/*
 * Copyright (c) 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
 * Copyright (c) 2003, 2004 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Jeffrey M. Hsu.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95
 * $FreeBSD: src/sys/netinet/tcp_timer.c,v 1.34.2.14 2003/02/03 02:33:41 hsu Exp $
 */

#include "opt_inet6.h"
#include "opt_tcpdebug.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/mbuf.h>
#include <sys/sysctl.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/thread.h>
#include <sys/globaldata.h>
#include <sys/thread2.h>
#include <sys/msgport2.h>

#include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */

#include <net/route.h>
#include <net/netmsg2.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_pcb.h>
#ifdef INET6
#include <netinet6/in6_pcb.h>
#endif
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_timer2.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif

#define TCP_TIMER_REXMT         0x01
#define TCP_TIMER_PERSIST       0x02
#define TCP_TIMER_KEEP          0x04
#define TCP_TIMER_2MSL          0x08
#define TCP_TIMER_DELACK        0x10

static struct tcpcb     *tcp_timer_rexmt_handler(struct tcpcb *);
static struct tcpcb     *tcp_timer_persist_handler(struct tcpcb *);
static struct tcpcb     *tcp_timer_keep_handler(struct tcpcb *);
static struct tcpcb     *tcp_timer_2msl_handler(struct tcpcb *);
static struct tcpcb     *tcp_timer_delack_handler(struct tcpcb *);

static const struct tcp_timer {
        uint32_t        tt_task;
        struct tcpcb    *(*tt_handler)(struct tcpcb *);
} tcp_timer_handlers[] = {
        { TCP_TIMER_DELACK,     tcp_timer_delack_handler },
        { TCP_TIMER_REXMT,      tcp_timer_rexmt_handler },
        { TCP_TIMER_PERSIST,    tcp_timer_persist_handler },
        { TCP_TIMER_KEEP,       tcp_timer_keep_handler },
        { TCP_TIMER_2MSL,       tcp_timer_2msl_handler },
        { 0, NULL }
};

static int
sysctl_msec_to_ticks(SYSCTL_HANDLER_ARGS)
{
        int error, s, tt;

        tt = *(int *)oidp->oid_arg1;
        s = (int)((int64_t)tt * 1000 / hz);

        error = sysctl_handle_int(oidp, &s, 0, req);
        if (error || !req->newptr)
                return (error);

        tt = (int)((int64_t)s * hz / 1000);
        if (tt < 1)
                return (EINVAL);

        *(int *)oidp->oid_arg1 = tt;
        return (0);
}

int     tcp_keepinit;
SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
    &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "Time to establish TCP connection");

int     tcp_keepidle;
SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
    &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "Time before TCP keepalive probes begin");

int     tcp_keepintvl;
SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
    &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "Time between TCP keepalive probes");

int     tcp_delacktime;
SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime,
    CTLTYPE_INT|CTLFLAG_RW, &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
    "Time before a delayed ACK is sent");

int     tcp_msl;
SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
    &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");

int     tcp_rexmit_min;
SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
    &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I", "Minimum Retransmission Timeout");

int     tcp_rexmit_slop;
SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
    &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
    "Retransmission Timer Slop");

static int      always_keepalive = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
    &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");

/* max idle probes */
int     tcp_keepcnt = TCPTV_KEEPCNT;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW,
    &tcp_keepcnt, 0, "Maximum number of keepalive probes to be sent");

static int tcp_do_eifel_response = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel_response, CTLFLAG_RW,
    &tcp_do_eifel_response, 0, "Eifel response algorithm (RFC 4015)");

int tcp_eifel_rtoinc = 2;
SYSCTL_PROC(_net_inet_tcp, OID_AUTO, eifel_rtoinc, CTLTYPE_INT|CTLFLAG_RW,
    &tcp_eifel_rtoinc, 0, sysctl_msec_to_ticks, "I",
    "Eifel response RTO increment");

/* max idle time in persist */
int     tcp_maxpersistidle;

/*
 * Cancel all timers for TCP tp.
 */
void
tcp_canceltimers(struct tcpcb *tp)
{
        tcp_callout_stop(tp, tp->tt_2msl);
        tcp_callout_stop(tp, tp->tt_persist);
        tcp_callout_stop(tp, tp->tt_keep);
        tcp_callout_stop(tp, tp->tt_rexmt);
}

/*
 * Caller should be in critical section
 */
static void
tcp_send_timermsg(struct tcpcb *tp, uint32_t task)
{
        struct netmsg_tcp_timer *tmsg = tp->tt_msg;

        KKASSERT(tmsg != NULL && tmsg->tt_cpuid == mycpuid &&
                 tmsg->tt_tcb != NULL);

        tmsg->tt_tasks |= task;
        if (tmsg->tt_msg.lmsg.ms_flags & MSGF_DONE)
                lwkt_sendmsg_oncpu(tmsg->tt_msgport, &tmsg->tt_msg.lmsg);
}

int     tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
    { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };

int     tcp_syn_backoff_low[TCP_MAXRXTSHIFT + 1] =
    { 1, 1, 2, 4, 8, 8, 16, 16, 32, 64, 64, 64, 64 };

int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };

static int tcp_totbackoff = 511;        /* sum of tcp_backoff[] */

/* Caller should be in critical section */
static struct tcpcb *
tcp_timer_delack_handler(struct tcpcb *tp)
{
        tp->t_flags |= TF_ACKNOW;
        tcpstat.tcps_delack++;
        tcp_output(tp);
        return tp;
}

/*
 * TCP timer processing.
 */
void
tcp_timer_delack(void *xtp)
{
        struct tcpcb *tp = xtp;
        struct callout *co = &tp->tt_delack->tc_callout;

        crit_enter();
        if (callout_pending(co) || !callout_active(co)) {
                crit_exit();
                return;
        }
        callout_deactivate(co);
        tcp_send_timermsg(tp, TCP_TIMER_DELACK);
        crit_exit();
}

/* Caller should be in critical section */
static struct tcpcb *
tcp_timer_2msl_handler(struct tcpcb *tp)
{
#ifdef TCPDEBUG
        int ostate;
#endif

#ifdef TCPDEBUG
        ostate = tp->t_state;
#endif
        /*
         * 2 MSL timeout in shutdown went off.  If we're closed but
         * still waiting for peer to close and connection has been idle
         * too long, or if 2MSL time is up from TIME_WAIT, delete connection
         * control block.  Otherwise, check again in a bit.
         */
        if (tp->t_state != TCPS_TIME_WAIT &&
            (ticks - tp->t_rcvtime) <= tp->t_maxidle) {
                tcp_callout_reset(tp, tp->tt_2msl, tp->t_keepintvl,
                                  tcp_timer_2msl);
        } else {
                tp = tcp_close(tp);
        }

#ifdef TCPDEBUG
        if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
                tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
#endif
        return tp;
}

void
tcp_timer_2msl(void *xtp)
{
        struct tcpcb *tp = xtp;
        struct callout *co = &tp->tt_2msl->tc_callout;

        crit_enter();
        if (callout_pending(co) || !callout_active(co)) {
                crit_exit();
                return;
        }
        callout_deactivate(co);
        tcp_send_timermsg(tp, TCP_TIMER_2MSL);
        crit_exit();
}

/* Caller should be in critical section */
static struct tcpcb *
tcp_timer_keep_handler(struct tcpcb *tp)
{
        struct tcptemp *t_template;
#ifdef TCPDEBUG
        int ostate = tp->t_state;
#endif

        /*
         * Keep-alive timer went off; send something
         * or drop connection if idle for too long.
         */
        tcpstat.tcps_keeptimeo++;
        if (tp->t_state < TCPS_ESTABLISHED)
                goto dropit;
        if ((always_keepalive || (tp->t_flags & TF_KEEPALIVE) ||
             (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE)) &&
            tp->t_state <= TCPS_CLOSING) {
                if ((ticks - tp->t_rcvtime) >= tp->t_keepidle + tp->t_maxidle)
                        goto dropit;
                /*
                 * Send a packet designed to force a response
                 * if the peer is up and reachable:
                 * either an ACK if the connection is still alive,
                 * or an RST if the peer has closed the connection
                 * due to timeout or reboot.
                 * Using sequence number tp->snd_una-1
                 * causes the transmitted zero-length segment
                 * to lie outside the receive window;
                 * by the protocol spec, this requires the
                 * correspondent TCP to respond.
                 */
                tcpstat.tcps_keepprobe++;
                t_template = tcp_maketemplate(tp);
                if (t_template) {
                        tcp_respond(tp, t_template->tt_ipgen,
                                    &t_template->tt_t, NULL,
                                    tp->rcv_nxt, tp->snd_una - 1, 0);
                        tcp_freetemplate(t_template);
                }
                tcp_callout_reset(tp, tp->tt_keep, tp->t_keepintvl,
                                  tcp_timer_keep);
        } else {
                tcp_callout_reset(tp, tp->tt_keep, tp->t_keepidle,
                                  tcp_timer_keep);
        }

#ifdef TCPDEBUG
        if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
                tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
#endif
        return tp;

dropit:
        tcpstat.tcps_keepdrops++;
        tp = tcp_drop(tp, ETIMEDOUT);

#ifdef TCPDEBUG
        if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
                tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
#endif
        return tp;
}

void
tcp_timer_keep(void *xtp)
{
        struct tcpcb *tp = xtp;
        struct callout *co = &tp->tt_keep->tc_callout;

        crit_enter();
        if (callout_pending(co) || !callout_active(co)) {
                crit_exit();
                return;
        }
        callout_deactivate(co);
        tcp_send_timermsg(tp, TCP_TIMER_KEEP);
        crit_exit();
}

/* Caller should be in critical section */
static struct tcpcb *
tcp_timer_persist_handler(struct tcpcb *tp)
{
#ifdef TCPDEBUG
        int ostate;
#endif

#ifdef TCPDEBUG
        ostate = tp->t_state;
#endif
        /*
         * Persistance timer into zero window.
         * Force a byte to be output, if possible.
         */
        tcpstat.tcps_persisttimeo++;
        /*
         * Hack: if the peer is dead/unreachable, we do not
         * time out if the window is closed.  After a full
         * backoff, drop the connection if the idle time
         * (no responses to probes) reaches the maximum
         * backoff that we would use if retransmitting.
         */
        if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
            ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle ||
             (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
                tcpstat.tcps_persistdrop++;
                tp = tcp_drop(tp, ETIMEDOUT);
                goto out;
        }
        tcp_setpersist(tp);
        tp->t_flags |= TF_FORCE;
        tcp_output(tp);
        tp->t_flags &= ~TF_FORCE;

out:
#ifdef TCPDEBUG
        if (tp && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
                tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
#endif
        return tp;
}

void
tcp_timer_persist(void *xtp)
{
        struct tcpcb *tp = xtp;
        struct callout *co = &tp->tt_persist->tc_callout;

        crit_enter();
        if (callout_pending(co) || !callout_active(co)){
                crit_exit();
                return;
        }
        callout_deactivate(co);
        tcp_send_timermsg(tp, TCP_TIMER_PERSIST);
        crit_exit();
}

void
tcp_save_congestion_state(struct tcpcb *tp)
{
        /*
         * Record connection's current states so that they could be
         * recovered, if this turns out to be a spurious retransmit.
         */
        tp->snd_cwnd_prev = tp->snd_cwnd;
        tp->snd_wacked_prev = tp->snd_wacked;
        tp->snd_ssthresh_prev = tp->snd_ssthresh;
        tp->snd_recover_prev = tp->snd_recover;

        /*
         * State for Eifel response after spurious timeout retransmit
         * is detected.  We save the current value of snd_max even if
         * we are called from fast retransmit code, so if RTO needs
         * rebase, it will be rebased using the RTT of segment that
         * is not sent during possible congestion.
         */
        tp->snd_max_prev = tp->snd_max;

        if (IN_FASTRECOVERY(tp))
                tp->rxt_flags |= TRXT_F_WASFRECOVERY;
        else
                tp->rxt_flags &= ~TRXT_F_WASFRECOVERY;
        if (tp->t_flags & TF_RCVD_TSTMP) {
                /* States for Eifel detection */
                tp->t_rexmtTS = ticks;
                tp->rxt_flags |= TRXT_F_FIRSTACCACK;
        }
#ifdef later
        tcp_sack_save_scoreboard(&tp->scb);
#endif
}

void
tcp_revert_congestion_state(struct tcpcb *tp)
{
        tp->snd_cwnd = tp->snd_cwnd_prev;
        tp->snd_wacked = tp->snd_wacked_prev;
        tp->snd_ssthresh = tp->snd_ssthresh_prev;
        tp->snd_recover = tp->snd_recover_prev;
        if (tp->rxt_flags & TRXT_F_WASFRECOVERY)
                ENTER_FASTRECOVERY(tp);
        if (tp->rxt_flags & TRXT_F_FASTREXMT) {
                ++tcpstat.tcps_sndfastrexmitbad;
                if (tp->rxt_flags & TRXT_F_EARLYREXMT)
                        ++tcpstat.tcps_sndearlyrexmitbad;
        } else {
                ++tcpstat.tcps_sndrtobad;
                tp->snd_last = ticks;
                if (tcp_do_eifel_response)
                        tp->rxt_flags |= TRXT_F_REBASERTO;
        }
        tp->t_badrxtwin = 0;
        tp->t_rxtshift = 0;
        tp->snd_nxt = tp->snd_max;
#ifdef later
        tcp_sack_revert_scoreboard(&tp->scb, tp->snd_una);
#endif
}

/* Caller should be in critical section */
static struct tcpcb *
tcp_timer_rexmt_handler(struct tcpcb *tp)
{
        int rexmt;
#ifdef TCPDEBUG
        int ostate;
#endif

#ifdef TCPDEBUG
        ostate = tp->t_state;
#endif
        /*
         * Retransmission timer went off.  Message has not
         * been acked within retransmit interval.  Back off
         * to a longer retransmit interval and retransmit one segment.
         */
        if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
                tp->t_rxtshift = TCP_MAXRXTSHIFT;
                tcpstat.tcps_timeoutdrop++;
                tp = tcp_drop(tp, tp->t_softerror ?
                              tp->t_softerror : ETIMEDOUT);
                goto out;
        }
        if (tp->t_rxtshift == 1) {
                /*
                 * First retransmit.
                 */

                /*
                 * State for "RTT based spurious timeout retransmit detection"
                 *
                 * RTT based spurious timeout retransmit detection:
                 * A retransmit is considered spurious if an ACK for this
                 * segment is received within RTT/2 interval; the assumption
                 * here is that the ACK was already in flight.  See
                 * "On Estimating End-to-End Network Path Properties" by
                 * Allman and Paxson for more details.
                 */
                tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));

                /*
                 * States for Eifel response after spurious timeout retransmit
                 * is detected.
                 */
                tp->t_rxtcur_prev = tp->t_rxtcur;
                tp->t_srtt_prev = tp->t_srtt +
                    (tcp_eifel_rtoinc << TCP_RTT_SHIFT);
                tp->t_rttvar_prev = tp->t_rttvar;

                tcp_save_congestion_state(tp);
                tp->rxt_flags &= ~(TRXT_F_FASTREXMT | TRXT_F_EARLYREXMT |
                    TRXT_F_REBASERTO);
        }
        if (tp->t_state == TCPS_SYN_SENT || tp->t_state == TCPS_SYN_RECEIVED) {
                /*
                 * Record the time that we spent in SYN or SYN|ACK
                 * retransmition.
                 *
                 * Needed by RFC3390 and RFC6298.
                 */
                tp->t_rxtsyn += tp->t_rxtcur;
        }
        /* Throw away SACK blocks on a RTO, as specified by RFC2018. */
        tcp_sack_discard(tp);
        tcpstat.tcps_rexmttimeo++;
        if (tp->t_state == TCPS_SYN_SENT) {
                if (tcp_low_rtobase) {
                        rexmt = TCP_REXMTVAL(tp) *
                                tcp_syn_backoff_low[tp->t_rxtshift];
                } else {
                        rexmt = TCP_REXMTVAL(tp) *
                                tcp_syn_backoff[tp->t_rxtshift];
                }
        } else {
                rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
        }
        TCPT_RANGESET(tp->t_rxtcur, rexmt,
                      tp->t_rttmin, TCPTV_REXMTMAX);
        /*
         * If losing, let the lower level know and try for
         * a better route.  Also, if we backed off this far,
         * our srtt estimate is probably bogus.  Clobber it
         * so we'll take the next rtt measurement as our srtt;
         * move the current srtt into rttvar to keep the current
         * retransmit times until then.
         */
        if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
#ifdef INET6
                if (INP_ISIPV6(tp->t_inpcb))
                        in6_losing(tp->t_inpcb);
                else
#endif
                in_losing(tp->t_inpcb);
                tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
                tp->t_srtt = 0;
        }
        tp->snd_nxt = tp->snd_una;
        tp->snd_recover = tp->snd_max;
        /*
         * Force a segment to be sent.
         */
        tp->t_flags |= TF_ACKNOW;
        /*
         * If timing a segment in this window, stop the timer.
         */
        tp->t_rtttime = 0;
        /*
         * Close the congestion window down to one segment
         * (we'll open it by one segment for each ack we get).
         * Since we probably have a window's worth of unacked
         * data accumulated, this "slow start" keeps us from
         * dumping all that data as back-to-back packets (which
         * might overwhelm an intermediate gateway).
         *
         * There are two phases to the opening: Initially we
         * open by one mss on each ack.  This makes the window
         * size increase exponentially with time.  If the
         * window is larger than the path can handle, this
         * exponential growth results in dropped packet(s)
         * almost immediately.  To get more time between
         * drops but still "push" the network to take advantage
         * of improving conditions, we switch from exponential
         * to linear window opening at some threshhold size.
         * For a threshhold, we use half the current window
         * size, truncated to a multiple of the mss.
         *
         * (the minimum cwnd that will give us exponential
         * growth is 2 mss.  We don't allow the threshhold
         * to go below this.)
         */
        {
                u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;

                if (win < 2)
                        win = 2;
                tp->snd_cwnd = tp->t_maxseg;
                tp->snd_wacked = 0;
                tp->snd_ssthresh = win * tp->t_maxseg;
                tp->t_dupacks = 0;
        }
        EXIT_FASTRECOVERY(tp);
        tcp_output(tp);

out:
#ifdef TCPDEBUG
        if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
                tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
#endif
        return tp;
}

void
tcp_timer_rexmt(void *xtp)
{
        struct tcpcb *tp = xtp;
        struct callout *co = &tp->tt_rexmt->tc_callout;

        crit_enter();
        if (callout_pending(co) || !callout_active(co)) {
                crit_exit();
                return;
        }
        callout_deactivate(co);
        tcp_send_timermsg(tp, TCP_TIMER_REXMT);
        crit_exit();
}

static void
tcp_timer_handler(netmsg_t msg)
{
        struct netmsg_tcp_timer *tmsg = (struct netmsg_tcp_timer *)msg;
        const struct tcp_timer *tt;
        struct tcpcb *tp;

        crit_enter();

        KKASSERT(tmsg->tt_cpuid == mycpuid && tmsg->tt_tcb != NULL);
        tp = tmsg->tt_tcb;

        /* Save pending tasks and reset the tasks in message */
        tmsg->tt_running_tasks = tmsg->tt_tasks;
        tmsg->tt_prev_tasks = tmsg->tt_tasks;
        tmsg->tt_tasks = 0;

        /* Reply ASAP */
        lwkt_replymsg(&tmsg->tt_msg.lmsg, 0);

        if (tmsg->tt_running_tasks == 0) {
                /*
                 * All of the timers are cancelled when the message
                 * is pending; bail out.
                 */
                crit_exit();
                return;
        }

        for (tt = tcp_timer_handlers; tt->tt_handler != NULL; ++tt) {
                if ((tmsg->tt_running_tasks & tt->tt_task) == 0)
                        continue;

                tmsg->tt_running_tasks &= ~tt->tt_task;
                tp = tt->tt_handler(tp);
                if (tp == NULL)
                        break;

                if (tmsg->tt_running_tasks == 0) /* nothing left to do */
                        break;
        }

        crit_exit();
}

void
tcp_create_timermsg(struct tcpcb *tp, struct lwkt_port *msgport)
{
        struct netmsg_tcp_timer *tmsg = tp->tt_msg;

        netmsg_init(&tmsg->tt_msg, NULL, &netisr_adone_rport,
                    MSGF_DROPABLE | MSGF_PRIORITY, tcp_timer_handler);
        tmsg->tt_cpuid = mycpuid;
        tmsg->tt_msgport = msgport;
        tmsg->tt_tcb = tp;
        tmsg->tt_tasks = 0;
}

void
tcp_destroy_timermsg(struct tcpcb *tp)
{
        struct netmsg_tcp_timer *tmsg = tp->tt_msg;

        if (tmsg == NULL ||             /* listen socket */
            tmsg->tt_tcb == NULL)       /* only tcp_attach() is called */
                return;

        KKASSERT(tmsg->tt_cpuid == mycpuid);

        /*
         * This message is still pending to be processed;
         * drop it.  Optimized.
         */
        crit_enter();
        if ((tmsg->tt_msg.lmsg.ms_flags & MSGF_DONE) == 0) {
                lwkt_dropmsg(&tmsg->tt_msg.lmsg);
        }
        crit_exit();
}

static __inline void
tcp_callout_init(struct tcp_callout *tc, uint32_t task)
{
        callout_init_mp(&tc->tc_callout);
        tc->tc_task = task;
}

void
tcp_inittimers(struct tcpcb *tp)
{
        tcp_callout_init(tp->tt_rexmt, TCP_TIMER_REXMT);
        tcp_callout_init(tp->tt_persist, TCP_TIMER_PERSIST);
        tcp_callout_init(tp->tt_keep, TCP_TIMER_KEEP);
        tcp_callout_init(tp->tt_2msl, TCP_TIMER_2MSL);
        tcp_callout_init(tp->tt_delack, TCP_TIMER_DELACK);
}