Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/netinet/tcp_output.c
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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 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95 34 * $FreeBSD: releng/5.0/sys/netinet/tcp_output.c 105291 2002-10-16 19:16:33Z dillon $ 35 */ 36 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_mac.h" 40 #include "opt_tcpdebug.h" 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/domain.h> 45 #include <sys/kernel.h> 46 #include <sys/lock.h> 47 #include <sys/mac.h> 48 #include <sys/mbuf.h> 49 #include <sys/mutex.h> 50 #include <sys/protosw.h> 51 #include <sys/socket.h> 52 #include <sys/socketvar.h> 53 #include <sys/sysctl.h> 54 55 #include <net/route.h> 56 57 #include <netinet/in.h> 58 #include <netinet/in_systm.h> 59 #include <netinet/ip.h> 60 #include <netinet/in_pcb.h> 61 #include <netinet/ip_var.h> 62 #ifdef INET6 63 #include <netinet6/in6_pcb.h> 64 #include <netinet/ip6.h> 65 #include <netinet6/ip6_var.h> 66 #endif 67 #include <netinet/tcp.h> 68 #define TCPOUTFLAGS 69 #include <netinet/tcp_fsm.h> 70 #include <netinet/tcp_seq.h> 71 #include <netinet/tcp_timer.h> 72 #include <netinet/tcp_var.h> 73 #include <netinet/tcpip.h> 74 #ifdef TCPDEBUG 75 #include <netinet/tcp_debug.h> 76 #endif 77 78 #ifdef IPSEC 79 #include <netinet6/ipsec.h> 80 #endif /*IPSEC*/ 81 82 #ifdef FAST_IPSEC 83 #include <netipsec/ipsec.h> 84 #define IPSEC 85 #endif /*FAST_IPSEC*/ 86 87 #include <machine/in_cksum.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 * Tcp output routine: figure out what should be sent and send it. 110 */ 111 int 112 tcp_output(struct tcpcb *tp) 113 { 114 struct socket *so = tp->t_inpcb->inp_socket; 115 long len, win; 116 int off, flags, error; 117 struct mbuf *m; 118 struct ip *ip = NULL; 119 struct ipovly *ipov = NULL; 120 struct tcphdr *th; 121 u_char opt[TCP_MAXOLEN]; 122 unsigned ipoptlen, optlen, hdrlen; 123 int idle, sendalot; 124 #if 0 125 int maxburst = TCP_MAXBURST; 126 #endif 127 struct rmxp_tao *taop; 128 struct rmxp_tao tao_noncached; 129 #ifdef INET6 130 struct ip6_hdr *ip6 = NULL; 131 int isipv6; 132 133 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0; 134 #endif 135 136 #ifndef INET6 137 mtx_assert(&tp->t_inpcb->inp_mtx, MA_OWNED); 138 #endif 139 140 /* 141 * Determine length of data that should be transmitted, 142 * and flags that will be used. 143 * If there is some data or critical controls (SYN, RST) 144 * to send, then transmit; otherwise, investigate further. 145 */ 146 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una); 147 if (idle && (ticks - tp->t_rcvtime) >= tp->t_rxtcur) { 148 /* 149 * We have been idle for "a while" and no acks are 150 * expected to clock out any data we send -- 151 * slow start to get ack "clock" running again. 152 * 153 * Set the slow-start flight size depending on whether 154 * this is a local network or not. 155 */ 156 int ss = ss_fltsz; 157 #ifdef INET6 158 if (isipv6) { 159 if (in6_localaddr(&tp->t_inpcb->in6p_faddr)) 160 ss = ss_fltsz_local; 161 } else 162 #endif /* INET6 */ 163 if (in_localaddr(tp->t_inpcb->inp_faddr)) 164 ss = ss_fltsz_local; 165 tp->snd_cwnd = tp->t_maxseg * ss; 166 } 167 tp->t_flags &= ~TF_LASTIDLE; 168 if (idle) { 169 if (tp->t_flags & TF_MORETOCOME) { 170 tp->t_flags |= TF_LASTIDLE; 171 idle = 0; 172 } 173 } 174 again: 175 sendalot = 0; 176 off = tp->snd_nxt - tp->snd_una; 177 win = min(tp->snd_wnd, tp->snd_cwnd); 178 win = min(win, tp->snd_bwnd); 179 180 flags = tcp_outflags[tp->t_state]; 181 /* 182 * Get standard flags, and add SYN or FIN if requested by 'hidden' 183 * state flags. 184 */ 185 if (tp->t_flags & TF_NEEDFIN) 186 flags |= TH_FIN; 187 if (tp->t_flags & TF_NEEDSYN) 188 flags |= TH_SYN; 189 190 /* 191 * If in persist timeout with window of 0, send 1 byte. 192 * Otherwise, if window is small but nonzero 193 * and timer expired, we will send what we can 194 * and go to transmit state. 195 */ 196 if (tp->t_force) { 197 if (win == 0) { 198 /* 199 * If we still have some data to send, then 200 * clear the FIN bit. Usually this would 201 * happen below when it realizes that we 202 * aren't sending all the data. However, 203 * if we have exactly 1 byte of unsent data, 204 * then it won't clear the FIN bit below, 205 * and if we are in persist state, we wind 206 * up sending the packet without recording 207 * that we sent the FIN bit. 208 * 209 * We can't just blindly clear the FIN bit, 210 * because if we don't have any more data 211 * to send then the probe will be the FIN 212 * itself. 213 */ 214 if (off < so->so_snd.sb_cc) 215 flags &= ~TH_FIN; 216 win = 1; 217 } else { 218 callout_stop(tp->tt_persist); 219 tp->t_rxtshift = 0; 220 } 221 } 222 223 /* 224 * If snd_nxt == snd_max and we have transmitted a FIN, the 225 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in 226 * a negative length. This can also occur when tcp opens up 227 * its congestion window while receiving additional duplicate 228 * acks after fast-retransmit because TCP will reset snd_nxt 229 * to snd_max after the fast-retransmit. 230 * 231 * In the normal retransmit-FIN-only case, however, snd_nxt will 232 * be set to snd_una, the offset will be 0, and the length may 233 * wind up 0. 234 */ 235 len = (long)ulmin(so->so_snd.sb_cc, win) - off; 236 237 if ((taop = tcp_gettaocache(&tp->t_inpcb->inp_inc)) == NULL) { 238 taop = &tao_noncached; 239 bzero(taop, sizeof(*taop)); 240 } 241 242 /* 243 * Lop off SYN bit if it has already been sent. However, if this 244 * is SYN-SENT state and if segment contains data and if we don't 245 * know that foreign host supports TAO, suppress sending segment. 246 */ 247 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) { 248 flags &= ~TH_SYN; 249 off--, len++; 250 if (len > 0 && tp->t_state == TCPS_SYN_SENT && 251 taop->tao_ccsent == 0) 252 return 0; 253 } 254 255 /* 256 * Be careful not to send data and/or FIN on SYN segments 257 * in cases when no CC option will be sent. 258 * This measure is needed to prevent interoperability problems 259 * with not fully conformant TCP implementations. 260 */ 261 if ((flags & TH_SYN) && 262 ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) || 263 ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) { 264 len = 0; 265 flags &= ~TH_FIN; 266 } 267 268 if (len < 0) { 269 /* 270 * If FIN has been sent but not acked, 271 * but we haven't been called to retransmit, 272 * len will be < 0. Otherwise, window shrank 273 * after we sent into it. If window shrank to 0, 274 * cancel pending retransmit, pull snd_nxt back 275 * to (closed) window, and set the persist timer 276 * if it isn't already going. If the window didn't 277 * close completely, just wait for an ACK. 278 */ 279 len = 0; 280 if (win == 0) { 281 callout_stop(tp->tt_rexmt); 282 tp->t_rxtshift = 0; 283 tp->snd_nxt = tp->snd_una; 284 if (!callout_active(tp->tt_persist)) 285 tcp_setpersist(tp); 286 } 287 } 288 289 /* 290 * len will be >= 0 after this point. Truncate to the maximum 291 * segment length and ensure that FIN is removed if the length 292 * no longer contains the last data byte. 293 */ 294 if (len > tp->t_maxseg) { 295 len = tp->t_maxseg; 296 sendalot = 1; 297 } 298 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) 299 flags &= ~TH_FIN; 300 301 win = sbspace(&so->so_rcv); 302 303 /* 304 * Sender silly window avoidance. We transmit under the following 305 * conditions when len is non-zero: 306 * 307 * - We have a full segment 308 * - This is the last buffer in a write()/send() and we are 309 * either idle or running NODELAY 310 * - we've timed out (e.g. persist timer) 311 * - we have more then 1/2 the maximum send window's worth of 312 * data (receiver may be limited the window size) 313 * - we need to retransmit 314 */ 315 if (len) { 316 if (len == tp->t_maxseg) 317 goto send; 318 /* 319 * NOTE! on localhost connections an 'ack' from the remote 320 * end may occur synchronously with the output and cause 321 * us to flush a buffer queued with moretocome. XXX 322 * 323 * note: the len + off check is almost certainly unnecessary. 324 */ 325 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */ 326 (idle || (tp->t_flags & TF_NODELAY)) && 327 len + off >= so->so_snd.sb_cc && 328 (tp->t_flags & TF_NOPUSH) == 0) { 329 goto send; 330 } 331 if (tp->t_force) /* typ. timeout case */ 332 goto send; 333 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0) 334 goto send; 335 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */ 336 goto send; 337 } 338 339 /* 340 * Compare available window to amount of window 341 * known to peer (as advertised window less 342 * next expected input). If the difference is at least two 343 * max size segments, or at least 50% of the maximum possible 344 * window, then want to send a window update to peer. 345 */ 346 if (win > 0) { 347 /* 348 * "adv" is the amount we can increase the window, 349 * taking into account that we are limited by 350 * TCP_MAXWIN << tp->rcv_scale. 351 */ 352 long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) - 353 (tp->rcv_adv - tp->rcv_nxt); 354 355 if (adv >= (long) (2 * tp->t_maxseg)) 356 goto send; 357 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 358 goto send; 359 } 360 361 /* 362 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW 363 * is also a catch-all for the retransmit timer timeout case. 364 */ 365 if (tp->t_flags & TF_ACKNOW) 366 goto send; 367 if ((flags & TH_RST) || 368 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0)) 369 goto send; 370 if (SEQ_GT(tp->snd_up, tp->snd_una)) 371 goto send; 372 /* 373 * If our state indicates that FIN should be sent 374 * and we have not yet done so, then we need to send. 375 */ 376 if (flags & TH_FIN && 377 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 378 goto send; 379 380 /* 381 * TCP window updates are not reliable, rather a polling protocol 382 * using ``persist'' packets is used to insure receipt of window 383 * updates. The three ``states'' for the output side are: 384 * idle not doing retransmits or persists 385 * persisting to move a small or zero window 386 * (re)transmitting and thereby not persisting 387 * 388 * callout_active(tp->tt_persist) 389 * is true when we are in persist state. 390 * tp->t_force 391 * is set when we are called to send a persist packet. 392 * callout_active(tp->tt_rexmt) 393 * is set when we are retransmitting 394 * The output side is idle when both timers are zero. 395 * 396 * If send window is too small, there is data to transmit, and no 397 * retransmit or persist is pending, then go to persist state. 398 * If nothing happens soon, send when timer expires: 399 * if window is nonzero, transmit what we can, 400 * otherwise force out a byte. 401 */ 402 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) && 403 !callout_active(tp->tt_persist)) { 404 tp->t_rxtshift = 0; 405 tcp_setpersist(tp); 406 } 407 408 /* 409 * No reason to send a segment, just return. 410 */ 411 return (0); 412 413 send: 414 /* 415 * Before ESTABLISHED, force sending of initial options 416 * unless TCP set not to do any options. 417 * NOTE: we assume that the IP/TCP header plus TCP options 418 * always fit in a single mbuf, leaving room for a maximum 419 * link header, i.e. 420 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 421 */ 422 optlen = 0; 423 #ifdef INET6 424 if (isipv6) 425 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr); 426 else 427 #endif 428 hdrlen = sizeof (struct tcpiphdr); 429 if (flags & TH_SYN) { 430 tp->snd_nxt = tp->iss; 431 if ((tp->t_flags & TF_NOOPT) == 0) { 432 u_short mss; 433 434 opt[0] = TCPOPT_MAXSEG; 435 opt[1] = TCPOLEN_MAXSEG; 436 mss = htons((u_short) tcp_mssopt(tp)); 437 (void)memcpy(opt + 2, &mss, sizeof(mss)); 438 optlen = TCPOLEN_MAXSEG; 439 440 if ((tp->t_flags & TF_REQ_SCALE) && 441 ((flags & TH_ACK) == 0 || 442 (tp->t_flags & TF_RCVD_SCALE))) { 443 *((u_int32_t *)(opt + optlen)) = htonl( 444 TCPOPT_NOP << 24 | 445 TCPOPT_WINDOW << 16 | 446 TCPOLEN_WINDOW << 8 | 447 tp->request_r_scale); 448 optlen += 4; 449 } 450 } 451 } 452 453 /* 454 * Send a timestamp and echo-reply if this is a SYN and our side 455 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 456 * and our peer have sent timestamps in our SYN's. 457 */ 458 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 459 (flags & TH_RST) == 0 && 460 ((flags & TH_ACK) == 0 || 461 (tp->t_flags & TF_RCVD_TSTMP))) { 462 u_int32_t *lp = (u_int32_t *)(opt + optlen); 463 464 /* Form timestamp option as shown in appendix A of RFC 1323. */ 465 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 466 *lp++ = htonl(ticks); 467 *lp = htonl(tp->ts_recent); 468 optlen += TCPOLEN_TSTAMP_APPA; 469 } 470 471 /* 472 * Send `CC-family' options if our side wants to use them (TF_REQ_CC), 473 * options are allowed (!TF_NOOPT) and it's not a RST. 474 */ 475 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC && 476 (flags & TH_RST) == 0) { 477 switch (flags & (TH_SYN|TH_ACK)) { 478 /* 479 * This is a normal ACK, send CC if we received CC before 480 * from our peer. 481 */ 482 case TH_ACK: 483 if (!(tp->t_flags & TF_RCVD_CC)) 484 break; 485 /*FALLTHROUGH*/ 486 487 /* 488 * We can only get here in T/TCP's SYN_SENT* state, when 489 * we're a sending a non-SYN segment without waiting for 490 * the ACK of our SYN. A check above assures that we only 491 * do this if our peer understands T/TCP. 492 */ 493 case 0: 494 opt[optlen++] = TCPOPT_NOP; 495 opt[optlen++] = TCPOPT_NOP; 496 opt[optlen++] = TCPOPT_CC; 497 opt[optlen++] = TCPOLEN_CC; 498 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send); 499 500 optlen += 4; 501 break; 502 503 /* 504 * This is our initial SYN, check whether we have to use 505 * CC or CC.new. 506 */ 507 case TH_SYN: 508 opt[optlen++] = TCPOPT_NOP; 509 opt[optlen++] = TCPOPT_NOP; 510 opt[optlen++] = tp->t_flags & TF_SENDCCNEW ? 511 TCPOPT_CCNEW : TCPOPT_CC; 512 opt[optlen++] = TCPOLEN_CC; 513 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send); 514 optlen += 4; 515 break; 516 517 /* 518 * This is a SYN,ACK; send CC and CC.echo if we received 519 * CC from our peer. 520 */ 521 case (TH_SYN|TH_ACK): 522 if (tp->t_flags & TF_RCVD_CC) { 523 opt[optlen++] = TCPOPT_NOP; 524 opt[optlen++] = TCPOPT_NOP; 525 opt[optlen++] = TCPOPT_CC; 526 opt[optlen++] = TCPOLEN_CC; 527 *(u_int32_t *)&opt[optlen] = 528 htonl(tp->cc_send); 529 optlen += 4; 530 opt[optlen++] = TCPOPT_NOP; 531 opt[optlen++] = TCPOPT_NOP; 532 opt[optlen++] = TCPOPT_CCECHO; 533 opt[optlen++] = TCPOLEN_CC; 534 *(u_int32_t *)&opt[optlen] = 535 htonl(tp->cc_recv); 536 optlen += 4; 537 } 538 break; 539 } 540 } 541 542 hdrlen += optlen; 543 544 #ifdef INET6 545 if (isipv6) 546 ipoptlen = ip6_optlen(tp->t_inpcb); 547 else 548 #endif 549 if (tp->t_inpcb->inp_options) 550 ipoptlen = tp->t_inpcb->inp_options->m_len - 551 offsetof(struct ipoption, ipopt_list); 552 else 553 ipoptlen = 0; 554 #ifdef IPSEC 555 ipoptlen += ipsec_hdrsiz_tcp(tp); 556 #endif 557 558 /* 559 * Adjust data length if insertion of options will 560 * bump the packet length beyond the t_maxopd length. 561 * Clear the FIN bit because we cut off the tail of 562 * the segment. 563 */ 564 if (len + optlen + ipoptlen > tp->t_maxopd) { 565 /* 566 * If there is still more to send, don't close the connection. 567 */ 568 flags &= ~TH_FIN; 569 len = tp->t_maxopd - optlen - ipoptlen; 570 sendalot = 1; 571 } 572 573 /*#ifdef DIAGNOSTIC*/ 574 #ifdef INET6 575 if (max_linkhdr + hdrlen > MCLBYTES) 576 #else 577 if (max_linkhdr + hdrlen > MHLEN) 578 #endif 579 panic("tcphdr too big"); 580 /*#endif*/ 581 582 /* 583 * Grab a header mbuf, attaching a copy of data to 584 * be transmitted, and initialize the header from 585 * the template for sends on this connection. 586 */ 587 if (len) { 588 if (tp->t_force && len == 1) 589 tcpstat.tcps_sndprobe++; 590 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 591 tcpstat.tcps_sndrexmitpack++; 592 tcpstat.tcps_sndrexmitbyte += len; 593 } else { 594 tcpstat.tcps_sndpack++; 595 tcpstat.tcps_sndbyte += len; 596 } 597 #ifdef notyet 598 if ((m = m_copypack(so->so_snd.sb_mb, off, 599 (int)len, max_linkhdr + hdrlen)) == 0) { 600 error = ENOBUFS; 601 goto out; 602 } 603 /* 604 * m_copypack left space for our hdr; use it. 605 */ 606 m->m_len += hdrlen; 607 m->m_data -= hdrlen; 608 #else 609 MGETHDR(m, M_DONTWAIT, MT_HEADER); 610 if (m == NULL) { 611 error = ENOBUFS; 612 goto out; 613 } 614 #ifdef INET6 615 if (MHLEN < hdrlen + max_linkhdr) { 616 MCLGET(m, M_DONTWAIT); 617 if ((m->m_flags & M_EXT) == 0) { 618 m_freem(m); 619 error = ENOBUFS; 620 goto out; 621 } 622 } 623 #endif 624 m->m_data += max_linkhdr; 625 m->m_len = hdrlen; 626 if (len <= MHLEN - hdrlen - max_linkhdr) { 627 m_copydata(so->so_snd.sb_mb, off, (int) len, 628 mtod(m, caddr_t) + hdrlen); 629 m->m_len += len; 630 } else { 631 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len); 632 if (m->m_next == 0) { 633 (void) m_free(m); 634 error = ENOBUFS; 635 goto out; 636 } 637 } 638 #endif 639 /* 640 * If we're sending everything we've got, set PUSH. 641 * (This will keep happy those implementations which only 642 * give data to the user when a buffer fills or 643 * a PUSH comes in.) 644 */ 645 if (off + len == so->so_snd.sb_cc) 646 flags |= TH_PUSH; 647 } else { 648 if (tp->t_flags & TF_ACKNOW) 649 tcpstat.tcps_sndacks++; 650 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 651 tcpstat.tcps_sndctrl++; 652 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 653 tcpstat.tcps_sndurg++; 654 else 655 tcpstat.tcps_sndwinup++; 656 657 MGETHDR(m, M_DONTWAIT, MT_HEADER); 658 if (m == NULL) { 659 error = ENOBUFS; 660 goto out; 661 } 662 #ifdef INET6 663 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) && 664 MHLEN >= hdrlen) { 665 MH_ALIGN(m, hdrlen); 666 } else 667 #endif 668 m->m_data += max_linkhdr; 669 m->m_len = hdrlen; 670 } 671 m->m_pkthdr.rcvif = (struct ifnet *)0; 672 #ifdef MAC 673 mac_create_mbuf_from_socket(so, m); 674 #endif 675 #ifdef INET6 676 if (isipv6) { 677 ip6 = mtod(m, struct ip6_hdr *); 678 th = (struct tcphdr *)(ip6 + 1); 679 tcp_fillheaders(tp, ip6, th); 680 } else 681 #endif /* INET6 */ 682 { 683 ip = mtod(m, struct ip *); 684 ipov = (struct ipovly *)ip; 685 th = (struct tcphdr *)(ip + 1); 686 /* this picks up the pseudo header (w/o the length) */ 687 tcp_fillheaders(tp, ip, th); 688 } 689 690 /* 691 * Fill in fields, remembering maximum advertised 692 * window for use in delaying messages about window sizes. 693 * If resending a FIN, be sure not to use a new sequence number. 694 */ 695 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 696 tp->snd_nxt == tp->snd_max) 697 tp->snd_nxt--; 698 /* 699 * If we are doing retransmissions, then snd_nxt will 700 * not reflect the first unsent octet. For ACK only 701 * packets, we do not want the sequence number of the 702 * retransmitted packet, we want the sequence number 703 * of the next unsent octet. So, if there is no data 704 * (and no SYN or FIN), use snd_max instead of snd_nxt 705 * when filling in ti_seq. But if we are in persist 706 * state, snd_max might reflect one byte beyond the 707 * right edge of the window, so use snd_nxt in that 708 * case, since we know we aren't doing a retransmission. 709 * (retransmit and persist are mutually exclusive...) 710 */ 711 if (len || (flags & (TH_SYN|TH_FIN)) 712 || callout_active(tp->tt_persist)) 713 th->th_seq = htonl(tp->snd_nxt); 714 else 715 th->th_seq = htonl(tp->snd_max); 716 th->th_ack = htonl(tp->rcv_nxt); 717 if (optlen) { 718 bcopy(opt, th + 1, optlen); 719 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 720 } 721 th->th_flags = flags; 722 /* 723 * Calculate receive window. Don't shrink window, 724 * but avoid silly window syndrome. 725 */ 726 if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg) 727 win = 0; 728 if (win < (long)(tp->rcv_adv - tp->rcv_nxt)) 729 win = (long)(tp->rcv_adv - tp->rcv_nxt); 730 if (win > (long)TCP_MAXWIN << tp->rcv_scale) 731 win = (long)TCP_MAXWIN << tp->rcv_scale; 732 th->th_win = htons((u_short) (win>>tp->rcv_scale)); 733 734 735 /* 736 * Adjust the RXWIN0SENT flag - indicate that we have advertised 737 * a 0 window. This may cause the remote transmitter to stall. This 738 * flag tells soreceive() to disable delayed acknowledgements when 739 * draining the buffer. This can occur if the receiver is attempting 740 * to read more data then can be buffered prior to transmitting on 741 * the connection. 742 */ 743 if (win == 0) 744 tp->t_flags |= TF_RXWIN0SENT; 745 else 746 tp->t_flags &= ~TF_RXWIN0SENT; 747 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 748 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 749 th->th_flags |= TH_URG; 750 } else 751 /* 752 * If no urgent pointer to send, then we pull 753 * the urgent pointer to the left edge of the send window 754 * so that it doesn't drift into the send window on sequence 755 * number wraparound. 756 */ 757 tp->snd_up = tp->snd_una; /* drag it along */ 758 759 /* 760 * Put TCP length in extended header, and then 761 * checksum extended header and data. 762 */ 763 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */ 764 #ifdef INET6 765 if (isipv6) 766 /* 767 * ip6_plen is not need to be filled now, and will be filled 768 * in ip6_output. 769 */ 770 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr), 771 sizeof(struct tcphdr) + optlen + len); 772 else 773 #endif /* INET6 */ 774 { 775 m->m_pkthdr.csum_flags = CSUM_TCP; 776 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 777 if (len + optlen) 778 th->th_sum = in_addword(th->th_sum, 779 htons((u_short)(optlen + len))); 780 781 /* IP version must be set here for ipv4/ipv6 checking later */ 782 KASSERT(ip->ip_v == IPVERSION, 783 ("%s: IP version incorrect: %d", __func__, ip->ip_v)); 784 } 785 786 /* 787 * In transmit state, time the transmission and arrange for 788 * the retransmit. In persist state, just set snd_max. 789 */ 790 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) { 791 tcp_seq startseq = tp->snd_nxt; 792 793 /* 794 * Advance snd_nxt over sequence space of this segment. 795 */ 796 if (flags & (TH_SYN|TH_FIN)) { 797 if (flags & TH_SYN) 798 tp->snd_nxt++; 799 if (flags & TH_FIN) { 800 tp->snd_nxt++; 801 tp->t_flags |= TF_SENTFIN; 802 } 803 } 804 tp->snd_nxt += len; 805 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 806 tp->snd_max = tp->snd_nxt; 807 /* 808 * Time this transmission if not a retransmission and 809 * not currently timing anything. 810 */ 811 if (tp->t_rtttime == 0) { 812 tp->t_rtttime = ticks; 813 tp->t_rtseq = startseq; 814 tcpstat.tcps_segstimed++; 815 } 816 } 817 818 /* 819 * Set retransmit timer if not currently set, 820 * and not doing a pure ack or a keep-alive probe. 821 * Initial value for retransmit timer is smoothed 822 * round-trip time + 2 * round-trip time variance. 823 * Initialize shift counter which is used for backoff 824 * of retransmit time. 825 */ 826 if (!callout_active(tp->tt_rexmt) && 827 tp->snd_nxt != tp->snd_una) { 828 if (callout_active(tp->tt_persist)) { 829 callout_stop(tp->tt_persist); 830 tp->t_rxtshift = 0; 831 } 832 callout_reset(tp->tt_rexmt, tp->t_rxtcur, 833 tcp_timer_rexmt, tp); 834 } 835 } else { 836 /* 837 * Persist case, update snd_max but since we are in 838 * persist mode (no window) we do not update snd_nxt. 839 */ 840 int xlen = len; 841 if (flags & TH_SYN) 842 ++xlen; 843 if (flags & TH_FIN) { 844 ++xlen; 845 tp->t_flags |= TF_SENTFIN; 846 } 847 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max)) 848 tp->snd_max = tp->snd_nxt + len; 849 } 850 851 #ifdef TCPDEBUG 852 /* 853 * Trace. 854 */ 855 if (so->so_options & SO_DEBUG) 856 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0); 857 #endif 858 859 /* 860 * Fill in IP length and desired time to live and 861 * send to IP level. There should be a better way 862 * to handle ttl and tos; we could keep them in 863 * the template, but need a way to checksum without them. 864 */ 865 /* 866 * m->m_pkthdr.len should have been set before cksum calcuration, 867 * because in6_cksum() need it. 868 */ 869 #ifdef INET6 870 if (isipv6) { 871 /* 872 * we separately set hoplimit for every segment, since the 873 * user might want to change the value via setsockopt. 874 * Also, desired default hop limit might be changed via 875 * Neighbor Discovery. 876 */ 877 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, 878 tp->t_inpcb->in6p_route.ro_rt ? 879 tp->t_inpcb->in6p_route.ro_rt->rt_ifp 880 : NULL); 881 882 /* TODO: IPv6 IP6TOS_ECT bit on */ 883 error = ip6_output(m, 884 tp->t_inpcb->in6p_outputopts, 885 &tp->t_inpcb->in6p_route, 886 (so->so_options & SO_DONTROUTE), NULL, NULL, 887 tp->t_inpcb); 888 } else 889 #endif /* INET6 */ 890 { 891 struct rtentry *rt; 892 ip->ip_len = m->m_pkthdr.len; 893 #ifdef INET6 894 if (INP_CHECK_SOCKAF(so, AF_INET6)) 895 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, 896 tp->t_inpcb->in6p_route.ro_rt ? 897 tp->t_inpcb->in6p_route.ro_rt->rt_ifp 898 : NULL); 899 else 900 #endif /* INET6 */ 901 ip->ip_ttl = tp->t_inpcb->inp_ip_ttl; /* XXX */ 902 ip->ip_tos = tp->t_inpcb->inp_ip_tos; /* XXX */ 903 /* 904 * See if we should do MTU discovery. We do it only if the following 905 * are true: 906 * 1) we have a valid route to the destination 907 * 2) the MTU is not locked (if it is, then discovery has been 908 * disabled) 909 */ 910 if (path_mtu_discovery 911 && (rt = tp->t_inpcb->inp_route.ro_rt) 912 && rt->rt_flags & RTF_UP 913 && !(rt->rt_rmx.rmx_locks & RTV_MTU)) { 914 ip->ip_off |= IP_DF; 915 } 916 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, 917 (so->so_options & SO_DONTROUTE), 0, tp->t_inpcb); 918 } 919 if (error) { 920 921 /* 922 * We know that the packet was lost, so back out the 923 * sequence number advance, if any. 924 */ 925 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) { 926 /* 927 * No need to check for TH_FIN here because 928 * the TF_SENTFIN flag handles that case. 929 */ 930 if ((flags & TH_SYN) == 0) 931 tp->snd_nxt -= len; 932 } 933 934 out: 935 if (error == ENOBUFS) { 936 if (!callout_active(tp->tt_rexmt) && 937 !callout_active(tp->tt_persist)) 938 callout_reset(tp->tt_rexmt, tp->t_rxtcur, 939 tcp_timer_rexmt, tp); 940 tcp_quench(tp->t_inpcb, 0); 941 return (0); 942 } 943 if (error == EMSGSIZE) { 944 /* 945 * ip_output() will have already fixed the route 946 * for us. tcp_mtudisc() will, as its last action, 947 * initiate retransmission, so it is important to 948 * not do so here. 949 */ 950 tcp_mtudisc(tp->t_inpcb, 0); 951 return 0; 952 } 953 if ((error == EHOSTUNREACH || error == ENETDOWN) 954 && TCPS_HAVERCVDSYN(tp->t_state)) { 955 tp->t_softerror = error; 956 return (0); 957 } 958 return (error); 959 } 960 tcpstat.tcps_sndtotal++; 961 962 /* 963 * Data sent (as far as we can tell). 964 * If this advertises a larger window than any other segment, 965 * then remember the size of the advertised window. 966 * Any pending ACK has now been sent. 967 */ 968 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 969 tp->rcv_adv = tp->rcv_nxt + win; 970 tp->last_ack_sent = tp->rcv_nxt; 971 tp->t_flags &= ~TF_ACKNOW; 972 if (tcp_delack_enabled) 973 callout_stop(tp->tt_delack); 974 #if 0 975 /* 976 * This completely breaks TCP if newreno is turned on. What happens 977 * is that if delayed-acks are turned on on the receiver, this code 978 * on the transmitter effectively destroys the TCP window, forcing 979 * it to four packets (1.5Kx4 = 6K window). 980 */ 981 if (sendalot && (!tcp_do_newreno || --maxburst)) 982 goto again; 983 #endif 984 if (sendalot) 985 goto again; 986 return (0); 987 } 988 989 void 990 tcp_setpersist(tp) 991 register struct tcpcb *tp; 992 { 993 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 994 int tt; 995 996 if (callout_active(tp->tt_rexmt)) 997 panic("tcp_setpersist: retransmit pending"); 998 /* 999 * Start/restart persistance timer. 1000 */ 1001 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], 1002 TCPTV_PERSMIN, TCPTV_PERSMAX); 1003 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp); 1004 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1005 tp->t_rxtshift++; 1006 }
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