Annotation of qemu/slirp/tcp_timer.c, revision 1.1.1.4

1.1       root        1: /*
                      2:  * Copyright (c) 1982, 1986, 1988, 1990, 1993
                      3:  *     The Regents of the University of California.  All rights reserved.
                      4:  *
                      5:  * Redistribution and use in source and binary forms, with or without
                      6:  * modification, are permitted provided that the following conditions
                      7:  * are met:
                      8:  * 1. Redistributions of source code must retain the above copyright
                      9:  *    notice, this list of conditions and the following disclaimer.
                     10:  * 2. Redistributions in binary form must reproduce the above copyright
                     11:  *    notice, this list of conditions and the following disclaimer in the
                     12:  *    documentation and/or other materials provided with the distribution.
1.1.1.3   root       13:  * 3. Neither the name of the University nor the names of its contributors
1.1       root       14:  *    may be used to endorse or promote products derived from this software
                     15:  *    without specific prior written permission.
                     16:  *
                     17:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
                     18:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
                     19:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
                     20:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
                     21:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
                     22:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
                     23:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
                     24:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
                     25:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
                     26:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
                     27:  * SUCH DAMAGE.
                     28:  *
                     29:  *     @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
                     30:  * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
                     31:  */
                     32: 
                     33: #include <slirp.h>
                     34: 
1.1.1.2   root       35: static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);
                     36: 
1.1       root       37: /*
                     38:  * Fast timeout routine for processing delayed acks
                     39:  */
                     40: void
1.1.1.4 ! root       41: tcp_fasttimo(Slirp *slirp)
1.1       root       42: {
                     43:        register struct socket *so;
                     44:        register struct tcpcb *tp;
                     45: 
                     46:        DEBUG_CALL("tcp_fasttimo");
1.1.1.2   root       47: 
1.1.1.4 ! root       48:        so = slirp->tcb.so_next;
1.1       root       49:        if (so)
1.1.1.4 ! root       50:        for (; so != &slirp->tcb; so = so->so_next)
1.1       root       51:                if ((tp = (struct tcpcb *)so->so_tcpcb) &&
                     52:                    (tp->t_flags & TF_DELACK)) {
                     53:                        tp->t_flags &= ~TF_DELACK;
                     54:                        tp->t_flags |= TF_ACKNOW;
                     55:                        (void) tcp_output(tp);
                     56:                }
                     57: }
                     58: 
                     59: /*
                     60:  * Tcp protocol timeout routine called every 500 ms.
                     61:  * Updates the timers in all active tcb's and
                     62:  * causes finite state machine actions if timers expire.
                     63:  */
                     64: void
1.1.1.4 ! root       65: tcp_slowtimo(Slirp *slirp)
1.1       root       66: {
                     67:        register struct socket *ip, *ipnxt;
                     68:        register struct tcpcb *tp;
                     69:        register int i;
                     70: 
                     71:        DEBUG_CALL("tcp_slowtimo");
1.1.1.2   root       72: 
1.1       root       73:        /*
                     74:         * Search through tcb's and update active timers.
                     75:         */
1.1.1.4 ! root       76:        ip = slirp->tcb.so_next;
        !            77:         if (ip == NULL) {
        !            78:             return;
        !            79:         }
        !            80:        for (; ip != &slirp->tcb; ip = ipnxt) {
1.1       root       81:                ipnxt = ip->so_next;
                     82:                tp = sototcpcb(ip);
1.1.1.4 ! root       83:                 if (tp == NULL) {
        !            84:                         continue;
        !            85:                 }
1.1       root       86:                for (i = 0; i < TCPT_NTIMERS; i++) {
                     87:                        if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
                     88:                                tcp_timers(tp,i);
                     89:                                if (ipnxt->so_prev != ip)
                     90:                                        goto tpgone;
                     91:                        }
                     92:                }
                     93:                tp->t_idle++;
                     94:                if (tp->t_rtt)
                     95:                   tp->t_rtt++;
                     96: tpgone:
                     97:                ;
                     98:        }
1.1.1.4 ! root       99:        slirp->tcp_iss += TCP_ISSINCR/PR_SLOWHZ;        /* increment iss */
        !           100:        slirp->tcp_now++;                               /* for timestamps */
1.1       root      101: }
                    102: 
                    103: /*
                    104:  * Cancel all timers for TCP tp.
                    105:  */
                    106: void
1.1.1.4 ! root      107: tcp_canceltimers(struct tcpcb *tp)
1.1       root      108: {
                    109:        register int i;
                    110: 
                    111:        for (i = 0; i < TCPT_NTIMERS; i++)
                    112:                tp->t_timer[i] = 0;
                    113: }
                    114: 
1.1.1.2   root      115: const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
1.1       root      116:    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
                    117: 
                    118: /*
                    119:  * TCP timer processing.
                    120:  */
1.1.1.2   root      121: static struct tcpcb *
                    122: tcp_timers(register struct tcpcb *tp, int timer)
1.1       root      123: {
                    124:        register int rexmt;
1.1.1.2   root      125: 
1.1       root      126:        DEBUG_CALL("tcp_timers");
1.1.1.2   root      127: 
1.1       root      128:        switch (timer) {
                    129: 
                    130:        /*
                    131:         * 2 MSL timeout in shutdown went off.  If we're closed but
                    132:         * still waiting for peer to close and connection has been idle
                    133:         * too long, or if 2MSL time is up from TIME_WAIT, delete connection
                    134:         * control block.  Otherwise, check again in a bit.
                    135:         */
                    136:        case TCPT_2MSL:
                    137:                if (tp->t_state != TCPS_TIME_WAIT &&
1.1.1.2   root      138:                    tp->t_idle <= TCP_MAXIDLE)
                    139:                        tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;
1.1       root      140:                else
                    141:                        tp = tcp_close(tp);
                    142:                break;
                    143: 
                    144:        /*
                    145:         * Retransmission timer went off.  Message has not
                    146:         * been acked within retransmit interval.  Back off
                    147:         * to a longer retransmit interval and retransmit one segment.
                    148:         */
                    149:        case TCPT_REXMT:
1.1.1.2   root      150: 
1.1       root      151:                /*
                    152:                 * XXXXX If a packet has timed out, then remove all the queued
                    153:                 * packets for that session.
                    154:                 */
1.1.1.2   root      155: 
1.1       root      156:                if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
                    157:                        /*
                    158:                         * This is a hack to suit our terminal server here at the uni of canberra
                    159:                         * since they have trouble with zeroes... It usually lets them through
                    160:                         * unharmed, but under some conditions, it'll eat the zeros.  If we
                    161:                         * keep retransmitting it, it'll keep eating the zeroes, so we keep
                    162:                         * retransmitting, and eventually the connection dies...
                    163:                         * (this only happens on incoming data)
1.1.1.2   root      164:                         *
1.1       root      165:                         * So, if we were gonna drop the connection from too many retransmits,
                    166:                         * don't... instead halve the t_maxseg, which might break up the NULLs and
                    167:                         * let them through
1.1.1.2   root      168:                         *
1.1       root      169:                         * *sigh*
                    170:                         */
1.1.1.2   root      171: 
1.1       root      172:                        tp->t_maxseg >>= 1;
                    173:                        if (tp->t_maxseg < 32) {
                    174:                                /*
                    175:                                 * We tried our best, now the connection must die!
                    176:                                 */
                    177:                                tp->t_rxtshift = TCP_MAXRXTSHIFT;
                    178:                                tp = tcp_drop(tp, tp->t_softerror);
                    179:                                /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
                    180:                                return (tp); /* XXX */
                    181:                        }
1.1.1.2   root      182: 
1.1       root      183:                        /*
                    184:                         * Set rxtshift to 6, which is still at the maximum
                    185:                         * backoff time
                    186:                         */
                    187:                        tp->t_rxtshift = 6;
                    188:                }
                    189:                rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
                    190:                TCPT_RANGESET(tp->t_rxtcur, rexmt,
                    191:                    (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
                    192:                tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
                    193:                /*
                    194:                 * If losing, let the lower level know and try for
                    195:                 * a better route.  Also, if we backed off this far,
                    196:                 * our srtt estimate is probably bogus.  Clobber it
                    197:                 * so we'll take the next rtt measurement as our srtt;
                    198:                 * move the current srtt into rttvar to keep the current
                    199:                 * retransmit times until then.
                    200:                 */
                    201:                if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
                    202:                        tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
                    203:                        tp->t_srtt = 0;
                    204:                }
                    205:                tp->snd_nxt = tp->snd_una;
                    206:                /*
                    207:                 * If timing a segment in this window, stop the timer.
                    208:                 */
                    209:                tp->t_rtt = 0;
                    210:                /*
                    211:                 * Close the congestion window down to one segment
                    212:                 * (we'll open it by one segment for each ack we get).
                    213:                 * Since we probably have a window's worth of unacked
                    214:                 * data accumulated, this "slow start" keeps us from
                    215:                 * dumping all that data as back-to-back packets (which
                    216:                 * might overwhelm an intermediate gateway).
                    217:                 *
                    218:                 * There are two phases to the opening: Initially we
                    219:                 * open by one mss on each ack.  This makes the window
                    220:                 * size increase exponentially with time.  If the
                    221:                 * window is larger than the path can handle, this
                    222:                 * exponential growth results in dropped packet(s)
1.1.1.2   root      223:                 * almost immediately.  To get more time between
1.1       root      224:                 * drops but still "push" the network to take advantage
                    225:                 * of improving conditions, we switch from exponential
                    226:                 * to linear window opening at some threshold size.
                    227:                 * For a threshold, we use half the current window
                    228:                 * size, truncated to a multiple of the mss.
                    229:                 *
                    230:                 * (the minimum cwnd that will give us exponential
                    231:                 * growth is 2 mss.  We don't allow the threshold
                    232:                 * to go below this.)
                    233:                 */
                    234:                {
                    235:                u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
                    236:                if (win < 2)
                    237:                        win = 2;
                    238:                tp->snd_cwnd = tp->t_maxseg;
                    239:                tp->snd_ssthresh = win * tp->t_maxseg;
                    240:                tp->t_dupacks = 0;
                    241:                }
                    242:                (void) tcp_output(tp);
                    243:                break;
                    244: 
                    245:        /*
                    246:         * Persistence timer into zero window.
                    247:         * Force a byte to be output, if possible.
                    248:         */
                    249:        case TCPT_PERSIST:
                    250:                tcp_setpersist(tp);
                    251:                tp->t_force = 1;
                    252:                (void) tcp_output(tp);
                    253:                tp->t_force = 0;
                    254:                break;
                    255: 
                    256:        /*
                    257:         * Keep-alive timer went off; send something
                    258:         * or drop connection if idle for too long.
                    259:         */
                    260:        case TCPT_KEEP:
                    261:                if (tp->t_state < TCPS_ESTABLISHED)
                    262:                        goto dropit;
                    263: 
1.1.1.2   root      264:                if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {
                    265:                        if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)
1.1       root      266:                                goto dropit;
                    267:                        /*
                    268:                         * Send a packet designed to force a response
                    269:                         * if the peer is up and reachable:
                    270:                         * either an ACK if the connection is still alive,
                    271:                         * or an RST if the peer has closed the connection
                    272:                         * due to timeout or reboot.
                    273:                         * Using sequence number tp->snd_una-1
                    274:                         * causes the transmitted zero-length segment
                    275:                         * to lie outside the receive window;
                    276:                         * by the protocol spec, this requires the
                    277:                         * correspondent TCP to respond.
                    278:                         */
                    279:                        tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
                    280:                            tp->rcv_nxt, tp->snd_una - 1, 0);
1.1.1.2   root      281:                        tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
1.1       root      282:                } else
1.1.1.2   root      283:                        tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
1.1       root      284:                break;
                    285: 
                    286:        dropit:
1.1.1.4 ! root      287:                tp = tcp_drop(tp, 0);
1.1       root      288:                break;
                    289:        }
                    290: 
                    291:        return (tp);
                    292: }

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