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 unsigned int sysctl_tcp_notsent_lowat __read_mostly
= UINT_MAX
;
69 EXPORT_SYMBOL(sysctl_tcp_notsent_lowat
);
71 static bool tcp_write_xmit(struct sock
*sk
, unsigned int mss_now
, int nonagle
,
72 int push_one
, gfp_t gfp
);
74 /* Account for new data that has been sent to the network. */
75 static void tcp_event_new_data_sent(struct sock
*sk
, const struct sk_buff
*skb
)
77 struct inet_connection_sock
*icsk
= inet_csk(sk
);
78 struct tcp_sock
*tp
= tcp_sk(sk
);
79 unsigned int prior_packets
= tp
->packets_out
;
81 tcp_advance_send_head(sk
, skb
);
82 tp
->snd_nxt
= TCP_SKB_CB(skb
)->end_seq
;
84 tp
->packets_out
+= tcp_skb_pcount(skb
);
85 if (!prior_packets
|| icsk
->icsk_pending
== ICSK_TIME_EARLY_RETRANS
||
86 icsk
->icsk_pending
== ICSK_TIME_LOSS_PROBE
) {
90 NET_ADD_STATS(sock_net(sk
), LINUX_MIB_TCPORIGDATASENT
,
94 /* SND.NXT, if window was not shrunk.
95 * If window has been shrunk, what should we make? It is not clear at all.
96 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
97 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
98 * invalid. OK, let's make this for now:
100 static inline __u32
tcp_acceptable_seq(const struct sock
*sk
)
102 const struct tcp_sock
*tp
= tcp_sk(sk
);
104 if (!before(tcp_wnd_end(tp
), tp
->snd_nxt
))
107 return tcp_wnd_end(tp
);
110 /* Calculate mss to advertise in SYN segment.
111 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
113 * 1. It is independent of path mtu.
114 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
115 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
116 * attached devices, because some buggy hosts are confused by
118 * 4. We do not make 3, we advertise MSS, calculated from first
119 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
120 * This may be overridden via information stored in routing table.
121 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
122 * probably even Jumbo".
124 static __u16
tcp_advertise_mss(struct sock
*sk
)
126 struct tcp_sock
*tp
= tcp_sk(sk
);
127 const struct dst_entry
*dst
= __sk_dst_get(sk
);
128 int mss
= tp
->advmss
;
131 unsigned int metric
= dst_metric_advmss(dst
);
142 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
143 * This is the first part of cwnd validation mechanism. */
144 static void tcp_cwnd_restart(struct sock
*sk
, const struct dst_entry
*dst
)
146 struct tcp_sock
*tp
= tcp_sk(sk
);
147 s32 delta
= tcp_time_stamp
- tp
->lsndtime
;
148 u32 restart_cwnd
= tcp_init_cwnd(tp
, dst
);
149 u32 cwnd
= tp
->snd_cwnd
;
151 tcp_ca_event(sk
, CA_EVENT_CWND_RESTART
);
153 tp
->snd_ssthresh
= tcp_current_ssthresh(sk
);
154 restart_cwnd
= min(restart_cwnd
, cwnd
);
156 while ((delta
-= inet_csk(sk
)->icsk_rto
) > 0 && cwnd
> restart_cwnd
)
158 tp
->snd_cwnd
= max(cwnd
, restart_cwnd
);
159 tp
->snd_cwnd_stamp
= tcp_time_stamp
;
160 tp
->snd_cwnd_used
= 0;
163 /* Congestion state accounting after a packet has been sent. */
164 static void tcp_event_data_sent(struct tcp_sock
*tp
,
167 struct inet_connection_sock
*icsk
= inet_csk(sk
);
168 const u32 now
= tcp_time_stamp
;
169 const struct dst_entry
*dst
= __sk_dst_get(sk
);
171 if (sysctl_tcp_slow_start_after_idle
&&
172 (!tp
->packets_out
&& (s32
)(now
- tp
->lsndtime
) > icsk
->icsk_rto
))
173 tcp_cwnd_restart(sk
, __sk_dst_get(sk
));
177 /* If it is a reply for ato after last received
178 * packet, enter pingpong mode.
180 if ((u32
)(now
- icsk
->icsk_ack
.lrcvtime
) < icsk
->icsk_ack
.ato
&&
181 (!dst
|| !dst_metric(dst
, RTAX_QUICKACK
)))
182 icsk
->icsk_ack
.pingpong
= 1;
185 /* Account for an ACK we sent. */
186 static inline void tcp_event_ack_sent(struct sock
*sk
, unsigned int pkts
)
188 tcp_dec_quickack_mode(sk
, pkts
);
189 inet_csk_clear_xmit_timer(sk
, ICSK_TIME_DACK
);
193 u32
tcp_default_init_rwnd(u32 mss
)
195 /* Initial receive window should be twice of TCP_INIT_CWND to
196 * enable proper sending of new unsent data during fast recovery
197 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
198 * limit when mss is larger than 1460.
200 u32 init_rwnd
= TCP_INIT_CWND
* 2;
203 init_rwnd
= max((1460 * init_rwnd
) / mss
, 2U);
207 /* Determine a window scaling and initial window to offer.
208 * Based on the assumption that the given amount of space
209 * will be offered. Store the results in the tp structure.
210 * NOTE: for smooth operation initial space offering should
211 * be a multiple of mss if possible. We assume here that mss >= 1.
212 * This MUST be enforced by all callers.
214 void tcp_select_initial_window(int __space
, __u32 mss
,
215 __u32
*rcv_wnd
, __u32
*window_clamp
,
216 int wscale_ok
, __u8
*rcv_wscale
,
219 unsigned int space
= (__space
< 0 ? 0 : __space
);
221 /* If no clamp set the clamp to the max possible scaled window */
222 if (*window_clamp
== 0)
223 (*window_clamp
) = (65535 << 14);
224 space
= min(*window_clamp
, space
);
226 /* Quantize space offering to a multiple of mss if possible. */
228 space
= (space
/ mss
) * mss
;
230 /* NOTE: offering an initial window larger than 32767
231 * will break some buggy TCP stacks. If the admin tells us
232 * it is likely we could be speaking with such a buggy stack
233 * we will truncate our initial window offering to 32K-1
234 * unless the remote has sent us a window scaling option,
235 * which we interpret as a sign the remote TCP is not
236 * misinterpreting the window field as a signed quantity.
238 if (sysctl_tcp_workaround_signed_windows
)
239 (*rcv_wnd
) = min(space
, MAX_TCP_WINDOW
);
245 /* Set window scaling on max possible window
246 * See RFC1323 for an explanation of the limit to 14
248 space
= max_t(u32
, sysctl_tcp_rmem
[2], sysctl_rmem_max
);
249 space
= min_t(u32
, space
, *window_clamp
);
250 while (space
> 65535 && (*rcv_wscale
) < 14) {
256 if (mss
> (1 << *rcv_wscale
)) {
257 if (!init_rcv_wnd
) /* Use default unless specified otherwise */
258 init_rcv_wnd
= tcp_default_init_rwnd(mss
);
259 *rcv_wnd
= min(*rcv_wnd
, init_rcv_wnd
* mss
);
262 /* Set the clamp no higher than max representable value */
263 (*window_clamp
) = min(65535U << (*rcv_wscale
), *window_clamp
);
265 EXPORT_SYMBOL(tcp_select_initial_window
);
267 /* Chose a new window to advertise, update state in tcp_sock for the
268 * socket, and return result with RFC1323 scaling applied. The return
269 * value can be stuffed directly into th->window for an outgoing
272 static u16
tcp_select_window(struct sock
*sk
)
274 struct tcp_sock
*tp
= tcp_sk(sk
);
275 u32 old_win
= tp
->rcv_wnd
;
276 u32 cur_win
= tcp_receive_window(tp
);
277 u32 new_win
= __tcp_select_window(sk
);
279 /* Never shrink the offered window */
280 if (new_win
< cur_win
) {
281 /* Danger Will Robinson!
282 * Don't update rcv_wup/rcv_wnd here or else
283 * we will not be able to advertise a zero
284 * window in time. --DaveM
286 * Relax Will Robinson.
289 NET_INC_STATS(sock_net(sk
),
290 LINUX_MIB_TCPWANTZEROWINDOWADV
);
291 new_win
= ALIGN(cur_win
, 1 << tp
->rx_opt
.rcv_wscale
);
293 tp
->rcv_wnd
= new_win
;
294 tp
->rcv_wup
= tp
->rcv_nxt
;
296 /* Make sure we do not exceed the maximum possible
299 if (!tp
->rx_opt
.rcv_wscale
&& sysctl_tcp_workaround_signed_windows
)
300 new_win
= min(new_win
, MAX_TCP_WINDOW
);
302 new_win
= min(new_win
, (65535U << tp
->rx_opt
.rcv_wscale
));
304 /* RFC1323 scaling applied */
305 new_win
>>= tp
->rx_opt
.rcv_wscale
;
307 /* If we advertise zero window, disable fast path. */
311 NET_INC_STATS(sock_net(sk
),
312 LINUX_MIB_TCPTOZEROWINDOWADV
);
313 } else if (old_win
== 0) {
314 NET_INC_STATS(sock_net(sk
), LINUX_MIB_TCPFROMZEROWINDOWADV
);
320 /* Packet ECN state for a SYN-ACK */
321 static inline void TCP_ECN_send_synack(const struct tcp_sock
*tp
, struct sk_buff
*skb
)
323 TCP_SKB_CB(skb
)->tcp_flags
&= ~TCPHDR_CWR
;
324 if (!(tp
->ecn_flags
& TCP_ECN_OK
))
325 TCP_SKB_CB(skb
)->tcp_flags
&= ~TCPHDR_ECE
;
328 /* Packet ECN state for a SYN. */
329 static inline void TCP_ECN_send_syn(struct sock
*sk
, struct sk_buff
*skb
)
331 struct tcp_sock
*tp
= tcp_sk(sk
);
334 if (sock_net(sk
)->ipv4
.sysctl_tcp_ecn
== 1) {
335 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_ECE
| TCPHDR_CWR
;
336 tp
->ecn_flags
= TCP_ECN_OK
;
340 static __inline__
void
341 TCP_ECN_make_synack(const struct request_sock
*req
, struct tcphdr
*th
)
343 if (inet_rsk(req
)->ecn_ok
)
347 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
350 static inline void TCP_ECN_send(struct sock
*sk
, struct sk_buff
*skb
,
353 struct tcp_sock
*tp
= tcp_sk(sk
);
355 if (tp
->ecn_flags
& TCP_ECN_OK
) {
356 /* Not-retransmitted data segment: set ECT and inject CWR. */
357 if (skb
->len
!= tcp_header_len
&&
358 !before(TCP_SKB_CB(skb
)->seq
, tp
->snd_nxt
)) {
360 if (tp
->ecn_flags
& TCP_ECN_QUEUE_CWR
) {
361 tp
->ecn_flags
&= ~TCP_ECN_QUEUE_CWR
;
362 tcp_hdr(skb
)->cwr
= 1;
363 skb_shinfo(skb
)->gso_type
|= SKB_GSO_TCP_ECN
;
366 /* ACK or retransmitted segment: clear ECT|CE */
367 INET_ECN_dontxmit(sk
);
369 if (tp
->ecn_flags
& TCP_ECN_DEMAND_CWR
)
370 tcp_hdr(skb
)->ece
= 1;
374 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
375 * auto increment end seqno.
377 static void tcp_init_nondata_skb(struct sk_buff
*skb
, u32 seq
, u8 flags
)
379 struct skb_shared_info
*shinfo
= skb_shinfo(skb
);
381 skb
->ip_summed
= CHECKSUM_PARTIAL
;
384 TCP_SKB_CB(skb
)->tcp_flags
= flags
;
385 TCP_SKB_CB(skb
)->sacked
= 0;
387 shinfo
->gso_segs
= 1;
388 shinfo
->gso_size
= 0;
389 shinfo
->gso_type
= 0;
391 TCP_SKB_CB(skb
)->seq
= seq
;
392 if (flags
& (TCPHDR_SYN
| TCPHDR_FIN
))
394 TCP_SKB_CB(skb
)->end_seq
= seq
;
397 static inline bool tcp_urg_mode(const struct tcp_sock
*tp
)
399 return tp
->snd_una
!= tp
->snd_up
;
402 #define OPTION_SACK_ADVERTISE (1 << 0)
403 #define OPTION_TS (1 << 1)
404 #define OPTION_MD5 (1 << 2)
405 #define OPTION_WSCALE (1 << 3)
406 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
408 struct tcp_out_options
{
409 u16 options
; /* bit field of OPTION_* */
410 u16 mss
; /* 0 to disable */
411 u8 ws
; /* window scale, 0 to disable */
412 u8 num_sack_blocks
; /* number of SACK blocks to include */
413 u8 hash_size
; /* bytes in hash_location */
414 __u8
*hash_location
; /* temporary pointer, overloaded */
415 __u32 tsval
, tsecr
; /* need to include OPTION_TS */
416 struct tcp_fastopen_cookie
*fastopen_cookie
; /* Fast open cookie */
419 /* Write previously computed TCP options to the packet.
421 * Beware: Something in the Internet is very sensitive to the ordering of
422 * TCP options, we learned this through the hard way, so be careful here.
423 * Luckily we can at least blame others for their non-compliance but from
424 * inter-operability perspective it seems that we're somewhat stuck with
425 * the ordering which we have been using if we want to keep working with
426 * those broken things (not that it currently hurts anybody as there isn't
427 * particular reason why the ordering would need to be changed).
429 * At least SACK_PERM as the first option is known to lead to a disaster
430 * (but it may well be that other scenarios fail similarly).
432 static void tcp_options_write(__be32
*ptr
, struct tcp_sock
*tp
,
433 struct tcp_out_options
*opts
)
435 u16 options
= opts
->options
; /* mungable copy */
437 if (unlikely(OPTION_MD5
& options
)) {
438 *ptr
++ = htonl((TCPOPT_NOP
<< 24) | (TCPOPT_NOP
<< 16) |
439 (TCPOPT_MD5SIG
<< 8) | TCPOLEN_MD5SIG
);
440 /* overload cookie hash location */
441 opts
->hash_location
= (__u8
*)ptr
;
445 if (unlikely(opts
->mss
)) {
446 *ptr
++ = htonl((TCPOPT_MSS
<< 24) |
447 (TCPOLEN_MSS
<< 16) |
451 if (likely(OPTION_TS
& options
)) {
452 if (unlikely(OPTION_SACK_ADVERTISE
& options
)) {
453 *ptr
++ = htonl((TCPOPT_SACK_PERM
<< 24) |
454 (TCPOLEN_SACK_PERM
<< 16) |
455 (TCPOPT_TIMESTAMP
<< 8) |
457 options
&= ~OPTION_SACK_ADVERTISE
;
459 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
461 (TCPOPT_TIMESTAMP
<< 8) |
464 *ptr
++ = htonl(opts
->tsval
);
465 *ptr
++ = htonl(opts
->tsecr
);
468 if (unlikely(OPTION_SACK_ADVERTISE
& options
)) {
469 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
471 (TCPOPT_SACK_PERM
<< 8) |
475 if (unlikely(OPTION_WSCALE
& options
)) {
476 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
477 (TCPOPT_WINDOW
<< 16) |
478 (TCPOLEN_WINDOW
<< 8) |
482 if (unlikely(opts
->num_sack_blocks
)) {
483 struct tcp_sack_block
*sp
= tp
->rx_opt
.dsack
?
484 tp
->duplicate_sack
: tp
->selective_acks
;
487 *ptr
++ = htonl((TCPOPT_NOP
<< 24) |
490 (TCPOLEN_SACK_BASE
+ (opts
->num_sack_blocks
*
491 TCPOLEN_SACK_PERBLOCK
)));
493 for (this_sack
= 0; this_sack
< opts
->num_sack_blocks
;
495 *ptr
++ = htonl(sp
[this_sack
].start_seq
);
496 *ptr
++ = htonl(sp
[this_sack
].end_seq
);
499 tp
->rx_opt
.dsack
= 0;
502 if (unlikely(OPTION_FAST_OPEN_COOKIE
& options
)) {
503 struct tcp_fastopen_cookie
*foc
= opts
->fastopen_cookie
;
505 *ptr
++ = htonl((TCPOPT_EXP
<< 24) |
506 ((TCPOLEN_EXP_FASTOPEN_BASE
+ foc
->len
) << 16) |
507 TCPOPT_FASTOPEN_MAGIC
);
509 memcpy(ptr
, foc
->val
, foc
->len
);
510 if ((foc
->len
& 3) == 2) {
511 u8
*align
= ((u8
*)ptr
) + foc
->len
;
512 align
[0] = align
[1] = TCPOPT_NOP
;
514 ptr
+= (foc
->len
+ 3) >> 2;
518 /* Compute TCP options for SYN packets. This is not the final
519 * network wire format yet.
521 static unsigned int tcp_syn_options(struct sock
*sk
, struct sk_buff
*skb
,
522 struct tcp_out_options
*opts
,
523 struct tcp_md5sig_key
**md5
)
525 struct tcp_sock
*tp
= tcp_sk(sk
);
526 unsigned int remaining
= MAX_TCP_OPTION_SPACE
;
527 struct tcp_fastopen_request
*fastopen
= tp
->fastopen_req
;
529 #ifdef CONFIG_TCP_MD5SIG
530 *md5
= tp
->af_specific
->md5_lookup(sk
, sk
);
532 opts
->options
|= OPTION_MD5
;
533 remaining
-= TCPOLEN_MD5SIG_ALIGNED
;
539 /* We always get an MSS option. The option bytes which will be seen in
540 * normal data packets should timestamps be used, must be in the MSS
541 * advertised. But we subtract them from tp->mss_cache so that
542 * calculations in tcp_sendmsg are simpler etc. So account for this
543 * fact here if necessary. If we don't do this correctly, as a
544 * receiver we won't recognize data packets as being full sized when we
545 * should, and thus we won't abide by the delayed ACK rules correctly.
546 * SACKs don't matter, we never delay an ACK when we have any of those
548 opts
->mss
= tcp_advertise_mss(sk
);
549 remaining
-= TCPOLEN_MSS_ALIGNED
;
551 if (likely(sysctl_tcp_timestamps
&& *md5
== NULL
)) {
552 opts
->options
|= OPTION_TS
;
553 opts
->tsval
= tcp_skb_timestamp(skb
) + tp
->tsoffset
;
554 opts
->tsecr
= tp
->rx_opt
.ts_recent
;
555 remaining
-= TCPOLEN_TSTAMP_ALIGNED
;
557 if (likely(sysctl_tcp_window_scaling
)) {
558 opts
->ws
= tp
->rx_opt
.rcv_wscale
;
559 opts
->options
|= OPTION_WSCALE
;
560 remaining
-= TCPOLEN_WSCALE_ALIGNED
;
562 if (likely(sysctl_tcp_sack
)) {
563 opts
->options
|= OPTION_SACK_ADVERTISE
;
564 if (unlikely(!(OPTION_TS
& opts
->options
)))
565 remaining
-= TCPOLEN_SACKPERM_ALIGNED
;
568 if (fastopen
&& fastopen
->cookie
.len
>= 0) {
569 u32 need
= TCPOLEN_EXP_FASTOPEN_BASE
+ fastopen
->cookie
.len
;
570 need
= (need
+ 3) & ~3U; /* Align to 32 bits */
571 if (remaining
>= need
) {
572 opts
->options
|= OPTION_FAST_OPEN_COOKIE
;
573 opts
->fastopen_cookie
= &fastopen
->cookie
;
575 tp
->syn_fastopen
= 1;
579 return MAX_TCP_OPTION_SPACE
- remaining
;
582 /* Set up TCP options for SYN-ACKs. */
583 static unsigned int tcp_synack_options(struct sock
*sk
,
584 struct request_sock
*req
,
585 unsigned int mss
, struct sk_buff
*skb
,
586 struct tcp_out_options
*opts
,
587 struct tcp_md5sig_key
**md5
,
588 struct tcp_fastopen_cookie
*foc
)
590 struct inet_request_sock
*ireq
= inet_rsk(req
);
591 unsigned int remaining
= MAX_TCP_OPTION_SPACE
;
593 #ifdef CONFIG_TCP_MD5SIG
594 *md5
= tcp_rsk(req
)->af_specific
->md5_lookup(sk
, req
);
596 opts
->options
|= OPTION_MD5
;
597 remaining
-= TCPOLEN_MD5SIG_ALIGNED
;
599 /* We can't fit any SACK blocks in a packet with MD5 + TS
600 * options. There was discussion about disabling SACK
601 * rather than TS in order to fit in better with old,
602 * buggy kernels, but that was deemed to be unnecessary.
604 ireq
->tstamp_ok
&= !ireq
->sack_ok
;
610 /* We always send an MSS option. */
612 remaining
-= TCPOLEN_MSS_ALIGNED
;
614 if (likely(ireq
->wscale_ok
)) {
615 opts
->ws
= ireq
->rcv_wscale
;
616 opts
->options
|= OPTION_WSCALE
;
617 remaining
-= TCPOLEN_WSCALE_ALIGNED
;
619 if (likely(ireq
->tstamp_ok
)) {
620 opts
->options
|= OPTION_TS
;
621 opts
->tsval
= tcp_skb_timestamp(skb
);
622 opts
->tsecr
= req
->ts_recent
;
623 remaining
-= TCPOLEN_TSTAMP_ALIGNED
;
625 if (likely(ireq
->sack_ok
)) {
626 opts
->options
|= OPTION_SACK_ADVERTISE
;
627 if (unlikely(!ireq
->tstamp_ok
))
628 remaining
-= TCPOLEN_SACKPERM_ALIGNED
;
630 if (foc
!= NULL
&& foc
->len
>= 0) {
631 u32 need
= TCPOLEN_EXP_FASTOPEN_BASE
+ foc
->len
;
632 need
= (need
+ 3) & ~3U; /* Align to 32 bits */
633 if (remaining
>= need
) {
634 opts
->options
|= OPTION_FAST_OPEN_COOKIE
;
635 opts
->fastopen_cookie
= foc
;
640 return MAX_TCP_OPTION_SPACE
- remaining
;
643 /* Compute TCP options for ESTABLISHED sockets. This is not the
644 * final wire format yet.
646 static unsigned int tcp_established_options(struct sock
*sk
, struct sk_buff
*skb
,
647 struct tcp_out_options
*opts
,
648 struct tcp_md5sig_key
**md5
)
650 struct tcp_sock
*tp
= tcp_sk(sk
);
651 unsigned int size
= 0;
652 unsigned int eff_sacks
;
656 #ifdef CONFIG_TCP_MD5SIG
657 *md5
= tp
->af_specific
->md5_lookup(sk
, sk
);
658 if (unlikely(*md5
)) {
659 opts
->options
|= OPTION_MD5
;
660 size
+= TCPOLEN_MD5SIG_ALIGNED
;
666 if (likely(tp
->rx_opt
.tstamp_ok
)) {
667 opts
->options
|= OPTION_TS
;
668 opts
->tsval
= skb
? tcp_skb_timestamp(skb
) + tp
->tsoffset
: 0;
669 opts
->tsecr
= tp
->rx_opt
.ts_recent
;
670 size
+= TCPOLEN_TSTAMP_ALIGNED
;
673 eff_sacks
= tp
->rx_opt
.num_sacks
+ tp
->rx_opt
.dsack
;
674 if (unlikely(eff_sacks
)) {
675 const unsigned int remaining
= MAX_TCP_OPTION_SPACE
- size
;
676 opts
->num_sack_blocks
=
677 min_t(unsigned int, eff_sacks
,
678 (remaining
- TCPOLEN_SACK_BASE_ALIGNED
) /
679 TCPOLEN_SACK_PERBLOCK
);
680 size
+= TCPOLEN_SACK_BASE_ALIGNED
+
681 opts
->num_sack_blocks
* TCPOLEN_SACK_PERBLOCK
;
688 /* TCP SMALL QUEUES (TSQ)
690 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
691 * to reduce RTT and bufferbloat.
692 * We do this using a special skb destructor (tcp_wfree).
694 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
695 * needs to be reallocated in a driver.
696 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
698 * Since transmit from skb destructor is forbidden, we use a tasklet
699 * to process all sockets that eventually need to send more skbs.
700 * We use one tasklet per cpu, with its own queue of sockets.
703 struct tasklet_struct tasklet
;
704 struct list_head head
; /* queue of tcp sockets */
706 static DEFINE_PER_CPU(struct tsq_tasklet
, tsq_tasklet
);
708 static void tcp_tsq_handler(struct sock
*sk
)
710 if ((1 << sk
->sk_state
) &
711 (TCPF_ESTABLISHED
| TCPF_FIN_WAIT1
| TCPF_CLOSING
|
712 TCPF_CLOSE_WAIT
| TCPF_LAST_ACK
))
713 tcp_write_xmit(sk
, tcp_current_mss(sk
), tcp_sk(sk
)->nonagle
,
717 * One tasklet per cpu tries to send more skbs.
718 * We run in tasklet context but need to disable irqs when
719 * transferring tsq->head because tcp_wfree() might
720 * interrupt us (non NAPI drivers)
722 static void tcp_tasklet_func(unsigned long data
)
724 struct tsq_tasklet
*tsq
= (struct tsq_tasklet
*)data
;
727 struct list_head
*q
, *n
;
731 local_irq_save(flags
);
732 list_splice_init(&tsq
->head
, &list
);
733 local_irq_restore(flags
);
735 list_for_each_safe(q
, n
, &list
) {
736 tp
= list_entry(q
, struct tcp_sock
, tsq_node
);
737 list_del(&tp
->tsq_node
);
739 sk
= (struct sock
*)tp
;
742 if (!sock_owned_by_user(sk
)) {
745 /* defer the work to tcp_release_cb() */
746 set_bit(TCP_TSQ_DEFERRED
, &tp
->tsq_flags
);
750 clear_bit(TSQ_QUEUED
, &tp
->tsq_flags
);
755 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
756 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
757 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
758 (1UL << TCP_MTU_REDUCED_DEFERRED))
760 * tcp_release_cb - tcp release_sock() callback
763 * called from release_sock() to perform protocol dependent
764 * actions before socket release.
766 void tcp_release_cb(struct sock
*sk
)
768 struct tcp_sock
*tp
= tcp_sk(sk
);
769 unsigned long flags
, nflags
;
771 /* perform an atomic operation only if at least one flag is set */
773 flags
= tp
->tsq_flags
;
774 if (!(flags
& TCP_DEFERRED_ALL
))
776 nflags
= flags
& ~TCP_DEFERRED_ALL
;
777 } while (cmpxchg(&tp
->tsq_flags
, flags
, nflags
) != flags
);
779 if (flags
& (1UL << TCP_TSQ_DEFERRED
))
782 /* Here begins the tricky part :
783 * We are called from release_sock() with :
785 * 2) sk_lock.slock spinlock held
786 * 3) socket owned by us (sk->sk_lock.owned == 1)
788 * But following code is meant to be called from BH handlers,
789 * so we should keep BH disabled, but early release socket ownership
791 sock_release_ownership(sk
);
793 if (flags
& (1UL << TCP_WRITE_TIMER_DEFERRED
)) {
794 tcp_write_timer_handler(sk
);
797 if (flags
& (1UL << TCP_DELACK_TIMER_DEFERRED
)) {
798 tcp_delack_timer_handler(sk
);
801 if (flags
& (1UL << TCP_MTU_REDUCED_DEFERRED
)) {
802 inet_csk(sk
)->icsk_af_ops
->mtu_reduced(sk
);
806 EXPORT_SYMBOL(tcp_release_cb
);
808 void __init
tcp_tasklet_init(void)
812 for_each_possible_cpu(i
) {
813 struct tsq_tasklet
*tsq
= &per_cpu(tsq_tasklet
, i
);
815 INIT_LIST_HEAD(&tsq
->head
);
816 tasklet_init(&tsq
->tasklet
,
823 * Write buffer destructor automatically called from kfree_skb.
824 * We can't xmit new skbs from this context, as we might already
827 void tcp_wfree(struct sk_buff
*skb
)
829 struct sock
*sk
= skb
->sk
;
830 struct tcp_sock
*tp
= tcp_sk(sk
);
832 if (test_and_clear_bit(TSQ_THROTTLED
, &tp
->tsq_flags
) &&
833 !test_and_set_bit(TSQ_QUEUED
, &tp
->tsq_flags
)) {
835 struct tsq_tasklet
*tsq
;
837 /* Keep a ref on socket.
838 * This last ref will be released in tcp_tasklet_func()
840 atomic_sub(skb
->truesize
- 1, &sk
->sk_wmem_alloc
);
842 /* queue this socket to tasklet queue */
843 local_irq_save(flags
);
844 tsq
= &__get_cpu_var(tsq_tasklet
);
845 list_add(&tp
->tsq_node
, &tsq
->head
);
846 tasklet_schedule(&tsq
->tasklet
);
847 local_irq_restore(flags
);
853 /* This routine actually transmits TCP packets queued in by
854 * tcp_do_sendmsg(). This is used by both the initial
855 * transmission and possible later retransmissions.
856 * All SKB's seen here are completely headerless. It is our
857 * job to build the TCP header, and pass the packet down to
858 * IP so it can do the same plus pass the packet off to the
861 * We are working here with either a clone of the original
862 * SKB, or a fresh unique copy made by the retransmit engine.
864 static int tcp_transmit_skb(struct sock
*sk
, struct sk_buff
*skb
, int clone_it
,
867 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
868 struct inet_sock
*inet
;
870 struct tcp_skb_cb
*tcb
;
871 struct tcp_out_options opts
;
872 unsigned int tcp_options_size
, tcp_header_size
;
873 struct tcp_md5sig_key
*md5
;
877 BUG_ON(!skb
|| !tcp_skb_pcount(skb
));
880 skb_mstamp_get(&skb
->skb_mstamp
);
882 if (unlikely(skb_cloned(skb
)))
883 skb
= pskb_copy(skb
, gfp_mask
);
885 skb
= skb_clone(skb
, gfp_mask
);
892 tcb
= TCP_SKB_CB(skb
);
893 memset(&opts
, 0, sizeof(opts
));
895 if (unlikely(tcb
->tcp_flags
& TCPHDR_SYN
))
896 tcp_options_size
= tcp_syn_options(sk
, skb
, &opts
, &md5
);
898 tcp_options_size
= tcp_established_options(sk
, skb
, &opts
,
900 tcp_header_size
= tcp_options_size
+ sizeof(struct tcphdr
);
902 if (tcp_packets_in_flight(tp
) == 0)
903 tcp_ca_event(sk
, CA_EVENT_TX_START
);
905 /* if no packet is in qdisc/device queue, then allow XPS to select
908 skb
->ooo_okay
= sk_wmem_alloc_get(sk
) == 0;
910 skb_push(skb
, tcp_header_size
);
911 skb_reset_transport_header(skb
);
915 skb
->destructor
= tcp_wfree
;
916 skb_set_hash_from_sk(skb
, sk
);
917 atomic_add(skb
->truesize
, &sk
->sk_wmem_alloc
);
919 /* Build TCP header and checksum it. */
921 th
->source
= inet
->inet_sport
;
922 th
->dest
= inet
->inet_dport
;
923 th
->seq
= htonl(tcb
->seq
);
924 th
->ack_seq
= htonl(tp
->rcv_nxt
);
925 *(((__be16
*)th
) + 6) = htons(((tcp_header_size
>> 2) << 12) |
928 if (unlikely(tcb
->tcp_flags
& TCPHDR_SYN
)) {
929 /* RFC1323: The window in SYN & SYN/ACK segments
932 th
->window
= htons(min(tp
->rcv_wnd
, 65535U));
934 th
->window
= htons(tcp_select_window(sk
));
939 /* The urg_mode check is necessary during a below snd_una win probe */
940 if (unlikely(tcp_urg_mode(tp
) && before(tcb
->seq
, tp
->snd_up
))) {
941 if (before(tp
->snd_up
, tcb
->seq
+ 0x10000)) {
942 th
->urg_ptr
= htons(tp
->snd_up
- tcb
->seq
);
944 } else if (after(tcb
->seq
+ 0xFFFF, tp
->snd_nxt
)) {
945 th
->urg_ptr
= htons(0xFFFF);
950 tcp_options_write((__be32
*)(th
+ 1), tp
, &opts
);
951 if (likely((tcb
->tcp_flags
& TCPHDR_SYN
) == 0))
952 TCP_ECN_send(sk
, skb
, tcp_header_size
);
954 #ifdef CONFIG_TCP_MD5SIG
955 /* Calculate the MD5 hash, as we have all we need now */
957 sk_nocaps_add(sk
, NETIF_F_GSO_MASK
);
958 tp
->af_specific
->calc_md5_hash(opts
.hash_location
,
963 icsk
->icsk_af_ops
->send_check(sk
, skb
);
965 if (likely(tcb
->tcp_flags
& TCPHDR_ACK
))
966 tcp_event_ack_sent(sk
, tcp_skb_pcount(skb
));
968 if (skb
->len
!= tcp_header_size
)
969 tcp_event_data_sent(tp
, sk
);
971 if (after(tcb
->end_seq
, tp
->snd_nxt
) || tcb
->seq
== tcb
->end_seq
)
972 TCP_ADD_STATS(sock_net(sk
), TCP_MIB_OUTSEGS
,
973 tcp_skb_pcount(skb
));
975 /* Our usage of tstamp should remain private */
976 skb
->tstamp
.tv64
= 0;
977 err
= icsk
->icsk_af_ops
->queue_xmit(sk
, skb
, &inet
->cork
.fl
);
979 if (likely(err
<= 0))
984 return net_xmit_eval(err
);
987 /* This routine just queues the buffer for sending.
989 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
990 * otherwise socket can stall.
992 static void tcp_queue_skb(struct sock
*sk
, struct sk_buff
*skb
)
994 struct tcp_sock
*tp
= tcp_sk(sk
);
996 /* Advance write_seq and place onto the write_queue. */
997 tp
->write_seq
= TCP_SKB_CB(skb
)->end_seq
;
998 skb_header_release(skb
);
999 tcp_add_write_queue_tail(sk
, skb
);
1000 sk
->sk_wmem_queued
+= skb
->truesize
;
1001 sk_mem_charge(sk
, skb
->truesize
);
1004 /* Initialize TSO segments for a packet. */
1005 static void tcp_set_skb_tso_segs(const struct sock
*sk
, struct sk_buff
*skb
,
1006 unsigned int mss_now
)
1008 struct skb_shared_info
*shinfo
= skb_shinfo(skb
);
1010 /* Make sure we own this skb before messing gso_size/gso_segs */
1011 WARN_ON_ONCE(skb_cloned(skb
));
1013 if (skb
->len
<= mss_now
|| skb
->ip_summed
== CHECKSUM_NONE
) {
1014 /* Avoid the costly divide in the normal
1017 shinfo
->gso_segs
= 1;
1018 shinfo
->gso_size
= 0;
1019 shinfo
->gso_type
= 0;
1021 shinfo
->gso_segs
= DIV_ROUND_UP(skb
->len
, mss_now
);
1022 shinfo
->gso_size
= mss_now
;
1023 shinfo
->gso_type
= sk
->sk_gso_type
;
1027 /* When a modification to fackets out becomes necessary, we need to check
1028 * skb is counted to fackets_out or not.
1030 static void tcp_adjust_fackets_out(struct sock
*sk
, const struct sk_buff
*skb
,
1033 struct tcp_sock
*tp
= tcp_sk(sk
);
1035 if (!tp
->sacked_out
|| tcp_is_reno(tp
))
1038 if (after(tcp_highest_sack_seq(tp
), TCP_SKB_CB(skb
)->seq
))
1039 tp
->fackets_out
-= decr
;
1042 /* Pcount in the middle of the write queue got changed, we need to do various
1043 * tweaks to fix counters
1045 static void tcp_adjust_pcount(struct sock
*sk
, const struct sk_buff
*skb
, int decr
)
1047 struct tcp_sock
*tp
= tcp_sk(sk
);
1049 tp
->packets_out
-= decr
;
1051 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_ACKED
)
1052 tp
->sacked_out
-= decr
;
1053 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_RETRANS
)
1054 tp
->retrans_out
-= decr
;
1055 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_LOST
)
1056 tp
->lost_out
-= decr
;
1058 /* Reno case is special. Sigh... */
1059 if (tcp_is_reno(tp
) && decr
> 0)
1060 tp
->sacked_out
-= min_t(u32
, tp
->sacked_out
, decr
);
1062 tcp_adjust_fackets_out(sk
, skb
, decr
);
1064 if (tp
->lost_skb_hint
&&
1065 before(TCP_SKB_CB(skb
)->seq
, TCP_SKB_CB(tp
->lost_skb_hint
)->seq
) &&
1066 (tcp_is_fack(tp
) || (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_ACKED
)))
1067 tp
->lost_cnt_hint
-= decr
;
1069 tcp_verify_left_out(tp
);
1072 static void tcp_fragment_tstamp(struct sk_buff
*skb
, struct sk_buff
*skb2
)
1074 struct skb_shared_info
*shinfo
= skb_shinfo(skb
);
1076 if (unlikely(shinfo
->tx_flags
& SKBTX_ANY_TSTAMP
) &&
1077 !before(shinfo
->tskey
, TCP_SKB_CB(skb2
)->seq
)) {
1078 struct skb_shared_info
*shinfo2
= skb_shinfo(skb2
);
1079 u8 tsflags
= shinfo
->tx_flags
& SKBTX_ANY_TSTAMP
;
1081 shinfo
->tx_flags
&= ~tsflags
;
1082 shinfo2
->tx_flags
|= tsflags
;
1083 swap(shinfo
->tskey
, shinfo2
->tskey
);
1087 /* Function to create two new TCP segments. Shrinks the given segment
1088 * to the specified size and appends a new segment with the rest of the
1089 * packet to the list. This won't be called frequently, I hope.
1090 * Remember, these are still headerless SKBs at this point.
1092 int tcp_fragment(struct sock
*sk
, struct sk_buff
*skb
, u32 len
,
1093 unsigned int mss_now
, gfp_t gfp
)
1095 struct tcp_sock
*tp
= tcp_sk(sk
);
1096 struct sk_buff
*buff
;
1097 int nsize
, old_factor
;
1101 if (WARN_ON(len
> skb
->len
))
1104 nsize
= skb_headlen(skb
) - len
;
1108 if (skb_unclone(skb
, gfp
))
1111 /* Get a new skb... force flag on. */
1112 buff
= sk_stream_alloc_skb(sk
, nsize
, gfp
);
1114 return -ENOMEM
; /* We'll just try again later. */
1116 sk
->sk_wmem_queued
+= buff
->truesize
;
1117 sk_mem_charge(sk
, buff
->truesize
);
1118 nlen
= skb
->len
- len
- nsize
;
1119 buff
->truesize
+= nlen
;
1120 skb
->truesize
-= nlen
;
1122 /* Correct the sequence numbers. */
1123 TCP_SKB_CB(buff
)->seq
= TCP_SKB_CB(skb
)->seq
+ len
;
1124 TCP_SKB_CB(buff
)->end_seq
= TCP_SKB_CB(skb
)->end_seq
;
1125 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(buff
)->seq
;
1127 /* PSH and FIN should only be set in the second packet. */
1128 flags
= TCP_SKB_CB(skb
)->tcp_flags
;
1129 TCP_SKB_CB(skb
)->tcp_flags
= flags
& ~(TCPHDR_FIN
| TCPHDR_PSH
);
1130 TCP_SKB_CB(buff
)->tcp_flags
= flags
;
1131 TCP_SKB_CB(buff
)->sacked
= TCP_SKB_CB(skb
)->sacked
;
1133 if (!skb_shinfo(skb
)->nr_frags
&& skb
->ip_summed
!= CHECKSUM_PARTIAL
) {
1134 /* Copy and checksum data tail into the new buffer. */
1135 buff
->csum
= csum_partial_copy_nocheck(skb
->data
+ len
,
1136 skb_put(buff
, nsize
),
1141 skb
->csum
= csum_block_sub(skb
->csum
, buff
->csum
, len
);
1143 skb
->ip_summed
= CHECKSUM_PARTIAL
;
1144 skb_split(skb
, buff
, len
);
1147 buff
->ip_summed
= skb
->ip_summed
;
1149 buff
->tstamp
= skb
->tstamp
;
1150 tcp_fragment_tstamp(skb
, buff
);
1152 old_factor
= tcp_skb_pcount(skb
);
1154 /* Fix up tso_factor for both original and new SKB. */
1155 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1156 tcp_set_skb_tso_segs(sk
, buff
, mss_now
);
1158 /* If this packet has been sent out already, we must
1159 * adjust the various packet counters.
1161 if (!before(tp
->snd_nxt
, TCP_SKB_CB(buff
)->end_seq
)) {
1162 int diff
= old_factor
- tcp_skb_pcount(skb
) -
1163 tcp_skb_pcount(buff
);
1166 tcp_adjust_pcount(sk
, skb
, diff
);
1169 /* Link BUFF into the send queue. */
1170 skb_header_release(buff
);
1171 tcp_insert_write_queue_after(skb
, buff
, sk
);
1176 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1177 * eventually). The difference is that pulled data not copied, but
1178 * immediately discarded.
1180 static void __pskb_trim_head(struct sk_buff
*skb
, int len
)
1182 struct skb_shared_info
*shinfo
;
1185 eat
= min_t(int, len
, skb_headlen(skb
));
1187 __skb_pull(skb
, eat
);
1194 shinfo
= skb_shinfo(skb
);
1195 for (i
= 0; i
< shinfo
->nr_frags
; i
++) {
1196 int size
= skb_frag_size(&shinfo
->frags
[i
]);
1199 skb_frag_unref(skb
, i
);
1202 shinfo
->frags
[k
] = shinfo
->frags
[i
];
1204 shinfo
->frags
[k
].page_offset
+= eat
;
1205 skb_frag_size_sub(&shinfo
->frags
[k
], eat
);
1211 shinfo
->nr_frags
= k
;
1213 skb_reset_tail_pointer(skb
);
1214 skb
->data_len
-= len
;
1215 skb
->len
= skb
->data_len
;
1218 /* Remove acked data from a packet in the transmit queue. */
1219 int tcp_trim_head(struct sock
*sk
, struct sk_buff
*skb
, u32 len
)
1221 if (skb_unclone(skb
, GFP_ATOMIC
))
1224 __pskb_trim_head(skb
, len
);
1226 TCP_SKB_CB(skb
)->seq
+= len
;
1227 skb
->ip_summed
= CHECKSUM_PARTIAL
;
1229 skb
->truesize
-= len
;
1230 sk
->sk_wmem_queued
-= len
;
1231 sk_mem_uncharge(sk
, len
);
1232 sock_set_flag(sk
, SOCK_QUEUE_SHRUNK
);
1234 /* Any change of skb->len requires recalculation of tso factor. */
1235 if (tcp_skb_pcount(skb
) > 1)
1236 tcp_set_skb_tso_segs(sk
, skb
, tcp_skb_mss(skb
));
1241 /* Calculate MSS not accounting any TCP options. */
1242 static inline int __tcp_mtu_to_mss(struct sock
*sk
, int pmtu
)
1244 const struct tcp_sock
*tp
= tcp_sk(sk
);
1245 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
1248 /* Calculate base mss without TCP options:
1249 It is MMS_S - sizeof(tcphdr) of rfc1122
1251 mss_now
= pmtu
- icsk
->icsk_af_ops
->net_header_len
- sizeof(struct tcphdr
);
1253 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1254 if (icsk
->icsk_af_ops
->net_frag_header_len
) {
1255 const struct dst_entry
*dst
= __sk_dst_get(sk
);
1257 if (dst
&& dst_allfrag(dst
))
1258 mss_now
-= icsk
->icsk_af_ops
->net_frag_header_len
;
1261 /* Clamp it (mss_clamp does not include tcp options) */
1262 if (mss_now
> tp
->rx_opt
.mss_clamp
)
1263 mss_now
= tp
->rx_opt
.mss_clamp
;
1265 /* Now subtract optional transport overhead */
1266 mss_now
-= icsk
->icsk_ext_hdr_len
;
1268 /* Then reserve room for full set of TCP options and 8 bytes of data */
1274 /* Calculate MSS. Not accounting for SACKs here. */
1275 int tcp_mtu_to_mss(struct sock
*sk
, int pmtu
)
1277 /* Subtract TCP options size, not including SACKs */
1278 return __tcp_mtu_to_mss(sk
, pmtu
) -
1279 (tcp_sk(sk
)->tcp_header_len
- sizeof(struct tcphdr
));
1282 /* Inverse of above */
1283 int tcp_mss_to_mtu(struct sock
*sk
, int mss
)
1285 const struct tcp_sock
*tp
= tcp_sk(sk
);
1286 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
1290 tp
->tcp_header_len
+
1291 icsk
->icsk_ext_hdr_len
+
1292 icsk
->icsk_af_ops
->net_header_len
;
1294 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1295 if (icsk
->icsk_af_ops
->net_frag_header_len
) {
1296 const struct dst_entry
*dst
= __sk_dst_get(sk
);
1298 if (dst
&& dst_allfrag(dst
))
1299 mtu
+= icsk
->icsk_af_ops
->net_frag_header_len
;
1304 /* MTU probing init per socket */
1305 void tcp_mtup_init(struct sock
*sk
)
1307 struct tcp_sock
*tp
= tcp_sk(sk
);
1308 struct inet_connection_sock
*icsk
= inet_csk(sk
);
1310 icsk
->icsk_mtup
.enabled
= sysctl_tcp_mtu_probing
> 1;
1311 icsk
->icsk_mtup
.search_high
= tp
->rx_opt
.mss_clamp
+ sizeof(struct tcphdr
) +
1312 icsk
->icsk_af_ops
->net_header_len
;
1313 icsk
->icsk_mtup
.search_low
= tcp_mss_to_mtu(sk
, sysctl_tcp_base_mss
);
1314 icsk
->icsk_mtup
.probe_size
= 0;
1316 EXPORT_SYMBOL(tcp_mtup_init
);
1318 /* This function synchronize snd mss to current pmtu/exthdr set.
1320 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1321 for TCP options, but includes only bare TCP header.
1323 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1324 It is minimum of user_mss and mss received with SYN.
1325 It also does not include TCP options.
1327 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1329 tp->mss_cache is current effective sending mss, including
1330 all tcp options except for SACKs. It is evaluated,
1331 taking into account current pmtu, but never exceeds
1332 tp->rx_opt.mss_clamp.
1334 NOTE1. rfc1122 clearly states that advertised MSS
1335 DOES NOT include either tcp or ip options.
1337 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1338 are READ ONLY outside this function. --ANK (980731)
1340 unsigned int tcp_sync_mss(struct sock
*sk
, u32 pmtu
)
1342 struct tcp_sock
*tp
= tcp_sk(sk
);
1343 struct inet_connection_sock
*icsk
= inet_csk(sk
);
1346 if (icsk
->icsk_mtup
.search_high
> pmtu
)
1347 icsk
->icsk_mtup
.search_high
= pmtu
;
1349 mss_now
= tcp_mtu_to_mss(sk
, pmtu
);
1350 mss_now
= tcp_bound_to_half_wnd(tp
, mss_now
);
1352 /* And store cached results */
1353 icsk
->icsk_pmtu_cookie
= pmtu
;
1354 if (icsk
->icsk_mtup
.enabled
)
1355 mss_now
= min(mss_now
, tcp_mtu_to_mss(sk
, icsk
->icsk_mtup
.search_low
));
1356 tp
->mss_cache
= mss_now
;
1360 EXPORT_SYMBOL(tcp_sync_mss
);
1362 /* Compute the current effective MSS, taking SACKs and IP options,
1363 * and even PMTU discovery events into account.
1365 unsigned int tcp_current_mss(struct sock
*sk
)
1367 const struct tcp_sock
*tp
= tcp_sk(sk
);
1368 const struct dst_entry
*dst
= __sk_dst_get(sk
);
1370 unsigned int header_len
;
1371 struct tcp_out_options opts
;
1372 struct tcp_md5sig_key
*md5
;
1374 mss_now
= tp
->mss_cache
;
1377 u32 mtu
= dst_mtu(dst
);
1378 if (mtu
!= inet_csk(sk
)->icsk_pmtu_cookie
)
1379 mss_now
= tcp_sync_mss(sk
, mtu
);
1382 header_len
= tcp_established_options(sk
, NULL
, &opts
, &md5
) +
1383 sizeof(struct tcphdr
);
1384 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1385 * some common options. If this is an odd packet (because we have SACK
1386 * blocks etc) then our calculated header_len will be different, and
1387 * we have to adjust mss_now correspondingly */
1388 if (header_len
!= tp
->tcp_header_len
) {
1389 int delta
= (int) header_len
- tp
->tcp_header_len
;
1396 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1397 * As additional protections, we do not touch cwnd in retransmission phases,
1398 * and if application hit its sndbuf limit recently.
1400 static void tcp_cwnd_application_limited(struct sock
*sk
)
1402 struct tcp_sock
*tp
= tcp_sk(sk
);
1404 if (inet_csk(sk
)->icsk_ca_state
== TCP_CA_Open
&&
1405 sk
->sk_socket
&& !test_bit(SOCK_NOSPACE
, &sk
->sk_socket
->flags
)) {
1406 /* Limited by application or receiver window. */
1407 u32 init_win
= tcp_init_cwnd(tp
, __sk_dst_get(sk
));
1408 u32 win_used
= max(tp
->snd_cwnd_used
, init_win
);
1409 if (win_used
< tp
->snd_cwnd
) {
1410 tp
->snd_ssthresh
= tcp_current_ssthresh(sk
);
1411 tp
->snd_cwnd
= (tp
->snd_cwnd
+ win_used
) >> 1;
1413 tp
->snd_cwnd_used
= 0;
1415 tp
->snd_cwnd_stamp
= tcp_time_stamp
;
1418 static void tcp_cwnd_validate(struct sock
*sk
, bool is_cwnd_limited
)
1420 struct tcp_sock
*tp
= tcp_sk(sk
);
1422 /* Track the maximum number of outstanding packets in each
1423 * window, and remember whether we were cwnd-limited then.
1425 if (!before(tp
->snd_una
, tp
->max_packets_seq
) ||
1426 tp
->packets_out
> tp
->max_packets_out
) {
1427 tp
->max_packets_out
= tp
->packets_out
;
1428 tp
->max_packets_seq
= tp
->snd_nxt
;
1429 tp
->is_cwnd_limited
= is_cwnd_limited
;
1432 if (tcp_is_cwnd_limited(sk
)) {
1433 /* Network is feed fully. */
1434 tp
->snd_cwnd_used
= 0;
1435 tp
->snd_cwnd_stamp
= tcp_time_stamp
;
1437 /* Network starves. */
1438 if (tp
->packets_out
> tp
->snd_cwnd_used
)
1439 tp
->snd_cwnd_used
= tp
->packets_out
;
1441 if (sysctl_tcp_slow_start_after_idle
&&
1442 (s32
)(tcp_time_stamp
- tp
->snd_cwnd_stamp
) >= inet_csk(sk
)->icsk_rto
)
1443 tcp_cwnd_application_limited(sk
);
1447 /* Minshall's variant of the Nagle send check. */
1448 static bool tcp_minshall_check(const struct tcp_sock
*tp
)
1450 return after(tp
->snd_sml
, tp
->snd_una
) &&
1451 !after(tp
->snd_sml
, tp
->snd_nxt
);
1454 /* Update snd_sml if this skb is under mss
1455 * Note that a TSO packet might end with a sub-mss segment
1456 * The test is really :
1457 * if ((skb->len % mss) != 0)
1458 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1459 * But we can avoid doing the divide again given we already have
1460 * skb_pcount = skb->len / mss_now
1462 static void tcp_minshall_update(struct tcp_sock
*tp
, unsigned int mss_now
,
1463 const struct sk_buff
*skb
)
1465 if (skb
->len
< tcp_skb_pcount(skb
) * mss_now
)
1466 tp
->snd_sml
= TCP_SKB_CB(skb
)->end_seq
;
1469 /* Return false, if packet can be sent now without violation Nagle's rules:
1470 * 1. It is full sized. (provided by caller in %partial bool)
1471 * 2. Or it contains FIN. (already checked by caller)
1472 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1473 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1474 * With Minshall's modification: all sent small packets are ACKed.
1476 static bool tcp_nagle_check(bool partial
, const struct tcp_sock
*tp
,
1480 ((nonagle
& TCP_NAGLE_CORK
) ||
1481 (!nonagle
&& tp
->packets_out
&& tcp_minshall_check(tp
)));
1483 /* Returns the portion of skb which can be sent right away */
1484 static unsigned int tcp_mss_split_point(const struct sock
*sk
,
1485 const struct sk_buff
*skb
,
1486 unsigned int mss_now
,
1487 unsigned int max_segs
,
1490 const struct tcp_sock
*tp
= tcp_sk(sk
);
1491 u32 partial
, needed
, window
, max_len
;
1493 window
= tcp_wnd_end(tp
) - TCP_SKB_CB(skb
)->seq
;
1494 max_len
= mss_now
* max_segs
;
1496 if (likely(max_len
<= window
&& skb
!= tcp_write_queue_tail(sk
)))
1499 needed
= min(skb
->len
, window
);
1501 if (max_len
<= needed
)
1504 partial
= needed
% mss_now
;
1505 /* If last segment is not a full MSS, check if Nagle rules allow us
1506 * to include this last segment in this skb.
1507 * Otherwise, we'll split the skb at last MSS boundary
1509 if (tcp_nagle_check(partial
!= 0, tp
, nonagle
))
1510 return needed
- partial
;
1515 /* Can at least one segment of SKB be sent right now, according to the
1516 * congestion window rules? If so, return how many segments are allowed.
1518 static inline unsigned int tcp_cwnd_test(const struct tcp_sock
*tp
,
1519 const struct sk_buff
*skb
)
1521 u32 in_flight
, cwnd
;
1523 /* Don't be strict about the congestion window for the final FIN. */
1524 if ((TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_FIN
) &&
1525 tcp_skb_pcount(skb
) == 1)
1528 in_flight
= tcp_packets_in_flight(tp
);
1529 cwnd
= tp
->snd_cwnd
;
1530 if (in_flight
< cwnd
)
1531 return (cwnd
- in_flight
);
1536 /* Initialize TSO state of a skb.
1537 * This must be invoked the first time we consider transmitting
1538 * SKB onto the wire.
1540 static int tcp_init_tso_segs(const struct sock
*sk
, struct sk_buff
*skb
,
1541 unsigned int mss_now
)
1543 int tso_segs
= tcp_skb_pcount(skb
);
1545 if (!tso_segs
|| (tso_segs
> 1 && tcp_skb_mss(skb
) != mss_now
)) {
1546 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1547 tso_segs
= tcp_skb_pcount(skb
);
1553 /* Return true if the Nagle test allows this packet to be
1556 static inline bool tcp_nagle_test(const struct tcp_sock
*tp
, const struct sk_buff
*skb
,
1557 unsigned int cur_mss
, int nonagle
)
1559 /* Nagle rule does not apply to frames, which sit in the middle of the
1560 * write_queue (they have no chances to get new data).
1562 * This is implemented in the callers, where they modify the 'nonagle'
1563 * argument based upon the location of SKB in the send queue.
1565 if (nonagle
& TCP_NAGLE_PUSH
)
1568 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1569 if (tcp_urg_mode(tp
) || (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_FIN
))
1572 if (!tcp_nagle_check(skb
->len
< cur_mss
, tp
, nonagle
))
1578 /* Does at least the first segment of SKB fit into the send window? */
1579 static bool tcp_snd_wnd_test(const struct tcp_sock
*tp
,
1580 const struct sk_buff
*skb
,
1581 unsigned int cur_mss
)
1583 u32 end_seq
= TCP_SKB_CB(skb
)->end_seq
;
1585 if (skb
->len
> cur_mss
)
1586 end_seq
= TCP_SKB_CB(skb
)->seq
+ cur_mss
;
1588 return !after(end_seq
, tcp_wnd_end(tp
));
1591 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1592 * should be put on the wire right now. If so, it returns the number of
1593 * packets allowed by the congestion window.
1595 static unsigned int tcp_snd_test(const struct sock
*sk
, struct sk_buff
*skb
,
1596 unsigned int cur_mss
, int nonagle
)
1598 const struct tcp_sock
*tp
= tcp_sk(sk
);
1599 unsigned int cwnd_quota
;
1601 tcp_init_tso_segs(sk
, skb
, cur_mss
);
1603 if (!tcp_nagle_test(tp
, skb
, cur_mss
, nonagle
))
1606 cwnd_quota
= tcp_cwnd_test(tp
, skb
);
1607 if (cwnd_quota
&& !tcp_snd_wnd_test(tp
, skb
, cur_mss
))
1613 /* Test if sending is allowed right now. */
1614 bool tcp_may_send_now(struct sock
*sk
)
1616 const struct tcp_sock
*tp
= tcp_sk(sk
);
1617 struct sk_buff
*skb
= tcp_send_head(sk
);
1620 tcp_snd_test(sk
, skb
, tcp_current_mss(sk
),
1621 (tcp_skb_is_last(sk
, skb
) ?
1622 tp
->nonagle
: TCP_NAGLE_PUSH
));
1625 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1626 * which is put after SKB on the list. It is very much like
1627 * tcp_fragment() except that it may make several kinds of assumptions
1628 * in order to speed up the splitting operation. In particular, we
1629 * know that all the data is in scatter-gather pages, and that the
1630 * packet has never been sent out before (and thus is not cloned).
1632 static int tso_fragment(struct sock
*sk
, struct sk_buff
*skb
, unsigned int len
,
1633 unsigned int mss_now
, gfp_t gfp
)
1635 struct sk_buff
*buff
;
1636 int nlen
= skb
->len
- len
;
1639 /* All of a TSO frame must be composed of paged data. */
1640 if (skb
->len
!= skb
->data_len
)
1641 return tcp_fragment(sk
, skb
, len
, mss_now
, gfp
);
1643 buff
= sk_stream_alloc_skb(sk
, 0, gfp
);
1644 if (unlikely(buff
== NULL
))
1647 sk
->sk_wmem_queued
+= buff
->truesize
;
1648 sk_mem_charge(sk
, buff
->truesize
);
1649 buff
->truesize
+= nlen
;
1650 skb
->truesize
-= nlen
;
1652 /* Correct the sequence numbers. */
1653 TCP_SKB_CB(buff
)->seq
= TCP_SKB_CB(skb
)->seq
+ len
;
1654 TCP_SKB_CB(buff
)->end_seq
= TCP_SKB_CB(skb
)->end_seq
;
1655 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(buff
)->seq
;
1657 /* PSH and FIN should only be set in the second packet. */
1658 flags
= TCP_SKB_CB(skb
)->tcp_flags
;
1659 TCP_SKB_CB(skb
)->tcp_flags
= flags
& ~(TCPHDR_FIN
| TCPHDR_PSH
);
1660 TCP_SKB_CB(buff
)->tcp_flags
= flags
;
1662 /* This packet was never sent out yet, so no SACK bits. */
1663 TCP_SKB_CB(buff
)->sacked
= 0;
1665 buff
->ip_summed
= skb
->ip_summed
= CHECKSUM_PARTIAL
;
1666 skb_split(skb
, buff
, len
);
1667 tcp_fragment_tstamp(skb
, buff
);
1669 /* Fix up tso_factor for both original and new SKB. */
1670 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1671 tcp_set_skb_tso_segs(sk
, buff
, mss_now
);
1673 /* Link BUFF into the send queue. */
1674 skb_header_release(buff
);
1675 tcp_insert_write_queue_after(skb
, buff
, sk
);
1680 /* Try to defer sending, if possible, in order to minimize the amount
1681 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1683 * This algorithm is from John Heffner.
1685 static bool tcp_tso_should_defer(struct sock
*sk
, struct sk_buff
*skb
,
1686 bool *is_cwnd_limited
)
1688 struct tcp_sock
*tp
= tcp_sk(sk
);
1689 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
1690 u32 send_win
, cong_win
, limit
, in_flight
;
1693 if (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_FIN
)
1696 if (icsk
->icsk_ca_state
!= TCP_CA_Open
)
1699 /* Defer for less than two clock ticks. */
1700 if (tp
->tso_deferred
&&
1701 (((u32
)jiffies
<< 1) >> 1) - (tp
->tso_deferred
>> 1) > 1)
1704 in_flight
= tcp_packets_in_flight(tp
);
1706 BUG_ON(tcp_skb_pcount(skb
) <= 1 || (tp
->snd_cwnd
<= in_flight
));
1708 send_win
= tcp_wnd_end(tp
) - TCP_SKB_CB(skb
)->seq
;
1710 /* From in_flight test above, we know that cwnd > in_flight. */
1711 cong_win
= (tp
->snd_cwnd
- in_flight
) * tp
->mss_cache
;
1713 limit
= min(send_win
, cong_win
);
1715 /* If a full-sized TSO skb can be sent, do it. */
1716 if (limit
>= min_t(unsigned int, sk
->sk_gso_max_size
,
1717 tp
->xmit_size_goal_segs
* tp
->mss_cache
))
1720 /* Middle in queue won't get any more data, full sendable already? */
1721 if ((skb
!= tcp_write_queue_tail(sk
)) && (limit
>= skb
->len
))
1724 win_divisor
= ACCESS_ONCE(sysctl_tcp_tso_win_divisor
);
1726 u32 chunk
= min(tp
->snd_wnd
, tp
->snd_cwnd
* tp
->mss_cache
);
1728 /* If at least some fraction of a window is available,
1731 chunk
/= win_divisor
;
1735 /* Different approach, try not to defer past a single
1736 * ACK. Receiver should ACK every other full sized
1737 * frame, so if we have space for more than 3 frames
1740 if (limit
> tcp_max_tso_deferred_mss(tp
) * tp
->mss_cache
)
1744 /* Ok, it looks like it is advisable to defer.
1745 * Do not rearm the timer if already set to not break TCP ACK clocking.
1747 if (!tp
->tso_deferred
)
1748 tp
->tso_deferred
= 1 | (jiffies
<< 1);
1750 if (cong_win
< send_win
&& cong_win
< skb
->len
)
1751 *is_cwnd_limited
= true;
1756 tp
->tso_deferred
= 0;
1760 /* Create a new MTU probe if we are ready.
1761 * MTU probe is regularly attempting to increase the path MTU by
1762 * deliberately sending larger packets. This discovers routing
1763 * changes resulting in larger path MTUs.
1765 * Returns 0 if we should wait to probe (no cwnd available),
1766 * 1 if a probe was sent,
1769 static int tcp_mtu_probe(struct sock
*sk
)
1771 struct tcp_sock
*tp
= tcp_sk(sk
);
1772 struct inet_connection_sock
*icsk
= inet_csk(sk
);
1773 struct sk_buff
*skb
, *nskb
, *next
;
1780 /* Not currently probing/verifying,
1782 * have enough cwnd, and
1783 * not SACKing (the variable headers throw things off) */
1784 if (!icsk
->icsk_mtup
.enabled
||
1785 icsk
->icsk_mtup
.probe_size
||
1786 inet_csk(sk
)->icsk_ca_state
!= TCP_CA_Open
||
1787 tp
->snd_cwnd
< 11 ||
1788 tp
->rx_opt
.num_sacks
|| tp
->rx_opt
.dsack
)
1791 /* Very simple search strategy: just double the MSS. */
1792 mss_now
= tcp_current_mss(sk
);
1793 probe_size
= 2 * tp
->mss_cache
;
1794 size_needed
= probe_size
+ (tp
->reordering
+ 1) * tp
->mss_cache
;
1795 if (probe_size
> tcp_mtu_to_mss(sk
, icsk
->icsk_mtup
.search_high
)) {
1796 /* TODO: set timer for probe_converge_event */
1800 /* Have enough data in the send queue to probe? */
1801 if (tp
->write_seq
- tp
->snd_nxt
< size_needed
)
1804 if (tp
->snd_wnd
< size_needed
)
1806 if (after(tp
->snd_nxt
+ size_needed
, tcp_wnd_end(tp
)))
1809 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1810 if (tcp_packets_in_flight(tp
) + 2 > tp
->snd_cwnd
) {
1811 if (!tcp_packets_in_flight(tp
))
1817 /* We're allowed to probe. Build it now. */
1818 if ((nskb
= sk_stream_alloc_skb(sk
, probe_size
, GFP_ATOMIC
)) == NULL
)
1820 sk
->sk_wmem_queued
+= nskb
->truesize
;
1821 sk_mem_charge(sk
, nskb
->truesize
);
1823 skb
= tcp_send_head(sk
);
1825 TCP_SKB_CB(nskb
)->seq
= TCP_SKB_CB(skb
)->seq
;
1826 TCP_SKB_CB(nskb
)->end_seq
= TCP_SKB_CB(skb
)->seq
+ probe_size
;
1827 TCP_SKB_CB(nskb
)->tcp_flags
= TCPHDR_ACK
;
1828 TCP_SKB_CB(nskb
)->sacked
= 0;
1830 nskb
->ip_summed
= skb
->ip_summed
;
1832 tcp_insert_write_queue_before(nskb
, skb
, sk
);
1835 tcp_for_write_queue_from_safe(skb
, next
, sk
) {
1836 copy
= min_t(int, skb
->len
, probe_size
- len
);
1837 if (nskb
->ip_summed
)
1838 skb_copy_bits(skb
, 0, skb_put(nskb
, copy
), copy
);
1840 nskb
->csum
= skb_copy_and_csum_bits(skb
, 0,
1841 skb_put(nskb
, copy
),
1844 if (skb
->len
<= copy
) {
1845 /* We've eaten all the data from this skb.
1847 TCP_SKB_CB(nskb
)->tcp_flags
|= TCP_SKB_CB(skb
)->tcp_flags
;
1848 tcp_unlink_write_queue(skb
, sk
);
1849 sk_wmem_free_skb(sk
, skb
);
1851 TCP_SKB_CB(nskb
)->tcp_flags
|= TCP_SKB_CB(skb
)->tcp_flags
&
1852 ~(TCPHDR_FIN
|TCPHDR_PSH
);
1853 if (!skb_shinfo(skb
)->nr_frags
) {
1854 skb_pull(skb
, copy
);
1855 if (skb
->ip_summed
!= CHECKSUM_PARTIAL
)
1856 skb
->csum
= csum_partial(skb
->data
,
1859 __pskb_trim_head(skb
, copy
);
1860 tcp_set_skb_tso_segs(sk
, skb
, mss_now
);
1862 TCP_SKB_CB(skb
)->seq
+= copy
;
1867 if (len
>= probe_size
)
1870 tcp_init_tso_segs(sk
, nskb
, nskb
->len
);
1872 /* We're ready to send. If this fails, the probe will
1873 * be resegmented into mss-sized pieces by tcp_write_xmit().
1875 if (!tcp_transmit_skb(sk
, nskb
, 1, GFP_ATOMIC
)) {
1876 /* Decrement cwnd here because we are sending
1877 * effectively two packets. */
1879 tcp_event_new_data_sent(sk
, nskb
);
1881 icsk
->icsk_mtup
.probe_size
= tcp_mss_to_mtu(sk
, nskb
->len
);
1882 tp
->mtu_probe
.probe_seq_start
= TCP_SKB_CB(nskb
)->seq
;
1883 tp
->mtu_probe
.probe_seq_end
= TCP_SKB_CB(nskb
)->end_seq
;
1891 /* This routine writes packets to the network. It advances the
1892 * send_head. This happens as incoming acks open up the remote
1895 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1896 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1897 * account rare use of URG, this is not a big flaw.
1899 * Send at most one packet when push_one > 0. Temporarily ignore
1900 * cwnd limit to force at most one packet out when push_one == 2.
1902 * Returns true, if no segments are in flight and we have queued segments,
1903 * but cannot send anything now because of SWS or another problem.
1905 static bool tcp_write_xmit(struct sock
*sk
, unsigned int mss_now
, int nonagle
,
1906 int push_one
, gfp_t gfp
)
1908 struct tcp_sock
*tp
= tcp_sk(sk
);
1909 struct sk_buff
*skb
;
1910 unsigned int tso_segs
, sent_pkts
;
1913 bool is_cwnd_limited
= false;
1918 /* Do MTU probing. */
1919 result
= tcp_mtu_probe(sk
);
1922 } else if (result
> 0) {
1927 while ((skb
= tcp_send_head(sk
))) {
1930 tso_segs
= tcp_init_tso_segs(sk
, skb
, mss_now
);
1933 if (unlikely(tp
->repair
) && tp
->repair_queue
== TCP_SEND_QUEUE
) {
1934 /* "skb_mstamp" is used as a start point for the retransmit timer */
1935 skb_mstamp_get(&skb
->skb_mstamp
);
1936 goto repair
; /* Skip network transmission */
1939 cwnd_quota
= tcp_cwnd_test(tp
, skb
);
1941 is_cwnd_limited
= true;
1943 /* Force out a loss probe pkt. */
1949 if (unlikely(!tcp_snd_wnd_test(tp
, skb
, mss_now
)))
1952 if (tso_segs
== 1) {
1953 if (unlikely(!tcp_nagle_test(tp
, skb
, mss_now
,
1954 (tcp_skb_is_last(sk
, skb
) ?
1955 nonagle
: TCP_NAGLE_PUSH
))))
1959 tcp_tso_should_defer(sk
, skb
, &is_cwnd_limited
))
1963 /* TCP Small Queues :
1964 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
1966 * - better RTT estimation and ACK scheduling
1969 * Alas, some drivers / subsystems require a fair amount
1970 * of queued bytes to ensure line rate.
1971 * One example is wifi aggregation (802.11 AMPDU)
1973 limit
= max_t(unsigned int, sysctl_tcp_limit_output_bytes
,
1974 sk
->sk_pacing_rate
>> 10);
1976 if (atomic_read(&sk
->sk_wmem_alloc
) > limit
) {
1977 set_bit(TSQ_THROTTLED
, &tp
->tsq_flags
);
1978 /* It is possible TX completion already happened
1979 * before we set TSQ_THROTTLED, so we must
1980 * test again the condition.
1982 smp_mb__after_atomic();
1983 if (atomic_read(&sk
->sk_wmem_alloc
) > limit
)
1988 if (tso_segs
> 1 && !tcp_urg_mode(tp
))
1989 limit
= tcp_mss_split_point(sk
, skb
, mss_now
,
1992 sk
->sk_gso_max_segs
),
1995 if (skb
->len
> limit
&&
1996 unlikely(tso_fragment(sk
, skb
, limit
, mss_now
, gfp
)))
1999 if (unlikely(tcp_transmit_skb(sk
, skb
, 1, gfp
)))
2003 /* Advance the send_head. This one is sent out.
2004 * This call will increment packets_out.
2006 tcp_event_new_data_sent(sk
, skb
);
2008 tcp_minshall_update(tp
, mss_now
, skb
);
2009 sent_pkts
+= tcp_skb_pcount(skb
);
2015 if (likely(sent_pkts
)) {
2016 if (tcp_in_cwnd_reduction(sk
))
2017 tp
->prr_out
+= sent_pkts
;
2019 /* Send one loss probe per tail loss episode. */
2021 tcp_schedule_loss_probe(sk
);
2022 tcp_cwnd_validate(sk
, is_cwnd_limited
);
2025 return (push_one
== 2) || (!tp
->packets_out
&& tcp_send_head(sk
));
2028 bool tcp_schedule_loss_probe(struct sock
*sk
)
2030 struct inet_connection_sock
*icsk
= inet_csk(sk
);
2031 struct tcp_sock
*tp
= tcp_sk(sk
);
2032 u32 timeout
, tlp_time_stamp
, rto_time_stamp
;
2033 u32 rtt
= usecs_to_jiffies(tp
->srtt_us
>> 3);
2035 if (WARN_ON(icsk
->icsk_pending
== ICSK_TIME_EARLY_RETRANS
))
2037 /* No consecutive loss probes. */
2038 if (WARN_ON(icsk
->icsk_pending
== ICSK_TIME_LOSS_PROBE
)) {
2042 /* Don't do any loss probe on a Fast Open connection before 3WHS
2045 if (sk
->sk_state
== TCP_SYN_RECV
)
2048 /* TLP is only scheduled when next timer event is RTO. */
2049 if (icsk
->icsk_pending
!= ICSK_TIME_RETRANS
)
2052 /* Schedule a loss probe in 2*RTT for SACK capable connections
2053 * in Open state, that are either limited by cwnd or application.
2055 if (sysctl_tcp_early_retrans
< 3 || !tp
->srtt_us
|| !tp
->packets_out
||
2056 !tcp_is_sack(tp
) || inet_csk(sk
)->icsk_ca_state
!= TCP_CA_Open
)
2059 if ((tp
->snd_cwnd
> tcp_packets_in_flight(tp
)) &&
2063 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2064 * for delayed ack when there's one outstanding packet.
2067 if (tp
->packets_out
== 1)
2068 timeout
= max_t(u32
, timeout
,
2069 (rtt
+ (rtt
>> 1) + TCP_DELACK_MAX
));
2070 timeout
= max_t(u32
, timeout
, msecs_to_jiffies(10));
2072 /* If RTO is shorter, just schedule TLP in its place. */
2073 tlp_time_stamp
= tcp_time_stamp
+ timeout
;
2074 rto_time_stamp
= (u32
)inet_csk(sk
)->icsk_timeout
;
2075 if ((s32
)(tlp_time_stamp
- rto_time_stamp
) > 0) {
2076 s32 delta
= rto_time_stamp
- tcp_time_stamp
;
2081 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_LOSS_PROBE
, timeout
,
2086 /* Thanks to skb fast clones, we can detect if a prior transmit of
2087 * a packet is still in a qdisc or driver queue.
2088 * In this case, there is very little point doing a retransmit !
2089 * Note: This is called from BH context only.
2091 static bool skb_still_in_host_queue(const struct sock
*sk
,
2092 const struct sk_buff
*skb
)
2094 const struct sk_buff
*fclone
= skb
+ 1;
2096 if (unlikely(skb
->fclone
== SKB_FCLONE_ORIG
&&
2097 fclone
->fclone
== SKB_FCLONE_CLONE
)) {
2098 NET_INC_STATS_BH(sock_net(sk
),
2099 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES
);
2105 /* When probe timeout (PTO) fires, send a new segment if one exists, else
2106 * retransmit the last segment.
2108 void tcp_send_loss_probe(struct sock
*sk
)
2110 struct tcp_sock
*tp
= tcp_sk(sk
);
2111 struct sk_buff
*skb
;
2113 int mss
= tcp_current_mss(sk
);
2116 if (tcp_send_head(sk
) != NULL
) {
2117 err
= tcp_write_xmit(sk
, mss
, TCP_NAGLE_OFF
, 2, GFP_ATOMIC
);
2121 /* At most one outstanding TLP retransmission. */
2122 if (tp
->tlp_high_seq
)
2125 /* Retransmit last segment. */
2126 skb
= tcp_write_queue_tail(sk
);
2130 if (skb_still_in_host_queue(sk
, skb
))
2133 pcount
= tcp_skb_pcount(skb
);
2134 if (WARN_ON(!pcount
))
2137 if ((pcount
> 1) && (skb
->len
> (pcount
- 1) * mss
)) {
2138 if (unlikely(tcp_fragment(sk
, skb
, (pcount
- 1) * mss
, mss
,
2141 skb
= tcp_write_queue_tail(sk
);
2144 if (WARN_ON(!skb
|| !tcp_skb_pcount(skb
)))
2147 err
= __tcp_retransmit_skb(sk
, skb
);
2149 /* Record snd_nxt for loss detection. */
2151 tp
->tlp_high_seq
= tp
->snd_nxt
;
2154 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
2155 inet_csk(sk
)->icsk_rto
,
2159 NET_INC_STATS_BH(sock_net(sk
),
2160 LINUX_MIB_TCPLOSSPROBES
);
2163 /* Push out any pending frames which were held back due to
2164 * TCP_CORK or attempt at coalescing tiny packets.
2165 * The socket must be locked by the caller.
2167 void __tcp_push_pending_frames(struct sock
*sk
, unsigned int cur_mss
,
2170 /* If we are closed, the bytes will have to remain here.
2171 * In time closedown will finish, we empty the write queue and
2172 * all will be happy.
2174 if (unlikely(sk
->sk_state
== TCP_CLOSE
))
2177 if (tcp_write_xmit(sk
, cur_mss
, nonagle
, 0,
2178 sk_gfp_atomic(sk
, GFP_ATOMIC
)))
2179 tcp_check_probe_timer(sk
);
2182 /* Send _single_ skb sitting at the send head. This function requires
2183 * true push pending frames to setup probe timer etc.
2185 void tcp_push_one(struct sock
*sk
, unsigned int mss_now
)
2187 struct sk_buff
*skb
= tcp_send_head(sk
);
2189 BUG_ON(!skb
|| skb
->len
< mss_now
);
2191 tcp_write_xmit(sk
, mss_now
, TCP_NAGLE_PUSH
, 1, sk
->sk_allocation
);
2194 /* This function returns the amount that we can raise the
2195 * usable window based on the following constraints
2197 * 1. The window can never be shrunk once it is offered (RFC 793)
2198 * 2. We limit memory per socket
2201 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2202 * RECV.NEXT + RCV.WIN fixed until:
2203 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2205 * i.e. don't raise the right edge of the window until you can raise
2206 * it at least MSS bytes.
2208 * Unfortunately, the recommended algorithm breaks header prediction,
2209 * since header prediction assumes th->window stays fixed.
2211 * Strictly speaking, keeping th->window fixed violates the receiver
2212 * side SWS prevention criteria. The problem is that under this rule
2213 * a stream of single byte packets will cause the right side of the
2214 * window to always advance by a single byte.
2216 * Of course, if the sender implements sender side SWS prevention
2217 * then this will not be a problem.
2219 * BSD seems to make the following compromise:
2221 * If the free space is less than the 1/4 of the maximum
2222 * space available and the free space is less than 1/2 mss,
2223 * then set the window to 0.
2224 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2225 * Otherwise, just prevent the window from shrinking
2226 * and from being larger than the largest representable value.
2228 * This prevents incremental opening of the window in the regime
2229 * where TCP is limited by the speed of the reader side taking
2230 * data out of the TCP receive queue. It does nothing about
2231 * those cases where the window is constrained on the sender side
2232 * because the pipeline is full.
2234 * BSD also seems to "accidentally" limit itself to windows that are a
2235 * multiple of MSS, at least until the free space gets quite small.
2236 * This would appear to be a side effect of the mbuf implementation.
2237 * Combining these two algorithms results in the observed behavior
2238 * of having a fixed window size at almost all times.
2240 * Below we obtain similar behavior by forcing the offered window to
2241 * a multiple of the mss when it is feasible to do so.
2243 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2244 * Regular options like TIMESTAMP are taken into account.
2246 u32
__tcp_select_window(struct sock
*sk
)
2248 struct inet_connection_sock
*icsk
= inet_csk(sk
);
2249 struct tcp_sock
*tp
= tcp_sk(sk
);
2250 /* MSS for the peer's data. Previous versions used mss_clamp
2251 * here. I don't know if the value based on our guesses
2252 * of peer's MSS is better for the performance. It's more correct
2253 * but may be worse for the performance because of rcv_mss
2254 * fluctuations. --SAW 1998/11/1
2256 int mss
= icsk
->icsk_ack
.rcv_mss
;
2257 int free_space
= tcp_space(sk
);
2258 int allowed_space
= tcp_full_space(sk
);
2259 int full_space
= min_t(int, tp
->window_clamp
, allowed_space
);
2262 if (mss
> full_space
)
2265 if (free_space
< (full_space
>> 1)) {
2266 icsk
->icsk_ack
.quick
= 0;
2268 if (sk_under_memory_pressure(sk
))
2269 tp
->rcv_ssthresh
= min(tp
->rcv_ssthresh
,
2272 /* free_space might become our new window, make sure we don't
2273 * increase it due to wscale.
2275 free_space
= round_down(free_space
, 1 << tp
->rx_opt
.rcv_wscale
);
2277 /* if free space is less than mss estimate, or is below 1/16th
2278 * of the maximum allowed, try to move to zero-window, else
2279 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2280 * new incoming data is dropped due to memory limits.
2281 * With large window, mss test triggers way too late in order
2282 * to announce zero window in time before rmem limit kicks in.
2284 if (free_space
< (allowed_space
>> 4) || free_space
< mss
)
2288 if (free_space
> tp
->rcv_ssthresh
)
2289 free_space
= tp
->rcv_ssthresh
;
2291 /* Don't do rounding if we are using window scaling, since the
2292 * scaled window will not line up with the MSS boundary anyway.
2294 window
= tp
->rcv_wnd
;
2295 if (tp
->rx_opt
.rcv_wscale
) {
2296 window
= free_space
;
2298 /* Advertise enough space so that it won't get scaled away.
2299 * Import case: prevent zero window announcement if
2300 * 1<<rcv_wscale > mss.
2302 if (((window
>> tp
->rx_opt
.rcv_wscale
) << tp
->rx_opt
.rcv_wscale
) != window
)
2303 window
= (((window
>> tp
->rx_opt
.rcv_wscale
) + 1)
2304 << tp
->rx_opt
.rcv_wscale
);
2306 /* Get the largest window that is a nice multiple of mss.
2307 * Window clamp already applied above.
2308 * If our current window offering is within 1 mss of the
2309 * free space we just keep it. This prevents the divide
2310 * and multiply from happening most of the time.
2311 * We also don't do any window rounding when the free space
2314 if (window
<= free_space
- mss
|| window
> free_space
)
2315 window
= (free_space
/ mss
) * mss
;
2316 else if (mss
== full_space
&&
2317 free_space
> window
+ (full_space
>> 1))
2318 window
= free_space
;
2324 /* Collapses two adjacent SKB's during retransmission. */
2325 static void tcp_collapse_retrans(struct sock
*sk
, struct sk_buff
*skb
)
2327 struct tcp_sock
*tp
= tcp_sk(sk
);
2328 struct sk_buff
*next_skb
= tcp_write_queue_next(sk
, skb
);
2329 int skb_size
, next_skb_size
;
2331 skb_size
= skb
->len
;
2332 next_skb_size
= next_skb
->len
;
2334 BUG_ON(tcp_skb_pcount(skb
) != 1 || tcp_skb_pcount(next_skb
) != 1);
2336 tcp_highest_sack_combine(sk
, next_skb
, skb
);
2338 tcp_unlink_write_queue(next_skb
, sk
);
2340 skb_copy_from_linear_data(next_skb
, skb_put(skb
, next_skb_size
),
2343 if (next_skb
->ip_summed
== CHECKSUM_PARTIAL
)
2344 skb
->ip_summed
= CHECKSUM_PARTIAL
;
2346 if (skb
->ip_summed
!= CHECKSUM_PARTIAL
)
2347 skb
->csum
= csum_block_add(skb
->csum
, next_skb
->csum
, skb_size
);
2349 /* Update sequence range on original skb. */
2350 TCP_SKB_CB(skb
)->end_seq
= TCP_SKB_CB(next_skb
)->end_seq
;
2352 /* Merge over control information. This moves PSH/FIN etc. over */
2353 TCP_SKB_CB(skb
)->tcp_flags
|= TCP_SKB_CB(next_skb
)->tcp_flags
;
2355 /* All done, get rid of second SKB and account for it so
2356 * packet counting does not break.
2358 TCP_SKB_CB(skb
)->sacked
|= TCP_SKB_CB(next_skb
)->sacked
& TCPCB_EVER_RETRANS
;
2360 /* changed transmit queue under us so clear hints */
2361 tcp_clear_retrans_hints_partial(tp
);
2362 if (next_skb
== tp
->retransmit_skb_hint
)
2363 tp
->retransmit_skb_hint
= skb
;
2365 tcp_adjust_pcount(sk
, next_skb
, tcp_skb_pcount(next_skb
));
2367 sk_wmem_free_skb(sk
, next_skb
);
2370 /* Check if coalescing SKBs is legal. */
2371 static bool tcp_can_collapse(const struct sock
*sk
, const struct sk_buff
*skb
)
2373 if (tcp_skb_pcount(skb
) > 1)
2375 /* TODO: SACK collapsing could be used to remove this condition */
2376 if (skb_shinfo(skb
)->nr_frags
!= 0)
2378 if (skb_cloned(skb
))
2380 if (skb
== tcp_send_head(sk
))
2382 /* Some heurestics for collapsing over SACK'd could be invented */
2383 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_ACKED
)
2389 /* Collapse packets in the retransmit queue to make to create
2390 * less packets on the wire. This is only done on retransmission.
2392 static void tcp_retrans_try_collapse(struct sock
*sk
, struct sk_buff
*to
,
2395 struct tcp_sock
*tp
= tcp_sk(sk
);
2396 struct sk_buff
*skb
= to
, *tmp
;
2399 if (!sysctl_tcp_retrans_collapse
)
2401 if (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_SYN
)
2404 tcp_for_write_queue_from_safe(skb
, tmp
, sk
) {
2405 if (!tcp_can_collapse(sk
, skb
))
2417 /* Punt if not enough space exists in the first SKB for
2418 * the data in the second
2420 if (skb
->len
> skb_availroom(to
))
2423 if (after(TCP_SKB_CB(skb
)->end_seq
, tcp_wnd_end(tp
)))
2426 tcp_collapse_retrans(sk
, to
);
2430 /* This retransmits one SKB. Policy decisions and retransmit queue
2431 * state updates are done by the caller. Returns non-zero if an
2432 * error occurred which prevented the send.
2434 int __tcp_retransmit_skb(struct sock
*sk
, struct sk_buff
*skb
)
2436 struct tcp_sock
*tp
= tcp_sk(sk
);
2437 struct inet_connection_sock
*icsk
= inet_csk(sk
);
2438 unsigned int cur_mss
;
2441 /* Inconslusive MTU probe */
2442 if (icsk
->icsk_mtup
.probe_size
) {
2443 icsk
->icsk_mtup
.probe_size
= 0;
2446 /* Do not sent more than we queued. 1/4 is reserved for possible
2447 * copying overhead: fragmentation, tunneling, mangling etc.
2449 if (atomic_read(&sk
->sk_wmem_alloc
) >
2450 min(sk
->sk_wmem_queued
+ (sk
->sk_wmem_queued
>> 2), sk
->sk_sndbuf
))
2453 if (skb_still_in_host_queue(sk
, skb
))
2456 if (before(TCP_SKB_CB(skb
)->seq
, tp
->snd_una
)) {
2457 if (before(TCP_SKB_CB(skb
)->end_seq
, tp
->snd_una
))
2459 if (tcp_trim_head(sk
, skb
, tp
->snd_una
- TCP_SKB_CB(skb
)->seq
))
2463 if (inet_csk(sk
)->icsk_af_ops
->rebuild_header(sk
))
2464 return -EHOSTUNREACH
; /* Routing failure or similar. */
2466 cur_mss
= tcp_current_mss(sk
);
2468 /* If receiver has shrunk his window, and skb is out of
2469 * new window, do not retransmit it. The exception is the
2470 * case, when window is shrunk to zero. In this case
2471 * our retransmit serves as a zero window probe.
2473 if (!before(TCP_SKB_CB(skb
)->seq
, tcp_wnd_end(tp
)) &&
2474 TCP_SKB_CB(skb
)->seq
!= tp
->snd_una
)
2477 if (skb
->len
> cur_mss
) {
2478 if (tcp_fragment(sk
, skb
, cur_mss
, cur_mss
, GFP_ATOMIC
))
2479 return -ENOMEM
; /* We'll try again later. */
2481 int oldpcount
= tcp_skb_pcount(skb
);
2483 if (unlikely(oldpcount
> 1)) {
2484 if (skb_unclone(skb
, GFP_ATOMIC
))
2486 tcp_init_tso_segs(sk
, skb
, cur_mss
);
2487 tcp_adjust_pcount(sk
, skb
, oldpcount
- tcp_skb_pcount(skb
));
2491 tcp_retrans_try_collapse(sk
, skb
, cur_mss
);
2493 /* Make a copy, if the first transmission SKB clone we made
2494 * is still in somebody's hands, else make a clone.
2497 /* make sure skb->data is aligned on arches that require it
2498 * and check if ack-trimming & collapsing extended the headroom
2499 * beyond what csum_start can cover.
2501 if (unlikely((NET_IP_ALIGN
&& ((unsigned long)skb
->data
& 3)) ||
2502 skb_headroom(skb
) >= 0xFFFF)) {
2503 struct sk_buff
*nskb
= __pskb_copy(skb
, MAX_TCP_HEADER
,
2505 err
= nskb
? tcp_transmit_skb(sk
, nskb
, 0, GFP_ATOMIC
) :
2508 err
= tcp_transmit_skb(sk
, skb
, 1, GFP_ATOMIC
);
2512 TCP_SKB_CB(skb
)->sacked
|= TCPCB_EVER_RETRANS
;
2513 /* Update global TCP statistics. */
2514 TCP_INC_STATS(sock_net(sk
), TCP_MIB_RETRANSSEGS
);
2515 if (TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_SYN
)
2516 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPSYNRETRANS
);
2517 tp
->total_retrans
++;
2522 int tcp_retransmit_skb(struct sock
*sk
, struct sk_buff
*skb
)
2524 struct tcp_sock
*tp
= tcp_sk(sk
);
2525 int err
= __tcp_retransmit_skb(sk
, skb
);
2528 #if FASTRETRANS_DEBUG > 0
2529 if (TCP_SKB_CB(skb
)->sacked
& TCPCB_SACKED_RETRANS
) {
2530 net_dbg_ratelimited("retrans_out leaked\n");
2533 if (!tp
->retrans_out
)
2534 tp
->lost_retrans_low
= tp
->snd_nxt
;
2535 TCP_SKB_CB(skb
)->sacked
|= TCPCB_RETRANS
;
2536 tp
->retrans_out
+= tcp_skb_pcount(skb
);
2538 /* Save stamp of the first retransmit. */
2539 if (!tp
->retrans_stamp
)
2540 tp
->retrans_stamp
= tcp_skb_timestamp(skb
);
2542 /* snd_nxt is stored to detect loss of retransmitted segment,
2543 * see tcp_input.c tcp_sacktag_write_queue().
2545 TCP_SKB_CB(skb
)->ack_seq
= tp
->snd_nxt
;
2546 } else if (err
!= -EBUSY
) {
2547 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPRETRANSFAIL
);
2550 if (tp
->undo_retrans
< 0)
2551 tp
->undo_retrans
= 0;
2552 tp
->undo_retrans
+= tcp_skb_pcount(skb
);
2556 /* Check if we forward retransmits are possible in the current
2557 * window/congestion state.
2559 static bool tcp_can_forward_retransmit(struct sock
*sk
)
2561 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
2562 const struct tcp_sock
*tp
= tcp_sk(sk
);
2564 /* Forward retransmissions are possible only during Recovery. */
2565 if (icsk
->icsk_ca_state
!= TCP_CA_Recovery
)
2568 /* No forward retransmissions in Reno are possible. */
2569 if (tcp_is_reno(tp
))
2572 /* Yeah, we have to make difficult choice between forward transmission
2573 * and retransmission... Both ways have their merits...
2575 * For now we do not retransmit anything, while we have some new
2576 * segments to send. In the other cases, follow rule 3 for
2577 * NextSeg() specified in RFC3517.
2580 if (tcp_may_send_now(sk
))
2586 /* This gets called after a retransmit timeout, and the initially
2587 * retransmitted data is acknowledged. It tries to continue
2588 * resending the rest of the retransmit queue, until either
2589 * we've sent it all or the congestion window limit is reached.
2590 * If doing SACK, the first ACK which comes back for a timeout
2591 * based retransmit packet might feed us FACK information again.
2592 * If so, we use it to avoid unnecessarily retransmissions.
2594 void tcp_xmit_retransmit_queue(struct sock
*sk
)
2596 const struct inet_connection_sock
*icsk
= inet_csk(sk
);
2597 struct tcp_sock
*tp
= tcp_sk(sk
);
2598 struct sk_buff
*skb
;
2599 struct sk_buff
*hole
= NULL
;
2602 int fwd_rexmitting
= 0;
2604 if (!tp
->packets_out
)
2608 tp
->retransmit_high
= tp
->snd_una
;
2610 if (tp
->retransmit_skb_hint
) {
2611 skb
= tp
->retransmit_skb_hint
;
2612 last_lost
= TCP_SKB_CB(skb
)->end_seq
;
2613 if (after(last_lost
, tp
->retransmit_high
))
2614 last_lost
= tp
->retransmit_high
;
2616 skb
= tcp_write_queue_head(sk
);
2617 last_lost
= tp
->snd_una
;
2620 tcp_for_write_queue_from(skb
, sk
) {
2621 __u8 sacked
= TCP_SKB_CB(skb
)->sacked
;
2623 if (skb
== tcp_send_head(sk
))
2625 /* we could do better than to assign each time */
2627 tp
->retransmit_skb_hint
= skb
;
2629 /* Assume this retransmit will generate
2630 * only one packet for congestion window
2631 * calculation purposes. This works because
2632 * tcp_retransmit_skb() will chop up the
2633 * packet to be MSS sized and all the
2634 * packet counting works out.
2636 if (tcp_packets_in_flight(tp
) >= tp
->snd_cwnd
)
2639 if (fwd_rexmitting
) {
2641 if (!before(TCP_SKB_CB(skb
)->seq
, tcp_highest_sack_seq(tp
)))
2643 mib_idx
= LINUX_MIB_TCPFORWARDRETRANS
;
2645 } else if (!before(TCP_SKB_CB(skb
)->seq
, tp
->retransmit_high
)) {
2646 tp
->retransmit_high
= last_lost
;
2647 if (!tcp_can_forward_retransmit(sk
))
2649 /* Backtrack if necessary to non-L'ed skb */
2657 } else if (!(sacked
& TCPCB_LOST
)) {
2658 if (hole
== NULL
&& !(sacked
& (TCPCB_SACKED_RETRANS
|TCPCB_SACKED_ACKED
)))
2663 last_lost
= TCP_SKB_CB(skb
)->end_seq
;
2664 if (icsk
->icsk_ca_state
!= TCP_CA_Loss
)
2665 mib_idx
= LINUX_MIB_TCPFASTRETRANS
;
2667 mib_idx
= LINUX_MIB_TCPSLOWSTARTRETRANS
;
2670 if (sacked
& (TCPCB_SACKED_ACKED
|TCPCB_SACKED_RETRANS
))
2673 if (tcp_retransmit_skb(sk
, skb
))
2676 NET_INC_STATS_BH(sock_net(sk
), mib_idx
);
2678 if (tcp_in_cwnd_reduction(sk
))
2679 tp
->prr_out
+= tcp_skb_pcount(skb
);
2681 if (skb
== tcp_write_queue_head(sk
))
2682 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
2683 inet_csk(sk
)->icsk_rto
,
2688 /* Send a fin. The caller locks the socket for us. This cannot be
2689 * allowed to fail queueing a FIN frame under any circumstances.
2691 void tcp_send_fin(struct sock
*sk
)
2693 struct tcp_sock
*tp
= tcp_sk(sk
);
2694 struct sk_buff
*skb
= tcp_write_queue_tail(sk
);
2697 /* Optimization, tack on the FIN if we have a queue of
2698 * unsent frames. But be careful about outgoing SACKS
2701 mss_now
= tcp_current_mss(sk
);
2703 if (tcp_send_head(sk
) != NULL
) {
2704 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_FIN
;
2705 TCP_SKB_CB(skb
)->end_seq
++;
2708 /* Socket is locked, keep trying until memory is available. */
2710 skb
= alloc_skb_fclone(MAX_TCP_HEADER
,
2717 /* Reserve space for headers and prepare control bits. */
2718 skb_reserve(skb
, MAX_TCP_HEADER
);
2719 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2720 tcp_init_nondata_skb(skb
, tp
->write_seq
,
2721 TCPHDR_ACK
| TCPHDR_FIN
);
2722 tcp_queue_skb(sk
, skb
);
2724 __tcp_push_pending_frames(sk
, mss_now
, TCP_NAGLE_OFF
);
2727 /* We get here when a process closes a file descriptor (either due to
2728 * an explicit close() or as a byproduct of exit()'ing) and there
2729 * was unread data in the receive queue. This behavior is recommended
2730 * by RFC 2525, section 2.17. -DaveM
2732 void tcp_send_active_reset(struct sock
*sk
, gfp_t priority
)
2734 struct sk_buff
*skb
;
2736 /* NOTE: No TCP options attached and we never retransmit this. */
2737 skb
= alloc_skb(MAX_TCP_HEADER
, priority
);
2739 NET_INC_STATS(sock_net(sk
), LINUX_MIB_TCPABORTFAILED
);
2743 /* Reserve space for headers and prepare control bits. */
2744 skb_reserve(skb
, MAX_TCP_HEADER
);
2745 tcp_init_nondata_skb(skb
, tcp_acceptable_seq(sk
),
2746 TCPHDR_ACK
| TCPHDR_RST
);
2748 if (tcp_transmit_skb(sk
, skb
, 0, priority
))
2749 NET_INC_STATS(sock_net(sk
), LINUX_MIB_TCPABORTFAILED
);
2751 TCP_INC_STATS(sock_net(sk
), TCP_MIB_OUTRSTS
);
2754 /* Send a crossed SYN-ACK during socket establishment.
2755 * WARNING: This routine must only be called when we have already sent
2756 * a SYN packet that crossed the incoming SYN that caused this routine
2757 * to get called. If this assumption fails then the initial rcv_wnd
2758 * and rcv_wscale values will not be correct.
2760 int tcp_send_synack(struct sock
*sk
)
2762 struct sk_buff
*skb
;
2764 skb
= tcp_write_queue_head(sk
);
2765 if (skb
== NULL
|| !(TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_SYN
)) {
2766 pr_debug("%s: wrong queue state\n", __func__
);
2769 if (!(TCP_SKB_CB(skb
)->tcp_flags
& TCPHDR_ACK
)) {
2770 if (skb_cloned(skb
)) {
2771 struct sk_buff
*nskb
= skb_copy(skb
, GFP_ATOMIC
);
2774 tcp_unlink_write_queue(skb
, sk
);
2775 skb_header_release(nskb
);
2776 __tcp_add_write_queue_head(sk
, nskb
);
2777 sk_wmem_free_skb(sk
, skb
);
2778 sk
->sk_wmem_queued
+= nskb
->truesize
;
2779 sk_mem_charge(sk
, nskb
->truesize
);
2783 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_ACK
;
2784 TCP_ECN_send_synack(tcp_sk(sk
), skb
);
2786 return tcp_transmit_skb(sk
, skb
, 1, GFP_ATOMIC
);
2790 * tcp_make_synack - Prepare a SYN-ACK.
2791 * sk: listener socket
2792 * dst: dst entry attached to the SYNACK
2793 * req: request_sock pointer
2795 * Allocate one skb and build a SYNACK packet.
2796 * @dst is consumed : Caller should not use it again.
2798 struct sk_buff
*tcp_make_synack(struct sock
*sk
, struct dst_entry
*dst
,
2799 struct request_sock
*req
,
2800 struct tcp_fastopen_cookie
*foc
)
2802 struct tcp_out_options opts
;
2803 struct inet_request_sock
*ireq
= inet_rsk(req
);
2804 struct tcp_sock
*tp
= tcp_sk(sk
);
2806 struct sk_buff
*skb
;
2807 struct tcp_md5sig_key
*md5
;
2808 int tcp_header_size
;
2811 skb
= sock_wmalloc(sk
, MAX_TCP_HEADER
, 1, GFP_ATOMIC
);
2812 if (unlikely(!skb
)) {
2816 /* Reserve space for headers. */
2817 skb_reserve(skb
, MAX_TCP_HEADER
);
2819 skb_dst_set(skb
, dst
);
2820 security_skb_owned_by(skb
, sk
);
2822 mss
= dst_metric_advmss(dst
);
2823 if (tp
->rx_opt
.user_mss
&& tp
->rx_opt
.user_mss
< mss
)
2824 mss
= tp
->rx_opt
.user_mss
;
2826 memset(&opts
, 0, sizeof(opts
));
2827 #ifdef CONFIG_SYN_COOKIES
2828 if (unlikely(req
->cookie_ts
))
2829 skb
->skb_mstamp
.stamp_jiffies
= cookie_init_timestamp(req
);
2832 skb_mstamp_get(&skb
->skb_mstamp
);
2833 tcp_header_size
= tcp_synack_options(sk
, req
, mss
, skb
, &opts
, &md5
,
2836 skb_push(skb
, tcp_header_size
);
2837 skb_reset_transport_header(skb
);
2840 memset(th
, 0, sizeof(struct tcphdr
));
2843 TCP_ECN_make_synack(req
, th
);
2844 th
->source
= htons(ireq
->ir_num
);
2845 th
->dest
= ireq
->ir_rmt_port
;
2846 /* Setting of flags are superfluous here for callers (and ECE is
2847 * not even correctly set)
2849 tcp_init_nondata_skb(skb
, tcp_rsk(req
)->snt_isn
,
2850 TCPHDR_SYN
| TCPHDR_ACK
);
2852 th
->seq
= htonl(TCP_SKB_CB(skb
)->seq
);
2853 /* XXX data is queued and acked as is. No buffer/window check */
2854 th
->ack_seq
= htonl(tcp_rsk(req
)->rcv_nxt
);
2856 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2857 th
->window
= htons(min(req
->rcv_wnd
, 65535U));
2858 tcp_options_write((__be32
*)(th
+ 1), tp
, &opts
);
2859 th
->doff
= (tcp_header_size
>> 2);
2860 TCP_INC_STATS_BH(sock_net(sk
), TCP_MIB_OUTSEGS
);
2862 #ifdef CONFIG_TCP_MD5SIG
2863 /* Okay, we have all we need - do the md5 hash if needed */
2865 tcp_rsk(req
)->af_specific
->calc_md5_hash(opts
.hash_location
,
2866 md5
, NULL
, req
, skb
);
2872 EXPORT_SYMBOL(tcp_make_synack
);
2874 /* Do all connect socket setups that can be done AF independent. */
2875 static void tcp_connect_init(struct sock
*sk
)
2877 const struct dst_entry
*dst
= __sk_dst_get(sk
);
2878 struct tcp_sock
*tp
= tcp_sk(sk
);
2881 /* We'll fix this up when we get a response from the other end.
2882 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2884 tp
->tcp_header_len
= sizeof(struct tcphdr
) +
2885 (sysctl_tcp_timestamps
? TCPOLEN_TSTAMP_ALIGNED
: 0);
2887 #ifdef CONFIG_TCP_MD5SIG
2888 if (tp
->af_specific
->md5_lookup(sk
, sk
) != NULL
)
2889 tp
->tcp_header_len
+= TCPOLEN_MD5SIG_ALIGNED
;
2892 /* If user gave his TCP_MAXSEG, record it to clamp */
2893 if (tp
->rx_opt
.user_mss
)
2894 tp
->rx_opt
.mss_clamp
= tp
->rx_opt
.user_mss
;
2897 tcp_sync_mss(sk
, dst_mtu(dst
));
2899 if (!tp
->window_clamp
)
2900 tp
->window_clamp
= dst_metric(dst
, RTAX_WINDOW
);
2901 tp
->advmss
= dst_metric_advmss(dst
);
2902 if (tp
->rx_opt
.user_mss
&& tp
->rx_opt
.user_mss
< tp
->advmss
)
2903 tp
->advmss
= tp
->rx_opt
.user_mss
;
2905 tcp_initialize_rcv_mss(sk
);
2907 /* limit the window selection if the user enforce a smaller rx buffer */
2908 if (sk
->sk_userlocks
& SOCK_RCVBUF_LOCK
&&
2909 (tp
->window_clamp
> tcp_full_space(sk
) || tp
->window_clamp
== 0))
2910 tp
->window_clamp
= tcp_full_space(sk
);
2912 tcp_select_initial_window(tcp_full_space(sk
),
2913 tp
->advmss
- (tp
->rx_opt
.ts_recent_stamp
? tp
->tcp_header_len
- sizeof(struct tcphdr
) : 0),
2916 sysctl_tcp_window_scaling
,
2918 dst_metric(dst
, RTAX_INITRWND
));
2920 tp
->rx_opt
.rcv_wscale
= rcv_wscale
;
2921 tp
->rcv_ssthresh
= tp
->rcv_wnd
;
2924 sock_reset_flag(sk
, SOCK_DONE
);
2927 tp
->snd_una
= tp
->write_seq
;
2928 tp
->snd_sml
= tp
->write_seq
;
2929 tp
->snd_up
= tp
->write_seq
;
2930 tp
->snd_nxt
= tp
->write_seq
;
2932 if (likely(!tp
->repair
))
2935 tp
->rcv_tstamp
= tcp_time_stamp
;
2936 tp
->rcv_wup
= tp
->rcv_nxt
;
2937 tp
->copied_seq
= tp
->rcv_nxt
;
2939 inet_csk(sk
)->icsk_rto
= TCP_TIMEOUT_INIT
;
2940 inet_csk(sk
)->icsk_retransmits
= 0;
2941 tcp_clear_retrans(tp
);
2944 static void tcp_connect_queue_skb(struct sock
*sk
, struct sk_buff
*skb
)
2946 struct tcp_sock
*tp
= tcp_sk(sk
);
2947 struct tcp_skb_cb
*tcb
= TCP_SKB_CB(skb
);
2949 tcb
->end_seq
+= skb
->len
;
2950 skb_header_release(skb
);
2951 __tcp_add_write_queue_tail(sk
, skb
);
2952 sk
->sk_wmem_queued
+= skb
->truesize
;
2953 sk_mem_charge(sk
, skb
->truesize
);
2954 tp
->write_seq
= tcb
->end_seq
;
2955 tp
->packets_out
+= tcp_skb_pcount(skb
);
2958 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
2959 * queue a data-only packet after the regular SYN, such that regular SYNs
2960 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
2961 * only the SYN sequence, the data are retransmitted in the first ACK.
2962 * If cookie is not cached or other error occurs, falls back to send a
2963 * regular SYN with Fast Open cookie request option.
2965 static int tcp_send_syn_data(struct sock
*sk
, struct sk_buff
*syn
)
2967 struct tcp_sock
*tp
= tcp_sk(sk
);
2968 struct tcp_fastopen_request
*fo
= tp
->fastopen_req
;
2969 int syn_loss
= 0, space
, i
, err
= 0, iovlen
= fo
->data
->msg_iovlen
;
2970 struct sk_buff
*syn_data
= NULL
, *data
;
2971 unsigned long last_syn_loss
= 0;
2973 tp
->rx_opt
.mss_clamp
= tp
->advmss
; /* If MSS is not cached */
2974 tcp_fastopen_cache_get(sk
, &tp
->rx_opt
.mss_clamp
, &fo
->cookie
,
2975 &syn_loss
, &last_syn_loss
);
2976 /* Recurring FO SYN losses: revert to regular handshake temporarily */
2978 time_before(jiffies
, last_syn_loss
+ (60*HZ
<< syn_loss
))) {
2979 fo
->cookie
.len
= -1;
2983 if (sysctl_tcp_fastopen
& TFO_CLIENT_NO_COOKIE
)
2984 fo
->cookie
.len
= -1;
2985 else if (fo
->cookie
.len
<= 0)
2988 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
2989 * user-MSS. Reserve maximum option space for middleboxes that add
2990 * private TCP options. The cost is reduced data space in SYN :(
2992 if (tp
->rx_opt
.user_mss
&& tp
->rx_opt
.user_mss
< tp
->rx_opt
.mss_clamp
)
2993 tp
->rx_opt
.mss_clamp
= tp
->rx_opt
.user_mss
;
2994 space
= __tcp_mtu_to_mss(sk
, inet_csk(sk
)->icsk_pmtu_cookie
) -
2995 MAX_TCP_OPTION_SPACE
;
2997 space
= min_t(size_t, space
, fo
->size
);
2999 /* limit to order-0 allocations */
3000 space
= min_t(size_t, space
, SKB_MAX_HEAD(MAX_TCP_HEADER
));
3002 syn_data
= skb_copy_expand(syn
, MAX_TCP_HEADER
, space
,
3004 if (syn_data
== NULL
)
3007 for (i
= 0; i
< iovlen
&& syn_data
->len
< space
; ++i
) {
3008 struct iovec
*iov
= &fo
->data
->msg_iov
[i
];
3009 unsigned char __user
*from
= iov
->iov_base
;
3010 int len
= iov
->iov_len
;
3012 if (syn_data
->len
+ len
> space
)
3013 len
= space
- syn_data
->len
;
3014 else if (i
+ 1 == iovlen
)
3015 /* No more data pending in inet_wait_for_connect() */
3018 if (skb_add_data(syn_data
, from
, len
))
3022 /* Queue a data-only packet after the regular SYN for retransmission */
3023 data
= pskb_copy(syn_data
, sk
->sk_allocation
);
3026 TCP_SKB_CB(data
)->seq
++;
3027 TCP_SKB_CB(data
)->tcp_flags
&= ~TCPHDR_SYN
;
3028 TCP_SKB_CB(data
)->tcp_flags
= (TCPHDR_ACK
|TCPHDR_PSH
);
3029 tcp_connect_queue_skb(sk
, data
);
3030 fo
->copied
= data
->len
;
3032 /* syn_data is about to be sent, we need to take current time stamps
3033 * for the packets that are in write queue : SYN packet and DATA
3035 skb_mstamp_get(&syn
->skb_mstamp
);
3036 data
->skb_mstamp
= syn
->skb_mstamp
;
3038 if (tcp_transmit_skb(sk
, syn_data
, 0, sk
->sk_allocation
) == 0) {
3039 tp
->syn_data
= (fo
->copied
> 0);
3040 NET_INC_STATS(sock_net(sk
), LINUX_MIB_TCPORIGDATASENT
);
3046 /* Send a regular SYN with Fast Open cookie request option */
3047 if (fo
->cookie
.len
> 0)
3049 err
= tcp_transmit_skb(sk
, syn
, 1, sk
->sk_allocation
);
3051 tp
->syn_fastopen
= 0;
3052 kfree_skb(syn_data
);
3054 fo
->cookie
.len
= -1; /* Exclude Fast Open option for SYN retries */
3058 /* Build a SYN and send it off. */
3059 int tcp_connect(struct sock
*sk
)
3061 struct tcp_sock
*tp
= tcp_sk(sk
);
3062 struct sk_buff
*buff
;
3065 tcp_connect_init(sk
);
3067 if (unlikely(tp
->repair
)) {
3068 tcp_finish_connect(sk
, NULL
);
3072 buff
= alloc_skb_fclone(MAX_TCP_HEADER
+ 15, sk
->sk_allocation
);
3073 if (unlikely(buff
== NULL
))
3076 /* Reserve space for headers. */
3077 skb_reserve(buff
, MAX_TCP_HEADER
);
3079 tcp_init_nondata_skb(buff
, tp
->write_seq
++, TCPHDR_SYN
);
3080 tp
->retrans_stamp
= tcp_time_stamp
;
3081 tcp_connect_queue_skb(sk
, buff
);
3082 TCP_ECN_send_syn(sk
, buff
);
3084 /* Send off SYN; include data in Fast Open. */
3085 err
= tp
->fastopen_req
? tcp_send_syn_data(sk
, buff
) :
3086 tcp_transmit_skb(sk
, buff
, 1, sk
->sk_allocation
);
3087 if (err
== -ECONNREFUSED
)
3090 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3091 * in order to make this packet get counted in tcpOutSegs.
3093 tp
->snd_nxt
= tp
->write_seq
;
3094 tp
->pushed_seq
= tp
->write_seq
;
3095 TCP_INC_STATS(sock_net(sk
), TCP_MIB_ACTIVEOPENS
);
3097 /* Timer for repeating the SYN until an answer. */
3098 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
3099 inet_csk(sk
)->icsk_rto
, TCP_RTO_MAX
);
3102 EXPORT_SYMBOL(tcp_connect
);
3104 /* Send out a delayed ack, the caller does the policy checking
3105 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3108 void tcp_send_delayed_ack(struct sock
*sk
)
3110 struct inet_connection_sock
*icsk
= inet_csk(sk
);
3111 int ato
= icsk
->icsk_ack
.ato
;
3112 unsigned long timeout
;
3114 if (ato
> TCP_DELACK_MIN
) {
3115 const struct tcp_sock
*tp
= tcp_sk(sk
);
3116 int max_ato
= HZ
/ 2;
3118 if (icsk
->icsk_ack
.pingpong
||
3119 (icsk
->icsk_ack
.pending
& ICSK_ACK_PUSHED
))
3120 max_ato
= TCP_DELACK_MAX
;
3122 /* Slow path, intersegment interval is "high". */
3124 /* If some rtt estimate is known, use it to bound delayed ack.
3125 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3129 int rtt
= max_t(int, usecs_to_jiffies(tp
->srtt_us
>> 3),
3136 ato
= min(ato
, max_ato
);
3139 /* Stay within the limit we were given */
3140 timeout
= jiffies
+ ato
;
3142 /* Use new timeout only if there wasn't a older one earlier. */
3143 if (icsk
->icsk_ack
.pending
& ICSK_ACK_TIMER
) {
3144 /* If delack timer was blocked or is about to expire,
3147 if (icsk
->icsk_ack
.blocked
||
3148 time_before_eq(icsk
->icsk_ack
.timeout
, jiffies
+ (ato
>> 2))) {
3153 if (!time_before(timeout
, icsk
->icsk_ack
.timeout
))
3154 timeout
= icsk
->icsk_ack
.timeout
;
3156 icsk
->icsk_ack
.pending
|= ICSK_ACK_SCHED
| ICSK_ACK_TIMER
;
3157 icsk
->icsk_ack
.timeout
= timeout
;
3158 sk_reset_timer(sk
, &icsk
->icsk_delack_timer
, timeout
);
3161 /* This routine sends an ack and also updates the window. */
3162 void tcp_send_ack(struct sock
*sk
)
3164 struct sk_buff
*buff
;
3166 /* If we have been reset, we may not send again. */
3167 if (sk
->sk_state
== TCP_CLOSE
)
3170 /* We are not putting this on the write queue, so
3171 * tcp_transmit_skb() will set the ownership to this
3174 buff
= alloc_skb(MAX_TCP_HEADER
, sk_gfp_atomic(sk
, GFP_ATOMIC
));
3176 inet_csk_schedule_ack(sk
);
3177 inet_csk(sk
)->icsk_ack
.ato
= TCP_ATO_MIN
;
3178 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_DACK
,
3179 TCP_DELACK_MAX
, TCP_RTO_MAX
);
3183 /* Reserve space for headers and prepare control bits. */
3184 skb_reserve(buff
, MAX_TCP_HEADER
);
3185 tcp_init_nondata_skb(buff
, tcp_acceptable_seq(sk
), TCPHDR_ACK
);
3187 /* Send it off, this clears delayed acks for us. */
3188 skb_mstamp_get(&buff
->skb_mstamp
);
3189 tcp_transmit_skb(sk
, buff
, 0, sk_gfp_atomic(sk
, GFP_ATOMIC
));
3192 /* This routine sends a packet with an out of date sequence
3193 * number. It assumes the other end will try to ack it.
3195 * Question: what should we make while urgent mode?
3196 * 4.4BSD forces sending single byte of data. We cannot send
3197 * out of window data, because we have SND.NXT==SND.MAX...
3199 * Current solution: to send TWO zero-length segments in urgent mode:
3200 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3201 * out-of-date with SND.UNA-1 to probe window.
3203 static int tcp_xmit_probe_skb(struct sock
*sk
, int urgent
)
3205 struct tcp_sock
*tp
= tcp_sk(sk
);
3206 struct sk_buff
*skb
;
3208 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3209 skb
= alloc_skb(MAX_TCP_HEADER
, sk_gfp_atomic(sk
, GFP_ATOMIC
));
3213 /* Reserve space for headers and set control bits. */
3214 skb_reserve(skb
, MAX_TCP_HEADER
);
3215 /* Use a previous sequence. This should cause the other
3216 * end to send an ack. Don't queue or clone SKB, just
3219 tcp_init_nondata_skb(skb
, tp
->snd_una
- !urgent
, TCPHDR_ACK
);
3220 skb_mstamp_get(&skb
->skb_mstamp
);
3221 return tcp_transmit_skb(sk
, skb
, 0, GFP_ATOMIC
);
3224 void tcp_send_window_probe(struct sock
*sk
)
3226 if (sk
->sk_state
== TCP_ESTABLISHED
) {
3227 tcp_sk(sk
)->snd_wl1
= tcp_sk(sk
)->rcv_nxt
- 1;
3228 tcp_xmit_probe_skb(sk
, 0);
3232 /* Initiate keepalive or window probe from timer. */
3233 int tcp_write_wakeup(struct sock
*sk
)
3235 struct tcp_sock
*tp
= tcp_sk(sk
);
3236 struct sk_buff
*skb
;
3238 if (sk
->sk_state
== TCP_CLOSE
)
3241 if ((skb
= tcp_send_head(sk
)) != NULL
&&
3242 before(TCP_SKB_CB(skb
)->seq
, tcp_wnd_end(tp
))) {
3244 unsigned int mss
= tcp_current_mss(sk
);
3245 unsigned int seg_size
= tcp_wnd_end(tp
) - TCP_SKB_CB(skb
)->seq
;
3247 if (before(tp
->pushed_seq
, TCP_SKB_CB(skb
)->end_seq
))
3248 tp
->pushed_seq
= TCP_SKB_CB(skb
)->end_seq
;
3250 /* We are probing the opening of a window
3251 * but the window size is != 0
3252 * must have been a result SWS avoidance ( sender )
3254 if (seg_size
< TCP_SKB_CB(skb
)->end_seq
- TCP_SKB_CB(skb
)->seq
||
3256 seg_size
= min(seg_size
, mss
);
3257 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_PSH
;
3258 if (tcp_fragment(sk
, skb
, seg_size
, mss
, GFP_ATOMIC
))
3260 } else if (!tcp_skb_pcount(skb
))
3261 tcp_set_skb_tso_segs(sk
, skb
, mss
);
3263 TCP_SKB_CB(skb
)->tcp_flags
|= TCPHDR_PSH
;
3264 err
= tcp_transmit_skb(sk
, skb
, 1, GFP_ATOMIC
);
3266 tcp_event_new_data_sent(sk
, skb
);
3269 if (between(tp
->snd_up
, tp
->snd_una
+ 1, tp
->snd_una
+ 0xFFFF))
3270 tcp_xmit_probe_skb(sk
, 1);
3271 return tcp_xmit_probe_skb(sk
, 0);
3275 /* A window probe timeout has occurred. If window is not closed send
3276 * a partial packet else a zero probe.
3278 void tcp_send_probe0(struct sock
*sk
)
3280 struct inet_connection_sock
*icsk
= inet_csk(sk
);
3281 struct tcp_sock
*tp
= tcp_sk(sk
);
3282 unsigned long probe_max
;
3285 err
= tcp_write_wakeup(sk
);
3287 if (tp
->packets_out
|| !tcp_send_head(sk
)) {
3288 /* Cancel probe timer, if it is not required. */
3289 icsk
->icsk_probes_out
= 0;
3290 icsk
->icsk_backoff
= 0;
3295 if (icsk
->icsk_backoff
< sysctl_tcp_retries2
)
3296 icsk
->icsk_backoff
++;
3297 icsk
->icsk_probes_out
++;
3298 probe_max
= TCP_RTO_MAX
;
3300 /* If packet was not sent due to local congestion,
3301 * do not backoff and do not remember icsk_probes_out.
3302 * Let local senders to fight for local resources.
3304 * Use accumulated backoff yet.
3306 if (!icsk
->icsk_probes_out
)
3307 icsk
->icsk_probes_out
= 1;
3308 probe_max
= TCP_RESOURCE_PROBE_INTERVAL
;
3310 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_PROBE0
,
3311 inet_csk_rto_backoff(icsk
, probe_max
),
3315 int tcp_rtx_synack(struct sock
*sk
, struct request_sock
*req
)
3317 const struct tcp_request_sock_ops
*af_ops
= tcp_rsk(req
)->af_specific
;
3321 res
= af_ops
->send_synack(sk
, NULL
, &fl
, req
, 0, NULL
);
3323 TCP_INC_STATS_BH(sock_net(sk
), TCP_MIB_RETRANSSEGS
);
3324 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPSYNRETRANS
);
3328 EXPORT_SYMBOL(tcp_rtx_synack
);