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Annotation of 43BSDTahoe/sys/netinet/tcp_timer.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1982, 1986 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  *
        !            17:  *     @(#)tcp_timer.c 7.14 (Berkeley) 6/29/88
        !            18:  */
        !            19: 
        !            20: #include "param.h"
        !            21: #include "systm.h"
        !            22: #include "mbuf.h"
        !            23: #include "socket.h"
        !            24: #include "socketvar.h"
        !            25: #include "protosw.h"
        !            26: #include "errno.h"
        !            27: 
        !            28: #include "../net/if.h"
        !            29: #include "../net/route.h"
        !            30: 
        !            31: #include "in.h"
        !            32: #include "in_pcb.h"
        !            33: #include "in_systm.h"
        !            34: #include "ip.h"
        !            35: #include "ip_var.h"
        !            36: #include "tcp.h"
        !            37: #include "tcp_fsm.h"
        !            38: #include "tcp_seq.h"
        !            39: #include "tcp_timer.h"
        !            40: #include "tcp_var.h"
        !            41: #include "tcpip.h"
        !            42: 
        !            43: int    tcp_keepidle = TCPTV_KEEP_IDLE;
        !            44: int    tcp_keepintvl = TCPTV_KEEPINTVL;
        !            45: int    tcp_maxidle;
        !            46: /*
        !            47:  * Fast timeout routine for processing delayed acks
        !            48:  */
        !            49: tcp_fasttimo()
        !            50: {
        !            51:        register struct inpcb *inp;
        !            52:        register struct tcpcb *tp;
        !            53:        int s = splnet();
        !            54: 
        !            55:        inp = tcb.inp_next;
        !            56:        if (inp)
        !            57:        for (; inp != &tcb; inp = inp->inp_next)
        !            58:                if ((tp = (struct tcpcb *)inp->inp_ppcb) &&
        !            59:                    (tp->t_flags & TF_DELACK)) {
        !            60:                        tp->t_flags &= ~TF_DELACK;
        !            61:                        tp->t_flags |= TF_ACKNOW;
        !            62:                        tcpstat.tcps_delack++;
        !            63:                        (void) tcp_output(tp);
        !            64:                }
        !            65:        splx(s);
        !            66: }
        !            67: 
        !            68: /*
        !            69:  * Tcp protocol timeout routine called every 500 ms.
        !            70:  * Updates the timers in all active tcb's and
        !            71:  * causes finite state machine actions if timers expire.
        !            72:  */
        !            73: tcp_slowtimo()
        !            74: {
        !            75:        register struct inpcb *ip, *ipnxt;
        !            76:        register struct tcpcb *tp;
        !            77:        int s = splnet();
        !            78:        register int i;
        !            79: 
        !            80:        tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl;
        !            81:        /*
        !            82:         * Search through tcb's and update active timers.
        !            83:         */
        !            84:        ip = tcb.inp_next;
        !            85:        if (ip == 0) {
        !            86:                splx(s);
        !            87:                return;
        !            88:        }
        !            89:        for (; ip != &tcb; ip = ipnxt) {
        !            90:                ipnxt = ip->inp_next;
        !            91:                tp = intotcpcb(ip);
        !            92:                if (tp == 0)
        !            93:                        continue;
        !            94:                for (i = 0; i < TCPT_NTIMERS; i++) {
        !            95:                        if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
        !            96:                                (void) tcp_usrreq(tp->t_inpcb->inp_socket,
        !            97:                                    PRU_SLOWTIMO, (struct mbuf *)0,
        !            98:                                    (struct mbuf *)i, (struct mbuf *)0);
        !            99:                                if (ipnxt->inp_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:        splx(s);
        !           115: }
        !           116: 
        !           117: /*
        !           118:  * Cancel all timers for TCP tp.
        !           119:  */
        !           120: tcp_canceltimers(tp)
        !           121:        struct tcpcb *tp;
        !           122: {
        !           123:        register int i;
        !           124: 
        !           125:        for (i = 0; i < TCPT_NTIMERS; i++)
        !           126:                tp->t_timer[i] = 0;
        !           127: }
        !           128: 
        !           129: int    tcp_backoff[TCP_MAXRXTSHIFT + 1] =
        !           130:     { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
        !           131: 
        !           132: /*
        !           133:  * TCP timer processing.
        !           134:  */
        !           135: struct tcpcb *
        !           136: tcp_timers(tp, timer)
        !           137:        register struct tcpcb *tp;
        !           138:        int timer;
        !           139: {
        !           140:        register int rexmt;
        !           141: 
        !           142:        switch (timer) {
        !           143: 
        !           144:        /*
        !           145:         * 2 MSL timeout in shutdown went off.  If we're closed but
        !           146:         * still waiting for peer to close and connection has been idle
        !           147:         * too long, or if 2MSL time is up from TIME_WAIT, delete connection
        !           148:         * control block.  Otherwise, check again in a bit.
        !           149:         */
        !           150:        case TCPT_2MSL:
        !           151:                if (tp->t_state != TCPS_TIME_WAIT &&
        !           152:                    tp->t_idle <= tcp_maxidle)
        !           153:                        tp->t_timer[TCPT_2MSL] = tcp_keepintvl;
        !           154:                else
        !           155:                        tp = tcp_close(tp);
        !           156:                break;
        !           157: 
        !           158:        /*
        !           159:         * Retransmission timer went off.  Message has not
        !           160:         * been acked within retransmit interval.  Back off
        !           161:         * to a longer retransmit interval and retransmit one segment.
        !           162:         */
        !           163:        case TCPT_REXMT:
        !           164:                if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
        !           165:                        tp->t_rxtshift = TCP_MAXRXTSHIFT;
        !           166:                        tcpstat.tcps_timeoutdrop++;
        !           167:                        tp = tcp_drop(tp, ETIMEDOUT);
        !           168:                        break;
        !           169:                }
        !           170:                tcpstat.tcps_rexmttimeo++;
        !           171:                rexmt = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
        !           172:                rexmt *= tcp_backoff[tp->t_rxtshift];
        !           173:                TCPT_RANGESET(tp->t_rxtcur, rexmt, TCPTV_MIN, TCPTV_REXMTMAX);
        !           174:                tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
        !           175:                /*
        !           176:                 * If losing, let the lower level know and try for
        !           177:                 * a better route.  Also, if we backed off this far,
        !           178:                 * our srtt estimate is probably bogus.  Clobber it
        !           179:                 * so we'll take the next rtt measurement as our srtt;
        !           180:                 * move the current srtt into rttvar to keep the current
        !           181:                 * retransmit times until then.
        !           182:                 */
        !           183:                if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
        !           184:                        in_losing(tp->t_inpcb);
        !           185:                        tp->t_rttvar += (tp->t_srtt >> 2);
        !           186:                        tp->t_srtt = 0;
        !           187:                }
        !           188:                tp->snd_nxt = tp->snd_una;
        !           189:                /*
        !           190:                 * If timing a segment in this window, stop the timer.
        !           191:                 */
        !           192:                tp->t_rtt = 0;
        !           193:                /*
        !           194:                 * Close the congestion window down to one segment
        !           195:                 * (we'll open it by one segment for each ack we get).
        !           196:                 * Since we probably have a window's worth of unacked
        !           197:                 * data accumulated, this "slow start" keeps us from
        !           198:                 * dumping all that data as back-to-back packets (which
        !           199:                 * might overwhelm an intermediate gateway).
        !           200:                 *
        !           201:                 * There are two phases to the opening: Initially we
        !           202:                 * open by one mss on each ack.  This makes the window
        !           203:                 * size increase exponentially with time.  If the
        !           204:                 * window is larger than the path can handle, this
        !           205:                 * exponential growth results in dropped packet(s)
        !           206:                 * almost immediately.  To get more time between 
        !           207:                 * drops but still "push" the network to take advantage
        !           208:                 * of improving conditions, we switch from exponential
        !           209:                 * to linear window opening at some threshhold size.
        !           210:                 * For a threshhold, we use half the current window
        !           211:                 * size, truncated to a multiple of the mss.
        !           212:                 *
        !           213:                 * (the minimum cwnd that will give us exponential
        !           214:                 * growth is 2 mss.  We don't allow the threshhold
        !           215:                 * to go below this.)
        !           216:                 */
        !           217:                {
        !           218:                u_int win = MIN(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
        !           219:                if (win < 2)
        !           220:                        win = 2;
        !           221:                tp->snd_cwnd = tp->t_maxseg;
        !           222:                tp->snd_ssthresh = win * tp->t_maxseg;
        !           223:                }
        !           224:                (void) tcp_output(tp);
        !           225:                break;
        !           226: 
        !           227:        /*
        !           228:         * Persistance timer into zero window.
        !           229:         * Force a byte to be output, if possible.
        !           230:         */
        !           231:        case TCPT_PERSIST:
        !           232:                tcpstat.tcps_persisttimeo++;
        !           233:                tcp_setpersist(tp);
        !           234:                tp->t_force = 1;
        !           235:                (void) tcp_output(tp);
        !           236:                tp->t_force = 0;
        !           237:                break;
        !           238: 
        !           239:        /*
        !           240:         * Keep-alive timer went off; send something
        !           241:         * or drop connection if idle for too long.
        !           242:         */
        !           243:        case TCPT_KEEP:
        !           244:                tcpstat.tcps_keeptimeo++;
        !           245:                if (tp->t_state < TCPS_ESTABLISHED)
        !           246:                        goto dropit;
        !           247:                if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE &&
        !           248:                    tp->t_state <= TCPS_CLOSE_WAIT) {
        !           249:                        if (tp->t_idle >= tcp_keepidle + tcp_maxidle)
        !           250:                                goto dropit;
        !           251:                        /*
        !           252:                         * Send a packet designed to force a response
        !           253:                         * if the peer is up and reachable:
        !           254:                         * either an ACK if the connection is still alive,
        !           255:                         * or an RST if the peer has closed the connection
        !           256:                         * due to timeout or reboot.
        !           257:                         * Using sequence number tp->snd_una-1
        !           258:                         * causes the transmitted zero-length segment
        !           259:                         * to lie outside the receive window;
        !           260:                         * by the protocol spec, this requires the
        !           261:                         * correspondent TCP to respond.
        !           262:                         */
        !           263:                        tcpstat.tcps_keepprobe++;
        !           264: #ifdef TCP_COMPAT_42
        !           265:                        /*
        !           266:                         * The keepalive packet must have nonzero length
        !           267:                         * to get a 4.2 host to respond.
        !           268:                         */
        !           269:                        tcp_respond(tp, tp->t_template,
        !           270:                            tp->rcv_nxt - 1, tp->snd_una - 1, 0);
        !           271: #else
        !           272:                        tcp_respond(tp, tp->t_template,
        !           273:                            tp->rcv_nxt, tp->snd_una - 1, 0);
        !           274: #endif
        !           275:                        tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
        !           276:                } else
        !           277:                        tp->t_timer[TCPT_KEEP] = tcp_keepidle;
        !           278:                break;
        !           279:        dropit:
        !           280:                tcpstat.tcps_keepdrops++;
        !           281:                tp = tcp_drop(tp, ETIMEDOUT);
        !           282:                break;
        !           283:        }
        !           284:        return (tp);
        !           285: }

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