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