xnu-7195.101.1.tar.gz

[apple/xnu.git] / bsd / kern / kern_event.c

/*
 * Copyright (c) 2000-2020 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 *
 */
/*-
 * Copyright (c) 1999,2000,2001 Jonathan Lemon <jlemon@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 *      @(#)kern_event.c       1.0 (3/31/2000)
 */
#include <stdint.h>
#include <machine/atomic.h>

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/malloc.h>
#include <sys/unistd.h>
#include <sys/file_internal.h>
#include <sys/fcntl.h>
#include <sys/select.h>
#include <sys/queue.h>
#include <sys/event.h>
#include <sys/eventvar.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/stat.h>
#include <sys/syscall.h> // SYS_* constants
#include <sys/sysctl.h>
#include <sys/uio.h>
#include <sys/sysproto.h>
#include <sys/user.h>
#include <sys/vnode_internal.h>
#include <string.h>
#include <sys/proc_info.h>
#include <sys/codesign.h>
#include <sys/pthread_shims.h>
#include <sys/kdebug.h>
#include <os/base.h>
#include <pexpert/pexpert.h>

#include <kern/locks.h>
#include <kern/clock.h>
#include <kern/cpu_data.h>
#include <kern/policy_internal.h>
#include <kern/thread_call.h>
#include <kern/sched_prim.h>
#include <kern/waitq.h>
#include <kern/zalloc.h>
#include <kern/kalloc.h>
#include <kern/assert.h>
#include <kern/ast.h>
#include <kern/thread.h>
#include <kern/kcdata.h>

#include <pthread/priority_private.h>
#include <pthread/workqueue_syscalls.h>
#include <pthread/workqueue_internal.h>
#include <libkern/libkern.h>

#include "net/net_str_id.h"

#include <mach/task.h>
#include <libkern/section_keywords.h>

#if CONFIG_MEMORYSTATUS
#include <sys/kern_memorystatus.h>
#endif

#if DEVELOPMENT || DEBUG
#define KEVENT_PANIC_ON_WORKLOOP_OWNERSHIP_LEAK  (1U << 0)
#define KEVENT_PANIC_ON_NON_ENQUEUED_PROCESS     (1U << 1)
TUNABLE(uint32_t, kevent_debug_flags, "kevent_debug", 0);
#endif

static LCK_GRP_DECLARE(kq_lck_grp, "kqueue");
SECURITY_READ_ONLY_EARLY(vm_packing_params_t) kn_kq_packing_params =
    VM_PACKING_PARAMS(KNOTE_KQ_PACKED);

extern mach_port_name_t ipc_entry_name_mask(mach_port_name_t name); /* osfmk/ipc/ipc_entry.h */
extern int cansignal(struct proc *, kauth_cred_t, struct proc *, int); /* bsd/kern/kern_sig.c */

#define KEV_EVTID(code) BSDDBG_CODE(DBG_BSD_KEVENT, (code))

/*
 * If you need accounting for KM_KQUEUE consider using
 * KALLOC_HEAP_DEFINE to define a zone view.
 */
#define KM_KQUEUE       KHEAP_DEFAULT

#define KQ_EVENT        NO_EVENT64

static int kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
    vfs_context_t ctx);
static int kqueue_close(struct fileglob *fg, vfs_context_t ctx);
static int kqueue_kqfilter(struct fileproc *fp, struct knote *kn,
    struct kevent_qos_s *kev);
static int kqueue_drain(struct fileproc *fp, vfs_context_t ctx);

static const struct fileops kqueueops = {
        .fo_type     = DTYPE_KQUEUE,
        .fo_read     = fo_no_read,
        .fo_write    = fo_no_write,
        .fo_ioctl    = fo_no_ioctl,
        .fo_select   = kqueue_select,
        .fo_close    = kqueue_close,
        .fo_drain    = kqueue_drain,
        .fo_kqfilter = kqueue_kqfilter,
};

static inline int kevent_modern_copyout(struct kevent_qos_s *, user_addr_t *);
static int kevent_register_wait_prepare(struct knote *kn, struct kevent_qos_s *kev, int result);
static void kevent_register_wait_block(struct turnstile *ts, thread_t handoff_thread,
    thread_continue_t cont, struct _kevent_register *cont_args) __dead2;
static void kevent_register_wait_return(struct _kevent_register *cont_args) __dead2;
static void kevent_register_wait_cleanup(struct knote *kn);

static struct kqtailq *kqueue_get_suppressed_queue(kqueue_t kq, struct knote *kn);
static void kqueue_threadreq_initiate(struct kqueue *kq, workq_threadreq_t, kq_index_t qos, int flags);

static void kqworkq_unbind(proc_t p, workq_threadreq_t);
static thread_qos_t kqworkq_unbind_locked(struct kqworkq *kqwq, workq_threadreq_t, thread_t thread);
static workq_threadreq_t kqworkq_get_request(struct kqworkq *kqwq, kq_index_t qos_index);

static void kqworkloop_unbind(struct kqworkloop *kwql);

enum kqwl_unbind_locked_mode {
        KQWL_OVERRIDE_DROP_IMMEDIATELY,
        KQWL_OVERRIDE_DROP_DELAYED,
};
static void kqworkloop_unbind_locked(struct kqworkloop *kwql, thread_t thread,
    enum kqwl_unbind_locked_mode how);
static void kqworkloop_unbind_delayed_override_drop(thread_t thread);
static kq_index_t kqworkloop_override(struct kqworkloop *kqwl);
static void kqworkloop_set_overcommit(struct kqworkloop *kqwl);
enum {
        KQWL_UTQ_NONE,
        /*
         * The wakeup qos is the qos of QUEUED knotes.
         *
         * This QoS is accounted for with the events override in the
         * kqr_override_index field. It is raised each time a new knote is queued at
         * a given QoS. The kqwl_wakeup_indexes field is a superset of the non empty
         * knote buckets and is recomputed after each event delivery.
         */
        KQWL_UTQ_UPDATE_WAKEUP_QOS,
        KQWL_UTQ_UPDATE_STAYACTIVE_QOS,
        KQWL_UTQ_RECOMPUTE_WAKEUP_QOS,
        KQWL_UTQ_UNBINDING, /* attempt to rebind */
        KQWL_UTQ_PARKING,
        /*
         * The wakeup override is for suppressed knotes that have fired again at
         * a higher QoS than the one for which they are suppressed already.
         * This override is cleared when the knote suppressed list becomes empty.
         */
        KQWL_UTQ_UPDATE_WAKEUP_OVERRIDE,
        KQWL_UTQ_RESET_WAKEUP_OVERRIDE,
        /*
         * The QoS is the maximum QoS of an event enqueued on this workloop in
         * userland. It is copied from the only EVFILT_WORKLOOP knote with
         * a NOTE_WL_THREAD_REQUEST bit set allowed on this workloop. If there is no
         * such knote, this QoS is 0.
         */
        KQWL_UTQ_SET_QOS_INDEX,
        KQWL_UTQ_REDRIVE_EVENTS,
};
static void kqworkloop_update_threads_qos(struct kqworkloop *kqwl, int op, kq_index_t qos);
static int kqworkloop_end_processing(struct kqworkloop *kqwl, int flags, int kevent_flags);

static struct knote *knote_alloc(void);
static void knote_free(struct knote *kn);
static int kq_add_knote(struct kqueue *kq, struct knote *kn,
    struct knote_lock_ctx *knlc, struct proc *p);
static struct knote *kq_find_knote_and_kq_lock(struct kqueue *kq,
    struct kevent_qos_s *kev, bool is_fd, struct proc *p);

static void knote_activate(kqueue_t kqu, struct knote *kn, int result);
static void knote_dequeue(kqueue_t kqu, struct knote *kn);

static void knote_apply_touch(kqueue_t kqu, struct knote *kn,
    struct kevent_qos_s *kev, int result);
static void knote_suppress(kqueue_t kqu, struct knote *kn);
static void knote_unsuppress(kqueue_t kqu, struct knote *kn);
static void knote_drop(kqueue_t kqu, struct knote *kn, struct knote_lock_ctx *knlc);

// both these functions may dequeue the knote and it is up to the caller
// to enqueue the knote back
static void knote_adjust_qos(struct kqueue *kq, struct knote *kn, int result);
static void knote_reset_priority(kqueue_t kqu, struct knote *kn, pthread_priority_t pp);

static ZONE_DECLARE(knote_zone, "knote zone",
    sizeof(struct knote), ZC_CACHING | ZC_ZFREE_CLEARMEM);
static ZONE_DECLARE(kqfile_zone, "kqueue file zone",
    sizeof(struct kqfile), ZC_ZFREE_CLEARMEM);
static ZONE_DECLARE(kqworkq_zone, "kqueue workq zone",
    sizeof(struct kqworkq), ZC_ZFREE_CLEARMEM);
static ZONE_DECLARE(kqworkloop_zone, "kqueue workloop zone",
    sizeof(struct kqworkloop), ZC_CACHING | ZC_ZFREE_CLEARMEM);

#define KN_HASH(val, mask)      (((val) ^ (val >> 8)) & (mask))

static int filt_no_attach(struct knote *kn, struct kevent_qos_s *kev);
static void filt_no_detach(struct knote *kn);
static int filt_bad_event(struct knote *kn, long hint);
static int filt_bad_touch(struct knote *kn, struct kevent_qos_s *kev);
static int filt_bad_process(struct knote *kn, struct kevent_qos_s *kev);

SECURITY_READ_ONLY_EARLY(static struct filterops) bad_filtops = {
        .f_attach  = filt_no_attach,
        .f_detach  = filt_no_detach,
        .f_event   = filt_bad_event,
        .f_touch   = filt_bad_touch,
        .f_process = filt_bad_process,
};

#if CONFIG_MEMORYSTATUS
extern const struct filterops memorystatus_filtops;
#endif /* CONFIG_MEMORYSTATUS */
extern const struct filterops fs_filtops;
extern const struct filterops sig_filtops;
extern const struct filterops machport_filtops;
extern const struct filterops pipe_nfiltops;
extern const struct filterops pipe_rfiltops;
extern const struct filterops pipe_wfiltops;
extern const struct filterops ptsd_kqops;
extern const struct filterops ptmx_kqops;
extern const struct filterops soread_filtops;
extern const struct filterops sowrite_filtops;
extern const struct filterops sock_filtops;
extern const struct filterops soexcept_filtops;
extern const struct filterops spec_filtops;
extern const struct filterops bpfread_filtops;
extern const struct filterops necp_fd_rfiltops;
extern const struct filterops fsevent_filtops;
extern const struct filterops vnode_filtops;
extern const struct filterops tty_filtops;

const static struct filterops file_filtops;
const static struct filterops kqread_filtops;
const static struct filterops proc_filtops;
const static struct filterops timer_filtops;
const static struct filterops user_filtops;
const static struct filterops workloop_filtops;

/*
 *
 * Rules for adding new filters to the system:
 * Public filters:
 * - Add a new "EVFILT_" option value to bsd/sys/event.h (typically a negative value)
 *   in the exported section of the header
 * - Update the EVFILT_SYSCOUNT value to reflect the new addition
 * - Add a filterops to the sysfilt_ops array. Public filters should be added at the end
 *   of the Public Filters section in the array.
 * Private filters:
 * - Add a new "EVFILT_" value to bsd/sys/event.h (typically a positive value)
 *   in the XNU_KERNEL_PRIVATE section of the header
 * - Update the EVFILTID_MAX value to reflect the new addition
 * - Add a filterops to the sysfilt_ops. Private filters should be added at the end of
 *   the Private filters section of the array.
 */
static_assert(EVFILTID_MAX < UINT8_MAX, "kn_filtid expects this to be true");
static const struct filterops * const sysfilt_ops[EVFILTID_MAX] = {
        /* Public Filters */
        [~EVFILT_READ]                  = &file_filtops,
        [~EVFILT_WRITE]                 = &file_filtops,
        [~EVFILT_AIO]                   = &bad_filtops,
        [~EVFILT_VNODE]                 = &file_filtops,
        [~EVFILT_PROC]                  = &proc_filtops,
        [~EVFILT_SIGNAL]                = &sig_filtops,
        [~EVFILT_TIMER]                 = &timer_filtops,
        [~EVFILT_MACHPORT]              = &machport_filtops,
        [~EVFILT_FS]                    = &fs_filtops,
        [~EVFILT_USER]                  = &user_filtops,
        [~EVFILT_UNUSED_11]             = &bad_filtops,
        [~EVFILT_VM]                    = &bad_filtops,
        [~EVFILT_SOCK]                  = &file_filtops,
#if CONFIG_MEMORYSTATUS
        [~EVFILT_MEMORYSTATUS]          = &memorystatus_filtops,
#else
        [~EVFILT_MEMORYSTATUS]          = &bad_filtops,
#endif
        [~EVFILT_EXCEPT]                = &file_filtops,
        [~EVFILT_WORKLOOP]              = &workloop_filtops,

        /* Private filters */
        [EVFILTID_KQREAD]               = &kqread_filtops,
        [EVFILTID_PIPE_N]               = &pipe_nfiltops,
        [EVFILTID_PIPE_R]               = &pipe_rfiltops,
        [EVFILTID_PIPE_W]               = &pipe_wfiltops,
        [EVFILTID_PTSD]                 = &ptsd_kqops,
        [EVFILTID_SOREAD]               = &soread_filtops,
        [EVFILTID_SOWRITE]              = &sowrite_filtops,
        [EVFILTID_SCK]                  = &sock_filtops,
        [EVFILTID_SOEXCEPT]             = &soexcept_filtops,
        [EVFILTID_SPEC]                 = &spec_filtops,
        [EVFILTID_BPFREAD]              = &bpfread_filtops,
        [EVFILTID_NECP_FD]              = &necp_fd_rfiltops,
        [EVFILTID_FSEVENT]              = &fsevent_filtops,
        [EVFILTID_VN]                   = &vnode_filtops,
        [EVFILTID_TTY]                  = &tty_filtops,
        [EVFILTID_PTMX]                 = &ptmx_kqops,

        /* fake filter for detached knotes, keep last */
        [EVFILTID_DETACHED]             = &bad_filtops,
};

/* waitq prepost callback */
void waitq_set__CALLING_PREPOST_HOOK__(waitq_set_prepost_hook_t *kq_hook);

static inline bool
kqr_thread_bound(workq_threadreq_t kqr)
{
        return kqr->tr_state == WORKQ_TR_STATE_BOUND;
}

static inline bool
kqr_thread_requested_pending(workq_threadreq_t kqr)
{
        workq_tr_state_t tr_state = kqr->tr_state;
        return tr_state > WORKQ_TR_STATE_IDLE && tr_state < WORKQ_TR_STATE_BOUND;
}

static inline bool
kqr_thread_requested(workq_threadreq_t kqr)
{
        return kqr->tr_state != WORKQ_TR_STATE_IDLE;
}

static inline thread_t
kqr_thread_fast(workq_threadreq_t kqr)
{
        assert(kqr_thread_bound(kqr));
        return kqr->tr_thread;
}

static inline thread_t
kqr_thread(workq_threadreq_t kqr)
{
        return kqr_thread_bound(kqr) ? kqr->tr_thread : THREAD_NULL;
}

static inline struct kqworkloop *
kqr_kqworkloop(workq_threadreq_t kqr)
{
        if (kqr->tr_flags & WORKQ_TR_FLAG_WORKLOOP) {
                return __container_of(kqr, struct kqworkloop, kqwl_request);
        }
        return NULL;
}

static inline kqueue_t
kqr_kqueue(proc_t p, workq_threadreq_t kqr)
{
        kqueue_t kqu;
        if (kqr->tr_flags & WORKQ_TR_FLAG_WORKLOOP) {
                kqu.kqwl = kqr_kqworkloop(kqr);
        } else {
                kqu.kqwq = p->p_fd->fd_wqkqueue;
                assert(kqr >= kqu.kqwq->kqwq_request &&
                    kqr < kqu.kqwq->kqwq_request + KQWQ_NBUCKETS);
        }
        return kqu;
}

/*
 * kqueue/note lock implementations
 *
 *      The kqueue lock guards the kq state, the state of its queues,
 *      and the kqueue-aware status and locks of individual knotes.
 *
 *      The kqueue workq lock is used to protect state guarding the
 *      interaction of the kqueue with the workq.  This state cannot
 *      be guarded by the kq lock - as it needs to be taken when we
 *      already have the waitq set lock held (during the waitq hook
 *      callback).  It might be better to use the waitq lock itself
 *      for this, but the IRQ requirements make that difficult).
 *
 *      Knote flags, filter flags, and associated data are protected
 *      by the underlying object lock - and are only ever looked at
 *      by calling the filter to get a [consistent] snapshot of that
 *      data.
 */

static inline void
kqlock(kqueue_t kqu)
{
        lck_spin_lock(&kqu.kq->kq_lock);
}

static inline void
kqlock_held(__assert_only kqueue_t kqu)
{
        LCK_SPIN_ASSERT(&kqu.kq->kq_lock, LCK_ASSERT_OWNED);
}

static inline void
kqunlock(kqueue_t kqu)
{
        lck_spin_unlock(&kqu.kq->kq_lock);
}

static inline void
knhash_lock(struct filedesc *fdp)
{
        lck_mtx_lock(&fdp->fd_knhashlock);
}

static inline void
knhash_unlock(struct filedesc *fdp)
{
        lck_mtx_unlock(&fdp->fd_knhashlock);
}

/* wait event for knote locks */
static inline event_t
knote_lock_wev(struct knote *kn)
{
        return (event_t)(&kn->kn_hook);
}

/* wait event for kevent_register_wait_* */
static inline event64_t
knote_filt_wev64(struct knote *kn)
{
        /* kdp_workloop_sync_wait_find_owner knows about this */
        return CAST_EVENT64_T(kn);
}

/* wait event for knote_post/knote_drop */
static inline event64_t
knote_post_wev64(struct knote *kn)
{
        return CAST_EVENT64_T(&kn->kn_kevent);
}

/*!
 * @function knote_has_qos
 *
 * @brief
 * Whether the knote has a regular QoS.
 *
 * @discussion
 * kn_qos_override is:
 * - 0 on kqfiles
 * - THREAD_QOS_LAST for special buckets (stayactive, manager)
 *
 * Other values mean the knote participates to QoS propagation.
 */
static inline bool
knote_has_qos(struct knote *kn)
{
        return kn->kn_qos_override > 0 && kn->kn_qos_override < THREAD_QOS_LAST;
}

#pragma mark knote locks

/*
 * Enum used by the knote_lock_* functions.
 *
 * KNOTE_KQ_LOCK_ALWAYS
 *   The function will always return with the kq lock held.
 *
 * KNOTE_KQ_LOCK_ON_SUCCESS
 *   The function will return with the kq lock held if it was successful
 *   (knote_lock() is the only function that can fail).
 *
 * KNOTE_KQ_LOCK_ON_FAILURE
 *   The function will return with the kq lock held if it was unsuccessful
 *   (knote_lock() is the only function that can fail).
 *
 * KNOTE_KQ_UNLOCK:
 *   The function returns with the kq unlocked.
 */
enum kqlocking {
        KNOTE_KQ_LOCK_ALWAYS,
        KNOTE_KQ_LOCK_ON_SUCCESS,
        KNOTE_KQ_LOCK_ON_FAILURE,
        KNOTE_KQ_UNLOCK,
};

static struct knote_lock_ctx *
knote_lock_ctx_find(kqueue_t kqu, struct knote *kn)
{
        struct knote_lock_ctx *ctx;
        LIST_FOREACH(ctx, &kqu.kq->kq_knlocks, knlc_link) {
                if (ctx->knlc_knote == kn) {
                        return ctx;
                }
        }
        panic("knote lock context not found: %p", kn);
        __builtin_trap();
}

/* slowpath of knote_lock() */
__attribute__((noinline))
static bool __result_use_check
knote_lock_slow(kqueue_t kqu, struct knote *kn,
    struct knote_lock_ctx *knlc, int kqlocking)
{
        struct knote_lock_ctx *owner_lc;
        struct uthread *uth = current_uthread();
        wait_result_t wr;

        kqlock_held(kqu);

        owner_lc = knote_lock_ctx_find(kqu, kn);
#if DEBUG || DEVELOPMENT
        knlc->knlc_state = KNOTE_LOCK_CTX_WAITING;
#endif
        owner_lc->knlc_waiters++;

        /*
         * Make our lock context visible to knote_unlock()
         */
        uth->uu_knlock = knlc;

        wr = lck_spin_sleep_with_inheritor(&kqu.kq->kq_lock, LCK_SLEEP_UNLOCK,
            knote_lock_wev(kn), owner_lc->knlc_thread,
            THREAD_UNINT | THREAD_WAIT_NOREPORT, TIMEOUT_WAIT_FOREVER);

        if (wr == THREAD_RESTART) {
                /*
                 * We haven't been woken up by knote_unlock() but knote_unlock_cancel.
                 * We need to cleanup the state since no one did.
                 */
                uth->uu_knlock = NULL;
#if DEBUG || DEVELOPMENT
                assert(knlc->knlc_state == KNOTE_LOCK_CTX_WAITING);
                knlc->knlc_state = KNOTE_LOCK_CTX_UNLOCKED;
#endif

                if (kqlocking == KNOTE_KQ_LOCK_ALWAYS ||
                    kqlocking == KNOTE_KQ_LOCK_ON_FAILURE) {
                        kqlock(kqu);
                }
                return false;
        } else {
                if (kqlocking == KNOTE_KQ_LOCK_ALWAYS ||
                    kqlocking == KNOTE_KQ_LOCK_ON_SUCCESS) {
                        kqlock(kqu);
#if DEBUG || DEVELOPMENT
                        /*
                         * This state is set under the lock so we can't
                         * really assert this unless we hold the lock.
                         */
                        assert(knlc->knlc_state == KNOTE_LOCK_CTX_LOCKED);
#endif
                }
                return true;
        }
}

/*
 * Attempts to take the "knote" lock.
 *
 * Called with the kqueue lock held.
 *
 * Returns true if the knote lock is acquired, false if it has been dropped
 */
static bool __result_use_check
knote_lock(kqueue_t kqu, struct knote *kn, struct knote_lock_ctx *knlc,
    enum kqlocking kqlocking)
{
        kqlock_held(kqu);

#if DEBUG || DEVELOPMENT
        assert(knlc->knlc_state == KNOTE_LOCK_CTX_UNLOCKED);
#endif
        knlc->knlc_knote = kn;
        knlc->knlc_thread = current_thread();
        knlc->knlc_waiters = 0;

        if (__improbable(kn->kn_status & KN_LOCKED)) {
                return knote_lock_slow(kqu, kn, knlc, kqlocking);
        }

        /*
         * When the knote will be dropped, the knote lock is taken before
         * KN_DROPPING is set, and then the knote will be removed from any
         * hash table that references it before the lock is canceled.
         */
        assert((kn->kn_status & KN_DROPPING) == 0);
        LIST_INSERT_HEAD(&kqu.kq->kq_knlocks, knlc, knlc_link);
        kn->kn_status |= KN_LOCKED;
#if DEBUG || DEVELOPMENT
        knlc->knlc_state = KNOTE_LOCK_CTX_LOCKED;
#endif

        if (kqlocking == KNOTE_KQ_UNLOCK ||
            kqlocking == KNOTE_KQ_LOCK_ON_FAILURE) {
                kqunlock(kqu);
        }
        return true;
}

/*
 * Unlocks a knote successfully locked with knote_lock().
 *
 * Called with the kqueue lock held.
 *
 * Returns with the kqueue lock held according to KNOTE_KQ_* mode.
 */
static void
knote_unlock(kqueue_t kqu, struct knote *kn,
    struct knote_lock_ctx *knlc, enum kqlocking kqlocking)
{
        kqlock_held(kqu);

        assert(knlc->knlc_knote == kn);
        assert(kn->kn_status & KN_LOCKED);
#if DEBUG || DEVELOPMENT
        assert(knlc->knlc_state == KNOTE_LOCK_CTX_LOCKED);
#endif

        LIST_REMOVE(knlc, knlc_link);

        if (knlc->knlc_waiters) {
                thread_t thread = THREAD_NULL;

                wakeup_one_with_inheritor(knote_lock_wev(kn), THREAD_AWAKENED,
                    LCK_WAKE_DEFAULT, &thread);

                /*
                 * knote_lock_slow() publishes the lock context of waiters
                 * in uthread::uu_knlock.
                 *
                 * Reach out and make this context the new owner.
                 */
                struct uthread *ut = get_bsdthread_info(thread);
                struct knote_lock_ctx *next_owner_lc = ut->uu_knlock;

                assert(next_owner_lc->knlc_knote == kn);
                next_owner_lc->knlc_waiters = knlc->knlc_waiters - 1;
                LIST_INSERT_HEAD(&kqu.kq->kq_knlocks, next_owner_lc, knlc_link);
#if DEBUG || DEVELOPMENT
                next_owner_lc->knlc_state = KNOTE_LOCK_CTX_LOCKED;
#endif
                ut->uu_knlock = NULL;
                thread_deallocate_safe(thread);
        } else {
                kn->kn_status &= ~KN_LOCKED;
        }

        if ((kn->kn_status & KN_MERGE_QOS) && !(kn->kn_status & KN_POSTING)) {
                /*
                 * No f_event() in flight anymore, we can leave QoS "Merge" mode
                 *
                 * See knote_adjust_qos()
                 */
                kn->kn_status &= ~KN_MERGE_QOS;
        }
        if (kqlocking == KNOTE_KQ_UNLOCK) {
                kqunlock(kqu);
        }
#if DEBUG || DEVELOPMENT
        knlc->knlc_state = KNOTE_LOCK_CTX_UNLOCKED;
#endif
}

/*
 * Aborts all waiters for a knote lock, and unlock the knote.
 *
 * Called with the kqueue lock held.
 *
 * Returns with the kqueue unlocked.
 */
static void
knote_unlock_cancel(struct kqueue *kq, struct knote *kn,
    struct knote_lock_ctx *knlc)
{
        kqlock_held(kq);

        assert(knlc->knlc_knote == kn);
        assert(kn->kn_status & KN_LOCKED);
        assert(kn->kn_status & KN_DROPPING);

        LIST_REMOVE(knlc, knlc_link);
        kn->kn_status &= ~KN_LOCKED;
        kqunlock(kq);

        if (knlc->knlc_waiters) {
                wakeup_all_with_inheritor(knote_lock_wev(kn), THREAD_RESTART);
        }
#if DEBUG || DEVELOPMENT
        knlc->knlc_state = KNOTE_LOCK_CTX_UNLOCKED;
#endif
}

/*
 * Call the f_event hook of a given filter.
 *
 * Takes a use count to protect against concurrent drops.
 */
static void
knote_post(struct knote *kn, long hint)
{
        struct kqueue *kq = knote_get_kq(kn);
        int dropping, result;

        kqlock(kq);

        if (__improbable(kn->kn_status & (KN_DROPPING | KN_VANISHED))) {
                return kqunlock(kq);
        }

        if (__improbable(kn->kn_status & KN_POSTING)) {
                panic("KNOTE() called concurrently on knote %p", kn);
        }

        kn->kn_status |= KN_POSTING;

        kqunlock(kq);
        result = filter_call(knote_fops(kn), f_event(kn, hint));
        kqlock(kq);

        dropping = (kn->kn_status & KN_DROPPING);

        if (!dropping && (result & FILTER_ACTIVE)) {
                knote_activate(kq, kn, result);
        }

        if ((kn->kn_status & KN_LOCKED) == 0) {
                /*
                 * There's no other f_* call in flight, we can leave QoS "Merge" mode.
                 *
                 * See knote_adjust_qos()
                 */
                kn->kn_status &= ~(KN_POSTING | KN_MERGE_QOS);
        } else {
                kn->kn_status &= ~KN_POSTING;
        }

        if (__improbable(dropping)) {
                waitq_wakeup64_all((struct waitq *)&kq->kq_wqs, knote_post_wev64(kn),
                    THREAD_AWAKENED, WAITQ_ALL_PRIORITIES);
        }

        kqunlock(kq);
}

/*
 * Called by knote_drop() to wait for the last f_event() caller to be done.
 *
 *      - kq locked at entry
 *      - kq unlocked at exit
 */
static void
knote_wait_for_post(struct kqueue *kq, struct knote *kn)
{
        wait_result_t wr = THREAD_NOT_WAITING;

        kqlock_held(kq);

        assert(kn->kn_status & KN_DROPPING);

        if (kn->kn_status & KN_POSTING) {
                wr = waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
                    knote_post_wev64(kn), THREAD_UNINT | THREAD_WAIT_NOREPORT,
                    TIMEOUT_WAIT_FOREVER);
        }
        kqunlock(kq);
        if (wr == THREAD_WAITING) {
                thread_block(THREAD_CONTINUE_NULL);
        }
}

#pragma mark knote helpers for filters

OS_ALWAYS_INLINE
void
knote_set_error(struct knote *kn, int error)
{
        kn->kn_flags |= EV_ERROR;
        kn->kn_sdata = error;
}

OS_ALWAYS_INLINE
int64_t
knote_low_watermark(const struct knote *kn)
{
        return (kn->kn_sfflags & NOTE_LOWAT) ? kn->kn_sdata : 1;
}

/*!
 * @function knote_fill_kevent_with_sdata
 *
 * @brief
 * Fills in a kevent from the current content of a knote.
 *
 * @discussion
 * This is meant to be called from filter's f_event hooks.
 * The kevent data is filled with kn->kn_sdata.
 *
 * kn->kn_fflags is cleared if kn->kn_flags has EV_CLEAR set.
 *
 * Using knote_fill_kevent is typically preferred.
 */
OS_ALWAYS_INLINE
void
knote_fill_kevent_with_sdata(struct knote *kn, struct kevent_qos_s *kev)
{
#define knote_assert_aliases(name1, offs1, name2) \
        static_assert(offsetof(struct kevent_qos_s, name1) + offs1 == \
            offsetof(struct kevent_internal_s, name2), \
                "kevent_qos_s::" #name1 " and kevent_internal_s::" #name2 "need to alias")
        /*
         * All the code makes assumptions on these aliasing,
         * so make sure we fail the build if we ever ever ever break them.
         */
        knote_assert_aliases(ident, 0, kei_ident);
#ifdef __LITTLE_ENDIAN__
        knote_assert_aliases(filter, 0, kei_filter);  // non trivial overlap
        knote_assert_aliases(filter, 1, kei_filtid);  // non trivial overlap
#else
        knote_assert_aliases(filter, 0, kei_filtid);  // non trivial overlap
        knote_assert_aliases(filter, 1, kei_filter);  // non trivial overlap
#endif
        knote_assert_aliases(flags, 0, kei_flags);
        knote_assert_aliases(qos, 0, kei_qos);
        knote_assert_aliases(udata, 0, kei_udata);
        knote_assert_aliases(fflags, 0, kei_fflags);
        knote_assert_aliases(xflags, 0, kei_sfflags); // non trivial overlap
        knote_assert_aliases(data, 0, kei_sdata);     // non trivial overlap
        knote_assert_aliases(ext, 0, kei_ext);
#undef knote_assert_aliases

        /*
         * Fix the differences between kevent_qos_s and kevent_internal_s:
         * - xflags is where kn_sfflags lives, we need to zero it
         * - fixup the high bits of `filter` where kn_filtid lives
         */
        *kev = *(struct kevent_qos_s *)&kn->kn_kevent;
        kev->xflags = 0;
        kev->filter |= 0xff00;
        if (kn->kn_flags & EV_CLEAR) {
                kn->kn_fflags = 0;
        }
}

/*!
 * @function knote_fill_kevent
 *
 * @brief
 * Fills in a kevent from the current content of a knote.
 *
 * @discussion
 * This is meant to be called from filter's f_event hooks.
 * The kevent data is filled with the passed in data.
 *
 * kn->kn_fflags is cleared if kn->kn_flags has EV_CLEAR set.
 */
OS_ALWAYS_INLINE
void
knote_fill_kevent(struct knote *kn, struct kevent_qos_s *kev, int64_t data)
{
        knote_fill_kevent_with_sdata(kn, kev);
        kev->filter = kn->kn_filter;
        kev->data = data;
}


#pragma mark file_filtops

static int
filt_fileattach(struct knote *kn, struct kevent_qos_s *kev)
{
        return fo_kqfilter(kn->kn_fp, kn, kev);
}

SECURITY_READ_ONLY_EARLY(static struct filterops) file_filtops = {
        .f_isfd = 1,
        .f_attach = filt_fileattach,
};

#pragma mark kqread_filtops

#define f_flag fp_glob->fg_flag
#define f_ops fp_glob->fg_ops
#define f_data fp_glob->fg_data
#define f_lflags fp_glob->fg_lflags

static void
filt_kqdetach(struct knote *kn)
{
        struct kqfile *kqf = (struct kqfile *)kn->kn_fp->f_data;
        struct kqueue *kq = &kqf->kqf_kqueue;

        kqlock(kq);
        KNOTE_DETACH(&kqf->kqf_sel.si_note, kn);
        kqunlock(kq);
}

static int
filt_kqueue(struct knote *kn, __unused long hint)
{
        struct kqueue *kq = (struct kqueue *)kn->kn_fp->f_data;

        return kq->kq_count > 0;
}

static int
filt_kqtouch(struct knote *kn, struct kevent_qos_s *kev)
{
#pragma unused(kev)
        struct kqueue *kq = (struct kqueue *)kn->kn_fp->f_data;
        int res;

        kqlock(kq);
        res = (kq->kq_count > 0);
        kqunlock(kq);

        return res;
}

static int
filt_kqprocess(struct knote *kn, struct kevent_qos_s *kev)
{
        struct kqueue *kq = (struct kqueue *)kn->kn_fp->f_data;
        int res = 0;

        kqlock(kq);
        if (kq->kq_count) {
                knote_fill_kevent(kn, kev, kq->kq_count);
                res = 1;
        }
        kqunlock(kq);

        return res;
}

SECURITY_READ_ONLY_EARLY(static struct filterops) kqread_filtops = {
        .f_isfd = 1,
        .f_detach = filt_kqdetach,
        .f_event = filt_kqueue,
        .f_touch = filt_kqtouch,
        .f_process = filt_kqprocess,
};

#pragma mark proc_filtops

static int
filt_procattach(struct knote *kn, __unused struct kevent_qos_s *kev)
{
        struct proc *p;

        assert(PID_MAX < NOTE_PDATAMASK);

        if ((kn->kn_sfflags & (NOTE_TRACK | NOTE_TRACKERR | NOTE_CHILD)) != 0) {
                knote_set_error(kn, ENOTSUP);
                return 0;
        }

        p = proc_find((int)kn->kn_id);
        if (p == NULL) {
                knote_set_error(kn, ESRCH);
                return 0;
        }

        const uint32_t NoteExitStatusBits = NOTE_EXIT | NOTE_EXITSTATUS;

        if ((kn->kn_sfflags & NoteExitStatusBits) == NoteExitStatusBits) {
                do {
                        pid_t selfpid = proc_selfpid();

                        if (p->p_ppid == selfpid) {
                                break;  /* parent => ok */
                        }
                        if ((p->p_lflag & P_LTRACED) != 0 &&
                            (p->p_oppid == selfpid)) {
                                break;  /* parent-in-waiting => ok */
                        }
                        if (cansignal(current_proc(), kauth_cred_get(), p, SIGKILL)) {
                                break; /* allowed to signal => ok */
                        }
                        proc_rele(p);
                        knote_set_error(kn, EACCES);
                        return 0;
                } while (0);
        }

        kn->kn_proc = p;
        kn->kn_flags |= EV_CLEAR;       /* automatically set */
        kn->kn_sdata = 0;               /* incoming data is ignored */

        proc_klist_lock();

        KNOTE_ATTACH(&p->p_klist, kn);

        proc_klist_unlock();

        proc_rele(p);

        /*
         * only captures edge-triggered events after this point
         * so it can't already be fired.
         */
        return 0;
}


/*
 * The knote may be attached to a different process, which may exit,
 * leaving nothing for the knote to be attached to.  In that case,
 * the pointer to the process will have already been nulled out.
 */
static void
filt_procdetach(struct knote *kn)
{
        struct proc *p;

        proc_klist_lock();

        p = kn->kn_proc;
        if (p != PROC_NULL) {
                kn->kn_proc = PROC_NULL;
                KNOTE_DETACH(&p->p_klist, kn);
        }

        proc_klist_unlock();
}

static int
filt_procevent(struct knote *kn, long hint)
{
        u_int event;

        /* ALWAYS CALLED WITH proc_klist_lock */

        /*
         * Note: a lot of bits in hint may be obtained from the knote
         * To free some of those bits, see <rdar://problem/12592988> Freeing up
         * bits in hint for filt_procevent
         *
         * mask off extra data
         */
        event = (u_int)hint & NOTE_PCTRLMASK;

        /*
         * termination lifecycle events can happen while a debugger
         * has reparented a process, in which case notifications
         * should be quashed except to the tracing parent. When
         * the debugger reaps the child (either via wait4(2) or
         * process exit), the child will be reparented to the original
         * parent and these knotes re-fired.
         */
        if (event & NOTE_EXIT) {
                if ((kn->kn_proc->p_oppid != 0)
                    && (knote_get_kq(kn)->kq_p->p_pid != kn->kn_proc->p_ppid)) {
                        /*
                         * This knote is not for the current ptrace(2) parent, ignore.
                         */
                        return 0;
                }
        }

        /*
         * if the user is interested in this event, record it.
         */
        if (kn->kn_sfflags & event) {
                kn->kn_fflags |= event;
        }

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
        if ((event == NOTE_REAP) || ((event == NOTE_EXIT) && !(kn->kn_sfflags & NOTE_REAP))) {
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
        }
#pragma clang diagnostic pop


        /*
         * The kernel has a wrapper in place that returns the same data
         * as is collected here, in kn_hook32.  Any changes to how
         * NOTE_EXITSTATUS and NOTE_EXIT_DETAIL are collected
         * should also be reflected in the proc_pidnoteexit() wrapper.
         */
        if (event == NOTE_EXIT) {
                kn->kn_hook32 = 0;
                if ((kn->kn_sfflags & NOTE_EXITSTATUS) != 0) {
                        kn->kn_fflags |= NOTE_EXITSTATUS;
                        kn->kn_hook32 |= (hint & NOTE_PDATAMASK);
                }
                if ((kn->kn_sfflags & NOTE_EXIT_DETAIL) != 0) {
                        kn->kn_fflags |= NOTE_EXIT_DETAIL;
                        if ((kn->kn_proc->p_lflag &
                            P_LTERM_DECRYPTFAIL) != 0) {
                                kn->kn_hook32 |= NOTE_EXIT_DECRYPTFAIL;
                        }
                        if ((kn->kn_proc->p_lflag &
                            P_LTERM_JETSAM) != 0) {
                                kn->kn_hook32 |= NOTE_EXIT_MEMORY;
                                switch (kn->kn_proc->p_lflag & P_JETSAM_MASK) {
                                case P_JETSAM_VMPAGESHORTAGE:
                                        kn->kn_hook32 |= NOTE_EXIT_MEMORY_VMPAGESHORTAGE;
                                        break;
                                case P_JETSAM_VMTHRASHING:
                                        kn->kn_hook32 |= NOTE_EXIT_MEMORY_VMTHRASHING;
                                        break;
                                case P_JETSAM_FCTHRASHING:
                                        kn->kn_hook32 |= NOTE_EXIT_MEMORY_FCTHRASHING;
                                        break;
                                case P_JETSAM_VNODE:
                                        kn->kn_hook32 |= NOTE_EXIT_MEMORY_VNODE;
                                        break;
                                case P_JETSAM_HIWAT:
                                        kn->kn_hook32 |= NOTE_EXIT_MEMORY_HIWAT;
                                        break;
                                case P_JETSAM_PID:
                                        kn->kn_hook32 |= NOTE_EXIT_MEMORY_PID;
                                        break;
                                case P_JETSAM_IDLEEXIT:
                                        kn->kn_hook32 |= NOTE_EXIT_MEMORY_IDLE;
                                        break;
                                }
                        }
                        if ((kn->kn_proc->p_csflags &
                            CS_KILLED) != 0) {
                                kn->kn_hook32 |= NOTE_EXIT_CSERROR;
                        }
                }
        }

        /* if we have any matching state, activate the knote */
        return kn->kn_fflags != 0;
}

static int
filt_proctouch(struct knote *kn, struct kevent_qos_s *kev)
{
        int res;

        proc_klist_lock();

        /* accept new filter flags and mask off output events no long interesting */
        kn->kn_sfflags = kev->fflags;

        /* restrict the current results to the (smaller?) set of new interest */
        /*
         * For compatibility with previous implementations, we leave kn_fflags
         * as they were before.
         */
        //kn->kn_fflags &= kn->kn_sfflags;

        res = (kn->kn_fflags != 0);

        proc_klist_unlock();

        return res;
}

static int
filt_procprocess(struct knote *kn, struct kevent_qos_s *kev)
{
        int res = 0;

        proc_klist_lock();
        if (kn->kn_fflags) {
                knote_fill_kevent(kn, kev, kn->kn_hook32);
                kn->kn_hook32 = 0;
                res = 1;
        }
        proc_klist_unlock();
        return res;
}

SECURITY_READ_ONLY_EARLY(static struct filterops) proc_filtops = {
        .f_attach  = filt_procattach,
        .f_detach  = filt_procdetach,
        .f_event   = filt_procevent,
        .f_touch   = filt_proctouch,
        .f_process = filt_procprocess,
};

#pragma mark timer_filtops

struct filt_timer_params {
        uint64_t deadline; /* deadline in abs/cont time
                            *                      (or 0 if NOTE_ABSOLUTE and deadline is in past) */
        uint64_t leeway;   /* leeway in abstime, or 0 if none */
        uint64_t interval; /* interval in abstime or 0 if non-repeating timer */
};

/*
 * Values stored in the knote at rest (using Mach absolute time units)
 *
 * kn->kn_thcall        where the thread_call object is stored
 * kn->kn_ext[0]        next deadline or 0 if immediate expiration
 * kn->kn_ext[1]        leeway value
 * kn->kn_sdata         interval timer: the interval
 *                      absolute/deadline timer: 0
 * kn->kn_hook32        timer state (with gencount)
 *
 * TIMER_IDLE:
 *   The timer has either never been scheduled or been cancelled.
 *   It is safe to schedule a new one in this state.
 *
 * TIMER_ARMED:
 *   The timer has been scheduled
 *
 * TIMER_FIRED
 *   The timer has fired and an event needs to be delivered.
 *   When in this state, the callout may still be running.
 *
 * TIMER_IMMEDIATE
 *   The timer has fired at registration time, and the callout was never
 *   dispatched.
 */
#define TIMER_IDLE       0x0
#define TIMER_ARMED      0x1
#define TIMER_FIRED      0x2
#define TIMER_IMMEDIATE  0x3
#define TIMER_STATE_MASK 0x3
#define TIMER_GEN_INC    0x4

static void
filt_timer_set_params(struct knote *kn, struct filt_timer_params *params)
{
        kn->kn_ext[0] = params->deadline;
        kn->kn_ext[1] = params->leeway;
        kn->kn_sdata  = params->interval;
}

/*
 * filt_timervalidate - process data from user
 *
 * Sets up the deadline, interval, and leeway from the provided user data
 *
 * Input:
 *      kn_sdata        timer deadline or interval time
 *      kn_sfflags      style of timer, unit of measurement
 *
 * Output:
 *      struct filter_timer_params to apply to the filter with
 *      filt_timer_set_params when changes are ready to be commited.
 *
 * Returns:
 *      EINVAL          Invalid user data parameters
 *      ERANGE          Various overflows with the parameters
 *
 * Called with timer filter lock held.
 */
static int
filt_timervalidate(const struct kevent_qos_s *kev,
    struct filt_timer_params *params)
{
        /*
         * There are 5 knobs that need to be chosen for a timer registration:
         *
         * A) Units of time (what is the time duration of the specified number)
         *      Absolute and interval take:
         *              NOTE_SECONDS, NOTE_USECONDS, NOTE_NSECONDS, NOTE_MACHTIME
         *      Defaults to milliseconds if not specified
         *
         * B) Clock epoch (what is the zero point of the specified number)
         *      For interval, there is none
         *      For absolute, defaults to the gettimeofday/calendar epoch
         *      With NOTE_MACHTIME, uses mach_absolute_time()
         *      With NOTE_MACHTIME and NOTE_MACH_CONTINUOUS_TIME, uses mach_continuous_time()
         *
         * C) The knote's behavior on delivery
         *      Interval timer causes the knote to arm for the next interval unless one-shot is set
         *      Absolute is a forced one-shot timer which deletes on delivery
         *      TODO: Add a way for absolute to be not forced one-shot
         *
         * D) Whether the time duration is relative to now or absolute
         *      Interval fires at now + duration when it is set up
         *      Absolute fires at now + difference between now walltime and passed in walltime
         *      With NOTE_MACHTIME it fires at an absolute MAT or MCT.
         *
         * E) Whether the timer continues to tick across sleep
         *      By default all three do not.
         *      For interval and absolute, NOTE_MACH_CONTINUOUS_TIME causes them to tick across sleep
         *      With NOTE_ABSOLUTE | NOTE_MACHTIME | NOTE_MACH_CONTINUOUS_TIME:
         *              expires when mach_continuous_time() is > the passed in value.
         */

        uint64_t multiplier;

        boolean_t use_abstime = FALSE;

        switch (kev->fflags & (NOTE_SECONDS | NOTE_USECONDS | NOTE_NSECONDS | NOTE_MACHTIME)) {
        case NOTE_SECONDS:
                multiplier = NSEC_PER_SEC;
                break;
        case NOTE_USECONDS:
                multiplier = NSEC_PER_USEC;
                break;
        case NOTE_NSECONDS:
                multiplier = 1;
                break;
        case NOTE_MACHTIME:
                multiplier = 0;
                use_abstime = TRUE;
                break;
        case 0: /* milliseconds (default) */
                multiplier = NSEC_PER_SEC / 1000;
                break;
        default:
                return EINVAL;
        }

        /* transform the leeway in kn_ext[1] to same time scale */
        if (kev->fflags & NOTE_LEEWAY) {
                uint64_t leeway_abs;

                if (use_abstime) {
                        leeway_abs = (uint64_t)kev->ext[1];
                } else {
                        uint64_t leeway_ns;
                        if (os_mul_overflow((uint64_t)kev->ext[1], multiplier, &leeway_ns)) {
                                return ERANGE;
                        }

                        nanoseconds_to_absolutetime(leeway_ns, &leeway_abs);
                }

                params->leeway = leeway_abs;
        } else {
                params->leeway = 0;
        }

        if (kev->fflags & NOTE_ABSOLUTE) {
                uint64_t deadline_abs;

                if (use_abstime) {
                        deadline_abs = (uint64_t)kev->data;
                } else {
                        uint64_t calendar_deadline_ns;

                        if (os_mul_overflow((uint64_t)kev->data, multiplier, &calendar_deadline_ns)) {
                                return ERANGE;
                        }

                        /* calendar_deadline_ns is in nanoseconds since the epoch */

                        clock_sec_t seconds;
                        clock_nsec_t nanoseconds;

                        /*
                         * Note that the conversion through wall-time is only done once.
                         *
                         * If the relationship between MAT and gettimeofday changes,
                         * the underlying timer does not update.
                         *
                         * TODO: build a wall-time denominated timer_call queue
                         * and a flag to request DTRTing with wall-time timers
                         */
                        clock_get_calendar_nanotime(&seconds, &nanoseconds);

                        uint64_t calendar_now_ns = (uint64_t)seconds * NSEC_PER_SEC + nanoseconds;

                        /* if deadline is in the future */
                        if (calendar_now_ns < calendar_deadline_ns) {
                                uint64_t interval_ns = calendar_deadline_ns - calendar_now_ns;
                                uint64_t interval_abs;

                                nanoseconds_to_absolutetime(interval_ns, &interval_abs);

                                /*
                                 * Note that the NOTE_MACH_CONTINUOUS_TIME flag here only
                                 * causes the timer to keep ticking across sleep, but
                                 * it does not change the calendar timebase.
                                 */

                                if (kev->fflags & NOTE_MACH_CONTINUOUS_TIME) {
                                        clock_continuoustime_interval_to_deadline(interval_abs,
                                            &deadline_abs);
                                } else {
                                        clock_absolutetime_interval_to_deadline(interval_abs,
                                            &deadline_abs);
                                }
                        } else {
                                deadline_abs = 0; /* cause immediate expiration */
                        }
                }

                params->deadline = deadline_abs;
                params->interval = 0; /* NOTE_ABSOLUTE is non-repeating */
        } else if (kev->data < 0) {
                /*
                 * Negative interval timers fire immediately, once.
                 *
                 * Ideally a negative interval would be an error, but certain clients
                 * pass negative values on accident, and expect an event back.
                 *
                 * In the old implementation the timer would repeat with no delay
                 * N times until mach_absolute_time() + (N * interval) underflowed,
                 * then it would wait ~forever by accidentally arming a timer for the far future.
                 *
                 * We now skip the power-wasting hot spin phase and go straight to the idle phase.
                 */

                params->deadline = 0; /* expire immediately */
                params->interval = 0; /* non-repeating */
        } else {
                uint64_t interval_abs = 0;

                if (use_abstime) {
                        interval_abs = (uint64_t)kev->data;
                } else {
                        uint64_t interval_ns;
                        if (os_mul_overflow((uint64_t)kev->data, multiplier, &interval_ns)) {
                                return ERANGE;
                        }

                        nanoseconds_to_absolutetime(interval_ns, &interval_abs);
                }

                uint64_t deadline = 0;

                if (kev->fflags & NOTE_MACH_CONTINUOUS_TIME) {
                        clock_continuoustime_interval_to_deadline(interval_abs, &deadline);
                } else {
                        clock_absolutetime_interval_to_deadline(interval_abs, &deadline);
                }

                params->deadline = deadline;
                params->interval = interval_abs;
        }

        return 0;
}

/*
 * filt_timerexpire - the timer callout routine
 */
static void
filt_timerexpire(void *knx, void *state_on_arm)
{
        struct knote *kn = knx;

        uint32_t state = (uint32_t)(uintptr_t)state_on_arm;
        uint32_t fired_state = state ^ TIMER_ARMED ^ TIMER_FIRED;

        if (os_atomic_cmpxchg(&kn->kn_hook32, state, fired_state, relaxed)) {
                // our f_event always would say FILTER_ACTIVE,
                // so be leaner and just do it.
                struct kqueue *kq = knote_get_kq(kn);
                kqlock(kq);
                knote_activate(kq, kn, FILTER_ACTIVE);
                kqunlock(kq);
        } else {
                /*
                 * The timer has been reprogrammed or canceled since it was armed,
                 * and this is a late firing for the timer, just ignore it.
                 */
        }
}

/*
 * Does this deadline needs a timer armed for it, or has it expired?
 */
static bool
filt_timer_is_ready(struct knote *kn)
{
        uint64_t now, deadline = kn->kn_ext[0];

        if (deadline == 0) {
                return true;
        }

        if (kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME) {
                now = mach_continuous_time();
        } else {
                now = mach_absolute_time();
        }
        return deadline <= now;
}

/*
 * Arm a timer
 *
 * It is the responsibility of the caller to make sure the timer call
 * has completed or been cancelled properly prior to arming it.
 */
static void
filt_timerarm(struct knote *kn)
{
        uint64_t deadline = kn->kn_ext[0];
        uint64_t leeway   = kn->kn_ext[1];
        uint32_t state;

        int filter_flags = kn->kn_sfflags;
        unsigned int timer_flags = 0;

        if (filter_flags & NOTE_CRITICAL) {
                timer_flags |= THREAD_CALL_DELAY_USER_CRITICAL;
        } else if (filter_flags & NOTE_BACKGROUND) {
                timer_flags |= THREAD_CALL_DELAY_USER_BACKGROUND;
        } else {
                timer_flags |= THREAD_CALL_DELAY_USER_NORMAL;
        }

        if (filter_flags & NOTE_LEEWAY) {
                timer_flags |= THREAD_CALL_DELAY_LEEWAY;
        }

        if (filter_flags & NOTE_MACH_CONTINUOUS_TIME) {
                timer_flags |= THREAD_CALL_CONTINUOUS;
        }

        /*
         * Move to ARMED.
         *
         * We increase the gencount, and setup the thread call with this expected
         * state. It means that if there was a previous generation of the timer in
         * flight that needs to be ignored, then 3 things are possible:
         *
         * - the timer fires first, filt_timerexpire() and sets the state to FIRED
         *   but we clobber it with ARMED and a new gencount. The knote will still
         *   be activated, but filt_timerprocess() which is serialized with this
         *   call will not see the FIRED bit set and will not deliver an event.
         *
         * - this code runs first, but filt_timerexpire() comes second. Because it
         *   knows an old gencount, it will debounce and not activate the knote.
         *
         * - filt_timerexpire() wasn't in flight yet, and thread_call_enter below
         *   will just cancel it properly.
         *
         * This is important as userspace expects to never be woken up for past
         * timers after filt_timertouch ran.
         */
        state = os_atomic_load(&kn->kn_hook32, relaxed);
        state &= ~TIMER_STATE_MASK;
        state += TIMER_GEN_INC + TIMER_ARMED;
        os_atomic_store(&kn->kn_hook32, state, relaxed);

        thread_call_enter_delayed_with_leeway(kn->kn_thcall,
            (void *)(uintptr_t)state, deadline, leeway, timer_flags);
}

/*
 * Mark a timer as "already fired" when it is being reprogrammed
 *
 * If there is a timer in flight, this will do a best effort at canceling it,
 * but will not wait. If the thread call was in flight, having set the
 * TIMER_IMMEDIATE bit will debounce a filt_timerexpire() racing with this
 * cancelation.
 */
static void
filt_timerfire_immediate(struct knote *kn)
{
        uint32_t state;

        static_assert(TIMER_IMMEDIATE == TIMER_STATE_MASK,
            "validate that this atomic or will transition to IMMEDIATE");
        state = os_atomic_or_orig(&kn->kn_hook32, TIMER_IMMEDIATE, relaxed);

        if ((state & TIMER_STATE_MASK) == TIMER_ARMED) {
                thread_call_cancel(kn->kn_thcall);
        }
}

/*
 * Allocate a thread call for the knote's lifetime, and kick off the timer.
 */
static int
filt_timerattach(struct knote *kn, struct kevent_qos_s *kev)
{
        thread_call_t callout;
        struct filt_timer_params params;
        int error;

        if ((error = filt_timervalidate(kev, &params)) != 0) {
                knote_set_error(kn, error);
                return 0;
        }

        callout = thread_call_allocate_with_options(filt_timerexpire,
            (thread_call_param_t)kn, THREAD_CALL_PRIORITY_HIGH,
            THREAD_CALL_OPTIONS_ONCE);

        if (NULL == callout) {
                knote_set_error(kn, ENOMEM);
                return 0;
        }

        filt_timer_set_params(kn, &params);
        kn->kn_thcall = callout;
        kn->kn_flags |= EV_CLEAR;
        os_atomic_store(&kn->kn_hook32, TIMER_IDLE, relaxed);

        /* NOTE_ABSOLUTE implies EV_ONESHOT */
        if (kn->kn_sfflags & NOTE_ABSOLUTE) {
                kn->kn_flags |= EV_ONESHOT;
        }

        if (filt_timer_is_ready(kn)) {
                os_atomic_store(&kn->kn_hook32, TIMER_IMMEDIATE, relaxed);
                return FILTER_ACTIVE;
        } else {
                filt_timerarm(kn);
                return 0;
        }
}

/*
 * Shut down the timer if it's running, and free the callout.
 */
static void
filt_timerdetach(struct knote *kn)
{
        __assert_only boolean_t freed;

        /*
         * Unconditionally cancel to make sure there can't be any filt_timerexpire()
         * running anymore.
         */
        thread_call_cancel_wait(kn->kn_thcall);
        freed = thread_call_free(kn->kn_thcall);
        assert(freed);
}

/*
 * filt_timertouch - update timer knote with new user input
 *
 * Cancel and restart the timer based on new user data. When
 * the user picks up a knote, clear the count of how many timer
 * pops have gone off (in kn_data).
 */
static int
filt_timertouch(struct knote *kn, struct kevent_qos_s *kev)
{
        struct filt_timer_params params;
        uint32_t changed_flags = (kn->kn_sfflags ^ kev->fflags);
        int error;

        if (changed_flags & NOTE_ABSOLUTE) {
                kev->flags |= EV_ERROR;
                kev->data = EINVAL;
                return 0;
        }

        if ((error = filt_timervalidate(kev, &params)) != 0) {
                kev->flags |= EV_ERROR;
                kev->data = error;
                return 0;
        }

        /* capture the new values used to compute deadline */
        filt_timer_set_params(kn, &params);
        kn->kn_sfflags = kev->fflags;

        if (filt_timer_is_ready(kn)) {
                filt_timerfire_immediate(kn);
                return FILTER_ACTIVE | FILTER_UPDATE_REQ_QOS;
        } else {
                filt_timerarm(kn);
                return FILTER_UPDATE_REQ_QOS;
        }
}

/*
 * filt_timerprocess - query state of knote and snapshot event data
 *
 * Determine if the timer has fired in the past, snapshot the state
 * of the kevent for returning to user-space, and clear pending event
 * counters for the next time.
 */
static int
filt_timerprocess(struct knote *kn, struct kevent_qos_s *kev)
{
        uint32_t state = os_atomic_load(&kn->kn_hook32, relaxed);

        /*
         * filt_timerprocess is serialized with any filter routine except for
         * filt_timerexpire which atomically does a TIMER_ARMED -> TIMER_FIRED
         * transition, and on success, activates the knote.
         *
         * Hence, we don't need atomic modifications of the state, only to peek at
         * whether we see any of the "FIRED" state, and if we do, it is safe to
         * do simple state machine transitions.
         */
        switch (state & TIMER_STATE_MASK) {
        case TIMER_IDLE:
        case TIMER_ARMED:
                /*
                 * This can happen if a touch resets a timer that had fired
                 * without being processed
                 */
                return 0;
        }

        os_atomic_store(&kn->kn_hook32, state & ~TIMER_STATE_MASK, relaxed);

        /*
         * Copy out the interesting kevent state,
         * but don't leak out the raw time calculations.
         *
         * TODO: potential enhancements - tell the user about:
         *      - deadline to which this timer thought it was expiring
         *      - return kn_sfflags in the fflags field so the client can know
         *        under what flags the timer fired
         */
        knote_fill_kevent(kn, kev, 1);
        kev->ext[0] = 0;
        /* kev->ext[1] = 0;  JMM - shouldn't we hide this too? */

        if (kn->kn_sdata != 0) {
                /*
                 * This is a 'repeating' timer, so we have to emit
                 * how many intervals expired between the arm
                 * and the process.
                 *
                 * A very strange style of interface, because
                 * this could easily be done in the client...
                 */

                uint64_t now;

                if (kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME) {
                        now = mach_continuous_time();
                } else {
                        now = mach_absolute_time();
                }

                uint64_t first_deadline = kn->kn_ext[0];
                uint64_t interval_abs   = kn->kn_sdata;
                uint64_t orig_arm_time  = first_deadline - interval_abs;

                assert(now > orig_arm_time);
                assert(now > first_deadline);

                uint64_t elapsed = now - orig_arm_time;

                uint64_t num_fired = elapsed / interval_abs;

                /*
                 * To reach this code, we must have seen the timer pop
                 * and be in repeating mode, so therefore it must have been
                 * more than 'interval' time since the attach or last
                 * successful touch.
                 */
                assert(num_fired > 0);

                /* report how many intervals have elapsed to the user */
                kev->data = (int64_t)num_fired;

                /* We only need to re-arm the timer if it's not about to be destroyed */
                if ((kn->kn_flags & EV_ONESHOT) == 0) {
                        /* fire at the end of the next interval */
                        uint64_t new_deadline = first_deadline + num_fired * interval_abs;

                        assert(new_deadline > now);

                        kn->kn_ext[0] = new_deadline;

                        /*
                         * This can't shortcut setting up the thread call, because
                         * knote_process deactivates EV_CLEAR knotes unconditionnally.
                         */
                        filt_timerarm(kn);
                }
        }

        return FILTER_ACTIVE;
}

SECURITY_READ_ONLY_EARLY(static struct filterops) timer_filtops = {
        .f_extended_codes = true,
        .f_attach   = filt_timerattach,
        .f_detach   = filt_timerdetach,
        .f_event    = filt_bad_event,
        .f_touch    = filt_timertouch,
        .f_process  = filt_timerprocess,
};

#pragma mark user_filtops

static int
filt_userattach(struct knote *kn, __unused struct kevent_qos_s *kev)
{
        if (kn->kn_sfflags & NOTE_TRIGGER) {
                kn->kn_hook32 = FILTER_ACTIVE;
        } else {
                kn->kn_hook32 = 0;
        }
        return kn->kn_hook32;
}

static int
filt_usertouch(struct knote *kn, struct kevent_qos_s *kev)
{
        uint32_t ffctrl;
        int fflags;

        ffctrl = kev->fflags & NOTE_FFCTRLMASK;
        fflags = kev->fflags & NOTE_FFLAGSMASK;
        switch (ffctrl) {
        case NOTE_FFNOP:
                break;
        case NOTE_FFAND:
                kn->kn_sfflags &= fflags;
                break;
        case NOTE_FFOR:
                kn->kn_sfflags |= fflags;
                break;
        case NOTE_FFCOPY:
                kn->kn_sfflags = fflags;
                break;
        }
        kn->kn_sdata = kev->data;

        if (kev->fflags & NOTE_TRIGGER) {
                kn->kn_hook32 = FILTER_ACTIVE;
        }
        return (int)kn->kn_hook32;
}

static int
filt_userprocess(struct knote *kn, struct kevent_qos_s *kev)
{
        int result = (int)kn->kn_hook32;

        if (result) {
                /* EVFILT_USER returns the data that was passed in */
                knote_fill_kevent_with_sdata(kn, kev);
                kev->fflags = kn->kn_sfflags;
                if (kn->kn_flags & EV_CLEAR) {
                        /* knote_fill_kevent cleared kn_fflags */
                        kn->kn_hook32 = 0;
                }
        }

        return result;
}

SECURITY_READ_ONLY_EARLY(static struct filterops) user_filtops = {
        .f_extended_codes = true,
        .f_attach  = filt_userattach,
        .f_detach  = filt_no_detach,
        .f_event   = filt_bad_event,
        .f_touch   = filt_usertouch,
        .f_process = filt_userprocess,
};

#pragma mark workloop_filtops

#define EPREEMPTDISABLED (-1)

static inline void
filt_wllock(struct kqworkloop *kqwl)
{
        lck_spin_lock(&kqwl->kqwl_statelock);
}

static inline void
filt_wlunlock(struct kqworkloop *kqwl)
{
        lck_spin_unlock(&kqwl->kqwl_statelock);
}

/*
 * Returns true when the interlock for the turnstile is the workqueue lock
 *
 * When this is the case, all turnstiles operations are delegated
 * to the workqueue subsystem.
 *
 * This is required because kqueue_threadreq_bind_prepost only holds the
 * workqueue lock but needs to move the inheritor from the workloop turnstile
 * away from the creator thread, so that this now fulfilled request cannot be
 * picked anymore by other threads.
 */
static inline bool
filt_wlturnstile_interlock_is_workq(struct kqworkloop *kqwl)
{
        return kqr_thread_requested_pending(&kqwl->kqwl_request);
}

static void
filt_wlupdate_inheritor(struct kqworkloop *kqwl, struct turnstile *ts,
    turnstile_update_flags_t flags)
{
        turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;
        workq_threadreq_t kqr = &kqwl->kqwl_request;

        /*
         * binding to the workq should always happen through
         * workq_kern_threadreq_update_inheritor()
         */
        assert(!filt_wlturnstile_interlock_is_workq(kqwl));

        if ((inheritor = kqwl->kqwl_owner)) {
                flags |= TURNSTILE_INHERITOR_THREAD;
        } else if ((inheritor = kqr_thread(kqr))) {
                flags |= TURNSTILE_INHERITOR_THREAD;
        }

        turnstile_update_inheritor(ts, inheritor, flags);
}

#define EVFILT_WORKLOOP_EFAULT_RETRY_COUNT 100
#define FILT_WLATTACH 0
#define FILT_WLTOUCH  1
#define FILT_WLDROP   2

__result_use_check
static int
filt_wlupdate(struct kqworkloop *kqwl, struct knote *kn,
    struct kevent_qos_s *kev, kq_index_t qos_index, int op)
{
        user_addr_t uaddr = CAST_USER_ADDR_T(kev->ext[EV_EXTIDX_WL_ADDR]);
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        thread_t cur_owner, new_owner, extra_thread_ref = THREAD_NULL;
        kq_index_t cur_override = THREAD_QOS_UNSPECIFIED;
        int efault_retry = EVFILT_WORKLOOP_EFAULT_RETRY_COUNT;
        int action = KQWL_UTQ_NONE, error = 0;
        bool wl_inheritor_updated = false, needs_wake = false;
        uint64_t kdata = kev->ext[EV_EXTIDX_WL_VALUE];
        uint64_t mask = kev->ext[EV_EXTIDX_WL_MASK];
        uint64_t udata = 0;
        struct turnstile *ts = TURNSTILE_NULL;

        filt_wllock(kqwl);

again:
        new_owner = cur_owner = kqwl->kqwl_owner;

        /*
         * Phase 1:
         *
         * If asked, load the uint64 value at the user provided address and compare
         * it against the passed in mask and expected value.
         *
         * If NOTE_WL_DISCOVER_OWNER is specified, translate the loaded name as
         * a thread reference.
         *
         * If NOTE_WL_END_OWNERSHIP is specified and the currently known owner is
         * the current thread, then end ownership.
         *
         * Lastly decide whether we need to perform a QoS update.
         */
        if (uaddr) {
                /*
                 * Until <rdar://problem/24999882> exists,
                 * disabling preemption copyin forces any
                 * vm_fault we encounter to fail.
                 */
                error = copyin_atomic64(uaddr, &udata);

                /*
                 * If we get EFAULT, drop locks, and retry.
                 * If we still get an error report it,
                 * else assume the memory has been faulted
                 * and attempt to copyin under lock again.
                 */
                switch (error) {
                case 0:
                        break;
                case EFAULT:
                        if (efault_retry-- > 0) {
                                filt_wlunlock(kqwl);
                                error = copyin_atomic64(uaddr, &udata);
                                filt_wllock(kqwl);
                                if (error == 0) {
                                        goto again;
                                }
                        }
                        OS_FALLTHROUGH;
                default:
                        goto out;
                }

                /* Update state as copied in.  */
                kev->ext[EV_EXTIDX_WL_VALUE] = udata;

                if ((udata & mask) != (kdata & mask)) {
                        error = ESTALE;
                } else if (kev->fflags & NOTE_WL_DISCOVER_OWNER) {
                        /*
                         * Decipher the owner port name, and translate accordingly.
                         * The low 2 bits were borrowed for other flags, so mask them off.
                         *
                         * Then attempt translation to a thread reference or fail.
                         */
                        mach_port_name_t name = (mach_port_name_t)udata & ~0x3;
                        if (name != MACH_PORT_NULL) {
                                name = ipc_entry_name_mask(name);
                                extra_thread_ref = port_name_to_thread(name,
                                    PORT_TO_THREAD_IN_CURRENT_TASK);
                                if (extra_thread_ref == THREAD_NULL) {
                                        error = EOWNERDEAD;
                                        goto out;
                                }
                                new_owner = extra_thread_ref;
                        }
                }
        }

        if ((kev->fflags & NOTE_WL_END_OWNERSHIP) && new_owner == current_thread()) {
                new_owner = THREAD_NULL;
        }

        if (error == 0) {
                if ((kev->fflags & NOTE_WL_THREAD_REQUEST) && (kev->flags & EV_DELETE)) {
                        action = KQWL_UTQ_SET_QOS_INDEX;
                } else if (qos_index && kqr->tr_kq_qos_index != qos_index) {
                        action = KQWL_UTQ_SET_QOS_INDEX;
                }

                if (op == FILT_WLTOUCH) {
                        /*
                         * Save off any additional fflags/data we just accepted
                         * But only keep the last round of "update" bits we acted on which helps
                         * debugging a lot.
                         */
                        kn->kn_sfflags &= ~NOTE_WL_UPDATES_MASK;
                        kn->kn_sfflags |= kev->fflags;
                        if (kev->fflags & NOTE_WL_SYNC_WAKE) {
                                needs_wake = (kn->kn_thread != THREAD_NULL);
                        }
                } else if (op == FILT_WLDROP) {
                        if ((kn->kn_sfflags & (NOTE_WL_SYNC_WAIT | NOTE_WL_SYNC_WAKE)) ==
                            NOTE_WL_SYNC_WAIT) {
                                /*
                                 * When deleting a SYNC_WAIT knote that hasn't been woken up
                                 * explicitly, issue a wake up.
                                 */
                                kn->kn_sfflags |= NOTE_WL_SYNC_WAKE;
                                needs_wake = (kn->kn_thread != THREAD_NULL);
                        }
                }
        }

        /*
         * Phase 2:
         *
         * Commit ownership and QoS changes if any, possibly wake up waiters
         */

        if (cur_owner == new_owner && action == KQWL_UTQ_NONE && !needs_wake) {
                goto out;
        }

        kqlock(kqwl);

        /* If already tracked as servicer, don't track as owner */
        if (new_owner == kqr_thread(kqr)) {
                new_owner = THREAD_NULL;
        }

        if (cur_owner != new_owner) {
                kqwl->kqwl_owner = new_owner;
                if (new_owner == extra_thread_ref) {
                        /* we just transfered this ref to kqwl_owner */
                        extra_thread_ref = THREAD_NULL;
                }
                cur_override = kqworkloop_override(kqwl);

                if (new_owner) {
                        /* override it before we drop the old */
                        if (cur_override != THREAD_QOS_UNSPECIFIED) {
                                thread_add_kevent_override(new_owner, cur_override);
                        }
                        if (kqr_thread_requested_pending(kqr)) {
                                if (action == KQWL_UTQ_NONE) {
                                        action = KQWL_UTQ_REDRIVE_EVENTS;
                                }
                        }
                } else {
                        if (!kqr_thread_requested(kqr) && kqr->tr_kq_wakeup) {
                                if (action == KQWL_UTQ_NONE) {
                                        action = KQWL_UTQ_REDRIVE_EVENTS;
                                }
                        }
                }
        }

        if (action != KQWL_UTQ_NONE) {
                kqworkloop_update_threads_qos(kqwl, action, qos_index);
        }

        ts = kqwl->kqwl_turnstile;
        if (cur_owner != new_owner && ts) {
                if (action == KQWL_UTQ_REDRIVE_EVENTS) {
                        /*
                         * Note that when action is KQWL_UTQ_REDRIVE_EVENTS,
                         * the code went through workq_kern_threadreq_initiate()
                         * and the workqueue has set the inheritor already
                         */
                        assert(filt_wlturnstile_interlock_is_workq(kqwl));
                } else if (filt_wlturnstile_interlock_is_workq(kqwl)) {
                        workq_kern_threadreq_lock(kqwl->kqwl_p);
                        workq_kern_threadreq_update_inheritor(kqwl->kqwl_p, kqr, new_owner,
                            ts, TURNSTILE_IMMEDIATE_UPDATE);
                        workq_kern_threadreq_unlock(kqwl->kqwl_p);
                        if (!filt_wlturnstile_interlock_is_workq(kqwl)) {
                                /*
                                 * If the workq is no longer the interlock, then
                                 * workq_kern_threadreq_update_inheritor() has finished a bind
                                 * and we need to fallback to the regular path.
                                 */
                                filt_wlupdate_inheritor(kqwl, ts, TURNSTILE_IMMEDIATE_UPDATE);
                        }
                        wl_inheritor_updated = true;
                } else {
                        filt_wlupdate_inheritor(kqwl, ts, TURNSTILE_IMMEDIATE_UPDATE);
                        wl_inheritor_updated = true;
                }

                /*
                 * We need a turnstile reference because we are dropping the interlock
                 * and the caller has not called turnstile_prepare.
                 */
                if (wl_inheritor_updated) {
                        turnstile_reference(ts);
                }
        }

        if (needs_wake && ts) {
                waitq_wakeup64_thread(&ts->ts_waitq, knote_filt_wev64(kn),
                    kn->kn_thread, THREAD_AWAKENED);
                if (op == FILT_WLATTACH || op == FILT_WLTOUCH) {
                        disable_preemption();
                        error = EPREEMPTDISABLED;
                }
        }

        kqunlock(kqwl);

out:
        /*
         * Phase 3:
         *
         * Unlock and cleanup various lingering references and things.
         */
        filt_wlunlock(kqwl);

#if CONFIG_WORKLOOP_DEBUG
        KQWL_HISTORY_WRITE_ENTRY(kqwl, {
                .updater = current_thread(),
                .servicer = kqr_thread(kqr), /* Note: racy */
                .old_owner = cur_owner,
                .new_owner = new_owner,

                .kev_ident  = kev->ident,
                .error      = (int16_t)error,
                .kev_flags  = kev->flags,
                .kev_fflags = kev->fflags,

                .kev_mask   = mask,
                .kev_value  = kdata,
                .in_value   = udata,
        });
#endif // CONFIG_WORKLOOP_DEBUG

        if (wl_inheritor_updated) {
                turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_NOT_HELD);
                turnstile_deallocate_safe(ts);
        }

        if (cur_owner && new_owner != cur_owner) {
                if (cur_override != THREAD_QOS_UNSPECIFIED) {
                        thread_drop_kevent_override(cur_owner);
                }
                thread_deallocate_safe(cur_owner);
        }
        if (extra_thread_ref) {
                thread_deallocate_safe(extra_thread_ref);
        }
        return error;
}

/*
 * Remembers the last updated that came in from userspace for debugging reasons.
 * - fflags is mirrored from the userspace kevent
 * - ext[i, i != VALUE] is mirrored from the userspace kevent
 * - ext[VALUE] is set to what the kernel loaded atomically
 * - data is set to the error if any
 */
static inline void
filt_wlremember_last_update(struct knote *kn, struct kevent_qos_s *kev,
    int error)
{
        kn->kn_fflags = kev->fflags;
        kn->kn_sdata = error;
        memcpy(kn->kn_ext, kev->ext, sizeof(kev->ext));
}

static int
filt_wlupdate_sync_ipc(struct kqworkloop *kqwl, struct knote *kn,
    struct kevent_qos_s *kev, int op)
{
        user_addr_t uaddr = (user_addr_t) kev->ext[EV_EXTIDX_WL_ADDR];
        uint64_t kdata = kev->ext[EV_EXTIDX_WL_VALUE];
        uint64_t mask  = kev->ext[EV_EXTIDX_WL_MASK];
        uint64_t udata = 0;
        int efault_retry = EVFILT_WORKLOOP_EFAULT_RETRY_COUNT;
        int error = 0;

        if (op == FILT_WLATTACH) {
                (void)kqueue_alloc_turnstile(&kqwl->kqwl_kqueue);
        } else if (uaddr == 0) {
                return 0;
        }

        filt_wllock(kqwl);

again:

        /*
         * Do the debounce thing, the lock serializing the state is the knote lock.
         */
        if (uaddr) {
                /*
                 * Until <rdar://problem/24999882> exists,
                 * disabling preemption copyin forces any
                 * vm_fault we encounter to fail.
                 */
                error = copyin_atomic64(uaddr, &udata);

                /*
                 * If we get EFAULT, drop locks, and retry.
                 * If we still get an error report it,
                 * else assume the memory has been faulted
                 * and attempt to copyin under lock again.
                 */
                switch (error) {
                case 0:
                        break;
                case EFAULT:
                        if (efault_retry-- > 0) {
                                filt_wlunlock(kqwl);
                                error = copyin_atomic64(uaddr, &udata);
                                filt_wllock(kqwl);
                                if (error == 0) {
                                        goto again;
                                }
                        }
                        OS_FALLTHROUGH;
                default:
                        goto out;
                }

                kev->ext[EV_EXTIDX_WL_VALUE] = udata;
                kn->kn_ext[EV_EXTIDX_WL_VALUE] = udata;

                if ((udata & mask) != (kdata & mask)) {
                        error = ESTALE;
                        goto out;
                }
        }

        if (op == FILT_WLATTACH) {
                error = filt_wlattach_sync_ipc(kn);
                if (error == 0) {
                        disable_preemption();
                        error = EPREEMPTDISABLED;
                }
        }

out:
        filt_wlunlock(kqwl);
        return error;
}

static int
filt_wlattach(struct knote *kn, struct kevent_qos_s *kev)
{
        struct kqueue *kq = knote_get_kq(kn);
        struct kqworkloop *kqwl = (struct kqworkloop *)kq;
        int error = 0, result = 0;
        kq_index_t qos_index = 0;

        if (__improbable((kq->kq_state & KQ_WORKLOOP) == 0)) {
                error = ENOTSUP;
                goto out;
        }

        uint32_t command = (kn->kn_sfflags & NOTE_WL_COMMANDS_MASK);
        switch (command) {
        case NOTE_WL_THREAD_REQUEST:
                if (kn->kn_id != kqwl->kqwl_dynamicid) {
                        error = EINVAL;
                        goto out;
                }
                qos_index = _pthread_priority_thread_qos(kn->kn_qos);
                if (qos_index == THREAD_QOS_UNSPECIFIED) {
                        error = ERANGE;
                        goto out;
                }
                if (kqwl->kqwl_request.tr_kq_qos_index) {
                        /*
                         * There already is a thread request, and well, you're only allowed
                         * one per workloop, so fail the attach.
                         */
                        error = EALREADY;
                        goto out;
                }
                break;
        case NOTE_WL_SYNC_WAIT:
        case NOTE_WL_SYNC_WAKE:
                if (kn->kn_id == kqwl->kqwl_dynamicid) {
                        error = EINVAL;
                        goto out;
                }
                if ((kn->kn_flags & EV_DISABLE) == 0) {
                        error = EINVAL;
                        goto out;
                }
                if (kn->kn_sfflags & NOTE_WL_END_OWNERSHIP) {
                        error = EINVAL;
                        goto out;
                }
                break;

        case NOTE_WL_SYNC_IPC:
                if ((kn->kn_flags & EV_DISABLE) == 0) {
                        error = EINVAL;
                        goto out;
                }
                if (kn->kn_sfflags & (NOTE_WL_UPDATE_QOS | NOTE_WL_DISCOVER_OWNER)) {
                        error = EINVAL;
                        goto out;
                }
                break;
        default:
                error = EINVAL;
                goto out;
        }

        if (command == NOTE_WL_SYNC_IPC) {
                error = filt_wlupdate_sync_ipc(kqwl, kn, kev, FILT_WLATTACH);
        } else {
                error = filt_wlupdate(kqwl, kn, kev, qos_index, FILT_WLATTACH);
        }

        if (error == EPREEMPTDISABLED) {
                error = 0;
                result = FILTER_THREADREQ_NODEFEER;
        }
out:
        if (error) {
                /* If userland wants ESTALE to be hidden, fail the attach anyway */
                if (error == ESTALE && (kn->kn_sfflags & NOTE_WL_IGNORE_ESTALE)) {
                        error = 0;
                }
                knote_set_error(kn, error);
                return result;
        }
        if (command == NOTE_WL_SYNC_WAIT) {
                return kevent_register_wait_prepare(kn, kev, result);
        }
        /* Just attaching the thread request successfully will fire it */
        if (command == NOTE_WL_THREAD_REQUEST) {
                /*
                 * Thread Request knotes need an explicit touch to be active again,
                 * so delivering an event needs to also consume it.
                 */
                kn->kn_flags |= EV_CLEAR;
                return result | FILTER_ACTIVE;
        }
        return result;
}

static void __dead2
filt_wlwait_continue(void *parameter, wait_result_t wr)
{
        struct _kevent_register *cont_args = parameter;
        struct kqworkloop *kqwl = cont_args->kqwl;

        kqlock(kqwl);
        if (filt_wlturnstile_interlock_is_workq(kqwl)) {
                workq_kern_threadreq_lock(kqwl->kqwl_p);
                turnstile_complete((uintptr_t)kqwl, &kqwl->kqwl_turnstile, NULL, TURNSTILE_WORKLOOPS);
                workq_kern_threadreq_unlock(kqwl->kqwl_p);
        } else {
                turnstile_complete((uintptr_t)kqwl, &kqwl->kqwl_turnstile, NULL, TURNSTILE_WORKLOOPS);
        }
        kqunlock(kqwl);

        turnstile_cleanup();

        if (wr == THREAD_INTERRUPTED) {
                cont_args->kev.flags |= EV_ERROR;
                cont_args->kev.data = EINTR;
        } else if (wr != THREAD_AWAKENED) {
                panic("Unexpected wait result: %d", wr);
        }

        kevent_register_wait_return(cont_args);
}

/*
 * Called with the workloop mutex held, most of the time never returns as it
 * calls filt_wlwait_continue through a continuation.
 */
static void __dead2
filt_wlpost_register_wait(struct uthread *uth, struct knote *kn,
    struct _kevent_register *cont_args)
{
        struct kqworkloop *kqwl = cont_args->kqwl;
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        struct turnstile *ts;
        bool workq_locked = false;

        kqlock_held(kqwl);

        if (filt_wlturnstile_interlock_is_workq(kqwl)) {
                workq_kern_threadreq_lock(kqwl->kqwl_p);
                workq_locked = true;
        }

        ts = turnstile_prepare((uintptr_t)kqwl, &kqwl->kqwl_turnstile,
            TURNSTILE_NULL, TURNSTILE_WORKLOOPS);

        if (workq_locked) {
                workq_kern_threadreq_update_inheritor(kqwl->kqwl_p,
                    &kqwl->kqwl_request, kqwl->kqwl_owner, ts,
                    TURNSTILE_DELAYED_UPDATE);
                if (!filt_wlturnstile_interlock_is_workq(kqwl)) {
                        /*
                         * if the interlock is no longer the workqueue lock,
                         * then we don't need to hold it anymore.
                         */
                        workq_kern_threadreq_unlock(kqwl->kqwl_p);
                        workq_locked = false;
                }
        }
        if (!workq_locked) {
                /*
                 * If the interlock is the workloop's, then it's our responsibility to
                 * call update_inheritor, so just do it.
                 */
                filt_wlupdate_inheritor(kqwl, ts, TURNSTILE_DELAYED_UPDATE);
        }

        thread_set_pending_block_hint(uth->uu_thread, kThreadWaitWorkloopSyncWait);
        waitq_assert_wait64(&ts->ts_waitq, knote_filt_wev64(kn),
            THREAD_ABORTSAFE, TIMEOUT_WAIT_FOREVER);

        if (workq_locked) {
                workq_kern_threadreq_unlock(kqwl->kqwl_p);
        }

        thread_t thread = kqwl->kqwl_owner ?: kqr_thread(kqr);
        if (thread) {
                thread_reference(thread);
        }

        kevent_register_wait_block(ts, thread, filt_wlwait_continue, cont_args);
}

/* called in stackshot context to report the thread responsible for blocking this thread */
void
kdp_workloop_sync_wait_find_owner(__assert_only thread_t thread,
    event64_t event, thread_waitinfo_t *waitinfo)
{
        extern zone_t thread_zone;
        struct knote *kn = (struct knote *)event;

        zone_require(knote_zone, kn);

        assert(kn->kn_thread == thread);

        struct kqueue *kq = knote_get_kq(kn);

        zone_require(kqworkloop_zone, kq);
        assert(kq->kq_state & KQ_WORKLOOP);

        struct kqworkloop *kqwl = (struct kqworkloop *)kq;
        workq_threadreq_t kqr = &kqwl->kqwl_request;

        thread_t kqwl_owner = kqwl->kqwl_owner;

        if (kqwl_owner != THREAD_NULL) {
                zone_require(thread_zone, kqwl_owner);
                waitinfo->owner = thread_tid(kqwl->kqwl_owner);
        } else if (kqr_thread_requested_pending(kqr)) {
                waitinfo->owner = STACKSHOT_WAITOWNER_THREQUESTED;
        } else if (kqr->tr_state >= WORKQ_TR_STATE_BINDING) {
                zone_require(thread_zone, kqr->tr_thread);
                waitinfo->owner = thread_tid(kqr->tr_thread);
        } else {
                waitinfo->owner = 0;
        }

        waitinfo->context = kqwl->kqwl_dynamicid;
}

static void
filt_wldetach(struct knote *kn)
{
        if (kn->kn_sfflags & NOTE_WL_SYNC_IPC) {
                filt_wldetach_sync_ipc(kn);
        } else if (kn->kn_thread) {
                kevent_register_wait_cleanup(kn);
        }
}

static int
filt_wlvalidate_kev_flags(struct knote *kn, struct kevent_qos_s *kev,
    thread_qos_t *qos_index)
{
        uint32_t new_commands = kev->fflags & NOTE_WL_COMMANDS_MASK;
        uint32_t sav_commands = kn->kn_sfflags & NOTE_WL_COMMANDS_MASK;

        if ((kev->fflags & NOTE_WL_DISCOVER_OWNER) && (kev->flags & EV_DELETE)) {
                return EINVAL;
        }
        if (kev->fflags & NOTE_WL_UPDATE_QOS) {
                if (kev->flags & EV_DELETE) {
                        return EINVAL;
                }
                if (sav_commands != NOTE_WL_THREAD_REQUEST) {
                        return EINVAL;
                }
                if (!(*qos_index = _pthread_priority_thread_qos(kev->qos))) {
                        return ERANGE;
                }
        }

        switch (new_commands) {
        case NOTE_WL_THREAD_REQUEST:
                /* thread requests can only update themselves */
                if (sav_commands != NOTE_WL_THREAD_REQUEST) {
                        return EINVAL;
                }
                break;

        case NOTE_WL_SYNC_WAIT:
                if (kev->fflags & NOTE_WL_END_OWNERSHIP) {
                        return EINVAL;
                }
                goto sync_checks;

        case NOTE_WL_SYNC_WAKE:
sync_checks:
                if (!(sav_commands & (NOTE_WL_SYNC_WAIT | NOTE_WL_SYNC_WAKE))) {
                        return EINVAL;
                }
                if ((kev->flags & (EV_ENABLE | EV_DELETE)) == EV_ENABLE) {
                        return EINVAL;
                }
                break;

        case NOTE_WL_SYNC_IPC:
                if (sav_commands != NOTE_WL_SYNC_IPC) {
                        return EINVAL;
                }
                if ((kev->flags & (EV_ENABLE | EV_DELETE)) == EV_ENABLE) {
                        return EINVAL;
                }
                break;

        default:
                return EINVAL;
        }
        return 0;
}

static int
filt_wltouch(struct knote *kn, struct kevent_qos_s *kev)
{
        struct kqworkloop *kqwl = (struct kqworkloop *)knote_get_kq(kn);
        thread_qos_t qos_index = THREAD_QOS_UNSPECIFIED;
        int result = 0;

        int error = filt_wlvalidate_kev_flags(kn, kev, &qos_index);
        if (error) {
                goto out;
        }

        uint32_t command = kev->fflags & NOTE_WL_COMMANDS_MASK;
        if (command == NOTE_WL_SYNC_IPC) {
                error = filt_wlupdate_sync_ipc(kqwl, kn, kev, FILT_WLTOUCH);
        } else {
                error = filt_wlupdate(kqwl, kn, kev, qos_index, FILT_WLTOUCH);
                filt_wlremember_last_update(kn, kev, error);
        }
        if (error == EPREEMPTDISABLED) {
                error = 0;
                result = FILTER_THREADREQ_NODEFEER;
        }

out:
        if (error) {
                if (error == ESTALE && (kev->fflags & NOTE_WL_IGNORE_ESTALE)) {
                        /* If userland wants ESTALE to be hidden, do not activate */
                        return result;
                }
                kev->flags |= EV_ERROR;
                kev->data = error;
                return result;
        }
        if (command == NOTE_WL_SYNC_WAIT && !(kn->kn_sfflags & NOTE_WL_SYNC_WAKE)) {
                return kevent_register_wait_prepare(kn, kev, result);
        }
        /* Just touching the thread request successfully will fire it */
        if (command == NOTE_WL_THREAD_REQUEST) {
                if (kev->fflags & NOTE_WL_UPDATE_QOS) {
                        result |= FILTER_UPDATE_REQ_QOS;
                }
                result |= FILTER_ACTIVE;
        }
        return result;
}

static bool
filt_wlallow_drop(struct knote *kn, struct kevent_qos_s *kev)
{
        struct kqworkloop *kqwl = (struct kqworkloop *)knote_get_kq(kn);

        int error = filt_wlvalidate_kev_flags(kn, kev, NULL);
        if (error) {
                goto out;
        }

        uint32_t command = (kev->fflags & NOTE_WL_COMMANDS_MASK);
        if (command == NOTE_WL_SYNC_IPC) {
                error = filt_wlupdate_sync_ipc(kqwl, kn, kev, FILT_WLDROP);
        } else {
                error = filt_wlupdate(kqwl, kn, kev, 0, FILT_WLDROP);
                filt_wlremember_last_update(kn, kev, error);
        }
        assert(error != EPREEMPTDISABLED);

out:
        if (error) {
                if (error == ESTALE && (kev->fflags & NOTE_WL_IGNORE_ESTALE)) {
                        return false;
                }
                kev->flags |= EV_ERROR;
                kev->data = error;
                return false;
        }
        return true;
}

static int
filt_wlprocess(struct knote *kn, struct kevent_qos_s *kev)
{
        struct kqworkloop *kqwl = (struct kqworkloop *)knote_get_kq(kn);
        int rc = 0;

        assert(kn->kn_sfflags & NOTE_WL_THREAD_REQUEST);

        kqlock(kqwl);

        if (kqwl->kqwl_owner) {
                /*
                 * <rdar://problem/33584321> userspace sometimes due to events being
                 * delivered but not triggering a drain session can cause a process
                 * of the thread request knote.
                 *
                 * When that happens, the automatic deactivation due to process
                 * would swallow the event, so we have to activate the knote again.
                 */
                knote_activate(kqwl, kn, FILTER_ACTIVE);
        } else {
#if DEBUG || DEVELOPMENT
                if (kevent_debug_flags & KEVENT_PANIC_ON_NON_ENQUEUED_PROCESS) {
                        /*
                         * see src/queue_internal.h in libdispatch
                         */
#define DISPATCH_QUEUE_ENQUEUED 0x1ull
                        user_addr_t addr = CAST_USER_ADDR_T(kn->kn_ext[EV_EXTIDX_WL_ADDR]);
                        task_t t = current_task();
                        uint64_t val;
                        if (addr && task_is_active(t) && !task_is_halting(t) &&
                            copyin_atomic64(addr, &val) == 0 &&
                            val && (val & DISPATCH_QUEUE_ENQUEUED) == 0 &&
                            (val >> 48) != 0xdead && (val >> 48) != 0 && (val >> 48) != 0xffff) {
                                panic("kevent: workloop %#016llx is not enqueued "
                                    "(kn:%p dq_state:%#016llx kev.dq_state:%#016llx)",
                                    kn->kn_udata, kn, val, kn->kn_ext[EV_EXTIDX_WL_VALUE]);
                        }
                }
#endif
                knote_fill_kevent(kn, kev, 0);
                kev->fflags = kn->kn_sfflags;
                rc |= FILTER_ACTIVE;
        }

        kqunlock(kqwl);

        if (rc & FILTER_ACTIVE) {
                workq_thread_set_max_qos(kqwl->kqwl_p, &kqwl->kqwl_request);
        }
        return rc;
}

SECURITY_READ_ONLY_EARLY(static struct filterops) workloop_filtops = {
        .f_extended_codes = true,
        .f_attach  = filt_wlattach,
        .f_detach  = filt_wldetach,
        .f_event   = filt_bad_event,
        .f_touch   = filt_wltouch,
        .f_process = filt_wlprocess,
        .f_allow_drop = filt_wlallow_drop,
        .f_post_register_wait = filt_wlpost_register_wait,
};

#pragma mark - kqueues allocation and deallocation

/*!
 * @enum kqworkloop_dealloc_flags_t
 *
 * @brief
 * Flags that alter kqworkloop_dealloc() behavior.
 *
 * @const KQWL_DEALLOC_NONE
 * Convenient name for "no flags".
 *
 * @const KQWL_DEALLOC_SKIP_HASH_REMOVE
 * Do not remove the workloop fromt he hash table.
 * This is used for process tear-down codepaths as the workloops have been
 * removed by the caller already.
 */
OS_OPTIONS(kqworkloop_dealloc_flags, unsigned,
    KQWL_DEALLOC_NONE               = 0x0000,
    KQWL_DEALLOC_SKIP_HASH_REMOVE   = 0x0001,
    );

static void
kqworkloop_dealloc(struct kqworkloop *, kqworkloop_dealloc_flags_t, uint32_t);

OS_NOINLINE OS_COLD OS_NORETURN
static void
kqworkloop_retain_panic(struct kqworkloop *kqwl, uint32_t previous)
{
        if (previous == 0) {
                panic("kq(%p) resurrection", kqwl);
        } else {
                panic("kq(%p) retain overflow", kqwl);
        }
}

OS_NOINLINE OS_COLD OS_NORETURN
static void
kqworkloop_release_panic(struct kqworkloop *kqwl)
{
        panic("kq(%p) over-release", kqwl);
}

OS_ALWAYS_INLINE
static inline bool
kqworkloop_try_retain(struct kqworkloop *kqwl)
{
        uint32_t old_ref, new_ref;
        os_atomic_rmw_loop(&kqwl->kqwl_retains, old_ref, new_ref, relaxed, {
                if (__improbable(old_ref == 0)) {
                        os_atomic_rmw_loop_give_up(return false);
                }
                if (__improbable(old_ref >= KQ_WORKLOOP_RETAINS_MAX)) {
                        kqworkloop_retain_panic(kqwl, old_ref);
                }
                new_ref = old_ref + 1;
        });
        return true;
}

OS_ALWAYS_INLINE
static inline void
kqworkloop_retain(struct kqworkloop *kqwl)
{
        uint32_t previous = os_atomic_inc_orig(&kqwl->kqwl_retains, relaxed);
        if (__improbable(previous == 0 || previous >= KQ_WORKLOOP_RETAINS_MAX)) {
                kqworkloop_retain_panic(kqwl, previous);
        }
}

OS_ALWAYS_INLINE
static inline void
kqueue_retain(kqueue_t kqu)
{
        if (kqu.kq->kq_state & KQ_DYNAMIC) {
                kqworkloop_retain(kqu.kqwl);
        }
}

OS_ALWAYS_INLINE
static inline void
kqworkloop_release_live(struct kqworkloop *kqwl)
{
        uint32_t refs = os_atomic_dec_orig(&kqwl->kqwl_retains, relaxed);
        if (__improbable(refs <= 1)) {
                kqworkloop_release_panic(kqwl);
        }
}

OS_ALWAYS_INLINE
static inline void
kqueue_release_live(kqueue_t kqu)
{
        if (kqu.kq->kq_state & KQ_DYNAMIC) {
                kqworkloop_release_live(kqu.kqwl);
        }
}

OS_ALWAYS_INLINE
static inline void
kqworkloop_release(struct kqworkloop *kqwl)
{
        uint32_t refs = os_atomic_dec_orig(&kqwl->kqwl_retains, relaxed);

        if (__improbable(refs <= 1)) {
                kqworkloop_dealloc(kqwl, KQWL_DEALLOC_NONE, refs - 1);
        }
}

OS_ALWAYS_INLINE
static inline void
kqueue_release(kqueue_t kqu)
{
        if (kqu.kq->kq_state & KQ_DYNAMIC) {
                kqworkloop_release(kqu.kqwl);
        }
}

/*!
 * @function kqueue_destroy
 *
 * @brief
 * Common part to all kqueue dealloc functions.
 */
OS_NOINLINE
static void
kqueue_destroy(kqueue_t kqu, zone_t zone)
{
        /*
         * waitq_set_deinit() remove the KQ's waitq set from
         * any select sets to which it may belong.
         *
         * The order of these deinits matter: before waitq_set_deinit() returns,
         * waitq_set__CALLING_PREPOST_HOOK__ may be called and it will take the
         * kq_lock.
         */
        waitq_set_deinit(&kqu.kq->kq_wqs);
        lck_spin_destroy(&kqu.kq->kq_lock, &kq_lck_grp);

        zfree(zone, kqu.kq);
}

/*!
 * @function kqueue_init
 *
 * @brief
 * Common part to all kqueue alloc functions.
 */
static kqueue_t
kqueue_init(kqueue_t kqu, waitq_set_prepost_hook_t *hook, int policy)
{
        waitq_set_init(&kqu.kq->kq_wqs, policy, NULL, hook);
        lck_spin_init(&kqu.kq->kq_lock, &kq_lck_grp, LCK_ATTR_NULL);
        return kqu;
}

#pragma mark kqfile allocation and deallocation

/*!
 * @function kqueue_dealloc
 *
 * @brief
 * Detach all knotes from a kqfile and free it.
 *
 * @discussion
 * We walk each list looking for knotes referencing this
 * this kqueue.  If we find one, we try to drop it.  But
 * if we fail to get a drop reference, that will wait
 * until it is dropped.  So, we can just restart again
 * safe in the assumption that the list will eventually
 * not contain any more references to this kqueue (either
 * we dropped them all, or someone else did).
 *
 * Assumes no new events are being added to the kqueue.
 * Nothing locked on entry or exit.
 */
void
kqueue_dealloc(struct kqueue *kq)
{
        KNOTE_LOCK_CTX(knlc);
        struct proc *p = kq->kq_p;
        struct filedesc *fdp = p->p_fd;
        struct knote *kn;

        assert(kq && (kq->kq_state & (KQ_WORKLOOP | KQ_WORKQ)) == 0);

        proc_fdlock(p);
        for (int i = 0; i < fdp->fd_knlistsize; i++) {
                kn = SLIST_FIRST(&fdp->fd_knlist[i]);
                while (kn != NULL) {
                        if (kq == knote_get_kq(kn)) {
                                kqlock(kq);
                                proc_fdunlock(p);
                                if (knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
                                        knote_drop(kq, kn, &knlc);
                                }
                                proc_fdlock(p);
                                /* start over at beginning of list */
                                kn = SLIST_FIRST(&fdp->fd_knlist[i]);
                                continue;
                        }
                        kn = SLIST_NEXT(kn, kn_link);
                }
        }

        knhash_lock(fdp);
        proc_fdunlock(p);

        if (fdp->fd_knhashmask != 0) {
                for (int i = 0; i < (int)fdp->fd_knhashmask + 1; i++) {
                        kn = SLIST_FIRST(&fdp->fd_knhash[i]);
                        while (kn != NULL) {
                                if (kq == knote_get_kq(kn)) {
                                        kqlock(kq);
                                        knhash_unlock(fdp);
                                        if (knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
                                                knote_drop(kq, kn, &knlc);
                                        }
                                        knhash_lock(fdp);
                                        /* start over at beginning of list */
                                        kn = SLIST_FIRST(&fdp->fd_knhash[i]);
                                        continue;
                                }
                                kn = SLIST_NEXT(kn, kn_link);
                        }
                }
        }
        knhash_unlock(fdp);

        kqueue_destroy(kq, kqfile_zone);
}

/*!
 * @function kqueue_alloc
 *
 * @brief
 * Allocate a kqfile.
 */
struct kqueue *
kqueue_alloc(struct proc *p)
{
        struct kqfile *kqf;

        /*
         * kqfiles are created with kqueue() so we need to wait for
         * the first kevent syscall to know which bit among
         * KQ_KEV_{32,64,QOS} will be set in kqf_state
         */
        kqf = zalloc_flags(kqfile_zone, Z_WAITOK | Z_ZERO);
        kqf->kqf_p = p;
        TAILQ_INIT_AFTER_BZERO(&kqf->kqf_queue);
        TAILQ_INIT_AFTER_BZERO(&kqf->kqf_suppressed);

        return kqueue_init(kqf, NULL, SYNC_POLICY_FIFO | SYNC_POLICY_PREPOST).kq;
}

/*!
 * @function kqueue_internal
 *
 * @brief
 * Core implementation for kqueue and guarded_kqueue_np()
 */
int
kqueue_internal(struct proc *p, fp_allocfn_t fp_zalloc, void *cra, int32_t *retval)
{
        struct kqueue *kq;
        struct fileproc *fp;
        int fd, error;

        error = falloc_withalloc(p, &fp, &fd, vfs_context_current(), fp_zalloc, cra);
        if (error) {
                return error;
        }

        kq = kqueue_alloc(p);
        if (kq == NULL) {
                fp_free(p, fd, fp);
                return ENOMEM;
        }

        fp->f_flag = FREAD | FWRITE;
        fp->f_ops = &kqueueops;
        fp->f_data = kq;
        fp->f_lflags |= FG_CONFINED;

        proc_fdlock(p);
        *fdflags(p, fd) |= UF_EXCLOSE | UF_FORKCLOSE;
        procfdtbl_releasefd(p, fd, NULL);
        fp_drop(p, fd, fp, 1);
        proc_fdunlock(p);

        *retval = fd;
        return error;
}

/*!
 * @function kqueue
 *
 * @brief
 * The kqueue syscall.
 */
int
kqueue(struct proc *p, __unused struct kqueue_args *uap, int32_t *retval)
{
        return kqueue_internal(p, fileproc_alloc_init, NULL, retval);
}

#pragma mark kqworkq allocation and deallocation

/*!
 * @function kqworkq_dealloc
 *
 * @brief
 * Deallocates a workqueue kqueue.
 *
 * @discussion
 * This only happens at process death, or for races with concurrent
 * kevent_get_kqwq calls, hence we don't have to care about knotes referencing
 * this kqueue, either there are none, or someone else took care of them.
 */
void
kqworkq_dealloc(struct kqworkq *kqwq)
{
        kqueue_destroy(kqwq, kqworkq_zone);
}

/*!
 * @function kqworkq_alloc
 *
 * @brief
 * Allocates a workqueue kqueue.
 *
 * @discussion
 * This is the slow path of kevent_get_kqwq.
 * This takes care of making sure procs have a single workq kqueue.
 */
OS_NOINLINE
static struct kqworkq *
kqworkq_alloc(struct proc *p, unsigned int flags)
{
        struct kqworkq *kqwq, *tmp;

        kqwq = zalloc_flags(kqworkq_zone, Z_WAITOK | Z_ZERO);

        assert((flags & KEVENT_FLAG_LEGACY32) == 0);
        if (flags & KEVENT_FLAG_LEGACY64) {
                kqwq->kqwq_state = KQ_WORKQ | KQ_KEV64;
        } else {
                kqwq->kqwq_state = KQ_WORKQ | KQ_KEV_QOS;
        }
        kqwq->kqwq_p = p;

        for (int i = 0; i < KQWQ_NBUCKETS; i++) {
                TAILQ_INIT_AFTER_BZERO(&kqwq->kqwq_queue[i]);
                TAILQ_INIT_AFTER_BZERO(&kqwq->kqwq_suppressed[i]);
        }
        for (int i = 0; i < KQWQ_NBUCKETS; i++) {
                /*
                 * Because of how the bucketized system works, we mix overcommit
                 * sources with not overcommit: each time we move a knote from
                 * one bucket to the next due to overrides, we'd had to track
                 * overcommitness, and it's really not worth it in the workloop
                 * enabled world that track this faithfully.
                 *
                 * Incidentally, this behaves like the original manager-based
                 * kqwq where event delivery always happened (hence is
                 * "overcommit")
                 */
                kqwq->kqwq_request[i].tr_state = WORKQ_TR_STATE_IDLE;
                kqwq->kqwq_request[i].tr_flags = WORKQ_TR_FLAG_KEVENT;
                if (i != KQWQ_QOS_MANAGER) {
                        kqwq->kqwq_request[i].tr_flags |= WORKQ_TR_FLAG_OVERCOMMIT;
                }
                kqwq->kqwq_request[i].tr_kq_qos_index = (kq_index_t)i;
        }

        kqueue_init(kqwq, &kqwq->kqwq_waitq_hook, SYNC_POLICY_FIFO);

        if (!os_atomic_cmpxchgv(&p->p_fd->fd_wqkqueue, NULL, kqwq, &tmp, release)) {
                kqworkq_dealloc(kqwq);
                return tmp;
        }

        return kqwq;
}

#pragma mark kqworkloop allocation and deallocation

#define KQ_HASH(val, mask)  (((val) ^ (val >> 8)) & (mask))
#define CONFIG_KQ_HASHSIZE  CONFIG_KN_HASHSIZE

OS_ALWAYS_INLINE
static inline void
kqhash_lock(struct filedesc *fdp)
{
        lck_mtx_lock_spin_always(&fdp->fd_kqhashlock);
}

OS_ALWAYS_INLINE
static inline void
kqhash_unlock(struct filedesc *fdp)
{
        lck_mtx_unlock(&fdp->fd_kqhashlock);
}

OS_ALWAYS_INLINE
static inline void
kqworkloop_hash_insert_locked(struct filedesc *fdp, kqueue_id_t id,
    struct kqworkloop *kqwl)
{
        struct kqwllist *list = &fdp->fd_kqhash[KQ_HASH(id, fdp->fd_kqhashmask)];
        LIST_INSERT_HEAD(list, kqwl, kqwl_hashlink);
}

OS_ALWAYS_INLINE
static inline struct kqworkloop *
kqworkloop_hash_lookup_locked(struct filedesc *fdp, kqueue_id_t id)
{
        struct kqwllist *list = &fdp->fd_kqhash[KQ_HASH(id, fdp->fd_kqhashmask)];
        struct kqworkloop *kqwl;

        LIST_FOREACH(kqwl, list, kqwl_hashlink) {
                if (kqwl->kqwl_dynamicid == id) {
                        return kqwl;
                }
        }
        return NULL;
}

static struct kqworkloop *
kqworkloop_hash_lookup_and_retain(struct filedesc *fdp, kqueue_id_t kq_id)
{
        struct kqworkloop *kqwl = NULL;

        kqhash_lock(fdp);
        if (__probable(fdp->fd_kqhash)) {
                kqwl = kqworkloop_hash_lookup_locked(fdp, kq_id);
                if (kqwl && !kqworkloop_try_retain(kqwl)) {
                        kqwl = NULL;
                }
        }
        kqhash_unlock(fdp);
        return kqwl;
}

OS_NOINLINE
static void
kqworkloop_hash_init(struct filedesc *fdp)
{
        struct kqwllist *alloc_hash;
        u_long alloc_mask;

        kqhash_unlock(fdp);
        alloc_hash = hashinit(CONFIG_KQ_HASHSIZE, M_KQUEUE, &alloc_mask);
        kqhash_lock(fdp);

        /* See if we won the race */
        if (__probable(fdp->fd_kqhashmask == 0)) {
                fdp->fd_kqhash = alloc_hash;
                fdp->fd_kqhashmask = alloc_mask;
        } else {
                kqhash_unlock(fdp);
                hashdestroy(alloc_hash, M_KQUEUE, alloc_mask);
                kqhash_lock(fdp);
        }
}

/*!
 * @function kqworkloop_dealloc
 *
 * @brief
 * Deallocates a workloop kqueue.
 *
 * @discussion
 * Knotes hold references on the workloop, so we can't really reach this
 * function unless all of these are already gone.
 *
 * Nothing locked on entry or exit.
 *
 * @param flags
 * Unless KQWL_DEALLOC_SKIP_HASH_REMOVE is set, the workloop is removed
 * from its hash table.
 *
 * @param current_ref
 * This function is also called to undo a kqworkloop_alloc in case of
 * allocation races, expected_ref is the current refcount that is expected
 * on the workloop object, usually 0, and 1 when a dealloc race is resolved.
 */
static void
kqworkloop_dealloc(struct kqworkloop *kqwl, kqworkloop_dealloc_flags_t flags,
    uint32_t current_ref)
{
        thread_t cur_owner;

        if (__improbable(current_ref > 1)) {
                kqworkloop_release_panic(kqwl);
        }
        assert(kqwl->kqwl_retains == current_ref);

        /* pair with kqunlock() and other kq locks */
        os_atomic_thread_fence(acquire);

        cur_owner = kqwl->kqwl_owner;
        if (cur_owner) {
                if (kqworkloop_override(kqwl) != THREAD_QOS_UNSPECIFIED) {
                        thread_drop_kevent_override(cur_owner);
                }
                thread_deallocate(cur_owner);
                kqwl->kqwl_owner = THREAD_NULL;
        }

        if (kqwl->kqwl_state & KQ_HAS_TURNSTILE) {
                struct turnstile *ts;
                turnstile_complete((uintptr_t)kqwl, &kqwl->kqwl_turnstile,
                    &ts, TURNSTILE_WORKLOOPS);
                turnstile_cleanup();
                turnstile_deallocate(ts);
        }

        if ((flags & KQWL_DEALLOC_SKIP_HASH_REMOVE) == 0) {
                struct filedesc *fdp = kqwl->kqwl_p->p_fd;

                kqhash_lock(fdp);
                LIST_REMOVE(kqwl, kqwl_hashlink);
                kqhash_unlock(fdp);
        }

        assert(TAILQ_EMPTY(&kqwl->kqwl_suppressed));
        assert(kqwl->kqwl_owner == THREAD_NULL);
        assert(kqwl->kqwl_turnstile == TURNSTILE_NULL);

        lck_spin_destroy(&kqwl->kqwl_statelock, &kq_lck_grp);
        kqueue_destroy(kqwl, kqworkloop_zone);
}

/*!
 * @function kqworkloop_alloc
 *
 * @brief
 * Allocates a workloop kqueue.
 */
static void
kqworkloop_init(struct kqworkloop *kqwl, proc_t p,
    kqueue_id_t id, workq_threadreq_param_t *trp)
{
        kqwl->kqwl_state     = KQ_WORKLOOP | KQ_DYNAMIC | KQ_KEV_QOS;
        kqwl->kqwl_retains   = 1; /* donate a retain to creator */
        kqwl->kqwl_dynamicid = id;
        kqwl->kqwl_p         = p;
        if (trp) {
                kqwl->kqwl_params = trp->trp_value;
        }

        workq_tr_flags_t tr_flags = WORKQ_TR_FLAG_WORKLOOP;
        if (trp) {
                if (trp->trp_flags & TRP_PRIORITY) {
                        tr_flags |= WORKQ_TR_FLAG_WL_OUTSIDE_QOS;
                }
                if (trp->trp_flags) {
                        tr_flags |= WORKQ_TR_FLAG_WL_PARAMS;
                }
        }
        kqwl->kqwl_request.tr_state = WORKQ_TR_STATE_IDLE;
        kqwl->kqwl_request.tr_flags = tr_flags;

        for (int i = 0; i < KQWL_NBUCKETS; i++) {
                TAILQ_INIT_AFTER_BZERO(&kqwl->kqwl_queue[i]);
        }
        TAILQ_INIT_AFTER_BZERO(&kqwl->kqwl_suppressed);

        lck_spin_init(&kqwl->kqwl_statelock, &kq_lck_grp, LCK_ATTR_NULL);

        kqueue_init(kqwl, &kqwl->kqwl_waitq_hook, SYNC_POLICY_FIFO);
}

/*!
 * @function kqworkloop_get_or_create
 *
 * @brief
 * Wrapper around kqworkloop_alloc that handles the uniquing of workloops.
 *
 * @returns
 * 0:      success
 * EINVAL: invalid parameters
 * EEXIST: KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST is set and a collision exists.
 * ENOENT: KEVENT_FLAG_DYNAMIC_KQ_MUST_EXIST is set and the entry wasn't found.
 * ENOMEM: allocation failed
 */
static int
kqworkloop_get_or_create(struct proc *p, kqueue_id_t id,
    workq_threadreq_param_t *trp, unsigned int flags, struct kqworkloop **kqwlp)
{
        struct filedesc *fdp = p->p_fd;
        struct kqworkloop *alloc_kqwl = NULL;
        struct kqworkloop *kqwl = NULL;
        int error = 0;

        assert(!trp || (flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST));

        if (id == 0 || id == (kqueue_id_t)-1) {
                return EINVAL;
        }

        for (;;) {
                kqhash_lock(fdp);
                if (__improbable(fdp->fd_kqhash == NULL)) {
                        kqworkloop_hash_init(fdp);
                }

                kqwl = kqworkloop_hash_lookup_locked(fdp, id);
                if (kqwl) {
                        if (__improbable(flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST)) {
                                /*
                                 * If MUST_NOT_EXIST was passed, even if we would have failed
                                 * the try_retain, it could have gone the other way, and
                                 * userspace can't tell. Let'em fix their race.
                                 */
                                error = EEXIST;
                                break;
                        }

                        if (__probable(kqworkloop_try_retain(kqwl))) {
                                /*
                                 * This is a valid live workloop !
                                 */
                                *kqwlp = kqwl;
                                error = 0;
                                break;
                        }
                }

                if (__improbable(flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_EXIST)) {
                        error = ENOENT;
                        break;
                }

                /*
                 * We didn't find what we were looking for.
                 *
                 * If this is the second time we reach this point (alloc_kqwl != NULL),
                 * then we're done.
                 *
                 * If this is the first time we reach this point (alloc_kqwl == NULL),
                 * then try to allocate one without blocking.
                 */
                if (__probable(alloc_kqwl == NULL)) {
                        alloc_kqwl = zalloc_flags(kqworkloop_zone, Z_NOWAIT | Z_ZERO);
                }
                if (__probable(alloc_kqwl)) {
                        kqworkloop_init(alloc_kqwl, p, id, trp);
                        kqworkloop_hash_insert_locked(fdp, id, alloc_kqwl);
                        kqhash_unlock(fdp);
                        *kqwlp = alloc_kqwl;
                        return 0;
                }

                /*
                 * We have to block to allocate a workloop, drop the lock,
                 * allocate one, but then we need to retry lookups as someone
                 * else could race with us.
                 */
                kqhash_unlock(fdp);

                alloc_kqwl = zalloc_flags(kqworkloop_zone, Z_WAITOK | Z_ZERO);
        }

        kqhash_unlock(fdp);

        if (__improbable(alloc_kqwl)) {
                zfree(kqworkloop_zone, alloc_kqwl);
        }

        return error;
}

#pragma mark - knotes

static int
filt_no_attach(struct knote *kn, __unused struct kevent_qos_s *kev)
{
        knote_set_error(kn, ENOTSUP);
        return 0;
}

static void
filt_no_detach(__unused struct knote *kn)
{
}

static int __dead2
filt_bad_event(struct knote *kn, long hint)
{
        panic("%s[%d](%p, %ld)", __func__, kn->kn_filter, kn, hint);
}

static int __dead2
filt_bad_touch(struct knote *kn, struct kevent_qos_s *kev)
{
        panic("%s[%d](%p, %p)", __func__, kn->kn_filter, kn, kev);
}

static int __dead2
filt_bad_process(struct knote *kn, struct kevent_qos_s *kev)
{
        panic("%s[%d](%p, %p)", __func__, kn->kn_filter, kn, kev);
}

/*
 * knotes_dealloc - detach all knotes for the process and drop them
 *
 *              Called with proc_fdlock held.
 *              Returns with it locked.
 *              May drop it temporarily.
 *              Process is in such a state that it will not try to allocate
 *              any more knotes during this process (stopped for exit or exec).
 */
void
knotes_dealloc(proc_t p)
{
        struct filedesc *fdp = p->p_fd;
        struct kqueue *kq;
        struct knote *kn;
        struct  klist *kn_hash = NULL;
        u_long kn_hashmask;
        int i;

        /* Close all the fd-indexed knotes up front */
        if (fdp->fd_knlistsize > 0) {
                for (i = 0; i < fdp->fd_knlistsize; i++) {
                        while ((kn = SLIST_FIRST(&fdp->fd_knlist[i])) != NULL) {
                                kq = knote_get_kq(kn);
                                kqlock(kq);
                                proc_fdunlock(p);
                                knote_drop(kq, kn, NULL);
                                proc_fdlock(p);
                        }
                }
                /* free the table */
                kheap_free(KM_KQUEUE, fdp->fd_knlist,
                    fdp->fd_knlistsize * sizeof(struct klist *));
        }
        fdp->fd_knlistsize = 0;

        knhash_lock(fdp);
        proc_fdunlock(p);

        /* Clean out all the hashed knotes as well */
        if (fdp->fd_knhashmask != 0) {
                for (i = 0; i <= (int)fdp->fd_knhashmask; i++) {
                        while ((kn = SLIST_FIRST(&fdp->fd_knhash[i])) != NULL) {
                                kq = knote_get_kq(kn);
                                kqlock(kq);
                                knhash_unlock(fdp);
                                knote_drop(kq, kn, NULL);
                                knhash_lock(fdp);
                        }
                }
                kn_hash = fdp->fd_knhash;
                kn_hashmask = fdp->fd_knhashmask;
                fdp->fd_knhashmask = 0;
                fdp->fd_knhash = NULL;
        }

        knhash_unlock(fdp);

        if (kn_hash) {
                hashdestroy(kn_hash, M_KQUEUE, kn_hashmask);
        }

        proc_fdlock(p);
}

/*
 * kqworkloops_dealloc - rebalance retains on kqworkloops created with
 * scheduling parameters
 *
 *              Called with proc_fdlock held.
 *              Returns with it locked.
 *              Process is in such a state that it will not try to allocate
 *              any more knotes during this process (stopped for exit or exec).
 */
void
kqworkloops_dealloc(proc_t p)
{
        struct filedesc *fdp = p->p_fd;
        struct kqworkloop *kqwl, *kqwln;
        struct kqwllist tofree;

        if (!(fdp->fd_flags & FD_WORKLOOP)) {
                return;
        }

        kqhash_lock(fdp);

        if (fdp->fd_kqhashmask == 0) {
                kqhash_unlock(fdp);
                return;
        }

        LIST_INIT(&tofree);

        for (size_t i = 0; i <= fdp->fd_kqhashmask; i++) {
                LIST_FOREACH_SAFE(kqwl, &fdp->fd_kqhash[i], kqwl_hashlink, kqwln) {
                        /*
                         * kqworkloops that have scheduling parameters have an
                         * implicit retain from kqueue_workloop_ctl that needs
                         * to be balanced on process exit.
                         */
                        assert(kqwl->kqwl_params);
                        LIST_REMOVE(kqwl, kqwl_hashlink);
                        LIST_INSERT_HEAD(&tofree, kqwl, kqwl_hashlink);
                }
        }

        kqhash_unlock(fdp);

        LIST_FOREACH_SAFE(kqwl, &tofree, kqwl_hashlink, kqwln) {
                kqworkloop_dealloc(kqwl, KQWL_DEALLOC_SKIP_HASH_REMOVE, 1);
        }
}

static int
kevent_register_validate_priority(struct kqueue *kq, struct knote *kn,
    struct kevent_qos_s *kev)
{
        /* We don't care about the priority of a disabled or deleted knote */
        if (kev->flags & (EV_DISABLE | EV_DELETE)) {
                return 0;
        }

        if (kq->kq_state & KQ_WORKLOOP) {
                /*
                 * Workloops need valid priorities with a QOS (excluding manager) for
                 * any enabled knote.
                 *
                 * When it is pre-existing, just make sure it has a valid QoS as
                 * kevent_register() will not use the incoming priority (filters who do
                 * have the responsibility to validate it again, see filt_wltouch).
                 *
                 * If the knote is being made, validate the incoming priority.
                 */
                if (!_pthread_priority_thread_qos(kn ? kn->kn_qos : kev->qos)) {
                        return ERANGE;
                }
        }

        return 0;
}

/*
 * Prepare a filter for waiting after register.
 *
 * The f_post_register_wait hook will be called later by kevent_register()
 * and should call kevent_register_wait_block()
 */
static int
kevent_register_wait_prepare(struct knote *kn, struct kevent_qos_s *kev, int rc)
{
        thread_t thread = current_thread();

        assert(knote_fops(kn)->f_extended_codes);

        if (kn->kn_thread == NULL) {
                thread_reference(thread);
                kn->kn_thread = thread;
        } else if (kn->kn_thread != thread) {
                /*
                 * kn_thread may be set from a previous aborted wait
                 * However, it has to be from the same thread.
                 */
                kev->flags |= EV_ERROR;
                kev->data = EXDEV;
                return 0;
        }

        return FILTER_REGISTER_WAIT | rc;
}

/*
 * Cleanup a kevent_register_wait_prepare() effect for threads that have been
 * aborted instead of properly woken up with thread_wakeup_thread().
 */
static void
kevent_register_wait_cleanup(struct knote *kn)
{
        thread_t thread = kn->kn_thread;
        kn->kn_thread = NULL;
        thread_deallocate(thread);
}

/*
 * Must be called at the end of a f_post_register_wait call from a filter.
 */
static void
kevent_register_wait_block(struct turnstile *ts, thread_t thread,
    thread_continue_t cont, struct _kevent_register *cont_args)
{
        turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_HELD);
        kqunlock(cont_args->kqwl);
        cont_args->handoff_thread = thread;
        thread_handoff_parameter(thread, cont, cont_args, THREAD_HANDOFF_NONE);
}

/*
 * Called by Filters using a f_post_register_wait to return from their wait.
 */
static void
kevent_register_wait_return(struct _kevent_register *cont_args)
{
        struct kqworkloop *kqwl = cont_args->kqwl;
        struct kevent_qos_s *kev = &cont_args->kev;
        int error = 0;

        if (cont_args->handoff_thread) {
                thread_deallocate(cont_args->handoff_thread);
        }

        if (kev->flags & (EV_ERROR | EV_RECEIPT)) {
                if ((kev->flags & EV_ERROR) == 0) {
                        kev->flags |= EV_ERROR;
                        kev->data = 0;
                }
                error = kevent_modern_copyout(kev, &cont_args->ueventlist);
                if (error == 0) {
                        cont_args->eventout++;
                }
        }

        kqworkloop_release(kqwl);
        if (error == 0) {
                *(int32_t *)&current_uthread()->uu_rval = cont_args->eventout;
        }
        unix_syscall_return(error);
}

/*
 * kevent_register - add a new event to a kqueue
 *
 *      Creates a mapping between the event source and
 *      the kqueue via a knote data structure.
 *
 *      Because many/most the event sources are file
 *      descriptor related, the knote is linked off
 *      the filedescriptor table for quick access.
 *
 *      called with nothing locked
 *      caller holds a reference on the kqueue
 */

int
kevent_register(struct kqueue *kq, struct kevent_qos_s *kev,
    struct knote **kn_out)
{
        struct proc *p = kq->kq_p;
        const struct filterops *fops;
        struct knote *kn = NULL;
        int result = 0, error = 0;
        unsigned short kev_flags = kev->flags;
        KNOTE_LOCK_CTX(knlc);

        if (__probable(kev->filter < 0 && kev->filter + EVFILT_SYSCOUNT >= 0)) {
                fops = sysfilt_ops[~kev->filter];       /* to 0-base index */
        } else {
                error = EINVAL;
                goto out;
        }

        /* restrict EV_VANISHED to adding udata-specific dispatch kevents */
        if (__improbable((kev->flags & EV_VANISHED) &&
            (kev->flags & (EV_ADD | EV_DISPATCH2)) != (EV_ADD | EV_DISPATCH2))) {
                error = EINVAL;
                goto out;
        }

        /* Simplify the flags - delete and disable overrule */
        if (kev->flags & EV_DELETE) {
                kev->flags &= ~EV_ADD;
        }
        if (kev->flags & EV_DISABLE) {
                kev->flags &= ~EV_ENABLE;
        }

        if (kq->kq_state & KQ_WORKLOOP) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_REGISTER),
                    ((struct kqworkloop *)kq)->kqwl_dynamicid,
                    kev->udata, kev->flags, kev->filter);
        } else if (kq->kq_state & KQ_WORKQ) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWQ_REGISTER),
                    0, kev->udata, kev->flags, kev->filter);
        } else {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQ_REGISTER),
                    VM_KERNEL_UNSLIDE_OR_PERM(kq),
                    kev->udata, kev->flags, kev->filter);
        }

restart:
        /* find the matching knote from the fd tables/hashes */
        kn = kq_find_knote_and_kq_lock(kq, kev, fops->f_isfd, p);
        error = kevent_register_validate_priority(kq, kn, kev);
        result = 0;
        if (error) {
                goto out;
        }

        if (kn == NULL && (kev->flags & EV_ADD) == 0) {
                /*
                 * No knote found, EV_ADD wasn't specified
                 */

                if ((kev_flags & EV_ADD) && (kev_flags & EV_DELETE) &&
                    (kq->kq_state & KQ_WORKLOOP)) {
                        /*
                         * For workloops, understand EV_ADD|EV_DELETE as a "soft" delete
                         * that doesn't care about ENOENT, so just pretend the deletion
                         * happened.
                         */
                } else {
                        error = ENOENT;
                }
                goto out;
        } else if (kn == NULL) {
                /*
                 * No knote found, need to attach a new one (attach)
                 */

                struct fileproc *knote_fp = NULL;

                /* grab a file reference for the new knote */
                if (fops->f_isfd) {
                        if ((error = fp_lookup(p, (int)kev->ident, &knote_fp, 0)) != 0) {
                                goto out;
                        }
                }

                kn = knote_alloc();
                if (kn == NULL) {
                        error = ENOMEM;
                        if (knote_fp != NULL) {
                                fp_drop(p, (int)kev->ident, knote_fp, 0);
                        }
                        goto out;
                }

                kn->kn_fp = knote_fp;
                kn->kn_is_fd = fops->f_isfd;
                kn->kn_kq_packed = VM_PACK_POINTER((vm_offset_t)kq, KNOTE_KQ_PACKED);
                kn->kn_status = 0;

                /* was vanish support requested */
                if (kev->flags & EV_VANISHED) {
                        kev->flags &= ~EV_VANISHED;
                        kn->kn_status |= KN_REQVANISH;
                }

                /* snapshot matching/dispatching protocol flags into knote */
                if (kev->flags & EV_DISABLE) {
                        kn->kn_status |= KN_DISABLED;
                }

                /*
                 * copy the kevent state into knote
                 * protocol is that fflags and data
                 * are saved off, and cleared before
                 * calling the attach routine.
                 *
                 * - kn->kn_sfflags aliases with kev->xflags
                 * - kn->kn_sdata   aliases with kev->data
                 * - kn->kn_filter  is the top 8 bits of kev->filter
                 */
                kn->kn_kevent  = *(struct kevent_internal_s *)kev;
                kn->kn_sfflags = kev->fflags;
                kn->kn_filtid  = (uint8_t)~kev->filter;
                kn->kn_fflags  = 0;
                knote_reset_priority(kq, kn, kev->qos);

                /* Add the knote for lookup thru the fd table */
                error = kq_add_knote(kq, kn, &knlc, p);
                if (error) {
                        knote_free(kn);
                        if (knote_fp != NULL) {
                                fp_drop(p, (int)kev->ident, knote_fp, 0);
                        }

                        if (error == ERESTART) {
                                goto restart;
                        }
                        goto out;
                }

                /* fp reference count now applies to knote */

                /*
                 * we can't use filter_call() because f_attach can change the filter ops
                 * for a filter that supports f_extended_codes, so we need to reload
                 * knote_fops() and not use `fops`.
                 */
                result = fops->f_attach(kn, kev);
                if (result && !knote_fops(kn)->f_extended_codes) {
                        result = FILTER_ACTIVE;
                }

                kqlock(kq);

                if (result & FILTER_THREADREQ_NODEFEER) {
                        enable_preemption();
                }

                if (kn->kn_flags & EV_ERROR) {
                        /*
                         * Failed to attach correctly, so drop.
                         */
                        kn->kn_filtid = EVFILTID_DETACHED;
                        error = (int)kn->kn_sdata;
                        knote_drop(kq, kn, &knlc);
                        result = 0;
                        goto out;
                }

                /*
                 * end "attaching" phase - now just attached
                 *
                 * Mark the thread request overcommit, if appropos
                 *
                 * If the attach routine indicated that an
                 * event is already fired, activate the knote.
                 */
                if ((kn->kn_qos & _PTHREAD_PRIORITY_OVERCOMMIT_FLAG) &&
                    (kq->kq_state & KQ_WORKLOOP)) {
                        kqworkloop_set_overcommit((struct kqworkloop *)kq);
                }
        } else if (!knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
                /*
                 * The knote was dropped while we were waiting for the lock,
                 * we need to re-evaluate entirely
                 */

                goto restart;
        } else if (kev->flags & EV_DELETE) {
                /*
                 * Deletion of a knote (drop)
                 *
                 * If the filter wants to filter drop events, let it do so.
                 *
                 * defer-delete: when trying to delete a disabled EV_DISPATCH2 knote,
                 * we must wait for the knote to be re-enabled (unless it is being
                 * re-enabled atomically here).
                 */

                if (knote_fops(kn)->f_allow_drop) {
                        bool drop;

                        kqunlock(kq);
                        drop = knote_fops(kn)->f_allow_drop(kn, kev);
                        kqlock(kq);

                        if (!drop) {
                                goto out_unlock;
                        }
                }

                if ((kev->flags & EV_ENABLE) == 0 &&
                    (kn->kn_flags & EV_DISPATCH2) == EV_DISPATCH2 &&
                    (kn->kn_status & KN_DISABLED) != 0) {
                        kn->kn_status |= KN_DEFERDELETE;
                        error = EINPROGRESS;
                        goto out_unlock;
                }

                knote_drop(kq, kn, &knlc);
                goto out;
        } else {
                /*
                 * Regular update of a knote (touch)
                 *
                 * Call touch routine to notify filter of changes in filter values
                 * (and to re-determine if any events are fired).
                 *
                 * If the knote is in defer-delete, avoid calling the filter touch
                 * routine (it has delivered its last event already).
                 *
                 * If the touch routine had no failure,
                 * apply the requested side effects to the knote.
                 */

                if (kn->kn_status & (KN_DEFERDELETE | KN_VANISHED)) {
                        if (kev->flags & EV_ENABLE) {
                                result = FILTER_ACTIVE;
                        }
                } else {
                        kqunlock(kq);
                        result = filter_call(knote_fops(kn), f_touch(kn, kev));
                        kqlock(kq);
                        if (result & FILTER_THREADREQ_NODEFEER) {
                                enable_preemption();
                        }
                }

                if (kev->flags & EV_ERROR) {
                        result = 0;
                        goto out_unlock;
                }

                if ((kn->kn_flags & EV_UDATA_SPECIFIC) == 0 &&
                    kn->kn_udata != kev->udata) {
                        // this allows klist_copy_udata() not to take locks
                        os_atomic_store_wide(&kn->kn_udata, kev->udata, relaxed);
                }
                if ((kev->flags & EV_DISABLE) && !(kn->kn_status & KN_DISABLED)) {
                        kn->kn_status |= KN_DISABLED;
                        knote_dequeue(kq, kn);
                }
        }

        /* accept new kevent state */
        knote_apply_touch(kq, kn, kev, result);

out_unlock:
        /*
         * When the filter asked for a post-register wait,
         * we leave the kqueue locked for kevent_register()
         * to call the filter's f_post_register_wait hook.
         */
        if (result & FILTER_REGISTER_WAIT) {
                knote_unlock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS);
                *kn_out = kn;
        } else {
                knote_unlock(kq, kn, &knlc, KNOTE_KQ_UNLOCK);
        }

out:
        /* output local errors through the kevent */
        if (error) {
                kev->flags |= EV_ERROR;
                kev->data = error;
        }
        return result;
}

/*
 * knote_process - process a triggered event
 *
 *      Validate that it is really still a triggered event
 *      by calling the filter routines (if necessary).  Hold
 *      a use reference on the knote to avoid it being detached.
 *
 *      If it is still considered triggered, we will have taken
 *      a copy of the state under the filter lock.  We use that
 *      snapshot to dispatch the knote for future processing (or
 *      not, if this was a lost event).
 *
 *      Our caller assures us that nobody else can be processing
 *      events from this knote during the whole operation. But
 *      others can be touching or posting events to the knote
 *      interspersed with our processing it.
 *
 *      caller holds a reference on the kqueue.
 *      kqueue locked on entry and exit - but may be dropped
 */
static int
knote_process(struct knote *kn, kevent_ctx_t kectx,
    kevent_callback_t callback)
{
        struct kevent_qos_s kev;
        struct kqueue *kq = knote_get_kq(kn);
        KNOTE_LOCK_CTX(knlc);
        int result = FILTER_ACTIVE;
        int error = 0;
        bool drop = false;

        /*
         * Must be active or stayactive
         * Must be queued and not disabled/suppressed or dropping
         */
        assert(kn->kn_status & KN_QUEUED);
        assert(kn->kn_status & (KN_ACTIVE | KN_STAYACTIVE));
        assert(!(kn->kn_status & (KN_DISABLED | KN_SUPPRESSED | KN_DROPPING)));

        if (kq->kq_state & KQ_WORKLOOP) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS),
                    ((struct kqworkloop *)kq)->kqwl_dynamicid,
                    kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
                    kn->kn_filtid);
        } else if (kq->kq_state & KQ_WORKQ) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWQ_PROCESS),
                    0, kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
                    kn->kn_filtid);
        } else {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQ_PROCESS),
                    VM_KERNEL_UNSLIDE_OR_PERM(kq), kn->kn_udata,
                    kn->kn_status | (kn->kn_id << 32), kn->kn_filtid);
        }

        if (!knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS)) {
                /*
                 * When the knote is dropping or has dropped,
                 * then there's nothing we want to process.
                 */
                return EJUSTRETURN;
        }

        /*
         * While waiting for the knote lock, we may have dropped the kq lock.
         * and a touch may have disabled and dequeued the knote.
         */
        if (!(kn->kn_status & KN_QUEUED)) {
                knote_unlock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS);
                return EJUSTRETURN;
        }

        /*
         * For deferred-drop or vanished events, we just create a fake
         * event to acknowledge end-of-life.  Otherwise, we call the
         * filter's process routine to snapshot the kevent state under
         * the filter's locking protocol.
         *
         * suppress knotes to avoid returning the same event multiple times in
         * a single call.
         */
        knote_suppress(kq, kn);

        if (kn->kn_status & (KN_DEFERDELETE | KN_VANISHED)) {
                uint16_t kev_flags = EV_DISPATCH2 | EV_ONESHOT;
                if (kn->kn_status & KN_DEFERDELETE) {
                        kev_flags |= EV_DELETE;
                } else {
                        kev_flags |= EV_VANISHED;
                }

                /* create fake event */
                kev = (struct kevent_qos_s){
                        .filter = kn->kn_filter,
                        .ident  = kn->kn_id,
                        .flags  = kev_flags,
                        .udata  = kn->kn_udata,
                };
        } else {
                kqunlock(kq);
                kev = (struct kevent_qos_s) { };
                result = filter_call(knote_fops(kn), f_process(kn, &kev));
                kqlock(kq);
        }

        /*
         * Determine how to dispatch the knote for future event handling.
         * not-fired: just return (do not callout, leave deactivated).
         * One-shot:  If dispatch2, enter deferred-delete mode (unless this is
         *            is the deferred delete event delivery itself).  Otherwise,
         *            drop it.
         * Dispatch:  don't clear state, just mark it disabled.
         * Cleared:   just leave it deactivated.
         * Others:    re-activate as there may be more events to handle.
         *            This will not wake up more handlers right now, but
         *            at the completion of handling events it may trigger
         *            more handler threads (TODO: optimize based on more than
         *            just this one event being detected by the filter).
         */
        if ((result & FILTER_ACTIVE) == 0) {
                if ((kn->kn_status & (KN_ACTIVE | KN_STAYACTIVE)) == 0) {
                        /*
                         * Stay active knotes should not be unsuppressed or we'd create an
                         * infinite loop.
                         *
                         * Some knotes (like EVFILT_WORKLOOP) can be reactivated from
                         * within f_process() but that doesn't necessarily make them
                         * ready to process, so we should leave them be.
                         *
                         * For other knotes, since we will not return an event,
                         * there's no point keeping the knote suppressed.
                         */
                        knote_unsuppress(kq, kn);
                }
                knote_unlock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS);
                return EJUSTRETURN;
        }

        if (result & FILTER_ADJUST_EVENT_QOS_BIT) {
                knote_adjust_qos(kq, kn, result);
        }
        kev.qos = _pthread_priority_combine(kn->kn_qos, kn->kn_qos_override);

        if (kev.flags & EV_ONESHOT) {
                if ((kn->kn_flags & EV_DISPATCH2) == EV_DISPATCH2 &&
                    (kn->kn_status & KN_DEFERDELETE) == 0) {
                        /* defer dropping non-delete oneshot dispatch2 events */
                        kn->kn_status |= KN_DEFERDELETE | KN_DISABLED;
                } else {
                        drop = true;
                }
        } else if (kn->kn_flags & EV_DISPATCH) {
                /* disable all dispatch knotes */
                kn->kn_status |= KN_DISABLED;
        } else if ((kn->kn_flags & EV_CLEAR) == 0) {
                /* re-activate in case there are more events */
                knote_activate(kq, kn, FILTER_ACTIVE);
        }

        /*
         * callback to handle each event as we find it.
         * If we have to detach and drop the knote, do
         * it while we have the kq unlocked.
         */
        if (drop) {
                knote_drop(kq, kn, &knlc);
        } else {
                knote_unlock(kq, kn, &knlc, KNOTE_KQ_UNLOCK);
        }

        if (kev.flags & EV_VANISHED) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KNOTE_VANISHED),
                    kev.ident, kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
                    kn->kn_filtid);
        }

        error = (callback)(&kev, kectx);
        kqlock(kq);
        return error;
}

/*
 * Returns -1 if the kqueue was unbound and processing should not happen
 */
#define KQWQAE_BEGIN_PROCESSING 1
#define KQWQAE_END_PROCESSING   2
#define KQWQAE_UNBIND           3
static int
kqworkq_acknowledge_events(struct kqworkq *kqwq, workq_threadreq_t kqr,
    int kevent_flags, int kqwqae_op)
{
        thread_qos_t old_override = THREAD_QOS_UNSPECIFIED;
        thread_t thread = kqr_thread_fast(kqr);
        struct knote *kn;
        int rc = 0;
        bool unbind;
        struct kqtailq *suppressq = &kqwq->kqwq_suppressed[kqr->tr_kq_qos_index];

        kqlock_held(&kqwq->kqwq_kqueue);

        if (!TAILQ_EMPTY(suppressq)) {
                /*
                 * Return suppressed knotes to their original state.
                 * For workq kqueues, suppressed ones that are still
                 * truly active (not just forced into the queue) will
                 * set flags we check below to see if anything got
                 * woken up.
                 */
                while ((kn = TAILQ_FIRST(suppressq)) != NULL) {
                        assert(kn->kn_status & KN_SUPPRESSED);
                        knote_unsuppress(kqwq, kn);
                }
        }

#if DEBUG || DEVELOPMENT
        thread_t self = current_thread();
        struct uthread *ut = get_bsdthread_info(self);

        assert(thread == self);
        assert(ut->uu_kqr_bound == kqr);
#endif // DEBUG || DEVELOPMENT

        if (kqwqae_op == KQWQAE_UNBIND) {
                unbind = true;
        } else if ((kevent_flags & KEVENT_FLAG_PARKING) == 0) {
                unbind = false;
        } else {
                unbind = !kqr->tr_kq_wakeup;
        }
        if (unbind) {
                old_override = kqworkq_unbind_locked(kqwq, kqr, thread);
                rc = -1;
                /*
                 * request a new thread if we didn't process the whole queue or real events
                 * have happened (not just putting stay-active events back).
                 */
                if (kqr->tr_kq_wakeup) {
                        kqueue_threadreq_initiate(&kqwq->kqwq_kqueue, kqr,
                            kqr->tr_kq_qos_index, 0);
                }
        }

        if (rc == 0) {
                /*
                 * Reset wakeup bit to notice events firing while we are processing,
                 * as we cannot rely on the bucket queue emptiness because of stay
                 * active knotes.
                 */
                kqr->tr_kq_wakeup = false;
        }

        if (old_override) {
                thread_drop_kevent_override(thread);
        }

        return rc;
}

/*
 * Return 0 to indicate that processing should proceed,
 * -1 if there is nothing to process.
 *
 * Called with kqueue locked and returns the same way,
 * but may drop lock temporarily.
 */
static int
kqworkq_begin_processing(struct kqworkq *kqwq, workq_threadreq_t kqr,
    int kevent_flags)
{
        int rc = 0;

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWQ_PROCESS_BEGIN) | DBG_FUNC_START,
            0, kqr->tr_kq_qos_index);

        rc = kqworkq_acknowledge_events(kqwq, kqr, kevent_flags,
            KQWQAE_BEGIN_PROCESSING);

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWQ_PROCESS_BEGIN) | DBG_FUNC_END,
            thread_tid(kqr_thread(kqr)), kqr->tr_kq_wakeup);

        return rc;
}

static thread_qos_t
kqworkloop_acknowledge_events(struct kqworkloop *kqwl)
{
        kq_index_t qos = THREAD_QOS_UNSPECIFIED;
        struct knote *kn, *tmp;

        kqlock_held(kqwl);

        TAILQ_FOREACH_SAFE(kn, &kqwl->kqwl_suppressed, kn_tqe, tmp) {
                /*
                 * If a knote that can adjust QoS is disabled because of the automatic
                 * behavior of EV_DISPATCH, the knotes should stay suppressed so that
                 * further overrides keep pushing.
                 */
                if (knote_fops(kn)->f_adjusts_qos && (kn->kn_status & KN_DISABLED) &&
                    (kn->kn_status & (KN_STAYACTIVE | KN_DROPPING)) == 0 &&
                    (kn->kn_flags & (EV_DISPATCH | EV_DISABLE)) == EV_DISPATCH) {
                        qos = MAX(qos, kn->kn_qos_override);
                        continue;
                }
                knote_unsuppress(kqwl, kn);
        }

        return qos;
}

static int
kqworkloop_begin_processing(struct kqworkloop *kqwl, unsigned int kevent_flags)
{
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        struct kqueue *kq = &kqwl->kqwl_kqueue;
        thread_qos_t qos_override;
        thread_t thread = kqr_thread_fast(kqr);
        int rc = 0, op = KQWL_UTQ_NONE;

        kqlock_held(kq);

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_BEGIN) | DBG_FUNC_START,
            kqwl->kqwl_dynamicid, 0, 0);

        /* nobody else should still be processing */
        assert((kq->kq_state & KQ_PROCESSING) == 0);

        kq->kq_state |= KQ_PROCESSING;

        if (!TAILQ_EMPTY(&kqwl->kqwl_suppressed)) {
                op = KQWL_UTQ_RESET_WAKEUP_OVERRIDE;
        }

        if (kevent_flags & KEVENT_FLAG_PARKING) {
                /*
                 * When "parking" we want to process events and if no events are found
                 * unbind.
                 *
                 * However, non overcommit threads sometimes park even when they have
                 * more work so that the pool can narrow.  For these, we need to unbind
                 * early, so that calling kqworkloop_update_threads_qos() can ask the
                 * workqueue subsystem whether the thread should park despite having
                 * pending events.
                 */
                if (kqr->tr_flags & WORKQ_TR_FLAG_OVERCOMMIT) {
                        op = KQWL_UTQ_PARKING;
                } else {
                        op = KQWL_UTQ_UNBINDING;
                }
        }
        if (op == KQWL_UTQ_NONE) {
                goto done;
        }

        qos_override = kqworkloop_acknowledge_events(kqwl);

        if (op == KQWL_UTQ_UNBINDING) {
                kqworkloop_unbind_locked(kqwl, thread, KQWL_OVERRIDE_DROP_IMMEDIATELY);
                kqworkloop_release_live(kqwl);
        }
        kqworkloop_update_threads_qos(kqwl, op, qos_override);
        if (op == KQWL_UTQ_PARKING) {
                if (!TAILQ_EMPTY(&kqwl->kqwl_queue[KQWL_BUCKET_STAYACTIVE])) {
                        /*
                         * We cannot trust tr_kq_wakeup when looking at stay active knotes.
                         * We need to process once, and kqworkloop_end_processing will
                         * handle the unbind.
                         */
                } else if (!kqr->tr_kq_wakeup || kqwl->kqwl_owner) {
                        kqworkloop_unbind_locked(kqwl, thread, KQWL_OVERRIDE_DROP_DELAYED);
                        kqworkloop_release_live(kqwl);
                        rc = -1;
                }
        } else if (op == KQWL_UTQ_UNBINDING) {
                if (kqr_thread(kqr) == thread) {
                        /*
                         * The thread request fired again, passed the admission check and
                         * got bound to the current thread again.
                         */
                } else {
                        rc = -1;
                }
        }

        if (rc == 0) {
                /*
                 * Reset wakeup bit to notice stay active events firing while we are
                 * processing, as we cannot rely on the stayactive bucket emptiness.
                 */
                kqwl->kqwl_wakeup_indexes &= ~KQWL_STAYACTIVE_FIRED_BIT;
        } else {
                kq->kq_state &= ~KQ_PROCESSING;
        }

        if (rc == -1) {
                kqworkloop_unbind_delayed_override_drop(thread);
        }

done:
        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_BEGIN) | DBG_FUNC_END,
            kqwl->kqwl_dynamicid, 0, 0);

        return rc;
}

/*
 * Return 0 to indicate that processing should proceed,
 * -1 if there is nothing to process.
 * EBADF if the kqueue is draining
 *
 * Called with kqueue locked and returns the same way,
 * but may drop lock temporarily.
 * May block.
 */
static int
kqfile_begin_processing(struct kqfile *kq)
{
        struct kqtailq *suppressq;

        kqlock_held(kq);

        assert((kq->kqf_state & (KQ_WORKQ | KQ_WORKLOOP)) == 0);
        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_START,
            VM_KERNEL_UNSLIDE_OR_PERM(kq), 0);

        /* wait to become the exclusive processing thread */
        for (;;) {
                if (kq->kqf_state & KQ_DRAIN) {
                        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_END,
                            VM_KERNEL_UNSLIDE_OR_PERM(kq), 2);
                        return EBADF;
                }

                if ((kq->kqf_state & KQ_PROCESSING) == 0) {
                        break;
                }

                /* if someone else is processing the queue, wait */
                kq->kqf_state |= KQ_PROCWAIT;
                suppressq = &kq->kqf_suppressed;
                waitq_assert_wait64((struct waitq *)&kq->kqf_wqs,
                    CAST_EVENT64_T(suppressq), THREAD_UNINT | THREAD_WAIT_NOREPORT,
                    TIMEOUT_WAIT_FOREVER);

                kqunlock(kq);
                thread_block(THREAD_CONTINUE_NULL);
                kqlock(kq);
        }

        /* Nobody else processing */

        /* clear pre-posts and KQ_WAKEUP now, in case we bail early */
        waitq_set_clear_preposts(&kq->kqf_wqs);
        kq->kqf_state &= ~KQ_WAKEUP;

        /* anything left to process? */
        if (TAILQ_EMPTY(&kq->kqf_queue)) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_END,
                    VM_KERNEL_UNSLIDE_OR_PERM(kq), 1);
                return -1;
        }

        /* convert to processing mode */
        kq->kqf_state |= KQ_PROCESSING;

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_END,
            VM_KERNEL_UNSLIDE_OR_PERM(kq));

        return 0;
}

/*
 * Try to end the processing, only called when a workq thread is attempting to
 * park (KEVENT_FLAG_PARKING is set).
 *
 * When returning -1, the kqworkq is setup again so that it is ready to be
 * processed.
 */
static int
kqworkq_end_processing(struct kqworkq *kqwq, workq_threadreq_t kqr,
    int kevent_flags)
{
        if (!TAILQ_EMPTY(&kqwq->kqwq_queue[kqr->tr_kq_qos_index])) {
                /* remember we didn't process everything */
                kqr->tr_kq_wakeup = true;
        }

        if (kevent_flags & KEVENT_FLAG_PARKING) {
                /*
                 * if acknowledge events "succeeds" it means there are events,
                 * which is a failure condition for end_processing.
                 */
                int rc = kqworkq_acknowledge_events(kqwq, kqr, kevent_flags,
                    KQWQAE_END_PROCESSING);
                if (rc == 0) {
                        return -1;
                }
        }

        return 0;
}

/*
 * Try to end the processing, only called when a workq thread is attempting to
 * park (KEVENT_FLAG_PARKING is set).
 *
 * When returning -1, the kqworkq is setup again so that it is ready to be
 * processed (as if kqworkloop_begin_processing had just been called).
 *
 * If successful and KEVENT_FLAG_PARKING was set in the kevent_flags,
 * the kqworkloop is unbound from its servicer as a side effect.
 */
static int
kqworkloop_end_processing(struct kqworkloop *kqwl, int flags, int kevent_flags)
{
        struct kqueue *kq = &kqwl->kqwl_kqueue;
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        thread_qos_t qos_override;
        thread_t thread = kqr_thread_fast(kqr);
        int rc = 0;

        kqlock_held(kq);

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_END) | DBG_FUNC_START,
            kqwl->kqwl_dynamicid, 0, 0);

        if (flags & KQ_PROCESSING) {
                assert(kq->kq_state & KQ_PROCESSING);

                /*
                 * If we still have queued stayactive knotes, remember we didn't finish
                 * processing all of them.  This should be extremely rare and would
                 * require to have a lot of them registered and fired.
                 */
                if (!TAILQ_EMPTY(&kqwl->kqwl_queue[KQWL_BUCKET_STAYACTIVE])) {
                        kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_UPDATE_WAKEUP_QOS,
                            KQWL_BUCKET_STAYACTIVE);
                }

                /*
                 * When KEVENT_FLAG_PARKING is set, we need to attempt an unbind while
                 * still under the lock.
                 *
                 * So we do everything kqworkloop_unbind() would do, but because we're
                 * inside kqueue_process(), if the workloop actually received events
                 * while our locks were dropped, we have the opportunity to fail the end
                 * processing and loop again.
                 *
                 * This avoids going through the process-wide workqueue lock hence
                 * scales better.
                 */
                if (kevent_flags & KEVENT_FLAG_PARKING) {
                        qos_override = kqworkloop_acknowledge_events(kqwl);
                }
        }

        if (kevent_flags & KEVENT_FLAG_PARKING) {
                kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_PARKING, qos_override);
                if (kqr->tr_kq_wakeup && !kqwl->kqwl_owner) {
                        /*
                         * Reset wakeup bit to notice stay active events firing while we are
                         * processing, as we cannot rely on the stayactive bucket emptiness.
                         */
                        kqwl->kqwl_wakeup_indexes &= ~KQWL_STAYACTIVE_FIRED_BIT;
                        rc = -1;
                } else {
                        kqworkloop_unbind_locked(kqwl, thread, KQWL_OVERRIDE_DROP_DELAYED);
                        kqworkloop_release_live(kqwl);
                        kq->kq_state &= ~flags;
                }
        } else {
                kq->kq_state &= ~flags;
                kq->kq_state |= KQ_R2K_ARMED;
                kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_RECOMPUTE_WAKEUP_QOS, 0);
        }

        if ((kevent_flags & KEVENT_FLAG_PARKING) && rc == 0) {
                kqworkloop_unbind_delayed_override_drop(thread);
        }

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_END) | DBG_FUNC_END,
            kqwl->kqwl_dynamicid, 0, 0);

        return rc;
}

/*
 * Called with kqueue lock held.
 *
 * 0: no more events
 * -1: has more events
 * EBADF: kqueue is in draining mode
 */
static int
kqfile_end_processing(struct kqfile *kq)
{
        struct kqtailq *suppressq = &kq->kqf_suppressed;
        struct knote *kn;
        int procwait;

        kqlock_held(kq);

        assert((kq->kqf_state & (KQ_WORKQ | KQ_WORKLOOP)) == 0);

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_END),
            VM_KERNEL_UNSLIDE_OR_PERM(kq), 0);

        /*
         * Return suppressed knotes to their original state.
         */
        while ((kn = TAILQ_FIRST(suppressq)) != NULL) {
                assert(kn->kn_status & KN_SUPPRESSED);
                knote_unsuppress(kq, kn);
        }

        procwait = (kq->kqf_state & KQ_PROCWAIT);
        kq->kqf_state &= ~(KQ_PROCESSING | KQ_PROCWAIT);

        if (procwait) {
                /* first wake up any thread already waiting to process */
                waitq_wakeup64_all((struct waitq *)&kq->kqf_wqs,
                    CAST_EVENT64_T(suppressq), THREAD_AWAKENED, WAITQ_ALL_PRIORITIES);
        }

        if (kq->kqf_state & KQ_DRAIN) {
                return EBADF;
        }
        return (kq->kqf_state & KQ_WAKEUP) ? -1 : 0;
}

static int
kqueue_workloop_ctl_internal(proc_t p, uintptr_t cmd, uint64_t __unused options,
    struct kqueue_workloop_params *params, int *retval)
{
        int error = 0;
        struct kqworkloop *kqwl;
        struct filedesc *fdp = p->p_fd;
        workq_threadreq_param_t trp = { };

        switch (cmd) {
        case KQ_WORKLOOP_CREATE:
                if (!params->kqwlp_flags) {
                        error = EINVAL;
                        break;
                }

                if ((params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_PRI) &&
                    (params->kqwlp_sched_pri < 1 ||
                    params->kqwlp_sched_pri > 63 /* MAXPRI_USER */)) {
                        error = EINVAL;
                        break;
                }

                if ((params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_POL) &&
                    invalid_policy(params->kqwlp_sched_pol)) {
                        error = EINVAL;
                        break;
                }

                if ((params->kqwlp_flags & KQ_WORKLOOP_CREATE_CPU_PERCENT) &&
                    (params->kqwlp_cpu_percent <= 0 ||
                    params->kqwlp_cpu_percent > 100 ||
                    params->kqwlp_cpu_refillms <= 0 ||
                    params->kqwlp_cpu_refillms > 0x00ffffff)) {
                        error = EINVAL;
                        break;
                }

                if (params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_PRI) {
                        trp.trp_flags |= TRP_PRIORITY;
                        trp.trp_pri = (uint8_t)params->kqwlp_sched_pri;
                }
                if (params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_POL) {
                        trp.trp_flags |= TRP_POLICY;
                        trp.trp_pol = (uint8_t)params->kqwlp_sched_pol;
                }
                if (params->kqwlp_flags & KQ_WORKLOOP_CREATE_CPU_PERCENT) {
                        trp.trp_flags |= TRP_CPUPERCENT;
                        trp.trp_cpupercent = (uint8_t)params->kqwlp_cpu_percent;
                        trp.trp_refillms = params->kqwlp_cpu_refillms;
                }

                error = kqworkloop_get_or_create(p, params->kqwlp_id, &trp,
                    KEVENT_FLAG_DYNAMIC_KQUEUE | KEVENT_FLAG_WORKLOOP |
                    KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST, &kqwl);
                if (error) {
                        break;
                }

                if (!(fdp->fd_flags & FD_WORKLOOP)) {
                        /* FD_WORKLOOP indicates we've ever created a workloop
                         * via this syscall but its only ever added to a process, never
                         * removed.
                         */
                        proc_fdlock(p);
                        fdp->fd_flags |= FD_WORKLOOP;
                        proc_fdunlock(p);
                }
                break;
        case KQ_WORKLOOP_DESTROY:
                error = kqworkloop_get_or_create(p, params->kqwlp_id, NULL,
                    KEVENT_FLAG_DYNAMIC_KQUEUE | KEVENT_FLAG_WORKLOOP |
                    KEVENT_FLAG_DYNAMIC_KQ_MUST_EXIST, &kqwl);
                if (error) {
                        break;
                }
                kqlock(kqwl);
                trp.trp_value = kqwl->kqwl_params;
                if (trp.trp_flags && !(trp.trp_flags & TRP_RELEASED)) {
                        trp.trp_flags |= TRP_RELEASED;
                        kqwl->kqwl_params = trp.trp_value;
                        kqworkloop_release_live(kqwl);
                } else {
                        error = EINVAL;
                }
                kqunlock(kqwl);
                kqworkloop_release(kqwl);
                break;
        }
        *retval = 0;
        return error;
}

int
kqueue_workloop_ctl(proc_t p, struct kqueue_workloop_ctl_args *uap, int *retval)
{
        struct kqueue_workloop_params params = {
                .kqwlp_id = 0,
        };
        if (uap->sz < sizeof(params.kqwlp_version)) {
                return EINVAL;
        }

        size_t copyin_sz = MIN(sizeof(params), uap->sz);
        int rv = copyin(uap->addr, &params, copyin_sz);
        if (rv) {
                return rv;
        }

        if (params.kqwlp_version != (int)uap->sz) {
                return EINVAL;
        }

        return kqueue_workloop_ctl_internal(p, uap->cmd, uap->options, &params,
                   retval);
}

/*ARGSUSED*/
static int
kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
    __unused vfs_context_t ctx)
{
        struct kqfile *kq = (struct kqfile *)fp->f_data;
        struct kqtailq *suppressq = &kq->kqf_suppressed;
        struct kqtailq *queue = &kq->kqf_queue;
        struct knote *kn;
        int retnum = 0;

        if (which != FREAD) {
                return 0;
        }

        kqlock(kq);

        assert((kq->kqf_state & KQ_WORKQ) == 0);

        /*
         * If this is the first pass, link the wait queue associated with the
         * the kqueue onto the wait queue set for the select().  Normally we
         * use selrecord() for this, but it uses the wait queue within the
         * selinfo structure and we need to use the main one for the kqueue to
         * catch events from KN_STAYQUEUED sources. So we do the linkage manually.
         * (The select() call will unlink them when it ends).
         */
        if (wq_link_id != NULL) {
                thread_t cur_act = current_thread();
                struct uthread * ut = get_bsdthread_info(cur_act);

                kq->kqf_state |= KQ_SEL;
                waitq_link((struct waitq *)&kq->kqf_wqs, ut->uu_wqset,
                    WAITQ_SHOULD_LOCK, (uint64_t *)wq_link_id);

                /* always consume the reserved link object */
                waitq_link_release(*(uint64_t *)wq_link_id);
                *(uint64_t *)wq_link_id = 0;

                /*
                 * selprocess() is expecting that we send it back the waitq
                 * that was just added to the thread's waitq set. In order
                 * to not change the selrecord() API (which is exported to
                 * kexts), we pass this value back through the
                 * void *wq_link_id pointer we were passed. We need to use
                 * memcpy here because the pointer may not be properly aligned
                 * on 32-bit systems.
                 */
                void *wqptr = &kq->kqf_wqs;
                memcpy(wq_link_id, (void *)&wqptr, sizeof(void *));
        }

        if (kqfile_begin_processing(kq) == -1) {
                kqunlock(kq);
                return 0;
        }

        if (!TAILQ_EMPTY(queue)) {
                /*
                 * there is something queued - but it might be a
                 * KN_STAYACTIVE knote, which may or may not have
                 * any events pending.  Otherwise, we have to walk
                 * the list of knotes to see, and peek at the
                 * (non-vanished) stay-active ones to be really sure.
                 */
                while ((kn = (struct knote *)TAILQ_FIRST(queue)) != NULL) {
                        if (kn->kn_status & KN_ACTIVE) {
                                retnum = 1;
                                goto out;
                        }
                        assert(kn->kn_status & KN_STAYACTIVE);
                        knote_suppress(kq, kn);
                }

                /*
                 * There were no regular events on the queue, so take
                 * a deeper look at the stay-queued ones we suppressed.
                 */
                while ((kn = (struct knote *)TAILQ_FIRST(suppressq)) != NULL) {
                        KNOTE_LOCK_CTX(knlc);
                        int result = 0;

                        /* If didn't vanish while suppressed - peek at it */
                        if ((kn->kn_status & KN_DROPPING) || !knote_lock(kq, kn, &knlc,
                            KNOTE_KQ_LOCK_ON_FAILURE)) {
                                continue;
                        }

                        result = filter_call(knote_fops(kn), f_peek(kn));

                        kqlock(kq);
                        knote_unlock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS);

                        /* unsuppress it */
                        knote_unsuppress(kq, kn);

                        /* has data or it has to report a vanish */
                        if (result & FILTER_ACTIVE) {
                                retnum = 1;
                                goto out;
                        }
                }
        }

out:
        kqfile_end_processing(kq);
        kqunlock(kq);
        return retnum;
}

/*
 * kqueue_close -
 */
/*ARGSUSED*/
static int
kqueue_close(struct fileglob *fg, __unused vfs_context_t ctx)
{
        struct kqfile *kqf = (struct kqfile *)fg->fg_data;

        assert((kqf->kqf_state & KQ_WORKQ) == 0);
        kqueue_dealloc(&kqf->kqf_kqueue);
        fg->fg_data = NULL;
        return 0;
}

/*
 * Max depth of the nested kq path that can be created.
 * Note that this has to be less than the size of kq_level
 * to avoid wrapping around and mislabeling the level.
 */
#define MAX_NESTED_KQ 1000

/*ARGSUSED*/
/*
 * The callers has taken a use-count reference on this kqueue and will donate it
 * to the kqueue we are being added to.  This keeps the kqueue from closing until
 * that relationship is torn down.
 */
static int
kqueue_kqfilter(struct fileproc *fp, struct knote *kn,
    __unused struct kevent_qos_s *kev)
{
        struct kqfile *kqf = (struct kqfile *)fp->f_data;
        struct kqueue *kq = &kqf->kqf_kqueue;
        struct kqueue *parentkq = knote_get_kq(kn);

        assert((kqf->kqf_state & KQ_WORKQ) == 0);

        if (parentkq == kq || kn->kn_filter != EVFILT_READ) {
                knote_set_error(kn, EINVAL);
                return 0;
        }

        /*
         * We have to avoid creating a cycle when nesting kqueues
         * inside another.  Rather than trying to walk the whole
         * potential DAG of nested kqueues, we just use a simple
         * ceiling protocol.  When a kqueue is inserted into another,
         * we check that the (future) parent is not already nested
         * into another kqueue at a lower level than the potenial
         * child (because it could indicate a cycle).  If that test
         * passes, we just mark the nesting levels accordingly.
         *
         * Only up to MAX_NESTED_KQ can be nested.
         *
         * Note: kqworkq and kqworkloop cannot be nested and have reused their
         *       kq_level field, so ignore these as parent.
         */

        kqlock(parentkq);

        if ((parentkq->kq_state & (KQ_WORKQ | KQ_WORKLOOP)) == 0) {
                if (parentkq->kq_level > 0 &&
                    parentkq->kq_level < kq->kq_level) {
                        kqunlock(parentkq);
                        knote_set_error(kn, EINVAL);
                        return 0;
                }

                /* set parent level appropriately */
                uint16_t plevel = (parentkq->kq_level == 0)? 2: parentkq->kq_level;
                if (plevel < kq->kq_level + 1) {
                        if (kq->kq_level + 1 > MAX_NESTED_KQ) {
                                kqunlock(parentkq);
                                knote_set_error(kn, EINVAL);
                                return 0;
                        }
                        plevel = kq->kq_level + 1;
                }

                parentkq->kq_level = plevel;
        }

        kqunlock(parentkq);

        kn->kn_filtid = EVFILTID_KQREAD;
        kqlock(kq);
        KNOTE_ATTACH(&kqf->kqf_sel.si_note, kn);
        /* indicate nesting in child, if needed */
        if (kq->kq_level == 0) {
                kq->kq_level = 1;
        }

        int count = kq->kq_count;
        kqunlock(kq);
        return count > 0;
}

/*
 * kqueue_drain - called when kq is closed
 */
/*ARGSUSED*/
static int
kqueue_drain(struct fileproc *fp, __unused vfs_context_t ctx)
{
        struct kqfile *kqf = (struct kqfile *)fp->fp_glob->fg_data;

        assert((kqf->kqf_state & KQ_WORKQ) == 0);

        kqlock(kqf);
        kqf->kqf_state |= KQ_DRAIN;

        /* wakeup sleeping threads */
        if ((kqf->kqf_state & (KQ_SLEEP | KQ_SEL)) != 0) {
                kqf->kqf_state &= ~(KQ_SLEEP | KQ_SEL);
                (void)waitq_wakeup64_all((struct waitq *)&kqf->kqf_wqs,
                    KQ_EVENT,
                    THREAD_RESTART,
                    WAITQ_ALL_PRIORITIES);
        }

        /* wakeup threads waiting their turn to process */
        if (kqf->kqf_state & KQ_PROCWAIT) {
                assert(kqf->kqf_state & KQ_PROCESSING);

                kqf->kqf_state &= ~KQ_PROCWAIT;
                (void)waitq_wakeup64_all((struct waitq *)&kqf->kqf_wqs,
                    CAST_EVENT64_T(&kqf->kqf_suppressed),
                    THREAD_RESTART, WAITQ_ALL_PRIORITIES);
        }

        kqunlock(kqf);
        return 0;
}

/*ARGSUSED*/
int
kqueue_stat(struct kqueue *kq, void *ub, int isstat64, proc_t p)
{
        assert((kq->kq_state & KQ_WORKQ) == 0);

        kqlock(kq);
        if (isstat64 != 0) {
                struct stat64 *sb64 = (struct stat64 *)ub;

                bzero((void *)sb64, sizeof(*sb64));
                sb64->st_size = kq->kq_count;
                if (kq->kq_state & KQ_KEV_QOS) {
                        sb64->st_blksize = sizeof(struct kevent_qos_s);
                } else if (kq->kq_state & KQ_KEV64) {
                        sb64->st_blksize = sizeof(struct kevent64_s);
                } else if (IS_64BIT_PROCESS(p)) {
                        sb64->st_blksize = sizeof(struct user64_kevent);
                } else {
                        sb64->st_blksize = sizeof(struct user32_kevent);
                }
                sb64->st_mode = S_IFIFO;
        } else {
                struct stat *sb = (struct stat *)ub;

                bzero((void *)sb, sizeof(*sb));
                sb->st_size = kq->kq_count;
                if (kq->kq_state & KQ_KEV_QOS) {
                        sb->st_blksize = sizeof(struct kevent_qos_s);
                } else if (kq->kq_state & KQ_KEV64) {
                        sb->st_blksize = sizeof(struct kevent64_s);
                } else if (IS_64BIT_PROCESS(p)) {
                        sb->st_blksize = sizeof(struct user64_kevent);
                } else {
                        sb->st_blksize = sizeof(struct user32_kevent);
                }
                sb->st_mode = S_IFIFO;
        }
        kqunlock(kq);
        return 0;
}

static inline bool
kqueue_threadreq_can_use_ast(struct kqueue *kq)
{
        if (current_proc() == kq->kq_p) {
                /*
                 * Setting an AST from a non BSD syscall is unsafe: mach_msg_trap() can
                 * do combined send/receive and in the case of self-IPC, the AST may bet
                 * set on a thread that will not return to userspace and needs the
                 * thread the AST would create to unblock itself.
                 *
                 * At this time, we really want to target:
                 *
                 * - kevent variants that can cause thread creations, and dispatch
                 *   really only uses kevent_qos and kevent_id,
                 *
                 * - workq_kernreturn (directly about thread creations)
                 *
                 * - bsdthread_ctl which is used for qos changes and has direct impact
                 *   on the creator thread scheduling decisions.
                 */
                switch (current_uthread()->syscall_code) {
                case SYS_kevent_qos:
                case SYS_kevent_id:
                case SYS_workq_kernreturn:
                case SYS_bsdthread_ctl:
                        return true;
                }
        }
        return false;
}

/*
 * Interact with the pthread kext to request a servicing there at a specific QoS
 * level.
 *
 * - Caller holds the workq request lock
 *
 * - May be called with the kqueue's wait queue set locked,
 *   so cannot do anything that could recurse on that.
 */
static void
kqueue_threadreq_initiate(struct kqueue *kq, workq_threadreq_t kqr,
    kq_index_t qos, int flags)
{
        assert(kqr->tr_kq_wakeup);
        assert(kqr_thread(kqr) == THREAD_NULL);
        assert(!kqr_thread_requested(kqr));
        struct turnstile *ts = TURNSTILE_NULL;

        if (workq_is_exiting(kq->kq_p)) {
                return;
        }

        kqlock_held(kq);

        if (kq->kq_state & KQ_WORKLOOP) {
                __assert_only struct kqworkloop *kqwl = (struct kqworkloop *)kq;

                assert(kqwl->kqwl_owner == THREAD_NULL);
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_THREQUEST),
                    kqwl->kqwl_dynamicid, 0, qos, kqr->tr_kq_wakeup);
                ts = kqwl->kqwl_turnstile;
                /* Add a thread request reference on the kqueue. */
                kqworkloop_retain(kqwl);
        } else {
                assert(kq->kq_state & KQ_WORKQ);
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWQ_THREQUEST),
                    -1, 0, qos, kqr->tr_kq_wakeup);
        }

        /*
         * New-style thread request supported.
         * Provide the pthread kext a pointer to a workq_threadreq_s structure for
         * its use until a corresponding kqueue_threadreq_bind callback.
         */
        if (kqueue_threadreq_can_use_ast(kq)) {
                flags |= WORKQ_THREADREQ_SET_AST_ON_FAILURE;
        }
        if (qos == KQWQ_QOS_MANAGER) {
                qos = WORKQ_THREAD_QOS_MANAGER;
        }
        if (!workq_kern_threadreq_initiate(kq->kq_p, kqr, ts, qos, flags)) {
                /*
                 * Process is shutting down or exec'ing.
                 * All the kqueues are going to be cleaned up
                 * soon. Forget we even asked for a thread -
                 * and make sure we don't ask for more.
                 */
                kq->kq_state &= ~KQ_R2K_ARMED;
                kqueue_release_live(kq);
        }
}

/*
 * kqueue_threadreq_bind_prepost - prepost the bind to kevent
 *
 * This is used when kqueue_threadreq_bind may cause a lock inversion.
 */
__attribute__((always_inline))
void
kqueue_threadreq_bind_prepost(struct proc *p __unused, workq_threadreq_t kqr,
    struct uthread *ut)
{
        ut->uu_kqr_bound = kqr;
        kqr->tr_thread = ut->uu_thread;
        kqr->tr_state = WORKQ_TR_STATE_BINDING;
}

/*
 * kqueue_threadreq_bind_commit - commit a bind prepost
 *
 * The workq code has to commit any binding prepost before the thread has
 * a chance to come back to userspace (and do kevent syscalls) or be aborted.
 */
void
kqueue_threadreq_bind_commit(struct proc *p, thread_t thread)
{
        struct uthread *ut = get_bsdthread_info(thread);
        workq_threadreq_t kqr = ut->uu_kqr_bound;
        kqueue_t kqu = kqr_kqueue(p, kqr);

        kqlock(kqu);
        if (kqr->tr_state == WORKQ_TR_STATE_BINDING) {
                kqueue_threadreq_bind(p, kqr, thread, 0);
        }
        kqunlock(kqu);
}

static void
kqueue_threadreq_modify(kqueue_t kqu, workq_threadreq_t kqr, kq_index_t qos,
    workq_kern_threadreq_flags_t flags)
{
        assert(kqr_thread_requested_pending(kqr));

        kqlock_held(kqu);

        if (kqueue_threadreq_can_use_ast(kqu.kq)) {
                flags |= WORKQ_THREADREQ_SET_AST_ON_FAILURE;
        }
        workq_kern_threadreq_modify(kqu.kq->kq_p, kqr, qos, flags);
}

/*
 * kqueue_threadreq_bind - bind thread to processing kqrequest
 *
 * The provided thread will be responsible for delivering events
 * associated with the given kqrequest.  Bind it and get ready for
 * the thread to eventually arrive.
 */
void
kqueue_threadreq_bind(struct proc *p, workq_threadreq_t kqr, thread_t thread,
    unsigned int flags)
{
        kqueue_t kqu = kqr_kqueue(p, kqr);
        struct uthread *ut = get_bsdthread_info(thread);

        kqlock_held(kqu);

        assert(ut->uu_kqueue_override == 0);

        if (kqr->tr_state == WORKQ_TR_STATE_BINDING) {
                assert(ut->uu_kqr_bound == kqr);
                assert(kqr->tr_thread == thread);
        } else {
                assert(kqr_thread_requested_pending(kqr));
                assert(kqr->tr_thread == THREAD_NULL);
                assert(ut->uu_kqr_bound == NULL);
                ut->uu_kqr_bound = kqr;
                kqr->tr_thread = thread;
        }

        kqr->tr_state = WORKQ_TR_STATE_BOUND;

        if (kqu.kq->kq_state & KQ_WORKLOOP) {
                struct turnstile *ts = kqu.kqwl->kqwl_turnstile;

                if (__improbable(thread == kqu.kqwl->kqwl_owner)) {
                        /*
                         * <rdar://problem/38626999> shows that asserting here is not ok.
                         *
                         * This is not supposed to happen for correct use of the interface,
                         * but it is sadly possible for userspace (with the help of memory
                         * corruption, such as over-release of a dispatch queue) to make
                         * the creator thread the "owner" of a workloop.
                         *
                         * Once that happens, and that creator thread picks up the same
                         * workloop as a servicer, we trip this codepath. We need to fixup
                         * the state to forget about this thread being the owner, as the
                         * entire workloop state machine expects servicers to never be
                         * owners and everything would basically go downhill from here.
                         */
                        kqu.kqwl->kqwl_owner = THREAD_NULL;
                        if (kqworkloop_override(kqu.kqwl)) {
                                thread_drop_kevent_override(thread);
                        }
                }

                if (ts && (flags & KQUEUE_THREADERQ_BIND_NO_INHERITOR_UPDATE) == 0) {
                        /*
                         * Past this point, the interlock is the kq req lock again,
                         * so we can fix the inheritor for good.
                         */
                        filt_wlupdate_inheritor(kqu.kqwl, ts, TURNSTILE_IMMEDIATE_UPDATE);
                        turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_HELD);
                }

                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_BIND), kqu.kqwl->kqwl_dynamicid,
                    thread_tid(thread), kqr->tr_kq_qos_index,
                    (kqr->tr_kq_override_index << 16) | kqr->tr_kq_wakeup);

                ut->uu_kqueue_override = kqr->tr_kq_override_index;
                if (kqr->tr_kq_override_index) {
                        thread_add_servicer_override(thread, kqr->tr_kq_override_index);
                }
        } else {
                assert(kqr->tr_kq_override_index == 0);

                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWQ_BIND), -1,
                    thread_tid(thread), kqr->tr_kq_qos_index,
                    (kqr->tr_kq_override_index << 16) | kqr->tr_kq_wakeup);
        }
}

/*
 * kqueue_threadreq_cancel - abort a pending thread request
 *
 * Called when exiting/exec'ing. Forget our pending request.
 */
void
kqueue_threadreq_cancel(struct proc *p, workq_threadreq_t kqr)
{
        kqueue_release(kqr_kqueue(p, kqr));
}

workq_threadreq_param_t
kqueue_threadreq_workloop_param(workq_threadreq_t kqr)
{
        struct kqworkloop *kqwl;
        workq_threadreq_param_t trp;

        assert(kqr->tr_flags & WORKQ_TR_FLAG_WORKLOOP);
        kqwl = __container_of(kqr, struct kqworkloop, kqwl_request);
        trp.trp_value = kqwl->kqwl_params;
        return trp;
}

/*
 *      kqueue_threadreq_unbind - unbind thread from processing kqueue
 *
 *      End processing the per-QoS bucket of events and allow other threads
 *      to be requested for future servicing.
 *
 *      caller holds a reference on the kqueue.
 */
void
kqueue_threadreq_unbind(struct proc *p, workq_threadreq_t kqr)
{
        if (kqr->tr_flags & WORKQ_TR_FLAG_WORKLOOP) {
                kqworkloop_unbind(kqr_kqworkloop(kqr));
        } else {
                kqworkq_unbind(p, kqr);
        }
}

/*
 * If we aren't already busy processing events [for this QoS],
 * request workq thread support as appropriate.
 *
 * TBD - for now, we don't segregate out processing by QoS.
 *
 * - May be called with the kqueue's wait queue set locked,
 *   so cannot do anything that could recurse on that.
 */
static void
kqworkq_wakeup(struct kqworkq *kqwq, kq_index_t qos_index)
{
        workq_threadreq_t kqr = kqworkq_get_request(kqwq, qos_index);

        /* convert to thread qos value */
        assert(qos_index < KQWQ_NBUCKETS);

        if (!kqr->tr_kq_wakeup) {
                kqr->tr_kq_wakeup = true;
                if (!kqr_thread_requested(kqr)) {
                        kqueue_threadreq_initiate(&kqwq->kqwq_kqueue, kqr, qos_index, 0);
                }
        }
}

/*
 * This represent the asynchronous QoS a given workloop contributes,
 * hence is the max of the current active knotes (override index)
 * and the workloop max qos (userspace async qos).
 */
static kq_index_t
kqworkloop_override(struct kqworkloop *kqwl)
{
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        return MAX(kqr->tr_kq_qos_index, kqr->tr_kq_override_index);
}

static inline void
kqworkloop_request_fire_r2k_notification(struct kqworkloop *kqwl)
{
        workq_threadreq_t kqr = &kqwl->kqwl_request;

        kqlock_held(kqwl);

        if (kqwl->kqwl_state & KQ_R2K_ARMED) {
                kqwl->kqwl_state &= ~KQ_R2K_ARMED;
                act_set_astkevent(kqr_thread_fast(kqr), AST_KEVENT_RETURN_TO_KERNEL);
        }
}

static void
kqworkloop_update_threads_qos(struct kqworkloop *kqwl, int op, kq_index_t qos)
{
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        struct kqueue *kq = &kqwl->kqwl_kqueue;
        kq_index_t old_override = kqworkloop_override(kqwl);
        kq_index_t i;

        kqlock_held(kqwl);

        switch (op) {
        case KQWL_UTQ_UPDATE_WAKEUP_QOS:
                if (qos == KQWL_BUCKET_STAYACTIVE) {
                        /*
                         * the KQWL_BUCKET_STAYACTIVE is not a QoS bucket, we only remember
                         * a high watermark (kqwl_stayactive_qos) of any stay active knote
                         * that was ever registered with this workloop.
                         *
                         * When waitq_set__CALLING_PREPOST_HOOK__() wakes up any stay active
                         * knote, we use this high-watermark as a wakeup-index, and also set
                         * the magic KQWL_BUCKET_STAYACTIVE bit to make sure we remember
                         * there is at least one stay active knote fired until the next full
                         * processing of this bucket.
                         */
                        kqwl->kqwl_wakeup_indexes |= KQWL_STAYACTIVE_FIRED_BIT;
                        qos = kqwl->kqwl_stayactive_qos;
                        assert(qos);
                }
                if (kqwl->kqwl_wakeup_indexes & (1 << qos)) {
                        assert(kqr->tr_kq_wakeup);
                        break;
                }

                kqwl->kqwl_wakeup_indexes |= (1 << qos);
                kqr->tr_kq_wakeup = true;
                kqworkloop_request_fire_r2k_notification(kqwl);
                goto recompute;

        case KQWL_UTQ_UPDATE_STAYACTIVE_QOS:
                assert(qos);
                if (kqwl->kqwl_stayactive_qos < qos) {
                        kqwl->kqwl_stayactive_qos = qos;
                        if (kqwl->kqwl_wakeup_indexes & KQWL_STAYACTIVE_FIRED_BIT) {
                                assert(kqr->tr_kq_wakeup);
                                kqwl->kqwl_wakeup_indexes |= (1 << qos);
                                goto recompute;
                        }
                }
                break;

        case KQWL_UTQ_PARKING:
        case KQWL_UTQ_UNBINDING:
                kqr->tr_kq_override_index = qos;
                OS_FALLTHROUGH;
        case KQWL_UTQ_RECOMPUTE_WAKEUP_QOS:
                if (op == KQWL_UTQ_RECOMPUTE_WAKEUP_QOS) {
                        assert(qos == THREAD_QOS_UNSPECIFIED);
                }
                i = KQWL_BUCKET_STAYACTIVE;
                if (TAILQ_EMPTY(&kqwl->kqwl_suppressed)) {
                        kqr->tr_kq_override_index = THREAD_QOS_UNSPECIFIED;
                }
                if (!TAILQ_EMPTY(&kqwl->kqwl_queue[i]) &&
                    (kqwl->kqwl_wakeup_indexes & KQWL_STAYACTIVE_FIRED_BIT)) {
                        /*
                         * If the KQWL_STAYACTIVE_FIRED_BIT is set, it means a stay active
                         * knote may have fired, so we need to merge in kqwl_stayactive_qos.
                         *
                         * Unlike other buckets, this one is never empty but could be idle.
                         */
                        kqwl->kqwl_wakeup_indexes &= KQWL_STAYACTIVE_FIRED_BIT;
                        kqwl->kqwl_wakeup_indexes |= (1 << kqwl->kqwl_stayactive_qos);
                } else {
                        kqwl->kqwl_wakeup_indexes = 0;
                }
                for (i = THREAD_QOS_UNSPECIFIED + 1; i < KQWL_BUCKET_STAYACTIVE; i++) {
                        if (!TAILQ_EMPTY(&kqwl->kqwl_queue[i])) {
                                kqwl->kqwl_wakeup_indexes |= (1 << i);
                        }
                }
                if (kqwl->kqwl_wakeup_indexes) {
                        kqr->tr_kq_wakeup = true;
                        kqworkloop_request_fire_r2k_notification(kqwl);
                } else {
                        kqr->tr_kq_wakeup = false;
                }
                goto recompute;

        case KQWL_UTQ_RESET_WAKEUP_OVERRIDE:
                kqr->tr_kq_override_index = qos;
                goto recompute;

        case KQWL_UTQ_UPDATE_WAKEUP_OVERRIDE:
recompute:
                /*
                 * When modifying the wakeup QoS or the override QoS, we always need to
                 * maintain our invariant that kqr_override_index is at least as large
                 * as the highest QoS for which an event is fired.
                 *
                 * However this override index can be larger when there is an overriden
                 * suppressed knote pushing on the kqueue.
                 */
                if (kqwl->kqwl_wakeup_indexes > (1 << qos)) {
                        qos = (uint8_t)(fls(kqwl->kqwl_wakeup_indexes) - 1); /* fls is 1-based */
                }
                if (kqr->tr_kq_override_index < qos) {
                        kqr->tr_kq_override_index = qos;
                }
                break;

        case KQWL_UTQ_REDRIVE_EVENTS:
                break;

        case KQWL_UTQ_SET_QOS_INDEX:
                kqr->tr_kq_qos_index = qos;
                break;

        default:
                panic("unknown kqwl thread qos update operation: %d", op);
        }

        thread_t kqwl_owner = kqwl->kqwl_owner;
        thread_t servicer = kqr_thread(kqr);
        boolean_t qos_changed = FALSE;
        kq_index_t new_override = kqworkloop_override(kqwl);

        /*
         * Apply the diffs to the owner if applicable
         */
        if (kqwl_owner) {
#if 0
                /* JMM - need new trace hooks for owner overrides */
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_THADJUST),
                    kqwl->kqwl_dynamicid, thread_tid(kqwl_owner), kqr->tr_kq_qos_index,
                    (kqr->tr_kq_override_index << 16) | kqr->tr_kq_wakeup);
#endif
                if (new_override == old_override) {
                        // nothing to do
                } else if (old_override == THREAD_QOS_UNSPECIFIED) {
                        thread_add_kevent_override(kqwl_owner, new_override);
                } else if (new_override == THREAD_QOS_UNSPECIFIED) {
                        thread_drop_kevent_override(kqwl_owner);
                } else { /*  old_override != new_override */
                        thread_update_kevent_override(kqwl_owner, new_override);
                }
        }

        /*
         * apply the diffs to the servicer
         */
        if (!kqr_thread_requested(kqr)) {
                /*
                 * No servicer, nor thread-request
                 *
                 * Make a new thread request, unless there is an owner (or the workloop
                 * is suspended in userland) or if there is no asynchronous work in the
                 * first place.
                 */

                if (kqwl_owner == NULL && kqr->tr_kq_wakeup) {
                        int initiate_flags = 0;
                        if (op == KQWL_UTQ_UNBINDING) {
                                initiate_flags = WORKQ_THREADREQ_ATTEMPT_REBIND;
                        }
                        kqueue_threadreq_initiate(kq, kqr, new_override, initiate_flags);
                }
        } else if (servicer) {
                /*
                 * Servicer in flight
                 *
                 * Just apply the diff to the servicer
                 */
                struct uthread *ut = get_bsdthread_info(servicer);
                if (ut->uu_kqueue_override != new_override) {
                        if (ut->uu_kqueue_override == THREAD_QOS_UNSPECIFIED) {
                                thread_add_servicer_override(servicer, new_override);
                        } else if (new_override == THREAD_QOS_UNSPECIFIED) {
                                thread_drop_servicer_override(servicer);
                        } else { /* ut->uu_kqueue_override != new_override */
                                thread_update_servicer_override(servicer, new_override);
                        }
                        ut->uu_kqueue_override = new_override;
                        qos_changed = TRUE;
                }
        } else if (new_override == THREAD_QOS_UNSPECIFIED) {
                /*
                 * No events to deliver anymore.
                 *
                 * However canceling with turnstiles is challenging, so the fact that
                 * the request isn't useful will be discovered by the servicer himself
                 * later on.
                 */
        } else if (old_override != new_override) {
                /*
                 * Request is in flight
                 *
                 * Apply the diff to the thread request
                 */
                kqueue_threadreq_modify(kq, kqr, new_override, WORKQ_THREADREQ_NONE);
                qos_changed = TRUE;
        }

        if (qos_changed) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_THADJUST), kqwl->kqwl_dynamicid,
                    thread_tid(servicer), kqr->tr_kq_qos_index,
                    (kqr->tr_kq_override_index << 16) | kqr->tr_kq_wakeup);
        }
}

static void
kqworkloop_wakeup(struct kqworkloop *kqwl, kq_index_t qos)
{
        if ((kqwl->kqwl_state & KQ_PROCESSING) &&
            kqr_thread(&kqwl->kqwl_request) == current_thread()) {
                /*
                 * kqworkloop_end_processing() will perform the required QoS
                 * computations when it unsets the processing mode.
                 */
                return;
        }

        kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_UPDATE_WAKEUP_QOS, qos);
}

static struct kqtailq *
kqueue_get_suppressed_queue(kqueue_t kq, struct knote *kn)
{
        if (kq.kq->kq_state & KQ_WORKLOOP) {
                return &kq.kqwl->kqwl_suppressed;
        } else if (kq.kq->kq_state & KQ_WORKQ) {
                return &kq.kqwq->kqwq_suppressed[kn->kn_qos_index];
        } else {
                return &kq.kqf->kqf_suppressed;
        }
}

struct turnstile *
kqueue_alloc_turnstile(kqueue_t kqu)
{
        struct kqworkloop *kqwl = kqu.kqwl;
        kq_state_t kq_state;

        kq_state = os_atomic_load(&kqu.kq->kq_state, dependency);
        if (kq_state & KQ_HAS_TURNSTILE) {
                /* force a dependency to pair with the atomic or with release below */
                return os_atomic_load_with_dependency_on(&kqwl->kqwl_turnstile,
                           (uintptr_t)kq_state);
        }

        if (!(kq_state & KQ_WORKLOOP)) {
                return TURNSTILE_NULL;
        }

        struct turnstile *ts = turnstile_alloc(), *free_ts = TURNSTILE_NULL;
        bool workq_locked = false;

        kqlock(kqu);

        if (filt_wlturnstile_interlock_is_workq(kqwl)) {
                workq_locked = true;
                workq_kern_threadreq_lock(kqwl->kqwl_p);
        }

        if (kqwl->kqwl_state & KQ_HAS_TURNSTILE) {
                free_ts = ts;
                ts = kqwl->kqwl_turnstile;
        } else {
                ts = turnstile_prepare((uintptr_t)kqwl, &kqwl->kqwl_turnstile,
                    ts, TURNSTILE_WORKLOOPS);

                /* release-barrier to pair with the unlocked load of kqwl_turnstile above */
                os_atomic_or(&kqwl->kqwl_state, KQ_HAS_TURNSTILE, release);

                if (filt_wlturnstile_interlock_is_workq(kqwl)) {
                        workq_kern_threadreq_update_inheritor(kqwl->kqwl_p,
                            &kqwl->kqwl_request, kqwl->kqwl_owner,
                            ts, TURNSTILE_IMMEDIATE_UPDATE);
                        /*
                         * The workq may no longer be the interlock after this.
                         * In which case the inheritor wasn't updated.
                         */
                }
                if (!filt_wlturnstile_interlock_is_workq(kqwl)) {
                        filt_wlupdate_inheritor(kqwl, ts, TURNSTILE_IMMEDIATE_UPDATE);
                }
        }

        if (workq_locked) {
                workq_kern_threadreq_unlock(kqwl->kqwl_p);
        }

        kqunlock(kqu);

        if (free_ts) {
                turnstile_deallocate(free_ts);
        } else {
                turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_NOT_HELD);
        }
        return ts;
}

__attribute__((always_inline))
struct turnstile *
kqueue_turnstile(kqueue_t kqu)
{
        kq_state_t kq_state = os_atomic_load(&kqu.kq->kq_state, relaxed);
        if (kq_state & KQ_WORKLOOP) {
                return os_atomic_load(&kqu.kqwl->kqwl_turnstile, relaxed);
        }
        return TURNSTILE_NULL;
}

__attribute__((always_inline))
struct turnstile *
kqueue_threadreq_get_turnstile(workq_threadreq_t kqr)
{
        struct kqworkloop *kqwl = kqr_kqworkloop(kqr);
        if (kqwl) {
                return os_atomic_load(&kqwl->kqwl_turnstile, relaxed);
        }
        return TURNSTILE_NULL;
}

static void
kqworkloop_set_overcommit(struct kqworkloop *kqwl)
{
        workq_threadreq_t kqr = &kqwl->kqwl_request;

        /*
         * This test is racy, but since we never remove this bit,
         * it allows us to avoid taking a lock.
         */
        if (kqr->tr_flags & WORKQ_TR_FLAG_OVERCOMMIT) {
                return;
        }

        kqlock_held(kqwl);

        if (kqr_thread_requested_pending(kqr)) {
                kqueue_threadreq_modify(kqwl, kqr, kqr->tr_qos,
                    WORKQ_THREADREQ_MAKE_OVERCOMMIT);
        } else {
                kqr->tr_flags |= WORKQ_TR_FLAG_OVERCOMMIT;
        }
}

static void
kqworkq_update_override(struct kqworkq *kqwq, struct knote *kn,
    kq_index_t override_index)
{
        workq_threadreq_t kqr;
        kq_index_t old_override_index;
        kq_index_t queue_index = kn->kn_qos_index;

        if (override_index <= queue_index) {
                return;
        }

        kqr = kqworkq_get_request(kqwq, queue_index);

        kqlock_held(kqwq);

        old_override_index = kqr->tr_kq_override_index;
        if (override_index > MAX(kqr->tr_kq_qos_index, old_override_index)) {
                thread_t servicer = kqr_thread(kqr);
                kqr->tr_kq_override_index = override_index;

                /* apply the override to [incoming?] servicing thread */
                if (servicer) {
                        if (old_override_index) {
                                thread_update_kevent_override(servicer, override_index);
                        } else {
                                thread_add_kevent_override(servicer, override_index);
                        }
                }
        }
}

static void
kqueue_update_override(kqueue_t kqu, struct knote *kn, thread_qos_t qos)
{
        if (kqu.kq->kq_state & KQ_WORKLOOP) {
                kqworkloop_update_threads_qos(kqu.kqwl, KQWL_UTQ_UPDATE_WAKEUP_OVERRIDE,
                    qos);
        } else {
                kqworkq_update_override(kqu.kqwq, kn, qos);
        }
}

static void
kqworkloop_unbind_locked(struct kqworkloop *kqwl, thread_t thread,
    enum kqwl_unbind_locked_mode how)
{
        struct uthread *ut = get_bsdthread_info(thread);
        workq_threadreq_t kqr = &kqwl->kqwl_request;

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWL_UNBIND), kqwl->kqwl_dynamicid,
            thread_tid(thread), 0, 0);

        kqlock_held(kqwl);

        assert(ut->uu_kqr_bound == kqr);
        ut->uu_kqr_bound = NULL;
        if (how == KQWL_OVERRIDE_DROP_IMMEDIATELY &&
            ut->uu_kqueue_override != THREAD_QOS_UNSPECIFIED) {
                thread_drop_servicer_override(thread);
                ut->uu_kqueue_override = THREAD_QOS_UNSPECIFIED;
        }

        if (kqwl->kqwl_owner == NULL && kqwl->kqwl_turnstile) {
                turnstile_update_inheritor(kqwl->kqwl_turnstile,
                    TURNSTILE_INHERITOR_NULL, TURNSTILE_IMMEDIATE_UPDATE);
                turnstile_update_inheritor_complete(kqwl->kqwl_turnstile,
                    TURNSTILE_INTERLOCK_HELD);
        }

        kqr->tr_thread = THREAD_NULL;
        kqr->tr_state = WORKQ_TR_STATE_IDLE;
        kqwl->kqwl_state &= ~KQ_R2K_ARMED;
}

static void
kqworkloop_unbind_delayed_override_drop(thread_t thread)
{
        struct uthread *ut = get_bsdthread_info(thread);
        assert(ut->uu_kqr_bound == NULL);
        if (ut->uu_kqueue_override != THREAD_QOS_UNSPECIFIED) {
                thread_drop_servicer_override(thread);
                ut->uu_kqueue_override = THREAD_QOS_UNSPECIFIED;
        }
}

/*
 *      kqworkloop_unbind - Unbind the servicer thread of a workloop kqueue
 *
 *      It will acknowledge events, and possibly request a new thread if:
 *      - there were active events left
 *      - we pended waitq hook callouts during processing
 *      - we pended wakeups while processing (or unsuppressing)
 *
 *      Called with kqueue lock held.
 */
static void
kqworkloop_unbind(struct kqworkloop *kqwl)
{
        struct kqueue *kq = &kqwl->kqwl_kqueue;
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        thread_t thread = kqr_thread_fast(kqr);
        int op = KQWL_UTQ_PARKING;
        kq_index_t qos_override = THREAD_QOS_UNSPECIFIED;

        assert(thread == current_thread());

        kqlock(kqwl);

        /*
         * Forcing the KQ_PROCESSING flag allows for QoS updates because of
         * unsuppressing knotes not to be applied until the eventual call to
         * kqworkloop_update_threads_qos() below.
         */
        assert((kq->kq_state & KQ_PROCESSING) == 0);
        if (!TAILQ_EMPTY(&kqwl->kqwl_suppressed)) {
                kq->kq_state |= KQ_PROCESSING;
                qos_override = kqworkloop_acknowledge_events(kqwl);
                kq->kq_state &= ~KQ_PROCESSING;
        }

        kqworkloop_unbind_locked(kqwl, thread, KQWL_OVERRIDE_DROP_DELAYED);
        kqworkloop_update_threads_qos(kqwl, op, qos_override);

        kqunlock(kqwl);

        /*
         * Drop the override on the current thread last, after the call to
         * kqworkloop_update_threads_qos above.
         */
        kqworkloop_unbind_delayed_override_drop(thread);

        /* If last reference, dealloc the workloop kq */
        kqworkloop_release(kqwl);
}

static thread_qos_t
kqworkq_unbind_locked(struct kqworkq *kqwq,
    workq_threadreq_t kqr, thread_t thread)
{
        struct uthread *ut = get_bsdthread_info(thread);
        kq_index_t old_override = kqr->tr_kq_override_index;

        KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KQWQ_UNBIND), -1,
            thread_tid(kqr_thread(kqr)), kqr->tr_kq_qos_index, 0);

        kqlock_held(kqwq);

        assert(ut->uu_kqr_bound == kqr);
        ut->uu_kqr_bound = NULL;
        kqr->tr_thread = THREAD_NULL;
        kqr->tr_state = WORKQ_TR_STATE_IDLE;
        kqr->tr_kq_override_index = THREAD_QOS_UNSPECIFIED;
        kqwq->kqwq_state &= ~KQ_R2K_ARMED;

        return old_override;
}

/*
 *      kqworkq_unbind - unbind of a workq kqueue from a thread
 *
 *      We may have to request new threads.
 *      This can happen there are no waiting processing threads and:
 *      - there were active events we never got to (count > 0)
 *      - we pended waitq hook callouts during processing
 *      - we pended wakeups while processing (or unsuppressing)
 */
static void
kqworkq_unbind(proc_t p, workq_threadreq_t kqr)
{
        struct kqworkq *kqwq = (struct kqworkq *)p->p_fd->fd_wqkqueue;
        __assert_only int rc;

        kqlock(kqwq);
        rc = kqworkq_acknowledge_events(kqwq, kqr, 0, KQWQAE_UNBIND);
        assert(rc == -1);
        kqunlock(kqwq);
}

workq_threadreq_t
kqworkq_get_request(struct kqworkq *kqwq, kq_index_t qos_index)
{
        assert(qos_index < KQWQ_NBUCKETS);
        return &kqwq->kqwq_request[qos_index];
}

static void
knote_reset_priority(kqueue_t kqu, struct knote *kn, pthread_priority_t pp)
{
        kq_index_t qos = _pthread_priority_thread_qos(pp);

        if (kqu.kq->kq_state & KQ_WORKLOOP) {
                assert((pp & _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG) == 0);
                pp = _pthread_priority_normalize(pp);
        } else if (kqu.kq->kq_state & KQ_WORKQ) {
                if (qos == THREAD_QOS_UNSPECIFIED) {
                        /* On workqueues, outside of QoS means MANAGER */
                        qos = KQWQ_QOS_MANAGER;
                        pp = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                } else {
                        pp = _pthread_priority_normalize(pp);
                }
        } else {
                pp = _pthread_unspecified_priority();
                qos = THREAD_QOS_UNSPECIFIED;
        }

        kn->kn_qos = (int32_t)pp;

        if ((kn->kn_status & KN_MERGE_QOS) == 0 || qos > kn->kn_qos_override) {
                /* Never lower QoS when in "Merge" mode */
                kn->kn_qos_override = qos;
        }

        /* only adjust in-use qos index when not suppressed */
        if (kn->kn_status & KN_SUPPRESSED) {
                kqueue_update_override(kqu, kn, qos);
        } else if (kn->kn_qos_index != qos) {
                knote_dequeue(kqu, kn);
                kn->kn_qos_index = qos;
        }
}

static void
knote_adjust_qos(struct kqueue *kq, struct knote *kn, int result)
{
        thread_qos_t qos_index = (result >> FILTER_ADJUST_EVENT_QOS_SHIFT) & 7;

        kqlock_held(kq);

        assert(result & FILTER_ADJUST_EVENT_QOS_BIT);
        assert(qos_index < THREAD_QOS_LAST);

        /*
         * Early exit for knotes that should not change QoS
         */
        if (__improbable(!knote_fops(kn)->f_adjusts_qos)) {
                panic("filter %d cannot change QoS", kn->kn_filtid);
        } else if (__improbable(!knote_has_qos(kn))) {
                return;
        }

        /*
         * knotes with the FALLBACK flag will only use their registration QoS if the
         * incoming event has no QoS, else, the registration QoS acts as a floor.
         */
        thread_qos_t req_qos = _pthread_priority_thread_qos_fast(kn->kn_qos);
        if (kn->kn_qos & _PTHREAD_PRIORITY_FALLBACK_FLAG) {
                if (qos_index == THREAD_QOS_UNSPECIFIED) {
                        qos_index = req_qos;
                }
        } else {
                if (qos_index < req_qos) {
                        qos_index = req_qos;
                }
        }
        if ((kn->kn_status & KN_MERGE_QOS) && (qos_index < kn->kn_qos_override)) {
                /* Never lower QoS when in "Merge" mode */
                return;
        }

        if ((kn->kn_status & KN_LOCKED) && (kn->kn_status & KN_POSTING)) {
                /*
                 * When we're trying to update the QoS override and that both an
                 * f_event() and other f_* calls are running concurrently, any of these
                 * in flight calls may want to perform overrides that aren't properly
                 * serialized with each other.
                 *
                 * The first update that observes this racy situation enters a "Merge"
                 * mode which causes subsequent override requests to saturate the
                 * override instead of replacing its value.
                 *
                 * This mode is left when knote_unlock() or knote_post()
                 * observe that no other f_* routine is in flight.
                 */
                kn->kn_status |= KN_MERGE_QOS;
        }

        /*
         * Now apply the override if it changed.
         */

        if (kn->kn_qos_override == qos_index) {
                return;
        }

        kn->kn_qos_override = qos_index;

        if (kn->kn_status & KN_SUPPRESSED) {
                /*
                 * For suppressed events, the kn_qos_index field cannot be touched as it
                 * allows us to know on which supress queue the knote is for a kqworkq.
                 *
                 * Also, there's no natural push applied on the kqueues when this field
                 * changes anyway. We hence need to apply manual overrides in this case,
                 * which will be cleared when the events are later acknowledged.
                 */
                kqueue_update_override(kq, kn, qos_index);
        } else if (kn->kn_qos_index != qos_index) {
                knote_dequeue(kq, kn);
                kn->kn_qos_index = qos_index;
        }
}

/*
 * Called back from waitq code when no threads waiting and the hook was set.
 *
 * Preemption is disabled - minimal work can be done in this context!!!
 */
void
waitq_set__CALLING_PREPOST_HOOK__(waitq_set_prepost_hook_t *kq_hook)
{
        kqueue_t kqu;

        kqu.kq = __container_of(kq_hook, struct kqueue, kq_waitq_hook);
        assert(kqu.kq->kq_state & (KQ_WORKQ | KQ_WORKLOOP));

        kqlock(kqu);

        if (kqu.kq->kq_count > 0) {
                if (kqu.kq->kq_state & KQ_WORKLOOP) {
                        kqworkloop_wakeup(kqu.kqwl, KQWL_BUCKET_STAYACTIVE);
                } else {
                        kqworkq_wakeup(kqu.kqwq, KQWQ_QOS_MANAGER);
                }
        }

        kqunlock(kqu);
}

void
klist_init(struct klist *list)
{
        SLIST_INIT(list);
}


/*
 * Query/Post each knote in the object's list
 *
 *      The object lock protects the list. It is assumed
 *      that the filter/event routine for the object can
 *      determine that the object is already locked (via
 *      the hint) and not deadlock itself.
 *
 *      The object lock should also hold off pending
 *      detach/drop operations.
 */
void
knote(struct klist *list, long hint)
{
        struct knote *kn;

        SLIST_FOREACH(kn, list, kn_selnext) {
                knote_post(kn, hint);
        }
}

/*
 * attach a knote to the specified list.  Return true if this is the first entry.
 * The list is protected by whatever lock the object it is associated with uses.
 */
int
knote_attach(struct klist *list, struct knote *kn)
{
        int ret = SLIST_EMPTY(list);
        SLIST_INSERT_HEAD(list, kn, kn_selnext);
        return ret;
}

/*
 * detach a knote from the specified list.  Return true if that was the last entry.
 * The list is protected by whatever lock the object it is associated with uses.
 */
int
knote_detach(struct klist *list, struct knote *kn)
{
        SLIST_REMOVE(list, kn, knote, kn_selnext);
        return SLIST_EMPTY(list);
}

/*
 * knote_vanish - Indicate that the source has vanished
 *
 * If the knote has requested EV_VANISHED delivery,
 * arrange for that. Otherwise, deliver a NOTE_REVOKE
 * event for backward compatibility.
 *
 * The knote is marked as having vanished, but is not
 * actually detached from the source in this instance.
 * The actual detach is deferred until the knote drop.
 *
 * Our caller already has the object lock held. Calling
 * the detach routine would try to take that lock
 * recursively - which likely is not supported.
 */
void
knote_vanish(struct klist *list, bool make_active)
{
        struct knote *kn;
        struct knote *kn_next;

        SLIST_FOREACH_SAFE(kn, list, kn_selnext, kn_next) {
                struct kqueue *kq = knote_get_kq(kn);

                kqlock(kq);
                if (__probable(kn->kn_status & KN_REQVANISH)) {
                        /*
                         * If EV_VANISH supported - prepare to deliver one
                         */
                        kn->kn_status |= KN_VANISHED;
                } else {
                        /*
                         * Handle the legacy way to indicate that the port/portset was
                         * deallocated or left the current Mach portspace (modern technique
                         * is with an EV_VANISHED protocol).
                         *
                         * Deliver an EV_EOF event for these changes (hopefully it will get
                         * delivered before the port name recycles to the same generation
                         * count and someone tries to re-register a kevent for it or the
                         * events are udata-specific - avoiding a conflict).
                         */
                        kn->kn_flags |= EV_EOF | EV_ONESHOT;
                }
                if (make_active) {
                        knote_activate(kq, kn, FILTER_ACTIVE);
                }
                kqunlock(kq);
        }
}

/*
 * Force a lazy allocation of the waitqset link
 * of the kq_wqs associated with the kn
 * if it wasn't already allocated.
 *
 * This allows knote_link_waitq to never block
 * if reserved_link is not NULL.
 */
void
knote_link_waitqset_lazy_alloc(struct knote *kn)
{
        struct kqueue *kq = knote_get_kq(kn);
        waitq_set_lazy_init_link(&kq->kq_wqs);
}

/*
 * Check if a lazy allocation for the waitqset link
 * of the kq_wqs is needed.
 */
boolean_t
knote_link_waitqset_should_lazy_alloc(struct knote *kn)
{
        struct kqueue *kq = knote_get_kq(kn);
        return waitq_set_should_lazy_init_link(&kq->kq_wqs);
}

/*
 * For a given knote, link a provided wait queue directly with the kqueue.
 * Wakeups will happen via recursive wait queue support.  But nothing will move
 * the knote to the active list at wakeup (nothing calls knote()).  Instead,
 * we permanently enqueue them here.
 *
 * kqueue and knote references are held by caller.
 * waitq locked by caller.
 *
 * caller provides the wait queue link structure and insures that the kq->kq_wqs
 * is linked by previously calling knote_link_waitqset_lazy_alloc.
 */
int
knote_link_waitq(struct knote *kn, struct waitq *wq, uint64_t *reserved_link)
{
        struct kqueue *kq = knote_get_kq(kn);
        kern_return_t kr;

        kr = waitq_link(wq, &kq->kq_wqs, WAITQ_ALREADY_LOCKED, reserved_link);
        if (kr == KERN_SUCCESS) {
                knote_markstayactive(kn);
                return 0;
        } else {
                return EINVAL;
        }
}

/*
 * Unlink the provided wait queue from the kqueue associated with a knote.
 * Also remove it from the magic list of directly attached knotes.
 *
 * Note that the unlink may have already happened from the other side, so
 * ignore any failures to unlink and just remove it from the kqueue list.
 *
 * On success, caller is responsible for the link structure
 */
int
knote_unlink_waitq(struct knote *kn, struct waitq *wq)
{
        struct kqueue *kq = knote_get_kq(kn);
        kern_return_t kr;

        kr = waitq_unlink(wq, &kq->kq_wqs);
        knote_clearstayactive(kn);
        return (kr != KERN_SUCCESS) ? EINVAL : 0;
}

/*
 * remove all knotes referencing a specified fd
 *
 * Entered with the proc_fd lock already held.
 * It returns the same way, but may drop it temporarily.
 */
void
knote_fdclose(struct proc *p, int fd)
{
        struct klist *list;
        struct knote *kn;
        KNOTE_LOCK_CTX(knlc);

restart:
        list = &p->p_fd->fd_knlist[fd];
        SLIST_FOREACH(kn, list, kn_link) {
                struct kqueue *kq = knote_get_kq(kn);

                kqlock(kq);

                if (kq->kq_p != p) {
                        panic("%s: proc mismatch (kq->kq_p=%p != p=%p)",
                            __func__, kq->kq_p, p);
                }

                /*
                 * If the knote supports EV_VANISHED delivery,
                 * transition it to vanished mode (or skip over
                 * it if already vanished).
                 */
                if (kn->kn_status & KN_VANISHED) {
                        kqunlock(kq);
                        continue;
                }

                proc_fdunlock(p);
                if (!knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
                        /* the knote was dropped by someone, nothing to do */
                } else if (kn->kn_status & KN_REQVANISH) {
                        kn->kn_status |= KN_VANISHED;

                        kqunlock(kq);
                        knote_fops(kn)->f_detach(kn);
                        if (kn->kn_is_fd) {
                                fp_drop(p, (int)kn->kn_id, kn->kn_fp, 0);
                        }
                        kn->kn_filtid = EVFILTID_DETACHED;
                        kqlock(kq);

                        knote_activate(kq, kn, FILTER_ACTIVE);
                        knote_unlock(kq, kn, &knlc, KNOTE_KQ_UNLOCK);
                } else {
                        knote_drop(kq, kn, &knlc);
                }

                proc_fdlock(p);
                goto restart;
        }
}

/*
 * knote_fdfind - lookup a knote in the fd table for process
 *
 * If the filter is file-based, lookup based on fd index.
 * Otherwise use a hash based on the ident.
 *
 * Matching is based on kq, filter, and ident. Optionally,
 * it may also be based on the udata field in the kevent -
 * allowing multiple event registration for the file object
 * per kqueue.
 *
 * fd_knhashlock or fdlock held on entry (and exit)
 */
static struct knote *
knote_fdfind(struct kqueue *kq,
    const struct kevent_internal_s *kev,
    bool is_fd,
    struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        struct klist *list = NULL;
        struct knote *kn = NULL;

        /*
         * determine where to look for the knote
         */
        if (is_fd) {
                /* fd-based knotes are linked off the fd table */
                if (kev->kei_ident < (u_int)fdp->fd_knlistsize) {
                        list = &fdp->fd_knlist[kev->kei_ident];
                }
        } else if (fdp->fd_knhashmask != 0) {
                /* hash non-fd knotes here too */
                list = &fdp->fd_knhash[KN_HASH((u_long)kev->kei_ident, fdp->fd_knhashmask)];
        }

        /*
         * scan the selected list looking for a match
         */
        if (list != NULL) {
                SLIST_FOREACH(kn, list, kn_link) {
                        if (kq == knote_get_kq(kn) &&
                            kev->kei_ident == kn->kn_id &&
                            kev->kei_filter == kn->kn_filter) {
                                if (kev->kei_flags & EV_UDATA_SPECIFIC) {
                                        if ((kn->kn_flags & EV_UDATA_SPECIFIC) &&
                                            kev->kei_udata == kn->kn_udata) {
                                                break; /* matching udata-specific knote */
                                        }
                                } else if ((kn->kn_flags & EV_UDATA_SPECIFIC) == 0) {
                                        break; /* matching non-udata-specific knote */
                                }
                        }
                }
        }
        return kn;
}

/*
 * kq_add_knote- Add knote to the fd table for process
 * while checking for duplicates.
 *
 * All file-based filters associate a list of knotes by file
 * descriptor index. All other filters hash the knote by ident.
 *
 * May have to grow the table of knote lists to cover the
 * file descriptor index presented.
 *
 * fd_knhashlock and fdlock unheld on entry (and exit).
 *
 * Takes a rwlock boost if inserting the knote is successful.
 */
static int
kq_add_knote(struct kqueue *kq, struct knote *kn, struct knote_lock_ctx *knlc,
    struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        struct klist *list = NULL;
        int ret = 0;
        bool is_fd = kn->kn_is_fd;
        uint64_t nofile = proc_limitgetcur(p, RLIMIT_NOFILE, TRUE);

        if (is_fd) {
                proc_fdlock(p);
        } else {
                knhash_lock(fdp);
        }

        if (knote_fdfind(kq, &kn->kn_kevent, is_fd, p) != NULL) {
                /* found an existing knote: we can't add this one */
                ret = ERESTART;
                goto out_locked;
        }

        /* knote was not found: add it now */
        if (!is_fd) {
                if (fdp->fd_knhashmask == 0) {
                        u_long size = 0;

                        list = hashinit(CONFIG_KN_HASHSIZE, M_KQUEUE, &size);
                        if (list == NULL) {
                                ret = ENOMEM;
                                goto out_locked;
                        }

                        fdp->fd_knhash = list;
                        fdp->fd_knhashmask = size;
                }

                list = &fdp->fd_knhash[KN_HASH(kn->kn_id, fdp->fd_knhashmask)];
                SLIST_INSERT_HEAD(list, kn, kn_link);
                ret = 0;
                goto out_locked;
        } else {
                /* knote is fd based */

                if ((u_int)fdp->fd_knlistsize <= kn->kn_id) {
                        u_int size = 0;

                        /* Make sure that fd stays below current process's soft limit AND system allowed per-process limits */
                        if (kn->kn_id >= (uint64_t) nofile
                            || kn->kn_id >= (uint64_t)maxfilesperproc) {
                                ret = EINVAL;
                                goto out_locked;
                        }
                        /* have to grow the fd_knlist */
                        size = fdp->fd_knlistsize;
                        while (size <= kn->kn_id) {
                                size += KQEXTENT;
                        }

                        if (size >= (UINT_MAX / sizeof(struct klist *))) {
                                ret = EINVAL;
                                goto out_locked;
                        }

                        list = kheap_alloc(KM_KQUEUE, size * sizeof(struct klist *),
                            Z_WAITOK);
                        if (list == NULL) {
                                ret = ENOMEM;
                                goto out_locked;
                        }

                        bcopy((caddr_t)fdp->fd_knlist, (caddr_t)list,
                            fdp->fd_knlistsize * sizeof(struct klist *));
                        bzero((caddr_t)list +
                            fdp->fd_knlistsize * sizeof(struct klist *),
                            (size - fdp->fd_knlistsize) * sizeof(struct klist *));
                        kheap_free(KM_KQUEUE, fdp->fd_knlist,
                            fdp->fd_knlistsize * sizeof(struct klist *));
                        fdp->fd_knlist = list;
                        fdp->fd_knlistsize = size;
                }

                list = &fdp->fd_knlist[kn->kn_id];
                SLIST_INSERT_HEAD(list, kn, kn_link);
                ret = 0;
                goto out_locked;
        }

out_locked:
        if (ret == 0) {
                kqlock(kq);
                assert((kn->kn_status & KN_LOCKED) == 0);
                (void)knote_lock(kq, kn, knlc, KNOTE_KQ_UNLOCK);
                kqueue_retain(kq); /* retain a kq ref */
        }
        if (is_fd) {
                proc_fdunlock(p);
        } else {
                knhash_unlock(fdp);
        }

        return ret;
}

/*
 * kq_remove_knote - remove a knote from the fd table for process
 *
 * If the filter is file-based, remove based on fd index.
 * Otherwise remove from the hash based on the ident.
 *
 * fd_knhashlock and fdlock unheld on entry (and exit).
 */
static void
kq_remove_knote(struct kqueue *kq, struct knote *kn, struct proc *p,
    struct knote_lock_ctx *knlc)
{
        struct filedesc *fdp = p->p_fd;
        struct klist *list = NULL;
        uint16_t kq_state;
        bool is_fd = kn->kn_is_fd;

        if (is_fd) {
                proc_fdlock(p);
        } else {
                knhash_lock(fdp);
        }

        if (is_fd) {
                assert((u_int)fdp->fd_knlistsize > kn->kn_id);
                list = &fdp->fd_knlist[kn->kn_id];
        } else {
                list = &fdp->fd_knhash[KN_HASH(kn->kn_id, fdp->fd_knhashmask)];
        }
        SLIST_REMOVE(list, kn, knote, kn_link);

        kqlock(kq);
        kq_state = kq->kq_state;
        if (knlc) {
                knote_unlock_cancel(kq, kn, knlc);
        } else {
                kqunlock(kq);
        }
        if (is_fd) {
                proc_fdunlock(p);
        } else {
                knhash_unlock(fdp);
        }

        if (kq_state & KQ_DYNAMIC) {
                kqworkloop_release((struct kqworkloop *)kq);
        }
}

/*
 * kq_find_knote_and_kq_lock - lookup a knote in the fd table for process
 * and, if the knote is found, acquires the kqlock while holding the fd table lock/spinlock.
 *
 * fd_knhashlock or fdlock unheld on entry (and exit)
 */

static struct knote *
kq_find_knote_and_kq_lock(struct kqueue *kq, struct kevent_qos_s *kev,
    bool is_fd, struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        struct knote *kn;

        if (is_fd) {
                proc_fdlock(p);
        } else {
                knhash_lock(fdp);
        }

        /*
         * Temporary horrible hack:
         * this cast is gross and will go away in a future change.
         * It is OK to do because we don't look at xflags/s_fflags,
         * and that when we cast down the kev this way,
         * the truncated filter field works.
         */
        kn = knote_fdfind(kq, (struct kevent_internal_s *)kev, is_fd, p);

        if (kn) {
                kqlock(kq);
                assert(knote_get_kq(kn) == kq);
        }

        if (is_fd) {
                proc_fdunlock(p);
        } else {
                knhash_unlock(fdp);
        }

        return kn;
}

__attribute__((noinline))
static void
kqfile_wakeup(struct kqfile *kqf, __unused kq_index_t qos)
{
        /* flag wakeups during processing */
        if (kqf->kqf_state & KQ_PROCESSING) {
                kqf->kqf_state |= KQ_WAKEUP;
        }

        /* wakeup a thread waiting on this queue */
        if (kqf->kqf_state & (KQ_SLEEP | KQ_SEL)) {
                kqf->kqf_state &= ~(KQ_SLEEP | KQ_SEL);
                waitq_wakeup64_all((struct waitq *)&kqf->kqf_wqs, KQ_EVENT,
                    THREAD_AWAKENED, WAITQ_ALL_PRIORITIES);
        }

        /* wakeup other kqueues/select sets we're inside */
        KNOTE(&kqf->kqf_sel.si_note, 0);
}

static struct kqtailq *
knote_get_tailq(kqueue_t kqu, struct knote *kn)
{
        kq_index_t qos_index = kn->kn_qos_index;

        if (kqu.kq->kq_state & KQ_WORKLOOP) {
                assert(qos_index < KQWL_NBUCKETS);
        } else if (kqu.kq->kq_state & KQ_WORKQ) {
                assert(qos_index < KQWQ_NBUCKETS);
        } else {
                assert(qos_index == QOS_INDEX_KQFILE);
        }
        static_assert(offsetof(struct kqueue, kq_queue) == sizeof(struct kqueue),
            "struct kqueue::kq_queue must be exactly at the end");
        return &kqu.kq->kq_queue[qos_index];
}

static void
knote_enqueue(kqueue_t kqu, struct knote *kn, kn_status_t wakeup_mask)
{
        kqlock_held(kqu);

        if ((kn->kn_status & (KN_ACTIVE | KN_STAYACTIVE)) == 0) {
                return;
        }

        if (kn->kn_status & (KN_DISABLED | KN_SUPPRESSED | KN_DROPPING)) {
                return;
        }

        if ((kn->kn_status & KN_QUEUED) == 0) {
                struct kqtailq *queue = knote_get_tailq(kqu, kn);

                TAILQ_INSERT_TAIL(queue, kn, kn_tqe);
                kn->kn_status |= KN_QUEUED;
                kqu.kq->kq_count++;
        } else if ((kn->kn_status & KN_STAYACTIVE) == 0) {
                return;
        }

        if (kn->kn_status & wakeup_mask) {
                if (kqu.kq->kq_state & KQ_WORKLOOP) {
                        kqworkloop_wakeup(kqu.kqwl, kn->kn_qos_index);
                } else if (kqu.kq->kq_state & KQ_WORKQ) {
                        kqworkq_wakeup(kqu.kqwq, kn->kn_qos_index);
                } else {
                        kqfile_wakeup(kqu.kqf, kn->kn_qos_index);
                }
        }
}

__attribute__((always_inline))
static inline void
knote_dequeue(kqueue_t kqu, struct knote *kn)
{
        if (kn->kn_status & KN_QUEUED) {
                struct kqtailq *queue = knote_get_tailq(kqu, kn);

                // attaching the knote calls knote_reset_priority() without
                // the kqlock which is fine, so we can't call kqlock_held()
                // if we're not queued.
                kqlock_held(kqu);

                TAILQ_REMOVE(queue, kn, kn_tqe);
                kn->kn_status &= ~KN_QUEUED;
                kqu.kq->kq_count--;
        }
}

/* called with kqueue lock held */
static void
knote_suppress(kqueue_t kqu, struct knote *kn)
{
        struct kqtailq *suppressq;

        kqlock_held(kqu);

        assert((kn->kn_status & KN_SUPPRESSED) == 0);
        assert(kn->kn_status & KN_QUEUED);

        knote_dequeue(kqu, kn);
        /* deactivate - so new activations indicate a wakeup */
        kn->kn_status &= ~KN_ACTIVE;
        kn->kn_status |= KN_SUPPRESSED;
        suppressq = kqueue_get_suppressed_queue(kqu, kn);
        TAILQ_INSERT_TAIL(suppressq, kn, kn_tqe);
}

__attribute__((always_inline))
static inline void
knote_unsuppress_noqueue(kqueue_t kqu, struct knote *kn)
{
        struct kqtailq *suppressq;

        kqlock_held(kqu);

        assert(kn->kn_status & KN_SUPPRESSED);

        kn->kn_status &= ~KN_SUPPRESSED;
        suppressq = kqueue_get_suppressed_queue(kqu, kn);
        TAILQ_REMOVE(suppressq, kn, kn_tqe);

        /*
         * If the knote is no longer active, reset its push,
         * and resynchronize kn_qos_index with kn_qos_override
         * for knotes with a real qos.
         */
        if ((kn->kn_status & KN_ACTIVE) == 0 && knote_has_qos(kn)) {
                kn->kn_qos_override = _pthread_priority_thread_qos_fast(kn->kn_qos);
        }
        kn->kn_qos_index = kn->kn_qos_override;
}

/* called with kqueue lock held */
static void
knote_unsuppress(kqueue_t kqu, struct knote *kn)
{
        if (kn->kn_status & KN_SUPPRESSED) {
                knote_unsuppress_noqueue(kqu, kn);

                /* don't wakeup if unsuppressing just a stay-active knote */
                knote_enqueue(kqu, kn, KN_ACTIVE);
        }
}

__attribute__((always_inline))
static inline void
knote_mark_active(struct knote *kn)
{
        if ((kn->kn_status & KN_ACTIVE) == 0) {
                KDBG_DEBUG(KEV_EVTID(BSD_KEVENT_KNOTE_ACTIVATE),
                    kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
                    kn->kn_filtid);
        }

        kn->kn_status |= KN_ACTIVE;
}

/* called with kqueue lock held */
static void
knote_activate(kqueue_t kqu, struct knote *kn, int result)
{
        assert(result & FILTER_ACTIVE);
        if (result & FILTER_ADJUST_EVENT_QOS_BIT) {
                // may dequeue the knote
                knote_adjust_qos(kqu.kq, kn, result);
        }
        knote_mark_active(kn);
        knote_enqueue(kqu, kn, KN_ACTIVE | KN_STAYACTIVE);
}

/*
 * This function applies changes requested by f_attach or f_touch for
 * a given filter. It proceeds in a carefully chosen order to help
 * every single transition do the minimal amount of work possible.
 */
static void
knote_apply_touch(kqueue_t kqu, struct knote *kn, struct kevent_qos_s *kev,
    int result)
{
        kn_status_t wakeup_mask = KN_ACTIVE;

        if ((kev->flags & EV_ENABLE) && (kn->kn_status & KN_DISABLED)) {
                /*
                 * When a stayactive knote is reenabled, we may have missed wakeups
                 * while it was disabled, so we need to poll it. To do so, ask
                 * knote_enqueue() below to reenqueue it.
                 */
                wakeup_mask |= KN_STAYACTIVE;
                kn->kn_status &= ~KN_DISABLED;

                /*
                 * it is possible for userland to have knotes registered for a given
                 * workloop `wl_orig` but really handled on another workloop `wl_new`.
                 *
                 * In that case, rearming will happen from the servicer thread of
                 * `wl_new` which if `wl_orig` is no longer being serviced, would cause
                 * this knote to stay suppressed forever if we only relied on
                 * kqworkloop_acknowledge_events to be called by `wl_orig`.
                 *
                 * However if we see the KQ_PROCESSING bit on `wl_orig` set, we can't
                 * unsuppress because that would mess with the processing phase of
                 * `wl_orig`, however it also means kqworkloop_acknowledge_events()
                 * will be called.
                 */
                if (__improbable(kn->kn_status & KN_SUPPRESSED)) {
                        if ((kqu.kq->kq_state & KQ_PROCESSING) == 0) {
                                knote_unsuppress_noqueue(kqu, kn);
                        }
                }
        }

        if ((result & FILTER_UPDATE_REQ_QOS) && kev->qos && kev->qos != kn->kn_qos) {
                // may dequeue the knote
                knote_reset_priority(kqu, kn, kev->qos);
        }

        /*
         * When we unsuppress above, or because of knote_reset_priority(),
         * the knote may have been dequeued, we need to restore the invariant
         * that if the knote is active it needs to be queued now that
         * we're done applying changes.
         */
        if (result & FILTER_ACTIVE) {
                knote_activate(kqu, kn, result);
        } else {
                knote_enqueue(kqu, kn, wakeup_mask);
        }

        if ((result & FILTER_THREADREQ_NODEFEER) &&
            act_clear_astkevent(current_thread(), AST_KEVENT_REDRIVE_THREADREQ)) {
                workq_kern_threadreq_redrive(kqu.kq->kq_p, WORKQ_THREADREQ_NONE);
        }
}

/*
 * knote_drop - disconnect and drop the knote
 *
 * Called with the kqueue locked, returns with the kqueue unlocked.
 *
 * If a knote locking context is passed, it is canceled.
 *
 * The knote may have already been detached from
 * (or not yet attached to) its source object.
 */
static void
knote_drop(struct kqueue *kq, struct knote *kn, struct knote_lock_ctx *knlc)
{
        struct proc *p = kq->kq_p;

        kqlock_held(kq);

        assert((kn->kn_status & KN_DROPPING) == 0);
        if (knlc == NULL) {
                assert((kn->kn_status & KN_LOCKED) == 0);
        }
        kn->kn_status |= KN_DROPPING;

        if (kn->kn_status & KN_SUPPRESSED) {
                knote_unsuppress_noqueue(kq, kn);
        } else {
                knote_dequeue(kq, kn);
        }
        knote_wait_for_post(kq, kn);

        knote_fops(kn)->f_detach(kn);

        /* kq may be freed when kq_remove_knote() returns */
        kq_remove_knote(kq, kn, p, knlc);
        if (kn->kn_is_fd && ((kn->kn_status & KN_VANISHED) == 0)) {
                fp_drop(p, (int)kn->kn_id, kn->kn_fp, 0);
        }

        knote_free(kn);
}

void
knote_init(void)
{
#if CONFIG_MEMORYSTATUS
        /* Initialize the memorystatus list lock */
        memorystatus_kevent_init(&kq_lck_grp, LCK_ATTR_NULL);
#endif
}
SYSINIT(knote, SI_SUB_PSEUDO, SI_ORDER_ANY, knote_init, NULL);

const struct filterops *
knote_fops(struct knote *kn)
{
        return sysfilt_ops[kn->kn_filtid];
}

static struct knote *
knote_alloc(void)
{
        return zalloc_flags(knote_zone, Z_WAITOK | Z_ZERO);
}

static void
knote_free(struct knote *kn)
{
        assert((kn->kn_status & (KN_LOCKED | KN_POSTING)) == 0);
        zfree(knote_zone, kn);
}

#pragma mark - syscalls: kevent, kevent64, kevent_qos, kevent_id

kevent_ctx_t
kevent_get_context(thread_t thread)
{
        uthread_t ut = get_bsdthread_info(thread);
        return &ut->uu_save.uus_kevent;
}

static inline bool
kevent_args_requesting_events(unsigned int flags, int nevents)
{
        return !(flags & KEVENT_FLAG_ERROR_EVENTS) && nevents > 0;
}

static inline int
kevent_adjust_flags_for_proc(proc_t p, int flags)
{
        __builtin_assume(p);
        return flags | (IS_64BIT_PROCESS(p) ? KEVENT_FLAG_PROC64 : 0);
}

/*!
 * @function kevent_get_kqfile
 *
 * @brief
 * Lookup a kqfile by fd.
 *
 * @discussion
 * Callers: kevent, kevent64, kevent_qos
 *
 * This is not assumed to be a fastpath (kqfile interfaces are legacy)
 */
OS_NOINLINE
static int
kevent_get_kqfile(struct proc *p, int fd, int flags,
    struct fileproc **fpp, struct kqueue **kqp)
{
        int error = 0;
        struct kqueue *kq;

        error = fp_get_ftype(p, fd, DTYPE_KQUEUE, EBADF, fpp);
        if (__improbable(error)) {
                return error;
        }
        kq = (struct kqueue *)(*fpp)->f_data;

        uint16_t kq_state = os_atomic_load(&kq->kq_state, relaxed);
        if (__improbable((kq_state & (KQ_KEV32 | KQ_KEV64 | KQ_KEV_QOS)) == 0)) {
                kqlock(kq);
                kq_state = kq->kq_state;
                if (!(kq_state & (KQ_KEV32 | KQ_KEV64 | KQ_KEV_QOS))) {
                        if (flags & KEVENT_FLAG_LEGACY32) {
                                kq_state |= KQ_KEV32;
                        } else if (flags & KEVENT_FLAG_LEGACY64) {
                                kq_state |= KQ_KEV64;
                        } else {
                                kq_state |= KQ_KEV_QOS;
                        }
                        kq->kq_state = kq_state;
                }
                kqunlock(kq);
        }

        /*
         * kqfiles can't be used through the legacy kevent()
         * and other interfaces at the same time.
         */
        if (__improbable((bool)(flags & KEVENT_FLAG_LEGACY32) !=
            (bool)(kq_state & KQ_KEV32))) {
                fp_drop(p, fd, *fpp, 0);
                return EINVAL;
        }

        *kqp = kq;
        return 0;
}

/*!
 * @function kevent_get_kqwq
 *
 * @brief
 * Lookup or create the process kqwq (faspath).
 *
 * @discussion
 * Callers: kevent64, kevent_qos
 */
OS_ALWAYS_INLINE
static int
kevent_get_kqwq(proc_t p, int flags, int nevents, struct kqueue **kqp)
{
        struct kqworkq *kqwq = p->p_fd->fd_wqkqueue;

        if (__improbable(kevent_args_requesting_events(flags, nevents))) {
                return EINVAL;
        }
        if (__improbable(kqwq == NULL)) {
                kqwq = kqworkq_alloc(p, flags);
                if (__improbable(kqwq == NULL)) {
                        return ENOMEM;
                }
        }

        *kqp = &kqwq->kqwq_kqueue;
        return 0;
}

#pragma mark kevent copyio

/*!
 * @function kevent_get_data_size
 *
 * @brief
 * Copies in the extra data size from user-space.
 */
static int
kevent_get_data_size(int flags, user_addr_t data_avail, user_addr_t data_out,
    kevent_ctx_t kectx)
{
        if (!data_avail || !data_out) {
                kectx->kec_data_size  = 0;
                kectx->kec_data_resid = 0;
        } else if (flags & KEVENT_FLAG_PROC64) {
                user64_size_t usize = 0;
                int error = copyin((user_addr_t)data_avail, &usize, sizeof(usize));
                if (__improbable(error)) {
                        return error;
                }
                kectx->kec_data_resid = kectx->kec_data_size = (user_size_t)usize;
        } else {
                user32_size_t usize = 0;
                int error = copyin((user_addr_t)data_avail, &usize, sizeof(usize));
                if (__improbable(error)) {
                        return error;
                }
                kectx->kec_data_avail = data_avail;
                kectx->kec_data_resid = kectx->kec_data_size = (user_size_t)usize;
        }
        kectx->kec_data_out   = data_out;
        kectx->kec_data_avail = data_avail;
        return 0;
}

/*!
 * @function kevent_put_data_size
 *
 * @brief
 * Copies out the residual data size to user-space if any has been used.
 */
static int
kevent_put_data_size(unsigned int flags, kevent_ctx_t kectx)
{
        if (kectx->kec_data_resid == kectx->kec_data_size) {
                return 0;
        }
        if (flags & KEVENT_FLAG_KERNEL) {
                *(user_size_t *)(uintptr_t)kectx->kec_data_avail = kectx->kec_data_resid;
                return 0;
        }
        if (flags & KEVENT_FLAG_PROC64) {
                user64_size_t usize = (user64_size_t)kectx->kec_data_resid;
                return copyout(&usize, (user_addr_t)kectx->kec_data_avail, sizeof(usize));
        } else {
                user32_size_t usize = (user32_size_t)kectx->kec_data_resid;
                return copyout(&usize, (user_addr_t)kectx->kec_data_avail, sizeof(usize));
        }
}

/*!
 * @function kevent_legacy_copyin
 *
 * @brief
 * Handles the copyin of a kevent/kevent64 event.
 */
static int
kevent_legacy_copyin(user_addr_t *addrp, struct kevent_qos_s *kevp, unsigned int flags)
{
        int error;

        assert((flags & (KEVENT_FLAG_LEGACY32 | KEVENT_FLAG_LEGACY64)) != 0);

        if (flags & KEVENT_FLAG_LEGACY64) {
                struct kevent64_s kev64;

                error = copyin(*addrp, (caddr_t)&kev64, sizeof(kev64));
                if (__improbable(error)) {
                        return error;
                }
                *addrp += sizeof(kev64);
                *kevp = (struct kevent_qos_s){
                        .ident  = kev64.ident,
                        .filter = kev64.filter,
                        /* Make sure user doesn't pass in any system flags */
                        .flags  = kev64.flags & ~EV_SYSFLAGS,
                        .udata  = kev64.udata,
                        .fflags = kev64.fflags,
                        .data   = kev64.data,
                        .ext[0] = kev64.ext[0],
                        .ext[1] = kev64.ext[1],
                };
        } else if (flags & KEVENT_FLAG_PROC64) {
                struct user64_kevent kev64;

                error = copyin(*addrp, (caddr_t)&kev64, sizeof(kev64));
                if (__improbable(error)) {
                        return error;
                }
                *addrp += sizeof(kev64);
                *kevp = (struct kevent_qos_s){
                        .ident  = kev64.ident,
                        .filter = kev64.filter,
                        /* Make sure user doesn't pass in any system flags */
                        .flags  = kev64.flags & ~EV_SYSFLAGS,
                        .udata  = kev64.udata,
                        .fflags = kev64.fflags,
                        .data   = kev64.data,
                };
        } else {
                struct user32_kevent kev32;

                error = copyin(*addrp, (caddr_t)&kev32, sizeof(kev32));
                if (__improbable(error)) {
                        return error;
                }
                *addrp += sizeof(kev32);
                *kevp = (struct kevent_qos_s){
                        .ident  = (uintptr_t)kev32.ident,
                        .filter = kev32.filter,
                        /* Make sure user doesn't pass in any system flags */
                        .flags  = kev32.flags & ~EV_SYSFLAGS,
                        .udata  = CAST_USER_ADDR_T(kev32.udata),
                        .fflags = kev32.fflags,
                        .data   = (intptr_t)kev32.data,
                };
        }

        return 0;
}

/*!
 * @function kevent_modern_copyin
 *
 * @brief
 * Handles the copyin of a kevent_qos/kevent_id event.
 */
static int
kevent_modern_copyin(user_addr_t *addrp, struct kevent_qos_s *kevp)
{
        int error = copyin(*addrp, (caddr_t)kevp, sizeof(struct kevent_qos_s));
        if (__probable(!error)) {
                /* Make sure user doesn't pass in any system flags */
                *addrp += sizeof(struct kevent_qos_s);
                kevp->flags &= ~EV_SYSFLAGS;
        }
        return error;
}

/*!
 * @function kevent_legacy_copyout
 *
 * @brief
 * Handles the copyout of a kevent/kevent64 event.
 */
static int
kevent_legacy_copyout(struct kevent_qos_s *kevp, user_addr_t *addrp, unsigned int flags)
{
        int advance;
        int error;

        assert((flags & (KEVENT_FLAG_LEGACY32 | KEVENT_FLAG_LEGACY64)) != 0);

        /*
         * fully initialize the differnt output event structure
         * types from the internal kevent (and some universal
         * defaults for fields not represented in the internal
         * form).
         *
         * Note: these structures have no padding hence the C99
         *       initializers below do not leak kernel info.
         */
        if (flags & KEVENT_FLAG_LEGACY64) {
                struct kevent64_s kev64 = {
                        .ident  = kevp->ident,
                        .filter = kevp->filter,
                        .flags  = kevp->flags,
                        .fflags = kevp->fflags,
                        .data   = (int64_t)kevp->data,
                        .udata  = kevp->udata,
                        .ext[0] = kevp->ext[0],
                        .ext[1] = kevp->ext[1],
                };
                advance = sizeof(struct kevent64_s);
                error = copyout((caddr_t)&kev64, *addrp, advance);
        } else if (flags & KEVENT_FLAG_PROC64) {
                /*
                 * deal with the special case of a user-supplied
                 * value of (uintptr_t)-1.
                 */
                uint64_t ident = (kevp->ident == (uintptr_t)-1) ?
                    (uint64_t)-1LL : (uint64_t)kevp->ident;
                struct user64_kevent kev64 = {
                        .ident  = ident,
                        .filter = kevp->filter,
                        .flags  = kevp->flags,
                        .fflags = kevp->fflags,
                        .data   = (int64_t) kevp->data,
                        .udata  = (user_addr_t) kevp->udata,
                };
                advance = sizeof(kev64);
                error = copyout((caddr_t)&kev64, *addrp, advance);
        } else {
                struct user32_kevent kev32 = {
                        .ident  = (uint32_t)kevp->ident,
                        .filter = kevp->filter,
                        .flags  = kevp->flags,
                        .fflags = kevp->fflags,
                        .data   = (int32_t)kevp->data,
                        .udata  = (uint32_t)kevp->udata,
                };
                advance = sizeof(kev32);
                error = copyout((caddr_t)&kev32, *addrp, advance);
        }
        if (__probable(!error)) {
                *addrp += advance;
        }
        return error;
}

/*!
 * @function kevent_modern_copyout
 *
 * @brief
 * Handles the copyout of a kevent_qos/kevent_id event.
 */
OS_ALWAYS_INLINE
static inline int
kevent_modern_copyout(struct kevent_qos_s *kevp, user_addr_t *addrp)
{
        int error = copyout((caddr_t)kevp, *addrp, sizeof(struct kevent_qos_s));
        if (__probable(!error)) {
                *addrp += sizeof(struct kevent_qos_s);
        }
        return error;
}

#pragma mark kevent core implementation

/*!
 * @function kevent_callback_inline
 *
 * @brief
 * Callback for each individual event
 *
 * @discussion
 * This is meant to be inlined in kevent_modern_callback and
 * kevent_legacy_callback.
 */
OS_ALWAYS_INLINE
static inline int
kevent_callback_inline(struct kevent_qos_s *kevp, kevent_ctx_t kectx, bool legacy)
{
        int error;

        assert(kectx->kec_process_noutputs < kectx->kec_process_nevents);

        /*
         * Copy out the appropriate amount of event data for this user.
         */
        if (legacy) {
                error = kevent_legacy_copyout(kevp, &kectx->kec_process_eventlist,
                    kectx->kec_process_flags);
        } else {
                error = kevent_modern_copyout(kevp, &kectx->kec_process_eventlist);
        }

        /*
         * If there isn't space for additional events, return
         * a harmless error to stop the processing here
         */
        if (error == 0 && ++kectx->kec_process_noutputs == kectx->kec_process_nevents) {
                error = EWOULDBLOCK;
        }
        return error;
}

/*!
 * @function kevent_modern_callback
 *
 * @brief
 * Callback for each individual modern event.
 *
 * @discussion
 * This callback handles kevent_qos/kevent_id events.
 */
static int
kevent_modern_callback(struct kevent_qos_s *kevp, kevent_ctx_t kectx)
{
        return kevent_callback_inline(kevp, kectx, /*legacy*/ false);
}

/*!
 * @function kevent_legacy_callback
 *
 * @brief
 * Callback for each individual legacy event.
 *
 * @discussion
 * This callback handles kevent/kevent64 events.
 */
static int
kevent_legacy_callback(struct kevent_qos_s *kevp, kevent_ctx_t kectx)
{
        return kevent_callback_inline(kevp, kectx, /*legacy*/ true);
}

/*!
 * @function kevent_cleanup
 *
 * @brief
 * Handles the cleanup returning from a kevent call.
 *
 * @discussion
 * kevent entry points will take a reference on workloops,
 * and a usecount on the fileglob of kqfiles.
 *
 * This function undoes this on the exit paths of kevents.
 *
 * @returns
 * The error to return to userspace.
 */
static int
kevent_cleanup(kqueue_t kqu, int flags, int error, kevent_ctx_t kectx)
{
        // poll should not call any codepath leading to this
        assert((flags & KEVENT_FLAG_POLL) == 0);

        if (flags & KEVENT_FLAG_WORKLOOP) {
                kqworkloop_release(kqu.kqwl);
        } else if (flags & KEVENT_FLAG_WORKQ) {
                /* nothing held */
        } else {
                fp_drop(kqu.kqf->kqf_p, kectx->kec_fd, kectx->kec_fp, 0);
        }

        /* don't restart after signals... */
        if (error == ERESTART) {
                error = EINTR;
        } else if (error == 0) {
                /* don't abandon other output just because of residual copyout failures */
                (void)kevent_put_data_size(flags, kectx);
        }

        if (flags & KEVENT_FLAG_PARKING) {
                thread_t th = current_thread();
                struct uthread *uth = get_bsdthread_info(th);
                if (uth->uu_kqr_bound) {
                        thread_unfreeze_base_pri(th);
                }
        }
        return error;
}

/*!
 * @function kqueue_process
 *
 * @brief
 * Process the triggered events in a kqueue.
 *
 * @discussion
 * Walk the queued knotes and validate that they are really still triggered
 * events by calling the filter routines (if necessary).
 *
 * For each event that is still considered triggered, invoke the callback
 * routine provided.
 *
 * caller holds a reference on the kqueue.
 * kqueue locked on entry and exit - but may be dropped
 * kqueue list locked (held for duration of call)
 *
 * This is only called by kqueue_scan() so that the compiler can inline it.
 *
 * @returns
 * - 0:            no event was returned, no other error occured
 * - EBADF:        the kqueue is being destroyed (KQ_DRAIN is set)
 * - EWOULDBLOCK:  (not an error) events have been found and we should return
 * - EFAULT:       copyout failed
 * - filter specific errors
 */
static int
kqueue_process(kqueue_t kqu, int flags, kevent_ctx_t kectx,
    kevent_callback_t callback)
{
        workq_threadreq_t kqr = current_uthread()->uu_kqr_bound;
        struct knote *kn;
        int error = 0, rc = 0;
        struct kqtailq *base_queue, *queue;
#if DEBUG || DEVELOPMENT
        int retries = 64;
#endif
        uint16_t kq_type = (kqu.kq->kq_state & (KQ_WORKQ | KQ_WORKLOOP));

        if (kq_type & KQ_WORKQ) {
                rc = kqworkq_begin_processing(kqu.kqwq, kqr, flags);
        } else if (kq_type & KQ_WORKLOOP) {
                rc = kqworkloop_begin_processing(kqu.kqwl, flags);
        } else {
kqfile_retry:
                rc = kqfile_begin_processing(kqu.kqf);
                if (rc == EBADF) {
                        return EBADF;
                }
        }

        if (rc == -1) {
                /* Nothing to process */
                return 0;
        }

        /*
         * loop through the enqueued knotes associated with this request,
         * processing each one. Each request may have several queues
         * of knotes to process (depending on the type of kqueue) so we
         * have to loop through all the queues as long as we have additional
         * space.
         */

process_again:
        if (kq_type & KQ_WORKQ) {
                base_queue = queue = &kqu.kqwq->kqwq_queue[kqr->tr_kq_qos_index];
        } else if (kq_type & KQ_WORKLOOP) {
                base_queue = &kqu.kqwl->kqwl_queue[0];
                queue = &kqu.kqwl->kqwl_queue[KQWL_NBUCKETS - 1];
        } else {
                base_queue = queue = &kqu.kqf->kqf_queue;
        }

        do {
                while ((kn = TAILQ_FIRST(queue)) != NULL) {
                        error = knote_process(kn, kectx, callback);
                        if (error == EJUSTRETURN) {
                                error = 0;
                        } else if (__improbable(error)) {
                                /* error is EWOULDBLOCK when the out event array is full */
                                goto stop_processing;
                        }
                }
        } while (queue-- > base_queue);

        if (kectx->kec_process_noutputs) {
                /* callers will transform this into no error */
                error = EWOULDBLOCK;
        }

stop_processing:
        /*
         * If KEVENT_FLAG_PARKING is set, and no kevents have been returned,
         * we want to unbind the kqrequest from the thread.
         *
         * However, because the kq locks are dropped several times during process,
         * new knotes may have fired again, in which case, we want to fail the end
         * processing and process again, until it converges.
         *
         * If we have an error or returned events, end processing never fails.
         */
        if (error) {
                flags &= ~KEVENT_FLAG_PARKING;
        }
        if (kq_type & KQ_WORKQ) {
                rc = kqworkq_end_processing(kqu.kqwq, kqr, flags);
        } else if (kq_type & KQ_WORKLOOP) {
                rc = kqworkloop_end_processing(kqu.kqwl, KQ_PROCESSING, flags);
        } else {
                rc = kqfile_end_processing(kqu.kqf);
        }

        if (__probable(error)) {
                return error;
        }

        if (__probable(rc >= 0)) {
                assert(rc == 0 || rc == EBADF);
                return rc;
        }

#if DEBUG || DEVELOPMENT
        if (retries-- == 0) {
                panic("kevent: way too many knote_process retries, kq: %p (0x%04x)",
                    kqu.kq, kqu.kq->kq_state);
        }
#endif
        if (kq_type & (KQ_WORKQ | KQ_WORKLOOP)) {
                assert(flags & KEVENT_FLAG_PARKING);
                goto process_again;
        } else {
                goto kqfile_retry;
        }
}

/*!
 * @function kqueue_scan_continue
 *
 * @brief
 * The continuation used by kqueue_scan for kevent entry points.
 *
 * @discussion
 * Assumes we inherit a use/ref count on the kq or its fileglob.
 *
 * This is called by kqueue_scan if neither KEVENT_FLAG_POLL nor
 * KEVENT_FLAG_KERNEL was set, and the caller had to wait.
 */
OS_NORETURN OS_NOINLINE
static void
kqueue_scan_continue(void *data, wait_result_t wait_result)
{
        uthread_t ut = current_uthread();
        kevent_ctx_t kectx = &ut->uu_save.uus_kevent;
        int error = 0, flags = kectx->kec_process_flags;
        struct kqueue *kq = data;

        /*
         * only kevent variants call in here, so we know the callback is
         * kevent_legacy_callback or kevent_modern_callback.
         */
        assert((flags & (KEVENT_FLAG_POLL | KEVENT_FLAG_KERNEL)) == 0);

        switch (wait_result) {
        case THREAD_AWAKENED:
                if (__improbable(flags & (KEVENT_FLAG_LEGACY32 | KEVENT_FLAG_LEGACY64))) {
                        error = kqueue_scan(kq, flags, kectx, kevent_legacy_callback);
                } else {
                        error = kqueue_scan(kq, flags, kectx, kevent_modern_callback);
                }
                break;
        case THREAD_TIMED_OUT:
                error = 0;
                break;
        case THREAD_INTERRUPTED:
                error = EINTR;
                break;
        case THREAD_RESTART:
                error = EBADF;
                break;
        default:
                panic("%s: - invalid wait_result (%d)", __func__, wait_result);
        }


        error = kevent_cleanup(kq, flags, error, kectx);
        *(int32_t *)&ut->uu_rval = kectx->kec_process_noutputs;
        unix_syscall_return(error);
}

/*!
 * @function kqueue_scan
 *
 * @brief
 * Scan and wait for events in a kqueue (used by poll & kevent).
 *
 * @discussion
 * Process the triggered events in a kqueue.
 *
 * If there are no events triggered arrange to wait for them:
 * - unless KEVENT_FLAG_IMMEDIATE is set in kectx->kec_process_flags
 * - possibly until kectx->kec_deadline expires
 *
 * When it waits, and that neither KEVENT_FLAG_POLL nor KEVENT_FLAG_KERNEL
 * are set, then it will wait in the kqueue_scan_continue continuation.
 *
 * poll() will block in place, and KEVENT_FLAG_KERNEL calls
 * all pass KEVENT_FLAG_IMMEDIATE and will not wait.
 *
 * @param kq
 * The kqueue being scanned.
 *
 * @param flags
 * The KEVENT_FLAG_* flags for this call.
 *
 * @param kectx
 * The context used for this scan.
 * The uthread_t::uu_save.uus_kevent storage is used for this purpose.
 *
 * @param callback
 * The callback to be called on events sucessfully processed.
 * (Either kevent_legacy_callback, kevent_modern_callback or poll_callback)
 */
int
kqueue_scan(struct kqueue *kq, int flags, kevent_ctx_t kectx,
    kevent_callback_t callback)
{
        int error;

        for (;;) {
                kqlock(kq);
                error = kqueue_process(kq, flags, kectx, callback);

                /*
                 * If we got an error, events returned (EWOULDBLOCK)
                 * or blocking was disallowed (KEVENT_FLAG_IMMEDIATE),
                 * just return.
                 */
                if (__probable(error || (flags & KEVENT_FLAG_IMMEDIATE))) {
                        kqunlock(kq);
                        return error == EWOULDBLOCK ? 0 : error;
                }

                waitq_assert_wait64_leeway((struct waitq *)&kq->kq_wqs,
                    KQ_EVENT, THREAD_ABORTSAFE, TIMEOUT_URGENCY_USER_NORMAL,
                    kectx->kec_deadline, TIMEOUT_NO_LEEWAY);
                kq->kq_state |= KQ_SLEEP;

                kqunlock(kq);

                if (__probable((flags & (KEVENT_FLAG_POLL | KEVENT_FLAG_KERNEL)) == 0)) {
                        thread_block_parameter(kqueue_scan_continue, kq);
                        __builtin_unreachable();
                }

                wait_result_t wr = thread_block(THREAD_CONTINUE_NULL);
                switch (wr) {
                case THREAD_AWAKENED:
                        break;
                case THREAD_TIMED_OUT:
                        return 0;
                case THREAD_INTERRUPTED:
                        return EINTR;
                case THREAD_RESTART:
                        return EBADF;
                default:
                        panic("%s: - bad wait_result (%d)", __func__, wr);
                }
        }
}

/*!
 * @function kevent_internal
 *
 * @brief
 * Common kevent code.
 *
 * @discussion
 * Needs to be inlined to specialize for legacy or modern and
 * eliminate dead code.
 *
 * This is the core logic of kevent entry points, that will:
 * - register kevents
 * - optionally scan the kqueue for events
 *
 * The caller is giving kevent_internal a reference on the kqueue
 * or its fileproc that needs to be cleaned up by kevent_cleanup().
 */
OS_ALWAYS_INLINE
static inline int
kevent_internal(kqueue_t kqu,
    user_addr_t changelist, int nchanges,
    user_addr_t ueventlist, int nevents,
    int flags, kevent_ctx_t kectx, int32_t *retval,
    bool legacy)
{
        int error = 0, noutputs = 0, register_rc;

        /* only bound threads can receive events on workloops */
        if (!legacy && (flags & KEVENT_FLAG_WORKLOOP)) {
#if CONFIG_WORKLOOP_DEBUG
                UU_KEVENT_HISTORY_WRITE_ENTRY(current_uthread(), {
                        .uu_kqid = kqu.kqwl->kqwl_dynamicid,
                        .uu_kq = error ? NULL : kqu.kq,
                        .uu_error = error,
                        .uu_nchanges = nchanges,
                        .uu_nevents = nevents,
                        .uu_flags = flags,
                });
#endif // CONFIG_WORKLOOP_DEBUG

                if (flags & KEVENT_FLAG_KERNEL) {
                        /* see kevent_workq_internal */
                        error = copyout(&kqu.kqwl->kqwl_dynamicid,
                            ueventlist - sizeof(kqueue_id_t), sizeof(kqueue_id_t));
                        kectx->kec_data_resid -= sizeof(kqueue_id_t);
                        if (__improbable(error)) {
                                goto out;
                        }
                }

                if (kevent_args_requesting_events(flags, nevents)) {
                        /*
                         * Disable the R2K notification while doing a register, if the
                         * caller wants events too, we don't want the AST to be set if we
                         * will process these events soon.
                         */
                        kqlock(kqu);
                        kqu.kq->kq_state &= ~KQ_R2K_ARMED;
                        kqunlock(kqu);
                        flags |= KEVENT_FLAG_NEEDS_END_PROCESSING;
                }
        }

        /* register all the change requests the user provided... */
        while (nchanges > 0 && error == 0) {
                struct kevent_qos_s kev;
                struct knote *kn = NULL;

                if (legacy) {
                        error = kevent_legacy_copyin(&changelist, &kev, flags);
                } else {
                        error = kevent_modern_copyin(&changelist, &kev);
                }
                if (error) {
                        break;
                }

                register_rc = kevent_register(kqu.kq, &kev, &kn);
                if (__improbable(!legacy && (register_rc & FILTER_REGISTER_WAIT))) {
                        thread_t thread = current_thread();

                        kqlock_held(kqu);

                        if (act_clear_astkevent(thread, AST_KEVENT_REDRIVE_THREADREQ)) {
                                workq_kern_threadreq_redrive(kqu.kq->kq_p, WORKQ_THREADREQ_NONE);
                        }

                        // f_post_register_wait is meant to call a continuation and not to
                        // return, which is why we don't support FILTER_REGISTER_WAIT if
                        // KEVENT_FLAG_ERROR_EVENTS is not passed, or if the event that
                        // waits isn't the last.
                        //
                        // It is implementable, but not used by any userspace code at the
                        // moment, so for now return ENOTSUP if someone tries to do it.
                        if (nchanges == 1 && noutputs < nevents &&
                            (flags & KEVENT_FLAG_KERNEL) == 0 &&
                            (flags & KEVENT_FLAG_PARKING) == 0 &&
                            (flags & KEVENT_FLAG_ERROR_EVENTS) &&
                            (flags & KEVENT_FLAG_WORKLOOP)) {
                                uthread_t ut = get_bsdthread_info(thread);

                                /*
                                 * store the continuation/completion data in the uthread
                                 *
                                 * Note: the kectx aliases with this,
                                 * and is destroyed in the process.
                                 */
                                ut->uu_save.uus_kevent_register = (struct _kevent_register){
                                        .kev        = kev,
                                        .kqwl       = kqu.kqwl,
                                        .eventout   = noutputs,
                                        .ueventlist = ueventlist,
                                };
                                knote_fops(kn)->f_post_register_wait(ut, kn,
                                    &ut->uu_save.uus_kevent_register);
                                __builtin_unreachable();
                        }
                        kqunlock(kqu);

                        kev.flags |= EV_ERROR;
                        kev.data = ENOTSUP;
                } else {
                        assert((register_rc & FILTER_REGISTER_WAIT) == 0);
                }

                // keep in sync with kevent_register_wait_return()
                if (noutputs < nevents && (kev.flags & (EV_ERROR | EV_RECEIPT))) {
                        if ((kev.flags & EV_ERROR) == 0) {
                                kev.flags |= EV_ERROR;
                                kev.data = 0;
                        }
                        if (legacy) {
                                error = kevent_legacy_copyout(&kev, &ueventlist, flags);
                        } else {
                                error = kevent_modern_copyout(&kev, &ueventlist);
                        }
                        if (error == 0) {
                                noutputs++;
                        }
                } else if (kev.flags & EV_ERROR) {
                        error = (int)kev.data;
                }
                nchanges--;
        }

        if ((flags & KEVENT_FLAG_ERROR_EVENTS) == 0 &&
            nevents > 0 && noutputs == 0 && error == 0) {
                kectx->kec_process_flags = flags;
                kectx->kec_process_nevents = nevents;
                kectx->kec_process_noutputs = 0;
                kectx->kec_process_eventlist = ueventlist;

                if (legacy) {
                        error = kqueue_scan(kqu.kq, flags, kectx, kevent_legacy_callback);
                } else {
                        error = kqueue_scan(kqu.kq, flags, kectx, kevent_modern_callback);
                }

                noutputs = kectx->kec_process_noutputs;
        } else if (!legacy && (flags & KEVENT_FLAG_NEEDS_END_PROCESSING)) {
                /*
                 * If we didn't through kqworkloop_end_processing(),
                 * we need to do it here.
                 *
                 * kqueue_scan will call kqworkloop_end_processing(),
                 * so we only need to do it if we didn't scan.
                 */
                kqlock(kqu);
                kqworkloop_end_processing(kqu.kqwl, 0, 0);
                kqunlock(kqu);
        }

        *retval = noutputs;
out:
        return kevent_cleanup(kqu.kq, flags, error, kectx);
}

#pragma mark modern syscalls: kevent_qos, kevent_id, kevent_workq_internal

/*!
 * @function kevent_modern_internal
 *
 * @brief
 * The backend of the kevent_id and kevent_workq_internal entry points.
 *
 * @discussion
 * Needs to be inline due to the number of arguments.
 */
OS_NOINLINE
static int
kevent_modern_internal(kqueue_t kqu,
    user_addr_t changelist, int nchanges,
    user_addr_t ueventlist, int nevents,
    int flags, kevent_ctx_t kectx, int32_t *retval)
{
        return kevent_internal(kqu.kq, changelist, nchanges,
                   ueventlist, nevents, flags, kectx, retval, /*legacy*/ false);
}

/*!
 * @function kevent_id
 *
 * @brief
 * The kevent_id() syscall.
 */
int
kevent_id(struct proc *p, struct kevent_id_args *uap, int32_t *retval)
{
        int error, flags = uap->flags & KEVENT_FLAG_USER;
        uthread_t uth = current_uthread();
        workq_threadreq_t kqr = uth->uu_kqr_bound;
        kevent_ctx_t kectx = &uth->uu_save.uus_kevent;
        kqueue_t kqu;

        flags = kevent_adjust_flags_for_proc(p, flags);
        flags |= KEVENT_FLAG_DYNAMIC_KQUEUE;

        if (__improbable((flags & (KEVENT_FLAG_WORKQ | KEVENT_FLAG_WORKLOOP)) !=
            KEVENT_FLAG_WORKLOOP)) {
                return EINVAL;
        }

        error = kevent_get_data_size(flags, uap->data_available, uap->data_out, kectx);
        if (__improbable(error)) {
                return error;
        }

        kectx->kec_deadline = 0;
        kectx->kec_fp       = NULL;
        kectx->kec_fd       = -1;
        /* the kec_process_* fields are filled if kqueue_scann is called only */

        /*
         * Get the kq we are going to be working on
         * As a fastpath, look at the currently bound workloop.
         */
        kqu.kqwl = kqr ? kqr_kqworkloop(kqr) : NULL;
        if (kqu.kqwl && kqu.kqwl->kqwl_dynamicid == uap->id) {
                if (__improbable(flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST)) {
                        return EEXIST;
                }
                kqworkloop_retain(kqu.kqwl);
        } else if (__improbable(kevent_args_requesting_events(flags, uap->nevents))) {
                return EXDEV;
        } else {
                error = kqworkloop_get_or_create(p, uap->id, NULL, flags, &kqu.kqwl);
                if (__improbable(error)) {
                        return error;
                }
        }

        return kevent_modern_internal(kqu, uap->changelist, uap->nchanges,
                   uap->eventlist, uap->nevents, flags, kectx, retval);
}

/**!
 * @function kevent_workq_internal
 *
 * @discussion
 * This function is exported for the sake of the workqueue subsystem.
 *
 * It is called in two ways:
 * - when a thread is about to go to userspace to ask for pending event
 * - when a thread is returning from userspace with events back
 *
 * the workqueue subsystem will only use the following flags:
 * - KEVENT_FLAG_STACK_DATA (always)
 * - KEVENT_FLAG_IMMEDIATE (always)
 * - KEVENT_FLAG_PARKING (depending on whether it is going to or returning from
 *   userspace).
 *
 * It implicitly acts on the bound kqueue, and for the case of workloops
 * will copyout the kqueue ID before anything else.
 *
 *
 * Pthread will have setup the various arguments to fit this stack layout:
 *
 * +-------....----+--------------+-----------+--------------------+
 * |  user stack   |  data avail  |  nevents  |   pthread_self()   |
 * +-------....----+--------------+-----------+--------------------+
 *                 ^              ^
 *             data_out       eventlist
 *
 * When a workloop is used, the workloop ID is copied out right before
 * the eventlist and is taken from the data buffer.
 *
 * @warning
 * This function is carefuly tailored to not make any call except the final tail
 * call into kevent_modern_internal. (LTO inlines current_uthread()).
 *
 * This function is performance sensitive due to the workq subsystem.
 */
int
kevent_workq_internal(struct proc *p,
    user_addr_t changelist, int nchanges,
    user_addr_t eventlist, int nevents,
    user_addr_t data_out, user_size_t *data_available,
    unsigned int flags, int32_t *retval)
{
        uthread_t uth = current_uthread();
        workq_threadreq_t kqr = uth->uu_kqr_bound;
        kevent_ctx_t kectx = &uth->uu_save.uus_kevent;
        kqueue_t kqu;

        assert(flags == (KEVENT_FLAG_STACK_DATA | KEVENT_FLAG_IMMEDIATE) ||
            flags == (KEVENT_FLAG_STACK_DATA | KEVENT_FLAG_IMMEDIATE | KEVENT_FLAG_PARKING));

        kectx->kec_data_out   = data_out;
        kectx->kec_data_avail = (uint64_t)data_available;
        kectx->kec_data_size  = *data_available;
        kectx->kec_data_resid = *data_available;
        kectx->kec_deadline   = 0;
        kectx->kec_fp         = NULL;
        kectx->kec_fd         = -1;
        /* the kec_process_* fields are filled if kqueue_scann is called only */

        flags = kevent_adjust_flags_for_proc(p, flags);

        if (kqr->tr_flags & WORKQ_TR_FLAG_WORKLOOP) {
                kqu.kqwl = __container_of(kqr, struct kqworkloop, kqwl_request);
                kqworkloop_retain(kqu.kqwl);

                flags |= KEVENT_FLAG_WORKLOOP | KEVENT_FLAG_DYNAMIC_KQUEUE |
                    KEVENT_FLAG_KERNEL;
        } else {
                kqu.kqwq = p->p_fd->fd_wqkqueue;

                flags |= KEVENT_FLAG_WORKQ | KEVENT_FLAG_KERNEL;
        }

        return kevent_modern_internal(kqu, changelist, nchanges,
                   eventlist, nevents, flags, kectx, retval);
}

/*!
 * @function kevent_qos
 *
 * @brief
 * The kevent_qos() syscall.
 */
int
kevent_qos(struct proc *p, struct kevent_qos_args *uap, int32_t *retval)
{
        uthread_t uth = current_uthread();
        kevent_ctx_t kectx = &uth->uu_save.uus_kevent;
        int error, flags = uap->flags & KEVENT_FLAG_USER;
        struct kqueue *kq;

        if (__improbable(flags & KEVENT_ID_FLAG_USER)) {
                return EINVAL;
        }

        flags = kevent_adjust_flags_for_proc(p, flags);

        error = kevent_get_data_size(flags, uap->data_available, uap->data_out, kectx);
        if (__improbable(error)) {
                return error;
        }

        kectx->kec_deadline = 0;
        kectx->kec_fp       = NULL;
        kectx->kec_fd       = uap->fd;
        /* the kec_process_* fields are filled if kqueue_scann is called only */

        /* get the kq we are going to be working on */
        if (__probable(flags & KEVENT_FLAG_WORKQ)) {
                error = kevent_get_kqwq(p, flags, uap->nevents, &kq);
        } else {
                error = kevent_get_kqfile(p, uap->fd, flags, &kectx->kec_fp, &kq);
        }
        if (__improbable(error)) {
                return error;
        }

        return kevent_modern_internal(kq, uap->changelist, uap->nchanges,
                   uap->eventlist, uap->nevents, flags, kectx, retval);
}

#pragma mark legacy syscalls: kevent, kevent64

/*!
 * @function kevent_legacy_get_deadline
 *
 * @brief
 * Compute the deadline for the legacy kevent syscalls.
 *
 * @discussion
 * This is not necessary if KEVENT_FLAG_IMMEDIATE is specified,
 * as this takes precedence over the deadline.
 *
 * This function will fail if utimeout is USER_ADDR_NULL
 * (the caller should check).
 */
static int
kevent_legacy_get_deadline(int flags, user_addr_t utimeout, uint64_t *deadline)
{
        struct timespec ts;

        if (flags & KEVENT_FLAG_PROC64) {
                struct user64_timespec ts64;
                int error = copyin(utimeout, &ts64, sizeof(ts64));
                if (__improbable(error)) {
                        return error;
                }
                ts.tv_sec = (unsigned long)ts64.tv_sec;
                ts.tv_nsec = (long)ts64.tv_nsec;
        } else {
                struct user32_timespec ts32;
                int error = copyin(utimeout, &ts32, sizeof(ts32));
                if (__improbable(error)) {
                        return error;
                }
                ts.tv_sec = ts32.tv_sec;
                ts.tv_nsec = ts32.tv_nsec;
        }
        if (!timespec_is_valid(&ts)) {
                return EINVAL;
        }

        clock_absolutetime_interval_to_deadline(tstoabstime(&ts), deadline);
        return 0;
}

/*!
 * @function kevent_legacy_internal
 *
 * @brief
 * The core implementation for kevent and kevent64
 */
OS_NOINLINE
static int
kevent_legacy_internal(struct proc *p, struct kevent64_args *uap,
    int32_t *retval, int flags)
{
        uthread_t uth = current_uthread();
        kevent_ctx_t kectx = &uth->uu_save.uus_kevent;
        struct kqueue *kq;
        int error;

        if (__improbable(uap->flags & KEVENT_ID_FLAG_USER)) {
                return EINVAL;
        }

        flags = kevent_adjust_flags_for_proc(p, flags);

        kectx->kec_data_out   = 0;
        kectx->kec_data_avail = 0;
        kectx->kec_data_size  = 0;
        kectx->kec_data_resid = 0;
        kectx->kec_deadline   = 0;
        kectx->kec_fp         = NULL;
        kectx->kec_fd         = uap->fd;
        /* the kec_process_* fields are filled if kqueue_scann is called only */

        /* convert timeout to absolute - if we have one (and not immediate) */
        if (__improbable(uap->timeout && !(flags & KEVENT_FLAG_IMMEDIATE))) {
                error = kevent_legacy_get_deadline(flags, uap->timeout,
                    &kectx->kec_deadline);
                if (__improbable(error)) {
                        return error;
                }
        }

        /* get the kq we are going to be working on */
        if (flags & KEVENT_FLAG_WORKQ) {
                error = kevent_get_kqwq(p, flags, uap->nevents, &kq);
        } else {
                error = kevent_get_kqfile(p, uap->fd, flags, &kectx->kec_fp, &kq);
        }
        if (__improbable(error)) {
                return error;
        }

        return kevent_internal(kq, uap->changelist, uap->nchanges,
                   uap->eventlist, uap->nevents, flags, kectx, retval,
                   /*legacy*/ true);
}

/*!
 * @function kevent
 *
 * @brief
 * The legacy kevent() syscall.
 */
int
kevent(struct proc *p, struct kevent_args *uap, int32_t *retval)
{
        struct kevent64_args args = {
                .fd         = uap->fd,
                .changelist = uap->changelist,
                .nchanges   = uap->nchanges,
                .eventlist  = uap->eventlist,
                .nevents    = uap->nevents,
                .timeout    = uap->timeout,
        };

        return kevent_legacy_internal(p, &args, retval, KEVENT_FLAG_LEGACY32);
}

/*!
 * @function kevent64
 *
 * @brief
 * The legacy kevent64() syscall.
 */
int
kevent64(struct proc *p, struct kevent64_args *uap, int32_t *retval)
{
        int flags = (uap->flags & KEVENT_FLAG_USER) | KEVENT_FLAG_LEGACY64;
        return kevent_legacy_internal(p, uap, retval, flags);
}

#pragma mark - socket interface

#if SOCKETS
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/protosw.h>
#include <sys/domain.h>
#include <sys/mbuf.h>
#include <sys/kern_event.h>
#include <sys/malloc.h>
#include <sys/sys_domain.h>
#include <sys/syslog.h>

#ifndef ROUNDUP64
#define ROUNDUP64(x) P2ROUNDUP((x), sizeof (u_int64_t))
#endif

#ifndef ADVANCE64
#define ADVANCE64(p, n) (void*)((char *)(p) + ROUNDUP64(n))
#endif

static LCK_GRP_DECLARE(kev_lck_grp, "Kernel Event Protocol");
static LCK_RW_DECLARE(kev_rwlock, &kev_lck_grp);

static int kev_attach(struct socket *so, int proto, struct proc *p);
static int kev_detach(struct socket *so);
static int kev_control(struct socket *so, u_long cmd, caddr_t data,
    struct ifnet *ifp, struct proc *p);
static lck_mtx_t * event_getlock(struct socket *, int);
static int event_lock(struct socket *, int, void *);
static int event_unlock(struct socket *, int, void *);

static int event_sofreelastref(struct socket *);
static void kev_delete(struct kern_event_pcb *);

static struct pr_usrreqs event_usrreqs = {
        .pru_attach =           kev_attach,
        .pru_control =          kev_control,
        .pru_detach =           kev_detach,
        .pru_soreceive =        soreceive,
};

static struct protosw eventsw[] = {
        {
                .pr_type =              SOCK_RAW,
                .pr_protocol =          SYSPROTO_EVENT,
                .pr_flags =             PR_ATOMIC,
                .pr_usrreqs =           &event_usrreqs,
                .pr_lock =              event_lock,
                .pr_unlock =            event_unlock,
                .pr_getlock =           event_getlock,
        }
};

__private_extern__ int kevt_getstat SYSCTL_HANDLER_ARGS;
__private_extern__ int kevt_pcblist SYSCTL_HANDLER_ARGS;

SYSCTL_NODE(_net_systm, OID_AUTO, kevt,
    CTLFLAG_RW | CTLFLAG_LOCKED, 0, "Kernel event family");

struct kevtstat kevtstat;
SYSCTL_PROC(_net_systm_kevt, OID_AUTO, stats,
    CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_LOCKED, 0, 0,
    kevt_getstat, "S,kevtstat", "");

SYSCTL_PROC(_net_systm_kevt, OID_AUTO, pcblist,
    CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_LOCKED, 0, 0,
    kevt_pcblist, "S,xkevtpcb", "");

static lck_mtx_t *
event_getlock(struct socket *so, int flags)
{
#pragma unused(flags)
        struct kern_event_pcb *ev_pcb = (struct kern_event_pcb *)so->so_pcb;

        if (so->so_pcb != NULL) {
                if (so->so_usecount < 0) {
                        panic("%s: so=%p usecount=%d lrh= %s\n", __func__,
                            so, so->so_usecount, solockhistory_nr(so));
                }
                /* NOTREACHED */
        } else {
                panic("%s: so=%p NULL NO so_pcb %s\n", __func__,
                    so, solockhistory_nr(so));
                /* NOTREACHED */
        }
        return &ev_pcb->evp_mtx;
}

static int
event_lock(struct socket *so, int refcount, void *lr)
{
        void *lr_saved;

        if (lr == NULL) {
                lr_saved = __builtin_return_address(0);
        } else {
                lr_saved = lr;
        }

        if (so->so_pcb != NULL) {
                lck_mtx_lock(&((struct kern_event_pcb *)so->so_pcb)->evp_mtx);
        } else {
                panic("%s: so=%p NO PCB! lr=%p lrh= %s\n", __func__,
                    so, lr_saved, solockhistory_nr(so));
                /* NOTREACHED */
        }

        if (so->so_usecount < 0) {
                panic("%s: so=%p so_pcb=%p lr=%p ref=%d lrh= %s\n", __func__,
                    so, so->so_pcb, lr_saved, so->so_usecount,
                    solockhistory_nr(so));
                /* NOTREACHED */
        }

        if (refcount) {
                so->so_usecount++;
        }

        so->lock_lr[so->next_lock_lr] = lr_saved;
        so->next_lock_lr = (so->next_lock_lr + 1) % SO_LCKDBG_MAX;
        return 0;
}

static int
event_unlock(struct socket *so, int refcount, void *lr)
{
        void *lr_saved;
        lck_mtx_t *mutex_held;

        if (lr == NULL) {
                lr_saved = __builtin_return_address(0);
        } else {
                lr_saved = lr;
        }

        if (refcount) {
                so->so_usecount--;
        }
        if (so->so_usecount < 0) {
                panic("%s: so=%p usecount=%d lrh= %s\n", __func__,
                    so, so->so_usecount, solockhistory_nr(so));
                /* NOTREACHED */
        }
        if (so->so_pcb == NULL) {
                panic("%s: so=%p NO PCB usecount=%d lr=%p lrh= %s\n", __func__,
                    so, so->so_usecount, (void *)lr_saved,
                    solockhistory_nr(so));
                /* NOTREACHED */
        }
        mutex_held = (&((struct kern_event_pcb *)so->so_pcb)->evp_mtx);

        LCK_MTX_ASSERT(mutex_held, LCK_MTX_ASSERT_OWNED);
        so->unlock_lr[so->next_unlock_lr] = lr_saved;
        so->next_unlock_lr = (so->next_unlock_lr + 1) % SO_LCKDBG_MAX;

        if (so->so_usecount == 0) {
                VERIFY(so->so_flags & SOF_PCBCLEARING);
                event_sofreelastref(so);
        } else {
                lck_mtx_unlock(mutex_held);
        }

        return 0;
}

static int
event_sofreelastref(struct socket *so)
{
        struct kern_event_pcb *ev_pcb = (struct kern_event_pcb *)so->so_pcb;

        LCK_MTX_ASSERT(&(ev_pcb->evp_mtx), LCK_MTX_ASSERT_OWNED);

        so->so_pcb = NULL;

        /*
         * Disable upcall in the event another thread is in kev_post_msg()
         * appending record to the receive socket buffer, since sbwakeup()
         * may release the socket lock otherwise.
         */
        so->so_rcv.sb_flags &= ~SB_UPCALL;
        so->so_snd.sb_flags &= ~SB_UPCALL;
        so->so_event = sonullevent;
        lck_mtx_unlock(&(ev_pcb->evp_mtx));

        LCK_MTX_ASSERT(&(ev_pcb->evp_mtx), LCK_MTX_ASSERT_NOTOWNED);
        lck_rw_lock_exclusive(&kev_rwlock);
        LIST_REMOVE(ev_pcb, evp_link);
        kevtstat.kes_pcbcount--;
        kevtstat.kes_gencnt++;
        lck_rw_done(&kev_rwlock);
        kev_delete(ev_pcb);

        sofreelastref(so, 1);
        return 0;
}

static int event_proto_count = (sizeof(eventsw) / sizeof(struct protosw));

static
struct kern_event_head kern_event_head;

static u_int32_t static_event_id = 0;

static ZONE_DECLARE(ev_pcb_zone, "kerneventpcb",
    sizeof(struct kern_event_pcb), ZC_ZFREE_CLEARMEM);

/*
 * Install the protosw's for the NKE manager.  Invoked at extension load time
 */
void
kern_event_init(struct domain *dp)
{
        struct protosw *pr;
        int i;

        VERIFY(!(dp->dom_flags & DOM_INITIALIZED));
        VERIFY(dp == systemdomain);

        for (i = 0, pr = &eventsw[0]; i < event_proto_count; i++, pr++) {
                net_add_proto(pr, dp, 1);
        }
}

static int
kev_attach(struct socket *so, __unused int proto, __unused struct proc *p)
{
        int error = 0;
        struct kern_event_pcb *ev_pcb;

        error = soreserve(so, KEV_SNDSPACE, KEV_RECVSPACE);
        if (error != 0) {
                return error;
        }

        ev_pcb = zalloc_flags(ev_pcb_zone, Z_WAITOK | Z_ZERO);
        lck_mtx_init(&ev_pcb->evp_mtx, &kev_lck_grp, LCK_ATTR_NULL);

        ev_pcb->evp_socket = so;
        ev_pcb->evp_vendor_code_filter = 0xffffffff;

        so->so_pcb = (caddr_t) ev_pcb;
        lck_rw_lock_exclusive(&kev_rwlock);
        LIST_INSERT_HEAD(&kern_event_head, ev_pcb, evp_link);
        kevtstat.kes_pcbcount++;
        kevtstat.kes_gencnt++;
        lck_rw_done(&kev_rwlock);

        return error;
}

static void
kev_delete(struct kern_event_pcb *ev_pcb)
{
        VERIFY(ev_pcb != NULL);
        lck_mtx_destroy(&ev_pcb->evp_mtx, &kev_lck_grp);
        zfree(ev_pcb_zone, ev_pcb);
}

static int
kev_detach(struct socket *so)
{
        struct kern_event_pcb *ev_pcb = (struct kern_event_pcb *) so->so_pcb;

        if (ev_pcb != NULL) {
                soisdisconnected(so);
                so->so_flags |= SOF_PCBCLEARING;
        }

        return 0;
}

/*
 * For now, kev_vendor_code and mbuf_tags use the same
 * mechanism.
 */
errno_t
kev_vendor_code_find(
        const char      *string,
        u_int32_t       *out_vendor_code)
{
        if (strlen(string) >= KEV_VENDOR_CODE_MAX_STR_LEN) {
                return EINVAL;
        }
        return net_str_id_find_internal(string, out_vendor_code,
                   NSI_VENDOR_CODE, 1);
}

errno_t
kev_msg_post(struct kev_msg *event_msg)
{
        mbuf_tag_id_t min_vendor, max_vendor;

        net_str_id_first_last(&min_vendor, &max_vendor, NSI_VENDOR_CODE);

        if (event_msg == NULL) {
                return EINVAL;
        }

        /*
         * Limit third parties to posting events for registered vendor codes
         * only
         */
        if (event_msg->vendor_code < min_vendor ||
            event_msg->vendor_code > max_vendor) {
                os_atomic_inc(&kevtstat.kes_badvendor, relaxed);
                return EINVAL;
        }
        return kev_post_msg(event_msg);
}

int
kev_post_msg(struct kev_msg *event_msg)
{
        struct mbuf *m, *m2;
        struct kern_event_pcb *ev_pcb;
        struct kern_event_msg *ev;
        char *tmp;
        u_int32_t total_size;
        int i;

        /* Verify the message is small enough to fit in one mbuf w/o cluster */
        total_size = KEV_MSG_HEADER_SIZE;

        for (i = 0; i < 5; i++) {
                if (event_msg->dv[i].data_length == 0) {
                        break;
                }
                total_size += event_msg->dv[i].data_length;
        }

        if (total_size > MLEN) {
                os_atomic_inc(&kevtstat.kes_toobig, relaxed);
                return EMSGSIZE;
        }

        m = m_get(M_WAIT, MT_DATA);
        if (m == 0) {
                os_atomic_inc(&kevtstat.kes_nomem, relaxed);
                return ENOMEM;
        }
        ev = mtod(m, struct kern_event_msg *);
        total_size = KEV_MSG_HEADER_SIZE;

        tmp = (char *) &ev->event_data[0];
        for (i = 0; i < 5; i++) {
                if (event_msg->dv[i].data_length == 0) {
                        break;
                }

                total_size += event_msg->dv[i].data_length;
                bcopy(event_msg->dv[i].data_ptr, tmp,
                    event_msg->dv[i].data_length);
                tmp += event_msg->dv[i].data_length;
        }

        ev->id = ++static_event_id;
        ev->total_size   = total_size;
        ev->vendor_code  = event_msg->vendor_code;
        ev->kev_class    = event_msg->kev_class;
        ev->kev_subclass = event_msg->kev_subclass;
        ev->event_code   = event_msg->event_code;

        m->m_len = total_size;
        lck_rw_lock_shared(&kev_rwlock);
        for (ev_pcb = LIST_FIRST(&kern_event_head);
            ev_pcb;
            ev_pcb = LIST_NEXT(ev_pcb, evp_link)) {
                lck_mtx_lock(&ev_pcb->evp_mtx);
                if (ev_pcb->evp_socket->so_pcb == NULL) {
                        lck_mtx_unlock(&ev_pcb->evp_mtx);
                        continue;
                }
                if (ev_pcb->evp_vendor_code_filter != KEV_ANY_VENDOR) {
                        if (ev_pcb->evp_vendor_code_filter != ev->vendor_code) {
                                lck_mtx_unlock(&ev_pcb->evp_mtx);
                                continue;
                        }

                        if (ev_pcb->evp_class_filter != KEV_ANY_CLASS) {
                                if (ev_pcb->evp_class_filter != ev->kev_class) {
                                        lck_mtx_unlock(&ev_pcb->evp_mtx);
                                        continue;
                                }

                                if ((ev_pcb->evp_subclass_filter !=
                                    KEV_ANY_SUBCLASS) &&
                                    (ev_pcb->evp_subclass_filter !=
                                    ev->kev_subclass)) {
                                        lck_mtx_unlock(&ev_pcb->evp_mtx);
                                        continue;
                                }
                        }
                }

                m2 = m_copym(m, 0, m->m_len, M_WAIT);
                if (m2 == 0) {
                        os_atomic_inc(&kevtstat.kes_nomem, relaxed);
                        m_free(m);
                        lck_mtx_unlock(&ev_pcb->evp_mtx);
                        lck_rw_done(&kev_rwlock);
                        return ENOMEM;
                }
                if (sbappendrecord(&ev_pcb->evp_socket->so_rcv, m2)) {
                        /*
                         * We use "m" for the socket stats as it would be
                         * unsafe to use "m2"
                         */
                        so_inc_recv_data_stat(ev_pcb->evp_socket,
                            1, m->m_len, MBUF_TC_BE);

                        sorwakeup(ev_pcb->evp_socket);
                        os_atomic_inc(&kevtstat.kes_posted, relaxed);
                } else {
                        os_atomic_inc(&kevtstat.kes_fullsock, relaxed);
                }
                lck_mtx_unlock(&ev_pcb->evp_mtx);
        }
        m_free(m);
        lck_rw_done(&kev_rwlock);

        return 0;
}

static int
kev_control(struct socket *so,
    u_long cmd,
    caddr_t data,
    __unused struct ifnet *ifp,
    __unused struct proc *p)
{
        struct kev_request *kev_req = (struct kev_request *) data;
        struct kern_event_pcb  *ev_pcb;
        struct kev_vendor_code *kev_vendor;
        u_int32_t  *id_value = (u_int32_t *) data;

        switch (cmd) {
        case SIOCGKEVID:
                *id_value = static_event_id;
                break;
        case SIOCSKEVFILT:
                ev_pcb = (struct kern_event_pcb *) so->so_pcb;
                ev_pcb->evp_vendor_code_filter = kev_req->vendor_code;
                ev_pcb->evp_class_filter = kev_req->kev_class;
                ev_pcb->evp_subclass_filter  = kev_req->kev_subclass;
                break;
        case SIOCGKEVFILT:
                ev_pcb = (struct kern_event_pcb *) so->so_pcb;
                kev_req->vendor_code = ev_pcb->evp_vendor_code_filter;
                kev_req->kev_class   = ev_pcb->evp_class_filter;
                kev_req->kev_subclass = ev_pcb->evp_subclass_filter;
                break;
        case SIOCGKEVVENDOR:
                kev_vendor = (struct kev_vendor_code *)data;
                /* Make sure string is NULL terminated */
                kev_vendor->vendor_string[KEV_VENDOR_CODE_MAX_STR_LEN - 1] = 0;
                return net_str_id_find_internal(kev_vendor->vendor_string,
                           &kev_vendor->vendor_code, NSI_VENDOR_CODE, 0);
        default:
                return ENOTSUP;
        }

        return 0;
}

int
kevt_getstat SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp, arg1, arg2)
        int error = 0;

        lck_rw_lock_shared(&kev_rwlock);

        if (req->newptr != USER_ADDR_NULL) {
                error = EPERM;
                goto done;
        }
        if (req->oldptr == USER_ADDR_NULL) {
                req->oldidx = sizeof(struct kevtstat);
                goto done;
        }

        error = SYSCTL_OUT(req, &kevtstat,
            MIN(sizeof(struct kevtstat), req->oldlen));
done:
        lck_rw_done(&kev_rwlock);

        return error;
}

__private_extern__ int
kevt_pcblist SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp, arg1, arg2)
        int error = 0;
        uint64_t n, i;
        struct xsystmgen xsg;
        void *buf = NULL;
        size_t item_size = ROUNDUP64(sizeof(struct xkevtpcb)) +
            ROUNDUP64(sizeof(struct xsocket_n)) +
            2 * ROUNDUP64(sizeof(struct xsockbuf_n)) +
            ROUNDUP64(sizeof(struct xsockstat_n));
        struct kern_event_pcb  *ev_pcb;

        buf = kheap_alloc(KHEAP_TEMP, item_size, Z_WAITOK | Z_ZERO);
        if (buf == NULL) {
                return ENOMEM;
        }

        lck_rw_lock_shared(&kev_rwlock);

        n = kevtstat.kes_pcbcount;

        if (req->oldptr == USER_ADDR_NULL) {
                req->oldidx = (size_t) ((n + n / 8) * item_size);
                goto done;
        }
        if (req->newptr != USER_ADDR_NULL) {
                error = EPERM;
                goto done;
        }
        bzero(&xsg, sizeof(xsg));
        xsg.xg_len = sizeof(xsg);
        xsg.xg_count = n;
        xsg.xg_gen = kevtstat.kes_gencnt;
        xsg.xg_sogen = so_gencnt;
        error = SYSCTL_OUT(req, &xsg, sizeof(xsg));
        if (error) {
                goto done;
        }
        /*
         * We are done if there is no pcb
         */
        if (n == 0) {
                goto done;
        }

        i = 0;
        for (i = 0, ev_pcb = LIST_FIRST(&kern_event_head);
            i < n && ev_pcb != NULL;
            i++, ev_pcb = LIST_NEXT(ev_pcb, evp_link)) {
                struct xkevtpcb *xk = (struct xkevtpcb *)buf;
                struct xsocket_n *xso = (struct xsocket_n *)
                    ADVANCE64(xk, sizeof(*xk));
                struct xsockbuf_n *xsbrcv = (struct xsockbuf_n *)
                    ADVANCE64(xso, sizeof(*xso));
                struct xsockbuf_n *xsbsnd = (struct xsockbuf_n *)
                    ADVANCE64(xsbrcv, sizeof(*xsbrcv));
                struct xsockstat_n *xsostats = (struct xsockstat_n *)
                    ADVANCE64(xsbsnd, sizeof(*xsbsnd));

                bzero(buf, item_size);

                lck_mtx_lock(&ev_pcb->evp_mtx);

                xk->kep_len = sizeof(struct xkevtpcb);
                xk->kep_kind = XSO_EVT;
                xk->kep_evtpcb = (uint64_t)VM_KERNEL_ADDRPERM(ev_pcb);
                xk->kep_vendor_code_filter = ev_pcb->evp_vendor_code_filter;
                xk->kep_class_filter = ev_pcb->evp_class_filter;
                xk->kep_subclass_filter = ev_pcb->evp_subclass_filter;

                sotoxsocket_n(ev_pcb->evp_socket, xso);
                sbtoxsockbuf_n(ev_pcb->evp_socket ?
                    &ev_pcb->evp_socket->so_rcv : NULL, xsbrcv);
                sbtoxsockbuf_n(ev_pcb->evp_socket ?
                    &ev_pcb->evp_socket->so_snd : NULL, xsbsnd);
                sbtoxsockstat_n(ev_pcb->evp_socket, xsostats);

                lck_mtx_unlock(&ev_pcb->evp_mtx);

                error = SYSCTL_OUT(req, buf, item_size);
        }

        if (error == 0) {
                /*
                 * Give the user an updated idea of our state.
                 * If the generation differs from what we told
                 * her before, she knows that something happened
                 * while we were processing this request, and it
                 * might be necessary to retry.
                 */
                bzero(&xsg, sizeof(xsg));
                xsg.xg_len = sizeof(xsg);
                xsg.xg_count = n;
                xsg.xg_gen = kevtstat.kes_gencnt;
                xsg.xg_sogen = so_gencnt;
                error = SYSCTL_OUT(req, &xsg, sizeof(xsg));
                if (error) {
                        goto done;
                }
        }

done:
        lck_rw_done(&kev_rwlock);

        kheap_free(KHEAP_TEMP, buf, item_size);
        return error;
}

#endif /* SOCKETS */


int
fill_kqueueinfo(struct kqueue *kq, struct kqueue_info * kinfo)
{
        struct vinfo_stat * st;

        st = &kinfo->kq_stat;

        st->vst_size = kq->kq_count;
        if (kq->kq_state & KQ_KEV_QOS) {
                st->vst_blksize = sizeof(struct kevent_qos_s);
        } else if (kq->kq_state & KQ_KEV64) {
                st->vst_blksize = sizeof(struct kevent64_s);
        } else {
                st->vst_blksize = sizeof(struct kevent);
        }
        st->vst_mode = S_IFIFO;
        st->vst_ino = (kq->kq_state & KQ_DYNAMIC) ?
            ((struct kqworkloop *)kq)->kqwl_dynamicid : 0;

        /* flags exported to libproc as PROC_KQUEUE_* (sys/proc_info.h) */
#define PROC_KQUEUE_MASK (KQ_SEL|KQ_SLEEP|KQ_KEV32|KQ_KEV64|KQ_KEV_QOS|KQ_WORKQ|KQ_WORKLOOP)
        kinfo->kq_state = kq->kq_state & PROC_KQUEUE_MASK;

        return 0;
}

static int
fill_kqueue_dyninfo(struct kqworkloop *kqwl, struct kqueue_dyninfo *kqdi)
{
        workq_threadreq_t kqr = &kqwl->kqwl_request;
        workq_threadreq_param_t trp = {};
        int err;

        if ((kqwl->kqwl_state & KQ_WORKLOOP) == 0) {
                return EINVAL;
        }

        if ((err = fill_kqueueinfo(&kqwl->kqwl_kqueue, &kqdi->kqdi_info))) {
                return err;
        }

        kqlock(kqwl);

        kqdi->kqdi_servicer = thread_tid(kqr_thread(kqr));
        kqdi->kqdi_owner = thread_tid(kqwl->kqwl_owner);
        kqdi->kqdi_request_state = kqr->tr_state;
        kqdi->kqdi_async_qos = kqr->tr_kq_qos_index;
        kqdi->kqdi_events_qos = kqr->tr_kq_override_index;
        kqdi->kqdi_sync_waiters = 0;
        kqdi->kqdi_sync_waiter_qos = 0;

        trp.trp_value = kqwl->kqwl_params;
        if (trp.trp_flags & TRP_PRIORITY) {
                kqdi->kqdi_pri = trp.trp_pri;
        } else {
                kqdi->kqdi_pri = 0;
        }

        if (trp.trp_flags & TRP_POLICY) {
                kqdi->kqdi_pol = trp.trp_pol;
        } else {
                kqdi->kqdi_pol = 0;
        }

        if (trp.trp_flags & TRP_CPUPERCENT) {
                kqdi->kqdi_cpupercent = trp.trp_cpupercent;
        } else {
                kqdi->kqdi_cpupercent = 0;
        }

        kqunlock(kqwl);

        return 0;
}


void
knote_markstayactive(struct knote *kn)
{
        struct kqueue *kq = knote_get_kq(kn);
        kq_index_t qos;

        kqlock(kq);
        kn->kn_status |= KN_STAYACTIVE;

        /*
         * Making a knote stay active is a property of the knote that must be
         * established before it is fully attached.
         */
        assert((kn->kn_status & (KN_QUEUED | KN_SUPPRESSED)) == 0);

        /* handle all stayactive knotes on the (appropriate) manager */
        if (kq->kq_state & KQ_WORKLOOP) {
                struct kqworkloop *kqwl = (struct kqworkloop *)kq;

                qos = _pthread_priority_thread_qos(kn->kn_qos);
                assert(qos && qos < THREAD_QOS_LAST);
                kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_UPDATE_STAYACTIVE_QOS, qos);
                qos = KQWL_BUCKET_STAYACTIVE;
        } else if (kq->kq_state & KQ_WORKQ) {
                qos = KQWQ_QOS_MANAGER;
        } else {
                qos = THREAD_QOS_UNSPECIFIED;
        }

        kn->kn_qos_override = qos;
        kn->kn_qos_index = qos;

        knote_activate(kq, kn, FILTER_ACTIVE);
        kqunlock(kq);
}

void
knote_clearstayactive(struct knote *kn)
{
        struct kqueue *kq = knote_get_kq(kn);
        kqlock(kq);
        kn->kn_status &= ~(KN_STAYACTIVE | KN_ACTIVE);
        knote_dequeue(kq, kn);
        kqunlock(kq);
}

static unsigned long
kevent_extinfo_emit(struct kqueue *kq, struct knote *kn, struct kevent_extinfo *buf,
    unsigned long buflen, unsigned long nknotes)
{
        for (; kn; kn = SLIST_NEXT(kn, kn_link)) {
                if (kq == knote_get_kq(kn)) {
                        if (nknotes < buflen) {
                                struct kevent_extinfo *info = &buf[nknotes];

                                kqlock(kq);

                                info->kqext_kev         = *(struct kevent_qos_s *)&kn->kn_kevent;
                                if (knote_has_qos(kn)) {
                                        info->kqext_kev.qos =
                                            _pthread_priority_thread_qos_fast(kn->kn_qos);
                                } else {
                                        info->kqext_kev.qos = kn->kn_qos_override;
                                }
                                info->kqext_kev.filter |= 0xff00; /* sign extend filter */
                                info->kqext_kev.xflags  = 0; /* this is where sfflags lives */
                                info->kqext_kev.data    = 0; /* this is where sdata lives */
                                info->kqext_sdata       = kn->kn_sdata;
                                info->kqext_status      = kn->kn_status;
                                info->kqext_sfflags     = kn->kn_sfflags;

                                kqunlock(kq);
                        }

                        /* we return total number of knotes, which may be more than requested */
                        nknotes++;
                }
        }

        return nknotes;
}

int
kevent_copyout_proc_dynkqids(void *proc, user_addr_t ubuf, uint32_t ubufsize,
    int32_t *nkqueues_out)
{
        proc_t p = (proc_t)proc;
        struct filedesc *fdp = p->p_fd;
        unsigned int nkqueues = 0;
        unsigned long ubuflen = ubufsize / sizeof(kqueue_id_t);
        size_t buflen, bufsize;
        kqueue_id_t *kq_ids = NULL;
        int err = 0;

        assert(p != NULL);

        if (ubuf == USER_ADDR_NULL && ubufsize != 0) {
                err = EINVAL;
                goto out;
        }

        buflen = MIN(ubuflen, PROC_PIDDYNKQUEUES_MAX);

        if (ubuflen != 0) {
                if (os_mul_overflow(sizeof(kqueue_id_t), buflen, &bufsize)) {
                        err = ERANGE;
                        goto out;
                }
                kq_ids = kheap_alloc(KHEAP_TEMP, bufsize, Z_WAITOK | Z_ZERO);
                if (!kq_ids) {
                        err = ENOMEM;
                        goto out;
                }
        }

        kqhash_lock(fdp);

        if (fdp->fd_kqhashmask > 0) {
                for (uint32_t i = 0; i < fdp->fd_kqhashmask + 1; i++) {
                        struct kqworkloop *kqwl;

                        LIST_FOREACH(kqwl, &fdp->fd_kqhash[i], kqwl_hashlink) {
                                /* report the number of kqueues, even if they don't all fit */
                                if (nkqueues < buflen) {
                                        kq_ids[nkqueues] = kqwl->kqwl_dynamicid;
                                }
                                nkqueues++;
                        }
                }
        }

        kqhash_unlock(fdp);

        if (kq_ids) {
                size_t copysize;
                if (os_mul_overflow(sizeof(kqueue_id_t), MIN(buflen, nkqueues), &copysize)) {
                        err = ERANGE;
                        goto out;
                }

                assert(ubufsize >= copysize);
                err = copyout(kq_ids, ubuf, copysize);
        }

out:
        if (kq_ids) {
                kheap_free(KHEAP_TEMP, kq_ids, bufsize);
        }

        if (!err) {
                *nkqueues_out = (int)min(nkqueues, PROC_PIDDYNKQUEUES_MAX);
        }
        return err;
}

int
kevent_copyout_dynkqinfo(void *proc, kqueue_id_t kq_id, user_addr_t ubuf,
    uint32_t ubufsize, int32_t *size_out)
{
        proc_t p = (proc_t)proc;
        struct kqworkloop *kqwl;
        int err = 0;
        struct kqueue_dyninfo kqdi = { };

        assert(p != NULL);

        if (ubufsize < sizeof(struct kqueue_info)) {
                return ENOBUFS;
        }

        kqwl = kqworkloop_hash_lookup_and_retain(p->p_fd, kq_id);
        if (!kqwl) {
                return ESRCH;
        }

        /*
         * backward compatibility: allow the argument to this call to only be
         * a struct kqueue_info
         */
        if (ubufsize >= sizeof(struct kqueue_dyninfo)) {
                ubufsize = sizeof(struct kqueue_dyninfo);
                err = fill_kqueue_dyninfo(kqwl, &kqdi);
        } else {
                ubufsize = sizeof(struct kqueue_info);
                err = fill_kqueueinfo(&kqwl->kqwl_kqueue, &kqdi.kqdi_info);
        }
        if (err == 0 && (err = copyout(&kqdi, ubuf, ubufsize)) == 0) {
                *size_out = ubufsize;
        }
        kqworkloop_release(kqwl);
        return err;
}

int
kevent_copyout_dynkqextinfo(void *proc, kqueue_id_t kq_id, user_addr_t ubuf,
    uint32_t ubufsize, int32_t *nknotes_out)
{
        proc_t p = (proc_t)proc;
        struct kqworkloop *kqwl;
        int err;

        kqwl = kqworkloop_hash_lookup_and_retain(p->p_fd, kq_id);
        if (!kqwl) {
                return ESRCH;
        }

        err = pid_kqueue_extinfo(p, &kqwl->kqwl_kqueue, ubuf, ubufsize, nknotes_out);
        kqworkloop_release(kqwl);
        return err;
}

int
pid_kqueue_extinfo(proc_t p, struct kqueue *kq, user_addr_t ubuf,
    uint32_t bufsize, int32_t *retval)
{
        struct knote *kn;
        int i;
        int err = 0;
        struct filedesc *fdp = p->p_fd;
        unsigned long nknotes = 0;
        unsigned long buflen = bufsize / sizeof(struct kevent_extinfo);
        struct kevent_extinfo *kqext = NULL;

        /* arbitrary upper limit to cap kernel memory usage, copyout size, etc. */
        buflen = MIN(buflen, PROC_PIDFDKQUEUE_KNOTES_MAX);

        kqext = kheap_alloc(KHEAP_TEMP,
            buflen * sizeof(struct kevent_extinfo), Z_WAITOK | Z_ZERO);
        if (kqext == NULL) {
                err = ENOMEM;
                goto out;
        }

        proc_fdlock(p);
        for (i = 0; i < fdp->fd_knlistsize; i++) {
                kn = SLIST_FIRST(&fdp->fd_knlist[i]);
                nknotes = kevent_extinfo_emit(kq, kn, kqext, buflen, nknotes);
        }
        proc_fdunlock(p);

        if (fdp->fd_knhashmask != 0) {
                for (i = 0; i < (int)fdp->fd_knhashmask + 1; i++) {
                        knhash_lock(fdp);
                        kn = SLIST_FIRST(&fdp->fd_knhash[i]);
                        nknotes = kevent_extinfo_emit(kq, kn, kqext, buflen, nknotes);
                        knhash_unlock(fdp);
                }
        }

        assert(bufsize >= sizeof(struct kevent_extinfo) * MIN(buflen, nknotes));
        err = copyout(kqext, ubuf, sizeof(struct kevent_extinfo) * MIN(buflen, nknotes));

out:
        kheap_free(KHEAP_TEMP, kqext, buflen * sizeof(struct kevent_extinfo));

        if (!err) {
                *retval = (int32_t)MIN(nknotes, PROC_PIDFDKQUEUE_KNOTES_MAX);
        }
        return err;
}

static unsigned int
klist_copy_udata(struct klist *list, uint64_t *buf,
    unsigned int buflen, unsigned int nknotes)
{
        struct knote *kn;
        SLIST_FOREACH(kn, list, kn_link) {
                if (nknotes < buflen) {
                        /*
                         * kevent_register will always set kn_udata atomically
                         * so that we don't have to take any kqlock here.
                         */
                        buf[nknotes] = os_atomic_load_wide(&kn->kn_udata, relaxed);
                }
                /* we return total number of knotes, which may be more than requested */
                nknotes++;
        }

        return nknotes;
}

int
kevent_proc_copy_uptrs(void *proc, uint64_t *buf, uint32_t bufsize)
{
        proc_t p = (proc_t)proc;
        struct filedesc *fdp = p->p_fd;
        unsigned int nuptrs = 0;
        unsigned int buflen = bufsize / sizeof(uint64_t);
        struct kqworkloop *kqwl;

        if (buflen > 0) {
                assert(buf != NULL);
        }

        proc_fdlock(p);
        for (int i = 0; i < fdp->fd_knlistsize; i++) {
                nuptrs = klist_copy_udata(&fdp->fd_knlist[i], buf, buflen, nuptrs);
        }
        proc_fdunlock(p);

        knhash_lock(fdp);
        if (fdp->fd_knhashmask != 0) {
                for (size_t i = 0; i < fdp->fd_knhashmask + 1; i++) {
                        nuptrs = klist_copy_udata(&fdp->fd_knhash[i], buf, buflen, nuptrs);
                }
        }
        knhash_unlock(fdp);

        kqhash_lock(fdp);
        if (fdp->fd_kqhashmask != 0) {
                for (size_t i = 0; i < fdp->fd_kqhashmask + 1; i++) {
                        LIST_FOREACH(kqwl, &fdp->fd_kqhash[i], kqwl_hashlink) {
                                if (nuptrs < buflen) {
                                        buf[nuptrs] = kqwl->kqwl_dynamicid;
                                }
                                nuptrs++;
                        }
                }
        }
        kqhash_unlock(fdp);

        return (int)nuptrs;
}

static void
kevent_set_return_to_kernel_user_tsd(proc_t p, thread_t thread)
{
        uint64_t ast_addr;
        bool proc_is_64bit = !!(p->p_flag & P_LP64);
        size_t user_addr_size = proc_is_64bit ? 8 : 4;
        uint32_t ast_flags32 = 0;
        uint64_t ast_flags64 = 0;
        struct uthread *ut = get_bsdthread_info(thread);

        if (ut->uu_kqr_bound != NULL) {
                ast_flags64 |= R2K_WORKLOOP_PENDING_EVENTS;
        }

        if (ast_flags64 == 0) {
                return;
        }

        if (!(p->p_flag & P_LP64)) {
                ast_flags32 = (uint32_t)ast_flags64;
                assert(ast_flags64 < 0x100000000ull);
        }

        ast_addr = thread_rettokern_addr(thread);
        if (ast_addr == 0) {
                return;
        }

        if (copyout((proc_is_64bit ? (void *)&ast_flags64 : (void *)&ast_flags32),
            (user_addr_t)ast_addr,
            user_addr_size) != 0) {
                printf("pid %d (tid:%llu): copyout of return_to_kernel ast flags failed with "
                    "ast_addr = %llu\n", p->p_pid, thread_tid(current_thread()), ast_addr);
        }
}

void
kevent_ast(thread_t thread, uint16_t bits)
{
        proc_t p = current_proc();

        if (bits & AST_KEVENT_REDRIVE_THREADREQ) {
                workq_kern_threadreq_redrive(p, WORKQ_THREADREQ_CAN_CREATE_THREADS);
        }
        if (bits & AST_KEVENT_RETURN_TO_KERNEL) {
                kevent_set_return_to_kernel_user_tsd(p, thread);
        }
}

#if DEVELOPMENT || DEBUG

#define KEVENT_SYSCTL_BOUND_ID 1

static int
kevent_sysctl SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp, arg2)
        uintptr_t type = (uintptr_t)arg1;
        uint64_t bound_id = 0;

        if (type != KEVENT_SYSCTL_BOUND_ID) {
                return EINVAL;
        }

        if (req->newptr) {
                return EINVAL;
        }

        struct uthread *ut = get_bsdthread_info(current_thread());
        if (!ut) {
                return EFAULT;
        }

        workq_threadreq_t kqr = ut->uu_kqr_bound;
        if (kqr) {
                if (kqr->tr_flags & WORKQ_TR_FLAG_WORKLOOP) {
                        bound_id = kqr_kqworkloop(kqr)->kqwl_dynamicid;
                } else {
                        bound_id = -1;
                }
        }

        return sysctl_io_number(req, bound_id, sizeof(bound_id), NULL, NULL);
}

SYSCTL_NODE(_kern, OID_AUTO, kevent, CTLFLAG_RW | CTLFLAG_LOCKED, 0,
    "kevent information");

SYSCTL_PROC(_kern_kevent, OID_AUTO, bound_id,
    CTLTYPE_QUAD | CTLFLAG_RD | CTLFLAG_LOCKED | CTLFLAG_MASKED,
    (void *)KEVENT_SYSCTL_BOUND_ID,
    sizeof(kqueue_id_t), kevent_sysctl, "Q",
    "get the ID of the bound kqueue");

#endif /* DEVELOPMENT || DEBUG */