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/*
 * 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. 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>

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

/*
 * Fast timeout routine for processing delayed acks
 */

void
tcp_fasttimo(Slirp *slirp)
{
        register struct socket *so;
        register struct tcpcb *tp;

        DEBUG_CALL("tcp_fasttimo");

        so = slirp->tcb.so_next;
        if (so)
        for (; so != &slirp->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;
                        (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(Slirp *slirp)
{
        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 = slirp->tcb.so_next;
        if (ip == NULL) {
            return;
        }
        for (; ip != &slirp->tcb; ip = ipnxt) {
                ipnxt = ip->so_next;
                tp = sototcpcb(ip);
                if (tp == NULL) {
                        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:
                ;
        }
        slirp->tcp_iss += TCP_ISSINCR/PR_SLOWHZ;        /* increment iss */
        slirp->tcp_now++;                               /* for timestamps */
}

/*
 * Cancel all timers for TCP tp.
 */

void
tcp_canceltimers(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;
                                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;
                }
                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) {
                        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:
                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:
                if (tp->t_state < TCPS_ESTABLISHED)
                        goto dropit;

                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.
                         */

                        tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
                            tp->rcv_nxt, tp->snd_una - 1, 0);
                        tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
                } else
                        tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
                break;

        dropit:
                tp = tcp_drop(tp, 0);
                break;
        }

        return (tp);
}