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Annotation of 43BSDTahoe/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.
        !             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_output.c        7.17 (Berkeley) 6/29/88
        !            18:  */
        !            19: 
        !            20: #include "param.h"
        !            21: #include "systm.h"
        !            22: #include "mbuf.h"
        !            23: #include "protosw.h"
        !            24: #include "socket.h"
        !            25: #include "socketvar.h"
        !            26: #include "errno.h"
        !            27: 
        !            28: #include "../net/route.h"
        !            29: 
        !            30: #include "in.h"
        !            31: #include "in_pcb.h"
        !            32: #include "in_systm.h"
        !            33: #include "ip.h"
        !            34: #include "ip_var.h"
        !            35: #include "tcp.h"
        !            36: #define        TCPOUTFLAGS
        !            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: #include "tcp_debug.h"
        !            43: 
        !            44: /*
        !            45:  * Initial options.
        !            46:  */
        !            47: u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
        !            48: 
        !            49: /*
        !            50:  * Tcp output routine: figure out what should be sent and send it.
        !            51:  */
        !            52: tcp_output(tp)
        !            53:        register struct tcpcb *tp;
        !            54: {
        !            55:        register struct socket *so = tp->t_inpcb->inp_socket;
        !            56:        register long len, win;
        !            57:        struct mbuf *m0;
        !            58:        int off, flags, error;
        !            59:        register struct mbuf *m;
        !            60:        register struct tcpiphdr *ti;
        !            61:        u_char *opt;
        !            62:        unsigned optlen = 0;
        !            63:        int idle, sendalot;
        !            64: 
        !            65:        /*
        !            66:         * Determine length of data that should be transmitted,
        !            67:         * and flags that will be used.
        !            68:         * If there is some data or critical controls (SYN, RST)
        !            69:         * to send, then transmit; otherwise, investigate further.
        !            70:         */
        !            71:        idle = (tp->snd_max == tp->snd_una);
        !            72: again:
        !            73:        sendalot = 0;
        !            74:        off = tp->snd_nxt - tp->snd_una;
        !            75:        win = MIN(tp->snd_wnd, tp->snd_cwnd);
        !            76: 
        !            77:        /*
        !            78:         * If in persist timeout with window of 0, send 1 byte.
        !            79:         * Otherwise, if window is small but nonzero
        !            80:         * and timer expired, we will send what we can
        !            81:         * and go to transmit state.
        !            82:         */
        !            83:        if (tp->t_force) {
        !            84:                if (win == 0)
        !            85:                        win = 1;
        !            86:                else {
        !            87:                        tp->t_timer[TCPT_PERSIST] = 0;
        !            88:                        tp->t_rxtshift = 0;
        !            89:                }
        !            90:        }
        !            91: 
        !            92:        len = MIN(so->so_snd.sb_cc, win) - off;
        !            93:        flags = tcp_outflags[tp->t_state];
        !            94: 
        !            95:        if (len < 0) {
        !            96:                /*
        !            97:                 * If FIN has been sent but not acked,
        !            98:                 * but we haven't been called to retransmit,
        !            99:                 * len will be -1.  Otherwise, window shrank
        !           100:                 * after we sent into it.  If window shrank to 0,
        !           101:                 * cancel pending retransmit and pull snd_nxt
        !           102:                 * back to (closed) window.  We will enter persist
        !           103:                 * state below.  If the window didn't close completely,
        !           104:                 * just wait for an ACK.
        !           105:                 */
        !           106:                len = 0;
        !           107:                if (win == 0) {
        !           108:                        tp->t_timer[TCPT_REXMT] = 0;
        !           109:                        tp->snd_nxt = tp->snd_una;
        !           110:                }
        !           111:        }
        !           112:        if (len > tp->t_maxseg) {
        !           113:                len = tp->t_maxseg;
        !           114:                sendalot = 1;
        !           115:        }
        !           116:        if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
        !           117:                flags &= ~TH_FIN;
        !           118:        win = sbspace(&so->so_rcv);
        !           119: 
        !           120: 
        !           121:        /*
        !           122:         * If our state indicates that FIN should be sent
        !           123:         * and we have not yet done so, or we're retransmitting the FIN,
        !           124:         * then we need to send.
        !           125:         */
        !           126:        if (flags & TH_FIN &&
        !           127:            ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
        !           128:                goto send;
        !           129:        /*
        !           130:         * Send if we owe peer an ACK.
        !           131:         */
        !           132:        if (tp->t_flags & TF_ACKNOW)
        !           133:                goto send;
        !           134:        if (flags & (TH_SYN|TH_RST))
        !           135:                goto send;
        !           136:        if (SEQ_GT(tp->snd_up, tp->snd_una))
        !           137:                goto send;
        !           138: 
        !           139:        /*
        !           140:         * Sender silly window avoidance.  If connection is idle
        !           141:         * and can send all data, a maximum segment,
        !           142:         * at least a maximum default-size segment do it,
        !           143:         * or are forced, do it; otherwise don't bother.
        !           144:         * If peer's buffer is tiny, then send
        !           145:         * when window is at least half open.
        !           146:         * If retransmitting (possibly after persist timer forced us
        !           147:         * to send into a small window), then must resend.
        !           148:         */
        !           149:        if (len) {
        !           150:                if (len == tp->t_maxseg)
        !           151:                        goto send;
        !           152:                if ((idle || tp->t_flags & TF_NODELAY) &&
        !           153:                    len + off >= so->so_snd.sb_cc)
        !           154:                        goto send;
        !           155:                if (tp->t_force)
        !           156:                        goto send;
        !           157:                if (len >= tp->max_sndwnd / 2)
        !           158:                        goto send;
        !           159:                if (SEQ_LT(tp->snd_nxt, tp->snd_max))
        !           160:                        goto send;
        !           161:        }
        !           162: 
        !           163:        /*
        !           164:         * Compare available window to amount of window
        !           165:         * known to peer (as advertised window less
        !           166:         * next expected input).  If the difference is at least two
        !           167:         * max size segments or at least 35% of the maximum possible
        !           168:         * window, then want to send a window update to peer.
        !           169:         */
        !           170:        if (win > 0) {
        !           171:                int adv = win - (tp->rcv_adv - tp->rcv_nxt);
        !           172: 
        !           173:                if (so->so_rcv.sb_cc == 0 && adv >= 2 * tp->t_maxseg)
        !           174:                        goto send;
        !           175:                if (100 * adv / so->so_rcv.sb_hiwat >= 35)
        !           176:                        goto send;
        !           177:        }
        !           178: 
        !           179:        /*
        !           180:         * TCP window updates are not reliable, rather a polling protocol
        !           181:         * using ``persist'' packets is used to insure receipt of window
        !           182:         * updates.  The three ``states'' for the output side are:
        !           183:         *      idle                    not doing retransmits or persists
        !           184:         *      persisting              to move a small or zero window
        !           185:         *      (re)transmitting        and thereby not persisting
        !           186:         *
        !           187:         * tp->t_timer[TCPT_PERSIST]
        !           188:         *      is set when we are in persist state.
        !           189:         * tp->t_force
        !           190:         *      is set when we are called to send a persist packet.
        !           191:         * tp->t_timer[TCPT_REXMT]
        !           192:         *      is set when we are retransmitting
        !           193:         * The output side is idle when both timers are zero.
        !           194:         *
        !           195:         * If send window is too small, there is data to transmit, and no
        !           196:         * retransmit or persist is pending, then go to persist state.
        !           197:         * If nothing happens soon, send when timer expires:
        !           198:         * if window is nonzero, transmit what we can,
        !           199:         * otherwise force out a byte.
        !           200:         */
        !           201:        if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
        !           202:            tp->t_timer[TCPT_PERSIST] == 0) {
        !           203:                tp->t_rxtshift = 0;
        !           204:                tcp_setpersist(tp);
        !           205:        }
        !           206: 
        !           207:        /*
        !           208:         * No reason to send a segment, just return.
        !           209:         */
        !           210:        return (0);
        !           211: 
        !           212: send:
        !           213:        /*
        !           214:         * Grab a header mbuf, attaching a copy of data to
        !           215:         * be transmitted, and initialize the header from
        !           216:         * the template for sends on this connection.
        !           217:         */
        !           218:        MGET(m, M_DONTWAIT, MT_HEADER);
        !           219:        if (m == NULL)
        !           220:                return (ENOBUFS);
        !           221: #define        MAXLINKHDR      32              /* belongs elsewhere */
        !           222: #define        DATASPACE  (MMAXOFF - (MMINOFF + MAXLINKHDR + sizeof (struct tcpiphdr)))
        !           223:        m->m_off = MMINOFF + MAXLINKHDR;
        !           224:        m->m_len = sizeof (struct tcpiphdr);
        !           225:        ti = mtod(m, struct tcpiphdr *);
        !           226:        if (len) {
        !           227:                if (tp->t_force && len == 1)
        !           228:                        tcpstat.tcps_sndprobe++;
        !           229:                else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
        !           230:                        tcpstat.tcps_sndrexmitpack++;
        !           231:                        tcpstat.tcps_sndrexmitbyte += len;
        !           232:                } else {
        !           233:                        tcpstat.tcps_sndpack++;
        !           234:                        tcpstat.tcps_sndbyte += len;
        !           235:                }
        !           236:                if (len <= DATASPACE) {
        !           237:                        m_copydata(so->so_snd.sb_mb, off, (int) len,
        !           238:                            mtod(m, caddr_t) + sizeof(struct tcpiphdr));
        !           239:                        m->m_len += len;
        !           240:                } else {
        !           241:                        m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
        !           242:                        if (m->m_next == 0)
        !           243:                                len = 0;
        !           244:                }
        !           245:        } else if (tp->t_flags & TF_ACKNOW)
        !           246:                tcpstat.tcps_sndacks++;
        !           247:        else if (flags & (TH_SYN|TH_FIN|TH_RST))
        !           248:                tcpstat.tcps_sndctrl++;
        !           249:        else if (SEQ_GT(tp->snd_up, tp->snd_una))
        !           250:                tcpstat.tcps_sndurg++;
        !           251:        else
        !           252:                tcpstat.tcps_sndwinup++;
        !           253: 
        !           254:        if (tp->t_template == 0)
        !           255:                panic("tcp_output");
        !           256:        bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
        !           257: 
        !           258:        /*
        !           259:         * Fill in fields, remembering maximum advertised
        !           260:         * window for use in delaying messages about window sizes.
        !           261:         * If resending a FIN, be sure not to use a new sequence number.
        !           262:         */
        !           263:        if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 
        !           264:            tp->snd_nxt == tp->snd_max)
        !           265:                tp->snd_nxt--;
        !           266:        ti->ti_seq = htonl(tp->snd_nxt);
        !           267:        ti->ti_ack = htonl(tp->rcv_nxt);
        !           268:        /*
        !           269:         * Before ESTABLISHED, force sending of initial options
        !           270:         * unless TCP set to not do any options.
        !           271:         */
        !           272:        opt = NULL;
        !           273:        if (flags & TH_SYN && (tp->t_flags & TF_NOOPT) == 0) {
        !           274:                u_short mss;
        !           275: 
        !           276:                mss = MIN(so->so_rcv.sb_hiwat / 2, tcp_mss(tp));
        !           277:                if (mss > IP_MSS - sizeof(struct tcpiphdr)) {
        !           278:                        opt = tcp_initopt;
        !           279:                        optlen = sizeof (tcp_initopt);
        !           280:                        *(u_short *)(opt + 2) = htons(mss);
        !           281:                }
        !           282:        }
        !           283:        if (opt) {
        !           284:                m0 = m->m_next;
        !           285:                m->m_next = m_get(M_DONTWAIT, MT_DATA);
        !           286:                if (m->m_next == 0) {
        !           287:                        (void) m_free(m);
        !           288:                        m_freem(m0);
        !           289:                        return (ENOBUFS);
        !           290:                }
        !           291:                m->m_next->m_next = m0;
        !           292:                m0 = m->m_next;
        !           293:                m0->m_len = optlen;
        !           294:                bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
        !           295:                opt = (u_char *)(mtod(m0, caddr_t) + optlen);
        !           296:                while (m0->m_len & 0x3) {
        !           297:                        *opt++ = TCPOPT_EOL;
        !           298:                        m0->m_len++;
        !           299:                }
        !           300:                optlen = m0->m_len;
        !           301:                ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
        !           302:        }
        !           303:        ti->ti_flags = flags;
        !           304:        /*
        !           305:         * Calculate receive window.  Don't shrink window,
        !           306:         * but avoid silly window syndrome.
        !           307:         */
        !           308:        if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg)
        !           309:                win = 0;
        !           310:        if (win > IP_MAXPACKET)
        !           311:                win = IP_MAXPACKET;
        !           312:        if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
        !           313:                win = (long)(tp->rcv_adv - tp->rcv_nxt);
        !           314:        ti->ti_win = htons((u_short)win);
        !           315:        if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
        !           316:                ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
        !           317:                ti->ti_flags |= TH_URG;
        !           318:        } else
        !           319:                /*
        !           320:                 * If no urgent pointer to send, then we pull
        !           321:                 * the urgent pointer to the left edge of the send window
        !           322:                 * so that it doesn't drift into the send window on sequence
        !           323:                 * number wraparound.
        !           324:                 */
        !           325:                tp->snd_up = tp->snd_una;               /* drag it along */
        !           326:        /*
        !           327:         * If anything to send and we can send it all, set PUSH.
        !           328:         * (This will keep happy those implementations which only
        !           329:         * give data to the user when a buffer fills or a PUSH comes in.)
        !           330:         */
        !           331:        if (len && off+len == so->so_snd.sb_cc)
        !           332:                ti->ti_flags |= TH_PUSH;
        !           333: 
        !           334:        /*
        !           335:         * Put TCP length in extended header, and then
        !           336:         * checksum extended header and data.
        !           337:         */
        !           338:        if (len + optlen)
        !           339:                ti->ti_len = htons((u_short)(sizeof(struct tcphdr) +
        !           340:                    optlen + len));
        !           341:        ti->ti_sum = in_cksum(m,
        !           342:            (int)(sizeof (struct tcpiphdr) + (int)optlen + len));
        !           343: 
        !           344:        /*
        !           345:         * In transmit state, time the transmission and arrange for
        !           346:         * the retransmit.  In persist state, just set snd_max.
        !           347:         */
        !           348:        if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
        !           349:                tcp_seq startseq = tp->snd_nxt;
        !           350: 
        !           351:                /*
        !           352:                 * Advance snd_nxt over sequence space of this segment.
        !           353:                 */
        !           354:                if (flags & TH_SYN)
        !           355:                        tp->snd_nxt++;
        !           356:                if (flags & TH_FIN) {
        !           357:                        tp->snd_nxt++;
        !           358:                        tp->t_flags |= TF_SENTFIN;
        !           359:                }
        !           360:                tp->snd_nxt += len;
        !           361:                if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
        !           362:                        tp->snd_max = tp->snd_nxt;
        !           363:                        /*
        !           364:                         * Time this transmission if not a retransmission and
        !           365:                         * not currently timing anything.
        !           366:                         */
        !           367:                        if (tp->t_rtt == 0) {
        !           368:                                tp->t_rtt = 1;
        !           369:                                tp->t_rtseq = startseq;
        !           370:                                tcpstat.tcps_segstimed++;
        !           371:                        }
        !           372:                }
        !           373: 
        !           374:                /*
        !           375:                 * Set retransmit timer if not currently set,
        !           376:                 * and not doing an ack or a keep-alive probe.
        !           377:                 * Initial value for retransmit timer is smoothed
        !           378:                 * round-trip time + 2 * round-trip time variance.
        !           379:                 * Initialize shift counter which is used for backoff
        !           380:                 * of retransmit time.
        !           381:                 */
        !           382:                if (tp->t_timer[TCPT_REXMT] == 0 &&
        !           383:                    tp->snd_nxt != tp->snd_una) {
        !           384:                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
        !           385:                        if (tp->t_timer[TCPT_PERSIST]) {
        !           386:                                tp->t_timer[TCPT_PERSIST] = 0;
        !           387:                                tp->t_rxtshift = 0;
        !           388:                        }
        !           389:                }
        !           390:        } else
        !           391:                if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
        !           392:                        tp->snd_max = tp->snd_nxt + len;
        !           393: 
        !           394:        /*
        !           395:         * Trace.
        !           396:         */
        !           397:        if (so->so_options & SO_DEBUG)
        !           398:                tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
        !           399: 
        !           400:        /*
        !           401:         * Fill in IP length and desired time to live and
        !           402:         * send to IP level.
        !           403:         */
        !           404:        ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
        !           405:        ((struct ip *)ti)->ip_ttl = TCP_TTL;
        !           406:        error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
        !           407:            so->so_options & SO_DONTROUTE);
        !           408:        if (error) {
        !           409:                if (error == ENOBUFS) {
        !           410:                        tcp_quench(tp->t_inpcb);
        !           411:                        return (0);
        !           412:                }
        !           413:                return (error);
        !           414:        }
        !           415:        tcpstat.tcps_sndtotal++;
        !           416: 
        !           417:        /*
        !           418:         * Data sent (as far as we can tell).
        !           419:         * If this advertises a larger window than any other segment,
        !           420:         * then remember the size of the advertised window.
        !           421:         * Any pending ACK has now been sent.
        !           422:         */
        !           423:        if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
        !           424:                tp->rcv_adv = tp->rcv_nxt + win;
        !           425:        tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
        !           426:        if (sendalot)
        !           427:                goto again;
        !           428:        return (0);
        !           429: }
        !           430: 
        !           431: tcp_setpersist(tp)
        !           432:        register struct tcpcb *tp;
        !           433: {
        !           434:        register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
        !           435: 
        !           436:        if (tp->t_timer[TCPT_REXMT])
        !           437:                panic("tcp_output REXMT");
        !           438:        /*
        !           439:         * Start/restart persistance timer.
        !           440:         */
        !           441:        TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
        !           442:            t * tcp_backoff[tp->t_rxtshift],
        !           443:            TCPTV_PERSMIN, TCPTV_PERSMAX);
        !           444:        if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
        !           445:                tp->t_rxtshift++;
        !           446: }

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