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 unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
66 EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);
68 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
69 int push_one, gfp_t gfp);
71 /* Account for new data that has been sent to the network. */
72 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
74 struct inet_connection_sock *icsk = inet_csk(sk);
75 struct tcp_sock *tp = tcp_sk(sk);
76 unsigned int prior_packets = tp->packets_out;
78 tcp_advance_send_head(sk, skb);
79 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
81 tp->packets_out += tcp_skb_pcount(skb);
82 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
83 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
87 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
91 /* SND.NXT, if window was not shrunk.
92 * If window has been shrunk, what should we make? It is not clear at all.
93 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
94 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
95 * invalid. OK, let's make this for now:
97 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
99 const struct tcp_sock *tp = tcp_sk(sk);
101 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
104 return tcp_wnd_end(tp);
107 /* Calculate mss to advertise in SYN segment.
108 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
110 * 1. It is independent of path mtu.
111 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
112 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
113 * attached devices, because some buggy hosts are confused by
115 * 4. We do not make 3, we advertise MSS, calculated from first
116 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
117 * This may be overridden via information stored in routing table.
118 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
119 * probably even Jumbo".
121 static __u16 tcp_advertise_mss(struct sock *sk)
123 struct tcp_sock *tp = tcp_sk(sk);
124 const struct dst_entry *dst = __sk_dst_get(sk);
125 int mss = tp->advmss;
128 unsigned int metric = dst_metric_advmss(dst);
139 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
140 * This is the first part of cwnd validation mechanism.
142 void tcp_cwnd_restart(struct sock *sk, s32 delta)
144 struct tcp_sock *tp = tcp_sk(sk);
145 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
146 u32 cwnd = tp->snd_cwnd;
148 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
150 tp->snd_ssthresh = tcp_current_ssthresh(sk);
151 restart_cwnd = min(restart_cwnd, cwnd);
153 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
155 tp->snd_cwnd = max(cwnd, restart_cwnd);
156 tp->snd_cwnd_stamp = tcp_time_stamp;
157 tp->snd_cwnd_used = 0;
160 /* Congestion state accounting after a packet has been sent. */
161 static void tcp_event_data_sent(struct tcp_sock *tp,
164 struct inet_connection_sock *icsk = inet_csk(sk);
165 const u32 now = tcp_time_stamp;
167 if (tcp_packets_in_flight(tp) == 0)
168 tcp_ca_event(sk, CA_EVENT_TX_START);
172 /* If it is a reply for ato after last received
173 * packet, enter pingpong mode.
175 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
176 icsk->icsk_ack.pingpong = 1;
179 /* Account for an ACK we sent. */
180 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
182 tcp_dec_quickack_mode(sk, pkts);
183 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
187 u32 tcp_default_init_rwnd(u32 mss)
189 /* Initial receive window should be twice of TCP_INIT_CWND to
190 * enable proper sending of new unsent data during fast recovery
191 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
192 * limit when mss is larger than 1460.
194 u32 init_rwnd = TCP_INIT_CWND * 2;
197 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
201 /* Determine a window scaling and initial window to offer.
202 * Based on the assumption that the given amount of space
203 * will be offered. Store the results in the tp structure.
204 * NOTE: for smooth operation initial space offering should
205 * be a multiple of mss if possible. We assume here that mss >= 1.
206 * This MUST be enforced by all callers.
208 void tcp_select_initial_window(int __space, __u32 mss,
209 __u32 *rcv_wnd, __u32 *window_clamp,
210 int wscale_ok, __u8 *rcv_wscale,
213 unsigned int space = (__space < 0 ? 0 : __space);
215 /* If no clamp set the clamp to the max possible scaled window */
216 if (*window_clamp == 0)
217 (*window_clamp) = (65535 << 14);
218 space = min(*window_clamp, space);
220 /* Quantize space offering to a multiple of mss if possible. */
222 space = (space / mss) * mss;
224 /* NOTE: offering an initial window larger than 32767
225 * will break some buggy TCP stacks. If the admin tells us
226 * it is likely we could be speaking with such a buggy stack
227 * we will truncate our initial window offering to 32K-1
228 * unless the remote has sent us a window scaling option,
229 * which we interpret as a sign the remote TCP is not
230 * misinterpreting the window field as a signed quantity.
232 if (sysctl_tcp_workaround_signed_windows)
233 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
239 /* Set window scaling on max possible window
240 * See RFC1323 for an explanation of the limit to 14
242 space = max_t(u32, space, sysctl_tcp_rmem[2]);
243 space = max_t(u32, space, sysctl_rmem_max);
244 space = min_t(u32, space, *window_clamp);
245 while (space > 65535 && (*rcv_wscale) < 14) {
251 if (mss > (1 << *rcv_wscale)) {
252 if (!init_rcv_wnd) /* Use default unless specified otherwise */
253 init_rcv_wnd = tcp_default_init_rwnd(mss);
254 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
257 /* Set the clamp no higher than max representable value */
258 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
260 EXPORT_SYMBOL(tcp_select_initial_window);
262 /* Chose a new window to advertise, update state in tcp_sock for the
263 * socket, and return result with RFC1323 scaling applied. The return
264 * value can be stuffed directly into th->window for an outgoing
267 static u16 tcp_select_window(struct sock *sk)
269 struct tcp_sock *tp = tcp_sk(sk);
270 u32 old_win = tp->rcv_wnd;
271 u32 cur_win = tcp_receive_window(tp);
272 u32 new_win = __tcp_select_window(sk);
274 /* Never shrink the offered window */
275 if (new_win < cur_win) {
276 /* Danger Will Robinson!
277 * Don't update rcv_wup/rcv_wnd here or else
278 * we will not be able to advertise a zero
279 * window in time. --DaveM
281 * Relax Will Robinson.
284 NET_INC_STATS(sock_net(sk),
285 LINUX_MIB_TCPWANTZEROWINDOWADV);
286 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
288 tp->rcv_wnd = new_win;
289 tp->rcv_wup = tp->rcv_nxt;
291 /* Make sure we do not exceed the maximum possible
294 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
295 new_win = min(new_win, MAX_TCP_WINDOW);
297 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
299 /* RFC1323 scaling applied */
300 new_win >>= tp->rx_opt.rcv_wscale;
302 /* If we advertise zero window, disable fast path. */
306 NET_INC_STATS(sock_net(sk),
307 LINUX_MIB_TCPTOZEROWINDOWADV);
308 } else if (old_win == 0) {
309 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
315 /* Packet ECN state for a SYN-ACK */
316 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
318 const struct tcp_sock *tp = tcp_sk(sk);
320 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
321 if (!(tp->ecn_flags & TCP_ECN_OK))
322 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
323 else if (tcp_ca_needs_ecn(sk))
327 /* Packet ECN state for a SYN. */
328 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
330 struct tcp_sock *tp = tcp_sk(sk);
331 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
332 tcp_ca_needs_ecn(sk);
335 const struct dst_entry *dst = __sk_dst_get(sk);
337 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
344 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
345 tp->ecn_flags = TCP_ECN_OK;
346 if (tcp_ca_needs_ecn(sk))
351 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
353 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
354 /* tp->ecn_flags are cleared at a later point in time when
355 * SYN ACK is ultimatively being received.
357 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
361 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
363 if (inet_rsk(req)->ecn_ok)
367 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
370 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
373 struct tcp_sock *tp = tcp_sk(sk);
375 if (tp->ecn_flags & TCP_ECN_OK) {
376 /* Not-retransmitted data segment: set ECT and inject CWR. */
377 if (skb->len != tcp_header_len &&
378 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
380 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
381 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
382 tcp_hdr(skb)->cwr = 1;
383 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
385 } else if (!tcp_ca_needs_ecn(sk)) {
386 /* ACK or retransmitted segment: clear ECT|CE */
387 INET_ECN_dontxmit(sk);
389 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
390 tcp_hdr(skb)->ece = 1;
394 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
395 * auto increment end seqno.
397 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
399 skb->ip_summed = CHECKSUM_PARTIAL;
402 TCP_SKB_CB(skb)->tcp_flags = flags;
403 TCP_SKB_CB(skb)->sacked = 0;
405 tcp_skb_pcount_set(skb, 1);
407 TCP_SKB_CB(skb)->seq = seq;
408 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
410 TCP_SKB_CB(skb)->end_seq = seq;
413 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
415 return tp->snd_una != tp->snd_up;
418 #define OPTION_SACK_ADVERTISE (1 << 0)
419 #define OPTION_TS (1 << 1)
420 #define OPTION_MD5 (1 << 2)
421 #define OPTION_WSCALE (1 << 3)
422 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
424 struct tcp_out_options {
425 u16 options; /* bit field of OPTION_* */
426 u16 mss; /* 0 to disable */
427 u8 ws; /* window scale, 0 to disable */
428 u8 num_sack_blocks; /* number of SACK blocks to include */
429 u8 hash_size; /* bytes in hash_location */
430 __u8 *hash_location; /* temporary pointer, overloaded */
431 __u32 tsval, tsecr; /* need to include OPTION_TS */
432 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
435 /* Write previously computed TCP options to the packet.
437 * Beware: Something in the Internet is very sensitive to the ordering of
438 * TCP options, we learned this through the hard way, so be careful here.
439 * Luckily we can at least blame others for their non-compliance but from
440 * inter-operability perspective it seems that we're somewhat stuck with
441 * the ordering which we have been using if we want to keep working with
442 * those broken things (not that it currently hurts anybody as there isn't
443 * particular reason why the ordering would need to be changed).
445 * At least SACK_PERM as the first option is known to lead to a disaster
446 * (but it may well be that other scenarios fail similarly).
448 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
449 struct tcp_out_options *opts)
451 u16 options = opts->options; /* mungable copy */
453 if (unlikely(OPTION_MD5 & options)) {
454 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
455 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
456 /* overload cookie hash location */
457 opts->hash_location = (__u8 *)ptr;
461 if (unlikely(opts->mss)) {
462 *ptr++ = htonl((TCPOPT_MSS << 24) |
463 (TCPOLEN_MSS << 16) |
467 if (likely(OPTION_TS & options)) {
468 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
469 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
470 (TCPOLEN_SACK_PERM << 16) |
471 (TCPOPT_TIMESTAMP << 8) |
473 options &= ~OPTION_SACK_ADVERTISE;
475 *ptr++ = htonl((TCPOPT_NOP << 24) |
477 (TCPOPT_TIMESTAMP << 8) |
480 *ptr++ = htonl(opts->tsval);
481 *ptr++ = htonl(opts->tsecr);
484 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
485 *ptr++ = htonl((TCPOPT_NOP << 24) |
487 (TCPOPT_SACK_PERM << 8) |
491 if (unlikely(OPTION_WSCALE & options)) {
492 *ptr++ = htonl((TCPOPT_NOP << 24) |
493 (TCPOPT_WINDOW << 16) |
494 (TCPOLEN_WINDOW << 8) |
498 if (unlikely(opts->num_sack_blocks)) {
499 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
500 tp->duplicate_sack : tp->selective_acks;
503 *ptr++ = htonl((TCPOPT_NOP << 24) |
506 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
507 TCPOLEN_SACK_PERBLOCK)));
509 for (this_sack = 0; this_sack < opts->num_sack_blocks;
511 *ptr++ = htonl(sp[this_sack].start_seq);
512 *ptr++ = htonl(sp[this_sack].end_seq);
515 tp->rx_opt.dsack = 0;
518 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
519 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
521 u32 len; /* Fast Open option length */
524 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
525 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
526 TCPOPT_FASTOPEN_MAGIC);
527 p += TCPOLEN_EXP_FASTOPEN_BASE;
529 len = TCPOLEN_FASTOPEN_BASE + foc->len;
530 *p++ = TCPOPT_FASTOPEN;
534 memcpy(p, foc->val, foc->len);
535 if ((len & 3) == 2) {
536 p[foc->len] = TCPOPT_NOP;
537 p[foc->len + 1] = TCPOPT_NOP;
539 ptr += (len + 3) >> 2;
543 /* Compute TCP options for SYN packets. This is not the final
544 * network wire format yet.
546 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
547 struct tcp_out_options *opts,
548 struct tcp_md5sig_key **md5)
550 struct tcp_sock *tp = tcp_sk(sk);
551 unsigned int remaining = MAX_TCP_OPTION_SPACE;
552 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
554 #ifdef CONFIG_TCP_MD5SIG
555 *md5 = tp->af_specific->md5_lookup(sk, sk);
557 opts->options |= OPTION_MD5;
558 remaining -= TCPOLEN_MD5SIG_ALIGNED;
564 /* We always get an MSS option. The option bytes which will be seen in
565 * normal data packets should timestamps be used, must be in the MSS
566 * advertised. But we subtract them from tp->mss_cache so that
567 * calculations in tcp_sendmsg are simpler etc. So account for this
568 * fact here if necessary. If we don't do this correctly, as a
569 * receiver we won't recognize data packets as being full sized when we
570 * should, and thus we won't abide by the delayed ACK rules correctly.
571 * SACKs don't matter, we never delay an ACK when we have any of those
573 opts->mss = tcp_advertise_mss(sk);
574 remaining -= TCPOLEN_MSS_ALIGNED;
576 if (likely(sysctl_tcp_timestamps && !*md5)) {
577 opts->options |= OPTION_TS;
578 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
579 opts->tsecr = tp->rx_opt.ts_recent;
580 remaining -= TCPOLEN_TSTAMP_ALIGNED;
582 if (likely(sysctl_tcp_window_scaling)) {
583 opts->ws = tp->rx_opt.rcv_wscale;
584 opts->options |= OPTION_WSCALE;
585 remaining -= TCPOLEN_WSCALE_ALIGNED;
587 if (likely(sysctl_tcp_sack)) {
588 opts->options |= OPTION_SACK_ADVERTISE;
589 if (unlikely(!(OPTION_TS & opts->options)))
590 remaining -= TCPOLEN_SACKPERM_ALIGNED;
593 if (fastopen && fastopen->cookie.len >= 0) {
594 u32 need = fastopen->cookie.len;
596 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
597 TCPOLEN_FASTOPEN_BASE;
598 need = (need + 3) & ~3U; /* Align to 32 bits */
599 if (remaining >= need) {
600 opts->options |= OPTION_FAST_OPEN_COOKIE;
601 opts->fastopen_cookie = &fastopen->cookie;
603 tp->syn_fastopen = 1;
604 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
608 return MAX_TCP_OPTION_SPACE - remaining;
611 /* Set up TCP options for SYN-ACKs. */
612 static unsigned int tcp_synack_options(struct request_sock *req,
613 unsigned int mss, struct sk_buff *skb,
614 struct tcp_out_options *opts,
615 const struct tcp_md5sig_key *md5,
616 struct tcp_fastopen_cookie *foc)
618 struct inet_request_sock *ireq = inet_rsk(req);
619 unsigned int remaining = MAX_TCP_OPTION_SPACE;
621 #ifdef CONFIG_TCP_MD5SIG
623 opts->options |= OPTION_MD5;
624 remaining -= TCPOLEN_MD5SIG_ALIGNED;
626 /* We can't fit any SACK blocks in a packet with MD5 + TS
627 * options. There was discussion about disabling SACK
628 * rather than TS in order to fit in better with old,
629 * buggy kernels, but that was deemed to be unnecessary.
631 ireq->tstamp_ok &= !ireq->sack_ok;
635 /* We always send an MSS option. */
637 remaining -= TCPOLEN_MSS_ALIGNED;
639 if (likely(ireq->wscale_ok)) {
640 opts->ws = ireq->rcv_wscale;
641 opts->options |= OPTION_WSCALE;
642 remaining -= TCPOLEN_WSCALE_ALIGNED;
644 if (likely(ireq->tstamp_ok)) {
645 opts->options |= OPTION_TS;
646 opts->tsval = tcp_skb_timestamp(skb);
647 opts->tsecr = req->ts_recent;
648 remaining -= TCPOLEN_TSTAMP_ALIGNED;
650 if (likely(ireq->sack_ok)) {
651 opts->options |= OPTION_SACK_ADVERTISE;
652 if (unlikely(!ireq->tstamp_ok))
653 remaining -= TCPOLEN_SACKPERM_ALIGNED;
655 if (foc != NULL && foc->len >= 0) {
658 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
659 TCPOLEN_FASTOPEN_BASE;
660 need = (need + 3) & ~3U; /* Align to 32 bits */
661 if (remaining >= need) {
662 opts->options |= OPTION_FAST_OPEN_COOKIE;
663 opts->fastopen_cookie = foc;
668 return MAX_TCP_OPTION_SPACE - remaining;
671 /* Compute TCP options for ESTABLISHED sockets. This is not the
672 * final wire format yet.
674 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
675 struct tcp_out_options *opts,
676 struct tcp_md5sig_key **md5)
678 struct tcp_sock *tp = tcp_sk(sk);
679 unsigned int size = 0;
680 unsigned int eff_sacks;
684 #ifdef CONFIG_TCP_MD5SIG
685 *md5 = tp->af_specific->md5_lookup(sk, sk);
686 if (unlikely(*md5)) {
687 opts->options |= OPTION_MD5;
688 size += TCPOLEN_MD5SIG_ALIGNED;
694 if (likely(tp->rx_opt.tstamp_ok)) {
695 opts->options |= OPTION_TS;
696 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
697 opts->tsecr = tp->rx_opt.ts_recent;
698 size += TCPOLEN_TSTAMP_ALIGNED;
701 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
702 if (unlikely(eff_sacks)) {
703 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
704 opts->num_sack_blocks =
705 min_t(unsigned int, eff_sacks,
706 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
707 TCPOLEN_SACK_PERBLOCK);
708 size += TCPOLEN_SACK_BASE_ALIGNED +
709 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
716 /* TCP SMALL QUEUES (TSQ)
718 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
719 * to reduce RTT and bufferbloat.
720 * We do this using a special skb destructor (tcp_wfree).
722 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
723 * needs to be reallocated in a driver.
724 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
726 * Since transmit from skb destructor is forbidden, we use a tasklet
727 * to process all sockets that eventually need to send more skbs.
728 * We use one tasklet per cpu, with its own queue of sockets.
731 struct tasklet_struct tasklet;
732 struct list_head head; /* queue of tcp sockets */
734 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
736 static void tcp_tsq_handler(struct sock *sk)
738 if ((1 << sk->sk_state) &
739 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
740 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
741 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
745 * One tasklet per cpu tries to send more skbs.
746 * We run in tasklet context but need to disable irqs when
747 * transferring tsq->head because tcp_wfree() might
748 * interrupt us (non NAPI drivers)
750 static void tcp_tasklet_func(unsigned long data)
752 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
755 struct list_head *q, *n;
759 local_irq_save(flags);
760 list_splice_init(&tsq->head, &list);
761 local_irq_restore(flags);
763 list_for_each_safe(q, n, &list) {
764 tp = list_entry(q, struct tcp_sock, tsq_node);
765 list_del(&tp->tsq_node);
767 sk = (struct sock *)tp;
770 if (!sock_owned_by_user(sk)) {
773 /* defer the work to tcp_release_cb() */
774 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
778 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
783 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
784 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
785 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
786 (1UL << TCP_MTU_REDUCED_DEFERRED))
788 * tcp_release_cb - tcp release_sock() callback
791 * called from release_sock() to perform protocol dependent
792 * actions before socket release.
794 void tcp_release_cb(struct sock *sk)
796 struct tcp_sock *tp = tcp_sk(sk);
797 unsigned long flags, nflags;
799 /* perform an atomic operation only if at least one flag is set */
801 flags = tp->tsq_flags;
802 if (!(flags & TCP_DEFERRED_ALL))
804 nflags = flags & ~TCP_DEFERRED_ALL;
805 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
807 if (flags & (1UL << TCP_TSQ_DEFERRED))
810 /* Here begins the tricky part :
811 * We are called from release_sock() with :
813 * 2) sk_lock.slock spinlock held
814 * 3) socket owned by us (sk->sk_lock.owned == 1)
816 * But following code is meant to be called from BH handlers,
817 * so we should keep BH disabled, but early release socket ownership
819 sock_release_ownership(sk);
821 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
822 tcp_write_timer_handler(sk);
825 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
826 tcp_delack_timer_handler(sk);
829 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
830 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
834 EXPORT_SYMBOL(tcp_release_cb);
836 void __init tcp_tasklet_init(void)
840 for_each_possible_cpu(i) {
841 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
843 INIT_LIST_HEAD(&tsq->head);
844 tasklet_init(&tsq->tasklet,
851 * Write buffer destructor automatically called from kfree_skb.
852 * We can't xmit new skbs from this context, as we might already
855 void tcp_wfree(struct sk_buff *skb)
857 struct sock *sk = skb->sk;
858 struct tcp_sock *tp = tcp_sk(sk);
861 /* Keep one reference on sk_wmem_alloc.
862 * Will be released by sk_free() from here or tcp_tasklet_func()
864 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
866 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
867 * Wait until our queues (qdisc + devices) are drained.
869 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
870 * - chance for incoming ACK (processed by another cpu maybe)
871 * to migrate this flow (skb->ooo_okay will be eventually set)
873 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
876 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
877 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
879 struct tsq_tasklet *tsq;
881 /* queue this socket to tasklet queue */
882 local_irq_save(flags);
883 tsq = this_cpu_ptr(&tsq_tasklet);
884 list_add(&tp->tsq_node, &tsq->head);
885 tasklet_schedule(&tsq->tasklet);
886 local_irq_restore(flags);
893 /* This routine actually transmits TCP packets queued in by
894 * tcp_do_sendmsg(). This is used by both the initial
895 * transmission and possible later retransmissions.
896 * All SKB's seen here are completely headerless. It is our
897 * job to build the TCP header, and pass the packet down to
898 * IP so it can do the same plus pass the packet off to the
901 * We are working here with either a clone of the original
902 * SKB, or a fresh unique copy made by the retransmit engine.
904 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
907 const struct inet_connection_sock *icsk = inet_csk(sk);
908 struct inet_sock *inet;
910 struct tcp_skb_cb *tcb;
911 struct tcp_out_options opts;
912 unsigned int tcp_options_size, tcp_header_size;
913 struct tcp_md5sig_key *md5;
917 BUG_ON(!skb || !tcp_skb_pcount(skb));
920 skb_mstamp_get(&skb->skb_mstamp);
922 if (unlikely(skb_cloned(skb)))
923 skb = pskb_copy(skb, gfp_mask);
925 skb = skb_clone(skb, gfp_mask);
932 tcb = TCP_SKB_CB(skb);
933 memset(&opts, 0, sizeof(opts));
935 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
936 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
938 tcp_options_size = tcp_established_options(sk, skb, &opts,
940 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
942 /* if no packet is in qdisc/device queue, then allow XPS to select
943 * another queue. We can be called from tcp_tsq_handler()
944 * which holds one reference to sk_wmem_alloc.
946 * TODO: Ideally, in-flight pure ACK packets should not matter here.
947 * One way to get this would be to set skb->truesize = 2 on them.
949 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
951 skb_push(skb, tcp_header_size);
952 skb_reset_transport_header(skb);
956 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
957 skb_set_hash_from_sk(skb, sk);
958 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
960 /* Build TCP header and checksum it. */
962 th->source = inet->inet_sport;
963 th->dest = inet->inet_dport;
964 th->seq = htonl(tcb->seq);
965 th->ack_seq = htonl(tp->rcv_nxt);
966 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
969 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
970 /* RFC1323: The window in SYN & SYN/ACK segments
973 th->window = htons(min(tp->rcv_wnd, 65535U));
975 th->window = htons(tcp_select_window(sk));
980 /* The urg_mode check is necessary during a below snd_una win probe */
981 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
982 if (before(tp->snd_up, tcb->seq + 0x10000)) {
983 th->urg_ptr = htons(tp->snd_up - tcb->seq);
985 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
986 th->urg_ptr = htons(0xFFFF);
991 tcp_options_write((__be32 *)(th + 1), tp, &opts);
992 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
993 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
994 tcp_ecn_send(sk, skb, tcp_header_size);
996 #ifdef CONFIG_TCP_MD5SIG
997 /* Calculate the MD5 hash, as we have all we need now */
999 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1000 tp->af_specific->calc_md5_hash(opts.hash_location,
1005 icsk->icsk_af_ops->send_check(sk, skb);
1007 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1008 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1010 if (skb->len != tcp_header_size)
1011 tcp_event_data_sent(tp, sk);
1013 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1014 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1015 tcp_skb_pcount(skb));
1017 tp->segs_out += tcp_skb_pcount(skb);
1018 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1019 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1020 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1022 /* Our usage of tstamp should remain private */
1023 skb->tstamp.tv64 = 0;
1025 /* Cleanup our debris for IP stacks */
1026 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1027 sizeof(struct inet6_skb_parm)));
1029 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1031 if (likely(err <= 0))
1036 return net_xmit_eval(err);
1039 /* This routine just queues the buffer for sending.
1041 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1042 * otherwise socket can stall.
1044 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1046 struct tcp_sock *tp = tcp_sk(sk);
1048 /* Advance write_seq and place onto the write_queue. */
1049 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1050 __skb_header_release(skb);
1051 tcp_add_write_queue_tail(sk, skb);
1052 sk->sk_wmem_queued += skb->truesize;
1053 sk_mem_charge(sk, skb->truesize);
1056 /* Initialize TSO segments for a packet. */
1057 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1059 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1060 /* Avoid the costly divide in the normal
1063 tcp_skb_pcount_set(skb, 1);
1064 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1066 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1067 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1071 /* When a modification to fackets out becomes necessary, we need to check
1072 * skb is counted to fackets_out or not.
1074 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1077 struct tcp_sock *tp = tcp_sk(sk);
1079 if (!tp->sacked_out || tcp_is_reno(tp))
1082 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1083 tp->fackets_out -= decr;
1086 /* Pcount in the middle of the write queue got changed, we need to do various
1087 * tweaks to fix counters
1089 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1091 struct tcp_sock *tp = tcp_sk(sk);
1093 tp->packets_out -= decr;
1095 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1096 tp->sacked_out -= decr;
1097 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1098 tp->retrans_out -= decr;
1099 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1100 tp->lost_out -= decr;
1102 /* Reno case is special. Sigh... */
1103 if (tcp_is_reno(tp) && decr > 0)
1104 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1106 tcp_adjust_fackets_out(sk, skb, decr);
1108 if (tp->lost_skb_hint &&
1109 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1110 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1111 tp->lost_cnt_hint -= decr;
1113 tcp_verify_left_out(tp);
1116 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1118 struct skb_shared_info *shinfo = skb_shinfo(skb);
1120 if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
1121 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1122 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1123 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1125 shinfo->tx_flags &= ~tsflags;
1126 shinfo2->tx_flags |= tsflags;
1127 swap(shinfo->tskey, shinfo2->tskey);
1131 /* Function to create two new TCP segments. Shrinks the given segment
1132 * to the specified size and appends a new segment with the rest of the
1133 * packet to the list. This won't be called frequently, I hope.
1134 * Remember, these are still headerless SKBs at this point.
1136 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1137 unsigned int mss_now, gfp_t gfp)
1139 struct tcp_sock *tp = tcp_sk(sk);
1140 struct sk_buff *buff;
1141 int nsize, old_factor;
1145 if (WARN_ON(len > skb->len))
1148 nsize = skb_headlen(skb) - len;
1152 if (skb_unclone(skb, gfp))
1155 /* Get a new skb... force flag on. */
1156 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1158 return -ENOMEM; /* We'll just try again later. */
1160 sk->sk_wmem_queued += buff->truesize;
1161 sk_mem_charge(sk, buff->truesize);
1162 nlen = skb->len - len - nsize;
1163 buff->truesize += nlen;
1164 skb->truesize -= nlen;
1166 /* Correct the sequence numbers. */
1167 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1168 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1169 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1171 /* PSH and FIN should only be set in the second packet. */
1172 flags = TCP_SKB_CB(skb)->tcp_flags;
1173 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1174 TCP_SKB_CB(buff)->tcp_flags = flags;
1175 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1177 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1178 /* Copy and checksum data tail into the new buffer. */
1179 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1180 skb_put(buff, nsize),
1185 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1187 skb->ip_summed = CHECKSUM_PARTIAL;
1188 skb_split(skb, buff, len);
1191 buff->ip_summed = skb->ip_summed;
1193 buff->tstamp = skb->tstamp;
1194 tcp_fragment_tstamp(skb, buff);
1196 old_factor = tcp_skb_pcount(skb);
1198 /* Fix up tso_factor for both original and new SKB. */
1199 tcp_set_skb_tso_segs(skb, mss_now);
1200 tcp_set_skb_tso_segs(buff, mss_now);
1202 /* If this packet has been sent out already, we must
1203 * adjust the various packet counters.
1205 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1206 int diff = old_factor - tcp_skb_pcount(skb) -
1207 tcp_skb_pcount(buff);
1210 tcp_adjust_pcount(sk, skb, diff);
1213 /* Link BUFF into the send queue. */
1214 __skb_header_release(buff);
1215 tcp_insert_write_queue_after(skb, buff, sk);
1220 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1221 * eventually). The difference is that pulled data not copied, but
1222 * immediately discarded.
1224 static void __pskb_trim_head(struct sk_buff *skb, int len)
1226 struct skb_shared_info *shinfo;
1229 eat = min_t(int, len, skb_headlen(skb));
1231 __skb_pull(skb, eat);
1238 shinfo = skb_shinfo(skb);
1239 for (i = 0; i < shinfo->nr_frags; i++) {
1240 int size = skb_frag_size(&shinfo->frags[i]);
1243 skb_frag_unref(skb, i);
1246 shinfo->frags[k] = shinfo->frags[i];
1248 shinfo->frags[k].page_offset += eat;
1249 skb_frag_size_sub(&shinfo->frags[k], eat);
1255 shinfo->nr_frags = k;
1257 skb_reset_tail_pointer(skb);
1258 skb->data_len -= len;
1259 skb->len = skb->data_len;
1262 /* Remove acked data from a packet in the transmit queue. */
1263 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1265 if (skb_unclone(skb, GFP_ATOMIC))
1268 __pskb_trim_head(skb, len);
1270 TCP_SKB_CB(skb)->seq += len;
1271 skb->ip_summed = CHECKSUM_PARTIAL;
1273 skb->truesize -= len;
1274 sk->sk_wmem_queued -= len;
1275 sk_mem_uncharge(sk, len);
1276 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1278 /* Any change of skb->len requires recalculation of tso factor. */
1279 if (tcp_skb_pcount(skb) > 1)
1280 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1285 /* Calculate MSS not accounting any TCP options. */
1286 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1288 const struct tcp_sock *tp = tcp_sk(sk);
1289 const struct inet_connection_sock *icsk = inet_csk(sk);
1292 /* Calculate base mss without TCP options:
1293 It is MMS_S - sizeof(tcphdr) of rfc1122
1295 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1297 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1298 if (icsk->icsk_af_ops->net_frag_header_len) {
1299 const struct dst_entry *dst = __sk_dst_get(sk);
1301 if (dst && dst_allfrag(dst))
1302 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1305 /* Clamp it (mss_clamp does not include tcp options) */
1306 if (mss_now > tp->rx_opt.mss_clamp)
1307 mss_now = tp->rx_opt.mss_clamp;
1309 /* Now subtract optional transport overhead */
1310 mss_now -= icsk->icsk_ext_hdr_len;
1312 /* Then reserve room for full set of TCP options and 8 bytes of data */
1318 /* Calculate MSS. Not accounting for SACKs here. */
1319 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1321 /* Subtract TCP options size, not including SACKs */
1322 return __tcp_mtu_to_mss(sk, pmtu) -
1323 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1326 /* Inverse of above */
1327 int tcp_mss_to_mtu(struct sock *sk, int mss)
1329 const struct tcp_sock *tp = tcp_sk(sk);
1330 const struct inet_connection_sock *icsk = inet_csk(sk);
1334 tp->tcp_header_len +
1335 icsk->icsk_ext_hdr_len +
1336 icsk->icsk_af_ops->net_header_len;
1338 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1339 if (icsk->icsk_af_ops->net_frag_header_len) {
1340 const struct dst_entry *dst = __sk_dst_get(sk);
1342 if (dst && dst_allfrag(dst))
1343 mtu += icsk->icsk_af_ops->net_frag_header_len;
1348 /* MTU probing init per socket */
1349 void tcp_mtup_init(struct sock *sk)
1351 struct tcp_sock *tp = tcp_sk(sk);
1352 struct inet_connection_sock *icsk = inet_csk(sk);
1353 struct net *net = sock_net(sk);
1355 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1356 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1357 icsk->icsk_af_ops->net_header_len;
1358 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1359 icsk->icsk_mtup.probe_size = 0;
1360 if (icsk->icsk_mtup.enabled)
1361 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1363 EXPORT_SYMBOL(tcp_mtup_init);
1365 /* This function synchronize snd mss to current pmtu/exthdr set.
1367 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1368 for TCP options, but includes only bare TCP header.
1370 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1371 It is minimum of user_mss and mss received with SYN.
1372 It also does not include TCP options.
1374 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1376 tp->mss_cache is current effective sending mss, including
1377 all tcp options except for SACKs. It is evaluated,
1378 taking into account current pmtu, but never exceeds
1379 tp->rx_opt.mss_clamp.
1381 NOTE1. rfc1122 clearly states that advertised MSS
1382 DOES NOT include either tcp or ip options.
1384 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1385 are READ ONLY outside this function. --ANK (980731)
1387 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1389 struct tcp_sock *tp = tcp_sk(sk);
1390 struct inet_connection_sock *icsk = inet_csk(sk);
1393 if (icsk->icsk_mtup.search_high > pmtu)
1394 icsk->icsk_mtup.search_high = pmtu;
1396 mss_now = tcp_mtu_to_mss(sk, pmtu);
1397 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1399 /* And store cached results */
1400 icsk->icsk_pmtu_cookie = pmtu;
1401 if (icsk->icsk_mtup.enabled)
1402 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1403 tp->mss_cache = mss_now;
1407 EXPORT_SYMBOL(tcp_sync_mss);
1409 /* Compute the current effective MSS, taking SACKs and IP options,
1410 * and even PMTU discovery events into account.
1412 unsigned int tcp_current_mss(struct sock *sk)
1414 const struct tcp_sock *tp = tcp_sk(sk);
1415 const struct dst_entry *dst = __sk_dst_get(sk);
1417 unsigned int header_len;
1418 struct tcp_out_options opts;
1419 struct tcp_md5sig_key *md5;
1421 mss_now = tp->mss_cache;
1424 u32 mtu = dst_mtu(dst);
1425 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1426 mss_now = tcp_sync_mss(sk, mtu);
1429 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1430 sizeof(struct tcphdr);
1431 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1432 * some common options. If this is an odd packet (because we have SACK
1433 * blocks etc) then our calculated header_len will be different, and
1434 * we have to adjust mss_now correspondingly */
1435 if (header_len != tp->tcp_header_len) {
1436 int delta = (int) header_len - tp->tcp_header_len;
1443 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1444 * As additional protections, we do not touch cwnd in retransmission phases,
1445 * and if application hit its sndbuf limit recently.
1447 static void tcp_cwnd_application_limited(struct sock *sk)
1449 struct tcp_sock *tp = tcp_sk(sk);
1451 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1452 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1453 /* Limited by application or receiver window. */
1454 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1455 u32 win_used = max(tp->snd_cwnd_used, init_win);
1456 if (win_used < tp->snd_cwnd) {
1457 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1458 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1460 tp->snd_cwnd_used = 0;
1462 tp->snd_cwnd_stamp = tcp_time_stamp;
1465 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1467 struct tcp_sock *tp = tcp_sk(sk);
1469 /* Track the maximum number of outstanding packets in each
1470 * window, and remember whether we were cwnd-limited then.
1472 if (!before(tp->snd_una, tp->max_packets_seq) ||
1473 tp->packets_out > tp->max_packets_out) {
1474 tp->max_packets_out = tp->packets_out;
1475 tp->max_packets_seq = tp->snd_nxt;
1476 tp->is_cwnd_limited = is_cwnd_limited;
1479 if (tcp_is_cwnd_limited(sk)) {
1480 /* Network is feed fully. */
1481 tp->snd_cwnd_used = 0;
1482 tp->snd_cwnd_stamp = tcp_time_stamp;
1484 /* Network starves. */
1485 if (tp->packets_out > tp->snd_cwnd_used)
1486 tp->snd_cwnd_used = tp->packets_out;
1488 if (sysctl_tcp_slow_start_after_idle &&
1489 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1490 tcp_cwnd_application_limited(sk);
1494 /* Minshall's variant of the Nagle send check. */
1495 static bool tcp_minshall_check(const struct tcp_sock *tp)
1497 return after(tp->snd_sml, tp->snd_una) &&
1498 !after(tp->snd_sml, tp->snd_nxt);
1501 /* Update snd_sml if this skb is under mss
1502 * Note that a TSO packet might end with a sub-mss segment
1503 * The test is really :
1504 * if ((skb->len % mss) != 0)
1505 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1506 * But we can avoid doing the divide again given we already have
1507 * skb_pcount = skb->len / mss_now
1509 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1510 const struct sk_buff *skb)
1512 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1513 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1516 /* Return false, if packet can be sent now without violation Nagle's rules:
1517 * 1. It is full sized. (provided by caller in %partial bool)
1518 * 2. Or it contains FIN. (already checked by caller)
1519 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1520 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1521 * With Minshall's modification: all sent small packets are ACKed.
1523 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1527 ((nonagle & TCP_NAGLE_CORK) ||
1528 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1531 /* Return how many segs we'd like on a TSO packet,
1532 * to send one TSO packet per ms
1534 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1538 bytes = min(sk->sk_pacing_rate >> 10,
1539 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1541 /* Goal is to send at least one packet per ms,
1542 * not one big TSO packet every 100 ms.
1543 * This preserves ACK clocking and is consistent
1544 * with tcp_tso_should_defer() heuristic.
1546 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1548 return min_t(u32, segs, sk->sk_gso_max_segs);
1551 /* Returns the portion of skb which can be sent right away */
1552 static unsigned int tcp_mss_split_point(const struct sock *sk,
1553 const struct sk_buff *skb,
1554 unsigned int mss_now,
1555 unsigned int max_segs,
1558 const struct tcp_sock *tp = tcp_sk(sk);
1559 u32 partial, needed, window, max_len;
1561 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1562 max_len = mss_now * max_segs;
1564 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1567 needed = min(skb->len, window);
1569 if (max_len <= needed)
1572 partial = needed % mss_now;
1573 /* If last segment is not a full MSS, check if Nagle rules allow us
1574 * to include this last segment in this skb.
1575 * Otherwise, we'll split the skb at last MSS boundary
1577 if (tcp_nagle_check(partial != 0, tp, nonagle))
1578 return needed - partial;
1583 /* Can at least one segment of SKB be sent right now, according to the
1584 * congestion window rules? If so, return how many segments are allowed.
1586 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1587 const struct sk_buff *skb)
1589 u32 in_flight, cwnd, halfcwnd;
1591 /* Don't be strict about the congestion window for the final FIN. */
1592 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1593 tcp_skb_pcount(skb) == 1)
1596 in_flight = tcp_packets_in_flight(tp);
1597 cwnd = tp->snd_cwnd;
1598 if (in_flight >= cwnd)
1601 /* For better scheduling, ensure we have at least
1602 * 2 GSO packets in flight.
1604 halfcwnd = max(cwnd >> 1, 1U);
1605 return min(halfcwnd, cwnd - in_flight);
1608 /* Initialize TSO state of a skb.
1609 * This must be invoked the first time we consider transmitting
1610 * SKB onto the wire.
1612 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1614 int tso_segs = tcp_skb_pcount(skb);
1616 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1617 tcp_set_skb_tso_segs(skb, mss_now);
1618 tso_segs = tcp_skb_pcount(skb);
1624 /* Return true if the Nagle test allows this packet to be
1627 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1628 unsigned int cur_mss, int nonagle)
1630 /* Nagle rule does not apply to frames, which sit in the middle of the
1631 * write_queue (they have no chances to get new data).
1633 * This is implemented in the callers, where they modify the 'nonagle'
1634 * argument based upon the location of SKB in the send queue.
1636 if (nonagle & TCP_NAGLE_PUSH)
1639 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1640 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1643 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1649 /* Does at least the first segment of SKB fit into the send window? */
1650 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1651 const struct sk_buff *skb,
1652 unsigned int cur_mss)
1654 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1656 if (skb->len > cur_mss)
1657 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1659 return !after(end_seq, tcp_wnd_end(tp));
1662 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1663 * should be put on the wire right now. If so, it returns the number of
1664 * packets allowed by the congestion window.
1666 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1667 unsigned int cur_mss, int nonagle)
1669 const struct tcp_sock *tp = tcp_sk(sk);
1670 unsigned int cwnd_quota;
1672 tcp_init_tso_segs(skb, cur_mss);
1674 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1677 cwnd_quota = tcp_cwnd_test(tp, skb);
1678 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1684 /* Test if sending is allowed right now. */
1685 bool tcp_may_send_now(struct sock *sk)
1687 const struct tcp_sock *tp = tcp_sk(sk);
1688 struct sk_buff *skb = tcp_send_head(sk);
1691 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1692 (tcp_skb_is_last(sk, skb) ?
1693 tp->nonagle : TCP_NAGLE_PUSH));
1696 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1697 * which is put after SKB on the list. It is very much like
1698 * tcp_fragment() except that it may make several kinds of assumptions
1699 * in order to speed up the splitting operation. In particular, we
1700 * know that all the data is in scatter-gather pages, and that the
1701 * packet has never been sent out before (and thus is not cloned).
1703 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1704 unsigned int mss_now, gfp_t gfp)
1706 struct sk_buff *buff;
1707 int nlen = skb->len - len;
1710 /* All of a TSO frame must be composed of paged data. */
1711 if (skb->len != skb->data_len)
1712 return tcp_fragment(sk, skb, len, mss_now, gfp);
1714 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1715 if (unlikely(!buff))
1718 sk->sk_wmem_queued += buff->truesize;
1719 sk_mem_charge(sk, buff->truesize);
1720 buff->truesize += nlen;
1721 skb->truesize -= nlen;
1723 /* Correct the sequence numbers. */
1724 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1725 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1726 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1728 /* PSH and FIN should only be set in the second packet. */
1729 flags = TCP_SKB_CB(skb)->tcp_flags;
1730 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1731 TCP_SKB_CB(buff)->tcp_flags = flags;
1733 /* This packet was never sent out yet, so no SACK bits. */
1734 TCP_SKB_CB(buff)->sacked = 0;
1736 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1737 skb_split(skb, buff, len);
1738 tcp_fragment_tstamp(skb, buff);
1740 /* Fix up tso_factor for both original and new SKB. */
1741 tcp_set_skb_tso_segs(skb, mss_now);
1742 tcp_set_skb_tso_segs(buff, mss_now);
1744 /* Link BUFF into the send queue. */
1745 __skb_header_release(buff);
1746 tcp_insert_write_queue_after(skb, buff, sk);
1751 /* Try to defer sending, if possible, in order to minimize the amount
1752 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1754 * This algorithm is from John Heffner.
1756 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1757 bool *is_cwnd_limited, u32 max_segs)
1759 const struct inet_connection_sock *icsk = inet_csk(sk);
1760 u32 age, send_win, cong_win, limit, in_flight;
1761 struct tcp_sock *tp = tcp_sk(sk);
1762 struct skb_mstamp now;
1763 struct sk_buff *head;
1766 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1769 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1772 /* Avoid bursty behavior by allowing defer
1773 * only if the last write was recent.
1775 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1778 in_flight = tcp_packets_in_flight(tp);
1780 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1782 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1784 /* From in_flight test above, we know that cwnd > in_flight. */
1785 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1787 limit = min(send_win, cong_win);
1789 /* If a full-sized TSO skb can be sent, do it. */
1790 if (limit >= max_segs * tp->mss_cache)
1793 /* Middle in queue won't get any more data, full sendable already? */
1794 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1797 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1799 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1801 /* If at least some fraction of a window is available,
1804 chunk /= win_divisor;
1808 /* Different approach, try not to defer past a single
1809 * ACK. Receiver should ACK every other full sized
1810 * frame, so if we have space for more than 3 frames
1813 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1817 head = tcp_write_queue_head(sk);
1818 skb_mstamp_get(&now);
1819 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1820 /* If next ACK is likely to come too late (half srtt), do not defer */
1821 if (age < (tp->srtt_us >> 4))
1824 /* Ok, it looks like it is advisable to defer. */
1826 if (cong_win < send_win && cong_win <= skb->len)
1827 *is_cwnd_limited = true;
1835 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1837 struct inet_connection_sock *icsk = inet_csk(sk);
1838 struct tcp_sock *tp = tcp_sk(sk);
1839 struct net *net = sock_net(sk);
1843 interval = net->ipv4.sysctl_tcp_probe_interval;
1844 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1845 if (unlikely(delta >= interval * HZ)) {
1846 int mss = tcp_current_mss(sk);
1848 /* Update current search range */
1849 icsk->icsk_mtup.probe_size = 0;
1850 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1851 sizeof(struct tcphdr) +
1852 icsk->icsk_af_ops->net_header_len;
1853 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1855 /* Update probe time stamp */
1856 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1860 /* Create a new MTU probe if we are ready.
1861 * MTU probe is regularly attempting to increase the path MTU by
1862 * deliberately sending larger packets. This discovers routing
1863 * changes resulting in larger path MTUs.
1865 * Returns 0 if we should wait to probe (no cwnd available),
1866 * 1 if a probe was sent,
1869 static int tcp_mtu_probe(struct sock *sk)
1871 struct tcp_sock *tp = tcp_sk(sk);
1872 struct inet_connection_sock *icsk = inet_csk(sk);
1873 struct sk_buff *skb, *nskb, *next;
1874 struct net *net = sock_net(sk);
1882 /* Not currently probing/verifying,
1884 * have enough cwnd, and
1885 * not SACKing (the variable headers throw things off) */
1886 if (!icsk->icsk_mtup.enabled ||
1887 icsk->icsk_mtup.probe_size ||
1888 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1889 tp->snd_cwnd < 11 ||
1890 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1893 /* Use binary search for probe_size between tcp_mss_base,
1894 * and current mss_clamp. if (search_high - search_low)
1895 * smaller than a threshold, backoff from probing.
1897 mss_now = tcp_current_mss(sk);
1898 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1899 icsk->icsk_mtup.search_low) >> 1);
1900 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1901 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1902 /* When misfortune happens, we are reprobing actively,
1903 * and then reprobe timer has expired. We stick with current
1904 * probing process by not resetting search range to its orignal.
1906 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1907 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1908 /* Check whether enough time has elaplased for
1909 * another round of probing.
1911 tcp_mtu_check_reprobe(sk);
1915 /* Have enough data in the send queue to probe? */
1916 if (tp->write_seq - tp->snd_nxt < size_needed)
1919 if (tp->snd_wnd < size_needed)
1921 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1924 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1925 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1926 if (!tcp_packets_in_flight(tp))
1932 /* We're allowed to probe. Build it now. */
1933 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1936 sk->sk_wmem_queued += nskb->truesize;
1937 sk_mem_charge(sk, nskb->truesize);
1939 skb = tcp_send_head(sk);
1941 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1942 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1943 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1944 TCP_SKB_CB(nskb)->sacked = 0;
1946 nskb->ip_summed = skb->ip_summed;
1948 tcp_insert_write_queue_before(nskb, skb, sk);
1951 tcp_for_write_queue_from_safe(skb, next, sk) {
1952 copy = min_t(int, skb->len, probe_size - len);
1953 if (nskb->ip_summed)
1954 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1956 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1957 skb_put(nskb, copy),
1960 if (skb->len <= copy) {
1961 /* We've eaten all the data from this skb.
1963 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1964 tcp_unlink_write_queue(skb, sk);
1965 sk_wmem_free_skb(sk, skb);
1967 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1968 ~(TCPHDR_FIN|TCPHDR_PSH);
1969 if (!skb_shinfo(skb)->nr_frags) {
1970 skb_pull(skb, copy);
1971 if (skb->ip_summed != CHECKSUM_PARTIAL)
1972 skb->csum = csum_partial(skb->data,
1975 __pskb_trim_head(skb, copy);
1976 tcp_set_skb_tso_segs(skb, mss_now);
1978 TCP_SKB_CB(skb)->seq += copy;
1983 if (len >= probe_size)
1986 tcp_init_tso_segs(nskb, nskb->len);
1988 /* We're ready to send. If this fails, the probe will
1989 * be resegmented into mss-sized pieces by tcp_write_xmit().
1991 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1992 /* Decrement cwnd here because we are sending
1993 * effectively two packets. */
1995 tcp_event_new_data_sent(sk, nskb);
1997 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1998 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1999 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2007 /* This routine writes packets to the network. It advances the
2008 * send_head. This happens as incoming acks open up the remote
2011 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2012 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2013 * account rare use of URG, this is not a big flaw.
2015 * Send at most one packet when push_one > 0. Temporarily ignore
2016 * cwnd limit to force at most one packet out when push_one == 2.
2018 * Returns true, if no segments are in flight and we have queued segments,
2019 * but cannot send anything now because of SWS or another problem.
2021 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2022 int push_one, gfp_t gfp)
2024 struct tcp_sock *tp = tcp_sk(sk);
2025 struct sk_buff *skb;
2026 unsigned int tso_segs, sent_pkts;
2029 bool is_cwnd_limited = false;
2035 /* Do MTU probing. */
2036 result = tcp_mtu_probe(sk);
2039 } else if (result > 0) {
2044 max_segs = tcp_tso_autosize(sk, mss_now);
2045 while ((skb = tcp_send_head(sk))) {
2048 tso_segs = tcp_init_tso_segs(skb, mss_now);
2051 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2052 /* "skb_mstamp" is used as a start point for the retransmit timer */
2053 skb_mstamp_get(&skb->skb_mstamp);
2054 goto repair; /* Skip network transmission */
2057 cwnd_quota = tcp_cwnd_test(tp, skb);
2060 /* Force out a loss probe pkt. */
2066 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2069 if (tso_segs == 1) {
2070 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2071 (tcp_skb_is_last(sk, skb) ?
2072 nonagle : TCP_NAGLE_PUSH))))
2076 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2082 if (tso_segs > 1 && !tcp_urg_mode(tp))
2083 limit = tcp_mss_split_point(sk, skb, mss_now,
2089 if (skb->len > limit &&
2090 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2093 /* TCP Small Queues :
2094 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2096 * - better RTT estimation and ACK scheduling
2099 * Alas, some drivers / subsystems require a fair amount
2100 * of queued bytes to ensure line rate.
2101 * One example is wifi aggregation (802.11 AMPDU)
2103 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2104 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2106 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2107 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2108 /* It is possible TX completion already happened
2109 * before we set TSQ_THROTTLED, so we must
2110 * test again the condition.
2112 smp_mb__after_atomic();
2113 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2117 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2121 /* Advance the send_head. This one is sent out.
2122 * This call will increment packets_out.
2124 tcp_event_new_data_sent(sk, skb);
2126 tcp_minshall_update(tp, mss_now, skb);
2127 sent_pkts += tcp_skb_pcount(skb);
2133 if (likely(sent_pkts)) {
2134 if (tcp_in_cwnd_reduction(sk))
2135 tp->prr_out += sent_pkts;
2137 /* Send one loss probe per tail loss episode. */
2139 tcp_schedule_loss_probe(sk);
2140 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2141 tcp_cwnd_validate(sk, is_cwnd_limited);
2144 return !tp->packets_out && tcp_send_head(sk);
2147 bool tcp_schedule_loss_probe(struct sock *sk)
2149 struct inet_connection_sock *icsk = inet_csk(sk);
2150 struct tcp_sock *tp = tcp_sk(sk);
2151 u32 timeout, tlp_time_stamp, rto_time_stamp;
2152 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2154 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2156 /* No consecutive loss probes. */
2157 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2161 /* Don't do any loss probe on a Fast Open connection before 3WHS
2164 if (tp->fastopen_rsk)
2167 /* TLP is only scheduled when next timer event is RTO. */
2168 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2171 /* Schedule a loss probe in 2*RTT for SACK capable connections
2172 * in Open state, that are either limited by cwnd or application.
2174 if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
2175 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2178 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2182 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2183 * for delayed ack when there's one outstanding packet. If no RTT
2184 * sample is available then probe after TCP_TIMEOUT_INIT.
2186 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2187 if (tp->packets_out == 1)
2188 timeout = max_t(u32, timeout,
2189 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2190 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2192 /* If RTO is shorter, just schedule TLP in its place. */
2193 tlp_time_stamp = tcp_time_stamp + timeout;
2194 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2195 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2196 s32 delta = rto_time_stamp - tcp_time_stamp;
2201 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2206 /* Thanks to skb fast clones, we can detect if a prior transmit of
2207 * a packet is still in a qdisc or driver queue.
2208 * In this case, there is very little point doing a retransmit !
2209 * Note: This is called from BH context only.
2211 static bool skb_still_in_host_queue(const struct sock *sk,
2212 const struct sk_buff *skb)
2214 if (unlikely(skb_fclone_busy(sk, skb))) {
2215 NET_INC_STATS_BH(sock_net(sk),
2216 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2222 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2223 * retransmit the last segment.
2225 void tcp_send_loss_probe(struct sock *sk)
2227 struct tcp_sock *tp = tcp_sk(sk);
2228 struct sk_buff *skb;
2230 int mss = tcp_current_mss(sk);
2232 skb = tcp_send_head(sk);
2234 if (tcp_snd_wnd_test(tp, skb, mss)) {
2235 pcount = tp->packets_out;
2236 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2237 if (tp->packets_out > pcount)
2241 skb = tcp_write_queue_prev(sk, skb);
2243 skb = tcp_write_queue_tail(sk);
2246 /* At most one outstanding TLP retransmission. */
2247 if (tp->tlp_high_seq)
2250 /* Retransmit last segment. */
2254 if (skb_still_in_host_queue(sk, skb))
2257 pcount = tcp_skb_pcount(skb);
2258 if (WARN_ON(!pcount))
2261 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2262 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2265 skb = tcp_write_queue_next(sk, skb);
2268 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2271 if (__tcp_retransmit_skb(sk, skb))
2274 /* Record snd_nxt for loss detection. */
2275 tp->tlp_high_seq = tp->snd_nxt;
2278 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2279 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2280 inet_csk(sk)->icsk_pending = 0;
2285 /* Push out any pending frames which were held back due to
2286 * TCP_CORK or attempt at coalescing tiny packets.
2287 * The socket must be locked by the caller.
2289 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2292 /* If we are closed, the bytes will have to remain here.
2293 * In time closedown will finish, we empty the write queue and
2294 * all will be happy.
2296 if (unlikely(sk->sk_state == TCP_CLOSE))
2299 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2300 sk_gfp_atomic(sk, GFP_ATOMIC)))
2301 tcp_check_probe_timer(sk);
2304 /* Send _single_ skb sitting at the send head. This function requires
2305 * true push pending frames to setup probe timer etc.
2307 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2309 struct sk_buff *skb = tcp_send_head(sk);
2311 BUG_ON(!skb || skb->len < mss_now);
2313 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2316 /* This function returns the amount that we can raise the
2317 * usable window based on the following constraints
2319 * 1. The window can never be shrunk once it is offered (RFC 793)
2320 * 2. We limit memory per socket
2323 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2324 * RECV.NEXT + RCV.WIN fixed until:
2325 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2327 * i.e. don't raise the right edge of the window until you can raise
2328 * it at least MSS bytes.
2330 * Unfortunately, the recommended algorithm breaks header prediction,
2331 * since header prediction assumes th->window stays fixed.
2333 * Strictly speaking, keeping th->window fixed violates the receiver
2334 * side SWS prevention criteria. The problem is that under this rule
2335 * a stream of single byte packets will cause the right side of the
2336 * window to always advance by a single byte.
2338 * Of course, if the sender implements sender side SWS prevention
2339 * then this will not be a problem.
2341 * BSD seems to make the following compromise:
2343 * If the free space is less than the 1/4 of the maximum
2344 * space available and the free space is less than 1/2 mss,
2345 * then set the window to 0.
2346 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2347 * Otherwise, just prevent the window from shrinking
2348 * and from being larger than the largest representable value.
2350 * This prevents incremental opening of the window in the regime
2351 * where TCP is limited by the speed of the reader side taking
2352 * data out of the TCP receive queue. It does nothing about
2353 * those cases where the window is constrained on the sender side
2354 * because the pipeline is full.
2356 * BSD also seems to "accidentally" limit itself to windows that are a
2357 * multiple of MSS, at least until the free space gets quite small.
2358 * This would appear to be a side effect of the mbuf implementation.
2359 * Combining these two algorithms results in the observed behavior
2360 * of having a fixed window size at almost all times.
2362 * Below we obtain similar behavior by forcing the offered window to
2363 * a multiple of the mss when it is feasible to do so.
2365 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2366 * Regular options like TIMESTAMP are taken into account.
2368 u32 __tcp_select_window(struct sock *sk)
2370 struct inet_connection_sock *icsk = inet_csk(sk);
2371 struct tcp_sock *tp = tcp_sk(sk);
2372 /* MSS for the peer's data. Previous versions used mss_clamp
2373 * here. I don't know if the value based on our guesses
2374 * of peer's MSS is better for the performance. It's more correct
2375 * but may be worse for the performance because of rcv_mss
2376 * fluctuations. --SAW 1998/11/1
2378 int mss = icsk->icsk_ack.rcv_mss;
2379 int free_space = tcp_space(sk);
2380 int allowed_space = tcp_full_space(sk);
2381 int full_space = min_t(int, tp->window_clamp, allowed_space);
2384 if (mss > full_space)
2387 if (free_space < (full_space >> 1)) {
2388 icsk->icsk_ack.quick = 0;
2390 if (tcp_under_memory_pressure(sk))
2391 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2394 /* free_space might become our new window, make sure we don't
2395 * increase it due to wscale.
2397 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2399 /* if free space is less than mss estimate, or is below 1/16th
2400 * of the maximum allowed, try to move to zero-window, else
2401 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2402 * new incoming data is dropped due to memory limits.
2403 * With large window, mss test triggers way too late in order
2404 * to announce zero window in time before rmem limit kicks in.
2406 if (free_space < (allowed_space >> 4) || free_space < mss)
2410 if (free_space > tp->rcv_ssthresh)
2411 free_space = tp->rcv_ssthresh;
2413 /* Don't do rounding if we are using window scaling, since the
2414 * scaled window will not line up with the MSS boundary anyway.
2416 window = tp->rcv_wnd;
2417 if (tp->rx_opt.rcv_wscale) {
2418 window = free_space;
2420 /* Advertise enough space so that it won't get scaled away.
2421 * Import case: prevent zero window announcement if
2422 * 1<<rcv_wscale > mss.
2424 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2425 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2426 << tp->rx_opt.rcv_wscale);
2428 /* Get the largest window that is a nice multiple of mss.
2429 * Window clamp already applied above.
2430 * If our current window offering is within 1 mss of the
2431 * free space we just keep it. This prevents the divide
2432 * and multiply from happening most of the time.
2433 * We also don't do any window rounding when the free space
2436 if (window <= free_space - mss || window > free_space)
2437 window = (free_space / mss) * mss;
2438 else if (mss == full_space &&
2439 free_space > window + (full_space >> 1))
2440 window = free_space;
2446 /* Collapses two adjacent SKB's during retransmission. */
2447 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2449 struct tcp_sock *tp = tcp_sk(sk);
2450 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2451 int skb_size, next_skb_size;
2453 skb_size = skb->len;
2454 next_skb_size = next_skb->len;
2456 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2458 tcp_highest_sack_combine(sk, next_skb, skb);
2460 tcp_unlink_write_queue(next_skb, sk);
2462 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2465 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2466 skb->ip_summed = CHECKSUM_PARTIAL;
2468 if (skb->ip_summed != CHECKSUM_PARTIAL)
2469 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2471 /* Update sequence range on original skb. */
2472 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2474 /* Merge over control information. This moves PSH/FIN etc. over */
2475 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2477 /* All done, get rid of second SKB and account for it so
2478 * packet counting does not break.
2480 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2482 /* changed transmit queue under us so clear hints */
2483 tcp_clear_retrans_hints_partial(tp);
2484 if (next_skb == tp->retransmit_skb_hint)
2485 tp->retransmit_skb_hint = skb;
2487 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2489 sk_wmem_free_skb(sk, next_skb);
2492 /* Check if coalescing SKBs is legal. */
2493 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2495 if (tcp_skb_pcount(skb) > 1)
2497 /* TODO: SACK collapsing could be used to remove this condition */
2498 if (skb_shinfo(skb)->nr_frags != 0)
2500 if (skb_cloned(skb))
2502 if (skb == tcp_send_head(sk))
2504 /* Some heurestics for collapsing over SACK'd could be invented */
2505 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2511 /* Collapse packets in the retransmit queue to make to create
2512 * less packets on the wire. This is only done on retransmission.
2514 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2517 struct tcp_sock *tp = tcp_sk(sk);
2518 struct sk_buff *skb = to, *tmp;
2521 if (!sysctl_tcp_retrans_collapse)
2523 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2526 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2527 if (!tcp_can_collapse(sk, skb))
2539 /* Punt if not enough space exists in the first SKB for
2540 * the data in the second
2542 if (skb->len > skb_availroom(to))
2545 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2548 tcp_collapse_retrans(sk, to);
2552 /* This retransmits one SKB. Policy decisions and retransmit queue
2553 * state updates are done by the caller. Returns non-zero if an
2554 * error occurred which prevented the send.
2556 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2558 struct tcp_sock *tp = tcp_sk(sk);
2559 struct inet_connection_sock *icsk = inet_csk(sk);
2560 unsigned int cur_mss;
2563 /* Inconslusive MTU probe */
2564 if (icsk->icsk_mtup.probe_size) {
2565 icsk->icsk_mtup.probe_size = 0;
2568 /* Do not sent more than we queued. 1/4 is reserved for possible
2569 * copying overhead: fragmentation, tunneling, mangling etc.
2571 if (atomic_read(&sk->sk_wmem_alloc) >
2572 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2575 if (skb_still_in_host_queue(sk, skb))
2578 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2579 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2581 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2585 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2586 return -EHOSTUNREACH; /* Routing failure or similar. */
2588 cur_mss = tcp_current_mss(sk);
2590 /* If receiver has shrunk his window, and skb is out of
2591 * new window, do not retransmit it. The exception is the
2592 * case, when window is shrunk to zero. In this case
2593 * our retransmit serves as a zero window probe.
2595 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2596 TCP_SKB_CB(skb)->seq != tp->snd_una)
2599 if (skb->len > cur_mss) {
2600 if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
2601 return -ENOMEM; /* We'll try again later. */
2603 int oldpcount = tcp_skb_pcount(skb);
2605 if (unlikely(oldpcount > 1)) {
2606 if (skb_unclone(skb, GFP_ATOMIC))
2608 tcp_init_tso_segs(skb, cur_mss);
2609 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2613 /* RFC3168, section 6.1.1.1. ECN fallback */
2614 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2615 tcp_ecn_clear_syn(sk, skb);
2617 tcp_retrans_try_collapse(sk, skb, cur_mss);
2619 /* Make a copy, if the first transmission SKB clone we made
2620 * is still in somebody's hands, else make a clone.
2623 /* make sure skb->data is aligned on arches that require it
2624 * and check if ack-trimming & collapsing extended the headroom
2625 * beyond what csum_start can cover.
2627 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2628 skb_headroom(skb) >= 0xFFFF)) {
2629 struct sk_buff *nskb;
2631 skb_mstamp_get(&skb->skb_mstamp);
2632 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2633 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2636 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2640 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2641 /* Update global TCP statistics. */
2642 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2643 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2644 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2645 tp->total_retrans++;
2650 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2652 struct tcp_sock *tp = tcp_sk(sk);
2653 int err = __tcp_retransmit_skb(sk, skb);
2656 #if FASTRETRANS_DEBUG > 0
2657 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2658 net_dbg_ratelimited("retrans_out leaked\n");
2661 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2662 tp->retrans_out += tcp_skb_pcount(skb);
2664 /* Save stamp of the first retransmit. */
2665 if (!tp->retrans_stamp)
2666 tp->retrans_stamp = tcp_skb_timestamp(skb);
2668 } else if (err != -EBUSY) {
2669 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2672 if (tp->undo_retrans < 0)
2673 tp->undo_retrans = 0;
2674 tp->undo_retrans += tcp_skb_pcount(skb);
2678 /* Check if we forward retransmits are possible in the current
2679 * window/congestion state.
2681 static bool tcp_can_forward_retransmit(struct sock *sk)
2683 const struct inet_connection_sock *icsk = inet_csk(sk);
2684 const struct tcp_sock *tp = tcp_sk(sk);
2686 /* Forward retransmissions are possible only during Recovery. */
2687 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2690 /* No forward retransmissions in Reno are possible. */
2691 if (tcp_is_reno(tp))
2694 /* Yeah, we have to make difficult choice between forward transmission
2695 * and retransmission... Both ways have their merits...
2697 * For now we do not retransmit anything, while we have some new
2698 * segments to send. In the other cases, follow rule 3 for
2699 * NextSeg() specified in RFC3517.
2702 if (tcp_may_send_now(sk))
2708 /* This gets called after a retransmit timeout, and the initially
2709 * retransmitted data is acknowledged. It tries to continue
2710 * resending the rest of the retransmit queue, until either
2711 * we've sent it all or the congestion window limit is reached.
2712 * If doing SACK, the first ACK which comes back for a timeout
2713 * based retransmit packet might feed us FACK information again.
2714 * If so, we use it to avoid unnecessarily retransmissions.
2716 void tcp_xmit_retransmit_queue(struct sock *sk)
2718 const struct inet_connection_sock *icsk = inet_csk(sk);
2719 struct tcp_sock *tp = tcp_sk(sk);
2720 struct sk_buff *skb;
2721 struct sk_buff *hole = NULL;
2724 int fwd_rexmitting = 0;
2726 if (!tp->packets_out)
2730 tp->retransmit_high = tp->snd_una;
2732 if (tp->retransmit_skb_hint) {
2733 skb = tp->retransmit_skb_hint;
2734 last_lost = TCP_SKB_CB(skb)->end_seq;
2735 if (after(last_lost, tp->retransmit_high))
2736 last_lost = tp->retransmit_high;
2738 skb = tcp_write_queue_head(sk);
2739 last_lost = tp->snd_una;
2742 tcp_for_write_queue_from(skb, sk) {
2743 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2745 if (skb == tcp_send_head(sk))
2747 /* we could do better than to assign each time */
2749 tp->retransmit_skb_hint = skb;
2751 /* Assume this retransmit will generate
2752 * only one packet for congestion window
2753 * calculation purposes. This works because
2754 * tcp_retransmit_skb() will chop up the
2755 * packet to be MSS sized and all the
2756 * packet counting works out.
2758 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2761 if (fwd_rexmitting) {
2763 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2765 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2767 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2768 tp->retransmit_high = last_lost;
2769 if (!tcp_can_forward_retransmit(sk))
2771 /* Backtrack if necessary to non-L'ed skb */
2779 } else if (!(sacked & TCPCB_LOST)) {
2780 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2785 last_lost = TCP_SKB_CB(skb)->end_seq;
2786 if (icsk->icsk_ca_state != TCP_CA_Loss)
2787 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2789 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2792 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2795 if (tcp_retransmit_skb(sk, skb))
2798 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2800 if (tcp_in_cwnd_reduction(sk))
2801 tp->prr_out += tcp_skb_pcount(skb);
2803 if (skb == tcp_write_queue_head(sk))
2804 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2805 inet_csk(sk)->icsk_rto,
2810 /* We allow to exceed memory limits for FIN packets to expedite
2811 * connection tear down and (memory) recovery.
2812 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2813 * or even be forced to close flow without any FIN.
2814 * In general, we want to allow one skb per socket to avoid hangs
2815 * with edge trigger epoll()
2817 void sk_forced_mem_schedule(struct sock *sk, int size)
2821 if (size <= sk->sk_forward_alloc)
2823 amt = sk_mem_pages(size);
2824 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2825 sk_memory_allocated_add(sk, amt, &status);
2828 /* Send a FIN. The caller locks the socket for us.
2829 * We should try to send a FIN packet really hard, but eventually give up.
2831 void tcp_send_fin(struct sock *sk)
2833 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2834 struct tcp_sock *tp = tcp_sk(sk);
2836 /* Optimization, tack on the FIN if we have one skb in write queue and
2837 * this skb was not yet sent, or we are under memory pressure.
2838 * Note: in the latter case, FIN packet will be sent after a timeout,
2839 * as TCP stack thinks it has already been transmitted.
2841 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2843 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
2844 TCP_SKB_CB(tskb)->end_seq++;
2846 if (!tcp_send_head(sk)) {
2847 /* This means tskb was already sent.
2848 * Pretend we included the FIN on previous transmit.
2849 * We need to set tp->snd_nxt to the value it would have
2850 * if FIN had been sent. This is because retransmit path
2851 * does not change tp->snd_nxt.
2857 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
2858 if (unlikely(!skb)) {
2863 skb_reserve(skb, MAX_TCP_HEADER);
2864 sk_forced_mem_schedule(sk, skb->truesize);
2865 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2866 tcp_init_nondata_skb(skb, tp->write_seq,
2867 TCPHDR_ACK | TCPHDR_FIN);
2868 tcp_queue_skb(sk, skb);
2870 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
2873 /* We get here when a process closes a file descriptor (either due to
2874 * an explicit close() or as a byproduct of exit()'ing) and there
2875 * was unread data in the receive queue. This behavior is recommended
2876 * by RFC 2525, section 2.17. -DaveM
2878 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2880 struct sk_buff *skb;
2882 /* NOTE: No TCP options attached and we never retransmit this. */
2883 skb = alloc_skb(MAX_TCP_HEADER, priority);
2885 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2889 /* Reserve space for headers and prepare control bits. */
2890 skb_reserve(skb, MAX_TCP_HEADER);
2891 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2892 TCPHDR_ACK | TCPHDR_RST);
2893 skb_mstamp_get(&skb->skb_mstamp);
2895 if (tcp_transmit_skb(sk, skb, 0, priority))
2896 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2898 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2901 /* Send a crossed SYN-ACK during socket establishment.
2902 * WARNING: This routine must only be called when we have already sent
2903 * a SYN packet that crossed the incoming SYN that caused this routine
2904 * to get called. If this assumption fails then the initial rcv_wnd
2905 * and rcv_wscale values will not be correct.
2907 int tcp_send_synack(struct sock *sk)
2909 struct sk_buff *skb;
2911 skb = tcp_write_queue_head(sk);
2912 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2913 pr_debug("%s: wrong queue state\n", __func__);
2916 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2917 if (skb_cloned(skb)) {
2918 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2921 tcp_unlink_write_queue(skb, sk);
2922 __skb_header_release(nskb);
2923 __tcp_add_write_queue_head(sk, nskb);
2924 sk_wmem_free_skb(sk, skb);
2925 sk->sk_wmem_queued += nskb->truesize;
2926 sk_mem_charge(sk, nskb->truesize);
2930 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2931 tcp_ecn_send_synack(sk, skb);
2933 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2937 * tcp_make_synack - Prepare a SYN-ACK.
2938 * sk: listener socket
2939 * dst: dst entry attached to the SYNACK
2940 * req: request_sock pointer
2942 * Allocate one skb and build a SYNACK packet.
2943 * @dst is consumed : Caller should not use it again.
2945 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
2946 struct request_sock *req,
2947 struct tcp_fastopen_cookie *foc,
2950 struct inet_request_sock *ireq = inet_rsk(req);
2951 const struct tcp_sock *tp = tcp_sk(sk);
2952 struct tcp_md5sig_key *md5 = NULL;
2953 struct tcp_out_options opts;
2954 struct sk_buff *skb;
2955 int tcp_header_size;
2960 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2961 if (unlikely(!skb)) {
2965 /* Reserve space for headers. */
2966 skb_reserve(skb, MAX_TCP_HEADER);
2969 skb_set_owner_w(skb, req_to_sk(req));
2971 /* sk is a const pointer, because we want to express multiple
2972 * cpu might call us concurrently.
2973 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
2975 skb_set_owner_w(skb, (struct sock *)sk);
2977 skb_dst_set(skb, dst);
2979 mss = dst_metric_advmss(dst);
2980 user_mss = READ_ONCE(tp->rx_opt.user_mss);
2981 if (user_mss && user_mss < mss)
2984 memset(&opts, 0, sizeof(opts));
2985 #ifdef CONFIG_SYN_COOKIES
2986 if (unlikely(req->cookie_ts))
2987 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
2990 skb_mstamp_get(&skb->skb_mstamp);
2992 #ifdef CONFIG_TCP_MD5SIG
2994 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
2996 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
2997 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3000 skb_push(skb, tcp_header_size);
3001 skb_reset_transport_header(skb);
3004 memset(th, 0, sizeof(struct tcphdr));
3007 tcp_ecn_make_synack(req, th);
3008 th->source = htons(ireq->ir_num);
3009 th->dest = ireq->ir_rmt_port;
3010 /* Setting of flags are superfluous here for callers (and ECE is
3011 * not even correctly set)
3013 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3014 TCPHDR_SYN | TCPHDR_ACK);
3016 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3017 /* XXX data is queued and acked as is. No buffer/window check */
3018 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3020 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3021 th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3022 tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3023 th->doff = (tcp_header_size >> 2);
3024 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
3026 #ifdef CONFIG_TCP_MD5SIG
3027 /* Okay, we have all we need - do the md5 hash if needed */
3029 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3030 md5, req_to_sk(req), skb);
3034 /* Do not fool tcpdump (if any), clean our debris */
3035 skb->tstamp.tv64 = 0;
3038 EXPORT_SYMBOL(tcp_make_synack);
3040 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3042 struct inet_connection_sock *icsk = inet_csk(sk);
3043 const struct tcp_congestion_ops *ca;
3044 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3046 if (ca_key == TCP_CA_UNSPEC)
3050 ca = tcp_ca_find_key(ca_key);
3051 if (likely(ca && try_module_get(ca->owner))) {
3052 module_put(icsk->icsk_ca_ops->owner);
3053 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3054 icsk->icsk_ca_ops = ca;
3059 /* Do all connect socket setups that can be done AF independent. */
3060 static void tcp_connect_init(struct sock *sk)
3062 const struct dst_entry *dst = __sk_dst_get(sk);
3063 struct tcp_sock *tp = tcp_sk(sk);
3066 /* We'll fix this up when we get a response from the other end.
3067 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3069 tp->tcp_header_len = sizeof(struct tcphdr) +
3070 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3072 #ifdef CONFIG_TCP_MD5SIG
3073 if (tp->af_specific->md5_lookup(sk, sk))
3074 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3077 /* If user gave his TCP_MAXSEG, record it to clamp */
3078 if (tp->rx_opt.user_mss)
3079 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3082 tcp_sync_mss(sk, dst_mtu(dst));
3084 tcp_ca_dst_init(sk, dst);
3086 if (!tp->window_clamp)
3087 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3088 tp->advmss = dst_metric_advmss(dst);
3089 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3090 tp->advmss = tp->rx_opt.user_mss;
3092 tcp_initialize_rcv_mss(sk);
3094 /* limit the window selection if the user enforce a smaller rx buffer */
3095 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3096 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3097 tp->window_clamp = tcp_full_space(sk);
3099 tcp_select_initial_window(tcp_full_space(sk),
3100 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3103 sysctl_tcp_window_scaling,
3105 dst_metric(dst, RTAX_INITRWND));
3107 tp->rx_opt.rcv_wscale = rcv_wscale;
3108 tp->rcv_ssthresh = tp->rcv_wnd;
3111 sock_reset_flag(sk, SOCK_DONE);
3114 tp->snd_una = tp->write_seq;
3115 tp->snd_sml = tp->write_seq;
3116 tp->snd_up = tp->write_seq;
3117 tp->snd_nxt = tp->write_seq;
3119 if (likely(!tp->repair))
3122 tp->rcv_tstamp = tcp_time_stamp;
3123 tp->rcv_wup = tp->rcv_nxt;
3124 tp->copied_seq = tp->rcv_nxt;
3126 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3127 inet_csk(sk)->icsk_retransmits = 0;
3128 tcp_clear_retrans(tp);
3131 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3133 struct tcp_sock *tp = tcp_sk(sk);
3134 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3136 tcb->end_seq += skb->len;
3137 __skb_header_release(skb);
3138 __tcp_add_write_queue_tail(sk, skb);
3139 sk->sk_wmem_queued += skb->truesize;
3140 sk_mem_charge(sk, skb->truesize);
3141 tp->write_seq = tcb->end_seq;
3142 tp->packets_out += tcp_skb_pcount(skb);
3145 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3146 * queue a data-only packet after the regular SYN, such that regular SYNs
3147 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3148 * only the SYN sequence, the data are retransmitted in the first ACK.
3149 * If cookie is not cached or other error occurs, falls back to send a
3150 * regular SYN with Fast Open cookie request option.
3152 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3154 struct tcp_sock *tp = tcp_sk(sk);
3155 struct tcp_fastopen_request *fo = tp->fastopen_req;
3156 int syn_loss = 0, space, err = 0;
3157 unsigned long last_syn_loss = 0;
3158 struct sk_buff *syn_data;
3160 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3161 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3162 &syn_loss, &last_syn_loss);
3163 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3165 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3166 fo->cookie.len = -1;
3170 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3171 fo->cookie.len = -1;
3172 else if (fo->cookie.len <= 0)
3175 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3176 * user-MSS. Reserve maximum option space for middleboxes that add
3177 * private TCP options. The cost is reduced data space in SYN :(
3179 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3180 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3181 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3182 MAX_TCP_OPTION_SPACE;
3184 space = min_t(size_t, space, fo->size);
3186 /* limit to order-0 allocations */
3187 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3189 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3192 syn_data->ip_summed = CHECKSUM_PARTIAL;
3193 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3195 int copied = copy_from_iter(skb_put(syn_data, space), space,
3196 &fo->data->msg_iter);
3197 if (unlikely(!copied)) {
3198 kfree_skb(syn_data);
3201 if (copied != space) {
3202 skb_trim(syn_data, copied);
3206 /* No more data pending in inet_wait_for_connect() */
3207 if (space == fo->size)
3211 tcp_connect_queue_skb(sk, syn_data);
3213 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3215 syn->skb_mstamp = syn_data->skb_mstamp;
3217 /* Now full SYN+DATA was cloned and sent (or not),
3218 * remove the SYN from the original skb (syn_data)
3219 * we keep in write queue in case of a retransmit, as we
3220 * also have the SYN packet (with no data) in the same queue.
3222 TCP_SKB_CB(syn_data)->seq++;
3223 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3225 tp->syn_data = (fo->copied > 0);
3226 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3231 /* Send a regular SYN with Fast Open cookie request option */
3232 if (fo->cookie.len > 0)
3234 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3236 tp->syn_fastopen = 0;
3238 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3242 /* Build a SYN and send it off. */
3243 int tcp_connect(struct sock *sk)
3245 struct tcp_sock *tp = tcp_sk(sk);
3246 struct sk_buff *buff;
3249 tcp_connect_init(sk);
3251 if (unlikely(tp->repair)) {
3252 tcp_finish_connect(sk, NULL);
3256 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3257 if (unlikely(!buff))
3260 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3261 tp->retrans_stamp = tcp_time_stamp;
3262 tcp_connect_queue_skb(sk, buff);
3263 tcp_ecn_send_syn(sk, buff);
3265 /* Send off SYN; include data in Fast Open. */
3266 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3267 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3268 if (err == -ECONNREFUSED)
3271 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3272 * in order to make this packet get counted in tcpOutSegs.
3274 tp->snd_nxt = tp->write_seq;
3275 tp->pushed_seq = tp->write_seq;
3276 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3278 /* Timer for repeating the SYN until an answer. */
3279 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3280 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3283 EXPORT_SYMBOL(tcp_connect);
3285 /* Send out a delayed ack, the caller does the policy checking
3286 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3289 void tcp_send_delayed_ack(struct sock *sk)
3291 struct inet_connection_sock *icsk = inet_csk(sk);
3292 int ato = icsk->icsk_ack.ato;
3293 unsigned long timeout;
3295 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3297 if (ato > TCP_DELACK_MIN) {
3298 const struct tcp_sock *tp = tcp_sk(sk);
3299 int max_ato = HZ / 2;
3301 if (icsk->icsk_ack.pingpong ||
3302 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3303 max_ato = TCP_DELACK_MAX;
3305 /* Slow path, intersegment interval is "high". */
3307 /* If some rtt estimate is known, use it to bound delayed ack.
3308 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3312 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3319 ato = min(ato, max_ato);
3322 /* Stay within the limit we were given */
3323 timeout = jiffies + ato;
3325 /* Use new timeout only if there wasn't a older one earlier. */
3326 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3327 /* If delack timer was blocked or is about to expire,
3330 if (icsk->icsk_ack.blocked ||
3331 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3336 if (!time_before(timeout, icsk->icsk_ack.timeout))
3337 timeout = icsk->icsk_ack.timeout;
3339 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3340 icsk->icsk_ack.timeout = timeout;
3341 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3344 /* This routine sends an ack and also updates the window. */
3345 void tcp_send_ack(struct sock *sk)
3347 struct sk_buff *buff;
3349 /* If we have been reset, we may not send again. */
3350 if (sk->sk_state == TCP_CLOSE)
3353 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3355 /* We are not putting this on the write queue, so
3356 * tcp_transmit_skb() will set the ownership to this
3359 buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3361 inet_csk_schedule_ack(sk);
3362 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3363 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3364 TCP_DELACK_MAX, TCP_RTO_MAX);
3368 /* Reserve space for headers and prepare control bits. */
3369 skb_reserve(buff, MAX_TCP_HEADER);
3370 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3372 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3374 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3375 * We also avoid tcp_wfree() overhead (cache line miss accessing
3376 * tp->tsq_flags) by using regular sock_wfree()
3378 skb_set_tcp_pure_ack(buff);
3380 /* Send it off, this clears delayed acks for us. */
3381 skb_mstamp_get(&buff->skb_mstamp);
3382 tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
3384 EXPORT_SYMBOL_GPL(tcp_send_ack);
3386 /* This routine sends a packet with an out of date sequence
3387 * number. It assumes the other end will try to ack it.
3389 * Question: what should we make while urgent mode?
3390 * 4.4BSD forces sending single byte of data. We cannot send
3391 * out of window data, because we have SND.NXT==SND.MAX...
3393 * Current solution: to send TWO zero-length segments in urgent mode:
3394 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3395 * out-of-date with SND.UNA-1 to probe window.
3397 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3399 struct tcp_sock *tp = tcp_sk(sk);
3400 struct sk_buff *skb;
3402 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3403 skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3407 /* Reserve space for headers and set control bits. */
3408 skb_reserve(skb, MAX_TCP_HEADER);
3409 /* Use a previous sequence. This should cause the other
3410 * end to send an ack. Don't queue or clone SKB, just
3413 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3414 skb_mstamp_get(&skb->skb_mstamp);
3415 NET_INC_STATS(sock_net(sk), mib);
3416 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3419 void tcp_send_window_probe(struct sock *sk)
3421 if (sk->sk_state == TCP_ESTABLISHED) {
3422 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3423 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3427 /* Initiate keepalive or window probe from timer. */
3428 int tcp_write_wakeup(struct sock *sk, int mib)
3430 struct tcp_sock *tp = tcp_sk(sk);
3431 struct sk_buff *skb;
3433 if (sk->sk_state == TCP_CLOSE)
3436 skb = tcp_send_head(sk);
3437 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3439 unsigned int mss = tcp_current_mss(sk);
3440 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3442 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3443 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3445 /* We are probing the opening of a window
3446 * but the window size is != 0
3447 * must have been a result SWS avoidance ( sender )
3449 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3451 seg_size = min(seg_size, mss);
3452 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3453 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3455 } else if (!tcp_skb_pcount(skb))
3456 tcp_set_skb_tso_segs(skb, mss);
3458 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3459 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3461 tcp_event_new_data_sent(sk, skb);
3464 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3465 tcp_xmit_probe_skb(sk, 1, mib);
3466 return tcp_xmit_probe_skb(sk, 0, mib);
3470 /* A window probe timeout has occurred. If window is not closed send
3471 * a partial packet else a zero probe.
3473 void tcp_send_probe0(struct sock *sk)
3475 struct inet_connection_sock *icsk = inet_csk(sk);
3476 struct tcp_sock *tp = tcp_sk(sk);
3477 unsigned long probe_max;
3480 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3482 if (tp->packets_out || !tcp_send_head(sk)) {
3483 /* Cancel probe timer, if it is not required. */
3484 icsk->icsk_probes_out = 0;
3485 icsk->icsk_backoff = 0;
3490 if (icsk->icsk_backoff < sysctl_tcp_retries2)
3491 icsk->icsk_backoff++;
3492 icsk->icsk_probes_out++;
3493 probe_max = TCP_RTO_MAX;
3495 /* If packet was not sent due to local congestion,
3496 * do not backoff and do not remember icsk_probes_out.
3497 * Let local senders to fight for local resources.
3499 * Use accumulated backoff yet.
3501 if (!icsk->icsk_probes_out)
3502 icsk->icsk_probes_out = 1;
3503 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3505 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3506 tcp_probe0_when(sk, probe_max),
3510 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3512 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3516 tcp_rsk(req)->txhash = net_tx_rndhash();
3517 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, true);
3519 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
3520 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3524 EXPORT_SYMBOL(tcp_rtx_synack);