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

/*
 * Copyright (c) 2012-2017 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 <kern/locks.h>
#include <kern/policy_internal.h>
#include <kern/zalloc.h>

#include <mach/sdt.h>

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

#include <net/content_filter.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_opt.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;
 *
 * 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.
 *
 * To handle events (read, write, control) from the subflows, we do direct
 * upcalls into the specific function.
 *
 * The whole MPTCP connection is protected by a single lock, the MPTCP socket's
 * lock. Incoming data on a subflow also ends up taking this single lock. To
 * achieve the latter, tcp_lock/unlock has been changed to rather use the lock
 * of the MPTCP-socket.
 *
 * 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.
 */

static void mptcp_attach_to_subf(struct socket *, struct mptcb *, uint8_t);
static void mptcp_detach_mptcb_from_subf(struct mptcb *, struct socket *);

static uint32_t mptcp_gc(struct mppcbinfo *);
static int mptcp_subflow_soreceive(struct socket *, struct sockaddr **,
    struct uio *, struct mbuf **, struct mbuf **, int *);
static int mptcp_subflow_sosend(struct socket *, struct sockaddr *,
    struct uio *, struct mbuf *, struct mbuf *, int);
static void mptcp_subflow_wupcall(struct socket *, void *, int);
static void mptcp_subflow_eupcall1(struct socket *, void *, uint32_t);
static void mptcp_update_last_owner(struct socket *so, struct socket *mp_so);
static void mptcp_drop_tfo_data(struct mptses *, struct mptsub *);

static void mptcp_subflow_abort(struct mptsub *, int);

static void mptcp_send_dfin(struct socket *so);
static void mptcp_set_cellicon(struct mptses *mpte, struct mptsub *mpts);
static int mptcp_freeq(struct mptcb *mp_tp);

/*
 * 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_propagate_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_nosrcaddr_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_failover_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_ifdenied_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_connected_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_disconnected_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_mpstatus_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_mustrst_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_mpcantrcvmore_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_mpsuberror_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_adaptive_rtimo_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);
static ev_ret_t mptcp_subflow_adaptive_wtimo_ev(struct mptses *, struct mptsub *, uint64_t *, uint64_t);

static void mptcp_do_sha1(mptcp_key_t *, char *);
static void mptcp_init_local_parms(struct mptses *);

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;

SYSCTL_DECL(_net_inet);

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

uint32_t mptcp_dbg_area = 31;           /* 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 = 1;
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");


static int mptcp_alternate_port = 0;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, alternate_port, CTLFLAG_RW | CTLFLAG_LOCKED,
    &mptcp_alternate_port, 0, "Set alternate port for MPTCP connections");

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 */

static uint8_t  mptcp_create_subflows_scheduled;

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,
                uint64_t event);
} mptsub_ev_entry_t;

/* 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;
static uint32_t mptcp_kern_skt_unit;
static symptoms_advisory_t mptcp_advisory;

uint32_t mptcp_cellicon_refcount = 0;

/*
 * XXX The order of the event handlers below is really
 * really important. Think twice before changing it.
 */
static mptsub_ev_entry_t mpsub_ev_entry_tbl[] = {
        {
                .sofilt_hint_mask = SO_FILT_HINT_MP_SUB_ERROR,
                .sofilt_hint_ev_hdlr = mptcp_subflow_mpsuberror_ev,
        },
        {
                .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_propagate_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_propagate_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_TIMEOUT,
                .sofilt_hint_ev_hdlr = mptcp_subflow_propagate_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_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_DISCONNECTED,
                .sofilt_hint_ev_hdlr = mptcp_subflow_disconnected_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_ADAPTIVE_RTIMO,
                .sofilt_hint_ev_hdlr = mptcp_subflow_adaptive_rtimo_ev,
        },
        {
                .sofilt_hint_mask = SO_FILT_HINT_ADAPTIVE_WTIMO,
                .sofilt_hint_ev_hdlr = mptcp_subflow_adaptive_wtimo_ev,
        },
};

os_log_t mptcp_log_handle;

/*
 * 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;

        mptcp_advisory.sa_wifi_status = SYMPTOMS_ADVISORY_WIFI_OK;

        /*
         * 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_sosend = mptcp_subflow_sosend;
        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_sosend = mptcp_subflow_sosend;
        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;

        /* 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);

        mptcp_log_handle = os_log_create("com.apple.xnu.net.mptcp", "mptcp");
}

int
mptcpstats_get_index_by_ifindex(struct mptcp_itf_stats *stats, int ifindex, boolean_t create)
{
        int i, index = -1;

        for (i = 0; i < MPTCP_ITFSTATS_SIZE; i++) {
                if (create && stats[i].ifindex == IFSCOPE_NONE) {
                        if (index < 0) {
                                index = i;
                        }
                        continue;
                }

                if (stats[i].ifindex == ifindex) {
                        index = i;
                        return index;
                }
        }

        if (index != -1) {
                stats[index].ifindex = ifindex;
        }

        return index;
}

static int
mptcpstats_get_index(struct mptcp_itf_stats *stats, const struct mptsub *mpts)
{
        const struct ifnet *ifp = sotoinpcb(mpts->mpts_socket)->inp_last_outifp;
        int index;

        if (ifp == NULL) {
                os_log_error(mptcp_log_handle, "%s - %lx: no ifp on subflow, state %u flags %#x\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpts->mpts_mpte),
                    sototcpcb(mpts->mpts_socket)->t_state, mpts->mpts_flags);
                return -1;
        }

        index = mptcpstats_get_index_by_ifindex(stats, ifp->if_index, true);

        if (index != -1) {
                if (stats[index].is_expensive == 0) {
                        stats[index].is_expensive = IFNET_IS_CELLULAR(ifp);
                }
        }

        return index;
}

void
mptcpstats_inc_switch(struct mptses *mpte, const struct mptsub *mpts)
{
        int index;

        tcpstat.tcps_mp_switches++;
        mpte->mpte_subflow_switches++;

        index = mptcpstats_get_index(mpte->mpte_itfstats, mpts);

        if (index != -1) {
                mpte->mpte_itfstats[index].switches++;
        }
}

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

        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));
}

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

        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;

        mptcp_init_urgency_timer(mpte);

        mpte->mpte_itfinfo = &mpte->_mpte_itfinfo[0];
        mpte->mpte_itfinfo_size = MPTE_ITFINFO_SIZE;

        if (mptcp_alternate_port) {
                mpte->mpte_alternate_port = htons(mptcp_alternate_port);
        }

        mpte->mpte_last_cellicon_set = tcp_now;

        /* MPTCP Protocol Control Block */
        bzero(mp_tp, sizeof(*mp_tp));
        mp_tp->mpt_mpte = mpte;
        mp_tp->mpt_state = MPTCPS_CLOSED;

        DTRACE_MPTCP1(session__create, struct mppcb *, mpp);

        return 0;
}

struct sockaddr *
mptcp_get_session_dst(struct mptses *mpte, boolean_t ipv6, boolean_t ipv4)
{
        if (!(mpte->mpte_flags & MPTE_UNICAST_IP)) {
                return &mpte->mpte_dst;
        }

        if (ipv6 && mpte->mpte_dst_unicast_v6.sin6_family == AF_INET6) {
                return (struct sockaddr *)&mpte->mpte_dst_unicast_v6;
        }

        if (ipv4 && mpte->mpte_dst_unicast_v4.sin_family == AF_INET) {
                return (struct sockaddr *)&mpte->mpte_dst_unicast_v4;
        }

        /* The interface has neither IPv4 nor IPv6 routes. Give our best guess,
         * meaning we prefer IPv6 over IPv4.
         */
        if (mpte->mpte_dst_unicast_v6.sin6_family == AF_INET6) {
                return (struct sockaddr *)&mpte->mpte_dst_unicast_v6;
        }

        if (mpte->mpte_dst_unicast_v4.sin_family == AF_INET) {
                return (struct sockaddr *)&mpte->mpte_dst_unicast_v4;
        }

        /* We don't yet have a unicast IP */
        return NULL;
}

static void
mptcpstats_get_bytes(struct mptses *mpte, boolean_t initial_cell,
    uint64_t *cellbytes, uint64_t *allbytes)
{
        int64_t mycellbytes = 0;
        uint64_t myallbytes = 0;
        int i;

        for (i = 0; i < MPTCP_ITFSTATS_SIZE; i++) {
                if (mpte->mpte_itfstats[i].is_expensive) {
                        mycellbytes += mpte->mpte_itfstats[i].mpis_txbytes;
                        mycellbytes += mpte->mpte_itfstats[i].mpis_rxbytes;
                }

                myallbytes += mpte->mpte_itfstats[i].mpis_txbytes;
                myallbytes += mpte->mpte_itfstats[i].mpis_rxbytes;
        }

        if (initial_cell) {
                mycellbytes -= mpte->mpte_init_txbytes;
                mycellbytes -= mpte->mpte_init_rxbytes;
        }

        if (mycellbytes < 0) {
                os_log_error(mptcp_log_handle, "%s - %lx: cellbytes is %lld\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mycellbytes);
                *cellbytes = 0;
                *allbytes = 0;
        } else {
                *cellbytes = mycellbytes;
                *allbytes = myallbytes;
        }
}

static void
mptcpstats_session_wrapup(struct mptses *mpte)
{
        boolean_t cell = mpte->mpte_initial_cell;

        switch (mpte->mpte_svctype) {
        case MPTCP_SVCTYPE_HANDOVER:
                if (mpte->mpte_flags & MPTE_FIRSTPARTY) {
                        tcpstat.tcps_mptcp_fp_handover_attempt++;

                        if (cell && mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_fp_handover_success_cell++;

                                if (mpte->mpte_used_wifi) {
                                        tcpstat.tcps_mptcp_handover_wifi_from_cell++;
                                }
                        } else if (mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_fp_handover_success_wifi++;

                                if (mpte->mpte_used_cell) {
                                        tcpstat.tcps_mptcp_handover_cell_from_wifi++;
                                }
                        }
                } else {
                        tcpstat.tcps_mptcp_handover_attempt++;

                        if (cell && mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_handover_success_cell++;

                                if (mpte->mpte_used_wifi) {
                                        tcpstat.tcps_mptcp_handover_wifi_from_cell++;
                                }
                        } else if (mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_handover_success_wifi++;

                                if (mpte->mpte_used_cell) {
                                        tcpstat.tcps_mptcp_handover_cell_from_wifi++;
                                }
                        }
                }

                if (mpte->mpte_handshake_success) {
                        uint64_t cellbytes;
                        uint64_t allbytes;

                        mptcpstats_get_bytes(mpte, cell, &cellbytes, &allbytes);

                        tcpstat.tcps_mptcp_handover_cell_bytes += cellbytes;
                        tcpstat.tcps_mptcp_handover_all_bytes += allbytes;
                }
                break;
        case MPTCP_SVCTYPE_INTERACTIVE:
                if (mpte->mpte_flags & MPTE_FIRSTPARTY) {
                        tcpstat.tcps_mptcp_fp_interactive_attempt++;

                        if (mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_fp_interactive_success++;

                                if (!cell && mpte->mpte_used_cell) {
                                        tcpstat.tcps_mptcp_interactive_cell_from_wifi++;
                                }
                        }
                } else {
                        tcpstat.tcps_mptcp_interactive_attempt++;

                        if (mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_interactive_success++;

                                if (!cell && mpte->mpte_used_cell) {
                                        tcpstat.tcps_mptcp_interactive_cell_from_wifi++;
                                }
                        }
                }

                if (mpte->mpte_handshake_success) {
                        uint64_t cellbytes;
                        uint64_t allbytes;

                        mptcpstats_get_bytes(mpte, cell, &cellbytes, &allbytes);

                        tcpstat.tcps_mptcp_interactive_cell_bytes += cellbytes;
                        tcpstat.tcps_mptcp_interactive_all_bytes += allbytes;
                }
                break;
        case MPTCP_SVCTYPE_AGGREGATE:
                if (mpte->mpte_flags & MPTE_FIRSTPARTY) {
                        tcpstat.tcps_mptcp_fp_aggregate_attempt++;

                        if (mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_fp_aggregate_success++;
                        }
                } else {
                        tcpstat.tcps_mptcp_aggregate_attempt++;

                        if (mpte->mpte_handshake_success) {
                                tcpstat.tcps_mptcp_aggregate_success++;
                        }
                }

                if (mpte->mpte_handshake_success) {
                        uint64_t cellbytes;
                        uint64_t allbytes;

                        mptcpstats_get_bytes(mpte, cell, &cellbytes, &allbytes);

                        tcpstat.tcps_mptcp_aggregate_cell_bytes += cellbytes;
                        tcpstat.tcps_mptcp_aggregate_all_bytes += allbytes;
                }
                break;
        }

        if (cell && mpte->mpte_handshake_success && mpte->mpte_used_wifi) {
                tcpstat.tcps_mptcp_back_to_wifi++;
        }

        if (mpte->mpte_triggered_cell) {
                tcpstat.tcps_mptcp_triggered_cell++;
        }
}

/*
 * Destroy an MPTCP session.
 */
static void
mptcp_session_destroy(struct mptses *mpte)
{
        struct mptcb *mp_tp = mpte->mpte_mptcb;

        VERIFY(mp_tp != NULL);
        VERIFY(TAILQ_EMPTY(&mpte->mpte_subflows) && mpte->mpte_numflows == 0);

        mptcpstats_session_wrapup(mpte);
        mptcp_unset_cellicon(mpte, NULL, mpte->mpte_cellicon_increments);
        mptcp_flush_sopts(mpte);

        if (mpte->mpte_itfinfo_size > MPTE_ITFINFO_SIZE) {
                _FREE(mpte->mpte_itfinfo, M_TEMP);
        }
        mpte->mpte_itfinfo = NULL;

        m_freem_list(mpte->mpte_reinjectq);

        os_log(mptcp_log_handle, "%s - %lx: Destroying session\n",
            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
}

boolean_t
mptcp_ok_to_create_subflows(struct mptcb *mp_tp)
{
        return mp_tp->mpt_state >= MPTCPS_ESTABLISHED &&
               mp_tp->mpt_state < MPTCPS_FIN_WAIT_1 &&
               !(mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP);
}

static int
mptcp_synthesize_nat64(struct in6_addr *addr, uint32_t len,
    const struct in_addr *addrv4)
{
        static const struct in6_addr well_known_prefix = {
                .__u6_addr.__u6_addr8 = {0x00, 0x64, 0xff, 0x9b, 0x00, 0x00,
                                         0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                                         0x00, 0x00, 0x00, 0x00},
        };
        const char *ptrv4 = (const char *)addrv4;
        char buf[MAX_IPv6_STR_LEN];
        char *ptr = (char *)addr;

        if (IN_ZERONET(ntohl(addrv4->s_addr)) || // 0.0.0.0/8 Source hosts on local network
            IN_LOOPBACK(ntohl(addrv4->s_addr)) || // 127.0.0.0/8 Loopback
            IN_LINKLOCAL(ntohl(addrv4->s_addr)) || // 169.254.0.0/16 Link Local
            IN_DS_LITE(ntohl(addrv4->s_addr)) || // 192.0.0.0/29 DS-Lite
            IN_6TO4_RELAY_ANYCAST(ntohl(addrv4->s_addr)) || // 192.88.99.0/24 6to4 Relay Anycast
            IN_MULTICAST(ntohl(addrv4->s_addr)) || // 224.0.0.0/4 Multicast
            INADDR_BROADCAST == addrv4->s_addr) { // 255.255.255.255/32 Limited Broadcast
                return -1;
        }

        /* Check for the well-known prefix */
        if (len == NAT64_PREFIX_LEN_96 &&
            IN6_ARE_ADDR_EQUAL(addr, &well_known_prefix)) {
                if (IN_PRIVATE(ntohl(addrv4->s_addr)) || // 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 Private-Use
                    IN_SHARED_ADDRESS_SPACE(ntohl(addrv4->s_addr))) { // 100.64.0.0/10 Shared Address Space
                        return -1;
                }
        }

        switch (len) {
        case NAT64_PREFIX_LEN_96:
                memcpy(ptr + 12, ptrv4, 4);
                break;
        case NAT64_PREFIX_LEN_64:
                memcpy(ptr + 9, ptrv4, 4);
                break;
        case NAT64_PREFIX_LEN_56:
                memcpy(ptr + 7, ptrv4, 1);
                memcpy(ptr + 9, ptrv4 + 1, 3);
                break;
        case NAT64_PREFIX_LEN_48:
                memcpy(ptr + 6, ptrv4, 2);
                memcpy(ptr + 9, ptrv4 + 2, 2);
                break;
        case NAT64_PREFIX_LEN_40:
                memcpy(ptr + 5, ptrv4, 3);
                memcpy(ptr + 9, ptrv4 + 3, 1);
                break;
        case NAT64_PREFIX_LEN_32:
                memcpy(ptr + 4, ptrv4, 4);
                break;
        default:
                panic("NAT64-prefix len is wrong: %u\n", len);
        }

        os_log_info(mptcp_log_handle, "%s: nat64prefix-len %u synthesized %s\n",
            __func__, len,
            inet_ntop(AF_INET6, (void *)addr, buf, sizeof(buf)));

        return 0;
}

static void
mptcp_trigger_cell_bringup(struct mptses *mpte)
{
        struct socket *mp_so = mptetoso(mpte);

        if (!uuid_is_null(mpsotomppcb(mp_so)->necp_client_uuid)) {
                uuid_string_t uuidstr;
                int err;

                socket_unlock(mp_so, 0);
                err = necp_client_assert_bb_radio_manager(mpsotomppcb(mp_so)->necp_client_uuid,
                    TRUE);
                socket_lock(mp_so, 0);

                if (err == 0) {
                        mpte->mpte_triggered_cell = 1;
                }

                uuid_unparse_upper(mpsotomppcb(mp_so)->necp_client_uuid, uuidstr);
                os_log_info(mptcp_log_handle, "%s - %lx: asked irat to bringup cell for uuid %s, err %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), uuidstr, err);
        } else {
                os_log_info(mptcp_log_handle, "%s - %lx: UUID is already null\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
        }
}

static boolean_t
mptcp_subflow_disconnecting(struct mptsub *mpts)
{
        if (mpts->mpts_socket->so_state & SS_ISDISCONNECTED) {
                return true;
        }

        if (mpts->mpts_flags & (MPTSF_DISCONNECTING | MPTSF_DISCONNECTED | MPTSF_CLOSE_REQD)) {
                return true;
        }

        if (sototcpcb(mpts->mpts_socket)->t_state == TCPS_CLOSED) {
                return true;
        }

        return false;
}

void
mptcp_check_subflows_and_add(struct mptses *mpte)
{
        struct mptcb *mp_tp = mpte->mpte_mptcb;
        boolean_t cellular_viable = FALSE;
        boolean_t want_cellular = TRUE;
        uint32_t i;

        if (!mptcp_ok_to_create_subflows(mp_tp)) {
                os_log_debug(mptcp_log_handle, "%s - %lx: not a good time for subflows, state %u flags %#x",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mp_tp->mpt_state, mp_tp->mpt_flags);
                return;
        }

        if (mptcp_get_session_dst(mpte, false, false) == NULL) {
                return;
        }

        for (i = 0; i < mpte->mpte_itfinfo_size; i++) {
                boolean_t need_to_ask_symptoms = FALSE, found = FALSE;
                struct mpt_itf_info *info;
                struct sockaddr_in6 nat64pre;
                struct sockaddr *dst;
                struct mptsub *mpts;
                struct ifnet *ifp;
                uint32_t ifindex;

                info = &mpte->mpte_itfinfo[i];

                ifindex = info->ifindex;
                if (ifindex == IFSCOPE_NONE) {
                        continue;
                }

                os_log(mptcp_log_handle, "%s - %lx: itf %u no support %u hasv4 %u has v6 %u hasnat64 %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), info->ifindex, info->no_mptcp_support,
                    info->has_v4_conn, info->has_v6_conn, info->has_nat64_conn);

                if (info->no_mptcp_support) {
                        continue;
                }

                ifnet_head_lock_shared();
                ifp = ifindex2ifnet[ifindex];
                ifnet_head_done();

                if (ifp == NULL) {
                        continue;
                }

                if (IFNET_IS_CELLULAR(ifp)) {
                        cellular_viable = TRUE;
                }

                TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                        const struct ifnet *subifp = sotoinpcb(mpts->mpts_socket)->inp_last_outifp;
                        struct tcpcb *tp = sototcpcb(mpts->mpts_socket);

                        if (subifp == NULL) {
                                continue;
                        }

                        /*
                         * If there is at least one functioning subflow on WiFi
                         * and we are checking for the cell interface, then
                         * we always need to ask symptoms for permission as
                         * cell is triggered even if WiFi is available.
                         */
                        if (!IFNET_IS_CELLULAR(subifp) &&
                            !mptcp_subflow_disconnecting(mpts) &&
                            IFNET_IS_CELLULAR(ifp)) {
                                need_to_ask_symptoms = TRUE;
                        }

                        /*
                         * In Handover mode, only create cell subflow if
                         * 1. Wi-Fi Assist is active
                         * 2. Symptoms marked WiFi as weak
                         * 3. We are experiencing RTOs or we are not sending data.
                         *
                         * This covers the scenario, where:
                         * 1. We send and get retransmission timeouts (thus,
                         *    we confirmed that WiFi is indeed bad).
                         * 2. We are not sending and the server tries to send.
                         *    Establshing a cell-subflow gives the server a
                         *    chance to send us some data over cell if WiFi
                         *    is dead. We establish the subflow with the
                         *    backup-bit set, so the server is not allowed to
                         *    send on this subflow as long as WiFi is providing
                         *    good performance.
                         */
                        if (mpte->mpte_svctype == MPTCP_SVCTYPE_HANDOVER &&
                            !IFNET_IS_CELLULAR(subifp) &&
                            !mptcp_subflow_disconnecting(mpts) &&
                            (mptcp_is_wifi_unusable_for_session(mpte) == 0 ||
                            (tp->t_rxtshift < mptcp_fail_thresh * 2 && mptetoso(mpte)->so_snd.sb_cc))) {
                                os_log_debug(mptcp_log_handle,
                                    "%s - %lx: handover, wifi state %d rxt %u first-party %u sb_cc %u ifindex %u this %u rtt %u rttvar %u rto %u\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                                    mptcp_is_wifi_unusable_for_session(mpte),
                                    tp->t_rxtshift,
                                    !!(mpte->mpte_flags & MPTE_FIRSTPARTY),
                                    mptetoso(mpte)->so_snd.sb_cc,
                                    ifindex, subifp->if_index,
                                    tp->t_srtt >> TCP_RTT_SHIFT,
                                    tp->t_rttvar >> TCP_RTTVAR_SHIFT,
                                    tp->t_rxtcur);
                                found = TRUE;

                                /* We found a proper subflow on WiFi - no need for cell */
                                want_cellular = FALSE;
                                break;
                        } else if (mpte->mpte_svctype == MPTCP_SVCTYPE_TARGET_BASED) {
                                uint64_t time_now = mach_continuous_time();

                                os_log(mptcp_log_handle,
                                    "%s - %lx: target-based: %llu now %llu unusable? %d cell %u sostat %#x mpts_flags %#x tcp-state %u\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpte->mpte_time_target,
                                    time_now, mptcp_is_wifi_unusable_for_session(mpte),
                                    IFNET_IS_CELLULAR(subifp), mpts->mpts_socket->so_state,
                                    mpts->mpts_flags, sototcpcb(mpts->mpts_socket)->t_state);

                                if (!IFNET_IS_CELLULAR(subifp) &&
                                    !mptcp_subflow_disconnecting(mpts) &&
                                    (mpte->mpte_time_target == 0 ||
                                    (int64_t)(mpte->mpte_time_target - time_now) > 0 ||
                                    !mptcp_is_wifi_unusable_for_session(mpte))) {
                                        found = TRUE;

                                        want_cellular = FALSE;
                                        break;
                                }
                        } else {
                                os_log_debug(mptcp_log_handle,
                                    "%s - %lx: svc %u cell %u flags %#x unusable %d rtx %u first %u sbcc %u rtt %u rttvar %u rto %u\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                                    mpte->mpte_svctype, IFNET_IS_CELLULAR(subifp), mpts->mpts_flags,
                                    mptcp_is_wifi_unusable_for_session(mpte), tp->t_rxtshift,
                                    !!(mpte->mpte_flags & MPTE_FIRSTPARTY), mptetoso(mpte)->so_snd.sb_cc,
                                    tp->t_srtt >> TCP_RTT_SHIFT,
                                    tp->t_rttvar >> TCP_RTTVAR_SHIFT,
                                    tp->t_rxtcur);
                        }

                        if (subifp->if_index == ifindex &&
                            !mptcp_subflow_disconnecting(mpts)) {
                                /*
                                 * We found a subflow on this interface.
                                 * No need to create a new one.
                                 */
                                found = TRUE;
                                break;
                        }
                }

                if (found) {
                        continue;
                }

                if (need_to_ask_symptoms &&
                    !(mpte->mpte_flags & MPTE_FIRSTPARTY) &&
                    !(mpte->mpte_flags & MPTE_ACCESS_GRANTED) &&
                    mptcp_developer_mode == 0) {
                        mptcp_ask_symptoms(mpte);
                        return;
                }

                dst = mptcp_get_session_dst(mpte, info->has_v6_conn, info->has_v4_conn);

                if (dst->sa_family == AF_INET &&
                    !info->has_v4_conn && info->has_nat64_conn) {
                        struct ipv6_prefix nat64prefixes[NAT64_MAX_NUM_PREFIXES];
                        int error, j;

                        bzero(&nat64pre, sizeof(struct sockaddr_in6));

                        error = ifnet_get_nat64prefix(ifp, nat64prefixes);
                        if (error) {
                                os_log_error(mptcp_log_handle, "%s - %lx: no NAT64-prefix on itf %s, error %d\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), ifp->if_name, error);
                                continue;
                        }

                        for (j = 0; j < NAT64_MAX_NUM_PREFIXES; j++) {
                                if (nat64prefixes[j].prefix_len != 0) {
                                        break;
                                }
                        }

                        VERIFY(j < NAT64_MAX_NUM_PREFIXES);

                        error = mptcp_synthesize_nat64(&nat64prefixes[j].ipv6_prefix,
                            nat64prefixes[j].prefix_len,
                            &((struct sockaddr_in *)(void *)dst)->sin_addr);
                        if (error != 0) {
                                os_log_info(mptcp_log_handle, "%s - %lx: cannot synthesize this addr\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
                                continue;
                        }

                        memcpy(&nat64pre.sin6_addr,
                            &nat64prefixes[j].ipv6_prefix,
                            sizeof(nat64pre.sin6_addr));
                        nat64pre.sin6_len = sizeof(struct sockaddr_in6);
                        nat64pre.sin6_family = AF_INET6;
                        nat64pre.sin6_port = ((struct sockaddr_in *)(void *)dst)->sin_port;
                        nat64pre.sin6_flowinfo = 0;
                        nat64pre.sin6_scope_id = 0;

                        dst = (struct sockaddr *)&nat64pre;
                }

                /* Initial subflow started on a NAT64'd address? */
                if (!(mpte->mpte_flags & MPTE_UNICAST_IP) &&
                    mpte->mpte_dst.sa_family == AF_INET6 &&
                    mpte->mpte_dst_v4_nat64.sin_family == AF_INET) {
                        dst = (struct sockaddr *)&mpte->mpte_dst_v4_nat64;
                }

                if (dst->sa_family == AF_INET && !info->has_v4_conn) {
                        continue;
                }
                if (dst->sa_family == AF_INET6 && !info->has_v6_conn) {
                        continue;
                }

                mptcp_subflow_add(mpte, NULL, dst, ifindex, NULL);
        }

        if (!cellular_viable && want_cellular) {
                /* Trigger Cell Bringup */
                mptcp_trigger_cell_bringup(mpte);
        }
}

static void
mptcp_remove_cell_subflows(struct mptses *mpte)
{
        struct mptsub *mpts, *tmpts;
        boolean_t found = false;

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                const struct ifnet *ifp = sotoinpcb(mpts->mpts_socket)->inp_last_outifp;

                if (ifp == NULL || IFNET_IS_CELLULAR(ifp)) {
                        continue;
                }

                /* We have a functioning subflow on WiFi. No need for cell! */
                if (mpts->mpts_flags & MPTSF_CONNECTED &&
                    !mptcp_subflow_disconnecting(mpts)) {
                        found = true;
                }
        }

        /* Didn't found functional sub on WiFi - stay on cell */
        if (!found) {
                return;
        }

        TAILQ_FOREACH_SAFE(mpts, &mpte->mpte_subflows, mpts_entry, tmpts) {
                const struct ifnet *ifp = sotoinpcb(mpts->mpts_socket)->inp_last_outifp;

                /* Only remove cellular subflows */
                if (ifp == NULL || !IFNET_IS_CELLULAR(ifp)) {
                        continue;
                }

                os_log(mptcp_log_handle, "%s - %lx: removing cell subflow\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));

                soevent(mpts->mpts_socket, SO_FILT_HINT_LOCKED | SO_FILT_HINT_MUSTRST);
        }

        return;
}

/* Returns true if it removed a subflow on cell */
static void
mptcp_handover_subflows_remove(struct mptses *mpte)
{
        int wifi_unusable = mptcp_is_wifi_unusable_for_session(mpte);
        boolean_t found_working_subflow = false;
        struct mptsub *mpts;

        /*
         * Look for a subflow that is on a non-cellular interface
         * and actually works (aka, no retransmission timeout).
         */
        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                const struct ifnet *ifp = sotoinpcb(mpts->mpts_socket)->inp_last_outifp;
                struct socket *so;
                struct tcpcb *tp;

                if (ifp == NULL || IFNET_IS_CELLULAR(ifp)) {
                        continue;
                }

                so = mpts->mpts_socket;
                tp = sototcpcb(so);

                if (!(mpts->mpts_flags & MPTSF_CONNECTED) ||
                    tp->t_state != TCPS_ESTABLISHED) {
                        continue;
                }

                os_log_debug(mptcp_log_handle, "%s - %lx: rxt %u sb_cc %u unusable %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), tp->t_rxtshift, mptetoso(mpte)->so_snd.sb_cc, wifi_unusable);

                /* Is this subflow in good condition? */
                if (tp->t_rxtshift == 0 && mptetoso(mpte)->so_snd.sb_cc) {
                        found_working_subflow = true;
                }

                /* Or WiFi is fine */
                if (!wifi_unusable) {
                        found_working_subflow = true;
                }
        }

        /*
         * Couldn't find a working subflow, let's not remove those on a cellular
         * interface.
         */
        if (!found_working_subflow) {
                return;
        }

        mptcp_remove_cell_subflows(mpte);
}

static void
mptcp_targetbased_subflows_remove(struct mptses *mpte)
{
        uint64_t time_now = mach_continuous_time();

        if (mpte->mpte_time_target != 0 &&
            (int64_t)(mpte->mpte_time_target - time_now) <= 0 &&
            mptcp_is_wifi_unusable_for_session(mpte)) {
                /* WiFi is bad and we are below the target - don't remove any subflows */
                return;
        }

        mptcp_remove_cell_subflows(mpte);
}

/*
 * Based on the MPTCP Service-type and the state of the subflows, we
 * will destroy subflows here.
 */
void
mptcp_check_subflows_and_remove(struct mptses *mpte)
{
        if (!mptcp_ok_to_create_subflows(mpte->mpte_mptcb)) {
                return;
        }

        socket_lock_assert_owned(mptetoso(mpte));

        if (mpte->mpte_svctype == MPTCP_SVCTYPE_HANDOVER) {
                mptcp_handover_subflows_remove(mpte);
        }

        if (mpte->mpte_svctype == MPTCP_SVCTYPE_TARGET_BASED) {
                mptcp_targetbased_subflows_remove(mpte);
        }
}

static void
mptcp_remove_subflows(struct mptses *mpte)
{
        struct mptsub *mpts, *tmpts;

        if (!mptcp_ok_to_create_subflows(mpte->mpte_mptcb)) {
                return;
        }

        TAILQ_FOREACH_SAFE(mpts, &mpte->mpte_subflows, mpts_entry, tmpts) {
                const struct ifnet *ifp = sotoinpcb(mpts->mpts_socket)->inp_last_outifp;
                boolean_t found = false;
                uint32_t ifindex;
                uint32_t i;

                if (mpts->mpts_flags & MPTSF_CLOSE_REQD) {
                        mpts->mpts_flags &= ~MPTSF_CLOSE_REQD;

                        os_log(mptcp_log_handle, "%s - %lx: itf %u close_reqd last itf %d\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpts->mpts_ifscope,
                            ifp ? ifp->if_index : -1);
                        soevent(mpts->mpts_socket,
                            SO_FILT_HINT_LOCKED | SO_FILT_HINT_NOSRCADDR);

                        continue;
                }

                if (ifp == NULL && mpts->mpts_ifscope == IFSCOPE_NONE) {
                        continue;
                }

                if (ifp) {
                        ifindex = ifp->if_index;
                } else {
                        ifindex = mpts->mpts_ifscope;
                }

                for (i = 0; i < mpte->mpte_itfinfo_size; i++) {
                        if (mpte->mpte_itfinfo[i].ifindex == IFSCOPE_NONE) {
                                continue;
                        }

                        if (mpte->mpte_itfinfo[i].ifindex == ifindex) {
                                if (mpts->mpts_dst.sa_family == AF_INET6 &&
                                    (mpte->mpte_itfinfo[i].has_v6_conn || mpte->mpte_itfinfo[i].has_nat64_conn)) {
                                        found = true;
                                        break;
                                }

                                if (mpts->mpts_dst.sa_family == AF_INET &&
                                    mpte->mpte_itfinfo[i].has_v4_conn) {
                                        found = true;
                                        break;
                                }
                        }
                }

                if (!found) {
                        os_log(mptcp_log_handle, "%s - %lx: itf %u killing %#x\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                            ifindex, mpts->mpts_flags);

                        soevent(mpts->mpts_socket,
                            SO_FILT_HINT_LOCKED | SO_FILT_HINT_NOSRCADDR);
                }
        }
}

static void
mptcp_create_subflows(__unused void *arg)
{
        struct mppcb *mpp;

        /*
         * Start with clearing, because we might be processing connections
         * while a new event comes in.
         */
        if (OSTestAndClear(0x01, &mptcp_create_subflows_scheduled)) {
                os_log_error(mptcp_log_handle, "%s: bit was already cleared!\n", __func__);
        }

        /* Iterate over all MPTCP connections */

        lck_mtx_lock(&mtcbinfo.mppi_lock);

        TAILQ_FOREACH(mpp, &mtcbinfo.mppi_pcbs, mpp_entry) {
                struct socket *mp_so = mpp->mpp_socket;
                struct mptses *mpte = mpp->mpp_pcbe;

                if (!(mpp->mpp_flags & MPP_CREATE_SUBFLOWS)) {
                        continue;
                }

                socket_lock(mp_so, 1);
                VERIFY(mp_so->so_usecount > 0);

                mpp->mpp_flags &= ~MPP_CREATE_SUBFLOWS;

                mptcp_check_subflows_and_add(mpte);
                mptcp_remove_subflows(mpte);

                mp_so->so_usecount--; /* See mptcp_sched_create_subflows */
                socket_unlock(mp_so, 1);
        }

        lck_mtx_unlock(&mtcbinfo.mppi_lock);
}

/*
 * We need this because we are coming from an NECP-event. This event gets posted
 * while holding NECP-locks. The creation of the subflow however leads us back
 * into NECP (e.g., to add the necp_cb and also from tcp_connect).
 * So, we would deadlock there as we already hold the NECP-lock.
 *
 * So, let's schedule this separately. It also gives NECP the chance to make
 * progress, without having to wait for MPTCP to finish its subflow creation.
 */
void
mptcp_sched_create_subflows(struct mptses *mpte)
{
        struct mppcb *mpp = mpte->mpte_mppcb;
        struct mptcb *mp_tp = mpte->mpte_mptcb;
        struct socket *mp_so = mpp->mpp_socket;

        if (!mptcp_ok_to_create_subflows(mp_tp)) {
                os_log_debug(mptcp_log_handle, "%s - %lx: not a good time for subflows, state %u flags %#x",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mp_tp->mpt_state, mp_tp->mpt_flags);
                return;
        }

        if (!(mpp->mpp_flags & MPP_CREATE_SUBFLOWS)) {
                mp_so->so_usecount++; /* To prevent it from being free'd in-between */
                mpp->mpp_flags |= MPP_CREATE_SUBFLOWS;
        }

        if (OSTestAndSet(0x01, &mptcp_create_subflows_scheduled)) {
                return;
        }

        /* Do the call in 100ms to allow NECP to schedule it on all sockets */
        timeout(mptcp_create_subflows, NULL, hz / 10);
}

/*
 * 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)
{
        socket_lock_assert_owned(mptetoso(mpte));
        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)
{
        socket_lock_assert_owned(mptetoso(mpte));
        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;

        socket_lock_assert_owned(mptetoso(mpte));

        TAILQ_FOREACH(mpo, &mpte->mpte_sopts, mpo_entry) {
                if (mpo->mpo_level == sopt->sopt_level &&
                    mpo->mpo_name == sopt->sopt_name) {
                        break;
                }
        }
        return mpo;
}

/*
 * Allocate a MPTCP subflow structure.
 */
static struct mptsub *
mptcp_subflow_alloc(void)
{
        struct mptsub *mpts = zalloc(mptsub_zone);

        if (mpts == NULL) {
                return NULL;
        }

        bzero(mpts, mptsub_zone_size);
        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.
 */
static void
mptcp_subflow_free(struct mptsub *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 != NULL) {
                FREE(mpts->mpts_src, M_SONAME);
                mpts->mpts_src = NULL;
        }

        zfree(mptsub_zone, mpts);
}

static void
mptcp_subflow_addref(struct mptsub *mpts)
{
        if (++mpts->mpts_refcnt == 0) {
                panic("%s: mpts %p wraparound refcnt\n", __func__, mpts);
        }
        /* NOTREACHED */
}

static void
mptcp_subflow_remref(struct mptsub *mpts)
{
        if (mpts->mpts_refcnt == 0) {
                panic("%s: mpts %p negative refcnt\n", __func__, mpts);
                /* NOTREACHED */
        }
        if (--mpts->mpts_refcnt > 0) {
                return;
        }

        /* callee will unlock and destroy lock */
        mptcp_subflow_free(mpts);
}

static void
mptcp_subflow_attach(struct mptses *mpte, struct mptsub *mpts, struct socket *so)
{
        struct socket *mp_so = mpte->mpte_mppcb->mpp_socket;
        struct tcpcb *tp = sototcpcb(so);

        /*
         * From this moment on, the subflow is linked to the MPTCP-connection.
         * Locking,... happens now at the MPTCP-layer
         */
        tp->t_mptcb = mpte->mpte_mptcb;
        so->so_flags |= SOF_MP_SUBFLOW;
        mp_so->so_usecount++;

        /*
         * 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;
        tp->t_mpsub = mpts;
        mptcp_subflow_addref(mpts);     /* for being in MPTCP subflow list */
        mptcp_subflow_addref(mpts);     /* for subflow socket */
}

static void
mptcp_subflow_necp_cb(void *handle, __unused int action,
    __unused uint32_t interface_index,
    uint32_t necp_flags, bool *viable)
{
        boolean_t low_power = !!(necp_flags & NECP_CLIENT_RESULT_FLAG_INTERFACE_LOW_POWER);
        struct inpcb *inp = (struct inpcb *)handle;
        struct socket *so = inp->inp_socket;
        struct mptsub *mpts;
        struct mptses *mpte;

        if (low_power) {
                action = NECP_CLIENT_CBACTION_NONVIABLE;
        }

        if (action != NECP_CLIENT_CBACTION_NONVIABLE) {
                return;
        }

        /*
         * The socket is being garbage-collected. There is nothing to be done
         * here.
         */
        if (in_pcb_checkstate(inp, WNT_ACQUIRE, 0) == WNT_STOPUSING) {
                return;
        }

        socket_lock(so, 1);

        /* Check again after we acquired the lock. */
        if (in_pcb_checkstate(inp, WNT_RELEASE, 1) == WNT_STOPUSING) {
                goto out;
        }

        mpte = tptomptp(sototcpcb(so))->mpt_mpte;
        mpts = sototcpcb(so)->t_mpsub;

        os_log_debug(mptcp_log_handle, "%s - %lx: Subflow on itf %u became non-viable, power %u",
            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpts->mpts_ifscope, low_power);

        mpts->mpts_flags |= MPTSF_CLOSE_REQD;

        mptcp_sched_create_subflows(mpte);

        if ((mpte->mpte_svctype == MPTCP_SVCTYPE_HANDOVER ||
            mpte->mpte_svctype == MPTCP_SVCTYPE_TARGET_BASED) &&
            viable != NULL) {
                *viable = 1;
        }

out:
        socket_unlock(so, 1);
}

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

        *so = NULL;

        mp_so = mptetoso(mpte);

        p = proc_find(mp_so->last_pid);
        if (p == PROC_NULL) {
                os_log_error(mptcp_log_handle, "%s - %lx: Couldn't find proc for pid %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mp_so->last_pid);

                return ESRCH;
        }

        /*
         * 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.
         */

        /*
         * Unlock, because tcp_usr_attach ends up in in_pcballoc, which takes
         * the ipi-lock. We cannot hold the socket-lock at that point.
         */
        socket_unlock(mp_so, 0);
        error = socreate_internal(dom, so, SOCK_STREAM, IPPROTO_TCP, p,
            SOCF_MPTCP, PROC_NULL);
        socket_lock(mp_so, 0);
        if (error) {
                os_log_error(mptcp_log_handle, "%s - %lx: unable to create subflow socket error %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), error);

                proc_rele(p);

                mptcp_subflow_free(mpts);
                return error;
        }

        /*
         * We need to protect the setting of SOF_MP_SUBFLOW with a lock, because
         * this marks the moment of lock-switch from the TCP-lock to the MPTCP-lock.
         * Which is why we also need to get the lock with pr_getlock, as after
         * setting the flag, socket_unlock will work on the MPTCP-level lock.
         */
        subflow_mtx = ((*so)->so_proto->pr_getlock)(*so, 0);
        lck_mtx_lock(subflow_mtx);

        /*
         * Must be the first thing we do, to make sure all pointers for this
         * subflow are set.
         */
        mptcp_subflow_attach(mpte, mpts, *so);

        /*
         * A multipath subflow socket is used internally in the kernel,
         * therefore it does not have a file desciptor associated by
         * default.
         */
        (*so)->so_state |= SS_NOFDREF;

        lck_mtx_unlock(subflow_mtx);

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

        /* Inherit preconnect and TFO data flags */
        if (mp_so->so_flags1 & SOF1_PRECONNECT_DATA) {
                (*so)->so_flags1 |= SOF1_PRECONNECT_DATA;
        }
        if (mp_so->so_flags1 & SOF1_DATA_IDEMPOTENT) {
                (*so)->so_flags1 |= SOF1_DATA_IDEMPOTENT;
        }

        /* Inherit uuid and create the related flow. */
        if (!uuid_is_null(mpsotomppcb(mp_so)->necp_client_uuid)) {
                struct mptcb *mp_tp = mpte->mpte_mptcb;

                sotoinpcb(*so)->necp_cb = mptcp_subflow_necp_cb;

                /*
                 * A note on the unlock: With MPTCP, we do multiple times a
                 * necp_client_register_socket_flow. This is problematic,
                 * because now the lock-ordering guarantee (first necp-locks,
                 * then socket-locks) is no more respected. So, we need to
                 * unlock here.
                 */
                socket_unlock(mp_so, 0);
                error = necp_client_register_socket_flow(mp_so->last_pid,
                    mpsotomppcb(mp_so)->necp_client_uuid, sotoinpcb(*so));
                socket_lock(mp_so, 0);

                if (error) {
                        os_log_error(mptcp_log_handle, "%s - %lx: necp_client_register_socket_flow failed with error %d\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), error);

                        goto out_err;
                }

                /* Possible state-change during the unlock above */
                if (mp_tp->mpt_state >= MPTCPS_TIME_WAIT ||
                    (mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP)) {
                        os_log_error(mptcp_log_handle, "%s - %lx: state changed during unlock: %u flags %#x\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                            mp_tp->mpt_state, mp_tp->mpt_flags);

                        error = EINVAL;
                        goto out_err;
                }

                uuid_copy(sotoinpcb(*so)->necp_client_uuid, mpsotomppcb(mp_so)->necp_client_uuid);
        }

        /* Needs to happen prior to the delegation! */
        (*so)->last_pid = mp_so->last_pid;

        if (mp_so->so_flags & SOF_DELEGATED) {
                if (mpte->mpte_epid) {
                        error = so_set_effective_pid(*so, mpte->mpte_epid, p, false);
                        if (error) {
                                os_log_error(mptcp_log_handle, "%s - %lx: so_set_effective_pid failed with error %d\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), error);
                                goto out_err;
                        }
                }
                if (!uuid_is_null(mpte->mpte_euuid)) {
                        error = so_set_effective_uuid(*so, mpte->mpte_euuid, p, false);
                        if (error) {
                                os_log_error(mptcp_log_handle, "%s - %lx: so_set_effective_uuid failed with error %d\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), error);
                                goto out_err;
                        }
                }
        }

        /* inherit the other socket options */
        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, mpts, &smpo)) != 0) {
                goto out_err;
        }

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

        if (mpte->mpte_mptcb->mpt_state >= MPTCPS_ESTABLISHED) {
                /*
                 * On secondary subflows we might need to set the cell-fallback
                 * flag (see conditions in mptcp_subflow_sosetopt).
                 */
                smpo.mpo_level = SOL_SOCKET;
                smpo.mpo_name = SO_MARK_CELLFALLBACK;
                smpo.mpo_intval = 1;
                if ((error = mptcp_subflow_sosetopt(mpte, mpts, &smpo)) != 0) {
                        goto out_err;
                }
        }

        /* 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, mpts, mpo) != 0 && interim) {
                        os_log_error(mptcp_log_handle, "%s - %lx: sopt %s val %d interim record removed\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                            mptcp_sopt2str(mpo->mpo_level, mpo->mpo_name),
                            mpo->mpo_intval);
                        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.
         */
        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 */
        }

        proc_rele(p);

        DTRACE_MPTCP3(subflow__create, struct mptses *, mpte,
            int, dom, int, error);

        return 0;

out_err:
        mptcp_subflow_abort(mpts, error);

        proc_rele(p);

        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 void
mptcp_subflow_soclose(struct mptsub *mpts)
{
        struct socket *so = mpts->mpts_socket;

        if (mpts->mpts_flags & MPTSF_CLOSED) {
                return;
        }

        VERIFY(so != NULL);
        VERIFY(so->so_flags & SOF_MP_SUBFLOW);
        VERIFY((so->so_state & (SS_NBIO | SS_NOFDREF)) == (SS_NBIO | SS_NOFDREF));

        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);

        mpts->mpts_flags |= MPTSF_CLOSED;

        if (so->so_retaincnt == 0) {
                soclose_locked(so);

                return;
        } else {
                VERIFY(so->so_usecount > 0);
                so->so_usecount--;
        }

        return;
}

/*
 * Connect an MPTCP subflow socket.
 *
 * 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)
{
        char dbuf[MAX_IPv6_STR_LEN];
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        struct sockaddr *dst;
        struct proc *p;
        int af, error, dport;

        mp_so = mptetoso(mpte);
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;
        af = mpts->mpts_dst.sa_family;
        dst = &mpts->mpts_dst;

        VERIFY((mpts->mpts_flags & (MPTSF_CONNECTING | MPTSF_CONNECTED)) == MPTSF_CONNECTING);
        VERIFY(mpts->mpts_socket != NULL);
        VERIFY(af == AF_INET || af == AF_INET6);

        if (af == AF_INET) {
                inet_ntop(af, &SIN(dst)->sin_addr.s_addr, dbuf, sizeof(dbuf));
                dport = ntohs(SIN(dst)->sin_port);
        } else {
                inet_ntop(af, &SIN6(dst)->sin6_addr, dbuf, sizeof(dbuf));
                dport = ntohs(SIN6(dst)->sin6_port);
        }

        os_log_info(mptcp_log_handle,
            "%s - %lx: ifindex %u dst %s:%d pended %u\n", __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
            mpts->mpts_ifscope, dbuf, dport, !!(mpts->mpts_flags & MPTSF_CONNECT_PENDING));

        p = proc_find(mp_so->last_pid);
        if (p == PROC_NULL) {
                os_log_error(mptcp_log_handle, "%s - %lx: Couldn't find proc for pid %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mp_so->last_pid);

                return ESRCH;
        }

        mpts->mpts_flags &= ~MPTSF_CONNECT_PENDING;

        mptcp_attach_to_subf(so, mpte->mpte_mptcb, mpte->mpte_addrid_last);

        /* connect the subflow socket */
        error = soconnectxlocked(so, mpts->mpts_src, &mpts->mpts_dst,
            p, mpts->mpts_ifscope,
            mpte->mpte_associd, NULL, 0, NULL, 0, NULL, NULL);

        mpts->mpts_iss = sototcpcb(so)->iss;

        /* See tcp_connect_complete */
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED &&
            (mp_so->so_flags1 & SOF1_PRECONNECT_DATA)) {
                mp_tp->mpt_sndwnd = sototcpcb(so)->snd_wnd;
        }

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

        proc_rele(p);

        DTRACE_MPTCP3(subflow__connect, struct mptses *, mpte,
            struct mptsub *, mpts, int, error);
        if (error) {
                os_log_error(mptcp_log_handle, "%s - %lx: connectx failed with error %d ifscope %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), error, mpts->mpts_ifscope);
        }

        return error;
}

static int
mptcp_adj_rmap(struct socket *so, struct mbuf *m, int off, uint64_t dsn,
    uint32_t rseq, uint16_t dlen)
{
        struct mptsub *mpts = sototcpcb(so)->t_mpsub;

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

        if ((m->m_flags & M_PKTHDR) && (m->m_pkthdr.pkt_flags & PKTF_MPTCP)) {
                if (off && (dsn != m->m_pkthdr.mp_dsn ||
                    rseq != m->m_pkthdr.mp_rseq ||
                    dlen != m->m_pkthdr.mp_rlen)) {
                        os_log_error(mptcp_log_handle, "%s - %lx: Received incorrect second mapping: %u - %u , %u - %u, %u - %u\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpts->mpts_mpte),
                            (uint32_t)dsn, (uint32_t)m->m_pkthdr.mp_dsn,
                            rseq, m->m_pkthdr.mp_rseq,
                            dlen, m->m_pkthdr.mp_rlen);

                        soevent(mpts->mpts_socket, SO_FILT_HINT_LOCKED | SO_FILT_HINT_MUSTRST);
                        return -1;
                }
                m->m_pkthdr.mp_dsn += off;
                m->m_pkthdr.mp_rseq += off;
                m->m_pkthdr.mp_rlen = m->m_pkthdr.len;
        } else {
                if (!(mpts->mpts_flags & MPTSF_FULLY_ESTABLISHED)) {
                        /* data arrived without an DSS option mapping */

                        /* initial subflow can fallback right after SYN handshake */
                        if (mpts->mpts_flags & MPTSF_INITIAL_SUB) {
                                mptcp_notify_mpfail(so);
                        } else {
                                soevent(mpts->mpts_socket, SO_FILT_HINT_LOCKED | SO_FILT_HINT_MUSTRST);

                                return -1;
                        }
                } else if (m->m_flags & M_PKTHDR) {
                        /* We need to fake the DATA-mapping */
                        m->m_pkthdr.pkt_flags |= PKTF_MPTCP;
                        m->m_pkthdr.mp_dsn = dsn + off;
                        m->m_pkthdr.mp_rseq = rseq + off;
                        m->m_pkthdr.mp_rlen = m->m_pkthdr.len;
                }
        }

        mpts->mpts_flags |= MPTSF_FULLY_ESTABLISHED;

        return 0;
}

/*
 * 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)
        struct socket *mp_so = mptetoso(tptomptp(sototcpcb(so))->mpt_mpte);
        int flags, error = 0;
        struct proc *p = current_proc();
        struct mbuf *m, **mp = mp0;
        boolean_t proc_held = FALSE;

        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) {
                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)) {
                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;
                /*
                 * 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__);
                }
                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)) {
                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) {
                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;
        }

        mptcp_update_last_owner(so, mp_so);

        if (mp_so->last_pid != proc_pid(p)) {
                p = proc_find(mp_so->last_pid);
                if (p == PROC_NULL) {
                        p = current_proc();
                } else {
                        proc_held = TRUE;
                }
        }

        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) {
                int dlen = 0, dfin = 0, error_out = 0;
                struct mbuf *start = m;
                uint64_t dsn;
                uint32_t sseq;
                uint16_t orig_dlen;
                uint16_t csum;

                VERIFY(m->m_nextpkt == NULL);

                if ((m->m_flags & M_PKTHDR) && (m->m_pkthdr.pkt_flags & PKTF_MPTCP)) {
                        orig_dlen = dlen = m->m_pkthdr.mp_rlen;
                        dsn = m->m_pkthdr.mp_dsn;
                        sseq = m->m_pkthdr.mp_rseq;
                        csum = m->m_pkthdr.mp_csum;
                } else {
                        /* We did fallback */
                        if (mptcp_adj_rmap(so, m, 0, 0, 0, 0)) {
                                error = EIO;
                                *mp0 = NULL;
                                goto release;
                        }

                        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) {
                                so->so_rcv.sb_lastrecord = m;
                        } else {
                                SB_EMPTY_FIXUP(&so->so_rcv);
                        }

                        continue;
                }

                if (m->m_pkthdr.pkt_flags & PKTF_MPTCP_DFIN) {
                        dfin = 1;
                }

                /*
                 * Check if the full mapping is now present
                 */
                if ((int)so->so_rcv.sb_cc < dlen - dfin) {
                        mptcplog((LOG_INFO, "%s not enough data (%u) need %u for dsn %u\n",
                            __func__, so->so_rcv.sb_cc, dlen, (uint32_t)dsn),
                            MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_LOG);

                        if (*mp0 == NULL) {
                                error = EWOULDBLOCK;
                        }
                        goto release;
                }

                /* Now, get the full mapping */
                while (dlen > 0) {
                        if (mptcp_adj_rmap(so, m, orig_dlen - dlen, dsn, sseq, orig_dlen)) {
                                error_out = 1;
                                error = EIO;
                                dlen = 0;
                                *mp0 = NULL;
                                break;
                        }

                        dlen -= m->m_len;
                        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 (dlen - dfin == 0) {
                                dlen = 0;
                        }

                        VERIFY(dlen <= 0 || m);
                }

                VERIFY(dlen == 0);

                if (m != NULL) {
                        so->so_rcv.sb_lastrecord = m;
                } else {
                        SB_EMPTY_FIXUP(&so->so_rcv);
                }

                if (error_out) {
                        goto release;
                }

                if (mptcp_validate_csum(sototcpcb(so), start, dsn, sseq, orig_dlen, csum, dfin)) {
                        error = EIO;
                        *mp0 = NULL;
                        goto release;
                }

                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);

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

release:
        sbunlock(&so->so_rcv, TRUE);

        if (proc_held) {
                proc_rele(p);
        }

        return error;
}

/*
 * MPTCP subflow socket send routine, derived from sosend().
 */
static int
mptcp_subflow_sosend(struct socket *so, struct sockaddr *addr, struct uio *uio,
    struct mbuf *top, struct mbuf *control, int flags)
{
        struct socket *mp_so = mptetoso(tptomptp(sototcpcb(so))->mpt_mpte);
        struct proc *p = current_proc();
        boolean_t en_tracing = FALSE, proc_held = FALSE;
        int en_tracing_val;
        int sblocked = 1; /* Pretend as if it is already locked, so we won't relock it */
        int error;

        VERIFY(control == NULL);
        VERIFY(addr == NULL);
        VERIFY(uio == NULL);
        VERIFY(flags == 0);
        VERIFY((so->so_flags & SOF_CONTENT_FILTER) == 0);

        VERIFY(top->m_pkthdr.len > 0 && top->m_pkthdr.len <= UINT16_MAX);
        VERIFY(top->m_pkthdr.pkt_flags & PKTF_MPTCP);

        /*
         * trace if tracing & network (vs. unix) sockets & and
         * non-loopback
         */
        if (ENTR_SHOULDTRACE &&
            (SOCK_CHECK_DOM(so, AF_INET) || SOCK_CHECK_DOM(so, AF_INET6))) {
                struct inpcb *inp = sotoinpcb(so);
                if (inp->inp_last_outifp != NULL &&
                    !(inp->inp_last_outifp->if_flags & IFF_LOOPBACK)) {
                        en_tracing = TRUE;
                        en_tracing_val = top->m_pkthdr.len;
                        KERNEL_ENERGYTRACE(kEnTrActKernSockWrite, DBG_FUNC_START,
                            (unsigned long)VM_KERNEL_ADDRPERM(so),
                            ((so->so_state & SS_NBIO) ? kEnTrFlagNonBlocking : 0),
                            (int64_t)en_tracing_val);
                }
        }

        mptcp_update_last_owner(so, mp_so);

        if (mp_so->last_pid != proc_pid(p)) {
                p = proc_find(mp_so->last_pid);
                if (p == PROC_NULL) {
                        p = current_proc();
                } else {
                        proc_held = TRUE;
                }
        }

#if NECP
        inp_update_necp_policy(sotoinpcb(so), NULL, NULL, 0);
#endif /* NECP */

        OSIncrementAtomicLong(&p->p_stats->p_ru.ru_msgsnd);

        error = sosendcheck(so, NULL, top->m_pkthdr.len, 0, 1, 0, &sblocked, NULL);
        if (error) {
                goto out;
        }

        error = (*so->so_proto->pr_usrreqs->pru_send)(so, 0, top, NULL, NULL, p);
        top = NULL;

out:
        if (top != NULL) {
                m_freem(top);
        }

        if (proc_held) {
                proc_rele(p);
        }

        soclearfastopen(so);

        if (en_tracing) {
                KERNEL_ENERGYTRACE(kEnTrActKernSockWrite, DBG_FUNC_END,
                    (unsigned long)VM_KERNEL_ADDRPERM(so),
                    ((error == EWOULDBLOCK) ? kEnTrFlagNoWork : 0),
                    (int64_t)en_tracing_val);
        }

        return error;
}

/*
 * 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 sockaddr *src,
    struct sockaddr *dst, uint32_t ifscope, sae_connid_t *pcid)
{
        struct socket *mp_so, *so = NULL;
        struct mptcb *mp_tp;
        struct mptsub *mpts = NULL;
        int af, error = 0;

        mp_so = mptetoso(mpte);
        mp_tp = mpte->mpte_mptcb;

        socket_lock_assert_owned(mp_so);

        if (mp_tp->mpt_state >= MPTCPS_CLOSE_WAIT) {
                /* If the remote end sends Data FIN, refuse subflow adds */
                os_log_error(mptcp_log_handle, "%s - %lx: state %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mp_tp->mpt_state);
                error = ENOTCONN;
                goto out_err;
        }

        mpts = mptcp_subflow_alloc();
        if (mpts == NULL) {
                os_log_error(mptcp_log_handle, "%s - %lx: malloc subflow failed\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
                error = ENOMEM;
                goto out_err;
        }

        if (src) {
                if (src->sa_family != AF_INET && src->sa_family != AF_INET6) {
                        error = EAFNOSUPPORT;
                        goto out_err;
                }

                if (src->sa_family == AF_INET &&
                    src->sa_len != sizeof(struct sockaddr_in)) {
                        error = EINVAL;
                        goto out_err;
                }

                if (src->sa_family == AF_INET6 &&
                    src->sa_len != sizeof(struct sockaddr_in6)) {
                        error = EINVAL;
                        goto out_err;
                }

                MALLOC(mpts->mpts_src, struct sockaddr *, src->sa_len, M_SONAME,
                    M_WAITOK | M_ZERO);
                if (mpts->mpts_src == NULL) {
                        error = ENOMEM;
                        goto out_err;
                }
                bcopy(src, mpts->mpts_src, src->sa_len);
        }

        if (dst->sa_family != AF_INET && dst->sa_family != AF_INET6) {
                error = EAFNOSUPPORT;
                goto out_err;
        }

        if (dst->sa_family == AF_INET &&
            dst->sa_len != sizeof(mpts->__mpts_dst_v4)) {
                error = EINVAL;
                goto out_err;
        }

        if (dst->sa_family == AF_INET6 &&
            dst->sa_len != sizeof(mpts->__mpts_dst_v6)) {
                error = EINVAL;
                goto out_err;
        }

        memcpy(&mpts->mpts_u_dst, dst, dst->sa_len);

        af = mpts->mpts_dst.sa_family;

        ifnet_head_lock_shared();
        if ((ifscope > (unsigned)if_index)) {
                ifnet_head_done();
                error = ENXIO;
                goto out_err;
        }
        ifnet_head_done();

        mpts->mpts_ifscope = ifscope;

        /* create the subflow socket */
        if ((error = mptcp_subflow_socreate(mpte, mpts, af, &so)) != 0) {
                /*
                 * Returning (error) and not cleaning up, because up to here
                 * all we did is creating mpts.
                 *
                 * And the contract is that the call to mptcp_subflow_socreate,
                 * moves ownership of mpts to mptcp_subflow_socreate.
                 */
                return error;
        }

        /*
         * We may be called from within the kernel. Still need to account this
         * one to the real app.
         */
        mptcp_update_last_owner(mpts->mpts_socket, mp_so);

        /*
         * 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;

        mpts->mpts_rel_seq = 1;

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

        /* register for subflow socket read/write events */
        sock_setupcalls_locked(so, NULL, NULL, mptcp_subflow_wupcall, mpts, 1);

        /* Register for subflow socket control events */
        sock_catchevents_locked(so, mptcp_subflow_eupcall1, mpts,
            SO_FILT_HINT_CONNRESET | SO_FILT_HINT_CANTRCVMORE |
            SO_FILT_HINT_TIMEOUT | SO_FILT_HINT_NOSRCADDR |
            SO_FILT_HINT_IFDENIED | SO_FILT_HINT_CONNECTED |
            SO_FILT_HINT_DISCONNECTED | SO_FILT_HINT_MPFAILOVER |
            SO_FILT_HINT_MPSTATUS | SO_FILT_HINT_MUSTRST |
            SO_FILT_HINT_MPCANTRCVMORE | SO_FILT_HINT_ADAPTIVE_RTIMO |
            SO_FILT_HINT_ADAPTIVE_WTIMO | SO_FILT_HINT_MP_SUB_ERROR);

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

        /*
         * 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.)
         */
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED && mpte->mpte_numflows == 1) {
                mpts->mpts_flags |= MPTSF_INITIAL_SUB;

                if (mp_tp->mpt_state == MPTCPS_CLOSED) {
                        mptcp_init_local_parms(mpte);
                }
                soisconnecting(mp_so);

                /* If fastopen is requested, set state in mpts */
                if (so->so_flags1 & SOF1_PRECONNECT_DATA) {
                        mpts->mpts_flags |= MPTSF_TFO_REQD;
                }
        } else {
                if (!(mp_tp->mpt_flags & MPTCPF_JOIN_READY)) {
                        mpts->mpts_flags |= MPTSF_CONNECT_PENDING;
                }
        }

        mpts->mpts_flags |= MPTSF_CONNECTING;

        /* 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);
        }

        if (error) {
                goto out_err_close;
        }

        if (pcid) {
                *pcid = mpts->mpts_connid;
        }

        return 0;

out_err_close:
        mptcp_subflow_abort(mpts, error);

        return error;

out_err:
        if (mpts) {
                mptcp_subflow_free(mpts);
        }

        return error;
}

void
mptcpstats_update(struct mptcp_itf_stats *stats, const struct mptsub *mpts)
{
        int index = mptcpstats_get_index(stats, mpts);

        if (index != -1) {
                struct inpcb *inp = sotoinpcb(mpts->mpts_socket);

                stats[index].mpis_txbytes += inp->inp_stat->txbytes;
                stats[index].mpis_rxbytes += inp->inp_stat->rxbytes;

                stats[index].mpis_wifi_txbytes += inp->inp_wstat->txbytes;
                stats[index].mpis_wifi_rxbytes += inp->inp_wstat->rxbytes;

                stats[index].mpis_wired_txbytes += inp->inp_Wstat->txbytes;
                stats[index].mpis_wired_rxbytes += inp->inp_Wstat->rxbytes;

                stats[index].mpis_cell_txbytes += inp->inp_cstat->txbytes;
                stats[index].mpis_cell_rxbytes += inp->inp_cstat->rxbytes;
        }
}

/*
 * 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.
 */
void
mptcp_subflow_del(struct mptses *mpte, struct mptsub *mpts)
{
        struct socket *mp_so = mptetoso(mpte);
        struct socket *so = mpts->mpts_socket;
        struct tcpcb *tp = sototcpcb(so);

        socket_lock_assert_owned(mp_so);
        VERIFY(mpts->mpts_mpte == mpte);
        VERIFY(mpts->mpts_flags & MPTSF_ATTACHED);
        VERIFY(mpte->mpte_numflows != 0);
        VERIFY(mp_so->so_usecount > 0);

        mptcpstats_update(mpte->mpte_itfstats, mpts);

        mptcp_unset_cellicon(mpte, mpts, 1);

        mpte->mpte_init_rxbytes = sotoinpcb(so)->inp_stat->rxbytes;
        mpte->mpte_init_txbytes = sotoinpcb(so)->inp_stat->txbytes;

        atomic_bitclear_32(&mpts->mpts_flags, MPTSF_ATTACHED);
        TAILQ_REMOVE(&mpte->mpte_subflows, mpts, mpts_entry);
        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.
         */
        sock_setupcalls_locked(so, NULL, NULL, NULL, NULL, 0);
        sock_catchevents_locked(so, NULL, NULL, 0);

        mptcp_detach_mptcb_from_subf(mpte->mpte_mptcb, so);

        mp_so->so_usecount--;           /* for subflow socket */
        mpts->mpts_mpte = NULL;
        mpts->mpts_socket = NULL;

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

        so->so_flags &= ~SOF_MP_SUBFLOW;
        tp->t_mptcb = NULL;
        tp->t_mpsub = NULL;
}

void
mptcp_subflow_shutdown(struct mptses *mpte, struct mptsub *mpts)
{
        struct socket *so = mpts->mpts_socket;
        struct mptcb *mp_tp = mpte->mpte_mptcb;
        int send_dfin = 0;

        if (mp_tp->mpt_state > MPTCPS_CLOSE_WAIT) {
                send_dfin = 1;
        }

        if (!(so->so_state & (SS_ISDISCONNECTING | SS_ISDISCONNECTED)) &&
            (so->so_state & SS_ISCONNECTED)) {
                mptcplog((LOG_DEBUG, "MPTCP subflow shutdown %s: cid %d fin %d\n",
                    __func__, mpts->mpts_connid, send_dfin),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                if (send_dfin) {
                        mptcp_send_dfin(so);
                }
                soshutdownlock(so, SHUT_WR);
        }
}

static void
mptcp_subflow_abort(struct mptsub *mpts, int error)
{
        struct socket *so = mpts->mpts_socket;
        struct tcpcb *tp = sototcpcb(so);

        if (mpts->mpts_flags & MPTSF_DISCONNECTED) {
                return;
        }

        mptcplog((LOG_DEBUG, "%s aborting connection state %u\n", __func__, tp->t_state),
            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

        if (tp->t_state != TCPS_CLOSED) {
                tcp_drop(tp, error);
        }

        mptcp_subflow_eupcall1(so, mpts, SO_FILT_HINT_DISCONNECTED);
}

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

        so = mpts->mpts_socket;
        mp_tp = mpte->mpte_mptcb;
        mp_so = mptetoso(mpte);

        socket_lock_assert_owned(mp_so);

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

        mptcp_unset_cellicon(mpte, mpts, 1);

        mpts->mpts_flags |= MPTSF_DISCONNECTING;

        if (mp_tp->mpt_state > MPTCPS_CLOSE_WAIT) {
                send_dfin = 1;
        }

        if (!(so->so_state & (SS_ISDISCONNECTING | SS_ISDISCONNECTED)) &&
            (so->so_state & SS_ISCONNECTED)) {
                mptcplog((LOG_DEBUG, "%s: cid %d fin %d\n",
                    __func__, mpts->mpts_connid, send_dfin),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                if (send_dfin) {
                        mptcp_send_dfin(so);
                }

                if (mp_so->so_flags & SOF_DEFUNCT) {
                        errno_t ret;

                        ret = sosetdefunct(NULL, so, SHUTDOWN_SOCKET_LEVEL_DISCONNECT_ALL, TRUE);
                        if (ret == 0) {
                                ret = sodefunct(NULL, so, SHUTDOWN_SOCKET_LEVEL_DISCONNECT_ALL);

                                if (ret != 0) {
                                        os_log_error(mptcp_log_handle, "%s - %lx: sodefunct failed with %d\n",
                                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), ret);
                                }
                        } else {
                                os_log_error(mptcp_log_handle, "%s - %lx: sosetdefunct failed with %d\n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), ret);
                        }
                } else {
                        (void) soshutdownlock(so, SHUT_RD);
                        (void) soshutdownlock(so, SHUT_WR);
                        (void) sodisconnectlocked(so);
                }
        }

        /*
         * 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.
         */
        mptcp_subflow_eupcall1(so, mpts, SO_FILT_HINT_DISCONNECTED);
}

/*
 * Subflow socket input.
 */
static void
mptcp_subflow_input(struct mptses *mpte, struct mptsub *mpts)
{
        struct socket *mp_so = mptetoso(mpte);
        struct mbuf *m = NULL;
        struct socket *so;
        int error, wakeup = 0;

        VERIFY(!(mpte->mpte_mppcb->mpp_flags & MPP_INSIDE_INPUT));
        mpte->mpte_mppcb->mpp_flags |= MPP_INSIDE_INPUT;

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

        if (!(mpts->mpts_flags & MPTSF_CONNECTED)) {
                goto out;
        }

        so = mpts->mpts_socket;

        error = sock_receive_internal(so, NULL, &m, 0, NULL);
        if (error != 0 && error != EWOULDBLOCK) {
                os_log_error(mptcp_log_handle, "%s - %lx: cid %d error %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpts->mpts_connid, error);
                if (error == ENODATA) {
                        /*
                         * Don't ignore ENODATA so as to discover
                         * nasty middleboxes.
                         */
                        mp_so->so_error = ENODATA;

                        wakeup = 1;
                        goto out;
                }
        } else if (error == 0) {
                mptcplog((LOG_DEBUG, "%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 (m && (mpts->mpts_flags & MPTSF_MP_DEGRADED) &&
            !(mpts->mpts_flags & MPTSF_ACTIVE)) {
                mptcplog((LOG_DEBUG, "%s: degraded and got data on non-active flow\n",
                    __func__), MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_VERBOSE);
                m_freem(m);
                goto out;
        }

        if (m != NULL) {
                if (IFNET_IS_CELLULAR(sotoinpcb(so)->inp_last_outifp)) {
                        mptcp_set_cellicon(mpte, mpts);

                        mpte->mpte_used_cell = 1;
                } else {
                        /*
                         * If during the past MPTCP_CELLICON_TOGGLE_RATE seconds we didn't
                         * explicitly set the cellicon, then we unset it again.
                         */
                        if (TSTMP_LT(mpte->mpte_last_cellicon_set + MPTCP_CELLICON_TOGGLE_RATE, tcp_now)) {
                                mptcp_unset_cellicon(mpte, NULL, 1);
                        }

                        mpte->mpte_used_wifi = 1;
                }

                mptcp_input(mpte, m);
        }

out:
        if (wakeup) {
                mpte->mpte_mppcb->mpp_flags |= MPP_SHOULD_RWAKEUP;
        }

        mptcp_handle_deferred_upcalls(mpte->mpte_mppcb, MPP_INSIDE_INPUT);
}

void
mptcp_handle_input(struct socket *so)
{
        struct mptsub *mpts, *tmpts;
        struct mptses *mpte;

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

        mpts = sototcpcb(so)->t_mpsub;
        mpte = mpts->mpts_mpte;

        socket_lock_assert_owned(mptetoso(mpte));

        if (mptcp_should_defer_upcall(mpte->mpte_mppcb)) {
                if (!(mpte->mpte_mppcb->mpp_flags & MPP_INPUT_HANDLE)) {
                        mpte->mpte_mppcb->mpp_flags |= MPP_SHOULD_RWAKEUP;
                }
                return;
        }

        mpte->mpte_mppcb->mpp_flags |= MPP_INPUT_HANDLE;
        TAILQ_FOREACH_SAFE(mpts, &mpte->mpte_subflows, mpts_entry, tmpts) {
                if (mpts->mpts_socket->so_usecount == 0) {
                        /* Will be removed soon by tcp_garbage_collect */
                        continue;
                }

                mptcp_subflow_addref(mpts);
                mpts->mpts_socket->so_usecount++;

                mptcp_subflow_input(mpte, mpts);

                mptcp_subflow_remref(mpts);             /* ours */

                VERIFY(mpts->mpts_socket->so_usecount != 0);
                mpts->mpts_socket->so_usecount--;
        }

        mptcp_handle_deferred_upcalls(mpte->mpte_mppcb, MPP_INPUT_HANDLE);
}

/*
 * Subflow socket write upcall.
 *
 * Called when the associated subflow socket posted a read event.
 */
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;

        VERIFY(mpte != NULL);

        if (mptcp_should_defer_upcall(mpte->mpte_mppcb)) {
                if (!(mpte->mpte_mppcb->mpp_flags & MPP_WUPCALL)) {
                        mpte->mpte_mppcb->mpp_flags |= MPP_SHOULD_WWAKEUP;
                }
                return;
        }

        mptcp_output(mpte);
}

static boolean_t
mptcp_search_seq_in_sub(struct mbuf *m, struct socket *so)
{
        struct mbuf *so_m = so->so_snd.sb_mb;
        uint64_t dsn = m->m_pkthdr.mp_dsn;

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

                /* Part of the segment is covered, don't reinject here */
                if (so_m->m_pkthdr.mp_dsn <= dsn &&
                    so_m->m_pkthdr.mp_dsn + so_m->m_pkthdr.mp_rlen > dsn) {
                        return TRUE;
                }

                so_m = so_m->m_next;
        }

        return FALSE;
}

/*
 * Subflow socket output.
 *
 * Called for sending data from MPTCP to the underlying subflow socket.
 */
int
mptcp_subflow_output(struct mptses *mpte, struct mptsub *mpts, int flags)
{
        struct mptcb *mp_tp = mpte->mpte_mptcb;
        struct mbuf *sb_mb, *m, *mpt_mbuf = NULL, *head, *tail;
        struct socket *mp_so, *so;
        struct tcpcb *tp;
        uint64_t mpt_dsn = 0, off = 0;
        int sb_cc = 0, error = 0, wakeup = 0;
        uint32_t dss_csum;
        uint16_t tot_sent = 0;
        boolean_t reinjected = FALSE;

        mp_so = mptetoso(mpte);
        so = mpts->mpts_socket;
        tp = sototcpcb(so);

        socket_lock_assert_owned(mp_so);

        VERIFY(!(mpte->mpte_mppcb->mpp_flags & MPP_INSIDE_OUTPUT));
        mpte->mpte_mppcb->mpp_flags |= MPP_INSIDE_OUTPUT;

        VERIFY(!INP_WAIT_FOR_IF_FEEDBACK(sotoinpcb(so)));
        VERIFY((mpts->mpts_flags & MPTSF_MP_CAPABLE) ||
            (mpts->mpts_flags & MPTSF_MP_DEGRADED) ||
            (mpts->mpts_flags & MPTSF_TFO_REQD));
        VERIFY(mptcp_subflow_cwnd_space(mpts->mpts_socket) > 0);

        mptcplog((LOG_DEBUG, "%s mpts_flags %#x, mpte_flags %#x cwnd_space %u\n",
            __func__, mpts->mpts_flags, mpte->mpte_flags,
            mptcp_subflow_cwnd_space(so)),
            MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
        DTRACE_MPTCP2(subflow__output, struct mptses *, mpte,
            struct mptsub *, mpts);

        /* Remove Addr Option is not sent reliably as per I-D */
        if (mpte->mpte_flags & MPTE_SND_REM_ADDR) {
                tp->t_rem_aid = mpte->mpte_lost_aid;
                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.
         */

        if (mpte->mpte_reinjectq) {
                sb_mb = mpte->mpte_reinjectq;
        } else {
                sb_mb = mp_so->so_snd.sb_mb;
        }

        if (sb_mb == NULL) {
                os_log_error(mptcp_log_handle, "%s - %lx: No data in MPTCP-sendbuffer! smax %u snxt %u suna %u state %u flags %#x\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                    (uint32_t)mp_tp->mpt_sndmax, (uint32_t)mp_tp->mpt_sndnxt,
                    (uint32_t)mp_tp->mpt_snduna, mp_tp->mpt_state, mp_so->so_flags1);

                /* Fix it to prevent looping */
                if (MPTCP_SEQ_LT(mp_tp->mpt_sndnxt, mp_tp->mpt_snduna)) {
                        mp_tp->mpt_sndnxt = mp_tp->mpt_snduna;
                }
                goto out;
        }

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

        if (sb_mb->m_pkthdr.mp_rlen == 0 &&
            !(so->so_state & SS_ISCONNECTED) &&
            (so->so_flags1 & SOF1_PRECONNECT_DATA)) {
                tp->t_mpflags |= TMPF_TFO_REQUEST;
                goto zero_len_write;
        }

        mpt_dsn = sb_mb->m_pkthdr.mp_dsn;

        /* First, drop acknowledged data */
        if (MPTCP_SEQ_LT(mpt_dsn, mp_tp->mpt_snduna)) {
                os_log_error(mptcp_log_handle, "%s - %lx: dropping data, should have been done earlier "
                    "dsn %u suna %u reinject? %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), (uint32_t)mpt_dsn,
                    (uint32_t)mp_tp->mpt_snduna, !!mpte->mpte_reinjectq);
                if (mpte->mpte_reinjectq) {
                        mptcp_clean_reinjectq(mpte);
                } else {
                        uint64_t len = 0;
                        len = mp_tp->mpt_snduna - mpt_dsn;
                        sbdrop(&mp_so->so_snd, (int)len);
                        wakeup = 1;
                }
        }

        /* Check again because of above sbdrop */
        if (mp_so->so_snd.sb_mb == NULL && mpte->mpte_reinjectq == NULL) {
                os_log_error(mptcp_log_handle, "%s - $%lx: send-buffer is empty\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
                goto out;
        }

        /*
         * In degraded mode, we don't receive data acks, so force free
         * mbufs less than snd_nxt
         */
        if ((mpts->mpts_flags & MPTSF_MP_DEGRADED) &&
            (mp_tp->mpt_flags & MPTCPF_POST_FALLBACK_SYNC) &&
            mp_so->so_snd.sb_mb) {
                mpt_dsn = mp_so->so_snd.sb_mb->m_pkthdr.mp_dsn;
                if (MPTCP_SEQ_LT(mpt_dsn, mp_tp->mpt_snduna)) {
                        uint64_t len = 0;
                        len = mp_tp->mpt_snduna - mpt_dsn;
                        sbdrop(&mp_so->so_snd, (int)len);
                        wakeup = 1;

                        os_log_error(mptcp_log_handle, "%s - %lx: dropping data in degraded mode, should have been done earlier dsn %u sndnxt %u suna %u\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                            (uint32_t)mpt_dsn, (uint32_t)mp_tp->mpt_sndnxt, (uint32_t)mp_tp->mpt_snduna);
                }
        }

        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;
        }

        /*
         * 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 */
        if (mpte->mpte_reinjectq) {
                sb_mb = mpte->mpte_reinjectq;
        } else {
dont_reinject:
                sb_mb = mp_so->so_snd.sb_mb;
        }
        if (sb_mb == NULL) {
                os_log_error(mptcp_log_handle, "%s - %lx: send-buffer is still empty\n", __func__,
                    (unsigned long)VM_KERNEL_ADDRPERM(mpte));
                goto out;
        }

        if (sb_mb == mpte->mpte_reinjectq) {
                sb_cc = sb_mb->m_pkthdr.mp_rlen;
                off = 0;

                if (mptcp_search_seq_in_sub(sb_mb, so)) {
                        if (mptcp_can_send_more(mp_tp, TRUE)) {
                                goto dont_reinject;
                        }

                        error = ECANCELED;
                        goto out;
                }

                reinjected = TRUE;
        } else if (flags & MPTCP_SUBOUT_PROBING) {
                sb_cc = sb_mb->m_pkthdr.mp_rlen;
                off = 0;
        } else {
                sb_cc = min(mp_so->so_snd.sb_cc, mp_tp->mpt_sndwnd);

                /*
                 * With TFO, there might be no data at all, thus still go into this
                 * code-path here.
                 */
                if ((mp_so->so_flags1 & SOF1_PRECONNECT_DATA) ||
                    MPTCP_SEQ_LT(mp_tp->mpt_sndnxt, mp_tp->mpt_sndmax)) {
                        off = mp_tp->mpt_sndnxt - mp_tp->mpt_snduna;
                        sb_cc -= off;
                } else {
                        os_log_error(mptcp_log_handle, "%s - %lx: this should not happen: sndnxt %u sndmax %u\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), (uint32_t)mp_tp->mpt_sndnxt,
                            (uint32_t)mp_tp->mpt_sndmax);

                        goto out;
                }
        }

        sb_cc = min(sb_cc, mptcp_subflow_cwnd_space(so));
        if (sb_cc <= 0) {
                os_log_error(mptcp_log_handle, "%s - %lx: sb_cc is %d, mp_so->sb_cc %u, sndwnd %u,sndnxt %u sndmax %u cwnd %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), sb_cc, mp_so->so_snd.sb_cc, mp_tp->mpt_sndwnd,
                    (uint32_t)mp_tp->mpt_sndnxt, (uint32_t)mp_tp->mpt_sndmax,
                    mptcp_subflow_cwnd_space(so));
        }

        sb_cc = min(sb_cc, UINT16_MAX);

        /*
         * Create a DSN mapping for the data we are about to send. It all
         * has the same mapping.
         */
        if (reinjected) {
                mpt_dsn = sb_mb->m_pkthdr.mp_dsn;
        } else {
                mpt_dsn = mp_tp->mpt_snduna + off;
        }

        mpt_mbuf = sb_mb;
        while (mpt_mbuf && reinjected == FALSE &&
            (mpt_mbuf->m_pkthdr.mp_rlen == 0 ||
            mpt_mbuf->m_pkthdr.mp_rlen <= (uint32_t)off)) {
                off -= mpt_mbuf->m_pkthdr.mp_rlen;
                mpt_mbuf = mpt_mbuf->m_next;
        }
        if (mpts->mpts_flags & MPTSF_MP_DEGRADED) {
                mptcplog((LOG_DEBUG, "%s: %u snduna = %u sndnxt = %u probe %d\n",
                    __func__, mpts->mpts_connid, (uint32_t)mp_tp->mpt_snduna, (uint32_t)mp_tp->mpt_sndnxt,
                    mpts->mpts_probecnt),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
        }

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

        head = tail = NULL;

        while (tot_sent < sb_cc) {
                ssize_t mlen;

                mlen = mpt_mbuf->m_len;
                mlen -= off;
                mlen = min(mlen, sb_cc - tot_sent);

                if (mlen < 0) {
                        os_log_error(mptcp_log_handle, "%s - %lx: mlen %d mp_rlen %u off %u sb_cc %u tot_sent %u\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), (int)mlen, mpt_mbuf->m_pkthdr.mp_rlen,
                            (uint32_t)off, sb_cc, tot_sent);
                        goto out;
                }

                if (mlen == 0) {
                        goto next;
                }

                m = m_copym_mode(mpt_mbuf, (int)off, mlen, M_DONTWAIT,
                    M_COPYM_MUST_COPY_HDR);
                if (m == NULL) {
                        os_log_error(mptcp_log_handle, "%s - %lx: m_copym_mode failed\n", __func__,
                            (unsigned long)VM_KERNEL_ADDRPERM(mpte));
                        error = ENOBUFS;
                        break;
                }

                /* Create a DSN mapping for the data (m_copym does it) */
                VERIFY(m->m_flags & M_PKTHDR);
                VERIFY(m->m_next == NULL);

                m->m_pkthdr.pkt_flags |= PKTF_MPTCP;
                m->m_pkthdr.pkt_flags &= ~PKTF_MPSO;
                m->m_pkthdr.mp_dsn = mpt_dsn;
                m->m_pkthdr.mp_rseq = mpts->mpts_rel_seq;
                m->m_pkthdr.len = mlen;

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

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

        if (reinjected) {
                if (sb_cc < sb_mb->m_pkthdr.mp_rlen) {
                        struct mbuf *n = sb_mb;

                        while (n) {
                                n->m_pkthdr.mp_dsn += sb_cc;
                                n->m_pkthdr.mp_rlen -= sb_cc;
                                n = n->m_next;
                        }
                        m_adj(sb_mb, sb_cc);
                } else {
                        mpte->mpte_reinjectq = sb_mb->m_nextpkt;
                        m_freem(sb_mb);
                }
        }

        mptcplog((LOG_DEBUG, "%s: Queued dsn %u ssn %u len %u on sub %u\n",
            __func__, (uint32_t)mpt_dsn, mpts->mpts_rel_seq,
            tot_sent, mpts->mpts_connid), MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);

        if (head && (mp_tp->mpt_flags & MPTCPF_CHECKSUM)) {
                dss_csum = mptcp_output_csum(head, mpt_dsn, mpts->mpts_rel_seq,
                    tot_sent);
        }

        /* Now, let's update rel-seq and the data-level length */
        mpts->mpts_rel_seq += tot_sent;
        m = head;
        while (m) {
                if (mp_tp->mpt_flags & MPTCPF_CHECKSUM) {
                        m->m_pkthdr.mp_csum = dss_csum;
                }
                m->m_pkthdr.mp_rlen = tot_sent;
                m = m->m_next;
        }

        if (head != NULL) {
                if ((mpts->mpts_flags & MPTSF_TFO_REQD) &&
                    (tp->t_tfo_stats == 0)) {
                        tp->t_mpflags |= TMPF_TFO_REQUEST;
                }

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

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

done_sending:
        if (error == 0 ||
            (error == EWOULDBLOCK && (tp->t_mpflags & TMPF_TFO_REQUEST))) {
                uint64_t new_sndnxt = mp_tp->mpt_sndnxt + tot_sent;

                if (mpts->mpts_probesoon && mpts->mpts_maxseg && tot_sent) {
                        tcpstat.tcps_mp_num_probes++;
                        if ((uint32_t)tot_sent < mpts->mpts_maxseg) {
                                mpts->mpts_probecnt += 1;
                        } else {
                                mpts->mpts_probecnt +=
                                    tot_sent / mpts->mpts_maxseg;
                        }
                }

                if (!reinjected && !(flags & MPTCP_SUBOUT_PROBING)) {
                        if (MPTCP_DATASEQ_HIGH32(new_sndnxt) >
                            MPTCP_DATASEQ_HIGH32(mp_tp->mpt_sndnxt)) {
                                mp_tp->mpt_flags |= MPTCPF_SND_64BITDSN;
                        }
                        mp_tp->mpt_sndnxt = new_sndnxt;
                }

                mptcp_cancel_timer(mp_tp, MPTT_REXMT);

                /* Must be here as mptcp_can_send_more() checks for this */
                soclearfastopen(mp_so);

                if ((mpts->mpts_flags & MPTSF_MP_DEGRADED) ||
                    (mpts->mpts_probesoon != 0)) {
                        mptcplog((LOG_DEBUG, "%s %u degraded %u wrote %d %d probe %d probedelta %d\n",
                            __func__, mpts->mpts_connid,
                            !!(mpts->mpts_flags & MPTSF_MP_DEGRADED),
                            tot_sent, (int) sb_cc, mpts->mpts_probecnt,
                            (tcp_now - mpts->mpts_probesoon)),
                            MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
                }

                if (IFNET_IS_CELLULAR(sotoinpcb(so)->inp_last_outifp)) {
                        mptcp_set_cellicon(mpte, mpts);

                        mpte->mpte_used_cell = 1;
                } else {
                        /*
                         * If during the past MPTCP_CELLICON_TOGGLE_RATE seconds we didn't
                         * explicitly set the cellicon, then we unset it again.
                         */
                        if (TSTMP_LT(mpte->mpte_last_cellicon_set + MPTCP_CELLICON_TOGGLE_RATE, tcp_now)) {
                                mptcp_unset_cellicon(mpte, NULL, 1);
                        }

                        mpte->mpte_used_wifi = 1;
                }

                /*
                 * Don't propagate EWOULDBLOCK - it's already taken care of
                 * in mptcp_usr_send for TFO.
                 */
                error = 0;
        } else {
                os_log_error(mptcp_log_handle, "%s - %lx: %u error %d len %d subflags %#x sostate %#x soerror %u hiwat %u lowat %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpts->mpts_connid, error, tot_sent, so->so_flags, so->so_state, so->so_error, so->so_snd.sb_hiwat, so->so_snd.sb_lowat);
        }
out:

        if (wakeup) {
                mpte->mpte_mppcb->mpp_flags |= MPP_SHOULD_WWAKEUP;
        }

        mptcp_handle_deferred_upcalls(mpte->mpte_mppcb, MPP_INSIDE_OUTPUT);
        return error;

zero_len_write:
        /* Opting to call pru_send as no mbuf at subflow level */
        error = (*so->so_proto->pr_usrreqs->pru_send)(so, 0, NULL, NULL,
            NULL, current_proc());

        goto done_sending;
}

static void
mptcp_add_reinjectq(struct mptses *mpte, struct mbuf *m)
{
        struct mbuf *n, *prev = NULL;

        mptcplog((LOG_DEBUG, "%s reinjecting dsn %u dlen %u rseq %u\n",
            __func__, (uint32_t)m->m_pkthdr.mp_dsn, m->m_pkthdr.mp_rlen,
            m->m_pkthdr.mp_rseq),
            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

        n = mpte->mpte_reinjectq;

        /* First, look for an mbuf n, whose data-sequence-number is bigger or
         * equal than m's sequence number.
         */
        while (n) {
                if (MPTCP_SEQ_GEQ(n->m_pkthdr.mp_dsn, m->m_pkthdr.mp_dsn)) {
                        break;
                }

                prev = n;

                n = n->m_nextpkt;
        }

        if (n) {
                /* m is already fully covered by the next mbuf in the queue */
                if (n->m_pkthdr.mp_dsn == m->m_pkthdr.mp_dsn &&
                    n->m_pkthdr.mp_rlen >= m->m_pkthdr.mp_rlen) {
                        mptcplog((LOG_DEBUG, "%s fully covered with len %u\n",
                            __func__, n->m_pkthdr.mp_rlen),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
                        goto dont_queue;
                }

                /* m is covering the next mbuf entirely, thus we remove this guy */
                if (m->m_pkthdr.mp_dsn + m->m_pkthdr.mp_rlen >= n->m_pkthdr.mp_dsn + n->m_pkthdr.mp_rlen) {
                        struct mbuf *tmp = n->m_nextpkt;

                        mptcplog((LOG_DEBUG, "%s m is covering that guy dsn %u len %u dsn %u len %u\n",
                            __func__, m->m_pkthdr.mp_dsn, m->m_pkthdr.mp_rlen,
                            n->m_pkthdr.mp_dsn, n->m_pkthdr.mp_rlen),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                        m->m_nextpkt = NULL;
                        if (prev == NULL) {
                                mpte->mpte_reinjectq = tmp;
                        } else {
                                prev->m_nextpkt = tmp;
                        }

                        m_freem(n);
                        n = tmp;
                }
        }

        if (prev) {
                /* m is already fully covered by the previous mbuf in the queue */
                if (prev->m_pkthdr.mp_dsn + prev->m_pkthdr.mp_rlen >= m->m_pkthdr.mp_dsn + m->m_pkthdr.len) {
                        mptcplog((LOG_DEBUG, "%s prev covers us from %u with len %u\n",
                            __func__, prev->m_pkthdr.mp_dsn, prev->m_pkthdr.mp_rlen),
                            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);
                        goto dont_queue;
                }
        }

        if (prev == NULL) {
                mpte->mpte_reinjectq = m;
        } else {
                prev->m_nextpkt = m;
        }

        m->m_nextpkt = n;

        return;

dont_queue:
        m_freem(m);
        return;
}

static struct mbuf *
mptcp_lookup_dsn(struct mptses *mpte, uint64_t dsn)
{
        struct socket *mp_so = mptetoso(mpte);
        struct mbuf *m;

        m = mp_so->so_snd.sb_mb;

        while (m) {
                /* If this segment covers what we are looking for, return it. */
                if (MPTCP_SEQ_LEQ(m->m_pkthdr.mp_dsn, dsn) &&
                    MPTCP_SEQ_GT(m->m_pkthdr.mp_dsn + m->m_pkthdr.mp_rlen, dsn)) {
                        break;
                }


                /* Segment is no more in the queue */
                if (MPTCP_SEQ_GT(m->m_pkthdr.mp_dsn, dsn)) {
                        return NULL;
                }

                m = m->m_next;
        }

        return m;
}

static struct mbuf *
mptcp_copy_mbuf_list(struct mptses *mpte, struct mbuf *m, int len)
{
        struct mbuf *top = NULL, *tail = NULL;
        uint64_t dsn;
        uint32_t dlen, rseq;

        dsn = m->m_pkthdr.mp_dsn;
        dlen = m->m_pkthdr.mp_rlen;
        rseq = m->m_pkthdr.mp_rseq;

        while (len > 0) {
                struct mbuf *n;

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

                n = m_copym_mode(m, 0, m->m_len, M_DONTWAIT, M_COPYM_MUST_COPY_HDR);
                if (n == NULL) {
                        os_log_error(mptcp_log_handle, "%s - %lx: m_copym_mode returned NULL\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
                        goto err;
                }

                VERIFY(n->m_flags & M_PKTHDR);
                VERIFY(n->m_next == NULL);
                VERIFY(n->m_pkthdr.mp_dsn == dsn);
                VERIFY(n->m_pkthdr.mp_rlen == dlen);
                VERIFY(n->m_pkthdr.mp_rseq == rseq);
                VERIFY(n->m_len == m->m_len);

                n->m_pkthdr.pkt_flags |= (PKTF_MPSO | PKTF_MPTCP);

                if (top == NULL) {
                        top = n;
                }

                if (tail != NULL) {
                        tail->m_next = n;
                }

                tail = n;

                len -= m->m_len;
                m = m->m_next;
        }

        return top;

err:
        if (top) {
                m_freem(top);
        }

        return NULL;
}

static void
mptcp_reinject_mbufs(struct socket *so)
{
        struct tcpcb *tp = sototcpcb(so);
        struct mptsub *mpts = tp->t_mpsub;
        struct mptcb *mp_tp = tptomptp(tp);
        struct mptses *mpte = mp_tp->mpt_mpte;;
        struct sockbuf *sb = &so->so_snd;
        struct mbuf *m;

        m = sb->sb_mb;
        while (m) {
                struct mbuf *n = m->m_next, *orig = m;

                mptcplog((LOG_DEBUG, "%s working on suna %u relseq %u iss %u len %u pktflags %#x\n",
                    __func__, tp->snd_una, m->m_pkthdr.mp_rseq, mpts->mpts_iss,
                    m->m_pkthdr.mp_rlen, m->m_pkthdr.pkt_flags),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);

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

                if (m->m_pkthdr.pkt_flags & PKTF_MPTCP_REINJ) {
                        goto next;
                }

                /* Has it all already been acknowledged at the data-level? */
                if (MPTCP_SEQ_GEQ(mp_tp->mpt_snduna, m->m_pkthdr.mp_dsn + m->m_pkthdr.mp_rlen)) {
                        goto next;
                }

                /* Part of this has already been acknowledged - lookup in the
                 * MPTCP-socket for the segment.
                 */
                if (SEQ_GT(tp->snd_una - mpts->mpts_iss, m->m_pkthdr.mp_rseq)) {
                        m = mptcp_lookup_dsn(mpte, m->m_pkthdr.mp_dsn);
                        if (m == NULL) {
                                goto next;
                        }
                }

                /* Copy the mbuf with headers (aka, DSN-numbers) */
                m = mptcp_copy_mbuf_list(mpte, m, m->m_pkthdr.mp_rlen);
                if (m == NULL) {
                        break;
                }

                VERIFY(m->m_nextpkt == NULL);

                /* Now, add to the reinject-queue, eliminating overlapping
                 * segments
                 */
                mptcp_add_reinjectq(mpte, m);

                orig->m_pkthdr.pkt_flags |= PKTF_MPTCP_REINJ;

next:
                /* mp_rlen can cover multiple mbufs, so advance to the end of it. */
                while (n) {
                        VERIFY((n->m_flags & M_PKTHDR) && (n->m_pkthdr.pkt_flags & PKTF_MPTCP));

                        if (n->m_pkthdr.mp_dsn != orig->m_pkthdr.mp_dsn) {
                                break;
                        }

                        n->m_pkthdr.pkt_flags |= PKTF_MPTCP_REINJ;
                        n = n->m_next;
                }

                m = n;
        }
}

void
mptcp_clean_reinjectq(struct mptses *mpte)
{
        struct mptcb *mp_tp = mpte->mpte_mptcb;

        socket_lock_assert_owned(mptetoso(mpte));

        while (mpte->mpte_reinjectq) {
                struct mbuf *m = mpte->mpte_reinjectq;

                if (MPTCP_SEQ_GEQ(m->m_pkthdr.mp_dsn, mp_tp->mpt_snduna) ||
                    MPTCP_SEQ_GT(m->m_pkthdr.mp_dsn + m->m_pkthdr.mp_rlen, mp_tp->mpt_snduna)) {
                        break;
                }

                mpte->mpte_reinjectq = m->m_nextpkt;
                m->m_nextpkt = NULL;
                m_freem(m);
        }
}

/*
 * Subflow socket control event upcall.
 */
static void
mptcp_subflow_eupcall1(struct socket *so, void *arg, uint32_t events)
{
#pragma unused(so)
        struct mptsub *mpts = arg;
        struct mptses *mpte = mpts->mpts_mpte;

        socket_lock_assert_owned(mptetoso(mpte));

        if ((mpts->mpts_evctl & events) == events) {
                return;
        }

        mpts->mpts_evctl |= events;

        if (mptcp_should_defer_upcall(mpte->mpte_mppcb)) {
                mpte->mpte_mppcb->mpp_flags |= MPP_SHOULD_WORKLOOP;
                return;
        }

        mptcp_subflow_workloop(mpte);
}

/*
 * 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)
{
        ev_ret_t ret = MPTS_EVRET_OK;
        int i, mpsub_ev_entry_count = sizeof(mpsub_ev_entry_tbl) /
            sizeof(mpsub_ev_entry_tbl[0]);

        /* bail if there's nothing to process */
        if (!mpts->mpts_evctl) {
                return ret;
        }

        if (mpts->mpts_evctl & (SO_FILT_HINT_CONNRESET | SO_FILT_HINT_MUSTRST |
            SO_FILT_HINT_CANTSENDMORE | SO_FILT_HINT_TIMEOUT |
            SO_FILT_HINT_NOSRCADDR | SO_FILT_HINT_IFDENIED |
            SO_FILT_HINT_DISCONNECTED)) {
                mpts->mpts_evctl |= SO_FILT_HINT_MPFAILOVER;
        }

        DTRACE_MPTCP3(subflow__events, struct mptses *, mpte,
            struct mptsub *, mpts, uint32_t, mpts->mpts_evctl);

        mptcplog((LOG_DEBUG, "%s cid %d events=%b\n", __func__,
            mpts->mpts_connid, mpts->mpts_evctl, 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 && mpts->mpts_evctl; i++) {
                /*
                 * Always execute the DISCONNECTED event, because it will wakeup
                 * the app.
                 */
                if ((mpts->mpts_evctl & mpsub_ev_entry_tbl[i].sofilt_hint_mask) &&
                    (ret >= MPTS_EVRET_OK ||
                    mpsub_ev_entry_tbl[i].sofilt_hint_mask == SO_FILT_HINT_DISCONNECTED)) {
                        mpts->mpts_evctl &= ~mpsub_ev_entry_tbl[i].sofilt_hint_mask;
                        ev_ret_t error =
                            mpsub_ev_entry_tbl[i].sofilt_hint_ev_hdlr(mpte, mpts, p_mpsofilt_hint, 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 (mpts->mpts_evctl || ret < MPTS_EVRET_OK) {
                mptcplog((LOG_WARNING, "%s%s: cid %d evret %d unhandled events=%b\n", __func__,
                    (mpts->mpts_evctl && ret == MPTS_EVRET_OK) ? "MPTCP_ERROR " : "",
                    mpts->mpts_connid,
                    ret, mpts->mpts_evctl, SO_FILT_HINT_BITS),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
        } else {
                mptcplog((LOG_DEBUG, "%s: Done, events %b\n", __func__,
                    mpts->mpts_evctl, SO_FILT_HINT_BITS),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_VERBOSE);
        }

        return ret;
}

static ev_ret_t
mptcp_subflow_propagate_ev(struct mptses *mpte, struct mptsub *mpts,
    uint64_t *p_mpsofilt_hint, uint64_t event)
{
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;

        mp_so = mptetoso(mpte);
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

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

        /*
         * We got an event for this subflow that might need to be propagated,
         * based on the state of the MPTCP connection.
         */
        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED ||
            (!(mp_tp->mpt_flags & MPTCPF_JOIN_READY) && !(mpts->mpts_flags & MPTSF_MP_READY)) ||
            ((mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP) && (mpts->mpts_flags & MPTSF_ACTIVE))) {
                mp_so->so_error = so->so_error;
                *p_mpsofilt_hint |= event;
        }

        return MPTS_EVRET_OK;
}

/*
 * 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, uint64_t event)
{
#pragma unused(p_mpsofilt_hint, event)
        struct socket *mp_so;
        struct tcpcb *tp;

        mp_so = mptetoso(mpte);
        tp = intotcpcb(sotoinpcb(mpts->mpts_socket));

        /*
         * 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;

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

        /*
         * The subflow connection has lost its source address.
         */
        mptcp_subflow_abort(mpts, EADDRNOTAVAIL);

        if (mp_so->so_flags & SOF_NOADDRAVAIL) {
                mptcp_subflow_propagate_ev(mpte, mpts, p_mpsofilt_hint, event);
        }

        return MPTS_EVRET_DELETE;
}

static ev_ret_t
mptcp_subflow_mpsuberror_ev(struct mptses *mpte, struct mptsub *mpts,
    uint64_t *p_mpsofilt_hint, uint64_t event)
{
#pragma unused(event, p_mpsofilt_hint)
        struct socket *so, *mp_so;

        so = mpts->mpts_socket;

        if (so->so_error != ENODATA) {
                return MPTS_EVRET_OK;
        }


        mp_so = mptetoso(mpte);

        mp_so->so_error = ENODATA;

        sorwakeup(mp_so);
        sowwakeup(mp_so);

        return MPTS_EVRET_OK;
}


/*
 * 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, uint64_t event)
{
#pragma unused(event)
        struct mptcb *mp_tp = mpte->mpte_mptcb;

        mptcplog((LOG_DEBUG, "%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.
         */
        if (mp_tp->mpt_state == MPTCPS_CLOSE_WAIT) {
                *p_mpsofilt_hint |= SO_FILT_HINT_CANTRCVMORE;
        }

        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, uint64_t event)
{
#pragma unused(event, p_mpsofilt_hint)
        struct mptsub *mpts_alt = NULL;
        struct socket *alt_so = NULL;
        struct socket *mp_so;
        int altpath_exists = 0;

        mp_so = mptetoso(mpte);
        os_log_info(mptcp_log_handle, "%s - %lx\n", __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));

        mptcp_reinject_mbufs(mpts->mpts_socket);

        mpts_alt = mptcp_get_subflow(mpte, NULL);

        /* If there is no alternate eligible subflow, ignore the failover hint. */
        if (mpts_alt == NULL || mpts_alt == mpts) {
                os_log(mptcp_log_handle, "%s - %lx no alternate path\n", __func__,
                    (unsigned long)VM_KERNEL_ADDRPERM(mpte));

                goto done;
        }

        altpath_exists = 1;
        alt_so = mpts_alt->mpts_socket;
        if (mpts_alt->mpts_flags & MPTSF_FAILINGOVER) {
                /* All data acknowledged and no RTT spike */
                if (alt_so->so_snd.sb_cc == 0 && mptcp_no_rto_spike(alt_so)) {
                        mpts_alt->mpts_flags &= ~MPTSF_FAILINGOVER;
                } else {
                        /* no alternate path available */
                        altpath_exists = 0;
                }
        }

        if (altpath_exists) {
                mpts_alt->mpts_flags |= MPTSF_ACTIVE;

                mpte->mpte_active_sub = mpts_alt;
                mpts->mpts_flags |= MPTSF_FAILINGOVER;
                mpts->mpts_flags &= ~MPTSF_ACTIVE;

                os_log_info(mptcp_log_handle, "%s - %lx: switched from %d to %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpts->mpts_connid, mpts_alt->mpts_connid);

                mptcpstats_inc_switch(mpte, mpts);

                sowwakeup(alt_so);
        } else {
                mptcplog((LOG_DEBUG, "%s: no alt cid = %d\n", __func__,
                    mpts->mpts_connid),
                    MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);
done:
                mpts->mpts_socket->so_flags &= ~SOF_MP_TRYFAILOVER;
        }

        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, uint64_t event)
{
        mptcplog((LOG_DEBUG, "%s: cid %d\n", __func__,
            mpts->mpts_connid), MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        /*
         * The subflow connection cannot use the outgoing interface, let's
         * close this subflow.
         */
        mptcp_subflow_abort(mpts, EPERM);

        mptcp_subflow_propagate_ev(mpte, mpts, p_mpsofilt_hint, event);

        return MPTS_EVRET_DELETE;
}

/*
 * https://tools.ietf.org/html/rfc6052#section-2
 * https://tools.ietf.org/html/rfc6147#section-5.2
 */
static boolean_t
mptcp_desynthesize_ipv6_addr(const struct in6_addr *addr,
    const struct ipv6_prefix *prefix,
    struct in_addr *addrv4)
{
        char buf[MAX_IPv4_STR_LEN];
        char *ptrv4 = (char *)addrv4;
        const char *ptr = (const char *)addr;

        if (memcmp(addr, &prefix->ipv6_prefix, prefix->prefix_len) != 0) {
                return false;
        }

        switch (prefix->prefix_len) {
        case NAT64_PREFIX_LEN_96:
                memcpy(ptrv4, ptr + 12, 4);
                break;
        case NAT64_PREFIX_LEN_64:
                memcpy(ptrv4, ptr + 9, 4);
                break;
        case NAT64_PREFIX_LEN_56:
                memcpy(ptrv4, ptr + 7, 1);
                memcpy(ptrv4 + 1, ptr + 9, 3);
                break;
        case NAT64_PREFIX_LEN_48:
                memcpy(ptrv4, ptr + 6, 2);
                memcpy(ptrv4 + 2, ptr + 9, 2);
                break;
        case NAT64_PREFIX_LEN_40:
                memcpy(ptrv4, ptr + 5, 3);
                memcpy(ptrv4 + 3, ptr + 9, 1);
                break;
        case NAT64_PREFIX_LEN_32:
                memcpy(ptrv4, ptr + 4, 4);
                break;
        default:
                panic("NAT64-prefix len is wrong: %u\n",
                    prefix->prefix_len);
        }

        os_log_info(mptcp_log_handle, "%s desynthesized to %s\n", __func__,
            inet_ntop(AF_INET, (void *)addrv4, buf, sizeof(buf)));

        return true;
}

static void
mptcp_handle_ipv6_connection(struct mptses *mpte, const struct mptsub *mpts)
{
        struct ipv6_prefix nat64prefixes[NAT64_MAX_NUM_PREFIXES];
        struct socket *so = mpts->mpts_socket;
        struct ifnet *ifp;
        int j;

        /* Subflow IPs will be steered directly by the server - no need to
         * desynthesize.
         */
        if (mpte->mpte_flags & MPTE_UNICAST_IP) {
                return;
        }

        ifp = sotoinpcb(so)->inp_last_outifp;

        if (ifnet_get_nat64prefix(ifp, nat64prefixes) == ENOENT) {
                mptcp_ask_for_nat64(ifp);
                return;
        }


        for (j = 0; j < NAT64_MAX_NUM_PREFIXES; j++) {
                int success;

                if (nat64prefixes[j].prefix_len == 0) {
                        continue;
                }

                success = mptcp_desynthesize_ipv6_addr(&mpte->__mpte_dst_v6.sin6_addr,
                    &nat64prefixes[j],
                    &mpte->mpte_dst_v4_nat64.sin_addr);
                if (success) {
                        mpte->mpte_dst_v4_nat64.sin_len = sizeof(mpte->mpte_dst_v4_nat64);
                        mpte->mpte_dst_v4_nat64.sin_family = AF_INET;
                        mpte->mpte_dst_v4_nat64.sin_port = mpte->__mpte_dst_v6.sin6_port;
                        break;
                }
        }
}

/*
 * 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, uint64_t event)
{
#pragma unused(event, p_mpsofilt_hint)
        struct socket *mp_so, *so;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct mptcb *mp_tp;
        int af;
        boolean_t mpok = FALSE;

        mp_so = mptetoso(mpte);
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;
        tp = sototcpcb(so);
        af = mpts->mpts_dst.sa_family;

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

        if ((mpts->mpts_flags & MPTSF_DISCONNECTED) ||
            (mpts->mpts_flags & MPTSF_DISCONNECTING)) {
                if (!(so->so_state & (SS_ISDISCONNECTING | SS_ISDISCONNECTED)) &&
                    (so->so_state & SS_ISCONNECTED)) {
                        mptcplog((LOG_DEBUG, "%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);
                }
                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,
         *      fallback to regular TCP by degrading this subflow.
         *
         *   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.
         *
         * Right now, we simply unblock any waiters at the MPTCP socket layer
         * if the MPTCP connection has not been established.
         */

        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.
                 */
                return MPTS_EVRET_OK;
        }

        if (mpts->mpts_flags & MPTSF_TFO_REQD) {
                mptcp_drop_tfo_data(mpte, mpts);
        }

        mpts->mpts_flags &= ~(MPTSF_CONNECTING | MPTSF_TFO_REQD);
        mpts->mpts_flags |= MPTSF_CONNECTED;

        if (tp->t_mpflags & TMPF_MPTCP_TRUE) {
                mpts->mpts_flags |= MPTSF_MP_CAPABLE;
        }

        tp->t_mpflags &= ~TMPF_TFO_REQUEST;

        /* get/verify the outbound interface */
        inp = sotoinpcb(so);

        mpts->mpts_maxseg = tp->t_maxseg;

        mptcplog((LOG_DEBUG, "%s: cid %d outif %s is %s\n", __func__, mpts->mpts_connid,
            ((inp->inp_last_outifp != NULL) ? inp->inp_last_outifp->if_xname : "NULL"),
            ((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);

        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED) {
                mp_tp->mpt_state = MPTCPS_ESTABLISHED;
                mpte->mpte_associd = mpts->mpts_connid;
                DTRACE_MPTCP2(state__change,
                    struct mptcb *, mp_tp,
                    uint32_t, 0 /* event */);

                if (SOCK_DOM(so) == AF_INET) {
                        in_getsockaddr_s(so, &mpte->__mpte_src_v4);
                } else {
                        in6_getsockaddr_s(so, &mpte->__mpte_src_v6);
                }

                mpts->mpts_flags |= MPTSF_ACTIVE;

                /* case (a) above */
                if (!mpok) {
                        tcpstat.tcps_mpcap_fallback++;

                        tp->t_mpflags |= TMPF_INFIN_SENT;
                        mptcp_notify_mpfail(so);
                } else {
                        if (IFNET_IS_CELLULAR(inp->inp_last_outifp) &&
                            mpte->mpte_svctype < MPTCP_SVCTYPE_AGGREGATE) {
                                tp->t_mpflags |= (TMPF_BACKUP_PATH | TMPF_SND_MPPRIO);
                        } else {
                                mpts->mpts_flags |= MPTSF_PREFERRED;
                        }
                        mpts->mpts_flags |= MPTSF_MPCAP_CTRSET;
                        mpte->mpte_nummpcapflows++;

                        if (SOCK_DOM(so) == AF_INET6) {
                                mptcp_handle_ipv6_connection(mpte, mpts);
                        }

                        mptcp_check_subflows_and_add(mpte);

                        if (IFNET_IS_CELLULAR(inp->inp_last_outifp)) {
                                mpte->mpte_initial_cell = 1;
                        }

                        mpte->mpte_handshake_success = 1;
                }

                mp_tp->mpt_sndwnd = tp->snd_wnd;
                mp_tp->mpt_sndwl1 = mp_tp->mpt_rcvnxt;
                mp_tp->mpt_sndwl2 = mp_tp->mpt_snduna;
                soisconnected(mp_so);
        } else if (mpok) {
                /*
                 * 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.
                 */
                if (IFNET_IS_CELLULAR(inp->inp_last_outifp) &&
                    !(tp->t_mpflags & TMPF_BACKUP_PATH) &&
                    mpte->mpte_svctype < MPTCP_SVCTYPE_AGGREGATE) {
                        tp->t_mpflags |= (TMPF_BACKUP_PATH | TMPF_SND_MPPRIO);
                        mpts->mpts_flags &= ~MPTSF_PREFERRED;
                } else {
                        mpts->mpts_flags |= MPTSF_PREFERRED;
                }

                mpts->mpts_flags |= MPTSF_MPCAP_CTRSET;
                mpte->mpte_nummpcapflows++;

                mpts->mpts_rel_seq = 1;

                mptcp_check_subflows_and_remove(mpte);
        } else {
                unsigned int i;

                /* Should we try the alternate port? */
                if (mpte->mpte_alternate_port &&
                    inp->inp_fport != mpte->mpte_alternate_port) {
                        union sockaddr_in_4_6 dst;
                        struct sockaddr_in *dst_in = (struct sockaddr_in *)&dst;

                        memcpy(&dst, &mpts->mpts_dst, mpts->mpts_dst.sa_len);

                        dst_in->sin_port = mpte->mpte_alternate_port;

                        mptcp_subflow_add(mpte, NULL, (struct sockaddr *)&dst,
                            mpts->mpts_ifscope, NULL);
                } else { /* Else, we tried all we could, mark this interface as non-MPTCP */
                        for (i = 0; i < mpte->mpte_itfinfo_size; i++) {
                                struct mpt_itf_info *info =  &mpte->mpte_itfinfo[i];

                                if (inp->inp_last_outifp->if_index == info->ifindex) {
                                        info->no_mptcp_support = 1;
                                        break;
                                }
                        }
                }

                tcpstat.tcps_join_fallback++;
                if (IFNET_IS_CELLULAR(inp->inp_last_outifp)) {
                        tcpstat.tcps_mptcp_cell_proxy++;
                } else {
                        tcpstat.tcps_mptcp_wifi_proxy++;
                }

                soevent(mpts->mpts_socket, SO_FILT_HINT_LOCKED | SO_FILT_HINT_MUSTRST);

                return MPTS_EVRET_OK;
        }

        /* This call, just to "book" an entry in the stats-table for this ifindex */
        mptcpstats_get_index(mpte->mpte_itfstats, mpts);

        mptcp_output(mpte);

        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, uint64_t event)
{
#pragma unused(event, p_mpsofilt_hint)
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;

        mp_so = mptetoso(mpte);
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        mptcplog((LOG_DEBUG, "%s: cid %d, so_err %d, mpt_state %u fallback %u active %u flags %#x\n",
            __func__, mpts->mpts_connid, so->so_error, mp_tp->mpt_state,
            !!(mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP),
            !!(mpts->mpts_flags & MPTSF_ACTIVE), sototcpcb(so)->t_mpflags),
            MPTCP_EVENTS_DBG, MPTCP_LOGLVL_LOG);

        if (mpts->mpts_flags & MPTSF_DISCONNECTED) {
                return MPTS_EVRET_DELETE;
        }

        mpts->mpts_flags |= MPTSF_DISCONNECTED;

        /* The subflow connection has been disconnected. */

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

        if (mp_tp->mpt_state < MPTCPS_ESTABLISHED ||
            ((mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP) && (mpts->mpts_flags & MPTSF_ACTIVE))) {
                mptcp_drop(mpte, mp_tp, so->so_error);
        }

        /*
         * 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_ACTIVE);

        return 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, uint64_t event)
{
#pragma unused(event, p_mpsofilt_hint)
        ev_ret_t ret = MPTS_EVRET_OK;
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;

        mp_so = mptetoso(mpte);
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

        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) {
                ret = MPTS_EVRET_DISCONNECT_FALLBACK;

                m_freem_list(mpte->mpte_reinjectq);
                mpte->mpte_reinjectq = NULL;
        } else if (mpts->mpts_flags & MPTSF_MP_READY) {
                mp_tp->mpt_flags |= MPTCPF_JOIN_READY;
                ret = MPTS_EVRET_CONNECT_PENDING;
        }

done:
        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, uint64_t event)
{
#pragma unused(event)
        struct socket *mp_so, *so;
        struct mptcb *mp_tp;
        boolean_t is_fastclose;

        mp_so = mptetoso(mpte);
        mp_tp = mpte->mpte_mptcb;
        so = mpts->mpts_socket;

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

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

        is_fastclose = !!(tp->t_mpflags & TMPF_FASTCLOSERCV);

        tp->t_mpflags |= TMPF_RESET;

        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));
        }

        if (!(mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP) && is_fastclose) {
                struct mptsub *iter, *tmp;

                *p_mpsofilt_hint |= SO_FILT_HINT_CONNRESET;

                mp_so->so_error = ECONNRESET;

                TAILQ_FOREACH_SAFE(iter, &mpte->mpte_subflows, mpts_entry, tmp) {
                        if (iter == mpts) {
                                continue;
                        }
                        mptcp_subflow_abort(iter, ECONNABORTED);
                }

                /*
                 * mptcp_drop is being called after processing the events, to fully
                 * close the MPTCP connection
                 */
                mptcp_drop(mpte, mp_tp, mp_so->so_error);
        }

        mptcp_subflow_abort(mpts, ECONNABORTED);


        if (mp_tp->mpt_gc_ticks == MPT_GC_TICKS) {
                mp_tp->mpt_gc_ticks = MPT_GC_TICKS_FAST;
        }

        return MPTS_EVRET_DELETE;
}

static ev_ret_t
mptcp_subflow_adaptive_rtimo_ev(struct mptses *mpte, struct mptsub *mpts,
    uint64_t *p_mpsofilt_hint, uint64_t event)
{
#pragma unused(event)
        bool found_active = false;

        mpts->mpts_flags |= MPTSF_READ_STALL;

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                struct tcpcb *tp = sototcpcb(mpts->mpts_socket);

                if (!TCPS_HAVEESTABLISHED(tp->t_state) ||
                    TCPS_HAVERCVDFIN2(tp->t_state)) {
                        continue;
                }

                if (!(mpts->mpts_flags & MPTSF_READ_STALL)) {
                        found_active = true;
                        break;
                }
        }

        if (!found_active) {
                *p_mpsofilt_hint |= SO_FILT_HINT_ADAPTIVE_RTIMO;
        }

        return MPTS_EVRET_OK;
}

static ev_ret_t
mptcp_subflow_adaptive_wtimo_ev(struct mptses *mpte, struct mptsub *mpts,
    uint64_t *p_mpsofilt_hint, uint64_t event)
{
#pragma unused(event)
        bool found_active = false;

        mpts->mpts_flags |= MPTSF_WRITE_STALL;

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                struct tcpcb *tp = sototcpcb(mpts->mpts_socket);

                if (!TCPS_HAVEESTABLISHED(tp->t_state) ||
                    tp->t_state > TCPS_CLOSE_WAIT) {
                        continue;
                }

                if (!(mpts->mpts_flags & MPTSF_WRITE_STALL)) {
                        found_active = true;
                        break;
                }
        }

        if (!found_active) {
                *p_mpsofilt_hint |= SO_FILT_HINT_ADAPTIVE_WTIMO;
        }

        return MPTS_EVRET_OK;
}

/*
 * 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 mptsub *mpts, struct mptopt *mpo)
{
        struct socket *mp_so, *so;
        struct sockopt sopt;
        int error;

        VERIFY(mpo->mpo_flags & MPOF_SUBFLOW_OK);

        mp_so = mptetoso(mpte);
        so = mpts->mpts_socket;

        socket_lock_assert_owned(mp_so);

        if (mpte->mpte_mptcb->mpt_state >= MPTCPS_ESTABLISHED &&
            mpo->mpo_level == SOL_SOCKET &&
            mpo->mpo_name == SO_MARK_CELLFALLBACK) {
                struct ifnet *ifp = ifindex2ifnet[mpts->mpts_ifscope];

                mptcplog((LOG_DEBUG, "%s Setting CELL_FALLBACK, mpte_flags %#x, svctype %u wifi unusable %d lastcell? %d boundcell? %d\n",
                    __func__, mpte->mpte_flags, mpte->mpte_svctype, mptcp_is_wifi_unusable_for_session(mpte),
                    sotoinpcb(so)->inp_last_outifp ? IFNET_IS_CELLULAR(sotoinpcb(so)->inp_last_outifp) : -1,
                    mpts->mpts_ifscope != IFSCOPE_NONE && ifp ? IFNET_IS_CELLULAR(ifp) : -1),
                    MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

                /*
                 * When we open a new subflow, mark it as cell fallback, if
                 * this subflow goes over cell.
                 *
                 * (except for first-party apps)
                 */

                if (mpte->mpte_flags & MPTE_FIRSTPARTY) {
                        return 0;
                }

                if (sotoinpcb(so)->inp_last_outifp &&
                    !IFNET_IS_CELLULAR(sotoinpcb(so)->inp_last_outifp)) {
                        return 0;
                }

                /*
                 * This here is an OR, because if the app is not binding to the
                 * interface, then it definitely is not a cell-fallback
                 * connection.
                 */
                if (mpts->mpts_ifscope == IFSCOPE_NONE || ifp == NULL ||
                    !IFNET_IS_CELLULAR(ifp)) {
                        return 0;
                }
        }

        mpo->mpo_flags &= ~MPOF_INTERIM;

        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);
        if (error) {
                os_log_error(mptcp_log_handle, "%s - %lx: sopt %s "
                    "val %d set error %d\n", __func__,
                    (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                    mptcp_sopt2str(mpo->mpo_level, mpo->mpo_name),
                    mpo->mpo_intval, error);
        }
        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;
        int error;

        VERIFY(mpo->mpo_flags & MPOF_SUBFLOW_OK);
        mp_so = mptetoso(mpte);

        socket_lock_assert_owned(mp_so);

        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) {
                os_log_error(mptcp_log_handle,
                    "%s - %lx: sopt %s get error %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                    mptcp_sopt2str(mpo->mpo_level, mpo->mpo_name), error);
        }
        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;

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

                if (!mpp_try_lock(mpp)) {
                        active++;
                        continue;
                }

                VERIFY(mpp->mpp_flags & MPP_ATTACHED);

                /* check again under the lock */
                if (mp_so->so_usecount > 0) {
                        boolean_t wakeup = FALSE;
                        struct mptsub *mpts, *tmpts;

                        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 (wakeup) {
                                TAILQ_FOREACH_SAFE(mpts,
                                    &mpte->mpte_subflows, mpts_entry, tmpts) {
                                        mptcp_subflow_eupcall1(mpts->mpts_socket,
                                            mpts, SO_FILT_HINT_DISCONNECTED);
                                }
                        }
                        socket_unlock(mp_so, 0);
                        active++;
                        continue;
                }

                if (mpp->mpp_state != MPPCB_STATE_DEAD) {
                        panic("%s - %lx: skipped state "
                            "[u=%d,r=%d,s=%d]\n", __func__,
                            (unsigned long)VM_KERNEL_ADDRPERM(mpte),
                            mp_so->so_usecount, mp_so->so_retaincnt,
                            mpp->mpp_state);
                }

                if (mp_tp->mpt_state == MPTCPS_TIME_WAIT) {
                        mptcp_close(mpte, mp_tp);
                }

                mptcp_session_destroy(mpte);

                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);
                sodealloc(mp_so);
        }

        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 = mptetoso(mpte);

        VERIFY(mpte->mpte_mptcb == mp_tp);

        socket_lock_assert_owned(mp_so);

        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 mptsub *mpts = NULL, *tmpts = NULL;
        struct socket *mp_so = mptetoso(mpte);

        socket_lock_assert_owned(mp_so);
        VERIFY(mpte->mpte_mptcb == mp_tp);

        mp_tp->mpt_state = MPTCPS_TERMINATE;

        mptcp_freeq(mp_tp);

        soisdisconnected(mp_so);

        /* Clean up all subflows */
        TAILQ_FOREACH_SAFE(mpts, &mpte->mpte_subflows, mpts_entry, tmpts) {
                mptcp_subflow_disconnect(mpte, mpts);
        }

        return NULL;
}

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

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

        mp_so = mptetoso(mpte);

        socket_lock_assert_owned(mp_so);

        if (mpte->mpte_flags & MPTE_IN_WORKLOOP) {
                mpte->mpte_flags |= MPTE_WORKLOOP_RELAUNCH;
                return;
        }
        mpte->mpte_flags |= MPTE_IN_WORKLOOP;

relaunch:
        mpte->mpte_flags &= ~MPTE_WORKLOOP_RELAUNCH;

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

                if (mpts->mpts_socket->so_usecount == 0) {
                        /* Will be removed soon by tcp_garbage_collect */
                        continue;
                }

                mptcp_subflow_addref(mpts);
                mpts->mpts_socket->so_usecount++;

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

                /*
                 * 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);
                }

                switch (ret) {
                case MPTS_EVRET_OK:
                        /* nothing to do */
                        break;
                case MPTS_EVRET_DELETE:
                        mptcp_subflow_soclose(mpts);
                        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;
                }
                mptcp_subflow_remref(mpts);             /* ours */

                VERIFY(mpts->mpts_socket->so_usecount != 0);
                mpts->mpts_socket->so_usecount--;
        }

        if (mpsofilt_hint_mask != SO_FILT_HINT_LOCKED) {
                VERIFY(mpsofilt_hint_mask & SO_FILT_HINT_LOCKED);

                if (mpsofilt_hint_mask & SO_FILT_HINT_CANTRCVMORE) {
                        mp_so->so_state |= SS_CANTRCVMORE;
                        sorwakeup(mp_so);
                }

                soevent(mp_so, mpsofilt_hint_mask);
        }

        if (!connect_pending && !disconnect_fallback) {
                goto exit;
        }

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

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

                        mpts->mpts_flags |= MPTSF_MP_DEGRADED;

                        if (mpts->mpts_flags & (MPTSF_DISCONNECTING |
                            MPTSF_DISCONNECTED | MPTSF_CONNECT_PENDING)) {
                                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.
                         */

                        inp = sotoinpcb(so);
                        tp = intotcpcb(inp);
                        tp->t_mpflags &=
                            ~(TMPF_MPTCP_READY | TMPF_MPTCP_TRUE);
                        tp->t_mpflags |= TMPF_TCP_FALLBACK;

                        soevent(so, SO_FILT_HINT_MUSTRST);
                } else if (connect_pending) {
                        /*
                         * 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) {
                                int error = mptcp_subflow_soconnectx(mpte, mpts);

                                if (error) {
                                        mptcp_subflow_abort(mpts, error);
                                }
                        }
                }
        }

exit:
        if (mpte->mpte_flags & MPTE_WORKLOOP_RELAUNCH) {
                goto relaunch;
        }

        mpte->mpte_flags &= ~MPTE_IN_WORKLOOP;
}

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

        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++;
                mpp->mpp_inside++;
        }
        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 = mpsotomppcb(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 */
        }
        socket_lock_assert_owned(mp_so);

        if (refcount != 0) {
                mp_so->so_usecount--;
                mpp->mpp_inside--;
        }

        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 */
        }
        if (mpp->mpp_inside < 0) {
                panic("%s: mpp=%p inside=%x lrh= %s\n", __func__,
                    mpp, mpp->mpp_inside, 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;
        mpp_unlock(mpp);

        return 0;
}

/*
 * Protocol pr_getlock callback.
 */
lck_mtx_t *
mptcp_getlock(struct socket *mp_so, int flags)
{
        struct mppcb *mpp = mpsotomppcb(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_getlock(mpp, flags);
}

/*
 * 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;

        /*
         * 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;
        }
        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;
        }
        LIST_INSERT_HEAD(&mp_tp->mpt_subauth_list, sauth_entry, msae_next);
}

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;

        tp = sototcpcb(so);
        if (tp == NULL) {
                return;
        }

        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);
        }

        if (found) {
                zfree(mpt_subauth_zone, sauth_entry);
        }
}

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;

        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;
                }
        }
}

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;

        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)) {
                                os_log_error(mptcp_log_handle, "%s - %lx: mismatched"
                                    " address ids %d %d \n", __func__, (unsigned long)VM_KERNEL_ADDRPERM(mp_tp->mpt_mpte),
                                    raddr_id, sauth_entry->msae_raddr_id);
                                return;
                        }
                        sauth_entry->msae_raddr_id = raddr_id;
                        if ((sauth_entry->msae_raddr_rand != 0) &&
                            (sauth_entry->msae_raddr_rand != raddr_rand)) {
                                os_log_error(mptcp_log_handle, "%s - %lx: "
                                    "dup SYN_ACK %d %d \n",
                                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mp_tp->mpt_mpte),
                                    raddr_rand, sauth_entry->msae_raddr_rand);
                                return;
                        }
                        sauth_entry->msae_raddr_rand = raddr_rand;
                        return;
                }
        }
}

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

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

void
mptcp_hmac_sha1(mptcp_key_t key1, mptcp_key_t key2,
    u_int32_t rand1, u_int32_t rand2, u_char *digest)
{
        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, SHA1_RESULTLEN);

        /* 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)
{
        uint32_t lrand, rrand;

        lrand = rrand = 0;
        mptcp_get_rands(aid, mp_tp, &lrand, &rrand);
        mptcp_hmac_sha1(mp_tp->mpt_localkey, mp_tp->mpt_remotekey, lrand, rrand,
            digest);
}

/*
 * Authentication data generation
 */
static void
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;
}

static void
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;
}

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;
}

static void
mptcp_init_local_parms(struct mptses *mpte)
{
        struct mptcb *mp_tp = mpte->mpte_mptcb;
        char key_digest[SHA1_RESULTLEN];

        read_frandom(&mp_tp->mpt_localkey, sizeof(mp_tp->mpt_localkey));
        mptcp_do_sha1(&mp_tp->mpt_localkey, key_digest);

        mptcp_generate_token(key_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_localtoken, sizeof(mp_tp->mpt_localtoken));
        mptcp_generate_idsn(key_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_local_idsn, sizeof(u_int64_t));

        /* 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;

        mptcp_conn_properties(mp_tp);
}

int
mptcp_init_remote_parms(struct mptcb *mp_tp)
{
        char remote_digest[SHA1_RESULTLEN];

        /* 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 */
        mptcp_do_sha1(&mp_tp->mpt_remotekey, remote_digest);
        mptcp_generate_token(remote_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_remotetoken, sizeof(mp_tp->mpt_remotetoken));
        mptcp_generate_idsn(remote_digest, SHA1_RESULTLEN,
            (caddr_t)&mp_tp->mpt_remote_idsn, sizeof(u_int64_t));
        mp_tp->mpt_rcvnxt = mp_tp->mpt_remote_idsn + 1;
        mp_tp->mpt_rcvadv = mp_tp->mpt_rcvnxt + mp_tp->mpt_rcvwnd;

        return 0;
}

static 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);

        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;
        }
}

void
mptcp_fallback_sbdrop(struct socket *so, struct mbuf *m, int len)
{
        struct mptcb *mp_tp = tptomptp(sototcpcb(so));
        uint64_t data_ack;
        uint64_t dsn;

        if (!m || len == 0) {
                return;
        }

        while (m && len > 0) {
                VERIFY(m->m_flags & M_PKTHDR);
                VERIFY(m->m_pkthdr.pkt_flags & PKTF_MPTCP);

                data_ack = m->m_pkthdr.mp_dsn + m->m_pkthdr.mp_rlen;
                dsn = m->m_pkthdr.mp_dsn;

                len -= m->m_len;
                m = m->m_next;
        }

        if (m && len == 0) {
                /*
                 * If there is one more mbuf in the chain, it automatically means
                 * that up to m->mp_dsn has been ack'ed.
                 *
                 * This means, we actually correct data_ack back down (compared
                 * to what we set inside the loop - dsn + data_len). Because in
                 * the loop we are "optimistic" and assume that the full mapping
                 * will be acked. If that's not the case and we get out of the
                 * loop with m != NULL, it means only up to m->mp_dsn has been
                 * really acked.
                 */
                data_ack = m->m_pkthdr.mp_dsn;
        }

        if (len < 0) {
                /*
                 * If len is negative, meaning we acked in the middle of an mbuf,
                 * only up to this mbuf's data-sequence number has been acked
                 * at the MPTCP-level.
                 */
                data_ack = dsn;
        }

        mptcplog((LOG_DEBUG, "%s inferred ack up to %u\n", __func__, (uint32_t)data_ack),
            MPTCP_SOCKET_DBG, MPTCP_LOGLVL_VERBOSE);

        /* We can have data in the subflow's send-queue that is being acked,
         * while the DATA_ACK has already advanced. Thus, we should check whether
         * or not the DATA_ACK is actually new here.
         */
        if (MPTCP_SEQ_LEQ(data_ack, mp_tp->mpt_sndmax) &&
            MPTCP_SEQ_GEQ(data_ack, mp_tp->mpt_snduna)) {
                mptcp_data_ack_rcvd(mp_tp, sototcpcb(so), data_ack);
        }
}

void
mptcp_preproc_sbdrop(struct socket *so, struct mbuf *m, unsigned int len)
{
        int rewinding = 0;

        /* TFO makes things complicated. */
        if (so->so_flags1 & SOF1_TFO_REWIND) {
                rewinding = 1;
                so->so_flags1 &= ~SOF1_TFO_REWIND;
        }

        while (m && (!(so->so_flags & SOF_MP_SUBFLOW) || rewinding)) {
                u_int32_t sub_len;
                VERIFY(m->m_flags & M_PKTHDR);
                VERIFY(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 */
                        if (rewinding == 0) {
                                m->m_pkthdr.mp_dsn += len;
                        }
                        if (!(m->m_pkthdr.pkt_flags & PKTF_MPSO)) {
                                if (rewinding == 0) {
                                        m->m_pkthdr.mp_rseq += len;
                                }
                        }
                        mptcplog((LOG_DEBUG, "%s: dsn %u ssn %u len %d %d\n",
                            __func__, (u_int32_t)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;
                        break;
                }
                m = m->m_next;
        }

        if (so->so_flags & SOF_MP_SUBFLOW &&
            !(sototcpcb(so)->t_mpflags & TMPF_TFO_REQUEST) &&
            !(sototcpcb(so)->t_mpflags & TMPF_RCVD_DACK)) {
                /*
                 * Received an ack without receiving a DATA_ACK.
                 * Need to fallback to regular TCP (or destroy this subflow).
                 */
                sototcpcb(so)->t_mpflags |= TMPF_INFIN_SENT;
                mptcp_notify_mpfail(so);
        }
}

/* Obtain the DSN mapping stored in the mbuf */
void
mptcp_output_getm_dsnmap32(struct socket *so, int off,
    uint32_t *dsn, uint32_t *relseq, uint16_t *data_len, uint16_t *dss_csum)
{
        u_int64_t dsn64;

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

void
mptcp_output_getm_dsnmap64(struct socket *so, int off, uint64_t *dsn,
    uint32_t *relseq, uint16_t *data_len,
    uint16_t *dss_csum)
{
        struct mbuf *m = so->so_snd.sb_mb;
        int off_orig = off;

        VERIFY(off >= 0);

        if (m == NULL && (so->so_flags & SOF_DEFUNCT)) {
                *dsn = 0;
                *relseq = 0;
                *data_len = 0;
                *dss_csum = 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_flags & M_PKTHDR);
                VERIFY(m->m_pkthdr.pkt_flags & PKTF_MPTCP);

                if (off >= m->m_len) {
                        off -= m->m_len;
                        m = m->m_next;
                } else {
                        break;
                }
        }

        VERIFY(off >= 0);
        VERIFY(m->m_pkthdr.mp_rlen <= UINT16_MAX);

        *dsn = m->m_pkthdr.mp_dsn;
        *relseq = m->m_pkthdr.mp_rseq;
        *data_len = m->m_pkthdr.mp_rlen;
        *dss_csum = m->m_pkthdr.mp_csum;

        mptcplog((LOG_DEBUG, "%s: dsn %u ssn %u data_len %d off %d off_orig %d\n",
            __func__, (u_int32_t)(*dsn), *relseq, *data_len, off, off_orig),
            MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
}

/*
 * 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, struct tcphdr *th)
{
        VERIFY(m->m_flags & M_PKTHDR);
        VERIFY(!(m->m_pkthdr.pkt_flags & PKTF_MPTCP));

        if (tp->t_mpflags & TMPF_EMBED_DSN) {
                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.mp_csum = tp->t_rcv_map.mpt_csum;
                if (tp->t_rcv_map.mpt_dfin) {
                        m->m_pkthdr.pkt_flags |= PKTF_MPTCP_DFIN;
                }

                m->m_pkthdr.pkt_flags |= PKTF_MPTCP;

                tp->t_mpflags &= ~TMPF_EMBED_DSN;
                tp->t_mpflags |= TMPF_MPTCP_ACKNOW;
        } else if (tp->t_mpflags & TMPF_TCP_FALLBACK) {
                if (th->th_flags & TH_FIN) {
                        m->m_pkthdr.pkt_flags |= PKTF_MPTCP_DFIN;
                }
        }
}

/*
 * 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, "%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.
         */

        os_log_error(mptcp_log_handle, "%s: %llu not found \n", __func__, dsn_fail);
        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)
{
        struct tcpcb *tp = sototcpcb(so);
        struct mptsub *mpts = tp->t_mpsub;
        uint64_t mdss_dsn;
        uint32_t mdss_subflow_seq;
        int mdss_subflow_off;
        uint16_t mdss_data_len;
        uint16_t dss_csum;

        if (so->so_snd.sb_mb == NULL && (so->so_flags & SOF_DEFUNCT)) {
                return 0;
        }

        mptcp_output_getm_dsnmap64(so, off, &mdss_dsn, &mdss_subflow_seq,
            &mdss_data_len, &dss_csum);

        /*
         * We need to compute how much of the mapping still remains.
         * So, we compute the offset in the send-buffer of the dss-sub-seq.
         */
        mdss_subflow_off = (mdss_subflow_seq + mpts->mpts_iss) - tp->snd_una;

        /*
         * When TFO is used, we are sending the mpts->mpts_iss although the relative
         * seq has been set to 1 (while it should be 0).
         */
        if (tp->t_mpflags & TMPF_TFO_REQUEST) {
                mdss_subflow_off--;
        }

        VERIFY(off >= mdss_subflow_off);

        return mdss_data_len - (off - mdss_subflow_off);
}

static uint32_t
mptcp_get_maxseg(struct mptses *mpte)
{
        struct mptsub *mpts;
        uint32_t maxseg = 0;

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                struct tcpcb *tp = sototcpcb(mpts->mpts_socket);

                if (!TCPS_HAVEESTABLISHED(tp->t_state) ||
                    TCPS_HAVERCVDFIN2(tp->t_state)) {
                        continue;
                }

                if (tp->t_maxseg > maxseg) {
                        maxseg = tp->t_maxseg;
                }
        }

        return maxseg;
}

static uint8_t
mptcp_get_rcvscale(struct mptses *mpte)
{
        struct mptsub *mpts;
        uint8_t rcvscale = UINT8_MAX;

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                struct tcpcb *tp = sototcpcb(mpts->mpts_socket);

                if (!TCPS_HAVEESTABLISHED(tp->t_state) ||
                    TCPS_HAVERCVDFIN2(tp->t_state)) {
                        continue;
                }

                if (tp->rcv_scale < rcvscale) {
                        rcvscale = tp->rcv_scale;
                }
        }

        return rcvscale;
}

/* Similar to tcp_sbrcv_reserve */
static void
mptcp_sbrcv_reserve(struct mptcb *mp_tp, struct sockbuf *sbrcv,
    u_int32_t newsize, u_int32_t idealsize)
{
        uint8_t rcvscale = mptcp_get_rcvscale(mp_tp->mpt_mpte);

        /* newsize should not exceed max */
        newsize = min(newsize, tcp_autorcvbuf_max);

        /* The receive window scale negotiated at the
         * beginning of the connection will also set a
         * limit on the socket buffer size
         */
        newsize = min(newsize, TCP_MAXWIN << rcvscale);

        /* Set new socket buffer size */
        if (newsize > sbrcv->sb_hiwat &&
            (sbreserve(sbrcv, newsize) == 1)) {
                sbrcv->sb_idealsize = min(max(sbrcv->sb_idealsize,
                    (idealsize != 0) ? idealsize : newsize), tcp_autorcvbuf_max);

                /* Again check the limit set by the advertised
                 * window scale
                 */
                sbrcv->sb_idealsize = min(sbrcv->sb_idealsize,
                    TCP_MAXWIN << rcvscale);
        }
}

void
mptcp_sbrcv_grow(struct mptcb *mp_tp)
{
        struct mptses *mpte = mp_tp->mpt_mpte;
        struct socket *mp_so = mpte->mpte_mppcb->mpp_socket;
        struct sockbuf *sbrcv = &mp_so->so_rcv;
        uint32_t hiwat_sum = 0;
        uint32_t ideal_sum = 0;
        struct mptsub *mpts;

        /*
         * Do not grow the receive socket buffer if
         * - auto resizing is disabled, globally or on this socket
         * - the high water mark already reached the maximum
         * - the stream is in background and receive side is being
         * throttled
         * - if there are segments in reassembly queue indicating loss,
         * do not need to increase recv window during recovery as more
         * data is not going to be sent. A duplicate ack sent during
         * recovery should not change the receive window
         */
        if (tcp_do_autorcvbuf == 0 ||
            (sbrcv->sb_flags & SB_AUTOSIZE) == 0 ||
            tcp_cansbgrow(sbrcv) == 0 ||
            sbrcv->sb_hiwat >= tcp_autorcvbuf_max ||
            (mp_so->so_flags1 & SOF1_EXTEND_BK_IDLE_WANTED) ||
            !LIST_EMPTY(&mp_tp->mpt_segq)) {
                /* Can not resize the socket buffer, just return */
                return;
        }

        /*
         * Ideally, we want the rbuf to be (sum_i {bw_i} * rtt_max * 2)
         *
         * But, for this we first need accurate receiver-RTT estimations, which
         * we currently don't have.
         *
         * Let's use a dummy algorithm for now, just taking the sum of all
         * subflow's receive-buffers. It's too low, but that's all we can get
         * for now.
         */

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                hiwat_sum += mpts->mpts_socket->so_rcv.sb_hiwat;
                ideal_sum += mpts->mpts_socket->so_rcv.sb_idealsize;
        }

        mptcp_sbrcv_reserve(mp_tp, sbrcv, hiwat_sum, ideal_sum);
}

/*
 * Determine if we can grow the recieve socket buffer to avoid sending
 * a zero window update to the peer. We allow even socket buffers that
 * have fixed size (set by the application) to grow if the resource
 * constraints are met. They will also be trimmed after the application
 * reads data.
 *
 * Similar to tcp_sbrcv_grow_rwin
 */
static void
mptcp_sbrcv_grow_rwin(struct mptcb *mp_tp, struct sockbuf *sb)
{
        struct socket *mp_so = mp_tp->mpt_mpte->mpte_mppcb->mpp_socket;
        u_int32_t rcvbufinc = mptcp_get_maxseg(mp_tp->mpt_mpte) << 4;
        u_int32_t rcvbuf = sb->sb_hiwat;

        if (tcp_recv_bg == 1 || IS_TCP_RECV_BG(mp_so)) {
                return;
        }

        if (tcp_do_autorcvbuf == 1 &&
            tcp_cansbgrow(sb) &&
            /* Diff to tcp_sbrcv_grow_rwin */
            (mp_so->so_flags1 & SOF1_EXTEND_BK_IDLE_WANTED) == 0 &&
            (rcvbuf - sb->sb_cc) < rcvbufinc &&
            rcvbuf < tcp_autorcvbuf_max &&
            (sb->sb_idealsize > 0 &&
            sb->sb_hiwat <= (sb->sb_idealsize + rcvbufinc))) {
                sbreserve(sb, min((sb->sb_hiwat + rcvbufinc), tcp_autorcvbuf_max));
        }
}

/* Similar to tcp_sbspace */
int32_t
mptcp_sbspace(struct mptcb *mp_tp)
{
        struct sockbuf *sb = &mp_tp->mpt_mpte->mpte_mppcb->mpp_socket->so_rcv;
        uint32_t rcvbuf;
        int32_t space;
        int32_t pending = 0;

        socket_lock_assert_owned(mptetoso(mp_tp->mpt_mpte));

        mptcp_sbrcv_grow_rwin(mp_tp, sb);

        /* hiwat might have changed */
        rcvbuf = sb->sb_hiwat;

        space =  ((int32_t) imin((rcvbuf - sb->sb_cc),
            (sb->sb_mbmax - sb->sb_mbcnt)));
        if (space < 0) {
                space = 0;
        }

#if CONTENT_FILTER
        /* Compensate for data being processed by content filters */
        pending = cfil_sock_data_space(sb);
#endif /* CONTENT_FILTER */
        if (pending > space) {
                space = 0;
        } else {
                space -= pending;
        }

        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;

        socket_lock_assert_owned(mptetoso(mp_tp->mpt_mpte));

        if (mp_tp->mpt_state >= MPTCPS_CLOSE_WAIT) {
                ret = 0;
        }
        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);  \
        if (mp_tp->mpt_flags & MPTCPF_CHECKSUM)         \
                mss_lower += 2;                         \
        else                                            \
        /* adjust to 32-bit boundary + EOL */   \
                mss_lower += 2;                         \
}
        if (mp_tp == NULL) {
                return 0;
        }

        socket_lock_assert_owned(mptetoso(mp_tp->mpt_mpte));

        /*
         * 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 (!mtudisc) {
                if (tp->t_mpflags & TMPF_MPTCP_TRUE &&
                    !(tp->t_mpflags & TMPF_JOINED_FLOW)) {
                        MPTCP_COMPUTE_LEN;
                }

                if (tp->t_mpflags & TMPF_PREESTABLISHED &&
                    tp->t_mpflags & TMPF_SENT_JOIN) {
                        MPTCP_COMPUTE_LEN;
                }
        } else {
                if (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 socket *so, struct socket *mp_so)
{
        if (so->last_pid != mp_so->last_pid ||
            so->last_upid != mp_so->last_upid) {
                so->last_upid = mp_so->last_upid;
                so->last_pid = mp_so->last_pid;
                uuid_copy(so->last_uuid, mp_so->last_uuid);
        }
        so_update_policy(so);
}

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_relseq = mpts->mpts_rel_seq;
        flow->flow_soerror = mpts->mpts_socket->so_error;
        flow->flow_probecnt = mpts->mpts_probecnt;
}

static int
mptcp_pcblist SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp, arg1, arg2)
        int error = 0, f;
        size_t 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);
        if (req->oldptr == USER_ADDR_NULL) {
                size_t n = mtcbinfo.mppi_count;
                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;
                socket_lock(mpp->mpp_socket, 1);
                VERIFY(mpp->mpp_flags & MPP_ATTACHED);
                mpte = mptompte(mpp);

                socket_lock_assert_owned(mptetoso(mpte));
                mp_tp = mpte->mpte_mptcb;

                bzero(&mptcpci, sizeof(mptcpci));
                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_rcvnxt;
                mptcpci.mptcpci_ridsn = mp_tp->mpt_remote_idsn;
                mptcpci.mptcpci_rcvwnd = mp_tp->mpt_rcvwnd;

                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) {
                                socket_unlock(mpp->mpp_socket, 1);
                                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) {
                        socket_unlock(mpp->mpp_socket, 1);
                        FREE(flows, M_TEMP);
                        break;
                }
                f = 0;
                TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                        so = mpts->mpts_socket;
                        fill_mptcp_subflow(so, &flows[f], mpts);
                        f++;
                }
                socket_unlock(mpp->mpp_socket, 1);
                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");

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

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

        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);
                return 1;
        }

        /* 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;
                if (mpts->mpts_flags & MPTSF_ACTIVE) {
                        struct socket *subf_so = mpts->mpts_socket;
                        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);
                        return retval;
                }
        }
        return 0;
}

static errno_t
mptcp_symptoms_ctl_connect(kern_ctl_ref kctlref, struct sockaddr_ctl *sac,
    void **unitinfo)
{
#pragma unused(kctlref, sac, unitinfo)

        if (OSIncrementAtomic(&mptcp_kern_skt_inuse) > 0) {
                os_log_error(mptcp_log_handle, "%s: MPTCP kernel-control socket for Symptoms already open!", __func__);
        }

        mptcp_kern_skt_unit = sac->sc_unit;

        return 0;
}

static void
mptcp_allow_uuid(uuid_t uuid, int32_t rssi)
{
        struct mppcb *mpp;

        /* Iterate over all MPTCP connections */

        lck_mtx_lock(&mtcbinfo.mppi_lock);

        TAILQ_FOREACH(mpp, &mtcbinfo.mppi_pcbs, mpp_entry) {
                struct socket *mp_so = mpp->mpp_socket;
                struct mptses *mpte = mpp->mpp_pcbe;

                socket_lock(mp_so, 1);

                if (mp_so->so_flags & SOF_DELEGATED &&
                    uuid_compare(uuid, mp_so->e_uuid)) {
                        goto next;
                } else if (!(mp_so->so_flags & SOF_DELEGATED) &&
                    uuid_compare(uuid, mp_so->last_uuid)) {
                        goto next;
                }

                os_log(mptcp_log_handle, "%s - %lx: Got allowance for useApp with rssi %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), rssi);

                mpte->mpte_flags |= MPTE_ACCESS_GRANTED;

                if (rssi > MPTCP_TARGET_BASED_RSSI_THRESHOLD) {
                        mpte->mpte_flags |= MPTE_CELL_PROHIBITED;
                }

                mptcp_check_subflows_and_add(mpte);
                mptcp_remove_subflows(mpte);

                mpte->mpte_flags &= ~(MPTE_ACCESS_GRANTED | MPTE_CELL_PROHIBITED);

next:
                socket_unlock(mp_so, 1);
        }

        lck_mtx_unlock(&mtcbinfo.mppi_lock);
}

static void
mptcp_wifi_status_changed(void)
{
        struct mppcb *mpp;

        /* Iterate over all MPTCP connections */

        lck_mtx_lock(&mtcbinfo.mppi_lock);

        TAILQ_FOREACH(mpp, &mtcbinfo.mppi_pcbs, mpp_entry) {
                struct socket *mp_so = mpp->mpp_socket;
                struct mptses *mpte = mpp->mpp_pcbe;

                socket_lock(mp_so, 1);

                /* Only handover- and urgency-mode are purely driven by Symptom's Wi-Fi status */
                if (mpte->mpte_svctype != MPTCP_SVCTYPE_HANDOVER &&
                    mpte->mpte_svctype != MPTCP_SVCTYPE_TARGET_BASED) {
                        goto next;
                }

                mptcp_check_subflows_and_add(mpte);
                mptcp_check_subflows_and_remove(mpte);

next:
                socket_unlock(mp_so, 1);
        }

        lck_mtx_unlock(&mtcbinfo.mppi_lock);
}

void
mptcp_ask_symptoms(struct mptses *mpte)
{
        struct mptcp_symptoms_ask_uuid ask;
        struct socket *mp_so;
        struct proc *p;
        int pid, prio, err;

        if (mptcp_kern_skt_unit == 0) {
                os_log_error(mptcp_log_handle, "%s - %lx: skt_unit is still 0\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
                return;
        }

        mp_so = mptetoso(mpte);

        if (mp_so->so_flags & SOF_DELEGATED) {
                pid = mp_so->e_pid;
        } else {
                pid = mp_so->last_pid;
        }

        p = proc_find(pid);
        if (p == PROC_NULL) {
                os_log_error(mptcp_log_handle, "%s - %lx: Couldn't find proc for pid %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), pid);
                return;
        }

        ask.cmd = MPTCP_SYMPTOMS_ASK_UUID;

        if (mp_so->so_flags & SOF_DELEGATED) {
                uuid_copy(ask.uuid, mp_so->e_uuid);
        } else {
                uuid_copy(ask.uuid, mp_so->last_uuid);
        }

        prio = proc_get_effective_task_policy(proc_task(p), TASK_POLICY_ROLE);

        if (prio == TASK_BACKGROUND_APPLICATION || prio == TASK_NONUI_APPLICATION ||
            prio == TASK_DARWINBG_APPLICATION) {
                ask.priority = MPTCP_SYMPTOMS_BACKGROUND;
        } else if (prio == TASK_FOREGROUND_APPLICATION) {
                ask.priority = MPTCP_SYMPTOMS_FOREGROUND;
        } else {
                ask.priority = MPTCP_SYMPTOMS_UNKNOWN;
        }

        err = ctl_enqueuedata(mptcp_kern_ctrl_ref, mptcp_kern_skt_unit,
            &ask, sizeof(ask), CTL_DATA_EOR);

        os_log(mptcp_log_handle, "%s - %lx: asked symptoms about pid %u, taskprio %u, prio %u, err %d\n",
            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), pid, prio, ask.priority, err);


        proc_rele(p);
}

static errno_t
mptcp_symptoms_ctl_disconnect(kern_ctl_ref kctlref, u_int32_t kcunit,
    void *unitinfo)
{
#pragma unused(kctlref, kcunit, unitinfo)

        OSDecrementAtomic(&mptcp_kern_skt_inuse);

        return 0;
}

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, unitinfo, flags)
        symptoms_advisory_t *sa = NULL;

        if (kcunit != mptcp_kern_skt_unit) {
                os_log_error(mptcp_log_handle, "%s: kcunit %u is different from expected one %u\n",
                    __func__, kcunit, mptcp_kern_skt_unit);
        }

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

        if (mbuf_len(m) < sizeof(*sa)) {
                os_log_error(mptcp_log_handle, "%s: mbuf is %lu but need %lu\n",
                    __func__, mbuf_len(m), sizeof(*sa));
                mbuf_freem(m);
                return EINVAL;
        }

        sa = mbuf_data(m);

        if (sa->sa_nwk_status != SYMPTOMS_ADVISORY_USEAPP) {
                os_log(mptcp_log_handle, "%s: wifi new,old: %d,%d, cell new, old: %d,%d\n", __func__,
                    sa->sa_wifi_status, mptcp_advisory.sa_wifi_status,
                    sa->sa_cell_status, mptcp_advisory.sa_cell_status);

                if (sa->sa_wifi_status != mptcp_advisory.sa_wifi_status) {
                        mptcp_advisory.sa_wifi_status = sa->sa_wifi_status;
                        mptcp_wifi_status_changed();
                }
        } else {
                struct mptcp_symptoms_answer answer;
                errno_t err;

                /* We temporarily allow different sizes for ease of submission */
                if (mbuf_len(m) != sizeof(uuid_t) + sizeof(*sa) &&
                    mbuf_len(m) != sizeof(answer)) {
                        os_log_error(mptcp_log_handle, "%s: mbuf is %lu but need %lu or %lu\n",
                            __func__, mbuf_len(m), sizeof(uuid_t) + sizeof(*sa),
                            sizeof(answer));
                        mbuf_free(m);
                        return EINVAL;
                }

                memset(&answer, 0, sizeof(answer));

                err = mbuf_copydata(m, 0, mbuf_len(m), &answer);
                if (err) {
                        os_log_error(mptcp_log_handle, "%s: mbuf_copydata returned %d\n", __func__, err);
                        mbuf_free(m);
                        return err;
                }

                mptcp_allow_uuid(answer.uuid, answer.rssi);
        }

        mbuf_freem(m);
        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);
}

/*
 * Three return-values:
 * 1  : WiFi is bad
 * 0  : WiFi is good
 * -1 : WiFi-state is unknown
 */
int
mptcp_is_wifi_unusable_for_session(struct mptses *mpte)
{
        if (mpte->mpte_flags & MPTE_FIRSTPARTY) {
                if (mptcp_advisory.sa_wifi_status) {
                        return symptoms_is_wifi_lossy() ? 1 : 0;
                }

                /*
                 * If it's a first-party app and we don't have any info
                 * about the Wi-Fi state, let's be pessimistic.
                 */
                return -1;
        } else {
                if (mptcp_advisory.sa_wifi_status & SYMPTOMS_ADVISORY_WIFI_BAD) {
                        return 1;
                }

                /*
                 * If we are target-based (meaning, we allow to be more lax on
                 * the "unusable" target. We only *know* about the state once
                 * we got the allowance from Symptoms (MPTE_ACCESS_GRANTED).
                 *
                 * If RSSI is not bad enough, MPTE_CELL_PROHIBITED will then
                 * be set.
                 *
                 * In any other case (while in target-mode), consider WiFi bad
                 * and we are going to ask for allowance from Symptoms anyway.
                 */
                if (mpte->mpte_svctype == MPTCP_SVCTYPE_TARGET_BASED) {
                        if (mpte->mpte_flags & MPTE_ACCESS_GRANTED &&
                            mpte->mpte_flags & MPTE_CELL_PROHIBITED) {
                                return 0;
                        }

                        return 1;
                }

                return 0;
        }
}

boolean_t
symptoms_is_wifi_lossy(void)
{
        return (mptcp_advisory.sa_wifi_status & SYMPTOMS_ADVISORY_WIFI_OK) ? false : true;
}

/* If TFO data is succesfully acked, it must be dropped from the mptcp so */
static void
mptcp_drop_tfo_data(struct mptses *mpte, struct mptsub *mpts)
{
        struct socket *mp_so = mptetoso(mpte);
        struct socket *so = mpts->mpts_socket;
        struct tcpcb *tp = intotcpcb(sotoinpcb(so));
        struct mptcb *mp_tp = mpte->mpte_mptcb;

        /* If data was sent with SYN, rewind state */
        if (tp->t_tfo_stats & TFO_S_SYN_DATA_ACKED) {
                u_int64_t mp_droplen = mp_tp->mpt_sndnxt - mp_tp->mpt_snduna;
                unsigned int tcp_droplen = tp->snd_una - tp->iss - 1;

                VERIFY(mp_droplen <= (UINT_MAX));
                VERIFY(mp_droplen >= tcp_droplen);

                mpts->mpts_flags &= ~MPTSF_TFO_REQD;
                mpts->mpts_iss += tcp_droplen;
                tp->t_mpflags &= ~TMPF_TFO_REQUEST;

                if (mp_droplen > tcp_droplen) {
                        /* handle partial TCP ack */
                        mp_so->so_flags1 |= SOF1_TFO_REWIND;
                        mp_tp->mpt_sndnxt = mp_tp->mpt_snduna + (mp_droplen - tcp_droplen);
                        mp_droplen = tcp_droplen;
                } else {
                        /* all data on SYN was acked */
                        mpts->mpts_rel_seq = 1;
                        mp_tp->mpt_sndnxt = mp_tp->mpt_snduna;
                }
                mp_tp->mpt_sndmax -= tcp_droplen;

                if (mp_droplen != 0) {
                        VERIFY(mp_so->so_snd.sb_mb != NULL);
                        sbdrop(&mp_so->so_snd, (int)mp_droplen);
                }
        }
}

int
mptcp_freeq(struct mptcb *mp_tp)
{
        struct tseg_qent *q;
        int rv = 0;

        while ((q = LIST_FIRST(&mp_tp->mpt_segq)) != NULL) {
                LIST_REMOVE(q, tqe_q);
                m_freem(q->tqe_m);
                zfree(tcp_reass_zone, q);
                rv = 1;
        }
        mp_tp->mpt_reassqlen = 0;
        return rv;
}

static int
mptcp_post_event(u_int32_t event_code, int value)
{
        struct kev_mptcp_data event_data;
        struct kev_msg ev_msg;

        memset(&ev_msg, 0, sizeof(ev_msg));

        ev_msg.vendor_code      = KEV_VENDOR_APPLE;
        ev_msg.kev_class        = KEV_NETWORK_CLASS;
        ev_msg.kev_subclass     = KEV_MPTCP_SUBCLASS;
        ev_msg.event_code       = event_code;

        event_data.value = value;

        ev_msg.dv[0].data_ptr    = &event_data;
        ev_msg.dv[0].data_length = sizeof(event_data);

        return kev_post_msg(&ev_msg);
}

static void
mptcp_set_cellicon(struct mptses *mpte, struct mptsub *mpts)
{
        struct tcpcb *tp = sototcpcb(mpts->mpts_socket);
        int error;

        /* First-party apps (Siri) don't flip the cellicon */
        if (mpte->mpte_flags & MPTE_FIRSTPARTY) {
                return;
        }

        /* Subflow is disappearing - don't set it on this one */
        if (mpts->mpts_flags & (MPTSF_DISCONNECTING | MPTSF_DISCONNECTED)) {
                return;
        }

        /* Fallen back connections are not triggering the cellicon */
        if (mpte->mpte_mptcb->mpt_flags & MPTCPF_FALLBACK_TO_TCP) {
                return;
        }

        /* Remember the last time we set the cellicon. Needed for debouncing */
        mpte->mpte_last_cellicon_set = tcp_now;

        tp->t_timer[TCPT_CELLICON] = OFFSET_FROM_START(tp, MPTCP_CELLICON_TOGGLE_RATE);
        tcp_sched_timers(tp);

        if (mpts->mpts_flags & MPTSF_CELLICON_SET &&
            mpte->mpte_cellicon_increments != 0) {
                if (mptcp_cellicon_refcount == 0) {
                        os_log_error(mptcp_log_handle, "%s - %lx: Cell should be set (count is %u), but it's zero!\n",
                            __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpte->mpte_cellicon_increments);

                        /* Continue, so that the icon gets set... */
                } else {
                        /*
                         * In this case, the cellicon is already set. No need to bump it
                         * even higher
                         */

                        return;
                }
        }

        /* When tearing down this subflow, we need to decrement the
         * reference counter
         */
        mpts->mpts_flags |= MPTSF_CELLICON_SET;

        /* This counter, so that when a session gets destroyed we decrement
         * the reference counter by whatever is left
         */
        mpte->mpte_cellicon_increments++;

        if (OSIncrementAtomic(&mptcp_cellicon_refcount)) {
                /* If cellicon is already set, get out of here! */
                return;
        }

        error = mptcp_post_event(KEV_MPTCP_CELLUSE, 1);

        if (error) {
                os_log_error(mptcp_log_handle, "%s - %lx: Setting cellicon failed with %d\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), error);
        } else {
                os_log(mptcp_log_handle, "%s - %lx: successfully set the cellicon\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte));
        }
}

void
mptcp_clear_cellicon(void)
{
        int error = mptcp_post_event(KEV_MPTCP_CELLUSE, 0);

        if (error) {
                os_log_error(mptcp_log_handle, "%s: Unsetting cellicon failed with %d\n",
                    __func__, error);
        } else {
                os_log(mptcp_log_handle, "%s: successfully unset the cellicon\n",
                    __func__);
        }
}

/*
 * Returns true if the icon has been flipped to WiFi.
 */
static boolean_t
__mptcp_unset_cellicon(long val)
{
        if (OSAddAtomic(-val, &mptcp_cellicon_refcount) != 1) {
                return false;
        }

        mptcp_clear_cellicon();

        return true;
}

void
mptcp_unset_cellicon(struct mptses *mpte, struct mptsub *mpts, uint32_t val)
{
        /* First-party apps (Siri) don't flip the cellicon */
        if (mpte->mpte_flags & MPTE_FIRSTPARTY) {
                return;
        }

        if (mpte->mpte_cellicon_increments == 0) {
                /* This flow never used cell - get out of here! */
                return;
        }

        if (mptcp_cellicon_refcount == 0) {
                os_log_error(mptcp_log_handle, "%s - %lx: Cell is off, but should be at least %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpte->mpte_cellicon_increments);

                return;
        }

        if (mpts) {
                if (!(mpts->mpts_flags & MPTSF_CELLICON_SET)) {
                        return;
                }

                mpts->mpts_flags &= ~MPTSF_CELLICON_SET;
        }

        if (mpte->mpte_cellicon_increments < val) {
                os_log_error(mptcp_log_handle, "%s - %lx: Increments is %u but want to dec by %u.\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpte->mpte_cellicon_increments, val);
                val = mpte->mpte_cellicon_increments;
        }

        mpte->mpte_cellicon_increments -= val;

        if (__mptcp_unset_cellicon(val) == false) {
                return;
        }

        /* All flows are gone - our counter should be at zero too! */
        if (mpte->mpte_cellicon_increments != 0) {
                os_log_error(mptcp_log_handle, "%s - %lx: Inconsistent state! Cell refcount is zero but increments are at %u\n",
                    __func__, (unsigned long)VM_KERNEL_ADDRPERM(mpte), mpte->mpte_cellicon_increments);
        }
}

void
mptcp_reset_rexmit_state(struct tcpcb *tp)
{
        struct mptsub *mpts;
        struct inpcb *inp;
        struct socket *so;

        inp = tp->t_inpcb;
        if (inp == NULL) {
                return;
        }

        so = inp->inp_socket;
        if (so == NULL) {
                return;
        }

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

        mpts = tp->t_mpsub;

        mpts->mpts_flags &= ~MPTSF_WRITE_STALL;
        so->so_flags &= ~SOF_MP_TRYFAILOVER;
}

void
mptcp_reset_keepalive(struct tcpcb *tp)
{
        struct mptsub *mpts = tp->t_mpsub;

        mpts->mpts_flags &= ~MPTSF_READ_STALL;
}