1 /* 2 * INET An implementation of the TCP/IP protocol suite for the LINUX 3 * operating system. INET is implemented using the BSD Socket 4 * interface as the means of communication with the user level. 5 * 6 * Implementation of the Transmission Control Protocol(TCP). 7 * 8 * Authors: Ross Biro 9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 10 * Mark Evans, <evansmp@uhura.aston.ac.uk> 11 * Corey Minyard <wf-rch!minyard@relay.EU.net> 12 * Florian La Roche, <flla@stud.uni-sb.de> 13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 14 * Linus Torvalds, <torvalds@cs.helsinki.fi> 15 * Alan Cox, <gw4pts@gw4pts.ampr.org> 16 * Matthew Dillon, <dillon@apollo.west.oic.com> 17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 18 * Jorge Cwik, <jorge@laser.satlink.net> 19 */ 20 21 /* 22 * Changes: Pedro Roque : Retransmit queue handled by TCP. 23 * : Fragmentation on mtu decrease 24 * : Segment collapse on retransmit 25 * : AF independence 26 * 27 * Linus Torvalds : send_delayed_ack 28 * David S. Miller : Charge memory using the right skb 29 * during syn/ack processing. 30 * David S. Miller : Output engine completely rewritten. 31 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr. 32 * Cacophonix Gaul : draft-minshall-nagle-01 33 * J Hadi Salim : ECN support 34 * 35 */ 36 37 #define pr_fmt(fmt) "TCP: " fmt 38 39 #include <net/tcp.h> 40 41 #include <linux/compiler.h> 42 #include <linux/gfp.h> 43 #include <linux/module.h> 44 45 /* People can turn this off for buggy TCP's found in printers etc. */ 46 int sysctl_tcp_retrans_collapse __read_mostly = 1; 47 48 /* People can turn this on to work with those rare, broken TCPs that 49 * interpret the window field as a signed quantity. 50 */ 51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0; 52 53 /* Default TSQ limit of two TSO segments */ 54 int sysctl_tcp_limit_output_bytes __read_mostly = 131072; 55 56 /* This limits the percentage of the congestion window which we 57 * will allow a single TSO frame to consume. Building TSO frames 58 * which are too large can cause TCP streams to be bursty. 59 */ 60 int sysctl_tcp_tso_win_divisor __read_mostly = 3; 61 62 /* By default, RFC2861 behavior. */ 63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1; 64 65 unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX; 66 EXPORT_SYMBOL(sysctl_tcp_notsent_lowat); 67 68 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, 69 int push_one, gfp_t gfp); 70 71 /* Account for new data that has been sent to the network. */ 72 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb) 73 { 74 struct inet_connection_sock *icsk = inet_csk(sk); 75 struct tcp_sock *tp = tcp_sk(sk); 76 unsigned int prior_packets = tp->packets_out; 77 78 tcp_advance_send_head(sk, skb); 79 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq; 80 81 tp->packets_out += tcp_skb_pcount(skb); 82 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS || 83 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) { 84 tcp_rearm_rto(sk); 85 } 86 87 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT, 88 tcp_skb_pcount(skb)); 89 } 90 91 /* SND.NXT, if window was not shrunk. 92 * If window has been shrunk, what should we make? It is not clear at all. 93 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( 94 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already 95 * invalid. OK, let's make this for now: 96 */ 97 static inline __u32 tcp_acceptable_seq(const struct sock *sk) 98 { 99 const struct tcp_sock *tp = tcp_sk(sk); 100 101 if (!before(tcp_wnd_end(tp), tp->snd_nxt)) 102 return tp->snd_nxt; 103 else 104 return tcp_wnd_end(tp); 105 } 106 107 /* Calculate mss to advertise in SYN segment. 108 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that: 109 * 110 * 1. It is independent of path mtu. 111 * 2. Ideally, it is maximal possible segment size i.e. 65535-40. 112 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of 113 * attached devices, because some buggy hosts are confused by 114 * large MSS. 115 * 4. We do not make 3, we advertise MSS, calculated from first 116 * hop device mtu, but allow to raise it to ip_rt_min_advmss. 117 * This may be overridden via information stored in routing table. 118 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible, 119 * probably even Jumbo". 120 */ 121 static __u16 tcp_advertise_mss(struct sock *sk) 122 { 123 struct tcp_sock *tp = tcp_sk(sk); 124 const struct dst_entry *dst = __sk_dst_get(sk); 125 int mss = tp->advmss; 126 127 if (dst) { 128 unsigned int metric = dst_metric_advmss(dst); 129 130 if (metric < mss) { 131 mss = metric; 132 tp->advmss = mss; 133 } 134 } 135 136 return (__u16)mss; 137 } 138 139 /* RFC2861. Reset CWND after idle period longer RTO to "restart window". 140 * This is the first part of cwnd validation mechanism. */ 141 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst) 142 { 143 struct tcp_sock *tp = tcp_sk(sk); 144 s32 delta = tcp_time_stamp - tp->lsndtime; 145 u32 restart_cwnd = tcp_init_cwnd(tp, dst); 146 u32 cwnd = tp->snd_cwnd; 147 148 tcp_ca_event(sk, CA_EVENT_CWND_RESTART); 149 150 tp->snd_ssthresh = tcp_current_ssthresh(sk); 151 restart_cwnd = min(restart_cwnd, cwnd); 152 153 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd) 154 cwnd >>= 1; 155 tp->snd_cwnd = max(cwnd, restart_cwnd); 156 tp->snd_cwnd_stamp = tcp_time_stamp; 157 tp->snd_cwnd_used = 0; 158 } 159 160 /* Congestion state accounting after a packet has been sent. */ 161 static void tcp_event_data_sent(struct tcp_sock *tp, 162 struct sock *sk) 163 { 164 struct inet_connection_sock *icsk = inet_csk(sk); 165 const u32 now = tcp_time_stamp; 166 const struct dst_entry *dst = __sk_dst_get(sk); 167 168 if (sysctl_tcp_slow_start_after_idle && 169 (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto)) 170 tcp_cwnd_restart(sk, __sk_dst_get(sk)); 171 172 tp->lsndtime = now; 173 174 /* If it is a reply for ato after last received 175 * packet, enter pingpong mode. 176 */ 177 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato && 178 (!dst || !dst_metric(dst, RTAX_QUICKACK))) 179 icsk->icsk_ack.pingpong = 1; 180 } 181 182 /* Account for an ACK we sent. */ 183 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts) 184 { 185 tcp_dec_quickack_mode(sk, pkts); 186 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); 187 } 188 189 190 u32 tcp_default_init_rwnd(u32 mss) 191 { 192 /* Initial receive window should be twice of TCP_INIT_CWND to 193 * enable proper sending of new unsent data during fast recovery 194 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a 195 * limit when mss is larger than 1460. 196 */ 197 u32 init_rwnd = TCP_INIT_CWND * 2; 198 199 if (mss > 1460) 200 init_rwnd = max((1460 * init_rwnd) / mss, 2U); 201 return init_rwnd; 202 } 203 204 /* Determine a window scaling and initial window to offer. 205 * Based on the assumption that the given amount of space 206 * will be offered. Store the results in the tp structure. 207 * NOTE: for smooth operation initial space offering should 208 * be a multiple of mss if possible. We assume here that mss >= 1. 209 * This MUST be enforced by all callers. 210 */ 211 void tcp_select_initial_window(int __space, __u32 mss, 212 __u32 *rcv_wnd, __u32 *window_clamp, 213 int wscale_ok, __u8 *rcv_wscale, 214 __u32 init_rcv_wnd) 215 { 216 unsigned int space = (__space < 0 ? 0 : __space); 217 218 /* If no clamp set the clamp to the max possible scaled window */ 219 if (*window_clamp == 0) 220 (*window_clamp) = (65535 << 14); 221 space = min(*window_clamp, space); 222 223 /* Quantize space offering to a multiple of mss if possible. */ 224 if (space > mss) 225 space = (space / mss) * mss; 226 227 /* NOTE: offering an initial window larger than 32767 228 * will break some buggy TCP stacks. If the admin tells us 229 * it is likely we could be speaking with such a buggy stack 230 * we will truncate our initial window offering to 32K-1 231 * unless the remote has sent us a window scaling option, 232 * which we interpret as a sign the remote TCP is not 233 * misinterpreting the window field as a signed quantity. 234 */ 235 if (sysctl_tcp_workaround_signed_windows) 236 (*rcv_wnd) = min(space, MAX_TCP_WINDOW); 237 else 238 (*rcv_wnd) = space; 239 240 (*rcv_wscale) = 0; 241 if (wscale_ok) { 242 /* Set window scaling on max possible window 243 * See RFC1323 for an explanation of the limit to 14 244 */ 245 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max); 246 space = min_t(u32, space, *window_clamp); 247 while (space > 65535 && (*rcv_wscale) < 14) { 248 space >>= 1; 249 (*rcv_wscale)++; 250 } 251 } 252 253 if (mss > (1 << *rcv_wscale)) { 254 if (!init_rcv_wnd) /* Use default unless specified otherwise */ 255 init_rcv_wnd = tcp_default_init_rwnd(mss); 256 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss); 257 } 258 259 /* Set the clamp no higher than max representable value */ 260 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp); 261 } 262 EXPORT_SYMBOL(tcp_select_initial_window); 263 264 /* Chose a new window to advertise, update state in tcp_sock for the 265 * socket, and return result with RFC1323 scaling applied. The return 266 * value can be stuffed directly into th->window for an outgoing 267 * frame. 268 */ 269 static u16 tcp_select_window(struct sock *sk) 270 { 271 struct tcp_sock *tp = tcp_sk(sk); 272 u32 old_win = tp->rcv_wnd; 273 u32 cur_win = tcp_receive_window(tp); 274 u32 new_win = __tcp_select_window(sk); 275 276 /* Never shrink the offered window */ 277 if (new_win < cur_win) { 278 /* Danger Will Robinson! 279 * Don't update rcv_wup/rcv_wnd here or else 280 * we will not be able to advertise a zero 281 * window in time. --DaveM 282 * 283 * Relax Will Robinson. 284 */ 285 if (new_win == 0) 286 NET_INC_STATS(sock_net(sk), 287 LINUX_MIB_TCPWANTZEROWINDOWADV); 288 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale); 289 } 290 tp->rcv_wnd = new_win; 291 tp->rcv_wup = tp->rcv_nxt; 292 293 /* Make sure we do not exceed the maximum possible 294 * scaled window. 295 */ 296 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows) 297 new_win = min(new_win, MAX_TCP_WINDOW); 298 else 299 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale)); 300 301 /* RFC1323 scaling applied */ 302 new_win >>= tp->rx_opt.rcv_wscale; 303 304 /* If we advertise zero window, disable fast path. */ 305 if (new_win == 0) { 306 tp->pred_flags = 0; 307 if (old_win) 308 NET_INC_STATS(sock_net(sk), 309 LINUX_MIB_TCPTOZEROWINDOWADV); 310 } else if (old_win == 0) { 311 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV); 312 } 313 314 return new_win; 315 } 316 317 /* Packet ECN state for a SYN-ACK */ 318 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb) 319 { 320 const struct tcp_sock *tp = tcp_sk(sk); 321 322 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR; 323 if (!(tp->ecn_flags & TCP_ECN_OK)) 324 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE; 325 else if (tcp_ca_needs_ecn(sk)) 326 INET_ECN_xmit(sk); 327 } 328 329 /* Packet ECN state for a SYN. */ 330 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb) 331 { 332 struct tcp_sock *tp = tcp_sk(sk); 333 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 || 334 tcp_ca_needs_ecn(sk); 335 336 if (!use_ecn) { 337 const struct dst_entry *dst = __sk_dst_get(sk); 338 339 if (dst && dst_feature(dst, RTAX_FEATURE_ECN)) 340 use_ecn = true; 341 } 342 343 tp->ecn_flags = 0; 344 345 if (use_ecn) { 346 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR; 347 tp->ecn_flags = TCP_ECN_OK; 348 if (tcp_ca_needs_ecn(sk)) 349 INET_ECN_xmit(sk); 350 } 351 } 352 353 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb) 354 { 355 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback) 356 /* tp->ecn_flags are cleared at a later point in time when 357 * SYN ACK is ultimatively being received. 358 */ 359 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR); 360 } 361 362 static void 363 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th, 364 struct sock *sk) 365 { 366 if (inet_rsk(req)->ecn_ok) { 367 th->ece = 1; 368 if (tcp_ca_needs_ecn(sk)) 369 INET_ECN_xmit(sk); 370 } 371 } 372 373 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to 374 * be sent. 375 */ 376 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb, 377 int tcp_header_len) 378 { 379 struct tcp_sock *tp = tcp_sk(sk); 380 381 if (tp->ecn_flags & TCP_ECN_OK) { 382 /* Not-retransmitted data segment: set ECT and inject CWR. */ 383 if (skb->len != tcp_header_len && 384 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) { 385 INET_ECN_xmit(sk); 386 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) { 387 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR; 388 tcp_hdr(skb)->cwr = 1; 389 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN; 390 } 391 } else if (!tcp_ca_needs_ecn(sk)) { 392 /* ACK or retransmitted segment: clear ECT|CE */ 393 INET_ECN_dontxmit(sk); 394 } 395 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR) 396 tcp_hdr(skb)->ece = 1; 397 } 398 } 399 400 /* Constructs common control bits of non-data skb. If SYN/FIN is present, 401 * auto increment end seqno. 402 */ 403 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags) 404 { 405 struct skb_shared_info *shinfo = skb_shinfo(skb); 406 407 skb->ip_summed = CHECKSUM_PARTIAL; 408 skb->csum = 0; 409 410 TCP_SKB_CB(skb)->tcp_flags = flags; 411 TCP_SKB_CB(skb)->sacked = 0; 412 413 tcp_skb_pcount_set(skb, 1); 414 shinfo->gso_size = 0; 415 shinfo->gso_type = 0; 416 417 TCP_SKB_CB(skb)->seq = seq; 418 if (flags & (TCPHDR_SYN | TCPHDR_FIN)) 419 seq++; 420 TCP_SKB_CB(skb)->end_seq = seq; 421 } 422 423 static inline bool tcp_urg_mode(const struct tcp_sock *tp) 424 { 425 return tp->snd_una != tp->snd_up; 426 } 427 428 #define OPTION_SACK_ADVERTISE (1 << 0) 429 #define OPTION_TS (1 << 1) 430 #define OPTION_MD5 (1 << 2) 431 #define OPTION_WSCALE (1 << 3) 432 #define OPTION_FAST_OPEN_COOKIE (1 << 8) 433 434 struct tcp_out_options { 435 u16 options; /* bit field of OPTION_* */ 436 u16 mss; /* 0 to disable */ 437 u8 ws; /* window scale, 0 to disable */ 438 u8 num_sack_blocks; /* number of SACK blocks to include */ 439 u8 hash_size; /* bytes in hash_location */ 440 __u8 *hash_location; /* temporary pointer, overloaded */ 441 __u32 tsval, tsecr; /* need to include OPTION_TS */ 442 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */ 443 }; 444 445 /* Write previously computed TCP options to the packet. 446 * 447 * Beware: Something in the Internet is very sensitive to the ordering of 448 * TCP options, we learned this through the hard way, so be careful here. 449 * Luckily we can at least blame others for their non-compliance but from 450 * inter-operability perspective it seems that we're somewhat stuck with 451 * the ordering which we have been using if we want to keep working with 452 * those broken things (not that it currently hurts anybody as there isn't 453 * particular reason why the ordering would need to be changed). 454 * 455 * At least SACK_PERM as the first option is known to lead to a disaster 456 * (but it may well be that other scenarios fail similarly). 457 */ 458 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp, 459 struct tcp_out_options *opts) 460 { 461 u16 options = opts->options; /* mungable copy */ 462 463 if (unlikely(OPTION_MD5 & options)) { 464 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | 465 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG); 466 /* overload cookie hash location */ 467 opts->hash_location = (__u8 *)ptr; 468 ptr += 4; 469 } 470 471 if (unlikely(opts->mss)) { 472 *ptr++ = htonl((TCPOPT_MSS << 24) | 473 (TCPOLEN_MSS << 16) | 474 opts->mss); 475 } 476 477 if (likely(OPTION_TS & options)) { 478 if (unlikely(OPTION_SACK_ADVERTISE & options)) { 479 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) | 480 (TCPOLEN_SACK_PERM << 16) | 481 (TCPOPT_TIMESTAMP << 8) | 482 TCPOLEN_TIMESTAMP); 483 options &= ~OPTION_SACK_ADVERTISE; 484 } else { 485 *ptr++ = htonl((TCPOPT_NOP << 24) | 486 (TCPOPT_NOP << 16) | 487 (TCPOPT_TIMESTAMP << 8) | 488 TCPOLEN_TIMESTAMP); 489 } 490 *ptr++ = htonl(opts->tsval); 491 *ptr++ = htonl(opts->tsecr); 492 } 493 494 if (unlikely(OPTION_SACK_ADVERTISE & options)) { 495 *ptr++ = htonl((TCPOPT_NOP << 24) | 496 (TCPOPT_NOP << 16) | 497 (TCPOPT_SACK_PERM << 8) | 498 TCPOLEN_SACK_PERM); 499 } 500 501 if (unlikely(OPTION_WSCALE & options)) { 502 *ptr++ = htonl((TCPOPT_NOP << 24) | 503 (TCPOPT_WINDOW << 16) | 504 (TCPOLEN_WINDOW << 8) | 505 opts->ws); 506 } 507 508 if (unlikely(opts->num_sack_blocks)) { 509 struct tcp_sack_block *sp = tp->rx_opt.dsack ? 510 tp->duplicate_sack : tp->selective_acks; 511 int this_sack; 512 513 *ptr++ = htonl((TCPOPT_NOP << 24) | 514 (TCPOPT_NOP << 16) | 515 (TCPOPT_SACK << 8) | 516 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks * 517 TCPOLEN_SACK_PERBLOCK))); 518 519 for (this_sack = 0; this_sack < opts->num_sack_blocks; 520 ++this_sack) { 521 *ptr++ = htonl(sp[this_sack].start_seq); 522 *ptr++ = htonl(sp[this_sack].end_seq); 523 } 524 525 tp->rx_opt.dsack = 0; 526 } 527 528 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) { 529 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie; 530 u8 *p = (u8 *)ptr; 531 u32 len; /* Fast Open option length */ 532 533 if (foc->exp) { 534 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len; 535 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) | 536 TCPOPT_FASTOPEN_MAGIC); 537 p += TCPOLEN_EXP_FASTOPEN_BASE; 538 } else { 539 len = TCPOLEN_FASTOPEN_BASE + foc->len; 540 *p++ = TCPOPT_FASTOPEN; 541 *p++ = len; 542 } 543 544 memcpy(p, foc->val, foc->len); 545 if ((len & 3) == 2) { 546 p[foc->len] = TCPOPT_NOP; 547 p[foc->len + 1] = TCPOPT_NOP; 548 } 549 ptr += (len + 3) >> 2; 550 } 551 } 552 553 /* Compute TCP options for SYN packets. This is not the final 554 * network wire format yet. 555 */ 556 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb, 557 struct tcp_out_options *opts, 558 struct tcp_md5sig_key **md5) 559 { 560 struct tcp_sock *tp = tcp_sk(sk); 561 unsigned int remaining = MAX_TCP_OPTION_SPACE; 562 struct tcp_fastopen_request *fastopen = tp->fastopen_req; 563 564 #ifdef CONFIG_TCP_MD5SIG 565 *md5 = tp->af_specific->md5_lookup(sk, sk); 566 if (*md5) { 567 opts->options |= OPTION_MD5; 568 remaining -= TCPOLEN_MD5SIG_ALIGNED; 569 } 570 #else 571 *md5 = NULL; 572 #endif 573 574 /* We always get an MSS option. The option bytes which will be seen in 575 * normal data packets should timestamps be used, must be in the MSS 576 * advertised. But we subtract them from tp->mss_cache so that 577 * calculations in tcp_sendmsg are simpler etc. So account for this 578 * fact here if necessary. If we don't do this correctly, as a 579 * receiver we won't recognize data packets as being full sized when we 580 * should, and thus we won't abide by the delayed ACK rules correctly. 581 * SACKs don't matter, we never delay an ACK when we have any of those 582 * going out. */ 583 opts->mss = tcp_advertise_mss(sk); 584 remaining -= TCPOLEN_MSS_ALIGNED; 585 586 if (likely(sysctl_tcp_timestamps && !*md5)) { 587 opts->options |= OPTION_TS; 588 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset; 589 opts->tsecr = tp->rx_opt.ts_recent; 590 remaining -= TCPOLEN_TSTAMP_ALIGNED; 591 } 592 if (likely(sysctl_tcp_window_scaling)) { 593 opts->ws = tp->rx_opt.rcv_wscale; 594 opts->options |= OPTION_WSCALE; 595 remaining -= TCPOLEN_WSCALE_ALIGNED; 596 } 597 if (likely(sysctl_tcp_sack)) { 598 opts->options |= OPTION_SACK_ADVERTISE; 599 if (unlikely(!(OPTION_TS & opts->options))) 600 remaining -= TCPOLEN_SACKPERM_ALIGNED; 601 } 602 603 if (fastopen && fastopen->cookie.len >= 0) { 604 u32 need = fastopen->cookie.len; 605 606 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE : 607 TCPOLEN_FASTOPEN_BASE; 608 need = (need + 3) & ~3U; /* Align to 32 bits */ 609 if (remaining >= need) { 610 opts->options |= OPTION_FAST_OPEN_COOKIE; 611 opts->fastopen_cookie = &fastopen->cookie; 612 remaining -= need; 613 tp->syn_fastopen = 1; 614 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0; 615 } 616 } 617 618 return MAX_TCP_OPTION_SPACE - remaining; 619 } 620 621 /* Set up TCP options for SYN-ACKs. */ 622 static unsigned int tcp_synack_options(struct sock *sk, 623 struct request_sock *req, 624 unsigned int mss, struct sk_buff *skb, 625 struct tcp_out_options *opts, 626 const struct tcp_md5sig_key *md5, 627 struct tcp_fastopen_cookie *foc) 628 { 629 struct inet_request_sock *ireq = inet_rsk(req); 630 unsigned int remaining = MAX_TCP_OPTION_SPACE; 631 632 #ifdef CONFIG_TCP_MD5SIG 633 if (md5) { 634 opts->options |= OPTION_MD5; 635 remaining -= TCPOLEN_MD5SIG_ALIGNED; 636 637 /* We can't fit any SACK blocks in a packet with MD5 + TS 638 * options. There was discussion about disabling SACK 639 * rather than TS in order to fit in better with old, 640 * buggy kernels, but that was deemed to be unnecessary. 641 */ 642 ireq->tstamp_ok &= !ireq->sack_ok; 643 } 644 #endif 645 646 /* We always send an MSS option. */ 647 opts->mss = mss; 648 remaining -= TCPOLEN_MSS_ALIGNED; 649 650 if (likely(ireq->wscale_ok)) { 651 opts->ws = ireq->rcv_wscale; 652 opts->options |= OPTION_WSCALE; 653 remaining -= TCPOLEN_WSCALE_ALIGNED; 654 } 655 if (likely(ireq->tstamp_ok)) { 656 opts->options |= OPTION_TS; 657 opts->tsval = tcp_skb_timestamp(skb); 658 opts->tsecr = req->ts_recent; 659 remaining -= TCPOLEN_TSTAMP_ALIGNED; 660 } 661 if (likely(ireq->sack_ok)) { 662 opts->options |= OPTION_SACK_ADVERTISE; 663 if (unlikely(!ireq->tstamp_ok)) 664 remaining -= TCPOLEN_SACKPERM_ALIGNED; 665 } 666 if (foc != NULL && foc->len >= 0) { 667 u32 need = foc->len; 668 669 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE : 670 TCPOLEN_FASTOPEN_BASE; 671 need = (need + 3) & ~3U; /* Align to 32 bits */ 672 if (remaining >= need) { 673 opts->options |= OPTION_FAST_OPEN_COOKIE; 674 opts->fastopen_cookie = foc; 675 remaining -= need; 676 } 677 } 678 679 return MAX_TCP_OPTION_SPACE - remaining; 680 } 681 682 /* Compute TCP options for ESTABLISHED sockets. This is not the 683 * final wire format yet. 684 */ 685 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb, 686 struct tcp_out_options *opts, 687 struct tcp_md5sig_key **md5) 688 { 689 struct tcp_sock *tp = tcp_sk(sk); 690 unsigned int size = 0; 691 unsigned int eff_sacks; 692 693 opts->options = 0; 694 695 #ifdef CONFIG_TCP_MD5SIG 696 *md5 = tp->af_specific->md5_lookup(sk, sk); 697 if (unlikely(*md5)) { 698 opts->options |= OPTION_MD5; 699 size += TCPOLEN_MD5SIG_ALIGNED; 700 } 701 #else 702 *md5 = NULL; 703 #endif 704 705 if (likely(tp->rx_opt.tstamp_ok)) { 706 opts->options |= OPTION_TS; 707 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0; 708 opts->tsecr = tp->rx_opt.ts_recent; 709 size += TCPOLEN_TSTAMP_ALIGNED; 710 } 711 712 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack; 713 if (unlikely(eff_sacks)) { 714 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size; 715 opts->num_sack_blocks = 716 min_t(unsigned int, eff_sacks, 717 (remaining - TCPOLEN_SACK_BASE_ALIGNED) / 718 TCPOLEN_SACK_PERBLOCK); 719 size += TCPOLEN_SACK_BASE_ALIGNED + 720 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK; 721 } 722 723 return size; 724 } 725 726 727 /* TCP SMALL QUEUES (TSQ) 728 * 729 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev) 730 * to reduce RTT and bufferbloat. 731 * We do this using a special skb destructor (tcp_wfree). 732 * 733 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb 734 * needs to be reallocated in a driver. 735 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc 736 * 737 * Since transmit from skb destructor is forbidden, we use a tasklet 738 * to process all sockets that eventually need to send more skbs. 739 * We use one tasklet per cpu, with its own queue of sockets. 740 */ 741 struct tsq_tasklet { 742 struct tasklet_struct tasklet; 743 struct list_head head; /* queue of tcp sockets */ 744 }; 745 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet); 746 747 static void tcp_tsq_handler(struct sock *sk) 748 { 749 if ((1 << sk->sk_state) & 750 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING | 751 TCPF_CLOSE_WAIT | TCPF_LAST_ACK)) 752 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle, 753 0, GFP_ATOMIC); 754 } 755 /* 756 * One tasklet per cpu tries to send more skbs. 757 * We run in tasklet context but need to disable irqs when 758 * transferring tsq->head because tcp_wfree() might 759 * interrupt us (non NAPI drivers) 760 */ 761 static void tcp_tasklet_func(unsigned long data) 762 { 763 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data; 764 LIST_HEAD(list); 765 unsigned long flags; 766 struct list_head *q, *n; 767 struct tcp_sock *tp; 768 struct sock *sk; 769 770 local_irq_save(flags); 771 list_splice_init(&tsq->head, &list); 772 local_irq_restore(flags); 773 774 list_for_each_safe(q, n, &list) { 775 tp = list_entry(q, struct tcp_sock, tsq_node); 776 list_del(&tp->tsq_node); 777 778 sk = (struct sock *)tp; 779 bh_lock_sock(sk); 780 781 if (!sock_owned_by_user(sk)) { 782 tcp_tsq_handler(sk); 783 } else { 784 /* defer the work to tcp_release_cb() */ 785 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags); 786 } 787 bh_unlock_sock(sk); 788 789 clear_bit(TSQ_QUEUED, &tp->tsq_flags); 790 sk_free(sk); 791 } 792 } 793 794 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \ 795 (1UL << TCP_WRITE_TIMER_DEFERRED) | \ 796 (1UL << TCP_DELACK_TIMER_DEFERRED) | \ 797 (1UL << TCP_MTU_REDUCED_DEFERRED)) 798 /** 799 * tcp_release_cb - tcp release_sock() callback 800 * @sk: socket 801 * 802 * called from release_sock() to perform protocol dependent 803 * actions before socket release. 804 */ 805 void tcp_release_cb(struct sock *sk) 806 { 807 struct tcp_sock *tp = tcp_sk(sk); 808 unsigned long flags, nflags; 809 810 /* perform an atomic operation only if at least one flag is set */ 811 do { 812 flags = tp->tsq_flags; 813 if (!(flags & TCP_DEFERRED_ALL)) 814 return; 815 nflags = flags & ~TCP_DEFERRED_ALL; 816 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags); 817 818 if (flags & (1UL << TCP_TSQ_DEFERRED)) 819 tcp_tsq_handler(sk); 820 821 /* Here begins the tricky part : 822 * We are called from release_sock() with : 823 * 1) BH disabled 824 * 2) sk_lock.slock spinlock held 825 * 3) socket owned by us (sk->sk_lock.owned == 1) 826 * 827 * But following code is meant to be called from BH handlers, 828 * so we should keep BH disabled, but early release socket ownership 829 */ 830 sock_release_ownership(sk); 831 832 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) { 833 tcp_write_timer_handler(sk); 834 __sock_put(sk); 835 } 836 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) { 837 tcp_delack_timer_handler(sk); 838 __sock_put(sk); 839 } 840 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) { 841 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk); 842 __sock_put(sk); 843 } 844 } 845 EXPORT_SYMBOL(tcp_release_cb); 846 847 void __init tcp_tasklet_init(void) 848 { 849 int i; 850 851 for_each_possible_cpu(i) { 852 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i); 853 854 INIT_LIST_HEAD(&tsq->head); 855 tasklet_init(&tsq->tasklet, 856 tcp_tasklet_func, 857 (unsigned long)tsq); 858 } 859 } 860 861 /* 862 * Write buffer destructor automatically called from kfree_skb. 863 * We can't xmit new skbs from this context, as we might already 864 * hold qdisc lock. 865 */ 866 void tcp_wfree(struct sk_buff *skb) 867 { 868 struct sock *sk = skb->sk; 869 struct tcp_sock *tp = tcp_sk(sk); 870 int wmem; 871 872 /* Keep one reference on sk_wmem_alloc. 873 * Will be released by sk_free() from here or tcp_tasklet_func() 874 */ 875 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc); 876 877 /* If this softirq is serviced by ksoftirqd, we are likely under stress. 878 * Wait until our queues (qdisc + devices) are drained. 879 * This gives : 880 * - less callbacks to tcp_write_xmit(), reducing stress (batches) 881 * - chance for incoming ACK (processed by another cpu maybe) 882 * to migrate this flow (skb->ooo_okay will be eventually set) 883 */ 884 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current) 885 goto out; 886 887 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) && 888 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) { 889 unsigned long flags; 890 struct tsq_tasklet *tsq; 891 892 /* queue this socket to tasklet queue */ 893 local_irq_save(flags); 894 tsq = this_cpu_ptr(&tsq_tasklet); 895 list_add(&tp->tsq_node, &tsq->head); 896 tasklet_schedule(&tsq->tasklet); 897 local_irq_restore(flags); 898 return; 899 } 900 out: 901 sk_free(sk); 902 } 903 904 /* This routine actually transmits TCP packets queued in by 905 * tcp_do_sendmsg(). This is used by both the initial 906 * transmission and possible later retransmissions. 907 * All SKB's seen here are completely headerless. It is our 908 * job to build the TCP header, and pass the packet down to 909 * IP so it can do the same plus pass the packet off to the 910 * device. 911 * 912 * We are working here with either a clone of the original 913 * SKB, or a fresh unique copy made by the retransmit engine. 914 */ 915 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, 916 gfp_t gfp_mask) 917 { 918 const struct inet_connection_sock *icsk = inet_csk(sk); 919 struct inet_sock *inet; 920 struct tcp_sock *tp; 921 struct tcp_skb_cb *tcb; 922 struct tcp_out_options opts; 923 unsigned int tcp_options_size, tcp_header_size; 924 struct tcp_md5sig_key *md5; 925 struct tcphdr *th; 926 int err; 927 928 BUG_ON(!skb || !tcp_skb_pcount(skb)); 929 930 if (clone_it) { 931 skb_mstamp_get(&skb->skb_mstamp); 932 933 if (unlikely(skb_cloned(skb))) 934 skb = pskb_copy(skb, gfp_mask); 935 else 936 skb = skb_clone(skb, gfp_mask); 937 if (unlikely(!skb)) 938 return -ENOBUFS; 939 } 940 941 inet = inet_sk(sk); 942 tp = tcp_sk(sk); 943 tcb = TCP_SKB_CB(skb); 944 memset(&opts, 0, sizeof(opts)); 945 946 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) 947 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5); 948 else 949 tcp_options_size = tcp_established_options(sk, skb, &opts, 950 &md5); 951 tcp_header_size = tcp_options_size + sizeof(struct tcphdr); 952 953 if (tcp_packets_in_flight(tp) == 0) 954 tcp_ca_event(sk, CA_EVENT_TX_START); 955 956 /* if no packet is in qdisc/device queue, then allow XPS to select 957 * another queue. We can be called from tcp_tsq_handler() 958 * which holds one reference to sk_wmem_alloc. 959 * 960 * TODO: Ideally, in-flight pure ACK packets should not matter here. 961 * One way to get this would be to set skb->truesize = 2 on them. 962 */ 963 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1); 964 965 skb_push(skb, tcp_header_size); 966 skb_reset_transport_header(skb); 967 968 skb_orphan(skb); 969 skb->sk = sk; 970 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree; 971 skb_set_hash_from_sk(skb, sk); 972 atomic_add(skb->truesize, &sk->sk_wmem_alloc); 973 974 /* Build TCP header and checksum it. */ 975 th = tcp_hdr(skb); 976 th->source = inet->inet_sport; 977 th->dest = inet->inet_dport; 978 th->seq = htonl(tcb->seq); 979 th->ack_seq = htonl(tp->rcv_nxt); 980 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | 981 tcb->tcp_flags); 982 983 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) { 984 /* RFC1323: The window in SYN & SYN/ACK segments 985 * is never scaled. 986 */ 987 th->window = htons(min(tp->rcv_wnd, 65535U)); 988 } else { 989 th->window = htons(tcp_select_window(sk)); 990 } 991 th->check = 0; 992 th->urg_ptr = 0; 993 994 /* The urg_mode check is necessary during a below snd_una win probe */ 995 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) { 996 if (before(tp->snd_up, tcb->seq + 0x10000)) { 997 th->urg_ptr = htons(tp->snd_up - tcb->seq); 998 th->urg = 1; 999 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) { 1000 th->urg_ptr = htons(0xFFFF); 1001 th->urg = 1; 1002 } 1003 } 1004 1005 tcp_options_write((__be32 *)(th + 1), tp, &opts); 1006 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0)) 1007 tcp_ecn_send(sk, skb, tcp_header_size); 1008 1009 #ifdef CONFIG_TCP_MD5SIG 1010 /* Calculate the MD5 hash, as we have all we need now */ 1011 if (md5) { 1012 sk_nocaps_add(sk, NETIF_F_GSO_MASK); 1013 tp->af_specific->calc_md5_hash(opts.hash_location, 1014 md5, sk, skb); 1015 } 1016 #endif 1017 1018 icsk->icsk_af_ops->send_check(sk, skb); 1019 1020 if (likely(tcb->tcp_flags & TCPHDR_ACK)) 1021 tcp_event_ack_sent(sk, tcp_skb_pcount(skb)); 1022 1023 if (skb->len != tcp_header_size) 1024 tcp_event_data_sent(tp, sk); 1025 1026 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq) 1027 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, 1028 tcp_skb_pcount(skb)); 1029 1030 tp->segs_out += tcp_skb_pcount(skb); 1031 /* OK, its time to fill skb_shinfo(skb)->gso_segs */ 1032 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb); 1033 1034 /* Our usage of tstamp should remain private */ 1035 skb->tstamp.tv64 = 0; 1036 1037 /* Cleanup our debris for IP stacks */ 1038 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm), 1039 sizeof(struct inet6_skb_parm))); 1040 1041 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl); 1042 1043 if (likely(err <= 0)) 1044 return err; 1045 1046 tcp_enter_cwr(sk); 1047 1048 return net_xmit_eval(err); 1049 } 1050 1051 /* This routine just queues the buffer for sending. 1052 * 1053 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames, 1054 * otherwise socket can stall. 1055 */ 1056 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb) 1057 { 1058 struct tcp_sock *tp = tcp_sk(sk); 1059 1060 /* Advance write_seq and place onto the write_queue. */ 1061 tp->write_seq = TCP_SKB_CB(skb)->end_seq; 1062 __skb_header_release(skb); 1063 tcp_add_write_queue_tail(sk, skb); 1064 sk->sk_wmem_queued += skb->truesize; 1065 sk_mem_charge(sk, skb->truesize); 1066 } 1067 1068 /* Initialize TSO segments for a packet. */ 1069 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb, 1070 unsigned int mss_now) 1071 { 1072 struct skb_shared_info *shinfo = skb_shinfo(skb); 1073 1074 /* Make sure we own this skb before messing gso_size/gso_segs */ 1075 WARN_ON_ONCE(skb_cloned(skb)); 1076 1077 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) { 1078 /* Avoid the costly divide in the normal 1079 * non-TSO case. 1080 */ 1081 tcp_skb_pcount_set(skb, 1); 1082 shinfo->gso_size = 0; 1083 shinfo->gso_type = 0; 1084 } else { 1085 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now)); 1086 shinfo->gso_size = mss_now; 1087 shinfo->gso_type = sk->sk_gso_type; 1088 } 1089 } 1090 1091 /* When a modification to fackets out becomes necessary, we need to check 1092 * skb is counted to fackets_out or not. 1093 */ 1094 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb, 1095 int decr) 1096 { 1097 struct tcp_sock *tp = tcp_sk(sk); 1098 1099 if (!tp->sacked_out || tcp_is_reno(tp)) 1100 return; 1101 1102 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq)) 1103 tp->fackets_out -= decr; 1104 } 1105 1106 /* Pcount in the middle of the write queue got changed, we need to do various 1107 * tweaks to fix counters 1108 */ 1109 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr) 1110 { 1111 struct tcp_sock *tp = tcp_sk(sk); 1112 1113 tp->packets_out -= decr; 1114 1115 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 1116 tp->sacked_out -= decr; 1117 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) 1118 tp->retrans_out -= decr; 1119 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) 1120 tp->lost_out -= decr; 1121 1122 /* Reno case is special. Sigh... */ 1123 if (tcp_is_reno(tp) && decr > 0) 1124 tp->sacked_out -= min_t(u32, tp->sacked_out, decr); 1125 1126 tcp_adjust_fackets_out(sk, skb, decr); 1127 1128 if (tp->lost_skb_hint && 1129 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) && 1130 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))) 1131 tp->lost_cnt_hint -= decr; 1132 1133 tcp_verify_left_out(tp); 1134 } 1135 1136 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2) 1137 { 1138 struct skb_shared_info *shinfo = skb_shinfo(skb); 1139 1140 if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) && 1141 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) { 1142 struct skb_shared_info *shinfo2 = skb_shinfo(skb2); 1143 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP; 1144 1145 shinfo->tx_flags &= ~tsflags; 1146 shinfo2->tx_flags |= tsflags; 1147 swap(shinfo->tskey, shinfo2->tskey); 1148 } 1149 } 1150 1151 /* Function to create two new TCP segments. Shrinks the given segment 1152 * to the specified size and appends a new segment with the rest of the 1153 * packet to the list. This won't be called frequently, I hope. 1154 * Remember, these are still headerless SKBs at this point. 1155 */ 1156 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, 1157 unsigned int mss_now, gfp_t gfp) 1158 { 1159 struct tcp_sock *tp = tcp_sk(sk); 1160 struct sk_buff *buff; 1161 int nsize, old_factor; 1162 int nlen; 1163 u8 flags; 1164 1165 if (WARN_ON(len > skb->len)) 1166 return -EINVAL; 1167 1168 nsize = skb_headlen(skb) - len; 1169 if (nsize < 0) 1170 nsize = 0; 1171 1172 if (skb_unclone(skb, gfp)) 1173 return -ENOMEM; 1174 1175 /* Get a new skb... force flag on. */ 1176 buff = sk_stream_alloc_skb(sk, nsize, gfp, true); 1177 if (!buff) 1178 return -ENOMEM; /* We'll just try again later. */ 1179 1180 sk->sk_wmem_queued += buff->truesize; 1181 sk_mem_charge(sk, buff->truesize); 1182 nlen = skb->len - len - nsize; 1183 buff->truesize += nlen; 1184 skb->truesize -= nlen; 1185 1186 /* Correct the sequence numbers. */ 1187 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 1188 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 1189 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 1190 1191 /* PSH and FIN should only be set in the second packet. */ 1192 flags = TCP_SKB_CB(skb)->tcp_flags; 1193 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); 1194 TCP_SKB_CB(buff)->tcp_flags = flags; 1195 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked; 1196 1197 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) { 1198 /* Copy and checksum data tail into the new buffer. */ 1199 buff->csum = csum_partial_copy_nocheck(skb->data + len, 1200 skb_put(buff, nsize), 1201 nsize, 0); 1202 1203 skb_trim(skb, len); 1204 1205 skb->csum = csum_block_sub(skb->csum, buff->csum, len); 1206 } else { 1207 skb->ip_summed = CHECKSUM_PARTIAL; 1208 skb_split(skb, buff, len); 1209 } 1210 1211 buff->ip_summed = skb->ip_summed; 1212 1213 buff->tstamp = skb->tstamp; 1214 tcp_fragment_tstamp(skb, buff); 1215 1216 old_factor = tcp_skb_pcount(skb); 1217 1218 /* Fix up tso_factor for both original and new SKB. */ 1219 tcp_set_skb_tso_segs(sk, skb, mss_now); 1220 tcp_set_skb_tso_segs(sk, buff, mss_now); 1221 1222 /* If this packet has been sent out already, we must 1223 * adjust the various packet counters. 1224 */ 1225 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) { 1226 int diff = old_factor - tcp_skb_pcount(skb) - 1227 tcp_skb_pcount(buff); 1228 1229 if (diff) 1230 tcp_adjust_pcount(sk, skb, diff); 1231 } 1232 1233 /* Link BUFF into the send queue. */ 1234 __skb_header_release(buff); 1235 tcp_insert_write_queue_after(skb, buff, sk); 1236 1237 return 0; 1238 } 1239 1240 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c 1241 * eventually). The difference is that pulled data not copied, but 1242 * immediately discarded. 1243 */ 1244 static void __pskb_trim_head(struct sk_buff *skb, int len) 1245 { 1246 struct skb_shared_info *shinfo; 1247 int i, k, eat; 1248 1249 eat = min_t(int, len, skb_headlen(skb)); 1250 if (eat) { 1251 __skb_pull(skb, eat); 1252 len -= eat; 1253 if (!len) 1254 return; 1255 } 1256 eat = len; 1257 k = 0; 1258 shinfo = skb_shinfo(skb); 1259 for (i = 0; i < shinfo->nr_frags; i++) { 1260 int size = skb_frag_size(&shinfo->frags[i]); 1261 1262 if (size <= eat) { 1263 skb_frag_unref(skb, i); 1264 eat -= size; 1265 } else { 1266 shinfo->frags[k] = shinfo->frags[i]; 1267 if (eat) { 1268 shinfo->frags[k].page_offset += eat; 1269 skb_frag_size_sub(&shinfo->frags[k], eat); 1270 eat = 0; 1271 } 1272 k++; 1273 } 1274 } 1275 shinfo->nr_frags = k; 1276 1277 skb_reset_tail_pointer(skb); 1278 skb->data_len -= len; 1279 skb->len = skb->data_len; 1280 } 1281 1282 /* Remove acked data from a packet in the transmit queue. */ 1283 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) 1284 { 1285 if (skb_unclone(skb, GFP_ATOMIC)) 1286 return -ENOMEM; 1287 1288 __pskb_trim_head(skb, len); 1289 1290 TCP_SKB_CB(skb)->seq += len; 1291 skb->ip_summed = CHECKSUM_PARTIAL; 1292 1293 skb->truesize -= len; 1294 sk->sk_wmem_queued -= len; 1295 sk_mem_uncharge(sk, len); 1296 sock_set_flag(sk, SOCK_QUEUE_SHRUNK); 1297 1298 /* Any change of skb->len requires recalculation of tso factor. */ 1299 if (tcp_skb_pcount(skb) > 1) 1300 tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb)); 1301 1302 return 0; 1303 } 1304 1305 /* Calculate MSS not accounting any TCP options. */ 1306 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu) 1307 { 1308 const struct tcp_sock *tp = tcp_sk(sk); 1309 const struct inet_connection_sock *icsk = inet_csk(sk); 1310 int mss_now; 1311 1312 /* Calculate base mss without TCP options: 1313 It is MMS_S - sizeof(tcphdr) of rfc1122 1314 */ 1315 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr); 1316 1317 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */ 1318 if (icsk->icsk_af_ops->net_frag_header_len) { 1319 const struct dst_entry *dst = __sk_dst_get(sk); 1320 1321 if (dst && dst_allfrag(dst)) 1322 mss_now -= icsk->icsk_af_ops->net_frag_header_len; 1323 } 1324 1325 /* Clamp it (mss_clamp does not include tcp options) */ 1326 if (mss_now > tp->rx_opt.mss_clamp) 1327 mss_now = tp->rx_opt.mss_clamp; 1328 1329 /* Now subtract optional transport overhead */ 1330 mss_now -= icsk->icsk_ext_hdr_len; 1331 1332 /* Then reserve room for full set of TCP options and 8 bytes of data */ 1333 if (mss_now < 48) 1334 mss_now = 48; 1335 return mss_now; 1336 } 1337 1338 /* Calculate MSS. Not accounting for SACKs here. */ 1339 int tcp_mtu_to_mss(struct sock *sk, int pmtu) 1340 { 1341 /* Subtract TCP options size, not including SACKs */ 1342 return __tcp_mtu_to_mss(sk, pmtu) - 1343 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr)); 1344 } 1345 1346 /* Inverse of above */ 1347 int tcp_mss_to_mtu(struct sock *sk, int mss) 1348 { 1349 const struct tcp_sock *tp = tcp_sk(sk); 1350 const struct inet_connection_sock *icsk = inet_csk(sk); 1351 int mtu; 1352 1353 mtu = mss + 1354 tp->tcp_header_len + 1355 icsk->icsk_ext_hdr_len + 1356 icsk->icsk_af_ops->net_header_len; 1357 1358 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */ 1359 if (icsk->icsk_af_ops->net_frag_header_len) { 1360 const struct dst_entry *dst = __sk_dst_get(sk); 1361 1362 if (dst && dst_allfrag(dst)) 1363 mtu += icsk->icsk_af_ops->net_frag_header_len; 1364 } 1365 return mtu; 1366 } 1367 1368 /* MTU probing init per socket */ 1369 void tcp_mtup_init(struct sock *sk) 1370 { 1371 struct tcp_sock *tp = tcp_sk(sk); 1372 struct inet_connection_sock *icsk = inet_csk(sk); 1373 struct net *net = sock_net(sk); 1374 1375 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1; 1376 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) + 1377 icsk->icsk_af_ops->net_header_len; 1378 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss); 1379 icsk->icsk_mtup.probe_size = 0; 1380 if (icsk->icsk_mtup.enabled) 1381 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; 1382 } 1383 EXPORT_SYMBOL(tcp_mtup_init); 1384 1385 /* This function synchronize snd mss to current pmtu/exthdr set. 1386 1387 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts 1388 for TCP options, but includes only bare TCP header. 1389 1390 tp->rx_opt.mss_clamp is mss negotiated at connection setup. 1391 It is minimum of user_mss and mss received with SYN. 1392 It also does not include TCP options. 1393 1394 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function. 1395 1396 tp->mss_cache is current effective sending mss, including 1397 all tcp options except for SACKs. It is evaluated, 1398 taking into account current pmtu, but never exceeds 1399 tp->rx_opt.mss_clamp. 1400 1401 NOTE1. rfc1122 clearly states that advertised MSS 1402 DOES NOT include either tcp or ip options. 1403 1404 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache 1405 are READ ONLY outside this function. --ANK (980731) 1406 */ 1407 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu) 1408 { 1409 struct tcp_sock *tp = tcp_sk(sk); 1410 struct inet_connection_sock *icsk = inet_csk(sk); 1411 int mss_now; 1412 1413 if (icsk->icsk_mtup.search_high > pmtu) 1414 icsk->icsk_mtup.search_high = pmtu; 1415 1416 mss_now = tcp_mtu_to_mss(sk, pmtu); 1417 mss_now = tcp_bound_to_half_wnd(tp, mss_now); 1418 1419 /* And store cached results */ 1420 icsk->icsk_pmtu_cookie = pmtu; 1421 if (icsk->icsk_mtup.enabled) 1422 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)); 1423 tp->mss_cache = mss_now; 1424 1425 return mss_now; 1426 } 1427 EXPORT_SYMBOL(tcp_sync_mss); 1428 1429 /* Compute the current effective MSS, taking SACKs and IP options, 1430 * and even PMTU discovery events into account. 1431 */ 1432 unsigned int tcp_current_mss(struct sock *sk) 1433 { 1434 const struct tcp_sock *tp = tcp_sk(sk); 1435 const struct dst_entry *dst = __sk_dst_get(sk); 1436 u32 mss_now; 1437 unsigned int header_len; 1438 struct tcp_out_options opts; 1439 struct tcp_md5sig_key *md5; 1440 1441 mss_now = tp->mss_cache; 1442 1443 if (dst) { 1444 u32 mtu = dst_mtu(dst); 1445 if (mtu != inet_csk(sk)->icsk_pmtu_cookie) 1446 mss_now = tcp_sync_mss(sk, mtu); 1447 } 1448 1449 header_len = tcp_established_options(sk, NULL, &opts, &md5) + 1450 sizeof(struct tcphdr); 1451 /* The mss_cache is sized based on tp->tcp_header_len, which assumes 1452 * some common options. If this is an odd packet (because we have SACK 1453 * blocks etc) then our calculated header_len will be different, and 1454 * we have to adjust mss_now correspondingly */ 1455 if (header_len != tp->tcp_header_len) { 1456 int delta = (int) header_len - tp->tcp_header_len; 1457 mss_now -= delta; 1458 } 1459 1460 return mss_now; 1461 } 1462 1463 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto. 1464 * As additional protections, we do not touch cwnd in retransmission phases, 1465 * and if application hit its sndbuf limit recently. 1466 */ 1467 static void tcp_cwnd_application_limited(struct sock *sk) 1468 { 1469 struct tcp_sock *tp = tcp_sk(sk); 1470 1471 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open && 1472 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { 1473 /* Limited by application or receiver window. */ 1474 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk)); 1475 u32 win_used = max(tp->snd_cwnd_used, init_win); 1476 if (win_used < tp->snd_cwnd) { 1477 tp->snd_ssthresh = tcp_current_ssthresh(sk); 1478 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1; 1479 } 1480 tp->snd_cwnd_used = 0; 1481 } 1482 tp->snd_cwnd_stamp = tcp_time_stamp; 1483 } 1484 1485 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited) 1486 { 1487 struct tcp_sock *tp = tcp_sk(sk); 1488 1489 /* Track the maximum number of outstanding packets in each 1490 * window, and remember whether we were cwnd-limited then. 1491 */ 1492 if (!before(tp->snd_una, tp->max_packets_seq) || 1493 tp->packets_out > tp->max_packets_out) { 1494 tp->max_packets_out = tp->packets_out; 1495 tp->max_packets_seq = tp->snd_nxt; 1496 tp->is_cwnd_limited = is_cwnd_limited; 1497 } 1498 1499 if (tcp_is_cwnd_limited(sk)) { 1500 /* Network is feed fully. */ 1501 tp->snd_cwnd_used = 0; 1502 tp->snd_cwnd_stamp = tcp_time_stamp; 1503 } else { 1504 /* Network starves. */ 1505 if (tp->packets_out > tp->snd_cwnd_used) 1506 tp->snd_cwnd_used = tp->packets_out; 1507 1508 if (sysctl_tcp_slow_start_after_idle && 1509 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto) 1510 tcp_cwnd_application_limited(sk); 1511 } 1512 } 1513 1514 /* Minshall's variant of the Nagle send check. */ 1515 static bool tcp_minshall_check(const struct tcp_sock *tp) 1516 { 1517 return after(tp->snd_sml, tp->snd_una) && 1518 !after(tp->snd_sml, tp->snd_nxt); 1519 } 1520 1521 /* Update snd_sml if this skb is under mss 1522 * Note that a TSO packet might end with a sub-mss segment 1523 * The test is really : 1524 * if ((skb->len % mss) != 0) 1525 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq; 1526 * But we can avoid doing the divide again given we already have 1527 * skb_pcount = skb->len / mss_now 1528 */ 1529 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now, 1530 const struct sk_buff *skb) 1531 { 1532 if (skb->len < tcp_skb_pcount(skb) * mss_now) 1533 tp->snd_sml = TCP_SKB_CB(skb)->end_seq; 1534 } 1535 1536 /* Return false, if packet can be sent now without violation Nagle's rules: 1537 * 1. It is full sized. (provided by caller in %partial bool) 1538 * 2. Or it contains FIN. (already checked by caller) 1539 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set. 1540 * 4. Or TCP_CORK is not set, and all sent packets are ACKed. 1541 * With Minshall's modification: all sent small packets are ACKed. 1542 */ 1543 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp, 1544 int nonagle) 1545 { 1546 return partial && 1547 ((nonagle & TCP_NAGLE_CORK) || 1548 (!nonagle && tp->packets_out && tcp_minshall_check(tp))); 1549 } 1550 1551 /* Return how many segs we'd like on a TSO packet, 1552 * to send one TSO packet per ms 1553 */ 1554 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now) 1555 { 1556 u32 bytes, segs; 1557 1558 bytes = min(sk->sk_pacing_rate >> 10, 1559 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER); 1560 1561 /* Goal is to send at least one packet per ms, 1562 * not one big TSO packet every 100 ms. 1563 * This preserves ACK clocking and is consistent 1564 * with tcp_tso_should_defer() heuristic. 1565 */ 1566 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs); 1567 1568 return min_t(u32, segs, sk->sk_gso_max_segs); 1569 } 1570 1571 /* Returns the portion of skb which can be sent right away */ 1572 static unsigned int tcp_mss_split_point(const struct sock *sk, 1573 const struct sk_buff *skb, 1574 unsigned int mss_now, 1575 unsigned int max_segs, 1576 int nonagle) 1577 { 1578 const struct tcp_sock *tp = tcp_sk(sk); 1579 u32 partial, needed, window, max_len; 1580 1581 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 1582 max_len = mss_now * max_segs; 1583 1584 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk))) 1585 return max_len; 1586 1587 needed = min(skb->len, window); 1588 1589 if (max_len <= needed) 1590 return max_len; 1591 1592 partial = needed % mss_now; 1593 /* If last segment is not a full MSS, check if Nagle rules allow us 1594 * to include this last segment in this skb. 1595 * Otherwise, we'll split the skb at last MSS boundary 1596 */ 1597 if (tcp_nagle_check(partial != 0, tp, nonagle)) 1598 return needed - partial; 1599 1600 return needed; 1601 } 1602 1603 /* Can at least one segment of SKB be sent right now, according to the 1604 * congestion window rules? If so, return how many segments are allowed. 1605 */ 1606 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp, 1607 const struct sk_buff *skb) 1608 { 1609 u32 in_flight, cwnd, halfcwnd; 1610 1611 /* Don't be strict about the congestion window for the final FIN. */ 1612 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) && 1613 tcp_skb_pcount(skb) == 1) 1614 return 1; 1615 1616 in_flight = tcp_packets_in_flight(tp); 1617 cwnd = tp->snd_cwnd; 1618 if (in_flight >= cwnd) 1619 return 0; 1620 1621 /* For better scheduling, ensure we have at least 1622 * 2 GSO packets in flight. 1623 */ 1624 halfcwnd = max(cwnd >> 1, 1U); 1625 return min(halfcwnd, cwnd - in_flight); 1626 } 1627 1628 /* Initialize TSO state of a skb. 1629 * This must be invoked the first time we consider transmitting 1630 * SKB onto the wire. 1631 */ 1632 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb, 1633 unsigned int mss_now) 1634 { 1635 int tso_segs = tcp_skb_pcount(skb); 1636 1637 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) { 1638 tcp_set_skb_tso_segs(sk, skb, mss_now); 1639 tso_segs = tcp_skb_pcount(skb); 1640 } 1641 return tso_segs; 1642 } 1643 1644 1645 /* Return true if the Nagle test allows this packet to be 1646 * sent now. 1647 */ 1648 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb, 1649 unsigned int cur_mss, int nonagle) 1650 { 1651 /* Nagle rule does not apply to frames, which sit in the middle of the 1652 * write_queue (they have no chances to get new data). 1653 * 1654 * This is implemented in the callers, where they modify the 'nonagle' 1655 * argument based upon the location of SKB in the send queue. 1656 */ 1657 if (nonagle & TCP_NAGLE_PUSH) 1658 return true; 1659 1660 /* Don't use the nagle rule for urgent data (or for the final FIN). */ 1661 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)) 1662 return true; 1663 1664 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle)) 1665 return true; 1666 1667 return false; 1668 } 1669 1670 /* Does at least the first segment of SKB fit into the send window? */ 1671 static bool tcp_snd_wnd_test(const struct tcp_sock *tp, 1672 const struct sk_buff *skb, 1673 unsigned int cur_mss) 1674 { 1675 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 1676 1677 if (skb->len > cur_mss) 1678 end_seq = TCP_SKB_CB(skb)->seq + cur_mss; 1679 1680 return !after(end_seq, tcp_wnd_end(tp)); 1681 } 1682 1683 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk)) 1684 * should be put on the wire right now. If so, it returns the number of 1685 * packets allowed by the congestion window. 1686 */ 1687 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb, 1688 unsigned int cur_mss, int nonagle) 1689 { 1690 const struct tcp_sock *tp = tcp_sk(sk); 1691 unsigned int cwnd_quota; 1692 1693 tcp_init_tso_segs(sk, skb, cur_mss); 1694 1695 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle)) 1696 return 0; 1697 1698 cwnd_quota = tcp_cwnd_test(tp, skb); 1699 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss)) 1700 cwnd_quota = 0; 1701 1702 return cwnd_quota; 1703 } 1704 1705 /* Test if sending is allowed right now. */ 1706 bool tcp_may_send_now(struct sock *sk) 1707 { 1708 const struct tcp_sock *tp = tcp_sk(sk); 1709 struct sk_buff *skb = tcp_send_head(sk); 1710 1711 return skb && 1712 tcp_snd_test(sk, skb, tcp_current_mss(sk), 1713 (tcp_skb_is_last(sk, skb) ? 1714 tp->nonagle : TCP_NAGLE_PUSH)); 1715 } 1716 1717 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet 1718 * which is put after SKB on the list. It is very much like 1719 * tcp_fragment() except that it may make several kinds of assumptions 1720 * in order to speed up the splitting operation. In particular, we 1721 * know that all the data is in scatter-gather pages, and that the 1722 * packet has never been sent out before (and thus is not cloned). 1723 */ 1724 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, 1725 unsigned int mss_now, gfp_t gfp) 1726 { 1727 struct sk_buff *buff; 1728 int nlen = skb->len - len; 1729 u8 flags; 1730 1731 /* All of a TSO frame must be composed of paged data. */ 1732 if (skb->len != skb->data_len) 1733 return tcp_fragment(sk, skb, len, mss_now, gfp); 1734 1735 buff = sk_stream_alloc_skb(sk, 0, gfp, true); 1736 if (unlikely(!buff)) 1737 return -ENOMEM; 1738 1739 sk->sk_wmem_queued += buff->truesize; 1740 sk_mem_charge(sk, buff->truesize); 1741 buff->truesize += nlen; 1742 skb->truesize -= nlen; 1743 1744 /* Correct the sequence numbers. */ 1745 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 1746 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 1747 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 1748 1749 /* PSH and FIN should only be set in the second packet. */ 1750 flags = TCP_SKB_CB(skb)->tcp_flags; 1751 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); 1752 TCP_SKB_CB(buff)->tcp_flags = flags; 1753 1754 /* This packet was never sent out yet, so no SACK bits. */ 1755 TCP_SKB_CB(buff)->sacked = 0; 1756 1757 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL; 1758 skb_split(skb, buff, len); 1759 tcp_fragment_tstamp(skb, buff); 1760 1761 /* Fix up tso_factor for both original and new SKB. */ 1762 tcp_set_skb_tso_segs(sk, skb, mss_now); 1763 tcp_set_skb_tso_segs(sk, buff, mss_now); 1764 1765 /* Link BUFF into the send queue. */ 1766 __skb_header_release(buff); 1767 tcp_insert_write_queue_after(skb, buff, sk); 1768 1769 return 0; 1770 } 1771 1772 /* Try to defer sending, if possible, in order to minimize the amount 1773 * of TSO splitting we do. View it as a kind of TSO Nagle test. 1774 * 1775 * This algorithm is from John Heffner. 1776 */ 1777 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb, 1778 bool *is_cwnd_limited, u32 max_segs) 1779 { 1780 const struct inet_connection_sock *icsk = inet_csk(sk); 1781 u32 age, send_win, cong_win, limit, in_flight; 1782 struct tcp_sock *tp = tcp_sk(sk); 1783 struct skb_mstamp now; 1784 struct sk_buff *head; 1785 int win_divisor; 1786 1787 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) 1788 goto send_now; 1789 1790 if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_CWR))) 1791 goto send_now; 1792 1793 /* Avoid bursty behavior by allowing defer 1794 * only if the last write was recent. 1795 */ 1796 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0) 1797 goto send_now; 1798 1799 in_flight = tcp_packets_in_flight(tp); 1800 1801 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight)); 1802 1803 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 1804 1805 /* From in_flight test above, we know that cwnd > in_flight. */ 1806 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache; 1807 1808 limit = min(send_win, cong_win); 1809 1810 /* If a full-sized TSO skb can be sent, do it. */ 1811 if (limit >= max_segs * tp->mss_cache) 1812 goto send_now; 1813 1814 /* Middle in queue won't get any more data, full sendable already? */ 1815 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len)) 1816 goto send_now; 1817 1818 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor); 1819 if (win_divisor) { 1820 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache); 1821 1822 /* If at least some fraction of a window is available, 1823 * just use it. 1824 */ 1825 chunk /= win_divisor; 1826 if (limit >= chunk) 1827 goto send_now; 1828 } else { 1829 /* Different approach, try not to defer past a single 1830 * ACK. Receiver should ACK every other full sized 1831 * frame, so if we have space for more than 3 frames 1832 * then send now. 1833 */ 1834 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache) 1835 goto send_now; 1836 } 1837 1838 head = tcp_write_queue_head(sk); 1839 skb_mstamp_get(&now); 1840 age = skb_mstamp_us_delta(&now, &head->skb_mstamp); 1841 /* If next ACK is likely to come too late (half srtt), do not defer */ 1842 if (age < (tp->srtt_us >> 4)) 1843 goto send_now; 1844 1845 /* Ok, it looks like it is advisable to defer. */ 1846 1847 if (cong_win < send_win && cong_win < skb->len) 1848 *is_cwnd_limited = true; 1849 1850 return true; 1851 1852 send_now: 1853 return false; 1854 } 1855 1856 static inline void tcp_mtu_check_reprobe(struct sock *sk) 1857 { 1858 struct inet_connection_sock *icsk = inet_csk(sk); 1859 struct tcp_sock *tp = tcp_sk(sk); 1860 struct net *net = sock_net(sk); 1861 u32 interval; 1862 s32 delta; 1863 1864 interval = net->ipv4.sysctl_tcp_probe_interval; 1865 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp; 1866 if (unlikely(delta >= interval * HZ)) { 1867 int mss = tcp_current_mss(sk); 1868 1869 /* Update current search range */ 1870 icsk->icsk_mtup.probe_size = 0; 1871 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + 1872 sizeof(struct tcphdr) + 1873 icsk->icsk_af_ops->net_header_len; 1874 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 1875 1876 /* Update probe time stamp */ 1877 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; 1878 } 1879 } 1880 1881 /* Create a new MTU probe if we are ready. 1882 * MTU probe is regularly attempting to increase the path MTU by 1883 * deliberately sending larger packets. This discovers routing 1884 * changes resulting in larger path MTUs. 1885 * 1886 * Returns 0 if we should wait to probe (no cwnd available), 1887 * 1 if a probe was sent, 1888 * -1 otherwise 1889 */ 1890 static int tcp_mtu_probe(struct sock *sk) 1891 { 1892 struct tcp_sock *tp = tcp_sk(sk); 1893 struct inet_connection_sock *icsk = inet_csk(sk); 1894 struct sk_buff *skb, *nskb, *next; 1895 struct net *net = sock_net(sk); 1896 int len; 1897 int probe_size; 1898 int size_needed; 1899 int copy; 1900 int mss_now; 1901 int interval; 1902 1903 /* Not currently probing/verifying, 1904 * not in recovery, 1905 * have enough cwnd, and 1906 * not SACKing (the variable headers throw things off) */ 1907 if (!icsk->icsk_mtup.enabled || 1908 icsk->icsk_mtup.probe_size || 1909 inet_csk(sk)->icsk_ca_state != TCP_CA_Open || 1910 tp->snd_cwnd < 11 || 1911 tp->rx_opt.num_sacks || tp->rx_opt.dsack) 1912 return -1; 1913 1914 /* Use binary search for probe_size between tcp_mss_base, 1915 * and current mss_clamp. if (search_high - search_low) 1916 * smaller than a threshold, backoff from probing. 1917 */ 1918 mss_now = tcp_current_mss(sk); 1919 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high + 1920 icsk->icsk_mtup.search_low) >> 1); 1921 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache; 1922 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low; 1923 /* When misfortune happens, we are reprobing actively, 1924 * and then reprobe timer has expired. We stick with current 1925 * probing process by not resetting search range to its orignal. 1926 */ 1927 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) || 1928 interval < net->ipv4.sysctl_tcp_probe_threshold) { 1929 /* Check whether enough time has elaplased for 1930 * another round of probing. 1931 */ 1932 tcp_mtu_check_reprobe(sk); 1933 return -1; 1934 } 1935 1936 /* Have enough data in the send queue to probe? */ 1937 if (tp->write_seq - tp->snd_nxt < size_needed) 1938 return -1; 1939 1940 if (tp->snd_wnd < size_needed) 1941 return -1; 1942 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp))) 1943 return 0; 1944 1945 /* Do we need to wait to drain cwnd? With none in flight, don't stall */ 1946 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) { 1947 if (!tcp_packets_in_flight(tp)) 1948 return -1; 1949 else 1950 return 0; 1951 } 1952 1953 /* We're allowed to probe. Build it now. */ 1954 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false); 1955 if (!nskb) 1956 return -1; 1957 sk->sk_wmem_queued += nskb->truesize; 1958 sk_mem_charge(sk, nskb->truesize); 1959 1960 skb = tcp_send_head(sk); 1961 1962 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq; 1963 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size; 1964 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK; 1965 TCP_SKB_CB(nskb)->sacked = 0; 1966 nskb->csum = 0; 1967 nskb->ip_summed = skb->ip_summed; 1968 1969 tcp_insert_write_queue_before(nskb, skb, sk); 1970 1971 len = 0; 1972 tcp_for_write_queue_from_safe(skb, next, sk) { 1973 copy = min_t(int, skb->len, probe_size - len); 1974 if (nskb->ip_summed) 1975 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy); 1976 else 1977 nskb->csum = skb_copy_and_csum_bits(skb, 0, 1978 skb_put(nskb, copy), 1979 copy, nskb->csum); 1980 1981 if (skb->len <= copy) { 1982 /* We've eaten all the data from this skb. 1983 * Throw it away. */ 1984 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; 1985 tcp_unlink_write_queue(skb, sk); 1986 sk_wmem_free_skb(sk, skb); 1987 } else { 1988 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags & 1989 ~(TCPHDR_FIN|TCPHDR_PSH); 1990 if (!skb_shinfo(skb)->nr_frags) { 1991 skb_pull(skb, copy); 1992 if (skb->ip_summed != CHECKSUM_PARTIAL) 1993 skb->csum = csum_partial(skb->data, 1994 skb->len, 0); 1995 } else { 1996 __pskb_trim_head(skb, copy); 1997 tcp_set_skb_tso_segs(sk, skb, mss_now); 1998 } 1999 TCP_SKB_CB(skb)->seq += copy; 2000 } 2001 2002 len += copy; 2003 2004 if (len >= probe_size) 2005 break; 2006 } 2007 tcp_init_tso_segs(sk, nskb, nskb->len); 2008 2009 /* We're ready to send. If this fails, the probe will 2010 * be resegmented into mss-sized pieces by tcp_write_xmit(). 2011 */ 2012 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) { 2013 /* Decrement cwnd here because we are sending 2014 * effectively two packets. */ 2015 tp->snd_cwnd--; 2016 tcp_event_new_data_sent(sk, nskb); 2017 2018 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len); 2019 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq; 2020 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq; 2021 2022 return 1; 2023 } 2024 2025 return -1; 2026 } 2027 2028 /* This routine writes packets to the network. It advances the 2029 * send_head. This happens as incoming acks open up the remote 2030 * window for us. 2031 * 2032 * LARGESEND note: !tcp_urg_mode is overkill, only frames between 2033 * snd_up-64k-mss .. snd_up cannot be large. However, taking into 2034 * account rare use of URG, this is not a big flaw. 2035 * 2036 * Send at most one packet when push_one > 0. Temporarily ignore 2037 * cwnd limit to force at most one packet out when push_one == 2. 2038 2039 * Returns true, if no segments are in flight and we have queued segments, 2040 * but cannot send anything now because of SWS or another problem. 2041 */ 2042 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, 2043 int push_one, gfp_t gfp) 2044 { 2045 struct tcp_sock *tp = tcp_sk(sk); 2046 struct sk_buff *skb; 2047 unsigned int tso_segs, sent_pkts; 2048 int cwnd_quota; 2049 int result; 2050 bool is_cwnd_limited = false; 2051 u32 max_segs; 2052 2053 sent_pkts = 0; 2054 2055 if (!push_one) { 2056 /* Do MTU probing. */ 2057 result = tcp_mtu_probe(sk); 2058 if (!result) { 2059 return false; 2060 } else if (result > 0) { 2061 sent_pkts = 1; 2062 } 2063 } 2064 2065 max_segs = tcp_tso_autosize(sk, mss_now); 2066 while ((skb = tcp_send_head(sk))) { 2067 unsigned int limit; 2068 2069 tso_segs = tcp_init_tso_segs(sk, skb, mss_now); 2070 BUG_ON(!tso_segs); 2071 2072 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) { 2073 /* "skb_mstamp" is used as a start point for the retransmit timer */ 2074 skb_mstamp_get(&skb->skb_mstamp); 2075 goto repair; /* Skip network transmission */ 2076 } 2077 2078 cwnd_quota = tcp_cwnd_test(tp, skb); 2079 if (!cwnd_quota) { 2080 is_cwnd_limited = true; 2081 if (push_one == 2) 2082 /* Force out a loss probe pkt. */ 2083 cwnd_quota = 1; 2084 else 2085 break; 2086 } 2087 2088 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) 2089 break; 2090 2091 if (tso_segs == 1) { 2092 if (unlikely(!tcp_nagle_test(tp, skb, mss_now, 2093 (tcp_skb_is_last(sk, skb) ? 2094 nonagle : TCP_NAGLE_PUSH)))) 2095 break; 2096 } else { 2097 if (!push_one && 2098 tcp_tso_should_defer(sk, skb, &is_cwnd_limited, 2099 max_segs)) 2100 break; 2101 } 2102 2103 limit = mss_now; 2104 if (tso_segs > 1 && !tcp_urg_mode(tp)) 2105 limit = tcp_mss_split_point(sk, skb, mss_now, 2106 min_t(unsigned int, 2107 cwnd_quota, 2108 max_segs), 2109 nonagle); 2110 2111 if (skb->len > limit && 2112 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp))) 2113 break; 2114 2115 /* TCP Small Queues : 2116 * Control number of packets in qdisc/devices to two packets / or ~1 ms. 2117 * This allows for : 2118 * - better RTT estimation and ACK scheduling 2119 * - faster recovery 2120 * - high rates 2121 * Alas, some drivers / subsystems require a fair amount 2122 * of queued bytes to ensure line rate. 2123 * One example is wifi aggregation (802.11 AMPDU) 2124 */ 2125 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10); 2126 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes); 2127 2128 if (atomic_read(&sk->sk_wmem_alloc) > limit) { 2129 set_bit(TSQ_THROTTLED, &tp->tsq_flags); 2130 /* It is possible TX completion already happened 2131 * before we set TSQ_THROTTLED, so we must 2132 * test again the condition. 2133 */ 2134 smp_mb__after_atomic(); 2135 if (atomic_read(&sk->sk_wmem_alloc) > limit) 2136 break; 2137 } 2138 2139 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp))) 2140 break; 2141 2142 repair: 2143 /* Advance the send_head. This one is sent out. 2144 * This call will increment packets_out. 2145 */ 2146 tcp_event_new_data_sent(sk, skb); 2147 2148 tcp_minshall_update(tp, mss_now, skb); 2149 sent_pkts += tcp_skb_pcount(skb); 2150 2151 if (push_one) 2152 break; 2153 } 2154 2155 if (likely(sent_pkts)) { 2156 if (tcp_in_cwnd_reduction(sk)) 2157 tp->prr_out += sent_pkts; 2158 2159 /* Send one loss probe per tail loss episode. */ 2160 if (push_one != 2) 2161 tcp_schedule_loss_probe(sk); 2162 tcp_cwnd_validate(sk, is_cwnd_limited); 2163 return false; 2164 } 2165 return (push_one == 2) || (!tp->packets_out && tcp_send_head(sk)); 2166 } 2167 2168 bool tcp_schedule_loss_probe(struct sock *sk) 2169 { 2170 struct inet_connection_sock *icsk = inet_csk(sk); 2171 struct tcp_sock *tp = tcp_sk(sk); 2172 u32 timeout, tlp_time_stamp, rto_time_stamp; 2173 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3); 2174 2175 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS)) 2176 return false; 2177 /* No consecutive loss probes. */ 2178 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) { 2179 tcp_rearm_rto(sk); 2180 return false; 2181 } 2182 /* Don't do any loss probe on a Fast Open connection before 3WHS 2183 * finishes. 2184 */ 2185 if (sk->sk_state == TCP_SYN_RECV) 2186 return false; 2187 2188 /* TLP is only scheduled when next timer event is RTO. */ 2189 if (icsk->icsk_pending != ICSK_TIME_RETRANS) 2190 return false; 2191 2192 /* Schedule a loss probe in 2*RTT for SACK capable connections 2193 * in Open state, that are either limited by cwnd or application. 2194 */ 2195 if (sysctl_tcp_early_retrans < 3 || !tp->srtt_us || !tp->packets_out || 2196 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open) 2197 return false; 2198 2199 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) && 2200 tcp_send_head(sk)) 2201 return false; 2202 2203 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account 2204 * for delayed ack when there's one outstanding packet. 2205 */ 2206 timeout = rtt << 1; 2207 if (tp->packets_out == 1) 2208 timeout = max_t(u32, timeout, 2209 (rtt + (rtt >> 1) + TCP_DELACK_MAX)); 2210 timeout = max_t(u32, timeout, msecs_to_jiffies(10)); 2211 2212 /* If RTO is shorter, just schedule TLP in its place. */ 2213 tlp_time_stamp = tcp_time_stamp + timeout; 2214 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout; 2215 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) { 2216 s32 delta = rto_time_stamp - tcp_time_stamp; 2217 if (delta > 0) 2218 timeout = delta; 2219 } 2220 2221 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout, 2222 TCP_RTO_MAX); 2223 return true; 2224 } 2225 2226 /* Thanks to skb fast clones, we can detect if a prior transmit of 2227 * a packet is still in a qdisc or driver queue. 2228 * In this case, there is very little point doing a retransmit ! 2229 * Note: This is called from BH context only. 2230 */ 2231 static bool skb_still_in_host_queue(const struct sock *sk, 2232 const struct sk_buff *skb) 2233 { 2234 if (unlikely(skb_fclone_busy(sk, skb))) { 2235 NET_INC_STATS_BH(sock_net(sk), 2236 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES); 2237 return true; 2238 } 2239 return false; 2240 } 2241 2242 /* When probe timeout (PTO) fires, send a new segment if one exists, else 2243 * retransmit the last segment. 2244 */ 2245 void tcp_send_loss_probe(struct sock *sk) 2246 { 2247 struct tcp_sock *tp = tcp_sk(sk); 2248 struct sk_buff *skb; 2249 int pcount; 2250 int mss = tcp_current_mss(sk); 2251 int err = -1; 2252 2253 if (tcp_send_head(sk)) { 2254 err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC); 2255 goto rearm_timer; 2256 } 2257 2258 /* At most one outstanding TLP retransmission. */ 2259 if (tp->tlp_high_seq) 2260 goto rearm_timer; 2261 2262 /* Retransmit last segment. */ 2263 skb = tcp_write_queue_tail(sk); 2264 if (WARN_ON(!skb)) 2265 goto rearm_timer; 2266 2267 if (skb_still_in_host_queue(sk, skb)) 2268 goto rearm_timer; 2269 2270 pcount = tcp_skb_pcount(skb); 2271 if (WARN_ON(!pcount)) 2272 goto rearm_timer; 2273 2274 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) { 2275 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss, 2276 GFP_ATOMIC))) 2277 goto rearm_timer; 2278 skb = tcp_write_queue_tail(sk); 2279 } 2280 2281 if (WARN_ON(!skb || !tcp_skb_pcount(skb))) 2282 goto rearm_timer; 2283 2284 err = __tcp_retransmit_skb(sk, skb); 2285 2286 /* Record snd_nxt for loss detection. */ 2287 if (likely(!err)) 2288 tp->tlp_high_seq = tp->snd_nxt; 2289 2290 rearm_timer: 2291 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 2292 inet_csk(sk)->icsk_rto, 2293 TCP_RTO_MAX); 2294 2295 if (likely(!err)) 2296 NET_INC_STATS_BH(sock_net(sk), 2297 LINUX_MIB_TCPLOSSPROBES); 2298 } 2299 2300 /* Push out any pending frames which were held back due to 2301 * TCP_CORK or attempt at coalescing tiny packets. 2302 * The socket must be locked by the caller. 2303 */ 2304 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss, 2305 int nonagle) 2306 { 2307 /* If we are closed, the bytes will have to remain here. 2308 * In time closedown will finish, we empty the write queue and 2309 * all will be happy. 2310 */ 2311 if (unlikely(sk->sk_state == TCP_CLOSE)) 2312 return; 2313 2314 if (tcp_write_xmit(sk, cur_mss, nonagle, 0, 2315 sk_gfp_atomic(sk, GFP_ATOMIC))) 2316 tcp_check_probe_timer(sk); 2317 } 2318 2319 /* Send _single_ skb sitting at the send head. This function requires 2320 * true push pending frames to setup probe timer etc. 2321 */ 2322 void tcp_push_one(struct sock *sk, unsigned int mss_now) 2323 { 2324 struct sk_buff *skb = tcp_send_head(sk); 2325 2326 BUG_ON(!skb || skb->len < mss_now); 2327 2328 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation); 2329 } 2330 2331 /* This function returns the amount that we can raise the 2332 * usable window based on the following constraints 2333 * 2334 * 1. The window can never be shrunk once it is offered (RFC 793) 2335 * 2. We limit memory per socket 2336 * 2337 * RFC 1122: 2338 * "the suggested [SWS] avoidance algorithm for the receiver is to keep 2339 * RECV.NEXT + RCV.WIN fixed until: 2340 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)" 2341 * 2342 * i.e. don't raise the right edge of the window until you can raise 2343 * it at least MSS bytes. 2344 * 2345 * Unfortunately, the recommended algorithm breaks header prediction, 2346 * since header prediction assumes th->window stays fixed. 2347 * 2348 * Strictly speaking, keeping th->window fixed violates the receiver 2349 * side SWS prevention criteria. The problem is that under this rule 2350 * a stream of single byte packets will cause the right side of the 2351 * window to always advance by a single byte. 2352 * 2353 * Of course, if the sender implements sender side SWS prevention 2354 * then this will not be a problem. 2355 * 2356 * BSD seems to make the following compromise: 2357 * 2358 * If the free space is less than the 1/4 of the maximum 2359 * space available and the free space is less than 1/2 mss, 2360 * then set the window to 0. 2361 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ] 2362 * Otherwise, just prevent the window from shrinking 2363 * and from being larger than the largest representable value. 2364 * 2365 * This prevents incremental opening of the window in the regime 2366 * where TCP is limited by the speed of the reader side taking 2367 * data out of the TCP receive queue. It does nothing about 2368 * those cases where the window is constrained on the sender side 2369 * because the pipeline is full. 2370 * 2371 * BSD also seems to "accidentally" limit itself to windows that are a 2372 * multiple of MSS, at least until the free space gets quite small. 2373 * This would appear to be a side effect of the mbuf implementation. 2374 * Combining these two algorithms results in the observed behavior 2375 * of having a fixed window size at almost all times. 2376 * 2377 * Below we obtain similar behavior by forcing the offered window to 2378 * a multiple of the mss when it is feasible to do so. 2379 * 2380 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes. 2381 * Regular options like TIMESTAMP are taken into account. 2382 */ 2383 u32 __tcp_select_window(struct sock *sk) 2384 { 2385 struct inet_connection_sock *icsk = inet_csk(sk); 2386 struct tcp_sock *tp = tcp_sk(sk); 2387 /* MSS for the peer's data. Previous versions used mss_clamp 2388 * here. I don't know if the value based on our guesses 2389 * of peer's MSS is better for the performance. It's more correct 2390 * but may be worse for the performance because of rcv_mss 2391 * fluctuations. --SAW 1998/11/1 2392 */ 2393 int mss = icsk->icsk_ack.rcv_mss; 2394 int free_space = tcp_space(sk); 2395 int allowed_space = tcp_full_space(sk); 2396 int full_space = min_t(int, tp->window_clamp, allowed_space); 2397 int window; 2398 2399 if (mss > full_space) 2400 mss = full_space; 2401 2402 if (free_space < (full_space >> 1)) { 2403 icsk->icsk_ack.quick = 0; 2404 2405 if (tcp_under_memory_pressure(sk)) 2406 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 2407 4U * tp->advmss); 2408 2409 /* free_space might become our new window, make sure we don't 2410 * increase it due to wscale. 2411 */ 2412 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale); 2413 2414 /* if free space is less than mss estimate, or is below 1/16th 2415 * of the maximum allowed, try to move to zero-window, else 2416 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and 2417 * new incoming data is dropped due to memory limits. 2418 * With large window, mss test triggers way too late in order 2419 * to announce zero window in time before rmem limit kicks in. 2420 */ 2421 if (free_space < (allowed_space >> 4) || free_space < mss) 2422 return 0; 2423 } 2424 2425 if (free_space > tp->rcv_ssthresh) 2426 free_space = tp->rcv_ssthresh; 2427 2428 /* Don't do rounding if we are using window scaling, since the 2429 * scaled window will not line up with the MSS boundary anyway. 2430 */ 2431 window = tp->rcv_wnd; 2432 if (tp->rx_opt.rcv_wscale) { 2433 window = free_space; 2434 2435 /* Advertise enough space so that it won't get scaled away. 2436 * Import case: prevent zero window announcement if 2437 * 1<<rcv_wscale > mss. 2438 */ 2439 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window) 2440 window = (((window >> tp->rx_opt.rcv_wscale) + 1) 2441 << tp->rx_opt.rcv_wscale); 2442 } else { 2443 /* Get the largest window that is a nice multiple of mss. 2444 * Window clamp already applied above. 2445 * If our current window offering is within 1 mss of the 2446 * free space we just keep it. This prevents the divide 2447 * and multiply from happening most of the time. 2448 * We also don't do any window rounding when the free space 2449 * is too small. 2450 */ 2451 if (window <= free_space - mss || window > free_space) 2452 window = (free_space / mss) * mss; 2453 else if (mss == full_space && 2454 free_space > window + (full_space >> 1)) 2455 window = free_space; 2456 } 2457 2458 return window; 2459 } 2460 2461 /* Collapses two adjacent SKB's during retransmission. */ 2462 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb) 2463 { 2464 struct tcp_sock *tp = tcp_sk(sk); 2465 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb); 2466 int skb_size, next_skb_size; 2467 2468 skb_size = skb->len; 2469 next_skb_size = next_skb->len; 2470 2471 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1); 2472 2473 tcp_highest_sack_combine(sk, next_skb, skb); 2474 2475 tcp_unlink_write_queue(next_skb, sk); 2476 2477 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size), 2478 next_skb_size); 2479 2480 if (next_skb->ip_summed == CHECKSUM_PARTIAL) 2481 skb->ip_summed = CHECKSUM_PARTIAL; 2482 2483 if (skb->ip_summed != CHECKSUM_PARTIAL) 2484 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size); 2485 2486 /* Update sequence range on original skb. */ 2487 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq; 2488 2489 /* Merge over control information. This moves PSH/FIN etc. over */ 2490 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags; 2491 2492 /* All done, get rid of second SKB and account for it so 2493 * packet counting does not break. 2494 */ 2495 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS; 2496 2497 /* changed transmit queue under us so clear hints */ 2498 tcp_clear_retrans_hints_partial(tp); 2499 if (next_skb == tp->retransmit_skb_hint) 2500 tp->retransmit_skb_hint = skb; 2501 2502 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb)); 2503 2504 sk_wmem_free_skb(sk, next_skb); 2505 } 2506 2507 /* Check if coalescing SKBs is legal. */ 2508 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb) 2509 { 2510 if (tcp_skb_pcount(skb) > 1) 2511 return false; 2512 /* TODO: SACK collapsing could be used to remove this condition */ 2513 if (skb_shinfo(skb)->nr_frags != 0) 2514 return false; 2515 if (skb_cloned(skb)) 2516 return false; 2517 if (skb == tcp_send_head(sk)) 2518 return false; 2519 /* Some heurestics for collapsing over SACK'd could be invented */ 2520 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 2521 return false; 2522 2523 return true; 2524 } 2525 2526 /* Collapse packets in the retransmit queue to make to create 2527 * less packets on the wire. This is only done on retransmission. 2528 */ 2529 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, 2530 int space) 2531 { 2532 struct tcp_sock *tp = tcp_sk(sk); 2533 struct sk_buff *skb = to, *tmp; 2534 bool first = true; 2535 2536 if (!sysctl_tcp_retrans_collapse) 2537 return; 2538 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN) 2539 return; 2540 2541 tcp_for_write_queue_from_safe(skb, tmp, sk) { 2542 if (!tcp_can_collapse(sk, skb)) 2543 break; 2544 2545 space -= skb->len; 2546 2547 if (first) { 2548 first = false; 2549 continue; 2550 } 2551 2552 if (space < 0) 2553 break; 2554 /* Punt if not enough space exists in the first SKB for 2555 * the data in the second 2556 */ 2557 if (skb->len > skb_availroom(to)) 2558 break; 2559 2560 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp))) 2561 break; 2562 2563 tcp_collapse_retrans(sk, to); 2564 } 2565 } 2566 2567 /* This retransmits one SKB. Policy decisions and retransmit queue 2568 * state updates are done by the caller. Returns non-zero if an 2569 * error occurred which prevented the send. 2570 */ 2571 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) 2572 { 2573 struct tcp_sock *tp = tcp_sk(sk); 2574 struct inet_connection_sock *icsk = inet_csk(sk); 2575 unsigned int cur_mss; 2576 int err; 2577 2578 /* Inconslusive MTU probe */ 2579 if (icsk->icsk_mtup.probe_size) { 2580 icsk->icsk_mtup.probe_size = 0; 2581 } 2582 2583 /* Do not sent more than we queued. 1/4 is reserved for possible 2584 * copying overhead: fragmentation, tunneling, mangling etc. 2585 */ 2586 if (atomic_read(&sk->sk_wmem_alloc) > 2587 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf)) 2588 return -EAGAIN; 2589 2590 if (skb_still_in_host_queue(sk, skb)) 2591 return -EBUSY; 2592 2593 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) { 2594 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 2595 BUG(); 2596 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) 2597 return -ENOMEM; 2598 } 2599 2600 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) 2601 return -EHOSTUNREACH; /* Routing failure or similar. */ 2602 2603 cur_mss = tcp_current_mss(sk); 2604 2605 /* If receiver has shrunk his window, and skb is out of 2606 * new window, do not retransmit it. The exception is the 2607 * case, when window is shrunk to zero. In this case 2608 * our retransmit serves as a zero window probe. 2609 */ 2610 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) && 2611 TCP_SKB_CB(skb)->seq != tp->snd_una) 2612 return -EAGAIN; 2613 2614 if (skb->len > cur_mss) { 2615 if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC)) 2616 return -ENOMEM; /* We'll try again later. */ 2617 } else { 2618 int oldpcount = tcp_skb_pcount(skb); 2619 2620 if (unlikely(oldpcount > 1)) { 2621 if (skb_unclone(skb, GFP_ATOMIC)) 2622 return -ENOMEM; 2623 tcp_init_tso_segs(sk, skb, cur_mss); 2624 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb)); 2625 } 2626 } 2627 2628 /* RFC3168, section 6.1.1.1. ECN fallback */ 2629 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN) 2630 tcp_ecn_clear_syn(sk, skb); 2631 2632 tcp_retrans_try_collapse(sk, skb, cur_mss); 2633 2634 /* Make a copy, if the first transmission SKB clone we made 2635 * is still in somebody's hands, else make a clone. 2636 */ 2637 2638 /* make sure skb->data is aligned on arches that require it 2639 * and check if ack-trimming & collapsing extended the headroom 2640 * beyond what csum_start can cover. 2641 */ 2642 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) || 2643 skb_headroom(skb) >= 0xFFFF)) { 2644 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER, 2645 GFP_ATOMIC); 2646 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) : 2647 -ENOBUFS; 2648 } else { 2649 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 2650 } 2651 2652 if (likely(!err)) { 2653 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS; 2654 /* Update global TCP statistics. */ 2655 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS); 2656 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN) 2657 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS); 2658 tp->total_retrans++; 2659 } 2660 return err; 2661 } 2662 2663 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) 2664 { 2665 struct tcp_sock *tp = tcp_sk(sk); 2666 int err = __tcp_retransmit_skb(sk, skb); 2667 2668 if (err == 0) { 2669 #if FASTRETRANS_DEBUG > 0 2670 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { 2671 net_dbg_ratelimited("retrans_out leaked\n"); 2672 } 2673 #endif 2674 if (!tp->retrans_out) 2675 tp->lost_retrans_low = tp->snd_nxt; 2676 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS; 2677 tp->retrans_out += tcp_skb_pcount(skb); 2678 2679 /* Save stamp of the first retransmit. */ 2680 if (!tp->retrans_stamp) 2681 tp->retrans_stamp = tcp_skb_timestamp(skb); 2682 2683 /* snd_nxt is stored to detect loss of retransmitted segment, 2684 * see tcp_input.c tcp_sacktag_write_queue(). 2685 */ 2686 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt; 2687 } else if (err != -EBUSY) { 2688 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL); 2689 } 2690 2691 if (tp->undo_retrans < 0) 2692 tp->undo_retrans = 0; 2693 tp->undo_retrans += tcp_skb_pcount(skb); 2694 return err; 2695 } 2696 2697 /* Check if we forward retransmits are possible in the current 2698 * window/congestion state. 2699 */ 2700 static bool tcp_can_forward_retransmit(struct sock *sk) 2701 { 2702 const struct inet_connection_sock *icsk = inet_csk(sk); 2703 const struct tcp_sock *tp = tcp_sk(sk); 2704 2705 /* Forward retransmissions are possible only during Recovery. */ 2706 if (icsk->icsk_ca_state != TCP_CA_Recovery) 2707 return false; 2708 2709 /* No forward retransmissions in Reno are possible. */ 2710 if (tcp_is_reno(tp)) 2711 return false; 2712 2713 /* Yeah, we have to make difficult choice between forward transmission 2714 * and retransmission... Both ways have their merits... 2715 * 2716 * For now we do not retransmit anything, while we have some new 2717 * segments to send. In the other cases, follow rule 3 for 2718 * NextSeg() specified in RFC3517. 2719 */ 2720 2721 if (tcp_may_send_now(sk)) 2722 return false; 2723 2724 return true; 2725 } 2726 2727 /* This gets called after a retransmit timeout, and the initially 2728 * retransmitted data is acknowledged. It tries to continue 2729 * resending the rest of the retransmit queue, until either 2730 * we've sent it all or the congestion window limit is reached. 2731 * If doing SACK, the first ACK which comes back for a timeout 2732 * based retransmit packet might feed us FACK information again. 2733 * If so, we use it to avoid unnecessarily retransmissions. 2734 */ 2735 void tcp_xmit_retransmit_queue(struct sock *sk) 2736 { 2737 const struct inet_connection_sock *icsk = inet_csk(sk); 2738 struct tcp_sock *tp = tcp_sk(sk); 2739 struct sk_buff *skb; 2740 struct sk_buff *hole = NULL; 2741 u32 last_lost; 2742 int mib_idx; 2743 int fwd_rexmitting = 0; 2744 2745 if (!tp->packets_out) 2746 return; 2747 2748 if (!tp->lost_out) 2749 tp->retransmit_high = tp->snd_una; 2750 2751 if (tp->retransmit_skb_hint) { 2752 skb = tp->retransmit_skb_hint; 2753 last_lost = TCP_SKB_CB(skb)->end_seq; 2754 if (after(last_lost, tp->retransmit_high)) 2755 last_lost = tp->retransmit_high; 2756 } else { 2757 skb = tcp_write_queue_head(sk); 2758 last_lost = tp->snd_una; 2759 } 2760 2761 tcp_for_write_queue_from(skb, sk) { 2762 __u8 sacked = TCP_SKB_CB(skb)->sacked; 2763 2764 if (skb == tcp_send_head(sk)) 2765 break; 2766 /* we could do better than to assign each time */ 2767 if (!hole) 2768 tp->retransmit_skb_hint = skb; 2769 2770 /* Assume this retransmit will generate 2771 * only one packet for congestion window 2772 * calculation purposes. This works because 2773 * tcp_retransmit_skb() will chop up the 2774 * packet to be MSS sized and all the 2775 * packet counting works out. 2776 */ 2777 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd) 2778 return; 2779 2780 if (fwd_rexmitting) { 2781 begin_fwd: 2782 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp))) 2783 break; 2784 mib_idx = LINUX_MIB_TCPFORWARDRETRANS; 2785 2786 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) { 2787 tp->retransmit_high = last_lost; 2788 if (!tcp_can_forward_retransmit(sk)) 2789 break; 2790 /* Backtrack if necessary to non-L'ed skb */ 2791 if (hole) { 2792 skb = hole; 2793 hole = NULL; 2794 } 2795 fwd_rexmitting = 1; 2796 goto begin_fwd; 2797 2798 } else if (!(sacked & TCPCB_LOST)) { 2799 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED))) 2800 hole = skb; 2801 continue; 2802 2803 } else { 2804 last_lost = TCP_SKB_CB(skb)->end_seq; 2805 if (icsk->icsk_ca_state != TCP_CA_Loss) 2806 mib_idx = LINUX_MIB_TCPFASTRETRANS; 2807 else 2808 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS; 2809 } 2810 2811 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS)) 2812 continue; 2813 2814 if (tcp_retransmit_skb(sk, skb)) 2815 return; 2816 2817 NET_INC_STATS_BH(sock_net(sk), mib_idx); 2818 2819 if (tcp_in_cwnd_reduction(sk)) 2820 tp->prr_out += tcp_skb_pcount(skb); 2821 2822 if (skb == tcp_write_queue_head(sk)) 2823 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 2824 inet_csk(sk)->icsk_rto, 2825 TCP_RTO_MAX); 2826 } 2827 } 2828 2829 /* We allow to exceed memory limits for FIN packets to expedite 2830 * connection tear down and (memory) recovery. 2831 * Otherwise tcp_send_fin() could be tempted to either delay FIN 2832 * or even be forced to close flow without any FIN. 2833 * In general, we want to allow one skb per socket to avoid hangs 2834 * with edge trigger epoll() 2835 */ 2836 void sk_forced_mem_schedule(struct sock *sk, int size) 2837 { 2838 int amt, status; 2839 2840 if (size <= sk->sk_forward_alloc) 2841 return; 2842 amt = sk_mem_pages(size); 2843 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM; 2844 sk_memory_allocated_add(sk, amt, &status); 2845 } 2846 2847 /* Send a FIN. The caller locks the socket for us. 2848 * We should try to send a FIN packet really hard, but eventually give up. 2849 */ 2850 void tcp_send_fin(struct sock *sk) 2851 { 2852 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk); 2853 struct tcp_sock *tp = tcp_sk(sk); 2854 2855 /* Optimization, tack on the FIN if we have one skb in write queue and 2856 * this skb was not yet sent, or we are under memory pressure. 2857 * Note: in the latter case, FIN packet will be sent after a timeout, 2858 * as TCP stack thinks it has already been transmitted. 2859 */ 2860 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) { 2861 coalesce: 2862 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN; 2863 TCP_SKB_CB(tskb)->end_seq++; 2864 tp->write_seq++; 2865 if (!tcp_send_head(sk)) { 2866 /* This means tskb was already sent. 2867 * Pretend we included the FIN on previous transmit. 2868 * We need to set tp->snd_nxt to the value it would have 2869 * if FIN had been sent. This is because retransmit path 2870 * does not change tp->snd_nxt. 2871 */ 2872 tp->snd_nxt++; 2873 return; 2874 } 2875 } else { 2876 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation); 2877 if (unlikely(!skb)) { 2878 if (tskb) 2879 goto coalesce; 2880 return; 2881 } 2882 skb_reserve(skb, MAX_TCP_HEADER); 2883 sk_forced_mem_schedule(sk, skb->truesize); 2884 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */ 2885 tcp_init_nondata_skb(skb, tp->write_seq, 2886 TCPHDR_ACK | TCPHDR_FIN); 2887 tcp_queue_skb(sk, skb); 2888 } 2889 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF); 2890 } 2891 2892 /* We get here when a process closes a file descriptor (either due to 2893 * an explicit close() or as a byproduct of exit()'ing) and there 2894 * was unread data in the receive queue. This behavior is recommended 2895 * by RFC 2525, section 2.17. -DaveM 2896 */ 2897 void tcp_send_active_reset(struct sock *sk, gfp_t priority) 2898 { 2899 struct sk_buff *skb; 2900 2901 /* NOTE: No TCP options attached and we never retransmit this. */ 2902 skb = alloc_skb(MAX_TCP_HEADER, priority); 2903 if (!skb) { 2904 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); 2905 return; 2906 } 2907 2908 /* Reserve space for headers and prepare control bits. */ 2909 skb_reserve(skb, MAX_TCP_HEADER); 2910 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk), 2911 TCPHDR_ACK | TCPHDR_RST); 2912 /* Send it off. */ 2913 if (tcp_transmit_skb(sk, skb, 0, priority)) 2914 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); 2915 2916 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS); 2917 } 2918 2919 /* Send a crossed SYN-ACK during socket establishment. 2920 * WARNING: This routine must only be called when we have already sent 2921 * a SYN packet that crossed the incoming SYN that caused this routine 2922 * to get called. If this assumption fails then the initial rcv_wnd 2923 * and rcv_wscale values will not be correct. 2924 */ 2925 int tcp_send_synack(struct sock *sk) 2926 { 2927 struct sk_buff *skb; 2928 2929 skb = tcp_write_queue_head(sk); 2930 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) { 2931 pr_debug("%s: wrong queue state\n", __func__); 2932 return -EFAULT; 2933 } 2934 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) { 2935 if (skb_cloned(skb)) { 2936 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC); 2937 if (!nskb) 2938 return -ENOMEM; 2939 tcp_unlink_write_queue(skb, sk); 2940 __skb_header_release(nskb); 2941 __tcp_add_write_queue_head(sk, nskb); 2942 sk_wmem_free_skb(sk, skb); 2943 sk->sk_wmem_queued += nskb->truesize; 2944 sk_mem_charge(sk, nskb->truesize); 2945 skb = nskb; 2946 } 2947 2948 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK; 2949 tcp_ecn_send_synack(sk, skb); 2950 } 2951 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 2952 } 2953 2954 /** 2955 * tcp_make_synack - Prepare a SYN-ACK. 2956 * sk: listener socket 2957 * dst: dst entry attached to the SYNACK 2958 * req: request_sock pointer 2959 * 2960 * Allocate one skb and build a SYNACK packet. 2961 * @dst is consumed : Caller should not use it again. 2962 */ 2963 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst, 2964 struct request_sock *req, 2965 struct tcp_fastopen_cookie *foc) 2966 { 2967 struct tcp_out_options opts; 2968 struct inet_request_sock *ireq = inet_rsk(req); 2969 struct tcp_sock *tp = tcp_sk(sk); 2970 struct tcphdr *th; 2971 struct sk_buff *skb; 2972 struct tcp_md5sig_key *md5 = NULL; 2973 int tcp_header_size; 2974 int mss; 2975 2976 skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC); 2977 if (unlikely(!skb)) { 2978 dst_release(dst); 2979 return NULL; 2980 } 2981 /* Reserve space for headers. */ 2982 skb_reserve(skb, MAX_TCP_HEADER); 2983 2984 skb_dst_set(skb, dst); 2985 2986 mss = dst_metric_advmss(dst); 2987 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss) 2988 mss = tp->rx_opt.user_mss; 2989 2990 memset(&opts, 0, sizeof(opts)); 2991 #ifdef CONFIG_SYN_COOKIES 2992 if (unlikely(req->cookie_ts)) 2993 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req); 2994 else 2995 #endif 2996 skb_mstamp_get(&skb->skb_mstamp); 2997 2998 #ifdef CONFIG_TCP_MD5SIG 2999 rcu_read_lock(); 3000 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req)); 3001 #endif 3002 tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5, 3003 foc) + sizeof(*th); 3004 3005 skb_push(skb, tcp_header_size); 3006 skb_reset_transport_header(skb); 3007 3008 th = tcp_hdr(skb); 3009 memset(th, 0, sizeof(struct tcphdr)); 3010 th->syn = 1; 3011 th->ack = 1; 3012 tcp_ecn_make_synack(req, th, sk); 3013 th->source = htons(ireq->ir_num); 3014 th->dest = ireq->ir_rmt_port; 3015 /* Setting of flags are superfluous here for callers (and ECE is 3016 * not even correctly set) 3017 */ 3018 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn, 3019 TCPHDR_SYN | TCPHDR_ACK); 3020 3021 th->seq = htonl(TCP_SKB_CB(skb)->seq); 3022 /* XXX data is queued and acked as is. No buffer/window check */ 3023 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt); 3024 3025 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */ 3026 th->window = htons(min(req->rcv_wnd, 65535U)); 3027 tcp_options_write((__be32 *)(th + 1), tp, &opts); 3028 th->doff = (tcp_header_size >> 2); 3029 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS); 3030 3031 #ifdef CONFIG_TCP_MD5SIG 3032 /* Okay, we have all we need - do the md5 hash if needed */ 3033 if (md5) 3034 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location, 3035 md5, req_to_sk(req), skb); 3036 rcu_read_unlock(); 3037 #endif 3038 3039 /* Do not fool tcpdump (if any), clean our debris */ 3040 skb->tstamp.tv64 = 0; 3041 return skb; 3042 } 3043 EXPORT_SYMBOL(tcp_make_synack); 3044 3045 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst) 3046 { 3047 struct inet_connection_sock *icsk = inet_csk(sk); 3048 const struct tcp_congestion_ops *ca; 3049 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 3050 3051 if (ca_key == TCP_CA_UNSPEC) 3052 return; 3053 3054 rcu_read_lock(); 3055 ca = tcp_ca_find_key(ca_key); 3056 if (likely(ca && try_module_get(ca->owner))) { 3057 module_put(icsk->icsk_ca_ops->owner); 3058 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 3059 icsk->icsk_ca_ops = ca; 3060 } 3061 rcu_read_unlock(); 3062 } 3063 3064 /* Do all connect socket setups that can be done AF independent. */ 3065 static void tcp_connect_init(struct sock *sk) 3066 { 3067 const struct dst_entry *dst = __sk_dst_get(sk); 3068 struct tcp_sock *tp = tcp_sk(sk); 3069 __u8 rcv_wscale; 3070 3071 /* We'll fix this up when we get a response from the other end. 3072 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT. 3073 */ 3074 tp->tcp_header_len = sizeof(struct tcphdr) + 3075 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0); 3076 3077 #ifdef CONFIG_TCP_MD5SIG 3078 if (tp->af_specific->md5_lookup(sk, sk)) 3079 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; 3080 #endif 3081 3082 /* If user gave his TCP_MAXSEG, record it to clamp */ 3083 if (tp->rx_opt.user_mss) 3084 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; 3085 tp->max_window = 0; 3086 tcp_mtup_init(sk); 3087 tcp_sync_mss(sk, dst_mtu(dst)); 3088 3089 tcp_ca_dst_init(sk, dst); 3090 3091 if (!tp->window_clamp) 3092 tp->window_clamp = dst_metric(dst, RTAX_WINDOW); 3093 tp->advmss = dst_metric_advmss(dst); 3094 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss) 3095 tp->advmss = tp->rx_opt.user_mss; 3096 3097 tcp_initialize_rcv_mss(sk); 3098 3099 /* limit the window selection if the user enforce a smaller rx buffer */ 3100 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && 3101 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0)) 3102 tp->window_clamp = tcp_full_space(sk); 3103 3104 tcp_select_initial_window(tcp_full_space(sk), 3105 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0), 3106 &tp->rcv_wnd, 3107 &tp->window_clamp, 3108 sysctl_tcp_window_scaling, 3109 &rcv_wscale, 3110 dst_metric(dst, RTAX_INITRWND)); 3111 3112 tp->rx_opt.rcv_wscale = rcv_wscale; 3113 tp->rcv_ssthresh = tp->rcv_wnd; 3114 3115 sk->sk_err = 0; 3116 sock_reset_flag(sk, SOCK_DONE); 3117 tp->snd_wnd = 0; 3118 tcp_init_wl(tp, 0); 3119 tp->snd_una = tp->write_seq; 3120 tp->snd_sml = tp->write_seq; 3121 tp->snd_up = tp->write_seq; 3122 tp->snd_nxt = tp->write_seq; 3123 3124 if (likely(!tp->repair)) 3125 tp->rcv_nxt = 0; 3126 else 3127 tp->rcv_tstamp = tcp_time_stamp; 3128 tp->rcv_wup = tp->rcv_nxt; 3129 tp->copied_seq = tp->rcv_nxt; 3130 3131 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; 3132 inet_csk(sk)->icsk_retransmits = 0; 3133 tcp_clear_retrans(tp); 3134 } 3135 3136 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb) 3137 { 3138 struct tcp_sock *tp = tcp_sk(sk); 3139 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb); 3140 3141 tcb->end_seq += skb->len; 3142 __skb_header_release(skb); 3143 __tcp_add_write_queue_tail(sk, skb); 3144 sk->sk_wmem_queued += skb->truesize; 3145 sk_mem_charge(sk, skb->truesize); 3146 tp->write_seq = tcb->end_seq; 3147 tp->packets_out += tcp_skb_pcount(skb); 3148 } 3149 3150 /* Build and send a SYN with data and (cached) Fast Open cookie. However, 3151 * queue a data-only packet after the regular SYN, such that regular SYNs 3152 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges 3153 * only the SYN sequence, the data are retransmitted in the first ACK. 3154 * If cookie is not cached or other error occurs, falls back to send a 3155 * regular SYN with Fast Open cookie request option. 3156 */ 3157 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn) 3158 { 3159 struct tcp_sock *tp = tcp_sk(sk); 3160 struct tcp_fastopen_request *fo = tp->fastopen_req; 3161 int syn_loss = 0, space, err = 0, copied; 3162 unsigned long last_syn_loss = 0; 3163 struct sk_buff *syn_data; 3164 3165 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */ 3166 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie, 3167 &syn_loss, &last_syn_loss); 3168 /* Recurring FO SYN losses: revert to regular handshake temporarily */ 3169 if (syn_loss > 1 && 3170 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) { 3171 fo->cookie.len = -1; 3172 goto fallback; 3173 } 3174 3175 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE) 3176 fo->cookie.len = -1; 3177 else if (fo->cookie.len <= 0) 3178 goto fallback; 3179 3180 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and 3181 * user-MSS. Reserve maximum option space for middleboxes that add 3182 * private TCP options. The cost is reduced data space in SYN :( 3183 */ 3184 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp) 3185 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; 3186 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) - 3187 MAX_TCP_OPTION_SPACE; 3188 3189 space = min_t(size_t, space, fo->size); 3190 3191 /* limit to order-0 allocations */ 3192 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER)); 3193 3194 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false); 3195 if (!syn_data) 3196 goto fallback; 3197 syn_data->ip_summed = CHECKSUM_PARTIAL; 3198 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb)); 3199 copied = copy_from_iter(skb_put(syn_data, space), space, 3200 &fo->data->msg_iter); 3201 if (unlikely(!copied)) { 3202 kfree_skb(syn_data); 3203 goto fallback; 3204 } 3205 if (copied != space) { 3206 skb_trim(syn_data, copied); 3207 space = copied; 3208 } 3209 3210 /* No more data pending in inet_wait_for_connect() */ 3211 if (space == fo->size) 3212 fo->data = NULL; 3213 fo->copied = space; 3214 3215 tcp_connect_queue_skb(sk, syn_data); 3216 3217 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation); 3218 3219 syn->skb_mstamp = syn_data->skb_mstamp; 3220 3221 /* Now full SYN+DATA was cloned and sent (or not), 3222 * remove the SYN from the original skb (syn_data) 3223 * we keep in write queue in case of a retransmit, as we 3224 * also have the SYN packet (with no data) in the same queue. 3225 */ 3226 TCP_SKB_CB(syn_data)->seq++; 3227 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH; 3228 if (!err) { 3229 tp->syn_data = (fo->copied > 0); 3230 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT); 3231 goto done; 3232 } 3233 3234 fallback: 3235 /* Send a regular SYN with Fast Open cookie request option */ 3236 if (fo->cookie.len > 0) 3237 fo->cookie.len = 0; 3238 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation); 3239 if (err) 3240 tp->syn_fastopen = 0; 3241 done: 3242 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */ 3243 return err; 3244 } 3245 3246 /* Build a SYN and send it off. */ 3247 int tcp_connect(struct sock *sk) 3248 { 3249 struct tcp_sock *tp = tcp_sk(sk); 3250 struct sk_buff *buff; 3251 int err; 3252 3253 tcp_connect_init(sk); 3254 3255 if (unlikely(tp->repair)) { 3256 tcp_finish_connect(sk, NULL); 3257 return 0; 3258 } 3259 3260 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true); 3261 if (unlikely(!buff)) 3262 return -ENOBUFS; 3263 3264 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN); 3265 tp->retrans_stamp = tcp_time_stamp; 3266 tcp_connect_queue_skb(sk, buff); 3267 tcp_ecn_send_syn(sk, buff); 3268 3269 /* Send off SYN; include data in Fast Open. */ 3270 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) : 3271 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation); 3272 if (err == -ECONNREFUSED) 3273 return err; 3274 3275 /* We change tp->snd_nxt after the tcp_transmit_skb() call 3276 * in order to make this packet get counted in tcpOutSegs. 3277 */ 3278 tp->snd_nxt = tp->write_seq; 3279 tp->pushed_seq = tp->write_seq; 3280 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS); 3281 3282 /* Timer for repeating the SYN until an answer. */ 3283 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 3284 inet_csk(sk)->icsk_rto, TCP_RTO_MAX); 3285 return 0; 3286 } 3287 EXPORT_SYMBOL(tcp_connect); 3288 3289 /* Send out a delayed ack, the caller does the policy checking 3290 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check() 3291 * for details. 3292 */ 3293 void tcp_send_delayed_ack(struct sock *sk) 3294 { 3295 struct inet_connection_sock *icsk = inet_csk(sk); 3296 int ato = icsk->icsk_ack.ato; 3297 unsigned long timeout; 3298 3299 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK); 3300 3301 if (ato > TCP_DELACK_MIN) { 3302 const struct tcp_sock *tp = tcp_sk(sk); 3303 int max_ato = HZ / 2; 3304 3305 if (icsk->icsk_ack.pingpong || 3306 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)) 3307 max_ato = TCP_DELACK_MAX; 3308 3309 /* Slow path, intersegment interval is "high". */ 3310 3311 /* If some rtt estimate is known, use it to bound delayed ack. 3312 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements 3313 * directly. 3314 */ 3315 if (tp->srtt_us) { 3316 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3), 3317 TCP_DELACK_MIN); 3318 3319 if (rtt < max_ato) 3320 max_ato = rtt; 3321 } 3322 3323 ato = min(ato, max_ato); 3324 } 3325 3326 /* Stay within the limit we were given */ 3327 timeout = jiffies + ato; 3328 3329 /* Use new timeout only if there wasn't a older one earlier. */ 3330 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) { 3331 /* If delack timer was blocked or is about to expire, 3332 * send ACK now. 3333 */ 3334 if (icsk->icsk_ack.blocked || 3335 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) { 3336 tcp_send_ack(sk); 3337 return; 3338 } 3339 3340 if (!time_before(timeout, icsk->icsk_ack.timeout)) 3341 timeout = icsk->icsk_ack.timeout; 3342 } 3343 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; 3344 icsk->icsk_ack.timeout = timeout; 3345 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); 3346 } 3347 3348 /* This routine sends an ack and also updates the window. */ 3349 void tcp_send_ack(struct sock *sk) 3350 { 3351 struct sk_buff *buff; 3352 3353 /* If we have been reset, we may not send again. */ 3354 if (sk->sk_state == TCP_CLOSE) 3355 return; 3356 3357 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK); 3358 3359 /* We are not putting this on the write queue, so 3360 * tcp_transmit_skb() will set the ownership to this 3361 * sock. 3362 */ 3363 buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC)); 3364 if (!buff) { 3365 inet_csk_schedule_ack(sk); 3366 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN; 3367 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 3368 TCP_DELACK_MAX, TCP_RTO_MAX); 3369 return; 3370 } 3371 3372 /* Reserve space for headers and prepare control bits. */ 3373 skb_reserve(buff, MAX_TCP_HEADER); 3374 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK); 3375 3376 /* We do not want pure acks influencing TCP Small Queues or fq/pacing 3377 * too much. 3378 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784 3379 * We also avoid tcp_wfree() overhead (cache line miss accessing 3380 * tp->tsq_flags) by using regular sock_wfree() 3381 */ 3382 skb_set_tcp_pure_ack(buff); 3383 3384 /* Send it off, this clears delayed acks for us. */ 3385 skb_mstamp_get(&buff->skb_mstamp); 3386 tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC)); 3387 } 3388 EXPORT_SYMBOL_GPL(tcp_send_ack); 3389 3390 /* This routine sends a packet with an out of date sequence 3391 * number. It assumes the other end will try to ack it. 3392 * 3393 * Question: what should we make while urgent mode? 3394 * 4.4BSD forces sending single byte of data. We cannot send 3395 * out of window data, because we have SND.NXT==SND.MAX... 3396 * 3397 * Current solution: to send TWO zero-length segments in urgent mode: 3398 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is 3399 * out-of-date with SND.UNA-1 to probe window. 3400 */ 3401 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib) 3402 { 3403 struct tcp_sock *tp = tcp_sk(sk); 3404 struct sk_buff *skb; 3405 3406 /* We don't queue it, tcp_transmit_skb() sets ownership. */ 3407 skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC)); 3408 if (!skb) 3409 return -1; 3410 3411 /* Reserve space for headers and set control bits. */ 3412 skb_reserve(skb, MAX_TCP_HEADER); 3413 /* Use a previous sequence. This should cause the other 3414 * end to send an ack. Don't queue or clone SKB, just 3415 * send it. 3416 */ 3417 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK); 3418 skb_mstamp_get(&skb->skb_mstamp); 3419 NET_INC_STATS_BH(sock_net(sk), mib); 3420 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC); 3421 } 3422 3423 void tcp_send_window_probe(struct sock *sk) 3424 { 3425 if (sk->sk_state == TCP_ESTABLISHED) { 3426 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1; 3427 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE); 3428 } 3429 } 3430 3431 /* Initiate keepalive or window probe from timer. */ 3432 int tcp_write_wakeup(struct sock *sk, int mib) 3433 { 3434 struct tcp_sock *tp = tcp_sk(sk); 3435 struct sk_buff *skb; 3436 3437 if (sk->sk_state == TCP_CLOSE) 3438 return -1; 3439 3440 skb = tcp_send_head(sk); 3441 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) { 3442 int err; 3443 unsigned int mss = tcp_current_mss(sk); 3444 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 3445 3446 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq)) 3447 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq; 3448 3449 /* We are probing the opening of a window 3450 * but the window size is != 0 3451 * must have been a result SWS avoidance ( sender ) 3452 */ 3453 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq || 3454 skb->len > mss) { 3455 seg_size = min(seg_size, mss); 3456 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH; 3457 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC)) 3458 return -1; 3459 } else if (!tcp_skb_pcount(skb)) 3460 tcp_set_skb_tso_segs(sk, skb, mss); 3461 3462 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH; 3463 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 3464 if (!err) 3465 tcp_event_new_data_sent(sk, skb); 3466 return err; 3467 } else { 3468 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF)) 3469 tcp_xmit_probe_skb(sk, 1, mib); 3470 return tcp_xmit_probe_skb(sk, 0, mib); 3471 } 3472 } 3473 3474 /* A window probe timeout has occurred. If window is not closed send 3475 * a partial packet else a zero probe. 3476 */ 3477 void tcp_send_probe0(struct sock *sk) 3478 { 3479 struct inet_connection_sock *icsk = inet_csk(sk); 3480 struct tcp_sock *tp = tcp_sk(sk); 3481 unsigned long probe_max; 3482 int err; 3483 3484 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE); 3485 3486 if (tp->packets_out || !tcp_send_head(sk)) { 3487 /* Cancel probe timer, if it is not required. */ 3488 icsk->icsk_probes_out = 0; 3489 icsk->icsk_backoff = 0; 3490 return; 3491 } 3492 3493 if (err <= 0) { 3494 if (icsk->icsk_backoff < sysctl_tcp_retries2) 3495 icsk->icsk_backoff++; 3496 icsk->icsk_probes_out++; 3497 probe_max = TCP_RTO_MAX; 3498 } else { 3499 /* If packet was not sent due to local congestion, 3500 * do not backoff and do not remember icsk_probes_out. 3501 * Let local senders to fight for local resources. 3502 * 3503 * Use accumulated backoff yet. 3504 */ 3505 if (!icsk->icsk_probes_out) 3506 icsk->icsk_probes_out = 1; 3507 probe_max = TCP_RESOURCE_PROBE_INTERVAL; 3508 } 3509 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 3510 tcp_probe0_when(sk, probe_max), 3511 TCP_RTO_MAX); 3512 } 3513 3514 int tcp_rtx_synack(struct sock *sk, struct request_sock *req) 3515 { 3516 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific; 3517 struct flowi fl; 3518 int res; 3519 3520 res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL); 3521 if (!res) { 3522 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS); 3523 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS); 3524 } 3525 return res; 3526 } 3527 EXPORT_SYMBOL(tcp_rtx_synack); 3528