Annotation of qemu/slirp/tcp_timer.c, revision 1.1

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.
        !            13:  * 3. All advertising materials mentioning features or use of this software
        !            14:  *    must display the following acknowledgement:
        !            15:  *     This product includes software developed by the University of
        !            16:  *     California, Berkeley and its contributors.
        !            17:  * 4. Neither the name of the University nor the names of its contributors
        !            18:  *    may be used to endorse or promote products derived from this software
        !            19:  *    without specific prior written permission.
        !            20:  *
        !            21:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            22:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            23:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            24:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            25:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            26:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            27:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            28:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            29:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            30:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            31:  * SUCH DAMAGE.
        !            32:  *
        !            33:  *     @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
        !            34:  * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
        !            35:  */
        !            36: 
        !            37: #include <slirp.h>
        !            38: 
        !            39: int    tcp_keepidle = TCPTV_KEEP_IDLE;
        !            40: int    tcp_keepintvl = TCPTV_KEEPINTVL;
        !            41: int    tcp_maxidle;
        !            42: int    so_options = DO_KEEPALIVE;
        !            43: 
        !            44: struct   tcpstat tcpstat;        /* tcp statistics */
        !            45: u_int32_t        tcp_now;                /* for RFC 1323 timestamps */
        !            46: 
        !            47: /*
        !            48:  * Fast timeout routine for processing delayed acks
        !            49:  */
        !            50: void
        !            51: tcp_fasttimo()
        !            52: {
        !            53:        register struct socket *so;
        !            54:        register struct tcpcb *tp;
        !            55: 
        !            56:        DEBUG_CALL("tcp_fasttimo");
        !            57:        
        !            58:        so = tcb.so_next;
        !            59:        if (so)
        !            60:        for (; so != &tcb; so = so->so_next)
        !            61:                if ((tp = (struct tcpcb *)so->so_tcpcb) &&
        !            62:                    (tp->t_flags & TF_DELACK)) {
        !            63:                        tp->t_flags &= ~TF_DELACK;
        !            64:                        tp->t_flags |= TF_ACKNOW;
        !            65:                        tcpstat.tcps_delack++;
        !            66:                        (void) tcp_output(tp);
        !            67:                }
        !            68: }
        !            69: 
        !            70: /*
        !            71:  * Tcp protocol timeout routine called every 500 ms.
        !            72:  * Updates the timers in all active tcb's and
        !            73:  * causes finite state machine actions if timers expire.
        !            74:  */
        !            75: void
        !            76: tcp_slowtimo()
        !            77: {
        !            78:        register struct socket *ip, *ipnxt;
        !            79:        register struct tcpcb *tp;
        !            80:        register int i;
        !            81: 
        !            82:        DEBUG_CALL("tcp_slowtimo");
        !            83:        
        !            84:        tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl;
        !            85:        /*
        !            86:         * Search through tcb's and update active timers.
        !            87:         */
        !            88:        ip = tcb.so_next;
        !            89:        if (ip == 0)
        !            90:           return;
        !            91:        for (; ip != &tcb; ip = ipnxt) {
        !            92:                ipnxt = ip->so_next;
        !            93:                tp = sototcpcb(ip);
        !            94:                if (tp == 0)
        !            95:                        continue;
        !            96:                for (i = 0; i < TCPT_NTIMERS; i++) {
        !            97:                        if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
        !            98:                                tcp_timers(tp,i);
        !            99:                                if (ipnxt->so_prev != ip)
        !           100:                                        goto tpgone;
        !           101:                        }
        !           102:                }
        !           103:                tp->t_idle++;
        !           104:                if (tp->t_rtt)
        !           105:                   tp->t_rtt++;
        !           106: tpgone:
        !           107:                ;
        !           108:        }
        !           109:        tcp_iss += TCP_ISSINCR/PR_SLOWHZ;               /* increment iss */
        !           110: #ifdef TCP_COMPAT_42
        !           111:        if ((int)tcp_iss < 0)
        !           112:                tcp_iss = 0;                            /* XXX */
        !           113: #endif
        !           114:        tcp_now++;                                      /* for timestamps */
        !           115: }
        !           116: 
        !           117: /*
        !           118:  * Cancel all timers for TCP tp.
        !           119:  */
        !           120: void
        !           121: tcp_canceltimers(tp)
        !           122:        struct tcpcb *tp;
        !           123: {
        !           124:        register int i;
        !           125: 
        !           126:        for (i = 0; i < TCPT_NTIMERS; i++)
        !           127:                tp->t_timer[i] = 0;
        !           128: }
        !           129: 
        !           130: int    tcp_backoff[TCP_MAXRXTSHIFT + 1] =
        !           131:    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
        !           132: 
        !           133: /*
        !           134:  * TCP timer processing.
        !           135:  */
        !           136: struct tcpcb *
        !           137: tcp_timers(tp, timer)
        !           138:        register struct tcpcb *tp;
        !           139:        int timer;
        !           140: {
        !           141:        register int rexmt;
        !           142:        
        !           143:        DEBUG_CALL("tcp_timers");
        !           144:        
        !           145:        switch (timer) {
        !           146: 
        !           147:        /*
        !           148:         * 2 MSL timeout in shutdown went off.  If we're closed but
        !           149:         * still waiting for peer to close and connection has been idle
        !           150:         * too long, or if 2MSL time is up from TIME_WAIT, delete connection
        !           151:         * control block.  Otherwise, check again in a bit.
        !           152:         */
        !           153:        case TCPT_2MSL:
        !           154:                if (tp->t_state != TCPS_TIME_WAIT &&
        !           155:                    tp->t_idle <= tcp_maxidle)
        !           156:                        tp->t_timer[TCPT_2MSL] = tcp_keepintvl;
        !           157:                else
        !           158:                        tp = tcp_close(tp);
        !           159:                break;
        !           160: 
        !           161:        /*
        !           162:         * Retransmission timer went off.  Message has not
        !           163:         * been acked within retransmit interval.  Back off
        !           164:         * to a longer retransmit interval and retransmit one segment.
        !           165:         */
        !           166:        case TCPT_REXMT:
        !           167:                
        !           168:                /*
        !           169:                 * XXXXX If a packet has timed out, then remove all the queued
        !           170:                 * packets for that session.
        !           171:                 */
        !           172:                
        !           173:                if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
        !           174:                        /*
        !           175:                         * This is a hack to suit our terminal server here at the uni of canberra
        !           176:                         * since they have trouble with zeroes... It usually lets them through
        !           177:                         * unharmed, but under some conditions, it'll eat the zeros.  If we
        !           178:                         * keep retransmitting it, it'll keep eating the zeroes, so we keep
        !           179:                         * retransmitting, and eventually the connection dies...
        !           180:                         * (this only happens on incoming data)
        !           181:                         * 
        !           182:                         * So, if we were gonna drop the connection from too many retransmits,
        !           183:                         * don't... instead halve the t_maxseg, which might break up the NULLs and
        !           184:                         * let them through
        !           185:                         * 
        !           186:                         * *sigh*
        !           187:                         */
        !           188:                        
        !           189:                        tp->t_maxseg >>= 1;
        !           190:                        if (tp->t_maxseg < 32) {
        !           191:                                /*
        !           192:                                 * We tried our best, now the connection must die!
        !           193:                                 */
        !           194:                                tp->t_rxtshift = TCP_MAXRXTSHIFT;
        !           195:                                tcpstat.tcps_timeoutdrop++;
        !           196:                                tp = tcp_drop(tp, tp->t_softerror);
        !           197:                                /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
        !           198:                                return (tp); /* XXX */
        !           199:                        }
        !           200:                        
        !           201:                        /*
        !           202:                         * Set rxtshift to 6, which is still at the maximum
        !           203:                         * backoff time
        !           204:                         */
        !           205:                        tp->t_rxtshift = 6;
        !           206:                }
        !           207:                tcpstat.tcps_rexmttimeo++;
        !           208:                rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
        !           209:                TCPT_RANGESET(tp->t_rxtcur, rexmt,
        !           210:                    (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
        !           211:                tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
        !           212:                /*
        !           213:                 * If losing, let the lower level know and try for
        !           214:                 * a better route.  Also, if we backed off this far,
        !           215:                 * our srtt estimate is probably bogus.  Clobber it
        !           216:                 * so we'll take the next rtt measurement as our srtt;
        !           217:                 * move the current srtt into rttvar to keep the current
        !           218:                 * retransmit times until then.
        !           219:                 */
        !           220:                if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
        !           221: /*                     in_losing(tp->t_inpcb); */
        !           222:                        tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
        !           223:                        tp->t_srtt = 0;
        !           224:                }
        !           225:                tp->snd_nxt = tp->snd_una;
        !           226:                /*
        !           227:                 * If timing a segment in this window, stop the timer.
        !           228:                 */
        !           229:                tp->t_rtt = 0;
        !           230:                /*
        !           231:                 * Close the congestion window down to one segment
        !           232:                 * (we'll open it by one segment for each ack we get).
        !           233:                 * Since we probably have a window's worth of unacked
        !           234:                 * data accumulated, this "slow start" keeps us from
        !           235:                 * dumping all that data as back-to-back packets (which
        !           236:                 * might overwhelm an intermediate gateway).
        !           237:                 *
        !           238:                 * There are two phases to the opening: Initially we
        !           239:                 * open by one mss on each ack.  This makes the window
        !           240:                 * size increase exponentially with time.  If the
        !           241:                 * window is larger than the path can handle, this
        !           242:                 * exponential growth results in dropped packet(s)
        !           243:                 * almost immediately.  To get more time between 
        !           244:                 * drops but still "push" the network to take advantage
        !           245:                 * of improving conditions, we switch from exponential
        !           246:                 * to linear window opening at some threshold size.
        !           247:                 * For a threshold, we use half the current window
        !           248:                 * size, truncated to a multiple of the mss.
        !           249:                 *
        !           250:                 * (the minimum cwnd that will give us exponential
        !           251:                 * growth is 2 mss.  We don't allow the threshold
        !           252:                 * to go below this.)
        !           253:                 */
        !           254:                {
        !           255:                u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
        !           256:                if (win < 2)
        !           257:                        win = 2;
        !           258:                tp->snd_cwnd = tp->t_maxseg;
        !           259:                tp->snd_ssthresh = win * tp->t_maxseg;
        !           260:                tp->t_dupacks = 0;
        !           261:                }
        !           262:                (void) tcp_output(tp);
        !           263:                break;
        !           264: 
        !           265:        /*
        !           266:         * Persistence timer into zero window.
        !           267:         * Force a byte to be output, if possible.
        !           268:         */
        !           269:        case TCPT_PERSIST:
        !           270:                tcpstat.tcps_persisttimeo++;
        !           271:                tcp_setpersist(tp);
        !           272:                tp->t_force = 1;
        !           273:                (void) tcp_output(tp);
        !           274:                tp->t_force = 0;
        !           275:                break;
        !           276: 
        !           277:        /*
        !           278:         * Keep-alive timer went off; send something
        !           279:         * or drop connection if idle for too long.
        !           280:         */
        !           281:        case TCPT_KEEP:
        !           282:                tcpstat.tcps_keeptimeo++;
        !           283:                if (tp->t_state < TCPS_ESTABLISHED)
        !           284:                        goto dropit;
        !           285: 
        !           286: /*             if (tp->t_socket->so_options & SO_KEEPALIVE && */
        !           287:                if ((so_options) && tp->t_state <= TCPS_CLOSE_WAIT) {
        !           288:                        if (tp->t_idle >= tcp_keepidle + tcp_maxidle)
        !           289:                                goto dropit;
        !           290:                        /*
        !           291:                         * Send a packet designed to force a response
        !           292:                         * if the peer is up and reachable:
        !           293:                         * either an ACK if the connection is still alive,
        !           294:                         * or an RST if the peer has closed the connection
        !           295:                         * due to timeout or reboot.
        !           296:                         * Using sequence number tp->snd_una-1
        !           297:                         * causes the transmitted zero-length segment
        !           298:                         * to lie outside the receive window;
        !           299:                         * by the protocol spec, this requires the
        !           300:                         * correspondent TCP to respond.
        !           301:                         */
        !           302:                        tcpstat.tcps_keepprobe++;
        !           303: #ifdef TCP_COMPAT_42
        !           304:                        /*
        !           305:                         * The keepalive packet must have nonzero length
        !           306:                         * to get a 4.2 host to respond.
        !           307:                         */
        !           308:                        tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
        !           309:                            tp->rcv_nxt - 1, tp->snd_una - 1, 0);
        !           310: #else
        !           311:                        tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
        !           312:                            tp->rcv_nxt, tp->snd_una - 1, 0);
        !           313: #endif
        !           314:                        tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
        !           315:                } else
        !           316:                        tp->t_timer[TCPT_KEEP] = tcp_keepidle;
        !           317:                break;
        !           318: 
        !           319:        dropit:
        !           320:                tcpstat.tcps_keepdrops++;
        !           321:                tp = tcp_drop(tp, 0); /* ETIMEDOUT); */
        !           322:                break;
        !           323:        }
        !           324: 
        !           325:        return (tp);
        !           326: }

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