2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * Implementation of the Transmission Control Protocol(TCP).
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
27 * Linus Torvalds : send_delayed_ack
28 * David S. Miller : Charge memory using the right skb
29 * during syn/ack processing.
30 * David S. Miller : Output engine completely rewritten.
31 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
32 * Cacophonix Gaul : draft-minshall-nagle-01
33 * J Hadi Salim : ECN support
37 #define pr_fmt(fmt) "TCP: " fmt
41 #include <linux/compiler.h>
42 #include <linux/gfp.h>
43 #include <linux/module.h>
45 /* People can turn this off for buggy TCP's found in printers etc. */
46 int sysctl_tcp_retrans_collapse __read_mostly
= 1;
48 /* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
51 int sysctl_tcp_workaround_signed_windows __read_mostly
= 0;
53 /* Default TSQ limit of two TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly
= 131072;
56 /* This limits the percentage of the congestion window which we
57 * will allow a single TSO frame to consume. Building TSO frames
58 * which are too large can cause TCP streams to be bursty.
60 int sysctl_tcp_tso_win_divisor __read_mostly
= 3;
62 int sysctl_tcp_mtu_probing __read_mostly
= 0;
63 int sysctl_tcp_base_mss __read_mostly
= TCP_BASE_MSS
;
65 /* By default, RFC2861 behavior. */
66 int sysctl_tcp_slow_start_after_idle __read_mostly
= 1;
68 static bool tcp_write_xmit(struct sock
*sk
, unsigned int mss_now
, int nonagle
,
69 int push_one
, gfp_t gfp
);
71 /* Account for new data that has been sent to the network. */
72 static void tcp_event_new_data_sent(struct sock
*sk
, const struct sk_buff
*skb
)
74 struct inet_connection_sock
*icsk
= inet_csk(sk
);
75 struct tcp_sock
*tp
= tcp_sk(sk
);
76 unsigned int prior_packets
= tp
->packets_out
;
78 tcp_advance_send_head(sk
, skb
);
79 tp
->snd_nxt
= TCP_SKB_CB(skb
)->end_seq
;
81 tp
->packets_out
+= tcp_skb_pcount(skb
);
82 if (!prior_packets
|| icsk
->icsk_pending
== ICSK_TIME_EARLY_RETRANS
||
83 icsk
->icsk_pending
== ICSK_TIME_LOSS_PROBE
)
87 /* SND.NXT, if window was not shrunk.
88 * If window has been shrunk, what should we make? It is not clear at all.
89 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
90 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
91 * invalid. OK, let's make this for now:
93 static inline __u32
tcp_acceptable_seq(const struct sock
*sk
)
95 const struct tcp_sock
*tp
= tcp_sk(sk
);
97 if (!before(tcp_wnd_end(tp
), tp
->snd_nxt
))
100 return tcp_wnd_end(tp
);
103 /* Calculate mss to advertise in SYN segment.
104 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
106 * 1. It is independent of path mtu.
107 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
108 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
109 * attached devices, because some buggy hosts are confused by
111 * 4. We do not make 3, we advertise MSS, calculated from first
112 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
113 * This may be overridden via information stored in routing table.
114 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
115 * probably even Jumbo".
117 static __u16
tcp_advertise_mss(struct sock
*sk
)
119 struct tcp_sock
*tp
= tcp_sk(sk
);
120 const struct dst_entry
*dst
= __sk_dst_get(sk
);
121 int mss
= tp
->advmss
;
124 unsigned int metric
= dst_metric_advmss(dst
);
135 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
136 * This is the first part of cwnd validation mechanism. */
137 static void tcp_cwnd_restart(struct sock
*sk
, const struct dst_entry
*dst
)
139 struct tcp_sock
*tp
= tcp_sk(sk
);
140 s32 delta
= tcp_time_stamp
- tp
->lsndtime
;
141 u32 restart_cwnd
= tcp_init_cwnd(tp
, dst
);
142 u32 cwnd
= tp
->snd_cwnd
;
144 tcp_ca_event(sk
, CA_EVENT_CWND_RESTART
);
146 tp
->snd_ssthresh
= tcp_current_ssthresh(sk
);
147 restart_cwnd
= min(restart_cwnd
, cwnd
);
149 while ((delta
-= inet_csk(sk
)->icsk_rto
) > 0 && cwnd
> restart_cwnd
)
151 tp
->snd_cwnd
= max(cwnd
, restart_cwnd
);
152 tp
->snd_cwnd_stamp
= tcp_time_stamp
;
153 tp
->snd_cwnd_used
= 0;
156 /* Congestion state accounting after a packet has been sent. */
157 static void tcp_event_data_sent(struct tcp_sock
*tp
,
160 struct inet_connection_sock
*icsk
= inet_csk(sk
);
161 const u32 now
= tcp_time_stamp
;
163 if (sysctl_tcp_slow_start_after_idle
&&
164 (!tp
->packets_out
&& (s32
)(now
- tp
->lsndtime
) > icsk
->icsk_rto
))
165 tcp_cwnd_restart(sk
, __sk_dst_get(sk
));
169 /* If it is a reply for ato after last received
170 * packet, enter pingpong mode.
172 if ((u32
)(now
- icsk
->icsk_ack
.lrcvtime
) < icsk
->icsk_ack
.ato
)
173 icsk
->icsk_ack
.pingpong
= 1;
176 /* Account for an ACK we sent. */
177 static inline void tcp_event_ack_sent(struct sock
*sk
, unsigned int pkts
)
179 tcp_dec_quickack_mode(sk
, pkts
);
180 inet_csk_clear_xmit_timer(sk
, ICSK_TIME_DACK
);
183 /* Determine a window scaling and initial window to offer.
184 * Based on the assumption that the given amount of space
185 * will be offered. Store the results in the tp structure.
186 * NOTE: for smooth operation initial space offering should
187 * be a multiple of mss if possible. We assume here that mss >= 1.
188 * This MUST be enforced by all callers.
190 void tcp_select_initial_window(int __space
, __u32 mss
,
191 __u32
*rcv_wnd
, __u32
*window_clamp
,
192 int wscale_ok
, __u8
*rcv_wscale
,
195 unsigned int space
= (__space
< 0 ? 0 : __space
);
197 /* If no clamp set the clamp to the max possible scaled window */
198 if (*window_clamp
== 0)
199 (*window_clamp
) = (65535 << 14);
200 space
= min(*window_clamp
, space
);
202 /* Quantize space offering to a multiple of mss if possible. */
204 space
= (space
/ mss
) * mss
;
206 /* NOTE: offering an initial window larger than 32767
207 * will break some buggy TCP stacks. If the admin tells us
208 * it is likely we could be speaking with such a buggy stack
209 * we will truncate our initial window offering to 32K-1
210 * unless the remote has sent us a window scaling option,
211 * which we interpret as a sign the remote TCP is not
212 * misinterpreting the window field as a signed quantity.
214 if (sysctl_tcp_workaround_signed_windows
)
215 (*rcv_wnd
) = min(space
, MAX_TCP_WINDOW
);
221 /* Set window scaling on max possible window
222 * See RFC1323 for an explanation of the limit to 14
224 space
= max_t(u32
, sysctl_tcp_rmem
[2], sysctl_rmem_max
);
225 space
= min_t(u32
, space
, *window_clamp
);
226 while (space
> 65535 && (*rcv_wscale
) < 14) {
232 /* Set initial window to a value enough for senders starting with
233 * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
234 * a limit on the initial window when mss is larger than 1460.
236 if (mss
> (1 << *rcv_wscale
)) {
237 int init_cwnd
= TCP_DEFAULT_INIT_RCVWND
;
240 max_t(u32
, (1460 * TCP_DEFAULT_INIT_RCVWND
) / mss
, 2);
241 /* when initializing use the value from init_rcv_wnd
242 * rather than the default from above
245 *rcv_wnd
= min(*rcv_wnd
, init_rcv_wnd
* mss
);
247 *rcv_wnd
= min(*rcv_wnd
, init_cwnd
* mss
);
250 /* Set the clamp no higher than max representable value */
251 (*window_clamp
) = min(65535U << (*rcv_wscale
), *window_clamp
);
253 EXPORT_SYMBOL(tcp_select_initial_window
);
255 /* Chose a new window to advertise, update state in tcp_sock for the
256 * socket, and return result with RFC1323 scaling applied. The return
257 * value can be stuffed directly into th->window for an outgoing
260 static u16
tcp_select_window(struct sock
*sk
)
262 struct tcp_sock
*tp
= tcp_sk(sk
);
263 u32 cur_win
= tcp_receive_window(tp
);
264 u32 new_win
= __tcp_select_window(sk
);
266 /* Never shrink the offered window */
267 if (new_win
< cur_win
) {
268 /* Danger Will Robinson!
269 * Don't update rcv_wup/rcv_wnd here or else
270 * we will not be able to advertise a zero
271 * window in time. --DaveM
273 * Relax Will Robinson.
275 new_win
= ALIGN(cur_win
, 1 << tp
->rx_opt
.rcv_wscale
);
277 tp
->rcv_wnd
= new_win
;
278 tp
->rcv_wup
= tp
->rcv_nxt
;
280 /* Make sure we do not exceed the maximum possible
283 if (!tp
->rx_opt
.rcv_wscale
&& sysctl_tcp_workaround_signed_windows
)
284 new_win
= min(new_win
, MAX_TCP_WINDOW
);
286 new_win
= min(new_win
, (65535U << tp
->rx_opt
.rcv_wscale
));
288 /* RFC1323 scaling applied */
289 new_win
>>= tp
->rx_opt
.rcv_wscale
;
291 /* If we advertise zero window, disable fast path. */
298 /* Packet ECN state for a SYN-ACK */
299 static inline void TCP_ECN_send_synack(const struct tcp_sock
*tp
, struct sk_buff
*skb
)
301 TCP_SKB_CB(skb
)->tcp_flags
&= ~TCPHDR_CWR
;
302 if (!(tp
->ecn_flags
& TCP_ECN_OK
))
303 TCP_SKB_CB(skb
)->tcp_flags
&= ~TCPHDR_ECE
;
306 /* Packet ECN state for a SYN. */
307 static inline void TCP_ECN_send_syn(struct sock
*sk
, struct sk_buff
*skb
)
309 struct tcp_sock
*tp
= tcp_sk(sk
);
312 if (sock_net(sk
)->ipv4
.sysctl_tcp_ecn
== 1) {
313 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_ECE
| TCPHDR_CWR
;
314 tp
->ecn_flags
= TCP_ECN_OK
;
318 static __inline__
void
319 TCP_ECN_make_synack(const struct request_sock
*req
, struct tcphdr
*th
)
321 if (inet_rsk(req
)->ecn_ok
)
325 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
328 static inline void TCP_ECN_send(struct sock
*sk
, struct sk_buff
*skb
,
331 struct tcp_sock
*tp
= tcp_sk(sk
);
333 if (tp
->ecn_flags
& TCP_ECN_OK
) {
334 /* Not-retransmitted data segment: set ECT and inject CWR. */
335 if (skb
->len
!= tcp_header_len
&&
336 !before(TCP_SKB_CB(skb
)->seq
, tp
->snd_nxt
)) {
338 if (tp
->ecn_flags
& TCP_ECN_QUEUE_CWR
) {
339 tp
->ecn_flags
&= ~TCP_ECN_QUEUE_CWR
;
340 tcp_hdr(skb
)->cwr
= 1;
341 skb_shinfo(skb
)->gso_type
|= SKB_GSO_TCP_ECN
;
344 /* ACK or retransmitted segment: clear ECT|CE */
345 INET_ECN_dontxmit(sk
);
347 if (tp
->ecn_flags
& TCP_ECN_DEMAND_CWR
)
348 tcp_hdr(skb
)->ece
= 1;
352 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
353 * auto increment end seqno.
355 static void tcp_init_nondata_skb(struct sk_buff
*skb
, u32 seq
, u8 flags
)
357 skb
->ip_summed
= CHECKSUM_PARTIAL
;
360 TCP_SKB_CB(skb
)->tcp_flags
= flags
;
361 TCP_SKB_CB(skb
)->sacked
= 0;
363 skb_shinfo(skb
)->gso_segs
= 1;
364 skb_shinfo(skb
)->gso_size
= 0;
365 skb_shinfo(skb
)->gso_type
= 0;
367 TCP_SKB_CB(skb
)->seq
= seq
;
368 if (flags
& (TCPHDR_SYN
| TCPHDR_FIN
))
370 TCP_SKB_CB(skb
)->end_seq
= seq
;
373 static inline bool tcp_urg_mode(const struct tcp_sock
*tp
)
375 return tp
->snd_una
!= tp
->snd_up
;
378 #define OPTION_SACK_ADVERTISE (1 << 0)
379 #define OPTION_TS (1 << 1)
380 #define OPTION_MD5 (1 << 2)
381 #define OPTION_WSCALE (1 << 3)
382 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
384 struct tcp_out_options
{
385 u16 options
; /* bit field of OPTION_* */
386 u16 mss
; /* 0 to disable */
387 u8 ws
; /* window scale, 0 to disable */
388 u8 num_sack_blocks
; /* number of SACK blocks to include */
389 u8 hash_size
; /* bytes in hash_location */
390 __u8
*hash_location
; /* temporary pointer, overloaded */
391 __u32 tsval
, tsecr
; /* need to include OPTION_TS */
392 struct tcp_fastopen_cookie
*fastopen_cookie
; /* Fast open cookie */
395 /* Write previously computed TCP options to the packet.
397 * Beware: Something in the Internet is very sensitive to the ordering of
398 * TCP options, we learned this through the hard way, so be careful here.
399 * Luckily we can at least blame others for their non-compliance but from
400 * inter-operatibility perspective it seems that we're somewhat stuck with
401 * the ordering which we have been using if we want to keep working with
402 * those broken things (not that it currently hurts anybody as there isn't
403 * particular reason why the ordering would need to be changed).
405 * At least SACK_PERM as the first option is known to lead to a disaster
406 * (but it may well be that other scenarios fail similarly).
408 static void tcp_options_write(__be32
*ptr
, struct tcp_sock
*tp
,
409 struct tcp_out_options
*opts
)
411 u16 options
= opts
->options
; /* mungable copy */
413 if (unlikely(OPTION_MD5
& options
)) {
414 *ptr
++ = htonl((TCPOPT_NOP
<< 24) | (TCPOPT_NOP
<< 16) |
415 (TCPOPT_MD5SIG
<< 8) | TCPOLEN_MD5SIG
);
416 /* overload cookie hash location */
417 opts
->hash_location
= (__u8
*)ptr
;
421 if (unlikely(opts
->mss
)) {
422 *ptr
++ = htonl((TCPOPT_MSS
<< 24) |
423 (TCPOLEN_MSS
<< 16) |
427 if (likely(OPTION_TS
& options
)) {
428 if (unlikely(OPTION_SACK_ADVERTISE
& options
)) {
429 *ptr
++ = htonl((TCPOPT_SACK_PERM
<< 24) |
430 (TCPOLEN_SACK_PERM
<< 16) |
431 (TCPOPT_TIMESTAMP
<< 8) |
433 options
&= ~OPTION_SACK_ADVERTISE
;
435 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
437 (TCPOPT_TIMESTAMP
<< 8) |
440 *ptr
++ = htonl(opts
->tsval
);
441 *ptr
++ = htonl(opts
->tsecr
);
444 if (unlikely(OPTION_SACK_ADVERTISE
& options
)) {
445 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
447 (TCPOPT_SACK_PERM
<< 8) |
451 if (unlikely(OPTION_WSCALE
& options
)) {
452 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
453 (TCPOPT_WINDOW
<< 16) |
454 (TCPOLEN_WINDOW
<< 8) |
458 if (unlikely(opts
->num_sack_blocks
)) {
459 struct tcp_sack_block
*sp
= tp
->rx_opt
.dsack
?
460 tp
->duplicate_sack
: tp
->selective_acks
;
463 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
466 (TCPOLEN_SACK_BASE
+ (opts
->num_sack_blocks
*
467 TCPOLEN_SACK_PERBLOCK
)));
469 for (this_sack
= 0; this_sack
< opts
->num_sack_blocks
;
471 *ptr
++ = htonl(sp
[this_sack
].start_seq
);
472 *ptr
++ = htonl(sp
[this_sack
].end_seq
);
475 tp
->rx_opt
.dsack
= 0;
478 if (unlikely(OPTION_FAST_OPEN_COOKIE
& options
)) {
479 struct tcp_fastopen_cookie
*foc
= opts
->fastopen_cookie
;
481 *ptr
++ = htonl((TCPOPT_EXP
<< 24) |
482 ((TCPOLEN_EXP_FASTOPEN_BASE
+ foc
->len
) << 16) |
483 TCPOPT_FASTOPEN_MAGIC
);
485 memcpy(ptr
, foc
->val
, foc
->len
);
486 if ((foc
->len
& 3) == 2) {
487 u8
*align
= ((u8
*)ptr
) + foc
->len
;
488 align
[0] = align
[1] = TCPOPT_NOP
;
490 ptr
+= (foc
->len
+ 3) >> 2;
494 /* Compute TCP options for SYN packets. This is not the final
495 * network wire format yet.
497 static unsigned int tcp_syn_options(struct sock
*sk
, struct sk_buff
*skb
,
498 struct tcp_out_options
*opts
,
499 struct tcp_md5sig_key
**md5
)
501 struct tcp_sock
*tp
= tcp_sk(sk
);
502 unsigned int remaining
= MAX_TCP_OPTION_SPACE
;
503 struct tcp_fastopen_request
*fastopen
= tp
->fastopen_req
;
505 #ifdef CONFIG_TCP_MD5SIG
506 *md5
= tp
->af_specific
->md5_lookup(sk
, sk
);
508 opts
->options
|= OPTION_MD5
;
509 remaining
-= TCPOLEN_MD5SIG_ALIGNED
;
515 /* We always get an MSS option. The option bytes which will be seen in
516 * normal data packets should timestamps be used, must be in the MSS
517 * advertised. But we subtract them from tp->mss_cache so that
518 * calculations in tcp_sendmsg are simpler etc. So account for this
519 * fact here if necessary. If we don't do this correctly, as a
520 * receiver we won't recognize data packets as being full sized when we
521 * should, and thus we won't abide by the delayed ACK rules correctly.
522 * SACKs don't matter, we never delay an ACK when we have any of those
524 opts
->mss
= tcp_advertise_mss(sk
);
525 remaining
-= TCPOLEN_MSS_ALIGNED
;
527 if (likely(sysctl_tcp_timestamps
&& *md5
== NULL
)) {
528 opts
->options
|= OPTION_TS
;
529 opts
->tsval
= TCP_SKB_CB(skb
)->when
+ tp
->tsoffset
;
530 opts
->tsecr
= tp
->rx_opt
.ts_recent
;
531 remaining
-= TCPOLEN_TSTAMP_ALIGNED
;
533 if (likely(sysctl_tcp_window_scaling
)) {
534 opts
->ws
= tp
->rx_opt
.rcv_wscale
;
535 opts
->options
|= OPTION_WSCALE
;
536 remaining
-= TCPOLEN_WSCALE_ALIGNED
;
538 if (likely(sysctl_tcp_sack
)) {
539 opts
->options
|= OPTION_SACK_ADVERTISE
;
540 if (unlikely(!(OPTION_TS
& opts
->options
)))
541 remaining
-= TCPOLEN_SACKPERM_ALIGNED
;
544 if (fastopen
&& fastopen
->cookie
.len
>= 0) {
545 u32 need
= TCPOLEN_EXP_FASTOPEN_BASE
+ fastopen
->cookie
.len
;
546 need
= (need
+ 3) & ~3U; /* Align to 32 bits */
547 if (remaining
>= need
) {
548 opts
->options
|= OPTION_FAST_OPEN_COOKIE
;
549 opts
->fastopen_cookie
= &fastopen
->cookie
;
551 tp
->syn_fastopen
= 1;
555 return MAX_TCP_OPTION_SPACE
- remaining
;
558 /* Set up TCP options for SYN-ACKs. */
559 static unsigned int tcp_synack_options(struct sock
*sk
,
560 struct request_sock
*req
,
561 unsigned int mss
, struct sk_buff
*skb
,
562 struct tcp_out_options
*opts
,
563 struct tcp_md5sig_key
**md5
,
564 struct tcp_fastopen_cookie
*foc
)
566 struct inet_request_sock
*ireq
= inet_rsk(req
);
567 unsigned int remaining
= MAX_TCP_OPTION_SPACE
;
569 #ifdef CONFIG_TCP_MD5SIG
570 *md5
= tcp_rsk(req
)->af_specific
->md5_lookup(sk
, req
);
572 opts
->options
|= OPTION_MD5
;
573 remaining
-= TCPOLEN_MD5SIG_ALIGNED
;
575 /* We can't fit any SACK blocks in a packet with MD5 + TS
576 * options. There was discussion about disabling SACK
577 * rather than TS in order to fit in better with old,
578 * buggy kernels, but that was deemed to be unnecessary.
580 ireq
->tstamp_ok
&= !ireq
->sack_ok
;
586 /* We always send an MSS option. */
588 remaining
-= TCPOLEN_MSS_ALIGNED
;
590 if (likely(ireq
->wscale_ok
)) {
591 opts
->ws
= ireq
->rcv_wscale
;
592 opts
->options
|= OPTION_WSCALE
;
593 remaining
-= TCPOLEN_WSCALE_ALIGNED
;
595 if (likely(ireq
->tstamp_ok
)) {
596 opts
->options
|= OPTION_TS
;
597 opts
->tsval
= TCP_SKB_CB(skb
)->when
;
598 opts
->tsecr
= req
->ts_recent
;
599 remaining
-= TCPOLEN_TSTAMP_ALIGNED
;
601 if (likely(ireq
->sack_ok
)) {
602 opts
->options
|= OPTION_SACK_ADVERTISE
;
603 if (unlikely(!ireq
->tstamp_ok
))
604 remaining
-= TCPOLEN_SACKPERM_ALIGNED
;
607 u32 need
= TCPOLEN_EXP_FASTOPEN_BASE
+ foc
->len
;
608 need
= (need
+ 3) & ~3U; /* Align to 32 bits */
609 if (remaining
>= need
) {
610 opts
->options
|= OPTION_FAST_OPEN_COOKIE
;
611 opts
->fastopen_cookie
= foc
;
616 return MAX_TCP_OPTION_SPACE
- remaining
;
619 /* Compute TCP options for ESTABLISHED sockets. This is not the
620 * final wire format yet.
622 static unsigned int tcp_established_options(struct sock
*sk
, struct sk_buff
*skb
,
623 struct tcp_out_options
*opts
,
624 struct tcp_md5sig_key
**md5
)
626 struct tcp_skb_cb
*tcb
= skb
? TCP_SKB_CB(skb
) : NULL
;
627 struct tcp_sock
*tp
= tcp_sk(sk
);
628 unsigned int size
= 0;
629 unsigned int eff_sacks
;
631 #ifdef CONFIG_TCP_MD5SIG
632 *md5
= tp
->af_specific
->md5_lookup(sk
, sk
);
633 if (unlikely(*md5
)) {
634 opts
->options
|= OPTION_MD5
;
635 size
+= TCPOLEN_MD5SIG_ALIGNED
;
641 if (likely(tp
->rx_opt
.tstamp_ok
)) {
642 opts
->options
|= OPTION_TS
;
643 opts
->tsval
= tcb
? tcb
->when
+ tp
->tsoffset
: 0;
644 opts
->tsecr
= tp
->rx_opt
.ts_recent
;
645 size
+= TCPOLEN_TSTAMP_ALIGNED
;
648 eff_sacks
= tp
->rx_opt
.num_sacks
+ tp
->rx_opt
.dsack
;
649 if (unlikely(eff_sacks
)) {
650 const unsigned int remaining
= MAX_TCP_OPTION_SPACE
- size
;
651 opts
->num_sack_blocks
=
652 min_t(unsigned int, eff_sacks
,
653 (remaining
- TCPOLEN_SACK_BASE_ALIGNED
) /
654 TCPOLEN_SACK_PERBLOCK
);
655 size
+= TCPOLEN_SACK_BASE_ALIGNED
+
656 opts
->num_sack_blocks
* TCPOLEN_SACK_PERBLOCK
;
663 /* TCP SMALL QUEUES (TSQ)
665 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
666 * to reduce RTT and bufferbloat.
667 * We do this using a special skb destructor (tcp_wfree).
669 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
670 * needs to be reallocated in a driver.
671 * The invariant being skb->truesize substracted from sk->sk_wmem_alloc
673 * Since transmit from skb destructor is forbidden, we use a tasklet
674 * to process all sockets that eventually need to send more skbs.
675 * We use one tasklet per cpu, with its own queue of sockets.
678 struct tasklet_struct tasklet
;
679 struct list_head head
; /* queue of tcp sockets */
681 static DEFINE_PER_CPU(struct tsq_tasklet
, tsq_tasklet
);
683 static void tcp_tsq_handler(struct sock
*sk
)
685 if ((1 << sk
->sk_state
) &
686 (TCPF_ESTABLISHED
| TCPF_FIN_WAIT1
| TCPF_CLOSING
|
687 TCPF_CLOSE_WAIT
| TCPF_LAST_ACK
))
688 tcp_write_xmit(sk
, tcp_current_mss(sk
), 0, 0, GFP_ATOMIC
);
691 * One tasklest per cpu tries to send more skbs.
692 * We run in tasklet context but need to disable irqs when
693 * transfering tsq->head because tcp_wfree() might
694 * interrupt us (non NAPI drivers)
696 static void tcp_tasklet_func(unsigned long data
)
698 struct tsq_tasklet
*tsq
= (struct tsq_tasklet
*)data
;
701 struct list_head
*q
, *n
;
705 local_irq_save(flags
);
706 list_splice_init(&tsq
->head
, &list
);
707 local_irq_restore(flags
);
709 list_for_each_safe(q
, n
, &list
) {
710 tp
= list_entry(q
, struct tcp_sock
, tsq_node
);
711 list_del(&tp
->tsq_node
);
713 sk
= (struct sock
*)tp
;
716 if (!sock_owned_by_user(sk
)) {
719 /* defer the work to tcp_release_cb() */
720 set_bit(TCP_TSQ_DEFERRED
, &tp
->tsq_flags
);
724 clear_bit(TSQ_QUEUED
, &tp
->tsq_flags
);
729 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
730 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
731 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
732 (1UL << TCP_MTU_REDUCED_DEFERRED))
734 * tcp_release_cb - tcp release_sock() callback
737 * called from release_sock() to perform protocol dependent
738 * actions before socket release.
740 void tcp_release_cb(struct sock
*sk
)
742 struct tcp_sock
*tp
= tcp_sk(sk
);
743 unsigned long flags
, nflags
;
745 /* perform an atomic operation only if at least one flag is set */
747 flags
= tp
->tsq_flags
;
748 if (!(flags
& TCP_DEFERRED_ALL
))
750 nflags
= flags
& ~TCP_DEFERRED_ALL
;
751 } while (cmpxchg(&tp
->tsq_flags
, flags
, nflags
) != flags
);
753 if (flags
& (1UL << TCP_TSQ_DEFERRED
))
756 if (flags
& (1UL << TCP_WRITE_TIMER_DEFERRED
)) {
757 tcp_write_timer_handler(sk
);
760 if (flags
& (1UL << TCP_DELACK_TIMER_DEFERRED
)) {
761 tcp_delack_timer_handler(sk
);
764 if (flags
& (1UL << TCP_MTU_REDUCED_DEFERRED
)) {
765 sk
->sk_prot
->mtu_reduced(sk
);
769 EXPORT_SYMBOL(tcp_release_cb
);
771 void __init
tcp_tasklet_init(void)
775 for_each_possible_cpu(i
) {
776 struct tsq_tasklet
*tsq
= &per_cpu(tsq_tasklet
, i
);
778 INIT_LIST_HEAD(&tsq
->head
);
779 tasklet_init(&tsq
->tasklet
,
786 * Write buffer destructor automatically called from kfree_skb.
787 * We cant xmit new skbs from this context, as we might already
790 void tcp_wfree(struct sk_buff
*skb
)
792 struct sock
*sk
= skb
->sk
;
793 struct tcp_sock
*tp
= tcp_sk(sk
);
795 if (test_and_clear_bit(TSQ_THROTTLED
, &tp
->tsq_flags
) &&
796 !test_and_set_bit(TSQ_QUEUED
, &tp
->tsq_flags
)) {
798 struct tsq_tasklet
*tsq
;
800 /* Keep a ref on socket.
801 * This last ref will be released in tcp_tasklet_func()
803 atomic_sub(skb
->truesize
- 1, &sk
->sk_wmem_alloc
);
805 /* queue this socket to tasklet queue */
806 local_irq_save(flags
);
807 tsq
= &__get_cpu_var(tsq_tasklet
);
808 list_add(&tp
->tsq_node
, &tsq
->head
);
809 tasklet_schedule(&tsq
->tasklet
);
810 local_irq_restore(flags
);
816 /* This routine actually transmits TCP packets queued in by
817 * tcp_do_sendmsg(). This is used by both the initial
818 * transmission and possible later retransmissions.
819 * All SKB's seen here are completely headerless. It is our
820 * job to build the TCP header, and pass the packet down to
821 * IP so it can do the same plus pass the packet off to the
824 * We are working here with either a clone of the original
825 * SKB, or a fresh unique copy made by the retransmit engine.
827 static int tcp_transmit_skb(struct sock
*sk
, struct sk_buff
*skb
, int clone_it
,
830 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
831 struct inet_sock
*inet
;
833 struct tcp_skb_cb
*tcb
;
834 struct tcp_out_options opts
;
835 unsigned int tcp_options_size
, tcp_header_size
;
836 struct tcp_md5sig_key
*md5
;
840 BUG_ON(!skb
|| !tcp_skb_pcount(skb
));
842 /* If congestion control is doing timestamping, we must
843 * take such a timestamp before we potentially clone/copy.
845 if (icsk
->icsk_ca_ops
->flags
& TCP_CONG_RTT_STAMP
)
846 __net_timestamp(skb
);
848 if (likely(clone_it
)) {
849 if (unlikely(skb_cloned(skb
)))
850 skb
= pskb_copy(skb
, gfp_mask
);
852 skb
= skb_clone(skb
, gfp_mask
);
859 tcb
= TCP_SKB_CB(skb
);
860 memset(&opts
, 0, sizeof(opts
));
862 if (unlikely(tcb
->tcp_flags
& TCPHDR_SYN
))
863 tcp_options_size
= tcp_syn_options(sk
, skb
, &opts
, &md5
);
865 tcp_options_size
= tcp_established_options(sk
, skb
, &opts
,
867 tcp_header_size
= tcp_options_size
+ sizeof(struct tcphdr
);
869 if (tcp_packets_in_flight(tp
) == 0) {
870 tcp_ca_event(sk
, CA_EVENT_TX_START
);
875 skb_push(skb
, tcp_header_size
);
876 skb_reset_transport_header(skb
);
880 skb
->destructor
= (sysctl_tcp_limit_output_bytes
> 0) ?
881 tcp_wfree
: sock_wfree
;
882 atomic_add(skb
->truesize
, &sk
->sk_wmem_alloc
);
884 /* Build TCP header and checksum it. */
886 th
->source
= inet
->inet_sport
;
887 th
->dest
= inet
->inet_dport
;
888 th
->seq
= htonl(tcb
->seq
);
889 th
->ack_seq
= htonl(tp
->rcv_nxt
);
890 *(((__be16
*)th
) + 6) = htons(((tcp_header_size
>> 2) << 12) |
893 if (unlikely(tcb
->tcp_flags
& TCPHDR_SYN
)) {
894 /* RFC1323: The window in SYN & SYN/ACK segments
897 th
->window
= htons(min(tp
->rcv_wnd
, 65535U));
899 th
->window
= htons(tcp_select_window(sk
));
904 /* The urg_mode check is necessary during a below snd_una win probe */
905 if (unlikely(tcp_urg_mode(tp
) && before(tcb
->seq
, tp
->snd_up
))) {
906 if (before(tp
->snd_up
, tcb
->seq
+ 0x10000)) {
907 th
->urg_ptr
= htons(tp
->snd_up
- tcb
->seq
);
909 } else if (after(tcb
->seq
+ 0xFFFF, tp
->snd_nxt
)) {
910 th
->urg_ptr
= htons(0xFFFF);
915 tcp_options_write((__be32
*)(th
+ 1), tp
, &opts
);
916 if (likely((tcb
->tcp_flags
& TCPHDR_SYN
) == 0))
917 TCP_ECN_send(sk
, skb
, tcp_header_size
);
919 #ifdef CONFIG_TCP_MD5SIG
920 /* Calculate the MD5 hash, as we have all we need now */
922 sk_nocaps_add(sk
, NETIF_F_GSO_MASK
);
923 tp
->af_specific
->calc_md5_hash(opts
.hash_location
,
928 icsk
->icsk_af_ops
->send_check(sk
, skb
);
930 if (likely(tcb
->tcp_flags
& TCPHDR_ACK
))
931 tcp_event_ack_sent(sk
, tcp_skb_pcount(skb
));
933 if (skb
->len
!= tcp_header_size
)
934 tcp_event_data_sent(tp
, sk
);
936 if (after(tcb
->end_seq
, tp
->snd_nxt
) || tcb
->seq
== tcb
->end_seq
)
937 TCP_ADD_STATS(sock_net(sk
), TCP_MIB_OUTSEGS
,
938 tcp_skb_pcount(skb
));
940 err
= icsk
->icsk_af_ops
->queue_xmit(skb
, &inet
->cork
.fl
);
941 if (likely(err
<= 0))
944 tcp_enter_cwr(sk
, 1);
946 return net_xmit_eval(err
);
949 /* This routine just queues the buffer for sending.
951 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
952 * otherwise socket can stall.
954 static void tcp_queue_skb(struct sock
*sk
, struct sk_buff
*skb
)
956 struct tcp_sock
*tp
= tcp_sk(sk
);
958 /* Advance write_seq and place onto the write_queue. */
959 tp
->write_seq
= TCP_SKB_CB(skb
)->end_seq
;
960 skb_header_release(skb
);
961 tcp_add_write_queue_tail(sk
, skb
);
962 sk
->sk_wmem_queued
+= skb
->truesize
;
963 sk_mem_charge(sk
, skb
->truesize
);
966 /* Initialize TSO segments for a packet. */
967 static void tcp_set_skb_tso_segs(const struct sock
*sk
, struct sk_buff
*skb
,
968 unsigned int mss_now
)
970 if (skb
->len
<= mss_now
|| !sk_can_gso(sk
) ||
971 skb
->ip_summed
== CHECKSUM_NONE
) {
972 /* Avoid the costly divide in the normal
975 skb_shinfo(skb
)->gso_segs
= 1;
976 skb_shinfo(skb
)->gso_size
= 0;
977 skb_shinfo(skb
)->gso_type
= 0;
979 skb_shinfo(skb
)->gso_segs
= DIV_ROUND_UP(skb
->len
, mss_now
);
980 skb_shinfo(skb
)->gso_size
= mss_now
;
981 skb_shinfo(skb
)->gso_type
= sk
->sk_gso_type
;
985 /* When a modification to fackets out becomes necessary, we need to check
986 * skb is counted to fackets_out or not.
988 static void tcp_adjust_fackets_out(struct sock
*sk
, const struct sk_buff
*skb
,
991 struct tcp_sock
*tp
= tcp_sk(sk
);
993 if (!tp
->sacked_out
|| tcp_is_reno(tp
))
996 if (after(tcp_highest_sack_seq(tp
), TCP_SKB_CB(skb
)->seq
))
997 tp
->fackets_out
-= decr
;
1000 /* Pcount in the middle of the write queue got changed, we need to do various
1001 * tweaks to fix counters
1003 static void tcp_adjust_pcount(struct sock
*sk
, const struct sk_buff
*skb
, int decr
)
1005 struct tcp_sock
*tp
= tcp_sk(sk
);
1007 tp
->packets_out
-= decr
;
1009 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_ACKED
)
1010 tp
->sacked_out
-= decr
;
1011 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_RETRANS
)
1012 tp
->retrans_out
-= decr
;
1013 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_LOST
)
1014 tp
->lost_out
-= decr
;
1016 /* Reno case is special. Sigh... */
1017 if (tcp_is_reno(tp
) && decr
> 0)
1018 tp
->sacked_out
-= min_t(u32
, tp
->sacked_out
, decr
);
1020 tcp_adjust_fackets_out(sk
, skb
, decr
);
1022 if (tp
->lost_skb_hint
&&
1023 before(TCP_SKB_CB(skb
)->seq
, TCP_SKB_CB(tp
->lost_skb_hint
)->seq
) &&
1024 (tcp_is_fack(tp
) || (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_ACKED
)))
1025 tp
->lost_cnt_hint
-= decr
;
1027 tcp_verify_left_out(tp
);
1030 /* Function to create two new TCP segments. Shrinks the given segment
1031 * to the specified size and appends a new segment with the rest of the
1032 * packet to the list. This won't be called frequently, I hope.
1033 * Remember, these are still headerless SKBs at this point.
1035 int tcp_fragment(struct sock
*sk
, struct sk_buff
*skb
, u32 len
,
1036 unsigned int mss_now
)
1038 struct tcp_sock
*tp
= tcp_sk(sk
);
1039 struct sk_buff
*buff
;
1040 int nsize
, old_factor
;
1044 if (WARN_ON(len
> skb
->len
))
1047 nsize
= skb_headlen(skb
) - len
;
1051 if (skb_cloned(skb
) &&
1052 skb_is_nonlinear(skb
) &&
1053 pskb_expand_head(skb
, 0, 0, GFP_ATOMIC
))
1056 /* Get a new skb... force flag on. */
1057 buff
= sk_stream_alloc_skb(sk
, nsize
, GFP_ATOMIC
);
1059 return -ENOMEM
; /* We'll just try again later. */
1061 sk
->sk_wmem_queued
+= buff
->truesize
;
1062 sk_mem_charge(sk
, buff
->truesize
);
1063 nlen
= skb
->len
- len
- nsize
;
1064 buff
->truesize
+= nlen
;
1065 skb
->truesize
-= nlen
;
1067 /* Correct the sequence numbers. */
1068 TCP_SKB_CB(buff
)->seq
= TCP_SKB_CB(skb
)->seq
+ len
;
1069 TCP_SKB_CB(buff
)->end_seq
= TCP_SKB_CB(skb
)->end_seq
;
1070 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(buff
)->seq
;
1072 /* PSH and FIN should only be set in the second packet. */
1073 flags
= TCP_SKB_CB(skb
)->tcp_flags
;
1074 TCP_SKB_CB(skb
)->tcp_flags
= flags
& ~(TCPHDR_FIN
| TCPHDR_PSH
);
1075 TCP_SKB_CB(buff
)->tcp_flags
= flags
;
1076 TCP_SKB_CB(buff
)->sacked
= TCP_SKB_CB(skb
)->sacked
;
1078 if (!skb_shinfo(skb
)->nr_frags
&& skb
->ip_summed
!= CHECKSUM_PARTIAL
) {
1079 /* Copy and checksum data tail into the new buffer. */
1080 buff
->csum
= csum_partial_copy_nocheck(skb
->data
+ len
,
1081 skb_put(buff
, nsize
),
1086 skb
->csum
= csum_block_sub(skb
->csum
, buff
->csum
, len
);
1088 skb
->ip_summed
= CHECKSUM_PARTIAL
;
1089 skb_split(skb
, buff
, len
);
1092 buff
->ip_summed
= skb
->ip_summed
;
1094 /* Looks stupid, but our code really uses when of
1095 * skbs, which it never sent before. --ANK
1097 TCP_SKB_CB(buff
)->when
= TCP_SKB_CB(skb
)->when
;
1098 buff
->tstamp
= skb
->tstamp
;
1100 old_factor
= tcp_skb_pcount(skb
);
1102 /* Fix up tso_factor for both original and new SKB. */
1103 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1104 tcp_set_skb_tso_segs(sk
, buff
, mss_now
);
1106 /* If this packet has been sent out already, we must
1107 * adjust the various packet counters.
1109 if (!before(tp
->snd_nxt
, TCP_SKB_CB(buff
)->end_seq
)) {
1110 int diff
= old_factor
- tcp_skb_pcount(skb
) -
1111 tcp_skb_pcount(buff
);
1114 tcp_adjust_pcount(sk
, skb
, diff
);
1117 /* Link BUFF into the send queue. */
1118 skb_header_release(buff
);
1119 tcp_insert_write_queue_after(skb
, buff
, sk
);
1124 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1125 * eventually). The difference is that pulled data not copied, but
1126 * immediately discarded.
1128 static void __pskb_trim_head(struct sk_buff
*skb
, int len
)
1132 eat
= min_t(int, len
, skb_headlen(skb
));
1134 __skb_pull(skb
, eat
);
1141 for (i
= 0; i
< skb_shinfo(skb
)->nr_frags
; i
++) {
1142 int size
= skb_frag_size(&skb_shinfo(skb
)->frags
[i
]);
1145 skb_frag_unref(skb
, i
);
1148 skb_shinfo(skb
)->frags
[k
] = skb_shinfo(skb
)->frags
[i
];
1150 skb_shinfo(skb
)->frags
[k
].page_offset
+= eat
;
1151 skb_frag_size_sub(&skb_shinfo(skb
)->frags
[k
], eat
);
1157 skb_shinfo(skb
)->nr_frags
= k
;
1159 skb_reset_tail_pointer(skb
);
1160 skb
->data_len
-= len
;
1161 skb
->len
= skb
->data_len
;
1164 /* Remove acked data from a packet in the transmit queue. */
1165 int tcp_trim_head(struct sock
*sk
, struct sk_buff
*skb
, u32 len
)
1167 if (skb_unclone(skb
, GFP_ATOMIC
))
1170 __pskb_trim_head(skb
, len
);
1172 TCP_SKB_CB(skb
)->seq
+= len
;
1173 skb
->ip_summed
= CHECKSUM_PARTIAL
;
1175 skb
->truesize
-= len
;
1176 sk
->sk_wmem_queued
-= len
;
1177 sk_mem_uncharge(sk
, len
);
1178 sock_set_flag(sk
, SOCK_QUEUE_SHRUNK
);
1180 /* Any change of skb->len requires recalculation of tso factor. */
1181 if (tcp_skb_pcount(skb
) > 1)
1182 tcp_set_skb_tso_segs(sk
, skb
, tcp_skb_mss(skb
));
1187 /* Calculate MSS not accounting any TCP options. */
1188 static inline int __tcp_mtu_to_mss(struct sock
*sk
, int pmtu
)
1190 const struct tcp_sock
*tp
= tcp_sk(sk
);
1191 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
1194 /* Calculate base mss without TCP options:
1195 It is MMS_S - sizeof(tcphdr) of rfc1122
1197 mss_now
= pmtu
- icsk
->icsk_af_ops
->net_header_len
- sizeof(struct tcphdr
);
1199 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1200 if (icsk
->icsk_af_ops
->net_frag_header_len
) {
1201 const struct dst_entry
*dst
= __sk_dst_get(sk
);
1203 if (dst
&& dst_allfrag(dst
))
1204 mss_now
-= icsk
->icsk_af_ops
->net_frag_header_len
;
1207 /* Clamp it (mss_clamp does not include tcp options) */
1208 if (mss_now
> tp
->rx_opt
.mss_clamp
)
1209 mss_now
= tp
->rx_opt
.mss_clamp
;
1211 /* Now subtract optional transport overhead */
1212 mss_now
-= icsk
->icsk_ext_hdr_len
;
1214 /* Then reserve room for full set of TCP options and 8 bytes of data */
1220 /* Calculate MSS. Not accounting for SACKs here. */
1221 int tcp_mtu_to_mss(struct sock
*sk
, int pmtu
)
1223 /* Subtract TCP options size, not including SACKs */
1224 return __tcp_mtu_to_mss(sk
, pmtu
) -
1225 (tcp_sk(sk
)->tcp_header_len
- sizeof(struct tcphdr
));
1228 /* Inverse of above */
1229 int tcp_mss_to_mtu(struct sock
*sk
, int mss
)
1231 const struct tcp_sock
*tp
= tcp_sk(sk
);
1232 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
1236 tp
->tcp_header_len
+
1237 icsk
->icsk_ext_hdr_len
+
1238 icsk
->icsk_af_ops
->net_header_len
;
1240 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1241 if (icsk
->icsk_af_ops
->net_frag_header_len
) {
1242 const struct dst_entry
*dst
= __sk_dst_get(sk
);
1244 if (dst
&& dst_allfrag(dst
))
1245 mtu
+= icsk
->icsk_af_ops
->net_frag_header_len
;
1250 /* MTU probing init per socket */
1251 void tcp_mtup_init(struct sock
*sk
)
1253 struct tcp_sock
*tp
= tcp_sk(sk
);
1254 struct inet_connection_sock
*icsk
= inet_csk(sk
);
1256 icsk
->icsk_mtup
.enabled
= sysctl_tcp_mtu_probing
> 1;
1257 icsk
->icsk_mtup
.search_high
= tp
->rx_opt
.mss_clamp
+ sizeof(struct tcphdr
) +
1258 icsk
->icsk_af_ops
->net_header_len
;
1259 icsk
->icsk_mtup
.search_low
= tcp_mss_to_mtu(sk
, sysctl_tcp_base_mss
);
1260 icsk
->icsk_mtup
.probe_size
= 0;
1262 EXPORT_SYMBOL(tcp_mtup_init
);
1264 /* This function synchronize snd mss to current pmtu/exthdr set.
1266 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1267 for TCP options, but includes only bare TCP header.
1269 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1270 It is minimum of user_mss and mss received with SYN.
1271 It also does not include TCP options.
1273 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1275 tp->mss_cache is current effective sending mss, including
1276 all tcp options except for SACKs. It is evaluated,
1277 taking into account current pmtu, but never exceeds
1278 tp->rx_opt.mss_clamp.
1280 NOTE1. rfc1122 clearly states that advertised MSS
1281 DOES NOT include either tcp or ip options.
1283 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1284 are READ ONLY outside this function. --ANK (980731)
1286 unsigned int tcp_sync_mss(struct sock
*sk
, u32 pmtu
)
1288 struct tcp_sock
*tp
= tcp_sk(sk
);
1289 struct inet_connection_sock
*icsk
= inet_csk(sk
);
1292 if (icsk
->icsk_mtup
.search_high
> pmtu
)
1293 icsk
->icsk_mtup
.search_high
= pmtu
;
1295 mss_now
= tcp_mtu_to_mss(sk
, pmtu
);
1296 mss_now
= tcp_bound_to_half_wnd(tp
, mss_now
);
1298 /* And store cached results */
1299 icsk
->icsk_pmtu_cookie
= pmtu
;
1300 if (icsk
->icsk_mtup
.enabled
)
1301 mss_now
= min(mss_now
, tcp_mtu_to_mss(sk
, icsk
->icsk_mtup
.search_low
));
1302 tp
->mss_cache
= mss_now
;
1306 EXPORT_SYMBOL(tcp_sync_mss
);
1308 /* Compute the current effective MSS, taking SACKs and IP options,
1309 * and even PMTU discovery events into account.
1311 unsigned int tcp_current_mss(struct sock
*sk
)
1313 const struct tcp_sock
*tp
= tcp_sk(sk
);
1314 const struct dst_entry
*dst
= __sk_dst_get(sk
);
1316 unsigned int header_len
;
1317 struct tcp_out_options opts
;
1318 struct tcp_md5sig_key
*md5
;
1320 mss_now
= tp
->mss_cache
;
1323 u32 mtu
= dst_mtu(dst
);
1324 if (mtu
!= inet_csk(sk
)->icsk_pmtu_cookie
)
1325 mss_now
= tcp_sync_mss(sk
, mtu
);
1328 header_len
= tcp_established_options(sk
, NULL
, &opts
, &md5
) +
1329 sizeof(struct tcphdr
);
1330 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1331 * some common options. If this is an odd packet (because we have SACK
1332 * blocks etc) then our calculated header_len will be different, and
1333 * we have to adjust mss_now correspondingly */
1334 if (header_len
!= tp
->tcp_header_len
) {
1335 int delta
= (int) header_len
- tp
->tcp_header_len
;
1342 /* Congestion window validation. (RFC2861) */
1343 static void tcp_cwnd_validate(struct sock
*sk
)
1345 struct tcp_sock
*tp
= tcp_sk(sk
);
1347 if (tp
->packets_out
>= tp
->snd_cwnd
) {
1348 /* Network is feed fully. */
1349 tp
->snd_cwnd_used
= 0;
1350 tp
->snd_cwnd_stamp
= tcp_time_stamp
;
1352 /* Network starves. */
1353 if (tp
->packets_out
> tp
->snd_cwnd_used
)
1354 tp
->snd_cwnd_used
= tp
->packets_out
;
1356 if (sysctl_tcp_slow_start_after_idle
&&
1357 (s32
)(tcp_time_stamp
- tp
->snd_cwnd_stamp
) >= inet_csk(sk
)->icsk_rto
)
1358 tcp_cwnd_application_limited(sk
);
1362 /* Returns the portion of skb which can be sent right away without
1363 * introducing MSS oddities to segment boundaries. In rare cases where
1364 * mss_now != mss_cache, we will request caller to create a small skb
1365 * per input skb which could be mostly avoided here (if desired).
1367 * We explicitly want to create a request for splitting write queue tail
1368 * to a small skb for Nagle purposes while avoiding unnecessary modulos,
1369 * thus all the complexity (cwnd_len is always MSS multiple which we
1370 * return whenever allowed by the other factors). Basically we need the
1371 * modulo only when the receiver window alone is the limiting factor or
1372 * when we would be allowed to send the split-due-to-Nagle skb fully.
1374 static unsigned int tcp_mss_split_point(const struct sock
*sk
, const struct sk_buff
*skb
,
1375 unsigned int mss_now
, unsigned int max_segs
)
1377 const struct tcp_sock
*tp
= tcp_sk(sk
);
1378 u32 needed
, window
, max_len
;
1380 window
= tcp_wnd_end(tp
) - TCP_SKB_CB(skb
)->seq
;
1381 max_len
= mss_now
* max_segs
;
1383 if (likely(max_len
<= window
&& skb
!= tcp_write_queue_tail(sk
)))
1386 needed
= min(skb
->len
, window
);
1388 if (max_len
<= needed
)
1391 return needed
- needed
% mss_now
;
1394 /* Can at least one segment of SKB be sent right now, according to the
1395 * congestion window rules? If so, return how many segments are allowed.
1397 static inline unsigned int tcp_cwnd_test(const struct tcp_sock
*tp
,
1398 const struct sk_buff
*skb
)
1400 u32 in_flight
, cwnd
;
1402 /* Don't be strict about the congestion window for the final FIN. */
1403 if ((TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_FIN
) &&
1404 tcp_skb_pcount(skb
) == 1)
1407 in_flight
= tcp_packets_in_flight(tp
);
1408 cwnd
= tp
->snd_cwnd
;
1409 if (in_flight
< cwnd
)
1410 return (cwnd
- in_flight
);
1415 /* Initialize TSO state of a skb.
1416 * This must be invoked the first time we consider transmitting
1417 * SKB onto the wire.
1419 static int tcp_init_tso_segs(const struct sock
*sk
, struct sk_buff
*skb
,
1420 unsigned int mss_now
)
1422 int tso_segs
= tcp_skb_pcount(skb
);
1424 if (!tso_segs
|| (tso_segs
> 1 && tcp_skb_mss(skb
) != mss_now
)) {
1425 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1426 tso_segs
= tcp_skb_pcount(skb
);
1431 /* Minshall's variant of the Nagle send check. */
1432 static inline bool tcp_minshall_check(const struct tcp_sock
*tp
)
1434 return after(tp
->snd_sml
, tp
->snd_una
) &&
1435 !after(tp
->snd_sml
, tp
->snd_nxt
);
1438 /* Return false, if packet can be sent now without violation Nagle's rules:
1439 * 1. It is full sized.
1440 * 2. Or it contains FIN. (already checked by caller)
1441 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1442 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1443 * With Minshall's modification: all sent small packets are ACKed.
1445 static inline bool tcp_nagle_check(const struct tcp_sock
*tp
,
1446 const struct sk_buff
*skb
,
1447 unsigned int mss_now
, int nonagle
)
1449 return skb
->len
< mss_now
&&
1450 ((nonagle
& TCP_NAGLE_CORK
) ||
1451 (!nonagle
&& tp
->packets_out
&& tcp_minshall_check(tp
)));
1454 /* Return true if the Nagle test allows this packet to be
1457 static inline bool tcp_nagle_test(const struct tcp_sock
*tp
, const struct sk_buff
*skb
,
1458 unsigned int cur_mss
, int nonagle
)
1460 /* Nagle rule does not apply to frames, which sit in the middle of the
1461 * write_queue (they have no chances to get new data).
1463 * This is implemented in the callers, where they modify the 'nonagle'
1464 * argument based upon the location of SKB in the send queue.
1466 if (nonagle
& TCP_NAGLE_PUSH
)
1469 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1470 if (tcp_urg_mode(tp
) || (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_FIN
))
1473 if (!tcp_nagle_check(tp
, skb
, cur_mss
, nonagle
))
1479 /* Does at least the first segment of SKB fit into the send window? */
1480 static bool tcp_snd_wnd_test(const struct tcp_sock
*tp
,
1481 const struct sk_buff
*skb
,
1482 unsigned int cur_mss
)
1484 u32 end_seq
= TCP_SKB_CB(skb
)->end_seq
;
1486 if (skb
->len
> cur_mss
)
1487 end_seq
= TCP_SKB_CB(skb
)->seq
+ cur_mss
;
1489 return !after(end_seq
, tcp_wnd_end(tp
));
1492 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1493 * should be put on the wire right now. If so, it returns the number of
1494 * packets allowed by the congestion window.
1496 static unsigned int tcp_snd_test(const struct sock
*sk
, struct sk_buff
*skb
,
1497 unsigned int cur_mss
, int nonagle
)
1499 const struct tcp_sock
*tp
= tcp_sk(sk
);
1500 unsigned int cwnd_quota
;
1502 tcp_init_tso_segs(sk
, skb
, cur_mss
);
1504 if (!tcp_nagle_test(tp
, skb
, cur_mss
, nonagle
))
1507 cwnd_quota
= tcp_cwnd_test(tp
, skb
);
1508 if (cwnd_quota
&& !tcp_snd_wnd_test(tp
, skb
, cur_mss
))
1514 /* Test if sending is allowed right now. */
1515 bool tcp_may_send_now(struct sock
*sk
)
1517 const struct tcp_sock
*tp
= tcp_sk(sk
);
1518 struct sk_buff
*skb
= tcp_send_head(sk
);
1521 tcp_snd_test(sk
, skb
, tcp_current_mss(sk
),
1522 (tcp_skb_is_last(sk
, skb
) ?
1523 tp
->nonagle
: TCP_NAGLE_PUSH
));
1526 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1527 * which is put after SKB on the list. It is very much like
1528 * tcp_fragment() except that it may make several kinds of assumptions
1529 * in order to speed up the splitting operation. In particular, we
1530 * know that all the data is in scatter-gather pages, and that the
1531 * packet has never been sent out before (and thus is not cloned).
1533 static int tso_fragment(struct sock
*sk
, struct sk_buff
*skb
, unsigned int len
,
1534 unsigned int mss_now
, gfp_t gfp
)
1536 struct sk_buff
*buff
;
1537 int nlen
= skb
->len
- len
;
1540 /* All of a TSO frame must be composed of paged data. */
1541 if (skb
->len
!= skb
->data_len
)
1542 return tcp_fragment(sk
, skb
, len
, mss_now
);
1544 buff
= sk_stream_alloc_skb(sk
, 0, gfp
);
1545 if (unlikely(buff
== NULL
))
1548 sk
->sk_wmem_queued
+= buff
->truesize
;
1549 sk_mem_charge(sk
, buff
->truesize
);
1550 buff
->truesize
+= nlen
;
1551 skb
->truesize
-= nlen
;
1553 /* Correct the sequence numbers. */
1554 TCP_SKB_CB(buff
)->seq
= TCP_SKB_CB(skb
)->seq
+ len
;
1555 TCP_SKB_CB(buff
)->end_seq
= TCP_SKB_CB(skb
)->end_seq
;
1556 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(buff
)->seq
;
1558 /* PSH and FIN should only be set in the second packet. */
1559 flags
= TCP_SKB_CB(skb
)->tcp_flags
;
1560 TCP_SKB_CB(skb
)->tcp_flags
= flags
& ~(TCPHDR_FIN
| TCPHDR_PSH
);
1561 TCP_SKB_CB(buff
)->tcp_flags
= flags
;
1563 /* This packet was never sent out yet, so no SACK bits. */
1564 TCP_SKB_CB(buff
)->sacked
= 0;
1566 buff
->ip_summed
= skb
->ip_summed
= CHECKSUM_PARTIAL
;
1567 skb_split(skb
, buff
, len
);
1569 /* Fix up tso_factor for both original and new SKB. */
1570 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1571 tcp_set_skb_tso_segs(sk
, buff
, mss_now
);
1573 /* Link BUFF into the send queue. */
1574 skb_header_release(buff
);
1575 tcp_insert_write_queue_after(skb
, buff
, sk
);
1580 /* Try to defer sending, if possible, in order to minimize the amount
1581 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1583 * This algorithm is from John Heffner.
1585 static bool tcp_tso_should_defer(struct sock
*sk
, struct sk_buff
*skb
)
1587 struct tcp_sock
*tp
= tcp_sk(sk
);
1588 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
1589 u32 send_win
, cong_win
, limit
, in_flight
;
1592 if (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_FIN
)
1595 if (icsk
->icsk_ca_state
!= TCP_CA_Open
)
1598 /* Defer for less than two clock ticks. */
1599 if (tp
->tso_deferred
&&
1600 (((u32
)jiffies
<< 1) >> 1) - (tp
->tso_deferred
>> 1) > 1)
1603 in_flight
= tcp_packets_in_flight(tp
);
1605 BUG_ON(tcp_skb_pcount(skb
) <= 1 || (tp
->snd_cwnd
<= in_flight
));
1607 send_win
= tcp_wnd_end(tp
) - TCP_SKB_CB(skb
)->seq
;
1609 /* From in_flight test above, we know that cwnd > in_flight. */
1610 cong_win
= (tp
->snd_cwnd
- in_flight
) * tp
->mss_cache
;
1612 limit
= min(send_win
, cong_win
);
1614 /* If a full-sized TSO skb can be sent, do it. */
1615 if (limit
>= min_t(unsigned int, sk
->sk_gso_max_size
,
1616 sk
->sk_gso_max_segs
* tp
->mss_cache
))
1619 /* Middle in queue won't get any more data, full sendable already? */
1620 if ((skb
!= tcp_write_queue_tail(sk
)) && (limit
>= skb
->len
))
1623 win_divisor
= ACCESS_ONCE(sysctl_tcp_tso_win_divisor
);
1625 u32 chunk
= min(tp
->snd_wnd
, tp
->snd_cwnd
* tp
->mss_cache
);
1627 /* If at least some fraction of a window is available,
1630 chunk
/= win_divisor
;
1634 /* Different approach, try not to defer past a single
1635 * ACK. Receiver should ACK every other full sized
1636 * frame, so if we have space for more than 3 frames
1639 if (limit
> tcp_max_tso_deferred_mss(tp
) * tp
->mss_cache
)
1643 /* Ok, it looks like it is advisable to defer.
1644 * Do not rearm the timer if already set to not break TCP ACK clocking.
1646 if (!tp
->tso_deferred
)
1647 tp
->tso_deferred
= 1 | (jiffies
<< 1);
1652 tp
->tso_deferred
= 0;
1656 /* Create a new MTU probe if we are ready.
1657 * MTU probe is regularly attempting to increase the path MTU by
1658 * deliberately sending larger packets. This discovers routing
1659 * changes resulting in larger path MTUs.
1661 * Returns 0 if we should wait to probe (no cwnd available),
1662 * 1 if a probe was sent,
1665 static int tcp_mtu_probe(struct sock
*sk
)
1667 struct tcp_sock
*tp
= tcp_sk(sk
);
1668 struct inet_connection_sock
*icsk
= inet_csk(sk
);
1669 struct sk_buff
*skb
, *nskb
, *next
;
1676 /* Not currently probing/verifying,
1678 * have enough cwnd, and
1679 * not SACKing (the variable headers throw things off) */
1680 if (!icsk
->icsk_mtup
.enabled
||
1681 icsk
->icsk_mtup
.probe_size
||
1682 inet_csk(sk
)->icsk_ca_state
!= TCP_CA_Open
||
1683 tp
->snd_cwnd
< 11 ||
1684 tp
->rx_opt
.num_sacks
|| tp
->rx_opt
.dsack
)
1687 /* Very simple search strategy: just double the MSS. */
1688 mss_now
= tcp_current_mss(sk
);
1689 probe_size
= 2 * tp
->mss_cache
;
1690 size_needed
= probe_size
+ (tp
->reordering
+ 1) * tp
->mss_cache
;
1691 if (probe_size
> tcp_mtu_to_mss(sk
, icsk
->icsk_mtup
.search_high
)) {
1692 /* TODO: set timer for probe_converge_event */
1696 /* Have enough data in the send queue to probe? */
1697 if (tp
->write_seq
- tp
->snd_nxt
< size_needed
)
1700 if (tp
->snd_wnd
< size_needed
)
1702 if (after(tp
->snd_nxt
+ size_needed
, tcp_wnd_end(tp
)))
1705 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1706 if (tcp_packets_in_flight(tp
) + 2 > tp
->snd_cwnd
) {
1707 if (!tcp_packets_in_flight(tp
))
1713 /* We're allowed to probe. Build it now. */
1714 if ((nskb
= sk_stream_alloc_skb(sk
, probe_size
, GFP_ATOMIC
)) == NULL
)
1716 sk
->sk_wmem_queued
+= nskb
->truesize
;
1717 sk_mem_charge(sk
, nskb
->truesize
);
1719 skb
= tcp_send_head(sk
);
1721 TCP_SKB_CB(nskb
)->seq
= TCP_SKB_CB(skb
)->seq
;
1722 TCP_SKB_CB(nskb
)->end_seq
= TCP_SKB_CB(skb
)->seq
+ probe_size
;
1723 TCP_SKB_CB(nskb
)->tcp_flags
= TCPHDR_ACK
;
1724 TCP_SKB_CB(nskb
)->sacked
= 0;
1726 nskb
->ip_summed
= skb
->ip_summed
;
1728 tcp_insert_write_queue_before(nskb
, skb
, sk
);
1731 tcp_for_write_queue_from_safe(skb
, next
, sk
) {
1732 copy
= min_t(int, skb
->len
, probe_size
- len
);
1733 if (nskb
->ip_summed
)
1734 skb_copy_bits(skb
, 0, skb_put(nskb
, copy
), copy
);
1736 nskb
->csum
= skb_copy_and_csum_bits(skb
, 0,
1737 skb_put(nskb
, copy
),
1740 if (skb
->len
<= copy
) {
1741 /* We've eaten all the data from this skb.
1743 TCP_SKB_CB(nskb
)->tcp_flags
|= TCP_SKB_CB(skb
)->tcp_flags
;
1744 tcp_unlink_write_queue(skb
, sk
);
1745 sk_wmem_free_skb(sk
, skb
);
1747 TCP_SKB_CB(nskb
)->tcp_flags
|= TCP_SKB_CB(skb
)->tcp_flags
&
1748 ~(TCPHDR_FIN
|TCPHDR_PSH
);
1749 if (!skb_shinfo(skb
)->nr_frags
) {
1750 skb_pull(skb
, copy
);
1751 if (skb
->ip_summed
!= CHECKSUM_PARTIAL
)
1752 skb
->csum
= csum_partial(skb
->data
,
1755 __pskb_trim_head(skb
, copy
);
1756 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1758 TCP_SKB_CB(skb
)->seq
+= copy
;
1763 if (len
>= probe_size
)
1766 tcp_init_tso_segs(sk
, nskb
, nskb
->len
);
1768 /* We're ready to send. If this fails, the probe will
1769 * be resegmented into mss-sized pieces by tcp_write_xmit(). */
1770 TCP_SKB_CB(nskb
)->when
= tcp_time_stamp
;
1771 if (!tcp_transmit_skb(sk
, nskb
, 1, GFP_ATOMIC
)) {
1772 /* Decrement cwnd here because we are sending
1773 * effectively two packets. */
1775 tcp_event_new_data_sent(sk
, nskb
);
1777 icsk
->icsk_mtup
.probe_size
= tcp_mss_to_mtu(sk
, nskb
->len
);
1778 tp
->mtu_probe
.probe_seq_start
= TCP_SKB_CB(nskb
)->seq
;
1779 tp
->mtu_probe
.probe_seq_end
= TCP_SKB_CB(nskb
)->end_seq
;
1787 /* This routine writes packets to the network. It advances the
1788 * send_head. This happens as incoming acks open up the remote
1791 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1792 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1793 * account rare use of URG, this is not a big flaw.
1795 * Send at most one packet when push_one > 0. Temporarily ignore
1796 * cwnd limit to force at most one packet out when push_one == 2.
1798 * Returns true, if no segments are in flight and we have queued segments,
1799 * but cannot send anything now because of SWS or another problem.
1801 static bool tcp_write_xmit(struct sock
*sk
, unsigned int mss_now
, int nonagle
,
1802 int push_one
, gfp_t gfp
)
1804 struct tcp_sock
*tp
= tcp_sk(sk
);
1805 struct sk_buff
*skb
;
1806 unsigned int tso_segs
, sent_pkts
;
1813 /* Do MTU probing. */
1814 result
= tcp_mtu_probe(sk
);
1817 } else if (result
> 0) {
1822 while ((skb
= tcp_send_head(sk
))) {
1826 tso_segs
= tcp_init_tso_segs(sk
, skb
, mss_now
);
1829 if (unlikely(tp
->repair
) && tp
->repair_queue
== TCP_SEND_QUEUE
)
1830 goto repair
; /* Skip network transmission */
1832 cwnd_quota
= tcp_cwnd_test(tp
, skb
);
1835 /* Force out a loss probe pkt. */
1841 if (unlikely(!tcp_snd_wnd_test(tp
, skb
, mss_now
)))
1844 if (tso_segs
== 1) {
1845 if (unlikely(!tcp_nagle_test(tp
, skb
, mss_now
,
1846 (tcp_skb_is_last(sk
, skb
) ?
1847 nonagle
: TCP_NAGLE_PUSH
))))
1850 if (!push_one
&& tcp_tso_should_defer(sk
, skb
))
1854 /* TSQ : sk_wmem_alloc accounts skb truesize,
1855 * including skb overhead. But thats OK.
1857 if (atomic_read(&sk
->sk_wmem_alloc
) >= sysctl_tcp_limit_output_bytes
) {
1858 set_bit(TSQ_THROTTLED
, &tp
->tsq_flags
);
1862 if (tso_segs
> 1 && !tcp_urg_mode(tp
))
1863 limit
= tcp_mss_split_point(sk
, skb
, mss_now
,
1866 sk
->sk_gso_max_segs
));
1868 if (skb
->len
> limit
&&
1869 unlikely(tso_fragment(sk
, skb
, limit
, mss_now
, gfp
)))
1872 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
1874 if (unlikely(tcp_transmit_skb(sk
, skb
, 1, gfp
)))
1878 /* Advance the send_head. This one is sent out.
1879 * This call will increment packets_out.
1881 tcp_event_new_data_sent(sk
, skb
);
1883 tcp_minshall_update(tp
, mss_now
, skb
);
1884 sent_pkts
+= tcp_skb_pcount(skb
);
1890 if (likely(sent_pkts
)) {
1891 if (tcp_in_cwnd_reduction(sk
))
1892 tp
->prr_out
+= sent_pkts
;
1894 /* Send one loss probe per tail loss episode. */
1896 tcp_schedule_loss_probe(sk
);
1897 tcp_cwnd_validate(sk
);
1900 return (push_one
== 2) || (!tp
->packets_out
&& tcp_send_head(sk
));
1903 bool tcp_schedule_loss_probe(struct sock
*sk
)
1905 struct inet_connection_sock
*icsk
= inet_csk(sk
);
1906 struct tcp_sock
*tp
= tcp_sk(sk
);
1907 u32 timeout
, tlp_time_stamp
, rto_time_stamp
;
1908 u32 rtt
= tp
->srtt
>> 3;
1910 if (WARN_ON(icsk
->icsk_pending
== ICSK_TIME_EARLY_RETRANS
))
1912 /* No consecutive loss probes. */
1913 if (WARN_ON(icsk
->icsk_pending
== ICSK_TIME_LOSS_PROBE
)) {
1917 /* Don't do any loss probe on a Fast Open connection before 3WHS
1920 if (sk
->sk_state
== TCP_SYN_RECV
)
1923 /* TLP is only scheduled when next timer event is RTO. */
1924 if (icsk
->icsk_pending
!= ICSK_TIME_RETRANS
)
1927 /* Schedule a loss probe in 2*RTT for SACK capable connections
1928 * in Open state, that are either limited by cwnd or application.
1930 if (sysctl_tcp_early_retrans
< 3 || !rtt
|| !tp
->packets_out
||
1931 !tcp_is_sack(tp
) || inet_csk(sk
)->icsk_ca_state
!= TCP_CA_Open
)
1934 if ((tp
->snd_cwnd
> tcp_packets_in_flight(tp
)) &&
1938 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
1939 * for delayed ack when there's one outstanding packet.
1942 if (tp
->packets_out
== 1)
1943 timeout
= max_t(u32
, timeout
,
1944 (rtt
+ (rtt
>> 1) + TCP_DELACK_MAX
));
1945 timeout
= max_t(u32
, timeout
, msecs_to_jiffies(10));
1947 /* If RTO is shorter, just schedule TLP in its place. */
1948 tlp_time_stamp
= tcp_time_stamp
+ timeout
;
1949 rto_time_stamp
= (u32
)inet_csk(sk
)->icsk_timeout
;
1950 if ((s32
)(tlp_time_stamp
- rto_time_stamp
) > 0) {
1951 s32 delta
= rto_time_stamp
- tcp_time_stamp
;
1956 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_LOSS_PROBE
, timeout
,
1961 /* When probe timeout (PTO) fires, send a new segment if one exists, else
1962 * retransmit the last segment.
1964 void tcp_send_loss_probe(struct sock
*sk
)
1966 struct tcp_sock
*tp
= tcp_sk(sk
);
1967 struct sk_buff
*skb
;
1969 int mss
= tcp_current_mss(sk
);
1972 if (tcp_send_head(sk
) != NULL
) {
1973 err
= tcp_write_xmit(sk
, mss
, TCP_NAGLE_OFF
, 2, GFP_ATOMIC
);
1977 /* At most one outstanding TLP retransmission. */
1978 if (tp
->tlp_high_seq
)
1981 /* Retransmit last segment. */
1982 skb
= tcp_write_queue_tail(sk
);
1986 pcount
= tcp_skb_pcount(skb
);
1987 if (WARN_ON(!pcount
))
1990 if ((pcount
> 1) && (skb
->len
> (pcount
- 1) * mss
)) {
1991 if (unlikely(tcp_fragment(sk
, skb
, (pcount
- 1) * mss
, mss
)))
1993 skb
= tcp_write_queue_tail(sk
);
1996 if (WARN_ON(!skb
|| !tcp_skb_pcount(skb
)))
1999 /* Probe with zero data doesn't trigger fast recovery. */
2001 err
= __tcp_retransmit_skb(sk
, skb
);
2003 /* Record snd_nxt for loss detection. */
2005 tp
->tlp_high_seq
= tp
->snd_nxt
;
2008 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
2009 inet_csk(sk
)->icsk_rto
,
2013 NET_INC_STATS_BH(sock_net(sk
),
2014 LINUX_MIB_TCPLOSSPROBES
);
2018 /* Push out any pending frames which were held back due to
2019 * TCP_CORK or attempt at coalescing tiny packets.
2020 * The socket must be locked by the caller.
2022 void __tcp_push_pending_frames(struct sock
*sk
, unsigned int cur_mss
,
2025 /* If we are closed, the bytes will have to remain here.
2026 * In time closedown will finish, we empty the write queue and
2027 * all will be happy.
2029 if (unlikely(sk
->sk_state
== TCP_CLOSE
))
2032 if (tcp_write_xmit(sk
, cur_mss
, nonagle
, 0,
2033 sk_gfp_atomic(sk
, GFP_ATOMIC
)))
2034 tcp_check_probe_timer(sk
);
2037 /* Send _single_ skb sitting at the send head. This function requires
2038 * true push pending frames to setup probe timer etc.
2040 void tcp_push_one(struct sock
*sk
, unsigned int mss_now
)
2042 struct sk_buff
*skb
= tcp_send_head(sk
);
2044 BUG_ON(!skb
|| skb
->len
< mss_now
);
2046 tcp_write_xmit(sk
, mss_now
, TCP_NAGLE_PUSH
, 1, sk
->sk_allocation
);
2049 /* This function returns the amount that we can raise the
2050 * usable window based on the following constraints
2052 * 1. The window can never be shrunk once it is offered (RFC 793)
2053 * 2. We limit memory per socket
2056 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2057 * RECV.NEXT + RCV.WIN fixed until:
2058 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2060 * i.e. don't raise the right edge of the window until you can raise
2061 * it at least MSS bytes.
2063 * Unfortunately, the recommended algorithm breaks header prediction,
2064 * since header prediction assumes th->window stays fixed.
2066 * Strictly speaking, keeping th->window fixed violates the receiver
2067 * side SWS prevention criteria. The problem is that under this rule
2068 * a stream of single byte packets will cause the right side of the
2069 * window to always advance by a single byte.
2071 * Of course, if the sender implements sender side SWS prevention
2072 * then this will not be a problem.
2074 * BSD seems to make the following compromise:
2076 * If the free space is less than the 1/4 of the maximum
2077 * space available and the free space is less than 1/2 mss,
2078 * then set the window to 0.
2079 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2080 * Otherwise, just prevent the window from shrinking
2081 * and from being larger than the largest representable value.
2083 * This prevents incremental opening of the window in the regime
2084 * where TCP is limited by the speed of the reader side taking
2085 * data out of the TCP receive queue. It does nothing about
2086 * those cases where the window is constrained on the sender side
2087 * because the pipeline is full.
2089 * BSD also seems to "accidentally" limit itself to windows that are a
2090 * multiple of MSS, at least until the free space gets quite small.
2091 * This would appear to be a side effect of the mbuf implementation.
2092 * Combining these two algorithms results in the observed behavior
2093 * of having a fixed window size at almost all times.
2095 * Below we obtain similar behavior by forcing the offered window to
2096 * a multiple of the mss when it is feasible to do so.
2098 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2099 * Regular options like TIMESTAMP are taken into account.
2101 u32
__tcp_select_window(struct sock
*sk
)
2103 struct inet_connection_sock
*icsk
= inet_csk(sk
);
2104 struct tcp_sock
*tp
= tcp_sk(sk
);
2105 /* MSS for the peer's data. Previous versions used mss_clamp
2106 * here. I don't know if the value based on our guesses
2107 * of peer's MSS is better for the performance. It's more correct
2108 * but may be worse for the performance because of rcv_mss
2109 * fluctuations. --SAW 1998/11/1
2111 int mss
= icsk
->icsk_ack
.rcv_mss
;
2112 int free_space
= tcp_space(sk
);
2113 int full_space
= min_t(int, tp
->window_clamp
, tcp_full_space(sk
));
2116 if (mss
> full_space
)
2119 if (free_space
< (full_space
>> 1)) {
2120 icsk
->icsk_ack
.quick
= 0;
2122 if (sk_under_memory_pressure(sk
))
2123 tp
->rcv_ssthresh
= min(tp
->rcv_ssthresh
,
2126 if (free_space
< mss
)
2130 if (free_space
> tp
->rcv_ssthresh
)
2131 free_space
= tp
->rcv_ssthresh
;
2133 /* Don't do rounding if we are using window scaling, since the
2134 * scaled window will not line up with the MSS boundary anyway.
2136 window
= tp
->rcv_wnd
;
2137 if (tp
->rx_opt
.rcv_wscale
) {
2138 window
= free_space
;
2140 /* Advertise enough space so that it won't get scaled away.
2141 * Import case: prevent zero window announcement if
2142 * 1<<rcv_wscale > mss.
2144 if (((window
>> tp
->rx_opt
.rcv_wscale
) << tp
->rx_opt
.rcv_wscale
) != window
)
2145 window
= (((window
>> tp
->rx_opt
.rcv_wscale
) + 1)
2146 << tp
->rx_opt
.rcv_wscale
);
2148 /* Get the largest window that is a nice multiple of mss.
2149 * Window clamp already applied above.
2150 * If our current window offering is within 1 mss of the
2151 * free space we just keep it. This prevents the divide
2152 * and multiply from happening most of the time.
2153 * We also don't do any window rounding when the free space
2156 if (window
<= free_space
- mss
|| window
> free_space
)
2157 window
= (free_space
/ mss
) * mss
;
2158 else if (mss
== full_space
&&
2159 free_space
> window
+ (full_space
>> 1))
2160 window
= free_space
;
2166 /* Collapses two adjacent SKB's during retransmission. */
2167 static void tcp_collapse_retrans(struct sock
*sk
, struct sk_buff
*skb
)
2169 struct tcp_sock
*tp
= tcp_sk(sk
);
2170 struct sk_buff
*next_skb
= tcp_write_queue_next(sk
, skb
);
2171 int skb_size
, next_skb_size
;
2173 skb_size
= skb
->len
;
2174 next_skb_size
= next_skb
->len
;
2176 BUG_ON(tcp_skb_pcount(skb
) != 1 || tcp_skb_pcount(next_skb
) != 1);
2178 tcp_highest_sack_combine(sk
, next_skb
, skb
);
2180 tcp_unlink_write_queue(next_skb
, sk
);
2182 skb_copy_from_linear_data(next_skb
, skb_put(skb
, next_skb_size
),
2185 if (next_skb
->ip_summed
== CHECKSUM_PARTIAL
)
2186 skb
->ip_summed
= CHECKSUM_PARTIAL
;
2188 if (skb
->ip_summed
!= CHECKSUM_PARTIAL
)
2189 skb
->csum
= csum_block_add(skb
->csum
, next_skb
->csum
, skb_size
);
2191 /* Update sequence range on original skb. */
2192 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(next_skb
)->end_seq
;
2194 /* Merge over control information. This moves PSH/FIN etc. over */
2195 TCP_SKB_CB(skb
)->tcp_flags
|= TCP_SKB_CB(next_skb
)->tcp_flags
;
2197 /* All done, get rid of second SKB and account for it so
2198 * packet counting does not break.
2200 TCP_SKB_CB(skb
)->sacked
|= TCP_SKB_CB(next_skb
)->sacked
& TCPCB_EVER_RETRANS
;
2202 /* changed transmit queue under us so clear hints */
2203 tcp_clear_retrans_hints_partial(tp
);
2204 if (next_skb
== tp
->retransmit_skb_hint
)
2205 tp
->retransmit_skb_hint
= skb
;
2207 tcp_adjust_pcount(sk
, next_skb
, tcp_skb_pcount(next_skb
));
2209 sk_wmem_free_skb(sk
, next_skb
);
2212 /* Check if coalescing SKBs is legal. */
2213 static bool tcp_can_collapse(const struct sock
*sk
, const struct sk_buff
*skb
)
2215 if (tcp_skb_pcount(skb
) > 1)
2217 /* TODO: SACK collapsing could be used to remove this condition */
2218 if (skb_shinfo(skb
)->nr_frags
!= 0)
2220 if (skb_cloned(skb
))
2222 if (skb
== tcp_send_head(sk
))
2224 /* Some heurestics for collapsing over SACK'd could be invented */
2225 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_ACKED
)
2231 /* Collapse packets in the retransmit queue to make to create
2232 * less packets on the wire. This is only done on retransmission.
2234 static void tcp_retrans_try_collapse(struct sock
*sk
, struct sk_buff
*to
,
2237 struct tcp_sock
*tp
= tcp_sk(sk
);
2238 struct sk_buff
*skb
= to
, *tmp
;
2241 if (!sysctl_tcp_retrans_collapse
)
2243 if (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_SYN
)
2246 tcp_for_write_queue_from_safe(skb
, tmp
, sk
) {
2247 if (!tcp_can_collapse(sk
, skb
))
2259 /* Punt if not enough space exists in the first SKB for
2260 * the data in the second
2262 if (skb
->len
> skb_availroom(to
))
2265 if (after(TCP_SKB_CB(skb
)->end_seq
, tcp_wnd_end(tp
)))
2268 tcp_collapse_retrans(sk
, to
);
2272 /* This retransmits one SKB. Policy decisions and retransmit queue
2273 * state updates are done by the caller. Returns non-zero if an
2274 * error occurred which prevented the send.
2276 int __tcp_retransmit_skb(struct sock
*sk
, struct sk_buff
*skb
)
2278 struct tcp_sock
*tp
= tcp_sk(sk
);
2279 struct inet_connection_sock
*icsk
= inet_csk(sk
);
2280 unsigned int cur_mss
;
2282 /* Inconslusive MTU probe */
2283 if (icsk
->icsk_mtup
.probe_size
) {
2284 icsk
->icsk_mtup
.probe_size
= 0;
2287 /* Do not sent more than we queued. 1/4 is reserved for possible
2288 * copying overhead: fragmentation, tunneling, mangling etc.
2290 if (atomic_read(&sk
->sk_wmem_alloc
) >
2291 min(sk
->sk_wmem_queued
+ (sk
->sk_wmem_queued
>> 2), sk
->sk_sndbuf
))
2294 if (before(TCP_SKB_CB(skb
)->seq
, tp
->snd_una
)) {
2295 if (before(TCP_SKB_CB(skb
)->end_seq
, tp
->snd_una
))
2297 if (tcp_trim_head(sk
, skb
, tp
->snd_una
- TCP_SKB_CB(skb
)->seq
))
2301 if (inet_csk(sk
)->icsk_af_ops
->rebuild_header(sk
))
2302 return -EHOSTUNREACH
; /* Routing failure or similar. */
2304 cur_mss
= tcp_current_mss(sk
);
2306 /* If receiver has shrunk his window, and skb is out of
2307 * new window, do not retransmit it. The exception is the
2308 * case, when window is shrunk to zero. In this case
2309 * our retransmit serves as a zero window probe.
2311 if (!before(TCP_SKB_CB(skb
)->seq
, tcp_wnd_end(tp
)) &&
2312 TCP_SKB_CB(skb
)->seq
!= tp
->snd_una
)
2315 if (skb
->len
> cur_mss
) {
2316 if (tcp_fragment(sk
, skb
, cur_mss
, cur_mss
))
2317 return -ENOMEM
; /* We'll try again later. */
2319 int oldpcount
= tcp_skb_pcount(skb
);
2321 if (unlikely(oldpcount
> 1)) {
2322 tcp_init_tso_segs(sk
, skb
, cur_mss
);
2323 tcp_adjust_pcount(sk
, skb
, oldpcount
- tcp_skb_pcount(skb
));
2327 tcp_retrans_try_collapse(sk
, skb
, cur_mss
);
2329 /* Some Solaris stacks overoptimize and ignore the FIN on a
2330 * retransmit when old data is attached. So strip it off
2331 * since it is cheap to do so and saves bytes on the network.
2334 (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_FIN
) &&
2335 tp
->snd_una
== (TCP_SKB_CB(skb
)->end_seq
- 1)) {
2336 if (!pskb_trim(skb
, 0)) {
2337 /* Reuse, even though it does some unnecessary work */
2338 tcp_init_nondata_skb(skb
, TCP_SKB_CB(skb
)->end_seq
- 1,
2339 TCP_SKB_CB(skb
)->tcp_flags
);
2340 skb
->ip_summed
= CHECKSUM_NONE
;
2344 /* Make a copy, if the first transmission SKB clone we made
2345 * is still in somebody's hands, else make a clone.
2347 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
2349 /* make sure skb->data is aligned on arches that require it */
2350 if (unlikely(NET_IP_ALIGN
&& ((unsigned long)skb
->data
& 3))) {
2351 struct sk_buff
*nskb
= __pskb_copy(skb
, MAX_TCP_HEADER
,
2353 return nskb
? tcp_transmit_skb(sk
, nskb
, 0, GFP_ATOMIC
) :
2356 return tcp_transmit_skb(sk
, skb
, 1, GFP_ATOMIC
);
2360 int tcp_retransmit_skb(struct sock
*sk
, struct sk_buff
*skb
)
2362 struct tcp_sock
*tp
= tcp_sk(sk
);
2363 int err
= __tcp_retransmit_skb(sk
, skb
);
2366 /* Update global TCP statistics. */
2367 TCP_INC_STATS(sock_net(sk
), TCP_MIB_RETRANSSEGS
);
2369 tp
->total_retrans
++;
2371 #if FASTRETRANS_DEBUG > 0
2372 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_RETRANS
) {
2373 net_dbg_ratelimited("retrans_out leaked\n");
2376 if (!tp
->retrans_out
)
2377 tp
->lost_retrans_low
= tp
->snd_nxt
;
2378 TCP_SKB_CB(skb
)->sacked
|= TCPCB_RETRANS
;
2379 tp
->retrans_out
+= tcp_skb_pcount(skb
);
2381 /* Save stamp of the first retransmit. */
2382 if (!tp
->retrans_stamp
)
2383 tp
->retrans_stamp
= TCP_SKB_CB(skb
)->when
;
2385 tp
->undo_retrans
+= tcp_skb_pcount(skb
);
2387 /* snd_nxt is stored to detect loss of retransmitted segment,
2388 * see tcp_input.c tcp_sacktag_write_queue().
2390 TCP_SKB_CB(skb
)->ack_seq
= tp
->snd_nxt
;
2395 /* Check if we forward retransmits are possible in the current
2396 * window/congestion state.
2398 static bool tcp_can_forward_retransmit(struct sock
*sk
)
2400 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
2401 const struct tcp_sock
*tp
= tcp_sk(sk
);
2403 /* Forward retransmissions are possible only during Recovery. */
2404 if (icsk
->icsk_ca_state
!= TCP_CA_Recovery
)
2407 /* No forward retransmissions in Reno are possible. */
2408 if (tcp_is_reno(tp
))
2411 /* Yeah, we have to make difficult choice between forward transmission
2412 * and retransmission... Both ways have their merits...
2414 * For now we do not retransmit anything, while we have some new
2415 * segments to send. In the other cases, follow rule 3 for
2416 * NextSeg() specified in RFC3517.
2419 if (tcp_may_send_now(sk
))
2425 /* This gets called after a retransmit timeout, and the initially
2426 * retransmitted data is acknowledged. It tries to continue
2427 * resending the rest of the retransmit queue, until either
2428 * we've sent it all or the congestion window limit is reached.
2429 * If doing SACK, the first ACK which comes back for a timeout
2430 * based retransmit packet might feed us FACK information again.
2431 * If so, we use it to avoid unnecessarily retransmissions.
2433 void tcp_xmit_retransmit_queue(struct sock
*sk
)
2435 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
2436 struct tcp_sock
*tp
= tcp_sk(sk
);
2437 struct sk_buff
*skb
;
2438 struct sk_buff
*hole
= NULL
;
2441 int fwd_rexmitting
= 0;
2443 if (!tp
->packets_out
)
2447 tp
->retransmit_high
= tp
->snd_una
;
2449 if (tp
->retransmit_skb_hint
) {
2450 skb
= tp
->retransmit_skb_hint
;
2451 last_lost
= TCP_SKB_CB(skb
)->end_seq
;
2452 if (after(last_lost
, tp
->retransmit_high
))
2453 last_lost
= tp
->retransmit_high
;
2455 skb
= tcp_write_queue_head(sk
);
2456 last_lost
= tp
->snd_una
;
2459 tcp_for_write_queue_from(skb
, sk
) {
2460 __u8 sacked
= TCP_SKB_CB(skb
)->sacked
;
2462 if (skb
== tcp_send_head(sk
))
2464 /* we could do better than to assign each time */
2466 tp
->retransmit_skb_hint
= skb
;
2468 /* Assume this retransmit will generate
2469 * only one packet for congestion window
2470 * calculation purposes. This works because
2471 * tcp_retransmit_skb() will chop up the
2472 * packet to be MSS sized and all the
2473 * packet counting works out.
2475 if (tcp_packets_in_flight(tp
) >= tp
->snd_cwnd
)
2478 if (fwd_rexmitting
) {
2480 if (!before(TCP_SKB_CB(skb
)->seq
, tcp_highest_sack_seq(tp
)))
2482 mib_idx
= LINUX_MIB_TCPFORWARDRETRANS
;
2484 } else if (!before(TCP_SKB_CB(skb
)->seq
, tp
->retransmit_high
)) {
2485 tp
->retransmit_high
= last_lost
;
2486 if (!tcp_can_forward_retransmit(sk
))
2488 /* Backtrack if necessary to non-L'ed skb */
2496 } else if (!(sacked
& TCPCB_LOST
)) {
2497 if (hole
== NULL
&& !(sacked
& (TCPCB_SACKED_RETRANS
|TCPCB_SACKED_ACKED
)))
2502 last_lost
= TCP_SKB_CB(skb
)->end_seq
;
2503 if (icsk
->icsk_ca_state
!= TCP_CA_Loss
)
2504 mib_idx
= LINUX_MIB_TCPFASTRETRANS
;
2506 mib_idx
= LINUX_MIB_TCPSLOWSTARTRETRANS
;
2509 if (sacked
& (TCPCB_SACKED_ACKED
|TCPCB_SACKED_RETRANS
))
2512 if (tcp_retransmit_skb(sk
, skb
)) {
2513 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPRETRANSFAIL
);
2516 NET_INC_STATS_BH(sock_net(sk
), mib_idx
);
2518 if (tcp_in_cwnd_reduction(sk
))
2519 tp
->prr_out
+= tcp_skb_pcount(skb
);
2521 if (skb
== tcp_write_queue_head(sk
))
2522 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
2523 inet_csk(sk
)->icsk_rto
,
2528 /* Send a fin. The caller locks the socket for us. This cannot be
2529 * allowed to fail queueing a FIN frame under any circumstances.
2531 void tcp_send_fin(struct sock
*sk
)
2533 struct tcp_sock
*tp
= tcp_sk(sk
);
2534 struct sk_buff
*skb
= tcp_write_queue_tail(sk
);
2537 /* Optimization, tack on the FIN if we have a queue of
2538 * unsent frames. But be careful about outgoing SACKS
2541 mss_now
= tcp_current_mss(sk
);
2543 if (tcp_send_head(sk
) != NULL
) {
2544 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_FIN
;
2545 TCP_SKB_CB(skb
)->end_seq
++;
2548 /* Socket is locked, keep trying until memory is available. */
2550 skb
= alloc_skb_fclone(MAX_TCP_HEADER
,
2557 /* Reserve space for headers and prepare control bits. */
2558 skb_reserve(skb
, MAX_TCP_HEADER
);
2559 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2560 tcp_init_nondata_skb(skb
, tp
->write_seq
,
2561 TCPHDR_ACK
| TCPHDR_FIN
);
2562 tcp_queue_skb(sk
, skb
);
2564 __tcp_push_pending_frames(sk
, mss_now
, TCP_NAGLE_OFF
);
2567 /* We get here when a process closes a file descriptor (either due to
2568 * an explicit close() or as a byproduct of exit()'ing) and there
2569 * was unread data in the receive queue. This behavior is recommended
2570 * by RFC 2525, section 2.17. -DaveM
2572 void tcp_send_active_reset(struct sock
*sk
, gfp_t priority
)
2574 struct sk_buff
*skb
;
2576 /* NOTE: No TCP options attached and we never retransmit this. */
2577 skb
= alloc_skb(MAX_TCP_HEADER
, priority
);
2579 NET_INC_STATS(sock_net(sk
), LINUX_MIB_TCPABORTFAILED
);
2583 /* Reserve space for headers and prepare control bits. */
2584 skb_reserve(skb
, MAX_TCP_HEADER
);
2585 tcp_init_nondata_skb(skb
, tcp_acceptable_seq(sk
),
2586 TCPHDR_ACK
| TCPHDR_RST
);
2588 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
2589 if (tcp_transmit_skb(sk
, skb
, 0, priority
))
2590 NET_INC_STATS(sock_net(sk
), LINUX_MIB_TCPABORTFAILED
);
2592 TCP_INC_STATS(sock_net(sk
), TCP_MIB_OUTRSTS
);
2595 /* Send a crossed SYN-ACK during socket establishment.
2596 * WARNING: This routine must only be called when we have already sent
2597 * a SYN packet that crossed the incoming SYN that caused this routine
2598 * to get called. If this assumption fails then the initial rcv_wnd
2599 * and rcv_wscale values will not be correct.
2601 int tcp_send_synack(struct sock
*sk
)
2603 struct sk_buff
*skb
;
2605 skb
= tcp_write_queue_head(sk
);
2606 if (skb
== NULL
|| !(TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_SYN
)) {
2607 pr_debug("%s: wrong queue state\n", __func__
);
2610 if (!(TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_ACK
)) {
2611 if (skb_cloned(skb
)) {
2612 struct sk_buff
*nskb
= skb_copy(skb
, GFP_ATOMIC
);
2615 tcp_unlink_write_queue(skb
, sk
);
2616 skb_header_release(nskb
);
2617 __tcp_add_write_queue_head(sk
, nskb
);
2618 sk_wmem_free_skb(sk
, skb
);
2619 sk
->sk_wmem_queued
+= nskb
->truesize
;
2620 sk_mem_charge(sk
, nskb
->truesize
);
2624 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_ACK
;
2625 TCP_ECN_send_synack(tcp_sk(sk
), skb
);
2627 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
2628 return tcp_transmit_skb(sk
, skb
, 1, GFP_ATOMIC
);
2632 * tcp_make_synack - Prepare a SYN-ACK.
2633 * sk: listener socket
2634 * dst: dst entry attached to the SYNACK
2635 * req: request_sock pointer
2637 * Allocate one skb and build a SYNACK packet.
2638 * @dst is consumed : Caller should not use it again.
2640 struct sk_buff
*tcp_make_synack(struct sock
*sk
, struct dst_entry
*dst
,
2641 struct request_sock
*req
,
2642 struct tcp_fastopen_cookie
*foc
)
2644 struct tcp_out_options opts
;
2645 struct inet_request_sock
*ireq
= inet_rsk(req
);
2646 struct tcp_sock
*tp
= tcp_sk(sk
);
2648 struct sk_buff
*skb
;
2649 struct tcp_md5sig_key
*md5
;
2650 int tcp_header_size
;
2653 skb
= alloc_skb(MAX_TCP_HEADER
+ 15, sk_gfp_atomic(sk
, GFP_ATOMIC
));
2654 if (unlikely(!skb
)) {
2658 /* Reserve space for headers. */
2659 skb_reserve(skb
, MAX_TCP_HEADER
);
2661 skb_dst_set(skb
, dst
);
2663 mss
= dst_metric_advmss(dst
);
2664 if (tp
->rx_opt
.user_mss
&& tp
->rx_opt
.user_mss
< mss
)
2665 mss
= tp
->rx_opt
.user_mss
;
2667 if (req
->rcv_wnd
== 0) { /* ignored for retransmitted syns */
2669 /* Set this up on the first call only */
2670 req
->window_clamp
= tp
->window_clamp
? : dst_metric(dst
, RTAX_WINDOW
);
2672 /* limit the window selection if the user enforce a smaller rx buffer */
2673 if (sk
->sk_userlocks
& SOCK_RCVBUF_LOCK
&&
2674 (req
->window_clamp
> tcp_full_space(sk
) || req
->window_clamp
== 0))
2675 req
->window_clamp
= tcp_full_space(sk
);
2677 /* tcp_full_space because it is guaranteed to be the first packet */
2678 tcp_select_initial_window(tcp_full_space(sk
),
2679 mss
- (ireq
->tstamp_ok
? TCPOLEN_TSTAMP_ALIGNED
: 0),
2684 dst_metric(dst
, RTAX_INITRWND
));
2685 ireq
->rcv_wscale
= rcv_wscale
;
2688 memset(&opts
, 0, sizeof(opts
));
2689 #ifdef CONFIG_SYN_COOKIES
2690 if (unlikely(req
->cookie_ts
))
2691 TCP_SKB_CB(skb
)->when
= cookie_init_timestamp(req
);
2694 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
2695 tcp_header_size
= tcp_synack_options(sk
, req
, mss
, skb
, &opts
, &md5
,
2698 skb_push(skb
, tcp_header_size
);
2699 skb_reset_transport_header(skb
);
2702 memset(th
, 0, sizeof(struct tcphdr
));
2705 TCP_ECN_make_synack(req
, th
);
2706 th
->source
= ireq
->loc_port
;
2707 th
->dest
= ireq
->rmt_port
;
2708 /* Setting of flags are superfluous here for callers (and ECE is
2709 * not even correctly set)
2711 tcp_init_nondata_skb(skb
, tcp_rsk(req
)->snt_isn
,
2712 TCPHDR_SYN
| TCPHDR_ACK
);
2714 th
->seq
= htonl(TCP_SKB_CB(skb
)->seq
);
2715 /* XXX data is queued and acked as is. No buffer/window check */
2716 th
->ack_seq
= htonl(tcp_rsk(req
)->rcv_nxt
);
2718 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2719 th
->window
= htons(min(req
->rcv_wnd
, 65535U));
2720 tcp_options_write((__be32
*)(th
+ 1), tp
, &opts
);
2721 th
->doff
= (tcp_header_size
>> 2);
2722 TCP_ADD_STATS(sock_net(sk
), TCP_MIB_OUTSEGS
, tcp_skb_pcount(skb
));
2724 #ifdef CONFIG_TCP_MD5SIG
2725 /* Okay, we have all we need - do the md5 hash if needed */
2727 tcp_rsk(req
)->af_specific
->calc_md5_hash(opts
.hash_location
,
2728 md5
, NULL
, req
, skb
);
2734 EXPORT_SYMBOL(tcp_make_synack
);
2736 /* Do all connect socket setups that can be done AF independent. */
2737 void tcp_connect_init(struct sock
*sk
)
2739 const struct dst_entry
*dst
= __sk_dst_get(sk
);
2740 struct tcp_sock
*tp
= tcp_sk(sk
);
2743 /* We'll fix this up when we get a response from the other end.
2744 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2746 tp
->tcp_header_len
= sizeof(struct tcphdr
) +
2747 (sysctl_tcp_timestamps
? TCPOLEN_TSTAMP_ALIGNED
: 0);
2749 #ifdef CONFIG_TCP_MD5SIG
2750 if (tp
->af_specific
->md5_lookup(sk
, sk
) != NULL
)
2751 tp
->tcp_header_len
+= TCPOLEN_MD5SIG_ALIGNED
;
2754 /* If user gave his TCP_MAXSEG, record it to clamp */
2755 if (tp
->rx_opt
.user_mss
)
2756 tp
->rx_opt
.mss_clamp
= tp
->rx_opt
.user_mss
;
2759 tcp_sync_mss(sk
, dst_mtu(dst
));
2761 if (!tp
->window_clamp
)
2762 tp
->window_clamp
= dst_metric(dst
, RTAX_WINDOW
);
2763 tp
->advmss
= dst_metric_advmss(dst
);
2764 if (tp
->rx_opt
.user_mss
&& tp
->rx_opt
.user_mss
< tp
->advmss
)
2765 tp
->advmss
= tp
->rx_opt
.user_mss
;
2767 tcp_initialize_rcv_mss(sk
);
2769 /* limit the window selection if the user enforce a smaller rx buffer */
2770 if (sk
->sk_userlocks
& SOCK_RCVBUF_LOCK
&&
2771 (tp
->window_clamp
> tcp_full_space(sk
) || tp
->window_clamp
== 0))
2772 tp
->window_clamp
= tcp_full_space(sk
);
2774 tcp_select_initial_window(tcp_full_space(sk
),
2775 tp
->advmss
- (tp
->rx_opt
.ts_recent_stamp
? tp
->tcp_header_len
- sizeof(struct tcphdr
) : 0),
2778 sysctl_tcp_window_scaling
,
2780 dst_metric(dst
, RTAX_INITRWND
));
2782 tp
->rx_opt
.rcv_wscale
= rcv_wscale
;
2783 tp
->rcv_ssthresh
= tp
->rcv_wnd
;
2786 sock_reset_flag(sk
, SOCK_DONE
);
2789 tp
->snd_una
= tp
->write_seq
;
2790 tp
->snd_sml
= tp
->write_seq
;
2791 tp
->snd_up
= tp
->write_seq
;
2792 tp
->snd_nxt
= tp
->write_seq
;
2794 if (likely(!tp
->repair
))
2796 tp
->rcv_wup
= tp
->rcv_nxt
;
2797 tp
->copied_seq
= tp
->rcv_nxt
;
2799 inet_csk(sk
)->icsk_rto
= TCP_TIMEOUT_INIT
;
2800 inet_csk(sk
)->icsk_retransmits
= 0;
2801 tcp_clear_retrans(tp
);
2804 static void tcp_connect_queue_skb(struct sock
*sk
, struct sk_buff
*skb
)
2806 struct tcp_sock
*tp
= tcp_sk(sk
);
2807 struct tcp_skb_cb
*tcb
= TCP_SKB_CB(skb
);
2809 tcb
->end_seq
+= skb
->len
;
2810 skb_header_release(skb
);
2811 __tcp_add_write_queue_tail(sk
, skb
);
2812 sk
->sk_wmem_queued
+= skb
->truesize
;
2813 sk_mem_charge(sk
, skb
->truesize
);
2814 tp
->write_seq
= tcb
->end_seq
;
2815 tp
->packets_out
+= tcp_skb_pcount(skb
);
2818 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
2819 * queue a data-only packet after the regular SYN, such that regular SYNs
2820 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
2821 * only the SYN sequence, the data are retransmitted in the first ACK.
2822 * If cookie is not cached or other error occurs, falls back to send a
2823 * regular SYN with Fast Open cookie request option.
2825 static int tcp_send_syn_data(struct sock
*sk
, struct sk_buff
*syn
)
2827 struct tcp_sock
*tp
= tcp_sk(sk
);
2828 struct tcp_fastopen_request
*fo
= tp
->fastopen_req
;
2829 int syn_loss
= 0, space
, i
, err
= 0, iovlen
= fo
->data
->msg_iovlen
;
2830 struct sk_buff
*syn_data
= NULL
, *data
;
2831 unsigned long last_syn_loss
= 0;
2833 tp
->rx_opt
.mss_clamp
= tp
->advmss
; /* If MSS is not cached */
2834 tcp_fastopen_cache_get(sk
, &tp
->rx_opt
.mss_clamp
, &fo
->cookie
,
2835 &syn_loss
, &last_syn_loss
);
2836 /* Recurring FO SYN losses: revert to regular handshake temporarily */
2838 time_before(jiffies
, last_syn_loss
+ (60*HZ
<< syn_loss
))) {
2839 fo
->cookie
.len
= -1;
2843 if (sysctl_tcp_fastopen
& TFO_CLIENT_NO_COOKIE
)
2844 fo
->cookie
.len
= -1;
2845 else if (fo
->cookie
.len
<= 0)
2848 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
2849 * user-MSS. Reserve maximum option space for middleboxes that add
2850 * private TCP options. The cost is reduced data space in SYN :(
2852 if (tp
->rx_opt
.user_mss
&& tp
->rx_opt
.user_mss
< tp
->rx_opt
.mss_clamp
)
2853 tp
->rx_opt
.mss_clamp
= tp
->rx_opt
.user_mss
;
2854 space
= __tcp_mtu_to_mss(sk
, inet_csk(sk
)->icsk_pmtu_cookie
) -
2855 MAX_TCP_OPTION_SPACE
;
2857 syn_data
= skb_copy_expand(syn
, skb_headroom(syn
), space
,
2859 if (syn_data
== NULL
)
2862 for (i
= 0; i
< iovlen
&& syn_data
->len
< space
; ++i
) {
2863 struct iovec
*iov
= &fo
->data
->msg_iov
[i
];
2864 unsigned char __user
*from
= iov
->iov_base
;
2865 int len
= iov
->iov_len
;
2867 if (syn_data
->len
+ len
> space
)
2868 len
= space
- syn_data
->len
;
2869 else if (i
+ 1 == iovlen
)
2870 /* No more data pending in inet_wait_for_connect() */
2873 if (skb_add_data(syn_data
, from
, len
))
2877 /* Queue a data-only packet after the regular SYN for retransmission */
2878 data
= pskb_copy(syn_data
, sk
->sk_allocation
);
2881 TCP_SKB_CB(data
)->seq
++;
2882 TCP_SKB_CB(data
)->tcp_flags
&= ~TCPHDR_SYN
;
2883 TCP_SKB_CB(data
)->tcp_flags
= (TCPHDR_ACK
|TCPHDR_PSH
);
2884 tcp_connect_queue_skb(sk
, data
);
2885 fo
->copied
= data
->len
;
2887 if (tcp_transmit_skb(sk
, syn_data
, 0, sk
->sk_allocation
) == 0) {
2888 tp
->syn_data
= (fo
->copied
> 0);
2889 NET_INC_STATS(sock_net(sk
), LINUX_MIB_TCPFASTOPENACTIVE
);
2895 /* Send a regular SYN with Fast Open cookie request option */
2896 if (fo
->cookie
.len
> 0)
2898 err
= tcp_transmit_skb(sk
, syn
, 1, sk
->sk_allocation
);
2900 tp
->syn_fastopen
= 0;
2901 kfree_skb(syn_data
);
2903 fo
->cookie
.len
= -1; /* Exclude Fast Open option for SYN retries */
2907 /* Build a SYN and send it off. */
2908 int tcp_connect(struct sock
*sk
)
2910 struct tcp_sock
*tp
= tcp_sk(sk
);
2911 struct sk_buff
*buff
;
2914 tcp_connect_init(sk
);
2916 if (unlikely(tp
->repair
)) {
2917 tcp_finish_connect(sk
, NULL
);
2921 buff
= alloc_skb_fclone(MAX_TCP_HEADER
+ 15, sk
->sk_allocation
);
2922 if (unlikely(buff
== NULL
))
2925 /* Reserve space for headers. */
2926 skb_reserve(buff
, MAX_TCP_HEADER
);
2928 tcp_init_nondata_skb(buff
, tp
->write_seq
++, TCPHDR_SYN
);
2929 tp
->retrans_stamp
= TCP_SKB_CB(buff
)->when
= tcp_time_stamp
;
2930 tcp_connect_queue_skb(sk
, buff
);
2931 TCP_ECN_send_syn(sk
, buff
);
2933 /* Send off SYN; include data in Fast Open. */
2934 err
= tp
->fastopen_req
? tcp_send_syn_data(sk
, buff
) :
2935 tcp_transmit_skb(sk
, buff
, 1, sk
->sk_allocation
);
2936 if (err
== -ECONNREFUSED
)
2939 /* We change tp->snd_nxt after the tcp_transmit_skb() call
2940 * in order to make this packet get counted in tcpOutSegs.
2942 tp
->snd_nxt
= tp
->write_seq
;
2943 tp
->pushed_seq
= tp
->write_seq
;
2944 TCP_INC_STATS(sock_net(sk
), TCP_MIB_ACTIVEOPENS
);
2946 /* Timer for repeating the SYN until an answer. */
2947 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
2948 inet_csk(sk
)->icsk_rto
, TCP_RTO_MAX
);
2951 EXPORT_SYMBOL(tcp_connect
);
2953 /* Send out a delayed ack, the caller does the policy checking
2954 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
2957 void tcp_send_delayed_ack(struct sock
*sk
)
2959 struct inet_connection_sock
*icsk
= inet_csk(sk
);
2960 int ato
= icsk
->icsk_ack
.ato
;
2961 unsigned long timeout
;
2963 if (ato
> TCP_DELACK_MIN
) {
2964 const struct tcp_sock
*tp
= tcp_sk(sk
);
2965 int max_ato
= HZ
/ 2;
2967 if (icsk
->icsk_ack
.pingpong
||
2968 (icsk
->icsk_ack
.pending
& ICSK_ACK_PUSHED
))
2969 max_ato
= TCP_DELACK_MAX
;
2971 /* Slow path, intersegment interval is "high". */
2973 /* If some rtt estimate is known, use it to bound delayed ack.
2974 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
2978 int rtt
= max(tp
->srtt
>> 3, TCP_DELACK_MIN
);
2984 ato
= min(ato
, max_ato
);
2987 /* Stay within the limit we were given */
2988 timeout
= jiffies
+ ato
;
2990 /* Use new timeout only if there wasn't a older one earlier. */
2991 if (icsk
->icsk_ack
.pending
& ICSK_ACK_TIMER
) {
2992 /* If delack timer was blocked or is about to expire,
2995 if (icsk
->icsk_ack
.blocked
||
2996 time_before_eq(icsk
->icsk_ack
.timeout
, jiffies
+ (ato
>> 2))) {
3001 if (!time_before(timeout
, icsk
->icsk_ack
.timeout
))
3002 timeout
= icsk
->icsk_ack
.timeout
;
3004 icsk
->icsk_ack
.pending
|= ICSK_ACK_SCHED
| ICSK_ACK_TIMER
;
3005 icsk
->icsk_ack
.timeout
= timeout
;
3006 sk_reset_timer(sk
, &icsk
->icsk_delack_timer
, timeout
);
3009 /* This routine sends an ack and also updates the window. */
3010 void tcp_send_ack(struct sock
*sk
)
3012 struct sk_buff
*buff
;
3014 /* If we have been reset, we may not send again. */
3015 if (sk
->sk_state
== TCP_CLOSE
)
3018 /* We are not putting this on the write queue, so
3019 * tcp_transmit_skb() will set the ownership to this
3022 buff
= alloc_skb(MAX_TCP_HEADER
, sk_gfp_atomic(sk
, GFP_ATOMIC
));
3024 inet_csk_schedule_ack(sk
);
3025 inet_csk(sk
)->icsk_ack
.ato
= TCP_ATO_MIN
;
3026 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_DACK
,
3027 TCP_DELACK_MAX
, TCP_RTO_MAX
);
3031 /* Reserve space for headers and prepare control bits. */
3032 skb_reserve(buff
, MAX_TCP_HEADER
);
3033 tcp_init_nondata_skb(buff
, tcp_acceptable_seq(sk
), TCPHDR_ACK
);
3035 /* Send it off, this clears delayed acks for us. */
3036 TCP_SKB_CB(buff
)->when
= tcp_time_stamp
;
3037 tcp_transmit_skb(sk
, buff
, 0, sk_gfp_atomic(sk
, GFP_ATOMIC
));
3040 /* This routine sends a packet with an out of date sequence
3041 * number. It assumes the other end will try to ack it.
3043 * Question: what should we make while urgent mode?
3044 * 4.4BSD forces sending single byte of data. We cannot send
3045 * out of window data, because we have SND.NXT==SND.MAX...
3047 * Current solution: to send TWO zero-length segments in urgent mode:
3048 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3049 * out-of-date with SND.UNA-1 to probe window.
3051 static int tcp_xmit_probe_skb(struct sock
*sk
, int urgent
)
3053 struct tcp_sock
*tp
= tcp_sk(sk
);
3054 struct sk_buff
*skb
;
3056 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3057 skb
= alloc_skb(MAX_TCP_HEADER
, sk_gfp_atomic(sk
, GFP_ATOMIC
));
3061 /* Reserve space for headers and set control bits. */
3062 skb_reserve(skb
, MAX_TCP_HEADER
);
3063 /* Use a previous sequence. This should cause the other
3064 * end to send an ack. Don't queue or clone SKB, just
3067 tcp_init_nondata_skb(skb
, tp
->snd_una
- !urgent
, TCPHDR_ACK
);
3068 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
3069 return tcp_transmit_skb(sk
, skb
, 0, GFP_ATOMIC
);
3072 void tcp_send_window_probe(struct sock
*sk
)
3074 if (sk
->sk_state
== TCP_ESTABLISHED
) {
3075 tcp_sk(sk
)->snd_wl1
= tcp_sk(sk
)->rcv_nxt
- 1;
3076 tcp_sk(sk
)->snd_nxt
= tcp_sk(sk
)->write_seq
;
3077 tcp_xmit_probe_skb(sk
, 0);
3081 /* Initiate keepalive or window probe from timer. */
3082 int tcp_write_wakeup(struct sock
*sk
)
3084 struct tcp_sock
*tp
= tcp_sk(sk
);
3085 struct sk_buff
*skb
;
3087 if (sk
->sk_state
== TCP_CLOSE
)
3090 if ((skb
= tcp_send_head(sk
)) != NULL
&&
3091 before(TCP_SKB_CB(skb
)->seq
, tcp_wnd_end(tp
))) {
3093 unsigned int mss
= tcp_current_mss(sk
);
3094 unsigned int seg_size
= tcp_wnd_end(tp
) - TCP_SKB_CB(skb
)->seq
;
3096 if (before(tp
->pushed_seq
, TCP_SKB_CB(skb
)->end_seq
))
3097 tp
->pushed_seq
= TCP_SKB_CB(skb
)->end_seq
;
3099 /* We are probing the opening of a window
3100 * but the window size is != 0
3101 * must have been a result SWS avoidance ( sender )
3103 if (seg_size
< TCP_SKB_CB(skb
)->end_seq
- TCP_SKB_CB(skb
)->seq
||
3105 seg_size
= min(seg_size
, mss
);
3106 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_PSH
;
3107 if (tcp_fragment(sk
, skb
, seg_size
, mss
))
3109 } else if (!tcp_skb_pcount(skb
))
3110 tcp_set_skb_tso_segs(sk
, skb
, mss
);
3112 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_PSH
;
3113 TCP_SKB_CB(skb
)->when
= tcp_time_stamp
;
3114 err
= tcp_transmit_skb(sk
, skb
, 1, GFP_ATOMIC
);
3116 tcp_event_new_data_sent(sk
, skb
);
3119 if (between(tp
->snd_up
, tp
->snd_una
+ 1, tp
->snd_una
+ 0xFFFF))
3120 tcp_xmit_probe_skb(sk
, 1);
3121 return tcp_xmit_probe_skb(sk
, 0);
3125 /* A window probe timeout has occurred. If window is not closed send
3126 * a partial packet else a zero probe.
3128 void tcp_send_probe0(struct sock
*sk
)
3130 struct inet_connection_sock
*icsk
= inet_csk(sk
);
3131 struct tcp_sock
*tp
= tcp_sk(sk
);
3134 err
= tcp_write_wakeup(sk
);
3136 if (tp
->packets_out
|| !tcp_send_head(sk
)) {
3137 /* Cancel probe timer, if it is not required. */
3138 icsk
->icsk_probes_out
= 0;
3139 icsk
->icsk_backoff
= 0;
3144 if (icsk
->icsk_backoff
< sysctl_tcp_retries2
)
3145 icsk
->icsk_backoff
++;
3146 icsk
->icsk_probes_out
++;
3147 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_PROBE0
,
3148 min(icsk
->icsk_rto
<< icsk
->icsk_backoff
, TCP_RTO_MAX
),
3151 /* If packet was not sent due to local congestion,
3152 * do not backoff and do not remember icsk_probes_out.
3153 * Let local senders to fight for local resources.
3155 * Use accumulated backoff yet.
3157 if (!icsk
->icsk_probes_out
)
3158 icsk
->icsk_probes_out
= 1;
3159 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_PROBE0
,
3160 min(icsk
->icsk_rto
<< icsk
->icsk_backoff
,
3161 TCP_RESOURCE_PROBE_INTERVAL
),