1 /* $OpenBSD: tcp_output.c,v 1.68 2004/05/31 20:04:44 brad Exp $ */ 2 /* $NetBSD: tcp_output.c,v 1.16 1997/06/03 16:17:09 kml Exp $ */ 3 4 /* 5 * Copyright (c) 1982, 1986, 1988, 1990, 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * @(#)COPYRIGHT 1.1 (NRL) 17 January 1995 33 * 34 * NRL grants permission for redistribution and use in source and binary 35 * forms, with or without modification, of the software and documentation 36 * created at NRL provided that the following conditions are met: 37 * 38 * 1. Redistributions of source code must retain the above copyright 39 * notice, this list of conditions and the following disclaimer. 40 * 2. Redistributions in binary form must reproduce the above copyright 41 * notice, this list of conditions and the following disclaimer in the 42 * documentation and/or other materials provided with the distribution. 43 * 3. All advertising materials mentioning features or use of this software 44 * must display the following acknowledgements: 45 * This product includes software developed by the University of 46 * California, Berkeley and its contributors. 47 * This product includes software developed at the Information 48 * Technology Division, US Naval Research Laboratory. 49 * 4. Neither the name of the NRL nor the names of its contributors 50 * may be used to endorse or promote products derived from this software 51 * without specific prior written permission. 52 * 53 * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS 54 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 55 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 56 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NRL OR 57 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 58 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 59 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 60 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 61 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 62 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 63 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 64 * 65 * The views and conclusions contained in the software and documentation 66 * are those of the authors and should not be interpreted as representing 67 * official policies, either expressed or implied, of the US Naval 68 * Research Laboratory (NRL). 69 */ 70 71 #include <sys/param.h> 72 #include <sys/systm.h> 73 #include <sys/mbuf.h> 74 #include <sys/protosw.h> 75 #include <sys/socket.h> 76 #include <sys/socketvar.h> 77 #include <sys/kernel.h> 78 79 #include <net/route.h> 80 #include <net/if.h> 81 82 #include <netinet/in.h> 83 #include <netinet/in_systm.h> 84 #include <netinet/ip.h> 85 #include <netinet/in_pcb.h> 86 #include <netinet/ip_var.h> 87 #include <netinet/tcp.h> 88 #define TCPOUTFLAGS 89 #include <netinet/tcp_fsm.h> 90 #include <netinet/tcp_seq.h> 91 #include <netinet/tcp_timer.h> 92 #include <netinet/tcp_var.h> 93 #include <netinet/tcpip.h> 94 #include <netinet/tcp_debug.h> 95 96 #ifdef TUBA 97 #include <netiso/iso.h> 98 #include <netiso/tuba_table.h> 99 #endif 100 101 #ifdef INET6 102 #include <netinet6/tcpipv6.h> 103 #include <netinet6/in6_var.h> 104 #endif /* INET6 */ 105 106 #ifdef TCP_SIGNATURE 107 #include <crypto/md5.h> 108 #endif /* TCP_SIGNATURE */ 109 110 #ifdef notyet 111 extern struct mbuf *m_copypack(); 112 #endif 113 114 #ifdef TCP_SACK 115 extern int tcprexmtthresh; 116 #endif 117 118 #ifdef TCP_SACK 119 #ifdef TCP_SACK_DEBUG 120 void tcp_print_holes(struct tcpcb *tp); 121 122 void 123 tcp_print_holes(struct tcpcb *tp) 124 { 125 struct sackhole *p = tp->snd_holes; 126 if (p == 0) 127 return; 128 printf("Hole report: start--end dups rxmit\n"); 129 while (p) { 130 printf("%x--%x d %d r %x\n", p->start, p->end, p->dups, 131 p->rxmit); 132 p = p->next; 133 } 134 printf("\n"); 135 } 136 #endif /* TCP_SACK_DEBUG */ 137 138 /* 139 * Returns pointer to a sackhole if there are any pending retransmissions; 140 * NULL otherwise. 141 */ 142 struct sackhole * 143 tcp_sack_output(struct tcpcb *tp) 144 { 145 struct sackhole *p; 146 147 if (!tp->sack_enable) 148 return (NULL); 149 p = tp->snd_holes; 150 while (p) { 151 #ifndef TCP_FACK 152 if (p->dups >= tcprexmtthresh && SEQ_LT(p->rxmit, p->end)) { 153 #else 154 /* In FACK, if p->dups is less than tcprexmtthresh, but 155 * snd_fack advances more than tcprextmtthresh * tp->t_maxseg, 156 * tcp_input() will try fast retransmit. This forces output. 157 */ 158 if ((p->dups >= tcprexmtthresh || 159 tp->t_dupacks == tcprexmtthresh) && 160 SEQ_LT(p->rxmit, p->end)) { 161 #endif /* TCP_FACK */ 162 if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */ 163 p = p->next; 164 continue; 165 } 166 #ifdef TCP_SACK_DEBUG 167 if (p) 168 tcp_print_holes(tp); 169 #endif 170 return (p); 171 } 172 p = p->next; 173 } 174 return (NULL); 175 } 176 177 /* 178 * After a timeout, the SACK list may be rebuilt. This SACK information 179 * should be used to avoid retransmitting SACKed data. This function 180 * traverses the SACK list to see if snd_nxt should be moved forward. 181 */ 182 183 void 184 tcp_sack_adjust(struct tcpcb *tp) 185 { 186 struct sackhole *cur = tp->snd_holes; 187 if (cur == NULL) 188 return; /* No holes */ 189 if (SEQ_GEQ(tp->snd_nxt, tp->rcv_lastsack)) 190 return; /* We're already beyond any SACKed blocks */ 191 /* 192 * Two cases for which we want to advance snd_nxt: 193 * i) snd_nxt lies between end of one hole and beginning of another 194 * ii) snd_nxt lies between end of last hole and rcv_lastsack 195 */ 196 while (cur->next) { 197 if (SEQ_LT(tp->snd_nxt, cur->end)) 198 return; 199 if (SEQ_GEQ(tp->snd_nxt, cur->next->start)) 200 cur = cur->next; 201 else { 202 tp->snd_nxt = cur->next->start; 203 return; 204 } 205 } 206 if (SEQ_LT(tp->snd_nxt, cur->end)) 207 return; 208 tp->snd_nxt = tp->rcv_lastsack; 209 return; 210 } 211 #endif /* TCP_SACK */ 212 213 /* 214 * Tcp output routine: figure out what should be sent and send it. 215 */ 216 int 217 tcp_output(tp) 218 struct tcpcb *tp; 219 { 220 struct socket *so = tp->t_inpcb->inp_socket; 221 long len, win, txmaxseg; 222 int off, flags, error; 223 struct mbuf *m; 224 struct tcphdr *th; 225 u_char opt[MAX_TCPOPTLEN]; 226 unsigned int optlen, hdrlen; 227 int idle, sendalot = 0; 228 #ifdef TCP_SACK 229 int i, sack_rxmit = 0; 230 struct sackhole *p; 231 #endif 232 #if defined(TCP_SACK) 233 int maxburst = TCP_MAXBURST; 234 #endif 235 #ifdef TCP_SIGNATURE 236 unsigned int sigoff; 237 #endif /* TCP_SIGNATURE */ 238 #ifdef TCP_ECN 239 int needect; 240 #endif 241 242 #if defined(TCP_SACK) && defined(TCP_SIGNATURE) && defined(DIAGNOSTIC) 243 if (tp->sack_enable && (tp->t_flags & TF_SIGNATURE)) 244 return (EINVAL); 245 #endif /* defined(TCP_SACK) && defined(TCP_SIGNATURE) && defined(DIAGNOSTIC) */ 246 247 /* 248 * Determine length of data that should be transmitted, 249 * and flags that will be used. 250 * If there is some data or critical controls (SYN, RST) 251 * to send, then transmit; otherwise, investigate further. 252 */ 253 idle = (tp->snd_max == tp->snd_una); 254 if (idle && (tcp_now - tp->t_rcvtime) >= tp->t_rxtcur) 255 /* 256 * We have been idle for "a while" and no acks are 257 * expected to clock out any data we send -- 258 * slow start to get ack "clock" running again. 259 */ 260 tp->snd_cwnd = tp->t_maxseg; 261 again: 262 #ifdef TCP_SACK 263 /* 264 * If we've recently taken a timeout, snd_max will be greater than 265 * snd_nxt. There may be SACK information that allows us to avoid 266 * resending already delivered data. Adjust snd_nxt accordingly. 267 */ 268 if (tp->sack_enable && SEQ_LT(tp->snd_nxt, tp->snd_max)) 269 tcp_sack_adjust(tp); 270 #endif 271 off = tp->snd_nxt - tp->snd_una; 272 #if defined(TCP_SACK) && defined(TCP_FACK) 273 /* Normally, sendable data is limited by off < tp->snd_cwnd. 274 * But in FACK, sendable data is limited by snd_awnd < snd_cwnd, 275 * regardless of offset. 276 */ 277 if (tp->sack_enable && (tp->t_dupacks > tcprexmtthresh)) 278 win = tp->snd_wnd; 279 else 280 #endif 281 win = ulmin(tp->snd_wnd, tp->snd_cwnd); 282 283 flags = tcp_outflags[tp->t_state]; 284 285 #ifdef TCP_SACK 286 /* 287 * Send any SACK-generated retransmissions. If we're explicitly trying 288 * to send out new data (when sendalot is 1), bypass this function. 289 * If we retransmit in fast recovery mode, decrement snd_cwnd, since 290 * we're replacing a (future) new transmission with a retransmission 291 * now, and we previously incremented snd_cwnd in tcp_input(). 292 */ 293 if (tp->sack_enable && !sendalot) { 294 if (tp->t_dupacks >= tcprexmtthresh && 295 (p = tcp_sack_output(tp))) { 296 off = p->rxmit - tp->snd_una; 297 sack_rxmit = 1; 298 #if 0 299 /* Coalesce holes into a single retransmission */ 300 #endif 301 len = min(tp->t_maxseg, p->end - p->rxmit); 302 #ifndef TCP_FACK 303 /* in FACK, hold snd_cwnd constant during recovery */ 304 if (SEQ_LT(tp->snd_una, tp->snd_last)) 305 tp->snd_cwnd -= tp->t_maxseg; 306 #endif 307 } 308 } 309 #endif /* TCP_SACK */ 310 311 sendalot = 0; 312 /* 313 * If in persist timeout with window of 0, send 1 byte. 314 * Otherwise, if window is small but nonzero 315 * and timer expired, we will send what we can 316 * and go to transmit state. 317 */ 318 if (tp->t_force) { 319 if (win == 0) { 320 /* 321 * If we still have some data to send, then 322 * clear the FIN bit. Usually this would 323 * happen below when it realizes that we 324 * aren't sending all the data. However, 325 * if we have exactly 1 byte of unset data, 326 * then it won't clear the FIN bit below, 327 * and if we are in persist state, we wind 328 * up sending the packet without recording 329 * that we sent the FIN bit. 330 * 331 * We can't just blindly clear the FIN bit, 332 * because if we don't have any more data 333 * to send then the probe will be the FIN 334 * itself. 335 */ 336 if (off < so->so_snd.sb_cc) 337 flags &= ~TH_FIN; 338 win = 1; 339 } else { 340 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 341 tp->t_rxtshift = 0; 342 } 343 } 344 345 #ifdef TCP_SACK 346 if (!sack_rxmit) { 347 #endif 348 len = ulmin(so->so_snd.sb_cc, win) - off; 349 350 #if defined(TCP_SACK) && defined(TCP_FACK) 351 /* 352 * If we're in fast recovery (SEQ_GT(tp->snd_last, tp->snd_una)), and 353 * amount of outstanding data (snd_awnd) is >= snd_cwnd, then 354 * do not send data (like zero window conditions) 355 */ 356 if (tp->sack_enable && len && SEQ_GT(tp->snd_last, tp->snd_una) && 357 (tp->snd_awnd >= tp->snd_cwnd)) 358 len = 0; 359 #endif /* TCP_FACK */ 360 #ifdef TCP_SACK 361 } 362 #endif 363 364 if (len < 0) { 365 /* 366 * If FIN has been sent but not acked, 367 * but we haven't been called to retransmit, 368 * len will be -1. Otherwise, window shrank 369 * after we sent into it. If window shrank to 0, 370 * cancel pending retransmit, pull snd_nxt back 371 * to (closed) window, and set the persist timer 372 * if it isn't already going. If the window didn't 373 * close completely, just wait for an ACK. 374 */ 375 len = 0; 376 if (win == 0) { 377 TCP_TIMER_DISARM(tp, TCPT_REXMT); 378 tp->t_rxtshift = 0; 379 tp->snd_nxt = tp->snd_una; 380 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) 381 tcp_setpersist(tp); 382 } 383 } 384 385 /* 386 * Never send more than half a buffer full. This insures that we can 387 * always keep 2 packets on the wire, no matter what SO_SNDBUF is, and 388 * therefore acks will never be delayed unless we run out of data to 389 * transmit. 390 */ 391 txmaxseg = ulmin(so->so_snd.sb_hiwat / 2, tp->t_maxseg); 392 393 if (len > txmaxseg) { 394 len = txmaxseg; 395 sendalot = 1; 396 } 397 if (off + len < so->so_snd.sb_cc) 398 flags &= ~TH_FIN; 399 400 win = sbspace(&so->so_rcv); 401 402 /* 403 * Sender silly window avoidance. If connection is idle 404 * and can send all data, a maximum segment, 405 * at least a maximum default-size segment do it, 406 * or are forced, do it; otherwise don't bother. 407 * If peer's buffer is tiny, then send 408 * when window is at least half open. 409 * If retransmitting (possibly after persist timer forced us 410 * to send into a small window), then must resend. 411 */ 412 if (len) { 413 if (len == txmaxseg) 414 goto send; 415 if ((idle || tp->t_flags & TF_NODELAY) && 416 len + off >= so->so_snd.sb_cc) 417 goto send; 418 if (tp->t_force) 419 goto send; 420 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0) 421 goto send; 422 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 423 goto send; 424 #ifdef TCP_SACK 425 if (sack_rxmit) 426 goto send; 427 #endif 428 } 429 430 /* 431 * Compare available window to amount of window 432 * known to peer (as advertised window less 433 * next expected input). If the difference is at least two 434 * max size segments, or at least 50% of the maximum possible 435 * window, then want to send a window update to peer. 436 */ 437 if (win > 0) { 438 /* 439 * "adv" is the amount we can increase the window, 440 * taking into account that we are limited by 441 * TCP_MAXWIN << tp->rcv_scale. 442 */ 443 long adv = lmin(win, (long)TCP_MAXWIN << tp->rcv_scale) - 444 (tp->rcv_adv - tp->rcv_nxt); 445 446 if (adv >= (long) (2 * tp->t_maxseg)) 447 goto send; 448 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 449 goto send; 450 } 451 452 /* 453 * Send if we owe peer an ACK. 454 */ 455 if (tp->t_flags & TF_ACKNOW) 456 goto send; 457 if (flags & (TH_SYN|TH_RST)) 458 goto send; 459 if (SEQ_GT(tp->snd_up, tp->snd_una)) 460 goto send; 461 /* 462 * If our state indicates that FIN should be sent 463 * and we have not yet done so, or we're retransmitting the FIN, 464 * then we need to send. 465 */ 466 if (flags & TH_FIN && 467 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 468 goto send; 469 #ifdef TCP_SACK 470 /* 471 * In SACK, it is possible for tcp_output to fail to send a segment 472 * after the retransmission timer has been turned off. Make sure 473 * that the retransmission timer is set. 474 */ 475 if (SEQ_GT(tp->snd_max, tp->snd_una) && 476 TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 477 TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 478 TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); 479 return (0); 480 } 481 #endif /* TCP_SACK */ 482 483 /* 484 * TCP window updates are not reliable, rather a polling protocol 485 * using ``persist'' packets is used to insure receipt of window 486 * updates. The three ``states'' for the output side are: 487 * idle not doing retransmits or persists 488 * persisting to move a small or zero window 489 * (re)transmitting and thereby not persisting 490 * 491 * tp->t_timer[TCPT_PERSIST] 492 * is set when we are in persist state. 493 * tp->t_force 494 * is set when we are called to send a persist packet. 495 * tp->t_timer[TCPT_REXMT] 496 * is set when we are retransmitting 497 * The output side is idle when both timers are zero. 498 * 499 * If send window is too small, there is data to transmit, and no 500 * retransmit or persist is pending, then go to persist state. 501 * If nothing happens soon, send when timer expires: 502 * if window is nonzero, transmit what we can, 503 * otherwise force out a byte. 504 */ 505 if (so->so_snd.sb_cc && TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 506 TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 507 tp->t_rxtshift = 0; 508 tcp_setpersist(tp); 509 } 510 511 /* 512 * No reason to send a segment, just return. 513 */ 514 return (0); 515 516 send: 517 /* 518 * Before ESTABLISHED, force sending of initial options 519 * unless TCP set not to do any options. 520 * NOTE: we assume that the IP/TCP header plus TCP options 521 * always fit in a single mbuf, leaving room for a maximum 522 * link header, i.e. 523 * max_linkhdr + sizeof(network header) + sizeof(struct tcphdr + 524 * optlen <= MHLEN 525 */ 526 optlen = 0; 527 528 switch (tp->pf) { 529 case 0: /*default to PF_INET*/ 530 #ifdef INET 531 case PF_INET: 532 hdrlen = sizeof(struct ip) + sizeof(struct tcphdr); 533 break; 534 #endif /* INET */ 535 #ifdef INET6 536 case PF_INET6: 537 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); 538 break; 539 #endif /* INET6 */ 540 default: 541 return (EPFNOSUPPORT); 542 } 543 544 if (flags & TH_SYN) { 545 tp->snd_nxt = tp->iss; 546 if ((tp->t_flags & TF_NOOPT) == 0) { 547 u_int16_t mss; 548 549 opt[0] = TCPOPT_MAXSEG; 550 opt[1] = 4; 551 mss = htons((u_int16_t) tcp_mss(tp, 0)); 552 bcopy((caddr_t)&mss, (caddr_t)(opt + 2), sizeof(mss)); 553 optlen = 4; 554 555 if (flags & TH_ACK) 556 tcp_mss_update(tp); 557 #ifdef TCP_SACK 558 /* 559 * If this is the first SYN of connection (not a SYN 560 * ACK), include SACK_PERMIT_HDR option. If this is a 561 * SYN ACK, include SACK_PERMIT_HDR option if peer has 562 * already done so. 563 */ 564 if (tp->sack_enable && ((flags & TH_ACK) == 0 || 565 (tp->t_flags & TF_SACK_PERMIT))) { 566 *((u_int32_t *) (opt + optlen)) = 567 htonl(TCPOPT_SACK_PERMIT_HDR); 568 optlen += 4; 569 } 570 #endif 571 572 if ((tp->t_flags & TF_REQ_SCALE) && 573 ((flags & TH_ACK) == 0 || 574 (tp->t_flags & TF_RCVD_SCALE))) { 575 *((u_int32_t *) (opt + optlen)) = htonl( 576 TCPOPT_NOP << 24 | 577 TCPOPT_WINDOW << 16 | 578 TCPOLEN_WINDOW << 8 | 579 tp->request_r_scale); 580 optlen += 4; 581 } 582 } 583 } 584 585 /* 586 * Send a timestamp and echo-reply if this is a SYN and our side 587 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 588 * and our peer have sent timestamps in our SYN's. 589 */ 590 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 591 (flags & TH_RST) == 0 && 592 ((flags & (TH_SYN|TH_ACK)) == TH_SYN || 593 (tp->t_flags & TF_RCVD_TSTMP))) { 594 u_int32_t *lp = (u_int32_t *)(opt + optlen); 595 596 /* Form timestamp option as shown in appendix A of RFC 1323. */ 597 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 598 *lp++ = htonl(tcp_now); 599 *lp = htonl(tp->ts_recent); 600 optlen += TCPOLEN_TSTAMP_APPA; 601 } 602 603 #ifdef TCP_SIGNATURE 604 if (tp->t_flags & TF_SIGNATURE) { 605 u_int8_t *bp = (u_int8_t *)(opt + optlen); 606 607 /* Send signature option */ 608 *(bp++) = TCPOPT_SIGNATURE; 609 *(bp++) = TCPOLEN_SIGNATURE; 610 sigoff = optlen + 2; 611 612 { 613 unsigned int i; 614 615 for (i = 0; i < 16; i++) 616 *(bp++) = 0; 617 } 618 619 620 /* Pad options list to the next 32 bit boundary and 621 * terminate it. 622 */ 623 *bp++ = TCPOPT_NOP; 624 *bp++ = TCPOPT_EOL; 625 626 optlen += TCPOLEN_SIGLEN; 627 } 628 #endif /* TCP_SIGNATURE */ 629 630 #ifdef TCP_SACK 631 /* 632 * Send SACKs if necessary. This should be the last option processed. 633 * Only as many SACKs are sent as are permitted by the maximum options 634 * size. No more than three SACKs are sent. 635 */ 636 if (tp->sack_enable && tp->t_state == TCPS_ESTABLISHED && 637 (tp->t_flags & (TF_SACK_PERMIT|TF_NOOPT)) == TF_SACK_PERMIT && 638 tp->rcv_numsacks) { 639 u_int32_t *lp = (u_int32_t *)(opt + optlen); 640 u_int32_t *olp = lp++; 641 int count = 0; /* actual number of SACKs inserted */ 642 int maxsack = (MAX_TCPOPTLEN - (optlen + 4))/TCPOLEN_SACK; 643 644 maxsack = min(maxsack, TCP_MAX_SACK); 645 for (i = 0; (i < tp->rcv_numsacks && count < maxsack); i++) { 646 struct sackblk sack = tp->sackblks[i]; 647 if (sack.start == 0 && sack.end == 0) 648 continue; 649 *lp++ = htonl(sack.start); 650 *lp++ = htonl(sack.end); 651 count++; 652 } 653 *olp = htonl(TCPOPT_SACK_HDR|(TCPOLEN_SACK*count+2)); 654 optlen += TCPOLEN_SACK*count + 4; /* including leading NOPs */ 655 } 656 #endif /* TCP_SACK */ 657 658 #ifdef DIAGNOSTIC 659 if (optlen > MAX_TCPOPTLEN) 660 panic("tcp_output: options too long"); 661 #endif /* DIAGNOSTIC */ 662 663 hdrlen += optlen; 664 665 /* 666 * Adjust data length if insertion of options will 667 * bump the packet length beyond the t_maxopd length. 668 */ 669 if (len > tp->t_maxopd - optlen) { 670 len = tp->t_maxopd - optlen; 671 sendalot = 1; 672 flags &= ~TH_FIN; 673 } 674 675 #ifdef DIAGNOSTIC 676 if (max_linkhdr + hdrlen > MCLBYTES) 677 panic("tcphdr too big"); 678 #endif 679 680 /* 681 * Grab a header mbuf, attaching a copy of data to 682 * be transmitted, and initialize the header from 683 * the template for sends on this connection. 684 */ 685 if (len) { 686 if (tp->t_force && len == 1) 687 tcpstat.tcps_sndprobe++; 688 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 689 tcpstat.tcps_sndrexmitpack++; 690 tcpstat.tcps_sndrexmitbyte += len; 691 } else { 692 tcpstat.tcps_sndpack++; 693 tcpstat.tcps_sndbyte += len; 694 } 695 #ifdef notyet 696 if ((m = m_copypack(so->so_snd.sb_mb, off, 697 (int)len, max_linkhdr + hdrlen)) == 0) { 698 error = ENOBUFS; 699 goto out; 700 } 701 /* 702 * m_copypack left space for our hdr; use it. 703 */ 704 m->m_len += hdrlen; 705 m->m_data -= hdrlen; 706 #else 707 MGETHDR(m, M_DONTWAIT, MT_HEADER); 708 if (m != NULL && max_linkhdr + hdrlen > MHLEN) { 709 MCLGET(m, M_DONTWAIT); 710 if ((m->m_flags & M_EXT) == 0) { 711 m_freem(m); 712 m = NULL; 713 } 714 } 715 if (m == NULL) { 716 error = ENOBUFS; 717 goto out; 718 } 719 m->m_data += max_linkhdr; 720 m->m_len = hdrlen; 721 if (len <= M_TRAILINGSPACE(m)) { 722 m_copydata(so->so_snd.sb_mb, off, (int) len, 723 mtod(m, caddr_t) + hdrlen); 724 m->m_len += len; 725 } else { 726 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len); 727 if (m->m_next == 0) { 728 (void) m_free(m); 729 error = ENOBUFS; 730 goto out; 731 } 732 } 733 #endif 734 /* 735 * If we're sending everything we've got, set PUSH. 736 * (This will keep happy those implementations which only 737 * give data to the user when a buffer fills or 738 * a PUSH comes in.) 739 */ 740 if (off + len == so->so_snd.sb_cc) 741 flags |= TH_PUSH; 742 } else { 743 if (tp->t_flags & TF_ACKNOW) 744 tcpstat.tcps_sndacks++; 745 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 746 tcpstat.tcps_sndctrl++; 747 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 748 tcpstat.tcps_sndurg++; 749 else 750 tcpstat.tcps_sndwinup++; 751 752 MGETHDR(m, M_DONTWAIT, MT_HEADER); 753 if (m != NULL && max_linkhdr + hdrlen > MHLEN) { 754 MCLGET(m, M_DONTWAIT); 755 if ((m->m_flags & M_EXT) == 0) { 756 m_freem(m); 757 m = NULL; 758 } 759 } 760 if (m == NULL) { 761 error = ENOBUFS; 762 goto out; 763 } 764 m->m_data += max_linkhdr; 765 m->m_len = hdrlen; 766 } 767 m->m_pkthdr.rcvif = (struct ifnet *)0; 768 769 if (!tp->t_template) 770 panic("tcp_output"); 771 #ifdef DIAGNOSTIC 772 if (tp->t_template->m_len != hdrlen - optlen) 773 panic("tcp_output: template len != hdrlen - optlen"); 774 #endif /* DIAGNOSTIC */ 775 bcopy(mtod(tp->t_template, caddr_t), mtod(m, caddr_t), 776 tp->t_template->m_len); 777 th = (struct tcphdr *)(mtod(m, caddr_t) + tp->t_template->m_len - 778 sizeof(struct tcphdr)); 779 780 /* 781 * Fill in fields, remembering maximum advertised 782 * window for use in delaying messages about window sizes. 783 * If resending a FIN, be sure not to use a new sequence number. 784 */ 785 if ((flags & TH_FIN) && (tp->t_flags & TF_SENTFIN) && 786 (tp->snd_nxt == tp->snd_max)) 787 tp->snd_nxt--; 788 /* 789 * If we are doing retransmissions, then snd_nxt will 790 * not reflect the first unsent octet. For ACK only 791 * packets, we do not want the sequence number of the 792 * retransmitted packet, we want the sequence number 793 * of the next unsent octet. So, if there is no data 794 * (and no SYN or FIN), use snd_max instead of snd_nxt 795 * when filling in ti_seq. But if we are in persist 796 * state, snd_max might reflect one byte beyond the 797 * right edge of the window, so use snd_nxt in that 798 * case, since we know we aren't doing a retransmission. 799 * (retransmit and persist are mutually exclusive...) 800 */ 801 if (len || (flags & (TH_SYN|TH_FIN)) || TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) 802 th->th_seq = htonl(tp->snd_nxt); 803 else 804 th->th_seq = htonl(tp->snd_max); 805 806 #ifdef TCP_SACK 807 if (sack_rxmit) { 808 /* 809 * If sendalot was turned on (due to option stuffing), turn it 810 * off. Properly set th_seq field. Advance the ret'x pointer 811 * by len. 812 */ 813 if (sendalot) 814 sendalot = 0; 815 th->th_seq = htonl(p->rxmit); 816 p->rxmit += len; 817 #if defined(TCP_SACK) && defined(TCP_FACK) 818 tp->retran_data += len; 819 #endif /* TCP_FACK */ 820 } 821 #endif /* TCP_SACK */ 822 823 th->th_ack = htonl(tp->rcv_nxt); 824 if (optlen) { 825 bcopy((caddr_t)opt, (caddr_t)(th + 1), optlen); 826 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 827 } 828 #ifdef TCP_ECN 829 if (tcp_do_ecn) { 830 /* 831 * if we have received congestion experienced segs, 832 * set ECE bit. 833 */ 834 if (tp->t_flags & TF_RCVD_CE) { 835 flags |= TH_ECE; 836 tcpstat.tcps_ecn_sndece++; 837 } 838 if (!(tp->t_flags & TF_DISABLE_ECN)) { 839 /* 840 * if this is a SYN seg, set ECE and CWR. 841 * set only ECE for SYN-ACK if peer supports ECN. 842 */ 843 if ((flags & (TH_SYN|TH_ACK)) == TH_SYN) 844 flags |= (TH_ECE|TH_CWR); 845 else if ((tp->t_flags & TF_ECN_PERMIT) && 846 (flags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) 847 flags |= TH_ECE; 848 } 849 /* 850 * if we have reduced the congestion window, notify 851 * the peer by setting CWR bit. 852 */ 853 if ((tp->t_flags & TF_ECN_PERMIT) && 854 (tp->t_flags & TF_SEND_CWR)) { 855 flags |= TH_CWR; 856 tp->t_flags &= ~TF_SEND_CWR; 857 tcpstat.tcps_ecn_sndcwr++; 858 } 859 } 860 #endif 861 th->th_flags = flags; 862 863 /* 864 * Calculate receive window. Don't shrink window, 865 * but avoid silly window syndrome. 866 */ 867 if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg) 868 win = 0; 869 if (win > (long)TCP_MAXWIN << tp->rcv_scale) 870 win = (long)TCP_MAXWIN << tp->rcv_scale; 871 if (win < (long)(int32_t)(tp->rcv_adv - tp->rcv_nxt)) 872 win = (long)(int32_t)(tp->rcv_adv - tp->rcv_nxt); 873 if (flags & TH_RST) 874 win = 0; 875 th->th_win = htons((u_int16_t) (win>>tp->rcv_scale)); 876 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 877 u_int32_t urp = tp->snd_up - tp->snd_nxt; 878 if (urp > IP_MAXPACKET) 879 urp = IP_MAXPACKET; 880 th->th_urp = htons((u_int16_t)urp); 881 th->th_flags |= TH_URG; 882 } else 883 /* 884 * If no urgent pointer to send, then we pull 885 * the urgent pointer to the left edge of the send window 886 * so that it doesn't drift into the send window on sequence 887 * number wraparound. 888 */ 889 tp->snd_up = tp->snd_una; /* drag it along */ 890 891 #ifdef TCP_SIGNATURE 892 if (tp->t_flags & TF_SIGNATURE) { 893 MD5_CTX ctx; 894 union sockaddr_union src, dst; 895 struct tdb *tdb; 896 897 bzero(&src, sizeof(union sockaddr_union)); 898 bzero(&dst, sizeof(union sockaddr_union)); 899 900 switch (tp->pf) { 901 case 0: /*default to PF_INET*/ 902 #ifdef INET 903 case AF_INET: 904 src.sa.sa_len = sizeof(struct sockaddr_in); 905 src.sa.sa_family = AF_INET; 906 src.sin.sin_addr = mtod(m, struct ip *)->ip_src; 907 dst.sa.sa_len = sizeof(struct sockaddr_in); 908 dst.sa.sa_family = AF_INET; 909 dst.sin.sin_addr = mtod(m, struct ip *)->ip_dst; 910 break; 911 #endif /* INET */ 912 #ifdef INET6 913 case AF_INET6: 914 src.sa.sa_len = sizeof(struct sockaddr_in6); 915 src.sa.sa_family = AF_INET6; 916 src.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_src; 917 dst.sa.sa_len = sizeof(struct sockaddr_in6); 918 dst.sa.sa_family = AF_INET6; 919 dst.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_dst; 920 break; 921 #endif /* INET6 */ 922 } 923 924 /* XXX gettdbbysrcdst() should really be called at spltdb(). */ 925 /* XXX this is splsoftnet(), currently they are the same. */ 926 tdb = gettdbbysrcdst(0, &src, &dst, IPPROTO_TCP); 927 if (tdb == NULL) 928 return (EPERM); 929 930 MD5Init(&ctx); 931 932 switch (tp->pf) { 933 case 0: /*default to PF_INET*/ 934 #ifdef INET 935 case AF_INET: 936 { 937 struct ippseudo ippseudo; 938 struct ipovly *ipovly; 939 940 ipovly = mtod(m, struct ipovly *); 941 942 ippseudo.ippseudo_src = ipovly->ih_src; 943 ippseudo.ippseudo_dst = ipovly->ih_dst; 944 ippseudo.ippseudo_pad = 0; 945 ippseudo.ippseudo_p = IPPROTO_TCP; 946 ippseudo.ippseudo_len = ntohs(ipovly->ih_len) + len + 947 optlen; 948 ippseudo.ippseudo_len = htons(ippseudo.ippseudo_len); 949 MD5Update(&ctx, (char *)&ippseudo, 950 sizeof(struct ippseudo)); 951 } 952 break; 953 #endif /* INET */ 954 #ifdef INET6 955 case AF_INET6: 956 { 957 struct ip6_hdr_pseudo ip6pseudo; 958 struct ip6_hdr *ip6; 959 960 ip6 = mtod(m, struct ip6_hdr *); 961 bzero(&ip6pseudo, sizeof(ip6pseudo)); 962 ip6pseudo.ip6ph_src = ip6->ip6_src; 963 ip6pseudo.ip6ph_dst = ip6->ip6_dst; 964 in6_clearscope(&ip6pseudo.ip6ph_src); 965 in6_clearscope(&ip6pseudo.ip6ph_dst); 966 ip6pseudo.ip6ph_nxt = IPPROTO_TCP; 967 ip6pseudo.ip6ph_len = 968 htonl(sizeof(struct tcphdr) + len + optlen); 969 970 MD5Update(&ctx, (char *)&ip6pseudo, 971 sizeof(ip6pseudo)); 972 } 973 break; 974 #endif /* INET6 */ 975 } 976 977 { 978 u_int16_t thsum = th->th_sum; 979 980 /* RFC 2385 requires th_sum == 0 */ 981 th->th_sum = 0; 982 MD5Update(&ctx, (char *)th, sizeof(struct tcphdr)); 983 th->th_sum = thsum; 984 } 985 986 if (len && m_apply(m, hdrlen, len, tcp_signature_apply, 987 (caddr_t)&ctx)) 988 return (EINVAL); 989 990 MD5Update(&ctx, tdb->tdb_amxkey, tdb->tdb_amxkeylen); 991 MD5Final(mtod(m, caddr_t) + hdrlen - optlen + sigoff, &ctx); 992 } 993 #endif /* TCP_SIGNATURE */ 994 995 /* 996 * Put TCP length in extended header, and then 997 * checksum extended header and data. 998 */ 999 switch (tp->pf) { 1000 case 0: /*default to PF_INET*/ 1001 #ifdef INET 1002 case AF_INET: 1003 /* Defer checksumming until later (ip_output() or hardware) */ 1004 m->m_pkthdr.csum |= M_TCPV4_CSUM_OUT; 1005 if (len + optlen) 1006 th->th_sum = in_cksum_addword(th->th_sum, 1007 htons((u_int16_t)(len + optlen))); 1008 break; 1009 #endif /* INET */ 1010 #ifdef INET6 1011 case AF_INET6: 1012 m->m_pkthdr.len = hdrlen + len; 1013 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr), 1014 hdrlen - sizeof(struct ip6_hdr) + len); 1015 break; 1016 #endif /* INET6 */ 1017 } 1018 1019 /* 1020 * In transmit state, time the transmission and arrange for 1021 * the retransmit. In persist state, just set snd_max. 1022 */ 1023 if (tp->t_force == 0 || TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 1024 tcp_seq startseq = tp->snd_nxt; 1025 1026 /* 1027 * Advance snd_nxt over sequence space of this segment. 1028 */ 1029 if (flags & (TH_SYN|TH_FIN)) { 1030 if (flags & TH_SYN) 1031 tp->snd_nxt++; 1032 if (flags & TH_FIN) { 1033 tp->snd_nxt++; 1034 tp->t_flags |= TF_SENTFIN; 1035 } 1036 } 1037 #ifdef TCP_SACK 1038 if (tp->sack_enable) { 1039 if (sack_rxmit && (p->rxmit != tp->snd_nxt)) { 1040 goto timer; 1041 } 1042 } 1043 #endif 1044 tp->snd_nxt += len; 1045 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1046 tp->snd_max = tp->snd_nxt; 1047 /* 1048 * Time this transmission if not a retransmission and 1049 * not currently timing anything. 1050 */ 1051 if (tp->t_rtttime == 0) { 1052 tp->t_rtttime = tcp_now; 1053 tp->t_rtseq = startseq; 1054 tcpstat.tcps_segstimed++; 1055 } 1056 } 1057 1058 /* 1059 * Set retransmit timer if not currently set, 1060 * and not doing an ack or a keep-alive probe. 1061 * Initial value for retransmit timer is smoothed 1062 * round-trip time + 2 * round-trip time variance. 1063 * Initialize shift counter which is used for backoff 1064 * of retransmit time. 1065 */ 1066 #ifdef TCP_SACK 1067 timer: 1068 if (tp->sack_enable && sack_rxmit && 1069 TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 1070 tp->snd_nxt != tp->snd_max) { 1071 TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); 1072 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) { 1073 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 1074 tp->t_rxtshift = 0; 1075 } 1076 } 1077 #endif 1078 1079 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 1080 tp->snd_nxt != tp->snd_una) { 1081 TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); 1082 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) { 1083 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 1084 tp->t_rxtshift = 0; 1085 } 1086 } 1087 } else 1088 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 1089 tp->snd_max = tp->snd_nxt + len; 1090 1091 /* 1092 * Trace. 1093 */ 1094 if (so->so_options & SO_DEBUG) 1095 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, caddr_t), 0, 1096 len); 1097 1098 /* 1099 * Fill in IP length and desired time to live and 1100 * send to IP level. There should be a better way 1101 * to handle ttl and tos; we could keep them in 1102 * the template, but need a way to checksum without them. 1103 */ 1104 m->m_pkthdr.len = hdrlen + len; 1105 1106 #ifdef TCP_ECN 1107 /* 1108 * if peer is ECN capable, set the ECT bit in the IP header. 1109 * but don't set ECT for a pure ack, a retransmit or a window probe. 1110 */ 1111 needect = 0; 1112 if (tcp_do_ecn && (tp->t_flags & TF_ECN_PERMIT)) { 1113 if (len == 0 || SEQ_LT(tp->snd_nxt, tp->snd_max) || 1114 (tp->t_force && len == 1)) { 1115 /* don't set ECT */ 1116 } else { 1117 needect = 1; 1118 tcpstat.tcps_ecn_sndect++; 1119 } 1120 } 1121 #endif 1122 1123 switch (tp->pf) { 1124 case 0: /*default to PF_INET*/ 1125 #ifdef INET 1126 case AF_INET: 1127 { 1128 struct ip *ip; 1129 1130 ip = mtod(m, struct ip *); 1131 ip->ip_len = htons(m->m_pkthdr.len); 1132 ip->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl; 1133 ip->ip_tos = tp->t_inpcb->inp_ip.ip_tos; 1134 #ifdef TCP_ECN 1135 if (needect) 1136 ip->ip_tos |= IPTOS_ECN_ECT0; 1137 #endif 1138 } 1139 error = ip_output(m, tp->t_inpcb->inp_options, 1140 &tp->t_inpcb->inp_route, 1141 (ip_mtudisc ? IP_MTUDISC : 0) | 1142 (so->so_options & SO_DONTROUTE), 1143 (void *)NULL, tp->t_inpcb); 1144 break; 1145 #endif /* INET */ 1146 #ifdef INET6 1147 case AF_INET6: 1148 { 1149 struct ip6_hdr *ip6; 1150 1151 ip6 = mtod(m, struct ip6_hdr *); 1152 ip6->ip6_plen = m->m_pkthdr.len - 1153 sizeof(struct ip6_hdr); 1154 ip6->ip6_nxt = IPPROTO_TCP; 1155 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL); 1156 #ifdef TCP_ECN 1157 if (needect) 1158 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20); 1159 #endif 1160 } 1161 error = ip6_output(m, tp->t_inpcb->inp_outputopts6, 1162 &tp->t_inpcb->inp_route6, 1163 (so->so_options & SO_DONTROUTE), NULL, NULL); 1164 break; 1165 #endif /* INET6 */ 1166 #ifdef TUBA 1167 case AF_ISO: 1168 if (tp->t_tuba_pcb) 1169 error = tuba_output(m, tp); 1170 break; 1171 #endif /* TUBA */ 1172 } 1173 1174 #if defined(TCP_SACK) && defined(TCP_FACK) 1175 /* Update snd_awnd to reflect the new data that was sent. */ 1176 tp->snd_awnd = tcp_seq_subtract(tp->snd_max, tp->snd_fack) + 1177 tp->retran_data; 1178 #endif /* defined(TCP_SACK) && defined(TCP_FACK) */ 1179 1180 if (error) { 1181 out: 1182 if (error == ENOBUFS) { 1183 tcp_quench(tp->t_inpcb, 0); 1184 return (0); 1185 } 1186 if (error == EMSGSIZE) { 1187 /* 1188 * ip_output() will have already fixed the route 1189 * for us. tcp_mtudisc() will, as its last action, 1190 * initiate retransmission, so it is important to 1191 * not do so here. 1192 */ 1193 tcp_mtudisc(tp->t_inpcb, -1); 1194 return (0); 1195 } 1196 if ((error == EHOSTUNREACH || error == ENETDOWN) && 1197 TCPS_HAVERCVDSYN(tp->t_state)) { 1198 tp->t_softerror = error; 1199 return (0); 1200 } 1201 1202 /* Restart the delayed ACK timer, if necessary. */ 1203 if (tp->t_flags & TF_DELACK) 1204 TCP_RESTART_DELACK(tp); 1205 1206 return (error); 1207 } 1208 tcpstat.tcps_sndtotal++; 1209 if (tp->t_flags & TF_DELACK) 1210 tcpstat.tcps_delack++; 1211 1212 /* 1213 * Data sent (as far as we can tell). 1214 * If this advertises a larger window than any other segment, 1215 * then remember the size of the advertised window. 1216 * Any pending ACK has now been sent. 1217 */ 1218 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 1219 tp->rcv_adv = tp->rcv_nxt + win; 1220 tp->last_ack_sent = tp->rcv_nxt; 1221 tp->t_flags &= ~TF_ACKNOW; 1222 TCP_CLEAR_DELACK(tp); 1223 #if defined(TCP_SACK) 1224 if (sendalot && --maxburst) 1225 #else 1226 if (sendalot) 1227 #endif 1228 goto again; 1229 return (0); 1230 } 1231 1232 void 1233 tcp_setpersist(struct tcpcb *tp) 1234 { 1235 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 1236 int nticks; 1237 1238 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT)) 1239 panic("tcp_output REXMT"); 1240 /* 1241 * Start/restart persistance timer. 1242 */ 1243 if (t < tp->t_rttmin) 1244 t = tp->t_rttmin; 1245 TCPT_RANGESET(nticks, t * tcp_backoff[tp->t_rxtshift], 1246 TCPTV_PERSMIN, TCPTV_PERSMAX); 1247 TCP_TIMER_ARM(tp, TCPT_PERSIST, nticks); 1248 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1249 tp->t_rxtshift++; 1250 } 1251