slirp/tcp_output.c

   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.
  13  * 3. Neither the name of the University nor the names of its contributors
  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.
  36  *
  37  * Please read the file COPYRIGHT for the
  38  * terms and conditions of the copyright.
  39  */
  40
  41 #include <slirp.h>
  42
  43 static const u_char  tcp_outflags[TCP_NSTATES] = {
  44         TH_RST|TH_ACK, 0,      TH_SYN,        TH_SYN|TH_ACK,
  45         TH_ACK,        TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK,
  46         TH_FIN|TH_ACK, TH_ACK, TH_ACK,
  47 };
  48
  49
  50 #undef MAX_TCPOPTLEN
  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
  57 tcp_output(struct tcpcb *tp)
  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;
  67
  68         DEBUG_CALL("tcp_output");
  69         DEBUG_ARG("tp = %lx", (long )tp);
  70
  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];
  91
  92         DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));
  93
  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         }
 146
 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) {
 188                 /*
 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) {
 267                         uint16_t mss;
 268
 269                         opt[0] = TCPOPT_MAXSEG;
 270                         opt[1] = 4;
 271                         mss = htons((uint16_t) tcp_mss(tp, 0));
 272                         memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));
 273                         optlen = 4;
 274                 }
 275         }
 276
 277         hdrlen += optlen;
 278
 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) {
 294                 m = m_get(so->slirp);
 295                 if (m == NULL) {
 296                         error = 1;
 297                         goto out;
 298                 }
 299                 m->m_data += IF_MAXLINKHDR;
 300                 m->m_len = hdrlen;
 301
 302                 sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);
 303                 m->m_len += len;
 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 {
 314                 m = m_get(so->slirp);
 315                 if (m == NULL) {
 316                         error = 1;
 317                         goto out;
 318                 }
 319                 m->m_data += IF_MAXLINKHDR;
 320                 m->m_len = hdrlen;
 321         }
 322
 323         ti = mtod(m, struct tcpiphdr *);
 324
 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          */
 332         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
 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);
 368         ti->ti_win = htons((uint16_t) (win>>tp->rcv_scale));
 369
 370         if (SEQ_GT(tp->snd_up, tp->snd_una)) {
 371                 ti->ti_urp = htons((uint16_t)(tp->snd_up - ntohl(ti->ti_seq)));
 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)
 387                 ti->ti_len = htons((uint16_t)(sizeof (struct tcphdr) +
 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 */
 449
 450     {
 451
 452         ((struct ip *)ti)->ip_len = m->m_len;
 453
 454         ((struct ip *)ti)->ip_ttl = IPDEFTTL;
 455         ((struct ip *)ti)->ip_tos = so->so_iptos;
 456
 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
 481 tcp_setpersist(struct tcpcb *tp)
 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 }