1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 5 * The Regents of the University of California. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the University nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 * 31 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95 32 */ 33 34 #include <sys/cdefs.h> 35 __FBSDID("$FreeBSD$"); 36 37 #include "opt_inet.h" 38 #include "opt_inet6.h" 39 #include "opt_ipsec.h" 40 #include "opt_tcpdebug.h" 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/domain.h> 45 #ifdef TCP_HHOOK 46 #include <sys/hhook.h> 47 #endif 48 #include <sys/kernel.h> 49 #include <sys/lock.h> 50 #include <sys/mbuf.h> 51 #include <sys/mutex.h> 52 #include <sys/protosw.h> 53 #include <sys/sdt.h> 54 #include <sys/socket.h> 55 #include <sys/socketvar.h> 56 #include <sys/sysctl.h> 57 58 #include <net/if.h> 59 #include <net/route.h> 60 #include <net/vnet.h> 61 62 #include <netinet/in.h> 63 #include <netinet/in_kdtrace.h> 64 #include <netinet/in_systm.h> 65 #include <netinet/ip.h> 66 #include <netinet/in_pcb.h> 67 #include <netinet/ip_var.h> 68 #include <netinet/ip_options.h> 69 #ifdef INET6 70 #include <netinet6/in6_pcb.h> 71 #include <netinet/ip6.h> 72 #include <netinet6/ip6_var.h> 73 #endif 74 #include <netinet/tcp.h> 75 #define TCPOUTFLAGS 76 #include <netinet/tcp_fsm.h> 77 #include <netinet/tcp_seq.h> 78 #include <netinet/tcp_timer.h> 79 #include <netinet/tcp_var.h> 80 #include <netinet/tcpip.h> 81 #include <netinet/cc/cc.h> 82 #include <netinet/tcp_fastopen.h> 83 #ifdef TCPPCAP 84 #include <netinet/tcp_pcap.h> 85 #endif 86 #ifdef TCPDEBUG 87 #include <netinet/tcp_debug.h> 88 #endif 89 #ifdef TCP_OFFLOAD 90 #include <netinet/tcp_offload.h> 91 #endif 92 93 #include <netipsec/ipsec_support.h> 94 95 #include <machine/in_cksum.h> 96 97 #include <security/mac/mac_framework.h> 98 99 VNET_DEFINE(int, path_mtu_discovery) = 1; 100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW, 101 &VNET_NAME(path_mtu_discovery), 1, 102 "Enable Path MTU Discovery"); 103 104 VNET_DEFINE(int, tcp_do_tso) = 1; 105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW, 106 &VNET_NAME(tcp_do_tso), 0, 107 "Enable TCP Segmentation Offload"); 108 109 VNET_DEFINE(int, tcp_sendspace) = 1024*32; 110 #define V_tcp_sendspace VNET(tcp_sendspace) 111 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW, 112 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size"); 113 114 VNET_DEFINE(int, tcp_do_autosndbuf) = 1; 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW, 116 &VNET_NAME(tcp_do_autosndbuf), 0, 117 "Enable automatic send buffer sizing"); 118 119 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024; 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW, 121 &VNET_NAME(tcp_autosndbuf_inc), 0, 122 "Incrementor step size of automatic send buffer"); 123 124 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024; 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW, 126 &VNET_NAME(tcp_autosndbuf_max), 0, 127 "Max size of automatic send buffer"); 128 129 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0; 130 #define V_tcp_sendbuf_auto_lowat VNET(tcp_sendbuf_auto_lowat) 131 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW, 132 &VNET_NAME(tcp_sendbuf_auto_lowat), 0, 133 "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT"); 134 135 /* 136 * Make sure that either retransmit or persist timer is set for SYN, FIN and 137 * non-ACK. 138 */ 139 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \ 140 KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\ 141 tcp_timer_active((tp), TT_REXMT) || \ 142 tcp_timer_active((tp), TT_PERSIST), \ 143 ("neither rexmt nor persist timer is set")) 144 145 #ifdef TCP_HHOOK 146 static void inline hhook_run_tcp_est_out(struct tcpcb *tp, 147 struct tcphdr *th, struct tcpopt *to, 148 uint32_t len, int tso); 149 #endif 150 static void inline cc_after_idle(struct tcpcb *tp); 151 152 #ifdef TCP_HHOOK 153 /* 154 * Wrapper for the TCP established output helper hook. 155 */ 156 static void inline 157 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th, 158 struct tcpopt *to, uint32_t len, int tso) 159 { 160 struct tcp_hhook_data hhook_data; 161 162 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) { 163 hhook_data.tp = tp; 164 hhook_data.th = th; 165 hhook_data.to = to; 166 hhook_data.len = len; 167 hhook_data.tso = tso; 168 169 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data, 170 tp->osd); 171 } 172 } 173 #endif 174 175 /* 176 * CC wrapper hook functions 177 */ 178 static void inline 179 cc_after_idle(struct tcpcb *tp) 180 { 181 INP_WLOCK_ASSERT(tp->t_inpcb); 182 183 if (CC_ALGO(tp)->after_idle != NULL) 184 CC_ALGO(tp)->after_idle(tp->ccv); 185 } 186 187 /* 188 * Tcp output routine: figure out what should be sent and send it. 189 */ 190 int 191 tcp_output(struct tcpcb *tp) 192 { 193 struct socket *so = tp->t_inpcb->inp_socket; 194 int32_t len; 195 uint32_t recwin, sendwin; 196 int off, flags, error = 0; /* Keep compiler happy */ 197 struct mbuf *m; 198 struct ip *ip = NULL; 199 #ifdef TCPDEBUG 200 struct ipovly *ipov = NULL; 201 #endif 202 struct tcphdr *th; 203 u_char opt[TCP_MAXOLEN]; 204 unsigned ipoptlen, optlen, hdrlen; 205 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 206 unsigned ipsec_optlen = 0; 207 #endif 208 int idle, sendalot; 209 int sack_rxmit, sack_bytes_rxmt; 210 struct sackhole *p; 211 int tso, mtu; 212 struct tcpopt to; 213 unsigned int wanted_cookie = 0; 214 unsigned int dont_sendalot = 0; 215 #if 0 216 int maxburst = TCP_MAXBURST; 217 #endif 218 #ifdef INET6 219 struct ip6_hdr *ip6 = NULL; 220 int isipv6; 221 222 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0; 223 #endif 224 225 INP_WLOCK_ASSERT(tp->t_inpcb); 226 227 #ifdef TCP_OFFLOAD 228 if (tp->t_flags & TF_TOE) 229 return (tcp_offload_output(tp)); 230 #endif 231 232 /* 233 * For TFO connections in SYN_RECEIVED, only allow the initial 234 * SYN|ACK and those sent by the retransmit timer. 235 */ 236 if (IS_FASTOPEN(tp->t_flags) && 237 (tp->t_state == TCPS_SYN_RECEIVED) && 238 SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN|ACK sent */ 239 (tp->snd_nxt != tp->snd_una)) /* not a retransmit */ 240 return (0); 241 242 /* 243 * Determine length of data that should be transmitted, 244 * and flags that will be used. 245 * If there is some data or critical controls (SYN, RST) 246 * to send, then transmit; otherwise, investigate further. 247 */ 248 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una); 249 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur) 250 cc_after_idle(tp); 251 tp->t_flags &= ~TF_LASTIDLE; 252 if (idle) { 253 if (tp->t_flags & TF_MORETOCOME) { 254 tp->t_flags |= TF_LASTIDLE; 255 idle = 0; 256 } 257 } 258 again: 259 /* 260 * If we've recently taken a timeout, snd_max will be greater than 261 * snd_nxt. There may be SACK information that allows us to avoid 262 * resending already delivered data. Adjust snd_nxt accordingly. 263 */ 264 if ((tp->t_flags & TF_SACK_PERMIT) && 265 SEQ_LT(tp->snd_nxt, tp->snd_max)) 266 tcp_sack_adjust(tp); 267 sendalot = 0; 268 tso = 0; 269 mtu = 0; 270 off = tp->snd_nxt - tp->snd_una; 271 sendwin = min(tp->snd_wnd, tp->snd_cwnd); 272 273 flags = tcp_outflags[tp->t_state]; 274 /* 275 * Send any SACK-generated retransmissions. If we're explicitly trying 276 * to send out new data (when sendalot is 1), bypass this function. 277 * If we retransmit in fast recovery mode, decrement snd_cwnd, since 278 * we're replacing a (future) new transmission with a retransmission 279 * now, and we previously incremented snd_cwnd in tcp_input(). 280 */ 281 /* 282 * Still in sack recovery , reset rxmit flag to zero. 283 */ 284 sack_rxmit = 0; 285 sack_bytes_rxmt = 0; 286 len = 0; 287 p = NULL; 288 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) && 289 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) { 290 uint32_t cwin; 291 292 cwin = 293 imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0); 294 /* Do not retransmit SACK segments beyond snd_recover */ 295 if (SEQ_GT(p->end, tp->snd_recover)) { 296 /* 297 * (At least) part of sack hole extends beyond 298 * snd_recover. Check to see if we can rexmit data 299 * for this hole. 300 */ 301 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) { 302 /* 303 * Can't rexmit any more data for this hole. 304 * That data will be rexmitted in the next 305 * sack recovery episode, when snd_recover 306 * moves past p->rxmit. 307 */ 308 p = NULL; 309 goto after_sack_rexmit; 310 } else 311 /* Can rexmit part of the current hole */ 312 len = ((int32_t)ulmin(cwin, 313 tp->snd_recover - p->rxmit)); 314 } else 315 len = ((int32_t)ulmin(cwin, p->end - p->rxmit)); 316 off = p->rxmit - tp->snd_una; 317 KASSERT(off >= 0,("%s: sack block to the left of una : %d", 318 __func__, off)); 319 if (len > 0) { 320 sack_rxmit = 1; 321 sendalot = 1; 322 TCPSTAT_INC(tcps_sack_rexmits); 323 TCPSTAT_ADD(tcps_sack_rexmit_bytes, 324 min(len, tp->t_maxseg)); 325 } 326 } 327 after_sack_rexmit: 328 /* 329 * Get standard flags, and add SYN or FIN if requested by 'hidden' 330 * state flags. 331 */ 332 if (tp->t_flags & TF_NEEDFIN) 333 flags |= TH_FIN; 334 if (tp->t_flags & TF_NEEDSYN) 335 flags |= TH_SYN; 336 337 SOCKBUF_LOCK(&so->so_snd); 338 /* 339 * If in persist timeout with window of 0, send 1 byte. 340 * Otherwise, if window is small but nonzero 341 * and timer expired, we will send what we can 342 * and go to transmit state. 343 */ 344 if (tp->t_flags & TF_FORCEDATA) { 345 if (sendwin == 0) { 346 /* 347 * If we still have some data to send, then 348 * clear the FIN bit. Usually this would 349 * happen below when it realizes that we 350 * aren't sending all the data. However, 351 * if we have exactly 1 byte of unsent data, 352 * then it won't clear the FIN bit below, 353 * and if we are in persist state, we wind 354 * up sending the packet without recording 355 * that we sent the FIN bit. 356 * 357 * We can't just blindly clear the FIN bit, 358 * because if we don't have any more data 359 * to send then the probe will be the FIN 360 * itself. 361 */ 362 if (off < sbused(&so->so_snd)) 363 flags &= ~TH_FIN; 364 sendwin = 1; 365 } else { 366 tcp_timer_activate(tp, TT_PERSIST, 0); 367 tp->t_rxtshift = 0; 368 } 369 } 370 371 /* 372 * If snd_nxt == snd_max and we have transmitted a FIN, the 373 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in 374 * a negative length. This can also occur when TCP opens up 375 * its congestion window while receiving additional duplicate 376 * acks after fast-retransmit because TCP will reset snd_nxt 377 * to snd_max after the fast-retransmit. 378 * 379 * In the normal retransmit-FIN-only case, however, snd_nxt will 380 * be set to snd_una, the offset will be 0, and the length may 381 * wind up 0. 382 * 383 * If sack_rxmit is true we are retransmitting from the scoreboard 384 * in which case len is already set. 385 */ 386 if (sack_rxmit == 0) { 387 if (sack_bytes_rxmt == 0) 388 len = ((int32_t)min(sbavail(&so->so_snd), sendwin) - 389 off); 390 else { 391 int32_t cwin; 392 393 /* 394 * We are inside of a SACK recovery episode and are 395 * sending new data, having retransmitted all the 396 * data possible in the scoreboard. 397 */ 398 len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) - 399 off); 400 /* 401 * Don't remove this (len > 0) check ! 402 * We explicitly check for len > 0 here (although it 403 * isn't really necessary), to work around a gcc 404 * optimization issue - to force gcc to compute 405 * len above. Without this check, the computation 406 * of len is bungled by the optimizer. 407 */ 408 if (len > 0) { 409 cwin = tp->snd_cwnd - 410 (tp->snd_nxt - tp->sack_newdata) - 411 sack_bytes_rxmt; 412 if (cwin < 0) 413 cwin = 0; 414 len = imin(len, cwin); 415 } 416 } 417 } 418 419 /* 420 * Lop off SYN bit if it has already been sent. However, if this 421 * is SYN-SENT state and if segment contains data and if we don't 422 * know that foreign host supports TAO, suppress sending segment. 423 */ 424 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) { 425 if (tp->t_state != TCPS_SYN_RECEIVED) 426 flags &= ~TH_SYN; 427 /* 428 * When sending additional segments following a TFO SYN|ACK, 429 * do not include the SYN bit. 430 */ 431 if (IS_FASTOPEN(tp->t_flags) && 432 (tp->t_state == TCPS_SYN_RECEIVED)) 433 flags &= ~TH_SYN; 434 off--, len++; 435 } 436 437 /* 438 * Be careful not to send data and/or FIN on SYN segments. 439 * This measure is needed to prevent interoperability problems 440 * with not fully conformant TCP implementations. 441 */ 442 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) { 443 len = 0; 444 flags &= ~TH_FIN; 445 } 446 447 /* 448 * On TFO sockets, ensure no data is sent in the following cases: 449 * 450 * - When retransmitting SYN|ACK on a passively-created socket 451 * 452 * - When retransmitting SYN on an actively created socket 453 * 454 * - When sending a zero-length cookie (cookie request) on an 455 * actively created socket 456 * 457 * - When the socket is in the CLOSED state (RST is being sent) 458 */ 459 if (IS_FASTOPEN(tp->t_flags) && 460 (((flags & TH_SYN) && (tp->t_rxtshift > 0)) || 461 ((tp->t_state == TCPS_SYN_SENT) && 462 (tp->t_tfo_client_cookie_len == 0)) || 463 (flags & TH_RST))) 464 len = 0; 465 if (len <= 0) { 466 /* 467 * If FIN has been sent but not acked, 468 * but we haven't been called to retransmit, 469 * len will be < 0. Otherwise, window shrank 470 * after we sent into it. If window shrank to 0, 471 * cancel pending retransmit, pull snd_nxt back 472 * to (closed) window, and set the persist timer 473 * if it isn't already going. If the window didn't 474 * close completely, just wait for an ACK. 475 * 476 * We also do a general check here to ensure that 477 * we will set the persist timer when we have data 478 * to send, but a 0-byte window. This makes sure 479 * the persist timer is set even if the packet 480 * hits one of the "goto send" lines below. 481 */ 482 len = 0; 483 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) && 484 (off < (int) sbavail(&so->so_snd))) { 485 tcp_timer_activate(tp, TT_REXMT, 0); 486 tp->t_rxtshift = 0; 487 tp->snd_nxt = tp->snd_una; 488 if (!tcp_timer_active(tp, TT_PERSIST)) 489 tcp_setpersist(tp); 490 } 491 } 492 493 /* len will be >= 0 after this point. */ 494 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__)); 495 496 tcp_sndbuf_autoscale(tp, so, sendwin); 497 498 /* 499 * Decide if we can use TCP Segmentation Offloading (if supported by 500 * hardware). 501 * 502 * TSO may only be used if we are in a pure bulk sending state. The 503 * presence of TCP-MD5, SACK retransmits, SACK advertizements and 504 * IP options prevent using TSO. With TSO the TCP header is the same 505 * (except for the sequence number) for all generated packets. This 506 * makes it impossible to transmit any options which vary per generated 507 * segment or packet. 508 * 509 * IPv4 handling has a clear separation of ip options and ip header 510 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does 511 * the right thing below to provide length of just ip options and thus 512 * checking for ipoptlen is enough to decide if ip options are present. 513 */ 514 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 515 /* 516 * Pre-calculate here as we save another lookup into the darknesses 517 * of IPsec that way and can actually decide if TSO is ok. 518 */ 519 #ifdef INET6 520 if (isipv6 && IPSEC_ENABLED(ipv6)) 521 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb); 522 #ifdef INET 523 else 524 #endif 525 #endif /* INET6 */ 526 #ifdef INET 527 if (IPSEC_ENABLED(ipv4)) 528 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb); 529 #endif /* INET */ 530 #endif /* IPSEC */ 531 #ifdef INET6 532 if (isipv6) 533 ipoptlen = ip6_optlen(tp->t_inpcb); 534 else 535 #endif 536 if (tp->t_inpcb->inp_options) 537 ipoptlen = tp->t_inpcb->inp_options->m_len - 538 offsetof(struct ipoption, ipopt_list); 539 else 540 ipoptlen = 0; 541 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 542 ipoptlen += ipsec_optlen; 543 #endif 544 545 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg && 546 ((tp->t_flags & TF_SIGNATURE) == 0) && 547 tp->rcv_numsacks == 0 && sack_rxmit == 0 && 548 ipoptlen == 0 && !(flags & TH_SYN)) 549 tso = 1; 550 551 if (sack_rxmit) { 552 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd))) 553 flags &= ~TH_FIN; 554 } else { 555 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + 556 sbused(&so->so_snd))) 557 flags &= ~TH_FIN; 558 } 559 560 recwin = lmin(lmax(sbspace(&so->so_rcv), 0), 561 (long)TCP_MAXWIN << tp->rcv_scale); 562 563 /* 564 * Sender silly window avoidance. We transmit under the following 565 * conditions when len is non-zero: 566 * 567 * - We have a full segment (or more with TSO) 568 * - This is the last buffer in a write()/send() and we are 569 * either idle or running NODELAY 570 * - we've timed out (e.g. persist timer) 571 * - we have more then 1/2 the maximum send window's worth of 572 * data (receiver may be limited the window size) 573 * - we need to retransmit 574 */ 575 if (len) { 576 if (len >= tp->t_maxseg) 577 goto send; 578 /* 579 * NOTE! on localhost connections an 'ack' from the remote 580 * end may occur synchronously with the output and cause 581 * us to flush a buffer queued with moretocome. XXX 582 * 583 * note: the len + off check is almost certainly unnecessary. 584 */ 585 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */ 586 (idle || (tp->t_flags & TF_NODELAY)) && 587 (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) && 588 (tp->t_flags & TF_NOPUSH) == 0) { 589 goto send; 590 } 591 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */ 592 goto send; 593 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0) 594 goto send; 595 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */ 596 goto send; 597 if (sack_rxmit) 598 goto send; 599 } 600 601 /* 602 * Sending of standalone window updates. 603 * 604 * Window updates are important when we close our window due to a 605 * full socket buffer and are opening it again after the application 606 * reads data from it. Once the window has opened again and the 607 * remote end starts to send again the ACK clock takes over and 608 * provides the most current window information. 609 * 610 * We must avoid the silly window syndrome whereas every read 611 * from the receive buffer, no matter how small, causes a window 612 * update to be sent. We also should avoid sending a flurry of 613 * window updates when the socket buffer had queued a lot of data 614 * and the application is doing small reads. 615 * 616 * Prevent a flurry of pointless window updates by only sending 617 * an update when we can increase the advertized window by more 618 * than 1/4th of the socket buffer capacity. When the buffer is 619 * getting full or is very small be more aggressive and send an 620 * update whenever we can increase by two mss sized segments. 621 * In all other situations the ACK's to new incoming data will 622 * carry further window increases. 623 * 624 * Don't send an independent window update if a delayed 625 * ACK is pending (it will get piggy-backed on it) or the 626 * remote side already has done a half-close and won't send 627 * more data. Skip this if the connection is in T/TCP 628 * half-open state. 629 */ 630 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) && 631 !(tp->t_flags & TF_DELACK) && 632 !TCPS_HAVERCVDFIN(tp->t_state)) { 633 /* 634 * "adv" is the amount we could increase the window, 635 * taking into account that we are limited by 636 * TCP_MAXWIN << tp->rcv_scale. 637 */ 638 int32_t adv; 639 int oldwin; 640 641 adv = recwin; 642 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) { 643 oldwin = (tp->rcv_adv - tp->rcv_nxt); 644 adv -= oldwin; 645 } else 646 oldwin = 0; 647 648 /* 649 * If the new window size ends up being the same as or less 650 * than the old size when it is scaled, then don't force 651 * a window update. 652 */ 653 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale) 654 goto dontupdate; 655 656 if (adv >= (int32_t)(2 * tp->t_maxseg) && 657 (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) || 658 recwin <= (so->so_rcv.sb_hiwat / 8) || 659 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg)) 660 goto send; 661 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat) 662 goto send; 663 } 664 dontupdate: 665 666 /* 667 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW 668 * is also a catch-all for the retransmit timer timeout case. 669 */ 670 if (tp->t_flags & TF_ACKNOW) 671 goto send; 672 if ((flags & TH_RST) || 673 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0)) 674 goto send; 675 if (SEQ_GT(tp->snd_up, tp->snd_una)) 676 goto send; 677 /* 678 * If our state indicates that FIN should be sent 679 * and we have not yet done so, then we need to send. 680 */ 681 if (flags & TH_FIN && 682 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 683 goto send; 684 /* 685 * In SACK, it is possible for tcp_output to fail to send a segment 686 * after the retransmission timer has been turned off. Make sure 687 * that the retransmission timer is set. 688 */ 689 if ((tp->t_flags & TF_SACK_PERMIT) && 690 SEQ_GT(tp->snd_max, tp->snd_una) && 691 !tcp_timer_active(tp, TT_REXMT) && 692 !tcp_timer_active(tp, TT_PERSIST)) { 693 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); 694 goto just_return; 695 } 696 /* 697 * TCP window updates are not reliable, rather a polling protocol 698 * using ``persist'' packets is used to insure receipt of window 699 * updates. The three ``states'' for the output side are: 700 * idle not doing retransmits or persists 701 * persisting to move a small or zero window 702 * (re)transmitting and thereby not persisting 703 * 704 * tcp_timer_active(tp, TT_PERSIST) 705 * is true when we are in persist state. 706 * (tp->t_flags & TF_FORCEDATA) 707 * is set when we are called to send a persist packet. 708 * tcp_timer_active(tp, TT_REXMT) 709 * is set when we are retransmitting 710 * The output side is idle when both timers are zero. 711 * 712 * If send window is too small, there is data to transmit, and no 713 * retransmit or persist is pending, then go to persist state. 714 * If nothing happens soon, send when timer expires: 715 * if window is nonzero, transmit what we can, 716 * otherwise force out a byte. 717 */ 718 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) && 719 !tcp_timer_active(tp, TT_PERSIST)) { 720 tp->t_rxtshift = 0; 721 tcp_setpersist(tp); 722 } 723 724 /* 725 * No reason to send a segment, just return. 726 */ 727 just_return: 728 SOCKBUF_UNLOCK(&so->so_snd); 729 return (0); 730 731 send: 732 SOCKBUF_LOCK_ASSERT(&so->so_snd); 733 if (len > 0) { 734 if (len >= tp->t_maxseg) 735 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT; 736 else 737 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT; 738 } 739 /* 740 * Before ESTABLISHED, force sending of initial options 741 * unless TCP set not to do any options. 742 * NOTE: we assume that the IP/TCP header plus TCP options 743 * always fit in a single mbuf, leaving room for a maximum 744 * link header, i.e. 745 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 746 */ 747 optlen = 0; 748 #ifdef INET6 749 if (isipv6) 750 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr); 751 else 752 #endif 753 hdrlen = sizeof (struct tcpiphdr); 754 755 /* 756 * Compute options for segment. 757 * We only have to care about SYN and established connection 758 * segments. Options for SYN-ACK segments are handled in TCP 759 * syncache. 760 */ 761 to.to_flags = 0; 762 if ((tp->t_flags & TF_NOOPT) == 0) { 763 /* Maximum segment size. */ 764 if (flags & TH_SYN) { 765 tp->snd_nxt = tp->iss; 766 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc); 767 to.to_flags |= TOF_MSS; 768 769 /* 770 * On SYN or SYN|ACK transmits on TFO connections, 771 * only include the TFO option if it is not a 772 * retransmit, as the presence of the TFO option may 773 * have caused the original SYN or SYN|ACK to have 774 * been dropped by a middlebox. 775 */ 776 if (IS_FASTOPEN(tp->t_flags) && 777 (tp->t_rxtshift == 0)) { 778 if (tp->t_state == TCPS_SYN_RECEIVED) { 779 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 780 to.to_tfo_cookie = 781 (u_int8_t *)&tp->t_tfo_cookie.server; 782 to.to_flags |= TOF_FASTOPEN; 783 wanted_cookie = 1; 784 } else if (tp->t_state == TCPS_SYN_SENT) { 785 to.to_tfo_len = 786 tp->t_tfo_client_cookie_len; 787 to.to_tfo_cookie = 788 tp->t_tfo_cookie.client; 789 to.to_flags |= TOF_FASTOPEN; 790 wanted_cookie = 1; 791 /* 792 * If we wind up having more data to 793 * send with the SYN than can fit in 794 * one segment, don't send any more 795 * until the SYN|ACK comes back from 796 * the other end. 797 */ 798 dont_sendalot = 1; 799 } 800 } 801 } 802 /* Window scaling. */ 803 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) { 804 to.to_wscale = tp->request_r_scale; 805 to.to_flags |= TOF_SCALE; 806 } 807 /* Timestamps. */ 808 if ((tp->t_flags & TF_RCVD_TSTMP) || 809 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) { 810 to.to_tsval = tcp_ts_getticks() + tp->ts_offset; 811 to.to_tsecr = tp->ts_recent; 812 to.to_flags |= TOF_TS; 813 } 814 815 /* Set receive buffer autosizing timestamp. */ 816 if (tp->rfbuf_ts == 0 && 817 (so->so_rcv.sb_flags & SB_AUTOSIZE)) 818 tp->rfbuf_ts = tcp_ts_getticks(); 819 820 /* Selective ACK's. */ 821 if (tp->t_flags & TF_SACK_PERMIT) { 822 if (flags & TH_SYN) 823 to.to_flags |= TOF_SACKPERM; 824 else if (TCPS_HAVEESTABLISHED(tp->t_state) && 825 (tp->t_flags & TF_SACK_PERMIT) && 826 tp->rcv_numsacks > 0) { 827 to.to_flags |= TOF_SACK; 828 to.to_nsacks = tp->rcv_numsacks; 829 to.to_sacks = (u_char *)tp->sackblks; 830 } 831 } 832 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 833 /* TCP-MD5 (RFC2385). */ 834 /* 835 * Check that TCP_MD5SIG is enabled in tcpcb to 836 * account the size needed to set this TCP option. 837 */ 838 if (tp->t_flags & TF_SIGNATURE) 839 to.to_flags |= TOF_SIGNATURE; 840 #endif /* TCP_SIGNATURE */ 841 842 /* Processing the options. */ 843 hdrlen += optlen = tcp_addoptions(&to, opt); 844 /* 845 * If we wanted a TFO option to be added, but it was unable 846 * to fit, ensure no data is sent. 847 */ 848 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie && 849 !(to.to_flags & TOF_FASTOPEN)) 850 len = 0; 851 } 852 853 /* 854 * Adjust data length if insertion of options will 855 * bump the packet length beyond the t_maxseg length. 856 * Clear the FIN bit because we cut off the tail of 857 * the segment. 858 */ 859 if (len + optlen + ipoptlen > tp->t_maxseg) { 860 flags &= ~TH_FIN; 861 862 if (tso) { 863 u_int if_hw_tsomax; 864 u_int if_hw_tsomaxsegcount; 865 u_int if_hw_tsomaxsegsize; 866 struct mbuf *mb; 867 u_int moff; 868 int max_len; 869 870 /* extract TSO information */ 871 if_hw_tsomax = tp->t_tsomax; 872 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount; 873 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize; 874 875 /* 876 * Limit a TSO burst to prevent it from 877 * overflowing or exceeding the maximum length 878 * allowed by the network interface: 879 */ 880 KASSERT(ipoptlen == 0, 881 ("%s: TSO can't do IP options", __func__)); 882 883 /* 884 * Check if we should limit by maximum payload 885 * length: 886 */ 887 if (if_hw_tsomax != 0) { 888 /* compute maximum TSO length */ 889 max_len = (if_hw_tsomax - hdrlen - 890 max_linkhdr); 891 if (max_len <= 0) { 892 len = 0; 893 } else if (len > max_len) { 894 sendalot = 1; 895 len = max_len; 896 } 897 } 898 899 /* 900 * Check if we should limit by maximum segment 901 * size and count: 902 */ 903 if (if_hw_tsomaxsegcount != 0 && 904 if_hw_tsomaxsegsize != 0) { 905 /* 906 * Subtract one segment for the LINK 907 * and TCP/IP headers mbuf that will 908 * be prepended to this mbuf chain 909 * after the code in this section 910 * limits the number of mbufs in the 911 * chain to if_hw_tsomaxsegcount. 912 */ 913 if_hw_tsomaxsegcount -= 1; 914 max_len = 0; 915 mb = sbsndmbuf(&so->so_snd, off, &moff); 916 917 while (mb != NULL && max_len < len) { 918 u_int mlen; 919 u_int frags; 920 921 /* 922 * Get length of mbuf fragment 923 * and how many hardware frags, 924 * rounded up, it would use: 925 */ 926 mlen = (mb->m_len - moff); 927 frags = howmany(mlen, 928 if_hw_tsomaxsegsize); 929 930 /* Handle special case: Zero Length Mbuf */ 931 if (frags == 0) 932 frags = 1; 933 934 /* 935 * Check if the fragment limit 936 * will be reached or exceeded: 937 */ 938 if (frags >= if_hw_tsomaxsegcount) { 939 max_len += min(mlen, 940 if_hw_tsomaxsegcount * 941 if_hw_tsomaxsegsize); 942 break; 943 } 944 max_len += mlen; 945 if_hw_tsomaxsegcount -= frags; 946 moff = 0; 947 mb = mb->m_next; 948 } 949 if (max_len <= 0) { 950 len = 0; 951 } else if (len > max_len) { 952 sendalot = 1; 953 len = max_len; 954 } 955 } 956 957 /* 958 * Prevent the last segment from being 959 * fractional unless the send sockbuf can be 960 * emptied: 961 */ 962 max_len = (tp->t_maxseg - optlen); 963 if (((uint32_t)off + (uint32_t)len) < 964 sbavail(&so->so_snd)) { 965 moff = len % max_len; 966 if (moff != 0) { 967 len -= moff; 968 sendalot = 1; 969 } 970 } 971 972 /* 973 * In case there are too many small fragments 974 * don't use TSO: 975 */ 976 if (len <= max_len) { 977 len = max_len; 978 sendalot = 1; 979 tso = 0; 980 } 981 982 /* 983 * Send the FIN in a separate segment 984 * after the bulk sending is done. 985 * We don't trust the TSO implementations 986 * to clear the FIN flag on all but the 987 * last segment. 988 */ 989 if (tp->t_flags & TF_NEEDFIN) 990 sendalot = 1; 991 992 } else { 993 len = tp->t_maxseg - optlen - ipoptlen; 994 sendalot = 1; 995 if (dont_sendalot) 996 sendalot = 0; 997 } 998 } else 999 tso = 0; 1000 1001 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET, 1002 ("%s: len > IP_MAXPACKET", __func__)); 1003 1004 /*#ifdef DIAGNOSTIC*/ 1005 #ifdef INET6 1006 if (max_linkhdr + hdrlen > MCLBYTES) 1007 #else 1008 if (max_linkhdr + hdrlen > MHLEN) 1009 #endif 1010 panic("tcphdr too big"); 1011 /*#endif*/ 1012 1013 /* 1014 * This KASSERT is here to catch edge cases at a well defined place. 1015 * Before, those had triggered (random) panic conditions further down. 1016 */ 1017 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__)); 1018 1019 /* 1020 * Grab a header mbuf, attaching a copy of data to 1021 * be transmitted, and initialize the header from 1022 * the template for sends on this connection. 1023 */ 1024 if (len) { 1025 struct mbuf *mb; 1026 u_int moff; 1027 1028 if ((tp->t_flags & TF_FORCEDATA) && len == 1) 1029 TCPSTAT_INC(tcps_sndprobe); 1030 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) { 1031 tp->t_sndrexmitpack++; 1032 TCPSTAT_INC(tcps_sndrexmitpack); 1033 TCPSTAT_ADD(tcps_sndrexmitbyte, len); 1034 } else { 1035 TCPSTAT_INC(tcps_sndpack); 1036 TCPSTAT_ADD(tcps_sndbyte, len); 1037 } 1038 #ifdef INET6 1039 if (MHLEN < hdrlen + max_linkhdr) 1040 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR); 1041 else 1042 #endif 1043 m = m_gethdr(M_NOWAIT, MT_DATA); 1044 1045 if (m == NULL) { 1046 SOCKBUF_UNLOCK(&so->so_snd); 1047 error = ENOBUFS; 1048 sack_rxmit = 0; 1049 goto out; 1050 } 1051 1052 m->m_data += max_linkhdr; 1053 m->m_len = hdrlen; 1054 1055 /* 1056 * Start the m_copy functions from the closest mbuf 1057 * to the offset in the socket buffer chain. 1058 */ 1059 mb = sbsndptr(&so->so_snd, off, len, &moff); 1060 1061 if (len <= MHLEN - hdrlen - max_linkhdr) { 1062 m_copydata(mb, moff, len, 1063 mtod(m, caddr_t) + hdrlen); 1064 m->m_len += len; 1065 } else { 1066 m->m_next = m_copym(mb, moff, len, M_NOWAIT); 1067 if (m->m_next == NULL) { 1068 SOCKBUF_UNLOCK(&so->so_snd); 1069 (void) m_free(m); 1070 error = ENOBUFS; 1071 sack_rxmit = 0; 1072 goto out; 1073 } 1074 } 1075 1076 /* 1077 * If we're sending everything we've got, set PUSH. 1078 * (This will keep happy those implementations which only 1079 * give data to the user when a buffer fills or 1080 * a PUSH comes in.) 1081 */ 1082 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) && 1083 !(flags & TH_SYN)) 1084 flags |= TH_PUSH; 1085 SOCKBUF_UNLOCK(&so->so_snd); 1086 } else { 1087 SOCKBUF_UNLOCK(&so->so_snd); 1088 if (tp->t_flags & TF_ACKNOW) 1089 TCPSTAT_INC(tcps_sndacks); 1090 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 1091 TCPSTAT_INC(tcps_sndctrl); 1092 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 1093 TCPSTAT_INC(tcps_sndurg); 1094 else 1095 TCPSTAT_INC(tcps_sndwinup); 1096 1097 m = m_gethdr(M_NOWAIT, MT_DATA); 1098 if (m == NULL) { 1099 error = ENOBUFS; 1100 sack_rxmit = 0; 1101 goto out; 1102 } 1103 #ifdef INET6 1104 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) && 1105 MHLEN >= hdrlen) { 1106 M_ALIGN(m, hdrlen); 1107 } else 1108 #endif 1109 m->m_data += max_linkhdr; 1110 m->m_len = hdrlen; 1111 } 1112 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); 1113 m->m_pkthdr.rcvif = (struct ifnet *)0; 1114 #ifdef MAC 1115 mac_inpcb_create_mbuf(tp->t_inpcb, m); 1116 #endif 1117 #ifdef INET6 1118 if (isipv6) { 1119 ip6 = mtod(m, struct ip6_hdr *); 1120 th = (struct tcphdr *)(ip6 + 1); 1121 tcpip_fillheaders(tp->t_inpcb, ip6, th); 1122 } else 1123 #endif /* INET6 */ 1124 { 1125 ip = mtod(m, struct ip *); 1126 #ifdef TCPDEBUG 1127 ipov = (struct ipovly *)ip; 1128 #endif 1129 th = (struct tcphdr *)(ip + 1); 1130 tcpip_fillheaders(tp->t_inpcb, ip, th); 1131 } 1132 1133 /* 1134 * Fill in fields, remembering maximum advertised 1135 * window for use in delaying messages about window sizes. 1136 * If resending a FIN, be sure not to use a new sequence number. 1137 */ 1138 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 1139 tp->snd_nxt == tp->snd_max) 1140 tp->snd_nxt--; 1141 /* 1142 * If we are starting a connection, send ECN setup 1143 * SYN packet. If we are on a retransmit, we may 1144 * resend those bits a number of times as per 1145 * RFC 3168. 1146 */ 1147 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) { 1148 if (tp->t_rxtshift >= 1) { 1149 if (tp->t_rxtshift <= V_tcp_ecn_maxretries) 1150 flags |= TH_ECE|TH_CWR; 1151 } else 1152 flags |= TH_ECE|TH_CWR; 1153 } 1154 1155 if (tp->t_state == TCPS_ESTABLISHED && 1156 (tp->t_flags & TF_ECN_PERMIT)) { 1157 /* 1158 * If the peer has ECN, mark data packets with 1159 * ECN capable transmission (ECT). 1160 * Ignore pure ack packets, retransmissions and window probes. 1161 */ 1162 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) && 1163 !((tp->t_flags & TF_FORCEDATA) && len == 1)) { 1164 #ifdef INET6 1165 if (isipv6) 1166 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20); 1167 else 1168 #endif 1169 ip->ip_tos |= IPTOS_ECN_ECT0; 1170 TCPSTAT_INC(tcps_ecn_ect0); 1171 } 1172 1173 /* 1174 * Reply with proper ECN notifications. 1175 */ 1176 if (tp->t_flags & TF_ECN_SND_CWR) { 1177 flags |= TH_CWR; 1178 tp->t_flags &= ~TF_ECN_SND_CWR; 1179 } 1180 if (tp->t_flags & TF_ECN_SND_ECE) 1181 flags |= TH_ECE; 1182 } 1183 1184 /* 1185 * If we are doing retransmissions, then snd_nxt will 1186 * not reflect the first unsent octet. For ACK only 1187 * packets, we do not want the sequence number of the 1188 * retransmitted packet, we want the sequence number 1189 * of the next unsent octet. So, if there is no data 1190 * (and no SYN or FIN), use snd_max instead of snd_nxt 1191 * when filling in ti_seq. But if we are in persist 1192 * state, snd_max might reflect one byte beyond the 1193 * right edge of the window, so use snd_nxt in that 1194 * case, since we know we aren't doing a retransmission. 1195 * (retransmit and persist are mutually exclusive...) 1196 */ 1197 if (sack_rxmit == 0) { 1198 if (len || (flags & (TH_SYN|TH_FIN)) || 1199 tcp_timer_active(tp, TT_PERSIST)) 1200 th->th_seq = htonl(tp->snd_nxt); 1201 else 1202 th->th_seq = htonl(tp->snd_max); 1203 } else { 1204 th->th_seq = htonl(p->rxmit); 1205 p->rxmit += len; 1206 tp->sackhint.sack_bytes_rexmit += len; 1207 } 1208 th->th_ack = htonl(tp->rcv_nxt); 1209 if (optlen) { 1210 bcopy(opt, th + 1, optlen); 1211 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 1212 } 1213 th->th_flags = flags; 1214 /* 1215 * Calculate receive window. Don't shrink window, 1216 * but avoid silly window syndrome. 1217 */ 1218 if (recwin < (so->so_rcv.sb_hiwat / 4) && 1219 recwin < tp->t_maxseg) 1220 recwin = 0; 1221 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) && 1222 recwin < (tp->rcv_adv - tp->rcv_nxt)) 1223 recwin = (tp->rcv_adv - tp->rcv_nxt); 1224 1225 /* 1226 * According to RFC1323 the window field in a SYN (i.e., a <SYN> 1227 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK> 1228 * case is handled in syncache. 1229 */ 1230 if (flags & TH_SYN) 1231 th->th_win = htons((u_short) 1232 (min(sbspace(&so->so_rcv), TCP_MAXWIN))); 1233 else 1234 th->th_win = htons((u_short)(recwin >> tp->rcv_scale)); 1235 1236 /* 1237 * Adjust the RXWIN0SENT flag - indicate that we have advertised 1238 * a 0 window. This may cause the remote transmitter to stall. This 1239 * flag tells soreceive() to disable delayed acknowledgements when 1240 * draining the buffer. This can occur if the receiver is attempting 1241 * to read more data than can be buffered prior to transmitting on 1242 * the connection. 1243 */ 1244 if (th->th_win == 0) { 1245 tp->t_sndzerowin++; 1246 tp->t_flags |= TF_RXWIN0SENT; 1247 } else 1248 tp->t_flags &= ~TF_RXWIN0SENT; 1249 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 1250 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 1251 th->th_flags |= TH_URG; 1252 } else 1253 /* 1254 * If no urgent pointer to send, then we pull 1255 * the urgent pointer to the left edge of the send window 1256 * so that it doesn't drift into the send window on sequence 1257 * number wraparound. 1258 */ 1259 tp->snd_up = tp->snd_una; /* drag it along */ 1260 1261 /* 1262 * Put TCP length in extended header, and then 1263 * checksum extended header and data. 1264 */ 1265 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */ 1266 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1267 1268 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1269 if (to.to_flags & TOF_SIGNATURE) { 1270 /* 1271 * Calculate MD5 signature and put it into the place 1272 * determined before. 1273 * NOTE: since TCP options buffer doesn't point into 1274 * mbuf's data, calculate offset and use it. 1275 */ 1276 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th, 1277 (u_char *)(th + 1) + (to.to_signature - opt))) != 0) { 1278 /* 1279 * Do not send segment if the calculation of MD5 1280 * digest has failed. 1281 */ 1282 m_freem(m); 1283 goto out; 1284 } 1285 } 1286 #endif 1287 #ifdef INET6 1288 if (isipv6) { 1289 /* 1290 * There is no need to fill in ip6_plen right now. 1291 * It will be filled later by ip6_output. 1292 */ 1293 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1294 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) + 1295 optlen + len, IPPROTO_TCP, 0); 1296 } 1297 #endif 1298 #if defined(INET6) && defined(INET) 1299 else 1300 #endif 1301 #ifdef INET 1302 { 1303 m->m_pkthdr.csum_flags = CSUM_TCP; 1304 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1305 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen)); 1306 1307 /* IP version must be set here for ipv4/ipv6 checking later */ 1308 KASSERT(ip->ip_v == IPVERSION, 1309 ("%s: IP version incorrect: %d", __func__, ip->ip_v)); 1310 } 1311 #endif 1312 1313 /* 1314 * Enable TSO and specify the size of the segments. 1315 * The TCP pseudo header checksum is always provided. 1316 */ 1317 if (tso) { 1318 KASSERT(len > tp->t_maxseg - optlen, 1319 ("%s: len <= tso_segsz", __func__)); 1320 m->m_pkthdr.csum_flags |= CSUM_TSO; 1321 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen; 1322 } 1323 1324 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 1325 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL), 1326 ("%s: mbuf chain shorter than expected: %d + %u + %u - %u != %u", 1327 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL))); 1328 #else 1329 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL), 1330 ("%s: mbuf chain shorter than expected: %d + %u + %u != %u", 1331 __func__, len, hdrlen, ipoptlen, m_length(m, NULL))); 1332 #endif 1333 1334 #ifdef TCP_HHOOK 1335 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */ 1336 hhook_run_tcp_est_out(tp, th, &to, len, tso); 1337 #endif 1338 1339 #ifdef TCPDEBUG 1340 /* 1341 * Trace. 1342 */ 1343 if (so->so_options & SO_DEBUG) { 1344 u_short save = 0; 1345 #ifdef INET6 1346 if (!isipv6) 1347 #endif 1348 { 1349 save = ipov->ih_len; 1350 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */); 1351 } 1352 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0); 1353 #ifdef INET6 1354 if (!isipv6) 1355 #endif 1356 ipov->ih_len = save; 1357 } 1358 #endif /* TCPDEBUG */ 1359 TCP_PROBE3(debug__output, tp, th, m); 1360 1361 /* 1362 * Fill in IP length and desired time to live and 1363 * send to IP level. There should be a better way 1364 * to handle ttl and tos; we could keep them in 1365 * the template, but need a way to checksum without them. 1366 */ 1367 /* 1368 * m->m_pkthdr.len should have been set before checksum calculation, 1369 * because in6_cksum() need it. 1370 */ 1371 #ifdef INET6 1372 if (isipv6) { 1373 /* 1374 * we separately set hoplimit for every segment, since the 1375 * user might want to change the value via setsockopt. 1376 * Also, desired default hop limit might be changed via 1377 * Neighbor Discovery. 1378 */ 1379 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL); 1380 1381 /* 1382 * Set the packet size here for the benefit of DTrace probes. 1383 * ip6_output() will set it properly; it's supposed to include 1384 * the option header lengths as well. 1385 */ 1386 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6)); 1387 1388 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) 1389 tp->t_flags2 |= TF2_PLPMTU_PMTUD; 1390 else 1391 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; 1392 1393 if (tp->t_state == TCPS_SYN_SENT) 1394 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th); 1395 1396 TCP_PROBE5(send, NULL, tp, ip6, tp, th); 1397 1398 #ifdef TCPPCAP 1399 /* Save packet, if requested. */ 1400 tcp_pcap_add(th, m, &(tp->t_outpkts)); 1401 #endif 1402 1403 /* TODO: IPv6 IP6TOS_ECT bit on */ 1404 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, 1405 &tp->t_inpcb->inp_route6, 1406 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 1407 NULL, NULL, tp->t_inpcb); 1408 1409 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_rt != NULL) 1410 mtu = tp->t_inpcb->inp_route6.ro_rt->rt_mtu; 1411 } 1412 #endif /* INET6 */ 1413 #if defined(INET) && defined(INET6) 1414 else 1415 #endif 1416 #ifdef INET 1417 { 1418 ip->ip_len = htons(m->m_pkthdr.len); 1419 #ifdef INET6 1420 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO) 1421 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL); 1422 #endif /* INET6 */ 1423 /* 1424 * If we do path MTU discovery, then we set DF on every packet. 1425 * This might not be the best thing to do according to RFC3390 1426 * Section 2. However the tcp hostcache migitates the problem 1427 * so it affects only the first tcp connection with a host. 1428 * 1429 * NB: Don't set DF on small MTU/MSS to have a safe fallback. 1430 */ 1431 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) { 1432 ip->ip_off |= htons(IP_DF); 1433 tp->t_flags2 |= TF2_PLPMTU_PMTUD; 1434 } else { 1435 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; 1436 } 1437 1438 if (tp->t_state == TCPS_SYN_SENT) 1439 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th); 1440 1441 TCP_PROBE5(send, NULL, tp, ip, tp, th); 1442 1443 #ifdef TCPPCAP 1444 /* Save packet, if requested. */ 1445 tcp_pcap_add(th, m, &(tp->t_outpkts)); 1446 #endif 1447 1448 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, 1449 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, 1450 tp->t_inpcb); 1451 1452 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL) 1453 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu; 1454 } 1455 #endif /* INET */ 1456 1457 out: 1458 /* 1459 * In transmit state, time the transmission and arrange for 1460 * the retransmit. In persist state, just set snd_max. 1461 */ 1462 if ((tp->t_flags & TF_FORCEDATA) == 0 || 1463 !tcp_timer_active(tp, TT_PERSIST)) { 1464 tcp_seq startseq = tp->snd_nxt; 1465 1466 /* 1467 * Advance snd_nxt over sequence space of this segment. 1468 */ 1469 if (flags & (TH_SYN|TH_FIN)) { 1470 if (flags & TH_SYN) 1471 tp->snd_nxt++; 1472 if (flags & TH_FIN) { 1473 tp->snd_nxt++; 1474 tp->t_flags |= TF_SENTFIN; 1475 } 1476 } 1477 if (sack_rxmit) 1478 goto timer; 1479 tp->snd_nxt += len; 1480 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1481 tp->snd_max = tp->snd_nxt; 1482 /* 1483 * Time this transmission if not a retransmission and 1484 * not currently timing anything. 1485 */ 1486 if (tp->t_rtttime == 0) { 1487 tp->t_rtttime = ticks; 1488 tp->t_rtseq = startseq; 1489 TCPSTAT_INC(tcps_segstimed); 1490 } 1491 } 1492 1493 /* 1494 * Set retransmit timer if not currently set, 1495 * and not doing a pure ack or a keep-alive probe. 1496 * Initial value for retransmit timer is smoothed 1497 * round-trip time + 2 * round-trip time variance. 1498 * Initialize shift counter which is used for backoff 1499 * of retransmit time. 1500 */ 1501 timer: 1502 if (!tcp_timer_active(tp, TT_REXMT) && 1503 ((sack_rxmit && tp->snd_nxt != tp->snd_max) || 1504 (tp->snd_nxt != tp->snd_una))) { 1505 if (tcp_timer_active(tp, TT_PERSIST)) { 1506 tcp_timer_activate(tp, TT_PERSIST, 0); 1507 tp->t_rxtshift = 0; 1508 } 1509 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); 1510 } else if (len == 0 && sbavail(&so->so_snd) && 1511 !tcp_timer_active(tp, TT_REXMT) && 1512 !tcp_timer_active(tp, TT_PERSIST)) { 1513 /* 1514 * Avoid a situation where we do not set persist timer 1515 * after a zero window condition. For example: 1516 * 1) A -> B: packet with enough data to fill the window 1517 * 2) B -> A: ACK for #1 + new data (0 window 1518 * advertisement) 1519 * 3) A -> B: ACK for #2, 0 len packet 1520 * 1521 * In this case, A will not activate the persist timer, 1522 * because it chose to send a packet. Unless tcp_output 1523 * is called for some other reason (delayed ack timer, 1524 * another input packet from B, socket syscall), A will 1525 * not send zero window probes. 1526 * 1527 * So, if you send a 0-length packet, but there is data 1528 * in the socket buffer, and neither the rexmt or 1529 * persist timer is already set, then activate the 1530 * persist timer. 1531 */ 1532 tp->t_rxtshift = 0; 1533 tcp_setpersist(tp); 1534 } 1535 } else { 1536 /* 1537 * Persist case, update snd_max but since we are in 1538 * persist mode (no window) we do not update snd_nxt. 1539 */ 1540 int xlen = len; 1541 if (flags & TH_SYN) 1542 ++xlen; 1543 if (flags & TH_FIN) { 1544 ++xlen; 1545 tp->t_flags |= TF_SENTFIN; 1546 } 1547 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max)) 1548 tp->snd_max = tp->snd_nxt + xlen; 1549 } 1550 1551 if (error) { 1552 1553 /* 1554 * We know that the packet was lost, so back out the 1555 * sequence number advance, if any. 1556 * 1557 * If the error is EPERM the packet got blocked by the 1558 * local firewall. Normally we should terminate the 1559 * connection but the blocking may have been spurious 1560 * due to a firewall reconfiguration cycle. So we treat 1561 * it like a packet loss and let the retransmit timer and 1562 * timeouts do their work over time. 1563 * XXX: It is a POLA question whether calling tcp_drop right 1564 * away would be the really correct behavior instead. 1565 */ 1566 if (((tp->t_flags & TF_FORCEDATA) == 0 || 1567 !tcp_timer_active(tp, TT_PERSIST)) && 1568 ((flags & TH_SYN) == 0) && 1569 (error != EPERM)) { 1570 if (sack_rxmit) { 1571 p->rxmit -= len; 1572 tp->sackhint.sack_bytes_rexmit -= len; 1573 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0, 1574 ("sackhint bytes rtx >= 0")); 1575 } else 1576 tp->snd_nxt -= len; 1577 } 1578 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */ 1579 switch (error) { 1580 case EACCES: 1581 tp->t_softerror = error; 1582 return (0); 1583 case EPERM: 1584 tp->t_softerror = error; 1585 return (error); 1586 case ENOBUFS: 1587 TCP_XMIT_TIMER_ASSERT(tp, len, flags); 1588 tp->snd_cwnd = tp->t_maxseg; 1589 return (0); 1590 case EMSGSIZE: 1591 /* 1592 * For some reason the interface we used initially 1593 * to send segments changed to another or lowered 1594 * its MTU. 1595 * If TSO was active we either got an interface 1596 * without TSO capabilits or TSO was turned off. 1597 * If we obtained mtu from ip_output() then update 1598 * it and try again. 1599 */ 1600 if (tso) 1601 tp->t_flags &= ~TF_TSO; 1602 if (mtu != 0) { 1603 tcp_mss_update(tp, -1, mtu, NULL, NULL); 1604 goto again; 1605 } 1606 return (error); 1607 case EHOSTDOWN: 1608 case EHOSTUNREACH: 1609 case ENETDOWN: 1610 case ENETUNREACH: 1611 if (TCPS_HAVERCVDSYN(tp->t_state)) { 1612 tp->t_softerror = error; 1613 return (0); 1614 } 1615 /* FALLTHROUGH */ 1616 default: 1617 return (error); 1618 } 1619 } 1620 TCPSTAT_INC(tcps_sndtotal); 1621 1622 /* 1623 * Data sent (as far as we can tell). 1624 * If this advertises a larger window than any other segment, 1625 * then remember the size of the advertised window. 1626 * Any pending ACK has now been sent. 1627 */ 1628 if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv)) 1629 tp->rcv_adv = tp->rcv_nxt + recwin; 1630 tp->last_ack_sent = tp->rcv_nxt; 1631 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK); 1632 if (tcp_timer_active(tp, TT_DELACK)) 1633 tcp_timer_activate(tp, TT_DELACK, 0); 1634 #if 0 1635 /* 1636 * This completely breaks TCP if newreno is turned on. What happens 1637 * is that if delayed-acks are turned on on the receiver, this code 1638 * on the transmitter effectively destroys the TCP window, forcing 1639 * it to four packets (1.5Kx4 = 6K window). 1640 */ 1641 if (sendalot && --maxburst) 1642 goto again; 1643 #endif 1644 if (sendalot) 1645 goto again; 1646 return (0); 1647 } 1648 1649 void 1650 tcp_setpersist(struct tcpcb *tp) 1651 { 1652 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 1653 int tt; 1654 1655 tp->t_flags &= ~TF_PREVVALID; 1656 if (tcp_timer_active(tp, TT_REXMT)) 1657 panic("tcp_setpersist: retransmit pending"); 1658 /* 1659 * Start/restart persistence timer. 1660 */ 1661 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], 1662 tcp_persmin, tcp_persmax); 1663 tcp_timer_activate(tp, TT_PERSIST, tt); 1664 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1665 tp->t_rxtshift++; 1666 } 1667 1668 /* 1669 * Insert TCP options according to the supplied parameters to the place 1670 * optp in a consistent way. Can handle unaligned destinations. 1671 * 1672 * The order of the option processing is crucial for optimal packing and 1673 * alignment for the scarce option space. 1674 * 1675 * The optimal order for a SYN/SYN-ACK segment is: 1676 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) + 1677 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40. 1678 * 1679 * The SACK options should be last. SACK blocks consume 8*n+2 bytes. 1680 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks). 1681 * At minimum we need 10 bytes (to generate 1 SACK block). If both 1682 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present, 1683 * we only have 10 bytes for SACK options (40 - (12 + 18)). 1684 */ 1685 int 1686 tcp_addoptions(struct tcpopt *to, u_char *optp) 1687 { 1688 u_int32_t mask, optlen = 0; 1689 1690 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) { 1691 if ((to->to_flags & mask) != mask) 1692 continue; 1693 if (optlen == TCP_MAXOLEN) 1694 break; 1695 switch (to->to_flags & mask) { 1696 case TOF_MSS: 1697 while (optlen % 4) { 1698 optlen += TCPOLEN_NOP; 1699 *optp++ = TCPOPT_NOP; 1700 } 1701 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG) 1702 continue; 1703 optlen += TCPOLEN_MAXSEG; 1704 *optp++ = TCPOPT_MAXSEG; 1705 *optp++ = TCPOLEN_MAXSEG; 1706 to->to_mss = htons(to->to_mss); 1707 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss)); 1708 optp += sizeof(to->to_mss); 1709 break; 1710 case TOF_SCALE: 1711 while (!optlen || optlen % 2 != 1) { 1712 optlen += TCPOLEN_NOP; 1713 *optp++ = TCPOPT_NOP; 1714 } 1715 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW) 1716 continue; 1717 optlen += TCPOLEN_WINDOW; 1718 *optp++ = TCPOPT_WINDOW; 1719 *optp++ = TCPOLEN_WINDOW; 1720 *optp++ = to->to_wscale; 1721 break; 1722 case TOF_SACKPERM: 1723 while (optlen % 2) { 1724 optlen += TCPOLEN_NOP; 1725 *optp++ = TCPOPT_NOP; 1726 } 1727 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED) 1728 continue; 1729 optlen += TCPOLEN_SACK_PERMITTED; 1730 *optp++ = TCPOPT_SACK_PERMITTED; 1731 *optp++ = TCPOLEN_SACK_PERMITTED; 1732 break; 1733 case TOF_TS: 1734 while (!optlen || optlen % 4 != 2) { 1735 optlen += TCPOLEN_NOP; 1736 *optp++ = TCPOPT_NOP; 1737 } 1738 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP) 1739 continue; 1740 optlen += TCPOLEN_TIMESTAMP; 1741 *optp++ = TCPOPT_TIMESTAMP; 1742 *optp++ = TCPOLEN_TIMESTAMP; 1743 to->to_tsval = htonl(to->to_tsval); 1744 to->to_tsecr = htonl(to->to_tsecr); 1745 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval)); 1746 optp += sizeof(to->to_tsval); 1747 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr)); 1748 optp += sizeof(to->to_tsecr); 1749 break; 1750 case TOF_SIGNATURE: 1751 { 1752 int siglen = TCPOLEN_SIGNATURE - 2; 1753 1754 while (!optlen || optlen % 4 != 2) { 1755 optlen += TCPOLEN_NOP; 1756 *optp++ = TCPOPT_NOP; 1757 } 1758 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) { 1759 to->to_flags &= ~TOF_SIGNATURE; 1760 continue; 1761 } 1762 optlen += TCPOLEN_SIGNATURE; 1763 *optp++ = TCPOPT_SIGNATURE; 1764 *optp++ = TCPOLEN_SIGNATURE; 1765 to->to_signature = optp; 1766 while (siglen--) 1767 *optp++ = 0; 1768 break; 1769 } 1770 case TOF_SACK: 1771 { 1772 int sackblks = 0; 1773 struct sackblk *sack = (struct sackblk *)to->to_sacks; 1774 tcp_seq sack_seq; 1775 1776 while (!optlen || optlen % 4 != 2) { 1777 optlen += TCPOLEN_NOP; 1778 *optp++ = TCPOPT_NOP; 1779 } 1780 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK) 1781 continue; 1782 optlen += TCPOLEN_SACKHDR; 1783 *optp++ = TCPOPT_SACK; 1784 sackblks = min(to->to_nsacks, 1785 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK); 1786 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK; 1787 while (sackblks--) { 1788 sack_seq = htonl(sack->start); 1789 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq)); 1790 optp += sizeof(sack_seq); 1791 sack_seq = htonl(sack->end); 1792 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq)); 1793 optp += sizeof(sack_seq); 1794 optlen += TCPOLEN_SACK; 1795 sack++; 1796 } 1797 TCPSTAT_INC(tcps_sack_send_blocks); 1798 break; 1799 } 1800 case TOF_FASTOPEN: 1801 { 1802 int total_len; 1803 1804 /* XXX is there any point to aligning this option? */ 1805 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len; 1806 if (TCP_MAXOLEN - optlen < total_len) { 1807 to->to_flags &= ~TOF_FASTOPEN; 1808 continue; 1809 } 1810 *optp++ = TCPOPT_FAST_OPEN; 1811 *optp++ = total_len; 1812 if (to->to_tfo_len > 0) { 1813 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len); 1814 optp += to->to_tfo_len; 1815 } 1816 optlen += total_len; 1817 break; 1818 } 1819 default: 1820 panic("%s: unknown TCP option type", __func__); 1821 break; 1822 } 1823 } 1824 1825 /* Terminate and pad TCP options to a 4 byte boundary. */ 1826 if (optlen % 4) { 1827 optlen += TCPOLEN_EOL; 1828 *optp++ = TCPOPT_EOL; 1829 } 1830 /* 1831 * According to RFC 793 (STD0007): 1832 * "The content of the header beyond the End-of-Option option 1833 * must be header padding (i.e., zero)." 1834 * and later: "The padding is composed of zeros." 1835 */ 1836 while (optlen % 4) { 1837 optlen += TCPOLEN_PAD; 1838 *optp++ = TCPOPT_PAD; 1839 } 1840 1841 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__)); 1842 return (optlen); 1843 } 1844 1845 void 1846 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin) 1847 { 1848 1849 /* 1850 * Automatic sizing of send socket buffer. Often the send buffer 1851 * size is not optimally adjusted to the actual network conditions 1852 * at hand (delay bandwidth product). Setting the buffer size too 1853 * small limits throughput on links with high bandwidth and high 1854 * delay (eg. trans-continental/oceanic links). Setting the 1855 * buffer size too big consumes too much real kernel memory, 1856 * especially with many connections on busy servers. 1857 * 1858 * The criteria to step up the send buffer one notch are: 1859 * 1. receive window of remote host is larger than send buffer 1860 * (with a fudge factor of 5/4th); 1861 * 2. send buffer is filled to 7/8th with data (so we actually 1862 * have data to make use of it); 1863 * 3. send buffer fill has not hit maximal automatic size; 1864 * 4. our send window (slow start and cogestion controlled) is 1865 * larger than sent but unacknowledged data in send buffer. 1866 * 1867 * The remote host receive window scaling factor may limit the 1868 * growing of the send buffer before it reaches its allowed 1869 * maximum. 1870 * 1871 * It scales directly with slow start or congestion window 1872 * and does at most one step per received ACK. This fast 1873 * scaling has the drawback of growing the send buffer beyond 1874 * what is strictly necessary to make full use of a given 1875 * delay*bandwidth product. However testing has shown this not 1876 * to be much of an problem. At worst we are trading wasting 1877 * of available bandwidth (the non-use of it) for wasting some 1878 * socket buffer memory. 1879 * 1880 * TODO: Shrink send buffer during idle periods together 1881 * with congestion window. Requires another timer. Has to 1882 * wait for upcoming tcp timer rewrite. 1883 * 1884 * XXXGL: should there be used sbused() or sbavail()? 1885 */ 1886 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) { 1887 int lowat; 1888 1889 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0; 1890 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat && 1891 sbused(&so->so_snd) >= 1892 (so->so_snd.sb_hiwat / 8 * 7) - lowat && 1893 sbused(&so->so_snd) < V_tcp_autosndbuf_max && 1894 sendwin >= (sbused(&so->so_snd) - 1895 (tp->snd_nxt - tp->snd_una))) { 1896 if (!sbreserve_locked(&so->so_snd, 1897 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc, 1898 V_tcp_autosndbuf_max), so, curthread)) 1899 so->so_snd.sb_flags &= ~SB_AUTOSIZE; 1900 } 1901 } 1902 } 1903