1 /*- 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 4. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95 30 * $FreeBSD$ 31 */ 32 33 #include "opt_inet.h" 34 #include "opt_inet6.h" 35 #include "opt_ipsec.h" 36 #include "opt_mac.h" 37 #include "opt_tcpdebug.h" 38 #include "opt_tcp_sack.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/domain.h> 43 #include <sys/kernel.h> 44 #include <sys/lock.h> 45 #include <sys/mbuf.h> 46 #include <sys/mutex.h> 47 #include <sys/protosw.h> 48 #include <sys/socket.h> 49 #include <sys/socketvar.h> 50 #include <sys/sysctl.h> 51 52 #include <net/route.h> 53 54 #include <netinet/in.h> 55 #include <netinet/in_systm.h> 56 #include <netinet/ip.h> 57 #include <netinet/in_pcb.h> 58 #include <netinet/ip_var.h> 59 #include <netinet/ip_options.h> 60 #ifdef INET6 61 #include <netinet6/in6_pcb.h> 62 #include <netinet/ip6.h> 63 #include <netinet6/ip6_var.h> 64 #endif 65 #include <netinet/tcp.h> 66 #define TCPOUTFLAGS 67 #include <netinet/tcp_fsm.h> 68 #include <netinet/tcp_seq.h> 69 #include <netinet/tcp_timer.h> 70 #include <netinet/tcp_var.h> 71 #include <netinet/tcpip.h> 72 #ifdef TCPDEBUG 73 #include <netinet/tcp_debug.h> 74 #endif 75 76 #ifdef IPSEC 77 #include <netinet6/ipsec.h> 78 #endif /*IPSEC*/ 79 80 #ifdef FAST_IPSEC 81 #include <netipsec/ipsec.h> 82 #define IPSEC 83 #endif /*FAST_IPSEC*/ 84 85 #include <machine/in_cksum.h> 86 87 #include <security/mac/mac_framework.h> 88 89 #ifdef notyet 90 extern struct mbuf *m_copypack(); 91 #endif 92 93 int path_mtu_discovery = 1; 94 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW, 95 &path_mtu_discovery, 1, "Enable Path MTU Discovery"); 96 97 int ss_fltsz = 1; 98 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW, 99 &ss_fltsz, 1, "Slow start flight size"); 100 101 int ss_fltsz_local = 4; 102 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW, 103 &ss_fltsz_local, 1, "Slow start flight size for local networks"); 104 105 int tcp_do_newreno = 1; 106 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, &tcp_do_newreno, 107 0, "Enable NewReno Algorithms"); 108 109 int tcp_do_tso = 1; 110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW, 111 &tcp_do_tso, 0, "Enable TCP Segmentation Offload"); 112 113 /* 114 * Tcp output routine: figure out what should be sent and send it. 115 */ 116 int 117 tcp_output(struct tcpcb *tp) 118 { 119 struct socket *so = tp->t_inpcb->inp_socket; 120 long len, recwin, sendwin; 121 int off, flags, error; 122 #ifdef TCP_SIGNATURE 123 int sigoff = 0; 124 #endif 125 struct mbuf *m; 126 struct ip *ip = NULL; 127 struct ipovly *ipov = NULL; 128 struct tcphdr *th; 129 u_char opt[TCP_MAXOLEN]; 130 unsigned ipoptlen, optlen, hdrlen; 131 int idle, sendalot; 132 int i, sack_rxmit; 133 int sack_bytes_rxmt; 134 struct sackhole *p; 135 int tso = 0; 136 #if 0 137 int maxburst = TCP_MAXBURST; 138 #endif 139 #ifdef INET6 140 struct ip6_hdr *ip6 = NULL; 141 int isipv6; 142 143 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0; 144 #endif 145 146 INP_LOCK_ASSERT(tp->t_inpcb); 147 148 /* 149 * Determine length of data that should be transmitted, 150 * and flags that will be used. 151 * If there is some data or critical controls (SYN, RST) 152 * to send, then transmit; otherwise, investigate further. 153 */ 154 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una); 155 if (idle && (ticks - tp->t_rcvtime) >= tp->t_rxtcur) { 156 /* 157 * We have been idle for "a while" and no acks are 158 * expected to clock out any data we send -- 159 * slow start to get ack "clock" running again. 160 * 161 * Set the slow-start flight size depending on whether 162 * this is a local network or not. 163 */ 164 int ss = ss_fltsz; 165 #ifdef INET6 166 if (isipv6) { 167 if (in6_localaddr(&tp->t_inpcb->in6p_faddr)) 168 ss = ss_fltsz_local; 169 } else 170 #endif /* INET6 */ 171 if (in_localaddr(tp->t_inpcb->inp_faddr)) 172 ss = ss_fltsz_local; 173 tp->snd_cwnd = tp->t_maxseg * ss; 174 } 175 tp->t_flags &= ~TF_LASTIDLE; 176 if (idle) { 177 if (tp->t_flags & TF_MORETOCOME) { 178 tp->t_flags |= TF_LASTIDLE; 179 idle = 0; 180 } 181 } 182 again: 183 /* 184 * If we've recently taken a timeout, snd_max will be greater than 185 * snd_nxt. There may be SACK information that allows us to avoid 186 * resending already delivered data. Adjust snd_nxt accordingly. 187 */ 188 if (tp->sack_enable && SEQ_LT(tp->snd_nxt, tp->snd_max)) 189 tcp_sack_adjust(tp); 190 sendalot = 0; 191 off = tp->snd_nxt - tp->snd_una; 192 sendwin = min(tp->snd_wnd, tp->snd_cwnd); 193 sendwin = min(sendwin, tp->snd_bwnd); 194 195 flags = tcp_outflags[tp->t_state]; 196 /* 197 * Send any SACK-generated retransmissions. If we're explicitly trying 198 * to send out new data (when sendalot is 1), bypass this function. 199 * If we retransmit in fast recovery mode, decrement snd_cwnd, since 200 * we're replacing a (future) new transmission with a retransmission 201 * now, and we previously incremented snd_cwnd in tcp_input(). 202 */ 203 /* 204 * Still in sack recovery , reset rxmit flag to zero. 205 */ 206 sack_rxmit = 0; 207 sack_bytes_rxmt = 0; 208 len = 0; 209 p = NULL; 210 if (tp->sack_enable && IN_FASTRECOVERY(tp) && 211 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) { 212 long cwin; 213 214 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt; 215 if (cwin < 0) 216 cwin = 0; 217 /* Do not retransmit SACK segments beyond snd_recover */ 218 if (SEQ_GT(p->end, tp->snd_recover)) { 219 /* 220 * (At least) part of sack hole extends beyond 221 * snd_recover. Check to see if we can rexmit data 222 * for this hole. 223 */ 224 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) { 225 /* 226 * Can't rexmit any more data for this hole. 227 * That data will be rexmitted in the next 228 * sack recovery episode, when snd_recover 229 * moves past p->rxmit. 230 */ 231 p = NULL; 232 goto after_sack_rexmit; 233 } else 234 /* Can rexmit part of the current hole */ 235 len = ((long)ulmin(cwin, 236 tp->snd_recover - p->rxmit)); 237 } else 238 len = ((long)ulmin(cwin, p->end - p->rxmit)); 239 off = p->rxmit - tp->snd_una; 240 KASSERT(off >= 0,("%s: sack block to the left of una : %d", 241 __func__, off)); 242 if (len > 0) { 243 sack_rxmit = 1; 244 sendalot = 1; 245 tcpstat.tcps_sack_rexmits++; 246 tcpstat.tcps_sack_rexmit_bytes += 247 min(len, tp->t_maxseg); 248 } 249 } 250 after_sack_rexmit: 251 /* 252 * Get standard flags, and add SYN or FIN if requested by 'hidden' 253 * state flags. 254 */ 255 if (tp->t_flags & TF_NEEDFIN) 256 flags |= TH_FIN; 257 if (tp->t_flags & TF_NEEDSYN) 258 flags |= TH_SYN; 259 260 SOCKBUF_LOCK(&so->so_snd); 261 /* 262 * If in persist timeout with window of 0, send 1 byte. 263 * Otherwise, if window is small but nonzero 264 * and timer expired, we will send what we can 265 * and go to transmit state. 266 */ 267 if (tp->t_flags & TF_FORCEDATA) { 268 if (sendwin == 0) { 269 /* 270 * If we still have some data to send, then 271 * clear the FIN bit. Usually this would 272 * happen below when it realizes that we 273 * aren't sending all the data. However, 274 * if we have exactly 1 byte of unsent data, 275 * then it won't clear the FIN bit below, 276 * and if we are in persist state, we wind 277 * up sending the packet without recording 278 * that we sent the FIN bit. 279 * 280 * We can't just blindly clear the FIN bit, 281 * because if we don't have any more data 282 * to send then the probe will be the FIN 283 * itself. 284 */ 285 if (off < so->so_snd.sb_cc) 286 flags &= ~TH_FIN; 287 sendwin = 1; 288 } else { 289 callout_stop(tp->tt_persist); 290 tp->t_rxtshift = 0; 291 } 292 } 293 294 /* 295 * If snd_nxt == snd_max and we have transmitted a FIN, the 296 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in 297 * a negative length. This can also occur when TCP opens up 298 * its congestion window while receiving additional duplicate 299 * acks after fast-retransmit because TCP will reset snd_nxt 300 * to snd_max after the fast-retransmit. 301 * 302 * In the normal retransmit-FIN-only case, however, snd_nxt will 303 * be set to snd_una, the offset will be 0, and the length may 304 * wind up 0. 305 * 306 * If sack_rxmit is true we are retransmitting from the scoreboard 307 * in which case len is already set. 308 */ 309 if (sack_rxmit == 0) { 310 if (sack_bytes_rxmt == 0) 311 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off); 312 else { 313 long cwin; 314 315 /* 316 * We are inside of a SACK recovery episode and are 317 * sending new data, having retransmitted all the 318 * data possible in the scoreboard. 319 */ 320 len = ((long)ulmin(so->so_snd.sb_cc, tp->snd_wnd) 321 - off); 322 /* 323 * Don't remove this (len > 0) check ! 324 * We explicitly check for len > 0 here (although it 325 * isn't really necessary), to work around a gcc 326 * optimization issue - to force gcc to compute 327 * len above. Without this check, the computation 328 * of len is bungled by the optimizer. 329 */ 330 if (len > 0) { 331 cwin = tp->snd_cwnd - 332 (tp->snd_nxt - tp->sack_newdata) - 333 sack_bytes_rxmt; 334 if (cwin < 0) 335 cwin = 0; 336 len = lmin(len, cwin); 337 } 338 } 339 } 340 341 /* 342 * Lop off SYN bit if it has already been sent. However, if this 343 * is SYN-SENT state and if segment contains data and if we don't 344 * know that foreign host supports TAO, suppress sending segment. 345 */ 346 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) { 347 if (tp->t_state != TCPS_SYN_RECEIVED) 348 flags &= ~TH_SYN; 349 off--, len++; 350 } 351 352 /* 353 * Be careful not to send data and/or FIN on SYN segments. 354 * This measure is needed to prevent interoperability problems 355 * with not fully conformant TCP implementations. 356 */ 357 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) { 358 len = 0; 359 flags &= ~TH_FIN; 360 } 361 362 if (len < 0) { 363 /* 364 * If FIN has been sent but not acked, 365 * but we haven't been called to retransmit, 366 * len will be < 0. Otherwise, window shrank 367 * after we sent into it. If window shrank to 0, 368 * cancel pending retransmit, pull snd_nxt back 369 * to (closed) window, and set the persist timer 370 * if it isn't already going. If the window didn't 371 * close completely, just wait for an ACK. 372 */ 373 len = 0; 374 if (sendwin == 0) { 375 callout_stop(tp->tt_rexmt); 376 tp->t_rxtshift = 0; 377 tp->snd_nxt = tp->snd_una; 378 if (!callout_active(tp->tt_persist)) 379 tcp_setpersist(tp); 380 } 381 } 382 383 /* 384 * len will be >= 0 after this point. Truncate to the maximum 385 * segment length or enable TCP Segmentation Offloading (if supported 386 * by hardware) and ensure that FIN is removed if the length no longer 387 * contains the last data byte. 388 * 389 * TSO may only be used if we are in a pure bulk sending state. The 390 * presence of TCP-MD5, SACK retransmits, SACK advertizements and 391 * IP options prevent using TSO. With TSO the TCP header is the same 392 * (except for the sequence number) for all generated packets. This 393 * makes it impossible to transmit any options which vary per generated 394 * segment or packet. 395 * 396 * The length of TSO bursts is limited to TCP_MAXWIN. That limit and 397 * removal of FIN (if not already catched here) are handled later after 398 * the exact length of the TCP options are known. 399 */ 400 if (len > tp->t_maxseg) { 401 if ((tp->t_flags & TF_TSO) && tcp_do_tso && 402 ((tp->t_flags & TF_SIGNATURE) == 0) && 403 tp->rcv_numsacks == 0 && sack_rxmit == 0 && 404 tp->t_inpcb->inp_options == NULL && 405 tp->t_inpcb->in6p_options == NULL && 406 tp->t_inpcb->inp_sp == NULL) { 407 tso = 1; 408 } else { 409 len = tp->t_maxseg; 410 sendalot = 1; 411 tso = 0; 412 } 413 } 414 if (sack_rxmit) { 415 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc)) 416 flags &= ~TH_FIN; 417 } else { 418 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) 419 flags &= ~TH_FIN; 420 } 421 422 recwin = sbspace(&so->so_rcv); 423 424 /* 425 * Sender silly window avoidance. We transmit under the following 426 * conditions when len is non-zero: 427 * 428 * - We have a full segment (or more with TSO) 429 * - This is the last buffer in a write()/send() and we are 430 * either idle or running NODELAY 431 * - we've timed out (e.g. persist timer) 432 * - we have more then 1/2 the maximum send window's worth of 433 * data (receiver may be limited the window size) 434 * - we need to retransmit 435 */ 436 if (len) { 437 if (len >= tp->t_maxseg) 438 goto send; 439 /* 440 * NOTE! on localhost connections an 'ack' from the remote 441 * end may occur synchronously with the output and cause 442 * us to flush a buffer queued with moretocome. XXX 443 * 444 * note: the len + off check is almost certainly unnecessary. 445 */ 446 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */ 447 (idle || (tp->t_flags & TF_NODELAY)) && 448 len + off >= so->so_snd.sb_cc && 449 (tp->t_flags & TF_NOPUSH) == 0) { 450 goto send; 451 } 452 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */ 453 goto send; 454 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0) 455 goto send; 456 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */ 457 goto send; 458 if (sack_rxmit) 459 goto send; 460 } 461 462 /* 463 * Compare available window to amount of window 464 * known to peer (as advertised window less 465 * next expected input). If the difference is at least two 466 * max size segments, or at least 50% of the maximum possible 467 * window, then want to send a window update to peer. 468 * Skip this if the connection is in T/TCP half-open state. 469 */ 470 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN)) { 471 /* 472 * "adv" is the amount we can increase the window, 473 * taking into account that we are limited by 474 * TCP_MAXWIN << tp->rcv_scale. 475 */ 476 long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) - 477 (tp->rcv_adv - tp->rcv_nxt); 478 479 if (adv >= (long) (2 * tp->t_maxseg)) 480 goto send; 481 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 482 goto send; 483 } 484 485 /* 486 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW 487 * is also a catch-all for the retransmit timer timeout case. 488 */ 489 if (tp->t_flags & TF_ACKNOW) 490 goto send; 491 if ((flags & TH_RST) || 492 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0)) 493 goto send; 494 if (SEQ_GT(tp->snd_up, tp->snd_una)) 495 goto send; 496 /* 497 * If our state indicates that FIN should be sent 498 * and we have not yet done so, then we need to send. 499 */ 500 if (flags & TH_FIN && 501 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 502 goto send; 503 /* 504 * In SACK, it is possible for tcp_output to fail to send a segment 505 * after the retransmission timer has been turned off. Make sure 506 * that the retransmission timer is set. 507 */ 508 if (tp->sack_enable && SEQ_GT(tp->snd_max, tp->snd_una) && 509 !callout_active(tp->tt_rexmt) && 510 !callout_active(tp->tt_persist)) { 511 callout_reset(tp->tt_rexmt, tp->t_rxtcur, 512 tcp_timer_rexmt, tp); 513 goto just_return; 514 } 515 /* 516 * TCP window updates are not reliable, rather a polling protocol 517 * using ``persist'' packets is used to insure receipt of window 518 * updates. The three ``states'' for the output side are: 519 * idle not doing retransmits or persists 520 * persisting to move a small or zero window 521 * (re)transmitting and thereby not persisting 522 * 523 * callout_active(tp->tt_persist) 524 * is true when we are in persist state. 525 * (tp->t_flags & TF_FORCEDATA) 526 * is set when we are called to send a persist packet. 527 * callout_active(tp->tt_rexmt) 528 * is set when we are retransmitting 529 * The output side is idle when both timers are zero. 530 * 531 * If send window is too small, there is data to transmit, and no 532 * retransmit or persist is pending, then go to persist state. 533 * If nothing happens soon, send when timer expires: 534 * if window is nonzero, transmit what we can, 535 * otherwise force out a byte. 536 */ 537 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) && 538 !callout_active(tp->tt_persist)) { 539 tp->t_rxtshift = 0; 540 tcp_setpersist(tp); 541 } 542 543 /* 544 * No reason to send a segment, just return. 545 */ 546 just_return: 547 SOCKBUF_UNLOCK(&so->so_snd); 548 return (0); 549 550 send: 551 SOCKBUF_LOCK_ASSERT(&so->so_snd); 552 /* 553 * Before ESTABLISHED, force sending of initial options 554 * unless TCP set not to do any options. 555 * NOTE: we assume that the IP/TCP header plus TCP options 556 * always fit in a single mbuf, leaving room for a maximum 557 * link header, i.e. 558 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 559 */ 560 optlen = 0; 561 #ifdef INET6 562 if (isipv6) 563 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr); 564 else 565 #endif 566 hdrlen = sizeof (struct tcpiphdr); 567 if (flags & TH_SYN) { 568 tp->snd_nxt = tp->iss; 569 if ((tp->t_flags & TF_NOOPT) == 0) { 570 u_short mss; 571 572 opt[0] = TCPOPT_MAXSEG; 573 opt[1] = TCPOLEN_MAXSEG; 574 mss = htons((u_short) tcp_mssopt(&tp->t_inpcb->inp_inc)); 575 (void)memcpy(opt + 2, &mss, sizeof(mss)); 576 optlen = TCPOLEN_MAXSEG; 577 578 if ((tp->t_flags & TF_REQ_SCALE) && 579 ((flags & TH_ACK) == 0 || 580 (tp->t_flags & TF_RCVD_SCALE))) { 581 *((u_int32_t *)(opt + optlen)) = htonl( 582 TCPOPT_NOP << 24 | 583 TCPOPT_WINDOW << 16 | 584 TCPOLEN_WINDOW << 8 | 585 tp->request_r_scale); 586 optlen += 4; 587 } 588 } 589 } 590 591 /* 592 * Send a timestamp and echo-reply if this is a SYN and our side 593 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 594 * and our peer have sent timestamps in our SYN's. 595 */ 596 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 597 (flags & TH_RST) == 0 && 598 ((flags & TH_ACK) == 0 || 599 (tp->t_flags & TF_RCVD_TSTMP))) { 600 u_int32_t *lp = (u_int32_t *)(opt + optlen); 601 602 /* Form timestamp option as shown in appendix A of RFC 1323. */ 603 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 604 *lp++ = htonl(ticks + tp->ts_offset); 605 *lp = htonl(tp->ts_recent); 606 optlen += TCPOLEN_TSTAMP_APPA; 607 } 608 609 #ifdef TCP_SIGNATURE 610 #ifdef INET6 611 if (!isipv6) 612 #endif 613 if (tp->t_flags & TF_SIGNATURE) { 614 int i; 615 u_char *bp; 616 617 /* Initialize TCP-MD5 option (RFC2385) */ 618 bp = (u_char *)opt + optlen; 619 *bp++ = TCPOPT_SIGNATURE; 620 *bp++ = TCPOLEN_SIGNATURE; 621 sigoff = optlen + 2; 622 for (i = 0; i < TCP_SIGLEN; i++) 623 *bp++ = 0; 624 optlen += TCPOLEN_SIGNATURE; 625 } 626 #endif /* TCP_SIGNATURE */ 627 628 if (tp->sack_enable && ((tp->t_flags & TF_NOOPT) == 0)) { 629 /* 630 * Tack on the SACK permitted option *last*. 631 * And do padding of options after tacking this on. 632 * This is because of MSS, TS, WinScale and Signatures are 633 * all present, we have just 2 bytes left for the SACK 634 * permitted option, which is just enough. 635 */ 636 /* 637 * If this is the first SYN of connection (not a SYN 638 * ACK), include SACK permitted option. If this is a 639 * SYN ACK, include SACK permitted option if peer has 640 * already done so. This is only for active connect, 641 * since the syncache takes care of the passive connect. 642 */ 643 if ((flags & TH_SYN) && 644 (!(flags & TH_ACK) || (tp->t_flags & TF_SACK_PERMIT))) { 645 u_char *bp; 646 bp = (u_char *)opt + optlen; 647 648 *bp++ = TCPOPT_SACK_PERMITTED; 649 *bp++ = TCPOLEN_SACK_PERMITTED; 650 optlen += TCPOLEN_SACK_PERMITTED; 651 } 652 653 /* 654 * Send SACKs if necessary. This should be the last 655 * option processed. Only as many SACKs are sent as 656 * are permitted by the maximum options size. 657 * 658 * In general, SACK blocks consume 8*n+2 bytes. 659 * So a full size SACK blocks option is 34 bytes 660 * (to generate 4 SACK blocks). At a minimum, 661 * we need 10 bytes (to generate 1 SACK block). 662 * If TCP Timestamps (12 bytes) and TCP Signatures 663 * (18 bytes) are both present, we'll just have 664 * 10 bytes for SACK options 40 - (12 + 18). 665 */ 666 if (TCPS_HAVEESTABLISHED(tp->t_state) && 667 (tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks > 0 && 668 MAX_TCPOPTLEN - optlen - 2 >= TCPOLEN_SACK) { 669 int nsack, sackoptlen, padlen; 670 u_char *bp = (u_char *)opt + optlen; 671 u_int32_t *lp; 672 673 nsack = (MAX_TCPOPTLEN - optlen - 2) / TCPOLEN_SACK; 674 nsack = min(nsack, tp->rcv_numsacks); 675 sackoptlen = (2 + nsack * TCPOLEN_SACK); 676 677 /* 678 * First we need to pad options so that the 679 * SACK blocks can start at a 4-byte boundary 680 * (sack option and length are at a 2 byte offset). 681 */ 682 padlen = (MAX_TCPOPTLEN - optlen - sackoptlen) % 4; 683 optlen += padlen; 684 while (padlen-- > 0) 685 *bp++ = TCPOPT_NOP; 686 687 tcpstat.tcps_sack_send_blocks++; 688 *bp++ = TCPOPT_SACK; 689 *bp++ = sackoptlen; 690 lp = (u_int32_t *)bp; 691 for (i = 0; i < nsack; i++) { 692 struct sackblk sack = tp->sackblks[i]; 693 *lp++ = htonl(sack.start); 694 *lp++ = htonl(sack.end); 695 } 696 optlen += sackoptlen; 697 } 698 } 699 700 /* Pad TCP options to a 4 byte boundary */ 701 if (optlen < MAX_TCPOPTLEN && (optlen % sizeof(u_int32_t))) { 702 int pad = sizeof(u_int32_t) - (optlen % sizeof(u_int32_t)); 703 u_char *bp = (u_char *)opt + optlen; 704 705 optlen += pad; 706 while (pad) { 707 *bp++ = TCPOPT_EOL; 708 pad--; 709 } 710 } 711 712 hdrlen += optlen; 713 714 #ifdef INET6 715 if (isipv6) 716 ipoptlen = ip6_optlen(tp->t_inpcb); 717 else 718 #endif 719 if (tp->t_inpcb->inp_options) 720 ipoptlen = tp->t_inpcb->inp_options->m_len - 721 offsetof(struct ipoption, ipopt_list); 722 else 723 ipoptlen = 0; 724 #ifdef IPSEC 725 ipoptlen += ipsec_hdrsiz_tcp(tp); 726 #endif 727 728 /* 729 * Adjust data length if insertion of options will 730 * bump the packet length beyond the t_maxopd length. 731 * Clear the FIN bit because we cut off the tail of 732 * the segment. 733 * 734 * When doing TSO limit a burst to TCP_MAXWIN minus the 735 * IP, TCP and Options length to keep ip->ip_len from 736 * overflowing. Prevent the last segment from being 737 * fractional thus making them all equal sized and set 738 * the flag to continue sending. 739 */ 740 if (len + optlen + ipoptlen > tp->t_maxopd) { 741 flags &= ~TH_FIN; 742 if (tso) { 743 if (len > TCP_MAXWIN - hdrlen) { 744 len = TCP_MAXWIN - hdrlen; 745 len = len - (len % (tp->t_maxopd - optlen)); 746 sendalot = 1; 747 } else if (tp->t_flags & TF_NEEDFIN) 748 sendalot = 1; 749 } else { 750 len = tp->t_maxopd - optlen - ipoptlen; 751 sendalot = 1; 752 } 753 } 754 755 /*#ifdef DIAGNOSTIC*/ 756 #ifdef INET6 757 if (max_linkhdr + hdrlen > MCLBYTES) 758 #else 759 if (max_linkhdr + hdrlen > MHLEN) 760 #endif 761 panic("tcphdr too big"); 762 /*#endif*/ 763 764 /* 765 * Grab a header mbuf, attaching a copy of data to 766 * be transmitted, and initialize the header from 767 * the template for sends on this connection. 768 */ 769 if (len) { 770 if ((tp->t_flags & TF_FORCEDATA) && len == 1) 771 tcpstat.tcps_sndprobe++; 772 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 773 tcpstat.tcps_sndrexmitpack++; 774 tcpstat.tcps_sndrexmitbyte += len; 775 } else { 776 tcpstat.tcps_sndpack++; 777 tcpstat.tcps_sndbyte += len; 778 } 779 #ifdef notyet 780 if ((m = m_copypack(so->so_snd.sb_mb, off, 781 (int)len, max_linkhdr + hdrlen)) == 0) { 782 SOCKBUF_UNLOCK(&so->so_snd); 783 error = ENOBUFS; 784 goto out; 785 } 786 /* 787 * m_copypack left space for our hdr; use it. 788 */ 789 m->m_len += hdrlen; 790 m->m_data -= hdrlen; 791 #else 792 MGETHDR(m, M_DONTWAIT, MT_DATA); 793 if (m == NULL) { 794 SOCKBUF_UNLOCK(&so->so_snd); 795 error = ENOBUFS; 796 goto out; 797 } 798 #ifdef INET6 799 if (MHLEN < hdrlen + max_linkhdr) { 800 MCLGET(m, M_DONTWAIT); 801 if ((m->m_flags & M_EXT) == 0) { 802 SOCKBUF_UNLOCK(&so->so_snd); 803 m_freem(m); 804 error = ENOBUFS; 805 goto out; 806 } 807 } 808 #endif 809 m->m_data += max_linkhdr; 810 m->m_len = hdrlen; 811 if (len <= MHLEN - hdrlen - max_linkhdr) { 812 m_copydata(so->so_snd.sb_mb, off, (int) len, 813 mtod(m, caddr_t) + hdrlen); 814 m->m_len += len; 815 } else { 816 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len); 817 if (m->m_next == 0) { 818 SOCKBUF_UNLOCK(&so->so_snd); 819 (void) m_free(m); 820 error = ENOBUFS; 821 goto out; 822 } 823 } 824 #endif 825 /* 826 * If we're sending everything we've got, set PUSH. 827 * (This will keep happy those implementations which only 828 * give data to the user when a buffer fills or 829 * a PUSH comes in.) 830 */ 831 if (off + len == so->so_snd.sb_cc) 832 flags |= TH_PUSH; 833 SOCKBUF_UNLOCK(&so->so_snd); 834 } else { 835 SOCKBUF_UNLOCK(&so->so_snd); 836 if (tp->t_flags & TF_ACKNOW) 837 tcpstat.tcps_sndacks++; 838 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 839 tcpstat.tcps_sndctrl++; 840 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 841 tcpstat.tcps_sndurg++; 842 else 843 tcpstat.tcps_sndwinup++; 844 845 MGETHDR(m, M_DONTWAIT, MT_DATA); 846 if (m == NULL) { 847 error = ENOBUFS; 848 goto out; 849 } 850 #ifdef INET6 851 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) && 852 MHLEN >= hdrlen) { 853 MH_ALIGN(m, hdrlen); 854 } else 855 #endif 856 m->m_data += max_linkhdr; 857 m->m_len = hdrlen; 858 } 859 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); 860 m->m_pkthdr.rcvif = (struct ifnet *)0; 861 #ifdef MAC 862 mac_create_mbuf_from_inpcb(tp->t_inpcb, m); 863 #endif 864 #ifdef INET6 865 if (isipv6) { 866 ip6 = mtod(m, struct ip6_hdr *); 867 th = (struct tcphdr *)(ip6 + 1); 868 tcpip_fillheaders(tp->t_inpcb, ip6, th); 869 } else 870 #endif /* INET6 */ 871 { 872 ip = mtod(m, struct ip *); 873 ipov = (struct ipovly *)ip; 874 th = (struct tcphdr *)(ip + 1); 875 tcpip_fillheaders(tp->t_inpcb, ip, th); 876 } 877 878 /* 879 * Fill in fields, remembering maximum advertised 880 * window for use in delaying messages about window sizes. 881 * If resending a FIN, be sure not to use a new sequence number. 882 */ 883 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 884 tp->snd_nxt == tp->snd_max) 885 tp->snd_nxt--; 886 /* 887 * If we are doing retransmissions, then snd_nxt will 888 * not reflect the first unsent octet. For ACK only 889 * packets, we do not want the sequence number of the 890 * retransmitted packet, we want the sequence number 891 * of the next unsent octet. So, if there is no data 892 * (and no SYN or FIN), use snd_max instead of snd_nxt 893 * when filling in ti_seq. But if we are in persist 894 * state, snd_max might reflect one byte beyond the 895 * right edge of the window, so use snd_nxt in that 896 * case, since we know we aren't doing a retransmission. 897 * (retransmit and persist are mutually exclusive...) 898 */ 899 if (sack_rxmit == 0) { 900 if (len || (flags & (TH_SYN|TH_FIN)) 901 || callout_active(tp->tt_persist)) 902 th->th_seq = htonl(tp->snd_nxt); 903 else 904 th->th_seq = htonl(tp->snd_max); 905 } else { 906 th->th_seq = htonl(p->rxmit); 907 p->rxmit += len; 908 tp->sackhint.sack_bytes_rexmit += len; 909 } 910 th->th_ack = htonl(tp->rcv_nxt); 911 if (optlen) { 912 bcopy(opt, th + 1, optlen); 913 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 914 } 915 th->th_flags = flags; 916 /* 917 * Calculate receive window. Don't shrink window, 918 * but avoid silly window syndrome. 919 */ 920 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) && 921 recwin < (long)tp->t_maxseg) 922 recwin = 0; 923 if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt)) 924 recwin = (long)(tp->rcv_adv - tp->rcv_nxt); 925 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale) 926 recwin = (long)TCP_MAXWIN << tp->rcv_scale; 927 th->th_win = htons((u_short) (recwin >> tp->rcv_scale)); 928 929 930 /* 931 * Adjust the RXWIN0SENT flag - indicate that we have advertised 932 * a 0 window. This may cause the remote transmitter to stall. This 933 * flag tells soreceive() to disable delayed acknowledgements when 934 * draining the buffer. This can occur if the receiver is attempting 935 * to read more data then can be buffered prior to transmitting on 936 * the connection. 937 */ 938 if (recwin == 0) 939 tp->t_flags |= TF_RXWIN0SENT; 940 else 941 tp->t_flags &= ~TF_RXWIN0SENT; 942 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 943 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 944 th->th_flags |= TH_URG; 945 } else 946 /* 947 * If no urgent pointer to send, then we pull 948 * the urgent pointer to the left edge of the send window 949 * so that it doesn't drift into the send window on sequence 950 * number wraparound. 951 */ 952 tp->snd_up = tp->snd_una; /* drag it along */ 953 954 #ifdef TCP_SIGNATURE 955 #ifdef INET6 956 if (!isipv6) 957 #endif 958 if (tp->t_flags & TF_SIGNATURE) 959 tcp_signature_compute(m, sizeof(struct ip), len, optlen, 960 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND); 961 #endif 962 963 /* 964 * Put TCP length in extended header, and then 965 * checksum extended header and data. 966 */ 967 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */ 968 #ifdef INET6 969 if (isipv6) 970 /* 971 * ip6_plen is not need to be filled now, and will be filled 972 * in ip6_output. 973 */ 974 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr), 975 sizeof(struct tcphdr) + optlen + len); 976 else 977 #endif /* INET6 */ 978 { 979 m->m_pkthdr.csum_flags = CSUM_TCP; 980 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 981 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 982 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen)); 983 984 /* IP version must be set here for ipv4/ipv6 checking later */ 985 KASSERT(ip->ip_v == IPVERSION, 986 ("%s: IP version incorrect: %d", __func__, ip->ip_v)); 987 } 988 989 /* 990 * Enable TSO and specify the size of the segments. 991 * The TCP pseudo header checksum is always provided. 992 * XXX: Fixme: This is currently not the case for IPv6. 993 */ 994 if (tso) { 995 m->m_pkthdr.csum_flags = CSUM_TSO; 996 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen; 997 } 998 999 /* 1000 * In transmit state, time the transmission and arrange for 1001 * the retransmit. In persist state, just set snd_max. 1002 */ 1003 if ((tp->t_flags & TF_FORCEDATA) == 0 || 1004 !callout_active(tp->tt_persist)) { 1005 tcp_seq startseq = tp->snd_nxt; 1006 1007 /* 1008 * Advance snd_nxt over sequence space of this segment. 1009 */ 1010 if (flags & (TH_SYN|TH_FIN)) { 1011 if (flags & TH_SYN) 1012 tp->snd_nxt++; 1013 if (flags & TH_FIN) { 1014 tp->snd_nxt++; 1015 tp->t_flags |= TF_SENTFIN; 1016 } 1017 } 1018 if (sack_rxmit) 1019 goto timer; 1020 tp->snd_nxt += len; 1021 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1022 tp->snd_max = tp->snd_nxt; 1023 /* 1024 * Time this transmission if not a retransmission and 1025 * not currently timing anything. 1026 */ 1027 if (tp->t_rtttime == 0) { 1028 tp->t_rtttime = ticks; 1029 tp->t_rtseq = startseq; 1030 tcpstat.tcps_segstimed++; 1031 } 1032 } 1033 1034 /* 1035 * Set retransmit timer if not currently set, 1036 * and not doing a pure ack or a keep-alive probe. 1037 * Initial value for retransmit timer is smoothed 1038 * round-trip time + 2 * round-trip time variance. 1039 * Initialize shift counter which is used for backoff 1040 * of retransmit time. 1041 */ 1042 timer: 1043 if (!callout_active(tp->tt_rexmt) && 1044 ((sack_rxmit && tp->snd_nxt != tp->snd_max) || 1045 (tp->snd_nxt != tp->snd_una))) { 1046 if (callout_active(tp->tt_persist)) { 1047 callout_stop(tp->tt_persist); 1048 tp->t_rxtshift = 0; 1049 } 1050 callout_reset(tp->tt_rexmt, tp->t_rxtcur, 1051 tcp_timer_rexmt, tp); 1052 } 1053 } else { 1054 /* 1055 * Persist case, update snd_max but since we are in 1056 * persist mode (no window) we do not update snd_nxt. 1057 */ 1058 int xlen = len; 1059 if (flags & TH_SYN) 1060 ++xlen; 1061 if (flags & TH_FIN) { 1062 ++xlen; 1063 tp->t_flags |= TF_SENTFIN; 1064 } 1065 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max)) 1066 tp->snd_max = tp->snd_nxt + len; 1067 } 1068 1069 #ifdef TCPDEBUG 1070 /* 1071 * Trace. 1072 */ 1073 if (so->so_options & SO_DEBUG) { 1074 u_short save = 0; 1075 #ifdef INET6 1076 if (!isipv6) 1077 #endif 1078 { 1079 save = ipov->ih_len; 1080 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */); 1081 } 1082 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0); 1083 #ifdef INET6 1084 if (!isipv6) 1085 #endif 1086 ipov->ih_len = save; 1087 } 1088 #endif 1089 1090 /* 1091 * Fill in IP length and desired time to live and 1092 * send to IP level. There should be a better way 1093 * to handle ttl and tos; we could keep them in 1094 * the template, but need a way to checksum without them. 1095 */ 1096 /* 1097 * m->m_pkthdr.len should have been set before cksum calcuration, 1098 * because in6_cksum() need it. 1099 */ 1100 #ifdef INET6 1101 if (isipv6) { 1102 /* 1103 * we separately set hoplimit for every segment, since the 1104 * user might want to change the value via setsockopt. 1105 * Also, desired default hop limit might be changed via 1106 * Neighbor Discovery. 1107 */ 1108 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL); 1109 1110 /* TODO: IPv6 IP6TOS_ECT bit on */ 1111 error = ip6_output(m, 1112 tp->t_inpcb->in6p_outputopts, NULL, 1113 ((so->so_options & SO_DONTROUTE) ? 1114 IP_ROUTETOIF : 0), NULL, NULL, tp->t_inpcb); 1115 } else 1116 #endif /* INET6 */ 1117 { 1118 ip->ip_len = m->m_pkthdr.len; 1119 #ifdef INET6 1120 if (INP_CHECK_SOCKAF(so, AF_INET6)) 1121 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL); 1122 #endif /* INET6 */ 1123 /* 1124 * If we do path MTU discovery, then we set DF on every packet. 1125 * This might not be the best thing to do according to RFC3390 1126 * Section 2. However the tcp hostcache migitates the problem 1127 * so it affects only the first tcp connection with a host. 1128 */ 1129 if (path_mtu_discovery) 1130 ip->ip_off |= IP_DF; 1131 1132 error = ip_output(m, tp->t_inpcb->inp_options, NULL, 1133 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, 1134 tp->t_inpcb); 1135 } 1136 if (error) { 1137 1138 /* 1139 * We know that the packet was lost, so back out the 1140 * sequence number advance, if any. 1141 * 1142 * If the error is EPERM the packet got blocked by the 1143 * local firewall. Normally we should terminate the 1144 * connection but the blocking may have been spurious 1145 * due to a firewall reconfiguration cycle. So we treat 1146 * it like a packet loss and let the retransmit timer and 1147 * timeouts do their work over time. 1148 * XXX: It is a POLA question whether calling tcp_drop right 1149 * away would be the really correct behavior instead. 1150 */ 1151 if (error != EPERM && ((tp->t_flags & TF_FORCEDATA) == 0 || 1152 !callout_active(tp->tt_persist))) { 1153 /* 1154 * No need to check for TH_FIN here because 1155 * the TF_SENTFIN flag handles that case. 1156 */ 1157 if ((flags & TH_SYN) == 0) { 1158 if (sack_rxmit) { 1159 p->rxmit -= len; 1160 tp->sackhint.sack_bytes_rexmit -= len; 1161 KASSERT(tp->sackhint.sack_bytes_rexmit 1162 >= 0, 1163 ("sackhint bytes rtx >= 0")); 1164 } else 1165 tp->snd_nxt -= len; 1166 } 1167 } 1168 if (error == EPERM) { 1169 tp->t_softerror = error; 1170 return (error); 1171 } 1172 1173 out: 1174 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */ 1175 if (error == ENOBUFS) { 1176 if (!callout_active(tp->tt_rexmt) && 1177 !callout_active(tp->tt_persist)) 1178 callout_reset(tp->tt_rexmt, tp->t_rxtcur, 1179 tcp_timer_rexmt, tp); 1180 tp->snd_cwnd = tp->t_maxseg; 1181 return (0); 1182 } 1183 if (error == EMSGSIZE) { 1184 /* 1185 * For some reason the interface we used initially 1186 * to send segments changed to another or lowered 1187 * its MTU. 1188 * 1189 * tcp_mtudisc() will find out the new MTU and as 1190 * its last action, initiate retransmission, so it 1191 * is important to not do so here. 1192 * 1193 * If TSO was active we either got an interface 1194 * without TSO capabilits or TSO was turned off. 1195 * Disable it for this connection as too and 1196 * immediatly retry with MSS sized segments generated 1197 * by this function. 1198 */ 1199 if (tso) 1200 tp->t_flags &= ~TF_TSO; 1201 tcp_mtudisc(tp->t_inpcb, 0); 1202 return 0; 1203 } 1204 if ((error == EHOSTUNREACH || error == ENETDOWN) 1205 && TCPS_HAVERCVDSYN(tp->t_state)) { 1206 tp->t_softerror = error; 1207 return (0); 1208 } 1209 return (error); 1210 } 1211 tcpstat.tcps_sndtotal++; 1212 1213 /* 1214 * Data sent (as far as we can tell). 1215 * If this advertises a larger window than any other segment, 1216 * then remember the size of the advertised window. 1217 * Any pending ACK has now been sent. 1218 */ 1219 if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv)) 1220 tp->rcv_adv = tp->rcv_nxt + recwin; 1221 tp->last_ack_sent = tp->rcv_nxt; 1222 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK); 1223 if (callout_active(tp->tt_delack)) 1224 callout_stop(tp->tt_delack); 1225 #if 0 1226 /* 1227 * This completely breaks TCP if newreno is turned on. What happens 1228 * is that if delayed-acks are turned on on the receiver, this code 1229 * on the transmitter effectively destroys the TCP window, forcing 1230 * it to four packets (1.5Kx4 = 6K window). 1231 */ 1232 if (sendalot && (!tcp_do_newreno || --maxburst)) 1233 goto again; 1234 #endif 1235 if (sendalot) 1236 goto again; 1237 return (0); 1238 } 1239 1240 void 1241 tcp_setpersist(tp) 1242 register struct tcpcb *tp; 1243 { 1244 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 1245 int tt; 1246 1247 if (callout_active(tp->tt_rexmt)) 1248 panic("tcp_setpersist: retransmit pending"); 1249 /* 1250 * Start/restart persistance timer. 1251 */ 1252 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], 1253 TCPTV_PERSMIN, TCPTV_PERSMAX); 1254 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp); 1255 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1256 tp->t_rxtshift++; 1257 } 1258