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 #ifdef TCP_RFC7413 75 #include <netinet/tcp_fastopen.h> 76 #endif 77 #include <netinet/tcp.h> 78 #define TCPOUTFLAGS 79 #include <netinet/tcp_fsm.h> 80 #include <netinet/tcp_seq.h> 81 #include <netinet/tcp_timer.h> 82 #include <netinet/tcp_var.h> 83 #include <netinet/tcpip.h> 84 #include <netinet/cc/cc.h> 85 #ifdef TCPPCAP 86 #include <netinet/tcp_pcap.h> 87 #endif 88 #ifdef TCPDEBUG 89 #include <netinet/tcp_debug.h> 90 #endif 91 #ifdef TCP_OFFLOAD 92 #include <netinet/tcp_offload.h> 93 #endif 94 95 #include <netipsec/ipsec_support.h> 96 97 #include <machine/in_cksum.h> 98 99 #include <security/mac/mac_framework.h> 100 101 VNET_DEFINE(int, path_mtu_discovery) = 1; 102 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW, 103 &VNET_NAME(path_mtu_discovery), 1, 104 "Enable Path MTU Discovery"); 105 106 VNET_DEFINE(int, tcp_do_tso) = 1; 107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW, 108 &VNET_NAME(tcp_do_tso), 0, 109 "Enable TCP Segmentation Offload"); 110 111 VNET_DEFINE(int, tcp_sendspace) = 1024*32; 112 #define V_tcp_sendspace VNET(tcp_sendspace) 113 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW, 114 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size"); 115 116 VNET_DEFINE(int, tcp_do_autosndbuf) = 1; 117 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW, 118 &VNET_NAME(tcp_do_autosndbuf), 0, 119 "Enable automatic send buffer sizing"); 120 121 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024; 122 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW, 123 &VNET_NAME(tcp_autosndbuf_inc), 0, 124 "Incrementor step size of automatic send buffer"); 125 126 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024; 127 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW, 128 &VNET_NAME(tcp_autosndbuf_max), 0, 129 "Max size of automatic send buffer"); 130 131 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0; 132 #define V_tcp_sendbuf_auto_lowat VNET(tcp_sendbuf_auto_lowat) 133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW, 134 &VNET_NAME(tcp_sendbuf_auto_lowat), 0, 135 "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT"); 136 137 /* 138 * Make sure that either retransmit or persist timer is set for SYN, FIN and 139 * non-ACK. 140 */ 141 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \ 142 KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\ 143 tcp_timer_active((tp), TT_REXMT) || \ 144 tcp_timer_active((tp), TT_PERSIST), \ 145 ("neither rexmt nor persist timer is set")) 146 147 #ifdef TCP_HHOOK 148 static void inline hhook_run_tcp_est_out(struct tcpcb *tp, 149 struct tcphdr *th, struct tcpopt *to, 150 uint32_t len, int tso); 151 #endif 152 static void inline cc_after_idle(struct tcpcb *tp); 153 154 #ifdef TCP_HHOOK 155 /* 156 * Wrapper for the TCP established output helper hook. 157 */ 158 static void inline 159 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th, 160 struct tcpopt *to, uint32_t len, int tso) 161 { 162 struct tcp_hhook_data hhook_data; 163 164 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) { 165 hhook_data.tp = tp; 166 hhook_data.th = th; 167 hhook_data.to = to; 168 hhook_data.len = len; 169 hhook_data.tso = tso; 170 171 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data, 172 tp->osd); 173 } 174 } 175 #endif 176 177 /* 178 * CC wrapper hook functions 179 */ 180 static void inline 181 cc_after_idle(struct tcpcb *tp) 182 { 183 INP_WLOCK_ASSERT(tp->t_inpcb); 184 185 if (CC_ALGO(tp)->after_idle != NULL) 186 CC_ALGO(tp)->after_idle(tp->ccv); 187 } 188 189 /* 190 * Tcp output routine: figure out what should be sent and send it. 191 */ 192 int 193 tcp_output(struct tcpcb *tp) 194 { 195 struct socket *so = tp->t_inpcb->inp_socket; 196 int32_t len; 197 uint32_t recwin, sendwin; 198 int off, flags, error = 0; /* Keep compiler happy */ 199 struct mbuf *m; 200 struct ip *ip = NULL; 201 #ifdef TCPDEBUG 202 struct ipovly *ipov = NULL; 203 #endif 204 struct tcphdr *th; 205 u_char opt[TCP_MAXOLEN]; 206 unsigned ipoptlen, optlen, hdrlen; 207 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 208 unsigned ipsec_optlen = 0; 209 #endif 210 int idle, sendalot; 211 int sack_rxmit, sack_bytes_rxmt; 212 struct sackhole *p; 213 int tso, mtu; 214 struct tcpopt to; 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 #ifdef TCP_RFC7413 233 /* 234 * For TFO connections in SYN_RECEIVED, only allow the initial 235 * SYN|ACK and those sent by the retransmit timer. 236 */ 237 if (IS_FASTOPEN(tp->t_flags) && 238 (tp->t_state == TCPS_SYN_RECEIVED) && 239 SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN|ACK sent */ 240 (tp->snd_nxt != tp->snd_una)) /* not a retransmit */ 241 return (0); 242 #endif 243 /* 244 * Determine length of data that should be transmitted, 245 * and flags that will be used. 246 * If there is some data or critical controls (SYN, RST) 247 * to send, then transmit; otherwise, investigate further. 248 */ 249 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una); 250 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur) 251 cc_after_idle(tp); 252 tp->t_flags &= ~TF_LASTIDLE; 253 if (idle) { 254 if (tp->t_flags & TF_MORETOCOME) { 255 tp->t_flags |= TF_LASTIDLE; 256 idle = 0; 257 } 258 } 259 again: 260 /* 261 * If we've recently taken a timeout, snd_max will be greater than 262 * snd_nxt. There may be SACK information that allows us to avoid 263 * resending already delivered data. Adjust snd_nxt accordingly. 264 */ 265 if ((tp->t_flags & TF_SACK_PERMIT) && 266 SEQ_LT(tp->snd_nxt, tp->snd_max)) 267 tcp_sack_adjust(tp); 268 sendalot = 0; 269 tso = 0; 270 mtu = 0; 271 off = tp->snd_nxt - tp->snd_una; 272 sendwin = min(tp->snd_wnd, tp->snd_cwnd); 273 274 flags = tcp_outflags[tp->t_state]; 275 /* 276 * Send any SACK-generated retransmissions. If we're explicitly trying 277 * to send out new data (when sendalot is 1), bypass this function. 278 * If we retransmit in fast recovery mode, decrement snd_cwnd, since 279 * we're replacing a (future) new transmission with a retransmission 280 * now, and we previously incremented snd_cwnd in tcp_input(). 281 */ 282 /* 283 * Still in sack recovery , reset rxmit flag to zero. 284 */ 285 sack_rxmit = 0; 286 sack_bytes_rxmt = 0; 287 len = 0; 288 p = NULL; 289 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) && 290 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) { 291 uint32_t cwin; 292 293 cwin = 294 imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0); 295 /* Do not retransmit SACK segments beyond snd_recover */ 296 if (SEQ_GT(p->end, tp->snd_recover)) { 297 /* 298 * (At least) part of sack hole extends beyond 299 * snd_recover. Check to see if we can rexmit data 300 * for this hole. 301 */ 302 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) { 303 /* 304 * Can't rexmit any more data for this hole. 305 * That data will be rexmitted in the next 306 * sack recovery episode, when snd_recover 307 * moves past p->rxmit. 308 */ 309 p = NULL; 310 goto after_sack_rexmit; 311 } else 312 /* Can rexmit part of the current hole */ 313 len = ((int32_t)ulmin(cwin, 314 tp->snd_recover - p->rxmit)); 315 } else 316 len = ((int32_t)ulmin(cwin, p->end - p->rxmit)); 317 off = p->rxmit - tp->snd_una; 318 KASSERT(off >= 0,("%s: sack block to the left of una : %d", 319 __func__, off)); 320 if (len > 0) { 321 sack_rxmit = 1; 322 sendalot = 1; 323 TCPSTAT_INC(tcps_sack_rexmits); 324 TCPSTAT_ADD(tcps_sack_rexmit_bytes, 325 min(len, tp->t_maxseg)); 326 } 327 } 328 after_sack_rexmit: 329 /* 330 * Get standard flags, and add SYN or FIN if requested by 'hidden' 331 * state flags. 332 */ 333 if (tp->t_flags & TF_NEEDFIN) 334 flags |= TH_FIN; 335 if (tp->t_flags & TF_NEEDSYN) 336 flags |= TH_SYN; 337 338 SOCKBUF_LOCK(&so->so_snd); 339 /* 340 * If in persist timeout with window of 0, send 1 byte. 341 * Otherwise, if window is small but nonzero 342 * and timer expired, we will send what we can 343 * and go to transmit state. 344 */ 345 if (tp->t_flags & TF_FORCEDATA) { 346 if (sendwin == 0) { 347 /* 348 * If we still have some data to send, then 349 * clear the FIN bit. Usually this would 350 * happen below when it realizes that we 351 * aren't sending all the data. However, 352 * if we have exactly 1 byte of unsent data, 353 * then it won't clear the FIN bit below, 354 * and if we are in persist state, we wind 355 * up sending the packet without recording 356 * that we sent the FIN bit. 357 * 358 * We can't just blindly clear the FIN bit, 359 * because if we don't have any more data 360 * to send then the probe will be the FIN 361 * itself. 362 */ 363 if (off < sbused(&so->so_snd)) 364 flags &= ~TH_FIN; 365 sendwin = 1; 366 } else { 367 tcp_timer_activate(tp, TT_PERSIST, 0); 368 tp->t_rxtshift = 0; 369 } 370 } 371 372 /* 373 * If snd_nxt == snd_max and we have transmitted a FIN, the 374 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in 375 * a negative length. This can also occur when TCP opens up 376 * its congestion window while receiving additional duplicate 377 * acks after fast-retransmit because TCP will reset snd_nxt 378 * to snd_max after the fast-retransmit. 379 * 380 * In the normal retransmit-FIN-only case, however, snd_nxt will 381 * be set to snd_una, the offset will be 0, and the length may 382 * wind up 0. 383 * 384 * If sack_rxmit is true we are retransmitting from the scoreboard 385 * in which case len is already set. 386 */ 387 if (sack_rxmit == 0) { 388 if (sack_bytes_rxmt == 0) 389 len = ((int32_t)min(sbavail(&so->so_snd), sendwin) - 390 off); 391 else { 392 int32_t cwin; 393 394 /* 395 * We are inside of a SACK recovery episode and are 396 * sending new data, having retransmitted all the 397 * data possible in the scoreboard. 398 */ 399 len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) - 400 off); 401 /* 402 * Don't remove this (len > 0) check ! 403 * We explicitly check for len > 0 here (although it 404 * isn't really necessary), to work around a gcc 405 * optimization issue - to force gcc to compute 406 * len above. Without this check, the computation 407 * of len is bungled by the optimizer. 408 */ 409 if (len > 0) { 410 cwin = tp->snd_cwnd - 411 (tp->snd_nxt - tp->sack_newdata) - 412 sack_bytes_rxmt; 413 if (cwin < 0) 414 cwin = 0; 415 len = imin(len, cwin); 416 } 417 } 418 } 419 420 /* 421 * Lop off SYN bit if it has already been sent. However, if this 422 * is SYN-SENT state and if segment contains data and if we don't 423 * know that foreign host supports TAO, suppress sending segment. 424 */ 425 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) { 426 if (tp->t_state != TCPS_SYN_RECEIVED) 427 flags &= ~TH_SYN; 428 #ifdef TCP_RFC7413 429 /* 430 * When sending additional segments following a TFO SYN|ACK, 431 * do not include the SYN bit. 432 */ 433 if (IS_FASTOPEN(tp->t_flags) && 434 (tp->t_state == TCPS_SYN_RECEIVED)) 435 flags &= ~TH_SYN; 436 #endif 437 off--, len++; 438 } 439 440 /* 441 * Be careful not to send data and/or FIN on SYN segments. 442 * This measure is needed to prevent interoperability problems 443 * with not fully conformant TCP implementations. 444 */ 445 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) { 446 len = 0; 447 flags &= ~TH_FIN; 448 } 449 450 #ifdef TCP_RFC7413 451 /* 452 * When retransmitting SYN|ACK on a passively-created TFO socket, 453 * don't include data, as the presence of data may have caused the 454 * original SYN|ACK to have been dropped by a middlebox. 455 */ 456 if (IS_FASTOPEN(tp->t_flags) && 457 (((tp->t_state == TCPS_SYN_RECEIVED) && (tp->t_rxtshift > 0)) || 458 (flags & TH_RST))) 459 len = 0; 460 #endif 461 if (len <= 0) { 462 /* 463 * If FIN has been sent but not acked, 464 * but we haven't been called to retransmit, 465 * len will be < 0. Otherwise, window shrank 466 * after we sent into it. If window shrank to 0, 467 * cancel pending retransmit, pull snd_nxt back 468 * to (closed) window, and set the persist timer 469 * if it isn't already going. If the window didn't 470 * close completely, just wait for an ACK. 471 * 472 * We also do a general check here to ensure that 473 * we will set the persist timer when we have data 474 * to send, but a 0-byte window. This makes sure 475 * the persist timer is set even if the packet 476 * hits one of the "goto send" lines below. 477 */ 478 len = 0; 479 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) && 480 (off < (int) sbavail(&so->so_snd))) { 481 tcp_timer_activate(tp, TT_REXMT, 0); 482 tp->t_rxtshift = 0; 483 tp->snd_nxt = tp->snd_una; 484 if (!tcp_timer_active(tp, TT_PERSIST)) 485 tcp_setpersist(tp); 486 } 487 } 488 489 /* len will be >= 0 after this point. */ 490 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__)); 491 492 tcp_sndbuf_autoscale(tp, so, sendwin); 493 494 /* 495 * Decide if we can use TCP Segmentation Offloading (if supported by 496 * hardware). 497 * 498 * TSO may only be used if we are in a pure bulk sending state. The 499 * presence of TCP-MD5, SACK retransmits, SACK advertizements and 500 * IP options prevent using TSO. With TSO the TCP header is the same 501 * (except for the sequence number) for all generated packets. This 502 * makes it impossible to transmit any options which vary per generated 503 * segment or packet. 504 * 505 * IPv4 handling has a clear separation of ip options and ip header 506 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does 507 * the right thing below to provide length of just ip options and thus 508 * checking for ipoptlen is enough to decide if ip options are present. 509 */ 510 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 511 /* 512 * Pre-calculate here as we save another lookup into the darknesses 513 * of IPsec that way and can actually decide if TSO is ok. 514 */ 515 #ifdef INET6 516 if (isipv6 && IPSEC_ENABLED(ipv6)) 517 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb); 518 #ifdef INET 519 else 520 #endif 521 #endif /* INET6 */ 522 #ifdef INET 523 if (IPSEC_ENABLED(ipv4)) 524 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb); 525 #endif /* INET */ 526 #endif /* IPSEC */ 527 #ifdef INET6 528 if (isipv6) 529 ipoptlen = ip6_optlen(tp->t_inpcb); 530 else 531 #endif 532 if (tp->t_inpcb->inp_options) 533 ipoptlen = tp->t_inpcb->inp_options->m_len - 534 offsetof(struct ipoption, ipopt_list); 535 else 536 ipoptlen = 0; 537 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 538 ipoptlen += ipsec_optlen; 539 #endif 540 541 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg && 542 ((tp->t_flags & TF_SIGNATURE) == 0) && 543 tp->rcv_numsacks == 0 && sack_rxmit == 0 && 544 ipoptlen == 0) 545 tso = 1; 546 547 if (sack_rxmit) { 548 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd))) 549 flags &= ~TH_FIN; 550 } else { 551 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + 552 sbused(&so->so_snd))) 553 flags &= ~TH_FIN; 554 } 555 556 recwin = lmin(lmax(sbspace(&so->so_rcv), 0), 557 (long)TCP_MAXWIN << tp->rcv_scale); 558 559 /* 560 * Sender silly window avoidance. We transmit under the following 561 * conditions when len is non-zero: 562 * 563 * - We have a full segment (or more with TSO) 564 * - This is the last buffer in a write()/send() and we are 565 * either idle or running NODELAY 566 * - we've timed out (e.g. persist timer) 567 * - we have more then 1/2 the maximum send window's worth of 568 * data (receiver may be limited the window size) 569 * - we need to retransmit 570 */ 571 if (len) { 572 if (len >= tp->t_maxseg) 573 goto send; 574 /* 575 * NOTE! on localhost connections an 'ack' from the remote 576 * end may occur synchronously with the output and cause 577 * us to flush a buffer queued with moretocome. XXX 578 * 579 * note: the len + off check is almost certainly unnecessary. 580 */ 581 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */ 582 (idle || (tp->t_flags & TF_NODELAY)) && 583 (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) && 584 (tp->t_flags & TF_NOPUSH) == 0) { 585 goto send; 586 } 587 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */ 588 goto send; 589 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0) 590 goto send; 591 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */ 592 goto send; 593 if (sack_rxmit) 594 goto send; 595 } 596 597 /* 598 * Sending of standalone window updates. 599 * 600 * Window updates are important when we close our window due to a 601 * full socket buffer and are opening it again after the application 602 * reads data from it. Once the window has opened again and the 603 * remote end starts to send again the ACK clock takes over and 604 * provides the most current window information. 605 * 606 * We must avoid the silly window syndrome whereas every read 607 * from the receive buffer, no matter how small, causes a window 608 * update to be sent. We also should avoid sending a flurry of 609 * window updates when the socket buffer had queued a lot of data 610 * and the application is doing small reads. 611 * 612 * Prevent a flurry of pointless window updates by only sending 613 * an update when we can increase the advertized window by more 614 * than 1/4th of the socket buffer capacity. When the buffer is 615 * getting full or is very small be more aggressive and send an 616 * update whenever we can increase by two mss sized segments. 617 * In all other situations the ACK's to new incoming data will 618 * carry further window increases. 619 * 620 * Don't send an independent window update if a delayed 621 * ACK is pending (it will get piggy-backed on it) or the 622 * remote side already has done a half-close and won't send 623 * more data. Skip this if the connection is in T/TCP 624 * half-open state. 625 */ 626 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) && 627 !(tp->t_flags & TF_DELACK) && 628 !TCPS_HAVERCVDFIN(tp->t_state)) { 629 /* 630 * "adv" is the amount we could increase the window, 631 * taking into account that we are limited by 632 * TCP_MAXWIN << tp->rcv_scale. 633 */ 634 int32_t adv; 635 int oldwin; 636 637 adv = recwin; 638 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) { 639 oldwin = (tp->rcv_adv - tp->rcv_nxt); 640 adv -= oldwin; 641 } else 642 oldwin = 0; 643 644 /* 645 * If the new window size ends up being the same as or less 646 * than the old size when it is scaled, then don't force 647 * a window update. 648 */ 649 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale) 650 goto dontupdate; 651 652 if (adv >= (int32_t)(2 * tp->t_maxseg) && 653 (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) || 654 recwin <= (so->so_rcv.sb_hiwat / 8) || 655 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg)) 656 goto send; 657 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat) 658 goto send; 659 } 660 dontupdate: 661 662 /* 663 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW 664 * is also a catch-all for the retransmit timer timeout case. 665 */ 666 if (tp->t_flags & TF_ACKNOW) 667 goto send; 668 if ((flags & TH_RST) || 669 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0)) 670 goto send; 671 if (SEQ_GT(tp->snd_up, tp->snd_una)) 672 goto send; 673 /* 674 * If our state indicates that FIN should be sent 675 * and we have not yet done so, then we need to send. 676 */ 677 if (flags & TH_FIN && 678 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 679 goto send; 680 /* 681 * In SACK, it is possible for tcp_output to fail to send a segment 682 * after the retransmission timer has been turned off. Make sure 683 * that the retransmission timer is set. 684 */ 685 if ((tp->t_flags & TF_SACK_PERMIT) && 686 SEQ_GT(tp->snd_max, tp->snd_una) && 687 !tcp_timer_active(tp, TT_REXMT) && 688 !tcp_timer_active(tp, TT_PERSIST)) { 689 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); 690 goto just_return; 691 } 692 /* 693 * TCP window updates are not reliable, rather a polling protocol 694 * using ``persist'' packets is used to insure receipt of window 695 * updates. The three ``states'' for the output side are: 696 * idle not doing retransmits or persists 697 * persisting to move a small or zero window 698 * (re)transmitting and thereby not persisting 699 * 700 * tcp_timer_active(tp, TT_PERSIST) 701 * is true when we are in persist state. 702 * (tp->t_flags & TF_FORCEDATA) 703 * is set when we are called to send a persist packet. 704 * tcp_timer_active(tp, TT_REXMT) 705 * is set when we are retransmitting 706 * The output side is idle when both timers are zero. 707 * 708 * If send window is too small, there is data to transmit, and no 709 * retransmit or persist is pending, then go to persist state. 710 * If nothing happens soon, send when timer expires: 711 * if window is nonzero, transmit what we can, 712 * otherwise force out a byte. 713 */ 714 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) && 715 !tcp_timer_active(tp, TT_PERSIST)) { 716 tp->t_rxtshift = 0; 717 tcp_setpersist(tp); 718 } 719 720 /* 721 * No reason to send a segment, just return. 722 */ 723 just_return: 724 SOCKBUF_UNLOCK(&so->so_snd); 725 return (0); 726 727 send: 728 SOCKBUF_LOCK_ASSERT(&so->so_snd); 729 if (len > 0) { 730 if (len >= tp->t_maxseg) 731 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT; 732 else 733 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT; 734 } 735 /* 736 * Before ESTABLISHED, force sending of initial options 737 * unless TCP set not to do any options. 738 * NOTE: we assume that the IP/TCP header plus TCP options 739 * always fit in a single mbuf, leaving room for a maximum 740 * link header, i.e. 741 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES 742 */ 743 optlen = 0; 744 #ifdef INET6 745 if (isipv6) 746 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr); 747 else 748 #endif 749 hdrlen = sizeof (struct tcpiphdr); 750 751 /* 752 * Compute options for segment. 753 * We only have to care about SYN and established connection 754 * segments. Options for SYN-ACK segments are handled in TCP 755 * syncache. 756 */ 757 to.to_flags = 0; 758 if ((tp->t_flags & TF_NOOPT) == 0) { 759 /* Maximum segment size. */ 760 if (flags & TH_SYN) { 761 tp->snd_nxt = tp->iss; 762 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc); 763 to.to_flags |= TOF_MSS; 764 #ifdef TCP_RFC7413 765 /* 766 * Only include the TFO option on the first 767 * transmission of the SYN|ACK on a 768 * passively-created TFO socket, as the presence of 769 * the TFO option may have caused the original 770 * SYN|ACK to have been dropped by a middlebox. 771 */ 772 if (IS_FASTOPEN(tp->t_flags) && 773 (tp->t_state == TCPS_SYN_RECEIVED) && 774 (tp->t_rxtshift == 0)) { 775 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 776 to.to_tfo_cookie = (u_char *)&tp->t_tfo_cookie; 777 to.to_flags |= TOF_FASTOPEN; 778 } 779 #endif 780 } 781 /* Window scaling. */ 782 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) { 783 to.to_wscale = tp->request_r_scale; 784 to.to_flags |= TOF_SCALE; 785 } 786 /* Timestamps. */ 787 if ((tp->t_flags & TF_RCVD_TSTMP) || 788 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) { 789 to.to_tsval = tcp_ts_getticks() + tp->ts_offset; 790 to.to_tsecr = tp->ts_recent; 791 to.to_flags |= TOF_TS; 792 } 793 794 /* Set receive buffer autosizing timestamp. */ 795 if (tp->rfbuf_ts == 0 && 796 (so->so_rcv.sb_flags & SB_AUTOSIZE)) 797 tp->rfbuf_ts = tcp_ts_getticks(); 798 799 /* Selective ACK's. */ 800 if (tp->t_flags & TF_SACK_PERMIT) { 801 if (flags & TH_SYN) 802 to.to_flags |= TOF_SACKPERM; 803 else if (TCPS_HAVEESTABLISHED(tp->t_state) && 804 (tp->t_flags & TF_SACK_PERMIT) && 805 tp->rcv_numsacks > 0) { 806 to.to_flags |= TOF_SACK; 807 to.to_nsacks = tp->rcv_numsacks; 808 to.to_sacks = (u_char *)tp->sackblks; 809 } 810 } 811 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 812 /* TCP-MD5 (RFC2385). */ 813 /* 814 * Check that TCP_MD5SIG is enabled in tcpcb to 815 * account the size needed to set this TCP option. 816 */ 817 if (tp->t_flags & TF_SIGNATURE) 818 to.to_flags |= TOF_SIGNATURE; 819 #endif /* TCP_SIGNATURE */ 820 821 /* Processing the options. */ 822 hdrlen += optlen = tcp_addoptions(&to, opt); 823 } 824 825 /* 826 * Adjust data length if insertion of options will 827 * bump the packet length beyond the t_maxseg length. 828 * Clear the FIN bit because we cut off the tail of 829 * the segment. 830 */ 831 if (len + optlen + ipoptlen > tp->t_maxseg) { 832 flags &= ~TH_FIN; 833 834 if (tso) { 835 u_int if_hw_tsomax; 836 u_int if_hw_tsomaxsegcount; 837 u_int if_hw_tsomaxsegsize; 838 struct mbuf *mb; 839 u_int moff; 840 int max_len; 841 842 /* extract TSO information */ 843 if_hw_tsomax = tp->t_tsomax; 844 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount; 845 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize; 846 847 /* 848 * Limit a TSO burst to prevent it from 849 * overflowing or exceeding the maximum length 850 * allowed by the network interface: 851 */ 852 KASSERT(ipoptlen == 0, 853 ("%s: TSO can't do IP options", __func__)); 854 855 /* 856 * Check if we should limit by maximum payload 857 * length: 858 */ 859 if (if_hw_tsomax != 0) { 860 /* compute maximum TSO length */ 861 max_len = (if_hw_tsomax - hdrlen - 862 max_linkhdr); 863 if (max_len <= 0) { 864 len = 0; 865 } else if (len > max_len) { 866 sendalot = 1; 867 len = max_len; 868 } 869 } 870 871 /* 872 * Check if we should limit by maximum segment 873 * size and count: 874 */ 875 if (if_hw_tsomaxsegcount != 0 && 876 if_hw_tsomaxsegsize != 0) { 877 /* 878 * Subtract one segment for the LINK 879 * and TCP/IP headers mbuf that will 880 * be prepended to this mbuf chain 881 * after the code in this section 882 * limits the number of mbufs in the 883 * chain to if_hw_tsomaxsegcount. 884 */ 885 if_hw_tsomaxsegcount -= 1; 886 max_len = 0; 887 mb = sbsndmbuf(&so->so_snd, off, &moff); 888 889 while (mb != NULL && max_len < len) { 890 u_int mlen; 891 u_int frags; 892 893 /* 894 * Get length of mbuf fragment 895 * and how many hardware frags, 896 * rounded up, it would use: 897 */ 898 mlen = (mb->m_len - moff); 899 frags = howmany(mlen, 900 if_hw_tsomaxsegsize); 901 902 /* Handle special case: Zero Length Mbuf */ 903 if (frags == 0) 904 frags = 1; 905 906 /* 907 * Check if the fragment limit 908 * will be reached or exceeded: 909 */ 910 if (frags >= if_hw_tsomaxsegcount) { 911 max_len += min(mlen, 912 if_hw_tsomaxsegcount * 913 if_hw_tsomaxsegsize); 914 break; 915 } 916 max_len += mlen; 917 if_hw_tsomaxsegcount -= frags; 918 moff = 0; 919 mb = mb->m_next; 920 } 921 if (max_len <= 0) { 922 len = 0; 923 } else if (len > max_len) { 924 sendalot = 1; 925 len = max_len; 926 } 927 } 928 929 /* 930 * Prevent the last segment from being 931 * fractional unless the send sockbuf can be 932 * emptied: 933 */ 934 max_len = (tp->t_maxseg - optlen); 935 if (((uint32_t)off + (uint32_t)len) < 936 sbavail(&so->so_snd)) { 937 moff = len % max_len; 938 if (moff != 0) { 939 len -= moff; 940 sendalot = 1; 941 } 942 } 943 944 /* 945 * In case there are too many small fragments 946 * don't use TSO: 947 */ 948 if (len <= max_len) { 949 len = max_len; 950 sendalot = 1; 951 tso = 0; 952 } 953 954 /* 955 * Send the FIN in a separate segment 956 * after the bulk sending is done. 957 * We don't trust the TSO implementations 958 * to clear the FIN flag on all but the 959 * last segment. 960 */ 961 if (tp->t_flags & TF_NEEDFIN) 962 sendalot = 1; 963 964 } else { 965 len = tp->t_maxseg - optlen - ipoptlen; 966 sendalot = 1; 967 } 968 } else 969 tso = 0; 970 971 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET, 972 ("%s: len > IP_MAXPACKET", __func__)); 973 974 /*#ifdef DIAGNOSTIC*/ 975 #ifdef INET6 976 if (max_linkhdr + hdrlen > MCLBYTES) 977 #else 978 if (max_linkhdr + hdrlen > MHLEN) 979 #endif 980 panic("tcphdr too big"); 981 /*#endif*/ 982 983 /* 984 * This KASSERT is here to catch edge cases at a well defined place. 985 * Before, those had triggered (random) panic conditions further down. 986 */ 987 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__)); 988 989 /* 990 * Grab a header mbuf, attaching a copy of data to 991 * be transmitted, and initialize the header from 992 * the template for sends on this connection. 993 */ 994 if (len) { 995 struct mbuf *mb; 996 u_int moff; 997 998 if ((tp->t_flags & TF_FORCEDATA) && len == 1) 999 TCPSTAT_INC(tcps_sndprobe); 1000 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) { 1001 tp->t_sndrexmitpack++; 1002 TCPSTAT_INC(tcps_sndrexmitpack); 1003 TCPSTAT_ADD(tcps_sndrexmitbyte, len); 1004 } else { 1005 TCPSTAT_INC(tcps_sndpack); 1006 TCPSTAT_ADD(tcps_sndbyte, len); 1007 } 1008 #ifdef INET6 1009 if (MHLEN < hdrlen + max_linkhdr) 1010 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR); 1011 else 1012 #endif 1013 m = m_gethdr(M_NOWAIT, MT_DATA); 1014 1015 if (m == NULL) { 1016 SOCKBUF_UNLOCK(&so->so_snd); 1017 error = ENOBUFS; 1018 sack_rxmit = 0; 1019 goto out; 1020 } 1021 1022 m->m_data += max_linkhdr; 1023 m->m_len = hdrlen; 1024 1025 /* 1026 * Start the m_copy functions from the closest mbuf 1027 * to the offset in the socket buffer chain. 1028 */ 1029 mb = sbsndptr(&so->so_snd, off, len, &moff); 1030 1031 if (len <= MHLEN - hdrlen - max_linkhdr) { 1032 m_copydata(mb, moff, len, 1033 mtod(m, caddr_t) + hdrlen); 1034 m->m_len += len; 1035 } else { 1036 m->m_next = m_copym(mb, moff, len, M_NOWAIT); 1037 if (m->m_next == NULL) { 1038 SOCKBUF_UNLOCK(&so->so_snd); 1039 (void) m_free(m); 1040 error = ENOBUFS; 1041 sack_rxmit = 0; 1042 goto out; 1043 } 1044 } 1045 1046 /* 1047 * If we're sending everything we've got, set PUSH. 1048 * (This will keep happy those implementations which only 1049 * give data to the user when a buffer fills or 1050 * a PUSH comes in.) 1051 */ 1052 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) && 1053 !(flags & TH_SYN)) 1054 flags |= TH_PUSH; 1055 SOCKBUF_UNLOCK(&so->so_snd); 1056 } else { 1057 SOCKBUF_UNLOCK(&so->so_snd); 1058 if (tp->t_flags & TF_ACKNOW) 1059 TCPSTAT_INC(tcps_sndacks); 1060 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 1061 TCPSTAT_INC(tcps_sndctrl); 1062 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 1063 TCPSTAT_INC(tcps_sndurg); 1064 else 1065 TCPSTAT_INC(tcps_sndwinup); 1066 1067 m = m_gethdr(M_NOWAIT, MT_DATA); 1068 if (m == NULL) { 1069 error = ENOBUFS; 1070 sack_rxmit = 0; 1071 goto out; 1072 } 1073 #ifdef INET6 1074 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) && 1075 MHLEN >= hdrlen) { 1076 M_ALIGN(m, hdrlen); 1077 } else 1078 #endif 1079 m->m_data += max_linkhdr; 1080 m->m_len = hdrlen; 1081 } 1082 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); 1083 m->m_pkthdr.rcvif = (struct ifnet *)0; 1084 #ifdef MAC 1085 mac_inpcb_create_mbuf(tp->t_inpcb, m); 1086 #endif 1087 #ifdef INET6 1088 if (isipv6) { 1089 ip6 = mtod(m, struct ip6_hdr *); 1090 th = (struct tcphdr *)(ip6 + 1); 1091 tcpip_fillheaders(tp->t_inpcb, ip6, th); 1092 } else 1093 #endif /* INET6 */ 1094 { 1095 ip = mtod(m, struct ip *); 1096 #ifdef TCPDEBUG 1097 ipov = (struct ipovly *)ip; 1098 #endif 1099 th = (struct tcphdr *)(ip + 1); 1100 tcpip_fillheaders(tp->t_inpcb, ip, th); 1101 } 1102 1103 /* 1104 * Fill in fields, remembering maximum advertised 1105 * window for use in delaying messages about window sizes. 1106 * If resending a FIN, be sure not to use a new sequence number. 1107 */ 1108 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 1109 tp->snd_nxt == tp->snd_max) 1110 tp->snd_nxt--; 1111 /* 1112 * If we are starting a connection, send ECN setup 1113 * SYN packet. If we are on a retransmit, we may 1114 * resend those bits a number of times as per 1115 * RFC 3168. 1116 */ 1117 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) { 1118 if (tp->t_rxtshift >= 1) { 1119 if (tp->t_rxtshift <= V_tcp_ecn_maxretries) 1120 flags |= TH_ECE|TH_CWR; 1121 } else 1122 flags |= TH_ECE|TH_CWR; 1123 } 1124 1125 if (tp->t_state == TCPS_ESTABLISHED && 1126 (tp->t_flags & TF_ECN_PERMIT)) { 1127 /* 1128 * If the peer has ECN, mark data packets with 1129 * ECN capable transmission (ECT). 1130 * Ignore pure ack packets, retransmissions and window probes. 1131 */ 1132 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) && 1133 !((tp->t_flags & TF_FORCEDATA) && len == 1)) { 1134 #ifdef INET6 1135 if (isipv6) 1136 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20); 1137 else 1138 #endif 1139 ip->ip_tos |= IPTOS_ECN_ECT0; 1140 TCPSTAT_INC(tcps_ecn_ect0); 1141 } 1142 1143 /* 1144 * Reply with proper ECN notifications. 1145 */ 1146 if (tp->t_flags & TF_ECN_SND_CWR) { 1147 flags |= TH_CWR; 1148 tp->t_flags &= ~TF_ECN_SND_CWR; 1149 } 1150 if (tp->t_flags & TF_ECN_SND_ECE) 1151 flags |= TH_ECE; 1152 } 1153 1154 /* 1155 * If we are doing retransmissions, then snd_nxt will 1156 * not reflect the first unsent octet. For ACK only 1157 * packets, we do not want the sequence number of the 1158 * retransmitted packet, we want the sequence number 1159 * of the next unsent octet. So, if there is no data 1160 * (and no SYN or FIN), use snd_max instead of snd_nxt 1161 * when filling in ti_seq. But if we are in persist 1162 * state, snd_max might reflect one byte beyond the 1163 * right edge of the window, so use snd_nxt in that 1164 * case, since we know we aren't doing a retransmission. 1165 * (retransmit and persist are mutually exclusive...) 1166 */ 1167 if (sack_rxmit == 0) { 1168 if (len || (flags & (TH_SYN|TH_FIN)) || 1169 tcp_timer_active(tp, TT_PERSIST)) 1170 th->th_seq = htonl(tp->snd_nxt); 1171 else 1172 th->th_seq = htonl(tp->snd_max); 1173 } else { 1174 th->th_seq = htonl(p->rxmit); 1175 p->rxmit += len; 1176 tp->sackhint.sack_bytes_rexmit += len; 1177 } 1178 th->th_ack = htonl(tp->rcv_nxt); 1179 if (optlen) { 1180 bcopy(opt, th + 1, optlen); 1181 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2; 1182 } 1183 th->th_flags = flags; 1184 /* 1185 * Calculate receive window. Don't shrink window, 1186 * but avoid silly window syndrome. 1187 */ 1188 if (recwin < (so->so_rcv.sb_hiwat / 4) && 1189 recwin < tp->t_maxseg) 1190 recwin = 0; 1191 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) && 1192 recwin < (tp->rcv_adv - tp->rcv_nxt)) 1193 recwin = (tp->rcv_adv - tp->rcv_nxt); 1194 1195 /* 1196 * According to RFC1323 the window field in a SYN (i.e., a <SYN> 1197 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK> 1198 * case is handled in syncache. 1199 */ 1200 if (flags & TH_SYN) 1201 th->th_win = htons((u_short) 1202 (min(sbspace(&so->so_rcv), TCP_MAXWIN))); 1203 else 1204 th->th_win = htons((u_short)(recwin >> tp->rcv_scale)); 1205 1206 /* 1207 * Adjust the RXWIN0SENT flag - indicate that we have advertised 1208 * a 0 window. This may cause the remote transmitter to stall. This 1209 * flag tells soreceive() to disable delayed acknowledgements when 1210 * draining the buffer. This can occur if the receiver is attempting 1211 * to read more data than can be buffered prior to transmitting on 1212 * the connection. 1213 */ 1214 if (th->th_win == 0) { 1215 tp->t_sndzerowin++; 1216 tp->t_flags |= TF_RXWIN0SENT; 1217 } else 1218 tp->t_flags &= ~TF_RXWIN0SENT; 1219 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 1220 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 1221 th->th_flags |= TH_URG; 1222 } else 1223 /* 1224 * If no urgent pointer to send, then we pull 1225 * the urgent pointer to the left edge of the send window 1226 * so that it doesn't drift into the send window on sequence 1227 * number wraparound. 1228 */ 1229 tp->snd_up = tp->snd_una; /* drag it along */ 1230 1231 /* 1232 * Put TCP length in extended header, and then 1233 * checksum extended header and data. 1234 */ 1235 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */ 1236 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1237 1238 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1239 if (to.to_flags & TOF_SIGNATURE) { 1240 /* 1241 * Calculate MD5 signature and put it into the place 1242 * determined before. 1243 * NOTE: since TCP options buffer doesn't point into 1244 * mbuf's data, calculate offset and use it. 1245 */ 1246 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th, 1247 (u_char *)(th + 1) + (to.to_signature - opt))) != 0) { 1248 /* 1249 * Do not send segment if the calculation of MD5 1250 * digest has failed. 1251 */ 1252 m_freem(m); 1253 goto out; 1254 } 1255 } 1256 #endif 1257 #ifdef INET6 1258 if (isipv6) { 1259 /* 1260 * There is no need to fill in ip6_plen right now. 1261 * It will be filled later by ip6_output. 1262 */ 1263 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1264 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) + 1265 optlen + len, IPPROTO_TCP, 0); 1266 } 1267 #endif 1268 #if defined(INET6) && defined(INET) 1269 else 1270 #endif 1271 #ifdef INET 1272 { 1273 m->m_pkthdr.csum_flags = CSUM_TCP; 1274 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1275 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen)); 1276 1277 /* IP version must be set here for ipv4/ipv6 checking later */ 1278 KASSERT(ip->ip_v == IPVERSION, 1279 ("%s: IP version incorrect: %d", __func__, ip->ip_v)); 1280 } 1281 #endif 1282 1283 /* 1284 * Enable TSO and specify the size of the segments. 1285 * The TCP pseudo header checksum is always provided. 1286 */ 1287 if (tso) { 1288 KASSERT(len > tp->t_maxseg - optlen, 1289 ("%s: len <= tso_segsz", __func__)); 1290 m->m_pkthdr.csum_flags |= CSUM_TSO; 1291 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen; 1292 } 1293 1294 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 1295 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL), 1296 ("%s: mbuf chain shorter than expected: %d + %u + %u - %u != %u", 1297 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL))); 1298 #else 1299 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL), 1300 ("%s: mbuf chain shorter than expected: %d + %u + %u != %u", 1301 __func__, len, hdrlen, ipoptlen, m_length(m, NULL))); 1302 #endif 1303 1304 #ifdef TCP_HHOOK 1305 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */ 1306 hhook_run_tcp_est_out(tp, th, &to, len, tso); 1307 #endif 1308 1309 #ifdef TCPDEBUG 1310 /* 1311 * Trace. 1312 */ 1313 if (so->so_options & SO_DEBUG) { 1314 u_short save = 0; 1315 #ifdef INET6 1316 if (!isipv6) 1317 #endif 1318 { 1319 save = ipov->ih_len; 1320 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */); 1321 } 1322 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0); 1323 #ifdef INET6 1324 if (!isipv6) 1325 #endif 1326 ipov->ih_len = save; 1327 } 1328 #endif /* TCPDEBUG */ 1329 TCP_PROBE3(debug__output, tp, th, m); 1330 1331 /* 1332 * Fill in IP length and desired time to live and 1333 * send to IP level. There should be a better way 1334 * to handle ttl and tos; we could keep them in 1335 * the template, but need a way to checksum without them. 1336 */ 1337 /* 1338 * m->m_pkthdr.len should have been set before checksum calculation, 1339 * because in6_cksum() need it. 1340 */ 1341 #ifdef INET6 1342 if (isipv6) { 1343 /* 1344 * we separately set hoplimit for every segment, since the 1345 * user might want to change the value via setsockopt. 1346 * Also, desired default hop limit might be changed via 1347 * Neighbor Discovery. 1348 */ 1349 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL); 1350 1351 /* 1352 * Set the packet size here for the benefit of DTrace probes. 1353 * ip6_output() will set it properly; it's supposed to include 1354 * the option header lengths as well. 1355 */ 1356 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6)); 1357 1358 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) 1359 tp->t_flags2 |= TF2_PLPMTU_PMTUD; 1360 else 1361 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; 1362 1363 if (tp->t_state == TCPS_SYN_SENT) 1364 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th); 1365 1366 TCP_PROBE5(send, NULL, tp, ip6, tp, th); 1367 1368 #ifdef TCPPCAP 1369 /* Save packet, if requested. */ 1370 tcp_pcap_add(th, m, &(tp->t_outpkts)); 1371 #endif 1372 1373 /* TODO: IPv6 IP6TOS_ECT bit on */ 1374 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, 1375 &tp->t_inpcb->inp_route6, 1376 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 1377 NULL, NULL, tp->t_inpcb); 1378 1379 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_rt != NULL) 1380 mtu = tp->t_inpcb->inp_route6.ro_rt->rt_mtu; 1381 } 1382 #endif /* INET6 */ 1383 #if defined(INET) && defined(INET6) 1384 else 1385 #endif 1386 #ifdef INET 1387 { 1388 ip->ip_len = htons(m->m_pkthdr.len); 1389 #ifdef INET6 1390 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO) 1391 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL); 1392 #endif /* INET6 */ 1393 /* 1394 * If we do path MTU discovery, then we set DF on every packet. 1395 * This might not be the best thing to do according to RFC3390 1396 * Section 2. However the tcp hostcache migitates the problem 1397 * so it affects only the first tcp connection with a host. 1398 * 1399 * NB: Don't set DF on small MTU/MSS to have a safe fallback. 1400 */ 1401 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) { 1402 ip->ip_off |= htons(IP_DF); 1403 tp->t_flags2 |= TF2_PLPMTU_PMTUD; 1404 } else { 1405 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; 1406 } 1407 1408 if (tp->t_state == TCPS_SYN_SENT) 1409 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th); 1410 1411 TCP_PROBE5(send, NULL, tp, ip, tp, th); 1412 1413 #ifdef TCPPCAP 1414 /* Save packet, if requested. */ 1415 tcp_pcap_add(th, m, &(tp->t_outpkts)); 1416 #endif 1417 1418 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, 1419 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, 1420 tp->t_inpcb); 1421 1422 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL) 1423 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu; 1424 } 1425 #endif /* INET */ 1426 1427 out: 1428 /* 1429 * In transmit state, time the transmission and arrange for 1430 * the retransmit. In persist state, just set snd_max. 1431 */ 1432 if ((tp->t_flags & TF_FORCEDATA) == 0 || 1433 !tcp_timer_active(tp, TT_PERSIST)) { 1434 tcp_seq startseq = tp->snd_nxt; 1435 1436 /* 1437 * Advance snd_nxt over sequence space of this segment. 1438 */ 1439 if (flags & (TH_SYN|TH_FIN)) { 1440 if (flags & TH_SYN) 1441 tp->snd_nxt++; 1442 if (flags & TH_FIN) { 1443 tp->snd_nxt++; 1444 tp->t_flags |= TF_SENTFIN; 1445 } 1446 } 1447 if (sack_rxmit) 1448 goto timer; 1449 tp->snd_nxt += len; 1450 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 1451 tp->snd_max = tp->snd_nxt; 1452 /* 1453 * Time this transmission if not a retransmission and 1454 * not currently timing anything. 1455 */ 1456 if (tp->t_rtttime == 0) { 1457 tp->t_rtttime = ticks; 1458 tp->t_rtseq = startseq; 1459 TCPSTAT_INC(tcps_segstimed); 1460 } 1461 } 1462 1463 /* 1464 * Set retransmit timer if not currently set, 1465 * and not doing a pure ack or a keep-alive probe. 1466 * Initial value for retransmit timer is smoothed 1467 * round-trip time + 2 * round-trip time variance. 1468 * Initialize shift counter which is used for backoff 1469 * of retransmit time. 1470 */ 1471 timer: 1472 if (!tcp_timer_active(tp, TT_REXMT) && 1473 ((sack_rxmit && tp->snd_nxt != tp->snd_max) || 1474 (tp->snd_nxt != tp->snd_una))) { 1475 if (tcp_timer_active(tp, TT_PERSIST)) { 1476 tcp_timer_activate(tp, TT_PERSIST, 0); 1477 tp->t_rxtshift = 0; 1478 } 1479 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); 1480 } else if (len == 0 && sbavail(&so->so_snd) && 1481 !tcp_timer_active(tp, TT_REXMT) && 1482 !tcp_timer_active(tp, TT_PERSIST)) { 1483 /* 1484 * Avoid a situation where we do not set persist timer 1485 * after a zero window condition. For example: 1486 * 1) A -> B: packet with enough data to fill the window 1487 * 2) B -> A: ACK for #1 + new data (0 window 1488 * advertisement) 1489 * 3) A -> B: ACK for #2, 0 len packet 1490 * 1491 * In this case, A will not activate the persist timer, 1492 * because it chose to send a packet. Unless tcp_output 1493 * is called for some other reason (delayed ack timer, 1494 * another input packet from B, socket syscall), A will 1495 * not send zero window probes. 1496 * 1497 * So, if you send a 0-length packet, but there is data 1498 * in the socket buffer, and neither the rexmt or 1499 * persist timer is already set, then activate the 1500 * persist timer. 1501 */ 1502 tp->t_rxtshift = 0; 1503 tcp_setpersist(tp); 1504 } 1505 } else { 1506 /* 1507 * Persist case, update snd_max but since we are in 1508 * persist mode (no window) we do not update snd_nxt. 1509 */ 1510 int xlen = len; 1511 if (flags & TH_SYN) 1512 ++xlen; 1513 if (flags & TH_FIN) { 1514 ++xlen; 1515 tp->t_flags |= TF_SENTFIN; 1516 } 1517 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max)) 1518 tp->snd_max = tp->snd_nxt + xlen; 1519 } 1520 1521 if (error) { 1522 1523 /* 1524 * We know that the packet was lost, so back out the 1525 * sequence number advance, if any. 1526 * 1527 * If the error is EPERM the packet got blocked by the 1528 * local firewall. Normally we should terminate the 1529 * connection but the blocking may have been spurious 1530 * due to a firewall reconfiguration cycle. So we treat 1531 * it like a packet loss and let the retransmit timer and 1532 * timeouts do their work over time. 1533 * XXX: It is a POLA question whether calling tcp_drop right 1534 * away would be the really correct behavior instead. 1535 */ 1536 if (((tp->t_flags & TF_FORCEDATA) == 0 || 1537 !tcp_timer_active(tp, TT_PERSIST)) && 1538 ((flags & TH_SYN) == 0) && 1539 (error != EPERM)) { 1540 if (sack_rxmit) { 1541 p->rxmit -= len; 1542 tp->sackhint.sack_bytes_rexmit -= len; 1543 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0, 1544 ("sackhint bytes rtx >= 0")); 1545 } else 1546 tp->snd_nxt -= len; 1547 } 1548 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */ 1549 switch (error) { 1550 case EACCES: 1551 tp->t_softerror = error; 1552 return (0); 1553 case EPERM: 1554 tp->t_softerror = error; 1555 return (error); 1556 case ENOBUFS: 1557 TCP_XMIT_TIMER_ASSERT(tp, len, flags); 1558 tp->snd_cwnd = tp->t_maxseg; 1559 return (0); 1560 case EMSGSIZE: 1561 /* 1562 * For some reason the interface we used initially 1563 * to send segments changed to another or lowered 1564 * its MTU. 1565 * If TSO was active we either got an interface 1566 * without TSO capabilits or TSO was turned off. 1567 * If we obtained mtu from ip_output() then update 1568 * it and try again. 1569 */ 1570 if (tso) 1571 tp->t_flags &= ~TF_TSO; 1572 if (mtu != 0) { 1573 tcp_mss_update(tp, -1, mtu, NULL, NULL); 1574 goto again; 1575 } 1576 return (error); 1577 case EHOSTDOWN: 1578 case EHOSTUNREACH: 1579 case ENETDOWN: 1580 case ENETUNREACH: 1581 if (TCPS_HAVERCVDSYN(tp->t_state)) { 1582 tp->t_softerror = error; 1583 return (0); 1584 } 1585 /* FALLTHROUGH */ 1586 default: 1587 return (error); 1588 } 1589 } 1590 TCPSTAT_INC(tcps_sndtotal); 1591 1592 /* 1593 * Data sent (as far as we can tell). 1594 * If this advertises a larger window than any other segment, 1595 * then remember the size of the advertised window. 1596 * Any pending ACK has now been sent. 1597 */ 1598 if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv)) 1599 tp->rcv_adv = tp->rcv_nxt + recwin; 1600 tp->last_ack_sent = tp->rcv_nxt; 1601 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK); 1602 if (tcp_timer_active(tp, TT_DELACK)) 1603 tcp_timer_activate(tp, TT_DELACK, 0); 1604 #if 0 1605 /* 1606 * This completely breaks TCP if newreno is turned on. What happens 1607 * is that if delayed-acks are turned on on the receiver, this code 1608 * on the transmitter effectively destroys the TCP window, forcing 1609 * it to four packets (1.5Kx4 = 6K window). 1610 */ 1611 if (sendalot && --maxburst) 1612 goto again; 1613 #endif 1614 if (sendalot) 1615 goto again; 1616 return (0); 1617 } 1618 1619 void 1620 tcp_setpersist(struct tcpcb *tp) 1621 { 1622 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 1623 int tt; 1624 1625 tp->t_flags &= ~TF_PREVVALID; 1626 if (tcp_timer_active(tp, TT_REXMT)) 1627 panic("tcp_setpersist: retransmit pending"); 1628 /* 1629 * Start/restart persistence timer. 1630 */ 1631 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], 1632 tcp_persmin, tcp_persmax); 1633 tcp_timer_activate(tp, TT_PERSIST, tt); 1634 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 1635 tp->t_rxtshift++; 1636 } 1637 1638 /* 1639 * Insert TCP options according to the supplied parameters to the place 1640 * optp in a consistent way. Can handle unaligned destinations. 1641 * 1642 * The order of the option processing is crucial for optimal packing and 1643 * alignment for the scarce option space. 1644 * 1645 * The optimal order for a SYN/SYN-ACK segment is: 1646 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) + 1647 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40. 1648 * 1649 * The SACK options should be last. SACK blocks consume 8*n+2 bytes. 1650 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks). 1651 * At minimum we need 10 bytes (to generate 1 SACK block). If both 1652 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present, 1653 * we only have 10 bytes for SACK options (40 - (12 + 18)). 1654 */ 1655 int 1656 tcp_addoptions(struct tcpopt *to, u_char *optp) 1657 { 1658 u_int32_t mask, optlen = 0; 1659 1660 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) { 1661 if ((to->to_flags & mask) != mask) 1662 continue; 1663 if (optlen == TCP_MAXOLEN) 1664 break; 1665 switch (to->to_flags & mask) { 1666 case TOF_MSS: 1667 while (optlen % 4) { 1668 optlen += TCPOLEN_NOP; 1669 *optp++ = TCPOPT_NOP; 1670 } 1671 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG) 1672 continue; 1673 optlen += TCPOLEN_MAXSEG; 1674 *optp++ = TCPOPT_MAXSEG; 1675 *optp++ = TCPOLEN_MAXSEG; 1676 to->to_mss = htons(to->to_mss); 1677 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss)); 1678 optp += sizeof(to->to_mss); 1679 break; 1680 case TOF_SCALE: 1681 while (!optlen || optlen % 2 != 1) { 1682 optlen += TCPOLEN_NOP; 1683 *optp++ = TCPOPT_NOP; 1684 } 1685 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW) 1686 continue; 1687 optlen += TCPOLEN_WINDOW; 1688 *optp++ = TCPOPT_WINDOW; 1689 *optp++ = TCPOLEN_WINDOW; 1690 *optp++ = to->to_wscale; 1691 break; 1692 case TOF_SACKPERM: 1693 while (optlen % 2) { 1694 optlen += TCPOLEN_NOP; 1695 *optp++ = TCPOPT_NOP; 1696 } 1697 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED) 1698 continue; 1699 optlen += TCPOLEN_SACK_PERMITTED; 1700 *optp++ = TCPOPT_SACK_PERMITTED; 1701 *optp++ = TCPOLEN_SACK_PERMITTED; 1702 break; 1703 case TOF_TS: 1704 while (!optlen || optlen % 4 != 2) { 1705 optlen += TCPOLEN_NOP; 1706 *optp++ = TCPOPT_NOP; 1707 } 1708 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP) 1709 continue; 1710 optlen += TCPOLEN_TIMESTAMP; 1711 *optp++ = TCPOPT_TIMESTAMP; 1712 *optp++ = TCPOLEN_TIMESTAMP; 1713 to->to_tsval = htonl(to->to_tsval); 1714 to->to_tsecr = htonl(to->to_tsecr); 1715 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval)); 1716 optp += sizeof(to->to_tsval); 1717 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr)); 1718 optp += sizeof(to->to_tsecr); 1719 break; 1720 case TOF_SIGNATURE: 1721 { 1722 int siglen = TCPOLEN_SIGNATURE - 2; 1723 1724 while (!optlen || optlen % 4 != 2) { 1725 optlen += TCPOLEN_NOP; 1726 *optp++ = TCPOPT_NOP; 1727 } 1728 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) { 1729 to->to_flags &= ~TOF_SIGNATURE; 1730 continue; 1731 } 1732 optlen += TCPOLEN_SIGNATURE; 1733 *optp++ = TCPOPT_SIGNATURE; 1734 *optp++ = TCPOLEN_SIGNATURE; 1735 to->to_signature = optp; 1736 while (siglen--) 1737 *optp++ = 0; 1738 break; 1739 } 1740 case TOF_SACK: 1741 { 1742 int sackblks = 0; 1743 struct sackblk *sack = (struct sackblk *)to->to_sacks; 1744 tcp_seq sack_seq; 1745 1746 while (!optlen || optlen % 4 != 2) { 1747 optlen += TCPOLEN_NOP; 1748 *optp++ = TCPOPT_NOP; 1749 } 1750 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK) 1751 continue; 1752 optlen += TCPOLEN_SACKHDR; 1753 *optp++ = TCPOPT_SACK; 1754 sackblks = min(to->to_nsacks, 1755 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK); 1756 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK; 1757 while (sackblks--) { 1758 sack_seq = htonl(sack->start); 1759 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq)); 1760 optp += sizeof(sack_seq); 1761 sack_seq = htonl(sack->end); 1762 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq)); 1763 optp += sizeof(sack_seq); 1764 optlen += TCPOLEN_SACK; 1765 sack++; 1766 } 1767 TCPSTAT_INC(tcps_sack_send_blocks); 1768 break; 1769 } 1770 #ifdef TCP_RFC7413 1771 case TOF_FASTOPEN: 1772 { 1773 int total_len; 1774 1775 /* XXX is there any point to aligning this option? */ 1776 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len; 1777 if (TCP_MAXOLEN - optlen < total_len) 1778 continue; 1779 *optp++ = TCPOPT_FAST_OPEN; 1780 *optp++ = total_len; 1781 if (to->to_tfo_len > 0) { 1782 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len); 1783 optp += to->to_tfo_len; 1784 } 1785 optlen += total_len; 1786 break; 1787 } 1788 #endif 1789 default: 1790 panic("%s: unknown TCP option type", __func__); 1791 break; 1792 } 1793 } 1794 1795 /* Terminate and pad TCP options to a 4 byte boundary. */ 1796 if (optlen % 4) { 1797 optlen += TCPOLEN_EOL; 1798 *optp++ = TCPOPT_EOL; 1799 } 1800 /* 1801 * According to RFC 793 (STD0007): 1802 * "The content of the header beyond the End-of-Option option 1803 * must be header padding (i.e., zero)." 1804 * and later: "The padding is composed of zeros." 1805 */ 1806 while (optlen % 4) { 1807 optlen += TCPOLEN_PAD; 1808 *optp++ = TCPOPT_PAD; 1809 } 1810 1811 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__)); 1812 return (optlen); 1813 } 1814 1815 void 1816 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin) 1817 { 1818 1819 /* 1820 * Automatic sizing of send socket buffer. Often the send buffer 1821 * size is not optimally adjusted to the actual network conditions 1822 * at hand (delay bandwidth product). Setting the buffer size too 1823 * small limits throughput on links with high bandwidth and high 1824 * delay (eg. trans-continental/oceanic links). Setting the 1825 * buffer size too big consumes too much real kernel memory, 1826 * especially with many connections on busy servers. 1827 * 1828 * The criteria to step up the send buffer one notch are: 1829 * 1. receive window of remote host is larger than send buffer 1830 * (with a fudge factor of 5/4th); 1831 * 2. send buffer is filled to 7/8th with data (so we actually 1832 * have data to make use of it); 1833 * 3. send buffer fill has not hit maximal automatic size; 1834 * 4. our send window (slow start and cogestion controlled) is 1835 * larger than sent but unacknowledged data in send buffer. 1836 * 1837 * The remote host receive window scaling factor may limit the 1838 * growing of the send buffer before it reaches its allowed 1839 * maximum. 1840 * 1841 * It scales directly with slow start or congestion window 1842 * and does at most one step per received ACK. This fast 1843 * scaling has the drawback of growing the send buffer beyond 1844 * what is strictly necessary to make full use of a given 1845 * delay*bandwidth product. However testing has shown this not 1846 * to be much of an problem. At worst we are trading wasting 1847 * of available bandwidth (the non-use of it) for wasting some 1848 * socket buffer memory. 1849 * 1850 * TODO: Shrink send buffer during idle periods together 1851 * with congestion window. Requires another timer. Has to 1852 * wait for upcoming tcp timer rewrite. 1853 * 1854 * XXXGL: should there be used sbused() or sbavail()? 1855 */ 1856 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) { 1857 int lowat; 1858 1859 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0; 1860 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat && 1861 sbused(&so->so_snd) >= 1862 (so->so_snd.sb_hiwat / 8 * 7) - lowat && 1863 sbused(&so->so_snd) < V_tcp_autosndbuf_max && 1864 sendwin >= (sbused(&so->so_snd) - 1865 (tp->snd_nxt - tp->snd_una))) { 1866 if (!sbreserve_locked(&so->so_snd, 1867 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc, 1868 V_tcp_autosndbuf_max), so, curthread)) 1869 so->so_snd.sb_flags &= ~SB_AUTOSIZE; 1870 } 1871 } 1872 } 1873