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-rw-r--r--net/ipv4/tcp_output.c1739
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diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
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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 * Version: $Id: tcp_output.c,v 1.146 2002/02/01 22:01:04 davem Exp $
9 *
10 * Authors: Ross Biro, <bir7@leland.Stanford.Edu>
11 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12 * Mark Evans, <evansmp@uhura.aston.ac.uk>
13 * Corey Minyard <wf-rch!minyard@relay.EU.net>
14 * Florian La Roche, <flla@stud.uni-sb.de>
15 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16 * Linus Torvalds, <torvalds@cs.helsinki.fi>
17 * Alan Cox, <gw4pts@gw4pts.ampr.org>
18 * Matthew Dillon, <dillon@apollo.west.oic.com>
19 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20 * Jorge Cwik, <jorge@laser.satlink.net>
21 */
22
23/*
24 * Changes: Pedro Roque : Retransmit queue handled by TCP.
25 * : Fragmentation on mtu decrease
26 * : Segment collapse on retransmit
27 * : AF independence
28 *
29 * Linus Torvalds : send_delayed_ack
30 * David S. Miller : Charge memory using the right skb
31 * during syn/ack processing.
32 * David S. Miller : Output engine completely rewritten.
33 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
34 * Cacophonix Gaul : draft-minshall-nagle-01
35 * J Hadi Salim : ECN support
36 *
37 */
38
39#include <net/tcp.h>
40
41#include <linux/compiler.h>
42#include <linux/module.h>
43#include <linux/smp_lock.h>
44
45/* People can turn this off for buggy TCP's found in printers etc. */
46int sysctl_tcp_retrans_collapse = 1;
47
48/* This limits the percentage of the congestion window which we
49 * will allow a single TSO frame to consume. Building TSO frames
50 * which are too large can cause TCP streams to be bursty.
51 */
52int sysctl_tcp_tso_win_divisor = 8;
53
54static inline void update_send_head(struct sock *sk, struct tcp_sock *tp,
55 struct sk_buff *skb)
56{
57 sk->sk_send_head = skb->next;
58 if (sk->sk_send_head == (struct sk_buff *)&sk->sk_write_queue)
59 sk->sk_send_head = NULL;
60 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
61 tcp_packets_out_inc(sk, tp, skb);
62}
63
64/* SND.NXT, if window was not shrunk.
65 * If window has been shrunk, what should we make? It is not clear at all.
66 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
67 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
68 * invalid. OK, let's make this for now:
69 */
70static inline __u32 tcp_acceptable_seq(struct sock *sk, struct tcp_sock *tp)
71{
72 if (!before(tp->snd_una+tp->snd_wnd, tp->snd_nxt))
73 return tp->snd_nxt;
74 else
75 return tp->snd_una+tp->snd_wnd;
76}
77
78/* Calculate mss to advertise in SYN segment.
79 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
80 *
81 * 1. It is independent of path mtu.
82 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
83 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
84 * attached devices, because some buggy hosts are confused by
85 * large MSS.
86 * 4. We do not make 3, we advertise MSS, calculated from first
87 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
88 * This may be overridden via information stored in routing table.
89 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
90 * probably even Jumbo".
91 */
92static __u16 tcp_advertise_mss(struct sock *sk)
93{
94 struct tcp_sock *tp = tcp_sk(sk);
95 struct dst_entry *dst = __sk_dst_get(sk);
96 int mss = tp->advmss;
97
98 if (dst && dst_metric(dst, RTAX_ADVMSS) < mss) {
99 mss = dst_metric(dst, RTAX_ADVMSS);
100 tp->advmss = mss;
101 }
102
103 return (__u16)mss;
104}
105
106/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
107 * This is the first part of cwnd validation mechanism. */
108static void tcp_cwnd_restart(struct tcp_sock *tp, struct dst_entry *dst)
109{
110 s32 delta = tcp_time_stamp - tp->lsndtime;
111 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
112 u32 cwnd = tp->snd_cwnd;
113
114 if (tcp_is_vegas(tp))
115 tcp_vegas_enable(tp);
116
117 tp->snd_ssthresh = tcp_current_ssthresh(tp);
118 restart_cwnd = min(restart_cwnd, cwnd);
119
120 while ((delta -= tp->rto) > 0 && cwnd > restart_cwnd)
121 cwnd >>= 1;
122 tp->snd_cwnd = max(cwnd, restart_cwnd);
123 tp->snd_cwnd_stamp = tcp_time_stamp;
124 tp->snd_cwnd_used = 0;
125}
126
127static inline void tcp_event_data_sent(struct tcp_sock *tp,
128 struct sk_buff *skb, struct sock *sk)
129{
130 u32 now = tcp_time_stamp;
131
132 if (!tp->packets_out && (s32)(now - tp->lsndtime) > tp->rto)
133 tcp_cwnd_restart(tp, __sk_dst_get(sk));
134
135 tp->lsndtime = now;
136
137 /* If it is a reply for ato after last received
138 * packet, enter pingpong mode.
139 */
140 if ((u32)(now - tp->ack.lrcvtime) < tp->ack.ato)
141 tp->ack.pingpong = 1;
142}
143
144static __inline__ void tcp_event_ack_sent(struct sock *sk)
145{
146 struct tcp_sock *tp = tcp_sk(sk);
147
148 tcp_dec_quickack_mode(tp);
149 tcp_clear_xmit_timer(sk, TCP_TIME_DACK);
150}
151
152/* Determine a window scaling and initial window to offer.
153 * Based on the assumption that the given amount of space
154 * will be offered. Store the results in the tp structure.
155 * NOTE: for smooth operation initial space offering should
156 * be a multiple of mss if possible. We assume here that mss >= 1.
157 * This MUST be enforced by all callers.
158 */
159void tcp_select_initial_window(int __space, __u32 mss,
160 __u32 *rcv_wnd, __u32 *window_clamp,
161 int wscale_ok, __u8 *rcv_wscale)
162{
163 unsigned int space = (__space < 0 ? 0 : __space);
164
165 /* If no clamp set the clamp to the max possible scaled window */
166 if (*window_clamp == 0)
167 (*window_clamp) = (65535 << 14);
168 space = min(*window_clamp, space);
169
170 /* Quantize space offering to a multiple of mss if possible. */
171 if (space > mss)
172 space = (space / mss) * mss;
173
174 /* NOTE: offering an initial window larger than 32767
175 * will break some buggy TCP stacks. We try to be nice.
176 * If we are not window scaling, then this truncates
177 * our initial window offering to 32k. There should also
178 * be a sysctl option to stop being nice.
179 */
180 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
181 (*rcv_wscale) = 0;
182 if (wscale_ok) {
183 /* Set window scaling on max possible window
184 * See RFC1323 for an explanation of the limit to 14
185 */
186 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
187 while (space > 65535 && (*rcv_wscale) < 14) {
188 space >>= 1;
189 (*rcv_wscale)++;
190 }
191 }
192
193 /* Set initial window to value enough for senders,
194 * following RFC1414. Senders, not following this RFC,
195 * will be satisfied with 2.
196 */
197 if (mss > (1<<*rcv_wscale)) {
198 int init_cwnd = 4;
199 if (mss > 1460*3)
200 init_cwnd = 2;
201 else if (mss > 1460)
202 init_cwnd = 3;
203 if (*rcv_wnd > init_cwnd*mss)
204 *rcv_wnd = init_cwnd*mss;
205 }
206
207 /* Set the clamp no higher than max representable value */
208 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
209}
210
211/* Chose a new window to advertise, update state in tcp_sock for the
212 * socket, and return result with RFC1323 scaling applied. The return
213 * value can be stuffed directly into th->window for an outgoing
214 * frame.
215 */
216static __inline__ u16 tcp_select_window(struct sock *sk)
217{
218 struct tcp_sock *tp = tcp_sk(sk);
219 u32 cur_win = tcp_receive_window(tp);
220 u32 new_win = __tcp_select_window(sk);
221
222 /* Never shrink the offered window */
223 if(new_win < cur_win) {
224 /* Danger Will Robinson!
225 * Don't update rcv_wup/rcv_wnd here or else
226 * we will not be able to advertise a zero
227 * window in time. --DaveM
228 *
229 * Relax Will Robinson.
230 */
231 new_win = cur_win;
232 }
233 tp->rcv_wnd = new_win;
234 tp->rcv_wup = tp->rcv_nxt;
235
236 /* Make sure we do not exceed the maximum possible
237 * scaled window.
238 */
239 if (!tp->rx_opt.rcv_wscale)
240 new_win = min(new_win, MAX_TCP_WINDOW);
241 else
242 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
243
244 /* RFC1323 scaling applied */
245 new_win >>= tp->rx_opt.rcv_wscale;
246
247 /* If we advertise zero window, disable fast path. */
248 if (new_win == 0)
249 tp->pred_flags = 0;
250
251 return new_win;
252}
253
254
255/* This routine actually transmits TCP packets queued in by
256 * tcp_do_sendmsg(). This is used by both the initial
257 * transmission and possible later retransmissions.
258 * All SKB's seen here are completely headerless. It is our
259 * job to build the TCP header, and pass the packet down to
260 * IP so it can do the same plus pass the packet off to the
261 * device.
262 *
263 * We are working here with either a clone of the original
264 * SKB, or a fresh unique copy made by the retransmit engine.
265 */
266static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb)
267{
268 if (skb != NULL) {
269 struct inet_sock *inet = inet_sk(sk);
270 struct tcp_sock *tp = tcp_sk(sk);
271 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
272 int tcp_header_size = tp->tcp_header_len;
273 struct tcphdr *th;
274 int sysctl_flags;
275 int err;
276
277 BUG_ON(!tcp_skb_pcount(skb));
278
279#define SYSCTL_FLAG_TSTAMPS 0x1
280#define SYSCTL_FLAG_WSCALE 0x2
281#define SYSCTL_FLAG_SACK 0x4
282
283 sysctl_flags = 0;
284 if (tcb->flags & TCPCB_FLAG_SYN) {
285 tcp_header_size = sizeof(struct tcphdr) + TCPOLEN_MSS;
286 if(sysctl_tcp_timestamps) {
287 tcp_header_size += TCPOLEN_TSTAMP_ALIGNED;
288 sysctl_flags |= SYSCTL_FLAG_TSTAMPS;
289 }
290 if(sysctl_tcp_window_scaling) {
291 tcp_header_size += TCPOLEN_WSCALE_ALIGNED;
292 sysctl_flags |= SYSCTL_FLAG_WSCALE;
293 }
294 if(sysctl_tcp_sack) {
295 sysctl_flags |= SYSCTL_FLAG_SACK;
296 if(!(sysctl_flags & SYSCTL_FLAG_TSTAMPS))
297 tcp_header_size += TCPOLEN_SACKPERM_ALIGNED;
298 }
299 } else if (tp->rx_opt.eff_sacks) {
300 /* A SACK is 2 pad bytes, a 2 byte header, plus
301 * 2 32-bit sequence numbers for each SACK block.
302 */
303 tcp_header_size += (TCPOLEN_SACK_BASE_ALIGNED +
304 (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
305 }
306
307 /*
308 * If the connection is idle and we are restarting,
309 * then we don't want to do any Vegas calculations
310 * until we get fresh RTT samples. So when we
311 * restart, we reset our Vegas state to a clean
312 * slate. After we get acks for this flight of
313 * packets, _then_ we can make Vegas calculations
314 * again.
315 */
316 if (tcp_is_vegas(tp) && tcp_packets_in_flight(tp) == 0)
317 tcp_vegas_enable(tp);
318
319 th = (struct tcphdr *) skb_push(skb, tcp_header_size);
320 skb->h.th = th;
321 skb_set_owner_w(skb, sk);
322
323 /* Build TCP header and checksum it. */
324 th->source = inet->sport;
325 th->dest = inet->dport;
326 th->seq = htonl(tcb->seq);
327 th->ack_seq = htonl(tp->rcv_nxt);
328 *(((__u16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | tcb->flags);
329 if (tcb->flags & TCPCB_FLAG_SYN) {
330 /* RFC1323: The window in SYN & SYN/ACK segments
331 * is never scaled.
332 */
333 th->window = htons(tp->rcv_wnd);
334 } else {
335 th->window = htons(tcp_select_window(sk));
336 }
337 th->check = 0;
338 th->urg_ptr = 0;
339
340 if (tp->urg_mode &&
341 between(tp->snd_up, tcb->seq+1, tcb->seq+0xFFFF)) {
342 th->urg_ptr = htons(tp->snd_up-tcb->seq);
343 th->urg = 1;
344 }
345
346 if (tcb->flags & TCPCB_FLAG_SYN) {
347 tcp_syn_build_options((__u32 *)(th + 1),
348 tcp_advertise_mss(sk),
349 (sysctl_flags & SYSCTL_FLAG_TSTAMPS),
350 (sysctl_flags & SYSCTL_FLAG_SACK),
351 (sysctl_flags & SYSCTL_FLAG_WSCALE),
352 tp->rx_opt.rcv_wscale,
353 tcb->when,
354 tp->rx_opt.ts_recent);
355 } else {
356 tcp_build_and_update_options((__u32 *)(th + 1),
357 tp, tcb->when);
358
359 TCP_ECN_send(sk, tp, skb, tcp_header_size);
360 }
361 tp->af_specific->send_check(sk, th, skb->len, skb);
362
363 if (tcb->flags & TCPCB_FLAG_ACK)
364 tcp_event_ack_sent(sk);
365
366 if (skb->len != tcp_header_size)
367 tcp_event_data_sent(tp, skb, sk);
368
369 TCP_INC_STATS(TCP_MIB_OUTSEGS);
370
371 err = tp->af_specific->queue_xmit(skb, 0);
372 if (err <= 0)
373 return err;
374
375 tcp_enter_cwr(tp);
376
377 /* NET_XMIT_CN is special. It does not guarantee,
378 * that this packet is lost. It tells that device
379 * is about to start to drop packets or already
380 * drops some packets of the same priority and
381 * invokes us to send less aggressively.
382 */
383 return err == NET_XMIT_CN ? 0 : err;
384 }
385 return -ENOBUFS;
386#undef SYSCTL_FLAG_TSTAMPS
387#undef SYSCTL_FLAG_WSCALE
388#undef SYSCTL_FLAG_SACK
389}
390
391
392/* This routine just queue's the buffer
393 *
394 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
395 * otherwise socket can stall.
396 */
397static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
398{
399 struct tcp_sock *tp = tcp_sk(sk);
400
401 /* Advance write_seq and place onto the write_queue. */
402 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
403 skb_header_release(skb);
404 __skb_queue_tail(&sk->sk_write_queue, skb);
405 sk_charge_skb(sk, skb);
406
407 /* Queue it, remembering where we must start sending. */
408 if (sk->sk_send_head == NULL)
409 sk->sk_send_head = skb;
410}
411
412static inline void tcp_tso_set_push(struct sk_buff *skb)
413{
414 /* Force push to be on for any TSO frames to workaround
415 * problems with busted implementations like Mac OS-X that
416 * hold off socket receive wakeups until push is seen.
417 */
418 if (tcp_skb_pcount(skb) > 1)
419 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
420}
421
422/* Send _single_ skb sitting at the send head. This function requires
423 * true push pending frames to setup probe timer etc.
424 */
425void tcp_push_one(struct sock *sk, unsigned cur_mss)
426{
427 struct tcp_sock *tp = tcp_sk(sk);
428 struct sk_buff *skb = sk->sk_send_head;
429
430 if (tcp_snd_test(tp, skb, cur_mss, TCP_NAGLE_PUSH)) {
431 /* Send it out now. */
432 TCP_SKB_CB(skb)->when = tcp_time_stamp;
433 tcp_tso_set_push(skb);
434 if (!tcp_transmit_skb(sk, skb_clone(skb, sk->sk_allocation))) {
435 sk->sk_send_head = NULL;
436 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
437 tcp_packets_out_inc(sk, tp, skb);
438 return;
439 }
440 }
441}
442
443void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_std)
444{
445 if (skb->len <= mss_std) {
446 /* Avoid the costly divide in the normal
447 * non-TSO case.
448 */
449 skb_shinfo(skb)->tso_segs = 1;
450 skb_shinfo(skb)->tso_size = 0;
451 } else {
452 unsigned int factor;
453
454 factor = skb->len + (mss_std - 1);
455 factor /= mss_std;
456 skb_shinfo(skb)->tso_segs = factor;
457 skb_shinfo(skb)->tso_size = mss_std;
458 }
459}
460
461/* Function to create two new TCP segments. Shrinks the given segment
462 * to the specified size and appends a new segment with the rest of the
463 * packet to the list. This won't be called frequently, I hope.
464 * Remember, these are still headerless SKBs at this point.
465 */
466static int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len)
467{
468 struct tcp_sock *tp = tcp_sk(sk);
469 struct sk_buff *buff;
470 int nsize;
471 u16 flags;
472
473 nsize = skb_headlen(skb) - len;
474 if (nsize < 0)
475 nsize = 0;
476
477 if (skb_cloned(skb) &&
478 skb_is_nonlinear(skb) &&
479 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
480 return -ENOMEM;
481
482 /* Get a new skb... force flag on. */
483 buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
484 if (buff == NULL)
485 return -ENOMEM; /* We'll just try again later. */
486 sk_charge_skb(sk, buff);
487
488 /* Correct the sequence numbers. */
489 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
490 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
491 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
492
493 /* PSH and FIN should only be set in the second packet. */
494 flags = TCP_SKB_CB(skb)->flags;
495 TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
496 TCP_SKB_CB(buff)->flags = flags;
497 TCP_SKB_CB(buff)->sacked =
498 (TCP_SKB_CB(skb)->sacked &
499 (TCPCB_LOST | TCPCB_EVER_RETRANS | TCPCB_AT_TAIL));
500 TCP_SKB_CB(skb)->sacked &= ~TCPCB_AT_TAIL;
501
502 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_HW) {
503 /* Copy and checksum data tail into the new buffer. */
504 buff->csum = csum_partial_copy_nocheck(skb->data + len, skb_put(buff, nsize),
505 nsize, 0);
506
507 skb_trim(skb, len);
508
509 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
510 } else {
511 skb->ip_summed = CHECKSUM_HW;
512 skb_split(skb, buff, len);
513 }
514
515 buff->ip_summed = skb->ip_summed;
516
517 /* Looks stupid, but our code really uses when of
518 * skbs, which it never sent before. --ANK
519 */
520 TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
521
522 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
523 tp->lost_out -= tcp_skb_pcount(skb);
524 tp->left_out -= tcp_skb_pcount(skb);
525 }
526
527 /* Fix up tso_factor for both original and new SKB. */
528 tcp_set_skb_tso_segs(skb, tp->mss_cache_std);
529 tcp_set_skb_tso_segs(buff, tp->mss_cache_std);
530
531 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
532 tp->lost_out += tcp_skb_pcount(skb);
533 tp->left_out += tcp_skb_pcount(skb);
534 }
535
536 if (TCP_SKB_CB(buff)->sacked&TCPCB_LOST) {
537 tp->lost_out += tcp_skb_pcount(buff);
538 tp->left_out += tcp_skb_pcount(buff);
539 }
540
541 /* Link BUFF into the send queue. */
542 __skb_append(skb, buff);
543
544 return 0;
545}
546
547/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
548 * eventually). The difference is that pulled data not copied, but
549 * immediately discarded.
550 */
551static unsigned char *__pskb_trim_head(struct sk_buff *skb, int len)
552{
553 int i, k, eat;
554
555 eat = len;
556 k = 0;
557 for (i=0; i<skb_shinfo(skb)->nr_frags; i++) {
558 if (skb_shinfo(skb)->frags[i].size <= eat) {
559 put_page(skb_shinfo(skb)->frags[i].page);
560 eat -= skb_shinfo(skb)->frags[i].size;
561 } else {
562 skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
563 if (eat) {
564 skb_shinfo(skb)->frags[k].page_offset += eat;
565 skb_shinfo(skb)->frags[k].size -= eat;
566 eat = 0;
567 }
568 k++;
569 }
570 }
571 skb_shinfo(skb)->nr_frags = k;
572
573 skb->tail = skb->data;
574 skb->data_len -= len;
575 skb->len = skb->data_len;
576 return skb->tail;
577}
578
579int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
580{
581 if (skb_cloned(skb) &&
582 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
583 return -ENOMEM;
584
585 if (len <= skb_headlen(skb)) {
586 __skb_pull(skb, len);
587 } else {
588 if (__pskb_trim_head(skb, len-skb_headlen(skb)) == NULL)
589 return -ENOMEM;
590 }
591
592 TCP_SKB_CB(skb)->seq += len;
593 skb->ip_summed = CHECKSUM_HW;
594
595 skb->truesize -= len;
596 sk->sk_wmem_queued -= len;
597 sk->sk_forward_alloc += len;
598 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
599
600 /* Any change of skb->len requires recalculation of tso
601 * factor and mss.
602 */
603 if (tcp_skb_pcount(skb) > 1)
604 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
605
606 return 0;
607}
608
609/* This function synchronize snd mss to current pmtu/exthdr set.
610
611 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
612 for TCP options, but includes only bare TCP header.
613
614 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
615 It is minumum of user_mss and mss received with SYN.
616 It also does not include TCP options.
617
618 tp->pmtu_cookie is last pmtu, seen by this function.
619
620 tp->mss_cache is current effective sending mss, including
621 all tcp options except for SACKs. It is evaluated,
622 taking into account current pmtu, but never exceeds
623 tp->rx_opt.mss_clamp.
624
625 NOTE1. rfc1122 clearly states that advertised MSS
626 DOES NOT include either tcp or ip options.
627
628 NOTE2. tp->pmtu_cookie and tp->mss_cache are READ ONLY outside
629 this function. --ANK (980731)
630 */
631
632unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
633{
634 struct tcp_sock *tp = tcp_sk(sk);
635 int mss_now;
636
637 /* Calculate base mss without TCP options:
638 It is MMS_S - sizeof(tcphdr) of rfc1122
639 */
640 mss_now = pmtu - tp->af_specific->net_header_len - sizeof(struct tcphdr);
641
642 /* Clamp it (mss_clamp does not include tcp options) */
643 if (mss_now > tp->rx_opt.mss_clamp)
644 mss_now = tp->rx_opt.mss_clamp;
645
646 /* Now subtract optional transport overhead */
647 mss_now -= tp->ext_header_len;
648
649 /* Then reserve room for full set of TCP options and 8 bytes of data */
650 if (mss_now < 48)
651 mss_now = 48;
652
653 /* Now subtract TCP options size, not including SACKs */
654 mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
655
656 /* Bound mss with half of window */
657 if (tp->max_window && mss_now > (tp->max_window>>1))
658 mss_now = max((tp->max_window>>1), 68U - tp->tcp_header_len);
659
660 /* And store cached results */
661 tp->pmtu_cookie = pmtu;
662 tp->mss_cache = tp->mss_cache_std = mss_now;
663
664 return mss_now;
665}
666
667/* Compute the current effective MSS, taking SACKs and IP options,
668 * and even PMTU discovery events into account.
669 *
670 * LARGESEND note: !urg_mode is overkill, only frames up to snd_up
671 * cannot be large. However, taking into account rare use of URG, this
672 * is not a big flaw.
673 */
674
675unsigned int tcp_current_mss(struct sock *sk, int large)
676{
677 struct tcp_sock *tp = tcp_sk(sk);
678 struct dst_entry *dst = __sk_dst_get(sk);
679 unsigned int do_large, mss_now;
680
681 mss_now = tp->mss_cache_std;
682 if (dst) {
683 u32 mtu = dst_mtu(dst);
684 if (mtu != tp->pmtu_cookie)
685 mss_now = tcp_sync_mss(sk, mtu);
686 }
687
688 do_large = (large &&
689 (sk->sk_route_caps & NETIF_F_TSO) &&
690 !tp->urg_mode);
691
692 if (do_large) {
693 unsigned int large_mss, factor, limit;
694
695 large_mss = 65535 - tp->af_specific->net_header_len -
696 tp->ext_header_len - tp->tcp_header_len;
697
698 if (tp->max_window && large_mss > (tp->max_window>>1))
699 large_mss = max((tp->max_window>>1),
700 68U - tp->tcp_header_len);
701
702 factor = large_mss / mss_now;
703
704 /* Always keep large mss multiple of real mss, but
705 * do not exceed 1/tso_win_divisor of the congestion window
706 * so we can keep the ACK clock ticking and minimize
707 * bursting.
708 */
709 limit = tp->snd_cwnd;
710 if (sysctl_tcp_tso_win_divisor)
711 limit /= sysctl_tcp_tso_win_divisor;
712 limit = max(1U, limit);
713 if (factor > limit)
714 factor = limit;
715
716 tp->mss_cache = mss_now * factor;
717
718 mss_now = tp->mss_cache;
719 }
720
721 if (tp->rx_opt.eff_sacks)
722 mss_now -= (TCPOLEN_SACK_BASE_ALIGNED +
723 (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
724 return mss_now;
725}
726
727/* This routine writes packets to the network. It advances the
728 * send_head. This happens as incoming acks open up the remote
729 * window for us.
730 *
731 * Returns 1, if no segments are in flight and we have queued segments, but
732 * cannot send anything now because of SWS or another problem.
733 */
734int tcp_write_xmit(struct sock *sk, int nonagle)
735{
736 struct tcp_sock *tp = tcp_sk(sk);
737 unsigned int mss_now;
738
739 /* If we are closed, the bytes will have to remain here.
740 * In time closedown will finish, we empty the write queue and all
741 * will be happy.
742 */
743 if (sk->sk_state != TCP_CLOSE) {
744 struct sk_buff *skb;
745 int sent_pkts = 0;
746
747 /* Account for SACKS, we may need to fragment due to this.
748 * It is just like the real MSS changing on us midstream.
749 * We also handle things correctly when the user adds some
750 * IP options mid-stream. Silly to do, but cover it.
751 */
752 mss_now = tcp_current_mss(sk, 1);
753
754 while ((skb = sk->sk_send_head) &&
755 tcp_snd_test(tp, skb, mss_now,
756 tcp_skb_is_last(sk, skb) ? nonagle :
757 TCP_NAGLE_PUSH)) {
758 if (skb->len > mss_now) {
759 if (tcp_fragment(sk, skb, mss_now))
760 break;
761 }
762
763 TCP_SKB_CB(skb)->when = tcp_time_stamp;
764 tcp_tso_set_push(skb);
765 if (tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC)))
766 break;
767
768 /* Advance the send_head. This one is sent out.
769 * This call will increment packets_out.
770 */
771 update_send_head(sk, tp, skb);
772
773 tcp_minshall_update(tp, mss_now, skb);
774 sent_pkts = 1;
775 }
776
777 if (sent_pkts) {
778 tcp_cwnd_validate(sk, tp);
779 return 0;
780 }
781
782 return !tp->packets_out && sk->sk_send_head;
783 }
784 return 0;
785}
786
787/* This function returns the amount that we can raise the
788 * usable window based on the following constraints
789 *
790 * 1. The window can never be shrunk once it is offered (RFC 793)
791 * 2. We limit memory per socket
792 *
793 * RFC 1122:
794 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
795 * RECV.NEXT + RCV.WIN fixed until:
796 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
797 *
798 * i.e. don't raise the right edge of the window until you can raise
799 * it at least MSS bytes.
800 *
801 * Unfortunately, the recommended algorithm breaks header prediction,
802 * since header prediction assumes th->window stays fixed.
803 *
804 * Strictly speaking, keeping th->window fixed violates the receiver
805 * side SWS prevention criteria. The problem is that under this rule
806 * a stream of single byte packets will cause the right side of the
807 * window to always advance by a single byte.
808 *
809 * Of course, if the sender implements sender side SWS prevention
810 * then this will not be a problem.
811 *
812 * BSD seems to make the following compromise:
813 *
814 * If the free space is less than the 1/4 of the maximum
815 * space available and the free space is less than 1/2 mss,
816 * then set the window to 0.
817 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
818 * Otherwise, just prevent the window from shrinking
819 * and from being larger than the largest representable value.
820 *
821 * This prevents incremental opening of the window in the regime
822 * where TCP is limited by the speed of the reader side taking
823 * data out of the TCP receive queue. It does nothing about
824 * those cases where the window is constrained on the sender side
825 * because the pipeline is full.
826 *
827 * BSD also seems to "accidentally" limit itself to windows that are a
828 * multiple of MSS, at least until the free space gets quite small.
829 * This would appear to be a side effect of the mbuf implementation.
830 * Combining these two algorithms results in the observed behavior
831 * of having a fixed window size at almost all times.
832 *
833 * Below we obtain similar behavior by forcing the offered window to
834 * a multiple of the mss when it is feasible to do so.
835 *
836 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
837 * Regular options like TIMESTAMP are taken into account.
838 */
839u32 __tcp_select_window(struct sock *sk)
840{
841 struct tcp_sock *tp = tcp_sk(sk);
842 /* MSS for the peer's data. Previous verions used mss_clamp
843 * here. I don't know if the value based on our guesses
844 * of peer's MSS is better for the performance. It's more correct
845 * but may be worse for the performance because of rcv_mss
846 * fluctuations. --SAW 1998/11/1
847 */
848 int mss = tp->ack.rcv_mss;
849 int free_space = tcp_space(sk);
850 int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
851 int window;
852
853 if (mss > full_space)
854 mss = full_space;
855
856 if (free_space < full_space/2) {
857 tp->ack.quick = 0;
858
859 if (tcp_memory_pressure)
860 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U*tp->advmss);
861
862 if (free_space < mss)
863 return 0;
864 }
865
866 if (free_space > tp->rcv_ssthresh)
867 free_space = tp->rcv_ssthresh;
868
869 /* Don't do rounding if we are using window scaling, since the
870 * scaled window will not line up with the MSS boundary anyway.
871 */
872 window = tp->rcv_wnd;
873 if (tp->rx_opt.rcv_wscale) {
874 window = free_space;
875
876 /* Advertise enough space so that it won't get scaled away.
877 * Import case: prevent zero window announcement if
878 * 1<<rcv_wscale > mss.
879 */
880 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
881 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
882 << tp->rx_opt.rcv_wscale);
883 } else {
884 /* Get the largest window that is a nice multiple of mss.
885 * Window clamp already applied above.
886 * If our current window offering is within 1 mss of the
887 * free space we just keep it. This prevents the divide
888 * and multiply from happening most of the time.
889 * We also don't do any window rounding when the free space
890 * is too small.
891 */
892 if (window <= free_space - mss || window > free_space)
893 window = (free_space/mss)*mss;
894 }
895
896 return window;
897}
898
899/* Attempt to collapse two adjacent SKB's during retransmission. */
900static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int mss_now)
901{
902 struct tcp_sock *tp = tcp_sk(sk);
903 struct sk_buff *next_skb = skb->next;
904
905 /* The first test we must make is that neither of these two
906 * SKB's are still referenced by someone else.
907 */
908 if (!skb_cloned(skb) && !skb_cloned(next_skb)) {
909 int skb_size = skb->len, next_skb_size = next_skb->len;
910 u16 flags = TCP_SKB_CB(skb)->flags;
911
912 /* Also punt if next skb has been SACK'd. */
913 if(TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED)
914 return;
915
916 /* Next skb is out of window. */
917 if (after(TCP_SKB_CB(next_skb)->end_seq, tp->snd_una+tp->snd_wnd))
918 return;
919
920 /* Punt if not enough space exists in the first SKB for
921 * the data in the second, or the total combined payload
922 * would exceed the MSS.
923 */
924 if ((next_skb_size > skb_tailroom(skb)) ||
925 ((skb_size + next_skb_size) > mss_now))
926 return;
927
928 BUG_ON(tcp_skb_pcount(skb) != 1 ||
929 tcp_skb_pcount(next_skb) != 1);
930
931 /* Ok. We will be able to collapse the packet. */
932 __skb_unlink(next_skb, next_skb->list);
933
934 memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
935
936 if (next_skb->ip_summed == CHECKSUM_HW)
937 skb->ip_summed = CHECKSUM_HW;
938
939 if (skb->ip_summed != CHECKSUM_HW)
940 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
941
942 /* Update sequence range on original skb. */
943 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
944
945 /* Merge over control information. */
946 flags |= TCP_SKB_CB(next_skb)->flags; /* This moves PSH/FIN etc. over */
947 TCP_SKB_CB(skb)->flags = flags;
948
949 /* All done, get rid of second SKB and account for it so
950 * packet counting does not break.
951 */
952 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked&(TCPCB_EVER_RETRANS|TCPCB_AT_TAIL);
953 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_SACKED_RETRANS)
954 tp->retrans_out -= tcp_skb_pcount(next_skb);
955 if (TCP_SKB_CB(next_skb)->sacked&TCPCB_LOST) {
956 tp->lost_out -= tcp_skb_pcount(next_skb);
957 tp->left_out -= tcp_skb_pcount(next_skb);
958 }
959 /* Reno case is special. Sigh... */
960 if (!tp->rx_opt.sack_ok && tp->sacked_out) {
961 tcp_dec_pcount_approx(&tp->sacked_out, next_skb);
962 tp->left_out -= tcp_skb_pcount(next_skb);
963 }
964
965 /* Not quite right: it can be > snd.fack, but
966 * it is better to underestimate fackets.
967 */
968 tcp_dec_pcount_approx(&tp->fackets_out, next_skb);
969 tcp_packets_out_dec(tp, next_skb);
970 sk_stream_free_skb(sk, next_skb);
971 }
972}
973
974/* Do a simple retransmit without using the backoff mechanisms in
975 * tcp_timer. This is used for path mtu discovery.
976 * The socket is already locked here.
977 */
978void tcp_simple_retransmit(struct sock *sk)
979{
980 struct tcp_sock *tp = tcp_sk(sk);
981 struct sk_buff *skb;
982 unsigned int mss = tcp_current_mss(sk, 0);
983 int lost = 0;
984
985 sk_stream_for_retrans_queue(skb, sk) {
986 if (skb->len > mss &&
987 !(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
988 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
989 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
990 tp->retrans_out -= tcp_skb_pcount(skb);
991 }
992 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_LOST)) {
993 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
994 tp->lost_out += tcp_skb_pcount(skb);
995 lost = 1;
996 }
997 }
998 }
999
1000 if (!lost)
1001 return;
1002
1003 tcp_sync_left_out(tp);
1004
1005 /* Don't muck with the congestion window here.
1006 * Reason is that we do not increase amount of _data_
1007 * in network, but units changed and effective
1008 * cwnd/ssthresh really reduced now.
1009 */
1010 if (tp->ca_state != TCP_CA_Loss) {
1011 tp->high_seq = tp->snd_nxt;
1012 tp->snd_ssthresh = tcp_current_ssthresh(tp);
1013 tp->prior_ssthresh = 0;
1014 tp->undo_marker = 0;
1015 tcp_set_ca_state(tp, TCP_CA_Loss);
1016 }
1017 tcp_xmit_retransmit_queue(sk);
1018}
1019
1020/* This retransmits one SKB. Policy decisions and retransmit queue
1021 * state updates are done by the caller. Returns non-zero if an
1022 * error occurred which prevented the send.
1023 */
1024int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
1025{
1026 struct tcp_sock *tp = tcp_sk(sk);
1027 unsigned int cur_mss = tcp_current_mss(sk, 0);
1028 int err;
1029
1030 /* Do not sent more than we queued. 1/4 is reserved for possible
1031 * copying overhead: frgagmentation, tunneling, mangling etc.
1032 */
1033 if (atomic_read(&sk->sk_wmem_alloc) >
1034 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
1035 return -EAGAIN;
1036
1037 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
1038 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1039 BUG();
1040
1041 if (sk->sk_route_caps & NETIF_F_TSO) {
1042 sk->sk_route_caps &= ~NETIF_F_TSO;
1043 sock_set_flag(sk, SOCK_NO_LARGESEND);
1044 tp->mss_cache = tp->mss_cache_std;
1045 }
1046
1047 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
1048 return -ENOMEM;
1049 }
1050
1051 /* If receiver has shrunk his window, and skb is out of
1052 * new window, do not retransmit it. The exception is the
1053 * case, when window is shrunk to zero. In this case
1054 * our retransmit serves as a zero window probe.
1055 */
1056 if (!before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)
1057 && TCP_SKB_CB(skb)->seq != tp->snd_una)
1058 return -EAGAIN;
1059
1060 if (skb->len > cur_mss) {
1061 int old_factor = tcp_skb_pcount(skb);
1062 int new_factor;
1063
1064 if (tcp_fragment(sk, skb, cur_mss))
1065 return -ENOMEM; /* We'll try again later. */
1066
1067 /* New SKB created, account for it. */
1068 new_factor = tcp_skb_pcount(skb);
1069 tp->packets_out -= old_factor - new_factor;
1070 tp->packets_out += tcp_skb_pcount(skb->next);
1071 }
1072
1073 /* Collapse two adjacent packets if worthwhile and we can. */
1074 if(!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) &&
1075 (skb->len < (cur_mss >> 1)) &&
1076 (skb->next != sk->sk_send_head) &&
1077 (skb->next != (struct sk_buff *)&sk->sk_write_queue) &&
1078 (skb_shinfo(skb)->nr_frags == 0 && skb_shinfo(skb->next)->nr_frags == 0) &&
1079 (tcp_skb_pcount(skb) == 1 && tcp_skb_pcount(skb->next) == 1) &&
1080 (sysctl_tcp_retrans_collapse != 0))
1081 tcp_retrans_try_collapse(sk, skb, cur_mss);
1082
1083 if(tp->af_specific->rebuild_header(sk))
1084 return -EHOSTUNREACH; /* Routing failure or similar. */
1085
1086 /* Some Solaris stacks overoptimize and ignore the FIN on a
1087 * retransmit when old data is attached. So strip it off
1088 * since it is cheap to do so and saves bytes on the network.
1089 */
1090 if(skb->len > 0 &&
1091 (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
1092 tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
1093 if (!pskb_trim(skb, 0)) {
1094 TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1;
1095 skb_shinfo(skb)->tso_segs = 1;
1096 skb_shinfo(skb)->tso_size = 0;
1097 skb->ip_summed = CHECKSUM_NONE;
1098 skb->csum = 0;
1099 }
1100 }
1101
1102 /* Make a copy, if the first transmission SKB clone we made
1103 * is still in somebody's hands, else make a clone.
1104 */
1105 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1106 tcp_tso_set_push(skb);
1107
1108 err = tcp_transmit_skb(sk, (skb_cloned(skb) ?
1109 pskb_copy(skb, GFP_ATOMIC):
1110 skb_clone(skb, GFP_ATOMIC)));
1111
1112 if (err == 0) {
1113 /* Update global TCP statistics. */
1114 TCP_INC_STATS(TCP_MIB_RETRANSSEGS);
1115
1116 tp->total_retrans++;
1117
1118#if FASTRETRANS_DEBUG > 0
1119 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
1120 if (net_ratelimit())
1121 printk(KERN_DEBUG "retrans_out leaked.\n");
1122 }
1123#endif
1124 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
1125 tp->retrans_out += tcp_skb_pcount(skb);
1126
1127 /* Save stamp of the first retransmit. */
1128 if (!tp->retrans_stamp)
1129 tp->retrans_stamp = TCP_SKB_CB(skb)->when;
1130
1131 tp->undo_retrans++;
1132
1133 /* snd_nxt is stored to detect loss of retransmitted segment,
1134 * see tcp_input.c tcp_sacktag_write_queue().
1135 */
1136 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
1137 }
1138 return err;
1139}
1140
1141/* This gets called after a retransmit timeout, and the initially
1142 * retransmitted data is acknowledged. It tries to continue
1143 * resending the rest of the retransmit queue, until either
1144 * we've sent it all or the congestion window limit is reached.
1145 * If doing SACK, the first ACK which comes back for a timeout
1146 * based retransmit packet might feed us FACK information again.
1147 * If so, we use it to avoid unnecessarily retransmissions.
1148 */
1149void tcp_xmit_retransmit_queue(struct sock *sk)
1150{
1151 struct tcp_sock *tp = tcp_sk(sk);
1152 struct sk_buff *skb;
1153 int packet_cnt = tp->lost_out;
1154
1155 /* First pass: retransmit lost packets. */
1156 if (packet_cnt) {
1157 sk_stream_for_retrans_queue(skb, sk) {
1158 __u8 sacked = TCP_SKB_CB(skb)->sacked;
1159
1160 /* Assume this retransmit will generate
1161 * only one packet for congestion window
1162 * calculation purposes. This works because
1163 * tcp_retransmit_skb() will chop up the
1164 * packet to be MSS sized and all the
1165 * packet counting works out.
1166 */
1167 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1168 return;
1169
1170 if (sacked&TCPCB_LOST) {
1171 if (!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
1172 if (tcp_retransmit_skb(sk, skb))
1173 return;
1174 if (tp->ca_state != TCP_CA_Loss)
1175 NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS);
1176 else
1177 NET_INC_STATS_BH(LINUX_MIB_TCPSLOWSTARTRETRANS);
1178
1179 if (skb ==
1180 skb_peek(&sk->sk_write_queue))
1181 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1182 }
1183
1184 packet_cnt -= tcp_skb_pcount(skb);
1185 if (packet_cnt <= 0)
1186 break;
1187 }
1188 }
1189 }
1190
1191 /* OK, demanded retransmission is finished. */
1192
1193 /* Forward retransmissions are possible only during Recovery. */
1194 if (tp->ca_state != TCP_CA_Recovery)
1195 return;
1196
1197 /* No forward retransmissions in Reno are possible. */
1198 if (!tp->rx_opt.sack_ok)
1199 return;
1200
1201 /* Yeah, we have to make difficult choice between forward transmission
1202 * and retransmission... Both ways have their merits...
1203 *
1204 * For now we do not retransmit anything, while we have some new
1205 * segments to send.
1206 */
1207
1208 if (tcp_may_send_now(sk, tp))
1209 return;
1210
1211 packet_cnt = 0;
1212
1213 sk_stream_for_retrans_queue(skb, sk) {
1214 /* Similar to the retransmit loop above we
1215 * can pretend that the retransmitted SKB
1216 * we send out here will be composed of one
1217 * real MSS sized packet because tcp_retransmit_skb()
1218 * will fragment it if necessary.
1219 */
1220 if (++packet_cnt > tp->fackets_out)
1221 break;
1222
1223 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1224 break;
1225
1226 if (TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS)
1227 continue;
1228
1229 /* Ok, retransmit it. */
1230 if (tcp_retransmit_skb(sk, skb))
1231 break;
1232
1233 if (skb == skb_peek(&sk->sk_write_queue))
1234 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1235
1236 NET_INC_STATS_BH(LINUX_MIB_TCPFORWARDRETRANS);
1237 }
1238}
1239
1240
1241/* Send a fin. The caller locks the socket for us. This cannot be
1242 * allowed to fail queueing a FIN frame under any circumstances.
1243 */
1244void tcp_send_fin(struct sock *sk)
1245{
1246 struct tcp_sock *tp = tcp_sk(sk);
1247 struct sk_buff *skb = skb_peek_tail(&sk->sk_write_queue);
1248 int mss_now;
1249
1250 /* Optimization, tack on the FIN if we have a queue of
1251 * unsent frames. But be careful about outgoing SACKS
1252 * and IP options.
1253 */
1254 mss_now = tcp_current_mss(sk, 1);
1255
1256 if (sk->sk_send_head != NULL) {
1257 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN;
1258 TCP_SKB_CB(skb)->end_seq++;
1259 tp->write_seq++;
1260 } else {
1261 /* Socket is locked, keep trying until memory is available. */
1262 for (;;) {
1263 skb = alloc_skb(MAX_TCP_HEADER, GFP_KERNEL);
1264 if (skb)
1265 break;
1266 yield();
1267 }
1268
1269 /* Reserve space for headers and prepare control bits. */
1270 skb_reserve(skb, MAX_TCP_HEADER);
1271 skb->csum = 0;
1272 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
1273 TCP_SKB_CB(skb)->sacked = 0;
1274 skb_shinfo(skb)->tso_segs = 1;
1275 skb_shinfo(skb)->tso_size = 0;
1276
1277 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
1278 TCP_SKB_CB(skb)->seq = tp->write_seq;
1279 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
1280 tcp_queue_skb(sk, skb);
1281 }
1282 __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_OFF);
1283}
1284
1285/* We get here when a process closes a file descriptor (either due to
1286 * an explicit close() or as a byproduct of exit()'ing) and there
1287 * was unread data in the receive queue. This behavior is recommended
1288 * by draft-ietf-tcpimpl-prob-03.txt section 3.10. -DaveM
1289 */
1290void tcp_send_active_reset(struct sock *sk, int priority)
1291{
1292 struct tcp_sock *tp = tcp_sk(sk);
1293 struct sk_buff *skb;
1294
1295 /* NOTE: No TCP options attached and we never retransmit this. */
1296 skb = alloc_skb(MAX_TCP_HEADER, priority);
1297 if (!skb) {
1298 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
1299 return;
1300 }
1301
1302 /* Reserve space for headers and prepare control bits. */
1303 skb_reserve(skb, MAX_TCP_HEADER);
1304 skb->csum = 0;
1305 TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
1306 TCP_SKB_CB(skb)->sacked = 0;
1307 skb_shinfo(skb)->tso_segs = 1;
1308 skb_shinfo(skb)->tso_size = 0;
1309
1310 /* Send it off. */
1311 TCP_SKB_CB(skb)->seq = tcp_acceptable_seq(sk, tp);
1312 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
1313 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1314 if (tcp_transmit_skb(sk, skb))
1315 NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
1316}
1317
1318/* WARNING: This routine must only be called when we have already sent
1319 * a SYN packet that crossed the incoming SYN that caused this routine
1320 * to get called. If this assumption fails then the initial rcv_wnd
1321 * and rcv_wscale values will not be correct.
1322 */
1323int tcp_send_synack(struct sock *sk)
1324{
1325 struct sk_buff* skb;
1326
1327 skb = skb_peek(&sk->sk_write_queue);
1328 if (skb == NULL || !(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_SYN)) {
1329 printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
1330 return -EFAULT;
1331 }
1332 if (!(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_ACK)) {
1333 if (skb_cloned(skb)) {
1334 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
1335 if (nskb == NULL)
1336 return -ENOMEM;
1337 __skb_unlink(skb, &sk->sk_write_queue);
1338 skb_header_release(nskb);
1339 __skb_queue_head(&sk->sk_write_queue, nskb);
1340 sk_stream_free_skb(sk, skb);
1341 sk_charge_skb(sk, nskb);
1342 skb = nskb;
1343 }
1344
1345 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK;
1346 TCP_ECN_send_synack(tcp_sk(sk), skb);
1347 }
1348 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1349 return tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC));
1350}
1351
1352/*
1353 * Prepare a SYN-ACK.
1354 */
1355struct sk_buff * tcp_make_synack(struct sock *sk, struct dst_entry *dst,
1356 struct open_request *req)
1357{
1358 struct tcp_sock *tp = tcp_sk(sk);
1359 struct tcphdr *th;
1360 int tcp_header_size;
1361 struct sk_buff *skb;
1362
1363 skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC);
1364 if (skb == NULL)
1365 return NULL;
1366
1367 /* Reserve space for headers. */
1368 skb_reserve(skb, MAX_TCP_HEADER);
1369
1370 skb->dst = dst_clone(dst);
1371
1372 tcp_header_size = (sizeof(struct tcphdr) + TCPOLEN_MSS +
1373 (req->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0) +
1374 (req->wscale_ok ? TCPOLEN_WSCALE_ALIGNED : 0) +
1375 /* SACK_PERM is in the place of NOP NOP of TS */
1376 ((req->sack_ok && !req->tstamp_ok) ? TCPOLEN_SACKPERM_ALIGNED : 0));
1377 skb->h.th = th = (struct tcphdr *) skb_push(skb, tcp_header_size);
1378
1379 memset(th, 0, sizeof(struct tcphdr));
1380 th->syn = 1;
1381 th->ack = 1;
1382 if (dst->dev->features&NETIF_F_TSO)
1383 req->ecn_ok = 0;
1384 TCP_ECN_make_synack(req, th);
1385 th->source = inet_sk(sk)->sport;
1386 th->dest = req->rmt_port;
1387 TCP_SKB_CB(skb)->seq = req->snt_isn;
1388 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
1389 TCP_SKB_CB(skb)->sacked = 0;
1390 skb_shinfo(skb)->tso_segs = 1;
1391 skb_shinfo(skb)->tso_size = 0;
1392 th->seq = htonl(TCP_SKB_CB(skb)->seq);
1393 th->ack_seq = htonl(req->rcv_isn + 1);
1394 if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
1395 __u8 rcv_wscale;
1396 /* Set this up on the first call only */
1397 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
1398 /* tcp_full_space because it is guaranteed to be the first packet */
1399 tcp_select_initial_window(tcp_full_space(sk),
1400 dst_metric(dst, RTAX_ADVMSS) - (req->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
1401 &req->rcv_wnd,
1402 &req->window_clamp,
1403 req->wscale_ok,
1404 &rcv_wscale);
1405 req->rcv_wscale = rcv_wscale;
1406 }
1407
1408 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
1409 th->window = htons(req->rcv_wnd);
1410
1411 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1412 tcp_syn_build_options((__u32 *)(th + 1), dst_metric(dst, RTAX_ADVMSS), req->tstamp_ok,
1413 req->sack_ok, req->wscale_ok, req->rcv_wscale,
1414 TCP_SKB_CB(skb)->when,
1415 req->ts_recent);
1416
1417 skb->csum = 0;
1418 th->doff = (tcp_header_size >> 2);
1419 TCP_INC_STATS(TCP_MIB_OUTSEGS);
1420 return skb;
1421}
1422
1423/*
1424 * Do all connect socket setups that can be done AF independent.
1425 */
1426static inline void tcp_connect_init(struct sock *sk)
1427{
1428 struct dst_entry *dst = __sk_dst_get(sk);
1429 struct tcp_sock *tp = tcp_sk(sk);
1430 __u8 rcv_wscale;
1431
1432 /* We'll fix this up when we get a response from the other end.
1433 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
1434 */
1435 tp->tcp_header_len = sizeof(struct tcphdr) +
1436 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
1437
1438 /* If user gave his TCP_MAXSEG, record it to clamp */
1439 if (tp->rx_opt.user_mss)
1440 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
1441 tp->max_window = 0;
1442 tcp_sync_mss(sk, dst_mtu(dst));
1443
1444 if (!tp->window_clamp)
1445 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
1446 tp->advmss = dst_metric(dst, RTAX_ADVMSS);
1447 tcp_initialize_rcv_mss(sk);
1448 tcp_ca_init(tp);
1449
1450 tcp_select_initial_window(tcp_full_space(sk),
1451 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
1452 &tp->rcv_wnd,
1453 &tp->window_clamp,
1454 sysctl_tcp_window_scaling,
1455 &rcv_wscale);
1456
1457 tp->rx_opt.rcv_wscale = rcv_wscale;
1458 tp->rcv_ssthresh = tp->rcv_wnd;
1459
1460 sk->sk_err = 0;
1461 sock_reset_flag(sk, SOCK_DONE);
1462 tp->snd_wnd = 0;
1463 tcp_init_wl(tp, tp->write_seq, 0);
1464 tp->snd_una = tp->write_seq;
1465 tp->snd_sml = tp->write_seq;
1466 tp->rcv_nxt = 0;
1467 tp->rcv_wup = 0;
1468 tp->copied_seq = 0;
1469
1470 tp->rto = TCP_TIMEOUT_INIT;
1471 tp->retransmits = 0;
1472 tcp_clear_retrans(tp);
1473}
1474
1475/*
1476 * Build a SYN and send it off.
1477 */
1478int tcp_connect(struct sock *sk)
1479{
1480 struct tcp_sock *tp = tcp_sk(sk);
1481 struct sk_buff *buff;
1482
1483 tcp_connect_init(sk);
1484
1485 buff = alloc_skb(MAX_TCP_HEADER + 15, sk->sk_allocation);
1486 if (unlikely(buff == NULL))
1487 return -ENOBUFS;
1488
1489 /* Reserve space for headers. */
1490 skb_reserve(buff, MAX_TCP_HEADER);
1491
1492 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN;
1493 TCP_ECN_send_syn(sk, tp, buff);
1494 TCP_SKB_CB(buff)->sacked = 0;
1495 skb_shinfo(buff)->tso_segs = 1;
1496 skb_shinfo(buff)->tso_size = 0;
1497 buff->csum = 0;
1498 TCP_SKB_CB(buff)->seq = tp->write_seq++;
1499 TCP_SKB_CB(buff)->end_seq = tp->write_seq;
1500 tp->snd_nxt = tp->write_seq;
1501 tp->pushed_seq = tp->write_seq;
1502 tcp_ca_init(tp);
1503
1504 /* Send it off. */
1505 TCP_SKB_CB(buff)->when = tcp_time_stamp;
1506 tp->retrans_stamp = TCP_SKB_CB(buff)->when;
1507 skb_header_release(buff);
1508 __skb_queue_tail(&sk->sk_write_queue, buff);
1509 sk_charge_skb(sk, buff);
1510 tp->packets_out += tcp_skb_pcount(buff);
1511 tcp_transmit_skb(sk, skb_clone(buff, GFP_KERNEL));
1512 TCP_INC_STATS(TCP_MIB_ACTIVEOPENS);
1513
1514 /* Timer for repeating the SYN until an answer. */
1515 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1516 return 0;
1517}
1518
1519/* Send out a delayed ack, the caller does the policy checking
1520 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
1521 * for details.
1522 */
1523void tcp_send_delayed_ack(struct sock *sk)
1524{
1525 struct tcp_sock *tp = tcp_sk(sk);
1526 int ato = tp->ack.ato;
1527 unsigned long timeout;
1528
1529 if (ato > TCP_DELACK_MIN) {
1530 int max_ato = HZ/2;
1531
1532 if (tp->ack.pingpong || (tp->ack.pending&TCP_ACK_PUSHED))
1533 max_ato = TCP_DELACK_MAX;
1534
1535 /* Slow path, intersegment interval is "high". */
1536
1537 /* If some rtt estimate is known, use it to bound delayed ack.
1538 * Do not use tp->rto here, use results of rtt measurements
1539 * directly.
1540 */
1541 if (tp->srtt) {
1542 int rtt = max(tp->srtt>>3, TCP_DELACK_MIN);
1543
1544 if (rtt < max_ato)
1545 max_ato = rtt;
1546 }
1547
1548 ato = min(ato, max_ato);
1549 }
1550
1551 /* Stay within the limit we were given */
1552 timeout = jiffies + ato;
1553
1554 /* Use new timeout only if there wasn't a older one earlier. */
1555 if (tp->ack.pending&TCP_ACK_TIMER) {
1556 /* If delack timer was blocked or is about to expire,
1557 * send ACK now.
1558 */
1559 if (tp->ack.blocked || time_before_eq(tp->ack.timeout, jiffies+(ato>>2))) {
1560 tcp_send_ack(sk);
1561 return;
1562 }
1563
1564 if (!time_before(timeout, tp->ack.timeout))
1565 timeout = tp->ack.timeout;
1566 }
1567 tp->ack.pending |= TCP_ACK_SCHED|TCP_ACK_TIMER;
1568 tp->ack.timeout = timeout;
1569 sk_reset_timer(sk, &tp->delack_timer, timeout);
1570}
1571
1572/* This routine sends an ack and also updates the window. */
1573void tcp_send_ack(struct sock *sk)
1574{
1575 /* If we have been reset, we may not send again. */
1576 if (sk->sk_state != TCP_CLOSE) {
1577 struct tcp_sock *tp = tcp_sk(sk);
1578 struct sk_buff *buff;
1579
1580 /* We are not putting this on the write queue, so
1581 * tcp_transmit_skb() will set the ownership to this
1582 * sock.
1583 */
1584 buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
1585 if (buff == NULL) {
1586 tcp_schedule_ack(tp);
1587 tp->ack.ato = TCP_ATO_MIN;
1588 tcp_reset_xmit_timer(sk, TCP_TIME_DACK, TCP_DELACK_MAX);
1589 return;
1590 }
1591
1592 /* Reserve space for headers and prepare control bits. */
1593 skb_reserve(buff, MAX_TCP_HEADER);
1594 buff->csum = 0;
1595 TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK;
1596 TCP_SKB_CB(buff)->sacked = 0;
1597 skb_shinfo(buff)->tso_segs = 1;
1598 skb_shinfo(buff)->tso_size = 0;
1599
1600 /* Send it off, this clears delayed acks for us. */
1601 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(buff)->end_seq = tcp_acceptable_seq(sk, tp);
1602 TCP_SKB_CB(buff)->when = tcp_time_stamp;
1603 tcp_transmit_skb(sk, buff);
1604 }
1605}
1606
1607/* This routine sends a packet with an out of date sequence
1608 * number. It assumes the other end will try to ack it.
1609 *
1610 * Question: what should we make while urgent mode?
1611 * 4.4BSD forces sending single byte of data. We cannot send
1612 * out of window data, because we have SND.NXT==SND.MAX...
1613 *
1614 * Current solution: to send TWO zero-length segments in urgent mode:
1615 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
1616 * out-of-date with SND.UNA-1 to probe window.
1617 */
1618static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
1619{
1620 struct tcp_sock *tp = tcp_sk(sk);
1621 struct sk_buff *skb;
1622
1623 /* We don't queue it, tcp_transmit_skb() sets ownership. */
1624 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
1625 if (skb == NULL)
1626 return -1;
1627
1628 /* Reserve space for headers and set control bits. */
1629 skb_reserve(skb, MAX_TCP_HEADER);
1630 skb->csum = 0;
1631 TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
1632 TCP_SKB_CB(skb)->sacked = urgent;
1633 skb_shinfo(skb)->tso_segs = 1;
1634 skb_shinfo(skb)->tso_size = 0;
1635
1636 /* Use a previous sequence. This should cause the other
1637 * end to send an ack. Don't queue or clone SKB, just
1638 * send it.
1639 */
1640 TCP_SKB_CB(skb)->seq = urgent ? tp->snd_una : tp->snd_una - 1;
1641 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
1642 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1643 return tcp_transmit_skb(sk, skb);
1644}
1645
1646int tcp_write_wakeup(struct sock *sk)
1647{
1648 if (sk->sk_state != TCP_CLOSE) {
1649 struct tcp_sock *tp = tcp_sk(sk);
1650 struct sk_buff *skb;
1651
1652 if ((skb = sk->sk_send_head) != NULL &&
1653 before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)) {
1654 int err;
1655 unsigned int mss = tcp_current_mss(sk, 0);
1656 unsigned int seg_size = tp->snd_una+tp->snd_wnd-TCP_SKB_CB(skb)->seq;
1657
1658 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
1659 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
1660
1661 /* We are probing the opening of a window
1662 * but the window size is != 0
1663 * must have been a result SWS avoidance ( sender )
1664 */
1665 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
1666 skb->len > mss) {
1667 seg_size = min(seg_size, mss);
1668 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
1669 if (tcp_fragment(sk, skb, seg_size))
1670 return -1;
1671 /* SWS override triggered forced fragmentation.
1672 * Disable TSO, the connection is too sick. */
1673 if (sk->sk_route_caps & NETIF_F_TSO) {
1674 sock_set_flag(sk, SOCK_NO_LARGESEND);
1675 sk->sk_route_caps &= ~NETIF_F_TSO;
1676 tp->mss_cache = tp->mss_cache_std;
1677 }
1678 } else if (!tcp_skb_pcount(skb))
1679 tcp_set_skb_tso_segs(skb, tp->mss_cache_std);
1680
1681 TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
1682 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1683 tcp_tso_set_push(skb);
1684 err = tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC));
1685 if (!err) {
1686 update_send_head(sk, tp, skb);
1687 }
1688 return err;
1689 } else {
1690 if (tp->urg_mode &&
1691 between(tp->snd_up, tp->snd_una+1, tp->snd_una+0xFFFF))
1692 tcp_xmit_probe_skb(sk, TCPCB_URG);
1693 return tcp_xmit_probe_skb(sk, 0);
1694 }
1695 }
1696 return -1;
1697}
1698
1699/* A window probe timeout has occurred. If window is not closed send
1700 * a partial packet else a zero probe.
1701 */
1702void tcp_send_probe0(struct sock *sk)
1703{
1704 struct tcp_sock *tp = tcp_sk(sk);
1705 int err;
1706
1707 err = tcp_write_wakeup(sk);
1708
1709 if (tp->packets_out || !sk->sk_send_head) {
1710 /* Cancel probe timer, if it is not required. */
1711 tp->probes_out = 0;
1712 tp->backoff = 0;
1713 return;
1714 }
1715
1716 if (err <= 0) {
1717 if (tp->backoff < sysctl_tcp_retries2)
1718 tp->backoff++;
1719 tp->probes_out++;
1720 tcp_reset_xmit_timer (sk, TCP_TIME_PROBE0,
1721 min(tp->rto << tp->backoff, TCP_RTO_MAX));
1722 } else {
1723 /* If packet was not sent due to local congestion,
1724 * do not backoff and do not remember probes_out.
1725 * Let local senders to fight for local resources.
1726 *
1727 * Use accumulated backoff yet.
1728 */
1729 if (!tp->probes_out)
1730 tp->probes_out=1;
1731 tcp_reset_xmit_timer (sk, TCP_TIME_PROBE0,
1732 min(tp->rto << tp->backoff, TCP_RESOURCE_PROBE_INTERVAL));
1733 }
1734}
1735
1736EXPORT_SYMBOL(tcp_connect);
1737EXPORT_SYMBOL(tcp_make_synack);
1738EXPORT_SYMBOL(tcp_simple_retransmit);
1739EXPORT_SYMBOL(tcp_sync_mss);
generated by cgit v1.2.2 (git 2.25.0) at 2024-12-27 13:51:28 -0500