1 /* $NetBSD: tcp_output.c,v 1.101 2003/08/22 22:00:38 itojun Exp $ */ 2 3 /* 4 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project. 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the project nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 /* 33 * @(#)COPYRIGHT 1.1 (NRL) 17 January 1995 34 * 35 * NRL grants permission for redistribution and use in source and binary 36 * forms, with or without modification, of the software and documentation 37 * created at NRL provided that the following conditions are met: 38 * 39 * 1. Redistributions of source code must retain the above copyright 40 * notice, this list of conditions and the following disclaimer. 41 * 2. Redistributions in binary form must reproduce the above copyright 42 * notice, this list of conditions and the following disclaimer in the 43 * documentation and/or other materials provided with the distribution. 44 * 3. All advertising materials mentioning features or use of this software 45 * must display the following acknowledgements: 46 * This product includes software developed by the University of 47 * California, Berkeley and its contributors. 48 * This product includes software developed at the Information 49 * Technology Division, US Naval Research Laboratory. 50 * 4. Neither the name of the NRL nor the names of its contributors 51 * may be used to endorse or promote products derived from this software 52 * without specific prior written permission. 53 * 54 * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS 55 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 56 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 57 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NRL OR 58 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 59 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 60 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 61 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 62 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 63 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 64 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 65 * 66 * The views and conclusions contained in the software and documentation 67 * are those of the authors and should not be interpreted as representing 68 * official policies, either expressed or implied, of the US Naval 69 * Research Laboratory (NRL). 70 */ 71 72 /*- 73 * Copyright (c) 1997, 1998, 2001 The NetBSD Foundation, Inc. 74 * All rights reserved. 75 * 76 * This code is derived from software contributed to The NetBSD Foundation 77 * by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation 78 * Facility, NASA Ames Research Center. 79 * 80 * Redistribution and use in source and binary forms, with or without 81 * modification, are permitted provided that the following conditions 82 * are met: 83 * 1. Redistributions of source code must retain the above copyright 84 * notice, this list of conditions and the following disclaimer. 85 * 2. Redistributions in binary form must reproduce the above copyright 86 * notice, this list of conditions and the following disclaimer in the 87 * documentation and/or other materials provided with the distribution. 88 * 3. All advertising materials mentioning features or use of this software 89 * must display the following acknowledgement: 90 * This product includes software developed by the NetBSD 91 * Foundation, Inc. and its contributors. 92 * 4. Neither the name of The NetBSD Foundation nor the names of its 93 * contributors may be used to endorse or promote products derived 94 * from this software without specific prior written permission. 95 * 96 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 97 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 98 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 99 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 100 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 101 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 102 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 103 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 104 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 105 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 106 * POSSIBILITY OF SUCH DAMAGE. 107 */ 108 109 /* 110 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 111 * The Regents of the University of California. All rights reserved. 112 * 113 * Redistribution and use in source and binary forms, with or without 114 * modification, are permitted provided that the following conditions 115 * are met: 116 * 1. Redistributions of source code must retain the above copyright 117 * notice, this list of conditions and the following disclaimer. 118 * 2. Redistributions in binary form must reproduce the above copyright 119 * notice, this list of conditions and the following disclaimer in the 120 * documentation and/or other materials provided with the distribution. 121 * 3. Neither the name of the University nor the names of its contributors 122 * may be used to endorse or promote products derived from this software 123 * without specific prior written permission. 124 * 125 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 126 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 127 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 128 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 129 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 130 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 131 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 132 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 133 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 134 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 135 * SUCH DAMAGE. 136 * 137 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95 138 */ 139 140 #include <sys/cdefs.h> 141 __KERNEL_RCSID(0, "$NetBSD: tcp_output.c,v 1.101 2003/08/22 22:00:38 itojun Exp $"); 142 143 #include "opt_inet.h" 144 #include "opt_ipsec.h" 145 #include "opt_tcp_debug.h" 146 147 #include <sys/param.h> 148 #include <sys/systm.h> 149 #include <sys/malloc.h> 150 #include <sys/mbuf.h> 151 #include <sys/protosw.h> 152 #include <sys/socket.h> 153 #include <sys/socketvar.h> 154 #include <sys/errno.h> 155 #include <sys/domain.h> 156 #include <sys/kernel.h> 157 158 #include <net/if.h> 159 #include <net/route.h> 160 161 #include <netinet/in.h> 162 #include <netinet/in_systm.h> 163 #include <netinet/ip.h> 164 #include <netinet/in_pcb.h> 165 #include <netinet/ip_var.h> 166 167 #ifdef INET6 168 #ifndef INET 169 #include <netinet/in.h> 170 #endif 171 #include <netinet/ip6.h> 172 #include <netinet6/in6_var.h> 173 #include <netinet6/ip6_var.h> 174 #include <netinet6/in6_pcb.h> 175 #include <netinet6/nd6.h> 176 #endif 177 178 #ifdef FAST_IPSEC 179 #include <netipsec/ipsec.h> 180 #endif /* FAST_IPSEC*/ 181 #ifdef IPSEC 182 #include <netinet6/ipsec.h> 183 #endif 184 185 #include <netinet/tcp.h> 186 #define TCPOUTFLAGS 187 #include <netinet/tcp_fsm.h> 188 #include <netinet/tcp_seq.h> 189 #include <netinet/tcp_timer.h> 190 #include <netinet/tcp_var.h> 191 #include <netinet/tcpip.h> 192 #include <netinet/tcp_debug.h> 193 194 #ifdef notyet 195 extern struct mbuf *m_copypack(); 196 #endif 197 198 #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */ 199 200 /* 201 * Knob to enable Congestion Window Monitoring, and control the 202 * the burst size it allows. Default burst is 4 packets, per 203 * the Internet draft. 204 */ 205 int tcp_cwm = 0; 206 int tcp_cwm_burstsize = 4; 207 208 #ifdef TCP_OUTPUT_COUNTERS 209 #include <sys/device.h> 210 211 extern struct evcnt tcp_output_bigheader; 212 extern struct evcnt tcp_output_copysmall; 213 extern struct evcnt tcp_output_copybig; 214 extern struct evcnt tcp_output_refbig; 215 216 #define TCP_OUTPUT_COUNTER_INCR(ev) (ev)->ev_count++ 217 #else 218 219 #define TCP_OUTPUT_COUNTER_INCR(ev) /* nothing */ 220 221 #endif /* TCP_OUTPUT_COUNTERS */ 222 223 static 224 #ifndef GPROF 225 __inline 226 #endif 227 void 228 tcp_segsize(struct tcpcb *tp, int *txsegsizep, int *rxsegsizep) 229 { 230 #ifdef INET 231 struct inpcb *inp = tp->t_inpcb; 232 #endif 233 #ifdef INET6 234 struct in6pcb *in6p = tp->t_in6pcb; 235 #endif 236 struct socket *so = NULL; 237 struct rtentry *rt; 238 struct ifnet *ifp; 239 int size; 240 int iphlen; 241 int optlen; 242 243 #ifdef DIAGNOSTIC 244 if (tp->t_inpcb && tp->t_in6pcb) 245 panic("tcp_segsize: both t_inpcb and t_in6pcb are set"); 246 #endif 247 switch (tp->t_family) { 248 #ifdef INET 249 case AF_INET: 250 iphlen = sizeof(struct ip); 251 break; 252 #endif 253 #ifdef INET6 254 case AF_INET6: 255 iphlen = sizeof(struct ip6_hdr); 256 break; 257 #endif 258 default: 259 size = tcp_mssdflt; 260 goto out; 261 } 262 263 rt = NULL; 264 #ifdef INET 265 if (inp) { 266 rt = in_pcbrtentry(inp); 267 so = inp->inp_socket; 268 } 269 #endif 270 #ifdef INET6 271 if (in6p) { 272 rt = in6_pcbrtentry(in6p); 273 so = in6p->in6p_socket; 274 } 275 #endif 276 if (rt == NULL) { 277 size = tcp_mssdflt; 278 goto out; 279 } 280 281 ifp = rt->rt_ifp; 282 283 size = tcp_mssdflt; 284 if (tp->t_mtudisc && rt->rt_rmx.rmx_mtu != 0) 285 size = rt->rt_rmx.rmx_mtu - iphlen - sizeof(struct tcphdr); 286 else if (ifp->if_flags & IFF_LOOPBACK) 287 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 288 #ifdef INET 289 else if (inp && tp->t_mtudisc) 290 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 291 else if (inp && in_localaddr(inp->inp_faddr)) 292 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 293 #endif 294 #ifdef INET6 295 else if (in6p) { 296 #ifdef INET 297 if (IN6_IS_ADDR_V4MAPPED(&in6p->in6p_faddr)) { 298 /* mapped addr case */ 299 struct in_addr d; 300 bcopy(&in6p->in6p_faddr.s6_addr32[3], &d, sizeof(d)); 301 if (tp->t_mtudisc || in_localaddr(d)) 302 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 303 } else 304 #endif 305 { 306 /* 307 * for IPv6, path MTU discovery is always turned on, 308 * or the node must use packet size <= 1280. 309 */ 310 size = tp->t_mtudisc ? IN6_LINKMTU(ifp) : IPV6_MMTU; 311 size -= (iphlen + sizeof(struct tcphdr)); 312 } 313 } 314 #endif 315 out: 316 /* 317 * Now we must make room for whatever extra TCP/IP options are in 318 * the packet. 319 */ 320 optlen = tcp_optlen(tp); 321 322 /* 323 * XXX tp->t_ourmss should have the right size, but without this code 324 * fragmentation will occur... need more investigation 325 */ 326 #ifdef INET 327 if (inp) { 328 #if defined(IPSEC) || defined(FAST_IPSEC) 329 optlen += ipsec4_hdrsiz_tcp(tp); 330 #endif 331 optlen += ip_optlen(inp); 332 } 333 #endif 334 #ifdef INET6 335 #ifdef INET 336 if (in6p && tp->t_family == AF_INET) { 337 #if defined(IPSEC) || defined(FAST_IPSEC) 338 optlen += ipsec4_hdrsiz_tcp(tp); 339 #endif 340 /* XXX size -= ip_optlen(in6p); */ 341 } else 342 #endif 343 if (in6p && tp->t_family == AF_INET6) { 344 #ifdef IPSEC 345 optlen += ipsec6_hdrsiz_tcp(tp); 346 #endif 347 optlen += ip6_optlen(in6p); 348 } 349 #endif 350 size -= optlen; 351 352 /* 353 * *rxsegsizep holds *estimated* inbound segment size (estimation 354 * assumes that path MTU is the same for both ways). this is only 355 * for silly window avoidance, do not use the value for other purposes. 356 * 357 * ipseclen is subtracted from both sides, this may not be right. 358 * I'm not quite sure about this (could someone comment). 359 */ 360 *txsegsizep = min(tp->t_peermss - optlen, size); 361 /* 362 * Never send more than half a buffer full. This insures that we can 363 * always keep 2 packets on the wire, no matter what SO_SNDBUF is, and 364 * therefore acks will never be delayed unless we run out of data to 365 * transmit. 366 */ 367 if (so) 368 *txsegsizep = min(so->so_snd.sb_hiwat >> 1, *txsegsizep); 369 *rxsegsizep = min(tp->t_ourmss - optlen, size); 370 371 if (*txsegsizep != tp->t_segsz) { 372 /* 373 * If the new segment size is larger, we don't want to 374 * mess up the congestion window, but if it is smaller 375 * we'll have to reduce the congestion window to ensure 376 * that we don't get into trouble with initial windows 377 * and the rest. In any case, if the segment size 378 * has changed, chances are the path has, too, and 379 * our congestion window will be different. 380 */ 381 if (*txsegsizep < tp->t_segsz) { 382 tp->snd_cwnd = max((tp->snd_cwnd / tp->t_segsz) 383 * *txsegsizep, *txsegsizep); 384 tp->snd_ssthresh = max((tp->snd_ssthresh / tp->t_segsz) 385 * *txsegsizep, *txsegsizep); 386 } 387 tp->t_segsz = *txsegsizep; 388 } 389 } 390 391 static 392 #ifndef GPROF 393 __inline 394 #endif 395 int 396 tcp_build_datapkt(struct tcpcb *tp, struct socket *so, int off, 397 long len, int hdrlen, struct mbuf **mp) 398 { 399 struct mbuf *m, *m0; 400 401 if (tp->t_force && len == 1) 402 tcpstat.tcps_sndprobe++; 403 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 404 tcpstat.tcps_sndrexmitpack++; 405 tcpstat.tcps_sndrexmitbyte += len; 406 } else { 407 tcpstat.tcps_sndpack++; 408 tcpstat.tcps_sndbyte += len; 409 } 410 #ifdef notyet 411 if ((m = m_copypack(so->so_snd.sb_mb, off, 412 (int)len, max_linkhdr + hdrlen)) == 0) 413 return (ENOBUFS); 414 /* 415 * m_copypack left space for our hdr; use it. 416 */ 417 m->m_len += hdrlen; 418 m->m_data -= hdrlen; 419 #else 420 MGETHDR(m, M_DONTWAIT, MT_HEADER); 421 if (__predict_false(m == NULL)) 422 return (ENOBUFS); 423 MCLAIM(m, &tcp_tx_mowner); 424 425 /* 426 * XXX Because other code assumes headers will fit in 427 * XXX one header mbuf. 428 * 429 * (This code should almost *never* be run.) 430 */ 431 if (__predict_false((max_linkhdr + hdrlen) > MHLEN)) { 432 TCP_OUTPUT_COUNTER_INCR(&tcp_output_bigheader); 433 MCLGET(m, M_DONTWAIT); 434 if ((m->m_flags & M_EXT) == 0) { 435 m_freem(m); 436 return (ENOBUFS); 437 } 438 } 439 440 m->m_data += max_linkhdr; 441 m->m_len = hdrlen; 442 443 /* 444 * To avoid traversing the whole sb_mb chain for correct 445 * data to send, remember last sent mbuf, its offset and 446 * the sent size. When called the next time, see if the 447 * data to send is the directly following the previous 448 * transfer. This is important for large TCP windows. 449 */ 450 #ifdef FAST_MBSEARCH 451 if (off == 0 || (tp->t_lastoff + tp->t_lastlen) != off) { 452 #else 453 if (1) { 454 #endif 455 /* 456 * Either a new packet or a retransmit. 457 * Start from the beginning. 458 */ 459 tp->t_lastm = so->so_snd.sb_mb; 460 tp->t_inoff = off; 461 } else 462 tp->t_inoff += tp->t_lastlen; 463 464 /* Traverse forward to next packet */ 465 while (tp->t_inoff > 0) { 466 if (tp->t_lastm == NULL) 467 panic("tp->t_lastm == NULL"); 468 if (tp->t_inoff < tp->t_lastm->m_len) 469 break; 470 tp->t_inoff -= tp->t_lastm->m_len; 471 tp->t_lastm = tp->t_lastm->m_next; 472 } 473 474 tp->t_lastoff = off; 475 tp->t_lastlen = len; 476 m0 = tp->t_lastm; 477 off = tp->t_inoff; 478 479 if (len <= M_TRAILINGSPACE(m)) { 480 m_copydata(m0, off, (int) len, mtod(m, caddr_t) + hdrlen); 481 m->m_len += len; 482 TCP_OUTPUT_COUNTER_INCR(&tcp_output_copysmall); 483 } else { 484 m->m_next = m_copy(m0, off, (int) len); 485 if (m->m_next == NULL) { 486 m_freem(m); 487 return (ENOBUFS); 488 } 489 #ifdef TCP_OUTPUT_COUNTERS 490 if (m->m_next->m_flags & M_EXT) 491 TCP_OUTPUT_COUNTER_INCR(&tcp_output_refbig); 492 else 493 TCP_OUTPUT_COUNTER_INCR(&tcp_output_copybig); 494 #endif /* TCP_OUTPUT_COUNTERS */ 495 } 496 #endif 497 498 *mp = m; 499 return (0); 500 } 501 502 /* 503 * Tcp output routine: figure out what should be sent and send it. 504 */ 505 int 506 tcp_output(tp) 507 struct tcpcb *tp; 508 { 509 struct socket *so; 510 struct route *ro; 511 long len, win; 512 int off, flags, error; 513 struct mbuf *m; 514 struct ip *ip; 515 #ifdef INET6 516 struct ip6_hdr *ip6; 517 #endif 518 struct tcphdr *th; 519 u_char opt[MAX_TCPOPTLEN]; 520 unsigned optlen, hdrlen; 521 int idle, sendalot, txsegsize, rxsegsize; 522 int maxburst = TCP_MAXBURST; 523 int af; /* address family on the wire */ 524 int iphdrlen; 525 526 #ifdef DIAGNOSTIC 527 if (tp->t_inpcb && tp->t_in6pcb) 528 panic("tcp_output: both t_inpcb and t_in6pcb are set"); 529 #endif 530 so = NULL; 531 ro = NULL; 532 if (tp->t_inpcb) { 533 so = tp->t_inpcb->inp_socket; 534 ro = &tp->t_inpcb->inp_route; 535 } 536 #ifdef INET6 537 else if (tp->t_in6pcb) { 538 so = tp->t_in6pcb->in6p_socket; 539 ro = (struct route *)&tp->t_in6pcb->in6p_route; 540 } 541 #endif 542 543 switch (af = tp->t_family) { 544 #ifdef INET 545 case AF_INET: 546 if (tp->t_inpcb) 547 break; 548 #ifdef INET6 549 /* mapped addr case */ 550 if (tp->t_in6pcb) 551 break; 552 #endif 553 return EINVAL; 554 #endif 555 #ifdef INET6 556 case AF_INET6: 557 if (tp->t_in6pcb) 558 break; 559 return EINVAL; 560 #endif 561 default: 562 return EAFNOSUPPORT; 563 } 564 565 tcp_segsize(tp, &txsegsize, &rxsegsize); 566 567 idle = (tp->snd_max == tp->snd_una); 568 569 /* 570 * Restart Window computation. From draft-floyd-incr-init-win-03: 571 * 572 * Optionally, a TCP MAY set the restart window to the 573 * minimum of the value used for the initial window and 574 * the current value of cwnd (in other words, using a 575 * larger value for the restart window should never increase 576 * the size of cwnd). 577 */ 578 if (tcp_cwm) { 579 /* 580 * Hughes/Touch/Heidemann Congestion Window Monitoring. 581 * Count the number of packets currently pending 582 * acknowledgement, and limit our congestion window 583 * to a pre-determined allowed burst size plus that count. 584 * This prevents bursting once all pending packets have 585 * been acknowledged (i.e. transmission is idle). 586 * 587 * XXX Link this to Initial Window? 588 */ 589 tp->snd_cwnd = min(tp->snd_cwnd, 590 (tcp_cwm_burstsize * txsegsize) + 591 (tp->snd_nxt - tp->snd_una)); 592 } else { 593 if (idle && (tcp_now - tp->t_rcvtime) >= tp->t_rxtcur) { 594 /* 595 * We have been idle for "a while" and no acks are 596 * expected to clock out any data we send -- 597 * slow start to get ack "clock" running again. 598 */ 599 int ss = tcp_init_win; 600 #ifdef INET 601 if (tp->t_inpcb && 602 in_localaddr(tp->t_inpcb->inp_faddr)) 603 ss = tcp_init_win_local; 604 #endif 605 #ifdef INET6 606 if (tp->t_in6pcb && 607 in6_localaddr(&tp->t_in6pcb->in6p_faddr)) 608 ss = tcp_init_win_local; 609 #endif 610 tp->snd_cwnd = min(tp->snd_cwnd, 611 TCP_INITIAL_WINDOW(ss, txsegsize)); 612 } 613 } 614 615 again: 616 /* 617 * Determine length of data that should be transmitted, and 618 * flags that should be used. If there is some data or critical 619 * controls (SYN, RST) to send, then transmit; otherwise, 620 * investigate further. 621 */ 622 sendalot = 0; 623 off = tp->snd_nxt - tp->snd_una; 624 win = min(tp->snd_wnd, tp->snd_cwnd); 625 626 flags = tcp_outflags[tp->t_state]; 627 /* 628 * If in persist timeout with window of 0, send 1 byte. 629 * Otherwise, if window is small but nonzero 630 * and timer expired, we will send what we can 631 * and go to transmit state. 632 */ 633 if (tp->t_force) { 634 if (win == 0) { 635 /* 636 * If we still have some data to send, then 637 * clear the FIN bit. Usually this would 638 * happen below when it realizes that we 639 * aren't sending all the data. However, 640 * if we have exactly 1 byte of unset data, 641 * then it won't clear the FIN bit below, 642 * and if we are in persist state, we wind 643 * up sending the packet without recording 644 * that we sent the FIN bit. 645 * 646 * We can't just blindly clear the FIN bit, 647 * because if we don't have any more data 648 * to send then the probe will be the FIN 649 * itself. 650 */ 651 if (off < so->so_snd.sb_cc) 652 flags &= ~TH_FIN; 653 win = 1; 654 } else { 655 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 656 tp->t_rxtshift = 0; 657 } 658 } 659 660 if (win < so->so_snd.sb_cc) { 661 len = win - off; 662 flags &= ~TH_FIN; 663 } else 664 len = so->so_snd.sb_cc - off; 665 666 if (len < 0) { 667 /* 668 * If FIN has been sent but not acked, 669 * but we haven't been called to retransmit, 670 * len will be -1. Otherwise, window shrank 671 * after we sent into it. If window shrank to 0, 672 * cancel pending retransmit, pull snd_nxt back 673 * to (closed) window, and set the persist timer 674 * if it isn't already going. If the window didn't 675 * close completely, just wait for an ACK. 676 * 677 * If we have a pending FIN, either it has already been 678 * transmitted or it is outside the window, so drop it. 679 * If the FIN has been transmitted, but this is not a 680 * retransmission, then len must be -1. Therefore we also 681 * prevent here the sending of `gratuitous FINs'. This 682 * eliminates the need to check for that case below (e.g. 683 * to back up snd_nxt before the FIN so that the sequence 684 * number is correct). 685 */ 686 len = 0; 687 flags &= ~TH_FIN; 688 if (win == 0) { 689 TCP_TIMER_DISARM(tp, TCPT_REXMT); 690 tp->t_rxtshift = 0; 691 tp->snd_nxt = tp->snd_una; 692 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) 693 tcp_setpersist(tp); 694 } 695 } 696 if (len > txsegsize) { 697 len = txsegsize; 698 flags &= ~TH_FIN; 699 sendalot = 1; 700 } 701 702 win = sbspace(&so->so_rcv); 703 704 /* 705 * Sender silly window avoidance. If connection is idle 706 * and can send all data, a maximum segment, 707 * at least a maximum default-size segment do it, 708 * or are forced, do it; otherwise don't bother. 709 * If peer's buffer is tiny, then send 710 * when window is at least half open. 711 * If retransmitting (possibly after persist timer forced us 712 * to send into a small window), then must resend. 713 */ 714 if (len) { 715 if (len == txsegsize) 716 goto send; 717 if ((so->so_state & SS_MORETOCOME) == 0 && 718 ((idle || tp->t_flags & TF_NODELAY) && 719 len + off >= so->so_snd.sb_cc)) 720 goto send; 721 if (tp->t_force) 722 goto send; 723 if (len >= tp->max_sndwnd / 2) 724 goto send; 725 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 726 goto send; 727 } 728 729 /* 730 * Compare available window to amount of window known to peer 731 * (as advertised window less next expected input). If the 732 * difference is at least twice the size of the largest segment 733 * we expect to receive (i.e. two segments) or at least 50% of 734 * the maximum possible window, then want to send a window update 735 * to peer. 736 */ 737 if (win > 0) { 738 /* 739 * "adv" is the amount we can increase the window, 740 * taking into account that we are limited by 741 * TCP_MAXWIN << tp->rcv_scale. 742 */ 743 long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) - 744 (tp->rcv_adv - tp->rcv_nxt); 745 746 if (adv >= (long) (2 * rxsegsize)) 747 goto send; 748 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 749 goto send; 750 } 751 752 /* 753 * Send if we owe peer an ACK. 754 */ 755 if (tp->t_flags & TF_ACKNOW) 756 goto send; 757 if (flags & (TH_SYN|TH_FIN|TH_RST)) 758 goto send; 759 if (SEQ_GT(tp->snd_up, tp->snd_una)) 760 goto send; 761 762 /* 763 * TCP window updates are not reliable, rather a polling protocol 764 * using ``persist'' packets is used to insure receipt of window 765 * updates. The three ``states'' for the output side are: 766 * idle not doing retransmits or persists 767 * persisting to move a small or zero window 768 * (re)transmitting and thereby not persisting 769 * 770 * tp->t_timer[TCPT_PERSIST] 771 * is set when we are in persist state. 772 * tp->t_force 773 * is set when we are called to send a persist packet. 774 * tp->t_timer[TCPT_REXMT] 775 * is set when we are retransmitting 776 * The output side is idle when both timers are zero. 777 * 778 * If send window is too small, there is data to transmit, and no 779 * retransmit or persist is pending, then go to persist state. 780 * If nothing happens soon, send when timer expires: 781 * if window is nonzero, transmit what we can, 782 * otherwise force out a byte. 783 */ 784 if (so->so_snd.sb_cc && TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 785 TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 786 tp->t_rxtshift = 0; 787 tcp_setpersist(tp); 788 } 789 790 /* 791 * No reason to send a segment, just return. 792 */ 793 return (0); 794 795 send: 796 /* 797 * Before ESTABLISHED, force sending of initial options 798 * unless TCP set not to do any options. 799 * NOTE: we assume that the IP/TCP header plus TCP options 800 * always fit in a single mbuf, leaving room for a maximum 801 * link header, i.e. 802 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 803 */ 804 optlen = 0; 805 switch (af) { 806 #ifdef INET 807 case AF_INET: 808 iphdrlen = sizeof(struct ip) + sizeof(struct tcphdr); 809 break; 810 #endif 811 #ifdef INET6 812 case AF_INET6: 813 iphdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); 814 break; 815 #endif 816 default: /*pacify gcc*/ 817 iphdrlen = 0; 818 break; 819 } 820 hdrlen = iphdrlen; 821 if (flags & TH_SYN) { 822 struct rtentry *rt; 823 824 rt = NULL; 825 #ifdef INET 826 if (tp->t_inpcb) 827 rt = in_pcbrtentry(tp->t_inpcb); 828 #endif 829 #ifdef INET6 830 if (tp->t_in6pcb) 831 rt = in6_pcbrtentry(tp->t_in6pcb); 832 #endif 833 834 tp->snd_nxt = tp->iss; 835 tp->t_ourmss = tcp_mss_to_advertise(rt != NULL ? 836 rt->rt_ifp : NULL, af); 837 if ((tp->t_flags & TF_NOOPT) == 0) { 838 opt[0] = TCPOPT_MAXSEG; 839 opt[1] = 4; 840 opt[2] = (tp->t_ourmss >> 8) & 0xff; 841 opt[3] = tp->t_ourmss & 0xff; 842 optlen = 4; 843 844 if ((tp->t_flags & TF_REQ_SCALE) && 845 ((flags & TH_ACK) == 0 || 846 (tp->t_flags & TF_RCVD_SCALE))) { 847 *((u_int32_t *) (opt + optlen)) = htonl( 848 TCPOPT_NOP << 24 | 849 TCPOPT_WINDOW << 16 | 850 TCPOLEN_WINDOW << 8 | 851 tp->request_r_scale); 852 optlen += 4; 853 } 854 } 855 } 856 857 /* 858 * Send a timestamp and echo-reply if this is a SYN and our side 859 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 860 * and our peer have sent timestamps in our SYN's. 861 */ 862 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 863 (flags & TH_RST) == 0 && 864 ((flags & (TH_SYN|TH_ACK)) == TH_SYN || 865 (tp->t_flags & TF_RCVD_TSTMP))) { 866 u_int32_t *lp = (u_int32_t *)(opt + optlen); 867 868 /* Form timestamp option as shown in appendix A of RFC 1323. */ 869 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 870 *lp++ = htonl(TCP_TIMESTAMP(tp)); 871 *lp = htonl(tp->ts_recent); 872 optlen += TCPOLEN_TSTAMP_APPA; 873 } 874 875 hdrlen += optlen; 876 877 #ifdef DIAGNOSTIC 878 if (len > txsegsize) 879 panic("tcp data to be sent is larger than segment"); 880 if (max_linkhdr + hdrlen > MCLBYTES) 881 panic("tcphdr too big"); 882 #endif 883 884 /* 885 * Grab a header mbuf, attaching a copy of data to 886 * be transmitted, and initialize the header from 887 * the template for sends on this connection. 888 */ 889 if (len) { 890 error = tcp_build_datapkt(tp, so, off, len, hdrlen, &m); 891 if (error) 892 goto out; 893 /* 894 * If we're sending everything we've got, set PUSH. 895 * (This will keep happy those implementations which only 896 * give data to the user when a buffer fills or 897 * a PUSH comes in.) 898 */ 899 if (off + len == so->so_snd.sb_cc) 900 flags |= TH_PUSH; 901 } else { 902 if (tp->t_flags & TF_ACKNOW) 903 tcpstat.tcps_sndacks++; 904 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 905 tcpstat.tcps_sndctrl++; 906 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 907 tcpstat.tcps_sndurg++; 908 else 909 tcpstat.tcps_sndwinup++; 910 911 MGETHDR(m, M_DONTWAIT, MT_HEADER); 912 if (m != NULL && max_linkhdr + hdrlen > MHLEN) { 913 MCLGET(m, M_DONTWAIT); 914 if ((m->m_flags & M_EXT) == 0) { 915 m_freem(m); 916 m = NULL; 917 } 918 } 919 if (m == NULL) { 920 error = ENOBUFS; 921 goto out; 922 } 923 MCLAIM(m, &tcp_tx_mowner); 924 m->m_data += max_linkhdr; 925 m->m_len = hdrlen; 926 } 927 m->m_pkthdr.rcvif = (struct ifnet *)0; 928 switch (af) { 929 #ifdef INET 930 case AF_INET: 931 ip = mtod(m, struct ip *); 932 #ifdef INET6 933 ip6 = NULL; 934 #endif 935 th = (struct tcphdr *)(ip + 1); 936 break; 937 #endif 938 #ifdef INET6 939 case AF_INET6: 940 ip = NULL; 941 ip6 = mtod(m, struct ip6_hdr *); 942 th = (struct tcphdr *)(ip6 + 1); 943 break; 944 #endif 945 default: /*pacify gcc*/ 946 ip = NULL; 947 #ifdef INET6 948 ip6 = NULL; 949 #endif 950 th = NULL; 951 break; 952 } 953 if (tp->t_template == 0) 954 panic("tcp_output"); 955 if (tp->t_template->m_len < iphdrlen) 956 panic("tcp_output"); 957 bcopy(mtod(tp->t_template, caddr_t), mtod(m, caddr_t), iphdrlen); 958 959 /* 960 * If we are doing retransmissions, then snd_nxt will 961 * not reflect the first unsent octet. For ACK only 962 * packets, we do not want the sequence number of the 963 * retransmitted packet, we want the sequence number 964 * of the next unsent octet. So, if there is no data 965 * (and no SYN or FIN), use snd_max instead of snd_nxt 966 * when filling in ti_seq. But if we are in persist 967 * state, snd_max might reflect one byte beyond the 968 * right edge of the window, so use snd_nxt in that 969 * case, since we know we aren't doing a retransmission. 970 * (retransmit and persist are mutually exclusive...) 971 */ 972 if (len || (flags & (TH_SYN|TH_FIN)) || 973 TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) 974 th->th_seq = htonl(tp->snd_nxt); 975 else 976 th->th_seq = htonl(tp->snd_max); 977 th->th_ack = htonl(tp->rcv_nxt); 978 if (optlen) { 979 bcopy((caddr_t)opt, (caddr_t)(th + 1), optlen); 980 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 981 } 982 th->th_flags = flags; 983 /* 984 * Calculate receive window. Don't shrink window, 985 * but avoid silly window syndrome. 986 */ 987 if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)rxsegsize) 988 win = 0; 989 if (win > (long)TCP_MAXWIN << tp->rcv_scale) 990 win = (long)TCP_MAXWIN << tp->rcv_scale; 991 if (win < (long)(tp->rcv_adv - tp->rcv_nxt)) 992 win = (long)(tp->rcv_adv - tp->rcv_nxt); 993 th->th_win = htons((u_int16_t) (win>>tp->rcv_scale)); 994 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 995 u_int32_t urp = tp->snd_up - tp->snd_nxt; 996 if (urp > IP_MAXPACKET) 997 urp = IP_MAXPACKET; 998 th->th_urp = htons((u_int16_t)urp); 999 th->th_flags |= TH_URG; 1000 } else 1001 /* 1002 * If no urgent pointer to send, then we pull 1003 * the urgent pointer to the left edge of the send window 1004 * so that it doesn't drift into the send window on sequence 1005 * number wraparound. 1006 */ 1007 tp->snd_up = tp->snd_una; /* drag it along */ 1008 1009 /* 1010 * Set ourselves up to be checksummed just before the packet 1011 * hits the wire. 1012 */ 1013 switch (af) { 1014 #ifdef INET 1015 case AF_INET: 1016 m->m_pkthdr.csum_flags = M_CSUM_TCPv4; 1017 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1018 if (len + optlen) { 1019 /* Fixup the pseudo-header checksum. */ 1020 /* XXXJRT Not IP Jumbogram safe. */ 1021 th->th_sum = in_cksum_addword(th->th_sum, 1022 htons((u_int16_t) (len + optlen))); 1023 } 1024 break; 1025 #endif 1026 #ifdef INET6 1027 case AF_INET6: 1028 /* 1029 * XXX Actually delaying the checksum is Hard 1030 * XXX (well, maybe not for Itojun, but it is 1031 * XXX for me), but we can still take advantage 1032 * XXX of the cached pseudo-header checksum. 1033 */ 1034 /* equals to hdrlen + len */ 1035 m->m_pkthdr.len = sizeof(struct ip6_hdr) 1036 + sizeof(struct tcphdr) + optlen + len; 1037 #ifdef notyet 1038 m->m_pkthdr.csum_flags = M_CSUM_TCPv6; 1039 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1040 #endif 1041 if (len + optlen) { 1042 /* Fixup the pseudo-header checksum. */ 1043 /* XXXJRT: Not IPv6 Jumbogram safe. */ 1044 th->th_sum = in_cksum_addword(th->th_sum, 1045 htons((u_int16_t) (len + optlen))); 1046 } 1047 #ifndef notyet 1048 th->th_sum = in6_cksum(m, 0, sizeof(struct ip6_hdr), 1049 sizeof(struct tcphdr) + optlen + len); 1050 #endif 1051 break; 1052 #endif 1053 } 1054 1055 /* 1056 * In transmit state, time the transmission and arrange for 1057 * the retransmit. In persist state, just set snd_max. 1058 */ 1059 if (tp->t_force == 0 || TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 1060 tcp_seq startseq = tp->snd_nxt; 1061 1062 /* 1063 * Advance snd_nxt over sequence space of this segment. 1064 * There are no states in which we send both a SYN and a FIN, 1065 * so we collapse the tests for these flags. 1066 */ 1067 if (flags & (TH_SYN|TH_FIN)) 1068 tp->snd_nxt++; 1069 tp->snd_nxt += len; 1070 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1071 tp->snd_max = tp->snd_nxt; 1072 /* 1073 * Time this transmission if not a retransmission and 1074 * not currently timing anything. 1075 */ 1076 if (tp->t_rtttime == 0) { 1077 tp->t_rtttime = tcp_now; 1078 tp->t_rtseq = startseq; 1079 tcpstat.tcps_segstimed++; 1080 } 1081 } 1082 1083 /* 1084 * Set retransmit timer if not currently set, 1085 * and not doing an ack or a keep-alive probe. 1086 * Initial value for retransmit timer is smoothed 1087 * round-trip time + 2 * round-trip time variance. 1088 * Initialize shift counter which is used for backoff 1089 * of retransmit time. 1090 */ 1091 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 1092 tp->snd_nxt != tp->snd_una) { 1093 TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); 1094 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) { 1095 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 1096 tp->t_rxtshift = 0; 1097 } 1098 } 1099 } else 1100 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 1101 tp->snd_max = tp->snd_nxt + len; 1102 1103 #ifdef TCP_DEBUG 1104 /* 1105 * Trace. 1106 */ 1107 if (so->so_options & SO_DEBUG) 1108 tcp_trace(TA_OUTPUT, tp->t_state, tp, m, 0); 1109 #endif 1110 1111 /* 1112 * Fill in IP length and desired time to live and 1113 * send to IP level. There should be a better way 1114 * to handle ttl and tos; we could keep them in 1115 * the template, but need a way to checksum without them. 1116 */ 1117 m->m_pkthdr.len = hdrlen + len; 1118 1119 switch (af) { 1120 #ifdef INET 1121 case AF_INET: 1122 ip->ip_len = htons(m->m_pkthdr.len); 1123 if (tp->t_inpcb) { 1124 ip->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl; 1125 ip->ip_tos = tp->t_inpcb->inp_ip.ip_tos; 1126 } 1127 #ifdef INET6 1128 else if (tp->t_in6pcb) { 1129 ip->ip_ttl = in6_selecthlim(tp->t_in6pcb, NULL); /*XXX*/ 1130 ip->ip_tos = 0; /*XXX*/ 1131 } 1132 #endif 1133 break; 1134 #endif 1135 #ifdef INET6 1136 case AF_INET6: 1137 ip6->ip6_nxt = IPPROTO_TCP; 1138 if (tp->t_in6pcb) { 1139 /* 1140 * we separately set hoplimit for every segment, since 1141 * the user might want to change the value via 1142 * setsockopt. Also, desired default hop limit might 1143 * be changed via Neighbor Discovery. 1144 */ 1145 ip6->ip6_hlim = in6_selecthlim(tp->t_in6pcb, 1146 ro->ro_rt ? ro->ro_rt->rt_ifp : NULL); 1147 } 1148 /* ip6->ip6_flow = ??? */ 1149 /* ip6_plen will be filled in ip6_output(). */ 1150 break; 1151 #endif 1152 } 1153 1154 switch (af) { 1155 #ifdef INET 1156 case AF_INET: 1157 { 1158 struct mbuf *opts; 1159 1160 if (tp->t_inpcb) 1161 opts = tp->t_inpcb->inp_options; 1162 else 1163 opts = NULL; 1164 error = ip_output(m, opts, ro, 1165 (tp->t_mtudisc ? IP_MTUDISC : 0) | 1166 (so->so_options & SO_DONTROUTE), 1167 (struct ip_moptions *)0, so); 1168 break; 1169 } 1170 #endif 1171 #ifdef INET6 1172 case AF_INET6: 1173 { 1174 struct ip6_pktopts *opts; 1175 1176 if (tp->t_in6pcb) 1177 opts = tp->t_in6pcb->in6p_outputopts; 1178 else 1179 opts = NULL; 1180 error = ip6_output(m, opts, (struct route_in6 *)ro, 1181 so->so_options & SO_DONTROUTE, 1182 (struct ip6_moptions *)0, so, NULL); 1183 break; 1184 } 1185 #endif 1186 default: 1187 error = EAFNOSUPPORT; 1188 break; 1189 } 1190 if (error) { 1191 out: 1192 if (error == ENOBUFS) { 1193 tcpstat.tcps_selfquench++; 1194 #ifdef INET 1195 if (tp->t_inpcb) 1196 tcp_quench(tp->t_inpcb, 0); 1197 #endif 1198 #ifdef INET6 1199 if (tp->t_in6pcb) 1200 tcp6_quench(tp->t_in6pcb, 0); 1201 #endif 1202 error = 0; 1203 } else if ((error == EHOSTUNREACH || error == ENETDOWN) && 1204 TCPS_HAVERCVDSYN(tp->t_state)) { 1205 tp->t_softerror = error; 1206 error = 0; 1207 } 1208 1209 /* Restart the delayed ACK timer, if necessary. */ 1210 if (tp->t_flags & TF_DELACK) 1211 TCP_RESTART_DELACK(tp); 1212 1213 return (error); 1214 } 1215 tcpstat.tcps_sndtotal++; 1216 if (tp->t_flags & TF_DELACK) 1217 tcpstat.tcps_delack++; 1218 1219 /* 1220 * Data sent (as far as we can tell). 1221 * If this advertises a larger window than any other segment, 1222 * then remember the size of the advertised window. 1223 * Any pending ACK has now been sent. 1224 */ 1225 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 1226 tp->rcv_adv = tp->rcv_nxt + win; 1227 tp->last_ack_sent = tp->rcv_nxt; 1228 tp->t_flags &= ~TF_ACKNOW; 1229 TCP_CLEAR_DELACK(tp); 1230 #ifdef DIAGNOSTIC 1231 if (maxburst < 0) 1232 printf("tcp_output: maxburst exceeded by %d\n", -maxburst); 1233 #endif 1234 if (sendalot && (!tcp_do_newreno || --maxburst)) 1235 goto again; 1236 return (0); 1237 } 1238 1239 void 1240 tcp_setpersist(tp) 1241 struct tcpcb *tp; 1242 { 1243 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> (1 + 2); 1244 int nticks; 1245 1246 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT)) 1247 panic("tcp_output REXMT"); 1248 /* 1249 * Start/restart persistance timer. 1250 */ 1251 if (t < tp->t_rttmin) 1252 t = tp->t_rttmin; 1253 TCPT_RANGESET(nticks, t * tcp_backoff[tp->t_rxtshift], 1254 TCPTV_PERSMIN, TCPTV_PERSMAX); 1255 TCP_TIMER_ARM(tp, TCPT_PERSIST, nticks); 1256 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1257 tp->t_rxtshift++; 1258 } 1259