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Annotation of researchv9/sys/inet/tcp_output.c, revision 1.1

1.1     ! root        1: /*     tcp_output.c    6.1     83/07/29        */
        !             2: #include "tcp.h"
        !             3: #if NTCP > 0
        !             4: 
        !             5: #include "../h/param.h"
        !             6: #include "../h/systm.h"
        !             7: #include "../h/stream.h"
        !             8: #include "../h/inet/mbuf.h"
        !             9: #include "../h/inet/in.h"
        !            10: #include "../h/inet/ip.h"
        !            11: #include "../h/inet/ip_var.h"
        !            12: #include "../h/inet/tcp.h"
        !            13: #define        TCPOUTFLAGS
        !            14: #include "../h/inet/tcp_fsm.h"
        !            15: #include "../h/inet/tcp_seq.h"
        !            16: #include "../h/inet/tcp_timer.h"
        !            17: #include "../h/inet/tcp_var.h"
        !            18: #include "../h/inet/tcpip.h"
        !            19: #include "../h/inet/socket.h"
        !            20: 
        !            21: int tcp_busy;  /* set/unset by tcp_output callers, to keep out timer */
        !            22: 
        !            23: /*
        !            24:  * Initial options.
        !            25:  */
        !            26: u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
        !            27: extern tcpprintfs;
        !            28: 
        !            29: /*
        !            30:  *  Settable maximum tcp segment size.
        !            31:  */
        !            32: extern int tcp_maxseg;
        !            33: 
        !            34: /*
        !            35:  * Tcp output routine: figure out what should be sent and send it.
        !            36:  */
        !            37: tcp_output(tp)
        !            38:        register struct tcpcb *tp;
        !            39: {
        !            40:        register struct socket *so = tp->t_socket;
        !            41:        register int len;
        !            42:        struct mbuf *m0;
        !            43:        int off, flags, win, error;
        !            44:        register struct mbuf *m;
        !            45:        register struct tcpiphdr *ti;
        !            46:        u_char *opt;
        !            47:        unsigned optlen = 0;
        !            48:        int sendalot;
        !            49: 
        !            50:        if(tcp_busy != 1)
        !            51:                panic("tcp_busy");
        !            52:        /*
        !            53:         * Determine length of data that should be transmitted,
        !            54:         * and flags that will be used.
        !            55:         * If there is some data or critical controls (SYN, RST)
        !            56:         * to send, then transmit; otherwise, investigate further.
        !            57:         */
        !            58: again:
        !            59:        sendalot = 0;
        !            60:        off = tp->snd_nxt - tp->snd_una;
        !            61:        len = MIN(sosndcc(so), tp->snd_wnd+tp->t_force) - off;
        !            62:        if (len < 0)
        !            63:                return (0);     /* ??? */       /* past FIN */
        !            64:        if (len > tp->t_maxseg) {
        !            65:                len = tp->t_maxseg;
        !            66:                sendalot = 1;
        !            67:        }
        !            68: 
        !            69:        flags = tcp_outflags[tp->t_state];
        !            70:        if (tp->snd_nxt + len < tp->snd_una + sosndcc(so))
        !            71:                flags &= ~TH_FIN;
        !            72:        if (flags & (TH_SYN|TH_RST|TH_FIN))
        !            73:                goto send;
        !            74:        if (SEQ_GT(tp->snd_up, tp->snd_una))
        !            75:                goto send;
        !            76: 
        !            77:        /*
        !            78:         * Sender silly window avoidance.  If can send all data,
        !            79:         * a maximum segment, at least 1/4 of window do it,
        !            80:         * or are forced, do it; otherwise don't bother.
        !            81:         */
        !            82:        if (len) {
        !            83:                if (len == tp->t_maxseg || off+len >= sosndcc(so))
        !            84:                        goto send;
        !            85:                if (len * 4 >= tp->snd_wnd)             /* a lot */
        !            86:                        goto send;
        !            87:                if (tp->t_force)
        !            88:                        goto send;
        !            89:        }
        !            90: 
        !            91:        /*
        !            92:         * Send if we owe peer an ACK.
        !            93:         */
        !            94:        if (tp->t_flags&TF_ACKNOW)
        !            95:                goto send;
        !            96: 
        !            97: 
        !            98:        /*
        !            99:         * Calculate available window in i, and also amount
        !           100:         * of window known to peer (as advertised window less
        !           101:         * next expected input.)  If this is 35% or more of the
        !           102:         * maximum possible window, then want to send a segment to peer.
        !           103:         */
        !           104:        win = sbrcvspace(so);
        !           105:        if (win > 0 &&
        !           106:            ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/sorcvhiwat(so)) >= 35))
        !           107:                goto send;
        !           108: 
        !           109:        /*
        !           110:         * TCP window updates are not reliable, rather a polling protocol
        !           111:         * using ``persist'' packets is used to insure receipt of window
        !           112:         * updates.  The three ``states'' for the output side are:
        !           113:         *      idle                    not doing retransmits or persists
        !           114:         *      persisting              to move a zero window
        !           115:         *      (re)transmitting        and thereby not persisting
        !           116:         *
        !           117:         * tp->t_timer[TCPT_PERSIST]
        !           118:         *      is set when we are in persist state.
        !           119:         * tp->t_force
        !           120:         *      is set when we are called to send a persist packet.
        !           121:         * tp->t_timer[TCPT_REXMT]
        !           122:         *      is set when we are retransmitting
        !           123:         * The output side is idle when both timers are zero.
        !           124:         *
        !           125:         * If send window is closed, there is data to transmit, and no
        !           126:         * retransmit or persist is pending, then go to persist state,
        !           127:         * arranging to force out a byte to get more current window information
        !           128:         * if nothing happens soon.
        !           129:         */
        !           130:        if (tp->snd_wnd == 0 && sosndcc(so) &&
        !           131:            tp->t_timer[TCPT_REXMT] == 0 && tp->t_timer[TCPT_PERSIST] == 0) {
        !           132:                tp->t_rxtshift = 0;
        !           133:                tcp_setpersist(tp);
        !           134:        }
        !           135: 
        !           136:        /*
        !           137:         * No reason to send a segment, just return.
        !           138:         */
        !           139:        return (0);
        !           140: 
        !           141: send:
        !           142:        /*
        !           143:         * Grab a header mbuf, attaching a copy of data to
        !           144:         * be transmitted, and initialize the header from
        !           145:         * the template for sends on this connection.
        !           146:         */
        !           147:        MGET(m, M_DONTWAIT, MT_HEADER);
        !           148:        if (m == NULL)
        !           149:                return (1);
        !           150:        m->next = 0;
        !           151:        m->wptr += sizeof (struct tcpiphdr);
        !           152:        if (len) {
        !           153:                m->m_next = m_copy(so->so_wq->first, off, len);
        !           154:                if (m->m_next == 0)
        !           155:                        len = 0;
        !           156:        }
        !           157:        ti = mtod(m, struct tcpiphdr *);
        !           158:        if (tp->t_template == 0)
        !           159:                panic("tcp_output");
        !           160:        bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
        !           161: 
        !           162:        /*
        !           163:         * Fill in fields, remembering maximum advertised
        !           164:         * window for use in delaying messages about window sizes.
        !           165:         */
        !           166:        ti->ti_seq = tp->snd_nxt;
        !           167:        ti->ti_ack = tp->rcv_nxt;
        !           168:        ti->ti_seq = htonl(ti->ti_seq);
        !           169:        ti->ti_ack = htonl(ti->ti_ack);
        !           170:        /*
        !           171:         * Before ESTABLISHED, force sending of initial options
        !           172:         * unless TCP set to not do any options.
        !           173:         */
        !           174:        if (tp->t_state < TCPS_ESTABLISHED) {
        !           175:                if (tp->t_flags&TF_NOOPT)
        !           176:                        goto noopt;
        !           177:                opt = tcp_initopt;
        !           178:                optlen = sizeof (tcp_initopt);
        !           179:                *(u_short *)(opt + 2) = tcp_maxseg;     /* 2048/2 in 4.2 */
        !           180:                *(u_short *)(opt + 2) = htons(*(u_short *)(opt + 2));
        !           181:        } else {
        !           182:                if (tp->t_tcpopt == 0)
        !           183:                        goto noopt;
        !           184:                opt = mtod(tp->t_tcpopt, u_char *);
        !           185:                optlen = BLEN(tp->t_tcpopt);
        !           186:        }
        !           187:        if (opt) {
        !           188:                m0 = m->m_next;
        !           189:                m->m_next = m_get(M_DONTWAIT, MT_DATA);
        !           190:                if (m->m_next == 0) {
        !           191:                        (void) m_free(m);
        !           192:                        m_freem(m0);
        !           193:                        return (1);
        !           194:                }
        !           195:                m->m_next->m_next = m0;
        !           196:                m0 = m->m_next;
        !           197:                m0->wptr += optlen;
        !           198:                bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
        !           199:                opt = (u_char *)(mtod(m0, caddr_t) + optlen);
        !           200:                while (BLEN(m0) & 0x3) {
        !           201:                        m0->wptr++;
        !           202:                        *opt++ = TCPOPT_EOL;
        !           203:                }
        !           204:                optlen = BLEN(m0);
        !           205:                ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
        !           206:        }
        !           207: noopt:
        !           208:        ti->ti_flags = flags;
        !           209:        win = sbrcvspace(so);
        !           210:        if (win < sorcvhiwat(so) / 4)   /* avoid silly window */
        !           211:                win = 0;
        !           212:        if (win > 0)
        !           213:                ti->ti_win = htons((u_short)win);
        !           214:        if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
        !           215:                ti->ti_urp = tp->snd_up - tp->snd_nxt;
        !           216:                ti->ti_urp = htons(ti->ti_urp);
        !           217:                ti->ti_flags |= TH_URG;
        !           218:        } else
        !           219:                /*
        !           220:                 * If no urgent pointer to send, then we pull
        !           221:                 * the urgent pointer to the left edge of the send window
        !           222:                 * so that it doesn't drift into the send window on sequence
        !           223:                 * number wraparound.
        !           224:                 */
        !           225:                tp->snd_up = tp->snd_una;               /* drag it along */
        !           226:        /*
        !           227:         * If anything to send and we can send it all, set PUSH.
        !           228:         * (This will keep happy those implementations which only
        !           229:         * give data to the user when a buffer fills or a PUSH comes in.)
        !           230:         */
        !           231:        if (len && off+len == sosndcc(so))
        !           232:                ti->ti_flags |= TH_PUSH;
        !           233: 
        !           234:        /*
        !           235:         * Put TCP length in extended header, and then
        !           236:         * checksum extended header and data.
        !           237:         */
        !           238:        if (len + optlen) {
        !           239:                ti->ti_len = sizeof (struct tcphdr) + optlen + len;
        !           240:                ti->ti_len = htons((u_short)ti->ti_len);
        !           241:        }
        !           242:        ti->ti_src = htonl(ti->ti_src);
        !           243:        ti->ti_dst = htonl(ti->ti_dst);
        !           244:        ti->ti_sport = htons(ti->ti_sport);
        !           245:        ti->ti_dport = htons(ti->ti_dport);
        !           246:        ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len);
        !           247:        tcp_debug(ti, 1);
        !           248:        ti->ti_src = ntohl(ti->ti_src);
        !           249:        ti->ti_dst = ntohl(ti->ti_dst);
        !           250: 
        !           251:        /*
        !           252:         * In transmit state, time the transmission and arrange for
        !           253:         * the retransmit.  In persist state, reset persist time for
        !           254:         * next persist.
        !           255:         */
        !           256:        if (tp->t_force == 0) {
        !           257:                /*
        !           258:                 * Advance snd_nxt over sequence space of this segment.
        !           259:                 */
        !           260:                if (flags & (TH_SYN|TH_FIN))
        !           261:                        tp->snd_nxt++;
        !           262:                tp->snd_nxt += len;
        !           263:                if (SEQ_GT(tp->snd_nxt, tp->snd_max))
        !           264:                        tp->snd_max = tp->snd_nxt;
        !           265: 
        !           266:                /*
        !           267:                 * Time this transmission if not a retransmission and
        !           268:                 * not currently timing anything.
        !           269:                 */
        !           270:                if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) {
        !           271:                        tp->t_rtt = 1;
        !           272:                        tp->t_rtseq = tp->snd_nxt - len;
        !           273:                }
        !           274: 
        !           275:                /*
        !           276:                 * Set retransmit timer if not currently set.
        !           277:                 * Initial value for retransmit timer to tcp_beta*tp->t_srtt.
        !           278:                 * Initialize shift counter which is used for exponential
        !           279:                 * backoff of retransmit time.
        !           280:                 */
        !           281:                if (tp->t_timer[TCPT_REXMT] == 0 &&
        !           282:                    tp->snd_nxt != tp->snd_una) {
        !           283:                        TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
        !           284:                            tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX);
        !           285:                        tp->t_rtt = 0;
        !           286:                        tp->t_rxtshift = 0;
        !           287:                }
        !           288:                tp->t_timer[TCPT_PERSIST] = 0;
        !           289:        } else {
        !           290:                if (SEQ_GT(tp->snd_una+1, tp->snd_max))
        !           291:                        tp->snd_max = tp->snd_una+1;
        !           292:        }
        !           293: 
        !           294:        /*
        !           295:         * Fill in IP length and desired time to live and
        !           296:         * send to IP level.
        !           297:         */
        !           298:        ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
        !           299:        ((struct ip *)ti)->ip_ttl = TCP_TTL;
        !           300:        error = tcp_ldout(m);
        !           301:        if (error)
        !           302:                return (error);
        !           303: 
        !           304: 
        !           305:        /*
        !           306:         * Data sent (as far as we can tell).
        !           307:         * If this advertises a larger window than any other segment,
        !           308:         * then remember the size of the advertised window.
        !           309:         * Drop send for purpose of ACK requirements.
        !           310:         */
        !           311:        if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
        !           312:                tp->rcv_adv = tp->rcv_nxt + win;
        !           313:        tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
        !           314:        if (sendalot && tp->t_force == 0)
        !           315:                goto again;
        !           316:        return (0);
        !           317: }
        !           318: 
        !           319: tcp_setpersist(tp)
        !           320:        register struct tcpcb *tp;
        !           321: {
        !           322: 
        !           323:        if (tp->t_timer[TCPT_REXMT])
        !           324:                panic("tcp_output REXMT");
        !           325:        /*
        !           326:         * Start/restart persistance timer.
        !           327:         */
        !           328:        TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
        !           329:            ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift,
        !           330:            TCPTV_PERSMIN, TCPTV_MAX);
        !           331:        tp->t_rxtshift++;
        !           332:        if (tp->t_rxtshift >= TCP_MAXRXTSHIFT)
        !           333:                tp->t_rxtshift = 0;
        !           334: }
        !           335: #endif

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