2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * Implementation of the Transmission Control Protocol(TCP).
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
27 * Linus Torvalds : send_delayed_ack
28 * David S. Miller : Charge memory using the right skb
29 * during syn/ack processing.
30 * David S. Miller : Output engine completely rewritten.
31 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
32 * Cacophonix Gaul : draft-minshall-nagle-01
33 * J Hadi Salim : ECN support
37 #define pr_fmt(fmt) "TCP: " fmt
41 #include <linux/compiler.h>
42 #include <linux/gfp.h>
43 #include <linux/module.h>
45 /* People can turn this off for buggy TCP's found in printers etc. */
46 int sysctl_tcp_retrans_collapse __read_mostly = 1;
48 /* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
53 /* Default TSQ limit of four TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
56 /* This limits the percentage of the congestion window which we
57 * will allow a single TSO frame to consume. Building TSO frames
58 * which are too large can cause TCP streams to be bursty.
60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
62 /* By default, RFC2861 behavior. */
63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
65 unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
66 EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);
68 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
69 int push_one, gfp_t gfp);
71 /* Account for new data that has been sent to the network. */
72 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
74 struct inet_connection_sock *icsk = inet_csk(sk);
75 struct tcp_sock *tp = tcp_sk(sk);
76 unsigned int prior_packets = tp->packets_out;
78 tcp_advance_send_head(sk, skb);
79 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
81 tp->packets_out += tcp_skb_pcount(skb);
82 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
83 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
87 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
91 /* SND.NXT, if window was not shrunk.
92 * If window has been shrunk, what should we make? It is not clear at all.
93 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
94 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
95 * invalid. OK, let's make this for now:
97 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
99 const struct tcp_sock *tp = tcp_sk(sk);
101 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
104 return tcp_wnd_end(tp);
107 /* Calculate mss to advertise in SYN segment.
108 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
110 * 1. It is independent of path mtu.
111 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
112 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
113 * attached devices, because some buggy hosts are confused by
115 * 4. We do not make 3, we advertise MSS, calculated from first
116 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
117 * This may be overridden via information stored in routing table.
118 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
119 * probably even Jumbo".
121 static __u16 tcp_advertise_mss(struct sock *sk)
123 struct tcp_sock *tp = tcp_sk(sk);
124 const struct dst_entry *dst = __sk_dst_get(sk);
125 int mss = tp->advmss;
128 unsigned int metric = dst_metric_advmss(dst);
139 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
140 * This is the first part of cwnd validation mechanism. */
141 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
143 struct tcp_sock *tp = tcp_sk(sk);
144 s32 delta = tcp_time_stamp - tp->lsndtime;
145 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
146 u32 cwnd = tp->snd_cwnd;
148 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
150 tp->snd_ssthresh = tcp_current_ssthresh(sk);
151 restart_cwnd = min(restart_cwnd, cwnd);
153 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
155 tp->snd_cwnd = max(cwnd, restart_cwnd);
156 tp->snd_cwnd_stamp = tcp_time_stamp;
157 tp->snd_cwnd_used = 0;
160 /* Congestion state accounting after a packet has been sent. */
161 static void tcp_event_data_sent(struct tcp_sock *tp,
164 struct inet_connection_sock *icsk = inet_csk(sk);
165 const u32 now = tcp_time_stamp;
167 if (sysctl_tcp_slow_start_after_idle &&
168 (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
169 tcp_cwnd_restart(sk, __sk_dst_get(sk));
173 /* If it is a reply for ato after last received
174 * packet, enter pingpong mode.
176 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
177 icsk->icsk_ack.pingpong = 1;
180 /* Account for an ACK we sent. */
181 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
183 tcp_dec_quickack_mode(sk, pkts);
184 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
188 u32 tcp_default_init_rwnd(u32 mss)
190 /* Initial receive window should be twice of TCP_INIT_CWND to
191 * enable proper sending of new unsent data during fast recovery
192 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
193 * limit when mss is larger than 1460.
195 u32 init_rwnd = TCP_INIT_CWND * 2;
198 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
202 /* Determine a window scaling and initial window to offer.
203 * Based on the assumption that the given amount of space
204 * will be offered. Store the results in the tp structure.
205 * NOTE: for smooth operation initial space offering should
206 * be a multiple of mss if possible. We assume here that mss >= 1.
207 * This MUST be enforced by all callers.
209 void tcp_select_initial_window(int __space, __u32 mss,
210 __u32 *rcv_wnd, __u32 *window_clamp,
211 int wscale_ok, __u8 *rcv_wscale,
214 unsigned int space = (__space < 0 ? 0 : __space);
216 /* If no clamp set the clamp to the max possible scaled window */
217 if (*window_clamp == 0)
218 (*window_clamp) = (65535 << 14);
219 space = min(*window_clamp, space);
221 /* Quantize space offering to a multiple of mss if possible. */
223 space = (space / mss) * mss;
225 /* NOTE: offering an initial window larger than 32767
226 * will break some buggy TCP stacks. If the admin tells us
227 * it is likely we could be speaking with such a buggy stack
228 * we will truncate our initial window offering to 32K-1
229 * unless the remote has sent us a window scaling option,
230 * which we interpret as a sign the remote TCP is not
231 * misinterpreting the window field as a signed quantity.
233 if (sysctl_tcp_workaround_signed_windows)
234 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
240 /* Set window scaling on max possible window
241 * See RFC1323 for an explanation of the limit to 14
243 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
244 space = min_t(u32, space, *window_clamp);
245 while (space > 65535 && (*rcv_wscale) < 14) {
251 if (mss > (1 << *rcv_wscale)) {
252 if (!init_rcv_wnd) /* Use default unless specified otherwise */
253 init_rcv_wnd = tcp_default_init_rwnd(mss);
254 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
257 /* Set the clamp no higher than max representable value */
258 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
260 EXPORT_SYMBOL(tcp_select_initial_window);
262 /* Chose a new window to advertise, update state in tcp_sock for the
263 * socket, and return result with RFC1323 scaling applied. The return
264 * value can be stuffed directly into th->window for an outgoing
267 static u16 tcp_select_window(struct sock *sk)
269 struct tcp_sock *tp = tcp_sk(sk);
270 u32 old_win = tp->rcv_wnd;
271 u32 cur_win = tcp_receive_window(tp);
272 u32 new_win = __tcp_select_window(sk);
274 /* Never shrink the offered window */
275 if (new_win < cur_win) {
276 /* Danger Will Robinson!
277 * Don't update rcv_wup/rcv_wnd here or else
278 * we will not be able to advertise a zero
279 * window in time. --DaveM
281 * Relax Will Robinson.
284 NET_INC_STATS(sock_net(sk),
285 LINUX_MIB_TCPWANTZEROWINDOWADV);
286 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
288 tp->rcv_wnd = new_win;
289 tp->rcv_wup = tp->rcv_nxt;
291 /* Make sure we do not exceed the maximum possible
294 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
295 new_win = min(new_win, MAX_TCP_WINDOW);
297 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
299 /* RFC1323 scaling applied */
300 new_win >>= tp->rx_opt.rcv_wscale;
302 /* If we advertise zero window, disable fast path. */
306 NET_INC_STATS(sock_net(sk),
307 LINUX_MIB_TCPTOZEROWINDOWADV);
308 } else if (old_win == 0) {
309 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
315 /* Packet ECN state for a SYN-ACK */
316 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
318 const struct tcp_sock *tp = tcp_sk(sk);
320 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
321 if (!(tp->ecn_flags & TCP_ECN_OK))
322 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
323 else if (tcp_ca_needs_ecn(sk))
327 /* Packet ECN state for a SYN. */
328 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
330 struct tcp_sock *tp = tcp_sk(sk);
331 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
332 tcp_ca_needs_ecn(sk);
335 const struct dst_entry *dst = __sk_dst_get(sk);
337 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
344 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
345 tp->ecn_flags = TCP_ECN_OK;
346 if (tcp_ca_needs_ecn(sk))
351 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
353 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
354 /* tp->ecn_flags are cleared at a later point in time when
355 * SYN ACK is ultimatively being received.
357 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
361 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th,
364 if (inet_rsk(req)->ecn_ok) {
366 if (tcp_ca_needs_ecn(sk))
371 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
374 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
377 struct tcp_sock *tp = tcp_sk(sk);
379 if (tp->ecn_flags & TCP_ECN_OK) {
380 /* Not-retransmitted data segment: set ECT and inject CWR. */
381 if (skb->len != tcp_header_len &&
382 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
384 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
385 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
386 tcp_hdr(skb)->cwr = 1;
387 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
389 } else if (!tcp_ca_needs_ecn(sk)) {
390 /* ACK or retransmitted segment: clear ECT|CE */
391 INET_ECN_dontxmit(sk);
393 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
394 tcp_hdr(skb)->ece = 1;
398 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
399 * auto increment end seqno.
401 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
403 skb->ip_summed = CHECKSUM_PARTIAL;
406 TCP_SKB_CB(skb)->tcp_flags = flags;
407 TCP_SKB_CB(skb)->sacked = 0;
409 tcp_skb_pcount_set(skb, 1);
411 TCP_SKB_CB(skb)->seq = seq;
412 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
414 TCP_SKB_CB(skb)->end_seq = seq;
417 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
419 return tp->snd_una != tp->snd_up;
422 #define OPTION_SACK_ADVERTISE (1 << 0)
423 #define OPTION_TS (1 << 1)
424 #define OPTION_MD5 (1 << 2)
425 #define OPTION_WSCALE (1 << 3)
426 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
428 struct tcp_out_options {
429 u16 options; /* bit field of OPTION_* */
430 u16 mss; /* 0 to disable */
431 u8 ws; /* window scale, 0 to disable */
432 u8 num_sack_blocks; /* number of SACK blocks to include */
433 u8 hash_size; /* bytes in hash_location */
434 __u8 *hash_location; /* temporary pointer, overloaded */
435 __u32 tsval, tsecr; /* need to include OPTION_TS */
436 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
439 /* Write previously computed TCP options to the packet.
441 * Beware: Something in the Internet is very sensitive to the ordering of
442 * TCP options, we learned this through the hard way, so be careful here.
443 * Luckily we can at least blame others for their non-compliance but from
444 * inter-operability perspective it seems that we're somewhat stuck with
445 * the ordering which we have been using if we want to keep working with
446 * those broken things (not that it currently hurts anybody as there isn't
447 * particular reason why the ordering would need to be changed).
449 * At least SACK_PERM as the first option is known to lead to a disaster
450 * (but it may well be that other scenarios fail similarly).
452 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
453 struct tcp_out_options *opts)
455 u16 options = opts->options; /* mungable copy */
457 if (unlikely(OPTION_MD5 & options)) {
458 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
459 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
460 /* overload cookie hash location */
461 opts->hash_location = (__u8 *)ptr;
465 if (unlikely(opts->mss)) {
466 *ptr++ = htonl((TCPOPT_MSS << 24) |
467 (TCPOLEN_MSS << 16) |
471 if (likely(OPTION_TS & options)) {
472 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
473 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
474 (TCPOLEN_SACK_PERM << 16) |
475 (TCPOPT_TIMESTAMP << 8) |
477 options &= ~OPTION_SACK_ADVERTISE;
479 *ptr++ = htonl((TCPOPT_NOP << 24) |
481 (TCPOPT_TIMESTAMP << 8) |
484 *ptr++ = htonl(opts->tsval);
485 *ptr++ = htonl(opts->tsecr);
488 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
489 *ptr++ = htonl((TCPOPT_NOP << 24) |
491 (TCPOPT_SACK_PERM << 8) |
495 if (unlikely(OPTION_WSCALE & options)) {
496 *ptr++ = htonl((TCPOPT_NOP << 24) |
497 (TCPOPT_WINDOW << 16) |
498 (TCPOLEN_WINDOW << 8) |
502 if (unlikely(opts->num_sack_blocks)) {
503 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
504 tp->duplicate_sack : tp->selective_acks;
507 *ptr++ = htonl((TCPOPT_NOP << 24) |
510 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
511 TCPOLEN_SACK_PERBLOCK)));
513 for (this_sack = 0; this_sack < opts->num_sack_blocks;
515 *ptr++ = htonl(sp[this_sack].start_seq);
516 *ptr++ = htonl(sp[this_sack].end_seq);
519 tp->rx_opt.dsack = 0;
522 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
523 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
525 u32 len; /* Fast Open option length */
528 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
529 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
530 TCPOPT_FASTOPEN_MAGIC);
531 p += TCPOLEN_EXP_FASTOPEN_BASE;
533 len = TCPOLEN_FASTOPEN_BASE + foc->len;
534 *p++ = TCPOPT_FASTOPEN;
538 memcpy(p, foc->val, foc->len);
539 if ((len & 3) == 2) {
540 p[foc->len] = TCPOPT_NOP;
541 p[foc->len + 1] = TCPOPT_NOP;
543 ptr += (len + 3) >> 2;
547 /* Compute TCP options for SYN packets. This is not the final
548 * network wire format yet.
550 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
551 struct tcp_out_options *opts,
552 struct tcp_md5sig_key **md5)
554 struct tcp_sock *tp = tcp_sk(sk);
555 unsigned int remaining = MAX_TCP_OPTION_SPACE;
556 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
558 #ifdef CONFIG_TCP_MD5SIG
559 *md5 = tp->af_specific->md5_lookup(sk, sk);
561 opts->options |= OPTION_MD5;
562 remaining -= TCPOLEN_MD5SIG_ALIGNED;
568 /* We always get an MSS option. The option bytes which will be seen in
569 * normal data packets should timestamps be used, must be in the MSS
570 * advertised. But we subtract them from tp->mss_cache so that
571 * calculations in tcp_sendmsg are simpler etc. So account for this
572 * fact here if necessary. If we don't do this correctly, as a
573 * receiver we won't recognize data packets as being full sized when we
574 * should, and thus we won't abide by the delayed ACK rules correctly.
575 * SACKs don't matter, we never delay an ACK when we have any of those
577 opts->mss = tcp_advertise_mss(sk);
578 remaining -= TCPOLEN_MSS_ALIGNED;
580 if (likely(sysctl_tcp_timestamps && !*md5)) {
581 opts->options |= OPTION_TS;
582 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
583 opts->tsecr = tp->rx_opt.ts_recent;
584 remaining -= TCPOLEN_TSTAMP_ALIGNED;
586 if (likely(sysctl_tcp_window_scaling)) {
587 opts->ws = tp->rx_opt.rcv_wscale;
588 opts->options |= OPTION_WSCALE;
589 remaining -= TCPOLEN_WSCALE_ALIGNED;
591 if (likely(sysctl_tcp_sack)) {
592 opts->options |= OPTION_SACK_ADVERTISE;
593 if (unlikely(!(OPTION_TS & opts->options)))
594 remaining -= TCPOLEN_SACKPERM_ALIGNED;
597 if (fastopen && fastopen->cookie.len >= 0) {
598 u32 need = fastopen->cookie.len;
600 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
601 TCPOLEN_FASTOPEN_BASE;
602 need = (need + 3) & ~3U; /* Align to 32 bits */
603 if (remaining >= need) {
604 opts->options |= OPTION_FAST_OPEN_COOKIE;
605 opts->fastopen_cookie = &fastopen->cookie;
607 tp->syn_fastopen = 1;
608 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
612 return MAX_TCP_OPTION_SPACE - remaining;
615 /* Set up TCP options for SYN-ACKs. */
616 static unsigned int tcp_synack_options(struct sock *sk,
617 struct request_sock *req,
618 unsigned int mss, struct sk_buff *skb,
619 struct tcp_out_options *opts,
620 const struct tcp_md5sig_key *md5,
621 struct tcp_fastopen_cookie *foc)
623 struct inet_request_sock *ireq = inet_rsk(req);
624 unsigned int remaining = MAX_TCP_OPTION_SPACE;
626 #ifdef CONFIG_TCP_MD5SIG
628 opts->options |= OPTION_MD5;
629 remaining -= TCPOLEN_MD5SIG_ALIGNED;
631 /* We can't fit any SACK blocks in a packet with MD5 + TS
632 * options. There was discussion about disabling SACK
633 * rather than TS in order to fit in better with old,
634 * buggy kernels, but that was deemed to be unnecessary.
636 ireq->tstamp_ok &= !ireq->sack_ok;
640 /* We always send an MSS option. */
642 remaining -= TCPOLEN_MSS_ALIGNED;
644 if (likely(ireq->wscale_ok)) {
645 opts->ws = ireq->rcv_wscale;
646 opts->options |= OPTION_WSCALE;
647 remaining -= TCPOLEN_WSCALE_ALIGNED;
649 if (likely(ireq->tstamp_ok)) {
650 opts->options |= OPTION_TS;
651 opts->tsval = tcp_skb_timestamp(skb);
652 opts->tsecr = req->ts_recent;
653 remaining -= TCPOLEN_TSTAMP_ALIGNED;
655 if (likely(ireq->sack_ok)) {
656 opts->options |= OPTION_SACK_ADVERTISE;
657 if (unlikely(!ireq->tstamp_ok))
658 remaining -= TCPOLEN_SACKPERM_ALIGNED;
660 if (foc != NULL && foc->len >= 0) {
663 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
664 TCPOLEN_FASTOPEN_BASE;
665 need = (need + 3) & ~3U; /* Align to 32 bits */
666 if (remaining >= need) {
667 opts->options |= OPTION_FAST_OPEN_COOKIE;
668 opts->fastopen_cookie = foc;
673 return MAX_TCP_OPTION_SPACE - remaining;
676 /* Compute TCP options for ESTABLISHED sockets. This is not the
677 * final wire format yet.
679 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
680 struct tcp_out_options *opts,
681 struct tcp_md5sig_key **md5)
683 struct tcp_sock *tp = tcp_sk(sk);
684 unsigned int size = 0;
685 unsigned int eff_sacks;
689 #ifdef CONFIG_TCP_MD5SIG
690 *md5 = tp->af_specific->md5_lookup(sk, sk);
691 if (unlikely(*md5)) {
692 opts->options |= OPTION_MD5;
693 size += TCPOLEN_MD5SIG_ALIGNED;
699 if (likely(tp->rx_opt.tstamp_ok)) {
700 opts->options |= OPTION_TS;
701 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
702 opts->tsecr = tp->rx_opt.ts_recent;
703 size += TCPOLEN_TSTAMP_ALIGNED;
706 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
707 if (unlikely(eff_sacks)) {
708 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
709 opts->num_sack_blocks =
710 min_t(unsigned int, eff_sacks,
711 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
712 TCPOLEN_SACK_PERBLOCK);
713 size += TCPOLEN_SACK_BASE_ALIGNED +
714 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
721 /* TCP SMALL QUEUES (TSQ)
723 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
724 * to reduce RTT and bufferbloat.
725 * We do this using a special skb destructor (tcp_wfree).
727 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
728 * needs to be reallocated in a driver.
729 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
731 * Since transmit from skb destructor is forbidden, we use a tasklet
732 * to process all sockets that eventually need to send more skbs.
733 * We use one tasklet per cpu, with its own queue of sockets.
736 struct tasklet_struct tasklet;
737 struct list_head head; /* queue of tcp sockets */
739 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
741 static void tcp_tsq_handler(struct sock *sk)
743 if ((1 << sk->sk_state) &
744 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
745 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
746 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
750 * One tasklet per cpu tries to send more skbs.
751 * We run in tasklet context but need to disable irqs when
752 * transferring tsq->head because tcp_wfree() might
753 * interrupt us (non NAPI drivers)
755 static void tcp_tasklet_func(unsigned long data)
757 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
760 struct list_head *q, *n;
764 local_irq_save(flags);
765 list_splice_init(&tsq->head, &list);
766 local_irq_restore(flags);
768 list_for_each_safe(q, n, &list) {
769 tp = list_entry(q, struct tcp_sock, tsq_node);
770 list_del(&tp->tsq_node);
772 sk = (struct sock *)tp;
775 if (!sock_owned_by_user(sk)) {
778 /* defer the work to tcp_release_cb() */
779 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
783 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
788 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
789 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
790 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
791 (1UL << TCP_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 struct tcp_sock *tp = tcp_sk(sk);
802 unsigned long flags, nflags;
804 /* perform an atomic operation only if at least one flag is set */
806 flags = tp->tsq_flags;
807 if (!(flags & TCP_DEFERRED_ALL))
809 nflags = flags & ~TCP_DEFERRED_ALL;
810 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
812 if (flags & (1UL << TCP_TSQ_DEFERRED))
815 /* Here begins the tricky part :
816 * We are called from release_sock() with :
818 * 2) sk_lock.slock spinlock held
819 * 3) socket owned by us (sk->sk_lock.owned == 1)
821 * But following code is meant to be called from BH handlers,
822 * so we should keep BH disabled, but early release socket ownership
824 sock_release_ownership(sk);
826 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
827 tcp_write_timer_handler(sk);
830 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
831 tcp_delack_timer_handler(sk);
834 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
835 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
839 EXPORT_SYMBOL(tcp_release_cb);
841 void __init tcp_tasklet_init(void)
845 for_each_possible_cpu(i) {
846 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
848 INIT_LIST_HEAD(&tsq->head);
849 tasklet_init(&tsq->tasklet,
856 * Write buffer destructor automatically called from kfree_skb.
857 * We can't xmit new skbs from this context, as we might already
860 void tcp_wfree(struct sk_buff *skb)
862 struct sock *sk = skb->sk;
863 struct tcp_sock *tp = tcp_sk(sk);
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 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
882 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
884 struct tsq_tasklet *tsq;
886 /* queue this socket to tasklet queue */
887 local_irq_save(flags);
888 tsq = this_cpu_ptr(&tsq_tasklet);
889 list_add(&tp->tsq_node, &tsq->head);
890 tasklet_schedule(&tsq->tasklet);
891 local_irq_restore(flags);
898 /* This routine actually transmits TCP packets queued in by
899 * tcp_do_sendmsg(). This is used by both the initial
900 * transmission and possible later retransmissions.
901 * All SKB's seen here are completely headerless. It is our
902 * job to build the TCP header, and pass the packet down to
903 * IP so it can do the same plus pass the packet off to the
906 * We are working here with either a clone of the original
907 * SKB, or a fresh unique copy made by the retransmit engine.
909 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
912 const struct inet_connection_sock *icsk = inet_csk(sk);
913 struct inet_sock *inet;
915 struct tcp_skb_cb *tcb;
916 struct tcp_out_options opts;
917 unsigned int tcp_options_size, tcp_header_size;
918 struct tcp_md5sig_key *md5;
922 BUG_ON(!skb || !tcp_skb_pcount(skb));
925 skb_mstamp_get(&skb->skb_mstamp);
927 if (unlikely(skb_cloned(skb)))
928 skb = pskb_copy(skb, gfp_mask);
930 skb = skb_clone(skb, gfp_mask);
937 tcb = TCP_SKB_CB(skb);
938 memset(&opts, 0, sizeof(opts));
940 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
941 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
943 tcp_options_size = tcp_established_options(sk, skb, &opts,
945 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
947 if (tcp_packets_in_flight(tp) == 0)
948 tcp_ca_event(sk, CA_EVENT_TX_START);
950 /* if no packet is in qdisc/device queue, then allow XPS to select
951 * another queue. We can be called from tcp_tsq_handler()
952 * which holds one reference to sk_wmem_alloc.
954 * TODO: Ideally, in-flight pure ACK packets should not matter here.
955 * One way to get this would be to set skb->truesize = 2 on them.
957 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
959 skb_push(skb, tcp_header_size);
960 skb_reset_transport_header(skb);
964 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
965 skb_set_hash_from_sk(skb, sk);
966 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
968 /* Build TCP header and checksum it. */
970 th->source = inet->inet_sport;
971 th->dest = inet->inet_dport;
972 th->seq = htonl(tcb->seq);
973 th->ack_seq = htonl(tp->rcv_nxt);
974 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
977 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
978 /* RFC1323: The window in SYN & SYN/ACK segments
981 th->window = htons(min(tp->rcv_wnd, 65535U));
983 th->window = htons(tcp_select_window(sk));
988 /* The urg_mode check is necessary during a below snd_una win probe */
989 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
990 if (before(tp->snd_up, tcb->seq + 0x10000)) {
991 th->urg_ptr = htons(tp->snd_up - tcb->seq);
993 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
994 th->urg_ptr = htons(0xFFFF);
999 tcp_options_write((__be32 *)(th + 1), tp, &opts);
1000 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1001 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
1002 tcp_ecn_send(sk, skb, tcp_header_size);
1004 #ifdef CONFIG_TCP_MD5SIG
1005 /* Calculate the MD5 hash, as we have all we need now */
1007 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1008 tp->af_specific->calc_md5_hash(opts.hash_location,
1013 icsk->icsk_af_ops->send_check(sk, skb);
1015 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1016 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1018 if (skb->len != tcp_header_size)
1019 tcp_event_data_sent(tp, sk);
1021 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1022 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1023 tcp_skb_pcount(skb));
1025 tp->segs_out += tcp_skb_pcount(skb);
1026 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1027 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1028 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1030 /* Our usage of tstamp should remain private */
1031 skb->tstamp.tv64 = 0;
1033 /* Cleanup our debris for IP stacks */
1034 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1035 sizeof(struct inet6_skb_parm)));
1037 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1039 if (likely(err <= 0))
1044 return net_xmit_eval(err);
1047 /* This routine just queues the buffer for sending.
1049 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1050 * otherwise socket can stall.
1052 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1054 struct tcp_sock *tp = tcp_sk(sk);
1056 /* Advance write_seq and place onto the write_queue. */
1057 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1058 __skb_header_release(skb);
1059 tcp_add_write_queue_tail(sk, skb);
1060 sk->sk_wmem_queued += skb->truesize;
1061 sk_mem_charge(sk, skb->truesize);
1064 /* Initialize TSO segments for a packet. */
1065 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1067 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1068 /* Avoid the costly divide in the normal
1071 tcp_skb_pcount_set(skb, 1);
1072 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1074 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1075 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1079 /* When a modification to fackets out becomes necessary, we need to check
1080 * skb is counted to fackets_out or not.
1082 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1085 struct tcp_sock *tp = tcp_sk(sk);
1087 if (!tp->sacked_out || tcp_is_reno(tp))
1090 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1091 tp->fackets_out -= decr;
1094 /* Pcount in the middle of the write queue got changed, we need to do various
1095 * tweaks to fix counters
1097 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1099 struct tcp_sock *tp = tcp_sk(sk);
1101 tp->packets_out -= decr;
1103 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1104 tp->sacked_out -= decr;
1105 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1106 tp->retrans_out -= decr;
1107 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1108 tp->lost_out -= decr;
1110 /* Reno case is special. Sigh... */
1111 if (tcp_is_reno(tp) && decr > 0)
1112 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1114 tcp_adjust_fackets_out(sk, skb, decr);
1116 if (tp->lost_skb_hint &&
1117 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1118 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1119 tp->lost_cnt_hint -= decr;
1121 tcp_verify_left_out(tp);
1124 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1126 struct skb_shared_info *shinfo = skb_shinfo(skb);
1128 if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
1129 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1130 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1131 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1133 shinfo->tx_flags &= ~tsflags;
1134 shinfo2->tx_flags |= tsflags;
1135 swap(shinfo->tskey, shinfo2->tskey);
1139 /* Function to create two new TCP segments. Shrinks the given segment
1140 * to the specified size and appends a new segment with the rest of the
1141 * packet to the list. This won't be called frequently, I hope.
1142 * Remember, these are still headerless SKBs at this point.
1144 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1145 unsigned int mss_now, gfp_t gfp)
1147 struct tcp_sock *tp = tcp_sk(sk);
1148 struct sk_buff *buff;
1149 int nsize, old_factor;
1153 if (WARN_ON(len > skb->len))
1156 nsize = skb_headlen(skb) - len;
1160 if (skb_unclone(skb, gfp))
1163 /* Get a new skb... force flag on. */
1164 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1166 return -ENOMEM; /* We'll just try again later. */
1168 sk->sk_wmem_queued += buff->truesize;
1169 sk_mem_charge(sk, buff->truesize);
1170 nlen = skb->len - len - nsize;
1171 buff->truesize += nlen;
1172 skb->truesize -= nlen;
1174 /* Correct the sequence numbers. */
1175 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1176 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1177 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1179 /* PSH and FIN should only be set in the second packet. */
1180 flags = TCP_SKB_CB(skb)->tcp_flags;
1181 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1182 TCP_SKB_CB(buff)->tcp_flags = flags;
1183 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1185 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1186 /* Copy and checksum data tail into the new buffer. */
1187 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1188 skb_put(buff, nsize),
1193 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1195 skb->ip_summed = CHECKSUM_PARTIAL;
1196 skb_split(skb, buff, len);
1199 buff->ip_summed = skb->ip_summed;
1201 buff->tstamp = skb->tstamp;
1202 tcp_fragment_tstamp(skb, buff);
1204 old_factor = tcp_skb_pcount(skb);
1206 /* Fix up tso_factor for both original and new SKB. */
1207 tcp_set_skb_tso_segs(skb, mss_now);
1208 tcp_set_skb_tso_segs(buff, mss_now);
1210 /* If this packet has been sent out already, we must
1211 * adjust the various packet counters.
1213 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1214 int diff = old_factor - tcp_skb_pcount(skb) -
1215 tcp_skb_pcount(buff);
1218 tcp_adjust_pcount(sk, skb, diff);
1221 /* Link BUFF into the send queue. */
1222 __skb_header_release(buff);
1223 tcp_insert_write_queue_after(skb, buff, sk);
1228 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1229 * eventually). The difference is that pulled data not copied, but
1230 * immediately discarded.
1232 static void __pskb_trim_head(struct sk_buff *skb, int len)
1234 struct skb_shared_info *shinfo;
1237 eat = min_t(int, len, skb_headlen(skb));
1239 __skb_pull(skb, eat);
1246 shinfo = skb_shinfo(skb);
1247 for (i = 0; i < shinfo->nr_frags; i++) {
1248 int size = skb_frag_size(&shinfo->frags[i]);
1251 skb_frag_unref(skb, i);
1254 shinfo->frags[k] = shinfo->frags[i];
1256 shinfo->frags[k].page_offset += eat;
1257 skb_frag_size_sub(&shinfo->frags[k], eat);
1263 shinfo->nr_frags = k;
1265 skb_reset_tail_pointer(skb);
1266 skb->data_len -= len;
1267 skb->len = skb->data_len;
1270 /* Remove acked data from a packet in the transmit queue. */
1271 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1273 if (skb_unclone(skb, GFP_ATOMIC))
1276 __pskb_trim_head(skb, len);
1278 TCP_SKB_CB(skb)->seq += len;
1279 skb->ip_summed = CHECKSUM_PARTIAL;
1281 skb->truesize -= len;
1282 sk->sk_wmem_queued -= len;
1283 sk_mem_uncharge(sk, len);
1284 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1286 /* Any change of skb->len requires recalculation of tso factor. */
1287 if (tcp_skb_pcount(skb) > 1)
1288 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1293 /* Calculate MSS not accounting any TCP options. */
1294 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1296 const struct tcp_sock *tp = tcp_sk(sk);
1297 const struct inet_connection_sock *icsk = inet_csk(sk);
1300 /* Calculate base mss without TCP options:
1301 It is MMS_S - sizeof(tcphdr) of rfc1122
1303 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1305 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1306 if (icsk->icsk_af_ops->net_frag_header_len) {
1307 const struct dst_entry *dst = __sk_dst_get(sk);
1309 if (dst && dst_allfrag(dst))
1310 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1313 /* Clamp it (mss_clamp does not include tcp options) */
1314 if (mss_now > tp->rx_opt.mss_clamp)
1315 mss_now = tp->rx_opt.mss_clamp;
1317 /* Now subtract optional transport overhead */
1318 mss_now -= icsk->icsk_ext_hdr_len;
1320 /* Then reserve room for full set of TCP options and 8 bytes of data */
1326 /* Calculate MSS. Not accounting for SACKs here. */
1327 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1329 /* Subtract TCP options size, not including SACKs */
1330 return __tcp_mtu_to_mss(sk, pmtu) -
1331 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1334 /* Inverse of above */
1335 int tcp_mss_to_mtu(struct sock *sk, int mss)
1337 const struct tcp_sock *tp = tcp_sk(sk);
1338 const struct inet_connection_sock *icsk = inet_csk(sk);
1342 tp->tcp_header_len +
1343 icsk->icsk_ext_hdr_len +
1344 icsk->icsk_af_ops->net_header_len;
1346 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1347 if (icsk->icsk_af_ops->net_frag_header_len) {
1348 const struct dst_entry *dst = __sk_dst_get(sk);
1350 if (dst && dst_allfrag(dst))
1351 mtu += icsk->icsk_af_ops->net_frag_header_len;
1356 /* MTU probing init per socket */
1357 void tcp_mtup_init(struct sock *sk)
1359 struct tcp_sock *tp = tcp_sk(sk);
1360 struct inet_connection_sock *icsk = inet_csk(sk);
1361 struct net *net = sock_net(sk);
1363 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1364 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1365 icsk->icsk_af_ops->net_header_len;
1366 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1367 icsk->icsk_mtup.probe_size = 0;
1368 if (icsk->icsk_mtup.enabled)
1369 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1371 EXPORT_SYMBOL(tcp_mtup_init);
1373 /* This function synchronize snd mss to current pmtu/exthdr set.
1375 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1376 for TCP options, but includes only bare TCP header.
1378 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1379 It is minimum of user_mss and mss received with SYN.
1380 It also does not include TCP options.
1382 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1384 tp->mss_cache is current effective sending mss, including
1385 all tcp options except for SACKs. It is evaluated,
1386 taking into account current pmtu, but never exceeds
1387 tp->rx_opt.mss_clamp.
1389 NOTE1. rfc1122 clearly states that advertised MSS
1390 DOES NOT include either tcp or ip options.
1392 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1393 are READ ONLY outside this function. --ANK (980731)
1395 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1397 struct tcp_sock *tp = tcp_sk(sk);
1398 struct inet_connection_sock *icsk = inet_csk(sk);
1401 if (icsk->icsk_mtup.search_high > pmtu)
1402 icsk->icsk_mtup.search_high = pmtu;
1404 mss_now = tcp_mtu_to_mss(sk, pmtu);
1405 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1407 /* And store cached results */
1408 icsk->icsk_pmtu_cookie = pmtu;
1409 if (icsk->icsk_mtup.enabled)
1410 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1411 tp->mss_cache = mss_now;
1415 EXPORT_SYMBOL(tcp_sync_mss);
1417 /* Compute the current effective MSS, taking SACKs and IP options,
1418 * and even PMTU discovery events into account.
1420 unsigned int tcp_current_mss(struct sock *sk)
1422 const struct tcp_sock *tp = tcp_sk(sk);
1423 const struct dst_entry *dst = __sk_dst_get(sk);
1425 unsigned int header_len;
1426 struct tcp_out_options opts;
1427 struct tcp_md5sig_key *md5;
1429 mss_now = tp->mss_cache;
1432 u32 mtu = dst_mtu(dst);
1433 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1434 mss_now = tcp_sync_mss(sk, mtu);
1437 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1438 sizeof(struct tcphdr);
1439 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1440 * some common options. If this is an odd packet (because we have SACK
1441 * blocks etc) then our calculated header_len will be different, and
1442 * we have to adjust mss_now correspondingly */
1443 if (header_len != tp->tcp_header_len) {
1444 int delta = (int) header_len - tp->tcp_header_len;
1451 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1452 * As additional protections, we do not touch cwnd in retransmission phases,
1453 * and if application hit its sndbuf limit recently.
1455 static void tcp_cwnd_application_limited(struct sock *sk)
1457 struct tcp_sock *tp = tcp_sk(sk);
1459 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1460 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1461 /* Limited by application or receiver window. */
1462 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1463 u32 win_used = max(tp->snd_cwnd_used, init_win);
1464 if (win_used < tp->snd_cwnd) {
1465 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1466 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1468 tp->snd_cwnd_used = 0;
1470 tp->snd_cwnd_stamp = tcp_time_stamp;
1473 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1475 struct tcp_sock *tp = tcp_sk(sk);
1477 /* Track the maximum number of outstanding packets in each
1478 * window, and remember whether we were cwnd-limited then.
1480 if (!before(tp->snd_una, tp->max_packets_seq) ||
1481 tp->packets_out > tp->max_packets_out) {
1482 tp->max_packets_out = tp->packets_out;
1483 tp->max_packets_seq = tp->snd_nxt;
1484 tp->is_cwnd_limited = is_cwnd_limited;
1487 if (tcp_is_cwnd_limited(sk)) {
1488 /* Network is feed fully. */
1489 tp->snd_cwnd_used = 0;
1490 tp->snd_cwnd_stamp = tcp_time_stamp;
1492 /* Network starves. */
1493 if (tp->packets_out > tp->snd_cwnd_used)
1494 tp->snd_cwnd_used = tp->packets_out;
1496 if (sysctl_tcp_slow_start_after_idle &&
1497 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1498 tcp_cwnd_application_limited(sk);
1502 /* Minshall's variant of the Nagle send check. */
1503 static bool tcp_minshall_check(const struct tcp_sock *tp)
1505 return after(tp->snd_sml, tp->snd_una) &&
1506 !after(tp->snd_sml, tp->snd_nxt);
1509 /* Update snd_sml if this skb is under mss
1510 * Note that a TSO packet might end with a sub-mss segment
1511 * The test is really :
1512 * if ((skb->len % mss) != 0)
1513 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1514 * But we can avoid doing the divide again given we already have
1515 * skb_pcount = skb->len / mss_now
1517 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1518 const struct sk_buff *skb)
1520 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1521 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1524 /* Return false, if packet can be sent now without violation Nagle's rules:
1525 * 1. It is full sized. (provided by caller in %partial bool)
1526 * 2. Or it contains FIN. (already checked by caller)
1527 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1528 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1529 * With Minshall's modification: all sent small packets are ACKed.
1531 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1535 ((nonagle & TCP_NAGLE_CORK) ||
1536 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1539 /* Return how many segs we'd like on a TSO packet,
1540 * to send one TSO packet per ms
1542 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1546 bytes = min(sk->sk_pacing_rate >> 10,
1547 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1549 /* Goal is to send at least one packet per ms,
1550 * not one big TSO packet every 100 ms.
1551 * This preserves ACK clocking and is consistent
1552 * with tcp_tso_should_defer() heuristic.
1554 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1556 return min_t(u32, segs, sk->sk_gso_max_segs);
1559 /* Returns the portion of skb which can be sent right away */
1560 static unsigned int tcp_mss_split_point(const struct sock *sk,
1561 const struct sk_buff *skb,
1562 unsigned int mss_now,
1563 unsigned int max_segs,
1566 const struct tcp_sock *tp = tcp_sk(sk);
1567 u32 partial, needed, window, max_len;
1569 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1570 max_len = mss_now * max_segs;
1572 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1575 needed = min(skb->len, window);
1577 if (max_len <= needed)
1580 partial = needed % mss_now;
1581 /* If last segment is not a full MSS, check if Nagle rules allow us
1582 * to include this last segment in this skb.
1583 * Otherwise, we'll split the skb at last MSS boundary
1585 if (tcp_nagle_check(partial != 0, tp, nonagle))
1586 return needed - partial;
1591 /* Can at least one segment of SKB be sent right now, according to the
1592 * congestion window rules? If so, return how many segments are allowed.
1594 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1595 const struct sk_buff *skb)
1597 u32 in_flight, cwnd, halfcwnd;
1599 /* Don't be strict about the congestion window for the final FIN. */
1600 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1601 tcp_skb_pcount(skb) == 1)
1604 in_flight = tcp_packets_in_flight(tp);
1605 cwnd = tp->snd_cwnd;
1606 if (in_flight >= cwnd)
1609 /* For better scheduling, ensure we have at least
1610 * 2 GSO packets in flight.
1612 halfcwnd = max(cwnd >> 1, 1U);
1613 return min(halfcwnd, cwnd - in_flight);
1616 /* Initialize TSO state of a skb.
1617 * This must be invoked the first time we consider transmitting
1618 * SKB onto the wire.
1620 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1622 int tso_segs = tcp_skb_pcount(skb);
1624 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1625 tcp_set_skb_tso_segs(skb, mss_now);
1626 tso_segs = tcp_skb_pcount(skb);
1632 /* Return true if the Nagle test allows this packet to be
1635 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1636 unsigned int cur_mss, int nonagle)
1638 /* Nagle rule does not apply to frames, which sit in the middle of the
1639 * write_queue (they have no chances to get new data).
1641 * This is implemented in the callers, where they modify the 'nonagle'
1642 * argument based upon the location of SKB in the send queue.
1644 if (nonagle & TCP_NAGLE_PUSH)
1647 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1648 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1651 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1657 /* Does at least the first segment of SKB fit into the send window? */
1658 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1659 const struct sk_buff *skb,
1660 unsigned int cur_mss)
1662 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1664 if (skb->len > cur_mss)
1665 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1667 return !after(end_seq, tcp_wnd_end(tp));
1670 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1671 * should be put on the wire right now. If so, it returns the number of
1672 * packets allowed by the congestion window.
1674 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1675 unsigned int cur_mss, int nonagle)
1677 const struct tcp_sock *tp = tcp_sk(sk);
1678 unsigned int cwnd_quota;
1680 tcp_init_tso_segs(skb, cur_mss);
1682 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1685 cwnd_quota = tcp_cwnd_test(tp, skb);
1686 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1692 /* Test if sending is allowed right now. */
1693 bool tcp_may_send_now(struct sock *sk)
1695 const struct tcp_sock *tp = tcp_sk(sk);
1696 struct sk_buff *skb = tcp_send_head(sk);
1699 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1700 (tcp_skb_is_last(sk, skb) ?
1701 tp->nonagle : TCP_NAGLE_PUSH));
1704 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1705 * which is put after SKB on the list. It is very much like
1706 * tcp_fragment() except that it may make several kinds of assumptions
1707 * in order to speed up the splitting operation. In particular, we
1708 * know that all the data is in scatter-gather pages, and that the
1709 * packet has never been sent out before (and thus is not cloned).
1711 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1712 unsigned int mss_now, gfp_t gfp)
1714 struct sk_buff *buff;
1715 int nlen = skb->len - len;
1718 /* All of a TSO frame must be composed of paged data. */
1719 if (skb->len != skb->data_len)
1720 return tcp_fragment(sk, skb, len, mss_now, gfp);
1722 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1723 if (unlikely(!buff))
1726 sk->sk_wmem_queued += buff->truesize;
1727 sk_mem_charge(sk, buff->truesize);
1728 buff->truesize += nlen;
1729 skb->truesize -= nlen;
1731 /* Correct the sequence numbers. */
1732 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1733 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1734 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1736 /* PSH and FIN should only be set in the second packet. */
1737 flags = TCP_SKB_CB(skb)->tcp_flags;
1738 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1739 TCP_SKB_CB(buff)->tcp_flags = flags;
1741 /* This packet was never sent out yet, so no SACK bits. */
1742 TCP_SKB_CB(buff)->sacked = 0;
1744 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1745 skb_split(skb, buff, len);
1746 tcp_fragment_tstamp(skb, buff);
1748 /* Fix up tso_factor for both original and new SKB. */
1749 tcp_set_skb_tso_segs(skb, mss_now);
1750 tcp_set_skb_tso_segs(buff, mss_now);
1752 /* Link BUFF into the send queue. */
1753 __skb_header_release(buff);
1754 tcp_insert_write_queue_after(skb, buff, sk);
1759 /* Try to defer sending, if possible, in order to minimize the amount
1760 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1762 * This algorithm is from John Heffner.
1764 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1765 bool *is_cwnd_limited, u32 max_segs)
1767 const struct inet_connection_sock *icsk = inet_csk(sk);
1768 u32 age, send_win, cong_win, limit, in_flight;
1769 struct tcp_sock *tp = tcp_sk(sk);
1770 struct skb_mstamp now;
1771 struct sk_buff *head;
1774 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1777 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1780 /* Avoid bursty behavior by allowing defer
1781 * only if the last write was recent.
1783 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1786 in_flight = tcp_packets_in_flight(tp);
1788 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1790 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1792 /* From in_flight test above, we know that cwnd > in_flight. */
1793 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1795 limit = min(send_win, cong_win);
1797 /* If a full-sized TSO skb can be sent, do it. */
1798 if (limit >= max_segs * tp->mss_cache)
1801 /* Middle in queue won't get any more data, full sendable already? */
1802 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1805 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1807 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1809 /* If at least some fraction of a window is available,
1812 chunk /= win_divisor;
1816 /* Different approach, try not to defer past a single
1817 * ACK. Receiver should ACK every other full sized
1818 * frame, so if we have space for more than 3 frames
1821 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1825 head = tcp_write_queue_head(sk);
1826 skb_mstamp_get(&now);
1827 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1828 /* If next ACK is likely to come too late (half srtt), do not defer */
1829 if (age < (tp->srtt_us >> 4))
1832 /* Ok, it looks like it is advisable to defer. */
1834 if (cong_win < send_win && cong_win < skb->len)
1835 *is_cwnd_limited = true;
1843 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1845 struct inet_connection_sock *icsk = inet_csk(sk);
1846 struct tcp_sock *tp = tcp_sk(sk);
1847 struct net *net = sock_net(sk);
1851 interval = net->ipv4.sysctl_tcp_probe_interval;
1852 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1853 if (unlikely(delta >= interval * HZ)) {
1854 int mss = tcp_current_mss(sk);
1856 /* Update current search range */
1857 icsk->icsk_mtup.probe_size = 0;
1858 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1859 sizeof(struct tcphdr) +
1860 icsk->icsk_af_ops->net_header_len;
1861 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1863 /* Update probe time stamp */
1864 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1868 /* Create a new MTU probe if we are ready.
1869 * MTU probe is regularly attempting to increase the path MTU by
1870 * deliberately sending larger packets. This discovers routing
1871 * changes resulting in larger path MTUs.
1873 * Returns 0 if we should wait to probe (no cwnd available),
1874 * 1 if a probe was sent,
1877 static int tcp_mtu_probe(struct sock *sk)
1879 struct tcp_sock *tp = tcp_sk(sk);
1880 struct inet_connection_sock *icsk = inet_csk(sk);
1881 struct sk_buff *skb, *nskb, *next;
1882 struct net *net = sock_net(sk);
1890 /* Not currently probing/verifying,
1892 * have enough cwnd, and
1893 * not SACKing (the variable headers throw things off) */
1894 if (!icsk->icsk_mtup.enabled ||
1895 icsk->icsk_mtup.probe_size ||
1896 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1897 tp->snd_cwnd < 11 ||
1898 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1901 /* Use binary search for probe_size between tcp_mss_base,
1902 * and current mss_clamp. if (search_high - search_low)
1903 * smaller than a threshold, backoff from probing.
1905 mss_now = tcp_current_mss(sk);
1906 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1907 icsk->icsk_mtup.search_low) >> 1);
1908 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1909 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1910 /* When misfortune happens, we are reprobing actively,
1911 * and then reprobe timer has expired. We stick with current
1912 * probing process by not resetting search range to its orignal.
1914 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1915 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1916 /* Check whether enough time has elaplased for
1917 * another round of probing.
1919 tcp_mtu_check_reprobe(sk);
1923 /* Have enough data in the send queue to probe? */
1924 if (tp->write_seq - tp->snd_nxt < size_needed)
1927 if (tp->snd_wnd < size_needed)
1929 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1932 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1933 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1934 if (!tcp_packets_in_flight(tp))
1940 /* We're allowed to probe. Build it now. */
1941 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1944 sk->sk_wmem_queued += nskb->truesize;
1945 sk_mem_charge(sk, nskb->truesize);
1947 skb = tcp_send_head(sk);
1949 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1950 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1951 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1952 TCP_SKB_CB(nskb)->sacked = 0;
1954 nskb->ip_summed = skb->ip_summed;
1956 tcp_insert_write_queue_before(nskb, skb, sk);
1959 tcp_for_write_queue_from_safe(skb, next, sk) {
1960 copy = min_t(int, skb->len, probe_size - len);
1961 if (nskb->ip_summed)
1962 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1964 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1965 skb_put(nskb, copy),
1968 if (skb->len <= copy) {
1969 /* We've eaten all the data from this skb.
1971 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1972 tcp_unlink_write_queue(skb, sk);
1973 sk_wmem_free_skb(sk, skb);
1975 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1976 ~(TCPHDR_FIN|TCPHDR_PSH);
1977 if (!skb_shinfo(skb)->nr_frags) {
1978 skb_pull(skb, copy);
1979 if (skb->ip_summed != CHECKSUM_PARTIAL)
1980 skb->csum = csum_partial(skb->data,
1983 __pskb_trim_head(skb, copy);
1984 tcp_set_skb_tso_segs(skb, mss_now);
1986 TCP_SKB_CB(skb)->seq += copy;
1991 if (len >= probe_size)
1994 tcp_init_tso_segs(nskb, nskb->len);
1996 /* We're ready to send. If this fails, the probe will
1997 * be resegmented into mss-sized pieces by tcp_write_xmit().
1999 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2000 /* Decrement cwnd here because we are sending
2001 * effectively two packets. */
2003 tcp_event_new_data_sent(sk, nskb);
2005 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2006 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2007 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2015 /* This routine writes packets to the network. It advances the
2016 * send_head. This happens as incoming acks open up the remote
2019 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2020 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2021 * account rare use of URG, this is not a big flaw.
2023 * Send at most one packet when push_one > 0. Temporarily ignore
2024 * cwnd limit to force at most one packet out when push_one == 2.
2026 * Returns true, if no segments are in flight and we have queued segments,
2027 * but cannot send anything now because of SWS or another problem.
2029 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2030 int push_one, gfp_t gfp)
2032 struct tcp_sock *tp = tcp_sk(sk);
2033 struct sk_buff *skb;
2034 unsigned int tso_segs, sent_pkts;
2037 bool is_cwnd_limited = false;
2043 /* Do MTU probing. */
2044 result = tcp_mtu_probe(sk);
2047 } else if (result > 0) {
2052 max_segs = tcp_tso_autosize(sk, mss_now);
2053 while ((skb = tcp_send_head(sk))) {
2056 tso_segs = tcp_init_tso_segs(skb, mss_now);
2059 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2060 /* "skb_mstamp" is used as a start point for the retransmit timer */
2061 skb_mstamp_get(&skb->skb_mstamp);
2062 goto repair; /* Skip network transmission */
2065 cwnd_quota = tcp_cwnd_test(tp, skb);
2067 is_cwnd_limited = true;
2069 /* Force out a loss probe pkt. */
2075 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2078 if (tso_segs == 1) {
2079 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2080 (tcp_skb_is_last(sk, skb) ?
2081 nonagle : TCP_NAGLE_PUSH))))
2085 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2091 if (tso_segs > 1 && !tcp_urg_mode(tp))
2092 limit = tcp_mss_split_point(sk, skb, mss_now,
2098 if (skb->len > limit &&
2099 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2102 /* TCP Small Queues :
2103 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2105 * - better RTT estimation and ACK scheduling
2108 * Alas, some drivers / subsystems require a fair amount
2109 * of queued bytes to ensure line rate.
2110 * One example is wifi aggregation (802.11 AMPDU)
2112 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2113 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2115 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2116 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2117 /* It is possible TX completion already happened
2118 * before we set TSQ_THROTTLED, so we must
2119 * test again the condition.
2121 smp_mb__after_atomic();
2122 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2126 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2130 /* Advance the send_head. This one is sent out.
2131 * This call will increment packets_out.
2133 tcp_event_new_data_sent(sk, skb);
2135 tcp_minshall_update(tp, mss_now, skb);
2136 sent_pkts += tcp_skb_pcount(skb);
2142 if (likely(sent_pkts)) {
2143 if (tcp_in_cwnd_reduction(sk))
2144 tp->prr_out += sent_pkts;
2146 /* Send one loss probe per tail loss episode. */
2148 tcp_schedule_loss_probe(sk);
2149 tcp_cwnd_validate(sk, is_cwnd_limited);
2152 return !tp->packets_out && tcp_send_head(sk);
2155 bool tcp_schedule_loss_probe(struct sock *sk)
2157 struct inet_connection_sock *icsk = inet_csk(sk);
2158 struct tcp_sock *tp = tcp_sk(sk);
2159 u32 timeout, tlp_time_stamp, rto_time_stamp;
2160 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2162 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2164 /* No consecutive loss probes. */
2165 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2169 /* Don't do any loss probe on a Fast Open connection before 3WHS
2172 if (sk->sk_state == TCP_SYN_RECV)
2175 /* TLP is only scheduled when next timer event is RTO. */
2176 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2179 /* Schedule a loss probe in 2*RTT for SACK capable connections
2180 * in Open state, that are either limited by cwnd or application.
2182 if (sysctl_tcp_early_retrans < 3 || !tp->srtt_us || !tp->packets_out ||
2183 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2186 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2190 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2191 * for delayed ack when there's one outstanding packet.
2194 if (tp->packets_out == 1)
2195 timeout = max_t(u32, timeout,
2196 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2197 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2199 /* If RTO is shorter, just schedule TLP in its place. */
2200 tlp_time_stamp = tcp_time_stamp + timeout;
2201 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2202 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2203 s32 delta = rto_time_stamp - tcp_time_stamp;
2208 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2213 /* Thanks to skb fast clones, we can detect if a prior transmit of
2214 * a packet is still in a qdisc or driver queue.
2215 * In this case, there is very little point doing a retransmit !
2216 * Note: This is called from BH context only.
2218 static bool skb_still_in_host_queue(const struct sock *sk,
2219 const struct sk_buff *skb)
2221 if (unlikely(skb_fclone_busy(sk, skb))) {
2222 NET_INC_STATS_BH(sock_net(sk),
2223 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2229 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2230 * retransmit the last segment.
2232 void tcp_send_loss_probe(struct sock *sk)
2234 struct tcp_sock *tp = tcp_sk(sk);
2235 struct sk_buff *skb;
2237 int mss = tcp_current_mss(sk);
2239 skb = tcp_send_head(sk);
2241 if (tcp_snd_wnd_test(tp, skb, mss)) {
2242 pcount = tp->packets_out;
2243 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2244 if (tp->packets_out > pcount)
2248 skb = tcp_write_queue_prev(sk, skb);
2250 skb = tcp_write_queue_tail(sk);
2253 /* At most one outstanding TLP retransmission. */
2254 if (tp->tlp_high_seq)
2257 /* Retransmit last segment. */
2261 if (skb_still_in_host_queue(sk, skb))
2264 pcount = tcp_skb_pcount(skb);
2265 if (WARN_ON(!pcount))
2268 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2269 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2272 skb = tcp_write_queue_next(sk, skb);
2275 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2278 if (__tcp_retransmit_skb(sk, skb))
2281 /* Record snd_nxt for loss detection. */
2282 tp->tlp_high_seq = tp->snd_nxt;
2285 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2286 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2287 inet_csk(sk)->icsk_pending = 0;
2292 /* Push out any pending frames which were held back due to
2293 * TCP_CORK or attempt at coalescing tiny packets.
2294 * The socket must be locked by the caller.
2296 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2299 /* If we are closed, the bytes will have to remain here.
2300 * In time closedown will finish, we empty the write queue and
2301 * all will be happy.
2303 if (unlikely(sk->sk_state == TCP_CLOSE))
2306 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2307 sk_gfp_atomic(sk, GFP_ATOMIC)))
2308 tcp_check_probe_timer(sk);
2311 /* Send _single_ skb sitting at the send head. This function requires
2312 * true push pending frames to setup probe timer etc.
2314 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2316 struct sk_buff *skb = tcp_send_head(sk);
2318 BUG_ON(!skb || skb->len < mss_now);
2320 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2323 /* This function returns the amount that we can raise the
2324 * usable window based on the following constraints
2326 * 1. The window can never be shrunk once it is offered (RFC 793)
2327 * 2. We limit memory per socket
2330 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2331 * RECV.NEXT + RCV.WIN fixed until:
2332 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2334 * i.e. don't raise the right edge of the window until you can raise
2335 * it at least MSS bytes.
2337 * Unfortunately, the recommended algorithm breaks header prediction,
2338 * since header prediction assumes th->window stays fixed.
2340 * Strictly speaking, keeping th->window fixed violates the receiver
2341 * side SWS prevention criteria. The problem is that under this rule
2342 * a stream of single byte packets will cause the right side of the
2343 * window to always advance by a single byte.
2345 * Of course, if the sender implements sender side SWS prevention
2346 * then this will not be a problem.
2348 * BSD seems to make the following compromise:
2350 * If the free space is less than the 1/4 of the maximum
2351 * space available and the free space is less than 1/2 mss,
2352 * then set the window to 0.
2353 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2354 * Otherwise, just prevent the window from shrinking
2355 * and from being larger than the largest representable value.
2357 * This prevents incremental opening of the window in the regime
2358 * where TCP is limited by the speed of the reader side taking
2359 * data out of the TCP receive queue. It does nothing about
2360 * those cases where the window is constrained on the sender side
2361 * because the pipeline is full.
2363 * BSD also seems to "accidentally" limit itself to windows that are a
2364 * multiple of MSS, at least until the free space gets quite small.
2365 * This would appear to be a side effect of the mbuf implementation.
2366 * Combining these two algorithms results in the observed behavior
2367 * of having a fixed window size at almost all times.
2369 * Below we obtain similar behavior by forcing the offered window to
2370 * a multiple of the mss when it is feasible to do so.
2372 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2373 * Regular options like TIMESTAMP are taken into account.
2375 u32 __tcp_select_window(struct sock *sk)
2377 struct inet_connection_sock *icsk = inet_csk(sk);
2378 struct tcp_sock *tp = tcp_sk(sk);
2379 /* MSS for the peer's data. Previous versions used mss_clamp
2380 * here. I don't know if the value based on our guesses
2381 * of peer's MSS is better for the performance. It's more correct
2382 * but may be worse for the performance because of rcv_mss
2383 * fluctuations. --SAW 1998/11/1
2385 int mss = icsk->icsk_ack.rcv_mss;
2386 int free_space = tcp_space(sk);
2387 int allowed_space = tcp_full_space(sk);
2388 int full_space = min_t(int, tp->window_clamp, allowed_space);
2391 if (mss > full_space)
2394 if (free_space < (full_space >> 1)) {
2395 icsk->icsk_ack.quick = 0;
2397 if (tcp_under_memory_pressure(sk))
2398 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2401 /* free_space might become our new window, make sure we don't
2402 * increase it due to wscale.
2404 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2406 /* if free space is less than mss estimate, or is below 1/16th
2407 * of the maximum allowed, try to move to zero-window, else
2408 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2409 * new incoming data is dropped due to memory limits.
2410 * With large window, mss test triggers way too late in order
2411 * to announce zero window in time before rmem limit kicks in.
2413 if (free_space < (allowed_space >> 4) || free_space < mss)
2417 if (free_space > tp->rcv_ssthresh)
2418 free_space = tp->rcv_ssthresh;
2420 /* Don't do rounding if we are using window scaling, since the
2421 * scaled window will not line up with the MSS boundary anyway.
2423 window = tp->rcv_wnd;
2424 if (tp->rx_opt.rcv_wscale) {
2425 window = free_space;
2427 /* Advertise enough space so that it won't get scaled away.
2428 * Import case: prevent zero window announcement if
2429 * 1<<rcv_wscale > mss.
2431 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2432 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2433 << tp->rx_opt.rcv_wscale);
2435 /* Get the largest window that is a nice multiple of mss.
2436 * Window clamp already applied above.
2437 * If our current window offering is within 1 mss of the
2438 * free space we just keep it. This prevents the divide
2439 * and multiply from happening most of the time.
2440 * We also don't do any window rounding when the free space
2443 if (window <= free_space - mss || window > free_space)
2444 window = (free_space / mss) * mss;
2445 else if (mss == full_space &&
2446 free_space > window + (full_space >> 1))
2447 window = free_space;
2453 /* Collapses two adjacent SKB's during retransmission. */
2454 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2456 struct tcp_sock *tp = tcp_sk(sk);
2457 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2458 int skb_size, next_skb_size;
2460 skb_size = skb->len;
2461 next_skb_size = next_skb->len;
2463 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2465 tcp_highest_sack_combine(sk, next_skb, skb);
2467 tcp_unlink_write_queue(next_skb, sk);
2469 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2472 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2473 skb->ip_summed = CHECKSUM_PARTIAL;
2475 if (skb->ip_summed != CHECKSUM_PARTIAL)
2476 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2478 /* Update sequence range on original skb. */
2479 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2481 /* Merge over control information. This moves PSH/FIN etc. over */
2482 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2484 /* All done, get rid of second SKB and account for it so
2485 * packet counting does not break.
2487 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2489 /* changed transmit queue under us so clear hints */
2490 tcp_clear_retrans_hints_partial(tp);
2491 if (next_skb == tp->retransmit_skb_hint)
2492 tp->retransmit_skb_hint = skb;
2494 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2496 sk_wmem_free_skb(sk, next_skb);
2499 /* Check if coalescing SKBs is legal. */
2500 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2502 if (tcp_skb_pcount(skb) > 1)
2504 /* TODO: SACK collapsing could be used to remove this condition */
2505 if (skb_shinfo(skb)->nr_frags != 0)
2507 if (skb_cloned(skb))
2509 if (skb == tcp_send_head(sk))
2511 /* Some heurestics for collapsing over SACK'd could be invented */
2512 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2518 /* Collapse packets in the retransmit queue to make to create
2519 * less packets on the wire. This is only done on retransmission.
2521 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2524 struct tcp_sock *tp = tcp_sk(sk);
2525 struct sk_buff *skb = to, *tmp;
2528 if (!sysctl_tcp_retrans_collapse)
2530 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2533 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2534 if (!tcp_can_collapse(sk, skb))
2546 /* Punt if not enough space exists in the first SKB for
2547 * the data in the second
2549 if (skb->len > skb_availroom(to))
2552 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2555 tcp_collapse_retrans(sk, to);
2559 /* This retransmits one SKB. Policy decisions and retransmit queue
2560 * state updates are done by the caller. Returns non-zero if an
2561 * error occurred which prevented the send.
2563 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2565 struct tcp_sock *tp = tcp_sk(sk);
2566 struct inet_connection_sock *icsk = inet_csk(sk);
2567 unsigned int cur_mss;
2570 /* Inconslusive MTU probe */
2571 if (icsk->icsk_mtup.probe_size) {
2572 icsk->icsk_mtup.probe_size = 0;
2575 /* Do not sent more than we queued. 1/4 is reserved for possible
2576 * copying overhead: fragmentation, tunneling, mangling etc.
2578 if (atomic_read(&sk->sk_wmem_alloc) >
2579 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2582 if (skb_still_in_host_queue(sk, skb))
2585 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2586 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2588 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2592 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2593 return -EHOSTUNREACH; /* Routing failure or similar. */
2595 cur_mss = tcp_current_mss(sk);
2597 /* If receiver has shrunk his window, and skb is out of
2598 * new window, do not retransmit it. The exception is the
2599 * case, when window is shrunk to zero. In this case
2600 * our retransmit serves as a zero window probe.
2602 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2603 TCP_SKB_CB(skb)->seq != tp->snd_una)
2606 if (skb->len > cur_mss) {
2607 if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
2608 return -ENOMEM; /* We'll try again later. */
2610 int oldpcount = tcp_skb_pcount(skb);
2612 if (unlikely(oldpcount > 1)) {
2613 if (skb_unclone(skb, GFP_ATOMIC))
2615 tcp_init_tso_segs(skb, cur_mss);
2616 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2620 /* RFC3168, section 6.1.1.1. ECN fallback */
2621 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2622 tcp_ecn_clear_syn(sk, skb);
2624 tcp_retrans_try_collapse(sk, skb, cur_mss);
2626 /* Make a copy, if the first transmission SKB clone we made
2627 * is still in somebody's hands, else make a clone.
2630 /* make sure skb->data is aligned on arches that require it
2631 * and check if ack-trimming & collapsing extended the headroom
2632 * beyond what csum_start can cover.
2634 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2635 skb_headroom(skb) >= 0xFFFF)) {
2636 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2638 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2641 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2645 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2646 /* Update global TCP statistics. */
2647 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2648 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2649 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2650 tp->total_retrans++;
2655 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2657 struct tcp_sock *tp = tcp_sk(sk);
2658 int err = __tcp_retransmit_skb(sk, skb);
2661 #if FASTRETRANS_DEBUG > 0
2662 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2663 net_dbg_ratelimited("retrans_out leaked\n");
2666 if (!tp->retrans_out)
2667 tp->lost_retrans_low = tp->snd_nxt;
2668 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2669 tp->retrans_out += tcp_skb_pcount(skb);
2671 /* Save stamp of the first retransmit. */
2672 if (!tp->retrans_stamp)
2673 tp->retrans_stamp = tcp_skb_timestamp(skb);
2675 /* snd_nxt is stored to detect loss of retransmitted segment,
2676 * see tcp_input.c tcp_sacktag_write_queue().
2678 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2679 } else if (err != -EBUSY) {
2680 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2683 if (tp->undo_retrans < 0)
2684 tp->undo_retrans = 0;
2685 tp->undo_retrans += tcp_skb_pcount(skb);
2689 /* Check if we forward retransmits are possible in the current
2690 * window/congestion state.
2692 static bool tcp_can_forward_retransmit(struct sock *sk)
2694 const struct inet_connection_sock *icsk = inet_csk(sk);
2695 const struct tcp_sock *tp = tcp_sk(sk);
2697 /* Forward retransmissions are possible only during Recovery. */
2698 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2701 /* No forward retransmissions in Reno are possible. */
2702 if (tcp_is_reno(tp))
2705 /* Yeah, we have to make difficult choice between forward transmission
2706 * and retransmission... Both ways have their merits...
2708 * For now we do not retransmit anything, while we have some new
2709 * segments to send. In the other cases, follow rule 3 for
2710 * NextSeg() specified in RFC3517.
2713 if (tcp_may_send_now(sk))
2719 /* This gets called after a retransmit timeout, and the initially
2720 * retransmitted data is acknowledged. It tries to continue
2721 * resending the rest of the retransmit queue, until either
2722 * we've sent it all or the congestion window limit is reached.
2723 * If doing SACK, the first ACK which comes back for a timeout
2724 * based retransmit packet might feed us FACK information again.
2725 * If so, we use it to avoid unnecessarily retransmissions.
2727 void tcp_xmit_retransmit_queue(struct sock *sk)
2729 const struct inet_connection_sock *icsk = inet_csk(sk);
2730 struct tcp_sock *tp = tcp_sk(sk);
2731 struct sk_buff *skb;
2732 struct sk_buff *hole = NULL;
2735 int fwd_rexmitting = 0;
2737 if (!tp->packets_out)
2741 tp->retransmit_high = tp->snd_una;
2743 if (tp->retransmit_skb_hint) {
2744 skb = tp->retransmit_skb_hint;
2745 last_lost = TCP_SKB_CB(skb)->end_seq;
2746 if (after(last_lost, tp->retransmit_high))
2747 last_lost = tp->retransmit_high;
2749 skb = tcp_write_queue_head(sk);
2750 last_lost = tp->snd_una;
2753 tcp_for_write_queue_from(skb, sk) {
2754 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2756 if (skb == tcp_send_head(sk))
2758 /* we could do better than to assign each time */
2760 tp->retransmit_skb_hint = skb;
2762 /* Assume this retransmit will generate
2763 * only one packet for congestion window
2764 * calculation purposes. This works because
2765 * tcp_retransmit_skb() will chop up the
2766 * packet to be MSS sized and all the
2767 * packet counting works out.
2769 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2772 if (fwd_rexmitting) {
2774 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2776 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2778 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2779 tp->retransmit_high = last_lost;
2780 if (!tcp_can_forward_retransmit(sk))
2782 /* Backtrack if necessary to non-L'ed skb */
2790 } else if (!(sacked & TCPCB_LOST)) {
2791 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2796 last_lost = TCP_SKB_CB(skb)->end_seq;
2797 if (icsk->icsk_ca_state != TCP_CA_Loss)
2798 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2800 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2803 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2806 if (tcp_retransmit_skb(sk, skb))
2809 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2811 if (tcp_in_cwnd_reduction(sk))
2812 tp->prr_out += tcp_skb_pcount(skb);
2814 if (skb == tcp_write_queue_head(sk))
2815 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2816 inet_csk(sk)->icsk_rto,
2821 /* We allow to exceed memory limits for FIN packets to expedite
2822 * connection tear down and (memory) recovery.
2823 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2824 * or even be forced to close flow without any FIN.
2825 * In general, we want to allow one skb per socket to avoid hangs
2826 * with edge trigger epoll()
2828 void sk_forced_mem_schedule(struct sock *sk, int size)
2832 if (size <= sk->sk_forward_alloc)
2834 amt = sk_mem_pages(size);
2835 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2836 sk_memory_allocated_add(sk, amt, &status);
2839 /* Send a FIN. The caller locks the socket for us.
2840 * We should try to send a FIN packet really hard, but eventually give up.
2842 void tcp_send_fin(struct sock *sk)
2844 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2845 struct tcp_sock *tp = tcp_sk(sk);
2847 /* Optimization, tack on the FIN if we have one skb in write queue and
2848 * this skb was not yet sent, or we are under memory pressure.
2849 * Note: in the latter case, FIN packet will be sent after a timeout,
2850 * as TCP stack thinks it has already been transmitted.
2852 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2854 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
2855 TCP_SKB_CB(tskb)->end_seq++;
2857 if (!tcp_send_head(sk)) {
2858 /* This means tskb was already sent.
2859 * Pretend we included the FIN on previous transmit.
2860 * We need to set tp->snd_nxt to the value it would have
2861 * if FIN had been sent. This is because retransmit path
2862 * does not change tp->snd_nxt.
2868 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
2869 if (unlikely(!skb)) {
2874 skb_reserve(skb, MAX_TCP_HEADER);
2875 sk_forced_mem_schedule(sk, skb->truesize);
2876 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2877 tcp_init_nondata_skb(skb, tp->write_seq,
2878 TCPHDR_ACK | TCPHDR_FIN);
2879 tcp_queue_skb(sk, skb);
2881 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
2884 /* We get here when a process closes a file descriptor (either due to
2885 * an explicit close() or as a byproduct of exit()'ing) and there
2886 * was unread data in the receive queue. This behavior is recommended
2887 * by RFC 2525, section 2.17. -DaveM
2889 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2891 struct sk_buff *skb;
2893 /* NOTE: No TCP options attached and we never retransmit this. */
2894 skb = alloc_skb(MAX_TCP_HEADER, priority);
2896 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2900 /* Reserve space for headers and prepare control bits. */
2901 skb_reserve(skb, MAX_TCP_HEADER);
2902 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2903 TCPHDR_ACK | TCPHDR_RST);
2905 if (tcp_transmit_skb(sk, skb, 0, priority))
2906 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2908 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2911 /* Send a crossed SYN-ACK during socket establishment.
2912 * WARNING: This routine must only be called when we have already sent
2913 * a SYN packet that crossed the incoming SYN that caused this routine
2914 * to get called. If this assumption fails then the initial rcv_wnd
2915 * and rcv_wscale values will not be correct.
2917 int tcp_send_synack(struct sock *sk)
2919 struct sk_buff *skb;
2921 skb = tcp_write_queue_head(sk);
2922 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2923 pr_debug("%s: wrong queue state\n", __func__);
2926 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2927 if (skb_cloned(skb)) {
2928 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2931 tcp_unlink_write_queue(skb, sk);
2932 __skb_header_release(nskb);
2933 __tcp_add_write_queue_head(sk, nskb);
2934 sk_wmem_free_skb(sk, skb);
2935 sk->sk_wmem_queued += nskb->truesize;
2936 sk_mem_charge(sk, nskb->truesize);
2940 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2941 tcp_ecn_send_synack(sk, skb);
2943 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2947 * tcp_make_synack - Prepare a SYN-ACK.
2948 * sk: listener socket
2949 * dst: dst entry attached to the SYNACK
2950 * req: request_sock pointer
2952 * Allocate one skb and build a SYNACK packet.
2953 * @dst is consumed : Caller should not use it again.
2955 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2956 struct request_sock *req,
2957 struct tcp_fastopen_cookie *foc)
2959 struct tcp_out_options opts;
2960 struct inet_request_sock *ireq = inet_rsk(req);
2961 struct tcp_sock *tp = tcp_sk(sk);
2963 struct sk_buff *skb;
2964 struct tcp_md5sig_key *md5 = NULL;
2965 int tcp_header_size;
2968 skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
2969 if (unlikely(!skb)) {
2973 /* Reserve space for headers. */
2974 skb_reserve(skb, MAX_TCP_HEADER);
2976 skb_dst_set(skb, dst);
2978 mss = dst_metric_advmss(dst);
2979 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2980 mss = tp->rx_opt.user_mss;
2982 memset(&opts, 0, sizeof(opts));
2983 #ifdef CONFIG_SYN_COOKIES
2984 if (unlikely(req->cookie_ts))
2985 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
2988 skb_mstamp_get(&skb->skb_mstamp);
2990 #ifdef CONFIG_TCP_MD5SIG
2992 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
2994 tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5,
2997 skb_push(skb, tcp_header_size);
2998 skb_reset_transport_header(skb);
3001 memset(th, 0, sizeof(struct tcphdr));
3004 tcp_ecn_make_synack(req, th, sk);
3005 th->source = htons(ireq->ir_num);
3006 th->dest = ireq->ir_rmt_port;
3007 /* Setting of flags are superfluous here for callers (and ECE is
3008 * not even correctly set)
3010 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3011 TCPHDR_SYN | TCPHDR_ACK);
3013 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3014 /* XXX data is queued and acked as is. No buffer/window check */
3015 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3017 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3018 th->window = htons(min(req->rcv_wnd, 65535U));
3019 tcp_options_write((__be32 *)(th + 1), tp, &opts);
3020 th->doff = (tcp_header_size >> 2);
3021 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
3023 #ifdef CONFIG_TCP_MD5SIG
3024 /* Okay, we have all we need - do the md5 hash if needed */
3026 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3027 md5, req_to_sk(req), skb);
3031 /* Do not fool tcpdump (if any), clean our debris */
3032 skb->tstamp.tv64 = 0;
3035 EXPORT_SYMBOL(tcp_make_synack);
3037 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3039 struct inet_connection_sock *icsk = inet_csk(sk);
3040 const struct tcp_congestion_ops *ca;
3041 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3043 if (ca_key == TCP_CA_UNSPEC)
3047 ca = tcp_ca_find_key(ca_key);
3048 if (likely(ca && try_module_get(ca->owner))) {
3049 module_put(icsk->icsk_ca_ops->owner);
3050 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3051 icsk->icsk_ca_ops = ca;
3056 /* Do all connect socket setups that can be done AF independent. */
3057 static void tcp_connect_init(struct sock *sk)
3059 const struct dst_entry *dst = __sk_dst_get(sk);
3060 struct tcp_sock *tp = tcp_sk(sk);
3063 /* We'll fix this up when we get a response from the other end.
3064 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3066 tp->tcp_header_len = sizeof(struct tcphdr) +
3067 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3069 #ifdef CONFIG_TCP_MD5SIG
3070 if (tp->af_specific->md5_lookup(sk, sk))
3071 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3074 /* If user gave his TCP_MAXSEG, record it to clamp */
3075 if (tp->rx_opt.user_mss)
3076 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3079 tcp_sync_mss(sk, dst_mtu(dst));
3081 tcp_ca_dst_init(sk, dst);
3083 if (!tp->window_clamp)
3084 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3085 tp->advmss = dst_metric_advmss(dst);
3086 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3087 tp->advmss = tp->rx_opt.user_mss;
3089 tcp_initialize_rcv_mss(sk);
3091 /* limit the window selection if the user enforce a smaller rx buffer */
3092 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3093 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3094 tp->window_clamp = tcp_full_space(sk);
3096 tcp_select_initial_window(tcp_full_space(sk),
3097 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3100 sysctl_tcp_window_scaling,
3102 dst_metric(dst, RTAX_INITRWND));
3104 tp->rx_opt.rcv_wscale = rcv_wscale;
3105 tp->rcv_ssthresh = tp->rcv_wnd;
3108 sock_reset_flag(sk, SOCK_DONE);
3111 tp->snd_una = tp->write_seq;
3112 tp->snd_sml = tp->write_seq;
3113 tp->snd_up = tp->write_seq;
3114 tp->snd_nxt = tp->write_seq;
3116 if (likely(!tp->repair))
3119 tp->rcv_tstamp = tcp_time_stamp;
3120 tp->rcv_wup = tp->rcv_nxt;
3121 tp->copied_seq = tp->rcv_nxt;
3123 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3124 inet_csk(sk)->icsk_retransmits = 0;
3125 tcp_clear_retrans(tp);
3128 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3130 struct tcp_sock *tp = tcp_sk(sk);
3131 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3133 tcb->end_seq += skb->len;
3134 __skb_header_release(skb);
3135 __tcp_add_write_queue_tail(sk, skb);
3136 sk->sk_wmem_queued += skb->truesize;
3137 sk_mem_charge(sk, skb->truesize);
3138 tp->write_seq = tcb->end_seq;
3139 tp->packets_out += tcp_skb_pcount(skb);
3142 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3143 * queue a data-only packet after the regular SYN, such that regular SYNs
3144 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3145 * only the SYN sequence, the data are retransmitted in the first ACK.
3146 * If cookie is not cached or other error occurs, falls back to send a
3147 * regular SYN with Fast Open cookie request option.
3149 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3151 struct tcp_sock *tp = tcp_sk(sk);
3152 struct tcp_fastopen_request *fo = tp->fastopen_req;
3153 int syn_loss = 0, space, err = 0, copied;
3154 unsigned long last_syn_loss = 0;
3155 struct sk_buff *syn_data;
3157 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3158 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3159 &syn_loss, &last_syn_loss);
3160 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3162 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3163 fo->cookie.len = -1;
3167 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3168 fo->cookie.len = -1;
3169 else if (fo->cookie.len <= 0)
3172 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3173 * user-MSS. Reserve maximum option space for middleboxes that add
3174 * private TCP options. The cost is reduced data space in SYN :(
3176 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3177 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3178 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3179 MAX_TCP_OPTION_SPACE;
3181 space = min_t(size_t, space, fo->size);
3183 /* limit to order-0 allocations */
3184 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3186 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3189 syn_data->ip_summed = CHECKSUM_PARTIAL;
3190 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3191 copied = copy_from_iter(skb_put(syn_data, space), space,
3192 &fo->data->msg_iter);
3193 if (unlikely(!copied)) {
3194 kfree_skb(syn_data);
3197 if (copied != space) {
3198 skb_trim(syn_data, copied);
3202 /* No more data pending in inet_wait_for_connect() */
3203 if (space == fo->size)
3207 tcp_connect_queue_skb(sk, syn_data);
3209 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3211 syn->skb_mstamp = syn_data->skb_mstamp;
3213 /* Now full SYN+DATA was cloned and sent (or not),
3214 * remove the SYN from the original skb (syn_data)
3215 * we keep in write queue in case of a retransmit, as we
3216 * also have the SYN packet (with no data) in the same queue.
3218 TCP_SKB_CB(syn_data)->seq++;
3219 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3221 tp->syn_data = (fo->copied > 0);
3222 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3227 /* Send a regular SYN with Fast Open cookie request option */
3228 if (fo->cookie.len > 0)
3230 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3232 tp->syn_fastopen = 0;
3234 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3238 /* Build a SYN and send it off. */
3239 int tcp_connect(struct sock *sk)
3241 struct tcp_sock *tp = tcp_sk(sk);
3242 struct sk_buff *buff;
3245 tcp_connect_init(sk);
3247 if (unlikely(tp->repair)) {
3248 tcp_finish_connect(sk, NULL);
3252 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3253 if (unlikely(!buff))
3256 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3257 tp->retrans_stamp = tcp_time_stamp;
3258 tcp_connect_queue_skb(sk, buff);
3259 tcp_ecn_send_syn(sk, buff);
3261 /* Send off SYN; include data in Fast Open. */
3262 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3263 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3264 if (err == -ECONNREFUSED)
3267 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3268 * in order to make this packet get counted in tcpOutSegs.
3270 tp->snd_nxt = tp->write_seq;
3271 tp->pushed_seq = tp->write_seq;
3272 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3274 /* Timer for repeating the SYN until an answer. */
3275 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3276 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3279 EXPORT_SYMBOL(tcp_connect);
3281 /* Send out a delayed ack, the caller does the policy checking
3282 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3285 void tcp_send_delayed_ack(struct sock *sk)
3287 struct inet_connection_sock *icsk = inet_csk(sk);
3288 int ato = icsk->icsk_ack.ato;
3289 unsigned long timeout;
3291 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3293 if (ato > TCP_DELACK_MIN) {
3294 const struct tcp_sock *tp = tcp_sk(sk);
3295 int max_ato = HZ / 2;
3297 if (icsk->icsk_ack.pingpong ||
3298 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3299 max_ato = TCP_DELACK_MAX;
3301 /* Slow path, intersegment interval is "high". */
3303 /* If some rtt estimate is known, use it to bound delayed ack.
3304 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3308 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3315 ato = min(ato, max_ato);
3318 /* Stay within the limit we were given */
3319 timeout = jiffies + ato;
3321 /* Use new timeout only if there wasn't a older one earlier. */
3322 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3323 /* If delack timer was blocked or is about to expire,
3326 if (icsk->icsk_ack.blocked ||
3327 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3332 if (!time_before(timeout, icsk->icsk_ack.timeout))
3333 timeout = icsk->icsk_ack.timeout;
3335 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3336 icsk->icsk_ack.timeout = timeout;
3337 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3340 /* This routine sends an ack and also updates the window. */
3341 void tcp_send_ack(struct sock *sk)
3343 struct sk_buff *buff;
3345 /* If we have been reset, we may not send again. */
3346 if (sk->sk_state == TCP_CLOSE)
3349 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3351 /* We are not putting this on the write queue, so
3352 * tcp_transmit_skb() will set the ownership to this
3355 buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3357 inet_csk_schedule_ack(sk);
3358 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3359 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3360 TCP_DELACK_MAX, TCP_RTO_MAX);
3364 /* Reserve space for headers and prepare control bits. */
3365 skb_reserve(buff, MAX_TCP_HEADER);
3366 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3368 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3370 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3371 * We also avoid tcp_wfree() overhead (cache line miss accessing
3372 * tp->tsq_flags) by using regular sock_wfree()
3374 skb_set_tcp_pure_ack(buff);
3376 /* Send it off, this clears delayed acks for us. */
3377 skb_mstamp_get(&buff->skb_mstamp);
3378 tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
3380 EXPORT_SYMBOL_GPL(tcp_send_ack);
3382 /* This routine sends a packet with an out of date sequence
3383 * number. It assumes the other end will try to ack it.
3385 * Question: what should we make while urgent mode?
3386 * 4.4BSD forces sending single byte of data. We cannot send
3387 * out of window data, because we have SND.NXT==SND.MAX...
3389 * Current solution: to send TWO zero-length segments in urgent mode:
3390 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3391 * out-of-date with SND.UNA-1 to probe window.
3393 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3395 struct tcp_sock *tp = tcp_sk(sk);
3396 struct sk_buff *skb;
3398 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3399 skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3403 /* Reserve space for headers and set control bits. */
3404 skb_reserve(skb, MAX_TCP_HEADER);
3405 /* Use a previous sequence. This should cause the other
3406 * end to send an ack. Don't queue or clone SKB, just
3409 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3410 skb_mstamp_get(&skb->skb_mstamp);
3411 NET_INC_STATS_BH(sock_net(sk), mib);
3412 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3415 void tcp_send_window_probe(struct sock *sk)
3417 if (sk->sk_state == TCP_ESTABLISHED) {
3418 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3419 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3423 /* Initiate keepalive or window probe from timer. */
3424 int tcp_write_wakeup(struct sock *sk, int mib)
3426 struct tcp_sock *tp = tcp_sk(sk);
3427 struct sk_buff *skb;
3429 if (sk->sk_state == TCP_CLOSE)
3432 skb = tcp_send_head(sk);
3433 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3435 unsigned int mss = tcp_current_mss(sk);
3436 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3438 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3439 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3441 /* We are probing the opening of a window
3442 * but the window size is != 0
3443 * must have been a result SWS avoidance ( sender )
3445 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3447 seg_size = min(seg_size, mss);
3448 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3449 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3451 } else if (!tcp_skb_pcount(skb))
3452 tcp_set_skb_tso_segs(skb, mss);
3454 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3455 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3457 tcp_event_new_data_sent(sk, skb);
3460 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3461 tcp_xmit_probe_skb(sk, 1, mib);
3462 return tcp_xmit_probe_skb(sk, 0, mib);
3466 /* A window probe timeout has occurred. If window is not closed send
3467 * a partial packet else a zero probe.
3469 void tcp_send_probe0(struct sock *sk)
3471 struct inet_connection_sock *icsk = inet_csk(sk);
3472 struct tcp_sock *tp = tcp_sk(sk);
3473 unsigned long probe_max;
3476 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3478 if (tp->packets_out || !tcp_send_head(sk)) {
3479 /* Cancel probe timer, if it is not required. */
3480 icsk->icsk_probes_out = 0;
3481 icsk->icsk_backoff = 0;
3486 if (icsk->icsk_backoff < sysctl_tcp_retries2)
3487 icsk->icsk_backoff++;
3488 icsk->icsk_probes_out++;
3489 probe_max = TCP_RTO_MAX;
3491 /* If packet was not sent due to local congestion,
3492 * do not backoff and do not remember icsk_probes_out.
3493 * Let local senders to fight for local resources.
3495 * Use accumulated backoff yet.
3497 if (!icsk->icsk_probes_out)
3498 icsk->icsk_probes_out = 1;
3499 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3501 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3502 tcp_probe0_when(sk, probe_max),
3506 int tcp_rtx_synack(struct sock *sk, struct request_sock *req)
3508 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3512 res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL);
3514 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
3515 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3519 EXPORT_SYMBOL(tcp_rtx_synack);