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tcp_timer.c

/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993
 *    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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    This product includes software developed by the University of
 *    California, Berkeley and its contributors.
 * 4. 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   8.1 (Berkeley) 6/10/93
 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
 */

#include <slirp.h>

#ifdef LOG_ENABLED
struct   tcpstat tcpstat;        /* tcp statistics */
#endif

u_int32_t        tcp_now;                /* for RFC 1323 timestamps */

static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);

/*
 * Fast timeout routine for processing delayed acks
 */
void
tcp_fasttimo()
{
      register struct socket *so;
      register struct tcpcb *tp;

      DEBUG_CALL("tcp_fasttimo");

      so = tcb.so_next;
      if (so)
      for (; so != &tcb; so = so->so_next)
            if ((tp = (struct tcpcb *)so->so_tcpcb) &&
                (tp->t_flags & TF_DELACK)) {
                  tp->t_flags &= ~TF_DELACK;
                  tp->t_flags |= TF_ACKNOW;
                  STAT(tcpstat.tcps_delack++);
                  (void) tcp_output(tp);
            }
}

/*
 * Tcp protocol timeout routine called every 500 ms.
 * Updates the timers in all active tcb's and
 * causes finite state machine actions if timers expire.
 */
void
tcp_slowtimo()
{
      register struct socket *ip, *ipnxt;
      register struct tcpcb *tp;
      register int i;

      DEBUG_CALL("tcp_slowtimo");

      /*
       * Search through tcb's and update active timers.
       */
      ip = tcb.so_next;
      if (ip == 0)
         return;
      for (; ip != &tcb; ip = ipnxt) {
            ipnxt = ip->so_next;
            tp = sototcpcb(ip);
            if (tp == 0)
                  continue;
            for (i = 0; i < TCPT_NTIMERS; i++) {
                  if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
                        tcp_timers(tp,i);
                        if (ipnxt->so_prev != ip)
                              goto tpgone;
                  }
            }
            tp->t_idle++;
            if (tp->t_rtt)
               tp->t_rtt++;
tpgone:
            ;
      }
      tcp_iss += TCP_ISSINCR/PR_SLOWHZ;         /* increment iss */
#ifdef TCP_COMPAT_42
      if ((int)tcp_iss < 0)
            tcp_iss = 0;                        /* XXX */
#endif
      tcp_now++;                          /* for timestamps */
}

/*
 * Cancel all timers for TCP tp.
 */
void
tcp_canceltimers(tp)
      struct tcpcb *tp;
{
      register int i;

      for (i = 0; i < TCPT_NTIMERS; i++)
            tp->t_timer[i] = 0;
}

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

/*
 * TCP timer processing.
 */
static struct tcpcb *
tcp_timers(register struct tcpcb *tp, int timer)
{
      register int rexmt;

      DEBUG_CALL("tcp_timers");

      switch (timer) {

      /*
       * 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.
       */
      case TCPT_2MSL:
            if (tp->t_state != TCPS_TIME_WAIT &&
                tp->t_idle <= TCP_MAXIDLE)
                  tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;
            else
                  tp = tcp_close(tp);
            break;

      /*
       * Retransmission timer went off.  Message has not
       * been acked within retransmit interval.  Back off
       * to a longer retransmit interval and retransmit one segment.
       */
      case TCPT_REXMT:

            /*
             * XXXXX If a packet has timed out, then remove all the queued
             * packets for that session.
             */

            if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
                  /*
                   * This is a hack to suit our terminal server here at the uni of canberra
                   * since they have trouble with zeroes... It usually lets them through
                   * unharmed, but under some conditions, it'll eat the zeros.  If we
                   * keep retransmitting it, it'll keep eating the zeroes, so we keep
                   * retransmitting, and eventually the connection dies...
                   * (this only happens on incoming data)
                   *
                   * So, if we were gonna drop the connection from too many retransmits,
                   * don't... instead halve the t_maxseg, which might break up the NULLs and
                   * let them through
                   *
                   * *sigh*
                   */

                  tp->t_maxseg >>= 1;
                  if (tp->t_maxseg < 32) {
                        /*
                         * We tried our best, now the connection must die!
                         */
                        tp->t_rxtshift = TCP_MAXRXTSHIFT;
                        STAT(tcpstat.tcps_timeoutdrop++);
                        tp = tcp_drop(tp, tp->t_softerror);
                        /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
                        return (tp); /* XXX */
                  }

                  /*
                   * Set rxtshift to 6, which is still at the maximum
                   * backoff time
                   */
                  tp->t_rxtshift = 6;
            }
            STAT(tcpstat.tcps_rexmttimeo++);
            rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
            TCPT_RANGESET(tp->t_rxtcur, rexmt,
                (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
            tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
            /*
             * 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) {
/*                in_losing(tp->t_inpcb); */
                  tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
                  tp->t_srtt = 0;
            }
            tp->snd_nxt = tp->snd_una;
            /*
             * If timing a segment in this window, stop the timer.
             */
            tp->t_rtt = 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 threshold size.
             * For a threshold, 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 threshold
             * 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_ssthresh = win * tp->t_maxseg;
            tp->t_dupacks = 0;
            }
            (void) tcp_output(tp);
            break;

      /*
       * Persistence timer into zero window.
       * Force a byte to be output, if possible.
       */
      case TCPT_PERSIST:
            STAT(tcpstat.tcps_persisttimeo++);
            tcp_setpersist(tp);
            tp->t_force = 1;
            (void) tcp_output(tp);
            tp->t_force = 0;
            break;

      /*
       * Keep-alive timer went off; send something
       * or drop connection if idle for too long.
       */
      case TCPT_KEEP:
            STAT(tcpstat.tcps_keeptimeo++);
            if (tp->t_state < TCPS_ESTABLISHED)
                  goto dropit;

/*          if (tp->t_socket->so_options & SO_KEEPALIVE && */
            if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {
                  if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_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.
                   */
                  STAT(tcpstat.tcps_keepprobe++);
#ifdef TCP_COMPAT_42
                  /*
                   * The keepalive packet must have nonzero length
                   * to get a 4.2 host to respond.
                   */
                  tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
                      tp->rcv_nxt - 1, tp->snd_una - 1, 0);
#else
                  tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
                      tp->rcv_nxt, tp->snd_una - 1, 0);
#endif
                  tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
            } else
                  tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
            break;

      dropit:
            STAT(tcpstat.tcps_keepdrops++);
            tp = tcp_drop(tp, 0); /* ETIMEDOUT); */
            break;
      }

      return (tp);
}

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