Annotation of qemu/slirp/tcp_output.c, revision 1.1.1.5

1.1       root        1: /*
                      2:  * Copyright (c) 1982, 1986, 1988, 1990, 1993
                      3:  *     The Regents of the University of California.  All rights reserved.
                      4:  *
                      5:  * Redistribution and use in source and binary forms, with or without
                      6:  * modification, are permitted provided that the following conditions
                      7:  * are met:
                      8:  * 1. Redistributions of source code must retain the above copyright
                      9:  *    notice, this list of conditions and the following disclaimer.
                     10:  * 2. Redistributions in binary form must reproduce the above copyright
                     11:  *    notice, this list of conditions and the following disclaimer in the
                     12:  *    documentation and/or other materials provided with the distribution.
1.1.1.3   root       13:  * 3. Neither the name of the University nor the names of its contributors
1.1       root       14:  *    may be used to endorse or promote products derived from this software
                     15:  *    without specific prior written permission.
                     16:  *
                     17:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
                     18:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
                     19:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
                     20:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
                     21:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
                     22:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
                     23:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
                     24:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
                     25:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
                     26:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
                     27:  * SUCH DAMAGE.
                     28:  *
                     29:  *     @(#)tcp_output.c        8.3 (Berkeley) 12/30/93
                     30:  * tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg Exp
                     31:  */
                     32: 
                     33: /*
                     34:  * Changes and additions relating to SLiRP
                     35:  * Copyright (c) 1995 Danny Gasparovski.
1.1.1.2   root       36:  *
                     37:  * Please read the file COPYRIGHT for the
1.1       root       38:  * terms and conditions of the copyright.
                     39:  */
                     40: 
                     41: #include <slirp.h>
                     42: 
1.1.1.2   root       43: static const u_char  tcp_outflags[TCP_NSTATES] = {
1.1       root       44:        TH_RST|TH_ACK, 0,      TH_SYN,        TH_SYN|TH_ACK,
1.1.1.2   root       45:        TH_ACK,        TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK,
1.1       root       46:        TH_FIN|TH_ACK, TH_ACK, TH_ACK,
                     47: };
                     48: 
                     49: 
                     50: #define MAX_TCPOPTLEN  32      /* max # bytes that go in options */
                     51: 
                     52: /*
                     53:  * Tcp output routine: figure out what should be sent and send it.
                     54:  */
                     55: int
1.1.1.4   root       56: tcp_output(struct tcpcb *tp)
1.1       root       57: {
                     58:        register struct socket *so = tp->t_socket;
                     59:        register long len, win;
                     60:        int off, flags, error;
                     61:        register struct mbuf *m;
                     62:        register struct tcpiphdr *ti;
                     63:        u_char opt[MAX_TCPOPTLEN];
                     64:        unsigned optlen, hdrlen;
                     65:        int idle, sendalot;
1.1.1.2   root       66: 
1.1       root       67:        DEBUG_CALL("tcp_output");
                     68:        DEBUG_ARG("tp = %lx", (long )tp);
1.1.1.2   root       69: 
1.1       root       70:        /*
                     71:         * Determine length of data that should be transmitted,
                     72:         * and flags that will be used.
                     73:         * If there is some data or critical controls (SYN, RST)
                     74:         * to send, then transmit; otherwise, investigate further.
                     75:         */
                     76:        idle = (tp->snd_max == tp->snd_una);
                     77:        if (idle && tp->t_idle >= tp->t_rxtcur)
                     78:                /*
                     79:                 * We have been idle for "a while" and no acks are
                     80:                 * expected to clock out any data we send --
                     81:                 * slow start to get ack "clock" running again.
                     82:                 */
                     83:                tp->snd_cwnd = tp->t_maxseg;
                     84: again:
                     85:        sendalot = 0;
                     86:        off = tp->snd_nxt - tp->snd_una;
                     87:        win = min(tp->snd_wnd, tp->snd_cwnd);
                     88: 
                     89:        flags = tcp_outflags[tp->t_state];
1.1.1.2   root       90: 
1.1       root       91:        DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));
1.1.1.2   root       92: 
1.1       root       93:        /*
                     94:         * If in persist timeout with window of 0, send 1 byte.
                     95:         * Otherwise, if window is small but nonzero
                     96:         * and timer expired, we will send what we can
                     97:         * and go to transmit state.
                     98:         */
                     99:        if (tp->t_force) {
                    100:                if (win == 0) {
                    101:                        /*
                    102:                         * If we still have some data to send, then
                    103:                         * clear the FIN bit.  Usually this would
                    104:                         * happen below when it realizes that we
                    105:                         * aren't sending all the data.  However,
                    106:                         * if we have exactly 1 byte of unset data,
                    107:                         * then it won't clear the FIN bit below,
                    108:                         * and if we are in persist state, we wind
                    109:                         * up sending the packet without recording
                    110:                         * that we sent the FIN bit.
                    111:                         *
                    112:                         * We can't just blindly clear the FIN bit,
                    113:                         * because if we don't have any more data
                    114:                         * to send then the probe will be the FIN
                    115:                         * itself.
                    116:                         */
                    117:                        if (off < so->so_snd.sb_cc)
                    118:                                flags &= ~TH_FIN;
                    119:                        win = 1;
                    120:                } else {
                    121:                        tp->t_timer[TCPT_PERSIST] = 0;
                    122:                        tp->t_rxtshift = 0;
                    123:                }
                    124:        }
                    125: 
                    126:        len = min(so->so_snd.sb_cc, win) - off;
                    127: 
                    128:        if (len < 0) {
                    129:                /*
                    130:                 * If FIN has been sent but not acked,
                    131:                 * but we haven't been called to retransmit,
                    132:                 * len will be -1.  Otherwise, window shrank
                    133:                 * after we sent into it.  If window shrank to 0,
                    134:                 * cancel pending retransmit and pull snd_nxt
                    135:                 * back to (closed) window.  We will enter persist
                    136:                 * state below.  If the window didn't close completely,
                    137:                 * just wait for an ACK.
                    138:                 */
                    139:                len = 0;
                    140:                if (win == 0) {
                    141:                        tp->t_timer[TCPT_REXMT] = 0;
                    142:                        tp->snd_nxt = tp->snd_una;
                    143:                }
                    144:        }
1.1.1.2   root      145: 
1.1       root      146:        if (len > tp->t_maxseg) {
                    147:                len = tp->t_maxseg;
                    148:                sendalot = 1;
                    149:        }
                    150:        if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
                    151:                flags &= ~TH_FIN;
                    152: 
                    153:        win = sbspace(&so->so_rcv);
                    154: 
                    155:        /*
                    156:         * Sender silly window avoidance.  If connection is idle
                    157:         * and can send all data, a maximum segment,
                    158:         * at least a maximum default-size segment do it,
                    159:         * or are forced, do it; otherwise don't bother.
                    160:         * If peer's buffer is tiny, then send
                    161:         * when window is at least half open.
                    162:         * If retransmitting (possibly after persist timer forced us
                    163:         * to send into a small window), then must resend.
                    164:         */
                    165:        if (len) {
                    166:                if (len == tp->t_maxseg)
                    167:                        goto send;
                    168:                if ((1 || idle || tp->t_flags & TF_NODELAY) &&
                    169:                    len + off >= so->so_snd.sb_cc)
                    170:                        goto send;
                    171:                if (tp->t_force)
                    172:                        goto send;
                    173:                if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
                    174:                        goto send;
                    175:                if (SEQ_LT(tp->snd_nxt, tp->snd_max))
                    176:                        goto send;
                    177:        }
                    178: 
                    179:        /*
                    180:         * Compare available window to amount of window
                    181:         * known to peer (as advertised window less
                    182:         * next expected input).  If the difference is at least two
                    183:         * max size segments, or at least 50% of the maximum possible
                    184:         * window, then want to send a window update to peer.
                    185:         */
                    186:        if (win > 0) {
1.1.1.2   root      187:                /*
1.1       root      188:                 * "adv" is the amount we can increase the window,
                    189:                 * taking into account that we are limited by
                    190:                 * TCP_MAXWIN << tp->rcv_scale.
                    191:                 */
                    192:                long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -
                    193:                        (tp->rcv_adv - tp->rcv_nxt);
                    194: 
                    195:                if (adv >= (long) (2 * tp->t_maxseg))
                    196:                        goto send;
                    197:                if (2 * adv >= (long) so->so_rcv.sb_datalen)
                    198:                        goto send;
                    199:        }
                    200: 
                    201:        /*
                    202:         * Send if we owe peer an ACK.
                    203:         */
                    204:        if (tp->t_flags & TF_ACKNOW)
                    205:                goto send;
                    206:        if (flags & (TH_SYN|TH_RST))
                    207:                goto send;
                    208:        if (SEQ_GT(tp->snd_up, tp->snd_una))
                    209:                goto send;
                    210:        /*
                    211:         * If our state indicates that FIN should be sent
                    212:         * and we have not yet done so, or we're retransmitting the FIN,
                    213:         * then we need to send.
                    214:         */
                    215:        if (flags & TH_FIN &&
                    216:            ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
                    217:                goto send;
                    218: 
                    219:        /*
                    220:         * TCP window updates are not reliable, rather a polling protocol
                    221:         * using ``persist'' packets is used to insure receipt of window
                    222:         * updates.  The three ``states'' for the output side are:
                    223:         *      idle                    not doing retransmits or persists
                    224:         *      persisting              to move a small or zero window
                    225:         *      (re)transmitting        and thereby not persisting
                    226:         *
                    227:         * tp->t_timer[TCPT_PERSIST]
                    228:         *      is set when we are in persist state.
                    229:         * tp->t_force
                    230:         *      is set when we are called to send a persist packet.
                    231:         * tp->t_timer[TCPT_REXMT]
                    232:         *      is set when we are retransmitting
                    233:         * The output side is idle when both timers are zero.
                    234:         *
                    235:         * If send window is too small, there is data to transmit, and no
                    236:         * retransmit or persist is pending, then go to persist state.
                    237:         * If nothing happens soon, send when timer expires:
                    238:         * if window is nonzero, transmit what we can,
                    239:         * otherwise force out a byte.
                    240:         */
                    241:        if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
                    242:            tp->t_timer[TCPT_PERSIST] == 0) {
                    243:                tp->t_rxtshift = 0;
                    244:                tcp_setpersist(tp);
                    245:        }
                    246: 
                    247:        /*
                    248:         * No reason to send a segment, just return.
                    249:         */
                    250:        return (0);
                    251: 
                    252: send:
                    253:        /*
                    254:         * Before ESTABLISHED, force sending of initial options
                    255:         * unless TCP set not to do any options.
                    256:         * NOTE: we assume that the IP/TCP header plus TCP options
                    257:         * always fit in a single mbuf, leaving room for a maximum
                    258:         * link header, i.e.
                    259:         *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN
                    260:         */
                    261:        optlen = 0;
                    262:        hdrlen = sizeof (struct tcpiphdr);
                    263:        if (flags & TH_SYN) {
                    264:                tp->snd_nxt = tp->iss;
                    265:                if ((tp->t_flags & TF_NOOPT) == 0) {
1.1.1.5 ! root      266:                        uint16_t mss;
1.1       root      267: 
                    268:                        opt[0] = TCPOPT_MAXSEG;
                    269:                        opt[1] = 4;
1.1.1.5 ! root      270:                        mss = htons((uint16_t) tcp_mss(tp, 0));
1.1       root      271:                        memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));
                    272:                        optlen = 4;
                    273:                }
                    274:        }
1.1.1.2   root      275: 
1.1       root      276:        hdrlen += optlen;
1.1.1.2   root      277: 
1.1       root      278:        /*
                    279:         * Adjust data length if insertion of options will
                    280:         * bump the packet length beyond the t_maxseg length.
                    281:         */
                    282:         if (len > tp->t_maxseg - optlen) {
                    283:                len = tp->t_maxseg - optlen;
                    284:                sendalot = 1;
                    285:         }
                    286: 
                    287:        /*
                    288:         * Grab a header mbuf, attaching a copy of data to
                    289:         * be transmitted, and initialize the header from
                    290:         * the template for sends on this connection.
                    291:         */
                    292:        if (len) {
1.1.1.4   root      293:                m = m_get(so->slirp);
1.1       root      294:                if (m == NULL) {
                    295:                        error = 1;
                    296:                        goto out;
                    297:                }
1.1.1.2   root      298:                m->m_data += IF_MAXLINKHDR;
1.1       root      299:                m->m_len = hdrlen;
1.1.1.2   root      300: 
1.1.1.4   root      301:                sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);
                    302:                m->m_len += len;
1.1       root      303: 
                    304:                /*
                    305:                 * If we're sending everything we've got, set PUSH.
                    306:                 * (This will keep happy those implementations which only
                    307:                 * give data to the user when a buffer fills or
                    308:                 * a PUSH comes in.)
                    309:                 */
                    310:                if (off + len == so->so_snd.sb_cc)
                    311:                        flags |= TH_PUSH;
                    312:        } else {
1.1.1.4   root      313:                m = m_get(so->slirp);
1.1       root      314:                if (m == NULL) {
                    315:                        error = 1;
                    316:                        goto out;
                    317:                }
1.1.1.2   root      318:                m->m_data += IF_MAXLINKHDR;
1.1       root      319:                m->m_len = hdrlen;
                    320:        }
                    321: 
                    322:        ti = mtod(m, struct tcpiphdr *);
1.1.1.2   root      323: 
1.1       root      324:        memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr));
                    325: 
                    326:        /*
                    327:         * Fill in fields, remembering maximum advertised
                    328:         * window for use in delaying messages about window sizes.
                    329:         * If resending a FIN, be sure not to use a new sequence number.
                    330:         */
1.1.1.2   root      331:        if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1.1       root      332:            tp->snd_nxt == tp->snd_max)
                    333:                tp->snd_nxt--;
                    334:        /*
                    335:         * If we are doing retransmissions, then snd_nxt will
                    336:         * not reflect the first unsent octet.  For ACK only
                    337:         * packets, we do not want the sequence number of the
                    338:         * retransmitted packet, we want the sequence number
                    339:         * of the next unsent octet.  So, if there is no data
                    340:         * (and no SYN or FIN), use snd_max instead of snd_nxt
                    341:         * when filling in ti_seq.  But if we are in persist
                    342:         * state, snd_max might reflect one byte beyond the
                    343:         * right edge of the window, so use snd_nxt in that
                    344:         * case, since we know we aren't doing a retransmission.
                    345:         * (retransmit and persist are mutually exclusive...)
                    346:         */
                    347:        if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])
                    348:                ti->ti_seq = htonl(tp->snd_nxt);
                    349:        else
                    350:                ti->ti_seq = htonl(tp->snd_max);
                    351:        ti->ti_ack = htonl(tp->rcv_nxt);
                    352:        if (optlen) {
                    353:                memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);
                    354:                ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
                    355:        }
                    356:        ti->ti_flags = flags;
                    357:        /*
                    358:         * Calculate receive window.  Don't shrink window,
                    359:         * but avoid silly window syndrome.
                    360:         */
                    361:        if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)
                    362:                win = 0;
                    363:        if (win > (long)TCP_MAXWIN << tp->rcv_scale)
                    364:                win = (long)TCP_MAXWIN << tp->rcv_scale;
                    365:        if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
                    366:                win = (long)(tp->rcv_adv - tp->rcv_nxt);
1.1.1.5 ! root      367:        ti->ti_win = htons((uint16_t) (win>>tp->rcv_scale));
1.1.1.2   root      368: 
1.1       root      369:        if (SEQ_GT(tp->snd_up, tp->snd_una)) {
1.1.1.5 ! root      370:                ti->ti_urp = htons((uint16_t)(tp->snd_up - ntohl(ti->ti_seq)));
1.1       root      371:                ti->ti_flags |= TH_URG;
                    372:        } else
                    373:                /*
                    374:                 * If no urgent pointer to send, then we pull
                    375:                 * the urgent pointer to the left edge of the send window
                    376:                 * so that it doesn't drift into the send window on sequence
                    377:                 * number wraparound.
                    378:                 */
                    379:                tp->snd_up = tp->snd_una;               /* drag it along */
                    380: 
                    381:        /*
                    382:         * Put TCP length in extended header, and then
                    383:         * checksum extended header and data.
                    384:         */
                    385:        if (len + optlen)
1.1.1.5 ! root      386:                ti->ti_len = htons((uint16_t)(sizeof (struct tcphdr) +
1.1       root      387:                    optlen + len));
                    388:        ti->ti_sum = cksum(m, (int)(hdrlen + len));
                    389: 
                    390:        /*
                    391:         * In transmit state, time the transmission and arrange for
                    392:         * the retransmit.  In persist state, just set snd_max.
                    393:         */
                    394:        if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
                    395:                tcp_seq startseq = tp->snd_nxt;
                    396: 
                    397:                /*
                    398:                 * Advance snd_nxt over sequence space of this segment.
                    399:                 */
                    400:                if (flags & (TH_SYN|TH_FIN)) {
                    401:                        if (flags & TH_SYN)
                    402:                                tp->snd_nxt++;
                    403:                        if (flags & TH_FIN) {
                    404:                                tp->snd_nxt++;
                    405:                                tp->t_flags |= TF_SENTFIN;
                    406:                        }
                    407:                }
                    408:                tp->snd_nxt += len;
                    409:                if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
                    410:                        tp->snd_max = tp->snd_nxt;
                    411:                        /*
                    412:                         * Time this transmission if not a retransmission and
                    413:                         * not currently timing anything.
                    414:                         */
                    415:                        if (tp->t_rtt == 0) {
                    416:                                tp->t_rtt = 1;
                    417:                                tp->t_rtseq = startseq;
                    418:                        }
                    419:                }
                    420: 
                    421:                /*
                    422:                 * Set retransmit timer if not currently set,
                    423:                 * and not doing an ack or a keep-alive probe.
                    424:                 * Initial value for retransmit timer is smoothed
                    425:                 * round-trip time + 2 * round-trip time variance.
                    426:                 * Initialize shift counter which is used for backoff
                    427:                 * of retransmit time.
                    428:                 */
                    429:                if (tp->t_timer[TCPT_REXMT] == 0 &&
                    430:                    tp->snd_nxt != tp->snd_una) {
                    431:                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
                    432:                        if (tp->t_timer[TCPT_PERSIST]) {
                    433:                                tp->t_timer[TCPT_PERSIST] = 0;
                    434:                                tp->t_rxtshift = 0;
                    435:                        }
                    436:                }
                    437:        } else
                    438:                if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
                    439:                        tp->snd_max = tp->snd_nxt + len;
                    440: 
                    441:        /*
                    442:         * Fill in IP length and desired time to live and
                    443:         * send to IP level.  There should be a better way
                    444:         * to handle ttl and tos; we could keep them in
                    445:         * the template, but need a way to checksum without them.
                    446:         */
                    447:        m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
1.1.1.2   root      448: 
1.1       root      449:     {
1.1.1.2   root      450: 
1.1       root      451:        ((struct ip *)ti)->ip_len = m->m_len;
                    452: 
1.1.1.2   root      453:        ((struct ip *)ti)->ip_ttl = IPDEFTTL;
1.1       root      454:        ((struct ip *)ti)->ip_tos = so->so_iptos;
1.1.1.2   root      455: 
1.1       root      456:        error = ip_output(so, m);
                    457:     }
                    458:        if (error) {
                    459: out:
                    460:                return (error);
                    461:        }
                    462: 
                    463:        /*
                    464:         * Data sent (as far as we can tell).
                    465:         * If this advertises a larger window than any other segment,
                    466:         * then remember the size of the advertised window.
                    467:         * Any pending ACK has now been sent.
                    468:         */
                    469:        if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
                    470:                tp->rcv_adv = tp->rcv_nxt + win;
                    471:        tp->last_ack_sent = tp->rcv_nxt;
                    472:        tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
                    473:        if (sendalot)
                    474:                goto again;
                    475: 
                    476:        return (0);
                    477: }
                    478: 
                    479: void
1.1.1.4   root      480: tcp_setpersist(struct tcpcb *tp)
1.1       root      481: {
                    482:     int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
                    483: 
                    484:        /*
                    485:         * Start/restart persistence timer.
                    486:         */
                    487:        TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
                    488:            t * tcp_backoff[tp->t_rxtshift],
                    489:            TCPTV_PERSMIN, TCPTV_PERSMAX);
                    490:        if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
                    491:                tp->t_rxtshift++;
                    492: }

unix.superglobalmegacorp.com