xnu-3247.1.106.tar.gz

[apple/xnu.git] / bsd / netinet / mptcp_subr.c

/*
 * Copyright (c) 2012-2015 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@
 */

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/mbuf.h>
#include <sys/mcache.h>
#include <sys/resourcevar.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/syslog.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/sysctl.h>

#include <kern/zalloc.h>
#include <kern/locks.h>

#include <mach/thread_act.h>
#include <mach/sdt.h>

#include <net/if.h>
#include <net/if_var.h>
#include <netinet/in.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>
#include <netinet/mptcp_var.h>
#include <netinet/mptcp.h>
#include <netinet/mptcp_seq.h>
#include <netinet/mptcp_timer.h>
#include <libkern/crypto/sha1.h>
#if INET6
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6protosw.h>
#endif /* INET6 */
#include <dev/random/randomdev.h>

/*
 * Notes on MPTCP implementation.
 *
 * MPTCP is implemented as <SOCK_STREAM,IPPROTO_TCP> protocol in PF_MULTIPATH
 * communication domain.  The structure mtcbinfo describes the MPTCP instance
 * of a Multipath protocol in that domain.  It is used to keep track of all
 * MPTCP PCB instances in the system, and is protected by the global lock
 * mppi_lock.
 *
 * An MPTCP socket is opened by calling socket(PF_MULTIPATH, SOCK_STREAM,
 * IPPROTO_TCP).  Upon success, a Multipath PCB gets allocated and along with
 * it comes an MPTCP Session and an MPTCP PCB.  All three structures are
 * allocated from the same memory block, and each structure has a pointer
 * to the adjacent ones.  The layout is defined by the mpp_mtp structure.
 * The socket lock (mpp_lock) is used to protect accesses to the Multipath
 * PCB (mppcb) as well as the MPTCP Session (mptses).
 *
 * The MPTCP Session is an MPTCP-specific extension to the Multipath PCB;
 * in particular, the list of subflows as well as the MPTCP thread.
 *
 * A functioning MPTCP Session consists of one or more subflow sockets.  Each
 * subflow socket is essentially a regular PF_INET/PF_INET6 TCP socket, and is
 * represented by the mptsub structure.  Because each subflow requires access
 * to the MPTCP Session, the MPTCP socket's so_usecount is bumped up for each
 * subflow.  This gets decremented prior to the subflow's destruction.  The
 * subflow lock (mpts_lock) is used to protect accesses to the subflow.
 *
 * To handle events (read, write, control) from the subflows, an MPTCP thread
 * is created; currently, there is one thread per MPTCP Session.  In order to
 * prevent the MPTCP socket from being destroyed while being accessed by the
 * MPTCP thread, we bump up the MPTCP socket's so_usecount for the thread,
 * which will be decremented prior to the thread's termination.  The thread
 * lock (mpte_thread_lock) is used to synchronize its signalling.
 *
 * Lock ordering is defined as follows:
 *
 *      mtcbinfo (mppi_lock)
 *              mp_so (mpp_lock)
 *                      mpts (mpts_lock)
 *                              so (inpcb_mtx)
 *                                      mptcb (mpt_lock)
 *
 * It is not a requirement that all of the above locks need to be acquired
 * in succession, but the correct lock ordering must be followed when there
 * are more than one locks that need to be held.  The MPTCP thread lock is
 * is not constrained by this arrangement, because none of the other locks
 * is ever acquired while holding mpte_thread_lock; therefore it may be called
 * at any moment to signal the thread.
 *
 * An MPTCP socket will be destroyed when its so_usecount drops to zero; this
 * work is done by the MPTCP garbage collector which is invoked on demand by
 * the PF_MULTIPATH garbage collector.  This process will take place once all
 * of the subflows have been destroyed, and the MPTCP thread be instructed to
 * self-terminate.
 */

static void mptcp_sesdestroy(struct mptses *);
static void mptcp_thread_signal_locked(struct mptses *);
static void mptcp_thread_terminate_signal(struct mptses *);
static void mptcp_thread_dowork(struct mptses *);
static void mptcp_thread_func(void *, wait_result_t);
static void mptcp_thread_destroy(struct mptses *);
static void mptcp_key_pool_init(void);
static void mptcp_attach_to_subf(struct socket *, struct mptcb *, uint8_t);
static void mptcp_detach_mptcb_from_subf(struct mptcb *, struct socket *);
static void mptcp_conn_properties(struct mptcb *);
static void mptcp_init_statevars(struct mptcb *);

static uint32_t mptcp_gc(struct mppcbinfo *);
static int mptcp_subflow_socreate(struct mptses *, struct mptsub *,
    int, struct proc *, struct socket **);
static int mptcp_subflow_soclose(struct mptsub *, struct socket *);
static int mptcp_subflow_soconnectx(struct mptses *, struct mptsub *);
static int mptcp_subflow_soreceive(struct socket *, struct sockaddr **,
    struct uio *, struct mbuf **, struct mbuf **, int *);
static void mptcp_subflow_rupcall(struct socket *, void *, int);
static void mptcp_subflow_input(struct mptses *, struct mptsub *);
static void mptcp_subflow_wupcall(struct socket *, void *, int);
static void mptcp_subflow_eupcall(struct socket *, void *, uint32_t);
static void mptcp_update_last_owner(struct mptsub *, struct socket *);
static void mptcp_output_needed(struct mptses *mpte, struct mptsub *to_mpts);
static void mptcp_get_rtt_measurement(struct mptsub *, struct mptses *);

/*
 * Possible return values for subflow event handlers.  Note that success
 * values must be greater or equal than MPTS_EVRET_OK.  Values less than that
 * indicate errors or actions which require immediate attention; they will
 * prevent the rest of the handlers from processing their respective events
 * until the next round of events processing.
 */
typedef enum {
        MPTS_EVRET_DELETE               = 1,    /* delete this subflow */
        MPTS_EVRET_OK                   = 2,    /* OK */
        MPTS_EVRET_CONNECT_PENDING      = 3,    /* resume pended connects */
        MPTS_EVRET_DISCONNECT_FALLBACK  = 4,    /* abort all but preferred */
} ev_ret_t;

static ev_ret_t mptcp_subflow_events(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_connreset_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_cantrcvmore_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_cantsendmore_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_timeout_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_nosrcaddr_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_failover_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_ifdenied_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_suspend_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_resume_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_connected_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_disconnected_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_mpstatus_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_mustrst_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_fastjoin_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_deleteok_ev(struct mptses *, struct mptsub *, uint64_t *);
static ev_ret_t mptcp_subflow_mpcantrcvmore_ev(struct mptses *, struct mptsub *, uint64_t *);

static const char *mptcp_evret2str(ev_ret_t);

static mptcp_key_t *mptcp_reserve_key(void);
static int mptcp_do_sha1(mptcp_key_t *, char *, int);
static int mptcp_init_authparms(struct mptcb *);

static unsigned int mptsub_zone_size;           /* size of mptsub */
static struct zone *mptsub_zone;                /* zone for mptsub */

static unsigned int mptopt_zone_size;           /* size of mptopt */
static struct zone *mptopt_zone;                /* zone for mptopt */

static unsigned int mpt_subauth_entry_size;     /* size of subf auth entry */
static struct zone *mpt_subauth_zone;           /* zone of subf auth entry */

struct mppcbinfo mtcbinfo;

static struct mptcp_keys_pool_head mptcp_keys_pool;

#define MPTCP_SUBFLOW_WRITELEN  (8 * 1024)      /* bytes to write each time */
#define MPTCP_SUBFLOW_READLEN   (8 * 1024)      /* bytes to read each time */

SYSCTL_DECL(_net_inet);

SYSCTL_NODE(_net_inet, OID_AUTO, mptcp, CTLFLAG_RW|CTLFLAG_LOCKED, 0, "MPTCP");

uint32_t mptcp_dbg_area = 0;            /* more noise if greater than 1 */
SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, dbg_area, CTLFLAG_RW|CTLFLAG_LOCKED,
        &mptcp_dbg_area, 0, "MPTCP debug area");

uint32_t mptcp_dbg_level = 0;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, dbg_level, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_dbg_level, 0, "MPTCP debug level");


SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, pcbcount, CTLFLAG_RD|CTLFLAG_LOCKED,
        &mtcbinfo.mppi_count, 0, "Number of active PCBs");

/*
 * Since there is one kernel thread per mptcp socket, imposing an artificial
 * limit on number of allowed mptcp sockets.
 */
uint32_t mptcp_socket_limit = MPPCB_LIMIT;
SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, sk_lim, CTLFLAG_RW|CTLFLAG_LOCKED,
        &mptcp_socket_limit, 0, "MPTCP socket limit");

/*
 * SYSCTL to turn on delayed cellular subflow start.
 */
uint32_t mptcp_delayed_subf_start = 0;
SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, delayed, CTLFLAG_RW|CTLFLAG_LOCKED,
        &mptcp_delayed_subf_start, 0, "MPTCP Delayed Subflow start");

/*
 * sysctl to use network status hints from symptomsd
 */
uint32_t mptcp_use_symptomsd = 1;
SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, usesymptoms, CTLFLAG_RW|CTLFLAG_LOCKED,
        &mptcp_use_symptomsd, 0, "MPTCP Use SymptomsD");

static struct protosw mptcp_subflow_protosw;
static struct pr_usrreqs mptcp_subflow_usrreqs;
#if INET6
static struct ip6protosw mptcp_subflow_protosw6;
static struct pr_usrreqs mptcp_subflow_usrreqs6;
#endif /* INET6 */

typedef struct mptcp_subflow_event_entry {
        uint64_t        sofilt_hint_mask;
        ev_ret_t        (*sofilt_hint_ev_hdlr)(
                            struct mptses *mpte,
                            struct mptsub *mpts,
                            uint64_t *p_mpsofilt_hint);
} mptsub_ev_entry_t;

static mptsub_ev_entry_t mpsub_ev_entry_tbl [] = {
        {
                .sofilt_hint_mask = SO_FILT_HINT_MPCANTRCVMORE,
                .sofilt_hint_ev_hdlr =  mptcp_subflow_mpcantrcvmore_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_MPFAILOVER,
                .sofilt_hint_ev_hdlr = mptcp_subflow_failover_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_CONNRESET,
                .sofilt_hint_ev_hdlr = mptcp_subflow_connreset_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_MUSTRST,
                .sofilt_hint_ev_hdlr = mptcp_subflow_mustrst_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_CANTRCVMORE,
                .sofilt_hint_ev_hdlr = mptcp_subflow_cantrcvmore_ev,
        },
        {       .sofilt_hint_mask = SO_FILT_HINT_CANTSENDMORE,
                .sofilt_hint_ev_hdlr = mptcp_subflow_cantsendmore_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_TIMEOUT,
                .sofilt_hint_ev_hdlr = mptcp_subflow_timeout_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_NOSRCADDR,
                .sofilt_hint_ev_hdlr = mptcp_subflow_nosrcaddr_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_IFDENIED,
                .sofilt_hint_ev_hdlr = mptcp_subflow_ifdenied_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_SUSPEND,
                .sofilt_hint_ev_hdlr = mptcp_subflow_suspend_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_RESUME,
                .sofilt_hint_ev_hdlr = mptcp_subflow_resume_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_CONNECTED,
                .sofilt_hint_ev_hdlr = mptcp_subflow_connected_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_MPSTATUS,
                .sofilt_hint_ev_hdlr = mptcp_subflow_mpstatus_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_DELETEOK,
                .sofilt_hint_ev_hdlr = mptcp_deleteok_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_DISCONNECTED,
                .sofilt_hint_ev_hdlr = mptcp_subflow_disconnected_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_MPFASTJ,
                .sofilt_hint_ev_hdlr = mptcp_fastjoin_ev,
        }
};

/*
 * Protocol pr_init callback.
 */
void
mptcp_init(struct protosw *pp, struct domain *dp)
{
#pragma unused(dp)
        static int mptcp_initialized = 0;
        struct protosw *prp;
#if INET6
        struct ip6protosw *prp6;
#endif /* INET6 */

        VERIFY((pp->pr_flags & (PR_INITIALIZED|PR_ATTACHED)) == PR_ATTACHED);

        /* do this only once */
        if (mptcp_initialized)
                return;
        mptcp_initialized = 1;

        /*
         * Since PF_MULTIPATH gets initialized after PF_INET/INET6,
         * we must be able to find IPPROTO_TCP entries for both.
         */
        prp = pffindproto_locked(PF_INET, IPPROTO_TCP, SOCK_STREAM);
        VERIFY(prp != NULL);
        bcopy(prp, &mptcp_subflow_protosw, sizeof (*prp));
        bcopy(prp->pr_usrreqs, &mptcp_subflow_usrreqs,
            sizeof (mptcp_subflow_usrreqs));
        mptcp_subflow_protosw.pr_entry.tqe_next = NULL;
        mptcp_subflow_protosw.pr_entry.tqe_prev = NULL;
        mptcp_subflow_protosw.pr_usrreqs = &mptcp_subflow_usrreqs;
        mptcp_subflow_usrreqs.pru_soreceive = mptcp_subflow_soreceive;
        mptcp_subflow_usrreqs.pru_rcvoob = pru_rcvoob_notsupp;
        /*
         * Socket filters shouldn't attach/detach to/from this protosw
         * since pr_protosw is to be used instead, which points to the
         * real protocol; if they do, it is a bug and we should panic.
         */
        mptcp_subflow_protosw.pr_filter_head.tqh_first =
            (struct socket_filter *)(uintptr_t)0xdeadbeefdeadbeef;
        mptcp_subflow_protosw.pr_filter_head.tqh_last =
            (struct socket_filter **)(uintptr_t)0xdeadbeefdeadbeef;

#if INET6
        prp6 = (struct ip6protosw *)pffindproto_locked(PF_INET6,
            IPPROTO_TCP, SOCK_STREAM);
        VERIFY(prp6 != NULL);
        bcopy(prp6, &mptcp_subflow_protosw6, sizeof (*prp6));
        bcopy(prp6->pr_usrreqs, &mptcp_subflow_usrreqs6,
            sizeof (mptcp_subflow_usrreqs6));
        mptcp_subflow_protosw6.pr_entry.tqe_next = NULL;
        mptcp_subflow_protosw6.pr_entry.tqe_prev = NULL;
        mptcp_subflow_protosw6.pr_usrreqs = &mptcp_subflow_usrreqs6;
        mptcp_subflow_usrreqs6.pru_soreceive = mptcp_subflow_soreceive;
        mptcp_subflow_usrreqs6.pru_rcvoob = pru_rcvoob_notsupp;
        /*
         * Socket filters shouldn't attach/detach to/from this protosw
         * since pr_protosw is to be used instead, which points to the
         * real protocol; if they do, it is a bug and we should panic.
         */
        mptcp_subflow_protosw6.pr_filter_head.tqh_first =
            (struct socket_filter *)(uintptr_t)0xdeadbeefdeadbeef;
        mptcp_subflow_protosw6.pr_filter_head.tqh_last =
            (struct socket_filter **)(uintptr_t)0xdeadbeefdeadbeef;
#endif /* INET6 */

        bzero(&mtcbinfo, sizeof (mtcbinfo));
        TAILQ_INIT(&mtcbinfo.mppi_pcbs);
        mtcbinfo.mppi_size = sizeof (struct mpp_mtp);
        if ((mtcbinfo.mppi_zone = zinit(mtcbinfo.mppi_size,
            1024 * mtcbinfo.mppi_size, 8192, "mptcb")) == NULL) {
                panic("%s: unable to allocate MPTCP PCB zone\n", __func__);
                /* NOTREACHED */
        }
        zone_change(mtcbinfo.mppi_zone, Z_CALLERACCT, FALSE);
        zone_change(mtcbinfo.mppi_zone, Z_EXPAND, TRUE);

        mtcbinfo.mppi_lock_grp_attr = lck_grp_attr_alloc_init();
        mtcbinfo.mppi_lock_grp = lck_grp_alloc_init("mppcb",
            mtcbinfo.mppi_lock_grp_attr);
        mtcbinfo.mppi_lock_attr = lck_attr_alloc_init();
        lck_mtx_init(&mtcbinfo.mppi_lock, mtcbinfo.mppi_lock_grp,
            mtcbinfo.mppi_lock_attr);

        mtcbinfo.mppi_gc = mptcp_gc;
        mtcbinfo.mppi_timer = mptcp_timer;
        mtcbinfo.mppi_pcbe_create = mptcp_sescreate;

        /* attach to MP domain for garbage collection to take place */
        mp_pcbinfo_attach(&mtcbinfo);

        mptsub_zone_size = sizeof (struct mptsub);
        if ((mptsub_zone = zinit(mptsub_zone_size, 1024 * mptsub_zone_size,
            8192, "mptsub")) == NULL) {
                panic("%s: unable to allocate MPTCP subflow zone\n", __func__);
                /* NOTREACHED */
        }
        zone_change(mptsub_zone, Z_CALLERACCT, FALSE);
        zone_change(mptsub_zone, Z_EXPAND, TRUE);

        mptopt_zone_size = sizeof (struct mptopt);
        if ((mptopt_zone = zinit(mptopt_zone_size, 128 * mptopt_zone_size,
            1024, "mptopt")) == NULL) {
                panic("%s: unable to allocate MPTCP option zone\n", __func__);
                /* NOTREACHED */
        }
        zone_change(mptopt_zone, Z_CALLERACCT, FALSE);
        zone_change(mptopt_zone, Z_EXPAND, TRUE);

        mpt_subauth_entry_size = sizeof (struct mptcp_subf_auth_entry);
        if ((mpt_subauth_zone = zinit(mpt_subauth_entry_size,
            1024 * mpt_subauth_entry_size, 8192, "mptauth")) == NULL) {
                panic("%s: unable to allocate MPTCP address auth zone \n",
                    __func__);
                /* NOTREACHED */
        }
        zone_change(mpt_subauth_zone, Z_CALLERACCT, FALSE);
        zone_change(mpt_subauth_zone, Z_EXPAND, TRUE);

        /* Set up a list of unique keys */
        mptcp_key_pool_init();
}

/*
 * Create an MPTCP session, called as a result of opening a MPTCP socket.
 */
void *
mptcp_sescreate(struct socket *mp_so, struct mppcb *mpp)
{
        struct mppcbinfo *mppi;
        struct mptses *mpte;
        struct mptcb *mp_tp;
        int error = 0;

        VERIFY(mpp != NULL);
        mppi = mpp->mpp_pcbinfo;
        VERIFY(mppi != NULL);

        __IGNORE_WCASTALIGN(mpte = &((struct mpp_mtp *)mpp)->mpp_ses);
        __IGNORE_WCASTALIGN(mp_tp = &((struct mpp_mtp *)mpp)->mtcb);

        /* MPTCP Multipath PCB Extension */
        bzero(mpte, sizeof (*mpte));
        VERIFY(mpp->mpp_pcbe == NULL);
        mpp->mpp_pcbe = mpte;
        mpte->mpte_mppcb = mpp;
        mpte->mpte_mptcb = mp_tp;

        TAILQ_INIT(&mpte->mpte_sopts);
        TAILQ_INIT(&mpte->mpte_subflows);
        mpte->mpte_associd = SAE_ASSOCID_ANY;
        mpte->mpte_connid_last = SAE_CONNID_ANY;

        lck_mtx_init(&mpte->mpte_thread_lock, mppi->mppi_lock_grp,
            mppi->mppi_lock_attr);

        /*
         * XXX: adi@apple.com
         *
         * This can be rather expensive if we have lots of MPTCP sockets,
         * but we need a kernel thread for this model to work.  Perhaps we
         * could amortize the costs by having one worker thread per a group
         * of MPTCP sockets.
         */
        if (kernel_thread_start(mptcp_thread_func, mpte,
            &mpte->mpte_thread) != KERN_SUCCESS) {
                error = ENOBUFS;
                goto out;
        }
        mp_so->so_usecount++;           /* for thread */

        /* MPTCP Protocol Control Block */
        bzero(mp_tp, sizeof (*mp_tp));
        lck_mtx_init(&mp_tp->mpt_lock, mppi->mppi_lock_grp,
            mppi->mppi_lock_attr);
        mp_tp->mpt_mpte = mpte;
        mp_tp->mpt_state = MPTCPS_CLOSED;
out:
        if (error != 0)
                lck_mtx_destroy(&mpte->mpte_thread_lock, mppi->mppi_lock_grp);
        DTRACE_MPTCP5(session__create, struct socket *, mp_so,
            struct sockbuf *, &mp_so->so_rcv,
            struct sockbuf *, &mp_so->so_snd,
            struct mppcb *, mpp, int, error);

        return ((error != 0) ? NULL : mpte);
}

/*
 * Destroy an MPTCP session.
 */
static void
mptcp_sesdestroy(struct mptses *mpte)
{
        struct mptcb *mp_tp;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */

        mp_tp = mpte->mpte_mptcb;
        VERIFY(mp_tp != NULL);

        /*
         * MPTCP Multipath PCB Extension section
         */
        mptcp_flush_sopts(mpte);
        VERIFY(TAILQ_EMPTY(&mpte->mpte_subflows) && mpte->mpte_numflows == 0);

        lck_mtx_destroy(&mpte->mpte_thread_lock,
            mpte->mpte_mppcb->mpp_pcbinfo->mppi_lock_grp);

        /*
         * MPTCP Protocol Control Block section
         */
        lck_mtx_destroy(&mp_tp->mpt_lock,
            mpte->mpte_mppcb->mpp_pcbinfo->mppi_lock_grp);

        DTRACE_MPTCP2(session__destroy, struct mptses *, mpte,
            struct mptcb *, mp_tp);
}

/*
 * Allocate an MPTCP socket option structure.
 */
struct mptopt *
mptcp_sopt_alloc(int how)
{
        struct mptopt *mpo;

        mpo = (how == M_WAITOK) ? zalloc(mptopt_zone) :
            zalloc_noblock(mptopt_zone);
        if (mpo != NULL) {
                bzero(mpo, mptopt_zone_size);
        }

        return (mpo);
}

/*
 * Free an MPTCP socket option structure.
 */
void
mptcp_sopt_free(struct mptopt *mpo)
{
        VERIFY(!(mpo->mpo_flags & MPOF_ATTACHED));

        zfree(mptopt_zone, mpo);
}

/*
 * Add a socket option to the MPTCP socket option list.
 */
void
mptcp_sopt_insert(struct mptses *mpte, struct mptopt *mpo)
{
        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        VERIFY(!(mpo->mpo_flags & MPOF_ATTACHED));
        mpo->mpo_flags |= MPOF_ATTACHED;
        TAILQ_INSERT_TAIL(&mpte->mpte_sopts, mpo, mpo_entry);
}

/*
 * Remove a socket option from the MPTCP socket option list.
 */
void
mptcp_sopt_remove(struct mptses *mpte, struct mptopt *mpo)
{
        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        VERIFY(mpo->mpo_flags & MPOF_ATTACHED);
        mpo->mpo_flags &= ~MPOF_ATTACHED;
        TAILQ_REMOVE(&mpte->mpte_sopts, mpo, mpo_entry);
}

/*
 * Search for an existing <sopt_level,sopt_name> socket option.
 */
struct mptopt *
mptcp_sopt_find(struct mptses *mpte, struct sockopt *sopt)
{
        struct mptopt *mpo;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */

        TAILQ_FOREACH(mpo, &mpte->mpte_sopts, mpo_entry) {
                if (mpo->mpo_level == sopt->sopt_level &&
                    mpo->mpo_name == sopt->sopt_name)
                        break;
        }
        VERIFY(mpo == NULL || sopt->sopt_valsize == sizeof (int));

        return (mpo);
}

/*
 * Flushes all recorded socket options from an MP socket.
 */
void
mptcp_flush_sopts(struct mptses *mpte)
{
        struct mptopt *mpo, *tmpo;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */

        TAILQ_FOREACH_SAFE(mpo, &mpte->mpte_sopts, mpo_entry, tmpo) {
                mptcp_sopt_remove(mpte, mpo);
                mptcp_sopt_free(mpo);
        }
        VERIFY(TAILQ_EMPTY(&mpte->mpte_sopts));
}

/*
 * Allocate a MPTCP subflow structure.
 */
struct mptsub *
mptcp_subflow_alloc(int how)
{
        struct mptsub *mpts;

        mpts = (how == M_WAITOK) ? zalloc(mptsub_zone) :
            zalloc_noblock(mptsub_zone);
        if (mpts != NULL) {
                bzero(mpts, mptsub_zone_size);
                lck_mtx_init(&mpts->mpts_lock, mtcbinfo.mppi_lock_grp,
                    mtcbinfo.mppi_lock_attr);
        }

        return (mpts);
}

/*
 * Deallocate a subflow structure, called when all of the references held
 * on it have been released.  This implies that the subflow has been deleted.
 */
void
mptcp_subflow_free(struct mptsub *mpts)
{
        MPTS_LOCK_ASSERT_HELD(mpts);

        VERIFY(mpts->mpts_refcnt == 0);
        VERIFY(!(mpts->mpts_flags & MPTSF_ATTACHED));
        VERIFY(mpts->mpts_mpte == NULL);
        VERIFY(mpts->mpts_socket == NULL);

        if (mpts->mpts_src_sl != NULL) {
                sockaddrlist_free(mpts->mpts_src_sl);
                mpts->mpts_src_sl = NULL;
        }
        if (mpts->mpts_dst_sl != NULL) {
                sockaddrlist_free(mpts->mpts_dst_sl);
                mpts->mpts_dst_sl = NULL;
        }
        MPTS_UNLOCK(mpts);
        lck_mtx_destroy(&mpts->mpts_lock, mtcbinfo.mppi_lock_grp);

        zfree(mptsub_zone, mpts);
}

/*
 * Create an MPTCP subflow socket.
 */
static int
mptcp_subflow_socreate(struct mptses *mpte, struct mptsub *mpts, int dom,
    struct proc *p, struct socket **so)
{
        struct mptopt smpo, *mpo, *tmpo;
        struct socket *mp_so;
        int error;

        *so = NULL;
        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        mp_so = mpte->mpte_mppcb->mpp_socket;

        /*
         * Create the subflow socket (multipath subflow, non-blocking.)
         *
         * This will cause SOF_MP_SUBFLOW socket flag to be set on the subflow
         * socket; it will be cleared when the socket is peeled off or closed.
         * It also indicates to the underlying TCP to handle MPTCP options.
         * A multipath subflow socket implies SS_NOFDREF state.
         */
        if ((error = socreate_internal(dom, so, SOCK_STREAM,
            IPPROTO_TCP, p, SOCF_ASYNC | SOCF_MP_SUBFLOW, PROC_NULL)) != 0) {
                mptcplog((LOG_ERR, "MPTCP Socket: subflow socreate mp_so 0x%llx"
                    " unable to create subflow socket error %d\n",
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so), error),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_ERR);
                return (error);
        }

        socket_lock(*so, 0);
        VERIFY((*so)->so_flags & SOF_MP_SUBFLOW);
        VERIFY(((*so)->so_state & (SS_NBIO|SS_NOFDREF)) ==
            (SS_NBIO|SS_NOFDREF));

        /* prevent the socket buffers from being compressed */
        (*so)->so_rcv.sb_flags |= SB_NOCOMPRESS;
        (*so)->so_snd.sb_flags |= SB_NOCOMPRESS;

        bzero(&smpo, sizeof (smpo));
        smpo.mpo_flags |= MPOF_SUBFLOW_OK;
        smpo.mpo_level = SOL_SOCKET;
        smpo.mpo_intval = 1;

        /* disable SIGPIPE */
        smpo.mpo_name = SO_NOSIGPIPE;
        if ((error = mptcp_subflow_sosetopt(mpte, *so, &smpo)) != 0)
                goto out;

        /* find out if the subflow's source address goes away */
        smpo.mpo_name = SO_NOADDRERR;
        if ((error = mptcp_subflow_sosetopt(mpte, *so, &smpo)) != 0)
                goto out;

        /* enable keepalive */
        smpo.mpo_name = SO_KEEPALIVE;
        if ((error = mptcp_subflow_sosetopt(mpte, *so, &smpo)) != 0)
                goto out;

        /*
         * Limit the receive socket buffer size to 64k.
         *
         * We need to take into consideration the window scale option
         * which could be negotiated in one subflow but disabled in
         * another subflow.
         * XXX This can be improved in the future.
         */
        smpo.mpo_name = SO_RCVBUF;
        smpo.mpo_intval = MPTCP_RWIN_MAX;
        if ((error = mptcp_subflow_sosetopt(mpte, *so, &smpo)) != 0)
                goto out;

        /* N.B.: set by sosetopt */
        VERIFY(!((*so)->so_rcv.sb_flags & SB_AUTOSIZE));
        /* Prevent automatic socket buffer sizing. */
        (*so)->so_snd.sb_flags &= ~SB_AUTOSIZE;

        smpo.mpo_level = IPPROTO_TCP;
        smpo.mpo_intval = mptcp_subflow_keeptime;
        smpo.mpo_name = TCP_KEEPALIVE;
        if ((error = mptcp_subflow_sosetopt(mpte, *so, &smpo)) != 0)
                goto out;

        /* replay setsockopt(2) on the subflow sockets for eligible options */
        TAILQ_FOREACH_SAFE(mpo, &mpte->mpte_sopts, mpo_entry, tmpo) {
                int interim;

                if (!(mpo->mpo_flags & MPOF_SUBFLOW_OK))
                        continue;

                /*
                 * Skip those that are handled internally; these options
                 * should not have been recorded and marked with the
                 * MPOF_SUBFLOW_OK by mptcp_setopt(), but just in case.
                 */
                if (mpo->mpo_level == SOL_SOCKET &&
                    (mpo->mpo_name == SO_NOSIGPIPE ||
                    mpo->mpo_name == SO_NOADDRERR ||
                    mpo->mpo_name == SO_KEEPALIVE))
                        continue;

                interim = (mpo->mpo_flags & MPOF_INTERIM);
                if (mptcp_subflow_sosetopt(mpte, *so, mpo) != 0 && interim) {
                        char buf[32];
                        mptcplog((LOG_ERR, "MPTCP Socket: subflow socreate"
                            " mp_so 0x%llx"
                            " sopt %s val %d interim record removed\n",
                            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                            mptcp_sopt2str(mpo->mpo_level, mpo->mpo_name,
                            buf, sizeof (buf)), mpo->mpo_intval),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_ERR);
                        mptcp_sopt_remove(mpte, mpo);
                        mptcp_sopt_free(mpo);
                        continue;
                }
        }

        /*
         * We need to receive everything that the subflow socket has,
         * so use a customized socket receive function.  We will undo
         * this when the socket is peeled off or closed.
         */
        mpts->mpts_oprotosw = (*so)->so_proto;
        switch (dom) {
        case PF_INET:
                (*so)->so_proto = &mptcp_subflow_protosw;
                break;
#if INET6
        case PF_INET6:
                (*so)->so_proto = (struct protosw *)&mptcp_subflow_protosw6;
                break;
#endif /* INET6 */
        default:
                VERIFY(0);
                /* NOTREACHED */
        }

out:
        socket_unlock(*so, 0);

        DTRACE_MPTCP4(subflow__create, struct mptses *, mpte,
            struct mptsub *, mpts, int, dom, int, error);

        return (error);
}

/*
 * Close an MPTCP subflow socket.
 *
 * Note that this may be called on an embryonic subflow, and the only
 * thing that is guaranteed valid is the protocol-user request.
 */
static int
mptcp_subflow_soclose(struct mptsub *mpts, struct socket *so)
{
        MPTS_LOCK_ASSERT_HELD(mpts);

        socket_lock(so, 0);
        VERIFY(so->so_flags & SOF_MP_SUBFLOW);
        VERIFY((so->so_state & (SS_NBIO|SS_NOFDREF)) == (SS_NBIO|SS_NOFDREF));

        /* restore protocol-user requests */
        VERIFY(mpts->mpts_oprotosw != NULL);
        so->so_proto = mpts->mpts_oprotosw;
        socket_unlock(so, 0);

        mpts->mpts_socket = NULL;       /* may already be NULL */

        DTRACE_MPTCP5(subflow__close, struct mptsub *, mpts,
            struct socket *, so,
            struct sockbuf *, &so->so_rcv,
            struct sockbuf *, &so->so_snd,
            struct mptses *, mpts->mpts_mpte);

        return (soclose(so));
}

/*
 * Connect an MPTCP subflow socket.
 *
 * This may be called inline as part of adding a subflow, or asynchronously
 * by the thread (upon progressing to MPTCPF_JOIN_READY).  Note that in the
 * pending connect case, the subflow socket may have been bound to an interface
 * and/or a source IP address which may no longer be around by the time this
 * routine is called; in that case the connect attempt will most likely fail.
 */
static int
mptcp_subflow_soconnectx(struct mptses *mpte, struct mptsub *mpts)
{
        struct socket *so;
        int af, error;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        VERIFY((mpts->mpts_flags & (MPTSF_CONNECTING|MPTSF_CONNECTED)) ==
            MPTSF_CONNECTING);
        VERIFY(mpts->mpts_socket != NULL);
        so = mpts->mpts_socket;
        af = mpts->mpts_family;

        if (af == AF_INET || af == AF_INET6) {
                struct sockaddr_entry *dst_se;
                char dbuf[MAX_IPv6_STR_LEN];

                dst_se = TAILQ_FIRST(&mpts->mpts_dst_sl->sl_head);
                VERIFY(dst_se != NULL);

                mptcplog((LOG_DEBUG, "MPTCP Socket: connectx mp_so 0x%llx "
                    "dst %s[%d] cid %d [pended %s]\n",
                    (u_int64_t)VM_KERNEL_ADDRPERM(mpte->mpte_mppcb->mpp_socket),
                    inet_ntop(af, ((af == AF_INET) ?
                    (void *)&SIN(dst_se->se_addr)->sin_addr.s_addr :
                    (void *)&SIN6(dst_se->se_addr)->sin6_addr),
                    dbuf, sizeof (dbuf)), ((af == AF_INET) ?
                    ntohs(SIN(dst_se->se_addr)->sin_port) :
                    ntohs(SIN6(dst_se->se_addr)->sin6_port)),
                    mpts->mpts_connid,
                    ((mpts->mpts_flags & MPTSF_CONNECT_PENDING) ?
                    "YES" : "NO")),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);
        }

        mpts->mpts_flags &= ~MPTSF_CONNECT_PENDING;

        socket_lock(so, 0);
        mptcp_attach_to_subf(so, mpte->mpte_mptcb, mpte->mpte_addrid_last);
        
        /* connect the subflow socket */
        error = soconnectxlocked(so, &mpts->mpts_src_sl, &mpts->mpts_dst_sl,
            mpts->mpts_mpcr.mpcr_proc, mpts->mpts_mpcr.mpcr_ifscope,
            mpte->mpte_associd, NULL, CONNREQF_MPTCP,
            &mpts->mpts_mpcr, sizeof (mpts->mpts_mpcr), NULL, NULL);
        socket_unlock(so, 0);

        /* Allocate a unique address id per subflow */
        mpte->mpte_addrid_last++;
        if (mpte->mpte_addrid_last == 0)
                mpte->mpte_addrid_last++;

        DTRACE_MPTCP3(subflow__connect, struct mptses *, mpte,
            struct mptsub *, mpts, int, error);

        return (error);
}

/*
 * MPTCP subflow socket receive routine, derived from soreceive().
 */
static int
mptcp_subflow_soreceive(struct socket *so, struct sockaddr **psa,
    struct uio *uio, struct mbuf **mp0, struct mbuf **controlp, int *flagsp)
{
#pragma unused(uio)
        int flags, error = 0;
        struct proc *p = current_proc();
        struct mbuf *m, **mp = mp0;
        struct mbuf *nextrecord;

        socket_lock(so, 1);
        VERIFY(so->so_proto->pr_flags & PR_CONNREQUIRED);

#ifdef MORE_LOCKING_DEBUG
        if (so->so_usecount == 1) {
                panic("%s: so=%x no other reference on socket\n", __func__, so);
                /* NOTREACHED */
        }
#endif
        /*
         * We return all that is there in the subflow's socket receive buffer
         * to the MPTCP layer, so we require that the caller passes in the
         * expected parameters.
         */
        if (mp == NULL || controlp != NULL) {
                socket_unlock(so, 1);
                return (EINVAL);
        }
        *mp = NULL;
        if (psa != NULL)
                *psa = NULL;
        if (flagsp != NULL)
                flags = *flagsp &~ MSG_EOR;
        else
                flags = 0;

        if (flags & (MSG_PEEK|MSG_OOB|MSG_NEEDSA|MSG_WAITALL|MSG_WAITSTREAM)) {
                socket_unlock(so, 1);
                return (EOPNOTSUPP);
        }
        flags |= (MSG_DONTWAIT|MSG_NBIO);

        /*
         * If a recv attempt is made on a previously-accepted socket
         * that has been marked as inactive (disconnected), reject
         * the request.
         */
        if (so->so_flags & SOF_DEFUNCT) {
                struct sockbuf *sb = &so->so_rcv;

                error = ENOTCONN;
                SODEFUNCTLOG(("%s[%d]: defunct so 0x%llx [%d,%d] (%d)\n",
                    __func__, proc_pid(p), (uint64_t)VM_KERNEL_ADDRPERM(so),
                    SOCK_DOM(so), SOCK_TYPE(so), error));
                /*
                 * This socket should have been disconnected and flushed
                 * prior to being returned from sodefunct(); there should
                 * be no data on its receive list, so panic otherwise.
                 */
                if (so->so_state & SS_DEFUNCT)
                        sb_empty_assert(sb, __func__);
                socket_unlock(so, 1);
                return (error);
        }

        /*
         * See if the socket has been closed (SS_NOFDREF|SS_CANTRCVMORE)
         * and if so just return to the caller.  This could happen when
         * soreceive() is called by a socket upcall function during the
         * time the socket is freed.  The socket buffer would have been
         * locked across the upcall, therefore we cannot put this thread
         * to sleep (else we will deadlock) or return EWOULDBLOCK (else
         * we may livelock), because the lock on the socket buffer will
         * only be released when the upcall routine returns to its caller.
         * Because the socket has been officially closed, there can be
         * no further read on it.
         *
         * A multipath subflow socket would have its SS_NOFDREF set by
         * default, so check for SOF_MP_SUBFLOW socket flag; when the
         * socket is closed for real, SOF_MP_SUBFLOW would be cleared.
         */
        if ((so->so_state & (SS_NOFDREF | SS_CANTRCVMORE)) ==
            (SS_NOFDREF | SS_CANTRCVMORE) && !(so->so_flags & SOF_MP_SUBFLOW)) {
                socket_unlock(so, 1);
                return (0);
        }

        /*
         * For consistency with soreceive() semantics, we need to obey
         * SB_LOCK in case some other code path has locked the buffer.
         */
        error = sblock(&so->so_rcv, 0);
        if (error != 0) {
                socket_unlock(so, 1);
                return (error);
        }

        m = so->so_rcv.sb_mb;
        if (m == NULL) {
                /*
                 * Panic if we notice inconsistencies in the socket's
                 * receive list; both sb_mb and sb_cc should correctly
                 * reflect the contents of the list, otherwise we may
                 * end up with false positives during select() or poll()
                 * which could put the application in a bad state.
                 */
                SB_MB_CHECK(&so->so_rcv);

                if (so->so_error != 0) {
                        error = so->so_error;
                        so->so_error = 0;
                        goto release;
                }

                if (so->so_state & SS_CANTRCVMORE) {
                        goto release;
                }

                if (!(so->so_state & (SS_ISCONNECTED|SS_ISCONNECTING))) {
                        error = ENOTCONN;
                        goto release;
                }

                /*
                 * MSG_DONTWAIT is implicitly defined and this routine will
                 * never block, so return EWOULDBLOCK when there is nothing.
                 */
                error = EWOULDBLOCK;
                goto release;
        }

        OSIncrementAtomicLong(&p->p_stats->p_ru.ru_msgrcv);
        SBLASTRECORDCHK(&so->so_rcv, "mptcp_subflow_soreceive 1");
        SBLASTMBUFCHK(&so->so_rcv, "mptcp_subflow_soreceive 1");

        while (m != NULL) {
                nextrecord = m->m_nextpkt;
                sbfree(&so->so_rcv, m);

                if (mp != NULL) {
                        *mp = m;
                        mp = &m->m_next;
                        so->so_rcv.sb_mb = m = m->m_next;
                        *mp = NULL;
                }

                if (m != NULL) {
                        m->m_nextpkt = nextrecord;
                        if (nextrecord == NULL)
                                so->so_rcv.sb_lastrecord = m;
                } else {
                        m = so->so_rcv.sb_mb = nextrecord;
                        SB_EMPTY_FIXUP(&so->so_rcv);
                }
                SBLASTRECORDCHK(&so->so_rcv, "mptcp_subflow_soreceive 2");
                SBLASTMBUFCHK(&so->so_rcv, "mptcp_subflow_soreceive 2");
        }

        DTRACE_MPTCP3(subflow__receive, struct socket *, so,
            struct sockbuf *, &so->so_rcv, struct sockbuf *, &so->so_snd);
        /* notify protocol that we drained all the data */
        if ((so->so_proto->pr_flags & PR_WANTRCVD) && so->so_pcb != NULL)
                (*so->so_proto->pr_usrreqs->pru_rcvd)(so, flags);

        if (flagsp != NULL)
                *flagsp |= flags;

release:
        sbunlock(&so->so_rcv, FALSE);   /* will unlock socket */
        return (error);

}


/*
 * Prepare an MPTCP subflow socket for peeloff(2); basically undo
 * the work done earlier when the subflow socket was created.
 */
void
mptcp_subflow_sopeeloff(struct mptses *mpte, struct mptsub *mpts,
    struct socket *so)
{
        struct mptopt smpo;
        struct socket *mp_so;
        int p, c;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        mp_so = mpte->mpte_mppcb->mpp_socket;
        MPTS_LOCK_ASSERT_HELD(mpts);

        socket_lock(so, 0);
        VERIFY(so->so_flags & SOF_MP_SUBFLOW);
        VERIFY((so->so_state & (SS_NBIO|SS_NOFDREF)) == (SS_NBIO|SS_NOFDREF));

        /* inherit MPTCP socket states */
        if (!(mp_so->so_state & SS_NBIO))
                so->so_state &= ~SS_NBIO;

        /*
         * At this point, the socket is not yet closed, as there is at least
         * one outstanding usecount previously held by mpts_socket from
         * socreate().  Atomically clear SOF_MP_SUBFLOW and SS_NOFDREF here.
         */
        so->so_flags &= ~SOF_MP_SUBFLOW;
        so->so_state &= ~SS_NOFDREF;
        so->so_flags &= ~SOF_MPTCP_TRUE;

        /* allow socket buffers to be compressed */
        so->so_rcv.sb_flags &= ~SB_NOCOMPRESS;
        so->so_snd.sb_flags &= ~SB_NOCOMPRESS;

        /*
         * Allow socket buffer auto sizing.
         *
         * This will increase the current 64k buffer size to whatever is best.
         */
        if (!(so->so_rcv.sb_flags & SB_USRSIZE))         
                so->so_rcv.sb_flags |= SB_AUTOSIZE;
        if (!(so->so_snd.sb_flags & SB_USRSIZE))
                so->so_snd.sb_flags |= SB_AUTOSIZE;

        /* restore protocol-user requests */
        VERIFY(mpts->mpts_oprotosw != NULL);
        so->so_proto = mpts->mpts_oprotosw;

        bzero(&smpo, sizeof (smpo));
        smpo.mpo_flags |= MPOF_SUBFLOW_OK;
        smpo.mpo_level = SOL_SOCKET;

        /* inherit SOF_NOSIGPIPE from parent MP socket */
        p = (mp_so->so_flags & SOF_NOSIGPIPE);
        c = (so->so_flags & SOF_NOSIGPIPE);
        smpo.mpo_intval = ((p - c) > 0) ? 1 : 0;
        smpo.mpo_name = SO_NOSIGPIPE;
        if ((p - c) != 0)
                (void) mptcp_subflow_sosetopt(mpte, so, &smpo);

        /* inherit SOF_NOADDRAVAIL from parent MP socket */
        p = (mp_so->so_flags & SOF_NOADDRAVAIL);
        c = (so->so_flags & SOF_NOADDRAVAIL);
        smpo.mpo_intval = ((p - c) > 0) ? 1 : 0;
        smpo.mpo_name = SO_NOADDRERR;
        if ((p - c) != 0)
                (void) mptcp_subflow_sosetopt(mpte, so, &smpo);

        /* inherit SO_KEEPALIVE from parent MP socket */
        p = (mp_so->so_options & SO_KEEPALIVE);
        c = (so->so_options & SO_KEEPALIVE);
        smpo.mpo_intval = ((p - c) > 0) ? 1 : 0;
        smpo.mpo_name = SO_KEEPALIVE;
        if ((p - c) != 0)
                (void) mptcp_subflow_sosetopt(mpte, so, &smpo);

        /* unset TCP level default keepalive option */
        p = (intotcpcb(sotoinpcb(mp_so)))->t_keepidle;
        c = (intotcpcb(sotoinpcb(so)))->t_keepidle;
        smpo.mpo_level = IPPROTO_TCP;
        smpo.mpo_intval = 0;
        smpo.mpo_name = TCP_KEEPALIVE;
        if ((p - c) != 0)
                (void) mptcp_subflow_sosetopt(mpte, so, &smpo);
        socket_unlock(so, 0);

        DTRACE_MPTCP5(subflow__peeloff, struct mptses *, mpte,
            struct mptsub *, mpts, struct socket *, so,
            struct sockbuf *, &so->so_rcv, struct sockbuf *, &so->so_snd);
}

/*
 * Establish an initial MPTCP connection (if first subflow and not yet
 * connected), or add a subflow to an existing MPTCP connection.
 */
int
mptcp_subflow_add(struct mptses *mpte, struct mptsub *mpts,
    struct proc *p, uint32_t ifscope)
{
        struct sockaddr_entry *se, *src_se = NULL, *dst_se = NULL;
        struct socket *mp_so, *so = NULL;
        struct mptsub_connreq mpcr;
        struct mptcb *mp_tp;
        int af, error = 0;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;

        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state >= MPTCPS_CLOSE_WAIT) {
                /* If the remote end sends Data FIN, refuse subflow adds */
                error = ENOTCONN;
                MPT_UNLOCK(mp_tp);
                return (error);
        }
        MPT_UNLOCK(mp_tp);

        MPTS_LOCK(mpts);
        VERIFY(!(mpts->mpts_flags & (MPTSF_CONNECTING|MPTSF_CONNECTED)));
        VERIFY(mpts->mpts_mpte == NULL);
        VERIFY(mpts->mpts_socket == NULL);
        VERIFY(mpts->mpts_dst_sl != NULL);
        VERIFY(mpts->mpts_connid == SAE_CONNID_ANY);

        /* select source (if specified) and destination addresses */
        if ((error = in_selectaddrs(AF_UNSPEC, &mpts->mpts_src_sl, &src_se,
            &mpts->mpts_dst_sl, &dst_se)) != 0)
                goto out;

        VERIFY(mpts->mpts_dst_sl != NULL && dst_se != NULL);
        VERIFY(src_se == NULL || mpts->mpts_src_sl != NULL);
        af = mpts->mpts_family = dst_se->se_addr->sa_family;
        VERIFY(src_se == NULL || src_se->se_addr->sa_family == af);
        VERIFY(af == AF_INET || af == AF_INET6);

        /*
         * If the source address is not specified, allocate a storage for
         * it, so that later on we can fill it in with the actual source
         * IP address chosen by the underlying layer for the subflow after
         * it is connected.
         */
        if (mpts->mpts_src_sl == NULL) {
                mpts->mpts_src_sl =
                    sockaddrlist_dup(mpts->mpts_dst_sl, M_WAITOK);
                if (mpts->mpts_src_sl == NULL) {
                        error = ENOBUFS;
                        goto out;
                }
                se = TAILQ_FIRST(&mpts->mpts_src_sl->sl_head);
                VERIFY(se != NULL && se->se_addr != NULL &&
                    se->se_addr->sa_len == dst_se->se_addr->sa_len);
                bzero(se->se_addr, se->se_addr->sa_len);
                se->se_addr->sa_len = dst_se->se_addr->sa_len;
                se->se_addr->sa_family = dst_se->se_addr->sa_family;
        }

        /* create the subflow socket */
        if ((error = mptcp_subflow_socreate(mpte, mpts, af, p, &so)) != 0)
                goto out;

        /* If fastjoin is requested, set state in mpts */
        if ((so->so_flags & SOF_MPTCP_FASTJOIN) &&
            (mp_tp->mpt_state == MPTCPS_ESTABLISHED) &&
            (mpte->mpte_nummpcapflows == 0)) {
                mpts->mpts_flags |= MPTSF_FASTJ_REQD;
                mpts->mpts_rel_seq = 1;
                MPT_LOCK(mp_tp);
                mpts->mpts_sndnxt = mp_tp->mpt_snduna;
                MPT_UNLOCK(mp_tp);
        }

        /*
         * Increment the counter, while avoiding 0 (SAE_CONNID_ANY) and
         * -1 (SAE_CONNID_ALL).
         */
        mpte->mpte_connid_last++;
        if (mpte->mpte_connid_last == SAE_CONNID_ALL ||
            mpte->mpte_connid_last == SAE_CONNID_ANY)
                mpte->mpte_connid_last++;

        mpts->mpts_connid = mpte->mpte_connid_last;
        VERIFY(mpts->mpts_connid != SAE_CONNID_ANY &&
            mpts->mpts_connid != SAE_CONNID_ALL);
        
        /* Allocate a unique address id per subflow */
        mpte->mpte_addrid_last++;
        if (mpte->mpte_addrid_last == 0)
                mpte->mpte_addrid_last++;

        /* bind subflow socket to the specified interface */
        if (ifscope != IFSCOPE_NONE) {
                socket_lock(so, 0);
                error = inp_bindif(sotoinpcb(so), ifscope, &mpts->mpts_outif);
                if (error != 0) {
                        socket_unlock(so, 0);
                        (void) mptcp_subflow_soclose(mpts, so);
                        goto out;
                }
                VERIFY(mpts->mpts_outif != NULL);
                mpts->mpts_flags |= MPTSF_BOUND_IF;

                mptcplog((LOG_DEBUG, "MPTCP Socket: subflow_add mp_so 0x%llx "
                    "bindif %s[%d] cid d\n",
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    mpts->mpts_outif->if_xname,
                    ifscope, mpts->mpts_connid),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
                socket_unlock(so, 0);
        }

        /* if source address and/or port is specified, bind to it */
        if (src_se != NULL) {
                struct sockaddr *sa = src_se->se_addr;
                uint32_t mpts_flags = 0;
                in_port_t lport;

                switch (af) {
                case AF_INET:
                        if (SIN(sa)->sin_addr.s_addr != INADDR_ANY)
                                mpts_flags |= MPTSF_BOUND_IP;
                        if ((lport = SIN(sa)->sin_port) != 0)
                                mpts_flags |= MPTSF_BOUND_PORT;
                        break;
#if INET6
                case AF_INET6:
                        VERIFY(af == AF_INET6);
                        if (!IN6_IS_ADDR_UNSPECIFIED(&SIN6(sa)->sin6_addr))
                                mpts_flags |= MPTSF_BOUND_IP;
                        if ((lport = SIN6(sa)->sin6_port) != 0)
                                mpts_flags |= MPTSF_BOUND_PORT;
                        break;
#endif /* INET6 */
                }

                error = sobindlock(so, sa, 1);  /* will lock/unlock socket */
                if (error != 0) {
                        (void) mptcp_subflow_soclose(mpts, so);
                        goto out;
                }
                mpts->mpts_flags |= mpts_flags;

                if (af == AF_INET || af == AF_INET6) {
                        char sbuf[MAX_IPv6_STR_LEN];

                        mptcplog((LOG_DEBUG, "MPTCP Socket: subflow_add "
                            "mp_so 0x%llx bindip %s[%d] cid %d\n",
                            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                            inet_ntop(af, ((af == AF_INET) ?
                            (void *)&SIN(sa)->sin_addr.s_addr :
                            (void *)&SIN6(sa)->sin6_addr), sbuf, sizeof (sbuf)),
                            ntohs(lport), mpts->mpts_connid),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);
                }
        }

        /*
         * Insert the subflow into the list, and associate the MPTCP PCB
         * as well as the the subflow socket.  From this point on, removing
         * the subflow needs to be done via mptcp_subflow_del().
         */
        TAILQ_INSERT_TAIL(&mpte->mpte_subflows, mpts, mpts_entry);
        mpte->mpte_numflows++;

        atomic_bitset_32(&mpts->mpts_flags, MPTSF_ATTACHED);
        mpts->mpts_mpte = mpte;
        mpts->mpts_socket = so;
        MPTS_ADDREF_LOCKED(mpts);       /* for being in MPTCP subflow list */
        MPTS_ADDREF_LOCKED(mpts);       /* for subflow socket */
        mp_so->so_usecount++;           /* for subflow socket */

        /* register for subflow socket read/write events */
        (void) sock_setupcalls(so, mptcp_subflow_rupcall, mpts,
            mptcp_subflow_wupcall, mpts);

        /*
         * Register for subflow socket control events; ignore
         * SO_FILT_HINT_CONNINFO_UPDATED from below since we
         * will generate it here.
         */
        (void) sock_catchevents(so, mptcp_subflow_eupcall, mpts,
            SO_FILT_HINT_CONNRESET | SO_FILT_HINT_CANTRCVMORE |
            SO_FILT_HINT_CANTSENDMORE | SO_FILT_HINT_TIMEOUT |
            SO_FILT_HINT_NOSRCADDR | SO_FILT_HINT_IFDENIED |
            SO_FILT_HINT_SUSPEND | SO_FILT_HINT_RESUME |
            SO_FILT_HINT_CONNECTED | SO_FILT_HINT_DISCONNECTED |
            SO_FILT_HINT_MPFAILOVER | SO_FILT_HINT_MPSTATUS |
            SO_FILT_HINT_MUSTRST | SO_FILT_HINT_MPFASTJ |
            SO_FILT_HINT_DELETEOK | SO_FILT_HINT_MPCANTRCVMORE);

        /* sanity check */
        VERIFY(!(mpts->mpts_flags &
            (MPTSF_CONNECTING|MPTSF_CONNECTED|MPTSF_CONNECT_PENDING)));

        bzero(&mpcr, sizeof (mpcr));
        mpcr.mpcr_proc = p;
        mpcr.mpcr_ifscope = ifscope;
        /*
         * Indicate to the TCP subflow whether or not it should establish
         * the initial MPTCP connection, or join an existing one.  Fill
         * in the connection request structure with additional info needed
         * by the underlying TCP (to be used in the TCP options, etc.)
         */
        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED && mpte->mpte_numflows == 1) {
                if (mp_tp->mpt_state == MPTCPS_CLOSED) {
                        mp_tp->mpt_localkey = mptcp_reserve_key();
                        mptcp_conn_properties(mp_tp);
                }
                MPT_UNLOCK(mp_tp);
                soisconnecting(mp_so);
                mpcr.mpcr_type = MPTSUB_CONNREQ_MP_ENABLE;
        } else {
                if (!(mp_tp->mpt_flags & MPTCPF_JOIN_READY))
                        mpts->mpts_flags |= MPTSF_CONNECT_PENDING;

                /* avoid starting up cellular subflow unless required */
                if ((mptcp_delayed_subf_start) &&
                    (IFNET_IS_CELLULAR(mpts->mpts_outif))) {
                        mpts->mpts_flags |= MPTSF_CONNECT_PENDING;
                }
                MPT_UNLOCK(mp_tp);
                mpcr.mpcr_type = MPTSUB_CONNREQ_MP_ADD;
        }

        mpts->mpts_mpcr = mpcr;
        mpts->mpts_flags |= MPTSF_CONNECTING;

        if (af == AF_INET || af == AF_INET6) {
                char dbuf[MAX_IPv6_STR_LEN];

                mptcplog((LOG_DEBUG, "MPTCP Socket: %s "
                    "mp_so 0x%llx dst %s[%d] cid %d "
                    "[pending %s]\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    inet_ntop(af, ((af == AF_INET) ?
                    (void *)&SIN(dst_se->se_addr)->sin_addr.s_addr :
                    (void *)&SIN6(dst_se->se_addr)->sin6_addr),
                    dbuf, sizeof (dbuf)), ((af == AF_INET) ?
                    ntohs(SIN(dst_se->se_addr)->sin_port) :
                    ntohs(SIN6(dst_se->se_addr)->sin6_port)),
                    mpts->mpts_connid,
                    ((mpts->mpts_flags & MPTSF_CONNECT_PENDING) ?
                    "YES" : "NO")),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);
        }

        /* connect right away if first attempt, or if join can be done now */
        if (!(mpts->mpts_flags & MPTSF_CONNECT_PENDING))
                error = mptcp_subflow_soconnectx(mpte, mpts);

out:
        MPTS_UNLOCK(mpts);
        if (error == 0) {
                soevent(mp_so, SO_FILT_HINT_LOCKED |
                    SO_FILT_HINT_CONNINFO_UPDATED);
        }
        return (error);
}

/*
 * Delete/remove a subflow from an MPTCP.  The underlying subflow socket
 * will no longer be accessible after a subflow is deleted, thus this
 * should occur only after the subflow socket has been disconnected.
 * If peeloff(2) is called, leave the socket open.
 */
void
mptcp_subflow_del(struct mptses *mpte, struct mptsub *mpts, boolean_t close)
{
        struct socket *mp_so, *so;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        mp_so = mpte->mpte_mppcb->mpp_socket;

        MPTS_LOCK(mpts);
        so = mpts->mpts_socket;
        VERIFY(so != NULL);
        
        if (close && !((mpts->mpts_flags & MPTSF_DELETEOK) &&
            (mpts->mpts_flags & MPTSF_USER_DISCONNECT))) {
                MPTS_UNLOCK(mpts);
                mptcplog((LOG_DEBUG, "MPTCP Socket: subflow_del returning"
                    " mp_so 0x%llx flags %x\n",
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so), mpts->mpts_flags),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);
                return;
        }

        mptcplog((LOG_DEBUG, "MPTCP Socket: subflow_del mp_so 0x%llx "
            "[u=%d,r=%d] cid %d [close %s] %d %x error %d\n",
            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
            mp_so->so_usecount,
            mp_so->so_retaincnt, mpts->mpts_connid,
            (close ? "YES" : "NO"), mpts->mpts_soerror,
            mpts->mpts_flags,
            mp_so->so_error),
            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);

        VERIFY(mpts->mpts_mpte == mpte);
        VERIFY(mpts->mpts_connid != SAE_CONNID_ANY &&
            mpts->mpts_connid != SAE_CONNID_ALL);

        VERIFY(mpts->mpts_flags & MPTSF_ATTACHED);
        atomic_bitclear_32(&mpts->mpts_flags, MPTSF_ATTACHED);
        TAILQ_REMOVE(&mpte->mpte_subflows, mpts, mpts_entry);
        VERIFY(mpte->mpte_numflows != 0);
        mpte->mpte_numflows--;
        if (mpte->mpte_active_sub == mpts)
                mpte->mpte_active_sub = NULL;

        /*
         * Drop references held by this subflow socket; there
         * will be no further upcalls made from this point.
         */
        (void) sock_setupcalls(so, NULL, NULL, NULL, NULL);
        (void) sock_catchevents(so, NULL, NULL, 0);

        mptcp_detach_mptcb_from_subf(mpte->mpte_mptcb, so);
        
        if (close)
                (void) mptcp_subflow_soclose(mpts, so);

        VERIFY(mp_so->so_usecount != 0);
        mp_so->so_usecount--;           /* for subflow socket */
        mpts->mpts_mpte = NULL;
        mpts->mpts_socket = NULL;
        MPTS_UNLOCK(mpts);

        MPTS_REMREF(mpts);              /* for MPTCP subflow list */
        MPTS_REMREF(mpts);              /* for subflow socket */

        soevent(mp_so, SO_FILT_HINT_LOCKED | SO_FILT_HINT_CONNINFO_UPDATED);
}

/*
 * Disconnect a subflow socket.
 */
void
mptcp_subflow_disconnect(struct mptses *mpte, struct mptsub *mpts,
    boolean_t deleteok)
{
        struct socket *so;
        struct mptcb *mp_tp;
        int send_dfin = 0;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        VERIFY(mpts->mpts_mpte == mpte);
        VERIFY(mpts->mpts_socket != NULL);
        VERIFY(mpts->mpts_connid != SAE_CONNID_ANY &&
            mpts->mpts_connid != SAE_CONNID_ALL);

        if (mpts->mpts_flags & (MPTSF_DISCONNECTING|MPTSF_DISCONNECTED))
                return;

        mpts->mpts_flags |= MPTSF_DISCONNECTING;

        /*
         * If this is coming from disconnectx(2) or issued as part of
         * closing the MPTCP socket, the subflow shouldn't stick around.
         * Otherwise let it linger around in case the upper layers need
         * to retrieve its conninfo.
         */
        if (deleteok)
                mpts->mpts_flags |= MPTSF_DELETEOK;

        so = mpts->mpts_socket;
        mp_tp = mpte->mpte_mptcb;
        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state > MPTCPS_ESTABLISHED)
                send_dfin = 1;
        MPT_UNLOCK(mp_tp);

        socket_lock(so, 0);
        if (!(so->so_state & (SS_ISDISCONNECTING | SS_ISDISCONNECTED)) &&
            (so->so_state & SS_ISCONNECTED)) {
                mptcplog((LOG_DEBUG, "MPTCP Socket %s: cid %d fin %d "
                    "[linger %s]\n", __func__, mpts->mpts_connid, send_dfin,
                    (deleteok ? "NO" : "YES")),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);

                if (send_dfin)
                        mptcp_send_dfin(so);
                (void) soshutdownlock(so, SHUT_RD);
                (void) soshutdownlock(so, SHUT_WR);
                (void) sodisconnectlocked(so);
        }
        socket_unlock(so, 0);
        /*
         * Generate a disconnect event for this subflow socket, in case
         * the lower layer doesn't do it; this is needed because the
         * subflow socket deletion relies on it.  This will also end up
         * generating SO_FILT_HINT_CONNINFO_UPDATED on the MPTCP socket;
         * we cannot do that here because subflow lock is currently held.
         */
        mptcp_subflow_eupcall(so, mpts, SO_FILT_HINT_DISCONNECTED);
}

/*
 * Subflow socket read upcall.
 *
 * Called when the associated subflow socket posted a read event.  The subflow
 * socket lock has been released prior to invoking the callback.  Note that the
 * upcall may occur synchronously as a result of MPTCP performing an action on
 * it, or asynchronously as a result of an event happening at the subflow layer.
 * Therefore, to maintain lock ordering, the only lock that can be acquired
 * here is the thread lock, for signalling purposes.
 */
static void
mptcp_subflow_rupcall(struct socket *so, void *arg, int waitf)
{
#pragma unused(so, waitf)
        struct mptsub *mpts = arg;
        struct mptses *mpte = mpts->mpts_mpte;

        /* 
         * mpte should never be NULL, except in a race with 
         * mptcp_subflow_del 
         */
        if (mpte == NULL)
                return;

        lck_mtx_lock(&mpte->mpte_thread_lock);
        mptcp_thread_signal_locked(mpte);
        lck_mtx_unlock(&mpte->mpte_thread_lock);
}

/*
 * Subflow socket input.
 *
 * Called in the context of the MPTCP thread, for reading data from the
 * underlying subflow socket and delivering it to MPTCP.
 */
static void
mptcp_subflow_input(struct mptses *mpte, struct mptsub *mpts)
{
        struct mbuf *m = NULL;
        struct socket *so;
        int error;
        struct mptsub *mpts_alt = NULL;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        DTRACE_MPTCP2(subflow__input, struct mptses *, mpte, 
            struct mptsub *, mpts);

        if (!(mpts->mpts_flags & MPTSF_CONNECTED))
                return;

        so = mpts->mpts_socket;

        error = sock_receive_internal(so, NULL, &m, 0, NULL);
        if (error != 0 && error != EWOULDBLOCK) {
                mptcplog((LOG_ERR, "MPTCP Receiver: %s cid %d error %d\n",
                    __func__, mpts->mpts_connid, error),
                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_ERR);
                MPTS_UNLOCK(mpts);
                mpts_alt = mptcp_get_subflow(mpte, mpts, NULL);
                if (mpts_alt == NULL) {
                        if (mptcp_delayed_subf_start) {
                                mpts_alt = mptcp_get_pending_subflow(mpte,
                                    mpts);
                                if (mpts_alt) {
                                        mptcplog((LOG_DEBUG,"MPTCP Receiver:"
                                        " %s: pending %d\n",
                                        __func__, mpts_alt->mpts_connid),
                                        MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_ERR);
                                } else {
                                        mptcplog((LOG_ERR, "MPTCP Receiver:"
                                            " %s: no pending flow for cid %d",
                                            __func__, mpts->mpts_connid),
                                            MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_ERR);
                                }
                        } else {
                                mptcplog((LOG_ERR, "MPTCP Receiver: %s: no alt"
                                    " path for cid %d\n", __func__, 
                                    mpts->mpts_connid),
                                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_ERR);
                        }
                }
                MPTS_LOCK(mpts);
        } else if (error == 0) {
                mptcplog((LOG_DEBUG, "MPTCP Receiver: %s: cid %d \n",
                    __func__, mpts->mpts_connid),
                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_VERBOSE);
        }

        /* In fallback, make sure to accept data on all but one subflow */
        if ((mpts->mpts_flags & MPTSF_MP_DEGRADED) &&
            (!(mpts->mpts_flags & MPTSF_ACTIVE))) {
                m_freem(m);
                return;
        }

        if (m != NULL) {

                /* Did we receive data on the backup subflow? */
                if (!(mpts->mpts_flags & MPTSF_ACTIVE))
                        mpts->mpts_peerswitch++;
                else
                        mpts->mpts_peerswitch = 0;

                /*
                 * Release subflow lock since this may trigger MPTCP to send,
                 * possibly on a different subflow.  An extra reference has
                 * been held on the subflow by the MPTCP thread before coming
                 * here, so we can be sure that it won't go away, in the event
                 * the MP socket lock gets released.
                 */
                MPTS_UNLOCK(mpts);
                mptcp_input(mpte, m);
                MPTS_LOCK(mpts);
        }
}

/*
 * Subflow socket write upcall.
 *
 * Called when the associated subflow socket posted a read event.  The subflow
 * socket lock has been released prior to invoking the callback.  Note that the
 * upcall may occur synchronously as a result of MPTCP performing an action on
 * it, or asynchronously as a result of an event happening at the subflow layer.
 * Therefore, to maintain lock ordering, the only lock that can be acquired
 * here is the thread lock, for signalling purposes.
 */
static void
mptcp_subflow_wupcall(struct socket *so, void *arg, int waitf)
{
#pragma unused(so, waitf)
        struct mptsub *mpts = arg;
        struct mptses *mpte = mpts->mpts_mpte;

        /*
         * mpte should never be NULL except in a race with 
         * mptcp_subflow_del which doesn't hold socket lock across critical
         * section. This upcall is made after releasing the socket lock.
         * Interleaving of socket operations becomes possible therefore.
         */
        if (mpte == NULL)
                return;

        lck_mtx_lock(&mpte->mpte_thread_lock);
        mptcp_thread_signal_locked(mpte);
        lck_mtx_unlock(&mpte->mpte_thread_lock);
}

/*
 * Subflow socket output.
 *
 * Called for sending data from MPTCP to the underlying subflow socket.
 */
int
mptcp_subflow_output(struct mptses *mpte, struct mptsub *mpts)
{
        struct socket *mp_so, *so;
        size_t sb_cc = 0, tot_sent = 0;
        struct mbuf *sb_mb;
        int error = 0;
        u_int64_t mpt_dsn = 0;
        struct mptcb *mp_tp = mpte->mpte_mptcb;
        struct mbuf *mpt_mbuf = NULL;
        u_int64_t off = 0;
        struct mbuf *head, *tail;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        so = mpts->mpts_socket;

        DTRACE_MPTCP2(subflow__output, struct mptses *, mpte, 
            struct mptsub *, mpts);

        /* subflow socket is suspended? */
        if (mpts->mpts_flags & MPTSF_SUSPENDED) {
                mptcplog((LOG_ERR, "MPTCP Sender: %s mp_so 0x%llx cid %d is "
                    "flow controlled\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so), mpts->mpts_connid),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_ERR);
                goto out;
        }

        /* subflow socket is not MPTCP capable? */
        if (!(mpts->mpts_flags & MPTSF_MP_CAPABLE) &&
            !(mpts->mpts_flags & MPTSF_MP_DEGRADED) &&
            !(mpts->mpts_flags & MPTSF_FASTJ_SEND)) {
                mptcplog((LOG_ERR, "MPTCP Sender: %s mp_so 0x%llx cid %d not "
                    "MPTCP capable\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so), mpts->mpts_connid),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_ERR);
                goto out;
        }

        /* Remove Addr Option is not sent reliably as per I-D */
        if (mpte->mpte_flags & MPTE_SND_REM_ADDR) {
                struct tcpcb *tp = intotcpcb(sotoinpcb(so));
                tp->t_rem_aid = mpte->mpte_lost_aid;
                if (mptcp_remaddr_enable)
                        tp->t_mpflags |= TMPF_SND_REM_ADDR;
                mpte->mpte_flags &= ~MPTE_SND_REM_ADDR;
        }

        /*
         * The mbuf chains containing the metadata (as well as pointing to
         * the user data sitting at the MPTCP output queue) would then be
         * sent down to the subflow socket.
         *
         * Some notes on data sequencing:
         *
         *   a. Each mbuf must be a M_PKTHDR.
         *   b. MPTCP metadata is stored in the mptcp_pktinfo structure
         *      in the mbuf pkthdr structure.
         *   c. Each mbuf containing the MPTCP metadata must have its
         *      pkt_flags marked with the PKTF_MPTCP flag.
         */

        /* First, drop acknowledged data */
        sb_mb = mp_so->so_snd.sb_mb;
        if (sb_mb == NULL) {
                goto out;
        }

        VERIFY(sb_mb->m_pkthdr.pkt_flags & PKTF_MPTCP);

        mpt_mbuf = sb_mb;
        while (mpt_mbuf && mpt_mbuf->m_pkthdr.mp_rlen == 0) {
                mpt_mbuf = mpt_mbuf->m_next;
        }
        if (mpt_mbuf && (mpt_mbuf->m_pkthdr.pkt_flags & PKTF_MPTCP)) {
                mpt_dsn = mpt_mbuf->m_pkthdr.mp_dsn;
        } else {
                goto out;
        }

        MPT_LOCK(mp_tp);
        if (MPTCP_SEQ_LT(mpt_dsn, mp_tp->mpt_snduna)) {
                u_int64_t len = 0;
                len = mp_tp->mpt_snduna - mpt_dsn;
                MPT_UNLOCK(mp_tp);
                sbdrop(&mp_so->so_snd, (int)len);
                MPT_LOCK(mp_tp);
        }

        /*
         * In degraded mode, we don't receive data acks, so force free
         * mbufs less than snd_nxt
         */
        if (mp_so->so_snd.sb_mb == NULL) {
                MPT_UNLOCK(mp_tp);
                goto out;
        }

        mpt_dsn = mp_so->so_snd.sb_mb->m_pkthdr.mp_dsn;
        if ((mpts->mpts_flags & MPTSF_MP_DEGRADED) &&
            (mp_tp->mpt_flags & MPTCPF_POST_FALLBACK_SYNC) &&
            MPTCP_SEQ_LT(mpt_dsn, mp_tp->mpt_sndnxt)) {
                u_int64_t len = 0;
                len = mp_tp->mpt_sndnxt - mpt_dsn;
                sbdrop(&mp_so->so_snd, (int)len);
                mp_tp->mpt_snduna = mp_tp->mpt_sndnxt;
        }

        if ((mpts->mpts_flags & MPTSF_MP_DEGRADED) &&
            !(mp_tp->mpt_flags & MPTCPF_POST_FALLBACK_SYNC)) {
                mp_tp->mpt_flags |= MPTCPF_POST_FALLBACK_SYNC;
                so->so_flags1 |= SOF1_POST_FALLBACK_SYNC;
                if (mp_tp->mpt_flags & MPTCPF_RECVD_MPFAIL)
                        mpts->mpts_sndnxt = mp_tp->mpt_dsn_at_csum_fail;
        }

        /*
         * Adjust the subflow's notion of next byte to send based on
         * the last unacknowledged byte
         */
        if (MPTCP_SEQ_LT(mpts->mpts_sndnxt, mp_tp->mpt_snduna)) {
                mpts->mpts_sndnxt = mp_tp->mpt_snduna;
                /*
                 * With FastJoin, a write before the fastjoin event will use
                 * an uninitialized relative sequence number.
                 */
                if (mpts->mpts_rel_seq == 0)
                        mpts->mpts_rel_seq = 1;
        }

        /*
         * Adjust the top level notion of next byte used for retransmissions
         * and sending FINs.
         */
        if (MPTCP_SEQ_LT(mp_tp->mpt_sndnxt, mp_tp->mpt_snduna)) {
                mp_tp->mpt_sndnxt = mp_tp->mpt_snduna;
        }


        /* Now determine the offset from which to start transmitting data */
        sb_mb = mp_so->so_snd.sb_mb;
        sb_cc = mp_so->so_snd.sb_cc;
        if (sb_mb == NULL) {
                MPT_UNLOCK(mp_tp);
                goto out;
        }
        if (MPTCP_SEQ_LT(mpts->mpts_sndnxt, mp_tp->mpt_sndmax)) {
                off = mpts->mpts_sndnxt - mp_tp->mpt_snduna;
                sb_cc -= (size_t)off;
        } else {
                MPT_UNLOCK(mp_tp);
                goto out;
        }
        MPT_UNLOCK(mp_tp);

        mpt_mbuf = sb_mb;
        mpt_dsn = mpt_mbuf->m_pkthdr.mp_dsn;

        while (mpt_mbuf && ((mpt_mbuf->m_pkthdr.mp_rlen == 0) ||
            (mpt_mbuf->m_pkthdr.mp_rlen <= (u_int32_t)off))) {
                off -= mpt_mbuf->m_pkthdr.mp_rlen;
                mpt_mbuf = mpt_mbuf->m_next;
                mpt_dsn = mpt_mbuf->m_pkthdr.mp_dsn;
        }
        if (mpts->mpts_flags & MPTSF_MP_DEGRADED)
                mptcplog((LOG_DEBUG, "MPTCP Sender: %s cid = %d "
                    "snduna = %llu sndnxt = %llu probe %d\n",
                    __func__, mpts->mpts_connid,
                    mp_tp->mpt_snduna, mpts->mpts_sndnxt,
                    mpts->mpts_probecnt),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);

        VERIFY(mpt_mbuf && (mpt_mbuf->m_pkthdr.pkt_flags & PKTF_MPTCP));

        head = tail = NULL;

        while (tot_sent < sb_cc) {
                struct mbuf *m;
                size_t mlen;

                mlen = mpt_mbuf->m_pkthdr.mp_rlen;
                mlen -= off;
                if (mlen == 0)
                        goto out;

                if (mlen > sb_cc) {
                        panic("%s: unexpected %lu %lu \n", __func__,
                            mlen, sb_cc);
                }

                m = m_copym_mode(mpt_mbuf, (int)off, mlen, M_DONTWAIT,
                    M_COPYM_MUST_COPY_HDR);
                if (m == NULL) {
                        error = ENOBUFS;
                        break;
                }

                /* Create a DSN mapping for the data (m_copym does it) */
                mpt_dsn = mpt_mbuf->m_pkthdr.mp_dsn;
                VERIFY(m->m_flags & M_PKTHDR);
                m->m_pkthdr.pkt_flags |= PKTF_MPTCP;
                m->m_pkthdr.pkt_flags &= ~PKTF_MPSO;
                m->m_pkthdr.mp_dsn = mpt_dsn + off;
                m->m_pkthdr.mp_rseq = mpts->mpts_rel_seq;
                m->m_pkthdr.mp_rlen = mlen;
                mpts->mpts_rel_seq += mlen;
                m->m_pkthdr.len = mlen;

                if (head == NULL) {
                         head = tail = m;
                } else {
                        tail->m_next = m;
                        tail = m;
                }

                tot_sent += mlen;
                off = 0;
                mpt_mbuf = mpt_mbuf->m_next;
        }

        if (head != NULL) {

                if (mpts->mpts_flags & MPTSF_FASTJ_SEND) {
                        struct tcpcb *tp = intotcpcb(sotoinpcb(so));
                        tp->t_mpflags |= TMPF_FASTJOIN_SEND;
                }

                error = sock_sendmbuf(so, NULL, head, 0, NULL);

                DTRACE_MPTCP7(send, struct mbuf *, head, struct socket *, so, 
                    struct sockbuf *, &so->so_rcv,
                    struct sockbuf *, &so->so_snd,
                    struct mptses *, mpte, struct mptsub *, mpts,
                    size_t, tot_sent);
        }

        if (error == 0) {
                mpts->mpts_sndnxt += tot_sent;

                if (mpts->mpts_probesoon && mpts->mpts_maxseg && tot_sent) {
                        tcpstat.tcps_mp_num_probes++;
                        if (tot_sent < mpts->mpts_maxseg)
                                mpts->mpts_probecnt += 1;
                        else
                                mpts->mpts_probecnt +=
                                    tot_sent/mpts->mpts_maxseg;
                }

                MPT_LOCK(mp_tp);

                if (MPTCP_SEQ_LT(mp_tp->mpt_sndnxt, mpts->mpts_sndnxt)) {
                        if (MPTCP_DATASEQ_HIGH32(mpts->mpts_sndnxt) >
                            MPTCP_DATASEQ_HIGH32(mp_tp->mpt_sndnxt))
                                mp_tp->mpt_flags |= MPTCPF_SND_64BITDSN;
                        mp_tp->mpt_sndnxt = mpts->mpts_sndnxt;
                }
                mptcp_cancel_timer(mp_tp, MPTT_REXMT);
                MPT_UNLOCK(mp_tp);

                /* Send once in SYN_SENT state to avoid sending SYN spam */
                if (mpts->mpts_flags & MPTSF_FASTJ_SEND) {
                        so->so_flags &= ~SOF_MPTCP_FASTJOIN;                
                        mpts->mpts_flags &= ~MPTSF_FASTJ_SEND;
                }

                if ((mpts->mpts_flags & MPTSF_MP_DEGRADED) ||
                    (mpts->mpts_probesoon != 0))
                        mptcplog((LOG_DEBUG, "MPTCP Sender: %s cid %d "
                            "wrote %d %d probe %d probedelta %d\n",
                            __func__, mpts->mpts_connid, (int)tot_sent,
                            (int) sb_cc, mpts->mpts_probecnt,
                            (tcp_now - mpts->mpts_probesoon)),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
        } else {
                mptcplog((LOG_ERR, "MPTCP Sender: %s cid %d error %d len %zd\n",
                    __func__, mpts->mpts_connid, error, tot_sent),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_ERR);
        }
out:
        return (error);
}

/*
 * Subflow socket control event upcall.
 *
 * Called when the associated subflow socket posted one or more control events.
 * The subflow socket lock has been released prior to invoking the callback.
 * Note that the upcall may occur synchronously as a result of MPTCP performing
 * an action on it, or asynchronously as a result of an event happening at the
 * subflow layer.  Therefore, to maintain lock ordering, the only lock that can
 * be acquired here is the thread lock, for signalling purposes.
 */
static void
mptcp_subflow_eupcall(struct socket *so, void *arg, uint32_t events)
{
#pragma unused(so)
        struct mptsub *mpts = arg;
        struct mptses *mpte = mpts->mpts_mpte;

        VERIFY(mpte != NULL);

        lck_mtx_lock(&mpte->mpte_thread_lock);
        atomic_bitset_32(&mpts->mpts_evctl, events);
        mptcp_thread_signal_locked(mpte);
        lck_mtx_unlock(&mpte->mpte_thread_lock);
}

/*
 * Subflow socket control events.
 *
 * Called for handling events related to the underlying subflow socket.
 */
static ev_ret_t
mptcp_subflow_events(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        uint32_t events, save_events;
        ev_ret_t ret = MPTS_EVRET_OK;
        int i = 0;
        int mpsub_ev_entry_count = sizeof(mpsub_ev_entry_tbl)/
                sizeof(mpsub_ev_entry_tbl[0]);
        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        /* bail if there's nothing to process */
        if ((events = mpts->mpts_evctl) == 0)
                return (ret);

        if (events & (SO_FILT_HINT_CONNRESET|SO_FILT_HINT_MUSTRST|
            SO_FILT_HINT_CANTRCVMORE|SO_FILT_HINT_CANTSENDMORE|
            SO_FILT_HINT_TIMEOUT|SO_FILT_HINT_NOSRCADDR|
            SO_FILT_HINT_IFDENIED|SO_FILT_HINT_SUSPEND|
            SO_FILT_HINT_DISCONNECTED)) {
                events |= SO_FILT_HINT_MPFAILOVER;
        }

        save_events = events;

        DTRACE_MPTCP3(subflow__events, struct mptses *, mpte,
            struct mptsub *, mpts, uint32_t, events);

        mptcplog((LOG_DEBUG, "MPTCP Events: %s cid %d events=%b\n", __func__,
            mpts->mpts_connid, events, SO_FILT_HINT_BITS),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_VERBOSE);

        /*
         * Process all the socket filter hints and reset the hint
         * once it is handled
         */
        for (i = 0; (i < mpsub_ev_entry_count) && events; i++) {
                if ((events & mpsub_ev_entry_tbl[i].sofilt_hint_mask) &&
                    (ret >= MPTS_EVRET_OK)) {
                        ev_ret_t error =
                                mpsub_ev_entry_tbl[i].sofilt_hint_ev_hdlr(mpte, mpts, p_mpsofilt_hint);
                        events &= ~mpsub_ev_entry_tbl[i].sofilt_hint_mask;
                        ret = ((error >= MPTS_EVRET_OK) ? MAX(error, ret) : error);
                }
        }

        /*
         * We should be getting only events specified via sock_catchevents(),
         * so loudly complain if we have any unprocessed one(s).
         */
        if (events != 0 || ret < MPTS_EVRET_OK) {
                mptcplog((LOG_ERR, "MPTCP Events %s%s: cid %d evret %s (%d)"
                    " unhandled events=%b\n",
                    (events != 0) && (ret == MPTS_EVRET_OK) ? "MPTCP_ERROR " : "", 
                    __func__, mpts->mpts_connid,
                    mptcp_evret2str(ret), ret, events, SO_FILT_HINT_BITS),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_ERR);
        }

        /* clear the ones we've processed */
        atomic_bitclear_32(&mpts->mpts_evctl, save_events);
        return (ret);
}

/*
 * Handle SO_FILT_HINT_CONNRESET subflow socket event.
 */
static ev_ret_t
mptcp_subflow_connreset_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        boolean_t linger;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        linger = (!(mpts->mpts_flags & MPTSF_DELETEOK) &&
            !(mp_so->so_flags & SOF_PCBCLEARING));

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d [linger %s]\n", __func__,
            mpts->mpts_connid, (linger ? "YES" : "NO")),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        /*
         * We got a TCP RST for this subflow connection.
         *
         * Right now, we simply propagate ECONNREFUSED to the MPTCP socket
         * client if the MPTCP connection has not been established or
         * if the connection has only one subflow and is a connection being
         * resumed. Otherwise we close the socket.
         */
        mptcp_subflow_disconnect(mpte, mpts, !linger);

        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED) {
                mpts->mpts_soerror = mp_so->so_error = ECONNREFUSED;
        } else if (mpte->mpte_nummpcapflows < 1) {
                mpts->mpts_soerror = mp_so->so_error = ECONNRESET;
                *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED | SO_FILT_HINT_CONNRESET;
        }
        MPT_UNLOCK(mp_tp);

        /*
         * Keep the subflow socket around, unless the MPTCP socket has
         * been detached or the subflow has been disconnected explicitly,
         * in which case it should be deleted right away.
         */
        return (linger ? MPTS_EVRET_OK : MPTS_EVRET_DELETE);
}

/*
 * Handle SO_FILT_HINT_CANTRCVMORE subflow socket event.
 */
static ev_ret_t
mptcp_subflow_cantrcvmore_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        struct socket *so;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        so = mpts->mpts_socket;

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d\n", __func__, mpts->mpts_connid),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        /*
         * We got a FIN for this subflow connection.  This subflow socket
         * is no longer available for receiving data;
         * The FIN may arrive with data. The data is handed up to the
         * mptcp socket and the subflow is disconnected.
         */

        return (MPTS_EVRET_OK); /* keep the subflow socket around */
}

/*
 * Handle SO_FILT_HINT_CANTSENDMORE subflow socket event.
 */
static ev_ret_t
mptcp_subflow_cantsendmore_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        struct socket *so;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        so = mpts->mpts_socket;

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d\n", __func__, mpts->mpts_connid),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        return (MPTS_EVRET_OK); /* keep the subflow socket around */
}

/*
 * Handle SO_FILT_HINT_TIMEOUT subflow socket event.
 */
static ev_ret_t
mptcp_subflow_timeout_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        boolean_t linger;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        linger = (!(mpts->mpts_flags & MPTSF_DELETEOK) &&
            !(mp_so->so_flags & SOF_PCBCLEARING));

        mptcplog((LOG_NOTICE, "MPTCP Events: "
            "%s: cid %d [linger %s]\n", __func__,
            mpts->mpts_connid, (linger ? "YES" : "NO")),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        if (mpts->mpts_soerror == 0)
                mpts->mpts_soerror = ETIMEDOUT;

        /*
         * The subflow connection has timed out.
         *
         * Right now, we simply propagate ETIMEDOUT to the MPTCP socket
         * client if the MPTCP connection has not been established. Otherwise
         * drop it.
         */
        mptcp_subflow_disconnect(mpte, mpts, !linger);

        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED) {
                mp_so->so_error = ETIMEDOUT;
        }
        MPT_UNLOCK(mp_tp);

        /*
         * Keep the subflow socket around, unless the MPTCP socket has
         * been detached or the subflow has been disconnected explicitly,
         * in which case it should be deleted right away.
         */
        return (linger ? MPTS_EVRET_OK : MPTS_EVRET_DELETE);
}

/*
 * Handle SO_FILT_HINT_NOSRCADDR subflow socket event.
 */
static ev_ret_t
mptcp_subflow_nosrcaddr_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        boolean_t linger;
        struct tcpcb *tp = NULL;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        /* Not grabbing socket lock as t_local_aid is write once only */
        tp = intotcpcb(sotoinpcb(so));
        /*
         * This overwrites any previous mpte_lost_aid to avoid storing
         * too much state when the typical case has only two subflows.
         */
        mpte->mpte_flags |= MPTE_SND_REM_ADDR;
        mpte->mpte_lost_aid = tp->t_local_aid;

        linger = (!(mpts->mpts_flags & MPTSF_DELETEOK) &&
            !(mp_so->so_flags & SOF_PCBCLEARING));

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s cid %d [linger %s]\n", __func__,
            mpts->mpts_connid, (linger ? "YES" : "NO")),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        if (mpts->mpts_soerror == 0)
                mpts->mpts_soerror = EADDRNOTAVAIL;

        /*
         * The subflow connection has lost its source address.
         *
         * Right now, we simply propagate EADDRNOTAVAIL to the MPTCP socket
         * client if the MPTCP connection has not been established.  If it
         * has been established with one subflow , we keep the MPTCP
         * connection valid without any subflows till closed by application.
         * This lets tcp connection manager decide whether to close this or
         * not as it reacts to reachability changes too.
         */
        mptcp_subflow_disconnect(mpte, mpts, !linger);

        MPT_LOCK(mp_tp);
        if ((mp_tp->mpt_state < MPTCPS_ESTABLISHED) &&
            (mp_so->so_flags & SOF_NOADDRAVAIL)) {
                mp_so->so_error = EADDRNOTAVAIL;
        }
        MPT_UNLOCK(mp_tp);

        /*
         * Keep the subflow socket around, unless the MPTCP socket has
         * been detached or the subflow has been disconnected explicitly,
         * in which case it should be deleted right away.
         */
        return (linger ? MPTS_EVRET_OK : MPTS_EVRET_DELETE);
}

/*
 * Handle SO_FILT_HINT_MPCANTRCVMORE subflow socket event that
 * indicates that the remote side sent a Data FIN
 */
static ev_ret_t
mptcp_subflow_mpcantrcvmore_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        struct socket *so, *mp_so;
        struct mptcb *mp_tp;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        so = mpts->mpts_socket;
        mp_tp = mpte->mpte_mptcb;

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d\n", __func__, mpts->mpts_connid),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
        
        /*
        * We got a Data FIN for the MPTCP connection.  
        * The FIN may arrive with data. The data is handed up to the
        * mptcp socket and the user is notified so that it may close
        * the socket if needed.
        */
        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state == MPTCPS_CLOSE_WAIT) {
                *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED | SO_FILT_HINT_CANTRCVMORE;
        }
        MPT_UNLOCK(mp_tp);
        return (MPTS_EVRET_OK); /* keep the subflow socket around */
}

/*
 * Handle SO_FILT_HINT_MPFAILOVER subflow socket event
 */
static ev_ret_t
mptcp_subflow_failover_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        struct mptsub *mpts_alt = NULL;
        struct socket *so = NULL;
        struct socket *mp_so;
        int altpath_exists = 0;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mptcplog((LOG_NOTICE, "MPTCP Events: "
            "%s: mp_so 0x%llx\n", __func__,
            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so)),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        MPTS_UNLOCK(mpts);
        mpts_alt = mptcp_get_subflow(mpte, mpts, NULL);

        /*
         * If there is no alternate eligible subflow, ignore the
         * failover hint.
         */
        if (mpts_alt == NULL) {
                mptcplog((LOG_WARNING, "MPTCP Events: "
                    "%s: no alternate path\n", __func__),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_ERR);

                if (mptcp_delayed_subf_start) {
                        mpts_alt = mptcp_get_pending_subflow(mpte, mpts);
                        if (mpts_alt != NULL) {
                                MPTS_LOCK(mpts_alt);
                                (void) mptcp_subflow_soconnectx(mpte,
                                    mpts_alt);
                                MPTS_UNLOCK(mpts_alt);  
                        }
                }
                MPTS_LOCK(mpts);
                goto done;
        }
        MPTS_LOCK(mpts_alt);
        altpath_exists = 1;
        so = mpts_alt->mpts_socket;
        if (mpts_alt->mpts_flags & MPTSF_FAILINGOVER) {
                socket_lock(so, 1);
                /* All data acknowledged and no RTT spike */
                if ((so->so_snd.sb_cc == 0) &&
                    (mptcp_no_rto_spike(so))) {
                        so->so_flags &= ~SOF_MP_TRYFAILOVER;
                        mpts_alt->mpts_flags &= ~MPTSF_FAILINGOVER;
                } else {
                        /* no alternate path available */
                        altpath_exists = 0;
                }
                socket_unlock(so, 1);
        }
        if (altpath_exists) {
                mptcplog((LOG_INFO, "MPTCP Events: "
                    "%s: cid = %d\n",
                    __func__, mpts_alt->mpts_connid),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
                mpts_alt->mpts_flags |= MPTSF_ACTIVE;
                mpts_alt->mpts_peerswitch = 0;
                struct mptcb *mp_tp = mpte->mpte_mptcb;
                /* Bring the subflow's notion of snd_nxt into the send window */
                MPT_LOCK(mp_tp);
                mpts_alt->mpts_sndnxt = mp_tp->mpt_snduna;
                MPT_UNLOCK(mp_tp);
                mpte->mpte_active_sub = mpts_alt;
                socket_lock(so, 1);
                sowwakeup(so);
                socket_unlock(so, 1);
        }
        MPTS_UNLOCK(mpts_alt);

        if (altpath_exists) {
                *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED | SO_FILT_HINT_CONNINFO_UPDATED;
                mptcplog((LOG_NOTICE, "MPTCP Events: "
                    "%s: mp_so 0x%llx switched from "
                    "%d to %d\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    mpts->mpts_connid, mpts_alt->mpts_connid),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
                tcpstat.tcps_mp_switches++;
        }

        MPTS_LOCK(mpts);
        if (altpath_exists) {
                mpts->mpts_flags |= MPTSF_FAILINGOVER;
                mpts->mpts_flags &= ~MPTSF_ACTIVE;
        } else {
                mptcplog((LOG_DEBUG, "MPTCP Events %s: no alt cid = %d\n",
                    __func__, mpts->mpts_connid),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
done:
                so = mpts->mpts_socket;
                socket_lock(so, 1);
                so->so_flags &= ~SOF_MP_TRYFAILOVER;
                socket_unlock(so, 1);
        }
        MPTS_LOCK_ASSERT_HELD(mpts);
        return (MPTS_EVRET_OK);
}

/*
 * Handle SO_FILT_HINT_IFDENIED subflow socket event.
 */
static ev_ret_t
mptcp_subflow_ifdenied_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        boolean_t linger;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        linger = (!(mpts->mpts_flags & MPTSF_DELETEOK) &&
            !(mp_so->so_flags & SOF_PCBCLEARING));

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d [linger %s]\n", __func__,
            mpts->mpts_connid, (linger ? "YES" : "NO")),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        if (mpts->mpts_soerror == 0)
                mpts->mpts_soerror = EHOSTUNREACH;

        /*
         * The subflow connection cannot use the outgoing interface.
         *
         * Right now, we simply propagate EHOSTUNREACH to the MPTCP socket
         * client if the MPTCP connection has not been established.  If it
         * has been established, let the upper layer call disconnectx.
         */
        mptcp_subflow_disconnect(mpte, mpts, !linger);
        *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED | SO_FILT_HINT_IFDENIED;

        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED) {
                mp_so->so_error = EHOSTUNREACH;
        }
        MPT_UNLOCK(mp_tp);

        /*
         * Keep the subflow socket around, unless the MPTCP socket has
         * been detached or the subflow has been disconnected explicitly,
         * in which case it should be deleted right away.
         */
        return (linger ? MPTS_EVRET_OK : MPTS_EVRET_DELETE);
}

/*
 * Handle SO_FILT_HINT_SUSPEND subflow socket event.
 */
static ev_ret_t
mptcp_subflow_suspend_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        struct socket *so;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        so = mpts->mpts_socket;

        /* the subflow connection is being flow controlled */
        mpts->mpts_flags |= MPTSF_SUSPENDED;

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d\n", __func__,
            mpts->mpts_connid), MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        return (MPTS_EVRET_OK); /* keep the subflow socket around */
}

/*
 * Handle SO_FILT_HINT_RESUME subflow socket event.
 */
static ev_ret_t
mptcp_subflow_resume_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        struct socket *so;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);

        so = mpts->mpts_socket;

        /* the subflow connection is no longer flow controlled */
        mpts->mpts_flags &= ~MPTSF_SUSPENDED;

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d\n", __func__, mpts->mpts_connid),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        return (MPTS_EVRET_OK); /* keep the subflow socket around */
}

/*
 * Handle SO_FILT_HINT_CONNECTED subflow socket event.
 */
static ev_ret_t
mptcp_subflow_connected_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        char buf0[MAX_IPv6_STR_LEN], buf1[MAX_IPv6_STR_LEN];
        struct sockaddr_entry *src_se, *dst_se;
        struct sockaddr_storage src;
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        struct ifnet *outifp;
        int af, error = 0;
        boolean_t mpok = FALSE;
        boolean_t cell = FALSE;
        boolean_t wifi = FALSE;
        boolean_t wired = FALSE;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;

        MPTS_LOCK_ASSERT_HELD(mpts);
        so = mpts->mpts_socket;
        af = mpts->mpts_family;

        if (mpts->mpts_flags & MPTSF_CONNECTED)
                return (MPTS_EVRET_OK);

        if ((mpts->mpts_flags & MPTSF_DISCONNECTED) ||
            (mpts->mpts_flags & MPTSF_DISCONNECTING)) {
                socket_lock(so, 0);
                if (!(so->so_state & (SS_ISDISCONNECTING | SS_ISDISCONNECTED)) &&
                    (so->so_state & SS_ISCONNECTED)) {
                    mptcplog((LOG_DEBUG, "MPTCP Events: "
                        "%s: cid %d disconnect before tcp connect\n",
                        __func__, mpts->mpts_connid),
                        MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
                        (void) soshutdownlock(so, SHUT_RD);
                        (void) soshutdownlock(so, SHUT_WR);
                        (void) sodisconnectlocked(so);
                }
                socket_unlock(so, 0);
                return (MPTS_EVRET_OK);
        }

        /*
         * The subflow connection has been connected.  Find out whether it
         * is connected as a regular TCP or as a MPTCP subflow.  The idea is:
         *
         *   a. If MPTCP connection is not yet established, then this must be
         *      the first subflow connection.  If MPTCP failed to negotiate,
         *      indicate to the MPTCP socket client via EPROTO, that the
         *      underlying TCP connection may be peeled off via peeloff(2).
         *      Otherwise, mark the MPTCP socket as connected.
         *
         *   b. If MPTCP connection has been established, then this must be
         *      one of the subsequent subflow connections. If MPTCP failed
         *      to negotiate, disconnect the connection since peeloff(2)
         *      is no longer possible.
         *
         * Right now, we simply unblock any waiters at the MPTCP socket layer
         * if the MPTCP connection has not been established.
         */
        socket_lock(so, 0);

        if (so->so_state & SS_ISDISCONNECTED) {
                /*
                 * With MPTCP joins, a connection is connected at the subflow
                 * level, but the 4th ACK from the server elevates the MPTCP
                 * subflow to connected state. So there is a small window 
                 * where the subflow could get disconnected before the 
                 * connected event is processed.
                 */
                socket_unlock(so, 0);
                return (MPTS_EVRET_OK);
        }

        mpts->mpts_soerror = 0;
        mpts->mpts_flags &= ~MPTSF_CONNECTING;
        mpts->mpts_flags |= MPTSF_CONNECTED;
        if (sototcpcb(so)->t_mpflags & TMPF_MPTCP_TRUE)
                mpts->mpts_flags |= MPTSF_MP_CAPABLE;

        VERIFY(mpts->mpts_dst_sl != NULL);
        dst_se = TAILQ_FIRST(&mpts->mpts_dst_sl->sl_head);
        VERIFY(dst_se != NULL && dst_se->se_addr != NULL &&
            dst_se->se_addr->sa_family == af);

        VERIFY(mpts->mpts_src_sl != NULL);
        src_se = TAILQ_FIRST(&mpts->mpts_src_sl->sl_head);
        VERIFY(src_se != NULL && src_se->se_addr != NULL &&
            src_se->se_addr->sa_family == af);

        /* get/check source IP address */
        switch (af) {
        case AF_INET: {
                error = in_getsockaddr_s(so, &src);
                if (error == 0) {
                        struct sockaddr_in *ms = SIN(src_se->se_addr);
                        struct sockaddr_in *s = SIN(&src);

                        VERIFY(s->sin_len == ms->sin_len);
                        VERIFY(ms->sin_family == AF_INET);

                        if ((mpts->mpts_flags & MPTSF_BOUND_IP) &&
                            bcmp(&ms->sin_addr, &s->sin_addr,
                            sizeof (ms->sin_addr)) != 0) {
                                mptcplog((LOG_ERR, "MPTCP Events: "
                                    "%s: cid %d local "
                                    "address %s (expected %s)\n", __func__,
                                    mpts->mpts_connid, inet_ntop(AF_INET,
                                    (void *)&s->sin_addr.s_addr, buf0,
                                    sizeof (buf0)), inet_ntop(AF_INET,
                                    (void *)&ms->sin_addr.s_addr, buf1,
                                    sizeof (buf1))),
                                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_ERR);
                        }
                        bcopy(s, ms, sizeof (*s));
                }
                break;
        }
#if INET6
        case AF_INET6: {
                error = in6_getsockaddr_s(so, &src);
                if (error == 0) {
                        struct sockaddr_in6 *ms = SIN6(src_se->se_addr);
                        struct sockaddr_in6 *s = SIN6(&src);

                        VERIFY(s->sin6_len == ms->sin6_len);
                        VERIFY(ms->sin6_family == AF_INET6);

                        if ((mpts->mpts_flags & MPTSF_BOUND_IP) &&
                            bcmp(&ms->sin6_addr, &s->sin6_addr,
                            sizeof (ms->sin6_addr)) != 0) {
                                mptcplog((LOG_ERR, "MPTCP Events: "
                                    "%s: cid %d local "
                                    "address %s (expected %s)\n", __func__,
                                    mpts->mpts_connid, inet_ntop(AF_INET6,
                                    (void *)&s->sin6_addr, buf0,
                                    sizeof (buf0)), inet_ntop(AF_INET6,
                                    (void *)&ms->sin6_addr, buf1,
                                    sizeof (buf1))),
                                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_ERR);
                        }
                        bcopy(s, ms, sizeof (*s));
                }
                break;
        }
#endif /* INET6 */
        default:
                VERIFY(0);
                /* NOTREACHED */
        }

        if (error != 0) {
                mptcplog((LOG_ERR, "MPTCP Events "
                    "%s: cid %d getsockaddr failed (%d)\n",
                    __func__, mpts->mpts_connid, error),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_ERR);
        }

        /* get/verify the outbound interface */
        outifp = sotoinpcb(so)->inp_last_outifp;        /* could be NULL */
        if (mpts->mpts_flags & MPTSF_BOUND_IF) {
                VERIFY(mpts->mpts_outif != NULL);
                if (mpts->mpts_outif != outifp) {
                        mptcplog((LOG_ERR, "MPTCP Events: %s: cid %d outif %s "
                            "(expected %s)\n", __func__, mpts->mpts_connid,
                            ((outifp != NULL) ? outifp->if_xname : "NULL"),
                            mpts->mpts_outif->if_xname),
                            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_ERR);

                        if (outifp == NULL)
                                outifp = mpts->mpts_outif;
                }
        } else {
                mpts->mpts_outif = outifp;
        }

        mpts->mpts_srtt = (intotcpcb(sotoinpcb(so)))->t_srtt;
        mpts->mpts_rxtcur = (intotcpcb(sotoinpcb(so)))->t_rxtcur;
        mpts->mpts_maxseg = (intotcpcb(sotoinpcb(so)))->t_maxseg;

        cell = IFNET_IS_CELLULAR(mpts->mpts_outif);
        wifi = (!cell && IFNET_IS_WIFI(mpts->mpts_outif));
        wired = (!wifi && IFNET_IS_WIRED(mpts->mpts_outif));

        if (cell)
                mpts->mpts_linktype |= MPTSL_CELL;
        else if (wifi)
                mpts->mpts_linktype |= MPTSL_WIFI;
        else if (wired)
                mpts->mpts_linktype |= MPTSL_WIRED;

        socket_unlock(so, 0);

        mptcplog((LOG_DEBUG, "MPTCP Sender: %s: cid %d "
            "establishment srtt %d \n", __func__,
            mpts->mpts_connid, (mpts->mpts_srtt >> 5)),
            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);


        mptcplog((LOG_DEBUG, "MPTCP Socket: "
            "%s: cid %d outif %s %s[%d] -> %s[%d] "
            "is %s\n", __func__, mpts->mpts_connid, ((outifp != NULL) ?
            outifp->if_xname : "NULL"), inet_ntop(af, (af == AF_INET) ?
            (void *)&SIN(src_se->se_addr)->sin_addr.s_addr :
            (void *)&SIN6(src_se->se_addr)->sin6_addr, buf0, sizeof (buf0)),
            ((af == AF_INET) ? ntohs(SIN(src_se->se_addr)->sin_port) :
            ntohs(SIN6(src_se->se_addr)->sin6_port)),
            inet_ntop(af, ((af == AF_INET) ?
            (void *)&SIN(dst_se->se_addr)->sin_addr.s_addr :
            (void *)&SIN6(dst_se->se_addr)->sin6_addr), buf1, sizeof (buf1)),
            ((af == AF_INET) ? ntohs(SIN(dst_se->se_addr)->sin_port) :
            ntohs(SIN6(dst_se->se_addr)->sin6_port)),
            ((mpts->mpts_flags & MPTSF_MP_CAPABLE) ?
            "MPTCP capable" : "a regular TCP")),
            (MPTCP_SOCKET_DBG | MPTCP_EVENTS_DBG), MPTCP_LOGLVL_LOG);

        mpok = (mpts->mpts_flags & MPTSF_MP_CAPABLE);
        MPTS_UNLOCK(mpts);

        *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED | SO_FILT_HINT_CONNINFO_UPDATED;

        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED) {
                /* case (a) above */
                if (!mpok) {
                        mp_tp->mpt_flags |= MPTCPF_PEEL_OFF;
                        (void) mptcp_drop(mpte, mp_tp, EPROTO);
                        MPT_UNLOCK(mp_tp);
                } else {
                        if (mptcp_init_authparms(mp_tp) != 0) {
                                mp_tp->mpt_flags |= MPTCPF_PEEL_OFF;
                                (void) mptcp_drop(mpte, mp_tp, EPROTO);
                                MPT_UNLOCK(mp_tp);
                                mpok = FALSE;
                        } else {
                                mptcplog((LOG_DEBUG, "MPTCP State: "
                                    "MPTCPS_ESTABLISHED for mp_so 0x%llx \n",
                                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so)),
                                    MPTCP_STATE_DBG, MPTCP_LOGLVL_LOG);
                                mp_tp->mpt_state = MPTCPS_ESTABLISHED;
                                mpte->mpte_associd = mpts->mpts_connid;
                                DTRACE_MPTCP2(state__change, 
                                    struct mptcb *, mp_tp, 
                                    uint32_t, 0 /* event */);
                                mptcp_init_statevars(mp_tp);
                                MPT_UNLOCK(mp_tp);

                                (void) mptcp_setconnorder(mpte,
                                    mpts->mpts_connid, 1);
                                soisconnected(mp_so);
                        }
                }
                MPTS_LOCK(mpts);
                if (mpok) {
                        /* Initialize the relative sequence number */
                        mpts->mpts_rel_seq = 1;
                        mpts->mpts_flags |= MPTSF_MPCAP_CTRSET;
                        mpte->mpte_nummpcapflows++;
                        MPT_LOCK_SPIN(mp_tp);
                        mpts->mpts_sndnxt = mp_tp->mpt_snduna;
                        MPT_UNLOCK(mp_tp);
                }
        } else if (mpok) {
                MPT_UNLOCK(mp_tp);
                if (mptcp_rwnotify && (mpte->mpte_nummpcapflows == 0)) {
                        /* Experimental code, disabled by default. */
                        sorwakeup(mp_so);
                        sowwakeup(mp_so);
                }
                /*
                 * case (b) above
                 * In case of additional flows, the MPTCP socket is not
                 * MPTSF_MP_CAPABLE until an ACK is received from server
                 * for 3-way handshake.  TCP would have guaranteed that this
                 * is an MPTCP subflow.
                 */
                MPTS_LOCK(mpts);
                mpts->mpts_flags |= MPTSF_MPCAP_CTRSET;
                mpts->mpts_flags &= ~MPTSF_FASTJ_REQD;
                mpte->mpte_nummpcapflows++;
                /* With Fastjoin, rel sequence will be nonzero */
                if (mpts->mpts_rel_seq == 0)
                        mpts->mpts_rel_seq = 1;
                MPT_LOCK_SPIN(mp_tp);
                /* With Fastjoin, sndnxt is updated before connected_ev */
                if (mpts->mpts_sndnxt == 0) {
                        mpts->mpts_sndnxt = mp_tp->mpt_snduna;
                } 
                MPT_UNLOCK(mp_tp);
                mptcp_output_needed(mpte, mpts);
        } else {
                MPT_UNLOCK(mp_tp);
                MPTS_LOCK(mpts);
        }

        MPTS_LOCK_ASSERT_HELD(mpts);

        return (MPTS_EVRET_OK); /* keep the subflow socket around */
}

/*
 * Handle SO_FILT_HINT_DISCONNECTED subflow socket event.
 */
static ev_ret_t
mptcp_subflow_disconnected_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        boolean_t linger;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        linger = (!(mpts->mpts_flags & MPTSF_DELETEOK) &&
            !(mp_so->so_flags & SOF_PCBCLEARING));

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: cid %d [linger %s]\n", __func__,
            mpts->mpts_connid, (linger ? "YES" : "NO")),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        if (mpts->mpts_flags & MPTSF_DISCONNECTED)
                return (linger ? MPTS_EVRET_OK : MPTS_EVRET_DELETE);

        /*
         * Clear flags that are used by getconninfo to return state.
         * Retain like MPTSF_DELETEOK for internal purposes.
         */
        mpts->mpts_flags &= ~(MPTSF_CONNECTING|MPTSF_CONNECT_PENDING|
            MPTSF_CONNECTED|MPTSF_DISCONNECTING|MPTSF_PREFERRED|
            MPTSF_MP_CAPABLE|MPTSF_MP_READY|MPTSF_MP_DEGRADED|
            MPTSF_SUSPENDED|MPTSF_ACTIVE);
        mpts->mpts_flags |= MPTSF_DISCONNECTED;

        /*
         * The subflow connection has been disconnected.
         *
         * Right now, we simply unblock any waiters at the MPTCP socket layer
         * if the MPTCP connection has not been established.
         */
        *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED | SO_FILT_HINT_CONNINFO_UPDATED;

        if (mpts->mpts_flags & MPTSF_MPCAP_CTRSET) {
                mpte->mpte_nummpcapflows--;
                if (mpte->mpte_active_sub == mpts) {
                        mpte->mpte_active_sub = NULL;
                        mptcplog((LOG_DEBUG, "MPTCP Events: "
                            "%s: resetting active subflow \n",
                            __func__), MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
                }
                mpts->mpts_flags &= ~MPTSF_MPCAP_CTRSET;
        }

        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED) {
                MPT_UNLOCK(mp_tp);
                MPTS_UNLOCK(mpts);
                soisdisconnected(mp_so);
                MPTS_LOCK(mpts);
        } else {
                MPT_UNLOCK(mp_tp);
        }

        /*
         * The underlying subflow socket has been disconnected;
         * it is no longer useful to us.  Keep the subflow socket
         * around, unless the MPTCP socket has been detached or
         * the subflow has been disconnected explicitly, in which
         * case it should be deleted right away.
         */
        return (linger ? MPTS_EVRET_OK : MPTS_EVRET_DELETE);
}

/*
 * Handle SO_FILT_HINT_MPSTATUS subflow socket event
 */
static ev_ret_t
mptcp_subflow_mpstatus_ev(struct mptses *mpte, struct mptsub *mpts,
                uint64_t *p_mpsofilt_hint)
{
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        ev_ret_t ret = MPTS_EVRET_OK;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;

        MPTS_LOCK_ASSERT_HELD(mpts);
        so = mpts->mpts_socket;

        socket_lock(so, 0);
        MPT_LOCK(mp_tp);

        if (sototcpcb(so)->t_mpflags & TMPF_MPTCP_TRUE)
                mpts->mpts_flags |= MPTSF_MP_CAPABLE;
        else
                mpts->mpts_flags &= ~MPTSF_MP_CAPABLE;

        if (sototcpcb(so)->t_mpflags & TMPF_TCP_FALLBACK) {
                if (mpts->mpts_flags & MPTSF_MP_DEGRADED)
                        goto done;
                mpts->mpts_flags |= MPTSF_MP_DEGRADED;
        }
        else
                mpts->mpts_flags &= ~MPTSF_MP_DEGRADED;

        if (sototcpcb(so)->t_mpflags & TMPF_MPTCP_READY)
                mpts->mpts_flags |= MPTSF_MP_READY;
        else
                mpts->mpts_flags &= ~MPTSF_MP_READY;

        if (mpts->mpts_flags & MPTSF_MP_DEGRADED) {
                mp_tp->mpt_flags |= MPTCPF_FALLBACK_TO_TCP;
                mp_tp->mpt_flags &= ~MPTCPF_JOIN_READY;
        }

        if (mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP) {
                VERIFY(!(mp_tp->mpt_flags & MPTCPF_JOIN_READY));
                ret = MPTS_EVRET_DISCONNECT_FALLBACK;
                *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED |
                        SO_FILT_HINT_CONNINFO_UPDATED;
        } else if (mpts->mpts_flags & MPTSF_MP_READY) {
                mp_tp->mpt_flags |= MPTCPF_JOIN_READY;
                ret = MPTS_EVRET_CONNECT_PENDING;
        } else {
                *p_mpsofilt_hint |= SO_FILT_HINT_LOCKED |
                        SO_FILT_HINT_CONNINFO_UPDATED;
        }

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s: mp_so 0x%llx mpt_flags=%b cid %d "
            "mptsf=%b\n", __func__,
            (u_int64_t)VM_KERNEL_ADDRPERM(mpte->mpte_mppcb->mpp_socket),
            mp_tp->mpt_flags, MPTCPF_BITS, mpts->mpts_connid,
            mpts->mpts_flags, MPTSF_BITS),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

done:
        MPT_UNLOCK(mp_tp);
        socket_unlock(so, 0);
        return (ret);
}

/*
 * Handle SO_FILT_HINT_MUSTRST subflow socket event
 */
static ev_ret_t
mptcp_subflow_mustrst_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        boolean_t linger;


        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        linger = (!(mpts->mpts_flags & MPTSF_DELETEOK) &&
            !(mp_so->so_flags & SOF_PCBCLEARING));

        if (mpts->mpts_soerror == 0)
                mpts->mpts_soerror = ECONNABORTED;

        /* We got an invalid option or a fast close */
        socket_lock(so, 0);
        struct tcptemp *t_template;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp = NULL;

        tp = intotcpcb(inp);
        so->so_error = ECONNABORTED;

        t_template = tcp_maketemplate(tp);
        if (t_template) {
                struct tcp_respond_args tra;

                bzero(&tra, sizeof(tra));
                if (inp->inp_flags & INP_BOUND_IF)
                        tra.ifscope = inp->inp_boundifp->if_index;
                else
                        tra.ifscope = IFSCOPE_NONE;
                tra.awdl_unrestricted = 1;

                tcp_respond(tp, t_template->tt_ipgen,
                    &t_template->tt_t, (struct mbuf *)NULL,
                    tp->rcv_nxt, tp->snd_una, TH_RST, &tra);
                (void) m_free(dtom(t_template));
                mptcplog((LOG_DEBUG, "MPTCP Events: "
                    "%s: mp_so 0x%llx cid %d \n",
                    __func__, (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    so, mpts->mpts_connid),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
        }
        socket_unlock(so, 0);
        mptcp_subflow_disconnect(mpte, mpts, !linger);

        *p_mpsofilt_hint |=  (SO_FILT_HINT_LOCKED | SO_FILT_HINT_CONNINFO_UPDATED);

        if (!(mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP))
                *p_mpsofilt_hint |= SO_FILT_HINT_CONNRESET;

        MPT_LOCK(mp_tp);
        if ((mp_tp->mpt_state < MPTCPS_ESTABLISHED) ||
            (mp_tp->mpt_state == MPTCPS_FASTCLOSE_WAIT)) {
                mp_so->so_error = ECONNABORTED;
        }
        /*
         * Ideally there should be a state transition for when a FASTCLOSE
         * is received. Right now we keep the connection in MPTCPS_ESTABLISHED
         * state and only go to terminal state when the user level code calls
         * close after processing the SO_FILT_HINT_CONNRESET event.
         */
        if (mp_tp->mpt_gc_ticks == MPT_GC_TICKS)
                mp_tp->mpt_gc_ticks = MPT_GC_TICKS_FAST;
        MPT_UNLOCK(mp_tp);

        /*
         * Keep the subflow socket around unless the subflow has been
         * disconnected explicitly.
         */
        return (linger ? MPTS_EVRET_OK : MPTS_EVRET_DELETE);
}

static ev_ret_t
mptcp_fastjoin_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPTS_LOCK_ASSERT_HELD(mpts);
        VERIFY(mpte->mpte_mppcb != NULL);
        
        if (mpte->mpte_nummpcapflows == 0) {
                struct mptcb *mp_tp = mpte->mpte_mptcb;
                mptcplog((LOG_DEBUG,"MPTCP Events: %s: %llx %llx \n",
                    __func__, mp_tp->mpt_snduna, mpts->mpts_sndnxt),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

                mpte->mpte_active_sub = mpts;
                mpts->mpts_flags |= (MPTSF_FASTJ_SEND | MPTSF_ACTIVE);
                MPT_LOCK(mp_tp);
                /*
                 * If mptcp_subflow_output is called before fastjoin_ev
                 * then mpts->mpts_sndnxt is initialized to mp_tp->mpt_snduna
                 * and further mpts->mpts_sndnxt is incremented by len copied.
                 */
                if (mpts->mpts_sndnxt == 0) {
                        mpts->mpts_sndnxt = mp_tp->mpt_snduna;
                        mpts->mpts_rel_seq = 1;
                }
                MPT_UNLOCK(mp_tp);
        }

        return (MPTS_EVRET_OK);
}

static ev_ret_t
mptcp_deleteok_ev(struct mptses *mpte, struct mptsub *mpts,
        uint64_t *p_mpsofilt_hint)
{
#pragma unused(p_mpsofilt_hint)
        MPTE_LOCK_ASSERT_HELD(mpte);
        MPTS_LOCK_ASSERT_HELD(mpts);
        VERIFY(mpte->mpte_mppcb != NULL);

        mptcplog((LOG_DEBUG, "MPTCP Events: "
            "%s cid %d\n", __func__, mpts->mpts_connid),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        mpts->mpts_flags |= MPTSF_DELETEOK;
        if (mpts->mpts_flags & MPTSF_DISCONNECTED)
                return (MPTS_EVRET_DELETE);
        else
                return (MPTS_EVRET_OK);
}

static const char *
mptcp_evret2str(ev_ret_t ret)
{
        const char *c = "UNKNOWN";

        switch (ret) {
        case MPTS_EVRET_DELETE:
                c = "MPTS_EVRET_DELETE";
                break;
        case MPTS_EVRET_CONNECT_PENDING:
                c = "MPTS_EVRET_CONNECT_PENDING";
                break;
        case MPTS_EVRET_DISCONNECT_FALLBACK:
                c = "MPTS_EVRET_DISCONNECT_FALLBACK";
                break;
        case MPTS_EVRET_OK:
                c = "MPTS_EVRET_OK";
                break;
        default:
                break;
        }
        return (c);
}

/*
 * Add a reference to a subflow structure; used by MPTS_ADDREF().
 */
void
mptcp_subflow_addref(struct mptsub *mpts, int locked)
{
        if (!locked)
                MPTS_LOCK(mpts);
        else
                MPTS_LOCK_ASSERT_HELD(mpts);

        if (++mpts->mpts_refcnt == 0) {
                panic("%s: mpts %p wraparound refcnt\n", __func__, mpts);
                /* NOTREACHED */
        }
        if (!locked)
                MPTS_UNLOCK(mpts);
}

/*
 * Remove a reference held on a subflow structure; used by MPTS_REMREF();
 */
void
mptcp_subflow_remref(struct mptsub *mpts)
{
        MPTS_LOCK(mpts);
        if (mpts->mpts_refcnt == 0) {
                panic("%s: mpts %p negative refcnt\n", __func__, mpts);
                /* NOTREACHED */
        }
        if (--mpts->mpts_refcnt > 0) {
                MPTS_UNLOCK(mpts);
                return;
        }
        /* callee will unlock and destroy lock */
        mptcp_subflow_free(mpts);
}

/*
 * Issues SOPT_SET on an MPTCP subflow socket; socket must already be locked,
 * caller must ensure that the option can be issued on subflow sockets, via
 * MPOF_SUBFLOW_OK flag.
 */
int
mptcp_subflow_sosetopt(struct mptses *mpte, struct socket *so,
    struct mptopt *mpo)
{
        struct socket *mp_so;
        struct sockopt sopt;
        char buf[32];
        int error;

        VERIFY(mpo->mpo_flags & MPOF_SUBFLOW_OK);
        mpo->mpo_flags &= ~MPOF_INTERIM;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        mp_so = mpte->mpte_mppcb->mpp_socket;

        bzero(&sopt, sizeof (sopt));
        sopt.sopt_dir = SOPT_SET;
        sopt.sopt_level = mpo->mpo_level;
        sopt.sopt_name = mpo->mpo_name;
        sopt.sopt_val = CAST_USER_ADDR_T(&mpo->mpo_intval);
        sopt.sopt_valsize = sizeof (int);
        sopt.sopt_p = kernproc;

        error = sosetoptlock(so, &sopt, 0);     /* already locked */
        if (error == 0) {
                mptcplog((LOG_DEBUG, "MPTCP Socket: "
                    "%s: mp_so 0x%llx sopt %s "
                    "val %d set successful\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    mptcp_sopt2str(mpo->mpo_level, mpo->mpo_name,
                    buf, sizeof (buf)), mpo->mpo_intval),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
        } else {
                mptcplog((LOG_ERR, "MPTCP Socket: "
                    "%s: mp_so 0x%llx sopt %s "
                    "val %d set error %d\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    mptcp_sopt2str(mpo->mpo_level, mpo->mpo_name,
                    buf, sizeof (buf)), mpo->mpo_intval, error),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
        }
        return (error);
}

/*
 * Issues SOPT_GET on an MPTCP subflow socket; socket must already be locked,
 * caller must ensure that the option can be issued on subflow sockets, via
 * MPOF_SUBFLOW_OK flag.
 */
int
mptcp_subflow_sogetopt(struct mptses *mpte, struct socket *so,
    struct mptopt *mpo)
{
        struct socket *mp_so;
        struct sockopt sopt;
        char buf[32];
        int error;

        VERIFY(mpo->mpo_flags & MPOF_SUBFLOW_OK);
        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        mp_so = mpte->mpte_mppcb->mpp_socket;

        bzero(&sopt, sizeof (sopt));
        sopt.sopt_dir = SOPT_GET;
        sopt.sopt_level = mpo->mpo_level;
        sopt.sopt_name = mpo->mpo_name;
        sopt.sopt_val = CAST_USER_ADDR_T(&mpo->mpo_intval);
        sopt.sopt_valsize = sizeof (int);
        sopt.sopt_p = kernproc;

        error = sogetoptlock(so, &sopt, 0);     /* already locked */
        if (error == 0) {
                mptcplog((LOG_DEBUG, "MPTCP Socket: "
                    "%s: mp_so 0x%llx sopt %s "
                    "val %d get successful\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    mptcp_sopt2str(mpo->mpo_level, mpo->mpo_name,
                    buf, sizeof (buf)), mpo->mpo_intval),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
        } else {
                mptcplog((LOG_ERR, "MPTCP Socket: "
                    "%s: mp_so 0x%llx sopt %s get error %d\n",
                    __func__, (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    mptcp_sopt2str(mpo->mpo_level,
                    mpo->mpo_name, buf, sizeof (buf)), error),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_ERR);
        }
        return (error);
}


/*
 * MPTCP garbage collector.
 *
 * This routine is called by the MP domain on-demand, periodic callout,
 * which is triggered when a MPTCP socket is closed.  The callout will
 * repeat as long as this routine returns a non-zero value.
 */
static uint32_t
mptcp_gc(struct mppcbinfo *mppi)
{
        struct mppcb *mpp, *tmpp;
        uint32_t active = 0;

        lck_mtx_assert(&mppi->mppi_lock, LCK_MTX_ASSERT_OWNED);

        TAILQ_FOREACH_SAFE(mpp, &mppi->mppi_pcbs, mpp_entry, tmpp) {
                struct socket *mp_so;
                struct mptses *mpte;
                struct mptcb *mp_tp;

                VERIFY(mpp->mpp_flags & MPP_ATTACHED);
                mp_so = mpp->mpp_socket;
                VERIFY(mp_so != NULL);
                mpte = mptompte(mpp);
                VERIFY(mpte != NULL);
                mp_tp = mpte->mpte_mptcb;
                VERIFY(mp_tp != NULL);

                mptcplog((LOG_DEBUG, "MPTCP Socket: "
                    "%s: mp_so 0x%llx found "
                    "(u=%d,r=%d,s=%d)\n", __func__,
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so), mp_so->so_usecount,
                    mp_so->so_retaincnt, mpp->mpp_state),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                if (!lck_mtx_try_lock(&mpp->mpp_lock)) {
                        mptcplog((LOG_DEBUG, "MPTCP Socket: "
                            "%s: mp_so 0x%llx skipped "
                            "(u=%d,r=%d)\n", __func__,
                            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                            mp_so->so_usecount, mp_so->so_retaincnt),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
                        active++;
                        continue;
                }

                /* check again under the lock */
                if (mp_so->so_usecount > 1) {
                        boolean_t wakeup = FALSE;
                        struct mptsub *mpts, *tmpts;

                        mptcplog((LOG_DEBUG, "MPTCP Socket: "
                            "%s: mp_so 0x%llx skipped "
                            "[u=%d,r=%d] %d %d\n", __func__,
                            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                            mp_so->so_usecount, mp_so->so_retaincnt,
                            mp_tp->mpt_gc_ticks,
                            mp_tp->mpt_state),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                        MPT_LOCK(mp_tp);
                        if (mp_tp->mpt_state >= MPTCPS_FIN_WAIT_1) {
                                if (mp_tp->mpt_gc_ticks > 0)
                                        mp_tp->mpt_gc_ticks--;
                                if (mp_tp->mpt_gc_ticks == 0) {
                                        wakeup = TRUE;
                                        if (mp_tp->mpt_localkey != NULL) {
                                                mptcp_free_key(
                                                    mp_tp->mpt_localkey);
                                                mp_tp->mpt_localkey = NULL;
                                        }
                                }
                        }
                        MPT_UNLOCK(mp_tp);
                        if (wakeup) {
                                TAILQ_FOREACH_SAFE(mpts,
                                    &mpte->mpte_subflows, mpts_entry, tmpts) {
                                        MPTS_LOCK(mpts);
                                        mpts->mpts_flags |= MPTSF_DELETEOK;
                                        if (mpts->mpts_soerror == 0)
                                                mpts->mpts_soerror = ETIMEDOUT;
                                        mptcp_subflow_eupcall(mpts->mpts_socket,
                                            mpts, SO_FILT_HINT_DISCONNECTED);
                                        MPTS_UNLOCK(mpts);
                                }
                        }
                        lck_mtx_unlock(&mpp->mpp_lock);
                        active++;
                        continue;
                }

                if (mpp->mpp_state != MPPCB_STATE_DEAD) {
                        mptcplog((LOG_DEBUG, "MPTCP Socket: "
                            "%s: mp_so 0x%llx skipped "
                            "[u=%d,r=%d,s=%d]\n", __func__,
                            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                            mp_so->so_usecount, mp_so->so_retaincnt,
                            mpp->mpp_state),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
                        lck_mtx_unlock(&mpp->mpp_lock);
                        active++;
                        continue;
                }

                /*
                 * The PCB has been detached, and there is exactly 1 refnct
                 * held by the MPTCP thread.  Signal that thread to terminate,
                 * after which the last refcnt will be released.  That will
                 * allow it to be destroyed below during the next round.
                 */
                if (mp_so->so_usecount == 1) {
                        mptcplog((LOG_DEBUG, "MPTCP Socket: "
                            "%s: mp_so 0x%llx scheduled for "
                            "termination [u=%d,r=%d]\n", __func__,
                            (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                            mp_so->so_usecount, mp_so->so_retaincnt),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                        /* signal MPTCP thread to terminate */
                        mptcp_thread_terminate_signal(mpte);
                        lck_mtx_unlock(&mpp->mpp_lock);
                        active++;
                        continue;
                }

                mptcplog((LOG_DEBUG, "MPTCP Socket: "
                    "%s: mp_so 0x%llx destroyed [u=%d,r=%d]\n",
                    __func__, (u_int64_t)VM_KERNEL_ADDRPERM(mp_so),
                    mp_so->so_usecount, mp_so->so_retaincnt),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                DTRACE_MPTCP4(dispose, struct socket *, mp_so, 
                    struct sockbuf *, &mp_so->so_rcv,
                    struct sockbuf *, &mp_so->so_snd,
                    struct mppcb *, mpp);

                mp_pcbdispose(mpp);
        }

        return (active);
}

/*
 * Drop a MPTCP connection, reporting the specified error.
 */
struct mptses *
mptcp_drop(struct mptses *mpte, struct mptcb *mp_tp, int errno)
{
        struct socket *mp_so;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPT_LOCK_ASSERT_HELD(mp_tp);
        VERIFY(mpte->mpte_mptcb == mp_tp);
        mp_so = mpte->mpte_mppcb->mpp_socket;

        mp_tp->mpt_state = MPTCPS_TERMINATE;
        DTRACE_MPTCP2(state__change, struct mptcb *, mp_tp, 
            uint32_t, 0 /* event */);

        if (errno == ETIMEDOUT && mp_tp->mpt_softerror != 0)
                errno = mp_tp->mpt_softerror;
        mp_so->so_error = errno;

        return (mptcp_close(mpte, mp_tp));
}

/*
 * Close a MPTCP control block.
 */
struct mptses *
mptcp_close(struct mptses *mpte, struct mptcb *mp_tp)
{
        struct socket *mp_so = NULL;
        struct mptsub *mpts = NULL, *tmpts = NULL;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        MPT_LOCK_ASSERT_HELD(mp_tp);
        VERIFY(mpte->mpte_mptcb == mp_tp);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        if (mp_tp->mpt_localkey != NULL) {
                mptcp_free_key(mp_tp->mpt_localkey);
                mp_tp->mpt_localkey = NULL;
        }

        MPT_UNLOCK(mp_tp);
        soisdisconnected(mp_so);

        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_flags & MPTCPF_PEEL_OFF) {
                return (NULL);
        }
        MPT_UNLOCK(mp_tp);

        /* Clean up all subflows */
        TAILQ_FOREACH_SAFE(mpts, &mpte->mpte_subflows, mpts_entry, tmpts) {
                MPTS_LOCK(mpts);
                mpts->mpts_flags |= MPTSF_USER_DISCONNECT;
                mptcp_subflow_disconnect(mpte, mpts, TRUE);
                MPTS_UNLOCK(mpts);
                mptcp_subflow_del(mpte, mpts, TRUE);
        }
        MPT_LOCK(mp_tp);

        return (NULL);
}

void
mptcp_notify_close(struct socket *so)
{
        soevent(so, (SO_FILT_HINT_LOCKED | SO_FILT_HINT_DISCONNECTED));
}

/*
 * Signal MPTCP thread to wake up.
 */
void
mptcp_thread_signal(struct mptses *mpte)
{
        lck_mtx_lock(&mpte->mpte_thread_lock);
        mptcp_thread_signal_locked(mpte);
        lck_mtx_unlock(&mpte->mpte_thread_lock);
}

/*
 * Signal MPTCP thread to wake up (locked version)
 */
static void
mptcp_thread_signal_locked(struct mptses *mpte)
{
        lck_mtx_assert(&mpte->mpte_thread_lock, LCK_MTX_ASSERT_OWNED);

        mpte->mpte_thread_reqs++;
        if (!mpte->mpte_thread_active && mpte->mpte_thread != THREAD_NULL)
                wakeup_one((caddr_t)&mpte->mpte_thread);
}

/*
 * Signal MPTCP thread to terminate.
 */
static void
mptcp_thread_terminate_signal(struct mptses *mpte)
{
        lck_mtx_lock(&mpte->mpte_thread_lock);
        if (mpte->mpte_thread != THREAD_NULL) {
                mpte->mpte_thread = THREAD_NULL;
                mpte->mpte_thread_reqs++;
                if (!mpte->mpte_thread_active)
                        wakeup_one((caddr_t)&mpte->mpte_thread);
        }
        lck_mtx_unlock(&mpte->mpte_thread_lock);
}

/*
 * MPTCP thread workloop.
 */
static void
mptcp_thread_dowork(struct mptses *mpte)
{
        struct socket *mp_so;
        struct mptsub *mpts, *tmpts;
        boolean_t connect_pending = FALSE, disconnect_fallback = FALSE;
        uint64_t mpsofilt_hint_mask = 0;

        MPTE_LOCK(mpte);                /* same as MP socket lock */
        VERIFY(mpte->mpte_mppcb != NULL);
        mp_so = mpte->mpte_mppcb->mpp_socket;
        VERIFY(mp_so != NULL);

        TAILQ_FOREACH_SAFE(mpts, &mpte->mpte_subflows, mpts_entry, tmpts) {
                ev_ret_t ret;

                MPTS_LOCK(mpts);
                MPTS_ADDREF_LOCKED(mpts);       /* for us */
                
                /* Update process ownership based on parent mptcp socket */
                mptcp_update_last_owner(mpts, mp_so);
                
                mptcp_subflow_input(mpte, mpts);

                mptcp_get_rtt_measurement(mpts, mpte);

                ret = mptcp_subflow_events(mpte, mpts, &mpsofilt_hint_mask);

                if (mpts->mpts_flags & MPTSF_ACTIVE) {
                        mptcplog((LOG_DEBUG, "MPTCP Socket: "
                            "%s: cid %d \n", __func__,
                            mpts->mpts_connid),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
                        (void) mptcp_subflow_output(mpte, mpts);
                }

                /*
                 * If MPTCP socket is closed, disconnect all subflows.
                 * This will generate a disconnect event which will
                 * be handled during the next iteration, causing a
                 * non-zero error to be returned above.
                 */
                if (mp_so->so_flags & SOF_PCBCLEARING)
                        mptcp_subflow_disconnect(mpte, mpts, FALSE);
                MPTS_UNLOCK(mpts);

                switch (ret) {
                case MPTS_EVRET_OK:
                        /* nothing to do */
                        break;
                case MPTS_EVRET_DELETE:
                        mptcp_subflow_del(mpte, mpts, TRUE);
                        break;
                case MPTS_EVRET_CONNECT_PENDING:
                        connect_pending = TRUE;
                        break;
                case MPTS_EVRET_DISCONNECT_FALLBACK:
                        disconnect_fallback = TRUE;
                        break;
                default:
                        mptcplog((LOG_DEBUG,
                            "MPTCP Socket: %s: mptcp_subflow_events "
                            "returned invalid value: %d\n",  __func__,
                            ret),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
                        break;
                }
                MPTS_REMREF(mpts);              /* ours */
        }

        if (mpsofilt_hint_mask) {
                soevent(mp_so, mpsofilt_hint_mask);
        }

        if (!connect_pending && !disconnect_fallback) {
                MPTE_UNLOCK(mpte);
                return;
        }

        TAILQ_FOREACH_SAFE(mpts, &mpte->mpte_subflows, mpts_entry, tmpts) {
                MPTS_LOCK(mpts);
                if (disconnect_fallback) {
                        struct socket *so = NULL;
                        struct inpcb *inp = NULL;
                        struct tcpcb *tp = NULL;

                        if (mpts->mpts_flags & MPTSF_MP_DEGRADED) {
                                MPTS_UNLOCK(mpts);
                                continue;
                        }

                        mpts->mpts_flags |= MPTSF_MP_DEGRADED;

                        if (mpts->mpts_flags & (MPTSF_DISCONNECTING|
                            MPTSF_DISCONNECTED|MPTSF_CONNECT_PENDING)) {
                                MPTS_UNLOCK(mpts);
                                continue;
                        }
                        so = mpts->mpts_socket;

                        /*
                         * The MPTCP connection has degraded to a fallback
                         * mode, so there is no point in keeping this subflow
                         * regardless of its MPTCP-readiness state, unless it
                         * is the primary one which we use for fallback.  This
                         * assumes that the subflow used for fallback is the
                         * ACTIVE one.
                         */

                        socket_lock(so, 1);
                        inp = sotoinpcb(so);
                        tp = intotcpcb(inp);
                        tp->t_mpflags &=
                            ~(TMPF_MPTCP_READY|TMPF_MPTCP_TRUE);
                        tp->t_mpflags |= TMPF_TCP_FALLBACK;
                        if (mpts->mpts_flags & MPTSF_ACTIVE) {
                                socket_unlock(so, 1);
                                MPTS_UNLOCK(mpts);
                                continue;
                        }
                        tp->t_mpflags |= TMPF_RESET;
                        soevent(so, SO_FILT_HINT_LOCKED | SO_FILT_HINT_MUSTRST);
                        socket_unlock(so, 1);

                } else if (connect_pending) {
                        /*
                         * If delayed subflow start is set and cellular,
                         * delay the connect till a retransmission timeout
                         */

                        if ((mptcp_delayed_subf_start) &&
                            (IFNET_IS_CELLULAR(mpts->mpts_outif))) {
                                MPTS_UNLOCK(mpts);
                                continue;
                        }

                        /*
                         * The MPTCP connection has progressed to a state
                         * where it supports full multipath semantics; allow
                         * additional joins to be attempted for all subflows
                         * that are in the PENDING state.
                         */
                        if (mpts->mpts_flags & MPTSF_CONNECT_PENDING) {
                                (void) mptcp_subflow_soconnectx(mpte, mpts);
                        }
                }
                MPTS_UNLOCK(mpts);
        }

        MPTE_UNLOCK(mpte);
}

/*
 * MPTCP thread.
 */
static void
mptcp_thread_func(void *v, wait_result_t w)
{
#pragma unused(w)
        struct mptses *mpte = v;
        struct timespec *ts = NULL;

        VERIFY(mpte != NULL);

        lck_mtx_lock_spin(&mpte->mpte_thread_lock);

        for (;;) {
                lck_mtx_assert(&mpte->mpte_thread_lock, LCK_MTX_ASSERT_OWNED);

                if (mpte->mpte_thread != THREAD_NULL) {
                        (void) msleep(&mpte->mpte_thread,
                            &mpte->mpte_thread_lock, (PZERO - 1) | PSPIN,
                            __func__, ts);
                }

                /* MPTCP socket is closed? */
                if (mpte->mpte_thread == THREAD_NULL) {
                        lck_mtx_unlock(&mpte->mpte_thread_lock);
                        /* callee will destroy thread lock */
                        mptcp_thread_destroy(mpte);
                        /* NOTREACHED */
                        return;
                }

                mpte->mpte_thread_active = 1;
                for (;;) {
                        uint32_t reqs = mpte->mpte_thread_reqs;

                        lck_mtx_unlock(&mpte->mpte_thread_lock);
                        mptcp_thread_dowork(mpte);
                        lck_mtx_lock_spin(&mpte->mpte_thread_lock);

                        /* if there's no pending request, we're done */
                        if (reqs == mpte->mpte_thread_reqs ||
                            mpte->mpte_thread == THREAD_NULL)
                                break;
                }
                mpte->mpte_thread_reqs = 0;
                mpte->mpte_thread_active = 0;
        }
}

/*
 * Destroy a MTCP thread, to be called in the MPTCP thread context
 * upon receiving an indication to self-terminate.  This routine
 * will not return, as the current thread is terminated at the end.
 */
static void
mptcp_thread_destroy(struct mptses *mpte)
{
        struct socket *mp_so;

        MPTE_LOCK(mpte);                /* same as MP socket lock */
        VERIFY(mpte->mpte_thread == THREAD_NULL);
        VERIFY(mpte->mpte_mppcb != NULL);

        mptcp_sesdestroy(mpte);

        mp_so = mpte->mpte_mppcb->mpp_socket;
        VERIFY(mp_so != NULL);
        VERIFY(mp_so->so_usecount != 0);
        mp_so->so_usecount--;           /* for thread */
        mpte->mpte_mppcb->mpp_flags |= MPP_DEFUNCT;
        MPTE_UNLOCK(mpte);

        /* for the extra refcnt from kernel_thread_start() */
        thread_deallocate(current_thread());
        /* this is the end */
        thread_terminate(current_thread());
        /* NOTREACHED */
}

/*
 * Protocol pr_lock callback.
 */
int
mptcp_lock(struct socket *mp_so, int refcount, void *lr)
{
        struct mppcb *mpp = sotomppcb(mp_so);
        void *lr_saved;

        if (lr == NULL)
                lr_saved = __builtin_return_address(0);
        else
                lr_saved = lr;

        if (mpp == NULL) {
                panic("%s: so=%p NO PCB! lr=%p lrh= %s\n", __func__,
                    mp_so, lr_saved, solockhistory_nr(mp_so));
                /* NOTREACHED */
        }
        lck_mtx_lock(&mpp->mpp_lock);

        if (mp_so->so_usecount < 0) {
                panic("%s: so=%p so_pcb=%p lr=%p ref=%x lrh= %s\n", __func__,
                    mp_so, mp_so->so_pcb, lr_saved, mp_so->so_usecount,
                    solockhistory_nr(mp_so));
                /* NOTREACHED */
        }
        if (refcount != 0)
                mp_so->so_usecount++;
        mp_so->lock_lr[mp_so->next_lock_lr] = lr_saved;
        mp_so->next_lock_lr = (mp_so->next_lock_lr + 1) % SO_LCKDBG_MAX;

        return (0);
}

/*
 * Protocol pr_unlock callback.
 */
int
mptcp_unlock(struct socket *mp_so, int refcount, void *lr)
{
        struct mppcb *mpp = sotomppcb(mp_so);
        void *lr_saved;

        if (lr == NULL)
                lr_saved = __builtin_return_address(0);
        else
                lr_saved = lr;

        if (mpp == NULL) {
                panic("%s: so=%p NO PCB usecount=%x lr=%p lrh= %s\n", __func__,
                    mp_so, mp_so->so_usecount, lr_saved,
                    solockhistory_nr(mp_so));
                /* NOTREACHED */
        }
        lck_mtx_assert(&mpp->mpp_lock, LCK_MTX_ASSERT_OWNED);

        if (refcount != 0)
                mp_so->so_usecount--;

        if (mp_so->so_usecount < 0) {
                panic("%s: so=%p usecount=%x lrh= %s\n", __func__,
                    mp_so, mp_so->so_usecount, solockhistory_nr(mp_so));
                /* NOTREACHED */
        }
        mp_so->unlock_lr[mp_so->next_unlock_lr] = lr_saved;
        mp_so->next_unlock_lr = (mp_so->next_unlock_lr + 1) % SO_LCKDBG_MAX;
        lck_mtx_unlock(&mpp->mpp_lock);

        return (0);
}

/*
 * Protocol pr_getlock callback.
 */
lck_mtx_t *
mptcp_getlock(struct socket *mp_so, int locktype)
{
#pragma unused(locktype)
        struct mppcb *mpp = sotomppcb(mp_so);

        if (mpp == NULL) {
                panic("%s: so=%p NULL so_pcb %s\n", __func__, mp_so,
                    solockhistory_nr(mp_so));
                /* NOTREACHED */
        }
        if (mp_so->so_usecount < 0) {
                panic("%s: so=%p usecount=%x lrh= %s\n", __func__,
                    mp_so, mp_so->so_usecount, solockhistory_nr(mp_so));
                /* NOTREACHED */
        }
        return (&mpp->mpp_lock);
}

/*
 * Key generation functions
 */
static void
mptcp_generate_unique_key(struct mptcp_key_entry *key_entry)
{
        struct mptcp_key_entry *key_elm;
try_again:
        read_random(&key_entry->mkey_value, sizeof (key_entry->mkey_value));
        if (key_entry->mkey_value == 0)
                goto try_again;
        mptcp_do_sha1(&key_entry->mkey_value, key_entry->mkey_digest,
            sizeof (key_entry->mkey_digest));

        LIST_FOREACH(key_elm, &mptcp_keys_pool, mkey_next) {
                if (key_elm->mkey_value == key_entry->mkey_value) {
                        goto try_again;
                }
                if (bcmp(key_elm->mkey_digest, key_entry->mkey_digest, 4) ==
                    0) {
                        goto try_again;
                }
        }
}

static mptcp_key_t *
mptcp_reserve_key(void)
{
        struct mptcp_key_entry *key_elm;
        struct mptcp_key_entry *found_elm = NULL;

        lck_mtx_lock(&mptcp_keys_pool.mkph_lock);
        LIST_FOREACH(key_elm, &mptcp_keys_pool, mkey_next) {
                if (key_elm->mkey_flags == MKEYF_FREE) {
                        key_elm->mkey_flags = MKEYF_INUSE;
                        found_elm = key_elm;
                        break;
                }
        }
        lck_mtx_unlock(&mptcp_keys_pool.mkph_lock);

        if (found_elm) {
                return (&found_elm->mkey_value);
        }

        key_elm = (struct mptcp_key_entry *)
            zalloc(mptcp_keys_pool.mkph_key_entry_zone);
        key_elm->mkey_flags = MKEYF_INUSE;

        lck_mtx_lock(&mptcp_keys_pool.mkph_lock);
        mptcp_generate_unique_key(key_elm);
        LIST_INSERT_HEAD(&mptcp_keys_pool, key_elm, mkey_next);
        mptcp_keys_pool.mkph_count += 1;
        lck_mtx_unlock(&mptcp_keys_pool.mkph_lock);
        return (&key_elm->mkey_value);
}

static caddr_t
mptcp_get_stored_digest(mptcp_key_t *key)
{
        struct mptcp_key_entry *key_holder;
        caddr_t digest = NULL;

        lck_mtx_lock(&mptcp_keys_pool.mkph_lock);
        key_holder = (struct mptcp_key_entry *)(void *)((caddr_t)key -
            offsetof(struct mptcp_key_entry, mkey_value));
        if (key_holder->mkey_flags != MKEYF_INUSE)
                panic_plain("%s", __func__);
        digest = &key_holder->mkey_digest[0];
        lck_mtx_unlock(&mptcp_keys_pool.mkph_lock);
        return (digest);
}

void
mptcp_free_key(mptcp_key_t *key)
{
        struct mptcp_key_entry *key_holder;
        struct mptcp_key_entry *key_elm;
        int pt = RandomULong();

        lck_mtx_lock(&mptcp_keys_pool.mkph_lock);
        key_holder = (struct mptcp_key_entry *)(void*)((caddr_t)key -
            offsetof(struct mptcp_key_entry, mkey_value));
        key_holder->mkey_flags = MKEYF_FREE;

        LIST_REMOVE(key_holder, mkey_next);
        mptcp_keys_pool.mkph_count -= 1;

        /* Free half the time */
        if (pt & 0x01) {
                zfree(mptcp_keys_pool.mkph_key_entry_zone, key_holder);
        } else {
                /* Insert it at random point to avoid early reuse */
                int i = 0;
                if (mptcp_keys_pool.mkph_count > 1) {
                        pt = pt % (mptcp_keys_pool.mkph_count - 1);
                        LIST_FOREACH(key_elm, &mptcp_keys_pool, mkey_next) {
                                if (++i >= pt) {
                                        LIST_INSERT_AFTER(key_elm, key_holder,
                                            mkey_next);
                                        break;
                                }
                        }
                        if (i < pt)
                                panic("missed insertion");
                } else {
                        LIST_INSERT_HEAD(&mptcp_keys_pool, key_holder,
                            mkey_next);
                }
                mptcp_keys_pool.mkph_count += 1;
        }
        lck_mtx_unlock(&mptcp_keys_pool.mkph_lock);
}

static void
mptcp_key_pool_init(void)
{
        int i;
        struct mptcp_key_entry *key_entry;

        LIST_INIT(&mptcp_keys_pool);
        mptcp_keys_pool.mkph_count = 0;

        mptcp_keys_pool.mkph_key_elm_sz = (vm_size_t)
            (sizeof (struct mptcp_key_entry));
        mptcp_keys_pool.mkph_key_entry_zone = zinit(
            mptcp_keys_pool.mkph_key_elm_sz,
            MPTCP_MX_KEY_ALLOCS * mptcp_keys_pool.mkph_key_elm_sz,
            MPTCP_MX_PREALLOC_ZONE_SZ, "mptkeys");
        if (mptcp_keys_pool.mkph_key_entry_zone == NULL) {
                panic("%s: unable to allocate MPTCP keys zone \n", __func__);
                /* NOTREACHED */
        }
        zone_change(mptcp_keys_pool.mkph_key_entry_zone, Z_CALLERACCT, FALSE);
        zone_change(mptcp_keys_pool.mkph_key_entry_zone, Z_EXPAND, TRUE);

        for (i = 0; i < MPTCP_KEY_PREALLOCS_MX; i++) {
                key_entry = (struct mptcp_key_entry *)
                    zalloc(mptcp_keys_pool.mkph_key_entry_zone);
                key_entry->mkey_flags = MKEYF_FREE;
                mptcp_generate_unique_key(key_entry);
                LIST_INSERT_HEAD(&mptcp_keys_pool, key_entry, mkey_next);
                mptcp_keys_pool.mkph_count += 1;
        }
        lck_mtx_init(&mptcp_keys_pool.mkph_lock, mtcbinfo.mppi_lock_grp,
            mtcbinfo.mppi_lock_attr);
}

/*
 * MPTCP Join support
 */

static void
mptcp_attach_to_subf(struct socket *so, struct mptcb *mp_tp,
    uint8_t addr_id)
{
        struct tcpcb *tp = sototcpcb(so);
        struct mptcp_subf_auth_entry *sauth_entry;
        MPT_LOCK_ASSERT_NOTHELD(mp_tp);

        MPT_LOCK_SPIN(mp_tp);
        tp->t_mptcb = mp_tp;
        /*
         * The address ID of the first flow is implicitly 0.
         */
        if (mp_tp->mpt_state == MPTCPS_CLOSED) {
                tp->t_local_aid = 0;
        } else {
                tp->t_local_aid = addr_id;
                tp->t_mpflags |= (TMPF_PREESTABLISHED | TMPF_JOINED_FLOW);
                so->so_flags |= SOF_MP_SEC_SUBFLOW;
        }
        MPT_UNLOCK(mp_tp);
        sauth_entry = zalloc(mpt_subauth_zone);
        sauth_entry->msae_laddr_id = tp->t_local_aid;
        sauth_entry->msae_raddr_id = 0;
        sauth_entry->msae_raddr_rand = 0;
try_again:
        sauth_entry->msae_laddr_rand = RandomULong();
        if (sauth_entry->msae_laddr_rand == 0)
                goto try_again;
        MPT_LOCK_SPIN(mp_tp);
        LIST_INSERT_HEAD(&mp_tp->mpt_subauth_list, sauth_entry, msae_next);
        MPT_UNLOCK(mp_tp);
}

static void
mptcp_detach_mptcb_from_subf(struct mptcb *mp_tp, struct socket *so)
{
        struct mptcp_subf_auth_entry *sauth_entry;
        struct tcpcb *tp = NULL;
        int found = 0;

        socket_lock(so, 0);
        tp = sototcpcb(so);
        if (tp == NULL) {
                socket_unlock(so, 0);
                return;
        }

        MPT_LOCK(mp_tp);
        LIST_FOREACH(sauth_entry, &mp_tp->mpt_subauth_list, msae_next) {
                if (sauth_entry->msae_laddr_id == tp->t_local_aid) {
                        found = 1;
                        break;
                }
        }
        if (found) {
                LIST_REMOVE(sauth_entry, msae_next);
        }
        MPT_UNLOCK(mp_tp);

        if (found)
                zfree(mpt_subauth_zone, sauth_entry);

        tp->t_mptcb = NULL;
        socket_unlock(so, 0);
}

void
mptcp_get_rands(mptcp_addr_id addr_id, struct mptcb *mp_tp, u_int32_t *lrand,
    u_int32_t *rrand)
{
        struct mptcp_subf_auth_entry *sauth_entry;
        MPT_LOCK_ASSERT_NOTHELD(mp_tp);

        MPT_LOCK(mp_tp);
        LIST_FOREACH(sauth_entry, &mp_tp->mpt_subauth_list, msae_next) {
                if (sauth_entry->msae_laddr_id == addr_id) {
                        if (lrand)
                                *lrand = sauth_entry->msae_laddr_rand;
                        if (rrand)
                                *rrand = sauth_entry->msae_raddr_rand;
                        break;
                }
        }
        MPT_UNLOCK(mp_tp);
}

void
mptcp_set_raddr_rand(mptcp_addr_id laddr_id, struct mptcb *mp_tp,
    mptcp_addr_id raddr_id, u_int32_t raddr_rand)
{
        struct mptcp_subf_auth_entry *sauth_entry;
        MPT_LOCK_ASSERT_NOTHELD(mp_tp);

        MPT_LOCK(mp_tp);
        LIST_FOREACH(sauth_entry, &mp_tp->mpt_subauth_list, msae_next) {
                if (sauth_entry->msae_laddr_id == laddr_id) {
                        if ((sauth_entry->msae_raddr_id != 0) &&
                            (sauth_entry->msae_raddr_id != raddr_id)) {
                                mptcplog((LOG_ERR, "MPTCP Socket: %s mismatched"
                                    " address ids %d %d \n", __func__, raddr_id,
                                    sauth_entry->msae_raddr_id),
                                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);
                                MPT_UNLOCK(mp_tp);
                                return;
                        }
                        sauth_entry->msae_raddr_id = raddr_id;
                        if ((sauth_entry->msae_raddr_rand != 0) &&
                            (sauth_entry->msae_raddr_rand != raddr_rand)) {
                                mptcplog((LOG_ERR, "MPTCP Socket: "
                                    "%s: dup SYN_ACK %d %d \n",
                                    __func__, raddr_rand,
                                    sauth_entry->msae_raddr_rand),
                                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);
                                MPT_UNLOCK(mp_tp);
                                return;
                        }
                        sauth_entry->msae_raddr_rand = raddr_rand;
                        MPT_UNLOCK(mp_tp);
                        return;
                }
        }
        MPT_UNLOCK(mp_tp);
}

/*
 * SHA1 support for MPTCP
 */
static int
mptcp_do_sha1(mptcp_key_t *key, char *sha_digest, int digest_len)
{
        SHA1_CTX sha1ctxt;
        const unsigned char *sha1_base;
        int sha1_size;

        if (digest_len != SHA1_RESULTLEN) {
                return (FALSE);
        }

        sha1_base = (const unsigned char *) key;
        sha1_size = sizeof (mptcp_key_t);
        SHA1Init(&sha1ctxt);
        SHA1Update(&sha1ctxt, sha1_base, sha1_size);
        SHA1Final(sha_digest, &sha1ctxt);
        return (TRUE);
}

void
mptcp_hmac_sha1(mptcp_key_t key1, mptcp_key_t key2,
        u_int32_t rand1, u_int32_t rand2, u_char *digest, int digest_len)
{
        SHA1_CTX  sha1ctxt;
        mptcp_key_t key_ipad[8] = {0}; /* key XOR'd with inner pad */
        mptcp_key_t key_opad[8] = {0}; /* key XOR'd with outer pad */
        u_int32_t data[2];
        int i;

        bzero(digest, digest_len);

        /* Set up the Key for HMAC */
        key_ipad[0] = key1;
        key_ipad[1] = key2;

        key_opad[0] = key1;
        key_opad[1] = key2;

        /* Set up the message for HMAC */
        data[0] = rand1;
        data[1] = rand2;

        /* Key is 512 block length, so no need to compute hash */

        /* Compute SHA1(Key XOR opad, SHA1(Key XOR ipad, data)) */

        for (i = 0; i < 8; i++) {
                key_ipad[i] ^= 0x3636363636363636;
                key_opad[i] ^= 0x5c5c5c5c5c5c5c5c;
        }

        /* Perform inner SHA1 */
        SHA1Init(&sha1ctxt);
        SHA1Update(&sha1ctxt, (unsigned char *)key_ipad, sizeof (key_ipad));
        SHA1Update(&sha1ctxt, (unsigned char *)data, sizeof (data));
        SHA1Final(digest, &sha1ctxt);

        /* Perform outer SHA1 */
        SHA1Init(&sha1ctxt);
        SHA1Update(&sha1ctxt, (unsigned char *)key_opad, sizeof (key_opad));
        SHA1Update(&sha1ctxt, (unsigned char *)digest, SHA1_RESULTLEN);
        SHA1Final(digest, &sha1ctxt);
}

/*
 * corresponds to MAC-B = MAC (Key=(Key-B+Key-A), Msg=(R-B+R-A))
 * corresponds to MAC-A = MAC (Key=(Key-A+Key-B), Msg=(R-A+R-B))
 */
void
mptcp_get_hmac(mptcp_addr_id aid, struct mptcb *mp_tp, u_char *digest,
    int digest_len)
{
        uint32_t lrand, rrand;
        mptcp_key_t localkey, remotekey;
        MPT_LOCK_ASSERT_NOTHELD(mp_tp);

        if (digest_len != SHA1_RESULTLEN)
                return;

        lrand = rrand = 0;
        mptcp_get_rands(aid, mp_tp, &lrand, &rrand);
        MPT_LOCK_SPIN(mp_tp);
        localkey = *mp_tp->mpt_localkey;
        remotekey = mp_tp->mpt_remotekey;
        MPT_UNLOCK(mp_tp);
        mptcp_hmac_sha1(localkey, remotekey, lrand, rrand, digest,
            digest_len);
}

u_int64_t
mptcp_get_trunced_hmac(mptcp_addr_id aid, struct mptcb *mp_tp)
{
        u_char digest[SHA1_RESULTLEN];
        u_int64_t trunced_digest;

        mptcp_get_hmac(aid, mp_tp, &digest[0], sizeof (digest));
        bcopy(digest, &trunced_digest, 8);
        return (trunced_digest);
}

/*
 * Authentication data generation
 */
int
mptcp_generate_token(char *sha_digest, int sha_digest_len, caddr_t token,
    int token_len)
{
        VERIFY(token_len == sizeof (u_int32_t));
        VERIFY(sha_digest_len == SHA1_RESULTLEN);

        /* Most significant 32 bits of the SHA1 hash */
        bcopy(sha_digest, token, sizeof (u_int32_t));
        return (TRUE);
}

int
mptcp_generate_idsn(char *sha_digest, int sha_digest_len, caddr_t idsn,
    int idsn_len)
{
        VERIFY(idsn_len == sizeof (u_int64_t));
        VERIFY(sha_digest_len == SHA1_RESULTLEN);

        /*
         * Least significant 64 bits of the SHA1 hash
         */

        idsn[7] = sha_digest[12];
        idsn[6] = sha_digest[13];
        idsn[5] = sha_digest[14];
        idsn[4] = sha_digest[15];
        idsn[3] = sha_digest[16];
        idsn[2] = sha_digest[17];
        idsn[1] = sha_digest[18];
        idsn[0] = sha_digest[19];
        return (TRUE);
}

static int
mptcp_init_authparms(struct mptcb *mp_tp)
{
        caddr_t local_digest = NULL;
        char remote_digest[MPTCP_SHA1_RESULTLEN];
        MPT_LOCK_ASSERT_HELD(mp_tp);

        /* Only Version 0 is supported for auth purposes */
        if (mp_tp->mpt_version != MPTCP_STD_VERSION_0)
                return (-1);

        /* Setup local and remote tokens and Initial DSNs */
        local_digest = mptcp_get_stored_digest(mp_tp->mpt_localkey);
        mptcp_generate_token(local_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_localtoken, sizeof (mp_tp->mpt_localtoken));
        mptcp_generate_idsn(local_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_local_idsn, sizeof (u_int64_t));

        if (!mptcp_do_sha1(&mp_tp->mpt_remotekey, remote_digest,
            SHA1_RESULTLEN)) {
                mptcplog((LOG_ERR, "MPTCP Socket: %s: unexpected failure",
                    __func__), MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);
                return (-1);
        }
        mptcp_generate_token(remote_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_remotetoken, sizeof (mp_tp->mpt_localtoken));
        mptcp_generate_idsn(remote_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_remote_idsn, sizeof (u_int64_t));
        return (0);
}

static void
mptcp_init_statevars(struct mptcb *mp_tp)
{
        MPT_LOCK_ASSERT_HELD(mp_tp);

        /* The subflow SYN is also first MPTCP byte */
        mp_tp->mpt_snduna = mp_tp->mpt_sndmax = mp_tp->mpt_local_idsn + 1;
        mp_tp->mpt_sndnxt = mp_tp->mpt_snduna;

        mp_tp->mpt_rcvatmark = mp_tp->mpt_rcvnxt = mp_tp->mpt_remote_idsn + 1;
}

static void
mptcp_conn_properties(struct mptcb *mp_tp)
{
        /* There is only Version 0 at this time */
        mp_tp->mpt_version = MPTCP_STD_VERSION_0;

        /* Set DSS checksum flag */
        if (mptcp_dss_csum)
                mp_tp->mpt_flags |= MPTCPF_CHECKSUM;

        /* Set up receive window */
        mp_tp->mpt_rcvwnd = mptcp_sbspace(mp_tp);

        /* Set up gc ticks */
        mp_tp->mpt_gc_ticks = MPT_GC_TICKS;
}

/*
 * Helper Functions
 */
mptcp_token_t
mptcp_get_localtoken(void* mptcb_arg)
{
        struct mptcb *mp_tp = (struct mptcb *)mptcb_arg;
        return (mp_tp->mpt_localtoken);
}

mptcp_token_t
mptcp_get_remotetoken(void* mptcb_arg)
{
        struct mptcb *mp_tp = (struct mptcb *)mptcb_arg;
        return (mp_tp->mpt_remotetoken);
}

u_int64_t
mptcp_get_localkey(void* mptcb_arg)
{
        struct mptcb *mp_tp = (struct mptcb *)mptcb_arg;
        if (mp_tp->mpt_localkey != NULL)
                return (*mp_tp->mpt_localkey);
        else
                return (0);
}

u_int64_t
mptcp_get_remotekey(void* mptcb_arg)
{
        struct mptcb *mp_tp = (struct mptcb *)mptcb_arg;
        return (mp_tp->mpt_remotekey);
}

void
mptcp_send_dfin(struct socket *so)
{
        struct tcpcb *tp = NULL;
        struct inpcb *inp = NULL;

        inp = sotoinpcb(so);
        if (!inp)
                return;

        tp = intotcpcb(inp);
        if (!tp)
                return;

        if (!(tp->t_mpflags & TMPF_RESET))
                tp->t_mpflags |= TMPF_SEND_DFIN;
}

/*
 * Data Sequence Mapping routines
 */
void
mptcp_insert_dsn(struct mppcb *mpp, struct mbuf *m)
{
        struct mptcb *mp_tp;

        if (m == NULL)
                return;

        __IGNORE_WCASTALIGN(mp_tp = &((struct mpp_mtp *)mpp)->mtcb);
        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED) {
                MPT_UNLOCK(mp_tp);
                panic("%s: data write before establishment.",
                    __func__);
                return;
        }

        while (m) {
                VERIFY(m->m_flags & M_PKTHDR);
                m->m_pkthdr.pkt_flags |= (PKTF_MPTCP | PKTF_MPSO);
                m->m_pkthdr.mp_dsn = mp_tp->mpt_sndmax;
                m->m_pkthdr.mp_rlen = m_pktlen(m);
                mp_tp->mpt_sndmax += m_pktlen(m);
                m = m->m_next;
        }
        MPT_UNLOCK(mp_tp);
}

void
mptcp_preproc_sbdrop(struct mbuf *m, unsigned int len)
{
        u_int32_t sub_len = 0;

        while (m) {
                VERIFY(m->m_flags & M_PKTHDR);

                if (m->m_pkthdr.pkt_flags & PKTF_MPTCP) {
                        sub_len = m->m_pkthdr.mp_rlen;

                        if (sub_len < len) {
                                m->m_pkthdr.mp_dsn += sub_len;
                                if (!(m->m_pkthdr.pkt_flags & PKTF_MPSO)) {
                                        m->m_pkthdr.mp_rseq += sub_len;
                                }
                                m->m_pkthdr.mp_rlen = 0;
                                len -= sub_len;
                        } else {
                                /* sub_len >= len */
                                m->m_pkthdr.mp_dsn += len;
                                if (!(m->m_pkthdr.pkt_flags & PKTF_MPSO)) {
                                        m->m_pkthdr.mp_rseq += len;
                                }
                                mptcplog((LOG_DEBUG, "MPTCP Sender: "
                                    "%s: dsn 0x%llu ssn %u len %d %d\n",
                                    __func__,
                                    m->m_pkthdr.mp_dsn, m->m_pkthdr.mp_rseq,
                                    m->m_pkthdr.mp_rlen, len),
                                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
                                m->m_pkthdr.mp_rlen -= len;
                                return;
                        }
                } else {
                        panic("%s: MPTCP tag not set", __func__);
                        /* NOTREACHED */
                }
                m = m->m_next;
        }
}

/* Obtain the DSN mapping stored in the mbuf */
void
mptcp_output_getm_dsnmap32(struct socket *so, int off, uint32_t datalen,
    u_int32_t *dsn, u_int32_t *relseq, u_int16_t *data_len, u_int64_t *dsn64p)
{
        u_int64_t dsn64;

        mptcp_output_getm_dsnmap64(so, off, datalen, &dsn64, relseq, data_len);
        *dsn = (u_int32_t)MPTCP_DATASEQ_LOW32(dsn64);
        *dsn64p = dsn64;
}

void
mptcp_output_getm_dsnmap64(struct socket *so, int off, uint32_t datalen,
    u_int64_t *dsn, u_int32_t *relseq, u_int16_t *data_len)
{
        struct mbuf *m = so->so_snd.sb_mb;
        struct mbuf *mnext = NULL;
        uint32_t runlen = 0;
        u_int64_t dsn64;
        uint32_t contig_len = 0;

        if (m == NULL)
                return;

        if (off < 0)
                return;
        /*
         * In the subflow socket, the DSN sequencing can be discontiguous,
         * but the subflow sequence mapping is contiguous. Use the subflow
         * sequence property to find the right mbuf and corresponding dsn
         * mapping.
         */

        while (m) {
                VERIFY(m->m_pkthdr.pkt_flags & PKTF_MPTCP);
                VERIFY(m->m_flags & M_PKTHDR);

                if ((unsigned int)off >= m->m_pkthdr.mp_rlen) {
                        off -= m->m_pkthdr.mp_rlen;
                        m = m->m_next;
                } else {
                        break;
                }
        }

        if (m == NULL) {
                panic("%s: bad offset", __func__);
                /* NOTREACHED */
        }

        dsn64 = m->m_pkthdr.mp_dsn + off;
        *dsn = dsn64;
        *relseq = m->m_pkthdr.mp_rseq + off;

        /*
         * Now find the last contiguous byte and its length from
         * start.
         */
        runlen = m->m_pkthdr.mp_rlen - off;
        contig_len = runlen;

        /* If datalen does not span multiple mbufs, return */
        if (datalen <= runlen) {
                *data_len = min(datalen, UINT16_MAX);
                return;
        }

        mnext = m->m_next;
        while (datalen > runlen) {
                if (mnext == NULL) {
                        panic("%s: bad datalen = %d, %d %d", __func__, datalen,
                            runlen, off);
                        /* NOTREACHED */
                }
                VERIFY(mnext->m_flags & M_PKTHDR);
                VERIFY(mnext->m_pkthdr.pkt_flags & PKTF_MPTCP);

                /*
                 * case A. contiguous DSN stream
                 * case B. discontiguous DSN stream
                 */
                if (mnext->m_pkthdr.mp_dsn == (dsn64 + runlen)) {
                        /* case A */
                        runlen += mnext->m_pkthdr.mp_rlen;
                        contig_len += mnext->m_pkthdr.mp_rlen;
                        mptcplog((LOG_DEBUG, "MPTCP Sender: %s: contig \n",
                            __func__), MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
                } else {
                        /* case B */
                        mptcplog((LOG_DEBUG, "MPTCP Sender: "
                            "%s: discontig datalen %d contig_len %d cc %d \n",
                            __func__, datalen, contig_len, so->so_snd.sb_cc),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
                        break;
                }
                mnext = mnext->m_next;
        }
        datalen = min(datalen, UINT16_MAX);
        *data_len = min(datalen, contig_len);
        mptcplog((LOG_DEBUG, "MPTCP Sender: "
            "%s: %llu %u %d %d \n", __func__,
            *dsn, *relseq, *data_len, off),
            MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
}

/*
 * MPTCP's notion of the next insequence Data Sequence number is adjusted
 * here. It must be called from mptcp_adj_rmap() which is called only after
 * reassembly of out of order data. The rcvnxt variable must
 * be updated only when atleast some insequence new data is received.
 */
static void
mptcp_adj_rcvnxt(struct tcpcb *tp, struct mbuf *m)
{
        struct mptcb *mp_tp = tptomptp(tp);

        if (mp_tp == NULL)
                return;
        MPT_LOCK(mp_tp);
        if ((MPTCP_SEQ_GEQ(mp_tp->mpt_rcvnxt, m->m_pkthdr.mp_dsn)) &&
            (MPTCP_SEQ_LEQ(mp_tp->mpt_rcvnxt, (m->m_pkthdr.mp_dsn +
            m->m_pkthdr.mp_rlen)))) {
                mp_tp->mpt_rcvnxt = m->m_pkthdr.mp_dsn + m->m_pkthdr.mp_rlen;
        }
        MPT_UNLOCK(mp_tp);
}

/*
 * Note that this is called only from tcp_input() via mptcp_input_preproc()
 * tcp_input() may trim data after the dsn mapping is inserted into the mbuf.
 * When it trims data tcp_input calls m_adj() which does not remove the
 * m_pkthdr even if the m_len becomes 0 as a result of trimming the mbuf.
 * The dsn map insertion cannot be delayed after trim, because data can be in
 * the reassembly queue for a while and the DSN option info in tp will be
 * overwritten for every new packet received.
 * The dsn map will be adjusted just prior to appending to subflow sockbuf
 * with mptcp_adj_rmap()
 */
void
mptcp_insert_rmap(struct tcpcb *tp, struct mbuf *m)
{
        VERIFY(!(m->m_pkthdr.pkt_flags & PKTF_MPTCP));

        if (tp->t_mpflags & TMPF_EMBED_DSN) {
                VERIFY(m->m_flags & M_PKTHDR);
                m->m_pkthdr.mp_dsn = tp->t_rcv_map.mpt_dsn;
                m->m_pkthdr.mp_rseq = tp->t_rcv_map.mpt_sseq;
                m->m_pkthdr.mp_rlen = tp->t_rcv_map.mpt_len;
                m->m_pkthdr.pkt_flags |= PKTF_MPTCP;
                tp->t_mpflags &= ~TMPF_EMBED_DSN;
                tp->t_mpflags |= TMPF_MPTCP_ACKNOW;
        }
}

int
mptcp_adj_rmap(struct socket *so, struct mbuf *m)
{
        u_int64_t dsn;
        u_int32_t sseq, datalen;
        struct tcpcb *tp = intotcpcb(sotoinpcb(so));
        u_int32_t old_rcvnxt = 0;

        if (m_pktlen(m) == 0)
                return 0;

        if (m->m_pkthdr.pkt_flags & PKTF_MPTCP) {
                VERIFY(m->m_flags & M_PKTHDR);

                dsn = m->m_pkthdr.mp_dsn;
                sseq = m->m_pkthdr.mp_rseq + tp->irs;
                datalen = m->m_pkthdr.mp_rlen;
        } else {
                /* data arrived without an DSS option mapping */

                /* initial subflow can fallback right after SYN handshake */
                mptcp_notify_mpfail(so);
                return 0;
        }

        /* In the common case, data is in window and in sequence */
        if (m->m_pkthdr.len == (int)datalen) {
                mptcp_adj_rcvnxt(tp, m);
                return 0;
        }

        old_rcvnxt = tp->rcv_nxt - m->m_pkthdr.len;
        if (SEQ_GT(old_rcvnxt, sseq)) {
                /* data trimmed from the left */
                int off = old_rcvnxt - sseq;
                m->m_pkthdr.mp_dsn += off;
                m->m_pkthdr.mp_rseq += off;
                m->m_pkthdr.mp_rlen = m->m_pkthdr.len;
        } else if (old_rcvnxt == sseq) {
                /*
                 * data was trimmed from the right
                 */
                m->m_pkthdr.mp_rlen = m->m_pkthdr.len;
        } else {
                mptcp_notify_mpfail(so);
                return (-1);
        }
        mptcp_adj_rcvnxt(tp, m);
        return 0;
}

/*
 * Following routines help with failure detection and failover of data
 * transfer from one subflow to another.
 */
void
mptcp_act_on_txfail(struct socket *so)
{
        struct tcpcb *tp = NULL;
        struct inpcb *inp = sotoinpcb(so);

        if (inp == NULL)
                return;

        tp = intotcpcb(inp);
        if (tp == NULL)
                return;

        if (so->so_flags & SOF_MP_TRYFAILOVER) {
                return;
        }

        so->so_flags |= SOF_MP_TRYFAILOVER;
        soevent(so, (SO_FILT_HINT_LOCKED | SO_FILT_HINT_MPFAILOVER));
}

/*
 * Support for MP_FAIL option
 */
int
mptcp_get_map_for_dsn(struct socket *so, u_int64_t dsn_fail, u_int32_t *tcp_seq)
{
        struct mbuf *m = so->so_snd.sb_mb;
        u_int64_t dsn;
        int off = 0;
        u_int32_t datalen;

        if (m == NULL)
                return (-1);

        while (m != NULL) {
                VERIFY(m->m_pkthdr.pkt_flags & PKTF_MPTCP);
                VERIFY(m->m_flags & M_PKTHDR);
                dsn = m->m_pkthdr.mp_dsn;
                datalen = m->m_pkthdr.mp_rlen;
                if (MPTCP_SEQ_LEQ(dsn, dsn_fail) &&
                    (MPTCP_SEQ_GEQ(dsn + datalen, dsn_fail))) {
                        off = dsn_fail - dsn;
                        *tcp_seq = m->m_pkthdr.mp_rseq + off;
                        mptcplog((LOG_DEBUG, "MPTCP Sender: %s: %llu %llu \n",
                            __func__, dsn, dsn_fail),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                        return (0);
                }

                m = m->m_next;
        }

        /*
         * If there was no mbuf data and a fallback to TCP occurred, there's
         * not much else to do.
         */

        mptcplog((LOG_ERR, "MPTCP Sender: "
            "%s: %llu not found \n", __func__, dsn_fail),
            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
        return (-1);
}

/*
 * Support for sending contiguous MPTCP bytes in subflow
 * Also for preventing sending data with ACK in 3-way handshake
 */
int32_t
mptcp_adj_sendlen(struct socket *so, int32_t off, int32_t len)
{
        u_int64_t       mdss_dsn = 0;
        u_int32_t       mdss_subflow_seq = 0;
        u_int16_t       mdss_data_len = 0;

        if (len == 0)
                return (len);

        mptcp_output_getm_dsnmap64(so, off, (u_int32_t)len,
            &mdss_dsn, &mdss_subflow_seq, &mdss_data_len);

        /* 
         * Special case handling for Fast Join. We want to send data right
         * after ACK of the 3-way handshake, but not piggyback the data
         * with the 3rd ACK of the 3WHS. TMPF_FASTJOINBY2_SEND and
         * mdss_data_len control this.
         */
        struct tcpcb *tp = NULL;
        tp = intotcpcb(sotoinpcb(so)); 
        if ((tp->t_mpflags & TMPF_JOINED_FLOW) &&
            (tp->t_mpflags & TMPF_PREESTABLISHED) &&
            (!(tp->t_mpflags & TMPF_RECVD_JOIN)) &&
            (tp->t_mpflags & TMPF_SENT_JOIN) &&
            (!(tp->t_mpflags & TMPF_MPTCP_TRUE)) &&
            (!(tp->t_mpflags & TMPF_FASTJOINBY2_SEND))) {
            mdss_data_len = 0;
            tp->t_mpflags |= TMPF_FASTJOINBY2_SEND;
        }    
        return (mdss_data_len);
}

int32_t
mptcp_sbspace(struct mptcb *mpt)
{
        struct sockbuf *sb;
        uint32_t rcvbuf;
        int32_t space;

        MPT_LOCK_ASSERT_HELD(mpt);
        MPTE_LOCK_ASSERT_HELD(mpt->mpt_mpte);

        sb = &mpt->mpt_mpte->mpte_mppcb->mpp_socket->so_rcv;
        rcvbuf = sb->sb_hiwat;
        space = ((int32_t)imin((rcvbuf - sb->sb_cc),
            (sb->sb_mbmax - sb->sb_mbcnt)));
        if (space < 0)
                space = 0;
        /* XXX check if it's too small? */

        return (space);
}

/*
 * Support Fallback to Regular TCP
 */
void
mptcp_notify_mpready(struct socket *so)
{
        struct tcpcb *tp = NULL;

        if (so == NULL)
                return;

        tp = intotcpcb(sotoinpcb(so));

        if (tp == NULL)
                return;

        DTRACE_MPTCP4(multipath__ready, struct socket *, so,
            struct sockbuf *, &so->so_rcv, struct sockbuf *, &so->so_snd,
            struct tcpcb *, tp);

        if (!(tp->t_mpflags & TMPF_MPTCP_TRUE))
                return;

        if (tp->t_mpflags & TMPF_MPTCP_READY)
                return;

        tp->t_mpflags &= ~TMPF_TCP_FALLBACK;
        tp->t_mpflags |= TMPF_MPTCP_READY;

        soevent(so, (SO_FILT_HINT_LOCKED | SO_FILT_HINT_MPSTATUS));
}

void
mptcp_notify_mpfail(struct socket *so)
{
        struct tcpcb *tp = NULL;

        if (so == NULL)
                return;

        tp = intotcpcb(sotoinpcb(so));

        if (tp == NULL)
                return;

        DTRACE_MPTCP4(multipath__failed, struct socket *, so,
            struct sockbuf *, &so->so_rcv, struct sockbuf *, &so->so_snd,
            struct tcpcb *, tp);

        if (tp->t_mpflags & TMPF_TCP_FALLBACK)
                return;

        tp->t_mpflags &= ~(TMPF_MPTCP_READY|TMPF_MPTCP_TRUE);
        tp->t_mpflags |= TMPF_TCP_FALLBACK;

        soevent(so, (SO_FILT_HINT_LOCKED | SO_FILT_HINT_MPSTATUS));
}

/*
 * Keepalive helper function
 */
boolean_t
mptcp_ok_to_keepalive(struct mptcb *mp_tp)
{
        boolean_t ret = 1;
        VERIFY(mp_tp != NULL);
        MPT_LOCK(mp_tp);
        if (mp_tp->mpt_state >= MPTCPS_CLOSE_WAIT) {
                ret = 0;
        }
        MPT_UNLOCK(mp_tp);
        return (ret);
}

/*
 * MPTCP t_maxseg adjustment function
 */
int
mptcp_adj_mss(struct tcpcb *tp, boolean_t mtudisc)
{
        int mss_lower = 0;
        struct mptcb *mp_tp = tptomptp(tp);

#define MPTCP_COMPUTE_LEN {                             \
        mss_lower = sizeof (struct mptcp_dss_ack_opt);  \
        MPT_LOCK(mp_tp);                                \
        if (mp_tp->mpt_flags & MPTCPF_CHECKSUM)         \
                mss_lower += 2;                         \
        else                                            \
                /* adjust to 32-bit boundary + EOL */   \
                mss_lower += 2;                         \
        MPT_UNLOCK(mp_tp);                              \
}
        if (mp_tp == NULL)
                return (0);

        /*
         * For the first subflow and subsequent subflows, adjust mss for
         * most common MPTCP option size, for case where tcp_mss is called
         * during option processing and MTU discovery.
         */
        if ((tp->t_mpflags & TMPF_PREESTABLISHED) &&
            (!(tp->t_mpflags & TMPF_JOINED_FLOW))) {
                MPTCP_COMPUTE_LEN;
        }

        if ((tp->t_mpflags & TMPF_PREESTABLISHED) &&
            (tp->t_mpflags & TMPF_SENT_JOIN)) {
                MPTCP_COMPUTE_LEN;
        }

        if ((mtudisc) && (tp->t_mpflags & TMPF_MPTCP_TRUE)) {
                MPTCP_COMPUTE_LEN;
        }

        return (mss_lower);
}

/*
 * Update the pid, upid, uuid of the subflow so, based on parent so
 */
void
mptcp_update_last_owner(struct mptsub *mpts, struct socket *parent_mpso)
{
        struct socket *subflow_so = mpts->mpts_socket;
        
        MPTS_LOCK_ASSERT_HELD(mpts);

        socket_lock(subflow_so, 0);
        if ((subflow_so->last_pid != parent_mpso->last_pid) ||
                (subflow_so->last_upid != parent_mpso->last_upid)) {
                subflow_so->last_upid = parent_mpso->last_upid;
                subflow_so->last_pid = parent_mpso->last_pid;
                uuid_copy(subflow_so->last_uuid, parent_mpso->last_uuid);
        }
        so_update_policy(subflow_so);
        socket_unlock(subflow_so, 0);
}

static void
fill_mptcp_subflow(struct socket *so, mptcp_flow_t *flow, struct mptsub *mpts)
{
        struct inpcb *inp;

        tcp_getconninfo(so, &flow->flow_ci);
        inp = sotoinpcb(so);
#if INET6
        if ((inp->inp_vflag & INP_IPV6) != 0) {
                flow->flow_src.ss_family = AF_INET6;
                flow->flow_dst.ss_family = AF_INET6;
                flow->flow_src.ss_len = sizeof(struct sockaddr_in6);
                flow->flow_dst.ss_len = sizeof(struct sockaddr_in6);
                SIN6(&flow->flow_src)->sin6_port = inp->in6p_lport;
                SIN6(&flow->flow_dst)->sin6_port = inp->in6p_fport;
                SIN6(&flow->flow_src)->sin6_addr = inp->in6p_laddr;
                SIN6(&flow->flow_dst)->sin6_addr = inp->in6p_faddr;
        } else 
#endif
        if ((inp->inp_vflag & INP_IPV4) != 0) {
                flow->flow_src.ss_family = AF_INET;
                flow->flow_dst.ss_family = AF_INET;
                flow->flow_src.ss_len = sizeof(struct sockaddr_in);
                flow->flow_dst.ss_len = sizeof(struct sockaddr_in);
                SIN(&flow->flow_src)->sin_port = inp->inp_lport;
                SIN(&flow->flow_dst)->sin_port = inp->inp_fport;
                SIN(&flow->flow_src)->sin_addr = inp->inp_laddr;
                SIN(&flow->flow_dst)->sin_addr = inp->inp_faddr;
        }
        flow->flow_len = sizeof(*flow);
        flow->flow_tcpci_offset = offsetof(mptcp_flow_t, flow_ci);
        flow->flow_flags = mpts->mpts_flags;
        flow->flow_cid = mpts->mpts_connid;
        flow->flow_sndnxt = mpts->mpts_sndnxt;
        flow->flow_relseq = mpts->mpts_rel_seq;
        flow->flow_soerror = mpts->mpts_soerror;
        flow->flow_probecnt = mpts->mpts_probecnt;
        flow->flow_peerswitch = mpts->mpts_peerswitch;
}

static int
mptcp_pcblist SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp, arg1, arg2)
        int error = 0, f;
        size_t n, len;
        struct mppcb *mpp;
        struct mptses *mpte;
        struct mptcb *mp_tp;
        struct mptsub *mpts;
        struct socket *so;
        conninfo_mptcp_t mptcpci;
        mptcp_flow_t *flows = NULL;

        if (req->newptr != USER_ADDR_NULL)
                return (EPERM);

        lck_mtx_lock(&mtcbinfo.mppi_lock);
        n = mtcbinfo.mppi_count;
        if (req->oldptr == USER_ADDR_NULL) {
                lck_mtx_unlock(&mtcbinfo.mppi_lock);
                req->oldidx = (n + n/8) * sizeof(conninfo_mptcp_t) + 
                    4 * (n + n/8)  * sizeof(mptcp_flow_t);
                return (0);
        }
        TAILQ_FOREACH(mpp, &mtcbinfo.mppi_pcbs, mpp_entry) {
                flows = NULL;
                lck_mtx_lock(&mpp->mpp_lock);
                VERIFY(mpp->mpp_flags & MPP_ATTACHED);
                if (mpp->mpp_flags & MPP_DEFUNCT) {
                        lck_mtx_unlock(&mpp->mpp_lock);
                        continue;
                }
                mpte = mptompte(mpp);
                VERIFY(mpte != NULL);
                mp_tp = mpte->mpte_mptcb;
                VERIFY(mp_tp != NULL);

                bzero(&mptcpci, sizeof(mptcpci));
                MPT_LOCK(mp_tp);
                mptcpci.mptcpci_state = mp_tp->mpt_state;
                mptcpci.mptcpci_flags = mp_tp->mpt_flags;
                mptcpci.mptcpci_ltoken = mp_tp->mpt_localtoken;
                mptcpci.mptcpci_rtoken = mp_tp->mpt_remotetoken;
                mptcpci.mptcpci_notsent_lowat = mp_tp->mpt_notsent_lowat;
                mptcpci.mptcpci_snduna = mp_tp->mpt_snduna;
                mptcpci.mptcpci_sndnxt = mp_tp->mpt_sndnxt;
                mptcpci.mptcpci_sndmax = mp_tp->mpt_sndmax;
                mptcpci.mptcpci_lidsn = mp_tp->mpt_local_idsn;
                mptcpci.mptcpci_sndwnd = mp_tp->mpt_sndwnd;
                mptcpci.mptcpci_rcvnxt = mp_tp->mpt_rcvnxt;
                mptcpci.mptcpci_rcvatmark = mp_tp->mpt_rcvatmark;
                mptcpci.mptcpci_ridsn = mp_tp->mpt_remote_idsn;
                mptcpci.mptcpci_rcvwnd = mp_tp->mpt_rcvwnd;
                MPT_UNLOCK(mp_tp);

                mptcpci.mptcpci_nflows = mpte->mpte_numflows;
                mptcpci.mptcpci_mpte_flags = mpte->mpte_flags;
                mptcpci.mptcpci_mpte_addrid = mpte->mpte_addrid_last;
                mptcpci.mptcpci_flow_offset =
                    offsetof(conninfo_mptcp_t, mptcpci_flows);

                len = sizeof(*flows) * mpte->mpte_numflows;
                if (mpte->mpte_numflows != 0) {
                        flows = _MALLOC(len, M_TEMP, M_WAITOK | M_ZERO);
                        if (flows == NULL) {
                                lck_mtx_unlock(&mpp->mpp_lock);
                                break;
                        }
                        mptcpci.mptcpci_len = sizeof(mptcpci) +
                            sizeof(*flows) * (mptcpci.mptcpci_nflows - 1);
                        error = SYSCTL_OUT(req, &mptcpci,
                            sizeof(mptcpci) - sizeof(mptcp_flow_t));
                } else {
                        mptcpci.mptcpci_len = sizeof(mptcpci);
                        error = SYSCTL_OUT(req, &mptcpci, sizeof(mptcpci));
                }   
                if (error) {
                        lck_mtx_unlock(&mpp->mpp_lock);
                        FREE(flows, M_TEMP);
                        break;
                }
                f = 0;
                TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                        MPTS_LOCK(mpts);
                        so = mpts->mpts_socket;
                        socket_lock(so, 0);
                        fill_mptcp_subflow(so, &flows[f], mpts);
                        socket_unlock(so, 0);
                        MPTS_UNLOCK(mpts);
                        f++;
                }
                lck_mtx_unlock(&mpp->mpp_lock);
                if (flows) {
                        error = SYSCTL_OUT(req, flows, len);
                        FREE(flows, M_TEMP);
                        if (error)
                                break;
                }
        }
        lck_mtx_unlock(&mtcbinfo.mppi_lock);

        return (error);
}

SYSCTL_PROC(_net_inet_mptcp, OID_AUTO, pcblist, CTLFLAG_RD | CTLFLAG_LOCKED,
    0, 0, mptcp_pcblist, "S,conninfo_mptcp_t", 
    "List of active MPTCP connections");

/*
 * Check the health of the other subflows and do an mptcp_output if
 * there is no other active or functional subflow at the time of
 * call of this function.
 */
static void
mptcp_output_needed(struct mptses *mpte, struct mptsub *to_mpts)
{
        struct mptsub *from_mpts = NULL;

        MPTE_LOCK_ASSERT_HELD(mpte);

        MPTS_UNLOCK(to_mpts);
        
        from_mpts = mpte->mpte_active_sub; 

        if (from_mpts == NULL)
                goto output_needed;

        MPTS_LOCK(from_mpts);

        if ((from_mpts->mpts_flags & MPTSF_DISCONNECTED) ||
            (from_mpts->mpts_flags & MPTSF_DISCONNECTING)) {
                MPTS_UNLOCK(from_mpts);
                goto output_needed;
        }

        MPTS_UNLOCK(from_mpts);
        MPTS_LOCK(to_mpts);
        return;

output_needed:  
        mptcp_output(mpte);     
        MPTS_LOCK(to_mpts);
}

/*
 * Set notsent lowat mark on the MPTCB
 */
int
mptcp_set_notsent_lowat(struct mptses *mpte, int optval)
{
        struct mptcb *mp_tp = NULL;
        int error = 0;

        if (mpte->mpte_mppcb->mpp_flags & MPP_ATTACHED)
                mp_tp = mpte->mpte_mptcb;

        if (mp_tp)
                mp_tp->mpt_notsent_lowat = optval;
        else
                error = EINVAL;

        return error;   
}

u_int32_t
mptcp_get_notsent_lowat(struct mptses *mpte)
{
        struct mptcb *mp_tp = NULL;

        if (mpte->mpte_mppcb->mpp_flags & MPP_ATTACHED)
                mp_tp = mpte->mpte_mptcb;

        if (mp_tp)
                return mp_tp->mpt_notsent_lowat;
        else
                return 0;
}

int                             
mptcp_notsent_lowat_check(struct socket *so) {
        struct mptses *mpte;
        struct mppcb *mpp;
        struct mptcb *mp_tp;
        struct mptsub *mpts;

        int notsent = 0;

        mpp = sotomppcb(so);
        if (mpp == NULL || mpp->mpp_state == MPPCB_STATE_DEAD) {
                return (0);
        }

        mpte = mptompte(mpp);
        mp_tp = mpte->mpte_mptcb;

        MPT_LOCK(mp_tp);
        notsent = so->so_snd.sb_cc;

        if ((notsent == 0) ||
            ((notsent - (mp_tp->mpt_sndnxt - mp_tp->mpt_snduna)) <=
            mp_tp->mpt_notsent_lowat)) {
                mptcplog((LOG_DEBUG, "MPTCP Sender: "
                    "lowat %d notsent %d actual %d \n",
                    mp_tp->mpt_notsent_lowat, notsent,
                    notsent - (mp_tp->mpt_sndnxt - mp_tp->mpt_snduna)),
                    MPTCP_SENDER_DBG , MPTCP_LOGLVL_VERBOSE);
                MPT_UNLOCK(mp_tp);
                return (1);
        }
        MPT_UNLOCK(mp_tp);

        /* When Nagle's algorithm is not disabled, it is better
         * to wakeup the client even before there is atleast one
         * maxseg of data to write.
         */
        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                int retval = 0;
                MPTS_LOCK(mpts);
                if (mpts->mpts_flags & MPTSF_ACTIVE) {
                        struct socket *subf_so = mpts->mpts_socket;
                        socket_lock(subf_so, 0);
                        struct tcpcb *tp = intotcpcb(sotoinpcb(subf_so));
                        
                        notsent = so->so_snd.sb_cc -
                           (tp->snd_nxt - tp->snd_una);
                        
                        if ((tp->t_flags & TF_NODELAY) == 0 &&
                            notsent > 0 && (notsent <= (int)tp->t_maxseg)) {
                                retval = 1;
                        }
                        mptcplog((LOG_DEBUG, "MPTCP Sender: lowat %d notsent %d"
                            " nodelay false \n",
                            mp_tp->mpt_notsent_lowat, notsent),
                            MPTCP_SENDER_DBG , MPTCP_LOGLVL_VERBOSE);
                        socket_unlock(subf_so, 0);
                        MPTS_UNLOCK(mpts);
                        return (retval);
                }
                MPTS_UNLOCK(mpts);
        }
        return (0);
}

static void
mptcp_get_rtt_measurement(struct mptsub *mpts, struct mptses *mpte)
{
        MPTE_LOCK_ASSERT_HELD(mpte);
        MPTS_LOCK_ASSERT_HELD(mpts);

        struct socket *subflow_so = mpts->mpts_socket;
        socket_lock(subflow_so, 0);
        mpts->mpts_srtt = (intotcpcb(sotoinpcb(subflow_so)))->t_srtt;
        mpts->mpts_rxtcur = (intotcpcb(sotoinpcb(subflow_so)))->t_rxtcur;
        socket_unlock(subflow_so, 0);
}

/* Using Symptoms Advisory to detect poor WiFi or poor Cell */
static kern_ctl_ref mptcp_kern_ctrl_ref = NULL;
static uint32_t mptcp_kern_skt_inuse = 0;
symptoms_advisory_t mptcp_advisory;

static errno_t
mptcp_symptoms_ctl_connect(kern_ctl_ref kctlref, struct sockaddr_ctl *sac,
        void **unitinfo)
{
#pragma unused(kctlref, sac, unitinfo)
        /*
         * We don't need to do anything here. But we can atleast ensure
         * only one user opens the MPTCP_KERN_CTL_NAME control socket.
         */
        if (OSCompareAndSwap(0, 1, &mptcp_kern_skt_inuse))
                return (0);
        else
                return (EALREADY);
}

static errno_t
mptcp_symptoms_ctl_disconnect(kern_ctl_ref kctlref, u_int32_t kcunit,
        void *unitinfo)
{
#pragma unused(kctlref, kcunit, unitinfo)
        if (OSCompareAndSwap(1, 0, &mptcp_kern_skt_inuse)) {
                /* TBD needs to be locked if the size grows more than an int */
                bzero(&mptcp_advisory, sizeof(mptcp_advisory));
                return (0);
        }
        else {
                return (EINVAL);
        }
}

static errno_t
mptcp_symptoms_ctl_send(kern_ctl_ref kctlref, u_int32_t kcunit, void *unitinfo,
       mbuf_t m, int flags)
{
#pragma unused(kctlref, kcunit, unitinfo, flags)
        symptoms_advisory_t     *sa = NULL;

        if (mbuf_pkthdr_len(m) < sizeof(*sa)) {
                mbuf_freem(m);
                return (EINVAL);
        }

        if (mbuf_len(m) >= sizeof(*sa))
                sa = mbuf_data(m);
        else
                return (EINVAL);

        if (mptcp_advisory.sa_nwk_status_int != sa->sa_nwk_status_int) {
                /*
                 * we could use this notification to notify all mptcp pcbs
                 * of the change in network status. But its difficult to
                 * define if sending REMOVE_ADDR or MP_PRIO is appropriate
                 * given that these are only soft indicators of the network
                 * state. Leaving this as TBD for now.
                 */
        }

        if (sa->sa_nwk_status != SYMPTOMS_ADVISORY_NOCOMMENT) {
                mptcplog((LOG_DEBUG, "MPTCP Events: %s wifi %d,%d cell %d,%d\n",
                    __func__, sa->sa_wifi_status, mptcp_advisory.sa_wifi_status,
                    sa->sa_cell_status, mptcp_advisory.sa_cell_status),
                    MPTCP_SOCKET_DBG | MPTCP_EVENTS_DBG,
                    MPTCP_LOGLVL_LOG);

                if ((sa->sa_wifi_status &
                    (SYMPTOMS_ADVISORY_WIFI_BAD | SYMPTOMS_ADVISORY_WIFI_OK)) !=
                    (SYMPTOMS_ADVISORY_WIFI_BAD | SYMPTOMS_ADVISORY_WIFI_OK)) {
                        mptcp_advisory.sa_wifi_status = sa->sa_wifi_status;
                }

                if ((sa->sa_cell_status &
                    (SYMPTOMS_ADVISORY_CELL_BAD | SYMPTOMS_ADVISORY_CELL_OK)) !=
                    (SYMPTOMS_ADVISORY_CELL_BAD | SYMPTOMS_ADVISORY_CELL_OK)) {
                        mptcp_advisory.sa_cell_status = sa->sa_cell_status;
                }
        } else {
                mptcplog((LOG_DEBUG, "MPTCP Events: %s NOCOMMENT "
                    "wifi %d cell %d\n", __func__,
                    mptcp_advisory.sa_wifi_status,
                    mptcp_advisory.sa_cell_status),
                    MPTCP_SOCKET_DBG | MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
        }
        return (0);
}

void
mptcp_control_register(void)
{
        /* Set up the advisory control socket */
        struct kern_ctl_reg mptcp_kern_ctl;

        bzero(&mptcp_kern_ctl, sizeof(mptcp_kern_ctl));
        strlcpy(mptcp_kern_ctl.ctl_name, MPTCP_KERN_CTL_NAME,
            sizeof(mptcp_kern_ctl.ctl_name));
        mptcp_kern_ctl.ctl_connect = mptcp_symptoms_ctl_connect;
        mptcp_kern_ctl.ctl_disconnect = mptcp_symptoms_ctl_disconnect;
        mptcp_kern_ctl.ctl_send = mptcp_symptoms_ctl_send;
        mptcp_kern_ctl.ctl_flags = CTL_FLAG_PRIVILEGED;

        (void)ctl_register(&mptcp_kern_ctl, &mptcp_kern_ctrl_ref);
}

int
mptcp_is_wifi_unusable(void)
{
        /* a false return val indicates there is no info or wifi is ok */
        return (mptcp_advisory.sa_wifi_status & SYMPTOMS_ADVISORY_WIFI_BAD);
}

int
mptcp_is_cell_unusable(void)
{
        /* a false return val indicates there is no info or cell is ok */
        return (mptcp_advisory.sa_cell_status & SYMPTOMS_ADVISORY_CELL_BAD);
}

struct mptsub*
mptcp_use_symptoms_hints(struct mptsub* best, struct mptsub *second_best)
{
        struct mptsub *cellsub = NULL;
        struct mptsub *wifisub = NULL;
        struct mptsub *wiredsub = NULL;

        VERIFY ((best != NULL) && (second_best != NULL));

        if (!mptcp_use_symptomsd)
                return (NULL);

        if (!mptcp_kern_skt_inuse)
                return (NULL);

        /*
         * There could be devices with more than one wifi interface or 
         * more than one wired or cell interfaces. 
         * TBD: SymptomsD is unavailable on such platforms as of now.
         * Try to prefer best when possible in general.
         * Also, SymptomsD sends notifications about wifi only when it
         * is primary.
         */
        if (best->mpts_linktype & MPTSL_WIFI)
                wifisub = best;
        else if (best->mpts_linktype & MPTSL_CELL)
                cellsub = best;
        else if (best->mpts_linktype & MPTSL_WIRED)
                wiredsub = best;

        /*
         * On platforms with wired paths, don't use hints about wifi or cell.
         * Currently, SymptomsD is not available on platforms with wired paths.
         */
        if (wiredsub)
                return (NULL);

        if ((wifisub == NULL) && (second_best->mpts_linktype & MPTSL_WIFI))
                wifisub = second_best;

        if ((cellsub == NULL) && (second_best->mpts_linktype & MPTSL_CELL))
                cellsub = second_best;

        if ((wiredsub == NULL) && (second_best->mpts_linktype & MPTSL_WIRED))
                wiredsub = second_best;

        if ((wifisub == best) && mptcp_is_wifi_unusable()) {
                tcpstat.tcps_mp_sel_symtomsd++;
                if (mptcp_is_cell_unusable()) {
                        mptcplog((LOG_DEBUG, "MPTCP Sender: SymptomsD hint"
                            " suggests both Wifi and Cell are bad. Wired %s.",
                            (wiredsub == NULL) ? "none" : "present"),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                        return (wiredsub);
                } else {
                        mptcplog((LOG_DEBUG, "MPTCP Sender: SymptomsD hint"
                            " suggests Wifi bad, Cell good. Wired %s.",
                            (wiredsub == NULL) ? "none" : "present"),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                        return ((wiredsub != NULL) ? wiredsub : cellsub);
                }
        }

        if ((cellsub == best) && (mptcp_is_cell_unusable())) {
                tcpstat.tcps_mp_sel_symtomsd++;
                if (mptcp_is_wifi_unusable()) {
                        mptcplog((LOG_DEBUG, "MPTCP Sender: SymptomsD hint"
                            " suggests both Cell and Wifi are bad. Wired %s.",
                            (wiredsub == NULL) ? "none" : "present"),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                        return (wiredsub);
                } else {
                        mptcplog((LOG_DEBUG, "MPTCP Sender: SymptomsD hint"
                            " suggests Cell bad, Wifi good. Wired %s.",
                            (wiredsub == NULL) ? "none" : "present"),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                        return ((wiredsub != NULL) ? wiredsub : wifisub);
                }
        }

        /* little is known about the state of the network or wifi is good */
        return (NULL); 
}