xref: /linux/net/ipv4/tcp_output.c (revision 4949009eb8d40a441dcddcd96e101e77d31cf1b2)
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 unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
69 EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);
70 
71 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
72 			   int push_one, gfp_t gfp);
73 
74 /* Account for new data that has been sent to the network. */
75 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
76 {
77 	struct inet_connection_sock *icsk = inet_csk(sk);
78 	struct tcp_sock *tp = tcp_sk(sk);
79 	unsigned int prior_packets = tp->packets_out;
80 
81 	tcp_advance_send_head(sk, skb);
82 	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
83 
84 	tp->packets_out += tcp_skb_pcount(skb);
85 	if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
86 	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
87 		tcp_rearm_rto(sk);
88 	}
89 
90 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
91 		      tcp_skb_pcount(skb));
92 }
93 
94 /* SND.NXT, if window was not shrunk.
95  * If window has been shrunk, what should we make? It is not clear at all.
96  * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
97  * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
98  * invalid. OK, let's make this for now:
99  */
100 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
101 {
102 	const struct tcp_sock *tp = tcp_sk(sk);
103 
104 	if (!before(tcp_wnd_end(tp), tp->snd_nxt))
105 		return tp->snd_nxt;
106 	else
107 		return tcp_wnd_end(tp);
108 }
109 
110 /* Calculate mss to advertise in SYN segment.
111  * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
112  *
113  * 1. It is independent of path mtu.
114  * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
115  * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
116  *    attached devices, because some buggy hosts are confused by
117  *    large MSS.
118  * 4. We do not make 3, we advertise MSS, calculated from first
119  *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
120  *    This may be overridden via information stored in routing table.
121  * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
122  *    probably even Jumbo".
123  */
124 static __u16 tcp_advertise_mss(struct sock *sk)
125 {
126 	struct tcp_sock *tp = tcp_sk(sk);
127 	const struct dst_entry *dst = __sk_dst_get(sk);
128 	int mss = tp->advmss;
129 
130 	if (dst) {
131 		unsigned int metric = dst_metric_advmss(dst);
132 
133 		if (metric < mss) {
134 			mss = metric;
135 			tp->advmss = mss;
136 		}
137 	}
138 
139 	return (__u16)mss;
140 }
141 
142 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
143  * This is the first part of cwnd validation mechanism. */
144 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
145 {
146 	struct tcp_sock *tp = tcp_sk(sk);
147 	s32 delta = tcp_time_stamp - tp->lsndtime;
148 	u32 restart_cwnd = tcp_init_cwnd(tp, dst);
149 	u32 cwnd = tp->snd_cwnd;
150 
151 	tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
152 
153 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
154 	restart_cwnd = min(restart_cwnd, cwnd);
155 
156 	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
157 		cwnd >>= 1;
158 	tp->snd_cwnd = max(cwnd, restart_cwnd);
159 	tp->snd_cwnd_stamp = tcp_time_stamp;
160 	tp->snd_cwnd_used = 0;
161 }
162 
163 /* Congestion state accounting after a packet has been sent. */
164 static void tcp_event_data_sent(struct tcp_sock *tp,
165 				struct sock *sk)
166 {
167 	struct inet_connection_sock *icsk = inet_csk(sk);
168 	const u32 now = tcp_time_stamp;
169 	const struct dst_entry *dst = __sk_dst_get(sk);
170 
171 	if (sysctl_tcp_slow_start_after_idle &&
172 	    (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
173 		tcp_cwnd_restart(sk, __sk_dst_get(sk));
174 
175 	tp->lsndtime = now;
176 
177 	/* If it is a reply for ato after last received
178 	 * packet, enter pingpong mode.
179 	 */
180 	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato &&
181 	    (!dst || !dst_metric(dst, RTAX_QUICKACK)))
182 			icsk->icsk_ack.pingpong = 1;
183 }
184 
185 /* Account for an ACK we sent. */
186 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
187 {
188 	tcp_dec_quickack_mode(sk, pkts);
189 	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
190 }
191 
192 
193 u32 tcp_default_init_rwnd(u32 mss)
194 {
195 	/* Initial receive window should be twice of TCP_INIT_CWND to
196 	 * enable proper sending of new unsent data during fast recovery
197 	 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
198 	 * limit when mss is larger than 1460.
199 	 */
200 	u32 init_rwnd = TCP_INIT_CWND * 2;
201 
202 	if (mss > 1460)
203 		init_rwnd = max((1460 * init_rwnd) / mss, 2U);
204 	return init_rwnd;
205 }
206 
207 /* Determine a window scaling and initial window to offer.
208  * Based on the assumption that the given amount of space
209  * will be offered. Store the results in the tp structure.
210  * NOTE: for smooth operation initial space offering should
211  * be a multiple of mss if possible. We assume here that mss >= 1.
212  * This MUST be enforced by all callers.
213  */
214 void tcp_select_initial_window(int __space, __u32 mss,
215 			       __u32 *rcv_wnd, __u32 *window_clamp,
216 			       int wscale_ok, __u8 *rcv_wscale,
217 			       __u32 init_rcv_wnd)
218 {
219 	unsigned int space = (__space < 0 ? 0 : __space);
220 
221 	/* If no clamp set the clamp to the max possible scaled window */
222 	if (*window_clamp == 0)
223 		(*window_clamp) = (65535 << 14);
224 	space = min(*window_clamp, space);
225 
226 	/* Quantize space offering to a multiple of mss if possible. */
227 	if (space > mss)
228 		space = (space / mss) * mss;
229 
230 	/* NOTE: offering an initial window larger than 32767
231 	 * will break some buggy TCP stacks. If the admin tells us
232 	 * it is likely we could be speaking with such a buggy stack
233 	 * we will truncate our initial window offering to 32K-1
234 	 * unless the remote has sent us a window scaling option,
235 	 * which we interpret as a sign the remote TCP is not
236 	 * misinterpreting the window field as a signed quantity.
237 	 */
238 	if (sysctl_tcp_workaround_signed_windows)
239 		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
240 	else
241 		(*rcv_wnd) = space;
242 
243 	(*rcv_wscale) = 0;
244 	if (wscale_ok) {
245 		/* Set window scaling on max possible window
246 		 * See RFC1323 for an explanation of the limit to 14
247 		 */
248 		space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
249 		space = min_t(u32, space, *window_clamp);
250 		while (space > 65535 && (*rcv_wscale) < 14) {
251 			space >>= 1;
252 			(*rcv_wscale)++;
253 		}
254 	}
255 
256 	if (mss > (1 << *rcv_wscale)) {
257 		if (!init_rcv_wnd) /* Use default unless specified otherwise */
258 			init_rcv_wnd = tcp_default_init_rwnd(mss);
259 		*rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
260 	}
261 
262 	/* Set the clamp no higher than max representable value */
263 	(*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
264 }
265 EXPORT_SYMBOL(tcp_select_initial_window);
266 
267 /* Chose a new window to advertise, update state in tcp_sock for the
268  * socket, and return result with RFC1323 scaling applied.  The return
269  * value can be stuffed directly into th->window for an outgoing
270  * frame.
271  */
272 static u16 tcp_select_window(struct sock *sk)
273 {
274 	struct tcp_sock *tp = tcp_sk(sk);
275 	u32 old_win = tp->rcv_wnd;
276 	u32 cur_win = tcp_receive_window(tp);
277 	u32 new_win = __tcp_select_window(sk);
278 
279 	/* Never shrink the offered window */
280 	if (new_win < cur_win) {
281 		/* Danger Will Robinson!
282 		 * Don't update rcv_wup/rcv_wnd here or else
283 		 * we will not be able to advertise a zero
284 		 * window in time.  --DaveM
285 		 *
286 		 * Relax Will Robinson.
287 		 */
288 		if (new_win == 0)
289 			NET_INC_STATS(sock_net(sk),
290 				      LINUX_MIB_TCPWANTZEROWINDOWADV);
291 		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
292 	}
293 	tp->rcv_wnd = new_win;
294 	tp->rcv_wup = tp->rcv_nxt;
295 
296 	/* Make sure we do not exceed the maximum possible
297 	 * scaled window.
298 	 */
299 	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
300 		new_win = min(new_win, MAX_TCP_WINDOW);
301 	else
302 		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
303 
304 	/* RFC1323 scaling applied */
305 	new_win >>= tp->rx_opt.rcv_wscale;
306 
307 	/* If we advertise zero window, disable fast path. */
308 	if (new_win == 0) {
309 		tp->pred_flags = 0;
310 		if (old_win)
311 			NET_INC_STATS(sock_net(sk),
312 				      LINUX_MIB_TCPTOZEROWINDOWADV);
313 	} else if (old_win == 0) {
314 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
315 	}
316 
317 	return new_win;
318 }
319 
320 /* Packet ECN state for a SYN-ACK */
321 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
322 {
323 	const struct tcp_sock *tp = tcp_sk(sk);
324 
325 	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
326 	if (!(tp->ecn_flags & TCP_ECN_OK))
327 		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
328 	else if (tcp_ca_needs_ecn(sk))
329 		INET_ECN_xmit(sk);
330 }
331 
332 /* Packet ECN state for a SYN.  */
333 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
334 {
335 	struct tcp_sock *tp = tcp_sk(sk);
336 	bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
337 		       tcp_ca_needs_ecn(sk);
338 
339 	if (!use_ecn) {
340 		const struct dst_entry *dst = __sk_dst_get(sk);
341 
342 		if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
343 			use_ecn = true;
344 	}
345 
346 	tp->ecn_flags = 0;
347 
348 	if (use_ecn) {
349 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
350 		tp->ecn_flags = TCP_ECN_OK;
351 		if (tcp_ca_needs_ecn(sk))
352 			INET_ECN_xmit(sk);
353 	}
354 }
355 
356 static void
357 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th,
358 		    struct sock *sk)
359 {
360 	if (inet_rsk(req)->ecn_ok) {
361 		th->ece = 1;
362 		if (tcp_ca_needs_ecn(sk))
363 			INET_ECN_xmit(sk);
364 	}
365 }
366 
367 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
368  * be sent.
369  */
370 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
371 				int tcp_header_len)
372 {
373 	struct tcp_sock *tp = tcp_sk(sk);
374 
375 	if (tp->ecn_flags & TCP_ECN_OK) {
376 		/* Not-retransmitted data segment: set ECT and inject CWR. */
377 		if (skb->len != tcp_header_len &&
378 		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
379 			INET_ECN_xmit(sk);
380 			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
381 				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
382 				tcp_hdr(skb)->cwr = 1;
383 				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
384 			}
385 		} else if (!tcp_ca_needs_ecn(sk)) {
386 			/* ACK or retransmitted segment: clear ECT|CE */
387 			INET_ECN_dontxmit(sk);
388 		}
389 		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
390 			tcp_hdr(skb)->ece = 1;
391 	}
392 }
393 
394 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
395  * auto increment end seqno.
396  */
397 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
398 {
399 	struct skb_shared_info *shinfo = skb_shinfo(skb);
400 
401 	skb->ip_summed = CHECKSUM_PARTIAL;
402 	skb->csum = 0;
403 
404 	TCP_SKB_CB(skb)->tcp_flags = flags;
405 	TCP_SKB_CB(skb)->sacked = 0;
406 
407 	tcp_skb_pcount_set(skb, 1);
408 	shinfo->gso_size = 0;
409 	shinfo->gso_type = 0;
410 
411 	TCP_SKB_CB(skb)->seq = seq;
412 	if (flags & (TCPHDR_SYN | TCPHDR_FIN))
413 		seq++;
414 	TCP_SKB_CB(skb)->end_seq = seq;
415 }
416 
417 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
418 {
419 	return tp->snd_una != tp->snd_up;
420 }
421 
422 #define OPTION_SACK_ADVERTISE	(1 << 0)
423 #define OPTION_TS		(1 << 1)
424 #define OPTION_MD5		(1 << 2)
425 #define OPTION_WSCALE		(1 << 3)
426 #define OPTION_FAST_OPEN_COOKIE	(1 << 8)
427 
428 struct tcp_out_options {
429 	u16 options;		/* bit field of OPTION_* */
430 	u16 mss;		/* 0 to disable */
431 	u8 ws;			/* window scale, 0 to disable */
432 	u8 num_sack_blocks;	/* number of SACK blocks to include */
433 	u8 hash_size;		/* bytes in hash_location */
434 	__u8 *hash_location;	/* temporary pointer, overloaded */
435 	__u32 tsval, tsecr;	/* need to include OPTION_TS */
436 	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */
437 };
438 
439 /* Write previously computed TCP options to the packet.
440  *
441  * Beware: Something in the Internet is very sensitive to the ordering of
442  * TCP options, we learned this through the hard way, so be careful here.
443  * Luckily we can at least blame others for their non-compliance but from
444  * inter-operability perspective it seems that we're somewhat stuck with
445  * the ordering which we have been using if we want to keep working with
446  * those broken things (not that it currently hurts anybody as there isn't
447  * particular reason why the ordering would need to be changed).
448  *
449  * At least SACK_PERM as the first option is known to lead to a disaster
450  * (but it may well be that other scenarios fail similarly).
451  */
452 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
453 			      struct tcp_out_options *opts)
454 {
455 	u16 options = opts->options;	/* mungable copy */
456 
457 	if (unlikely(OPTION_MD5 & options)) {
458 		*ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
459 			       (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
460 		/* overload cookie hash location */
461 		opts->hash_location = (__u8 *)ptr;
462 		ptr += 4;
463 	}
464 
465 	if (unlikely(opts->mss)) {
466 		*ptr++ = htonl((TCPOPT_MSS << 24) |
467 			       (TCPOLEN_MSS << 16) |
468 			       opts->mss);
469 	}
470 
471 	if (likely(OPTION_TS & options)) {
472 		if (unlikely(OPTION_SACK_ADVERTISE & options)) {
473 			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
474 				       (TCPOLEN_SACK_PERM << 16) |
475 				       (TCPOPT_TIMESTAMP << 8) |
476 				       TCPOLEN_TIMESTAMP);
477 			options &= ~OPTION_SACK_ADVERTISE;
478 		} else {
479 			*ptr++ = htonl((TCPOPT_NOP << 24) |
480 				       (TCPOPT_NOP << 16) |
481 				       (TCPOPT_TIMESTAMP << 8) |
482 				       TCPOLEN_TIMESTAMP);
483 		}
484 		*ptr++ = htonl(opts->tsval);
485 		*ptr++ = htonl(opts->tsecr);
486 	}
487 
488 	if (unlikely(OPTION_SACK_ADVERTISE & options)) {
489 		*ptr++ = htonl((TCPOPT_NOP << 24) |
490 			       (TCPOPT_NOP << 16) |
491 			       (TCPOPT_SACK_PERM << 8) |
492 			       TCPOLEN_SACK_PERM);
493 	}
494 
495 	if (unlikely(OPTION_WSCALE & options)) {
496 		*ptr++ = htonl((TCPOPT_NOP << 24) |
497 			       (TCPOPT_WINDOW << 16) |
498 			       (TCPOLEN_WINDOW << 8) |
499 			       opts->ws);
500 	}
501 
502 	if (unlikely(opts->num_sack_blocks)) {
503 		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
504 			tp->duplicate_sack : tp->selective_acks;
505 		int this_sack;
506 
507 		*ptr++ = htonl((TCPOPT_NOP  << 24) |
508 			       (TCPOPT_NOP  << 16) |
509 			       (TCPOPT_SACK <<  8) |
510 			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
511 						     TCPOLEN_SACK_PERBLOCK)));
512 
513 		for (this_sack = 0; this_sack < opts->num_sack_blocks;
514 		     ++this_sack) {
515 			*ptr++ = htonl(sp[this_sack].start_seq);
516 			*ptr++ = htonl(sp[this_sack].end_seq);
517 		}
518 
519 		tp->rx_opt.dsack = 0;
520 	}
521 
522 	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
523 		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
524 
525 		*ptr++ = htonl((TCPOPT_EXP << 24) |
526 			       ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
527 			       TCPOPT_FASTOPEN_MAGIC);
528 
529 		memcpy(ptr, foc->val, foc->len);
530 		if ((foc->len & 3) == 2) {
531 			u8 *align = ((u8 *)ptr) + foc->len;
532 			align[0] = align[1] = TCPOPT_NOP;
533 		}
534 		ptr += (foc->len + 3) >> 2;
535 	}
536 }
537 
538 /* Compute TCP options for SYN packets. This is not the final
539  * network wire format yet.
540  */
541 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
542 				struct tcp_out_options *opts,
543 				struct tcp_md5sig_key **md5)
544 {
545 	struct tcp_sock *tp = tcp_sk(sk);
546 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
547 	struct tcp_fastopen_request *fastopen = tp->fastopen_req;
548 
549 #ifdef CONFIG_TCP_MD5SIG
550 	*md5 = tp->af_specific->md5_lookup(sk, sk);
551 	if (*md5) {
552 		opts->options |= OPTION_MD5;
553 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
554 	}
555 #else
556 	*md5 = NULL;
557 #endif
558 
559 	/* We always get an MSS option.  The option bytes which will be seen in
560 	 * normal data packets should timestamps be used, must be in the MSS
561 	 * advertised.  But we subtract them from tp->mss_cache so that
562 	 * calculations in tcp_sendmsg are simpler etc.  So account for this
563 	 * fact here if necessary.  If we don't do this correctly, as a
564 	 * receiver we won't recognize data packets as being full sized when we
565 	 * should, and thus we won't abide by the delayed ACK rules correctly.
566 	 * SACKs don't matter, we never delay an ACK when we have any of those
567 	 * going out.  */
568 	opts->mss = tcp_advertise_mss(sk);
569 	remaining -= TCPOLEN_MSS_ALIGNED;
570 
571 	if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
572 		opts->options |= OPTION_TS;
573 		opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
574 		opts->tsecr = tp->rx_opt.ts_recent;
575 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
576 	}
577 	if (likely(sysctl_tcp_window_scaling)) {
578 		opts->ws = tp->rx_opt.rcv_wscale;
579 		opts->options |= OPTION_WSCALE;
580 		remaining -= TCPOLEN_WSCALE_ALIGNED;
581 	}
582 	if (likely(sysctl_tcp_sack)) {
583 		opts->options |= OPTION_SACK_ADVERTISE;
584 		if (unlikely(!(OPTION_TS & opts->options)))
585 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
586 	}
587 
588 	if (fastopen && fastopen->cookie.len >= 0) {
589 		u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
590 		need = (need + 3) & ~3U;  /* Align to 32 bits */
591 		if (remaining >= need) {
592 			opts->options |= OPTION_FAST_OPEN_COOKIE;
593 			opts->fastopen_cookie = &fastopen->cookie;
594 			remaining -= need;
595 			tp->syn_fastopen = 1;
596 		}
597 	}
598 
599 	return MAX_TCP_OPTION_SPACE - remaining;
600 }
601 
602 /* Set up TCP options for SYN-ACKs. */
603 static unsigned int tcp_synack_options(struct sock *sk,
604 				   struct request_sock *req,
605 				   unsigned int mss, struct sk_buff *skb,
606 				   struct tcp_out_options *opts,
607 				   struct tcp_md5sig_key **md5,
608 				   struct tcp_fastopen_cookie *foc)
609 {
610 	struct inet_request_sock *ireq = inet_rsk(req);
611 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
612 
613 #ifdef CONFIG_TCP_MD5SIG
614 	*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
615 	if (*md5) {
616 		opts->options |= OPTION_MD5;
617 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
618 
619 		/* We can't fit any SACK blocks in a packet with MD5 + TS
620 		 * options. There was discussion about disabling SACK
621 		 * rather than TS in order to fit in better with old,
622 		 * buggy kernels, but that was deemed to be unnecessary.
623 		 */
624 		ireq->tstamp_ok &= !ireq->sack_ok;
625 	}
626 #else
627 	*md5 = NULL;
628 #endif
629 
630 	/* We always send an MSS option. */
631 	opts->mss = mss;
632 	remaining -= TCPOLEN_MSS_ALIGNED;
633 
634 	if (likely(ireq->wscale_ok)) {
635 		opts->ws = ireq->rcv_wscale;
636 		opts->options |= OPTION_WSCALE;
637 		remaining -= TCPOLEN_WSCALE_ALIGNED;
638 	}
639 	if (likely(ireq->tstamp_ok)) {
640 		opts->options |= OPTION_TS;
641 		opts->tsval = tcp_skb_timestamp(skb);
642 		opts->tsecr = req->ts_recent;
643 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
644 	}
645 	if (likely(ireq->sack_ok)) {
646 		opts->options |= OPTION_SACK_ADVERTISE;
647 		if (unlikely(!ireq->tstamp_ok))
648 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
649 	}
650 	if (foc != NULL && foc->len >= 0) {
651 		u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
652 		need = (need + 3) & ~3U;  /* Align to 32 bits */
653 		if (remaining >= need) {
654 			opts->options |= OPTION_FAST_OPEN_COOKIE;
655 			opts->fastopen_cookie = foc;
656 			remaining -= need;
657 		}
658 	}
659 
660 	return MAX_TCP_OPTION_SPACE - remaining;
661 }
662 
663 /* Compute TCP options for ESTABLISHED sockets. This is not the
664  * final wire format yet.
665  */
666 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
667 					struct tcp_out_options *opts,
668 					struct tcp_md5sig_key **md5)
669 {
670 	struct tcp_sock *tp = tcp_sk(sk);
671 	unsigned int size = 0;
672 	unsigned int eff_sacks;
673 
674 	opts->options = 0;
675 
676 #ifdef CONFIG_TCP_MD5SIG
677 	*md5 = tp->af_specific->md5_lookup(sk, sk);
678 	if (unlikely(*md5)) {
679 		opts->options |= OPTION_MD5;
680 		size += TCPOLEN_MD5SIG_ALIGNED;
681 	}
682 #else
683 	*md5 = NULL;
684 #endif
685 
686 	if (likely(tp->rx_opt.tstamp_ok)) {
687 		opts->options |= OPTION_TS;
688 		opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
689 		opts->tsecr = tp->rx_opt.ts_recent;
690 		size += TCPOLEN_TSTAMP_ALIGNED;
691 	}
692 
693 	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
694 	if (unlikely(eff_sacks)) {
695 		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
696 		opts->num_sack_blocks =
697 			min_t(unsigned int, eff_sacks,
698 			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
699 			      TCPOLEN_SACK_PERBLOCK);
700 		size += TCPOLEN_SACK_BASE_ALIGNED +
701 			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
702 	}
703 
704 	return size;
705 }
706 
707 
708 /* TCP SMALL QUEUES (TSQ)
709  *
710  * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
711  * to reduce RTT and bufferbloat.
712  * We do this using a special skb destructor (tcp_wfree).
713  *
714  * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
715  * needs to be reallocated in a driver.
716  * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
717  *
718  * Since transmit from skb destructor is forbidden, we use a tasklet
719  * to process all sockets that eventually need to send more skbs.
720  * We use one tasklet per cpu, with its own queue of sockets.
721  */
722 struct tsq_tasklet {
723 	struct tasklet_struct	tasklet;
724 	struct list_head	head; /* queue of tcp sockets */
725 };
726 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
727 
728 static void tcp_tsq_handler(struct sock *sk)
729 {
730 	if ((1 << sk->sk_state) &
731 	    (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
732 	     TCPF_CLOSE_WAIT  | TCPF_LAST_ACK))
733 		tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
734 			       0, GFP_ATOMIC);
735 }
736 /*
737  * One tasklet per cpu tries to send more skbs.
738  * We run in tasklet context but need to disable irqs when
739  * transferring tsq->head because tcp_wfree() might
740  * interrupt us (non NAPI drivers)
741  */
742 static void tcp_tasklet_func(unsigned long data)
743 {
744 	struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
745 	LIST_HEAD(list);
746 	unsigned long flags;
747 	struct list_head *q, *n;
748 	struct tcp_sock *tp;
749 	struct sock *sk;
750 
751 	local_irq_save(flags);
752 	list_splice_init(&tsq->head, &list);
753 	local_irq_restore(flags);
754 
755 	list_for_each_safe(q, n, &list) {
756 		tp = list_entry(q, struct tcp_sock, tsq_node);
757 		list_del(&tp->tsq_node);
758 
759 		sk = (struct sock *)tp;
760 		bh_lock_sock(sk);
761 
762 		if (!sock_owned_by_user(sk)) {
763 			tcp_tsq_handler(sk);
764 		} else {
765 			/* defer the work to tcp_release_cb() */
766 			set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
767 		}
768 		bh_unlock_sock(sk);
769 
770 		clear_bit(TSQ_QUEUED, &tp->tsq_flags);
771 		sk_free(sk);
772 	}
773 }
774 
775 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) |		\
776 			  (1UL << TCP_WRITE_TIMER_DEFERRED) |	\
777 			  (1UL << TCP_DELACK_TIMER_DEFERRED) |	\
778 			  (1UL << TCP_MTU_REDUCED_DEFERRED))
779 /**
780  * tcp_release_cb - tcp release_sock() callback
781  * @sk: socket
782  *
783  * called from release_sock() to perform protocol dependent
784  * actions before socket release.
785  */
786 void tcp_release_cb(struct sock *sk)
787 {
788 	struct tcp_sock *tp = tcp_sk(sk);
789 	unsigned long flags, nflags;
790 
791 	/* perform an atomic operation only if at least one flag is set */
792 	do {
793 		flags = tp->tsq_flags;
794 		if (!(flags & TCP_DEFERRED_ALL))
795 			return;
796 		nflags = flags & ~TCP_DEFERRED_ALL;
797 	} while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
798 
799 	if (flags & (1UL << TCP_TSQ_DEFERRED))
800 		tcp_tsq_handler(sk);
801 
802 	/* Here begins the tricky part :
803 	 * We are called from release_sock() with :
804 	 * 1) BH disabled
805 	 * 2) sk_lock.slock spinlock held
806 	 * 3) socket owned by us (sk->sk_lock.owned == 1)
807 	 *
808 	 * But following code is meant to be called from BH handlers,
809 	 * so we should keep BH disabled, but early release socket ownership
810 	 */
811 	sock_release_ownership(sk);
812 
813 	if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
814 		tcp_write_timer_handler(sk);
815 		__sock_put(sk);
816 	}
817 	if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
818 		tcp_delack_timer_handler(sk);
819 		__sock_put(sk);
820 	}
821 	if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
822 		inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
823 		__sock_put(sk);
824 	}
825 }
826 EXPORT_SYMBOL(tcp_release_cb);
827 
828 void __init tcp_tasklet_init(void)
829 {
830 	int i;
831 
832 	for_each_possible_cpu(i) {
833 		struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
834 
835 		INIT_LIST_HEAD(&tsq->head);
836 		tasklet_init(&tsq->tasklet,
837 			     tcp_tasklet_func,
838 			     (unsigned long)tsq);
839 	}
840 }
841 
842 /*
843  * Write buffer destructor automatically called from kfree_skb.
844  * We can't xmit new skbs from this context, as we might already
845  * hold qdisc lock.
846  */
847 void tcp_wfree(struct sk_buff *skb)
848 {
849 	struct sock *sk = skb->sk;
850 	struct tcp_sock *tp = tcp_sk(sk);
851 	int wmem;
852 
853 	/* Keep one reference on sk_wmem_alloc.
854 	 * Will be released by sk_free() from here or tcp_tasklet_func()
855 	 */
856 	wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
857 
858 	/* If this softirq is serviced by ksoftirqd, we are likely under stress.
859 	 * Wait until our queues (qdisc + devices) are drained.
860 	 * This gives :
861 	 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
862 	 * - chance for incoming ACK (processed by another cpu maybe)
863 	 *   to migrate this flow (skb->ooo_okay will be eventually set)
864 	 */
865 	if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
866 		goto out;
867 
868 	if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
869 	    !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
870 		unsigned long flags;
871 		struct tsq_tasklet *tsq;
872 
873 		/* queue this socket to tasklet queue */
874 		local_irq_save(flags);
875 		tsq = this_cpu_ptr(&tsq_tasklet);
876 		list_add(&tp->tsq_node, &tsq->head);
877 		tasklet_schedule(&tsq->tasklet);
878 		local_irq_restore(flags);
879 		return;
880 	}
881 out:
882 	sk_free(sk);
883 }
884 
885 /* This routine actually transmits TCP packets queued in by
886  * tcp_do_sendmsg().  This is used by both the initial
887  * transmission and possible later retransmissions.
888  * All SKB's seen here are completely headerless.  It is our
889  * job to build the TCP header, and pass the packet down to
890  * IP so it can do the same plus pass the packet off to the
891  * device.
892  *
893  * We are working here with either a clone of the original
894  * SKB, or a fresh unique copy made by the retransmit engine.
895  */
896 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
897 			    gfp_t gfp_mask)
898 {
899 	const struct inet_connection_sock *icsk = inet_csk(sk);
900 	struct inet_sock *inet;
901 	struct tcp_sock *tp;
902 	struct tcp_skb_cb *tcb;
903 	struct tcp_out_options opts;
904 	unsigned int tcp_options_size, tcp_header_size;
905 	struct tcp_md5sig_key *md5;
906 	struct tcphdr *th;
907 	int err;
908 
909 	BUG_ON(!skb || !tcp_skb_pcount(skb));
910 
911 	if (clone_it) {
912 		skb_mstamp_get(&skb->skb_mstamp);
913 
914 		if (unlikely(skb_cloned(skb)))
915 			skb = pskb_copy(skb, gfp_mask);
916 		else
917 			skb = skb_clone(skb, gfp_mask);
918 		if (unlikely(!skb))
919 			return -ENOBUFS;
920 	}
921 
922 	inet = inet_sk(sk);
923 	tp = tcp_sk(sk);
924 	tcb = TCP_SKB_CB(skb);
925 	memset(&opts, 0, sizeof(opts));
926 
927 	if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
928 		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
929 	else
930 		tcp_options_size = tcp_established_options(sk, skb, &opts,
931 							   &md5);
932 	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
933 
934 	if (tcp_packets_in_flight(tp) == 0)
935 		tcp_ca_event(sk, CA_EVENT_TX_START);
936 
937 	/* if no packet is in qdisc/device queue, then allow XPS to select
938 	 * another queue. We can be called from tcp_tsq_handler()
939 	 * which holds one reference to sk_wmem_alloc.
940 	 *
941 	 * TODO: Ideally, in-flight pure ACK packets should not matter here.
942 	 * One way to get this would be to set skb->truesize = 2 on them.
943 	 */
944 	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
945 
946 	skb_push(skb, tcp_header_size);
947 	skb_reset_transport_header(skb);
948 
949 	skb_orphan(skb);
950 	skb->sk = sk;
951 	skb->destructor = tcp_wfree;
952 	skb_set_hash_from_sk(skb, sk);
953 	atomic_add(skb->truesize, &sk->sk_wmem_alloc);
954 
955 	/* Build TCP header and checksum it. */
956 	th = tcp_hdr(skb);
957 	th->source		= inet->inet_sport;
958 	th->dest		= inet->inet_dport;
959 	th->seq			= htonl(tcb->seq);
960 	th->ack_seq		= htonl(tp->rcv_nxt);
961 	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
962 					tcb->tcp_flags);
963 
964 	if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
965 		/* RFC1323: The window in SYN & SYN/ACK segments
966 		 * is never scaled.
967 		 */
968 		th->window	= htons(min(tp->rcv_wnd, 65535U));
969 	} else {
970 		th->window	= htons(tcp_select_window(sk));
971 	}
972 	th->check		= 0;
973 	th->urg_ptr		= 0;
974 
975 	/* The urg_mode check is necessary during a below snd_una win probe */
976 	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
977 		if (before(tp->snd_up, tcb->seq + 0x10000)) {
978 			th->urg_ptr = htons(tp->snd_up - tcb->seq);
979 			th->urg = 1;
980 		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
981 			th->urg_ptr = htons(0xFFFF);
982 			th->urg = 1;
983 		}
984 	}
985 
986 	tcp_options_write((__be32 *)(th + 1), tp, &opts);
987 	if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
988 		tcp_ecn_send(sk, skb, tcp_header_size);
989 
990 #ifdef CONFIG_TCP_MD5SIG
991 	/* Calculate the MD5 hash, as we have all we need now */
992 	if (md5) {
993 		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
994 		tp->af_specific->calc_md5_hash(opts.hash_location,
995 					       md5, sk, NULL, skb);
996 	}
997 #endif
998 
999 	icsk->icsk_af_ops->send_check(sk, skb);
1000 
1001 	if (likely(tcb->tcp_flags & TCPHDR_ACK))
1002 		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1003 
1004 	if (skb->len != tcp_header_size)
1005 		tcp_event_data_sent(tp, sk);
1006 
1007 	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1008 		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1009 			      tcp_skb_pcount(skb));
1010 
1011 	/* OK, its time to fill skb_shinfo(skb)->gso_segs */
1012 	skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1013 
1014 	/* Our usage of tstamp should remain private */
1015 	skb->tstamp.tv64 = 0;
1016 
1017 	/* Cleanup our debris for IP stacks */
1018 	memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1019 			       sizeof(struct inet6_skb_parm)));
1020 
1021 	err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1022 
1023 	if (likely(err <= 0))
1024 		return err;
1025 
1026 	tcp_enter_cwr(sk);
1027 
1028 	return net_xmit_eval(err);
1029 }
1030 
1031 /* This routine just queues the buffer for sending.
1032  *
1033  * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1034  * otherwise socket can stall.
1035  */
1036 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1037 {
1038 	struct tcp_sock *tp = tcp_sk(sk);
1039 
1040 	/* Advance write_seq and place onto the write_queue. */
1041 	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1042 	__skb_header_release(skb);
1043 	tcp_add_write_queue_tail(sk, skb);
1044 	sk->sk_wmem_queued += skb->truesize;
1045 	sk_mem_charge(sk, skb->truesize);
1046 }
1047 
1048 /* Initialize TSO segments for a packet. */
1049 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
1050 				 unsigned int mss_now)
1051 {
1052 	struct skb_shared_info *shinfo = skb_shinfo(skb);
1053 
1054 	/* Make sure we own this skb before messing gso_size/gso_segs */
1055 	WARN_ON_ONCE(skb_cloned(skb));
1056 
1057 	if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1058 		/* Avoid the costly divide in the normal
1059 		 * non-TSO case.
1060 		 */
1061 		tcp_skb_pcount_set(skb, 1);
1062 		shinfo->gso_size = 0;
1063 		shinfo->gso_type = 0;
1064 	} else {
1065 		tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1066 		shinfo->gso_size = mss_now;
1067 		shinfo->gso_type = sk->sk_gso_type;
1068 	}
1069 }
1070 
1071 /* When a modification to fackets out becomes necessary, we need to check
1072  * skb is counted to fackets_out or not.
1073  */
1074 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1075 				   int decr)
1076 {
1077 	struct tcp_sock *tp = tcp_sk(sk);
1078 
1079 	if (!tp->sacked_out || tcp_is_reno(tp))
1080 		return;
1081 
1082 	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1083 		tp->fackets_out -= decr;
1084 }
1085 
1086 /* Pcount in the middle of the write queue got changed, we need to do various
1087  * tweaks to fix counters
1088  */
1089 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1090 {
1091 	struct tcp_sock *tp = tcp_sk(sk);
1092 
1093 	tp->packets_out -= decr;
1094 
1095 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1096 		tp->sacked_out -= decr;
1097 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1098 		tp->retrans_out -= decr;
1099 	if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1100 		tp->lost_out -= decr;
1101 
1102 	/* Reno case is special. Sigh... */
1103 	if (tcp_is_reno(tp) && decr > 0)
1104 		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1105 
1106 	tcp_adjust_fackets_out(sk, skb, decr);
1107 
1108 	if (tp->lost_skb_hint &&
1109 	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1110 	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1111 		tp->lost_cnt_hint -= decr;
1112 
1113 	tcp_verify_left_out(tp);
1114 }
1115 
1116 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1117 {
1118 	struct skb_shared_info *shinfo = skb_shinfo(skb);
1119 
1120 	if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
1121 	    !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1122 		struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1123 		u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1124 
1125 		shinfo->tx_flags &= ~tsflags;
1126 		shinfo2->tx_flags |= tsflags;
1127 		swap(shinfo->tskey, shinfo2->tskey);
1128 	}
1129 }
1130 
1131 /* Function to create two new TCP segments.  Shrinks the given segment
1132  * to the specified size and appends a new segment with the rest of the
1133  * packet to the list.  This won't be called frequently, I hope.
1134  * Remember, these are still headerless SKBs at this point.
1135  */
1136 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1137 		 unsigned int mss_now, gfp_t gfp)
1138 {
1139 	struct tcp_sock *tp = tcp_sk(sk);
1140 	struct sk_buff *buff;
1141 	int nsize, old_factor;
1142 	int nlen;
1143 	u8 flags;
1144 
1145 	if (WARN_ON(len > skb->len))
1146 		return -EINVAL;
1147 
1148 	nsize = skb_headlen(skb) - len;
1149 	if (nsize < 0)
1150 		nsize = 0;
1151 
1152 	if (skb_unclone(skb, gfp))
1153 		return -ENOMEM;
1154 
1155 	/* Get a new skb... force flag on. */
1156 	buff = sk_stream_alloc_skb(sk, nsize, gfp);
1157 	if (buff == NULL)
1158 		return -ENOMEM; /* We'll just try again later. */
1159 
1160 	sk->sk_wmem_queued += buff->truesize;
1161 	sk_mem_charge(sk, buff->truesize);
1162 	nlen = skb->len - len - nsize;
1163 	buff->truesize += nlen;
1164 	skb->truesize -= nlen;
1165 
1166 	/* Correct the sequence numbers. */
1167 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1168 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1169 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1170 
1171 	/* PSH and FIN should only be set in the second packet. */
1172 	flags = TCP_SKB_CB(skb)->tcp_flags;
1173 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1174 	TCP_SKB_CB(buff)->tcp_flags = flags;
1175 	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1176 
1177 	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1178 		/* Copy and checksum data tail into the new buffer. */
1179 		buff->csum = csum_partial_copy_nocheck(skb->data + len,
1180 						       skb_put(buff, nsize),
1181 						       nsize, 0);
1182 
1183 		skb_trim(skb, len);
1184 
1185 		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1186 	} else {
1187 		skb->ip_summed = CHECKSUM_PARTIAL;
1188 		skb_split(skb, buff, len);
1189 	}
1190 
1191 	buff->ip_summed = skb->ip_summed;
1192 
1193 	buff->tstamp = skb->tstamp;
1194 	tcp_fragment_tstamp(skb, buff);
1195 
1196 	old_factor = tcp_skb_pcount(skb);
1197 
1198 	/* Fix up tso_factor for both original and new SKB.  */
1199 	tcp_set_skb_tso_segs(sk, skb, mss_now);
1200 	tcp_set_skb_tso_segs(sk, buff, mss_now);
1201 
1202 	/* If this packet has been sent out already, we must
1203 	 * adjust the various packet counters.
1204 	 */
1205 	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1206 		int diff = old_factor - tcp_skb_pcount(skb) -
1207 			tcp_skb_pcount(buff);
1208 
1209 		if (diff)
1210 			tcp_adjust_pcount(sk, skb, diff);
1211 	}
1212 
1213 	/* Link BUFF into the send queue. */
1214 	__skb_header_release(buff);
1215 	tcp_insert_write_queue_after(skb, buff, sk);
1216 
1217 	return 0;
1218 }
1219 
1220 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1221  * eventually). The difference is that pulled data not copied, but
1222  * immediately discarded.
1223  */
1224 static void __pskb_trim_head(struct sk_buff *skb, int len)
1225 {
1226 	struct skb_shared_info *shinfo;
1227 	int i, k, eat;
1228 
1229 	eat = min_t(int, len, skb_headlen(skb));
1230 	if (eat) {
1231 		__skb_pull(skb, eat);
1232 		len -= eat;
1233 		if (!len)
1234 			return;
1235 	}
1236 	eat = len;
1237 	k = 0;
1238 	shinfo = skb_shinfo(skb);
1239 	for (i = 0; i < shinfo->nr_frags; i++) {
1240 		int size = skb_frag_size(&shinfo->frags[i]);
1241 
1242 		if (size <= eat) {
1243 			skb_frag_unref(skb, i);
1244 			eat -= size;
1245 		} else {
1246 			shinfo->frags[k] = shinfo->frags[i];
1247 			if (eat) {
1248 				shinfo->frags[k].page_offset += eat;
1249 				skb_frag_size_sub(&shinfo->frags[k], eat);
1250 				eat = 0;
1251 			}
1252 			k++;
1253 		}
1254 	}
1255 	shinfo->nr_frags = k;
1256 
1257 	skb_reset_tail_pointer(skb);
1258 	skb->data_len -= len;
1259 	skb->len = skb->data_len;
1260 }
1261 
1262 /* Remove acked data from a packet in the transmit queue. */
1263 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1264 {
1265 	if (skb_unclone(skb, GFP_ATOMIC))
1266 		return -ENOMEM;
1267 
1268 	__pskb_trim_head(skb, len);
1269 
1270 	TCP_SKB_CB(skb)->seq += len;
1271 	skb->ip_summed = CHECKSUM_PARTIAL;
1272 
1273 	skb->truesize	     -= len;
1274 	sk->sk_wmem_queued   -= len;
1275 	sk_mem_uncharge(sk, len);
1276 	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1277 
1278 	/* Any change of skb->len requires recalculation of tso factor. */
1279 	if (tcp_skb_pcount(skb) > 1)
1280 		tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
1281 
1282 	return 0;
1283 }
1284 
1285 /* Calculate MSS not accounting any TCP options.  */
1286 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1287 {
1288 	const struct tcp_sock *tp = tcp_sk(sk);
1289 	const struct inet_connection_sock *icsk = inet_csk(sk);
1290 	int mss_now;
1291 
1292 	/* Calculate base mss without TCP options:
1293 	   It is MMS_S - sizeof(tcphdr) of rfc1122
1294 	 */
1295 	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1296 
1297 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1298 	if (icsk->icsk_af_ops->net_frag_header_len) {
1299 		const struct dst_entry *dst = __sk_dst_get(sk);
1300 
1301 		if (dst && dst_allfrag(dst))
1302 			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1303 	}
1304 
1305 	/* Clamp it (mss_clamp does not include tcp options) */
1306 	if (mss_now > tp->rx_opt.mss_clamp)
1307 		mss_now = tp->rx_opt.mss_clamp;
1308 
1309 	/* Now subtract optional transport overhead */
1310 	mss_now -= icsk->icsk_ext_hdr_len;
1311 
1312 	/* Then reserve room for full set of TCP options and 8 bytes of data */
1313 	if (mss_now < 48)
1314 		mss_now = 48;
1315 	return mss_now;
1316 }
1317 
1318 /* Calculate MSS. Not accounting for SACKs here.  */
1319 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1320 {
1321 	/* Subtract TCP options size, not including SACKs */
1322 	return __tcp_mtu_to_mss(sk, pmtu) -
1323 	       (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1324 }
1325 
1326 /* Inverse of above */
1327 int tcp_mss_to_mtu(struct sock *sk, int mss)
1328 {
1329 	const struct tcp_sock *tp = tcp_sk(sk);
1330 	const struct inet_connection_sock *icsk = inet_csk(sk);
1331 	int mtu;
1332 
1333 	mtu = mss +
1334 	      tp->tcp_header_len +
1335 	      icsk->icsk_ext_hdr_len +
1336 	      icsk->icsk_af_ops->net_header_len;
1337 
1338 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1339 	if (icsk->icsk_af_ops->net_frag_header_len) {
1340 		const struct dst_entry *dst = __sk_dst_get(sk);
1341 
1342 		if (dst && dst_allfrag(dst))
1343 			mtu += icsk->icsk_af_ops->net_frag_header_len;
1344 	}
1345 	return mtu;
1346 }
1347 
1348 /* MTU probing init per socket */
1349 void tcp_mtup_init(struct sock *sk)
1350 {
1351 	struct tcp_sock *tp = tcp_sk(sk);
1352 	struct inet_connection_sock *icsk = inet_csk(sk);
1353 
1354 	icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
1355 	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1356 			       icsk->icsk_af_ops->net_header_len;
1357 	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
1358 	icsk->icsk_mtup.probe_size = 0;
1359 }
1360 EXPORT_SYMBOL(tcp_mtup_init);
1361 
1362 /* This function synchronize snd mss to current pmtu/exthdr set.
1363 
1364    tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1365    for TCP options, but includes only bare TCP header.
1366 
1367    tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1368    It is minimum of user_mss and mss received with SYN.
1369    It also does not include TCP options.
1370 
1371    inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1372 
1373    tp->mss_cache is current effective sending mss, including
1374    all tcp options except for SACKs. It is evaluated,
1375    taking into account current pmtu, but never exceeds
1376    tp->rx_opt.mss_clamp.
1377 
1378    NOTE1. rfc1122 clearly states that advertised MSS
1379    DOES NOT include either tcp or ip options.
1380 
1381    NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1382    are READ ONLY outside this function.		--ANK (980731)
1383  */
1384 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1385 {
1386 	struct tcp_sock *tp = tcp_sk(sk);
1387 	struct inet_connection_sock *icsk = inet_csk(sk);
1388 	int mss_now;
1389 
1390 	if (icsk->icsk_mtup.search_high > pmtu)
1391 		icsk->icsk_mtup.search_high = pmtu;
1392 
1393 	mss_now = tcp_mtu_to_mss(sk, pmtu);
1394 	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1395 
1396 	/* And store cached results */
1397 	icsk->icsk_pmtu_cookie = pmtu;
1398 	if (icsk->icsk_mtup.enabled)
1399 		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1400 	tp->mss_cache = mss_now;
1401 
1402 	return mss_now;
1403 }
1404 EXPORT_SYMBOL(tcp_sync_mss);
1405 
1406 /* Compute the current effective MSS, taking SACKs and IP options,
1407  * and even PMTU discovery events into account.
1408  */
1409 unsigned int tcp_current_mss(struct sock *sk)
1410 {
1411 	const struct tcp_sock *tp = tcp_sk(sk);
1412 	const struct dst_entry *dst = __sk_dst_get(sk);
1413 	u32 mss_now;
1414 	unsigned int header_len;
1415 	struct tcp_out_options opts;
1416 	struct tcp_md5sig_key *md5;
1417 
1418 	mss_now = tp->mss_cache;
1419 
1420 	if (dst) {
1421 		u32 mtu = dst_mtu(dst);
1422 		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1423 			mss_now = tcp_sync_mss(sk, mtu);
1424 	}
1425 
1426 	header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1427 		     sizeof(struct tcphdr);
1428 	/* The mss_cache is sized based on tp->tcp_header_len, which assumes
1429 	 * some common options. If this is an odd packet (because we have SACK
1430 	 * blocks etc) then our calculated header_len will be different, and
1431 	 * we have to adjust mss_now correspondingly */
1432 	if (header_len != tp->tcp_header_len) {
1433 		int delta = (int) header_len - tp->tcp_header_len;
1434 		mss_now -= delta;
1435 	}
1436 
1437 	return mss_now;
1438 }
1439 
1440 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1441  * As additional protections, we do not touch cwnd in retransmission phases,
1442  * and if application hit its sndbuf limit recently.
1443  */
1444 static void tcp_cwnd_application_limited(struct sock *sk)
1445 {
1446 	struct tcp_sock *tp = tcp_sk(sk);
1447 
1448 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1449 	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1450 		/* Limited by application or receiver window. */
1451 		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1452 		u32 win_used = max(tp->snd_cwnd_used, init_win);
1453 		if (win_used < tp->snd_cwnd) {
1454 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
1455 			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1456 		}
1457 		tp->snd_cwnd_used = 0;
1458 	}
1459 	tp->snd_cwnd_stamp = tcp_time_stamp;
1460 }
1461 
1462 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1463 {
1464 	struct tcp_sock *tp = tcp_sk(sk);
1465 
1466 	/* Track the maximum number of outstanding packets in each
1467 	 * window, and remember whether we were cwnd-limited then.
1468 	 */
1469 	if (!before(tp->snd_una, tp->max_packets_seq) ||
1470 	    tp->packets_out > tp->max_packets_out) {
1471 		tp->max_packets_out = tp->packets_out;
1472 		tp->max_packets_seq = tp->snd_nxt;
1473 		tp->is_cwnd_limited = is_cwnd_limited;
1474 	}
1475 
1476 	if (tcp_is_cwnd_limited(sk)) {
1477 		/* Network is feed fully. */
1478 		tp->snd_cwnd_used = 0;
1479 		tp->snd_cwnd_stamp = tcp_time_stamp;
1480 	} else {
1481 		/* Network starves. */
1482 		if (tp->packets_out > tp->snd_cwnd_used)
1483 			tp->snd_cwnd_used = tp->packets_out;
1484 
1485 		if (sysctl_tcp_slow_start_after_idle &&
1486 		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1487 			tcp_cwnd_application_limited(sk);
1488 	}
1489 }
1490 
1491 /* Minshall's variant of the Nagle send check. */
1492 static bool tcp_minshall_check(const struct tcp_sock *tp)
1493 {
1494 	return after(tp->snd_sml, tp->snd_una) &&
1495 		!after(tp->snd_sml, tp->snd_nxt);
1496 }
1497 
1498 /* Update snd_sml if this skb is under mss
1499  * Note that a TSO packet might end with a sub-mss segment
1500  * The test is really :
1501  * if ((skb->len % mss) != 0)
1502  *        tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1503  * But we can avoid doing the divide again given we already have
1504  *  skb_pcount = skb->len / mss_now
1505  */
1506 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1507 				const struct sk_buff *skb)
1508 {
1509 	if (skb->len < tcp_skb_pcount(skb) * mss_now)
1510 		tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1511 }
1512 
1513 /* Return false, if packet can be sent now without violation Nagle's rules:
1514  * 1. It is full sized. (provided by caller in %partial bool)
1515  * 2. Or it contains FIN. (already checked by caller)
1516  * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1517  * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1518  *    With Minshall's modification: all sent small packets are ACKed.
1519  */
1520 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1521 			    int nonagle)
1522 {
1523 	return partial &&
1524 		((nonagle & TCP_NAGLE_CORK) ||
1525 		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1526 }
1527 
1528 /* Return how many segs we'd like on a TSO packet,
1529  * to send one TSO packet per ms
1530  */
1531 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1532 {
1533 	u32 bytes, segs;
1534 
1535 	bytes = min(sk->sk_pacing_rate >> 10,
1536 		    sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1537 
1538 	/* Goal is to send at least one packet per ms,
1539 	 * not one big TSO packet every 100 ms.
1540 	 * This preserves ACK clocking and is consistent
1541 	 * with tcp_tso_should_defer() heuristic.
1542 	 */
1543 	segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1544 
1545 	return min_t(u32, segs, sk->sk_gso_max_segs);
1546 }
1547 
1548 /* Returns the portion of skb which can be sent right away */
1549 static unsigned int tcp_mss_split_point(const struct sock *sk,
1550 					const struct sk_buff *skb,
1551 					unsigned int mss_now,
1552 					unsigned int max_segs,
1553 					int nonagle)
1554 {
1555 	const struct tcp_sock *tp = tcp_sk(sk);
1556 	u32 partial, needed, window, max_len;
1557 
1558 	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1559 	max_len = mss_now * max_segs;
1560 
1561 	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1562 		return max_len;
1563 
1564 	needed = min(skb->len, window);
1565 
1566 	if (max_len <= needed)
1567 		return max_len;
1568 
1569 	partial = needed % mss_now;
1570 	/* If last segment is not a full MSS, check if Nagle rules allow us
1571 	 * to include this last segment in this skb.
1572 	 * Otherwise, we'll split the skb at last MSS boundary
1573 	 */
1574 	if (tcp_nagle_check(partial != 0, tp, nonagle))
1575 		return needed - partial;
1576 
1577 	return needed;
1578 }
1579 
1580 /* Can at least one segment of SKB be sent right now, according to the
1581  * congestion window rules?  If so, return how many segments are allowed.
1582  */
1583 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1584 					 const struct sk_buff *skb)
1585 {
1586 	u32 in_flight, cwnd, halfcwnd;
1587 
1588 	/* Don't be strict about the congestion window for the final FIN.  */
1589 	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1590 	    tcp_skb_pcount(skb) == 1)
1591 		return 1;
1592 
1593 	in_flight = tcp_packets_in_flight(tp);
1594 	cwnd = tp->snd_cwnd;
1595 	if (in_flight >= cwnd)
1596 		return 0;
1597 
1598 	/* For better scheduling, ensure we have at least
1599 	 * 2 GSO packets in flight.
1600 	 */
1601 	halfcwnd = max(cwnd >> 1, 1U);
1602 	return min(halfcwnd, cwnd - in_flight);
1603 }
1604 
1605 /* Initialize TSO state of a skb.
1606  * This must be invoked the first time we consider transmitting
1607  * SKB onto the wire.
1608  */
1609 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
1610 			     unsigned int mss_now)
1611 {
1612 	int tso_segs = tcp_skb_pcount(skb);
1613 
1614 	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1615 		tcp_set_skb_tso_segs(sk, skb, mss_now);
1616 		tso_segs = tcp_skb_pcount(skb);
1617 	}
1618 	return tso_segs;
1619 }
1620 
1621 
1622 /* Return true if the Nagle test allows this packet to be
1623  * sent now.
1624  */
1625 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1626 				  unsigned int cur_mss, int nonagle)
1627 {
1628 	/* Nagle rule does not apply to frames, which sit in the middle of the
1629 	 * write_queue (they have no chances to get new data).
1630 	 *
1631 	 * This is implemented in the callers, where they modify the 'nonagle'
1632 	 * argument based upon the location of SKB in the send queue.
1633 	 */
1634 	if (nonagle & TCP_NAGLE_PUSH)
1635 		return true;
1636 
1637 	/* Don't use the nagle rule for urgent data (or for the final FIN). */
1638 	if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1639 		return true;
1640 
1641 	if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1642 		return true;
1643 
1644 	return false;
1645 }
1646 
1647 /* Does at least the first segment of SKB fit into the send window? */
1648 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1649 			     const struct sk_buff *skb,
1650 			     unsigned int cur_mss)
1651 {
1652 	u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1653 
1654 	if (skb->len > cur_mss)
1655 		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1656 
1657 	return !after(end_seq, tcp_wnd_end(tp));
1658 }
1659 
1660 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1661  * should be put on the wire right now.  If so, it returns the number of
1662  * packets allowed by the congestion window.
1663  */
1664 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1665 				 unsigned int cur_mss, int nonagle)
1666 {
1667 	const struct tcp_sock *tp = tcp_sk(sk);
1668 	unsigned int cwnd_quota;
1669 
1670 	tcp_init_tso_segs(sk, skb, cur_mss);
1671 
1672 	if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1673 		return 0;
1674 
1675 	cwnd_quota = tcp_cwnd_test(tp, skb);
1676 	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1677 		cwnd_quota = 0;
1678 
1679 	return cwnd_quota;
1680 }
1681 
1682 /* Test if sending is allowed right now. */
1683 bool tcp_may_send_now(struct sock *sk)
1684 {
1685 	const struct tcp_sock *tp = tcp_sk(sk);
1686 	struct sk_buff *skb = tcp_send_head(sk);
1687 
1688 	return skb &&
1689 		tcp_snd_test(sk, skb, tcp_current_mss(sk),
1690 			     (tcp_skb_is_last(sk, skb) ?
1691 			      tp->nonagle : TCP_NAGLE_PUSH));
1692 }
1693 
1694 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1695  * which is put after SKB on the list.  It is very much like
1696  * tcp_fragment() except that it may make several kinds of assumptions
1697  * in order to speed up the splitting operation.  In particular, we
1698  * know that all the data is in scatter-gather pages, and that the
1699  * packet has never been sent out before (and thus is not cloned).
1700  */
1701 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1702 			unsigned int mss_now, gfp_t gfp)
1703 {
1704 	struct sk_buff *buff;
1705 	int nlen = skb->len - len;
1706 	u8 flags;
1707 
1708 	/* All of a TSO frame must be composed of paged data.  */
1709 	if (skb->len != skb->data_len)
1710 		return tcp_fragment(sk, skb, len, mss_now, gfp);
1711 
1712 	buff = sk_stream_alloc_skb(sk, 0, gfp);
1713 	if (unlikely(buff == NULL))
1714 		return -ENOMEM;
1715 
1716 	sk->sk_wmem_queued += buff->truesize;
1717 	sk_mem_charge(sk, buff->truesize);
1718 	buff->truesize += nlen;
1719 	skb->truesize -= nlen;
1720 
1721 	/* Correct the sequence numbers. */
1722 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1723 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1724 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1725 
1726 	/* PSH and FIN should only be set in the second packet. */
1727 	flags = TCP_SKB_CB(skb)->tcp_flags;
1728 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1729 	TCP_SKB_CB(buff)->tcp_flags = flags;
1730 
1731 	/* This packet was never sent out yet, so no SACK bits. */
1732 	TCP_SKB_CB(buff)->sacked = 0;
1733 
1734 	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1735 	skb_split(skb, buff, len);
1736 	tcp_fragment_tstamp(skb, buff);
1737 
1738 	/* Fix up tso_factor for both original and new SKB.  */
1739 	tcp_set_skb_tso_segs(sk, skb, mss_now);
1740 	tcp_set_skb_tso_segs(sk, buff, mss_now);
1741 
1742 	/* Link BUFF into the send queue. */
1743 	__skb_header_release(buff);
1744 	tcp_insert_write_queue_after(skb, buff, sk);
1745 
1746 	return 0;
1747 }
1748 
1749 /* Try to defer sending, if possible, in order to minimize the amount
1750  * of TSO splitting we do.  View it as a kind of TSO Nagle test.
1751  *
1752  * This algorithm is from John Heffner.
1753  */
1754 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1755 				 bool *is_cwnd_limited, u32 max_segs)
1756 {
1757 	struct tcp_sock *tp = tcp_sk(sk);
1758 	const struct inet_connection_sock *icsk = inet_csk(sk);
1759 	u32 send_win, cong_win, limit, in_flight;
1760 	int win_divisor;
1761 
1762 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1763 		goto send_now;
1764 
1765 	if (icsk->icsk_ca_state != TCP_CA_Open)
1766 		goto send_now;
1767 
1768 	/* Defer for less than two clock ticks. */
1769 	if (tp->tso_deferred &&
1770 	    (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
1771 		goto send_now;
1772 
1773 	in_flight = tcp_packets_in_flight(tp);
1774 
1775 	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1776 
1777 	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1778 
1779 	/* From in_flight test above, we know that cwnd > in_flight.  */
1780 	cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1781 
1782 	limit = min(send_win, cong_win);
1783 
1784 	/* If a full-sized TSO skb can be sent, do it. */
1785 	if (limit >= max_segs * tp->mss_cache)
1786 		goto send_now;
1787 
1788 	/* Middle in queue won't get any more data, full sendable already? */
1789 	if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1790 		goto send_now;
1791 
1792 	win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1793 	if (win_divisor) {
1794 		u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1795 
1796 		/* If at least some fraction of a window is available,
1797 		 * just use it.
1798 		 */
1799 		chunk /= win_divisor;
1800 		if (limit >= chunk)
1801 			goto send_now;
1802 	} else {
1803 		/* Different approach, try not to defer past a single
1804 		 * ACK.  Receiver should ACK every other full sized
1805 		 * frame, so if we have space for more than 3 frames
1806 		 * then send now.
1807 		 */
1808 		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1809 			goto send_now;
1810 	}
1811 
1812 	/* Ok, it looks like it is advisable to defer.
1813 	 * Do not rearm the timer if already set to not break TCP ACK clocking.
1814 	 */
1815 	if (!tp->tso_deferred)
1816 		tp->tso_deferred = 1 | (jiffies << 1);
1817 
1818 	if (cong_win < send_win && cong_win < skb->len)
1819 		*is_cwnd_limited = true;
1820 
1821 	return true;
1822 
1823 send_now:
1824 	tp->tso_deferred = 0;
1825 	return false;
1826 }
1827 
1828 /* Create a new MTU probe if we are ready.
1829  * MTU probe is regularly attempting to increase the path MTU by
1830  * deliberately sending larger packets.  This discovers routing
1831  * changes resulting in larger path MTUs.
1832  *
1833  * Returns 0 if we should wait to probe (no cwnd available),
1834  *         1 if a probe was sent,
1835  *         -1 otherwise
1836  */
1837 static int tcp_mtu_probe(struct sock *sk)
1838 {
1839 	struct tcp_sock *tp = tcp_sk(sk);
1840 	struct inet_connection_sock *icsk = inet_csk(sk);
1841 	struct sk_buff *skb, *nskb, *next;
1842 	int len;
1843 	int probe_size;
1844 	int size_needed;
1845 	int copy;
1846 	int mss_now;
1847 
1848 	/* Not currently probing/verifying,
1849 	 * not in recovery,
1850 	 * have enough cwnd, and
1851 	 * not SACKing (the variable headers throw things off) */
1852 	if (!icsk->icsk_mtup.enabled ||
1853 	    icsk->icsk_mtup.probe_size ||
1854 	    inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1855 	    tp->snd_cwnd < 11 ||
1856 	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1857 		return -1;
1858 
1859 	/* Very simple search strategy: just double the MSS. */
1860 	mss_now = tcp_current_mss(sk);
1861 	probe_size = 2 * tp->mss_cache;
1862 	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1863 	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
1864 		/* TODO: set timer for probe_converge_event */
1865 		return -1;
1866 	}
1867 
1868 	/* Have enough data in the send queue to probe? */
1869 	if (tp->write_seq - tp->snd_nxt < size_needed)
1870 		return -1;
1871 
1872 	if (tp->snd_wnd < size_needed)
1873 		return -1;
1874 	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1875 		return 0;
1876 
1877 	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
1878 	if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1879 		if (!tcp_packets_in_flight(tp))
1880 			return -1;
1881 		else
1882 			return 0;
1883 	}
1884 
1885 	/* We're allowed to probe.  Build it now. */
1886 	if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
1887 		return -1;
1888 	sk->sk_wmem_queued += nskb->truesize;
1889 	sk_mem_charge(sk, nskb->truesize);
1890 
1891 	skb = tcp_send_head(sk);
1892 
1893 	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1894 	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1895 	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1896 	TCP_SKB_CB(nskb)->sacked = 0;
1897 	nskb->csum = 0;
1898 	nskb->ip_summed = skb->ip_summed;
1899 
1900 	tcp_insert_write_queue_before(nskb, skb, sk);
1901 
1902 	len = 0;
1903 	tcp_for_write_queue_from_safe(skb, next, sk) {
1904 		copy = min_t(int, skb->len, probe_size - len);
1905 		if (nskb->ip_summed)
1906 			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1907 		else
1908 			nskb->csum = skb_copy_and_csum_bits(skb, 0,
1909 							    skb_put(nskb, copy),
1910 							    copy, nskb->csum);
1911 
1912 		if (skb->len <= copy) {
1913 			/* We've eaten all the data from this skb.
1914 			 * Throw it away. */
1915 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1916 			tcp_unlink_write_queue(skb, sk);
1917 			sk_wmem_free_skb(sk, skb);
1918 		} else {
1919 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1920 						   ~(TCPHDR_FIN|TCPHDR_PSH);
1921 			if (!skb_shinfo(skb)->nr_frags) {
1922 				skb_pull(skb, copy);
1923 				if (skb->ip_summed != CHECKSUM_PARTIAL)
1924 					skb->csum = csum_partial(skb->data,
1925 								 skb->len, 0);
1926 			} else {
1927 				__pskb_trim_head(skb, copy);
1928 				tcp_set_skb_tso_segs(sk, skb, mss_now);
1929 			}
1930 			TCP_SKB_CB(skb)->seq += copy;
1931 		}
1932 
1933 		len += copy;
1934 
1935 		if (len >= probe_size)
1936 			break;
1937 	}
1938 	tcp_init_tso_segs(sk, nskb, nskb->len);
1939 
1940 	/* We're ready to send.  If this fails, the probe will
1941 	 * be resegmented into mss-sized pieces by tcp_write_xmit().
1942 	 */
1943 	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1944 		/* Decrement cwnd here because we are sending
1945 		 * effectively two packets. */
1946 		tp->snd_cwnd--;
1947 		tcp_event_new_data_sent(sk, nskb);
1948 
1949 		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1950 		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1951 		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1952 
1953 		return 1;
1954 	}
1955 
1956 	return -1;
1957 }
1958 
1959 /* This routine writes packets to the network.  It advances the
1960  * send_head.  This happens as incoming acks open up the remote
1961  * window for us.
1962  *
1963  * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1964  * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1965  * account rare use of URG, this is not a big flaw.
1966  *
1967  * Send at most one packet when push_one > 0. Temporarily ignore
1968  * cwnd limit to force at most one packet out when push_one == 2.
1969 
1970  * Returns true, if no segments are in flight and we have queued segments,
1971  * but cannot send anything now because of SWS or another problem.
1972  */
1973 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
1974 			   int push_one, gfp_t gfp)
1975 {
1976 	struct tcp_sock *tp = tcp_sk(sk);
1977 	struct sk_buff *skb;
1978 	unsigned int tso_segs, sent_pkts;
1979 	int cwnd_quota;
1980 	int result;
1981 	bool is_cwnd_limited = false;
1982 	u32 max_segs;
1983 
1984 	sent_pkts = 0;
1985 
1986 	if (!push_one) {
1987 		/* Do MTU probing. */
1988 		result = tcp_mtu_probe(sk);
1989 		if (!result) {
1990 			return false;
1991 		} else if (result > 0) {
1992 			sent_pkts = 1;
1993 		}
1994 	}
1995 
1996 	max_segs = tcp_tso_autosize(sk, mss_now);
1997 	while ((skb = tcp_send_head(sk))) {
1998 		unsigned int limit;
1999 
2000 		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
2001 		BUG_ON(!tso_segs);
2002 
2003 		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2004 			/* "skb_mstamp" is used as a start point for the retransmit timer */
2005 			skb_mstamp_get(&skb->skb_mstamp);
2006 			goto repair; /* Skip network transmission */
2007 		}
2008 
2009 		cwnd_quota = tcp_cwnd_test(tp, skb);
2010 		if (!cwnd_quota) {
2011 			is_cwnd_limited = true;
2012 			if (push_one == 2)
2013 				/* Force out a loss probe pkt. */
2014 				cwnd_quota = 1;
2015 			else
2016 				break;
2017 		}
2018 
2019 		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2020 			break;
2021 
2022 		if (tso_segs == 1 || !max_segs) {
2023 			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2024 						     (tcp_skb_is_last(sk, skb) ?
2025 						      nonagle : TCP_NAGLE_PUSH))))
2026 				break;
2027 		} else {
2028 			if (!push_one &&
2029 			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2030 						 max_segs))
2031 				break;
2032 		}
2033 
2034 		limit = mss_now;
2035 		if (tso_segs > 1 && max_segs && !tcp_urg_mode(tp))
2036 			limit = tcp_mss_split_point(sk, skb, mss_now,
2037 						    min_t(unsigned int,
2038 							  cwnd_quota,
2039 							  max_segs),
2040 						    nonagle);
2041 
2042 		if (skb->len > limit &&
2043 		    unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2044 			break;
2045 
2046 		/* TCP Small Queues :
2047 		 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2048 		 * This allows for :
2049 		 *  - better RTT estimation and ACK scheduling
2050 		 *  - faster recovery
2051 		 *  - high rates
2052 		 * Alas, some drivers / subsystems require a fair amount
2053 		 * of queued bytes to ensure line rate.
2054 		 * One example is wifi aggregation (802.11 AMPDU)
2055 		 */
2056 		limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2057 		limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2058 
2059 		if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2060 			set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2061 			/* It is possible TX completion already happened
2062 			 * before we set TSQ_THROTTLED, so we must
2063 			 * test again the condition.
2064 			 */
2065 			smp_mb__after_atomic();
2066 			if (atomic_read(&sk->sk_wmem_alloc) > limit)
2067 				break;
2068 		}
2069 
2070 		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2071 			break;
2072 
2073 repair:
2074 		/* Advance the send_head.  This one is sent out.
2075 		 * This call will increment packets_out.
2076 		 */
2077 		tcp_event_new_data_sent(sk, skb);
2078 
2079 		tcp_minshall_update(tp, mss_now, skb);
2080 		sent_pkts += tcp_skb_pcount(skb);
2081 
2082 		if (push_one)
2083 			break;
2084 	}
2085 
2086 	if (likely(sent_pkts)) {
2087 		if (tcp_in_cwnd_reduction(sk))
2088 			tp->prr_out += sent_pkts;
2089 
2090 		/* Send one loss probe per tail loss episode. */
2091 		if (push_one != 2)
2092 			tcp_schedule_loss_probe(sk);
2093 		tcp_cwnd_validate(sk, is_cwnd_limited);
2094 		return false;
2095 	}
2096 	return (push_one == 2) || (!tp->packets_out && tcp_send_head(sk));
2097 }
2098 
2099 bool tcp_schedule_loss_probe(struct sock *sk)
2100 {
2101 	struct inet_connection_sock *icsk = inet_csk(sk);
2102 	struct tcp_sock *tp = tcp_sk(sk);
2103 	u32 timeout, tlp_time_stamp, rto_time_stamp;
2104 	u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2105 
2106 	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2107 		return false;
2108 	/* No consecutive loss probes. */
2109 	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2110 		tcp_rearm_rto(sk);
2111 		return false;
2112 	}
2113 	/* Don't do any loss probe on a Fast Open connection before 3WHS
2114 	 * finishes.
2115 	 */
2116 	if (sk->sk_state == TCP_SYN_RECV)
2117 		return false;
2118 
2119 	/* TLP is only scheduled when next timer event is RTO. */
2120 	if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2121 		return false;
2122 
2123 	/* Schedule a loss probe in 2*RTT for SACK capable connections
2124 	 * in Open state, that are either limited by cwnd or application.
2125 	 */
2126 	if (sysctl_tcp_early_retrans < 3 || !tp->srtt_us || !tp->packets_out ||
2127 	    !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2128 		return false;
2129 
2130 	if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2131 	     tcp_send_head(sk))
2132 		return false;
2133 
2134 	/* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2135 	 * for delayed ack when there's one outstanding packet.
2136 	 */
2137 	timeout = rtt << 1;
2138 	if (tp->packets_out == 1)
2139 		timeout = max_t(u32, timeout,
2140 				(rtt + (rtt >> 1) + TCP_DELACK_MAX));
2141 	timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2142 
2143 	/* If RTO is shorter, just schedule TLP in its place. */
2144 	tlp_time_stamp = tcp_time_stamp + timeout;
2145 	rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2146 	if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2147 		s32 delta = rto_time_stamp - tcp_time_stamp;
2148 		if (delta > 0)
2149 			timeout = delta;
2150 	}
2151 
2152 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2153 				  TCP_RTO_MAX);
2154 	return true;
2155 }
2156 
2157 /* Thanks to skb fast clones, we can detect if a prior transmit of
2158  * a packet is still in a qdisc or driver queue.
2159  * In this case, there is very little point doing a retransmit !
2160  * Note: This is called from BH context only.
2161  */
2162 static bool skb_still_in_host_queue(const struct sock *sk,
2163 				    const struct sk_buff *skb)
2164 {
2165 	if (unlikely(skb_fclone_busy(sk, skb))) {
2166 		NET_INC_STATS_BH(sock_net(sk),
2167 				 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2168 		return true;
2169 	}
2170 	return false;
2171 }
2172 
2173 /* When probe timeout (PTO) fires, send a new segment if one exists, else
2174  * retransmit the last segment.
2175  */
2176 void tcp_send_loss_probe(struct sock *sk)
2177 {
2178 	struct tcp_sock *tp = tcp_sk(sk);
2179 	struct sk_buff *skb;
2180 	int pcount;
2181 	int mss = tcp_current_mss(sk);
2182 	int err = -1;
2183 
2184 	if (tcp_send_head(sk) != NULL) {
2185 		err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2186 		goto rearm_timer;
2187 	}
2188 
2189 	/* At most one outstanding TLP retransmission. */
2190 	if (tp->tlp_high_seq)
2191 		goto rearm_timer;
2192 
2193 	/* Retransmit last segment. */
2194 	skb = tcp_write_queue_tail(sk);
2195 	if (WARN_ON(!skb))
2196 		goto rearm_timer;
2197 
2198 	if (skb_still_in_host_queue(sk, skb))
2199 		goto rearm_timer;
2200 
2201 	pcount = tcp_skb_pcount(skb);
2202 	if (WARN_ON(!pcount))
2203 		goto rearm_timer;
2204 
2205 	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2206 		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2207 					  GFP_ATOMIC)))
2208 			goto rearm_timer;
2209 		skb = tcp_write_queue_tail(sk);
2210 	}
2211 
2212 	if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2213 		goto rearm_timer;
2214 
2215 	err = __tcp_retransmit_skb(sk, skb);
2216 
2217 	/* Record snd_nxt for loss detection. */
2218 	if (likely(!err))
2219 		tp->tlp_high_seq = tp->snd_nxt;
2220 
2221 rearm_timer:
2222 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2223 				  inet_csk(sk)->icsk_rto,
2224 				  TCP_RTO_MAX);
2225 
2226 	if (likely(!err))
2227 		NET_INC_STATS_BH(sock_net(sk),
2228 				 LINUX_MIB_TCPLOSSPROBES);
2229 }
2230 
2231 /* Push out any pending frames which were held back due to
2232  * TCP_CORK or attempt at coalescing tiny packets.
2233  * The socket must be locked by the caller.
2234  */
2235 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2236 			       int nonagle)
2237 {
2238 	/* If we are closed, the bytes will have to remain here.
2239 	 * In time closedown will finish, we empty the write queue and
2240 	 * all will be happy.
2241 	 */
2242 	if (unlikely(sk->sk_state == TCP_CLOSE))
2243 		return;
2244 
2245 	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2246 			   sk_gfp_atomic(sk, GFP_ATOMIC)))
2247 		tcp_check_probe_timer(sk);
2248 }
2249 
2250 /* Send _single_ skb sitting at the send head. This function requires
2251  * true push pending frames to setup probe timer etc.
2252  */
2253 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2254 {
2255 	struct sk_buff *skb = tcp_send_head(sk);
2256 
2257 	BUG_ON(!skb || skb->len < mss_now);
2258 
2259 	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2260 }
2261 
2262 /* This function returns the amount that we can raise the
2263  * usable window based on the following constraints
2264  *
2265  * 1. The window can never be shrunk once it is offered (RFC 793)
2266  * 2. We limit memory per socket
2267  *
2268  * RFC 1122:
2269  * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2270  *  RECV.NEXT + RCV.WIN fixed until:
2271  *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2272  *
2273  * i.e. don't raise the right edge of the window until you can raise
2274  * it at least MSS bytes.
2275  *
2276  * Unfortunately, the recommended algorithm breaks header prediction,
2277  * since header prediction assumes th->window stays fixed.
2278  *
2279  * Strictly speaking, keeping th->window fixed violates the receiver
2280  * side SWS prevention criteria. The problem is that under this rule
2281  * a stream of single byte packets will cause the right side of the
2282  * window to always advance by a single byte.
2283  *
2284  * Of course, if the sender implements sender side SWS prevention
2285  * then this will not be a problem.
2286  *
2287  * BSD seems to make the following compromise:
2288  *
2289  *	If the free space is less than the 1/4 of the maximum
2290  *	space available and the free space is less than 1/2 mss,
2291  *	then set the window to 0.
2292  *	[ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2293  *	Otherwise, just prevent the window from shrinking
2294  *	and from being larger than the largest representable value.
2295  *
2296  * This prevents incremental opening of the window in the regime
2297  * where TCP is limited by the speed of the reader side taking
2298  * data out of the TCP receive queue. It does nothing about
2299  * those cases where the window is constrained on the sender side
2300  * because the pipeline is full.
2301  *
2302  * BSD also seems to "accidentally" limit itself to windows that are a
2303  * multiple of MSS, at least until the free space gets quite small.
2304  * This would appear to be a side effect of the mbuf implementation.
2305  * Combining these two algorithms results in the observed behavior
2306  * of having a fixed window size at almost all times.
2307  *
2308  * Below we obtain similar behavior by forcing the offered window to
2309  * a multiple of the mss when it is feasible to do so.
2310  *
2311  * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2312  * Regular options like TIMESTAMP are taken into account.
2313  */
2314 u32 __tcp_select_window(struct sock *sk)
2315 {
2316 	struct inet_connection_sock *icsk = inet_csk(sk);
2317 	struct tcp_sock *tp = tcp_sk(sk);
2318 	/* MSS for the peer's data.  Previous versions used mss_clamp
2319 	 * here.  I don't know if the value based on our guesses
2320 	 * of peer's MSS is better for the performance.  It's more correct
2321 	 * but may be worse for the performance because of rcv_mss
2322 	 * fluctuations.  --SAW  1998/11/1
2323 	 */
2324 	int mss = icsk->icsk_ack.rcv_mss;
2325 	int free_space = tcp_space(sk);
2326 	int allowed_space = tcp_full_space(sk);
2327 	int full_space = min_t(int, tp->window_clamp, allowed_space);
2328 	int window;
2329 
2330 	if (mss > full_space)
2331 		mss = full_space;
2332 
2333 	if (free_space < (full_space >> 1)) {
2334 		icsk->icsk_ack.quick = 0;
2335 
2336 		if (sk_under_memory_pressure(sk))
2337 			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2338 					       4U * tp->advmss);
2339 
2340 		/* free_space might become our new window, make sure we don't
2341 		 * increase it due to wscale.
2342 		 */
2343 		free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2344 
2345 		/* if free space is less than mss estimate, or is below 1/16th
2346 		 * of the maximum allowed, try to move to zero-window, else
2347 		 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2348 		 * new incoming data is dropped due to memory limits.
2349 		 * With large window, mss test triggers way too late in order
2350 		 * to announce zero window in time before rmem limit kicks in.
2351 		 */
2352 		if (free_space < (allowed_space >> 4) || free_space < mss)
2353 			return 0;
2354 	}
2355 
2356 	if (free_space > tp->rcv_ssthresh)
2357 		free_space = tp->rcv_ssthresh;
2358 
2359 	/* Don't do rounding if we are using window scaling, since the
2360 	 * scaled window will not line up with the MSS boundary anyway.
2361 	 */
2362 	window = tp->rcv_wnd;
2363 	if (tp->rx_opt.rcv_wscale) {
2364 		window = free_space;
2365 
2366 		/* Advertise enough space so that it won't get scaled away.
2367 		 * Import case: prevent zero window announcement if
2368 		 * 1<<rcv_wscale > mss.
2369 		 */
2370 		if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2371 			window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2372 				  << tp->rx_opt.rcv_wscale);
2373 	} else {
2374 		/* Get the largest window that is a nice multiple of mss.
2375 		 * Window clamp already applied above.
2376 		 * If our current window offering is within 1 mss of the
2377 		 * free space we just keep it. This prevents the divide
2378 		 * and multiply from happening most of the time.
2379 		 * We also don't do any window rounding when the free space
2380 		 * is too small.
2381 		 */
2382 		if (window <= free_space - mss || window > free_space)
2383 			window = (free_space / mss) * mss;
2384 		else if (mss == full_space &&
2385 			 free_space > window + (full_space >> 1))
2386 			window = free_space;
2387 	}
2388 
2389 	return window;
2390 }
2391 
2392 /* Collapses two adjacent SKB's during retransmission. */
2393 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2394 {
2395 	struct tcp_sock *tp = tcp_sk(sk);
2396 	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2397 	int skb_size, next_skb_size;
2398 
2399 	skb_size = skb->len;
2400 	next_skb_size = next_skb->len;
2401 
2402 	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2403 
2404 	tcp_highest_sack_combine(sk, next_skb, skb);
2405 
2406 	tcp_unlink_write_queue(next_skb, sk);
2407 
2408 	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2409 				  next_skb_size);
2410 
2411 	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2412 		skb->ip_summed = CHECKSUM_PARTIAL;
2413 
2414 	if (skb->ip_summed != CHECKSUM_PARTIAL)
2415 		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2416 
2417 	/* Update sequence range on original skb. */
2418 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2419 
2420 	/* Merge over control information. This moves PSH/FIN etc. over */
2421 	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2422 
2423 	/* All done, get rid of second SKB and account for it so
2424 	 * packet counting does not break.
2425 	 */
2426 	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2427 
2428 	/* changed transmit queue under us so clear hints */
2429 	tcp_clear_retrans_hints_partial(tp);
2430 	if (next_skb == tp->retransmit_skb_hint)
2431 		tp->retransmit_skb_hint = skb;
2432 
2433 	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2434 
2435 	sk_wmem_free_skb(sk, next_skb);
2436 }
2437 
2438 /* Check if coalescing SKBs is legal. */
2439 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2440 {
2441 	if (tcp_skb_pcount(skb) > 1)
2442 		return false;
2443 	/* TODO: SACK collapsing could be used to remove this condition */
2444 	if (skb_shinfo(skb)->nr_frags != 0)
2445 		return false;
2446 	if (skb_cloned(skb))
2447 		return false;
2448 	if (skb == tcp_send_head(sk))
2449 		return false;
2450 	/* Some heurestics for collapsing over SACK'd could be invented */
2451 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2452 		return false;
2453 
2454 	return true;
2455 }
2456 
2457 /* Collapse packets in the retransmit queue to make to create
2458  * less packets on the wire. This is only done on retransmission.
2459  */
2460 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2461 				     int space)
2462 {
2463 	struct tcp_sock *tp = tcp_sk(sk);
2464 	struct sk_buff *skb = to, *tmp;
2465 	bool first = true;
2466 
2467 	if (!sysctl_tcp_retrans_collapse)
2468 		return;
2469 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2470 		return;
2471 
2472 	tcp_for_write_queue_from_safe(skb, tmp, sk) {
2473 		if (!tcp_can_collapse(sk, skb))
2474 			break;
2475 
2476 		space -= skb->len;
2477 
2478 		if (first) {
2479 			first = false;
2480 			continue;
2481 		}
2482 
2483 		if (space < 0)
2484 			break;
2485 		/* Punt if not enough space exists in the first SKB for
2486 		 * the data in the second
2487 		 */
2488 		if (skb->len > skb_availroom(to))
2489 			break;
2490 
2491 		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2492 			break;
2493 
2494 		tcp_collapse_retrans(sk, to);
2495 	}
2496 }
2497 
2498 /* This retransmits one SKB.  Policy decisions and retransmit queue
2499  * state updates are done by the caller.  Returns non-zero if an
2500  * error occurred which prevented the send.
2501  */
2502 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2503 {
2504 	struct tcp_sock *tp = tcp_sk(sk);
2505 	struct inet_connection_sock *icsk = inet_csk(sk);
2506 	unsigned int cur_mss;
2507 	int err;
2508 
2509 	/* Inconslusive MTU probe */
2510 	if (icsk->icsk_mtup.probe_size) {
2511 		icsk->icsk_mtup.probe_size = 0;
2512 	}
2513 
2514 	/* Do not sent more than we queued. 1/4 is reserved for possible
2515 	 * copying overhead: fragmentation, tunneling, mangling etc.
2516 	 */
2517 	if (atomic_read(&sk->sk_wmem_alloc) >
2518 	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2519 		return -EAGAIN;
2520 
2521 	if (skb_still_in_host_queue(sk, skb))
2522 		return -EBUSY;
2523 
2524 	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2525 		if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2526 			BUG();
2527 		if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2528 			return -ENOMEM;
2529 	}
2530 
2531 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2532 		return -EHOSTUNREACH; /* Routing failure or similar. */
2533 
2534 	cur_mss = tcp_current_mss(sk);
2535 
2536 	/* If receiver has shrunk his window, and skb is out of
2537 	 * new window, do not retransmit it. The exception is the
2538 	 * case, when window is shrunk to zero. In this case
2539 	 * our retransmit serves as a zero window probe.
2540 	 */
2541 	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2542 	    TCP_SKB_CB(skb)->seq != tp->snd_una)
2543 		return -EAGAIN;
2544 
2545 	if (skb->len > cur_mss) {
2546 		if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
2547 			return -ENOMEM; /* We'll try again later. */
2548 	} else {
2549 		int oldpcount = tcp_skb_pcount(skb);
2550 
2551 		if (unlikely(oldpcount > 1)) {
2552 			if (skb_unclone(skb, GFP_ATOMIC))
2553 				return -ENOMEM;
2554 			tcp_init_tso_segs(sk, skb, cur_mss);
2555 			tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2556 		}
2557 	}
2558 
2559 	tcp_retrans_try_collapse(sk, skb, cur_mss);
2560 
2561 	/* Make a copy, if the first transmission SKB clone we made
2562 	 * is still in somebody's hands, else make a clone.
2563 	 */
2564 
2565 	/* make sure skb->data is aligned on arches that require it
2566 	 * and check if ack-trimming & collapsing extended the headroom
2567 	 * beyond what csum_start can cover.
2568 	 */
2569 	if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2570 		     skb_headroom(skb) >= 0xFFFF)) {
2571 		struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2572 						   GFP_ATOMIC);
2573 		err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2574 			     -ENOBUFS;
2575 	} else {
2576 		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2577 	}
2578 
2579 	if (likely(!err)) {
2580 		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2581 		/* Update global TCP statistics. */
2582 		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2583 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2584 			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2585 		tp->total_retrans++;
2586 	}
2587 	return err;
2588 }
2589 
2590 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2591 {
2592 	struct tcp_sock *tp = tcp_sk(sk);
2593 	int err = __tcp_retransmit_skb(sk, skb);
2594 
2595 	if (err == 0) {
2596 #if FASTRETRANS_DEBUG > 0
2597 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2598 			net_dbg_ratelimited("retrans_out leaked\n");
2599 		}
2600 #endif
2601 		if (!tp->retrans_out)
2602 			tp->lost_retrans_low = tp->snd_nxt;
2603 		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2604 		tp->retrans_out += tcp_skb_pcount(skb);
2605 
2606 		/* Save stamp of the first retransmit. */
2607 		if (!tp->retrans_stamp)
2608 			tp->retrans_stamp = tcp_skb_timestamp(skb);
2609 
2610 		/* snd_nxt is stored to detect loss of retransmitted segment,
2611 		 * see tcp_input.c tcp_sacktag_write_queue().
2612 		 */
2613 		TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2614 	} else if (err != -EBUSY) {
2615 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2616 	}
2617 
2618 	if (tp->undo_retrans < 0)
2619 		tp->undo_retrans = 0;
2620 	tp->undo_retrans += tcp_skb_pcount(skb);
2621 	return err;
2622 }
2623 
2624 /* Check if we forward retransmits are possible in the current
2625  * window/congestion state.
2626  */
2627 static bool tcp_can_forward_retransmit(struct sock *sk)
2628 {
2629 	const struct inet_connection_sock *icsk = inet_csk(sk);
2630 	const struct tcp_sock *tp = tcp_sk(sk);
2631 
2632 	/* Forward retransmissions are possible only during Recovery. */
2633 	if (icsk->icsk_ca_state != TCP_CA_Recovery)
2634 		return false;
2635 
2636 	/* No forward retransmissions in Reno are possible. */
2637 	if (tcp_is_reno(tp))
2638 		return false;
2639 
2640 	/* Yeah, we have to make difficult choice between forward transmission
2641 	 * and retransmission... Both ways have their merits...
2642 	 *
2643 	 * For now we do not retransmit anything, while we have some new
2644 	 * segments to send. In the other cases, follow rule 3 for
2645 	 * NextSeg() specified in RFC3517.
2646 	 */
2647 
2648 	if (tcp_may_send_now(sk))
2649 		return false;
2650 
2651 	return true;
2652 }
2653 
2654 /* This gets called after a retransmit timeout, and the initially
2655  * retransmitted data is acknowledged.  It tries to continue
2656  * resending the rest of the retransmit queue, until either
2657  * we've sent it all or the congestion window limit is reached.
2658  * If doing SACK, the first ACK which comes back for a timeout
2659  * based retransmit packet might feed us FACK information again.
2660  * If so, we use it to avoid unnecessarily retransmissions.
2661  */
2662 void tcp_xmit_retransmit_queue(struct sock *sk)
2663 {
2664 	const struct inet_connection_sock *icsk = inet_csk(sk);
2665 	struct tcp_sock *tp = tcp_sk(sk);
2666 	struct sk_buff *skb;
2667 	struct sk_buff *hole = NULL;
2668 	u32 last_lost;
2669 	int mib_idx;
2670 	int fwd_rexmitting = 0;
2671 
2672 	if (!tp->packets_out)
2673 		return;
2674 
2675 	if (!tp->lost_out)
2676 		tp->retransmit_high = tp->snd_una;
2677 
2678 	if (tp->retransmit_skb_hint) {
2679 		skb = tp->retransmit_skb_hint;
2680 		last_lost = TCP_SKB_CB(skb)->end_seq;
2681 		if (after(last_lost, tp->retransmit_high))
2682 			last_lost = tp->retransmit_high;
2683 	} else {
2684 		skb = tcp_write_queue_head(sk);
2685 		last_lost = tp->snd_una;
2686 	}
2687 
2688 	tcp_for_write_queue_from(skb, sk) {
2689 		__u8 sacked = TCP_SKB_CB(skb)->sacked;
2690 
2691 		if (skb == tcp_send_head(sk))
2692 			break;
2693 		/* we could do better than to assign each time */
2694 		if (hole == NULL)
2695 			tp->retransmit_skb_hint = skb;
2696 
2697 		/* Assume this retransmit will generate
2698 		 * only one packet for congestion window
2699 		 * calculation purposes.  This works because
2700 		 * tcp_retransmit_skb() will chop up the
2701 		 * packet to be MSS sized and all the
2702 		 * packet counting works out.
2703 		 */
2704 		if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2705 			return;
2706 
2707 		if (fwd_rexmitting) {
2708 begin_fwd:
2709 			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2710 				break;
2711 			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2712 
2713 		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2714 			tp->retransmit_high = last_lost;
2715 			if (!tcp_can_forward_retransmit(sk))
2716 				break;
2717 			/* Backtrack if necessary to non-L'ed skb */
2718 			if (hole != NULL) {
2719 				skb = hole;
2720 				hole = NULL;
2721 			}
2722 			fwd_rexmitting = 1;
2723 			goto begin_fwd;
2724 
2725 		} else if (!(sacked & TCPCB_LOST)) {
2726 			if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2727 				hole = skb;
2728 			continue;
2729 
2730 		} else {
2731 			last_lost = TCP_SKB_CB(skb)->end_seq;
2732 			if (icsk->icsk_ca_state != TCP_CA_Loss)
2733 				mib_idx = LINUX_MIB_TCPFASTRETRANS;
2734 			else
2735 				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2736 		}
2737 
2738 		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2739 			continue;
2740 
2741 		if (tcp_retransmit_skb(sk, skb))
2742 			return;
2743 
2744 		NET_INC_STATS_BH(sock_net(sk), mib_idx);
2745 
2746 		if (tcp_in_cwnd_reduction(sk))
2747 			tp->prr_out += tcp_skb_pcount(skb);
2748 
2749 		if (skb == tcp_write_queue_head(sk))
2750 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2751 						  inet_csk(sk)->icsk_rto,
2752 						  TCP_RTO_MAX);
2753 	}
2754 }
2755 
2756 /* Send a fin.  The caller locks the socket for us.  This cannot be
2757  * allowed to fail queueing a FIN frame under any circumstances.
2758  */
2759 void tcp_send_fin(struct sock *sk)
2760 {
2761 	struct tcp_sock *tp = tcp_sk(sk);
2762 	struct sk_buff *skb = tcp_write_queue_tail(sk);
2763 	int mss_now;
2764 
2765 	/* Optimization, tack on the FIN if we have a queue of
2766 	 * unsent frames.  But be careful about outgoing SACKS
2767 	 * and IP options.
2768 	 */
2769 	mss_now = tcp_current_mss(sk);
2770 
2771 	if (tcp_send_head(sk) != NULL) {
2772 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
2773 		TCP_SKB_CB(skb)->end_seq++;
2774 		tp->write_seq++;
2775 	} else {
2776 		/* Socket is locked, keep trying until memory is available. */
2777 		for (;;) {
2778 			skb = alloc_skb_fclone(MAX_TCP_HEADER,
2779 					       sk->sk_allocation);
2780 			if (skb)
2781 				break;
2782 			yield();
2783 		}
2784 
2785 		/* Reserve space for headers and prepare control bits. */
2786 		skb_reserve(skb, MAX_TCP_HEADER);
2787 		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2788 		tcp_init_nondata_skb(skb, tp->write_seq,
2789 				     TCPHDR_ACK | TCPHDR_FIN);
2790 		tcp_queue_skb(sk, skb);
2791 	}
2792 	__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
2793 }
2794 
2795 /* We get here when a process closes a file descriptor (either due to
2796  * an explicit close() or as a byproduct of exit()'ing) and there
2797  * was unread data in the receive queue.  This behavior is recommended
2798  * by RFC 2525, section 2.17.  -DaveM
2799  */
2800 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2801 {
2802 	struct sk_buff *skb;
2803 
2804 	/* NOTE: No TCP options attached and we never retransmit this. */
2805 	skb = alloc_skb(MAX_TCP_HEADER, priority);
2806 	if (!skb) {
2807 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2808 		return;
2809 	}
2810 
2811 	/* Reserve space for headers and prepare control bits. */
2812 	skb_reserve(skb, MAX_TCP_HEADER);
2813 	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2814 			     TCPHDR_ACK | TCPHDR_RST);
2815 	/* Send it off. */
2816 	if (tcp_transmit_skb(sk, skb, 0, priority))
2817 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2818 
2819 	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2820 }
2821 
2822 /* Send a crossed SYN-ACK during socket establishment.
2823  * WARNING: This routine must only be called when we have already sent
2824  * a SYN packet that crossed the incoming SYN that caused this routine
2825  * to get called. If this assumption fails then the initial rcv_wnd
2826  * and rcv_wscale values will not be correct.
2827  */
2828 int tcp_send_synack(struct sock *sk)
2829 {
2830 	struct sk_buff *skb;
2831 
2832 	skb = tcp_write_queue_head(sk);
2833 	if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2834 		pr_debug("%s: wrong queue state\n", __func__);
2835 		return -EFAULT;
2836 	}
2837 	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2838 		if (skb_cloned(skb)) {
2839 			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2840 			if (nskb == NULL)
2841 				return -ENOMEM;
2842 			tcp_unlink_write_queue(skb, sk);
2843 			__skb_header_release(nskb);
2844 			__tcp_add_write_queue_head(sk, nskb);
2845 			sk_wmem_free_skb(sk, skb);
2846 			sk->sk_wmem_queued += nskb->truesize;
2847 			sk_mem_charge(sk, nskb->truesize);
2848 			skb = nskb;
2849 		}
2850 
2851 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2852 		tcp_ecn_send_synack(sk, skb);
2853 	}
2854 	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2855 }
2856 
2857 /**
2858  * tcp_make_synack - Prepare a SYN-ACK.
2859  * sk: listener socket
2860  * dst: dst entry attached to the SYNACK
2861  * req: request_sock pointer
2862  *
2863  * Allocate one skb and build a SYNACK packet.
2864  * @dst is consumed : Caller should not use it again.
2865  */
2866 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2867 				struct request_sock *req,
2868 				struct tcp_fastopen_cookie *foc)
2869 {
2870 	struct tcp_out_options opts;
2871 	struct inet_request_sock *ireq = inet_rsk(req);
2872 	struct tcp_sock *tp = tcp_sk(sk);
2873 	struct tcphdr *th;
2874 	struct sk_buff *skb;
2875 	struct tcp_md5sig_key *md5;
2876 	int tcp_header_size;
2877 	int mss;
2878 
2879 	skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
2880 	if (unlikely(!skb)) {
2881 		dst_release(dst);
2882 		return NULL;
2883 	}
2884 	/* Reserve space for headers. */
2885 	skb_reserve(skb, MAX_TCP_HEADER);
2886 
2887 	skb_dst_set(skb, dst);
2888 	security_skb_owned_by(skb, sk);
2889 
2890 	mss = dst_metric_advmss(dst);
2891 	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2892 		mss = tp->rx_opt.user_mss;
2893 
2894 	memset(&opts, 0, sizeof(opts));
2895 #ifdef CONFIG_SYN_COOKIES
2896 	if (unlikely(req->cookie_ts))
2897 		skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
2898 	else
2899 #endif
2900 	skb_mstamp_get(&skb->skb_mstamp);
2901 	tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, &md5,
2902 					     foc) + sizeof(*th);
2903 
2904 	skb_push(skb, tcp_header_size);
2905 	skb_reset_transport_header(skb);
2906 
2907 	th = tcp_hdr(skb);
2908 	memset(th, 0, sizeof(struct tcphdr));
2909 	th->syn = 1;
2910 	th->ack = 1;
2911 	tcp_ecn_make_synack(req, th, sk);
2912 	th->source = htons(ireq->ir_num);
2913 	th->dest = ireq->ir_rmt_port;
2914 	/* Setting of flags are superfluous here for callers (and ECE is
2915 	 * not even correctly set)
2916 	 */
2917 	tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
2918 			     TCPHDR_SYN | TCPHDR_ACK);
2919 
2920 	th->seq = htonl(TCP_SKB_CB(skb)->seq);
2921 	/* XXX data is queued and acked as is. No buffer/window check */
2922 	th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
2923 
2924 	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2925 	th->window = htons(min(req->rcv_wnd, 65535U));
2926 	tcp_options_write((__be32 *)(th + 1), tp, &opts);
2927 	th->doff = (tcp_header_size >> 2);
2928 	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
2929 
2930 #ifdef CONFIG_TCP_MD5SIG
2931 	/* Okay, we have all we need - do the md5 hash if needed */
2932 	if (md5) {
2933 		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
2934 					       md5, NULL, req, skb);
2935 	}
2936 #endif
2937 
2938 	return skb;
2939 }
2940 EXPORT_SYMBOL(tcp_make_synack);
2941 
2942 /* Do all connect socket setups that can be done AF independent. */
2943 static void tcp_connect_init(struct sock *sk)
2944 {
2945 	const struct dst_entry *dst = __sk_dst_get(sk);
2946 	struct tcp_sock *tp = tcp_sk(sk);
2947 	__u8 rcv_wscale;
2948 
2949 	/* We'll fix this up when we get a response from the other end.
2950 	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2951 	 */
2952 	tp->tcp_header_len = sizeof(struct tcphdr) +
2953 		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
2954 
2955 #ifdef CONFIG_TCP_MD5SIG
2956 	if (tp->af_specific->md5_lookup(sk, sk) != NULL)
2957 		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
2958 #endif
2959 
2960 	/* If user gave his TCP_MAXSEG, record it to clamp */
2961 	if (tp->rx_opt.user_mss)
2962 		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2963 	tp->max_window = 0;
2964 	tcp_mtup_init(sk);
2965 	tcp_sync_mss(sk, dst_mtu(dst));
2966 
2967 	if (!tp->window_clamp)
2968 		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
2969 	tp->advmss = dst_metric_advmss(dst);
2970 	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
2971 		tp->advmss = tp->rx_opt.user_mss;
2972 
2973 	tcp_initialize_rcv_mss(sk);
2974 
2975 	/* limit the window selection if the user enforce a smaller rx buffer */
2976 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2977 	    (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
2978 		tp->window_clamp = tcp_full_space(sk);
2979 
2980 	tcp_select_initial_window(tcp_full_space(sk),
2981 				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
2982 				  &tp->rcv_wnd,
2983 				  &tp->window_clamp,
2984 				  sysctl_tcp_window_scaling,
2985 				  &rcv_wscale,
2986 				  dst_metric(dst, RTAX_INITRWND));
2987 
2988 	tp->rx_opt.rcv_wscale = rcv_wscale;
2989 	tp->rcv_ssthresh = tp->rcv_wnd;
2990 
2991 	sk->sk_err = 0;
2992 	sock_reset_flag(sk, SOCK_DONE);
2993 	tp->snd_wnd = 0;
2994 	tcp_init_wl(tp, 0);
2995 	tp->snd_una = tp->write_seq;
2996 	tp->snd_sml = tp->write_seq;
2997 	tp->snd_up = tp->write_seq;
2998 	tp->snd_nxt = tp->write_seq;
2999 
3000 	if (likely(!tp->repair))
3001 		tp->rcv_nxt = 0;
3002 	else
3003 		tp->rcv_tstamp = tcp_time_stamp;
3004 	tp->rcv_wup = tp->rcv_nxt;
3005 	tp->copied_seq = tp->rcv_nxt;
3006 
3007 	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3008 	inet_csk(sk)->icsk_retransmits = 0;
3009 	tcp_clear_retrans(tp);
3010 }
3011 
3012 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3013 {
3014 	struct tcp_sock *tp = tcp_sk(sk);
3015 	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3016 
3017 	tcb->end_seq += skb->len;
3018 	__skb_header_release(skb);
3019 	__tcp_add_write_queue_tail(sk, skb);
3020 	sk->sk_wmem_queued += skb->truesize;
3021 	sk_mem_charge(sk, skb->truesize);
3022 	tp->write_seq = tcb->end_seq;
3023 	tp->packets_out += tcp_skb_pcount(skb);
3024 }
3025 
3026 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3027  * queue a data-only packet after the regular SYN, such that regular SYNs
3028  * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3029  * only the SYN sequence, the data are retransmitted in the first ACK.
3030  * If cookie is not cached or other error occurs, falls back to send a
3031  * regular SYN with Fast Open cookie request option.
3032  */
3033 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3034 {
3035 	struct tcp_sock *tp = tcp_sk(sk);
3036 	struct tcp_fastopen_request *fo = tp->fastopen_req;
3037 	int syn_loss = 0, space, err = 0;
3038 	unsigned long last_syn_loss = 0;
3039 	struct sk_buff *syn_data;
3040 
3041 	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
3042 	tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3043 			       &syn_loss, &last_syn_loss);
3044 	/* Recurring FO SYN losses: revert to regular handshake temporarily */
3045 	if (syn_loss > 1 &&
3046 	    time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3047 		fo->cookie.len = -1;
3048 		goto fallback;
3049 	}
3050 
3051 	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3052 		fo->cookie.len = -1;
3053 	else if (fo->cookie.len <= 0)
3054 		goto fallback;
3055 
3056 	/* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3057 	 * user-MSS. Reserve maximum option space for middleboxes that add
3058 	 * private TCP options. The cost is reduced data space in SYN :(
3059 	 */
3060 	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3061 		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3062 	space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3063 		MAX_TCP_OPTION_SPACE;
3064 
3065 	space = min_t(size_t, space, fo->size);
3066 
3067 	/* limit to order-0 allocations */
3068 	space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3069 
3070 	syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation);
3071 	if (!syn_data)
3072 		goto fallback;
3073 	syn_data->ip_summed = CHECKSUM_PARTIAL;
3074 	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3075 	if (unlikely(memcpy_fromiovecend(skb_put(syn_data, space),
3076 					 fo->data->msg_iter.iov, 0, space))) {
3077 		kfree_skb(syn_data);
3078 		goto fallback;
3079 	}
3080 
3081 	/* No more data pending in inet_wait_for_connect() */
3082 	if (space == fo->size)
3083 		fo->data = NULL;
3084 	fo->copied = space;
3085 
3086 	tcp_connect_queue_skb(sk, syn_data);
3087 
3088 	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3089 
3090 	syn->skb_mstamp = syn_data->skb_mstamp;
3091 
3092 	/* Now full SYN+DATA was cloned and sent (or not),
3093 	 * remove the SYN from the original skb (syn_data)
3094 	 * we keep in write queue in case of a retransmit, as we
3095 	 * also have the SYN packet (with no data) in the same queue.
3096 	 */
3097 	TCP_SKB_CB(syn_data)->seq++;
3098 	TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3099 	if (!err) {
3100 		tp->syn_data = (fo->copied > 0);
3101 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3102 		goto done;
3103 	}
3104 
3105 fallback:
3106 	/* Send a regular SYN with Fast Open cookie request option */
3107 	if (fo->cookie.len > 0)
3108 		fo->cookie.len = 0;
3109 	err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3110 	if (err)
3111 		tp->syn_fastopen = 0;
3112 done:
3113 	fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
3114 	return err;
3115 }
3116 
3117 /* Build a SYN and send it off. */
3118 int tcp_connect(struct sock *sk)
3119 {
3120 	struct tcp_sock *tp = tcp_sk(sk);
3121 	struct sk_buff *buff;
3122 	int err;
3123 
3124 	tcp_connect_init(sk);
3125 
3126 	if (unlikely(tp->repair)) {
3127 		tcp_finish_connect(sk, NULL);
3128 		return 0;
3129 	}
3130 
3131 	buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
3132 	if (unlikely(!buff))
3133 		return -ENOBUFS;
3134 
3135 	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3136 	tp->retrans_stamp = tcp_time_stamp;
3137 	tcp_connect_queue_skb(sk, buff);
3138 	tcp_ecn_send_syn(sk, buff);
3139 
3140 	/* Send off SYN; include data in Fast Open. */
3141 	err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3142 	      tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3143 	if (err == -ECONNREFUSED)
3144 		return err;
3145 
3146 	/* We change tp->snd_nxt after the tcp_transmit_skb() call
3147 	 * in order to make this packet get counted in tcpOutSegs.
3148 	 */
3149 	tp->snd_nxt = tp->write_seq;
3150 	tp->pushed_seq = tp->write_seq;
3151 	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3152 
3153 	/* Timer for repeating the SYN until an answer. */
3154 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3155 				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3156 	return 0;
3157 }
3158 EXPORT_SYMBOL(tcp_connect);
3159 
3160 /* Send out a delayed ack, the caller does the policy checking
3161  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
3162  * for details.
3163  */
3164 void tcp_send_delayed_ack(struct sock *sk)
3165 {
3166 	struct inet_connection_sock *icsk = inet_csk(sk);
3167 	int ato = icsk->icsk_ack.ato;
3168 	unsigned long timeout;
3169 
3170 	tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3171 
3172 	if (ato > TCP_DELACK_MIN) {
3173 		const struct tcp_sock *tp = tcp_sk(sk);
3174 		int max_ato = HZ / 2;
3175 
3176 		if (icsk->icsk_ack.pingpong ||
3177 		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3178 			max_ato = TCP_DELACK_MAX;
3179 
3180 		/* Slow path, intersegment interval is "high". */
3181 
3182 		/* If some rtt estimate is known, use it to bound delayed ack.
3183 		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3184 		 * directly.
3185 		 */
3186 		if (tp->srtt_us) {
3187 			int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3188 					TCP_DELACK_MIN);
3189 
3190 			if (rtt < max_ato)
3191 				max_ato = rtt;
3192 		}
3193 
3194 		ato = min(ato, max_ato);
3195 	}
3196 
3197 	/* Stay within the limit we were given */
3198 	timeout = jiffies + ato;
3199 
3200 	/* Use new timeout only if there wasn't a older one earlier. */
3201 	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3202 		/* If delack timer was blocked or is about to expire,
3203 		 * send ACK now.
3204 		 */
3205 		if (icsk->icsk_ack.blocked ||
3206 		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3207 			tcp_send_ack(sk);
3208 			return;
3209 		}
3210 
3211 		if (!time_before(timeout, icsk->icsk_ack.timeout))
3212 			timeout = icsk->icsk_ack.timeout;
3213 	}
3214 	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3215 	icsk->icsk_ack.timeout = timeout;
3216 	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3217 }
3218 
3219 /* This routine sends an ack and also updates the window. */
3220 void tcp_send_ack(struct sock *sk)
3221 {
3222 	struct sk_buff *buff;
3223 
3224 	/* If we have been reset, we may not send again. */
3225 	if (sk->sk_state == TCP_CLOSE)
3226 		return;
3227 
3228 	tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3229 
3230 	/* We are not putting this on the write queue, so
3231 	 * tcp_transmit_skb() will set the ownership to this
3232 	 * sock.
3233 	 */
3234 	buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3235 	if (buff == NULL) {
3236 		inet_csk_schedule_ack(sk);
3237 		inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3238 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3239 					  TCP_DELACK_MAX, TCP_RTO_MAX);
3240 		return;
3241 	}
3242 
3243 	/* Reserve space for headers and prepare control bits. */
3244 	skb_reserve(buff, MAX_TCP_HEADER);
3245 	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3246 
3247 	/* Send it off, this clears delayed acks for us. */
3248 	skb_mstamp_get(&buff->skb_mstamp);
3249 	tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
3250 }
3251 EXPORT_SYMBOL_GPL(tcp_send_ack);
3252 
3253 /* This routine sends a packet with an out of date sequence
3254  * number. It assumes the other end will try to ack it.
3255  *
3256  * Question: what should we make while urgent mode?
3257  * 4.4BSD forces sending single byte of data. We cannot send
3258  * out of window data, because we have SND.NXT==SND.MAX...
3259  *
3260  * Current solution: to send TWO zero-length segments in urgent mode:
3261  * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3262  * out-of-date with SND.UNA-1 to probe window.
3263  */
3264 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
3265 {
3266 	struct tcp_sock *tp = tcp_sk(sk);
3267 	struct sk_buff *skb;
3268 
3269 	/* We don't queue it, tcp_transmit_skb() sets ownership. */
3270 	skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3271 	if (skb == NULL)
3272 		return -1;
3273 
3274 	/* Reserve space for headers and set control bits. */
3275 	skb_reserve(skb, MAX_TCP_HEADER);
3276 	/* Use a previous sequence.  This should cause the other
3277 	 * end to send an ack.  Don't queue or clone SKB, just
3278 	 * send it.
3279 	 */
3280 	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3281 	skb_mstamp_get(&skb->skb_mstamp);
3282 	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3283 }
3284 
3285 void tcp_send_window_probe(struct sock *sk)
3286 {
3287 	if (sk->sk_state == TCP_ESTABLISHED) {
3288 		tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3289 		tcp_xmit_probe_skb(sk, 0);
3290 	}
3291 }
3292 
3293 /* Initiate keepalive or window probe from timer. */
3294 int tcp_write_wakeup(struct sock *sk)
3295 {
3296 	struct tcp_sock *tp = tcp_sk(sk);
3297 	struct sk_buff *skb;
3298 
3299 	if (sk->sk_state == TCP_CLOSE)
3300 		return -1;
3301 
3302 	if ((skb = tcp_send_head(sk)) != NULL &&
3303 	    before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3304 		int err;
3305 		unsigned int mss = tcp_current_mss(sk);
3306 		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3307 
3308 		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3309 			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3310 
3311 		/* We are probing the opening of a window
3312 		 * but the window size is != 0
3313 		 * must have been a result SWS avoidance ( sender )
3314 		 */
3315 		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3316 		    skb->len > mss) {
3317 			seg_size = min(seg_size, mss);
3318 			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3319 			if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3320 				return -1;
3321 		} else if (!tcp_skb_pcount(skb))
3322 			tcp_set_skb_tso_segs(sk, skb, mss);
3323 
3324 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3325 		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3326 		if (!err)
3327 			tcp_event_new_data_sent(sk, skb);
3328 		return err;
3329 	} else {
3330 		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3331 			tcp_xmit_probe_skb(sk, 1);
3332 		return tcp_xmit_probe_skb(sk, 0);
3333 	}
3334 }
3335 
3336 /* A window probe timeout has occurred.  If window is not closed send
3337  * a partial packet else a zero probe.
3338  */
3339 void tcp_send_probe0(struct sock *sk)
3340 {
3341 	struct inet_connection_sock *icsk = inet_csk(sk);
3342 	struct tcp_sock *tp = tcp_sk(sk);
3343 	unsigned long probe_max;
3344 	int err;
3345 
3346 	err = tcp_write_wakeup(sk);
3347 
3348 	if (tp->packets_out || !tcp_send_head(sk)) {
3349 		/* Cancel probe timer, if it is not required. */
3350 		icsk->icsk_probes_out = 0;
3351 		icsk->icsk_backoff = 0;
3352 		return;
3353 	}
3354 
3355 	if (err <= 0) {
3356 		if (icsk->icsk_backoff < sysctl_tcp_retries2)
3357 			icsk->icsk_backoff++;
3358 		icsk->icsk_probes_out++;
3359 		probe_max = TCP_RTO_MAX;
3360 	} else {
3361 		/* If packet was not sent due to local congestion,
3362 		 * do not backoff and do not remember icsk_probes_out.
3363 		 * Let local senders to fight for local resources.
3364 		 *
3365 		 * Use accumulated backoff yet.
3366 		 */
3367 		if (!icsk->icsk_probes_out)
3368 			icsk->icsk_probes_out = 1;
3369 		probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3370 	}
3371 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3372 				  inet_csk_rto_backoff(icsk, probe_max),
3373 				  TCP_RTO_MAX);
3374 }
3375 
3376 int tcp_rtx_synack(struct sock *sk, struct request_sock *req)
3377 {
3378 	const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3379 	struct flowi fl;
3380 	int res;
3381 
3382 	res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL);
3383 	if (!res) {
3384 		TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
3385 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3386 	}
3387 	return res;
3388 }
3389 EXPORT_SYMBOL(tcp_rtx_synack);
3390