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 */ 31 32 #include <sys/cdefs.h> 33 __FBSDID("$FreeBSD$"); 34 35 #include "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_ipsec.h" 38 #include "opt_mac.h" 39 #include "opt_tcpdebug.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/domain.h> 44 #include <sys/kernel.h> 45 #include <sys/lock.h> 46 #include <sys/mbuf.h> 47 #include <sys/mutex.h> 48 #include <sys/protosw.h> 49 #include <sys/socket.h> 50 #include <sys/socketvar.h> 51 #include <sys/sysctl.h> 52 53 #include <net/route.h> 54 55 #include <netinet/in.h> 56 #include <netinet/in_systm.h> 57 #include <netinet/ip.h> 58 #include <netinet/in_pcb.h> 59 #include <netinet/ip_var.h> 60 #include <netinet/ip_options.h> 61 #ifdef INET6 62 #include <netinet6/in6_pcb.h> 63 #include <netinet/ip6.h> 64 #include <netinet6/ip6_var.h> 65 #endif 66 #include <netinet/tcp.h> 67 #define TCPOUTFLAGS 68 #include <netinet/tcp_fsm.h> 69 #include <netinet/tcp_seq.h> 70 #include <netinet/tcp_timer.h> 71 #include <netinet/tcp_var.h> 72 #include <netinet/tcpip.h> 73 #ifdef TCPDEBUG 74 #include <netinet/tcp_debug.h> 75 #endif 76 77 #ifdef IPSEC 78 #include <netipsec/ipsec.h> 79 #endif /*IPSEC*/ 80 81 #include <machine/in_cksum.h> 82 83 #include <security/mac/mac_framework.h> 84 85 #ifdef notyet 86 extern struct mbuf *m_copypack(); 87 #endif 88 89 int path_mtu_discovery = 1; 90 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW, 91 &path_mtu_discovery, 1, "Enable Path MTU Discovery"); 92 93 int ss_fltsz = 1; 94 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW, 95 &ss_fltsz, 1, "Slow start flight size"); 96 97 int ss_fltsz_local = 4; 98 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW, 99 &ss_fltsz_local, 1, "Slow start flight size for local networks"); 100 101 int tcp_do_newreno = 1; 102 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, 103 &tcp_do_newreno, 0, "Enable NewReno Algorithms"); 104 105 int tcp_do_tso = 1; 106 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW, 107 &tcp_do_tso, 0, "Enable TCP Segmentation Offload"); 108 109 int tcp_do_autosndbuf = 1; 110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW, 111 &tcp_do_autosndbuf, 0, "Enable automatic send buffer sizing"); 112 113 int tcp_autosndbuf_inc = 8*1024; 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW, 115 &tcp_autosndbuf_inc, 0, "Incrementor step size of automatic send buffer"); 116 117 int tcp_autosndbuf_max = 256*1024; 118 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW, 119 &tcp_autosndbuf_max, 0, "Max size of automatic send buffer"); 120 121 122 /* 123 * Tcp output routine: figure out what should be sent and send it. 124 */ 125 int 126 tcp_output(struct tcpcb *tp) 127 { 128 struct socket *so = tp->t_inpcb->inp_socket; 129 long len, recwin, sendwin; 130 int off, flags, error; 131 #ifdef TCP_SIGNATURE 132 int sigoff = 0; 133 #endif 134 struct mbuf *m; 135 struct ip *ip = NULL; 136 struct ipovly *ipov = NULL; 137 struct tcphdr *th; 138 u_char opt[TCP_MAXOLEN]; 139 unsigned ipoptlen, optlen, hdrlen; 140 int idle, sendalot; 141 int sack_rxmit, sack_bytes_rxmt; 142 struct sackhole *p; 143 int tso = 0; 144 struct tcpopt to; 145 #if 0 146 int maxburst = TCP_MAXBURST; 147 #endif 148 #ifdef INET6 149 struct ip6_hdr *ip6 = NULL; 150 int isipv6; 151 152 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0; 153 #endif 154 155 INP_LOCK_ASSERT(tp->t_inpcb); 156 157 /* 158 * Determine length of data that should be transmitted, 159 * and flags that will be used. 160 * If there is some data or critical controls (SYN, RST) 161 * to send, then transmit; otherwise, investigate further. 162 */ 163 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una); 164 if (idle && (ticks - tp->t_rcvtime) >= tp->t_rxtcur) { 165 /* 166 * We have been idle for "a while" and no acks are 167 * expected to clock out any data we send -- 168 * slow start to get ack "clock" running again. 169 * 170 * Set the slow-start flight size depending on whether 171 * this is a local network or not. 172 */ 173 int ss = ss_fltsz; 174 #ifdef INET6 175 if (isipv6) { 176 if (in6_localaddr(&tp->t_inpcb->in6p_faddr)) 177 ss = ss_fltsz_local; 178 } else 179 #endif /* INET6 */ 180 if (in_localaddr(tp->t_inpcb->inp_faddr)) 181 ss = ss_fltsz_local; 182 tp->snd_cwnd = tp->t_maxseg * ss; 183 } 184 tp->t_flags &= ~TF_LASTIDLE; 185 if (idle) { 186 if (tp->t_flags & TF_MORETOCOME) { 187 tp->t_flags |= TF_LASTIDLE; 188 idle = 0; 189 } 190 } 191 again: 192 /* 193 * If we've recently taken a timeout, snd_max will be greater than 194 * snd_nxt. There may be SACK information that allows us to avoid 195 * resending already delivered data. Adjust snd_nxt accordingly. 196 */ 197 if ((tp->t_flags & TF_SACK_PERMIT) && 198 SEQ_LT(tp->snd_nxt, tp->snd_max)) 199 tcp_sack_adjust(tp); 200 sendalot = 0; 201 off = tp->snd_nxt - tp->snd_una; 202 sendwin = min(tp->snd_wnd, tp->snd_cwnd); 203 sendwin = min(sendwin, tp->snd_bwnd); 204 205 flags = tcp_outflags[tp->t_state]; 206 /* 207 * Send any SACK-generated retransmissions. If we're explicitly trying 208 * to send out new data (when sendalot is 1), bypass this function. 209 * If we retransmit in fast recovery mode, decrement snd_cwnd, since 210 * we're replacing a (future) new transmission with a retransmission 211 * now, and we previously incremented snd_cwnd in tcp_input(). 212 */ 213 /* 214 * Still in sack recovery , reset rxmit flag to zero. 215 */ 216 sack_rxmit = 0; 217 sack_bytes_rxmt = 0; 218 len = 0; 219 p = NULL; 220 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp) && 221 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) { 222 long cwin; 223 224 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt; 225 if (cwin < 0) 226 cwin = 0; 227 /* Do not retransmit SACK segments beyond snd_recover */ 228 if (SEQ_GT(p->end, tp->snd_recover)) { 229 /* 230 * (At least) part of sack hole extends beyond 231 * snd_recover. Check to see if we can rexmit data 232 * for this hole. 233 */ 234 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) { 235 /* 236 * Can't rexmit any more data for this hole. 237 * That data will be rexmitted in the next 238 * sack recovery episode, when snd_recover 239 * moves past p->rxmit. 240 */ 241 p = NULL; 242 goto after_sack_rexmit; 243 } else 244 /* Can rexmit part of the current hole */ 245 len = ((long)ulmin(cwin, 246 tp->snd_recover - p->rxmit)); 247 } else 248 len = ((long)ulmin(cwin, p->end - p->rxmit)); 249 off = p->rxmit - tp->snd_una; 250 KASSERT(off >= 0,("%s: sack block to the left of una : %d", 251 __func__, off)); 252 if (len > 0) { 253 sack_rxmit = 1; 254 sendalot = 1; 255 tcpstat.tcps_sack_rexmits++; 256 tcpstat.tcps_sack_rexmit_bytes += 257 min(len, tp->t_maxseg); 258 } 259 } 260 after_sack_rexmit: 261 /* 262 * Get standard flags, and add SYN or FIN if requested by 'hidden' 263 * state flags. 264 */ 265 if (tp->t_flags & TF_NEEDFIN) 266 flags |= TH_FIN; 267 if (tp->t_flags & TF_NEEDSYN) 268 flags |= TH_SYN; 269 270 SOCKBUF_LOCK(&so->so_snd); 271 /* 272 * If in persist timeout with window of 0, send 1 byte. 273 * Otherwise, if window is small but nonzero 274 * and timer expired, we will send what we can 275 * and go to transmit state. 276 */ 277 if (tp->t_flags & TF_FORCEDATA) { 278 if (sendwin == 0) { 279 /* 280 * If we still have some data to send, then 281 * clear the FIN bit. Usually this would 282 * happen below when it realizes that we 283 * aren't sending all the data. However, 284 * if we have exactly 1 byte of unsent data, 285 * then it won't clear the FIN bit below, 286 * and if we are in persist state, we wind 287 * up sending the packet without recording 288 * that we sent the FIN bit. 289 * 290 * We can't just blindly clear the FIN bit, 291 * because if we don't have any more data 292 * to send then the probe will be the FIN 293 * itself. 294 */ 295 if (off < so->so_snd.sb_cc) 296 flags &= ~TH_FIN; 297 sendwin = 1; 298 } else { 299 tcp_timer_activate(tp, TT_PERSIST, 0); 300 tp->t_rxtshift = 0; 301 } 302 } 303 304 /* 305 * If snd_nxt == snd_max and we have transmitted a FIN, the 306 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in 307 * a negative length. This can also occur when TCP opens up 308 * its congestion window while receiving additional duplicate 309 * acks after fast-retransmit because TCP will reset snd_nxt 310 * to snd_max after the fast-retransmit. 311 * 312 * In the normal retransmit-FIN-only case, however, snd_nxt will 313 * be set to snd_una, the offset will be 0, and the length may 314 * wind up 0. 315 * 316 * If sack_rxmit is true we are retransmitting from the scoreboard 317 * in which case len is already set. 318 */ 319 if (sack_rxmit == 0) { 320 if (sack_bytes_rxmt == 0) 321 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off); 322 else { 323 long cwin; 324 325 /* 326 * We are inside of a SACK recovery episode and are 327 * sending new data, having retransmitted all the 328 * data possible in the scoreboard. 329 */ 330 len = ((long)ulmin(so->so_snd.sb_cc, tp->snd_wnd) 331 - off); 332 /* 333 * Don't remove this (len > 0) check ! 334 * We explicitly check for len > 0 here (although it 335 * isn't really necessary), to work around a gcc 336 * optimization issue - to force gcc to compute 337 * len above. Without this check, the computation 338 * of len is bungled by the optimizer. 339 */ 340 if (len > 0) { 341 cwin = tp->snd_cwnd - 342 (tp->snd_nxt - tp->sack_newdata) - 343 sack_bytes_rxmt; 344 if (cwin < 0) 345 cwin = 0; 346 len = lmin(len, cwin); 347 } 348 } 349 } 350 351 /* 352 * Lop off SYN bit if it has already been sent. However, if this 353 * is SYN-SENT state and if segment contains data and if we don't 354 * know that foreign host supports TAO, suppress sending segment. 355 */ 356 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) { 357 if (tp->t_state != TCPS_SYN_RECEIVED) 358 flags &= ~TH_SYN; 359 off--, len++; 360 } 361 362 /* 363 * Be careful not to send data and/or FIN on SYN segments. 364 * This measure is needed to prevent interoperability problems 365 * with not fully conformant TCP implementations. 366 */ 367 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) { 368 len = 0; 369 flags &= ~TH_FIN; 370 } 371 372 if (len < 0) { 373 /* 374 * If FIN has been sent but not acked, 375 * but we haven't been called to retransmit, 376 * len will be < 0. Otherwise, window shrank 377 * after we sent into it. If window shrank to 0, 378 * cancel pending retransmit, pull snd_nxt back 379 * to (closed) window, and set the persist timer 380 * if it isn't already going. If the window didn't 381 * close completely, just wait for an ACK. 382 */ 383 len = 0; 384 if (sendwin == 0) { 385 tcp_timer_activate(tp, TT_REXMT, 0); 386 tp->t_rxtshift = 0; 387 tp->snd_nxt = tp->snd_una; 388 if (!tcp_timer_active(tp, TT_PERSIST)) 389 tcp_setpersist(tp); 390 } 391 } 392 393 /* len will be >= 0 after this point. */ 394 KASSERT(len >= 0, ("%s: len < 0", __func__)); 395 396 /* 397 * Automatic sizing of send socket buffer. Often the send buffer 398 * size is not optimally adjusted to the actual network conditions 399 * at hand (delay bandwidth product). Setting the buffer size too 400 * small limits throughput on links with high bandwidth and high 401 * delay (eg. trans-continental/oceanic links). Setting the 402 * buffer size too big consumes too much real kernel memory, 403 * especially with many connections on busy servers. 404 * 405 * The criteria to step up the send buffer one notch are: 406 * 1. receive window of remote host is larger than send buffer 407 * (with a fudge factor of 5/4th); 408 * 2. send buffer is filled to 7/8th with data (so we actually 409 * have data to make use of it); 410 * 3. send buffer fill has not hit maximal automatic size; 411 * 4. our send window (slow start and cogestion controlled) is 412 * larger than sent but unacknowledged data in send buffer. 413 * 414 * The remote host receive window scaling factor may limit the 415 * growing of the send buffer before it reaches its allowed 416 * maximum. 417 * 418 * It scales directly with slow start or congestion window 419 * and does at most one step per received ACK. This fast 420 * scaling has the drawback of growing the send buffer beyond 421 * what is strictly necessary to make full use of a given 422 * delay*bandwith product. However testing has shown this not 423 * to be much of an problem. At worst we are trading wasting 424 * of available bandwith (the non-use of it) for wasting some 425 * socket buffer memory. 426 * 427 * TODO: Shrink send buffer during idle periods together 428 * with congestion window. Requires another timer. Has to 429 * wait for upcoming tcp timer rewrite. 430 */ 431 if (tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) { 432 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat && 433 so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) && 434 so->so_snd.sb_cc < tcp_autosndbuf_max && 435 sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) { 436 if (!sbreserve_locked(&so->so_snd, 437 min(so->so_snd.sb_hiwat + tcp_autosndbuf_inc, 438 tcp_autosndbuf_max), so, curthread)) 439 so->so_snd.sb_flags &= ~SB_AUTOSIZE; 440 } 441 } 442 443 /* 444 * Truncate to the maximum segment length or enable TCP Segmentation 445 * Offloading (if supported by hardware) and ensure that FIN is removed 446 * if the length no longer contains the last data byte. 447 * 448 * TSO may only be used if we are in a pure bulk sending state. The 449 * presence of TCP-MD5, SACK retransmits, SACK advertizements and 450 * IP options prevent using TSO. With TSO the TCP header is the same 451 * (except for the sequence number) for all generated packets. This 452 * makes it impossible to transmit any options which vary per generated 453 * segment or packet. 454 * 455 * The length of TSO bursts is limited to TCP_MAXWIN. That limit and 456 * removal of FIN (if not already catched here) are handled later after 457 * the exact length of the TCP options are known. 458 */ 459 if (len > tp->t_maxseg) { 460 if ((tp->t_flags & TF_TSO) && tcp_do_tso && 461 ((tp->t_flags & TF_SIGNATURE) == 0) && 462 tp->rcv_numsacks == 0 && sack_rxmit == 0 && 463 tp->t_inpcb->inp_options == NULL && 464 tp->t_inpcb->in6p_options == NULL && 465 tp->t_inpcb->inp_sp == NULL) { 466 tso = 1; 467 } else { 468 len = tp->t_maxseg; 469 sendalot = 1; 470 tso = 0; 471 } 472 } 473 if (sack_rxmit) { 474 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc)) 475 flags &= ~TH_FIN; 476 } else { 477 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) 478 flags &= ~TH_FIN; 479 } 480 481 recwin = sbspace(&so->so_rcv); 482 483 /* 484 * Sender silly window avoidance. We transmit under the following 485 * conditions when len is non-zero: 486 * 487 * - We have a full segment (or more with TSO) 488 * - This is the last buffer in a write()/send() and we are 489 * either idle or running NODELAY 490 * - we've timed out (e.g. persist timer) 491 * - we have more then 1/2 the maximum send window's worth of 492 * data (receiver may be limited the window size) 493 * - we need to retransmit 494 */ 495 if (len) { 496 if (len >= tp->t_maxseg) 497 goto send; 498 /* 499 * NOTE! on localhost connections an 'ack' from the remote 500 * end may occur synchronously with the output and cause 501 * us to flush a buffer queued with moretocome. XXX 502 * 503 * note: the len + off check is almost certainly unnecessary. 504 */ 505 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */ 506 (idle || (tp->t_flags & TF_NODELAY)) && 507 len + off >= so->so_snd.sb_cc && 508 (tp->t_flags & TF_NOPUSH) == 0) { 509 goto send; 510 } 511 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */ 512 goto send; 513 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0) 514 goto send; 515 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */ 516 goto send; 517 if (sack_rxmit) 518 goto send; 519 } 520 521 /* 522 * Compare available window to amount of window 523 * known to peer (as advertised window less 524 * next expected input). If the difference is at least two 525 * max size segments, or at least 50% of the maximum possible 526 * window, then want to send a window update to peer. 527 * Skip this if the connection is in T/TCP half-open state. 528 * Don't send pure window updates when the peer has closed 529 * the connection and won't ever send more data. 530 */ 531 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) && 532 !TCPS_HAVERCVDFIN(tp->t_state)) { 533 /* 534 * "adv" is the amount we can increase the window, 535 * taking into account that we are limited by 536 * TCP_MAXWIN << tp->rcv_scale. 537 */ 538 long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) - 539 (tp->rcv_adv - tp->rcv_nxt); 540 541 if (adv >= (long) (2 * tp->t_maxseg)) 542 goto send; 543 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 544 goto send; 545 } 546 547 /* 548 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW 549 * is also a catch-all for the retransmit timer timeout case. 550 */ 551 if (tp->t_flags & TF_ACKNOW) 552 goto send; 553 if ((flags & TH_RST) || 554 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0)) 555 goto send; 556 if (SEQ_GT(tp->snd_up, tp->snd_una)) 557 goto send; 558 /* 559 * If our state indicates that FIN should be sent 560 * and we have not yet done so, then we need to send. 561 */ 562 if (flags & TH_FIN && 563 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 564 goto send; 565 /* 566 * In SACK, it is possible for tcp_output to fail to send a segment 567 * after the retransmission timer has been turned off. Make sure 568 * that the retransmission timer is set. 569 */ 570 if ((tp->t_flags & TF_SACK_PERMIT) && 571 SEQ_GT(tp->snd_max, tp->snd_una) && 572 !tcp_timer_active(tp, TT_REXMT) && 573 !tcp_timer_active(tp, TT_PERSIST)) { 574 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); 575 goto just_return; 576 } 577 /* 578 * TCP window updates are not reliable, rather a polling protocol 579 * using ``persist'' packets is used to insure receipt of window 580 * updates. The three ``states'' for the output side are: 581 * idle not doing retransmits or persists 582 * persisting to move a small or zero window 583 * (re)transmitting and thereby not persisting 584 * 585 * tcp_timer_active(tp, TT_PERSIST) 586 * is true when we are in persist state. 587 * (tp->t_flags & TF_FORCEDATA) 588 * is set when we are called to send a persist packet. 589 * tcp_timer_active(tp, TT_REXMT) 590 * is set when we are retransmitting 591 * The output side is idle when both timers are zero. 592 * 593 * If send window is too small, there is data to transmit, and no 594 * retransmit or persist is pending, then go to persist state. 595 * If nothing happens soon, send when timer expires: 596 * if window is nonzero, transmit what we can, 597 * otherwise force out a byte. 598 */ 599 if (so->so_snd.sb_cc && !tcp_timer_active(tp, TT_REXMT) && 600 !tcp_timer_active(tp, TT_PERSIST)) { 601 tp->t_rxtshift = 0; 602 tcp_setpersist(tp); 603 } 604 605 /* 606 * No reason to send a segment, just return. 607 */ 608 just_return: 609 SOCKBUF_UNLOCK(&so->so_snd); 610 return (0); 611 612 send: 613 SOCKBUF_LOCK_ASSERT(&so->so_snd); 614 /* 615 * Before ESTABLISHED, force sending of initial options 616 * unless TCP set not to do any options. 617 * NOTE: we assume that the IP/TCP header plus TCP options 618 * always fit in a single mbuf, leaving room for a maximum 619 * link header, i.e. 620 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 621 */ 622 optlen = 0; 623 #ifdef INET6 624 if (isipv6) 625 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr); 626 else 627 #endif 628 hdrlen = sizeof (struct tcpiphdr); 629 630 /* 631 * Compute options for segment. 632 * We only have to care about SYN and established connection 633 * segments. Options for SYN-ACK segments are handled in TCP 634 * syncache. 635 */ 636 if ((tp->t_flags & TF_NOOPT) == 0) { 637 to.to_flags = 0; 638 /* Maximum segment size. */ 639 if (flags & TH_SYN) { 640 tp->snd_nxt = tp->iss; 641 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc); 642 to.to_flags |= TOF_MSS; 643 } 644 /* Window scaling. */ 645 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) { 646 to.to_wscale = tp->request_r_scale; 647 to.to_flags |= TOF_SCALE; 648 } 649 /* Timestamps. */ 650 if ((tp->t_flags & TF_RCVD_TSTMP) || 651 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) { 652 to.to_tsval = ticks + tp->ts_offset; 653 to.to_tsecr = tp->ts_recent; 654 to.to_flags |= TOF_TS; 655 /* Set receive buffer autosizing timestamp. */ 656 if (tp->rfbuf_ts == 0 && 657 (so->so_rcv.sb_flags & SB_AUTOSIZE)) 658 tp->rfbuf_ts = ticks; 659 } 660 /* Selective ACK's. */ 661 if (tp->t_flags & TF_SACK_PERMIT) { 662 if (flags & TH_SYN) 663 to.to_flags |= TOF_SACKPERM; 664 else if (TCPS_HAVEESTABLISHED(tp->t_state) && 665 (tp->t_flags & TF_SACK_PERMIT) && 666 tp->rcv_numsacks > 0) { 667 to.to_flags |= TOF_SACK; 668 to.to_nsacks = tp->rcv_numsacks; 669 to.to_sacks = (u_char *)tp->sackblks; 670 } 671 } 672 #ifdef TCP_SIGNATURE 673 /* TCP-MD5 (RFC2385). */ 674 #ifdef INET6 675 if (!isipv6 && (tp->t_flags & TF_SIGNATURE)) 676 #else 677 if (tp->t_flags & TF_SIGNATURE) 678 #endif /* INET6 */ 679 to.to_flags |= TOF_SIGNATURE; 680 #endif /* TCP_SIGNATURE */ 681 682 /* Processing the options. */ 683 hdrlen += optlen = tcp_addoptions(&to, (u_char *)&opt); 684 685 #ifdef TCP_SIGNATURE 686 sigoff = to.to_signature - (u_char *)&to; 687 #endif /* TCP_SIGNATURE */ 688 } 689 690 #ifdef INET6 691 if (isipv6) 692 ipoptlen = ip6_optlen(tp->t_inpcb); 693 else 694 #endif 695 if (tp->t_inpcb->inp_options) 696 ipoptlen = tp->t_inpcb->inp_options->m_len - 697 offsetof(struct ipoption, ipopt_list); 698 else 699 ipoptlen = 0; 700 #ifdef IPSEC 701 ipoptlen += ipsec_hdrsiz_tcp(tp); 702 #endif 703 704 /* 705 * Adjust data length if insertion of options will 706 * bump the packet length beyond the t_maxopd length. 707 * Clear the FIN bit because we cut off the tail of 708 * the segment. 709 * 710 * When doing TSO limit a burst to TCP_MAXWIN minus the 711 * IP, TCP and Options length to keep ip->ip_len from 712 * overflowing. Prevent the last segment from being 713 * fractional thus making them all equal sized and set 714 * the flag to continue sending. TSO is disabled when 715 * IP options or IPSEC are present. 716 */ 717 if (len + optlen + ipoptlen > tp->t_maxopd) { 718 flags &= ~TH_FIN; 719 if (tso) { 720 if (len > TCP_MAXWIN - hdrlen - optlen) { 721 len = TCP_MAXWIN - hdrlen - optlen; 722 len = len - (len % (tp->t_maxopd - optlen)); 723 sendalot = 1; 724 } else if (tp->t_flags & TF_NEEDFIN) 725 sendalot = 1; 726 } else { 727 len = tp->t_maxopd - optlen - ipoptlen; 728 sendalot = 1; 729 } 730 } 731 732 /*#ifdef DIAGNOSTIC*/ 733 #ifdef INET6 734 if (max_linkhdr + hdrlen > MCLBYTES) 735 #else 736 if (max_linkhdr + hdrlen > MHLEN) 737 #endif 738 panic("tcphdr too big"); 739 /*#endif*/ 740 741 /* 742 * Grab a header mbuf, attaching a copy of data to 743 * be transmitted, and initialize the header from 744 * the template for sends on this connection. 745 */ 746 if (len) { 747 struct mbuf *mb; 748 u_int moff; 749 750 if ((tp->t_flags & TF_FORCEDATA) && len == 1) 751 tcpstat.tcps_sndprobe++; 752 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) { 753 tcpstat.tcps_sndrexmitpack++; 754 tcpstat.tcps_sndrexmitbyte += len; 755 } else { 756 tcpstat.tcps_sndpack++; 757 tcpstat.tcps_sndbyte += len; 758 } 759 #ifdef notyet 760 if ((m = m_copypack(so->so_snd.sb_mb, off, 761 (int)len, max_linkhdr + hdrlen)) == 0) { 762 SOCKBUF_UNLOCK(&so->so_snd); 763 error = ENOBUFS; 764 goto out; 765 } 766 /* 767 * m_copypack left space for our hdr; use it. 768 */ 769 m->m_len += hdrlen; 770 m->m_data -= hdrlen; 771 #else 772 MGETHDR(m, M_DONTWAIT, MT_DATA); 773 if (m == NULL) { 774 SOCKBUF_UNLOCK(&so->so_snd); 775 error = ENOBUFS; 776 goto out; 777 } 778 #ifdef INET6 779 if (MHLEN < hdrlen + max_linkhdr) { 780 MCLGET(m, M_DONTWAIT); 781 if ((m->m_flags & M_EXT) == 0) { 782 SOCKBUF_UNLOCK(&so->so_snd); 783 m_freem(m); 784 error = ENOBUFS; 785 goto out; 786 } 787 } 788 #endif 789 m->m_data += max_linkhdr; 790 m->m_len = hdrlen; 791 792 /* 793 * Start the m_copy functions from the closest mbuf 794 * to the offset in the socket buffer chain. 795 */ 796 mb = sbsndptr(&so->so_snd, off, len, &moff); 797 798 if (len <= MHLEN - hdrlen - max_linkhdr) { 799 m_copydata(mb, moff, (int)len, 800 mtod(m, caddr_t) + hdrlen); 801 m->m_len += len; 802 } else { 803 m->m_next = m_copy(mb, moff, (int)len); 804 if (m->m_next == NULL) { 805 SOCKBUF_UNLOCK(&so->so_snd); 806 (void) m_free(m); 807 error = ENOBUFS; 808 goto out; 809 } 810 } 811 #endif 812 /* 813 * If we're sending everything we've got, set PUSH. 814 * (This will keep happy those implementations which only 815 * give data to the user when a buffer fills or 816 * a PUSH comes in.) 817 */ 818 if (off + len == so->so_snd.sb_cc) 819 flags |= TH_PUSH; 820 SOCKBUF_UNLOCK(&so->so_snd); 821 } else { 822 SOCKBUF_UNLOCK(&so->so_snd); 823 if (tp->t_flags & TF_ACKNOW) 824 tcpstat.tcps_sndacks++; 825 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 826 tcpstat.tcps_sndctrl++; 827 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 828 tcpstat.tcps_sndurg++; 829 else 830 tcpstat.tcps_sndwinup++; 831 832 MGETHDR(m, M_DONTWAIT, MT_DATA); 833 if (m == NULL) { 834 error = ENOBUFS; 835 goto out; 836 } 837 #ifdef INET6 838 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) && 839 MHLEN >= hdrlen) { 840 MH_ALIGN(m, hdrlen); 841 } else 842 #endif 843 m->m_data += max_linkhdr; 844 m->m_len = hdrlen; 845 } 846 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); 847 m->m_pkthdr.rcvif = (struct ifnet *)0; 848 #ifdef MAC 849 mac_create_mbuf_from_inpcb(tp->t_inpcb, m); 850 #endif 851 #ifdef INET6 852 if (isipv6) { 853 ip6 = mtod(m, struct ip6_hdr *); 854 th = (struct tcphdr *)(ip6 + 1); 855 tcpip_fillheaders(tp->t_inpcb, ip6, th); 856 } else 857 #endif /* INET6 */ 858 { 859 ip = mtod(m, struct ip *); 860 ipov = (struct ipovly *)ip; 861 th = (struct tcphdr *)(ip + 1); 862 tcpip_fillheaders(tp->t_inpcb, ip, th); 863 } 864 865 /* 866 * Fill in fields, remembering maximum advertised 867 * window for use in delaying messages about window sizes. 868 * If resending a FIN, be sure not to use a new sequence number. 869 */ 870 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 871 tp->snd_nxt == tp->snd_max) 872 tp->snd_nxt--; 873 /* 874 * If we are doing retransmissions, then snd_nxt will 875 * not reflect the first unsent octet. For ACK only 876 * packets, we do not want the sequence number of the 877 * retransmitted packet, we want the sequence number 878 * of the next unsent octet. So, if there is no data 879 * (and no SYN or FIN), use snd_max instead of snd_nxt 880 * when filling in ti_seq. But if we are in persist 881 * state, snd_max might reflect one byte beyond the 882 * right edge of the window, so use snd_nxt in that 883 * case, since we know we aren't doing a retransmission. 884 * (retransmit and persist are mutually exclusive...) 885 */ 886 if (sack_rxmit == 0) { 887 if (len || (flags & (TH_SYN|TH_FIN)) || 888 tcp_timer_active(tp, TT_PERSIST)) 889 th->th_seq = htonl(tp->snd_nxt); 890 else 891 th->th_seq = htonl(tp->snd_max); 892 } else { 893 th->th_seq = htonl(p->rxmit); 894 p->rxmit += len; 895 tp->sackhint.sack_bytes_rexmit += len; 896 } 897 th->th_ack = htonl(tp->rcv_nxt); 898 if (optlen) { 899 bcopy(opt, th + 1, optlen); 900 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 901 } 902 th->th_flags = flags; 903 /* 904 * Calculate receive window. Don't shrink window, 905 * but avoid silly window syndrome. 906 */ 907 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) && 908 recwin < (long)tp->t_maxseg) 909 recwin = 0; 910 if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt)) 911 recwin = (long)(tp->rcv_adv - tp->rcv_nxt); 912 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale) 913 recwin = (long)TCP_MAXWIN << tp->rcv_scale; 914 915 /* 916 * According to RFC1323 the window field in a SYN (i.e., a <SYN> 917 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK> 918 * case is handled in syncache. 919 */ 920 if (flags & TH_SYN) 921 th->th_win = htons((u_short) 922 (min(sbspace(&so->so_rcv), TCP_MAXWIN))); 923 else 924 th->th_win = htons((u_short)(recwin >> tp->rcv_scale)); 925 926 /* 927 * Adjust the RXWIN0SENT flag - indicate that we have advertised 928 * a 0 window. This may cause the remote transmitter to stall. This 929 * flag tells soreceive() to disable delayed acknowledgements when 930 * draining the buffer. This can occur if the receiver is attempting 931 * to read more data then can be buffered prior to transmitting on 932 * the connection. 933 */ 934 if (recwin == 0) 935 tp->t_flags |= TF_RXWIN0SENT; 936 else 937 tp->t_flags &= ~TF_RXWIN0SENT; 938 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 939 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 940 th->th_flags |= TH_URG; 941 } else 942 /* 943 * If no urgent pointer to send, then we pull 944 * the urgent pointer to the left edge of the send window 945 * so that it doesn't drift into the send window on sequence 946 * number wraparound. 947 */ 948 tp->snd_up = tp->snd_una; /* drag it along */ 949 950 #ifdef TCP_SIGNATURE 951 #ifdef INET6 952 if (!isipv6) 953 #endif 954 if (tp->t_flags & TF_SIGNATURE) 955 tcp_signature_compute(m, sizeof(struct ip), len, optlen, 956 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND); 957 #endif 958 959 /* 960 * Put TCP length in extended header, and then 961 * checksum extended header and data. 962 */ 963 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */ 964 #ifdef INET6 965 if (isipv6) 966 /* 967 * ip6_plen is not need to be filled now, and will be filled 968 * in ip6_output. 969 */ 970 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr), 971 sizeof(struct tcphdr) + optlen + len); 972 else 973 #endif /* INET6 */ 974 { 975 m->m_pkthdr.csum_flags = CSUM_TCP; 976 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 977 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 978 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen)); 979 980 /* IP version must be set here for ipv4/ipv6 checking later */ 981 KASSERT(ip->ip_v == IPVERSION, 982 ("%s: IP version incorrect: %d", __func__, ip->ip_v)); 983 } 984 985 /* 986 * Enable TSO and specify the size of the segments. 987 * The TCP pseudo header checksum is always provided. 988 * XXX: Fixme: This is currently not the case for IPv6. 989 */ 990 if (tso) { 991 m->m_pkthdr.csum_flags = CSUM_TSO; 992 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen; 993 } 994 995 /* 996 * In transmit state, time the transmission and arrange for 997 * the retransmit. In persist state, just set snd_max. 998 */ 999 if ((tp->t_flags & TF_FORCEDATA) == 0 || 1000 !tcp_timer_active(tp, TT_PERSIST)) { 1001 tcp_seq startseq = tp->snd_nxt; 1002 1003 /* 1004 * Advance snd_nxt over sequence space of this segment. 1005 */ 1006 if (flags & (TH_SYN|TH_FIN)) { 1007 if (flags & TH_SYN) 1008 tp->snd_nxt++; 1009 if (flags & TH_FIN) { 1010 tp->snd_nxt++; 1011 tp->t_flags |= TF_SENTFIN; 1012 } 1013 } 1014 if (sack_rxmit) 1015 goto timer; 1016 tp->snd_nxt += len; 1017 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1018 tp->snd_max = tp->snd_nxt; 1019 /* 1020 * Time this transmission if not a retransmission and 1021 * not currently timing anything. 1022 */ 1023 if (tp->t_rtttime == 0) { 1024 tp->t_rtttime = ticks; 1025 tp->t_rtseq = startseq; 1026 tcpstat.tcps_segstimed++; 1027 } 1028 } 1029 1030 /* 1031 * Set retransmit timer if not currently set, 1032 * and not doing a pure ack or a keep-alive probe. 1033 * Initial value for retransmit timer is smoothed 1034 * round-trip time + 2 * round-trip time variance. 1035 * Initialize shift counter which is used for backoff 1036 * of retransmit time. 1037 */ 1038 timer: 1039 if (!tcp_timer_active(tp, TT_REXMT) && 1040 ((sack_rxmit && tp->snd_nxt != tp->snd_max) || 1041 (tp->snd_nxt != tp->snd_una))) { 1042 if (tcp_timer_active(tp, TT_PERSIST)) { 1043 tcp_timer_activate(tp, TT_PERSIST, 0); 1044 tp->t_rxtshift = 0; 1045 } 1046 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); 1047 } 1048 } else { 1049 /* 1050 * Persist case, update snd_max but since we are in 1051 * persist mode (no window) we do not update snd_nxt. 1052 */ 1053 int xlen = len; 1054 if (flags & TH_SYN) 1055 ++xlen; 1056 if (flags & TH_FIN) { 1057 ++xlen; 1058 tp->t_flags |= TF_SENTFIN; 1059 } 1060 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max)) 1061 tp->snd_max = tp->snd_nxt + len; 1062 } 1063 1064 #ifdef TCPDEBUG 1065 /* 1066 * Trace. 1067 */ 1068 if (so->so_options & SO_DEBUG) { 1069 u_short save = 0; 1070 #ifdef INET6 1071 if (!isipv6) 1072 #endif 1073 { 1074 save = ipov->ih_len; 1075 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */); 1076 } 1077 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0); 1078 #ifdef INET6 1079 if (!isipv6) 1080 #endif 1081 ipov->ih_len = save; 1082 } 1083 #endif 1084 1085 /* 1086 * Fill in IP length and desired time to live and 1087 * send to IP level. There should be a better way 1088 * to handle ttl and tos; we could keep them in 1089 * the template, but need a way to checksum without them. 1090 */ 1091 /* 1092 * m->m_pkthdr.len should have been set before cksum calcuration, 1093 * because in6_cksum() need it. 1094 */ 1095 #ifdef INET6 1096 if (isipv6) { 1097 /* 1098 * we separately set hoplimit for every segment, since the 1099 * user might want to change the value via setsockopt. 1100 * Also, desired default hop limit might be changed via 1101 * Neighbor Discovery. 1102 */ 1103 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL); 1104 1105 /* TODO: IPv6 IP6TOS_ECT bit on */ 1106 error = ip6_output(m, 1107 tp->t_inpcb->in6p_outputopts, NULL, 1108 ((so->so_options & SO_DONTROUTE) ? 1109 IP_ROUTETOIF : 0), NULL, NULL, tp->t_inpcb); 1110 } else 1111 #endif /* INET6 */ 1112 { 1113 ip->ip_len = m->m_pkthdr.len; 1114 #ifdef INET6 1115 if (INP_CHECK_SOCKAF(so, AF_INET6)) 1116 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL); 1117 #endif /* INET6 */ 1118 /* 1119 * If we do path MTU discovery, then we set DF on every packet. 1120 * This might not be the best thing to do according to RFC3390 1121 * Section 2. However the tcp hostcache migitates the problem 1122 * so it affects only the first tcp connection with a host. 1123 */ 1124 if (path_mtu_discovery) 1125 ip->ip_off |= IP_DF; 1126 1127 error = ip_output(m, tp->t_inpcb->inp_options, NULL, 1128 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, 1129 tp->t_inpcb); 1130 } 1131 if (error) { 1132 1133 /* 1134 * We know that the packet was lost, so back out the 1135 * sequence number advance, if any. 1136 * 1137 * If the error is EPERM the packet got blocked by the 1138 * local firewall. Normally we should terminate the 1139 * connection but the blocking may have been spurious 1140 * due to a firewall reconfiguration cycle. So we treat 1141 * it like a packet loss and let the retransmit timer and 1142 * timeouts do their work over time. 1143 * XXX: It is a POLA question whether calling tcp_drop right 1144 * away would be the really correct behavior instead. 1145 */ 1146 if (((tp->t_flags & TF_FORCEDATA) == 0 || 1147 !tcp_timer_active(tp, TT_PERSIST)) && 1148 ((flags & TH_SYN) == 0) && 1149 (error != EPERM)) { 1150 if (sack_rxmit) { 1151 p->rxmit -= len; 1152 tp->sackhint.sack_bytes_rexmit -= len; 1153 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0, 1154 ("sackhint bytes rtx >= 0")); 1155 } else 1156 tp->snd_nxt -= len; 1157 } 1158 out: 1159 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */ 1160 switch (error) { 1161 case EPERM: 1162 tp->t_softerror = error; 1163 return (error); 1164 case ENOBUFS: 1165 if (!tcp_timer_active(tp, TT_REXMT) && 1166 !tcp_timer_active(tp, TT_PERSIST)) 1167 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); 1168 tp->snd_cwnd = tp->t_maxseg; 1169 return (0); 1170 case EMSGSIZE: 1171 /* 1172 * For some reason the interface we used initially 1173 * to send segments changed to another or lowered 1174 * its MTU. 1175 * 1176 * tcp_mtudisc() will find out the new MTU and as 1177 * its last action, initiate retransmission, so it 1178 * is important to not do so here. 1179 * 1180 * If TSO was active we either got an interface 1181 * without TSO capabilits or TSO was turned off. 1182 * Disable it for this connection as too and 1183 * immediatly retry with MSS sized segments generated 1184 * by this function. 1185 */ 1186 if (tso) 1187 tp->t_flags &= ~TF_TSO; 1188 tcp_mtudisc(tp->t_inpcb, 0); 1189 return (0); 1190 case EHOSTDOWN: 1191 case EHOSTUNREACH: 1192 case ENETDOWN: 1193 case ENETUNREACH: 1194 if (TCPS_HAVERCVDSYN(tp->t_state)) { 1195 tp->t_softerror = error; 1196 return (0); 1197 } 1198 /* FALLTHROUGH */ 1199 default: 1200 return (error); 1201 } 1202 } 1203 tcpstat.tcps_sndtotal++; 1204 1205 /* 1206 * Data sent (as far as we can tell). 1207 * If this advertises a larger window than any other segment, 1208 * then remember the size of the advertised window. 1209 * Any pending ACK has now been sent. 1210 */ 1211 if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv)) 1212 tp->rcv_adv = tp->rcv_nxt + recwin; 1213 tp->last_ack_sent = tp->rcv_nxt; 1214 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK); 1215 if (tcp_timer_active(tp, TT_DELACK)) 1216 tcp_timer_activate(tp, TT_DELACK, 0); 1217 #if 0 1218 /* 1219 * This completely breaks TCP if newreno is turned on. What happens 1220 * is that if delayed-acks are turned on on the receiver, this code 1221 * on the transmitter effectively destroys the TCP window, forcing 1222 * it to four packets (1.5Kx4 = 6K window). 1223 */ 1224 if (sendalot && (!tcp_do_newreno || --maxburst)) 1225 goto again; 1226 #endif 1227 if (sendalot) 1228 goto again; 1229 return (0); 1230 } 1231 1232 void 1233 tcp_setpersist(struct tcpcb *tp) 1234 { 1235 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 1236 int tt; 1237 1238 if (tcp_timer_active(tp, TT_REXMT)) 1239 panic("tcp_setpersist: retransmit pending"); 1240 /* 1241 * Start/restart persistance timer. 1242 */ 1243 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], 1244 TCPTV_PERSMIN, TCPTV_PERSMAX); 1245 tcp_timer_activate(tp, TT_PERSIST, tt); 1246 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1247 tp->t_rxtshift++; 1248 } 1249 1250 /* 1251 * Insert TCP options according to the supplied parameters to the place 1252 * optp in a consistent way. Can handle unaligned destinations. 1253 * 1254 * The order of the option processing is crucial for optimal packing and 1255 * alignment for the scarce option space. 1256 * 1257 * The optimal order for a SYN/SYN-ACK segment is: 1258 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) + 1259 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40. 1260 * 1261 * The SACK options should be last. SACK blocks consume 8*n+2 bytes. 1262 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks). 1263 * At minimum we need 10 bytes (to generate 1 SACK block). If both 1264 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present, 1265 * we only have 10 bytes for SACK options (40 - (12 + 18)). 1266 */ 1267 int 1268 tcp_addoptions(struct tcpopt *to, u_char *optp) 1269 { 1270 u_int mask, optlen = 0; 1271 1272 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) { 1273 if ((to->to_flags & mask) != mask) 1274 continue; 1275 switch (to->to_flags & mask) { 1276 case TOF_MSS: 1277 while (optlen % 4) { 1278 optlen += TCPOLEN_NOP; 1279 *optp++ = TCPOPT_NOP; 1280 } 1281 optlen += TCPOLEN_MAXSEG; 1282 *optp++ = TCPOPT_MAXSEG; 1283 *optp++ = TCPOLEN_MAXSEG; 1284 to->to_mss = htons(to->to_mss); 1285 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss)); 1286 optp += sizeof(to->to_mss); 1287 break; 1288 case TOF_SCALE: 1289 while (!optlen || optlen % 2 != 1) { 1290 optlen += TCPOLEN_NOP; 1291 *optp++ = TCPOPT_NOP; 1292 } 1293 optlen += TCPOLEN_WINDOW; 1294 *optp++ = TCPOPT_WINDOW; 1295 *optp++ = TCPOLEN_WINDOW; 1296 *optp++ = to->to_wscale; 1297 break; 1298 case TOF_SACKPERM: 1299 while (optlen % 2) { 1300 optlen += TCPOLEN_NOP; 1301 *optp++ = TCPOPT_NOP; 1302 } 1303 optlen += TCPOLEN_SACK_PERMITTED; 1304 *optp++ = TCPOPT_SACK_PERMITTED; 1305 *optp++ = TCPOLEN_SACK_PERMITTED; 1306 break; 1307 case TOF_TS: 1308 while (!optlen || optlen % 4 != 2) { 1309 optlen += TCPOLEN_NOP; 1310 *optp++ = TCPOPT_NOP; 1311 } 1312 optlen += TCPOLEN_TIMESTAMP; 1313 *optp++ = TCPOPT_TIMESTAMP; 1314 *optp++ = TCPOLEN_TIMESTAMP; 1315 to->to_tsval = htonl(to->to_tsval); 1316 to->to_tsecr = htonl(to->to_tsecr); 1317 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval)); 1318 optp += sizeof(to->to_tsval); 1319 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr)); 1320 optp += sizeof(to->to_tsecr); 1321 break; 1322 case TOF_SIGNATURE: 1323 { 1324 int siglen = TCPOLEN_SIGNATURE - 2; 1325 1326 while (!optlen || optlen % 4 != 2) { 1327 optlen += TCPOLEN_NOP; 1328 *optp++ = TCPOPT_NOP; 1329 } 1330 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) 1331 continue; 1332 optlen += TCPOLEN_SIGNATURE; 1333 *optp++ = TCPOPT_SIGNATURE; 1334 *optp++ = TCPOLEN_SIGNATURE; 1335 to->to_signature = optp; 1336 while (siglen--) 1337 *optp++ = 0; 1338 break; 1339 } 1340 case TOF_SACK: 1341 { 1342 int sackblks = 0; 1343 struct sackblk *sack = (struct sackblk *)to->to_sacks; 1344 tcp_seq sack_seq; 1345 1346 while (!optlen || optlen % 4 != 2) { 1347 optlen += TCPOLEN_NOP; 1348 *optp++ = TCPOPT_NOP; 1349 } 1350 if (TCP_MAXOLEN - optlen < 2 + TCPOLEN_SACK) 1351 continue; 1352 optlen += TCPOLEN_SACKHDR; 1353 *optp++ = TCPOPT_SACK; 1354 sackblks = min(to->to_nsacks, 1355 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK); 1356 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK; 1357 while (sackblks--) { 1358 sack_seq = htonl(sack->start); 1359 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq)); 1360 optp += sizeof(sack_seq); 1361 sack_seq = htonl(sack->end); 1362 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq)); 1363 optp += sizeof(sack_seq); 1364 optlen += TCPOLEN_SACK; 1365 sack++; 1366 } 1367 tcpstat.tcps_sack_send_blocks++; 1368 break; 1369 } 1370 default: 1371 panic("%s: unknown TCP option type", __func__); 1372 break; 1373 } 1374 } 1375 1376 /* Terminate and pad TCP options to a 4 byte boundary. */ 1377 if (optlen % 4) { 1378 optlen += TCPOLEN_EOL; 1379 *optp++ = TCPOPT_EOL; 1380 } 1381 while (optlen % 4) { 1382 optlen += TCPOLEN_NOP; 1383 *optp++ = TCPOPT_NOP; 1384 } 1385 1386 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__)); 1387 return (optlen); 1388 } 1389