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/* 44 * Since this is only used in "stats socket", we give meaning 45 * names instead of the REAL names 46 */ 47const char * const tcpstates[] = { 48/* "CLOSED", "LISTEN", "SYN_SENT", "SYN_RCVD", */ 49 "REDIRECT", "LISTEN", "SYN_SENT", "SYN_RCVD", 50 "ESTABLISHED", "CLOSE_WAIT", "FIN_WAIT_1", "CLOSING", 51 "LAST_ACK", "FIN_WAIT_2", "TIME_WAIT", 52}; 53 54static const u_char tcp_outflags[TCP_NSTATES] = { 55 TH_RST|TH_ACK, 0, TH_SYN, TH_SYN|TH_ACK, 56 TH_ACK, TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK, 57 TH_FIN|TH_ACK, TH_ACK, TH_ACK, 58}; 59 60 61#define MAX_TCPOPTLEN 32 /* max # bytes that go in options */ 62 63/* 64 * Tcp output routine: figure out what should be sent and send it. 65 */ 66int 67tcp_output(tp) 68 register struct tcpcb *tp; 69{ 70 register struct socket *so = tp->t_socket; 71 register long len, win; 72 int off, flags, error; 73 register struct mbuf *m; 74 register struct tcpiphdr *ti; 75 u_char opt[MAX_TCPOPTLEN]; 76 unsigned optlen, hdrlen; 77 int idle, sendalot; 78 79 DEBUG_CALL("tcp_output"); 80 DEBUG_ARG("tp = %lx", (long )tp); 81 82 /* 83 * Determine length of data that should be transmitted, 84 * and flags that will be used. 85 * If there is some data or critical controls (SYN, RST) 86 * to send, then transmit; otherwise, investigate further. 87 */ 88 idle = (tp->snd_max == tp->snd_una); 89 if (idle && tp->t_idle >= tp->t_rxtcur) 90 /* 91 * We have been idle for "a while" and no acks are 92 * expected to clock out any data we send -- 93 * slow start to get ack "clock" running again. 94 */ 95 tp->snd_cwnd = tp->t_maxseg; 96again: 97 sendalot = 0; 98 off = tp->snd_nxt - tp->snd_una; 99 win = min(tp->snd_wnd, tp->snd_cwnd); 100 101 flags = tcp_outflags[tp->t_state]; 102 103 DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags)); 104 105 /* 106 * If in persist timeout with window of 0, send 1 byte. 107 * Otherwise, if window is small but nonzero 108 * and timer expired, we will send what we can 109 * and go to transmit state. 110 */ 111 if (tp->t_force) { 112 if (win == 0) { 113 /* 114 * If we still have some data to send, then 115 * clear the FIN bit. Usually this would 116 * happen below when it realizes that we 117 * aren't sending all the data. However, 118 * if we have exactly 1 byte of unset data, 119 * then it won't clear the FIN bit below, 120 * and if we are in persist state, we wind 121 * up sending the packet without recording 122 * that we sent the FIN bit. 123 * 124 * We can't just blindly clear the FIN bit, 125 * because if we don't have any more data 126 * to send then the probe will be the FIN 127 * itself. 128 */ 129 if (off < so->so_snd.sb_cc) 130 flags &= ~TH_FIN; 131 win = 1; 132 } else { 133 tp->t_timer[TCPT_PERSIST] = 0; 134 tp->t_rxtshift = 0; 135 } 136 } 137 138 len = min(so->so_snd.sb_cc, win) - off; 139 140 if (len < 0) { 141 /* 142 * If FIN has been sent but not acked, 143 * but we haven't been called to retransmit, 144 * len will be -1. Otherwise, window shrank 145 * after we sent into it. If window shrank to 0, 146 * cancel pending retransmit and pull snd_nxt 147 * back to (closed) window. We will enter persist 148 * state below. If the window didn't close completely, 149 * just wait for an ACK. 150 */ 151 len = 0; 152 if (win == 0) { 153 tp->t_timer[TCPT_REXMT] = 0; 154 tp->snd_nxt = tp->snd_una; 155 } 156 } 157 158 if (len > tp->t_maxseg) { 159 len = tp->t_maxseg; 160 sendalot = 1; 161 } 162 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) 163 flags &= ~TH_FIN; 164 165 win = sbspace(&so->so_rcv); 166 167 /* 168 * Sender silly window avoidance. If connection is idle 169 * and can send all data, a maximum segment, 170 * at least a maximum default-size segment do it, 171 * or are forced, do it; otherwise don't bother. 172 * If peer's buffer is tiny, then send 173 * when window is at least half open. 174 * If retransmitting (possibly after persist timer forced us 175 * to send into a small window), then must resend. 176 */ 177 if (len) { 178 if (len == tp->t_maxseg) 179 goto send; 180 if ((1 || idle || tp->t_flags & TF_NODELAY) && 181 len + off >= so->so_snd.sb_cc) 182 goto send; 183 if (tp->t_force) 184 goto send; 185 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0) 186 goto send; 187 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 188 goto send; 189 } 190 191 /* 192 * Compare available window to amount of window 193 * known to peer (as advertised window less 194 * next expected input). If the difference is at least two 195 * max size segments, or at least 50% of the maximum possible 196 * window, then want to send a window update to peer. 197 */ 198 if (win > 0) { 199 /* 200 * "adv" is the amount we can increase the window, 201 * taking into account that we are limited by 202 * TCP_MAXWIN << tp->rcv_scale. 203 */ 204 long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) - 205 (tp->rcv_adv - tp->rcv_nxt); 206 207 if (adv >= (long) (2 * tp->t_maxseg)) 208 goto send; 209 if (2 * adv >= (long) so->so_rcv.sb_datalen) 210 goto send; 211 } 212 213 /* 214 * Send if we owe peer an ACK. 215 */ 216 if (tp->t_flags & TF_ACKNOW) 217 goto send; 218 if (flags & (TH_SYN|TH_RST)) 219 goto send; 220 if (SEQ_GT(tp->snd_up, tp->snd_una)) 221 goto send; 222 /* 223 * If our state indicates that FIN should be sent 224 * and we have not yet done so, or we're retransmitting the FIN, 225 * then we need to send. 226 */ 227 if (flags & TH_FIN && 228 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 229 goto send; 230 231 /* 232 * TCP window updates are not reliable, rather a polling protocol 233 * using ``persist'' packets is used to insure receipt of window 234 * updates. The three ``states'' for the output side are: 235 * idle not doing retransmits or persists 236 * persisting to move a small or zero window 237 * (re)transmitting and thereby not persisting 238 * 239 * tp->t_timer[TCPT_PERSIST] 240 * is set when we are in persist state. 241 * tp->t_force 242 * is set when we are called to send a persist packet. 243 * tp->t_timer[TCPT_REXMT] 244 * is set when we are retransmitting 245 * The output side is idle when both timers are zero. 246 * 247 * If send window is too small, there is data to transmit, and no 248 * retransmit or persist is pending, then go to persist state. 249 * If nothing happens soon, send when timer expires: 250 * if window is nonzero, transmit what we can, 251 * otherwise force out a byte. 252 */ 253 if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 && 254 tp->t_timer[TCPT_PERSIST] == 0) { 255 tp->t_rxtshift = 0; 256 tcp_setpersist(tp); 257 } 258 259 /* 260 * No reason to send a segment, just return. 261 */ 262 STAT(tcpstat.tcps_didnuttin++); 263 264 return (0); 265 266send: 267 /* 268 * Before ESTABLISHED, force sending of initial options 269 * unless TCP set not to do any options. 270 * NOTE: we assume that the IP/TCP header plus TCP options 271 * always fit in a single mbuf, leaving room for a maximum 272 * link header, i.e. 273 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN 274 */ 275 optlen = 0; 276 hdrlen = sizeof (struct tcpiphdr); 277 if (flags & TH_SYN) { 278 tp->snd_nxt = tp->iss; 279 if ((tp->t_flags & TF_NOOPT) == 0) { 280 u_int16_t mss; 281 282 opt[0] = TCPOPT_MAXSEG; 283 opt[1] = 4; 284 mss = htons((u_int16_t) tcp_mss(tp, 0)); 285 memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss)); 286 optlen = 4; 287 288/* if ((tp->t_flags & TF_REQ_SCALE) && 289 * ((flags & TH_ACK) == 0 || 290 * (tp->t_flags & TF_RCVD_SCALE))) { 291 * *((u_int32_t *) (opt + optlen)) = htonl( 292 * TCPOPT_NOP << 24 | 293 * TCPOPT_WINDOW << 16 | 294 * TCPOLEN_WINDOW << 8 | 295 * tp->request_r_scale); 296 * optlen += 4; 297 * } 298 */ 299 } 300 } 301 302 /* 303 * Send a timestamp and echo-reply if this is a SYN and our side 304 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 305 * and our peer have sent timestamps in our SYN's. 306 */ 307/* if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 308 * (flags & TH_RST) == 0 && 309 * ((flags & (TH_SYN|TH_ACK)) == TH_SYN || 310 * (tp->t_flags & TF_RCVD_TSTMP))) { 311 * u_int32_t *lp = (u_int32_t *)(opt + optlen); 312 * 313 * / * Form timestamp option as shown in appendix A of RFC 1323. * / 314 * *lp++ = htonl(TCPOPT_TSTAMP_HDR); 315 * *lp++ = htonl(tcp_now); 316 * *lp = htonl(tp->ts_recent); 317 * optlen += TCPOLEN_TSTAMP_APPA; 318 * } 319 */ 320 hdrlen += optlen; 321 322 /* 323 * Adjust data length if insertion of options will 324 * bump the packet length beyond the t_maxseg length. 325 */ 326 if (len > tp->t_maxseg - optlen) { 327 len = tp->t_maxseg - optlen; 328 sendalot = 1; 329 } 330 331 /* 332 * Grab a header mbuf, attaching a copy of data to 333 * be transmitted, and initialize the header from 334 * the template for sends on this connection. 335 */ 336 if (len) { 337 if (tp->t_force && len == 1) 338 STAT(tcpstat.tcps_sndprobe++); 339 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 340 STAT(tcpstat.tcps_sndrexmitpack++); 341 STAT(tcpstat.tcps_sndrexmitbyte += len); 342 } else { 343 STAT(tcpstat.tcps_sndpack++); 344 STAT(tcpstat.tcps_sndbyte += len); 345 } 346 347 m = m_get(); 348 if (m == NULL) { 349/* error = ENOBUFS; */ 350 error = 1; 351 goto out; 352 } 353 m->m_data += IF_MAXLINKHDR; 354 m->m_len = hdrlen; 355 356 /* 357 * This will always succeed, since we make sure our mbufs 358 * are big enough to hold one MSS packet + header + ... etc. 359 */ 360/* if (len <= MHLEN - hdrlen - max_linkhdr) { */ 361 362 sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen); 363 m->m_len += len; 364 365/* } else { 366 * m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len); 367 * if (m->m_next == 0) 368 * len = 0; 369 * } 370 */ 371 /* 372 * If we're sending everything we've got, set PUSH. 373 * (This will keep happy those implementations which only 374 * give data to the user when a buffer fills or 375 * a PUSH comes in.) 376 */ 377 if (off + len == so->so_snd.sb_cc) 378 flags |= TH_PUSH; 379 } else { 380 if (tp->t_flags & TF_ACKNOW) 381 STAT(tcpstat.tcps_sndacks++); 382 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 383 STAT(tcpstat.tcps_sndctrl++); 384 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 385 STAT(tcpstat.tcps_sndurg++); 386 else 387 STAT(tcpstat.tcps_sndwinup++); 388 389 m = m_get(); 390 if (m == NULL) { 391/* error = ENOBUFS; */ 392 error = 1; 393 goto out; 394 } 395 m->m_data += IF_MAXLINKHDR; 396 m->m_len = hdrlen; 397 } 398 399 ti = mtod(m, struct tcpiphdr *); 400 401 memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr)); 402 403 /* 404 * Fill in fields, remembering maximum advertised 405 * window for use in delaying messages about window sizes. 406 * If resending a FIN, be sure not to use a new sequence number. 407 */ 408 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 409 tp->snd_nxt == tp->snd_max) 410 tp->snd_nxt--; 411 /* 412 * If we are doing retransmissions, then snd_nxt will 413 * not reflect the first unsent octet. For ACK only 414 * packets, we do not want the sequence number of the 415 * retransmitted packet, we want the sequence number 416 * of the next unsent octet. So, if there is no data 417 * (and no SYN or FIN), use snd_max instead of snd_nxt 418 * when filling in ti_seq. But if we are in persist 419 * state, snd_max might reflect one byte beyond the 420 * right edge of the window, so use snd_nxt in that 421 * case, since we know we aren't doing a retransmission. 422 * (retransmit and persist are mutually exclusive...) 423 */ 424 if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST]) 425 ti->ti_seq = htonl(tp->snd_nxt); 426 else 427 ti->ti_seq = htonl(tp->snd_max); 428 ti->ti_ack = htonl(tp->rcv_nxt); 429 if (optlen) { 430 memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen); 431 ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; 432 } 433 ti->ti_flags = flags; 434 /* 435 * Calculate receive window. Don't shrink window, 436 * but avoid silly window syndrome. 437 */ 438 if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg) 439 win = 0; 440 if (win > (long)TCP_MAXWIN << tp->rcv_scale) 441 win = (long)TCP_MAXWIN << tp->rcv_scale; 442 if (win < (long)(tp->rcv_adv - tp->rcv_nxt)) 443 win = (long)(tp->rcv_adv - tp->rcv_nxt); 444 ti->ti_win = htons((u_int16_t) (win>>tp->rcv_scale)); 445 446 if (SEQ_GT(tp->snd_up, tp->snd_una)) { 447 ti->ti_urp = htons((u_int16_t)(tp->snd_up - ntohl(ti->ti_seq))); 448#ifdef notdef 449 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 450 ti->ti_urp = htons((u_int16_t)(tp->snd_up - tp->snd_nxt)); 451#endif 452 ti->ti_flags |= TH_URG; 453 } else 454 /* 455 * If no urgent pointer to send, then we pull 456 * the urgent pointer to the left edge of the send window 457 * so that it doesn't drift into the send window on sequence 458 * number wraparound. 459 */ 460 tp->snd_up = tp->snd_una; /* drag it along */ 461 462 /* 463 * Put TCP length in extended header, and then 464 * checksum extended header and data. 465 */ 466 if (len + optlen) 467 ti->ti_len = htons((u_int16_t)(sizeof (struct tcphdr) + 468 optlen + len)); 469 ti->ti_sum = cksum(m, (int)(hdrlen + len)); 470 471 /* 472 * In transmit state, time the transmission and arrange for 473 * the retransmit. In persist state, just set snd_max. 474 */ 475 if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) { 476 tcp_seq startseq = tp->snd_nxt; 477 478 /* 479 * Advance snd_nxt over sequence space of this segment. 480 */ 481 if (flags & (TH_SYN|TH_FIN)) { 482 if (flags & TH_SYN) 483 tp->snd_nxt++; 484 if (flags & TH_FIN) { 485 tp->snd_nxt++; 486 tp->t_flags |= TF_SENTFIN; 487 } 488 } 489 tp->snd_nxt += len; 490 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 491 tp->snd_max = tp->snd_nxt; 492 /* 493 * Time this transmission if not a retransmission and 494 * not currently timing anything. 495 */ 496 if (tp->t_rtt == 0) { 497 tp->t_rtt = 1; 498 tp->t_rtseq = startseq; 499 STAT(tcpstat.tcps_segstimed++); 500 } 501 } 502 503 /* 504 * Set retransmit timer if not currently set, 505 * and not doing an ack or a keep-alive probe. 506 * Initial value for retransmit timer is smoothed 507 * round-trip time + 2 * round-trip time variance. 508 * Initialize shift counter which is used for backoff 509 * of retransmit time. 510 */ 511 if (tp->t_timer[TCPT_REXMT] == 0 && 512 tp->snd_nxt != tp->snd_una) { 513 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 514 if (tp->t_timer[TCPT_PERSIST]) { 515 tp->t_timer[TCPT_PERSIST] = 0; 516 tp->t_rxtshift = 0; 517 } 518 } 519 } else 520 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 521 tp->snd_max = tp->snd_nxt + len; 522 523 /* 524 * Fill in IP length and desired time to live and 525 * send to IP level. There should be a better way 526 * to handle ttl and tos; we could keep them in 527 * the template, but need a way to checksum without them. 528 */ 529 m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */ 530 531 { 532 533 ((struct ip *)ti)->ip_len = m->m_len; 534 535 ((struct ip *)ti)->ip_ttl = IPDEFTTL; 536 ((struct ip *)ti)->ip_tos = so->so_iptos; 537 538/* #if BSD >= 43 */ 539 /* Don't do IP options... */ 540/* error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, 541 * so->so_options & SO_DONTROUTE, 0); 542 */ 543 error = ip_output(so, m); 544 545/* #else 546 * error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route, 547 * so->so_options & SO_DONTROUTE); 548 * #endif 549 */ 550 } 551 if (error) { 552out: 553/* if (error == ENOBUFS) { 554 * tcp_quench(tp->t_inpcb, 0); 555 * return (0); 556 * } 557 */ 558/* if ((error == EHOSTUNREACH || error == ENETDOWN) 559 * && TCPS_HAVERCVDSYN(tp->t_state)) { 560 * tp->t_softerror = error; 561 * return (0); 562 * } 563 */ 564 return (error); 565 } 566 STAT(tcpstat.tcps_sndtotal++); 567 568 /* 569 * Data sent (as far as we can tell). 570 * If this advertises a larger window than any other segment, 571 * then remember the size of the advertised window. 572 * Any pending ACK has now been sent. 573 */ 574 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 575 tp->rcv_adv = tp->rcv_nxt + win; 576 tp->last_ack_sent = tp->rcv_nxt; 577 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 578 if (sendalot) 579 goto again; 580 581 return (0); 582} 583 584void 585tcp_setpersist(tp) 586 register struct tcpcb *tp; 587{ 588 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 589 590/* if (tp->t_timer[TCPT_REXMT]) 591 * panic("tcp_output REXMT"); 592 */ 593 /* 594 * Start/restart persistence timer. 595 */ 596 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 597 t * tcp_backoff[tp->t_rxtshift], 598 TCPTV_PERSMIN, TCPTV_PERSMAX); 599 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 600 tp->t_rxtshift++; 601} 602