xref: /openbmc/linux/net/ipv4/tcp_output.c (revision ee89bd6b)
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. */
46 int 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  */
51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
52 
53 /* Default TSQ limit of two TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 131072;
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  */
60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
61 
62 int sysctl_tcp_mtu_probing __read_mostly = 0;
63 int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;
64 
65 /* By default, RFC2861 behavior.  */
66 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
67 
68 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
69 			   int push_one, gfp_t gfp);
70 
71 /* Account for new data that has been sent to the network. */
72 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
73 {
74 	struct inet_connection_sock *icsk = inet_csk(sk);
75 	struct tcp_sock *tp = tcp_sk(sk);
76 	unsigned int prior_packets = tp->packets_out;
77 
78 	tcp_advance_send_head(sk, skb);
79 	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
80 
81 	tp->packets_out += tcp_skb_pcount(skb);
82 	if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
83 	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
84 		tcp_rearm_rto(sk);
85 	}
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  */
94 static 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  */
118 static __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 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
139 {
140 	struct tcp_sock *tp = tcp_sk(sk);
141 	s32 delta = tcp_time_stamp - tp->lsndtime;
142 	u32 restart_cwnd = tcp_init_cwnd(tp, dst);
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. */
158 static 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 (sysctl_tcp_slow_start_after_idle &&
165 	    (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
166 		tcp_cwnd_restart(sk, __sk_dst_get(sk));
167 
168 	tp->lsndtime = now;
169 
170 	/* If it is a reply for ato after last received
171 	 * packet, enter pingpong mode.
172 	 */
173 	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
174 		icsk->icsk_ack.pingpong = 1;
175 }
176 
177 /* Account for an ACK we sent. */
178 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
179 {
180 	tcp_dec_quickack_mode(sk, pkts);
181 	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
182 }
183 
184 /* Determine a window scaling and initial window to offer.
185  * Based on the assumption that the given amount of space
186  * will be offered. Store the results in the tp structure.
187  * NOTE: for smooth operation initial space offering should
188  * be a multiple of mss if possible. We assume here that mss >= 1.
189  * This MUST be enforced by all callers.
190  */
191 void tcp_select_initial_window(int __space, __u32 mss,
192 			       __u32 *rcv_wnd, __u32 *window_clamp,
193 			       int wscale_ok, __u8 *rcv_wscale,
194 			       __u32 init_rcv_wnd)
195 {
196 	unsigned int space = (__space < 0 ? 0 : __space);
197 
198 	/* If no clamp set the clamp to the max possible scaled window */
199 	if (*window_clamp == 0)
200 		(*window_clamp) = (65535 << 14);
201 	space = min(*window_clamp, space);
202 
203 	/* Quantize space offering to a multiple of mss if possible. */
204 	if (space > mss)
205 		space = (space / mss) * mss;
206 
207 	/* NOTE: offering an initial window larger than 32767
208 	 * will break some buggy TCP stacks. If the admin tells us
209 	 * it is likely we could be speaking with such a buggy stack
210 	 * we will truncate our initial window offering to 32K-1
211 	 * unless the remote has sent us a window scaling option,
212 	 * which we interpret as a sign the remote TCP is not
213 	 * misinterpreting the window field as a signed quantity.
214 	 */
215 	if (sysctl_tcp_workaround_signed_windows)
216 		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
217 	else
218 		(*rcv_wnd) = space;
219 
220 	(*rcv_wscale) = 0;
221 	if (wscale_ok) {
222 		/* Set window scaling on max possible window
223 		 * See RFC1323 for an explanation of the limit to 14
224 		 */
225 		space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
226 		space = min_t(u32, space, *window_clamp);
227 		while (space > 65535 && (*rcv_wscale) < 14) {
228 			space >>= 1;
229 			(*rcv_wscale)++;
230 		}
231 	}
232 
233 	/* Set initial window to a value enough for senders starting with
234 	 * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
235 	 * a limit on the initial window when mss is larger than 1460.
236 	 */
237 	if (mss > (1 << *rcv_wscale)) {
238 		int init_cwnd = TCP_DEFAULT_INIT_RCVWND;
239 		if (mss > 1460)
240 			init_cwnd =
241 			max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
242 		/* when initializing use the value from init_rcv_wnd
243 		 * rather than the default from above
244 		 */
245 		if (init_rcv_wnd)
246 			*rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
247 		else
248 			*rcv_wnd = min(*rcv_wnd, init_cwnd * mss);
249 	}
250 
251 	/* Set the clamp no higher than max representable value */
252 	(*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
253 }
254 EXPORT_SYMBOL(tcp_select_initial_window);
255 
256 /* Chose a new window to advertise, update state in tcp_sock for the
257  * socket, and return result with RFC1323 scaling applied.  The return
258  * value can be stuffed directly into th->window for an outgoing
259  * frame.
260  */
261 static u16 tcp_select_window(struct sock *sk)
262 {
263 	struct tcp_sock *tp = tcp_sk(sk);
264 	u32 cur_win = tcp_receive_window(tp);
265 	u32 new_win = __tcp_select_window(sk);
266 
267 	/* Never shrink the offered window */
268 	if (new_win < cur_win) {
269 		/* Danger Will Robinson!
270 		 * Don't update rcv_wup/rcv_wnd here or else
271 		 * we will not be able to advertise a zero
272 		 * window in time.  --DaveM
273 		 *
274 		 * Relax Will Robinson.
275 		 */
276 		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
277 	}
278 	tp->rcv_wnd = new_win;
279 	tp->rcv_wup = tp->rcv_nxt;
280 
281 	/* Make sure we do not exceed the maximum possible
282 	 * scaled window.
283 	 */
284 	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
285 		new_win = min(new_win, MAX_TCP_WINDOW);
286 	else
287 		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
288 
289 	/* RFC1323 scaling applied */
290 	new_win >>= tp->rx_opt.rcv_wscale;
291 
292 	/* If we advertise zero window, disable fast path. */
293 	if (new_win == 0)
294 		tp->pred_flags = 0;
295 
296 	return new_win;
297 }
298 
299 /* Packet ECN state for a SYN-ACK */
300 static inline void TCP_ECN_send_synack(const struct tcp_sock *tp, struct sk_buff *skb)
301 {
302 	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
303 	if (!(tp->ecn_flags & TCP_ECN_OK))
304 		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
305 }
306 
307 /* Packet ECN state for a SYN.  */
308 static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
309 {
310 	struct tcp_sock *tp = tcp_sk(sk);
311 
312 	tp->ecn_flags = 0;
313 	if (sock_net(sk)->ipv4.sysctl_tcp_ecn == 1) {
314 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
315 		tp->ecn_flags = TCP_ECN_OK;
316 	}
317 }
318 
319 static __inline__ void
320 TCP_ECN_make_synack(const struct request_sock *req, struct tcphdr *th)
321 {
322 	if (inet_rsk(req)->ecn_ok)
323 		th->ece = 1;
324 }
325 
326 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
327  * be sent.
328  */
329 static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
330 				int tcp_header_len)
331 {
332 	struct tcp_sock *tp = tcp_sk(sk);
333 
334 	if (tp->ecn_flags & TCP_ECN_OK) {
335 		/* Not-retransmitted data segment: set ECT and inject CWR. */
336 		if (skb->len != tcp_header_len &&
337 		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
338 			INET_ECN_xmit(sk);
339 			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
340 				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
341 				tcp_hdr(skb)->cwr = 1;
342 				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
343 			}
344 		} else {
345 			/* ACK or retransmitted segment: clear ECT|CE */
346 			INET_ECN_dontxmit(sk);
347 		}
348 		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
349 			tcp_hdr(skb)->ece = 1;
350 	}
351 }
352 
353 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
354  * auto increment end seqno.
355  */
356 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
357 {
358 	skb->ip_summed = CHECKSUM_PARTIAL;
359 	skb->csum = 0;
360 
361 	TCP_SKB_CB(skb)->tcp_flags = flags;
362 	TCP_SKB_CB(skb)->sacked = 0;
363 
364 	skb_shinfo(skb)->gso_segs = 1;
365 	skb_shinfo(skb)->gso_size = 0;
366 	skb_shinfo(skb)->gso_type = 0;
367 
368 	TCP_SKB_CB(skb)->seq = seq;
369 	if (flags & (TCPHDR_SYN | TCPHDR_FIN))
370 		seq++;
371 	TCP_SKB_CB(skb)->end_seq = seq;
372 }
373 
374 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
375 {
376 	return tp->snd_una != tp->snd_up;
377 }
378 
379 #define OPTION_SACK_ADVERTISE	(1 << 0)
380 #define OPTION_TS		(1 << 1)
381 #define OPTION_MD5		(1 << 2)
382 #define OPTION_WSCALE		(1 << 3)
383 #define OPTION_FAST_OPEN_COOKIE	(1 << 8)
384 
385 struct tcp_out_options {
386 	u16 options;		/* bit field of OPTION_* */
387 	u16 mss;		/* 0 to disable */
388 	u8 ws;			/* window scale, 0 to disable */
389 	u8 num_sack_blocks;	/* number of SACK blocks to include */
390 	u8 hash_size;		/* bytes in hash_location */
391 	__u8 *hash_location;	/* temporary pointer, overloaded */
392 	__u32 tsval, tsecr;	/* need to include OPTION_TS */
393 	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */
394 };
395 
396 /* Write previously computed TCP options to the packet.
397  *
398  * Beware: Something in the Internet is very sensitive to the ordering of
399  * TCP options, we learned this through the hard way, so be careful here.
400  * Luckily we can at least blame others for their non-compliance but from
401  * inter-operatibility perspective it seems that we're somewhat stuck with
402  * the ordering which we have been using if we want to keep working with
403  * those broken things (not that it currently hurts anybody as there isn't
404  * particular reason why the ordering would need to be changed).
405  *
406  * At least SACK_PERM as the first option is known to lead to a disaster
407  * (but it may well be that other scenarios fail similarly).
408  */
409 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
410 			      struct tcp_out_options *opts)
411 {
412 	u16 options = opts->options;	/* mungable copy */
413 
414 	if (unlikely(OPTION_MD5 & options)) {
415 		*ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
416 			       (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
417 		/* overload cookie hash location */
418 		opts->hash_location = (__u8 *)ptr;
419 		ptr += 4;
420 	}
421 
422 	if (unlikely(opts->mss)) {
423 		*ptr++ = htonl((TCPOPT_MSS << 24) |
424 			       (TCPOLEN_MSS << 16) |
425 			       opts->mss);
426 	}
427 
428 	if (likely(OPTION_TS & options)) {
429 		if (unlikely(OPTION_SACK_ADVERTISE & options)) {
430 			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
431 				       (TCPOLEN_SACK_PERM << 16) |
432 				       (TCPOPT_TIMESTAMP << 8) |
433 				       TCPOLEN_TIMESTAMP);
434 			options &= ~OPTION_SACK_ADVERTISE;
435 		} else {
436 			*ptr++ = htonl((TCPOPT_NOP << 24) |
437 				       (TCPOPT_NOP << 16) |
438 				       (TCPOPT_TIMESTAMP << 8) |
439 				       TCPOLEN_TIMESTAMP);
440 		}
441 		*ptr++ = htonl(opts->tsval);
442 		*ptr++ = htonl(opts->tsecr);
443 	}
444 
445 	if (unlikely(OPTION_SACK_ADVERTISE & options)) {
446 		*ptr++ = htonl((TCPOPT_NOP << 24) |
447 			       (TCPOPT_NOP << 16) |
448 			       (TCPOPT_SACK_PERM << 8) |
449 			       TCPOLEN_SACK_PERM);
450 	}
451 
452 	if (unlikely(OPTION_WSCALE & options)) {
453 		*ptr++ = htonl((TCPOPT_NOP << 24) |
454 			       (TCPOPT_WINDOW << 16) |
455 			       (TCPOLEN_WINDOW << 8) |
456 			       opts->ws);
457 	}
458 
459 	if (unlikely(opts->num_sack_blocks)) {
460 		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
461 			tp->duplicate_sack : tp->selective_acks;
462 		int this_sack;
463 
464 		*ptr++ = htonl((TCPOPT_NOP  << 24) |
465 			       (TCPOPT_NOP  << 16) |
466 			       (TCPOPT_SACK <<  8) |
467 			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
468 						     TCPOLEN_SACK_PERBLOCK)));
469 
470 		for (this_sack = 0; this_sack < opts->num_sack_blocks;
471 		     ++this_sack) {
472 			*ptr++ = htonl(sp[this_sack].start_seq);
473 			*ptr++ = htonl(sp[this_sack].end_seq);
474 		}
475 
476 		tp->rx_opt.dsack = 0;
477 	}
478 
479 	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
480 		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
481 
482 		*ptr++ = htonl((TCPOPT_EXP << 24) |
483 			       ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
484 			       TCPOPT_FASTOPEN_MAGIC);
485 
486 		memcpy(ptr, foc->val, foc->len);
487 		if ((foc->len & 3) == 2) {
488 			u8 *align = ((u8 *)ptr) + foc->len;
489 			align[0] = align[1] = TCPOPT_NOP;
490 		}
491 		ptr += (foc->len + 3) >> 2;
492 	}
493 }
494 
495 /* Compute TCP options for SYN packets. This is not the final
496  * network wire format yet.
497  */
498 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
499 				struct tcp_out_options *opts,
500 				struct tcp_md5sig_key **md5)
501 {
502 	struct tcp_sock *tp = tcp_sk(sk);
503 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
504 	struct tcp_fastopen_request *fastopen = tp->fastopen_req;
505 
506 #ifdef CONFIG_TCP_MD5SIG
507 	*md5 = tp->af_specific->md5_lookup(sk, sk);
508 	if (*md5) {
509 		opts->options |= OPTION_MD5;
510 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
511 	}
512 #else
513 	*md5 = NULL;
514 #endif
515 
516 	/* We always get an MSS option.  The option bytes which will be seen in
517 	 * normal data packets should timestamps be used, must be in the MSS
518 	 * advertised.  But we subtract them from tp->mss_cache so that
519 	 * calculations in tcp_sendmsg are simpler etc.  So account for this
520 	 * fact here if necessary.  If we don't do this correctly, as a
521 	 * receiver we won't recognize data packets as being full sized when we
522 	 * should, and thus we won't abide by the delayed ACK rules correctly.
523 	 * SACKs don't matter, we never delay an ACK when we have any of those
524 	 * going out.  */
525 	opts->mss = tcp_advertise_mss(sk);
526 	remaining -= TCPOLEN_MSS_ALIGNED;
527 
528 	if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
529 		opts->options |= OPTION_TS;
530 		opts->tsval = TCP_SKB_CB(skb)->when + tp->tsoffset;
531 		opts->tsecr = tp->rx_opt.ts_recent;
532 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
533 	}
534 	if (likely(sysctl_tcp_window_scaling)) {
535 		opts->ws = tp->rx_opt.rcv_wscale;
536 		opts->options |= OPTION_WSCALE;
537 		remaining -= TCPOLEN_WSCALE_ALIGNED;
538 	}
539 	if (likely(sysctl_tcp_sack)) {
540 		opts->options |= OPTION_SACK_ADVERTISE;
541 		if (unlikely(!(OPTION_TS & opts->options)))
542 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
543 	}
544 
545 	if (fastopen && fastopen->cookie.len >= 0) {
546 		u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
547 		need = (need + 3) & ~3U;  /* Align to 32 bits */
548 		if (remaining >= need) {
549 			opts->options |= OPTION_FAST_OPEN_COOKIE;
550 			opts->fastopen_cookie = &fastopen->cookie;
551 			remaining -= need;
552 			tp->syn_fastopen = 1;
553 		}
554 	}
555 
556 	return MAX_TCP_OPTION_SPACE - remaining;
557 }
558 
559 /* Set up TCP options for SYN-ACKs. */
560 static unsigned int tcp_synack_options(struct sock *sk,
561 				   struct request_sock *req,
562 				   unsigned int mss, struct sk_buff *skb,
563 				   struct tcp_out_options *opts,
564 				   struct tcp_md5sig_key **md5,
565 				   struct tcp_fastopen_cookie *foc)
566 {
567 	struct inet_request_sock *ireq = inet_rsk(req);
568 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
569 
570 #ifdef CONFIG_TCP_MD5SIG
571 	*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
572 	if (*md5) {
573 		opts->options |= OPTION_MD5;
574 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
575 
576 		/* We can't fit any SACK blocks in a packet with MD5 + TS
577 		 * options. There was discussion about disabling SACK
578 		 * rather than TS in order to fit in better with old,
579 		 * buggy kernels, but that was deemed to be unnecessary.
580 		 */
581 		ireq->tstamp_ok &= !ireq->sack_ok;
582 	}
583 #else
584 	*md5 = NULL;
585 #endif
586 
587 	/* We always send an MSS option. */
588 	opts->mss = mss;
589 	remaining -= TCPOLEN_MSS_ALIGNED;
590 
591 	if (likely(ireq->wscale_ok)) {
592 		opts->ws = ireq->rcv_wscale;
593 		opts->options |= OPTION_WSCALE;
594 		remaining -= TCPOLEN_WSCALE_ALIGNED;
595 	}
596 	if (likely(ireq->tstamp_ok)) {
597 		opts->options |= OPTION_TS;
598 		opts->tsval = TCP_SKB_CB(skb)->when;
599 		opts->tsecr = req->ts_recent;
600 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
601 	}
602 	if (likely(ireq->sack_ok)) {
603 		opts->options |= OPTION_SACK_ADVERTISE;
604 		if (unlikely(!ireq->tstamp_ok))
605 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
606 	}
607 	if (foc != NULL) {
608 		u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
609 		need = (need + 3) & ~3U;  /* Align to 32 bits */
610 		if (remaining >= need) {
611 			opts->options |= OPTION_FAST_OPEN_COOKIE;
612 			opts->fastopen_cookie = foc;
613 			remaining -= need;
614 		}
615 	}
616 
617 	return MAX_TCP_OPTION_SPACE - remaining;
618 }
619 
620 /* Compute TCP options for ESTABLISHED sockets. This is not the
621  * final wire format yet.
622  */
623 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
624 					struct tcp_out_options *opts,
625 					struct tcp_md5sig_key **md5)
626 {
627 	struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
628 	struct tcp_sock *tp = tcp_sk(sk);
629 	unsigned int size = 0;
630 	unsigned int eff_sacks;
631 
632 #ifdef CONFIG_TCP_MD5SIG
633 	*md5 = tp->af_specific->md5_lookup(sk, sk);
634 	if (unlikely(*md5)) {
635 		opts->options |= OPTION_MD5;
636 		size += TCPOLEN_MD5SIG_ALIGNED;
637 	}
638 #else
639 	*md5 = NULL;
640 #endif
641 
642 	if (likely(tp->rx_opt.tstamp_ok)) {
643 		opts->options |= OPTION_TS;
644 		opts->tsval = tcb ? tcb->when + tp->tsoffset : 0;
645 		opts->tsecr = tp->rx_opt.ts_recent;
646 		size += TCPOLEN_TSTAMP_ALIGNED;
647 	}
648 
649 	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
650 	if (unlikely(eff_sacks)) {
651 		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
652 		opts->num_sack_blocks =
653 			min_t(unsigned int, eff_sacks,
654 			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
655 			      TCPOLEN_SACK_PERBLOCK);
656 		size += TCPOLEN_SACK_BASE_ALIGNED +
657 			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
658 	}
659 
660 	return size;
661 }
662 
663 
664 /* TCP SMALL QUEUES (TSQ)
665  *
666  * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
667  * to reduce RTT and bufferbloat.
668  * We do this using a special skb destructor (tcp_wfree).
669  *
670  * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
671  * needs to be reallocated in a driver.
672  * The invariant being skb->truesize substracted from sk->sk_wmem_alloc
673  *
674  * Since transmit from skb destructor is forbidden, we use a tasklet
675  * to process all sockets that eventually need to send more skbs.
676  * We use one tasklet per cpu, with its own queue of sockets.
677  */
678 struct tsq_tasklet {
679 	struct tasklet_struct	tasklet;
680 	struct list_head	head; /* queue of tcp sockets */
681 };
682 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
683 
684 static void tcp_tsq_handler(struct sock *sk)
685 {
686 	if ((1 << sk->sk_state) &
687 	    (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
688 	     TCPF_CLOSE_WAIT  | TCPF_LAST_ACK))
689 		tcp_write_xmit(sk, tcp_current_mss(sk), 0, 0, GFP_ATOMIC);
690 }
691 /*
692  * One tasklest per cpu tries to send more skbs.
693  * We run in tasklet context but need to disable irqs when
694  * transfering tsq->head because tcp_wfree() might
695  * interrupt us (non NAPI drivers)
696  */
697 static void tcp_tasklet_func(unsigned long data)
698 {
699 	struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
700 	LIST_HEAD(list);
701 	unsigned long flags;
702 	struct list_head *q, *n;
703 	struct tcp_sock *tp;
704 	struct sock *sk;
705 
706 	local_irq_save(flags);
707 	list_splice_init(&tsq->head, &list);
708 	local_irq_restore(flags);
709 
710 	list_for_each_safe(q, n, &list) {
711 		tp = list_entry(q, struct tcp_sock, tsq_node);
712 		list_del(&tp->tsq_node);
713 
714 		sk = (struct sock *)tp;
715 		bh_lock_sock(sk);
716 
717 		if (!sock_owned_by_user(sk)) {
718 			tcp_tsq_handler(sk);
719 		} else {
720 			/* defer the work to tcp_release_cb() */
721 			set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
722 		}
723 		bh_unlock_sock(sk);
724 
725 		clear_bit(TSQ_QUEUED, &tp->tsq_flags);
726 		sk_free(sk);
727 	}
728 }
729 
730 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) |		\
731 			  (1UL << TCP_WRITE_TIMER_DEFERRED) |	\
732 			  (1UL << TCP_DELACK_TIMER_DEFERRED) |	\
733 			  (1UL << TCP_MTU_REDUCED_DEFERRED))
734 /**
735  * tcp_release_cb - tcp release_sock() callback
736  * @sk: socket
737  *
738  * called from release_sock() to perform protocol dependent
739  * actions before socket release.
740  */
741 void tcp_release_cb(struct sock *sk)
742 {
743 	struct tcp_sock *tp = tcp_sk(sk);
744 	unsigned long flags, nflags;
745 
746 	/* perform an atomic operation only if at least one flag is set */
747 	do {
748 		flags = tp->tsq_flags;
749 		if (!(flags & TCP_DEFERRED_ALL))
750 			return;
751 		nflags = flags & ~TCP_DEFERRED_ALL;
752 	} while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
753 
754 	if (flags & (1UL << TCP_TSQ_DEFERRED))
755 		tcp_tsq_handler(sk);
756 
757 	if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
758 		tcp_write_timer_handler(sk);
759 		__sock_put(sk);
760 	}
761 	if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
762 		tcp_delack_timer_handler(sk);
763 		__sock_put(sk);
764 	}
765 	if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
766 		sk->sk_prot->mtu_reduced(sk);
767 		__sock_put(sk);
768 	}
769 }
770 EXPORT_SYMBOL(tcp_release_cb);
771 
772 void __init tcp_tasklet_init(void)
773 {
774 	int i;
775 
776 	for_each_possible_cpu(i) {
777 		struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
778 
779 		INIT_LIST_HEAD(&tsq->head);
780 		tasklet_init(&tsq->tasklet,
781 			     tcp_tasklet_func,
782 			     (unsigned long)tsq);
783 	}
784 }
785 
786 /*
787  * Write buffer destructor automatically called from kfree_skb.
788  * We cant xmit new skbs from this context, as we might already
789  * hold qdisc lock.
790  */
791 void tcp_wfree(struct sk_buff *skb)
792 {
793 	struct sock *sk = skb->sk;
794 	struct tcp_sock *tp = tcp_sk(sk);
795 
796 	if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
797 	    !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
798 		unsigned long flags;
799 		struct tsq_tasklet *tsq;
800 
801 		/* Keep a ref on socket.
802 		 * This last ref will be released in tcp_tasklet_func()
803 		 */
804 		atomic_sub(skb->truesize - 1, &sk->sk_wmem_alloc);
805 
806 		/* queue this socket to tasklet queue */
807 		local_irq_save(flags);
808 		tsq = &__get_cpu_var(tsq_tasklet);
809 		list_add(&tp->tsq_node, &tsq->head);
810 		tasklet_schedule(&tsq->tasklet);
811 		local_irq_restore(flags);
812 	} else {
813 		sock_wfree(skb);
814 	}
815 }
816 
817 /* This routine actually transmits TCP packets queued in by
818  * tcp_do_sendmsg().  This is used by both the initial
819  * transmission and possible later retransmissions.
820  * All SKB's seen here are completely headerless.  It is our
821  * job to build the TCP header, and pass the packet down to
822  * IP so it can do the same plus pass the packet off to the
823  * device.
824  *
825  * We are working here with either a clone of the original
826  * SKB, or a fresh unique copy made by the retransmit engine.
827  */
828 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
829 			    gfp_t gfp_mask)
830 {
831 	const struct inet_connection_sock *icsk = inet_csk(sk);
832 	struct inet_sock *inet;
833 	struct tcp_sock *tp;
834 	struct tcp_skb_cb *tcb;
835 	struct tcp_out_options opts;
836 	unsigned int tcp_options_size, tcp_header_size;
837 	struct tcp_md5sig_key *md5;
838 	struct tcphdr *th;
839 	int err;
840 
841 	BUG_ON(!skb || !tcp_skb_pcount(skb));
842 
843 	/* If congestion control is doing timestamping, we must
844 	 * take such a timestamp before we potentially clone/copy.
845 	 */
846 	if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
847 		__net_timestamp(skb);
848 
849 	if (likely(clone_it)) {
850 		const struct sk_buff *fclone = skb + 1;
851 
852 		if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
853 			     fclone->fclone == SKB_FCLONE_CLONE))
854 			NET_INC_STATS_BH(sock_net(sk),
855 					 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
856 
857 		if (unlikely(skb_cloned(skb)))
858 			skb = pskb_copy(skb, gfp_mask);
859 		else
860 			skb = skb_clone(skb, gfp_mask);
861 		if (unlikely(!skb))
862 			return -ENOBUFS;
863 	}
864 
865 	inet = inet_sk(sk);
866 	tp = tcp_sk(sk);
867 	tcb = TCP_SKB_CB(skb);
868 	memset(&opts, 0, sizeof(opts));
869 
870 	if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
871 		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
872 	else
873 		tcp_options_size = tcp_established_options(sk, skb, &opts,
874 							   &md5);
875 	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
876 
877 	if (tcp_packets_in_flight(tp) == 0)
878 		tcp_ca_event(sk, CA_EVENT_TX_START);
879 
880 	/* if no packet is in qdisc/device queue, then allow XPS to select
881 	 * another queue.
882 	 */
883 	skb->ooo_okay = sk_wmem_alloc_get(sk) == 0;
884 
885 	skb_push(skb, tcp_header_size);
886 	skb_reset_transport_header(skb);
887 
888 	skb_orphan(skb);
889 	skb->sk = sk;
890 	skb->destructor = (sysctl_tcp_limit_output_bytes > 0) ?
891 			  tcp_wfree : sock_wfree;
892 	atomic_add(skb->truesize, &sk->sk_wmem_alloc);
893 
894 	/* Build TCP header and checksum it. */
895 	th = tcp_hdr(skb);
896 	th->source		= inet->inet_sport;
897 	th->dest		= inet->inet_dport;
898 	th->seq			= htonl(tcb->seq);
899 	th->ack_seq		= htonl(tp->rcv_nxt);
900 	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
901 					tcb->tcp_flags);
902 
903 	if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
904 		/* RFC1323: The window in SYN & SYN/ACK segments
905 		 * is never scaled.
906 		 */
907 		th->window	= htons(min(tp->rcv_wnd, 65535U));
908 	} else {
909 		th->window	= htons(tcp_select_window(sk));
910 	}
911 	th->check		= 0;
912 	th->urg_ptr		= 0;
913 
914 	/* The urg_mode check is necessary during a below snd_una win probe */
915 	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
916 		if (before(tp->snd_up, tcb->seq + 0x10000)) {
917 			th->urg_ptr = htons(tp->snd_up - tcb->seq);
918 			th->urg = 1;
919 		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
920 			th->urg_ptr = htons(0xFFFF);
921 			th->urg = 1;
922 		}
923 	}
924 
925 	tcp_options_write((__be32 *)(th + 1), tp, &opts);
926 	if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
927 		TCP_ECN_send(sk, skb, tcp_header_size);
928 
929 #ifdef CONFIG_TCP_MD5SIG
930 	/* Calculate the MD5 hash, as we have all we need now */
931 	if (md5) {
932 		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
933 		tp->af_specific->calc_md5_hash(opts.hash_location,
934 					       md5, sk, NULL, skb);
935 	}
936 #endif
937 
938 	icsk->icsk_af_ops->send_check(sk, skb);
939 
940 	if (likely(tcb->tcp_flags & TCPHDR_ACK))
941 		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
942 
943 	if (skb->len != tcp_header_size)
944 		tcp_event_data_sent(tp, sk);
945 
946 	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
947 		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
948 			      tcp_skb_pcount(skb));
949 
950 	err = icsk->icsk_af_ops->queue_xmit(skb, &inet->cork.fl);
951 	if (likely(err <= 0))
952 		return err;
953 
954 	tcp_enter_cwr(sk, 1);
955 
956 	return net_xmit_eval(err);
957 }
958 
959 /* This routine just queues the buffer for sending.
960  *
961  * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
962  * otherwise socket can stall.
963  */
964 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
965 {
966 	struct tcp_sock *tp = tcp_sk(sk);
967 
968 	/* Advance write_seq and place onto the write_queue. */
969 	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
970 	skb_header_release(skb);
971 	tcp_add_write_queue_tail(sk, skb);
972 	sk->sk_wmem_queued += skb->truesize;
973 	sk_mem_charge(sk, skb->truesize);
974 }
975 
976 /* Initialize TSO segments for a packet. */
977 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
978 				 unsigned int mss_now)
979 {
980 	if (skb->len <= mss_now || !sk_can_gso(sk) ||
981 	    skb->ip_summed == CHECKSUM_NONE) {
982 		/* Avoid the costly divide in the normal
983 		 * non-TSO case.
984 		 */
985 		skb_shinfo(skb)->gso_segs = 1;
986 		skb_shinfo(skb)->gso_size = 0;
987 		skb_shinfo(skb)->gso_type = 0;
988 	} else {
989 		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
990 		skb_shinfo(skb)->gso_size = mss_now;
991 		skb_shinfo(skb)->gso_type = sk->sk_gso_type;
992 	}
993 }
994 
995 /* When a modification to fackets out becomes necessary, we need to check
996  * skb is counted to fackets_out or not.
997  */
998 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
999 				   int decr)
1000 {
1001 	struct tcp_sock *tp = tcp_sk(sk);
1002 
1003 	if (!tp->sacked_out || tcp_is_reno(tp))
1004 		return;
1005 
1006 	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1007 		tp->fackets_out -= decr;
1008 }
1009 
1010 /* Pcount in the middle of the write queue got changed, we need to do various
1011  * tweaks to fix counters
1012  */
1013 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1014 {
1015 	struct tcp_sock *tp = tcp_sk(sk);
1016 
1017 	tp->packets_out -= decr;
1018 
1019 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1020 		tp->sacked_out -= decr;
1021 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1022 		tp->retrans_out -= decr;
1023 	if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1024 		tp->lost_out -= decr;
1025 
1026 	/* Reno case is special. Sigh... */
1027 	if (tcp_is_reno(tp) && decr > 0)
1028 		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1029 
1030 	tcp_adjust_fackets_out(sk, skb, decr);
1031 
1032 	if (tp->lost_skb_hint &&
1033 	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1034 	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1035 		tp->lost_cnt_hint -= decr;
1036 
1037 	tcp_verify_left_out(tp);
1038 }
1039 
1040 /* Function to create two new TCP segments.  Shrinks the given segment
1041  * to the specified size and appends a new segment with the rest of the
1042  * packet to the list.  This won't be called frequently, I hope.
1043  * Remember, these are still headerless SKBs at this point.
1044  */
1045 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1046 		 unsigned int mss_now)
1047 {
1048 	struct tcp_sock *tp = tcp_sk(sk);
1049 	struct sk_buff *buff;
1050 	int nsize, old_factor;
1051 	int nlen;
1052 	u8 flags;
1053 
1054 	if (WARN_ON(len > skb->len))
1055 		return -EINVAL;
1056 
1057 	nsize = skb_headlen(skb) - len;
1058 	if (nsize < 0)
1059 		nsize = 0;
1060 
1061 	if (skb_cloned(skb) &&
1062 	    skb_is_nonlinear(skb) &&
1063 	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
1064 		return -ENOMEM;
1065 
1066 	/* Get a new skb... force flag on. */
1067 	buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
1068 	if (buff == NULL)
1069 		return -ENOMEM; /* We'll just try again later. */
1070 
1071 	sk->sk_wmem_queued += buff->truesize;
1072 	sk_mem_charge(sk, buff->truesize);
1073 	nlen = skb->len - len - nsize;
1074 	buff->truesize += nlen;
1075 	skb->truesize -= nlen;
1076 
1077 	/* Correct the sequence numbers. */
1078 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1079 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1080 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1081 
1082 	/* PSH and FIN should only be set in the second packet. */
1083 	flags = TCP_SKB_CB(skb)->tcp_flags;
1084 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1085 	TCP_SKB_CB(buff)->tcp_flags = flags;
1086 	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1087 
1088 	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1089 		/* Copy and checksum data tail into the new buffer. */
1090 		buff->csum = csum_partial_copy_nocheck(skb->data + len,
1091 						       skb_put(buff, nsize),
1092 						       nsize, 0);
1093 
1094 		skb_trim(skb, len);
1095 
1096 		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1097 	} else {
1098 		skb->ip_summed = CHECKSUM_PARTIAL;
1099 		skb_split(skb, buff, len);
1100 	}
1101 
1102 	buff->ip_summed = skb->ip_summed;
1103 
1104 	/* Looks stupid, but our code really uses when of
1105 	 * skbs, which it never sent before. --ANK
1106 	 */
1107 	TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
1108 	buff->tstamp = skb->tstamp;
1109 
1110 	old_factor = tcp_skb_pcount(skb);
1111 
1112 	/* Fix up tso_factor for both original and new SKB.  */
1113 	tcp_set_skb_tso_segs(sk, skb, mss_now);
1114 	tcp_set_skb_tso_segs(sk, buff, mss_now);
1115 
1116 	/* If this packet has been sent out already, we must
1117 	 * adjust the various packet counters.
1118 	 */
1119 	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1120 		int diff = old_factor - tcp_skb_pcount(skb) -
1121 			tcp_skb_pcount(buff);
1122 
1123 		if (diff)
1124 			tcp_adjust_pcount(sk, skb, diff);
1125 	}
1126 
1127 	/* Link BUFF into the send queue. */
1128 	skb_header_release(buff);
1129 	tcp_insert_write_queue_after(skb, buff, sk);
1130 
1131 	return 0;
1132 }
1133 
1134 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1135  * eventually). The difference is that pulled data not copied, but
1136  * immediately discarded.
1137  */
1138 static void __pskb_trim_head(struct sk_buff *skb, int len)
1139 {
1140 	int i, k, eat;
1141 
1142 	eat = min_t(int, len, skb_headlen(skb));
1143 	if (eat) {
1144 		__skb_pull(skb, eat);
1145 		len -= eat;
1146 		if (!len)
1147 			return;
1148 	}
1149 	eat = len;
1150 	k = 0;
1151 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
1152 		int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
1153 
1154 		if (size <= eat) {
1155 			skb_frag_unref(skb, i);
1156 			eat -= size;
1157 		} else {
1158 			skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
1159 			if (eat) {
1160 				skb_shinfo(skb)->frags[k].page_offset += eat;
1161 				skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
1162 				eat = 0;
1163 			}
1164 			k++;
1165 		}
1166 	}
1167 	skb_shinfo(skb)->nr_frags = k;
1168 
1169 	skb_reset_tail_pointer(skb);
1170 	skb->data_len -= len;
1171 	skb->len = skb->data_len;
1172 }
1173 
1174 /* Remove acked data from a packet in the transmit queue. */
1175 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1176 {
1177 	if (skb_unclone(skb, GFP_ATOMIC))
1178 		return -ENOMEM;
1179 
1180 	__pskb_trim_head(skb, len);
1181 
1182 	TCP_SKB_CB(skb)->seq += len;
1183 	skb->ip_summed = CHECKSUM_PARTIAL;
1184 
1185 	skb->truesize	     -= len;
1186 	sk->sk_wmem_queued   -= len;
1187 	sk_mem_uncharge(sk, len);
1188 	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1189 
1190 	/* Any change of skb->len requires recalculation of tso factor. */
1191 	if (tcp_skb_pcount(skb) > 1)
1192 		tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
1193 
1194 	return 0;
1195 }
1196 
1197 /* Calculate MSS not accounting any TCP options.  */
1198 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1199 {
1200 	const struct tcp_sock *tp = tcp_sk(sk);
1201 	const struct inet_connection_sock *icsk = inet_csk(sk);
1202 	int mss_now;
1203 
1204 	/* Calculate base mss without TCP options:
1205 	   It is MMS_S - sizeof(tcphdr) of rfc1122
1206 	 */
1207 	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1208 
1209 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1210 	if (icsk->icsk_af_ops->net_frag_header_len) {
1211 		const struct dst_entry *dst = __sk_dst_get(sk);
1212 
1213 		if (dst && dst_allfrag(dst))
1214 			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1215 	}
1216 
1217 	/* Clamp it (mss_clamp does not include tcp options) */
1218 	if (mss_now > tp->rx_opt.mss_clamp)
1219 		mss_now = tp->rx_opt.mss_clamp;
1220 
1221 	/* Now subtract optional transport overhead */
1222 	mss_now -= icsk->icsk_ext_hdr_len;
1223 
1224 	/* Then reserve room for full set of TCP options and 8 bytes of data */
1225 	if (mss_now < 48)
1226 		mss_now = 48;
1227 	return mss_now;
1228 }
1229 
1230 /* Calculate MSS. Not accounting for SACKs here.  */
1231 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1232 {
1233 	/* Subtract TCP options size, not including SACKs */
1234 	return __tcp_mtu_to_mss(sk, pmtu) -
1235 	       (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1236 }
1237 
1238 /* Inverse of above */
1239 int tcp_mss_to_mtu(struct sock *sk, int mss)
1240 {
1241 	const struct tcp_sock *tp = tcp_sk(sk);
1242 	const struct inet_connection_sock *icsk = inet_csk(sk);
1243 	int mtu;
1244 
1245 	mtu = mss +
1246 	      tp->tcp_header_len +
1247 	      icsk->icsk_ext_hdr_len +
1248 	      icsk->icsk_af_ops->net_header_len;
1249 
1250 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1251 	if (icsk->icsk_af_ops->net_frag_header_len) {
1252 		const struct dst_entry *dst = __sk_dst_get(sk);
1253 
1254 		if (dst && dst_allfrag(dst))
1255 			mtu += icsk->icsk_af_ops->net_frag_header_len;
1256 	}
1257 	return mtu;
1258 }
1259 
1260 /* MTU probing init per socket */
1261 void tcp_mtup_init(struct sock *sk)
1262 {
1263 	struct tcp_sock *tp = tcp_sk(sk);
1264 	struct inet_connection_sock *icsk = inet_csk(sk);
1265 
1266 	icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
1267 	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1268 			       icsk->icsk_af_ops->net_header_len;
1269 	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
1270 	icsk->icsk_mtup.probe_size = 0;
1271 }
1272 EXPORT_SYMBOL(tcp_mtup_init);
1273 
1274 /* This function synchronize snd mss to current pmtu/exthdr set.
1275 
1276    tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1277    for TCP options, but includes only bare TCP header.
1278 
1279    tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1280    It is minimum of user_mss and mss received with SYN.
1281    It also does not include TCP options.
1282 
1283    inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1284 
1285    tp->mss_cache is current effective sending mss, including
1286    all tcp options except for SACKs. It is evaluated,
1287    taking into account current pmtu, but never exceeds
1288    tp->rx_opt.mss_clamp.
1289 
1290    NOTE1. rfc1122 clearly states that advertised MSS
1291    DOES NOT include either tcp or ip options.
1292 
1293    NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1294    are READ ONLY outside this function.		--ANK (980731)
1295  */
1296 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1297 {
1298 	struct tcp_sock *tp = tcp_sk(sk);
1299 	struct inet_connection_sock *icsk = inet_csk(sk);
1300 	int mss_now;
1301 
1302 	if (icsk->icsk_mtup.search_high > pmtu)
1303 		icsk->icsk_mtup.search_high = pmtu;
1304 
1305 	mss_now = tcp_mtu_to_mss(sk, pmtu);
1306 	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1307 
1308 	/* And store cached results */
1309 	icsk->icsk_pmtu_cookie = pmtu;
1310 	if (icsk->icsk_mtup.enabled)
1311 		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1312 	tp->mss_cache = mss_now;
1313 
1314 	return mss_now;
1315 }
1316 EXPORT_SYMBOL(tcp_sync_mss);
1317 
1318 /* Compute the current effective MSS, taking SACKs and IP options,
1319  * and even PMTU discovery events into account.
1320  */
1321 unsigned int tcp_current_mss(struct sock *sk)
1322 {
1323 	const struct tcp_sock *tp = tcp_sk(sk);
1324 	const struct dst_entry *dst = __sk_dst_get(sk);
1325 	u32 mss_now;
1326 	unsigned int header_len;
1327 	struct tcp_out_options opts;
1328 	struct tcp_md5sig_key *md5;
1329 
1330 	mss_now = tp->mss_cache;
1331 
1332 	if (dst) {
1333 		u32 mtu = dst_mtu(dst);
1334 		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1335 			mss_now = tcp_sync_mss(sk, mtu);
1336 	}
1337 
1338 	header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1339 		     sizeof(struct tcphdr);
1340 	/* The mss_cache is sized based on tp->tcp_header_len, which assumes
1341 	 * some common options. If this is an odd packet (because we have SACK
1342 	 * blocks etc) then our calculated header_len will be different, and
1343 	 * we have to adjust mss_now correspondingly */
1344 	if (header_len != tp->tcp_header_len) {
1345 		int delta = (int) header_len - tp->tcp_header_len;
1346 		mss_now -= delta;
1347 	}
1348 
1349 	return mss_now;
1350 }
1351 
1352 /* Congestion window validation. (RFC2861) */
1353 static void tcp_cwnd_validate(struct sock *sk)
1354 {
1355 	struct tcp_sock *tp = tcp_sk(sk);
1356 
1357 	if (tp->packets_out >= tp->snd_cwnd) {
1358 		/* Network is feed fully. */
1359 		tp->snd_cwnd_used = 0;
1360 		tp->snd_cwnd_stamp = tcp_time_stamp;
1361 	} else {
1362 		/* Network starves. */
1363 		if (tp->packets_out > tp->snd_cwnd_used)
1364 			tp->snd_cwnd_used = tp->packets_out;
1365 
1366 		if (sysctl_tcp_slow_start_after_idle &&
1367 		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1368 			tcp_cwnd_application_limited(sk);
1369 	}
1370 }
1371 
1372 /* Returns the portion of skb which can be sent right away without
1373  * introducing MSS oddities to segment boundaries. In rare cases where
1374  * mss_now != mss_cache, we will request caller to create a small skb
1375  * per input skb which could be mostly avoided here (if desired).
1376  *
1377  * We explicitly want to create a request for splitting write queue tail
1378  * to a small skb for Nagle purposes while avoiding unnecessary modulos,
1379  * thus all the complexity (cwnd_len is always MSS multiple which we
1380  * return whenever allowed by the other factors). Basically we need the
1381  * modulo only when the receiver window alone is the limiting factor or
1382  * when we would be allowed to send the split-due-to-Nagle skb fully.
1383  */
1384 static unsigned int tcp_mss_split_point(const struct sock *sk, const struct sk_buff *skb,
1385 					unsigned int mss_now, unsigned int max_segs)
1386 {
1387 	const struct tcp_sock *tp = tcp_sk(sk);
1388 	u32 needed, window, max_len;
1389 
1390 	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1391 	max_len = mss_now * max_segs;
1392 
1393 	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1394 		return max_len;
1395 
1396 	needed = min(skb->len, window);
1397 
1398 	if (max_len <= needed)
1399 		return max_len;
1400 
1401 	return needed - needed % mss_now;
1402 }
1403 
1404 /* Can at least one segment of SKB be sent right now, according to the
1405  * congestion window rules?  If so, return how many segments are allowed.
1406  */
1407 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1408 					 const struct sk_buff *skb)
1409 {
1410 	u32 in_flight, cwnd;
1411 
1412 	/* Don't be strict about the congestion window for the final FIN.  */
1413 	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1414 	    tcp_skb_pcount(skb) == 1)
1415 		return 1;
1416 
1417 	in_flight = tcp_packets_in_flight(tp);
1418 	cwnd = tp->snd_cwnd;
1419 	if (in_flight < cwnd)
1420 		return (cwnd - in_flight);
1421 
1422 	return 0;
1423 }
1424 
1425 /* Initialize TSO state of a skb.
1426  * This must be invoked the first time we consider transmitting
1427  * SKB onto the wire.
1428  */
1429 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
1430 			     unsigned int mss_now)
1431 {
1432 	int tso_segs = tcp_skb_pcount(skb);
1433 
1434 	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1435 		tcp_set_skb_tso_segs(sk, skb, mss_now);
1436 		tso_segs = tcp_skb_pcount(skb);
1437 	}
1438 	return tso_segs;
1439 }
1440 
1441 /* Minshall's variant of the Nagle send check. */
1442 static inline bool tcp_minshall_check(const struct tcp_sock *tp)
1443 {
1444 	return after(tp->snd_sml, tp->snd_una) &&
1445 		!after(tp->snd_sml, tp->snd_nxt);
1446 }
1447 
1448 /* Return false, if packet can be sent now without violation Nagle's rules:
1449  * 1. It is full sized.
1450  * 2. Or it contains FIN. (already checked by caller)
1451  * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1452  * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1453  *    With Minshall's modification: all sent small packets are ACKed.
1454  */
1455 static inline bool tcp_nagle_check(const struct tcp_sock *tp,
1456 				  const struct sk_buff *skb,
1457 				  unsigned int mss_now, int nonagle)
1458 {
1459 	return skb->len < mss_now &&
1460 		((nonagle & TCP_NAGLE_CORK) ||
1461 		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1462 }
1463 
1464 /* Return true if the Nagle test allows this packet to be
1465  * sent now.
1466  */
1467 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1468 				  unsigned int cur_mss, int nonagle)
1469 {
1470 	/* Nagle rule does not apply to frames, which sit in the middle of the
1471 	 * write_queue (they have no chances to get new data).
1472 	 *
1473 	 * This is implemented in the callers, where they modify the 'nonagle'
1474 	 * argument based upon the location of SKB in the send queue.
1475 	 */
1476 	if (nonagle & TCP_NAGLE_PUSH)
1477 		return true;
1478 
1479 	/* Don't use the nagle rule for urgent data (or for the final FIN). */
1480 	if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1481 		return true;
1482 
1483 	if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
1484 		return true;
1485 
1486 	return false;
1487 }
1488 
1489 /* Does at least the first segment of SKB fit into the send window? */
1490 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1491 			     const struct sk_buff *skb,
1492 			     unsigned int cur_mss)
1493 {
1494 	u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1495 
1496 	if (skb->len > cur_mss)
1497 		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1498 
1499 	return !after(end_seq, tcp_wnd_end(tp));
1500 }
1501 
1502 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1503  * should be put on the wire right now.  If so, it returns the number of
1504  * packets allowed by the congestion window.
1505  */
1506 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1507 				 unsigned int cur_mss, int nonagle)
1508 {
1509 	const struct tcp_sock *tp = tcp_sk(sk);
1510 	unsigned int cwnd_quota;
1511 
1512 	tcp_init_tso_segs(sk, skb, cur_mss);
1513 
1514 	if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1515 		return 0;
1516 
1517 	cwnd_quota = tcp_cwnd_test(tp, skb);
1518 	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1519 		cwnd_quota = 0;
1520 
1521 	return cwnd_quota;
1522 }
1523 
1524 /* Test if sending is allowed right now. */
1525 bool tcp_may_send_now(struct sock *sk)
1526 {
1527 	const struct tcp_sock *tp = tcp_sk(sk);
1528 	struct sk_buff *skb = tcp_send_head(sk);
1529 
1530 	return skb &&
1531 		tcp_snd_test(sk, skb, tcp_current_mss(sk),
1532 			     (tcp_skb_is_last(sk, skb) ?
1533 			      tp->nonagle : TCP_NAGLE_PUSH));
1534 }
1535 
1536 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1537  * which is put after SKB on the list.  It is very much like
1538  * tcp_fragment() except that it may make several kinds of assumptions
1539  * in order to speed up the splitting operation.  In particular, we
1540  * know that all the data is in scatter-gather pages, and that the
1541  * packet has never been sent out before (and thus is not cloned).
1542  */
1543 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1544 			unsigned int mss_now, gfp_t gfp)
1545 {
1546 	struct sk_buff *buff;
1547 	int nlen = skb->len - len;
1548 	u8 flags;
1549 
1550 	/* All of a TSO frame must be composed of paged data.  */
1551 	if (skb->len != skb->data_len)
1552 		return tcp_fragment(sk, skb, len, mss_now);
1553 
1554 	buff = sk_stream_alloc_skb(sk, 0, gfp);
1555 	if (unlikely(buff == NULL))
1556 		return -ENOMEM;
1557 
1558 	sk->sk_wmem_queued += buff->truesize;
1559 	sk_mem_charge(sk, buff->truesize);
1560 	buff->truesize += nlen;
1561 	skb->truesize -= nlen;
1562 
1563 	/* Correct the sequence numbers. */
1564 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1565 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1566 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1567 
1568 	/* PSH and FIN should only be set in the second packet. */
1569 	flags = TCP_SKB_CB(skb)->tcp_flags;
1570 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1571 	TCP_SKB_CB(buff)->tcp_flags = flags;
1572 
1573 	/* This packet was never sent out yet, so no SACK bits. */
1574 	TCP_SKB_CB(buff)->sacked = 0;
1575 
1576 	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1577 	skb_split(skb, buff, len);
1578 
1579 	/* Fix up tso_factor for both original and new SKB.  */
1580 	tcp_set_skb_tso_segs(sk, skb, mss_now);
1581 	tcp_set_skb_tso_segs(sk, buff, mss_now);
1582 
1583 	/* Link BUFF into the send queue. */
1584 	skb_header_release(buff);
1585 	tcp_insert_write_queue_after(skb, buff, sk);
1586 
1587 	return 0;
1588 }
1589 
1590 /* Try to defer sending, if possible, in order to minimize the amount
1591  * of TSO splitting we do.  View it as a kind of TSO Nagle test.
1592  *
1593  * This algorithm is from John Heffner.
1594  */
1595 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1596 {
1597 	struct tcp_sock *tp = tcp_sk(sk);
1598 	const struct inet_connection_sock *icsk = inet_csk(sk);
1599 	u32 send_win, cong_win, limit, in_flight;
1600 	int win_divisor;
1601 
1602 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1603 		goto send_now;
1604 
1605 	if (icsk->icsk_ca_state != TCP_CA_Open)
1606 		goto send_now;
1607 
1608 	/* Defer for less than two clock ticks. */
1609 	if (tp->tso_deferred &&
1610 	    (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
1611 		goto send_now;
1612 
1613 	in_flight = tcp_packets_in_flight(tp);
1614 
1615 	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1616 
1617 	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1618 
1619 	/* From in_flight test above, we know that cwnd > in_flight.  */
1620 	cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1621 
1622 	limit = min(send_win, cong_win);
1623 
1624 	/* If a full-sized TSO skb can be sent, do it. */
1625 	if (limit >= min_t(unsigned int, sk->sk_gso_max_size,
1626 			   sk->sk_gso_max_segs * tp->mss_cache))
1627 		goto send_now;
1628 
1629 	/* Middle in queue won't get any more data, full sendable already? */
1630 	if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1631 		goto send_now;
1632 
1633 	win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1634 	if (win_divisor) {
1635 		u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1636 
1637 		/* If at least some fraction of a window is available,
1638 		 * just use it.
1639 		 */
1640 		chunk /= win_divisor;
1641 		if (limit >= chunk)
1642 			goto send_now;
1643 	} else {
1644 		/* Different approach, try not to defer past a single
1645 		 * ACK.  Receiver should ACK every other full sized
1646 		 * frame, so if we have space for more than 3 frames
1647 		 * then send now.
1648 		 */
1649 		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1650 			goto send_now;
1651 	}
1652 
1653 	/* Ok, it looks like it is advisable to defer.
1654 	 * Do not rearm the timer if already set to not break TCP ACK clocking.
1655 	 */
1656 	if (!tp->tso_deferred)
1657 		tp->tso_deferred = 1 | (jiffies << 1);
1658 
1659 	return true;
1660 
1661 send_now:
1662 	tp->tso_deferred = 0;
1663 	return false;
1664 }
1665 
1666 /* Create a new MTU probe if we are ready.
1667  * MTU probe is regularly attempting to increase the path MTU by
1668  * deliberately sending larger packets.  This discovers routing
1669  * changes resulting in larger path MTUs.
1670  *
1671  * Returns 0 if we should wait to probe (no cwnd available),
1672  *         1 if a probe was sent,
1673  *         -1 otherwise
1674  */
1675 static int tcp_mtu_probe(struct sock *sk)
1676 {
1677 	struct tcp_sock *tp = tcp_sk(sk);
1678 	struct inet_connection_sock *icsk = inet_csk(sk);
1679 	struct sk_buff *skb, *nskb, *next;
1680 	int len;
1681 	int probe_size;
1682 	int size_needed;
1683 	int copy;
1684 	int mss_now;
1685 
1686 	/* Not currently probing/verifying,
1687 	 * not in recovery,
1688 	 * have enough cwnd, and
1689 	 * not SACKing (the variable headers throw things off) */
1690 	if (!icsk->icsk_mtup.enabled ||
1691 	    icsk->icsk_mtup.probe_size ||
1692 	    inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1693 	    tp->snd_cwnd < 11 ||
1694 	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1695 		return -1;
1696 
1697 	/* Very simple search strategy: just double the MSS. */
1698 	mss_now = tcp_current_mss(sk);
1699 	probe_size = 2 * tp->mss_cache;
1700 	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1701 	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
1702 		/* TODO: set timer for probe_converge_event */
1703 		return -1;
1704 	}
1705 
1706 	/* Have enough data in the send queue to probe? */
1707 	if (tp->write_seq - tp->snd_nxt < size_needed)
1708 		return -1;
1709 
1710 	if (tp->snd_wnd < size_needed)
1711 		return -1;
1712 	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1713 		return 0;
1714 
1715 	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
1716 	if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1717 		if (!tcp_packets_in_flight(tp))
1718 			return -1;
1719 		else
1720 			return 0;
1721 	}
1722 
1723 	/* We're allowed to probe.  Build it now. */
1724 	if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
1725 		return -1;
1726 	sk->sk_wmem_queued += nskb->truesize;
1727 	sk_mem_charge(sk, nskb->truesize);
1728 
1729 	skb = tcp_send_head(sk);
1730 
1731 	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1732 	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1733 	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1734 	TCP_SKB_CB(nskb)->sacked = 0;
1735 	nskb->csum = 0;
1736 	nskb->ip_summed = skb->ip_summed;
1737 
1738 	tcp_insert_write_queue_before(nskb, skb, sk);
1739 
1740 	len = 0;
1741 	tcp_for_write_queue_from_safe(skb, next, sk) {
1742 		copy = min_t(int, skb->len, probe_size - len);
1743 		if (nskb->ip_summed)
1744 			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1745 		else
1746 			nskb->csum = skb_copy_and_csum_bits(skb, 0,
1747 							    skb_put(nskb, copy),
1748 							    copy, nskb->csum);
1749 
1750 		if (skb->len <= copy) {
1751 			/* We've eaten all the data from this skb.
1752 			 * Throw it away. */
1753 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1754 			tcp_unlink_write_queue(skb, sk);
1755 			sk_wmem_free_skb(sk, skb);
1756 		} else {
1757 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1758 						   ~(TCPHDR_FIN|TCPHDR_PSH);
1759 			if (!skb_shinfo(skb)->nr_frags) {
1760 				skb_pull(skb, copy);
1761 				if (skb->ip_summed != CHECKSUM_PARTIAL)
1762 					skb->csum = csum_partial(skb->data,
1763 								 skb->len, 0);
1764 			} else {
1765 				__pskb_trim_head(skb, copy);
1766 				tcp_set_skb_tso_segs(sk, skb, mss_now);
1767 			}
1768 			TCP_SKB_CB(skb)->seq += copy;
1769 		}
1770 
1771 		len += copy;
1772 
1773 		if (len >= probe_size)
1774 			break;
1775 	}
1776 	tcp_init_tso_segs(sk, nskb, nskb->len);
1777 
1778 	/* We're ready to send.  If this fails, the probe will
1779 	 * be resegmented into mss-sized pieces by tcp_write_xmit(). */
1780 	TCP_SKB_CB(nskb)->when = tcp_time_stamp;
1781 	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1782 		/* Decrement cwnd here because we are sending
1783 		 * effectively two packets. */
1784 		tp->snd_cwnd--;
1785 		tcp_event_new_data_sent(sk, nskb);
1786 
1787 		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1788 		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1789 		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1790 
1791 		return 1;
1792 	}
1793 
1794 	return -1;
1795 }
1796 
1797 /* This routine writes packets to the network.  It advances the
1798  * send_head.  This happens as incoming acks open up the remote
1799  * window for us.
1800  *
1801  * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1802  * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1803  * account rare use of URG, this is not a big flaw.
1804  *
1805  * Send at most one packet when push_one > 0. Temporarily ignore
1806  * cwnd limit to force at most one packet out when push_one == 2.
1807 
1808  * Returns true, if no segments are in flight and we have queued segments,
1809  * but cannot send anything now because of SWS or another problem.
1810  */
1811 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
1812 			   int push_one, gfp_t gfp)
1813 {
1814 	struct tcp_sock *tp = tcp_sk(sk);
1815 	struct sk_buff *skb;
1816 	unsigned int tso_segs, sent_pkts;
1817 	int cwnd_quota;
1818 	int result;
1819 
1820 	sent_pkts = 0;
1821 
1822 	if (!push_one) {
1823 		/* Do MTU probing. */
1824 		result = tcp_mtu_probe(sk);
1825 		if (!result) {
1826 			return false;
1827 		} else if (result > 0) {
1828 			sent_pkts = 1;
1829 		}
1830 	}
1831 
1832 	while ((skb = tcp_send_head(sk))) {
1833 		unsigned int limit;
1834 
1835 
1836 		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1837 		BUG_ON(!tso_segs);
1838 
1839 		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE)
1840 			goto repair; /* Skip network transmission */
1841 
1842 		cwnd_quota = tcp_cwnd_test(tp, skb);
1843 		if (!cwnd_quota) {
1844 			if (push_one == 2)
1845 				/* Force out a loss probe pkt. */
1846 				cwnd_quota = 1;
1847 			else
1848 				break;
1849 		}
1850 
1851 		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
1852 			break;
1853 
1854 		if (tso_segs == 1) {
1855 			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
1856 						     (tcp_skb_is_last(sk, skb) ?
1857 						      nonagle : TCP_NAGLE_PUSH))))
1858 				break;
1859 		} else {
1860 			if (!push_one && tcp_tso_should_defer(sk, skb))
1861 				break;
1862 		}
1863 
1864 		/* TSQ : sk_wmem_alloc accounts skb truesize,
1865 		 * including skb overhead. But thats OK.
1866 		 */
1867 		if (atomic_read(&sk->sk_wmem_alloc) >= sysctl_tcp_limit_output_bytes) {
1868 			set_bit(TSQ_THROTTLED, &tp->tsq_flags);
1869 			break;
1870 		}
1871 		limit = mss_now;
1872 		if (tso_segs > 1 && !tcp_urg_mode(tp))
1873 			limit = tcp_mss_split_point(sk, skb, mss_now,
1874 						    min_t(unsigned int,
1875 							  cwnd_quota,
1876 							  sk->sk_gso_max_segs));
1877 
1878 		if (skb->len > limit &&
1879 		    unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
1880 			break;
1881 
1882 		TCP_SKB_CB(skb)->when = tcp_time_stamp;
1883 
1884 		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
1885 			break;
1886 
1887 repair:
1888 		/* Advance the send_head.  This one is sent out.
1889 		 * This call will increment packets_out.
1890 		 */
1891 		tcp_event_new_data_sent(sk, skb);
1892 
1893 		tcp_minshall_update(tp, mss_now, skb);
1894 		sent_pkts += tcp_skb_pcount(skb);
1895 
1896 		if (push_one)
1897 			break;
1898 	}
1899 
1900 	if (likely(sent_pkts)) {
1901 		if (tcp_in_cwnd_reduction(sk))
1902 			tp->prr_out += sent_pkts;
1903 
1904 		/* Send one loss probe per tail loss episode. */
1905 		if (push_one != 2)
1906 			tcp_schedule_loss_probe(sk);
1907 		tcp_cwnd_validate(sk);
1908 		return false;
1909 	}
1910 	return (push_one == 2) || (!tp->packets_out && tcp_send_head(sk));
1911 }
1912 
1913 bool tcp_schedule_loss_probe(struct sock *sk)
1914 {
1915 	struct inet_connection_sock *icsk = inet_csk(sk);
1916 	struct tcp_sock *tp = tcp_sk(sk);
1917 	u32 timeout, tlp_time_stamp, rto_time_stamp;
1918 	u32 rtt = tp->srtt >> 3;
1919 
1920 	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
1921 		return false;
1922 	/* No consecutive loss probes. */
1923 	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
1924 		tcp_rearm_rto(sk);
1925 		return false;
1926 	}
1927 	/* Don't do any loss probe on a Fast Open connection before 3WHS
1928 	 * finishes.
1929 	 */
1930 	if (sk->sk_state == TCP_SYN_RECV)
1931 		return false;
1932 
1933 	/* TLP is only scheduled when next timer event is RTO. */
1934 	if (icsk->icsk_pending != ICSK_TIME_RETRANS)
1935 		return false;
1936 
1937 	/* Schedule a loss probe in 2*RTT for SACK capable connections
1938 	 * in Open state, that are either limited by cwnd or application.
1939 	 */
1940 	if (sysctl_tcp_early_retrans < 3 || !rtt || !tp->packets_out ||
1941 	    !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
1942 		return false;
1943 
1944 	if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
1945 	     tcp_send_head(sk))
1946 		return false;
1947 
1948 	/* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
1949 	 * for delayed ack when there's one outstanding packet.
1950 	 */
1951 	timeout = rtt << 1;
1952 	if (tp->packets_out == 1)
1953 		timeout = max_t(u32, timeout,
1954 				(rtt + (rtt >> 1) + TCP_DELACK_MAX));
1955 	timeout = max_t(u32, timeout, msecs_to_jiffies(10));
1956 
1957 	/* If RTO is shorter, just schedule TLP in its place. */
1958 	tlp_time_stamp = tcp_time_stamp + timeout;
1959 	rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
1960 	if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
1961 		s32 delta = rto_time_stamp - tcp_time_stamp;
1962 		if (delta > 0)
1963 			timeout = delta;
1964 	}
1965 
1966 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
1967 				  TCP_RTO_MAX);
1968 	return true;
1969 }
1970 
1971 /* When probe timeout (PTO) fires, send a new segment if one exists, else
1972  * retransmit the last segment.
1973  */
1974 void tcp_send_loss_probe(struct sock *sk)
1975 {
1976 	struct tcp_sock *tp = tcp_sk(sk);
1977 	struct sk_buff *skb;
1978 	int pcount;
1979 	int mss = tcp_current_mss(sk);
1980 	int err = -1;
1981 
1982 	if (tcp_send_head(sk) != NULL) {
1983 		err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
1984 		goto rearm_timer;
1985 	}
1986 
1987 	/* At most one outstanding TLP retransmission. */
1988 	if (tp->tlp_high_seq)
1989 		goto rearm_timer;
1990 
1991 	/* Retransmit last segment. */
1992 	skb = tcp_write_queue_tail(sk);
1993 	if (WARN_ON(!skb))
1994 		goto rearm_timer;
1995 
1996 	pcount = tcp_skb_pcount(skb);
1997 	if (WARN_ON(!pcount))
1998 		goto rearm_timer;
1999 
2000 	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2001 		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss)))
2002 			goto rearm_timer;
2003 		skb = tcp_write_queue_tail(sk);
2004 	}
2005 
2006 	if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2007 		goto rearm_timer;
2008 
2009 	/* Probe with zero data doesn't trigger fast recovery. */
2010 	if (skb->len > 0)
2011 		err = __tcp_retransmit_skb(sk, skb);
2012 
2013 	/* Record snd_nxt for loss detection. */
2014 	if (likely(!err))
2015 		tp->tlp_high_seq = tp->snd_nxt;
2016 
2017 rearm_timer:
2018 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2019 				  inet_csk(sk)->icsk_rto,
2020 				  TCP_RTO_MAX);
2021 
2022 	if (likely(!err))
2023 		NET_INC_STATS_BH(sock_net(sk),
2024 				 LINUX_MIB_TCPLOSSPROBES);
2025 	return;
2026 }
2027 
2028 /* Push out any pending frames which were held back due to
2029  * TCP_CORK or attempt at coalescing tiny packets.
2030  * The socket must be locked by the caller.
2031  */
2032 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2033 			       int nonagle)
2034 {
2035 	/* If we are closed, the bytes will have to remain here.
2036 	 * In time closedown will finish, we empty the write queue and
2037 	 * all will be happy.
2038 	 */
2039 	if (unlikely(sk->sk_state == TCP_CLOSE))
2040 		return;
2041 
2042 	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2043 			   sk_gfp_atomic(sk, GFP_ATOMIC)))
2044 		tcp_check_probe_timer(sk);
2045 }
2046 
2047 /* Send _single_ skb sitting at the send head. This function requires
2048  * true push pending frames to setup probe timer etc.
2049  */
2050 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2051 {
2052 	struct sk_buff *skb = tcp_send_head(sk);
2053 
2054 	BUG_ON(!skb || skb->len < mss_now);
2055 
2056 	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2057 }
2058 
2059 /* This function returns the amount that we can raise the
2060  * usable window based on the following constraints
2061  *
2062  * 1. The window can never be shrunk once it is offered (RFC 793)
2063  * 2. We limit memory per socket
2064  *
2065  * RFC 1122:
2066  * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2067  *  RECV.NEXT + RCV.WIN fixed until:
2068  *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2069  *
2070  * i.e. don't raise the right edge of the window until you can raise
2071  * it at least MSS bytes.
2072  *
2073  * Unfortunately, the recommended algorithm breaks header prediction,
2074  * since header prediction assumes th->window stays fixed.
2075  *
2076  * Strictly speaking, keeping th->window fixed violates the receiver
2077  * side SWS prevention criteria. The problem is that under this rule
2078  * a stream of single byte packets will cause the right side of the
2079  * window to always advance by a single byte.
2080  *
2081  * Of course, if the sender implements sender side SWS prevention
2082  * then this will not be a problem.
2083  *
2084  * BSD seems to make the following compromise:
2085  *
2086  *	If the free space is less than the 1/4 of the maximum
2087  *	space available and the free space is less than 1/2 mss,
2088  *	then set the window to 0.
2089  *	[ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2090  *	Otherwise, just prevent the window from shrinking
2091  *	and from being larger than the largest representable value.
2092  *
2093  * This prevents incremental opening of the window in the regime
2094  * where TCP is limited by the speed of the reader side taking
2095  * data out of the TCP receive queue. It does nothing about
2096  * those cases where the window is constrained on the sender side
2097  * because the pipeline is full.
2098  *
2099  * BSD also seems to "accidentally" limit itself to windows that are a
2100  * multiple of MSS, at least until the free space gets quite small.
2101  * This would appear to be a side effect of the mbuf implementation.
2102  * Combining these two algorithms results in the observed behavior
2103  * of having a fixed window size at almost all times.
2104  *
2105  * Below we obtain similar behavior by forcing the offered window to
2106  * a multiple of the mss when it is feasible to do so.
2107  *
2108  * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2109  * Regular options like TIMESTAMP are taken into account.
2110  */
2111 u32 __tcp_select_window(struct sock *sk)
2112 {
2113 	struct inet_connection_sock *icsk = inet_csk(sk);
2114 	struct tcp_sock *tp = tcp_sk(sk);
2115 	/* MSS for the peer's data.  Previous versions used mss_clamp
2116 	 * here.  I don't know if the value based on our guesses
2117 	 * of peer's MSS is better for the performance.  It's more correct
2118 	 * but may be worse for the performance because of rcv_mss
2119 	 * fluctuations.  --SAW  1998/11/1
2120 	 */
2121 	int mss = icsk->icsk_ack.rcv_mss;
2122 	int free_space = tcp_space(sk);
2123 	int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
2124 	int window;
2125 
2126 	if (mss > full_space)
2127 		mss = full_space;
2128 
2129 	if (free_space < (full_space >> 1)) {
2130 		icsk->icsk_ack.quick = 0;
2131 
2132 		if (sk_under_memory_pressure(sk))
2133 			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2134 					       4U * tp->advmss);
2135 
2136 		if (free_space < mss)
2137 			return 0;
2138 	}
2139 
2140 	if (free_space > tp->rcv_ssthresh)
2141 		free_space = tp->rcv_ssthresh;
2142 
2143 	/* Don't do rounding if we are using window scaling, since the
2144 	 * scaled window will not line up with the MSS boundary anyway.
2145 	 */
2146 	window = tp->rcv_wnd;
2147 	if (tp->rx_opt.rcv_wscale) {
2148 		window = free_space;
2149 
2150 		/* Advertise enough space so that it won't get scaled away.
2151 		 * Import case: prevent zero window announcement if
2152 		 * 1<<rcv_wscale > mss.
2153 		 */
2154 		if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2155 			window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2156 				  << tp->rx_opt.rcv_wscale);
2157 	} else {
2158 		/* Get the largest window that is a nice multiple of mss.
2159 		 * Window clamp already applied above.
2160 		 * If our current window offering is within 1 mss of the
2161 		 * free space we just keep it. This prevents the divide
2162 		 * and multiply from happening most of the time.
2163 		 * We also don't do any window rounding when the free space
2164 		 * is too small.
2165 		 */
2166 		if (window <= free_space - mss || window > free_space)
2167 			window = (free_space / mss) * mss;
2168 		else if (mss == full_space &&
2169 			 free_space > window + (full_space >> 1))
2170 			window = free_space;
2171 	}
2172 
2173 	return window;
2174 }
2175 
2176 /* Collapses two adjacent SKB's during retransmission. */
2177 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2178 {
2179 	struct tcp_sock *tp = tcp_sk(sk);
2180 	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2181 	int skb_size, next_skb_size;
2182 
2183 	skb_size = skb->len;
2184 	next_skb_size = next_skb->len;
2185 
2186 	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2187 
2188 	tcp_highest_sack_combine(sk, next_skb, skb);
2189 
2190 	tcp_unlink_write_queue(next_skb, sk);
2191 
2192 	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2193 				  next_skb_size);
2194 
2195 	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2196 		skb->ip_summed = CHECKSUM_PARTIAL;
2197 
2198 	if (skb->ip_summed != CHECKSUM_PARTIAL)
2199 		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2200 
2201 	/* Update sequence range on original skb. */
2202 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2203 
2204 	/* Merge over control information. This moves PSH/FIN etc. over */
2205 	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2206 
2207 	/* All done, get rid of second SKB and account for it so
2208 	 * packet counting does not break.
2209 	 */
2210 	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2211 
2212 	/* changed transmit queue under us so clear hints */
2213 	tcp_clear_retrans_hints_partial(tp);
2214 	if (next_skb == tp->retransmit_skb_hint)
2215 		tp->retransmit_skb_hint = skb;
2216 
2217 	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2218 
2219 	sk_wmem_free_skb(sk, next_skb);
2220 }
2221 
2222 /* Check if coalescing SKBs is legal. */
2223 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2224 {
2225 	if (tcp_skb_pcount(skb) > 1)
2226 		return false;
2227 	/* TODO: SACK collapsing could be used to remove this condition */
2228 	if (skb_shinfo(skb)->nr_frags != 0)
2229 		return false;
2230 	if (skb_cloned(skb))
2231 		return false;
2232 	if (skb == tcp_send_head(sk))
2233 		return false;
2234 	/* Some heurestics for collapsing over SACK'd could be invented */
2235 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2236 		return false;
2237 
2238 	return true;
2239 }
2240 
2241 /* Collapse packets in the retransmit queue to make to create
2242  * less packets on the wire. This is only done on retransmission.
2243  */
2244 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2245 				     int space)
2246 {
2247 	struct tcp_sock *tp = tcp_sk(sk);
2248 	struct sk_buff *skb = to, *tmp;
2249 	bool first = true;
2250 
2251 	if (!sysctl_tcp_retrans_collapse)
2252 		return;
2253 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2254 		return;
2255 
2256 	tcp_for_write_queue_from_safe(skb, tmp, sk) {
2257 		if (!tcp_can_collapse(sk, skb))
2258 			break;
2259 
2260 		space -= skb->len;
2261 
2262 		if (first) {
2263 			first = false;
2264 			continue;
2265 		}
2266 
2267 		if (space < 0)
2268 			break;
2269 		/* Punt if not enough space exists in the first SKB for
2270 		 * the data in the second
2271 		 */
2272 		if (skb->len > skb_availroom(to))
2273 			break;
2274 
2275 		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2276 			break;
2277 
2278 		tcp_collapse_retrans(sk, to);
2279 	}
2280 }
2281 
2282 /* This retransmits one SKB.  Policy decisions and retransmit queue
2283  * state updates are done by the caller.  Returns non-zero if an
2284  * error occurred which prevented the send.
2285  */
2286 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2287 {
2288 	struct tcp_sock *tp = tcp_sk(sk);
2289 	struct inet_connection_sock *icsk = inet_csk(sk);
2290 	unsigned int cur_mss;
2291 
2292 	/* Inconslusive MTU probe */
2293 	if (icsk->icsk_mtup.probe_size) {
2294 		icsk->icsk_mtup.probe_size = 0;
2295 	}
2296 
2297 	/* Do not sent more than we queued. 1/4 is reserved for possible
2298 	 * copying overhead: fragmentation, tunneling, mangling etc.
2299 	 */
2300 	if (atomic_read(&sk->sk_wmem_alloc) >
2301 	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2302 		return -EAGAIN;
2303 
2304 	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2305 		if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2306 			BUG();
2307 		if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2308 			return -ENOMEM;
2309 	}
2310 
2311 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2312 		return -EHOSTUNREACH; /* Routing failure or similar. */
2313 
2314 	cur_mss = tcp_current_mss(sk);
2315 
2316 	/* If receiver has shrunk his window, and skb is out of
2317 	 * new window, do not retransmit it. The exception is the
2318 	 * case, when window is shrunk to zero. In this case
2319 	 * our retransmit serves as a zero window probe.
2320 	 */
2321 	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2322 	    TCP_SKB_CB(skb)->seq != tp->snd_una)
2323 		return -EAGAIN;
2324 
2325 	if (skb->len > cur_mss) {
2326 		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
2327 			return -ENOMEM; /* We'll try again later. */
2328 	} else {
2329 		int oldpcount = tcp_skb_pcount(skb);
2330 
2331 		if (unlikely(oldpcount > 1)) {
2332 			tcp_init_tso_segs(sk, skb, cur_mss);
2333 			tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2334 		}
2335 	}
2336 
2337 	tcp_retrans_try_collapse(sk, skb, cur_mss);
2338 
2339 	/* Some Solaris stacks overoptimize and ignore the FIN on a
2340 	 * retransmit when old data is attached.  So strip it off
2341 	 * since it is cheap to do so and saves bytes on the network.
2342 	 */
2343 	if (skb->len > 0 &&
2344 	    (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
2345 	    tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
2346 		if (!pskb_trim(skb, 0)) {
2347 			/* Reuse, even though it does some unnecessary work */
2348 			tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1,
2349 					     TCP_SKB_CB(skb)->tcp_flags);
2350 			skb->ip_summed = CHECKSUM_NONE;
2351 		}
2352 	}
2353 
2354 	/* Make a copy, if the first transmission SKB clone we made
2355 	 * is still in somebody's hands, else make a clone.
2356 	 */
2357 	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2358 
2359 	/* make sure skb->data is aligned on arches that require it
2360 	 * and check if ack-trimming & collapsing extended the headroom
2361 	 * beyond what csum_start can cover.
2362 	 */
2363 	if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2364 		     skb_headroom(skb) >= 0xFFFF)) {
2365 		struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2366 						   GFP_ATOMIC);
2367 		return nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2368 			      -ENOBUFS;
2369 	} else {
2370 		return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2371 	}
2372 }
2373 
2374 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2375 {
2376 	struct tcp_sock *tp = tcp_sk(sk);
2377 	int err = __tcp_retransmit_skb(sk, skb);
2378 
2379 	if (err == 0) {
2380 		/* Update global TCP statistics. */
2381 		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2382 
2383 		tp->total_retrans++;
2384 
2385 #if FASTRETRANS_DEBUG > 0
2386 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2387 			net_dbg_ratelimited("retrans_out leaked\n");
2388 		}
2389 #endif
2390 		if (!tp->retrans_out)
2391 			tp->lost_retrans_low = tp->snd_nxt;
2392 		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2393 		tp->retrans_out += tcp_skb_pcount(skb);
2394 
2395 		/* Save stamp of the first retransmit. */
2396 		if (!tp->retrans_stamp)
2397 			tp->retrans_stamp = TCP_SKB_CB(skb)->when;
2398 
2399 		tp->undo_retrans += tcp_skb_pcount(skb);
2400 
2401 		/* snd_nxt is stored to detect loss of retransmitted segment,
2402 		 * see tcp_input.c tcp_sacktag_write_queue().
2403 		 */
2404 		TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2405 	}
2406 	return err;
2407 }
2408 
2409 /* Check if we forward retransmits are possible in the current
2410  * window/congestion state.
2411  */
2412 static bool tcp_can_forward_retransmit(struct sock *sk)
2413 {
2414 	const struct inet_connection_sock *icsk = inet_csk(sk);
2415 	const struct tcp_sock *tp = tcp_sk(sk);
2416 
2417 	/* Forward retransmissions are possible only during Recovery. */
2418 	if (icsk->icsk_ca_state != TCP_CA_Recovery)
2419 		return false;
2420 
2421 	/* No forward retransmissions in Reno are possible. */
2422 	if (tcp_is_reno(tp))
2423 		return false;
2424 
2425 	/* Yeah, we have to make difficult choice between forward transmission
2426 	 * and retransmission... Both ways have their merits...
2427 	 *
2428 	 * For now we do not retransmit anything, while we have some new
2429 	 * segments to send. In the other cases, follow rule 3 for
2430 	 * NextSeg() specified in RFC3517.
2431 	 */
2432 
2433 	if (tcp_may_send_now(sk))
2434 		return false;
2435 
2436 	return true;
2437 }
2438 
2439 /* This gets called after a retransmit timeout, and the initially
2440  * retransmitted data is acknowledged.  It tries to continue
2441  * resending the rest of the retransmit queue, until either
2442  * we've sent it all or the congestion window limit is reached.
2443  * If doing SACK, the first ACK which comes back for a timeout
2444  * based retransmit packet might feed us FACK information again.
2445  * If so, we use it to avoid unnecessarily retransmissions.
2446  */
2447 void tcp_xmit_retransmit_queue(struct sock *sk)
2448 {
2449 	const struct inet_connection_sock *icsk = inet_csk(sk);
2450 	struct tcp_sock *tp = tcp_sk(sk);
2451 	struct sk_buff *skb;
2452 	struct sk_buff *hole = NULL;
2453 	u32 last_lost;
2454 	int mib_idx;
2455 	int fwd_rexmitting = 0;
2456 
2457 	if (!tp->packets_out)
2458 		return;
2459 
2460 	if (!tp->lost_out)
2461 		tp->retransmit_high = tp->snd_una;
2462 
2463 	if (tp->retransmit_skb_hint) {
2464 		skb = tp->retransmit_skb_hint;
2465 		last_lost = TCP_SKB_CB(skb)->end_seq;
2466 		if (after(last_lost, tp->retransmit_high))
2467 			last_lost = tp->retransmit_high;
2468 	} else {
2469 		skb = tcp_write_queue_head(sk);
2470 		last_lost = tp->snd_una;
2471 	}
2472 
2473 	tcp_for_write_queue_from(skb, sk) {
2474 		__u8 sacked = TCP_SKB_CB(skb)->sacked;
2475 
2476 		if (skb == tcp_send_head(sk))
2477 			break;
2478 		/* we could do better than to assign each time */
2479 		if (hole == NULL)
2480 			tp->retransmit_skb_hint = skb;
2481 
2482 		/* Assume this retransmit will generate
2483 		 * only one packet for congestion window
2484 		 * calculation purposes.  This works because
2485 		 * tcp_retransmit_skb() will chop up the
2486 		 * packet to be MSS sized and all the
2487 		 * packet counting works out.
2488 		 */
2489 		if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2490 			return;
2491 
2492 		if (fwd_rexmitting) {
2493 begin_fwd:
2494 			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2495 				break;
2496 			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2497 
2498 		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2499 			tp->retransmit_high = last_lost;
2500 			if (!tcp_can_forward_retransmit(sk))
2501 				break;
2502 			/* Backtrack if necessary to non-L'ed skb */
2503 			if (hole != NULL) {
2504 				skb = hole;
2505 				hole = NULL;
2506 			}
2507 			fwd_rexmitting = 1;
2508 			goto begin_fwd;
2509 
2510 		} else if (!(sacked & TCPCB_LOST)) {
2511 			if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2512 				hole = skb;
2513 			continue;
2514 
2515 		} else {
2516 			last_lost = TCP_SKB_CB(skb)->end_seq;
2517 			if (icsk->icsk_ca_state != TCP_CA_Loss)
2518 				mib_idx = LINUX_MIB_TCPFASTRETRANS;
2519 			else
2520 				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2521 		}
2522 
2523 		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2524 			continue;
2525 
2526 		if (tcp_retransmit_skb(sk, skb)) {
2527 			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2528 			return;
2529 		}
2530 		NET_INC_STATS_BH(sock_net(sk), mib_idx);
2531 
2532 		if (tcp_in_cwnd_reduction(sk))
2533 			tp->prr_out += tcp_skb_pcount(skb);
2534 
2535 		if (skb == tcp_write_queue_head(sk))
2536 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2537 						  inet_csk(sk)->icsk_rto,
2538 						  TCP_RTO_MAX);
2539 	}
2540 }
2541 
2542 /* Send a fin.  The caller locks the socket for us.  This cannot be
2543  * allowed to fail queueing a FIN frame under any circumstances.
2544  */
2545 void tcp_send_fin(struct sock *sk)
2546 {
2547 	struct tcp_sock *tp = tcp_sk(sk);
2548 	struct sk_buff *skb = tcp_write_queue_tail(sk);
2549 	int mss_now;
2550 
2551 	/* Optimization, tack on the FIN if we have a queue of
2552 	 * unsent frames.  But be careful about outgoing SACKS
2553 	 * and IP options.
2554 	 */
2555 	mss_now = tcp_current_mss(sk);
2556 
2557 	if (tcp_send_head(sk) != NULL) {
2558 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
2559 		TCP_SKB_CB(skb)->end_seq++;
2560 		tp->write_seq++;
2561 	} else {
2562 		/* Socket is locked, keep trying until memory is available. */
2563 		for (;;) {
2564 			skb = alloc_skb_fclone(MAX_TCP_HEADER,
2565 					       sk->sk_allocation);
2566 			if (skb)
2567 				break;
2568 			yield();
2569 		}
2570 
2571 		/* Reserve space for headers and prepare control bits. */
2572 		skb_reserve(skb, MAX_TCP_HEADER);
2573 		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2574 		tcp_init_nondata_skb(skb, tp->write_seq,
2575 				     TCPHDR_ACK | TCPHDR_FIN);
2576 		tcp_queue_skb(sk, skb);
2577 	}
2578 	__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
2579 }
2580 
2581 /* We get here when a process closes a file descriptor (either due to
2582  * an explicit close() or as a byproduct of exit()'ing) and there
2583  * was unread data in the receive queue.  This behavior is recommended
2584  * by RFC 2525, section 2.17.  -DaveM
2585  */
2586 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2587 {
2588 	struct sk_buff *skb;
2589 
2590 	/* NOTE: No TCP options attached and we never retransmit this. */
2591 	skb = alloc_skb(MAX_TCP_HEADER, priority);
2592 	if (!skb) {
2593 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2594 		return;
2595 	}
2596 
2597 	/* Reserve space for headers and prepare control bits. */
2598 	skb_reserve(skb, MAX_TCP_HEADER);
2599 	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2600 			     TCPHDR_ACK | TCPHDR_RST);
2601 	/* Send it off. */
2602 	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2603 	if (tcp_transmit_skb(sk, skb, 0, priority))
2604 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2605 
2606 	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2607 }
2608 
2609 /* Send a crossed SYN-ACK during socket establishment.
2610  * WARNING: This routine must only be called when we have already sent
2611  * a SYN packet that crossed the incoming SYN that caused this routine
2612  * to get called. If this assumption fails then the initial rcv_wnd
2613  * and rcv_wscale values will not be correct.
2614  */
2615 int tcp_send_synack(struct sock *sk)
2616 {
2617 	struct sk_buff *skb;
2618 
2619 	skb = tcp_write_queue_head(sk);
2620 	if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2621 		pr_debug("%s: wrong queue state\n", __func__);
2622 		return -EFAULT;
2623 	}
2624 	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2625 		if (skb_cloned(skb)) {
2626 			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2627 			if (nskb == NULL)
2628 				return -ENOMEM;
2629 			tcp_unlink_write_queue(skb, sk);
2630 			skb_header_release(nskb);
2631 			__tcp_add_write_queue_head(sk, nskb);
2632 			sk_wmem_free_skb(sk, skb);
2633 			sk->sk_wmem_queued += nskb->truesize;
2634 			sk_mem_charge(sk, nskb->truesize);
2635 			skb = nskb;
2636 		}
2637 
2638 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2639 		TCP_ECN_send_synack(tcp_sk(sk), skb);
2640 	}
2641 	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2642 	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2643 }
2644 
2645 /**
2646  * tcp_make_synack - Prepare a SYN-ACK.
2647  * sk: listener socket
2648  * dst: dst entry attached to the SYNACK
2649  * req: request_sock pointer
2650  *
2651  * Allocate one skb and build a SYNACK packet.
2652  * @dst is consumed : Caller should not use it again.
2653  */
2654 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2655 				struct request_sock *req,
2656 				struct tcp_fastopen_cookie *foc)
2657 {
2658 	struct tcp_out_options opts;
2659 	struct inet_request_sock *ireq = inet_rsk(req);
2660 	struct tcp_sock *tp = tcp_sk(sk);
2661 	struct tcphdr *th;
2662 	struct sk_buff *skb;
2663 	struct tcp_md5sig_key *md5;
2664 	int tcp_header_size;
2665 	int mss;
2666 
2667 	skb = alloc_skb(MAX_TCP_HEADER + 15, sk_gfp_atomic(sk, GFP_ATOMIC));
2668 	if (unlikely(!skb)) {
2669 		dst_release(dst);
2670 		return NULL;
2671 	}
2672 	/* Reserve space for headers. */
2673 	skb_reserve(skb, MAX_TCP_HEADER);
2674 
2675 	skb_dst_set(skb, dst);
2676 	security_skb_owned_by(skb, sk);
2677 
2678 	mss = dst_metric_advmss(dst);
2679 	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2680 		mss = tp->rx_opt.user_mss;
2681 
2682 	if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
2683 		__u8 rcv_wscale;
2684 		/* Set this up on the first call only */
2685 		req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
2686 
2687 		/* limit the window selection if the user enforce a smaller rx buffer */
2688 		if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2689 		    (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
2690 			req->window_clamp = tcp_full_space(sk);
2691 
2692 		/* tcp_full_space because it is guaranteed to be the first packet */
2693 		tcp_select_initial_window(tcp_full_space(sk),
2694 			mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
2695 			&req->rcv_wnd,
2696 			&req->window_clamp,
2697 			ireq->wscale_ok,
2698 			&rcv_wscale,
2699 			dst_metric(dst, RTAX_INITRWND));
2700 		ireq->rcv_wscale = rcv_wscale;
2701 	}
2702 
2703 	memset(&opts, 0, sizeof(opts));
2704 #ifdef CONFIG_SYN_COOKIES
2705 	if (unlikely(req->cookie_ts))
2706 		TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
2707 	else
2708 #endif
2709 	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2710 	tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, &md5,
2711 					     foc) + sizeof(*th);
2712 
2713 	skb_push(skb, tcp_header_size);
2714 	skb_reset_transport_header(skb);
2715 
2716 	th = tcp_hdr(skb);
2717 	memset(th, 0, sizeof(struct tcphdr));
2718 	th->syn = 1;
2719 	th->ack = 1;
2720 	TCP_ECN_make_synack(req, th);
2721 	th->source = ireq->loc_port;
2722 	th->dest = ireq->rmt_port;
2723 	/* Setting of flags are superfluous here for callers (and ECE is
2724 	 * not even correctly set)
2725 	 */
2726 	tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
2727 			     TCPHDR_SYN | TCPHDR_ACK);
2728 
2729 	th->seq = htonl(TCP_SKB_CB(skb)->seq);
2730 	/* XXX data is queued and acked as is. No buffer/window check */
2731 	th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
2732 
2733 	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2734 	th->window = htons(min(req->rcv_wnd, 65535U));
2735 	tcp_options_write((__be32 *)(th + 1), tp, &opts);
2736 	th->doff = (tcp_header_size >> 2);
2737 	TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb));
2738 
2739 #ifdef CONFIG_TCP_MD5SIG
2740 	/* Okay, we have all we need - do the md5 hash if needed */
2741 	if (md5) {
2742 		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
2743 					       md5, NULL, req, skb);
2744 	}
2745 #endif
2746 
2747 	return skb;
2748 }
2749 EXPORT_SYMBOL(tcp_make_synack);
2750 
2751 /* Do all connect socket setups that can be done AF independent. */
2752 void tcp_connect_init(struct sock *sk)
2753 {
2754 	const struct dst_entry *dst = __sk_dst_get(sk);
2755 	struct tcp_sock *tp = tcp_sk(sk);
2756 	__u8 rcv_wscale;
2757 
2758 	/* We'll fix this up when we get a response from the other end.
2759 	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2760 	 */
2761 	tp->tcp_header_len = sizeof(struct tcphdr) +
2762 		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
2763 
2764 #ifdef CONFIG_TCP_MD5SIG
2765 	if (tp->af_specific->md5_lookup(sk, sk) != NULL)
2766 		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
2767 #endif
2768 
2769 	/* If user gave his TCP_MAXSEG, record it to clamp */
2770 	if (tp->rx_opt.user_mss)
2771 		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2772 	tp->max_window = 0;
2773 	tcp_mtup_init(sk);
2774 	tcp_sync_mss(sk, dst_mtu(dst));
2775 
2776 	if (!tp->window_clamp)
2777 		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
2778 	tp->advmss = dst_metric_advmss(dst);
2779 	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
2780 		tp->advmss = tp->rx_opt.user_mss;
2781 
2782 	tcp_initialize_rcv_mss(sk);
2783 
2784 	/* limit the window selection if the user enforce a smaller rx buffer */
2785 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2786 	    (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
2787 		tp->window_clamp = tcp_full_space(sk);
2788 
2789 	tcp_select_initial_window(tcp_full_space(sk),
2790 				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
2791 				  &tp->rcv_wnd,
2792 				  &tp->window_clamp,
2793 				  sysctl_tcp_window_scaling,
2794 				  &rcv_wscale,
2795 				  dst_metric(dst, RTAX_INITRWND));
2796 
2797 	tp->rx_opt.rcv_wscale = rcv_wscale;
2798 	tp->rcv_ssthresh = tp->rcv_wnd;
2799 
2800 	sk->sk_err = 0;
2801 	sock_reset_flag(sk, SOCK_DONE);
2802 	tp->snd_wnd = 0;
2803 	tcp_init_wl(tp, 0);
2804 	tp->snd_una = tp->write_seq;
2805 	tp->snd_sml = tp->write_seq;
2806 	tp->snd_up = tp->write_seq;
2807 	tp->snd_nxt = tp->write_seq;
2808 
2809 	if (likely(!tp->repair))
2810 		tp->rcv_nxt = 0;
2811 	tp->rcv_wup = tp->rcv_nxt;
2812 	tp->copied_seq = tp->rcv_nxt;
2813 
2814 	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
2815 	inet_csk(sk)->icsk_retransmits = 0;
2816 	tcp_clear_retrans(tp);
2817 }
2818 
2819 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
2820 {
2821 	struct tcp_sock *tp = tcp_sk(sk);
2822 	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
2823 
2824 	tcb->end_seq += skb->len;
2825 	skb_header_release(skb);
2826 	__tcp_add_write_queue_tail(sk, skb);
2827 	sk->sk_wmem_queued += skb->truesize;
2828 	sk_mem_charge(sk, skb->truesize);
2829 	tp->write_seq = tcb->end_seq;
2830 	tp->packets_out += tcp_skb_pcount(skb);
2831 }
2832 
2833 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
2834  * queue a data-only packet after the regular SYN, such that regular SYNs
2835  * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
2836  * only the SYN sequence, the data are retransmitted in the first ACK.
2837  * If cookie is not cached or other error occurs, falls back to send a
2838  * regular SYN with Fast Open cookie request option.
2839  */
2840 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
2841 {
2842 	struct tcp_sock *tp = tcp_sk(sk);
2843 	struct tcp_fastopen_request *fo = tp->fastopen_req;
2844 	int syn_loss = 0, space, i, err = 0, iovlen = fo->data->msg_iovlen;
2845 	struct sk_buff *syn_data = NULL, *data;
2846 	unsigned long last_syn_loss = 0;
2847 
2848 	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
2849 	tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
2850 			       &syn_loss, &last_syn_loss);
2851 	/* Recurring FO SYN losses: revert to regular handshake temporarily */
2852 	if (syn_loss > 1 &&
2853 	    time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
2854 		fo->cookie.len = -1;
2855 		goto fallback;
2856 	}
2857 
2858 	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
2859 		fo->cookie.len = -1;
2860 	else if (fo->cookie.len <= 0)
2861 		goto fallback;
2862 
2863 	/* MSS for SYN-data is based on cached MSS and bounded by PMTU and
2864 	 * user-MSS. Reserve maximum option space for middleboxes that add
2865 	 * private TCP options. The cost is reduced data space in SYN :(
2866 	 */
2867 	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
2868 		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2869 	space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
2870 		MAX_TCP_OPTION_SPACE;
2871 
2872 	syn_data = skb_copy_expand(syn, skb_headroom(syn), space,
2873 				   sk->sk_allocation);
2874 	if (syn_data == NULL)
2875 		goto fallback;
2876 
2877 	for (i = 0; i < iovlen && syn_data->len < space; ++i) {
2878 		struct iovec *iov = &fo->data->msg_iov[i];
2879 		unsigned char __user *from = iov->iov_base;
2880 		int len = iov->iov_len;
2881 
2882 		if (syn_data->len + len > space)
2883 			len = space - syn_data->len;
2884 		else if (i + 1 == iovlen)
2885 			/* No more data pending in inet_wait_for_connect() */
2886 			fo->data = NULL;
2887 
2888 		if (skb_add_data(syn_data, from, len))
2889 			goto fallback;
2890 	}
2891 
2892 	/* Queue a data-only packet after the regular SYN for retransmission */
2893 	data = pskb_copy(syn_data, sk->sk_allocation);
2894 	if (data == NULL)
2895 		goto fallback;
2896 	TCP_SKB_CB(data)->seq++;
2897 	TCP_SKB_CB(data)->tcp_flags &= ~TCPHDR_SYN;
2898 	TCP_SKB_CB(data)->tcp_flags = (TCPHDR_ACK|TCPHDR_PSH);
2899 	tcp_connect_queue_skb(sk, data);
2900 	fo->copied = data->len;
2901 
2902 	if (tcp_transmit_skb(sk, syn_data, 0, sk->sk_allocation) == 0) {
2903 		tp->syn_data = (fo->copied > 0);
2904 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
2905 		goto done;
2906 	}
2907 	syn_data = NULL;
2908 
2909 fallback:
2910 	/* Send a regular SYN with Fast Open cookie request option */
2911 	if (fo->cookie.len > 0)
2912 		fo->cookie.len = 0;
2913 	err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
2914 	if (err)
2915 		tp->syn_fastopen = 0;
2916 	kfree_skb(syn_data);
2917 done:
2918 	fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
2919 	return err;
2920 }
2921 
2922 /* Build a SYN and send it off. */
2923 int tcp_connect(struct sock *sk)
2924 {
2925 	struct tcp_sock *tp = tcp_sk(sk);
2926 	struct sk_buff *buff;
2927 	int err;
2928 
2929 	tcp_connect_init(sk);
2930 
2931 	if (unlikely(tp->repair)) {
2932 		tcp_finish_connect(sk, NULL);
2933 		return 0;
2934 	}
2935 
2936 	buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
2937 	if (unlikely(buff == NULL))
2938 		return -ENOBUFS;
2939 
2940 	/* Reserve space for headers. */
2941 	skb_reserve(buff, MAX_TCP_HEADER);
2942 
2943 	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
2944 	tp->retrans_stamp = TCP_SKB_CB(buff)->when = tcp_time_stamp;
2945 	tcp_connect_queue_skb(sk, buff);
2946 	TCP_ECN_send_syn(sk, buff);
2947 
2948 	/* Send off SYN; include data in Fast Open. */
2949 	err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
2950 	      tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
2951 	if (err == -ECONNREFUSED)
2952 		return err;
2953 
2954 	/* We change tp->snd_nxt after the tcp_transmit_skb() call
2955 	 * in order to make this packet get counted in tcpOutSegs.
2956 	 */
2957 	tp->snd_nxt = tp->write_seq;
2958 	tp->pushed_seq = tp->write_seq;
2959 	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
2960 
2961 	/* Timer for repeating the SYN until an answer. */
2962 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2963 				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2964 	return 0;
2965 }
2966 EXPORT_SYMBOL(tcp_connect);
2967 
2968 /* Send out a delayed ack, the caller does the policy checking
2969  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
2970  * for details.
2971  */
2972 void tcp_send_delayed_ack(struct sock *sk)
2973 {
2974 	struct inet_connection_sock *icsk = inet_csk(sk);
2975 	int ato = icsk->icsk_ack.ato;
2976 	unsigned long timeout;
2977 
2978 	if (ato > TCP_DELACK_MIN) {
2979 		const struct tcp_sock *tp = tcp_sk(sk);
2980 		int max_ato = HZ / 2;
2981 
2982 		if (icsk->icsk_ack.pingpong ||
2983 		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
2984 			max_ato = TCP_DELACK_MAX;
2985 
2986 		/* Slow path, intersegment interval is "high". */
2987 
2988 		/* If some rtt estimate is known, use it to bound delayed ack.
2989 		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
2990 		 * directly.
2991 		 */
2992 		if (tp->srtt) {
2993 			int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
2994 
2995 			if (rtt < max_ato)
2996 				max_ato = rtt;
2997 		}
2998 
2999 		ato = min(ato, max_ato);
3000 	}
3001 
3002 	/* Stay within the limit we were given */
3003 	timeout = jiffies + ato;
3004 
3005 	/* Use new timeout only if there wasn't a older one earlier. */
3006 	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3007 		/* If delack timer was blocked or is about to expire,
3008 		 * send ACK now.
3009 		 */
3010 		if (icsk->icsk_ack.blocked ||
3011 		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3012 			tcp_send_ack(sk);
3013 			return;
3014 		}
3015 
3016 		if (!time_before(timeout, icsk->icsk_ack.timeout))
3017 			timeout = icsk->icsk_ack.timeout;
3018 	}
3019 	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3020 	icsk->icsk_ack.timeout = timeout;
3021 	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3022 }
3023 
3024 /* This routine sends an ack and also updates the window. */
3025 void tcp_send_ack(struct sock *sk)
3026 {
3027 	struct sk_buff *buff;
3028 
3029 	/* If we have been reset, we may not send again. */
3030 	if (sk->sk_state == TCP_CLOSE)
3031 		return;
3032 
3033 	/* We are not putting this on the write queue, so
3034 	 * tcp_transmit_skb() will set the ownership to this
3035 	 * sock.
3036 	 */
3037 	buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3038 	if (buff == NULL) {
3039 		inet_csk_schedule_ack(sk);
3040 		inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3041 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3042 					  TCP_DELACK_MAX, TCP_RTO_MAX);
3043 		return;
3044 	}
3045 
3046 	/* Reserve space for headers and prepare control bits. */
3047 	skb_reserve(buff, MAX_TCP_HEADER);
3048 	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3049 
3050 	/* Send it off, this clears delayed acks for us. */
3051 	TCP_SKB_CB(buff)->when = tcp_time_stamp;
3052 	tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
3053 }
3054 
3055 /* This routine sends a packet with an out of date sequence
3056  * number. It assumes the other end will try to ack it.
3057  *
3058  * Question: what should we make while urgent mode?
3059  * 4.4BSD forces sending single byte of data. We cannot send
3060  * out of window data, because we have SND.NXT==SND.MAX...
3061  *
3062  * Current solution: to send TWO zero-length segments in urgent mode:
3063  * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3064  * out-of-date with SND.UNA-1 to probe window.
3065  */
3066 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
3067 {
3068 	struct tcp_sock *tp = tcp_sk(sk);
3069 	struct sk_buff *skb;
3070 
3071 	/* We don't queue it, tcp_transmit_skb() sets ownership. */
3072 	skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3073 	if (skb == NULL)
3074 		return -1;
3075 
3076 	/* Reserve space for headers and set control bits. */
3077 	skb_reserve(skb, MAX_TCP_HEADER);
3078 	/* Use a previous sequence.  This should cause the other
3079 	 * end to send an ack.  Don't queue or clone SKB, just
3080 	 * send it.
3081 	 */
3082 	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3083 	TCP_SKB_CB(skb)->when = tcp_time_stamp;
3084 	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3085 }
3086 
3087 void tcp_send_window_probe(struct sock *sk)
3088 {
3089 	if (sk->sk_state == TCP_ESTABLISHED) {
3090 		tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3091 		tcp_sk(sk)->snd_nxt = tcp_sk(sk)->write_seq;
3092 		tcp_xmit_probe_skb(sk, 0);
3093 	}
3094 }
3095 
3096 /* Initiate keepalive or window probe from timer. */
3097 int tcp_write_wakeup(struct sock *sk)
3098 {
3099 	struct tcp_sock *tp = tcp_sk(sk);
3100 	struct sk_buff *skb;
3101 
3102 	if (sk->sk_state == TCP_CLOSE)
3103 		return -1;
3104 
3105 	if ((skb = tcp_send_head(sk)) != NULL &&
3106 	    before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3107 		int err;
3108 		unsigned int mss = tcp_current_mss(sk);
3109 		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3110 
3111 		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3112 			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3113 
3114 		/* We are probing the opening of a window
3115 		 * but the window size is != 0
3116 		 * must have been a result SWS avoidance ( sender )
3117 		 */
3118 		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3119 		    skb->len > mss) {
3120 			seg_size = min(seg_size, mss);
3121 			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3122 			if (tcp_fragment(sk, skb, seg_size, mss))
3123 				return -1;
3124 		} else if (!tcp_skb_pcount(skb))
3125 			tcp_set_skb_tso_segs(sk, skb, mss);
3126 
3127 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3128 		TCP_SKB_CB(skb)->when = tcp_time_stamp;
3129 		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3130 		if (!err)
3131 			tcp_event_new_data_sent(sk, skb);
3132 		return err;
3133 	} else {
3134 		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3135 			tcp_xmit_probe_skb(sk, 1);
3136 		return tcp_xmit_probe_skb(sk, 0);
3137 	}
3138 }
3139 
3140 /* A window probe timeout has occurred.  If window is not closed send
3141  * a partial packet else a zero probe.
3142  */
3143 void tcp_send_probe0(struct sock *sk)
3144 {
3145 	struct inet_connection_sock *icsk = inet_csk(sk);
3146 	struct tcp_sock *tp = tcp_sk(sk);
3147 	int err;
3148 
3149 	err = tcp_write_wakeup(sk);
3150 
3151 	if (tp->packets_out || !tcp_send_head(sk)) {
3152 		/* Cancel probe timer, if it is not required. */
3153 		icsk->icsk_probes_out = 0;
3154 		icsk->icsk_backoff = 0;
3155 		return;
3156 	}
3157 
3158 	if (err <= 0) {
3159 		if (icsk->icsk_backoff < sysctl_tcp_retries2)
3160 			icsk->icsk_backoff++;
3161 		icsk->icsk_probes_out++;
3162 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3163 					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3164 					  TCP_RTO_MAX);
3165 	} else {
3166 		/* If packet was not sent due to local congestion,
3167 		 * do not backoff and do not remember icsk_probes_out.
3168 		 * Let local senders to fight for local resources.
3169 		 *
3170 		 * Use accumulated backoff yet.
3171 		 */
3172 		if (!icsk->icsk_probes_out)
3173 			icsk->icsk_probes_out = 1;
3174 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3175 					  min(icsk->icsk_rto << icsk->icsk_backoff,
3176 					      TCP_RESOURCE_PROBE_INTERVAL),
3177 					  TCP_RTO_MAX);
3178 	}
3179 }
3180