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

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1982, 1986, 1988, 1990 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution is only permitted until one year after the first shipment
        !             6:  * of 4.4BSD by the Regents.  Otherwise, redistribution and use in source and
        !             7:  * binary forms are permitted provided that: (1) source distributions retain
        !             8:  * this entire copyright notice and comment, and (2) distributions including
        !             9:  * binaries display the following acknowledgement:  This product includes
        !            10:  * software developed by the University of California, Berkeley and its
        !            11:  * contributors'' in the documentation or other materials provided with the
        !            12:  * distribution and in all advertising materials mentioning features or use
        !            13:  * of this software.  Neither the name of the University nor the names of
        !            14:  * its contributors may be used to endorse or promote products derived from
        !            15:  * this software without specific prior written permission.
        !            16:  * THIS SOFTWARE IS PROVIDED AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
        !            17:  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
        !            18:  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            19:  *
        !            20:  *     @(#)tcp_output.c        7.21 (Berkeley) 6/28/90
        !            21:  */
        !            22: 
        !            23: #include "param.h"
        !            24: #include "systm.h"
        !            25: #include "malloc.h"
        !            26: #include "mbuf.h"
        !            27: #include "protosw.h"
        !            28: #include "socket.h"
        !            29: #include "socketvar.h"
        !            30: #include "errno.h"
        !            31: 
        !            32: #include "../net/route.h"
        !            33: 
        !            34: #include "in.h"
        !            35: #include "in_systm.h"
        !            36: #include "ip.h"
        !            37: #include "in_pcb.h"
        !            38: #include "ip_var.h"
        !            39: #include "tcp.h"
        !            40: #define        TCPOUTFLAGS
        !            41: #include "tcp_fsm.h"
        !            42: #include "tcp_seq.h"
        !            43: #include "tcp_timer.h"
        !            44: #include "tcp_var.h"
        !            45: #include "tcpip.h"
        !            46: #include "tcp_debug.h"
        !            47: 
        !            48: #ifdef notyet
        !            49: extern struct mbuf *m_copypack();
        !            50: #endif
        !            51: 
        !            52: /*
        !            53:  * Initial options.
        !            54:  */
        !            55: u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
        !            56: 
        !            57: /*
        !            58:  * Tcp output routine: figure out what should be sent and send it.
        !            59:  */
        !            60: tcp_output(tp)
        !            61:        register struct tcpcb *tp;
        !            62: {
        !            63:        register struct socket *so = tp->t_inpcb->inp_socket;
        !            64:        register long len, win;
        !            65:        int off, flags, error;
        !            66:        register struct mbuf *m;
        !            67:        register struct tcpiphdr *ti;
        !            68:        u_char *opt;
        !            69:        unsigned optlen, hdrlen;
        !            70:        int idle, sendalot;
        !            71: 
        !            72:        /*
        !            73:         * Determine length of data that should be transmitted,
        !            74:         * and flags that will be used.
        !            75:         * If there is some data or critical controls (SYN, RST)
        !            76:         * to send, then transmit; otherwise, investigate further.
        !            77:         */
        !            78:        idle = (tp->snd_max == tp->snd_una);
        !            79:        if (idle && tp->t_idle >= tp->t_rxtcur)
        !            80:                /*
        !            81:                 * We have been idle for "a while" and no acks are
        !            82:                 * expected to clock out any data we send --
        !            83:                 * slow start to get ack "clock" running again.
        !            84:                 */
        !            85:                tp->snd_cwnd = tp->t_maxseg;
        !            86: again:
        !            87:        sendalot = 0;
        !            88:        off = tp->snd_nxt - tp->snd_una;
        !            89:        win = min(tp->snd_wnd, tp->snd_cwnd);
        !            90: 
        !            91:        /*
        !            92:         * If in persist timeout with window of 0, send 1 byte.
        !            93:         * Otherwise, if window is small but nonzero
        !            94:         * and timer expired, we will send what we can
        !            95:         * and go to transmit state.
        !            96:         */
        !            97:        if (tp->t_force) {
        !            98:                if (win == 0)
        !            99:                        win = 1;
        !           100:                else {
        !           101:                        tp->t_timer[TCPT_PERSIST] = 0;
        !           102:                        tp->t_rxtshift = 0;
        !           103:                }
        !           104:        }
        !           105: 
        !           106:        flags = tcp_outflags[tp->t_state];
        !           107:        len = min(so->so_snd.sb_cc, win) - off;
        !           108: 
        !           109:        if (len < 0) {
        !           110:                /*
        !           111:                 * If FIN has been sent but not acked,
        !           112:                 * but we haven't been called to retransmit,
        !           113:                 * len will be -1.  Otherwise, window shrank
        !           114:                 * after we sent into it.  If window shrank to 0,
        !           115:                 * cancel pending retransmit and pull snd_nxt
        !           116:                 * back to (closed) window.  We will enter persist
        !           117:                 * state below.  If the window didn't close completely,
        !           118:                 * just wait for an ACK.
        !           119:                 */
        !           120:                len = 0;
        !           121:                if (win == 0) {
        !           122:                        tp->t_timer[TCPT_REXMT] = 0;
        !           123:                        tp->snd_nxt = tp->snd_una;
        !           124:                }
        !           125:        }
        !           126:        if (len > tp->t_maxseg) {
        !           127:                len = tp->t_maxseg;
        !           128:                sendalot = 1;
        !           129:        }
        !           130:        if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
        !           131:                flags &= ~TH_FIN;
        !           132: 
        !           133:        win = sbspace(&so->so_rcv);
        !           134: 
        !           135:        /*
        !           136:         * Sender silly window avoidance.  If connection is idle
        !           137:         * and can send all data, a maximum segment,
        !           138:         * at least a maximum default-size segment do it,
        !           139:         * or are forced, do it; otherwise don't bother.
        !           140:         * If peer's buffer is tiny, then send
        !           141:         * when window is at least half open.
        !           142:         * If retransmitting (possibly after persist timer forced us
        !           143:         * to send into a small window), then must resend.
        !           144:         */
        !           145:        if (len) {
        !           146:                if (len == tp->t_maxseg)
        !           147:                        goto send;
        !           148:                if ((idle || tp->t_flags & TF_NODELAY) &&
        !           149:                    len + off >= so->so_snd.sb_cc)
        !           150:                        goto send;
        !           151:                if (tp->t_force)
        !           152:                        goto send;
        !           153:                if (len >= tp->max_sndwnd / 2)
        !           154:                        goto send;
        !           155:                if (SEQ_LT(tp->snd_nxt, tp->snd_max))
        !           156:                        goto send;
        !           157:        }
        !           158: 
        !           159:        /*
        !           160:         * Compare available window to amount of window
        !           161:         * known to peer (as advertised window less
        !           162:         * next expected input).  If the difference is at least two
        !           163:         * max size segments, or at least 50% of the maximum possible
        !           164:         * window, then want to send a window update to peer.
        !           165:         */
        !           166:        if (win > 0) {
        !           167:                int adv = win - (tp->rcv_adv - tp->rcv_nxt);
        !           168: 
        !           169:                /* this was:                                    XXX
        !           170:                 * if (so->so_rcv.sb_cc == 0 && adv >= 2 * tp->t_maxseg)
        !           171:                 */
        !           172:                if (adv >= 2 * tp->t_maxseg)
        !           173:                        goto send;
        !           174:                if (2 * adv >= so->so_rcv.sb_hiwat)
        !           175:                        goto send;
        !           176:        }
        !           177: 
        !           178:        /*
        !           179:         * Send if we owe peer an ACK.
        !           180:         */
        !           181:        if (tp->t_flags & TF_ACKNOW)
        !           182:                goto send;
        !           183:        if (flags & (TH_SYN|TH_RST))
        !           184:                goto send;
        !           185:        if (SEQ_GT(tp->snd_up, tp->snd_una))
        !           186:                goto send;
        !           187:        /*
        !           188:         * If our state indicates that FIN should be sent
        !           189:         * and we have not yet done so, or we're retransmitting the FIN,
        !           190:         * then we need to send.
        !           191:         */
        !           192:        if (flags & TH_FIN &&
        !           193:            ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
        !           194:                goto send;
        !           195: 
        !           196:        /*
        !           197:         * TCP window updates are not reliable, rather a polling protocol
        !           198:         * using ``persist'' packets is used to insure receipt of window
        !           199:         * updates.  The three ``states'' for the output side are:
        !           200:         *      idle                    not doing retransmits or persists
        !           201:         *      persisting              to move a small or zero window
        !           202:         *      (re)transmitting        and thereby not persisting
        !           203:         *
        !           204:         * tp->t_timer[TCPT_PERSIST]
        !           205:         *      is set when we are in persist state.
        !           206:         * tp->t_force
        !           207:         *      is set when we are called to send a persist packet.
        !           208:         * tp->t_timer[TCPT_REXMT]
        !           209:         *      is set when we are retransmitting
        !           210:         * The output side is idle when both timers are zero.
        !           211:         *
        !           212:         * If send window is too small, there is data to transmit, and no
        !           213:         * retransmit or persist is pending, then go to persist state.
        !           214:         * If nothing happens soon, send when timer expires:
        !           215:         * if window is nonzero, transmit what we can,
        !           216:         * otherwise force out a byte.
        !           217:         */
        !           218:        if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
        !           219:            tp->t_timer[TCPT_PERSIST] == 0) {
        !           220:                tp->t_rxtshift = 0;
        !           221:                tcp_setpersist(tp);
        !           222:        }
        !           223: 
        !           224:        /*
        !           225:         * No reason to send a segment, just return.
        !           226:         */
        !           227:        return (0);
        !           228: 
        !           229: send:
        !           230:        /*
        !           231:         * Before ESTABLISHED, force sending of initial options
        !           232:         * unless TCP set not to do any options.
        !           233:         * NOTE: we assume that the IP/TCP header plus TCP options
        !           234:         * always fit in a single mbuf, leaving room for a maximum
        !           235:         * link header, i.e.
        !           236:         *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN
        !           237:         */
        !           238:        optlen = 0;
        !           239:        hdrlen = sizeof (struct tcpiphdr);
        !           240:        if (flags & TH_SYN && (tp->t_flags & TF_NOOPT) == 0) {
        !           241:                opt = tcp_initopt;
        !           242:                optlen = sizeof (tcp_initopt);
        !           243:                hdrlen += sizeof (tcp_initopt);
        !           244:                *(u_short *)(opt + 2) = htons((u_short) tcp_mss(tp, 0));
        !           245: #ifdef DIAGNOSTIC
        !           246:                if (max_linkhdr + hdrlen > MHLEN)
        !           247:                        panic("tcphdr too big");
        !           248: #endif
        !           249:        }
        !           250: 
        !           251:        /*
        !           252:         * Grab a header mbuf, attaching a copy of data to
        !           253:         * be transmitted, and initialize the header from
        !           254:         * the template for sends on this connection.
        !           255:         */
        !           256:        if (len) {
        !           257:                if (tp->t_force && len == 1)
        !           258:                        tcpstat.tcps_sndprobe++;
        !           259:                else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
        !           260:                        tcpstat.tcps_sndrexmitpack++;
        !           261:                        tcpstat.tcps_sndrexmitbyte += len;
        !           262:                } else {
        !           263:                        tcpstat.tcps_sndpack++;
        !           264:                        tcpstat.tcps_sndbyte += len;
        !           265:                }
        !           266: #ifdef notyet
        !           267:                if ((m = m_copypack(so->so_snd.sb_mb, off,
        !           268:                    (int)len, max_linkhdr + hdrlen)) == 0) {
        !           269:                        error = ENOBUFS;
        !           270:                        goto out;
        !           271:                }
        !           272:                /*
        !           273:                 * m_copypack left space for our hdr; use it.
        !           274:                 */
        !           275:                m->m_len += hdrlen;
        !           276:                m->m_data -= hdrlen;
        !           277: #else
        !           278:                MGETHDR(m, M_DONTWAIT, MT_HEADER);
        !           279:                if (m == NULL) {
        !           280:                        error = ENOBUFS;
        !           281:                        goto out;
        !           282:                }
        !           283:                m->m_data += max_linkhdr;
        !           284:                m->m_len = hdrlen;
        !           285:                if (len <= MHLEN - hdrlen - max_linkhdr) {
        !           286:                        m_copydata(so->so_snd.sb_mb, off, (int) len,
        !           287:                            mtod(m, caddr_t) + hdrlen);
        !           288:                        m->m_len += len;
        !           289:                } else {
        !           290:                        m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
        !           291:                        if (m->m_next == 0)
        !           292:                                len = 0;
        !           293:                }
        !           294: #endif
        !           295:                /*
        !           296:                 * If we're sending everything we've got, set PUSH.
        !           297:                 * (This will keep happy those implementations which only
        !           298:                 * give data to the user when a buffer fills or
        !           299:                 * a PUSH comes in.)
        !           300:                 */
        !           301:                if (off + len == so->so_snd.sb_cc)
        !           302:                        flags |= TH_PUSH;
        !           303:        } else {
        !           304:                if (tp->t_flags & TF_ACKNOW)
        !           305:                        tcpstat.tcps_sndacks++;
        !           306:                else if (flags & (TH_SYN|TH_FIN|TH_RST))
        !           307:                        tcpstat.tcps_sndctrl++;
        !           308:                else if (SEQ_GT(tp->snd_up, tp->snd_una))
        !           309:                        tcpstat.tcps_sndurg++;
        !           310:                else
        !           311:                        tcpstat.tcps_sndwinup++;
        !           312: 
        !           313:                MGETHDR(m, M_DONTWAIT, MT_HEADER);
        !           314:                if (m == NULL) {
        !           315:                        error = ENOBUFS;
        !           316:                        goto out;
        !           317:                }
        !           318:                m->m_data += max_linkhdr;
        !           319:                m->m_len = hdrlen;
        !           320:        }
        !           321:        m->m_pkthdr.rcvif = (struct ifnet *)0;
        !           322:        ti = mtod(m, struct tcpiphdr *);
        !           323:        if (tp->t_template == 0)
        !           324:                panic("tcp_output");
        !           325:        bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
        !           326: 
        !           327:        /*
        !           328:         * Fill in fields, remembering maximum advertised
        !           329:         * window for use in delaying messages about window sizes.
        !           330:         * If resending a FIN, be sure not to use a new sequence number.
        !           331:         */
        !           332:        if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 
        !           333:            tp->snd_nxt == tp->snd_max)
        !           334:                tp->snd_nxt--;
        !           335:        ti->ti_seq = htonl(tp->snd_nxt);
        !           336:        ti->ti_ack = htonl(tp->rcv_nxt);
        !           337:        if (optlen) {
        !           338:                bcopy((caddr_t)opt, (caddr_t)(ti + 1), optlen);
        !           339:                ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
        !           340:        }
        !           341:        ti->ti_flags = flags;
        !           342:        /*
        !           343:         * Calculate receive window.  Don't shrink window,
        !           344:         * but avoid silly window syndrome.
        !           345:         */
        !           346:        if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg)
        !           347:                win = 0;
        !           348:        if (win > TCP_MAXWIN)
        !           349:                win = TCP_MAXWIN;
        !           350:        if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
        !           351:                win = (long)(tp->rcv_adv - tp->rcv_nxt);
        !           352:        ti->ti_win = htons((u_short)win);
        !           353:        if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
        !           354:                ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
        !           355:                ti->ti_flags |= TH_URG;
        !           356:        } else
        !           357:                /*
        !           358:                 * If no urgent pointer to send, then we pull
        !           359:                 * the urgent pointer to the left edge of the send window
        !           360:                 * so that it doesn't drift into the send window on sequence
        !           361:                 * number wraparound.
        !           362:                 */
        !           363:                tp->snd_up = tp->snd_una;               /* drag it along */
        !           364: 
        !           365:        /*
        !           366:         * Put TCP length in extended header, and then
        !           367:         * checksum extended header and data.
        !           368:         */
        !           369:        if (len + optlen)
        !           370:                ti->ti_len = htons((u_short)(sizeof (struct tcphdr) +
        !           371:                    optlen + len));
        !           372:        ti->ti_sum = in_cksum(m, (int)(hdrlen + len));
        !           373: 
        !           374:        /*
        !           375:         * In transmit state, time the transmission and arrange for
        !           376:         * the retransmit.  In persist state, just set snd_max.
        !           377:         */
        !           378:        if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
        !           379:                tcp_seq startseq = tp->snd_nxt;
        !           380: 
        !           381:                /*
        !           382:                 * Advance snd_nxt over sequence space of this segment.
        !           383:                 */
        !           384:                if (flags & (TH_SYN|TH_FIN)) {
        !           385:                        if (flags & TH_SYN)
        !           386:                                tp->snd_nxt++;
        !           387:                        if (flags & TH_FIN) {
        !           388:                                tp->snd_nxt++;
        !           389:                                tp->t_flags |= TF_SENTFIN;
        !           390:                        }
        !           391:                }
        !           392:                tp->snd_nxt += len;
        !           393:                if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
        !           394:                        tp->snd_max = tp->snd_nxt;
        !           395:                        /*
        !           396:                         * Time this transmission if not a retransmission and
        !           397:                         * not currently timing anything.
        !           398:                         */
        !           399:                        if (tp->t_rtt == 0) {
        !           400:                                tp->t_rtt = 1;
        !           401:                                tp->t_rtseq = startseq;
        !           402:                                tcpstat.tcps_segstimed++;
        !           403:                        }
        !           404:                }
        !           405: 
        !           406:                /*
        !           407:                 * Set retransmit timer if not currently set,
        !           408:                 * and not doing an ack or a keep-alive probe.
        !           409:                 * Initial value for retransmit timer is smoothed
        !           410:                 * round-trip time + 2 * round-trip time variance.
        !           411:                 * Initialize shift counter which is used for backoff
        !           412:                 * of retransmit time.
        !           413:                 */
        !           414:                if (tp->t_timer[TCPT_REXMT] == 0 &&
        !           415:                    tp->snd_nxt != tp->snd_una) {
        !           416:                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
        !           417:                        if (tp->t_timer[TCPT_PERSIST]) {
        !           418:                                tp->t_timer[TCPT_PERSIST] = 0;
        !           419:                                tp->t_rxtshift = 0;
        !           420:                        }
        !           421:                }
        !           422:        } else
        !           423:                if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
        !           424:                        tp->snd_max = tp->snd_nxt + len;
        !           425: 
        !           426:        /*
        !           427:         * Trace.
        !           428:         */
        !           429:        if (so->so_options & SO_DEBUG)
        !           430:                tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
        !           431: 
        !           432:        /*
        !           433:         * Fill in IP length and desired time to live and
        !           434:         * send to IP level.  There should be a better way
        !           435:         * to handle ttl and tos; we could keep them in
        !           436:         * the template, but need a way to checksum without them.
        !           437:         */
        !           438:        m->m_pkthdr.len = hdrlen + len;
        !           439:        ((struct ip *)ti)->ip_len = m->m_pkthdr.len;
        !           440:        ((struct ip *)ti)->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl; /* XXX */
        !           441:        ((struct ip *)ti)->ip_tos = tp->t_inpcb->inp_ip.ip_tos; /* XXX */
        !           442: #if BSD >= 43
        !           443:        error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
        !           444:            so->so_options & SO_DONTROUTE);
        !           445: #else
        !           446:        error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route, 
        !           447:            so->so_options & SO_DONTROUTE);
        !           448: #endif
        !           449:        if (error) {
        !           450: out:
        !           451:                if (error == ENOBUFS) {
        !           452:                        tcp_quench(tp->t_inpcb);
        !           453:                        return (0);
        !           454:                }
        !           455:                if ((error == EHOSTUNREACH || error == ENETDOWN)
        !           456:                    && TCPS_HAVERCVDSYN(tp->t_state)) {
        !           457:                        tp->t_softerror = error;
        !           458:                        return (0);
        !           459:                }
        !           460:                return (error);
        !           461:        }
        !           462:        tcpstat.tcps_sndtotal++;
        !           463: 
        !           464:        /*
        !           465:         * Data sent (as far as we can tell).
        !           466:         * If this advertises a larger window than any other segment,
        !           467:         * then remember the size of the advertised window.
        !           468:         * Any pending ACK has now been sent.
        !           469:         */
        !           470:        if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
        !           471:                tp->rcv_adv = tp->rcv_nxt + win;
        !           472:        tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
        !           473:        if (sendalot)
        !           474:                goto again;
        !           475:        return (0);
        !           476: }
        !           477: 
        !           478: tcp_setpersist(tp)
        !           479:        register struct tcpcb *tp;
        !           480: {
        !           481:        register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
        !           482: 
        !           483:        if (tp->t_timer[TCPT_REXMT])
        !           484:                panic("tcp_output REXMT");
        !           485:        /*
        !           486:         * Start/restart persistance timer.
        !           487:         */
        !           488:        TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
        !           489:            t * tcp_backoff[tp->t_rxtshift],
        !           490:            TCPTV_PERSMIN, TCPTV_PERSMAX);
        !           491:        if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
        !           492:                tp->t_rxtshift++;
        !           493: }

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