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, sysctl_tcp_rmem[2], sysctl_rmem_max);
243 space = min_t(u32, space, *window_clamp);
244 while (space > 65535 && (*rcv_wscale) < 14) {
250 if (mss > (1 << *rcv_wscale)) {
251 if (!init_rcv_wnd) /* Use default unless specified otherwise */
252 init_rcv_wnd = tcp_default_init_rwnd(mss);
253 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
256 /* Set the clamp no higher than max representable value */
257 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
259 EXPORT_SYMBOL(tcp_select_initial_window);
261 /* Chose a new window to advertise, update state in tcp_sock for the
262 * socket, and return result with RFC1323 scaling applied. The return
263 * value can be stuffed directly into th->window for an outgoing
266 static u16 tcp_select_window(struct sock *sk)
268 struct tcp_sock *tp = tcp_sk(sk);
269 u32 old_win = tp->rcv_wnd;
270 u32 cur_win = tcp_receive_window(tp);
271 u32 new_win = __tcp_select_window(sk);
273 /* Never shrink the offered window */
274 if (new_win < cur_win) {
275 /* Danger Will Robinson!
276 * Don't update rcv_wup/rcv_wnd here or else
277 * we will not be able to advertise a zero
278 * window in time. --DaveM
280 * Relax Will Robinson.
283 NET_INC_STATS(sock_net(sk),
284 LINUX_MIB_TCPWANTZEROWINDOWADV);
285 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
287 tp->rcv_wnd = new_win;
288 tp->rcv_wup = tp->rcv_nxt;
290 /* Make sure we do not exceed the maximum possible
293 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
294 new_win = min(new_win, MAX_TCP_WINDOW);
296 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
298 /* RFC1323 scaling applied */
299 new_win >>= tp->rx_opt.rcv_wscale;
301 /* If we advertise zero window, disable fast path. */
305 NET_INC_STATS(sock_net(sk),
306 LINUX_MIB_TCPTOZEROWINDOWADV);
307 } else if (old_win == 0) {
308 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
314 /* Packet ECN state for a SYN-ACK */
315 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
317 const struct tcp_sock *tp = tcp_sk(sk);
319 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
320 if (!(tp->ecn_flags & TCP_ECN_OK))
321 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
322 else if (tcp_ca_needs_ecn(sk))
326 /* Packet ECN state for a SYN. */
327 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
329 struct tcp_sock *tp = tcp_sk(sk);
330 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
331 tcp_ca_needs_ecn(sk);
334 const struct dst_entry *dst = __sk_dst_get(sk);
336 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
343 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
344 tp->ecn_flags = TCP_ECN_OK;
345 if (tcp_ca_needs_ecn(sk))
350 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
352 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
353 /* tp->ecn_flags are cleared at a later point in time when
354 * SYN ACK is ultimatively being received.
356 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
360 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th,
363 if (inet_rsk(req)->ecn_ok) {
365 if (tcp_ca_needs_ecn(sk))
370 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
373 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
376 struct tcp_sock *tp = tcp_sk(sk);
378 if (tp->ecn_flags & TCP_ECN_OK) {
379 /* Not-retransmitted data segment: set ECT and inject CWR. */
380 if (skb->len != tcp_header_len &&
381 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
383 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
384 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
385 tcp_hdr(skb)->cwr = 1;
386 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
388 } else if (!tcp_ca_needs_ecn(sk)) {
389 /* ACK or retransmitted segment: clear ECT|CE */
390 INET_ECN_dontxmit(sk);
392 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
393 tcp_hdr(skb)->ece = 1;
397 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
398 * auto increment end seqno.
400 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
402 skb->ip_summed = CHECKSUM_PARTIAL;
405 TCP_SKB_CB(skb)->tcp_flags = flags;
406 TCP_SKB_CB(skb)->sacked = 0;
408 tcp_skb_pcount_set(skb, 1);
410 TCP_SKB_CB(skb)->seq = seq;
411 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
413 TCP_SKB_CB(skb)->end_seq = seq;
416 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
418 return tp->snd_una != tp->snd_up;
421 #define OPTION_SACK_ADVERTISE (1 << 0)
422 #define OPTION_TS (1 << 1)
423 #define OPTION_MD5 (1 << 2)
424 #define OPTION_WSCALE (1 << 3)
425 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
427 struct tcp_out_options {
428 u16 options; /* bit field of OPTION_* */
429 u16 mss; /* 0 to disable */
430 u8 ws; /* window scale, 0 to disable */
431 u8 num_sack_blocks; /* number of SACK blocks to include */
432 u8 hash_size; /* bytes in hash_location */
433 __u8 *hash_location; /* temporary pointer, overloaded */
434 __u32 tsval, tsecr; /* need to include OPTION_TS */
435 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
438 /* Write previously computed TCP options to the packet.
440 * Beware: Something in the Internet is very sensitive to the ordering of
441 * TCP options, we learned this through the hard way, so be careful here.
442 * Luckily we can at least blame others for their non-compliance but from
443 * inter-operability perspective it seems that we're somewhat stuck with
444 * the ordering which we have been using if we want to keep working with
445 * those broken things (not that it currently hurts anybody as there isn't
446 * particular reason why the ordering would need to be changed).
448 * At least SACK_PERM as the first option is known to lead to a disaster
449 * (but it may well be that other scenarios fail similarly).
451 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
452 struct tcp_out_options *opts)
454 u16 options = opts->options; /* mungable copy */
456 if (unlikely(OPTION_MD5 & options)) {
457 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
458 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
459 /* overload cookie hash location */
460 opts->hash_location = (__u8 *)ptr;
464 if (unlikely(opts->mss)) {
465 *ptr++ = htonl((TCPOPT_MSS << 24) |
466 (TCPOLEN_MSS << 16) |
470 if (likely(OPTION_TS & options)) {
471 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
472 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
473 (TCPOLEN_SACK_PERM << 16) |
474 (TCPOPT_TIMESTAMP << 8) |
476 options &= ~OPTION_SACK_ADVERTISE;
478 *ptr++ = htonl((TCPOPT_NOP << 24) |
480 (TCPOPT_TIMESTAMP << 8) |
483 *ptr++ = htonl(opts->tsval);
484 *ptr++ = htonl(opts->tsecr);
487 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
488 *ptr++ = htonl((TCPOPT_NOP << 24) |
490 (TCPOPT_SACK_PERM << 8) |
494 if (unlikely(OPTION_WSCALE & options)) {
495 *ptr++ = htonl((TCPOPT_NOP << 24) |
496 (TCPOPT_WINDOW << 16) |
497 (TCPOLEN_WINDOW << 8) |
501 if (unlikely(opts->num_sack_blocks)) {
502 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
503 tp->duplicate_sack : tp->selective_acks;
506 *ptr++ = htonl((TCPOPT_NOP << 24) |
509 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
510 TCPOLEN_SACK_PERBLOCK)));
512 for (this_sack = 0; this_sack < opts->num_sack_blocks;
514 *ptr++ = htonl(sp[this_sack].start_seq);
515 *ptr++ = htonl(sp[this_sack].end_seq);
518 tp->rx_opt.dsack = 0;
521 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
522 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
524 u32 len; /* Fast Open option length */
527 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
528 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
529 TCPOPT_FASTOPEN_MAGIC);
530 p += TCPOLEN_EXP_FASTOPEN_BASE;
532 len = TCPOLEN_FASTOPEN_BASE + foc->len;
533 *p++ = TCPOPT_FASTOPEN;
537 memcpy(p, foc->val, foc->len);
538 if ((len & 3) == 2) {
539 p[foc->len] = TCPOPT_NOP;
540 p[foc->len + 1] = TCPOPT_NOP;
542 ptr += (len + 3) >> 2;
546 /* Compute TCP options for SYN packets. This is not the final
547 * network wire format yet.
549 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
550 struct tcp_out_options *opts,
551 struct tcp_md5sig_key **md5)
553 struct tcp_sock *tp = tcp_sk(sk);
554 unsigned int remaining = MAX_TCP_OPTION_SPACE;
555 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
557 #ifdef CONFIG_TCP_MD5SIG
558 *md5 = tp->af_specific->md5_lookup(sk, sk);
560 opts->options |= OPTION_MD5;
561 remaining -= TCPOLEN_MD5SIG_ALIGNED;
567 /* We always get an MSS option. The option bytes which will be seen in
568 * normal data packets should timestamps be used, must be in the MSS
569 * advertised. But we subtract them from tp->mss_cache so that
570 * calculations in tcp_sendmsg are simpler etc. So account for this
571 * fact here if necessary. If we don't do this correctly, as a
572 * receiver we won't recognize data packets as being full sized when we
573 * should, and thus we won't abide by the delayed ACK rules correctly.
574 * SACKs don't matter, we never delay an ACK when we have any of those
576 opts->mss = tcp_advertise_mss(sk);
577 remaining -= TCPOLEN_MSS_ALIGNED;
579 if (likely(sysctl_tcp_timestamps && !*md5)) {
580 opts->options |= OPTION_TS;
581 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
582 opts->tsecr = tp->rx_opt.ts_recent;
583 remaining -= TCPOLEN_TSTAMP_ALIGNED;
585 if (likely(sysctl_tcp_window_scaling)) {
586 opts->ws = tp->rx_opt.rcv_wscale;
587 opts->options |= OPTION_WSCALE;
588 remaining -= TCPOLEN_WSCALE_ALIGNED;
590 if (likely(sysctl_tcp_sack)) {
591 opts->options |= OPTION_SACK_ADVERTISE;
592 if (unlikely(!(OPTION_TS & opts->options)))
593 remaining -= TCPOLEN_SACKPERM_ALIGNED;
596 if (fastopen && fastopen->cookie.len >= 0) {
597 u32 need = fastopen->cookie.len;
599 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
600 TCPOLEN_FASTOPEN_BASE;
601 need = (need + 3) & ~3U; /* Align to 32 bits */
602 if (remaining >= need) {
603 opts->options |= OPTION_FAST_OPEN_COOKIE;
604 opts->fastopen_cookie = &fastopen->cookie;
606 tp->syn_fastopen = 1;
607 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
611 return MAX_TCP_OPTION_SPACE - remaining;
614 /* Set up TCP options for SYN-ACKs. */
615 static unsigned int tcp_synack_options(struct sock *sk,
616 struct request_sock *req,
617 unsigned int mss, struct sk_buff *skb,
618 struct tcp_out_options *opts,
619 const struct tcp_md5sig_key *md5,
620 struct tcp_fastopen_cookie *foc)
622 struct inet_request_sock *ireq = inet_rsk(req);
623 unsigned int remaining = MAX_TCP_OPTION_SPACE;
625 #ifdef CONFIG_TCP_MD5SIG
627 opts->options |= OPTION_MD5;
628 remaining -= TCPOLEN_MD5SIG_ALIGNED;
630 /* We can't fit any SACK blocks in a packet with MD5 + TS
631 * options. There was discussion about disabling SACK
632 * rather than TS in order to fit in better with old,
633 * buggy kernels, but that was deemed to be unnecessary.
635 ireq->tstamp_ok &= !ireq->sack_ok;
639 /* We always send an MSS option. */
641 remaining -= TCPOLEN_MSS_ALIGNED;
643 if (likely(ireq->wscale_ok)) {
644 opts->ws = ireq->rcv_wscale;
645 opts->options |= OPTION_WSCALE;
646 remaining -= TCPOLEN_WSCALE_ALIGNED;
648 if (likely(ireq->tstamp_ok)) {
649 opts->options |= OPTION_TS;
650 opts->tsval = tcp_skb_timestamp(skb);
651 opts->tsecr = req->ts_recent;
652 remaining -= TCPOLEN_TSTAMP_ALIGNED;
654 if (likely(ireq->sack_ok)) {
655 opts->options |= OPTION_SACK_ADVERTISE;
656 if (unlikely(!ireq->tstamp_ok))
657 remaining -= TCPOLEN_SACKPERM_ALIGNED;
659 if (foc != NULL && foc->len >= 0) {
662 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
663 TCPOLEN_FASTOPEN_BASE;
664 need = (need + 3) & ~3U; /* Align to 32 bits */
665 if (remaining >= need) {
666 opts->options |= OPTION_FAST_OPEN_COOKIE;
667 opts->fastopen_cookie = foc;
672 return MAX_TCP_OPTION_SPACE - remaining;
675 /* Compute TCP options for ESTABLISHED sockets. This is not the
676 * final wire format yet.
678 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
679 struct tcp_out_options *opts,
680 struct tcp_md5sig_key **md5)
682 struct tcp_sock *tp = tcp_sk(sk);
683 unsigned int size = 0;
684 unsigned int eff_sacks;
688 #ifdef CONFIG_TCP_MD5SIG
689 *md5 = tp->af_specific->md5_lookup(sk, sk);
690 if (unlikely(*md5)) {
691 opts->options |= OPTION_MD5;
692 size += TCPOLEN_MD5SIG_ALIGNED;
698 if (likely(tp->rx_opt.tstamp_ok)) {
699 opts->options |= OPTION_TS;
700 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
701 opts->tsecr = tp->rx_opt.ts_recent;
702 size += TCPOLEN_TSTAMP_ALIGNED;
705 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
706 if (unlikely(eff_sacks)) {
707 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
708 opts->num_sack_blocks =
709 min_t(unsigned int, eff_sacks,
710 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
711 TCPOLEN_SACK_PERBLOCK);
712 size += TCPOLEN_SACK_BASE_ALIGNED +
713 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
720 /* TCP SMALL QUEUES (TSQ)
722 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
723 * to reduce RTT and bufferbloat.
724 * We do this using a special skb destructor (tcp_wfree).
726 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
727 * needs to be reallocated in a driver.
728 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
730 * Since transmit from skb destructor is forbidden, we use a tasklet
731 * to process all sockets that eventually need to send more skbs.
732 * We use one tasklet per cpu, with its own queue of sockets.
735 struct tasklet_struct tasklet;
736 struct list_head head; /* queue of tcp sockets */
738 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
740 static void tcp_tsq_handler(struct sock *sk)
742 if ((1 << sk->sk_state) &
743 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
744 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
745 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
749 * One tasklet per cpu tries to send more skbs.
750 * We run in tasklet context but need to disable irqs when
751 * transferring tsq->head because tcp_wfree() might
752 * interrupt us (non NAPI drivers)
754 static void tcp_tasklet_func(unsigned long data)
756 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
759 struct list_head *q, *n;
763 local_irq_save(flags);
764 list_splice_init(&tsq->head, &list);
765 local_irq_restore(flags);
767 list_for_each_safe(q, n, &list) {
768 tp = list_entry(q, struct tcp_sock, tsq_node);
769 list_del(&tp->tsq_node);
771 sk = (struct sock *)tp;
774 if (!sock_owned_by_user(sk)) {
777 /* defer the work to tcp_release_cb() */
778 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
782 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
787 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
788 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
789 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
790 (1UL << TCP_MTU_REDUCED_DEFERRED))
792 * tcp_release_cb - tcp release_sock() callback
795 * called from release_sock() to perform protocol dependent
796 * actions before socket release.
798 void tcp_release_cb(struct sock *sk)
800 struct tcp_sock *tp = tcp_sk(sk);
801 unsigned long flags, nflags;
803 /* perform an atomic operation only if at least one flag is set */
805 flags = tp->tsq_flags;
806 if (!(flags & TCP_DEFERRED_ALL))
808 nflags = flags & ~TCP_DEFERRED_ALL;
809 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
811 if (flags & (1UL << TCP_TSQ_DEFERRED))
814 /* Here begins the tricky part :
815 * We are called from release_sock() with :
817 * 2) sk_lock.slock spinlock held
818 * 3) socket owned by us (sk->sk_lock.owned == 1)
820 * But following code is meant to be called from BH handlers,
821 * so we should keep BH disabled, but early release socket ownership
823 sock_release_ownership(sk);
825 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
826 tcp_write_timer_handler(sk);
829 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
830 tcp_delack_timer_handler(sk);
833 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
834 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
838 EXPORT_SYMBOL(tcp_release_cb);
840 void __init tcp_tasklet_init(void)
844 for_each_possible_cpu(i) {
845 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
847 INIT_LIST_HEAD(&tsq->head);
848 tasklet_init(&tsq->tasklet,
855 * Write buffer destructor automatically called from kfree_skb.
856 * We can't xmit new skbs from this context, as we might already
859 void tcp_wfree(struct sk_buff *skb)
861 struct sock *sk = skb->sk;
862 struct tcp_sock *tp = tcp_sk(sk);
865 /* Keep one reference on sk_wmem_alloc.
866 * Will be released by sk_free() from here or tcp_tasklet_func()
868 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
870 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
871 * Wait until our queues (qdisc + devices) are drained.
873 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
874 * - chance for incoming ACK (processed by another cpu maybe)
875 * to migrate this flow (skb->ooo_okay will be eventually set)
877 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
880 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
881 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
883 struct tsq_tasklet *tsq;
885 /* queue this socket to tasklet queue */
886 local_irq_save(flags);
887 tsq = this_cpu_ptr(&tsq_tasklet);
888 list_add(&tp->tsq_node, &tsq->head);
889 tasklet_schedule(&tsq->tasklet);
890 local_irq_restore(flags);
897 /* This routine actually transmits TCP packets queued in by
898 * tcp_do_sendmsg(). This is used by both the initial
899 * transmission and possible later retransmissions.
900 * All SKB's seen here are completely headerless. It is our
901 * job to build the TCP header, and pass the packet down to
902 * IP so it can do the same plus pass the packet off to the
905 * We are working here with either a clone of the original
906 * SKB, or a fresh unique copy made by the retransmit engine.
908 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
911 const struct inet_connection_sock *icsk = inet_csk(sk);
912 struct inet_sock *inet;
914 struct tcp_skb_cb *tcb;
915 struct tcp_out_options opts;
916 unsigned int tcp_options_size, tcp_header_size;
917 struct tcp_md5sig_key *md5;
921 BUG_ON(!skb || !tcp_skb_pcount(skb));
924 skb_mstamp_get(&skb->skb_mstamp);
926 if (unlikely(skb_cloned(skb)))
927 skb = pskb_copy(skb, gfp_mask);
929 skb = skb_clone(skb, gfp_mask);
936 tcb = TCP_SKB_CB(skb);
937 memset(&opts, 0, sizeof(opts));
939 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
940 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
942 tcp_options_size = tcp_established_options(sk, skb, &opts,
944 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
946 /* if no packet is in qdisc/device queue, then allow XPS to select
947 * another queue. We can be called from tcp_tsq_handler()
948 * which holds one reference to sk_wmem_alloc.
950 * TODO: Ideally, in-flight pure ACK packets should not matter here.
951 * One way to get this would be to set skb->truesize = 2 on them.
953 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
955 skb_push(skb, tcp_header_size);
956 skb_reset_transport_header(skb);
960 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
961 skb_set_hash_from_sk(skb, sk);
962 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
964 /* Build TCP header and checksum it. */
966 th->source = inet->inet_sport;
967 th->dest = inet->inet_dport;
968 th->seq = htonl(tcb->seq);
969 th->ack_seq = htonl(tp->rcv_nxt);
970 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
973 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
974 /* RFC1323: The window in SYN & SYN/ACK segments
977 th->window = htons(min(tp->rcv_wnd, 65535U));
979 th->window = htons(tcp_select_window(sk));
984 /* The urg_mode check is necessary during a below snd_una win probe */
985 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
986 if (before(tp->snd_up, tcb->seq + 0x10000)) {
987 th->urg_ptr = htons(tp->snd_up - tcb->seq);
989 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
990 th->urg_ptr = htons(0xFFFF);
995 tcp_options_write((__be32 *)(th + 1), tp, &opts);
996 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
997 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
998 tcp_ecn_send(sk, skb, tcp_header_size);
1000 #ifdef CONFIG_TCP_MD5SIG
1001 /* Calculate the MD5 hash, as we have all we need now */
1003 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1004 tp->af_specific->calc_md5_hash(opts.hash_location,
1009 icsk->icsk_af_ops->send_check(sk, skb);
1011 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1012 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1014 if (skb->len != tcp_header_size)
1015 tcp_event_data_sent(tp, sk);
1017 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1018 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1019 tcp_skb_pcount(skb));
1021 tp->segs_out += tcp_skb_pcount(skb);
1022 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1023 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1024 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1026 /* Our usage of tstamp should remain private */
1027 skb->tstamp.tv64 = 0;
1029 /* Cleanup our debris for IP stacks */
1030 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1031 sizeof(struct inet6_skb_parm)));
1033 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1035 if (likely(err <= 0))
1040 return net_xmit_eval(err);
1043 /* This routine just queues the buffer for sending.
1045 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1046 * otherwise socket can stall.
1048 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1050 struct tcp_sock *tp = tcp_sk(sk);
1052 /* Advance write_seq and place onto the write_queue. */
1053 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1054 __skb_header_release(skb);
1055 tcp_add_write_queue_tail(sk, skb);
1056 sk->sk_wmem_queued += skb->truesize;
1057 sk_mem_charge(sk, skb->truesize);
1060 /* Initialize TSO segments for a packet. */
1061 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1063 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1064 /* Avoid the costly divide in the normal
1067 tcp_skb_pcount_set(skb, 1);
1068 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1070 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1071 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1075 /* When a modification to fackets out becomes necessary, we need to check
1076 * skb is counted to fackets_out or not.
1078 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1081 struct tcp_sock *tp = tcp_sk(sk);
1083 if (!tp->sacked_out || tcp_is_reno(tp))
1086 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1087 tp->fackets_out -= decr;
1090 /* Pcount in the middle of the write queue got changed, we need to do various
1091 * tweaks to fix counters
1093 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1095 struct tcp_sock *tp = tcp_sk(sk);
1097 tp->packets_out -= decr;
1099 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1100 tp->sacked_out -= decr;
1101 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1102 tp->retrans_out -= decr;
1103 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1104 tp->lost_out -= decr;
1106 /* Reno case is special. Sigh... */
1107 if (tcp_is_reno(tp) && decr > 0)
1108 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1110 tcp_adjust_fackets_out(sk, skb, decr);
1112 if (tp->lost_skb_hint &&
1113 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1114 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1115 tp->lost_cnt_hint -= decr;
1117 tcp_verify_left_out(tp);
1120 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1122 struct skb_shared_info *shinfo = skb_shinfo(skb);
1124 if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
1125 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1126 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1127 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1129 shinfo->tx_flags &= ~tsflags;
1130 shinfo2->tx_flags |= tsflags;
1131 swap(shinfo->tskey, shinfo2->tskey);
1135 /* Function to create two new TCP segments. Shrinks the given segment
1136 * to the specified size and appends a new segment with the rest of the
1137 * packet to the list. This won't be called frequently, I hope.
1138 * Remember, these are still headerless SKBs at this point.
1140 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1141 unsigned int mss_now, gfp_t gfp)
1143 struct tcp_sock *tp = tcp_sk(sk);
1144 struct sk_buff *buff;
1145 int nsize, old_factor;
1149 if (WARN_ON(len > skb->len))
1152 nsize = skb_headlen(skb) - len;
1156 if (skb_unclone(skb, gfp))
1159 /* Get a new skb... force flag on. */
1160 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1162 return -ENOMEM; /* We'll just try again later. */
1164 sk->sk_wmem_queued += buff->truesize;
1165 sk_mem_charge(sk, buff->truesize);
1166 nlen = skb->len - len - nsize;
1167 buff->truesize += nlen;
1168 skb->truesize -= nlen;
1170 /* Correct the sequence numbers. */
1171 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1172 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1173 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1175 /* PSH and FIN should only be set in the second packet. */
1176 flags = TCP_SKB_CB(skb)->tcp_flags;
1177 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1178 TCP_SKB_CB(buff)->tcp_flags = flags;
1179 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1181 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1182 /* Copy and checksum data tail into the new buffer. */
1183 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1184 skb_put(buff, nsize),
1189 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1191 skb->ip_summed = CHECKSUM_PARTIAL;
1192 skb_split(skb, buff, len);
1195 buff->ip_summed = skb->ip_summed;
1197 buff->tstamp = skb->tstamp;
1198 tcp_fragment_tstamp(skb, buff);
1200 old_factor = tcp_skb_pcount(skb);
1202 /* Fix up tso_factor for both original and new SKB. */
1203 tcp_set_skb_tso_segs(skb, mss_now);
1204 tcp_set_skb_tso_segs(buff, mss_now);
1206 /* If this packet has been sent out already, we must
1207 * adjust the various packet counters.
1209 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1210 int diff = old_factor - tcp_skb_pcount(skb) -
1211 tcp_skb_pcount(buff);
1214 tcp_adjust_pcount(sk, skb, diff);
1217 /* Link BUFF into the send queue. */
1218 __skb_header_release(buff);
1219 tcp_insert_write_queue_after(skb, buff, sk);
1224 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1225 * eventually). The difference is that pulled data not copied, but
1226 * immediately discarded.
1228 static void __pskb_trim_head(struct sk_buff *skb, int len)
1230 struct skb_shared_info *shinfo;
1233 eat = min_t(int, len, skb_headlen(skb));
1235 __skb_pull(skb, eat);
1242 shinfo = skb_shinfo(skb);
1243 for (i = 0; i < shinfo->nr_frags; i++) {
1244 int size = skb_frag_size(&shinfo->frags[i]);
1247 skb_frag_unref(skb, i);
1250 shinfo->frags[k] = shinfo->frags[i];
1252 shinfo->frags[k].page_offset += eat;
1253 skb_frag_size_sub(&shinfo->frags[k], eat);
1259 shinfo->nr_frags = k;
1261 skb_reset_tail_pointer(skb);
1262 skb->data_len -= len;
1263 skb->len = skb->data_len;
1266 /* Remove acked data from a packet in the transmit queue. */
1267 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1269 if (skb_unclone(skb, GFP_ATOMIC))
1272 __pskb_trim_head(skb, len);
1274 TCP_SKB_CB(skb)->seq += len;
1275 skb->ip_summed = CHECKSUM_PARTIAL;
1277 skb->truesize -= len;
1278 sk->sk_wmem_queued -= len;
1279 sk_mem_uncharge(sk, len);
1280 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1282 /* Any change of skb->len requires recalculation of tso factor. */
1283 if (tcp_skb_pcount(skb) > 1)
1284 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1289 /* Calculate MSS not accounting any TCP options. */
1290 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1292 const struct tcp_sock *tp = tcp_sk(sk);
1293 const struct inet_connection_sock *icsk = inet_csk(sk);
1296 /* Calculate base mss without TCP options:
1297 It is MMS_S - sizeof(tcphdr) of rfc1122
1299 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1301 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1302 if (icsk->icsk_af_ops->net_frag_header_len) {
1303 const struct dst_entry *dst = __sk_dst_get(sk);
1305 if (dst && dst_allfrag(dst))
1306 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1309 /* Clamp it (mss_clamp does not include tcp options) */
1310 if (mss_now > tp->rx_opt.mss_clamp)
1311 mss_now = tp->rx_opt.mss_clamp;
1313 /* Now subtract optional transport overhead */
1314 mss_now -= icsk->icsk_ext_hdr_len;
1316 /* Then reserve room for full set of TCP options and 8 bytes of data */
1322 /* Calculate MSS. Not accounting for SACKs here. */
1323 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1325 /* Subtract TCP options size, not including SACKs */
1326 return __tcp_mtu_to_mss(sk, pmtu) -
1327 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1330 /* Inverse of above */
1331 int tcp_mss_to_mtu(struct sock *sk, int mss)
1333 const struct tcp_sock *tp = tcp_sk(sk);
1334 const struct inet_connection_sock *icsk = inet_csk(sk);
1338 tp->tcp_header_len +
1339 icsk->icsk_ext_hdr_len +
1340 icsk->icsk_af_ops->net_header_len;
1342 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1343 if (icsk->icsk_af_ops->net_frag_header_len) {
1344 const struct dst_entry *dst = __sk_dst_get(sk);
1346 if (dst && dst_allfrag(dst))
1347 mtu += icsk->icsk_af_ops->net_frag_header_len;
1352 /* MTU probing init per socket */
1353 void tcp_mtup_init(struct sock *sk)
1355 struct tcp_sock *tp = tcp_sk(sk);
1356 struct inet_connection_sock *icsk = inet_csk(sk);
1357 struct net *net = sock_net(sk);
1359 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1360 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1361 icsk->icsk_af_ops->net_header_len;
1362 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1363 icsk->icsk_mtup.probe_size = 0;
1364 if (icsk->icsk_mtup.enabled)
1365 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1367 EXPORT_SYMBOL(tcp_mtup_init);
1369 /* This function synchronize snd mss to current pmtu/exthdr set.
1371 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1372 for TCP options, but includes only bare TCP header.
1374 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1375 It is minimum of user_mss and mss received with SYN.
1376 It also does not include TCP options.
1378 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1380 tp->mss_cache is current effective sending mss, including
1381 all tcp options except for SACKs. It is evaluated,
1382 taking into account current pmtu, but never exceeds
1383 tp->rx_opt.mss_clamp.
1385 NOTE1. rfc1122 clearly states that advertised MSS
1386 DOES NOT include either tcp or ip options.
1388 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1389 are READ ONLY outside this function. --ANK (980731)
1391 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1393 struct tcp_sock *tp = tcp_sk(sk);
1394 struct inet_connection_sock *icsk = inet_csk(sk);
1397 if (icsk->icsk_mtup.search_high > pmtu)
1398 icsk->icsk_mtup.search_high = pmtu;
1400 mss_now = tcp_mtu_to_mss(sk, pmtu);
1401 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1403 /* And store cached results */
1404 icsk->icsk_pmtu_cookie = pmtu;
1405 if (icsk->icsk_mtup.enabled)
1406 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1407 tp->mss_cache = mss_now;
1411 EXPORT_SYMBOL(tcp_sync_mss);
1413 /* Compute the current effective MSS, taking SACKs and IP options,
1414 * and even PMTU discovery events into account.
1416 unsigned int tcp_current_mss(struct sock *sk)
1418 const struct tcp_sock *tp = tcp_sk(sk);
1419 const struct dst_entry *dst = __sk_dst_get(sk);
1421 unsigned int header_len;
1422 struct tcp_out_options opts;
1423 struct tcp_md5sig_key *md5;
1425 mss_now = tp->mss_cache;
1428 u32 mtu = dst_mtu(dst);
1429 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1430 mss_now = tcp_sync_mss(sk, mtu);
1433 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1434 sizeof(struct tcphdr);
1435 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1436 * some common options. If this is an odd packet (because we have SACK
1437 * blocks etc) then our calculated header_len will be different, and
1438 * we have to adjust mss_now correspondingly */
1439 if (header_len != tp->tcp_header_len) {
1440 int delta = (int) header_len - tp->tcp_header_len;
1447 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1448 * As additional protections, we do not touch cwnd in retransmission phases,
1449 * and if application hit its sndbuf limit recently.
1451 static void tcp_cwnd_application_limited(struct sock *sk)
1453 struct tcp_sock *tp = tcp_sk(sk);
1455 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1456 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1457 /* Limited by application or receiver window. */
1458 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1459 u32 win_used = max(tp->snd_cwnd_used, init_win);
1460 if (win_used < tp->snd_cwnd) {
1461 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1462 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1464 tp->snd_cwnd_used = 0;
1466 tp->snd_cwnd_stamp = tcp_time_stamp;
1469 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1471 struct tcp_sock *tp = tcp_sk(sk);
1473 /* Track the maximum number of outstanding packets in each
1474 * window, and remember whether we were cwnd-limited then.
1476 if (!before(tp->snd_una, tp->max_packets_seq) ||
1477 tp->packets_out > tp->max_packets_out) {
1478 tp->max_packets_out = tp->packets_out;
1479 tp->max_packets_seq = tp->snd_nxt;
1480 tp->is_cwnd_limited = is_cwnd_limited;
1483 if (tcp_is_cwnd_limited(sk)) {
1484 /* Network is feed fully. */
1485 tp->snd_cwnd_used = 0;
1486 tp->snd_cwnd_stamp = tcp_time_stamp;
1488 /* Network starves. */
1489 if (tp->packets_out > tp->snd_cwnd_used)
1490 tp->snd_cwnd_used = tp->packets_out;
1492 if (sysctl_tcp_slow_start_after_idle &&
1493 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1494 tcp_cwnd_application_limited(sk);
1498 /* Minshall's variant of the Nagle send check. */
1499 static bool tcp_minshall_check(const struct tcp_sock *tp)
1501 return after(tp->snd_sml, tp->snd_una) &&
1502 !after(tp->snd_sml, tp->snd_nxt);
1505 /* Update snd_sml if this skb is under mss
1506 * Note that a TSO packet might end with a sub-mss segment
1507 * The test is really :
1508 * if ((skb->len % mss) != 0)
1509 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1510 * But we can avoid doing the divide again given we already have
1511 * skb_pcount = skb->len / mss_now
1513 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1514 const struct sk_buff *skb)
1516 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1517 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1520 /* Return false, if packet can be sent now without violation Nagle's rules:
1521 * 1. It is full sized. (provided by caller in %partial bool)
1522 * 2. Or it contains FIN. (already checked by caller)
1523 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1524 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1525 * With Minshall's modification: all sent small packets are ACKed.
1527 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1531 ((nonagle & TCP_NAGLE_CORK) ||
1532 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1535 /* Return how many segs we'd like on a TSO packet,
1536 * to send one TSO packet per ms
1538 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1542 bytes = min(sk->sk_pacing_rate >> 10,
1543 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1545 /* Goal is to send at least one packet per ms,
1546 * not one big TSO packet every 100 ms.
1547 * This preserves ACK clocking and is consistent
1548 * with tcp_tso_should_defer() heuristic.
1550 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1552 return min_t(u32, segs, sk->sk_gso_max_segs);
1555 /* Returns the portion of skb which can be sent right away */
1556 static unsigned int tcp_mss_split_point(const struct sock *sk,
1557 const struct sk_buff *skb,
1558 unsigned int mss_now,
1559 unsigned int max_segs,
1562 const struct tcp_sock *tp = tcp_sk(sk);
1563 u32 partial, needed, window, max_len;
1565 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1566 max_len = mss_now * max_segs;
1568 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1571 needed = min(skb->len, window);
1573 if (max_len <= needed)
1576 partial = needed % mss_now;
1577 /* If last segment is not a full MSS, check if Nagle rules allow us
1578 * to include this last segment in this skb.
1579 * Otherwise, we'll split the skb at last MSS boundary
1581 if (tcp_nagle_check(partial != 0, tp, nonagle))
1582 return needed - partial;
1587 /* Can at least one segment of SKB be sent right now, according to the
1588 * congestion window rules? If so, return how many segments are allowed.
1590 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1591 const struct sk_buff *skb)
1593 u32 in_flight, cwnd, halfcwnd;
1595 /* Don't be strict about the congestion window for the final FIN. */
1596 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1597 tcp_skb_pcount(skb) == 1)
1600 in_flight = tcp_packets_in_flight(tp);
1601 cwnd = tp->snd_cwnd;
1602 if (in_flight >= cwnd)
1605 /* For better scheduling, ensure we have at least
1606 * 2 GSO packets in flight.
1608 halfcwnd = max(cwnd >> 1, 1U);
1609 return min(halfcwnd, cwnd - in_flight);
1612 /* Initialize TSO state of a skb.
1613 * This must be invoked the first time we consider transmitting
1614 * SKB onto the wire.
1616 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1618 int tso_segs = tcp_skb_pcount(skb);
1620 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1621 tcp_set_skb_tso_segs(skb, mss_now);
1622 tso_segs = tcp_skb_pcount(skb);
1628 /* Return true if the Nagle test allows this packet to be
1631 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1632 unsigned int cur_mss, int nonagle)
1634 /* Nagle rule does not apply to frames, which sit in the middle of the
1635 * write_queue (they have no chances to get new data).
1637 * This is implemented in the callers, where they modify the 'nonagle'
1638 * argument based upon the location of SKB in the send queue.
1640 if (nonagle & TCP_NAGLE_PUSH)
1643 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1644 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1647 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1653 /* Does at least the first segment of SKB fit into the send window? */
1654 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1655 const struct sk_buff *skb,
1656 unsigned int cur_mss)
1658 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1660 if (skb->len > cur_mss)
1661 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1663 return !after(end_seq, tcp_wnd_end(tp));
1666 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1667 * should be put on the wire right now. If so, it returns the number of
1668 * packets allowed by the congestion window.
1670 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1671 unsigned int cur_mss, int nonagle)
1673 const struct tcp_sock *tp = tcp_sk(sk);
1674 unsigned int cwnd_quota;
1676 tcp_init_tso_segs(skb, cur_mss);
1678 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1681 cwnd_quota = tcp_cwnd_test(tp, skb);
1682 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1688 /* Test if sending is allowed right now. */
1689 bool tcp_may_send_now(struct sock *sk)
1691 const struct tcp_sock *tp = tcp_sk(sk);
1692 struct sk_buff *skb = tcp_send_head(sk);
1695 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1696 (tcp_skb_is_last(sk, skb) ?
1697 tp->nonagle : TCP_NAGLE_PUSH));
1700 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1701 * which is put after SKB on the list. It is very much like
1702 * tcp_fragment() except that it may make several kinds of assumptions
1703 * in order to speed up the splitting operation. In particular, we
1704 * know that all the data is in scatter-gather pages, and that the
1705 * packet has never been sent out before (and thus is not cloned).
1707 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1708 unsigned int mss_now, gfp_t gfp)
1710 struct sk_buff *buff;
1711 int nlen = skb->len - len;
1714 /* All of a TSO frame must be composed of paged data. */
1715 if (skb->len != skb->data_len)
1716 return tcp_fragment(sk, skb, len, mss_now, gfp);
1718 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1719 if (unlikely(!buff))
1722 sk->sk_wmem_queued += buff->truesize;
1723 sk_mem_charge(sk, buff->truesize);
1724 buff->truesize += nlen;
1725 skb->truesize -= nlen;
1727 /* Correct the sequence numbers. */
1728 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1729 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1730 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1732 /* PSH and FIN should only be set in the second packet. */
1733 flags = TCP_SKB_CB(skb)->tcp_flags;
1734 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1735 TCP_SKB_CB(buff)->tcp_flags = flags;
1737 /* This packet was never sent out yet, so no SACK bits. */
1738 TCP_SKB_CB(buff)->sacked = 0;
1740 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1741 skb_split(skb, buff, len);
1742 tcp_fragment_tstamp(skb, buff);
1744 /* Fix up tso_factor for both original and new SKB. */
1745 tcp_set_skb_tso_segs(skb, mss_now);
1746 tcp_set_skb_tso_segs(buff, mss_now);
1748 /* Link BUFF into the send queue. */
1749 __skb_header_release(buff);
1750 tcp_insert_write_queue_after(skb, buff, sk);
1755 /* Try to defer sending, if possible, in order to minimize the amount
1756 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1758 * This algorithm is from John Heffner.
1760 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1761 bool *is_cwnd_limited, u32 max_segs)
1763 const struct inet_connection_sock *icsk = inet_csk(sk);
1764 u32 age, send_win, cong_win, limit, in_flight;
1765 struct tcp_sock *tp = tcp_sk(sk);
1766 struct skb_mstamp now;
1767 struct sk_buff *head;
1770 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1773 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1776 /* Avoid bursty behavior by allowing defer
1777 * only if the last write was recent.
1779 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1782 in_flight = tcp_packets_in_flight(tp);
1784 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1786 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1788 /* From in_flight test above, we know that cwnd > in_flight. */
1789 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1791 limit = min(send_win, cong_win);
1793 /* If a full-sized TSO skb can be sent, do it. */
1794 if (limit >= max_segs * tp->mss_cache)
1797 /* Middle in queue won't get any more data, full sendable already? */
1798 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1801 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1803 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1805 /* If at least some fraction of a window is available,
1808 chunk /= win_divisor;
1812 /* Different approach, try not to defer past a single
1813 * ACK. Receiver should ACK every other full sized
1814 * frame, so if we have space for more than 3 frames
1817 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1821 head = tcp_write_queue_head(sk);
1822 skb_mstamp_get(&now);
1823 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1824 /* If next ACK is likely to come too late (half srtt), do not defer */
1825 if (age < (tp->srtt_us >> 4))
1828 /* Ok, it looks like it is advisable to defer. */
1830 if (cong_win < send_win && cong_win < skb->len)
1831 *is_cwnd_limited = true;
1839 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1841 struct inet_connection_sock *icsk = inet_csk(sk);
1842 struct tcp_sock *tp = tcp_sk(sk);
1843 struct net *net = sock_net(sk);
1847 interval = net->ipv4.sysctl_tcp_probe_interval;
1848 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1849 if (unlikely(delta >= interval * HZ)) {
1850 int mss = tcp_current_mss(sk);
1852 /* Update current search range */
1853 icsk->icsk_mtup.probe_size = 0;
1854 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1855 sizeof(struct tcphdr) +
1856 icsk->icsk_af_ops->net_header_len;
1857 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1859 /* Update probe time stamp */
1860 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1864 /* Create a new MTU probe if we are ready.
1865 * MTU probe is regularly attempting to increase the path MTU by
1866 * deliberately sending larger packets. This discovers routing
1867 * changes resulting in larger path MTUs.
1869 * Returns 0 if we should wait to probe (no cwnd available),
1870 * 1 if a probe was sent,
1873 static int tcp_mtu_probe(struct sock *sk)
1875 struct tcp_sock *tp = tcp_sk(sk);
1876 struct inet_connection_sock *icsk = inet_csk(sk);
1877 struct sk_buff *skb, *nskb, *next;
1878 struct net *net = sock_net(sk);
1886 /* Not currently probing/verifying,
1888 * have enough cwnd, and
1889 * not SACKing (the variable headers throw things off) */
1890 if (!icsk->icsk_mtup.enabled ||
1891 icsk->icsk_mtup.probe_size ||
1892 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1893 tp->snd_cwnd < 11 ||
1894 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1897 /* Use binary search for probe_size between tcp_mss_base,
1898 * and current mss_clamp. if (search_high - search_low)
1899 * smaller than a threshold, backoff from probing.
1901 mss_now = tcp_current_mss(sk);
1902 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1903 icsk->icsk_mtup.search_low) >> 1);
1904 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1905 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1906 /* When misfortune happens, we are reprobing actively,
1907 * and then reprobe timer has expired. We stick with current
1908 * probing process by not resetting search range to its orignal.
1910 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1911 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1912 /* Check whether enough time has elaplased for
1913 * another round of probing.
1915 tcp_mtu_check_reprobe(sk);
1919 /* Have enough data in the send queue to probe? */
1920 if (tp->write_seq - tp->snd_nxt < size_needed)
1923 if (tp->snd_wnd < size_needed)
1925 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1928 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1929 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1930 if (!tcp_packets_in_flight(tp))
1936 /* We're allowed to probe. Build it now. */
1937 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1940 sk->sk_wmem_queued += nskb->truesize;
1941 sk_mem_charge(sk, nskb->truesize);
1943 skb = tcp_send_head(sk);
1945 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1946 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1947 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1948 TCP_SKB_CB(nskb)->sacked = 0;
1950 nskb->ip_summed = skb->ip_summed;
1952 tcp_insert_write_queue_before(nskb, skb, sk);
1955 tcp_for_write_queue_from_safe(skb, next, sk) {
1956 copy = min_t(int, skb->len, probe_size - len);
1957 if (nskb->ip_summed)
1958 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1960 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1961 skb_put(nskb, copy),
1964 if (skb->len <= copy) {
1965 /* We've eaten all the data from this skb.
1967 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1968 tcp_unlink_write_queue(skb, sk);
1969 sk_wmem_free_skb(sk, skb);
1971 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1972 ~(TCPHDR_FIN|TCPHDR_PSH);
1973 if (!skb_shinfo(skb)->nr_frags) {
1974 skb_pull(skb, copy);
1975 if (skb->ip_summed != CHECKSUM_PARTIAL)
1976 skb->csum = csum_partial(skb->data,
1979 __pskb_trim_head(skb, copy);
1980 tcp_set_skb_tso_segs(skb, mss_now);
1982 TCP_SKB_CB(skb)->seq += copy;
1987 if (len >= probe_size)
1990 tcp_init_tso_segs(nskb, nskb->len);
1992 /* We're ready to send. If this fails, the probe will
1993 * be resegmented into mss-sized pieces by tcp_write_xmit().
1995 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1996 /* Decrement cwnd here because we are sending
1997 * effectively two packets. */
1999 tcp_event_new_data_sent(sk, nskb);
2001 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2002 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2003 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2011 /* This routine writes packets to the network. It advances the
2012 * send_head. This happens as incoming acks open up the remote
2015 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2016 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2017 * account rare use of URG, this is not a big flaw.
2019 * Send at most one packet when push_one > 0. Temporarily ignore
2020 * cwnd limit to force at most one packet out when push_one == 2.
2022 * Returns true, if no segments are in flight and we have queued segments,
2023 * but cannot send anything now because of SWS or another problem.
2025 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2026 int push_one, gfp_t gfp)
2028 struct tcp_sock *tp = tcp_sk(sk);
2029 struct sk_buff *skb;
2030 unsigned int tso_segs, sent_pkts;
2033 bool is_cwnd_limited = false;
2039 /* Do MTU probing. */
2040 result = tcp_mtu_probe(sk);
2043 } else if (result > 0) {
2048 max_segs = tcp_tso_autosize(sk, mss_now);
2049 while ((skb = tcp_send_head(sk))) {
2052 tso_segs = tcp_init_tso_segs(skb, mss_now);
2055 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2056 /* "skb_mstamp" is used as a start point for the retransmit timer */
2057 skb_mstamp_get(&skb->skb_mstamp);
2058 goto repair; /* Skip network transmission */
2061 cwnd_quota = tcp_cwnd_test(tp, skb);
2063 is_cwnd_limited = true;
2065 /* Force out a loss probe pkt. */
2071 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2074 if (tso_segs == 1) {
2075 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2076 (tcp_skb_is_last(sk, skb) ?
2077 nonagle : TCP_NAGLE_PUSH))))
2081 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2087 if (tso_segs > 1 && !tcp_urg_mode(tp))
2088 limit = tcp_mss_split_point(sk, skb, mss_now,
2094 if (skb->len > limit &&
2095 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2098 /* TCP Small Queues :
2099 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2101 * - better RTT estimation and ACK scheduling
2104 * Alas, some drivers / subsystems require a fair amount
2105 * of queued bytes to ensure line rate.
2106 * One example is wifi aggregation (802.11 AMPDU)
2108 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2109 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2111 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2112 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2113 /* It is possible TX completion already happened
2114 * before we set TSQ_THROTTLED, so we must
2115 * test again the condition.
2117 smp_mb__after_atomic();
2118 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2122 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2126 /* Advance the send_head. This one is sent out.
2127 * This call will increment packets_out.
2129 tcp_event_new_data_sent(sk, skb);
2131 tcp_minshall_update(tp, mss_now, skb);
2132 sent_pkts += tcp_skb_pcount(skb);
2138 if (likely(sent_pkts)) {
2139 if (tcp_in_cwnd_reduction(sk))
2140 tp->prr_out += sent_pkts;
2142 /* Send one loss probe per tail loss episode. */
2144 tcp_schedule_loss_probe(sk);
2145 tcp_cwnd_validate(sk, is_cwnd_limited);
2148 return !tp->packets_out && tcp_send_head(sk);
2151 bool tcp_schedule_loss_probe(struct sock *sk)
2153 struct inet_connection_sock *icsk = inet_csk(sk);
2154 struct tcp_sock *tp = tcp_sk(sk);
2155 u32 timeout, tlp_time_stamp, rto_time_stamp;
2156 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2158 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2160 /* No consecutive loss probes. */
2161 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2165 /* Don't do any loss probe on a Fast Open connection before 3WHS
2168 if (sk->sk_state == TCP_SYN_RECV)
2171 /* TLP is only scheduled when next timer event is RTO. */
2172 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2175 /* Schedule a loss probe in 2*RTT for SACK capable connections
2176 * in Open state, that are either limited by cwnd or application.
2178 if (sysctl_tcp_early_retrans < 3 || !tp->srtt_us || !tp->packets_out ||
2179 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2182 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2186 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2187 * for delayed ack when there's one outstanding packet.
2190 if (tp->packets_out == 1)
2191 timeout = max_t(u32, timeout,
2192 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2193 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2195 /* If RTO is shorter, just schedule TLP in its place. */
2196 tlp_time_stamp = tcp_time_stamp + timeout;
2197 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2198 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2199 s32 delta = rto_time_stamp - tcp_time_stamp;
2204 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2209 /* Thanks to skb fast clones, we can detect if a prior transmit of
2210 * a packet is still in a qdisc or driver queue.
2211 * In this case, there is very little point doing a retransmit !
2212 * Note: This is called from BH context only.
2214 static bool skb_still_in_host_queue(const struct sock *sk,
2215 const struct sk_buff *skb)
2217 if (unlikely(skb_fclone_busy(sk, skb))) {
2218 NET_INC_STATS_BH(sock_net(sk),
2219 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2225 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2226 * retransmit the last segment.
2228 void tcp_send_loss_probe(struct sock *sk)
2230 struct tcp_sock *tp = tcp_sk(sk);
2231 struct sk_buff *skb;
2233 int mss = tcp_current_mss(sk);
2235 skb = tcp_send_head(sk);
2237 if (tcp_snd_wnd_test(tp, skb, mss)) {
2238 pcount = tp->packets_out;
2239 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2240 if (tp->packets_out > pcount)
2244 skb = tcp_write_queue_prev(sk, skb);
2246 skb = tcp_write_queue_tail(sk);
2249 /* At most one outstanding TLP retransmission. */
2250 if (tp->tlp_high_seq)
2253 /* Retransmit last segment. */
2257 if (skb_still_in_host_queue(sk, skb))
2260 pcount = tcp_skb_pcount(skb);
2261 if (WARN_ON(!pcount))
2264 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2265 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2268 skb = tcp_write_queue_next(sk, skb);
2271 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2274 if (__tcp_retransmit_skb(sk, skb))
2277 /* Record snd_nxt for loss detection. */
2278 tp->tlp_high_seq = tp->snd_nxt;
2281 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2282 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2283 inet_csk(sk)->icsk_pending = 0;
2288 /* Push out any pending frames which were held back due to
2289 * TCP_CORK or attempt at coalescing tiny packets.
2290 * The socket must be locked by the caller.
2292 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2295 /* If we are closed, the bytes will have to remain here.
2296 * In time closedown will finish, we empty the write queue and
2297 * all will be happy.
2299 if (unlikely(sk->sk_state == TCP_CLOSE))
2302 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2303 sk_gfp_atomic(sk, GFP_ATOMIC)))
2304 tcp_check_probe_timer(sk);
2307 /* Send _single_ skb sitting at the send head. This function requires
2308 * true push pending frames to setup probe timer etc.
2310 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2312 struct sk_buff *skb = tcp_send_head(sk);
2314 BUG_ON(!skb || skb->len < mss_now);
2316 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2319 /* This function returns the amount that we can raise the
2320 * usable window based on the following constraints
2322 * 1. The window can never be shrunk once it is offered (RFC 793)
2323 * 2. We limit memory per socket
2326 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2327 * RECV.NEXT + RCV.WIN fixed until:
2328 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2330 * i.e. don't raise the right edge of the window until you can raise
2331 * it at least MSS bytes.
2333 * Unfortunately, the recommended algorithm breaks header prediction,
2334 * since header prediction assumes th->window stays fixed.
2336 * Strictly speaking, keeping th->window fixed violates the receiver
2337 * side SWS prevention criteria. The problem is that under this rule
2338 * a stream of single byte packets will cause the right side of the
2339 * window to always advance by a single byte.
2341 * Of course, if the sender implements sender side SWS prevention
2342 * then this will not be a problem.
2344 * BSD seems to make the following compromise:
2346 * If the free space is less than the 1/4 of the maximum
2347 * space available and the free space is less than 1/2 mss,
2348 * then set the window to 0.
2349 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2350 * Otherwise, just prevent the window from shrinking
2351 * and from being larger than the largest representable value.
2353 * This prevents incremental opening of the window in the regime
2354 * where TCP is limited by the speed of the reader side taking
2355 * data out of the TCP receive queue. It does nothing about
2356 * those cases where the window is constrained on the sender side
2357 * because the pipeline is full.
2359 * BSD also seems to "accidentally" limit itself to windows that are a
2360 * multiple of MSS, at least until the free space gets quite small.
2361 * This would appear to be a side effect of the mbuf implementation.
2362 * Combining these two algorithms results in the observed behavior
2363 * of having a fixed window size at almost all times.
2365 * Below we obtain similar behavior by forcing the offered window to
2366 * a multiple of the mss when it is feasible to do so.
2368 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2369 * Regular options like TIMESTAMP are taken into account.
2371 u32 __tcp_select_window(struct sock *sk)
2373 struct inet_connection_sock *icsk = inet_csk(sk);
2374 struct tcp_sock *tp = tcp_sk(sk);
2375 /* MSS for the peer's data. Previous versions used mss_clamp
2376 * here. I don't know if the value based on our guesses
2377 * of peer's MSS is better for the performance. It's more correct
2378 * but may be worse for the performance because of rcv_mss
2379 * fluctuations. --SAW 1998/11/1
2381 int mss = icsk->icsk_ack.rcv_mss;
2382 int free_space = tcp_space(sk);
2383 int allowed_space = tcp_full_space(sk);
2384 int full_space = min_t(int, tp->window_clamp, allowed_space);
2387 if (mss > full_space)
2390 if (free_space < (full_space >> 1)) {
2391 icsk->icsk_ack.quick = 0;
2393 if (tcp_under_memory_pressure(sk))
2394 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2397 /* free_space might become our new window, make sure we don't
2398 * increase it due to wscale.
2400 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2402 /* if free space is less than mss estimate, or is below 1/16th
2403 * of the maximum allowed, try to move to zero-window, else
2404 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2405 * new incoming data is dropped due to memory limits.
2406 * With large window, mss test triggers way too late in order
2407 * to announce zero window in time before rmem limit kicks in.
2409 if (free_space < (allowed_space >> 4) || free_space < mss)
2413 if (free_space > tp->rcv_ssthresh)
2414 free_space = tp->rcv_ssthresh;
2416 /* Don't do rounding if we are using window scaling, since the
2417 * scaled window will not line up with the MSS boundary anyway.
2419 window = tp->rcv_wnd;
2420 if (tp->rx_opt.rcv_wscale) {
2421 window = free_space;
2423 /* Advertise enough space so that it won't get scaled away.
2424 * Import case: prevent zero window announcement if
2425 * 1<<rcv_wscale > mss.
2427 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2428 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2429 << tp->rx_opt.rcv_wscale);
2431 /* Get the largest window that is a nice multiple of mss.
2432 * Window clamp already applied above.
2433 * If our current window offering is within 1 mss of the
2434 * free space we just keep it. This prevents the divide
2435 * and multiply from happening most of the time.
2436 * We also don't do any window rounding when the free space
2439 if (window <= free_space - mss || window > free_space)
2440 window = (free_space / mss) * mss;
2441 else if (mss == full_space &&
2442 free_space > window + (full_space >> 1))
2443 window = free_space;
2449 /* Collapses two adjacent SKB's during retransmission. */
2450 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2452 struct tcp_sock *tp = tcp_sk(sk);
2453 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2454 int skb_size, next_skb_size;
2456 skb_size = skb->len;
2457 next_skb_size = next_skb->len;
2459 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2461 tcp_highest_sack_combine(sk, next_skb, skb);
2463 tcp_unlink_write_queue(next_skb, sk);
2465 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2468 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2469 skb->ip_summed = CHECKSUM_PARTIAL;
2471 if (skb->ip_summed != CHECKSUM_PARTIAL)
2472 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2474 /* Update sequence range on original skb. */
2475 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2477 /* Merge over control information. This moves PSH/FIN etc. over */
2478 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2480 /* All done, get rid of second SKB and account for it so
2481 * packet counting does not break.
2483 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2485 /* changed transmit queue under us so clear hints */
2486 tcp_clear_retrans_hints_partial(tp);
2487 if (next_skb == tp->retransmit_skb_hint)
2488 tp->retransmit_skb_hint = skb;
2490 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2492 sk_wmem_free_skb(sk, next_skb);
2495 /* Check if coalescing SKBs is legal. */
2496 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2498 if (tcp_skb_pcount(skb) > 1)
2500 /* TODO: SACK collapsing could be used to remove this condition */
2501 if (skb_shinfo(skb)->nr_frags != 0)
2503 if (skb_cloned(skb))
2505 if (skb == tcp_send_head(sk))
2507 /* Some heurestics for collapsing over SACK'd could be invented */
2508 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2514 /* Collapse packets in the retransmit queue to make to create
2515 * less packets on the wire. This is only done on retransmission.
2517 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2520 struct tcp_sock *tp = tcp_sk(sk);
2521 struct sk_buff *skb = to, *tmp;
2524 if (!sysctl_tcp_retrans_collapse)
2526 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2529 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2530 if (!tcp_can_collapse(sk, skb))
2542 /* Punt if not enough space exists in the first SKB for
2543 * the data in the second
2545 if (skb->len > skb_availroom(to))
2548 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2551 tcp_collapse_retrans(sk, to);
2555 /* This retransmits one SKB. Policy decisions and retransmit queue
2556 * state updates are done by the caller. Returns non-zero if an
2557 * error occurred which prevented the send.
2559 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2561 struct tcp_sock *tp = tcp_sk(sk);
2562 struct inet_connection_sock *icsk = inet_csk(sk);
2563 unsigned int cur_mss;
2566 /* Inconslusive MTU probe */
2567 if (icsk->icsk_mtup.probe_size) {
2568 icsk->icsk_mtup.probe_size = 0;
2571 /* Do not sent more than we queued. 1/4 is reserved for possible
2572 * copying overhead: fragmentation, tunneling, mangling etc.
2574 if (atomic_read(&sk->sk_wmem_alloc) >
2575 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2578 if (skb_still_in_host_queue(sk, skb))
2581 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2582 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2584 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2588 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2589 return -EHOSTUNREACH; /* Routing failure or similar. */
2591 cur_mss = tcp_current_mss(sk);
2593 /* If receiver has shrunk his window, and skb is out of
2594 * new window, do not retransmit it. The exception is the
2595 * case, when window is shrunk to zero. In this case
2596 * our retransmit serves as a zero window probe.
2598 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2599 TCP_SKB_CB(skb)->seq != tp->snd_una)
2602 if (skb->len > cur_mss) {
2603 if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
2604 return -ENOMEM; /* We'll try again later. */
2606 int oldpcount = tcp_skb_pcount(skb);
2608 if (unlikely(oldpcount > 1)) {
2609 if (skb_unclone(skb, GFP_ATOMIC))
2611 tcp_init_tso_segs(skb, cur_mss);
2612 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2616 /* RFC3168, section 6.1.1.1. ECN fallback */
2617 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2618 tcp_ecn_clear_syn(sk, skb);
2620 tcp_retrans_try_collapse(sk, skb, cur_mss);
2622 /* Make a copy, if the first transmission SKB clone we made
2623 * is still in somebody's hands, else make a clone.
2626 /* make sure skb->data is aligned on arches that require it
2627 * and check if ack-trimming & collapsing extended the headroom
2628 * beyond what csum_start can cover.
2630 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2631 skb_headroom(skb) >= 0xFFFF)) {
2632 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2634 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2637 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2641 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2642 /* Update global TCP statistics. */
2643 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2644 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2645 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2646 tp->total_retrans++;
2651 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2653 struct tcp_sock *tp = tcp_sk(sk);
2654 int err = __tcp_retransmit_skb(sk, skb);
2657 #if FASTRETRANS_DEBUG > 0
2658 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2659 net_dbg_ratelimited("retrans_out leaked\n");
2662 if (!tp->retrans_out)
2663 tp->lost_retrans_low = tp->snd_nxt;
2664 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2665 tp->retrans_out += tcp_skb_pcount(skb);
2667 /* Save stamp of the first retransmit. */
2668 if (!tp->retrans_stamp)
2669 tp->retrans_stamp = tcp_skb_timestamp(skb);
2671 /* snd_nxt is stored to detect loss of retransmitted segment,
2672 * see tcp_input.c tcp_sacktag_write_queue().
2674 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2675 } else if (err != -EBUSY) {
2676 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2679 if (tp->undo_retrans < 0)
2680 tp->undo_retrans = 0;
2681 tp->undo_retrans += tcp_skb_pcount(skb);
2685 /* Check if we forward retransmits are possible in the current
2686 * window/congestion state.
2688 static bool tcp_can_forward_retransmit(struct sock *sk)
2690 const struct inet_connection_sock *icsk = inet_csk(sk);
2691 const struct tcp_sock *tp = tcp_sk(sk);
2693 /* Forward retransmissions are possible only during Recovery. */
2694 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2697 /* No forward retransmissions in Reno are possible. */
2698 if (tcp_is_reno(tp))
2701 /* Yeah, we have to make difficult choice between forward transmission
2702 * and retransmission... Both ways have their merits...
2704 * For now we do not retransmit anything, while we have some new
2705 * segments to send. In the other cases, follow rule 3 for
2706 * NextSeg() specified in RFC3517.
2709 if (tcp_may_send_now(sk))
2715 /* This gets called after a retransmit timeout, and the initially
2716 * retransmitted data is acknowledged. It tries to continue
2717 * resending the rest of the retransmit queue, until either
2718 * we've sent it all or the congestion window limit is reached.
2719 * If doing SACK, the first ACK which comes back for a timeout
2720 * based retransmit packet might feed us FACK information again.
2721 * If so, we use it to avoid unnecessarily retransmissions.
2723 void tcp_xmit_retransmit_queue(struct sock *sk)
2725 const struct inet_connection_sock *icsk = inet_csk(sk);
2726 struct tcp_sock *tp = tcp_sk(sk);
2727 struct sk_buff *skb;
2728 struct sk_buff *hole = NULL;
2731 int fwd_rexmitting = 0;
2733 if (!tp->packets_out)
2737 tp->retransmit_high = tp->snd_una;
2739 if (tp->retransmit_skb_hint) {
2740 skb = tp->retransmit_skb_hint;
2741 last_lost = TCP_SKB_CB(skb)->end_seq;
2742 if (after(last_lost, tp->retransmit_high))
2743 last_lost = tp->retransmit_high;
2745 skb = tcp_write_queue_head(sk);
2746 last_lost = tp->snd_una;
2749 tcp_for_write_queue_from(skb, sk) {
2750 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2752 if (skb == tcp_send_head(sk))
2754 /* we could do better than to assign each time */
2756 tp->retransmit_skb_hint = skb;
2758 /* Assume this retransmit will generate
2759 * only one packet for congestion window
2760 * calculation purposes. This works because
2761 * tcp_retransmit_skb() will chop up the
2762 * packet to be MSS sized and all the
2763 * packet counting works out.
2765 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2768 if (fwd_rexmitting) {
2770 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2772 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2774 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2775 tp->retransmit_high = last_lost;
2776 if (!tcp_can_forward_retransmit(sk))
2778 /* Backtrack if necessary to non-L'ed skb */
2786 } else if (!(sacked & TCPCB_LOST)) {
2787 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2792 last_lost = TCP_SKB_CB(skb)->end_seq;
2793 if (icsk->icsk_ca_state != TCP_CA_Loss)
2794 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2796 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2799 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2802 if (tcp_retransmit_skb(sk, skb))
2805 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2807 if (tcp_in_cwnd_reduction(sk))
2808 tp->prr_out += tcp_skb_pcount(skb);
2810 if (skb == tcp_write_queue_head(sk))
2811 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2812 inet_csk(sk)->icsk_rto,
2817 /* We allow to exceed memory limits for FIN packets to expedite
2818 * connection tear down and (memory) recovery.
2819 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2820 * or even be forced to close flow without any FIN.
2821 * In general, we want to allow one skb per socket to avoid hangs
2822 * with edge trigger epoll()
2824 void sk_forced_mem_schedule(struct sock *sk, int size)
2828 if (size <= sk->sk_forward_alloc)
2830 amt = sk_mem_pages(size);
2831 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2832 sk_memory_allocated_add(sk, amt, &status);
2835 /* Send a FIN. The caller locks the socket for us.
2836 * We should try to send a FIN packet really hard, but eventually give up.
2838 void tcp_send_fin(struct sock *sk)
2840 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2841 struct tcp_sock *tp = tcp_sk(sk);
2843 /* Optimization, tack on the FIN if we have one skb in write queue and
2844 * this skb was not yet sent, or we are under memory pressure.
2845 * Note: in the latter case, FIN packet will be sent after a timeout,
2846 * as TCP stack thinks it has already been transmitted.
2848 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2850 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
2851 TCP_SKB_CB(tskb)->end_seq++;
2853 if (!tcp_send_head(sk)) {
2854 /* This means tskb was already sent.
2855 * Pretend we included the FIN on previous transmit.
2856 * We need to set tp->snd_nxt to the value it would have
2857 * if FIN had been sent. This is because retransmit path
2858 * does not change tp->snd_nxt.
2864 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
2865 if (unlikely(!skb)) {
2870 skb_reserve(skb, MAX_TCP_HEADER);
2871 sk_forced_mem_schedule(sk, skb->truesize);
2872 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2873 tcp_init_nondata_skb(skb, tp->write_seq,
2874 TCPHDR_ACK | TCPHDR_FIN);
2875 tcp_queue_skb(sk, skb);
2877 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
2880 /* We get here when a process closes a file descriptor (either due to
2881 * an explicit close() or as a byproduct of exit()'ing) and there
2882 * was unread data in the receive queue. This behavior is recommended
2883 * by RFC 2525, section 2.17. -DaveM
2885 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2887 struct sk_buff *skb;
2889 /* NOTE: No TCP options attached and we never retransmit this. */
2890 skb = alloc_skb(MAX_TCP_HEADER, priority);
2892 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2896 /* Reserve space for headers and prepare control bits. */
2897 skb_reserve(skb, MAX_TCP_HEADER);
2898 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2899 TCPHDR_ACK | TCPHDR_RST);
2900 skb_mstamp_get(&skb->skb_mstamp);
2902 if (tcp_transmit_skb(sk, skb, 0, priority))
2903 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2905 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2908 /* Send a crossed SYN-ACK during socket establishment.
2909 * WARNING: This routine must only be called when we have already sent
2910 * a SYN packet that crossed the incoming SYN that caused this routine
2911 * to get called. If this assumption fails then the initial rcv_wnd
2912 * and rcv_wscale values will not be correct.
2914 int tcp_send_synack(struct sock *sk)
2916 struct sk_buff *skb;
2918 skb = tcp_write_queue_head(sk);
2919 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2920 pr_debug("%s: wrong queue state\n", __func__);
2923 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2924 if (skb_cloned(skb)) {
2925 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2928 tcp_unlink_write_queue(skb, sk);
2929 __skb_header_release(nskb);
2930 __tcp_add_write_queue_head(sk, nskb);
2931 sk_wmem_free_skb(sk, skb);
2932 sk->sk_wmem_queued += nskb->truesize;
2933 sk_mem_charge(sk, nskb->truesize);
2937 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2938 tcp_ecn_send_synack(sk, skb);
2940 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2944 * tcp_make_synack - Prepare a SYN-ACK.
2945 * sk: listener socket
2946 * dst: dst entry attached to the SYNACK
2947 * req: request_sock pointer
2949 * Allocate one skb and build a SYNACK packet.
2950 * @dst is consumed : Caller should not use it again.
2952 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2953 struct request_sock *req,
2954 struct tcp_fastopen_cookie *foc)
2956 struct tcp_out_options opts;
2957 struct inet_request_sock *ireq = inet_rsk(req);
2958 struct tcp_sock *tp = tcp_sk(sk);
2960 struct sk_buff *skb;
2961 struct tcp_md5sig_key *md5 = NULL;
2962 int tcp_header_size;
2965 skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
2966 if (unlikely(!skb)) {
2970 /* Reserve space for headers. */
2971 skb_reserve(skb, MAX_TCP_HEADER);
2973 skb_dst_set(skb, dst);
2975 mss = dst_metric_advmss(dst);
2976 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2977 mss = tp->rx_opt.user_mss;
2979 memset(&opts, 0, sizeof(opts));
2980 #ifdef CONFIG_SYN_COOKIES
2981 if (unlikely(req->cookie_ts))
2982 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
2985 skb_mstamp_get(&skb->skb_mstamp);
2987 #ifdef CONFIG_TCP_MD5SIG
2989 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
2991 tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5,
2994 skb_push(skb, tcp_header_size);
2995 skb_reset_transport_header(skb);
2998 memset(th, 0, sizeof(struct tcphdr));
3001 tcp_ecn_make_synack(req, th, sk);
3002 th->source = htons(ireq->ir_num);
3003 th->dest = ireq->ir_rmt_port;
3004 /* Setting of flags are superfluous here for callers (and ECE is
3005 * not even correctly set)
3007 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3008 TCPHDR_SYN | TCPHDR_ACK);
3010 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3011 /* XXX data is queued and acked as is. No buffer/window check */
3012 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3014 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3015 th->window = htons(min(req->rcv_wnd, 65535U));
3016 tcp_options_write((__be32 *)(th + 1), tp, &opts);
3017 th->doff = (tcp_header_size >> 2);
3018 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
3020 #ifdef CONFIG_TCP_MD5SIG
3021 /* Okay, we have all we need - do the md5 hash if needed */
3023 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3024 md5, req_to_sk(req), skb);
3028 /* Do not fool tcpdump (if any), clean our debris */
3029 skb->tstamp.tv64 = 0;
3032 EXPORT_SYMBOL(tcp_make_synack);
3034 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3036 struct inet_connection_sock *icsk = inet_csk(sk);
3037 const struct tcp_congestion_ops *ca;
3038 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3040 if (ca_key == TCP_CA_UNSPEC)
3044 ca = tcp_ca_find_key(ca_key);
3045 if (likely(ca && try_module_get(ca->owner))) {
3046 module_put(icsk->icsk_ca_ops->owner);
3047 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3048 icsk->icsk_ca_ops = ca;
3053 /* Do all connect socket setups that can be done AF independent. */
3054 static void tcp_connect_init(struct sock *sk)
3056 const struct dst_entry *dst = __sk_dst_get(sk);
3057 struct tcp_sock *tp = tcp_sk(sk);
3060 /* We'll fix this up when we get a response from the other end.
3061 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3063 tp->tcp_header_len = sizeof(struct tcphdr) +
3064 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3066 #ifdef CONFIG_TCP_MD5SIG
3067 if (tp->af_specific->md5_lookup(sk, sk))
3068 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3071 /* If user gave his TCP_MAXSEG, record it to clamp */
3072 if (tp->rx_opt.user_mss)
3073 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3076 tcp_sync_mss(sk, dst_mtu(dst));
3078 tcp_ca_dst_init(sk, dst);
3080 if (!tp->window_clamp)
3081 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3082 tp->advmss = dst_metric_advmss(dst);
3083 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3084 tp->advmss = tp->rx_opt.user_mss;
3086 tcp_initialize_rcv_mss(sk);
3088 /* limit the window selection if the user enforce a smaller rx buffer */
3089 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3090 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3091 tp->window_clamp = tcp_full_space(sk);
3093 tcp_select_initial_window(tcp_full_space(sk),
3094 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3097 sysctl_tcp_window_scaling,
3099 dst_metric(dst, RTAX_INITRWND));
3101 tp->rx_opt.rcv_wscale = rcv_wscale;
3102 tp->rcv_ssthresh = tp->rcv_wnd;
3105 sock_reset_flag(sk, SOCK_DONE);
3108 tp->snd_una = tp->write_seq;
3109 tp->snd_sml = tp->write_seq;
3110 tp->snd_up = tp->write_seq;
3111 tp->snd_nxt = tp->write_seq;
3113 if (likely(!tp->repair))
3116 tp->rcv_tstamp = tcp_time_stamp;
3117 tp->rcv_wup = tp->rcv_nxt;
3118 tp->copied_seq = tp->rcv_nxt;
3120 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3121 inet_csk(sk)->icsk_retransmits = 0;
3122 tcp_clear_retrans(tp);
3125 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3127 struct tcp_sock *tp = tcp_sk(sk);
3128 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3130 tcb->end_seq += skb->len;
3131 __skb_header_release(skb);
3132 __tcp_add_write_queue_tail(sk, skb);
3133 sk->sk_wmem_queued += skb->truesize;
3134 sk_mem_charge(sk, skb->truesize);
3135 tp->write_seq = tcb->end_seq;
3136 tp->packets_out += tcp_skb_pcount(skb);
3139 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3140 * queue a data-only packet after the regular SYN, such that regular SYNs
3141 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3142 * only the SYN sequence, the data are retransmitted in the first ACK.
3143 * If cookie is not cached or other error occurs, falls back to send a
3144 * regular SYN with Fast Open cookie request option.
3146 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3148 struct tcp_sock *tp = tcp_sk(sk);
3149 struct tcp_fastopen_request *fo = tp->fastopen_req;
3150 int syn_loss = 0, space, err = 0, copied;
3151 unsigned long last_syn_loss = 0;
3152 struct sk_buff *syn_data;
3154 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3155 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3156 &syn_loss, &last_syn_loss);
3157 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3159 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3160 fo->cookie.len = -1;
3164 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3165 fo->cookie.len = -1;
3166 else if (fo->cookie.len <= 0)
3169 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3170 * user-MSS. Reserve maximum option space for middleboxes that add
3171 * private TCP options. The cost is reduced data space in SYN :(
3173 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3174 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3175 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3176 MAX_TCP_OPTION_SPACE;
3178 space = min_t(size_t, space, fo->size);
3180 /* limit to order-0 allocations */
3181 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3183 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3186 syn_data->ip_summed = CHECKSUM_PARTIAL;
3187 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3188 copied = copy_from_iter(skb_put(syn_data, space), space,
3189 &fo->data->msg_iter);
3190 if (unlikely(!copied)) {
3191 kfree_skb(syn_data);
3194 if (copied != space) {
3195 skb_trim(syn_data, copied);
3199 /* No more data pending in inet_wait_for_connect() */
3200 if (space == fo->size)
3204 tcp_connect_queue_skb(sk, syn_data);
3206 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3208 syn->skb_mstamp = syn_data->skb_mstamp;
3210 /* Now full SYN+DATA was cloned and sent (or not),
3211 * remove the SYN from the original skb (syn_data)
3212 * we keep in write queue in case of a retransmit, as we
3213 * also have the SYN packet (with no data) in the same queue.
3215 TCP_SKB_CB(syn_data)->seq++;
3216 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3218 tp->syn_data = (fo->copied > 0);
3219 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3224 /* Send a regular SYN with Fast Open cookie request option */
3225 if (fo->cookie.len > 0)
3227 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3229 tp->syn_fastopen = 0;
3231 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3235 /* Build a SYN and send it off. */
3236 int tcp_connect(struct sock *sk)
3238 struct tcp_sock *tp = tcp_sk(sk);
3239 struct sk_buff *buff;
3242 tcp_connect_init(sk);
3244 if (unlikely(tp->repair)) {
3245 tcp_finish_connect(sk, NULL);
3249 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3250 if (unlikely(!buff))
3253 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3254 tp->retrans_stamp = tcp_time_stamp;
3255 tcp_connect_queue_skb(sk, buff);
3256 tcp_ecn_send_syn(sk, buff);
3258 /* Send off SYN; include data in Fast Open. */
3259 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3260 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3261 if (err == -ECONNREFUSED)
3264 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3265 * in order to make this packet get counted in tcpOutSegs.
3267 tp->snd_nxt = tp->write_seq;
3268 tp->pushed_seq = tp->write_seq;
3269 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3271 /* Timer for repeating the SYN until an answer. */
3272 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3273 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3276 EXPORT_SYMBOL(tcp_connect);
3278 /* Send out a delayed ack, the caller does the policy checking
3279 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3282 void tcp_send_delayed_ack(struct sock *sk)
3284 struct inet_connection_sock *icsk = inet_csk(sk);
3285 int ato = icsk->icsk_ack.ato;
3286 unsigned long timeout;
3288 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3290 if (ato > TCP_DELACK_MIN) {
3291 const struct tcp_sock *tp = tcp_sk(sk);
3292 int max_ato = HZ / 2;
3294 if (icsk->icsk_ack.pingpong ||
3295 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3296 max_ato = TCP_DELACK_MAX;
3298 /* Slow path, intersegment interval is "high". */
3300 /* If some rtt estimate is known, use it to bound delayed ack.
3301 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3305 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3312 ato = min(ato, max_ato);
3315 /* Stay within the limit we were given */
3316 timeout = jiffies + ato;
3318 /* Use new timeout only if there wasn't a older one earlier. */
3319 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3320 /* If delack timer was blocked or is about to expire,
3323 if (icsk->icsk_ack.blocked ||
3324 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3329 if (!time_before(timeout, icsk->icsk_ack.timeout))
3330 timeout = icsk->icsk_ack.timeout;
3332 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3333 icsk->icsk_ack.timeout = timeout;
3334 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3337 /* This routine sends an ack and also updates the window. */
3338 void tcp_send_ack(struct sock *sk)
3340 struct sk_buff *buff;
3342 /* If we have been reset, we may not send again. */
3343 if (sk->sk_state == TCP_CLOSE)
3346 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3348 /* We are not putting this on the write queue, so
3349 * tcp_transmit_skb() will set the ownership to this
3352 buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3354 inet_csk_schedule_ack(sk);
3355 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3356 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3357 TCP_DELACK_MAX, TCP_RTO_MAX);
3361 /* Reserve space for headers and prepare control bits. */
3362 skb_reserve(buff, MAX_TCP_HEADER);
3363 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3365 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3367 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3368 * We also avoid tcp_wfree() overhead (cache line miss accessing
3369 * tp->tsq_flags) by using regular sock_wfree()
3371 skb_set_tcp_pure_ack(buff);
3373 /* Send it off, this clears delayed acks for us. */
3374 skb_mstamp_get(&buff->skb_mstamp);
3375 tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
3377 EXPORT_SYMBOL_GPL(tcp_send_ack);
3379 /* This routine sends a packet with an out of date sequence
3380 * number. It assumes the other end will try to ack it.
3382 * Question: what should we make while urgent mode?
3383 * 4.4BSD forces sending single byte of data. We cannot send
3384 * out of window data, because we have SND.NXT==SND.MAX...
3386 * Current solution: to send TWO zero-length segments in urgent mode:
3387 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3388 * out-of-date with SND.UNA-1 to probe window.
3390 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3392 struct tcp_sock *tp = tcp_sk(sk);
3393 struct sk_buff *skb;
3395 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3396 skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3400 /* Reserve space for headers and set control bits. */
3401 skb_reserve(skb, MAX_TCP_HEADER);
3402 /* Use a previous sequence. This should cause the other
3403 * end to send an ack. Don't queue or clone SKB, just
3406 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3407 skb_mstamp_get(&skb->skb_mstamp);
3408 NET_INC_STATS(sock_net(sk), mib);
3409 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3412 void tcp_send_window_probe(struct sock *sk)
3414 if (sk->sk_state == TCP_ESTABLISHED) {
3415 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3416 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3420 /* Initiate keepalive or window probe from timer. */
3421 int tcp_write_wakeup(struct sock *sk, int mib)
3423 struct tcp_sock *tp = tcp_sk(sk);
3424 struct sk_buff *skb;
3426 if (sk->sk_state == TCP_CLOSE)
3429 skb = tcp_send_head(sk);
3430 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3432 unsigned int mss = tcp_current_mss(sk);
3433 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3435 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3436 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3438 /* We are probing the opening of a window
3439 * but the window size is != 0
3440 * must have been a result SWS avoidance ( sender )
3442 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3444 seg_size = min(seg_size, mss);
3445 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3446 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3448 } else if (!tcp_skb_pcount(skb))
3449 tcp_set_skb_tso_segs(skb, mss);
3451 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3452 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3454 tcp_event_new_data_sent(sk, skb);
3457 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3458 tcp_xmit_probe_skb(sk, 1, mib);
3459 return tcp_xmit_probe_skb(sk, 0, mib);
3463 /* A window probe timeout has occurred. If window is not closed send
3464 * a partial packet else a zero probe.
3466 void tcp_send_probe0(struct sock *sk)
3468 struct inet_connection_sock *icsk = inet_csk(sk);
3469 struct tcp_sock *tp = tcp_sk(sk);
3470 unsigned long probe_max;
3473 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3475 if (tp->packets_out || !tcp_send_head(sk)) {
3476 /* Cancel probe timer, if it is not required. */
3477 icsk->icsk_probes_out = 0;
3478 icsk->icsk_backoff = 0;
3483 if (icsk->icsk_backoff < sysctl_tcp_retries2)
3484 icsk->icsk_backoff++;
3485 icsk->icsk_probes_out++;
3486 probe_max = TCP_RTO_MAX;
3488 /* If packet was not sent due to local congestion,
3489 * do not backoff and do not remember icsk_probes_out.
3490 * Let local senders to fight for local resources.
3492 * Use accumulated backoff yet.
3494 if (!icsk->icsk_probes_out)
3495 icsk->icsk_probes_out = 1;
3496 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3498 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3499 tcp_probe0_when(sk, probe_max),
3503 int tcp_rtx_synack(struct sock *sk, struct request_sock *req)
3505 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3509 res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL);
3511 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
3512 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3516 EXPORT_SYMBOL(tcp_rtx_synack);