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 $
10 * Authors: Ross Biro, <bir7@leland.Stanford.Edu>
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 if (tcp_is_vegas(tp
))
115 tcp_vegas_enable(tp
);
117 tp
->snd_ssthresh
= tcp_current_ssthresh(tp
);
118 restart_cwnd
= min(restart_cwnd
, cwnd
);
120 while ((delta
-= tp
->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 u32 now
= tcp_time_stamp
;
132 if (!tp
->packets_out
&& (s32
)(now
- tp
->lsndtime
) > tp
->rto
)
133 tcp_cwnd_restart(tp
, __sk_dst_get(sk
));
137 /* If it is a reply for ato after last received
138 * packet, enter pingpong mode.
140 if ((u32
)(now
- tp
->ack
.lrcvtime
) < tp
->ack
.ato
)
141 tp
->ack
.pingpong
= 1;
144 static __inline__
void tcp_event_ack_sent(struct sock
*sk
)
146 struct tcp_sock
*tp
= tcp_sk(sk
);
148 tcp_dec_quickack_mode(tp
);
149 tcp_clear_xmit_timer(sk
, TCP_TIME_DACK
);
152 /* Determine a window scaling and initial window to offer.
153 * Based on the assumption that the given amount of space
154 * will be offered. Store the results in the tp structure.
155 * NOTE: for smooth operation initial space offering should
156 * be a multiple of mss if possible. We assume here that mss >= 1.
157 * This MUST be enforced by all callers.
159 void tcp_select_initial_window(int __space
, __u32 mss
,
160 __u32
*rcv_wnd
, __u32
*window_clamp
,
161 int wscale_ok
, __u8
*rcv_wscale
)
163 unsigned int space
= (__space
< 0 ? 0 : __space
);
165 /* If no clamp set the clamp to the max possible scaled window */
166 if (*window_clamp
== 0)
167 (*window_clamp
) = (65535 << 14);
168 space
= min(*window_clamp
, space
);
170 /* Quantize space offering to a multiple of mss if possible. */
172 space
= (space
/ mss
) * mss
;
174 /* NOTE: offering an initial window larger than 32767
175 * will break some buggy TCP stacks. We try to be nice.
176 * If we are not window scaling, then this truncates
177 * our initial window offering to 32k. There should also
178 * be a sysctl option to stop being nice.
180 (*rcv_wnd
) = min(space
, MAX_TCP_WINDOW
);
183 /* Set window scaling on max possible window
184 * See RFC1323 for an explanation of the limit to 14
186 space
= max_t(u32
, sysctl_tcp_rmem
[2], sysctl_rmem_max
);
187 while (space
> 65535 && (*rcv_wscale
) < 14) {
193 /* Set initial window to value enough for senders,
194 * following RFC1414. Senders, not following this RFC,
195 * will be satisfied with 2.
197 if (mss
> (1<<*rcv_wscale
)) {
203 if (*rcv_wnd
> init_cwnd
*mss
)
204 *rcv_wnd
= init_cwnd
*mss
;
207 /* Set the clamp no higher than max representable value */
208 (*window_clamp
) = min(65535U << (*rcv_wscale
), *window_clamp
);
211 /* Chose a new window to advertise, update state in tcp_sock for the
212 * socket, and return result with RFC1323 scaling applied. The return
213 * value can be stuffed directly into th->window for an outgoing
216 static __inline__ u16
tcp_select_window(struct sock
*sk
)
218 struct tcp_sock
*tp
= tcp_sk(sk
);
219 u32 cur_win
= tcp_receive_window(tp
);
220 u32 new_win
= __tcp_select_window(sk
);
222 /* Never shrink the offered window */
223 if(new_win
< cur_win
) {
224 /* Danger Will Robinson!
225 * Don't update rcv_wup/rcv_wnd here or else
226 * we will not be able to advertise a zero
227 * window in time. --DaveM
229 * Relax Will Robinson.
233 tp
->rcv_wnd
= new_win
;
234 tp
->rcv_wup
= tp
->rcv_nxt
;
236 /* Make sure we do not exceed the maximum possible
239 if (!tp
->rx_opt
.rcv_wscale
)
240 new_win
= min(new_win
, MAX_TCP_WINDOW
);
242 new_win
= min(new_win
, (65535U << tp
->rx_opt
.rcv_wscale
));
244 /* RFC1323 scaling applied */
245 new_win
>>= tp
->rx_opt
.rcv_wscale
;
247 /* If we advertise zero window, disable fast path. */
255 /* This routine actually transmits TCP packets queued in by
256 * tcp_do_sendmsg(). This is used by both the initial
257 * transmission and possible later retransmissions.
258 * All SKB's seen here are completely headerless. It is our
259 * job to build the TCP header, and pass the packet down to
260 * IP so it can do the same plus pass the packet off to the
263 * We are working here with either a clone of the original
264 * SKB, or a fresh unique copy made by the retransmit engine.
266 static int tcp_transmit_skb(struct sock
*sk
, struct sk_buff
*skb
)
269 struct inet_sock
*inet
= inet_sk(sk
);
270 struct tcp_sock
*tp
= tcp_sk(sk
);
271 struct tcp_skb_cb
*tcb
= TCP_SKB_CB(skb
);
272 int tcp_header_size
= tp
->tcp_header_len
;
277 BUG_ON(!tcp_skb_pcount(skb
));
279 #define SYSCTL_FLAG_TSTAMPS 0x1
280 #define SYSCTL_FLAG_WSCALE 0x2
281 #define SYSCTL_FLAG_SACK 0x4
284 if (tcb
->flags
& TCPCB_FLAG_SYN
) {
285 tcp_header_size
= sizeof(struct tcphdr
) + TCPOLEN_MSS
;
286 if(sysctl_tcp_timestamps
) {
287 tcp_header_size
+= TCPOLEN_TSTAMP_ALIGNED
;
288 sysctl_flags
|= SYSCTL_FLAG_TSTAMPS
;
290 if(sysctl_tcp_window_scaling
) {
291 tcp_header_size
+= TCPOLEN_WSCALE_ALIGNED
;
292 sysctl_flags
|= SYSCTL_FLAG_WSCALE
;
294 if(sysctl_tcp_sack
) {
295 sysctl_flags
|= SYSCTL_FLAG_SACK
;
296 if(!(sysctl_flags
& SYSCTL_FLAG_TSTAMPS
))
297 tcp_header_size
+= TCPOLEN_SACKPERM_ALIGNED
;
299 } else if (tp
->rx_opt
.eff_sacks
) {
300 /* A SACK is 2 pad bytes, a 2 byte header, plus
301 * 2 32-bit sequence numbers for each SACK block.
303 tcp_header_size
+= (TCPOLEN_SACK_BASE_ALIGNED
+
304 (tp
->rx_opt
.eff_sacks
* TCPOLEN_SACK_PERBLOCK
));
308 * If the connection is idle and we are restarting,
309 * then we don't want to do any Vegas calculations
310 * until we get fresh RTT samples. So when we
311 * restart, we reset our Vegas state to a clean
312 * slate. After we get acks for this flight of
313 * packets, _then_ we can make Vegas calculations
316 if (tcp_is_vegas(tp
) && tcp_packets_in_flight(tp
) == 0)
317 tcp_vegas_enable(tp
);
319 th
= (struct tcphdr
*) skb_push(skb
, tcp_header_size
);
321 skb_set_owner_w(skb
, sk
);
323 /* Build TCP header and checksum it. */
324 th
->source
= inet
->sport
;
325 th
->dest
= inet
->dport
;
326 th
->seq
= htonl(tcb
->seq
);
327 th
->ack_seq
= htonl(tp
->rcv_nxt
);
328 *(((__u16
*)th
) + 6) = htons(((tcp_header_size
>> 2) << 12) | tcb
->flags
);
329 if (tcb
->flags
& TCPCB_FLAG_SYN
) {
330 /* RFC1323: The window in SYN & SYN/ACK segments
333 th
->window
= htons(tp
->rcv_wnd
);
335 th
->window
= htons(tcp_select_window(sk
));
341 between(tp
->snd_up
, tcb
->seq
+1, tcb
->seq
+0xFFFF)) {
342 th
->urg_ptr
= htons(tp
->snd_up
-tcb
->seq
);
346 if (tcb
->flags
& TCPCB_FLAG_SYN
) {
347 tcp_syn_build_options((__u32
*)(th
+ 1),
348 tcp_advertise_mss(sk
),
349 (sysctl_flags
& SYSCTL_FLAG_TSTAMPS
),
350 (sysctl_flags
& SYSCTL_FLAG_SACK
),
351 (sysctl_flags
& SYSCTL_FLAG_WSCALE
),
352 tp
->rx_opt
.rcv_wscale
,
354 tp
->rx_opt
.ts_recent
);
356 tcp_build_and_update_options((__u32
*)(th
+ 1),
359 TCP_ECN_send(sk
, tp
, skb
, tcp_header_size
);
361 tp
->af_specific
->send_check(sk
, th
, skb
->len
, skb
);
363 if (tcb
->flags
& TCPCB_FLAG_ACK
)
364 tcp_event_ack_sent(sk
);
366 if (skb
->len
!= tcp_header_size
)
367 tcp_event_data_sent(tp
, skb
, sk
);
369 TCP_INC_STATS(TCP_MIB_OUTSEGS
);
371 err
= tp
->af_specific
->queue_xmit(skb
, 0);
377 /* NET_XMIT_CN is special. It does not guarantee,
378 * that this packet is lost. It tells that device
379 * is about to start to drop packets or already
380 * drops some packets of the same priority and
381 * invokes us to send less aggressively.
383 return err
== NET_XMIT_CN
? 0 : err
;
386 #undef SYSCTL_FLAG_TSTAMPS
387 #undef SYSCTL_FLAG_WSCALE
388 #undef SYSCTL_FLAG_SACK
392 /* This routine just queue's the buffer
394 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
395 * otherwise socket can stall.
397 static void tcp_queue_skb(struct sock
*sk
, struct sk_buff
*skb
)
399 struct tcp_sock
*tp
= tcp_sk(sk
);
401 /* Advance write_seq and place onto the write_queue. */
402 tp
->write_seq
= TCP_SKB_CB(skb
)->end_seq
;
403 skb_header_release(skb
);
404 __skb_queue_tail(&sk
->sk_write_queue
, skb
);
405 sk_charge_skb(sk
, skb
);
407 /* Queue it, remembering where we must start sending. */
408 if (sk
->sk_send_head
== NULL
)
409 sk
->sk_send_head
= skb
;
412 static inline void tcp_tso_set_push(struct sk_buff
*skb
)
414 /* Force push to be on for any TSO frames to workaround
415 * problems with busted implementations like Mac OS-X that
416 * hold off socket receive wakeups until push is seen.
418 if (tcp_skb_pcount(skb
) > 1)
419 TCP_SKB_CB(skb
)->flags
|= TCPCB_FLAG_PSH
;
422 /* Send _single_ skb sitting at the send head. This function requires
423 * true push pending frames to setup probe timer etc.
425 void tcp_push_one(struct sock
*sk
, unsigned cur_mss
)
427 struct tcp_sock
*tp
= tcp_sk(sk
);
428 struct sk_buff
*skb
= sk
->sk_send_head
;
430 if (tcp_snd_test(tp
, skb
, cur_mss
, TCP_NAGLE_PUSH
)) {
431 /* Send it out now. */
432 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
433 tcp_tso_set_push(skb
);
434 if (!tcp_transmit_skb(sk
, skb_clone(skb
, sk
->sk_allocation
))) {
435 sk
->sk_send_head
= NULL
;
436 tp
->snd_nxt
= TCP_SKB_CB(skb
)->end_seq
;
437 tcp_packets_out_inc(sk
, tp
, skb
);
443 void tcp_set_skb_tso_segs(struct sk_buff
*skb
, unsigned int mss_std
)
445 if (skb
->len
<= mss_std
) {
446 /* Avoid the costly divide in the normal
449 skb_shinfo(skb
)->tso_segs
= 1;
450 skb_shinfo(skb
)->tso_size
= 0;
454 factor
= skb
->len
+ (mss_std
- 1);
456 skb_shinfo(skb
)->tso_segs
= factor
;
457 skb_shinfo(skb
)->tso_size
= mss_std
;
461 /* Function to create two new TCP segments. Shrinks the given segment
462 * to the specified size and appends a new segment with the rest of the
463 * packet to the list. This won't be called frequently, I hope.
464 * Remember, these are still headerless SKBs at this point.
466 static int tcp_fragment(struct sock
*sk
, struct sk_buff
*skb
, u32 len
)
468 struct tcp_sock
*tp
= tcp_sk(sk
);
469 struct sk_buff
*buff
;
473 nsize
= skb_headlen(skb
) - len
;
477 if (skb_cloned(skb
) &&
478 skb_is_nonlinear(skb
) &&
479 pskb_expand_head(skb
, 0, 0, GFP_ATOMIC
))
482 /* Get a new skb... force flag on. */
483 buff
= sk_stream_alloc_skb(sk
, nsize
, GFP_ATOMIC
);
485 return -ENOMEM
; /* We'll just try again later. */
486 sk_charge_skb(sk
, buff
);
488 /* Correct the sequence numbers. */
489 TCP_SKB_CB(buff
)->seq
= TCP_SKB_CB(skb
)->seq
+ len
;
490 TCP_SKB_CB(buff
)->end_seq
= TCP_SKB_CB(skb
)->end_seq
;
491 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(buff
)->seq
;
493 /* PSH and FIN should only be set in the second packet. */
494 flags
= TCP_SKB_CB(skb
)->flags
;
495 TCP_SKB_CB(skb
)->flags
= flags
& ~(TCPCB_FLAG_FIN
|TCPCB_FLAG_PSH
);
496 TCP_SKB_CB(buff
)->flags
= flags
;
497 TCP_SKB_CB(buff
)->sacked
=
498 (TCP_SKB_CB(skb
)->sacked
&
499 (TCPCB_LOST
| TCPCB_EVER_RETRANS
| TCPCB_AT_TAIL
));
500 TCP_SKB_CB(skb
)->sacked
&= ~TCPCB_AT_TAIL
;
502 if (!skb_shinfo(skb
)->nr_frags
&& skb
->ip_summed
!= CHECKSUM_HW
) {
503 /* Copy and checksum data tail into the new buffer. */
504 buff
->csum
= csum_partial_copy_nocheck(skb
->data
+ len
, skb_put(buff
, nsize
),
509 skb
->csum
= csum_block_sub(skb
->csum
, buff
->csum
, len
);
511 skb
->ip_summed
= CHECKSUM_HW
;
512 skb_split(skb
, buff
, len
);
515 buff
->ip_summed
= skb
->ip_summed
;
517 /* Looks stupid, but our code really uses when of
518 * skbs, which it never sent before. --ANK
520 TCP_SKB_CB(buff
)->when
= TCP_SKB_CB(skb
)->when
;
522 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_LOST
) {
523 tp
->lost_out
-= tcp_skb_pcount(skb
);
524 tp
->left_out
-= tcp_skb_pcount(skb
);
527 /* Fix up tso_factor for both original and new SKB. */
528 tcp_set_skb_tso_segs(skb
, tp
->mss_cache_std
);
529 tcp_set_skb_tso_segs(buff
, tp
->mss_cache_std
);
531 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_LOST
) {
532 tp
->lost_out
+= tcp_skb_pcount(skb
);
533 tp
->left_out
+= tcp_skb_pcount(skb
);
536 if (TCP_SKB_CB(buff
)->sacked
&TCPCB_LOST
) {
537 tp
->lost_out
+= tcp_skb_pcount(buff
);
538 tp
->left_out
+= tcp_skb_pcount(buff
);
541 /* Link BUFF into the send queue. */
542 __skb_append(skb
, buff
);
547 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
548 * eventually). The difference is that pulled data not copied, but
549 * immediately discarded.
551 static unsigned char *__pskb_trim_head(struct sk_buff
*skb
, int len
)
557 for (i
=0; i
<skb_shinfo(skb
)->nr_frags
; i
++) {
558 if (skb_shinfo(skb
)->frags
[i
].size
<= eat
) {
559 put_page(skb_shinfo(skb
)->frags
[i
].page
);
560 eat
-= skb_shinfo(skb
)->frags
[i
].size
;
562 skb_shinfo(skb
)->frags
[k
] = skb_shinfo(skb
)->frags
[i
];
564 skb_shinfo(skb
)->frags
[k
].page_offset
+= eat
;
565 skb_shinfo(skb
)->frags
[k
].size
-= eat
;
571 skb_shinfo(skb
)->nr_frags
= k
;
573 skb
->tail
= skb
->data
;
574 skb
->data_len
-= len
;
575 skb
->len
= skb
->data_len
;
579 int tcp_trim_head(struct sock
*sk
, struct sk_buff
*skb
, u32 len
)
581 if (skb_cloned(skb
) &&
582 pskb_expand_head(skb
, 0, 0, GFP_ATOMIC
))
585 if (len
<= skb_headlen(skb
)) {
586 __skb_pull(skb
, len
);
588 if (__pskb_trim_head(skb
, len
-skb_headlen(skb
)) == NULL
)
592 TCP_SKB_CB(skb
)->seq
+= len
;
593 skb
->ip_summed
= CHECKSUM_HW
;
595 skb
->truesize
-= len
;
596 sk
->sk_wmem_queued
-= len
;
597 sk
->sk_forward_alloc
+= len
;
598 sock_set_flag(sk
, SOCK_QUEUE_SHRUNK
);
600 /* Any change of skb->len requires recalculation of tso
603 if (tcp_skb_pcount(skb
) > 1)
604 tcp_set_skb_tso_segs(skb
, tcp_skb_mss(skb
));
609 /* This function synchronize snd mss to current pmtu/exthdr set.
611 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
612 for TCP options, but includes only bare TCP header.
614 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
615 It is minumum of user_mss and mss received with SYN.
616 It also does not include TCP options.
618 tp->pmtu_cookie is last pmtu, seen by this function.
620 tp->mss_cache is current effective sending mss, including
621 all tcp options except for SACKs. It is evaluated,
622 taking into account current pmtu, but never exceeds
623 tp->rx_opt.mss_clamp.
625 NOTE1. rfc1122 clearly states that advertised MSS
626 DOES NOT include either tcp or ip options.
628 NOTE2. tp->pmtu_cookie and tp->mss_cache are READ ONLY outside
629 this function. --ANK (980731)
632 unsigned int tcp_sync_mss(struct sock
*sk
, u32 pmtu
)
634 struct tcp_sock
*tp
= tcp_sk(sk
);
637 /* Calculate base mss without TCP options:
638 It is MMS_S - sizeof(tcphdr) of rfc1122
640 mss_now
= pmtu
- tp
->af_specific
->net_header_len
- sizeof(struct tcphdr
);
642 /* Clamp it (mss_clamp does not include tcp options) */
643 if (mss_now
> tp
->rx_opt
.mss_clamp
)
644 mss_now
= tp
->rx_opt
.mss_clamp
;
646 /* Now subtract optional transport overhead */
647 mss_now
-= tp
->ext_header_len
;
649 /* Then reserve room for full set of TCP options and 8 bytes of data */
653 /* Now subtract TCP options size, not including SACKs */
654 mss_now
-= tp
->tcp_header_len
- sizeof(struct tcphdr
);
656 /* Bound mss with half of window */
657 if (tp
->max_window
&& mss_now
> (tp
->max_window
>>1))
658 mss_now
= max((tp
->max_window
>>1), 68U - tp
->tcp_header_len
);
660 /* And store cached results */
661 tp
->pmtu_cookie
= pmtu
;
662 tp
->mss_cache
= tp
->mss_cache_std
= mss_now
;
667 /* Compute the current effective MSS, taking SACKs and IP options,
668 * and even PMTU discovery events into account.
670 * LARGESEND note: !urg_mode is overkill, only frames up to snd_up
671 * cannot be large. However, taking into account rare use of URG, this
675 unsigned int tcp_current_mss(struct sock
*sk
, int large
)
677 struct tcp_sock
*tp
= tcp_sk(sk
);
678 struct dst_entry
*dst
= __sk_dst_get(sk
);
679 unsigned int do_large
, mss_now
;
681 mss_now
= tp
->mss_cache_std
;
683 u32 mtu
= dst_mtu(dst
);
684 if (mtu
!= tp
->pmtu_cookie
)
685 mss_now
= tcp_sync_mss(sk
, mtu
);
689 (sk
->sk_route_caps
& NETIF_F_TSO
) &&
693 unsigned int large_mss
, factor
, limit
;
695 large_mss
= 65535 - tp
->af_specific
->net_header_len
-
696 tp
->ext_header_len
- tp
->tcp_header_len
;
698 if (tp
->max_window
&& large_mss
> (tp
->max_window
>>1))
699 large_mss
= max((tp
->max_window
>>1),
700 68U - tp
->tcp_header_len
);
702 factor
= large_mss
/ mss_now
;
704 /* Always keep large mss multiple of real mss, but
705 * do not exceed 1/tso_win_divisor of the congestion window
706 * so we can keep the ACK clock ticking and minimize
709 limit
= tp
->snd_cwnd
;
710 if (sysctl_tcp_tso_win_divisor
)
711 limit
/= sysctl_tcp_tso_win_divisor
;
712 limit
= max(1U, limit
);
716 tp
->mss_cache
= mss_now
* factor
;
718 mss_now
= tp
->mss_cache
;
721 if (tp
->rx_opt
.eff_sacks
)
722 mss_now
-= (TCPOLEN_SACK_BASE_ALIGNED
+
723 (tp
->rx_opt
.eff_sacks
* TCPOLEN_SACK_PERBLOCK
));
727 /* This routine writes packets to the network. It advances the
728 * send_head. This happens as incoming acks open up the remote
731 * Returns 1, if no segments are in flight and we have queued segments, but
732 * cannot send anything now because of SWS or another problem.
734 int tcp_write_xmit(struct sock
*sk
, int nonagle
)
736 struct tcp_sock
*tp
= tcp_sk(sk
);
737 unsigned int mss_now
;
739 /* If we are closed, the bytes will have to remain here.
740 * In time closedown will finish, we empty the write queue and all
743 if (sk
->sk_state
!= TCP_CLOSE
) {
747 /* Account for SACKS, we may need to fragment due to this.
748 * It is just like the real MSS changing on us midstream.
749 * We also handle things correctly when the user adds some
750 * IP options mid-stream. Silly to do, but cover it.
752 mss_now
= tcp_current_mss(sk
, 1);
754 while ((skb
= sk
->sk_send_head
) &&
755 tcp_snd_test(tp
, skb
, mss_now
,
756 tcp_skb_is_last(sk
, skb
) ? nonagle
:
758 if (skb
->len
> mss_now
) {
759 if (tcp_fragment(sk
, skb
, mss_now
))
763 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
764 tcp_tso_set_push(skb
);
765 if (tcp_transmit_skb(sk
, skb_clone(skb
, GFP_ATOMIC
)))
768 /* Advance the send_head. This one is sent out.
769 * This call will increment packets_out.
771 update_send_head(sk
, tp
, skb
);
773 tcp_minshall_update(tp
, mss_now
, skb
);
778 tcp_cwnd_validate(sk
, tp
);
782 return !tp
->packets_out
&& sk
->sk_send_head
;
787 /* This function returns the amount that we can raise the
788 * usable window based on the following constraints
790 * 1. The window can never be shrunk once it is offered (RFC 793)
791 * 2. We limit memory per socket
794 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
795 * RECV.NEXT + RCV.WIN fixed until:
796 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
798 * i.e. don't raise the right edge of the window until you can raise
799 * it at least MSS bytes.
801 * Unfortunately, the recommended algorithm breaks header prediction,
802 * since header prediction assumes th->window stays fixed.
804 * Strictly speaking, keeping th->window fixed violates the receiver
805 * side SWS prevention criteria. The problem is that under this rule
806 * a stream of single byte packets will cause the right side of the
807 * window to always advance by a single byte.
809 * Of course, if the sender implements sender side SWS prevention
810 * then this will not be a problem.
812 * BSD seems to make the following compromise:
814 * If the free space is less than the 1/4 of the maximum
815 * space available and the free space is less than 1/2 mss,
816 * then set the window to 0.
817 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
818 * Otherwise, just prevent the window from shrinking
819 * and from being larger than the largest representable value.
821 * This prevents incremental opening of the window in the regime
822 * where TCP is limited by the speed of the reader side taking
823 * data out of the TCP receive queue. It does nothing about
824 * those cases where the window is constrained on the sender side
825 * because the pipeline is full.
827 * BSD also seems to "accidentally" limit itself to windows that are a
828 * multiple of MSS, at least until the free space gets quite small.
829 * This would appear to be a side effect of the mbuf implementation.
830 * Combining these two algorithms results in the observed behavior
831 * of having a fixed window size at almost all times.
833 * Below we obtain similar behavior by forcing the offered window to
834 * a multiple of the mss when it is feasible to do so.
836 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
837 * Regular options like TIMESTAMP are taken into account.
839 u32
__tcp_select_window(struct sock
*sk
)
841 struct tcp_sock
*tp
= tcp_sk(sk
);
842 /* MSS for the peer's data. Previous verions used mss_clamp
843 * here. I don't know if the value based on our guesses
844 * of peer's MSS is better for the performance. It's more correct
845 * but may be worse for the performance because of rcv_mss
846 * fluctuations. --SAW 1998/11/1
848 int mss
= tp
->ack
.rcv_mss
;
849 int free_space
= tcp_space(sk
);
850 int full_space
= min_t(int, tp
->window_clamp
, tcp_full_space(sk
));
853 if (mss
> full_space
)
856 if (free_space
< full_space
/2) {
859 if (tcp_memory_pressure
)
860 tp
->rcv_ssthresh
= min(tp
->rcv_ssthresh
, 4U*tp
->advmss
);
862 if (free_space
< mss
)
866 if (free_space
> tp
->rcv_ssthresh
)
867 free_space
= tp
->rcv_ssthresh
;
869 /* Don't do rounding if we are using window scaling, since the
870 * scaled window will not line up with the MSS boundary anyway.
872 window
= tp
->rcv_wnd
;
873 if (tp
->rx_opt
.rcv_wscale
) {
876 /* Advertise enough space so that it won't get scaled away.
877 * Import case: prevent zero window announcement if
878 * 1<<rcv_wscale > mss.
880 if (((window
>> tp
->rx_opt
.rcv_wscale
) << tp
->rx_opt
.rcv_wscale
) != window
)
881 window
= (((window
>> tp
->rx_opt
.rcv_wscale
) + 1)
882 << tp
->rx_opt
.rcv_wscale
);
884 /* Get the largest window that is a nice multiple of mss.
885 * Window clamp already applied above.
886 * If our current window offering is within 1 mss of the
887 * free space we just keep it. This prevents the divide
888 * and multiply from happening most of the time.
889 * We also don't do any window rounding when the free space
892 if (window
<= free_space
- mss
|| window
> free_space
)
893 window
= (free_space
/mss
)*mss
;
899 /* Attempt to collapse two adjacent SKB's during retransmission. */
900 static void tcp_retrans_try_collapse(struct sock
*sk
, struct sk_buff
*skb
, int mss_now
)
902 struct tcp_sock
*tp
= tcp_sk(sk
);
903 struct sk_buff
*next_skb
= skb
->next
;
905 /* The first test we must make is that neither of these two
906 * SKB's are still referenced by someone else.
908 if (!skb_cloned(skb
) && !skb_cloned(next_skb
)) {
909 int skb_size
= skb
->len
, next_skb_size
= next_skb
->len
;
910 u16 flags
= TCP_SKB_CB(skb
)->flags
;
912 /* Also punt if next skb has been SACK'd. */
913 if(TCP_SKB_CB(next_skb
)->sacked
& TCPCB_SACKED_ACKED
)
916 /* Next skb is out of window. */
917 if (after(TCP_SKB_CB(next_skb
)->end_seq
, tp
->snd_una
+tp
->snd_wnd
))
920 /* Punt if not enough space exists in the first SKB for
921 * the data in the second, or the total combined payload
922 * would exceed the MSS.
924 if ((next_skb_size
> skb_tailroom(skb
)) ||
925 ((skb_size
+ next_skb_size
) > mss_now
))
928 BUG_ON(tcp_skb_pcount(skb
) != 1 ||
929 tcp_skb_pcount(next_skb
) != 1);
931 /* Ok. We will be able to collapse the packet. */
932 __skb_unlink(next_skb
, next_skb
->list
);
934 memcpy(skb_put(skb
, next_skb_size
), next_skb
->data
, next_skb_size
);
936 if (next_skb
->ip_summed
== CHECKSUM_HW
)
937 skb
->ip_summed
= CHECKSUM_HW
;
939 if (skb
->ip_summed
!= CHECKSUM_HW
)
940 skb
->csum
= csum_block_add(skb
->csum
, next_skb
->csum
, skb_size
);
942 /* Update sequence range on original skb. */
943 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(next_skb
)->end_seq
;
945 /* Merge over control information. */
946 flags
|= TCP_SKB_CB(next_skb
)->flags
; /* This moves PSH/FIN etc. over */
947 TCP_SKB_CB(skb
)->flags
= flags
;
949 /* All done, get rid of second SKB and account for it so
950 * packet counting does not break.
952 TCP_SKB_CB(skb
)->sacked
|= TCP_SKB_CB(next_skb
)->sacked
&(TCPCB_EVER_RETRANS
|TCPCB_AT_TAIL
);
953 if (TCP_SKB_CB(next_skb
)->sacked
&TCPCB_SACKED_RETRANS
)
954 tp
->retrans_out
-= tcp_skb_pcount(next_skb
);
955 if (TCP_SKB_CB(next_skb
)->sacked
&TCPCB_LOST
) {
956 tp
->lost_out
-= tcp_skb_pcount(next_skb
);
957 tp
->left_out
-= tcp_skb_pcount(next_skb
);
959 /* Reno case is special. Sigh... */
960 if (!tp
->rx_opt
.sack_ok
&& tp
->sacked_out
) {
961 tcp_dec_pcount_approx(&tp
->sacked_out
, next_skb
);
962 tp
->left_out
-= tcp_skb_pcount(next_skb
);
965 /* Not quite right: it can be > snd.fack, but
966 * it is better to underestimate fackets.
968 tcp_dec_pcount_approx(&tp
->fackets_out
, next_skb
);
969 tcp_packets_out_dec(tp
, next_skb
);
970 sk_stream_free_skb(sk
, next_skb
);
974 /* Do a simple retransmit without using the backoff mechanisms in
975 * tcp_timer. This is used for path mtu discovery.
976 * The socket is already locked here.
978 void tcp_simple_retransmit(struct sock
*sk
)
980 struct tcp_sock
*tp
= tcp_sk(sk
);
982 unsigned int mss
= tcp_current_mss(sk
, 0);
985 sk_stream_for_retrans_queue(skb
, sk
) {
986 if (skb
->len
> mss
&&
987 !(TCP_SKB_CB(skb
)->sacked
&TCPCB_SACKED_ACKED
)) {
988 if (TCP_SKB_CB(skb
)->sacked
&TCPCB_SACKED_RETRANS
) {
989 TCP_SKB_CB(skb
)->sacked
&= ~TCPCB_SACKED_RETRANS
;
990 tp
->retrans_out
-= tcp_skb_pcount(skb
);
992 if (!(TCP_SKB_CB(skb
)->sacked
&TCPCB_LOST
)) {
993 TCP_SKB_CB(skb
)->sacked
|= TCPCB_LOST
;
994 tp
->lost_out
+= tcp_skb_pcount(skb
);
1003 tcp_sync_left_out(tp
);
1005 /* Don't muck with the congestion window here.
1006 * Reason is that we do not increase amount of _data_
1007 * in network, but units changed and effective
1008 * cwnd/ssthresh really reduced now.
1010 if (tp
->ca_state
!= TCP_CA_Loss
) {
1011 tp
->high_seq
= tp
->snd_nxt
;
1012 tp
->snd_ssthresh
= tcp_current_ssthresh(tp
);
1013 tp
->prior_ssthresh
= 0;
1014 tp
->undo_marker
= 0;
1015 tcp_set_ca_state(tp
, TCP_CA_Loss
);
1017 tcp_xmit_retransmit_queue(sk
);
1020 /* This retransmits one SKB. Policy decisions and retransmit queue
1021 * state updates are done by the caller. Returns non-zero if an
1022 * error occurred which prevented the send.
1024 int tcp_retransmit_skb(struct sock
*sk
, struct sk_buff
*skb
)
1026 struct tcp_sock
*tp
= tcp_sk(sk
);
1027 unsigned int cur_mss
= tcp_current_mss(sk
, 0);
1030 /* Do not sent more than we queued. 1/4 is reserved for possible
1031 * copying overhead: frgagmentation, tunneling, mangling etc.
1033 if (atomic_read(&sk
->sk_wmem_alloc
) >
1034 min(sk
->sk_wmem_queued
+ (sk
->sk_wmem_queued
>> 2), sk
->sk_sndbuf
))
1037 if (before(TCP_SKB_CB(skb
)->seq
, tp
->snd_una
)) {
1038 if (before(TCP_SKB_CB(skb
)->end_seq
, tp
->snd_una
))
1041 if (sk
->sk_route_caps
& NETIF_F_TSO
) {
1042 sk
->sk_route_caps
&= ~NETIF_F_TSO
;
1043 sock_set_flag(sk
, SOCK_NO_LARGESEND
);
1044 tp
->mss_cache
= tp
->mss_cache_std
;
1047 if (tcp_trim_head(sk
, skb
, tp
->snd_una
- TCP_SKB_CB(skb
)->seq
))
1051 /* If receiver has shrunk his window, and skb is out of
1052 * new window, do not retransmit it. The exception is the
1053 * case, when window is shrunk to zero. In this case
1054 * our retransmit serves as a zero window probe.
1056 if (!before(TCP_SKB_CB(skb
)->seq
, tp
->snd_una
+tp
->snd_wnd
)
1057 && TCP_SKB_CB(skb
)->seq
!= tp
->snd_una
)
1060 if (skb
->len
> cur_mss
) {
1061 int old_factor
= tcp_skb_pcount(skb
);
1064 if (tcp_fragment(sk
, skb
, cur_mss
))
1065 return -ENOMEM
; /* We'll try again later. */
1067 /* New SKB created, account for it. */
1068 new_factor
= tcp_skb_pcount(skb
);
1069 tp
->packets_out
-= old_factor
- new_factor
;
1070 tp
->packets_out
+= tcp_skb_pcount(skb
->next
);
1073 /* Collapse two adjacent packets if worthwhile and we can. */
1074 if(!(TCP_SKB_CB(skb
)->flags
& TCPCB_FLAG_SYN
) &&
1075 (skb
->len
< (cur_mss
>> 1)) &&
1076 (skb
->next
!= sk
->sk_send_head
) &&
1077 (skb
->next
!= (struct sk_buff
*)&sk
->sk_write_queue
) &&
1078 (skb_shinfo(skb
)->nr_frags
== 0 && skb_shinfo(skb
->next
)->nr_frags
== 0) &&
1079 (tcp_skb_pcount(skb
) == 1 && tcp_skb_pcount(skb
->next
) == 1) &&
1080 (sysctl_tcp_retrans_collapse
!= 0))
1081 tcp_retrans_try_collapse(sk
, skb
, cur_mss
);
1083 if(tp
->af_specific
->rebuild_header(sk
))
1084 return -EHOSTUNREACH
; /* Routing failure or similar. */
1086 /* Some Solaris stacks overoptimize and ignore the FIN on a
1087 * retransmit when old data is attached. So strip it off
1088 * since it is cheap to do so and saves bytes on the network.
1091 (TCP_SKB_CB(skb
)->flags
& TCPCB_FLAG_FIN
) &&
1092 tp
->snd_una
== (TCP_SKB_CB(skb
)->end_seq
- 1)) {
1093 if (!pskb_trim(skb
, 0)) {
1094 TCP_SKB_CB(skb
)->seq
= TCP_SKB_CB(skb
)->end_seq
- 1;
1095 skb_shinfo(skb
)->tso_segs
= 1;
1096 skb_shinfo(skb
)->tso_size
= 0;
1097 skb
->ip_summed
= CHECKSUM_NONE
;
1102 /* Make a copy, if the first transmission SKB clone we made
1103 * is still in somebody's hands, else make a clone.
1105 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
1106 tcp_tso_set_push(skb
);
1108 err
= tcp_transmit_skb(sk
, (skb_cloned(skb
) ?
1109 pskb_copy(skb
, GFP_ATOMIC
):
1110 skb_clone(skb
, GFP_ATOMIC
)));
1113 /* Update global TCP statistics. */
1114 TCP_INC_STATS(TCP_MIB_RETRANSSEGS
);
1116 tp
->total_retrans
++;
1118 #if FASTRETRANS_DEBUG > 0
1119 if (TCP_SKB_CB(skb
)->sacked
&TCPCB_SACKED_RETRANS
) {
1120 if (net_ratelimit())
1121 printk(KERN_DEBUG
"retrans_out leaked.\n");
1124 TCP_SKB_CB(skb
)->sacked
|= TCPCB_RETRANS
;
1125 tp
->retrans_out
+= tcp_skb_pcount(skb
);
1127 /* Save stamp of the first retransmit. */
1128 if (!tp
->retrans_stamp
)
1129 tp
->retrans_stamp
= TCP_SKB_CB(skb
)->when
;
1133 /* snd_nxt is stored to detect loss of retransmitted segment,
1134 * see tcp_input.c tcp_sacktag_write_queue().
1136 TCP_SKB_CB(skb
)->ack_seq
= tp
->snd_nxt
;
1141 /* This gets called after a retransmit timeout, and the initially
1142 * retransmitted data is acknowledged. It tries to continue
1143 * resending the rest of the retransmit queue, until either
1144 * we've sent it all or the congestion window limit is reached.
1145 * If doing SACK, the first ACK which comes back for a timeout
1146 * based retransmit packet might feed us FACK information again.
1147 * If so, we use it to avoid unnecessarily retransmissions.
1149 void tcp_xmit_retransmit_queue(struct sock
*sk
)
1151 struct tcp_sock
*tp
= tcp_sk(sk
);
1152 struct sk_buff
*skb
;
1153 int packet_cnt
= tp
->lost_out
;
1155 /* First pass: retransmit lost packets. */
1157 sk_stream_for_retrans_queue(skb
, sk
) {
1158 __u8 sacked
= TCP_SKB_CB(skb
)->sacked
;
1160 /* Assume this retransmit will generate
1161 * only one packet for congestion window
1162 * calculation purposes. This works because
1163 * tcp_retransmit_skb() will chop up the
1164 * packet to be MSS sized and all the
1165 * packet counting works out.
1167 if (tcp_packets_in_flight(tp
) >= tp
->snd_cwnd
)
1170 if (sacked
&TCPCB_LOST
) {
1171 if (!(sacked
&(TCPCB_SACKED_ACKED
|TCPCB_SACKED_RETRANS
))) {
1172 if (tcp_retransmit_skb(sk
, skb
))
1174 if (tp
->ca_state
!= TCP_CA_Loss
)
1175 NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS
);
1177 NET_INC_STATS_BH(LINUX_MIB_TCPSLOWSTARTRETRANS
);
1180 skb_peek(&sk
->sk_write_queue
))
1181 tcp_reset_xmit_timer(sk
, TCP_TIME_RETRANS
, tp
->rto
);
1184 packet_cnt
-= tcp_skb_pcount(skb
);
1185 if (packet_cnt
<= 0)
1191 /* OK, demanded retransmission is finished. */
1193 /* Forward retransmissions are possible only during Recovery. */
1194 if (tp
->ca_state
!= TCP_CA_Recovery
)
1197 /* No forward retransmissions in Reno are possible. */
1198 if (!tp
->rx_opt
.sack_ok
)
1201 /* Yeah, we have to make difficult choice between forward transmission
1202 * and retransmission... Both ways have their merits...
1204 * For now we do not retransmit anything, while we have some new
1208 if (tcp_may_send_now(sk
, tp
))
1213 sk_stream_for_retrans_queue(skb
, sk
) {
1214 /* Similar to the retransmit loop above we
1215 * can pretend that the retransmitted SKB
1216 * we send out here will be composed of one
1217 * real MSS sized packet because tcp_retransmit_skb()
1218 * will fragment it if necessary.
1220 if (++packet_cnt
> tp
->fackets_out
)
1223 if (tcp_packets_in_flight(tp
) >= tp
->snd_cwnd
)
1226 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_TAGBITS
)
1229 /* Ok, retransmit it. */
1230 if (tcp_retransmit_skb(sk
, skb
))
1233 if (skb
== skb_peek(&sk
->sk_write_queue
))
1234 tcp_reset_xmit_timer(sk
, TCP_TIME_RETRANS
, tp
->rto
);
1236 NET_INC_STATS_BH(LINUX_MIB_TCPFORWARDRETRANS
);
1241 /* Send a fin. The caller locks the socket for us. This cannot be
1242 * allowed to fail queueing a FIN frame under any circumstances.
1244 void tcp_send_fin(struct sock
*sk
)
1246 struct tcp_sock
*tp
= tcp_sk(sk
);
1247 struct sk_buff
*skb
= skb_peek_tail(&sk
->sk_write_queue
);
1250 /* Optimization, tack on the FIN if we have a queue of
1251 * unsent frames. But be careful about outgoing SACKS
1254 mss_now
= tcp_current_mss(sk
, 1);
1256 if (sk
->sk_send_head
!= NULL
) {
1257 TCP_SKB_CB(skb
)->flags
|= TCPCB_FLAG_FIN
;
1258 TCP_SKB_CB(skb
)->end_seq
++;
1261 /* Socket is locked, keep trying until memory is available. */
1263 skb
= alloc_skb(MAX_TCP_HEADER
, GFP_KERNEL
);
1269 /* Reserve space for headers and prepare control bits. */
1270 skb_reserve(skb
, MAX_TCP_HEADER
);
1272 TCP_SKB_CB(skb
)->flags
= (TCPCB_FLAG_ACK
| TCPCB_FLAG_FIN
);
1273 TCP_SKB_CB(skb
)->sacked
= 0;
1274 skb_shinfo(skb
)->tso_segs
= 1;
1275 skb_shinfo(skb
)->tso_size
= 0;
1277 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
1278 TCP_SKB_CB(skb
)->seq
= tp
->write_seq
;
1279 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(skb
)->seq
+ 1;
1280 tcp_queue_skb(sk
, skb
);
1282 __tcp_push_pending_frames(sk
, tp
, mss_now
, TCP_NAGLE_OFF
);
1285 /* We get here when a process closes a file descriptor (either due to
1286 * an explicit close() or as a byproduct of exit()'ing) and there
1287 * was unread data in the receive queue. This behavior is recommended
1288 * by draft-ietf-tcpimpl-prob-03.txt section 3.10. -DaveM
1290 void tcp_send_active_reset(struct sock
*sk
, int priority
)
1292 struct tcp_sock
*tp
= tcp_sk(sk
);
1293 struct sk_buff
*skb
;
1295 /* NOTE: No TCP options attached and we never retransmit this. */
1296 skb
= alloc_skb(MAX_TCP_HEADER
, priority
);
1298 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED
);
1302 /* Reserve space for headers and prepare control bits. */
1303 skb_reserve(skb
, MAX_TCP_HEADER
);
1305 TCP_SKB_CB(skb
)->flags
= (TCPCB_FLAG_ACK
| TCPCB_FLAG_RST
);
1306 TCP_SKB_CB(skb
)->sacked
= 0;
1307 skb_shinfo(skb
)->tso_segs
= 1;
1308 skb_shinfo(skb
)->tso_size
= 0;
1311 TCP_SKB_CB(skb
)->seq
= tcp_acceptable_seq(sk
, tp
);
1312 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(skb
)->seq
;
1313 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
1314 if (tcp_transmit_skb(sk
, skb
))
1315 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED
);
1318 /* WARNING: This routine must only be called when we have already sent
1319 * a SYN packet that crossed the incoming SYN that caused this routine
1320 * to get called. If this assumption fails then the initial rcv_wnd
1321 * and rcv_wscale values will not be correct.
1323 int tcp_send_synack(struct sock
*sk
)
1325 struct sk_buff
* skb
;
1327 skb
= skb_peek(&sk
->sk_write_queue
);
1328 if (skb
== NULL
|| !(TCP_SKB_CB(skb
)->flags
&TCPCB_FLAG_SYN
)) {
1329 printk(KERN_DEBUG
"tcp_send_synack: wrong queue state\n");
1332 if (!(TCP_SKB_CB(skb
)->flags
&TCPCB_FLAG_ACK
)) {
1333 if (skb_cloned(skb
)) {
1334 struct sk_buff
*nskb
= skb_copy(skb
, GFP_ATOMIC
);
1337 __skb_unlink(skb
, &sk
->sk_write_queue
);
1338 skb_header_release(nskb
);
1339 __skb_queue_head(&sk
->sk_write_queue
, nskb
);
1340 sk_stream_free_skb(sk
, skb
);
1341 sk_charge_skb(sk
, nskb
);
1345 TCP_SKB_CB(skb
)->flags
|= TCPCB_FLAG_ACK
;
1346 TCP_ECN_send_synack(tcp_sk(sk
), skb
);
1348 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
1349 return tcp_transmit_skb(sk
, skb_clone(skb
, GFP_ATOMIC
));
1353 * Prepare a SYN-ACK.
1355 struct sk_buff
* tcp_make_synack(struct sock
*sk
, struct dst_entry
*dst
,
1356 struct open_request
*req
)
1358 struct tcp_sock
*tp
= tcp_sk(sk
);
1360 int tcp_header_size
;
1361 struct sk_buff
*skb
;
1363 skb
= sock_wmalloc(sk
, MAX_TCP_HEADER
+ 15, 1, GFP_ATOMIC
);
1367 /* Reserve space for headers. */
1368 skb_reserve(skb
, MAX_TCP_HEADER
);
1370 skb
->dst
= dst_clone(dst
);
1372 tcp_header_size
= (sizeof(struct tcphdr
) + TCPOLEN_MSS
+
1373 (req
->tstamp_ok
? TCPOLEN_TSTAMP_ALIGNED
: 0) +
1374 (req
->wscale_ok
? TCPOLEN_WSCALE_ALIGNED
: 0) +
1375 /* SACK_PERM is in the place of NOP NOP of TS */
1376 ((req
->sack_ok
&& !req
->tstamp_ok
) ? TCPOLEN_SACKPERM_ALIGNED
: 0));
1377 skb
->h
.th
= th
= (struct tcphdr
*) skb_push(skb
, tcp_header_size
);
1379 memset(th
, 0, sizeof(struct tcphdr
));
1382 if (dst
->dev
->features
&NETIF_F_TSO
)
1384 TCP_ECN_make_synack(req
, th
);
1385 th
->source
= inet_sk(sk
)->sport
;
1386 th
->dest
= req
->rmt_port
;
1387 TCP_SKB_CB(skb
)->seq
= req
->snt_isn
;
1388 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(skb
)->seq
+ 1;
1389 TCP_SKB_CB(skb
)->sacked
= 0;
1390 skb_shinfo(skb
)->tso_segs
= 1;
1391 skb_shinfo(skb
)->tso_size
= 0;
1392 th
->seq
= htonl(TCP_SKB_CB(skb
)->seq
);
1393 th
->ack_seq
= htonl(req
->rcv_isn
+ 1);
1394 if (req
->rcv_wnd
== 0) { /* ignored for retransmitted syns */
1396 /* Set this up on the first call only */
1397 req
->window_clamp
= tp
->window_clamp
? : dst_metric(dst
, RTAX_WINDOW
);
1398 /* tcp_full_space because it is guaranteed to be the first packet */
1399 tcp_select_initial_window(tcp_full_space(sk
),
1400 dst_metric(dst
, RTAX_ADVMSS
) - (req
->tstamp_ok
? TCPOLEN_TSTAMP_ALIGNED
: 0),
1405 req
->rcv_wscale
= rcv_wscale
;
1408 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
1409 th
->window
= htons(req
->rcv_wnd
);
1411 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
1412 tcp_syn_build_options((__u32
*)(th
+ 1), dst_metric(dst
, RTAX_ADVMSS
), req
->tstamp_ok
,
1413 req
->sack_ok
, req
->wscale_ok
, req
->rcv_wscale
,
1414 TCP_SKB_CB(skb
)->when
,
1418 th
->doff
= (tcp_header_size
>> 2);
1419 TCP_INC_STATS(TCP_MIB_OUTSEGS
);
1424 * Do all connect socket setups that can be done AF independent.
1426 static inline void tcp_connect_init(struct sock
*sk
)
1428 struct dst_entry
*dst
= __sk_dst_get(sk
);
1429 struct tcp_sock
*tp
= tcp_sk(sk
);
1432 /* We'll fix this up when we get a response from the other end.
1433 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
1435 tp
->tcp_header_len
= sizeof(struct tcphdr
) +
1436 (sysctl_tcp_timestamps
? TCPOLEN_TSTAMP_ALIGNED
: 0);
1438 /* If user gave his TCP_MAXSEG, record it to clamp */
1439 if (tp
->rx_opt
.user_mss
)
1440 tp
->rx_opt
.mss_clamp
= tp
->rx_opt
.user_mss
;
1442 tcp_sync_mss(sk
, dst_mtu(dst
));
1444 if (!tp
->window_clamp
)
1445 tp
->window_clamp
= dst_metric(dst
, RTAX_WINDOW
);
1446 tp
->advmss
= dst_metric(dst
, RTAX_ADVMSS
);
1447 tcp_initialize_rcv_mss(sk
);
1450 tcp_select_initial_window(tcp_full_space(sk
),
1451 tp
->advmss
- (tp
->rx_opt
.ts_recent_stamp
? tp
->tcp_header_len
- sizeof(struct tcphdr
) : 0),
1454 sysctl_tcp_window_scaling
,
1457 tp
->rx_opt
.rcv_wscale
= rcv_wscale
;
1458 tp
->rcv_ssthresh
= tp
->rcv_wnd
;
1461 sock_reset_flag(sk
, SOCK_DONE
);
1463 tcp_init_wl(tp
, tp
->write_seq
, 0);
1464 tp
->snd_una
= tp
->write_seq
;
1465 tp
->snd_sml
= tp
->write_seq
;
1470 tp
->rto
= TCP_TIMEOUT_INIT
;
1471 tp
->retransmits
= 0;
1472 tcp_clear_retrans(tp
);
1476 * Build a SYN and send it off.
1478 int tcp_connect(struct sock
*sk
)
1480 struct tcp_sock
*tp
= tcp_sk(sk
);
1481 struct sk_buff
*buff
;
1483 tcp_connect_init(sk
);
1485 buff
= alloc_skb(MAX_TCP_HEADER
+ 15, sk
->sk_allocation
);
1486 if (unlikely(buff
== NULL
))
1489 /* Reserve space for headers. */
1490 skb_reserve(buff
, MAX_TCP_HEADER
);
1492 TCP_SKB_CB(buff
)->flags
= TCPCB_FLAG_SYN
;
1493 TCP_ECN_send_syn(sk
, tp
, buff
);
1494 TCP_SKB_CB(buff
)->sacked
= 0;
1495 skb_shinfo(buff
)->tso_segs
= 1;
1496 skb_shinfo(buff
)->tso_size
= 0;
1498 TCP_SKB_CB(buff
)->seq
= tp
->write_seq
++;
1499 TCP_SKB_CB(buff
)->end_seq
= tp
->write_seq
;
1500 tp
->snd_nxt
= tp
->write_seq
;
1501 tp
->pushed_seq
= tp
->write_seq
;
1505 TCP_SKB_CB(buff
)->when
= tcp_time_stamp
;
1506 tp
->retrans_stamp
= TCP_SKB_CB(buff
)->when
;
1507 skb_header_release(buff
);
1508 __skb_queue_tail(&sk
->sk_write_queue
, buff
);
1509 sk_charge_skb(sk
, buff
);
1510 tp
->packets_out
+= tcp_skb_pcount(buff
);
1511 tcp_transmit_skb(sk
, skb_clone(buff
, GFP_KERNEL
));
1512 TCP_INC_STATS(TCP_MIB_ACTIVEOPENS
);
1514 /* Timer for repeating the SYN until an answer. */
1515 tcp_reset_xmit_timer(sk
, TCP_TIME_RETRANS
, tp
->rto
);
1519 /* Send out a delayed ack, the caller does the policy checking
1520 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
1523 void tcp_send_delayed_ack(struct sock
*sk
)
1525 struct tcp_sock
*tp
= tcp_sk(sk
);
1526 int ato
= tp
->ack
.ato
;
1527 unsigned long timeout
;
1529 if (ato
> TCP_DELACK_MIN
) {
1532 if (tp
->ack
.pingpong
|| (tp
->ack
.pending
&TCP_ACK_PUSHED
))
1533 max_ato
= TCP_DELACK_MAX
;
1535 /* Slow path, intersegment interval is "high". */
1537 /* If some rtt estimate is known, use it to bound delayed ack.
1538 * Do not use tp->rto here, use results of rtt measurements
1542 int rtt
= max(tp
->srtt
>>3, TCP_DELACK_MIN
);
1548 ato
= min(ato
, max_ato
);
1551 /* Stay within the limit we were given */
1552 timeout
= jiffies
+ ato
;
1554 /* Use new timeout only if there wasn't a older one earlier. */
1555 if (tp
->ack
.pending
&TCP_ACK_TIMER
) {
1556 /* If delack timer was blocked or is about to expire,
1559 if (tp
->ack
.blocked
|| time_before_eq(tp
->ack
.timeout
, jiffies
+(ato
>>2))) {
1564 if (!time_before(timeout
, tp
->ack
.timeout
))
1565 timeout
= tp
->ack
.timeout
;
1567 tp
->ack
.pending
|= TCP_ACK_SCHED
|TCP_ACK_TIMER
;
1568 tp
->ack
.timeout
= timeout
;
1569 sk_reset_timer(sk
, &tp
->delack_timer
, timeout
);
1572 /* This routine sends an ack and also updates the window. */
1573 void tcp_send_ack(struct sock
*sk
)
1575 /* If we have been reset, we may not send again. */
1576 if (sk
->sk_state
!= TCP_CLOSE
) {
1577 struct tcp_sock
*tp
= tcp_sk(sk
);
1578 struct sk_buff
*buff
;
1580 /* We are not putting this on the write queue, so
1581 * tcp_transmit_skb() will set the ownership to this
1584 buff
= alloc_skb(MAX_TCP_HEADER
, GFP_ATOMIC
);
1586 tcp_schedule_ack(tp
);
1587 tp
->ack
.ato
= TCP_ATO_MIN
;
1588 tcp_reset_xmit_timer(sk
, TCP_TIME_DACK
, TCP_DELACK_MAX
);
1592 /* Reserve space for headers and prepare control bits. */
1593 skb_reserve(buff
, MAX_TCP_HEADER
);
1595 TCP_SKB_CB(buff
)->flags
= TCPCB_FLAG_ACK
;
1596 TCP_SKB_CB(buff
)->sacked
= 0;
1597 skb_shinfo(buff
)->tso_segs
= 1;
1598 skb_shinfo(buff
)->tso_size
= 0;
1600 /* Send it off, this clears delayed acks for us. */
1601 TCP_SKB_CB(buff
)->seq
= TCP_SKB_CB(buff
)->end_seq
= tcp_acceptable_seq(sk
, tp
);
1602 TCP_SKB_CB(buff
)->when
= tcp_time_stamp
;
1603 tcp_transmit_skb(sk
, buff
);
1607 /* This routine sends a packet with an out of date sequence
1608 * number. It assumes the other end will try to ack it.
1610 * Question: what should we make while urgent mode?
1611 * 4.4BSD forces sending single byte of data. We cannot send
1612 * out of window data, because we have SND.NXT==SND.MAX...
1614 * Current solution: to send TWO zero-length segments in urgent mode:
1615 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
1616 * out-of-date with SND.UNA-1 to probe window.
1618 static int tcp_xmit_probe_skb(struct sock
*sk
, int urgent
)
1620 struct tcp_sock
*tp
= tcp_sk(sk
);
1621 struct sk_buff
*skb
;
1623 /* We don't queue it, tcp_transmit_skb() sets ownership. */
1624 skb
= alloc_skb(MAX_TCP_HEADER
, GFP_ATOMIC
);
1628 /* Reserve space for headers and set control bits. */
1629 skb_reserve(skb
, MAX_TCP_HEADER
);
1631 TCP_SKB_CB(skb
)->flags
= TCPCB_FLAG_ACK
;
1632 TCP_SKB_CB(skb
)->sacked
= urgent
;
1633 skb_shinfo(skb
)->tso_segs
= 1;
1634 skb_shinfo(skb
)->tso_size
= 0;
1636 /* Use a previous sequence. This should cause the other
1637 * end to send an ack. Don't queue or clone SKB, just
1640 TCP_SKB_CB(skb
)->seq
= urgent
? tp
->snd_una
: tp
->snd_una
- 1;
1641 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(skb
)->seq
;
1642 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
1643 return tcp_transmit_skb(sk
, skb
);
1646 int tcp_write_wakeup(struct sock
*sk
)
1648 if (sk
->sk_state
!= TCP_CLOSE
) {
1649 struct tcp_sock
*tp
= tcp_sk(sk
);
1650 struct sk_buff
*skb
;
1652 if ((skb
= sk
->sk_send_head
) != NULL
&&
1653 before(TCP_SKB_CB(skb
)->seq
, tp
->snd_una
+tp
->snd_wnd
)) {
1655 unsigned int mss
= tcp_current_mss(sk
, 0);
1656 unsigned int seg_size
= tp
->snd_una
+tp
->snd_wnd
-TCP_SKB_CB(skb
)->seq
;
1658 if (before(tp
->pushed_seq
, TCP_SKB_CB(skb
)->end_seq
))
1659 tp
->pushed_seq
= TCP_SKB_CB(skb
)->end_seq
;
1661 /* We are probing the opening of a window
1662 * but the window size is != 0
1663 * must have been a result SWS avoidance ( sender )
1665 if (seg_size
< TCP_SKB_CB(skb
)->end_seq
- TCP_SKB_CB(skb
)->seq
||
1667 seg_size
= min(seg_size
, mss
);
1668 TCP_SKB_CB(skb
)->flags
|= TCPCB_FLAG_PSH
;
1669 if (tcp_fragment(sk
, skb
, seg_size
))
1671 /* SWS override triggered forced fragmentation.
1672 * Disable TSO, the connection is too sick. */
1673 if (sk
->sk_route_caps
& NETIF_F_TSO
) {
1674 sock_set_flag(sk
, SOCK_NO_LARGESEND
);
1675 sk
->sk_route_caps
&= ~NETIF_F_TSO
;
1676 tp
->mss_cache
= tp
->mss_cache_std
;
1678 } else if (!tcp_skb_pcount(skb
))
1679 tcp_set_skb_tso_segs(skb
, tp
->mss_cache_std
);
1681 TCP_SKB_CB(skb
)->flags
|= TCPCB_FLAG_PSH
;
1682 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
1683 tcp_tso_set_push(skb
);
1684 err
= tcp_transmit_skb(sk
, skb_clone(skb
, GFP_ATOMIC
));
1686 update_send_head(sk
, tp
, skb
);
1691 between(tp
->snd_up
, tp
->snd_una
+1, tp
->snd_una
+0xFFFF))
1692 tcp_xmit_probe_skb(sk
, TCPCB_URG
);
1693 return tcp_xmit_probe_skb(sk
, 0);
1699 /* A window probe timeout has occurred. If window is not closed send
1700 * a partial packet else a zero probe.
1702 void tcp_send_probe0(struct sock
*sk
)
1704 struct tcp_sock
*tp
= tcp_sk(sk
);
1707 err
= tcp_write_wakeup(sk
);
1709 if (tp
->packets_out
|| !sk
->sk_send_head
) {
1710 /* Cancel probe timer, if it is not required. */
1717 if (tp
->backoff
< sysctl_tcp_retries2
)
1720 tcp_reset_xmit_timer (sk
, TCP_TIME_PROBE0
,
1721 min(tp
->rto
<< tp
->backoff
, TCP_RTO_MAX
));
1723 /* If packet was not sent due to local congestion,
1724 * do not backoff and do not remember probes_out.
1725 * Let local senders to fight for local resources.
1727 * Use accumulated backoff yet.
1729 if (!tp
->probes_out
)
1731 tcp_reset_xmit_timer (sk
, TCP_TIME_PROBE0
,
1732 min(tp
->rto
<< tp
->backoff
, TCP_RESOURCE_PROBE_INTERVAL
));
1736 EXPORT_SYMBOL(tcp_connect
);
1737 EXPORT_SYMBOL(tcp_make_synack
);
1738 EXPORT_SYMBOL(tcp_simple_retransmit
);
1739 EXPORT_SYMBOL(tcp_sync_mss
);