xref: /openbmc/linux/net/ipv4/tcp_output.c (revision 6f52b16c5b29b89d92c0e7236f4655dc8491ad70)
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 four TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
55 
56 /* This limits the percentage of the congestion window which we
57  * will allow a single TSO frame to consume.  Building TSO frames
58  * which are too large can cause TCP streams to be bursty.
59  */
60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
61 
62 /* By default, RFC2861 behavior.  */
63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
64 
65 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
66 			   int push_one, gfp_t gfp);
67 
68 /* Account for new data that has been sent to the network. */
69 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
70 {
71 	struct inet_connection_sock *icsk = inet_csk(sk);
72 	struct tcp_sock *tp = tcp_sk(sk);
73 	unsigned int prior_packets = tp->packets_out;
74 
75 	tcp_advance_send_head(sk, skb);
76 	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
77 
78 	tp->packets_out += tcp_skb_pcount(skb);
79 	if (!prior_packets || icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
80 		tcp_rearm_rto(sk);
81 
82 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
83 		      tcp_skb_pcount(skb));
84 }
85 
86 /* SND.NXT, if window was not shrunk or the amount of shrunk was less than one
87  * window scaling factor due to loss of precision.
88  * If window has been shrunk, what should we make? It is not clear at all.
89  * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
90  * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
91  * invalid. OK, let's make this for now:
92  */
93 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
94 {
95 	const struct tcp_sock *tp = tcp_sk(sk);
96 
97 	if (!before(tcp_wnd_end(tp), tp->snd_nxt) ||
98 	    (tp->rx_opt.wscale_ok &&
99 	     ((tp->snd_nxt - tcp_wnd_end(tp)) < (1 << tp->rx_opt.rcv_wscale))))
100 		return tp->snd_nxt;
101 	else
102 		return tcp_wnd_end(tp);
103 }
104 
105 /* Calculate mss to advertise in SYN segment.
106  * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
107  *
108  * 1. It is independent of path mtu.
109  * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
110  * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
111  *    attached devices, because some buggy hosts are confused by
112  *    large MSS.
113  * 4. We do not make 3, we advertise MSS, calculated from first
114  *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
115  *    This may be overridden via information stored in routing table.
116  * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
117  *    probably even Jumbo".
118  */
119 static __u16 tcp_advertise_mss(struct sock *sk)
120 {
121 	struct tcp_sock *tp = tcp_sk(sk);
122 	const struct dst_entry *dst = __sk_dst_get(sk);
123 	int mss = tp->advmss;
124 
125 	if (dst) {
126 		unsigned int metric = dst_metric_advmss(dst);
127 
128 		if (metric < mss) {
129 			mss = metric;
130 			tp->advmss = mss;
131 		}
132 	}
133 
134 	return (__u16)mss;
135 }
136 
137 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
138  * This is the first part of cwnd validation mechanism.
139  */
140 void tcp_cwnd_restart(struct sock *sk, s32 delta)
141 {
142 	struct tcp_sock *tp = tcp_sk(sk);
143 	u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
144 	u32 cwnd = tp->snd_cwnd;
145 
146 	tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
147 
148 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
149 	restart_cwnd = min(restart_cwnd, cwnd);
150 
151 	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
152 		cwnd >>= 1;
153 	tp->snd_cwnd = max(cwnd, restart_cwnd);
154 	tp->snd_cwnd_stamp = tcp_jiffies32;
155 	tp->snd_cwnd_used = 0;
156 }
157 
158 /* Congestion state accounting after a packet has been sent. */
159 static void tcp_event_data_sent(struct tcp_sock *tp,
160 				struct sock *sk)
161 {
162 	struct inet_connection_sock *icsk = inet_csk(sk);
163 	const u32 now = tcp_jiffies32;
164 
165 	if (tcp_packets_in_flight(tp) == 0)
166 		tcp_ca_event(sk, CA_EVENT_TX_START);
167 
168 	tp->lsndtime = now;
169 
170 	/* If it is a reply for ato after last received
171 	 * packet, enter pingpong mode.
172 	 */
173 	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
174 		icsk->icsk_ack.pingpong = 1;
175 }
176 
177 /* Account for an ACK we sent. */
178 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
179 {
180 	tcp_dec_quickack_mode(sk, pkts);
181 	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
182 }
183 
184 
185 u32 tcp_default_init_rwnd(u32 mss)
186 {
187 	/* Initial receive window should be twice of TCP_INIT_CWND to
188 	 * enable proper sending of new unsent data during fast recovery
189 	 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
190 	 * limit when mss is larger than 1460.
191 	 */
192 	u32 init_rwnd = TCP_INIT_CWND * 2;
193 
194 	if (mss > 1460)
195 		init_rwnd = max((1460 * init_rwnd) / mss, 2U);
196 	return init_rwnd;
197 }
198 
199 /* Determine a window scaling and initial window to offer.
200  * Based on the assumption that the given amount of space
201  * will be offered. Store the results in the tp structure.
202  * NOTE: for smooth operation initial space offering should
203  * be a multiple of mss if possible. We assume here that mss >= 1.
204  * This MUST be enforced by all callers.
205  */
206 void tcp_select_initial_window(int __space, __u32 mss,
207 			       __u32 *rcv_wnd, __u32 *window_clamp,
208 			       int wscale_ok, __u8 *rcv_wscale,
209 			       __u32 init_rcv_wnd)
210 {
211 	unsigned int space = (__space < 0 ? 0 : __space);
212 
213 	/* If no clamp set the clamp to the max possible scaled window */
214 	if (*window_clamp == 0)
215 		(*window_clamp) = (U16_MAX << TCP_MAX_WSCALE);
216 	space = min(*window_clamp, space);
217 
218 	/* Quantize space offering to a multiple of mss if possible. */
219 	if (space > mss)
220 		space = rounddown(space, mss);
221 
222 	/* NOTE: offering an initial window larger than 32767
223 	 * will break some buggy TCP stacks. If the admin tells us
224 	 * it is likely we could be speaking with such a buggy stack
225 	 * we will truncate our initial window offering to 32K-1
226 	 * unless the remote has sent us a window scaling option,
227 	 * which we interpret as a sign the remote TCP is not
228 	 * misinterpreting the window field as a signed quantity.
229 	 */
230 	if (sysctl_tcp_workaround_signed_windows)
231 		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
232 	else
233 		(*rcv_wnd) = space;
234 
235 	(*rcv_wscale) = 0;
236 	if (wscale_ok) {
237 		/* Set window scaling on max possible window */
238 		space = max_t(u32, space, sysctl_tcp_rmem[2]);
239 		space = max_t(u32, space, sysctl_rmem_max);
240 		space = min_t(u32, space, *window_clamp);
241 		while (space > U16_MAX && (*rcv_wscale) < TCP_MAX_WSCALE) {
242 			space >>= 1;
243 			(*rcv_wscale)++;
244 		}
245 	}
246 
247 	if (mss > (1 << *rcv_wscale)) {
248 		if (!init_rcv_wnd) /* Use default unless specified otherwise */
249 			init_rcv_wnd = tcp_default_init_rwnd(mss);
250 		*rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
251 	}
252 
253 	/* Set the clamp no higher than max representable value */
254 	(*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale), *window_clamp);
255 }
256 EXPORT_SYMBOL(tcp_select_initial_window);
257 
258 /* Chose a new window to advertise, update state in tcp_sock for the
259  * socket, and return result with RFC1323 scaling applied.  The return
260  * value can be stuffed directly into th->window for an outgoing
261  * frame.
262  */
263 static u16 tcp_select_window(struct sock *sk)
264 {
265 	struct tcp_sock *tp = tcp_sk(sk);
266 	u32 old_win = tp->rcv_wnd;
267 	u32 cur_win = tcp_receive_window(tp);
268 	u32 new_win = __tcp_select_window(sk);
269 
270 	/* Never shrink the offered window */
271 	if (new_win < cur_win) {
272 		/* Danger Will Robinson!
273 		 * Don't update rcv_wup/rcv_wnd here or else
274 		 * we will not be able to advertise a zero
275 		 * window in time.  --DaveM
276 		 *
277 		 * Relax Will Robinson.
278 		 */
279 		if (new_win == 0)
280 			NET_INC_STATS(sock_net(sk),
281 				      LINUX_MIB_TCPWANTZEROWINDOWADV);
282 		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
283 	}
284 	tp->rcv_wnd = new_win;
285 	tp->rcv_wup = tp->rcv_nxt;
286 
287 	/* Make sure we do not exceed the maximum possible
288 	 * scaled window.
289 	 */
290 	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
291 		new_win = min(new_win, MAX_TCP_WINDOW);
292 	else
293 		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
294 
295 	/* RFC1323 scaling applied */
296 	new_win >>= tp->rx_opt.rcv_wscale;
297 
298 	/* If we advertise zero window, disable fast path. */
299 	if (new_win == 0) {
300 		tp->pred_flags = 0;
301 		if (old_win)
302 			NET_INC_STATS(sock_net(sk),
303 				      LINUX_MIB_TCPTOZEROWINDOWADV);
304 	} else if (old_win == 0) {
305 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
306 	}
307 
308 	return new_win;
309 }
310 
311 /* Packet ECN state for a SYN-ACK */
312 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
313 {
314 	const struct tcp_sock *tp = tcp_sk(sk);
315 
316 	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
317 	if (!(tp->ecn_flags & TCP_ECN_OK))
318 		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
319 	else if (tcp_ca_needs_ecn(sk) ||
320 		 tcp_bpf_ca_needs_ecn(sk))
321 		INET_ECN_xmit(sk);
322 }
323 
324 /* Packet ECN state for a SYN.  */
325 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
326 {
327 	struct tcp_sock *tp = tcp_sk(sk);
328 	bool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk);
329 	bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
330 		tcp_ca_needs_ecn(sk) || bpf_needs_ecn;
331 
332 	if (!use_ecn) {
333 		const struct dst_entry *dst = __sk_dst_get(sk);
334 
335 		if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
336 			use_ecn = true;
337 	}
338 
339 	tp->ecn_flags = 0;
340 
341 	if (use_ecn) {
342 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
343 		tp->ecn_flags = TCP_ECN_OK;
344 		if (tcp_ca_needs_ecn(sk) || bpf_needs_ecn)
345 			INET_ECN_xmit(sk);
346 	}
347 }
348 
349 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
350 {
351 	if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
352 		/* tp->ecn_flags are cleared at a later point in time when
353 		 * SYN ACK is ultimatively being received.
354 		 */
355 		TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
356 }
357 
358 static void
359 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
360 {
361 	if (inet_rsk(req)->ecn_ok)
362 		th->ece = 1;
363 }
364 
365 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
366  * be sent.
367  */
368 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
369 			 struct tcphdr *th, int tcp_header_len)
370 {
371 	struct tcp_sock *tp = tcp_sk(sk);
372 
373 	if (tp->ecn_flags & TCP_ECN_OK) {
374 		/* Not-retransmitted data segment: set ECT and inject CWR. */
375 		if (skb->len != tcp_header_len &&
376 		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
377 			INET_ECN_xmit(sk);
378 			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
379 				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
380 				th->cwr = 1;
381 				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
382 			}
383 		} else if (!tcp_ca_needs_ecn(sk)) {
384 			/* ACK or retransmitted segment: clear ECT|CE */
385 			INET_ECN_dontxmit(sk);
386 		}
387 		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
388 			th->ece = 1;
389 	}
390 }
391 
392 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
393  * auto increment end seqno.
394  */
395 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
396 {
397 	skb->ip_summed = CHECKSUM_PARTIAL;
398 	skb->csum = 0;
399 
400 	TCP_SKB_CB(skb)->tcp_flags = flags;
401 	TCP_SKB_CB(skb)->sacked = 0;
402 
403 	tcp_skb_pcount_set(skb, 1);
404 
405 	TCP_SKB_CB(skb)->seq = seq;
406 	if (flags & (TCPHDR_SYN | TCPHDR_FIN))
407 		seq++;
408 	TCP_SKB_CB(skb)->end_seq = seq;
409 }
410 
411 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
412 {
413 	return tp->snd_una != tp->snd_up;
414 }
415 
416 #define OPTION_SACK_ADVERTISE	(1 << 0)
417 #define OPTION_TS		(1 << 1)
418 #define OPTION_MD5		(1 << 2)
419 #define OPTION_WSCALE		(1 << 3)
420 #define OPTION_FAST_OPEN_COOKIE	(1 << 8)
421 
422 struct tcp_out_options {
423 	u16 options;		/* bit field of OPTION_* */
424 	u16 mss;		/* 0 to disable */
425 	u8 ws;			/* window scale, 0 to disable */
426 	u8 num_sack_blocks;	/* number of SACK blocks to include */
427 	u8 hash_size;		/* bytes in hash_location */
428 	__u8 *hash_location;	/* temporary pointer, overloaded */
429 	__u32 tsval, tsecr;	/* need to include OPTION_TS */
430 	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */
431 };
432 
433 /* Write previously computed TCP options to the packet.
434  *
435  * Beware: Something in the Internet is very sensitive to the ordering of
436  * TCP options, we learned this through the hard way, so be careful here.
437  * Luckily we can at least blame others for their non-compliance but from
438  * inter-operability perspective it seems that we're somewhat stuck with
439  * the ordering which we have been using if we want to keep working with
440  * those broken things (not that it currently hurts anybody as there isn't
441  * particular reason why the ordering would need to be changed).
442  *
443  * At least SACK_PERM as the first option is known to lead to a disaster
444  * (but it may well be that other scenarios fail similarly).
445  */
446 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
447 			      struct tcp_out_options *opts)
448 {
449 	u16 options = opts->options;	/* mungable copy */
450 
451 	if (unlikely(OPTION_MD5 & options)) {
452 		*ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
453 			       (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
454 		/* overload cookie hash location */
455 		opts->hash_location = (__u8 *)ptr;
456 		ptr += 4;
457 	}
458 
459 	if (unlikely(opts->mss)) {
460 		*ptr++ = htonl((TCPOPT_MSS << 24) |
461 			       (TCPOLEN_MSS << 16) |
462 			       opts->mss);
463 	}
464 
465 	if (likely(OPTION_TS & options)) {
466 		if (unlikely(OPTION_SACK_ADVERTISE & options)) {
467 			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
468 				       (TCPOLEN_SACK_PERM << 16) |
469 				       (TCPOPT_TIMESTAMP << 8) |
470 				       TCPOLEN_TIMESTAMP);
471 			options &= ~OPTION_SACK_ADVERTISE;
472 		} else {
473 			*ptr++ = htonl((TCPOPT_NOP << 24) |
474 				       (TCPOPT_NOP << 16) |
475 				       (TCPOPT_TIMESTAMP << 8) |
476 				       TCPOLEN_TIMESTAMP);
477 		}
478 		*ptr++ = htonl(opts->tsval);
479 		*ptr++ = htonl(opts->tsecr);
480 	}
481 
482 	if (unlikely(OPTION_SACK_ADVERTISE & options)) {
483 		*ptr++ = htonl((TCPOPT_NOP << 24) |
484 			       (TCPOPT_NOP << 16) |
485 			       (TCPOPT_SACK_PERM << 8) |
486 			       TCPOLEN_SACK_PERM);
487 	}
488 
489 	if (unlikely(OPTION_WSCALE & options)) {
490 		*ptr++ = htonl((TCPOPT_NOP << 24) |
491 			       (TCPOPT_WINDOW << 16) |
492 			       (TCPOLEN_WINDOW << 8) |
493 			       opts->ws);
494 	}
495 
496 	if (unlikely(opts->num_sack_blocks)) {
497 		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
498 			tp->duplicate_sack : tp->selective_acks;
499 		int this_sack;
500 
501 		*ptr++ = htonl((TCPOPT_NOP  << 24) |
502 			       (TCPOPT_NOP  << 16) |
503 			       (TCPOPT_SACK <<  8) |
504 			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
505 						     TCPOLEN_SACK_PERBLOCK)));
506 
507 		for (this_sack = 0; this_sack < opts->num_sack_blocks;
508 		     ++this_sack) {
509 			*ptr++ = htonl(sp[this_sack].start_seq);
510 			*ptr++ = htonl(sp[this_sack].end_seq);
511 		}
512 
513 		tp->rx_opt.dsack = 0;
514 	}
515 
516 	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
517 		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
518 		u8 *p = (u8 *)ptr;
519 		u32 len; /* Fast Open option length */
520 
521 		if (foc->exp) {
522 			len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
523 			*ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
524 				     TCPOPT_FASTOPEN_MAGIC);
525 			p += TCPOLEN_EXP_FASTOPEN_BASE;
526 		} else {
527 			len = TCPOLEN_FASTOPEN_BASE + foc->len;
528 			*p++ = TCPOPT_FASTOPEN;
529 			*p++ = len;
530 		}
531 
532 		memcpy(p, foc->val, foc->len);
533 		if ((len & 3) == 2) {
534 			p[foc->len] = TCPOPT_NOP;
535 			p[foc->len + 1] = TCPOPT_NOP;
536 		}
537 		ptr += (len + 3) >> 2;
538 	}
539 }
540 
541 /* Compute TCP options for SYN packets. This is not the final
542  * network wire format yet.
543  */
544 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
545 				struct tcp_out_options *opts,
546 				struct tcp_md5sig_key **md5)
547 {
548 	struct tcp_sock *tp = tcp_sk(sk);
549 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
550 	struct tcp_fastopen_request *fastopen = tp->fastopen_req;
551 
552 #ifdef CONFIG_TCP_MD5SIG
553 	*md5 = tp->af_specific->md5_lookup(sk, sk);
554 	if (*md5) {
555 		opts->options |= OPTION_MD5;
556 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
557 	}
558 #else
559 	*md5 = NULL;
560 #endif
561 
562 	/* We always get an MSS option.  The option bytes which will be seen in
563 	 * normal data packets should timestamps be used, must be in the MSS
564 	 * advertised.  But we subtract them from tp->mss_cache so that
565 	 * calculations in tcp_sendmsg are simpler etc.  So account for this
566 	 * fact here if necessary.  If we don't do this correctly, as a
567 	 * receiver we won't recognize data packets as being full sized when we
568 	 * should, and thus we won't abide by the delayed ACK rules correctly.
569 	 * SACKs don't matter, we never delay an ACK when we have any of those
570 	 * going out.  */
571 	opts->mss = tcp_advertise_mss(sk);
572 	remaining -= TCPOLEN_MSS_ALIGNED;
573 
574 	if (likely(sock_net(sk)->ipv4.sysctl_tcp_timestamps && !*md5)) {
575 		opts->options |= OPTION_TS;
576 		opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
577 		opts->tsecr = tp->rx_opt.ts_recent;
578 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
579 	}
580 	if (likely(sock_net(sk)->ipv4.sysctl_tcp_window_scaling)) {
581 		opts->ws = tp->rx_opt.rcv_wscale;
582 		opts->options |= OPTION_WSCALE;
583 		remaining -= TCPOLEN_WSCALE_ALIGNED;
584 	}
585 	if (likely(sock_net(sk)->ipv4.sysctl_tcp_sack)) {
586 		opts->options |= OPTION_SACK_ADVERTISE;
587 		if (unlikely(!(OPTION_TS & opts->options)))
588 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
589 	}
590 
591 	if (fastopen && fastopen->cookie.len >= 0) {
592 		u32 need = fastopen->cookie.len;
593 
594 		need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
595 					       TCPOLEN_FASTOPEN_BASE;
596 		need = (need + 3) & ~3U;  /* Align to 32 bits */
597 		if (remaining >= need) {
598 			opts->options |= OPTION_FAST_OPEN_COOKIE;
599 			opts->fastopen_cookie = &fastopen->cookie;
600 			remaining -= need;
601 			tp->syn_fastopen = 1;
602 			tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
603 		}
604 	}
605 
606 	return MAX_TCP_OPTION_SPACE - remaining;
607 }
608 
609 /* Set up TCP options for SYN-ACKs. */
610 static unsigned int tcp_synack_options(struct request_sock *req,
611 				       unsigned int mss, struct sk_buff *skb,
612 				       struct tcp_out_options *opts,
613 				       const struct tcp_md5sig_key *md5,
614 				       struct tcp_fastopen_cookie *foc)
615 {
616 	struct inet_request_sock *ireq = inet_rsk(req);
617 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
618 
619 #ifdef CONFIG_TCP_MD5SIG
620 	if (md5) {
621 		opts->options |= OPTION_MD5;
622 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
623 
624 		/* We can't fit any SACK blocks in a packet with MD5 + TS
625 		 * options. There was discussion about disabling SACK
626 		 * rather than TS in order to fit in better with old,
627 		 * buggy kernels, but that was deemed to be unnecessary.
628 		 */
629 		ireq->tstamp_ok &= !ireq->sack_ok;
630 	}
631 #endif
632 
633 	/* We always send an MSS option. */
634 	opts->mss = mss;
635 	remaining -= TCPOLEN_MSS_ALIGNED;
636 
637 	if (likely(ireq->wscale_ok)) {
638 		opts->ws = ireq->rcv_wscale;
639 		opts->options |= OPTION_WSCALE;
640 		remaining -= TCPOLEN_WSCALE_ALIGNED;
641 	}
642 	if (likely(ireq->tstamp_ok)) {
643 		opts->options |= OPTION_TS;
644 		opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
645 		opts->tsecr = req->ts_recent;
646 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
647 	}
648 	if (likely(ireq->sack_ok)) {
649 		opts->options |= OPTION_SACK_ADVERTISE;
650 		if (unlikely(!ireq->tstamp_ok))
651 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
652 	}
653 	if (foc != NULL && foc->len >= 0) {
654 		u32 need = foc->len;
655 
656 		need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
657 				   TCPOLEN_FASTOPEN_BASE;
658 		need = (need + 3) & ~3U;  /* Align to 32 bits */
659 		if (remaining >= need) {
660 			opts->options |= OPTION_FAST_OPEN_COOKIE;
661 			opts->fastopen_cookie = foc;
662 			remaining -= need;
663 		}
664 	}
665 
666 	return MAX_TCP_OPTION_SPACE - remaining;
667 }
668 
669 /* Compute TCP options for ESTABLISHED sockets. This is not the
670  * final wire format yet.
671  */
672 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
673 					struct tcp_out_options *opts,
674 					struct tcp_md5sig_key **md5)
675 {
676 	struct tcp_sock *tp = tcp_sk(sk);
677 	unsigned int size = 0;
678 	unsigned int eff_sacks;
679 
680 	opts->options = 0;
681 
682 #ifdef CONFIG_TCP_MD5SIG
683 	*md5 = tp->af_specific->md5_lookup(sk, sk);
684 	if (unlikely(*md5)) {
685 		opts->options |= OPTION_MD5;
686 		size += TCPOLEN_MD5SIG_ALIGNED;
687 	}
688 #else
689 	*md5 = NULL;
690 #endif
691 
692 	if (likely(tp->rx_opt.tstamp_ok)) {
693 		opts->options |= OPTION_TS;
694 		opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
695 		opts->tsecr = tp->rx_opt.ts_recent;
696 		size += TCPOLEN_TSTAMP_ALIGNED;
697 	}
698 
699 	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
700 	if (unlikely(eff_sacks)) {
701 		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
702 		opts->num_sack_blocks =
703 			min_t(unsigned int, eff_sacks,
704 			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
705 			      TCPOLEN_SACK_PERBLOCK);
706 		size += TCPOLEN_SACK_BASE_ALIGNED +
707 			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
708 	}
709 
710 	return size;
711 }
712 
713 
714 /* TCP SMALL QUEUES (TSQ)
715  *
716  * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
717  * to reduce RTT and bufferbloat.
718  * We do this using a special skb destructor (tcp_wfree).
719  *
720  * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
721  * needs to be reallocated in a driver.
722  * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
723  *
724  * Since transmit from skb destructor is forbidden, we use a tasklet
725  * to process all sockets that eventually need to send more skbs.
726  * We use one tasklet per cpu, with its own queue of sockets.
727  */
728 struct tsq_tasklet {
729 	struct tasklet_struct	tasklet;
730 	struct list_head	head; /* queue of tcp sockets */
731 };
732 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
733 
734 static void tcp_tsq_handler(struct sock *sk)
735 {
736 	if ((1 << sk->sk_state) &
737 	    (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
738 	     TCPF_CLOSE_WAIT  | TCPF_LAST_ACK)) {
739 		struct tcp_sock *tp = tcp_sk(sk);
740 
741 		if (tp->lost_out > tp->retrans_out &&
742 		    tp->snd_cwnd > tcp_packets_in_flight(tp))
743 			tcp_xmit_retransmit_queue(sk);
744 
745 		tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
746 			       0, GFP_ATOMIC);
747 	}
748 }
749 /*
750  * One tasklet per cpu tries to send more skbs.
751  * We run in tasklet context but need to disable irqs when
752  * transferring tsq->head because tcp_wfree() might
753  * interrupt us (non NAPI drivers)
754  */
755 static void tcp_tasklet_func(unsigned long data)
756 {
757 	struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
758 	LIST_HEAD(list);
759 	unsigned long flags;
760 	struct list_head *q, *n;
761 	struct tcp_sock *tp;
762 	struct sock *sk;
763 
764 	local_irq_save(flags);
765 	list_splice_init(&tsq->head, &list);
766 	local_irq_restore(flags);
767 
768 	list_for_each_safe(q, n, &list) {
769 		tp = list_entry(q, struct tcp_sock, tsq_node);
770 		list_del(&tp->tsq_node);
771 
772 		sk = (struct sock *)tp;
773 		smp_mb__before_atomic();
774 		clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags);
775 
776 		if (!sk->sk_lock.owned &&
777 		    test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) {
778 			bh_lock_sock(sk);
779 			if (!sock_owned_by_user(sk)) {
780 				clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
781 				tcp_tsq_handler(sk);
782 			}
783 			bh_unlock_sock(sk);
784 		}
785 
786 		sk_free(sk);
787 	}
788 }
789 
790 #define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED |		\
791 			  TCPF_WRITE_TIMER_DEFERRED |	\
792 			  TCPF_DELACK_TIMER_DEFERRED |	\
793 			  TCPF_MTU_REDUCED_DEFERRED)
794 /**
795  * tcp_release_cb - tcp release_sock() callback
796  * @sk: socket
797  *
798  * called from release_sock() to perform protocol dependent
799  * actions before socket release.
800  */
801 void tcp_release_cb(struct sock *sk)
802 {
803 	unsigned long flags, nflags;
804 
805 	/* perform an atomic operation only if at least one flag is set */
806 	do {
807 		flags = sk->sk_tsq_flags;
808 		if (!(flags & TCP_DEFERRED_ALL))
809 			return;
810 		nflags = flags & ~TCP_DEFERRED_ALL;
811 	} while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);
812 
813 	if (flags & TCPF_TSQ_DEFERRED)
814 		tcp_tsq_handler(sk);
815 
816 	/* Here begins the tricky part :
817 	 * We are called from release_sock() with :
818 	 * 1) BH disabled
819 	 * 2) sk_lock.slock spinlock held
820 	 * 3) socket owned by us (sk->sk_lock.owned == 1)
821 	 *
822 	 * But following code is meant to be called from BH handlers,
823 	 * so we should keep BH disabled, but early release socket ownership
824 	 */
825 	sock_release_ownership(sk);
826 
827 	if (flags & TCPF_WRITE_TIMER_DEFERRED) {
828 		tcp_write_timer_handler(sk);
829 		__sock_put(sk);
830 	}
831 	if (flags & TCPF_DELACK_TIMER_DEFERRED) {
832 		tcp_delack_timer_handler(sk);
833 		__sock_put(sk);
834 	}
835 	if (flags & TCPF_MTU_REDUCED_DEFERRED) {
836 		inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
837 		__sock_put(sk);
838 	}
839 }
840 EXPORT_SYMBOL(tcp_release_cb);
841 
842 void __init tcp_tasklet_init(void)
843 {
844 	int i;
845 
846 	for_each_possible_cpu(i) {
847 		struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
848 
849 		INIT_LIST_HEAD(&tsq->head);
850 		tasklet_init(&tsq->tasklet,
851 			     tcp_tasklet_func,
852 			     (unsigned long)tsq);
853 	}
854 }
855 
856 /*
857  * Write buffer destructor automatically called from kfree_skb.
858  * We can't xmit new skbs from this context, as we might already
859  * hold qdisc lock.
860  */
861 void tcp_wfree(struct sk_buff *skb)
862 {
863 	struct sock *sk = skb->sk;
864 	struct tcp_sock *tp = tcp_sk(sk);
865 	unsigned long flags, nval, oval;
866 
867 	/* Keep one reference on sk_wmem_alloc.
868 	 * Will be released by sk_free() from here or tcp_tasklet_func()
869 	 */
870 	WARN_ON(refcount_sub_and_test(skb->truesize - 1, &sk->sk_wmem_alloc));
871 
872 	/* If this softirq is serviced by ksoftirqd, we are likely under stress.
873 	 * Wait until our queues (qdisc + devices) are drained.
874 	 * This gives :
875 	 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
876 	 * - chance for incoming ACK (processed by another cpu maybe)
877 	 *   to migrate this flow (skb->ooo_okay will be eventually set)
878 	 */
879 	if (refcount_read(&sk->sk_wmem_alloc) >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
880 		goto out;
881 
882 	for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
883 		struct tsq_tasklet *tsq;
884 		bool empty;
885 
886 		if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
887 			goto out;
888 
889 		nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
890 		nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
891 		if (nval != oval)
892 			continue;
893 
894 		/* queue this socket to tasklet queue */
895 		local_irq_save(flags);
896 		tsq = this_cpu_ptr(&tsq_tasklet);
897 		empty = list_empty(&tsq->head);
898 		list_add(&tp->tsq_node, &tsq->head);
899 		if (empty)
900 			tasklet_schedule(&tsq->tasklet);
901 		local_irq_restore(flags);
902 		return;
903 	}
904 out:
905 	sk_free(sk);
906 }
907 
908 /* Note: Called under hard irq.
909  * We can not call TCP stack right away.
910  */
911 enum hrtimer_restart tcp_pace_kick(struct hrtimer *timer)
912 {
913 	struct tcp_sock *tp = container_of(timer, struct tcp_sock, pacing_timer);
914 	struct sock *sk = (struct sock *)tp;
915 	unsigned long nval, oval;
916 
917 	for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
918 		struct tsq_tasklet *tsq;
919 		bool empty;
920 
921 		if (oval & TSQF_QUEUED)
922 			break;
923 
924 		nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
925 		nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
926 		if (nval != oval)
927 			continue;
928 
929 		if (!refcount_inc_not_zero(&sk->sk_wmem_alloc))
930 			break;
931 		/* queue this socket to tasklet queue */
932 		tsq = this_cpu_ptr(&tsq_tasklet);
933 		empty = list_empty(&tsq->head);
934 		list_add(&tp->tsq_node, &tsq->head);
935 		if (empty)
936 			tasklet_schedule(&tsq->tasklet);
937 		break;
938 	}
939 	return HRTIMER_NORESTART;
940 }
941 
942 /* BBR congestion control needs pacing.
943  * Same remark for SO_MAX_PACING_RATE.
944  * sch_fq packet scheduler is efficiently handling pacing,
945  * but is not always installed/used.
946  * Return true if TCP stack should pace packets itself.
947  */
948 static bool tcp_needs_internal_pacing(const struct sock *sk)
949 {
950 	return smp_load_acquire(&sk->sk_pacing_status) == SK_PACING_NEEDED;
951 }
952 
953 static void tcp_internal_pacing(struct sock *sk, const struct sk_buff *skb)
954 {
955 	u64 len_ns;
956 	u32 rate;
957 
958 	if (!tcp_needs_internal_pacing(sk))
959 		return;
960 	rate = sk->sk_pacing_rate;
961 	if (!rate || rate == ~0U)
962 		return;
963 
964 	/* Should account for header sizes as sch_fq does,
965 	 * but lets make things simple.
966 	 */
967 	len_ns = (u64)skb->len * NSEC_PER_SEC;
968 	do_div(len_ns, rate);
969 	hrtimer_start(&tcp_sk(sk)->pacing_timer,
970 		      ktime_add_ns(ktime_get(), len_ns),
971 		      HRTIMER_MODE_ABS_PINNED);
972 }
973 
974 /* This routine actually transmits TCP packets queued in by
975  * tcp_do_sendmsg().  This is used by both the initial
976  * transmission and possible later retransmissions.
977  * All SKB's seen here are completely headerless.  It is our
978  * job to build the TCP header, and pass the packet down to
979  * IP so it can do the same plus pass the packet off to the
980  * device.
981  *
982  * We are working here with either a clone of the original
983  * SKB, or a fresh unique copy made by the retransmit engine.
984  */
985 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
986 			    gfp_t gfp_mask)
987 {
988 	const struct inet_connection_sock *icsk = inet_csk(sk);
989 	struct inet_sock *inet;
990 	struct tcp_sock *tp;
991 	struct tcp_skb_cb *tcb;
992 	struct tcp_out_options opts;
993 	unsigned int tcp_options_size, tcp_header_size;
994 	struct sk_buff *oskb = NULL;
995 	struct tcp_md5sig_key *md5;
996 	struct tcphdr *th;
997 	int err;
998 
999 	BUG_ON(!skb || !tcp_skb_pcount(skb));
1000 	tp = tcp_sk(sk);
1001 
1002 	if (clone_it) {
1003 		TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
1004 			- tp->snd_una;
1005 		oskb = skb;
1006 		if (unlikely(skb_cloned(skb)))
1007 			skb = pskb_copy(skb, gfp_mask);
1008 		else
1009 			skb = skb_clone(skb, gfp_mask);
1010 		if (unlikely(!skb))
1011 			return -ENOBUFS;
1012 	}
1013 	skb->skb_mstamp = tp->tcp_mstamp;
1014 
1015 	inet = inet_sk(sk);
1016 	tcb = TCP_SKB_CB(skb);
1017 	memset(&opts, 0, sizeof(opts));
1018 
1019 	if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
1020 		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
1021 	else
1022 		tcp_options_size = tcp_established_options(sk, skb, &opts,
1023 							   &md5);
1024 	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
1025 
1026 	/* if no packet is in qdisc/device queue, then allow XPS to select
1027 	 * another queue. We can be called from tcp_tsq_handler()
1028 	 * which holds one reference to sk_wmem_alloc.
1029 	 *
1030 	 * TODO: Ideally, in-flight pure ACK packets should not matter here.
1031 	 * One way to get this would be to set skb->truesize = 2 on them.
1032 	 */
1033 	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
1034 
1035 	/* If we had to use memory reserve to allocate this skb,
1036 	 * this might cause drops if packet is looped back :
1037 	 * Other socket might not have SOCK_MEMALLOC.
1038 	 * Packets not looped back do not care about pfmemalloc.
1039 	 */
1040 	skb->pfmemalloc = 0;
1041 
1042 	skb_push(skb, tcp_header_size);
1043 	skb_reset_transport_header(skb);
1044 
1045 	skb_orphan(skb);
1046 	skb->sk = sk;
1047 	skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
1048 	skb_set_hash_from_sk(skb, sk);
1049 	refcount_add(skb->truesize, &sk->sk_wmem_alloc);
1050 
1051 	skb_set_dst_pending_confirm(skb, sk->sk_dst_pending_confirm);
1052 
1053 	/* Build TCP header and checksum it. */
1054 	th = (struct tcphdr *)skb->data;
1055 	th->source		= inet->inet_sport;
1056 	th->dest		= inet->inet_dport;
1057 	th->seq			= htonl(tcb->seq);
1058 	th->ack_seq		= htonl(tp->rcv_nxt);
1059 	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
1060 					tcb->tcp_flags);
1061 
1062 	th->check		= 0;
1063 	th->urg_ptr		= 0;
1064 
1065 	/* The urg_mode check is necessary during a below snd_una win probe */
1066 	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
1067 		if (before(tp->snd_up, tcb->seq + 0x10000)) {
1068 			th->urg_ptr = htons(tp->snd_up - tcb->seq);
1069 			th->urg = 1;
1070 		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
1071 			th->urg_ptr = htons(0xFFFF);
1072 			th->urg = 1;
1073 		}
1074 	}
1075 
1076 	tcp_options_write((__be32 *)(th + 1), tp, &opts);
1077 	skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1078 	if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
1079 		th->window      = htons(tcp_select_window(sk));
1080 		tcp_ecn_send(sk, skb, th, tcp_header_size);
1081 	} else {
1082 		/* RFC1323: The window in SYN & SYN/ACK segments
1083 		 * is never scaled.
1084 		 */
1085 		th->window	= htons(min(tp->rcv_wnd, 65535U));
1086 	}
1087 #ifdef CONFIG_TCP_MD5SIG
1088 	/* Calculate the MD5 hash, as we have all we need now */
1089 	if (md5) {
1090 		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1091 		tp->af_specific->calc_md5_hash(opts.hash_location,
1092 					       md5, sk, skb);
1093 	}
1094 #endif
1095 
1096 	icsk->icsk_af_ops->send_check(sk, skb);
1097 
1098 	if (likely(tcb->tcp_flags & TCPHDR_ACK))
1099 		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1100 
1101 	if (skb->len != tcp_header_size) {
1102 		tcp_event_data_sent(tp, sk);
1103 		tp->data_segs_out += tcp_skb_pcount(skb);
1104 		tcp_internal_pacing(sk, skb);
1105 	}
1106 
1107 	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1108 		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1109 			      tcp_skb_pcount(skb));
1110 
1111 	tp->segs_out += tcp_skb_pcount(skb);
1112 	/* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1113 	skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1114 	skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1115 
1116 	/* Our usage of tstamp should remain private */
1117 	skb->tstamp = 0;
1118 
1119 	/* Cleanup our debris for IP stacks */
1120 	memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1121 			       sizeof(struct inet6_skb_parm)));
1122 
1123 	err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1124 
1125 	if (unlikely(err > 0)) {
1126 		tcp_enter_cwr(sk);
1127 		err = net_xmit_eval(err);
1128 	}
1129 	if (!err && oskb) {
1130 		oskb->skb_mstamp = tp->tcp_mstamp;
1131 		tcp_rate_skb_sent(sk, oskb);
1132 	}
1133 	return err;
1134 }
1135 
1136 /* This routine just queues the buffer for sending.
1137  *
1138  * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1139  * otherwise socket can stall.
1140  */
1141 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1142 {
1143 	struct tcp_sock *tp = tcp_sk(sk);
1144 
1145 	/* Advance write_seq and place onto the write_queue. */
1146 	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1147 	__skb_header_release(skb);
1148 	tcp_add_write_queue_tail(sk, skb);
1149 	sk->sk_wmem_queued += skb->truesize;
1150 	sk_mem_charge(sk, skb->truesize);
1151 }
1152 
1153 /* Initialize TSO segments for a packet. */
1154 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1155 {
1156 	if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1157 		/* Avoid the costly divide in the normal
1158 		 * non-TSO case.
1159 		 */
1160 		tcp_skb_pcount_set(skb, 1);
1161 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1162 	} else {
1163 		tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1164 		TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1165 	}
1166 }
1167 
1168 /* When a modification to fackets out becomes necessary, we need to check
1169  * skb is counted to fackets_out or not.
1170  */
1171 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1172 				   int decr)
1173 {
1174 	struct tcp_sock *tp = tcp_sk(sk);
1175 
1176 	if (!tp->sacked_out || tcp_is_reno(tp))
1177 		return;
1178 
1179 	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1180 		tp->fackets_out -= decr;
1181 }
1182 
1183 /* Pcount in the middle of the write queue got changed, we need to do various
1184  * tweaks to fix counters
1185  */
1186 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1187 {
1188 	struct tcp_sock *tp = tcp_sk(sk);
1189 
1190 	tp->packets_out -= decr;
1191 
1192 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1193 		tp->sacked_out -= decr;
1194 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1195 		tp->retrans_out -= decr;
1196 	if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1197 		tp->lost_out -= decr;
1198 
1199 	/* Reno case is special. Sigh... */
1200 	if (tcp_is_reno(tp) && decr > 0)
1201 		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1202 
1203 	tcp_adjust_fackets_out(sk, skb, decr);
1204 
1205 	if (tp->lost_skb_hint &&
1206 	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1207 	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1208 		tp->lost_cnt_hint -= decr;
1209 
1210 	tcp_verify_left_out(tp);
1211 }
1212 
1213 static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
1214 {
1215 	return TCP_SKB_CB(skb)->txstamp_ack ||
1216 		(skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
1217 }
1218 
1219 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1220 {
1221 	struct skb_shared_info *shinfo = skb_shinfo(skb);
1222 
1223 	if (unlikely(tcp_has_tx_tstamp(skb)) &&
1224 	    !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1225 		struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1226 		u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1227 
1228 		shinfo->tx_flags &= ~tsflags;
1229 		shinfo2->tx_flags |= tsflags;
1230 		swap(shinfo->tskey, shinfo2->tskey);
1231 		TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
1232 		TCP_SKB_CB(skb)->txstamp_ack = 0;
1233 	}
1234 }
1235 
1236 static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
1237 {
1238 	TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
1239 	TCP_SKB_CB(skb)->eor = 0;
1240 }
1241 
1242 /* Function to create two new TCP segments.  Shrinks the given segment
1243  * to the specified size and appends a new segment with the rest of the
1244  * packet to the list.  This won't be called frequently, I hope.
1245  * Remember, these are still headerless SKBs at this point.
1246  */
1247 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1248 		 unsigned int mss_now, gfp_t gfp)
1249 {
1250 	struct tcp_sock *tp = tcp_sk(sk);
1251 	struct sk_buff *buff;
1252 	int nsize, old_factor;
1253 	int nlen;
1254 	u8 flags;
1255 
1256 	if (WARN_ON(len > skb->len))
1257 		return -EINVAL;
1258 
1259 	nsize = skb_headlen(skb) - len;
1260 	if (nsize < 0)
1261 		nsize = 0;
1262 
1263 	if (skb_unclone(skb, gfp))
1264 		return -ENOMEM;
1265 
1266 	/* Get a new skb... force flag on. */
1267 	buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1268 	if (!buff)
1269 		return -ENOMEM; /* We'll just try again later. */
1270 
1271 	sk->sk_wmem_queued += buff->truesize;
1272 	sk_mem_charge(sk, buff->truesize);
1273 	nlen = skb->len - len - nsize;
1274 	buff->truesize += nlen;
1275 	skb->truesize -= nlen;
1276 
1277 	/* Correct the sequence numbers. */
1278 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1279 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1280 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1281 
1282 	/* PSH and FIN should only be set in the second packet. */
1283 	flags = TCP_SKB_CB(skb)->tcp_flags;
1284 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1285 	TCP_SKB_CB(buff)->tcp_flags = flags;
1286 	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1287 	tcp_skb_fragment_eor(skb, buff);
1288 
1289 	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1290 		/* Copy and checksum data tail into the new buffer. */
1291 		buff->csum = csum_partial_copy_nocheck(skb->data + len,
1292 						       skb_put(buff, nsize),
1293 						       nsize, 0);
1294 
1295 		skb_trim(skb, len);
1296 
1297 		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1298 	} else {
1299 		skb->ip_summed = CHECKSUM_PARTIAL;
1300 		skb_split(skb, buff, len);
1301 	}
1302 
1303 	buff->ip_summed = skb->ip_summed;
1304 
1305 	buff->tstamp = skb->tstamp;
1306 	tcp_fragment_tstamp(skb, buff);
1307 
1308 	old_factor = tcp_skb_pcount(skb);
1309 
1310 	/* Fix up tso_factor for both original and new SKB.  */
1311 	tcp_set_skb_tso_segs(skb, mss_now);
1312 	tcp_set_skb_tso_segs(buff, mss_now);
1313 
1314 	/* Update delivered info for the new segment */
1315 	TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;
1316 
1317 	/* If this packet has been sent out already, we must
1318 	 * adjust the various packet counters.
1319 	 */
1320 	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1321 		int diff = old_factor - tcp_skb_pcount(skb) -
1322 			tcp_skb_pcount(buff);
1323 
1324 		if (diff)
1325 			tcp_adjust_pcount(sk, skb, diff);
1326 	}
1327 
1328 	/* Link BUFF into the send queue. */
1329 	__skb_header_release(buff);
1330 	tcp_insert_write_queue_after(skb, buff, sk);
1331 
1332 	return 0;
1333 }
1334 
1335 /* This is similar to __pskb_pull_tail(). The difference is that pulled
1336  * data is not copied, but immediately discarded.
1337  */
1338 static int __pskb_trim_head(struct sk_buff *skb, int len)
1339 {
1340 	struct skb_shared_info *shinfo;
1341 	int i, k, eat;
1342 
1343 	eat = min_t(int, len, skb_headlen(skb));
1344 	if (eat) {
1345 		__skb_pull(skb, eat);
1346 		len -= eat;
1347 		if (!len)
1348 			return 0;
1349 	}
1350 	eat = len;
1351 	k = 0;
1352 	shinfo = skb_shinfo(skb);
1353 	for (i = 0; i < shinfo->nr_frags; i++) {
1354 		int size = skb_frag_size(&shinfo->frags[i]);
1355 
1356 		if (size <= eat) {
1357 			skb_frag_unref(skb, i);
1358 			eat -= size;
1359 		} else {
1360 			shinfo->frags[k] = shinfo->frags[i];
1361 			if (eat) {
1362 				shinfo->frags[k].page_offset += eat;
1363 				skb_frag_size_sub(&shinfo->frags[k], eat);
1364 				eat = 0;
1365 			}
1366 			k++;
1367 		}
1368 	}
1369 	shinfo->nr_frags = k;
1370 
1371 	skb->data_len -= len;
1372 	skb->len = skb->data_len;
1373 	return len;
1374 }
1375 
1376 /* Remove acked data from a packet in the transmit queue. */
1377 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1378 {
1379 	u32 delta_truesize;
1380 
1381 	if (skb_unclone(skb, GFP_ATOMIC))
1382 		return -ENOMEM;
1383 
1384 	delta_truesize = __pskb_trim_head(skb, len);
1385 
1386 	TCP_SKB_CB(skb)->seq += len;
1387 	skb->ip_summed = CHECKSUM_PARTIAL;
1388 
1389 	if (delta_truesize) {
1390 		skb->truesize	   -= delta_truesize;
1391 		sk->sk_wmem_queued -= delta_truesize;
1392 		sk_mem_uncharge(sk, delta_truesize);
1393 		sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1394 	}
1395 
1396 	/* Any change of skb->len requires recalculation of tso factor. */
1397 	if (tcp_skb_pcount(skb) > 1)
1398 		tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1399 
1400 	return 0;
1401 }
1402 
1403 /* Calculate MSS not accounting any TCP options.  */
1404 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1405 {
1406 	const struct tcp_sock *tp = tcp_sk(sk);
1407 	const struct inet_connection_sock *icsk = inet_csk(sk);
1408 	int mss_now;
1409 
1410 	/* Calculate base mss without TCP options:
1411 	   It is MMS_S - sizeof(tcphdr) of rfc1122
1412 	 */
1413 	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1414 
1415 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1416 	if (icsk->icsk_af_ops->net_frag_header_len) {
1417 		const struct dst_entry *dst = __sk_dst_get(sk);
1418 
1419 		if (dst && dst_allfrag(dst))
1420 			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1421 	}
1422 
1423 	/* Clamp it (mss_clamp does not include tcp options) */
1424 	if (mss_now > tp->rx_opt.mss_clamp)
1425 		mss_now = tp->rx_opt.mss_clamp;
1426 
1427 	/* Now subtract optional transport overhead */
1428 	mss_now -= icsk->icsk_ext_hdr_len;
1429 
1430 	/* Then reserve room for full set of TCP options and 8 bytes of data */
1431 	if (mss_now < 48)
1432 		mss_now = 48;
1433 	return mss_now;
1434 }
1435 
1436 /* Calculate MSS. Not accounting for SACKs here.  */
1437 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1438 {
1439 	/* Subtract TCP options size, not including SACKs */
1440 	return __tcp_mtu_to_mss(sk, pmtu) -
1441 	       (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1442 }
1443 
1444 /* Inverse of above */
1445 int tcp_mss_to_mtu(struct sock *sk, int mss)
1446 {
1447 	const struct tcp_sock *tp = tcp_sk(sk);
1448 	const struct inet_connection_sock *icsk = inet_csk(sk);
1449 	int mtu;
1450 
1451 	mtu = mss +
1452 	      tp->tcp_header_len +
1453 	      icsk->icsk_ext_hdr_len +
1454 	      icsk->icsk_af_ops->net_header_len;
1455 
1456 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1457 	if (icsk->icsk_af_ops->net_frag_header_len) {
1458 		const struct dst_entry *dst = __sk_dst_get(sk);
1459 
1460 		if (dst && dst_allfrag(dst))
1461 			mtu += icsk->icsk_af_ops->net_frag_header_len;
1462 	}
1463 	return mtu;
1464 }
1465 EXPORT_SYMBOL(tcp_mss_to_mtu);
1466 
1467 /* MTU probing init per socket */
1468 void tcp_mtup_init(struct sock *sk)
1469 {
1470 	struct tcp_sock *tp = tcp_sk(sk);
1471 	struct inet_connection_sock *icsk = inet_csk(sk);
1472 	struct net *net = sock_net(sk);
1473 
1474 	icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1475 	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1476 			       icsk->icsk_af_ops->net_header_len;
1477 	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1478 	icsk->icsk_mtup.probe_size = 0;
1479 	if (icsk->icsk_mtup.enabled)
1480 		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
1481 }
1482 EXPORT_SYMBOL(tcp_mtup_init);
1483 
1484 /* This function synchronize snd mss to current pmtu/exthdr set.
1485 
1486    tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1487    for TCP options, but includes only bare TCP header.
1488 
1489    tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1490    It is minimum of user_mss and mss received with SYN.
1491    It also does not include TCP options.
1492 
1493    inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1494 
1495    tp->mss_cache is current effective sending mss, including
1496    all tcp options except for SACKs. It is evaluated,
1497    taking into account current pmtu, but never exceeds
1498    tp->rx_opt.mss_clamp.
1499 
1500    NOTE1. rfc1122 clearly states that advertised MSS
1501    DOES NOT include either tcp or ip options.
1502 
1503    NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1504    are READ ONLY outside this function.		--ANK (980731)
1505  */
1506 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1507 {
1508 	struct tcp_sock *tp = tcp_sk(sk);
1509 	struct inet_connection_sock *icsk = inet_csk(sk);
1510 	int mss_now;
1511 
1512 	if (icsk->icsk_mtup.search_high > pmtu)
1513 		icsk->icsk_mtup.search_high = pmtu;
1514 
1515 	mss_now = tcp_mtu_to_mss(sk, pmtu);
1516 	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1517 
1518 	/* And store cached results */
1519 	icsk->icsk_pmtu_cookie = pmtu;
1520 	if (icsk->icsk_mtup.enabled)
1521 		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1522 	tp->mss_cache = mss_now;
1523 
1524 	return mss_now;
1525 }
1526 EXPORT_SYMBOL(tcp_sync_mss);
1527 
1528 /* Compute the current effective MSS, taking SACKs and IP options,
1529  * and even PMTU discovery events into account.
1530  */
1531 unsigned int tcp_current_mss(struct sock *sk)
1532 {
1533 	const struct tcp_sock *tp = tcp_sk(sk);
1534 	const struct dst_entry *dst = __sk_dst_get(sk);
1535 	u32 mss_now;
1536 	unsigned int header_len;
1537 	struct tcp_out_options opts;
1538 	struct tcp_md5sig_key *md5;
1539 
1540 	mss_now = tp->mss_cache;
1541 
1542 	if (dst) {
1543 		u32 mtu = dst_mtu(dst);
1544 		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1545 			mss_now = tcp_sync_mss(sk, mtu);
1546 	}
1547 
1548 	header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1549 		     sizeof(struct tcphdr);
1550 	/* The mss_cache is sized based on tp->tcp_header_len, which assumes
1551 	 * some common options. If this is an odd packet (because we have SACK
1552 	 * blocks etc) then our calculated header_len will be different, and
1553 	 * we have to adjust mss_now correspondingly */
1554 	if (header_len != tp->tcp_header_len) {
1555 		int delta = (int) header_len - tp->tcp_header_len;
1556 		mss_now -= delta;
1557 	}
1558 
1559 	return mss_now;
1560 }
1561 
1562 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1563  * As additional protections, we do not touch cwnd in retransmission phases,
1564  * and if application hit its sndbuf limit recently.
1565  */
1566 static void tcp_cwnd_application_limited(struct sock *sk)
1567 {
1568 	struct tcp_sock *tp = tcp_sk(sk);
1569 
1570 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1571 	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1572 		/* Limited by application or receiver window. */
1573 		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1574 		u32 win_used = max(tp->snd_cwnd_used, init_win);
1575 		if (win_used < tp->snd_cwnd) {
1576 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
1577 			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1578 		}
1579 		tp->snd_cwnd_used = 0;
1580 	}
1581 	tp->snd_cwnd_stamp = tcp_jiffies32;
1582 }
1583 
1584 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1585 {
1586 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1587 	struct tcp_sock *tp = tcp_sk(sk);
1588 
1589 	/* Track the maximum number of outstanding packets in each
1590 	 * window, and remember whether we were cwnd-limited then.
1591 	 */
1592 	if (!before(tp->snd_una, tp->max_packets_seq) ||
1593 	    tp->packets_out > tp->max_packets_out) {
1594 		tp->max_packets_out = tp->packets_out;
1595 		tp->max_packets_seq = tp->snd_nxt;
1596 		tp->is_cwnd_limited = is_cwnd_limited;
1597 	}
1598 
1599 	if (tcp_is_cwnd_limited(sk)) {
1600 		/* Network is feed fully. */
1601 		tp->snd_cwnd_used = 0;
1602 		tp->snd_cwnd_stamp = tcp_jiffies32;
1603 	} else {
1604 		/* Network starves. */
1605 		if (tp->packets_out > tp->snd_cwnd_used)
1606 			tp->snd_cwnd_used = tp->packets_out;
1607 
1608 		if (sysctl_tcp_slow_start_after_idle &&
1609 		    (s32)(tcp_jiffies32 - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
1610 		    !ca_ops->cong_control)
1611 			tcp_cwnd_application_limited(sk);
1612 
1613 		/* The following conditions together indicate the starvation
1614 		 * is caused by insufficient sender buffer:
1615 		 * 1) just sent some data (see tcp_write_xmit)
1616 		 * 2) not cwnd limited (this else condition)
1617 		 * 3) no more data to send (null tcp_send_head )
1618 		 * 4) application is hitting buffer limit (SOCK_NOSPACE)
1619 		 */
1620 		if (!tcp_send_head(sk) && sk->sk_socket &&
1621 		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
1622 		    (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
1623 			tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
1624 	}
1625 }
1626 
1627 /* Minshall's variant of the Nagle send check. */
1628 static bool tcp_minshall_check(const struct tcp_sock *tp)
1629 {
1630 	return after(tp->snd_sml, tp->snd_una) &&
1631 		!after(tp->snd_sml, tp->snd_nxt);
1632 }
1633 
1634 /* Update snd_sml if this skb is under mss
1635  * Note that a TSO packet might end with a sub-mss segment
1636  * The test is really :
1637  * if ((skb->len % mss) != 0)
1638  *        tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1639  * But we can avoid doing the divide again given we already have
1640  *  skb_pcount = skb->len / mss_now
1641  */
1642 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1643 				const struct sk_buff *skb)
1644 {
1645 	if (skb->len < tcp_skb_pcount(skb) * mss_now)
1646 		tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1647 }
1648 
1649 /* Return false, if packet can be sent now without violation Nagle's rules:
1650  * 1. It is full sized. (provided by caller in %partial bool)
1651  * 2. Or it contains FIN. (already checked by caller)
1652  * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1653  * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1654  *    With Minshall's modification: all sent small packets are ACKed.
1655  */
1656 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1657 			    int nonagle)
1658 {
1659 	return partial &&
1660 		((nonagle & TCP_NAGLE_CORK) ||
1661 		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1662 }
1663 
1664 /* Return how many segs we'd like on a TSO packet,
1665  * to send one TSO packet per ms
1666  */
1667 u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
1668 		     int min_tso_segs)
1669 {
1670 	u32 bytes, segs;
1671 
1672 	bytes = min(sk->sk_pacing_rate >> 10,
1673 		    sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1674 
1675 	/* Goal is to send at least one packet per ms,
1676 	 * not one big TSO packet every 100 ms.
1677 	 * This preserves ACK clocking and is consistent
1678 	 * with tcp_tso_should_defer() heuristic.
1679 	 */
1680 	segs = max_t(u32, bytes / mss_now, min_tso_segs);
1681 
1682 	return min_t(u32, segs, sk->sk_gso_max_segs);
1683 }
1684 EXPORT_SYMBOL(tcp_tso_autosize);
1685 
1686 /* Return the number of segments we want in the skb we are transmitting.
1687  * See if congestion control module wants to decide; otherwise, autosize.
1688  */
1689 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
1690 {
1691 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1692 	u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;
1693 
1694 	return tso_segs ? :
1695 		tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs);
1696 }
1697 
1698 /* Returns the portion of skb which can be sent right away */
1699 static unsigned int tcp_mss_split_point(const struct sock *sk,
1700 					const struct sk_buff *skb,
1701 					unsigned int mss_now,
1702 					unsigned int max_segs,
1703 					int nonagle)
1704 {
1705 	const struct tcp_sock *tp = tcp_sk(sk);
1706 	u32 partial, needed, window, max_len;
1707 
1708 	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1709 	max_len = mss_now * max_segs;
1710 
1711 	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1712 		return max_len;
1713 
1714 	needed = min(skb->len, window);
1715 
1716 	if (max_len <= needed)
1717 		return max_len;
1718 
1719 	partial = needed % mss_now;
1720 	/* If last segment is not a full MSS, check if Nagle rules allow us
1721 	 * to include this last segment in this skb.
1722 	 * Otherwise, we'll split the skb at last MSS boundary
1723 	 */
1724 	if (tcp_nagle_check(partial != 0, tp, nonagle))
1725 		return needed - partial;
1726 
1727 	return needed;
1728 }
1729 
1730 /* Can at least one segment of SKB be sent right now, according to the
1731  * congestion window rules?  If so, return how many segments are allowed.
1732  */
1733 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1734 					 const struct sk_buff *skb)
1735 {
1736 	u32 in_flight, cwnd, halfcwnd;
1737 
1738 	/* Don't be strict about the congestion window for the final FIN.  */
1739 	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1740 	    tcp_skb_pcount(skb) == 1)
1741 		return 1;
1742 
1743 	in_flight = tcp_packets_in_flight(tp);
1744 	cwnd = tp->snd_cwnd;
1745 	if (in_flight >= cwnd)
1746 		return 0;
1747 
1748 	/* For better scheduling, ensure we have at least
1749 	 * 2 GSO packets in flight.
1750 	 */
1751 	halfcwnd = max(cwnd >> 1, 1U);
1752 	return min(halfcwnd, cwnd - in_flight);
1753 }
1754 
1755 /* Initialize TSO state of a skb.
1756  * This must be invoked the first time we consider transmitting
1757  * SKB onto the wire.
1758  */
1759 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1760 {
1761 	int tso_segs = tcp_skb_pcount(skb);
1762 
1763 	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1764 		tcp_set_skb_tso_segs(skb, mss_now);
1765 		tso_segs = tcp_skb_pcount(skb);
1766 	}
1767 	return tso_segs;
1768 }
1769 
1770 
1771 /* Return true if the Nagle test allows this packet to be
1772  * sent now.
1773  */
1774 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1775 				  unsigned int cur_mss, int nonagle)
1776 {
1777 	/* Nagle rule does not apply to frames, which sit in the middle of the
1778 	 * write_queue (they have no chances to get new data).
1779 	 *
1780 	 * This is implemented in the callers, where they modify the 'nonagle'
1781 	 * argument based upon the location of SKB in the send queue.
1782 	 */
1783 	if (nonagle & TCP_NAGLE_PUSH)
1784 		return true;
1785 
1786 	/* Don't use the nagle rule for urgent data (or for the final FIN). */
1787 	if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1788 		return true;
1789 
1790 	if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1791 		return true;
1792 
1793 	return false;
1794 }
1795 
1796 /* Does at least the first segment of SKB fit into the send window? */
1797 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1798 			     const struct sk_buff *skb,
1799 			     unsigned int cur_mss)
1800 {
1801 	u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1802 
1803 	if (skb->len > cur_mss)
1804 		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1805 
1806 	return !after(end_seq, tcp_wnd_end(tp));
1807 }
1808 
1809 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1810  * which is put after SKB on the list.  It is very much like
1811  * tcp_fragment() except that it may make several kinds of assumptions
1812  * in order to speed up the splitting operation.  In particular, we
1813  * know that all the data is in scatter-gather pages, and that the
1814  * packet has never been sent out before (and thus is not cloned).
1815  */
1816 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1817 			unsigned int mss_now, gfp_t gfp)
1818 {
1819 	struct sk_buff *buff;
1820 	int nlen = skb->len - len;
1821 	u8 flags;
1822 
1823 	/* All of a TSO frame must be composed of paged data.  */
1824 	if (skb->len != skb->data_len)
1825 		return tcp_fragment(sk, skb, len, mss_now, gfp);
1826 
1827 	buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1828 	if (unlikely(!buff))
1829 		return -ENOMEM;
1830 
1831 	sk->sk_wmem_queued += buff->truesize;
1832 	sk_mem_charge(sk, buff->truesize);
1833 	buff->truesize += nlen;
1834 	skb->truesize -= nlen;
1835 
1836 	/* Correct the sequence numbers. */
1837 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1838 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1839 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1840 
1841 	/* PSH and FIN should only be set in the second packet. */
1842 	flags = TCP_SKB_CB(skb)->tcp_flags;
1843 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1844 	TCP_SKB_CB(buff)->tcp_flags = flags;
1845 
1846 	/* This packet was never sent out yet, so no SACK bits. */
1847 	TCP_SKB_CB(buff)->sacked = 0;
1848 
1849 	tcp_skb_fragment_eor(skb, buff);
1850 
1851 	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1852 	skb_split(skb, buff, len);
1853 	tcp_fragment_tstamp(skb, buff);
1854 
1855 	/* Fix up tso_factor for both original and new SKB.  */
1856 	tcp_set_skb_tso_segs(skb, mss_now);
1857 	tcp_set_skb_tso_segs(buff, mss_now);
1858 
1859 	/* Link BUFF into the send queue. */
1860 	__skb_header_release(buff);
1861 	tcp_insert_write_queue_after(skb, buff, sk);
1862 
1863 	return 0;
1864 }
1865 
1866 /* Try to defer sending, if possible, in order to minimize the amount
1867  * of TSO splitting we do.  View it as a kind of TSO Nagle test.
1868  *
1869  * This algorithm is from John Heffner.
1870  */
1871 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1872 				 bool *is_cwnd_limited, u32 max_segs)
1873 {
1874 	const struct inet_connection_sock *icsk = inet_csk(sk);
1875 	u32 age, send_win, cong_win, limit, in_flight;
1876 	struct tcp_sock *tp = tcp_sk(sk);
1877 	struct sk_buff *head;
1878 	int win_divisor;
1879 
1880 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1881 		goto send_now;
1882 
1883 	if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1884 		goto send_now;
1885 
1886 	/* Avoid bursty behavior by allowing defer
1887 	 * only if the last write was recent.
1888 	 */
1889 	if ((s32)(tcp_jiffies32 - tp->lsndtime) > 0)
1890 		goto send_now;
1891 
1892 	in_flight = tcp_packets_in_flight(tp);
1893 
1894 	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1895 
1896 	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1897 
1898 	/* From in_flight test above, we know that cwnd > in_flight.  */
1899 	cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1900 
1901 	limit = min(send_win, cong_win);
1902 
1903 	/* If a full-sized TSO skb can be sent, do it. */
1904 	if (limit >= max_segs * tp->mss_cache)
1905 		goto send_now;
1906 
1907 	/* Middle in queue won't get any more data, full sendable already? */
1908 	if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1909 		goto send_now;
1910 
1911 	win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1912 	if (win_divisor) {
1913 		u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1914 
1915 		/* If at least some fraction of a window is available,
1916 		 * just use it.
1917 		 */
1918 		chunk /= win_divisor;
1919 		if (limit >= chunk)
1920 			goto send_now;
1921 	} else {
1922 		/* Different approach, try not to defer past a single
1923 		 * ACK.  Receiver should ACK every other full sized
1924 		 * frame, so if we have space for more than 3 frames
1925 		 * then send now.
1926 		 */
1927 		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1928 			goto send_now;
1929 	}
1930 
1931 	head = tcp_write_queue_head(sk);
1932 
1933 	age = tcp_stamp_us_delta(tp->tcp_mstamp, head->skb_mstamp);
1934 	/* If next ACK is likely to come too late (half srtt), do not defer */
1935 	if (age < (tp->srtt_us >> 4))
1936 		goto send_now;
1937 
1938 	/* Ok, it looks like it is advisable to defer. */
1939 
1940 	if (cong_win < send_win && cong_win <= skb->len)
1941 		*is_cwnd_limited = true;
1942 
1943 	return true;
1944 
1945 send_now:
1946 	return false;
1947 }
1948 
1949 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1950 {
1951 	struct inet_connection_sock *icsk = inet_csk(sk);
1952 	struct tcp_sock *tp = tcp_sk(sk);
1953 	struct net *net = sock_net(sk);
1954 	u32 interval;
1955 	s32 delta;
1956 
1957 	interval = net->ipv4.sysctl_tcp_probe_interval;
1958 	delta = tcp_jiffies32 - icsk->icsk_mtup.probe_timestamp;
1959 	if (unlikely(delta >= interval * HZ)) {
1960 		int mss = tcp_current_mss(sk);
1961 
1962 		/* Update current search range */
1963 		icsk->icsk_mtup.probe_size = 0;
1964 		icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1965 			sizeof(struct tcphdr) +
1966 			icsk->icsk_af_ops->net_header_len;
1967 		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1968 
1969 		/* Update probe time stamp */
1970 		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
1971 	}
1972 }
1973 
1974 /* Create a new MTU probe if we are ready.
1975  * MTU probe is regularly attempting to increase the path MTU by
1976  * deliberately sending larger packets.  This discovers routing
1977  * changes resulting in larger path MTUs.
1978  *
1979  * Returns 0 if we should wait to probe (no cwnd available),
1980  *         1 if a probe was sent,
1981  *         -1 otherwise
1982  */
1983 static int tcp_mtu_probe(struct sock *sk)
1984 {
1985 	struct inet_connection_sock *icsk = inet_csk(sk);
1986 	struct tcp_sock *tp = tcp_sk(sk);
1987 	struct sk_buff *skb, *nskb, *next;
1988 	struct net *net = sock_net(sk);
1989 	int probe_size;
1990 	int size_needed;
1991 	int copy, len;
1992 	int mss_now;
1993 	int interval;
1994 
1995 	/* Not currently probing/verifying,
1996 	 * not in recovery,
1997 	 * have enough cwnd, and
1998 	 * not SACKing (the variable headers throw things off)
1999 	 */
2000 	if (likely(!icsk->icsk_mtup.enabled ||
2001 		   icsk->icsk_mtup.probe_size ||
2002 		   inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
2003 		   tp->snd_cwnd < 11 ||
2004 		   tp->rx_opt.num_sacks || tp->rx_opt.dsack))
2005 		return -1;
2006 
2007 	/* Use binary search for probe_size between tcp_mss_base,
2008 	 * and current mss_clamp. if (search_high - search_low)
2009 	 * smaller than a threshold, backoff from probing.
2010 	 */
2011 	mss_now = tcp_current_mss(sk);
2012 	probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
2013 				    icsk->icsk_mtup.search_low) >> 1);
2014 	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
2015 	interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
2016 	/* When misfortune happens, we are reprobing actively,
2017 	 * and then reprobe timer has expired. We stick with current
2018 	 * probing process by not resetting search range to its orignal.
2019 	 */
2020 	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
2021 		interval < net->ipv4.sysctl_tcp_probe_threshold) {
2022 		/* Check whether enough time has elaplased for
2023 		 * another round of probing.
2024 		 */
2025 		tcp_mtu_check_reprobe(sk);
2026 		return -1;
2027 	}
2028 
2029 	/* Have enough data in the send queue to probe? */
2030 	if (tp->write_seq - tp->snd_nxt < size_needed)
2031 		return -1;
2032 
2033 	if (tp->snd_wnd < size_needed)
2034 		return -1;
2035 	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
2036 		return 0;
2037 
2038 	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
2039 	if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
2040 		if (!tcp_packets_in_flight(tp))
2041 			return -1;
2042 		else
2043 			return 0;
2044 	}
2045 
2046 	/* We're allowed to probe.  Build it now. */
2047 	nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
2048 	if (!nskb)
2049 		return -1;
2050 	sk->sk_wmem_queued += nskb->truesize;
2051 	sk_mem_charge(sk, nskb->truesize);
2052 
2053 	skb = tcp_send_head(sk);
2054 
2055 	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
2056 	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
2057 	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
2058 	TCP_SKB_CB(nskb)->sacked = 0;
2059 	nskb->csum = 0;
2060 	nskb->ip_summed = skb->ip_summed;
2061 
2062 	tcp_insert_write_queue_before(nskb, skb, sk);
2063 
2064 	len = 0;
2065 	tcp_for_write_queue_from_safe(skb, next, sk) {
2066 		copy = min_t(int, skb->len, probe_size - len);
2067 		if (nskb->ip_summed) {
2068 			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
2069 		} else {
2070 			__wsum csum = skb_copy_and_csum_bits(skb, 0,
2071 							     skb_put(nskb, copy),
2072 							     copy, 0);
2073 			nskb->csum = csum_block_add(nskb->csum, csum, len);
2074 		}
2075 
2076 		if (skb->len <= copy) {
2077 			/* We've eaten all the data from this skb.
2078 			 * Throw it away. */
2079 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2080 			tcp_unlink_write_queue(skb, sk);
2081 			sk_wmem_free_skb(sk, skb);
2082 		} else {
2083 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
2084 						   ~(TCPHDR_FIN|TCPHDR_PSH);
2085 			if (!skb_shinfo(skb)->nr_frags) {
2086 				skb_pull(skb, copy);
2087 				if (skb->ip_summed != CHECKSUM_PARTIAL)
2088 					skb->csum = csum_partial(skb->data,
2089 								 skb->len, 0);
2090 			} else {
2091 				__pskb_trim_head(skb, copy);
2092 				tcp_set_skb_tso_segs(skb, mss_now);
2093 			}
2094 			TCP_SKB_CB(skb)->seq += copy;
2095 		}
2096 
2097 		len += copy;
2098 
2099 		if (len >= probe_size)
2100 			break;
2101 	}
2102 	tcp_init_tso_segs(nskb, nskb->len);
2103 
2104 	/* We're ready to send.  If this fails, the probe will
2105 	 * be resegmented into mss-sized pieces by tcp_write_xmit().
2106 	 */
2107 	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2108 		/* Decrement cwnd here because we are sending
2109 		 * effectively two packets. */
2110 		tp->snd_cwnd--;
2111 		tcp_event_new_data_sent(sk, nskb);
2112 
2113 		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2114 		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2115 		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2116 
2117 		return 1;
2118 	}
2119 
2120 	return -1;
2121 }
2122 
2123 static bool tcp_pacing_check(const struct sock *sk)
2124 {
2125 	return tcp_needs_internal_pacing(sk) &&
2126 	       hrtimer_active(&tcp_sk(sk)->pacing_timer);
2127 }
2128 
2129 /* TCP Small Queues :
2130  * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2131  * (These limits are doubled for retransmits)
2132  * This allows for :
2133  *  - better RTT estimation and ACK scheduling
2134  *  - faster recovery
2135  *  - high rates
2136  * Alas, some drivers / subsystems require a fair amount
2137  * of queued bytes to ensure line rate.
2138  * One example is wifi aggregation (802.11 AMPDU)
2139  */
2140 static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
2141 				  unsigned int factor)
2142 {
2143 	unsigned int limit;
2144 
2145 	limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2146 	limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2147 	limit <<= factor;
2148 
2149 	if (refcount_read(&sk->sk_wmem_alloc) > limit) {
2150 		/* Always send the 1st or 2nd skb in write queue.
2151 		 * No need to wait for TX completion to call us back,
2152 		 * after softirq/tasklet schedule.
2153 		 * This helps when TX completions are delayed too much.
2154 		 */
2155 		if (skb == sk->sk_write_queue.next ||
2156 		    skb->prev == sk->sk_write_queue.next)
2157 			return false;
2158 
2159 		set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
2160 		/* It is possible TX completion already happened
2161 		 * before we set TSQ_THROTTLED, so we must
2162 		 * test again the condition.
2163 		 */
2164 		smp_mb__after_atomic();
2165 		if (refcount_read(&sk->sk_wmem_alloc) > limit)
2166 			return true;
2167 	}
2168 	return false;
2169 }
2170 
2171 static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
2172 {
2173 	const u32 now = tcp_jiffies32;
2174 	enum tcp_chrono old = tp->chrono_type;
2175 
2176 	if (old > TCP_CHRONO_UNSPEC)
2177 		tp->chrono_stat[old - 1] += now - tp->chrono_start;
2178 	tp->chrono_start = now;
2179 	tp->chrono_type = new;
2180 }
2181 
2182 void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
2183 {
2184 	struct tcp_sock *tp = tcp_sk(sk);
2185 
2186 	/* If there are multiple conditions worthy of tracking in a
2187 	 * chronograph then the highest priority enum takes precedence
2188 	 * over the other conditions. So that if something "more interesting"
2189 	 * starts happening, stop the previous chrono and start a new one.
2190 	 */
2191 	if (type > tp->chrono_type)
2192 		tcp_chrono_set(tp, type);
2193 }
2194 
2195 void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
2196 {
2197 	struct tcp_sock *tp = tcp_sk(sk);
2198 
2199 
2200 	/* There are multiple conditions worthy of tracking in a
2201 	 * chronograph, so that the highest priority enum takes
2202 	 * precedence over the other conditions (see tcp_chrono_start).
2203 	 * If a condition stops, we only stop chrono tracking if
2204 	 * it's the "most interesting" or current chrono we are
2205 	 * tracking and starts busy chrono if we have pending data.
2206 	 */
2207 	if (tcp_write_queue_empty(sk))
2208 		tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
2209 	else if (type == tp->chrono_type)
2210 		tcp_chrono_set(tp, TCP_CHRONO_BUSY);
2211 }
2212 
2213 /* This routine writes packets to the network.  It advances the
2214  * send_head.  This happens as incoming acks open up the remote
2215  * window for us.
2216  *
2217  * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2218  * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2219  * account rare use of URG, this is not a big flaw.
2220  *
2221  * Send at most one packet when push_one > 0. Temporarily ignore
2222  * cwnd limit to force at most one packet out when push_one == 2.
2223 
2224  * Returns true, if no segments are in flight and we have queued segments,
2225  * but cannot send anything now because of SWS or another problem.
2226  */
2227 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2228 			   int push_one, gfp_t gfp)
2229 {
2230 	struct tcp_sock *tp = tcp_sk(sk);
2231 	struct sk_buff *skb;
2232 	unsigned int tso_segs, sent_pkts;
2233 	int cwnd_quota;
2234 	int result;
2235 	bool is_cwnd_limited = false, is_rwnd_limited = false;
2236 	u32 max_segs;
2237 
2238 	sent_pkts = 0;
2239 
2240 	if (!push_one) {
2241 		/* Do MTU probing. */
2242 		result = tcp_mtu_probe(sk);
2243 		if (!result) {
2244 			return false;
2245 		} else if (result > 0) {
2246 			sent_pkts = 1;
2247 		}
2248 	}
2249 
2250 	max_segs = tcp_tso_segs(sk, mss_now);
2251 	tcp_mstamp_refresh(tp);
2252 	while ((skb = tcp_send_head(sk))) {
2253 		unsigned int limit;
2254 
2255 		if (tcp_pacing_check(sk))
2256 			break;
2257 
2258 		tso_segs = tcp_init_tso_segs(skb, mss_now);
2259 		BUG_ON(!tso_segs);
2260 
2261 		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2262 			/* "skb_mstamp" is used as a start point for the retransmit timer */
2263 			skb->skb_mstamp = tp->tcp_mstamp;
2264 			goto repair; /* Skip network transmission */
2265 		}
2266 
2267 		cwnd_quota = tcp_cwnd_test(tp, skb);
2268 		if (!cwnd_quota) {
2269 			if (push_one == 2)
2270 				/* Force out a loss probe pkt. */
2271 				cwnd_quota = 1;
2272 			else
2273 				break;
2274 		}
2275 
2276 		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
2277 			is_rwnd_limited = true;
2278 			break;
2279 		}
2280 
2281 		if (tso_segs == 1) {
2282 			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2283 						     (tcp_skb_is_last(sk, skb) ?
2284 						      nonagle : TCP_NAGLE_PUSH))))
2285 				break;
2286 		} else {
2287 			if (!push_one &&
2288 			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2289 						 max_segs))
2290 				break;
2291 		}
2292 
2293 		limit = mss_now;
2294 		if (tso_segs > 1 && !tcp_urg_mode(tp))
2295 			limit = tcp_mss_split_point(sk, skb, mss_now,
2296 						    min_t(unsigned int,
2297 							  cwnd_quota,
2298 							  max_segs),
2299 						    nonagle);
2300 
2301 		if (skb->len > limit &&
2302 		    unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2303 			break;
2304 
2305 		if (test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags))
2306 			clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
2307 		if (tcp_small_queue_check(sk, skb, 0))
2308 			break;
2309 
2310 		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2311 			break;
2312 
2313 repair:
2314 		/* Advance the send_head.  This one is sent out.
2315 		 * This call will increment packets_out.
2316 		 */
2317 		tcp_event_new_data_sent(sk, skb);
2318 
2319 		tcp_minshall_update(tp, mss_now, skb);
2320 		sent_pkts += tcp_skb_pcount(skb);
2321 
2322 		if (push_one)
2323 			break;
2324 	}
2325 
2326 	if (is_rwnd_limited)
2327 		tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
2328 	else
2329 		tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
2330 
2331 	if (likely(sent_pkts)) {
2332 		if (tcp_in_cwnd_reduction(sk))
2333 			tp->prr_out += sent_pkts;
2334 
2335 		/* Send one loss probe per tail loss episode. */
2336 		if (push_one != 2)
2337 			tcp_schedule_loss_probe(sk);
2338 		is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2339 		tcp_cwnd_validate(sk, is_cwnd_limited);
2340 		return false;
2341 	}
2342 	return !tp->packets_out && tcp_send_head(sk);
2343 }
2344 
2345 bool tcp_schedule_loss_probe(struct sock *sk)
2346 {
2347 	struct inet_connection_sock *icsk = inet_csk(sk);
2348 	struct tcp_sock *tp = tcp_sk(sk);
2349 	u32 timeout, rto_delta_us;
2350 
2351 	/* Don't do any loss probe on a Fast Open connection before 3WHS
2352 	 * finishes.
2353 	 */
2354 	if (tp->fastopen_rsk)
2355 		return false;
2356 
2357 	/* Schedule a loss probe in 2*RTT for SACK capable connections
2358 	 * in Open state, that are either limited by cwnd or application.
2359 	 */
2360 	if ((sysctl_tcp_early_retrans != 3 && sysctl_tcp_early_retrans != 4) ||
2361 	    !tp->packets_out || !tcp_is_sack(tp) ||
2362 	    icsk->icsk_ca_state != TCP_CA_Open)
2363 		return false;
2364 
2365 	if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2366 	     tcp_send_head(sk))
2367 		return false;
2368 
2369 	/* Probe timeout is 2*rtt. Add minimum RTO to account
2370 	 * for delayed ack when there's one outstanding packet. If no RTT
2371 	 * sample is available then probe after TCP_TIMEOUT_INIT.
2372 	 */
2373 	if (tp->srtt_us) {
2374 		timeout = usecs_to_jiffies(tp->srtt_us >> 2);
2375 		if (tp->packets_out == 1)
2376 			timeout += TCP_RTO_MIN;
2377 		else
2378 			timeout += TCP_TIMEOUT_MIN;
2379 	} else {
2380 		timeout = TCP_TIMEOUT_INIT;
2381 	}
2382 
2383 	/* If the RTO formula yields an earlier time, then use that time. */
2384 	rto_delta_us = tcp_rto_delta_us(sk);  /* How far in future is RTO? */
2385 	if (rto_delta_us > 0)
2386 		timeout = min_t(u32, timeout, usecs_to_jiffies(rto_delta_us));
2387 
2388 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2389 				  TCP_RTO_MAX);
2390 	return true;
2391 }
2392 
2393 /* Thanks to skb fast clones, we can detect if a prior transmit of
2394  * a packet is still in a qdisc or driver queue.
2395  * In this case, there is very little point doing a retransmit !
2396  */
2397 static bool skb_still_in_host_queue(const struct sock *sk,
2398 				    const struct sk_buff *skb)
2399 {
2400 	if (unlikely(skb_fclone_busy(sk, skb))) {
2401 		NET_INC_STATS(sock_net(sk),
2402 			      LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2403 		return true;
2404 	}
2405 	return false;
2406 }
2407 
2408 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2409  * retransmit the last segment.
2410  */
2411 void tcp_send_loss_probe(struct sock *sk)
2412 {
2413 	struct tcp_sock *tp = tcp_sk(sk);
2414 	struct sk_buff *skb;
2415 	int pcount;
2416 	int mss = tcp_current_mss(sk);
2417 
2418 	skb = tcp_send_head(sk);
2419 	if (skb) {
2420 		if (tcp_snd_wnd_test(tp, skb, mss)) {
2421 			pcount = tp->packets_out;
2422 			tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2423 			if (tp->packets_out > pcount)
2424 				goto probe_sent;
2425 			goto rearm_timer;
2426 		}
2427 		skb = tcp_write_queue_prev(sk, skb);
2428 	} else {
2429 		skb = tcp_write_queue_tail(sk);
2430 	}
2431 
2432 	/* At most one outstanding TLP retransmission. */
2433 	if (tp->tlp_high_seq)
2434 		goto rearm_timer;
2435 
2436 	/* Retransmit last segment. */
2437 	if (WARN_ON(!skb))
2438 		goto rearm_timer;
2439 
2440 	if (skb_still_in_host_queue(sk, skb))
2441 		goto rearm_timer;
2442 
2443 	pcount = tcp_skb_pcount(skb);
2444 	if (WARN_ON(!pcount))
2445 		goto rearm_timer;
2446 
2447 	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2448 		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2449 					  GFP_ATOMIC)))
2450 			goto rearm_timer;
2451 		skb = tcp_write_queue_next(sk, skb);
2452 	}
2453 
2454 	if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2455 		goto rearm_timer;
2456 
2457 	if (__tcp_retransmit_skb(sk, skb, 1))
2458 		goto rearm_timer;
2459 
2460 	/* Record snd_nxt for loss detection. */
2461 	tp->tlp_high_seq = tp->snd_nxt;
2462 
2463 probe_sent:
2464 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2465 	/* Reset s.t. tcp_rearm_rto will restart timer from now */
2466 	inet_csk(sk)->icsk_pending = 0;
2467 rearm_timer:
2468 	tcp_rearm_rto(sk);
2469 }
2470 
2471 /* Push out any pending frames which were held back due to
2472  * TCP_CORK or attempt at coalescing tiny packets.
2473  * The socket must be locked by the caller.
2474  */
2475 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2476 			       int nonagle)
2477 {
2478 	/* If we are closed, the bytes will have to remain here.
2479 	 * In time closedown will finish, we empty the write queue and
2480 	 * all will be happy.
2481 	 */
2482 	if (unlikely(sk->sk_state == TCP_CLOSE))
2483 		return;
2484 
2485 	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2486 			   sk_gfp_mask(sk, GFP_ATOMIC)))
2487 		tcp_check_probe_timer(sk);
2488 }
2489 
2490 /* Send _single_ skb sitting at the send head. This function requires
2491  * true push pending frames to setup probe timer etc.
2492  */
2493 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2494 {
2495 	struct sk_buff *skb = tcp_send_head(sk);
2496 
2497 	BUG_ON(!skb || skb->len < mss_now);
2498 
2499 	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2500 }
2501 
2502 /* This function returns the amount that we can raise the
2503  * usable window based on the following constraints
2504  *
2505  * 1. The window can never be shrunk once it is offered (RFC 793)
2506  * 2. We limit memory per socket
2507  *
2508  * RFC 1122:
2509  * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2510  *  RECV.NEXT + RCV.WIN fixed until:
2511  *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2512  *
2513  * i.e. don't raise the right edge of the window until you can raise
2514  * it at least MSS bytes.
2515  *
2516  * Unfortunately, the recommended algorithm breaks header prediction,
2517  * since header prediction assumes th->window stays fixed.
2518  *
2519  * Strictly speaking, keeping th->window fixed violates the receiver
2520  * side SWS prevention criteria. The problem is that under this rule
2521  * a stream of single byte packets will cause the right side of the
2522  * window to always advance by a single byte.
2523  *
2524  * Of course, if the sender implements sender side SWS prevention
2525  * then this will not be a problem.
2526  *
2527  * BSD seems to make the following compromise:
2528  *
2529  *	If the free space is less than the 1/4 of the maximum
2530  *	space available and the free space is less than 1/2 mss,
2531  *	then set the window to 0.
2532  *	[ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2533  *	Otherwise, just prevent the window from shrinking
2534  *	and from being larger than the largest representable value.
2535  *
2536  * This prevents incremental opening of the window in the regime
2537  * where TCP is limited by the speed of the reader side taking
2538  * data out of the TCP receive queue. It does nothing about
2539  * those cases where the window is constrained on the sender side
2540  * because the pipeline is full.
2541  *
2542  * BSD also seems to "accidentally" limit itself to windows that are a
2543  * multiple of MSS, at least until the free space gets quite small.
2544  * This would appear to be a side effect of the mbuf implementation.
2545  * Combining these two algorithms results in the observed behavior
2546  * of having a fixed window size at almost all times.
2547  *
2548  * Below we obtain similar behavior by forcing the offered window to
2549  * a multiple of the mss when it is feasible to do so.
2550  *
2551  * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2552  * Regular options like TIMESTAMP are taken into account.
2553  */
2554 u32 __tcp_select_window(struct sock *sk)
2555 {
2556 	struct inet_connection_sock *icsk = inet_csk(sk);
2557 	struct tcp_sock *tp = tcp_sk(sk);
2558 	/* MSS for the peer's data.  Previous versions used mss_clamp
2559 	 * here.  I don't know if the value based on our guesses
2560 	 * of peer's MSS is better for the performance.  It's more correct
2561 	 * but may be worse for the performance because of rcv_mss
2562 	 * fluctuations.  --SAW  1998/11/1
2563 	 */
2564 	int mss = icsk->icsk_ack.rcv_mss;
2565 	int free_space = tcp_space(sk);
2566 	int allowed_space = tcp_full_space(sk);
2567 	int full_space = min_t(int, tp->window_clamp, allowed_space);
2568 	int window;
2569 
2570 	if (unlikely(mss > full_space)) {
2571 		mss = full_space;
2572 		if (mss <= 0)
2573 			return 0;
2574 	}
2575 	if (free_space < (full_space >> 1)) {
2576 		icsk->icsk_ack.quick = 0;
2577 
2578 		if (tcp_under_memory_pressure(sk))
2579 			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2580 					       4U * tp->advmss);
2581 
2582 		/* free_space might become our new window, make sure we don't
2583 		 * increase it due to wscale.
2584 		 */
2585 		free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2586 
2587 		/* if free space is less than mss estimate, or is below 1/16th
2588 		 * of the maximum allowed, try to move to zero-window, else
2589 		 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2590 		 * new incoming data is dropped due to memory limits.
2591 		 * With large window, mss test triggers way too late in order
2592 		 * to announce zero window in time before rmem limit kicks in.
2593 		 */
2594 		if (free_space < (allowed_space >> 4) || free_space < mss)
2595 			return 0;
2596 	}
2597 
2598 	if (free_space > tp->rcv_ssthresh)
2599 		free_space = tp->rcv_ssthresh;
2600 
2601 	/* Don't do rounding if we are using window scaling, since the
2602 	 * scaled window will not line up with the MSS boundary anyway.
2603 	 */
2604 	if (tp->rx_opt.rcv_wscale) {
2605 		window = free_space;
2606 
2607 		/* Advertise enough space so that it won't get scaled away.
2608 		 * Import case: prevent zero window announcement if
2609 		 * 1<<rcv_wscale > mss.
2610 		 */
2611 		window = ALIGN(window, (1 << tp->rx_opt.rcv_wscale));
2612 	} else {
2613 		window = tp->rcv_wnd;
2614 		/* Get the largest window that is a nice multiple of mss.
2615 		 * Window clamp already applied above.
2616 		 * If our current window offering is within 1 mss of the
2617 		 * free space we just keep it. This prevents the divide
2618 		 * and multiply from happening most of the time.
2619 		 * We also don't do any window rounding when the free space
2620 		 * is too small.
2621 		 */
2622 		if (window <= free_space - mss || window > free_space)
2623 			window = rounddown(free_space, mss);
2624 		else if (mss == full_space &&
2625 			 free_space > window + (full_space >> 1))
2626 			window = free_space;
2627 	}
2628 
2629 	return window;
2630 }
2631 
2632 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
2633 			     const struct sk_buff *next_skb)
2634 {
2635 	if (unlikely(tcp_has_tx_tstamp(next_skb))) {
2636 		const struct skb_shared_info *next_shinfo =
2637 			skb_shinfo(next_skb);
2638 		struct skb_shared_info *shinfo = skb_shinfo(skb);
2639 
2640 		shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2641 		shinfo->tskey = next_shinfo->tskey;
2642 		TCP_SKB_CB(skb)->txstamp_ack |=
2643 			TCP_SKB_CB(next_skb)->txstamp_ack;
2644 	}
2645 }
2646 
2647 /* Collapses two adjacent SKB's during retransmission. */
2648 static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2649 {
2650 	struct tcp_sock *tp = tcp_sk(sk);
2651 	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2652 	int skb_size, next_skb_size;
2653 
2654 	skb_size = skb->len;
2655 	next_skb_size = next_skb->len;
2656 
2657 	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2658 
2659 	if (next_skb_size) {
2660 		if (next_skb_size <= skb_availroom(skb))
2661 			skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size),
2662 				      next_skb_size);
2663 		else if (!skb_shift(skb, next_skb, next_skb_size))
2664 			return false;
2665 	}
2666 	tcp_highest_sack_combine(sk, next_skb, skb);
2667 
2668 	tcp_unlink_write_queue(next_skb, sk);
2669 
2670 	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2671 		skb->ip_summed = CHECKSUM_PARTIAL;
2672 
2673 	if (skb->ip_summed != CHECKSUM_PARTIAL)
2674 		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2675 
2676 	/* Update sequence range on original skb. */
2677 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2678 
2679 	/* Merge over control information. This moves PSH/FIN etc. over */
2680 	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2681 
2682 	/* All done, get rid of second SKB and account for it so
2683 	 * packet counting does not break.
2684 	 */
2685 	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2686 	TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2687 
2688 	/* changed transmit queue under us so clear hints */
2689 	tcp_clear_retrans_hints_partial(tp);
2690 	if (next_skb == tp->retransmit_skb_hint)
2691 		tp->retransmit_skb_hint = skb;
2692 
2693 	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2694 
2695 	tcp_skb_collapse_tstamp(skb, next_skb);
2696 
2697 	sk_wmem_free_skb(sk, next_skb);
2698 	return true;
2699 }
2700 
2701 /* Check if coalescing SKBs is legal. */
2702 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2703 {
2704 	if (tcp_skb_pcount(skb) > 1)
2705 		return false;
2706 	if (skb_cloned(skb))
2707 		return false;
2708 	if (skb == tcp_send_head(sk))
2709 		return false;
2710 	/* Some heuristics for collapsing over SACK'd could be invented */
2711 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2712 		return false;
2713 
2714 	return true;
2715 }
2716 
2717 /* Collapse packets in the retransmit queue to make to create
2718  * less packets on the wire. This is only done on retransmission.
2719  */
2720 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2721 				     int space)
2722 {
2723 	struct tcp_sock *tp = tcp_sk(sk);
2724 	struct sk_buff *skb = to, *tmp;
2725 	bool first = true;
2726 
2727 	if (!sysctl_tcp_retrans_collapse)
2728 		return;
2729 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2730 		return;
2731 
2732 	tcp_for_write_queue_from_safe(skb, tmp, sk) {
2733 		if (!tcp_can_collapse(sk, skb))
2734 			break;
2735 
2736 		if (!tcp_skb_can_collapse_to(to))
2737 			break;
2738 
2739 		space -= skb->len;
2740 
2741 		if (first) {
2742 			first = false;
2743 			continue;
2744 		}
2745 
2746 		if (space < 0)
2747 			break;
2748 
2749 		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2750 			break;
2751 
2752 		if (!tcp_collapse_retrans(sk, to))
2753 			break;
2754 	}
2755 }
2756 
2757 /* This retransmits one SKB.  Policy decisions and retransmit queue
2758  * state updates are done by the caller.  Returns non-zero if an
2759  * error occurred which prevented the send.
2760  */
2761 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2762 {
2763 	struct inet_connection_sock *icsk = inet_csk(sk);
2764 	struct tcp_sock *tp = tcp_sk(sk);
2765 	unsigned int cur_mss;
2766 	int diff, len, err;
2767 
2768 
2769 	/* Inconclusive MTU probe */
2770 	if (icsk->icsk_mtup.probe_size)
2771 		icsk->icsk_mtup.probe_size = 0;
2772 
2773 	/* Do not sent more than we queued. 1/4 is reserved for possible
2774 	 * copying overhead: fragmentation, tunneling, mangling etc.
2775 	 */
2776 	if (refcount_read(&sk->sk_wmem_alloc) >
2777 	    min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
2778 		  sk->sk_sndbuf))
2779 		return -EAGAIN;
2780 
2781 	if (skb_still_in_host_queue(sk, skb))
2782 		return -EBUSY;
2783 
2784 	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2785 		if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2786 			BUG();
2787 		if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2788 			return -ENOMEM;
2789 	}
2790 
2791 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2792 		return -EHOSTUNREACH; /* Routing failure or similar. */
2793 
2794 	cur_mss = tcp_current_mss(sk);
2795 
2796 	/* If receiver has shrunk his window, and skb is out of
2797 	 * new window, do not retransmit it. The exception is the
2798 	 * case, when window is shrunk to zero. In this case
2799 	 * our retransmit serves as a zero window probe.
2800 	 */
2801 	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2802 	    TCP_SKB_CB(skb)->seq != tp->snd_una)
2803 		return -EAGAIN;
2804 
2805 	len = cur_mss * segs;
2806 	if (skb->len > len) {
2807 		if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
2808 			return -ENOMEM; /* We'll try again later. */
2809 	} else {
2810 		if (skb_unclone(skb, GFP_ATOMIC))
2811 			return -ENOMEM;
2812 
2813 		diff = tcp_skb_pcount(skb);
2814 		tcp_set_skb_tso_segs(skb, cur_mss);
2815 		diff -= tcp_skb_pcount(skb);
2816 		if (diff)
2817 			tcp_adjust_pcount(sk, skb, diff);
2818 		if (skb->len < cur_mss)
2819 			tcp_retrans_try_collapse(sk, skb, cur_mss);
2820 	}
2821 
2822 	/* RFC3168, section 6.1.1.1. ECN fallback */
2823 	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2824 		tcp_ecn_clear_syn(sk, skb);
2825 
2826 	/* Update global and local TCP statistics. */
2827 	segs = tcp_skb_pcount(skb);
2828 	TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2829 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2830 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2831 	tp->total_retrans += segs;
2832 
2833 	/* make sure skb->data is aligned on arches that require it
2834 	 * and check if ack-trimming & collapsing extended the headroom
2835 	 * beyond what csum_start can cover.
2836 	 */
2837 	if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2838 		     skb_headroom(skb) >= 0xFFFF)) {
2839 		struct sk_buff *nskb;
2840 
2841 		nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2842 		err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2843 			     -ENOBUFS;
2844 		if (!err)
2845 			skb->skb_mstamp = tp->tcp_mstamp;
2846 	} else {
2847 		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2848 	}
2849 
2850 	if (likely(!err)) {
2851 		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2852 	} else if (err != -EBUSY) {
2853 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2854 	}
2855 	return err;
2856 }
2857 
2858 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2859 {
2860 	struct tcp_sock *tp = tcp_sk(sk);
2861 	int err = __tcp_retransmit_skb(sk, skb, segs);
2862 
2863 	if (err == 0) {
2864 #if FASTRETRANS_DEBUG > 0
2865 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2866 			net_dbg_ratelimited("retrans_out leaked\n");
2867 		}
2868 #endif
2869 		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2870 		tp->retrans_out += tcp_skb_pcount(skb);
2871 
2872 		/* Save stamp of the first retransmit. */
2873 		if (!tp->retrans_stamp)
2874 			tp->retrans_stamp = tcp_skb_timestamp(skb);
2875 
2876 	}
2877 
2878 	if (tp->undo_retrans < 0)
2879 		tp->undo_retrans = 0;
2880 	tp->undo_retrans += tcp_skb_pcount(skb);
2881 	return err;
2882 }
2883 
2884 /* This gets called after a retransmit timeout, and the initially
2885  * retransmitted data is acknowledged.  It tries to continue
2886  * resending the rest of the retransmit queue, until either
2887  * we've sent it all or the congestion window limit is reached.
2888  * If doing SACK, the first ACK which comes back for a timeout
2889  * based retransmit packet might feed us FACK information again.
2890  * If so, we use it to avoid unnecessarily retransmissions.
2891  */
2892 void tcp_xmit_retransmit_queue(struct sock *sk)
2893 {
2894 	const struct inet_connection_sock *icsk = inet_csk(sk);
2895 	struct tcp_sock *tp = tcp_sk(sk);
2896 	struct sk_buff *skb;
2897 	struct sk_buff *hole = NULL;
2898 	u32 max_segs;
2899 	int mib_idx;
2900 
2901 	if (!tp->packets_out)
2902 		return;
2903 
2904 	if (tp->retransmit_skb_hint) {
2905 		skb = tp->retransmit_skb_hint;
2906 	} else {
2907 		skb = tcp_write_queue_head(sk);
2908 	}
2909 
2910 	max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
2911 	tcp_for_write_queue_from(skb, sk) {
2912 		__u8 sacked;
2913 		int segs;
2914 
2915 		if (skb == tcp_send_head(sk))
2916 			break;
2917 
2918 		if (tcp_pacing_check(sk))
2919 			break;
2920 
2921 		/* we could do better than to assign each time */
2922 		if (!hole)
2923 			tp->retransmit_skb_hint = skb;
2924 
2925 		segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
2926 		if (segs <= 0)
2927 			return;
2928 		sacked = TCP_SKB_CB(skb)->sacked;
2929 		/* In case tcp_shift_skb_data() have aggregated large skbs,
2930 		 * we need to make sure not sending too bigs TSO packets
2931 		 */
2932 		segs = min_t(int, segs, max_segs);
2933 
2934 		if (tp->retrans_out >= tp->lost_out) {
2935 			break;
2936 		} else if (!(sacked & TCPCB_LOST)) {
2937 			if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2938 				hole = skb;
2939 			continue;
2940 
2941 		} else {
2942 			if (icsk->icsk_ca_state != TCP_CA_Loss)
2943 				mib_idx = LINUX_MIB_TCPFASTRETRANS;
2944 			else
2945 				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2946 		}
2947 
2948 		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2949 			continue;
2950 
2951 		if (tcp_small_queue_check(sk, skb, 1))
2952 			return;
2953 
2954 		if (tcp_retransmit_skb(sk, skb, segs))
2955 			return;
2956 
2957 		NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb));
2958 
2959 		if (tcp_in_cwnd_reduction(sk))
2960 			tp->prr_out += tcp_skb_pcount(skb);
2961 
2962 		if (skb == tcp_write_queue_head(sk) &&
2963 		    icsk->icsk_pending != ICSK_TIME_REO_TIMEOUT)
2964 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2965 						  inet_csk(sk)->icsk_rto,
2966 						  TCP_RTO_MAX);
2967 	}
2968 }
2969 
2970 /* We allow to exceed memory limits for FIN packets to expedite
2971  * connection tear down and (memory) recovery.
2972  * Otherwise tcp_send_fin() could be tempted to either delay FIN
2973  * or even be forced to close flow without any FIN.
2974  * In general, we want to allow one skb per socket to avoid hangs
2975  * with edge trigger epoll()
2976  */
2977 void sk_forced_mem_schedule(struct sock *sk, int size)
2978 {
2979 	int amt;
2980 
2981 	if (size <= sk->sk_forward_alloc)
2982 		return;
2983 	amt = sk_mem_pages(size);
2984 	sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2985 	sk_memory_allocated_add(sk, amt);
2986 
2987 	if (mem_cgroup_sockets_enabled && sk->sk_memcg)
2988 		mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2989 }
2990 
2991 /* Send a FIN. The caller locks the socket for us.
2992  * We should try to send a FIN packet really hard, but eventually give up.
2993  */
2994 void tcp_send_fin(struct sock *sk)
2995 {
2996 	struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2997 	struct tcp_sock *tp = tcp_sk(sk);
2998 
2999 	/* Optimization, tack on the FIN if we have one skb in write queue and
3000 	 * this skb was not yet sent, or we are under memory pressure.
3001 	 * Note: in the latter case, FIN packet will be sent after a timeout,
3002 	 * as TCP stack thinks it has already been transmitted.
3003 	 */
3004 	if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
3005 coalesce:
3006 		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
3007 		TCP_SKB_CB(tskb)->end_seq++;
3008 		tp->write_seq++;
3009 		if (!tcp_send_head(sk)) {
3010 			/* This means tskb was already sent.
3011 			 * Pretend we included the FIN on previous transmit.
3012 			 * We need to set tp->snd_nxt to the value it would have
3013 			 * if FIN had been sent. This is because retransmit path
3014 			 * does not change tp->snd_nxt.
3015 			 */
3016 			tp->snd_nxt++;
3017 			return;
3018 		}
3019 	} else {
3020 		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
3021 		if (unlikely(!skb)) {
3022 			if (tskb)
3023 				goto coalesce;
3024 			return;
3025 		}
3026 		skb_reserve(skb, MAX_TCP_HEADER);
3027 		sk_forced_mem_schedule(sk, skb->truesize);
3028 		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
3029 		tcp_init_nondata_skb(skb, tp->write_seq,
3030 				     TCPHDR_ACK | TCPHDR_FIN);
3031 		tcp_queue_skb(sk, skb);
3032 	}
3033 	__tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
3034 }
3035 
3036 /* We get here when a process closes a file descriptor (either due to
3037  * an explicit close() or as a byproduct of exit()'ing) and there
3038  * was unread data in the receive queue.  This behavior is recommended
3039  * by RFC 2525, section 2.17.  -DaveM
3040  */
3041 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
3042 {
3043 	struct sk_buff *skb;
3044 
3045 	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
3046 
3047 	/* NOTE: No TCP options attached and we never retransmit this. */
3048 	skb = alloc_skb(MAX_TCP_HEADER, priority);
3049 	if (!skb) {
3050 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3051 		return;
3052 	}
3053 
3054 	/* Reserve space for headers and prepare control bits. */
3055 	skb_reserve(skb, MAX_TCP_HEADER);
3056 	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
3057 			     TCPHDR_ACK | TCPHDR_RST);
3058 	tcp_mstamp_refresh(tcp_sk(sk));
3059 	/* Send it off. */
3060 	if (tcp_transmit_skb(sk, skb, 0, priority))
3061 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3062 }
3063 
3064 /* Send a crossed SYN-ACK during socket establishment.
3065  * WARNING: This routine must only be called when we have already sent
3066  * a SYN packet that crossed the incoming SYN that caused this routine
3067  * to get called. If this assumption fails then the initial rcv_wnd
3068  * and rcv_wscale values will not be correct.
3069  */
3070 int tcp_send_synack(struct sock *sk)
3071 {
3072 	struct sk_buff *skb;
3073 
3074 	skb = tcp_write_queue_head(sk);
3075 	if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
3076 		pr_debug("%s: wrong queue state\n", __func__);
3077 		return -EFAULT;
3078 	}
3079 	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
3080 		if (skb_cloned(skb)) {
3081 			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
3082 			if (!nskb)
3083 				return -ENOMEM;
3084 			tcp_unlink_write_queue(skb, sk);
3085 			__skb_header_release(nskb);
3086 			__tcp_add_write_queue_head(sk, nskb);
3087 			sk_wmem_free_skb(sk, skb);
3088 			sk->sk_wmem_queued += nskb->truesize;
3089 			sk_mem_charge(sk, nskb->truesize);
3090 			skb = nskb;
3091 		}
3092 
3093 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
3094 		tcp_ecn_send_synack(sk, skb);
3095 	}
3096 	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3097 }
3098 
3099 /**
3100  * tcp_make_synack - Prepare a SYN-ACK.
3101  * sk: listener socket
3102  * dst: dst entry attached to the SYNACK
3103  * req: request_sock pointer
3104  *
3105  * Allocate one skb and build a SYNACK packet.
3106  * @dst is consumed : Caller should not use it again.
3107  */
3108 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3109 				struct request_sock *req,
3110 				struct tcp_fastopen_cookie *foc,
3111 				enum tcp_synack_type synack_type)
3112 {
3113 	struct inet_request_sock *ireq = inet_rsk(req);
3114 	const struct tcp_sock *tp = tcp_sk(sk);
3115 	struct tcp_md5sig_key *md5 = NULL;
3116 	struct tcp_out_options opts;
3117 	struct sk_buff *skb;
3118 	int tcp_header_size;
3119 	struct tcphdr *th;
3120 	int mss;
3121 
3122 	skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3123 	if (unlikely(!skb)) {
3124 		dst_release(dst);
3125 		return NULL;
3126 	}
3127 	/* Reserve space for headers. */
3128 	skb_reserve(skb, MAX_TCP_HEADER);
3129 
3130 	switch (synack_type) {
3131 	case TCP_SYNACK_NORMAL:
3132 		skb_set_owner_w(skb, req_to_sk(req));
3133 		break;
3134 	case TCP_SYNACK_COOKIE:
3135 		/* Under synflood, we do not attach skb to a socket,
3136 		 * to avoid false sharing.
3137 		 */
3138 		break;
3139 	case TCP_SYNACK_FASTOPEN:
3140 		/* sk is a const pointer, because we want to express multiple
3141 		 * cpu might call us concurrently.
3142 		 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3143 		 */
3144 		skb_set_owner_w(skb, (struct sock *)sk);
3145 		break;
3146 	}
3147 	skb_dst_set(skb, dst);
3148 
3149 	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
3150 
3151 	memset(&opts, 0, sizeof(opts));
3152 #ifdef CONFIG_SYN_COOKIES
3153 	if (unlikely(req->cookie_ts))
3154 		skb->skb_mstamp = cookie_init_timestamp(req);
3155 	else
3156 #endif
3157 		skb->skb_mstamp = tcp_clock_us();
3158 
3159 #ifdef CONFIG_TCP_MD5SIG
3160 	rcu_read_lock();
3161 	md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3162 #endif
3163 	skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3164 	tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3165 			  sizeof(*th);
3166 
3167 	skb_push(skb, tcp_header_size);
3168 	skb_reset_transport_header(skb);
3169 
3170 	th = (struct tcphdr *)skb->data;
3171 	memset(th, 0, sizeof(struct tcphdr));
3172 	th->syn = 1;
3173 	th->ack = 1;
3174 	tcp_ecn_make_synack(req, th);
3175 	th->source = htons(ireq->ir_num);
3176 	th->dest = ireq->ir_rmt_port;
3177 	skb->mark = ireq->ir_mark;
3178 	/* Setting of flags are superfluous here for callers (and ECE is
3179 	 * not even correctly set)
3180 	 */
3181 	tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3182 			     TCPHDR_SYN | TCPHDR_ACK);
3183 
3184 	th->seq = htonl(TCP_SKB_CB(skb)->seq);
3185 	/* XXX data is queued and acked as is. No buffer/window check */
3186 	th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3187 
3188 	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3189 	th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3190 	tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3191 	th->doff = (tcp_header_size >> 2);
3192 	__TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3193 
3194 #ifdef CONFIG_TCP_MD5SIG
3195 	/* Okay, we have all we need - do the md5 hash if needed */
3196 	if (md5)
3197 		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3198 					       md5, req_to_sk(req), skb);
3199 	rcu_read_unlock();
3200 #endif
3201 
3202 	/* Do not fool tcpdump (if any), clean our debris */
3203 	skb->tstamp = 0;
3204 	return skb;
3205 }
3206 EXPORT_SYMBOL(tcp_make_synack);
3207 
3208 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3209 {
3210 	struct inet_connection_sock *icsk = inet_csk(sk);
3211 	const struct tcp_congestion_ops *ca;
3212 	u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3213 
3214 	if (ca_key == TCP_CA_UNSPEC)
3215 		return;
3216 
3217 	rcu_read_lock();
3218 	ca = tcp_ca_find_key(ca_key);
3219 	if (likely(ca && try_module_get(ca->owner))) {
3220 		module_put(icsk->icsk_ca_ops->owner);
3221 		icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3222 		icsk->icsk_ca_ops = ca;
3223 	}
3224 	rcu_read_unlock();
3225 }
3226 
3227 /* Do all connect socket setups that can be done AF independent. */
3228 static void tcp_connect_init(struct sock *sk)
3229 {
3230 	const struct dst_entry *dst = __sk_dst_get(sk);
3231 	struct tcp_sock *tp = tcp_sk(sk);
3232 	__u8 rcv_wscale;
3233 	u32 rcv_wnd;
3234 
3235 	/* We'll fix this up when we get a response from the other end.
3236 	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3237 	 */
3238 	tp->tcp_header_len = sizeof(struct tcphdr);
3239 	if (sock_net(sk)->ipv4.sysctl_tcp_timestamps)
3240 		tp->tcp_header_len += TCPOLEN_TSTAMP_ALIGNED;
3241 
3242 #ifdef CONFIG_TCP_MD5SIG
3243 	if (tp->af_specific->md5_lookup(sk, sk))
3244 		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3245 #endif
3246 
3247 	/* If user gave his TCP_MAXSEG, record it to clamp */
3248 	if (tp->rx_opt.user_mss)
3249 		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3250 	tp->max_window = 0;
3251 	tcp_mtup_init(sk);
3252 	tcp_sync_mss(sk, dst_mtu(dst));
3253 
3254 	tcp_ca_dst_init(sk, dst);
3255 
3256 	if (!tp->window_clamp)
3257 		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3258 	tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
3259 
3260 	tcp_initialize_rcv_mss(sk);
3261 
3262 	/* limit the window selection if the user enforce a smaller rx buffer */
3263 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3264 	    (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3265 		tp->window_clamp = tcp_full_space(sk);
3266 
3267 	rcv_wnd = tcp_rwnd_init_bpf(sk);
3268 	if (rcv_wnd == 0)
3269 		rcv_wnd = dst_metric(dst, RTAX_INITRWND);
3270 
3271 	tcp_select_initial_window(tcp_full_space(sk),
3272 				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3273 				  &tp->rcv_wnd,
3274 				  &tp->window_clamp,
3275 				  sock_net(sk)->ipv4.sysctl_tcp_window_scaling,
3276 				  &rcv_wscale,
3277 				  rcv_wnd);
3278 
3279 	tp->rx_opt.rcv_wscale = rcv_wscale;
3280 	tp->rcv_ssthresh = tp->rcv_wnd;
3281 
3282 	sk->sk_err = 0;
3283 	sock_reset_flag(sk, SOCK_DONE);
3284 	tp->snd_wnd = 0;
3285 	tcp_init_wl(tp, 0);
3286 	tp->snd_una = tp->write_seq;
3287 	tp->snd_sml = tp->write_seq;
3288 	tp->snd_up = tp->write_seq;
3289 	tp->snd_nxt = tp->write_seq;
3290 
3291 	if (likely(!tp->repair))
3292 		tp->rcv_nxt = 0;
3293 	else
3294 		tp->rcv_tstamp = tcp_jiffies32;
3295 	tp->rcv_wup = tp->rcv_nxt;
3296 	tp->copied_seq = tp->rcv_nxt;
3297 
3298 	inet_csk(sk)->icsk_rto = tcp_timeout_init(sk);
3299 	inet_csk(sk)->icsk_retransmits = 0;
3300 	tcp_clear_retrans(tp);
3301 }
3302 
3303 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3304 {
3305 	struct tcp_sock *tp = tcp_sk(sk);
3306 	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3307 
3308 	tcb->end_seq += skb->len;
3309 	__skb_header_release(skb);
3310 	__tcp_add_write_queue_tail(sk, skb);
3311 	sk->sk_wmem_queued += skb->truesize;
3312 	sk_mem_charge(sk, skb->truesize);
3313 	tp->write_seq = tcb->end_seq;
3314 	tp->packets_out += tcp_skb_pcount(skb);
3315 }
3316 
3317 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3318  * queue a data-only packet after the regular SYN, such that regular SYNs
3319  * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3320  * only the SYN sequence, the data are retransmitted in the first ACK.
3321  * If cookie is not cached or other error occurs, falls back to send a
3322  * regular SYN with Fast Open cookie request option.
3323  */
3324 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3325 {
3326 	struct tcp_sock *tp = tcp_sk(sk);
3327 	struct tcp_fastopen_request *fo = tp->fastopen_req;
3328 	int space, err = 0;
3329 	struct sk_buff *syn_data;
3330 
3331 	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
3332 	if (!tcp_fastopen_cookie_check(sk, &tp->rx_opt.mss_clamp, &fo->cookie))
3333 		goto fallback;
3334 
3335 	/* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3336 	 * user-MSS. Reserve maximum option space for middleboxes that add
3337 	 * private TCP options. The cost is reduced data space in SYN :(
3338 	 */
3339 	tp->rx_opt.mss_clamp = tcp_mss_clamp(tp, tp->rx_opt.mss_clamp);
3340 
3341 	space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3342 		MAX_TCP_OPTION_SPACE;
3343 
3344 	space = min_t(size_t, space, fo->size);
3345 
3346 	/* limit to order-0 allocations */
3347 	space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3348 
3349 	syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3350 	if (!syn_data)
3351 		goto fallback;
3352 	syn_data->ip_summed = CHECKSUM_PARTIAL;
3353 	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3354 	if (space) {
3355 		int copied = copy_from_iter(skb_put(syn_data, space), space,
3356 					    &fo->data->msg_iter);
3357 		if (unlikely(!copied)) {
3358 			kfree_skb(syn_data);
3359 			goto fallback;
3360 		}
3361 		if (copied != space) {
3362 			skb_trim(syn_data, copied);
3363 			space = copied;
3364 		}
3365 	}
3366 	/* No more data pending in inet_wait_for_connect() */
3367 	if (space == fo->size)
3368 		fo->data = NULL;
3369 	fo->copied = space;
3370 
3371 	tcp_connect_queue_skb(sk, syn_data);
3372 	if (syn_data->len)
3373 		tcp_chrono_start(sk, TCP_CHRONO_BUSY);
3374 
3375 	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3376 
3377 	syn->skb_mstamp = syn_data->skb_mstamp;
3378 
3379 	/* Now full SYN+DATA was cloned and sent (or not),
3380 	 * remove the SYN from the original skb (syn_data)
3381 	 * we keep in write queue in case of a retransmit, as we
3382 	 * also have the SYN packet (with no data) in the same queue.
3383 	 */
3384 	TCP_SKB_CB(syn_data)->seq++;
3385 	TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3386 	if (!err) {
3387 		tp->syn_data = (fo->copied > 0);
3388 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3389 		goto done;
3390 	}
3391 
3392 	/* data was not sent, this is our new send_head */
3393 	sk->sk_send_head = syn_data;
3394 	tp->packets_out -= tcp_skb_pcount(syn_data);
3395 
3396 fallback:
3397 	/* Send a regular SYN with Fast Open cookie request option */
3398 	if (fo->cookie.len > 0)
3399 		fo->cookie.len = 0;
3400 	err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3401 	if (err)
3402 		tp->syn_fastopen = 0;
3403 done:
3404 	fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
3405 	return err;
3406 }
3407 
3408 /* Build a SYN and send it off. */
3409 int tcp_connect(struct sock *sk)
3410 {
3411 	struct tcp_sock *tp = tcp_sk(sk);
3412 	struct sk_buff *buff;
3413 	int err;
3414 
3415 	tcp_call_bpf(sk, BPF_SOCK_OPS_TCP_CONNECT_CB);
3416 
3417 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
3418 		return -EHOSTUNREACH; /* Routing failure or similar. */
3419 
3420 	tcp_connect_init(sk);
3421 
3422 	if (unlikely(tp->repair)) {
3423 		tcp_finish_connect(sk, NULL);
3424 		return 0;
3425 	}
3426 
3427 	buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3428 	if (unlikely(!buff))
3429 		return -ENOBUFS;
3430 
3431 	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3432 	tcp_mstamp_refresh(tp);
3433 	tp->retrans_stamp = tcp_time_stamp(tp);
3434 	tcp_connect_queue_skb(sk, buff);
3435 	tcp_ecn_send_syn(sk, buff);
3436 
3437 	/* Send off SYN; include data in Fast Open. */
3438 	err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3439 	      tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3440 	if (err == -ECONNREFUSED)
3441 		return err;
3442 
3443 	/* We change tp->snd_nxt after the tcp_transmit_skb() call
3444 	 * in order to make this packet get counted in tcpOutSegs.
3445 	 */
3446 	tp->snd_nxt = tp->write_seq;
3447 	tp->pushed_seq = tp->write_seq;
3448 	buff = tcp_send_head(sk);
3449 	if (unlikely(buff)) {
3450 		tp->snd_nxt	= TCP_SKB_CB(buff)->seq;
3451 		tp->pushed_seq	= TCP_SKB_CB(buff)->seq;
3452 	}
3453 	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3454 
3455 	/* Timer for repeating the SYN until an answer. */
3456 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3457 				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3458 	return 0;
3459 }
3460 EXPORT_SYMBOL(tcp_connect);
3461 
3462 /* Send out a delayed ack, the caller does the policy checking
3463  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
3464  * for details.
3465  */
3466 void tcp_send_delayed_ack(struct sock *sk)
3467 {
3468 	struct inet_connection_sock *icsk = inet_csk(sk);
3469 	int ato = icsk->icsk_ack.ato;
3470 	unsigned long timeout;
3471 
3472 	tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3473 
3474 	if (ato > TCP_DELACK_MIN) {
3475 		const struct tcp_sock *tp = tcp_sk(sk);
3476 		int max_ato = HZ / 2;
3477 
3478 		if (icsk->icsk_ack.pingpong ||
3479 		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3480 			max_ato = TCP_DELACK_MAX;
3481 
3482 		/* Slow path, intersegment interval is "high". */
3483 
3484 		/* If some rtt estimate is known, use it to bound delayed ack.
3485 		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3486 		 * directly.
3487 		 */
3488 		if (tp->srtt_us) {
3489 			int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3490 					TCP_DELACK_MIN);
3491 
3492 			if (rtt < max_ato)
3493 				max_ato = rtt;
3494 		}
3495 
3496 		ato = min(ato, max_ato);
3497 	}
3498 
3499 	/* Stay within the limit we were given */
3500 	timeout = jiffies + ato;
3501 
3502 	/* Use new timeout only if there wasn't a older one earlier. */
3503 	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3504 		/* If delack timer was blocked or is about to expire,
3505 		 * send ACK now.
3506 		 */
3507 		if (icsk->icsk_ack.blocked ||
3508 		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3509 			tcp_send_ack(sk);
3510 			return;
3511 		}
3512 
3513 		if (!time_before(timeout, icsk->icsk_ack.timeout))
3514 			timeout = icsk->icsk_ack.timeout;
3515 	}
3516 	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3517 	icsk->icsk_ack.timeout = timeout;
3518 	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3519 }
3520 
3521 /* This routine sends an ack and also updates the window. */
3522 void tcp_send_ack(struct sock *sk)
3523 {
3524 	struct sk_buff *buff;
3525 
3526 	/* If we have been reset, we may not send again. */
3527 	if (sk->sk_state == TCP_CLOSE)
3528 		return;
3529 
3530 	tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3531 
3532 	/* We are not putting this on the write queue, so
3533 	 * tcp_transmit_skb() will set the ownership to this
3534 	 * sock.
3535 	 */
3536 	buff = alloc_skb(MAX_TCP_HEADER,
3537 			 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3538 	if (unlikely(!buff)) {
3539 		inet_csk_schedule_ack(sk);
3540 		inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3541 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3542 					  TCP_DELACK_MAX, TCP_RTO_MAX);
3543 		return;
3544 	}
3545 
3546 	/* Reserve space for headers and prepare control bits. */
3547 	skb_reserve(buff, MAX_TCP_HEADER);
3548 	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3549 
3550 	/* We do not want pure acks influencing TCP Small Queues or fq/pacing
3551 	 * too much.
3552 	 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3553 	 */
3554 	skb_set_tcp_pure_ack(buff);
3555 
3556 	/* Send it off, this clears delayed acks for us. */
3557 	tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
3558 }
3559 EXPORT_SYMBOL_GPL(tcp_send_ack);
3560 
3561 /* This routine sends a packet with an out of date sequence
3562  * number. It assumes the other end will try to ack it.
3563  *
3564  * Question: what should we make while urgent mode?
3565  * 4.4BSD forces sending single byte of data. We cannot send
3566  * out of window data, because we have SND.NXT==SND.MAX...
3567  *
3568  * Current solution: to send TWO zero-length segments in urgent mode:
3569  * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3570  * out-of-date with SND.UNA-1 to probe window.
3571  */
3572 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3573 {
3574 	struct tcp_sock *tp = tcp_sk(sk);
3575 	struct sk_buff *skb;
3576 
3577 	/* We don't queue it, tcp_transmit_skb() sets ownership. */
3578 	skb = alloc_skb(MAX_TCP_HEADER,
3579 			sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3580 	if (!skb)
3581 		return -1;
3582 
3583 	/* Reserve space for headers and set control bits. */
3584 	skb_reserve(skb, MAX_TCP_HEADER);
3585 	/* Use a previous sequence.  This should cause the other
3586 	 * end to send an ack.  Don't queue or clone SKB, just
3587 	 * send it.
3588 	 */
3589 	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3590 	NET_INC_STATS(sock_net(sk), mib);
3591 	return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
3592 }
3593 
3594 /* Called from setsockopt( ... TCP_REPAIR ) */
3595 void tcp_send_window_probe(struct sock *sk)
3596 {
3597 	if (sk->sk_state == TCP_ESTABLISHED) {
3598 		tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3599 		tcp_mstamp_refresh(tcp_sk(sk));
3600 		tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3601 	}
3602 }
3603 
3604 /* Initiate keepalive or window probe from timer. */
3605 int tcp_write_wakeup(struct sock *sk, int mib)
3606 {
3607 	struct tcp_sock *tp = tcp_sk(sk);
3608 	struct sk_buff *skb;
3609 
3610 	if (sk->sk_state == TCP_CLOSE)
3611 		return -1;
3612 
3613 	skb = tcp_send_head(sk);
3614 	if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3615 		int err;
3616 		unsigned int mss = tcp_current_mss(sk);
3617 		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3618 
3619 		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3620 			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3621 
3622 		/* We are probing the opening of a window
3623 		 * but the window size is != 0
3624 		 * must have been a result SWS avoidance ( sender )
3625 		 */
3626 		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3627 		    skb->len > mss) {
3628 			seg_size = min(seg_size, mss);
3629 			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3630 			if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3631 				return -1;
3632 		} else if (!tcp_skb_pcount(skb))
3633 			tcp_set_skb_tso_segs(skb, mss);
3634 
3635 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3636 		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3637 		if (!err)
3638 			tcp_event_new_data_sent(sk, skb);
3639 		return err;
3640 	} else {
3641 		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3642 			tcp_xmit_probe_skb(sk, 1, mib);
3643 		return tcp_xmit_probe_skb(sk, 0, mib);
3644 	}
3645 }
3646 
3647 /* A window probe timeout has occurred.  If window is not closed send
3648  * a partial packet else a zero probe.
3649  */
3650 void tcp_send_probe0(struct sock *sk)
3651 {
3652 	struct inet_connection_sock *icsk = inet_csk(sk);
3653 	struct tcp_sock *tp = tcp_sk(sk);
3654 	struct net *net = sock_net(sk);
3655 	unsigned long probe_max;
3656 	int err;
3657 
3658 	err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3659 
3660 	if (tp->packets_out || !tcp_send_head(sk)) {
3661 		/* Cancel probe timer, if it is not required. */
3662 		icsk->icsk_probes_out = 0;
3663 		icsk->icsk_backoff = 0;
3664 		return;
3665 	}
3666 
3667 	if (err <= 0) {
3668 		if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3669 			icsk->icsk_backoff++;
3670 		icsk->icsk_probes_out++;
3671 		probe_max = TCP_RTO_MAX;
3672 	} else {
3673 		/* If packet was not sent due to local congestion,
3674 		 * do not backoff and do not remember icsk_probes_out.
3675 		 * Let local senders to fight for local resources.
3676 		 *
3677 		 * Use accumulated backoff yet.
3678 		 */
3679 		if (!icsk->icsk_probes_out)
3680 			icsk->icsk_probes_out = 1;
3681 		probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3682 	}
3683 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3684 				  tcp_probe0_when(sk, probe_max),
3685 				  TCP_RTO_MAX);
3686 }
3687 
3688 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3689 {
3690 	const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3691 	struct flowi fl;
3692 	int res;
3693 
3694 	tcp_rsk(req)->txhash = net_tx_rndhash();
3695 	res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3696 	if (!res) {
3697 		__TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3698 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3699 		if (unlikely(tcp_passive_fastopen(sk)))
3700 			tcp_sk(sk)->total_retrans++;
3701 	}
3702 	return res;
3703 }
3704 EXPORT_SYMBOL(tcp_rtx_synack);
3705