xnu-3248.50.21.tar.gz

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

/*
 * Copyright (c) 2012-2015 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

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

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

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

#include <dev/random/randomdev.h>

#include <net/if.h>
#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>
#include <netinet/mptcp_var.h>
#include <netinet/mptcp.h>
#include <netinet/mptcp_seq.h>
#include <netinet/mptcp_opt.h>
#include <netinet/mptcp_timer.h>

int mptcp_enable = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, enable, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_enable, 0, "Enable Multipath TCP Support");

/* Number of times to try negotiating MPTCP on SYN retransmissions */
int mptcp_mpcap_retries = MPTCP_CAPABLE_RETRIES;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, mptcp_cap_retr,
        CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_mpcap_retries, 0, "Number of MP Capable SYN Retries");

/*
 * By default, DSS checksum is turned off, revisit if we ever do
 * MPTCP for non SSL Traffic.
 */
int mptcp_dss_csum = 0;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, dss_csum, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_dss_csum, 0, "Enable DSS checksum");

/*
 * When mptcp_fail_thresh number of retransmissions are sent, subflow failover
 * is attempted on a different path.
 */
int mptcp_fail_thresh = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, fail, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_fail_thresh, 0, "Failover threshold");


/*
 * MPTCP subflows have TCP keepalives set to ON. Set a conservative keeptime
 * as carrier networks mostly have a 30 minute to 60 minute NAT Timeout.
 * Some carrier networks have a timeout of 10 or 15 minutes.
 */
int mptcp_subflow_keeptime = 60*14;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, keepalive, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_subflow_keeptime, 0, "Keepalive in seconds");

/*
 * MP_PRIO option.
 */
int mptcp_mpprio_enable = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, mpprio, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_mpprio_enable, 0, "Enable MP_PRIO option");

/*
 * REMOVE_ADDR option.
 */
int mptcp_remaddr_enable = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, remaddr, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_remaddr_enable, 0, "Enable REMOVE_ADDR option");

/*
 * FastJoin Option
 */
int mptcp_fastjoin = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, fastjoin, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_fastjoin, 0, "Enable FastJoin Option");

int mptcp_zerortt_fastjoin = 0;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, zerortt_fastjoin, CTLFLAG_RW |
        CTLFLAG_LOCKED, &mptcp_zerortt_fastjoin, 0,
        "Enable Zero RTT Fast Join");

/*
 * R/W Notification on resume
 */
int mptcp_rwnotify = 0;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, rwnotify, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_rwnotify, 0, "Enable RW notify on resume");

/*
 * Using RTT history for sending new data
 */
int mptcp_use_rtthist = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, rtthist, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_use_rtthist, 0, "Disable RTT History");

#define MPTCP_RTTHIST_MINTHRESH 500
int mptcp_rtthist_rtthresh = 600;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, rtthist_thresh, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_rtthist_rtthresh, 0, "Rtt threshold");

/*
 * Use RTO history for sending new data
 */
int mptcp_use_rto = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, userto, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_use_rto, 0, "Disable RTO for subflow selection");

#define MPTCP_RTO_MINTHRESH 1000
int mptcp_rtothresh = 1500;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, rto_thresh, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_rtothresh, 0, "RTO threshold");

/*
 * Use server's chosen path for sending new data
 */
int mptcp_peerswitch = 1;
SYSCTL_INT(_net_inet_mptcp, OID_AUTO, use_peer, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_peerswitch, 0, "Use peer");

#define MPTCP_PEERSWITCH_CNTMIN 3
uint32_t mptcp_peerswitch_cnt = 3;
SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, peerswitchno, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_peerswitch_cnt, 0, "Set threshold based on peer's data arrival");

/*
 * Probe the preferred path, when it is not in use
 */
#define MPTCP_PROBETO_MIN 500
uint32_t mptcp_probeto = 1000;
SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, probeto, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_probeto, 0, "Disable probing by setting to 0");

#define MPTCP_PROBE_MX 15
uint32_t mptcp_probecnt = 5;
SYSCTL_UINT(_net_inet_mptcp, OID_AUTO, probecnt, CTLFLAG_RW | CTLFLAG_LOCKED,
        &mptcp_probecnt, 0, "Number of probe writes");

/*
 * Static declarations
 */
static int mptcp_validate_csum(struct tcpcb *, struct mbuf *, int);
static uint16_t mptcp_input_csum(struct tcpcb *, struct mbuf *, int);

/*
 * MPTCP input, called when data has been read from a subflow socket.
 */
void
mptcp_input(struct mptses *mpte, struct mbuf *m)
{
        struct socket *mp_so;
        struct mptcb *mp_tp = NULL;
        u_int64_t mb_dsn;
        u_int32_t mb_datalen;
        int count = 0;
        struct mbuf *save = NULL, *prev = NULL;
        struct mbuf *freelist = NULL, *tail = NULL;
        boolean_t in_fallback = FALSE;

        VERIFY(m->m_flags & M_PKTHDR);

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

        DTRACE_MPTCP(input);

        /*
         * Each mbuf contains MPTCP Data Sequence Map
         * Process the data for reassembly, delivery to MPTCP socket
         * client, etc.
         *
         */
        count = mp_so->so_rcv.sb_cc;

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

        /* Ok to check for this flag without lock as its set in this thread */
        in_fallback = (mp_tp->mpt_flags & MPTCPF_FALLBACK_TO_TCP);

        /*
         * In the degraded fallback case, data is accepted without DSS map
         */
        if (in_fallback) {
fallback: 
                /* 
                 * assume degraded flow as this may be the first packet 
                 * without DSS, and the subflow state is not updated yet. 
                 */
                if (sbappendstream(&mp_so->so_rcv, m))
                        sorwakeup(mp_so);
                DTRACE_MPTCP5(receive__degraded, struct mbuf *, m,
                    struct socket *, mp_so,
                    struct sockbuf *, &mp_so->so_rcv,
                    struct sockbuf *, &mp_so->so_snd,
                    struct mptses *, mpte);
                count = mp_so->so_rcv.sb_cc - count;
                mptcplog((LOG_DEBUG, "MPTCP Receiver: Fallback read %d bytes\n",
                    count), MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_VERBOSE);
                return;
        }

        MPT_LOCK(mp_tp);
        do {
                /* If fallback occurs, mbufs will not have PKTF_MPTCP set */
                if (!(m->m_pkthdr.pkt_flags & PKTF_MPTCP)) {
                        MPT_UNLOCK(mp_tp);
                        goto fallback;
                }

                save = m->m_next;
                /*
                 * A single TCP packet formed of multiple mbufs
                 * holds DSS mapping in the first mbuf of the chain.
                 * Other mbufs in the chain may have M_PKTHDR set
                 * even though they belong to the same TCP packet
                 * and therefore use the DSS mapping stored in the
                 * first mbuf of the mbuf chain. mptcp_input() can
                 * get an mbuf chain with multiple TCP packets.
                 */
                while (save && (!(save->m_flags & M_PKTHDR) ||
                    !(save->m_pkthdr.pkt_flags & PKTF_MPTCP))) {
                        prev = save;
                        save = save->m_next;
                }
                if (prev)
                        prev->m_next = NULL;
                else
                        m->m_next = NULL;

                mb_dsn = m->m_pkthdr.mp_dsn;
                mb_datalen = m->m_pkthdr.mp_rlen;

                if (MPTCP_SEQ_GT(mb_dsn, mp_tp->mpt_rcvatmark)) {
                        tcpstat.tcps_mp_oodata++;
                        MPT_UNLOCK(mp_tp);
                        m_freem(m);
                        return;
                        /*
                         * Reassembly queue support here in future. Per spec,
                         * senders must implement retransmission timer to
                         * retransmit unacked data. Dropping out of order
                         * gives a slight hit on performance but allows us to
                         * deploy MPTCP and protects us against in-window DoS
                         * attacks that attempt to use up memory by sending
                         * out of order data. When doing load sharing across
                         * subflows, out of order support is a must.
                         */
                }

                if (MPTCP_SEQ_LT(mb_dsn, mp_tp->mpt_rcvatmark)) {
                        if (MPTCP_SEQ_LEQ((mb_dsn + mb_datalen),
                            mp_tp->mpt_rcvatmark)) {
                                if (freelist == NULL)
                                        freelist = m;
                                else
                                        tail->m_next = m;

                                if (prev != NULL)
                                        tail = prev;
                                else
                                        tail = m;

                                m = save;
                                prev = save = NULL;
                                continue;
                        } else {
                                m_adj(m, (mp_tp->mpt_rcvatmark - mb_dsn));
                        }
                        mptcplog((LOG_INFO, "MPTCP Receiver: Left Edge %llu\n",
                            mp_tp->mpt_rcvatmark),
                            MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_VERBOSE);
                }

                MPT_UNLOCK(mp_tp);
                if (sbappendstream(&mp_so->so_rcv, m)) {
                        sorwakeup(mp_so);
                }
                DTRACE_MPTCP6(receive, struct mbuf *, m, struct socket *, mp_so,
                    struct sockbuf *, &mp_so->so_rcv,
                    struct sockbuf *, &mp_so->so_snd,
                    struct mptses *, mpte,
                    struct mptcb *, mp_tp);
                MPT_LOCK(mp_tp);
                count = mp_so->so_rcv.sb_cc - count;
                tcpstat.tcps_mp_rcvtotal++;
                tcpstat.tcps_mp_rcvbytes += count;
                mptcplog((LOG_DEBUG, "MPTCP Receiver: Read %d bytes\n", count),
                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_VERBOSE);

                /*
                 * The data received at the MPTCP layer will never exceed the
                 * receive window because anything to the right of the
                 * receive window will be trimmed at the subflow level.
                 */
                mp_tp->mpt_rcvwnd = mptcp_sbspace(mp_tp);
                mp_tp->mpt_rcvatmark += count;
                m = save;
                prev = save = NULL;
                count = mp_so->so_rcv.sb_cc;
        } while (m);
        MPT_UNLOCK(mp_tp);

        if (freelist)
                m_freem(freelist);
}

/*
 * MPTCP output.
 */
int
mptcp_output(struct mptses *mpte)
{
        struct mptsub *mpts;
        struct mptsub *mpts_tried = NULL;
        struct socket *mp_so;
        struct mptsub *preferred_mpts = NULL;
        int error = 0;

        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */
        mp_so = mpte->mpte_mppcb->mpp_socket;
        if (mp_so->so_state & SS_CANTSENDMORE) {
                mptcplog((LOG_DEBUG, "MPTCP Sender: cantsendmore\n"),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
                return (EPIPE);
        }

try_again:
        /* get the "best" subflow to be used for transmission */
        mpts = mptcp_get_subflow(mpte, NULL, &preferred_mpts);
        if (mpts == NULL) {
                mptcplog((LOG_ERR, "MPTCP Sender: mp_so 0x%llx no subflow\n",
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so)),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                goto out;
        }

        mptcplog((LOG_DEBUG, "MPTCP Sender: mp_so 0x%llx using cid %d \n",
            (uint64_t)VM_KERNEL_ADDRPERM(mp_so), mpts->mpts_connid),
            MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);

        /* In case there's just one flow, we reattempt later */
        MPTS_LOCK(mpts);
        if ((mpts_tried != NULL) && ((mpts == mpts_tried) ||
            (mpts->mpts_flags & MPTSF_FAILINGOVER))) {
                MPTS_UNLOCK(mpts);
                MPTS_LOCK(mpts_tried);
                mpts_tried->mpts_flags &= ~MPTSF_FAILINGOVER;
                mpts_tried->mpts_flags |= MPTSF_ACTIVE;
                MPTS_UNLOCK(mpts_tried);
                mptcp_start_timer(mpte, MPTT_REXMT);
                mptcplog((LOG_DEBUG, "MPTCP Sender: mp_so 0x%llx retry later\n",
                    (u_int64_t)VM_KERNEL_ADDRPERM(mp_so)),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
                goto out;
        }

        DTRACE_MPTCP3(output, struct mptses *, mpte, struct mptsub *, mpts,
            struct socket *, mp_so);
        error = mptcp_subflow_output(mpte, mpts);
        if (error && error != EWOULDBLOCK) {
                /* can be a temporary loss of source address or other error */
                mpts->mpts_flags |= MPTSF_FAILINGOVER;
                mpts->mpts_flags &= ~MPTSF_ACTIVE;
                mpts_tried = mpts;
                MPTS_UNLOCK(mpts);
                mptcplog((LOG_INFO, "MPTCP Sender: %s Error = %d \n",
                    __func__, error),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                goto try_again;
        }
        /* The model is to have only one active flow at a time */
        mpts->mpts_flags |= MPTSF_ACTIVE;
        mpts->mpts_probesoon = mpts->mpts_probecnt = 0;
        MPTS_UNLOCK(mpts);

        /* Allows us to update the smoothed rtt */
        if ((mptcp_probeto) && (mptcp_probeto >= MPTCP_PROBETO_MIN) &&
            (mpts != preferred_mpts) && (preferred_mpts != NULL)) {
                MPTS_LOCK(preferred_mpts);
                if (preferred_mpts->mpts_probesoon) {
                        if ((tcp_now - preferred_mpts->mpts_probesoon) >
                            mptcp_probeto) {
                                (void) mptcp_subflow_output(mpte, preferred_mpts);
                                if (preferred_mpts->mpts_probecnt >=
                                    MIN(mptcp_probecnt, MPTCP_PROBE_MX)) {
                                        preferred_mpts->mpts_probesoon = 0;
                                        preferred_mpts->mpts_probecnt = 0;
                                }
                        }
                } else {
                        preferred_mpts->mpts_probesoon = tcp_now;
                        preferred_mpts->mpts_probecnt = 0;
                }
                MPTS_UNLOCK(preferred_mpts);
        }

        if (mpte->mpte_active_sub == NULL) {
                mpte->mpte_active_sub = mpts;
        } else if (mpte->mpte_active_sub != mpts) {
                mptcplog((LOG_DEBUG, "MPTCP Sender: switch [cid %d, srtt %d]"
                    "to [cid %d, srtt %d]\n",
                    mpte->mpte_active_sub->mpts_connid,
                    mpte->mpte_active_sub->mpts_srtt >> 5,
                    mpts->mpts_connid,
                    mpts->mpts_srtt >> 5),
                    MPTCP_SENDER_DBG | MPTCP_SOCKET_DBG, MPTCP_LOGLVL_LOG);

                MPTS_LOCK(mpte->mpte_active_sub);
                mpte->mpte_active_sub->mpts_flags &= ~MPTSF_ACTIVE;
                mpts->mpts_peerswitch = 0;
                MPTS_UNLOCK(mpte->mpte_active_sub);
                mpte->mpte_active_sub = mpts;
                tcpstat.tcps_mp_switches++;
        }
out:
        /* subflow errors should not be percolated back up */
        return (0);
}

/*
 * Return the most eligible subflow to be used for sending data.
 * This function also serves to check if any alternate subflow is available
 * or not. best and second_best flows are chosen by their priority. third_best
 * could be best or second_best but is under loss at the time of evaluation.
 */
struct mptsub *
mptcp_get_subflow(struct mptses *mpte, struct mptsub *ignore, struct mptsub **preferred)
{
        struct mptsub *mpts;
        struct mptsub *best = NULL;
        struct mptsub *second_best = NULL;
        struct mptsub *third_best = NULL;
        struct mptsub *symptoms_best = NULL;
        struct socket *so = NULL;

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

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                MPTS_LOCK(mpts);

                if ((ignore) && (mpts == ignore)) {
                        MPTS_UNLOCK(mpts);
                        continue;
                }

                /* There can only be one subflow in degraded state */
                if (mpts->mpts_flags & MPTSF_MP_DEGRADED) {
                        MPTS_UNLOCK(mpts);
                        best = mpts;
                        break;
                }

                /*
                 * Subflows with TFO or Fastjoin allow data to be written before
                 * the subflow is mp capable.
                 */
                if (!(mpts->mpts_flags & MPTSF_MP_CAPABLE) &&
                    !(mpts->mpts_flags & MPTSF_FASTJ_REQD) &&
                    !(mpts->mpts_flags & MPTSF_TFO_REQD)) {
                        MPTS_UNLOCK(mpts);
                        continue;
                }

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

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

                if (mpts->mpts_flags & MPTSF_FAILINGOVER) {
                        so = mpts->mpts_socket;
                        if ((so) && (!(so->so_flags & SOF_PCBCLEARING))) {
                                socket_lock(so, 1);
                                if ((so->so_snd.sb_cc == 0) &&
                                    (mptcp_no_rto_spike(so))) {
                                        mpts->mpts_flags &= ~MPTSF_FAILINGOVER;
                                        so->so_flags &= ~SOF_MP_TRYFAILOVER;
                                        socket_unlock(so, 1);
                                } else {
                                        third_best = mpts;
                                        mptcplog((LOG_DEBUG, "MPTCP Sender: "
                                            "%s cid %d in failover\n",
                                            __func__, third_best->mpts_connid),
                                            MPTCP_SENDER_DBG,
                                            MPTCP_LOGLVL_VERBOSE);
                                        socket_unlock(so, 1);
                                        MPTS_UNLOCK(mpts);
                                        continue;
                                }
                        } else {
                                MPTS_UNLOCK(mpts);
                                continue;
                        }
                }

                /* When there are no preferred flows, use first one in list */
                if ((!second_best) && !(mpts->mpts_flags & MPTSF_PREFERRED))
                        second_best = mpts;

                if (mpts->mpts_flags & MPTSF_PREFERRED) {
                        best = mpts;
                }

                MPTS_UNLOCK(mpts);
        }

        /*
         * If there is no preferred or backup subflow, and there is no active
         * subflow use the last usable subflow.
         */
        if (best == NULL) {
                return (second_best ? second_best : third_best);
        }

        if (second_best == NULL) {
                return (best ? best : third_best);
        }

        if (preferred != NULL)
                *preferred = best;

        /* Use a hint from symptomsd if it exists */
        symptoms_best = mptcp_use_symptoms_hints(best, second_best);
        if (symptoms_best != NULL)
                return (symptoms_best);

        /* Compare RTTs, select second_best if best's rtt exceeds rttthresh */
        if ((mptcp_use_rtthist) &&
            (best->mpts_srtt) && (second_best->mpts_srtt) &&
            (best->mpts_srtt > second_best->mpts_srtt) &&
            (best->mpts_srtt >= MAX((MPTCP_RTTHIST_MINTHRESH << 5),
            (mptcp_rtthist_rtthresh << 5)))) {
                tcpstat.tcps_mp_sel_rtt++;
                mptcplog((LOG_DEBUG, "MPTCP Sender: %s best cid %d"
                    " at rtt %d,  second cid %d at rtt %d\n", __func__,
                    best->mpts_connid, best->mpts_srtt >> 5,
                    second_best->mpts_connid,
                    second_best->mpts_srtt >> 5),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);
                return (second_best);
        }

        /* Compare RTOs, select second_best if best's rto exceeds rtothresh */
        if ((mptcp_use_rto) &&
            (best->mpts_rxtcur) && (second_best->mpts_rxtcur) &&
            (best->mpts_rxtcur > second_best->mpts_rxtcur) &&
            (best->mpts_rxtcur >=
            MAX(MPTCP_RTO_MINTHRESH, mptcp_rtothresh))) {
                tcpstat.tcps_mp_sel_rto++;
                mptcplog((LOG_DEBUG, "MPTCP Sender: %s best cid %d"
                    " at rto %d, second cid %d at rto %d\n", __func__,
                    best->mpts_connid, best->mpts_rxtcur,
                    second_best->mpts_connid, second_best->mpts_rxtcur),
                    MPTCP_SENDER_DBG, MPTCP_LOGLVL_LOG);

                return (second_best);
        }

        /* If second_best received data, use second_best */
        if (mptcp_peerswitch &&
            (second_best->mpts_peerswitch >
            MAX(MPTCP_PEERSWITCH_CNTMIN, mptcp_peerswitch_cnt))) {
                tcpstat.tcps_mp_sel_peer++;
                mptcplog((LOG_DEBUG, "MPTCP Sender: %s: best cid %d"
                    " but using cid %d after receiving %d segments\n",
                    __func__, best->mpts_connid, second_best->mpts_connid,
                    second_best->mpts_peerswitch), MPTCP_SENDER_DBG,
                    MPTCP_LOGLVL_LOG);
                return (second_best);
        }
        return (best);
}

struct mptsub *
mptcp_get_pending_subflow(struct mptses *mpte, struct mptsub *ignore)
{
        struct mptsub *mpts = NULL;
        
        MPTE_LOCK_ASSERT_HELD(mpte);    /* same as MP socket lock */

        TAILQ_FOREACH(mpts, &mpte->mpte_subflows, mpts_entry) {
                MPTS_LOCK(mpts);

                if ((ignore) && (mpts == ignore)) {
                        MPTS_UNLOCK(mpts);
                        continue;
                }

                if (mpts->mpts_flags & MPTSF_CONNECT_PENDING) {
                        MPTS_UNLOCK(mpts);
                        break;
                }

                MPTS_UNLOCK(mpts);
        }
        return (mpts);
}

static const char *
mptcp_event_to_str(uint32_t event)
{
        const char *c = "UNDEFINED";
        switch (event) {
        case MPCE_CLOSE:
                c = "MPCE_CLOSE";
                break;
        case MPCE_RECV_DATA_ACK:
                c = "MPCE_RECV_DATA_ACK";
                break;
        case MPCE_RECV_DATA_FIN:
                c = "MPCE_RECV_DATA_FIN";
                break;
        }
        return (c);
}

static const char *
mptcp_state_to_str(mptcp_state_t state)
{
        const char *c = "UNDEFINED";
        switch (state) {
        case MPTCPS_CLOSED:
                c = "MPTCPS_CLOSED";
                break;
        case MPTCPS_LISTEN:
                c = "MPTCPS_LISTEN";
                break;
        case MPTCPS_ESTABLISHED:
                c = "MPTCPS_ESTABLISHED";
                break;
        case MPTCPS_CLOSE_WAIT:
                c = "MPTCPS_CLOSE_WAIT";
                break;
        case MPTCPS_FIN_WAIT_1:
                c = "MPTCPS_FIN_WAIT_1";
                break;
        case MPTCPS_CLOSING:
                c = "MPTCPS_CLOSING";
                break;
        case MPTCPS_LAST_ACK:
                c = "MPTCPS_LAST_ACK";
                break;
        case MPTCPS_FIN_WAIT_2:
                c = "MPTCPS_FIN_WAIT_2";
                break;
        case MPTCPS_TIME_WAIT:
                c = "MPTCPS_TIME_WAIT";
                break;
        case MPTCPS_FASTCLOSE_WAIT:
                c = "MPTCPS_FASTCLOSE_WAIT";
                break;
        case MPTCPS_TERMINATE:
                c = "MPTCPS_TERMINATE";
                break;
        }
        return (c);
}

void
mptcp_close_fsm(struct mptcb *mp_tp, uint32_t event)
{
        MPT_LOCK_ASSERT_HELD(mp_tp);
        mptcp_state_t old_state = mp_tp->mpt_state;

        DTRACE_MPTCP2(state__change, struct mptcb *, mp_tp, 
            uint32_t, event);

        switch (mp_tp->mpt_state) {
        case MPTCPS_CLOSED:
        case MPTCPS_LISTEN:
                mp_tp->mpt_state = MPTCPS_CLOSED;
                break;

        case MPTCPS_ESTABLISHED:
                if (event == MPCE_CLOSE) {
                        mp_tp->mpt_state = MPTCPS_FIN_WAIT_1;
                        mp_tp->mpt_sndmax += 1; /* adjust for Data FIN */
                }       
                else if (event == MPCE_RECV_DATA_FIN) {
                        mp_tp->mpt_rcvnxt += 1; /* adj remote data FIN */
                        mp_tp->mpt_state = MPTCPS_CLOSE_WAIT;
                }       
                break;

        case MPTCPS_CLOSE_WAIT:
                if (event == MPCE_CLOSE) {
                        mp_tp->mpt_state = MPTCPS_LAST_ACK;
                        mp_tp->mpt_sndmax += 1; /* adjust for Data FIN */
                }       
                break;

        case MPTCPS_FIN_WAIT_1:
                if (event == MPCE_RECV_DATA_ACK)
                        mp_tp->mpt_state = MPTCPS_FIN_WAIT_2;
                else if (event == MPCE_RECV_DATA_FIN) {
                        mp_tp->mpt_rcvnxt += 1; /* adj remote data FIN */
                        mp_tp->mpt_state = MPTCPS_CLOSING;
                }       
                break;

        case MPTCPS_CLOSING:
                if (event == MPCE_RECV_DATA_ACK)
                        mp_tp->mpt_state = MPTCPS_TIME_WAIT;
                break;

        case MPTCPS_LAST_ACK:
                if (event == MPCE_RECV_DATA_ACK)
                        mp_tp->mpt_state = MPTCPS_TERMINATE;
                break;

        case MPTCPS_FIN_WAIT_2:
                if (event == MPCE_RECV_DATA_FIN) {
                        mp_tp->mpt_rcvnxt += 1; /* adj remote data FIN */
                        mp_tp->mpt_state = MPTCPS_TIME_WAIT;
                }       
                break;

        case MPTCPS_TIME_WAIT:
                break;

        case MPTCPS_FASTCLOSE_WAIT:
                if (event == MPCE_CLOSE) {
                        /* no need to adjust for data FIN */
                        mp_tp->mpt_state = MPTCPS_TERMINATE;
                }
                break;
        case MPTCPS_TERMINATE:
                break;
        default:
                VERIFY(0);
                /* NOTREACHED */
        }
        DTRACE_MPTCP2(state__change, struct mptcb *, mp_tp, 
            uint32_t, event);
        mptcplog((LOG_INFO, "MPTCP State: %s to %s on event %s\n",
            mptcp_state_to_str(old_state),
            mptcp_state_to_str(mp_tp->mpt_state),
            mptcp_event_to_str(event)),
            MPTCP_STATE_DBG, MPTCP_LOGLVL_LOG);
}

/*
 * Update the mptcb send state variables, but the actual sbdrop occurs
 * in MPTCP layer
 */
void
mptcp_data_ack_rcvd(struct mptcb *mp_tp, struct tcpcb *tp, u_int64_t full_dack)
{
        u_int64_t acked = 0;

        acked = full_dack - mp_tp->mpt_snduna;

        if (acked) {
                mp_tp->mpt_snduna += acked;
                /* In degraded mode, we may get some Data ACKs */
                if ((tp->t_mpflags & TMPF_TCP_FALLBACK) &&
                        !(mp_tp->mpt_flags & MPTCPF_POST_FALLBACK_SYNC) &&
                        MPTCP_SEQ_GT(mp_tp->mpt_sndnxt, mp_tp->mpt_snduna)) {
                        /* bring back sndnxt to retransmit MPTCP data */
                        mp_tp->mpt_sndnxt = mp_tp->mpt_dsn_at_csum_fail;
                        mp_tp->mpt_flags |= MPTCPF_POST_FALLBACK_SYNC;
                        tp->t_inpcb->inp_socket->so_flags1 |= 
                            SOF1_POST_FALLBACK_SYNC;
                }
        }
        if ((full_dack == mp_tp->mpt_sndmax) &&
            (mp_tp->mpt_state >= MPTCPS_FIN_WAIT_1)) {
                mptcp_close_fsm(mp_tp, MPCE_RECV_DATA_ACK);
                tp->t_mpflags &= ~TMPF_SEND_DFIN;
        }
}

/* If you change this function, match up mptcp_update_rcv_state_f */
void
mptcp_update_dss_rcv_state(struct mptcp_dsn_opt *dss_info, struct tcpcb *tp,
    uint16_t csum)
{
        struct mptcb *mp_tp = tptomptp(tp);
        u_int64_t full_dsn = 0;

        NTOHL(dss_info->mdss_dsn);
        NTOHL(dss_info->mdss_subflow_seqn);
        NTOHS(dss_info->mdss_data_len);

        /* XXX for autosndbuf grow sb here */
        MPT_LOCK(mp_tp);
        MPTCP_EXTEND_DSN(mp_tp->mpt_rcvnxt, dss_info->mdss_dsn, full_dsn);
        MPT_UNLOCK(mp_tp);
        mptcp_update_rcv_state_meat(mp_tp, tp,
            full_dsn, dss_info->mdss_subflow_seqn, dss_info->mdss_data_len,
            csum);

}

void
mptcp_update_rcv_state_meat(struct mptcb *mp_tp, struct tcpcb *tp,
    u_int64_t full_dsn, u_int32_t seqn, u_int16_t mdss_data_len,
    uint16_t csum)
{
        if (mdss_data_len == 0) {
                mptcplog((LOG_INFO, "MPTCP Receiver: Infinite Mapping.\n"),
                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_LOG);

                if ((mp_tp->mpt_flags & MPTCPF_CHECKSUM) && (csum != 0)) {
                        mptcplog((LOG_ERR, "MPTCP Receiver: Bad checksum %x \n",
                            csum), MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_ERR);
                }
                mptcp_notify_mpfail(tp->t_inpcb->inp_socket);
                return;
        }
        MPT_LOCK(mp_tp);
                mptcplog((LOG_DEBUG,
                    "MPTCP Receiver: seqn = %x len = %x full = %llx "
                    "rcvnxt = %llu \n",
                    seqn, mdss_data_len, full_dsn, mp_tp->mpt_rcvnxt),
                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_VERBOSE);

        /* Process a Data FIN packet , handled in mptcp_do_fin_opt */
        if ((seqn == 0) && (mdss_data_len == 1)) {
                mptcplog((LOG_INFO, "MPTCP Receiver: Data FIN in %s state \n",
                    mptcp_state_to_str(mp_tp->mpt_state)),
                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_LOG);
                MPT_UNLOCK(mp_tp);
                return;
        }
        MPT_UNLOCK(mp_tp);
        mptcp_notify_mpready(tp->t_inpcb->inp_socket);
        tp->t_rcv_map.mpt_dsn = full_dsn;
        tp->t_rcv_map.mpt_sseq = seqn;
        tp->t_rcv_map.mpt_len = mdss_data_len;
        tp->t_rcv_map.mpt_csum = csum;
        tp->t_mpflags |= TMPF_EMBED_DSN;
}


void
mptcp_update_rcv_state_f(struct mptcp_dss_ack_opt *dss_info, struct tcpcb *tp,
    uint16_t csum)
{
        u_int64_t full_dsn = 0;
        struct mptcb *mp_tp = tptomptp(tp);

        /*
         * May happen, because the caller of this function does an soevent.
         * Review after rdar://problem/24083886
         */
        if (!mp_tp)
                return;

        NTOHL(dss_info->mdss_dsn);
        NTOHL(dss_info->mdss_subflow_seqn);
        NTOHS(dss_info->mdss_data_len);
        MPT_LOCK(mp_tp);
        MPTCP_EXTEND_DSN(mp_tp->mpt_rcvnxt, dss_info->mdss_dsn, full_dsn);
        MPT_UNLOCK(mp_tp);
        mptcp_update_rcv_state_meat(mp_tp, tp,
            full_dsn,
            dss_info->mdss_subflow_seqn,
            dss_info->mdss_data_len,
            csum);
}

void
mptcp_update_rcv_state_g(struct mptcp_dss64_ack32_opt *dss_info,
    struct tcpcb *tp, uint16_t csum)
{
        u_int64_t dsn = mptcp_ntoh64(dss_info->mdss_dsn);
        struct mptcb *mp_tp = tptomptp(tp);

        /*
         * May happen, because the caller of this function does an soevent.
         * Review after rdar://problem/24083886
         */
        if (!mp_tp)
                return;

        NTOHL(dss_info->mdss_subflow_seqn);
        NTOHS(dss_info->mdss_data_len);
        mptcp_update_rcv_state_meat(mp_tp, tp,
            dsn,
            dss_info->mdss_subflow_seqn,
            dss_info->mdss_data_len,
            csum);
}

static int
mptcp_validate_dss_map(struct socket *so, struct tcpcb *tp, struct mbuf *m,
    int hdrlen)
{
        u_int32_t sseq, datalen;

        if (!(m->m_pkthdr.pkt_flags & PKTF_MPTCP))
                return 0;

        sseq = m->m_pkthdr.mp_rseq + tp->irs;
        datalen = m->m_pkthdr.mp_rlen;

#if 0
        /* enable this to test TCP fallback post connection establishment */
        if (SEQ_GT(sseq, (tp->irs+1)))
                datalen = m->m_pkthdr.len - hdrlen - 1;
#endif

        /* unacceptable DSS option, fallback to TCP */
        if (m->m_pkthdr.len > ((int) datalen + hdrlen)) {
                mptcplog((LOG_ERR, "MPTCP Receiver: "
                    "%s: mbuf len %d, MPTCP expected %d",
                    __func__, m->m_pkthdr.len, datalen),
                    MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_LOG);
        } else {
                return 0;
        }
        tp->t_mpflags |= TMPF_SND_MPFAIL;
        mptcp_notify_mpfail(so);
        m_freem(m);
        return -1;
}

int
mptcp_input_preproc(struct tcpcb *tp, struct mbuf *m, int drop_hdrlen)
{
        if (mptcp_validate_csum(tp, m, drop_hdrlen) != 0)
                return -1;

        mptcp_insert_rmap(tp, m);
        if (mptcp_validate_dss_map(tp->t_inpcb->inp_socket, tp, m,
            drop_hdrlen) != 0)
                return -1;
        return 0;
}

/*
 * MPTCP Checksum support
 * The checksum is calculated whenever the MPTCP DSS option is included
 * in the TCP packet. The checksum includes the sum of the MPTCP psuedo
 * header and the actual data indicated by the length specified in the
 * DSS option.
 */

static int
mptcp_validate_csum(struct tcpcb *tp, struct mbuf *m, int drop_hdrlen)
{
        uint16_t mptcp_csum = 0;
        mptcp_csum = mptcp_input_csum(tp, m, drop_hdrlen);
        if (mptcp_csum) {
                tp->t_mpflags |= TMPF_SND_MPFAIL;
                tp->t_mpflags &= ~TMPF_EMBED_DSN;
                mptcp_notify_mpfail(tp->t_inpcb->inp_socket);
                m_freem(m);
                tcpstat.tcps_mp_badcsum++;
                return -1;
        }
        return 0;
}

static uint16_t
mptcp_input_csum(struct tcpcb *tp, struct mbuf *m, int off)
{
        struct mptcb *mp_tp = tptomptp(tp);
        uint32_t sum = 0;
        uint64_t dsn;
        uint32_t sseq;
        uint16_t len;
        uint16_t csum;

        if (mp_tp == NULL)
                return (0);

        if (!(mp_tp->mpt_flags & MPTCPF_CHECKSUM))
                return (0);

        if (!(tp->t_mpflags & TMPF_EMBED_DSN))
                return (0);

        if (tp->t_mpflags & TMPF_TCP_FALLBACK)
                return (0);

        /* 
         * The remote side may send a packet with fewer bytes than the
         * claimed DSS checksum length.
         */
        if ((int)m_length2(m, NULL) < (off + tp->t_rcv_map.mpt_len))
                return (0xffff);

        if (tp->t_rcv_map.mpt_len != 0)
                sum = m_sum16(m, off, tp->t_rcv_map.mpt_len);

        dsn = mptcp_hton64(tp->t_rcv_map.mpt_dsn);
        sseq = htonl(tp->t_rcv_map.mpt_sseq);
        len = htons(tp->t_rcv_map.mpt_len);
        csum = tp->t_rcv_map.mpt_csum;
        sum += in_pseudo64(dsn, sseq, (len + csum));
        ADDCARRY(sum);
        DTRACE_MPTCP3(checksum__result, struct tcpcb *, tp, struct mbuf *, m,
            uint32_t, sum);
        mptcplog((LOG_DEBUG, "MPTCP Receiver: sum = %x \n", sum),
            MPTCP_RECEIVER_DBG, MPTCP_LOGLVL_VERBOSE);
        return (~sum & 0xffff);
}

void
mptcp_output_csum(struct tcpcb *tp, struct mbuf *m, int32_t len,
    unsigned hdrlen, u_int64_t dss_val, u_int32_t *sseqp)
{
        struct mptcb *mp_tp = tptomptp(tp);
        u_int32_t sum = 0;
        uint32_t sseq;
        uint16_t dss_len;
        uint16_t csum = 0;
        uint16_t *csump = NULL;

        if (mp_tp == NULL)
                return;

        if (!(mp_tp->mpt_flags & MPTCPF_CHECKSUM))
                return;

        if (sseqp == NULL)
                return;

        if (len)
                sum = m_sum16(m, hdrlen, len);

        dss_val = mptcp_hton64(dss_val);
        sseq = *sseqp;
        dss_len = *(uint16_t *)(void *)((u_char*)sseqp + sizeof (u_int32_t));
        sum += in_pseudo64(dss_val, sseq, (dss_len + csum));

        ADDCARRY(sum);
        sum = ~sum & 0xffff;
        csump = (uint16_t *)(void *)((u_char*)sseqp + sizeof (u_int32_t) +
            sizeof (uint16_t));
        DTRACE_MPTCP3(checksum__result, struct tcpcb *, tp, struct mbuf *, m,
            uint32_t, sum);
        *csump = sum;
        mptcplog((LOG_DEBUG, "MPTCP Sender: sum = %x \n", sum),
            MPTCP_SENDER_DBG, MPTCP_LOGLVL_VERBOSE);
}

/*
 * When WiFi signal starts fading, there's more loss and RTT spikes.
 * Check if there has been a large spike by comparing against
 * a tolerable RTT spike threshold.
 */
boolean_t
mptcp_no_rto_spike(struct socket *so)
{
        struct tcpcb *tp = intotcpcb(sotoinpcb(so));
        int32_t spike = 0;

        if (tp->t_rxtcur > MAX(mptcp_rtothresh, MPTCP_RTO_MINTHRESH)) {
                spike = tp->t_rxtcur - mptcp_rtothresh;

                mptcplog((LOG_DEBUG, "MPTCP Socket: %s: spike = %d rto = %d"
                    "best = %d cur = %d\n", __func__, spike,
                    tp->t_rxtcur, tp->t_rttbest >> TCP_RTT_SHIFT,
                    tp->t_rttcur),
                    (MPTCP_SOCKET_DBG|MPTCP_SENDER_DBG), MPTCP_LOGLVL_LOG);

        }

        if (spike > 0 ) {
                return (FALSE);
        } else {
                return (TRUE);
        }
}