powerpc/powernv: Report size of OPAL memcons log
[linux/fpc-iii.git] / net / ipv4 / tcp_output.c
blob1d5331a1b1dc2677316148ba9852c191e7ed0fd4
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.
6 * Implementation of the Transmission Control Protocol(TCP).
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>
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
25 * : AF independence
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
37 #define pr_fmt(fmt) "TCP: " fmt
39 #include <net/tcp.h>
41 #include <linux/compiler.h>
42 #include <linux/gfp.h>
43 #include <linux/module.h>
45 /* People can turn this off for buggy TCP's found in printers etc. */
46 int sysctl_tcp_retrans_collapse __read_mostly = 1;
48 /* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
53 /* Default TSQ limit of four TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
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.
60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
62 /* By default, RFC2861 behavior. */
63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
65 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
66 int push_one, gfp_t gfp);
68 /* Account for new data that has been sent to the network. */
69 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
71 struct inet_connection_sock *icsk = inet_csk(sk);
72 struct tcp_sock *tp = tcp_sk(sk);
73 unsigned int prior_packets = tp->packets_out;
75 tcp_advance_send_head(sk, skb);
76 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
78 tp->packets_out += tcp_skb_pcount(skb);
79 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
80 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
81 tcp_rearm_rto(sk);
84 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
85 tcp_skb_pcount(skb));
88 /* SND.NXT, if window was not shrunk.
89 * If window has been shrunk, what should we make? It is not clear at all.
90 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
91 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
92 * invalid. OK, let's make this for now:
94 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
96 const struct tcp_sock *tp = tcp_sk(sk);
98 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
99 return tp->snd_nxt;
100 else
101 return tcp_wnd_end(tp);
104 /* Calculate mss to advertise in SYN segment.
105 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
107 * 1. It is independent of path mtu.
108 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
109 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
110 * attached devices, because some buggy hosts are confused by
111 * large MSS.
112 * 4. We do not make 3, we advertise MSS, calculated from first
113 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
114 * This may be overridden via information stored in routing table.
115 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
116 * probably even Jumbo".
118 static __u16 tcp_advertise_mss(struct sock *sk)
120 struct tcp_sock *tp = tcp_sk(sk);
121 const struct dst_entry *dst = __sk_dst_get(sk);
122 int mss = tp->advmss;
124 if (dst) {
125 unsigned int metric = dst_metric_advmss(dst);
127 if (metric < mss) {
128 mss = metric;
129 tp->advmss = mss;
133 return (__u16)mss;
136 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
137 * This is the first part of cwnd validation mechanism.
139 void tcp_cwnd_restart(struct sock *sk, s32 delta)
141 struct tcp_sock *tp = tcp_sk(sk);
142 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
143 u32 cwnd = tp->snd_cwnd;
145 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
147 tp->snd_ssthresh = tcp_current_ssthresh(sk);
148 restart_cwnd = min(restart_cwnd, cwnd);
150 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
151 cwnd >>= 1;
152 tp->snd_cwnd = max(cwnd, restart_cwnd);
153 tp->snd_cwnd_stamp = tcp_time_stamp;
154 tp->snd_cwnd_used = 0;
157 /* Congestion state accounting after a packet has been sent. */
158 static void tcp_event_data_sent(struct tcp_sock *tp,
159 struct sock *sk)
161 struct inet_connection_sock *icsk = inet_csk(sk);
162 const u32 now = tcp_time_stamp;
164 if (tcp_packets_in_flight(tp) == 0)
165 tcp_ca_event(sk, CA_EVENT_TX_START);
167 tp->lsndtime = now;
169 /* If it is a reply for ato after last received
170 * packet, enter pingpong mode.
172 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
173 icsk->icsk_ack.pingpong = 1;
176 /* Account for an ACK we sent. */
177 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
179 tcp_dec_quickack_mode(sk, pkts);
180 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
184 u32 tcp_default_init_rwnd(u32 mss)
186 /* Initial receive window should be twice of TCP_INIT_CWND to
187 * enable proper sending of new unsent data during fast recovery
188 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
189 * limit when mss is larger than 1460.
191 u32 init_rwnd = TCP_INIT_CWND * 2;
193 if (mss > 1460)
194 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
195 return init_rwnd;
198 /* Determine a window scaling and initial window to offer.
199 * Based on the assumption that the given amount of space
200 * will be offered. Store the results in the tp structure.
201 * NOTE: for smooth operation initial space offering should
202 * be a multiple of mss if possible. We assume here that mss >= 1.
203 * This MUST be enforced by all callers.
205 void tcp_select_initial_window(int __space, __u32 mss,
206 __u32 *rcv_wnd, __u32 *window_clamp,
207 int wscale_ok, __u8 *rcv_wscale,
208 __u32 init_rcv_wnd)
210 unsigned int space = (__space < 0 ? 0 : __space);
212 /* If no clamp set the clamp to the max possible scaled window */
213 if (*window_clamp == 0)
214 (*window_clamp) = (65535 << 14);
215 space = min(*window_clamp, space);
217 /* Quantize space offering to a multiple of mss if possible. */
218 if (space > mss)
219 space = (space / mss) * mss;
221 /* NOTE: offering an initial window larger than 32767
222 * will break some buggy TCP stacks. If the admin tells us
223 * it is likely we could be speaking with such a buggy stack
224 * we will truncate our initial window offering to 32K-1
225 * unless the remote has sent us a window scaling option,
226 * which we interpret as a sign the remote TCP is not
227 * misinterpreting the window field as a signed quantity.
229 if (sysctl_tcp_workaround_signed_windows)
230 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
231 else
232 (*rcv_wnd) = space;
234 (*rcv_wscale) = 0;
235 if (wscale_ok) {
236 /* Set window scaling on max possible window
237 * See RFC1323 for an explanation of the limit to 14
239 space = max_t(u32, space, sysctl_tcp_rmem[2]);
240 space = max_t(u32, space, sysctl_rmem_max);
241 space = min_t(u32, space, *window_clamp);
242 while (space > 65535 && (*rcv_wscale) < 14) {
243 space >>= 1;
244 (*rcv_wscale)++;
248 if (mss > (1 << *rcv_wscale)) {
249 if (!init_rcv_wnd) /* Use default unless specified otherwise */
250 init_rcv_wnd = tcp_default_init_rwnd(mss);
251 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
254 /* Set the clamp no higher than max representable value */
255 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
257 EXPORT_SYMBOL(tcp_select_initial_window);
259 /* Chose a new window to advertise, update state in tcp_sock for the
260 * socket, and return result with RFC1323 scaling applied. The return
261 * value can be stuffed directly into th->window for an outgoing
262 * frame.
264 static u16 tcp_select_window(struct sock *sk)
266 struct tcp_sock *tp = tcp_sk(sk);
267 u32 old_win = tp->rcv_wnd;
268 u32 cur_win = tcp_receive_window(tp);
269 u32 new_win = __tcp_select_window(sk);
271 /* Never shrink the offered window */
272 if (new_win < cur_win) {
273 /* Danger Will Robinson!
274 * Don't update rcv_wup/rcv_wnd here or else
275 * we will not be able to advertise a zero
276 * window in time. --DaveM
278 * Relax Will Robinson.
280 if (new_win == 0)
281 NET_INC_STATS(sock_net(sk),
282 LINUX_MIB_TCPWANTZEROWINDOWADV);
283 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
285 tp->rcv_wnd = new_win;
286 tp->rcv_wup = tp->rcv_nxt;
288 /* Make sure we do not exceed the maximum possible
289 * scaled window.
291 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
292 new_win = min(new_win, MAX_TCP_WINDOW);
293 else
294 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
296 /* RFC1323 scaling applied */
297 new_win >>= tp->rx_opt.rcv_wscale;
299 /* If we advertise zero window, disable fast path. */
300 if (new_win == 0) {
301 tp->pred_flags = 0;
302 if (old_win)
303 NET_INC_STATS(sock_net(sk),
304 LINUX_MIB_TCPTOZEROWINDOWADV);
305 } else if (old_win == 0) {
306 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
309 return new_win;
312 /* Packet ECN state for a SYN-ACK */
313 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
315 const struct tcp_sock *tp = tcp_sk(sk);
317 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
318 if (!(tp->ecn_flags & TCP_ECN_OK))
319 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
320 else if (tcp_ca_needs_ecn(sk))
321 INET_ECN_xmit(sk);
324 /* Packet ECN state for a SYN. */
325 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
327 struct tcp_sock *tp = tcp_sk(sk);
328 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
329 tcp_ca_needs_ecn(sk);
331 if (!use_ecn) {
332 const struct dst_entry *dst = __sk_dst_get(sk);
334 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
335 use_ecn = true;
338 tp->ecn_flags = 0;
340 if (use_ecn) {
341 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
342 tp->ecn_flags = TCP_ECN_OK;
343 if (tcp_ca_needs_ecn(sk))
344 INET_ECN_xmit(sk);
348 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
350 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
351 /* tp->ecn_flags are cleared at a later point in time when
352 * SYN ACK is ultimatively being received.
354 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
357 static void
358 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
360 if (inet_rsk(req)->ecn_ok)
361 th->ece = 1;
364 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
365 * be sent.
367 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
368 struct tcphdr *th, int tcp_header_len)
370 struct tcp_sock *tp = tcp_sk(sk);
372 if (tp->ecn_flags & TCP_ECN_OK) {
373 /* Not-retransmitted data segment: set ECT and inject CWR. */
374 if (skb->len != tcp_header_len &&
375 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
376 INET_ECN_xmit(sk);
377 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
378 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
379 th->cwr = 1;
380 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
382 } else if (!tcp_ca_needs_ecn(sk)) {
383 /* ACK or retransmitted segment: clear ECT|CE */
384 INET_ECN_dontxmit(sk);
386 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
387 th->ece = 1;
391 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
392 * auto increment end seqno.
394 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
396 skb->ip_summed = CHECKSUM_PARTIAL;
397 skb->csum = 0;
399 TCP_SKB_CB(skb)->tcp_flags = flags;
400 TCP_SKB_CB(skb)->sacked = 0;
402 tcp_skb_pcount_set(skb, 1);
404 TCP_SKB_CB(skb)->seq = seq;
405 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
406 seq++;
407 TCP_SKB_CB(skb)->end_seq = seq;
410 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
412 return tp->snd_una != tp->snd_up;
415 #define OPTION_SACK_ADVERTISE (1 << 0)
416 #define OPTION_TS (1 << 1)
417 #define OPTION_MD5 (1 << 2)
418 #define OPTION_WSCALE (1 << 3)
419 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
421 struct tcp_out_options {
422 u16 options; /* bit field of OPTION_* */
423 u16 mss; /* 0 to disable */
424 u8 ws; /* window scale, 0 to disable */
425 u8 num_sack_blocks; /* number of SACK blocks to include */
426 u8 hash_size; /* bytes in hash_location */
427 __u8 *hash_location; /* temporary pointer, overloaded */
428 __u32 tsval, tsecr; /* need to include OPTION_TS */
429 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
432 /* Write previously computed TCP options to the packet.
434 * Beware: Something in the Internet is very sensitive to the ordering of
435 * TCP options, we learned this through the hard way, so be careful here.
436 * Luckily we can at least blame others for their non-compliance but from
437 * inter-operability perspective it seems that we're somewhat stuck with
438 * the ordering which we have been using if we want to keep working with
439 * those broken things (not that it currently hurts anybody as there isn't
440 * particular reason why the ordering would need to be changed).
442 * At least SACK_PERM as the first option is known to lead to a disaster
443 * (but it may well be that other scenarios fail similarly).
445 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
446 struct tcp_out_options *opts)
448 u16 options = opts->options; /* mungable copy */
450 if (unlikely(OPTION_MD5 & options)) {
451 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
452 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
453 /* overload cookie hash location */
454 opts->hash_location = (__u8 *)ptr;
455 ptr += 4;
458 if (unlikely(opts->mss)) {
459 *ptr++ = htonl((TCPOPT_MSS << 24) |
460 (TCPOLEN_MSS << 16) |
461 opts->mss);
464 if (likely(OPTION_TS & options)) {
465 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
466 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
467 (TCPOLEN_SACK_PERM << 16) |
468 (TCPOPT_TIMESTAMP << 8) |
469 TCPOLEN_TIMESTAMP);
470 options &= ~OPTION_SACK_ADVERTISE;
471 } else {
472 *ptr++ = htonl((TCPOPT_NOP << 24) |
473 (TCPOPT_NOP << 16) |
474 (TCPOPT_TIMESTAMP << 8) |
475 TCPOLEN_TIMESTAMP);
477 *ptr++ = htonl(opts->tsval);
478 *ptr++ = htonl(opts->tsecr);
481 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
482 *ptr++ = htonl((TCPOPT_NOP << 24) |
483 (TCPOPT_NOP << 16) |
484 (TCPOPT_SACK_PERM << 8) |
485 TCPOLEN_SACK_PERM);
488 if (unlikely(OPTION_WSCALE & options)) {
489 *ptr++ = htonl((TCPOPT_NOP << 24) |
490 (TCPOPT_WINDOW << 16) |
491 (TCPOLEN_WINDOW << 8) |
492 opts->ws);
495 if (unlikely(opts->num_sack_blocks)) {
496 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
497 tp->duplicate_sack : tp->selective_acks;
498 int this_sack;
500 *ptr++ = htonl((TCPOPT_NOP << 24) |
501 (TCPOPT_NOP << 16) |
502 (TCPOPT_SACK << 8) |
503 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
504 TCPOLEN_SACK_PERBLOCK)));
506 for (this_sack = 0; this_sack < opts->num_sack_blocks;
507 ++this_sack) {
508 *ptr++ = htonl(sp[this_sack].start_seq);
509 *ptr++ = htonl(sp[this_sack].end_seq);
512 tp->rx_opt.dsack = 0;
515 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
516 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
517 u8 *p = (u8 *)ptr;
518 u32 len; /* Fast Open option length */
520 if (foc->exp) {
521 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
522 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
523 TCPOPT_FASTOPEN_MAGIC);
524 p += TCPOLEN_EXP_FASTOPEN_BASE;
525 } else {
526 len = TCPOLEN_FASTOPEN_BASE + foc->len;
527 *p++ = TCPOPT_FASTOPEN;
528 *p++ = len;
531 memcpy(p, foc->val, foc->len);
532 if ((len & 3) == 2) {
533 p[foc->len] = TCPOPT_NOP;
534 p[foc->len + 1] = TCPOPT_NOP;
536 ptr += (len + 3) >> 2;
540 /* Compute TCP options for SYN packets. This is not the final
541 * network wire format yet.
543 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
544 struct tcp_out_options *opts,
545 struct tcp_md5sig_key **md5)
547 struct tcp_sock *tp = tcp_sk(sk);
548 unsigned int remaining = MAX_TCP_OPTION_SPACE;
549 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
551 #ifdef CONFIG_TCP_MD5SIG
552 *md5 = tp->af_specific->md5_lookup(sk, sk);
553 if (*md5) {
554 opts->options |= OPTION_MD5;
555 remaining -= TCPOLEN_MD5SIG_ALIGNED;
557 #else
558 *md5 = NULL;
559 #endif
561 /* We always get an MSS option. The option bytes which will be seen in
562 * normal data packets should timestamps be used, must be in the MSS
563 * advertised. But we subtract them from tp->mss_cache so that
564 * calculations in tcp_sendmsg are simpler etc. So account for this
565 * fact here if necessary. If we don't do this correctly, as a
566 * receiver we won't recognize data packets as being full sized when we
567 * should, and thus we won't abide by the delayed ACK rules correctly.
568 * SACKs don't matter, we never delay an ACK when we have any of those
569 * going out. */
570 opts->mss = tcp_advertise_mss(sk);
571 remaining -= TCPOLEN_MSS_ALIGNED;
573 if (likely(sysctl_tcp_timestamps && !*md5)) {
574 opts->options |= OPTION_TS;
575 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
576 opts->tsecr = tp->rx_opt.ts_recent;
577 remaining -= TCPOLEN_TSTAMP_ALIGNED;
579 if (likely(sysctl_tcp_window_scaling)) {
580 opts->ws = tp->rx_opt.rcv_wscale;
581 opts->options |= OPTION_WSCALE;
582 remaining -= TCPOLEN_WSCALE_ALIGNED;
584 if (likely(sysctl_tcp_sack)) {
585 opts->options |= OPTION_SACK_ADVERTISE;
586 if (unlikely(!(OPTION_TS & opts->options)))
587 remaining -= TCPOLEN_SACKPERM_ALIGNED;
590 if (fastopen && fastopen->cookie.len >= 0) {
591 u32 need = fastopen->cookie.len;
593 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
594 TCPOLEN_FASTOPEN_BASE;
595 need = (need + 3) & ~3U; /* Align to 32 bits */
596 if (remaining >= need) {
597 opts->options |= OPTION_FAST_OPEN_COOKIE;
598 opts->fastopen_cookie = &fastopen->cookie;
599 remaining -= need;
600 tp->syn_fastopen = 1;
601 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
605 return MAX_TCP_OPTION_SPACE - remaining;
608 /* Set up TCP options for SYN-ACKs. */
609 static unsigned int tcp_synack_options(struct request_sock *req,
610 unsigned int mss, struct sk_buff *skb,
611 struct tcp_out_options *opts,
612 const struct tcp_md5sig_key *md5,
613 struct tcp_fastopen_cookie *foc)
615 struct inet_request_sock *ireq = inet_rsk(req);
616 unsigned int remaining = MAX_TCP_OPTION_SPACE;
618 #ifdef CONFIG_TCP_MD5SIG
619 if (md5) {
620 opts->options |= OPTION_MD5;
621 remaining -= TCPOLEN_MD5SIG_ALIGNED;
623 /* We can't fit any SACK blocks in a packet with MD5 + TS
624 * options. There was discussion about disabling SACK
625 * rather than TS in order to fit in better with old,
626 * buggy kernels, but that was deemed to be unnecessary.
628 ireq->tstamp_ok &= !ireq->sack_ok;
630 #endif
632 /* We always send an MSS option. */
633 opts->mss = mss;
634 remaining -= TCPOLEN_MSS_ALIGNED;
636 if (likely(ireq->wscale_ok)) {
637 opts->ws = ireq->rcv_wscale;
638 opts->options |= OPTION_WSCALE;
639 remaining -= TCPOLEN_WSCALE_ALIGNED;
641 if (likely(ireq->tstamp_ok)) {
642 opts->options |= OPTION_TS;
643 opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
644 opts->tsecr = req->ts_recent;
645 remaining -= TCPOLEN_TSTAMP_ALIGNED;
647 if (likely(ireq->sack_ok)) {
648 opts->options |= OPTION_SACK_ADVERTISE;
649 if (unlikely(!ireq->tstamp_ok))
650 remaining -= TCPOLEN_SACKPERM_ALIGNED;
652 if (foc != NULL && foc->len >= 0) {
653 u32 need = foc->len;
655 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
656 TCPOLEN_FASTOPEN_BASE;
657 need = (need + 3) & ~3U; /* Align to 32 bits */
658 if (remaining >= need) {
659 opts->options |= OPTION_FAST_OPEN_COOKIE;
660 opts->fastopen_cookie = foc;
661 remaining -= need;
665 return MAX_TCP_OPTION_SPACE - remaining;
668 /* Compute TCP options for ESTABLISHED sockets. This is not the
669 * final wire format yet.
671 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
672 struct tcp_out_options *opts,
673 struct tcp_md5sig_key **md5)
675 struct tcp_sock *tp = tcp_sk(sk);
676 unsigned int size = 0;
677 unsigned int eff_sacks;
679 opts->options = 0;
681 #ifdef CONFIG_TCP_MD5SIG
682 *md5 = tp->af_specific->md5_lookup(sk, sk);
683 if (unlikely(*md5)) {
684 opts->options |= OPTION_MD5;
685 size += TCPOLEN_MD5SIG_ALIGNED;
687 #else
688 *md5 = NULL;
689 #endif
691 if (likely(tp->rx_opt.tstamp_ok)) {
692 opts->options |= OPTION_TS;
693 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
694 opts->tsecr = tp->rx_opt.ts_recent;
695 size += TCPOLEN_TSTAMP_ALIGNED;
698 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
699 if (unlikely(eff_sacks)) {
700 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
701 opts->num_sack_blocks =
702 min_t(unsigned int, eff_sacks,
703 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
704 TCPOLEN_SACK_PERBLOCK);
705 size += TCPOLEN_SACK_BASE_ALIGNED +
706 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
709 return size;
713 /* TCP SMALL QUEUES (TSQ)
715 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
716 * to reduce RTT and bufferbloat.
717 * We do this using a special skb destructor (tcp_wfree).
719 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
720 * needs to be reallocated in a driver.
721 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
723 * Since transmit from skb destructor is forbidden, we use a tasklet
724 * to process all sockets that eventually need to send more skbs.
725 * We use one tasklet per cpu, with its own queue of sockets.
727 struct tsq_tasklet {
728 struct tasklet_struct tasklet;
729 struct list_head head; /* queue of tcp sockets */
731 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
733 static void tcp_tsq_handler(struct sock *sk)
735 if ((1 << sk->sk_state) &
736 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
737 TCPF_CLOSE_WAIT | TCPF_LAST_ACK)) {
738 struct tcp_sock *tp = tcp_sk(sk);
740 if (tp->lost_out > tp->retrans_out &&
741 tp->snd_cwnd > tcp_packets_in_flight(tp))
742 tcp_xmit_retransmit_queue(sk);
744 tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
745 0, GFP_ATOMIC);
749 * One tasklet per cpu tries to send more skbs.
750 * We run in tasklet context but need to disable irqs when
751 * transferring tsq->head because tcp_wfree() might
752 * interrupt us (non NAPI drivers)
754 static void tcp_tasklet_func(unsigned long data)
756 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
757 LIST_HEAD(list);
758 unsigned long flags;
759 struct list_head *q, *n;
760 struct tcp_sock *tp;
761 struct sock *sk;
763 local_irq_save(flags);
764 list_splice_init(&tsq->head, &list);
765 local_irq_restore(flags);
767 list_for_each_safe(q, n, &list) {
768 tp = list_entry(q, struct tcp_sock, tsq_node);
769 list_del(&tp->tsq_node);
771 sk = (struct sock *)tp;
772 smp_mb__before_atomic();
773 clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags);
775 if (!sk->sk_lock.owned &&
776 test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) {
777 bh_lock_sock(sk);
778 if (!sock_owned_by_user(sk)) {
779 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
780 tcp_tsq_handler(sk);
782 bh_unlock_sock(sk);
785 sk_free(sk);
789 #define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED | \
790 TCPF_WRITE_TIMER_DEFERRED | \
791 TCPF_DELACK_TIMER_DEFERRED | \
792 TCPF_MTU_REDUCED_DEFERRED)
794 * tcp_release_cb - tcp release_sock() callback
795 * @sk: socket
797 * called from release_sock() to perform protocol dependent
798 * actions before socket release.
800 void tcp_release_cb(struct sock *sk)
802 unsigned long flags, nflags;
804 /* perform an atomic operation only if at least one flag is set */
805 do {
806 flags = sk->sk_tsq_flags;
807 if (!(flags & TCP_DEFERRED_ALL))
808 return;
809 nflags = flags & ~TCP_DEFERRED_ALL;
810 } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);
812 if (flags & TCPF_TSQ_DEFERRED)
813 tcp_tsq_handler(sk);
815 /* Here begins the tricky part :
816 * We are called from release_sock() with :
817 * 1) BH disabled
818 * 2) sk_lock.slock spinlock held
819 * 3) socket owned by us (sk->sk_lock.owned == 1)
821 * But following code is meant to be called from BH handlers,
822 * so we should keep BH disabled, but early release socket ownership
824 sock_release_ownership(sk);
826 if (flags & TCPF_WRITE_TIMER_DEFERRED) {
827 tcp_write_timer_handler(sk);
828 __sock_put(sk);
830 if (flags & TCPF_DELACK_TIMER_DEFERRED) {
831 tcp_delack_timer_handler(sk);
832 __sock_put(sk);
834 if (flags & TCPF_MTU_REDUCED_DEFERRED) {
835 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
836 __sock_put(sk);
839 EXPORT_SYMBOL(tcp_release_cb);
841 void __init tcp_tasklet_init(void)
843 int i;
845 for_each_possible_cpu(i) {
846 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
848 INIT_LIST_HEAD(&tsq->head);
849 tasklet_init(&tsq->tasklet,
850 tcp_tasklet_func,
851 (unsigned long)tsq);
856 * Write buffer destructor automatically called from kfree_skb.
857 * We can't xmit new skbs from this context, as we might already
858 * hold qdisc lock.
860 void tcp_wfree(struct sk_buff *skb)
862 struct sock *sk = skb->sk;
863 struct tcp_sock *tp = tcp_sk(sk);
864 unsigned long flags, nval, oval;
865 int wmem;
867 /* Keep one reference on sk_wmem_alloc.
868 * Will be released by sk_free() from here or tcp_tasklet_func()
870 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
872 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
873 * Wait until our queues (qdisc + devices) are drained.
874 * This gives :
875 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
876 * - chance for incoming ACK (processed by another cpu maybe)
877 * to migrate this flow (skb->ooo_okay will be eventually set)
879 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
880 goto out;
882 for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
883 struct tsq_tasklet *tsq;
884 bool empty;
886 if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
887 goto out;
889 nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
890 nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
891 if (nval != oval)
892 continue;
894 /* queue this socket to tasklet queue */
895 local_irq_save(flags);
896 tsq = this_cpu_ptr(&tsq_tasklet);
897 empty = list_empty(&tsq->head);
898 list_add(&tp->tsq_node, &tsq->head);
899 if (empty)
900 tasklet_schedule(&tsq->tasklet);
901 local_irq_restore(flags);
902 return;
904 out:
905 sk_free(sk);
908 /* This routine actually transmits TCP packets queued in by
909 * tcp_do_sendmsg(). This is used by both the initial
910 * transmission and possible later retransmissions.
911 * All SKB's seen here are completely headerless. It is our
912 * job to build the TCP header, and pass the packet down to
913 * IP so it can do the same plus pass the packet off to the
914 * device.
916 * We are working here with either a clone of the original
917 * SKB, or a fresh unique copy made by the retransmit engine.
919 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
920 gfp_t gfp_mask)
922 const struct inet_connection_sock *icsk = inet_csk(sk);
923 struct inet_sock *inet;
924 struct tcp_sock *tp;
925 struct tcp_skb_cb *tcb;
926 struct tcp_out_options opts;
927 unsigned int tcp_options_size, tcp_header_size;
928 struct tcp_md5sig_key *md5;
929 struct tcphdr *th;
930 int err;
932 BUG_ON(!skb || !tcp_skb_pcount(skb));
933 tp = tcp_sk(sk);
935 if (clone_it) {
936 skb_mstamp_get(&skb->skb_mstamp);
937 TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
938 - tp->snd_una;
939 tcp_rate_skb_sent(sk, skb);
941 if (unlikely(skb_cloned(skb)))
942 skb = pskb_copy(skb, gfp_mask);
943 else
944 skb = skb_clone(skb, gfp_mask);
945 if (unlikely(!skb))
946 return -ENOBUFS;
949 inet = inet_sk(sk);
950 tcb = TCP_SKB_CB(skb);
951 memset(&opts, 0, sizeof(opts));
953 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
954 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
955 else
956 tcp_options_size = tcp_established_options(sk, skb, &opts,
957 &md5);
958 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
960 /* if no packet is in qdisc/device queue, then allow XPS to select
961 * another queue. We can be called from tcp_tsq_handler()
962 * which holds one reference to sk_wmem_alloc.
964 * TODO: Ideally, in-flight pure ACK packets should not matter here.
965 * One way to get this would be to set skb->truesize = 2 on them.
967 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
969 skb_push(skb, tcp_header_size);
970 skb_reset_transport_header(skb);
972 skb_orphan(skb);
973 skb->sk = sk;
974 skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
975 skb_set_hash_from_sk(skb, sk);
976 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
978 /* Build TCP header and checksum it. */
979 th = (struct tcphdr *)skb->data;
980 th->source = inet->inet_sport;
981 th->dest = inet->inet_dport;
982 th->seq = htonl(tcb->seq);
983 th->ack_seq = htonl(tp->rcv_nxt);
984 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
985 tcb->tcp_flags);
987 th->check = 0;
988 th->urg_ptr = 0;
990 /* The urg_mode check is necessary during a below snd_una win probe */
991 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
992 if (before(tp->snd_up, tcb->seq + 0x10000)) {
993 th->urg_ptr = htons(tp->snd_up - tcb->seq);
994 th->urg = 1;
995 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
996 th->urg_ptr = htons(0xFFFF);
997 th->urg = 1;
1001 tcp_options_write((__be32 *)(th + 1), tp, &opts);
1002 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1003 if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
1004 th->window = htons(tcp_select_window(sk));
1005 tcp_ecn_send(sk, skb, th, tcp_header_size);
1006 } else {
1007 /* RFC1323: The window in SYN & SYN/ACK segments
1008 * is never scaled.
1010 th->window = htons(min(tp->rcv_wnd, 65535U));
1012 #ifdef CONFIG_TCP_MD5SIG
1013 /* Calculate the MD5 hash, as we have all we need now */
1014 if (md5) {
1015 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1016 tp->af_specific->calc_md5_hash(opts.hash_location,
1017 md5, sk, skb);
1019 #endif
1021 icsk->icsk_af_ops->send_check(sk, skb);
1023 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1024 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1026 if (skb->len != tcp_header_size) {
1027 tcp_event_data_sent(tp, sk);
1028 tp->data_segs_out += tcp_skb_pcount(skb);
1031 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1032 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1033 tcp_skb_pcount(skb));
1035 tp->segs_out += tcp_skb_pcount(skb);
1036 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1037 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1038 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1040 /* Our usage of tstamp should remain private */
1041 skb->tstamp = 0;
1043 /* Cleanup our debris for IP stacks */
1044 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1045 sizeof(struct inet6_skb_parm)));
1047 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1049 if (likely(err <= 0))
1050 return err;
1052 tcp_enter_cwr(sk);
1054 return net_xmit_eval(err);
1057 /* This routine just queues the buffer for sending.
1059 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1060 * otherwise socket can stall.
1062 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1064 struct tcp_sock *tp = tcp_sk(sk);
1066 /* Advance write_seq and place onto the write_queue. */
1067 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1068 __skb_header_release(skb);
1069 tcp_add_write_queue_tail(sk, skb);
1070 sk->sk_wmem_queued += skb->truesize;
1071 sk_mem_charge(sk, skb->truesize);
1074 /* Initialize TSO segments for a packet. */
1075 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1077 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1078 /* Avoid the costly divide in the normal
1079 * non-TSO case.
1081 tcp_skb_pcount_set(skb, 1);
1082 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1083 } else {
1084 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1085 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1089 /* When a modification to fackets out becomes necessary, we need to check
1090 * skb is counted to fackets_out or not.
1092 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1093 int decr)
1095 struct tcp_sock *tp = tcp_sk(sk);
1097 if (!tp->sacked_out || tcp_is_reno(tp))
1098 return;
1100 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1101 tp->fackets_out -= decr;
1104 /* Pcount in the middle of the write queue got changed, we need to do various
1105 * tweaks to fix counters
1107 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1109 struct tcp_sock *tp = tcp_sk(sk);
1111 tp->packets_out -= decr;
1113 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1114 tp->sacked_out -= decr;
1115 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1116 tp->retrans_out -= decr;
1117 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1118 tp->lost_out -= decr;
1120 /* Reno case is special. Sigh... */
1121 if (tcp_is_reno(tp) && decr > 0)
1122 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1124 tcp_adjust_fackets_out(sk, skb, decr);
1126 if (tp->lost_skb_hint &&
1127 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1128 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1129 tp->lost_cnt_hint -= decr;
1131 tcp_verify_left_out(tp);
1134 static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
1136 return TCP_SKB_CB(skb)->txstamp_ack ||
1137 (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
1140 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1142 struct skb_shared_info *shinfo = skb_shinfo(skb);
1144 if (unlikely(tcp_has_tx_tstamp(skb)) &&
1145 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1146 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1147 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1149 shinfo->tx_flags &= ~tsflags;
1150 shinfo2->tx_flags |= tsflags;
1151 swap(shinfo->tskey, shinfo2->tskey);
1152 TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
1153 TCP_SKB_CB(skb)->txstamp_ack = 0;
1157 static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
1159 TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
1160 TCP_SKB_CB(skb)->eor = 0;
1163 /* Function to create two new TCP segments. Shrinks the given segment
1164 * to the specified size and appends a new segment with the rest of the
1165 * packet to the list. This won't be called frequently, I hope.
1166 * Remember, these are still headerless SKBs at this point.
1168 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1169 unsigned int mss_now, gfp_t gfp)
1171 struct tcp_sock *tp = tcp_sk(sk);
1172 struct sk_buff *buff;
1173 int nsize, old_factor;
1174 int nlen;
1175 u8 flags;
1177 if (WARN_ON(len > skb->len))
1178 return -EINVAL;
1180 nsize = skb_headlen(skb) - len;
1181 if (nsize < 0)
1182 nsize = 0;
1184 if (skb_unclone(skb, gfp))
1185 return -ENOMEM;
1187 /* Get a new skb... force flag on. */
1188 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1189 if (!buff)
1190 return -ENOMEM; /* We'll just try again later. */
1192 sk->sk_wmem_queued += buff->truesize;
1193 sk_mem_charge(sk, buff->truesize);
1194 nlen = skb->len - len - nsize;
1195 buff->truesize += nlen;
1196 skb->truesize -= nlen;
1198 /* Correct the sequence numbers. */
1199 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1200 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1201 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1203 /* PSH and FIN should only be set in the second packet. */
1204 flags = TCP_SKB_CB(skb)->tcp_flags;
1205 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1206 TCP_SKB_CB(buff)->tcp_flags = flags;
1207 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1208 tcp_skb_fragment_eor(skb, buff);
1210 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1211 /* Copy and checksum data tail into the new buffer. */
1212 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1213 skb_put(buff, nsize),
1214 nsize, 0);
1216 skb_trim(skb, len);
1218 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1219 } else {
1220 skb->ip_summed = CHECKSUM_PARTIAL;
1221 skb_split(skb, buff, len);
1224 buff->ip_summed = skb->ip_summed;
1226 buff->tstamp = skb->tstamp;
1227 tcp_fragment_tstamp(skb, buff);
1229 old_factor = tcp_skb_pcount(skb);
1231 /* Fix up tso_factor for both original and new SKB. */
1232 tcp_set_skb_tso_segs(skb, mss_now);
1233 tcp_set_skb_tso_segs(buff, mss_now);
1235 /* Update delivered info for the new segment */
1236 TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;
1238 /* If this packet has been sent out already, we must
1239 * adjust the various packet counters.
1241 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1242 int diff = old_factor - tcp_skb_pcount(skb) -
1243 tcp_skb_pcount(buff);
1245 if (diff)
1246 tcp_adjust_pcount(sk, skb, diff);
1249 /* Link BUFF into the send queue. */
1250 __skb_header_release(buff);
1251 tcp_insert_write_queue_after(skb, buff, sk);
1253 return 0;
1256 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1257 * eventually). The difference is that pulled data not copied, but
1258 * immediately discarded.
1260 static void __pskb_trim_head(struct sk_buff *skb, int len)
1262 struct skb_shared_info *shinfo;
1263 int i, k, eat;
1265 eat = min_t(int, len, skb_headlen(skb));
1266 if (eat) {
1267 __skb_pull(skb, eat);
1268 len -= eat;
1269 if (!len)
1270 return;
1272 eat = len;
1273 k = 0;
1274 shinfo = skb_shinfo(skb);
1275 for (i = 0; i < shinfo->nr_frags; i++) {
1276 int size = skb_frag_size(&shinfo->frags[i]);
1278 if (size <= eat) {
1279 skb_frag_unref(skb, i);
1280 eat -= size;
1281 } else {
1282 shinfo->frags[k] = shinfo->frags[i];
1283 if (eat) {
1284 shinfo->frags[k].page_offset += eat;
1285 skb_frag_size_sub(&shinfo->frags[k], eat);
1286 eat = 0;
1288 k++;
1291 shinfo->nr_frags = k;
1293 skb_reset_tail_pointer(skb);
1294 skb->data_len -= len;
1295 skb->len = skb->data_len;
1298 /* Remove acked data from a packet in the transmit queue. */
1299 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1301 if (skb_unclone(skb, GFP_ATOMIC))
1302 return -ENOMEM;
1304 __pskb_trim_head(skb, len);
1306 TCP_SKB_CB(skb)->seq += len;
1307 skb->ip_summed = CHECKSUM_PARTIAL;
1309 skb->truesize -= len;
1310 sk->sk_wmem_queued -= len;
1311 sk_mem_uncharge(sk, len);
1312 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1314 /* Any change of skb->len requires recalculation of tso factor. */
1315 if (tcp_skb_pcount(skb) > 1)
1316 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1318 return 0;
1321 /* Calculate MSS not accounting any TCP options. */
1322 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1324 const struct tcp_sock *tp = tcp_sk(sk);
1325 const struct inet_connection_sock *icsk = inet_csk(sk);
1326 int mss_now;
1328 /* Calculate base mss without TCP options:
1329 It is MMS_S - sizeof(tcphdr) of rfc1122
1331 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1333 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1334 if (icsk->icsk_af_ops->net_frag_header_len) {
1335 const struct dst_entry *dst = __sk_dst_get(sk);
1337 if (dst && dst_allfrag(dst))
1338 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1341 /* Clamp it (mss_clamp does not include tcp options) */
1342 if (mss_now > tp->rx_opt.mss_clamp)
1343 mss_now = tp->rx_opt.mss_clamp;
1345 /* Now subtract optional transport overhead */
1346 mss_now -= icsk->icsk_ext_hdr_len;
1348 /* Then reserve room for full set of TCP options and 8 bytes of data */
1349 if (mss_now < 48)
1350 mss_now = 48;
1351 return mss_now;
1354 /* Calculate MSS. Not accounting for SACKs here. */
1355 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1357 /* Subtract TCP options size, not including SACKs */
1358 return __tcp_mtu_to_mss(sk, pmtu) -
1359 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1362 /* Inverse of above */
1363 int tcp_mss_to_mtu(struct sock *sk, int mss)
1365 const struct tcp_sock *tp = tcp_sk(sk);
1366 const struct inet_connection_sock *icsk = inet_csk(sk);
1367 int mtu;
1369 mtu = mss +
1370 tp->tcp_header_len +
1371 icsk->icsk_ext_hdr_len +
1372 icsk->icsk_af_ops->net_header_len;
1374 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1375 if (icsk->icsk_af_ops->net_frag_header_len) {
1376 const struct dst_entry *dst = __sk_dst_get(sk);
1378 if (dst && dst_allfrag(dst))
1379 mtu += icsk->icsk_af_ops->net_frag_header_len;
1381 return mtu;
1383 EXPORT_SYMBOL(tcp_mss_to_mtu);
1385 /* MTU probing init per socket */
1386 void tcp_mtup_init(struct sock *sk)
1388 struct tcp_sock *tp = tcp_sk(sk);
1389 struct inet_connection_sock *icsk = inet_csk(sk);
1390 struct net *net = sock_net(sk);
1392 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1393 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1394 icsk->icsk_af_ops->net_header_len;
1395 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1396 icsk->icsk_mtup.probe_size = 0;
1397 if (icsk->icsk_mtup.enabled)
1398 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1400 EXPORT_SYMBOL(tcp_mtup_init);
1402 /* This function synchronize snd mss to current pmtu/exthdr set.
1404 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1405 for TCP options, but includes only bare TCP header.
1407 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1408 It is minimum of user_mss and mss received with SYN.
1409 It also does not include TCP options.
1411 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1413 tp->mss_cache is current effective sending mss, including
1414 all tcp options except for SACKs. It is evaluated,
1415 taking into account current pmtu, but never exceeds
1416 tp->rx_opt.mss_clamp.
1418 NOTE1. rfc1122 clearly states that advertised MSS
1419 DOES NOT include either tcp or ip options.
1421 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1422 are READ ONLY outside this function. --ANK (980731)
1424 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1426 struct tcp_sock *tp = tcp_sk(sk);
1427 struct inet_connection_sock *icsk = inet_csk(sk);
1428 int mss_now;
1430 if (icsk->icsk_mtup.search_high > pmtu)
1431 icsk->icsk_mtup.search_high = pmtu;
1433 mss_now = tcp_mtu_to_mss(sk, pmtu);
1434 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1436 /* And store cached results */
1437 icsk->icsk_pmtu_cookie = pmtu;
1438 if (icsk->icsk_mtup.enabled)
1439 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1440 tp->mss_cache = mss_now;
1442 return mss_now;
1444 EXPORT_SYMBOL(tcp_sync_mss);
1446 /* Compute the current effective MSS, taking SACKs and IP options,
1447 * and even PMTU discovery events into account.
1449 unsigned int tcp_current_mss(struct sock *sk)
1451 const struct tcp_sock *tp = tcp_sk(sk);
1452 const struct dst_entry *dst = __sk_dst_get(sk);
1453 u32 mss_now;
1454 unsigned int header_len;
1455 struct tcp_out_options opts;
1456 struct tcp_md5sig_key *md5;
1458 mss_now = tp->mss_cache;
1460 if (dst) {
1461 u32 mtu = dst_mtu(dst);
1462 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1463 mss_now = tcp_sync_mss(sk, mtu);
1466 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1467 sizeof(struct tcphdr);
1468 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1469 * some common options. If this is an odd packet (because we have SACK
1470 * blocks etc) then our calculated header_len will be different, and
1471 * we have to adjust mss_now correspondingly */
1472 if (header_len != tp->tcp_header_len) {
1473 int delta = (int) header_len - tp->tcp_header_len;
1474 mss_now -= delta;
1477 return mss_now;
1480 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1481 * As additional protections, we do not touch cwnd in retransmission phases,
1482 * and if application hit its sndbuf limit recently.
1484 static void tcp_cwnd_application_limited(struct sock *sk)
1486 struct tcp_sock *tp = tcp_sk(sk);
1488 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1489 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1490 /* Limited by application or receiver window. */
1491 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1492 u32 win_used = max(tp->snd_cwnd_used, init_win);
1493 if (win_used < tp->snd_cwnd) {
1494 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1495 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1497 tp->snd_cwnd_used = 0;
1499 tp->snd_cwnd_stamp = tcp_time_stamp;
1502 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1504 struct tcp_sock *tp = tcp_sk(sk);
1506 /* Track the maximum number of outstanding packets in each
1507 * window, and remember whether we were cwnd-limited then.
1509 if (!before(tp->snd_una, tp->max_packets_seq) ||
1510 tp->packets_out > tp->max_packets_out) {
1511 tp->max_packets_out = tp->packets_out;
1512 tp->max_packets_seq = tp->snd_nxt;
1513 tp->is_cwnd_limited = is_cwnd_limited;
1516 if (tcp_is_cwnd_limited(sk)) {
1517 /* Network is feed fully. */
1518 tp->snd_cwnd_used = 0;
1519 tp->snd_cwnd_stamp = tcp_time_stamp;
1520 } else {
1521 /* Network starves. */
1522 if (tp->packets_out > tp->snd_cwnd_used)
1523 tp->snd_cwnd_used = tp->packets_out;
1525 if (sysctl_tcp_slow_start_after_idle &&
1526 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1527 tcp_cwnd_application_limited(sk);
1529 /* The following conditions together indicate the starvation
1530 * is caused by insufficient sender buffer:
1531 * 1) just sent some data (see tcp_write_xmit)
1532 * 2) not cwnd limited (this else condition)
1533 * 3) no more data to send (null tcp_send_head )
1534 * 4) application is hitting buffer limit (SOCK_NOSPACE)
1536 if (!tcp_send_head(sk) && sk->sk_socket &&
1537 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
1538 (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
1539 tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
1543 /* Minshall's variant of the Nagle send check. */
1544 static bool tcp_minshall_check(const struct tcp_sock *tp)
1546 return after(tp->snd_sml, tp->snd_una) &&
1547 !after(tp->snd_sml, tp->snd_nxt);
1550 /* Update snd_sml if this skb is under mss
1551 * Note that a TSO packet might end with a sub-mss segment
1552 * The test is really :
1553 * if ((skb->len % mss) != 0)
1554 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1555 * But we can avoid doing the divide again given we already have
1556 * skb_pcount = skb->len / mss_now
1558 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1559 const struct sk_buff *skb)
1561 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1562 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1565 /* Return false, if packet can be sent now without violation Nagle's rules:
1566 * 1. It is full sized. (provided by caller in %partial bool)
1567 * 2. Or it contains FIN. (already checked by caller)
1568 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1569 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1570 * With Minshall's modification: all sent small packets are ACKed.
1572 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1573 int nonagle)
1575 return partial &&
1576 ((nonagle & TCP_NAGLE_CORK) ||
1577 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1580 /* Return how many segs we'd like on a TSO packet,
1581 * to send one TSO packet per ms
1583 u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
1584 int min_tso_segs)
1586 u32 bytes, segs;
1588 bytes = min(sk->sk_pacing_rate >> 10,
1589 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1591 /* Goal is to send at least one packet per ms,
1592 * not one big TSO packet every 100 ms.
1593 * This preserves ACK clocking and is consistent
1594 * with tcp_tso_should_defer() heuristic.
1596 segs = max_t(u32, bytes / mss_now, min_tso_segs);
1598 return min_t(u32, segs, sk->sk_gso_max_segs);
1600 EXPORT_SYMBOL(tcp_tso_autosize);
1602 /* Return the number of segments we want in the skb we are transmitting.
1603 * See if congestion control module wants to decide; otherwise, autosize.
1605 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
1607 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1608 u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;
1610 return tso_segs ? :
1611 tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs);
1614 /* Returns the portion of skb which can be sent right away */
1615 static unsigned int tcp_mss_split_point(const struct sock *sk,
1616 const struct sk_buff *skb,
1617 unsigned int mss_now,
1618 unsigned int max_segs,
1619 int nonagle)
1621 const struct tcp_sock *tp = tcp_sk(sk);
1622 u32 partial, needed, window, max_len;
1624 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1625 max_len = mss_now * max_segs;
1627 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1628 return max_len;
1630 needed = min(skb->len, window);
1632 if (max_len <= needed)
1633 return max_len;
1635 partial = needed % mss_now;
1636 /* If last segment is not a full MSS, check if Nagle rules allow us
1637 * to include this last segment in this skb.
1638 * Otherwise, we'll split the skb at last MSS boundary
1640 if (tcp_nagle_check(partial != 0, tp, nonagle))
1641 return needed - partial;
1643 return needed;
1646 /* Can at least one segment of SKB be sent right now, according to the
1647 * congestion window rules? If so, return how many segments are allowed.
1649 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1650 const struct sk_buff *skb)
1652 u32 in_flight, cwnd, halfcwnd;
1654 /* Don't be strict about the congestion window for the final FIN. */
1655 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1656 tcp_skb_pcount(skb) == 1)
1657 return 1;
1659 in_flight = tcp_packets_in_flight(tp);
1660 cwnd = tp->snd_cwnd;
1661 if (in_flight >= cwnd)
1662 return 0;
1664 /* For better scheduling, ensure we have at least
1665 * 2 GSO packets in flight.
1667 halfcwnd = max(cwnd >> 1, 1U);
1668 return min(halfcwnd, cwnd - in_flight);
1671 /* Initialize TSO state of a skb.
1672 * This must be invoked the first time we consider transmitting
1673 * SKB onto the wire.
1675 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1677 int tso_segs = tcp_skb_pcount(skb);
1679 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1680 tcp_set_skb_tso_segs(skb, mss_now);
1681 tso_segs = tcp_skb_pcount(skb);
1683 return tso_segs;
1687 /* Return true if the Nagle test allows this packet to be
1688 * sent now.
1690 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1691 unsigned int cur_mss, int nonagle)
1693 /* Nagle rule does not apply to frames, which sit in the middle of the
1694 * write_queue (they have no chances to get new data).
1696 * This is implemented in the callers, where they modify the 'nonagle'
1697 * argument based upon the location of SKB in the send queue.
1699 if (nonagle & TCP_NAGLE_PUSH)
1700 return true;
1702 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1703 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1704 return true;
1706 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1707 return true;
1709 return false;
1712 /* Does at least the first segment of SKB fit into the send window? */
1713 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1714 const struct sk_buff *skb,
1715 unsigned int cur_mss)
1717 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1719 if (skb->len > cur_mss)
1720 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1722 return !after(end_seq, tcp_wnd_end(tp));
1725 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1726 * should be put on the wire right now. If so, it returns the number of
1727 * packets allowed by the congestion window.
1729 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1730 unsigned int cur_mss, int nonagle)
1732 const struct tcp_sock *tp = tcp_sk(sk);
1733 unsigned int cwnd_quota;
1735 tcp_init_tso_segs(skb, cur_mss);
1737 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1738 return 0;
1740 cwnd_quota = tcp_cwnd_test(tp, skb);
1741 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1742 cwnd_quota = 0;
1744 return cwnd_quota;
1747 /* Test if sending is allowed right now. */
1748 bool tcp_may_send_now(struct sock *sk)
1750 const struct tcp_sock *tp = tcp_sk(sk);
1751 struct sk_buff *skb = tcp_send_head(sk);
1753 return skb &&
1754 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1755 (tcp_skb_is_last(sk, skb) ?
1756 tp->nonagle : TCP_NAGLE_PUSH));
1759 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1760 * which is put after SKB on the list. It is very much like
1761 * tcp_fragment() except that it may make several kinds of assumptions
1762 * in order to speed up the splitting operation. In particular, we
1763 * know that all the data is in scatter-gather pages, and that the
1764 * packet has never been sent out before (and thus is not cloned).
1766 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1767 unsigned int mss_now, gfp_t gfp)
1769 struct sk_buff *buff;
1770 int nlen = skb->len - len;
1771 u8 flags;
1773 /* All of a TSO frame must be composed of paged data. */
1774 if (skb->len != skb->data_len)
1775 return tcp_fragment(sk, skb, len, mss_now, gfp);
1777 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1778 if (unlikely(!buff))
1779 return -ENOMEM;
1781 sk->sk_wmem_queued += buff->truesize;
1782 sk_mem_charge(sk, buff->truesize);
1783 buff->truesize += nlen;
1784 skb->truesize -= nlen;
1786 /* Correct the sequence numbers. */
1787 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1788 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1789 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1791 /* PSH and FIN should only be set in the second packet. */
1792 flags = TCP_SKB_CB(skb)->tcp_flags;
1793 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1794 TCP_SKB_CB(buff)->tcp_flags = flags;
1796 /* This packet was never sent out yet, so no SACK bits. */
1797 TCP_SKB_CB(buff)->sacked = 0;
1799 tcp_skb_fragment_eor(skb, buff);
1801 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1802 skb_split(skb, buff, len);
1803 tcp_fragment_tstamp(skb, buff);
1805 /* Fix up tso_factor for both original and new SKB. */
1806 tcp_set_skb_tso_segs(skb, mss_now);
1807 tcp_set_skb_tso_segs(buff, mss_now);
1809 /* Link BUFF into the send queue. */
1810 __skb_header_release(buff);
1811 tcp_insert_write_queue_after(skb, buff, sk);
1813 return 0;
1816 /* Try to defer sending, if possible, in order to minimize the amount
1817 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1819 * This algorithm is from John Heffner.
1821 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1822 bool *is_cwnd_limited, u32 max_segs)
1824 const struct inet_connection_sock *icsk = inet_csk(sk);
1825 u32 age, send_win, cong_win, limit, in_flight;
1826 struct tcp_sock *tp = tcp_sk(sk);
1827 struct skb_mstamp now;
1828 struct sk_buff *head;
1829 int win_divisor;
1831 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1832 goto send_now;
1834 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1835 goto send_now;
1837 /* Avoid bursty behavior by allowing defer
1838 * only if the last write was recent.
1840 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1841 goto send_now;
1843 in_flight = tcp_packets_in_flight(tp);
1845 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1847 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1849 /* From in_flight test above, we know that cwnd > in_flight. */
1850 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1852 limit = min(send_win, cong_win);
1854 /* If a full-sized TSO skb can be sent, do it. */
1855 if (limit >= max_segs * tp->mss_cache)
1856 goto send_now;
1858 /* Middle in queue won't get any more data, full sendable already? */
1859 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1860 goto send_now;
1862 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1863 if (win_divisor) {
1864 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1866 /* If at least some fraction of a window is available,
1867 * just use it.
1869 chunk /= win_divisor;
1870 if (limit >= chunk)
1871 goto send_now;
1872 } else {
1873 /* Different approach, try not to defer past a single
1874 * ACK. Receiver should ACK every other full sized
1875 * frame, so if we have space for more than 3 frames
1876 * then send now.
1878 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1879 goto send_now;
1882 head = tcp_write_queue_head(sk);
1883 skb_mstamp_get(&now);
1884 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1885 /* If next ACK is likely to come too late (half srtt), do not defer */
1886 if (age < (tp->srtt_us >> 4))
1887 goto send_now;
1889 /* Ok, it looks like it is advisable to defer. */
1891 if (cong_win < send_win && cong_win <= skb->len)
1892 *is_cwnd_limited = true;
1894 return true;
1896 send_now:
1897 return false;
1900 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1902 struct inet_connection_sock *icsk = inet_csk(sk);
1903 struct tcp_sock *tp = tcp_sk(sk);
1904 struct net *net = sock_net(sk);
1905 u32 interval;
1906 s32 delta;
1908 interval = net->ipv4.sysctl_tcp_probe_interval;
1909 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1910 if (unlikely(delta >= interval * HZ)) {
1911 int mss = tcp_current_mss(sk);
1913 /* Update current search range */
1914 icsk->icsk_mtup.probe_size = 0;
1915 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1916 sizeof(struct tcphdr) +
1917 icsk->icsk_af_ops->net_header_len;
1918 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1920 /* Update probe time stamp */
1921 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1925 /* Create a new MTU probe if we are ready.
1926 * MTU probe is regularly attempting to increase the path MTU by
1927 * deliberately sending larger packets. This discovers routing
1928 * changes resulting in larger path MTUs.
1930 * Returns 0 if we should wait to probe (no cwnd available),
1931 * 1 if a probe was sent,
1932 * -1 otherwise
1934 static int tcp_mtu_probe(struct sock *sk)
1936 struct inet_connection_sock *icsk = inet_csk(sk);
1937 struct tcp_sock *tp = tcp_sk(sk);
1938 struct sk_buff *skb, *nskb, *next;
1939 struct net *net = sock_net(sk);
1940 int probe_size;
1941 int size_needed;
1942 int copy, len;
1943 int mss_now;
1944 int interval;
1946 /* Not currently probing/verifying,
1947 * not in recovery,
1948 * have enough cwnd, and
1949 * not SACKing (the variable headers throw things off)
1951 if (likely(!icsk->icsk_mtup.enabled ||
1952 icsk->icsk_mtup.probe_size ||
1953 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1954 tp->snd_cwnd < 11 ||
1955 tp->rx_opt.num_sacks || tp->rx_opt.dsack))
1956 return -1;
1958 /* Use binary search for probe_size between tcp_mss_base,
1959 * and current mss_clamp. if (search_high - search_low)
1960 * smaller than a threshold, backoff from probing.
1962 mss_now = tcp_current_mss(sk);
1963 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1964 icsk->icsk_mtup.search_low) >> 1);
1965 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1966 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1967 /* When misfortune happens, we are reprobing actively,
1968 * and then reprobe timer has expired. We stick with current
1969 * probing process by not resetting search range to its orignal.
1971 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1972 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1973 /* Check whether enough time has elaplased for
1974 * another round of probing.
1976 tcp_mtu_check_reprobe(sk);
1977 return -1;
1980 /* Have enough data in the send queue to probe? */
1981 if (tp->write_seq - tp->snd_nxt < size_needed)
1982 return -1;
1984 if (tp->snd_wnd < size_needed)
1985 return -1;
1986 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1987 return 0;
1989 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1990 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1991 if (!tcp_packets_in_flight(tp))
1992 return -1;
1993 else
1994 return 0;
1997 /* We're allowed to probe. Build it now. */
1998 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1999 if (!nskb)
2000 return -1;
2001 sk->sk_wmem_queued += nskb->truesize;
2002 sk_mem_charge(sk, nskb->truesize);
2004 skb = tcp_send_head(sk);
2006 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
2007 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
2008 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
2009 TCP_SKB_CB(nskb)->sacked = 0;
2010 nskb->csum = 0;
2011 nskb->ip_summed = skb->ip_summed;
2013 tcp_insert_write_queue_before(nskb, skb, sk);
2015 len = 0;
2016 tcp_for_write_queue_from_safe(skb, next, sk) {
2017 copy = min_t(int, skb->len, probe_size - len);
2018 if (nskb->ip_summed) {
2019 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
2020 } else {
2021 __wsum csum = skb_copy_and_csum_bits(skb, 0,
2022 skb_put(nskb, copy),
2023 copy, 0);
2024 nskb->csum = csum_block_add(nskb->csum, csum, len);
2027 if (skb->len <= copy) {
2028 /* We've eaten all the data from this skb.
2029 * Throw it away. */
2030 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2031 tcp_unlink_write_queue(skb, sk);
2032 sk_wmem_free_skb(sk, skb);
2033 } else {
2034 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
2035 ~(TCPHDR_FIN|TCPHDR_PSH);
2036 if (!skb_shinfo(skb)->nr_frags) {
2037 skb_pull(skb, copy);
2038 if (skb->ip_summed != CHECKSUM_PARTIAL)
2039 skb->csum = csum_partial(skb->data,
2040 skb->len, 0);
2041 } else {
2042 __pskb_trim_head(skb, copy);
2043 tcp_set_skb_tso_segs(skb, mss_now);
2045 TCP_SKB_CB(skb)->seq += copy;
2048 len += copy;
2050 if (len >= probe_size)
2051 break;
2053 tcp_init_tso_segs(nskb, nskb->len);
2055 /* We're ready to send. If this fails, the probe will
2056 * be resegmented into mss-sized pieces by tcp_write_xmit().
2058 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2059 /* Decrement cwnd here because we are sending
2060 * effectively two packets. */
2061 tp->snd_cwnd--;
2062 tcp_event_new_data_sent(sk, nskb);
2064 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2065 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2066 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2068 return 1;
2071 return -1;
2074 /* TCP Small Queues :
2075 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2076 * (These limits are doubled for retransmits)
2077 * This allows for :
2078 * - better RTT estimation and ACK scheduling
2079 * - faster recovery
2080 * - high rates
2081 * Alas, some drivers / subsystems require a fair amount
2082 * of queued bytes to ensure line rate.
2083 * One example is wifi aggregation (802.11 AMPDU)
2085 static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
2086 unsigned int factor)
2088 unsigned int limit;
2090 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2091 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2092 limit <<= factor;
2094 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2095 /* Always send the 1st or 2nd skb in write queue.
2096 * No need to wait for TX completion to call us back,
2097 * after softirq/tasklet schedule.
2098 * This helps when TX completions are delayed too much.
2100 if (skb == sk->sk_write_queue.next ||
2101 skb->prev == sk->sk_write_queue.next)
2102 return false;
2104 set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
2105 /* It is possible TX completion already happened
2106 * before we set TSQ_THROTTLED, so we must
2107 * test again the condition.
2109 smp_mb__after_atomic();
2110 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2111 return true;
2113 return false;
2116 static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
2118 const u32 now = tcp_time_stamp;
2120 if (tp->chrono_type > TCP_CHRONO_UNSPEC)
2121 tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;
2122 tp->chrono_start = now;
2123 tp->chrono_type = new;
2126 void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
2128 struct tcp_sock *tp = tcp_sk(sk);
2130 /* If there are multiple conditions worthy of tracking in a
2131 * chronograph then the highest priority enum takes precedence
2132 * over the other conditions. So that if something "more interesting"
2133 * starts happening, stop the previous chrono and start a new one.
2135 if (type > tp->chrono_type)
2136 tcp_chrono_set(tp, type);
2139 void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
2141 struct tcp_sock *tp = tcp_sk(sk);
2144 /* There are multiple conditions worthy of tracking in a
2145 * chronograph, so that the highest priority enum takes
2146 * precedence over the other conditions (see tcp_chrono_start).
2147 * If a condition stops, we only stop chrono tracking if
2148 * it's the "most interesting" or current chrono we are
2149 * tracking and starts busy chrono if we have pending data.
2151 if (tcp_write_queue_empty(sk))
2152 tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
2153 else if (type == tp->chrono_type)
2154 tcp_chrono_set(tp, TCP_CHRONO_BUSY);
2157 /* This routine writes packets to the network. It advances the
2158 * send_head. This happens as incoming acks open up the remote
2159 * window for us.
2161 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2162 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2163 * account rare use of URG, this is not a big flaw.
2165 * Send at most one packet when push_one > 0. Temporarily ignore
2166 * cwnd limit to force at most one packet out when push_one == 2.
2168 * Returns true, if no segments are in flight and we have queued segments,
2169 * but cannot send anything now because of SWS or another problem.
2171 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2172 int push_one, gfp_t gfp)
2174 struct tcp_sock *tp = tcp_sk(sk);
2175 struct sk_buff *skb;
2176 unsigned int tso_segs, sent_pkts;
2177 int cwnd_quota;
2178 int result;
2179 bool is_cwnd_limited = false, is_rwnd_limited = false;
2180 u32 max_segs;
2182 sent_pkts = 0;
2184 if (!push_one) {
2185 /* Do MTU probing. */
2186 result = tcp_mtu_probe(sk);
2187 if (!result) {
2188 return false;
2189 } else if (result > 0) {
2190 sent_pkts = 1;
2194 max_segs = tcp_tso_segs(sk, mss_now);
2195 while ((skb = tcp_send_head(sk))) {
2196 unsigned int limit;
2198 tso_segs = tcp_init_tso_segs(skb, mss_now);
2199 BUG_ON(!tso_segs);
2201 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2202 /* "skb_mstamp" is used as a start point for the retransmit timer */
2203 skb_mstamp_get(&skb->skb_mstamp);
2204 goto repair; /* Skip network transmission */
2207 cwnd_quota = tcp_cwnd_test(tp, skb);
2208 if (!cwnd_quota) {
2209 if (push_one == 2)
2210 /* Force out a loss probe pkt. */
2211 cwnd_quota = 1;
2212 else
2213 break;
2216 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
2217 is_rwnd_limited = true;
2218 break;
2221 if (tso_segs == 1) {
2222 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2223 (tcp_skb_is_last(sk, skb) ?
2224 nonagle : TCP_NAGLE_PUSH))))
2225 break;
2226 } else {
2227 if (!push_one &&
2228 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2229 max_segs))
2230 break;
2233 limit = mss_now;
2234 if (tso_segs > 1 && !tcp_urg_mode(tp))
2235 limit = tcp_mss_split_point(sk, skb, mss_now,
2236 min_t(unsigned int,
2237 cwnd_quota,
2238 max_segs),
2239 nonagle);
2241 if (skb->len > limit &&
2242 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2243 break;
2245 if (test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags))
2246 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
2247 if (tcp_small_queue_check(sk, skb, 0))
2248 break;
2250 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2251 break;
2253 repair:
2254 /* Advance the send_head. This one is sent out.
2255 * This call will increment packets_out.
2257 tcp_event_new_data_sent(sk, skb);
2259 tcp_minshall_update(tp, mss_now, skb);
2260 sent_pkts += tcp_skb_pcount(skb);
2262 if (push_one)
2263 break;
2266 if (is_rwnd_limited)
2267 tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
2268 else
2269 tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
2271 if (likely(sent_pkts)) {
2272 if (tcp_in_cwnd_reduction(sk))
2273 tp->prr_out += sent_pkts;
2275 /* Send one loss probe per tail loss episode. */
2276 if (push_one != 2)
2277 tcp_schedule_loss_probe(sk);
2278 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2279 tcp_cwnd_validate(sk, is_cwnd_limited);
2280 return false;
2282 return !tp->packets_out && tcp_send_head(sk);
2285 bool tcp_schedule_loss_probe(struct sock *sk)
2287 struct inet_connection_sock *icsk = inet_csk(sk);
2288 struct tcp_sock *tp = tcp_sk(sk);
2289 u32 timeout, tlp_time_stamp, rto_time_stamp;
2290 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2292 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2293 return false;
2294 /* No consecutive loss probes. */
2295 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2296 tcp_rearm_rto(sk);
2297 return false;
2299 /* Don't do any loss probe on a Fast Open connection before 3WHS
2300 * finishes.
2302 if (tp->fastopen_rsk)
2303 return false;
2305 /* TLP is only scheduled when next timer event is RTO. */
2306 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2307 return false;
2309 /* Schedule a loss probe in 2*RTT for SACK capable connections
2310 * in Open state, that are either limited by cwnd or application.
2312 if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
2313 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2314 return false;
2316 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2317 tcp_send_head(sk))
2318 return false;
2320 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2321 * for delayed ack when there's one outstanding packet. If no RTT
2322 * sample is available then probe after TCP_TIMEOUT_INIT.
2324 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2325 if (tp->packets_out == 1)
2326 timeout = max_t(u32, timeout,
2327 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2328 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2330 /* If RTO is shorter, just schedule TLP in its place. */
2331 tlp_time_stamp = tcp_time_stamp + timeout;
2332 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2333 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2334 s32 delta = rto_time_stamp - tcp_time_stamp;
2335 if (delta > 0)
2336 timeout = delta;
2339 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2340 TCP_RTO_MAX);
2341 return true;
2344 /* Thanks to skb fast clones, we can detect if a prior transmit of
2345 * a packet is still in a qdisc or driver queue.
2346 * In this case, there is very little point doing a retransmit !
2348 static bool skb_still_in_host_queue(const struct sock *sk,
2349 const struct sk_buff *skb)
2351 if (unlikely(skb_fclone_busy(sk, skb))) {
2352 NET_INC_STATS(sock_net(sk),
2353 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2354 return true;
2356 return false;
2359 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2360 * retransmit the last segment.
2362 void tcp_send_loss_probe(struct sock *sk)
2364 struct tcp_sock *tp = tcp_sk(sk);
2365 struct sk_buff *skb;
2366 int pcount;
2367 int mss = tcp_current_mss(sk);
2369 skb = tcp_send_head(sk);
2370 if (skb) {
2371 if (tcp_snd_wnd_test(tp, skb, mss)) {
2372 pcount = tp->packets_out;
2373 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2374 if (tp->packets_out > pcount)
2375 goto probe_sent;
2376 goto rearm_timer;
2378 skb = tcp_write_queue_prev(sk, skb);
2379 } else {
2380 skb = tcp_write_queue_tail(sk);
2383 /* At most one outstanding TLP retransmission. */
2384 if (tp->tlp_high_seq)
2385 goto rearm_timer;
2387 /* Retransmit last segment. */
2388 if (WARN_ON(!skb))
2389 goto rearm_timer;
2391 if (skb_still_in_host_queue(sk, skb))
2392 goto rearm_timer;
2394 pcount = tcp_skb_pcount(skb);
2395 if (WARN_ON(!pcount))
2396 goto rearm_timer;
2398 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2399 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2400 GFP_ATOMIC)))
2401 goto rearm_timer;
2402 skb = tcp_write_queue_next(sk, skb);
2405 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2406 goto rearm_timer;
2408 if (__tcp_retransmit_skb(sk, skb, 1))
2409 goto rearm_timer;
2411 /* Record snd_nxt for loss detection. */
2412 tp->tlp_high_seq = tp->snd_nxt;
2414 probe_sent:
2415 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2416 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2417 inet_csk(sk)->icsk_pending = 0;
2418 rearm_timer:
2419 tcp_rearm_rto(sk);
2422 /* Push out any pending frames which were held back due to
2423 * TCP_CORK or attempt at coalescing tiny packets.
2424 * The socket must be locked by the caller.
2426 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2427 int nonagle)
2429 /* If we are closed, the bytes will have to remain here.
2430 * In time closedown will finish, we empty the write queue and
2431 * all will be happy.
2433 if (unlikely(sk->sk_state == TCP_CLOSE))
2434 return;
2436 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2437 sk_gfp_mask(sk, GFP_ATOMIC)))
2438 tcp_check_probe_timer(sk);
2441 /* Send _single_ skb sitting at the send head. This function requires
2442 * true push pending frames to setup probe timer etc.
2444 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2446 struct sk_buff *skb = tcp_send_head(sk);
2448 BUG_ON(!skb || skb->len < mss_now);
2450 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2453 /* This function returns the amount that we can raise the
2454 * usable window based on the following constraints
2456 * 1. The window can never be shrunk once it is offered (RFC 793)
2457 * 2. We limit memory per socket
2459 * RFC 1122:
2460 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2461 * RECV.NEXT + RCV.WIN fixed until:
2462 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2464 * i.e. don't raise the right edge of the window until you can raise
2465 * it at least MSS bytes.
2467 * Unfortunately, the recommended algorithm breaks header prediction,
2468 * since header prediction assumes th->window stays fixed.
2470 * Strictly speaking, keeping th->window fixed violates the receiver
2471 * side SWS prevention criteria. The problem is that under this rule
2472 * a stream of single byte packets will cause the right side of the
2473 * window to always advance by a single byte.
2475 * Of course, if the sender implements sender side SWS prevention
2476 * then this will not be a problem.
2478 * BSD seems to make the following compromise:
2480 * If the free space is less than the 1/4 of the maximum
2481 * space available and the free space is less than 1/2 mss,
2482 * then set the window to 0.
2483 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2484 * Otherwise, just prevent the window from shrinking
2485 * and from being larger than the largest representable value.
2487 * This prevents incremental opening of the window in the regime
2488 * where TCP is limited by the speed of the reader side taking
2489 * data out of the TCP receive queue. It does nothing about
2490 * those cases where the window is constrained on the sender side
2491 * because the pipeline is full.
2493 * BSD also seems to "accidentally" limit itself to windows that are a
2494 * multiple of MSS, at least until the free space gets quite small.
2495 * This would appear to be a side effect of the mbuf implementation.
2496 * Combining these two algorithms results in the observed behavior
2497 * of having a fixed window size at almost all times.
2499 * Below we obtain similar behavior by forcing the offered window to
2500 * a multiple of the mss when it is feasible to do so.
2502 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2503 * Regular options like TIMESTAMP are taken into account.
2505 u32 __tcp_select_window(struct sock *sk)
2507 struct inet_connection_sock *icsk = inet_csk(sk);
2508 struct tcp_sock *tp = tcp_sk(sk);
2509 /* MSS for the peer's data. Previous versions used mss_clamp
2510 * here. I don't know if the value based on our guesses
2511 * of peer's MSS is better for the performance. It's more correct
2512 * but may be worse for the performance because of rcv_mss
2513 * fluctuations. --SAW 1998/11/1
2515 int mss = icsk->icsk_ack.rcv_mss;
2516 int free_space = tcp_space(sk);
2517 int allowed_space = tcp_full_space(sk);
2518 int full_space = min_t(int, tp->window_clamp, allowed_space);
2519 int window;
2521 if (mss > full_space)
2522 mss = full_space;
2524 if (free_space < (full_space >> 1)) {
2525 icsk->icsk_ack.quick = 0;
2527 if (tcp_under_memory_pressure(sk))
2528 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2529 4U * tp->advmss);
2531 /* free_space might become our new window, make sure we don't
2532 * increase it due to wscale.
2534 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2536 /* if free space is less than mss estimate, or is below 1/16th
2537 * of the maximum allowed, try to move to zero-window, else
2538 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2539 * new incoming data is dropped due to memory limits.
2540 * With large window, mss test triggers way too late in order
2541 * to announce zero window in time before rmem limit kicks in.
2543 if (free_space < (allowed_space >> 4) || free_space < mss)
2544 return 0;
2547 if (free_space > tp->rcv_ssthresh)
2548 free_space = tp->rcv_ssthresh;
2550 /* Don't do rounding if we are using window scaling, since the
2551 * scaled window will not line up with the MSS boundary anyway.
2553 window = tp->rcv_wnd;
2554 if (tp->rx_opt.rcv_wscale) {
2555 window = free_space;
2557 /* Advertise enough space so that it won't get scaled away.
2558 * Import case: prevent zero window announcement if
2559 * 1<<rcv_wscale > mss.
2561 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2562 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2563 << tp->rx_opt.rcv_wscale);
2564 } else {
2565 /* Get the largest window that is a nice multiple of mss.
2566 * Window clamp already applied above.
2567 * If our current window offering is within 1 mss of the
2568 * free space we just keep it. This prevents the divide
2569 * and multiply from happening most of the time.
2570 * We also don't do any window rounding when the free space
2571 * is too small.
2573 if (window <= free_space - mss || window > free_space)
2574 window = (free_space / mss) * mss;
2575 else if (mss == full_space &&
2576 free_space > window + (full_space >> 1))
2577 window = free_space;
2580 return window;
2583 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
2584 const struct sk_buff *next_skb)
2586 if (unlikely(tcp_has_tx_tstamp(next_skb))) {
2587 const struct skb_shared_info *next_shinfo =
2588 skb_shinfo(next_skb);
2589 struct skb_shared_info *shinfo = skb_shinfo(skb);
2591 shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2592 shinfo->tskey = next_shinfo->tskey;
2593 TCP_SKB_CB(skb)->txstamp_ack |=
2594 TCP_SKB_CB(next_skb)->txstamp_ack;
2598 /* Collapses two adjacent SKB's during retransmission. */
2599 static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2601 struct tcp_sock *tp = tcp_sk(sk);
2602 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2603 int skb_size, next_skb_size;
2605 skb_size = skb->len;
2606 next_skb_size = next_skb->len;
2608 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2610 if (next_skb_size) {
2611 if (next_skb_size <= skb_availroom(skb))
2612 skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size),
2613 next_skb_size);
2614 else if (!skb_shift(skb, next_skb, next_skb_size))
2615 return false;
2617 tcp_highest_sack_combine(sk, next_skb, skb);
2619 tcp_unlink_write_queue(next_skb, sk);
2621 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2622 skb->ip_summed = CHECKSUM_PARTIAL;
2624 if (skb->ip_summed != CHECKSUM_PARTIAL)
2625 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2627 /* Update sequence range on original skb. */
2628 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2630 /* Merge over control information. This moves PSH/FIN etc. over */
2631 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2633 /* All done, get rid of second SKB and account for it so
2634 * packet counting does not break.
2636 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2637 TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2639 /* changed transmit queue under us so clear hints */
2640 tcp_clear_retrans_hints_partial(tp);
2641 if (next_skb == tp->retransmit_skb_hint)
2642 tp->retransmit_skb_hint = skb;
2644 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2646 tcp_skb_collapse_tstamp(skb, next_skb);
2648 sk_wmem_free_skb(sk, next_skb);
2649 return true;
2652 /* Check if coalescing SKBs is legal. */
2653 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2655 if (tcp_skb_pcount(skb) > 1)
2656 return false;
2657 if (skb_cloned(skb))
2658 return false;
2659 if (skb == tcp_send_head(sk))
2660 return false;
2661 /* Some heuristics for collapsing over SACK'd could be invented */
2662 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2663 return false;
2665 return true;
2668 /* Collapse packets in the retransmit queue to make to create
2669 * less packets on the wire. This is only done on retransmission.
2671 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2672 int space)
2674 struct tcp_sock *tp = tcp_sk(sk);
2675 struct sk_buff *skb = to, *tmp;
2676 bool first = true;
2678 if (!sysctl_tcp_retrans_collapse)
2679 return;
2680 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2681 return;
2683 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2684 if (!tcp_can_collapse(sk, skb))
2685 break;
2687 if (!tcp_skb_can_collapse_to(to))
2688 break;
2690 space -= skb->len;
2692 if (first) {
2693 first = false;
2694 continue;
2697 if (space < 0)
2698 break;
2700 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2701 break;
2703 if (!tcp_collapse_retrans(sk, to))
2704 break;
2708 /* This retransmits one SKB. Policy decisions and retransmit queue
2709 * state updates are done by the caller. Returns non-zero if an
2710 * error occurred which prevented the send.
2712 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2714 struct inet_connection_sock *icsk = inet_csk(sk);
2715 struct tcp_sock *tp = tcp_sk(sk);
2716 unsigned int cur_mss;
2717 int diff, len, err;
2720 /* Inconclusive MTU probe */
2721 if (icsk->icsk_mtup.probe_size)
2722 icsk->icsk_mtup.probe_size = 0;
2724 /* Do not sent more than we queued. 1/4 is reserved for possible
2725 * copying overhead: fragmentation, tunneling, mangling etc.
2727 if (atomic_read(&sk->sk_wmem_alloc) >
2728 min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
2729 sk->sk_sndbuf))
2730 return -EAGAIN;
2732 if (skb_still_in_host_queue(sk, skb))
2733 return -EBUSY;
2735 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2736 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2737 BUG();
2738 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2739 return -ENOMEM;
2742 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2743 return -EHOSTUNREACH; /* Routing failure or similar. */
2745 cur_mss = tcp_current_mss(sk);
2747 /* If receiver has shrunk his window, and skb is out of
2748 * new window, do not retransmit it. The exception is the
2749 * case, when window is shrunk to zero. In this case
2750 * our retransmit serves as a zero window probe.
2752 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2753 TCP_SKB_CB(skb)->seq != tp->snd_una)
2754 return -EAGAIN;
2756 len = cur_mss * segs;
2757 if (skb->len > len) {
2758 if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
2759 return -ENOMEM; /* We'll try again later. */
2760 } else {
2761 if (skb_unclone(skb, GFP_ATOMIC))
2762 return -ENOMEM;
2764 diff = tcp_skb_pcount(skb);
2765 tcp_set_skb_tso_segs(skb, cur_mss);
2766 diff -= tcp_skb_pcount(skb);
2767 if (diff)
2768 tcp_adjust_pcount(sk, skb, diff);
2769 if (skb->len < cur_mss)
2770 tcp_retrans_try_collapse(sk, skb, cur_mss);
2773 /* RFC3168, section 6.1.1.1. ECN fallback */
2774 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2775 tcp_ecn_clear_syn(sk, skb);
2777 /* make sure skb->data is aligned on arches that require it
2778 * and check if ack-trimming & collapsing extended the headroom
2779 * beyond what csum_start can cover.
2781 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2782 skb_headroom(skb) >= 0xFFFF)) {
2783 struct sk_buff *nskb;
2785 skb_mstamp_get(&skb->skb_mstamp);
2786 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2787 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2788 -ENOBUFS;
2789 } else {
2790 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2793 if (likely(!err)) {
2794 segs = tcp_skb_pcount(skb);
2796 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2797 /* Update global TCP statistics. */
2798 TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2799 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2800 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2801 tp->total_retrans += segs;
2803 return err;
2806 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2808 struct tcp_sock *tp = tcp_sk(sk);
2809 int err = __tcp_retransmit_skb(sk, skb, segs);
2811 if (err == 0) {
2812 #if FASTRETRANS_DEBUG > 0
2813 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2814 net_dbg_ratelimited("retrans_out leaked\n");
2816 #endif
2817 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2818 tp->retrans_out += tcp_skb_pcount(skb);
2820 /* Save stamp of the first retransmit. */
2821 if (!tp->retrans_stamp)
2822 tp->retrans_stamp = tcp_skb_timestamp(skb);
2824 } else if (err != -EBUSY) {
2825 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2828 if (tp->undo_retrans < 0)
2829 tp->undo_retrans = 0;
2830 tp->undo_retrans += tcp_skb_pcount(skb);
2831 return err;
2834 /* Check if we forward retransmits are possible in the current
2835 * window/congestion state.
2837 static bool tcp_can_forward_retransmit(struct sock *sk)
2839 const struct inet_connection_sock *icsk = inet_csk(sk);
2840 const struct tcp_sock *tp = tcp_sk(sk);
2842 /* Forward retransmissions are possible only during Recovery. */
2843 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2844 return false;
2846 /* No forward retransmissions in Reno are possible. */
2847 if (tcp_is_reno(tp))
2848 return false;
2850 /* Yeah, we have to make difficult choice between forward transmission
2851 * and retransmission... Both ways have their merits...
2853 * For now we do not retransmit anything, while we have some new
2854 * segments to send. In the other cases, follow rule 3 for
2855 * NextSeg() specified in RFC3517.
2858 if (tcp_may_send_now(sk))
2859 return false;
2861 return true;
2864 /* This gets called after a retransmit timeout, and the initially
2865 * retransmitted data is acknowledged. It tries to continue
2866 * resending the rest of the retransmit queue, until either
2867 * we've sent it all or the congestion window limit is reached.
2868 * If doing SACK, the first ACK which comes back for a timeout
2869 * based retransmit packet might feed us FACK information again.
2870 * If so, we use it to avoid unnecessarily retransmissions.
2872 void tcp_xmit_retransmit_queue(struct sock *sk)
2874 const struct inet_connection_sock *icsk = inet_csk(sk);
2875 struct tcp_sock *tp = tcp_sk(sk);
2876 struct sk_buff *skb;
2877 struct sk_buff *hole = NULL;
2878 u32 max_segs, last_lost;
2879 int mib_idx;
2880 int fwd_rexmitting = 0;
2882 if (!tp->packets_out)
2883 return;
2885 if (!tp->lost_out)
2886 tp->retransmit_high = tp->snd_una;
2888 if (tp->retransmit_skb_hint) {
2889 skb = tp->retransmit_skb_hint;
2890 last_lost = TCP_SKB_CB(skb)->end_seq;
2891 if (after(last_lost, tp->retransmit_high))
2892 last_lost = tp->retransmit_high;
2893 } else {
2894 skb = tcp_write_queue_head(sk);
2895 last_lost = tp->snd_una;
2898 max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
2899 tcp_for_write_queue_from(skb, sk) {
2900 __u8 sacked;
2901 int segs;
2903 if (skb == tcp_send_head(sk))
2904 break;
2905 /* we could do better than to assign each time */
2906 if (!hole)
2907 tp->retransmit_skb_hint = skb;
2909 segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
2910 if (segs <= 0)
2911 return;
2912 sacked = TCP_SKB_CB(skb)->sacked;
2913 /* In case tcp_shift_skb_data() have aggregated large skbs,
2914 * we need to make sure not sending too bigs TSO packets
2916 segs = min_t(int, segs, max_segs);
2918 if (fwd_rexmitting) {
2919 begin_fwd:
2920 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2921 break;
2922 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2924 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2925 tp->retransmit_high = last_lost;
2926 if (!tcp_can_forward_retransmit(sk))
2927 break;
2928 /* Backtrack if necessary to non-L'ed skb */
2929 if (hole) {
2930 skb = hole;
2931 hole = NULL;
2933 fwd_rexmitting = 1;
2934 goto begin_fwd;
2936 } else if (!(sacked & TCPCB_LOST)) {
2937 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2938 hole = skb;
2939 continue;
2941 } else {
2942 last_lost = TCP_SKB_CB(skb)->end_seq;
2943 if (icsk->icsk_ca_state != TCP_CA_Loss)
2944 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2945 else
2946 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2949 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2950 continue;
2952 if (tcp_small_queue_check(sk, skb, 1))
2953 return;
2955 if (tcp_retransmit_skb(sk, skb, segs))
2956 return;
2958 NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb));
2960 if (tcp_in_cwnd_reduction(sk))
2961 tp->prr_out += tcp_skb_pcount(skb);
2963 if (skb == tcp_write_queue_head(sk))
2964 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2965 inet_csk(sk)->icsk_rto,
2966 TCP_RTO_MAX);
2970 /* We allow to exceed memory limits for FIN packets to expedite
2971 * connection tear down and (memory) recovery.
2972 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2973 * or even be forced to close flow without any FIN.
2974 * In general, we want to allow one skb per socket to avoid hangs
2975 * with edge trigger epoll()
2977 void sk_forced_mem_schedule(struct sock *sk, int size)
2979 int amt;
2981 if (size <= sk->sk_forward_alloc)
2982 return;
2983 amt = sk_mem_pages(size);
2984 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2985 sk_memory_allocated_add(sk, amt);
2987 if (mem_cgroup_sockets_enabled && sk->sk_memcg)
2988 mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2991 /* Send a FIN. The caller locks the socket for us.
2992 * We should try to send a FIN packet really hard, but eventually give up.
2994 void tcp_send_fin(struct sock *sk)
2996 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2997 struct tcp_sock *tp = tcp_sk(sk);
2999 /* Optimization, tack on the FIN if we have one skb in write queue and
3000 * this skb was not yet sent, or we are under memory pressure.
3001 * Note: in the latter case, FIN packet will be sent after a timeout,
3002 * as TCP stack thinks it has already been transmitted.
3004 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
3005 coalesce:
3006 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
3007 TCP_SKB_CB(tskb)->end_seq++;
3008 tp->write_seq++;
3009 if (!tcp_send_head(sk)) {
3010 /* This means tskb was already sent.
3011 * Pretend we included the FIN on previous transmit.
3012 * We need to set tp->snd_nxt to the value it would have
3013 * if FIN had been sent. This is because retransmit path
3014 * does not change tp->snd_nxt.
3016 tp->snd_nxt++;
3017 return;
3019 } else {
3020 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
3021 if (unlikely(!skb)) {
3022 if (tskb)
3023 goto coalesce;
3024 return;
3026 skb_reserve(skb, MAX_TCP_HEADER);
3027 sk_forced_mem_schedule(sk, skb->truesize);
3028 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
3029 tcp_init_nondata_skb(skb, tp->write_seq,
3030 TCPHDR_ACK | TCPHDR_FIN);
3031 tcp_queue_skb(sk, skb);
3033 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
3036 /* We get here when a process closes a file descriptor (either due to
3037 * an explicit close() or as a byproduct of exit()'ing) and there
3038 * was unread data in the receive queue. This behavior is recommended
3039 * by RFC 2525, section 2.17. -DaveM
3041 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
3043 struct sk_buff *skb;
3045 /* NOTE: No TCP options attached and we never retransmit this. */
3046 skb = alloc_skb(MAX_TCP_HEADER, priority);
3047 if (!skb) {
3048 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3049 return;
3052 /* Reserve space for headers and prepare control bits. */
3053 skb_reserve(skb, MAX_TCP_HEADER);
3054 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
3055 TCPHDR_ACK | TCPHDR_RST);
3056 skb_mstamp_get(&skb->skb_mstamp);
3057 /* Send it off. */
3058 if (tcp_transmit_skb(sk, skb, 0, priority))
3059 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3061 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
3064 /* Send a crossed SYN-ACK during socket establishment.
3065 * WARNING: This routine must only be called when we have already sent
3066 * a SYN packet that crossed the incoming SYN that caused this routine
3067 * to get called. If this assumption fails then the initial rcv_wnd
3068 * and rcv_wscale values will not be correct.
3070 int tcp_send_synack(struct sock *sk)
3072 struct sk_buff *skb;
3074 skb = tcp_write_queue_head(sk);
3075 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
3076 pr_debug("%s: wrong queue state\n", __func__);
3077 return -EFAULT;
3079 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
3080 if (skb_cloned(skb)) {
3081 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
3082 if (!nskb)
3083 return -ENOMEM;
3084 tcp_unlink_write_queue(skb, sk);
3085 __skb_header_release(nskb);
3086 __tcp_add_write_queue_head(sk, nskb);
3087 sk_wmem_free_skb(sk, skb);
3088 sk->sk_wmem_queued += nskb->truesize;
3089 sk_mem_charge(sk, nskb->truesize);
3090 skb = nskb;
3093 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
3094 tcp_ecn_send_synack(sk, skb);
3096 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3100 * tcp_make_synack - Prepare a SYN-ACK.
3101 * sk: listener socket
3102 * dst: dst entry attached to the SYNACK
3103 * req: request_sock pointer
3105 * Allocate one skb and build a SYNACK packet.
3106 * @dst is consumed : Caller should not use it again.
3108 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3109 struct request_sock *req,
3110 struct tcp_fastopen_cookie *foc,
3111 enum tcp_synack_type synack_type)
3113 struct inet_request_sock *ireq = inet_rsk(req);
3114 const struct tcp_sock *tp = tcp_sk(sk);
3115 struct tcp_md5sig_key *md5 = NULL;
3116 struct tcp_out_options opts;
3117 struct sk_buff *skb;
3118 int tcp_header_size;
3119 struct tcphdr *th;
3120 u16 user_mss;
3121 int mss;
3123 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3124 if (unlikely(!skb)) {
3125 dst_release(dst);
3126 return NULL;
3128 /* Reserve space for headers. */
3129 skb_reserve(skb, MAX_TCP_HEADER);
3131 switch (synack_type) {
3132 case TCP_SYNACK_NORMAL:
3133 skb_set_owner_w(skb, req_to_sk(req));
3134 break;
3135 case TCP_SYNACK_COOKIE:
3136 /* Under synflood, we do not attach skb to a socket,
3137 * to avoid false sharing.
3139 break;
3140 case TCP_SYNACK_FASTOPEN:
3141 /* sk is a const pointer, because we want to express multiple
3142 * cpu might call us concurrently.
3143 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3145 skb_set_owner_w(skb, (struct sock *)sk);
3146 break;
3148 skb_dst_set(skb, dst);
3150 mss = dst_metric_advmss(dst);
3151 user_mss = READ_ONCE(tp->rx_opt.user_mss);
3152 if (user_mss && user_mss < mss)
3153 mss = user_mss;
3155 memset(&opts, 0, sizeof(opts));
3156 #ifdef CONFIG_SYN_COOKIES
3157 if (unlikely(req->cookie_ts))
3158 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3159 else
3160 #endif
3161 skb_mstamp_get(&skb->skb_mstamp);
3163 #ifdef CONFIG_TCP_MD5SIG
3164 rcu_read_lock();
3165 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3166 #endif
3167 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3168 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3169 sizeof(*th);
3171 skb_push(skb, tcp_header_size);
3172 skb_reset_transport_header(skb);
3174 th = (struct tcphdr *)skb->data;
3175 memset(th, 0, sizeof(struct tcphdr));
3176 th->syn = 1;
3177 th->ack = 1;
3178 tcp_ecn_make_synack(req, th);
3179 th->source = htons(ireq->ir_num);
3180 th->dest = ireq->ir_rmt_port;
3181 /* Setting of flags are superfluous here for callers (and ECE is
3182 * not even correctly set)
3184 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3185 TCPHDR_SYN | TCPHDR_ACK);
3187 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3188 /* XXX data is queued and acked as is. No buffer/window check */
3189 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3191 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3192 th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3193 tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3194 th->doff = (tcp_header_size >> 2);
3195 __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3197 #ifdef CONFIG_TCP_MD5SIG
3198 /* Okay, we have all we need - do the md5 hash if needed */
3199 if (md5)
3200 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3201 md5, req_to_sk(req), skb);
3202 rcu_read_unlock();
3203 #endif
3205 /* Do not fool tcpdump (if any), clean our debris */
3206 skb->tstamp = 0;
3207 return skb;
3209 EXPORT_SYMBOL(tcp_make_synack);
3211 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3213 struct inet_connection_sock *icsk = inet_csk(sk);
3214 const struct tcp_congestion_ops *ca;
3215 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3217 if (ca_key == TCP_CA_UNSPEC)
3218 return;
3220 rcu_read_lock();
3221 ca = tcp_ca_find_key(ca_key);
3222 if (likely(ca && try_module_get(ca->owner))) {
3223 module_put(icsk->icsk_ca_ops->owner);
3224 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3225 icsk->icsk_ca_ops = ca;
3227 rcu_read_unlock();
3230 /* Do all connect socket setups that can be done AF independent. */
3231 static void tcp_connect_init(struct sock *sk)
3233 const struct dst_entry *dst = __sk_dst_get(sk);
3234 struct tcp_sock *tp = tcp_sk(sk);
3235 __u8 rcv_wscale;
3237 /* We'll fix this up when we get a response from the other end.
3238 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3240 tp->tcp_header_len = sizeof(struct tcphdr) +
3241 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3243 #ifdef CONFIG_TCP_MD5SIG
3244 if (tp->af_specific->md5_lookup(sk, sk))
3245 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3246 #endif
3248 /* If user gave his TCP_MAXSEG, record it to clamp */
3249 if (tp->rx_opt.user_mss)
3250 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3251 tp->max_window = 0;
3252 tcp_mtup_init(sk);
3253 tcp_sync_mss(sk, dst_mtu(dst));
3255 tcp_ca_dst_init(sk, dst);
3257 if (!tp->window_clamp)
3258 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3259 tp->advmss = dst_metric_advmss(dst);
3260 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3261 tp->advmss = tp->rx_opt.user_mss;
3263 tcp_initialize_rcv_mss(sk);
3265 /* limit the window selection if the user enforce a smaller rx buffer */
3266 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3267 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3268 tp->window_clamp = tcp_full_space(sk);
3270 tcp_select_initial_window(tcp_full_space(sk),
3271 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3272 &tp->rcv_wnd,
3273 &tp->window_clamp,
3274 sysctl_tcp_window_scaling,
3275 &rcv_wscale,
3276 dst_metric(dst, RTAX_INITRWND));
3278 tp->rx_opt.rcv_wscale = rcv_wscale;
3279 tp->rcv_ssthresh = tp->rcv_wnd;
3281 sk->sk_err = 0;
3282 sock_reset_flag(sk, SOCK_DONE);
3283 tp->snd_wnd = 0;
3284 tcp_init_wl(tp, 0);
3285 tp->snd_una = tp->write_seq;
3286 tp->snd_sml = tp->write_seq;
3287 tp->snd_up = tp->write_seq;
3288 tp->snd_nxt = tp->write_seq;
3290 if (likely(!tp->repair))
3291 tp->rcv_nxt = 0;
3292 else
3293 tp->rcv_tstamp = tcp_time_stamp;
3294 tp->rcv_wup = tp->rcv_nxt;
3295 tp->copied_seq = tp->rcv_nxt;
3297 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3298 inet_csk(sk)->icsk_retransmits = 0;
3299 tcp_clear_retrans(tp);
3302 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3304 struct tcp_sock *tp = tcp_sk(sk);
3305 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3307 tcb->end_seq += skb->len;
3308 __skb_header_release(skb);
3309 __tcp_add_write_queue_tail(sk, skb);
3310 sk->sk_wmem_queued += skb->truesize;
3311 sk_mem_charge(sk, skb->truesize);
3312 tp->write_seq = tcb->end_seq;
3313 tp->packets_out += tcp_skb_pcount(skb);
3316 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3317 * queue a data-only packet after the regular SYN, such that regular SYNs
3318 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3319 * only the SYN sequence, the data are retransmitted in the first ACK.
3320 * If cookie is not cached or other error occurs, falls back to send a
3321 * regular SYN with Fast Open cookie request option.
3323 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3325 struct tcp_sock *tp = tcp_sk(sk);
3326 struct tcp_fastopen_request *fo = tp->fastopen_req;
3327 int syn_loss = 0, space, err = 0;
3328 unsigned long last_syn_loss = 0;
3329 struct sk_buff *syn_data;
3331 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3332 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3333 &syn_loss, &last_syn_loss);
3334 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3335 if (syn_loss > 1 &&
3336 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3337 fo->cookie.len = -1;
3338 goto fallback;
3341 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3342 fo->cookie.len = -1;
3343 else if (fo->cookie.len <= 0)
3344 goto fallback;
3346 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3347 * user-MSS. Reserve maximum option space for middleboxes that add
3348 * private TCP options. The cost is reduced data space in SYN :(
3350 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3351 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3352 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3353 MAX_TCP_OPTION_SPACE;
3355 space = min_t(size_t, space, fo->size);
3357 /* limit to order-0 allocations */
3358 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3360 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3361 if (!syn_data)
3362 goto fallback;
3363 syn_data->ip_summed = CHECKSUM_PARTIAL;
3364 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3365 if (space) {
3366 int copied = copy_from_iter(skb_put(syn_data, space), space,
3367 &fo->data->msg_iter);
3368 if (unlikely(!copied)) {
3369 kfree_skb(syn_data);
3370 goto fallback;
3372 if (copied != space) {
3373 skb_trim(syn_data, copied);
3374 space = copied;
3377 /* No more data pending in inet_wait_for_connect() */
3378 if (space == fo->size)
3379 fo->data = NULL;
3380 fo->copied = space;
3382 tcp_connect_queue_skb(sk, syn_data);
3383 if (syn_data->len)
3384 tcp_chrono_start(sk, TCP_CHRONO_BUSY);
3386 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3388 syn->skb_mstamp = syn_data->skb_mstamp;
3390 /* Now full SYN+DATA was cloned and sent (or not),
3391 * remove the SYN from the original skb (syn_data)
3392 * we keep in write queue in case of a retransmit, as we
3393 * also have the SYN packet (with no data) in the same queue.
3395 TCP_SKB_CB(syn_data)->seq++;
3396 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3397 if (!err) {
3398 tp->syn_data = (fo->copied > 0);
3399 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3400 goto done;
3403 fallback:
3404 /* Send a regular SYN with Fast Open cookie request option */
3405 if (fo->cookie.len > 0)
3406 fo->cookie.len = 0;
3407 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3408 if (err)
3409 tp->syn_fastopen = 0;
3410 done:
3411 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3412 return err;
3415 /* Build a SYN and send it off. */
3416 int tcp_connect(struct sock *sk)
3418 struct tcp_sock *tp = tcp_sk(sk);
3419 struct sk_buff *buff;
3420 int err;
3422 tcp_connect_init(sk);
3424 if (unlikely(tp->repair)) {
3425 tcp_finish_connect(sk, NULL);
3426 return 0;
3429 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3430 if (unlikely(!buff))
3431 return -ENOBUFS;
3433 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3434 tp->retrans_stamp = tcp_time_stamp;
3435 tcp_connect_queue_skb(sk, buff);
3436 tcp_ecn_send_syn(sk, buff);
3438 /* Send off SYN; include data in Fast Open. */
3439 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3440 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3441 if (err == -ECONNREFUSED)
3442 return err;
3444 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3445 * in order to make this packet get counted in tcpOutSegs.
3447 tp->snd_nxt = tp->write_seq;
3448 tp->pushed_seq = tp->write_seq;
3449 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3451 /* Timer for repeating the SYN until an answer. */
3452 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3453 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3454 return 0;
3456 EXPORT_SYMBOL(tcp_connect);
3458 /* Send out a delayed ack, the caller does the policy checking
3459 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3460 * for details.
3462 void tcp_send_delayed_ack(struct sock *sk)
3464 struct inet_connection_sock *icsk = inet_csk(sk);
3465 int ato = icsk->icsk_ack.ato;
3466 unsigned long timeout;
3468 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3470 if (ato > TCP_DELACK_MIN) {
3471 const struct tcp_sock *tp = tcp_sk(sk);
3472 int max_ato = HZ / 2;
3474 if (icsk->icsk_ack.pingpong ||
3475 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3476 max_ato = TCP_DELACK_MAX;
3478 /* Slow path, intersegment interval is "high". */
3480 /* If some rtt estimate is known, use it to bound delayed ack.
3481 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3482 * directly.
3484 if (tp->srtt_us) {
3485 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3486 TCP_DELACK_MIN);
3488 if (rtt < max_ato)
3489 max_ato = rtt;
3492 ato = min(ato, max_ato);
3495 /* Stay within the limit we were given */
3496 timeout = jiffies + ato;
3498 /* Use new timeout only if there wasn't a older one earlier. */
3499 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3500 /* If delack timer was blocked or is about to expire,
3501 * send ACK now.
3503 if (icsk->icsk_ack.blocked ||
3504 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3505 tcp_send_ack(sk);
3506 return;
3509 if (!time_before(timeout, icsk->icsk_ack.timeout))
3510 timeout = icsk->icsk_ack.timeout;
3512 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3513 icsk->icsk_ack.timeout = timeout;
3514 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3517 /* This routine sends an ack and also updates the window. */
3518 void tcp_send_ack(struct sock *sk)
3520 struct sk_buff *buff;
3522 /* If we have been reset, we may not send again. */
3523 if (sk->sk_state == TCP_CLOSE)
3524 return;
3526 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3528 /* We are not putting this on the write queue, so
3529 * tcp_transmit_skb() will set the ownership to this
3530 * sock.
3532 buff = alloc_skb(MAX_TCP_HEADER,
3533 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3534 if (unlikely(!buff)) {
3535 inet_csk_schedule_ack(sk);
3536 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3537 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3538 TCP_DELACK_MAX, TCP_RTO_MAX);
3539 return;
3542 /* Reserve space for headers and prepare control bits. */
3543 skb_reserve(buff, MAX_TCP_HEADER);
3544 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3546 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3547 * too much.
3548 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3550 skb_set_tcp_pure_ack(buff);
3552 /* Send it off, this clears delayed acks for us. */
3553 skb_mstamp_get(&buff->skb_mstamp);
3554 tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
3556 EXPORT_SYMBOL_GPL(tcp_send_ack);
3558 /* This routine sends a packet with an out of date sequence
3559 * number. It assumes the other end will try to ack it.
3561 * Question: what should we make while urgent mode?
3562 * 4.4BSD forces sending single byte of data. We cannot send
3563 * out of window data, because we have SND.NXT==SND.MAX...
3565 * Current solution: to send TWO zero-length segments in urgent mode:
3566 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3567 * out-of-date with SND.UNA-1 to probe window.
3569 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3571 struct tcp_sock *tp = tcp_sk(sk);
3572 struct sk_buff *skb;
3574 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3575 skb = alloc_skb(MAX_TCP_HEADER,
3576 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3577 if (!skb)
3578 return -1;
3580 /* Reserve space for headers and set control bits. */
3581 skb_reserve(skb, MAX_TCP_HEADER);
3582 /* Use a previous sequence. This should cause the other
3583 * end to send an ack. Don't queue or clone SKB, just
3584 * send it.
3586 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3587 skb_mstamp_get(&skb->skb_mstamp);
3588 NET_INC_STATS(sock_net(sk), mib);
3589 return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
3592 void tcp_send_window_probe(struct sock *sk)
3594 if (sk->sk_state == TCP_ESTABLISHED) {
3595 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3596 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3600 /* Initiate keepalive or window probe from timer. */
3601 int tcp_write_wakeup(struct sock *sk, int mib)
3603 struct tcp_sock *tp = tcp_sk(sk);
3604 struct sk_buff *skb;
3606 if (sk->sk_state == TCP_CLOSE)
3607 return -1;
3609 skb = tcp_send_head(sk);
3610 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3611 int err;
3612 unsigned int mss = tcp_current_mss(sk);
3613 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3615 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3616 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3618 /* We are probing the opening of a window
3619 * but the window size is != 0
3620 * must have been a result SWS avoidance ( sender )
3622 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3623 skb->len > mss) {
3624 seg_size = min(seg_size, mss);
3625 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3626 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3627 return -1;
3628 } else if (!tcp_skb_pcount(skb))
3629 tcp_set_skb_tso_segs(skb, mss);
3631 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3632 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3633 if (!err)
3634 tcp_event_new_data_sent(sk, skb);
3635 return err;
3636 } else {
3637 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3638 tcp_xmit_probe_skb(sk, 1, mib);
3639 return tcp_xmit_probe_skb(sk, 0, mib);
3643 /* A window probe timeout has occurred. If window is not closed send
3644 * a partial packet else a zero probe.
3646 void tcp_send_probe0(struct sock *sk)
3648 struct inet_connection_sock *icsk = inet_csk(sk);
3649 struct tcp_sock *tp = tcp_sk(sk);
3650 struct net *net = sock_net(sk);
3651 unsigned long probe_max;
3652 int err;
3654 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3656 if (tp->packets_out || !tcp_send_head(sk)) {
3657 /* Cancel probe timer, if it is not required. */
3658 icsk->icsk_probes_out = 0;
3659 icsk->icsk_backoff = 0;
3660 return;
3663 if (err <= 0) {
3664 if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3665 icsk->icsk_backoff++;
3666 icsk->icsk_probes_out++;
3667 probe_max = TCP_RTO_MAX;
3668 } else {
3669 /* If packet was not sent due to local congestion,
3670 * do not backoff and do not remember icsk_probes_out.
3671 * Let local senders to fight for local resources.
3673 * Use accumulated backoff yet.
3675 if (!icsk->icsk_probes_out)
3676 icsk->icsk_probes_out = 1;
3677 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3679 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3680 tcp_probe0_when(sk, probe_max),
3681 TCP_RTO_MAX);
3684 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3686 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3687 struct flowi fl;
3688 int res;
3690 tcp_rsk(req)->txhash = net_tx_rndhash();
3691 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3692 if (!res) {
3693 __TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3694 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3695 if (unlikely(tcp_passive_fastopen(sk)))
3696 tcp_sk(sk)->total_retrans++;
3698 return res;
3700 EXPORT_SYMBOL(tcp_rtx_synack);