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 two TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 131072;
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 int sysctl_tcp_mtu_probing __read_mostly = 0;
63 int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;
65 /* By default, RFC2861 behavior. */
66 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
68 int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
69 EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size);
71 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
72 int push_one, gfp_t gfp);
74 /* Account for new data that has been sent to the network. */
75 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
77 struct tcp_sock *tp = tcp_sk(sk);
78 unsigned int prior_packets = tp->packets_out;
80 tcp_advance_send_head(sk, skb);
81 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
83 /* Don't override Nagle indefinitely with F-RTO */
84 if (tp->frto_counter == 2)
87 tp->packets_out += tcp_skb_pcount(skb);
88 if (!prior_packets || tp->early_retrans_delayed)
92 /* SND.NXT, if window was not shrunk.
93 * If window has been shrunk, what should we make? It is not clear at all.
94 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
95 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
96 * invalid. OK, let's make this for now:
98 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
100 const struct tcp_sock *tp = tcp_sk(sk);
102 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
105 return tcp_wnd_end(tp);
108 /* Calculate mss to advertise in SYN segment.
109 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
111 * 1. It is independent of path mtu.
112 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
113 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
114 * attached devices, because some buggy hosts are confused by
116 * 4. We do not make 3, we advertise MSS, calculated from first
117 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
118 * This may be overridden via information stored in routing table.
119 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
120 * probably even Jumbo".
122 static __u16 tcp_advertise_mss(struct sock *sk)
124 struct tcp_sock *tp = tcp_sk(sk);
125 const struct dst_entry *dst = __sk_dst_get(sk);
126 int mss = tp->advmss;
129 unsigned int metric = dst_metric_advmss(dst);
140 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
141 * This is the first part of cwnd validation mechanism. */
142 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
144 struct tcp_sock *tp = tcp_sk(sk);
145 s32 delta = tcp_time_stamp - tp->lsndtime;
146 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
147 u32 cwnd = tp->snd_cwnd;
149 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
151 tp->snd_ssthresh = tcp_current_ssthresh(sk);
152 restart_cwnd = min(restart_cwnd, cwnd);
154 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
156 tp->snd_cwnd = max(cwnd, restart_cwnd);
157 tp->snd_cwnd_stamp = tcp_time_stamp;
158 tp->snd_cwnd_used = 0;
161 /* Congestion state accounting after a packet has been sent. */
162 static void tcp_event_data_sent(struct tcp_sock *tp,
165 struct inet_connection_sock *icsk = inet_csk(sk);
166 const u32 now = tcp_time_stamp;
168 if (sysctl_tcp_slow_start_after_idle &&
169 (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
170 tcp_cwnd_restart(sk, __sk_dst_get(sk));
174 /* If it is a reply for ato after last received
175 * packet, enter pingpong mode.
177 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
178 icsk->icsk_ack.pingpong = 1;
181 /* Account for an ACK we sent. */
182 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
184 tcp_dec_quickack_mode(sk, pkts);
185 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
188 /* Determine a window scaling and initial window to offer.
189 * Based on the assumption that the given amount of space
190 * will be offered. Store the results in the tp structure.
191 * NOTE: for smooth operation initial space offering should
192 * be a multiple of mss if possible. We assume here that mss >= 1.
193 * This MUST be enforced by all callers.
195 void tcp_select_initial_window(int __space, __u32 mss,
196 __u32 *rcv_wnd, __u32 *window_clamp,
197 int wscale_ok, __u8 *rcv_wscale,
200 unsigned int space = (__space < 0 ? 0 : __space);
202 /* If no clamp set the clamp to the max possible scaled window */
203 if (*window_clamp == 0)
204 (*window_clamp) = (65535 << 14);
205 space = min(*window_clamp, space);
207 /* Quantize space offering to a multiple of mss if possible. */
209 space = (space / mss) * mss;
211 /* NOTE: offering an initial window larger than 32767
212 * will break some buggy TCP stacks. If the admin tells us
213 * it is likely we could be speaking with such a buggy stack
214 * we will truncate our initial window offering to 32K-1
215 * unless the remote has sent us a window scaling option,
216 * which we interpret as a sign the remote TCP is not
217 * misinterpreting the window field as a signed quantity.
219 if (sysctl_tcp_workaround_signed_windows)
220 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
226 /* Set window scaling on max possible window
227 * See RFC1323 for an explanation of the limit to 14
229 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
230 space = min_t(u32, space, *window_clamp);
231 while (space > 65535 && (*rcv_wscale) < 14) {
237 /* Set initial window to a value enough for senders starting with
238 * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
239 * a limit on the initial window when mss is larger than 1460.
241 if (mss > (1 << *rcv_wscale)) {
242 int init_cwnd = TCP_DEFAULT_INIT_RCVWND;
245 max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
246 /* when initializing use the value from init_rcv_wnd
247 * rather than the default from above
250 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
252 *rcv_wnd = min(*rcv_wnd, init_cwnd * mss);
255 /* Set the clamp no higher than max representable value */
256 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
258 EXPORT_SYMBOL(tcp_select_initial_window);
260 /* Chose a new window to advertise, update state in tcp_sock for the
261 * socket, and return result with RFC1323 scaling applied. The return
262 * value can be stuffed directly into th->window for an outgoing
265 static u16 tcp_select_window(struct sock *sk)
267 struct tcp_sock *tp = tcp_sk(sk);
268 u32 cur_win = tcp_receive_window(tp);
269 u32 new_win = __tcp_select_window(sk);
271 /* Never shrink the offered window */
272 if (new_win < cur_win) {
273 /* Danger Will Robinson!
274 * Don't update rcv_wup/rcv_wnd here or else
275 * we will not be able to advertise a zero
276 * window in time. --DaveM
278 * Relax Will Robinson.
280 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
282 tp->rcv_wnd = new_win;
283 tp->rcv_wup = tp->rcv_nxt;
285 /* Make sure we do not exceed the maximum possible
288 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
289 new_win = min(new_win, MAX_TCP_WINDOW);
291 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
293 /* RFC1323 scaling applied */
294 new_win >>= tp->rx_opt.rcv_wscale;
296 /* If we advertise zero window, disable fast path. */
303 /* Packet ECN state for a SYN-ACK */
304 static inline void TCP_ECN_send_synack(const struct tcp_sock *tp, struct sk_buff *skb)
306 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
307 if (!(tp->ecn_flags & TCP_ECN_OK))
308 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
311 /* Packet ECN state for a SYN. */
312 static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
314 struct tcp_sock *tp = tcp_sk(sk);
317 if (sysctl_tcp_ecn == 1) {
318 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
319 tp->ecn_flags = TCP_ECN_OK;
323 static __inline__ void
324 TCP_ECN_make_synack(const struct request_sock *req, struct tcphdr *th)
326 if (inet_rsk(req)->ecn_ok)
330 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
333 static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
336 struct tcp_sock *tp = tcp_sk(sk);
338 if (tp->ecn_flags & TCP_ECN_OK) {
339 /* Not-retransmitted data segment: set ECT and inject CWR. */
340 if (skb->len != tcp_header_len &&
341 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
343 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
344 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
345 tcp_hdr(skb)->cwr = 1;
346 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
349 /* ACK or retransmitted segment: clear ECT|CE */
350 INET_ECN_dontxmit(sk);
352 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
353 tcp_hdr(skb)->ece = 1;
357 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
358 * auto increment end seqno.
360 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
362 skb->ip_summed = CHECKSUM_PARTIAL;
365 TCP_SKB_CB(skb)->tcp_flags = flags;
366 TCP_SKB_CB(skb)->sacked = 0;
368 skb_shinfo(skb)->gso_segs = 1;
369 skb_shinfo(skb)->gso_size = 0;
370 skb_shinfo(skb)->gso_type = 0;
372 TCP_SKB_CB(skb)->seq = seq;
373 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
375 TCP_SKB_CB(skb)->end_seq = seq;
378 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
380 return tp->snd_una != tp->snd_up;
383 #define OPTION_SACK_ADVERTISE (1 << 0)
384 #define OPTION_TS (1 << 1)
385 #define OPTION_MD5 (1 << 2)
386 #define OPTION_WSCALE (1 << 3)
387 #define OPTION_COOKIE_EXTENSION (1 << 4)
388 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
390 struct tcp_out_options {
391 u16 options; /* bit field of OPTION_* */
392 u16 mss; /* 0 to disable */
393 u8 ws; /* window scale, 0 to disable */
394 u8 num_sack_blocks; /* number of SACK blocks to include */
395 u8 hash_size; /* bytes in hash_location */
396 __u8 *hash_location; /* temporary pointer, overloaded */
397 __u32 tsval, tsecr; /* need to include OPTION_TS */
398 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
401 /* The sysctl int routines are generic, so check consistency here.
403 static u8 tcp_cookie_size_check(u8 desired)
408 /* previously specified */
411 cookie_size = ACCESS_ONCE(sysctl_tcp_cookie_size);
412 if (cookie_size <= 0)
413 /* no default specified */
416 if (cookie_size <= TCP_COOKIE_MIN)
417 /* value too small, specify minimum */
418 return TCP_COOKIE_MIN;
420 if (cookie_size >= TCP_COOKIE_MAX)
421 /* value too large, specify maximum */
422 return TCP_COOKIE_MAX;
425 /* 8-bit multiple, illegal, fix it */
428 return (u8)cookie_size;
431 /* Write previously computed TCP options to the packet.
433 * Beware: Something in the Internet is very sensitive to the ordering of
434 * TCP options, we learned this through the hard way, so be careful here.
435 * Luckily we can at least blame others for their non-compliance but from
436 * inter-operatibility perspective it seems that we're somewhat stuck with
437 * the ordering which we have been using if we want to keep working with
438 * those broken things (not that it currently hurts anybody as there isn't
439 * particular reason why the ordering would need to be changed).
441 * At least SACK_PERM as the first option is known to lead to a disaster
442 * (but it may well be that other scenarios fail similarly).
444 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
445 struct tcp_out_options *opts)
447 u16 options = opts->options; /* mungable copy */
449 /* Having both authentication and cookies for security is redundant,
450 * and there's certainly not enough room. Instead, the cookie-less
451 * extension variant is proposed.
453 * Consider the pessimal case with authentication. The options
455 * COOKIE|MD5(20) + MSS(4) + SACK|TS(12) + WSCALE(4) == 40
457 if (unlikely(OPTION_MD5 & options)) {
458 if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
459 *ptr++ = htonl((TCPOPT_COOKIE << 24) |
460 (TCPOLEN_COOKIE_BASE << 16) |
461 (TCPOPT_MD5SIG << 8) |
464 *ptr++ = htonl((TCPOPT_NOP << 24) |
466 (TCPOPT_MD5SIG << 8) |
469 options &= ~OPTION_COOKIE_EXTENSION;
470 /* overload cookie hash location */
471 opts->hash_location = (__u8 *)ptr;
475 if (unlikely(opts->mss)) {
476 *ptr++ = htonl((TCPOPT_MSS << 24) |
477 (TCPOLEN_MSS << 16) |
481 if (likely(OPTION_TS & options)) {
482 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
483 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
484 (TCPOLEN_SACK_PERM << 16) |
485 (TCPOPT_TIMESTAMP << 8) |
487 options &= ~OPTION_SACK_ADVERTISE;
489 *ptr++ = htonl((TCPOPT_NOP << 24) |
491 (TCPOPT_TIMESTAMP << 8) |
494 *ptr++ = htonl(opts->tsval);
495 *ptr++ = htonl(opts->tsecr);
498 /* Specification requires after timestamp, so do it now.
500 * Consider the pessimal case without authentication. The options
502 * MSS(4) + SACK|TS(12) + COOKIE(20) + WSCALE(4) == 40
504 if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
505 __u8 *cookie_copy = opts->hash_location;
506 u8 cookie_size = opts->hash_size;
508 /* 8-bit multiple handled in tcp_cookie_size_check() above,
511 if (0x2 & cookie_size) {
512 __u8 *p = (__u8 *)ptr;
514 /* 16-bit multiple */
515 *p++ = TCPOPT_COOKIE;
516 *p++ = TCPOLEN_COOKIE_BASE + cookie_size;
517 *p++ = *cookie_copy++;
518 *p++ = *cookie_copy++;
522 /* 32-bit multiple */
523 *ptr++ = htonl(((TCPOPT_NOP << 24) |
525 (TCPOPT_COOKIE << 8) |
526 TCPOLEN_COOKIE_BASE) +
530 if (cookie_size > 0) {
531 memcpy(ptr, cookie_copy, cookie_size);
532 ptr += (cookie_size / 4);
536 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
537 *ptr++ = htonl((TCPOPT_NOP << 24) |
539 (TCPOPT_SACK_PERM << 8) |
543 if (unlikely(OPTION_WSCALE & options)) {
544 *ptr++ = htonl((TCPOPT_NOP << 24) |
545 (TCPOPT_WINDOW << 16) |
546 (TCPOLEN_WINDOW << 8) |
550 if (unlikely(opts->num_sack_blocks)) {
551 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
552 tp->duplicate_sack : tp->selective_acks;
555 *ptr++ = htonl((TCPOPT_NOP << 24) |
558 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
559 TCPOLEN_SACK_PERBLOCK)));
561 for (this_sack = 0; this_sack < opts->num_sack_blocks;
563 *ptr++ = htonl(sp[this_sack].start_seq);
564 *ptr++ = htonl(sp[this_sack].end_seq);
567 tp->rx_opt.dsack = 0;
570 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
571 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
573 *ptr++ = htonl((TCPOPT_EXP << 24) |
574 ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
575 TCPOPT_FASTOPEN_MAGIC);
577 memcpy(ptr, foc->val, foc->len);
578 if ((foc->len & 3) == 2) {
579 u8 *align = ((u8 *)ptr) + foc->len;
580 align[0] = align[1] = TCPOPT_NOP;
582 ptr += (foc->len + 3) >> 2;
586 /* Compute TCP options for SYN packets. This is not the final
587 * network wire format yet.
589 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
590 struct tcp_out_options *opts,
591 struct tcp_md5sig_key **md5)
593 struct tcp_sock *tp = tcp_sk(sk);
594 struct tcp_cookie_values *cvp = tp->cookie_values;
595 unsigned int remaining = MAX_TCP_OPTION_SPACE;
596 u8 cookie_size = (!tp->rx_opt.cookie_out_never && cvp != NULL) ?
597 tcp_cookie_size_check(cvp->cookie_desired) :
599 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
601 #ifdef CONFIG_TCP_MD5SIG
602 *md5 = tp->af_specific->md5_lookup(sk, sk);
604 opts->options |= OPTION_MD5;
605 remaining -= TCPOLEN_MD5SIG_ALIGNED;
611 /* We always get an MSS option. The option bytes which will be seen in
612 * normal data packets should timestamps be used, must be in the MSS
613 * advertised. But we subtract them from tp->mss_cache so that
614 * calculations in tcp_sendmsg are simpler etc. So account for this
615 * fact here if necessary. If we don't do this correctly, as a
616 * receiver we won't recognize data packets as being full sized when we
617 * should, and thus we won't abide by the delayed ACK rules correctly.
618 * SACKs don't matter, we never delay an ACK when we have any of those
620 opts->mss = tcp_advertise_mss(sk);
621 remaining -= TCPOLEN_MSS_ALIGNED;
623 if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
624 opts->options |= OPTION_TS;
625 opts->tsval = TCP_SKB_CB(skb)->when;
626 opts->tsecr = tp->rx_opt.ts_recent;
627 remaining -= TCPOLEN_TSTAMP_ALIGNED;
629 if (likely(sysctl_tcp_window_scaling)) {
630 opts->ws = tp->rx_opt.rcv_wscale;
631 opts->options |= OPTION_WSCALE;
632 remaining -= TCPOLEN_WSCALE_ALIGNED;
634 if (likely(sysctl_tcp_sack)) {
635 opts->options |= OPTION_SACK_ADVERTISE;
636 if (unlikely(!(OPTION_TS & opts->options)))
637 remaining -= TCPOLEN_SACKPERM_ALIGNED;
640 if (fastopen && fastopen->cookie.len >= 0) {
641 u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
642 need = (need + 3) & ~3U; /* Align to 32 bits */
643 if (remaining >= need) {
644 opts->options |= OPTION_FAST_OPEN_COOKIE;
645 opts->fastopen_cookie = &fastopen->cookie;
647 tp->syn_fastopen = 1;
650 /* Note that timestamps are required by the specification.
652 * Odd numbers of bytes are prohibited by the specification, ensuring
653 * that the cookie is 16-bit aligned, and the resulting cookie pair is
657 (OPTION_TS & opts->options) &&
659 int need = TCPOLEN_COOKIE_BASE + cookie_size;
662 /* 32-bit multiple */
663 need += 2; /* NOPs */
665 if (need > remaining) {
666 /* try shrinking cookie to fit */
671 while (need > remaining && TCP_COOKIE_MIN <= cookie_size) {
675 if (TCP_COOKIE_MIN <= cookie_size) {
676 opts->options |= OPTION_COOKIE_EXTENSION;
677 opts->hash_location = (__u8 *)&cvp->cookie_pair[0];
678 opts->hash_size = cookie_size;
680 /* Remember for future incarnations. */
681 cvp->cookie_desired = cookie_size;
683 if (cvp->cookie_desired != cvp->cookie_pair_size) {
684 /* Currently use random bytes as a nonce,
685 * assuming these are completely unpredictable
686 * by hostile users of the same system.
688 get_random_bytes(&cvp->cookie_pair[0],
690 cvp->cookie_pair_size = cookie_size;
696 return MAX_TCP_OPTION_SPACE - remaining;
699 /* Set up TCP options for SYN-ACKs. */
700 static unsigned int tcp_synack_options(struct sock *sk,
701 struct request_sock *req,
702 unsigned int mss, struct sk_buff *skb,
703 struct tcp_out_options *opts,
704 struct tcp_md5sig_key **md5,
705 struct tcp_extend_values *xvp)
707 struct inet_request_sock *ireq = inet_rsk(req);
708 unsigned int remaining = MAX_TCP_OPTION_SPACE;
709 u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
713 #ifdef CONFIG_TCP_MD5SIG
714 *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
716 opts->options |= OPTION_MD5;
717 remaining -= TCPOLEN_MD5SIG_ALIGNED;
719 /* We can't fit any SACK blocks in a packet with MD5 + TS
720 * options. There was discussion about disabling SACK
721 * rather than TS in order to fit in better with old,
722 * buggy kernels, but that was deemed to be unnecessary.
724 ireq->tstamp_ok &= !ireq->sack_ok;
730 /* We always send an MSS option. */
732 remaining -= TCPOLEN_MSS_ALIGNED;
734 if (likely(ireq->wscale_ok)) {
735 opts->ws = ireq->rcv_wscale;
736 opts->options |= OPTION_WSCALE;
737 remaining -= TCPOLEN_WSCALE_ALIGNED;
739 if (likely(ireq->tstamp_ok)) {
740 opts->options |= OPTION_TS;
741 opts->tsval = TCP_SKB_CB(skb)->when;
742 opts->tsecr = req->ts_recent;
743 remaining -= TCPOLEN_TSTAMP_ALIGNED;
745 if (likely(ireq->sack_ok)) {
746 opts->options |= OPTION_SACK_ADVERTISE;
747 if (unlikely(!ireq->tstamp_ok))
748 remaining -= TCPOLEN_SACKPERM_ALIGNED;
751 /* Similar rationale to tcp_syn_options() applies here, too.
752 * If the <SYN> options fit, the same options should fit now!
756 cookie_plus > TCPOLEN_COOKIE_BASE) {
757 int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */
760 /* 32-bit multiple */
761 need += 2; /* NOPs */
763 if (need <= remaining) {
764 opts->options |= OPTION_COOKIE_EXTENSION;
765 opts->hash_size = cookie_plus - TCPOLEN_COOKIE_BASE;
768 /* There's no error return, so flag it. */
769 xvp->cookie_out_never = 1; /* true */
773 return MAX_TCP_OPTION_SPACE - remaining;
776 /* Compute TCP options for ESTABLISHED sockets. This is not the
777 * final wire format yet.
779 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
780 struct tcp_out_options *opts,
781 struct tcp_md5sig_key **md5)
783 struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
784 struct tcp_sock *tp = tcp_sk(sk);
785 unsigned int size = 0;
786 unsigned int eff_sacks;
788 #ifdef CONFIG_TCP_MD5SIG
789 *md5 = tp->af_specific->md5_lookup(sk, sk);
790 if (unlikely(*md5)) {
791 opts->options |= OPTION_MD5;
792 size += TCPOLEN_MD5SIG_ALIGNED;
798 if (likely(tp->rx_opt.tstamp_ok)) {
799 opts->options |= OPTION_TS;
800 opts->tsval = tcb ? tcb->when : 0;
801 opts->tsecr = tp->rx_opt.ts_recent;
802 size += TCPOLEN_TSTAMP_ALIGNED;
805 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
806 if (unlikely(eff_sacks)) {
807 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
808 opts->num_sack_blocks =
809 min_t(unsigned int, eff_sacks,
810 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
811 TCPOLEN_SACK_PERBLOCK);
812 size += TCPOLEN_SACK_BASE_ALIGNED +
813 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
820 /* TCP SMALL QUEUES (TSQ)
822 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
823 * to reduce RTT and bufferbloat.
824 * We do this using a special skb destructor (tcp_wfree).
826 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
827 * needs to be reallocated in a driver.
828 * The invariant being skb->truesize substracted from sk->sk_wmem_alloc
830 * Since transmit from skb destructor is forbidden, we use a tasklet
831 * to process all sockets that eventually need to send more skbs.
832 * We use one tasklet per cpu, with its own queue of sockets.
835 struct tasklet_struct tasklet;
836 struct list_head head; /* queue of tcp sockets */
838 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
840 static void tcp_tsq_handler(struct sock *sk)
842 if ((1 << sk->sk_state) &
843 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
844 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
845 tcp_write_xmit(sk, tcp_current_mss(sk), 0, 0, GFP_ATOMIC);
848 * One tasklest per cpu tries to send more skbs.
849 * We run in tasklet context but need to disable irqs when
850 * transfering tsq->head because tcp_wfree() might
851 * interrupt us (non NAPI drivers)
853 static void tcp_tasklet_func(unsigned long data)
855 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
858 struct list_head *q, *n;
862 local_irq_save(flags);
863 list_splice_init(&tsq->head, &list);
864 local_irq_restore(flags);
866 list_for_each_safe(q, n, &list) {
867 tp = list_entry(q, struct tcp_sock, tsq_node);
868 list_del(&tp->tsq_node);
870 sk = (struct sock *)tp;
873 if (!sock_owned_by_user(sk)) {
876 /* defer the work to tcp_release_cb() */
877 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
881 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
886 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
887 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
888 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
889 (1UL << TCP_MTU_REDUCED_DEFERRED))
891 * tcp_release_cb - tcp release_sock() callback
894 * called from release_sock() to perform protocol dependent
895 * actions before socket release.
897 void tcp_release_cb(struct sock *sk)
899 struct tcp_sock *tp = tcp_sk(sk);
900 unsigned long flags, nflags;
902 /* perform an atomic operation only if at least one flag is set */
904 flags = tp->tsq_flags;
905 if (!(flags & TCP_DEFERRED_ALL))
907 nflags = flags & ~TCP_DEFERRED_ALL;
908 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
910 if (flags & (1UL << TCP_TSQ_DEFERRED))
913 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED))
914 tcp_write_timer_handler(sk);
916 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED))
917 tcp_delack_timer_handler(sk);
919 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED))
920 sk->sk_prot->mtu_reduced(sk);
922 EXPORT_SYMBOL(tcp_release_cb);
924 void __init tcp_tasklet_init(void)
928 for_each_possible_cpu(i) {
929 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
931 INIT_LIST_HEAD(&tsq->head);
932 tasklet_init(&tsq->tasklet,
939 * Write buffer destructor automatically called from kfree_skb.
940 * We cant xmit new skbs from this context, as we might already
943 void tcp_wfree(struct sk_buff *skb)
945 struct sock *sk = skb->sk;
946 struct tcp_sock *tp = tcp_sk(sk);
948 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
949 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
951 struct tsq_tasklet *tsq;
953 /* Keep a ref on socket.
954 * This last ref will be released in tcp_tasklet_func()
956 atomic_sub(skb->truesize - 1, &sk->sk_wmem_alloc);
958 /* queue this socket to tasklet queue */
959 local_irq_save(flags);
960 tsq = &__get_cpu_var(tsq_tasklet);
961 list_add(&tp->tsq_node, &tsq->head);
962 tasklet_schedule(&tsq->tasklet);
963 local_irq_restore(flags);
969 /* This routine actually transmits TCP packets queued in by
970 * tcp_do_sendmsg(). This is used by both the initial
971 * transmission and possible later retransmissions.
972 * All SKB's seen here are completely headerless. It is our
973 * job to build the TCP header, and pass the packet down to
974 * IP so it can do the same plus pass the packet off to the
977 * We are working here with either a clone of the original
978 * SKB, or a fresh unique copy made by the retransmit engine.
980 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
983 const struct inet_connection_sock *icsk = inet_csk(sk);
984 struct inet_sock *inet;
986 struct tcp_skb_cb *tcb;
987 struct tcp_out_options opts;
988 unsigned int tcp_options_size, tcp_header_size;
989 struct tcp_md5sig_key *md5;
993 BUG_ON(!skb || !tcp_skb_pcount(skb));
995 /* If congestion control is doing timestamping, we must
996 * take such a timestamp before we potentially clone/copy.
998 if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
999 __net_timestamp(skb);
1001 if (likely(clone_it)) {
1002 if (unlikely(skb_cloned(skb)))
1003 skb = pskb_copy(skb, gfp_mask);
1005 skb = skb_clone(skb, gfp_mask);
1012 tcb = TCP_SKB_CB(skb);
1013 memset(&opts, 0, sizeof(opts));
1015 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
1016 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
1018 tcp_options_size = tcp_established_options(sk, skb, &opts,
1020 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
1022 if (tcp_packets_in_flight(tp) == 0) {
1023 tcp_ca_event(sk, CA_EVENT_TX_START);
1028 skb_push(skb, tcp_header_size);
1029 skb_reset_transport_header(skb);
1033 skb->destructor = (sysctl_tcp_limit_output_bytes > 0) ?
1034 tcp_wfree : sock_wfree;
1035 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
1037 /* Build TCP header and checksum it. */
1039 th->source = inet->inet_sport;
1040 th->dest = inet->inet_dport;
1041 th->seq = htonl(tcb->seq);
1042 th->ack_seq = htonl(tp->rcv_nxt);
1043 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
1046 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
1047 /* RFC1323: The window in SYN & SYN/ACK segments
1050 th->window = htons(min(tp->rcv_wnd, 65535U));
1052 th->window = htons(tcp_select_window(sk));
1057 /* The urg_mode check is necessary during a below snd_una win probe */
1058 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
1059 if (before(tp->snd_up, tcb->seq + 0x10000)) {
1060 th->urg_ptr = htons(tp->snd_up - tcb->seq);
1062 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
1063 th->urg_ptr = htons(0xFFFF);
1068 tcp_options_write((__be32 *)(th + 1), tp, &opts);
1069 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
1070 TCP_ECN_send(sk, skb, tcp_header_size);
1072 #ifdef CONFIG_TCP_MD5SIG
1073 /* Calculate the MD5 hash, as we have all we need now */
1075 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1076 tp->af_specific->calc_md5_hash(opts.hash_location,
1077 md5, sk, NULL, skb);
1081 icsk->icsk_af_ops->send_check(sk, skb);
1083 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1084 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1086 if (skb->len != tcp_header_size)
1087 tcp_event_data_sent(tp, sk);
1089 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1090 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1091 tcp_skb_pcount(skb));
1093 err = icsk->icsk_af_ops->queue_xmit(skb, &inet->cork.fl);
1094 if (likely(err <= 0))
1097 tcp_enter_cwr(sk, 1);
1099 return net_xmit_eval(err);
1102 /* This routine just queues the buffer for sending.
1104 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1105 * otherwise socket can stall.
1107 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1109 struct tcp_sock *tp = tcp_sk(sk);
1111 /* Advance write_seq and place onto the write_queue. */
1112 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1113 skb_header_release(skb);
1114 tcp_add_write_queue_tail(sk, skb);
1115 sk->sk_wmem_queued += skb->truesize;
1116 sk_mem_charge(sk, skb->truesize);
1119 /* Initialize TSO segments for a packet. */
1120 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
1121 unsigned int mss_now)
1123 if (skb->len <= mss_now || !sk_can_gso(sk) ||
1124 skb->ip_summed == CHECKSUM_NONE) {
1125 /* Avoid the costly divide in the normal
1128 skb_shinfo(skb)->gso_segs = 1;
1129 skb_shinfo(skb)->gso_size = 0;
1130 skb_shinfo(skb)->gso_type = 0;
1132 skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
1133 skb_shinfo(skb)->gso_size = mss_now;
1134 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1138 /* When a modification to fackets out becomes necessary, we need to check
1139 * skb is counted to fackets_out or not.
1141 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1144 struct tcp_sock *tp = tcp_sk(sk);
1146 if (!tp->sacked_out || tcp_is_reno(tp))
1149 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1150 tp->fackets_out -= decr;
1153 /* Pcount in the middle of the write queue got changed, we need to do various
1154 * tweaks to fix counters
1156 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1158 struct tcp_sock *tp = tcp_sk(sk);
1160 tp->packets_out -= decr;
1162 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1163 tp->sacked_out -= decr;
1164 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1165 tp->retrans_out -= decr;
1166 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1167 tp->lost_out -= decr;
1169 /* Reno case is special. Sigh... */
1170 if (tcp_is_reno(tp) && decr > 0)
1171 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1173 tcp_adjust_fackets_out(sk, skb, decr);
1175 if (tp->lost_skb_hint &&
1176 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1177 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1178 tp->lost_cnt_hint -= decr;
1180 tcp_verify_left_out(tp);
1183 /* Function to create two new TCP segments. Shrinks the given segment
1184 * to the specified size and appends a new segment with the rest of the
1185 * packet to the list. This won't be called frequently, I hope.
1186 * Remember, these are still headerless SKBs at this point.
1188 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1189 unsigned int mss_now)
1191 struct tcp_sock *tp = tcp_sk(sk);
1192 struct sk_buff *buff;
1193 int nsize, old_factor;
1197 if (WARN_ON(len > skb->len))
1200 nsize = skb_headlen(skb) - len;
1204 if (skb_cloned(skb) &&
1205 skb_is_nonlinear(skb) &&
1206 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
1209 /* Get a new skb... force flag on. */
1210 buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
1212 return -ENOMEM; /* We'll just try again later. */
1214 sk->sk_wmem_queued += buff->truesize;
1215 sk_mem_charge(sk, buff->truesize);
1216 nlen = skb->len - len - nsize;
1217 buff->truesize += nlen;
1218 skb->truesize -= nlen;
1220 /* Correct the sequence numbers. */
1221 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1222 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1223 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1225 /* PSH and FIN should only be set in the second packet. */
1226 flags = TCP_SKB_CB(skb)->tcp_flags;
1227 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1228 TCP_SKB_CB(buff)->tcp_flags = flags;
1229 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1231 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1232 /* Copy and checksum data tail into the new buffer. */
1233 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1234 skb_put(buff, nsize),
1239 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1241 skb->ip_summed = CHECKSUM_PARTIAL;
1242 skb_split(skb, buff, len);
1245 buff->ip_summed = skb->ip_summed;
1247 /* Looks stupid, but our code really uses when of
1248 * skbs, which it never sent before. --ANK
1250 TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
1251 buff->tstamp = skb->tstamp;
1253 old_factor = tcp_skb_pcount(skb);
1255 /* Fix up tso_factor for both original and new SKB. */
1256 tcp_set_skb_tso_segs(sk, skb, mss_now);
1257 tcp_set_skb_tso_segs(sk, buff, mss_now);
1259 /* If this packet has been sent out already, we must
1260 * adjust the various packet counters.
1262 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1263 int diff = old_factor - tcp_skb_pcount(skb) -
1264 tcp_skb_pcount(buff);
1267 tcp_adjust_pcount(sk, skb, diff);
1270 /* Link BUFF into the send queue. */
1271 skb_header_release(buff);
1272 tcp_insert_write_queue_after(skb, buff, sk);
1277 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1278 * eventually). The difference is that pulled data not copied, but
1279 * immediately discarded.
1281 static void __pskb_trim_head(struct sk_buff *skb, int len)
1285 eat = min_t(int, len, skb_headlen(skb));
1287 __skb_pull(skb, eat);
1288 skb->avail_size -= eat;
1295 for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
1296 int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
1299 skb_frag_unref(skb, i);
1302 skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
1304 skb_shinfo(skb)->frags[k].page_offset += eat;
1305 skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
1311 skb_shinfo(skb)->nr_frags = k;
1313 skb_reset_tail_pointer(skb);
1314 skb->data_len -= len;
1315 skb->len = skb->data_len;
1318 /* Remove acked data from a packet in the transmit queue. */
1319 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1321 if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
1324 __pskb_trim_head(skb, len);
1326 TCP_SKB_CB(skb)->seq += len;
1327 skb->ip_summed = CHECKSUM_PARTIAL;
1329 skb->truesize -= len;
1330 sk->sk_wmem_queued -= len;
1331 sk_mem_uncharge(sk, len);
1332 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1334 /* Any change of skb->len requires recalculation of tso factor. */
1335 if (tcp_skb_pcount(skb) > 1)
1336 tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
1341 /* Calculate MSS. Not accounting for SACKs here. */
1342 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1344 const struct tcp_sock *tp = tcp_sk(sk);
1345 const struct inet_connection_sock *icsk = inet_csk(sk);
1348 /* Calculate base mss without TCP options:
1349 It is MMS_S - sizeof(tcphdr) of rfc1122
1351 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1353 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1354 if (icsk->icsk_af_ops->net_frag_header_len) {
1355 const struct dst_entry *dst = __sk_dst_get(sk);
1357 if (dst && dst_allfrag(dst))
1358 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1361 /* Clamp it (mss_clamp does not include tcp options) */
1362 if (mss_now > tp->rx_opt.mss_clamp)
1363 mss_now = tp->rx_opt.mss_clamp;
1365 /* Now subtract optional transport overhead */
1366 mss_now -= icsk->icsk_ext_hdr_len;
1368 /* Then reserve room for full set of TCP options and 8 bytes of data */
1372 /* Now subtract TCP options size, not including SACKs */
1373 mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
1378 /* Inverse of above */
1379 int tcp_mss_to_mtu(struct sock *sk, int mss)
1381 const struct tcp_sock *tp = tcp_sk(sk);
1382 const struct inet_connection_sock *icsk = inet_csk(sk);
1386 tp->tcp_header_len +
1387 icsk->icsk_ext_hdr_len +
1388 icsk->icsk_af_ops->net_header_len;
1390 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1391 if (icsk->icsk_af_ops->net_frag_header_len) {
1392 const struct dst_entry *dst = __sk_dst_get(sk);
1394 if (dst && dst_allfrag(dst))
1395 mtu += icsk->icsk_af_ops->net_frag_header_len;
1400 /* MTU probing init per socket */
1401 void tcp_mtup_init(struct sock *sk)
1403 struct tcp_sock *tp = tcp_sk(sk);
1404 struct inet_connection_sock *icsk = inet_csk(sk);
1406 icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
1407 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1408 icsk->icsk_af_ops->net_header_len;
1409 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
1410 icsk->icsk_mtup.probe_size = 0;
1412 EXPORT_SYMBOL(tcp_mtup_init);
1414 /* This function synchronize snd mss to current pmtu/exthdr set.
1416 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1417 for TCP options, but includes only bare TCP header.
1419 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1420 It is minimum of user_mss and mss received with SYN.
1421 It also does not include TCP options.
1423 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1425 tp->mss_cache is current effective sending mss, including
1426 all tcp options except for SACKs. It is evaluated,
1427 taking into account current pmtu, but never exceeds
1428 tp->rx_opt.mss_clamp.
1430 NOTE1. rfc1122 clearly states that advertised MSS
1431 DOES NOT include either tcp or ip options.
1433 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1434 are READ ONLY outside this function. --ANK (980731)
1436 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1438 struct tcp_sock *tp = tcp_sk(sk);
1439 struct inet_connection_sock *icsk = inet_csk(sk);
1442 if (icsk->icsk_mtup.search_high > pmtu)
1443 icsk->icsk_mtup.search_high = pmtu;
1445 mss_now = tcp_mtu_to_mss(sk, pmtu);
1446 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1448 /* And store cached results */
1449 icsk->icsk_pmtu_cookie = pmtu;
1450 if (icsk->icsk_mtup.enabled)
1451 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1452 tp->mss_cache = mss_now;
1456 EXPORT_SYMBOL(tcp_sync_mss);
1458 /* Compute the current effective MSS, taking SACKs and IP options,
1459 * and even PMTU discovery events into account.
1461 unsigned int tcp_current_mss(struct sock *sk)
1463 const struct tcp_sock *tp = tcp_sk(sk);
1464 const struct dst_entry *dst = __sk_dst_get(sk);
1466 unsigned int header_len;
1467 struct tcp_out_options opts;
1468 struct tcp_md5sig_key *md5;
1470 mss_now = tp->mss_cache;
1473 u32 mtu = dst_mtu(dst);
1474 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1475 mss_now = tcp_sync_mss(sk, mtu);
1478 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1479 sizeof(struct tcphdr);
1480 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1481 * some common options. If this is an odd packet (because we have SACK
1482 * blocks etc) then our calculated header_len will be different, and
1483 * we have to adjust mss_now correspondingly */
1484 if (header_len != tp->tcp_header_len) {
1485 int delta = (int) header_len - tp->tcp_header_len;
1492 /* Congestion window validation. (RFC2861) */
1493 static void tcp_cwnd_validate(struct sock *sk)
1495 struct tcp_sock *tp = tcp_sk(sk);
1497 if (tp->packets_out >= tp->snd_cwnd) {
1498 /* Network is feed fully. */
1499 tp->snd_cwnd_used = 0;
1500 tp->snd_cwnd_stamp = tcp_time_stamp;
1502 /* Network starves. */
1503 if (tp->packets_out > tp->snd_cwnd_used)
1504 tp->snd_cwnd_used = tp->packets_out;
1506 if (sysctl_tcp_slow_start_after_idle &&
1507 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1508 tcp_cwnd_application_limited(sk);
1512 /* Returns the portion of skb which can be sent right away without
1513 * introducing MSS oddities to segment boundaries. In rare cases where
1514 * mss_now != mss_cache, we will request caller to create a small skb
1515 * per input skb which could be mostly avoided here (if desired).
1517 * We explicitly want to create a request for splitting write queue tail
1518 * to a small skb for Nagle purposes while avoiding unnecessary modulos,
1519 * thus all the complexity (cwnd_len is always MSS multiple which we
1520 * return whenever allowed by the other factors). Basically we need the
1521 * modulo only when the receiver window alone is the limiting factor or
1522 * when we would be allowed to send the split-due-to-Nagle skb fully.
1524 static unsigned int tcp_mss_split_point(const struct sock *sk, const struct sk_buff *skb,
1525 unsigned int mss_now, unsigned int cwnd)
1527 const struct tcp_sock *tp = tcp_sk(sk);
1528 u32 needed, window, cwnd_len;
1530 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1531 cwnd_len = mss_now * cwnd;
1533 if (likely(cwnd_len <= window && skb != tcp_write_queue_tail(sk)))
1536 needed = min(skb->len, window);
1538 if (cwnd_len <= needed)
1541 return needed - needed % mss_now;
1544 /* Can at least one segment of SKB be sent right now, according to the
1545 * congestion window rules? If so, return how many segments are allowed.
1547 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1548 const struct sk_buff *skb)
1550 u32 in_flight, cwnd;
1552 /* Don't be strict about the congestion window for the final FIN. */
1553 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1554 tcp_skb_pcount(skb) == 1)
1557 in_flight = tcp_packets_in_flight(tp);
1558 cwnd = tp->snd_cwnd;
1559 if (in_flight < cwnd)
1560 return (cwnd - in_flight);
1565 /* Initialize TSO state of a skb.
1566 * This must be invoked the first time we consider transmitting
1567 * SKB onto the wire.
1569 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
1570 unsigned int mss_now)
1572 int tso_segs = tcp_skb_pcount(skb);
1574 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1575 tcp_set_skb_tso_segs(sk, skb, mss_now);
1576 tso_segs = tcp_skb_pcount(skb);
1581 /* Minshall's variant of the Nagle send check. */
1582 static inline bool tcp_minshall_check(const struct tcp_sock *tp)
1584 return after(tp->snd_sml, tp->snd_una) &&
1585 !after(tp->snd_sml, tp->snd_nxt);
1588 /* Return false, if packet can be sent now without violation Nagle's rules:
1589 * 1. It is full sized.
1590 * 2. Or it contains FIN. (already checked by caller)
1591 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1592 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1593 * With Minshall's modification: all sent small packets are ACKed.
1595 static inline bool tcp_nagle_check(const struct tcp_sock *tp,
1596 const struct sk_buff *skb,
1597 unsigned int mss_now, int nonagle)
1599 return skb->len < mss_now &&
1600 ((nonagle & TCP_NAGLE_CORK) ||
1601 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1604 /* Return true if the Nagle test allows this packet to be
1607 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1608 unsigned int cur_mss, int nonagle)
1610 /* Nagle rule does not apply to frames, which sit in the middle of the
1611 * write_queue (they have no chances to get new data).
1613 * This is implemented in the callers, where they modify the 'nonagle'
1614 * argument based upon the location of SKB in the send queue.
1616 if (nonagle & TCP_NAGLE_PUSH)
1619 /* Don't use the nagle rule for urgent data (or for the final FIN).
1620 * Nagle can be ignored during F-RTO too (see RFC4138).
1622 if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
1623 (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1626 if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
1632 /* Does at least the first segment of SKB fit into the send window? */
1633 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1634 const struct sk_buff *skb,
1635 unsigned int cur_mss)
1637 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1639 if (skb->len > cur_mss)
1640 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1642 return !after(end_seq, tcp_wnd_end(tp));
1645 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1646 * should be put on the wire right now. If so, it returns the number of
1647 * packets allowed by the congestion window.
1649 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1650 unsigned int cur_mss, int nonagle)
1652 const struct tcp_sock *tp = tcp_sk(sk);
1653 unsigned int cwnd_quota;
1655 tcp_init_tso_segs(sk, skb, cur_mss);
1657 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1660 cwnd_quota = tcp_cwnd_test(tp, skb);
1661 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1667 /* Test if sending is allowed right now. */
1668 bool tcp_may_send_now(struct sock *sk)
1670 const struct tcp_sock *tp = tcp_sk(sk);
1671 struct sk_buff *skb = tcp_send_head(sk);
1674 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1675 (tcp_skb_is_last(sk, skb) ?
1676 tp->nonagle : TCP_NAGLE_PUSH));
1679 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1680 * which is put after SKB on the list. It is very much like
1681 * tcp_fragment() except that it may make several kinds of assumptions
1682 * in order to speed up the splitting operation. In particular, we
1683 * know that all the data is in scatter-gather pages, and that the
1684 * packet has never been sent out before (and thus is not cloned).
1686 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1687 unsigned int mss_now, gfp_t gfp)
1689 struct sk_buff *buff;
1690 int nlen = skb->len - len;
1693 /* All of a TSO frame must be composed of paged data. */
1694 if (skb->len != skb->data_len)
1695 return tcp_fragment(sk, skb, len, mss_now);
1697 buff = sk_stream_alloc_skb(sk, 0, gfp);
1698 if (unlikely(buff == NULL))
1701 sk->sk_wmem_queued += buff->truesize;
1702 sk_mem_charge(sk, buff->truesize);
1703 buff->truesize += nlen;
1704 skb->truesize -= nlen;
1706 /* Correct the sequence numbers. */
1707 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1708 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1709 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1711 /* PSH and FIN should only be set in the second packet. */
1712 flags = TCP_SKB_CB(skb)->tcp_flags;
1713 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1714 TCP_SKB_CB(buff)->tcp_flags = flags;
1716 /* This packet was never sent out yet, so no SACK bits. */
1717 TCP_SKB_CB(buff)->sacked = 0;
1719 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1720 skb_split(skb, buff, len);
1722 /* Fix up tso_factor for both original and new SKB. */
1723 tcp_set_skb_tso_segs(sk, skb, mss_now);
1724 tcp_set_skb_tso_segs(sk, buff, mss_now);
1726 /* Link BUFF into the send queue. */
1727 skb_header_release(buff);
1728 tcp_insert_write_queue_after(skb, buff, sk);
1733 /* Try to defer sending, if possible, in order to minimize the amount
1734 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1736 * This algorithm is from John Heffner.
1738 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1740 struct tcp_sock *tp = tcp_sk(sk);
1741 const struct inet_connection_sock *icsk = inet_csk(sk);
1742 u32 send_win, cong_win, limit, in_flight;
1745 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1748 if (icsk->icsk_ca_state != TCP_CA_Open)
1751 /* Defer for less than two clock ticks. */
1752 if (tp->tso_deferred &&
1753 (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
1756 in_flight = tcp_packets_in_flight(tp);
1758 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1760 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1762 /* From in_flight test above, we know that cwnd > in_flight. */
1763 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1765 limit = min(send_win, cong_win);
1767 /* If a full-sized TSO skb can be sent, do it. */
1768 if (limit >= sk->sk_gso_max_size)
1771 /* Middle in queue won't get any more data, full sendable already? */
1772 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1775 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1777 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1779 /* If at least some fraction of a window is available,
1782 chunk /= win_divisor;
1786 /* Different approach, try not to defer past a single
1787 * ACK. Receiver should ACK every other full sized
1788 * frame, so if we have space for more than 3 frames
1791 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1795 /* Ok, it looks like it is advisable to defer. */
1796 tp->tso_deferred = 1 | (jiffies << 1);
1801 tp->tso_deferred = 0;
1805 /* Create a new MTU probe if we are ready.
1806 * MTU probe is regularly attempting to increase the path MTU by
1807 * deliberately sending larger packets. This discovers routing
1808 * changes resulting in larger path MTUs.
1810 * Returns 0 if we should wait to probe (no cwnd available),
1811 * 1 if a probe was sent,
1814 static int tcp_mtu_probe(struct sock *sk)
1816 struct tcp_sock *tp = tcp_sk(sk);
1817 struct inet_connection_sock *icsk = inet_csk(sk);
1818 struct sk_buff *skb, *nskb, *next;
1825 /* Not currently probing/verifying,
1827 * have enough cwnd, and
1828 * not SACKing (the variable headers throw things off) */
1829 if (!icsk->icsk_mtup.enabled ||
1830 icsk->icsk_mtup.probe_size ||
1831 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1832 tp->snd_cwnd < 11 ||
1833 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1836 /* Very simple search strategy: just double the MSS. */
1837 mss_now = tcp_current_mss(sk);
1838 probe_size = 2 * tp->mss_cache;
1839 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1840 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
1841 /* TODO: set timer for probe_converge_event */
1845 /* Have enough data in the send queue to probe? */
1846 if (tp->write_seq - tp->snd_nxt < size_needed)
1849 if (tp->snd_wnd < size_needed)
1851 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1854 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1855 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1856 if (!tcp_packets_in_flight(tp))
1862 /* We're allowed to probe. Build it now. */
1863 if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
1865 sk->sk_wmem_queued += nskb->truesize;
1866 sk_mem_charge(sk, nskb->truesize);
1868 skb = tcp_send_head(sk);
1870 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1871 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1872 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1873 TCP_SKB_CB(nskb)->sacked = 0;
1875 nskb->ip_summed = skb->ip_summed;
1877 tcp_insert_write_queue_before(nskb, skb, sk);
1880 tcp_for_write_queue_from_safe(skb, next, sk) {
1881 copy = min_t(int, skb->len, probe_size - len);
1882 if (nskb->ip_summed)
1883 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1885 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1886 skb_put(nskb, copy),
1889 if (skb->len <= copy) {
1890 /* We've eaten all the data from this skb.
1892 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1893 tcp_unlink_write_queue(skb, sk);
1894 sk_wmem_free_skb(sk, skb);
1896 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1897 ~(TCPHDR_FIN|TCPHDR_PSH);
1898 if (!skb_shinfo(skb)->nr_frags) {
1899 skb_pull(skb, copy);
1900 if (skb->ip_summed != CHECKSUM_PARTIAL)
1901 skb->csum = csum_partial(skb->data,
1904 __pskb_trim_head(skb, copy);
1905 tcp_set_skb_tso_segs(sk, skb, mss_now);
1907 TCP_SKB_CB(skb)->seq += copy;
1912 if (len >= probe_size)
1915 tcp_init_tso_segs(sk, nskb, nskb->len);
1917 /* We're ready to send. If this fails, the probe will
1918 * be resegmented into mss-sized pieces by tcp_write_xmit(). */
1919 TCP_SKB_CB(nskb)->when = tcp_time_stamp;
1920 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1921 /* Decrement cwnd here because we are sending
1922 * effectively two packets. */
1924 tcp_event_new_data_sent(sk, nskb);
1926 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1927 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1928 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1936 /* This routine writes packets to the network. It advances the
1937 * send_head. This happens as incoming acks open up the remote
1940 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1941 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1942 * account rare use of URG, this is not a big flaw.
1944 * Returns true, if no segments are in flight and we have queued segments,
1945 * but cannot send anything now because of SWS or another problem.
1947 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
1948 int push_one, gfp_t gfp)
1950 struct tcp_sock *tp = tcp_sk(sk);
1951 struct sk_buff *skb;
1952 unsigned int tso_segs, sent_pkts;
1959 /* Do MTU probing. */
1960 result = tcp_mtu_probe(sk);
1963 } else if (result > 0) {
1968 while ((skb = tcp_send_head(sk))) {
1972 tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1975 cwnd_quota = tcp_cwnd_test(tp, skb);
1979 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
1982 if (tso_segs == 1) {
1983 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
1984 (tcp_skb_is_last(sk, skb) ?
1985 nonagle : TCP_NAGLE_PUSH))))
1988 if (!push_one && tcp_tso_should_defer(sk, skb))
1992 /* TSQ : sk_wmem_alloc accounts skb truesize,
1993 * including skb overhead. But thats OK.
1995 if (atomic_read(&sk->sk_wmem_alloc) >= sysctl_tcp_limit_output_bytes) {
1996 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2000 if (tso_segs > 1 && !tcp_urg_mode(tp))
2001 limit = tcp_mss_split_point(sk, skb, mss_now,
2004 if (skb->len > limit &&
2005 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2008 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2010 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2013 /* Advance the send_head. This one is sent out.
2014 * This call will increment packets_out.
2016 tcp_event_new_data_sent(sk, skb);
2018 tcp_minshall_update(tp, mss_now, skb);
2019 sent_pkts += tcp_skb_pcount(skb);
2024 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)
2025 tp->prr_out += sent_pkts;
2027 if (likely(sent_pkts)) {
2028 tcp_cwnd_validate(sk);
2031 return !tp->packets_out && tcp_send_head(sk);
2034 /* Push out any pending frames which were held back due to
2035 * TCP_CORK or attempt at coalescing tiny packets.
2036 * The socket must be locked by the caller.
2038 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2041 /* If we are closed, the bytes will have to remain here.
2042 * In time closedown will finish, we empty the write queue and
2043 * all will be happy.
2045 if (unlikely(sk->sk_state == TCP_CLOSE))
2048 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2049 sk_gfp_atomic(sk, GFP_ATOMIC)))
2050 tcp_check_probe_timer(sk);
2053 /* Send _single_ skb sitting at the send head. This function requires
2054 * true push pending frames to setup probe timer etc.
2056 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2058 struct sk_buff *skb = tcp_send_head(sk);
2060 BUG_ON(!skb || skb->len < mss_now);
2062 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2065 /* This function returns the amount that we can raise the
2066 * usable window based on the following constraints
2068 * 1. The window can never be shrunk once it is offered (RFC 793)
2069 * 2. We limit memory per socket
2072 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2073 * RECV.NEXT + RCV.WIN fixed until:
2074 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2076 * i.e. don't raise the right edge of the window until you can raise
2077 * it at least MSS bytes.
2079 * Unfortunately, the recommended algorithm breaks header prediction,
2080 * since header prediction assumes th->window stays fixed.
2082 * Strictly speaking, keeping th->window fixed violates the receiver
2083 * side SWS prevention criteria. The problem is that under this rule
2084 * a stream of single byte packets will cause the right side of the
2085 * window to always advance by a single byte.
2087 * Of course, if the sender implements sender side SWS prevention
2088 * then this will not be a problem.
2090 * BSD seems to make the following compromise:
2092 * If the free space is less than the 1/4 of the maximum
2093 * space available and the free space is less than 1/2 mss,
2094 * then set the window to 0.
2095 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2096 * Otherwise, just prevent the window from shrinking
2097 * and from being larger than the largest representable value.
2099 * This prevents incremental opening of the window in the regime
2100 * where TCP is limited by the speed of the reader side taking
2101 * data out of the TCP receive queue. It does nothing about
2102 * those cases where the window is constrained on the sender side
2103 * because the pipeline is full.
2105 * BSD also seems to "accidentally" limit itself to windows that are a
2106 * multiple of MSS, at least until the free space gets quite small.
2107 * This would appear to be a side effect of the mbuf implementation.
2108 * Combining these two algorithms results in the observed behavior
2109 * of having a fixed window size at almost all times.
2111 * Below we obtain similar behavior by forcing the offered window to
2112 * a multiple of the mss when it is feasible to do so.
2114 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2115 * Regular options like TIMESTAMP are taken into account.
2117 u32 __tcp_select_window(struct sock *sk)
2119 struct inet_connection_sock *icsk = inet_csk(sk);
2120 struct tcp_sock *tp = tcp_sk(sk);
2121 /* MSS for the peer's data. Previous versions used mss_clamp
2122 * here. I don't know if the value based on our guesses
2123 * of peer's MSS is better for the performance. It's more correct
2124 * but may be worse for the performance because of rcv_mss
2125 * fluctuations. --SAW 1998/11/1
2127 int mss = icsk->icsk_ack.rcv_mss;
2128 int free_space = tcp_space(sk);
2129 int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
2132 if (mss > full_space)
2135 if (free_space < (full_space >> 1)) {
2136 icsk->icsk_ack.quick = 0;
2138 if (sk_under_memory_pressure(sk))
2139 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2142 if (free_space < mss)
2146 if (free_space > tp->rcv_ssthresh)
2147 free_space = tp->rcv_ssthresh;
2149 /* Don't do rounding if we are using window scaling, since the
2150 * scaled window will not line up with the MSS boundary anyway.
2152 window = tp->rcv_wnd;
2153 if (tp->rx_opt.rcv_wscale) {
2154 window = free_space;
2156 /* Advertise enough space so that it won't get scaled away.
2157 * Import case: prevent zero window announcement if
2158 * 1<<rcv_wscale > mss.
2160 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2161 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2162 << tp->rx_opt.rcv_wscale);
2164 /* Get the largest window that is a nice multiple of mss.
2165 * Window clamp already applied above.
2166 * If our current window offering is within 1 mss of the
2167 * free space we just keep it. This prevents the divide
2168 * and multiply from happening most of the time.
2169 * We also don't do any window rounding when the free space
2172 if (window <= free_space - mss || window > free_space)
2173 window = (free_space / mss) * mss;
2174 else if (mss == full_space &&
2175 free_space > window + (full_space >> 1))
2176 window = free_space;
2182 /* Collapses two adjacent SKB's during retransmission. */
2183 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2185 struct tcp_sock *tp = tcp_sk(sk);
2186 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2187 int skb_size, next_skb_size;
2189 skb_size = skb->len;
2190 next_skb_size = next_skb->len;
2192 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2194 tcp_highest_sack_combine(sk, next_skb, skb);
2196 tcp_unlink_write_queue(next_skb, sk);
2198 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2201 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2202 skb->ip_summed = CHECKSUM_PARTIAL;
2204 if (skb->ip_summed != CHECKSUM_PARTIAL)
2205 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2207 /* Update sequence range on original skb. */
2208 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2210 /* Merge over control information. This moves PSH/FIN etc. over */
2211 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2213 /* All done, get rid of second SKB and account for it so
2214 * packet counting does not break.
2216 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2218 /* changed transmit queue under us so clear hints */
2219 tcp_clear_retrans_hints_partial(tp);
2220 if (next_skb == tp->retransmit_skb_hint)
2221 tp->retransmit_skb_hint = skb;
2223 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2225 sk_wmem_free_skb(sk, next_skb);
2228 /* Check if coalescing SKBs is legal. */
2229 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2231 if (tcp_skb_pcount(skb) > 1)
2233 /* TODO: SACK collapsing could be used to remove this condition */
2234 if (skb_shinfo(skb)->nr_frags != 0)
2236 if (skb_cloned(skb))
2238 if (skb == tcp_send_head(sk))
2240 /* Some heurestics for collapsing over SACK'd could be invented */
2241 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2247 /* Collapse packets in the retransmit queue to make to create
2248 * less packets on the wire. This is only done on retransmission.
2250 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2253 struct tcp_sock *tp = tcp_sk(sk);
2254 struct sk_buff *skb = to, *tmp;
2257 if (!sysctl_tcp_retrans_collapse)
2259 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2262 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2263 if (!tcp_can_collapse(sk, skb))
2275 /* Punt if not enough space exists in the first SKB for
2276 * the data in the second
2278 if (skb->len > skb_availroom(to))
2281 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2284 tcp_collapse_retrans(sk, to);
2288 /* This retransmits one SKB. Policy decisions and retransmit queue
2289 * state updates are done by the caller. Returns non-zero if an
2290 * error occurred which prevented the send.
2292 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2294 struct tcp_sock *tp = tcp_sk(sk);
2295 struct inet_connection_sock *icsk = inet_csk(sk);
2296 unsigned int cur_mss;
2299 /* Inconslusive MTU probe */
2300 if (icsk->icsk_mtup.probe_size) {
2301 icsk->icsk_mtup.probe_size = 0;
2304 /* Do not sent more than we queued. 1/4 is reserved for possible
2305 * copying overhead: fragmentation, tunneling, mangling etc.
2307 if (atomic_read(&sk->sk_wmem_alloc) >
2308 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2311 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2312 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2314 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2318 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2319 return -EHOSTUNREACH; /* Routing failure or similar. */
2321 cur_mss = tcp_current_mss(sk);
2323 /* If receiver has shrunk his window, and skb is out of
2324 * new window, do not retransmit it. The exception is the
2325 * case, when window is shrunk to zero. In this case
2326 * our retransmit serves as a zero window probe.
2328 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2329 TCP_SKB_CB(skb)->seq != tp->snd_una)
2332 if (skb->len > cur_mss) {
2333 if (tcp_fragment(sk, skb, cur_mss, cur_mss))
2334 return -ENOMEM; /* We'll try again later. */
2336 int oldpcount = tcp_skb_pcount(skb);
2338 if (unlikely(oldpcount > 1)) {
2339 tcp_init_tso_segs(sk, skb, cur_mss);
2340 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2344 tcp_retrans_try_collapse(sk, skb, cur_mss);
2346 /* Some Solaris stacks overoptimize and ignore the FIN on a
2347 * retransmit when old data is attached. So strip it off
2348 * since it is cheap to do so and saves bytes on the network.
2351 (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
2352 tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
2353 if (!pskb_trim(skb, 0)) {
2354 /* Reuse, even though it does some unnecessary work */
2355 tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1,
2356 TCP_SKB_CB(skb)->tcp_flags);
2357 skb->ip_summed = CHECKSUM_NONE;
2361 /* Make a copy, if the first transmission SKB clone we made
2362 * is still in somebody's hands, else make a clone.
2364 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2366 /* make sure skb->data is aligned on arches that require it */
2367 if (unlikely(NET_IP_ALIGN && ((unsigned long)skb->data & 3))) {
2368 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2370 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2373 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2377 /* Update global TCP statistics. */
2378 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2380 tp->total_retrans++;
2382 #if FASTRETRANS_DEBUG > 0
2383 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2384 net_dbg_ratelimited("retrans_out leaked\n");
2387 if (!tp->retrans_out)
2388 tp->lost_retrans_low = tp->snd_nxt;
2389 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2390 tp->retrans_out += tcp_skb_pcount(skb);
2392 /* Save stamp of the first retransmit. */
2393 if (!tp->retrans_stamp)
2394 tp->retrans_stamp = TCP_SKB_CB(skb)->when;
2396 tp->undo_retrans += tcp_skb_pcount(skb);
2398 /* snd_nxt is stored to detect loss of retransmitted segment,
2399 * see tcp_input.c tcp_sacktag_write_queue().
2401 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2406 /* Check if we forward retransmits are possible in the current
2407 * window/congestion state.
2409 static bool tcp_can_forward_retransmit(struct sock *sk)
2411 const struct inet_connection_sock *icsk = inet_csk(sk);
2412 const struct tcp_sock *tp = tcp_sk(sk);
2414 /* Forward retransmissions are possible only during Recovery. */
2415 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2418 /* No forward retransmissions in Reno are possible. */
2419 if (tcp_is_reno(tp))
2422 /* Yeah, we have to make difficult choice between forward transmission
2423 * and retransmission... Both ways have their merits...
2425 * For now we do not retransmit anything, while we have some new
2426 * segments to send. In the other cases, follow rule 3 for
2427 * NextSeg() specified in RFC3517.
2430 if (tcp_may_send_now(sk))
2436 /* This gets called after a retransmit timeout, and the initially
2437 * retransmitted data is acknowledged. It tries to continue
2438 * resending the rest of the retransmit queue, until either
2439 * we've sent it all or the congestion window limit is reached.
2440 * If doing SACK, the first ACK which comes back for a timeout
2441 * based retransmit packet might feed us FACK information again.
2442 * If so, we use it to avoid unnecessarily retransmissions.
2444 void tcp_xmit_retransmit_queue(struct sock *sk)
2446 const struct inet_connection_sock *icsk = inet_csk(sk);
2447 struct tcp_sock *tp = tcp_sk(sk);
2448 struct sk_buff *skb;
2449 struct sk_buff *hole = NULL;
2452 int fwd_rexmitting = 0;
2454 if (!tp->packets_out)
2458 tp->retransmit_high = tp->snd_una;
2460 if (tp->retransmit_skb_hint) {
2461 skb = tp->retransmit_skb_hint;
2462 last_lost = TCP_SKB_CB(skb)->end_seq;
2463 if (after(last_lost, tp->retransmit_high))
2464 last_lost = tp->retransmit_high;
2466 skb = tcp_write_queue_head(sk);
2467 last_lost = tp->snd_una;
2470 tcp_for_write_queue_from(skb, sk) {
2471 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2473 if (skb == tcp_send_head(sk))
2475 /* we could do better than to assign each time */
2477 tp->retransmit_skb_hint = skb;
2479 /* Assume this retransmit will generate
2480 * only one packet for congestion window
2481 * calculation purposes. This works because
2482 * tcp_retransmit_skb() will chop up the
2483 * packet to be MSS sized and all the
2484 * packet counting works out.
2486 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2489 if (fwd_rexmitting) {
2491 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2493 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2495 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2496 tp->retransmit_high = last_lost;
2497 if (!tcp_can_forward_retransmit(sk))
2499 /* Backtrack if necessary to non-L'ed skb */
2507 } else if (!(sacked & TCPCB_LOST)) {
2508 if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2513 last_lost = TCP_SKB_CB(skb)->end_seq;
2514 if (icsk->icsk_ca_state != TCP_CA_Loss)
2515 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2517 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2520 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2523 if (tcp_retransmit_skb(sk, skb)) {
2524 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2527 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2529 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)
2530 tp->prr_out += tcp_skb_pcount(skb);
2532 if (skb == tcp_write_queue_head(sk))
2533 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2534 inet_csk(sk)->icsk_rto,
2539 /* Send a fin. The caller locks the socket for us. This cannot be
2540 * allowed to fail queueing a FIN frame under any circumstances.
2542 void tcp_send_fin(struct sock *sk)
2544 struct tcp_sock *tp = tcp_sk(sk);
2545 struct sk_buff *skb = tcp_write_queue_tail(sk);
2548 /* Optimization, tack on the FIN if we have a queue of
2549 * unsent frames. But be careful about outgoing SACKS
2552 mss_now = tcp_current_mss(sk);
2554 if (tcp_send_head(sk) != NULL) {
2555 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
2556 TCP_SKB_CB(skb)->end_seq++;
2559 /* Socket is locked, keep trying until memory is available. */
2561 skb = alloc_skb_fclone(MAX_TCP_HEADER,
2568 /* Reserve space for headers and prepare control bits. */
2569 skb_reserve(skb, MAX_TCP_HEADER);
2570 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2571 tcp_init_nondata_skb(skb, tp->write_seq,
2572 TCPHDR_ACK | TCPHDR_FIN);
2573 tcp_queue_skb(sk, skb);
2575 __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
2578 /* We get here when a process closes a file descriptor (either due to
2579 * an explicit close() or as a byproduct of exit()'ing) and there
2580 * was unread data in the receive queue. This behavior is recommended
2581 * by RFC 2525, section 2.17. -DaveM
2583 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2585 struct sk_buff *skb;
2587 /* NOTE: No TCP options attached and we never retransmit this. */
2588 skb = alloc_skb(MAX_TCP_HEADER, priority);
2590 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2594 /* Reserve space for headers and prepare control bits. */
2595 skb_reserve(skb, MAX_TCP_HEADER);
2596 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2597 TCPHDR_ACK | TCPHDR_RST);
2599 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2600 if (tcp_transmit_skb(sk, skb, 0, priority))
2601 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2603 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2606 /* Send a crossed SYN-ACK during socket establishment.
2607 * WARNING: This routine must only be called when we have already sent
2608 * a SYN packet that crossed the incoming SYN that caused this routine
2609 * to get called. If this assumption fails then the initial rcv_wnd
2610 * and rcv_wscale values will not be correct.
2612 int tcp_send_synack(struct sock *sk)
2614 struct sk_buff *skb;
2616 skb = tcp_write_queue_head(sk);
2617 if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2618 pr_debug("%s: wrong queue state\n", __func__);
2621 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2622 if (skb_cloned(skb)) {
2623 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2626 tcp_unlink_write_queue(skb, sk);
2627 skb_header_release(nskb);
2628 __tcp_add_write_queue_head(sk, nskb);
2629 sk_wmem_free_skb(sk, skb);
2630 sk->sk_wmem_queued += nskb->truesize;
2631 sk_mem_charge(sk, nskb->truesize);
2635 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2636 TCP_ECN_send_synack(tcp_sk(sk), skb);
2638 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2639 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2643 * tcp_make_synack - Prepare a SYN-ACK.
2644 * sk: listener socket
2645 * dst: dst entry attached to the SYNACK
2646 * req: request_sock pointer
2647 * rvp: request_values pointer
2649 * Allocate one skb and build a SYNACK packet.
2650 * @dst is consumed : Caller should not use it again.
2652 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2653 struct request_sock *req,
2654 struct request_values *rvp)
2656 struct tcp_out_options opts;
2657 struct tcp_extend_values *xvp = tcp_xv(rvp);
2658 struct inet_request_sock *ireq = inet_rsk(req);
2659 struct tcp_sock *tp = tcp_sk(sk);
2660 const struct tcp_cookie_values *cvp = tp->cookie_values;
2662 struct sk_buff *skb;
2663 struct tcp_md5sig_key *md5;
2664 int tcp_header_size;
2666 int s_data_desired = 0;
2668 if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)
2669 s_data_desired = cvp->s_data_desired;
2670 skb = alloc_skb(MAX_TCP_HEADER + 15 + s_data_desired,
2671 sk_gfp_atomic(sk, GFP_ATOMIC));
2672 if (unlikely(!skb)) {
2676 /* Reserve space for headers. */
2677 skb_reserve(skb, MAX_TCP_HEADER);
2679 skb_dst_set(skb, dst);
2681 mss = dst_metric_advmss(dst);
2682 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2683 mss = tp->rx_opt.user_mss;
2685 if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
2687 /* Set this up on the first call only */
2688 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
2690 /* limit the window selection if the user enforce a smaller rx buffer */
2691 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2692 (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
2693 req->window_clamp = tcp_full_space(sk);
2695 /* tcp_full_space because it is guaranteed to be the first packet */
2696 tcp_select_initial_window(tcp_full_space(sk),
2697 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
2702 dst_metric(dst, RTAX_INITRWND));
2703 ireq->rcv_wscale = rcv_wscale;
2706 memset(&opts, 0, sizeof(opts));
2707 #ifdef CONFIG_SYN_COOKIES
2708 if (unlikely(req->cookie_ts))
2709 TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
2712 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2713 tcp_header_size = tcp_synack_options(sk, req, mss,
2714 skb, &opts, &md5, xvp)
2717 skb_push(skb, tcp_header_size);
2718 skb_reset_transport_header(skb);
2721 memset(th, 0, sizeof(struct tcphdr));
2724 TCP_ECN_make_synack(req, th);
2725 th->source = ireq->loc_port;
2726 th->dest = ireq->rmt_port;
2727 /* Setting of flags are superfluous here for callers (and ECE is
2728 * not even correctly set)
2730 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
2731 TCPHDR_SYN | TCPHDR_ACK);
2733 if (OPTION_COOKIE_EXTENSION & opts.options) {
2734 if (s_data_desired) {
2735 u8 *buf = skb_put(skb, s_data_desired);
2737 /* copy data directly from the listening socket. */
2738 memcpy(buf, cvp->s_data_payload, s_data_desired);
2739 TCP_SKB_CB(skb)->end_seq += s_data_desired;
2742 if (opts.hash_size > 0) {
2743 __u32 workspace[SHA_WORKSPACE_WORDS];
2744 u32 *mess = &xvp->cookie_bakery[COOKIE_DIGEST_WORDS];
2745 u32 *tail = &mess[COOKIE_MESSAGE_WORDS-1];
2747 /* Secret recipe depends on the Timestamp, (future)
2748 * Sequence and Acknowledgment Numbers, Initiator
2749 * Cookie, and others handled by IP variant caller.
2751 *tail-- ^= opts.tsval;
2752 *tail-- ^= tcp_rsk(req)->rcv_isn + 1;
2753 *tail-- ^= TCP_SKB_CB(skb)->seq + 1;
2756 *tail-- ^= (((__force u32)th->dest << 16) | (__force u32)th->source);
2757 *tail-- ^= (u32)(unsigned long)cvp; /* per sockopt */
2759 sha_transform((__u32 *)&xvp->cookie_bakery[0],
2762 opts.hash_location =
2763 (__u8 *)&xvp->cookie_bakery[0];
2767 th->seq = htonl(TCP_SKB_CB(skb)->seq);
2768 th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
2770 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2771 th->window = htons(min(req->rcv_wnd, 65535U));
2772 tcp_options_write((__be32 *)(th + 1), tp, &opts);
2773 th->doff = (tcp_header_size >> 2);
2774 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb));
2776 #ifdef CONFIG_TCP_MD5SIG
2777 /* Okay, we have all we need - do the md5 hash if needed */
2779 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
2780 md5, NULL, req, skb);
2786 EXPORT_SYMBOL(tcp_make_synack);
2788 /* Do all connect socket setups that can be done AF independent. */
2789 void tcp_connect_init(struct sock *sk)
2791 const struct dst_entry *dst = __sk_dst_get(sk);
2792 struct tcp_sock *tp = tcp_sk(sk);
2795 /* We'll fix this up when we get a response from the other end.
2796 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2798 tp->tcp_header_len = sizeof(struct tcphdr) +
2799 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
2801 #ifdef CONFIG_TCP_MD5SIG
2802 if (tp->af_specific->md5_lookup(sk, sk) != NULL)
2803 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
2806 /* If user gave his TCP_MAXSEG, record it to clamp */
2807 if (tp->rx_opt.user_mss)
2808 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2811 tcp_sync_mss(sk, dst_mtu(dst));
2813 if (!tp->window_clamp)
2814 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
2815 tp->advmss = dst_metric_advmss(dst);
2816 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
2817 tp->advmss = tp->rx_opt.user_mss;
2819 tcp_initialize_rcv_mss(sk);
2821 /* limit the window selection if the user enforce a smaller rx buffer */
2822 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2823 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
2824 tp->window_clamp = tcp_full_space(sk);
2826 tcp_select_initial_window(tcp_full_space(sk),
2827 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
2830 sysctl_tcp_window_scaling,
2832 dst_metric(dst, RTAX_INITRWND));
2834 tp->rx_opt.rcv_wscale = rcv_wscale;
2835 tp->rcv_ssthresh = tp->rcv_wnd;
2838 sock_reset_flag(sk, SOCK_DONE);
2841 tp->snd_una = tp->write_seq;
2842 tp->snd_sml = tp->write_seq;
2843 tp->snd_up = tp->write_seq;
2844 tp->snd_nxt = tp->write_seq;
2846 if (likely(!tp->repair))
2848 tp->rcv_wup = tp->rcv_nxt;
2849 tp->copied_seq = tp->rcv_nxt;
2851 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
2852 inet_csk(sk)->icsk_retransmits = 0;
2853 tcp_clear_retrans(tp);
2856 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
2858 struct tcp_sock *tp = tcp_sk(sk);
2859 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
2861 tcb->end_seq += skb->len;
2862 skb_header_release(skb);
2863 __tcp_add_write_queue_tail(sk, skb);
2864 sk->sk_wmem_queued += skb->truesize;
2865 sk_mem_charge(sk, skb->truesize);
2866 tp->write_seq = tcb->end_seq;
2867 tp->packets_out += tcp_skb_pcount(skb);
2870 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
2871 * queue a data-only packet after the regular SYN, such that regular SYNs
2872 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
2873 * only the SYN sequence, the data are retransmitted in the first ACK.
2874 * If cookie is not cached or other error occurs, falls back to send a
2875 * regular SYN with Fast Open cookie request option.
2877 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
2879 struct tcp_sock *tp = tcp_sk(sk);
2880 struct tcp_fastopen_request *fo = tp->fastopen_req;
2881 int syn_loss = 0, space, i, err = 0, iovlen = fo->data->msg_iovlen;
2882 struct sk_buff *syn_data = NULL, *data;
2883 unsigned long last_syn_loss = 0;
2885 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
2886 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
2887 &syn_loss, &last_syn_loss);
2888 /* Recurring FO SYN losses: revert to regular handshake temporarily */
2890 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
2891 fo->cookie.len = -1;
2895 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
2896 fo->cookie.len = -1;
2897 else if (fo->cookie.len <= 0)
2900 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
2901 * user-MSS. Reserve maximum option space for middleboxes that add
2902 * private TCP options. The cost is reduced data space in SYN :(
2904 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
2905 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2906 space = tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
2907 MAX_TCP_OPTION_SPACE;
2909 syn_data = skb_copy_expand(syn, skb_headroom(syn), space,
2911 if (syn_data == NULL)
2914 for (i = 0; i < iovlen && syn_data->len < space; ++i) {
2915 struct iovec *iov = &fo->data->msg_iov[i];
2916 unsigned char __user *from = iov->iov_base;
2917 int len = iov->iov_len;
2919 if (syn_data->len + len > space)
2920 len = space - syn_data->len;
2921 else if (i + 1 == iovlen)
2922 /* No more data pending in inet_wait_for_connect() */
2925 if (skb_add_data(syn_data, from, len))
2929 /* Queue a data-only packet after the regular SYN for retransmission */
2930 data = pskb_copy(syn_data, sk->sk_allocation);
2933 TCP_SKB_CB(data)->seq++;
2934 TCP_SKB_CB(data)->tcp_flags &= ~TCPHDR_SYN;
2935 TCP_SKB_CB(data)->tcp_flags = (TCPHDR_ACK|TCPHDR_PSH);
2936 tcp_connect_queue_skb(sk, data);
2937 fo->copied = data->len;
2939 if (tcp_transmit_skb(sk, syn_data, 0, sk->sk_allocation) == 0) {
2940 tp->syn_data = (fo->copied > 0);
2941 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
2947 /* Send a regular SYN with Fast Open cookie request option */
2948 if (fo->cookie.len > 0)
2950 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
2952 tp->syn_fastopen = 0;
2953 kfree_skb(syn_data);
2955 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
2959 /* Build a SYN and send it off. */
2960 int tcp_connect(struct sock *sk)
2962 struct tcp_sock *tp = tcp_sk(sk);
2963 struct sk_buff *buff;
2966 tcp_connect_init(sk);
2968 buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
2969 if (unlikely(buff == NULL))
2972 /* Reserve space for headers. */
2973 skb_reserve(buff, MAX_TCP_HEADER);
2975 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
2976 tp->retrans_stamp = TCP_SKB_CB(buff)->when = tcp_time_stamp;
2977 tcp_connect_queue_skb(sk, buff);
2978 TCP_ECN_send_syn(sk, buff);
2980 /* Send off SYN; include data in Fast Open. */
2981 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
2982 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
2983 if (err == -ECONNREFUSED)
2986 /* We change tp->snd_nxt after the tcp_transmit_skb() call
2987 * in order to make this packet get counted in tcpOutSegs.
2989 tp->snd_nxt = tp->write_seq;
2990 tp->pushed_seq = tp->write_seq;
2991 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
2993 /* Timer for repeating the SYN until an answer. */
2994 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2995 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2998 EXPORT_SYMBOL(tcp_connect);
3000 /* Send out a delayed ack, the caller does the policy checking
3001 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3004 void tcp_send_delayed_ack(struct sock *sk)
3006 struct inet_connection_sock *icsk = inet_csk(sk);
3007 int ato = icsk->icsk_ack.ato;
3008 unsigned long timeout;
3010 if (ato > TCP_DELACK_MIN) {
3011 const struct tcp_sock *tp = tcp_sk(sk);
3012 int max_ato = HZ / 2;
3014 if (icsk->icsk_ack.pingpong ||
3015 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3016 max_ato = TCP_DELACK_MAX;
3018 /* Slow path, intersegment interval is "high". */
3020 /* If some rtt estimate is known, use it to bound delayed ack.
3021 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3025 int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
3031 ato = min(ato, max_ato);
3034 /* Stay within the limit we were given */
3035 timeout = jiffies + ato;
3037 /* Use new timeout only if there wasn't a older one earlier. */
3038 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3039 /* If delack timer was blocked or is about to expire,
3042 if (icsk->icsk_ack.blocked ||
3043 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3048 if (!time_before(timeout, icsk->icsk_ack.timeout))
3049 timeout = icsk->icsk_ack.timeout;
3051 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3052 icsk->icsk_ack.timeout = timeout;
3053 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3056 /* This routine sends an ack and also updates the window. */
3057 void tcp_send_ack(struct sock *sk)
3059 struct sk_buff *buff;
3061 /* If we have been reset, we may not send again. */
3062 if (sk->sk_state == TCP_CLOSE)
3065 /* We are not putting this on the write queue, so
3066 * tcp_transmit_skb() will set the ownership to this
3069 buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3071 inet_csk_schedule_ack(sk);
3072 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3073 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3074 TCP_DELACK_MAX, TCP_RTO_MAX);
3078 /* Reserve space for headers and prepare control bits. */
3079 skb_reserve(buff, MAX_TCP_HEADER);
3080 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3082 /* Send it off, this clears delayed acks for us. */
3083 TCP_SKB_CB(buff)->when = tcp_time_stamp;
3084 tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
3087 /* This routine sends a packet with an out of date sequence
3088 * number. It assumes the other end will try to ack it.
3090 * Question: what should we make while urgent mode?
3091 * 4.4BSD forces sending single byte of data. We cannot send
3092 * out of window data, because we have SND.NXT==SND.MAX...
3094 * Current solution: to send TWO zero-length segments in urgent mode:
3095 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3096 * out-of-date with SND.UNA-1 to probe window.
3098 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
3100 struct tcp_sock *tp = tcp_sk(sk);
3101 struct sk_buff *skb;
3103 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3104 skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3108 /* Reserve space for headers and set control bits. */
3109 skb_reserve(skb, MAX_TCP_HEADER);
3110 /* Use a previous sequence. This should cause the other
3111 * end to send an ack. Don't queue or clone SKB, just
3114 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3115 TCP_SKB_CB(skb)->when = tcp_time_stamp;
3116 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3119 void tcp_send_window_probe(struct sock *sk)
3121 if (sk->sk_state == TCP_ESTABLISHED) {
3122 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3123 tcp_sk(sk)->snd_nxt = tcp_sk(sk)->write_seq;
3124 tcp_xmit_probe_skb(sk, 0);
3128 /* Initiate keepalive or window probe from timer. */
3129 int tcp_write_wakeup(struct sock *sk)
3131 struct tcp_sock *tp = tcp_sk(sk);
3132 struct sk_buff *skb;
3134 if (sk->sk_state == TCP_CLOSE)
3137 if ((skb = tcp_send_head(sk)) != NULL &&
3138 before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3140 unsigned int mss = tcp_current_mss(sk);
3141 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3143 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3144 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3146 /* We are probing the opening of a window
3147 * but the window size is != 0
3148 * must have been a result SWS avoidance ( sender )
3150 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3152 seg_size = min(seg_size, mss);
3153 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3154 if (tcp_fragment(sk, skb, seg_size, mss))
3156 } else if (!tcp_skb_pcount(skb))
3157 tcp_set_skb_tso_segs(sk, skb, mss);
3159 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3160 TCP_SKB_CB(skb)->when = tcp_time_stamp;
3161 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3163 tcp_event_new_data_sent(sk, skb);
3166 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3167 tcp_xmit_probe_skb(sk, 1);
3168 return tcp_xmit_probe_skb(sk, 0);
3172 /* A window probe timeout has occurred. If window is not closed send
3173 * a partial packet else a zero probe.
3175 void tcp_send_probe0(struct sock *sk)
3177 struct inet_connection_sock *icsk = inet_csk(sk);
3178 struct tcp_sock *tp = tcp_sk(sk);
3181 err = tcp_write_wakeup(sk);
3183 if (tp->packets_out || !tcp_send_head(sk)) {
3184 /* Cancel probe timer, if it is not required. */
3185 icsk->icsk_probes_out = 0;
3186 icsk->icsk_backoff = 0;
3191 if (icsk->icsk_backoff < sysctl_tcp_retries2)
3192 icsk->icsk_backoff++;
3193 icsk->icsk_probes_out++;
3194 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3195 min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3198 /* If packet was not sent due to local congestion,
3199 * do not backoff and do not remember icsk_probes_out.
3200 * Let local senders to fight for local resources.
3202 * Use accumulated backoff yet.
3204 if (!icsk->icsk_probes_out)
3205 icsk->icsk_probes_out = 1;
3206 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3207 min(icsk->icsk_rto << icsk->icsk_backoff,
3208 TCP_RESOURCE_PROBE_INTERVAL),