1 /* $NetBSD: tcp_output.c,v 1.97 2003/08/07 16:33:17 agc 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 1.97 2003/08/07 16:33:17 agc 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 IPSEC 179 #include <netinet6/ipsec.h> 180 #endif 181 182 #include <netinet/tcp.h> 183 #define TCPOUTFLAGS 184 #include <netinet/tcp_fsm.h> 185 #include <netinet/tcp_seq.h> 186 #include <netinet/tcp_timer.h> 187 #include <netinet/tcp_var.h> 188 #include <netinet/tcpip.h> 189 #include <netinet/tcp_debug.h> 190 191 #ifdef notyet 192 extern struct mbuf *m_copypack(); 193 #endif 194 195 #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */ 196 197 /* 198 * Knob to enable Congestion Window Monitoring, and control the 199 * the burst size it allows. Default burst is 4 packets, per 200 * the Internet draft. 201 */ 202 int tcp_cwm = 0; 203 int tcp_cwm_burstsize = 4; 204 205 #ifdef TCP_OUTPUT_COUNTERS 206 #include <sys/device.h> 207 208 extern struct evcnt tcp_output_bigheader; 209 extern struct evcnt tcp_output_copysmall; 210 extern struct evcnt tcp_output_copybig; 211 extern struct evcnt tcp_output_refbig; 212 213 #define TCP_OUTPUT_COUNTER_INCR(ev) (ev)->ev_count++ 214 #else 215 216 #define TCP_OUTPUT_COUNTER_INCR(ev) /* nothing */ 217 218 #endif /* TCP_OUTPUT_COUNTERS */ 219 220 static 221 #ifndef GPROF 222 __inline 223 #endif 224 void 225 tcp_segsize(struct tcpcb *tp, int *txsegsizep, int *rxsegsizep) 226 { 227 #ifdef INET 228 struct inpcb *inp = tp->t_inpcb; 229 #endif 230 #ifdef INET6 231 struct in6pcb *in6p = tp->t_in6pcb; 232 #endif 233 struct socket *so = NULL; 234 struct rtentry *rt; 235 struct ifnet *ifp; 236 int size; 237 int iphlen; 238 int optlen; 239 240 #ifdef DIAGNOSTIC 241 if (tp->t_inpcb && tp->t_in6pcb) 242 panic("tcp_segsize: both t_inpcb and t_in6pcb are set"); 243 #endif 244 switch (tp->t_family) { 245 #ifdef INET 246 case AF_INET: 247 iphlen = sizeof(struct ip); 248 break; 249 #endif 250 #ifdef INET6 251 case AF_INET6: 252 iphlen = sizeof(struct ip6_hdr); 253 break; 254 #endif 255 default: 256 size = tcp_mssdflt; 257 goto out; 258 } 259 260 rt = NULL; 261 #ifdef INET 262 if (inp) { 263 rt = in_pcbrtentry(inp); 264 so = inp->inp_socket; 265 } 266 #endif 267 #ifdef INET6 268 if (in6p) { 269 rt = in6_pcbrtentry(in6p); 270 so = in6p->in6p_socket; 271 } 272 #endif 273 if (rt == NULL) { 274 size = tcp_mssdflt; 275 goto out; 276 } 277 278 ifp = rt->rt_ifp; 279 280 size = tcp_mssdflt; 281 if (tp->t_mtudisc && rt->rt_rmx.rmx_mtu != 0) 282 size = rt->rt_rmx.rmx_mtu - iphlen - sizeof(struct tcphdr); 283 else if (ifp->if_flags & IFF_LOOPBACK) 284 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 285 #ifdef INET 286 else if (inp && tp->t_mtudisc) 287 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 288 else if (inp && in_localaddr(inp->inp_faddr)) 289 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 290 #endif 291 #ifdef INET6 292 else if (in6p) { 293 #ifdef INET 294 if (IN6_IS_ADDR_V4MAPPED(&in6p->in6p_faddr)) { 295 /* mapped addr case */ 296 struct in_addr d; 297 bcopy(&in6p->in6p_faddr.s6_addr32[3], &d, sizeof(d)); 298 if (tp->t_mtudisc || in_localaddr(d)) 299 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 300 } else 301 #endif 302 { 303 /* 304 * for IPv6, path MTU discovery is always turned on, 305 * or the node must use packet size <= 1280. 306 */ 307 size = tp->t_mtudisc ? IN6_LINKMTU(ifp) : IPV6_MMTU; 308 size -= (iphlen + sizeof(struct tcphdr)); 309 } 310 } 311 #endif 312 out: 313 /* 314 * Now we must make room for whatever extra TCP/IP options are in 315 * the packet. 316 */ 317 optlen = tcp_optlen(tp); 318 319 /* 320 * XXX tp->t_ourmss should have the right size, but without this code 321 * fragmentation will occur... need more investigation 322 */ 323 #ifdef INET 324 if (inp) { 325 #ifdef IPSEC 326 optlen += ipsec4_hdrsiz_tcp(tp); 327 #endif 328 optlen += ip_optlen(inp); 329 } 330 #endif 331 #ifdef INET6 332 #ifdef INET 333 if (in6p && tp->t_family == AF_INET) { 334 #ifdef IPSEC 335 optlen += ipsec4_hdrsiz_tcp(tp); 336 #endif 337 /* XXX size -= ip_optlen(in6p); */ 338 } else 339 #endif 340 if (in6p && tp->t_family == AF_INET6) { 341 #ifdef IPSEC 342 optlen += ipsec6_hdrsiz_tcp(tp); 343 #endif 344 optlen += ip6_optlen(in6p); 345 } 346 #endif 347 size -= optlen; 348 349 /* 350 * *rxsegsizep holds *estimated* inbound segment size (estimation 351 * assumes that path MTU is the same for both ways). this is only 352 * for silly window avoidance, do not use the value for other purposes. 353 * 354 * ipseclen is subtracted from both sides, this may not be right. 355 * I'm not quite sure about this (could someone comment). 356 */ 357 *txsegsizep = min(tp->t_peermss - optlen, size); 358 /* 359 * Never send more than half a buffer full. This insures that we can 360 * always keep 2 packets on the wire, no matter what SO_SNDBUF is, and 361 * therefore acks will never be delayed unless we run out of data to 362 * transmit. 363 */ 364 if (so) 365 *txsegsizep = min(so->so_snd.sb_hiwat >> 1, *txsegsizep); 366 *rxsegsizep = min(tp->t_ourmss - optlen, size); 367 368 if (*txsegsizep != tp->t_segsz) { 369 /* 370 * If the new segment size is larger, we don't want to 371 * mess up the congestion window, but if it is smaller 372 * we'll have to reduce the congestion window to ensure 373 * that we don't get into trouble with initial windows 374 * and the rest. In any case, if the segment size 375 * has changed, chances are the path has, too, and 376 * our congestion window will be different. 377 */ 378 if (*txsegsizep < tp->t_segsz) { 379 tp->snd_cwnd = max((tp->snd_cwnd / tp->t_segsz) 380 * *txsegsizep, *txsegsizep); 381 tp->snd_ssthresh = max((tp->snd_ssthresh / tp->t_segsz) 382 * *txsegsizep, *txsegsizep); 383 } 384 tp->t_segsz = *txsegsizep; 385 } 386 } 387 388 static 389 #ifndef GPROF 390 __inline 391 #endif 392 int 393 tcp_build_datapkt(struct tcpcb *tp, struct socket *so, int off, 394 long len, int hdrlen, struct mbuf **mp) 395 { 396 struct mbuf *m, *m0; 397 398 if (tp->t_force && len == 1) 399 tcpstat.tcps_sndprobe++; 400 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 401 tcpstat.tcps_sndrexmitpack++; 402 tcpstat.tcps_sndrexmitbyte += len; 403 } else { 404 tcpstat.tcps_sndpack++; 405 tcpstat.tcps_sndbyte += len; 406 } 407 #ifdef notyet 408 if ((m = m_copypack(so->so_snd.sb_mb, off, 409 (int)len, max_linkhdr + hdrlen)) == 0) 410 return (ENOBUFS); 411 /* 412 * m_copypack left space for our hdr; use it. 413 */ 414 m->m_len += hdrlen; 415 m->m_data -= hdrlen; 416 #else 417 MGETHDR(m, M_DONTWAIT, MT_HEADER); 418 if (__predict_false(m == NULL)) 419 return (ENOBUFS); 420 MCLAIM(m, &tcp_tx_mowner); 421 422 /* 423 * XXX Because other code assumes headers will fit in 424 * XXX one header mbuf. 425 * 426 * (This code should almost *never* be run.) 427 */ 428 if (__predict_false((max_linkhdr + hdrlen) > MHLEN)) { 429 TCP_OUTPUT_COUNTER_INCR(&tcp_output_bigheader); 430 MCLGET(m, M_DONTWAIT); 431 if ((m->m_flags & M_EXT) == 0) { 432 m_freem(m); 433 return (ENOBUFS); 434 } 435 } 436 437 m->m_data += max_linkhdr; 438 m->m_len = hdrlen; 439 440 /* 441 * To avoid traversing the whole sb_mb chain for correct 442 * data to send, remember last sent mbuf, its offset and 443 * the sent size. When called the next time, see if the 444 * data to send is the directly following the previous 445 * transfer. This is important for large TCP windows. 446 */ 447 #ifdef FAST_MBSEARCH 448 if (off == 0 || (tp->t_lastoff + tp->t_lastlen) != off) { 449 #else 450 if (1) { 451 #endif 452 /* 453 * Either a new packet or a retransmit. 454 * Start from the beginning. 455 */ 456 tp->t_lastm = so->so_snd.sb_mb; 457 tp->t_inoff = off; 458 } else 459 tp->t_inoff += tp->t_lastlen; 460 461 /* Traverse forward to next packet */ 462 while (tp->t_inoff > 0) { 463 if (tp->t_lastm == NULL) 464 panic("tp->t_lastm == NULL"); 465 if (tp->t_inoff < tp->t_lastm->m_len) 466 break; 467 tp->t_inoff -= tp->t_lastm->m_len; 468 tp->t_lastm = tp->t_lastm->m_next; 469 } 470 471 tp->t_lastoff = off; 472 tp->t_lastlen = len; 473 m0 = tp->t_lastm; 474 off = tp->t_inoff; 475 476 if (len <= M_TRAILINGSPACE(m)) { 477 m_copydata(m0, off, (int) len, mtod(m, caddr_t) + hdrlen); 478 m->m_len += len; 479 TCP_OUTPUT_COUNTER_INCR(&tcp_output_copysmall); 480 } else { 481 m->m_next = m_copy(m0, off, (int) len); 482 if (m->m_next == NULL) { 483 m_freem(m); 484 return (ENOBUFS); 485 } 486 #ifdef TCP_OUTPUT_COUNTERS 487 if (m->m_next->m_flags & M_EXT) 488 TCP_OUTPUT_COUNTER_INCR(&tcp_output_refbig); 489 else 490 TCP_OUTPUT_COUNTER_INCR(&tcp_output_copybig); 491 #endif /* TCP_OUTPUT_COUNTERS */ 492 } 493 #endif 494 495 *mp = m; 496 return (0); 497 } 498 499 /* 500 * Tcp output routine: figure out what should be sent and send it. 501 */ 502 int 503 tcp_output(tp) 504 struct tcpcb *tp; 505 { 506 struct socket *so; 507 struct route *ro; 508 long len, win; 509 int off, flags, error; 510 struct mbuf *m; 511 struct ip *ip; 512 #ifdef INET6 513 struct ip6_hdr *ip6; 514 #endif 515 struct tcphdr *th; 516 u_char opt[MAX_TCPOPTLEN]; 517 unsigned optlen, hdrlen; 518 int idle, sendalot, txsegsize, rxsegsize; 519 int maxburst = TCP_MAXBURST; 520 int af; /* address family on the wire */ 521 int iphdrlen; 522 523 #ifdef DIAGNOSTIC 524 if (tp->t_inpcb && tp->t_in6pcb) 525 panic("tcp_output: both t_inpcb and t_in6pcb are set"); 526 #endif 527 so = NULL; 528 ro = NULL; 529 if (tp->t_inpcb) { 530 so = tp->t_inpcb->inp_socket; 531 ro = &tp->t_inpcb->inp_route; 532 } 533 #ifdef INET6 534 else if (tp->t_in6pcb) { 535 so = tp->t_in6pcb->in6p_socket; 536 ro = (struct route *)&tp->t_in6pcb->in6p_route; 537 } 538 #endif 539 540 switch (af = tp->t_family) { 541 #ifdef INET 542 case AF_INET: 543 if (tp->t_inpcb) 544 break; 545 #ifdef INET6 546 /* mapped addr case */ 547 if (tp->t_in6pcb) 548 break; 549 #endif 550 return EINVAL; 551 #endif 552 #ifdef INET6 553 case AF_INET6: 554 if (tp->t_in6pcb) 555 break; 556 return EINVAL; 557 #endif 558 default: 559 return EAFNOSUPPORT; 560 } 561 562 tcp_segsize(tp, &txsegsize, &rxsegsize); 563 564 idle = (tp->snd_max == tp->snd_una); 565 566 /* 567 * Restart Window computation. From draft-floyd-incr-init-win-03: 568 * 569 * Optionally, a TCP MAY set the restart window to the 570 * minimum of the value used for the initial window and 571 * the current value of cwnd (in other words, using a 572 * larger value for the restart window should never increase 573 * the size of cwnd). 574 */ 575 if (tcp_cwm) { 576 /* 577 * Hughes/Touch/Heidemann Congestion Window Monitoring. 578 * Count the number of packets currently pending 579 * acknowledgement, and limit our congestion window 580 * to a pre-determined allowed burst size plus that count. 581 * This prevents bursting once all pending packets have 582 * been acknowledged (i.e. transmission is idle). 583 * 584 * XXX Link this to Initial Window? 585 */ 586 tp->snd_cwnd = min(tp->snd_cwnd, 587 (tcp_cwm_burstsize * txsegsize) + 588 (tp->snd_nxt - tp->snd_una)); 589 } else { 590 if (idle && (tcp_now - tp->t_rcvtime) >= tp->t_rxtcur) { 591 /* 592 * We have been idle for "a while" and no acks are 593 * expected to clock out any data we send -- 594 * slow start to get ack "clock" running again. 595 */ 596 int ss = tcp_init_win; 597 #ifdef INET 598 if (tp->t_inpcb && 599 in_localaddr(tp->t_inpcb->inp_faddr)) 600 ss = tcp_init_win_local; 601 #endif 602 #ifdef INET6 603 if (tp->t_in6pcb && 604 in6_localaddr(&tp->t_in6pcb->in6p_faddr)) 605 ss = tcp_init_win_local; 606 #endif 607 tp->snd_cwnd = min(tp->snd_cwnd, 608 TCP_INITIAL_WINDOW(ss, txsegsize)); 609 } 610 } 611 612 again: 613 /* 614 * Determine length of data that should be transmitted, and 615 * flags that should be used. If there is some data or critical 616 * controls (SYN, RST) to send, then transmit; otherwise, 617 * investigate further. 618 */ 619 sendalot = 0; 620 off = tp->snd_nxt - tp->snd_una; 621 win = min(tp->snd_wnd, tp->snd_cwnd); 622 623 flags = tcp_outflags[tp->t_state]; 624 /* 625 * If in persist timeout with window of 0, send 1 byte. 626 * Otherwise, if window is small but nonzero 627 * and timer expired, we will send what we can 628 * and go to transmit state. 629 */ 630 if (tp->t_force) { 631 if (win == 0) { 632 /* 633 * If we still have some data to send, then 634 * clear the FIN bit. Usually this would 635 * happen below when it realizes that we 636 * aren't sending all the data. However, 637 * if we have exactly 1 byte of unset data, 638 * then it won't clear the FIN bit below, 639 * and if we are in persist state, we wind 640 * up sending the packet without recording 641 * that we sent the FIN bit. 642 * 643 * We can't just blindly clear the FIN bit, 644 * because if we don't have any more data 645 * to send then the probe will be the FIN 646 * itself. 647 */ 648 if (off < so->so_snd.sb_cc) 649 flags &= ~TH_FIN; 650 win = 1; 651 } else { 652 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 653 tp->t_rxtshift = 0; 654 } 655 } 656 657 if (win < so->so_snd.sb_cc) { 658 len = win - off; 659 flags &= ~TH_FIN; 660 } else 661 len = so->so_snd.sb_cc - off; 662 663 if (len < 0) { 664 /* 665 * If FIN has been sent but not acked, 666 * but we haven't been called to retransmit, 667 * len will be -1. Otherwise, window shrank 668 * after we sent into it. If window shrank to 0, 669 * cancel pending retransmit, pull snd_nxt back 670 * to (closed) window, and set the persist timer 671 * if it isn't already going. If the window didn't 672 * close completely, just wait for an ACK. 673 * 674 * If we have a pending FIN, either it has already been 675 * transmitted or it is outside the window, so drop it. 676 * If the FIN has been transmitted, but this is not a 677 * retransmission, then len must be -1. Therefore we also 678 * prevent here the sending of `gratuitous FINs'. This 679 * eliminates the need to check for that case below (e.g. 680 * to back up snd_nxt before the FIN so that the sequence 681 * number is correct). 682 */ 683 len = 0; 684 flags &= ~TH_FIN; 685 if (win == 0) { 686 TCP_TIMER_DISARM(tp, TCPT_REXMT); 687 tp->t_rxtshift = 0; 688 tp->snd_nxt = tp->snd_una; 689 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) 690 tcp_setpersist(tp); 691 } 692 } 693 if (len > txsegsize) { 694 len = txsegsize; 695 flags &= ~TH_FIN; 696 sendalot = 1; 697 } 698 699 win = sbspace(&so->so_rcv); 700 701 /* 702 * Sender silly window avoidance. If connection is idle 703 * and can send all data, a maximum segment, 704 * at least a maximum default-size segment do it, 705 * or are forced, do it; otherwise don't bother. 706 * If peer's buffer is tiny, then send 707 * when window is at least half open. 708 * If retransmitting (possibly after persist timer forced us 709 * to send into a small window), then must resend. 710 */ 711 if (len) { 712 if (len == txsegsize) 713 goto send; 714 if ((so->so_state & SS_MORETOCOME) == 0 && 715 ((idle || tp->t_flags & TF_NODELAY) && 716 len + off >= so->so_snd.sb_cc)) 717 goto send; 718 if (tp->t_force) 719 goto send; 720 if (len >= tp->max_sndwnd / 2) 721 goto send; 722 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 723 goto send; 724 } 725 726 /* 727 * Compare available window to amount of window known to peer 728 * (as advertised window less next expected input). If the 729 * difference is at least twice the size of the largest segment 730 * we expect to receive (i.e. two segments) or at least 50% of 731 * the maximum possible window, then want to send a window update 732 * to peer. 733 */ 734 if (win > 0) { 735 /* 736 * "adv" is the amount we can increase the window, 737 * taking into account that we are limited by 738 * TCP_MAXWIN << tp->rcv_scale. 739 */ 740 long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) - 741 (tp->rcv_adv - tp->rcv_nxt); 742 743 if (adv >= (long) (2 * rxsegsize)) 744 goto send; 745 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 746 goto send; 747 } 748 749 /* 750 * Send if we owe peer an ACK. 751 */ 752 if (tp->t_flags & TF_ACKNOW) 753 goto send; 754 if (flags & (TH_SYN|TH_FIN|TH_RST)) 755 goto send; 756 if (SEQ_GT(tp->snd_up, tp->snd_una)) 757 goto send; 758 759 /* 760 * TCP window updates are not reliable, rather a polling protocol 761 * using ``persist'' packets is used to insure receipt of window 762 * updates. The three ``states'' for the output side are: 763 * idle not doing retransmits or persists 764 * persisting to move a small or zero window 765 * (re)transmitting and thereby not persisting 766 * 767 * tp->t_timer[TCPT_PERSIST] 768 * is set when we are in persist state. 769 * tp->t_force 770 * is set when we are called to send a persist packet. 771 * tp->t_timer[TCPT_REXMT] 772 * is set when we are retransmitting 773 * The output side is idle when both timers are zero. 774 * 775 * If send window is too small, there is data to transmit, and no 776 * retransmit or persist is pending, then go to persist state. 777 * If nothing happens soon, send when timer expires: 778 * if window is nonzero, transmit what we can, 779 * otherwise force out a byte. 780 */ 781 if (so->so_snd.sb_cc && TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 782 TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 783 tp->t_rxtshift = 0; 784 tcp_setpersist(tp); 785 } 786 787 /* 788 * No reason to send a segment, just return. 789 */ 790 return (0); 791 792 send: 793 /* 794 * Before ESTABLISHED, force sending of initial options 795 * unless TCP set not to do any options. 796 * NOTE: we assume that the IP/TCP header plus TCP options 797 * always fit in a single mbuf, leaving room for a maximum 798 * link header, i.e. 799 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 800 */ 801 optlen = 0; 802 switch (af) { 803 #ifdef INET 804 case AF_INET: 805 iphdrlen = sizeof(struct ip) + sizeof(struct tcphdr); 806 break; 807 #endif 808 #ifdef INET6 809 case AF_INET6: 810 iphdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); 811 break; 812 #endif 813 default: /*pacify gcc*/ 814 iphdrlen = 0; 815 break; 816 } 817 hdrlen = iphdrlen; 818 if (flags & TH_SYN) { 819 struct rtentry *rt; 820 821 rt = NULL; 822 #ifdef INET 823 if (tp->t_inpcb) 824 rt = in_pcbrtentry(tp->t_inpcb); 825 #endif 826 #ifdef INET6 827 if (tp->t_in6pcb) 828 rt = in6_pcbrtentry(tp->t_in6pcb); 829 #endif 830 831 tp->snd_nxt = tp->iss; 832 tp->t_ourmss = tcp_mss_to_advertise(rt != NULL ? 833 rt->rt_ifp : NULL, af); 834 if ((tp->t_flags & TF_NOOPT) == 0) { 835 opt[0] = TCPOPT_MAXSEG; 836 opt[1] = 4; 837 opt[2] = (tp->t_ourmss >> 8) & 0xff; 838 opt[3] = tp->t_ourmss & 0xff; 839 optlen = 4; 840 841 if ((tp->t_flags & TF_REQ_SCALE) && 842 ((flags & TH_ACK) == 0 || 843 (tp->t_flags & TF_RCVD_SCALE))) { 844 *((u_int32_t *) (opt + optlen)) = htonl( 845 TCPOPT_NOP << 24 | 846 TCPOPT_WINDOW << 16 | 847 TCPOLEN_WINDOW << 8 | 848 tp->request_r_scale); 849 optlen += 4; 850 } 851 } 852 } 853 854 /* 855 * Send a timestamp and echo-reply if this is a SYN and our side 856 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 857 * and our peer have sent timestamps in our SYN's. 858 */ 859 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 860 (flags & TH_RST) == 0 && 861 ((flags & (TH_SYN|TH_ACK)) == TH_SYN || 862 (tp->t_flags & TF_RCVD_TSTMP))) { 863 u_int32_t *lp = (u_int32_t *)(opt + optlen); 864 865 /* Form timestamp option as shown in appendix A of RFC 1323. */ 866 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 867 *lp++ = htonl(TCP_TIMESTAMP(tp)); 868 *lp = htonl(tp->ts_recent); 869 optlen += TCPOLEN_TSTAMP_APPA; 870 } 871 872 hdrlen += optlen; 873 874 #ifdef DIAGNOSTIC 875 if (len > txsegsize) 876 panic("tcp data to be sent is larger than segment"); 877 if (max_linkhdr + hdrlen > MCLBYTES) 878 panic("tcphdr too big"); 879 #endif 880 881 /* 882 * Grab a header mbuf, attaching a copy of data to 883 * be transmitted, and initialize the header from 884 * the template for sends on this connection. 885 */ 886 if (len) { 887 error = tcp_build_datapkt(tp, so, off, len, hdrlen, &m); 888 if (error) 889 goto out; 890 /* 891 * If we're sending everything we've got, set PUSH. 892 * (This will keep happy those implementations which only 893 * give data to the user when a buffer fills or 894 * a PUSH comes in.) 895 */ 896 if (off + len == so->so_snd.sb_cc) 897 flags |= TH_PUSH; 898 } else { 899 if (tp->t_flags & TF_ACKNOW) 900 tcpstat.tcps_sndacks++; 901 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 902 tcpstat.tcps_sndctrl++; 903 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 904 tcpstat.tcps_sndurg++; 905 else 906 tcpstat.tcps_sndwinup++; 907 908 MGETHDR(m, M_DONTWAIT, MT_HEADER); 909 if (m != NULL && max_linkhdr + hdrlen > MHLEN) { 910 MCLGET(m, M_DONTWAIT); 911 if ((m->m_flags & M_EXT) == 0) { 912 m_freem(m); 913 m = NULL; 914 } 915 } 916 if (m == NULL) { 917 error = ENOBUFS; 918 goto out; 919 } 920 MCLAIM(m, &tcp_tx_mowner); 921 m->m_data += max_linkhdr; 922 m->m_len = hdrlen; 923 } 924 m->m_pkthdr.rcvif = (struct ifnet *)0; 925 switch (af) { 926 #ifdef INET 927 case AF_INET: 928 ip = mtod(m, struct ip *); 929 #ifdef INET6 930 ip6 = NULL; 931 #endif 932 th = (struct tcphdr *)(ip + 1); 933 break; 934 #endif 935 #ifdef INET6 936 case AF_INET6: 937 ip = NULL; 938 ip6 = mtod(m, struct ip6_hdr *); 939 th = (struct tcphdr *)(ip6 + 1); 940 break; 941 #endif 942 default: /*pacify gcc*/ 943 ip = NULL; 944 #ifdef INET6 945 ip6 = NULL; 946 #endif 947 th = NULL; 948 break; 949 } 950 if (tp->t_template == 0) 951 panic("tcp_output"); 952 if (tp->t_template->m_len < iphdrlen) 953 panic("tcp_output"); 954 bcopy(mtod(tp->t_template, caddr_t), mtod(m, caddr_t), iphdrlen); 955 956 /* 957 * If we are doing retransmissions, then snd_nxt will 958 * not reflect the first unsent octet. For ACK only 959 * packets, we do not want the sequence number of the 960 * retransmitted packet, we want the sequence number 961 * of the next unsent octet. So, if there is no data 962 * (and no SYN or FIN), use snd_max instead of snd_nxt 963 * when filling in ti_seq. But if we are in persist 964 * state, snd_max might reflect one byte beyond the 965 * right edge of the window, so use snd_nxt in that 966 * case, since we know we aren't doing a retransmission. 967 * (retransmit and persist are mutually exclusive...) 968 */ 969 if (len || (flags & (TH_SYN|TH_FIN)) || 970 TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) 971 th->th_seq = htonl(tp->snd_nxt); 972 else 973 th->th_seq = htonl(tp->snd_max); 974 th->th_ack = htonl(tp->rcv_nxt); 975 if (optlen) { 976 bcopy((caddr_t)opt, (caddr_t)(th + 1), optlen); 977 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 978 } 979 th->th_flags = flags; 980 /* 981 * Calculate receive window. Don't shrink window, 982 * but avoid silly window syndrome. 983 */ 984 if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)rxsegsize) 985 win = 0; 986 if (win > (long)TCP_MAXWIN << tp->rcv_scale) 987 win = (long)TCP_MAXWIN << tp->rcv_scale; 988 if (win < (long)(tp->rcv_adv - tp->rcv_nxt)) 989 win = (long)(tp->rcv_adv - tp->rcv_nxt); 990 th->th_win = htons((u_int16_t) (win>>tp->rcv_scale)); 991 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 992 u_int32_t urp = tp->snd_up - tp->snd_nxt; 993 if (urp > IP_MAXPACKET) 994 urp = IP_MAXPACKET; 995 th->th_urp = htons((u_int16_t)urp); 996 th->th_flags |= TH_URG; 997 } else 998 /* 999 * If no urgent pointer to send, then we pull 1000 * the urgent pointer to the left edge of the send window 1001 * so that it doesn't drift into the send window on sequence 1002 * number wraparound. 1003 */ 1004 tp->snd_up = tp->snd_una; /* drag it along */ 1005 1006 /* 1007 * Set ourselves up to be checksummed just before the packet 1008 * hits the wire. 1009 */ 1010 switch (af) { 1011 #ifdef INET 1012 case AF_INET: 1013 m->m_pkthdr.csum_flags = M_CSUM_TCPv4; 1014 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1015 if (len + optlen) { 1016 /* Fixup the pseudo-header checksum. */ 1017 /* XXXJRT Not IP Jumbogram safe. */ 1018 th->th_sum = in_cksum_addword(th->th_sum, 1019 htons((u_int16_t) (len + optlen))); 1020 } 1021 break; 1022 #endif 1023 #ifdef INET6 1024 case AF_INET6: 1025 /* 1026 * XXX Actually delaying the checksum is Hard 1027 * XXX (well, maybe not for Itojun, but it is 1028 * XXX for me), but we can still take advantage 1029 * XXX of the cached pseudo-header checksum. 1030 */ 1031 /* equals to hdrlen + len */ 1032 m->m_pkthdr.len = sizeof(struct ip6_hdr) 1033 + sizeof(struct tcphdr) + optlen + len; 1034 #ifdef notyet 1035 m->m_pkthdr.csum_flags = M_CSUM_TCPv6; 1036 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1037 #endif 1038 if (len + optlen) { 1039 /* Fixup the pseudo-header checksum. */ 1040 /* XXXJRT: Not IPv6 Jumbogram safe. */ 1041 th->th_sum = in_cksum_addword(th->th_sum, 1042 htons((u_int16_t) (len + optlen))); 1043 } 1044 #ifndef notyet 1045 th->th_sum = in6_cksum(m, 0, sizeof(struct ip6_hdr), 1046 sizeof(struct tcphdr) + optlen + len); 1047 #endif 1048 break; 1049 #endif 1050 } 1051 1052 /* 1053 * In transmit state, time the transmission and arrange for 1054 * the retransmit. In persist state, just set snd_max. 1055 */ 1056 if (tp->t_force == 0 || TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 1057 tcp_seq startseq = tp->snd_nxt; 1058 1059 /* 1060 * Advance snd_nxt over sequence space of this segment. 1061 * There are no states in which we send both a SYN and a FIN, 1062 * so we collapse the tests for these flags. 1063 */ 1064 if (flags & (TH_SYN|TH_FIN)) 1065 tp->snd_nxt++; 1066 tp->snd_nxt += len; 1067 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1068 tp->snd_max = tp->snd_nxt; 1069 /* 1070 * Time this transmission if not a retransmission and 1071 * not currently timing anything. 1072 */ 1073 if (tp->t_rtttime == 0) { 1074 tp->t_rtttime = tcp_now; 1075 tp->t_rtseq = startseq; 1076 tcpstat.tcps_segstimed++; 1077 } 1078 } 1079 1080 /* 1081 * Set retransmit timer if not currently set, 1082 * and not doing an ack or a keep-alive probe. 1083 * Initial value for retransmit timer is smoothed 1084 * round-trip time + 2 * round-trip time variance. 1085 * Initialize shift counter which is used for backoff 1086 * of retransmit time. 1087 */ 1088 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 1089 tp->snd_nxt != tp->snd_una) { 1090 TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); 1091 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) { 1092 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 1093 tp->t_rxtshift = 0; 1094 } 1095 } 1096 } else 1097 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 1098 tp->snd_max = tp->snd_nxt + len; 1099 1100 #ifdef TCP_DEBUG 1101 /* 1102 * Trace. 1103 */ 1104 if (so->so_options & SO_DEBUG) 1105 tcp_trace(TA_OUTPUT, tp->t_state, tp, m, 0); 1106 #endif 1107 1108 /* 1109 * Fill in IP length and desired time to live and 1110 * send to IP level. There should be a better way 1111 * to handle ttl and tos; we could keep them in 1112 * the template, but need a way to checksum without them. 1113 */ 1114 m->m_pkthdr.len = hdrlen + len; 1115 1116 switch (af) { 1117 #ifdef INET 1118 case AF_INET: 1119 ip->ip_len = htons(m->m_pkthdr.len); 1120 if (tp->t_inpcb) { 1121 ip->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl; 1122 ip->ip_tos = tp->t_inpcb->inp_ip.ip_tos; 1123 } 1124 #ifdef INET6 1125 else if (tp->t_in6pcb) { 1126 ip->ip_ttl = in6_selecthlim(tp->t_in6pcb, NULL); /*XXX*/ 1127 ip->ip_tos = 0; /*XXX*/ 1128 } 1129 #endif 1130 break; 1131 #endif 1132 #ifdef INET6 1133 case AF_INET6: 1134 ip6->ip6_nxt = IPPROTO_TCP; 1135 if (tp->t_in6pcb) { 1136 /* 1137 * we separately set hoplimit for every segment, since 1138 * the user might want to change the value via 1139 * setsockopt. Also, desired default hop limit might 1140 * be changed via Neighbor Discovery. 1141 */ 1142 ip6->ip6_hlim = in6_selecthlim(tp->t_in6pcb, 1143 ro->ro_rt ? ro->ro_rt->rt_ifp : NULL); 1144 } 1145 /* ip6->ip6_flow = ??? */ 1146 /* ip6_plen will be filled in ip6_output(). */ 1147 break; 1148 #endif 1149 } 1150 1151 #ifdef IPSEC 1152 if (ipsec_setsocket(m, so) != 0) { 1153 m_freem(m); 1154 error = ENOBUFS; 1155 goto out; 1156 } 1157 #endif /*IPSEC*/ 1158 1159 switch (af) { 1160 #ifdef INET 1161 case AF_INET: 1162 { 1163 struct mbuf *opts; 1164 1165 if (tp->t_inpcb) 1166 opts = tp->t_inpcb->inp_options; 1167 else 1168 opts = NULL; 1169 error = ip_output(m, opts, ro, 1170 (tp->t_mtudisc ? IP_MTUDISC : 0) | 1171 (so->so_options & SO_DONTROUTE), 1172 0); 1173 break; 1174 } 1175 #endif 1176 #ifdef INET6 1177 case AF_INET6: 1178 { 1179 struct ip6_pktopts *opts; 1180 1181 if (tp->t_in6pcb) 1182 opts = tp->t_in6pcb->in6p_outputopts; 1183 else 1184 opts = NULL; 1185 error = ip6_output(m, opts, (struct route_in6 *)ro, 1186 so->so_options & SO_DONTROUTE, 0, NULL); 1187 break; 1188 } 1189 #endif 1190 default: 1191 error = EAFNOSUPPORT; 1192 break; 1193 } 1194 if (error) { 1195 out: 1196 if (error == ENOBUFS) { 1197 tcpstat.tcps_selfquench++; 1198 #ifdef INET 1199 if (tp->t_inpcb) 1200 tcp_quench(tp->t_inpcb, 0); 1201 #endif 1202 #ifdef INET6 1203 if (tp->t_in6pcb) 1204 tcp6_quench(tp->t_in6pcb, 0); 1205 #endif 1206 error = 0; 1207 } else if ((error == EHOSTUNREACH || error == ENETDOWN) && 1208 TCPS_HAVERCVDSYN(tp->t_state)) { 1209 tp->t_softerror = error; 1210 error = 0; 1211 } 1212 1213 /* Restart the delayed ACK timer, if necessary. */ 1214 if (tp->t_flags & TF_DELACK) 1215 TCP_RESTART_DELACK(tp); 1216 1217 return (error); 1218 } 1219 tcpstat.tcps_sndtotal++; 1220 if (tp->t_flags & TF_DELACK) 1221 tcpstat.tcps_delack++; 1222 1223 /* 1224 * Data sent (as far as we can tell). 1225 * If this advertises a larger window than any other segment, 1226 * then remember the size of the advertised window. 1227 * Any pending ACK has now been sent. 1228 */ 1229 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 1230 tp->rcv_adv = tp->rcv_nxt + win; 1231 tp->last_ack_sent = tp->rcv_nxt; 1232 tp->t_flags &= ~TF_ACKNOW; 1233 TCP_CLEAR_DELACK(tp); 1234 #ifdef DIAGNOSTIC 1235 if (maxburst < 0) 1236 printf("tcp_output: maxburst exceeded by %d\n", -maxburst); 1237 #endif 1238 if (sendalot && (!tcp_do_newreno || --maxburst)) 1239 goto again; 1240 return (0); 1241 } 1242 1243 void 1244 tcp_setpersist(tp) 1245 struct tcpcb *tp; 1246 { 1247 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> (1 + 2); 1248 int nticks; 1249 1250 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT)) 1251 panic("tcp_output REXMT"); 1252 /* 1253 * Start/restart persistance timer. 1254 */ 1255 if (t < tp->t_rttmin) 1256 t = tp->t_rttmin; 1257 TCPT_RANGESET(nticks, t * tcp_backoff[tp->t_rxtshift], 1258 TCPTV_PERSMIN, TCPTV_PERSMAX); 1259 TCP_TIMER_ARM(tp, TCPT_PERSIST, nticks); 1260 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1261 tp->t_rxtshift++; 1262 } 1263