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 = 8;
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 tcp_sock *tp, struct dst_entry *dst)
110 s32 delta = tcp_time_stamp - tp->lsndtime;
111 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
112 u32 cwnd = tp->snd_cwnd;
114 tcp_ca_event(tp, CA_EVENT_CWND_RESTART);
116 tp->snd_ssthresh = tcp_current_ssthresh(tp);
117 restart_cwnd = min(restart_cwnd, cwnd);
119 while ((delta -= tp->rto) > 0 && cwnd > restart_cwnd)
121 tp->snd_cwnd = max(cwnd, restart_cwnd);
122 tp->snd_cwnd_stamp = tcp_time_stamp;
123 tp->snd_cwnd_used = 0;
126 static inline void tcp_event_data_sent(struct tcp_sock *tp,
127 struct sk_buff *skb, struct sock *sk)
129 u32 now = tcp_time_stamp;
131 if (!tp->packets_out && (s32)(now - tp->lsndtime) > tp->rto)
132 tcp_cwnd_restart(tp, __sk_dst_get(sk));
136 /* If it is a reply for ato after last received
137 * packet, enter pingpong mode.
139 if ((u32)(now - tp->ack.lrcvtime) < tp->ack.ato)
140 tp->ack.pingpong = 1;
143 static __inline__ void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
145 struct tcp_sock *tp = tcp_sk(sk);
147 tcp_dec_quickack_mode(tp, pkts);
148 tcp_clear_xmit_timer(sk, TCP_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 RFC1414. 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)
268 struct inet_sock *inet = inet_sk(sk);
269 struct tcp_sock *tp = tcp_sk(sk);
270 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
271 int tcp_header_size = tp->tcp_header_len;
276 BUG_ON(!tcp_skb_pcount(skb));
278 #define SYSCTL_FLAG_TSTAMPS 0x1
279 #define SYSCTL_FLAG_WSCALE 0x2
280 #define SYSCTL_FLAG_SACK 0x4
282 /* If congestion control is doing timestamping */
283 if (tp->ca_ops->rtt_sample)
284 do_gettimeofday(&skb->stamp);
287 if (tcb->flags & TCPCB_FLAG_SYN) {
288 tcp_header_size = sizeof(struct tcphdr) + TCPOLEN_MSS;
289 if(sysctl_tcp_timestamps) {
290 tcp_header_size += TCPOLEN_TSTAMP_ALIGNED;
291 sysctl_flags |= SYSCTL_FLAG_TSTAMPS;
293 if(sysctl_tcp_window_scaling) {
294 tcp_header_size += TCPOLEN_WSCALE_ALIGNED;
295 sysctl_flags |= SYSCTL_FLAG_WSCALE;
297 if(sysctl_tcp_sack) {
298 sysctl_flags |= SYSCTL_FLAG_SACK;
299 if(!(sysctl_flags & SYSCTL_FLAG_TSTAMPS))
300 tcp_header_size += TCPOLEN_SACKPERM_ALIGNED;
302 } else if (tp->rx_opt.eff_sacks) {
303 /* A SACK is 2 pad bytes, a 2 byte header, plus
304 * 2 32-bit sequence numbers for each SACK block.
306 tcp_header_size += (TCPOLEN_SACK_BASE_ALIGNED +
307 (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
310 if (tcp_packets_in_flight(tp) == 0)
311 tcp_ca_event(tp, CA_EVENT_TX_START);
313 th = (struct tcphdr *) skb_push(skb, tcp_header_size);
315 skb_set_owner_w(skb, sk);
317 /* Build TCP header and checksum it. */
318 th->source = inet->sport;
319 th->dest = inet->dport;
320 th->seq = htonl(tcb->seq);
321 th->ack_seq = htonl(tp->rcv_nxt);
322 *(((__u16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | tcb->flags);
323 if (tcb->flags & TCPCB_FLAG_SYN) {
324 /* RFC1323: The window in SYN & SYN/ACK segments
327 th->window = htons(tp->rcv_wnd);
329 th->window = htons(tcp_select_window(sk));
335 between(tp->snd_up, tcb->seq+1, tcb->seq+0xFFFF)) {
336 th->urg_ptr = htons(tp->snd_up-tcb->seq);
340 if (tcb->flags & TCPCB_FLAG_SYN) {
341 tcp_syn_build_options((__u32 *)(th + 1),
342 tcp_advertise_mss(sk),
343 (sysctl_flags & SYSCTL_FLAG_TSTAMPS),
344 (sysctl_flags & SYSCTL_FLAG_SACK),
345 (sysctl_flags & SYSCTL_FLAG_WSCALE),
346 tp->rx_opt.rcv_wscale,
348 tp->rx_opt.ts_recent);
350 tcp_build_and_update_options((__u32 *)(th + 1),
353 TCP_ECN_send(sk, tp, skb, tcp_header_size);
355 tp->af_specific->send_check(sk, th, skb->len, skb);
357 if (tcb->flags & TCPCB_FLAG_ACK)
358 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
360 if (skb->len != tcp_header_size)
361 tcp_event_data_sent(tp, skb, sk);
363 TCP_INC_STATS(TCP_MIB_OUTSEGS);
365 err = tp->af_specific->queue_xmit(skb, 0);
371 /* NET_XMIT_CN is special. It does not guarantee,
372 * that this packet is lost. It tells that device
373 * is about to start to drop packets or already
374 * drops some packets of the same priority and
375 * invokes us to send less aggressively.
377 return err == NET_XMIT_CN ? 0 : err;
380 #undef SYSCTL_FLAG_TSTAMPS
381 #undef SYSCTL_FLAG_WSCALE
382 #undef SYSCTL_FLAG_SACK
386 /* This routine just queue's the buffer
388 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
389 * otherwise socket can stall.
391 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
393 struct tcp_sock *tp = tcp_sk(sk);
395 /* Advance write_seq and place onto the write_queue. */
396 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
397 skb_header_release(skb);
398 __skb_queue_tail(&sk->sk_write_queue, skb);
399 sk_charge_skb(sk, skb);
401 /* Queue it, remembering where we must start sending. */
402 if (sk->sk_send_head == NULL)
403 sk->sk_send_head = skb;
406 static inline void tcp_tso_set_push(struct sk_buff *skb)
408 /* Force push to be on for any TSO frames to workaround
409 * problems with busted implementations like Mac OS-X that
410 * hold off socket receive wakeups until push is seen.
412 if (tcp_skb_pcount(skb) > 1)
413 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
416 static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb)
418 struct tcp_sock *tp = tcp_sk(sk);
420 if (skb->len <= tp->mss_cache_std ||
421 !(sk->sk_route_caps & NETIF_F_TSO)) {
422 /* Avoid the costly divide in the normal
425 skb_shinfo(skb)->tso_segs = 1;
426 skb_shinfo(skb)->tso_size = 0;
430 factor = skb->len + (tp->mss_cache_std - 1);
431 factor /= tp->mss_cache_std;
432 skb_shinfo(skb)->tso_segs = factor;
433 skb_shinfo(skb)->tso_size = tp->mss_cache_std;
437 static inline int tcp_minshall_check(const struct tcp_sock *tp)
439 return after(tp->snd_sml,tp->snd_una) &&
440 !after(tp->snd_sml, tp->snd_nxt);
443 /* Return 0, if packet can be sent now without violation Nagle's rules:
444 * 1. It is full sized.
445 * 2. Or it contains FIN.
446 * 3. Or TCP_NODELAY was set.
447 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
448 * With Minshall's modification: all sent small packets are ACKed.
451 static inline int tcp_nagle_check(const struct tcp_sock *tp,
452 const struct sk_buff *skb,
453 unsigned mss_now, int nonagle)
455 return (skb->len < mss_now &&
456 !(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
457 ((nonagle&TCP_NAGLE_CORK) ||
460 tcp_minshall_check(tp))));
463 /* This checks if the data bearing packet SKB (usually sk->sk_send_head)
464 * should be put on the wire right now.
466 static int tcp_snd_test(struct sock *sk, struct sk_buff *skb,
467 unsigned cur_mss, int nonagle)
469 struct tcp_sock *tp = tcp_sk(sk);
470 int pkts = tcp_skb_pcount(skb);
473 tcp_set_skb_tso_segs(sk, skb);
474 pkts = tcp_skb_pcount(skb);
477 /* RFC 1122 - section 4.2.3.4
481 * a) The right edge of this frame exceeds the window
482 * b) There are packets in flight and we have a small segment
483 * [SWS avoidance and Nagle algorithm]
484 * (part of SWS is done on packetization)
485 * Minshall version sounds: there are no _small_
486 * segments in flight. (tcp_nagle_check)
487 * c) We have too many packets 'in flight'
489 * Don't use the nagle rule for urgent data (or
490 * for the final FIN -DaveM).
492 * Also, Nagle rule does not apply to frames, which
493 * sit in the middle of queue (they have no chances
494 * to get new data) and if room at tail of skb is
495 * not enough to save something seriously (<32 for now).
498 /* Don't be strict about the congestion window for the
499 * final FIN frame. -DaveM
501 return (((nonagle&TCP_NAGLE_PUSH) || tp->urg_mode
502 || !tcp_nagle_check(tp, skb, cur_mss, nonagle)) &&
503 (((tcp_packets_in_flight(tp) + (pkts-1)) < tp->snd_cwnd) ||
504 (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)) &&
505 !after(TCP_SKB_CB(skb)->end_seq, tp->snd_una + tp->snd_wnd));
508 static inline int tcp_skb_is_last(const struct sock *sk,
509 const struct sk_buff *skb)
511 return skb->next == (struct sk_buff *)&sk->sk_write_queue;
514 /* Push out any pending frames which were held back due to
515 * TCP_CORK or attempt at coalescing tiny packets.
516 * The socket must be locked by the caller.
518 void __tcp_push_pending_frames(struct sock *sk, struct tcp_sock *tp,
519 unsigned cur_mss, int nonagle)
521 struct sk_buff *skb = sk->sk_send_head;
524 if (!tcp_skb_is_last(sk, skb))
525 nonagle = TCP_NAGLE_PUSH;
526 if (!tcp_snd_test(sk, skb, cur_mss, nonagle) ||
527 tcp_write_xmit(sk, nonagle))
528 tcp_check_probe_timer(sk, tp);
530 tcp_cwnd_validate(sk, tp);
533 int tcp_may_send_now(struct sock *sk, struct tcp_sock *tp)
535 struct sk_buff *skb = sk->sk_send_head;
538 tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
539 (tcp_skb_is_last(sk, skb) ?
545 /* Send _single_ skb sitting at the send head. This function requires
546 * true push pending frames to setup probe timer etc.
548 void tcp_push_one(struct sock *sk, unsigned cur_mss)
550 struct tcp_sock *tp = tcp_sk(sk);
551 struct sk_buff *skb = sk->sk_send_head;
553 if (tcp_snd_test(sk, skb, cur_mss, TCP_NAGLE_PUSH)) {
554 /* Send it out now. */
555 TCP_SKB_CB(skb)->when = tcp_time_stamp;
556 tcp_tso_set_push(skb);
557 if (!tcp_transmit_skb(sk, skb_clone(skb, sk->sk_allocation))) {
558 sk->sk_send_head = NULL;
559 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
560 tcp_packets_out_inc(sk, tp, skb);
566 /* Function to create two new TCP segments. Shrinks the given segment
567 * to the specified size and appends a new segment with the rest of the
568 * packet to the list. This won't be called frequently, I hope.
569 * Remember, these are still headerless SKBs at this point.
571 static int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len)
573 struct tcp_sock *tp = tcp_sk(sk);
574 struct sk_buff *buff;
578 nsize = skb_headlen(skb) - len;
582 if (skb_cloned(skb) &&
583 skb_is_nonlinear(skb) &&
584 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
587 /* Get a new skb... force flag on. */
588 buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
590 return -ENOMEM; /* We'll just try again later. */
591 sk_charge_skb(sk, buff);
593 /* Correct the sequence numbers. */
594 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
595 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
596 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
598 /* PSH and FIN should only be set in the second packet. */
599 flags = TCP_SKB_CB(skb)->flags;
600 TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
601 TCP_SKB_CB(buff)->flags = flags;
602 TCP_SKB_CB(buff)->sacked =
603 (TCP_SKB_CB(skb)->sacked &
604 (TCPCB_LOST | TCPCB_EVER_RETRANS | TCPCB_AT_TAIL));
605 TCP_SKB_CB(skb)->sacked &= ~TCPCB_AT_TAIL;
607 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_HW) {
608 /* Copy and checksum data tail into the new buffer. */
609 buff->csum = csum_partial_copy_nocheck(skb->data + len, skb_put(buff, nsize),
614 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
616 skb->ip_summed = CHECKSUM_HW;
617 skb_split(skb, buff, len);
620 buff->ip_summed = skb->ip_summed;
622 /* Looks stupid, but our code really uses when of
623 * skbs, which it never sent before. --ANK
625 TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
626 buff->stamp = skb->stamp;
628 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
629 tp->lost_out -= tcp_skb_pcount(skb);
630 tp->left_out -= tcp_skb_pcount(skb);
633 /* Fix up tso_factor for both original and new SKB. */
634 tcp_set_skb_tso_segs(sk, skb);
635 tcp_set_skb_tso_segs(sk, buff);
637 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
638 tp->lost_out += tcp_skb_pcount(skb);
639 tp->left_out += tcp_skb_pcount(skb);
642 if (TCP_SKB_CB(buff)->sacked&TCPCB_LOST) {
643 tp->lost_out += tcp_skb_pcount(buff);
644 tp->left_out += tcp_skb_pcount(buff);
647 /* Link BUFF into the send queue. */
648 __skb_append(skb, buff);
653 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
654 * eventually). The difference is that pulled data not copied, but
655 * immediately discarded.
657 static unsigned char *__pskb_trim_head(struct sk_buff *skb, int len)
663 for (i=0; i<skb_shinfo(skb)->nr_frags; i++) {
664 if (skb_shinfo(skb)->frags[i].size <= eat) {
665 put_page(skb_shinfo(skb)->frags[i].page);
666 eat -= skb_shinfo(skb)->frags[i].size;
668 skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
670 skb_shinfo(skb)->frags[k].page_offset += eat;
671 skb_shinfo(skb)->frags[k].size -= eat;
677 skb_shinfo(skb)->nr_frags = k;
679 skb->tail = skb->data;
680 skb->data_len -= len;
681 skb->len = skb->data_len;
685 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
687 if (skb_cloned(skb) &&
688 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
691 if (len <= skb_headlen(skb)) {
692 __skb_pull(skb, len);
694 if (__pskb_trim_head(skb, len-skb_headlen(skb)) == NULL)
698 TCP_SKB_CB(skb)->seq += len;
699 skb->ip_summed = CHECKSUM_HW;
701 skb->truesize -= len;
702 sk->sk_wmem_queued -= len;
703 sk->sk_forward_alloc += len;
704 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
706 /* Any change of skb->len requires recalculation of tso
709 if (tcp_skb_pcount(skb) > 1)
710 tcp_set_skb_tso_segs(sk, skb);
715 /* This function synchronize snd mss to current pmtu/exthdr set.
717 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
718 for TCP options, but includes only bare TCP header.
720 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
721 It is minumum of user_mss and mss received with SYN.
722 It also does not include TCP options.
724 tp->pmtu_cookie is last pmtu, seen by this function.
726 tp->mss_cache is current effective sending mss, including
727 all tcp options except for SACKs. It is evaluated,
728 taking into account current pmtu, but never exceeds
729 tp->rx_opt.mss_clamp.
731 NOTE1. rfc1122 clearly states that advertised MSS
732 DOES NOT include either tcp or ip options.
734 NOTE2. tp->pmtu_cookie and tp->mss_cache are READ ONLY outside
735 this function. --ANK (980731)
738 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
740 struct tcp_sock *tp = tcp_sk(sk);
743 /* Calculate base mss without TCP options:
744 It is MMS_S - sizeof(tcphdr) of rfc1122
746 mss_now = pmtu - tp->af_specific->net_header_len - sizeof(struct tcphdr);
748 /* Clamp it (mss_clamp does not include tcp options) */
749 if (mss_now > tp->rx_opt.mss_clamp)
750 mss_now = tp->rx_opt.mss_clamp;
752 /* Now subtract optional transport overhead */
753 mss_now -= tp->ext_header_len;
755 /* Then reserve room for full set of TCP options and 8 bytes of data */
759 /* Now subtract TCP options size, not including SACKs */
760 mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
762 /* Bound mss with half of window */
763 if (tp->max_window && mss_now > (tp->max_window>>1))
764 mss_now = max((tp->max_window>>1), 68U - tp->tcp_header_len);
766 /* And store cached results */
767 tp->pmtu_cookie = pmtu;
768 tp->mss_cache = tp->mss_cache_std = mss_now;
773 /* Compute the current effective MSS, taking SACKs and IP options,
774 * and even PMTU discovery events into account.
776 * LARGESEND note: !urg_mode is overkill, only frames up to snd_up
777 * cannot be large. However, taking into account rare use of URG, this
781 unsigned int tcp_current_mss(struct sock *sk, int large)
783 struct tcp_sock *tp = tcp_sk(sk);
784 struct dst_entry *dst = __sk_dst_get(sk);
785 unsigned int do_large, mss_now;
787 mss_now = tp->mss_cache_std;
789 u32 mtu = dst_mtu(dst);
790 if (mtu != tp->pmtu_cookie)
791 mss_now = tcp_sync_mss(sk, mtu);
795 (sk->sk_route_caps & NETIF_F_TSO) &&
799 unsigned int large_mss, factor, limit;
801 large_mss = 65535 - tp->af_specific->net_header_len -
802 tp->ext_header_len - tp->tcp_header_len;
804 if (tp->max_window && large_mss > (tp->max_window>>1))
805 large_mss = max((tp->max_window>>1),
806 68U - tp->tcp_header_len);
808 factor = large_mss / mss_now;
810 /* Always keep large mss multiple of real mss, but
811 * do not exceed 1/tso_win_divisor of the congestion window
812 * so we can keep the ACK clock ticking and minimize
815 limit = tp->snd_cwnd;
816 if (sysctl_tcp_tso_win_divisor)
817 limit /= sysctl_tcp_tso_win_divisor;
818 limit = max(1U, limit);
822 tp->mss_cache = mss_now * factor;
824 mss_now = tp->mss_cache;
827 if (tp->rx_opt.eff_sacks)
828 mss_now -= (TCPOLEN_SACK_BASE_ALIGNED +
829 (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
833 /* This routine writes packets to the network. It advances the
834 * send_head. This happens as incoming acks open up the remote
837 * Returns 1, if no segments are in flight and we have queued segments, but
838 * cannot send anything now because of SWS or another problem.
840 int tcp_write_xmit(struct sock *sk, int nonagle)
842 struct tcp_sock *tp = tcp_sk(sk);
843 unsigned int mss_now;
845 /* If we are closed, the bytes will have to remain here.
846 * In time closedown will finish, we empty the write queue and all
849 if (sk->sk_state != TCP_CLOSE) {
853 /* Account for SACKS, we may need to fragment due to this.
854 * It is just like the real MSS changing on us midstream.
855 * We also handle things correctly when the user adds some
856 * IP options mid-stream. Silly to do, but cover it.
858 mss_now = tcp_current_mss(sk, 1);
860 while ((skb = sk->sk_send_head) &&
861 tcp_snd_test(sk, skb, mss_now,
862 tcp_skb_is_last(sk, skb) ? nonagle :
864 if (skb->len > mss_now) {
865 if (tcp_fragment(sk, skb, mss_now))
869 TCP_SKB_CB(skb)->when = tcp_time_stamp;
870 tcp_tso_set_push(skb);
871 if (tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC)))
874 /* Advance the send_head. This one is sent out.
875 * This call will increment packets_out.
877 update_send_head(sk, tp, skb);
879 tcp_minshall_update(tp, mss_now, skb);
884 tcp_cwnd_validate(sk, tp);
888 return !tp->packets_out && sk->sk_send_head;
893 /* This function returns the amount that we can raise the
894 * usable window based on the following constraints
896 * 1. The window can never be shrunk once it is offered (RFC 793)
897 * 2. We limit memory per socket
900 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
901 * RECV.NEXT + RCV.WIN fixed until:
902 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
904 * i.e. don't raise the right edge of the window until you can raise
905 * it at least MSS bytes.
907 * Unfortunately, the recommended algorithm breaks header prediction,
908 * since header prediction assumes th->window stays fixed.
910 * Strictly speaking, keeping th->window fixed violates the receiver
911 * side SWS prevention criteria. The problem is that under this rule
912 * a stream of single byte packets will cause the right side of the
913 * window to always advance by a single byte.
915 * Of course, if the sender implements sender side SWS prevention
916 * then this will not be a problem.
918 * BSD seems to make the following compromise:
920 * If the free space is less than the 1/4 of the maximum
921 * space available and the free space is less than 1/2 mss,
922 * then set the window to 0.
923 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
924 * Otherwise, just prevent the window from shrinking
925 * and from being larger than the largest representable value.
927 * This prevents incremental opening of the window in the regime
928 * where TCP is limited by the speed of the reader side taking
929 * data out of the TCP receive queue. It does nothing about
930 * those cases where the window is constrained on the sender side
931 * because the pipeline is full.
933 * BSD also seems to "accidentally" limit itself to windows that are a
934 * multiple of MSS, at least until the free space gets quite small.
935 * This would appear to be a side effect of the mbuf implementation.
936 * Combining these two algorithms results in the observed behavior
937 * of having a fixed window size at almost all times.
939 * Below we obtain similar behavior by forcing the offered window to
940 * a multiple of the mss when it is feasible to do so.
942 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
943 * Regular options like TIMESTAMP are taken into account.
945 u32 __tcp_select_window(struct sock *sk)
947 struct tcp_sock *tp = tcp_sk(sk);
948 /* MSS for the peer's data. Previous verions used mss_clamp
949 * here. I don't know if the value based on our guesses
950 * of peer's MSS is better for the performance. It's more correct
951 * but may be worse for the performance because of rcv_mss
952 * fluctuations. --SAW 1998/11/1
954 int mss = tp->ack.rcv_mss;
955 int free_space = tcp_space(sk);
956 int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
959 if (mss > full_space)
962 if (free_space < full_space/2) {
965 if (tcp_memory_pressure)
966 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U*tp->advmss);
968 if (free_space < mss)
972 if (free_space > tp->rcv_ssthresh)
973 free_space = tp->rcv_ssthresh;
975 /* Don't do rounding if we are using window scaling, since the
976 * scaled window will not line up with the MSS boundary anyway.
978 window = tp->rcv_wnd;
979 if (tp->rx_opt.rcv_wscale) {
982 /* Advertise enough space so that it won't get scaled away.
983 * Import case: prevent zero window announcement if
984 * 1<<rcv_wscale > mss.
986 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
987 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
988 << tp->rx_opt.rcv_wscale);
990 /* Get the largest window that is a nice multiple of mss.
991 * Window clamp already applied above.
992 * If our current window offering is within 1 mss of the
993 * free space we just keep it. This prevents the divide
994 * and multiply from happening most of the time.
995 * We also don't do any window rounding when the free space
998 if (window <= free_space - mss || window > free_space)
999 window = (free_space/mss)*mss;
1005 /* Attempt to collapse two adjacent SKB's during retransmission. */
1006 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int mss_now)
1008 struct tcp_sock *tp = tcp_sk(sk);
1009 struct sk_buff *next_skb = skb->next;
1011 /* The first test we must make is that neither of these two
1012 * SKB's are still referenced by someone else.
1014 if (!skb_cloned(skb) && !skb_cloned(next_skb)) {
1015 int skb_size = skb->len, next_skb_size = next_skb->len;
1016 u16 flags = TCP_SKB_CB(skb)->flags;
1018 /* Also punt if next skb has been SACK'd. */
1019 if(TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED)
1022 /* Next skb is out of window. */
1023 if (after(TCP_SKB_CB(next_skb)->end_seq, tp->snd_una+tp->snd_wnd))
1026 /* Punt if not enough space exists in the first SKB for
1027 * the data in the second, or the total combined payload
1028 * would exceed the MSS.
1030 if ((next_skb_size > skb_tailroom(skb)) ||
1031 ((skb_size + next_skb_size) > mss_now))
1034 BUG_ON(tcp_skb_pcount(skb) != 1 ||
1035 tcp_skb_pcount(next_skb) != 1);
1037 /* Ok. We will be able to collapse the packet. */
1038 __skb_unlink(next_skb, next_skb->list);
1040 memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
1042 if (next_skb->ip_summed == CHECKSUM_HW)
1043 skb->ip_summed = CHECKSUM_HW;
1045 if (skb->ip_summed != CHECKSUM_HW)
1046 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
1048 /* Update sequence range on original skb. */
1049 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
1051 /* Merge over control information. */
1052 flags |= TCP_SKB_CB(next_skb)->flags; /* This moves PSH/FIN etc. over */
1053 TCP_SKB_CB(skb)->flags = flags;
1055 /* All done, get rid of second SKB and account for it so
1056 * packet counting does not break.
1058 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked&(TCPCB_EVER_RETRANS|TCPCB_AT_TAIL);
1059 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_SACKED_RETRANS)
1060 tp->retrans_out -= tcp_skb_pcount(next_skb);
1061 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_LOST) {
1062 tp->lost_out -= tcp_skb_pcount(next_skb);
1063 tp->left_out -= tcp_skb_pcount(next_skb);
1065 /* Reno case is special. Sigh... */
1066 if (!tp->rx_opt.sack_ok && tp->sacked_out) {
1067 tcp_dec_pcount_approx(&tp->sacked_out, next_skb);
1068 tp->left_out -= tcp_skb_pcount(next_skb);
1071 /* Not quite right: it can be > snd.fack, but
1072 * it is better to underestimate fackets.
1074 tcp_dec_pcount_approx(&tp->fackets_out, next_skb);
1075 tcp_packets_out_dec(tp, next_skb);
1076 sk_stream_free_skb(sk, next_skb);
1080 /* Do a simple retransmit without using the backoff mechanisms in
1081 * tcp_timer. This is used for path mtu discovery.
1082 * The socket is already locked here.
1084 void tcp_simple_retransmit(struct sock *sk)
1086 struct tcp_sock *tp = tcp_sk(sk);
1087 struct sk_buff *skb;
1088 unsigned int mss = tcp_current_mss(sk, 0);
1091 sk_stream_for_retrans_queue(skb, sk) {
1092 if (skb->len > mss &&
1093 !(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1094 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
1095 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1096 tp->retrans_out -= tcp_skb_pcount(skb);
1098 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_LOST)) {
1099 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1100 tp->lost_out += tcp_skb_pcount(skb);
1109 tcp_sync_left_out(tp);
1111 /* Don't muck with the congestion window here.
1112 * Reason is that we do not increase amount of _data_
1113 * in network, but units changed and effective
1114 * cwnd/ssthresh really reduced now.
1116 if (tp->ca_state != TCP_CA_Loss) {
1117 tp->high_seq = tp->snd_nxt;
1118 tp->snd_ssthresh = tcp_current_ssthresh(tp);
1119 tp->prior_ssthresh = 0;
1120 tp->undo_marker = 0;
1121 tcp_set_ca_state(tp, TCP_CA_Loss);
1123 tcp_xmit_retransmit_queue(sk);
1126 /* This retransmits one SKB. Policy decisions and retransmit queue
1127 * state updates are done by the caller. Returns non-zero if an
1128 * error occurred which prevented the send.
1130 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
1132 struct tcp_sock *tp = tcp_sk(sk);
1133 unsigned int cur_mss = tcp_current_mss(sk, 0);
1136 /* Do not sent more than we queued. 1/4 is reserved for possible
1137 * copying overhead: frgagmentation, tunneling, mangling etc.
1139 if (atomic_read(&sk->sk_wmem_alloc) >
1140 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
1143 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
1144 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1147 if (sk->sk_route_caps & NETIF_F_TSO) {
1148 sk->sk_route_caps &= ~NETIF_F_TSO;
1149 sock_set_flag(sk, SOCK_NO_LARGESEND);
1150 tp->mss_cache = tp->mss_cache_std;
1153 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
1157 /* If receiver has shrunk his window, and skb is out of
1158 * new window, do not retransmit it. The exception is the
1159 * case, when window is shrunk to zero. In this case
1160 * our retransmit serves as a zero window probe.
1162 if (!before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)
1163 && TCP_SKB_CB(skb)->seq != tp->snd_una)
1166 if (skb->len > cur_mss) {
1167 int old_factor = tcp_skb_pcount(skb);
1170 if (tcp_fragment(sk, skb, cur_mss))
1171 return -ENOMEM; /* We'll try again later. */
1173 /* New SKB created, account for it. */
1174 new_factor = tcp_skb_pcount(skb);
1175 tp->packets_out -= old_factor - new_factor;
1176 tp->packets_out += tcp_skb_pcount(skb->next);
1179 /* Collapse two adjacent packets if worthwhile and we can. */
1180 if(!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) &&
1181 (skb->len < (cur_mss >> 1)) &&
1182 (skb->next != sk->sk_send_head) &&
1183 (skb->next != (struct sk_buff *)&sk->sk_write_queue) &&
1184 (skb_shinfo(skb)->nr_frags == 0 && skb_shinfo(skb->next)->nr_frags == 0) &&
1185 (tcp_skb_pcount(skb) == 1 && tcp_skb_pcount(skb->next) == 1) &&
1186 (sysctl_tcp_retrans_collapse != 0))
1187 tcp_retrans_try_collapse(sk, skb, cur_mss);
1189 if(tp->af_specific->rebuild_header(sk))
1190 return -EHOSTUNREACH; /* Routing failure or similar. */
1192 /* Some Solaris stacks overoptimize and ignore the FIN on a
1193 * retransmit when old data is attached. So strip it off
1194 * since it is cheap to do so and saves bytes on the network.
1197 (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
1198 tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
1199 if (!pskb_trim(skb, 0)) {
1200 TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1;
1201 skb_shinfo(skb)->tso_segs = 1;
1202 skb_shinfo(skb)->tso_size = 0;
1203 skb->ip_summed = CHECKSUM_NONE;
1208 /* Make a copy, if the first transmission SKB clone we made
1209 * is still in somebody's hands, else make a clone.
1211 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1212 tcp_tso_set_push(skb);
1214 err = tcp_transmit_skb(sk, (skb_cloned(skb) ?
1215 pskb_copy(skb, GFP_ATOMIC):
1216 skb_clone(skb, GFP_ATOMIC)));
1219 /* Update global TCP statistics. */
1220 TCP_INC_STATS(TCP_MIB_RETRANSSEGS);
1222 tp->total_retrans++;
1224 #if FASTRETRANS_DEBUG > 0
1225 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
1226 if (net_ratelimit())
1227 printk(KERN_DEBUG "retrans_out leaked.\n");
1230 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
1231 tp->retrans_out += tcp_skb_pcount(skb);
1233 /* Save stamp of the first retransmit. */
1234 if (!tp->retrans_stamp)
1235 tp->retrans_stamp = TCP_SKB_CB(skb)->when;
1239 /* snd_nxt is stored to detect loss of retransmitted segment,
1240 * see tcp_input.c tcp_sacktag_write_queue().
1242 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
1247 /* This gets called after a retransmit timeout, and the initially
1248 * retransmitted data is acknowledged. It tries to continue
1249 * resending the rest of the retransmit queue, until either
1250 * we've sent it all or the congestion window limit is reached.
1251 * If doing SACK, the first ACK which comes back for a timeout
1252 * based retransmit packet might feed us FACK information again.
1253 * If so, we use it to avoid unnecessarily retransmissions.
1255 void tcp_xmit_retransmit_queue(struct sock *sk)
1257 struct tcp_sock *tp = tcp_sk(sk);
1258 struct sk_buff *skb;
1259 int packet_cnt = tp->lost_out;
1261 /* First pass: retransmit lost packets. */
1263 sk_stream_for_retrans_queue(skb, sk) {
1264 __u8 sacked = TCP_SKB_CB(skb)->sacked;
1266 /* Assume this retransmit will generate
1267 * only one packet for congestion window
1268 * calculation purposes. This works because
1269 * tcp_retransmit_skb() will chop up the
1270 * packet to be MSS sized and all the
1271 * packet counting works out.
1273 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1276 if (sacked&TCPCB_LOST) {
1277 if (!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
1278 if (tcp_retransmit_skb(sk, skb))
1280 if (tp->ca_state != TCP_CA_Loss)
1281 NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS);
1283 NET_INC_STATS_BH(LINUX_MIB_TCPSLOWSTARTRETRANS);
1286 skb_peek(&sk->sk_write_queue))
1287 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1290 packet_cnt -= tcp_skb_pcount(skb);
1291 if (packet_cnt <= 0)
1297 /* OK, demanded retransmission is finished. */
1299 /* Forward retransmissions are possible only during Recovery. */
1300 if (tp->ca_state != TCP_CA_Recovery)
1303 /* No forward retransmissions in Reno are possible. */
1304 if (!tp->rx_opt.sack_ok)
1307 /* Yeah, we have to make difficult choice between forward transmission
1308 * and retransmission... Both ways have their merits...
1310 * For now we do not retransmit anything, while we have some new
1314 if (tcp_may_send_now(sk, tp))
1319 sk_stream_for_retrans_queue(skb, sk) {
1320 /* Similar to the retransmit loop above we
1321 * can pretend that the retransmitted SKB
1322 * we send out here will be composed of one
1323 * real MSS sized packet because tcp_retransmit_skb()
1324 * will fragment it if necessary.
1326 if (++packet_cnt > tp->fackets_out)
1329 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1332 if (TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS)
1335 /* Ok, retransmit it. */
1336 if (tcp_retransmit_skb(sk, skb))
1339 if (skb == skb_peek(&sk->sk_write_queue))
1340 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1342 NET_INC_STATS_BH(LINUX_MIB_TCPFORWARDRETRANS);
1347 /* Send a fin. The caller locks the socket for us. This cannot be
1348 * allowed to fail queueing a FIN frame under any circumstances.
1350 void tcp_send_fin(struct sock *sk)
1352 struct tcp_sock *tp = tcp_sk(sk);
1353 struct sk_buff *skb = skb_peek_tail(&sk->sk_write_queue);
1356 /* Optimization, tack on the FIN if we have a queue of
1357 * unsent frames. But be careful about outgoing SACKS
1360 mss_now = tcp_current_mss(sk, 1);
1362 if (sk->sk_send_head != NULL) {
1363 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN;
1364 TCP_SKB_CB(skb)->end_seq++;
1367 /* Socket is locked, keep trying until memory is available. */
1369 skb = alloc_skb(MAX_TCP_HEADER, GFP_KERNEL);
1375 /* Reserve space for headers and prepare control bits. */
1376 skb_reserve(skb, MAX_TCP_HEADER);
1378 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
1379 TCP_SKB_CB(skb)->sacked = 0;
1380 skb_shinfo(skb)->tso_segs = 1;
1381 skb_shinfo(skb)->tso_size = 0;
1383 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
1384 TCP_SKB_CB(skb)->seq = tp->write_seq;
1385 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
1386 tcp_queue_skb(sk, skb);
1388 __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_OFF);
1391 /* We get here when a process closes a file descriptor (either due to
1392 * an explicit close() or as a byproduct of exit()'ing) and there
1393 * was unread data in the receive queue. This behavior is recommended
1394 * by draft-ietf-tcpimpl-prob-03.txt section 3.10. -DaveM
1396 void tcp_send_active_reset(struct sock *sk, int priority)
1398 struct tcp_sock *tp = tcp_sk(sk);
1399 struct sk_buff *skb;
1401 /* NOTE: No TCP options attached and we never retransmit this. */
1402 skb = alloc_skb(MAX_TCP_HEADER, priority);
1404 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
1408 /* Reserve space for headers and prepare control bits. */
1409 skb_reserve(skb, MAX_TCP_HEADER);
1411 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
1412 TCP_SKB_CB(skb)->sacked = 0;
1413 skb_shinfo(skb)->tso_segs = 1;
1414 skb_shinfo(skb)->tso_size = 0;
1417 TCP_SKB_CB(skb)->seq = tcp_acceptable_seq(sk, tp);
1418 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
1419 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1420 if (tcp_transmit_skb(sk, skb))
1421 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
1424 /* WARNING: This routine must only be called when we have already sent
1425 * a SYN packet that crossed the incoming SYN that caused this routine
1426 * to get called. If this assumption fails then the initial rcv_wnd
1427 * and rcv_wscale values will not be correct.
1429 int tcp_send_synack(struct sock *sk)
1431 struct sk_buff* skb;
1433 skb = skb_peek(&sk->sk_write_queue);
1434 if (skb == NULL || !(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_SYN)) {
1435 printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
1438 if (!(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_ACK)) {
1439 if (skb_cloned(skb)) {
1440 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
1443 __skb_unlink(skb, &sk->sk_write_queue);
1444 skb_header_release(nskb);
1445 __skb_queue_head(&sk->sk_write_queue, nskb);
1446 sk_stream_free_skb(sk, skb);
1447 sk_charge_skb(sk, nskb);
1451 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK;
1452 TCP_ECN_send_synack(tcp_sk(sk), skb);
1454 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1455 return tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC));
1459 * Prepare a SYN-ACK.
1461 struct sk_buff * tcp_make_synack(struct sock *sk, struct dst_entry *dst,
1462 struct request_sock *req)
1464 struct inet_request_sock *ireq = inet_rsk(req);
1465 struct tcp_sock *tp = tcp_sk(sk);
1467 int tcp_header_size;
1468 struct sk_buff *skb;
1470 skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC);
1474 /* Reserve space for headers. */
1475 skb_reserve(skb, MAX_TCP_HEADER);
1477 skb->dst = dst_clone(dst);
1479 tcp_header_size = (sizeof(struct tcphdr) + TCPOLEN_MSS +
1480 (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0) +
1481 (ireq->wscale_ok ? TCPOLEN_WSCALE_ALIGNED : 0) +
1482 /* SACK_PERM is in the place of NOP NOP of TS */
1483 ((ireq->sack_ok && !ireq->tstamp_ok) ? TCPOLEN_SACKPERM_ALIGNED : 0));
1484 skb->h.th = th = (struct tcphdr *) skb_push(skb, tcp_header_size);
1486 memset(th, 0, sizeof(struct tcphdr));
1489 if (dst->dev->features&NETIF_F_TSO)
1491 TCP_ECN_make_synack(req, th);
1492 th->source = inet_sk(sk)->sport;
1493 th->dest = ireq->rmt_port;
1494 TCP_SKB_CB(skb)->seq = tcp_rsk(req)->snt_isn;
1495 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
1496 TCP_SKB_CB(skb)->sacked = 0;
1497 skb_shinfo(skb)->tso_segs = 1;
1498 skb_shinfo(skb)->tso_size = 0;
1499 th->seq = htonl(TCP_SKB_CB(skb)->seq);
1500 th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
1501 if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
1503 /* Set this up on the first call only */
1504 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
1505 /* tcp_full_space because it is guaranteed to be the first packet */
1506 tcp_select_initial_window(tcp_full_space(sk),
1507 dst_metric(dst, RTAX_ADVMSS) - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
1512 ireq->rcv_wscale = rcv_wscale;
1515 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
1516 th->window = htons(req->rcv_wnd);
1518 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1519 tcp_syn_build_options((__u32 *)(th + 1), dst_metric(dst, RTAX_ADVMSS), ireq->tstamp_ok,
1520 ireq->sack_ok, ireq->wscale_ok, ireq->rcv_wscale,
1521 TCP_SKB_CB(skb)->when,
1525 th->doff = (tcp_header_size >> 2);
1526 TCP_INC_STATS(TCP_MIB_OUTSEGS);
1531 * Do all connect socket setups that can be done AF independent.
1533 static inline void tcp_connect_init(struct sock *sk)
1535 struct dst_entry *dst = __sk_dst_get(sk);
1536 struct tcp_sock *tp = tcp_sk(sk);
1539 /* We'll fix this up when we get a response from the other end.
1540 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
1542 tp->tcp_header_len = sizeof(struct tcphdr) +
1543 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
1545 /* If user gave his TCP_MAXSEG, record it to clamp */
1546 if (tp->rx_opt.user_mss)
1547 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
1549 tcp_sync_mss(sk, dst_mtu(dst));
1551 if (!tp->window_clamp)
1552 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
1553 tp->advmss = dst_metric(dst, RTAX_ADVMSS);
1554 tcp_initialize_rcv_mss(sk);
1556 tcp_select_initial_window(tcp_full_space(sk),
1557 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
1560 sysctl_tcp_window_scaling,
1563 tp->rx_opt.rcv_wscale = rcv_wscale;
1564 tp->rcv_ssthresh = tp->rcv_wnd;
1567 sock_reset_flag(sk, SOCK_DONE);
1569 tcp_init_wl(tp, tp->write_seq, 0);
1570 tp->snd_una = tp->write_seq;
1571 tp->snd_sml = tp->write_seq;
1576 tp->rto = TCP_TIMEOUT_INIT;
1577 tp->retransmits = 0;
1578 tcp_clear_retrans(tp);
1582 * Build a SYN and send it off.
1584 int tcp_connect(struct sock *sk)
1586 struct tcp_sock *tp = tcp_sk(sk);
1587 struct sk_buff *buff;
1589 tcp_connect_init(sk);
1591 buff = alloc_skb(MAX_TCP_HEADER + 15, sk->sk_allocation);
1592 if (unlikely(buff == NULL))
1595 /* Reserve space for headers. */
1596 skb_reserve(buff, MAX_TCP_HEADER);
1598 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN;
1599 TCP_ECN_send_syn(sk, tp, buff);
1600 TCP_SKB_CB(buff)->sacked = 0;
1601 skb_shinfo(buff)->tso_segs = 1;
1602 skb_shinfo(buff)->tso_size = 0;
1604 TCP_SKB_CB(buff)->seq = tp->write_seq++;
1605 TCP_SKB_CB(buff)->end_seq = tp->write_seq;
1606 tp->snd_nxt = tp->write_seq;
1607 tp->pushed_seq = tp->write_seq;
1610 TCP_SKB_CB(buff)->when = tcp_time_stamp;
1611 tp->retrans_stamp = TCP_SKB_CB(buff)->when;
1612 skb_header_release(buff);
1613 __skb_queue_tail(&sk->sk_write_queue, buff);
1614 sk_charge_skb(sk, buff);
1615 tp->packets_out += tcp_skb_pcount(buff);
1616 tcp_transmit_skb(sk, skb_clone(buff, GFP_KERNEL));
1617 TCP_INC_STATS(TCP_MIB_ACTIVEOPENS);
1619 /* Timer for repeating the SYN until an answer. */
1620 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1624 /* Send out a delayed ack, the caller does the policy checking
1625 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
1628 void tcp_send_delayed_ack(struct sock *sk)
1630 struct tcp_sock *tp = tcp_sk(sk);
1631 int ato = tp->ack.ato;
1632 unsigned long timeout;
1634 if (ato > TCP_DELACK_MIN) {
1637 if (tp->ack.pingpong || (tp->ack.pending&TCP_ACK_PUSHED))
1638 max_ato = TCP_DELACK_MAX;
1640 /* Slow path, intersegment interval is "high". */
1642 /* If some rtt estimate is known, use it to bound delayed ack.
1643 * Do not use tp->rto here, use results of rtt measurements
1647 int rtt = max(tp->srtt>>3, TCP_DELACK_MIN);
1653 ato = min(ato, max_ato);
1656 /* Stay within the limit we were given */
1657 timeout = jiffies + ato;
1659 /* Use new timeout only if there wasn't a older one earlier. */
1660 if (tp->ack.pending&TCP_ACK_TIMER) {
1661 /* If delack timer was blocked or is about to expire,
1664 if (tp->ack.blocked || time_before_eq(tp->ack.timeout, jiffies+(ato>>2))) {
1669 if (!time_before(timeout, tp->ack.timeout))
1670 timeout = tp->ack.timeout;
1672 tp->ack.pending |= TCP_ACK_SCHED|TCP_ACK_TIMER;
1673 tp->ack.timeout = timeout;
1674 sk_reset_timer(sk, &tp->delack_timer, timeout);
1677 /* This routine sends an ack and also updates the window. */
1678 void tcp_send_ack(struct sock *sk)
1680 /* If we have been reset, we may not send again. */
1681 if (sk->sk_state != TCP_CLOSE) {
1682 struct tcp_sock *tp = tcp_sk(sk);
1683 struct sk_buff *buff;
1685 /* We are not putting this on the write queue, so
1686 * tcp_transmit_skb() will set the ownership to this
1689 buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
1691 tcp_schedule_ack(tp);
1692 tp->ack.ato = TCP_ATO_MIN;
1693 tcp_reset_xmit_timer(sk, TCP_TIME_DACK, TCP_DELACK_MAX);
1697 /* Reserve space for headers and prepare control bits. */
1698 skb_reserve(buff, MAX_TCP_HEADER);
1700 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK;
1701 TCP_SKB_CB(buff)->sacked = 0;
1702 skb_shinfo(buff)->tso_segs = 1;
1703 skb_shinfo(buff)->tso_size = 0;
1705 /* Send it off, this clears delayed acks for us. */
1706 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(buff)->end_seq = tcp_acceptable_seq(sk, tp);
1707 TCP_SKB_CB(buff)->when = tcp_time_stamp;
1708 tcp_transmit_skb(sk, buff);
1712 /* This routine sends a packet with an out of date sequence
1713 * number. It assumes the other end will try to ack it.
1715 * Question: what should we make while urgent mode?
1716 * 4.4BSD forces sending single byte of data. We cannot send
1717 * out of window data, because we have SND.NXT==SND.MAX...
1719 * Current solution: to send TWO zero-length segments in urgent mode:
1720 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
1721 * out-of-date with SND.UNA-1 to probe window.
1723 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
1725 struct tcp_sock *tp = tcp_sk(sk);
1726 struct sk_buff *skb;
1728 /* We don't queue it, tcp_transmit_skb() sets ownership. */
1729 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
1733 /* Reserve space for headers and set control bits. */
1734 skb_reserve(skb, MAX_TCP_HEADER);
1736 TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
1737 TCP_SKB_CB(skb)->sacked = urgent;
1738 skb_shinfo(skb)->tso_segs = 1;
1739 skb_shinfo(skb)->tso_size = 0;
1741 /* Use a previous sequence. This should cause the other
1742 * end to send an ack. Don't queue or clone SKB, just
1745 TCP_SKB_CB(skb)->seq = urgent ? tp->snd_una : tp->snd_una - 1;
1746 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
1747 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1748 return tcp_transmit_skb(sk, skb);
1751 int tcp_write_wakeup(struct sock *sk)
1753 if (sk->sk_state != TCP_CLOSE) {
1754 struct tcp_sock *tp = tcp_sk(sk);
1755 struct sk_buff *skb;
1757 if ((skb = sk->sk_send_head) != NULL &&
1758 before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)) {
1760 unsigned int mss = tcp_current_mss(sk, 0);
1761 unsigned int seg_size = tp->snd_una+tp->snd_wnd-TCP_SKB_CB(skb)->seq;
1763 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
1764 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
1766 /* We are probing the opening of a window
1767 * but the window size is != 0
1768 * must have been a result SWS avoidance ( sender )
1770 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
1772 seg_size = min(seg_size, mss);
1773 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
1774 if (tcp_fragment(sk, skb, seg_size))
1776 /* SWS override triggered forced fragmentation.
1777 * Disable TSO, the connection is too sick. */
1778 if (sk->sk_route_caps & NETIF_F_TSO) {
1779 sock_set_flag(sk, SOCK_NO_LARGESEND);
1780 sk->sk_route_caps &= ~NETIF_F_TSO;
1781 tp->mss_cache = tp->mss_cache_std;
1783 } else if (!tcp_skb_pcount(skb))
1784 tcp_set_skb_tso_segs(sk, skb);
1786 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
1787 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1788 tcp_tso_set_push(skb);
1789 err = tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC));
1791 update_send_head(sk, tp, skb);
1796 between(tp->snd_up, tp->snd_una+1, tp->snd_una+0xFFFF))
1797 tcp_xmit_probe_skb(sk, TCPCB_URG);
1798 return tcp_xmit_probe_skb(sk, 0);
1804 /* A window probe timeout has occurred. If window is not closed send
1805 * a partial packet else a zero probe.
1807 void tcp_send_probe0(struct sock *sk)
1809 struct tcp_sock *tp = tcp_sk(sk);
1812 err = tcp_write_wakeup(sk);
1814 if (tp->packets_out || !sk->sk_send_head) {
1815 /* Cancel probe timer, if it is not required. */
1822 if (tp->backoff < sysctl_tcp_retries2)
1825 tcp_reset_xmit_timer (sk, TCP_TIME_PROBE0,
1826 min(tp->rto << tp->backoff, TCP_RTO_MAX));
1828 /* If packet was not sent due to local congestion,
1829 * do not backoff and do not remember probes_out.
1830 * Let local senders to fight for local resources.
1832 * Use accumulated backoff yet.
1834 if (!tp->probes_out)
1836 tcp_reset_xmit_timer (sk, TCP_TIME_PROBE0,
1837 min(tp->rto << tp->backoff, TCP_RESOURCE_PROBE_INTERVAL));
1841 EXPORT_SYMBOL(tcp_connect);
1842 EXPORT_SYMBOL(tcp_make_synack);
1843 EXPORT_SYMBOL(tcp_simple_retransmit);
1844 EXPORT_SYMBOL(tcp_sync_mss);