1 /* $NetBSD: tcp_output.c,v 1.96 2003/07/02 21:43:49 ragge 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. All advertising materials mentioning features or use of this software 122 * must display the following acknowledgement: 123 * This product includes software developed by the University of 124 * California, Berkeley and its contributors. 125 * 4. Neither the name of the University nor the names of its contributors 126 * may be used to endorse or promote products derived from this software 127 * without specific prior written permission. 128 * 129 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 130 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 131 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 132 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 133 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 134 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 135 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 136 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 137 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 138 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 139 * SUCH DAMAGE. 140 * 141 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95 142 */ 143 144 #include <sys/cdefs.h> 145 __KERNEL_RCSID(0, "$NetBSD: tcp_output.c,v 1.96 2003/07/02 21:43:49 ragge Exp $"); 146 147 #include "opt_inet.h" 148 #include "opt_ipsec.h" 149 #include "opt_tcp_debug.h" 150 151 #include <sys/param.h> 152 #include <sys/systm.h> 153 #include <sys/malloc.h> 154 #include <sys/mbuf.h> 155 #include <sys/protosw.h> 156 #include <sys/socket.h> 157 #include <sys/socketvar.h> 158 #include <sys/errno.h> 159 #include <sys/domain.h> 160 #include <sys/kernel.h> 161 162 #include <net/if.h> 163 #include <net/route.h> 164 165 #include <netinet/in.h> 166 #include <netinet/in_systm.h> 167 #include <netinet/ip.h> 168 #include <netinet/in_pcb.h> 169 #include <netinet/ip_var.h> 170 171 #ifdef INET6 172 #ifndef INET 173 #include <netinet/in.h> 174 #endif 175 #include <netinet/ip6.h> 176 #include <netinet6/in6_var.h> 177 #include <netinet6/ip6_var.h> 178 #include <netinet6/in6_pcb.h> 179 #include <netinet6/nd6.h> 180 #endif 181 182 #ifdef IPSEC 183 #include <netinet6/ipsec.h> 184 #endif 185 186 #include <netinet/tcp.h> 187 #define TCPOUTFLAGS 188 #include <netinet/tcp_fsm.h> 189 #include <netinet/tcp_seq.h> 190 #include <netinet/tcp_timer.h> 191 #include <netinet/tcp_var.h> 192 #include <netinet/tcpip.h> 193 #include <netinet/tcp_debug.h> 194 195 #ifdef notyet 196 extern struct mbuf *m_copypack(); 197 #endif 198 199 #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */ 200 201 /* 202 * Knob to enable Congestion Window Monitoring, and control the 203 * the burst size it allows. Default burst is 4 packets, per 204 * the Internet draft. 205 */ 206 int tcp_cwm = 0; 207 int tcp_cwm_burstsize = 4; 208 209 #ifdef TCP_OUTPUT_COUNTERS 210 #include <sys/device.h> 211 212 extern struct evcnt tcp_output_bigheader; 213 extern struct evcnt tcp_output_copysmall; 214 extern struct evcnt tcp_output_copybig; 215 extern struct evcnt tcp_output_refbig; 216 217 #define TCP_OUTPUT_COUNTER_INCR(ev) (ev)->ev_count++ 218 #else 219 220 #define TCP_OUTPUT_COUNTER_INCR(ev) /* nothing */ 221 222 #endif /* TCP_OUTPUT_COUNTERS */ 223 224 static 225 #ifndef GPROF 226 __inline 227 #endif 228 void 229 tcp_segsize(struct tcpcb *tp, int *txsegsizep, int *rxsegsizep) 230 { 231 #ifdef INET 232 struct inpcb *inp = tp->t_inpcb; 233 #endif 234 #ifdef INET6 235 struct in6pcb *in6p = tp->t_in6pcb; 236 #endif 237 struct socket *so = NULL; 238 struct rtentry *rt; 239 struct ifnet *ifp; 240 int size; 241 int iphlen; 242 int optlen; 243 244 #ifdef DIAGNOSTIC 245 if (tp->t_inpcb && tp->t_in6pcb) 246 panic("tcp_segsize: both t_inpcb and t_in6pcb are set"); 247 #endif 248 switch (tp->t_family) { 249 #ifdef INET 250 case AF_INET: 251 iphlen = sizeof(struct ip); 252 break; 253 #endif 254 #ifdef INET6 255 case AF_INET6: 256 iphlen = sizeof(struct ip6_hdr); 257 break; 258 #endif 259 default: 260 size = tcp_mssdflt; 261 goto out; 262 } 263 264 rt = NULL; 265 #ifdef INET 266 if (inp) { 267 rt = in_pcbrtentry(inp); 268 so = inp->inp_socket; 269 } 270 #endif 271 #ifdef INET6 272 if (in6p) { 273 rt = in6_pcbrtentry(in6p); 274 so = in6p->in6p_socket; 275 } 276 #endif 277 if (rt == NULL) { 278 size = tcp_mssdflt; 279 goto out; 280 } 281 282 ifp = rt->rt_ifp; 283 284 size = tcp_mssdflt; 285 if (tp->t_mtudisc && rt->rt_rmx.rmx_mtu != 0) 286 size = rt->rt_rmx.rmx_mtu - iphlen - sizeof(struct tcphdr); 287 else if (ifp->if_flags & IFF_LOOPBACK) 288 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 289 #ifdef INET 290 else if (inp && tp->t_mtudisc) 291 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 292 else if (inp && in_localaddr(inp->inp_faddr)) 293 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 294 #endif 295 #ifdef INET6 296 else if (in6p) { 297 #ifdef INET 298 if (IN6_IS_ADDR_V4MAPPED(&in6p->in6p_faddr)) { 299 /* mapped addr case */ 300 struct in_addr d; 301 bcopy(&in6p->in6p_faddr.s6_addr32[3], &d, sizeof(d)); 302 if (tp->t_mtudisc || in_localaddr(d)) 303 size = ifp->if_mtu - iphlen - sizeof(struct tcphdr); 304 } else 305 #endif 306 { 307 /* 308 * for IPv6, path MTU discovery is always turned on, 309 * or the node must use packet size <= 1280. 310 */ 311 size = tp->t_mtudisc ? IN6_LINKMTU(ifp) : IPV6_MMTU; 312 size -= (iphlen + sizeof(struct tcphdr)); 313 } 314 } 315 #endif 316 out: 317 /* 318 * Now we must make room for whatever extra TCP/IP options are in 319 * the packet. 320 */ 321 optlen = tcp_optlen(tp); 322 323 /* 324 * XXX tp->t_ourmss should have the right size, but without this code 325 * fragmentation will occur... need more investigation 326 */ 327 #ifdef INET 328 if (inp) { 329 #ifdef IPSEC 330 optlen += ipsec4_hdrsiz_tcp(tp); 331 #endif 332 optlen += ip_optlen(inp); 333 } 334 #endif 335 #ifdef INET6 336 #ifdef INET 337 if (in6p && tp->t_family == AF_INET) { 338 #ifdef IPSEC 339 optlen += ipsec4_hdrsiz_tcp(tp); 340 #endif 341 /* XXX size -= ip_optlen(in6p); */ 342 } else 343 #endif 344 if (in6p && tp->t_family == AF_INET6) { 345 #ifdef IPSEC 346 optlen += ipsec6_hdrsiz_tcp(tp); 347 #endif 348 optlen += ip6_optlen(in6p); 349 } 350 #endif 351 size -= optlen; 352 353 /* 354 * *rxsegsizep holds *estimated* inbound segment size (estimation 355 * assumes that path MTU is the same for both ways). this is only 356 * for silly window avoidance, do not use the value for other purposes. 357 * 358 * ipseclen is subtracted from both sides, this may not be right. 359 * I'm not quite sure about this (could someone comment). 360 */ 361 *txsegsizep = min(tp->t_peermss - optlen, size); 362 /* 363 * Never send more than half a buffer full. This insures that we can 364 * always keep 2 packets on the wire, no matter what SO_SNDBUF is, and 365 * therefore acks will never be delayed unless we run out of data to 366 * transmit. 367 */ 368 if (so) 369 *txsegsizep = min(so->so_snd.sb_hiwat >> 1, *txsegsizep); 370 *rxsegsizep = min(tp->t_ourmss - optlen, size); 371 372 if (*txsegsizep != tp->t_segsz) { 373 /* 374 * If the new segment size is larger, we don't want to 375 * mess up the congestion window, but if it is smaller 376 * we'll have to reduce the congestion window to ensure 377 * that we don't get into trouble with initial windows 378 * and the rest. In any case, if the segment size 379 * has changed, chances are the path has, too, and 380 * our congestion window will be different. 381 */ 382 if (*txsegsizep < tp->t_segsz) { 383 tp->snd_cwnd = max((tp->snd_cwnd / tp->t_segsz) 384 * *txsegsizep, *txsegsizep); 385 tp->snd_ssthresh = max((tp->snd_ssthresh / tp->t_segsz) 386 * *txsegsizep, *txsegsizep); 387 } 388 tp->t_segsz = *txsegsizep; 389 } 390 } 391 392 static 393 #ifndef GPROF 394 __inline 395 #endif 396 int 397 tcp_build_datapkt(struct tcpcb *tp, struct socket *so, int off, 398 long len, int hdrlen, struct mbuf **mp) 399 { 400 struct mbuf *m, *m0; 401 402 if (tp->t_force && len == 1) 403 tcpstat.tcps_sndprobe++; 404 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 405 tcpstat.tcps_sndrexmitpack++; 406 tcpstat.tcps_sndrexmitbyte += len; 407 } else { 408 tcpstat.tcps_sndpack++; 409 tcpstat.tcps_sndbyte += len; 410 } 411 #ifdef notyet 412 if ((m = m_copypack(so->so_snd.sb_mb, off, 413 (int)len, max_linkhdr + hdrlen)) == 0) 414 return (ENOBUFS); 415 /* 416 * m_copypack left space for our hdr; use it. 417 */ 418 m->m_len += hdrlen; 419 m->m_data -= hdrlen; 420 #else 421 MGETHDR(m, M_DONTWAIT, MT_HEADER); 422 if (__predict_false(m == NULL)) 423 return (ENOBUFS); 424 MCLAIM(m, &tcp_tx_mowner); 425 426 /* 427 * XXX Because other code assumes headers will fit in 428 * XXX one header mbuf. 429 * 430 * (This code should almost *never* be run.) 431 */ 432 if (__predict_false((max_linkhdr + hdrlen) > MHLEN)) { 433 TCP_OUTPUT_COUNTER_INCR(&tcp_output_bigheader); 434 MCLGET(m, M_DONTWAIT); 435 if ((m->m_flags & M_EXT) == 0) { 436 m_freem(m); 437 return (ENOBUFS); 438 } 439 } 440 441 m->m_data += max_linkhdr; 442 m->m_len = hdrlen; 443 444 /* 445 * To avoid traversing the whole sb_mb chain for correct 446 * data to send, remember last sent mbuf, its offset and 447 * the sent size. When called the next time, see if the 448 * data to send is the directly following the previous 449 * transfer. This is important for large TCP windows. 450 */ 451 #ifdef FAST_MBSEARCH 452 if (off == 0 || (tp->t_lastoff + tp->t_lastlen) != off) { 453 #else 454 if (1) { 455 #endif 456 /* 457 * Either a new packet or a retransmit. 458 * Start from the beginning. 459 */ 460 tp->t_lastm = so->so_snd.sb_mb; 461 tp->t_inoff = off; 462 } else 463 tp->t_inoff += tp->t_lastlen; 464 465 /* Traverse forward to next packet */ 466 while (tp->t_inoff > 0) { 467 if (tp->t_lastm == NULL) 468 panic("tp->t_lastm == NULL"); 469 if (tp->t_inoff < tp->t_lastm->m_len) 470 break; 471 tp->t_inoff -= tp->t_lastm->m_len; 472 tp->t_lastm = tp->t_lastm->m_next; 473 } 474 475 tp->t_lastoff = off; 476 tp->t_lastlen = len; 477 m0 = tp->t_lastm; 478 off = tp->t_inoff; 479 480 if (len <= M_TRAILINGSPACE(m)) { 481 m_copydata(m0, off, (int) len, mtod(m, caddr_t) + hdrlen); 482 m->m_len += len; 483 TCP_OUTPUT_COUNTER_INCR(&tcp_output_copysmall); 484 } else { 485 m->m_next = m_copy(m0, off, (int) len); 486 if (m->m_next == NULL) { 487 m_freem(m); 488 return (ENOBUFS); 489 } 490 #ifdef TCP_OUTPUT_COUNTERS 491 if (m->m_next->m_flags & M_EXT) 492 TCP_OUTPUT_COUNTER_INCR(&tcp_output_refbig); 493 else 494 TCP_OUTPUT_COUNTER_INCR(&tcp_output_copybig); 495 #endif /* TCP_OUTPUT_COUNTERS */ 496 } 497 #endif 498 499 *mp = m; 500 return (0); 501 } 502 503 /* 504 * Tcp output routine: figure out what should be sent and send it. 505 */ 506 int 507 tcp_output(tp) 508 struct tcpcb *tp; 509 { 510 struct socket *so; 511 struct route *ro; 512 long len, win; 513 int off, flags, error; 514 struct mbuf *m; 515 struct ip *ip; 516 #ifdef INET6 517 struct ip6_hdr *ip6; 518 #endif 519 struct tcphdr *th; 520 u_char opt[MAX_TCPOPTLEN]; 521 unsigned optlen, hdrlen; 522 int idle, sendalot, txsegsize, rxsegsize; 523 int maxburst = TCP_MAXBURST; 524 int af; /* address family on the wire */ 525 int iphdrlen; 526 527 #ifdef DIAGNOSTIC 528 if (tp->t_inpcb && tp->t_in6pcb) 529 panic("tcp_output: both t_inpcb and t_in6pcb are set"); 530 #endif 531 so = NULL; 532 ro = NULL; 533 if (tp->t_inpcb) { 534 so = tp->t_inpcb->inp_socket; 535 ro = &tp->t_inpcb->inp_route; 536 } 537 #ifdef INET6 538 else if (tp->t_in6pcb) { 539 so = tp->t_in6pcb->in6p_socket; 540 ro = (struct route *)&tp->t_in6pcb->in6p_route; 541 } 542 #endif 543 544 switch (af = tp->t_family) { 545 #ifdef INET 546 case AF_INET: 547 if (tp->t_inpcb) 548 break; 549 #ifdef INET6 550 /* mapped addr case */ 551 if (tp->t_in6pcb) 552 break; 553 #endif 554 return EINVAL; 555 #endif 556 #ifdef INET6 557 case AF_INET6: 558 if (tp->t_in6pcb) 559 break; 560 return EINVAL; 561 #endif 562 default: 563 return EAFNOSUPPORT; 564 } 565 566 tcp_segsize(tp, &txsegsize, &rxsegsize); 567 568 idle = (tp->snd_max == tp->snd_una); 569 570 /* 571 * Restart Window computation. From draft-floyd-incr-init-win-03: 572 * 573 * Optionally, a TCP MAY set the restart window to the 574 * minimum of the value used for the initial window and 575 * the current value of cwnd (in other words, using a 576 * larger value for the restart window should never increase 577 * the size of cwnd). 578 */ 579 if (tcp_cwm) { 580 /* 581 * Hughes/Touch/Heidemann Congestion Window Monitoring. 582 * Count the number of packets currently pending 583 * acknowledgement, and limit our congestion window 584 * to a pre-determined allowed burst size plus that count. 585 * This prevents bursting once all pending packets have 586 * been acknowledged (i.e. transmission is idle). 587 * 588 * XXX Link this to Initial Window? 589 */ 590 tp->snd_cwnd = min(tp->snd_cwnd, 591 (tcp_cwm_burstsize * txsegsize) + 592 (tp->snd_nxt - tp->snd_una)); 593 } else { 594 if (idle && (tcp_now - tp->t_rcvtime) >= tp->t_rxtcur) { 595 /* 596 * We have been idle for "a while" and no acks are 597 * expected to clock out any data we send -- 598 * slow start to get ack "clock" running again. 599 */ 600 int ss = tcp_init_win; 601 #ifdef INET 602 if (tp->t_inpcb && 603 in_localaddr(tp->t_inpcb->inp_faddr)) 604 ss = tcp_init_win_local; 605 #endif 606 #ifdef INET6 607 if (tp->t_in6pcb && 608 in6_localaddr(&tp->t_in6pcb->in6p_faddr)) 609 ss = tcp_init_win_local; 610 #endif 611 tp->snd_cwnd = min(tp->snd_cwnd, 612 TCP_INITIAL_WINDOW(ss, txsegsize)); 613 } 614 } 615 616 again: 617 /* 618 * Determine length of data that should be transmitted, and 619 * flags that should be used. If there is some data or critical 620 * controls (SYN, RST) to send, then transmit; otherwise, 621 * investigate further. 622 */ 623 sendalot = 0; 624 off = tp->snd_nxt - tp->snd_una; 625 win = min(tp->snd_wnd, tp->snd_cwnd); 626 627 flags = tcp_outflags[tp->t_state]; 628 /* 629 * If in persist timeout with window of 0, send 1 byte. 630 * Otherwise, if window is small but nonzero 631 * and timer expired, we will send what we can 632 * and go to transmit state. 633 */ 634 if (tp->t_force) { 635 if (win == 0) { 636 /* 637 * If we still have some data to send, then 638 * clear the FIN bit. Usually this would 639 * happen below when it realizes that we 640 * aren't sending all the data. However, 641 * if we have exactly 1 byte of unset data, 642 * then it won't clear the FIN bit below, 643 * and if we are in persist state, we wind 644 * up sending the packet without recording 645 * that we sent the FIN bit. 646 * 647 * We can't just blindly clear the FIN bit, 648 * because if we don't have any more data 649 * to send then the probe will be the FIN 650 * itself. 651 */ 652 if (off < so->so_snd.sb_cc) 653 flags &= ~TH_FIN; 654 win = 1; 655 } else { 656 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 657 tp->t_rxtshift = 0; 658 } 659 } 660 661 if (win < so->so_snd.sb_cc) { 662 len = win - off; 663 flags &= ~TH_FIN; 664 } else 665 len = so->so_snd.sb_cc - off; 666 667 if (len < 0) { 668 /* 669 * If FIN has been sent but not acked, 670 * but we haven't been called to retransmit, 671 * len will be -1. Otherwise, window shrank 672 * after we sent into it. If window shrank to 0, 673 * cancel pending retransmit, pull snd_nxt back 674 * to (closed) window, and set the persist timer 675 * if it isn't already going. If the window didn't 676 * close completely, just wait for an ACK. 677 * 678 * If we have a pending FIN, either it has already been 679 * transmitted or it is outside the window, so drop it. 680 * If the FIN has been transmitted, but this is not a 681 * retransmission, then len must be -1. Therefore we also 682 * prevent here the sending of `gratuitous FINs'. This 683 * eliminates the need to check for that case below (e.g. 684 * to back up snd_nxt before the FIN so that the sequence 685 * number is correct). 686 */ 687 len = 0; 688 flags &= ~TH_FIN; 689 if (win == 0) { 690 TCP_TIMER_DISARM(tp, TCPT_REXMT); 691 tp->t_rxtshift = 0; 692 tp->snd_nxt = tp->snd_una; 693 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) 694 tcp_setpersist(tp); 695 } 696 } 697 if (len > txsegsize) { 698 len = txsegsize; 699 flags &= ~TH_FIN; 700 sendalot = 1; 701 } 702 703 win = sbspace(&so->so_rcv); 704 705 /* 706 * Sender silly window avoidance. If connection is idle 707 * and can send all data, a maximum segment, 708 * at least a maximum default-size segment do it, 709 * or are forced, do it; otherwise don't bother. 710 * If peer's buffer is tiny, then send 711 * when window is at least half open. 712 * If retransmitting (possibly after persist timer forced us 713 * to send into a small window), then must resend. 714 */ 715 if (len) { 716 if (len == txsegsize) 717 goto send; 718 if ((so->so_state & SS_MORETOCOME) == 0 && 719 ((idle || tp->t_flags & TF_NODELAY) && 720 len + off >= so->so_snd.sb_cc)) 721 goto send; 722 if (tp->t_force) 723 goto send; 724 if (len >= tp->max_sndwnd / 2) 725 goto send; 726 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 727 goto send; 728 } 729 730 /* 731 * Compare available window to amount of window known to peer 732 * (as advertised window less next expected input). If the 733 * difference is at least twice the size of the largest segment 734 * we expect to receive (i.e. two segments) or at least 50% of 735 * the maximum possible window, then want to send a window update 736 * to peer. 737 */ 738 if (win > 0) { 739 /* 740 * "adv" is the amount we can increase the window, 741 * taking into account that we are limited by 742 * TCP_MAXWIN << tp->rcv_scale. 743 */ 744 long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) - 745 (tp->rcv_adv - tp->rcv_nxt); 746 747 if (adv >= (long) (2 * rxsegsize)) 748 goto send; 749 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 750 goto send; 751 } 752 753 /* 754 * Send if we owe peer an ACK. 755 */ 756 if (tp->t_flags & TF_ACKNOW) 757 goto send; 758 if (flags & (TH_SYN|TH_FIN|TH_RST)) 759 goto send; 760 if (SEQ_GT(tp->snd_up, tp->snd_una)) 761 goto send; 762 763 /* 764 * TCP window updates are not reliable, rather a polling protocol 765 * using ``persist'' packets is used to insure receipt of window 766 * updates. The three ``states'' for the output side are: 767 * idle not doing retransmits or persists 768 * persisting to move a small or zero window 769 * (re)transmitting and thereby not persisting 770 * 771 * tp->t_timer[TCPT_PERSIST] 772 * is set when we are in persist state. 773 * tp->t_force 774 * is set when we are called to send a persist packet. 775 * tp->t_timer[TCPT_REXMT] 776 * is set when we are retransmitting 777 * The output side is idle when both timers are zero. 778 * 779 * If send window is too small, there is data to transmit, and no 780 * retransmit or persist is pending, then go to persist state. 781 * If nothing happens soon, send when timer expires: 782 * if window is nonzero, transmit what we can, 783 * otherwise force out a byte. 784 */ 785 if (so->so_snd.sb_cc && TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 786 TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 787 tp->t_rxtshift = 0; 788 tcp_setpersist(tp); 789 } 790 791 /* 792 * No reason to send a segment, just return. 793 */ 794 return (0); 795 796 send: 797 /* 798 * Before ESTABLISHED, force sending of initial options 799 * unless TCP set not to do any options. 800 * NOTE: we assume that the IP/TCP header plus TCP options 801 * always fit in a single mbuf, leaving room for a maximum 802 * link header, i.e. 803 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 804 */ 805 optlen = 0; 806 switch (af) { 807 #ifdef INET 808 case AF_INET: 809 iphdrlen = sizeof(struct ip) + sizeof(struct tcphdr); 810 break; 811 #endif 812 #ifdef INET6 813 case AF_INET6: 814 iphdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); 815 break; 816 #endif 817 default: /*pacify gcc*/ 818 iphdrlen = 0; 819 break; 820 } 821 hdrlen = iphdrlen; 822 if (flags & TH_SYN) { 823 struct rtentry *rt; 824 825 rt = NULL; 826 #ifdef INET 827 if (tp->t_inpcb) 828 rt = in_pcbrtentry(tp->t_inpcb); 829 #endif 830 #ifdef INET6 831 if (tp->t_in6pcb) 832 rt = in6_pcbrtentry(tp->t_in6pcb); 833 #endif 834 835 tp->snd_nxt = tp->iss; 836 tp->t_ourmss = tcp_mss_to_advertise(rt != NULL ? 837 rt->rt_ifp : NULL, af); 838 if ((tp->t_flags & TF_NOOPT) == 0) { 839 opt[0] = TCPOPT_MAXSEG; 840 opt[1] = 4; 841 opt[2] = (tp->t_ourmss >> 8) & 0xff; 842 opt[3] = tp->t_ourmss & 0xff; 843 optlen = 4; 844 845 if ((tp->t_flags & TF_REQ_SCALE) && 846 ((flags & TH_ACK) == 0 || 847 (tp->t_flags & TF_RCVD_SCALE))) { 848 *((u_int32_t *) (opt + optlen)) = htonl( 849 TCPOPT_NOP << 24 | 850 TCPOPT_WINDOW << 16 | 851 TCPOLEN_WINDOW << 8 | 852 tp->request_r_scale); 853 optlen += 4; 854 } 855 } 856 } 857 858 /* 859 * Send a timestamp and echo-reply if this is a SYN and our side 860 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 861 * and our peer have sent timestamps in our SYN's. 862 */ 863 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 864 (flags & TH_RST) == 0 && 865 ((flags & (TH_SYN|TH_ACK)) == TH_SYN || 866 (tp->t_flags & TF_RCVD_TSTMP))) { 867 u_int32_t *lp = (u_int32_t *)(opt + optlen); 868 869 /* Form timestamp option as shown in appendix A of RFC 1323. */ 870 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 871 *lp++ = htonl(TCP_TIMESTAMP(tp)); 872 *lp = htonl(tp->ts_recent); 873 optlen += TCPOLEN_TSTAMP_APPA; 874 } 875 876 hdrlen += optlen; 877 878 #ifdef DIAGNOSTIC 879 if (len > txsegsize) 880 panic("tcp data to be sent is larger than segment"); 881 if (max_linkhdr + hdrlen > MCLBYTES) 882 panic("tcphdr too big"); 883 #endif 884 885 /* 886 * Grab a header mbuf, attaching a copy of data to 887 * be transmitted, and initialize the header from 888 * the template for sends on this connection. 889 */ 890 if (len) { 891 error = tcp_build_datapkt(tp, so, off, len, hdrlen, &m); 892 if (error) 893 goto out; 894 /* 895 * If we're sending everything we've got, set PUSH. 896 * (This will keep happy those implementations which only 897 * give data to the user when a buffer fills or 898 * a PUSH comes in.) 899 */ 900 if (off + len == so->so_snd.sb_cc) 901 flags |= TH_PUSH; 902 } else { 903 if (tp->t_flags & TF_ACKNOW) 904 tcpstat.tcps_sndacks++; 905 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 906 tcpstat.tcps_sndctrl++; 907 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 908 tcpstat.tcps_sndurg++; 909 else 910 tcpstat.tcps_sndwinup++; 911 912 MGETHDR(m, M_DONTWAIT, MT_HEADER); 913 if (m != NULL && max_linkhdr + hdrlen > MHLEN) { 914 MCLGET(m, M_DONTWAIT); 915 if ((m->m_flags & M_EXT) == 0) { 916 m_freem(m); 917 m = NULL; 918 } 919 } 920 if (m == NULL) { 921 error = ENOBUFS; 922 goto out; 923 } 924 MCLAIM(m, &tcp_tx_mowner); 925 m->m_data += max_linkhdr; 926 m->m_len = hdrlen; 927 } 928 m->m_pkthdr.rcvif = (struct ifnet *)0; 929 switch (af) { 930 #ifdef INET 931 case AF_INET: 932 ip = mtod(m, struct ip *); 933 #ifdef INET6 934 ip6 = NULL; 935 #endif 936 th = (struct tcphdr *)(ip + 1); 937 break; 938 #endif 939 #ifdef INET6 940 case AF_INET6: 941 ip = NULL; 942 ip6 = mtod(m, struct ip6_hdr *); 943 th = (struct tcphdr *)(ip6 + 1); 944 break; 945 #endif 946 default: /*pacify gcc*/ 947 ip = NULL; 948 #ifdef INET6 949 ip6 = NULL; 950 #endif 951 th = NULL; 952 break; 953 } 954 if (tp->t_template == 0) 955 panic("tcp_output"); 956 if (tp->t_template->m_len < iphdrlen) 957 panic("tcp_output"); 958 bcopy(mtod(tp->t_template, caddr_t), mtod(m, caddr_t), iphdrlen); 959 960 /* 961 * If we are doing retransmissions, then snd_nxt will 962 * not reflect the first unsent octet. For ACK only 963 * packets, we do not want the sequence number of the 964 * retransmitted packet, we want the sequence number 965 * of the next unsent octet. So, if there is no data 966 * (and no SYN or FIN), use snd_max instead of snd_nxt 967 * when filling in ti_seq. But if we are in persist 968 * state, snd_max might reflect one byte beyond the 969 * right edge of the window, so use snd_nxt in that 970 * case, since we know we aren't doing a retransmission. 971 * (retransmit and persist are mutually exclusive...) 972 */ 973 if (len || (flags & (TH_SYN|TH_FIN)) || 974 TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) 975 th->th_seq = htonl(tp->snd_nxt); 976 else 977 th->th_seq = htonl(tp->snd_max); 978 th->th_ack = htonl(tp->rcv_nxt); 979 if (optlen) { 980 bcopy((caddr_t)opt, (caddr_t)(th + 1), optlen); 981 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 982 } 983 th->th_flags = flags; 984 /* 985 * Calculate receive window. Don't shrink window, 986 * but avoid silly window syndrome. 987 */ 988 if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)rxsegsize) 989 win = 0; 990 if (win > (long)TCP_MAXWIN << tp->rcv_scale) 991 win = (long)TCP_MAXWIN << tp->rcv_scale; 992 if (win < (long)(tp->rcv_adv - tp->rcv_nxt)) 993 win = (long)(tp->rcv_adv - tp->rcv_nxt); 994 th->th_win = htons((u_int16_t) (win>>tp->rcv_scale)); 995 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 996 u_int32_t urp = tp->snd_up - tp->snd_nxt; 997 if (urp > IP_MAXPACKET) 998 urp = IP_MAXPACKET; 999 th->th_urp = htons((u_int16_t)urp); 1000 th->th_flags |= TH_URG; 1001 } else 1002 /* 1003 * If no urgent pointer to send, then we pull 1004 * the urgent pointer to the left edge of the send window 1005 * so that it doesn't drift into the send window on sequence 1006 * number wraparound. 1007 */ 1008 tp->snd_up = tp->snd_una; /* drag it along */ 1009 1010 /* 1011 * Set ourselves up to be checksummed just before the packet 1012 * hits the wire. 1013 */ 1014 switch (af) { 1015 #ifdef INET 1016 case AF_INET: 1017 m->m_pkthdr.csum_flags = M_CSUM_TCPv4; 1018 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1019 if (len + optlen) { 1020 /* Fixup the pseudo-header checksum. */ 1021 /* XXXJRT Not IP Jumbogram safe. */ 1022 th->th_sum = in_cksum_addword(th->th_sum, 1023 htons((u_int16_t) (len + optlen))); 1024 } 1025 break; 1026 #endif 1027 #ifdef INET6 1028 case AF_INET6: 1029 /* 1030 * XXX Actually delaying the checksum is Hard 1031 * XXX (well, maybe not for Itojun, but it is 1032 * XXX for me), but we can still take advantage 1033 * XXX of the cached pseudo-header checksum. 1034 */ 1035 /* equals to hdrlen + len */ 1036 m->m_pkthdr.len = sizeof(struct ip6_hdr) 1037 + sizeof(struct tcphdr) + optlen + len; 1038 #ifdef notyet 1039 m->m_pkthdr.csum_flags = M_CSUM_TCPv6; 1040 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1041 #endif 1042 if (len + optlen) { 1043 /* Fixup the pseudo-header checksum. */ 1044 /* XXXJRT: Not IPv6 Jumbogram safe. */ 1045 th->th_sum = in_cksum_addword(th->th_sum, 1046 htons((u_int16_t) (len + optlen))); 1047 } 1048 #ifndef notyet 1049 th->th_sum = in6_cksum(m, 0, sizeof(struct ip6_hdr), 1050 sizeof(struct tcphdr) + optlen + len); 1051 #endif 1052 break; 1053 #endif 1054 } 1055 1056 /* 1057 * In transmit state, time the transmission and arrange for 1058 * the retransmit. In persist state, just set snd_max. 1059 */ 1060 if (tp->t_force == 0 || TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0) { 1061 tcp_seq startseq = tp->snd_nxt; 1062 1063 /* 1064 * Advance snd_nxt over sequence space of this segment. 1065 * There are no states in which we send both a SYN and a FIN, 1066 * so we collapse the tests for these flags. 1067 */ 1068 if (flags & (TH_SYN|TH_FIN)) 1069 tp->snd_nxt++; 1070 tp->snd_nxt += len; 1071 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1072 tp->snd_max = tp->snd_nxt; 1073 /* 1074 * Time this transmission if not a retransmission and 1075 * not currently timing anything. 1076 */ 1077 if (tp->t_rtttime == 0) { 1078 tp->t_rtttime = tcp_now; 1079 tp->t_rtseq = startseq; 1080 tcpstat.tcps_segstimed++; 1081 } 1082 } 1083 1084 /* 1085 * Set retransmit timer if not currently set, 1086 * and not doing an ack or a keep-alive probe. 1087 * Initial value for retransmit timer is smoothed 1088 * round-trip time + 2 * round-trip time variance. 1089 * Initialize shift counter which is used for backoff 1090 * of retransmit time. 1091 */ 1092 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 && 1093 tp->snd_nxt != tp->snd_una) { 1094 TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); 1095 if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST)) { 1096 TCP_TIMER_DISARM(tp, TCPT_PERSIST); 1097 tp->t_rxtshift = 0; 1098 } 1099 } 1100 } else 1101 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 1102 tp->snd_max = tp->snd_nxt + len; 1103 1104 #ifdef TCP_DEBUG 1105 /* 1106 * Trace. 1107 */ 1108 if (so->so_options & SO_DEBUG) 1109 tcp_trace(TA_OUTPUT, tp->t_state, tp, m, 0); 1110 #endif 1111 1112 /* 1113 * Fill in IP length and desired time to live and 1114 * send to IP level. There should be a better way 1115 * to handle ttl and tos; we could keep them in 1116 * the template, but need a way to checksum without them. 1117 */ 1118 m->m_pkthdr.len = hdrlen + len; 1119 1120 switch (af) { 1121 #ifdef INET 1122 case AF_INET: 1123 ip->ip_len = htons(m->m_pkthdr.len); 1124 if (tp->t_inpcb) { 1125 ip->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl; 1126 ip->ip_tos = tp->t_inpcb->inp_ip.ip_tos; 1127 } 1128 #ifdef INET6 1129 else if (tp->t_in6pcb) { 1130 ip->ip_ttl = in6_selecthlim(tp->t_in6pcb, NULL); /*XXX*/ 1131 ip->ip_tos = 0; /*XXX*/ 1132 } 1133 #endif 1134 break; 1135 #endif 1136 #ifdef INET6 1137 case AF_INET6: 1138 ip6->ip6_nxt = IPPROTO_TCP; 1139 if (tp->t_in6pcb) { 1140 /* 1141 * we separately set hoplimit for every segment, since 1142 * the user might want to change the value via 1143 * setsockopt. Also, desired default hop limit might 1144 * be changed via Neighbor Discovery. 1145 */ 1146 ip6->ip6_hlim = in6_selecthlim(tp->t_in6pcb, 1147 ro->ro_rt ? ro->ro_rt->rt_ifp : NULL); 1148 } 1149 /* ip6->ip6_flow = ??? */ 1150 /* ip6_plen will be filled in ip6_output(). */ 1151 break; 1152 #endif 1153 } 1154 1155 #ifdef IPSEC 1156 if (ipsec_setsocket(m, so) != 0) { 1157 m_freem(m); 1158 error = ENOBUFS; 1159 goto out; 1160 } 1161 #endif /*IPSEC*/ 1162 1163 switch (af) { 1164 #ifdef INET 1165 case AF_INET: 1166 { 1167 struct mbuf *opts; 1168 1169 if (tp->t_inpcb) 1170 opts = tp->t_inpcb->inp_options; 1171 else 1172 opts = NULL; 1173 error = ip_output(m, opts, ro, 1174 (tp->t_mtudisc ? IP_MTUDISC : 0) | 1175 (so->so_options & SO_DONTROUTE), 1176 0); 1177 break; 1178 } 1179 #endif 1180 #ifdef INET6 1181 case AF_INET6: 1182 { 1183 struct ip6_pktopts *opts; 1184 1185 if (tp->t_in6pcb) 1186 opts = tp->t_in6pcb->in6p_outputopts; 1187 else 1188 opts = NULL; 1189 error = ip6_output(m, opts, (struct route_in6 *)ro, 1190 so->so_options & SO_DONTROUTE, 0, NULL); 1191 break; 1192 } 1193 #endif 1194 default: 1195 error = EAFNOSUPPORT; 1196 break; 1197 } 1198 if (error) { 1199 out: 1200 if (error == ENOBUFS) { 1201 tcpstat.tcps_selfquench++; 1202 #ifdef INET 1203 if (tp->t_inpcb) 1204 tcp_quench(tp->t_inpcb, 0); 1205 #endif 1206 #ifdef INET6 1207 if (tp->t_in6pcb) 1208 tcp6_quench(tp->t_in6pcb, 0); 1209 #endif 1210 error = 0; 1211 } else if ((error == EHOSTUNREACH || error == ENETDOWN) && 1212 TCPS_HAVERCVDSYN(tp->t_state)) { 1213 tp->t_softerror = error; 1214 error = 0; 1215 } 1216 1217 /* Restart the delayed ACK timer, if necessary. */ 1218 if (tp->t_flags & TF_DELACK) 1219 TCP_RESTART_DELACK(tp); 1220 1221 return (error); 1222 } 1223 tcpstat.tcps_sndtotal++; 1224 if (tp->t_flags & TF_DELACK) 1225 tcpstat.tcps_delack++; 1226 1227 /* 1228 * Data sent (as far as we can tell). 1229 * If this advertises a larger window than any other segment, 1230 * then remember the size of the advertised window. 1231 * Any pending ACK has now been sent. 1232 */ 1233 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 1234 tp->rcv_adv = tp->rcv_nxt + win; 1235 tp->last_ack_sent = tp->rcv_nxt; 1236 tp->t_flags &= ~TF_ACKNOW; 1237 TCP_CLEAR_DELACK(tp); 1238 #ifdef DIAGNOSTIC 1239 if (maxburst < 0) 1240 printf("tcp_output: maxburst exceeded by %d\n", -maxburst); 1241 #endif 1242 if (sendalot && (!tcp_do_newreno || --maxburst)) 1243 goto again; 1244 return (0); 1245 } 1246 1247 void 1248 tcp_setpersist(tp) 1249 struct tcpcb *tp; 1250 { 1251 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> (1 + 2); 1252 int nticks; 1253 1254 if (TCP_TIMER_ISARMED(tp, TCPT_REXMT)) 1255 panic("tcp_output REXMT"); 1256 /* 1257 * Start/restart persistance timer. 1258 */ 1259 if (t < tp->t_rttmin) 1260 t = tp->t_rttmin; 1261 TCPT_RANGESET(nticks, t * tcp_backoff[tp->t_rxtshift], 1262 TCPTV_PERSMIN, TCPTV_PERSMAX); 1263 TCP_TIMER_ARM(tp, TCPT_PERSIST, nticks); 1264 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1265 tp->t_rxtshift++; 1266 } 1267