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).
8 * Version: $Id: tcp_output.c,v 1.146 2002/02/01 22:01:04 davem Exp $
11 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12 * Mark Evans, <evansmp@uhura.aston.ac.uk>
13 * Corey Minyard <wf-rch!minyard@relay.EU.net>
14 * Florian La Roche, <flla@stud.uni-sb.de>
15 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16 * Linus Torvalds, <torvalds@cs.helsinki.fi>
17 * Alan Cox, <gw4pts@gw4pts.ampr.org>
18 * Matthew Dillon, <dillon@apollo.west.oic.com>
19 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20 * Jorge Cwik, <jorge@laser.satlink.net>
24 * Changes: Pedro Roque : Retransmit queue handled by TCP.
25 * : Fragmentation on mtu decrease
26 * : Segment collapse on retransmit
29 * Linus Torvalds : send_delayed_ack
30 * David S. Miller : Charge memory using the right skb
31 * during syn/ack processing.
32 * David S. Miller : Output engine completely rewritten.
33 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
34 * Cacophonix Gaul : draft-minshall-nagle-01
35 * J Hadi Salim : ECN support
41 #include <linux/compiler.h>
42 #include <linux/module.h>
43 #include <linux/smp_lock.h>
45 /* People can turn this off for buggy TCP's found in printers etc. */
46 int sysctl_tcp_retrans_collapse = 1;
48 /* This limits the percentage of the congestion window which we
49 * will allow a single TSO frame to consume. Building TSO frames
50 * which are too large can cause TCP streams to be bursty.
52 int sysctl_tcp_tso_win_divisor = 3;
54 static inline void update_send_head(struct sock *sk, struct tcp_sock *tp,
57 sk->sk_send_head = skb->next;
58 if (sk->sk_send_head == (struct sk_buff *)&sk->sk_write_queue)
59 sk->sk_send_head = NULL;
60 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
61 tcp_packets_out_inc(sk, tp, skb);
64 /* SND.NXT, if window was not shrunk.
65 * If window has been shrunk, what should we make? It is not clear at all.
66 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
67 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
68 * invalid. OK, let's make this for now:
70 static inline __u32 tcp_acceptable_seq(struct sock *sk, struct tcp_sock *tp)
72 if (!before(tp->snd_una+tp->snd_wnd, tp->snd_nxt))
75 return tp->snd_una+tp->snd_wnd;
78 /* Calculate mss to advertise in SYN segment.
79 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
81 * 1. It is independent of path mtu.
82 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
83 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
84 * attached devices, because some buggy hosts are confused by
86 * 4. We do not make 3, we advertise MSS, calculated from first
87 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
88 * This may be overridden via information stored in routing table.
89 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
90 * probably even Jumbo".
92 static __u16 tcp_advertise_mss(struct sock *sk)
94 struct tcp_sock *tp = tcp_sk(sk);
95 struct dst_entry *dst = __sk_dst_get(sk);
98 if (dst && dst_metric(dst, RTAX_ADVMSS) < mss) {
99 mss = dst_metric(dst, RTAX_ADVMSS);
106 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
107 * This is the first part of cwnd validation mechanism. */
108 static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst)
110 struct tcp_sock *tp = tcp_sk(sk);
111 s32 delta = tcp_time_stamp - tp->lsndtime;
112 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
113 u32 cwnd = tp->snd_cwnd;
115 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
117 tp->snd_ssthresh = tcp_current_ssthresh(sk);
118 restart_cwnd = min(restart_cwnd, cwnd);
120 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
122 tp->snd_cwnd = max(cwnd, restart_cwnd);
123 tp->snd_cwnd_stamp = tcp_time_stamp;
124 tp->snd_cwnd_used = 0;
127 static inline void tcp_event_data_sent(struct tcp_sock *tp,
128 struct sk_buff *skb, struct sock *sk)
130 struct inet_connection_sock *icsk = inet_csk(sk);
131 const u32 now = tcp_time_stamp;
133 if (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto)
134 tcp_cwnd_restart(sk, __sk_dst_get(sk));
138 /* If it is a reply for ato after last received
139 * packet, enter pingpong mode.
141 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
142 icsk->icsk_ack.pingpong = 1;
145 static __inline__ void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
147 tcp_dec_quickack_mode(sk, pkts);
148 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
151 /* Determine a window scaling and initial window to offer.
152 * Based on the assumption that the given amount of space
153 * will be offered. Store the results in the tp structure.
154 * NOTE: for smooth operation initial space offering should
155 * be a multiple of mss if possible. We assume here that mss >= 1.
156 * This MUST be enforced by all callers.
158 void tcp_select_initial_window(int __space, __u32 mss,
159 __u32 *rcv_wnd, __u32 *window_clamp,
160 int wscale_ok, __u8 *rcv_wscale)
162 unsigned int space = (__space < 0 ? 0 : __space);
164 /* If no clamp set the clamp to the max possible scaled window */
165 if (*window_clamp == 0)
166 (*window_clamp) = (65535 << 14);
167 space = min(*window_clamp, space);
169 /* Quantize space offering to a multiple of mss if possible. */
171 space = (space / mss) * mss;
173 /* NOTE: offering an initial window larger than 32767
174 * will break some buggy TCP stacks. We try to be nice.
175 * If we are not window scaling, then this truncates
176 * our initial window offering to 32k. There should also
177 * be a sysctl option to stop being nice.
179 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
182 /* Set window scaling on max possible window
183 * See RFC1323 for an explanation of the limit to 14
185 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
186 while (space > 65535 && (*rcv_wscale) < 14) {
192 /* Set initial window to value enough for senders,
193 * following RFC2414. Senders, not following this RFC,
194 * will be satisfied with 2.
196 if (mss > (1<<*rcv_wscale)) {
202 if (*rcv_wnd > init_cwnd*mss)
203 *rcv_wnd = init_cwnd*mss;
206 /* Set the clamp no higher than max representable value */
207 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
210 /* Chose a new window to advertise, update state in tcp_sock for the
211 * socket, and return result with RFC1323 scaling applied. The return
212 * value can be stuffed directly into th->window for an outgoing
215 static __inline__ u16 tcp_select_window(struct sock *sk)
217 struct tcp_sock *tp = tcp_sk(sk);
218 u32 cur_win = tcp_receive_window(tp);
219 u32 new_win = __tcp_select_window(sk);
221 /* Never shrink the offered window */
222 if(new_win < cur_win) {
223 /* Danger Will Robinson!
224 * Don't update rcv_wup/rcv_wnd here or else
225 * we will not be able to advertise a zero
226 * window in time. --DaveM
228 * Relax Will Robinson.
232 tp->rcv_wnd = new_win;
233 tp->rcv_wup = tp->rcv_nxt;
235 /* Make sure we do not exceed the maximum possible
238 if (!tp->rx_opt.rcv_wscale)
239 new_win = min(new_win, MAX_TCP_WINDOW);
241 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
243 /* RFC1323 scaling applied */
244 new_win >>= tp->rx_opt.rcv_wscale;
246 /* If we advertise zero window, disable fast path. */
254 /* This routine actually transmits TCP packets queued in by
255 * tcp_do_sendmsg(). This is used by both the initial
256 * transmission and possible later retransmissions.
257 * All SKB's seen here are completely headerless. It is our
258 * job to build the TCP header, and pass the packet down to
259 * IP so it can do the same plus pass the packet off to the
262 * We are working here with either a clone of the original
263 * SKB, or a fresh unique copy made by the retransmit engine.
265 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, gfp_t gfp_mask)
267 const struct inet_connection_sock *icsk = inet_csk(sk);
268 struct inet_sock *inet;
270 struct tcp_skb_cb *tcb;
276 BUG_ON(!skb || !tcp_skb_pcount(skb));
278 /* If congestion control is doing timestamping, we must
279 * take such a timestamp before we potentially clone/copy.
281 if (icsk->icsk_ca_ops->rtt_sample)
282 __net_timestamp(skb);
284 if (likely(clone_it)) {
285 if (unlikely(skb_cloned(skb)))
286 skb = pskb_copy(skb, gfp_mask);
288 skb = skb_clone(skb, gfp_mask);
295 tcb = TCP_SKB_CB(skb);
296 tcp_header_size = tp->tcp_header_len;
298 #define SYSCTL_FLAG_TSTAMPS 0x1
299 #define SYSCTL_FLAG_WSCALE 0x2
300 #define SYSCTL_FLAG_SACK 0x4
303 if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
304 tcp_header_size = sizeof(struct tcphdr) + TCPOLEN_MSS;
305 if(sysctl_tcp_timestamps) {
306 tcp_header_size += TCPOLEN_TSTAMP_ALIGNED;
307 sysctl_flags |= SYSCTL_FLAG_TSTAMPS;
309 if (sysctl_tcp_window_scaling) {
310 tcp_header_size += TCPOLEN_WSCALE_ALIGNED;
311 sysctl_flags |= SYSCTL_FLAG_WSCALE;
313 if (sysctl_tcp_sack) {
314 sysctl_flags |= SYSCTL_FLAG_SACK;
315 if (!(sysctl_flags & SYSCTL_FLAG_TSTAMPS))
316 tcp_header_size += TCPOLEN_SACKPERM_ALIGNED;
318 } else if (unlikely(tp->rx_opt.eff_sacks)) {
319 /* A SACK is 2 pad bytes, a 2 byte header, plus
320 * 2 32-bit sequence numbers for each SACK block.
322 tcp_header_size += (TCPOLEN_SACK_BASE_ALIGNED +
323 (tp->rx_opt.eff_sacks *
324 TCPOLEN_SACK_PERBLOCK));
327 if (tcp_packets_in_flight(tp) == 0)
328 tcp_ca_event(sk, CA_EVENT_TX_START);
330 th = (struct tcphdr *) skb_push(skb, tcp_header_size);
332 skb_set_owner_w(skb, sk);
334 /* Build TCP header and checksum it. */
335 th->source = inet->sport;
336 th->dest = inet->dport;
337 th->seq = htonl(tcb->seq);
338 th->ack_seq = htonl(tp->rcv_nxt);
339 *(((__u16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
342 if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
343 /* RFC1323: The window in SYN & SYN/ACK segments
346 th->window = htons(tp->rcv_wnd);
348 th->window = htons(tcp_select_window(sk));
353 if (unlikely(tp->urg_mode &&
354 between(tp->snd_up, tcb->seq+1, tcb->seq+0xFFFF))) {
355 th->urg_ptr = htons(tp->snd_up-tcb->seq);
359 if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
360 tcp_syn_build_options((__u32 *)(th + 1),
361 tcp_advertise_mss(sk),
362 (sysctl_flags & SYSCTL_FLAG_TSTAMPS),
363 (sysctl_flags & SYSCTL_FLAG_SACK),
364 (sysctl_flags & SYSCTL_FLAG_WSCALE),
365 tp->rx_opt.rcv_wscale,
367 tp->rx_opt.ts_recent);
369 tcp_build_and_update_options((__u32 *)(th + 1),
371 TCP_ECN_send(sk, tp, skb, tcp_header_size);
374 tp->af_specific->send_check(sk, th, skb->len, skb);
376 if (likely(tcb->flags & TCPCB_FLAG_ACK))
377 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
379 if (skb->len != tcp_header_size)
380 tcp_event_data_sent(tp, skb, sk);
382 TCP_INC_STATS(TCP_MIB_OUTSEGS);
384 err = tp->af_specific->queue_xmit(skb, 0);
385 if (unlikely(err <= 0))
390 /* NET_XMIT_CN is special. It does not guarantee,
391 * that this packet is lost. It tells that device
392 * is about to start to drop packets or already
393 * drops some packets of the same priority and
394 * invokes us to send less aggressively.
396 return err == NET_XMIT_CN ? 0 : err;
398 #undef SYSCTL_FLAG_TSTAMPS
399 #undef SYSCTL_FLAG_WSCALE
400 #undef SYSCTL_FLAG_SACK
404 /* This routine just queue's the buffer
406 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
407 * otherwise socket can stall.
409 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
411 struct tcp_sock *tp = tcp_sk(sk);
413 /* Advance write_seq and place onto the write_queue. */
414 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
415 skb_header_release(skb);
416 __skb_queue_tail(&sk->sk_write_queue, skb);
417 sk_charge_skb(sk, skb);
419 /* Queue it, remembering where we must start sending. */
420 if (sk->sk_send_head == NULL)
421 sk->sk_send_head = skb;
424 static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now)
426 if (skb->len <= mss_now ||
427 !(sk->sk_route_caps & NETIF_F_TSO)) {
428 /* Avoid the costly divide in the normal
431 skb_shinfo(skb)->tso_segs = 1;
432 skb_shinfo(skb)->tso_size = 0;
436 factor = skb->len + (mss_now - 1);
438 skb_shinfo(skb)->tso_segs = factor;
439 skb_shinfo(skb)->tso_size = mss_now;
443 /* Function to create two new TCP segments. Shrinks the given segment
444 * to the specified size and appends a new segment with the rest of the
445 * packet to the list. This won't be called frequently, I hope.
446 * Remember, these are still headerless SKBs at this point.
448 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss_now)
450 struct tcp_sock *tp = tcp_sk(sk);
451 struct sk_buff *buff;
452 int nsize, old_factor;
455 BUG_ON(len > skb->len);
457 clear_all_retrans_hints(tp);
458 nsize = skb_headlen(skb) - len;
462 if (skb_cloned(skb) &&
463 skb_is_nonlinear(skb) &&
464 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
467 /* Get a new skb... force flag on. */
468 buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
470 return -ENOMEM; /* We'll just try again later. */
471 sk_charge_skb(sk, buff);
473 /* Correct the sequence numbers. */
474 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
475 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
476 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
478 /* PSH and FIN should only be set in the second packet. */
479 flags = TCP_SKB_CB(skb)->flags;
480 TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
481 TCP_SKB_CB(buff)->flags = flags;
482 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
483 TCP_SKB_CB(skb)->sacked &= ~TCPCB_AT_TAIL;
485 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_HW) {
486 /* Copy and checksum data tail into the new buffer. */
487 buff->csum = csum_partial_copy_nocheck(skb->data + len, skb_put(buff, nsize),
492 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
494 skb->ip_summed = CHECKSUM_HW;
495 skb_split(skb, buff, len);
498 buff->ip_summed = skb->ip_summed;
500 /* Looks stupid, but our code really uses when of
501 * skbs, which it never sent before. --ANK
503 TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
504 buff->tstamp = skb->tstamp;
506 old_factor = tcp_skb_pcount(skb);
508 /* Fix up tso_factor for both original and new SKB. */
509 tcp_set_skb_tso_segs(sk, skb, mss_now);
510 tcp_set_skb_tso_segs(sk, buff, mss_now);
512 /* If this packet has been sent out already, we must
513 * adjust the various packet counters.
515 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
516 int diff = old_factor - tcp_skb_pcount(skb) -
517 tcp_skb_pcount(buff);
519 tp->packets_out -= diff;
521 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
522 tp->sacked_out -= diff;
523 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
524 tp->retrans_out -= diff;
526 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
527 tp->lost_out -= diff;
528 tp->left_out -= diff;
532 /* Adjust Reno SACK estimate. */
533 if (!tp->rx_opt.sack_ok) {
534 tp->sacked_out -= diff;
535 if ((int)tp->sacked_out < 0)
537 tcp_sync_left_out(tp);
540 tp->fackets_out -= diff;
541 if ((int)tp->fackets_out < 0)
546 /* Link BUFF into the send queue. */
547 skb_header_release(buff);
548 __skb_append(skb, buff, &sk->sk_write_queue);
553 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
554 * eventually). The difference is that pulled data not copied, but
555 * immediately discarded.
557 static unsigned char *__pskb_trim_head(struct sk_buff *skb, int len)
563 for (i=0; i<skb_shinfo(skb)->nr_frags; i++) {
564 if (skb_shinfo(skb)->frags[i].size <= eat) {
565 put_page(skb_shinfo(skb)->frags[i].page);
566 eat -= skb_shinfo(skb)->frags[i].size;
568 skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
570 skb_shinfo(skb)->frags[k].page_offset += eat;
571 skb_shinfo(skb)->frags[k].size -= eat;
577 skb_shinfo(skb)->nr_frags = k;
579 skb->tail = skb->data;
580 skb->data_len -= len;
581 skb->len = skb->data_len;
585 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
587 if (skb_cloned(skb) &&
588 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
591 if (len <= skb_headlen(skb)) {
592 __skb_pull(skb, len);
594 if (__pskb_trim_head(skb, len-skb_headlen(skb)) == NULL)
598 TCP_SKB_CB(skb)->seq += len;
599 skb->ip_summed = CHECKSUM_HW;
601 skb->truesize -= len;
602 sk->sk_wmem_queued -= len;
603 sk->sk_forward_alloc += len;
604 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
606 /* Any change of skb->len requires recalculation of tso
609 if (tcp_skb_pcount(skb) > 1)
610 tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1));
615 /* This function synchronize snd mss to current pmtu/exthdr set.
617 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
618 for TCP options, but includes only bare TCP header.
620 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
621 It is minimum of user_mss and mss received with SYN.
622 It also does not include TCP options.
624 tp->pmtu_cookie is last pmtu, seen by this function.
626 tp->mss_cache is current effective sending mss, including
627 all tcp options except for SACKs. It is evaluated,
628 taking into account current pmtu, but never exceeds
629 tp->rx_opt.mss_clamp.
631 NOTE1. rfc1122 clearly states that advertised MSS
632 DOES NOT include either tcp or ip options.
634 NOTE2. tp->pmtu_cookie and tp->mss_cache are READ ONLY outside
635 this function. --ANK (980731)
638 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
640 struct tcp_sock *tp = tcp_sk(sk);
643 /* Calculate base mss without TCP options:
644 It is MMS_S - sizeof(tcphdr) of rfc1122
646 mss_now = pmtu - tp->af_specific->net_header_len - sizeof(struct tcphdr);
648 /* Clamp it (mss_clamp does not include tcp options) */
649 if (mss_now > tp->rx_opt.mss_clamp)
650 mss_now = tp->rx_opt.mss_clamp;
652 /* Now subtract optional transport overhead */
653 mss_now -= tp->ext_header_len;
655 /* Then reserve room for full set of TCP options and 8 bytes of data */
659 /* Now subtract TCP options size, not including SACKs */
660 mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
662 /* Bound mss with half of window */
663 if (tp->max_window && mss_now > (tp->max_window>>1))
664 mss_now = max((tp->max_window>>1), 68U - tp->tcp_header_len);
666 /* And store cached results */
667 tp->pmtu_cookie = pmtu;
668 tp->mss_cache = mss_now;
673 /* Compute the current effective MSS, taking SACKs and IP options,
674 * and even PMTU discovery events into account.
676 * LARGESEND note: !urg_mode is overkill, only frames up to snd_up
677 * cannot be large. However, taking into account rare use of URG, this
680 unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
682 struct tcp_sock *tp = tcp_sk(sk);
683 struct dst_entry *dst = __sk_dst_get(sk);
688 mss_now = tp->mss_cache;
691 (sk->sk_route_caps & NETIF_F_TSO) &&
696 u32 mtu = dst_mtu(dst);
697 if (mtu != tp->pmtu_cookie)
698 mss_now = tcp_sync_mss(sk, mtu);
701 if (tp->rx_opt.eff_sacks)
702 mss_now -= (TCPOLEN_SACK_BASE_ALIGNED +
703 (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
705 xmit_size_goal = mss_now;
708 xmit_size_goal = 65535 -
709 tp->af_specific->net_header_len -
710 tp->ext_header_len - tp->tcp_header_len;
712 if (tp->max_window &&
713 (xmit_size_goal > (tp->max_window >> 1)))
714 xmit_size_goal = max((tp->max_window >> 1),
715 68U - tp->tcp_header_len);
717 xmit_size_goal -= (xmit_size_goal % mss_now);
719 tp->xmit_size_goal = xmit_size_goal;
724 /* Congestion window validation. (RFC2861) */
726 static inline void tcp_cwnd_validate(struct sock *sk, struct tcp_sock *tp)
728 __u32 packets_out = tp->packets_out;
730 if (packets_out >= tp->snd_cwnd) {
731 /* Network is feed fully. */
732 tp->snd_cwnd_used = 0;
733 tp->snd_cwnd_stamp = tcp_time_stamp;
735 /* Network starves. */
736 if (tp->packets_out > tp->snd_cwnd_used)
737 tp->snd_cwnd_used = tp->packets_out;
739 if ((s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
740 tcp_cwnd_application_limited(sk);
744 static unsigned int tcp_window_allows(struct tcp_sock *tp, struct sk_buff *skb, unsigned int mss_now, unsigned int cwnd)
746 u32 window, cwnd_len;
748 window = (tp->snd_una + tp->snd_wnd - TCP_SKB_CB(skb)->seq);
749 cwnd_len = mss_now * cwnd;
750 return min(window, cwnd_len);
753 /* Can at least one segment of SKB be sent right now, according to the
754 * congestion window rules? If so, return how many segments are allowed.
756 static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, struct sk_buff *skb)
760 /* Don't be strict about the congestion window for the final FIN. */
761 if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
764 in_flight = tcp_packets_in_flight(tp);
766 if (in_flight < cwnd)
767 return (cwnd - in_flight);
772 /* This must be invoked the first time we consider transmitting
775 static inline int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now)
777 int tso_segs = tcp_skb_pcount(skb);
781 skb_shinfo(skb)->tso_size != mss_now)) {
782 tcp_set_skb_tso_segs(sk, skb, mss_now);
783 tso_segs = tcp_skb_pcount(skb);
788 static inline int tcp_minshall_check(const struct tcp_sock *tp)
790 return after(tp->snd_sml,tp->snd_una) &&
791 !after(tp->snd_sml, tp->snd_nxt);
794 /* Return 0, if packet can be sent now without violation Nagle's rules:
795 * 1. It is full sized.
796 * 2. Or it contains FIN. (already checked by caller)
797 * 3. Or TCP_NODELAY was set.
798 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
799 * With Minshall's modification: all sent small packets are ACKed.
802 static inline int tcp_nagle_check(const struct tcp_sock *tp,
803 const struct sk_buff *skb,
804 unsigned mss_now, int nonagle)
806 return (skb->len < mss_now &&
807 ((nonagle&TCP_NAGLE_CORK) ||
810 tcp_minshall_check(tp))));
813 /* Return non-zero if the Nagle test allows this packet to be
816 static inline int tcp_nagle_test(struct tcp_sock *tp, struct sk_buff *skb,
817 unsigned int cur_mss, int nonagle)
819 /* Nagle rule does not apply to frames, which sit in the middle of the
820 * write_queue (they have no chances to get new data).
822 * This is implemented in the callers, where they modify the 'nonagle'
823 * argument based upon the location of SKB in the send queue.
825 if (nonagle & TCP_NAGLE_PUSH)
828 /* Don't use the nagle rule for urgent data (or for the final FIN). */
830 (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN))
833 if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
839 /* Does at least the first segment of SKB fit into the send window? */
840 static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb, unsigned int cur_mss)
842 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
844 if (skb->len > cur_mss)
845 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
847 return !after(end_seq, tp->snd_una + tp->snd_wnd);
850 /* This checks if the data bearing packet SKB (usually sk->sk_send_head)
851 * should be put on the wire right now. If so, it returns the number of
852 * packets allowed by the congestion window.
854 static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb,
855 unsigned int cur_mss, int nonagle)
857 struct tcp_sock *tp = tcp_sk(sk);
858 unsigned int cwnd_quota;
860 tcp_init_tso_segs(sk, skb, cur_mss);
862 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
865 cwnd_quota = tcp_cwnd_test(tp, skb);
867 !tcp_snd_wnd_test(tp, skb, cur_mss))
873 static inline int tcp_skb_is_last(const struct sock *sk,
874 const struct sk_buff *skb)
876 return skb->next == (struct sk_buff *)&sk->sk_write_queue;
879 int tcp_may_send_now(struct sock *sk, struct tcp_sock *tp)
881 struct sk_buff *skb = sk->sk_send_head;
884 tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
885 (tcp_skb_is_last(sk, skb) ?
890 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
891 * which is put after SKB on the list. It is very much like
892 * tcp_fragment() except that it may make several kinds of assumptions
893 * in order to speed up the splitting operation. In particular, we
894 * know that all the data is in scatter-gather pages, and that the
895 * packet has never been sent out before (and thus is not cloned).
897 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, unsigned int mss_now)
899 struct sk_buff *buff;
900 int nlen = skb->len - len;
903 /* All of a TSO frame must be composed of paged data. */
904 if (skb->len != skb->data_len)
905 return tcp_fragment(sk, skb, len, mss_now);
907 buff = sk_stream_alloc_pskb(sk, 0, 0, GFP_ATOMIC);
908 if (unlikely(buff == NULL))
911 buff->truesize = nlen;
912 skb->truesize -= nlen;
914 /* Correct the sequence numbers. */
915 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
916 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
917 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
919 /* PSH and FIN should only be set in the second packet. */
920 flags = TCP_SKB_CB(skb)->flags;
921 TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
922 TCP_SKB_CB(buff)->flags = flags;
924 /* This packet was never sent out yet, so no SACK bits. */
925 TCP_SKB_CB(buff)->sacked = 0;
927 buff->ip_summed = skb->ip_summed = CHECKSUM_HW;
928 skb_split(skb, buff, len);
930 /* Fix up tso_factor for both original and new SKB. */
931 tcp_set_skb_tso_segs(sk, skb, mss_now);
932 tcp_set_skb_tso_segs(sk, buff, mss_now);
934 /* Link BUFF into the send queue. */
935 skb_header_release(buff);
936 __skb_append(skb, buff, &sk->sk_write_queue);
941 /* Try to defer sending, if possible, in order to minimize the amount
942 * of TSO splitting we do. View it as a kind of TSO Nagle test.
944 * This algorithm is from John Heffner.
946 static int tcp_tso_should_defer(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
948 const struct inet_connection_sock *icsk = inet_csk(sk);
949 u32 send_win, cong_win, limit, in_flight;
951 if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
954 if (icsk->icsk_ca_state != TCP_CA_Open)
957 in_flight = tcp_packets_in_flight(tp);
959 BUG_ON(tcp_skb_pcount(skb) <= 1 ||
960 (tp->snd_cwnd <= in_flight));
962 send_win = (tp->snd_una + tp->snd_wnd) - TCP_SKB_CB(skb)->seq;
964 /* From in_flight test above, we know that cwnd > in_flight. */
965 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
967 limit = min(send_win, cong_win);
969 if (sysctl_tcp_tso_win_divisor) {
970 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
972 /* If at least some fraction of a window is available,
975 chunk /= sysctl_tcp_tso_win_divisor;
979 /* Different approach, try not to defer past a single
980 * ACK. Receiver should ACK every other full sized
981 * frame, so if we have space for more than 3 frames
984 if (limit > tcp_max_burst(tp) * tp->mss_cache)
988 /* Ok, it looks like it is advisable to defer. */
992 /* This routine writes packets to the network. It advances the
993 * send_head. This happens as incoming acks open up the remote
996 * Returns 1, if no segments are in flight and we have queued segments, but
997 * cannot send anything now because of SWS or another problem.
999 static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
1001 struct tcp_sock *tp = tcp_sk(sk);
1002 struct sk_buff *skb;
1003 unsigned int tso_segs, sent_pkts;
1006 /* If we are closed, the bytes will have to remain here.
1007 * In time closedown will finish, we empty the write queue and all
1010 if (unlikely(sk->sk_state == TCP_CLOSE))
1014 while ((skb = sk->sk_send_head)) {
1017 tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1020 cwnd_quota = tcp_cwnd_test(tp, skb);
1024 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
1027 if (tso_segs == 1) {
1028 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
1029 (tcp_skb_is_last(sk, skb) ?
1030 nonagle : TCP_NAGLE_PUSH))))
1033 if (tcp_tso_should_defer(sk, tp, skb))
1039 limit = tcp_window_allows(tp, skb,
1040 mss_now, cwnd_quota);
1042 if (skb->len < limit) {
1043 unsigned int trim = skb->len % mss_now;
1046 limit = skb->len - trim;
1050 if (skb->len > limit &&
1051 unlikely(tso_fragment(sk, skb, limit, mss_now)))
1054 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1056 if (unlikely(tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC)))
1059 /* Advance the send_head. This one is sent out.
1060 * This call will increment packets_out.
1062 update_send_head(sk, tp, skb);
1064 tcp_minshall_update(tp, mss_now, skb);
1068 if (likely(sent_pkts)) {
1069 tcp_cwnd_validate(sk, tp);
1072 return !tp->packets_out && sk->sk_send_head;
1075 /* Push out any pending frames which were held back due to
1076 * TCP_CORK or attempt at coalescing tiny packets.
1077 * The socket must be locked by the caller.
1079 void __tcp_push_pending_frames(struct sock *sk, struct tcp_sock *tp,
1080 unsigned int cur_mss, int nonagle)
1082 struct sk_buff *skb = sk->sk_send_head;
1085 if (tcp_write_xmit(sk, cur_mss, nonagle))
1086 tcp_check_probe_timer(sk, tp);
1090 /* Send _single_ skb sitting at the send head. This function requires
1091 * true push pending frames to setup probe timer etc.
1093 void tcp_push_one(struct sock *sk, unsigned int mss_now)
1095 struct tcp_sock *tp = tcp_sk(sk);
1096 struct sk_buff *skb = sk->sk_send_head;
1097 unsigned int tso_segs, cwnd_quota;
1099 BUG_ON(!skb || skb->len < mss_now);
1101 tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1102 cwnd_quota = tcp_snd_test(sk, skb, mss_now, TCP_NAGLE_PUSH);
1104 if (likely(cwnd_quota)) {
1111 limit = tcp_window_allows(tp, skb,
1112 mss_now, cwnd_quota);
1114 if (skb->len < limit) {
1115 unsigned int trim = skb->len % mss_now;
1118 limit = skb->len - trim;
1122 if (skb->len > limit &&
1123 unlikely(tso_fragment(sk, skb, limit, mss_now)))
1126 /* Send it out now. */
1127 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1129 if (likely(!tcp_transmit_skb(sk, skb, 1, sk->sk_allocation))) {
1130 update_send_head(sk, tp, skb);
1131 tcp_cwnd_validate(sk, tp);
1137 /* This function returns the amount that we can raise the
1138 * usable window based on the following constraints
1140 * 1. The window can never be shrunk once it is offered (RFC 793)
1141 * 2. We limit memory per socket
1144 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
1145 * RECV.NEXT + RCV.WIN fixed until:
1146 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
1148 * i.e. don't raise the right edge of the window until you can raise
1149 * it at least MSS bytes.
1151 * Unfortunately, the recommended algorithm breaks header prediction,
1152 * since header prediction assumes th->window stays fixed.
1154 * Strictly speaking, keeping th->window fixed violates the receiver
1155 * side SWS prevention criteria. The problem is that under this rule
1156 * a stream of single byte packets will cause the right side of the
1157 * window to always advance by a single byte.
1159 * Of course, if the sender implements sender side SWS prevention
1160 * then this will not be a problem.
1162 * BSD seems to make the following compromise:
1164 * If the free space is less than the 1/4 of the maximum
1165 * space available and the free space is less than 1/2 mss,
1166 * then set the window to 0.
1167 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
1168 * Otherwise, just prevent the window from shrinking
1169 * and from being larger than the largest representable value.
1171 * This prevents incremental opening of the window in the regime
1172 * where TCP is limited by the speed of the reader side taking
1173 * data out of the TCP receive queue. It does nothing about
1174 * those cases where the window is constrained on the sender side
1175 * because the pipeline is full.
1177 * BSD also seems to "accidentally" limit itself to windows that are a
1178 * multiple of MSS, at least until the free space gets quite small.
1179 * This would appear to be a side effect of the mbuf implementation.
1180 * Combining these two algorithms results in the observed behavior
1181 * of having a fixed window size at almost all times.
1183 * Below we obtain similar behavior by forcing the offered window to
1184 * a multiple of the mss when it is feasible to do so.
1186 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
1187 * Regular options like TIMESTAMP are taken into account.
1189 u32 __tcp_select_window(struct sock *sk)
1191 struct inet_connection_sock *icsk = inet_csk(sk);
1192 struct tcp_sock *tp = tcp_sk(sk);
1193 /* MSS for the peer's data. Previous versions used mss_clamp
1194 * here. I don't know if the value based on our guesses
1195 * of peer's MSS is better for the performance. It's more correct
1196 * but may be worse for the performance because of rcv_mss
1197 * fluctuations. --SAW 1998/11/1
1199 int mss = icsk->icsk_ack.rcv_mss;
1200 int free_space = tcp_space(sk);
1201 int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
1204 if (mss > full_space)
1207 if (free_space < full_space/2) {
1208 icsk->icsk_ack.quick = 0;
1210 if (tcp_memory_pressure)
1211 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U*tp->advmss);
1213 if (free_space < mss)
1217 if (free_space > tp->rcv_ssthresh)
1218 free_space = tp->rcv_ssthresh;
1220 /* Don't do rounding if we are using window scaling, since the
1221 * scaled window will not line up with the MSS boundary anyway.
1223 window = tp->rcv_wnd;
1224 if (tp->rx_opt.rcv_wscale) {
1225 window = free_space;
1227 /* Advertise enough space so that it won't get scaled away.
1228 * Import case: prevent zero window announcement if
1229 * 1<<rcv_wscale > mss.
1231 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
1232 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
1233 << tp->rx_opt.rcv_wscale);
1235 /* Get the largest window that is a nice multiple of mss.
1236 * Window clamp already applied above.
1237 * If our current window offering is within 1 mss of the
1238 * free space we just keep it. This prevents the divide
1239 * and multiply from happening most of the time.
1240 * We also don't do any window rounding when the free space
1243 if (window <= free_space - mss || window > free_space)
1244 window = (free_space/mss)*mss;
1250 /* Attempt to collapse two adjacent SKB's during retransmission. */
1251 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int mss_now)
1253 struct tcp_sock *tp = tcp_sk(sk);
1254 struct sk_buff *next_skb = skb->next;
1256 /* The first test we must make is that neither of these two
1257 * SKB's are still referenced by someone else.
1259 if (!skb_cloned(skb) && !skb_cloned(next_skb)) {
1260 int skb_size = skb->len, next_skb_size = next_skb->len;
1261 u16 flags = TCP_SKB_CB(skb)->flags;
1263 /* Also punt if next skb has been SACK'd. */
1264 if(TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED)
1267 /* Next skb is out of window. */
1268 if (after(TCP_SKB_CB(next_skb)->end_seq, tp->snd_una+tp->snd_wnd))
1271 /* Punt if not enough space exists in the first SKB for
1272 * the data in the second, or the total combined payload
1273 * would exceed the MSS.
1275 if ((next_skb_size > skb_tailroom(skb)) ||
1276 ((skb_size + next_skb_size) > mss_now))
1279 BUG_ON(tcp_skb_pcount(skb) != 1 ||
1280 tcp_skb_pcount(next_skb) != 1);
1282 /* changing transmit queue under us so clear hints */
1283 clear_all_retrans_hints(tp);
1285 /* Ok. We will be able to collapse the packet. */
1286 __skb_unlink(next_skb, &sk->sk_write_queue);
1288 memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
1290 if (next_skb->ip_summed == CHECKSUM_HW)
1291 skb->ip_summed = CHECKSUM_HW;
1293 if (skb->ip_summed != CHECKSUM_HW)
1294 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
1296 /* Update sequence range on original skb. */
1297 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
1299 /* Merge over control information. */
1300 flags |= TCP_SKB_CB(next_skb)->flags; /* This moves PSH/FIN etc. over */
1301 TCP_SKB_CB(skb)->flags = flags;
1303 /* All done, get rid of second SKB and account for it so
1304 * packet counting does not break.
1306 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked&(TCPCB_EVER_RETRANS|TCPCB_AT_TAIL);
1307 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_SACKED_RETRANS)
1308 tp->retrans_out -= tcp_skb_pcount(next_skb);
1309 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_LOST) {
1310 tp->lost_out -= tcp_skb_pcount(next_skb);
1311 tp->left_out -= tcp_skb_pcount(next_skb);
1313 /* Reno case is special. Sigh... */
1314 if (!tp->rx_opt.sack_ok && tp->sacked_out) {
1315 tcp_dec_pcount_approx(&tp->sacked_out, next_skb);
1316 tp->left_out -= tcp_skb_pcount(next_skb);
1319 /* Not quite right: it can be > snd.fack, but
1320 * it is better to underestimate fackets.
1322 tcp_dec_pcount_approx(&tp->fackets_out, next_skb);
1323 tcp_packets_out_dec(tp, next_skb);
1324 sk_stream_free_skb(sk, next_skb);
1328 /* Do a simple retransmit without using the backoff mechanisms in
1329 * tcp_timer. This is used for path mtu discovery.
1330 * The socket is already locked here.
1332 void tcp_simple_retransmit(struct sock *sk)
1334 const struct inet_connection_sock *icsk = inet_csk(sk);
1335 struct tcp_sock *tp = tcp_sk(sk);
1336 struct sk_buff *skb;
1337 unsigned int mss = tcp_current_mss(sk, 0);
1340 sk_stream_for_retrans_queue(skb, sk) {
1341 if (skb->len > mss &&
1342 !(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1343 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
1344 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1345 tp->retrans_out -= tcp_skb_pcount(skb);
1347 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_LOST)) {
1348 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1349 tp->lost_out += tcp_skb_pcount(skb);
1355 clear_all_retrans_hints(tp);
1360 tcp_sync_left_out(tp);
1362 /* Don't muck with the congestion window here.
1363 * Reason is that we do not increase amount of _data_
1364 * in network, but units changed and effective
1365 * cwnd/ssthresh really reduced now.
1367 if (icsk->icsk_ca_state != TCP_CA_Loss) {
1368 tp->high_seq = tp->snd_nxt;
1369 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1370 tp->prior_ssthresh = 0;
1371 tp->undo_marker = 0;
1372 tcp_set_ca_state(sk, TCP_CA_Loss);
1374 tcp_xmit_retransmit_queue(sk);
1377 /* This retransmits one SKB. Policy decisions and retransmit queue
1378 * state updates are done by the caller. Returns non-zero if an
1379 * error occurred which prevented the send.
1381 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
1383 struct tcp_sock *tp = tcp_sk(sk);
1384 unsigned int cur_mss = tcp_current_mss(sk, 0);
1387 /* Do not sent more than we queued. 1/4 is reserved for possible
1388 * copying overhead: fragmentation, tunneling, mangling etc.
1390 if (atomic_read(&sk->sk_wmem_alloc) >
1391 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
1394 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
1395 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1397 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
1401 /* If receiver has shrunk his window, and skb is out of
1402 * new window, do not retransmit it. The exception is the
1403 * case, when window is shrunk to zero. In this case
1404 * our retransmit serves as a zero window probe.
1406 if (!before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)
1407 && TCP_SKB_CB(skb)->seq != tp->snd_una)
1410 if (skb->len > cur_mss) {
1411 if (tcp_fragment(sk, skb, cur_mss, cur_mss))
1412 return -ENOMEM; /* We'll try again later. */
1415 /* Collapse two adjacent packets if worthwhile and we can. */
1416 if(!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) &&
1417 (skb->len < (cur_mss >> 1)) &&
1418 (skb->next != sk->sk_send_head) &&
1419 (skb->next != (struct sk_buff *)&sk->sk_write_queue) &&
1420 (skb_shinfo(skb)->nr_frags == 0 && skb_shinfo(skb->next)->nr_frags == 0) &&
1421 (tcp_skb_pcount(skb) == 1 && tcp_skb_pcount(skb->next) == 1) &&
1422 (sysctl_tcp_retrans_collapse != 0))
1423 tcp_retrans_try_collapse(sk, skb, cur_mss);
1425 if(tp->af_specific->rebuild_header(sk))
1426 return -EHOSTUNREACH; /* Routing failure or similar. */
1428 /* Some Solaris stacks overoptimize and ignore the FIN on a
1429 * retransmit when old data is attached. So strip it off
1430 * since it is cheap to do so and saves bytes on the network.
1433 (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
1434 tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
1435 if (!pskb_trim(skb, 0)) {
1436 TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1;
1437 skb_shinfo(skb)->tso_segs = 1;
1438 skb_shinfo(skb)->tso_size = 0;
1439 skb->ip_summed = CHECKSUM_NONE;
1444 /* Make a copy, if the first transmission SKB clone we made
1445 * is still in somebody's hands, else make a clone.
1447 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1449 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
1452 /* Update global TCP statistics. */
1453 TCP_INC_STATS(TCP_MIB_RETRANSSEGS);
1455 tp->total_retrans++;
1457 #if FASTRETRANS_DEBUG > 0
1458 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
1459 if (net_ratelimit())
1460 printk(KERN_DEBUG "retrans_out leaked.\n");
1463 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
1464 tp->retrans_out += tcp_skb_pcount(skb);
1466 /* Save stamp of the first retransmit. */
1467 if (!tp->retrans_stamp)
1468 tp->retrans_stamp = TCP_SKB_CB(skb)->when;
1472 /* snd_nxt is stored to detect loss of retransmitted segment,
1473 * see tcp_input.c tcp_sacktag_write_queue().
1475 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
1480 /* This gets called after a retransmit timeout, and the initially
1481 * retransmitted data is acknowledged. It tries to continue
1482 * resending the rest of the retransmit queue, until either
1483 * we've sent it all or the congestion window limit is reached.
1484 * If doing SACK, the first ACK which comes back for a timeout
1485 * based retransmit packet might feed us FACK information again.
1486 * If so, we use it to avoid unnecessarily retransmissions.
1488 void tcp_xmit_retransmit_queue(struct sock *sk)
1490 const struct inet_connection_sock *icsk = inet_csk(sk);
1491 struct tcp_sock *tp = tcp_sk(sk);
1492 struct sk_buff *skb;
1495 if (tp->retransmit_skb_hint) {
1496 skb = tp->retransmit_skb_hint;
1497 packet_cnt = tp->retransmit_cnt_hint;
1499 skb = sk->sk_write_queue.next;
1503 /* First pass: retransmit lost packets. */
1505 sk_stream_for_retrans_queue_from(skb, sk) {
1506 __u8 sacked = TCP_SKB_CB(skb)->sacked;
1508 /* we could do better than to assign each time */
1509 tp->retransmit_skb_hint = skb;
1510 tp->retransmit_cnt_hint = packet_cnt;
1512 /* Assume this retransmit will generate
1513 * only one packet for congestion window
1514 * calculation purposes. This works because
1515 * tcp_retransmit_skb() will chop up the
1516 * packet to be MSS sized and all the
1517 * packet counting works out.
1519 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1522 if (sacked & TCPCB_LOST) {
1523 if (!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
1524 if (tcp_retransmit_skb(sk, skb)) {
1525 tp->retransmit_skb_hint = NULL;
1528 if (icsk->icsk_ca_state != TCP_CA_Loss)
1529 NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS);
1531 NET_INC_STATS_BH(LINUX_MIB_TCPSLOWSTARTRETRANS);
1534 skb_peek(&sk->sk_write_queue))
1535 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1536 inet_csk(sk)->icsk_rto,
1540 packet_cnt += tcp_skb_pcount(skb);
1541 if (packet_cnt >= tp->lost_out)
1547 /* OK, demanded retransmission is finished. */
1549 /* Forward retransmissions are possible only during Recovery. */
1550 if (icsk->icsk_ca_state != TCP_CA_Recovery)
1553 /* No forward retransmissions in Reno are possible. */
1554 if (!tp->rx_opt.sack_ok)
1557 /* Yeah, we have to make difficult choice between forward transmission
1558 * and retransmission... Both ways have their merits...
1560 * For now we do not retransmit anything, while we have some new
1564 if (tcp_may_send_now(sk, tp))
1567 if (tp->forward_skb_hint) {
1568 skb = tp->forward_skb_hint;
1569 packet_cnt = tp->forward_cnt_hint;
1571 skb = sk->sk_write_queue.next;
1575 sk_stream_for_retrans_queue_from(skb, sk) {
1576 tp->forward_cnt_hint = packet_cnt;
1577 tp->forward_skb_hint = skb;
1579 /* Similar to the retransmit loop above we
1580 * can pretend that the retransmitted SKB
1581 * we send out here will be composed of one
1582 * real MSS sized packet because tcp_retransmit_skb()
1583 * will fragment it if necessary.
1585 if (++packet_cnt > tp->fackets_out)
1588 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1591 if (TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS)
1594 /* Ok, retransmit it. */
1595 if (tcp_retransmit_skb(sk, skb)) {
1596 tp->forward_skb_hint = NULL;
1600 if (skb == skb_peek(&sk->sk_write_queue))
1601 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1602 inet_csk(sk)->icsk_rto,
1605 NET_INC_STATS_BH(LINUX_MIB_TCPFORWARDRETRANS);
1610 /* Send a fin. The caller locks the socket for us. This cannot be
1611 * allowed to fail queueing a FIN frame under any circumstances.
1613 void tcp_send_fin(struct sock *sk)
1615 struct tcp_sock *tp = tcp_sk(sk);
1616 struct sk_buff *skb = skb_peek_tail(&sk->sk_write_queue);
1619 /* Optimization, tack on the FIN if we have a queue of
1620 * unsent frames. But be careful about outgoing SACKS
1623 mss_now = tcp_current_mss(sk, 1);
1625 if (sk->sk_send_head != NULL) {
1626 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN;
1627 TCP_SKB_CB(skb)->end_seq++;
1630 /* Socket is locked, keep trying until memory is available. */
1632 skb = alloc_skb_fclone(MAX_TCP_HEADER, GFP_KERNEL);
1638 /* Reserve space for headers and prepare control bits. */
1639 skb_reserve(skb, MAX_TCP_HEADER);
1641 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
1642 TCP_SKB_CB(skb)->sacked = 0;
1643 skb_shinfo(skb)->tso_segs = 1;
1644 skb_shinfo(skb)->tso_size = 0;
1646 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
1647 TCP_SKB_CB(skb)->seq = tp->write_seq;
1648 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
1649 tcp_queue_skb(sk, skb);
1651 __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_OFF);
1654 /* We get here when a process closes a file descriptor (either due to
1655 * an explicit close() or as a byproduct of exit()'ing) and there
1656 * was unread data in the receive queue. This behavior is recommended
1657 * by draft-ietf-tcpimpl-prob-03.txt section 3.10. -DaveM
1659 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
1661 struct tcp_sock *tp = tcp_sk(sk);
1662 struct sk_buff *skb;
1664 /* NOTE: No TCP options attached and we never retransmit this. */
1665 skb = alloc_skb(MAX_TCP_HEADER, priority);
1667 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
1671 /* Reserve space for headers and prepare control bits. */
1672 skb_reserve(skb, MAX_TCP_HEADER);
1674 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
1675 TCP_SKB_CB(skb)->sacked = 0;
1676 skb_shinfo(skb)->tso_segs = 1;
1677 skb_shinfo(skb)->tso_size = 0;
1680 TCP_SKB_CB(skb)->seq = tcp_acceptable_seq(sk, tp);
1681 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
1682 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1683 if (tcp_transmit_skb(sk, skb, 0, priority))
1684 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
1687 /* WARNING: This routine must only be called when we have already sent
1688 * a SYN packet that crossed the incoming SYN that caused this routine
1689 * to get called. If this assumption fails then the initial rcv_wnd
1690 * and rcv_wscale values will not be correct.
1692 int tcp_send_synack(struct sock *sk)
1694 struct sk_buff* skb;
1696 skb = skb_peek(&sk->sk_write_queue);
1697 if (skb == NULL || !(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_SYN)) {
1698 printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
1701 if (!(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_ACK)) {
1702 if (skb_cloned(skb)) {
1703 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
1706 __skb_unlink(skb, &sk->sk_write_queue);
1707 skb_header_release(nskb);
1708 __skb_queue_head(&sk->sk_write_queue, nskb);
1709 sk_stream_free_skb(sk, skb);
1710 sk_charge_skb(sk, nskb);
1714 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK;
1715 TCP_ECN_send_synack(tcp_sk(sk), skb);
1717 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1718 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
1722 * Prepare a SYN-ACK.
1724 struct sk_buff * tcp_make_synack(struct sock *sk, struct dst_entry *dst,
1725 struct request_sock *req)
1727 struct inet_request_sock *ireq = inet_rsk(req);
1728 struct tcp_sock *tp = tcp_sk(sk);
1730 int tcp_header_size;
1731 struct sk_buff *skb;
1733 skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC);
1737 /* Reserve space for headers. */
1738 skb_reserve(skb, MAX_TCP_HEADER);
1740 skb->dst = dst_clone(dst);
1742 tcp_header_size = (sizeof(struct tcphdr) + TCPOLEN_MSS +
1743 (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0) +
1744 (ireq->wscale_ok ? TCPOLEN_WSCALE_ALIGNED : 0) +
1745 /* SACK_PERM is in the place of NOP NOP of TS */
1746 ((ireq->sack_ok && !ireq->tstamp_ok) ? TCPOLEN_SACKPERM_ALIGNED : 0));
1747 skb->h.th = th = (struct tcphdr *) skb_push(skb, tcp_header_size);
1749 memset(th, 0, sizeof(struct tcphdr));
1752 if (dst->dev->features&NETIF_F_TSO)
1754 TCP_ECN_make_synack(req, th);
1755 th->source = inet_sk(sk)->sport;
1756 th->dest = ireq->rmt_port;
1757 TCP_SKB_CB(skb)->seq = tcp_rsk(req)->snt_isn;
1758 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
1759 TCP_SKB_CB(skb)->sacked = 0;
1760 skb_shinfo(skb)->tso_segs = 1;
1761 skb_shinfo(skb)->tso_size = 0;
1762 th->seq = htonl(TCP_SKB_CB(skb)->seq);
1763 th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
1764 if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
1766 /* Set this up on the first call only */
1767 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
1768 /* tcp_full_space because it is guaranteed to be the first packet */
1769 tcp_select_initial_window(tcp_full_space(sk),
1770 dst_metric(dst, RTAX_ADVMSS) - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
1775 ireq->rcv_wscale = rcv_wscale;
1778 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
1779 th->window = htons(req->rcv_wnd);
1781 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1782 tcp_syn_build_options((__u32 *)(th + 1), dst_metric(dst, RTAX_ADVMSS), ireq->tstamp_ok,
1783 ireq->sack_ok, ireq->wscale_ok, ireq->rcv_wscale,
1784 TCP_SKB_CB(skb)->when,
1788 th->doff = (tcp_header_size >> 2);
1789 TCP_INC_STATS(TCP_MIB_OUTSEGS);
1794 * Do all connect socket setups that can be done AF independent.
1796 static inline void tcp_connect_init(struct sock *sk)
1798 struct dst_entry *dst = __sk_dst_get(sk);
1799 struct tcp_sock *tp = tcp_sk(sk);
1802 /* We'll fix this up when we get a response from the other end.
1803 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
1805 tp->tcp_header_len = sizeof(struct tcphdr) +
1806 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
1808 /* If user gave his TCP_MAXSEG, record it to clamp */
1809 if (tp->rx_opt.user_mss)
1810 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
1812 tcp_sync_mss(sk, dst_mtu(dst));
1814 if (!tp->window_clamp)
1815 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
1816 tp->advmss = dst_metric(dst, RTAX_ADVMSS);
1817 tcp_initialize_rcv_mss(sk);
1819 tcp_select_initial_window(tcp_full_space(sk),
1820 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
1823 sysctl_tcp_window_scaling,
1826 tp->rx_opt.rcv_wscale = rcv_wscale;
1827 tp->rcv_ssthresh = tp->rcv_wnd;
1830 sock_reset_flag(sk, SOCK_DONE);
1832 tcp_init_wl(tp, tp->write_seq, 0);
1833 tp->snd_una = tp->write_seq;
1834 tp->snd_sml = tp->write_seq;
1839 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
1840 inet_csk(sk)->icsk_retransmits = 0;
1841 tcp_clear_retrans(tp);
1845 * Build a SYN and send it off.
1847 int tcp_connect(struct sock *sk)
1849 struct tcp_sock *tp = tcp_sk(sk);
1850 struct sk_buff *buff;
1852 tcp_connect_init(sk);
1854 buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
1855 if (unlikely(buff == NULL))
1858 /* Reserve space for headers. */
1859 skb_reserve(buff, MAX_TCP_HEADER);
1861 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN;
1862 TCP_ECN_send_syn(sk, tp, buff);
1863 TCP_SKB_CB(buff)->sacked = 0;
1864 skb_shinfo(buff)->tso_segs = 1;
1865 skb_shinfo(buff)->tso_size = 0;
1867 TCP_SKB_CB(buff)->seq = tp->write_seq++;
1868 TCP_SKB_CB(buff)->end_seq = tp->write_seq;
1869 tp->snd_nxt = tp->write_seq;
1870 tp->pushed_seq = tp->write_seq;
1873 TCP_SKB_CB(buff)->when = tcp_time_stamp;
1874 tp->retrans_stamp = TCP_SKB_CB(buff)->when;
1875 skb_header_release(buff);
1876 __skb_queue_tail(&sk->sk_write_queue, buff);
1877 sk_charge_skb(sk, buff);
1878 tp->packets_out += tcp_skb_pcount(buff);
1879 tcp_transmit_skb(sk, buff, 1, GFP_KERNEL);
1880 TCP_INC_STATS(TCP_MIB_ACTIVEOPENS);
1882 /* Timer for repeating the SYN until an answer. */
1883 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1884 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
1888 /* Send out a delayed ack, the caller does the policy checking
1889 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
1892 void tcp_send_delayed_ack(struct sock *sk)
1894 struct inet_connection_sock *icsk = inet_csk(sk);
1895 int ato = icsk->icsk_ack.ato;
1896 unsigned long timeout;
1898 if (ato > TCP_DELACK_MIN) {
1899 const struct tcp_sock *tp = tcp_sk(sk);
1902 if (icsk->icsk_ack.pingpong || (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
1903 max_ato = TCP_DELACK_MAX;
1905 /* Slow path, intersegment interval is "high". */
1907 /* If some rtt estimate is known, use it to bound delayed ack.
1908 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
1912 int rtt = max(tp->srtt>>3, TCP_DELACK_MIN);
1918 ato = min(ato, max_ato);
1921 /* Stay within the limit we were given */
1922 timeout = jiffies + ato;
1924 /* Use new timeout only if there wasn't a older one earlier. */
1925 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
1926 /* If delack timer was blocked or is about to expire,
1929 if (icsk->icsk_ack.blocked ||
1930 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
1935 if (!time_before(timeout, icsk->icsk_ack.timeout))
1936 timeout = icsk->icsk_ack.timeout;
1938 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
1939 icsk->icsk_ack.timeout = timeout;
1940 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
1943 /* This routine sends an ack and also updates the window. */
1944 void tcp_send_ack(struct sock *sk)
1946 /* If we have been reset, we may not send again. */
1947 if (sk->sk_state != TCP_CLOSE) {
1948 struct tcp_sock *tp = tcp_sk(sk);
1949 struct sk_buff *buff;
1951 /* We are not putting this on the write queue, so
1952 * tcp_transmit_skb() will set the ownership to this
1955 buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
1957 inet_csk_schedule_ack(sk);
1958 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
1959 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
1960 TCP_DELACK_MAX, TCP_RTO_MAX);
1964 /* Reserve space for headers and prepare control bits. */
1965 skb_reserve(buff, MAX_TCP_HEADER);
1967 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK;
1968 TCP_SKB_CB(buff)->sacked = 0;
1969 skb_shinfo(buff)->tso_segs = 1;
1970 skb_shinfo(buff)->tso_size = 0;
1972 /* Send it off, this clears delayed acks for us. */
1973 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(buff)->end_seq = tcp_acceptable_seq(sk, tp);
1974 TCP_SKB_CB(buff)->when = tcp_time_stamp;
1975 tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC);
1979 /* This routine sends a packet with an out of date sequence
1980 * number. It assumes the other end will try to ack it.
1982 * Question: what should we make while urgent mode?
1983 * 4.4BSD forces sending single byte of data. We cannot send
1984 * out of window data, because we have SND.NXT==SND.MAX...
1986 * Current solution: to send TWO zero-length segments in urgent mode:
1987 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
1988 * out-of-date with SND.UNA-1 to probe window.
1990 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
1992 struct tcp_sock *tp = tcp_sk(sk);
1993 struct sk_buff *skb;
1995 /* We don't queue it, tcp_transmit_skb() sets ownership. */
1996 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2000 /* Reserve space for headers and set control bits. */
2001 skb_reserve(skb, MAX_TCP_HEADER);
2003 TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
2004 TCP_SKB_CB(skb)->sacked = urgent;
2005 skb_shinfo(skb)->tso_segs = 1;
2006 skb_shinfo(skb)->tso_size = 0;
2008 /* Use a previous sequence. This should cause the other
2009 * end to send an ack. Don't queue or clone SKB, just
2012 TCP_SKB_CB(skb)->seq = urgent ? tp->snd_una : tp->snd_una - 1;
2013 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
2014 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2015 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
2018 int tcp_write_wakeup(struct sock *sk)
2020 if (sk->sk_state != TCP_CLOSE) {
2021 struct tcp_sock *tp = tcp_sk(sk);
2022 struct sk_buff *skb;
2024 if ((skb = sk->sk_send_head) != NULL &&
2025 before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)) {
2027 unsigned int mss = tcp_current_mss(sk, 0);
2028 unsigned int seg_size = tp->snd_una+tp->snd_wnd-TCP_SKB_CB(skb)->seq;
2030 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
2031 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
2033 /* We are probing the opening of a window
2034 * but the window size is != 0
2035 * must have been a result SWS avoidance ( sender )
2037 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
2039 seg_size = min(seg_size, mss);
2040 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
2041 if (tcp_fragment(sk, skb, seg_size, mss))
2043 } else if (!tcp_skb_pcount(skb))
2044 tcp_set_skb_tso_segs(sk, skb, mss);
2046 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
2047 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2048 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2050 update_send_head(sk, tp, skb);
2055 between(tp->snd_up, tp->snd_una+1, tp->snd_una+0xFFFF))
2056 tcp_xmit_probe_skb(sk, TCPCB_URG);
2057 return tcp_xmit_probe_skb(sk, 0);
2063 /* A window probe timeout has occurred. If window is not closed send
2064 * a partial packet else a zero probe.
2066 void tcp_send_probe0(struct sock *sk)
2068 struct inet_connection_sock *icsk = inet_csk(sk);
2069 struct tcp_sock *tp = tcp_sk(sk);
2072 err = tcp_write_wakeup(sk);
2074 if (tp->packets_out || !sk->sk_send_head) {
2075 /* Cancel probe timer, if it is not required. */
2076 icsk->icsk_probes_out = 0;
2077 icsk->icsk_backoff = 0;
2082 if (icsk->icsk_backoff < sysctl_tcp_retries2)
2083 icsk->icsk_backoff++;
2084 icsk->icsk_probes_out++;
2085 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2086 min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2089 /* If packet was not sent due to local congestion,
2090 * do not backoff and do not remember icsk_probes_out.
2091 * Let local senders to fight for local resources.
2093 * Use accumulated backoff yet.
2095 if (!icsk->icsk_probes_out)
2096 icsk->icsk_probes_out = 1;
2097 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2098 min(icsk->icsk_rto << icsk->icsk_backoff,
2099 TCP_RESOURCE_PROBE_INTERVAL),
2104 EXPORT_SYMBOL(tcp_connect);
2105 EXPORT_SYMBOL(tcp_make_synack);
2106 EXPORT_SYMBOL(tcp_simple_retransmit);
2107 EXPORT_SYMBOL(tcp_sync_mss);
2108 EXPORT_SYMBOL(sysctl_tcp_tso_win_divisor);