2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * Implementation of the Transmission Control Protocol(TCP).
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
27 * Linus Torvalds : send_delayed_ack
28 * David S. Miller : Charge memory using the right skb
29 * during syn/ack processing.
30 * David S. Miller : Output engine completely rewritten.
31 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
32 * Cacophonix Gaul : draft-minshall-nagle-01
33 * J Hadi Salim : ECN support
37 #define pr_fmt(fmt) "TCP: " fmt
41 #include <linux/compiler.h>
42 #include <linux/gfp.h>
43 #include <linux/module.h>
45 /* People can turn this off for buggy TCP's found in printers etc. */
46 int sysctl_tcp_retrans_collapse __read_mostly = 1;
48 /* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
53 /* Default TSQ limit of four TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
56 /* This limits the percentage of the congestion window which we
57 * will allow a single TSO frame to consume. Building TSO frames
58 * which are too large can cause TCP streams to be bursty.
60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
62 /* By default, RFC2861 behavior. */
63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
65 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
66 int push_one, gfp_t gfp);
68 /* Account for new data that has been sent to the network. */
69 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
71 struct inet_connection_sock *icsk = inet_csk(sk);
72 struct tcp_sock *tp = tcp_sk(sk);
73 unsigned int prior_packets = tp->packets_out;
75 tcp_advance_send_head(sk, skb);
76 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
78 tp->packets_out += tcp_skb_pcount(skb);
79 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
82 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
86 /* SND.NXT, if window was not shrunk or the amount of shrunk was less than one
87 * window scaling factor due to loss of precision.
88 * If window has been shrunk, what should we make? It is not clear at all.
89 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
90 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
91 * invalid. OK, let's make this for now:
93 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
95 const struct tcp_sock *tp = tcp_sk(sk);
97 if (!before(tcp_wnd_end(tp), tp->snd_nxt) ||
98 (tp->rx_opt.wscale_ok &&
99 ((tp->snd_nxt - tcp_wnd_end(tp)) < (1 << tp->rx_opt.rcv_wscale))))
102 return tcp_wnd_end(tp);
105 /* Calculate mss to advertise in SYN segment.
106 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
108 * 1. It is independent of path mtu.
109 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
110 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
111 * attached devices, because some buggy hosts are confused by
113 * 4. We do not make 3, we advertise MSS, calculated from first
114 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
115 * This may be overridden via information stored in routing table.
116 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
117 * probably even Jumbo".
119 static __u16 tcp_advertise_mss(struct sock *sk)
121 struct tcp_sock *tp = tcp_sk(sk);
122 const struct dst_entry *dst = __sk_dst_get(sk);
123 int mss = tp->advmss;
126 unsigned int metric = dst_metric_advmss(dst);
137 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
138 * This is the first part of cwnd validation mechanism.
140 void tcp_cwnd_restart(struct sock *sk, s32 delta)
142 struct tcp_sock *tp = tcp_sk(sk);
143 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
144 u32 cwnd = tp->snd_cwnd;
146 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
148 tp->snd_ssthresh = tcp_current_ssthresh(sk);
149 restart_cwnd = min(restart_cwnd, cwnd);
151 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
153 tp->snd_cwnd = max(cwnd, restart_cwnd);
154 tp->snd_cwnd_stamp = tcp_jiffies32;
155 tp->snd_cwnd_used = 0;
158 /* Congestion state accounting after a packet has been sent. */
159 static void tcp_event_data_sent(struct tcp_sock *tp,
162 struct inet_connection_sock *icsk = inet_csk(sk);
163 const u32 now = tcp_jiffies32;
165 if (tcp_packets_in_flight(tp) == 0)
166 tcp_ca_event(sk, CA_EVENT_TX_START);
170 /* If it is a reply for ato after last received
171 * packet, enter pingpong mode.
173 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
174 icsk->icsk_ack.pingpong = 1;
177 /* Account for an ACK we sent. */
178 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
180 tcp_dec_quickack_mode(sk, pkts);
181 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
185 u32 tcp_default_init_rwnd(u32 mss)
187 /* Initial receive window should be twice of TCP_INIT_CWND to
188 * enable proper sending of new unsent data during fast recovery
189 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
190 * limit when mss is larger than 1460.
192 u32 init_rwnd = TCP_INIT_CWND * 2;
195 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
199 /* Determine a window scaling and initial window to offer.
200 * Based on the assumption that the given amount of space
201 * will be offered. Store the results in the tp structure.
202 * NOTE: for smooth operation initial space offering should
203 * be a multiple of mss if possible. We assume here that mss >= 1.
204 * This MUST be enforced by all callers.
206 void tcp_select_initial_window(int __space, __u32 mss,
207 __u32 *rcv_wnd, __u32 *window_clamp,
208 int wscale_ok, __u8 *rcv_wscale,
211 unsigned int space = (__space < 0 ? 0 : __space);
213 /* If no clamp set the clamp to the max possible scaled window */
214 if (*window_clamp == 0)
215 (*window_clamp) = (U16_MAX << TCP_MAX_WSCALE);
216 space = min(*window_clamp, space);
218 /* Quantize space offering to a multiple of mss if possible. */
220 space = rounddown(space, mss);
222 /* NOTE: offering an initial window larger than 32767
223 * will break some buggy TCP stacks. If the admin tells us
224 * it is likely we could be speaking with such a buggy stack
225 * we will truncate our initial window offering to 32K-1
226 * unless the remote has sent us a window scaling option,
227 * which we interpret as a sign the remote TCP is not
228 * misinterpreting the window field as a signed quantity.
230 if (sysctl_tcp_workaround_signed_windows)
231 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
237 /* Set window scaling on max possible window */
238 space = max_t(u32, space, sysctl_tcp_rmem[2]);
239 space = max_t(u32, space, sysctl_rmem_max);
240 space = min_t(u32, space, *window_clamp);
241 while (space > U16_MAX && (*rcv_wscale) < TCP_MAX_WSCALE) {
247 if (mss > (1 << *rcv_wscale)) {
248 if (!init_rcv_wnd) /* Use default unless specified otherwise */
249 init_rcv_wnd = tcp_default_init_rwnd(mss);
250 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
253 /* Set the clamp no higher than max representable value */
254 (*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale), *window_clamp);
256 EXPORT_SYMBOL(tcp_select_initial_window);
258 /* Chose a new window to advertise, update state in tcp_sock for the
259 * socket, and return result with RFC1323 scaling applied. The return
260 * value can be stuffed directly into th->window for an outgoing
263 static u16 tcp_select_window(struct sock *sk)
265 struct tcp_sock *tp = tcp_sk(sk);
266 u32 old_win = tp->rcv_wnd;
267 u32 cur_win = tcp_receive_window(tp);
268 u32 new_win = __tcp_select_window(sk);
270 /* Never shrink the offered window */
271 if (new_win < cur_win) {
272 /* Danger Will Robinson!
273 * Don't update rcv_wup/rcv_wnd here or else
274 * we will not be able to advertise a zero
275 * window in time. --DaveM
277 * Relax Will Robinson.
280 NET_INC_STATS(sock_net(sk),
281 LINUX_MIB_TCPWANTZEROWINDOWADV);
282 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
284 tp->rcv_wnd = new_win;
285 tp->rcv_wup = tp->rcv_nxt;
287 /* Make sure we do not exceed the maximum possible
290 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
291 new_win = min(new_win, MAX_TCP_WINDOW);
293 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
295 /* RFC1323 scaling applied */
296 new_win >>= tp->rx_opt.rcv_wscale;
298 /* If we advertise zero window, disable fast path. */
302 NET_INC_STATS(sock_net(sk),
303 LINUX_MIB_TCPTOZEROWINDOWADV);
304 } else if (old_win == 0) {
305 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
311 /* Packet ECN state for a SYN-ACK */
312 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
314 const struct tcp_sock *tp = tcp_sk(sk);
316 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
317 if (!(tp->ecn_flags & TCP_ECN_OK))
318 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
319 else if (tcp_ca_needs_ecn(sk))
323 /* Packet ECN state for a SYN. */
324 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
326 struct tcp_sock *tp = tcp_sk(sk);
327 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
328 tcp_ca_needs_ecn(sk);
331 const struct dst_entry *dst = __sk_dst_get(sk);
333 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
340 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
341 tp->ecn_flags = TCP_ECN_OK;
342 if (tcp_ca_needs_ecn(sk))
347 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
349 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
350 /* tp->ecn_flags are cleared at a later point in time when
351 * SYN ACK is ultimatively being received.
353 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
357 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
359 if (inet_rsk(req)->ecn_ok)
363 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
366 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
367 struct tcphdr *th, int tcp_header_len)
369 struct tcp_sock *tp = tcp_sk(sk);
371 if (tp->ecn_flags & TCP_ECN_OK) {
372 /* Not-retransmitted data segment: set ECT and inject CWR. */
373 if (skb->len != tcp_header_len &&
374 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
376 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
377 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
379 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
381 } else if (!tcp_ca_needs_ecn(sk)) {
382 /* ACK or retransmitted segment: clear ECT|CE */
383 INET_ECN_dontxmit(sk);
385 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
390 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
391 * auto increment end seqno.
393 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
395 skb->ip_summed = CHECKSUM_PARTIAL;
398 TCP_SKB_CB(skb)->tcp_flags = flags;
399 TCP_SKB_CB(skb)->sacked = 0;
401 tcp_skb_pcount_set(skb, 1);
403 TCP_SKB_CB(skb)->seq = seq;
404 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
406 TCP_SKB_CB(skb)->end_seq = seq;
409 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
411 return tp->snd_una != tp->snd_up;
414 #define OPTION_SACK_ADVERTISE (1 << 0)
415 #define OPTION_TS (1 << 1)
416 #define OPTION_MD5 (1 << 2)
417 #define OPTION_WSCALE (1 << 3)
418 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
420 struct tcp_out_options {
421 u16 options; /* bit field of OPTION_* */
422 u16 mss; /* 0 to disable */
423 u8 ws; /* window scale, 0 to disable */
424 u8 num_sack_blocks; /* number of SACK blocks to include */
425 u8 hash_size; /* bytes in hash_location */
426 __u8 *hash_location; /* temporary pointer, overloaded */
427 __u32 tsval, tsecr; /* need to include OPTION_TS */
428 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
431 /* Write previously computed TCP options to the packet.
433 * Beware: Something in the Internet is very sensitive to the ordering of
434 * TCP options, we learned this through the hard way, so be careful here.
435 * Luckily we can at least blame others for their non-compliance but from
436 * inter-operability perspective it seems that we're somewhat stuck with
437 * the ordering which we have been using if we want to keep working with
438 * those broken things (not that it currently hurts anybody as there isn't
439 * particular reason why the ordering would need to be changed).
441 * At least SACK_PERM as the first option is known to lead to a disaster
442 * (but it may well be that other scenarios fail similarly).
444 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
445 struct tcp_out_options *opts)
447 u16 options = opts->options; /* mungable copy */
449 if (unlikely(OPTION_MD5 & options)) {
450 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
451 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
452 /* overload cookie hash location */
453 opts->hash_location = (__u8 *)ptr;
457 if (unlikely(opts->mss)) {
458 *ptr++ = htonl((TCPOPT_MSS << 24) |
459 (TCPOLEN_MSS << 16) |
463 if (likely(OPTION_TS & options)) {
464 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
465 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
466 (TCPOLEN_SACK_PERM << 16) |
467 (TCPOPT_TIMESTAMP << 8) |
469 options &= ~OPTION_SACK_ADVERTISE;
471 *ptr++ = htonl((TCPOPT_NOP << 24) |
473 (TCPOPT_TIMESTAMP << 8) |
476 *ptr++ = htonl(opts->tsval);
477 *ptr++ = htonl(opts->tsecr);
480 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
481 *ptr++ = htonl((TCPOPT_NOP << 24) |
483 (TCPOPT_SACK_PERM << 8) |
487 if (unlikely(OPTION_WSCALE & options)) {
488 *ptr++ = htonl((TCPOPT_NOP << 24) |
489 (TCPOPT_WINDOW << 16) |
490 (TCPOLEN_WINDOW << 8) |
494 if (unlikely(opts->num_sack_blocks)) {
495 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
496 tp->duplicate_sack : tp->selective_acks;
499 *ptr++ = htonl((TCPOPT_NOP << 24) |
502 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
503 TCPOLEN_SACK_PERBLOCK)));
505 for (this_sack = 0; this_sack < opts->num_sack_blocks;
507 *ptr++ = htonl(sp[this_sack].start_seq);
508 *ptr++ = htonl(sp[this_sack].end_seq);
511 tp->rx_opt.dsack = 0;
514 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
515 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
517 u32 len; /* Fast Open option length */
520 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
521 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
522 TCPOPT_FASTOPEN_MAGIC);
523 p += TCPOLEN_EXP_FASTOPEN_BASE;
525 len = TCPOLEN_FASTOPEN_BASE + foc->len;
526 *p++ = TCPOPT_FASTOPEN;
530 memcpy(p, foc->val, foc->len);
531 if ((len & 3) == 2) {
532 p[foc->len] = TCPOPT_NOP;
533 p[foc->len + 1] = TCPOPT_NOP;
535 ptr += (len + 3) >> 2;
539 /* Compute TCP options for SYN packets. This is not the final
540 * network wire format yet.
542 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
543 struct tcp_out_options *opts,
544 struct tcp_md5sig_key **md5)
546 struct tcp_sock *tp = tcp_sk(sk);
547 unsigned int remaining = MAX_TCP_OPTION_SPACE;
548 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
550 #ifdef CONFIG_TCP_MD5SIG
551 *md5 = tp->af_specific->md5_lookup(sk, sk);
553 opts->options |= OPTION_MD5;
554 remaining -= TCPOLEN_MD5SIG_ALIGNED;
560 /* We always get an MSS option. The option bytes which will be seen in
561 * normal data packets should timestamps be used, must be in the MSS
562 * advertised. But we subtract them from tp->mss_cache so that
563 * calculations in tcp_sendmsg are simpler etc. So account for this
564 * fact here if necessary. If we don't do this correctly, as a
565 * receiver we won't recognize data packets as being full sized when we
566 * should, and thus we won't abide by the delayed ACK rules correctly.
567 * SACKs don't matter, we never delay an ACK when we have any of those
569 opts->mss = tcp_advertise_mss(sk);
570 remaining -= TCPOLEN_MSS_ALIGNED;
572 if (likely(sysctl_tcp_timestamps && !*md5)) {
573 opts->options |= OPTION_TS;
574 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
575 opts->tsecr = tp->rx_opt.ts_recent;
576 remaining -= TCPOLEN_TSTAMP_ALIGNED;
578 if (likely(sock_net(sk)->ipv4.sysctl_tcp_window_scaling)) {
579 opts->ws = tp->rx_opt.rcv_wscale;
580 opts->options |= OPTION_WSCALE;
581 remaining -= TCPOLEN_WSCALE_ALIGNED;
583 if (likely(sock_net(sk)->ipv4.sysctl_tcp_sack)) {
584 opts->options |= OPTION_SACK_ADVERTISE;
585 if (unlikely(!(OPTION_TS & opts->options)))
586 remaining -= TCPOLEN_SACKPERM_ALIGNED;
589 if (fastopen && fastopen->cookie.len >= 0) {
590 u32 need = fastopen->cookie.len;
592 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
593 TCPOLEN_FASTOPEN_BASE;
594 need = (need + 3) & ~3U; /* Align to 32 bits */
595 if (remaining >= need) {
596 opts->options |= OPTION_FAST_OPEN_COOKIE;
597 opts->fastopen_cookie = &fastopen->cookie;
599 tp->syn_fastopen = 1;
600 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
604 return MAX_TCP_OPTION_SPACE - remaining;
607 /* Set up TCP options for SYN-ACKs. */
608 static unsigned int tcp_synack_options(struct request_sock *req,
609 unsigned int mss, struct sk_buff *skb,
610 struct tcp_out_options *opts,
611 const struct tcp_md5sig_key *md5,
612 struct tcp_fastopen_cookie *foc)
614 struct inet_request_sock *ireq = inet_rsk(req);
615 unsigned int remaining = MAX_TCP_OPTION_SPACE;
617 #ifdef CONFIG_TCP_MD5SIG
619 opts->options |= OPTION_MD5;
620 remaining -= TCPOLEN_MD5SIG_ALIGNED;
622 /* We can't fit any SACK blocks in a packet with MD5 + TS
623 * options. There was discussion about disabling SACK
624 * rather than TS in order to fit in better with old,
625 * buggy kernels, but that was deemed to be unnecessary.
627 ireq->tstamp_ok &= !ireq->sack_ok;
631 /* We always send an MSS option. */
633 remaining -= TCPOLEN_MSS_ALIGNED;
635 if (likely(ireq->wscale_ok)) {
636 opts->ws = ireq->rcv_wscale;
637 opts->options |= OPTION_WSCALE;
638 remaining -= TCPOLEN_WSCALE_ALIGNED;
640 if (likely(ireq->tstamp_ok)) {
641 opts->options |= OPTION_TS;
642 opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
643 opts->tsecr = req->ts_recent;
644 remaining -= TCPOLEN_TSTAMP_ALIGNED;
646 if (likely(ireq->sack_ok)) {
647 opts->options |= OPTION_SACK_ADVERTISE;
648 if (unlikely(!ireq->tstamp_ok))
649 remaining -= TCPOLEN_SACKPERM_ALIGNED;
651 if (foc != NULL && foc->len >= 0) {
654 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
655 TCPOLEN_FASTOPEN_BASE;
656 need = (need + 3) & ~3U; /* Align to 32 bits */
657 if (remaining >= need) {
658 opts->options |= OPTION_FAST_OPEN_COOKIE;
659 opts->fastopen_cookie = foc;
664 return MAX_TCP_OPTION_SPACE - remaining;
667 /* Compute TCP options for ESTABLISHED sockets. This is not the
668 * final wire format yet.
670 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
671 struct tcp_out_options *opts,
672 struct tcp_md5sig_key **md5)
674 struct tcp_sock *tp = tcp_sk(sk);
675 unsigned int size = 0;
676 unsigned int eff_sacks;
680 #ifdef CONFIG_TCP_MD5SIG
681 *md5 = tp->af_specific->md5_lookup(sk, sk);
682 if (unlikely(*md5)) {
683 opts->options |= OPTION_MD5;
684 size += TCPOLEN_MD5SIG_ALIGNED;
690 if (likely(tp->rx_opt.tstamp_ok)) {
691 opts->options |= OPTION_TS;
692 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
693 opts->tsecr = tp->rx_opt.ts_recent;
694 size += TCPOLEN_TSTAMP_ALIGNED;
697 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
698 if (unlikely(eff_sacks)) {
699 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
700 opts->num_sack_blocks =
701 min_t(unsigned int, eff_sacks,
702 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
703 TCPOLEN_SACK_PERBLOCK);
704 size += TCPOLEN_SACK_BASE_ALIGNED +
705 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
712 /* TCP SMALL QUEUES (TSQ)
714 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
715 * to reduce RTT and bufferbloat.
716 * We do this using a special skb destructor (tcp_wfree).
718 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
719 * needs to be reallocated in a driver.
720 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
722 * Since transmit from skb destructor is forbidden, we use a tasklet
723 * to process all sockets that eventually need to send more skbs.
724 * We use one tasklet per cpu, with its own queue of sockets.
727 struct tasklet_struct tasklet;
728 struct list_head head; /* queue of tcp sockets */
730 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
732 static void tcp_tsq_handler(struct sock *sk)
734 if ((1 << sk->sk_state) &
735 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
736 TCPF_CLOSE_WAIT | TCPF_LAST_ACK)) {
737 struct tcp_sock *tp = tcp_sk(sk);
739 if (tp->lost_out > tp->retrans_out &&
740 tp->snd_cwnd > tcp_packets_in_flight(tp))
741 tcp_xmit_retransmit_queue(sk);
743 tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
748 * One tasklet per cpu tries to send more skbs.
749 * We run in tasklet context but need to disable irqs when
750 * transferring tsq->head because tcp_wfree() might
751 * interrupt us (non NAPI drivers)
753 static void tcp_tasklet_func(unsigned long data)
755 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
758 struct list_head *q, *n;
762 local_irq_save(flags);
763 list_splice_init(&tsq->head, &list);
764 local_irq_restore(flags);
766 list_for_each_safe(q, n, &list) {
767 tp = list_entry(q, struct tcp_sock, tsq_node);
768 list_del(&tp->tsq_node);
770 sk = (struct sock *)tp;
771 smp_mb__before_atomic();
772 clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags);
774 if (!sk->sk_lock.owned &&
775 test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) {
777 if (!sock_owned_by_user(sk)) {
778 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
788 #define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED | \
789 TCPF_WRITE_TIMER_DEFERRED | \
790 TCPF_DELACK_TIMER_DEFERRED | \
791 TCPF_MTU_REDUCED_DEFERRED)
793 * tcp_release_cb - tcp release_sock() callback
796 * called from release_sock() to perform protocol dependent
797 * actions before socket release.
799 void tcp_release_cb(struct sock *sk)
801 unsigned long flags, nflags;
803 /* perform an atomic operation only if at least one flag is set */
805 flags = sk->sk_tsq_flags;
806 if (!(flags & TCP_DEFERRED_ALL))
808 nflags = flags & ~TCP_DEFERRED_ALL;
809 } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);
811 if (flags & TCPF_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 & TCPF_WRITE_TIMER_DEFERRED) {
826 tcp_write_timer_handler(sk);
829 if (flags & TCPF_DELACK_TIMER_DEFERRED) {
830 tcp_delack_timer_handler(sk);
833 if (flags & TCPF_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);
863 unsigned long flags, nval, oval;
866 /* Keep one reference on sk_wmem_alloc.
867 * Will be released by sk_free() from here or tcp_tasklet_func()
869 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
871 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
872 * Wait until our queues (qdisc + devices) are drained.
874 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
875 * - chance for incoming ACK (processed by another cpu maybe)
876 * to migrate this flow (skb->ooo_okay will be eventually set)
878 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
881 for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
882 struct tsq_tasklet *tsq;
885 if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
888 nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
889 nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
893 /* queue this socket to tasklet queue */
894 local_irq_save(flags);
895 tsq = this_cpu_ptr(&tsq_tasklet);
896 empty = list_empty(&tsq->head);
897 list_add(&tp->tsq_node, &tsq->head);
899 tasklet_schedule(&tsq->tasklet);
900 local_irq_restore(flags);
907 /* Note: Called under hard irq.
908 * We can not call TCP stack right away.
910 enum hrtimer_restart tcp_pace_kick(struct hrtimer *timer)
912 struct tcp_sock *tp = container_of(timer, struct tcp_sock, pacing_timer);
913 struct sock *sk = (struct sock *)tp;
914 unsigned long nval, oval;
916 for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
917 struct tsq_tasklet *tsq;
920 if (oval & TSQF_QUEUED)
923 nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
924 nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
928 if (!atomic_inc_not_zero(&sk->sk_wmem_alloc))
930 /* queue this socket to tasklet queue */
931 tsq = this_cpu_ptr(&tsq_tasklet);
932 empty = list_empty(&tsq->head);
933 list_add(&tp->tsq_node, &tsq->head);
935 tasklet_schedule(&tsq->tasklet);
938 return HRTIMER_NORESTART;
941 /* BBR congestion control needs pacing.
942 * Same remark for SO_MAX_PACING_RATE.
943 * sch_fq packet scheduler is efficiently handling pacing,
944 * but is not always installed/used.
945 * Return true if TCP stack should pace packets itself.
947 static bool tcp_needs_internal_pacing(const struct sock *sk)
949 return smp_load_acquire(&sk->sk_pacing_status) == SK_PACING_NEEDED;
952 static void tcp_internal_pacing(struct sock *sk, const struct sk_buff *skb)
957 if (!tcp_needs_internal_pacing(sk))
959 rate = sk->sk_pacing_rate;
960 if (!rate || rate == ~0U)
963 /* Should account for header sizes as sch_fq does,
964 * but lets make things simple.
966 len_ns = (u64)skb->len * NSEC_PER_SEC;
967 do_div(len_ns, rate);
968 hrtimer_start(&tcp_sk(sk)->pacing_timer,
969 ktime_add_ns(ktime_get(), len_ns),
970 HRTIMER_MODE_ABS_PINNED);
973 /* This routine actually transmits TCP packets queued in by
974 * tcp_do_sendmsg(). This is used by both the initial
975 * transmission and possible later retransmissions.
976 * All SKB's seen here are completely headerless. It is our
977 * job to build the TCP header, and pass the packet down to
978 * IP so it can do the same plus pass the packet off to the
981 * We are working here with either a clone of the original
982 * SKB, or a fresh unique copy made by the retransmit engine.
984 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
987 const struct inet_connection_sock *icsk = inet_csk(sk);
988 struct inet_sock *inet;
990 struct tcp_skb_cb *tcb;
991 struct tcp_out_options opts;
992 unsigned int tcp_options_size, tcp_header_size;
993 struct tcp_md5sig_key *md5;
997 BUG_ON(!skb || !tcp_skb_pcount(skb));
1000 skb->skb_mstamp = tp->tcp_mstamp;
1002 TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
1004 tcp_rate_skb_sent(sk, skb);
1006 if (unlikely(skb_cloned(skb)))
1007 skb = pskb_copy(skb, gfp_mask);
1009 skb = skb_clone(skb, gfp_mask);
1015 tcb = TCP_SKB_CB(skb);
1016 memset(&opts, 0, sizeof(opts));
1018 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
1019 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
1021 tcp_options_size = tcp_established_options(sk, skb, &opts,
1023 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
1025 /* if no packet is in qdisc/device queue, then allow XPS to select
1026 * another queue. We can be called from tcp_tsq_handler()
1027 * which holds one reference to sk_wmem_alloc.
1029 * TODO: Ideally, in-flight pure ACK packets should not matter here.
1030 * One way to get this would be to set skb->truesize = 2 on them.
1032 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
1034 /* If we had to use memory reserve to allocate this skb,
1035 * this might cause drops if packet is looped back :
1036 * Other socket might not have SOCK_MEMALLOC.
1037 * Packets not looped back do not care about pfmemalloc.
1039 skb->pfmemalloc = 0;
1041 skb_push(skb, tcp_header_size);
1042 skb_reset_transport_header(skb);
1046 skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
1047 skb_set_hash_from_sk(skb, sk);
1048 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
1050 skb_set_dst_pending_confirm(skb, sk->sk_dst_pending_confirm);
1052 /* Build TCP header and checksum it. */
1053 th = (struct tcphdr *)skb->data;
1054 th->source = inet->inet_sport;
1055 th->dest = inet->inet_dport;
1056 th->seq = htonl(tcb->seq);
1057 th->ack_seq = htonl(tp->rcv_nxt);
1058 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
1064 /* The urg_mode check is necessary during a below snd_una win probe */
1065 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
1066 if (before(tp->snd_up, tcb->seq + 0x10000)) {
1067 th->urg_ptr = htons(tp->snd_up - tcb->seq);
1069 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
1070 th->urg_ptr = htons(0xFFFF);
1075 tcp_options_write((__be32 *)(th + 1), tp, &opts);
1076 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1077 if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
1078 th->window = htons(tcp_select_window(sk));
1079 tcp_ecn_send(sk, skb, th, tcp_header_size);
1081 /* RFC1323: The window in SYN & SYN/ACK segments
1084 th->window = htons(min(tp->rcv_wnd, 65535U));
1086 #ifdef CONFIG_TCP_MD5SIG
1087 /* Calculate the MD5 hash, as we have all we need now */
1089 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1090 tp->af_specific->calc_md5_hash(opts.hash_location,
1095 icsk->icsk_af_ops->send_check(sk, skb);
1097 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1098 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1100 if (skb->len != tcp_header_size) {
1101 tcp_event_data_sent(tp, sk);
1102 tp->data_segs_out += tcp_skb_pcount(skb);
1103 tcp_internal_pacing(sk, skb);
1106 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1107 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1108 tcp_skb_pcount(skb));
1110 tp->segs_out += tcp_skb_pcount(skb);
1111 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1112 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1113 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1115 /* Our usage of tstamp should remain private */
1118 /* Cleanup our debris for IP stacks */
1119 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1120 sizeof(struct inet6_skb_parm)));
1122 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1124 if (likely(err <= 0))
1129 return net_xmit_eval(err);
1132 /* This routine just queues the buffer for sending.
1134 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1135 * otherwise socket can stall.
1137 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1139 struct tcp_sock *tp = tcp_sk(sk);
1141 /* Advance write_seq and place onto the write_queue. */
1142 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1143 __skb_header_release(skb);
1144 tcp_add_write_queue_tail(sk, skb);
1145 sk->sk_wmem_queued += skb->truesize;
1146 sk_mem_charge(sk, skb->truesize);
1149 /* Initialize TSO segments for a packet. */
1150 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1152 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1153 /* Avoid the costly divide in the normal
1156 tcp_skb_pcount_set(skb, 1);
1157 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1159 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1160 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1164 /* When a modification to fackets out becomes necessary, we need to check
1165 * skb is counted to fackets_out or not.
1167 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1170 struct tcp_sock *tp = tcp_sk(sk);
1172 if (!tp->sacked_out || tcp_is_reno(tp))
1175 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1176 tp->fackets_out -= decr;
1179 /* Pcount in the middle of the write queue got changed, we need to do various
1180 * tweaks to fix counters
1182 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1184 struct tcp_sock *tp = tcp_sk(sk);
1186 tp->packets_out -= decr;
1188 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1189 tp->sacked_out -= decr;
1190 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1191 tp->retrans_out -= decr;
1192 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1193 tp->lost_out -= decr;
1195 /* Reno case is special. Sigh... */
1196 if (tcp_is_reno(tp) && decr > 0)
1197 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1199 tcp_adjust_fackets_out(sk, skb, decr);
1201 if (tp->lost_skb_hint &&
1202 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1203 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1204 tp->lost_cnt_hint -= decr;
1206 tcp_verify_left_out(tp);
1209 static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
1211 return TCP_SKB_CB(skb)->txstamp_ack ||
1212 (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
1215 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1217 struct skb_shared_info *shinfo = skb_shinfo(skb);
1219 if (unlikely(tcp_has_tx_tstamp(skb)) &&
1220 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1221 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1222 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1224 shinfo->tx_flags &= ~tsflags;
1225 shinfo2->tx_flags |= tsflags;
1226 swap(shinfo->tskey, shinfo2->tskey);
1227 TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
1228 TCP_SKB_CB(skb)->txstamp_ack = 0;
1232 static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
1234 TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
1235 TCP_SKB_CB(skb)->eor = 0;
1238 /* Function to create two new TCP segments. Shrinks the given segment
1239 * to the specified size and appends a new segment with the rest of the
1240 * packet to the list. This won't be called frequently, I hope.
1241 * Remember, these are still headerless SKBs at this point.
1243 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1244 unsigned int mss_now, gfp_t gfp)
1246 struct tcp_sock *tp = tcp_sk(sk);
1247 struct sk_buff *buff;
1248 int nsize, old_factor;
1252 if (WARN_ON(len > skb->len))
1255 nsize = skb_headlen(skb) - len;
1259 if (skb_unclone(skb, gfp))
1262 /* Get a new skb... force flag on. */
1263 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1265 return -ENOMEM; /* We'll just try again later. */
1267 sk->sk_wmem_queued += buff->truesize;
1268 sk_mem_charge(sk, buff->truesize);
1269 nlen = skb->len - len - nsize;
1270 buff->truesize += nlen;
1271 skb->truesize -= nlen;
1273 /* Correct the sequence numbers. */
1274 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1275 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1276 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1278 /* PSH and FIN should only be set in the second packet. */
1279 flags = TCP_SKB_CB(skb)->tcp_flags;
1280 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1281 TCP_SKB_CB(buff)->tcp_flags = flags;
1282 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1283 tcp_skb_fragment_eor(skb, buff);
1285 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1286 /* Copy and checksum data tail into the new buffer. */
1287 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1288 skb_put(buff, nsize),
1293 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1295 skb->ip_summed = CHECKSUM_PARTIAL;
1296 skb_split(skb, buff, len);
1299 buff->ip_summed = skb->ip_summed;
1301 buff->tstamp = skb->tstamp;
1302 tcp_fragment_tstamp(skb, buff);
1304 old_factor = tcp_skb_pcount(skb);
1306 /* Fix up tso_factor for both original and new SKB. */
1307 tcp_set_skb_tso_segs(skb, mss_now);
1308 tcp_set_skb_tso_segs(buff, mss_now);
1310 /* Update delivered info for the new segment */
1311 TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;
1313 /* If this packet has been sent out already, we must
1314 * adjust the various packet counters.
1316 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1317 int diff = old_factor - tcp_skb_pcount(skb) -
1318 tcp_skb_pcount(buff);
1321 tcp_adjust_pcount(sk, skb, diff);
1324 /* Link BUFF into the send queue. */
1325 __skb_header_release(buff);
1326 tcp_insert_write_queue_after(skb, buff, sk);
1331 /* This is similar to __pskb_pull_tail(). The difference is that pulled
1332 * data is not copied, but immediately discarded.
1334 static int __pskb_trim_head(struct sk_buff *skb, int len)
1336 struct skb_shared_info *shinfo;
1339 eat = min_t(int, len, skb_headlen(skb));
1341 __skb_pull(skb, eat);
1348 shinfo = skb_shinfo(skb);
1349 for (i = 0; i < shinfo->nr_frags; i++) {
1350 int size = skb_frag_size(&shinfo->frags[i]);
1353 skb_frag_unref(skb, i);
1356 shinfo->frags[k] = shinfo->frags[i];
1358 shinfo->frags[k].page_offset += eat;
1359 skb_frag_size_sub(&shinfo->frags[k], eat);
1365 shinfo->nr_frags = k;
1367 skb->data_len -= len;
1368 skb->len = skb->data_len;
1372 /* Remove acked data from a packet in the transmit queue. */
1373 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1377 if (skb_unclone(skb, GFP_ATOMIC))
1380 delta_truesize = __pskb_trim_head(skb, len);
1382 TCP_SKB_CB(skb)->seq += len;
1383 skb->ip_summed = CHECKSUM_PARTIAL;
1385 if (delta_truesize) {
1386 skb->truesize -= delta_truesize;
1387 sk->sk_wmem_queued -= delta_truesize;
1388 sk_mem_uncharge(sk, delta_truesize);
1389 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1392 /* Any change of skb->len requires recalculation of tso factor. */
1393 if (tcp_skb_pcount(skb) > 1)
1394 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1399 /* Calculate MSS not accounting any TCP options. */
1400 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1402 const struct tcp_sock *tp = tcp_sk(sk);
1403 const struct inet_connection_sock *icsk = inet_csk(sk);
1406 /* Calculate base mss without TCP options:
1407 It is MMS_S - sizeof(tcphdr) of rfc1122
1409 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1411 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1412 if (icsk->icsk_af_ops->net_frag_header_len) {
1413 const struct dst_entry *dst = __sk_dst_get(sk);
1415 if (dst && dst_allfrag(dst))
1416 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1419 /* Clamp it (mss_clamp does not include tcp options) */
1420 if (mss_now > tp->rx_opt.mss_clamp)
1421 mss_now = tp->rx_opt.mss_clamp;
1423 /* Now subtract optional transport overhead */
1424 mss_now -= icsk->icsk_ext_hdr_len;
1426 /* Then reserve room for full set of TCP options and 8 bytes of data */
1432 /* Calculate MSS. Not accounting for SACKs here. */
1433 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1435 /* Subtract TCP options size, not including SACKs */
1436 return __tcp_mtu_to_mss(sk, pmtu) -
1437 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1440 /* Inverse of above */
1441 int tcp_mss_to_mtu(struct sock *sk, int mss)
1443 const struct tcp_sock *tp = tcp_sk(sk);
1444 const struct inet_connection_sock *icsk = inet_csk(sk);
1448 tp->tcp_header_len +
1449 icsk->icsk_ext_hdr_len +
1450 icsk->icsk_af_ops->net_header_len;
1452 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1453 if (icsk->icsk_af_ops->net_frag_header_len) {
1454 const struct dst_entry *dst = __sk_dst_get(sk);
1456 if (dst && dst_allfrag(dst))
1457 mtu += icsk->icsk_af_ops->net_frag_header_len;
1461 EXPORT_SYMBOL(tcp_mss_to_mtu);
1463 /* MTU probing init per socket */
1464 void tcp_mtup_init(struct sock *sk)
1466 struct tcp_sock *tp = tcp_sk(sk);
1467 struct inet_connection_sock *icsk = inet_csk(sk);
1468 struct net *net = sock_net(sk);
1470 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1471 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1472 icsk->icsk_af_ops->net_header_len;
1473 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1474 icsk->icsk_mtup.probe_size = 0;
1475 if (icsk->icsk_mtup.enabled)
1476 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
1478 EXPORT_SYMBOL(tcp_mtup_init);
1480 /* This function synchronize snd mss to current pmtu/exthdr set.
1482 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1483 for TCP options, but includes only bare TCP header.
1485 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1486 It is minimum of user_mss and mss received with SYN.
1487 It also does not include TCP options.
1489 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1491 tp->mss_cache is current effective sending mss, including
1492 all tcp options except for SACKs. It is evaluated,
1493 taking into account current pmtu, but never exceeds
1494 tp->rx_opt.mss_clamp.
1496 NOTE1. rfc1122 clearly states that advertised MSS
1497 DOES NOT include either tcp or ip options.
1499 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1500 are READ ONLY outside this function. --ANK (980731)
1502 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1504 struct tcp_sock *tp = tcp_sk(sk);
1505 struct inet_connection_sock *icsk = inet_csk(sk);
1508 if (icsk->icsk_mtup.search_high > pmtu)
1509 icsk->icsk_mtup.search_high = pmtu;
1511 mss_now = tcp_mtu_to_mss(sk, pmtu);
1512 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1514 /* And store cached results */
1515 icsk->icsk_pmtu_cookie = pmtu;
1516 if (icsk->icsk_mtup.enabled)
1517 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1518 tp->mss_cache = mss_now;
1522 EXPORT_SYMBOL(tcp_sync_mss);
1524 /* Compute the current effective MSS, taking SACKs and IP options,
1525 * and even PMTU discovery events into account.
1527 unsigned int tcp_current_mss(struct sock *sk)
1529 const struct tcp_sock *tp = tcp_sk(sk);
1530 const struct dst_entry *dst = __sk_dst_get(sk);
1532 unsigned int header_len;
1533 struct tcp_out_options opts;
1534 struct tcp_md5sig_key *md5;
1536 mss_now = tp->mss_cache;
1539 u32 mtu = dst_mtu(dst);
1540 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1541 mss_now = tcp_sync_mss(sk, mtu);
1544 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1545 sizeof(struct tcphdr);
1546 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1547 * some common options. If this is an odd packet (because we have SACK
1548 * blocks etc) then our calculated header_len will be different, and
1549 * we have to adjust mss_now correspondingly */
1550 if (header_len != tp->tcp_header_len) {
1551 int delta = (int) header_len - tp->tcp_header_len;
1558 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1559 * As additional protections, we do not touch cwnd in retransmission phases,
1560 * and if application hit its sndbuf limit recently.
1562 static void tcp_cwnd_application_limited(struct sock *sk)
1564 struct tcp_sock *tp = tcp_sk(sk);
1566 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1567 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1568 /* Limited by application or receiver window. */
1569 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1570 u32 win_used = max(tp->snd_cwnd_used, init_win);
1571 if (win_used < tp->snd_cwnd) {
1572 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1573 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1575 tp->snd_cwnd_used = 0;
1577 tp->snd_cwnd_stamp = tcp_jiffies32;
1580 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1582 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1583 struct tcp_sock *tp = tcp_sk(sk);
1585 /* Track the maximum number of outstanding packets in each
1586 * window, and remember whether we were cwnd-limited then.
1588 if (!before(tp->snd_una, tp->max_packets_seq) ||
1589 tp->packets_out > tp->max_packets_out) {
1590 tp->max_packets_out = tp->packets_out;
1591 tp->max_packets_seq = tp->snd_nxt;
1592 tp->is_cwnd_limited = is_cwnd_limited;
1595 if (tcp_is_cwnd_limited(sk)) {
1596 /* Network is feed fully. */
1597 tp->snd_cwnd_used = 0;
1598 tp->snd_cwnd_stamp = tcp_jiffies32;
1600 /* Network starves. */
1601 if (tp->packets_out > tp->snd_cwnd_used)
1602 tp->snd_cwnd_used = tp->packets_out;
1604 if (sysctl_tcp_slow_start_after_idle &&
1605 (s32)(tcp_jiffies32 - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
1606 !ca_ops->cong_control)
1607 tcp_cwnd_application_limited(sk);
1609 /* The following conditions together indicate the starvation
1610 * is caused by insufficient sender buffer:
1611 * 1) just sent some data (see tcp_write_xmit)
1612 * 2) not cwnd limited (this else condition)
1613 * 3) no more data to send (null tcp_send_head )
1614 * 4) application is hitting buffer limit (SOCK_NOSPACE)
1616 if (!tcp_send_head(sk) && sk->sk_socket &&
1617 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
1618 (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
1619 tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
1623 /* Minshall's variant of the Nagle send check. */
1624 static bool tcp_minshall_check(const struct tcp_sock *tp)
1626 return after(tp->snd_sml, tp->snd_una) &&
1627 !after(tp->snd_sml, tp->snd_nxt);
1630 /* Update snd_sml if this skb is under mss
1631 * Note that a TSO packet might end with a sub-mss segment
1632 * The test is really :
1633 * if ((skb->len % mss) != 0)
1634 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1635 * But we can avoid doing the divide again given we already have
1636 * skb_pcount = skb->len / mss_now
1638 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1639 const struct sk_buff *skb)
1641 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1642 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1645 /* Return false, if packet can be sent now without violation Nagle's rules:
1646 * 1. It is full sized. (provided by caller in %partial bool)
1647 * 2. Or it contains FIN. (already checked by caller)
1648 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1649 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1650 * With Minshall's modification: all sent small packets are ACKed.
1652 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1656 ((nonagle & TCP_NAGLE_CORK) ||
1657 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1660 /* Return how many segs we'd like on a TSO packet,
1661 * to send one TSO packet per ms
1663 u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
1668 bytes = min(sk->sk_pacing_rate >> 10,
1669 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1671 /* Goal is to send at least one packet per ms,
1672 * not one big TSO packet every 100 ms.
1673 * This preserves ACK clocking and is consistent
1674 * with tcp_tso_should_defer() heuristic.
1676 segs = max_t(u32, bytes / mss_now, min_tso_segs);
1678 return min_t(u32, segs, sk->sk_gso_max_segs);
1680 EXPORT_SYMBOL(tcp_tso_autosize);
1682 /* Return the number of segments we want in the skb we are transmitting.
1683 * See if congestion control module wants to decide; otherwise, autosize.
1685 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
1687 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1688 u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;
1691 tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs);
1694 /* Returns the portion of skb which can be sent right away */
1695 static unsigned int tcp_mss_split_point(const struct sock *sk,
1696 const struct sk_buff *skb,
1697 unsigned int mss_now,
1698 unsigned int max_segs,
1701 const struct tcp_sock *tp = tcp_sk(sk);
1702 u32 partial, needed, window, max_len;
1704 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1705 max_len = mss_now * max_segs;
1707 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1710 needed = min(skb->len, window);
1712 if (max_len <= needed)
1715 partial = needed % mss_now;
1716 /* If last segment is not a full MSS, check if Nagle rules allow us
1717 * to include this last segment in this skb.
1718 * Otherwise, we'll split the skb at last MSS boundary
1720 if (tcp_nagle_check(partial != 0, tp, nonagle))
1721 return needed - partial;
1726 /* Can at least one segment of SKB be sent right now, according to the
1727 * congestion window rules? If so, return how many segments are allowed.
1729 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1730 const struct sk_buff *skb)
1732 u32 in_flight, cwnd, halfcwnd;
1734 /* Don't be strict about the congestion window for the final FIN. */
1735 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1736 tcp_skb_pcount(skb) == 1)
1739 in_flight = tcp_packets_in_flight(tp);
1740 cwnd = tp->snd_cwnd;
1741 if (in_flight >= cwnd)
1744 /* For better scheduling, ensure we have at least
1745 * 2 GSO packets in flight.
1747 halfcwnd = max(cwnd >> 1, 1U);
1748 return min(halfcwnd, cwnd - in_flight);
1751 /* Initialize TSO state of a skb.
1752 * This must be invoked the first time we consider transmitting
1753 * SKB onto the wire.
1755 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1757 int tso_segs = tcp_skb_pcount(skb);
1759 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1760 tcp_set_skb_tso_segs(skb, mss_now);
1761 tso_segs = tcp_skb_pcount(skb);
1767 /* Return true if the Nagle test allows this packet to be
1770 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1771 unsigned int cur_mss, int nonagle)
1773 /* Nagle rule does not apply to frames, which sit in the middle of the
1774 * write_queue (they have no chances to get new data).
1776 * This is implemented in the callers, where they modify the 'nonagle'
1777 * argument based upon the location of SKB in the send queue.
1779 if (nonagle & TCP_NAGLE_PUSH)
1782 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1783 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1786 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1792 /* Does at least the first segment of SKB fit into the send window? */
1793 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1794 const struct sk_buff *skb,
1795 unsigned int cur_mss)
1797 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1799 if (skb->len > cur_mss)
1800 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1802 return !after(end_seq, tcp_wnd_end(tp));
1805 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1806 * should be put on the wire right now. If so, it returns the number of
1807 * packets allowed by the congestion window.
1809 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1810 unsigned int cur_mss, int nonagle)
1812 const struct tcp_sock *tp = tcp_sk(sk);
1813 unsigned int cwnd_quota;
1815 tcp_init_tso_segs(skb, cur_mss);
1817 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1820 cwnd_quota = tcp_cwnd_test(tp, skb);
1821 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1827 /* Test if sending is allowed right now. */
1828 bool tcp_may_send_now(struct sock *sk)
1830 const struct tcp_sock *tp = tcp_sk(sk);
1831 struct sk_buff *skb = tcp_send_head(sk);
1834 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1835 (tcp_skb_is_last(sk, skb) ?
1836 tp->nonagle : TCP_NAGLE_PUSH));
1839 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1840 * which is put after SKB on the list. It is very much like
1841 * tcp_fragment() except that it may make several kinds of assumptions
1842 * in order to speed up the splitting operation. In particular, we
1843 * know that all the data is in scatter-gather pages, and that the
1844 * packet has never been sent out before (and thus is not cloned).
1846 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1847 unsigned int mss_now, gfp_t gfp)
1849 struct sk_buff *buff;
1850 int nlen = skb->len - len;
1853 /* All of a TSO frame must be composed of paged data. */
1854 if (skb->len != skb->data_len)
1855 return tcp_fragment(sk, skb, len, mss_now, gfp);
1857 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1858 if (unlikely(!buff))
1861 sk->sk_wmem_queued += buff->truesize;
1862 sk_mem_charge(sk, buff->truesize);
1863 buff->truesize += nlen;
1864 skb->truesize -= nlen;
1866 /* Correct the sequence numbers. */
1867 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1868 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1869 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1871 /* PSH and FIN should only be set in the second packet. */
1872 flags = TCP_SKB_CB(skb)->tcp_flags;
1873 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1874 TCP_SKB_CB(buff)->tcp_flags = flags;
1876 /* This packet was never sent out yet, so no SACK bits. */
1877 TCP_SKB_CB(buff)->sacked = 0;
1879 tcp_skb_fragment_eor(skb, buff);
1881 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1882 skb_split(skb, buff, len);
1883 tcp_fragment_tstamp(skb, buff);
1885 /* Fix up tso_factor for both original and new SKB. */
1886 tcp_set_skb_tso_segs(skb, mss_now);
1887 tcp_set_skb_tso_segs(buff, mss_now);
1889 /* Link BUFF into the send queue. */
1890 __skb_header_release(buff);
1891 tcp_insert_write_queue_after(skb, buff, sk);
1896 /* Try to defer sending, if possible, in order to minimize the amount
1897 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1899 * This algorithm is from John Heffner.
1901 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1902 bool *is_cwnd_limited, u32 max_segs)
1904 const struct inet_connection_sock *icsk = inet_csk(sk);
1905 u32 age, send_win, cong_win, limit, in_flight;
1906 struct tcp_sock *tp = tcp_sk(sk);
1907 struct sk_buff *head;
1910 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1913 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1916 /* Avoid bursty behavior by allowing defer
1917 * only if the last write was recent.
1919 if ((s32)(tcp_jiffies32 - tp->lsndtime) > 0)
1922 in_flight = tcp_packets_in_flight(tp);
1924 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1926 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1928 /* From in_flight test above, we know that cwnd > in_flight. */
1929 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1931 limit = min(send_win, cong_win);
1933 /* If a full-sized TSO skb can be sent, do it. */
1934 if (limit >= max_segs * tp->mss_cache)
1937 /* Middle in queue won't get any more data, full sendable already? */
1938 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1941 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1943 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1945 /* If at least some fraction of a window is available,
1948 chunk /= win_divisor;
1952 /* Different approach, try not to defer past a single
1953 * ACK. Receiver should ACK every other full sized
1954 * frame, so if we have space for more than 3 frames
1957 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1961 head = tcp_write_queue_head(sk);
1963 age = tcp_stamp_us_delta(tp->tcp_mstamp, head->skb_mstamp);
1964 /* If next ACK is likely to come too late (half srtt), do not defer */
1965 if (age < (tp->srtt_us >> 4))
1968 /* Ok, it looks like it is advisable to defer. */
1970 if (cong_win < send_win && cong_win <= skb->len)
1971 *is_cwnd_limited = true;
1979 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1981 struct inet_connection_sock *icsk = inet_csk(sk);
1982 struct tcp_sock *tp = tcp_sk(sk);
1983 struct net *net = sock_net(sk);
1987 interval = net->ipv4.sysctl_tcp_probe_interval;
1988 delta = tcp_jiffies32 - icsk->icsk_mtup.probe_timestamp;
1989 if (unlikely(delta >= interval * HZ)) {
1990 int mss = tcp_current_mss(sk);
1992 /* Update current search range */
1993 icsk->icsk_mtup.probe_size = 0;
1994 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1995 sizeof(struct tcphdr) +
1996 icsk->icsk_af_ops->net_header_len;
1997 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1999 /* Update probe time stamp */
2000 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
2004 /* Create a new MTU probe if we are ready.
2005 * MTU probe is regularly attempting to increase the path MTU by
2006 * deliberately sending larger packets. This discovers routing
2007 * changes resulting in larger path MTUs.
2009 * Returns 0 if we should wait to probe (no cwnd available),
2010 * 1 if a probe was sent,
2013 static int tcp_mtu_probe(struct sock *sk)
2015 struct inet_connection_sock *icsk = inet_csk(sk);
2016 struct tcp_sock *tp = tcp_sk(sk);
2017 struct sk_buff *skb, *nskb, *next;
2018 struct net *net = sock_net(sk);
2025 /* Not currently probing/verifying,
2027 * have enough cwnd, and
2028 * not SACKing (the variable headers throw things off)
2030 if (likely(!icsk->icsk_mtup.enabled ||
2031 icsk->icsk_mtup.probe_size ||
2032 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
2033 tp->snd_cwnd < 11 ||
2034 tp->rx_opt.num_sacks || tp->rx_opt.dsack))
2037 /* Use binary search for probe_size between tcp_mss_base,
2038 * and current mss_clamp. if (search_high - search_low)
2039 * smaller than a threshold, backoff from probing.
2041 mss_now = tcp_current_mss(sk);
2042 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
2043 icsk->icsk_mtup.search_low) >> 1);
2044 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
2045 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
2046 /* When misfortune happens, we are reprobing actively,
2047 * and then reprobe timer has expired. We stick with current
2048 * probing process by not resetting search range to its orignal.
2050 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
2051 interval < net->ipv4.sysctl_tcp_probe_threshold) {
2052 /* Check whether enough time has elaplased for
2053 * another round of probing.
2055 tcp_mtu_check_reprobe(sk);
2059 /* Have enough data in the send queue to probe? */
2060 if (tp->write_seq - tp->snd_nxt < size_needed)
2063 if (tp->snd_wnd < size_needed)
2065 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
2068 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
2069 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
2070 if (!tcp_packets_in_flight(tp))
2076 /* We're allowed to probe. Build it now. */
2077 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
2080 sk->sk_wmem_queued += nskb->truesize;
2081 sk_mem_charge(sk, nskb->truesize);
2083 skb = tcp_send_head(sk);
2085 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
2086 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
2087 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
2088 TCP_SKB_CB(nskb)->sacked = 0;
2090 nskb->ip_summed = skb->ip_summed;
2092 tcp_insert_write_queue_before(nskb, skb, sk);
2095 tcp_for_write_queue_from_safe(skb, next, sk) {
2096 copy = min_t(int, skb->len, probe_size - len);
2097 if (nskb->ip_summed) {
2098 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
2100 __wsum csum = skb_copy_and_csum_bits(skb, 0,
2101 skb_put(nskb, copy),
2103 nskb->csum = csum_block_add(nskb->csum, csum, len);
2106 if (skb->len <= copy) {
2107 /* We've eaten all the data from this skb.
2109 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2110 tcp_unlink_write_queue(skb, sk);
2111 sk_wmem_free_skb(sk, skb);
2113 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
2114 ~(TCPHDR_FIN|TCPHDR_PSH);
2115 if (!skb_shinfo(skb)->nr_frags) {
2116 skb_pull(skb, copy);
2117 if (skb->ip_summed != CHECKSUM_PARTIAL)
2118 skb->csum = csum_partial(skb->data,
2121 __pskb_trim_head(skb, copy);
2122 tcp_set_skb_tso_segs(skb, mss_now);
2124 TCP_SKB_CB(skb)->seq += copy;
2129 if (len >= probe_size)
2132 tcp_init_tso_segs(nskb, nskb->len);
2134 /* We're ready to send. If this fails, the probe will
2135 * be resegmented into mss-sized pieces by tcp_write_xmit().
2137 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2138 /* Decrement cwnd here because we are sending
2139 * effectively two packets. */
2141 tcp_event_new_data_sent(sk, nskb);
2143 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2144 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2145 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2153 static bool tcp_pacing_check(const struct sock *sk)
2155 return tcp_needs_internal_pacing(sk) &&
2156 hrtimer_active(&tcp_sk(sk)->pacing_timer);
2159 /* TCP Small Queues :
2160 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2161 * (These limits are doubled for retransmits)
2163 * - better RTT estimation and ACK scheduling
2166 * Alas, some drivers / subsystems require a fair amount
2167 * of queued bytes to ensure line rate.
2168 * One example is wifi aggregation (802.11 AMPDU)
2170 static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
2171 unsigned int factor)
2175 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2176 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2179 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2180 /* Always send the 1st or 2nd skb in write queue.
2181 * No need to wait for TX completion to call us back,
2182 * after softirq/tasklet schedule.
2183 * This helps when TX completions are delayed too much.
2185 if (skb == sk->sk_write_queue.next ||
2186 skb->prev == sk->sk_write_queue.next)
2189 set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
2190 /* It is possible TX completion already happened
2191 * before we set TSQ_THROTTLED, so we must
2192 * test again the condition.
2194 smp_mb__after_atomic();
2195 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2201 static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
2203 const u32 now = tcp_jiffies32;
2205 if (tp->chrono_type > TCP_CHRONO_UNSPEC)
2206 tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;
2207 tp->chrono_start = now;
2208 tp->chrono_type = new;
2211 void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
2213 struct tcp_sock *tp = tcp_sk(sk);
2215 /* If there are multiple conditions worthy of tracking in a
2216 * chronograph then the highest priority enum takes precedence
2217 * over the other conditions. So that if something "more interesting"
2218 * starts happening, stop the previous chrono and start a new one.
2220 if (type > tp->chrono_type)
2221 tcp_chrono_set(tp, type);
2224 void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
2226 struct tcp_sock *tp = tcp_sk(sk);
2229 /* There are multiple conditions worthy of tracking in a
2230 * chronograph, so that the highest priority enum takes
2231 * precedence over the other conditions (see tcp_chrono_start).
2232 * If a condition stops, we only stop chrono tracking if
2233 * it's the "most interesting" or current chrono we are
2234 * tracking and starts busy chrono if we have pending data.
2236 if (tcp_write_queue_empty(sk))
2237 tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
2238 else if (type == tp->chrono_type)
2239 tcp_chrono_set(tp, TCP_CHRONO_BUSY);
2242 /* This routine writes packets to the network. It advances the
2243 * send_head. This happens as incoming acks open up the remote
2246 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2247 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2248 * account rare use of URG, this is not a big flaw.
2250 * Send at most one packet when push_one > 0. Temporarily ignore
2251 * cwnd limit to force at most one packet out when push_one == 2.
2253 * Returns true, if no segments are in flight and we have queued segments,
2254 * but cannot send anything now because of SWS or another problem.
2256 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2257 int push_one, gfp_t gfp)
2259 struct tcp_sock *tp = tcp_sk(sk);
2260 struct sk_buff *skb;
2261 unsigned int tso_segs, sent_pkts;
2264 bool is_cwnd_limited = false, is_rwnd_limited = false;
2270 /* Do MTU probing. */
2271 result = tcp_mtu_probe(sk);
2274 } else if (result > 0) {
2279 max_segs = tcp_tso_segs(sk, mss_now);
2280 tcp_mstamp_refresh(tp);
2281 while ((skb = tcp_send_head(sk))) {
2284 if (tcp_pacing_check(sk))
2287 tso_segs = tcp_init_tso_segs(skb, mss_now);
2290 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2291 /* "skb_mstamp" is used as a start point for the retransmit timer */
2292 skb->skb_mstamp = tp->tcp_mstamp;
2293 goto repair; /* Skip network transmission */
2296 cwnd_quota = tcp_cwnd_test(tp, skb);
2299 /* Force out a loss probe pkt. */
2305 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
2306 is_rwnd_limited = true;
2310 if (tso_segs == 1) {
2311 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2312 (tcp_skb_is_last(sk, skb) ?
2313 nonagle : TCP_NAGLE_PUSH))))
2317 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2323 if (tso_segs > 1 && !tcp_urg_mode(tp))
2324 limit = tcp_mss_split_point(sk, skb, mss_now,
2330 if (skb->len > limit &&
2331 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2334 if (test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags))
2335 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
2336 if (tcp_small_queue_check(sk, skb, 0))
2339 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2343 /* Advance the send_head. This one is sent out.
2344 * This call will increment packets_out.
2346 tcp_event_new_data_sent(sk, skb);
2348 tcp_minshall_update(tp, mss_now, skb);
2349 sent_pkts += tcp_skb_pcount(skb);
2355 if (is_rwnd_limited)
2356 tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
2358 tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
2360 if (likely(sent_pkts)) {
2361 if (tcp_in_cwnd_reduction(sk))
2362 tp->prr_out += sent_pkts;
2364 /* Send one loss probe per tail loss episode. */
2366 tcp_schedule_loss_probe(sk);
2367 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2368 tcp_cwnd_validate(sk, is_cwnd_limited);
2371 return !tp->packets_out && tcp_send_head(sk);
2374 bool tcp_schedule_loss_probe(struct sock *sk)
2376 struct inet_connection_sock *icsk = inet_csk(sk);
2377 struct tcp_sock *tp = tcp_sk(sk);
2378 u32 timeout, tlp_time_stamp, rto_time_stamp;
2379 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2381 /* No consecutive loss probes. */
2382 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2386 /* Don't do any loss probe on a Fast Open connection before 3WHS
2389 if (tp->fastopen_rsk)
2392 /* TLP is only scheduled when next timer event is RTO. */
2393 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2396 /* Schedule a loss probe in 2*RTT for SACK capable connections
2397 * in Open state, that are either limited by cwnd or application.
2399 if ((sysctl_tcp_early_retrans != 3 && sysctl_tcp_early_retrans != 4) ||
2400 !tp->packets_out || !tcp_is_sack(tp) ||
2401 icsk->icsk_ca_state != TCP_CA_Open)
2404 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2408 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2409 * for delayed ack when there's one outstanding packet. If no RTT
2410 * sample is available then probe after TCP_TIMEOUT_INIT.
2412 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2413 if (tp->packets_out == 1)
2414 timeout = max_t(u32, timeout,
2415 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2416 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2418 /* If RTO is shorter, just schedule TLP in its place. */
2419 tlp_time_stamp = tcp_jiffies32 + timeout;
2420 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2421 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2422 s32 delta = rto_time_stamp - tcp_jiffies32;
2427 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2432 /* Thanks to skb fast clones, we can detect if a prior transmit of
2433 * a packet is still in a qdisc or driver queue.
2434 * In this case, there is very little point doing a retransmit !
2436 static bool skb_still_in_host_queue(const struct sock *sk,
2437 const struct sk_buff *skb)
2439 if (unlikely(skb_fclone_busy(sk, skb))) {
2440 NET_INC_STATS(sock_net(sk),
2441 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2447 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2448 * retransmit the last segment.
2450 void tcp_send_loss_probe(struct sock *sk)
2452 struct tcp_sock *tp = tcp_sk(sk);
2453 struct sk_buff *skb;
2455 int mss = tcp_current_mss(sk);
2457 skb = tcp_send_head(sk);
2459 if (tcp_snd_wnd_test(tp, skb, mss)) {
2460 pcount = tp->packets_out;
2461 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2462 if (tp->packets_out > pcount)
2466 skb = tcp_write_queue_prev(sk, skb);
2468 skb = tcp_write_queue_tail(sk);
2471 /* At most one outstanding TLP retransmission. */
2472 if (tp->tlp_high_seq)
2475 /* Retransmit last segment. */
2479 if (skb_still_in_host_queue(sk, skb))
2482 pcount = tcp_skb_pcount(skb);
2483 if (WARN_ON(!pcount))
2486 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2487 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2490 skb = tcp_write_queue_next(sk, skb);
2493 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2496 if (__tcp_retransmit_skb(sk, skb, 1))
2499 /* Record snd_nxt for loss detection. */
2500 tp->tlp_high_seq = tp->snd_nxt;
2503 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2504 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2505 inet_csk(sk)->icsk_pending = 0;
2510 /* Push out any pending frames which were held back due to
2511 * TCP_CORK or attempt at coalescing tiny packets.
2512 * The socket must be locked by the caller.
2514 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2517 /* If we are closed, the bytes will have to remain here.
2518 * In time closedown will finish, we empty the write queue and
2519 * all will be happy.
2521 if (unlikely(sk->sk_state == TCP_CLOSE))
2524 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2525 sk_gfp_mask(sk, GFP_ATOMIC)))
2526 tcp_check_probe_timer(sk);
2529 /* Send _single_ skb sitting at the send head. This function requires
2530 * true push pending frames to setup probe timer etc.
2532 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2534 struct sk_buff *skb = tcp_send_head(sk);
2536 BUG_ON(!skb || skb->len < mss_now);
2538 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2541 /* This function returns the amount that we can raise the
2542 * usable window based on the following constraints
2544 * 1. The window can never be shrunk once it is offered (RFC 793)
2545 * 2. We limit memory per socket
2548 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2549 * RECV.NEXT + RCV.WIN fixed until:
2550 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2552 * i.e. don't raise the right edge of the window until you can raise
2553 * it at least MSS bytes.
2555 * Unfortunately, the recommended algorithm breaks header prediction,
2556 * since header prediction assumes th->window stays fixed.
2558 * Strictly speaking, keeping th->window fixed violates the receiver
2559 * side SWS prevention criteria. The problem is that under this rule
2560 * a stream of single byte packets will cause the right side of the
2561 * window to always advance by a single byte.
2563 * Of course, if the sender implements sender side SWS prevention
2564 * then this will not be a problem.
2566 * BSD seems to make the following compromise:
2568 * If the free space is less than the 1/4 of the maximum
2569 * space available and the free space is less than 1/2 mss,
2570 * then set the window to 0.
2571 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2572 * Otherwise, just prevent the window from shrinking
2573 * and from being larger than the largest representable value.
2575 * This prevents incremental opening of the window in the regime
2576 * where TCP is limited by the speed of the reader side taking
2577 * data out of the TCP receive queue. It does nothing about
2578 * those cases where the window is constrained on the sender side
2579 * because the pipeline is full.
2581 * BSD also seems to "accidentally" limit itself to windows that are a
2582 * multiple of MSS, at least until the free space gets quite small.
2583 * This would appear to be a side effect of the mbuf implementation.
2584 * Combining these two algorithms results in the observed behavior
2585 * of having a fixed window size at almost all times.
2587 * Below we obtain similar behavior by forcing the offered window to
2588 * a multiple of the mss when it is feasible to do so.
2590 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2591 * Regular options like TIMESTAMP are taken into account.
2593 u32 __tcp_select_window(struct sock *sk)
2595 struct inet_connection_sock *icsk = inet_csk(sk);
2596 struct tcp_sock *tp = tcp_sk(sk);
2597 /* MSS for the peer's data. Previous versions used mss_clamp
2598 * here. I don't know if the value based on our guesses
2599 * of peer's MSS is better for the performance. It's more correct
2600 * but may be worse for the performance because of rcv_mss
2601 * fluctuations. --SAW 1998/11/1
2603 int mss = icsk->icsk_ack.rcv_mss;
2604 int free_space = tcp_space(sk);
2605 int allowed_space = tcp_full_space(sk);
2606 int full_space = min_t(int, tp->window_clamp, allowed_space);
2609 if (unlikely(mss > full_space)) {
2614 if (free_space < (full_space >> 1)) {
2615 icsk->icsk_ack.quick = 0;
2617 if (tcp_under_memory_pressure(sk))
2618 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2621 /* free_space might become our new window, make sure we don't
2622 * increase it due to wscale.
2624 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2626 /* if free space is less than mss estimate, or is below 1/16th
2627 * of the maximum allowed, try to move to zero-window, else
2628 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2629 * new incoming data is dropped due to memory limits.
2630 * With large window, mss test triggers way too late in order
2631 * to announce zero window in time before rmem limit kicks in.
2633 if (free_space < (allowed_space >> 4) || free_space < mss)
2637 if (free_space > tp->rcv_ssthresh)
2638 free_space = tp->rcv_ssthresh;
2640 /* Don't do rounding if we are using window scaling, since the
2641 * scaled window will not line up with the MSS boundary anyway.
2643 if (tp->rx_opt.rcv_wscale) {
2644 window = free_space;
2646 /* Advertise enough space so that it won't get scaled away.
2647 * Import case: prevent zero window announcement if
2648 * 1<<rcv_wscale > mss.
2650 window = ALIGN(window, (1 << tp->rx_opt.rcv_wscale));
2652 window = tp->rcv_wnd;
2653 /* Get the largest window that is a nice multiple of mss.
2654 * Window clamp already applied above.
2655 * If our current window offering is within 1 mss of the
2656 * free space we just keep it. This prevents the divide
2657 * and multiply from happening most of the time.
2658 * We also don't do any window rounding when the free space
2661 if (window <= free_space - mss || window > free_space)
2662 window = rounddown(free_space, mss);
2663 else if (mss == full_space &&
2664 free_space > window + (full_space >> 1))
2665 window = free_space;
2671 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
2672 const struct sk_buff *next_skb)
2674 if (unlikely(tcp_has_tx_tstamp(next_skb))) {
2675 const struct skb_shared_info *next_shinfo =
2676 skb_shinfo(next_skb);
2677 struct skb_shared_info *shinfo = skb_shinfo(skb);
2679 shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2680 shinfo->tskey = next_shinfo->tskey;
2681 TCP_SKB_CB(skb)->txstamp_ack |=
2682 TCP_SKB_CB(next_skb)->txstamp_ack;
2686 /* Collapses two adjacent SKB's during retransmission. */
2687 static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2689 struct tcp_sock *tp = tcp_sk(sk);
2690 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2691 int skb_size, next_skb_size;
2693 skb_size = skb->len;
2694 next_skb_size = next_skb->len;
2696 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2698 if (next_skb_size) {
2699 if (next_skb_size <= skb_availroom(skb))
2700 skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size),
2702 else if (!skb_shift(skb, next_skb, next_skb_size))
2705 tcp_highest_sack_combine(sk, next_skb, skb);
2707 tcp_unlink_write_queue(next_skb, sk);
2709 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2710 skb->ip_summed = CHECKSUM_PARTIAL;
2712 if (skb->ip_summed != CHECKSUM_PARTIAL)
2713 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2715 /* Update sequence range on original skb. */
2716 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2718 /* Merge over control information. This moves PSH/FIN etc. over */
2719 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2721 /* All done, get rid of second SKB and account for it so
2722 * packet counting does not break.
2724 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2725 TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2727 /* changed transmit queue under us so clear hints */
2728 tcp_clear_retrans_hints_partial(tp);
2729 if (next_skb == tp->retransmit_skb_hint)
2730 tp->retransmit_skb_hint = skb;
2732 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2734 tcp_skb_collapse_tstamp(skb, next_skb);
2736 sk_wmem_free_skb(sk, next_skb);
2740 /* Check if coalescing SKBs is legal. */
2741 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2743 if (tcp_skb_pcount(skb) > 1)
2745 if (skb_cloned(skb))
2747 if (skb == tcp_send_head(sk))
2749 /* Some heuristics for collapsing over SACK'd could be invented */
2750 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2756 /* Collapse packets in the retransmit queue to make to create
2757 * less packets on the wire. This is only done on retransmission.
2759 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2762 struct tcp_sock *tp = tcp_sk(sk);
2763 struct sk_buff *skb = to, *tmp;
2766 if (!sysctl_tcp_retrans_collapse)
2768 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2771 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2772 if (!tcp_can_collapse(sk, skb))
2775 if (!tcp_skb_can_collapse_to(to))
2788 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2791 if (!tcp_collapse_retrans(sk, to))
2796 /* This retransmits one SKB. Policy decisions and retransmit queue
2797 * state updates are done by the caller. Returns non-zero if an
2798 * error occurred which prevented the send.
2800 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2802 struct inet_connection_sock *icsk = inet_csk(sk);
2803 struct tcp_sock *tp = tcp_sk(sk);
2804 unsigned int cur_mss;
2808 /* Inconclusive MTU probe */
2809 if (icsk->icsk_mtup.probe_size)
2810 icsk->icsk_mtup.probe_size = 0;
2812 /* Do not sent more than we queued. 1/4 is reserved for possible
2813 * copying overhead: fragmentation, tunneling, mangling etc.
2815 if (atomic_read(&sk->sk_wmem_alloc) >
2816 min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
2820 if (skb_still_in_host_queue(sk, skb))
2823 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2824 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2826 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2830 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2831 return -EHOSTUNREACH; /* Routing failure or similar. */
2833 cur_mss = tcp_current_mss(sk);
2835 /* If receiver has shrunk his window, and skb is out of
2836 * new window, do not retransmit it. The exception is the
2837 * case, when window is shrunk to zero. In this case
2838 * our retransmit serves as a zero window probe.
2840 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2841 TCP_SKB_CB(skb)->seq != tp->snd_una)
2844 len = cur_mss * segs;
2845 if (skb->len > len) {
2846 if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
2847 return -ENOMEM; /* We'll try again later. */
2849 if (skb_unclone(skb, GFP_ATOMIC))
2852 diff = tcp_skb_pcount(skb);
2853 tcp_set_skb_tso_segs(skb, cur_mss);
2854 diff -= tcp_skb_pcount(skb);
2856 tcp_adjust_pcount(sk, skb, diff);
2857 if (skb->len < cur_mss)
2858 tcp_retrans_try_collapse(sk, skb, cur_mss);
2861 /* RFC3168, section 6.1.1.1. ECN fallback */
2862 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2863 tcp_ecn_clear_syn(sk, skb);
2865 /* Update global and local TCP statistics. */
2866 segs = tcp_skb_pcount(skb);
2867 TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2868 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2869 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2870 tp->total_retrans += segs;
2872 /* make sure skb->data is aligned on arches that require it
2873 * and check if ack-trimming & collapsing extended the headroom
2874 * beyond what csum_start can cover.
2876 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2877 skb_headroom(skb) >= 0xFFFF)) {
2878 struct sk_buff *nskb;
2880 skb->skb_mstamp = tp->tcp_mstamp;
2881 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2882 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2885 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2889 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2890 } else if (err != -EBUSY) {
2891 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2896 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2898 struct tcp_sock *tp = tcp_sk(sk);
2899 int err = __tcp_retransmit_skb(sk, skb, segs);
2902 #if FASTRETRANS_DEBUG > 0
2903 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2904 net_dbg_ratelimited("retrans_out leaked\n");
2907 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2908 tp->retrans_out += tcp_skb_pcount(skb);
2910 /* Save stamp of the first retransmit. */
2911 if (!tp->retrans_stamp)
2912 tp->retrans_stamp = tcp_skb_timestamp(skb);
2916 if (tp->undo_retrans < 0)
2917 tp->undo_retrans = 0;
2918 tp->undo_retrans += tcp_skb_pcount(skb);
2922 /* This gets called after a retransmit timeout, and the initially
2923 * retransmitted data is acknowledged. It tries to continue
2924 * resending the rest of the retransmit queue, until either
2925 * we've sent it all or the congestion window limit is reached.
2926 * If doing SACK, the first ACK which comes back for a timeout
2927 * based retransmit packet might feed us FACK information again.
2928 * If so, we use it to avoid unnecessarily retransmissions.
2930 void tcp_xmit_retransmit_queue(struct sock *sk)
2932 const struct inet_connection_sock *icsk = inet_csk(sk);
2933 struct tcp_sock *tp = tcp_sk(sk);
2934 struct sk_buff *skb;
2935 struct sk_buff *hole = NULL;
2939 if (!tp->packets_out)
2942 if (tp->retransmit_skb_hint) {
2943 skb = tp->retransmit_skb_hint;
2945 skb = tcp_write_queue_head(sk);
2948 max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
2949 tcp_for_write_queue_from(skb, sk) {
2953 if (skb == tcp_send_head(sk))
2956 if (tcp_pacing_check(sk))
2959 /* we could do better than to assign each time */
2961 tp->retransmit_skb_hint = skb;
2963 segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
2966 sacked = TCP_SKB_CB(skb)->sacked;
2967 /* In case tcp_shift_skb_data() have aggregated large skbs,
2968 * we need to make sure not sending too bigs TSO packets
2970 segs = min_t(int, segs, max_segs);
2972 if (tp->retrans_out >= tp->lost_out) {
2974 } else if (!(sacked & TCPCB_LOST)) {
2975 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2980 if (icsk->icsk_ca_state != TCP_CA_Loss)
2981 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2983 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2986 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2989 if (tcp_small_queue_check(sk, skb, 1))
2992 if (tcp_retransmit_skb(sk, skb, segs))
2995 NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb));
2997 if (tcp_in_cwnd_reduction(sk))
2998 tp->prr_out += tcp_skb_pcount(skb);
3000 if (skb == tcp_write_queue_head(sk) &&
3001 icsk->icsk_pending != ICSK_TIME_REO_TIMEOUT)
3002 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3003 inet_csk(sk)->icsk_rto,
3008 /* We allow to exceed memory limits for FIN packets to expedite
3009 * connection tear down and (memory) recovery.
3010 * Otherwise tcp_send_fin() could be tempted to either delay FIN
3011 * or even be forced to close flow without any FIN.
3012 * In general, we want to allow one skb per socket to avoid hangs
3013 * with edge trigger epoll()
3015 void sk_forced_mem_schedule(struct sock *sk, int size)
3019 if (size <= sk->sk_forward_alloc)
3021 amt = sk_mem_pages(size);
3022 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
3023 sk_memory_allocated_add(sk, amt);
3025 if (mem_cgroup_sockets_enabled && sk->sk_memcg)
3026 mem_cgroup_charge_skmem(sk->sk_memcg, amt);
3029 /* Send a FIN. The caller locks the socket for us.
3030 * We should try to send a FIN packet really hard, but eventually give up.
3032 void tcp_send_fin(struct sock *sk)
3034 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
3035 struct tcp_sock *tp = tcp_sk(sk);
3037 /* Optimization, tack on the FIN if we have one skb in write queue and
3038 * this skb was not yet sent, or we are under memory pressure.
3039 * Note: in the latter case, FIN packet will be sent after a timeout,
3040 * as TCP stack thinks it has already been transmitted.
3042 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
3044 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
3045 TCP_SKB_CB(tskb)->end_seq++;
3047 if (!tcp_send_head(sk)) {
3048 /* This means tskb was already sent.
3049 * Pretend we included the FIN on previous transmit.
3050 * We need to set tp->snd_nxt to the value it would have
3051 * if FIN had been sent. This is because retransmit path
3052 * does not change tp->snd_nxt.
3058 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
3059 if (unlikely(!skb)) {
3064 skb_reserve(skb, MAX_TCP_HEADER);
3065 sk_forced_mem_schedule(sk, skb->truesize);
3066 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
3067 tcp_init_nondata_skb(skb, tp->write_seq,
3068 TCPHDR_ACK | TCPHDR_FIN);
3069 tcp_queue_skb(sk, skb);
3071 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
3074 /* We get here when a process closes a file descriptor (either due to
3075 * an explicit close() or as a byproduct of exit()'ing) and there
3076 * was unread data in the receive queue. This behavior is recommended
3077 * by RFC 2525, section 2.17. -DaveM
3079 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
3081 struct sk_buff *skb;
3083 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
3085 /* NOTE: No TCP options attached and we never retransmit this. */
3086 skb = alloc_skb(MAX_TCP_HEADER, priority);
3088 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3092 /* Reserve space for headers and prepare control bits. */
3093 skb_reserve(skb, MAX_TCP_HEADER);
3094 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
3095 TCPHDR_ACK | TCPHDR_RST);
3096 tcp_mstamp_refresh(tcp_sk(sk));
3098 if (tcp_transmit_skb(sk, skb, 0, priority))
3099 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3102 /* Send a crossed SYN-ACK during socket establishment.
3103 * WARNING: This routine must only be called when we have already sent
3104 * a SYN packet that crossed the incoming SYN that caused this routine
3105 * to get called. If this assumption fails then the initial rcv_wnd
3106 * and rcv_wscale values will not be correct.
3108 int tcp_send_synack(struct sock *sk)
3110 struct sk_buff *skb;
3112 skb = tcp_write_queue_head(sk);
3113 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
3114 pr_debug("%s: wrong queue state\n", __func__);
3117 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
3118 if (skb_cloned(skb)) {
3119 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
3122 tcp_unlink_write_queue(skb, sk);
3123 __skb_header_release(nskb);
3124 __tcp_add_write_queue_head(sk, nskb);
3125 sk_wmem_free_skb(sk, skb);
3126 sk->sk_wmem_queued += nskb->truesize;
3127 sk_mem_charge(sk, nskb->truesize);
3131 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
3132 tcp_ecn_send_synack(sk, skb);
3134 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3138 * tcp_make_synack - Prepare a SYN-ACK.
3139 * sk: listener socket
3140 * dst: dst entry attached to the SYNACK
3141 * req: request_sock pointer
3143 * Allocate one skb and build a SYNACK packet.
3144 * @dst is consumed : Caller should not use it again.
3146 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3147 struct request_sock *req,
3148 struct tcp_fastopen_cookie *foc,
3149 enum tcp_synack_type synack_type)
3151 struct inet_request_sock *ireq = inet_rsk(req);
3152 const struct tcp_sock *tp = tcp_sk(sk);
3153 struct tcp_md5sig_key *md5 = NULL;
3154 struct tcp_out_options opts;
3155 struct sk_buff *skb;
3156 int tcp_header_size;
3160 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3161 if (unlikely(!skb)) {
3165 /* Reserve space for headers. */
3166 skb_reserve(skb, MAX_TCP_HEADER);
3168 switch (synack_type) {
3169 case TCP_SYNACK_NORMAL:
3170 skb_set_owner_w(skb, req_to_sk(req));
3172 case TCP_SYNACK_COOKIE:
3173 /* Under synflood, we do not attach skb to a socket,
3174 * to avoid false sharing.
3177 case TCP_SYNACK_FASTOPEN:
3178 /* sk is a const pointer, because we want to express multiple
3179 * cpu might call us concurrently.
3180 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3182 skb_set_owner_w(skb, (struct sock *)sk);
3185 skb_dst_set(skb, dst);
3187 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
3189 memset(&opts, 0, sizeof(opts));
3190 #ifdef CONFIG_SYN_COOKIES
3191 if (unlikely(req->cookie_ts))
3192 skb->skb_mstamp = cookie_init_timestamp(req);
3195 skb->skb_mstamp = tcp_clock_us();
3197 #ifdef CONFIG_TCP_MD5SIG
3199 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3201 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3202 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3205 skb_push(skb, tcp_header_size);
3206 skb_reset_transport_header(skb);
3208 th = (struct tcphdr *)skb->data;
3209 memset(th, 0, sizeof(struct tcphdr));
3212 tcp_ecn_make_synack(req, th);
3213 th->source = htons(ireq->ir_num);
3214 th->dest = ireq->ir_rmt_port;
3215 /* Setting of flags are superfluous here for callers (and ECE is
3216 * not even correctly set)
3218 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3219 TCPHDR_SYN | TCPHDR_ACK);
3221 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3222 /* XXX data is queued and acked as is. No buffer/window check */
3223 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3225 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3226 th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3227 tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3228 th->doff = (tcp_header_size >> 2);
3229 __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3231 #ifdef CONFIG_TCP_MD5SIG
3232 /* Okay, we have all we need - do the md5 hash if needed */
3234 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3235 md5, req_to_sk(req), skb);
3239 /* Do not fool tcpdump (if any), clean our debris */
3243 EXPORT_SYMBOL(tcp_make_synack);
3245 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3247 struct inet_connection_sock *icsk = inet_csk(sk);
3248 const struct tcp_congestion_ops *ca;
3249 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3251 if (ca_key == TCP_CA_UNSPEC)
3255 ca = tcp_ca_find_key(ca_key);
3256 if (likely(ca && try_module_get(ca->owner))) {
3257 module_put(icsk->icsk_ca_ops->owner);
3258 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3259 icsk->icsk_ca_ops = ca;
3264 /* Do all connect socket setups that can be done AF independent. */
3265 static void tcp_connect_init(struct sock *sk)
3267 const struct dst_entry *dst = __sk_dst_get(sk);
3268 struct tcp_sock *tp = tcp_sk(sk);
3271 /* We'll fix this up when we get a response from the other end.
3272 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3274 tp->tcp_header_len = sizeof(struct tcphdr) +
3275 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3277 #ifdef CONFIG_TCP_MD5SIG
3278 if (tp->af_specific->md5_lookup(sk, sk))
3279 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3282 /* If user gave his TCP_MAXSEG, record it to clamp */
3283 if (tp->rx_opt.user_mss)
3284 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3287 tcp_sync_mss(sk, dst_mtu(dst));
3289 tcp_ca_dst_init(sk, dst);
3291 if (!tp->window_clamp)
3292 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3293 tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
3295 tcp_initialize_rcv_mss(sk);
3297 /* limit the window selection if the user enforce a smaller rx buffer */
3298 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3299 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3300 tp->window_clamp = tcp_full_space(sk);
3302 tcp_select_initial_window(tcp_full_space(sk),
3303 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3306 sock_net(sk)->ipv4.sysctl_tcp_window_scaling,
3308 dst_metric(dst, RTAX_INITRWND));
3310 tp->rx_opt.rcv_wscale = rcv_wscale;
3311 tp->rcv_ssthresh = tp->rcv_wnd;
3314 sock_reset_flag(sk, SOCK_DONE);
3317 tp->snd_una = tp->write_seq;
3318 tp->snd_sml = tp->write_seq;
3319 tp->snd_up = tp->write_seq;
3320 tp->snd_nxt = tp->write_seq;
3322 if (likely(!tp->repair))
3325 tp->rcv_tstamp = tcp_jiffies32;
3326 tp->rcv_wup = tp->rcv_nxt;
3327 tp->copied_seq = tp->rcv_nxt;
3329 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3330 inet_csk(sk)->icsk_retransmits = 0;
3331 tcp_clear_retrans(tp);
3334 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3336 struct tcp_sock *tp = tcp_sk(sk);
3337 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3339 tcb->end_seq += skb->len;
3340 __skb_header_release(skb);
3341 __tcp_add_write_queue_tail(sk, skb);
3342 sk->sk_wmem_queued += skb->truesize;
3343 sk_mem_charge(sk, skb->truesize);
3344 tp->write_seq = tcb->end_seq;
3345 tp->packets_out += tcp_skb_pcount(skb);
3348 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3349 * queue a data-only packet after the regular SYN, such that regular SYNs
3350 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3351 * only the SYN sequence, the data are retransmitted in the first ACK.
3352 * If cookie is not cached or other error occurs, falls back to send a
3353 * regular SYN with Fast Open cookie request option.
3355 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3357 struct tcp_sock *tp = tcp_sk(sk);
3358 struct tcp_fastopen_request *fo = tp->fastopen_req;
3360 struct sk_buff *syn_data;
3362 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3363 if (!tcp_fastopen_cookie_check(sk, &tp->rx_opt.mss_clamp, &fo->cookie))
3366 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3367 * user-MSS. Reserve maximum option space for middleboxes that add
3368 * private TCP options. The cost is reduced data space in SYN :(
3370 tp->rx_opt.mss_clamp = tcp_mss_clamp(tp, tp->rx_opt.mss_clamp);
3372 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3373 MAX_TCP_OPTION_SPACE;
3375 space = min_t(size_t, space, fo->size);
3377 /* limit to order-0 allocations */
3378 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3380 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3383 syn_data->ip_summed = CHECKSUM_PARTIAL;
3384 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3386 int copied = copy_from_iter(skb_put(syn_data, space), space,
3387 &fo->data->msg_iter);
3388 if (unlikely(!copied)) {
3389 kfree_skb(syn_data);
3392 if (copied != space) {
3393 skb_trim(syn_data, copied);
3397 /* No more data pending in inet_wait_for_connect() */
3398 if (space == fo->size)
3402 tcp_connect_queue_skb(sk, syn_data);
3404 tcp_chrono_start(sk, TCP_CHRONO_BUSY);
3406 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3408 syn->skb_mstamp = syn_data->skb_mstamp;
3410 /* Now full SYN+DATA was cloned and sent (or not),
3411 * remove the SYN from the original skb (syn_data)
3412 * we keep in write queue in case of a retransmit, as we
3413 * also have the SYN packet (with no data) in the same queue.
3415 TCP_SKB_CB(syn_data)->seq++;
3416 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3418 tp->syn_data = (fo->copied > 0);
3419 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3424 /* Send a regular SYN with Fast Open cookie request option */
3425 if (fo->cookie.len > 0)
3427 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3429 tp->syn_fastopen = 0;
3431 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3435 /* Build a SYN and send it off. */
3436 int tcp_connect(struct sock *sk)
3438 struct tcp_sock *tp = tcp_sk(sk);
3439 struct sk_buff *buff;
3442 tcp_connect_init(sk);
3444 if (unlikely(tp->repair)) {
3445 tcp_finish_connect(sk, NULL);
3449 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3450 if (unlikely(!buff))
3453 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3454 tcp_mstamp_refresh(tp);
3455 tp->retrans_stamp = tcp_time_stamp(tp);
3456 tcp_connect_queue_skb(sk, buff);
3457 tcp_ecn_send_syn(sk, buff);
3459 /* Send off SYN; include data in Fast Open. */
3460 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3461 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3462 if (err == -ECONNREFUSED)
3465 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3466 * in order to make this packet get counted in tcpOutSegs.
3468 tp->snd_nxt = tp->write_seq;
3469 tp->pushed_seq = tp->write_seq;
3470 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3472 /* Timer for repeating the SYN until an answer. */
3473 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3474 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3477 EXPORT_SYMBOL(tcp_connect);
3479 /* Send out a delayed ack, the caller does the policy checking
3480 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3483 void tcp_send_delayed_ack(struct sock *sk)
3485 struct inet_connection_sock *icsk = inet_csk(sk);
3486 int ato = icsk->icsk_ack.ato;
3487 unsigned long timeout;
3489 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3491 if (ato > TCP_DELACK_MIN) {
3492 const struct tcp_sock *tp = tcp_sk(sk);
3493 int max_ato = HZ / 2;
3495 if (icsk->icsk_ack.pingpong ||
3496 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3497 max_ato = TCP_DELACK_MAX;
3499 /* Slow path, intersegment interval is "high". */
3501 /* If some rtt estimate is known, use it to bound delayed ack.
3502 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3506 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3513 ato = min(ato, max_ato);
3516 /* Stay within the limit we were given */
3517 timeout = jiffies + ato;
3519 /* Use new timeout only if there wasn't a older one earlier. */
3520 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3521 /* If delack timer was blocked or is about to expire,
3524 if (icsk->icsk_ack.blocked ||
3525 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3530 if (!time_before(timeout, icsk->icsk_ack.timeout))
3531 timeout = icsk->icsk_ack.timeout;
3533 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3534 icsk->icsk_ack.timeout = timeout;
3535 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3538 /* This routine sends an ack and also updates the window. */
3539 void tcp_send_ack(struct sock *sk)
3541 struct sk_buff *buff;
3543 /* If we have been reset, we may not send again. */
3544 if (sk->sk_state == TCP_CLOSE)
3547 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3549 /* We are not putting this on the write queue, so
3550 * tcp_transmit_skb() will set the ownership to this
3553 buff = alloc_skb(MAX_TCP_HEADER,
3554 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3555 if (unlikely(!buff)) {
3556 inet_csk_schedule_ack(sk);
3557 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3558 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3559 TCP_DELACK_MAX, TCP_RTO_MAX);
3563 /* Reserve space for headers and prepare control bits. */
3564 skb_reserve(buff, MAX_TCP_HEADER);
3565 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3567 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3569 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3571 skb_set_tcp_pure_ack(buff);
3573 /* Send it off, this clears delayed acks for us. */
3574 tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
3576 EXPORT_SYMBOL_GPL(tcp_send_ack);
3578 /* This routine sends a packet with an out of date sequence
3579 * number. It assumes the other end will try to ack it.
3581 * Question: what should we make while urgent mode?
3582 * 4.4BSD forces sending single byte of data. We cannot send
3583 * out of window data, because we have SND.NXT==SND.MAX...
3585 * Current solution: to send TWO zero-length segments in urgent mode:
3586 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3587 * out-of-date with SND.UNA-1 to probe window.
3589 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3591 struct tcp_sock *tp = tcp_sk(sk);
3592 struct sk_buff *skb;
3594 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3595 skb = alloc_skb(MAX_TCP_HEADER,
3596 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3600 /* Reserve space for headers and set control bits. */
3601 skb_reserve(skb, MAX_TCP_HEADER);
3602 /* Use a previous sequence. This should cause the other
3603 * end to send an ack. Don't queue or clone SKB, just
3606 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3607 NET_INC_STATS(sock_net(sk), mib);
3608 return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
3611 /* Called from setsockopt( ... TCP_REPAIR ) */
3612 void tcp_send_window_probe(struct sock *sk)
3614 if (sk->sk_state == TCP_ESTABLISHED) {
3615 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3616 tcp_mstamp_refresh(tcp_sk(sk));
3617 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3621 /* Initiate keepalive or window probe from timer. */
3622 int tcp_write_wakeup(struct sock *sk, int mib)
3624 struct tcp_sock *tp = tcp_sk(sk);
3625 struct sk_buff *skb;
3627 if (sk->sk_state == TCP_CLOSE)
3630 skb = tcp_send_head(sk);
3631 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3633 unsigned int mss = tcp_current_mss(sk);
3634 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3636 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3637 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3639 /* We are probing the opening of a window
3640 * but the window size is != 0
3641 * must have been a result SWS avoidance ( sender )
3643 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3645 seg_size = min(seg_size, mss);
3646 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3647 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3649 } else if (!tcp_skb_pcount(skb))
3650 tcp_set_skb_tso_segs(skb, mss);
3652 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3653 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3655 tcp_event_new_data_sent(sk, skb);
3658 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3659 tcp_xmit_probe_skb(sk, 1, mib);
3660 return tcp_xmit_probe_skb(sk, 0, mib);
3664 /* A window probe timeout has occurred. If window is not closed send
3665 * a partial packet else a zero probe.
3667 void tcp_send_probe0(struct sock *sk)
3669 struct inet_connection_sock *icsk = inet_csk(sk);
3670 struct tcp_sock *tp = tcp_sk(sk);
3671 struct net *net = sock_net(sk);
3672 unsigned long probe_max;
3675 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3677 if (tp->packets_out || !tcp_send_head(sk)) {
3678 /* Cancel probe timer, if it is not required. */
3679 icsk->icsk_probes_out = 0;
3680 icsk->icsk_backoff = 0;
3685 if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3686 icsk->icsk_backoff++;
3687 icsk->icsk_probes_out++;
3688 probe_max = TCP_RTO_MAX;
3690 /* If packet was not sent due to local congestion,
3691 * do not backoff and do not remember icsk_probes_out.
3692 * Let local senders to fight for local resources.
3694 * Use accumulated backoff yet.
3696 if (!icsk->icsk_probes_out)
3697 icsk->icsk_probes_out = 1;
3698 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3700 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3701 tcp_probe0_when(sk, probe_max),
3705 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3707 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3711 tcp_rsk(req)->txhash = net_tx_rndhash();
3712 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3714 __TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3715 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3716 if (unlikely(tcp_passive_fastopen(sk)))
3717 tcp_sk(sk)->total_retrans++;
3721 EXPORT_SYMBOL(tcp_rtx_synack);