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 * Version: $Id: tcp_output.c,v 1.146 2002/02/01 22:01:04 davem Exp $ 9 * 10 * Authors: Ross Biro 11 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 12 * Mark Evans, <evansmp@uhura.aston.ac.uk> 13 * Corey Minyard <wf-rch!minyard@relay.EU.net> 14 * Florian La Roche, <flla@stud.uni-sb.de> 15 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 16 * Linus Torvalds, <torvalds@cs.helsinki.fi> 17 * Alan Cox, <gw4pts@gw4pts.ampr.org> 18 * Matthew Dillon, <dillon@apollo.west.oic.com> 19 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 20 * Jorge Cwik, <jorge@laser.satlink.net> 21 */ 22 23 /* 24 * Changes: Pedro Roque : Retransmit queue handled by TCP. 25 * : Fragmentation on mtu decrease 26 * : Segment collapse on retransmit 27 * : AF independence 28 * 29 * Linus Torvalds : send_delayed_ack 30 * David S. Miller : Charge memory using the right skb 31 * during syn/ack processing. 32 * David S. Miller : Output engine completely rewritten. 33 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr. 34 * Cacophonix Gaul : draft-minshall-nagle-01 35 * J Hadi Salim : ECN support 36 * 37 */ 38 39 #include <net/tcp.h> 40 41 #include <linux/compiler.h> 42 #include <linux/module.h> 43 #include <linux/smp_lock.h> 44 45 /* People can turn this off for buggy TCP's found in printers etc. */ 46 int sysctl_tcp_retrans_collapse = 1; 47 48 /* This limits the percentage of the congestion window which we 49 * will allow a single TSO frame to consume. Building TSO frames 50 * which are too large can cause TCP streams to be bursty. 51 */ 52 int sysctl_tcp_tso_win_divisor = 3; 53 54 static void update_send_head(struct sock *sk, struct tcp_sock *tp, 55 struct sk_buff *skb) 56 { 57 sk->sk_send_head = skb->next; 58 if (sk->sk_send_head == (struct sk_buff *)&sk->sk_write_queue) 59 sk->sk_send_head = NULL; 60 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq; 61 tcp_packets_out_inc(sk, tp, skb); 62 } 63 64 /* SND.NXT, if window was not shrunk. 65 * If window has been shrunk, what should we make? It is not clear at all. 66 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( 67 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already 68 * invalid. OK, let's make this for now: 69 */ 70 static inline __u32 tcp_acceptable_seq(struct sock *sk, struct tcp_sock *tp) 71 { 72 if (!before(tp->snd_una+tp->snd_wnd, tp->snd_nxt)) 73 return tp->snd_nxt; 74 else 75 return tp->snd_una+tp->snd_wnd; 76 } 77 78 /* Calculate mss to advertise in SYN segment. 79 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that: 80 * 81 * 1. It is independent of path mtu. 82 * 2. Ideally, it is maximal possible segment size i.e. 65535-40. 83 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of 84 * attached devices, because some buggy hosts are confused by 85 * large MSS. 86 * 4. We do not make 3, we advertise MSS, calculated from first 87 * hop device mtu, but allow to raise it to ip_rt_min_advmss. 88 * This may be overridden via information stored in routing table. 89 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible, 90 * probably even Jumbo". 91 */ 92 static __u16 tcp_advertise_mss(struct sock *sk) 93 { 94 struct tcp_sock *tp = tcp_sk(sk); 95 struct dst_entry *dst = __sk_dst_get(sk); 96 int mss = tp->advmss; 97 98 if (dst && dst_metric(dst, RTAX_ADVMSS) < mss) { 99 mss = dst_metric(dst, RTAX_ADVMSS); 100 tp->advmss = mss; 101 } 102 103 return (__u16)mss; 104 } 105 106 /* RFC2861. Reset CWND after idle period longer RTO to "restart window". 107 * This is the first part of cwnd validation mechanism. */ 108 static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst) 109 { 110 struct tcp_sock *tp = tcp_sk(sk); 111 s32 delta = tcp_time_stamp - tp->lsndtime; 112 u32 restart_cwnd = tcp_init_cwnd(tp, dst); 113 u32 cwnd = tp->snd_cwnd; 114 115 tcp_ca_event(sk, CA_EVENT_CWND_RESTART); 116 117 tp->snd_ssthresh = tcp_current_ssthresh(sk); 118 restart_cwnd = min(restart_cwnd, cwnd); 119 120 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd) 121 cwnd >>= 1; 122 tp->snd_cwnd = max(cwnd, restart_cwnd); 123 tp->snd_cwnd_stamp = tcp_time_stamp; 124 tp->snd_cwnd_used = 0; 125 } 126 127 static void tcp_event_data_sent(struct tcp_sock *tp, 128 struct sk_buff *skb, struct sock *sk) 129 { 130 struct inet_connection_sock *icsk = inet_csk(sk); 131 const u32 now = tcp_time_stamp; 132 133 if (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto) 134 tcp_cwnd_restart(sk, __sk_dst_get(sk)); 135 136 tp->lsndtime = now; 137 138 /* If it is a reply for ato after last received 139 * packet, enter pingpong mode. 140 */ 141 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) 142 icsk->icsk_ack.pingpong = 1; 143 } 144 145 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts) 146 { 147 tcp_dec_quickack_mode(sk, pkts); 148 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); 149 } 150 151 /* Determine a window scaling and initial window to offer. 152 * Based on the assumption that the given amount of space 153 * will be offered. Store the results in the tp structure. 154 * NOTE: for smooth operation initial space offering should 155 * be a multiple of mss if possible. We assume here that mss >= 1. 156 * This MUST be enforced by all callers. 157 */ 158 void tcp_select_initial_window(int __space, __u32 mss, 159 __u32 *rcv_wnd, __u32 *window_clamp, 160 int wscale_ok, __u8 *rcv_wscale) 161 { 162 unsigned int space = (__space < 0 ? 0 : __space); 163 164 /* If no clamp set the clamp to the max possible scaled window */ 165 if (*window_clamp == 0) 166 (*window_clamp) = (65535 << 14); 167 space = min(*window_clamp, space); 168 169 /* Quantize space offering to a multiple of mss if possible. */ 170 if (space > mss) 171 space = (space / mss) * mss; 172 173 /* NOTE: offering an initial window larger than 32767 174 * will break some buggy TCP stacks. We try to be nice. 175 * If we are not window scaling, then this truncates 176 * our initial window offering to 32k. There should also 177 * be a sysctl option to stop being nice. 178 */ 179 (*rcv_wnd) = min(space, MAX_TCP_WINDOW); 180 (*rcv_wscale) = 0; 181 if (wscale_ok) { 182 /* Set window scaling on max possible window 183 * See RFC1323 for an explanation of the limit to 14 184 */ 185 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max); 186 while (space > 65535 && (*rcv_wscale) < 14) { 187 space >>= 1; 188 (*rcv_wscale)++; 189 } 190 } 191 192 /* Set initial window to value enough for senders, 193 * following RFC2414. Senders, not following this RFC, 194 * will be satisfied with 2. 195 */ 196 if (mss > (1<<*rcv_wscale)) { 197 int init_cwnd = 4; 198 if (mss > 1460*3) 199 init_cwnd = 2; 200 else if (mss > 1460) 201 init_cwnd = 3; 202 if (*rcv_wnd > init_cwnd*mss) 203 *rcv_wnd = init_cwnd*mss; 204 } 205 206 /* Set the clamp no higher than max representable value */ 207 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp); 208 } 209 210 /* Chose a new window to advertise, update state in tcp_sock for the 211 * socket, and return result with RFC1323 scaling applied. The return 212 * value can be stuffed directly into th->window for an outgoing 213 * frame. 214 */ 215 static u16 tcp_select_window(struct sock *sk) 216 { 217 struct tcp_sock *tp = tcp_sk(sk); 218 u32 cur_win = tcp_receive_window(tp); 219 u32 new_win = __tcp_select_window(sk); 220 221 /* Never shrink the offered window */ 222 if(new_win < cur_win) { 223 /* Danger Will Robinson! 224 * Don't update rcv_wup/rcv_wnd here or else 225 * we will not be able to advertise a zero 226 * window in time. --DaveM 227 * 228 * Relax Will Robinson. 229 */ 230 new_win = cur_win; 231 } 232 tp->rcv_wnd = new_win; 233 tp->rcv_wup = tp->rcv_nxt; 234 235 /* Make sure we do not exceed the maximum possible 236 * scaled window. 237 */ 238 if (!tp->rx_opt.rcv_wscale) 239 new_win = min(new_win, MAX_TCP_WINDOW); 240 else 241 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale)); 242 243 /* RFC1323 scaling applied */ 244 new_win >>= tp->rx_opt.rcv_wscale; 245 246 /* If we advertise zero window, disable fast path. */ 247 if (new_win == 0) 248 tp->pred_flags = 0; 249 250 return new_win; 251 } 252 253 static void tcp_build_and_update_options(__u32 *ptr, struct tcp_sock *tp, 254 __u32 tstamp) 255 { 256 if (tp->rx_opt.tstamp_ok) { 257 *ptr++ = __constant_htonl((TCPOPT_NOP << 24) | 258 (TCPOPT_NOP << 16) | 259 (TCPOPT_TIMESTAMP << 8) | 260 TCPOLEN_TIMESTAMP); 261 *ptr++ = htonl(tstamp); 262 *ptr++ = htonl(tp->rx_opt.ts_recent); 263 } 264 if (tp->rx_opt.eff_sacks) { 265 struct tcp_sack_block *sp = tp->rx_opt.dsack ? tp->duplicate_sack : tp->selective_acks; 266 int this_sack; 267 268 *ptr++ = htonl((TCPOPT_NOP << 24) | 269 (TCPOPT_NOP << 16) | 270 (TCPOPT_SACK << 8) | 271 (TCPOLEN_SACK_BASE + (tp->rx_opt.eff_sacks * 272 TCPOLEN_SACK_PERBLOCK))); 273 for(this_sack = 0; this_sack < tp->rx_opt.eff_sacks; this_sack++) { 274 *ptr++ = htonl(sp[this_sack].start_seq); 275 *ptr++ = htonl(sp[this_sack].end_seq); 276 } 277 if (tp->rx_opt.dsack) { 278 tp->rx_opt.dsack = 0; 279 tp->rx_opt.eff_sacks--; 280 } 281 } 282 } 283 284 /* Construct a tcp options header for a SYN or SYN_ACK packet. 285 * If this is every changed make sure to change the definition of 286 * MAX_SYN_SIZE to match the new maximum number of options that you 287 * can generate. 288 */ 289 static void tcp_syn_build_options(__u32 *ptr, int mss, int ts, int sack, 290 int offer_wscale, int wscale, __u32 tstamp, 291 __u32 ts_recent) 292 { 293 /* We always get an MSS option. 294 * The option bytes which will be seen in normal data 295 * packets should timestamps be used, must be in the MSS 296 * advertised. But we subtract them from tp->mss_cache so 297 * that calculations in tcp_sendmsg are simpler etc. 298 * So account for this fact here if necessary. If we 299 * don't do this correctly, as a receiver we won't 300 * recognize data packets as being full sized when we 301 * should, and thus we won't abide by the delayed ACK 302 * rules correctly. 303 * SACKs don't matter, we never delay an ACK when we 304 * have any of those going out. 305 */ 306 *ptr++ = htonl((TCPOPT_MSS << 24) | (TCPOLEN_MSS << 16) | mss); 307 if (ts) { 308 if(sack) 309 *ptr++ = __constant_htonl((TCPOPT_SACK_PERM << 24) | (TCPOLEN_SACK_PERM << 16) | 310 (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); 311 else 312 *ptr++ = __constant_htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | 313 (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); 314 *ptr++ = htonl(tstamp); /* TSVAL */ 315 *ptr++ = htonl(ts_recent); /* TSECR */ 316 } else if(sack) 317 *ptr++ = __constant_htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | 318 (TCPOPT_SACK_PERM << 8) | TCPOLEN_SACK_PERM); 319 if (offer_wscale) 320 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_WINDOW << 16) | (TCPOLEN_WINDOW << 8) | (wscale)); 321 } 322 323 /* This routine actually transmits TCP packets queued in by 324 * tcp_do_sendmsg(). This is used by both the initial 325 * transmission and possible later retransmissions. 326 * All SKB's seen here are completely headerless. It is our 327 * job to build the TCP header, and pass the packet down to 328 * IP so it can do the same plus pass the packet off to the 329 * device. 330 * 331 * We are working here with either a clone of the original 332 * SKB, or a fresh unique copy made by the retransmit engine. 333 */ 334 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, gfp_t gfp_mask) 335 { 336 const struct inet_connection_sock *icsk = inet_csk(sk); 337 struct inet_sock *inet; 338 struct tcp_sock *tp; 339 struct tcp_skb_cb *tcb; 340 int tcp_header_size; 341 struct tcphdr *th; 342 int sysctl_flags; 343 int err; 344 345 BUG_ON(!skb || !tcp_skb_pcount(skb)); 346 347 /* If congestion control is doing timestamping, we must 348 * take such a timestamp before we potentially clone/copy. 349 */ 350 if (icsk->icsk_ca_ops->rtt_sample) 351 __net_timestamp(skb); 352 353 if (likely(clone_it)) { 354 if (unlikely(skb_cloned(skb))) 355 skb = pskb_copy(skb, gfp_mask); 356 else 357 skb = skb_clone(skb, gfp_mask); 358 if (unlikely(!skb)) 359 return -ENOBUFS; 360 } 361 362 inet = inet_sk(sk); 363 tp = tcp_sk(sk); 364 tcb = TCP_SKB_CB(skb); 365 tcp_header_size = tp->tcp_header_len; 366 367 #define SYSCTL_FLAG_TSTAMPS 0x1 368 #define SYSCTL_FLAG_WSCALE 0x2 369 #define SYSCTL_FLAG_SACK 0x4 370 371 sysctl_flags = 0; 372 if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) { 373 tcp_header_size = sizeof(struct tcphdr) + TCPOLEN_MSS; 374 if(sysctl_tcp_timestamps) { 375 tcp_header_size += TCPOLEN_TSTAMP_ALIGNED; 376 sysctl_flags |= SYSCTL_FLAG_TSTAMPS; 377 } 378 if (sysctl_tcp_window_scaling) { 379 tcp_header_size += TCPOLEN_WSCALE_ALIGNED; 380 sysctl_flags |= SYSCTL_FLAG_WSCALE; 381 } 382 if (sysctl_tcp_sack) { 383 sysctl_flags |= SYSCTL_FLAG_SACK; 384 if (!(sysctl_flags & SYSCTL_FLAG_TSTAMPS)) 385 tcp_header_size += TCPOLEN_SACKPERM_ALIGNED; 386 } 387 } else if (unlikely(tp->rx_opt.eff_sacks)) { 388 /* A SACK is 2 pad bytes, a 2 byte header, plus 389 * 2 32-bit sequence numbers for each SACK block. 390 */ 391 tcp_header_size += (TCPOLEN_SACK_BASE_ALIGNED + 392 (tp->rx_opt.eff_sacks * 393 TCPOLEN_SACK_PERBLOCK)); 394 } 395 396 if (tcp_packets_in_flight(tp) == 0) 397 tcp_ca_event(sk, CA_EVENT_TX_START); 398 399 th = (struct tcphdr *) skb_push(skb, tcp_header_size); 400 skb->h.th = th; 401 skb_set_owner_w(skb, sk); 402 403 /* Build TCP header and checksum it. */ 404 th->source = inet->sport; 405 th->dest = inet->dport; 406 th->seq = htonl(tcb->seq); 407 th->ack_seq = htonl(tp->rcv_nxt); 408 *(((__u16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | 409 tcb->flags); 410 411 if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) { 412 /* RFC1323: The window in SYN & SYN/ACK segments 413 * is never scaled. 414 */ 415 th->window = htons(tp->rcv_wnd); 416 } else { 417 th->window = htons(tcp_select_window(sk)); 418 } 419 th->check = 0; 420 th->urg_ptr = 0; 421 422 if (unlikely(tp->urg_mode && 423 between(tp->snd_up, tcb->seq+1, tcb->seq+0xFFFF))) { 424 th->urg_ptr = htons(tp->snd_up-tcb->seq); 425 th->urg = 1; 426 } 427 428 if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) { 429 tcp_syn_build_options((__u32 *)(th + 1), 430 tcp_advertise_mss(sk), 431 (sysctl_flags & SYSCTL_FLAG_TSTAMPS), 432 (sysctl_flags & SYSCTL_FLAG_SACK), 433 (sysctl_flags & SYSCTL_FLAG_WSCALE), 434 tp->rx_opt.rcv_wscale, 435 tcb->when, 436 tp->rx_opt.ts_recent); 437 } else { 438 tcp_build_and_update_options((__u32 *)(th + 1), 439 tp, tcb->when); 440 TCP_ECN_send(sk, tp, skb, tcp_header_size); 441 } 442 443 icsk->icsk_af_ops->send_check(sk, skb->len, skb); 444 445 if (likely(tcb->flags & TCPCB_FLAG_ACK)) 446 tcp_event_ack_sent(sk, tcp_skb_pcount(skb)); 447 448 if (skb->len != tcp_header_size) 449 tcp_event_data_sent(tp, skb, sk); 450 451 TCP_INC_STATS(TCP_MIB_OUTSEGS); 452 453 err = icsk->icsk_af_ops->queue_xmit(skb, 0); 454 if (unlikely(err <= 0)) 455 return err; 456 457 tcp_enter_cwr(sk); 458 459 /* NET_XMIT_CN is special. It does not guarantee, 460 * that this packet is lost. It tells that device 461 * is about to start to drop packets or already 462 * drops some packets of the same priority and 463 * invokes us to send less aggressively. 464 */ 465 return err == NET_XMIT_CN ? 0 : err; 466 467 #undef SYSCTL_FLAG_TSTAMPS 468 #undef SYSCTL_FLAG_WSCALE 469 #undef SYSCTL_FLAG_SACK 470 } 471 472 473 /* This routine just queue's the buffer 474 * 475 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames, 476 * otherwise socket can stall. 477 */ 478 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb) 479 { 480 struct tcp_sock *tp = tcp_sk(sk); 481 482 /* Advance write_seq and place onto the write_queue. */ 483 tp->write_seq = TCP_SKB_CB(skb)->end_seq; 484 skb_header_release(skb); 485 __skb_queue_tail(&sk->sk_write_queue, skb); 486 sk_charge_skb(sk, skb); 487 488 /* Queue it, remembering where we must start sending. */ 489 if (sk->sk_send_head == NULL) 490 sk->sk_send_head = skb; 491 } 492 493 static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now) 494 { 495 if (skb->len <= mss_now || 496 !(sk->sk_route_caps & NETIF_F_TSO)) { 497 /* Avoid the costly divide in the normal 498 * non-TSO case. 499 */ 500 skb_shinfo(skb)->tso_segs = 1; 501 skb_shinfo(skb)->tso_size = 0; 502 } else { 503 unsigned int factor; 504 505 factor = skb->len + (mss_now - 1); 506 factor /= mss_now; 507 skb_shinfo(skb)->tso_segs = factor; 508 skb_shinfo(skb)->tso_size = mss_now; 509 } 510 } 511 512 /* Function to create two new TCP segments. Shrinks the given segment 513 * to the specified size and appends a new segment with the rest of the 514 * packet to the list. This won't be called frequently, I hope. 515 * Remember, these are still headerless SKBs at this point. 516 */ 517 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss_now) 518 { 519 struct tcp_sock *tp = tcp_sk(sk); 520 struct sk_buff *buff; 521 int nsize, old_factor; 522 u16 flags; 523 524 BUG_ON(len > skb->len); 525 526 clear_all_retrans_hints(tp); 527 nsize = skb_headlen(skb) - len; 528 if (nsize < 0) 529 nsize = 0; 530 531 if (skb_cloned(skb) && 532 skb_is_nonlinear(skb) && 533 pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) 534 return -ENOMEM; 535 536 /* Get a new skb... force flag on. */ 537 buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC); 538 if (buff == NULL) 539 return -ENOMEM; /* We'll just try again later. */ 540 sk_charge_skb(sk, buff); 541 542 /* Correct the sequence numbers. */ 543 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 544 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 545 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 546 547 /* PSH and FIN should only be set in the second packet. */ 548 flags = TCP_SKB_CB(skb)->flags; 549 TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH); 550 TCP_SKB_CB(buff)->flags = flags; 551 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked; 552 TCP_SKB_CB(skb)->sacked &= ~TCPCB_AT_TAIL; 553 554 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_HW) { 555 /* Copy and checksum data tail into the new buffer. */ 556 buff->csum = csum_partial_copy_nocheck(skb->data + len, skb_put(buff, nsize), 557 nsize, 0); 558 559 skb_trim(skb, len); 560 561 skb->csum = csum_block_sub(skb->csum, buff->csum, len); 562 } else { 563 skb->ip_summed = CHECKSUM_HW; 564 skb_split(skb, buff, len); 565 } 566 567 buff->ip_summed = skb->ip_summed; 568 569 /* Looks stupid, but our code really uses when of 570 * skbs, which it never sent before. --ANK 571 */ 572 TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when; 573 buff->tstamp = skb->tstamp; 574 575 old_factor = tcp_skb_pcount(skb); 576 577 /* Fix up tso_factor for both original and new SKB. */ 578 tcp_set_skb_tso_segs(sk, skb, mss_now); 579 tcp_set_skb_tso_segs(sk, buff, mss_now); 580 581 /* If this packet has been sent out already, we must 582 * adjust the various packet counters. 583 */ 584 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) { 585 int diff = old_factor - tcp_skb_pcount(skb) - 586 tcp_skb_pcount(buff); 587 588 tp->packets_out -= diff; 589 590 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 591 tp->sacked_out -= diff; 592 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) 593 tp->retrans_out -= diff; 594 595 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) { 596 tp->lost_out -= diff; 597 tp->left_out -= diff; 598 } 599 600 if (diff > 0) { 601 /* Adjust Reno SACK estimate. */ 602 if (!tp->rx_opt.sack_ok) { 603 tp->sacked_out -= diff; 604 if ((int)tp->sacked_out < 0) 605 tp->sacked_out = 0; 606 tcp_sync_left_out(tp); 607 } 608 609 tp->fackets_out -= diff; 610 if ((int)tp->fackets_out < 0) 611 tp->fackets_out = 0; 612 } 613 } 614 615 /* Link BUFF into the send queue. */ 616 skb_header_release(buff); 617 __skb_append(skb, buff, &sk->sk_write_queue); 618 619 return 0; 620 } 621 622 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c 623 * eventually). The difference is that pulled data not copied, but 624 * immediately discarded. 625 */ 626 static unsigned char *__pskb_trim_head(struct sk_buff *skb, int len) 627 { 628 int i, k, eat; 629 630 eat = len; 631 k = 0; 632 for (i=0; i<skb_shinfo(skb)->nr_frags; i++) { 633 if (skb_shinfo(skb)->frags[i].size <= eat) { 634 put_page(skb_shinfo(skb)->frags[i].page); 635 eat -= skb_shinfo(skb)->frags[i].size; 636 } else { 637 skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i]; 638 if (eat) { 639 skb_shinfo(skb)->frags[k].page_offset += eat; 640 skb_shinfo(skb)->frags[k].size -= eat; 641 eat = 0; 642 } 643 k++; 644 } 645 } 646 skb_shinfo(skb)->nr_frags = k; 647 648 skb->tail = skb->data; 649 skb->data_len -= len; 650 skb->len = skb->data_len; 651 return skb->tail; 652 } 653 654 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) 655 { 656 if (skb_cloned(skb) && 657 pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) 658 return -ENOMEM; 659 660 if (len <= skb_headlen(skb)) { 661 __skb_pull(skb, len); 662 } else { 663 if (__pskb_trim_head(skb, len-skb_headlen(skb)) == NULL) 664 return -ENOMEM; 665 } 666 667 TCP_SKB_CB(skb)->seq += len; 668 skb->ip_summed = CHECKSUM_HW; 669 670 skb->truesize -= len; 671 sk->sk_wmem_queued -= len; 672 sk->sk_forward_alloc += len; 673 sock_set_flag(sk, SOCK_QUEUE_SHRUNK); 674 675 /* Any change of skb->len requires recalculation of tso 676 * factor and mss. 677 */ 678 if (tcp_skb_pcount(skb) > 1) 679 tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1)); 680 681 return 0; 682 } 683 684 /* This function synchronize snd mss to current pmtu/exthdr set. 685 686 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts 687 for TCP options, but includes only bare TCP header. 688 689 tp->rx_opt.mss_clamp is mss negotiated at connection setup. 690 It is minimum of user_mss and mss received with SYN. 691 It also does not include TCP options. 692 693 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function. 694 695 tp->mss_cache is current effective sending mss, including 696 all tcp options except for SACKs. It is evaluated, 697 taking into account current pmtu, but never exceeds 698 tp->rx_opt.mss_clamp. 699 700 NOTE1. rfc1122 clearly states that advertised MSS 701 DOES NOT include either tcp or ip options. 702 703 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache 704 are READ ONLY outside this function. --ANK (980731) 705 */ 706 707 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu) 708 { 709 struct tcp_sock *tp = tcp_sk(sk); 710 struct inet_connection_sock *icsk = inet_csk(sk); 711 /* Calculate base mss without TCP options: 712 It is MMS_S - sizeof(tcphdr) of rfc1122 713 */ 714 int mss_now = (pmtu - icsk->icsk_af_ops->net_header_len - 715 sizeof(struct tcphdr)); 716 717 /* Clamp it (mss_clamp does not include tcp options) */ 718 if (mss_now > tp->rx_opt.mss_clamp) 719 mss_now = tp->rx_opt.mss_clamp; 720 721 /* Now subtract optional transport overhead */ 722 mss_now -= icsk->icsk_ext_hdr_len; 723 724 /* Then reserve room for full set of TCP options and 8 bytes of data */ 725 if (mss_now < 48) 726 mss_now = 48; 727 728 /* Now subtract TCP options size, not including SACKs */ 729 mss_now -= tp->tcp_header_len - sizeof(struct tcphdr); 730 731 /* Bound mss with half of window */ 732 if (tp->max_window && mss_now > (tp->max_window>>1)) 733 mss_now = max((tp->max_window>>1), 68U - tp->tcp_header_len); 734 735 /* And store cached results */ 736 icsk->icsk_pmtu_cookie = pmtu; 737 tp->mss_cache = mss_now; 738 739 return mss_now; 740 } 741 742 /* Compute the current effective MSS, taking SACKs and IP options, 743 * and even PMTU discovery events into account. 744 * 745 * LARGESEND note: !urg_mode is overkill, only frames up to snd_up 746 * cannot be large. However, taking into account rare use of URG, this 747 * is not a big flaw. 748 */ 749 unsigned int tcp_current_mss(struct sock *sk, int large_allowed) 750 { 751 struct tcp_sock *tp = tcp_sk(sk); 752 struct dst_entry *dst = __sk_dst_get(sk); 753 u32 mss_now; 754 u16 xmit_size_goal; 755 int doing_tso = 0; 756 757 mss_now = tp->mss_cache; 758 759 if (large_allowed && 760 (sk->sk_route_caps & NETIF_F_TSO) && 761 !tp->urg_mode) 762 doing_tso = 1; 763 764 if (dst) { 765 u32 mtu = dst_mtu(dst); 766 if (mtu != inet_csk(sk)->icsk_pmtu_cookie) 767 mss_now = tcp_sync_mss(sk, mtu); 768 } 769 770 if (tp->rx_opt.eff_sacks) 771 mss_now -= (TCPOLEN_SACK_BASE_ALIGNED + 772 (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK)); 773 774 xmit_size_goal = mss_now; 775 776 if (doing_tso) { 777 xmit_size_goal = (65535 - 778 inet_csk(sk)->icsk_af_ops->net_header_len - 779 inet_csk(sk)->icsk_ext_hdr_len - 780 tp->tcp_header_len); 781 782 if (tp->max_window && 783 (xmit_size_goal > (tp->max_window >> 1))) 784 xmit_size_goal = max((tp->max_window >> 1), 785 68U - tp->tcp_header_len); 786 787 xmit_size_goal -= (xmit_size_goal % mss_now); 788 } 789 tp->xmit_size_goal = xmit_size_goal; 790 791 return mss_now; 792 } 793 794 /* Congestion window validation. (RFC2861) */ 795 796 static void tcp_cwnd_validate(struct sock *sk, struct tcp_sock *tp) 797 { 798 __u32 packets_out = tp->packets_out; 799 800 if (packets_out >= tp->snd_cwnd) { 801 /* Network is feed fully. */ 802 tp->snd_cwnd_used = 0; 803 tp->snd_cwnd_stamp = tcp_time_stamp; 804 } else { 805 /* Network starves. */ 806 if (tp->packets_out > tp->snd_cwnd_used) 807 tp->snd_cwnd_used = tp->packets_out; 808 809 if ((s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto) 810 tcp_cwnd_application_limited(sk); 811 } 812 } 813 814 static unsigned int tcp_window_allows(struct tcp_sock *tp, struct sk_buff *skb, unsigned int mss_now, unsigned int cwnd) 815 { 816 u32 window, cwnd_len; 817 818 window = (tp->snd_una + tp->snd_wnd - TCP_SKB_CB(skb)->seq); 819 cwnd_len = mss_now * cwnd; 820 return min(window, cwnd_len); 821 } 822 823 /* Can at least one segment of SKB be sent right now, according to the 824 * congestion window rules? If so, return how many segments are allowed. 825 */ 826 static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, struct sk_buff *skb) 827 { 828 u32 in_flight, cwnd; 829 830 /* Don't be strict about the congestion window for the final FIN. */ 831 if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) 832 return 1; 833 834 in_flight = tcp_packets_in_flight(tp); 835 cwnd = tp->snd_cwnd; 836 if (in_flight < cwnd) 837 return (cwnd - in_flight); 838 839 return 0; 840 } 841 842 /* This must be invoked the first time we consider transmitting 843 * SKB onto the wire. 844 */ 845 static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now) 846 { 847 int tso_segs = tcp_skb_pcount(skb); 848 849 if (!tso_segs || 850 (tso_segs > 1 && 851 skb_shinfo(skb)->tso_size != mss_now)) { 852 tcp_set_skb_tso_segs(sk, skb, mss_now); 853 tso_segs = tcp_skb_pcount(skb); 854 } 855 return tso_segs; 856 } 857 858 static inline int tcp_minshall_check(const struct tcp_sock *tp) 859 { 860 return after(tp->snd_sml,tp->snd_una) && 861 !after(tp->snd_sml, tp->snd_nxt); 862 } 863 864 /* Return 0, if packet can be sent now without violation Nagle's rules: 865 * 1. It is full sized. 866 * 2. Or it contains FIN. (already checked by caller) 867 * 3. Or TCP_NODELAY was set. 868 * 4. Or TCP_CORK is not set, and all sent packets are ACKed. 869 * With Minshall's modification: all sent small packets are ACKed. 870 */ 871 872 static inline int tcp_nagle_check(const struct tcp_sock *tp, 873 const struct sk_buff *skb, 874 unsigned mss_now, int nonagle) 875 { 876 return (skb->len < mss_now && 877 ((nonagle&TCP_NAGLE_CORK) || 878 (!nonagle && 879 tp->packets_out && 880 tcp_minshall_check(tp)))); 881 } 882 883 /* Return non-zero if the Nagle test allows this packet to be 884 * sent now. 885 */ 886 static inline int tcp_nagle_test(struct tcp_sock *tp, struct sk_buff *skb, 887 unsigned int cur_mss, int nonagle) 888 { 889 /* Nagle rule does not apply to frames, which sit in the middle of the 890 * write_queue (they have no chances to get new data). 891 * 892 * This is implemented in the callers, where they modify the 'nonagle' 893 * argument based upon the location of SKB in the send queue. 894 */ 895 if (nonagle & TCP_NAGLE_PUSH) 896 return 1; 897 898 /* Don't use the nagle rule for urgent data (or for the final FIN). */ 899 if (tp->urg_mode || 900 (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)) 901 return 1; 902 903 if (!tcp_nagle_check(tp, skb, cur_mss, nonagle)) 904 return 1; 905 906 return 0; 907 } 908 909 /* Does at least the first segment of SKB fit into the send window? */ 910 static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb, unsigned int cur_mss) 911 { 912 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 913 914 if (skb->len > cur_mss) 915 end_seq = TCP_SKB_CB(skb)->seq + cur_mss; 916 917 return !after(end_seq, tp->snd_una + tp->snd_wnd); 918 } 919 920 /* This checks if the data bearing packet SKB (usually sk->sk_send_head) 921 * should be put on the wire right now. If so, it returns the number of 922 * packets allowed by the congestion window. 923 */ 924 static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb, 925 unsigned int cur_mss, int nonagle) 926 { 927 struct tcp_sock *tp = tcp_sk(sk); 928 unsigned int cwnd_quota; 929 930 tcp_init_tso_segs(sk, skb, cur_mss); 931 932 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle)) 933 return 0; 934 935 cwnd_quota = tcp_cwnd_test(tp, skb); 936 if (cwnd_quota && 937 !tcp_snd_wnd_test(tp, skb, cur_mss)) 938 cwnd_quota = 0; 939 940 return cwnd_quota; 941 } 942 943 static inline int tcp_skb_is_last(const struct sock *sk, 944 const struct sk_buff *skb) 945 { 946 return skb->next == (struct sk_buff *)&sk->sk_write_queue; 947 } 948 949 int tcp_may_send_now(struct sock *sk, struct tcp_sock *tp) 950 { 951 struct sk_buff *skb = sk->sk_send_head; 952 953 return (skb && 954 tcp_snd_test(sk, skb, tcp_current_mss(sk, 1), 955 (tcp_skb_is_last(sk, skb) ? 956 TCP_NAGLE_PUSH : 957 tp->nonagle))); 958 } 959 960 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet 961 * which is put after SKB on the list. It is very much like 962 * tcp_fragment() except that it may make several kinds of assumptions 963 * in order to speed up the splitting operation. In particular, we 964 * know that all the data is in scatter-gather pages, and that the 965 * packet has never been sent out before (and thus is not cloned). 966 */ 967 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, unsigned int mss_now) 968 { 969 struct sk_buff *buff; 970 int nlen = skb->len - len; 971 u16 flags; 972 973 /* All of a TSO frame must be composed of paged data. */ 974 if (skb->len != skb->data_len) 975 return tcp_fragment(sk, skb, len, mss_now); 976 977 buff = sk_stream_alloc_pskb(sk, 0, 0, GFP_ATOMIC); 978 if (unlikely(buff == NULL)) 979 return -ENOMEM; 980 981 buff->truesize = nlen; 982 skb->truesize -= nlen; 983 984 /* Correct the sequence numbers. */ 985 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 986 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 987 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 988 989 /* PSH and FIN should only be set in the second packet. */ 990 flags = TCP_SKB_CB(skb)->flags; 991 TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH); 992 TCP_SKB_CB(buff)->flags = flags; 993 994 /* This packet was never sent out yet, so no SACK bits. */ 995 TCP_SKB_CB(buff)->sacked = 0; 996 997 buff->ip_summed = skb->ip_summed = CHECKSUM_HW; 998 skb_split(skb, buff, len); 999 1000 /* Fix up tso_factor for both original and new SKB. */ 1001 tcp_set_skb_tso_segs(sk, skb, mss_now); 1002 tcp_set_skb_tso_segs(sk, buff, mss_now); 1003 1004 /* Link BUFF into the send queue. */ 1005 skb_header_release(buff); 1006 __skb_append(skb, buff, &sk->sk_write_queue); 1007 1008 return 0; 1009 } 1010 1011 /* Try to defer sending, if possible, in order to minimize the amount 1012 * of TSO splitting we do. View it as a kind of TSO Nagle test. 1013 * 1014 * This algorithm is from John Heffner. 1015 */ 1016 static int tcp_tso_should_defer(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb) 1017 { 1018 const struct inet_connection_sock *icsk = inet_csk(sk); 1019 u32 send_win, cong_win, limit, in_flight; 1020 1021 if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) 1022 return 0; 1023 1024 if (icsk->icsk_ca_state != TCP_CA_Open) 1025 return 0; 1026 1027 in_flight = tcp_packets_in_flight(tp); 1028 1029 BUG_ON(tcp_skb_pcount(skb) <= 1 || 1030 (tp->snd_cwnd <= in_flight)); 1031 1032 send_win = (tp->snd_una + tp->snd_wnd) - TCP_SKB_CB(skb)->seq; 1033 1034 /* From in_flight test above, we know that cwnd > in_flight. */ 1035 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache; 1036 1037 limit = min(send_win, cong_win); 1038 1039 /* If a full-sized TSO skb can be sent, do it. */ 1040 if (limit >= 65536) 1041 return 0; 1042 1043 if (sysctl_tcp_tso_win_divisor) { 1044 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache); 1045 1046 /* If at least some fraction of a window is available, 1047 * just use it. 1048 */ 1049 chunk /= sysctl_tcp_tso_win_divisor; 1050 if (limit >= chunk) 1051 return 0; 1052 } else { 1053 /* Different approach, try not to defer past a single 1054 * ACK. Receiver should ACK every other full sized 1055 * frame, so if we have space for more than 3 frames 1056 * then send now. 1057 */ 1058 if (limit > tcp_max_burst(tp) * tp->mss_cache) 1059 return 0; 1060 } 1061 1062 /* Ok, it looks like it is advisable to defer. */ 1063 return 1; 1064 } 1065 1066 /* This routine writes packets to the network. It advances the 1067 * send_head. This happens as incoming acks open up the remote 1068 * window for us. 1069 * 1070 * Returns 1, if no segments are in flight and we have queued segments, but 1071 * cannot send anything now because of SWS or another problem. 1072 */ 1073 static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle) 1074 { 1075 struct tcp_sock *tp = tcp_sk(sk); 1076 struct sk_buff *skb; 1077 unsigned int tso_segs, sent_pkts; 1078 int cwnd_quota; 1079 1080 /* If we are closed, the bytes will have to remain here. 1081 * In time closedown will finish, we empty the write queue and all 1082 * will be happy. 1083 */ 1084 if (unlikely(sk->sk_state == TCP_CLOSE)) 1085 return 0; 1086 1087 sent_pkts = 0; 1088 while ((skb = sk->sk_send_head)) { 1089 unsigned int limit; 1090 1091 tso_segs = tcp_init_tso_segs(sk, skb, mss_now); 1092 BUG_ON(!tso_segs); 1093 1094 cwnd_quota = tcp_cwnd_test(tp, skb); 1095 if (!cwnd_quota) 1096 break; 1097 1098 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) 1099 break; 1100 1101 if (tso_segs == 1) { 1102 if (unlikely(!tcp_nagle_test(tp, skb, mss_now, 1103 (tcp_skb_is_last(sk, skb) ? 1104 nonagle : TCP_NAGLE_PUSH)))) 1105 break; 1106 } else { 1107 if (tcp_tso_should_defer(sk, tp, skb)) 1108 break; 1109 } 1110 1111 limit = mss_now; 1112 if (tso_segs > 1) { 1113 limit = tcp_window_allows(tp, skb, 1114 mss_now, cwnd_quota); 1115 1116 if (skb->len < limit) { 1117 unsigned int trim = skb->len % mss_now; 1118 1119 if (trim) 1120 limit = skb->len - trim; 1121 } 1122 } 1123 1124 if (skb->len > limit && 1125 unlikely(tso_fragment(sk, skb, limit, mss_now))) 1126 break; 1127 1128 TCP_SKB_CB(skb)->when = tcp_time_stamp; 1129 1130 if (unlikely(tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC))) 1131 break; 1132 1133 /* Advance the send_head. This one is sent out. 1134 * This call will increment packets_out. 1135 */ 1136 update_send_head(sk, tp, skb); 1137 1138 tcp_minshall_update(tp, mss_now, skb); 1139 sent_pkts++; 1140 } 1141 1142 if (likely(sent_pkts)) { 1143 tcp_cwnd_validate(sk, tp); 1144 return 0; 1145 } 1146 return !tp->packets_out && sk->sk_send_head; 1147 } 1148 1149 /* Push out any pending frames which were held back due to 1150 * TCP_CORK or attempt at coalescing tiny packets. 1151 * The socket must be locked by the caller. 1152 */ 1153 void __tcp_push_pending_frames(struct sock *sk, struct tcp_sock *tp, 1154 unsigned int cur_mss, int nonagle) 1155 { 1156 struct sk_buff *skb = sk->sk_send_head; 1157 1158 if (skb) { 1159 if (tcp_write_xmit(sk, cur_mss, nonagle)) 1160 tcp_check_probe_timer(sk, tp); 1161 } 1162 } 1163 1164 /* Send _single_ skb sitting at the send head. This function requires 1165 * true push pending frames to setup probe timer etc. 1166 */ 1167 void tcp_push_one(struct sock *sk, unsigned int mss_now) 1168 { 1169 struct tcp_sock *tp = tcp_sk(sk); 1170 struct sk_buff *skb = sk->sk_send_head; 1171 unsigned int tso_segs, cwnd_quota; 1172 1173 BUG_ON(!skb || skb->len < mss_now); 1174 1175 tso_segs = tcp_init_tso_segs(sk, skb, mss_now); 1176 cwnd_quota = tcp_snd_test(sk, skb, mss_now, TCP_NAGLE_PUSH); 1177 1178 if (likely(cwnd_quota)) { 1179 unsigned int limit; 1180 1181 BUG_ON(!tso_segs); 1182 1183 limit = mss_now; 1184 if (tso_segs > 1) { 1185 limit = tcp_window_allows(tp, skb, 1186 mss_now, cwnd_quota); 1187 1188 if (skb->len < limit) { 1189 unsigned int trim = skb->len % mss_now; 1190 1191 if (trim) 1192 limit = skb->len - trim; 1193 } 1194 } 1195 1196 if (skb->len > limit && 1197 unlikely(tso_fragment(sk, skb, limit, mss_now))) 1198 return; 1199 1200 /* Send it out now. */ 1201 TCP_SKB_CB(skb)->when = tcp_time_stamp; 1202 1203 if (likely(!tcp_transmit_skb(sk, skb, 1, sk->sk_allocation))) { 1204 update_send_head(sk, tp, skb); 1205 tcp_cwnd_validate(sk, tp); 1206 return; 1207 } 1208 } 1209 } 1210 1211 /* This function returns the amount that we can raise the 1212 * usable window based on the following constraints 1213 * 1214 * 1. The window can never be shrunk once it is offered (RFC 793) 1215 * 2. We limit memory per socket 1216 * 1217 * RFC 1122: 1218 * "the suggested [SWS] avoidance algorithm for the receiver is to keep 1219 * RECV.NEXT + RCV.WIN fixed until: 1220 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)" 1221 * 1222 * i.e. don't raise the right edge of the window until you can raise 1223 * it at least MSS bytes. 1224 * 1225 * Unfortunately, the recommended algorithm breaks header prediction, 1226 * since header prediction assumes th->window stays fixed. 1227 * 1228 * Strictly speaking, keeping th->window fixed violates the receiver 1229 * side SWS prevention criteria. The problem is that under this rule 1230 * a stream of single byte packets will cause the right side of the 1231 * window to always advance by a single byte. 1232 * 1233 * Of course, if the sender implements sender side SWS prevention 1234 * then this will not be a problem. 1235 * 1236 * BSD seems to make the following compromise: 1237 * 1238 * If the free space is less than the 1/4 of the maximum 1239 * space available and the free space is less than 1/2 mss, 1240 * then set the window to 0. 1241 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ] 1242 * Otherwise, just prevent the window from shrinking 1243 * and from being larger than the largest representable value. 1244 * 1245 * This prevents incremental opening of the window in the regime 1246 * where TCP is limited by the speed of the reader side taking 1247 * data out of the TCP receive queue. It does nothing about 1248 * those cases where the window is constrained on the sender side 1249 * because the pipeline is full. 1250 * 1251 * BSD also seems to "accidentally" limit itself to windows that are a 1252 * multiple of MSS, at least until the free space gets quite small. 1253 * This would appear to be a side effect of the mbuf implementation. 1254 * Combining these two algorithms results in the observed behavior 1255 * of having a fixed window size at almost all times. 1256 * 1257 * Below we obtain similar behavior by forcing the offered window to 1258 * a multiple of the mss when it is feasible to do so. 1259 * 1260 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes. 1261 * Regular options like TIMESTAMP are taken into account. 1262 */ 1263 u32 __tcp_select_window(struct sock *sk) 1264 { 1265 struct inet_connection_sock *icsk = inet_csk(sk); 1266 struct tcp_sock *tp = tcp_sk(sk); 1267 /* MSS for the peer's data. Previous versions used mss_clamp 1268 * here. I don't know if the value based on our guesses 1269 * of peer's MSS is better for the performance. It's more correct 1270 * but may be worse for the performance because of rcv_mss 1271 * fluctuations. --SAW 1998/11/1 1272 */ 1273 int mss = icsk->icsk_ack.rcv_mss; 1274 int free_space = tcp_space(sk); 1275 int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk)); 1276 int window; 1277 1278 if (mss > full_space) 1279 mss = full_space; 1280 1281 if (free_space < full_space/2) { 1282 icsk->icsk_ack.quick = 0; 1283 1284 if (tcp_memory_pressure) 1285 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U*tp->advmss); 1286 1287 if (free_space < mss) 1288 return 0; 1289 } 1290 1291 if (free_space > tp->rcv_ssthresh) 1292 free_space = tp->rcv_ssthresh; 1293 1294 /* Don't do rounding if we are using window scaling, since the 1295 * scaled window will not line up with the MSS boundary anyway. 1296 */ 1297 window = tp->rcv_wnd; 1298 if (tp->rx_opt.rcv_wscale) { 1299 window = free_space; 1300 1301 /* Advertise enough space so that it won't get scaled away. 1302 * Import case: prevent zero window announcement if 1303 * 1<<rcv_wscale > mss. 1304 */ 1305 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window) 1306 window = (((window >> tp->rx_opt.rcv_wscale) + 1) 1307 << tp->rx_opt.rcv_wscale); 1308 } else { 1309 /* Get the largest window that is a nice multiple of mss. 1310 * Window clamp already applied above. 1311 * If our current window offering is within 1 mss of the 1312 * free space we just keep it. This prevents the divide 1313 * and multiply from happening most of the time. 1314 * We also don't do any window rounding when the free space 1315 * is too small. 1316 */ 1317 if (window <= free_space - mss || window > free_space) 1318 window = (free_space/mss)*mss; 1319 } 1320 1321 return window; 1322 } 1323 1324 /* Attempt to collapse two adjacent SKB's during retransmission. */ 1325 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int mss_now) 1326 { 1327 struct tcp_sock *tp = tcp_sk(sk); 1328 struct sk_buff *next_skb = skb->next; 1329 1330 /* The first test we must make is that neither of these two 1331 * SKB's are still referenced by someone else. 1332 */ 1333 if (!skb_cloned(skb) && !skb_cloned(next_skb)) { 1334 int skb_size = skb->len, next_skb_size = next_skb->len; 1335 u16 flags = TCP_SKB_CB(skb)->flags; 1336 1337 /* Also punt if next skb has been SACK'd. */ 1338 if(TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED) 1339 return; 1340 1341 /* Next skb is out of window. */ 1342 if (after(TCP_SKB_CB(next_skb)->end_seq, tp->snd_una+tp->snd_wnd)) 1343 return; 1344 1345 /* Punt if not enough space exists in the first SKB for 1346 * the data in the second, or the total combined payload 1347 * would exceed the MSS. 1348 */ 1349 if ((next_skb_size > skb_tailroom(skb)) || 1350 ((skb_size + next_skb_size) > mss_now)) 1351 return; 1352 1353 BUG_ON(tcp_skb_pcount(skb) != 1 || 1354 tcp_skb_pcount(next_skb) != 1); 1355 1356 /* changing transmit queue under us so clear hints */ 1357 clear_all_retrans_hints(tp); 1358 1359 /* Ok. We will be able to collapse the packet. */ 1360 __skb_unlink(next_skb, &sk->sk_write_queue); 1361 1362 memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size); 1363 1364 if (next_skb->ip_summed == CHECKSUM_HW) 1365 skb->ip_summed = CHECKSUM_HW; 1366 1367 if (skb->ip_summed != CHECKSUM_HW) 1368 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size); 1369 1370 /* Update sequence range on original skb. */ 1371 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq; 1372 1373 /* Merge over control information. */ 1374 flags |= TCP_SKB_CB(next_skb)->flags; /* This moves PSH/FIN etc. over */ 1375 TCP_SKB_CB(skb)->flags = flags; 1376 1377 /* All done, get rid of second SKB and account for it so 1378 * packet counting does not break. 1379 */ 1380 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked&(TCPCB_EVER_RETRANS|TCPCB_AT_TAIL); 1381 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_SACKED_RETRANS) 1382 tp->retrans_out -= tcp_skb_pcount(next_skb); 1383 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_LOST) { 1384 tp->lost_out -= tcp_skb_pcount(next_skb); 1385 tp->left_out -= tcp_skb_pcount(next_skb); 1386 } 1387 /* Reno case is special. Sigh... */ 1388 if (!tp->rx_opt.sack_ok && tp->sacked_out) { 1389 tcp_dec_pcount_approx(&tp->sacked_out, next_skb); 1390 tp->left_out -= tcp_skb_pcount(next_skb); 1391 } 1392 1393 /* Not quite right: it can be > snd.fack, but 1394 * it is better to underestimate fackets. 1395 */ 1396 tcp_dec_pcount_approx(&tp->fackets_out, next_skb); 1397 tcp_packets_out_dec(tp, next_skb); 1398 sk_stream_free_skb(sk, next_skb); 1399 } 1400 } 1401 1402 /* Do a simple retransmit without using the backoff mechanisms in 1403 * tcp_timer. This is used for path mtu discovery. 1404 * The socket is already locked here. 1405 */ 1406 void tcp_simple_retransmit(struct sock *sk) 1407 { 1408 const struct inet_connection_sock *icsk = inet_csk(sk); 1409 struct tcp_sock *tp = tcp_sk(sk); 1410 struct sk_buff *skb; 1411 unsigned int mss = tcp_current_mss(sk, 0); 1412 int lost = 0; 1413 1414 sk_stream_for_retrans_queue(skb, sk) { 1415 if (skb->len > mss && 1416 !(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) { 1417 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) { 1418 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 1419 tp->retrans_out -= tcp_skb_pcount(skb); 1420 } 1421 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_LOST)) { 1422 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1423 tp->lost_out += tcp_skb_pcount(skb); 1424 lost = 1; 1425 } 1426 } 1427 } 1428 1429 clear_all_retrans_hints(tp); 1430 1431 if (!lost) 1432 return; 1433 1434 tcp_sync_left_out(tp); 1435 1436 /* Don't muck with the congestion window here. 1437 * Reason is that we do not increase amount of _data_ 1438 * in network, but units changed and effective 1439 * cwnd/ssthresh really reduced now. 1440 */ 1441 if (icsk->icsk_ca_state != TCP_CA_Loss) { 1442 tp->high_seq = tp->snd_nxt; 1443 tp->snd_ssthresh = tcp_current_ssthresh(sk); 1444 tp->prior_ssthresh = 0; 1445 tp->undo_marker = 0; 1446 tcp_set_ca_state(sk, TCP_CA_Loss); 1447 } 1448 tcp_xmit_retransmit_queue(sk); 1449 } 1450 1451 /* This retransmits one SKB. Policy decisions and retransmit queue 1452 * state updates are done by the caller. Returns non-zero if an 1453 * error occurred which prevented the send. 1454 */ 1455 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) 1456 { 1457 struct tcp_sock *tp = tcp_sk(sk); 1458 unsigned int cur_mss = tcp_current_mss(sk, 0); 1459 int err; 1460 1461 /* Do not sent more than we queued. 1/4 is reserved for possible 1462 * copying overhead: fragmentation, tunneling, mangling etc. 1463 */ 1464 if (atomic_read(&sk->sk_wmem_alloc) > 1465 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf)) 1466 return -EAGAIN; 1467 1468 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) { 1469 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 1470 BUG(); 1471 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) 1472 return -ENOMEM; 1473 } 1474 1475 /* If receiver has shrunk his window, and skb is out of 1476 * new window, do not retransmit it. The exception is the 1477 * case, when window is shrunk to zero. In this case 1478 * our retransmit serves as a zero window probe. 1479 */ 1480 if (!before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd) 1481 && TCP_SKB_CB(skb)->seq != tp->snd_una) 1482 return -EAGAIN; 1483 1484 if (skb->len > cur_mss) { 1485 if (tcp_fragment(sk, skb, cur_mss, cur_mss)) 1486 return -ENOMEM; /* We'll try again later. */ 1487 } 1488 1489 /* Collapse two adjacent packets if worthwhile and we can. */ 1490 if(!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) && 1491 (skb->len < (cur_mss >> 1)) && 1492 (skb->next != sk->sk_send_head) && 1493 (skb->next != (struct sk_buff *)&sk->sk_write_queue) && 1494 (skb_shinfo(skb)->nr_frags == 0 && skb_shinfo(skb->next)->nr_frags == 0) && 1495 (tcp_skb_pcount(skb) == 1 && tcp_skb_pcount(skb->next) == 1) && 1496 (sysctl_tcp_retrans_collapse != 0)) 1497 tcp_retrans_try_collapse(sk, skb, cur_mss); 1498 1499 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) 1500 return -EHOSTUNREACH; /* Routing failure or similar. */ 1501 1502 /* Some Solaris stacks overoptimize and ignore the FIN on a 1503 * retransmit when old data is attached. So strip it off 1504 * since it is cheap to do so and saves bytes on the network. 1505 */ 1506 if(skb->len > 0 && 1507 (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) && 1508 tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) { 1509 if (!pskb_trim(skb, 0)) { 1510 TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1; 1511 skb_shinfo(skb)->tso_segs = 1; 1512 skb_shinfo(skb)->tso_size = 0; 1513 skb->ip_summed = CHECKSUM_NONE; 1514 skb->csum = 0; 1515 } 1516 } 1517 1518 /* Make a copy, if the first transmission SKB clone we made 1519 * is still in somebody's hands, else make a clone. 1520 */ 1521 TCP_SKB_CB(skb)->when = tcp_time_stamp; 1522 1523 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 1524 1525 if (err == 0) { 1526 /* Update global TCP statistics. */ 1527 TCP_INC_STATS(TCP_MIB_RETRANSSEGS); 1528 1529 tp->total_retrans++; 1530 1531 #if FASTRETRANS_DEBUG > 0 1532 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) { 1533 if (net_ratelimit()) 1534 printk(KERN_DEBUG "retrans_out leaked.\n"); 1535 } 1536 #endif 1537 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS; 1538 tp->retrans_out += tcp_skb_pcount(skb); 1539 1540 /* Save stamp of the first retransmit. */ 1541 if (!tp->retrans_stamp) 1542 tp->retrans_stamp = TCP_SKB_CB(skb)->when; 1543 1544 tp->undo_retrans++; 1545 1546 /* snd_nxt is stored to detect loss of retransmitted segment, 1547 * see tcp_input.c tcp_sacktag_write_queue(). 1548 */ 1549 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt; 1550 } 1551 return err; 1552 } 1553 1554 /* This gets called after a retransmit timeout, and the initially 1555 * retransmitted data is acknowledged. It tries to continue 1556 * resending the rest of the retransmit queue, until either 1557 * we've sent it all or the congestion window limit is reached. 1558 * If doing SACK, the first ACK which comes back for a timeout 1559 * based retransmit packet might feed us FACK information again. 1560 * If so, we use it to avoid unnecessarily retransmissions. 1561 */ 1562 void tcp_xmit_retransmit_queue(struct sock *sk) 1563 { 1564 const struct inet_connection_sock *icsk = inet_csk(sk); 1565 struct tcp_sock *tp = tcp_sk(sk); 1566 struct sk_buff *skb; 1567 int packet_cnt; 1568 1569 if (tp->retransmit_skb_hint) { 1570 skb = tp->retransmit_skb_hint; 1571 packet_cnt = tp->retransmit_cnt_hint; 1572 }else{ 1573 skb = sk->sk_write_queue.next; 1574 packet_cnt = 0; 1575 } 1576 1577 /* First pass: retransmit lost packets. */ 1578 if (tp->lost_out) { 1579 sk_stream_for_retrans_queue_from(skb, sk) { 1580 __u8 sacked = TCP_SKB_CB(skb)->sacked; 1581 1582 /* we could do better than to assign each time */ 1583 tp->retransmit_skb_hint = skb; 1584 tp->retransmit_cnt_hint = packet_cnt; 1585 1586 /* Assume this retransmit will generate 1587 * only one packet for congestion window 1588 * calculation purposes. This works because 1589 * tcp_retransmit_skb() will chop up the 1590 * packet to be MSS sized and all the 1591 * packet counting works out. 1592 */ 1593 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd) 1594 return; 1595 1596 if (sacked & TCPCB_LOST) { 1597 if (!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) { 1598 if (tcp_retransmit_skb(sk, skb)) { 1599 tp->retransmit_skb_hint = NULL; 1600 return; 1601 } 1602 if (icsk->icsk_ca_state != TCP_CA_Loss) 1603 NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS); 1604 else 1605 NET_INC_STATS_BH(LINUX_MIB_TCPSLOWSTARTRETRANS); 1606 1607 if (skb == 1608 skb_peek(&sk->sk_write_queue)) 1609 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 1610 inet_csk(sk)->icsk_rto, 1611 TCP_RTO_MAX); 1612 } 1613 1614 packet_cnt += tcp_skb_pcount(skb); 1615 if (packet_cnt >= tp->lost_out) 1616 break; 1617 } 1618 } 1619 } 1620 1621 /* OK, demanded retransmission is finished. */ 1622 1623 /* Forward retransmissions are possible only during Recovery. */ 1624 if (icsk->icsk_ca_state != TCP_CA_Recovery) 1625 return; 1626 1627 /* No forward retransmissions in Reno are possible. */ 1628 if (!tp->rx_opt.sack_ok) 1629 return; 1630 1631 /* Yeah, we have to make difficult choice between forward transmission 1632 * and retransmission... Both ways have their merits... 1633 * 1634 * For now we do not retransmit anything, while we have some new 1635 * segments to send. 1636 */ 1637 1638 if (tcp_may_send_now(sk, tp)) 1639 return; 1640 1641 if (tp->forward_skb_hint) { 1642 skb = tp->forward_skb_hint; 1643 packet_cnt = tp->forward_cnt_hint; 1644 } else{ 1645 skb = sk->sk_write_queue.next; 1646 packet_cnt = 0; 1647 } 1648 1649 sk_stream_for_retrans_queue_from(skb, sk) { 1650 tp->forward_cnt_hint = packet_cnt; 1651 tp->forward_skb_hint = skb; 1652 1653 /* Similar to the retransmit loop above we 1654 * can pretend that the retransmitted SKB 1655 * we send out here will be composed of one 1656 * real MSS sized packet because tcp_retransmit_skb() 1657 * will fragment it if necessary. 1658 */ 1659 if (++packet_cnt > tp->fackets_out) 1660 break; 1661 1662 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd) 1663 break; 1664 1665 if (TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) 1666 continue; 1667 1668 /* Ok, retransmit it. */ 1669 if (tcp_retransmit_skb(sk, skb)) { 1670 tp->forward_skb_hint = NULL; 1671 break; 1672 } 1673 1674 if (skb == skb_peek(&sk->sk_write_queue)) 1675 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 1676 inet_csk(sk)->icsk_rto, 1677 TCP_RTO_MAX); 1678 1679 NET_INC_STATS_BH(LINUX_MIB_TCPFORWARDRETRANS); 1680 } 1681 } 1682 1683 1684 /* Send a fin. The caller locks the socket for us. This cannot be 1685 * allowed to fail queueing a FIN frame under any circumstances. 1686 */ 1687 void tcp_send_fin(struct sock *sk) 1688 { 1689 struct tcp_sock *tp = tcp_sk(sk); 1690 struct sk_buff *skb = skb_peek_tail(&sk->sk_write_queue); 1691 int mss_now; 1692 1693 /* Optimization, tack on the FIN if we have a queue of 1694 * unsent frames. But be careful about outgoing SACKS 1695 * and IP options. 1696 */ 1697 mss_now = tcp_current_mss(sk, 1); 1698 1699 if (sk->sk_send_head != NULL) { 1700 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN; 1701 TCP_SKB_CB(skb)->end_seq++; 1702 tp->write_seq++; 1703 } else { 1704 /* Socket is locked, keep trying until memory is available. */ 1705 for (;;) { 1706 skb = alloc_skb_fclone(MAX_TCP_HEADER, GFP_KERNEL); 1707 if (skb) 1708 break; 1709 yield(); 1710 } 1711 1712 /* Reserve space for headers and prepare control bits. */ 1713 skb_reserve(skb, MAX_TCP_HEADER); 1714 skb->csum = 0; 1715 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_FIN); 1716 TCP_SKB_CB(skb)->sacked = 0; 1717 skb_shinfo(skb)->tso_segs = 1; 1718 skb_shinfo(skb)->tso_size = 0; 1719 1720 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */ 1721 TCP_SKB_CB(skb)->seq = tp->write_seq; 1722 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1; 1723 tcp_queue_skb(sk, skb); 1724 } 1725 __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_OFF); 1726 } 1727 1728 /* We get here when a process closes a file descriptor (either due to 1729 * an explicit close() or as a byproduct of exit()'ing) and there 1730 * was unread data in the receive queue. This behavior is recommended 1731 * by draft-ietf-tcpimpl-prob-03.txt section 3.10. -DaveM 1732 */ 1733 void tcp_send_active_reset(struct sock *sk, gfp_t priority) 1734 { 1735 struct tcp_sock *tp = tcp_sk(sk); 1736 struct sk_buff *skb; 1737 1738 /* NOTE: No TCP options attached and we never retransmit this. */ 1739 skb = alloc_skb(MAX_TCP_HEADER, priority); 1740 if (!skb) { 1741 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED); 1742 return; 1743 } 1744 1745 /* Reserve space for headers and prepare control bits. */ 1746 skb_reserve(skb, MAX_TCP_HEADER); 1747 skb->csum = 0; 1748 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_RST); 1749 TCP_SKB_CB(skb)->sacked = 0; 1750 skb_shinfo(skb)->tso_segs = 1; 1751 skb_shinfo(skb)->tso_size = 0; 1752 1753 /* Send it off. */ 1754 TCP_SKB_CB(skb)->seq = tcp_acceptable_seq(sk, tp); 1755 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq; 1756 TCP_SKB_CB(skb)->when = tcp_time_stamp; 1757 if (tcp_transmit_skb(sk, skb, 0, priority)) 1758 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED); 1759 } 1760 1761 /* WARNING: This routine must only be called when we have already sent 1762 * a SYN packet that crossed the incoming SYN that caused this routine 1763 * to get called. If this assumption fails then the initial rcv_wnd 1764 * and rcv_wscale values will not be correct. 1765 */ 1766 int tcp_send_synack(struct sock *sk) 1767 { 1768 struct sk_buff* skb; 1769 1770 skb = skb_peek(&sk->sk_write_queue); 1771 if (skb == NULL || !(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_SYN)) { 1772 printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n"); 1773 return -EFAULT; 1774 } 1775 if (!(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_ACK)) { 1776 if (skb_cloned(skb)) { 1777 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC); 1778 if (nskb == NULL) 1779 return -ENOMEM; 1780 __skb_unlink(skb, &sk->sk_write_queue); 1781 skb_header_release(nskb); 1782 __skb_queue_head(&sk->sk_write_queue, nskb); 1783 sk_stream_free_skb(sk, skb); 1784 sk_charge_skb(sk, nskb); 1785 skb = nskb; 1786 } 1787 1788 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK; 1789 TCP_ECN_send_synack(tcp_sk(sk), skb); 1790 } 1791 TCP_SKB_CB(skb)->when = tcp_time_stamp; 1792 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 1793 } 1794 1795 /* 1796 * Prepare a SYN-ACK. 1797 */ 1798 struct sk_buff * tcp_make_synack(struct sock *sk, struct dst_entry *dst, 1799 struct request_sock *req) 1800 { 1801 struct inet_request_sock *ireq = inet_rsk(req); 1802 struct tcp_sock *tp = tcp_sk(sk); 1803 struct tcphdr *th; 1804 int tcp_header_size; 1805 struct sk_buff *skb; 1806 1807 skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC); 1808 if (skb == NULL) 1809 return NULL; 1810 1811 /* Reserve space for headers. */ 1812 skb_reserve(skb, MAX_TCP_HEADER); 1813 1814 skb->dst = dst_clone(dst); 1815 1816 tcp_header_size = (sizeof(struct tcphdr) + TCPOLEN_MSS + 1817 (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0) + 1818 (ireq->wscale_ok ? TCPOLEN_WSCALE_ALIGNED : 0) + 1819 /* SACK_PERM is in the place of NOP NOP of TS */ 1820 ((ireq->sack_ok && !ireq->tstamp_ok) ? TCPOLEN_SACKPERM_ALIGNED : 0)); 1821 skb->h.th = th = (struct tcphdr *) skb_push(skb, tcp_header_size); 1822 1823 memset(th, 0, sizeof(struct tcphdr)); 1824 th->syn = 1; 1825 th->ack = 1; 1826 if (dst->dev->features&NETIF_F_TSO) 1827 ireq->ecn_ok = 0; 1828 TCP_ECN_make_synack(req, th); 1829 th->source = inet_sk(sk)->sport; 1830 th->dest = ireq->rmt_port; 1831 TCP_SKB_CB(skb)->seq = tcp_rsk(req)->snt_isn; 1832 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1; 1833 TCP_SKB_CB(skb)->sacked = 0; 1834 skb_shinfo(skb)->tso_segs = 1; 1835 skb_shinfo(skb)->tso_size = 0; 1836 th->seq = htonl(TCP_SKB_CB(skb)->seq); 1837 th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1); 1838 if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */ 1839 __u8 rcv_wscale; 1840 /* Set this up on the first call only */ 1841 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW); 1842 /* tcp_full_space because it is guaranteed to be the first packet */ 1843 tcp_select_initial_window(tcp_full_space(sk), 1844 dst_metric(dst, RTAX_ADVMSS) - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 1845 &req->rcv_wnd, 1846 &req->window_clamp, 1847 ireq->wscale_ok, 1848 &rcv_wscale); 1849 ireq->rcv_wscale = rcv_wscale; 1850 } 1851 1852 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */ 1853 th->window = htons(req->rcv_wnd); 1854 1855 TCP_SKB_CB(skb)->when = tcp_time_stamp; 1856 tcp_syn_build_options((__u32 *)(th + 1), dst_metric(dst, RTAX_ADVMSS), ireq->tstamp_ok, 1857 ireq->sack_ok, ireq->wscale_ok, ireq->rcv_wscale, 1858 TCP_SKB_CB(skb)->when, 1859 req->ts_recent); 1860 1861 skb->csum = 0; 1862 th->doff = (tcp_header_size >> 2); 1863 TCP_INC_STATS(TCP_MIB_OUTSEGS); 1864 return skb; 1865 } 1866 1867 /* 1868 * Do all connect socket setups that can be done AF independent. 1869 */ 1870 static void tcp_connect_init(struct sock *sk) 1871 { 1872 struct dst_entry *dst = __sk_dst_get(sk); 1873 struct tcp_sock *tp = tcp_sk(sk); 1874 __u8 rcv_wscale; 1875 1876 /* We'll fix this up when we get a response from the other end. 1877 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT. 1878 */ 1879 tp->tcp_header_len = sizeof(struct tcphdr) + 1880 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0); 1881 1882 /* If user gave his TCP_MAXSEG, record it to clamp */ 1883 if (tp->rx_opt.user_mss) 1884 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; 1885 tp->max_window = 0; 1886 tcp_sync_mss(sk, dst_mtu(dst)); 1887 1888 if (!tp->window_clamp) 1889 tp->window_clamp = dst_metric(dst, RTAX_WINDOW); 1890 tp->advmss = dst_metric(dst, RTAX_ADVMSS); 1891 tcp_initialize_rcv_mss(sk); 1892 1893 tcp_select_initial_window(tcp_full_space(sk), 1894 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0), 1895 &tp->rcv_wnd, 1896 &tp->window_clamp, 1897 sysctl_tcp_window_scaling, 1898 &rcv_wscale); 1899 1900 tp->rx_opt.rcv_wscale = rcv_wscale; 1901 tp->rcv_ssthresh = tp->rcv_wnd; 1902 1903 sk->sk_err = 0; 1904 sock_reset_flag(sk, SOCK_DONE); 1905 tp->snd_wnd = 0; 1906 tcp_init_wl(tp, tp->write_seq, 0); 1907 tp->snd_una = tp->write_seq; 1908 tp->snd_sml = tp->write_seq; 1909 tp->rcv_nxt = 0; 1910 tp->rcv_wup = 0; 1911 tp->copied_seq = 0; 1912 1913 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; 1914 inet_csk(sk)->icsk_retransmits = 0; 1915 tcp_clear_retrans(tp); 1916 } 1917 1918 /* 1919 * Build a SYN and send it off. 1920 */ 1921 int tcp_connect(struct sock *sk) 1922 { 1923 struct tcp_sock *tp = tcp_sk(sk); 1924 struct sk_buff *buff; 1925 1926 tcp_connect_init(sk); 1927 1928 buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation); 1929 if (unlikely(buff == NULL)) 1930 return -ENOBUFS; 1931 1932 /* Reserve space for headers. */ 1933 skb_reserve(buff, MAX_TCP_HEADER); 1934 1935 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN; 1936 TCP_ECN_send_syn(sk, tp, buff); 1937 TCP_SKB_CB(buff)->sacked = 0; 1938 skb_shinfo(buff)->tso_segs = 1; 1939 skb_shinfo(buff)->tso_size = 0; 1940 buff->csum = 0; 1941 TCP_SKB_CB(buff)->seq = tp->write_seq++; 1942 TCP_SKB_CB(buff)->end_seq = tp->write_seq; 1943 tp->snd_nxt = tp->write_seq; 1944 tp->pushed_seq = tp->write_seq; 1945 1946 /* Send it off. */ 1947 TCP_SKB_CB(buff)->when = tcp_time_stamp; 1948 tp->retrans_stamp = TCP_SKB_CB(buff)->when; 1949 skb_header_release(buff); 1950 __skb_queue_tail(&sk->sk_write_queue, buff); 1951 sk_charge_skb(sk, buff); 1952 tp->packets_out += tcp_skb_pcount(buff); 1953 tcp_transmit_skb(sk, buff, 1, GFP_KERNEL); 1954 TCP_INC_STATS(TCP_MIB_ACTIVEOPENS); 1955 1956 /* Timer for repeating the SYN until an answer. */ 1957 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 1958 inet_csk(sk)->icsk_rto, TCP_RTO_MAX); 1959 return 0; 1960 } 1961 1962 /* Send out a delayed ack, the caller does the policy checking 1963 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check() 1964 * for details. 1965 */ 1966 void tcp_send_delayed_ack(struct sock *sk) 1967 { 1968 struct inet_connection_sock *icsk = inet_csk(sk); 1969 int ato = icsk->icsk_ack.ato; 1970 unsigned long timeout; 1971 1972 if (ato > TCP_DELACK_MIN) { 1973 const struct tcp_sock *tp = tcp_sk(sk); 1974 int max_ato = HZ/2; 1975 1976 if (icsk->icsk_ack.pingpong || (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)) 1977 max_ato = TCP_DELACK_MAX; 1978 1979 /* Slow path, intersegment interval is "high". */ 1980 1981 /* If some rtt estimate is known, use it to bound delayed ack. 1982 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements 1983 * directly. 1984 */ 1985 if (tp->srtt) { 1986 int rtt = max(tp->srtt>>3, TCP_DELACK_MIN); 1987 1988 if (rtt < max_ato) 1989 max_ato = rtt; 1990 } 1991 1992 ato = min(ato, max_ato); 1993 } 1994 1995 /* Stay within the limit we were given */ 1996 timeout = jiffies + ato; 1997 1998 /* Use new timeout only if there wasn't a older one earlier. */ 1999 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) { 2000 /* If delack timer was blocked or is about to expire, 2001 * send ACK now. 2002 */ 2003 if (icsk->icsk_ack.blocked || 2004 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) { 2005 tcp_send_ack(sk); 2006 return; 2007 } 2008 2009 if (!time_before(timeout, icsk->icsk_ack.timeout)) 2010 timeout = icsk->icsk_ack.timeout; 2011 } 2012 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; 2013 icsk->icsk_ack.timeout = timeout; 2014 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); 2015 } 2016 2017 /* This routine sends an ack and also updates the window. */ 2018 void tcp_send_ack(struct sock *sk) 2019 { 2020 /* If we have been reset, we may not send again. */ 2021 if (sk->sk_state != TCP_CLOSE) { 2022 struct tcp_sock *tp = tcp_sk(sk); 2023 struct sk_buff *buff; 2024 2025 /* We are not putting this on the write queue, so 2026 * tcp_transmit_skb() will set the ownership to this 2027 * sock. 2028 */ 2029 buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC); 2030 if (buff == NULL) { 2031 inet_csk_schedule_ack(sk); 2032 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN; 2033 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 2034 TCP_DELACK_MAX, TCP_RTO_MAX); 2035 return; 2036 } 2037 2038 /* Reserve space for headers and prepare control bits. */ 2039 skb_reserve(buff, MAX_TCP_HEADER); 2040 buff->csum = 0; 2041 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK; 2042 TCP_SKB_CB(buff)->sacked = 0; 2043 skb_shinfo(buff)->tso_segs = 1; 2044 skb_shinfo(buff)->tso_size = 0; 2045 2046 /* Send it off, this clears delayed acks for us. */ 2047 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(buff)->end_seq = tcp_acceptable_seq(sk, tp); 2048 TCP_SKB_CB(buff)->when = tcp_time_stamp; 2049 tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC); 2050 } 2051 } 2052 2053 /* This routine sends a packet with an out of date sequence 2054 * number. It assumes the other end will try to ack it. 2055 * 2056 * Question: what should we make while urgent mode? 2057 * 4.4BSD forces sending single byte of data. We cannot send 2058 * out of window data, because we have SND.NXT==SND.MAX... 2059 * 2060 * Current solution: to send TWO zero-length segments in urgent mode: 2061 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is 2062 * out-of-date with SND.UNA-1 to probe window. 2063 */ 2064 static int tcp_xmit_probe_skb(struct sock *sk, int urgent) 2065 { 2066 struct tcp_sock *tp = tcp_sk(sk); 2067 struct sk_buff *skb; 2068 2069 /* We don't queue it, tcp_transmit_skb() sets ownership. */ 2070 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC); 2071 if (skb == NULL) 2072 return -1; 2073 2074 /* Reserve space for headers and set control bits. */ 2075 skb_reserve(skb, MAX_TCP_HEADER); 2076 skb->csum = 0; 2077 TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK; 2078 TCP_SKB_CB(skb)->sacked = urgent; 2079 skb_shinfo(skb)->tso_segs = 1; 2080 skb_shinfo(skb)->tso_size = 0; 2081 2082 /* Use a previous sequence. This should cause the other 2083 * end to send an ack. Don't queue or clone SKB, just 2084 * send it. 2085 */ 2086 TCP_SKB_CB(skb)->seq = urgent ? tp->snd_una : tp->snd_una - 1; 2087 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq; 2088 TCP_SKB_CB(skb)->when = tcp_time_stamp; 2089 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC); 2090 } 2091 2092 int tcp_write_wakeup(struct sock *sk) 2093 { 2094 if (sk->sk_state != TCP_CLOSE) { 2095 struct tcp_sock *tp = tcp_sk(sk); 2096 struct sk_buff *skb; 2097 2098 if ((skb = sk->sk_send_head) != NULL && 2099 before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)) { 2100 int err; 2101 unsigned int mss = tcp_current_mss(sk, 0); 2102 unsigned int seg_size = tp->snd_una+tp->snd_wnd-TCP_SKB_CB(skb)->seq; 2103 2104 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq)) 2105 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq; 2106 2107 /* We are probing the opening of a window 2108 * but the window size is != 0 2109 * must have been a result SWS avoidance ( sender ) 2110 */ 2111 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq || 2112 skb->len > mss) { 2113 seg_size = min(seg_size, mss); 2114 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH; 2115 if (tcp_fragment(sk, skb, seg_size, mss)) 2116 return -1; 2117 } else if (!tcp_skb_pcount(skb)) 2118 tcp_set_skb_tso_segs(sk, skb, mss); 2119 2120 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH; 2121 TCP_SKB_CB(skb)->when = tcp_time_stamp; 2122 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 2123 if (!err) { 2124 update_send_head(sk, tp, skb); 2125 } 2126 return err; 2127 } else { 2128 if (tp->urg_mode && 2129 between(tp->snd_up, tp->snd_una+1, tp->snd_una+0xFFFF)) 2130 tcp_xmit_probe_skb(sk, TCPCB_URG); 2131 return tcp_xmit_probe_skb(sk, 0); 2132 } 2133 } 2134 return -1; 2135 } 2136 2137 /* A window probe timeout has occurred. If window is not closed send 2138 * a partial packet else a zero probe. 2139 */ 2140 void tcp_send_probe0(struct sock *sk) 2141 { 2142 struct inet_connection_sock *icsk = inet_csk(sk); 2143 struct tcp_sock *tp = tcp_sk(sk); 2144 int err; 2145 2146 err = tcp_write_wakeup(sk); 2147 2148 if (tp->packets_out || !sk->sk_send_head) { 2149 /* Cancel probe timer, if it is not required. */ 2150 icsk->icsk_probes_out = 0; 2151 icsk->icsk_backoff = 0; 2152 return; 2153 } 2154 2155 if (err <= 0) { 2156 if (icsk->icsk_backoff < sysctl_tcp_retries2) 2157 icsk->icsk_backoff++; 2158 icsk->icsk_probes_out++; 2159 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 2160 min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX), 2161 TCP_RTO_MAX); 2162 } else { 2163 /* If packet was not sent due to local congestion, 2164 * do not backoff and do not remember icsk_probes_out. 2165 * Let local senders to fight for local resources. 2166 * 2167 * Use accumulated backoff yet. 2168 */ 2169 if (!icsk->icsk_probes_out) 2170 icsk->icsk_probes_out = 1; 2171 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 2172 min(icsk->icsk_rto << icsk->icsk_backoff, 2173 TCP_RESOURCE_PROBE_INTERVAL), 2174 TCP_RTO_MAX); 2175 } 2176 } 2177 2178 EXPORT_SYMBOL(tcp_connect); 2179 EXPORT_SYMBOL(tcp_make_synack); 2180 EXPORT_SYMBOL(tcp_simple_retransmit); 2181 EXPORT_SYMBOL(tcp_sync_mss); 2182 EXPORT_SYMBOL(sysctl_tcp_tso_win_divisor); 2183