Archipelago » qemu

/*

 * 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);

}