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1/*
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.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
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>
19 */
20
21/*
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
25 * : AF independence
26 *
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
34 *
35 */
36
37#define pr_fmt(fmt) "TCP: " fmt
38
39#include <net/tcp.h>
40
41#include <linux/compiler.h>
42#include <linux/gfp.h>
43#include <linux/module.h>
44
45/* People can turn this off for buggy TCP's found in printers etc. */
46int sysctl_tcp_retrans_collapse __read_mostly = 1;
47
48/* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
50 */
51int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
52
53/* Default TSQ limit of four TSO segments */
54int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
55
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.
59 */
60int sysctl_tcp_tso_win_divisor __read_mostly = 3;
61
62/* By default, RFC2861 behavior. */
63int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
64
65static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
66 int push_one, gfp_t gfp);
67
68/* Account for new data that has been sent to the network. */
69static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
70{
71 struct inet_connection_sock *icsk = inet_csk(sk);
72 struct tcp_sock *tp = tcp_sk(sk);
73 unsigned int prior_packets = tp->packets_out;
74
75 tcp_advance_send_head(sk, skb);
76 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
77
78 tp->packets_out += tcp_skb_pcount(skb);
79 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
80 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
81 tcp_rearm_rto(sk);
82 }
83
84 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
85 tcp_skb_pcount(skb));
86}
87
88/* SND.NXT, if window was not shrunk.
89 * If window has been shrunk, what should we make? It is not clear at all.
90 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
91 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
92 * invalid. OK, let's make this for now:
93 */
94static inline __u32 tcp_acceptable_seq(const struct sock *sk)
95{
96 const struct tcp_sock *tp = tcp_sk(sk);
97
98 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
99 return tp->snd_nxt;
100 else
101 return tcp_wnd_end(tp);
102}
103
104/* Calculate mss to advertise in SYN segment.
105 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
106 *
107 * 1. It is independent of path mtu.
108 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
109 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
110 * attached devices, because some buggy hosts are confused by
111 * large MSS.
112 * 4. We do not make 3, we advertise MSS, calculated from first
113 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
114 * This may be overridden via information stored in routing table.
115 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
116 * probably even Jumbo".
117 */
118static __u16 tcp_advertise_mss(struct sock *sk)
119{
120 struct tcp_sock *tp = tcp_sk(sk);
121 const struct dst_entry *dst = __sk_dst_get(sk);
122 int mss = tp->advmss;
123
124 if (dst) {
125 unsigned int metric = dst_metric_advmss(dst);
126
127 if (metric < mss) {
128 mss = metric;
129 tp->advmss = mss;
130 }
131 }
132
133 return (__u16)mss;
134}
135
136/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
137 * This is the first part of cwnd validation mechanism.
138 */
139void tcp_cwnd_restart(struct sock *sk, s32 delta)
140{
141 struct tcp_sock *tp = tcp_sk(sk);
142 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
143 u32 cwnd = tp->snd_cwnd;
144
145 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
146
147 tp->snd_ssthresh = tcp_current_ssthresh(sk);
148 restart_cwnd = min(restart_cwnd, cwnd);
149
150 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
151 cwnd >>= 1;
152 tp->snd_cwnd = max(cwnd, restart_cwnd);
153 tp->snd_cwnd_stamp = tcp_time_stamp;
154 tp->snd_cwnd_used = 0;
155}
156
157/* Congestion state accounting after a packet has been sent. */
158static void tcp_event_data_sent(struct tcp_sock *tp,
159 struct sock *sk)
160{
161 struct inet_connection_sock *icsk = inet_csk(sk);
162 const u32 now = tcp_time_stamp;
163
164 if (tcp_packets_in_flight(tp) == 0)
165 tcp_ca_event(sk, CA_EVENT_TX_START);
166
167 tp->lsndtime = now;
168
169 /* If it is a reply for ato after last received
170 * packet, enter pingpong mode.
171 */
172 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
173 icsk->icsk_ack.pingpong = 1;
174}
175
176/* Account for an ACK we sent. */
177static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
178{
179 tcp_dec_quickack_mode(sk, pkts);
180 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
181}
182
183
184u32 tcp_default_init_rwnd(u32 mss)
185{
186 /* Initial receive window should be twice of TCP_INIT_CWND to
187 * enable proper sending of new unsent data during fast recovery
188 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
189 * limit when mss is larger than 1460.
190 */
191 u32 init_rwnd = TCP_INIT_CWND * 2;
192
193 if (mss > 1460)
194 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
195 return init_rwnd;
196}
197
198/* Determine a window scaling and initial window to offer.
199 * Based on the assumption that the given amount of space
200 * will be offered. Store the results in the tp structure.
201 * NOTE: for smooth operation initial space offering should
202 * be a multiple of mss if possible. We assume here that mss >= 1.
203 * This MUST be enforced by all callers.
204 */
205void tcp_select_initial_window(int __space, __u32 mss,
206 __u32 *rcv_wnd, __u32 *window_clamp,
207 int wscale_ok, __u8 *rcv_wscale,
208 __u32 init_rcv_wnd)
209{
210 unsigned int space = (__space < 0 ? 0 : __space);
211
212 /* If no clamp set the clamp to the max possible scaled window */
213 if (*window_clamp == 0)
214 (*window_clamp) = (65535 << 14);
215 space = min(*window_clamp, space);
216
217 /* Quantize space offering to a multiple of mss if possible. */
218 if (space > mss)
219 space = (space / mss) * mss;
220
221 /* NOTE: offering an initial window larger than 32767
222 * will break some buggy TCP stacks. If the admin tells us
223 * it is likely we could be speaking with such a buggy stack
224 * we will truncate our initial window offering to 32K-1
225 * unless the remote has sent us a window scaling option,
226 * which we interpret as a sign the remote TCP is not
227 * misinterpreting the window field as a signed quantity.
228 */
229 if (sysctl_tcp_workaround_signed_windows)
230 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
231 else
232 (*rcv_wnd) = space;
233
234 (*rcv_wscale) = 0;
235 if (wscale_ok) {
236 /* Set window scaling on max possible window
237 * See RFC1323 for an explanation of the limit to 14
238 */
239 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
240 space = min_t(u32, space, *window_clamp);
241 while (space > 65535 && (*rcv_wscale) < 14) {
242 space >>= 1;
243 (*rcv_wscale)++;
244 }
245 }
246
247 if (mss > (1 << *rcv_wscale)) {
248 if (!init_rcv_wnd) /* Use default unless specified otherwise */
249 init_rcv_wnd = tcp_default_init_rwnd(mss);
250 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
251 }
252
253 /* Set the clamp no higher than max representable value */
254 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
255}
256EXPORT_SYMBOL(tcp_select_initial_window);
257
258/* Chose a new window to advertise, update state in tcp_sock for the
259 * socket, and return result with RFC1323 scaling applied. The return
260 * value can be stuffed directly into th->window for an outgoing
261 * frame.
262 */
263static u16 tcp_select_window(struct sock *sk)
264{
265 struct tcp_sock *tp = tcp_sk(sk);
266 u32 old_win = tp->rcv_wnd;
267 u32 cur_win = tcp_receive_window(tp);
268 u32 new_win = __tcp_select_window(sk);
269
270 /* Never shrink the offered window */
271 if (new_win < cur_win) {
272 /* Danger Will Robinson!
273 * Don't update rcv_wup/rcv_wnd here or else
274 * we will not be able to advertise a zero
275 * window in time. --DaveM
276 *
277 * Relax Will Robinson.
278 */
279 if (new_win == 0)
280 NET_INC_STATS(sock_net(sk),
281 LINUX_MIB_TCPWANTZEROWINDOWADV);
282 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
283 }
284 tp->rcv_wnd = new_win;
285 tp->rcv_wup = tp->rcv_nxt;
286
287 /* Make sure we do not exceed the maximum possible
288 * scaled window.
289 */
290 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
291 new_win = min(new_win, MAX_TCP_WINDOW);
292 else
293 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
294
295 /* RFC1323 scaling applied */
296 new_win >>= tp->rx_opt.rcv_wscale;
297
298 /* If we advertise zero window, disable fast path. */
299 if (new_win == 0) {
300 tp->pred_flags = 0;
301 if (old_win)
302 NET_INC_STATS(sock_net(sk),
303 LINUX_MIB_TCPTOZEROWINDOWADV);
304 } else if (old_win == 0) {
305 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
306 }
307
308 return new_win;
309}
310
311/* Packet ECN state for a SYN-ACK */
312static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
313{
314 const struct tcp_sock *tp = tcp_sk(sk);
315
316 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
317 if (!(tp->ecn_flags & TCP_ECN_OK))
318 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
319 else if (tcp_ca_needs_ecn(sk))
320 INET_ECN_xmit(sk);
321}
322
323/* Packet ECN state for a SYN. */
324static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
325{
326 struct tcp_sock *tp = tcp_sk(sk);
327 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
328 tcp_ca_needs_ecn(sk);
329
330 if (!use_ecn) {
331 const struct dst_entry *dst = __sk_dst_get(sk);
332
333 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
334 use_ecn = true;
335 }
336
337 tp->ecn_flags = 0;
338
339 if (use_ecn) {
340 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
341 tp->ecn_flags = TCP_ECN_OK;
342 if (tcp_ca_needs_ecn(sk))
343 INET_ECN_xmit(sk);
344 }
345}
346
347static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
348{
349 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
350 /* tp->ecn_flags are cleared at a later point in time when
351 * SYN ACK is ultimatively being received.
352 */
353 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
354}
355
356static void
357tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
358{
359 if (inet_rsk(req)->ecn_ok)
360 th->ece = 1;
361}
362
363/* Set up ECN state for a packet on a ESTABLISHED socket that is about to
364 * be sent.
365 */
366static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
367 int tcp_header_len)
368{
369 struct tcp_sock *tp = tcp_sk(sk);
370
371 if (tp->ecn_flags & TCP_ECN_OK) {
372 /* Not-retransmitted data segment: set ECT and inject CWR. */
373 if (skb->len != tcp_header_len &&
374 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
375 INET_ECN_xmit(sk);
376 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
377 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
378 tcp_hdr(skb)->cwr = 1;
379 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
380 }
381 } else if (!tcp_ca_needs_ecn(sk)) {
382 /* ACK or retransmitted segment: clear ECT|CE */
383 INET_ECN_dontxmit(sk);
384 }
385 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
386 tcp_hdr(skb)->ece = 1;
387 }
388}
389
390/* Constructs common control bits of non-data skb. If SYN/FIN is present,
391 * auto increment end seqno.
392 */
393static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
394{
395 skb->ip_summed = CHECKSUM_PARTIAL;
396 skb->csum = 0;
397
398 TCP_SKB_CB(skb)->tcp_flags = flags;
399 TCP_SKB_CB(skb)->sacked = 0;
400
401 tcp_skb_pcount_set(skb, 1);
402
403 TCP_SKB_CB(skb)->seq = seq;
404 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
405 seq++;
406 TCP_SKB_CB(skb)->end_seq = seq;
407}
408
409static inline bool tcp_urg_mode(const struct tcp_sock *tp)
410{
411 return tp->snd_una != tp->snd_up;
412}
413
414#define OPTION_SACK_ADVERTISE (1 << 0)
415#define OPTION_TS (1 << 1)
416#define OPTION_MD5 (1 << 2)
417#define OPTION_WSCALE (1 << 3)
418#define OPTION_FAST_OPEN_COOKIE (1 << 8)
419
420struct tcp_out_options {
421 u16 options; /* bit field of OPTION_* */
422 u16 mss; /* 0 to disable */
423 u8 ws; /* window scale, 0 to disable */
424 u8 num_sack_blocks; /* number of SACK blocks to include */
425 u8 hash_size; /* bytes in hash_location */
426 __u8 *hash_location; /* temporary pointer, overloaded */
427 __u32 tsval, tsecr; /* need to include OPTION_TS */
428 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
429};
430
431/* Write previously computed TCP options to the packet.
432 *
433 * Beware: Something in the Internet is very sensitive to the ordering of
434 * TCP options, we learned this through the hard way, so be careful here.
435 * Luckily we can at least blame others for their non-compliance but from
436 * inter-operability perspective it seems that we're somewhat stuck with
437 * the ordering which we have been using if we want to keep working with
438 * those broken things (not that it currently hurts anybody as there isn't
439 * particular reason why the ordering would need to be changed).
440 *
441 * At least SACK_PERM as the first option is known to lead to a disaster
442 * (but it may well be that other scenarios fail similarly).
443 */
444static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
445 struct tcp_out_options *opts)
446{
447 u16 options = opts->options; /* mungable copy */
448
449 if (unlikely(OPTION_MD5 & options)) {
450 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
451 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
452 /* overload cookie hash location */
453 opts->hash_location = (__u8 *)ptr;
454 ptr += 4;
455 }
456
457 if (unlikely(opts->mss)) {
458 *ptr++ = htonl((TCPOPT_MSS << 24) |
459 (TCPOLEN_MSS << 16) |
460 opts->mss);
461 }
462
463 if (likely(OPTION_TS & options)) {
464 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
465 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
466 (TCPOLEN_SACK_PERM << 16) |
467 (TCPOPT_TIMESTAMP << 8) |
468 TCPOLEN_TIMESTAMP);
469 options &= ~OPTION_SACK_ADVERTISE;
470 } else {
471 *ptr++ = htonl((TCPOPT_NOP << 24) |
472 (TCPOPT_NOP << 16) |
473 (TCPOPT_TIMESTAMP << 8) |
474 TCPOLEN_TIMESTAMP);
475 }
476 *ptr++ = htonl(opts->tsval);
477 *ptr++ = htonl(opts->tsecr);
478 }
479
480 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
481 *ptr++ = htonl((TCPOPT_NOP << 24) |
482 (TCPOPT_NOP << 16) |
483 (TCPOPT_SACK_PERM << 8) |
484 TCPOLEN_SACK_PERM);
485 }
486
487 if (unlikely(OPTION_WSCALE & options)) {
488 *ptr++ = htonl((TCPOPT_NOP << 24) |
489 (TCPOPT_WINDOW << 16) |
490 (TCPOLEN_WINDOW << 8) |
491 opts->ws);
492 }
493
494 if (unlikely(opts->num_sack_blocks)) {
495 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
496 tp->duplicate_sack : tp->selective_acks;
497 int this_sack;
498
499 *ptr++ = htonl((TCPOPT_NOP << 24) |
500 (TCPOPT_NOP << 16) |
501 (TCPOPT_SACK << 8) |
502 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
503 TCPOLEN_SACK_PERBLOCK)));
504
505 for (this_sack = 0; this_sack < opts->num_sack_blocks;
506 ++this_sack) {
507 *ptr++ = htonl(sp[this_sack].start_seq);
508 *ptr++ = htonl(sp[this_sack].end_seq);
509 }
510
511 tp->rx_opt.dsack = 0;
512 }
513
514 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
515 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
516 u8 *p = (u8 *)ptr;
517 u32 len; /* Fast Open option length */
518
519 if (foc->exp) {
520 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
521 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
522 TCPOPT_FASTOPEN_MAGIC);
523 p += TCPOLEN_EXP_FASTOPEN_BASE;
524 } else {
525 len = TCPOLEN_FASTOPEN_BASE + foc->len;
526 *p++ = TCPOPT_FASTOPEN;
527 *p++ = len;
528 }
529
530 memcpy(p, foc->val, foc->len);
531 if ((len & 3) == 2) {
532 p[foc->len] = TCPOPT_NOP;
533 p[foc->len + 1] = TCPOPT_NOP;
534 }
535 ptr += (len + 3) >> 2;
536 }
537}
538
539/* Compute TCP options for SYN packets. This is not the final
540 * network wire format yet.
541 */
542static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
543 struct tcp_out_options *opts,
544 struct tcp_md5sig_key **md5)
545{
546 struct tcp_sock *tp = tcp_sk(sk);
547 unsigned int remaining = MAX_TCP_OPTION_SPACE;
548 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
549
550#ifdef CONFIG_TCP_MD5SIG
551 *md5 = tp->af_specific->md5_lookup(sk, sk);
552 if (*md5) {
553 opts->options |= OPTION_MD5;
554 remaining -= TCPOLEN_MD5SIG_ALIGNED;
555 }
556#else
557 *md5 = NULL;
558#endif
559
560 /* We always get an MSS option. The option bytes which will be seen in
561 * normal data packets should timestamps be used, must be in the MSS
562 * advertised. But we subtract them from tp->mss_cache so that
563 * calculations in tcp_sendmsg are simpler etc. So account for this
564 * fact here if necessary. If we don't do this correctly, as a
565 * receiver we won't recognize data packets as being full sized when we
566 * should, and thus we won't abide by the delayed ACK rules correctly.
567 * SACKs don't matter, we never delay an ACK when we have any of those
568 * going out. */
569 opts->mss = tcp_advertise_mss(sk);
570 remaining -= TCPOLEN_MSS_ALIGNED;
571
572 if (likely(sysctl_tcp_timestamps && !*md5)) {
573 opts->options |= OPTION_TS;
574 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
575 opts->tsecr = tp->rx_opt.ts_recent;
576 remaining -= TCPOLEN_TSTAMP_ALIGNED;
577 }
578 if (likely(sysctl_tcp_window_scaling)) {
579 opts->ws = tp->rx_opt.rcv_wscale;
580 opts->options |= OPTION_WSCALE;
581 remaining -= TCPOLEN_WSCALE_ALIGNED;
582 }
583 if (likely(sysctl_tcp_sack)) {
584 opts->options |= OPTION_SACK_ADVERTISE;
585 if (unlikely(!(OPTION_TS & opts->options)))
586 remaining -= TCPOLEN_SACKPERM_ALIGNED;
587 }
588
589 if (fastopen && fastopen->cookie.len >= 0) {
590 u32 need = fastopen->cookie.len;
591
592 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
593 TCPOLEN_FASTOPEN_BASE;
594 need = (need + 3) & ~3U; /* Align to 32 bits */
595 if (remaining >= need) {
596 opts->options |= OPTION_FAST_OPEN_COOKIE;
597 opts->fastopen_cookie = &fastopen->cookie;
598 remaining -= need;
599 tp->syn_fastopen = 1;
600 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
601 }
602 }
603
604 return MAX_TCP_OPTION_SPACE - remaining;
605}
606
607/* Set up TCP options for SYN-ACKs. */
608static unsigned int tcp_synack_options(struct request_sock *req,
609 unsigned int mss, struct sk_buff *skb,
610 struct tcp_out_options *opts,
611 const struct tcp_md5sig_key *md5,
612 struct tcp_fastopen_cookie *foc)
613{
614 struct inet_request_sock *ireq = inet_rsk(req);
615 unsigned int remaining = MAX_TCP_OPTION_SPACE;
616
617#ifdef CONFIG_TCP_MD5SIG
618 if (md5) {
619 opts->options |= OPTION_MD5;
620 remaining -= TCPOLEN_MD5SIG_ALIGNED;
621
622 /* We can't fit any SACK blocks in a packet with MD5 + TS
623 * options. There was discussion about disabling SACK
624 * rather than TS in order to fit in better with old,
625 * buggy kernels, but that was deemed to be unnecessary.
626 */
627 ireq->tstamp_ok &= !ireq->sack_ok;
628 }
629#endif
630
631 /* We always send an MSS option. */
632 opts->mss = mss;
633 remaining -= TCPOLEN_MSS_ALIGNED;
634
635 if (likely(ireq->wscale_ok)) {
636 opts->ws = ireq->rcv_wscale;
637 opts->options |= OPTION_WSCALE;
638 remaining -= TCPOLEN_WSCALE_ALIGNED;
639 }
640 if (likely(ireq->tstamp_ok)) {
641 opts->options |= OPTION_TS;
642 opts->tsval = tcp_skb_timestamp(skb);
643 opts->tsecr = req->ts_recent;
644 remaining -= TCPOLEN_TSTAMP_ALIGNED;
645 }
646 if (likely(ireq->sack_ok)) {
647 opts->options |= OPTION_SACK_ADVERTISE;
648 if (unlikely(!ireq->tstamp_ok))
649 remaining -= TCPOLEN_SACKPERM_ALIGNED;
650 }
651 if (foc != NULL && foc->len >= 0) {
652 u32 need = foc->len;
653
654 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
655 TCPOLEN_FASTOPEN_BASE;
656 need = (need + 3) & ~3U; /* Align to 32 bits */
657 if (remaining >= need) {
658 opts->options |= OPTION_FAST_OPEN_COOKIE;
659 opts->fastopen_cookie = foc;
660 remaining -= need;
661 }
662 }
663
664 return MAX_TCP_OPTION_SPACE - remaining;
665}
666
667/* Compute TCP options for ESTABLISHED sockets. This is not the
668 * final wire format yet.
669 */
670static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
671 struct tcp_out_options *opts,
672 struct tcp_md5sig_key **md5)
673{
674 struct tcp_sock *tp = tcp_sk(sk);
675 unsigned int size = 0;
676 unsigned int eff_sacks;
677
678 opts->options = 0;
679
680#ifdef CONFIG_TCP_MD5SIG
681 *md5 = tp->af_specific->md5_lookup(sk, sk);
682 if (unlikely(*md5)) {
683 opts->options |= OPTION_MD5;
684 size += TCPOLEN_MD5SIG_ALIGNED;
685 }
686#else
687 *md5 = NULL;
688#endif
689
690 if (likely(tp->rx_opt.tstamp_ok)) {
691 opts->options |= OPTION_TS;
692 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
693 opts->tsecr = tp->rx_opt.ts_recent;
694 size += TCPOLEN_TSTAMP_ALIGNED;
695 }
696
697 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
698 if (unlikely(eff_sacks)) {
699 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
700 opts->num_sack_blocks =
701 min_t(unsigned int, eff_sacks,
702 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
703 TCPOLEN_SACK_PERBLOCK);
704 size += TCPOLEN_SACK_BASE_ALIGNED +
705 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
706 }
707
708 return size;
709}
710
711
712/* TCP SMALL QUEUES (TSQ)
713 *
714 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
715 * to reduce RTT and bufferbloat.
716 * We do this using a special skb destructor (tcp_wfree).
717 *
718 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
719 * needs to be reallocated in a driver.
720 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
721 *
722 * Since transmit from skb destructor is forbidden, we use a tasklet
723 * to process all sockets that eventually need to send more skbs.
724 * We use one tasklet per cpu, with its own queue of sockets.
725 */
726struct tsq_tasklet {
727 struct tasklet_struct tasklet;
728 struct list_head head; /* queue of tcp sockets */
729};
730static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
731
732static void tcp_tsq_handler(struct sock *sk)
733{
734 if ((1 << sk->sk_state) &
735 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
736 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
737 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
738 0, GFP_ATOMIC);
739}
740/*
741 * One tasklet per cpu tries to send more skbs.
742 * We run in tasklet context but need to disable irqs when
743 * transferring tsq->head because tcp_wfree() might
744 * interrupt us (non NAPI drivers)
745 */
746static void tcp_tasklet_func(unsigned long data)
747{
748 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
749 LIST_HEAD(list);
750 unsigned long flags;
751 struct list_head *q, *n;
752 struct tcp_sock *tp;
753 struct sock *sk;
754
755 local_irq_save(flags);
756 list_splice_init(&tsq->head, &list);
757 local_irq_restore(flags);
758
759 list_for_each_safe(q, n, &list) {
760 tp = list_entry(q, struct tcp_sock, tsq_node);
761 list_del(&tp->tsq_node);
762
763 sk = (struct sock *)tp;
764 bh_lock_sock(sk);
765
766 if (!sock_owned_by_user(sk)) {
767 tcp_tsq_handler(sk);
768 } else {
769 /* defer the work to tcp_release_cb() */
770 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
771 }
772 bh_unlock_sock(sk);
773
774 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
775 sk_free(sk);
776 }
777}
778
779#define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
780 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
781 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
782 (1UL << TCP_MTU_REDUCED_DEFERRED))
783/**
784 * tcp_release_cb - tcp release_sock() callback
785 * @sk: socket
786 *
787 * called from release_sock() to perform protocol dependent
788 * actions before socket release.
789 */
790void tcp_release_cb(struct sock *sk)
791{
792 struct tcp_sock *tp = tcp_sk(sk);
793 unsigned long flags, nflags;
794
795 /* perform an atomic operation only if at least one flag is set */
796 do {
797 flags = tp->tsq_flags;
798 if (!(flags & TCP_DEFERRED_ALL))
799 return;
800 nflags = flags & ~TCP_DEFERRED_ALL;
801 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
802
803 if (flags & (1UL << TCP_TSQ_DEFERRED))
804 tcp_tsq_handler(sk);
805
806 /* Here begins the tricky part :
807 * We are called from release_sock() with :
808 * 1) BH disabled
809 * 2) sk_lock.slock spinlock held
810 * 3) socket owned by us (sk->sk_lock.owned == 1)
811 *
812 * But following code is meant to be called from BH handlers,
813 * so we should keep BH disabled, but early release socket ownership
814 */
815 sock_release_ownership(sk);
816
817 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
818 tcp_write_timer_handler(sk);
819 __sock_put(sk);
820 }
821 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
822 tcp_delack_timer_handler(sk);
823 __sock_put(sk);
824 }
825 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
826 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
827 __sock_put(sk);
828 }
829}
830EXPORT_SYMBOL(tcp_release_cb);
831
832void __init tcp_tasklet_init(void)
833{
834 int i;
835
836 for_each_possible_cpu(i) {
837 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
838
839 INIT_LIST_HEAD(&tsq->head);
840 tasklet_init(&tsq->tasklet,
841 tcp_tasklet_func,
842 (unsigned long)tsq);
843 }
844}
845
846/*
847 * Write buffer destructor automatically called from kfree_skb.
848 * We can't xmit new skbs from this context, as we might already
849 * hold qdisc lock.
850 */
851void tcp_wfree(struct sk_buff *skb)
852{
853 struct sock *sk = skb->sk;
854 struct tcp_sock *tp = tcp_sk(sk);
855 int wmem;
856
857 /* Keep one reference on sk_wmem_alloc.
858 * Will be released by sk_free() from here or tcp_tasklet_func()
859 */
860 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
861
862 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
863 * Wait until our queues (qdisc + devices) are drained.
864 * This gives :
865 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
866 * - chance for incoming ACK (processed by another cpu maybe)
867 * to migrate this flow (skb->ooo_okay will be eventually set)
868 */
869 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
870 goto out;
871
872 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
873 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
874 unsigned long flags;
875 struct tsq_tasklet *tsq;
876
877 /* queue this socket to tasklet queue */
878 local_irq_save(flags);
879 tsq = this_cpu_ptr(&tsq_tasklet);
880 list_add(&tp->tsq_node, &tsq->head);
881 tasklet_schedule(&tsq->tasklet);
882 local_irq_restore(flags);
883 return;
884 }
885out:
886 sk_free(sk);
887}
888
889/* This routine actually transmits TCP packets queued in by
890 * tcp_do_sendmsg(). This is used by both the initial
891 * transmission and possible later retransmissions.
892 * All SKB's seen here are completely headerless. It is our
893 * job to build the TCP header, and pass the packet down to
894 * IP so it can do the same plus pass the packet off to the
895 * device.
896 *
897 * We are working here with either a clone of the original
898 * SKB, or a fresh unique copy made by the retransmit engine.
899 */
900static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
901 gfp_t gfp_mask)
902{
903 const struct inet_connection_sock *icsk = inet_csk(sk);
904 struct inet_sock *inet;
905 struct tcp_sock *tp;
906 struct tcp_skb_cb *tcb;
907 struct tcp_out_options opts;
908 unsigned int tcp_options_size, tcp_header_size;
909 struct tcp_md5sig_key *md5;
910 struct tcphdr *th;
911 int err;
912
913 BUG_ON(!skb || !tcp_skb_pcount(skb));
914
915 if (clone_it) {
916 skb_mstamp_get(&skb->skb_mstamp);
917
918 if (unlikely(skb_cloned(skb)))
919 skb = pskb_copy(skb, gfp_mask);
920 else
921 skb = skb_clone(skb, gfp_mask);
922 if (unlikely(!skb))
923 return -ENOBUFS;
924 }
925
926 inet = inet_sk(sk);
927 tp = tcp_sk(sk);
928 tcb = TCP_SKB_CB(skb);
929 memset(&opts, 0, sizeof(opts));
930
931 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
932 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
933 else
934 tcp_options_size = tcp_established_options(sk, skb, &opts,
935 &md5);
936 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
937
938 /* if no packet is in qdisc/device queue, then allow XPS to select
939 * another queue. We can be called from tcp_tsq_handler()
940 * which holds one reference to sk_wmem_alloc.
941 *
942 * TODO: Ideally, in-flight pure ACK packets should not matter here.
943 * One way to get this would be to set skb->truesize = 2 on them.
944 */
945 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
946
947 skb_push(skb, tcp_header_size);
948 skb_reset_transport_header(skb);
949
950 skb_orphan(skb);
951 skb->sk = sk;
952 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
953 skb_set_hash_from_sk(skb, sk);
954 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
955
956 /* Build TCP header and checksum it. */
957 th = tcp_hdr(skb);
958 th->source = inet->inet_sport;
959 th->dest = inet->inet_dport;
960 th->seq = htonl(tcb->seq);
961 th->ack_seq = htonl(tp->rcv_nxt);
962 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
963 tcb->tcp_flags);
964
965 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
966 /* RFC1323: The window in SYN & SYN/ACK segments
967 * is never scaled.
968 */
969 th->window = htons(min(tp->rcv_wnd, 65535U));
970 } else {
971 th->window = htons(tcp_select_window(sk));
972 }
973 th->check = 0;
974 th->urg_ptr = 0;
975
976 /* The urg_mode check is necessary during a below snd_una win probe */
977 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
978 if (before(tp->snd_up, tcb->seq + 0x10000)) {
979 th->urg_ptr = htons(tp->snd_up - tcb->seq);
980 th->urg = 1;
981 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
982 th->urg_ptr = htons(0xFFFF);
983 th->urg = 1;
984 }
985 }
986
987 tcp_options_write((__be32 *)(th + 1), tp, &opts);
988 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
989 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
990 tcp_ecn_send(sk, skb, tcp_header_size);
991
992#ifdef CONFIG_TCP_MD5SIG
993 /* Calculate the MD5 hash, as we have all we need now */
994 if (md5) {
995 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
996 tp->af_specific->calc_md5_hash(opts.hash_location,
997 md5, sk, skb);
998 }
999#endif
1000
1001 icsk->icsk_af_ops->send_check(sk, skb);
1002
1003 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1004 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1005
1006 if (skb->len != tcp_header_size) {
1007 tcp_event_data_sent(tp, sk);
1008 tp->data_segs_out += tcp_skb_pcount(skb);
1009 }
1010
1011 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1012 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1013 tcp_skb_pcount(skb));
1014
1015 tp->segs_out += tcp_skb_pcount(skb);
1016 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1017 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1018 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1019
1020 /* Our usage of tstamp should remain private */
1021 skb->tstamp.tv64 = 0;
1022
1023 /* Cleanup our debris for IP stacks */
1024 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1025 sizeof(struct inet6_skb_parm)));
1026
1027 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1028
1029 if (likely(err <= 0))
1030 return err;
1031
1032 tcp_enter_cwr(sk);
1033
1034 return net_xmit_eval(err);
1035}
1036
1037/* This routine just queues the buffer for sending.
1038 *
1039 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1040 * otherwise socket can stall.
1041 */
1042static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1043{
1044 struct tcp_sock *tp = tcp_sk(sk);
1045
1046 /* Advance write_seq and place onto the write_queue. */
1047 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1048 __skb_header_release(skb);
1049 tcp_add_write_queue_tail(sk, skb);
1050 sk->sk_wmem_queued += skb->truesize;
1051 sk_mem_charge(sk, skb->truesize);
1052}
1053
1054/* Initialize TSO segments for a packet. */
1055static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1056{
1057 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1058 /* Avoid the costly divide in the normal
1059 * non-TSO case.
1060 */
1061 tcp_skb_pcount_set(skb, 1);
1062 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1063 } else {
1064 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1065 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1066 }
1067}
1068
1069/* When a modification to fackets out becomes necessary, we need to check
1070 * skb is counted to fackets_out or not.
1071 */
1072static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1073 int decr)
1074{
1075 struct tcp_sock *tp = tcp_sk(sk);
1076
1077 if (!tp->sacked_out || tcp_is_reno(tp))
1078 return;
1079
1080 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1081 tp->fackets_out -= decr;
1082}
1083
1084/* Pcount in the middle of the write queue got changed, we need to do various
1085 * tweaks to fix counters
1086 */
1087static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1088{
1089 struct tcp_sock *tp = tcp_sk(sk);
1090
1091 tp->packets_out -= decr;
1092
1093 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1094 tp->sacked_out -= decr;
1095 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1096 tp->retrans_out -= decr;
1097 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1098 tp->lost_out -= decr;
1099
1100 /* Reno case is special. Sigh... */
1101 if (tcp_is_reno(tp) && decr > 0)
1102 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1103
1104 tcp_adjust_fackets_out(sk, skb, decr);
1105
1106 if (tp->lost_skb_hint &&
1107 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1108 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1109 tp->lost_cnt_hint -= decr;
1110
1111 tcp_verify_left_out(tp);
1112}
1113
1114static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1115{
1116 struct skb_shared_info *shinfo = skb_shinfo(skb);
1117
1118 if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
1119 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1120 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1121 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1122
1123 shinfo->tx_flags &= ~tsflags;
1124 shinfo2->tx_flags |= tsflags;
1125 swap(shinfo->tskey, shinfo2->tskey);
1126 }
1127}
1128
1129/* Function to create two new TCP segments. Shrinks the given segment
1130 * to the specified size and appends a new segment with the rest of the
1131 * packet to the list. This won't be called frequently, I hope.
1132 * Remember, these are still headerless SKBs at this point.
1133 */
1134int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1135 unsigned int mss_now, gfp_t gfp)
1136{
1137 struct tcp_sock *tp = tcp_sk(sk);
1138 struct sk_buff *buff;
1139 int nsize, old_factor;
1140 int nlen;
1141 u8 flags;
1142
1143 if (WARN_ON(len > skb->len))
1144 return -EINVAL;
1145
1146 nsize = skb_headlen(skb) - len;
1147 if (nsize < 0)
1148 nsize = 0;
1149
1150 if (skb_unclone(skb, gfp))
1151 return -ENOMEM;
1152
1153 /* Get a new skb... force flag on. */
1154 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1155 if (!buff)
1156 return -ENOMEM; /* We'll just try again later. */
1157
1158 sk->sk_wmem_queued += buff->truesize;
1159 sk_mem_charge(sk, buff->truesize);
1160 nlen = skb->len - len - nsize;
1161 buff->truesize += nlen;
1162 skb->truesize -= nlen;
1163
1164 /* Correct the sequence numbers. */
1165 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1166 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1167 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1168
1169 /* PSH and FIN should only be set in the second packet. */
1170 flags = TCP_SKB_CB(skb)->tcp_flags;
1171 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1172 TCP_SKB_CB(buff)->tcp_flags = flags;
1173 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1174
1175 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1176 /* Copy and checksum data tail into the new buffer. */
1177 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1178 skb_put(buff, nsize),
1179 nsize, 0);
1180
1181 skb_trim(skb, len);
1182
1183 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1184 } else {
1185 skb->ip_summed = CHECKSUM_PARTIAL;
1186 skb_split(skb, buff, len);
1187 }
1188
1189 buff->ip_summed = skb->ip_summed;
1190
1191 buff->tstamp = skb->tstamp;
1192 tcp_fragment_tstamp(skb, buff);
1193
1194 old_factor = tcp_skb_pcount(skb);
1195
1196 /* Fix up tso_factor for both original and new SKB. */
1197 tcp_set_skb_tso_segs(skb, mss_now);
1198 tcp_set_skb_tso_segs(buff, mss_now);
1199
1200 /* If this packet has been sent out already, we must
1201 * adjust the various packet counters.
1202 */
1203 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1204 int diff = old_factor - tcp_skb_pcount(skb) -
1205 tcp_skb_pcount(buff);
1206
1207 if (diff)
1208 tcp_adjust_pcount(sk, skb, diff);
1209 }
1210
1211 /* Link BUFF into the send queue. */
1212 __skb_header_release(buff);
1213 tcp_insert_write_queue_after(skb, buff, sk);
1214
1215 return 0;
1216}
1217
1218/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1219 * eventually). The difference is that pulled data not copied, but
1220 * immediately discarded.
1221 */
1222static void __pskb_trim_head(struct sk_buff *skb, int len)
1223{
1224 struct skb_shared_info *shinfo;
1225 int i, k, eat;
1226
1227 eat = min_t(int, len, skb_headlen(skb));
1228 if (eat) {
1229 __skb_pull(skb, eat);
1230 len -= eat;
1231 if (!len)
1232 return;
1233 }
1234 eat = len;
1235 k = 0;
1236 shinfo = skb_shinfo(skb);
1237 for (i = 0; i < shinfo->nr_frags; i++) {
1238 int size = skb_frag_size(&shinfo->frags[i]);
1239
1240 if (size <= eat) {
1241 skb_frag_unref(skb, i);
1242 eat -= size;
1243 } else {
1244 shinfo->frags[k] = shinfo->frags[i];
1245 if (eat) {
1246 shinfo->frags[k].page_offset += eat;
1247 skb_frag_size_sub(&shinfo->frags[k], eat);
1248 eat = 0;
1249 }
1250 k++;
1251 }
1252 }
1253 shinfo->nr_frags = k;
1254
1255 skb_reset_tail_pointer(skb);
1256 skb->data_len -= len;
1257 skb->len = skb->data_len;
1258}
1259
1260/* Remove acked data from a packet in the transmit queue. */
1261int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1262{
1263 if (skb_unclone(skb, GFP_ATOMIC))
1264 return -ENOMEM;
1265
1266 __pskb_trim_head(skb, len);
1267
1268 TCP_SKB_CB(skb)->seq += len;
1269 skb->ip_summed = CHECKSUM_PARTIAL;
1270
1271 skb->truesize -= len;
1272 sk->sk_wmem_queued -= len;
1273 sk_mem_uncharge(sk, len);
1274 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1275
1276 /* Any change of skb->len requires recalculation of tso factor. */
1277 if (tcp_skb_pcount(skb) > 1)
1278 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1279
1280 return 0;
1281}
1282
1283/* Calculate MSS not accounting any TCP options. */
1284static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1285{
1286 const struct tcp_sock *tp = tcp_sk(sk);
1287 const struct inet_connection_sock *icsk = inet_csk(sk);
1288 int mss_now;
1289
1290 /* Calculate base mss without TCP options:
1291 It is MMS_S - sizeof(tcphdr) of rfc1122
1292 */
1293 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1294
1295 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1296 if (icsk->icsk_af_ops->net_frag_header_len) {
1297 const struct dst_entry *dst = __sk_dst_get(sk);
1298
1299 if (dst && dst_allfrag(dst))
1300 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1301 }
1302
1303 /* Clamp it (mss_clamp does not include tcp options) */
1304 if (mss_now > tp->rx_opt.mss_clamp)
1305 mss_now = tp->rx_opt.mss_clamp;
1306
1307 /* Now subtract optional transport overhead */
1308 mss_now -= icsk->icsk_ext_hdr_len;
1309
1310 /* Then reserve room for full set of TCP options and 8 bytes of data */
1311 if (mss_now < 48)
1312 mss_now = 48;
1313 return mss_now;
1314}
1315
1316/* Calculate MSS. Not accounting for SACKs here. */
1317int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1318{
1319 /* Subtract TCP options size, not including SACKs */
1320 return __tcp_mtu_to_mss(sk, pmtu) -
1321 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1322}
1323
1324/* Inverse of above */
1325int tcp_mss_to_mtu(struct sock *sk, int mss)
1326{
1327 const struct tcp_sock *tp = tcp_sk(sk);
1328 const struct inet_connection_sock *icsk = inet_csk(sk);
1329 int mtu;
1330
1331 mtu = mss +
1332 tp->tcp_header_len +
1333 icsk->icsk_ext_hdr_len +
1334 icsk->icsk_af_ops->net_header_len;
1335
1336 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1337 if (icsk->icsk_af_ops->net_frag_header_len) {
1338 const struct dst_entry *dst = __sk_dst_get(sk);
1339
1340 if (dst && dst_allfrag(dst))
1341 mtu += icsk->icsk_af_ops->net_frag_header_len;
1342 }
1343 return mtu;
1344}
1345
1346/* MTU probing init per socket */
1347void tcp_mtup_init(struct sock *sk)
1348{
1349 struct tcp_sock *tp = tcp_sk(sk);
1350 struct inet_connection_sock *icsk = inet_csk(sk);
1351 struct net *net = sock_net(sk);
1352
1353 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1354 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1355 icsk->icsk_af_ops->net_header_len;
1356 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1357 icsk->icsk_mtup.probe_size = 0;
1358 if (icsk->icsk_mtup.enabled)
1359 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1360}
1361EXPORT_SYMBOL(tcp_mtup_init);
1362
1363/* This function synchronize snd mss to current pmtu/exthdr set.
1364
1365 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1366 for TCP options, but includes only bare TCP header.
1367
1368 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1369 It is minimum of user_mss and mss received with SYN.
1370 It also does not include TCP options.
1371
1372 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1373
1374 tp->mss_cache is current effective sending mss, including
1375 all tcp options except for SACKs. It is evaluated,
1376 taking into account current pmtu, but never exceeds
1377 tp->rx_opt.mss_clamp.
1378
1379 NOTE1. rfc1122 clearly states that advertised MSS
1380 DOES NOT include either tcp or ip options.
1381
1382 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1383 are READ ONLY outside this function. --ANK (980731)
1384 */
1385unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1386{
1387 struct tcp_sock *tp = tcp_sk(sk);
1388 struct inet_connection_sock *icsk = inet_csk(sk);
1389 int mss_now;
1390
1391 if (icsk->icsk_mtup.search_high > pmtu)
1392 icsk->icsk_mtup.search_high = pmtu;
1393
1394 mss_now = tcp_mtu_to_mss(sk, pmtu);
1395 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1396
1397 /* And store cached results */
1398 icsk->icsk_pmtu_cookie = pmtu;
1399 if (icsk->icsk_mtup.enabled)
1400 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1401 tp->mss_cache = mss_now;
1402
1403 return mss_now;
1404}
1405EXPORT_SYMBOL(tcp_sync_mss);
1406
1407/* Compute the current effective MSS, taking SACKs and IP options,
1408 * and even PMTU discovery events into account.
1409 */
1410unsigned int tcp_current_mss(struct sock *sk)
1411{
1412 const struct tcp_sock *tp = tcp_sk(sk);
1413 const struct dst_entry *dst = __sk_dst_get(sk);
1414 u32 mss_now;
1415 unsigned int header_len;
1416 struct tcp_out_options opts;
1417 struct tcp_md5sig_key *md5;
1418
1419 mss_now = tp->mss_cache;
1420
1421 if (dst) {
1422 u32 mtu = dst_mtu(dst);
1423 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1424 mss_now = tcp_sync_mss(sk, mtu);
1425 }
1426
1427 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1428 sizeof(struct tcphdr);
1429 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1430 * some common options. If this is an odd packet (because we have SACK
1431 * blocks etc) then our calculated header_len will be different, and
1432 * we have to adjust mss_now correspondingly */
1433 if (header_len != tp->tcp_header_len) {
1434 int delta = (int) header_len - tp->tcp_header_len;
1435 mss_now -= delta;
1436 }
1437
1438 return mss_now;
1439}
1440
1441/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1442 * As additional protections, we do not touch cwnd in retransmission phases,
1443 * and if application hit its sndbuf limit recently.
1444 */
1445static void tcp_cwnd_application_limited(struct sock *sk)
1446{
1447 struct tcp_sock *tp = tcp_sk(sk);
1448
1449 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1450 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1451 /* Limited by application or receiver window. */
1452 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1453 u32 win_used = max(tp->snd_cwnd_used, init_win);
1454 if (win_used < tp->snd_cwnd) {
1455 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1456 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1457 }
1458 tp->snd_cwnd_used = 0;
1459 }
1460 tp->snd_cwnd_stamp = tcp_time_stamp;
1461}
1462
1463static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1464{
1465 struct tcp_sock *tp = tcp_sk(sk);
1466
1467 /* Track the maximum number of outstanding packets in each
1468 * window, and remember whether we were cwnd-limited then.
1469 */
1470 if (!before(tp->snd_una, tp->max_packets_seq) ||
1471 tp->packets_out > tp->max_packets_out) {
1472 tp->max_packets_out = tp->packets_out;
1473 tp->max_packets_seq = tp->snd_nxt;
1474 tp->is_cwnd_limited = is_cwnd_limited;
1475 }
1476
1477 if (tcp_is_cwnd_limited(sk)) {
1478 /* Network is feed fully. */
1479 tp->snd_cwnd_used = 0;
1480 tp->snd_cwnd_stamp = tcp_time_stamp;
1481 } else {
1482 /* Network starves. */
1483 if (tp->packets_out > tp->snd_cwnd_used)
1484 tp->snd_cwnd_used = tp->packets_out;
1485
1486 if (sysctl_tcp_slow_start_after_idle &&
1487 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1488 tcp_cwnd_application_limited(sk);
1489 }
1490}
1491
1492/* Minshall's variant of the Nagle send check. */
1493static bool tcp_minshall_check(const struct tcp_sock *tp)
1494{
1495 return after(tp->snd_sml, tp->snd_una) &&
1496 !after(tp->snd_sml, tp->snd_nxt);
1497}
1498
1499/* Update snd_sml if this skb is under mss
1500 * Note that a TSO packet might end with a sub-mss segment
1501 * The test is really :
1502 * if ((skb->len % mss) != 0)
1503 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1504 * But we can avoid doing the divide again given we already have
1505 * skb_pcount = skb->len / mss_now
1506 */
1507static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1508 const struct sk_buff *skb)
1509{
1510 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1511 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1512}
1513
1514/* Return false, if packet can be sent now without violation Nagle's rules:
1515 * 1. It is full sized. (provided by caller in %partial bool)
1516 * 2. Or it contains FIN. (already checked by caller)
1517 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1518 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1519 * With Minshall's modification: all sent small packets are ACKed.
1520 */
1521static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1522 int nonagle)
1523{
1524 return partial &&
1525 ((nonagle & TCP_NAGLE_CORK) ||
1526 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1527}
1528
1529/* Return how many segs we'd like on a TSO packet,
1530 * to send one TSO packet per ms
1531 */
1532static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1533{
1534 u32 bytes, segs;
1535
1536 bytes = min(sk->sk_pacing_rate >> 10,
1537 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1538
1539 /* Goal is to send at least one packet per ms,
1540 * not one big TSO packet every 100 ms.
1541 * This preserves ACK clocking and is consistent
1542 * with tcp_tso_should_defer() heuristic.
1543 */
1544 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1545
1546 return min_t(u32, segs, sk->sk_gso_max_segs);
1547}
1548
1549/* Returns the portion of skb which can be sent right away */
1550static unsigned int tcp_mss_split_point(const struct sock *sk,
1551 const struct sk_buff *skb,
1552 unsigned int mss_now,
1553 unsigned int max_segs,
1554 int nonagle)
1555{
1556 const struct tcp_sock *tp = tcp_sk(sk);
1557 u32 partial, needed, window, max_len;
1558
1559 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1560 max_len = mss_now * max_segs;
1561
1562 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1563 return max_len;
1564
1565 needed = min(skb->len, window);
1566
1567 if (max_len <= needed)
1568 return max_len;
1569
1570 partial = needed % mss_now;
1571 /* If last segment is not a full MSS, check if Nagle rules allow us
1572 * to include this last segment in this skb.
1573 * Otherwise, we'll split the skb at last MSS boundary
1574 */
1575 if (tcp_nagle_check(partial != 0, tp, nonagle))
1576 return needed - partial;
1577
1578 return needed;
1579}
1580
1581/* Can at least one segment of SKB be sent right now, according to the
1582 * congestion window rules? If so, return how many segments are allowed.
1583 */
1584static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1585 const struct sk_buff *skb)
1586{
1587 u32 in_flight, cwnd, halfcwnd;
1588
1589 /* Don't be strict about the congestion window for the final FIN. */
1590 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1591 tcp_skb_pcount(skb) == 1)
1592 return 1;
1593
1594 in_flight = tcp_packets_in_flight(tp);
1595 cwnd = tp->snd_cwnd;
1596 if (in_flight >= cwnd)
1597 return 0;
1598
1599 /* For better scheduling, ensure we have at least
1600 * 2 GSO packets in flight.
1601 */
1602 halfcwnd = max(cwnd >> 1, 1U);
1603 return min(halfcwnd, cwnd - in_flight);
1604}
1605
1606/* Initialize TSO state of a skb.
1607 * This must be invoked the first time we consider transmitting
1608 * SKB onto the wire.
1609 */
1610static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1611{
1612 int tso_segs = tcp_skb_pcount(skb);
1613
1614 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1615 tcp_set_skb_tso_segs(skb, mss_now);
1616 tso_segs = tcp_skb_pcount(skb);
1617 }
1618 return tso_segs;
1619}
1620
1621
1622/* Return true if the Nagle test allows this packet to be
1623 * sent now.
1624 */
1625static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1626 unsigned int cur_mss, int nonagle)
1627{
1628 /* Nagle rule does not apply to frames, which sit in the middle of the
1629 * write_queue (they have no chances to get new data).
1630 *
1631 * This is implemented in the callers, where they modify the 'nonagle'
1632 * argument based upon the location of SKB in the send queue.
1633 */
1634 if (nonagle & TCP_NAGLE_PUSH)
1635 return true;
1636
1637 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1638 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1639 return true;
1640
1641 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1642 return true;
1643
1644 return false;
1645}
1646
1647/* Does at least the first segment of SKB fit into the send window? */
1648static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1649 const struct sk_buff *skb,
1650 unsigned int cur_mss)
1651{
1652 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1653
1654 if (skb->len > cur_mss)
1655 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1656
1657 return !after(end_seq, tcp_wnd_end(tp));
1658}
1659
1660/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1661 * should be put on the wire right now. If so, it returns the number of
1662 * packets allowed by the congestion window.
1663 */
1664static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1665 unsigned int cur_mss, int nonagle)
1666{
1667 const struct tcp_sock *tp = tcp_sk(sk);
1668 unsigned int cwnd_quota;
1669
1670 tcp_init_tso_segs(skb, cur_mss);
1671
1672 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1673 return 0;
1674
1675 cwnd_quota = tcp_cwnd_test(tp, skb);
1676 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1677 cwnd_quota = 0;
1678
1679 return cwnd_quota;
1680}
1681
1682/* Test if sending is allowed right now. */
1683bool tcp_may_send_now(struct sock *sk)
1684{
1685 const struct tcp_sock *tp = tcp_sk(sk);
1686 struct sk_buff *skb = tcp_send_head(sk);
1687
1688 return skb &&
1689 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1690 (tcp_skb_is_last(sk, skb) ?
1691 tp->nonagle : TCP_NAGLE_PUSH));
1692}
1693
1694/* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1695 * which is put after SKB on the list. It is very much like
1696 * tcp_fragment() except that it may make several kinds of assumptions
1697 * in order to speed up the splitting operation. In particular, we
1698 * know that all the data is in scatter-gather pages, and that the
1699 * packet has never been sent out before (and thus is not cloned).
1700 */
1701static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1702 unsigned int mss_now, gfp_t gfp)
1703{
1704 struct sk_buff *buff;
1705 int nlen = skb->len - len;
1706 u8 flags;
1707
1708 /* All of a TSO frame must be composed of paged data. */
1709 if (skb->len != skb->data_len)
1710 return tcp_fragment(sk, skb, len, mss_now, gfp);
1711
1712 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1713 if (unlikely(!buff))
1714 return -ENOMEM;
1715
1716 sk->sk_wmem_queued += buff->truesize;
1717 sk_mem_charge(sk, buff->truesize);
1718 buff->truesize += nlen;
1719 skb->truesize -= nlen;
1720
1721 /* Correct the sequence numbers. */
1722 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1723 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1724 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1725
1726 /* PSH and FIN should only be set in the second packet. */
1727 flags = TCP_SKB_CB(skb)->tcp_flags;
1728 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1729 TCP_SKB_CB(buff)->tcp_flags = flags;
1730
1731 /* This packet was never sent out yet, so no SACK bits. */
1732 TCP_SKB_CB(buff)->sacked = 0;
1733
1734 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1735 skb_split(skb, buff, len);
1736 tcp_fragment_tstamp(skb, buff);
1737
1738 /* Fix up tso_factor for both original and new SKB. */
1739 tcp_set_skb_tso_segs(skb, mss_now);
1740 tcp_set_skb_tso_segs(buff, mss_now);
1741
1742 /* Link BUFF into the send queue. */
1743 __skb_header_release(buff);
1744 tcp_insert_write_queue_after(skb, buff, sk);
1745
1746 return 0;
1747}
1748
1749/* Try to defer sending, if possible, in order to minimize the amount
1750 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1751 *
1752 * This algorithm is from John Heffner.
1753 */
1754static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1755 bool *is_cwnd_limited, u32 max_segs)
1756{
1757 const struct inet_connection_sock *icsk = inet_csk(sk);
1758 u32 age, send_win, cong_win, limit, in_flight;
1759 struct tcp_sock *tp = tcp_sk(sk);
1760 struct skb_mstamp now;
1761 struct sk_buff *head;
1762 int win_divisor;
1763
1764 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1765 goto send_now;
1766
1767 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1768 goto send_now;
1769
1770 /* Avoid bursty behavior by allowing defer
1771 * only if the last write was recent.
1772 */
1773 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1774 goto send_now;
1775
1776 in_flight = tcp_packets_in_flight(tp);
1777
1778 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1779
1780 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1781
1782 /* From in_flight test above, we know that cwnd > in_flight. */
1783 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1784
1785 limit = min(send_win, cong_win);
1786
1787 /* If a full-sized TSO skb can be sent, do it. */
1788 if (limit >= max_segs * tp->mss_cache)
1789 goto send_now;
1790
1791 /* Middle in queue won't get any more data, full sendable already? */
1792 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1793 goto send_now;
1794
1795 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1796 if (win_divisor) {
1797 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1798
1799 /* If at least some fraction of a window is available,
1800 * just use it.
1801 */
1802 chunk /= win_divisor;
1803 if (limit >= chunk)
1804 goto send_now;
1805 } else {
1806 /* Different approach, try not to defer past a single
1807 * ACK. Receiver should ACK every other full sized
1808 * frame, so if we have space for more than 3 frames
1809 * then send now.
1810 */
1811 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1812 goto send_now;
1813 }
1814
1815 head = tcp_write_queue_head(sk);
1816 skb_mstamp_get(&now);
1817 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1818 /* If next ACK is likely to come too late (half srtt), do not defer */
1819 if (age < (tp->srtt_us >> 4))
1820 goto send_now;
1821
1822 /* Ok, it looks like it is advisable to defer. */
1823
1824 if (cong_win < send_win && cong_win <= skb->len)
1825 *is_cwnd_limited = true;
1826
1827 return true;
1828
1829send_now:
1830 return false;
1831}
1832
1833static inline void tcp_mtu_check_reprobe(struct sock *sk)
1834{
1835 struct inet_connection_sock *icsk = inet_csk(sk);
1836 struct tcp_sock *tp = tcp_sk(sk);
1837 struct net *net = sock_net(sk);
1838 u32 interval;
1839 s32 delta;
1840
1841 interval = net->ipv4.sysctl_tcp_probe_interval;
1842 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1843 if (unlikely(delta >= interval * HZ)) {
1844 int mss = tcp_current_mss(sk);
1845
1846 /* Update current search range */
1847 icsk->icsk_mtup.probe_size = 0;
1848 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1849 sizeof(struct tcphdr) +
1850 icsk->icsk_af_ops->net_header_len;
1851 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1852
1853 /* Update probe time stamp */
1854 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1855 }
1856}
1857
1858/* Create a new MTU probe if we are ready.
1859 * MTU probe is regularly attempting to increase the path MTU by
1860 * deliberately sending larger packets. This discovers routing
1861 * changes resulting in larger path MTUs.
1862 *
1863 * Returns 0 if we should wait to probe (no cwnd available),
1864 * 1 if a probe was sent,
1865 * -1 otherwise
1866 */
1867static int tcp_mtu_probe(struct sock *sk)
1868{
1869 struct tcp_sock *tp = tcp_sk(sk);
1870 struct inet_connection_sock *icsk = inet_csk(sk);
1871 struct sk_buff *skb, *nskb, *next;
1872 struct net *net = sock_net(sk);
1873 int len;
1874 int probe_size;
1875 int size_needed;
1876 int copy;
1877 int mss_now;
1878 int interval;
1879
1880 /* Not currently probing/verifying,
1881 * not in recovery,
1882 * have enough cwnd, and
1883 * not SACKing (the variable headers throw things off) */
1884 if (!icsk->icsk_mtup.enabled ||
1885 icsk->icsk_mtup.probe_size ||
1886 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1887 tp->snd_cwnd < 11 ||
1888 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1889 return -1;
1890
1891 /* Use binary search for probe_size between tcp_mss_base,
1892 * and current mss_clamp. if (search_high - search_low)
1893 * smaller than a threshold, backoff from probing.
1894 */
1895 mss_now = tcp_current_mss(sk);
1896 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1897 icsk->icsk_mtup.search_low) >> 1);
1898 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1899 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1900 /* When misfortune happens, we are reprobing actively,
1901 * and then reprobe timer has expired. We stick with current
1902 * probing process by not resetting search range to its orignal.
1903 */
1904 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1905 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1906 /* Check whether enough time has elaplased for
1907 * another round of probing.
1908 */
1909 tcp_mtu_check_reprobe(sk);
1910 return -1;
1911 }
1912
1913 /* Have enough data in the send queue to probe? */
1914 if (tp->write_seq - tp->snd_nxt < size_needed)
1915 return -1;
1916
1917 if (tp->snd_wnd < size_needed)
1918 return -1;
1919 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1920 return 0;
1921
1922 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1923 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1924 if (!tcp_packets_in_flight(tp))
1925 return -1;
1926 else
1927 return 0;
1928 }
1929
1930 /* We're allowed to probe. Build it now. */
1931 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1932 if (!nskb)
1933 return -1;
1934 sk->sk_wmem_queued += nskb->truesize;
1935 sk_mem_charge(sk, nskb->truesize);
1936
1937 skb = tcp_send_head(sk);
1938
1939 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1940 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1941 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1942 TCP_SKB_CB(nskb)->sacked = 0;
1943 nskb->csum = 0;
1944 nskb->ip_summed = skb->ip_summed;
1945
1946 tcp_insert_write_queue_before(nskb, skb, sk);
1947
1948 len = 0;
1949 tcp_for_write_queue_from_safe(skb, next, sk) {
1950 copy = min_t(int, skb->len, probe_size - len);
1951 if (nskb->ip_summed)
1952 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1953 else
1954 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1955 skb_put(nskb, copy),
1956 copy, nskb->csum);
1957
1958 if (skb->len <= copy) {
1959 /* We've eaten all the data from this skb.
1960 * Throw it away. */
1961 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1962 tcp_unlink_write_queue(skb, sk);
1963 sk_wmem_free_skb(sk, skb);
1964 } else {
1965 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1966 ~(TCPHDR_FIN|TCPHDR_PSH);
1967 if (!skb_shinfo(skb)->nr_frags) {
1968 skb_pull(skb, copy);
1969 if (skb->ip_summed != CHECKSUM_PARTIAL)
1970 skb->csum = csum_partial(skb->data,
1971 skb->len, 0);
1972 } else {
1973 __pskb_trim_head(skb, copy);
1974 tcp_set_skb_tso_segs(skb, mss_now);
1975 }
1976 TCP_SKB_CB(skb)->seq += copy;
1977 }
1978
1979 len += copy;
1980
1981 if (len >= probe_size)
1982 break;
1983 }
1984 tcp_init_tso_segs(nskb, nskb->len);
1985
1986 /* We're ready to send. If this fails, the probe will
1987 * be resegmented into mss-sized pieces by tcp_write_xmit().
1988 */
1989 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1990 /* Decrement cwnd here because we are sending
1991 * effectively two packets. */
1992 tp->snd_cwnd--;
1993 tcp_event_new_data_sent(sk, nskb);
1994
1995 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1996 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1997 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1998
1999 return 1;
2000 }
2001
2002 return -1;
2003}
2004
2005/* This routine writes packets to the network. It advances the
2006 * send_head. This happens as incoming acks open up the remote
2007 * window for us.
2008 *
2009 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2010 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2011 * account rare use of URG, this is not a big flaw.
2012 *
2013 * Send at most one packet when push_one > 0. Temporarily ignore
2014 * cwnd limit to force at most one packet out when push_one == 2.
2015
2016 * Returns true, if no segments are in flight and we have queued segments,
2017 * but cannot send anything now because of SWS or another problem.
2018 */
2019static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2020 int push_one, gfp_t gfp)
2021{
2022 struct tcp_sock *tp = tcp_sk(sk);
2023 struct sk_buff *skb;
2024 unsigned int tso_segs, sent_pkts;
2025 int cwnd_quota;
2026 int result;
2027 bool is_cwnd_limited = false;
2028 u32 max_segs;
2029
2030 sent_pkts = 0;
2031
2032 if (!push_one) {
2033 /* Do MTU probing. */
2034 result = tcp_mtu_probe(sk);
2035 if (!result) {
2036 return false;
2037 } else if (result > 0) {
2038 sent_pkts = 1;
2039 }
2040 }
2041
2042 max_segs = tcp_tso_autosize(sk, mss_now);
2043 while ((skb = tcp_send_head(sk))) {
2044 unsigned int limit;
2045
2046 tso_segs = tcp_init_tso_segs(skb, mss_now);
2047 BUG_ON(!tso_segs);
2048
2049 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2050 /* "skb_mstamp" is used as a start point for the retransmit timer */
2051 skb_mstamp_get(&skb->skb_mstamp);
2052 goto repair; /* Skip network transmission */
2053 }
2054
2055 cwnd_quota = tcp_cwnd_test(tp, skb);
2056 if (!cwnd_quota) {
2057 if (push_one == 2)
2058 /* Force out a loss probe pkt. */
2059 cwnd_quota = 1;
2060 else
2061 break;
2062 }
2063
2064 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2065 break;
2066
2067 if (tso_segs == 1) {
2068 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2069 (tcp_skb_is_last(sk, skb) ?
2070 nonagle : TCP_NAGLE_PUSH))))
2071 break;
2072 } else {
2073 if (!push_one &&
2074 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2075 max_segs))
2076 break;
2077 }
2078
2079 limit = mss_now;
2080 if (tso_segs > 1 && !tcp_urg_mode(tp))
2081 limit = tcp_mss_split_point(sk, skb, mss_now,
2082 min_t(unsigned int,
2083 cwnd_quota,
2084 max_segs),
2085 nonagle);
2086
2087 if (skb->len > limit &&
2088 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2089 break;
2090
2091 /* TCP Small Queues :
2092 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2093 * This allows for :
2094 * - better RTT estimation and ACK scheduling
2095 * - faster recovery
2096 * - high rates
2097 * Alas, some drivers / subsystems require a fair amount
2098 * of queued bytes to ensure line rate.
2099 * One example is wifi aggregation (802.11 AMPDU)
2100 */
2101 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2102 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2103
2104 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2105 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2106 /* It is possible TX completion already happened
2107 * before we set TSQ_THROTTLED, so we must
2108 * test again the condition.
2109 */
2110 smp_mb__after_atomic();
2111 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2112 break;
2113 }
2114
2115 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2116 break;
2117
2118repair:
2119 /* Advance the send_head. This one is sent out.
2120 * This call will increment packets_out.
2121 */
2122 tcp_event_new_data_sent(sk, skb);
2123
2124 tcp_minshall_update(tp, mss_now, skb);
2125 sent_pkts += tcp_skb_pcount(skb);
2126
2127 if (push_one)
2128 break;
2129 }
2130
2131 if (likely(sent_pkts)) {
2132 if (tcp_in_cwnd_reduction(sk))
2133 tp->prr_out += sent_pkts;
2134
2135 /* Send one loss probe per tail loss episode. */
2136 if (push_one != 2)
2137 tcp_schedule_loss_probe(sk);
2138 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2139 tcp_cwnd_validate(sk, is_cwnd_limited);
2140 return false;
2141 }
2142 return !tp->packets_out && tcp_send_head(sk);
2143}
2144
2145bool tcp_schedule_loss_probe(struct sock *sk)
2146{
2147 struct inet_connection_sock *icsk = inet_csk(sk);
2148 struct tcp_sock *tp = tcp_sk(sk);
2149 u32 timeout, tlp_time_stamp, rto_time_stamp;
2150 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2151
2152 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2153 return false;
2154 /* No consecutive loss probes. */
2155 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2156 tcp_rearm_rto(sk);
2157 return false;
2158 }
2159 /* Don't do any loss probe on a Fast Open connection before 3WHS
2160 * finishes.
2161 */
2162 if (tp->fastopen_rsk)
2163 return false;
2164
2165 /* TLP is only scheduled when next timer event is RTO. */
2166 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2167 return false;
2168
2169 /* Schedule a loss probe in 2*RTT for SACK capable connections
2170 * in Open state, that are either limited by cwnd or application.
2171 */
2172 if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
2173 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2174 return false;
2175
2176 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2177 tcp_send_head(sk))
2178 return false;
2179
2180 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2181 * for delayed ack when there's one outstanding packet. If no RTT
2182 * sample is available then probe after TCP_TIMEOUT_INIT.
2183 */
2184 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2185 if (tp->packets_out == 1)
2186 timeout = max_t(u32, timeout,
2187 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2188 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2189
2190 /* If RTO is shorter, just schedule TLP in its place. */
2191 tlp_time_stamp = tcp_time_stamp + timeout;
2192 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2193 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2194 s32 delta = rto_time_stamp - tcp_time_stamp;
2195 if (delta > 0)
2196 timeout = delta;
2197 }
2198
2199 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2200 TCP_RTO_MAX);
2201 return true;
2202}
2203
2204/* Thanks to skb fast clones, we can detect if a prior transmit of
2205 * a packet is still in a qdisc or driver queue.
2206 * In this case, there is very little point doing a retransmit !
2207 * Note: This is called from BH context only.
2208 */
2209static bool skb_still_in_host_queue(const struct sock *sk,
2210 const struct sk_buff *skb)
2211{
2212 if (unlikely(skb_fclone_busy(sk, skb))) {
2213 NET_INC_STATS_BH(sock_net(sk),
2214 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2215 return true;
2216 }
2217 return false;
2218}
2219
2220/* When probe timeout (PTO) fires, try send a new segment if possible, else
2221 * retransmit the last segment.
2222 */
2223void tcp_send_loss_probe(struct sock *sk)
2224{
2225 struct tcp_sock *tp = tcp_sk(sk);
2226 struct sk_buff *skb;
2227 int pcount;
2228 int mss = tcp_current_mss(sk);
2229
2230 skb = tcp_send_head(sk);
2231 if (skb) {
2232 if (tcp_snd_wnd_test(tp, skb, mss)) {
2233 pcount = tp->packets_out;
2234 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2235 if (tp->packets_out > pcount)
2236 goto probe_sent;
2237 goto rearm_timer;
2238 }
2239 skb = tcp_write_queue_prev(sk, skb);
2240 } else {
2241 skb = tcp_write_queue_tail(sk);
2242 }
2243
2244 /* At most one outstanding TLP retransmission. */
2245 if (tp->tlp_high_seq)
2246 goto rearm_timer;
2247
2248 /* Retransmit last segment. */
2249 if (WARN_ON(!skb))
2250 goto rearm_timer;
2251
2252 if (skb_still_in_host_queue(sk, skb))
2253 goto rearm_timer;
2254
2255 pcount = tcp_skb_pcount(skb);
2256 if (WARN_ON(!pcount))
2257 goto rearm_timer;
2258
2259 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2260 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2261 GFP_ATOMIC)))
2262 goto rearm_timer;
2263 skb = tcp_write_queue_next(sk, skb);
2264 }
2265
2266 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2267 goto rearm_timer;
2268
2269 if (__tcp_retransmit_skb(sk, skb))
2270 goto rearm_timer;
2271
2272 /* Record snd_nxt for loss detection. */
2273 tp->tlp_high_seq = tp->snd_nxt;
2274
2275probe_sent:
2276 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2277 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2278 inet_csk(sk)->icsk_pending = 0;
2279rearm_timer:
2280 tcp_rearm_rto(sk);
2281}
2282
2283/* Push out any pending frames which were held back due to
2284 * TCP_CORK or attempt at coalescing tiny packets.
2285 * The socket must be locked by the caller.
2286 */
2287void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2288 int nonagle)
2289{
2290 /* If we are closed, the bytes will have to remain here.
2291 * In time closedown will finish, we empty the write queue and
2292 * all will be happy.
2293 */
2294 if (unlikely(sk->sk_state == TCP_CLOSE))
2295 return;
2296
2297 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2298 sk_gfp_mask(sk, GFP_ATOMIC)))
2299 tcp_check_probe_timer(sk);
2300}
2301
2302/* Send _single_ skb sitting at the send head. This function requires
2303 * true push pending frames to setup probe timer etc.
2304 */
2305void tcp_push_one(struct sock *sk, unsigned int mss_now)
2306{
2307 struct sk_buff *skb = tcp_send_head(sk);
2308
2309 BUG_ON(!skb || skb->len < mss_now);
2310
2311 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2312}
2313
2314/* This function returns the amount that we can raise the
2315 * usable window based on the following constraints
2316 *
2317 * 1. The window can never be shrunk once it is offered (RFC 793)
2318 * 2. We limit memory per socket
2319 *
2320 * RFC 1122:
2321 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2322 * RECV.NEXT + RCV.WIN fixed until:
2323 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2324 *
2325 * i.e. don't raise the right edge of the window until you can raise
2326 * it at least MSS bytes.
2327 *
2328 * Unfortunately, the recommended algorithm breaks header prediction,
2329 * since header prediction assumes th->window stays fixed.
2330 *
2331 * Strictly speaking, keeping th->window fixed violates the receiver
2332 * side SWS prevention criteria. The problem is that under this rule
2333 * a stream of single byte packets will cause the right side of the
2334 * window to always advance by a single byte.
2335 *
2336 * Of course, if the sender implements sender side SWS prevention
2337 * then this will not be a problem.
2338 *
2339 * BSD seems to make the following compromise:
2340 *
2341 * If the free space is less than the 1/4 of the maximum
2342 * space available and the free space is less than 1/2 mss,
2343 * then set the window to 0.
2344 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2345 * Otherwise, just prevent the window from shrinking
2346 * and from being larger than the largest representable value.
2347 *
2348 * This prevents incremental opening of the window in the regime
2349 * where TCP is limited by the speed of the reader side taking
2350 * data out of the TCP receive queue. It does nothing about
2351 * those cases where the window is constrained on the sender side
2352 * because the pipeline is full.
2353 *
2354 * BSD also seems to "accidentally" limit itself to windows that are a
2355 * multiple of MSS, at least until the free space gets quite small.
2356 * This would appear to be a side effect of the mbuf implementation.
2357 * Combining these two algorithms results in the observed behavior
2358 * of having a fixed window size at almost all times.
2359 *
2360 * Below we obtain similar behavior by forcing the offered window to
2361 * a multiple of the mss when it is feasible to do so.
2362 *
2363 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2364 * Regular options like TIMESTAMP are taken into account.
2365 */
2366u32 __tcp_select_window(struct sock *sk)
2367{
2368 struct inet_connection_sock *icsk = inet_csk(sk);
2369 struct tcp_sock *tp = tcp_sk(sk);
2370 /* MSS for the peer's data. Previous versions used mss_clamp
2371 * here. I don't know if the value based on our guesses
2372 * of peer's MSS is better for the performance. It's more correct
2373 * but may be worse for the performance because of rcv_mss
2374 * fluctuations. --SAW 1998/11/1
2375 */
2376 int mss = icsk->icsk_ack.rcv_mss;
2377 int free_space = tcp_space(sk);
2378 int allowed_space = tcp_full_space(sk);
2379 int full_space = min_t(int, tp->window_clamp, allowed_space);
2380 int window;
2381
2382 if (mss > full_space)
2383 mss = full_space;
2384
2385 if (free_space < (full_space >> 1)) {
2386 icsk->icsk_ack.quick = 0;
2387
2388 if (tcp_under_memory_pressure(sk))
2389 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2390 4U * tp->advmss);
2391
2392 /* free_space might become our new window, make sure we don't
2393 * increase it due to wscale.
2394 */
2395 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2396
2397 /* if free space is less than mss estimate, or is below 1/16th
2398 * of the maximum allowed, try to move to zero-window, else
2399 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2400 * new incoming data is dropped due to memory limits.
2401 * With large window, mss test triggers way too late in order
2402 * to announce zero window in time before rmem limit kicks in.
2403 */
2404 if (free_space < (allowed_space >> 4) || free_space < mss)
2405 return 0;
2406 }
2407
2408 if (free_space > tp->rcv_ssthresh)
2409 free_space = tp->rcv_ssthresh;
2410
2411 /* Don't do rounding if we are using window scaling, since the
2412 * scaled window will not line up with the MSS boundary anyway.
2413 */
2414 window = tp->rcv_wnd;
2415 if (tp->rx_opt.rcv_wscale) {
2416 window = free_space;
2417
2418 /* Advertise enough space so that it won't get scaled away.
2419 * Import case: prevent zero window announcement if
2420 * 1<<rcv_wscale > mss.
2421 */
2422 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2423 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2424 << tp->rx_opt.rcv_wscale);
2425 } else {
2426 /* Get the largest window that is a nice multiple of mss.
2427 * Window clamp already applied above.
2428 * If our current window offering is within 1 mss of the
2429 * free space we just keep it. This prevents the divide
2430 * and multiply from happening most of the time.
2431 * We also don't do any window rounding when the free space
2432 * is too small.
2433 */
2434 if (window <= free_space - mss || window > free_space)
2435 window = (free_space / mss) * mss;
2436 else if (mss == full_space &&
2437 free_space > window + (full_space >> 1))
2438 window = free_space;
2439 }
2440
2441 return window;
2442}
2443
2444void tcp_skb_collapse_tstamp(struct sk_buff *skb,
2445 const struct sk_buff *next_skb)
2446{
2447 const struct skb_shared_info *next_shinfo = skb_shinfo(next_skb);
2448 u8 tsflags = next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2449
2450 if (unlikely(tsflags)) {
2451 struct skb_shared_info *shinfo = skb_shinfo(skb);
2452
2453 shinfo->tx_flags |= tsflags;
2454 shinfo->tskey = next_shinfo->tskey;
2455 }
2456}
2457
2458/* Collapses two adjacent SKB's during retransmission. */
2459static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2460{
2461 struct tcp_sock *tp = tcp_sk(sk);
2462 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2463 int skb_size, next_skb_size;
2464
2465 skb_size = skb->len;
2466 next_skb_size = next_skb->len;
2467
2468 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2469
2470 tcp_highest_sack_combine(sk, next_skb, skb);
2471
2472 tcp_unlink_write_queue(next_skb, sk);
2473
2474 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2475 next_skb_size);
2476
2477 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2478 skb->ip_summed = CHECKSUM_PARTIAL;
2479
2480 if (skb->ip_summed != CHECKSUM_PARTIAL)
2481 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2482
2483 /* Update sequence range on original skb. */
2484 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2485
2486 /* Merge over control information. This moves PSH/FIN etc. over */
2487 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2488
2489 /* All done, get rid of second SKB and account for it so
2490 * packet counting does not break.
2491 */
2492 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2493
2494 /* changed transmit queue under us so clear hints */
2495 tcp_clear_retrans_hints_partial(tp);
2496 if (next_skb == tp->retransmit_skb_hint)
2497 tp->retransmit_skb_hint = skb;
2498
2499 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2500
2501 tcp_skb_collapse_tstamp(skb, next_skb);
2502
2503 sk_wmem_free_skb(sk, next_skb);
2504}
2505
2506/* Check if coalescing SKBs is legal. */
2507static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2508{
2509 if (tcp_skb_pcount(skb) > 1)
2510 return false;
2511 /* TODO: SACK collapsing could be used to remove this condition */
2512 if (skb_shinfo(skb)->nr_frags != 0)
2513 return false;
2514 if (skb_cloned(skb))
2515 return false;
2516 if (skb == tcp_send_head(sk))
2517 return false;
2518 /* Some heurestics for collapsing over SACK'd could be invented */
2519 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2520 return false;
2521
2522 return true;
2523}
2524
2525/* Collapse packets in the retransmit queue to make to create
2526 * less packets on the wire. This is only done on retransmission.
2527 */
2528static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2529 int space)
2530{
2531 struct tcp_sock *tp = tcp_sk(sk);
2532 struct sk_buff *skb = to, *tmp;
2533 bool first = true;
2534
2535 if (!sysctl_tcp_retrans_collapse)
2536 return;
2537 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2538 return;
2539
2540 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2541 if (!tcp_can_collapse(sk, skb))
2542 break;
2543
2544 space -= skb->len;
2545
2546 if (first) {
2547 first = false;
2548 continue;
2549 }
2550
2551 if (space < 0)
2552 break;
2553 /* Punt if not enough space exists in the first SKB for
2554 * the data in the second
2555 */
2556 if (skb->len > skb_availroom(to))
2557 break;
2558
2559 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2560 break;
2561
2562 tcp_collapse_retrans(sk, to);
2563 }
2564}
2565
2566/* This retransmits one SKB. Policy decisions and retransmit queue
2567 * state updates are done by the caller. Returns non-zero if an
2568 * error occurred which prevented the send.
2569 */
2570int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2571{
2572 struct tcp_sock *tp = tcp_sk(sk);
2573 struct inet_connection_sock *icsk = inet_csk(sk);
2574 unsigned int cur_mss;
2575 int err;
2576
2577 /* Inconslusive MTU probe */
2578 if (icsk->icsk_mtup.probe_size) {
2579 icsk->icsk_mtup.probe_size = 0;
2580 }
2581
2582 /* Do not sent more than we queued. 1/4 is reserved for possible
2583 * copying overhead: fragmentation, tunneling, mangling etc.
2584 */
2585 if (atomic_read(&sk->sk_wmem_alloc) >
2586 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2587 return -EAGAIN;
2588
2589 if (skb_still_in_host_queue(sk, skb))
2590 return -EBUSY;
2591
2592 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2593 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2594 BUG();
2595 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2596 return -ENOMEM;
2597 }
2598
2599 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2600 return -EHOSTUNREACH; /* Routing failure or similar. */
2601
2602 cur_mss = tcp_current_mss(sk);
2603
2604 /* If receiver has shrunk his window, and skb is out of
2605 * new window, do not retransmit it. The exception is the
2606 * case, when window is shrunk to zero. In this case
2607 * our retransmit serves as a zero window probe.
2608 */
2609 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2610 TCP_SKB_CB(skb)->seq != tp->snd_una)
2611 return -EAGAIN;
2612
2613 if (skb->len > cur_mss) {
2614 if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
2615 return -ENOMEM; /* We'll try again later. */
2616 } else {
2617 int oldpcount = tcp_skb_pcount(skb);
2618
2619 if (unlikely(oldpcount > 1)) {
2620 if (skb_unclone(skb, GFP_ATOMIC))
2621 return -ENOMEM;
2622 tcp_init_tso_segs(skb, cur_mss);
2623 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2624 }
2625 }
2626
2627 /* RFC3168, section 6.1.1.1. ECN fallback */
2628 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2629 tcp_ecn_clear_syn(sk, skb);
2630
2631 tcp_retrans_try_collapse(sk, skb, cur_mss);
2632
2633 /* Make a copy, if the first transmission SKB clone we made
2634 * is still in somebody's hands, else make a clone.
2635 */
2636
2637 /* make sure skb->data is aligned on arches that require it
2638 * and check if ack-trimming & collapsing extended the headroom
2639 * beyond what csum_start can cover.
2640 */
2641 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2642 skb_headroom(skb) >= 0xFFFF)) {
2643 struct sk_buff *nskb;
2644
2645 skb_mstamp_get(&skb->skb_mstamp);
2646 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2647 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2648 -ENOBUFS;
2649 } else {
2650 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2651 }
2652
2653 if (likely(!err)) {
2654 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2655 /* Update global TCP statistics. */
2656 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2657 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2658 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2659 tp->total_retrans++;
2660 }
2661 return err;
2662}
2663
2664int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2665{
2666 struct tcp_sock *tp = tcp_sk(sk);
2667 int err = __tcp_retransmit_skb(sk, skb);
2668
2669 if (err == 0) {
2670#if FASTRETRANS_DEBUG > 0
2671 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2672 net_dbg_ratelimited("retrans_out leaked\n");
2673 }
2674#endif
2675 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2676 tp->retrans_out += tcp_skb_pcount(skb);
2677
2678 /* Save stamp of the first retransmit. */
2679 if (!tp->retrans_stamp)
2680 tp->retrans_stamp = tcp_skb_timestamp(skb);
2681
2682 } else if (err != -EBUSY) {
2683 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2684 }
2685
2686 if (tp->undo_retrans < 0)
2687 tp->undo_retrans = 0;
2688 tp->undo_retrans += tcp_skb_pcount(skb);
2689 return err;
2690}
2691
2692/* Check if we forward retransmits are possible in the current
2693 * window/congestion state.
2694 */
2695static bool tcp_can_forward_retransmit(struct sock *sk)
2696{
2697 const struct inet_connection_sock *icsk = inet_csk(sk);
2698 const struct tcp_sock *tp = tcp_sk(sk);
2699
2700 /* Forward retransmissions are possible only during Recovery. */
2701 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2702 return false;
2703
2704 /* No forward retransmissions in Reno are possible. */
2705 if (tcp_is_reno(tp))
2706 return false;
2707
2708 /* Yeah, we have to make difficult choice between forward transmission
2709 * and retransmission... Both ways have their merits...
2710 *
2711 * For now we do not retransmit anything, while we have some new
2712 * segments to send. In the other cases, follow rule 3 for
2713 * NextSeg() specified in RFC3517.
2714 */
2715
2716 if (tcp_may_send_now(sk))
2717 return false;
2718
2719 return true;
2720}
2721
2722/* This gets called after a retransmit timeout, and the initially
2723 * retransmitted data is acknowledged. It tries to continue
2724 * resending the rest of the retransmit queue, until either
2725 * we've sent it all or the congestion window limit is reached.
2726 * If doing SACK, the first ACK which comes back for a timeout
2727 * based retransmit packet might feed us FACK information again.
2728 * If so, we use it to avoid unnecessarily retransmissions.
2729 */
2730void tcp_xmit_retransmit_queue(struct sock *sk)
2731{
2732 const struct inet_connection_sock *icsk = inet_csk(sk);
2733 struct tcp_sock *tp = tcp_sk(sk);
2734 struct sk_buff *skb;
2735 struct sk_buff *hole = NULL;
2736 u32 last_lost;
2737 int mib_idx;
2738 int fwd_rexmitting = 0;
2739
2740 if (!tp->packets_out)
2741 return;
2742
2743 if (!tp->lost_out)
2744 tp->retransmit_high = tp->snd_una;
2745
2746 if (tp->retransmit_skb_hint) {
2747 skb = tp->retransmit_skb_hint;
2748 last_lost = TCP_SKB_CB(skb)->end_seq;
2749 if (after(last_lost, tp->retransmit_high))
2750 last_lost = tp->retransmit_high;
2751 } else {
2752 skb = tcp_write_queue_head(sk);
2753 last_lost = tp->snd_una;
2754 }
2755
2756 tcp_for_write_queue_from(skb, sk) {
2757 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2758
2759 if (skb == tcp_send_head(sk))
2760 break;
2761 /* we could do better than to assign each time */
2762 if (!hole)
2763 tp->retransmit_skb_hint = skb;
2764
2765 /* Assume this retransmit will generate
2766 * only one packet for congestion window
2767 * calculation purposes. This works because
2768 * tcp_retransmit_skb() will chop up the
2769 * packet to be MSS sized and all the
2770 * packet counting works out.
2771 */
2772 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2773 return;
2774
2775 if (fwd_rexmitting) {
2776begin_fwd:
2777 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2778 break;
2779 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2780
2781 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2782 tp->retransmit_high = last_lost;
2783 if (!tcp_can_forward_retransmit(sk))
2784 break;
2785 /* Backtrack if necessary to non-L'ed skb */
2786 if (hole) {
2787 skb = hole;
2788 hole = NULL;
2789 }
2790 fwd_rexmitting = 1;
2791 goto begin_fwd;
2792
2793 } else if (!(sacked & TCPCB_LOST)) {
2794 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2795 hole = skb;
2796 continue;
2797
2798 } else {
2799 last_lost = TCP_SKB_CB(skb)->end_seq;
2800 if (icsk->icsk_ca_state != TCP_CA_Loss)
2801 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2802 else
2803 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2804 }
2805
2806 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2807 continue;
2808
2809 if (tcp_retransmit_skb(sk, skb))
2810 return;
2811
2812 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2813
2814 if (tcp_in_cwnd_reduction(sk))
2815 tp->prr_out += tcp_skb_pcount(skb);
2816
2817 if (skb == tcp_write_queue_head(sk))
2818 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2819 inet_csk(sk)->icsk_rto,
2820 TCP_RTO_MAX);
2821 }
2822}
2823
2824/* We allow to exceed memory limits for FIN packets to expedite
2825 * connection tear down and (memory) recovery.
2826 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2827 * or even be forced to close flow without any FIN.
2828 * In general, we want to allow one skb per socket to avoid hangs
2829 * with edge trigger epoll()
2830 */
2831void sk_forced_mem_schedule(struct sock *sk, int size)
2832{
2833 int amt;
2834
2835 if (size <= sk->sk_forward_alloc)
2836 return;
2837 amt = sk_mem_pages(size);
2838 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2839 sk_memory_allocated_add(sk, amt);
2840
2841 if (mem_cgroup_sockets_enabled && sk->sk_memcg)
2842 mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2843}
2844
2845/* Send a FIN. The caller locks the socket for us.
2846 * We should try to send a FIN packet really hard, but eventually give up.
2847 */
2848void tcp_send_fin(struct sock *sk)
2849{
2850 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2851 struct tcp_sock *tp = tcp_sk(sk);
2852
2853 /* Optimization, tack on the FIN if we have one skb in write queue and
2854 * this skb was not yet sent, or we are under memory pressure.
2855 * Note: in the latter case, FIN packet will be sent after a timeout,
2856 * as TCP stack thinks it has already been transmitted.
2857 */
2858 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2859coalesce:
2860 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
2861 TCP_SKB_CB(tskb)->end_seq++;
2862 tp->write_seq++;
2863 if (!tcp_send_head(sk)) {
2864 /* This means tskb was already sent.
2865 * Pretend we included the FIN on previous transmit.
2866 * We need to set tp->snd_nxt to the value it would have
2867 * if FIN had been sent. This is because retransmit path
2868 * does not change tp->snd_nxt.
2869 */
2870 tp->snd_nxt++;
2871 return;
2872 }
2873 } else {
2874 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
2875 if (unlikely(!skb)) {
2876 if (tskb)
2877 goto coalesce;
2878 return;
2879 }
2880 skb_reserve(skb, MAX_TCP_HEADER);
2881 sk_forced_mem_schedule(sk, skb->truesize);
2882 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2883 tcp_init_nondata_skb(skb, tp->write_seq,
2884 TCPHDR_ACK | TCPHDR_FIN);
2885 tcp_queue_skb(sk, skb);
2886 }
2887 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
2888}
2889
2890/* We get here when a process closes a file descriptor (either due to
2891 * an explicit close() or as a byproduct of exit()'ing) and there
2892 * was unread data in the receive queue. This behavior is recommended
2893 * by RFC 2525, section 2.17. -DaveM
2894 */
2895void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2896{
2897 struct sk_buff *skb;
2898
2899 /* NOTE: No TCP options attached and we never retransmit this. */
2900 skb = alloc_skb(MAX_TCP_HEADER, priority);
2901 if (!skb) {
2902 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2903 return;
2904 }
2905
2906 /* Reserve space for headers and prepare control bits. */
2907 skb_reserve(skb, MAX_TCP_HEADER);
2908 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2909 TCPHDR_ACK | TCPHDR_RST);
2910 skb_mstamp_get(&skb->skb_mstamp);
2911 /* Send it off. */
2912 if (tcp_transmit_skb(sk, skb, 0, priority))
2913 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2914
2915 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2916}
2917
2918/* Send a crossed SYN-ACK during socket establishment.
2919 * WARNING: This routine must only be called when we have already sent
2920 * a SYN packet that crossed the incoming SYN that caused this routine
2921 * to get called. If this assumption fails then the initial rcv_wnd
2922 * and rcv_wscale values will not be correct.
2923 */
2924int tcp_send_synack(struct sock *sk)
2925{
2926 struct sk_buff *skb;
2927
2928 skb = tcp_write_queue_head(sk);
2929 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2930 pr_debug("%s: wrong queue state\n", __func__);
2931 return -EFAULT;
2932 }
2933 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2934 if (skb_cloned(skb)) {
2935 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2936 if (!nskb)
2937 return -ENOMEM;
2938 tcp_unlink_write_queue(skb, sk);
2939 __skb_header_release(nskb);
2940 __tcp_add_write_queue_head(sk, nskb);
2941 sk_wmem_free_skb(sk, skb);
2942 sk->sk_wmem_queued += nskb->truesize;
2943 sk_mem_charge(sk, nskb->truesize);
2944 skb = nskb;
2945 }
2946
2947 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2948 tcp_ecn_send_synack(sk, skb);
2949 }
2950 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2951}
2952
2953/**
2954 * tcp_make_synack - Prepare a SYN-ACK.
2955 * sk: listener socket
2956 * dst: dst entry attached to the SYNACK
2957 * req: request_sock pointer
2958 *
2959 * Allocate one skb and build a SYNACK packet.
2960 * @dst is consumed : Caller should not use it again.
2961 */
2962struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
2963 struct request_sock *req,
2964 struct tcp_fastopen_cookie *foc,
2965 bool attach_req)
2966{
2967 struct inet_request_sock *ireq = inet_rsk(req);
2968 const struct tcp_sock *tp = tcp_sk(sk);
2969 struct tcp_md5sig_key *md5 = NULL;
2970 struct tcp_out_options opts;
2971 struct sk_buff *skb;
2972 int tcp_header_size;
2973 struct tcphdr *th;
2974 u16 user_mss;
2975 int mss;
2976
2977 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2978 if (unlikely(!skb)) {
2979 dst_release(dst);
2980 return NULL;
2981 }
2982 /* Reserve space for headers. */
2983 skb_reserve(skb, MAX_TCP_HEADER);
2984
2985 if (attach_req) {
2986 skb_set_owner_w(skb, req_to_sk(req));
2987 } else {
2988 /* sk is a const pointer, because we want to express multiple
2989 * cpu might call us concurrently.
2990 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
2991 */
2992 skb_set_owner_w(skb, (struct sock *)sk);
2993 }
2994 skb_dst_set(skb, dst);
2995
2996 mss = dst_metric_advmss(dst);
2997 user_mss = READ_ONCE(tp->rx_opt.user_mss);
2998 if (user_mss && user_mss < mss)
2999 mss = user_mss;
3000
3001 memset(&opts, 0, sizeof(opts));
3002#ifdef CONFIG_SYN_COOKIES
3003 if (unlikely(req->cookie_ts))
3004 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3005 else
3006#endif
3007 skb_mstamp_get(&skb->skb_mstamp);
3008
3009#ifdef CONFIG_TCP_MD5SIG
3010 rcu_read_lock();
3011 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3012#endif
3013 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3014 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3015 sizeof(*th);
3016
3017 skb_push(skb, tcp_header_size);
3018 skb_reset_transport_header(skb);
3019
3020 th = tcp_hdr(skb);
3021 memset(th, 0, sizeof(struct tcphdr));
3022 th->syn = 1;
3023 th->ack = 1;
3024 tcp_ecn_make_synack(req, th);
3025 th->source = htons(ireq->ir_num);
3026 th->dest = ireq->ir_rmt_port;
3027 /* Setting of flags are superfluous here for callers (and ECE is
3028 * not even correctly set)
3029 */
3030 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3031 TCPHDR_SYN | TCPHDR_ACK);
3032
3033 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3034 /* XXX data is queued and acked as is. No buffer/window check */
3035 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3036
3037 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3038 th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3039 tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3040 th->doff = (tcp_header_size >> 2);
3041 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
3042
3043#ifdef CONFIG_TCP_MD5SIG
3044 /* Okay, we have all we need - do the md5 hash if needed */
3045 if (md5)
3046 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3047 md5, req_to_sk(req), skb);
3048 rcu_read_unlock();
3049#endif
3050
3051 /* Do not fool tcpdump (if any), clean our debris */
3052 skb->tstamp.tv64 = 0;
3053 return skb;
3054}
3055EXPORT_SYMBOL(tcp_make_synack);
3056
3057static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3058{
3059 struct inet_connection_sock *icsk = inet_csk(sk);
3060 const struct tcp_congestion_ops *ca;
3061 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3062
3063 if (ca_key == TCP_CA_UNSPEC)
3064 return;
3065
3066 rcu_read_lock();
3067 ca = tcp_ca_find_key(ca_key);
3068 if (likely(ca && try_module_get(ca->owner))) {
3069 module_put(icsk->icsk_ca_ops->owner);
3070 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3071 icsk->icsk_ca_ops = ca;
3072 }
3073 rcu_read_unlock();
3074}
3075
3076/* Do all connect socket setups that can be done AF independent. */
3077static void tcp_connect_init(struct sock *sk)
3078{
3079 const struct dst_entry *dst = __sk_dst_get(sk);
3080 struct tcp_sock *tp = tcp_sk(sk);
3081 __u8 rcv_wscale;
3082
3083 /* We'll fix this up when we get a response from the other end.
3084 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3085 */
3086 tp->tcp_header_len = sizeof(struct tcphdr) +
3087 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3088
3089#ifdef CONFIG_TCP_MD5SIG
3090 if (tp->af_specific->md5_lookup(sk, sk))
3091 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3092#endif
3093
3094 /* If user gave his TCP_MAXSEG, record it to clamp */
3095 if (tp->rx_opt.user_mss)
3096 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3097 tp->max_window = 0;
3098 tcp_mtup_init(sk);
3099 tcp_sync_mss(sk, dst_mtu(dst));
3100
3101 tcp_ca_dst_init(sk, dst);
3102
3103 if (!tp->window_clamp)
3104 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3105 tp->advmss = dst_metric_advmss(dst);
3106 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3107 tp->advmss = tp->rx_opt.user_mss;
3108
3109 tcp_initialize_rcv_mss(sk);
3110
3111 /* limit the window selection if the user enforce a smaller rx buffer */
3112 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3113 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3114 tp->window_clamp = tcp_full_space(sk);
3115
3116 tcp_select_initial_window(tcp_full_space(sk),
3117 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3118 &tp->rcv_wnd,
3119 &tp->window_clamp,
3120 sysctl_tcp_window_scaling,
3121 &rcv_wscale,
3122 dst_metric(dst, RTAX_INITRWND));
3123
3124 tp->rx_opt.rcv_wscale = rcv_wscale;
3125 tp->rcv_ssthresh = tp->rcv_wnd;
3126
3127 sk->sk_err = 0;
3128 sock_reset_flag(sk, SOCK_DONE);
3129 tp->snd_wnd = 0;
3130 tcp_init_wl(tp, 0);
3131 tp->snd_una = tp->write_seq;
3132 tp->snd_sml = tp->write_seq;
3133 tp->snd_up = tp->write_seq;
3134 tp->snd_nxt = tp->write_seq;
3135
3136 if (likely(!tp->repair))
3137 tp->rcv_nxt = 0;
3138 else
3139 tp->rcv_tstamp = tcp_time_stamp;
3140 tp->rcv_wup = tp->rcv_nxt;
3141 tp->copied_seq = tp->rcv_nxt;
3142
3143 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3144 inet_csk(sk)->icsk_retransmits = 0;
3145 tcp_clear_retrans(tp);
3146}
3147
3148static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3149{
3150 struct tcp_sock *tp = tcp_sk(sk);
3151 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3152
3153 tcb->end_seq += skb->len;
3154 __skb_header_release(skb);
3155 __tcp_add_write_queue_tail(sk, skb);
3156 sk->sk_wmem_queued += skb->truesize;
3157 sk_mem_charge(sk, skb->truesize);
3158 tp->write_seq = tcb->end_seq;
3159 tp->packets_out += tcp_skb_pcount(skb);
3160}
3161
3162/* Build and send a SYN with data and (cached) Fast Open cookie. However,
3163 * queue a data-only packet after the regular SYN, such that regular SYNs
3164 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3165 * only the SYN sequence, the data are retransmitted in the first ACK.
3166 * If cookie is not cached or other error occurs, falls back to send a
3167 * regular SYN with Fast Open cookie request option.
3168 */
3169static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3170{
3171 struct tcp_sock *tp = tcp_sk(sk);
3172 struct tcp_fastopen_request *fo = tp->fastopen_req;
3173 int syn_loss = 0, space, err = 0;
3174 unsigned long last_syn_loss = 0;
3175 struct sk_buff *syn_data;
3176
3177 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3178 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3179 &syn_loss, &last_syn_loss);
3180 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3181 if (syn_loss > 1 &&
3182 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3183 fo->cookie.len = -1;
3184 goto fallback;
3185 }
3186
3187 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3188 fo->cookie.len = -1;
3189 else if (fo->cookie.len <= 0)
3190 goto fallback;
3191
3192 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3193 * user-MSS. Reserve maximum option space for middleboxes that add
3194 * private TCP options. The cost is reduced data space in SYN :(
3195 */
3196 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3197 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3198 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3199 MAX_TCP_OPTION_SPACE;
3200
3201 space = min_t(size_t, space, fo->size);
3202
3203 /* limit to order-0 allocations */
3204 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3205
3206 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3207 if (!syn_data)
3208 goto fallback;
3209 syn_data->ip_summed = CHECKSUM_PARTIAL;
3210 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3211 if (space) {
3212 int copied = copy_from_iter(skb_put(syn_data, space), space,
3213 &fo->data->msg_iter);
3214 if (unlikely(!copied)) {
3215 kfree_skb(syn_data);
3216 goto fallback;
3217 }
3218 if (copied != space) {
3219 skb_trim(syn_data, copied);
3220 space = copied;
3221 }
3222 }
3223 /* No more data pending in inet_wait_for_connect() */
3224 if (space == fo->size)
3225 fo->data = NULL;
3226 fo->copied = space;
3227
3228 tcp_connect_queue_skb(sk, syn_data);
3229
3230 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3231
3232 syn->skb_mstamp = syn_data->skb_mstamp;
3233
3234 /* Now full SYN+DATA was cloned and sent (or not),
3235 * remove the SYN from the original skb (syn_data)
3236 * we keep in write queue in case of a retransmit, as we
3237 * also have the SYN packet (with no data) in the same queue.
3238 */
3239 TCP_SKB_CB(syn_data)->seq++;
3240 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3241 if (!err) {
3242 tp->syn_data = (fo->copied > 0);
3243 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3244 goto done;
3245 }
3246
3247fallback:
3248 /* Send a regular SYN with Fast Open cookie request option */
3249 if (fo->cookie.len > 0)
3250 fo->cookie.len = 0;
3251 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3252 if (err)
3253 tp->syn_fastopen = 0;
3254done:
3255 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3256 return err;
3257}
3258
3259/* Build a SYN and send it off. */
3260int tcp_connect(struct sock *sk)
3261{
3262 struct tcp_sock *tp = tcp_sk(sk);
3263 struct sk_buff *buff;
3264 int err;
3265
3266 tcp_connect_init(sk);
3267
3268 if (unlikely(tp->repair)) {
3269 tcp_finish_connect(sk, NULL);
3270 return 0;
3271 }
3272
3273 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3274 if (unlikely(!buff))
3275 return -ENOBUFS;
3276
3277 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3278 tp->retrans_stamp = tcp_time_stamp;
3279 tcp_connect_queue_skb(sk, buff);
3280 tcp_ecn_send_syn(sk, buff);
3281
3282 /* Send off SYN; include data in Fast Open. */
3283 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3284 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3285 if (err == -ECONNREFUSED)
3286 return err;
3287
3288 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3289 * in order to make this packet get counted in tcpOutSegs.
3290 */
3291 tp->snd_nxt = tp->write_seq;
3292 tp->pushed_seq = tp->write_seq;
3293 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3294
3295 /* Timer for repeating the SYN until an answer. */
3296 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3297 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3298 return 0;
3299}
3300EXPORT_SYMBOL(tcp_connect);
3301
3302/* Send out a delayed ack, the caller does the policy checking
3303 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3304 * for details.
3305 */
3306void tcp_send_delayed_ack(struct sock *sk)
3307{
3308 struct inet_connection_sock *icsk = inet_csk(sk);
3309 int ato = icsk->icsk_ack.ato;
3310 unsigned long timeout;
3311
3312 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3313
3314 if (ato > TCP_DELACK_MIN) {
3315 const struct tcp_sock *tp = tcp_sk(sk);
3316 int max_ato = HZ / 2;
3317
3318 if (icsk->icsk_ack.pingpong ||
3319 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3320 max_ato = TCP_DELACK_MAX;
3321
3322 /* Slow path, intersegment interval is "high". */
3323
3324 /* If some rtt estimate is known, use it to bound delayed ack.
3325 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3326 * directly.
3327 */
3328 if (tp->srtt_us) {
3329 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3330 TCP_DELACK_MIN);
3331
3332 if (rtt < max_ato)
3333 max_ato = rtt;
3334 }
3335
3336 ato = min(ato, max_ato);
3337 }
3338
3339 /* Stay within the limit we were given */
3340 timeout = jiffies + ato;
3341
3342 /* Use new timeout only if there wasn't a older one earlier. */
3343 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3344 /* If delack timer was blocked or is about to expire,
3345 * send ACK now.
3346 */
3347 if (icsk->icsk_ack.blocked ||
3348 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3349 tcp_send_ack(sk);
3350 return;
3351 }
3352
3353 if (!time_before(timeout, icsk->icsk_ack.timeout))
3354 timeout = icsk->icsk_ack.timeout;
3355 }
3356 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3357 icsk->icsk_ack.timeout = timeout;
3358 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3359}
3360
3361/* This routine sends an ack and also updates the window. */
3362void tcp_send_ack(struct sock *sk)
3363{
3364 struct sk_buff *buff;
3365
3366 /* If we have been reset, we may not send again. */
3367 if (sk->sk_state == TCP_CLOSE)
3368 return;
3369
3370 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3371
3372 /* We are not putting this on the write queue, so
3373 * tcp_transmit_skb() will set the ownership to this
3374 * sock.
3375 */
3376 buff = alloc_skb(MAX_TCP_HEADER,
3377 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3378 if (unlikely(!buff)) {
3379 inet_csk_schedule_ack(sk);
3380 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3381 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3382 TCP_DELACK_MAX, TCP_RTO_MAX);
3383 return;
3384 }
3385
3386 /* Reserve space for headers and prepare control bits. */
3387 skb_reserve(buff, MAX_TCP_HEADER);
3388 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3389
3390 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3391 * too much.
3392 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3393 * We also avoid tcp_wfree() overhead (cache line miss accessing
3394 * tp->tsq_flags) by using regular sock_wfree()
3395 */
3396 skb_set_tcp_pure_ack(buff);
3397
3398 /* Send it off, this clears delayed acks for us. */
3399 skb_mstamp_get(&buff->skb_mstamp);
3400 tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
3401}
3402EXPORT_SYMBOL_GPL(tcp_send_ack);
3403
3404/* This routine sends a packet with an out of date sequence
3405 * number. It assumes the other end will try to ack it.
3406 *
3407 * Question: what should we make while urgent mode?
3408 * 4.4BSD forces sending single byte of data. We cannot send
3409 * out of window data, because we have SND.NXT==SND.MAX...
3410 *
3411 * Current solution: to send TWO zero-length segments in urgent mode:
3412 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3413 * out-of-date with SND.UNA-1 to probe window.
3414 */
3415static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3416{
3417 struct tcp_sock *tp = tcp_sk(sk);
3418 struct sk_buff *skb;
3419
3420 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3421 skb = alloc_skb(MAX_TCP_HEADER,
3422 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3423 if (!skb)
3424 return -1;
3425
3426 /* Reserve space for headers and set control bits. */
3427 skb_reserve(skb, MAX_TCP_HEADER);
3428 /* Use a previous sequence. This should cause the other
3429 * end to send an ack. Don't queue or clone SKB, just
3430 * send it.
3431 */
3432 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3433 skb_mstamp_get(&skb->skb_mstamp);
3434 NET_INC_STATS(sock_net(sk), mib);
3435 return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
3436}
3437
3438void tcp_send_window_probe(struct sock *sk)
3439{
3440 if (sk->sk_state == TCP_ESTABLISHED) {
3441 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3442 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3443 }
3444}
3445
3446/* Initiate keepalive or window probe from timer. */
3447int tcp_write_wakeup(struct sock *sk, int mib)
3448{
3449 struct tcp_sock *tp = tcp_sk(sk);
3450 struct sk_buff *skb;
3451
3452 if (sk->sk_state == TCP_CLOSE)
3453 return -1;
3454
3455 skb = tcp_send_head(sk);
3456 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3457 int err;
3458 unsigned int mss = tcp_current_mss(sk);
3459 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3460
3461 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3462 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3463
3464 /* We are probing the opening of a window
3465 * but the window size is != 0
3466 * must have been a result SWS avoidance ( sender )
3467 */
3468 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3469 skb->len > mss) {
3470 seg_size = min(seg_size, mss);
3471 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3472 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3473 return -1;
3474 } else if (!tcp_skb_pcount(skb))
3475 tcp_set_skb_tso_segs(skb, mss);
3476
3477 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3478 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3479 if (!err)
3480 tcp_event_new_data_sent(sk, skb);
3481 return err;
3482 } else {
3483 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3484 tcp_xmit_probe_skb(sk, 1, mib);
3485 return tcp_xmit_probe_skb(sk, 0, mib);
3486 }
3487}
3488
3489/* A window probe timeout has occurred. If window is not closed send
3490 * a partial packet else a zero probe.
3491 */
3492void tcp_send_probe0(struct sock *sk)
3493{
3494 struct inet_connection_sock *icsk = inet_csk(sk);
3495 struct tcp_sock *tp = tcp_sk(sk);
3496 struct net *net = sock_net(sk);
3497 unsigned long probe_max;
3498 int err;
3499
3500 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3501
3502 if (tp->packets_out || !tcp_send_head(sk)) {
3503 /* Cancel probe timer, if it is not required. */
3504 icsk->icsk_probes_out = 0;
3505 icsk->icsk_backoff = 0;
3506 return;
3507 }
3508
3509 if (err <= 0) {
3510 if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3511 icsk->icsk_backoff++;
3512 icsk->icsk_probes_out++;
3513 probe_max = TCP_RTO_MAX;
3514 } else {
3515 /* If packet was not sent due to local congestion,
3516 * do not backoff and do not remember icsk_probes_out.
3517 * Let local senders to fight for local resources.
3518 *
3519 * Use accumulated backoff yet.
3520 */
3521 if (!icsk->icsk_probes_out)
3522 icsk->icsk_probes_out = 1;
3523 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3524 }
3525 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3526 tcp_probe0_when(sk, probe_max),
3527 TCP_RTO_MAX);
3528}
3529
3530int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3531{
3532 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3533 struct flowi fl;
3534 int res;
3535
3536 tcp_rsk(req)->txhash = net_tx_rndhash();
3537 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, true);
3538 if (!res) {
3539 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
3540 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3541 }
3542 return res;
3543}
3544EXPORT_SYMBOL(tcp_rtx_synack);
1/*
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.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
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>
19 */
20
21/*
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
25 * : AF independence
26 *
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
34 *
35 */
36
37#define pr_fmt(fmt) "TCP: " fmt
38
39#include <net/tcp.h>
40
41#include <linux/compiler.h>
42#include <linux/gfp.h>
43#include <linux/module.h>
44
45/* People can turn this off for buggy TCP's found in printers etc. */
46int sysctl_tcp_retrans_collapse __read_mostly = 1;
47
48/* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
50 */
51int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
52
53/* Default TSQ limit of four TSO segments */
54int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
55
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.
59 */
60int sysctl_tcp_tso_win_divisor __read_mostly = 3;
61
62/* By default, RFC2861 behavior. */
63int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
64
65static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
66 int push_one, gfp_t gfp);
67
68/* Account for new data that has been sent to the network. */
69static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
70{
71 struct inet_connection_sock *icsk = inet_csk(sk);
72 struct tcp_sock *tp = tcp_sk(sk);
73 unsigned int prior_packets = tp->packets_out;
74
75 tcp_advance_send_head(sk, skb);
76 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
77
78 tp->packets_out += tcp_skb_pcount(skb);
79 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
80 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
81 tcp_rearm_rto(sk);
82 }
83
84 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
85 tcp_skb_pcount(skb));
86}
87
88/* SND.NXT, if window was not shrunk.
89 * If window has been shrunk, what should we make? It is not clear at all.
90 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
91 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
92 * invalid. OK, let's make this for now:
93 */
94static inline __u32 tcp_acceptable_seq(const struct sock *sk)
95{
96 const struct tcp_sock *tp = tcp_sk(sk);
97
98 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
99 return tp->snd_nxt;
100 else
101 return tcp_wnd_end(tp);
102}
103
104/* Calculate mss to advertise in SYN segment.
105 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
106 *
107 * 1. It is independent of path mtu.
108 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
109 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
110 * attached devices, because some buggy hosts are confused by
111 * large MSS.
112 * 4. We do not make 3, we advertise MSS, calculated from first
113 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
114 * This may be overridden via information stored in routing table.
115 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
116 * probably even Jumbo".
117 */
118static __u16 tcp_advertise_mss(struct sock *sk)
119{
120 struct tcp_sock *tp = tcp_sk(sk);
121 const struct dst_entry *dst = __sk_dst_get(sk);
122 int mss = tp->advmss;
123
124 if (dst) {
125 unsigned int metric = dst_metric_advmss(dst);
126
127 if (metric < mss) {
128 mss = metric;
129 tp->advmss = mss;
130 }
131 }
132
133 return (__u16)mss;
134}
135
136/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
137 * This is the first part of cwnd validation mechanism.
138 */
139void tcp_cwnd_restart(struct sock *sk, s32 delta)
140{
141 struct tcp_sock *tp = tcp_sk(sk);
142 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
143 u32 cwnd = tp->snd_cwnd;
144
145 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
146
147 tp->snd_ssthresh = tcp_current_ssthresh(sk);
148 restart_cwnd = min(restart_cwnd, cwnd);
149
150 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
151 cwnd >>= 1;
152 tp->snd_cwnd = max(cwnd, restart_cwnd);
153 tp->snd_cwnd_stamp = tcp_time_stamp;
154 tp->snd_cwnd_used = 0;
155}
156
157/* Congestion state accounting after a packet has been sent. */
158static void tcp_event_data_sent(struct tcp_sock *tp,
159 struct sock *sk)
160{
161 struct inet_connection_sock *icsk = inet_csk(sk);
162 const u32 now = tcp_time_stamp;
163
164 if (tcp_packets_in_flight(tp) == 0)
165 tcp_ca_event(sk, CA_EVENT_TX_START);
166
167 tp->lsndtime = now;
168
169 /* If it is a reply for ato after last received
170 * packet, enter pingpong mode.
171 */
172 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
173 icsk->icsk_ack.pingpong = 1;
174}
175
176/* Account for an ACK we sent. */
177static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
178{
179 tcp_dec_quickack_mode(sk, pkts);
180 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
181}
182
183
184u32 tcp_default_init_rwnd(u32 mss)
185{
186 /* Initial receive window should be twice of TCP_INIT_CWND to
187 * enable proper sending of new unsent data during fast recovery
188 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
189 * limit when mss is larger than 1460.
190 */
191 u32 init_rwnd = TCP_INIT_CWND * 2;
192
193 if (mss > 1460)
194 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
195 return init_rwnd;
196}
197
198/* Determine a window scaling and initial window to offer.
199 * Based on the assumption that the given amount of space
200 * will be offered. Store the results in the tp structure.
201 * NOTE: for smooth operation initial space offering should
202 * be a multiple of mss if possible. We assume here that mss >= 1.
203 * This MUST be enforced by all callers.
204 */
205void tcp_select_initial_window(int __space, __u32 mss,
206 __u32 *rcv_wnd, __u32 *window_clamp,
207 int wscale_ok, __u8 *rcv_wscale,
208 __u32 init_rcv_wnd)
209{
210 unsigned int space = (__space < 0 ? 0 : __space);
211
212 /* If no clamp set the clamp to the max possible scaled window */
213 if (*window_clamp == 0)
214 (*window_clamp) = (65535 << 14);
215 space = min(*window_clamp, space);
216
217 /* Quantize space offering to a multiple of mss if possible. */
218 if (space > mss)
219 space = (space / mss) * mss;
220
221 /* NOTE: offering an initial window larger than 32767
222 * will break some buggy TCP stacks. If the admin tells us
223 * it is likely we could be speaking with such a buggy stack
224 * we will truncate our initial window offering to 32K-1
225 * unless the remote has sent us a window scaling option,
226 * which we interpret as a sign the remote TCP is not
227 * misinterpreting the window field as a signed quantity.
228 */
229 if (sysctl_tcp_workaround_signed_windows)
230 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
231 else
232 (*rcv_wnd) = space;
233
234 (*rcv_wscale) = 0;
235 if (wscale_ok) {
236 /* Set window scaling on max possible window
237 * See RFC1323 for an explanation of the limit to 14
238 */
239 space = max_t(u32, space, sysctl_tcp_rmem[2]);
240 space = max_t(u32, space, sysctl_rmem_max);
241 space = min_t(u32, space, *window_clamp);
242 while (space > 65535 && (*rcv_wscale) < 14) {
243 space >>= 1;
244 (*rcv_wscale)++;
245 }
246 }
247
248 if (mss > (1 << *rcv_wscale)) {
249 if (!init_rcv_wnd) /* Use default unless specified otherwise */
250 init_rcv_wnd = tcp_default_init_rwnd(mss);
251 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
252 }
253
254 /* Set the clamp no higher than max representable value */
255 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
256}
257EXPORT_SYMBOL(tcp_select_initial_window);
258
259/* Chose a new window to advertise, update state in tcp_sock for the
260 * socket, and return result with RFC1323 scaling applied. The return
261 * value can be stuffed directly into th->window for an outgoing
262 * frame.
263 */
264static u16 tcp_select_window(struct sock *sk)
265{
266 struct tcp_sock *tp = tcp_sk(sk);
267 u32 old_win = tp->rcv_wnd;
268 u32 cur_win = tcp_receive_window(tp);
269 u32 new_win = __tcp_select_window(sk);
270
271 /* Never shrink the offered window */
272 if (new_win < cur_win) {
273 /* Danger Will Robinson!
274 * Don't update rcv_wup/rcv_wnd here or else
275 * we will not be able to advertise a zero
276 * window in time. --DaveM
277 *
278 * Relax Will Robinson.
279 */
280 if (new_win == 0)
281 NET_INC_STATS(sock_net(sk),
282 LINUX_MIB_TCPWANTZEROWINDOWADV);
283 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
284 }
285 tp->rcv_wnd = new_win;
286 tp->rcv_wup = tp->rcv_nxt;
287
288 /* Make sure we do not exceed the maximum possible
289 * scaled window.
290 */
291 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
292 new_win = min(new_win, MAX_TCP_WINDOW);
293 else
294 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
295
296 /* RFC1323 scaling applied */
297 new_win >>= tp->rx_opt.rcv_wscale;
298
299 /* If we advertise zero window, disable fast path. */
300 if (new_win == 0) {
301 tp->pred_flags = 0;
302 if (old_win)
303 NET_INC_STATS(sock_net(sk),
304 LINUX_MIB_TCPTOZEROWINDOWADV);
305 } else if (old_win == 0) {
306 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
307 }
308
309 return new_win;
310}
311
312/* Packet ECN state for a SYN-ACK */
313static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
314{
315 const struct tcp_sock *tp = tcp_sk(sk);
316
317 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
318 if (!(tp->ecn_flags & TCP_ECN_OK))
319 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
320 else if (tcp_ca_needs_ecn(sk))
321 INET_ECN_xmit(sk);
322}
323
324/* Packet ECN state for a SYN. */
325static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
326{
327 struct tcp_sock *tp = tcp_sk(sk);
328 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
329 tcp_ca_needs_ecn(sk);
330
331 if (!use_ecn) {
332 const struct dst_entry *dst = __sk_dst_get(sk);
333
334 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
335 use_ecn = true;
336 }
337
338 tp->ecn_flags = 0;
339
340 if (use_ecn) {
341 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
342 tp->ecn_flags = TCP_ECN_OK;
343 if (tcp_ca_needs_ecn(sk))
344 INET_ECN_xmit(sk);
345 }
346}
347
348static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
349{
350 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
351 /* tp->ecn_flags are cleared at a later point in time when
352 * SYN ACK is ultimatively being received.
353 */
354 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
355}
356
357static void
358tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
359{
360 if (inet_rsk(req)->ecn_ok)
361 th->ece = 1;
362}
363
364/* Set up ECN state for a packet on a ESTABLISHED socket that is about to
365 * be sent.
366 */
367static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
368 struct tcphdr *th, int tcp_header_len)
369{
370 struct tcp_sock *tp = tcp_sk(sk);
371
372 if (tp->ecn_flags & TCP_ECN_OK) {
373 /* Not-retransmitted data segment: set ECT and inject CWR. */
374 if (skb->len != tcp_header_len &&
375 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
376 INET_ECN_xmit(sk);
377 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
378 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
379 th->cwr = 1;
380 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
381 }
382 } else if (!tcp_ca_needs_ecn(sk)) {
383 /* ACK or retransmitted segment: clear ECT|CE */
384 INET_ECN_dontxmit(sk);
385 }
386 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
387 th->ece = 1;
388 }
389}
390
391/* Constructs common control bits of non-data skb. If SYN/FIN is present,
392 * auto increment end seqno.
393 */
394static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
395{
396 skb->ip_summed = CHECKSUM_PARTIAL;
397 skb->csum = 0;
398
399 TCP_SKB_CB(skb)->tcp_flags = flags;
400 TCP_SKB_CB(skb)->sacked = 0;
401
402 tcp_skb_pcount_set(skb, 1);
403
404 TCP_SKB_CB(skb)->seq = seq;
405 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
406 seq++;
407 TCP_SKB_CB(skb)->end_seq = seq;
408}
409
410static inline bool tcp_urg_mode(const struct tcp_sock *tp)
411{
412 return tp->snd_una != tp->snd_up;
413}
414
415#define OPTION_SACK_ADVERTISE (1 << 0)
416#define OPTION_TS (1 << 1)
417#define OPTION_MD5 (1 << 2)
418#define OPTION_WSCALE (1 << 3)
419#define OPTION_FAST_OPEN_COOKIE (1 << 8)
420
421struct tcp_out_options {
422 u16 options; /* bit field of OPTION_* */
423 u16 mss; /* 0 to disable */
424 u8 ws; /* window scale, 0 to disable */
425 u8 num_sack_blocks; /* number of SACK blocks to include */
426 u8 hash_size; /* bytes in hash_location */
427 __u8 *hash_location; /* temporary pointer, overloaded */
428 __u32 tsval, tsecr; /* need to include OPTION_TS */
429 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
430};
431
432/* Write previously computed TCP options to the packet.
433 *
434 * Beware: Something in the Internet is very sensitive to the ordering of
435 * TCP options, we learned this through the hard way, so be careful here.
436 * Luckily we can at least blame others for their non-compliance but from
437 * inter-operability perspective it seems that we're somewhat stuck with
438 * the ordering which we have been using if we want to keep working with
439 * those broken things (not that it currently hurts anybody as there isn't
440 * particular reason why the ordering would need to be changed).
441 *
442 * At least SACK_PERM as the first option is known to lead to a disaster
443 * (but it may well be that other scenarios fail similarly).
444 */
445static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
446 struct tcp_out_options *opts)
447{
448 u16 options = opts->options; /* mungable copy */
449
450 if (unlikely(OPTION_MD5 & options)) {
451 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
452 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
453 /* overload cookie hash location */
454 opts->hash_location = (__u8 *)ptr;
455 ptr += 4;
456 }
457
458 if (unlikely(opts->mss)) {
459 *ptr++ = htonl((TCPOPT_MSS << 24) |
460 (TCPOLEN_MSS << 16) |
461 opts->mss);
462 }
463
464 if (likely(OPTION_TS & options)) {
465 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
466 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
467 (TCPOLEN_SACK_PERM << 16) |
468 (TCPOPT_TIMESTAMP << 8) |
469 TCPOLEN_TIMESTAMP);
470 options &= ~OPTION_SACK_ADVERTISE;
471 } else {
472 *ptr++ = htonl((TCPOPT_NOP << 24) |
473 (TCPOPT_NOP << 16) |
474 (TCPOPT_TIMESTAMP << 8) |
475 TCPOLEN_TIMESTAMP);
476 }
477 *ptr++ = htonl(opts->tsval);
478 *ptr++ = htonl(opts->tsecr);
479 }
480
481 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
482 *ptr++ = htonl((TCPOPT_NOP << 24) |
483 (TCPOPT_NOP << 16) |
484 (TCPOPT_SACK_PERM << 8) |
485 TCPOLEN_SACK_PERM);
486 }
487
488 if (unlikely(OPTION_WSCALE & options)) {
489 *ptr++ = htonl((TCPOPT_NOP << 24) |
490 (TCPOPT_WINDOW << 16) |
491 (TCPOLEN_WINDOW << 8) |
492 opts->ws);
493 }
494
495 if (unlikely(opts->num_sack_blocks)) {
496 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
497 tp->duplicate_sack : tp->selective_acks;
498 int this_sack;
499
500 *ptr++ = htonl((TCPOPT_NOP << 24) |
501 (TCPOPT_NOP << 16) |
502 (TCPOPT_SACK << 8) |
503 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
504 TCPOLEN_SACK_PERBLOCK)));
505
506 for (this_sack = 0; this_sack < opts->num_sack_blocks;
507 ++this_sack) {
508 *ptr++ = htonl(sp[this_sack].start_seq);
509 *ptr++ = htonl(sp[this_sack].end_seq);
510 }
511
512 tp->rx_opt.dsack = 0;
513 }
514
515 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
516 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
517 u8 *p = (u8 *)ptr;
518 u32 len; /* Fast Open option length */
519
520 if (foc->exp) {
521 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
522 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
523 TCPOPT_FASTOPEN_MAGIC);
524 p += TCPOLEN_EXP_FASTOPEN_BASE;
525 } else {
526 len = TCPOLEN_FASTOPEN_BASE + foc->len;
527 *p++ = TCPOPT_FASTOPEN;
528 *p++ = len;
529 }
530
531 memcpy(p, foc->val, foc->len);
532 if ((len & 3) == 2) {
533 p[foc->len] = TCPOPT_NOP;
534 p[foc->len + 1] = TCPOPT_NOP;
535 }
536 ptr += (len + 3) >> 2;
537 }
538}
539
540/* Compute TCP options for SYN packets. This is not the final
541 * network wire format yet.
542 */
543static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
544 struct tcp_out_options *opts,
545 struct tcp_md5sig_key **md5)
546{
547 struct tcp_sock *tp = tcp_sk(sk);
548 unsigned int remaining = MAX_TCP_OPTION_SPACE;
549 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
550
551#ifdef CONFIG_TCP_MD5SIG
552 *md5 = tp->af_specific->md5_lookup(sk, sk);
553 if (*md5) {
554 opts->options |= OPTION_MD5;
555 remaining -= TCPOLEN_MD5SIG_ALIGNED;
556 }
557#else
558 *md5 = NULL;
559#endif
560
561 /* We always get an MSS option. The option bytes which will be seen in
562 * normal data packets should timestamps be used, must be in the MSS
563 * advertised. But we subtract them from tp->mss_cache so that
564 * calculations in tcp_sendmsg are simpler etc. So account for this
565 * fact here if necessary. If we don't do this correctly, as a
566 * receiver we won't recognize data packets as being full sized when we
567 * should, and thus we won't abide by the delayed ACK rules correctly.
568 * SACKs don't matter, we never delay an ACK when we have any of those
569 * going out. */
570 opts->mss = tcp_advertise_mss(sk);
571 remaining -= TCPOLEN_MSS_ALIGNED;
572
573 if (likely(sysctl_tcp_timestamps && !*md5)) {
574 opts->options |= OPTION_TS;
575 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
576 opts->tsecr = tp->rx_opt.ts_recent;
577 remaining -= TCPOLEN_TSTAMP_ALIGNED;
578 }
579 if (likely(sysctl_tcp_window_scaling)) {
580 opts->ws = tp->rx_opt.rcv_wscale;
581 opts->options |= OPTION_WSCALE;
582 remaining -= TCPOLEN_WSCALE_ALIGNED;
583 }
584 if (likely(sysctl_tcp_sack)) {
585 opts->options |= OPTION_SACK_ADVERTISE;
586 if (unlikely(!(OPTION_TS & opts->options)))
587 remaining -= TCPOLEN_SACKPERM_ALIGNED;
588 }
589
590 if (fastopen && fastopen->cookie.len >= 0) {
591 u32 need = fastopen->cookie.len;
592
593 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
594 TCPOLEN_FASTOPEN_BASE;
595 need = (need + 3) & ~3U; /* Align to 32 bits */
596 if (remaining >= need) {
597 opts->options |= OPTION_FAST_OPEN_COOKIE;
598 opts->fastopen_cookie = &fastopen->cookie;
599 remaining -= need;
600 tp->syn_fastopen = 1;
601 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
602 }
603 }
604
605 return MAX_TCP_OPTION_SPACE - remaining;
606}
607
608/* Set up TCP options for SYN-ACKs. */
609static unsigned int tcp_synack_options(struct request_sock *req,
610 unsigned int mss, struct sk_buff *skb,
611 struct tcp_out_options *opts,
612 const struct tcp_md5sig_key *md5,
613 struct tcp_fastopen_cookie *foc)
614{
615 struct inet_request_sock *ireq = inet_rsk(req);
616 unsigned int remaining = MAX_TCP_OPTION_SPACE;
617
618#ifdef CONFIG_TCP_MD5SIG
619 if (md5) {
620 opts->options |= OPTION_MD5;
621 remaining -= TCPOLEN_MD5SIG_ALIGNED;
622
623 /* We can't fit any SACK blocks in a packet with MD5 + TS
624 * options. There was discussion about disabling SACK
625 * rather than TS in order to fit in better with old,
626 * buggy kernels, but that was deemed to be unnecessary.
627 */
628 ireq->tstamp_ok &= !ireq->sack_ok;
629 }
630#endif
631
632 /* We always send an MSS option. */
633 opts->mss = mss;
634 remaining -= TCPOLEN_MSS_ALIGNED;
635
636 if (likely(ireq->wscale_ok)) {
637 opts->ws = ireq->rcv_wscale;
638 opts->options |= OPTION_WSCALE;
639 remaining -= TCPOLEN_WSCALE_ALIGNED;
640 }
641 if (likely(ireq->tstamp_ok)) {
642 opts->options |= OPTION_TS;
643 opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
644 opts->tsecr = req->ts_recent;
645 remaining -= TCPOLEN_TSTAMP_ALIGNED;
646 }
647 if (likely(ireq->sack_ok)) {
648 opts->options |= OPTION_SACK_ADVERTISE;
649 if (unlikely(!ireq->tstamp_ok))
650 remaining -= TCPOLEN_SACKPERM_ALIGNED;
651 }
652 if (foc != NULL && foc->len >= 0) {
653 u32 need = foc->len;
654
655 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
656 TCPOLEN_FASTOPEN_BASE;
657 need = (need + 3) & ~3U; /* Align to 32 bits */
658 if (remaining >= need) {
659 opts->options |= OPTION_FAST_OPEN_COOKIE;
660 opts->fastopen_cookie = foc;
661 remaining -= need;
662 }
663 }
664
665 return MAX_TCP_OPTION_SPACE - remaining;
666}
667
668/* Compute TCP options for ESTABLISHED sockets. This is not the
669 * final wire format yet.
670 */
671static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
672 struct tcp_out_options *opts,
673 struct tcp_md5sig_key **md5)
674{
675 struct tcp_sock *tp = tcp_sk(sk);
676 unsigned int size = 0;
677 unsigned int eff_sacks;
678
679 opts->options = 0;
680
681#ifdef CONFIG_TCP_MD5SIG
682 *md5 = tp->af_specific->md5_lookup(sk, sk);
683 if (unlikely(*md5)) {
684 opts->options |= OPTION_MD5;
685 size += TCPOLEN_MD5SIG_ALIGNED;
686 }
687#else
688 *md5 = NULL;
689#endif
690
691 if (likely(tp->rx_opt.tstamp_ok)) {
692 opts->options |= OPTION_TS;
693 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
694 opts->tsecr = tp->rx_opt.ts_recent;
695 size += TCPOLEN_TSTAMP_ALIGNED;
696 }
697
698 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
699 if (unlikely(eff_sacks)) {
700 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
701 opts->num_sack_blocks =
702 min_t(unsigned int, eff_sacks,
703 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
704 TCPOLEN_SACK_PERBLOCK);
705 size += TCPOLEN_SACK_BASE_ALIGNED +
706 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
707 }
708
709 return size;
710}
711
712
713/* TCP SMALL QUEUES (TSQ)
714 *
715 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
716 * to reduce RTT and bufferbloat.
717 * We do this using a special skb destructor (tcp_wfree).
718 *
719 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
720 * needs to be reallocated in a driver.
721 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
722 *
723 * Since transmit from skb destructor is forbidden, we use a tasklet
724 * to process all sockets that eventually need to send more skbs.
725 * We use one tasklet per cpu, with its own queue of sockets.
726 */
727struct tsq_tasklet {
728 struct tasklet_struct tasklet;
729 struct list_head head; /* queue of tcp sockets */
730};
731static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
732
733static void tcp_tsq_handler(struct sock *sk)
734{
735 if ((1 << sk->sk_state) &
736 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
737 TCPF_CLOSE_WAIT | TCPF_LAST_ACK)) {
738 struct tcp_sock *tp = tcp_sk(sk);
739
740 if (tp->lost_out > tp->retrans_out &&
741 tp->snd_cwnd > tcp_packets_in_flight(tp))
742 tcp_xmit_retransmit_queue(sk);
743
744 tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
745 0, GFP_ATOMIC);
746 }
747}
748/*
749 * One tasklet per cpu tries to send more skbs.
750 * We run in tasklet context but need to disable irqs when
751 * transferring tsq->head because tcp_wfree() might
752 * interrupt us (non NAPI drivers)
753 */
754static void tcp_tasklet_func(unsigned long data)
755{
756 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
757 LIST_HEAD(list);
758 unsigned long flags;
759 struct list_head *q, *n;
760 struct tcp_sock *tp;
761 struct sock *sk;
762
763 local_irq_save(flags);
764 list_splice_init(&tsq->head, &list);
765 local_irq_restore(flags);
766
767 list_for_each_safe(q, n, &list) {
768 tp = list_entry(q, struct tcp_sock, tsq_node);
769 list_del(&tp->tsq_node);
770
771 sk = (struct sock *)tp;
772 smp_mb__before_atomic();
773 clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags);
774
775 if (!sk->sk_lock.owned &&
776 test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) {
777 bh_lock_sock(sk);
778 if (!sock_owned_by_user(sk)) {
779 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
780 tcp_tsq_handler(sk);
781 }
782 bh_unlock_sock(sk);
783 }
784
785 sk_free(sk);
786 }
787}
788
789#define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED | \
790 TCPF_WRITE_TIMER_DEFERRED | \
791 TCPF_DELACK_TIMER_DEFERRED | \
792 TCPF_MTU_REDUCED_DEFERRED)
793/**
794 * tcp_release_cb - tcp release_sock() callback
795 * @sk: socket
796 *
797 * called from release_sock() to perform protocol dependent
798 * actions before socket release.
799 */
800void tcp_release_cb(struct sock *sk)
801{
802 unsigned long flags, nflags;
803
804 /* perform an atomic operation only if at least one flag is set */
805 do {
806 flags = sk->sk_tsq_flags;
807 if (!(flags & TCP_DEFERRED_ALL))
808 return;
809 nflags = flags & ~TCP_DEFERRED_ALL;
810 } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);
811
812 if (flags & TCPF_TSQ_DEFERRED)
813 tcp_tsq_handler(sk);
814
815 /* Here begins the tricky part :
816 * We are called from release_sock() with :
817 * 1) BH disabled
818 * 2) sk_lock.slock spinlock held
819 * 3) socket owned by us (sk->sk_lock.owned == 1)
820 *
821 * But following code is meant to be called from BH handlers,
822 * so we should keep BH disabled, but early release socket ownership
823 */
824 sock_release_ownership(sk);
825
826 if (flags & TCPF_WRITE_TIMER_DEFERRED) {
827 tcp_write_timer_handler(sk);
828 __sock_put(sk);
829 }
830 if (flags & TCPF_DELACK_TIMER_DEFERRED) {
831 tcp_delack_timer_handler(sk);
832 __sock_put(sk);
833 }
834 if (flags & TCPF_MTU_REDUCED_DEFERRED) {
835 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
836 __sock_put(sk);
837 }
838}
839EXPORT_SYMBOL(tcp_release_cb);
840
841void __init tcp_tasklet_init(void)
842{
843 int i;
844
845 for_each_possible_cpu(i) {
846 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
847
848 INIT_LIST_HEAD(&tsq->head);
849 tasklet_init(&tsq->tasklet,
850 tcp_tasklet_func,
851 (unsigned long)tsq);
852 }
853}
854
855/*
856 * Write buffer destructor automatically called from kfree_skb.
857 * We can't xmit new skbs from this context, as we might already
858 * hold qdisc lock.
859 */
860void tcp_wfree(struct sk_buff *skb)
861{
862 struct sock *sk = skb->sk;
863 struct tcp_sock *tp = tcp_sk(sk);
864 unsigned long flags, nval, oval;
865 int wmem;
866
867 /* Keep one reference on sk_wmem_alloc.
868 * Will be released by sk_free() from here or tcp_tasklet_func()
869 */
870 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
871
872 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
873 * Wait until our queues (qdisc + devices) are drained.
874 * This gives :
875 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
876 * - chance for incoming ACK (processed by another cpu maybe)
877 * to migrate this flow (skb->ooo_okay will be eventually set)
878 */
879 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
880 goto out;
881
882 for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
883 struct tsq_tasklet *tsq;
884 bool empty;
885
886 if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
887 goto out;
888
889 nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
890 nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
891 if (nval != oval)
892 continue;
893
894 /* queue this socket to tasklet queue */
895 local_irq_save(flags);
896 tsq = this_cpu_ptr(&tsq_tasklet);
897 empty = list_empty(&tsq->head);
898 list_add(&tp->tsq_node, &tsq->head);
899 if (empty)
900 tasklet_schedule(&tsq->tasklet);
901 local_irq_restore(flags);
902 return;
903 }
904out:
905 sk_free(sk);
906}
907
908/* This routine actually transmits TCP packets queued in by
909 * tcp_do_sendmsg(). This is used by both the initial
910 * transmission and possible later retransmissions.
911 * All SKB's seen here are completely headerless. It is our
912 * job to build the TCP header, and pass the packet down to
913 * IP so it can do the same plus pass the packet off to the
914 * device.
915 *
916 * We are working here with either a clone of the original
917 * SKB, or a fresh unique copy made by the retransmit engine.
918 */
919static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
920 gfp_t gfp_mask)
921{
922 const struct inet_connection_sock *icsk = inet_csk(sk);
923 struct inet_sock *inet;
924 struct tcp_sock *tp;
925 struct tcp_skb_cb *tcb;
926 struct tcp_out_options opts;
927 unsigned int tcp_options_size, tcp_header_size;
928 struct tcp_md5sig_key *md5;
929 struct tcphdr *th;
930 int err;
931
932 BUG_ON(!skb || !tcp_skb_pcount(skb));
933 tp = tcp_sk(sk);
934
935 if (clone_it) {
936 skb_mstamp_get(&skb->skb_mstamp);
937 TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
938 - tp->snd_una;
939 tcp_rate_skb_sent(sk, skb);
940
941 if (unlikely(skb_cloned(skb)))
942 skb = pskb_copy(skb, gfp_mask);
943 else
944 skb = skb_clone(skb, gfp_mask);
945 if (unlikely(!skb))
946 return -ENOBUFS;
947 }
948
949 inet = inet_sk(sk);
950 tcb = TCP_SKB_CB(skb);
951 memset(&opts, 0, sizeof(opts));
952
953 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
954 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
955 else
956 tcp_options_size = tcp_established_options(sk, skb, &opts,
957 &md5);
958 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
959
960 /* if no packet is in qdisc/device queue, then allow XPS to select
961 * another queue. We can be called from tcp_tsq_handler()
962 * which holds one reference to sk_wmem_alloc.
963 *
964 * TODO: Ideally, in-flight pure ACK packets should not matter here.
965 * One way to get this would be to set skb->truesize = 2 on them.
966 */
967 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
968
969 skb_push(skb, tcp_header_size);
970 skb_reset_transport_header(skb);
971
972 skb_orphan(skb);
973 skb->sk = sk;
974 skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
975 skb_set_hash_from_sk(skb, sk);
976 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
977
978 /* Build TCP header and checksum it. */
979 th = (struct tcphdr *)skb->data;
980 th->source = inet->inet_sport;
981 th->dest = inet->inet_dport;
982 th->seq = htonl(tcb->seq);
983 th->ack_seq = htonl(tp->rcv_nxt);
984 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
985 tcb->tcp_flags);
986
987 th->check = 0;
988 th->urg_ptr = 0;
989
990 /* The urg_mode check is necessary during a below snd_una win probe */
991 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
992 if (before(tp->snd_up, tcb->seq + 0x10000)) {
993 th->urg_ptr = htons(tp->snd_up - tcb->seq);
994 th->urg = 1;
995 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
996 th->urg_ptr = htons(0xFFFF);
997 th->urg = 1;
998 }
999 }
1000
1001 tcp_options_write((__be32 *)(th + 1), tp, &opts);
1002 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1003 if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
1004 th->window = htons(tcp_select_window(sk));
1005 tcp_ecn_send(sk, skb, th, tcp_header_size);
1006 } else {
1007 /* RFC1323: The window in SYN & SYN/ACK segments
1008 * is never scaled.
1009 */
1010 th->window = htons(min(tp->rcv_wnd, 65535U));
1011 }
1012#ifdef CONFIG_TCP_MD5SIG
1013 /* Calculate the MD5 hash, as we have all we need now */
1014 if (md5) {
1015 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1016 tp->af_specific->calc_md5_hash(opts.hash_location,
1017 md5, sk, skb);
1018 }
1019#endif
1020
1021 icsk->icsk_af_ops->send_check(sk, skb);
1022
1023 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1024 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1025
1026 if (skb->len != tcp_header_size) {
1027 tcp_event_data_sent(tp, sk);
1028 tp->data_segs_out += tcp_skb_pcount(skb);
1029 }
1030
1031 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1032 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1033 tcp_skb_pcount(skb));
1034
1035 tp->segs_out += tcp_skb_pcount(skb);
1036 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1037 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1038 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1039
1040 /* Our usage of tstamp should remain private */
1041 skb->tstamp = 0;
1042
1043 /* Cleanup our debris for IP stacks */
1044 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1045 sizeof(struct inet6_skb_parm)));
1046
1047 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1048
1049 if (likely(err <= 0))
1050 return err;
1051
1052 tcp_enter_cwr(sk);
1053
1054 return net_xmit_eval(err);
1055}
1056
1057/* This routine just queues the buffer for sending.
1058 *
1059 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1060 * otherwise socket can stall.
1061 */
1062static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1063{
1064 struct tcp_sock *tp = tcp_sk(sk);
1065
1066 /* Advance write_seq and place onto the write_queue. */
1067 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1068 __skb_header_release(skb);
1069 tcp_add_write_queue_tail(sk, skb);
1070 sk->sk_wmem_queued += skb->truesize;
1071 sk_mem_charge(sk, skb->truesize);
1072}
1073
1074/* Initialize TSO segments for a packet. */
1075static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1076{
1077 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1078 /* Avoid the costly divide in the normal
1079 * non-TSO case.
1080 */
1081 tcp_skb_pcount_set(skb, 1);
1082 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1083 } else {
1084 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1085 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1086 }
1087}
1088
1089/* When a modification to fackets out becomes necessary, we need to check
1090 * skb is counted to fackets_out or not.
1091 */
1092static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1093 int decr)
1094{
1095 struct tcp_sock *tp = tcp_sk(sk);
1096
1097 if (!tp->sacked_out || tcp_is_reno(tp))
1098 return;
1099
1100 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1101 tp->fackets_out -= decr;
1102}
1103
1104/* Pcount in the middle of the write queue got changed, we need to do various
1105 * tweaks to fix counters
1106 */
1107static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1108{
1109 struct tcp_sock *tp = tcp_sk(sk);
1110
1111 tp->packets_out -= decr;
1112
1113 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1114 tp->sacked_out -= decr;
1115 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1116 tp->retrans_out -= decr;
1117 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1118 tp->lost_out -= decr;
1119
1120 /* Reno case is special. Sigh... */
1121 if (tcp_is_reno(tp) && decr > 0)
1122 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1123
1124 tcp_adjust_fackets_out(sk, skb, decr);
1125
1126 if (tp->lost_skb_hint &&
1127 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1128 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1129 tp->lost_cnt_hint -= decr;
1130
1131 tcp_verify_left_out(tp);
1132}
1133
1134static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
1135{
1136 return TCP_SKB_CB(skb)->txstamp_ack ||
1137 (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
1138}
1139
1140static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1141{
1142 struct skb_shared_info *shinfo = skb_shinfo(skb);
1143
1144 if (unlikely(tcp_has_tx_tstamp(skb)) &&
1145 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1146 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1147 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1148
1149 shinfo->tx_flags &= ~tsflags;
1150 shinfo2->tx_flags |= tsflags;
1151 swap(shinfo->tskey, shinfo2->tskey);
1152 TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
1153 TCP_SKB_CB(skb)->txstamp_ack = 0;
1154 }
1155}
1156
1157static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
1158{
1159 TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
1160 TCP_SKB_CB(skb)->eor = 0;
1161}
1162
1163/* Function to create two new TCP segments. Shrinks the given segment
1164 * to the specified size and appends a new segment with the rest of the
1165 * packet to the list. This won't be called frequently, I hope.
1166 * Remember, these are still headerless SKBs at this point.
1167 */
1168int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1169 unsigned int mss_now, gfp_t gfp)
1170{
1171 struct tcp_sock *tp = tcp_sk(sk);
1172 struct sk_buff *buff;
1173 int nsize, old_factor;
1174 int nlen;
1175 u8 flags;
1176
1177 if (WARN_ON(len > skb->len))
1178 return -EINVAL;
1179
1180 nsize = skb_headlen(skb) - len;
1181 if (nsize < 0)
1182 nsize = 0;
1183
1184 if (skb_unclone(skb, gfp))
1185 return -ENOMEM;
1186
1187 /* Get a new skb... force flag on. */
1188 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1189 if (!buff)
1190 return -ENOMEM; /* We'll just try again later. */
1191
1192 sk->sk_wmem_queued += buff->truesize;
1193 sk_mem_charge(sk, buff->truesize);
1194 nlen = skb->len - len - nsize;
1195 buff->truesize += nlen;
1196 skb->truesize -= nlen;
1197
1198 /* Correct the sequence numbers. */
1199 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1200 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1201 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1202
1203 /* PSH and FIN should only be set in the second packet. */
1204 flags = TCP_SKB_CB(skb)->tcp_flags;
1205 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1206 TCP_SKB_CB(buff)->tcp_flags = flags;
1207 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1208 tcp_skb_fragment_eor(skb, buff);
1209
1210 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1211 /* Copy and checksum data tail into the new buffer. */
1212 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1213 skb_put(buff, nsize),
1214 nsize, 0);
1215
1216 skb_trim(skb, len);
1217
1218 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1219 } else {
1220 skb->ip_summed = CHECKSUM_PARTIAL;
1221 skb_split(skb, buff, len);
1222 }
1223
1224 buff->ip_summed = skb->ip_summed;
1225
1226 buff->tstamp = skb->tstamp;
1227 tcp_fragment_tstamp(skb, buff);
1228
1229 old_factor = tcp_skb_pcount(skb);
1230
1231 /* Fix up tso_factor for both original and new SKB. */
1232 tcp_set_skb_tso_segs(skb, mss_now);
1233 tcp_set_skb_tso_segs(buff, mss_now);
1234
1235 /* Update delivered info for the new segment */
1236 TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;
1237
1238 /* If this packet has been sent out already, we must
1239 * adjust the various packet counters.
1240 */
1241 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1242 int diff = old_factor - tcp_skb_pcount(skb) -
1243 tcp_skb_pcount(buff);
1244
1245 if (diff)
1246 tcp_adjust_pcount(sk, skb, diff);
1247 }
1248
1249 /* Link BUFF into the send queue. */
1250 __skb_header_release(buff);
1251 tcp_insert_write_queue_after(skb, buff, sk);
1252
1253 return 0;
1254}
1255
1256/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1257 * eventually). The difference is that pulled data not copied, but
1258 * immediately discarded.
1259 */
1260static void __pskb_trim_head(struct sk_buff *skb, int len)
1261{
1262 struct skb_shared_info *shinfo;
1263 int i, k, eat;
1264
1265 eat = min_t(int, len, skb_headlen(skb));
1266 if (eat) {
1267 __skb_pull(skb, eat);
1268 len -= eat;
1269 if (!len)
1270 return;
1271 }
1272 eat = len;
1273 k = 0;
1274 shinfo = skb_shinfo(skb);
1275 for (i = 0; i < shinfo->nr_frags; i++) {
1276 int size = skb_frag_size(&shinfo->frags[i]);
1277
1278 if (size <= eat) {
1279 skb_frag_unref(skb, i);
1280 eat -= size;
1281 } else {
1282 shinfo->frags[k] = shinfo->frags[i];
1283 if (eat) {
1284 shinfo->frags[k].page_offset += eat;
1285 skb_frag_size_sub(&shinfo->frags[k], eat);
1286 eat = 0;
1287 }
1288 k++;
1289 }
1290 }
1291 shinfo->nr_frags = k;
1292
1293 skb_reset_tail_pointer(skb);
1294 skb->data_len -= len;
1295 skb->len = skb->data_len;
1296}
1297
1298/* Remove acked data from a packet in the transmit queue. */
1299int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1300{
1301 if (skb_unclone(skb, GFP_ATOMIC))
1302 return -ENOMEM;
1303
1304 __pskb_trim_head(skb, len);
1305
1306 TCP_SKB_CB(skb)->seq += len;
1307 skb->ip_summed = CHECKSUM_PARTIAL;
1308
1309 skb->truesize -= len;
1310 sk->sk_wmem_queued -= len;
1311 sk_mem_uncharge(sk, len);
1312 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1313
1314 /* Any change of skb->len requires recalculation of tso factor. */
1315 if (tcp_skb_pcount(skb) > 1)
1316 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1317
1318 return 0;
1319}
1320
1321/* Calculate MSS not accounting any TCP options. */
1322static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1323{
1324 const struct tcp_sock *tp = tcp_sk(sk);
1325 const struct inet_connection_sock *icsk = inet_csk(sk);
1326 int mss_now;
1327
1328 /* Calculate base mss without TCP options:
1329 It is MMS_S - sizeof(tcphdr) of rfc1122
1330 */
1331 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1332
1333 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1334 if (icsk->icsk_af_ops->net_frag_header_len) {
1335 const struct dst_entry *dst = __sk_dst_get(sk);
1336
1337 if (dst && dst_allfrag(dst))
1338 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1339 }
1340
1341 /* Clamp it (mss_clamp does not include tcp options) */
1342 if (mss_now > tp->rx_opt.mss_clamp)
1343 mss_now = tp->rx_opt.mss_clamp;
1344
1345 /* Now subtract optional transport overhead */
1346 mss_now -= icsk->icsk_ext_hdr_len;
1347
1348 /* Then reserve room for full set of TCP options and 8 bytes of data */
1349 if (mss_now < 48)
1350 mss_now = 48;
1351 return mss_now;
1352}
1353
1354/* Calculate MSS. Not accounting for SACKs here. */
1355int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1356{
1357 /* Subtract TCP options size, not including SACKs */
1358 return __tcp_mtu_to_mss(sk, pmtu) -
1359 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1360}
1361
1362/* Inverse of above */
1363int tcp_mss_to_mtu(struct sock *sk, int mss)
1364{
1365 const struct tcp_sock *tp = tcp_sk(sk);
1366 const struct inet_connection_sock *icsk = inet_csk(sk);
1367 int mtu;
1368
1369 mtu = mss +
1370 tp->tcp_header_len +
1371 icsk->icsk_ext_hdr_len +
1372 icsk->icsk_af_ops->net_header_len;
1373
1374 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1375 if (icsk->icsk_af_ops->net_frag_header_len) {
1376 const struct dst_entry *dst = __sk_dst_get(sk);
1377
1378 if (dst && dst_allfrag(dst))
1379 mtu += icsk->icsk_af_ops->net_frag_header_len;
1380 }
1381 return mtu;
1382}
1383EXPORT_SYMBOL(tcp_mss_to_mtu);
1384
1385/* MTU probing init per socket */
1386void tcp_mtup_init(struct sock *sk)
1387{
1388 struct tcp_sock *tp = tcp_sk(sk);
1389 struct inet_connection_sock *icsk = inet_csk(sk);
1390 struct net *net = sock_net(sk);
1391
1392 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1393 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1394 icsk->icsk_af_ops->net_header_len;
1395 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1396 icsk->icsk_mtup.probe_size = 0;
1397 if (icsk->icsk_mtup.enabled)
1398 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1399}
1400EXPORT_SYMBOL(tcp_mtup_init);
1401
1402/* This function synchronize snd mss to current pmtu/exthdr set.
1403
1404 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1405 for TCP options, but includes only bare TCP header.
1406
1407 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1408 It is minimum of user_mss and mss received with SYN.
1409 It also does not include TCP options.
1410
1411 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1412
1413 tp->mss_cache is current effective sending mss, including
1414 all tcp options except for SACKs. It is evaluated,
1415 taking into account current pmtu, but never exceeds
1416 tp->rx_opt.mss_clamp.
1417
1418 NOTE1. rfc1122 clearly states that advertised MSS
1419 DOES NOT include either tcp or ip options.
1420
1421 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1422 are READ ONLY outside this function. --ANK (980731)
1423 */
1424unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1425{
1426 struct tcp_sock *tp = tcp_sk(sk);
1427 struct inet_connection_sock *icsk = inet_csk(sk);
1428 int mss_now;
1429
1430 if (icsk->icsk_mtup.search_high > pmtu)
1431 icsk->icsk_mtup.search_high = pmtu;
1432
1433 mss_now = tcp_mtu_to_mss(sk, pmtu);
1434 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1435
1436 /* And store cached results */
1437 icsk->icsk_pmtu_cookie = pmtu;
1438 if (icsk->icsk_mtup.enabled)
1439 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1440 tp->mss_cache = mss_now;
1441
1442 return mss_now;
1443}
1444EXPORT_SYMBOL(tcp_sync_mss);
1445
1446/* Compute the current effective MSS, taking SACKs and IP options,
1447 * and even PMTU discovery events into account.
1448 */
1449unsigned int tcp_current_mss(struct sock *sk)
1450{
1451 const struct tcp_sock *tp = tcp_sk(sk);
1452 const struct dst_entry *dst = __sk_dst_get(sk);
1453 u32 mss_now;
1454 unsigned int header_len;
1455 struct tcp_out_options opts;
1456 struct tcp_md5sig_key *md5;
1457
1458 mss_now = tp->mss_cache;
1459
1460 if (dst) {
1461 u32 mtu = dst_mtu(dst);
1462 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1463 mss_now = tcp_sync_mss(sk, mtu);
1464 }
1465
1466 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1467 sizeof(struct tcphdr);
1468 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1469 * some common options. If this is an odd packet (because we have SACK
1470 * blocks etc) then our calculated header_len will be different, and
1471 * we have to adjust mss_now correspondingly */
1472 if (header_len != tp->tcp_header_len) {
1473 int delta = (int) header_len - tp->tcp_header_len;
1474 mss_now -= delta;
1475 }
1476
1477 return mss_now;
1478}
1479
1480/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1481 * As additional protections, we do not touch cwnd in retransmission phases,
1482 * and if application hit its sndbuf limit recently.
1483 */
1484static void tcp_cwnd_application_limited(struct sock *sk)
1485{
1486 struct tcp_sock *tp = tcp_sk(sk);
1487
1488 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1489 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1490 /* Limited by application or receiver window. */
1491 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1492 u32 win_used = max(tp->snd_cwnd_used, init_win);
1493 if (win_used < tp->snd_cwnd) {
1494 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1495 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1496 }
1497 tp->snd_cwnd_used = 0;
1498 }
1499 tp->snd_cwnd_stamp = tcp_time_stamp;
1500}
1501
1502static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1503{
1504 struct tcp_sock *tp = tcp_sk(sk);
1505
1506 /* Track the maximum number of outstanding packets in each
1507 * window, and remember whether we were cwnd-limited then.
1508 */
1509 if (!before(tp->snd_una, tp->max_packets_seq) ||
1510 tp->packets_out > tp->max_packets_out) {
1511 tp->max_packets_out = tp->packets_out;
1512 tp->max_packets_seq = tp->snd_nxt;
1513 tp->is_cwnd_limited = is_cwnd_limited;
1514 }
1515
1516 if (tcp_is_cwnd_limited(sk)) {
1517 /* Network is feed fully. */
1518 tp->snd_cwnd_used = 0;
1519 tp->snd_cwnd_stamp = tcp_time_stamp;
1520 } else {
1521 /* Network starves. */
1522 if (tp->packets_out > tp->snd_cwnd_used)
1523 tp->snd_cwnd_used = tp->packets_out;
1524
1525 if (sysctl_tcp_slow_start_after_idle &&
1526 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1527 tcp_cwnd_application_limited(sk);
1528
1529 /* The following conditions together indicate the starvation
1530 * is caused by insufficient sender buffer:
1531 * 1) just sent some data (see tcp_write_xmit)
1532 * 2) not cwnd limited (this else condition)
1533 * 3) no more data to send (null tcp_send_head )
1534 * 4) application is hitting buffer limit (SOCK_NOSPACE)
1535 */
1536 if (!tcp_send_head(sk) && sk->sk_socket &&
1537 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
1538 (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
1539 tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
1540 }
1541}
1542
1543/* Minshall's variant of the Nagle send check. */
1544static bool tcp_minshall_check(const struct tcp_sock *tp)
1545{
1546 return after(tp->snd_sml, tp->snd_una) &&
1547 !after(tp->snd_sml, tp->snd_nxt);
1548}
1549
1550/* Update snd_sml if this skb is under mss
1551 * Note that a TSO packet might end with a sub-mss segment
1552 * The test is really :
1553 * if ((skb->len % mss) != 0)
1554 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1555 * But we can avoid doing the divide again given we already have
1556 * skb_pcount = skb->len / mss_now
1557 */
1558static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1559 const struct sk_buff *skb)
1560{
1561 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1562 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1563}
1564
1565/* Return false, if packet can be sent now without violation Nagle's rules:
1566 * 1. It is full sized. (provided by caller in %partial bool)
1567 * 2. Or it contains FIN. (already checked by caller)
1568 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1569 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1570 * With Minshall's modification: all sent small packets are ACKed.
1571 */
1572static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1573 int nonagle)
1574{
1575 return partial &&
1576 ((nonagle & TCP_NAGLE_CORK) ||
1577 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1578}
1579
1580/* Return how many segs we'd like on a TSO packet,
1581 * to send one TSO packet per ms
1582 */
1583u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
1584 int min_tso_segs)
1585{
1586 u32 bytes, segs;
1587
1588 bytes = min(sk->sk_pacing_rate >> 10,
1589 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1590
1591 /* Goal is to send at least one packet per ms,
1592 * not one big TSO packet every 100 ms.
1593 * This preserves ACK clocking and is consistent
1594 * with tcp_tso_should_defer() heuristic.
1595 */
1596 segs = max_t(u32, bytes / mss_now, min_tso_segs);
1597
1598 return min_t(u32, segs, sk->sk_gso_max_segs);
1599}
1600EXPORT_SYMBOL(tcp_tso_autosize);
1601
1602/* Return the number of segments we want in the skb we are transmitting.
1603 * See if congestion control module wants to decide; otherwise, autosize.
1604 */
1605static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
1606{
1607 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1608 u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;
1609
1610 return tso_segs ? :
1611 tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs);
1612}
1613
1614/* Returns the portion of skb which can be sent right away */
1615static unsigned int tcp_mss_split_point(const struct sock *sk,
1616 const struct sk_buff *skb,
1617 unsigned int mss_now,
1618 unsigned int max_segs,
1619 int nonagle)
1620{
1621 const struct tcp_sock *tp = tcp_sk(sk);
1622 u32 partial, needed, window, max_len;
1623
1624 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1625 max_len = mss_now * max_segs;
1626
1627 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1628 return max_len;
1629
1630 needed = min(skb->len, window);
1631
1632 if (max_len <= needed)
1633 return max_len;
1634
1635 partial = needed % mss_now;
1636 /* If last segment is not a full MSS, check if Nagle rules allow us
1637 * to include this last segment in this skb.
1638 * Otherwise, we'll split the skb at last MSS boundary
1639 */
1640 if (tcp_nagle_check(partial != 0, tp, nonagle))
1641 return needed - partial;
1642
1643 return needed;
1644}
1645
1646/* Can at least one segment of SKB be sent right now, according to the
1647 * congestion window rules? If so, return how many segments are allowed.
1648 */
1649static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1650 const struct sk_buff *skb)
1651{
1652 u32 in_flight, cwnd, halfcwnd;
1653
1654 /* Don't be strict about the congestion window for the final FIN. */
1655 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1656 tcp_skb_pcount(skb) == 1)
1657 return 1;
1658
1659 in_flight = tcp_packets_in_flight(tp);
1660 cwnd = tp->snd_cwnd;
1661 if (in_flight >= cwnd)
1662 return 0;
1663
1664 /* For better scheduling, ensure we have at least
1665 * 2 GSO packets in flight.
1666 */
1667 halfcwnd = max(cwnd >> 1, 1U);
1668 return min(halfcwnd, cwnd - in_flight);
1669}
1670
1671/* Initialize TSO state of a skb.
1672 * This must be invoked the first time we consider transmitting
1673 * SKB onto the wire.
1674 */
1675static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1676{
1677 int tso_segs = tcp_skb_pcount(skb);
1678
1679 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1680 tcp_set_skb_tso_segs(skb, mss_now);
1681 tso_segs = tcp_skb_pcount(skb);
1682 }
1683 return tso_segs;
1684}
1685
1686
1687/* Return true if the Nagle test allows this packet to be
1688 * sent now.
1689 */
1690static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1691 unsigned int cur_mss, int nonagle)
1692{
1693 /* Nagle rule does not apply to frames, which sit in the middle of the
1694 * write_queue (they have no chances to get new data).
1695 *
1696 * This is implemented in the callers, where they modify the 'nonagle'
1697 * argument based upon the location of SKB in the send queue.
1698 */
1699 if (nonagle & TCP_NAGLE_PUSH)
1700 return true;
1701
1702 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1703 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1704 return true;
1705
1706 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1707 return true;
1708
1709 return false;
1710}
1711
1712/* Does at least the first segment of SKB fit into the send window? */
1713static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1714 const struct sk_buff *skb,
1715 unsigned int cur_mss)
1716{
1717 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1718
1719 if (skb->len > cur_mss)
1720 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1721
1722 return !after(end_seq, tcp_wnd_end(tp));
1723}
1724
1725/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1726 * should be put on the wire right now. If so, it returns the number of
1727 * packets allowed by the congestion window.
1728 */
1729static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1730 unsigned int cur_mss, int nonagle)
1731{
1732 const struct tcp_sock *tp = tcp_sk(sk);
1733 unsigned int cwnd_quota;
1734
1735 tcp_init_tso_segs(skb, cur_mss);
1736
1737 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1738 return 0;
1739
1740 cwnd_quota = tcp_cwnd_test(tp, skb);
1741 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1742 cwnd_quota = 0;
1743
1744 return cwnd_quota;
1745}
1746
1747/* Test if sending is allowed right now. */
1748bool tcp_may_send_now(struct sock *sk)
1749{
1750 const struct tcp_sock *tp = tcp_sk(sk);
1751 struct sk_buff *skb = tcp_send_head(sk);
1752
1753 return skb &&
1754 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1755 (tcp_skb_is_last(sk, skb) ?
1756 tp->nonagle : TCP_NAGLE_PUSH));
1757}
1758
1759/* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1760 * which is put after SKB on the list. It is very much like
1761 * tcp_fragment() except that it may make several kinds of assumptions
1762 * in order to speed up the splitting operation. In particular, we
1763 * know that all the data is in scatter-gather pages, and that the
1764 * packet has never been sent out before (and thus is not cloned).
1765 */
1766static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1767 unsigned int mss_now, gfp_t gfp)
1768{
1769 struct sk_buff *buff;
1770 int nlen = skb->len - len;
1771 u8 flags;
1772
1773 /* All of a TSO frame must be composed of paged data. */
1774 if (skb->len != skb->data_len)
1775 return tcp_fragment(sk, skb, len, mss_now, gfp);
1776
1777 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1778 if (unlikely(!buff))
1779 return -ENOMEM;
1780
1781 sk->sk_wmem_queued += buff->truesize;
1782 sk_mem_charge(sk, buff->truesize);
1783 buff->truesize += nlen;
1784 skb->truesize -= nlen;
1785
1786 /* Correct the sequence numbers. */
1787 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1788 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1789 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1790
1791 /* PSH and FIN should only be set in the second packet. */
1792 flags = TCP_SKB_CB(skb)->tcp_flags;
1793 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1794 TCP_SKB_CB(buff)->tcp_flags = flags;
1795
1796 /* This packet was never sent out yet, so no SACK bits. */
1797 TCP_SKB_CB(buff)->sacked = 0;
1798
1799 tcp_skb_fragment_eor(skb, buff);
1800
1801 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1802 skb_split(skb, buff, len);
1803 tcp_fragment_tstamp(skb, buff);
1804
1805 /* Fix up tso_factor for both original and new SKB. */
1806 tcp_set_skb_tso_segs(skb, mss_now);
1807 tcp_set_skb_tso_segs(buff, mss_now);
1808
1809 /* Link BUFF into the send queue. */
1810 __skb_header_release(buff);
1811 tcp_insert_write_queue_after(skb, buff, sk);
1812
1813 return 0;
1814}
1815
1816/* Try to defer sending, if possible, in order to minimize the amount
1817 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1818 *
1819 * This algorithm is from John Heffner.
1820 */
1821static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1822 bool *is_cwnd_limited, u32 max_segs)
1823{
1824 const struct inet_connection_sock *icsk = inet_csk(sk);
1825 u32 age, send_win, cong_win, limit, in_flight;
1826 struct tcp_sock *tp = tcp_sk(sk);
1827 struct skb_mstamp now;
1828 struct sk_buff *head;
1829 int win_divisor;
1830
1831 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1832 goto send_now;
1833
1834 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1835 goto send_now;
1836
1837 /* Avoid bursty behavior by allowing defer
1838 * only if the last write was recent.
1839 */
1840 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1841 goto send_now;
1842
1843 in_flight = tcp_packets_in_flight(tp);
1844
1845 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1846
1847 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1848
1849 /* From in_flight test above, we know that cwnd > in_flight. */
1850 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1851
1852 limit = min(send_win, cong_win);
1853
1854 /* If a full-sized TSO skb can be sent, do it. */
1855 if (limit >= max_segs * tp->mss_cache)
1856 goto send_now;
1857
1858 /* Middle in queue won't get any more data, full sendable already? */
1859 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1860 goto send_now;
1861
1862 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1863 if (win_divisor) {
1864 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1865
1866 /* If at least some fraction of a window is available,
1867 * just use it.
1868 */
1869 chunk /= win_divisor;
1870 if (limit >= chunk)
1871 goto send_now;
1872 } else {
1873 /* Different approach, try not to defer past a single
1874 * ACK. Receiver should ACK every other full sized
1875 * frame, so if we have space for more than 3 frames
1876 * then send now.
1877 */
1878 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1879 goto send_now;
1880 }
1881
1882 head = tcp_write_queue_head(sk);
1883 skb_mstamp_get(&now);
1884 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1885 /* If next ACK is likely to come too late (half srtt), do not defer */
1886 if (age < (tp->srtt_us >> 4))
1887 goto send_now;
1888
1889 /* Ok, it looks like it is advisable to defer. */
1890
1891 if (cong_win < send_win && cong_win <= skb->len)
1892 *is_cwnd_limited = true;
1893
1894 return true;
1895
1896send_now:
1897 return false;
1898}
1899
1900static inline void tcp_mtu_check_reprobe(struct sock *sk)
1901{
1902 struct inet_connection_sock *icsk = inet_csk(sk);
1903 struct tcp_sock *tp = tcp_sk(sk);
1904 struct net *net = sock_net(sk);
1905 u32 interval;
1906 s32 delta;
1907
1908 interval = net->ipv4.sysctl_tcp_probe_interval;
1909 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1910 if (unlikely(delta >= interval * HZ)) {
1911 int mss = tcp_current_mss(sk);
1912
1913 /* Update current search range */
1914 icsk->icsk_mtup.probe_size = 0;
1915 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1916 sizeof(struct tcphdr) +
1917 icsk->icsk_af_ops->net_header_len;
1918 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1919
1920 /* Update probe time stamp */
1921 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1922 }
1923}
1924
1925/* Create a new MTU probe if we are ready.
1926 * MTU probe is regularly attempting to increase the path MTU by
1927 * deliberately sending larger packets. This discovers routing
1928 * changes resulting in larger path MTUs.
1929 *
1930 * Returns 0 if we should wait to probe (no cwnd available),
1931 * 1 if a probe was sent,
1932 * -1 otherwise
1933 */
1934static int tcp_mtu_probe(struct sock *sk)
1935{
1936 struct inet_connection_sock *icsk = inet_csk(sk);
1937 struct tcp_sock *tp = tcp_sk(sk);
1938 struct sk_buff *skb, *nskb, *next;
1939 struct net *net = sock_net(sk);
1940 int probe_size;
1941 int size_needed;
1942 int copy, len;
1943 int mss_now;
1944 int interval;
1945
1946 /* Not currently probing/verifying,
1947 * not in recovery,
1948 * have enough cwnd, and
1949 * not SACKing (the variable headers throw things off)
1950 */
1951 if (likely(!icsk->icsk_mtup.enabled ||
1952 icsk->icsk_mtup.probe_size ||
1953 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1954 tp->snd_cwnd < 11 ||
1955 tp->rx_opt.num_sacks || tp->rx_opt.dsack))
1956 return -1;
1957
1958 /* Use binary search for probe_size between tcp_mss_base,
1959 * and current mss_clamp. if (search_high - search_low)
1960 * smaller than a threshold, backoff from probing.
1961 */
1962 mss_now = tcp_current_mss(sk);
1963 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1964 icsk->icsk_mtup.search_low) >> 1);
1965 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1966 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1967 /* When misfortune happens, we are reprobing actively,
1968 * and then reprobe timer has expired. We stick with current
1969 * probing process by not resetting search range to its orignal.
1970 */
1971 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1972 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1973 /* Check whether enough time has elaplased for
1974 * another round of probing.
1975 */
1976 tcp_mtu_check_reprobe(sk);
1977 return -1;
1978 }
1979
1980 /* Have enough data in the send queue to probe? */
1981 if (tp->write_seq - tp->snd_nxt < size_needed)
1982 return -1;
1983
1984 if (tp->snd_wnd < size_needed)
1985 return -1;
1986 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1987 return 0;
1988
1989 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1990 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1991 if (!tcp_packets_in_flight(tp))
1992 return -1;
1993 else
1994 return 0;
1995 }
1996
1997 /* We're allowed to probe. Build it now. */
1998 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1999 if (!nskb)
2000 return -1;
2001 sk->sk_wmem_queued += nskb->truesize;
2002 sk_mem_charge(sk, nskb->truesize);
2003
2004 skb = tcp_send_head(sk);
2005
2006 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
2007 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
2008 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
2009 TCP_SKB_CB(nskb)->sacked = 0;
2010 nskb->csum = 0;
2011 nskb->ip_summed = skb->ip_summed;
2012
2013 tcp_insert_write_queue_before(nskb, skb, sk);
2014
2015 len = 0;
2016 tcp_for_write_queue_from_safe(skb, next, sk) {
2017 copy = min_t(int, skb->len, probe_size - len);
2018 if (nskb->ip_summed) {
2019 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
2020 } else {
2021 __wsum csum = skb_copy_and_csum_bits(skb, 0,
2022 skb_put(nskb, copy),
2023 copy, 0);
2024 nskb->csum = csum_block_add(nskb->csum, csum, len);
2025 }
2026
2027 if (skb->len <= copy) {
2028 /* We've eaten all the data from this skb.
2029 * Throw it away. */
2030 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2031 tcp_unlink_write_queue(skb, sk);
2032 sk_wmem_free_skb(sk, skb);
2033 } else {
2034 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
2035 ~(TCPHDR_FIN|TCPHDR_PSH);
2036 if (!skb_shinfo(skb)->nr_frags) {
2037 skb_pull(skb, copy);
2038 if (skb->ip_summed != CHECKSUM_PARTIAL)
2039 skb->csum = csum_partial(skb->data,
2040 skb->len, 0);
2041 } else {
2042 __pskb_trim_head(skb, copy);
2043 tcp_set_skb_tso_segs(skb, mss_now);
2044 }
2045 TCP_SKB_CB(skb)->seq += copy;
2046 }
2047
2048 len += copy;
2049
2050 if (len >= probe_size)
2051 break;
2052 }
2053 tcp_init_tso_segs(nskb, nskb->len);
2054
2055 /* We're ready to send. If this fails, the probe will
2056 * be resegmented into mss-sized pieces by tcp_write_xmit().
2057 */
2058 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2059 /* Decrement cwnd here because we are sending
2060 * effectively two packets. */
2061 tp->snd_cwnd--;
2062 tcp_event_new_data_sent(sk, nskb);
2063
2064 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2065 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2066 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2067
2068 return 1;
2069 }
2070
2071 return -1;
2072}
2073
2074/* TCP Small Queues :
2075 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2076 * (These limits are doubled for retransmits)
2077 * This allows for :
2078 * - better RTT estimation and ACK scheduling
2079 * - faster recovery
2080 * - high rates
2081 * Alas, some drivers / subsystems require a fair amount
2082 * of queued bytes to ensure line rate.
2083 * One example is wifi aggregation (802.11 AMPDU)
2084 */
2085static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
2086 unsigned int factor)
2087{
2088 unsigned int limit;
2089
2090 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2091 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2092 limit <<= factor;
2093
2094 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2095 /* Always send the 1st or 2nd skb in write queue.
2096 * No need to wait for TX completion to call us back,
2097 * after softirq/tasklet schedule.
2098 * This helps when TX completions are delayed too much.
2099 */
2100 if (skb == sk->sk_write_queue.next ||
2101 skb->prev == sk->sk_write_queue.next)
2102 return false;
2103
2104 set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
2105 /* It is possible TX completion already happened
2106 * before we set TSQ_THROTTLED, so we must
2107 * test again the condition.
2108 */
2109 smp_mb__after_atomic();
2110 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2111 return true;
2112 }
2113 return false;
2114}
2115
2116static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
2117{
2118 const u32 now = tcp_time_stamp;
2119
2120 if (tp->chrono_type > TCP_CHRONO_UNSPEC)
2121 tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;
2122 tp->chrono_start = now;
2123 tp->chrono_type = new;
2124}
2125
2126void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
2127{
2128 struct tcp_sock *tp = tcp_sk(sk);
2129
2130 /* If there are multiple conditions worthy of tracking in a
2131 * chronograph then the highest priority enum takes precedence
2132 * over the other conditions. So that if something "more interesting"
2133 * starts happening, stop the previous chrono and start a new one.
2134 */
2135 if (type > tp->chrono_type)
2136 tcp_chrono_set(tp, type);
2137}
2138
2139void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
2140{
2141 struct tcp_sock *tp = tcp_sk(sk);
2142
2143
2144 /* There are multiple conditions worthy of tracking in a
2145 * chronograph, so that the highest priority enum takes
2146 * precedence over the other conditions (see tcp_chrono_start).
2147 * If a condition stops, we only stop chrono tracking if
2148 * it's the "most interesting" or current chrono we are
2149 * tracking and starts busy chrono if we have pending data.
2150 */
2151 if (tcp_write_queue_empty(sk))
2152 tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
2153 else if (type == tp->chrono_type)
2154 tcp_chrono_set(tp, TCP_CHRONO_BUSY);
2155}
2156
2157/* This routine writes packets to the network. It advances the
2158 * send_head. This happens as incoming acks open up the remote
2159 * window for us.
2160 *
2161 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2162 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2163 * account rare use of URG, this is not a big flaw.
2164 *
2165 * Send at most one packet when push_one > 0. Temporarily ignore
2166 * cwnd limit to force at most one packet out when push_one == 2.
2167
2168 * Returns true, if no segments are in flight and we have queued segments,
2169 * but cannot send anything now because of SWS or another problem.
2170 */
2171static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2172 int push_one, gfp_t gfp)
2173{
2174 struct tcp_sock *tp = tcp_sk(sk);
2175 struct sk_buff *skb;
2176 unsigned int tso_segs, sent_pkts;
2177 int cwnd_quota;
2178 int result;
2179 bool is_cwnd_limited = false, is_rwnd_limited = false;
2180 u32 max_segs;
2181
2182 sent_pkts = 0;
2183
2184 if (!push_one) {
2185 /* Do MTU probing. */
2186 result = tcp_mtu_probe(sk);
2187 if (!result) {
2188 return false;
2189 } else if (result > 0) {
2190 sent_pkts = 1;
2191 }
2192 }
2193
2194 max_segs = tcp_tso_segs(sk, mss_now);
2195 while ((skb = tcp_send_head(sk))) {
2196 unsigned int limit;
2197
2198 tso_segs = tcp_init_tso_segs(skb, mss_now);
2199 BUG_ON(!tso_segs);
2200
2201 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2202 /* "skb_mstamp" is used as a start point for the retransmit timer */
2203 skb_mstamp_get(&skb->skb_mstamp);
2204 goto repair; /* Skip network transmission */
2205 }
2206
2207 cwnd_quota = tcp_cwnd_test(tp, skb);
2208 if (!cwnd_quota) {
2209 if (push_one == 2)
2210 /* Force out a loss probe pkt. */
2211 cwnd_quota = 1;
2212 else
2213 break;
2214 }
2215
2216 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
2217 is_rwnd_limited = true;
2218 break;
2219 }
2220
2221 if (tso_segs == 1) {
2222 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2223 (tcp_skb_is_last(sk, skb) ?
2224 nonagle : TCP_NAGLE_PUSH))))
2225 break;
2226 } else {
2227 if (!push_one &&
2228 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2229 max_segs))
2230 break;
2231 }
2232
2233 limit = mss_now;
2234 if (tso_segs > 1 && !tcp_urg_mode(tp))
2235 limit = tcp_mss_split_point(sk, skb, mss_now,
2236 min_t(unsigned int,
2237 cwnd_quota,
2238 max_segs),
2239 nonagle);
2240
2241 if (skb->len > limit &&
2242 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2243 break;
2244
2245 if (test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags))
2246 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
2247 if (tcp_small_queue_check(sk, skb, 0))
2248 break;
2249
2250 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2251 break;
2252
2253repair:
2254 /* Advance the send_head. This one is sent out.
2255 * This call will increment packets_out.
2256 */
2257 tcp_event_new_data_sent(sk, skb);
2258
2259 tcp_minshall_update(tp, mss_now, skb);
2260 sent_pkts += tcp_skb_pcount(skb);
2261
2262 if (push_one)
2263 break;
2264 }
2265
2266 if (is_rwnd_limited)
2267 tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
2268 else
2269 tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
2270
2271 if (likely(sent_pkts)) {
2272 if (tcp_in_cwnd_reduction(sk))
2273 tp->prr_out += sent_pkts;
2274
2275 /* Send one loss probe per tail loss episode. */
2276 if (push_one != 2)
2277 tcp_schedule_loss_probe(sk);
2278 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2279 tcp_cwnd_validate(sk, is_cwnd_limited);
2280 return false;
2281 }
2282 return !tp->packets_out && tcp_send_head(sk);
2283}
2284
2285bool tcp_schedule_loss_probe(struct sock *sk)
2286{
2287 struct inet_connection_sock *icsk = inet_csk(sk);
2288 struct tcp_sock *tp = tcp_sk(sk);
2289 u32 timeout, tlp_time_stamp, rto_time_stamp;
2290 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2291
2292 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2293 return false;
2294 /* No consecutive loss probes. */
2295 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2296 tcp_rearm_rto(sk);
2297 return false;
2298 }
2299 /* Don't do any loss probe on a Fast Open connection before 3WHS
2300 * finishes.
2301 */
2302 if (tp->fastopen_rsk)
2303 return false;
2304
2305 /* TLP is only scheduled when next timer event is RTO. */
2306 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2307 return false;
2308
2309 /* Schedule a loss probe in 2*RTT for SACK capable connections
2310 * in Open state, that are either limited by cwnd or application.
2311 */
2312 if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
2313 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2314 return false;
2315
2316 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2317 tcp_send_head(sk))
2318 return false;
2319
2320 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2321 * for delayed ack when there's one outstanding packet. If no RTT
2322 * sample is available then probe after TCP_TIMEOUT_INIT.
2323 */
2324 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2325 if (tp->packets_out == 1)
2326 timeout = max_t(u32, timeout,
2327 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2328 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2329
2330 /* If RTO is shorter, just schedule TLP in its place. */
2331 tlp_time_stamp = tcp_time_stamp + timeout;
2332 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2333 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2334 s32 delta = rto_time_stamp - tcp_time_stamp;
2335 if (delta > 0)
2336 timeout = delta;
2337 }
2338
2339 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2340 TCP_RTO_MAX);
2341 return true;
2342}
2343
2344/* Thanks to skb fast clones, we can detect if a prior transmit of
2345 * a packet is still in a qdisc or driver queue.
2346 * In this case, there is very little point doing a retransmit !
2347 */
2348static bool skb_still_in_host_queue(const struct sock *sk,
2349 const struct sk_buff *skb)
2350{
2351 if (unlikely(skb_fclone_busy(sk, skb))) {
2352 NET_INC_STATS(sock_net(sk),
2353 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2354 return true;
2355 }
2356 return false;
2357}
2358
2359/* When probe timeout (PTO) fires, try send a new segment if possible, else
2360 * retransmit the last segment.
2361 */
2362void tcp_send_loss_probe(struct sock *sk)
2363{
2364 struct tcp_sock *tp = tcp_sk(sk);
2365 struct sk_buff *skb;
2366 int pcount;
2367 int mss = tcp_current_mss(sk);
2368
2369 skb = tcp_send_head(sk);
2370 if (skb) {
2371 if (tcp_snd_wnd_test(tp, skb, mss)) {
2372 pcount = tp->packets_out;
2373 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2374 if (tp->packets_out > pcount)
2375 goto probe_sent;
2376 goto rearm_timer;
2377 }
2378 skb = tcp_write_queue_prev(sk, skb);
2379 } else {
2380 skb = tcp_write_queue_tail(sk);
2381 }
2382
2383 /* At most one outstanding TLP retransmission. */
2384 if (tp->tlp_high_seq)
2385 goto rearm_timer;
2386
2387 /* Retransmit last segment. */
2388 if (WARN_ON(!skb))
2389 goto rearm_timer;
2390
2391 if (skb_still_in_host_queue(sk, skb))
2392 goto rearm_timer;
2393
2394 pcount = tcp_skb_pcount(skb);
2395 if (WARN_ON(!pcount))
2396 goto rearm_timer;
2397
2398 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2399 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2400 GFP_ATOMIC)))
2401 goto rearm_timer;
2402 skb = tcp_write_queue_next(sk, skb);
2403 }
2404
2405 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2406 goto rearm_timer;
2407
2408 if (__tcp_retransmit_skb(sk, skb, 1))
2409 goto rearm_timer;
2410
2411 /* Record snd_nxt for loss detection. */
2412 tp->tlp_high_seq = tp->snd_nxt;
2413
2414probe_sent:
2415 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2416 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2417 inet_csk(sk)->icsk_pending = 0;
2418rearm_timer:
2419 tcp_rearm_rto(sk);
2420}
2421
2422/* Push out any pending frames which were held back due to
2423 * TCP_CORK or attempt at coalescing tiny packets.
2424 * The socket must be locked by the caller.
2425 */
2426void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2427 int nonagle)
2428{
2429 /* If we are closed, the bytes will have to remain here.
2430 * In time closedown will finish, we empty the write queue and
2431 * all will be happy.
2432 */
2433 if (unlikely(sk->sk_state == TCP_CLOSE))
2434 return;
2435
2436 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2437 sk_gfp_mask(sk, GFP_ATOMIC)))
2438 tcp_check_probe_timer(sk);
2439}
2440
2441/* Send _single_ skb sitting at the send head. This function requires
2442 * true push pending frames to setup probe timer etc.
2443 */
2444void tcp_push_one(struct sock *sk, unsigned int mss_now)
2445{
2446 struct sk_buff *skb = tcp_send_head(sk);
2447
2448 BUG_ON(!skb || skb->len < mss_now);
2449
2450 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2451}
2452
2453/* This function returns the amount that we can raise the
2454 * usable window based on the following constraints
2455 *
2456 * 1. The window can never be shrunk once it is offered (RFC 793)
2457 * 2. We limit memory per socket
2458 *
2459 * RFC 1122:
2460 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2461 * RECV.NEXT + RCV.WIN fixed until:
2462 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2463 *
2464 * i.e. don't raise the right edge of the window until you can raise
2465 * it at least MSS bytes.
2466 *
2467 * Unfortunately, the recommended algorithm breaks header prediction,
2468 * since header prediction assumes th->window stays fixed.
2469 *
2470 * Strictly speaking, keeping th->window fixed violates the receiver
2471 * side SWS prevention criteria. The problem is that under this rule
2472 * a stream of single byte packets will cause the right side of the
2473 * window to always advance by a single byte.
2474 *
2475 * Of course, if the sender implements sender side SWS prevention
2476 * then this will not be a problem.
2477 *
2478 * BSD seems to make the following compromise:
2479 *
2480 * If the free space is less than the 1/4 of the maximum
2481 * space available and the free space is less than 1/2 mss,
2482 * then set the window to 0.
2483 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2484 * Otherwise, just prevent the window from shrinking
2485 * and from being larger than the largest representable value.
2486 *
2487 * This prevents incremental opening of the window in the regime
2488 * where TCP is limited by the speed of the reader side taking
2489 * data out of the TCP receive queue. It does nothing about
2490 * those cases where the window is constrained on the sender side
2491 * because the pipeline is full.
2492 *
2493 * BSD also seems to "accidentally" limit itself to windows that are a
2494 * multiple of MSS, at least until the free space gets quite small.
2495 * This would appear to be a side effect of the mbuf implementation.
2496 * Combining these two algorithms results in the observed behavior
2497 * of having a fixed window size at almost all times.
2498 *
2499 * Below we obtain similar behavior by forcing the offered window to
2500 * a multiple of the mss when it is feasible to do so.
2501 *
2502 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2503 * Regular options like TIMESTAMP are taken into account.
2504 */
2505u32 __tcp_select_window(struct sock *sk)
2506{
2507 struct inet_connection_sock *icsk = inet_csk(sk);
2508 struct tcp_sock *tp = tcp_sk(sk);
2509 /* MSS for the peer's data. Previous versions used mss_clamp
2510 * here. I don't know if the value based on our guesses
2511 * of peer's MSS is better for the performance. It's more correct
2512 * but may be worse for the performance because of rcv_mss
2513 * fluctuations. --SAW 1998/11/1
2514 */
2515 int mss = icsk->icsk_ack.rcv_mss;
2516 int free_space = tcp_space(sk);
2517 int allowed_space = tcp_full_space(sk);
2518 int full_space = min_t(int, tp->window_clamp, allowed_space);
2519 int window;
2520
2521 if (unlikely(mss > full_space)) {
2522 mss = full_space;
2523 if (mss <= 0)
2524 return 0;
2525 }
2526 if (free_space < (full_space >> 1)) {
2527 icsk->icsk_ack.quick = 0;
2528
2529 if (tcp_under_memory_pressure(sk))
2530 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2531 4U * tp->advmss);
2532
2533 /* free_space might become our new window, make sure we don't
2534 * increase it due to wscale.
2535 */
2536 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2537
2538 /* if free space is less than mss estimate, or is below 1/16th
2539 * of the maximum allowed, try to move to zero-window, else
2540 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2541 * new incoming data is dropped due to memory limits.
2542 * With large window, mss test triggers way too late in order
2543 * to announce zero window in time before rmem limit kicks in.
2544 */
2545 if (free_space < (allowed_space >> 4) || free_space < mss)
2546 return 0;
2547 }
2548
2549 if (free_space > tp->rcv_ssthresh)
2550 free_space = tp->rcv_ssthresh;
2551
2552 /* Don't do rounding if we are using window scaling, since the
2553 * scaled window will not line up with the MSS boundary anyway.
2554 */
2555 window = tp->rcv_wnd;
2556 if (tp->rx_opt.rcv_wscale) {
2557 window = free_space;
2558
2559 /* Advertise enough space so that it won't get scaled away.
2560 * Import case: prevent zero window announcement if
2561 * 1<<rcv_wscale > mss.
2562 */
2563 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2564 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2565 << tp->rx_opt.rcv_wscale);
2566 } else {
2567 /* Get the largest window that is a nice multiple of mss.
2568 * Window clamp already applied above.
2569 * If our current window offering is within 1 mss of the
2570 * free space we just keep it. This prevents the divide
2571 * and multiply from happening most of the time.
2572 * We also don't do any window rounding when the free space
2573 * is too small.
2574 */
2575 if (window <= free_space - mss || window > free_space)
2576 window = (free_space / mss) * mss;
2577 else if (mss == full_space &&
2578 free_space > window + (full_space >> 1))
2579 window = free_space;
2580 }
2581
2582 return window;
2583}
2584
2585void tcp_skb_collapse_tstamp(struct sk_buff *skb,
2586 const struct sk_buff *next_skb)
2587{
2588 if (unlikely(tcp_has_tx_tstamp(next_skb))) {
2589 const struct skb_shared_info *next_shinfo =
2590 skb_shinfo(next_skb);
2591 struct skb_shared_info *shinfo = skb_shinfo(skb);
2592
2593 shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2594 shinfo->tskey = next_shinfo->tskey;
2595 TCP_SKB_CB(skb)->txstamp_ack |=
2596 TCP_SKB_CB(next_skb)->txstamp_ack;
2597 }
2598}
2599
2600/* Collapses two adjacent SKB's during retransmission. */
2601static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2602{
2603 struct tcp_sock *tp = tcp_sk(sk);
2604 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2605 int skb_size, next_skb_size;
2606
2607 skb_size = skb->len;
2608 next_skb_size = next_skb->len;
2609
2610 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2611
2612 if (next_skb_size) {
2613 if (next_skb_size <= skb_availroom(skb))
2614 skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size),
2615 next_skb_size);
2616 else if (!skb_shift(skb, next_skb, next_skb_size))
2617 return false;
2618 }
2619 tcp_highest_sack_combine(sk, next_skb, skb);
2620
2621 tcp_unlink_write_queue(next_skb, sk);
2622
2623 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2624 skb->ip_summed = CHECKSUM_PARTIAL;
2625
2626 if (skb->ip_summed != CHECKSUM_PARTIAL)
2627 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2628
2629 /* Update sequence range on original skb. */
2630 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2631
2632 /* Merge over control information. This moves PSH/FIN etc. over */
2633 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2634
2635 /* All done, get rid of second SKB and account for it so
2636 * packet counting does not break.
2637 */
2638 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2639 TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2640
2641 /* changed transmit queue under us so clear hints */
2642 tcp_clear_retrans_hints_partial(tp);
2643 if (next_skb == tp->retransmit_skb_hint)
2644 tp->retransmit_skb_hint = skb;
2645
2646 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2647
2648 tcp_skb_collapse_tstamp(skb, next_skb);
2649
2650 sk_wmem_free_skb(sk, next_skb);
2651 return true;
2652}
2653
2654/* Check if coalescing SKBs is legal. */
2655static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2656{
2657 if (tcp_skb_pcount(skb) > 1)
2658 return false;
2659 if (skb_cloned(skb))
2660 return false;
2661 if (skb == tcp_send_head(sk))
2662 return false;
2663 /* Some heuristics for collapsing over SACK'd could be invented */
2664 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2665 return false;
2666
2667 return true;
2668}
2669
2670/* Collapse packets in the retransmit queue to make to create
2671 * less packets on the wire. This is only done on retransmission.
2672 */
2673static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2674 int space)
2675{
2676 struct tcp_sock *tp = tcp_sk(sk);
2677 struct sk_buff *skb = to, *tmp;
2678 bool first = true;
2679
2680 if (!sysctl_tcp_retrans_collapse)
2681 return;
2682 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2683 return;
2684
2685 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2686 if (!tcp_can_collapse(sk, skb))
2687 break;
2688
2689 if (!tcp_skb_can_collapse_to(to))
2690 break;
2691
2692 space -= skb->len;
2693
2694 if (first) {
2695 first = false;
2696 continue;
2697 }
2698
2699 if (space < 0)
2700 break;
2701
2702 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2703 break;
2704
2705 if (!tcp_collapse_retrans(sk, to))
2706 break;
2707 }
2708}
2709
2710/* This retransmits one SKB. Policy decisions and retransmit queue
2711 * state updates are done by the caller. Returns non-zero if an
2712 * error occurred which prevented the send.
2713 */
2714int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2715{
2716 struct inet_connection_sock *icsk = inet_csk(sk);
2717 struct tcp_sock *tp = tcp_sk(sk);
2718 unsigned int cur_mss;
2719 int diff, len, err;
2720
2721
2722 /* Inconclusive MTU probe */
2723 if (icsk->icsk_mtup.probe_size)
2724 icsk->icsk_mtup.probe_size = 0;
2725
2726 /* Do not sent more than we queued. 1/4 is reserved for possible
2727 * copying overhead: fragmentation, tunneling, mangling etc.
2728 */
2729 if (atomic_read(&sk->sk_wmem_alloc) >
2730 min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
2731 sk->sk_sndbuf))
2732 return -EAGAIN;
2733
2734 if (skb_still_in_host_queue(sk, skb))
2735 return -EBUSY;
2736
2737 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2738 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2739 BUG();
2740 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2741 return -ENOMEM;
2742 }
2743
2744 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2745 return -EHOSTUNREACH; /* Routing failure or similar. */
2746
2747 cur_mss = tcp_current_mss(sk);
2748
2749 /* If receiver has shrunk his window, and skb is out of
2750 * new window, do not retransmit it. The exception is the
2751 * case, when window is shrunk to zero. In this case
2752 * our retransmit serves as a zero window probe.
2753 */
2754 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2755 TCP_SKB_CB(skb)->seq != tp->snd_una)
2756 return -EAGAIN;
2757
2758 len = cur_mss * segs;
2759 if (skb->len > len) {
2760 if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
2761 return -ENOMEM; /* We'll try again later. */
2762 } else {
2763 if (skb_unclone(skb, GFP_ATOMIC))
2764 return -ENOMEM;
2765
2766 diff = tcp_skb_pcount(skb);
2767 tcp_set_skb_tso_segs(skb, cur_mss);
2768 diff -= tcp_skb_pcount(skb);
2769 if (diff)
2770 tcp_adjust_pcount(sk, skb, diff);
2771 if (skb->len < cur_mss)
2772 tcp_retrans_try_collapse(sk, skb, cur_mss);
2773 }
2774
2775 /* RFC3168, section 6.1.1.1. ECN fallback */
2776 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2777 tcp_ecn_clear_syn(sk, skb);
2778
2779 /* make sure skb->data is aligned on arches that require it
2780 * and check if ack-trimming & collapsing extended the headroom
2781 * beyond what csum_start can cover.
2782 */
2783 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2784 skb_headroom(skb) >= 0xFFFF)) {
2785 struct sk_buff *nskb;
2786
2787 skb_mstamp_get(&skb->skb_mstamp);
2788 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2789 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2790 -ENOBUFS;
2791 } else {
2792 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2793 }
2794
2795 if (likely(!err)) {
2796 segs = tcp_skb_pcount(skb);
2797
2798 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2799 /* Update global TCP statistics. */
2800 TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2801 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2802 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2803 tp->total_retrans += segs;
2804 }
2805 return err;
2806}
2807
2808int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2809{
2810 struct tcp_sock *tp = tcp_sk(sk);
2811 int err = __tcp_retransmit_skb(sk, skb, segs);
2812
2813 if (err == 0) {
2814#if FASTRETRANS_DEBUG > 0
2815 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2816 net_dbg_ratelimited("retrans_out leaked\n");
2817 }
2818#endif
2819 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2820 tp->retrans_out += tcp_skb_pcount(skb);
2821
2822 /* Save stamp of the first retransmit. */
2823 if (!tp->retrans_stamp)
2824 tp->retrans_stamp = tcp_skb_timestamp(skb);
2825
2826 } else if (err != -EBUSY) {
2827 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2828 }
2829
2830 if (tp->undo_retrans < 0)
2831 tp->undo_retrans = 0;
2832 tp->undo_retrans += tcp_skb_pcount(skb);
2833 return err;
2834}
2835
2836/* Check if we forward retransmits are possible in the current
2837 * window/congestion state.
2838 */
2839static bool tcp_can_forward_retransmit(struct sock *sk)
2840{
2841 const struct inet_connection_sock *icsk = inet_csk(sk);
2842 const struct tcp_sock *tp = tcp_sk(sk);
2843
2844 /* Forward retransmissions are possible only during Recovery. */
2845 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2846 return false;
2847
2848 /* No forward retransmissions in Reno are possible. */
2849 if (tcp_is_reno(tp))
2850 return false;
2851
2852 /* Yeah, we have to make difficult choice between forward transmission
2853 * and retransmission... Both ways have their merits...
2854 *
2855 * For now we do not retransmit anything, while we have some new
2856 * segments to send. In the other cases, follow rule 3 for
2857 * NextSeg() specified in RFC3517.
2858 */
2859
2860 if (tcp_may_send_now(sk))
2861 return false;
2862
2863 return true;
2864}
2865
2866/* This gets called after a retransmit timeout, and the initially
2867 * retransmitted data is acknowledged. It tries to continue
2868 * resending the rest of the retransmit queue, until either
2869 * we've sent it all or the congestion window limit is reached.
2870 * If doing SACK, the first ACK which comes back for a timeout
2871 * based retransmit packet might feed us FACK information again.
2872 * If so, we use it to avoid unnecessarily retransmissions.
2873 */
2874void tcp_xmit_retransmit_queue(struct sock *sk)
2875{
2876 const struct inet_connection_sock *icsk = inet_csk(sk);
2877 struct tcp_sock *tp = tcp_sk(sk);
2878 struct sk_buff *skb;
2879 struct sk_buff *hole = NULL;
2880 u32 max_segs, last_lost;
2881 int mib_idx;
2882 int fwd_rexmitting = 0;
2883
2884 if (!tp->packets_out)
2885 return;
2886
2887 if (!tp->lost_out)
2888 tp->retransmit_high = tp->snd_una;
2889
2890 if (tp->retransmit_skb_hint) {
2891 skb = tp->retransmit_skb_hint;
2892 last_lost = TCP_SKB_CB(skb)->end_seq;
2893 if (after(last_lost, tp->retransmit_high))
2894 last_lost = tp->retransmit_high;
2895 } else {
2896 skb = tcp_write_queue_head(sk);
2897 last_lost = tp->snd_una;
2898 }
2899
2900 max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
2901 tcp_for_write_queue_from(skb, sk) {
2902 __u8 sacked;
2903 int segs;
2904
2905 if (skb == tcp_send_head(sk))
2906 break;
2907 /* we could do better than to assign each time */
2908 if (!hole)
2909 tp->retransmit_skb_hint = skb;
2910
2911 segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
2912 if (segs <= 0)
2913 return;
2914 sacked = TCP_SKB_CB(skb)->sacked;
2915 /* In case tcp_shift_skb_data() have aggregated large skbs,
2916 * we need to make sure not sending too bigs TSO packets
2917 */
2918 segs = min_t(int, segs, max_segs);
2919
2920 if (fwd_rexmitting) {
2921begin_fwd:
2922 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2923 break;
2924 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2925
2926 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2927 tp->retransmit_high = last_lost;
2928 if (!tcp_can_forward_retransmit(sk))
2929 break;
2930 /* Backtrack if necessary to non-L'ed skb */
2931 if (hole) {
2932 skb = hole;
2933 hole = NULL;
2934 }
2935 fwd_rexmitting = 1;
2936 goto begin_fwd;
2937
2938 } else if (!(sacked & TCPCB_LOST)) {
2939 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2940 hole = skb;
2941 continue;
2942
2943 } else {
2944 last_lost = TCP_SKB_CB(skb)->end_seq;
2945 if (icsk->icsk_ca_state != TCP_CA_Loss)
2946 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2947 else
2948 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2949 }
2950
2951 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2952 continue;
2953
2954 if (tcp_small_queue_check(sk, skb, 1))
2955 return;
2956
2957 if (tcp_retransmit_skb(sk, skb, segs))
2958 return;
2959
2960 NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb));
2961
2962 if (tcp_in_cwnd_reduction(sk))
2963 tp->prr_out += tcp_skb_pcount(skb);
2964
2965 if (skb == tcp_write_queue_head(sk))
2966 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2967 inet_csk(sk)->icsk_rto,
2968 TCP_RTO_MAX);
2969 }
2970}
2971
2972/* We allow to exceed memory limits for FIN packets to expedite
2973 * connection tear down and (memory) recovery.
2974 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2975 * or even be forced to close flow without any FIN.
2976 * In general, we want to allow one skb per socket to avoid hangs
2977 * with edge trigger epoll()
2978 */
2979void sk_forced_mem_schedule(struct sock *sk, int size)
2980{
2981 int amt;
2982
2983 if (size <= sk->sk_forward_alloc)
2984 return;
2985 amt = sk_mem_pages(size);
2986 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2987 sk_memory_allocated_add(sk, amt);
2988
2989 if (mem_cgroup_sockets_enabled && sk->sk_memcg)
2990 mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2991}
2992
2993/* Send a FIN. The caller locks the socket for us.
2994 * We should try to send a FIN packet really hard, but eventually give up.
2995 */
2996void tcp_send_fin(struct sock *sk)
2997{
2998 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2999 struct tcp_sock *tp = tcp_sk(sk);
3000
3001 /* Optimization, tack on the FIN if we have one skb in write queue and
3002 * this skb was not yet sent, or we are under memory pressure.
3003 * Note: in the latter case, FIN packet will be sent after a timeout,
3004 * as TCP stack thinks it has already been transmitted.
3005 */
3006 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
3007coalesce:
3008 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
3009 TCP_SKB_CB(tskb)->end_seq++;
3010 tp->write_seq++;
3011 if (!tcp_send_head(sk)) {
3012 /* This means tskb was already sent.
3013 * Pretend we included the FIN on previous transmit.
3014 * We need to set tp->snd_nxt to the value it would have
3015 * if FIN had been sent. This is because retransmit path
3016 * does not change tp->snd_nxt.
3017 */
3018 tp->snd_nxt++;
3019 return;
3020 }
3021 } else {
3022 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
3023 if (unlikely(!skb)) {
3024 if (tskb)
3025 goto coalesce;
3026 return;
3027 }
3028 skb_reserve(skb, MAX_TCP_HEADER);
3029 sk_forced_mem_schedule(sk, skb->truesize);
3030 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
3031 tcp_init_nondata_skb(skb, tp->write_seq,
3032 TCPHDR_ACK | TCPHDR_FIN);
3033 tcp_queue_skb(sk, skb);
3034 }
3035 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
3036}
3037
3038/* We get here when a process closes a file descriptor (either due to
3039 * an explicit close() or as a byproduct of exit()'ing) and there
3040 * was unread data in the receive queue. This behavior is recommended
3041 * by RFC 2525, section 2.17. -DaveM
3042 */
3043void tcp_send_active_reset(struct sock *sk, gfp_t priority)
3044{
3045 struct sk_buff *skb;
3046
3047 /* NOTE: No TCP options attached and we never retransmit this. */
3048 skb = alloc_skb(MAX_TCP_HEADER, priority);
3049 if (!skb) {
3050 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3051 return;
3052 }
3053
3054 /* Reserve space for headers and prepare control bits. */
3055 skb_reserve(skb, MAX_TCP_HEADER);
3056 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
3057 TCPHDR_ACK | TCPHDR_RST);
3058 skb_mstamp_get(&skb->skb_mstamp);
3059 /* Send it off. */
3060 if (tcp_transmit_skb(sk, skb, 0, priority))
3061 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3062
3063 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
3064}
3065
3066/* Send a crossed SYN-ACK during socket establishment.
3067 * WARNING: This routine must only be called when we have already sent
3068 * a SYN packet that crossed the incoming SYN that caused this routine
3069 * to get called. If this assumption fails then the initial rcv_wnd
3070 * and rcv_wscale values will not be correct.
3071 */
3072int tcp_send_synack(struct sock *sk)
3073{
3074 struct sk_buff *skb;
3075
3076 skb = tcp_write_queue_head(sk);
3077 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
3078 pr_debug("%s: wrong queue state\n", __func__);
3079 return -EFAULT;
3080 }
3081 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
3082 if (skb_cloned(skb)) {
3083 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
3084 if (!nskb)
3085 return -ENOMEM;
3086 tcp_unlink_write_queue(skb, sk);
3087 __skb_header_release(nskb);
3088 __tcp_add_write_queue_head(sk, nskb);
3089 sk_wmem_free_skb(sk, skb);
3090 sk->sk_wmem_queued += nskb->truesize;
3091 sk_mem_charge(sk, nskb->truesize);
3092 skb = nskb;
3093 }
3094
3095 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
3096 tcp_ecn_send_synack(sk, skb);
3097 }
3098 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3099}
3100
3101/**
3102 * tcp_make_synack - Prepare a SYN-ACK.
3103 * sk: listener socket
3104 * dst: dst entry attached to the SYNACK
3105 * req: request_sock pointer
3106 *
3107 * Allocate one skb and build a SYNACK packet.
3108 * @dst is consumed : Caller should not use it again.
3109 */
3110struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3111 struct request_sock *req,
3112 struct tcp_fastopen_cookie *foc,
3113 enum tcp_synack_type synack_type)
3114{
3115 struct inet_request_sock *ireq = inet_rsk(req);
3116 const struct tcp_sock *tp = tcp_sk(sk);
3117 struct tcp_md5sig_key *md5 = NULL;
3118 struct tcp_out_options opts;
3119 struct sk_buff *skb;
3120 int tcp_header_size;
3121 struct tcphdr *th;
3122 u16 user_mss;
3123 int mss;
3124
3125 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3126 if (unlikely(!skb)) {
3127 dst_release(dst);
3128 return NULL;
3129 }
3130 /* Reserve space for headers. */
3131 skb_reserve(skb, MAX_TCP_HEADER);
3132
3133 switch (synack_type) {
3134 case TCP_SYNACK_NORMAL:
3135 skb_set_owner_w(skb, req_to_sk(req));
3136 break;
3137 case TCP_SYNACK_COOKIE:
3138 /* Under synflood, we do not attach skb to a socket,
3139 * to avoid false sharing.
3140 */
3141 break;
3142 case TCP_SYNACK_FASTOPEN:
3143 /* sk is a const pointer, because we want to express multiple
3144 * cpu might call us concurrently.
3145 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3146 */
3147 skb_set_owner_w(skb, (struct sock *)sk);
3148 break;
3149 }
3150 skb_dst_set(skb, dst);
3151
3152 mss = dst_metric_advmss(dst);
3153 user_mss = READ_ONCE(tp->rx_opt.user_mss);
3154 if (user_mss && user_mss < mss)
3155 mss = user_mss;
3156
3157 memset(&opts, 0, sizeof(opts));
3158#ifdef CONFIG_SYN_COOKIES
3159 if (unlikely(req->cookie_ts))
3160 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3161 else
3162#endif
3163 skb_mstamp_get(&skb->skb_mstamp);
3164
3165#ifdef CONFIG_TCP_MD5SIG
3166 rcu_read_lock();
3167 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3168#endif
3169 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3170 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3171 sizeof(*th);
3172
3173 skb_push(skb, tcp_header_size);
3174 skb_reset_transport_header(skb);
3175
3176 th = (struct tcphdr *)skb->data;
3177 memset(th, 0, sizeof(struct tcphdr));
3178 th->syn = 1;
3179 th->ack = 1;
3180 tcp_ecn_make_synack(req, th);
3181 th->source = htons(ireq->ir_num);
3182 th->dest = ireq->ir_rmt_port;
3183 /* Setting of flags are superfluous here for callers (and ECE is
3184 * not even correctly set)
3185 */
3186 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3187 TCPHDR_SYN | TCPHDR_ACK);
3188
3189 th->seq = htonl(TCP_SKB_CB(skb)->seq);
3190 /* XXX data is queued and acked as is. No buffer/window check */
3191 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3192
3193 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3194 th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3195 tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3196 th->doff = (tcp_header_size >> 2);
3197 __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3198
3199#ifdef CONFIG_TCP_MD5SIG
3200 /* Okay, we have all we need - do the md5 hash if needed */
3201 if (md5)
3202 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3203 md5, req_to_sk(req), skb);
3204 rcu_read_unlock();
3205#endif
3206
3207 /* Do not fool tcpdump (if any), clean our debris */
3208 skb->tstamp = 0;
3209 return skb;
3210}
3211EXPORT_SYMBOL(tcp_make_synack);
3212
3213static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3214{
3215 struct inet_connection_sock *icsk = inet_csk(sk);
3216 const struct tcp_congestion_ops *ca;
3217 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3218
3219 if (ca_key == TCP_CA_UNSPEC)
3220 return;
3221
3222 rcu_read_lock();
3223 ca = tcp_ca_find_key(ca_key);
3224 if (likely(ca && try_module_get(ca->owner))) {
3225 module_put(icsk->icsk_ca_ops->owner);
3226 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3227 icsk->icsk_ca_ops = ca;
3228 }
3229 rcu_read_unlock();
3230}
3231
3232/* Do all connect socket setups that can be done AF independent. */
3233static void tcp_connect_init(struct sock *sk)
3234{
3235 const struct dst_entry *dst = __sk_dst_get(sk);
3236 struct tcp_sock *tp = tcp_sk(sk);
3237 __u8 rcv_wscale;
3238
3239 /* We'll fix this up when we get a response from the other end.
3240 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3241 */
3242 tp->tcp_header_len = sizeof(struct tcphdr) +
3243 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3244
3245#ifdef CONFIG_TCP_MD5SIG
3246 if (tp->af_specific->md5_lookup(sk, sk))
3247 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3248#endif
3249
3250 /* If user gave his TCP_MAXSEG, record it to clamp */
3251 if (tp->rx_opt.user_mss)
3252 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3253 tp->max_window = 0;
3254 tcp_mtup_init(sk);
3255 tcp_sync_mss(sk, dst_mtu(dst));
3256
3257 tcp_ca_dst_init(sk, dst);
3258
3259 if (!tp->window_clamp)
3260 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3261 tp->advmss = dst_metric_advmss(dst);
3262 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3263 tp->advmss = tp->rx_opt.user_mss;
3264
3265 tcp_initialize_rcv_mss(sk);
3266
3267 /* limit the window selection if the user enforce a smaller rx buffer */
3268 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3269 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3270 tp->window_clamp = tcp_full_space(sk);
3271
3272 tcp_select_initial_window(tcp_full_space(sk),
3273 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3274 &tp->rcv_wnd,
3275 &tp->window_clamp,
3276 sysctl_tcp_window_scaling,
3277 &rcv_wscale,
3278 dst_metric(dst, RTAX_INITRWND));
3279
3280 tp->rx_opt.rcv_wscale = rcv_wscale;
3281 tp->rcv_ssthresh = tp->rcv_wnd;
3282
3283 sk->sk_err = 0;
3284 sock_reset_flag(sk, SOCK_DONE);
3285 tp->snd_wnd = 0;
3286 tcp_init_wl(tp, 0);
3287 tp->snd_una = tp->write_seq;
3288 tp->snd_sml = tp->write_seq;
3289 tp->snd_up = tp->write_seq;
3290 tp->snd_nxt = tp->write_seq;
3291
3292 if (likely(!tp->repair))
3293 tp->rcv_nxt = 0;
3294 else
3295 tp->rcv_tstamp = tcp_time_stamp;
3296 tp->rcv_wup = tp->rcv_nxt;
3297 tp->copied_seq = tp->rcv_nxt;
3298
3299 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3300 inet_csk(sk)->icsk_retransmits = 0;
3301 tcp_clear_retrans(tp);
3302}
3303
3304static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3305{
3306 struct tcp_sock *tp = tcp_sk(sk);
3307 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3308
3309 tcb->end_seq += skb->len;
3310 __skb_header_release(skb);
3311 __tcp_add_write_queue_tail(sk, skb);
3312 sk->sk_wmem_queued += skb->truesize;
3313 sk_mem_charge(sk, skb->truesize);
3314 tp->write_seq = tcb->end_seq;
3315 tp->packets_out += tcp_skb_pcount(skb);
3316}
3317
3318/* Build and send a SYN with data and (cached) Fast Open cookie. However,
3319 * queue a data-only packet after the regular SYN, such that regular SYNs
3320 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3321 * only the SYN sequence, the data are retransmitted in the first ACK.
3322 * If cookie is not cached or other error occurs, falls back to send a
3323 * regular SYN with Fast Open cookie request option.
3324 */
3325static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3326{
3327 struct tcp_sock *tp = tcp_sk(sk);
3328 struct tcp_fastopen_request *fo = tp->fastopen_req;
3329 int syn_loss = 0, space, err = 0;
3330 unsigned long last_syn_loss = 0;
3331 struct sk_buff *syn_data;
3332
3333 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3334 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3335 &syn_loss, &last_syn_loss);
3336 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3337 if (syn_loss > 1 &&
3338 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3339 fo->cookie.len = -1;
3340 goto fallback;
3341 }
3342
3343 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3344 fo->cookie.len = -1;
3345 else if (fo->cookie.len <= 0)
3346 goto fallback;
3347
3348 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3349 * user-MSS. Reserve maximum option space for middleboxes that add
3350 * private TCP options. The cost is reduced data space in SYN :(
3351 */
3352 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3353 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3354 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3355 MAX_TCP_OPTION_SPACE;
3356
3357 space = min_t(size_t, space, fo->size);
3358
3359 /* limit to order-0 allocations */
3360 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3361
3362 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3363 if (!syn_data)
3364 goto fallback;
3365 syn_data->ip_summed = CHECKSUM_PARTIAL;
3366 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3367 if (space) {
3368 int copied = copy_from_iter(skb_put(syn_data, space), space,
3369 &fo->data->msg_iter);
3370 if (unlikely(!copied)) {
3371 kfree_skb(syn_data);
3372 goto fallback;
3373 }
3374 if (copied != space) {
3375 skb_trim(syn_data, copied);
3376 space = copied;
3377 }
3378 }
3379 /* No more data pending in inet_wait_for_connect() */
3380 if (space == fo->size)
3381 fo->data = NULL;
3382 fo->copied = space;
3383
3384 tcp_connect_queue_skb(sk, syn_data);
3385 if (syn_data->len)
3386 tcp_chrono_start(sk, TCP_CHRONO_BUSY);
3387
3388 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3389
3390 syn->skb_mstamp = syn_data->skb_mstamp;
3391
3392 /* Now full SYN+DATA was cloned and sent (or not),
3393 * remove the SYN from the original skb (syn_data)
3394 * we keep in write queue in case of a retransmit, as we
3395 * also have the SYN packet (with no data) in the same queue.
3396 */
3397 TCP_SKB_CB(syn_data)->seq++;
3398 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3399 if (!err) {
3400 tp->syn_data = (fo->copied > 0);
3401 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3402 goto done;
3403 }
3404
3405fallback:
3406 /* Send a regular SYN with Fast Open cookie request option */
3407 if (fo->cookie.len > 0)
3408 fo->cookie.len = 0;
3409 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3410 if (err)
3411 tp->syn_fastopen = 0;
3412done:
3413 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3414 return err;
3415}
3416
3417/* Build a SYN and send it off. */
3418int tcp_connect(struct sock *sk)
3419{
3420 struct tcp_sock *tp = tcp_sk(sk);
3421 struct sk_buff *buff;
3422 int err;
3423
3424 tcp_connect_init(sk);
3425
3426 if (unlikely(tp->repair)) {
3427 tcp_finish_connect(sk, NULL);
3428 return 0;
3429 }
3430
3431 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3432 if (unlikely(!buff))
3433 return -ENOBUFS;
3434
3435 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3436 tp->retrans_stamp = tcp_time_stamp;
3437 tcp_connect_queue_skb(sk, buff);
3438 tcp_ecn_send_syn(sk, buff);
3439
3440 /* Send off SYN; include data in Fast Open. */
3441 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3442 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3443 if (err == -ECONNREFUSED)
3444 return err;
3445
3446 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3447 * in order to make this packet get counted in tcpOutSegs.
3448 */
3449 tp->snd_nxt = tp->write_seq;
3450 tp->pushed_seq = tp->write_seq;
3451 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3452
3453 /* Timer for repeating the SYN until an answer. */
3454 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3455 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3456 return 0;
3457}
3458EXPORT_SYMBOL(tcp_connect);
3459
3460/* Send out a delayed ack, the caller does the policy checking
3461 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3462 * for details.
3463 */
3464void tcp_send_delayed_ack(struct sock *sk)
3465{
3466 struct inet_connection_sock *icsk = inet_csk(sk);
3467 int ato = icsk->icsk_ack.ato;
3468 unsigned long timeout;
3469
3470 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3471
3472 if (ato > TCP_DELACK_MIN) {
3473 const struct tcp_sock *tp = tcp_sk(sk);
3474 int max_ato = HZ / 2;
3475
3476 if (icsk->icsk_ack.pingpong ||
3477 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3478 max_ato = TCP_DELACK_MAX;
3479
3480 /* Slow path, intersegment interval is "high". */
3481
3482 /* If some rtt estimate is known, use it to bound delayed ack.
3483 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3484 * directly.
3485 */
3486 if (tp->srtt_us) {
3487 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3488 TCP_DELACK_MIN);
3489
3490 if (rtt < max_ato)
3491 max_ato = rtt;
3492 }
3493
3494 ato = min(ato, max_ato);
3495 }
3496
3497 /* Stay within the limit we were given */
3498 timeout = jiffies + ato;
3499
3500 /* Use new timeout only if there wasn't a older one earlier. */
3501 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3502 /* If delack timer was blocked or is about to expire,
3503 * send ACK now.
3504 */
3505 if (icsk->icsk_ack.blocked ||
3506 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3507 tcp_send_ack(sk);
3508 return;
3509 }
3510
3511 if (!time_before(timeout, icsk->icsk_ack.timeout))
3512 timeout = icsk->icsk_ack.timeout;
3513 }
3514 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3515 icsk->icsk_ack.timeout = timeout;
3516 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3517}
3518
3519/* This routine sends an ack and also updates the window. */
3520void tcp_send_ack(struct sock *sk)
3521{
3522 struct sk_buff *buff;
3523
3524 /* If we have been reset, we may not send again. */
3525 if (sk->sk_state == TCP_CLOSE)
3526 return;
3527
3528 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3529
3530 /* We are not putting this on the write queue, so
3531 * tcp_transmit_skb() will set the ownership to this
3532 * sock.
3533 */
3534 buff = alloc_skb(MAX_TCP_HEADER,
3535 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3536 if (unlikely(!buff)) {
3537 inet_csk_schedule_ack(sk);
3538 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3539 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3540 TCP_DELACK_MAX, TCP_RTO_MAX);
3541 return;
3542 }
3543
3544 /* Reserve space for headers and prepare control bits. */
3545 skb_reserve(buff, MAX_TCP_HEADER);
3546 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3547
3548 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3549 * too much.
3550 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3551 */
3552 skb_set_tcp_pure_ack(buff);
3553
3554 /* Send it off, this clears delayed acks for us. */
3555 skb_mstamp_get(&buff->skb_mstamp);
3556 tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
3557}
3558EXPORT_SYMBOL_GPL(tcp_send_ack);
3559
3560/* This routine sends a packet with an out of date sequence
3561 * number. It assumes the other end will try to ack it.
3562 *
3563 * Question: what should we make while urgent mode?
3564 * 4.4BSD forces sending single byte of data. We cannot send
3565 * out of window data, because we have SND.NXT==SND.MAX...
3566 *
3567 * Current solution: to send TWO zero-length segments in urgent mode:
3568 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3569 * out-of-date with SND.UNA-1 to probe window.
3570 */
3571static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3572{
3573 struct tcp_sock *tp = tcp_sk(sk);
3574 struct sk_buff *skb;
3575
3576 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3577 skb = alloc_skb(MAX_TCP_HEADER,
3578 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3579 if (!skb)
3580 return -1;
3581
3582 /* Reserve space for headers and set control bits. */
3583 skb_reserve(skb, MAX_TCP_HEADER);
3584 /* Use a previous sequence. This should cause the other
3585 * end to send an ack. Don't queue or clone SKB, just
3586 * send it.
3587 */
3588 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3589 skb_mstamp_get(&skb->skb_mstamp);
3590 NET_INC_STATS(sock_net(sk), mib);
3591 return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
3592}
3593
3594void tcp_send_window_probe(struct sock *sk)
3595{
3596 if (sk->sk_state == TCP_ESTABLISHED) {
3597 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3598 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3599 }
3600}
3601
3602/* Initiate keepalive or window probe from timer. */
3603int tcp_write_wakeup(struct sock *sk, int mib)
3604{
3605 struct tcp_sock *tp = tcp_sk(sk);
3606 struct sk_buff *skb;
3607
3608 if (sk->sk_state == TCP_CLOSE)
3609 return -1;
3610
3611 skb = tcp_send_head(sk);
3612 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3613 int err;
3614 unsigned int mss = tcp_current_mss(sk);
3615 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3616
3617 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3618 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3619
3620 /* We are probing the opening of a window
3621 * but the window size is != 0
3622 * must have been a result SWS avoidance ( sender )
3623 */
3624 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3625 skb->len > mss) {
3626 seg_size = min(seg_size, mss);
3627 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3628 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3629 return -1;
3630 } else if (!tcp_skb_pcount(skb))
3631 tcp_set_skb_tso_segs(skb, mss);
3632
3633 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3634 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3635 if (!err)
3636 tcp_event_new_data_sent(sk, skb);
3637 return err;
3638 } else {
3639 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3640 tcp_xmit_probe_skb(sk, 1, mib);
3641 return tcp_xmit_probe_skb(sk, 0, mib);
3642 }
3643}
3644
3645/* A window probe timeout has occurred. If window is not closed send
3646 * a partial packet else a zero probe.
3647 */
3648void tcp_send_probe0(struct sock *sk)
3649{
3650 struct inet_connection_sock *icsk = inet_csk(sk);
3651 struct tcp_sock *tp = tcp_sk(sk);
3652 struct net *net = sock_net(sk);
3653 unsigned long probe_max;
3654 int err;
3655
3656 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3657
3658 if (tp->packets_out || !tcp_send_head(sk)) {
3659 /* Cancel probe timer, if it is not required. */
3660 icsk->icsk_probes_out = 0;
3661 icsk->icsk_backoff = 0;
3662 return;
3663 }
3664
3665 if (err <= 0) {
3666 if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3667 icsk->icsk_backoff++;
3668 icsk->icsk_probes_out++;
3669 probe_max = TCP_RTO_MAX;
3670 } else {
3671 /* If packet was not sent due to local congestion,
3672 * do not backoff and do not remember icsk_probes_out.
3673 * Let local senders to fight for local resources.
3674 *
3675 * Use accumulated backoff yet.
3676 */
3677 if (!icsk->icsk_probes_out)
3678 icsk->icsk_probes_out = 1;
3679 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3680 }
3681 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3682 tcp_probe0_when(sk, probe_max),
3683 TCP_RTO_MAX);
3684}
3685
3686int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3687{
3688 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3689 struct flowi fl;
3690 int res;
3691
3692 tcp_rsk(req)->txhash = net_tx_rndhash();
3693 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3694 if (!res) {
3695 __TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3696 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3697 if (unlikely(tcp_passive_fastopen(sk)))
3698 tcp_sk(sk)->total_retrans++;
3699 }
3700 return res;
3701}
3702EXPORT_SYMBOL(tcp_rtx_synack);