xnu-6153.61.1.tar.gz

[apple/xnu.git] / osfmk / ipc / ipc_pset.c

/*
 * Copyright (c) 2000-2004 Apple Computer, 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
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 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/*
 * Mach Operating System
 * Copyright (c) 1991,1990,1989 Carnegie Mellon University
 * All Rights Reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */
/*
 *      File:   ipc/ipc_pset.c
 *      Author: Rich Draves
 *      Date:   1989
 *
 *      Functions to manipulate IPC port sets.
 */

#include <mach/port.h>
#include <mach/kern_return.h>
#include <mach/message.h>
#include <ipc/ipc_mqueue.h>
#include <ipc/ipc_object.h>
#include <ipc/ipc_pset.h>
#include <ipc/ipc_right.h>
#include <ipc/ipc_space.h>
#include <ipc/ipc_port.h>

#include <kern/kern_types.h>

#include <vm/vm_map.h>
#include <libkern/section_keywords.h>

/*
 *      Routine:        ipc_pset_alloc
 *      Purpose:
 *              Allocate a port set.
 *      Conditions:
 *              Nothing locked.  If successful, the port set is returned
 *              locked.  (The caller doesn't have a reference.)
 *      Returns:
 *              KERN_SUCCESS            The port set is allocated.
 *              KERN_INVALID_TASK       The space is dead.
 *              KERN_NO_SPACE           No room for an entry in the space.
 *              KERN_RESOURCE_SHORTAGE  Couldn't allocate memory.
 */

kern_return_t
ipc_pset_alloc(
        ipc_space_t             space,
        mach_port_name_t        *namep,
        ipc_pset_t              *psetp)
{
        ipc_pset_t pset;
        mach_port_name_t name;
        kern_return_t kr;

        kr = ipc_object_alloc(space, IOT_PORT_SET,
            MACH_PORT_TYPE_PORT_SET, 0,
            &name, (ipc_object_t *) &pset);
        if (kr != KERN_SUCCESS) {
                return kr;
        }
        /* pset and space are locked */

        ipc_mqueue_init(&pset->ips_messages, IPC_MQUEUE_KIND_SET);
        is_write_unlock(space);

        *namep = name;
        *psetp = pset;
        return KERN_SUCCESS;
}

/*
 *      Routine:        ipc_pset_alloc_name
 *      Purpose:
 *              Allocate a port set, with a specific name.
 *      Conditions:
 *              Nothing locked.  If successful, the port set is returned
 *              locked.  (The caller doesn't have a reference.)
 *      Returns:
 *              KERN_SUCCESS            The port set is allocated.
 *              KERN_INVALID_TASK       The space is dead.
 *              KERN_NAME_EXISTS        The name already denotes a right.
 *              KERN_RESOURCE_SHORTAGE  Couldn't allocate memory.
 */

kern_return_t
ipc_pset_alloc_name(
        ipc_space_t             space,
        mach_port_name_t        name,
        ipc_pset_t              *psetp)
{
        ipc_pset_t pset;
        kern_return_t kr;

        kr = ipc_object_alloc_name(space, IOT_PORT_SET,
            MACH_PORT_TYPE_PORT_SET, 0,
            name, (ipc_object_t *) &pset);
        if (kr != KERN_SUCCESS) {
                return kr;
        }
        /* pset is locked */

        ipc_mqueue_init(&pset->ips_messages, IPC_MQUEUE_KIND_SET);

        *psetp = pset;
        return KERN_SUCCESS;
}


/*
 *      Routine:        ipc_pset_alloc_special
 *      Purpose:
 *              Allocate a port set in a special space.
 *              The new port set is returned with one ref.
 *              If unsuccessful, IPS_NULL is returned.
 *      Conditions:
 *              Nothing locked.
 */
ipc_pset_t
ipc_pset_alloc_special(
        __assert_only ipc_space_t space)
{
        ipc_pset_t pset;

        assert(space != IS_NULL);
        assert(space->is_table == IE_NULL);
        assert(!is_active(space));

        pset = ips_object_to_pset(io_alloc(IOT_PORT_SET));
        if (pset == IPS_NULL) {
                return IPS_NULL;
        }

        bzero((char *)pset, sizeof(*pset));

        io_lock_init(ips_to_object(pset));
        pset->ips_references = 1;
        pset->ips_object.io_bits = io_makebits(TRUE, IOT_PORT_SET, 0);

        ipc_mqueue_init(&pset->ips_messages, IPC_MQUEUE_KIND_SET);

        return pset;
}


/*
 *      Routine:        ipc_pset_member
 *      Purpose:
 *              Checks to see if a port is a member of a pset
 *      Conditions:
 *              Both port and port set are locked.
 *              The port must be active.
 */
boolean_t
ipc_pset_member(
        ipc_pset_t      pset,
        ipc_port_t      port)
{
        require_ip_active(port);

        return ipc_mqueue_member(&port->ip_messages, &pset->ips_messages);
}


/*
 *      Routine:        ipc_pset_add
 *      Purpose:
 *              Puts a port into a port set.
 *      Conditions:
 *              Both port and port set are locked and active.
 *              The owner of the port set is also receiver for the port.
 */

kern_return_t
ipc_pset_add(
        ipc_pset_t        pset,
        ipc_port_t        port,
        uint64_t         *reserved_link,
        uint64_t         *reserved_prepost)
{
        kern_return_t kr;

        assert(ips_active(pset));
        require_ip_active(port);

        kr = ipc_mqueue_add(&port->ip_messages, &pset->ips_messages,
            reserved_link, reserved_prepost);

        return kr;
}



/*
 *      Routine:        ipc_pset_remove
 *      Purpose:
 *              Removes a port from a port set.
 *              The port set loses a reference.
 *      Conditions:
 *              Both port and port set are locked.
 *              The port must be active.
 */

kern_return_t
ipc_pset_remove(
        ipc_pset_t        pset,
        ipc_port_t        port)
{
        kern_return_t kr;
        require_ip_active(port);

        if (port->ip_in_pset == 0) {
                return KERN_NOT_IN_SET;
        }

        kr = ipc_mqueue_remove(&port->ip_messages, &pset->ips_messages);

        return kr;
}

/*
 *      Routine:        ipc_pset_lazy_allocate
 *      Purpose:
 *              lazily initialize the wqset of a port set.
 *      Conditions:
 *              Nothing locked.
 */

kern_return_t
ipc_pset_lazy_allocate(
        ipc_space_t space,
        mach_port_name_t psname)
{
        kern_return_t kr;
        ipc_entry_t entry;
        ipc_object_t psobj;
        ipc_pset_t pset;

        kr = ipc_right_lookup_read(space, psname, &entry);
        if (kr != KERN_SUCCESS) {
                return kr;
        }

        /* space is read-locked and active */
        if ((entry->ie_bits & MACH_PORT_TYPE_PORT_SET) == 0) {
                is_read_unlock(space);
                kr = KERN_INVALID_RIGHT;
                return kr;
        }

        psobj = entry->ie_object;
        pset = ips_object_to_pset(psobj);
        assert(pset != NULL);
        ipc_mqueue_t set_mqueue = &pset->ips_messages;
        struct waitq_set *wqset =  &set_mqueue->imq_set_queue;

        io_reference(psobj);
        is_read_unlock(space);

        /*
         * lazily initialize the wqset to avoid
         * possible allocation while linking
         * under spinlocks.
         */
        waitq_set_lazy_init_link(wqset);
        io_release(psobj);

        return KERN_SUCCESS;
}

/*
 *      Routine:        ipc_pset_remove_from_all
 *      Purpose:
 *              Removes a port from all it's port sets.
 *      Conditions:
 *              port is locked and active.
 */

kern_return_t
ipc_pset_remove_from_all(
        ipc_port_t      port)
{
        if (port->ip_in_pset == 0) {
                return KERN_NOT_IN_SET;
        }

        /*
         * Remove the port's mqueue from all sets
         */
        ipc_mqueue_remove_from_all(&port->ip_messages);
        return KERN_SUCCESS;
}


/*
 *      Routine:        ipc_pset_destroy
 *      Purpose:
 *              Destroys a port_set.
 *      Conditions:
 *              The port_set is locked and alive.
 *              The caller has a reference, which is consumed.
 *              Afterwards, the port_set is unlocked and dead.
 */

void
ipc_pset_destroy(
        ipc_space_t     space,
        ipc_pset_t      pset)
{
        assert(ips_active(pset));

        pset->ips_object.io_bits &= ~IO_BITS_ACTIVE;

        /*
         * remove all the member message queues
         * AND remove this message queue from any containing sets
         */
        ipc_mqueue_remove_all(&pset->ips_messages);

        /*
         * Set all waiters on the portset running to
         * discover the change.
         */
        imq_lock(&pset->ips_messages);
        ipc_mqueue_changed(space, &pset->ips_messages);
        imq_unlock(&pset->ips_messages);

        ipc_mqueue_deinit(&pset->ips_messages);

        ips_unlock(pset);
        ips_release(pset);       /* consume the ref our caller gave us */
}

/*
 * Kqueue EVFILT_MACHPORT support
 *
 * - kn_mqueue points to the monitored mqueue
 *
 * - (in/out) ext[0] holds a mach_vm_address_t to a userspace buffer
 *   that can be used to direct-deliver messages when
 *   MACH_RCV_MSG is set in kn_sfflags
 *
 * - (in/out) ext[1] holds a mach_msg_size_t representing the size
 *   of the userspace buffer held in ext[0].
 *
 * - (out)    ext[2] is used to deliver qos information
 *   about the send queue to userspace.
 *
 * - (abused) ext[3] is used in kernel to hold a reference to the first port
 *   with a turnstile that participate to sync IPC override.
 *
 * - kn_hook is optionally a "knote" turnstile. It is used as the inheritor
 *   of turnstiles for rights copied out as part of direct message delivery
 *   when they can participate to sync IPC override.
 *
 *   It is used to atomically neuter the sync IPC override when the knote is
 *   re-enabled.
 *
 */

#include <sys/event.h>
#include <sys/errno.h>

static int
filt_machport_adjust_qos(struct knote *kn, ipc_kmsg_t first)
{
        if (kn->kn_sfflags & MACH_RCV_MSG) {
                int qos = _pthread_priority_thread_qos(first->ikm_qos_override);
                return FILTER_ADJUST_EVENT_QOS(qos);
        }
        return 0;
}

struct turnstile *
filt_ipc_kqueue_turnstile(struct knote *kn)
{
        assert(kn->kn_filter == EVFILT_MACHPORT || kn->kn_filter == EVFILT_WORKLOOP);
        return kqueue_turnstile(knote_get_kq(kn));
}

bool
filt_machport_kqueue_has_turnstile(struct knote *kn)
{
        assert(kn->kn_filter == EVFILT_MACHPORT);
        return ((kn->kn_sfflags & MACH_RCV_MSG) || (kn->kn_sfflags & MACH_RCV_SYNC_PEEK))
               && (kn->kn_flags & EV_DISPATCH);
}

/*
 * Stashes a port that participate to sync IPC override until the knote
 * is being re-enabled.
 *
 * It returns:
 * - the turnstile to use as an inheritor for the stashed port
 * - the kind of stash that happened as PORT_SYNC_* value among:
 *   o not stashed (no sync IPC support)
 *   o stashed in the knote (in kn_ext[3])
 *   o to be hooked to the kn_hook knote
 */
struct turnstile *
filt_machport_stash_port(struct knote *kn, ipc_port_t port, int *link)
{
        struct turnstile *ts = TURNSTILE_NULL;

        if (kn->kn_filter == EVFILT_WORKLOOP) {
                assert(kn->kn_mqueue == NULL);
                kn->kn_mqueue = &port->ip_messages;
                ip_reference(port);
                if (link) {
                        *link = PORT_SYNC_LINK_WORKLOOP_KNOTE;
                }
                ts = filt_ipc_kqueue_turnstile(kn);
        } else if (!filt_machport_kqueue_has_turnstile(kn)) {
                if (link) {
                        *link = PORT_SYNC_LINK_NO_LINKAGE;
                }
        } else if (kn->kn_ext[3] == 0) {
                ip_reference(port);
                kn->kn_ext[3] = (uintptr_t)port;
                ts = filt_ipc_kqueue_turnstile(kn);
                if (link) {
                        *link = PORT_SYNC_LINK_WORKLOOP_KNOTE;
                }
        } else {
                ts = (struct turnstile *)kn->kn_hook;
                if (link) {
                        *link = PORT_SYNC_LINK_WORKLOOP_STASH;
                }
        }

        return ts;
}

/*
 * Lazily prepare a turnstile so that filt_machport_stash_port()
 * can be called with the mqueue lock held.
 *
 * It will allocate a turnstile in kn_hook if:
 * - the knote supports sync IPC override,
 * - we already stashed a port in kn_ext[3],
 * - the object that will be copied out has a chance to ask to be stashed.
 *
 * It is setup so that its inheritor is the workloop turnstile that has been
 * allocated when this knote was attached.
 */
void
filt_machport_turnstile_prepare_lazily(
        struct knote *kn,
        mach_msg_type_name_t msgt_name,
        ipc_port_t port)
{
        /* This is called from within filt_machportprocess */
        assert((kn->kn_status & KN_SUPPRESSED) && (kn->kn_status & KN_LOCKED));

        if (!filt_machport_kqueue_has_turnstile(kn)) {
                return;
        }

        if (kn->kn_ext[3] == 0 || kn->kn_hook) {
                return;
        }

        struct turnstile *ts = filt_ipc_kqueue_turnstile(kn);
        if ((msgt_name == MACH_MSG_TYPE_PORT_SEND_ONCE && port->ip_specialreply) ||
            (msgt_name == MACH_MSG_TYPE_PORT_RECEIVE)) {
                struct turnstile *kn_ts = turnstile_alloc();
                kn_ts = turnstile_prepare((uintptr_t)kn,
                    (struct turnstile **)&kn->kn_hook, kn_ts, TURNSTILE_KNOTE);
                turnstile_update_inheritor(kn_ts, ts,
                    TURNSTILE_IMMEDIATE_UPDATE | TURNSTILE_INHERITOR_TURNSTILE);
                turnstile_cleanup();
        }
}

static void
filt_machport_turnstile_complete_port(struct knote *kn, ipc_port_t port,
    ipc_mqueue_t mqueue)
{
        struct turnstile *ts = TURNSTILE_NULL;

        ip_lock(port);
        if (port->ip_specialreply) {
                /*
                 * If the reply has been sent to the special reply port already,
                 * then the special reply port may already be reused to do something
                 * entirely different.
                 *
                 * However, the only reason for it to still point to this knote is
                 * that it's still waiting for a reply, so when this is the case,
                 * neuter the linkage.
                 */
                if (port->ip_sync_link_state == PORT_SYNC_LINK_WORKLOOP_KNOTE &&
                    port->ip_sync_inheritor_knote == kn) {
                        ipc_port_adjust_special_reply_port_locked(port, NULL,
                            (IPC_PORT_ADJUST_SR_NONE | IPC_PORT_ADJUST_SR_ENABLE_EVENT), FALSE);
                } else {
                        ip_unlock(port);
                }
        } else {
                /*
                 * For receive rights, if their IMQ_KNOTE() is still this
                 * knote, then sever the link.
                 */
                imq_lock(mqueue);
                if (port->ip_sync_link_state == PORT_SYNC_LINK_WORKLOOP_KNOTE &&
                    mqueue->imq_inheritor_knote == kn) {
                        ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);
                        ts = port_send_turnstile(port);
                }
                if (ts) {
                        turnstile_reference(ts);
                        turnstile_update_inheritor(ts, TURNSTILE_INHERITOR_NULL,
                            TURNSTILE_IMMEDIATE_UPDATE);
                }
                imq_unlock(mqueue);
                ip_unlock(port);

                if (ts) {
                        turnstile_update_inheritor_complete(ts,
                            TURNSTILE_INTERLOCK_NOT_HELD);
                        turnstile_deallocate(ts);
                }
        }

        ip_release(port);
}

void
filt_wldetach_sync_ipc(struct knote *kn)
{
        ipc_mqueue_t mqueue = kn->kn_mqueue;
        filt_machport_turnstile_complete_port(kn, ip_from_mq(mqueue), mqueue);
        kn->kn_mqueue = NULL;
}

/*
 * Other half of filt_machport_turnstile_prepare_lazily()
 *
 * This is serialized by the knote state machine.
 */
static void
filt_machport_turnstile_complete(struct knote *kn)
{
        if (kn->kn_ext[3]) {
                ipc_port_t port = (ipc_port_t)kn->kn_ext[3];
                filt_machport_turnstile_complete_port(kn, port, &port->ip_messages);
                kn->kn_ext[3] = 0;
        }

        if (kn->kn_hook) {
                struct turnstile *ts = kn->kn_hook;

                turnstile_update_inheritor(ts, TURNSTILE_INHERITOR_NULL,
                    TURNSTILE_IMMEDIATE_UPDATE);
                turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_HELD);

                turnstile_complete((uintptr_t)kn, (struct turnstile **)&kn->kn_hook, &ts, TURNSTILE_KNOTE);
                turnstile_cleanup();

                assert(ts);
                turnstile_deallocate(ts);
        }
}

static void
filt_machport_link(ipc_mqueue_t mqueue, struct knote *kn)
{
        struct knote *hd = SLIST_FIRST(&mqueue->imq_klist);

        if (hd && filt_machport_kqueue_has_turnstile(kn)) {
                SLIST_INSERT_AFTER(hd, kn, kn_selnext);
        } else {
                SLIST_INSERT_HEAD(&mqueue->imq_klist, kn, kn_selnext);
        }
}

static void
filt_machport_unlink(ipc_mqueue_t mqueue, struct knote *kn)
{
        struct knote **knprev;

        KNOTE_DETACH(&mqueue->imq_klist, kn);

        /* make sure the first knote is a knote we can push on */
        SLIST_FOREACH_PREVPTR(kn, knprev, &mqueue->imq_klist, kn_selnext) {
                if (filt_machport_kqueue_has_turnstile(kn)) {
                        *knprev = SLIST_NEXT(kn, kn_selnext);
                        SLIST_INSERT_HEAD(&mqueue->imq_klist, kn, kn_selnext);
                        break;
                }
        }
}

int
filt_wlattach_sync_ipc(struct knote *kn)
{
        mach_port_name_t name = (mach_port_name_t)kn->kn_id;
        ipc_space_t space = current_space();
        ipc_entry_t entry;
        ipc_port_t port = IP_NULL;
        int error = 0;

        if (ipc_right_lookup_read(space, name, &entry) != KERN_SUCCESS) {
                return ENOENT;
        }

        /* space is read-locked */

        if (entry->ie_bits & MACH_PORT_TYPE_RECEIVE) {
                port = ip_object_to_port(entry->ie_object);
                if (port->ip_specialreply) {
                        error = ENOENT;
                }
        } else if (entry->ie_bits & MACH_PORT_TYPE_SEND_ONCE) {
                port = ip_object_to_port(entry->ie_object);
                if (!port->ip_specialreply) {
                        error = ENOENT;
                }
        } else {
                error = ENOENT;
        }
        if (error) {
                is_read_unlock(space);
                return error;
        }

        ip_lock(port);
        is_read_unlock(space);

        if (port->ip_sync_link_state == PORT_SYNC_LINK_ANY) {
                ip_unlock(port);
                /*
                 * We cannot start a sync IPC inheritance chain, only further one
                 * Note: this can also happen if the inheritance chain broke
                 * because the original requestor died.
                 */
                return ENOENT;
        }

        if (port->ip_specialreply) {
                ipc_port_adjust_special_reply_port_locked(port, kn,
                    IPC_PORT_ADJUST_SR_LINK_WORKLOOP, FALSE);
        } else {
                ipc_port_adjust_port_locked(port, kn, FALSE);
        }

        /* make sure the port was stashed */
        assert(kn->kn_mqueue == &port->ip_messages);

        /* port has been unlocked by ipc_port_adjust_* */

        return 0;
}

static int
filt_machportattach(
        struct knote *kn,
        __unused struct kevent_qos_s *kev)
{
        mach_port_name_t name = (mach_port_name_t)kn->kn_id;
        uint64_t wq_link_id = waitq_link_reserve(NULL);
        ipc_space_t space = current_space();
        ipc_kmsg_t first;
        struct turnstile *send_turnstile = TURNSTILE_NULL;

        int error;
        int result = 0;
        kern_return_t kr;
        ipc_entry_t entry;
        ipc_mqueue_t mqueue;

        kn->kn_flags &= ~EV_EOF;
        kn->kn_ext[3] = 0;

        if (filt_machport_kqueue_has_turnstile(kn)) {
                /*
                 * If the filter is likely to support sync IPC override,
                 * and it happens to be attaching to a workloop,
                 * make sure the workloop has an allocated turnstile.
                 */
                kqueue_alloc_turnstile(knote_get_kq(kn));
        }

lookup_again:
        kr = ipc_right_lookup_read(space, name, &entry);

        if (kr != KERN_SUCCESS) {
                error = ENOENT;
                goto out;
        }

        /* space is read-locked and active */

        if ((entry->ie_bits & MACH_PORT_TYPE_PORT_SET) &&
            knote_link_waitqset_should_lazy_alloc(kn)) {
                is_read_unlock(space);

                /*
                 * We need to link the portset of the kn,
                 * to insure that the link is allocated before taking
                 * any spinlocks.
                 *
                 * Because we have to drop the space lock so that
                 * knote_link_waitqset_lazy_alloc() can allocate memory,
                 * we will need to redo the lookup.
                 */
                knote_link_waitqset_lazy_alloc(kn);
                goto lookup_again;
        }

        if (entry->ie_bits & MACH_PORT_TYPE_PORT_SET) {
                ipc_pset_t pset;

                pset = ips_object_to_pset(entry->ie_object);
                mqueue = &pset->ips_messages;
                ips_reference(pset);

                imq_lock(mqueue);
                kn->kn_mqueue = mqueue;

                /*
                 * Bind the portset wait queue directly to knote/kqueue.
                 * This allows us to just use wait_queue foo to effect a wakeup,
                 * rather than having to call knote() from the Mach code on each
                 * message.  We still attach the knote to the mqueue klist for
                 * NOTE_REVOKE purposes only.
                 */
                error = knote_link_waitq(kn, &mqueue->imq_wait_queue, &wq_link_id);
                if (!error) {
                        filt_machport_link(mqueue, kn);
                        imq_unlock(mqueue);
                } else {
                        kn->kn_mqueue = IMQ_NULL;
                        imq_unlock(mqueue);
                        ips_release(pset);
                }

                is_read_unlock(space);

                /*
                 * linked knotes are marked stay-active and therefore don't
                 * need an indication of their fired state to be returned
                 * from the attach operation.
                 */
        } else if (entry->ie_bits & MACH_PORT_TYPE_RECEIVE) {
                ipc_port_t port = ip_object_to_port(entry->ie_object);

                if (port->ip_specialreply) {
                        /*
                         * Registering for kevents on special reply ports
                         * isn't supported for two reasons:
                         *
                         * 1. it really makes very little sense for a port that
                         *    is supposed to be used synchronously
                         *
                         * 2. their mqueue's imq_klist field will be used to
                         *    store the receive turnstile, so we can't possibly
                         *    attach them anyway.
                         */
                        is_read_unlock(space);
                        error = ENOTSUP;
                        goto out;
                }

                mqueue = &port->ip_messages;
                ip_reference(port);

                /*
                 * attach knote to port and determine result
                 * If the filter requested direct message receipt,
                 * we may need to adjust the qos of the knote to
                 * reflect the requested and override qos of the
                 * first message in the queue.
                 */
                ip_lock(port);
                imq_lock(mqueue);

                kn->kn_mqueue = mqueue;
                if (port->ip_sync_link_state != PORT_SYNC_LINK_ANY) {
                        /*
                         * We're attaching a port that used to have an IMQ_KNOTE,
                         * clobber this state, we'll fixup its turnstile inheritor below.
                         */
                        ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);
                }
                filt_machport_link(mqueue, kn);

                if ((first = ipc_kmsg_queue_first(&mqueue->imq_messages)) != IKM_NULL) {
                        result = FILTER_ACTIVE | filt_machport_adjust_qos(kn, first);
                }

                /*
                 * Update the port's turnstile inheritor
                 *
                 * Unlike filt_machportdetach(), we don't have to care about races for
                 * turnstile_workloop_pusher_info(): filt_machport_link() doesn't affect
                 * already pushing knotes, and if the current one becomes the new
                 * pusher, it'll only be visible when turnstile_workloop_pusher_info()
                 * returns.
                 */
                send_turnstile = port_send_turnstile(port);
                if (send_turnstile) {
                        turnstile_reference(send_turnstile);
                        ipc_port_send_update_inheritor(port, send_turnstile,
                            TURNSTILE_IMMEDIATE_UPDATE);

                        /*
                         * rdar://problem/48861190
                         *
                         * When a listener connection resumes a peer,
                         * updating the inheritor above has moved the push
                         * from the current thread to the workloop.
                         *
                         * However, we haven't told the workloop yet
                         * that it needs a thread request, and we risk
                         * to be preeempted as soon as we drop the space
                         * lock below.
                         *
                         * To avoid this disable preemption and let kevent
                         * reenable it after it takes the kqlock.
                         */
                        disable_preemption();
                        result |= FILTER_THREADREQ_NODEFEER;
                }

                imq_unlock(mqueue);
                ip_unlock(port);

                is_read_unlock(space);
                if (send_turnstile) {
                        turnstile_update_inheritor_complete(send_turnstile,
                            TURNSTILE_INTERLOCK_NOT_HELD);
                        turnstile_deallocate_safe(send_turnstile);
                }

                error = 0;
        } else {
                is_read_unlock(space);
                error = ENOTSUP;
        }

out:
        waitq_link_release(wq_link_id);

        /* bail out on errors */
        if (error) {
                knote_set_error(kn, error);
                return 0;
        }

        return result;
}

/* Validate imq_to_object implementation "works" */
_Static_assert(offsetof(struct ipc_pset, ips_messages) ==
    offsetof(struct ipc_port, ip_messages),
    "Make sure the mqueue aliases in both ports and psets");

static void
filt_machportdetach(
        struct knote *kn)
{
        ipc_mqueue_t mqueue = kn->kn_mqueue;
        ipc_object_t object = imq_to_object(mqueue);
        struct turnstile *send_turnstile = TURNSTILE_NULL;

        filt_machport_turnstile_complete(kn);

        imq_lock(mqueue);
        if ((kn->kn_status & KN_VANISHED) || (kn->kn_flags & EV_EOF)) {
                /*
                 * ipc_mqueue_changed() already unhooked this knote from the mqueue,
                 */
        } else {
                ipc_port_t port = IP_NULL;

                /*
                 * When the knote being detached is the first one in the list,
                 * then unlinking the knote *and* updating the turnstile inheritor
                 * need to happen atomically with respect to the callers of
                 * turnstile_workloop_pusher_info().
                 *
                 * The caller of turnstile_workloop_pusher_info() will use the kq req
                 * lock (and hence the kqlock), so we just need to hold the kqlock too.
                 */
                if (io_otype(object) == IOT_PORT) {
                        port = ip_object_to_port(object);
                        assert(port->ip_sync_link_state == PORT_SYNC_LINK_ANY);
                        if (kn == SLIST_FIRST(&mqueue->imq_klist)) {
                                send_turnstile = port_send_turnstile(port);
                        }
                }

                filt_machport_unlink(mqueue, kn);

                if (send_turnstile) {
                        turnstile_reference(send_turnstile);
                        ipc_port_send_update_inheritor(port, send_turnstile,
                            TURNSTILE_IMMEDIATE_UPDATE);
                }
        }

        /* Clear the knote pointer once the knote has been removed from turnstile */
        kn->kn_mqueue = IMQ_NULL;
        imq_unlock(mqueue);

        if (send_turnstile) {
                turnstile_update_inheritor_complete(send_turnstile,
                    TURNSTILE_INTERLOCK_NOT_HELD);
                turnstile_deallocate(send_turnstile);
        }

        if (io_otype(object) == IOT_PORT_SET) {
                /*
                 * Unlink the portset wait queue from knote/kqueue.
                 * JMM - Does this need to be atomic under the mq lock?
                 */
                (void)knote_unlink_waitq(kn, &mqueue->imq_wait_queue);
        }
        io_release(object);
}

/*
 * filt_machportevent - deliver events into the mach port filter
 *
 * Mach port message arrival events are currently only posted via the
 * kqueue filter routine for ports. Port sets are marked stay-active
 * and the wait queue code will break any kqueue waiters out to go
 * poll the stay-queued knotes again.
 *
 * If there is a message at the head of the queue,
 * we indicate that the knote should go active.  If
 * the message is to be direct-received, we adjust the
 * QoS of the knote according the requested and override
 * QoS of that first message.
 */
static int
filt_machportevent(struct knote *kn, long hint __assert_only)
{
        ipc_mqueue_t mqueue = kn->kn_mqueue;
        ipc_kmsg_t first;
        int result = 0;

        /* mqueue locked by caller */
        assert(imq_held(mqueue));
        assert(hint != NOTE_REVOKE);
        if (imq_is_valid(mqueue)) {
                assert(!imq_is_set(mqueue));
                if ((first = ipc_kmsg_queue_first(&mqueue->imq_messages)) != IKM_NULL) {
                        result = FILTER_ACTIVE | filt_machport_adjust_qos(kn, first);
                }
        }

        return result;
}

static int
filt_machporttouch(
        struct knote *kn,
        struct kevent_qos_s *kev)
{
        ipc_mqueue_t mqueue = kn->kn_mqueue;
        ipc_kmsg_t first;
        int result = 0;

        /* copy in new settings and save off new input fflags */
        kn->kn_sfflags = kev->fflags;
        kn->kn_ext[0] = kev->ext[0];
        kn->kn_ext[1] = kev->ext[1];

        if (kev->flags & EV_ENABLE) {
                /*
                 * If the knote is being enabled, make sure there's no lingering
                 * IPC overrides from the previous message delivery.
                 */
                filt_machport_turnstile_complete(kn);
        }

        /*
         * If the mqueue is a valid port and there is a message
         * that will be direct-received from the knote, update
         * the knote qos based on the first message and trigger
         * the event. If there are no more messages, reset the
         * QoS to the value provided by the kevent.
         */
        imq_lock(mqueue);
        if (imq_is_valid(mqueue) && !imq_is_set(mqueue) &&
            (first = ipc_kmsg_queue_first(&mqueue->imq_messages)) != IKM_NULL) {
                result = FILTER_ACTIVE | filt_machport_adjust_qos(kn, first);
        } else if (kn->kn_sfflags & MACH_RCV_MSG) {
                result = FILTER_RESET_EVENT_QOS;
        }
        imq_unlock(mqueue);

        return result;
}

static int
filt_machportprocess(struct knote *kn, struct kevent_qos_s *kev)
{
        ipc_mqueue_t mqueue = kn->kn_mqueue;
        ipc_object_t object = imq_to_object(mqueue);
        thread_t self = current_thread();
        kevent_ctx_t kectx = NULL;

        wait_result_t wresult;
        mach_msg_option_t option;
        mach_vm_address_t addr;
        mach_msg_size_t size;

        /* Capture current state */
        knote_fill_kevent(kn, kev, MACH_PORT_NULL);
        kev->ext[3] = 0; /* hide our port reference from userspace */

        /* If already deallocated/moved return one last EOF event */
        if (kev->flags & EV_EOF) {
                return FILTER_ACTIVE | FILTER_RESET_EVENT_QOS;
        }

        /*
         * Only honor supported receive options. If no options are
         * provided, just force a MACH_RCV_TOO_LARGE to detect the
         * name of the port and sizeof the waiting message.
         */
        option = kn->kn_sfflags & (MACH_RCV_MSG | MACH_RCV_LARGE | MACH_RCV_LARGE_IDENTITY |
            MACH_RCV_TRAILER_MASK | MACH_RCV_VOUCHER | MACH_MSG_STRICT_REPLY);

        if (option & MACH_RCV_MSG) {
                addr = (mach_vm_address_t) kn->kn_ext[0];
                size = (mach_msg_size_t) kn->kn_ext[1];

                /*
                 * If the kevent didn't specify a buffer and length, carve a buffer
                 * from the filter processing data according to the flags.
                 */
                if (size == 0) {
                        kectx = kevent_get_context(self);
                        addr  = (mach_vm_address_t)kectx->kec_data_out;
                        size  = (mach_msg_size_t)kectx->kec_data_resid;
                        option |= (MACH_RCV_LARGE | MACH_RCV_LARGE_IDENTITY);
                        if (kectx->kec_process_flags & KEVENT_FLAG_STACK_DATA) {
                                option |= MACH_RCV_STACK;
                        }
                }
        } else {
                /* just detect the port name (if a set) and size of the first message */
                option = MACH_RCV_LARGE;
                addr = 0;
                size = 0;
        }

        imq_lock(mqueue);

        /* just use the reference from here on out */
        io_reference(object);

        /*
         * Set up to receive a message or the notification of a
         * too large message.  But never allow this call to wait.
         * If the user provided aditional options, like trailer
         * options, pass those through here.  But we don't support
         * scatter lists through this interface.
         */
        self->ith_object = object;
        self->ith_msg_addr = addr;
        self->ith_rsize = size;
        self->ith_msize = 0;
        self->ith_option = option;
        self->ith_receiver_name = MACH_PORT_NULL;
        self->ith_continuation = NULL;
        option |= MACH_RCV_TIMEOUT; // never wait
        self->ith_state = MACH_RCV_IN_PROGRESS;
        self->ith_knote = kn;

        wresult = ipc_mqueue_receive_on_thread(
                mqueue,
                option,
                size,         /* max_size */
                0,         /* immediate timeout */
                THREAD_INTERRUPTIBLE,
                self);
        /* mqueue unlocked */

        /*
         * If we timed out, or the process is exiting, just release the
         * reference on the ipc_object and return zero.
         */
        if (wresult == THREAD_RESTART || self->ith_state == MACH_RCV_TIMED_OUT) {
                assert(self->turnstile != TURNSTILE_NULL);
                io_release(object);
                return 0;
        }

        assert(wresult == THREAD_NOT_WAITING);
        assert(self->ith_state != MACH_RCV_IN_PROGRESS);

        /*
         * If we weren't attempting to receive a message
         * directly, we need to return the port name in
         * the kevent structure.
         */
        if ((option & MACH_RCV_MSG) != MACH_RCV_MSG) {
                assert(self->ith_state == MACH_RCV_TOO_LARGE);
                assert(self->ith_kmsg == IKM_NULL);
                kev->data = self->ith_receiver_name;
                io_release(object);
                return FILTER_ACTIVE;
        }

        /*
         * Attempt to receive the message directly, returning
         * the results in the fflags field.
         */
        kev->fflags = mach_msg_receive_results(&size);

        /* kmsg and object reference consumed */

        /*
         * if the user asked for the identity of ports containing a
         * a too-large message, return it in the data field (as we
         * do for messages we didn't try to receive).
         */
        if (kev->fflags == MACH_RCV_TOO_LARGE) {
                kev->ext[1] = self->ith_msize;
                if (option & MACH_RCV_LARGE_IDENTITY) {
                        kev->data = self->ith_receiver_name;
                } else {
                        kev->data = MACH_PORT_NULL;
                }
        } else {
                kev->ext[1] = size;
                kev->data = MACH_PORT_NULL;
        }

        /*
         * If we used a data buffer carved out from the filt_process data,
         * store the address used in the knote and adjust the residual and
         * other parameters for future use.
         */
        if (kectx) {
                assert(kectx->kec_data_resid >= size);
                kectx->kec_data_resid -= size;
                if ((kectx->kec_process_flags & KEVENT_FLAG_STACK_DATA) == 0) {
                        kev->ext[0] = kectx->kec_data_out;
                        kectx->kec_data_out += size;
                } else {
                        assert(option & MACH_RCV_STACK);
                        kev->ext[0] = kectx->kec_data_out + kectx->kec_data_resid;
                }
        }

        /*
         * Apply message-based QoS values to output kevent as prescribed.
         * The kev->ext[2] field gets (msg-qos << 32) | (override-qos).
         *
         * The mach_msg_receive_results() call saved off the message
         * QoS values in the continuation save area on successful receive.
         */
        if (kev->fflags == MACH_MSG_SUCCESS) {
                kev->ext[2] = ((uint64_t)self->ith_qos << 32) |
                    (uint64_t)self->ith_qos_override;
        }

        return FILTER_ACTIVE;
}

/*
 * Peek to see if the message queue associated with the knote has any
 * events. This pre-hook is called when a filter uses the stay-
 * on-queue mechanism (as the knote_link_waitq mechanism does for
 * portsets) and someone calls select() against the containing kqueue.
 *
 * Just peek at the pre-post status of the portset's wait queue
 * to determine if it has anything interesting.  We can do it
 * without holding the lock, as it is just a snapshot in time
 * (if this is used as part of really waiting for events, we
 * will catch changes in this status when the event gets posted
 * up to the knote's kqueue).
 */
static int
filt_machportpeek(struct knote *kn)
{
        ipc_mqueue_t mqueue = kn->kn_mqueue;

        return ipc_mqueue_set_peek(mqueue) ? FILTER_ACTIVE : 0;
}

SECURITY_READ_ONLY_EARLY(struct filterops) machport_filtops = {
        .f_adjusts_qos = true,
        .f_extended_codes = true,
        .f_attach = filt_machportattach,
        .f_detach = filt_machportdetach,
        .f_event = filt_machportevent,
        .f_touch = filt_machporttouch,
        .f_process = filt_machportprocess,
        .f_peek = filt_machportpeek,
};