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).
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
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
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) {
84 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
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))
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
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;
125 unsigned int metric = dst_metric_advmss(dst);
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)
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,
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);
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;
194 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
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,
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. */
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);
236 /* Set window scaling on max possible window
237 * See RFC1323 for an explanation of the limit to 14
239 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
240 space = min_t(u32, space, *window_clamp);
241 while (space > 65535 && (*rcv_wscale) < 14) {
247 if (mss > (1 << *rcv_wscale)) {
248 if (!init_rcv_wnd) /* Use default unless specified otherwise */
249 init_rcv_wnd = tcp_default_init_rwnd(mss);
250 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
253 /* Set the clamp no higher than max representable value */
254 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
256 EXPORT_SYMBOL(tcp_select_initial_window);
258 /* Chose a new window to advertise, update state in tcp_sock for the
259 * socket, and return result with RFC1323 scaling applied. The return
260 * value can be stuffed directly into th->window for an outgoing
263 static u16 tcp_select_window(struct sock *sk)
265 struct tcp_sock *tp = tcp_sk(sk);
266 u32 old_win = tp->rcv_wnd;
267 u32 cur_win = tcp_receive_window(tp);
268 u32 new_win = __tcp_select_window(sk);
270 /* Never shrink the offered window */
271 if (new_win < cur_win) {
272 /* Danger Will Robinson!
273 * Don't update rcv_wup/rcv_wnd here or else
274 * we will not be able to advertise a zero
275 * window in time. --DaveM
277 * Relax Will Robinson.
280 NET_INC_STATS(sock_net(sk),
281 LINUX_MIB_TCPWANTZEROWINDOWADV);
282 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
284 tp->rcv_wnd = new_win;
285 tp->rcv_wup = tp->rcv_nxt;
287 /* Make sure we do not exceed the maximum possible
290 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
291 new_win = min(new_win, MAX_TCP_WINDOW);
293 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
295 /* RFC1323 scaling applied */
296 new_win >>= tp->rx_opt.rcv_wscale;
298 /* If we advertise zero window, disable fast path. */
302 NET_INC_STATS(sock_net(sk),
303 LINUX_MIB_TCPTOZEROWINDOWADV);
304 } else if (old_win == 0) {
305 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
311 /* Packet ECN state for a SYN-ACK */
312 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
314 const struct tcp_sock *tp = tcp_sk(sk);
316 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
317 if (!(tp->ecn_flags & TCP_ECN_OK))
318 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
319 else if (tcp_ca_needs_ecn(sk))
323 /* Packet ECN state for a SYN. */
324 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
326 struct tcp_sock *tp = tcp_sk(sk);
327 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
328 tcp_ca_needs_ecn(sk);
331 const struct dst_entry *dst = __sk_dst_get(sk);
333 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
340 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
341 tp->ecn_flags = TCP_ECN_OK;
342 if (tcp_ca_needs_ecn(sk))
347 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
349 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
350 /* tp->ecn_flags are cleared at a later point in time when
351 * SYN ACK is ultimatively being received.
353 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
357 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
359 if (inet_rsk(req)->ecn_ok)
363 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
366 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
369 struct tcp_sock *tp = tcp_sk(sk);
371 if (tp->ecn_flags & TCP_ECN_OK) {
372 /* Not-retransmitted data segment: set ECT and inject CWR. */
373 if (skb->len != tcp_header_len &&
374 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
376 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
377 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
378 tcp_hdr(skb)->cwr = 1;
379 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
381 } else if (!tcp_ca_needs_ecn(sk)) {
382 /* ACK or retransmitted segment: clear ECT|CE */
383 INET_ECN_dontxmit(sk);
385 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
386 tcp_hdr(skb)->ece = 1;
390 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
391 * auto increment end seqno.
393 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
395 skb->ip_summed = CHECKSUM_PARTIAL;
398 TCP_SKB_CB(skb)->tcp_flags = flags;
399 TCP_SKB_CB(skb)->sacked = 0;
401 tcp_skb_pcount_set(skb, 1);
403 TCP_SKB_CB(skb)->seq = seq;
404 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
406 TCP_SKB_CB(skb)->end_seq = seq;
409 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
411 return tp->snd_una != tp->snd_up;
414 #define OPTION_SACK_ADVERTISE (1 << 0)
415 #define OPTION_TS (1 << 1)
416 #define OPTION_MD5 (1 << 2)
417 #define OPTION_WSCALE (1 << 3)
418 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
420 struct tcp_out_options {
421 u16 options; /* bit field of OPTION_* */
422 u16 mss; /* 0 to disable */
423 u8 ws; /* window scale, 0 to disable */
424 u8 num_sack_blocks; /* number of SACK blocks to include */
425 u8 hash_size; /* bytes in hash_location */
426 __u8 *hash_location; /* temporary pointer, overloaded */
427 __u32 tsval, tsecr; /* need to include OPTION_TS */
428 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
431 /* Write previously computed TCP options to the packet.
433 * Beware: Something in the Internet is very sensitive to the ordering of
434 * TCP options, we learned this through the hard way, so be careful here.
435 * Luckily we can at least blame others for their non-compliance but from
436 * inter-operability perspective it seems that we're somewhat stuck with
437 * the ordering which we have been using if we want to keep working with
438 * those broken things (not that it currently hurts anybody as there isn't
439 * particular reason why the ordering would need to be changed).
441 * At least SACK_PERM as the first option is known to lead to a disaster
442 * (but it may well be that other scenarios fail similarly).
444 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
445 struct tcp_out_options *opts)
447 u16 options = opts->options; /* mungable copy */
449 if (unlikely(OPTION_MD5 & options)) {
450 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
451 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
452 /* overload cookie hash location */
453 opts->hash_location = (__u8 *)ptr;
457 if (unlikely(opts->mss)) {
458 *ptr++ = htonl((TCPOPT_MSS << 24) |
459 (TCPOLEN_MSS << 16) |
463 if (likely(OPTION_TS & options)) {
464 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
465 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
466 (TCPOLEN_SACK_PERM << 16) |
467 (TCPOPT_TIMESTAMP << 8) |
469 options &= ~OPTION_SACK_ADVERTISE;
471 *ptr++ = htonl((TCPOPT_NOP << 24) |
473 (TCPOPT_TIMESTAMP << 8) |
476 *ptr++ = htonl(opts->tsval);
477 *ptr++ = htonl(opts->tsecr);
480 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
481 *ptr++ = htonl((TCPOPT_NOP << 24) |
483 (TCPOPT_SACK_PERM << 8) |
487 if (unlikely(OPTION_WSCALE & options)) {
488 *ptr++ = htonl((TCPOPT_NOP << 24) |
489 (TCPOPT_WINDOW << 16) |
490 (TCPOLEN_WINDOW << 8) |
494 if (unlikely(opts->num_sack_blocks)) {
495 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
496 tp->duplicate_sack : tp->selective_acks;
499 *ptr++ = htonl((TCPOPT_NOP << 24) |
502 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
503 TCPOLEN_SACK_PERBLOCK)));
505 for (this_sack = 0; this_sack < opts->num_sack_blocks;
507 *ptr++ = htonl(sp[this_sack].start_seq);
508 *ptr++ = htonl(sp[this_sack].end_seq);
511 tp->rx_opt.dsack = 0;
514 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
515 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
517 u32 len; /* Fast Open option length */
520 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
521 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
522 TCPOPT_FASTOPEN_MAGIC);
523 p += TCPOLEN_EXP_FASTOPEN_BASE;
525 len = TCPOLEN_FASTOPEN_BASE + foc->len;
526 *p++ = TCPOPT_FASTOPEN;
530 memcpy(p, foc->val, foc->len);
531 if ((len & 3) == 2) {
532 p[foc->len] = TCPOPT_NOP;
533 p[foc->len + 1] = TCPOPT_NOP;
535 ptr += (len + 3) >> 2;
539 /* Compute TCP options for SYN packets. This is not the final
540 * network wire format yet.
542 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
543 struct tcp_out_options *opts,
544 struct tcp_md5sig_key **md5)
546 struct tcp_sock *tp = tcp_sk(sk);
547 unsigned int remaining = MAX_TCP_OPTION_SPACE;
548 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
550 #ifdef CONFIG_TCP_MD5SIG
551 *md5 = tp->af_specific->md5_lookup(sk, sk);
553 opts->options |= OPTION_MD5;
554 remaining -= TCPOLEN_MD5SIG_ALIGNED;
560 /* We always get an MSS option. The option bytes which will be seen in
561 * normal data packets should timestamps be used, must be in the MSS
562 * advertised. But we subtract them from tp->mss_cache so that
563 * calculations in tcp_sendmsg are simpler etc. So account for this
564 * fact here if necessary. If we don't do this correctly, as a
565 * receiver we won't recognize data packets as being full sized when we
566 * should, and thus we won't abide by the delayed ACK rules correctly.
567 * SACKs don't matter, we never delay an ACK when we have any of those
569 opts->mss = tcp_advertise_mss(sk);
570 remaining -= TCPOLEN_MSS_ALIGNED;
572 if (likely(sysctl_tcp_timestamps && !*md5)) {
573 opts->options |= OPTION_TS;
574 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
575 opts->tsecr = tp->rx_opt.ts_recent;
576 remaining -= TCPOLEN_TSTAMP_ALIGNED;
578 if (likely(sysctl_tcp_window_scaling)) {
579 opts->ws = tp->rx_opt.rcv_wscale;
580 opts->options |= OPTION_WSCALE;
581 remaining -= TCPOLEN_WSCALE_ALIGNED;
583 if (likely(sysctl_tcp_sack)) {
584 opts->options |= OPTION_SACK_ADVERTISE;
585 if (unlikely(!(OPTION_TS & opts->options)))
586 remaining -= TCPOLEN_SACKPERM_ALIGNED;
589 if (fastopen && fastopen->cookie.len >= 0) {
590 u32 need = fastopen->cookie.len;
592 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
593 TCPOLEN_FASTOPEN_BASE;
594 need = (need + 3) & ~3U; /* Align to 32 bits */
595 if (remaining >= need) {
596 opts->options |= OPTION_FAST_OPEN_COOKIE;
597 opts->fastopen_cookie = &fastopen->cookie;
599 tp->syn_fastopen = 1;
600 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
604 return MAX_TCP_OPTION_SPACE - remaining;
607 /* Set up TCP options for SYN-ACKs. */
608 static unsigned int tcp_synack_options(struct request_sock *req,
609 unsigned int mss, struct sk_buff *skb,
610 struct tcp_out_options *opts,
611 const struct tcp_md5sig_key *md5,
612 struct tcp_fastopen_cookie *foc)
614 struct inet_request_sock *ireq = inet_rsk(req);
615 unsigned int remaining = MAX_TCP_OPTION_SPACE;
617 #ifdef CONFIG_TCP_MD5SIG
619 opts->options |= OPTION_MD5;
620 remaining -= TCPOLEN_MD5SIG_ALIGNED;
622 /* We can't fit any SACK blocks in a packet with MD5 + TS
623 * options. There was discussion about disabling SACK
624 * rather than TS in order to fit in better with old,
625 * buggy kernels, but that was deemed to be unnecessary.
627 ireq->tstamp_ok &= !ireq->sack_ok;
631 /* We always send an MSS option. */
633 remaining -= TCPOLEN_MSS_ALIGNED;
635 if (likely(ireq->wscale_ok)) {
636 opts->ws = ireq->rcv_wscale;
637 opts->options |= OPTION_WSCALE;
638 remaining -= TCPOLEN_WSCALE_ALIGNED;
640 if (likely(ireq->tstamp_ok)) {
641 opts->options |= OPTION_TS;
642 opts->tsval = tcp_skb_timestamp(skb);
643 opts->tsecr = req->ts_recent;
644 remaining -= TCPOLEN_TSTAMP_ALIGNED;
646 if (likely(ireq->sack_ok)) {
647 opts->options |= OPTION_SACK_ADVERTISE;
648 if (unlikely(!ireq->tstamp_ok))
649 remaining -= TCPOLEN_SACKPERM_ALIGNED;
651 if (foc != NULL && foc->len >= 0) {
654 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
655 TCPOLEN_FASTOPEN_BASE;
656 need = (need + 3) & ~3U; /* Align to 32 bits */
657 if (remaining >= need) {
658 opts->options |= OPTION_FAST_OPEN_COOKIE;
659 opts->fastopen_cookie = foc;
664 return MAX_TCP_OPTION_SPACE - remaining;
667 /* Compute TCP options for ESTABLISHED sockets. This is not the
668 * final wire format yet.
670 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
671 struct tcp_out_options *opts,
672 struct tcp_md5sig_key **md5)
674 struct tcp_sock *tp = tcp_sk(sk);
675 unsigned int size = 0;
676 unsigned int eff_sacks;
680 #ifdef CONFIG_TCP_MD5SIG
681 *md5 = tp->af_specific->md5_lookup(sk, sk);
682 if (unlikely(*md5)) {
683 opts->options |= OPTION_MD5;
684 size += TCPOLEN_MD5SIG_ALIGNED;
690 if (likely(tp->rx_opt.tstamp_ok)) {
691 opts->options |= OPTION_TS;
692 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
693 opts->tsecr = tp->rx_opt.ts_recent;
694 size += TCPOLEN_TSTAMP_ALIGNED;
697 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
698 if (unlikely(eff_sacks)) {
699 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
700 opts->num_sack_blocks =
701 min_t(unsigned int, eff_sacks,
702 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
703 TCPOLEN_SACK_PERBLOCK);
704 size += TCPOLEN_SACK_BASE_ALIGNED +
705 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
712 /* TCP SMALL QUEUES (TSQ)
714 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
715 * to reduce RTT and bufferbloat.
716 * We do this using a special skb destructor (tcp_wfree).
718 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
719 * needs to be reallocated in a driver.
720 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
722 * Since transmit from skb destructor is forbidden, we use a tasklet
723 * to process all sockets that eventually need to send more skbs.
724 * We use one tasklet per cpu, with its own queue of sockets.
727 struct tasklet_struct tasklet;
728 struct list_head head; /* queue of tcp sockets */
730 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
732 static void tcp_tsq_handler(struct sock *sk)
734 if ((1 << sk->sk_state) &
735 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
736 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
737 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
741 * One tasklet per cpu tries to send more skbs.
742 * We run in tasklet context but need to disable irqs when
743 * transferring tsq->head because tcp_wfree() might
744 * interrupt us (non NAPI drivers)
746 static void tcp_tasklet_func(unsigned long data)
748 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
751 struct list_head *q, *n;
755 local_irq_save(flags);
756 list_splice_init(&tsq->head, &list);
757 local_irq_restore(flags);
759 list_for_each_safe(q, n, &list) {
760 tp = list_entry(q, struct tcp_sock, tsq_node);
761 list_del(&tp->tsq_node);
763 sk = (struct sock *)tp;
766 if (!sock_owned_by_user(sk)) {
769 /* defer the work to tcp_release_cb() */
770 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
774 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
779 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
780 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
781 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
782 (1UL << TCP_MTU_REDUCED_DEFERRED))
784 * tcp_release_cb - tcp release_sock() callback
787 * called from release_sock() to perform protocol dependent
788 * actions before socket release.
790 void tcp_release_cb(struct sock *sk)
792 struct tcp_sock *tp = tcp_sk(sk);
793 unsigned long flags, nflags;
795 /* perform an atomic operation only if at least one flag is set */
797 flags = tp->tsq_flags;
798 if (!(flags & TCP_DEFERRED_ALL))
800 nflags = flags & ~TCP_DEFERRED_ALL;
801 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
803 if (flags & (1UL << TCP_TSQ_DEFERRED))
806 /* Here begins the tricky part :
807 * We are called from release_sock() with :
809 * 2) sk_lock.slock spinlock held
810 * 3) socket owned by us (sk->sk_lock.owned == 1)
812 * But following code is meant to be called from BH handlers,
813 * so we should keep BH disabled, but early release socket ownership
815 sock_release_ownership(sk);
817 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
818 tcp_write_timer_handler(sk);
821 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
822 tcp_delack_timer_handler(sk);
825 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
826 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
830 EXPORT_SYMBOL(tcp_release_cb);
832 void __init tcp_tasklet_init(void)
836 for_each_possible_cpu(i) {
837 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
839 INIT_LIST_HEAD(&tsq->head);
840 tasklet_init(&tsq->tasklet,
847 * Write buffer destructor automatically called from kfree_skb.
848 * We can't xmit new skbs from this context, as we might already
851 void tcp_wfree(struct sk_buff *skb)
853 struct sock *sk = skb->sk;
854 struct tcp_sock *tp = tcp_sk(sk);
857 /* Keep one reference on sk_wmem_alloc.
858 * Will be released by sk_free() from here or tcp_tasklet_func()
860 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
862 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
863 * Wait until our queues (qdisc + devices) are drained.
865 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
866 * - chance for incoming ACK (processed by another cpu maybe)
867 * to migrate this flow (skb->ooo_okay will be eventually set)
869 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
872 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
873 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
875 struct tsq_tasklet *tsq;
877 /* queue this socket to tasklet queue */
878 local_irq_save(flags);
879 tsq = this_cpu_ptr(&tsq_tasklet);
880 list_add(&tp->tsq_node, &tsq->head);
881 tasklet_schedule(&tsq->tasklet);
882 local_irq_restore(flags);
889 /* This routine actually transmits TCP packets queued in by
890 * tcp_do_sendmsg(). This is used by both the initial
891 * transmission and possible later retransmissions.
892 * All SKB's seen here are completely headerless. It is our
893 * job to build the TCP header, and pass the packet down to
894 * IP so it can do the same plus pass the packet off to the
897 * We are working here with either a clone of the original
898 * SKB, or a fresh unique copy made by the retransmit engine.
900 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
903 const struct inet_connection_sock *icsk = inet_csk(sk);
904 struct inet_sock *inet;
906 struct tcp_skb_cb *tcb;
907 struct tcp_out_options opts;
908 unsigned int tcp_options_size, tcp_header_size;
909 struct tcp_md5sig_key *md5;
913 BUG_ON(!skb || !tcp_skb_pcount(skb));
916 skb_mstamp_get(&skb->skb_mstamp);
918 if (unlikely(skb_cloned(skb)))
919 skb = pskb_copy(skb, gfp_mask);
921 skb = skb_clone(skb, gfp_mask);
928 tcb = TCP_SKB_CB(skb);
929 memset(&opts, 0, sizeof(opts));
931 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
932 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
934 tcp_options_size = tcp_established_options(sk, skb, &opts,
936 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
938 /* if no packet is in qdisc/device queue, then allow XPS to select
939 * another queue. We can be called from tcp_tsq_handler()
940 * which holds one reference to sk_wmem_alloc.
942 * TODO: Ideally, in-flight pure ACK packets should not matter here.
943 * One way to get this would be to set skb->truesize = 2 on them.
945 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
947 skb_push(skb, tcp_header_size);
948 skb_reset_transport_header(skb);
952 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
953 skb_set_hash_from_sk(skb, sk);
954 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
956 /* Build TCP header and checksum it. */
958 th->source = inet->inet_sport;
959 th->dest = inet->inet_dport;
960 th->seq = htonl(tcb->seq);
961 th->ack_seq = htonl(tp->rcv_nxt);
962 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
965 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
966 /* RFC1323: The window in SYN & SYN/ACK segments
969 th->window = htons(min(tp->rcv_wnd, 65535U));
971 th->window = htons(tcp_select_window(sk));
976 /* The urg_mode check is necessary during a below snd_una win probe */
977 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
978 if (before(tp->snd_up, tcb->seq + 0x10000)) {
979 th->urg_ptr = htons(tp->snd_up - tcb->seq);
981 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
982 th->urg_ptr = htons(0xFFFF);
987 tcp_options_write((__be32 *)(th + 1), tp, &opts);
988 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
989 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
990 tcp_ecn_send(sk, skb, tcp_header_size);
992 #ifdef CONFIG_TCP_MD5SIG
993 /* Calculate the MD5 hash, as we have all we need now */
995 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
996 tp->af_specific->calc_md5_hash(opts.hash_location,
1001 icsk->icsk_af_ops->send_check(sk, skb);
1003 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1004 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1006 if (skb->len != tcp_header_size) {
1007 tcp_event_data_sent(tp, sk);
1008 tp->data_segs_out += tcp_skb_pcount(skb);
1011 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1012 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1013 tcp_skb_pcount(skb));
1015 tp->segs_out += tcp_skb_pcount(skb);
1016 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1017 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1018 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1020 /* Our usage of tstamp should remain private */
1021 skb->tstamp.tv64 = 0;
1023 /* Cleanup our debris for IP stacks */
1024 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1025 sizeof(struct inet6_skb_parm)));
1027 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1029 if (likely(err <= 0))
1034 return net_xmit_eval(err);
1037 /* This routine just queues the buffer for sending.
1039 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1040 * otherwise socket can stall.
1042 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1044 struct tcp_sock *tp = tcp_sk(sk);
1046 /* Advance write_seq and place onto the write_queue. */
1047 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1048 __skb_header_release(skb);
1049 tcp_add_write_queue_tail(sk, skb);
1050 sk->sk_wmem_queued += skb->truesize;
1051 sk_mem_charge(sk, skb->truesize);
1054 /* Initialize TSO segments for a packet. */
1055 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1057 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1058 /* Avoid the costly divide in the normal
1061 tcp_skb_pcount_set(skb, 1);
1062 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1064 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1065 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1069 /* When a modification to fackets out becomes necessary, we need to check
1070 * skb is counted to fackets_out or not.
1072 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1075 struct tcp_sock *tp = tcp_sk(sk);
1077 if (!tp->sacked_out || tcp_is_reno(tp))
1080 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1081 tp->fackets_out -= decr;
1084 /* Pcount in the middle of the write queue got changed, we need to do various
1085 * tweaks to fix counters
1087 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1089 struct tcp_sock *tp = tcp_sk(sk);
1091 tp->packets_out -= decr;
1093 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1094 tp->sacked_out -= decr;
1095 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1096 tp->retrans_out -= decr;
1097 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1098 tp->lost_out -= decr;
1100 /* Reno case is special. Sigh... */
1101 if (tcp_is_reno(tp) && decr > 0)
1102 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1104 tcp_adjust_fackets_out(sk, skb, decr);
1106 if (tp->lost_skb_hint &&
1107 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1108 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1109 tp->lost_cnt_hint -= decr;
1111 tcp_verify_left_out(tp);
1114 static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
1116 return TCP_SKB_CB(skb)->txstamp_ack ||
1117 (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
1120 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1122 struct skb_shared_info *shinfo = skb_shinfo(skb);
1124 if (unlikely(tcp_has_tx_tstamp(skb)) &&
1125 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1126 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1127 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1129 shinfo->tx_flags &= ~tsflags;
1130 shinfo2->tx_flags |= tsflags;
1131 swap(shinfo->tskey, shinfo2->tskey);
1132 TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
1133 TCP_SKB_CB(skb)->txstamp_ack = 0;
1137 /* Function to create two new TCP segments. Shrinks the given segment
1138 * to the specified size and appends a new segment with the rest of the
1139 * packet to the list. This won't be called frequently, I hope.
1140 * Remember, these are still headerless SKBs at this point.
1142 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1143 unsigned int mss_now, gfp_t gfp)
1145 struct tcp_sock *tp = tcp_sk(sk);
1146 struct sk_buff *buff;
1147 int nsize, old_factor;
1151 if (WARN_ON(len > skb->len))
1154 nsize = skb_headlen(skb) - len;
1158 if (skb_unclone(skb, gfp))
1161 /* Get a new skb... force flag on. */
1162 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1164 return -ENOMEM; /* We'll just try again later. */
1166 sk->sk_wmem_queued += buff->truesize;
1167 sk_mem_charge(sk, buff->truesize);
1168 nlen = skb->len - len - nsize;
1169 buff->truesize += nlen;
1170 skb->truesize -= nlen;
1172 /* Correct the sequence numbers. */
1173 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1174 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1175 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1177 /* PSH and FIN should only be set in the second packet. */
1178 flags = TCP_SKB_CB(skb)->tcp_flags;
1179 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1180 TCP_SKB_CB(buff)->tcp_flags = flags;
1181 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1183 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1184 /* Copy and checksum data tail into the new buffer. */
1185 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1186 skb_put(buff, nsize),
1191 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1193 skb->ip_summed = CHECKSUM_PARTIAL;
1194 skb_split(skb, buff, len);
1197 buff->ip_summed = skb->ip_summed;
1199 buff->tstamp = skb->tstamp;
1200 tcp_fragment_tstamp(skb, buff);
1202 old_factor = tcp_skb_pcount(skb);
1204 /* Fix up tso_factor for both original and new SKB. */
1205 tcp_set_skb_tso_segs(skb, mss_now);
1206 tcp_set_skb_tso_segs(buff, mss_now);
1208 /* If this packet has been sent out already, we must
1209 * adjust the various packet counters.
1211 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1212 int diff = old_factor - tcp_skb_pcount(skb) -
1213 tcp_skb_pcount(buff);
1216 tcp_adjust_pcount(sk, skb, diff);
1219 /* Link BUFF into the send queue. */
1220 __skb_header_release(buff);
1221 tcp_insert_write_queue_after(skb, buff, sk);
1226 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1227 * eventually). The difference is that pulled data not copied, but
1228 * immediately discarded.
1230 static void __pskb_trim_head(struct sk_buff *skb, int len)
1232 struct skb_shared_info *shinfo;
1235 eat = min_t(int, len, skb_headlen(skb));
1237 __skb_pull(skb, eat);
1244 shinfo = skb_shinfo(skb);
1245 for (i = 0; i < shinfo->nr_frags; i++) {
1246 int size = skb_frag_size(&shinfo->frags[i]);
1249 skb_frag_unref(skb, i);
1252 shinfo->frags[k] = shinfo->frags[i];
1254 shinfo->frags[k].page_offset += eat;
1255 skb_frag_size_sub(&shinfo->frags[k], eat);
1261 shinfo->nr_frags = k;
1263 skb_reset_tail_pointer(skb);
1264 skb->data_len -= len;
1265 skb->len = skb->data_len;
1268 /* Remove acked data from a packet in the transmit queue. */
1269 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1271 if (skb_unclone(skb, GFP_ATOMIC))
1274 __pskb_trim_head(skb, len);
1276 TCP_SKB_CB(skb)->seq += len;
1277 skb->ip_summed = CHECKSUM_PARTIAL;
1279 skb->truesize -= len;
1280 sk->sk_wmem_queued -= len;
1281 sk_mem_uncharge(sk, len);
1282 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1284 /* Any change of skb->len requires recalculation of tso factor. */
1285 if (tcp_skb_pcount(skb) > 1)
1286 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1291 /* Calculate MSS not accounting any TCP options. */
1292 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1294 const struct tcp_sock *tp = tcp_sk(sk);
1295 const struct inet_connection_sock *icsk = inet_csk(sk);
1298 /* Calculate base mss without TCP options:
1299 It is MMS_S - sizeof(tcphdr) of rfc1122
1301 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1303 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1304 if (icsk->icsk_af_ops->net_frag_header_len) {
1305 const struct dst_entry *dst = __sk_dst_get(sk);
1307 if (dst && dst_allfrag(dst))
1308 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1311 /* Clamp it (mss_clamp does not include tcp options) */
1312 if (mss_now > tp->rx_opt.mss_clamp)
1313 mss_now = tp->rx_opt.mss_clamp;
1315 /* Now subtract optional transport overhead */
1316 mss_now -= icsk->icsk_ext_hdr_len;
1318 /* Then reserve room for full set of TCP options and 8 bytes of data */
1324 /* Calculate MSS. Not accounting for SACKs here. */
1325 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1327 /* Subtract TCP options size, not including SACKs */
1328 return __tcp_mtu_to_mss(sk, pmtu) -
1329 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1332 /* Inverse of above */
1333 int tcp_mss_to_mtu(struct sock *sk, int mss)
1335 const struct tcp_sock *tp = tcp_sk(sk);
1336 const struct inet_connection_sock *icsk = inet_csk(sk);
1340 tp->tcp_header_len +
1341 icsk->icsk_ext_hdr_len +
1342 icsk->icsk_af_ops->net_header_len;
1344 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1345 if (icsk->icsk_af_ops->net_frag_header_len) {
1346 const struct dst_entry *dst = __sk_dst_get(sk);
1348 if (dst && dst_allfrag(dst))
1349 mtu += icsk->icsk_af_ops->net_frag_header_len;
1354 /* MTU probing init per socket */
1355 void tcp_mtup_init(struct sock *sk)
1357 struct tcp_sock *tp = tcp_sk(sk);
1358 struct inet_connection_sock *icsk = inet_csk(sk);
1359 struct net *net = sock_net(sk);
1361 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1362 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1363 icsk->icsk_af_ops->net_header_len;
1364 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1365 icsk->icsk_mtup.probe_size = 0;
1366 if (icsk->icsk_mtup.enabled)
1367 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1369 EXPORT_SYMBOL(tcp_mtup_init);
1371 /* This function synchronize snd mss to current pmtu/exthdr set.
1373 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1374 for TCP options, but includes only bare TCP header.
1376 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1377 It is minimum of user_mss and mss received with SYN.
1378 It also does not include TCP options.
1380 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1382 tp->mss_cache is current effective sending mss, including
1383 all tcp options except for SACKs. It is evaluated,
1384 taking into account current pmtu, but never exceeds
1385 tp->rx_opt.mss_clamp.
1387 NOTE1. rfc1122 clearly states that advertised MSS
1388 DOES NOT include either tcp or ip options.
1390 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1391 are READ ONLY outside this function. --ANK (980731)
1393 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1395 struct tcp_sock *tp = tcp_sk(sk);
1396 struct inet_connection_sock *icsk = inet_csk(sk);
1399 if (icsk->icsk_mtup.search_high > pmtu)
1400 icsk->icsk_mtup.search_high = pmtu;
1402 mss_now = tcp_mtu_to_mss(sk, pmtu);
1403 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1405 /* And store cached results */
1406 icsk->icsk_pmtu_cookie = pmtu;
1407 if (icsk->icsk_mtup.enabled)
1408 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1409 tp->mss_cache = mss_now;
1413 EXPORT_SYMBOL(tcp_sync_mss);
1415 /* Compute the current effective MSS, taking SACKs and IP options,
1416 * and even PMTU discovery events into account.
1418 unsigned int tcp_current_mss(struct sock *sk)
1420 const struct tcp_sock *tp = tcp_sk(sk);
1421 const struct dst_entry *dst = __sk_dst_get(sk);
1423 unsigned int header_len;
1424 struct tcp_out_options opts;
1425 struct tcp_md5sig_key *md5;
1427 mss_now = tp->mss_cache;
1430 u32 mtu = dst_mtu(dst);
1431 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1432 mss_now = tcp_sync_mss(sk, mtu);
1435 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1436 sizeof(struct tcphdr);
1437 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1438 * some common options. If this is an odd packet (because we have SACK
1439 * blocks etc) then our calculated header_len will be different, and
1440 * we have to adjust mss_now correspondingly */
1441 if (header_len != tp->tcp_header_len) {
1442 int delta = (int) header_len - tp->tcp_header_len;
1449 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1450 * As additional protections, we do not touch cwnd in retransmission phases,
1451 * and if application hit its sndbuf limit recently.
1453 static void tcp_cwnd_application_limited(struct sock *sk)
1455 struct tcp_sock *tp = tcp_sk(sk);
1457 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1458 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1459 /* Limited by application or receiver window. */
1460 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1461 u32 win_used = max(tp->snd_cwnd_used, init_win);
1462 if (win_used < tp->snd_cwnd) {
1463 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1464 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1466 tp->snd_cwnd_used = 0;
1468 tp->snd_cwnd_stamp = tcp_time_stamp;
1471 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1473 struct tcp_sock *tp = tcp_sk(sk);
1475 /* Track the maximum number of outstanding packets in each
1476 * window, and remember whether we were cwnd-limited then.
1478 if (!before(tp->snd_una, tp->max_packets_seq) ||
1479 tp->packets_out > tp->max_packets_out) {
1480 tp->max_packets_out = tp->packets_out;
1481 tp->max_packets_seq = tp->snd_nxt;
1482 tp->is_cwnd_limited = is_cwnd_limited;
1485 if (tcp_is_cwnd_limited(sk)) {
1486 /* Network is feed fully. */
1487 tp->snd_cwnd_used = 0;
1488 tp->snd_cwnd_stamp = tcp_time_stamp;
1490 /* Network starves. */
1491 if (tp->packets_out > tp->snd_cwnd_used)
1492 tp->snd_cwnd_used = tp->packets_out;
1494 if (sysctl_tcp_slow_start_after_idle &&
1495 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1496 tcp_cwnd_application_limited(sk);
1500 /* Minshall's variant of the Nagle send check. */
1501 static bool tcp_minshall_check(const struct tcp_sock *tp)
1503 return after(tp->snd_sml, tp->snd_una) &&
1504 !after(tp->snd_sml, tp->snd_nxt);
1507 /* Update snd_sml if this skb is under mss
1508 * Note that a TSO packet might end with a sub-mss segment
1509 * The test is really :
1510 * if ((skb->len % mss) != 0)
1511 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1512 * But we can avoid doing the divide again given we already have
1513 * skb_pcount = skb->len / mss_now
1515 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1516 const struct sk_buff *skb)
1518 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1519 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1522 /* Return false, if packet can be sent now without violation Nagle's rules:
1523 * 1. It is full sized. (provided by caller in %partial bool)
1524 * 2. Or it contains FIN. (already checked by caller)
1525 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1526 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1527 * With Minshall's modification: all sent small packets are ACKed.
1529 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1533 ((nonagle & TCP_NAGLE_CORK) ||
1534 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1537 /* Return how many segs we'd like on a TSO packet,
1538 * to send one TSO packet per ms
1540 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1544 bytes = min(sk->sk_pacing_rate >> 10,
1545 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1547 /* Goal is to send at least one packet per ms,
1548 * not one big TSO packet every 100 ms.
1549 * This preserves ACK clocking and is consistent
1550 * with tcp_tso_should_defer() heuristic.
1552 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1554 return min_t(u32, segs, sk->sk_gso_max_segs);
1557 /* Returns the portion of skb which can be sent right away */
1558 static unsigned int tcp_mss_split_point(const struct sock *sk,
1559 const struct sk_buff *skb,
1560 unsigned int mss_now,
1561 unsigned int max_segs,
1564 const struct tcp_sock *tp = tcp_sk(sk);
1565 u32 partial, needed, window, max_len;
1567 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1568 max_len = mss_now * max_segs;
1570 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1573 needed = min(skb->len, window);
1575 if (max_len <= needed)
1578 partial = needed % mss_now;
1579 /* If last segment is not a full MSS, check if Nagle rules allow us
1580 * to include this last segment in this skb.
1581 * Otherwise, we'll split the skb at last MSS boundary
1583 if (tcp_nagle_check(partial != 0, tp, nonagle))
1584 return needed - partial;
1589 /* Can at least one segment of SKB be sent right now, according to the
1590 * congestion window rules? If so, return how many segments are allowed.
1592 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1593 const struct sk_buff *skb)
1595 u32 in_flight, cwnd, halfcwnd;
1597 /* Don't be strict about the congestion window for the final FIN. */
1598 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1599 tcp_skb_pcount(skb) == 1)
1602 in_flight = tcp_packets_in_flight(tp);
1603 cwnd = tp->snd_cwnd;
1604 if (in_flight >= cwnd)
1607 /* For better scheduling, ensure we have at least
1608 * 2 GSO packets in flight.
1610 halfcwnd = max(cwnd >> 1, 1U);
1611 return min(halfcwnd, cwnd - in_flight);
1614 /* Initialize TSO state of a skb.
1615 * This must be invoked the first time we consider transmitting
1616 * SKB onto the wire.
1618 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1620 int tso_segs = tcp_skb_pcount(skb);
1622 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1623 tcp_set_skb_tso_segs(skb, mss_now);
1624 tso_segs = tcp_skb_pcount(skb);
1630 /* Return true if the Nagle test allows this packet to be
1633 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1634 unsigned int cur_mss, int nonagle)
1636 /* Nagle rule does not apply to frames, which sit in the middle of the
1637 * write_queue (they have no chances to get new data).
1639 * This is implemented in the callers, where they modify the 'nonagle'
1640 * argument based upon the location of SKB in the send queue.
1642 if (nonagle & TCP_NAGLE_PUSH)
1645 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1646 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1649 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1655 /* Does at least the first segment of SKB fit into the send window? */
1656 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1657 const struct sk_buff *skb,
1658 unsigned int cur_mss)
1660 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1662 if (skb->len > cur_mss)
1663 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1665 return !after(end_seq, tcp_wnd_end(tp));
1668 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1669 * should be put on the wire right now. If so, it returns the number of
1670 * packets allowed by the congestion window.
1672 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1673 unsigned int cur_mss, int nonagle)
1675 const struct tcp_sock *tp = tcp_sk(sk);
1676 unsigned int cwnd_quota;
1678 tcp_init_tso_segs(skb, cur_mss);
1680 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1683 cwnd_quota = tcp_cwnd_test(tp, skb);
1684 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1690 /* Test if sending is allowed right now. */
1691 bool tcp_may_send_now(struct sock *sk)
1693 const struct tcp_sock *tp = tcp_sk(sk);
1694 struct sk_buff *skb = tcp_send_head(sk);
1697 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1698 (tcp_skb_is_last(sk, skb) ?
1699 tp->nonagle : TCP_NAGLE_PUSH));
1702 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1703 * which is put after SKB on the list. It is very much like
1704 * tcp_fragment() except that it may make several kinds of assumptions
1705 * in order to speed up the splitting operation. In particular, we
1706 * know that all the data is in scatter-gather pages, and that the
1707 * packet has never been sent out before (and thus is not cloned).
1709 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1710 unsigned int mss_now, gfp_t gfp)
1712 struct sk_buff *buff;
1713 int nlen = skb->len - len;
1716 /* All of a TSO frame must be composed of paged data. */
1717 if (skb->len != skb->data_len)
1718 return tcp_fragment(sk, skb, len, mss_now, gfp);
1720 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1721 if (unlikely(!buff))
1724 sk->sk_wmem_queued += buff->truesize;
1725 sk_mem_charge(sk, buff->truesize);
1726 buff->truesize += nlen;
1727 skb->truesize -= nlen;
1729 /* Correct the sequence numbers. */
1730 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1731 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1732 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1734 /* PSH and FIN should only be set in the second packet. */
1735 flags = TCP_SKB_CB(skb)->tcp_flags;
1736 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1737 TCP_SKB_CB(buff)->tcp_flags = flags;
1739 /* This packet was never sent out yet, so no SACK bits. */
1740 TCP_SKB_CB(buff)->sacked = 0;
1742 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1743 skb_split(skb, buff, len);
1744 tcp_fragment_tstamp(skb, buff);
1746 /* Fix up tso_factor for both original and new SKB. */
1747 tcp_set_skb_tso_segs(skb, mss_now);
1748 tcp_set_skb_tso_segs(buff, mss_now);
1750 /* Link BUFF into the send queue. */
1751 __skb_header_release(buff);
1752 tcp_insert_write_queue_after(skb, buff, sk);
1757 /* Try to defer sending, if possible, in order to minimize the amount
1758 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1760 * This algorithm is from John Heffner.
1762 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1763 bool *is_cwnd_limited, u32 max_segs)
1765 const struct inet_connection_sock *icsk = inet_csk(sk);
1766 u32 age, send_win, cong_win, limit, in_flight;
1767 struct tcp_sock *tp = tcp_sk(sk);
1768 struct skb_mstamp now;
1769 struct sk_buff *head;
1772 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1775 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1778 /* Avoid bursty behavior by allowing defer
1779 * only if the last write was recent.
1781 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1784 in_flight = tcp_packets_in_flight(tp);
1786 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1788 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1790 /* From in_flight test above, we know that cwnd > in_flight. */
1791 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1793 limit = min(send_win, cong_win);
1795 /* If a full-sized TSO skb can be sent, do it. */
1796 if (limit >= max_segs * tp->mss_cache)
1799 /* Middle in queue won't get any more data, full sendable already? */
1800 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1803 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1805 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1807 /* If at least some fraction of a window is available,
1810 chunk /= win_divisor;
1814 /* Different approach, try not to defer past a single
1815 * ACK. Receiver should ACK every other full sized
1816 * frame, so if we have space for more than 3 frames
1819 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1823 head = tcp_write_queue_head(sk);
1824 skb_mstamp_get(&now);
1825 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1826 /* If next ACK is likely to come too late (half srtt), do not defer */
1827 if (age < (tp->srtt_us >> 4))
1830 /* Ok, it looks like it is advisable to defer. */
1832 if (cong_win < send_win && cong_win <= skb->len)
1833 *is_cwnd_limited = true;
1841 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1843 struct inet_connection_sock *icsk = inet_csk(sk);
1844 struct tcp_sock *tp = tcp_sk(sk);
1845 struct net *net = sock_net(sk);
1849 interval = net->ipv4.sysctl_tcp_probe_interval;
1850 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1851 if (unlikely(delta >= interval * HZ)) {
1852 int mss = tcp_current_mss(sk);
1854 /* Update current search range */
1855 icsk->icsk_mtup.probe_size = 0;
1856 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1857 sizeof(struct tcphdr) +
1858 icsk->icsk_af_ops->net_header_len;
1859 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1861 /* Update probe time stamp */
1862 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1866 /* Create a new MTU probe if we are ready.
1867 * MTU probe is regularly attempting to increase the path MTU by
1868 * deliberately sending larger packets. This discovers routing
1869 * changes resulting in larger path MTUs.
1871 * Returns 0 if we should wait to probe (no cwnd available),
1872 * 1 if a probe was sent,
1875 static int tcp_mtu_probe(struct sock *sk)
1877 struct tcp_sock *tp = tcp_sk(sk);
1878 struct inet_connection_sock *icsk = inet_csk(sk);
1879 struct sk_buff *skb, *nskb, *next;
1880 struct net *net = sock_net(sk);
1888 /* Not currently probing/verifying,
1890 * have enough cwnd, and
1891 * not SACKing (the variable headers throw things off) */
1892 if (!icsk->icsk_mtup.enabled ||
1893 icsk->icsk_mtup.probe_size ||
1894 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1895 tp->snd_cwnd < 11 ||
1896 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1899 /* Use binary search for probe_size between tcp_mss_base,
1900 * and current mss_clamp. if (search_high - search_low)
1901 * smaller than a threshold, backoff from probing.
1903 mss_now = tcp_current_mss(sk);
1904 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1905 icsk->icsk_mtup.search_low) >> 1);
1906 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1907 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1908 /* When misfortune happens, we are reprobing actively,
1909 * and then reprobe timer has expired. We stick with current
1910 * probing process by not resetting search range to its orignal.
1912 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1913 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1914 /* Check whether enough time has elaplased for
1915 * another round of probing.
1917 tcp_mtu_check_reprobe(sk);
1921 /* Have enough data in the send queue to probe? */
1922 if (tp->write_seq - tp->snd_nxt < size_needed)
1925 if (tp->snd_wnd < size_needed)
1927 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1930 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1931 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1932 if (!tcp_packets_in_flight(tp))
1938 /* We're allowed to probe. Build it now. */
1939 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1942 sk->sk_wmem_queued += nskb->truesize;
1943 sk_mem_charge(sk, nskb->truesize);
1945 skb = tcp_send_head(sk);
1947 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1948 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1949 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1950 TCP_SKB_CB(nskb)->sacked = 0;
1952 nskb->ip_summed = skb->ip_summed;
1954 tcp_insert_write_queue_before(nskb, skb, sk);
1957 tcp_for_write_queue_from_safe(skb, next, sk) {
1958 copy = min_t(int, skb->len, probe_size - len);
1959 if (nskb->ip_summed)
1960 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1962 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1963 skb_put(nskb, copy),
1966 if (skb->len <= copy) {
1967 /* We've eaten all the data from this skb.
1969 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1970 tcp_unlink_write_queue(skb, sk);
1971 sk_wmem_free_skb(sk, skb);
1973 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1974 ~(TCPHDR_FIN|TCPHDR_PSH);
1975 if (!skb_shinfo(skb)->nr_frags) {
1976 skb_pull(skb, copy);
1977 if (skb->ip_summed != CHECKSUM_PARTIAL)
1978 skb->csum = csum_partial(skb->data,
1981 __pskb_trim_head(skb, copy);
1982 tcp_set_skb_tso_segs(skb, mss_now);
1984 TCP_SKB_CB(skb)->seq += copy;
1989 if (len >= probe_size)
1992 tcp_init_tso_segs(nskb, nskb->len);
1994 /* We're ready to send. If this fails, the probe will
1995 * be resegmented into mss-sized pieces by tcp_write_xmit().
1997 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1998 /* Decrement cwnd here because we are sending
1999 * effectively two packets. */
2001 tcp_event_new_data_sent(sk, nskb);
2003 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2004 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2005 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2013 /* This routine writes packets to the network. It advances the
2014 * send_head. This happens as incoming acks open up the remote
2017 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2018 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2019 * account rare use of URG, this is not a big flaw.
2021 * Send at most one packet when push_one > 0. Temporarily ignore
2022 * cwnd limit to force at most one packet out when push_one == 2.
2024 * Returns true, if no segments are in flight and we have queued segments,
2025 * but cannot send anything now because of SWS or another problem.
2027 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2028 int push_one, gfp_t gfp)
2030 struct tcp_sock *tp = tcp_sk(sk);
2031 struct sk_buff *skb;
2032 unsigned int tso_segs, sent_pkts;
2035 bool is_cwnd_limited = false;
2041 /* Do MTU probing. */
2042 result = tcp_mtu_probe(sk);
2045 } else if (result > 0) {
2050 max_segs = tcp_tso_autosize(sk, mss_now);
2051 while ((skb = tcp_send_head(sk))) {
2054 tso_segs = tcp_init_tso_segs(skb, mss_now);
2057 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2058 /* "skb_mstamp" is used as a start point for the retransmit timer */
2059 skb_mstamp_get(&skb->skb_mstamp);
2060 goto repair; /* Skip network transmission */
2063 cwnd_quota = tcp_cwnd_test(tp, skb);
2066 /* Force out a loss probe pkt. */
2072 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2075 if (tso_segs == 1) {
2076 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2077 (tcp_skb_is_last(sk, skb) ?
2078 nonagle : TCP_NAGLE_PUSH))))
2082 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2088 if (tso_segs > 1 && !tcp_urg_mode(tp))
2089 limit = tcp_mss_split_point(sk, skb, mss_now,
2095 if (skb->len > limit &&
2096 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2099 /* TCP Small Queues :
2100 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2102 * - better RTT estimation and ACK scheduling
2105 * Alas, some drivers / subsystems require a fair amount
2106 * of queued bytes to ensure line rate.
2107 * One example is wifi aggregation (802.11 AMPDU)
2109 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2110 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2112 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2113 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2114 /* It is possible TX completion already happened
2115 * before we set TSQ_THROTTLED, so we must
2116 * test again the condition.
2118 smp_mb__after_atomic();
2119 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2123 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2127 /* Advance the send_head. This one is sent out.
2128 * This call will increment packets_out.
2130 tcp_event_new_data_sent(sk, skb);
2132 tcp_minshall_update(tp, mss_now, skb);
2133 sent_pkts += tcp_skb_pcount(skb);
2139 if (likely(sent_pkts)) {
2140 if (tcp_in_cwnd_reduction(sk))
2141 tp->prr_out += sent_pkts;
2143 /* Send one loss probe per tail loss episode. */
2145 tcp_schedule_loss_probe(sk);
2146 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2147 tcp_cwnd_validate(sk, is_cwnd_limited);
2150 return !tp->packets_out && tcp_send_head(sk);
2153 bool tcp_schedule_loss_probe(struct sock *sk)
2155 struct inet_connection_sock *icsk = inet_csk(sk);
2156 struct tcp_sock *tp = tcp_sk(sk);
2157 u32 timeout, tlp_time_stamp, rto_time_stamp;
2158 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2160 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2162 /* No consecutive loss probes. */
2163 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2167 /* Don't do any loss probe on a Fast Open connection before 3WHS
2170 if (tp->fastopen_rsk)
2173 /* TLP is only scheduled when next timer event is RTO. */
2174 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2177 /* Schedule a loss probe in 2*RTT for SACK capable connections
2178 * in Open state, that are either limited by cwnd or application.
2180 if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
2181 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2184 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2188 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2189 * for delayed ack when there's one outstanding packet. If no RTT
2190 * sample is available then probe after TCP_TIMEOUT_INIT.
2192 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2193 if (tp->packets_out == 1)
2194 timeout = max_t(u32, timeout,
2195 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2196 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2198 /* If RTO is shorter, just schedule TLP in its place. */
2199 tlp_time_stamp = tcp_time_stamp + timeout;
2200 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2201 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2202 s32 delta = rto_time_stamp - tcp_time_stamp;
2207 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2212 /* Thanks to skb fast clones, we can detect if a prior transmit of
2213 * a packet is still in a qdisc or driver queue.
2214 * In this case, there is very little point doing a retransmit !
2215 * Note: This is called from BH context only.
2217 static bool skb_still_in_host_queue(const struct sock *sk,
2218 const struct sk_buff *skb)
2220 if (unlikely(skb_fclone_busy(sk, skb))) {
2221 __NET_INC_STATS(sock_net(sk),
2222 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2228 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2229 * retransmit the last segment.
2231 void tcp_send_loss_probe(struct sock *sk)
2233 struct tcp_sock *tp = tcp_sk(sk);
2234 struct sk_buff *skb;
2236 int mss = tcp_current_mss(sk);
2238 skb = tcp_send_head(sk);
2240 if (tcp_snd_wnd_test(tp, skb, mss)) {
2241 pcount = tp->packets_out;
2242 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2243 if (tp->packets_out > pcount)
2247 skb = tcp_write_queue_prev(sk, skb);
2249 skb = tcp_write_queue_tail(sk);
2252 /* At most one outstanding TLP retransmission. */
2253 if (tp->tlp_high_seq)
2256 /* Retransmit last segment. */
2260 if (skb_still_in_host_queue(sk, skb))
2263 pcount = tcp_skb_pcount(skb);
2264 if (WARN_ON(!pcount))
2267 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2268 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2271 skb = tcp_write_queue_next(sk, skb);
2274 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2277 if (__tcp_retransmit_skb(sk, skb, 1))
2280 /* Record snd_nxt for loss detection. */
2281 tp->tlp_high_seq = tp->snd_nxt;
2284 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2285 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2286 inet_csk(sk)->icsk_pending = 0;
2291 /* Push out any pending frames which were held back due to
2292 * TCP_CORK or attempt at coalescing tiny packets.
2293 * The socket must be locked by the caller.
2295 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2298 /* If we are closed, the bytes will have to remain here.
2299 * In time closedown will finish, we empty the write queue and
2300 * all will be happy.
2302 if (unlikely(sk->sk_state == TCP_CLOSE))
2305 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2306 sk_gfp_mask(sk, GFP_ATOMIC)))
2307 tcp_check_probe_timer(sk);
2310 /* Send _single_ skb sitting at the send head. This function requires
2311 * true push pending frames to setup probe timer etc.
2313 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2315 struct sk_buff *skb = tcp_send_head(sk);
2317 BUG_ON(!skb || skb->len < mss_now);
2319 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2322 /* This function returns the amount that we can raise the
2323 * usable window based on the following constraints
2325 * 1. The window can never be shrunk once it is offered (RFC 793)
2326 * 2. We limit memory per socket
2329 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2330 * RECV.NEXT + RCV.WIN fixed until:
2331 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2333 * i.e. don't raise the right edge of the window until you can raise
2334 * it at least MSS bytes.
2336 * Unfortunately, the recommended algorithm breaks header prediction,
2337 * since header prediction assumes th->window stays fixed.
2339 * Strictly speaking, keeping th->window fixed violates the receiver
2340 * side SWS prevention criteria. The problem is that under this rule
2341 * a stream of single byte packets will cause the right side of the
2342 * window to always advance by a single byte.
2344 * Of course, if the sender implements sender side SWS prevention
2345 * then this will not be a problem.
2347 * BSD seems to make the following compromise:
2349 * If the free space is less than the 1/4 of the maximum
2350 * space available and the free space is less than 1/2 mss,
2351 * then set the window to 0.
2352 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2353 * Otherwise, just prevent the window from shrinking
2354 * and from being larger than the largest representable value.
2356 * This prevents incremental opening of the window in the regime
2357 * where TCP is limited by the speed of the reader side taking
2358 * data out of the TCP receive queue. It does nothing about
2359 * those cases where the window is constrained on the sender side
2360 * because the pipeline is full.
2362 * BSD also seems to "accidentally" limit itself to windows that are a
2363 * multiple of MSS, at least until the free space gets quite small.
2364 * This would appear to be a side effect of the mbuf implementation.
2365 * Combining these two algorithms results in the observed behavior
2366 * of having a fixed window size at almost all times.
2368 * Below we obtain similar behavior by forcing the offered window to
2369 * a multiple of the mss when it is feasible to do so.
2371 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2372 * Regular options like TIMESTAMP are taken into account.
2374 u32 __tcp_select_window(struct sock *sk)
2376 struct inet_connection_sock *icsk = inet_csk(sk);
2377 struct tcp_sock *tp = tcp_sk(sk);
2378 /* MSS for the peer's data. Previous versions used mss_clamp
2379 * here. I don't know if the value based on our guesses
2380 * of peer's MSS is better for the performance. It's more correct
2381 * but may be worse for the performance because of rcv_mss
2382 * fluctuations. --SAW 1998/11/1
2384 int mss = icsk->icsk_ack.rcv_mss;
2385 int free_space = tcp_space(sk);
2386 int allowed_space = tcp_full_space(sk);
2387 int full_space = min_t(int, tp->window_clamp, allowed_space);
2390 if (mss > full_space)
2393 if (free_space < (full_space >> 1)) {
2394 icsk->icsk_ack.quick = 0;
2396 if (tcp_under_memory_pressure(sk))
2397 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2400 /* free_space might become our new window, make sure we don't
2401 * increase it due to wscale.
2403 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2405 /* if free space is less than mss estimate, or is below 1/16th
2406 * of the maximum allowed, try to move to zero-window, else
2407 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2408 * new incoming data is dropped due to memory limits.
2409 * With large window, mss test triggers way too late in order
2410 * to announce zero window in time before rmem limit kicks in.
2412 if (free_space < (allowed_space >> 4) || free_space < mss)
2416 if (free_space > tp->rcv_ssthresh)
2417 free_space = tp->rcv_ssthresh;
2419 /* Don't do rounding if we are using window scaling, since the
2420 * scaled window will not line up with the MSS boundary anyway.
2422 window = tp->rcv_wnd;
2423 if (tp->rx_opt.rcv_wscale) {
2424 window = free_space;
2426 /* Advertise enough space so that it won't get scaled away.
2427 * Import case: prevent zero window announcement if
2428 * 1<<rcv_wscale > mss.
2430 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2431 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2432 << tp->rx_opt.rcv_wscale);
2434 /* Get the largest window that is a nice multiple of mss.
2435 * Window clamp already applied above.
2436 * If our current window offering is within 1 mss of the
2437 * free space we just keep it. This prevents the divide
2438 * and multiply from happening most of the time.
2439 * We also don't do any window rounding when the free space
2442 if (window <= free_space - mss || window > free_space)
2443 window = (free_space / mss) * mss;
2444 else if (mss == full_space &&
2445 free_space > window + (full_space >> 1))
2446 window = free_space;
2452 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
2453 const struct sk_buff *next_skb)
2455 if (unlikely(tcp_has_tx_tstamp(next_skb))) {
2456 const struct skb_shared_info *next_shinfo =
2457 skb_shinfo(next_skb);
2458 struct skb_shared_info *shinfo = skb_shinfo(skb);
2460 shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2461 shinfo->tskey = next_shinfo->tskey;
2462 TCP_SKB_CB(skb)->txstamp_ack |=
2463 TCP_SKB_CB(next_skb)->txstamp_ack;
2467 /* Collapses two adjacent SKB's during retransmission. */
2468 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2470 struct tcp_sock *tp = tcp_sk(sk);
2471 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2472 int skb_size, next_skb_size;
2474 skb_size = skb->len;
2475 next_skb_size = next_skb->len;
2477 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2479 tcp_highest_sack_combine(sk, next_skb, skb);
2481 tcp_unlink_write_queue(next_skb, sk);
2483 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2486 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2487 skb->ip_summed = CHECKSUM_PARTIAL;
2489 if (skb->ip_summed != CHECKSUM_PARTIAL)
2490 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2492 /* Update sequence range on original skb. */
2493 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2495 /* Merge over control information. This moves PSH/FIN etc. over */
2496 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2498 /* All done, get rid of second SKB and account for it so
2499 * packet counting does not break.
2501 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2502 TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2504 /* changed transmit queue under us so clear hints */
2505 tcp_clear_retrans_hints_partial(tp);
2506 if (next_skb == tp->retransmit_skb_hint)
2507 tp->retransmit_skb_hint = skb;
2509 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2511 tcp_skb_collapse_tstamp(skb, next_skb);
2513 sk_wmem_free_skb(sk, next_skb);
2516 /* Check if coalescing SKBs is legal. */
2517 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2519 if (tcp_skb_pcount(skb) > 1)
2521 /* TODO: SACK collapsing could be used to remove this condition */
2522 if (skb_shinfo(skb)->nr_frags != 0)
2524 if (skb_cloned(skb))
2526 if (skb == tcp_send_head(sk))
2528 /* Some heurestics for collapsing over SACK'd could be invented */
2529 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2535 /* Collapse packets in the retransmit queue to make to create
2536 * less packets on the wire. This is only done on retransmission.
2538 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2541 struct tcp_sock *tp = tcp_sk(sk);
2542 struct sk_buff *skb = to, *tmp;
2545 if (!sysctl_tcp_retrans_collapse)
2547 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2550 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2551 if (!tcp_can_collapse(sk, skb))
2554 if (!tcp_skb_can_collapse_to(to))
2566 /* Punt if not enough space exists in the first SKB for
2567 * the data in the second
2569 if (skb->len > skb_availroom(to))
2572 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2575 tcp_collapse_retrans(sk, to);
2579 /* This retransmits one SKB. Policy decisions and retransmit queue
2580 * state updates are done by the caller. Returns non-zero if an
2581 * error occurred which prevented the send.
2583 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2585 struct inet_connection_sock *icsk = inet_csk(sk);
2586 struct tcp_sock *tp = tcp_sk(sk);
2587 unsigned int cur_mss;
2591 /* Inconclusive MTU probe */
2592 if (icsk->icsk_mtup.probe_size)
2593 icsk->icsk_mtup.probe_size = 0;
2595 /* Do not sent more than we queued. 1/4 is reserved for possible
2596 * copying overhead: fragmentation, tunneling, mangling etc.
2598 if (atomic_read(&sk->sk_wmem_alloc) >
2599 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2602 if (skb_still_in_host_queue(sk, skb))
2605 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2606 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2608 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2612 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2613 return -EHOSTUNREACH; /* Routing failure or similar. */
2615 cur_mss = tcp_current_mss(sk);
2617 /* If receiver has shrunk his window, and skb is out of
2618 * new window, do not retransmit it. The exception is the
2619 * case, when window is shrunk to zero. In this case
2620 * our retransmit serves as a zero window probe.
2622 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2623 TCP_SKB_CB(skb)->seq != tp->snd_una)
2626 len = cur_mss * segs;
2627 if (skb->len > len) {
2628 if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
2629 return -ENOMEM; /* We'll try again later. */
2631 if (skb_unclone(skb, GFP_ATOMIC))
2634 diff = tcp_skb_pcount(skb);
2635 tcp_set_skb_tso_segs(skb, cur_mss);
2636 diff -= tcp_skb_pcount(skb);
2638 tcp_adjust_pcount(sk, skb, diff);
2639 if (skb->len < cur_mss)
2640 tcp_retrans_try_collapse(sk, skb, cur_mss);
2643 /* RFC3168, section 6.1.1.1. ECN fallback */
2644 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2645 tcp_ecn_clear_syn(sk, skb);
2647 /* make sure skb->data is aligned on arches that require it
2648 * and check if ack-trimming & collapsing extended the headroom
2649 * beyond what csum_start can cover.
2651 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2652 skb_headroom(skb) >= 0xFFFF)) {
2653 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2655 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2658 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2662 segs = tcp_skb_pcount(skb);
2664 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2665 /* Update global TCP statistics. */
2666 TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2667 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2668 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2669 tp->total_retrans += segs;
2674 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2676 struct tcp_sock *tp = tcp_sk(sk);
2677 int err = __tcp_retransmit_skb(sk, skb, segs);
2680 #if FASTRETRANS_DEBUG > 0
2681 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2682 net_dbg_ratelimited("retrans_out leaked\n");
2685 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2686 tp->retrans_out += tcp_skb_pcount(skb);
2688 /* Save stamp of the first retransmit. */
2689 if (!tp->retrans_stamp)
2690 tp->retrans_stamp = tcp_skb_timestamp(skb);
2692 } else if (err != -EBUSY) {
2693 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2696 if (tp->undo_retrans < 0)
2697 tp->undo_retrans = 0;
2698 tp->undo_retrans += tcp_skb_pcount(skb);
2702 /* Check if we forward retransmits are possible in the current
2703 * window/congestion state.
2705 static bool tcp_can_forward_retransmit(struct sock *sk)
2707 const struct inet_connection_sock *icsk = inet_csk(sk);
2708 const struct tcp_sock *tp = tcp_sk(sk);
2710 /* Forward retransmissions are possible only during Recovery. */
2711 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2714 /* No forward retransmissions in Reno are possible. */
2715 if (tcp_is_reno(tp))
2718 /* Yeah, we have to make difficult choice between forward transmission
2719 * and retransmission... Both ways have their merits...
2721 * For now we do not retransmit anything, while we have some new
2722 * segments to send. In the other cases, follow rule 3 for
2723 * NextSeg() specified in RFC3517.
2726 if (tcp_may_send_now(sk))
2732 /* This gets called after a retransmit timeout, and the initially
2733 * retransmitted data is acknowledged. It tries to continue
2734 * resending the rest of the retransmit queue, until either
2735 * we've sent it all or the congestion window limit is reached.
2736 * If doing SACK, the first ACK which comes back for a timeout
2737 * based retransmit packet might feed us FACK information again.
2738 * If so, we use it to avoid unnecessarily retransmissions.
2740 void tcp_xmit_retransmit_queue(struct sock *sk)
2742 const struct inet_connection_sock *icsk = inet_csk(sk);
2743 struct tcp_sock *tp = tcp_sk(sk);
2744 struct sk_buff *skb;
2745 struct sk_buff *hole = NULL;
2748 int fwd_rexmitting = 0;
2750 if (!tp->packets_out)
2754 tp->retransmit_high = tp->snd_una;
2756 if (tp->retransmit_skb_hint) {
2757 skb = tp->retransmit_skb_hint;
2758 last_lost = TCP_SKB_CB(skb)->end_seq;
2759 if (after(last_lost, tp->retransmit_high))
2760 last_lost = tp->retransmit_high;
2762 skb = tcp_write_queue_head(sk);
2763 last_lost = tp->snd_una;
2766 tcp_for_write_queue_from(skb, sk) {
2767 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2770 if (skb == tcp_send_head(sk))
2772 /* we could do better than to assign each time */
2774 tp->retransmit_skb_hint = skb;
2776 segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
2780 if (fwd_rexmitting) {
2782 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2784 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2786 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2787 tp->retransmit_high = last_lost;
2788 if (!tcp_can_forward_retransmit(sk))
2790 /* Backtrack if necessary to non-L'ed skb */
2798 } else if (!(sacked & TCPCB_LOST)) {
2799 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2804 last_lost = TCP_SKB_CB(skb)->end_seq;
2805 if (icsk->icsk_ca_state != TCP_CA_Loss)
2806 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2808 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2811 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2814 if (tcp_retransmit_skb(sk, skb, segs))
2817 __NET_INC_STATS(sock_net(sk), mib_idx);
2819 if (tcp_in_cwnd_reduction(sk))
2820 tp->prr_out += tcp_skb_pcount(skb);
2822 if (skb == tcp_write_queue_head(sk))
2823 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2824 inet_csk(sk)->icsk_rto,
2829 /* We allow to exceed memory limits for FIN packets to expedite
2830 * connection tear down and (memory) recovery.
2831 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2832 * or even be forced to close flow without any FIN.
2833 * In general, we want to allow one skb per socket to avoid hangs
2834 * with edge trigger epoll()
2836 void sk_forced_mem_schedule(struct sock *sk, int size)
2840 if (size <= sk->sk_forward_alloc)
2842 amt = sk_mem_pages(size);
2843 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2844 sk_memory_allocated_add(sk, amt);
2846 if (mem_cgroup_sockets_enabled && sk->sk_memcg)
2847 mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2850 /* Send a FIN. The caller locks the socket for us.
2851 * We should try to send a FIN packet really hard, but eventually give up.
2853 void tcp_send_fin(struct sock *sk)
2855 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2856 struct tcp_sock *tp = tcp_sk(sk);
2858 /* Optimization, tack on the FIN if we have one skb in write queue and
2859 * this skb was not yet sent, or we are under memory pressure.
2860 * Note: in the latter case, FIN packet will be sent after a timeout,
2861 * as TCP stack thinks it has already been transmitted.
2863 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2865 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
2866 TCP_SKB_CB(tskb)->end_seq++;
2868 if (!tcp_send_head(sk)) {
2869 /* This means tskb was already sent.
2870 * Pretend we included the FIN on previous transmit.
2871 * We need to set tp->snd_nxt to the value it would have
2872 * if FIN had been sent. This is because retransmit path
2873 * does not change tp->snd_nxt.
2879 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
2880 if (unlikely(!skb)) {
2885 skb_reserve(skb, MAX_TCP_HEADER);
2886 sk_forced_mem_schedule(sk, skb->truesize);
2887 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2888 tcp_init_nondata_skb(skb, tp->write_seq,
2889 TCPHDR_ACK | TCPHDR_FIN);
2890 tcp_queue_skb(sk, skb);
2892 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
2895 /* We get here when a process closes a file descriptor (either due to
2896 * an explicit close() or as a byproduct of exit()'ing) and there
2897 * was unread data in the receive queue. This behavior is recommended
2898 * by RFC 2525, section 2.17. -DaveM
2900 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2902 struct sk_buff *skb;
2904 /* NOTE: No TCP options attached and we never retransmit this. */
2905 skb = alloc_skb(MAX_TCP_HEADER, priority);
2907 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2911 /* Reserve space for headers and prepare control bits. */
2912 skb_reserve(skb, MAX_TCP_HEADER);
2913 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2914 TCPHDR_ACK | TCPHDR_RST);
2915 skb_mstamp_get(&skb->skb_mstamp);
2917 if (tcp_transmit_skb(sk, skb, 0, priority))
2918 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2920 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2923 /* Send a crossed SYN-ACK during socket establishment.
2924 * WARNING: This routine must only be called when we have already sent
2925 * a SYN packet that crossed the incoming SYN that caused this routine
2926 * to get called. If this assumption fails then the initial rcv_wnd
2927 * and rcv_wscale values will not be correct.
2929 int tcp_send_synack(struct sock *sk)
2931 struct sk_buff *skb;
2933 skb = tcp_write_queue_head(sk);
2934 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2935 pr_debug("%s: wrong queue state\n", __func__);
2938 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2939 if (skb_cloned(skb)) {
2940 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2943 tcp_unlink_write_queue(skb, sk);
2944 __skb_header_release(nskb);
2945 __tcp_add_write_queue_head(sk, nskb);
2946 sk_wmem_free_skb(sk, skb);
2947 sk->sk_wmem_queued += nskb->truesize;
2948 sk_mem_charge(sk, nskb->truesize);
2952 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2953 tcp_ecn_send_synack(sk, skb);
2955 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2959 * tcp_make_synack - Prepare a SYN-ACK.
2960 * sk: listener socket
2961 * dst: dst entry attached to the SYNACK
2962 * req: request_sock pointer
2964 * Allocate one skb and build a SYNACK packet.
2965 * @dst is consumed : Caller should not use it again.
2967 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
2968 struct request_sock *req,
2969 struct tcp_fastopen_cookie *foc,
2970 enum tcp_synack_type synack_type)
2972 struct inet_request_sock *ireq = inet_rsk(req);
2973 const struct tcp_sock *tp = tcp_sk(sk);
2974 struct tcp_md5sig_key *md5 = NULL;
2975 struct tcp_out_options opts;
2976 struct sk_buff *skb;
2977 int tcp_header_size;
2982 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2983 if (unlikely(!skb)) {
2987 /* Reserve space for headers. */
2988 skb_reserve(skb, MAX_TCP_HEADER);
2990 switch (synack_type) {
2991 case TCP_SYNACK_NORMAL:
2992 skb_set_owner_w(skb, req_to_sk(req));
2994 case TCP_SYNACK_COOKIE:
2995 /* Under synflood, we do not attach skb to a socket,
2996 * to avoid false sharing.
2999 case TCP_SYNACK_FASTOPEN:
3000 /* sk is a const pointer, because we want to express multiple
3001 * cpu might call us concurrently.
3002 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3004 skb_set_owner_w(skb, (struct sock *)sk);
3007 skb_dst_set(skb, dst);
3009 mss = dst_metric_advmss(dst);
3010 user_mss = READ_ONCE(tp->rx_opt.user_mss);
3011 if (user_mss && user_mss < mss)
3014 memset(&opts, 0, sizeof(opts));
3015 #ifdef CONFIG_SYN_COOKIES
3016 if (unlikely(req->cookie_ts))
3017 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3020 skb_mstamp_get(&skb->skb_mstamp);
3022 #ifdef CONFIG_TCP_MD5SIG
3024 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3026 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3027 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3030 skb_push(skb, tcp_header_size);
3031 skb_reset_transport_header(skb);
3034 memset(th, 0, sizeof(struct tcphdr));
3037 tcp_ecn_make_synack(req, th);
3038 th->source = htons(ireq->ir_num);
3039 th->dest = ireq->ir_rmt_port;
3040 /* Setting of flags are superfluous here for callers (and ECE is
3041 * not even correctly set)
3043 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3044 TCPHDR_SYN | TCPHDR_ACK);
3046 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3047 /* XXX data is queued and acked as is. No buffer/window check */
3048 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3050 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3051 th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3052 tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3053 th->doff = (tcp_header_size >> 2);
3054 __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3056 #ifdef CONFIG_TCP_MD5SIG
3057 /* Okay, we have all we need - do the md5 hash if needed */
3059 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3060 md5, req_to_sk(req), skb);
3064 /* Do not fool tcpdump (if any), clean our debris */
3065 skb->tstamp.tv64 = 0;
3068 EXPORT_SYMBOL(tcp_make_synack);
3070 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3072 struct inet_connection_sock *icsk = inet_csk(sk);
3073 const struct tcp_congestion_ops *ca;
3074 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3076 if (ca_key == TCP_CA_UNSPEC)
3080 ca = tcp_ca_find_key(ca_key);
3081 if (likely(ca && try_module_get(ca->owner))) {
3082 module_put(icsk->icsk_ca_ops->owner);
3083 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3084 icsk->icsk_ca_ops = ca;
3089 /* Do all connect socket setups that can be done AF independent. */
3090 static void tcp_connect_init(struct sock *sk)
3092 const struct dst_entry *dst = __sk_dst_get(sk);
3093 struct tcp_sock *tp = tcp_sk(sk);
3096 /* We'll fix this up when we get a response from the other end.
3097 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3099 tp->tcp_header_len = sizeof(struct tcphdr) +
3100 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3102 #ifdef CONFIG_TCP_MD5SIG
3103 if (tp->af_specific->md5_lookup(sk, sk))
3104 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3107 /* If user gave his TCP_MAXSEG, record it to clamp */
3108 if (tp->rx_opt.user_mss)
3109 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3112 tcp_sync_mss(sk, dst_mtu(dst));
3114 tcp_ca_dst_init(sk, dst);
3116 if (!tp->window_clamp)
3117 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3118 tp->advmss = dst_metric_advmss(dst);
3119 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3120 tp->advmss = tp->rx_opt.user_mss;
3122 tcp_initialize_rcv_mss(sk);
3124 /* limit the window selection if the user enforce a smaller rx buffer */
3125 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3126 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3127 tp->window_clamp = tcp_full_space(sk);
3129 tcp_select_initial_window(tcp_full_space(sk),
3130 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3133 sysctl_tcp_window_scaling,
3135 dst_metric(dst, RTAX_INITRWND));
3137 tp->rx_opt.rcv_wscale = rcv_wscale;
3138 tp->rcv_ssthresh = tp->rcv_wnd;
3141 sock_reset_flag(sk, SOCK_DONE);
3144 tp->snd_una = tp->write_seq;
3145 tp->snd_sml = tp->write_seq;
3146 tp->snd_up = tp->write_seq;
3147 tp->snd_nxt = tp->write_seq;
3149 if (likely(!tp->repair))
3152 tp->rcv_tstamp = tcp_time_stamp;
3153 tp->rcv_wup = tp->rcv_nxt;
3154 tp->copied_seq = tp->rcv_nxt;
3156 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3157 inet_csk(sk)->icsk_retransmits = 0;
3158 tcp_clear_retrans(tp);
3161 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3163 struct tcp_sock *tp = tcp_sk(sk);
3164 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3166 tcb->end_seq += skb->len;
3167 __skb_header_release(skb);
3168 __tcp_add_write_queue_tail(sk, skb);
3169 sk->sk_wmem_queued += skb->truesize;
3170 sk_mem_charge(sk, skb->truesize);
3171 tp->write_seq = tcb->end_seq;
3172 tp->packets_out += tcp_skb_pcount(skb);
3175 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3176 * queue a data-only packet after the regular SYN, such that regular SYNs
3177 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3178 * only the SYN sequence, the data are retransmitted in the first ACK.
3179 * If cookie is not cached or other error occurs, falls back to send a
3180 * regular SYN with Fast Open cookie request option.
3182 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3184 struct tcp_sock *tp = tcp_sk(sk);
3185 struct tcp_fastopen_request *fo = tp->fastopen_req;
3186 int syn_loss = 0, space, err = 0;
3187 unsigned long last_syn_loss = 0;
3188 struct sk_buff *syn_data;
3190 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3191 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3192 &syn_loss, &last_syn_loss);
3193 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3195 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3196 fo->cookie.len = -1;
3200 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3201 fo->cookie.len = -1;
3202 else if (fo->cookie.len <= 0)
3205 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3206 * user-MSS. Reserve maximum option space for middleboxes that add
3207 * private TCP options. The cost is reduced data space in SYN :(
3209 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3210 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3211 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3212 MAX_TCP_OPTION_SPACE;
3214 space = min_t(size_t, space, fo->size);
3216 /* limit to order-0 allocations */
3217 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3219 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3222 syn_data->ip_summed = CHECKSUM_PARTIAL;
3223 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3225 int copied = copy_from_iter(skb_put(syn_data, space), space,
3226 &fo->data->msg_iter);
3227 if (unlikely(!copied)) {
3228 kfree_skb(syn_data);
3231 if (copied != space) {
3232 skb_trim(syn_data, copied);
3236 /* No more data pending in inet_wait_for_connect() */
3237 if (space == fo->size)
3241 tcp_connect_queue_skb(sk, syn_data);
3243 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3245 syn->skb_mstamp = syn_data->skb_mstamp;
3247 /* Now full SYN+DATA was cloned and sent (or not),
3248 * remove the SYN from the original skb (syn_data)
3249 * we keep in write queue in case of a retransmit, as we
3250 * also have the SYN packet (with no data) in the same queue.
3252 TCP_SKB_CB(syn_data)->seq++;
3253 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3255 tp->syn_data = (fo->copied > 0);
3256 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3261 /* Send a regular SYN with Fast Open cookie request option */
3262 if (fo->cookie.len > 0)
3264 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3266 tp->syn_fastopen = 0;
3268 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3272 /* Build a SYN and send it off. */
3273 int tcp_connect(struct sock *sk)
3275 struct tcp_sock *tp = tcp_sk(sk);
3276 struct sk_buff *buff;
3279 tcp_connect_init(sk);
3281 if (unlikely(tp->repair)) {
3282 tcp_finish_connect(sk, NULL);
3286 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3287 if (unlikely(!buff))
3290 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3291 tp->retrans_stamp = tcp_time_stamp;
3292 tcp_connect_queue_skb(sk, buff);
3293 tcp_ecn_send_syn(sk, buff);
3295 /* Send off SYN; include data in Fast Open. */
3296 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3297 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3298 if (err == -ECONNREFUSED)
3301 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3302 * in order to make this packet get counted in tcpOutSegs.
3304 tp->snd_nxt = tp->write_seq;
3305 tp->pushed_seq = tp->write_seq;
3306 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3308 /* Timer for repeating the SYN until an answer. */
3309 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3310 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3313 EXPORT_SYMBOL(tcp_connect);
3315 /* Send out a delayed ack, the caller does the policy checking
3316 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3319 void tcp_send_delayed_ack(struct sock *sk)
3321 struct inet_connection_sock *icsk = inet_csk(sk);
3322 int ato = icsk->icsk_ack.ato;
3323 unsigned long timeout;
3325 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3327 if (ato > TCP_DELACK_MIN) {
3328 const struct tcp_sock *tp = tcp_sk(sk);
3329 int max_ato = HZ / 2;
3331 if (icsk->icsk_ack.pingpong ||
3332 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3333 max_ato = TCP_DELACK_MAX;
3335 /* Slow path, intersegment interval is "high". */
3337 /* If some rtt estimate is known, use it to bound delayed ack.
3338 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3342 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3349 ato = min(ato, max_ato);
3352 /* Stay within the limit we were given */
3353 timeout = jiffies + ato;
3355 /* Use new timeout only if there wasn't a older one earlier. */
3356 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3357 /* If delack timer was blocked or is about to expire,
3360 if (icsk->icsk_ack.blocked ||
3361 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3366 if (!time_before(timeout, icsk->icsk_ack.timeout))
3367 timeout = icsk->icsk_ack.timeout;
3369 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3370 icsk->icsk_ack.timeout = timeout;
3371 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3374 /* This routine sends an ack and also updates the window. */
3375 void tcp_send_ack(struct sock *sk)
3377 struct sk_buff *buff;
3379 /* If we have been reset, we may not send again. */
3380 if (sk->sk_state == TCP_CLOSE)
3383 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3385 /* We are not putting this on the write queue, so
3386 * tcp_transmit_skb() will set the ownership to this
3389 buff = alloc_skb(MAX_TCP_HEADER,
3390 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3391 if (unlikely(!buff)) {
3392 inet_csk_schedule_ack(sk);
3393 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3394 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3395 TCP_DELACK_MAX, TCP_RTO_MAX);
3399 /* Reserve space for headers and prepare control bits. */
3400 skb_reserve(buff, MAX_TCP_HEADER);
3401 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3403 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3405 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3406 * We also avoid tcp_wfree() overhead (cache line miss accessing
3407 * tp->tsq_flags) by using regular sock_wfree()
3409 skb_set_tcp_pure_ack(buff);
3411 /* Send it off, this clears delayed acks for us. */
3412 skb_mstamp_get(&buff->skb_mstamp);
3413 tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
3415 EXPORT_SYMBOL_GPL(tcp_send_ack);
3417 /* This routine sends a packet with an out of date sequence
3418 * number. It assumes the other end will try to ack it.
3420 * Question: what should we make while urgent mode?
3421 * 4.4BSD forces sending single byte of data. We cannot send
3422 * out of window data, because we have SND.NXT==SND.MAX...
3424 * Current solution: to send TWO zero-length segments in urgent mode:
3425 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3426 * out-of-date with SND.UNA-1 to probe window.
3428 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3430 struct tcp_sock *tp = tcp_sk(sk);
3431 struct sk_buff *skb;
3433 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3434 skb = alloc_skb(MAX_TCP_HEADER,
3435 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3439 /* Reserve space for headers and set control bits. */
3440 skb_reserve(skb, MAX_TCP_HEADER);
3441 /* Use a previous sequence. This should cause the other
3442 * end to send an ack. Don't queue or clone SKB, just
3445 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3446 skb_mstamp_get(&skb->skb_mstamp);
3447 NET_INC_STATS(sock_net(sk), mib);
3448 return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
3451 void tcp_send_window_probe(struct sock *sk)
3453 if (sk->sk_state == TCP_ESTABLISHED) {
3454 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3455 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3459 /* Initiate keepalive or window probe from timer. */
3460 int tcp_write_wakeup(struct sock *sk, int mib)
3462 struct tcp_sock *tp = tcp_sk(sk);
3463 struct sk_buff *skb;
3465 if (sk->sk_state == TCP_CLOSE)
3468 skb = tcp_send_head(sk);
3469 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3471 unsigned int mss = tcp_current_mss(sk);
3472 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3474 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3475 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3477 /* We are probing the opening of a window
3478 * but the window size is != 0
3479 * must have been a result SWS avoidance ( sender )
3481 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3483 seg_size = min(seg_size, mss);
3484 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3485 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3487 } else if (!tcp_skb_pcount(skb))
3488 tcp_set_skb_tso_segs(skb, mss);
3490 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3491 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3493 tcp_event_new_data_sent(sk, skb);
3496 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3497 tcp_xmit_probe_skb(sk, 1, mib);
3498 return tcp_xmit_probe_skb(sk, 0, mib);
3502 /* A window probe timeout has occurred. If window is not closed send
3503 * a partial packet else a zero probe.
3505 void tcp_send_probe0(struct sock *sk)
3507 struct inet_connection_sock *icsk = inet_csk(sk);
3508 struct tcp_sock *tp = tcp_sk(sk);
3509 struct net *net = sock_net(sk);
3510 unsigned long probe_max;
3513 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3515 if (tp->packets_out || !tcp_send_head(sk)) {
3516 /* Cancel probe timer, if it is not required. */
3517 icsk->icsk_probes_out = 0;
3518 icsk->icsk_backoff = 0;
3523 if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3524 icsk->icsk_backoff++;
3525 icsk->icsk_probes_out++;
3526 probe_max = TCP_RTO_MAX;
3528 /* If packet was not sent due to local congestion,
3529 * do not backoff and do not remember icsk_probes_out.
3530 * Let local senders to fight for local resources.
3532 * Use accumulated backoff yet.
3534 if (!icsk->icsk_probes_out)
3535 icsk->icsk_probes_out = 1;
3536 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3538 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3539 tcp_probe0_when(sk, probe_max),
3543 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3545 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3549 tcp_rsk(req)->txhash = net_tx_rndhash();
3550 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3552 __TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3553 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3557 EXPORT_SYMBOL(tcp_rtx_synack);