Annotation of qemu/slirp/tcp_output.c, revision 1.1.1.6

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: 
1.1.1.6 ! root       50: #undef MAX_TCPOPTLEN
1.1       root       51: #define MAX_TCPOPTLEN  32      /* max # bytes that go in options */
                     52: 
                     53: /*
                     54:  * Tcp output routine: figure out what should be sent and send it.
                     55:  */
                     56: int
1.1.1.4   root       57: tcp_output(struct tcpcb *tp)
1.1       root       58: {
                     59:        register struct socket *so = tp->t_socket;
                     60:        register long len, win;
                     61:        int off, flags, error;
                     62:        register struct mbuf *m;
                     63:        register struct tcpiphdr *ti;
                     64:        u_char opt[MAX_TCPOPTLEN];
                     65:        unsigned optlen, hdrlen;
                     66:        int idle, sendalot;
1.1.1.2   root       67: 
1.1       root       68:        DEBUG_CALL("tcp_output");
                     69:        DEBUG_ARG("tp = %lx", (long )tp);
1.1.1.2   root       70: 
1.1       root       71:        /*
                     72:         * Determine length of data that should be transmitted,
                     73:         * and flags that will be used.
                     74:         * If there is some data or critical controls (SYN, RST)
                     75:         * to send, then transmit; otherwise, investigate further.
                     76:         */
                     77:        idle = (tp->snd_max == tp->snd_una);
                     78:        if (idle && tp->t_idle >= tp->t_rxtcur)
                     79:                /*
                     80:                 * We have been idle for "a while" and no acks are
                     81:                 * expected to clock out any data we send --
                     82:                 * slow start to get ack "clock" running again.
                     83:                 */
                     84:                tp->snd_cwnd = tp->t_maxseg;
                     85: again:
                     86:        sendalot = 0;
                     87:        off = tp->snd_nxt - tp->snd_una;
                     88:        win = min(tp->snd_wnd, tp->snd_cwnd);
                     89: 
                     90:        flags = tcp_outflags[tp->t_state];
1.1.1.2   root       91: 
1.1       root       92:        DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));
1.1.1.2   root       93: 
1.1       root       94:        /*
                     95:         * If in persist timeout with window of 0, send 1 byte.
                     96:         * Otherwise, if window is small but nonzero
                     97:         * and timer expired, we will send what we can
                     98:         * and go to transmit state.
                     99:         */
                    100:        if (tp->t_force) {
                    101:                if (win == 0) {
                    102:                        /*
                    103:                         * If we still have some data to send, then
                    104:                         * clear the FIN bit.  Usually this would
                    105:                         * happen below when it realizes that we
                    106:                         * aren't sending all the data.  However,
                    107:                         * if we have exactly 1 byte of unset data,
                    108:                         * then it won't clear the FIN bit below,
                    109:                         * and if we are in persist state, we wind
                    110:                         * up sending the packet without recording
                    111:                         * that we sent the FIN bit.
                    112:                         *
                    113:                         * We can't just blindly clear the FIN bit,
                    114:                         * because if we don't have any more data
                    115:                         * to send then the probe will be the FIN
                    116:                         * itself.
                    117:                         */
                    118:                        if (off < so->so_snd.sb_cc)
                    119:                                flags &= ~TH_FIN;
                    120:                        win = 1;
                    121:                } else {
                    122:                        tp->t_timer[TCPT_PERSIST] = 0;
                    123:                        tp->t_rxtshift = 0;
                    124:                }
                    125:        }
                    126: 
                    127:        len = min(so->so_snd.sb_cc, win) - off;
                    128: 
                    129:        if (len < 0) {
                    130:                /*
                    131:                 * If FIN has been sent but not acked,
                    132:                 * but we haven't been called to retransmit,
                    133:                 * len will be -1.  Otherwise, window shrank
                    134:                 * after we sent into it.  If window shrank to 0,
                    135:                 * cancel pending retransmit and pull snd_nxt
                    136:                 * back to (closed) window.  We will enter persist
                    137:                 * state below.  If the window didn't close completely,
                    138:                 * just wait for an ACK.
                    139:                 */
                    140:                len = 0;
                    141:                if (win == 0) {
                    142:                        tp->t_timer[TCPT_REXMT] = 0;
                    143:                        tp->snd_nxt = tp->snd_una;
                    144:                }
                    145:        }
1.1.1.2   root      146: 
1.1       root      147:        if (len > tp->t_maxseg) {
                    148:                len = tp->t_maxseg;
                    149:                sendalot = 1;
                    150:        }
                    151:        if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
                    152:                flags &= ~TH_FIN;
                    153: 
                    154:        win = sbspace(&so->so_rcv);
                    155: 
                    156:        /*
                    157:         * Sender silly window avoidance.  If connection is idle
                    158:         * and can send all data, a maximum segment,
                    159:         * at least a maximum default-size segment do it,
                    160:         * or are forced, do it; otherwise don't bother.
                    161:         * If peer's buffer is tiny, then send
                    162:         * when window is at least half open.
                    163:         * If retransmitting (possibly after persist timer forced us
                    164:         * to send into a small window), then must resend.
                    165:         */
                    166:        if (len) {
                    167:                if (len == tp->t_maxseg)
                    168:                        goto send;
                    169:                if ((1 || idle || tp->t_flags & TF_NODELAY) &&
                    170:                    len + off >= so->so_snd.sb_cc)
                    171:                        goto send;
                    172:                if (tp->t_force)
                    173:                        goto send;
                    174:                if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
                    175:                        goto send;
                    176:                if (SEQ_LT(tp->snd_nxt, tp->snd_max))
                    177:                        goto send;
                    178:        }
                    179: 
                    180:        /*
                    181:         * Compare available window to amount of window
                    182:         * known to peer (as advertised window less
                    183:         * next expected input).  If the difference is at least two
                    184:         * max size segments, or at least 50% of the maximum possible
                    185:         * window, then want to send a window update to peer.
                    186:         */
                    187:        if (win > 0) {
1.1.1.2   root      188:                /*
1.1       root      189:                 * "adv" is the amount we can increase the window,
                    190:                 * taking into account that we are limited by
                    191:                 * TCP_MAXWIN << tp->rcv_scale.
                    192:                 */
                    193:                long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -
                    194:                        (tp->rcv_adv - tp->rcv_nxt);
                    195: 
                    196:                if (adv >= (long) (2 * tp->t_maxseg))
                    197:                        goto send;
                    198:                if (2 * adv >= (long) so->so_rcv.sb_datalen)
                    199:                        goto send;
                    200:        }
                    201: 
                    202:        /*
                    203:         * Send if we owe peer an ACK.
                    204:         */
                    205:        if (tp->t_flags & TF_ACKNOW)
                    206:                goto send;
                    207:        if (flags & (TH_SYN|TH_RST))
                    208:                goto send;
                    209:        if (SEQ_GT(tp->snd_up, tp->snd_una))
                    210:                goto send;
                    211:        /*
                    212:         * If our state indicates that FIN should be sent
                    213:         * and we have not yet done so, or we're retransmitting the FIN,
                    214:         * then we need to send.
                    215:         */
                    216:        if (flags & TH_FIN &&
                    217:            ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
                    218:                goto send;
                    219: 
                    220:        /*
                    221:         * TCP window updates are not reliable, rather a polling protocol
                    222:         * using ``persist'' packets is used to insure receipt of window
                    223:         * updates.  The three ``states'' for the output side are:
                    224:         *      idle                    not doing retransmits or persists
                    225:         *      persisting              to move a small or zero window
                    226:         *      (re)transmitting        and thereby not persisting
                    227:         *
                    228:         * tp->t_timer[TCPT_PERSIST]
                    229:         *      is set when we are in persist state.
                    230:         * tp->t_force
                    231:         *      is set when we are called to send a persist packet.
                    232:         * tp->t_timer[TCPT_REXMT]
                    233:         *      is set when we are retransmitting
                    234:         * The output side is idle when both timers are zero.
                    235:         *
                    236:         * If send window is too small, there is data to transmit, and no
                    237:         * retransmit or persist is pending, then go to persist state.
                    238:         * If nothing happens soon, send when timer expires:
                    239:         * if window is nonzero, transmit what we can,
                    240:         * otherwise force out a byte.
                    241:         */
                    242:        if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
                    243:            tp->t_timer[TCPT_PERSIST] == 0) {
                    244:                tp->t_rxtshift = 0;
                    245:                tcp_setpersist(tp);
                    246:        }
                    247: 
                    248:        /*
                    249:         * No reason to send a segment, just return.
                    250:         */
                    251:        return (0);
                    252: 
                    253: send:
                    254:        /*
                    255:         * Before ESTABLISHED, force sending of initial options
                    256:         * unless TCP set not to do any options.
                    257:         * NOTE: we assume that the IP/TCP header plus TCP options
                    258:         * always fit in a single mbuf, leaving room for a maximum
                    259:         * link header, i.e.
                    260:         *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN
                    261:         */
                    262:        optlen = 0;
                    263:        hdrlen = sizeof (struct tcpiphdr);
                    264:        if (flags & TH_SYN) {
                    265:                tp->snd_nxt = tp->iss;
                    266:                if ((tp->t_flags & TF_NOOPT) == 0) {
1.1.1.5   root      267:                        uint16_t mss;
1.1       root      268: 
                    269:                        opt[0] = TCPOPT_MAXSEG;
                    270:                        opt[1] = 4;
1.1.1.5   root      271:                        mss = htons((uint16_t) tcp_mss(tp, 0));
1.1       root      272:                        memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));
                    273:                        optlen = 4;
                    274:                }
                    275:        }
1.1.1.2   root      276: 
1.1       root      277:        hdrlen += optlen;
1.1.1.2   root      278: 
1.1       root      279:        /*
                    280:         * Adjust data length if insertion of options will
                    281:         * bump the packet length beyond the t_maxseg length.
                    282:         */
                    283:         if (len > tp->t_maxseg - optlen) {
                    284:                len = tp->t_maxseg - optlen;
                    285:                sendalot = 1;
                    286:         }
                    287: 
                    288:        /*
                    289:         * Grab a header mbuf, attaching a copy of data to
                    290:         * be transmitted, and initialize the header from
                    291:         * the template for sends on this connection.
                    292:         */
                    293:        if (len) {
1.1.1.4   root      294:                m = m_get(so->slirp);
1.1       root      295:                if (m == NULL) {
                    296:                        error = 1;
                    297:                        goto out;
                    298:                }
1.1.1.2   root      299:                m->m_data += IF_MAXLINKHDR;
1.1       root      300:                m->m_len = hdrlen;
1.1.1.2   root      301: 
1.1.1.4   root      302:                sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);
                    303:                m->m_len += len;
1.1       root      304: 
                    305:                /*
                    306:                 * If we're sending everything we've got, set PUSH.
                    307:                 * (This will keep happy those implementations which only
                    308:                 * give data to the user when a buffer fills or
                    309:                 * a PUSH comes in.)
                    310:                 */
                    311:                if (off + len == so->so_snd.sb_cc)
                    312:                        flags |= TH_PUSH;
                    313:        } else {
1.1.1.4   root      314:                m = m_get(so->slirp);
1.1       root      315:                if (m == NULL) {
                    316:                        error = 1;
                    317:                        goto out;
                    318:                }
1.1.1.2   root      319:                m->m_data += IF_MAXLINKHDR;
1.1       root      320:                m->m_len = hdrlen;
                    321:        }
                    322: 
                    323:        ti = mtod(m, struct tcpiphdr *);
1.1.1.2   root      324: 
1.1       root      325:        memcpy((caddr_t)ti, &tp->t_template, 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:         */
1.1.1.2   root      332:        if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1.1       root      333:            tp->snd_nxt == tp->snd_max)
                    334:                tp->snd_nxt--;
                    335:        /*
                    336:         * If we are doing retransmissions, then snd_nxt will
                    337:         * not reflect the first unsent octet.  For ACK only
                    338:         * packets, we do not want the sequence number of the
                    339:         * retransmitted packet, we want the sequence number
                    340:         * of the next unsent octet.  So, if there is no data
                    341:         * (and no SYN or FIN), use snd_max instead of snd_nxt
                    342:         * when filling in ti_seq.  But if we are in persist
                    343:         * state, snd_max might reflect one byte beyond the
                    344:         * right edge of the window, so use snd_nxt in that
                    345:         * case, since we know we aren't doing a retransmission.
                    346:         * (retransmit and persist are mutually exclusive...)
                    347:         */
                    348:        if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])
                    349:                ti->ti_seq = htonl(tp->snd_nxt);
                    350:        else
                    351:                ti->ti_seq = htonl(tp->snd_max);
                    352:        ti->ti_ack = htonl(tp->rcv_nxt);
                    353:        if (optlen) {
                    354:                memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);
                    355:                ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
                    356:        }
                    357:        ti->ti_flags = flags;
                    358:        /*
                    359:         * Calculate receive window.  Don't shrink window,
                    360:         * but avoid silly window syndrome.
                    361:         */
                    362:        if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)
                    363:                win = 0;
                    364:        if (win > (long)TCP_MAXWIN << tp->rcv_scale)
                    365:                win = (long)TCP_MAXWIN << tp->rcv_scale;
                    366:        if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
                    367:                win = (long)(tp->rcv_adv - tp->rcv_nxt);
1.1.1.5   root      368:        ti->ti_win = htons((uint16_t) (win>>tp->rcv_scale));
1.1.1.2   root      369: 
1.1       root      370:        if (SEQ_GT(tp->snd_up, tp->snd_una)) {
1.1.1.5   root      371:                ti->ti_urp = htons((uint16_t)(tp->snd_up - ntohl(ti->ti_seq)));
1.1       root      372:                ti->ti_flags |= TH_URG;
                    373:        } else
                    374:                /*
                    375:                 * If no urgent pointer to send, then we pull
                    376:                 * the urgent pointer to the left edge of the send window
                    377:                 * so that it doesn't drift into the send window on sequence
                    378:                 * number wraparound.
                    379:                 */
                    380:                tp->snd_up = tp->snd_una;               /* drag it along */
                    381: 
                    382:        /*
                    383:         * Put TCP length in extended header, and then
                    384:         * checksum extended header and data.
                    385:         */
                    386:        if (len + optlen)
1.1.1.5   root      387:                ti->ti_len = htons((uint16_t)(sizeof (struct tcphdr) +
1.1       root      388:                    optlen + len));
                    389:        ti->ti_sum = cksum(m, (int)(hdrlen + len));
                    390: 
                    391:        /*
                    392:         * In transmit state, time the transmission and arrange for
                    393:         * the retransmit.  In persist state, just set snd_max.
                    394:         */
                    395:        if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
                    396:                tcp_seq startseq = tp->snd_nxt;
                    397: 
                    398:                /*
                    399:                 * Advance snd_nxt over sequence space of this segment.
                    400:                 */
                    401:                if (flags & (TH_SYN|TH_FIN)) {
                    402:                        if (flags & TH_SYN)
                    403:                                tp->snd_nxt++;
                    404:                        if (flags & TH_FIN) {
                    405:                                tp->snd_nxt++;
                    406:                                tp->t_flags |= TF_SENTFIN;
                    407:                        }
                    408:                }
                    409:                tp->snd_nxt += len;
                    410:                if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
                    411:                        tp->snd_max = tp->snd_nxt;
                    412:                        /*
                    413:                         * Time this transmission if not a retransmission and
                    414:                         * not currently timing anything.
                    415:                         */
                    416:                        if (tp->t_rtt == 0) {
                    417:                                tp->t_rtt = 1;
                    418:                                tp->t_rtseq = startseq;
                    419:                        }
                    420:                }
                    421: 
                    422:                /*
                    423:                 * Set retransmit timer if not currently set,
                    424:                 * and not doing an ack or a keep-alive probe.
                    425:                 * Initial value for retransmit timer is smoothed
                    426:                 * round-trip time + 2 * round-trip time variance.
                    427:                 * Initialize shift counter which is used for backoff
                    428:                 * of retransmit time.
                    429:                 */
                    430:                if (tp->t_timer[TCPT_REXMT] == 0 &&
                    431:                    tp->snd_nxt != tp->snd_una) {
                    432:                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
                    433:                        if (tp->t_timer[TCPT_PERSIST]) {
                    434:                                tp->t_timer[TCPT_PERSIST] = 0;
                    435:                                tp->t_rxtshift = 0;
                    436:                        }
                    437:                }
                    438:        } else
                    439:                if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
                    440:                        tp->snd_max = tp->snd_nxt + len;
                    441: 
                    442:        /*
                    443:         * Fill in IP length and desired time to live and
                    444:         * send to IP level.  There should be a better way
                    445:         * to handle ttl and tos; we could keep them in
                    446:         * the template, but need a way to checksum without them.
                    447:         */
                    448:        m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
1.1.1.2   root      449: 
1.1       root      450:     {
1.1.1.2   root      451: 
1.1       root      452:        ((struct ip *)ti)->ip_len = m->m_len;
                    453: 
1.1.1.2   root      454:        ((struct ip *)ti)->ip_ttl = IPDEFTTL;
1.1       root      455:        ((struct ip *)ti)->ip_tos = so->so_iptos;
1.1.1.2   root      456: 
1.1       root      457:        error = ip_output(so, m);
                    458:     }
                    459:        if (error) {
                    460: out:
                    461:                return (error);
                    462:        }
                    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->last_ack_sent = tp->rcv_nxt;
                    473:        tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
                    474:        if (sendalot)
                    475:                goto again;
                    476: 
                    477:        return (0);
                    478: }
                    479: 
                    480: void
1.1.1.4   root      481: tcp_setpersist(struct tcpcb *tp)
1.1       root      482: {
                    483:     int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
                    484: 
                    485:        /*
                    486:         * Start/restart persistence 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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