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Annotation of 43BSD/sys/netinet/tcp_output.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1982, 1986 Regents of the University of California.
        !             3:  * All rights reserved.  The Berkeley software License Agreement
        !             4:  * specifies the terms and conditions for redistribution.
        !             5:  *
        !             6:  *     @(#)tcp_output.c        7.2 (Berkeley) 8/20/86
        !             7:  */
        !             8: 
        !             9: #include "param.h"
        !            10: #include "systm.h"
        !            11: #include "mbuf.h"
        !            12: #include "protosw.h"
        !            13: #include "socket.h"
        !            14: #include "socketvar.h"
        !            15: #include "errno.h"
        !            16: 
        !            17: #include "../net/route.h"
        !            18: 
        !            19: #include "in.h"
        !            20: #include "in_pcb.h"
        !            21: #include "in_systm.h"
        !            22: #include "ip.h"
        !            23: #include "ip_var.h"
        !            24: #include "tcp.h"
        !            25: #define        TCPOUTFLAGS
        !            26: #include "tcp_fsm.h"
        !            27: #include "tcp_seq.h"
        !            28: #include "tcp_timer.h"
        !            29: #include "tcp_var.h"
        !            30: #include "tcpip.h"
        !            31: #include "tcp_debug.h"
        !            32: 
        !            33: /*
        !            34:  * Initial options.
        !            35:  */
        !            36: u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
        !            37: 
        !            38: /*
        !            39:  * Tcp output routine: figure out what should be sent and send it.
        !            40:  */
        !            41: tcp_output(tp)
        !            42:        register struct tcpcb *tp;
        !            43: {
        !            44:        register struct socket *so = tp->t_inpcb->inp_socket;
        !            45:        register int len, win;
        !            46:        struct mbuf *m0;
        !            47:        int off, flags, error;
        !            48:        register struct mbuf *m;
        !            49:        register struct tcpiphdr *ti;
        !            50:        u_char *opt;
        !            51:        unsigned optlen = 0;
        !            52:        int idle, sendalot;
        !            53: 
        !            54:        /*
        !            55:         * Determine length of data that should be transmitted,
        !            56:         * and flags that will be used.
        !            57:         * If there is some data or critical controls (SYN, RST)
        !            58:         * to send, then transmit; otherwise, investigate further.
        !            59:         */
        !            60:        idle = (tp->snd_max == tp->snd_una);
        !            61: again:
        !            62:        sendalot = 0;
        !            63:        off = tp->snd_nxt - tp->snd_una;
        !            64:        win = MIN(tp->snd_wnd, tp->snd_cwnd);
        !            65: 
        !            66:        /*
        !            67:         * If in persist timeout with window of 0, send 1 byte.
        !            68:         * Otherwise, if window is small but nonzero
        !            69:         * and timer expired, we will send what we can
        !            70:         * and go to transmit state.
        !            71:         */
        !            72:        if (tp->t_force) {
        !            73:                if (win == 0)
        !            74:                        win = 1;
        !            75:                else {
        !            76:                        tp->t_timer[TCPT_PERSIST] = 0;
        !            77:                        tp->t_rxtshift = 0;
        !            78:                }
        !            79:        }
        !            80: 
        !            81:        len = MIN(so->so_snd.sb_cc, win) - off;
        !            82:        flags = tcp_outflags[tp->t_state];
        !            83: 
        !            84:        if (len < 0) {
        !            85:                /*
        !            86:                 * If FIN has been sent but not acked,
        !            87:                 * but we haven't been called to retransmit,
        !            88:                 * len will be -1; transmit if acking, otherwise no need.
        !            89:                 * Otherwise, window shrank after we sent into it.
        !            90:                 * If window shrank to 0, cancel pending retransmit
        !            91:                 * and pull snd_nxt back to (closed) window.
        !            92:                 * We will enter persist state below.
        !            93:                 * If the window didn't close completely,
        !            94:                 * just wait for an ACK.
        !            95:                 */
        !            96:                if (flags & TH_FIN) {
        !            97:                        if (tp->t_flags & TF_ACKNOW)
        !            98:                                len = 0;
        !            99:                        else
        !           100:                                return (0);
        !           101:                } else if (win == 0) {
        !           102:                        tp->t_timer[TCPT_REXMT] = 0;
        !           103:                        tp->snd_nxt = tp->snd_una;
        !           104:                        len = 0;
        !           105:                } else
        !           106:                        return (0);
        !           107:        }
        !           108:        if (len > tp->t_maxseg) {
        !           109:                len = tp->t_maxseg;
        !           110:                /*
        !           111:                 * Don't send more than one segment if retransmitting
        !           112:                 * (or persisting, but then we shouldn't be here).
        !           113:                 */
        !           114:                if (tp->t_rxtshift == 0)
        !           115:                        sendalot = 1;
        !           116:        }
        !           117:        if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
        !           118:                flags &= ~TH_FIN;
        !           119:        win = sbspace(&so->so_rcv);
        !           120: 
        !           121: 
        !           122:        /*
        !           123:         * If our state indicates that FIN should be sent
        !           124:         * and we have not yet done so, or we're retransmitting the FIN,
        !           125:         * then we need to send.
        !           126:         */
        !           127:        if (flags & TH_FIN &&
        !           128:            ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
        !           129:                goto send;
        !           130:        /*
        !           131:         * Send if we owe peer an ACK.
        !           132:         */
        !           133:        if (tp->t_flags & TF_ACKNOW)
        !           134:                goto send;
        !           135:        if (flags & (TH_SYN|TH_RST))
        !           136:                goto send;
        !           137:        if (SEQ_GT(tp->snd_up, tp->snd_una))
        !           138:                goto send;
        !           139: 
        !           140:        /*
        !           141:         * Sender silly window avoidance.  If connection is idle
        !           142:         * and can send all data, a maximum segment,
        !           143:         * at least a maximum default-size segment do it,
        !           144:         * or are forced, do it; otherwise don't bother.
        !           145:         * If peer's buffer is tiny, then send
        !           146:         * when window is at least half open.
        !           147:         * If retransmitting (possibly after persist timer forced us
        !           148:         * to send into a small window), then must resend.
        !           149:         */
        !           150:        if (len) {
        !           151:                if (len == tp->t_maxseg || len >= TCP_MSS)      /* a lot */
        !           152:                        goto send;
        !           153:                if ((idle || tp->t_flags & TF_NODELAY) &&
        !           154:                    len + off >= so->so_snd.sb_cc)
        !           155:                        goto send;
        !           156:                if (tp->t_force)
        !           157:                        goto send;
        !           158:                if (len >= tp->max_sndwnd / 2)
        !           159:                        goto send;
        !           160:                if (SEQ_LT(tp->snd_nxt, tp->snd_max))
        !           161:                        goto send;
        !           162:        }
        !           163: 
        !           164:        /*
        !           165:         * Compare available window to amount of window
        !           166:         * known to peer (as advertised window less
        !           167:         * next expected input.)  If the difference is 35% or more of the
        !           168:         * maximum possible window, then want to send a window update to peer.
        !           169:         */
        !           170:        if (win > 0 &&
        !           171:            ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35))
        !           172:                goto send;
        !           173: 
        !           174:        /*
        !           175:         * TCP window updates are not reliable, rather a polling protocol
        !           176:         * using ``persist'' packets is used to insure receipt of window
        !           177:         * updates.  The three ``states'' for the output side are:
        !           178:         *      idle                    not doing retransmits or persists
        !           179:         *      persisting              to move a small or zero window
        !           180:         *      (re)transmitting        and thereby not persisting
        !           181:         *
        !           182:         * tp->t_timer[TCPT_PERSIST]
        !           183:         *      is set when we are in persist state.
        !           184:         * tp->t_force
        !           185:         *      is set when we are called to send a persist packet.
        !           186:         * tp->t_timer[TCPT_REXMT]
        !           187:         *      is set when we are retransmitting
        !           188:         * The output side is idle when both timers are zero.
        !           189:         *
        !           190:         * If send window is too small, there is data to transmit, and no
        !           191:         * retransmit or persist is pending, then go to persist state.
        !           192:         * If nothing happens soon, send when timer expires:
        !           193:         * if window is nonzero, transmit what we can,
        !           194:         * otherwise force out a byte.
        !           195:         */
        !           196:        if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
        !           197:            tp->t_timer[TCPT_PERSIST] == 0) {
        !           198:                tp->t_rxtshift = 0;
        !           199:                tcp_setpersist(tp);
        !           200:        }
        !           201: 
        !           202:        /*
        !           203:         * No reason to send a segment, just return.
        !           204:         */
        !           205:        return (0);
        !           206: 
        !           207: send:
        !           208:        /*
        !           209:         * Grab a header mbuf, attaching a copy of data to
        !           210:         * be transmitted, and initialize the header from
        !           211:         * the template for sends on this connection.
        !           212:         */
        !           213:        MGET(m, M_DONTWAIT, MT_HEADER);
        !           214:        if (m == NULL)
        !           215:                return (ENOBUFS);
        !           216:        m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
        !           217:        m->m_len = sizeof (struct tcpiphdr);
        !           218:        if (len) {
        !           219:                m->m_next = m_copy(so->so_snd.sb_mb, off, len);
        !           220:                if (m->m_next == 0)
        !           221:                        len = 0;
        !           222:        }
        !           223:        ti = mtod(m, struct tcpiphdr *);
        !           224:        if (tp->t_template == 0)
        !           225:                panic("tcp_output");
        !           226:        bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
        !           227: 
        !           228:        /*
        !           229:         * Fill in fields, remembering maximum advertised
        !           230:         * window for use in delaying messages about window sizes.
        !           231:         * If resending a FIN, be sure not to use a new sequence number.
        !           232:         */
        !           233:        if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
        !           234:            tp->snd_nxt != tp->snd_una)
        !           235:                tp->snd_nxt--;
        !           236:        ti->ti_seq = htonl(tp->snd_nxt);
        !           237:        ti->ti_ack = htonl(tp->rcv_nxt);
        !           238:        /*
        !           239:         * Before ESTABLISHED, force sending of initial options
        !           240:         * unless TCP set to not do any options.
        !           241:         */
        !           242:        opt = NULL;
        !           243:        if (tp->t_state < TCPS_ESTABLISHED && (tp->t_flags & TF_NOOPT) == 0) {
        !           244:                u_short mss;
        !           245: 
        !           246:                mss = MIN(so->so_rcv.sb_hiwat / 2, tcp_mss(tp));
        !           247:                if (mss > IP_MSS - sizeof(struct tcpiphdr)) {
        !           248:                        opt = tcp_initopt;
        !           249:                        optlen = sizeof (tcp_initopt);
        !           250:                        *(u_short *)(opt + 2) = htons(mss);
        !           251:                }
        !           252:        } else if (tp->t_tcpopt) {
        !           253:                opt = mtod(tp->t_tcpopt, u_char *);
        !           254:                optlen = tp->t_tcpopt->m_len;
        !           255:        }
        !           256:        if (opt) {
        !           257:                m0 = m->m_next;
        !           258:                m->m_next = m_get(M_DONTWAIT, MT_DATA);
        !           259:                if (m->m_next == 0) {
        !           260:                        (void) m_free(m);
        !           261:                        m_freem(m0);
        !           262:                        return (ENOBUFS);
        !           263:                }
        !           264:                m->m_next->m_next = m0;
        !           265:                m0 = m->m_next;
        !           266:                m0->m_len = optlen;
        !           267:                bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
        !           268:                opt = (u_char *)(mtod(m0, caddr_t) + optlen);
        !           269:                while (m0->m_len & 0x3) {
        !           270:                        *opt++ = TCPOPT_EOL;
        !           271:                        m0->m_len++;
        !           272:                }
        !           273:                optlen = m0->m_len;
        !           274:                ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
        !           275:        }
        !           276:        ti->ti_flags = flags;
        !           277:        /*
        !           278:         * Calculate receive window.  Don't shrink window,
        !           279:         * but avoid silly window syndrome.
        !           280:         */
        !           281:        if (win < so->so_rcv.sb_hiwat / 4 && win < tp->t_maxseg)
        !           282:                win = 0;
        !           283:        if (win < (int)(tp->rcv_adv - tp->rcv_nxt))
        !           284:                win = (int)(tp->rcv_adv - tp->rcv_nxt);
        !           285:        ti->ti_win = htons((u_short)win);
        !           286:        if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
        !           287:                ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
        !           288:                ti->ti_flags |= TH_URG;
        !           289:        } else
        !           290:                /*
        !           291:                 * If no urgent pointer to send, then we pull
        !           292:                 * the urgent pointer to the left edge of the send window
        !           293:                 * so that it doesn't drift into the send window on sequence
        !           294:                 * number wraparound.
        !           295:                 */
        !           296:                tp->snd_up = tp->snd_una;               /* drag it along */
        !           297:        /*
        !           298:         * If anything to send and we can send it all, set PUSH.
        !           299:         * (This will keep happy those implementations which only
        !           300:         * give data to the user when a buffer fills or a PUSH comes in.)
        !           301:         */
        !           302:        if (len && off+len == so->so_snd.sb_cc)
        !           303:                ti->ti_flags |= TH_PUSH;
        !           304: 
        !           305:        /*
        !           306:         * Put TCP length in extended header, and then
        !           307:         * checksum extended header and data.
        !           308:         */
        !           309:        if (len + optlen)
        !           310:                ti->ti_len = htons((u_short)(sizeof(struct tcphdr) +
        !           311:                    optlen + len));
        !           312:        ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len);
        !           313: 
        !           314:        /*
        !           315:         * In transmit state, time the transmission and arrange for
        !           316:         * the retransmit.  In persist state, just set snd_max.
        !           317:         */
        !           318:        if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
        !           319:                /*
        !           320:                 * Advance snd_nxt over sequence space of this segment.
        !           321:                 */
        !           322:                if (flags & TH_SYN)
        !           323:                        tp->snd_nxt++;
        !           324:                if (flags & TH_FIN) {
        !           325:                        tp->snd_nxt++;
        !           326:                        tp->t_flags |= TF_SENTFIN;
        !           327:                }
        !           328:                tp->snd_nxt += len;
        !           329:                if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
        !           330:                        tp->snd_max = tp->snd_nxt;
        !           331:                        /*
        !           332:                         * Time this transmission if not a retransmission and
        !           333:                         * not currently timing anything.
        !           334:                         */
        !           335:                        if (tp->t_rtt == 0) {
        !           336:                                tp->t_rtt = 1;
        !           337:                                tp->t_rtseq = tp->snd_nxt - len;
        !           338:                        }
        !           339:                }
        !           340: 
        !           341:                /*
        !           342:                 * Set retransmit timer if not currently set,
        !           343:                 * and not doing an ack or a keep-alive probe.
        !           344:                 * Initial value for retransmit timer is tcp_beta*tp->t_srtt.
        !           345:                 * Initialize shift counter which is used for backoff
        !           346:                 * of retransmit time.
        !           347:                 */
        !           348:                if (tp->t_timer[TCPT_REXMT] == 0 &&
        !           349:                    tp->snd_nxt != tp->snd_una) {
        !           350:                        TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
        !           351:                          tcp_beta * (tp->t_srtt ? tp->t_srtt : TCPTV_SRTTDFLT),
        !           352:                          TCPTV_MIN, TCPTV_MAX);
        !           353:                        tp->t_rxtshift = 0;
        !           354:                        tp->t_timer[TCPT_PERSIST] = 0;
        !           355:                }
        !           356:        } else
        !           357:                if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
        !           358:                        tp->snd_max = tp->snd_nxt + len;
        !           359: 
        !           360:        /*
        !           361:         * Trace.
        !           362:         */
        !           363:        if (so->so_options & SO_DEBUG)
        !           364:                tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
        !           365: 
        !           366:        /*
        !           367:         * Fill in IP length and desired time to live and
        !           368:         * send to IP level.
        !           369:         */
        !           370:        ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
        !           371:        ((struct ip *)ti)->ip_ttl = TCP_TTL;
        !           372:        error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
        !           373:            so->so_options & SO_DONTROUTE);
        !           374:        if (error)
        !           375:                return (error);
        !           376: 
        !           377:        /*
        !           378:         * Data sent (as far as we can tell).
        !           379:         * If this advertises a larger window than any other segment,
        !           380:         * then remember the size of the advertised window.
        !           381:         * Any pending ACK has now been sent.
        !           382:         */
        !           383:        if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
        !           384:                tp->rcv_adv = tp->rcv_nxt + win;
        !           385:        tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
        !           386:        if (sendalot)
        !           387:                goto again;
        !           388:        return (0);
        !           389: }
        !           390: 
        !           391: tcp_setpersist(tp)
        !           392:        register struct tcpcb *tp;
        !           393: {
        !           394: 
        !           395:        if (tp->t_timer[TCPT_REXMT])
        !           396:                panic("tcp_output REXMT");
        !           397:        /*
        !           398:         * Start/restart persistance timer.
        !           399:         */
        !           400:        TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
        !           401:            ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift,
        !           402:            TCPTV_PERSMIN, TCPTV_MAX);
        !           403:        tp->t_rxtshift++;
        !           404:        if (tp->t_rxtshift >= TCP_MAXRXTSHIFT)
        !           405:                tp->t_rxtshift = 0;
        !           406: }

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