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 /* This limits the percentage of the congestion window which we
54 * will allow a single TSO frame to consume. Building TSO frames
55 * which are too large can cause TCP streams to be bursty.
57 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
59 int sysctl_tcp_mtu_probing __read_mostly = 0;
60 int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;
62 /* By default, RFC2861 behavior. */
63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
65 int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
66 EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size);
69 /* Account for new data that has been sent to the network. */
70 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
72 struct tcp_sock *tp = tcp_sk(sk);
73 unsigned int prior_packets = tp->packets_out;
75 tcp_advance_send_head(sk, skb);
76 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
78 /* Don't override Nagle indefinitely with F-RTO */
79 if (tp->frto_counter == 2)
82 tp->packets_out += tcp_skb_pcount(skb);
83 if (!prior_packets || tp->early_retrans_delayed)
87 /* SND.NXT, if window was not shrunk.
88 * If window has been shrunk, what should we make? It is not clear at all.
89 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
90 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
91 * invalid. OK, let's make this for now:
93 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
95 const struct tcp_sock *tp = tcp_sk(sk);
97 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
100 return tcp_wnd_end(tp);
103 /* Calculate mss to advertise in SYN segment.
104 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
106 * 1. It is independent of path mtu.
107 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
108 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
109 * attached devices, because some buggy hosts are confused by
111 * 4. We do not make 3, we advertise MSS, calculated from first
112 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
113 * This may be overridden via information stored in routing table.
114 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
115 * probably even Jumbo".
117 static __u16 tcp_advertise_mss(struct sock *sk)
119 struct tcp_sock *tp = tcp_sk(sk);
120 const struct dst_entry *dst = __sk_dst_get(sk);
121 int mss = tp->advmss;
124 unsigned int metric = dst_metric_advmss(dst);
135 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
136 * This is the first part of cwnd validation mechanism. */
137 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
139 struct tcp_sock *tp = tcp_sk(sk);
140 s32 delta = tcp_time_stamp - tp->lsndtime;
141 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
142 u32 cwnd = tp->snd_cwnd;
144 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
146 tp->snd_ssthresh = tcp_current_ssthresh(sk);
147 restart_cwnd = min(restart_cwnd, cwnd);
149 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
151 tp->snd_cwnd = max(cwnd, restart_cwnd);
152 tp->snd_cwnd_stamp = tcp_time_stamp;
153 tp->snd_cwnd_used = 0;
156 /* Congestion state accounting after a packet has been sent. */
157 static void tcp_event_data_sent(struct tcp_sock *tp,
160 struct inet_connection_sock *icsk = inet_csk(sk);
161 const u32 now = tcp_time_stamp;
163 if (sysctl_tcp_slow_start_after_idle &&
164 (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
165 tcp_cwnd_restart(sk, __sk_dst_get(sk));
169 /* If it is a reply for ato after last received
170 * packet, enter pingpong mode.
172 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
173 icsk->icsk_ack.pingpong = 1;
176 /* Account for an ACK we sent. */
177 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
179 tcp_dec_quickack_mode(sk, pkts);
180 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
183 /* Determine a window scaling and initial window to offer.
184 * Based on the assumption that the given amount of space
185 * will be offered. Store the results in the tp structure.
186 * NOTE: for smooth operation initial space offering should
187 * be a multiple of mss if possible. We assume here that mss >= 1.
188 * This MUST be enforced by all callers.
190 void tcp_select_initial_window(int __space, __u32 mss,
191 __u32 *rcv_wnd, __u32 *window_clamp,
192 int wscale_ok, __u8 *rcv_wscale,
195 unsigned int space = (__space < 0 ? 0 : __space);
197 /* If no clamp set the clamp to the max possible scaled window */
198 if (*window_clamp == 0)
199 (*window_clamp) = (65535 << 14);
200 space = min(*window_clamp, space);
202 /* Quantize space offering to a multiple of mss if possible. */
204 space = (space / mss) * mss;
206 /* NOTE: offering an initial window larger than 32767
207 * will break some buggy TCP stacks. If the admin tells us
208 * it is likely we could be speaking with such a buggy stack
209 * we will truncate our initial window offering to 32K-1
210 * unless the remote has sent us a window scaling option,
211 * which we interpret as a sign the remote TCP is not
212 * misinterpreting the window field as a signed quantity.
214 if (sysctl_tcp_workaround_signed_windows)
215 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
221 /* Set window scaling on max possible window
222 * See RFC1323 for an explanation of the limit to 14
224 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
225 space = min_t(u32, space, *window_clamp);
226 while (space > 65535 && (*rcv_wscale) < 14) {
232 /* Set initial window to a value enough for senders starting with
233 * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
234 * a limit on the initial window when mss is larger than 1460.
236 if (mss > (1 << *rcv_wscale)) {
237 int init_cwnd = TCP_DEFAULT_INIT_RCVWND;
240 max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
241 /* when initializing use the value from init_rcv_wnd
242 * rather than the default from above
245 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
247 *rcv_wnd = min(*rcv_wnd, init_cwnd * mss);
250 /* Set the clamp no higher than max representable value */
251 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
253 EXPORT_SYMBOL(tcp_select_initial_window);
255 /* Chose a new window to advertise, update state in tcp_sock for the
256 * socket, and return result with RFC1323 scaling applied. The return
257 * value can be stuffed directly into th->window for an outgoing
260 static u16 tcp_select_window(struct sock *sk)
262 struct tcp_sock *tp = tcp_sk(sk);
263 u32 cur_win = tcp_receive_window(tp);
264 u32 new_win = __tcp_select_window(sk);
266 /* Never shrink the offered window */
267 if (new_win < cur_win) {
268 /* Danger Will Robinson!
269 * Don't update rcv_wup/rcv_wnd here or else
270 * we will not be able to advertise a zero
271 * window in time. --DaveM
273 * Relax Will Robinson.
275 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
277 tp->rcv_wnd = new_win;
278 tp->rcv_wup = tp->rcv_nxt;
280 /* Make sure we do not exceed the maximum possible
283 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
284 new_win = min(new_win, MAX_TCP_WINDOW);
286 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
288 /* RFC1323 scaling applied */
289 new_win >>= tp->rx_opt.rcv_wscale;
291 /* If we advertise zero window, disable fast path. */
298 /* Packet ECN state for a SYN-ACK */
299 static inline void TCP_ECN_send_synack(const struct tcp_sock *tp, struct sk_buff *skb)
301 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
302 if (!(tp->ecn_flags & TCP_ECN_OK))
303 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
306 /* Packet ECN state for a SYN. */
307 static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
309 struct tcp_sock *tp = tcp_sk(sk);
312 if (sysctl_tcp_ecn == 1) {
313 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
314 tp->ecn_flags = TCP_ECN_OK;
318 static __inline__ void
319 TCP_ECN_make_synack(const struct request_sock *req, struct tcphdr *th)
321 if (inet_rsk(req)->ecn_ok)
325 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
328 static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
331 struct tcp_sock *tp = tcp_sk(sk);
333 if (tp->ecn_flags & TCP_ECN_OK) {
334 /* Not-retransmitted data segment: set ECT and inject CWR. */
335 if (skb->len != tcp_header_len &&
336 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
338 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
339 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
340 tcp_hdr(skb)->cwr = 1;
341 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
344 /* ACK or retransmitted segment: clear ECT|CE */
345 INET_ECN_dontxmit(sk);
347 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
348 tcp_hdr(skb)->ece = 1;
352 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
353 * auto increment end seqno.
355 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
357 skb->ip_summed = CHECKSUM_PARTIAL;
360 TCP_SKB_CB(skb)->tcp_flags = flags;
361 TCP_SKB_CB(skb)->sacked = 0;
363 skb_shinfo(skb)->gso_segs = 1;
364 skb_shinfo(skb)->gso_size = 0;
365 skb_shinfo(skb)->gso_type = 0;
367 TCP_SKB_CB(skb)->seq = seq;
368 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
370 TCP_SKB_CB(skb)->end_seq = seq;
373 static inline int tcp_urg_mode(const struct tcp_sock *tp)
375 return tp->snd_una != tp->snd_up;
378 #define OPTION_SACK_ADVERTISE (1 << 0)
379 #define OPTION_TS (1 << 1)
380 #define OPTION_MD5 (1 << 2)
381 #define OPTION_WSCALE (1 << 3)
382 #define OPTION_COOKIE_EXTENSION (1 << 4)
384 struct tcp_out_options {
385 u8 options; /* bit field of OPTION_* */
386 u8 ws; /* window scale, 0 to disable */
387 u8 num_sack_blocks; /* number of SACK blocks to include */
388 u8 hash_size; /* bytes in hash_location */
389 u16 mss; /* 0 to disable */
390 __u32 tsval, tsecr; /* need to include OPTION_TS */
391 __u8 *hash_location; /* temporary pointer, overloaded */
394 /* The sysctl int routines are generic, so check consistency here.
396 static u8 tcp_cookie_size_check(u8 desired)
401 /* previously specified */
404 cookie_size = ACCESS_ONCE(sysctl_tcp_cookie_size);
405 if (cookie_size <= 0)
406 /* no default specified */
409 if (cookie_size <= TCP_COOKIE_MIN)
410 /* value too small, specify minimum */
411 return TCP_COOKIE_MIN;
413 if (cookie_size >= TCP_COOKIE_MAX)
414 /* value too large, specify maximum */
415 return TCP_COOKIE_MAX;
418 /* 8-bit multiple, illegal, fix it */
421 return (u8)cookie_size;
424 /* Write previously computed TCP options to the packet.
426 * Beware: Something in the Internet is very sensitive to the ordering of
427 * TCP options, we learned this through the hard way, so be careful here.
428 * Luckily we can at least blame others for their non-compliance but from
429 * inter-operatibility perspective it seems that we're somewhat stuck with
430 * the ordering which we have been using if we want to keep working with
431 * those broken things (not that it currently hurts anybody as there isn't
432 * particular reason why the ordering would need to be changed).
434 * At least SACK_PERM as the first option is known to lead to a disaster
435 * (but it may well be that other scenarios fail similarly).
437 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
438 struct tcp_out_options *opts)
440 u8 options = opts->options; /* mungable copy */
442 /* Having both authentication and cookies for security is redundant,
443 * and there's certainly not enough room. Instead, the cookie-less
444 * extension variant is proposed.
446 * Consider the pessimal case with authentication. The options
448 * COOKIE|MD5(20) + MSS(4) + SACK|TS(12) + WSCALE(4) == 40
450 if (unlikely(OPTION_MD5 & options)) {
451 if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
452 *ptr++ = htonl((TCPOPT_COOKIE << 24) |
453 (TCPOLEN_COOKIE_BASE << 16) |
454 (TCPOPT_MD5SIG << 8) |
457 *ptr++ = htonl((TCPOPT_NOP << 24) |
459 (TCPOPT_MD5SIG << 8) |
462 options &= ~OPTION_COOKIE_EXTENSION;
463 /* overload cookie hash location */
464 opts->hash_location = (__u8 *)ptr;
468 if (unlikely(opts->mss)) {
469 *ptr++ = htonl((TCPOPT_MSS << 24) |
470 (TCPOLEN_MSS << 16) |
474 if (likely(OPTION_TS & options)) {
475 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
476 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
477 (TCPOLEN_SACK_PERM << 16) |
478 (TCPOPT_TIMESTAMP << 8) |
480 options &= ~OPTION_SACK_ADVERTISE;
482 *ptr++ = htonl((TCPOPT_NOP << 24) |
484 (TCPOPT_TIMESTAMP << 8) |
487 *ptr++ = htonl(opts->tsval);
488 *ptr++ = htonl(opts->tsecr);
491 /* Specification requires after timestamp, so do it now.
493 * Consider the pessimal case without authentication. The options
495 * MSS(4) + SACK|TS(12) + COOKIE(20) + WSCALE(4) == 40
497 if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
498 __u8 *cookie_copy = opts->hash_location;
499 u8 cookie_size = opts->hash_size;
501 /* 8-bit multiple handled in tcp_cookie_size_check() above,
504 if (0x2 & cookie_size) {
505 __u8 *p = (__u8 *)ptr;
507 /* 16-bit multiple */
508 *p++ = TCPOPT_COOKIE;
509 *p++ = TCPOLEN_COOKIE_BASE + cookie_size;
510 *p++ = *cookie_copy++;
511 *p++ = *cookie_copy++;
515 /* 32-bit multiple */
516 *ptr++ = htonl(((TCPOPT_NOP << 24) |
518 (TCPOPT_COOKIE << 8) |
519 TCPOLEN_COOKIE_BASE) +
523 if (cookie_size > 0) {
524 memcpy(ptr, cookie_copy, cookie_size);
525 ptr += (cookie_size / 4);
529 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
530 *ptr++ = htonl((TCPOPT_NOP << 24) |
532 (TCPOPT_SACK_PERM << 8) |
536 if (unlikely(OPTION_WSCALE & options)) {
537 *ptr++ = htonl((TCPOPT_NOP << 24) |
538 (TCPOPT_WINDOW << 16) |
539 (TCPOLEN_WINDOW << 8) |
543 if (unlikely(opts->num_sack_blocks)) {
544 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
545 tp->duplicate_sack : tp->selective_acks;
548 *ptr++ = htonl((TCPOPT_NOP << 24) |
551 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
552 TCPOLEN_SACK_PERBLOCK)));
554 for (this_sack = 0; this_sack < opts->num_sack_blocks;
556 *ptr++ = htonl(sp[this_sack].start_seq);
557 *ptr++ = htonl(sp[this_sack].end_seq);
560 tp->rx_opt.dsack = 0;
564 /* Compute TCP options for SYN packets. This is not the final
565 * network wire format yet.
567 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
568 struct tcp_out_options *opts,
569 struct tcp_md5sig_key **md5)
571 struct tcp_sock *tp = tcp_sk(sk);
572 struct tcp_cookie_values *cvp = tp->cookie_values;
573 unsigned int remaining = MAX_TCP_OPTION_SPACE;
574 u8 cookie_size = (!tp->rx_opt.cookie_out_never && cvp != NULL) ?
575 tcp_cookie_size_check(cvp->cookie_desired) :
578 #ifdef CONFIG_TCP_MD5SIG
579 *md5 = tp->af_specific->md5_lookup(sk, sk);
581 opts->options |= OPTION_MD5;
582 remaining -= TCPOLEN_MD5SIG_ALIGNED;
588 /* We always get an MSS option. The option bytes which will be seen in
589 * normal data packets should timestamps be used, must be in the MSS
590 * advertised. But we subtract them from tp->mss_cache so that
591 * calculations in tcp_sendmsg are simpler etc. So account for this
592 * fact here if necessary. If we don't do this correctly, as a
593 * receiver we won't recognize data packets as being full sized when we
594 * should, and thus we won't abide by the delayed ACK rules correctly.
595 * SACKs don't matter, we never delay an ACK when we have any of those
597 opts->mss = tcp_advertise_mss(sk);
598 remaining -= TCPOLEN_MSS_ALIGNED;
600 if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
601 opts->options |= OPTION_TS;
602 opts->tsval = TCP_SKB_CB(skb)->when;
603 opts->tsecr = tp->rx_opt.ts_recent;
604 remaining -= TCPOLEN_TSTAMP_ALIGNED;
606 if (likely(sysctl_tcp_window_scaling)) {
607 opts->ws = tp->rx_opt.rcv_wscale;
608 opts->options |= OPTION_WSCALE;
609 remaining -= TCPOLEN_WSCALE_ALIGNED;
611 if (likely(sysctl_tcp_sack)) {
612 opts->options |= OPTION_SACK_ADVERTISE;
613 if (unlikely(!(OPTION_TS & opts->options)))
614 remaining -= TCPOLEN_SACKPERM_ALIGNED;
617 /* Note that timestamps are required by the specification.
619 * Odd numbers of bytes are prohibited by the specification, ensuring
620 * that the cookie is 16-bit aligned, and the resulting cookie pair is
624 (OPTION_TS & opts->options) &&
626 int need = TCPOLEN_COOKIE_BASE + cookie_size;
629 /* 32-bit multiple */
630 need += 2; /* NOPs */
632 if (need > remaining) {
633 /* try shrinking cookie to fit */
638 while (need > remaining && TCP_COOKIE_MIN <= cookie_size) {
642 if (TCP_COOKIE_MIN <= cookie_size) {
643 opts->options |= OPTION_COOKIE_EXTENSION;
644 opts->hash_location = (__u8 *)&cvp->cookie_pair[0];
645 opts->hash_size = cookie_size;
647 /* Remember for future incarnations. */
648 cvp->cookie_desired = cookie_size;
650 if (cvp->cookie_desired != cvp->cookie_pair_size) {
651 /* Currently use random bytes as a nonce,
652 * assuming these are completely unpredictable
653 * by hostile users of the same system.
655 get_random_bytes(&cvp->cookie_pair[0],
657 cvp->cookie_pair_size = cookie_size;
663 return MAX_TCP_OPTION_SPACE - remaining;
666 /* Set up TCP options for SYN-ACKs. */
667 static unsigned int tcp_synack_options(struct sock *sk,
668 struct request_sock *req,
669 unsigned int mss, struct sk_buff *skb,
670 struct tcp_out_options *opts,
671 struct tcp_md5sig_key **md5,
672 struct tcp_extend_values *xvp)
674 struct inet_request_sock *ireq = inet_rsk(req);
675 unsigned int remaining = MAX_TCP_OPTION_SPACE;
676 u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
680 #ifdef CONFIG_TCP_MD5SIG
681 *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
683 opts->options |= OPTION_MD5;
684 remaining -= TCPOLEN_MD5SIG_ALIGNED;
686 /* We can't fit any SACK blocks in a packet with MD5 + TS
687 * options. There was discussion about disabling SACK
688 * rather than TS in order to fit in better with old,
689 * buggy kernels, but that was deemed to be unnecessary.
691 ireq->tstamp_ok &= !ireq->sack_ok;
697 /* We always send an MSS option. */
699 remaining -= TCPOLEN_MSS_ALIGNED;
701 if (likely(ireq->wscale_ok)) {
702 opts->ws = ireq->rcv_wscale;
703 opts->options |= OPTION_WSCALE;
704 remaining -= TCPOLEN_WSCALE_ALIGNED;
706 if (likely(ireq->tstamp_ok)) {
707 opts->options |= OPTION_TS;
708 opts->tsval = TCP_SKB_CB(skb)->when;
709 opts->tsecr = req->ts_recent;
710 remaining -= TCPOLEN_TSTAMP_ALIGNED;
712 if (likely(ireq->sack_ok)) {
713 opts->options |= OPTION_SACK_ADVERTISE;
714 if (unlikely(!ireq->tstamp_ok))
715 remaining -= TCPOLEN_SACKPERM_ALIGNED;
718 /* Similar rationale to tcp_syn_options() applies here, too.
719 * If the <SYN> options fit, the same options should fit now!
723 cookie_plus > TCPOLEN_COOKIE_BASE) {
724 int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */
727 /* 32-bit multiple */
728 need += 2; /* NOPs */
730 if (need <= remaining) {
731 opts->options |= OPTION_COOKIE_EXTENSION;
732 opts->hash_size = cookie_plus - TCPOLEN_COOKIE_BASE;
735 /* There's no error return, so flag it. */
736 xvp->cookie_out_never = 1; /* true */
740 return MAX_TCP_OPTION_SPACE - remaining;
743 /* Compute TCP options for ESTABLISHED sockets. This is not the
744 * final wire format yet.
746 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
747 struct tcp_out_options *opts,
748 struct tcp_md5sig_key **md5)
750 struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
751 struct tcp_sock *tp = tcp_sk(sk);
752 unsigned int size = 0;
753 unsigned int eff_sacks;
755 #ifdef CONFIG_TCP_MD5SIG
756 *md5 = tp->af_specific->md5_lookup(sk, sk);
757 if (unlikely(*md5)) {
758 opts->options |= OPTION_MD5;
759 size += TCPOLEN_MD5SIG_ALIGNED;
765 if (likely(tp->rx_opt.tstamp_ok)) {
766 opts->options |= OPTION_TS;
767 opts->tsval = tcb ? tcb->when : 0;
768 opts->tsecr = tp->rx_opt.ts_recent;
769 size += TCPOLEN_TSTAMP_ALIGNED;
772 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
773 if (unlikely(eff_sacks)) {
774 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
775 opts->num_sack_blocks =
776 min_t(unsigned int, eff_sacks,
777 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
778 TCPOLEN_SACK_PERBLOCK);
779 size += TCPOLEN_SACK_BASE_ALIGNED +
780 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
786 /* This routine actually transmits TCP packets queued in by
787 * tcp_do_sendmsg(). This is used by both the initial
788 * transmission and possible later retransmissions.
789 * All SKB's seen here are completely headerless. It is our
790 * job to build the TCP header, and pass the packet down to
791 * IP so it can do the same plus pass the packet off to the
794 * We are working here with either a clone of the original
795 * SKB, or a fresh unique copy made by the retransmit engine.
797 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
800 const struct inet_connection_sock *icsk = inet_csk(sk);
801 struct inet_sock *inet;
803 struct tcp_skb_cb *tcb;
804 struct tcp_out_options opts;
805 unsigned int tcp_options_size, tcp_header_size;
806 struct tcp_md5sig_key *md5;
810 BUG_ON(!skb || !tcp_skb_pcount(skb));
812 /* If congestion control is doing timestamping, we must
813 * take such a timestamp before we potentially clone/copy.
815 if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
816 __net_timestamp(skb);
818 if (likely(clone_it)) {
819 if (unlikely(skb_cloned(skb)))
820 skb = pskb_copy(skb, gfp_mask);
822 skb = skb_clone(skb, gfp_mask);
829 tcb = TCP_SKB_CB(skb);
830 memset(&opts, 0, sizeof(opts));
832 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
833 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
835 tcp_options_size = tcp_established_options(sk, skb, &opts,
837 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
839 if (tcp_packets_in_flight(tp) == 0) {
840 tcp_ca_event(sk, CA_EVENT_TX_START);
845 skb_push(skb, tcp_header_size);
846 skb_reset_transport_header(skb);
847 skb_set_owner_w(skb, sk);
849 /* Build TCP header and checksum it. */
851 th->source = inet->inet_sport;
852 th->dest = inet->inet_dport;
853 th->seq = htonl(tcb->seq);
854 th->ack_seq = htonl(tp->rcv_nxt);
855 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
858 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
859 /* RFC1323: The window in SYN & SYN/ACK segments
862 th->window = htons(min(tp->rcv_wnd, 65535U));
864 th->window = htons(tcp_select_window(sk));
869 /* The urg_mode check is necessary during a below snd_una win probe */
870 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
871 if (before(tp->snd_up, tcb->seq + 0x10000)) {
872 th->urg_ptr = htons(tp->snd_up - tcb->seq);
874 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
875 th->urg_ptr = htons(0xFFFF);
880 tcp_options_write((__be32 *)(th + 1), tp, &opts);
881 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
882 TCP_ECN_send(sk, skb, tcp_header_size);
884 #ifdef CONFIG_TCP_MD5SIG
885 /* Calculate the MD5 hash, as we have all we need now */
887 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
888 tp->af_specific->calc_md5_hash(opts.hash_location,
893 icsk->icsk_af_ops->send_check(sk, skb);
895 if (likely(tcb->tcp_flags & TCPHDR_ACK))
896 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
898 if (skb->len != tcp_header_size)
899 tcp_event_data_sent(tp, sk);
901 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
902 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
903 tcp_skb_pcount(skb));
905 err = icsk->icsk_af_ops->queue_xmit(skb, &inet->cork.fl);
906 if (likely(err <= 0))
909 tcp_enter_cwr(sk, 1);
911 return net_xmit_eval(err);
914 /* This routine just queues the buffer for sending.
916 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
917 * otherwise socket can stall.
919 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
921 struct tcp_sock *tp = tcp_sk(sk);
923 /* Advance write_seq and place onto the write_queue. */
924 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
925 skb_header_release(skb);
926 tcp_add_write_queue_tail(sk, skb);
927 sk->sk_wmem_queued += skb->truesize;
928 sk_mem_charge(sk, skb->truesize);
931 /* Initialize TSO segments for a packet. */
932 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
933 unsigned int mss_now)
935 if (skb->len <= mss_now || !sk_can_gso(sk) ||
936 skb->ip_summed == CHECKSUM_NONE) {
937 /* Avoid the costly divide in the normal
940 skb_shinfo(skb)->gso_segs = 1;
941 skb_shinfo(skb)->gso_size = 0;
942 skb_shinfo(skb)->gso_type = 0;
944 skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
945 skb_shinfo(skb)->gso_size = mss_now;
946 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
950 /* When a modification to fackets out becomes necessary, we need to check
951 * skb is counted to fackets_out or not.
953 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
956 struct tcp_sock *tp = tcp_sk(sk);
958 if (!tp->sacked_out || tcp_is_reno(tp))
961 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
962 tp->fackets_out -= decr;
965 /* Pcount in the middle of the write queue got changed, we need to do various
966 * tweaks to fix counters
968 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
970 struct tcp_sock *tp = tcp_sk(sk);
972 tp->packets_out -= decr;
974 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
975 tp->sacked_out -= decr;
976 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
977 tp->retrans_out -= decr;
978 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
979 tp->lost_out -= decr;
981 /* Reno case is special. Sigh... */
982 if (tcp_is_reno(tp) && decr > 0)
983 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
985 tcp_adjust_fackets_out(sk, skb, decr);
987 if (tp->lost_skb_hint &&
988 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
989 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
990 tp->lost_cnt_hint -= decr;
992 tcp_verify_left_out(tp);
995 /* Function to create two new TCP segments. Shrinks the given segment
996 * to the specified size and appends a new segment with the rest of the
997 * packet to the list. This won't be called frequently, I hope.
998 * Remember, these are still headerless SKBs at this point.
1000 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1001 unsigned int mss_now)
1003 struct tcp_sock *tp = tcp_sk(sk);
1004 struct sk_buff *buff;
1005 int nsize, old_factor;
1009 if (WARN_ON(len > skb->len))
1012 nsize = skb_headlen(skb) - len;
1016 if (skb_cloned(skb) &&
1017 skb_is_nonlinear(skb) &&
1018 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
1021 /* Get a new skb... force flag on. */
1022 buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
1024 return -ENOMEM; /* We'll just try again later. */
1026 sk->sk_wmem_queued += buff->truesize;
1027 sk_mem_charge(sk, buff->truesize);
1028 nlen = skb->len - len - nsize;
1029 buff->truesize += nlen;
1030 skb->truesize -= nlen;
1032 /* Correct the sequence numbers. */
1033 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1034 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1035 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1037 /* PSH and FIN should only be set in the second packet. */
1038 flags = TCP_SKB_CB(skb)->tcp_flags;
1039 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1040 TCP_SKB_CB(buff)->tcp_flags = flags;
1041 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1043 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1044 /* Copy and checksum data tail into the new buffer. */
1045 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1046 skb_put(buff, nsize),
1051 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1053 skb->ip_summed = CHECKSUM_PARTIAL;
1054 skb_split(skb, buff, len);
1057 buff->ip_summed = skb->ip_summed;
1059 /* Looks stupid, but our code really uses when of
1060 * skbs, which it never sent before. --ANK
1062 TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
1063 buff->tstamp = skb->tstamp;
1065 old_factor = tcp_skb_pcount(skb);
1067 /* Fix up tso_factor for both original and new SKB. */
1068 tcp_set_skb_tso_segs(sk, skb, mss_now);
1069 tcp_set_skb_tso_segs(sk, buff, mss_now);
1071 /* If this packet has been sent out already, we must
1072 * adjust the various packet counters.
1074 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1075 int diff = old_factor - tcp_skb_pcount(skb) -
1076 tcp_skb_pcount(buff);
1079 tcp_adjust_pcount(sk, skb, diff);
1082 /* Link BUFF into the send queue. */
1083 skb_header_release(buff);
1084 tcp_insert_write_queue_after(skb, buff, sk);
1089 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1090 * eventually). The difference is that pulled data not copied, but
1091 * immediately discarded.
1093 static void __pskb_trim_head(struct sk_buff *skb, int len)
1097 eat = min_t(int, len, skb_headlen(skb));
1099 __skb_pull(skb, eat);
1100 skb->avail_size -= eat;
1107 for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
1108 int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
1111 skb_frag_unref(skb, i);
1114 skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
1116 skb_shinfo(skb)->frags[k].page_offset += eat;
1117 skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
1123 skb_shinfo(skb)->nr_frags = k;
1125 skb_reset_tail_pointer(skb);
1126 skb->data_len -= len;
1127 skb->len = skb->data_len;
1130 /* Remove acked data from a packet in the transmit queue. */
1131 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1133 if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
1136 __pskb_trim_head(skb, len);
1138 TCP_SKB_CB(skb)->seq += len;
1139 skb->ip_summed = CHECKSUM_PARTIAL;
1141 skb->truesize -= len;
1142 sk->sk_wmem_queued -= len;
1143 sk_mem_uncharge(sk, len);
1144 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1146 /* Any change of skb->len requires recalculation of tso factor. */
1147 if (tcp_skb_pcount(skb) > 1)
1148 tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
1153 /* Calculate MSS. Not accounting for SACKs here. */
1154 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1156 const struct tcp_sock *tp = tcp_sk(sk);
1157 const struct inet_connection_sock *icsk = inet_csk(sk);
1160 /* Calculate base mss without TCP options:
1161 It is MMS_S - sizeof(tcphdr) of rfc1122
1163 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1165 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1166 if (icsk->icsk_af_ops->net_frag_header_len) {
1167 const struct dst_entry *dst = __sk_dst_get(sk);
1169 if (dst && dst_allfrag(dst))
1170 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1173 /* Clamp it (mss_clamp does not include tcp options) */
1174 if (mss_now > tp->rx_opt.mss_clamp)
1175 mss_now = tp->rx_opt.mss_clamp;
1177 /* Now subtract optional transport overhead */
1178 mss_now -= icsk->icsk_ext_hdr_len;
1180 /* Then reserve room for full set of TCP options and 8 bytes of data */
1184 /* Now subtract TCP options size, not including SACKs */
1185 mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
1190 /* Inverse of above */
1191 int tcp_mss_to_mtu(struct sock *sk, int mss)
1193 const struct tcp_sock *tp = tcp_sk(sk);
1194 const struct inet_connection_sock *icsk = inet_csk(sk);
1198 tp->tcp_header_len +
1199 icsk->icsk_ext_hdr_len +
1200 icsk->icsk_af_ops->net_header_len;
1202 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1203 if (icsk->icsk_af_ops->net_frag_header_len) {
1204 const struct dst_entry *dst = __sk_dst_get(sk);
1206 if (dst && dst_allfrag(dst))
1207 mtu += icsk->icsk_af_ops->net_frag_header_len;
1212 /* MTU probing init per socket */
1213 void tcp_mtup_init(struct sock *sk)
1215 struct tcp_sock *tp = tcp_sk(sk);
1216 struct inet_connection_sock *icsk = inet_csk(sk);
1218 icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
1219 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1220 icsk->icsk_af_ops->net_header_len;
1221 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
1222 icsk->icsk_mtup.probe_size = 0;
1224 EXPORT_SYMBOL(tcp_mtup_init);
1226 /* This function synchronize snd mss to current pmtu/exthdr set.
1228 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1229 for TCP options, but includes only bare TCP header.
1231 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1232 It is minimum of user_mss and mss received with SYN.
1233 It also does not include TCP options.
1235 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1237 tp->mss_cache is current effective sending mss, including
1238 all tcp options except for SACKs. It is evaluated,
1239 taking into account current pmtu, but never exceeds
1240 tp->rx_opt.mss_clamp.
1242 NOTE1. rfc1122 clearly states that advertised MSS
1243 DOES NOT include either tcp or ip options.
1245 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1246 are READ ONLY outside this function. --ANK (980731)
1248 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1250 struct tcp_sock *tp = tcp_sk(sk);
1251 struct inet_connection_sock *icsk = inet_csk(sk);
1254 if (icsk->icsk_mtup.search_high > pmtu)
1255 icsk->icsk_mtup.search_high = pmtu;
1257 mss_now = tcp_mtu_to_mss(sk, pmtu);
1258 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1260 /* And store cached results */
1261 icsk->icsk_pmtu_cookie = pmtu;
1262 if (icsk->icsk_mtup.enabled)
1263 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1264 tp->mss_cache = mss_now;
1268 EXPORT_SYMBOL(tcp_sync_mss);
1270 /* Compute the current effective MSS, taking SACKs and IP options,
1271 * and even PMTU discovery events into account.
1273 unsigned int tcp_current_mss(struct sock *sk)
1275 const struct tcp_sock *tp = tcp_sk(sk);
1276 const struct dst_entry *dst = __sk_dst_get(sk);
1278 unsigned int header_len;
1279 struct tcp_out_options opts;
1280 struct tcp_md5sig_key *md5;
1282 mss_now = tp->mss_cache;
1285 u32 mtu = dst_mtu(dst);
1286 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1287 mss_now = tcp_sync_mss(sk, mtu);
1290 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1291 sizeof(struct tcphdr);
1292 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1293 * some common options. If this is an odd packet (because we have SACK
1294 * blocks etc) then our calculated header_len will be different, and
1295 * we have to adjust mss_now correspondingly */
1296 if (header_len != tp->tcp_header_len) {
1297 int delta = (int) header_len - tp->tcp_header_len;
1304 /* Congestion window validation. (RFC2861) */
1305 static void tcp_cwnd_validate(struct sock *sk)
1307 struct tcp_sock *tp = tcp_sk(sk);
1309 if (tp->packets_out >= tp->snd_cwnd) {
1310 /* Network is feed fully. */
1311 tp->snd_cwnd_used = 0;
1312 tp->snd_cwnd_stamp = tcp_time_stamp;
1314 /* Network starves. */
1315 if (tp->packets_out > tp->snd_cwnd_used)
1316 tp->snd_cwnd_used = tp->packets_out;
1318 if (sysctl_tcp_slow_start_after_idle &&
1319 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1320 tcp_cwnd_application_limited(sk);
1324 /* Returns the portion of skb which can be sent right away without
1325 * introducing MSS oddities to segment boundaries. In rare cases where
1326 * mss_now != mss_cache, we will request caller to create a small skb
1327 * per input skb which could be mostly avoided here (if desired).
1329 * We explicitly want to create a request for splitting write queue tail
1330 * to a small skb for Nagle purposes while avoiding unnecessary modulos,
1331 * thus all the complexity (cwnd_len is always MSS multiple which we
1332 * return whenever allowed by the other factors). Basically we need the
1333 * modulo only when the receiver window alone is the limiting factor or
1334 * when we would be allowed to send the split-due-to-Nagle skb fully.
1336 static unsigned int tcp_mss_split_point(const struct sock *sk, const struct sk_buff *skb,
1337 unsigned int mss_now, unsigned int cwnd)
1339 const struct tcp_sock *tp = tcp_sk(sk);
1340 u32 needed, window, cwnd_len;
1342 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1343 cwnd_len = mss_now * cwnd;
1345 if (likely(cwnd_len <= window && skb != tcp_write_queue_tail(sk)))
1348 needed = min(skb->len, window);
1350 if (cwnd_len <= needed)
1353 return needed - needed % mss_now;
1356 /* Can at least one segment of SKB be sent right now, according to the
1357 * congestion window rules? If so, return how many segments are allowed.
1359 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1360 const struct sk_buff *skb)
1362 u32 in_flight, cwnd;
1364 /* Don't be strict about the congestion window for the final FIN. */
1365 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1366 tcp_skb_pcount(skb) == 1)
1369 in_flight = tcp_packets_in_flight(tp);
1370 cwnd = tp->snd_cwnd;
1371 if (in_flight < cwnd)
1372 return (cwnd - in_flight);
1377 /* Initialize TSO state of a skb.
1378 * This must be invoked the first time we consider transmitting
1379 * SKB onto the wire.
1381 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
1382 unsigned int mss_now)
1384 int tso_segs = tcp_skb_pcount(skb);
1386 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1387 tcp_set_skb_tso_segs(sk, skb, mss_now);
1388 tso_segs = tcp_skb_pcount(skb);
1393 /* Minshall's variant of the Nagle send check. */
1394 static inline int tcp_minshall_check(const struct tcp_sock *tp)
1396 return after(tp->snd_sml, tp->snd_una) &&
1397 !after(tp->snd_sml, tp->snd_nxt);
1400 /* Return 0, if packet can be sent now without violation Nagle's rules:
1401 * 1. It is full sized.
1402 * 2. Or it contains FIN. (already checked by caller)
1403 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1404 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1405 * With Minshall's modification: all sent small packets are ACKed.
1407 static inline int tcp_nagle_check(const struct tcp_sock *tp,
1408 const struct sk_buff *skb,
1409 unsigned int mss_now, int nonagle)
1411 return skb->len < mss_now &&
1412 ((nonagle & TCP_NAGLE_CORK) ||
1413 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1416 /* Return non-zero if the Nagle test allows this packet to be
1419 static inline int tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1420 unsigned int cur_mss, int nonagle)
1422 /* Nagle rule does not apply to frames, which sit in the middle of the
1423 * write_queue (they have no chances to get new data).
1425 * This is implemented in the callers, where they modify the 'nonagle'
1426 * argument based upon the location of SKB in the send queue.
1428 if (nonagle & TCP_NAGLE_PUSH)
1431 /* Don't use the nagle rule for urgent data (or for the final FIN).
1432 * Nagle can be ignored during F-RTO too (see RFC4138).
1434 if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
1435 (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1438 if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
1444 /* Does at least the first segment of SKB fit into the send window? */
1445 static inline int tcp_snd_wnd_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1446 unsigned int cur_mss)
1448 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1450 if (skb->len > cur_mss)
1451 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1453 return !after(end_seq, tcp_wnd_end(tp));
1456 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1457 * should be put on the wire right now. If so, it returns the number of
1458 * packets allowed by the congestion window.
1460 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1461 unsigned int cur_mss, int nonagle)
1463 const struct tcp_sock *tp = tcp_sk(sk);
1464 unsigned int cwnd_quota;
1466 tcp_init_tso_segs(sk, skb, cur_mss);
1468 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1471 cwnd_quota = tcp_cwnd_test(tp, skb);
1472 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1478 /* Test if sending is allowed right now. */
1479 int tcp_may_send_now(struct sock *sk)
1481 const struct tcp_sock *tp = tcp_sk(sk);
1482 struct sk_buff *skb = tcp_send_head(sk);
1485 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1486 (tcp_skb_is_last(sk, skb) ?
1487 tp->nonagle : TCP_NAGLE_PUSH));
1490 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1491 * which is put after SKB on the list. It is very much like
1492 * tcp_fragment() except that it may make several kinds of assumptions
1493 * in order to speed up the splitting operation. In particular, we
1494 * know that all the data is in scatter-gather pages, and that the
1495 * packet has never been sent out before (and thus is not cloned).
1497 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1498 unsigned int mss_now, gfp_t gfp)
1500 struct sk_buff *buff;
1501 int nlen = skb->len - len;
1504 /* All of a TSO frame must be composed of paged data. */
1505 if (skb->len != skb->data_len)
1506 return tcp_fragment(sk, skb, len, mss_now);
1508 buff = sk_stream_alloc_skb(sk, 0, gfp);
1509 if (unlikely(buff == NULL))
1512 sk->sk_wmem_queued += buff->truesize;
1513 sk_mem_charge(sk, buff->truesize);
1514 buff->truesize += nlen;
1515 skb->truesize -= nlen;
1517 /* Correct the sequence numbers. */
1518 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1519 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1520 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1522 /* PSH and FIN should only be set in the second packet. */
1523 flags = TCP_SKB_CB(skb)->tcp_flags;
1524 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1525 TCP_SKB_CB(buff)->tcp_flags = flags;
1527 /* This packet was never sent out yet, so no SACK bits. */
1528 TCP_SKB_CB(buff)->sacked = 0;
1530 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1531 skb_split(skb, buff, len);
1533 /* Fix up tso_factor for both original and new SKB. */
1534 tcp_set_skb_tso_segs(sk, skb, mss_now);
1535 tcp_set_skb_tso_segs(sk, buff, mss_now);
1537 /* Link BUFF into the send queue. */
1538 skb_header_release(buff);
1539 tcp_insert_write_queue_after(skb, buff, sk);
1544 /* Try to defer sending, if possible, in order to minimize the amount
1545 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1547 * This algorithm is from John Heffner.
1549 static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1551 struct tcp_sock *tp = tcp_sk(sk);
1552 const struct inet_connection_sock *icsk = inet_csk(sk);
1553 u32 send_win, cong_win, limit, in_flight;
1556 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1559 if (icsk->icsk_ca_state != TCP_CA_Open)
1562 /* Defer for less than two clock ticks. */
1563 if (tp->tso_deferred &&
1564 (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
1567 in_flight = tcp_packets_in_flight(tp);
1569 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1571 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1573 /* From in_flight test above, we know that cwnd > in_flight. */
1574 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1576 limit = min(send_win, cong_win);
1578 /* If a full-sized TSO skb can be sent, do it. */
1579 if (limit >= sk->sk_gso_max_size)
1582 /* Middle in queue won't get any more data, full sendable already? */
1583 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1586 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1588 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1590 /* If at least some fraction of a window is available,
1593 chunk /= win_divisor;
1597 /* Different approach, try not to defer past a single
1598 * ACK. Receiver should ACK every other full sized
1599 * frame, so if we have space for more than 3 frames
1602 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1606 /* Ok, it looks like it is advisable to defer. */
1607 tp->tso_deferred = 1 | (jiffies << 1);
1612 tp->tso_deferred = 0;
1616 /* Create a new MTU probe if we are ready.
1617 * MTU probe is regularly attempting to increase the path MTU by
1618 * deliberately sending larger packets. This discovers routing
1619 * changes resulting in larger path MTUs.
1621 * Returns 0 if we should wait to probe (no cwnd available),
1622 * 1 if a probe was sent,
1625 static int tcp_mtu_probe(struct sock *sk)
1627 struct tcp_sock *tp = tcp_sk(sk);
1628 struct inet_connection_sock *icsk = inet_csk(sk);
1629 struct sk_buff *skb, *nskb, *next;
1636 /* Not currently probing/verifying,
1638 * have enough cwnd, and
1639 * not SACKing (the variable headers throw things off) */
1640 if (!icsk->icsk_mtup.enabled ||
1641 icsk->icsk_mtup.probe_size ||
1642 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1643 tp->snd_cwnd < 11 ||
1644 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1647 /* Very simple search strategy: just double the MSS. */
1648 mss_now = tcp_current_mss(sk);
1649 probe_size = 2 * tp->mss_cache;
1650 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1651 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
1652 /* TODO: set timer for probe_converge_event */
1656 /* Have enough data in the send queue to probe? */
1657 if (tp->write_seq - tp->snd_nxt < size_needed)
1660 if (tp->snd_wnd < size_needed)
1662 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1665 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1666 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1667 if (!tcp_packets_in_flight(tp))
1673 /* We're allowed to probe. Build it now. */
1674 if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
1676 sk->sk_wmem_queued += nskb->truesize;
1677 sk_mem_charge(sk, nskb->truesize);
1679 skb = tcp_send_head(sk);
1681 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1682 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1683 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1684 TCP_SKB_CB(nskb)->sacked = 0;
1686 nskb->ip_summed = skb->ip_summed;
1688 tcp_insert_write_queue_before(nskb, skb, sk);
1691 tcp_for_write_queue_from_safe(skb, next, sk) {
1692 copy = min_t(int, skb->len, probe_size - len);
1693 if (nskb->ip_summed)
1694 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1696 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1697 skb_put(nskb, copy),
1700 if (skb->len <= copy) {
1701 /* We've eaten all the data from this skb.
1703 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1704 tcp_unlink_write_queue(skb, sk);
1705 sk_wmem_free_skb(sk, skb);
1707 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1708 ~(TCPHDR_FIN|TCPHDR_PSH);
1709 if (!skb_shinfo(skb)->nr_frags) {
1710 skb_pull(skb, copy);
1711 if (skb->ip_summed != CHECKSUM_PARTIAL)
1712 skb->csum = csum_partial(skb->data,
1715 __pskb_trim_head(skb, copy);
1716 tcp_set_skb_tso_segs(sk, skb, mss_now);
1718 TCP_SKB_CB(skb)->seq += copy;
1723 if (len >= probe_size)
1726 tcp_init_tso_segs(sk, nskb, nskb->len);
1728 /* We're ready to send. If this fails, the probe will
1729 * be resegmented into mss-sized pieces by tcp_write_xmit(). */
1730 TCP_SKB_CB(nskb)->when = tcp_time_stamp;
1731 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1732 /* Decrement cwnd here because we are sending
1733 * effectively two packets. */
1735 tcp_event_new_data_sent(sk, nskb);
1737 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1738 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1739 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1747 /* This routine writes packets to the network. It advances the
1748 * send_head. This happens as incoming acks open up the remote
1751 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1752 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1753 * account rare use of URG, this is not a big flaw.
1755 * Returns 1, if no segments are in flight and we have queued segments, but
1756 * cannot send anything now because of SWS or another problem.
1758 static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
1759 int push_one, gfp_t gfp)
1761 struct tcp_sock *tp = tcp_sk(sk);
1762 struct sk_buff *skb;
1763 unsigned int tso_segs, sent_pkts;
1770 /* Do MTU probing. */
1771 result = tcp_mtu_probe(sk);
1774 } else if (result > 0) {
1779 while ((skb = tcp_send_head(sk))) {
1782 tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1785 cwnd_quota = tcp_cwnd_test(tp, skb);
1789 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
1792 if (tso_segs == 1) {
1793 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
1794 (tcp_skb_is_last(sk, skb) ?
1795 nonagle : TCP_NAGLE_PUSH))))
1798 if (!push_one && tcp_tso_should_defer(sk, skb))
1803 if (tso_segs > 1 && !tcp_urg_mode(tp))
1804 limit = tcp_mss_split_point(sk, skb, mss_now,
1807 if (skb->len > limit &&
1808 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
1811 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1813 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
1816 /* Advance the send_head. This one is sent out.
1817 * This call will increment packets_out.
1819 tcp_event_new_data_sent(sk, skb);
1821 tcp_minshall_update(tp, mss_now, skb);
1822 sent_pkts += tcp_skb_pcount(skb);
1827 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)
1828 tp->prr_out += sent_pkts;
1830 if (likely(sent_pkts)) {
1831 tcp_cwnd_validate(sk);
1834 return !tp->packets_out && tcp_send_head(sk);
1837 /* Push out any pending frames which were held back due to
1838 * TCP_CORK or attempt at coalescing tiny packets.
1839 * The socket must be locked by the caller.
1841 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
1844 /* If we are closed, the bytes will have to remain here.
1845 * In time closedown will finish, we empty the write queue and
1846 * all will be happy.
1848 if (unlikely(sk->sk_state == TCP_CLOSE))
1851 if (tcp_write_xmit(sk, cur_mss, nonagle, 0, GFP_ATOMIC))
1852 tcp_check_probe_timer(sk);
1855 /* Send _single_ skb sitting at the send head. This function requires
1856 * true push pending frames to setup probe timer etc.
1858 void tcp_push_one(struct sock *sk, unsigned int mss_now)
1860 struct sk_buff *skb = tcp_send_head(sk);
1862 BUG_ON(!skb || skb->len < mss_now);
1864 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
1867 /* This function returns the amount that we can raise the
1868 * usable window based on the following constraints
1870 * 1. The window can never be shrunk once it is offered (RFC 793)
1871 * 2. We limit memory per socket
1874 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
1875 * RECV.NEXT + RCV.WIN fixed until:
1876 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
1878 * i.e. don't raise the right edge of the window until you can raise
1879 * it at least MSS bytes.
1881 * Unfortunately, the recommended algorithm breaks header prediction,
1882 * since header prediction assumes th->window stays fixed.
1884 * Strictly speaking, keeping th->window fixed violates the receiver
1885 * side SWS prevention criteria. The problem is that under this rule
1886 * a stream of single byte packets will cause the right side of the
1887 * window to always advance by a single byte.
1889 * Of course, if the sender implements sender side SWS prevention
1890 * then this will not be a problem.
1892 * BSD seems to make the following compromise:
1894 * If the free space is less than the 1/4 of the maximum
1895 * space available and the free space is less than 1/2 mss,
1896 * then set the window to 0.
1897 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
1898 * Otherwise, just prevent the window from shrinking
1899 * and from being larger than the largest representable value.
1901 * This prevents incremental opening of the window in the regime
1902 * where TCP is limited by the speed of the reader side taking
1903 * data out of the TCP receive queue. It does nothing about
1904 * those cases where the window is constrained on the sender side
1905 * because the pipeline is full.
1907 * BSD also seems to "accidentally" limit itself to windows that are a
1908 * multiple of MSS, at least until the free space gets quite small.
1909 * This would appear to be a side effect of the mbuf implementation.
1910 * Combining these two algorithms results in the observed behavior
1911 * of having a fixed window size at almost all times.
1913 * Below we obtain similar behavior by forcing the offered window to
1914 * a multiple of the mss when it is feasible to do so.
1916 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
1917 * Regular options like TIMESTAMP are taken into account.
1919 u32 __tcp_select_window(struct sock *sk)
1921 struct inet_connection_sock *icsk = inet_csk(sk);
1922 struct tcp_sock *tp = tcp_sk(sk);
1923 /* MSS for the peer's data. Previous versions used mss_clamp
1924 * here. I don't know if the value based on our guesses
1925 * of peer's MSS is better for the performance. It's more correct
1926 * but may be worse for the performance because of rcv_mss
1927 * fluctuations. --SAW 1998/11/1
1929 int mss = icsk->icsk_ack.rcv_mss;
1930 int free_space = tcp_space(sk);
1931 int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
1934 if (mss > full_space)
1937 if (free_space < (full_space >> 1)) {
1938 icsk->icsk_ack.quick = 0;
1940 if (sk_under_memory_pressure(sk))
1941 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
1944 if (free_space < mss)
1948 if (free_space > tp->rcv_ssthresh)
1949 free_space = tp->rcv_ssthresh;
1951 /* Don't do rounding if we are using window scaling, since the
1952 * scaled window will not line up with the MSS boundary anyway.
1954 window = tp->rcv_wnd;
1955 if (tp->rx_opt.rcv_wscale) {
1956 window = free_space;
1958 /* Advertise enough space so that it won't get scaled away.
1959 * Import case: prevent zero window announcement if
1960 * 1<<rcv_wscale > mss.
1962 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
1963 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
1964 << tp->rx_opt.rcv_wscale);
1966 /* Get the largest window that is a nice multiple of mss.
1967 * Window clamp already applied above.
1968 * If our current window offering is within 1 mss of the
1969 * free space we just keep it. This prevents the divide
1970 * and multiply from happening most of the time.
1971 * We also don't do any window rounding when the free space
1974 if (window <= free_space - mss || window > free_space)
1975 window = (free_space / mss) * mss;
1976 else if (mss == full_space &&
1977 free_space > window + (full_space >> 1))
1978 window = free_space;
1984 /* Collapses two adjacent SKB's during retransmission. */
1985 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
1987 struct tcp_sock *tp = tcp_sk(sk);
1988 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
1989 int skb_size, next_skb_size;
1991 skb_size = skb->len;
1992 next_skb_size = next_skb->len;
1994 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
1996 tcp_highest_sack_combine(sk, next_skb, skb);
1998 tcp_unlink_write_queue(next_skb, sk);
2000 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2003 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2004 skb->ip_summed = CHECKSUM_PARTIAL;
2006 if (skb->ip_summed != CHECKSUM_PARTIAL)
2007 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2009 /* Update sequence range on original skb. */
2010 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2012 /* Merge over control information. This moves PSH/FIN etc. over */
2013 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2015 /* All done, get rid of second SKB and account for it so
2016 * packet counting does not break.
2018 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2020 /* changed transmit queue under us so clear hints */
2021 tcp_clear_retrans_hints_partial(tp);
2022 if (next_skb == tp->retransmit_skb_hint)
2023 tp->retransmit_skb_hint = skb;
2025 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2027 sk_wmem_free_skb(sk, next_skb);
2030 /* Check if coalescing SKBs is legal. */
2031 static int tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2033 if (tcp_skb_pcount(skb) > 1)
2035 /* TODO: SACK collapsing could be used to remove this condition */
2036 if (skb_shinfo(skb)->nr_frags != 0)
2038 if (skb_cloned(skb))
2040 if (skb == tcp_send_head(sk))
2042 /* Some heurestics for collapsing over SACK'd could be invented */
2043 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2049 /* Collapse packets in the retransmit queue to make to create
2050 * less packets on the wire. This is only done on retransmission.
2052 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2055 struct tcp_sock *tp = tcp_sk(sk);
2056 struct sk_buff *skb = to, *tmp;
2059 if (!sysctl_tcp_retrans_collapse)
2061 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2064 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2065 if (!tcp_can_collapse(sk, skb))
2077 /* Punt if not enough space exists in the first SKB for
2078 * the data in the second
2080 if (skb->len > skb_availroom(to))
2083 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2086 tcp_collapse_retrans(sk, to);
2090 /* This retransmits one SKB. Policy decisions and retransmit queue
2091 * state updates are done by the caller. Returns non-zero if an
2092 * error occurred which prevented the send.
2094 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2096 struct tcp_sock *tp = tcp_sk(sk);
2097 struct inet_connection_sock *icsk = inet_csk(sk);
2098 unsigned int cur_mss;
2101 /* Inconslusive MTU probe */
2102 if (icsk->icsk_mtup.probe_size) {
2103 icsk->icsk_mtup.probe_size = 0;
2106 /* Do not sent more than we queued. 1/4 is reserved for possible
2107 * copying overhead: fragmentation, tunneling, mangling etc.
2109 if (atomic_read(&sk->sk_wmem_alloc) >
2110 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2113 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2114 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2116 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2120 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2121 return -EHOSTUNREACH; /* Routing failure or similar. */
2123 cur_mss = tcp_current_mss(sk);
2125 /* If receiver has shrunk his window, and skb is out of
2126 * new window, do not retransmit it. The exception is the
2127 * case, when window is shrunk to zero. In this case
2128 * our retransmit serves as a zero window probe.
2130 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2131 TCP_SKB_CB(skb)->seq != tp->snd_una)
2134 if (skb->len > cur_mss) {
2135 if (tcp_fragment(sk, skb, cur_mss, cur_mss))
2136 return -ENOMEM; /* We'll try again later. */
2138 int oldpcount = tcp_skb_pcount(skb);
2140 if (unlikely(oldpcount > 1)) {
2141 tcp_init_tso_segs(sk, skb, cur_mss);
2142 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2146 tcp_retrans_try_collapse(sk, skb, cur_mss);
2148 /* Some Solaris stacks overoptimize and ignore the FIN on a
2149 * retransmit when old data is attached. So strip it off
2150 * since it is cheap to do so and saves bytes on the network.
2153 (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
2154 tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
2155 if (!pskb_trim(skb, 0)) {
2156 /* Reuse, even though it does some unnecessary work */
2157 tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1,
2158 TCP_SKB_CB(skb)->tcp_flags);
2159 skb->ip_summed = CHECKSUM_NONE;
2163 /* Make a copy, if the first transmission SKB clone we made
2164 * is still in somebody's hands, else make a clone.
2166 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2168 /* make sure skb->data is aligned on arches that require it */
2169 if (unlikely(NET_IP_ALIGN && ((unsigned long)skb->data & 3))) {
2170 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2172 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2175 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2179 /* Update global TCP statistics. */
2180 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2182 tp->total_retrans++;
2184 #if FASTRETRANS_DEBUG > 0
2185 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2186 net_dbg_ratelimited("retrans_out leaked\n");
2189 if (!tp->retrans_out)
2190 tp->lost_retrans_low = tp->snd_nxt;
2191 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2192 tp->retrans_out += tcp_skb_pcount(skb);
2194 /* Save stamp of the first retransmit. */
2195 if (!tp->retrans_stamp)
2196 tp->retrans_stamp = TCP_SKB_CB(skb)->when;
2198 tp->undo_retrans += tcp_skb_pcount(skb);
2200 /* snd_nxt is stored to detect loss of retransmitted segment,
2201 * see tcp_input.c tcp_sacktag_write_queue().
2203 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2208 /* Check if we forward retransmits are possible in the current
2209 * window/congestion state.
2211 static int tcp_can_forward_retransmit(struct sock *sk)
2213 const struct inet_connection_sock *icsk = inet_csk(sk);
2214 const struct tcp_sock *tp = tcp_sk(sk);
2216 /* Forward retransmissions are possible only during Recovery. */
2217 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2220 /* No forward retransmissions in Reno are possible. */
2221 if (tcp_is_reno(tp))
2224 /* Yeah, we have to make difficult choice between forward transmission
2225 * and retransmission... Both ways have their merits...
2227 * For now we do not retransmit anything, while we have some new
2228 * segments to send. In the other cases, follow rule 3 for
2229 * NextSeg() specified in RFC3517.
2232 if (tcp_may_send_now(sk))
2238 /* This gets called after a retransmit timeout, and the initially
2239 * retransmitted data is acknowledged. It tries to continue
2240 * resending the rest of the retransmit queue, until either
2241 * we've sent it all or the congestion window limit is reached.
2242 * If doing SACK, the first ACK which comes back for a timeout
2243 * based retransmit packet might feed us FACK information again.
2244 * If so, we use it to avoid unnecessarily retransmissions.
2246 void tcp_xmit_retransmit_queue(struct sock *sk)
2248 const struct inet_connection_sock *icsk = inet_csk(sk);
2249 struct tcp_sock *tp = tcp_sk(sk);
2250 struct sk_buff *skb;
2251 struct sk_buff *hole = NULL;
2254 int fwd_rexmitting = 0;
2256 if (!tp->packets_out)
2260 tp->retransmit_high = tp->snd_una;
2262 if (tp->retransmit_skb_hint) {
2263 skb = tp->retransmit_skb_hint;
2264 last_lost = TCP_SKB_CB(skb)->end_seq;
2265 if (after(last_lost, tp->retransmit_high))
2266 last_lost = tp->retransmit_high;
2268 skb = tcp_write_queue_head(sk);
2269 last_lost = tp->snd_una;
2272 tcp_for_write_queue_from(skb, sk) {
2273 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2275 if (skb == tcp_send_head(sk))
2277 /* we could do better than to assign each time */
2279 tp->retransmit_skb_hint = skb;
2281 /* Assume this retransmit will generate
2282 * only one packet for congestion window
2283 * calculation purposes. This works because
2284 * tcp_retransmit_skb() will chop up the
2285 * packet to be MSS sized and all the
2286 * packet counting works out.
2288 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2291 if (fwd_rexmitting) {
2293 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2295 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2297 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2298 tp->retransmit_high = last_lost;
2299 if (!tcp_can_forward_retransmit(sk))
2301 /* Backtrack if necessary to non-L'ed skb */
2309 } else if (!(sacked & TCPCB_LOST)) {
2310 if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2315 last_lost = TCP_SKB_CB(skb)->end_seq;
2316 if (icsk->icsk_ca_state != TCP_CA_Loss)
2317 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2319 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2322 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2325 if (tcp_retransmit_skb(sk, skb)) {
2326 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2329 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2331 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)
2332 tp->prr_out += tcp_skb_pcount(skb);
2334 if (skb == tcp_write_queue_head(sk))
2335 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2336 inet_csk(sk)->icsk_rto,
2341 /* Send a fin. The caller locks the socket for us. This cannot be
2342 * allowed to fail queueing a FIN frame under any circumstances.
2344 void tcp_send_fin(struct sock *sk)
2346 struct tcp_sock *tp = tcp_sk(sk);
2347 struct sk_buff *skb = tcp_write_queue_tail(sk);
2350 /* Optimization, tack on the FIN if we have a queue of
2351 * unsent frames. But be careful about outgoing SACKS
2354 mss_now = tcp_current_mss(sk);
2356 if (tcp_send_head(sk) != NULL) {
2357 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
2358 TCP_SKB_CB(skb)->end_seq++;
2361 /* Socket is locked, keep trying until memory is available. */
2363 skb = alloc_skb_fclone(MAX_TCP_HEADER,
2370 /* Reserve space for headers and prepare control bits. */
2371 skb_reserve(skb, MAX_TCP_HEADER);
2372 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2373 tcp_init_nondata_skb(skb, tp->write_seq,
2374 TCPHDR_ACK | TCPHDR_FIN);
2375 tcp_queue_skb(sk, skb);
2377 __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
2380 /* We get here when a process closes a file descriptor (either due to
2381 * an explicit close() or as a byproduct of exit()'ing) and there
2382 * was unread data in the receive queue. This behavior is recommended
2383 * by RFC 2525, section 2.17. -DaveM
2385 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2387 struct sk_buff *skb;
2389 /* NOTE: No TCP options attached and we never retransmit this. */
2390 skb = alloc_skb(MAX_TCP_HEADER, priority);
2392 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2396 /* Reserve space for headers and prepare control bits. */
2397 skb_reserve(skb, MAX_TCP_HEADER);
2398 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2399 TCPHDR_ACK | TCPHDR_RST);
2401 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2402 if (tcp_transmit_skb(sk, skb, 0, priority))
2403 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2405 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2408 /* Send a crossed SYN-ACK during socket establishment.
2409 * WARNING: This routine must only be called when we have already sent
2410 * a SYN packet that crossed the incoming SYN that caused this routine
2411 * to get called. If this assumption fails then the initial rcv_wnd
2412 * and rcv_wscale values will not be correct.
2414 int tcp_send_synack(struct sock *sk)
2416 struct sk_buff *skb;
2418 skb = tcp_write_queue_head(sk);
2419 if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2420 pr_debug("%s: wrong queue state\n", __func__);
2423 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2424 if (skb_cloned(skb)) {
2425 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2428 tcp_unlink_write_queue(skb, sk);
2429 skb_header_release(nskb);
2430 __tcp_add_write_queue_head(sk, nskb);
2431 sk_wmem_free_skb(sk, skb);
2432 sk->sk_wmem_queued += nskb->truesize;
2433 sk_mem_charge(sk, nskb->truesize);
2437 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2438 TCP_ECN_send_synack(tcp_sk(sk), skb);
2440 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2441 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2444 /* Prepare a SYN-ACK. */
2445 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2446 struct request_sock *req,
2447 struct request_values *rvp)
2449 struct tcp_out_options opts;
2450 struct tcp_extend_values *xvp = tcp_xv(rvp);
2451 struct inet_request_sock *ireq = inet_rsk(req);
2452 struct tcp_sock *tp = tcp_sk(sk);
2453 const struct tcp_cookie_values *cvp = tp->cookie_values;
2455 struct sk_buff *skb;
2456 struct tcp_md5sig_key *md5;
2457 int tcp_header_size;
2459 int s_data_desired = 0;
2461 if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)
2462 s_data_desired = cvp->s_data_desired;
2463 skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15 + s_data_desired, 1, GFP_ATOMIC);
2467 /* Reserve space for headers. */
2468 skb_reserve(skb, MAX_TCP_HEADER);
2470 skb_dst_set(skb, dst_clone(dst));
2472 mss = dst_metric_advmss(dst);
2473 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2474 mss = tp->rx_opt.user_mss;
2476 if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
2478 /* Set this up on the first call only */
2479 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
2481 /* limit the window selection if the user enforce a smaller rx buffer */
2482 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2483 (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
2484 req->window_clamp = tcp_full_space(sk);
2486 /* tcp_full_space because it is guaranteed to be the first packet */
2487 tcp_select_initial_window(tcp_full_space(sk),
2488 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
2493 dst_metric(dst, RTAX_INITRWND));
2494 ireq->rcv_wscale = rcv_wscale;
2497 memset(&opts, 0, sizeof(opts));
2498 #ifdef CONFIG_SYN_COOKIES
2499 if (unlikely(req->cookie_ts))
2500 TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
2503 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2504 tcp_header_size = tcp_synack_options(sk, req, mss,
2505 skb, &opts, &md5, xvp)
2508 skb_push(skb, tcp_header_size);
2509 skb_reset_transport_header(skb);
2512 memset(th, 0, sizeof(struct tcphdr));
2515 TCP_ECN_make_synack(req, th);
2516 th->source = ireq->loc_port;
2517 th->dest = ireq->rmt_port;
2518 /* Setting of flags are superfluous here for callers (and ECE is
2519 * not even correctly set)
2521 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
2522 TCPHDR_SYN | TCPHDR_ACK);
2524 if (OPTION_COOKIE_EXTENSION & opts.options) {
2525 if (s_data_desired) {
2526 u8 *buf = skb_put(skb, s_data_desired);
2528 /* copy data directly from the listening socket. */
2529 memcpy(buf, cvp->s_data_payload, s_data_desired);
2530 TCP_SKB_CB(skb)->end_seq += s_data_desired;
2533 if (opts.hash_size > 0) {
2534 __u32 workspace[SHA_WORKSPACE_WORDS];
2535 u32 *mess = &xvp->cookie_bakery[COOKIE_DIGEST_WORDS];
2536 u32 *tail = &mess[COOKIE_MESSAGE_WORDS-1];
2538 /* Secret recipe depends on the Timestamp, (future)
2539 * Sequence and Acknowledgment Numbers, Initiator
2540 * Cookie, and others handled by IP variant caller.
2542 *tail-- ^= opts.tsval;
2543 *tail-- ^= tcp_rsk(req)->rcv_isn + 1;
2544 *tail-- ^= TCP_SKB_CB(skb)->seq + 1;
2547 *tail-- ^= (((__force u32)th->dest << 16) | (__force u32)th->source);
2548 *tail-- ^= (u32)(unsigned long)cvp; /* per sockopt */
2550 sha_transform((__u32 *)&xvp->cookie_bakery[0],
2553 opts.hash_location =
2554 (__u8 *)&xvp->cookie_bakery[0];
2558 th->seq = htonl(TCP_SKB_CB(skb)->seq);
2559 th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
2561 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2562 th->window = htons(min(req->rcv_wnd, 65535U));
2563 tcp_options_write((__be32 *)(th + 1), tp, &opts);
2564 th->doff = (tcp_header_size >> 2);
2565 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb));
2567 #ifdef CONFIG_TCP_MD5SIG
2568 /* Okay, we have all we need - do the md5 hash if needed */
2570 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
2571 md5, NULL, req, skb);
2577 EXPORT_SYMBOL(tcp_make_synack);
2579 /* Do all connect socket setups that can be done AF independent. */
2580 void tcp_connect_init(struct sock *sk)
2582 const struct dst_entry *dst = __sk_dst_get(sk);
2583 struct tcp_sock *tp = tcp_sk(sk);
2586 /* We'll fix this up when we get a response from the other end.
2587 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2589 tp->tcp_header_len = sizeof(struct tcphdr) +
2590 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
2592 #ifdef CONFIG_TCP_MD5SIG
2593 if (tp->af_specific->md5_lookup(sk, sk) != NULL)
2594 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
2597 /* If user gave his TCP_MAXSEG, record it to clamp */
2598 if (tp->rx_opt.user_mss)
2599 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2602 tcp_sync_mss(sk, dst_mtu(dst));
2604 if (!tp->window_clamp)
2605 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
2606 tp->advmss = dst_metric_advmss(dst);
2607 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
2608 tp->advmss = tp->rx_opt.user_mss;
2610 tcp_initialize_rcv_mss(sk);
2612 /* limit the window selection if the user enforce a smaller rx buffer */
2613 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2614 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
2615 tp->window_clamp = tcp_full_space(sk);
2617 tcp_select_initial_window(tcp_full_space(sk),
2618 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
2621 sysctl_tcp_window_scaling,
2623 dst_metric(dst, RTAX_INITRWND));
2625 tp->rx_opt.rcv_wscale = rcv_wscale;
2626 tp->rcv_ssthresh = tp->rcv_wnd;
2629 sock_reset_flag(sk, SOCK_DONE);
2632 tp->snd_una = tp->write_seq;
2633 tp->snd_sml = tp->write_seq;
2634 tp->snd_up = tp->write_seq;
2635 tp->snd_nxt = tp->write_seq;
2637 if (likely(!tp->repair))
2639 tp->rcv_wup = tp->rcv_nxt;
2640 tp->copied_seq = tp->rcv_nxt;
2642 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
2643 inet_csk(sk)->icsk_retransmits = 0;
2644 tcp_clear_retrans(tp);
2647 /* Build a SYN and send it off. */
2648 int tcp_connect(struct sock *sk)
2650 struct tcp_sock *tp = tcp_sk(sk);
2651 struct sk_buff *buff;
2654 tcp_connect_init(sk);
2656 buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
2657 if (unlikely(buff == NULL))
2660 /* Reserve space for headers. */
2661 skb_reserve(buff, MAX_TCP_HEADER);
2663 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
2664 TCP_ECN_send_syn(sk, buff);
2667 TCP_SKB_CB(buff)->when = tcp_time_stamp;
2668 tp->retrans_stamp = TCP_SKB_CB(buff)->when;
2669 skb_header_release(buff);
2670 __tcp_add_write_queue_tail(sk, buff);
2671 sk->sk_wmem_queued += buff->truesize;
2672 sk_mem_charge(sk, buff->truesize);
2673 tp->packets_out += tcp_skb_pcount(buff);
2674 err = tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
2675 if (err == -ECONNREFUSED)
2678 /* We change tp->snd_nxt after the tcp_transmit_skb() call
2679 * in order to make this packet get counted in tcpOutSegs.
2681 tp->snd_nxt = tp->write_seq;
2682 tp->pushed_seq = tp->write_seq;
2683 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
2685 /* Timer for repeating the SYN until an answer. */
2686 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2687 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2690 EXPORT_SYMBOL(tcp_connect);
2692 /* Send out a delayed ack, the caller does the policy checking
2693 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
2696 void tcp_send_delayed_ack(struct sock *sk)
2698 struct inet_connection_sock *icsk = inet_csk(sk);
2699 int ato = icsk->icsk_ack.ato;
2700 unsigned long timeout;
2702 if (ato > TCP_DELACK_MIN) {
2703 const struct tcp_sock *tp = tcp_sk(sk);
2704 int max_ato = HZ / 2;
2706 if (icsk->icsk_ack.pingpong ||
2707 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
2708 max_ato = TCP_DELACK_MAX;
2710 /* Slow path, intersegment interval is "high". */
2712 /* If some rtt estimate is known, use it to bound delayed ack.
2713 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
2717 int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
2723 ato = min(ato, max_ato);
2726 /* Stay within the limit we were given */
2727 timeout = jiffies + ato;
2729 /* Use new timeout only if there wasn't a older one earlier. */
2730 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
2731 /* If delack timer was blocked or is about to expire,
2734 if (icsk->icsk_ack.blocked ||
2735 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
2740 if (!time_before(timeout, icsk->icsk_ack.timeout))
2741 timeout = icsk->icsk_ack.timeout;
2743 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
2744 icsk->icsk_ack.timeout = timeout;
2745 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
2748 /* This routine sends an ack and also updates the window. */
2749 void tcp_send_ack(struct sock *sk)
2751 struct sk_buff *buff;
2753 /* If we have been reset, we may not send again. */
2754 if (sk->sk_state == TCP_CLOSE)
2757 /* We are not putting this on the write queue, so
2758 * tcp_transmit_skb() will set the ownership to this
2761 buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2763 inet_csk_schedule_ack(sk);
2764 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
2765 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
2766 TCP_DELACK_MAX, TCP_RTO_MAX);
2770 /* Reserve space for headers and prepare control bits. */
2771 skb_reserve(buff, MAX_TCP_HEADER);
2772 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
2774 /* Send it off, this clears delayed acks for us. */
2775 TCP_SKB_CB(buff)->when = tcp_time_stamp;
2776 tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC);
2779 /* This routine sends a packet with an out of date sequence
2780 * number. It assumes the other end will try to ack it.
2782 * Question: what should we make while urgent mode?
2783 * 4.4BSD forces sending single byte of data. We cannot send
2784 * out of window data, because we have SND.NXT==SND.MAX...
2786 * Current solution: to send TWO zero-length segments in urgent mode:
2787 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
2788 * out-of-date with SND.UNA-1 to probe window.
2790 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
2792 struct tcp_sock *tp = tcp_sk(sk);
2793 struct sk_buff *skb;
2795 /* We don't queue it, tcp_transmit_skb() sets ownership. */
2796 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2800 /* Reserve space for headers and set control bits. */
2801 skb_reserve(skb, MAX_TCP_HEADER);
2802 /* Use a previous sequence. This should cause the other
2803 * end to send an ack. Don't queue or clone SKB, just
2806 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
2807 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2808 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
2811 void tcp_send_window_probe(struct sock *sk)
2813 if (sk->sk_state == TCP_ESTABLISHED) {
2814 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
2815 tcp_sk(sk)->snd_nxt = tcp_sk(sk)->write_seq;
2816 tcp_xmit_probe_skb(sk, 0);
2820 /* Initiate keepalive or window probe from timer. */
2821 int tcp_write_wakeup(struct sock *sk)
2823 struct tcp_sock *tp = tcp_sk(sk);
2824 struct sk_buff *skb;
2826 if (sk->sk_state == TCP_CLOSE)
2829 if ((skb = tcp_send_head(sk)) != NULL &&
2830 before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
2832 unsigned int mss = tcp_current_mss(sk);
2833 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
2835 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
2836 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
2838 /* We are probing the opening of a window
2839 * but the window size is != 0
2840 * must have been a result SWS avoidance ( sender )
2842 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
2844 seg_size = min(seg_size, mss);
2845 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
2846 if (tcp_fragment(sk, skb, seg_size, mss))
2848 } else if (!tcp_skb_pcount(skb))
2849 tcp_set_skb_tso_segs(sk, skb, mss);
2851 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
2852 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2853 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2855 tcp_event_new_data_sent(sk, skb);
2858 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
2859 tcp_xmit_probe_skb(sk, 1);
2860 return tcp_xmit_probe_skb(sk, 0);
2864 /* A window probe timeout has occurred. If window is not closed send
2865 * a partial packet else a zero probe.
2867 void tcp_send_probe0(struct sock *sk)
2869 struct inet_connection_sock *icsk = inet_csk(sk);
2870 struct tcp_sock *tp = tcp_sk(sk);
2873 err = tcp_write_wakeup(sk);
2875 if (tp->packets_out || !tcp_send_head(sk)) {
2876 /* Cancel probe timer, if it is not required. */
2877 icsk->icsk_probes_out = 0;
2878 icsk->icsk_backoff = 0;
2883 if (icsk->icsk_backoff < sysctl_tcp_retries2)
2884 icsk->icsk_backoff++;
2885 icsk->icsk_probes_out++;
2886 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2887 min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2890 /* If packet was not sent due to local congestion,
2891 * do not backoff and do not remember icsk_probes_out.
2892 * Let local senders to fight for local resources.
2894 * Use accumulated backoff yet.
2896 if (!icsk->icsk_probes_out)
2897 icsk->icsk_probes_out = 1;
2898 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2899 min(icsk->icsk_rto << icsk->icsk_backoff,
2900 TCP_RESOURCE_PROBE_INTERVAL),