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Annotation of 42BSD/sys/netinet/tcp_output.c, revision 1.1

1.1     ! root        1: /*     tcp_output.c    6.1     83/07/29        */
        !             2: 
        !             3: #include "../h/param.h"
        !             4: #include "../h/systm.h"
        !             5: #include "../h/mbuf.h"
        !             6: #include "../h/protosw.h"
        !             7: #include "../h/socket.h"
        !             8: #include "../h/socketvar.h"
        !             9: #include "../h/errno.h"
        !            10: 
        !            11: #include "../net/route.h"
        !            12: 
        !            13: #include "../netinet/in.h"
        !            14: #include "../netinet/in_pcb.h"
        !            15: #include "../netinet/in_systm.h"
        !            16: #include "../netinet/ip.h"
        !            17: #include "../netinet/ip_var.h"
        !            18: #include "../netinet/tcp.h"
        !            19: #define        TCPOUTFLAGS
        !            20: #include "../netinet/tcp_fsm.h"
        !            21: #include "../netinet/tcp_seq.h"
        !            22: #include "../netinet/tcp_timer.h"
        !            23: #include "../netinet/tcp_var.h"
        !            24: #include "../netinet/tcpip.h"
        !            25: #include "../netinet/tcp_debug.h"
        !            26: 
        !            27: /*
        !            28:  * Initial options.
        !            29:  */
        !            30: u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
        !            31: 
        !            32: /*
        !            33:  * Tcp output routine: figure out what should be sent and send it.
        !            34:  */
        !            35: tcp_output(tp)
        !            36:        register struct tcpcb *tp;
        !            37: {
        !            38:        register struct socket *so = tp->t_inpcb->inp_socket;
        !            39:        register int len;
        !            40:        struct mbuf *m0;
        !            41:        int off, flags, win, error;
        !            42:        register struct mbuf *m;
        !            43:        register struct tcpiphdr *ti;
        !            44:        u_char *opt;
        !            45:        unsigned optlen = 0;
        !            46:        int sendalot;
        !            47: 
        !            48:        /*
        !            49:         * Determine length of data that should be transmitted,
        !            50:         * and flags that will be used.
        !            51:         * If there is some data or critical controls (SYN, RST)
        !            52:         * to send, then transmit; otherwise, investigate further.
        !            53:         */
        !            54: again:
        !            55:        sendalot = 0;
        !            56:        off = tp->snd_nxt - tp->snd_una;
        !            57:        len = MIN(so->so_snd.sb_cc, tp->snd_wnd+tp->t_force) - off;
        !            58:        if (len < 0)
        !            59:                return (0);     /* ??? */       /* past FIN */
        !            60:        if (len > tp->t_maxseg) {
        !            61:                len = tp->t_maxseg;
        !            62:                sendalot = 1;
        !            63:        }
        !            64: 
        !            65:        flags = tcp_outflags[tp->t_state];
        !            66:        if (tp->snd_nxt + len < tp->snd_una + so->so_snd.sb_cc)
        !            67:                flags &= ~TH_FIN;
        !            68:        if (flags & (TH_SYN|TH_RST|TH_FIN))
        !            69:                goto send;
        !            70:        if (SEQ_GT(tp->snd_up, tp->snd_una))
        !            71:                goto send;
        !            72: 
        !            73:        /*
        !            74:         * Sender silly window avoidance.  If can send all data,
        !            75:         * a maximum segment, at least 1/4 of window do it,
        !            76:         * or are forced, do it; otherwise don't bother.
        !            77:         */
        !            78:        if (len) {
        !            79:                if (len == tp->t_maxseg || off+len >= so->so_snd.sb_cc)
        !            80:                        goto send;
        !            81:                if (len * 4 >= tp->snd_wnd)             /* a lot */
        !            82:                        goto send;
        !            83:                if (tp->t_force)
        !            84:                        goto send;
        !            85:        }
        !            86: 
        !            87:        /*
        !            88:         * Send if we owe peer an ACK.
        !            89:         */
        !            90:        if (tp->t_flags&TF_ACKNOW)
        !            91:                goto send;
        !            92: 
        !            93: 
        !            94:        /*
        !            95:         * Calculate available window in i, and also amount
        !            96:         * of window known to peer (as advertised window less
        !            97:         * next expected input.)  If this is 35% or more of the
        !            98:         * maximum possible window, then want to send a segment to peer.
        !            99:         */
        !           100:        win = sbspace(&so->so_rcv);
        !           101:        if (win > 0 &&
        !           102:            ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35))
        !           103:                goto send;
        !           104: 
        !           105:        /*
        !           106:         * TCP window updates are not reliable, rather a polling protocol
        !           107:         * using ``persist'' packets is used to insure receipt of window
        !           108:         * updates.  The three ``states'' for the output side are:
        !           109:         *      idle                    not doing retransmits or persists
        !           110:         *      persisting              to move a zero window
        !           111:         *      (re)transmitting        and thereby not persisting
        !           112:         *
        !           113:         * tp->t_timer[TCPT_PERSIST]
        !           114:         *      is set when we are in persist state.
        !           115:         * tp->t_force
        !           116:         *      is set when we are called to send a persist packet.
        !           117:         * tp->t_timer[TCPT_REXMT]
        !           118:         *      is set when we are retransmitting
        !           119:         * The output side is idle when both timers are zero.
        !           120:         *
        !           121:         * If send window is closed, there is data to transmit, and no
        !           122:         * retransmit or persist is pending, then go to persist state,
        !           123:         * arranging to force out a byte to get more current window information
        !           124:         * if nothing happens soon.
        !           125:         */
        !           126:        if (tp->snd_wnd == 0 && so->so_snd.sb_cc &&
        !           127:            tp->t_timer[TCPT_REXMT] == 0 && tp->t_timer[TCPT_PERSIST] == 0) {
        !           128:                tp->t_rxtshift = 0;
        !           129:                tcp_setpersist(tp);
        !           130:        }
        !           131: 
        !           132:        /*
        !           133:         * No reason to send a segment, just return.
        !           134:         */
        !           135:        return (0);
        !           136: 
        !           137: send:
        !           138:        /*
        !           139:         * Grab a header mbuf, attaching a copy of data to
        !           140:         * be transmitted, and initialize the header from
        !           141:         * the template for sends on this connection.
        !           142:         */
        !           143:        MGET(m, M_DONTWAIT, MT_HEADER);
        !           144:        if (m == NULL)
        !           145:                return (ENOBUFS);
        !           146:        m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
        !           147:        m->m_len = sizeof (struct tcpiphdr);
        !           148:        if (len) {
        !           149:                m->m_next = m_copy(so->so_snd.sb_mb, off, len);
        !           150:                if (m->m_next == 0)
        !           151:                        len = 0;
        !           152:        }
        !           153:        ti = mtod(m, struct tcpiphdr *);
        !           154:        if (tp->t_template == 0)
        !           155:                panic("tcp_output");
        !           156:        bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
        !           157: 
        !           158:        /*
        !           159:         * Fill in fields, remembering maximum advertised
        !           160:         * window for use in delaying messages about window sizes.
        !           161:         */
        !           162:        ti->ti_seq = tp->snd_nxt;
        !           163:        ti->ti_ack = tp->rcv_nxt;
        !           164:        ti->ti_seq = htonl(ti->ti_seq);
        !           165:        ti->ti_ack = htonl(ti->ti_ack);
        !           166:        /*
        !           167:         * Before ESTABLISHED, force sending of initial options
        !           168:         * unless TCP set to not do any options.
        !           169:         */
        !           170:        if (tp->t_state < TCPS_ESTABLISHED) {
        !           171:                if (tp->t_flags&TF_NOOPT)
        !           172:                        goto noopt;
        !           173:                opt = tcp_initopt;
        !           174:                optlen = sizeof (tcp_initopt);
        !           175:                *(u_short *)(opt + 2) = MIN(so->so_rcv.sb_hiwat / 2, 1024);
        !           176:                *(u_short *)(opt + 2) = htons(*(u_short *)(opt + 2));
        !           177:        } else {
        !           178:                if (tp->t_tcpopt == 0)
        !           179:                        goto noopt;
        !           180:                opt = mtod(tp->t_tcpopt, u_char *);
        !           181:                optlen = tp->t_tcpopt->m_len;
        !           182:        }
        !           183:        if (opt) {
        !           184:                m0 = m->m_next;
        !           185:                m->m_next = m_get(M_DONTWAIT, MT_DATA);
        !           186:                if (m->m_next == 0) {
        !           187:                        (void) m_free(m);
        !           188:                        m_freem(m0);
        !           189:                        return (ENOBUFS);
        !           190:                }
        !           191:                m->m_next->m_next = m0;
        !           192:                m0 = m->m_next;
        !           193:                m0->m_len = optlen;
        !           194:                bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
        !           195:                opt = (u_char *)(mtod(m0, caddr_t) + optlen);
        !           196:                while (m0->m_len & 0x3) {
        !           197:                        *opt++ = TCPOPT_EOL;
        !           198:                        m0->m_len++;
        !           199:                }
        !           200:                optlen = m0->m_len;
        !           201:                ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
        !           202:        }
        !           203: noopt:
        !           204:        ti->ti_flags = flags;
        !           205:        win = sbspace(&so->so_rcv);
        !           206:        if (win < so->so_rcv.sb_hiwat / 4)      /* avoid silly window */
        !           207:                win = 0;
        !           208:        if (win > 0)
        !           209:                ti->ti_win = htons((u_short)win);
        !           210:        if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
        !           211:                ti->ti_urp = tp->snd_up - tp->snd_nxt;
        !           212:                ti->ti_urp = htons(ti->ti_urp);
        !           213:                ti->ti_flags |= TH_URG;
        !           214:        } else
        !           215:                /*
        !           216:                 * If no urgent pointer to send, then we pull
        !           217:                 * the urgent pointer to the left edge of the send window
        !           218:                 * so that it doesn't drift into the send window on sequence
        !           219:                 * number wraparound.
        !           220:                 */
        !           221:                tp->snd_up = tp->snd_una;               /* drag it along */
        !           222:        /*
        !           223:         * If anything to send and we can send it all, set PUSH.
        !           224:         * (This will keep happy those implementations which only
        !           225:         * give data to the user when a buffer fills or a PUSH comes in.)
        !           226:         */
        !           227:        if (len && off+len == so->so_snd.sb_cc)
        !           228:                ti->ti_flags |= TH_PUSH;
        !           229: 
        !           230:        /*
        !           231:         * Put TCP length in extended header, and then
        !           232:         * checksum extended header and data.
        !           233:         */
        !           234:        if (len + optlen) {
        !           235:                ti->ti_len = sizeof (struct tcphdr) + optlen + len;
        !           236:                ti->ti_len = htons((u_short)ti->ti_len);
        !           237:        }
        !           238:        ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len);
        !           239: 
        !           240:        /*
        !           241:         * In transmit state, time the transmission and arrange for
        !           242:         * the retransmit.  In persist state, reset persist time for
        !           243:         * next persist.
        !           244:         */
        !           245:        if (tp->t_force == 0) {
        !           246:                /*
        !           247:                 * Advance snd_nxt over sequence space of this segment.
        !           248:                 */
        !           249:                if (flags & (TH_SYN|TH_FIN))
        !           250:                        tp->snd_nxt++;
        !           251:                tp->snd_nxt += len;
        !           252:                if (SEQ_GT(tp->snd_nxt, tp->snd_max))
        !           253:                        tp->snd_max = tp->snd_nxt;
        !           254: 
        !           255:                /*
        !           256:                 * Time this transmission if not a retransmission and
        !           257:                 * not currently timing anything.
        !           258:                 */
        !           259:                if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) {
        !           260:                        tp->t_rtt = 1;
        !           261:                        tp->t_rtseq = tp->snd_nxt - len;
        !           262:                }
        !           263: 
        !           264:                /*
        !           265:                 * Set retransmit timer if not currently set.
        !           266:                 * Initial value for retransmit timer to tcp_beta*tp->t_srtt.
        !           267:                 * Initialize shift counter which is used for exponential
        !           268:                 * backoff of retransmit time.
        !           269:                 */
        !           270:                if (tp->t_timer[TCPT_REXMT] == 0 &&
        !           271:                    tp->snd_nxt != tp->snd_una) {
        !           272:                        TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
        !           273:                            tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX);
        !           274:                        tp->t_rtt = 0;
        !           275:                        tp->t_rxtshift = 0;
        !           276:                }
        !           277:                tp->t_timer[TCPT_PERSIST] = 0;
        !           278:        } else {
        !           279:                if (SEQ_GT(tp->snd_una+1, tp->snd_max))
        !           280:                        tp->snd_max = tp->snd_una+1;
        !           281:        }
        !           282: 
        !           283:        /*
        !           284:         * Trace.
        !           285:         */
        !           286:        if (so->so_options & SO_DEBUG)
        !           287:                tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
        !           288: 
        !           289:        /*
        !           290:         * Fill in IP length and desired time to live and
        !           291:         * send to IP level.
        !           292:         */
        !           293:        ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
        !           294:        ((struct ip *)ti)->ip_ttl = TCP_TTL;
        !           295:        if (so->so_options & SO_DONTROUTE)
        !           296:                error =
        !           297:                   ip_output(m, tp->t_ipopt, (struct route *)0, IP_ROUTETOIF);
        !           298:        else
        !           299:                error = ip_output(m, tp->t_ipopt, &tp->t_inpcb->inp_route, 0);
        !           300:        if (error)
        !           301:                return (error);
        !           302: 
        !           303:        /*
        !           304:         * Data sent (as far as we can tell).
        !           305:         * If this advertises a larger window than any other segment,
        !           306:         * then remember the size of the advertised window.
        !           307:         * Drop send for purpose of ACK requirements.
        !           308:         */
        !           309:        if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
        !           310:                tp->rcv_adv = tp->rcv_nxt + win;
        !           311:        tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
        !           312:        if (sendalot && tp->t_force == 0)
        !           313:                goto again;
        !           314:        return (0);
        !           315: }
        !           316: 
        !           317: tcp_setpersist(tp)
        !           318:        register struct tcpcb *tp;
        !           319: {
        !           320: 
        !           321:        if (tp->t_timer[TCPT_REXMT])
        !           322:                panic("tcp_output REXMT");
        !           323:        /*
        !           324:         * Start/restart persistance timer.
        !           325:         */
        !           326:        TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
        !           327:            ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift,
        !           328:            TCPTV_PERSMIN, TCPTV_MAX);
        !           329:        tp->t_rxtshift++;
        !           330:        if (tp->t_rxtshift >= TCP_MAXRXTSHIFT)
        !           331:                tp->t_rxtshift = 0;
        !           332: }

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