xref: /openbmc/linux/net/ipv4/tcp_input.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
1 /*
2  * INET		An implementation of the TCP/IP protocol suite for the LINUX
3  *		operating system.  INET is implemented using the  BSD Socket
4  *		interface as the means of communication with the user level.
5  *
6  *		Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Version:	$Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
9  *
10  * Authors:	Ross Biro
11  *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  *		Mark Evans, <evansmp@uhura.aston.ac.uk>
13  *		Corey Minyard <wf-rch!minyard@relay.EU.net>
14  *		Florian La Roche, <flla@stud.uni-sb.de>
15  *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16  *		Linus Torvalds, <torvalds@cs.helsinki.fi>
17  *		Alan Cox, <gw4pts@gw4pts.ampr.org>
18  *		Matthew Dillon, <dillon@apollo.west.oic.com>
19  *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20  *		Jorge Cwik, <jorge@laser.satlink.net>
21  */
22 
23 /*
24  * Changes:
25  *		Pedro Roque	:	Fast Retransmit/Recovery.
26  *					Two receive queues.
27  *					Retransmit queue handled by TCP.
28  *					Better retransmit timer handling.
29  *					New congestion avoidance.
30  *					Header prediction.
31  *					Variable renaming.
32  *
33  *		Eric		:	Fast Retransmit.
34  *		Randy Scott	:	MSS option defines.
35  *		Eric Schenk	:	Fixes to slow start algorithm.
36  *		Eric Schenk	:	Yet another double ACK bug.
37  *		Eric Schenk	:	Delayed ACK bug fixes.
38  *		Eric Schenk	:	Floyd style fast retrans war avoidance.
39  *		David S. Miller	:	Don't allow zero congestion window.
40  *		Eric Schenk	:	Fix retransmitter so that it sends
41  *					next packet on ack of previous packet.
42  *		Andi Kleen	:	Moved open_request checking here
43  *					and process RSTs for open_requests.
44  *		Andi Kleen	:	Better prune_queue, and other fixes.
45  *		Andrey Savochkin:	Fix RTT measurements in the presnce of
46  *					timestamps.
47  *		Andrey Savochkin:	Check sequence numbers correctly when
48  *					removing SACKs due to in sequence incoming
49  *					data segments.
50  *		Andi Kleen:		Make sure we never ack data there is not
51  *					enough room for. Also make this condition
52  *					a fatal error if it might still happen.
53  *		Andi Kleen:		Add tcp_measure_rcv_mss to make
54  *					connections with MSS<min(MTU,ann. MSS)
55  *					work without delayed acks.
56  *		Andi Kleen:		Process packets with PSH set in the
57  *					fast path.
58  *		J Hadi Salim:		ECN support
59  *	 	Andrei Gurtov,
60  *		Pasi Sarolahti,
61  *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
62  *					engine. Lots of bugs are found.
63  *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
64  */
65 
66 #include <linux/config.h>
67 #include <linux/mm.h>
68 #include <linux/module.h>
69 #include <linux/sysctl.h>
70 #include <net/tcp.h>
71 #include <net/inet_common.h>
72 #include <linux/ipsec.h>
73 #include <asm/unaligned.h>
74 
75 int sysctl_tcp_timestamps = 1;
76 int sysctl_tcp_window_scaling = 1;
77 int sysctl_tcp_sack = 1;
78 int sysctl_tcp_fack = 1;
79 int sysctl_tcp_reordering = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn;
81 int sysctl_tcp_dsack = 1;
82 int sysctl_tcp_app_win = 31;
83 int sysctl_tcp_adv_win_scale = 2;
84 
85 int sysctl_tcp_stdurg;
86 int sysctl_tcp_rfc1337;
87 int sysctl_tcp_max_orphans = NR_FILE;
88 int sysctl_tcp_frto;
89 int sysctl_tcp_nometrics_save;
90 
91 int sysctl_tcp_moderate_rcvbuf = 1;
92 
93 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
94 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
95 #define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
96 #define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
97 #define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
98 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
99 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
100 #define FLAG_DATA_LOST		0x80 /* SACK detected data lossage.		*/
101 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
102 
103 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
104 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
105 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
106 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
107 
108 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
109 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
110 #define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
111 
112 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
113 
114 /* Adapt the MSS value used to make delayed ack decision to the
115  * real world.
116  */
117 static inline void tcp_measure_rcv_mss(struct sock *sk,
118 				       const struct sk_buff *skb)
119 {
120 	struct inet_connection_sock *icsk = inet_csk(sk);
121 	const unsigned int lss = icsk->icsk_ack.last_seg_size;
122 	unsigned int len;
123 
124 	icsk->icsk_ack.last_seg_size = 0;
125 
126 	/* skb->len may jitter because of SACKs, even if peer
127 	 * sends good full-sized frames.
128 	 */
129 	len = skb->len;
130 	if (len >= icsk->icsk_ack.rcv_mss) {
131 		icsk->icsk_ack.rcv_mss = len;
132 	} else {
133 		/* Otherwise, we make more careful check taking into account,
134 		 * that SACKs block is variable.
135 		 *
136 		 * "len" is invariant segment length, including TCP header.
137 		 */
138 		len += skb->data - skb->h.raw;
139 		if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
140 		    /* If PSH is not set, packet should be
141 		     * full sized, provided peer TCP is not badly broken.
142 		     * This observation (if it is correct 8)) allows
143 		     * to handle super-low mtu links fairly.
144 		     */
145 		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
146 		     !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) {
147 			/* Subtract also invariant (if peer is RFC compliant),
148 			 * tcp header plus fixed timestamp option length.
149 			 * Resulting "len" is MSS free of SACK jitter.
150 			 */
151 			len -= tcp_sk(sk)->tcp_header_len;
152 			icsk->icsk_ack.last_seg_size = len;
153 			if (len == lss) {
154 				icsk->icsk_ack.rcv_mss = len;
155 				return;
156 			}
157 		}
158 		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
159 	}
160 }
161 
162 static void tcp_incr_quickack(struct sock *sk)
163 {
164 	struct inet_connection_sock *icsk = inet_csk(sk);
165 	unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
166 
167 	if (quickacks==0)
168 		quickacks=2;
169 	if (quickacks > icsk->icsk_ack.quick)
170 		icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
171 }
172 
173 void tcp_enter_quickack_mode(struct sock *sk)
174 {
175 	struct inet_connection_sock *icsk = inet_csk(sk);
176 	tcp_incr_quickack(sk);
177 	icsk->icsk_ack.pingpong = 0;
178 	icsk->icsk_ack.ato = TCP_ATO_MIN;
179 }
180 
181 /* Send ACKs quickly, if "quick" count is not exhausted
182  * and the session is not interactive.
183  */
184 
185 static inline int tcp_in_quickack_mode(const struct sock *sk)
186 {
187 	const struct inet_connection_sock *icsk = inet_csk(sk);
188 	return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
189 }
190 
191 /* Buffer size and advertised window tuning.
192  *
193  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
194  */
195 
196 static void tcp_fixup_sndbuf(struct sock *sk)
197 {
198 	int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
199 		     sizeof(struct sk_buff);
200 
201 	if (sk->sk_sndbuf < 3 * sndmem)
202 		sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
203 }
204 
205 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
206  *
207  * All tcp_full_space() is split to two parts: "network" buffer, allocated
208  * forward and advertised in receiver window (tp->rcv_wnd) and
209  * "application buffer", required to isolate scheduling/application
210  * latencies from network.
211  * window_clamp is maximal advertised window. It can be less than
212  * tcp_full_space(), in this case tcp_full_space() - window_clamp
213  * is reserved for "application" buffer. The less window_clamp is
214  * the smoother our behaviour from viewpoint of network, but the lower
215  * throughput and the higher sensitivity of the connection to losses. 8)
216  *
217  * rcv_ssthresh is more strict window_clamp used at "slow start"
218  * phase to predict further behaviour of this connection.
219  * It is used for two goals:
220  * - to enforce header prediction at sender, even when application
221  *   requires some significant "application buffer". It is check #1.
222  * - to prevent pruning of receive queue because of misprediction
223  *   of receiver window. Check #2.
224  *
225  * The scheme does not work when sender sends good segments opening
226  * window and then starts to feed us spagetti. But it should work
227  * in common situations. Otherwise, we have to rely on queue collapsing.
228  */
229 
230 /* Slow part of check#2. */
231 static int __tcp_grow_window(const struct sock *sk, struct tcp_sock *tp,
232 			     const struct sk_buff *skb)
233 {
234 	/* Optimize this! */
235 	int truesize = tcp_win_from_space(skb->truesize)/2;
236 	int window = tcp_full_space(sk)/2;
237 
238 	while (tp->rcv_ssthresh <= window) {
239 		if (truesize <= skb->len)
240 			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
241 
242 		truesize >>= 1;
243 		window >>= 1;
244 	}
245 	return 0;
246 }
247 
248 static inline void tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
249 				   struct sk_buff *skb)
250 {
251 	/* Check #1 */
252 	if (tp->rcv_ssthresh < tp->window_clamp &&
253 	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
254 	    !tcp_memory_pressure) {
255 		int incr;
256 
257 		/* Check #2. Increase window, if skb with such overhead
258 		 * will fit to rcvbuf in future.
259 		 */
260 		if (tcp_win_from_space(skb->truesize) <= skb->len)
261 			incr = 2*tp->advmss;
262 		else
263 			incr = __tcp_grow_window(sk, tp, skb);
264 
265 		if (incr) {
266 			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
267 			inet_csk(sk)->icsk_ack.quick |= 1;
268 		}
269 	}
270 }
271 
272 /* 3. Tuning rcvbuf, when connection enters established state. */
273 
274 static void tcp_fixup_rcvbuf(struct sock *sk)
275 {
276 	struct tcp_sock *tp = tcp_sk(sk);
277 	int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
278 
279 	/* Try to select rcvbuf so that 4 mss-sized segments
280 	 * will fit to window and correspoding skbs will fit to our rcvbuf.
281 	 * (was 3; 4 is minimum to allow fast retransmit to work.)
282 	 */
283 	while (tcp_win_from_space(rcvmem) < tp->advmss)
284 		rcvmem += 128;
285 	if (sk->sk_rcvbuf < 4 * rcvmem)
286 		sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
287 }
288 
289 /* 4. Try to fixup all. It is made iimediately after connection enters
290  *    established state.
291  */
292 static void tcp_init_buffer_space(struct sock *sk)
293 {
294 	struct tcp_sock *tp = tcp_sk(sk);
295 	int maxwin;
296 
297 	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
298 		tcp_fixup_rcvbuf(sk);
299 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
300 		tcp_fixup_sndbuf(sk);
301 
302 	tp->rcvq_space.space = tp->rcv_wnd;
303 
304 	maxwin = tcp_full_space(sk);
305 
306 	if (tp->window_clamp >= maxwin) {
307 		tp->window_clamp = maxwin;
308 
309 		if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
310 			tp->window_clamp = max(maxwin -
311 					       (maxwin >> sysctl_tcp_app_win),
312 					       4 * tp->advmss);
313 	}
314 
315 	/* Force reservation of one segment. */
316 	if (sysctl_tcp_app_win &&
317 	    tp->window_clamp > 2 * tp->advmss &&
318 	    tp->window_clamp + tp->advmss > maxwin)
319 		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
320 
321 	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
322 	tp->snd_cwnd_stamp = tcp_time_stamp;
323 }
324 
325 /* 5. Recalculate window clamp after socket hit its memory bounds. */
326 static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp)
327 {
328 	struct inet_connection_sock *icsk = inet_csk(sk);
329 	struct sk_buff *skb;
330 	unsigned int app_win = tp->rcv_nxt - tp->copied_seq;
331 	int ofo_win = 0;
332 
333 	icsk->icsk_ack.quick = 0;
334 
335 	skb_queue_walk(&tp->out_of_order_queue, skb) {
336 		ofo_win += skb->len;
337 	}
338 
339 	/* If overcommit is due to out of order segments,
340 	 * do not clamp window. Try to expand rcvbuf instead.
341 	 */
342 	if (ofo_win) {
343 		if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
344 		    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
345 		    !tcp_memory_pressure &&
346 		    atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0])
347 			sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
348 					    sysctl_tcp_rmem[2]);
349 	}
350 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) {
351 		app_win += ofo_win;
352 		if (atomic_read(&sk->sk_rmem_alloc) >= 2 * sk->sk_rcvbuf)
353 			app_win >>= 1;
354 		if (app_win > icsk->icsk_ack.rcv_mss)
355 			app_win -= icsk->icsk_ack.rcv_mss;
356 		app_win = max(app_win, 2U*tp->advmss);
357 
358 		tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
359 	}
360 }
361 
362 /* Receiver "autotuning" code.
363  *
364  * The algorithm for RTT estimation w/o timestamps is based on
365  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
366  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
367  *
368  * More detail on this code can be found at
369  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
370  * though this reference is out of date.  A new paper
371  * is pending.
372  */
373 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
374 {
375 	u32 new_sample = tp->rcv_rtt_est.rtt;
376 	long m = sample;
377 
378 	if (m == 0)
379 		m = 1;
380 
381 	if (new_sample != 0) {
382 		/* If we sample in larger samples in the non-timestamp
383 		 * case, we could grossly overestimate the RTT especially
384 		 * with chatty applications or bulk transfer apps which
385 		 * are stalled on filesystem I/O.
386 		 *
387 		 * Also, since we are only going for a minimum in the
388 		 * non-timestamp case, we do not smoothe things out
389 		 * else with timestamps disabled convergance takes too
390 		 * long.
391 		 */
392 		if (!win_dep) {
393 			m -= (new_sample >> 3);
394 			new_sample += m;
395 		} else if (m < new_sample)
396 			new_sample = m << 3;
397 	} else {
398 		/* No previous mesaure. */
399 		new_sample = m << 3;
400 	}
401 
402 	if (tp->rcv_rtt_est.rtt != new_sample)
403 		tp->rcv_rtt_est.rtt = new_sample;
404 }
405 
406 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
407 {
408 	if (tp->rcv_rtt_est.time == 0)
409 		goto new_measure;
410 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
411 		return;
412 	tcp_rcv_rtt_update(tp,
413 			   jiffies - tp->rcv_rtt_est.time,
414 			   1);
415 
416 new_measure:
417 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
418 	tp->rcv_rtt_est.time = tcp_time_stamp;
419 }
420 
421 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
422 {
423 	struct tcp_sock *tp = tcp_sk(sk);
424 	if (tp->rx_opt.rcv_tsecr &&
425 	    (TCP_SKB_CB(skb)->end_seq -
426 	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
427 		tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
428 }
429 
430 /*
431  * This function should be called every time data is copied to user space.
432  * It calculates the appropriate TCP receive buffer space.
433  */
434 void tcp_rcv_space_adjust(struct sock *sk)
435 {
436 	struct tcp_sock *tp = tcp_sk(sk);
437 	int time;
438 	int space;
439 
440 	if (tp->rcvq_space.time == 0)
441 		goto new_measure;
442 
443 	time = tcp_time_stamp - tp->rcvq_space.time;
444 	if (time < (tp->rcv_rtt_est.rtt >> 3) ||
445 	    tp->rcv_rtt_est.rtt == 0)
446 		return;
447 
448 	space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
449 
450 	space = max(tp->rcvq_space.space, space);
451 
452 	if (tp->rcvq_space.space != space) {
453 		int rcvmem;
454 
455 		tp->rcvq_space.space = space;
456 
457 		if (sysctl_tcp_moderate_rcvbuf) {
458 			int new_clamp = space;
459 
460 			/* Receive space grows, normalize in order to
461 			 * take into account packet headers and sk_buff
462 			 * structure overhead.
463 			 */
464 			space /= tp->advmss;
465 			if (!space)
466 				space = 1;
467 			rcvmem = (tp->advmss + MAX_TCP_HEADER +
468 				  16 + sizeof(struct sk_buff));
469 			while (tcp_win_from_space(rcvmem) < tp->advmss)
470 				rcvmem += 128;
471 			space *= rcvmem;
472 			space = min(space, sysctl_tcp_rmem[2]);
473 			if (space > sk->sk_rcvbuf) {
474 				sk->sk_rcvbuf = space;
475 
476 				/* Make the window clamp follow along.  */
477 				tp->window_clamp = new_clamp;
478 			}
479 		}
480 	}
481 
482 new_measure:
483 	tp->rcvq_space.seq = tp->copied_seq;
484 	tp->rcvq_space.time = tcp_time_stamp;
485 }
486 
487 /* There is something which you must keep in mind when you analyze the
488  * behavior of the tp->ato delayed ack timeout interval.  When a
489  * connection starts up, we want to ack as quickly as possible.  The
490  * problem is that "good" TCP's do slow start at the beginning of data
491  * transmission.  The means that until we send the first few ACK's the
492  * sender will sit on his end and only queue most of his data, because
493  * he can only send snd_cwnd unacked packets at any given time.  For
494  * each ACK we send, he increments snd_cwnd and transmits more of his
495  * queue.  -DaveM
496  */
497 static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
498 {
499 	struct inet_connection_sock *icsk = inet_csk(sk);
500 	u32 now;
501 
502 	inet_csk_schedule_ack(sk);
503 
504 	tcp_measure_rcv_mss(sk, skb);
505 
506 	tcp_rcv_rtt_measure(tp);
507 
508 	now = tcp_time_stamp;
509 
510 	if (!icsk->icsk_ack.ato) {
511 		/* The _first_ data packet received, initialize
512 		 * delayed ACK engine.
513 		 */
514 		tcp_incr_quickack(sk);
515 		icsk->icsk_ack.ato = TCP_ATO_MIN;
516 	} else {
517 		int m = now - icsk->icsk_ack.lrcvtime;
518 
519 		if (m <= TCP_ATO_MIN/2) {
520 			/* The fastest case is the first. */
521 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
522 		} else if (m < icsk->icsk_ack.ato) {
523 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
524 			if (icsk->icsk_ack.ato > icsk->icsk_rto)
525 				icsk->icsk_ack.ato = icsk->icsk_rto;
526 		} else if (m > icsk->icsk_rto) {
527 			/* Too long gap. Apparently sender falled to
528 			 * restart window, so that we send ACKs quickly.
529 			 */
530 			tcp_incr_quickack(sk);
531 			sk_stream_mem_reclaim(sk);
532 		}
533 	}
534 	icsk->icsk_ack.lrcvtime = now;
535 
536 	TCP_ECN_check_ce(tp, skb);
537 
538 	if (skb->len >= 128)
539 		tcp_grow_window(sk, tp, skb);
540 }
541 
542 /* Called to compute a smoothed rtt estimate. The data fed to this
543  * routine either comes from timestamps, or from segments that were
544  * known _not_ to have been retransmitted [see Karn/Partridge
545  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
546  * piece by Van Jacobson.
547  * NOTE: the next three routines used to be one big routine.
548  * To save cycles in the RFC 1323 implementation it was better to break
549  * it up into three procedures. -- erics
550  */
551 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt, u32 *usrtt)
552 {
553 	struct tcp_sock *tp = tcp_sk(sk);
554 	const struct inet_connection_sock *icsk = inet_csk(sk);
555 	long m = mrtt; /* RTT */
556 
557 	/*	The following amusing code comes from Jacobson's
558 	 *	article in SIGCOMM '88.  Note that rtt and mdev
559 	 *	are scaled versions of rtt and mean deviation.
560 	 *	This is designed to be as fast as possible
561 	 *	m stands for "measurement".
562 	 *
563 	 *	On a 1990 paper the rto value is changed to:
564 	 *	RTO = rtt + 4 * mdev
565 	 *
566 	 * Funny. This algorithm seems to be very broken.
567 	 * These formulae increase RTO, when it should be decreased, increase
568 	 * too slowly, when it should be incresed fastly, decrease too fastly
569 	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
570 	 * does not matter how to _calculate_ it. Seems, it was trap
571 	 * that VJ failed to avoid. 8)
572 	 */
573 	if(m == 0)
574 		m = 1;
575 	if (tp->srtt != 0) {
576 		m -= (tp->srtt >> 3);	/* m is now error in rtt est */
577 		tp->srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
578 		if (m < 0) {
579 			m = -m;		/* m is now abs(error) */
580 			m -= (tp->mdev >> 2);   /* similar update on mdev */
581 			/* This is similar to one of Eifel findings.
582 			 * Eifel blocks mdev updates when rtt decreases.
583 			 * This solution is a bit different: we use finer gain
584 			 * for mdev in this case (alpha*beta).
585 			 * Like Eifel it also prevents growth of rto,
586 			 * but also it limits too fast rto decreases,
587 			 * happening in pure Eifel.
588 			 */
589 			if (m > 0)
590 				m >>= 3;
591 		} else {
592 			m -= (tp->mdev >> 2);   /* similar update on mdev */
593 		}
594 		tp->mdev += m;	    	/* mdev = 3/4 mdev + 1/4 new */
595 		if (tp->mdev > tp->mdev_max) {
596 			tp->mdev_max = tp->mdev;
597 			if (tp->mdev_max > tp->rttvar)
598 				tp->rttvar = tp->mdev_max;
599 		}
600 		if (after(tp->snd_una, tp->rtt_seq)) {
601 			if (tp->mdev_max < tp->rttvar)
602 				tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
603 			tp->rtt_seq = tp->snd_nxt;
604 			tp->mdev_max = TCP_RTO_MIN;
605 		}
606 	} else {
607 		/* no previous measure. */
608 		tp->srtt = m<<3;	/* take the measured time to be rtt */
609 		tp->mdev = m<<1;	/* make sure rto = 3*rtt */
610 		tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
611 		tp->rtt_seq = tp->snd_nxt;
612 	}
613 
614 	if (icsk->icsk_ca_ops->rtt_sample)
615 		icsk->icsk_ca_ops->rtt_sample(sk, *usrtt);
616 }
617 
618 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
619  * routine referred to above.
620  */
621 static inline void tcp_set_rto(struct sock *sk)
622 {
623 	const struct tcp_sock *tp = tcp_sk(sk);
624 	/* Old crap is replaced with new one. 8)
625 	 *
626 	 * More seriously:
627 	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
628 	 *    It cannot be less due to utterly erratic ACK generation made
629 	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
630 	 *    to do with delayed acks, because at cwnd>2 true delack timeout
631 	 *    is invisible. Actually, Linux-2.4 also generates erratic
632 	 *    ACKs in some curcumstances.
633 	 */
634 	inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
635 
636 	/* 2. Fixups made earlier cannot be right.
637 	 *    If we do not estimate RTO correctly without them,
638 	 *    all the algo is pure shit and should be replaced
639 	 *    with correct one. It is exaclty, which we pretend to do.
640 	 */
641 }
642 
643 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
644  * guarantees that rto is higher.
645  */
646 static inline void tcp_bound_rto(struct sock *sk)
647 {
648 	if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
649 		inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
650 }
651 
652 /* Save metrics learned by this TCP session.
653    This function is called only, when TCP finishes successfully
654    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
655  */
656 void tcp_update_metrics(struct sock *sk)
657 {
658 	struct tcp_sock *tp = tcp_sk(sk);
659 	struct dst_entry *dst = __sk_dst_get(sk);
660 
661 	if (sysctl_tcp_nometrics_save)
662 		return;
663 
664 	dst_confirm(dst);
665 
666 	if (dst && (dst->flags&DST_HOST)) {
667 		const struct inet_connection_sock *icsk = inet_csk(sk);
668 		int m;
669 
670 		if (icsk->icsk_backoff || !tp->srtt) {
671 			/* This session failed to estimate rtt. Why?
672 			 * Probably, no packets returned in time.
673 			 * Reset our results.
674 			 */
675 			if (!(dst_metric_locked(dst, RTAX_RTT)))
676 				dst->metrics[RTAX_RTT-1] = 0;
677 			return;
678 		}
679 
680 		m = dst_metric(dst, RTAX_RTT) - tp->srtt;
681 
682 		/* If newly calculated rtt larger than stored one,
683 		 * store new one. Otherwise, use EWMA. Remember,
684 		 * rtt overestimation is always better than underestimation.
685 		 */
686 		if (!(dst_metric_locked(dst, RTAX_RTT))) {
687 			if (m <= 0)
688 				dst->metrics[RTAX_RTT-1] = tp->srtt;
689 			else
690 				dst->metrics[RTAX_RTT-1] -= (m>>3);
691 		}
692 
693 		if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
694 			if (m < 0)
695 				m = -m;
696 
697 			/* Scale deviation to rttvar fixed point */
698 			m >>= 1;
699 			if (m < tp->mdev)
700 				m = tp->mdev;
701 
702 			if (m >= dst_metric(dst, RTAX_RTTVAR))
703 				dst->metrics[RTAX_RTTVAR-1] = m;
704 			else
705 				dst->metrics[RTAX_RTTVAR-1] -=
706 					(dst->metrics[RTAX_RTTVAR-1] - m)>>2;
707 		}
708 
709 		if (tp->snd_ssthresh >= 0xFFFF) {
710 			/* Slow start still did not finish. */
711 			if (dst_metric(dst, RTAX_SSTHRESH) &&
712 			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
713 			    (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
714 				dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
715 			if (!dst_metric_locked(dst, RTAX_CWND) &&
716 			    tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
717 				dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
718 		} else if (tp->snd_cwnd > tp->snd_ssthresh &&
719 			   icsk->icsk_ca_state == TCP_CA_Open) {
720 			/* Cong. avoidance phase, cwnd is reliable. */
721 			if (!dst_metric_locked(dst, RTAX_SSTHRESH))
722 				dst->metrics[RTAX_SSTHRESH-1] =
723 					max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
724 			if (!dst_metric_locked(dst, RTAX_CWND))
725 				dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
726 		} else {
727 			/* Else slow start did not finish, cwnd is non-sense,
728 			   ssthresh may be also invalid.
729 			 */
730 			if (!dst_metric_locked(dst, RTAX_CWND))
731 				dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
732 			if (dst->metrics[RTAX_SSTHRESH-1] &&
733 			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
734 			    tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
735 				dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
736 		}
737 
738 		if (!dst_metric_locked(dst, RTAX_REORDERING)) {
739 			if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
740 			    tp->reordering != sysctl_tcp_reordering)
741 				dst->metrics[RTAX_REORDERING-1] = tp->reordering;
742 		}
743 	}
744 }
745 
746 /* Numbers are taken from RFC2414.  */
747 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
748 {
749 	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
750 
751 	if (!cwnd) {
752 		if (tp->mss_cache > 1460)
753 			cwnd = 2;
754 		else
755 			cwnd = (tp->mss_cache > 1095) ? 3 : 4;
756 	}
757 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
758 }
759 
760 /* Initialize metrics on socket. */
761 
762 static void tcp_init_metrics(struct sock *sk)
763 {
764 	struct tcp_sock *tp = tcp_sk(sk);
765 	struct dst_entry *dst = __sk_dst_get(sk);
766 
767 	if (dst == NULL)
768 		goto reset;
769 
770 	dst_confirm(dst);
771 
772 	if (dst_metric_locked(dst, RTAX_CWND))
773 		tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
774 	if (dst_metric(dst, RTAX_SSTHRESH)) {
775 		tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
776 		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
777 			tp->snd_ssthresh = tp->snd_cwnd_clamp;
778 	}
779 	if (dst_metric(dst, RTAX_REORDERING) &&
780 	    tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
781 		tp->rx_opt.sack_ok &= ~2;
782 		tp->reordering = dst_metric(dst, RTAX_REORDERING);
783 	}
784 
785 	if (dst_metric(dst, RTAX_RTT) == 0)
786 		goto reset;
787 
788 	if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
789 		goto reset;
790 
791 	/* Initial rtt is determined from SYN,SYN-ACK.
792 	 * The segment is small and rtt may appear much
793 	 * less than real one. Use per-dst memory
794 	 * to make it more realistic.
795 	 *
796 	 * A bit of theory. RTT is time passed after "normal" sized packet
797 	 * is sent until it is ACKed. In normal curcumstances sending small
798 	 * packets force peer to delay ACKs and calculation is correct too.
799 	 * The algorithm is adaptive and, provided we follow specs, it
800 	 * NEVER underestimate RTT. BUT! If peer tries to make some clever
801 	 * tricks sort of "quick acks" for time long enough to decrease RTT
802 	 * to low value, and then abruptly stops to do it and starts to delay
803 	 * ACKs, wait for troubles.
804 	 */
805 	if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
806 		tp->srtt = dst_metric(dst, RTAX_RTT);
807 		tp->rtt_seq = tp->snd_nxt;
808 	}
809 	if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
810 		tp->mdev = dst_metric(dst, RTAX_RTTVAR);
811 		tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
812 	}
813 	tcp_set_rto(sk);
814 	tcp_bound_rto(sk);
815 	if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
816 		goto reset;
817 	tp->snd_cwnd = tcp_init_cwnd(tp, dst);
818 	tp->snd_cwnd_stamp = tcp_time_stamp;
819 	return;
820 
821 reset:
822 	/* Play conservative. If timestamps are not
823 	 * supported, TCP will fail to recalculate correct
824 	 * rtt, if initial rto is too small. FORGET ALL AND RESET!
825 	 */
826 	if (!tp->rx_opt.saw_tstamp && tp->srtt) {
827 		tp->srtt = 0;
828 		tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
829 		inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
830 	}
831 }
832 
833 static void tcp_update_reordering(struct sock *sk, const int metric,
834 				  const int ts)
835 {
836 	struct tcp_sock *tp = tcp_sk(sk);
837 	if (metric > tp->reordering) {
838 		tp->reordering = min(TCP_MAX_REORDERING, metric);
839 
840 		/* This exciting event is worth to be remembered. 8) */
841 		if (ts)
842 			NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
843 		else if (IsReno(tp))
844 			NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
845 		else if (IsFack(tp))
846 			NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
847 		else
848 			NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
849 #if FASTRETRANS_DEBUG > 1
850 		printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
851 		       tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
852 		       tp->reordering,
853 		       tp->fackets_out,
854 		       tp->sacked_out,
855 		       tp->undo_marker ? tp->undo_retrans : 0);
856 #endif
857 		/* Disable FACK yet. */
858 		tp->rx_opt.sack_ok &= ~2;
859 	}
860 }
861 
862 /* This procedure tags the retransmission queue when SACKs arrive.
863  *
864  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
865  * Packets in queue with these bits set are counted in variables
866  * sacked_out, retrans_out and lost_out, correspondingly.
867  *
868  * Valid combinations are:
869  * Tag  InFlight	Description
870  * 0	1		- orig segment is in flight.
871  * S	0		- nothing flies, orig reached receiver.
872  * L	0		- nothing flies, orig lost by net.
873  * R	2		- both orig and retransmit are in flight.
874  * L|R	1		- orig is lost, retransmit is in flight.
875  * S|R  1		- orig reached receiver, retrans is still in flight.
876  * (L|S|R is logically valid, it could occur when L|R is sacked,
877  *  but it is equivalent to plain S and code short-curcuits it to S.
878  *  L|S is logically invalid, it would mean -1 packet in flight 8))
879  *
880  * These 6 states form finite state machine, controlled by the following events:
881  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
882  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
883  * 3. Loss detection event of one of three flavors:
884  *	A. Scoreboard estimator decided the packet is lost.
885  *	   A'. Reno "three dupacks" marks head of queue lost.
886  *	   A''. Its FACK modfication, head until snd.fack is lost.
887  *	B. SACK arrives sacking data transmitted after never retransmitted
888  *	   hole was sent out.
889  *	C. SACK arrives sacking SND.NXT at the moment, when the
890  *	   segment was retransmitted.
891  * 4. D-SACK added new rule: D-SACK changes any tag to S.
892  *
893  * It is pleasant to note, that state diagram turns out to be commutative,
894  * so that we are allowed not to be bothered by order of our actions,
895  * when multiple events arrive simultaneously. (see the function below).
896  *
897  * Reordering detection.
898  * --------------------
899  * Reordering metric is maximal distance, which a packet can be displaced
900  * in packet stream. With SACKs we can estimate it:
901  *
902  * 1. SACK fills old hole and the corresponding segment was not
903  *    ever retransmitted -> reordering. Alas, we cannot use it
904  *    when segment was retransmitted.
905  * 2. The last flaw is solved with D-SACK. D-SACK arrives
906  *    for retransmitted and already SACKed segment -> reordering..
907  * Both of these heuristics are not used in Loss state, when we cannot
908  * account for retransmits accurately.
909  */
910 static int
911 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
912 {
913 	const struct inet_connection_sock *icsk = inet_csk(sk);
914 	struct tcp_sock *tp = tcp_sk(sk);
915 	unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
916 	struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2);
917 	int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
918 	int reord = tp->packets_out;
919 	int prior_fackets;
920 	u32 lost_retrans = 0;
921 	int flag = 0;
922 	int i;
923 
924 	if (!tp->sacked_out)
925 		tp->fackets_out = 0;
926 	prior_fackets = tp->fackets_out;
927 
928 	for (i=0; i<num_sacks; i++, sp++) {
929 		struct sk_buff *skb;
930 		__u32 start_seq = ntohl(sp->start_seq);
931 		__u32 end_seq = ntohl(sp->end_seq);
932 		int fack_count = 0;
933 		int dup_sack = 0;
934 
935 		/* Check for D-SACK. */
936 		if (i == 0) {
937 			u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;
938 
939 			if (before(start_seq, ack)) {
940 				dup_sack = 1;
941 				tp->rx_opt.sack_ok |= 4;
942 				NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
943 			} else if (num_sacks > 1 &&
944 				   !after(end_seq, ntohl(sp[1].end_seq)) &&
945 				   !before(start_seq, ntohl(sp[1].start_seq))) {
946 				dup_sack = 1;
947 				tp->rx_opt.sack_ok |= 4;
948 				NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
949 			}
950 
951 			/* D-SACK for already forgotten data...
952 			 * Do dumb counting. */
953 			if (dup_sack &&
954 			    !after(end_seq, prior_snd_una) &&
955 			    after(end_seq, tp->undo_marker))
956 				tp->undo_retrans--;
957 
958 			/* Eliminate too old ACKs, but take into
959 			 * account more or less fresh ones, they can
960 			 * contain valid SACK info.
961 			 */
962 			if (before(ack, prior_snd_una - tp->max_window))
963 				return 0;
964 		}
965 
966 		/* Event "B" in the comment above. */
967 		if (after(end_seq, tp->high_seq))
968 			flag |= FLAG_DATA_LOST;
969 
970 		sk_stream_for_retrans_queue(skb, sk) {
971 			int in_sack, pcount;
972 			u8 sacked;
973 
974 			/* The retransmission queue is always in order, so
975 			 * we can short-circuit the walk early.
976 			 */
977 			if (!before(TCP_SKB_CB(skb)->seq, end_seq))
978 				break;
979 
980 			in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
981 				!before(end_seq, TCP_SKB_CB(skb)->end_seq);
982 
983 			pcount = tcp_skb_pcount(skb);
984 
985 			if (pcount > 1 && !in_sack &&
986 			    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
987 				unsigned int pkt_len;
988 
989 				in_sack = !after(start_seq,
990 						 TCP_SKB_CB(skb)->seq);
991 
992 				if (!in_sack)
993 					pkt_len = (start_seq -
994 						   TCP_SKB_CB(skb)->seq);
995 				else
996 					pkt_len = (end_seq -
997 						   TCP_SKB_CB(skb)->seq);
998 				if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->tso_size))
999 					break;
1000 				pcount = tcp_skb_pcount(skb);
1001 			}
1002 
1003 			fack_count += pcount;
1004 
1005 			sacked = TCP_SKB_CB(skb)->sacked;
1006 
1007 			/* Account D-SACK for retransmitted packet. */
1008 			if ((dup_sack && in_sack) &&
1009 			    (sacked & TCPCB_RETRANS) &&
1010 			    after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1011 				tp->undo_retrans--;
1012 
1013 			/* The frame is ACKed. */
1014 			if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1015 				if (sacked&TCPCB_RETRANS) {
1016 					if ((dup_sack && in_sack) &&
1017 					    (sacked&TCPCB_SACKED_ACKED))
1018 						reord = min(fack_count, reord);
1019 				} else {
1020 					/* If it was in a hole, we detected reordering. */
1021 					if (fack_count < prior_fackets &&
1022 					    !(sacked&TCPCB_SACKED_ACKED))
1023 						reord = min(fack_count, reord);
1024 				}
1025 
1026 				/* Nothing to do; acked frame is about to be dropped. */
1027 				continue;
1028 			}
1029 
1030 			if ((sacked&TCPCB_SACKED_RETRANS) &&
1031 			    after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1032 			    (!lost_retrans || after(end_seq, lost_retrans)))
1033 				lost_retrans = end_seq;
1034 
1035 			if (!in_sack)
1036 				continue;
1037 
1038 			if (!(sacked&TCPCB_SACKED_ACKED)) {
1039 				if (sacked & TCPCB_SACKED_RETRANS) {
1040 					/* If the segment is not tagged as lost,
1041 					 * we do not clear RETRANS, believing
1042 					 * that retransmission is still in flight.
1043 					 */
1044 					if (sacked & TCPCB_LOST) {
1045 						TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1046 						tp->lost_out -= tcp_skb_pcount(skb);
1047 						tp->retrans_out -= tcp_skb_pcount(skb);
1048 					}
1049 				} else {
1050 					/* New sack for not retransmitted frame,
1051 					 * which was in hole. It is reordering.
1052 					 */
1053 					if (!(sacked & TCPCB_RETRANS) &&
1054 					    fack_count < prior_fackets)
1055 						reord = min(fack_count, reord);
1056 
1057 					if (sacked & TCPCB_LOST) {
1058 						TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1059 						tp->lost_out -= tcp_skb_pcount(skb);
1060 					}
1061 				}
1062 
1063 				TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1064 				flag |= FLAG_DATA_SACKED;
1065 				tp->sacked_out += tcp_skb_pcount(skb);
1066 
1067 				if (fack_count > tp->fackets_out)
1068 					tp->fackets_out = fack_count;
1069 			} else {
1070 				if (dup_sack && (sacked&TCPCB_RETRANS))
1071 					reord = min(fack_count, reord);
1072 			}
1073 
1074 			/* D-SACK. We can detect redundant retransmission
1075 			 * in S|R and plain R frames and clear it.
1076 			 * undo_retrans is decreased above, L|R frames
1077 			 * are accounted above as well.
1078 			 */
1079 			if (dup_sack &&
1080 			    (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1081 				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1082 				tp->retrans_out -= tcp_skb_pcount(skb);
1083 			}
1084 		}
1085 	}
1086 
1087 	/* Check for lost retransmit. This superb idea is
1088 	 * borrowed from "ratehalving". Event "C".
1089 	 * Later note: FACK people cheated me again 8),
1090 	 * we have to account for reordering! Ugly,
1091 	 * but should help.
1092 	 */
1093 	if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
1094 		struct sk_buff *skb;
1095 
1096 		sk_stream_for_retrans_queue(skb, sk) {
1097 			if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1098 				break;
1099 			if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1100 				continue;
1101 			if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1102 			    after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1103 			    (IsFack(tp) ||
1104 			     !before(lost_retrans,
1105 				     TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1106 				     tp->mss_cache))) {
1107 				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1108 				tp->retrans_out -= tcp_skb_pcount(skb);
1109 
1110 				if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1111 					tp->lost_out += tcp_skb_pcount(skb);
1112 					TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1113 					flag |= FLAG_DATA_SACKED;
1114 					NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1115 				}
1116 			}
1117 		}
1118 	}
1119 
1120 	tp->left_out = tp->sacked_out + tp->lost_out;
1121 
1122 	if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss)
1123 		tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1124 
1125 #if FASTRETRANS_DEBUG > 0
1126 	BUG_TRAP((int)tp->sacked_out >= 0);
1127 	BUG_TRAP((int)tp->lost_out >= 0);
1128 	BUG_TRAP((int)tp->retrans_out >= 0);
1129 	BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1130 #endif
1131 	return flag;
1132 }
1133 
1134 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new
1135  * segments to see from the next ACKs whether any data was really missing.
1136  * If the RTO was spurious, new ACKs should arrive.
1137  */
1138 void tcp_enter_frto(struct sock *sk)
1139 {
1140 	const struct inet_connection_sock *icsk = inet_csk(sk);
1141 	struct tcp_sock *tp = tcp_sk(sk);
1142 	struct sk_buff *skb;
1143 
1144 	tp->frto_counter = 1;
1145 
1146 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1147             tp->snd_una == tp->high_seq ||
1148             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1149 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
1150 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1151 		tcp_ca_event(sk, CA_EVENT_FRTO);
1152 	}
1153 
1154 	/* Have to clear retransmission markers here to keep the bookkeeping
1155 	 * in shape, even though we are not yet in Loss state.
1156 	 * If something was really lost, it is eventually caught up
1157 	 * in tcp_enter_frto_loss.
1158 	 */
1159 	tp->retrans_out = 0;
1160 	tp->undo_marker = tp->snd_una;
1161 	tp->undo_retrans = 0;
1162 
1163 	sk_stream_for_retrans_queue(skb, sk) {
1164 		TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
1165 	}
1166 	tcp_sync_left_out(tp);
1167 
1168 	tcp_set_ca_state(sk, TCP_CA_Open);
1169 	tp->frto_highmark = tp->snd_nxt;
1170 }
1171 
1172 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1173  * which indicates that we should follow the traditional RTO recovery,
1174  * i.e. mark everything lost and do go-back-N retransmission.
1175  */
1176 static void tcp_enter_frto_loss(struct sock *sk)
1177 {
1178 	struct tcp_sock *tp = tcp_sk(sk);
1179 	struct sk_buff *skb;
1180 	int cnt = 0;
1181 
1182 	tp->sacked_out = 0;
1183 	tp->lost_out = 0;
1184 	tp->fackets_out = 0;
1185 
1186 	sk_stream_for_retrans_queue(skb, sk) {
1187 		cnt += tcp_skb_pcount(skb);
1188 		TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1189 		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1190 
1191 			/* Do not mark those segments lost that were
1192 			 * forward transmitted after RTO
1193 			 */
1194 			if (!after(TCP_SKB_CB(skb)->end_seq,
1195 				   tp->frto_highmark)) {
1196 				TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1197 				tp->lost_out += tcp_skb_pcount(skb);
1198 			}
1199 		} else {
1200 			tp->sacked_out += tcp_skb_pcount(skb);
1201 			tp->fackets_out = cnt;
1202 		}
1203 	}
1204 	tcp_sync_left_out(tp);
1205 
1206 	tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
1207 	tp->snd_cwnd_cnt = 0;
1208 	tp->snd_cwnd_stamp = tcp_time_stamp;
1209 	tp->undo_marker = 0;
1210 	tp->frto_counter = 0;
1211 
1212 	tp->reordering = min_t(unsigned int, tp->reordering,
1213 					     sysctl_tcp_reordering);
1214 	tcp_set_ca_state(sk, TCP_CA_Loss);
1215 	tp->high_seq = tp->frto_highmark;
1216 	TCP_ECN_queue_cwr(tp);
1217 }
1218 
1219 void tcp_clear_retrans(struct tcp_sock *tp)
1220 {
1221 	tp->left_out = 0;
1222 	tp->retrans_out = 0;
1223 
1224 	tp->fackets_out = 0;
1225 	tp->sacked_out = 0;
1226 	tp->lost_out = 0;
1227 
1228 	tp->undo_marker = 0;
1229 	tp->undo_retrans = 0;
1230 }
1231 
1232 /* Enter Loss state. If "how" is not zero, forget all SACK information
1233  * and reset tags completely, otherwise preserve SACKs. If receiver
1234  * dropped its ofo queue, we will know this due to reneging detection.
1235  */
1236 void tcp_enter_loss(struct sock *sk, int how)
1237 {
1238 	const struct inet_connection_sock *icsk = inet_csk(sk);
1239 	struct tcp_sock *tp = tcp_sk(sk);
1240 	struct sk_buff *skb;
1241 	int cnt = 0;
1242 
1243 	/* Reduce ssthresh if it has not yet been made inside this window. */
1244 	if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1245 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1246 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
1247 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1248 		tcp_ca_event(sk, CA_EVENT_LOSS);
1249 	}
1250 	tp->snd_cwnd	   = 1;
1251 	tp->snd_cwnd_cnt   = 0;
1252 	tp->snd_cwnd_stamp = tcp_time_stamp;
1253 
1254 	tcp_clear_retrans(tp);
1255 
1256 	/* Push undo marker, if it was plain RTO and nothing
1257 	 * was retransmitted. */
1258 	if (!how)
1259 		tp->undo_marker = tp->snd_una;
1260 
1261 	sk_stream_for_retrans_queue(skb, sk) {
1262 		cnt += tcp_skb_pcount(skb);
1263 		if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1264 			tp->undo_marker = 0;
1265 		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1266 		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1267 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1268 			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1269 			tp->lost_out += tcp_skb_pcount(skb);
1270 		} else {
1271 			tp->sacked_out += tcp_skb_pcount(skb);
1272 			tp->fackets_out = cnt;
1273 		}
1274 	}
1275 	tcp_sync_left_out(tp);
1276 
1277 	tp->reordering = min_t(unsigned int, tp->reordering,
1278 					     sysctl_tcp_reordering);
1279 	tcp_set_ca_state(sk, TCP_CA_Loss);
1280 	tp->high_seq = tp->snd_nxt;
1281 	TCP_ECN_queue_cwr(tp);
1282 }
1283 
1284 static int tcp_check_sack_reneging(struct sock *sk)
1285 {
1286 	struct sk_buff *skb;
1287 
1288 	/* If ACK arrived pointing to a remembered SACK,
1289 	 * it means that our remembered SACKs do not reflect
1290 	 * real state of receiver i.e.
1291 	 * receiver _host_ is heavily congested (or buggy).
1292 	 * Do processing similar to RTO timeout.
1293 	 */
1294 	if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
1295 	    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1296 		struct inet_connection_sock *icsk = inet_csk(sk);
1297 		NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1298 
1299 		tcp_enter_loss(sk, 1);
1300 		icsk->icsk_retransmits++;
1301 		tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
1302 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1303 					  icsk->icsk_rto, TCP_RTO_MAX);
1304 		return 1;
1305 	}
1306 	return 0;
1307 }
1308 
1309 static inline int tcp_fackets_out(struct tcp_sock *tp)
1310 {
1311 	return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1312 }
1313 
1314 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1315 {
1316 	return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1317 }
1318 
1319 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
1320 {
1321 	return tp->packets_out &&
1322 	       tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
1323 }
1324 
1325 /* Linux NewReno/SACK/FACK/ECN state machine.
1326  * --------------------------------------
1327  *
1328  * "Open"	Normal state, no dubious events, fast path.
1329  * "Disorder"   In all the respects it is "Open",
1330  *		but requires a bit more attention. It is entered when
1331  *		we see some SACKs or dupacks. It is split of "Open"
1332  *		mainly to move some processing from fast path to slow one.
1333  * "CWR"	CWND was reduced due to some Congestion Notification event.
1334  *		It can be ECN, ICMP source quench, local device congestion.
1335  * "Recovery"	CWND was reduced, we are fast-retransmitting.
1336  * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
1337  *
1338  * tcp_fastretrans_alert() is entered:
1339  * - each incoming ACK, if state is not "Open"
1340  * - when arrived ACK is unusual, namely:
1341  *	* SACK
1342  *	* Duplicate ACK.
1343  *	* ECN ECE.
1344  *
1345  * Counting packets in flight is pretty simple.
1346  *
1347  *	in_flight = packets_out - left_out + retrans_out
1348  *
1349  *	packets_out is SND.NXT-SND.UNA counted in packets.
1350  *
1351  *	retrans_out is number of retransmitted segments.
1352  *
1353  *	left_out is number of segments left network, but not ACKed yet.
1354  *
1355  *		left_out = sacked_out + lost_out
1356  *
1357  *     sacked_out: Packets, which arrived to receiver out of order
1358  *		   and hence not ACKed. With SACKs this number is simply
1359  *		   amount of SACKed data. Even without SACKs
1360  *		   it is easy to give pretty reliable estimate of this number,
1361  *		   counting duplicate ACKs.
1362  *
1363  *       lost_out: Packets lost by network. TCP has no explicit
1364  *		   "loss notification" feedback from network (for now).
1365  *		   It means that this number can be only _guessed_.
1366  *		   Actually, it is the heuristics to predict lossage that
1367  *		   distinguishes different algorithms.
1368  *
1369  *	F.e. after RTO, when all the queue is considered as lost,
1370  *	lost_out = packets_out and in_flight = retrans_out.
1371  *
1372  *		Essentially, we have now two algorithms counting
1373  *		lost packets.
1374  *
1375  *		FACK: It is the simplest heuristics. As soon as we decided
1376  *		that something is lost, we decide that _all_ not SACKed
1377  *		packets until the most forward SACK are lost. I.e.
1378  *		lost_out = fackets_out - sacked_out and left_out = fackets_out.
1379  *		It is absolutely correct estimate, if network does not reorder
1380  *		packets. And it loses any connection to reality when reordering
1381  *		takes place. We use FACK by default until reordering
1382  *		is suspected on the path to this destination.
1383  *
1384  *		NewReno: when Recovery is entered, we assume that one segment
1385  *		is lost (classic Reno). While we are in Recovery and
1386  *		a partial ACK arrives, we assume that one more packet
1387  *		is lost (NewReno). This heuristics are the same in NewReno
1388  *		and SACK.
1389  *
1390  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1391  *  deflation etc. CWND is real congestion window, never inflated, changes
1392  *  only according to classic VJ rules.
1393  *
1394  * Really tricky (and requiring careful tuning) part of algorithm
1395  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1396  * The first determines the moment _when_ we should reduce CWND and,
1397  * hence, slow down forward transmission. In fact, it determines the moment
1398  * when we decide that hole is caused by loss, rather than by a reorder.
1399  *
1400  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1401  * holes, caused by lost packets.
1402  *
1403  * And the most logically complicated part of algorithm is undo
1404  * heuristics. We detect false retransmits due to both too early
1405  * fast retransmit (reordering) and underestimated RTO, analyzing
1406  * timestamps and D-SACKs. When we detect that some segments were
1407  * retransmitted by mistake and CWND reduction was wrong, we undo
1408  * window reduction and abort recovery phase. This logic is hidden
1409  * inside several functions named tcp_try_undo_<something>.
1410  */
1411 
1412 /* This function decides, when we should leave Disordered state
1413  * and enter Recovery phase, reducing congestion window.
1414  *
1415  * Main question: may we further continue forward transmission
1416  * with the same cwnd?
1417  */
1418 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
1419 {
1420 	__u32 packets_out;
1421 
1422 	/* Trick#1: The loss is proven. */
1423 	if (tp->lost_out)
1424 		return 1;
1425 
1426 	/* Not-A-Trick#2 : Classic rule... */
1427 	if (tcp_fackets_out(tp) > tp->reordering)
1428 		return 1;
1429 
1430 	/* Trick#3 : when we use RFC2988 timer restart, fast
1431 	 * retransmit can be triggered by timeout of queue head.
1432 	 */
1433 	if (tcp_head_timedout(sk, tp))
1434 		return 1;
1435 
1436 	/* Trick#4: It is still not OK... But will it be useful to delay
1437 	 * recovery more?
1438 	 */
1439 	packets_out = tp->packets_out;
1440 	if (packets_out <= tp->reordering &&
1441 	    tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1442 	    !tcp_may_send_now(sk, tp)) {
1443 		/* We have nothing to send. This connection is limited
1444 		 * either by receiver window or by application.
1445 		 */
1446 		return 1;
1447 	}
1448 
1449 	return 0;
1450 }
1451 
1452 /* If we receive more dupacks than we expected counting segments
1453  * in assumption of absent reordering, interpret this as reordering.
1454  * The only another reason could be bug in receiver TCP.
1455  */
1456 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1457 {
1458 	struct tcp_sock *tp = tcp_sk(sk);
1459 	u32 holes;
1460 
1461 	holes = max(tp->lost_out, 1U);
1462 	holes = min(holes, tp->packets_out);
1463 
1464 	if ((tp->sacked_out + holes) > tp->packets_out) {
1465 		tp->sacked_out = tp->packets_out - holes;
1466 		tcp_update_reordering(sk, tp->packets_out + addend, 0);
1467 	}
1468 }
1469 
1470 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1471 
1472 static void tcp_add_reno_sack(struct sock *sk)
1473 {
1474 	struct tcp_sock *tp = tcp_sk(sk);
1475 	tp->sacked_out++;
1476 	tcp_check_reno_reordering(sk, 0);
1477 	tcp_sync_left_out(tp);
1478 }
1479 
1480 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1481 
1482 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
1483 {
1484 	if (acked > 0) {
1485 		/* One ACK acked hole. The rest eat duplicate ACKs. */
1486 		if (acked-1 >= tp->sacked_out)
1487 			tp->sacked_out = 0;
1488 		else
1489 			tp->sacked_out -= acked-1;
1490 	}
1491 	tcp_check_reno_reordering(sk, acked);
1492 	tcp_sync_left_out(tp);
1493 }
1494 
1495 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1496 {
1497 	tp->sacked_out = 0;
1498 	tp->left_out = tp->lost_out;
1499 }
1500 
1501 /* Mark head of queue up as lost. */
1502 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
1503 			       int packets, u32 high_seq)
1504 {
1505 	struct sk_buff *skb;
1506 	int cnt = packets;
1507 
1508 	BUG_TRAP(cnt <= tp->packets_out);
1509 
1510 	sk_stream_for_retrans_queue(skb, sk) {
1511 		cnt -= tcp_skb_pcount(skb);
1512 		if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1513 			break;
1514 		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1515 			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1516 			tp->lost_out += tcp_skb_pcount(skb);
1517 		}
1518 	}
1519 	tcp_sync_left_out(tp);
1520 }
1521 
1522 /* Account newly detected lost packet(s) */
1523 
1524 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
1525 {
1526 	if (IsFack(tp)) {
1527 		int lost = tp->fackets_out - tp->reordering;
1528 		if (lost <= 0)
1529 			lost = 1;
1530 		tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
1531 	} else {
1532 		tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
1533 	}
1534 
1535 	/* New heuristics: it is possible only after we switched
1536 	 * to restart timer each time when something is ACKed.
1537 	 * Hence, we can detect timed out packets during fast
1538 	 * retransmit without falling to slow start.
1539 	 */
1540 	if (tcp_head_timedout(sk, tp)) {
1541 		struct sk_buff *skb;
1542 
1543 		sk_stream_for_retrans_queue(skb, sk) {
1544 			if (tcp_skb_timedout(sk, skb) &&
1545 			    !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1546 				TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1547 				tp->lost_out += tcp_skb_pcount(skb);
1548 			}
1549 		}
1550 		tcp_sync_left_out(tp);
1551 	}
1552 }
1553 
1554 /* CWND moderation, preventing bursts due to too big ACKs
1555  * in dubious situations.
1556  */
1557 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1558 {
1559 	tp->snd_cwnd = min(tp->snd_cwnd,
1560 			   tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1561 	tp->snd_cwnd_stamp = tcp_time_stamp;
1562 }
1563 
1564 /* Decrease cwnd each second ack. */
1565 static void tcp_cwnd_down(struct sock *sk)
1566 {
1567 	const struct inet_connection_sock *icsk = inet_csk(sk);
1568 	struct tcp_sock *tp = tcp_sk(sk);
1569 	int decr = tp->snd_cwnd_cnt + 1;
1570 
1571 	tp->snd_cwnd_cnt = decr&1;
1572 	decr >>= 1;
1573 
1574 	if (decr && tp->snd_cwnd > icsk->icsk_ca_ops->min_cwnd(sk))
1575 		tp->snd_cwnd -= decr;
1576 
1577 	tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1578 	tp->snd_cwnd_stamp = tcp_time_stamp;
1579 }
1580 
1581 /* Nothing was retransmitted or returned timestamp is less
1582  * than timestamp of the first retransmission.
1583  */
1584 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1585 {
1586 	return !tp->retrans_stamp ||
1587 		(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1588 		 (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1589 }
1590 
1591 /* Undo procedures. */
1592 
1593 #if FASTRETRANS_DEBUG > 1
1594 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
1595 {
1596 	struct inet_sock *inet = inet_sk(sk);
1597 	printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1598 	       msg,
1599 	       NIPQUAD(inet->daddr), ntohs(inet->dport),
1600 	       tp->snd_cwnd, tp->left_out,
1601 	       tp->snd_ssthresh, tp->prior_ssthresh,
1602 	       tp->packets_out);
1603 }
1604 #else
1605 #define DBGUNDO(x...) do { } while (0)
1606 #endif
1607 
1608 static void tcp_undo_cwr(struct sock *sk, const int undo)
1609 {
1610 	struct tcp_sock *tp = tcp_sk(sk);
1611 
1612 	if (tp->prior_ssthresh) {
1613 		const struct inet_connection_sock *icsk = inet_csk(sk);
1614 
1615 		if (icsk->icsk_ca_ops->undo_cwnd)
1616 			tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
1617 		else
1618 			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1619 
1620 		if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1621 			tp->snd_ssthresh = tp->prior_ssthresh;
1622 			TCP_ECN_withdraw_cwr(tp);
1623 		}
1624 	} else {
1625 		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1626 	}
1627 	tcp_moderate_cwnd(tp);
1628 	tp->snd_cwnd_stamp = tcp_time_stamp;
1629 }
1630 
1631 static inline int tcp_may_undo(struct tcp_sock *tp)
1632 {
1633 	return tp->undo_marker &&
1634 		(!tp->undo_retrans || tcp_packet_delayed(tp));
1635 }
1636 
1637 /* People celebrate: "We love our President!" */
1638 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
1639 {
1640 	if (tcp_may_undo(tp)) {
1641 		/* Happy end! We did not retransmit anything
1642 		 * or our original transmission succeeded.
1643 		 */
1644 		DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
1645 		tcp_undo_cwr(sk, 1);
1646 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
1647 			NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1648 		else
1649 			NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1650 		tp->undo_marker = 0;
1651 	}
1652 	if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1653 		/* Hold old state until something *above* high_seq
1654 		 * is ACKed. For Reno it is MUST to prevent false
1655 		 * fast retransmits (RFC2582). SACK TCP is safe. */
1656 		tcp_moderate_cwnd(tp);
1657 		return 1;
1658 	}
1659 	tcp_set_ca_state(sk, TCP_CA_Open);
1660 	return 0;
1661 }
1662 
1663 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1664 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
1665 {
1666 	if (tp->undo_marker && !tp->undo_retrans) {
1667 		DBGUNDO(sk, tp, "D-SACK");
1668 		tcp_undo_cwr(sk, 1);
1669 		tp->undo_marker = 0;
1670 		NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1671 	}
1672 }
1673 
1674 /* Undo during fast recovery after partial ACK. */
1675 
1676 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
1677 				int acked)
1678 {
1679 	/* Partial ACK arrived. Force Hoe's retransmit. */
1680 	int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1681 
1682 	if (tcp_may_undo(tp)) {
1683 		/* Plain luck! Hole if filled with delayed
1684 		 * packet, rather than with a retransmit.
1685 		 */
1686 		if (tp->retrans_out == 0)
1687 			tp->retrans_stamp = 0;
1688 
1689 		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
1690 
1691 		DBGUNDO(sk, tp, "Hoe");
1692 		tcp_undo_cwr(sk, 0);
1693 		NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1694 
1695 		/* So... Do not make Hoe's retransmit yet.
1696 		 * If the first packet was delayed, the rest
1697 		 * ones are most probably delayed as well.
1698 		 */
1699 		failed = 0;
1700 	}
1701 	return failed;
1702 }
1703 
1704 /* Undo during loss recovery after partial ACK. */
1705 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
1706 {
1707 	if (tcp_may_undo(tp)) {
1708 		struct sk_buff *skb;
1709 		sk_stream_for_retrans_queue(skb, sk) {
1710 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1711 		}
1712 		DBGUNDO(sk, tp, "partial loss");
1713 		tp->lost_out = 0;
1714 		tp->left_out = tp->sacked_out;
1715 		tcp_undo_cwr(sk, 1);
1716 		NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1717 		inet_csk(sk)->icsk_retransmits = 0;
1718 		tp->undo_marker = 0;
1719 		if (!IsReno(tp))
1720 			tcp_set_ca_state(sk, TCP_CA_Open);
1721 		return 1;
1722 	}
1723 	return 0;
1724 }
1725 
1726 static inline void tcp_complete_cwr(struct sock *sk)
1727 {
1728 	struct tcp_sock *tp = tcp_sk(sk);
1729 	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
1730 	tp->snd_cwnd_stamp = tcp_time_stamp;
1731 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
1732 }
1733 
1734 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
1735 {
1736 	tp->left_out = tp->sacked_out;
1737 
1738 	if (tp->retrans_out == 0)
1739 		tp->retrans_stamp = 0;
1740 
1741 	if (flag&FLAG_ECE)
1742 		tcp_enter_cwr(sk);
1743 
1744 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
1745 		int state = TCP_CA_Open;
1746 
1747 		if (tp->left_out || tp->retrans_out || tp->undo_marker)
1748 			state = TCP_CA_Disorder;
1749 
1750 		if (inet_csk(sk)->icsk_ca_state != state) {
1751 			tcp_set_ca_state(sk, state);
1752 			tp->high_seq = tp->snd_nxt;
1753 		}
1754 		tcp_moderate_cwnd(tp);
1755 	} else {
1756 		tcp_cwnd_down(sk);
1757 	}
1758 }
1759 
1760 /* Process an event, which can update packets-in-flight not trivially.
1761  * Main goal of this function is to calculate new estimate for left_out,
1762  * taking into account both packets sitting in receiver's buffer and
1763  * packets lost by network.
1764  *
1765  * Besides that it does CWND reduction, when packet loss is detected
1766  * and changes state of machine.
1767  *
1768  * It does _not_ decide what to send, it is made in function
1769  * tcp_xmit_retransmit_queue().
1770  */
1771 static void
1772 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
1773 		      int prior_packets, int flag)
1774 {
1775 	struct inet_connection_sock *icsk = inet_csk(sk);
1776 	struct tcp_sock *tp = tcp_sk(sk);
1777 	int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
1778 
1779 	/* Some technical things:
1780 	 * 1. Reno does not count dupacks (sacked_out) automatically. */
1781 	if (!tp->packets_out)
1782 		tp->sacked_out = 0;
1783         /* 2. SACK counts snd_fack in packets inaccurately. */
1784 	if (tp->sacked_out == 0)
1785 		tp->fackets_out = 0;
1786 
1787         /* Now state machine starts.
1788 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
1789 	if (flag&FLAG_ECE)
1790 		tp->prior_ssthresh = 0;
1791 
1792 	/* B. In all the states check for reneging SACKs. */
1793 	if (tp->sacked_out && tcp_check_sack_reneging(sk))
1794 		return;
1795 
1796 	/* C. Process data loss notification, provided it is valid. */
1797 	if ((flag&FLAG_DATA_LOST) &&
1798 	    before(tp->snd_una, tp->high_seq) &&
1799 	    icsk->icsk_ca_state != TCP_CA_Open &&
1800 	    tp->fackets_out > tp->reordering) {
1801 		tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
1802 		NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
1803 	}
1804 
1805 	/* D. Synchronize left_out to current state. */
1806 	tcp_sync_left_out(tp);
1807 
1808 	/* E. Check state exit conditions. State can be terminated
1809 	 *    when high_seq is ACKed. */
1810 	if (icsk->icsk_ca_state == TCP_CA_Open) {
1811 		if (!sysctl_tcp_frto)
1812 			BUG_TRAP(tp->retrans_out == 0);
1813 		tp->retrans_stamp = 0;
1814 	} else if (!before(tp->snd_una, tp->high_seq)) {
1815 		switch (icsk->icsk_ca_state) {
1816 		case TCP_CA_Loss:
1817 			icsk->icsk_retransmits = 0;
1818 			if (tcp_try_undo_recovery(sk, tp))
1819 				return;
1820 			break;
1821 
1822 		case TCP_CA_CWR:
1823 			/* CWR is to be held something *above* high_seq
1824 			 * is ACKed for CWR bit to reach receiver. */
1825 			if (tp->snd_una != tp->high_seq) {
1826 				tcp_complete_cwr(sk);
1827 				tcp_set_ca_state(sk, TCP_CA_Open);
1828 			}
1829 			break;
1830 
1831 		case TCP_CA_Disorder:
1832 			tcp_try_undo_dsack(sk, tp);
1833 			if (!tp->undo_marker ||
1834 			    /* For SACK case do not Open to allow to undo
1835 			     * catching for all duplicate ACKs. */
1836 			    IsReno(tp) || tp->snd_una != tp->high_seq) {
1837 				tp->undo_marker = 0;
1838 				tcp_set_ca_state(sk, TCP_CA_Open);
1839 			}
1840 			break;
1841 
1842 		case TCP_CA_Recovery:
1843 			if (IsReno(tp))
1844 				tcp_reset_reno_sack(tp);
1845 			if (tcp_try_undo_recovery(sk, tp))
1846 				return;
1847 			tcp_complete_cwr(sk);
1848 			break;
1849 		}
1850 	}
1851 
1852 	/* F. Process state. */
1853 	switch (icsk->icsk_ca_state) {
1854 	case TCP_CA_Recovery:
1855 		if (prior_snd_una == tp->snd_una) {
1856 			if (IsReno(tp) && is_dupack)
1857 				tcp_add_reno_sack(sk);
1858 		} else {
1859 			int acked = prior_packets - tp->packets_out;
1860 			if (IsReno(tp))
1861 				tcp_remove_reno_sacks(sk, tp, acked);
1862 			is_dupack = tcp_try_undo_partial(sk, tp, acked);
1863 		}
1864 		break;
1865 	case TCP_CA_Loss:
1866 		if (flag&FLAG_DATA_ACKED)
1867 			icsk->icsk_retransmits = 0;
1868 		if (!tcp_try_undo_loss(sk, tp)) {
1869 			tcp_moderate_cwnd(tp);
1870 			tcp_xmit_retransmit_queue(sk);
1871 			return;
1872 		}
1873 		if (icsk->icsk_ca_state != TCP_CA_Open)
1874 			return;
1875 		/* Loss is undone; fall through to processing in Open state. */
1876 	default:
1877 		if (IsReno(tp)) {
1878 			if (tp->snd_una != prior_snd_una)
1879 				tcp_reset_reno_sack(tp);
1880 			if (is_dupack)
1881 				tcp_add_reno_sack(sk);
1882 		}
1883 
1884 		if (icsk->icsk_ca_state == TCP_CA_Disorder)
1885 			tcp_try_undo_dsack(sk, tp);
1886 
1887 		if (!tcp_time_to_recover(sk, tp)) {
1888 			tcp_try_to_open(sk, tp, flag);
1889 			return;
1890 		}
1891 
1892 		/* Otherwise enter Recovery state */
1893 
1894 		if (IsReno(tp))
1895 			NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
1896 		else
1897 			NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
1898 
1899 		tp->high_seq = tp->snd_nxt;
1900 		tp->prior_ssthresh = 0;
1901 		tp->undo_marker = tp->snd_una;
1902 		tp->undo_retrans = tp->retrans_out;
1903 
1904 		if (icsk->icsk_ca_state < TCP_CA_CWR) {
1905 			if (!(flag&FLAG_ECE))
1906 				tp->prior_ssthresh = tcp_current_ssthresh(sk);
1907 			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1908 			TCP_ECN_queue_cwr(tp);
1909 		}
1910 
1911 		tp->snd_cwnd_cnt = 0;
1912 		tcp_set_ca_state(sk, TCP_CA_Recovery);
1913 	}
1914 
1915 	if (is_dupack || tcp_head_timedout(sk, tp))
1916 		tcp_update_scoreboard(sk, tp);
1917 	tcp_cwnd_down(sk);
1918 	tcp_xmit_retransmit_queue(sk);
1919 }
1920 
1921 /* Read draft-ietf-tcplw-high-performance before mucking
1922  * with this code. (Superceeds RFC1323)
1923  */
1924 static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
1925 {
1926 	/* RTTM Rule: A TSecr value received in a segment is used to
1927 	 * update the averaged RTT measurement only if the segment
1928 	 * acknowledges some new data, i.e., only if it advances the
1929 	 * left edge of the send window.
1930 	 *
1931 	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
1932 	 * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
1933 	 *
1934 	 * Changed: reset backoff as soon as we see the first valid sample.
1935 	 * If we do not, we get strongly overstimated rto. With timestamps
1936 	 * samples are accepted even from very old segments: f.e., when rtt=1
1937 	 * increases to 8, we retransmit 5 times and after 8 seconds delayed
1938 	 * answer arrives rto becomes 120 seconds! If at least one of segments
1939 	 * in window is lost... Voila.	 			--ANK (010210)
1940 	 */
1941 	struct tcp_sock *tp = tcp_sk(sk);
1942 	const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
1943 	tcp_rtt_estimator(sk, seq_rtt, usrtt);
1944 	tcp_set_rto(sk);
1945 	inet_csk(sk)->icsk_backoff = 0;
1946 	tcp_bound_rto(sk);
1947 }
1948 
1949 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag)
1950 {
1951 	/* We don't have a timestamp. Can only use
1952 	 * packets that are not retransmitted to determine
1953 	 * rtt estimates. Also, we must not reset the
1954 	 * backoff for rto until we get a non-retransmitted
1955 	 * packet. This allows us to deal with a situation
1956 	 * where the network delay has increased suddenly.
1957 	 * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
1958 	 */
1959 
1960 	if (flag & FLAG_RETRANS_DATA_ACKED)
1961 		return;
1962 
1963 	tcp_rtt_estimator(sk, seq_rtt, usrtt);
1964 	tcp_set_rto(sk);
1965 	inet_csk(sk)->icsk_backoff = 0;
1966 	tcp_bound_rto(sk);
1967 }
1968 
1969 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
1970 				      const s32 seq_rtt, u32 *usrtt)
1971 {
1972 	const struct tcp_sock *tp = tcp_sk(sk);
1973 	/* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
1974 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
1975 		tcp_ack_saw_tstamp(sk, usrtt, flag);
1976 	else if (seq_rtt >= 0)
1977 		tcp_ack_no_tstamp(sk, seq_rtt, usrtt, flag);
1978 }
1979 
1980 static inline void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
1981 				  u32 in_flight, int good)
1982 {
1983 	const struct inet_connection_sock *icsk = inet_csk(sk);
1984 	icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
1985 	tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
1986 }
1987 
1988 /* Restart timer after forward progress on connection.
1989  * RFC2988 recommends to restart timer to now+rto.
1990  */
1991 
1992 static inline void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
1993 {
1994 	if (!tp->packets_out) {
1995 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
1996 	} else {
1997 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
1998 	}
1999 }
2000 
2001 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
2002 			 __u32 now, __s32 *seq_rtt)
2003 {
2004 	struct tcp_sock *tp = tcp_sk(sk);
2005 	struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
2006 	__u32 seq = tp->snd_una;
2007 	__u32 packets_acked;
2008 	int acked = 0;
2009 
2010 	/* If we get here, the whole TSO packet has not been
2011 	 * acked.
2012 	 */
2013 	BUG_ON(!after(scb->end_seq, seq));
2014 
2015 	packets_acked = tcp_skb_pcount(skb);
2016 	if (tcp_trim_head(sk, skb, seq - scb->seq))
2017 		return 0;
2018 	packets_acked -= tcp_skb_pcount(skb);
2019 
2020 	if (packets_acked) {
2021 		__u8 sacked = scb->sacked;
2022 
2023 		acked |= FLAG_DATA_ACKED;
2024 		if (sacked) {
2025 			if (sacked & TCPCB_RETRANS) {
2026 				if (sacked & TCPCB_SACKED_RETRANS)
2027 					tp->retrans_out -= packets_acked;
2028 				acked |= FLAG_RETRANS_DATA_ACKED;
2029 				*seq_rtt = -1;
2030 			} else if (*seq_rtt < 0)
2031 				*seq_rtt = now - scb->when;
2032 			if (sacked & TCPCB_SACKED_ACKED)
2033 				tp->sacked_out -= packets_acked;
2034 			if (sacked & TCPCB_LOST)
2035 				tp->lost_out -= packets_acked;
2036 			if (sacked & TCPCB_URG) {
2037 				if (tp->urg_mode &&
2038 				    !before(seq, tp->snd_up))
2039 					tp->urg_mode = 0;
2040 			}
2041 		} else if (*seq_rtt < 0)
2042 			*seq_rtt = now - scb->when;
2043 
2044 		if (tp->fackets_out) {
2045 			__u32 dval = min(tp->fackets_out, packets_acked);
2046 			tp->fackets_out -= dval;
2047 		}
2048 		tp->packets_out -= packets_acked;
2049 
2050 		BUG_ON(tcp_skb_pcount(skb) == 0);
2051 		BUG_ON(!before(scb->seq, scb->end_seq));
2052 	}
2053 
2054 	return acked;
2055 }
2056 
2057 
2058 /* Remove acknowledged frames from the retransmission queue. */
2059 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt)
2060 {
2061 	struct tcp_sock *tp = tcp_sk(sk);
2062 	struct sk_buff *skb;
2063 	__u32 now = tcp_time_stamp;
2064 	int acked = 0;
2065 	__s32 seq_rtt = -1;
2066 	struct timeval usnow;
2067 	u32 pkts_acked = 0;
2068 
2069 	if (seq_usrtt)
2070 		do_gettimeofday(&usnow);
2071 
2072 	while ((skb = skb_peek(&sk->sk_write_queue)) &&
2073 	       skb != sk->sk_send_head) {
2074 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
2075 		__u8 sacked = scb->sacked;
2076 
2077 		/* If our packet is before the ack sequence we can
2078 		 * discard it as it's confirmed to have arrived at
2079 		 * the other end.
2080 		 */
2081 		if (after(scb->end_seq, tp->snd_una)) {
2082 			if (tcp_skb_pcount(skb) > 1 &&
2083 			    after(tp->snd_una, scb->seq))
2084 				acked |= tcp_tso_acked(sk, skb,
2085 						       now, &seq_rtt);
2086 			break;
2087 		}
2088 
2089 		/* Initial outgoing SYN's get put onto the write_queue
2090 		 * just like anything else we transmit.  It is not
2091 		 * true data, and if we misinform our callers that
2092 		 * this ACK acks real data, we will erroneously exit
2093 		 * connection startup slow start one packet too
2094 		 * quickly.  This is severely frowned upon behavior.
2095 		 */
2096 		if (!(scb->flags & TCPCB_FLAG_SYN)) {
2097 			acked |= FLAG_DATA_ACKED;
2098 			++pkts_acked;
2099 		} else {
2100 			acked |= FLAG_SYN_ACKED;
2101 			tp->retrans_stamp = 0;
2102 		}
2103 
2104 		if (sacked) {
2105 			if (sacked & TCPCB_RETRANS) {
2106 				if(sacked & TCPCB_SACKED_RETRANS)
2107 					tp->retrans_out -= tcp_skb_pcount(skb);
2108 				acked |= FLAG_RETRANS_DATA_ACKED;
2109 				seq_rtt = -1;
2110 			} else if (seq_rtt < 0)
2111 				seq_rtt = now - scb->when;
2112 			if (seq_usrtt) {
2113 				struct timeval tv;
2114 
2115 				skb_get_timestamp(skb, &tv);
2116 				*seq_usrtt = (usnow.tv_sec - tv.tv_sec) * 1000000
2117 					+ (usnow.tv_usec - tv.tv_usec);
2118 			}
2119 
2120 			if (sacked & TCPCB_SACKED_ACKED)
2121 				tp->sacked_out -= tcp_skb_pcount(skb);
2122 			if (sacked & TCPCB_LOST)
2123 				tp->lost_out -= tcp_skb_pcount(skb);
2124 			if (sacked & TCPCB_URG) {
2125 				if (tp->urg_mode &&
2126 				    !before(scb->end_seq, tp->snd_up))
2127 					tp->urg_mode = 0;
2128 			}
2129 		} else if (seq_rtt < 0)
2130 			seq_rtt = now - scb->when;
2131 		tcp_dec_pcount_approx(&tp->fackets_out, skb);
2132 		tcp_packets_out_dec(tp, skb);
2133 		__skb_unlink(skb, &sk->sk_write_queue);
2134 		sk_stream_free_skb(sk, skb);
2135 	}
2136 
2137 	if (acked&FLAG_ACKED) {
2138 		const struct inet_connection_sock *icsk = inet_csk(sk);
2139 		tcp_ack_update_rtt(sk, acked, seq_rtt, seq_usrtt);
2140 		tcp_ack_packets_out(sk, tp);
2141 
2142 		if (icsk->icsk_ca_ops->pkts_acked)
2143 			icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
2144 	}
2145 
2146 #if FASTRETRANS_DEBUG > 0
2147 	BUG_TRAP((int)tp->sacked_out >= 0);
2148 	BUG_TRAP((int)tp->lost_out >= 0);
2149 	BUG_TRAP((int)tp->retrans_out >= 0);
2150 	if (!tp->packets_out && tp->rx_opt.sack_ok) {
2151 		const struct inet_connection_sock *icsk = inet_csk(sk);
2152 		if (tp->lost_out) {
2153 			printk(KERN_DEBUG "Leak l=%u %d\n",
2154 			       tp->lost_out, icsk->icsk_ca_state);
2155 			tp->lost_out = 0;
2156 		}
2157 		if (tp->sacked_out) {
2158 			printk(KERN_DEBUG "Leak s=%u %d\n",
2159 			       tp->sacked_out, icsk->icsk_ca_state);
2160 			tp->sacked_out = 0;
2161 		}
2162 		if (tp->retrans_out) {
2163 			printk(KERN_DEBUG "Leak r=%u %d\n",
2164 			       tp->retrans_out, icsk->icsk_ca_state);
2165 			tp->retrans_out = 0;
2166 		}
2167 	}
2168 #endif
2169 	*seq_rtt_p = seq_rtt;
2170 	return acked;
2171 }
2172 
2173 static void tcp_ack_probe(struct sock *sk)
2174 {
2175 	const struct tcp_sock *tp = tcp_sk(sk);
2176 	struct inet_connection_sock *icsk = inet_csk(sk);
2177 
2178 	/* Was it a usable window open? */
2179 
2180 	if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
2181 		   tp->snd_una + tp->snd_wnd)) {
2182 		icsk->icsk_backoff = 0;
2183 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2184 		/* Socket must be waked up by subsequent tcp_data_snd_check().
2185 		 * This function is not for random using!
2186 		 */
2187 	} else {
2188 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2189 					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2190 					  TCP_RTO_MAX);
2191 	}
2192 }
2193 
2194 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2195 {
2196 	return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2197 		inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2198 }
2199 
2200 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2201 {
2202 	const struct tcp_sock *tp = tcp_sk(sk);
2203 	return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2204 		!((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2205 }
2206 
2207 /* Check that window update is acceptable.
2208  * The function assumes that snd_una<=ack<=snd_next.
2209  */
2210 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2211 					const u32 ack_seq, const u32 nwin)
2212 {
2213 	return (after(ack, tp->snd_una) ||
2214 		after(ack_seq, tp->snd_wl1) ||
2215 		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2216 }
2217 
2218 /* Update our send window.
2219  *
2220  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2221  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2222  */
2223 static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
2224 				 struct sk_buff *skb, u32 ack, u32 ack_seq)
2225 {
2226 	int flag = 0;
2227 	u32 nwin = ntohs(skb->h.th->window);
2228 
2229 	if (likely(!skb->h.th->syn))
2230 		nwin <<= tp->rx_opt.snd_wscale;
2231 
2232 	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2233 		flag |= FLAG_WIN_UPDATE;
2234 		tcp_update_wl(tp, ack, ack_seq);
2235 
2236 		if (tp->snd_wnd != nwin) {
2237 			tp->snd_wnd = nwin;
2238 
2239 			/* Note, it is the only place, where
2240 			 * fast path is recovered for sending TCP.
2241 			 */
2242 			tp->pred_flags = 0;
2243 			tcp_fast_path_check(sk, tp);
2244 
2245 			if (nwin > tp->max_window) {
2246 				tp->max_window = nwin;
2247 				tcp_sync_mss(sk, tp->pmtu_cookie);
2248 			}
2249 		}
2250 	}
2251 
2252 	tp->snd_una = ack;
2253 
2254 	return flag;
2255 }
2256 
2257 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
2258 {
2259 	struct tcp_sock *tp = tcp_sk(sk);
2260 
2261 	tcp_sync_left_out(tp);
2262 
2263 	if (tp->snd_una == prior_snd_una ||
2264 	    !before(tp->snd_una, tp->frto_highmark)) {
2265 		/* RTO was caused by loss, start retransmitting in
2266 		 * go-back-N slow start
2267 		 */
2268 		tcp_enter_frto_loss(sk);
2269 		return;
2270 	}
2271 
2272 	if (tp->frto_counter == 1) {
2273 		/* First ACK after RTO advances the window: allow two new
2274 		 * segments out.
2275 		 */
2276 		tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2277 	} else {
2278 		/* Also the second ACK after RTO advances the window.
2279 		 * The RTO was likely spurious. Reduce cwnd and continue
2280 		 * in congestion avoidance
2281 		 */
2282 		tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2283 		tcp_moderate_cwnd(tp);
2284 	}
2285 
2286 	/* F-RTO affects on two new ACKs following RTO.
2287 	 * At latest on third ACK the TCP behavor is back to normal.
2288 	 */
2289 	tp->frto_counter = (tp->frto_counter + 1) % 3;
2290 }
2291 
2292 /* This routine deals with incoming acks, but not outgoing ones. */
2293 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2294 {
2295 	struct inet_connection_sock *icsk = inet_csk(sk);
2296 	struct tcp_sock *tp = tcp_sk(sk);
2297 	u32 prior_snd_una = tp->snd_una;
2298 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
2299 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
2300 	u32 prior_in_flight;
2301 	s32 seq_rtt;
2302 	s32 seq_usrtt = 0;
2303 	int prior_packets;
2304 
2305 	/* If the ack is newer than sent or older than previous acks
2306 	 * then we can probably ignore it.
2307 	 */
2308 	if (after(ack, tp->snd_nxt))
2309 		goto uninteresting_ack;
2310 
2311 	if (before(ack, prior_snd_una))
2312 		goto old_ack;
2313 
2314 	if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
2315 		/* Window is constant, pure forward advance.
2316 		 * No more checks are required.
2317 		 * Note, we use the fact that SND.UNA>=SND.WL2.
2318 		 */
2319 		tcp_update_wl(tp, ack, ack_seq);
2320 		tp->snd_una = ack;
2321 		flag |= FLAG_WIN_UPDATE;
2322 
2323 		tcp_ca_event(sk, CA_EVENT_FAST_ACK);
2324 
2325 		NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
2326 	} else {
2327 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
2328 			flag |= FLAG_DATA;
2329 		else
2330 			NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
2331 
2332 		flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);
2333 
2334 		if (TCP_SKB_CB(skb)->sacked)
2335 			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2336 
2337 		if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
2338 			flag |= FLAG_ECE;
2339 
2340 		tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
2341 	}
2342 
2343 	/* We passed data and got it acked, remove any soft error
2344 	 * log. Something worked...
2345 	 */
2346 	sk->sk_err_soft = 0;
2347 	tp->rcv_tstamp = tcp_time_stamp;
2348 	prior_packets = tp->packets_out;
2349 	if (!prior_packets)
2350 		goto no_queue;
2351 
2352 	prior_in_flight = tcp_packets_in_flight(tp);
2353 
2354 	/* See if we can take anything off of the retransmit queue. */
2355 	flag |= tcp_clean_rtx_queue(sk, &seq_rtt,
2356 				    icsk->icsk_ca_ops->rtt_sample ? &seq_usrtt : NULL);
2357 
2358 	if (tp->frto_counter)
2359 		tcp_process_frto(sk, prior_snd_una);
2360 
2361 	if (tcp_ack_is_dubious(sk, flag)) {
2362 		/* Advanve CWND, if state allows this. */
2363 		if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
2364 			tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
2365 		tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2366 	} else {
2367 		if ((flag & FLAG_DATA_ACKED))
2368 			tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
2369 	}
2370 
2371 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2372 		dst_confirm(sk->sk_dst_cache);
2373 
2374 	return 1;
2375 
2376 no_queue:
2377 	icsk->icsk_probes_out = 0;
2378 
2379 	/* If this ack opens up a zero window, clear backoff.  It was
2380 	 * being used to time the probes, and is probably far higher than
2381 	 * it needs to be for normal retransmission.
2382 	 */
2383 	if (sk->sk_send_head)
2384 		tcp_ack_probe(sk);
2385 	return 1;
2386 
2387 old_ack:
2388 	if (TCP_SKB_CB(skb)->sacked)
2389 		tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2390 
2391 uninteresting_ack:
2392 	SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2393 	return 0;
2394 }
2395 
2396 
2397 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2398  * But, this can also be called on packets in the established flow when
2399  * the fast version below fails.
2400  */
2401 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2402 {
2403 	unsigned char *ptr;
2404 	struct tcphdr *th = skb->h.th;
2405 	int length=(th->doff*4)-sizeof(struct tcphdr);
2406 
2407 	ptr = (unsigned char *)(th + 1);
2408 	opt_rx->saw_tstamp = 0;
2409 
2410 	while(length>0) {
2411 	  	int opcode=*ptr++;
2412 		int opsize;
2413 
2414 		switch (opcode) {
2415 			case TCPOPT_EOL:
2416 				return;
2417 			case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
2418 				length--;
2419 				continue;
2420 			default:
2421 				opsize=*ptr++;
2422 				if (opsize < 2) /* "silly options" */
2423 					return;
2424 				if (opsize > length)
2425 					return;	/* don't parse partial options */
2426 	  			switch(opcode) {
2427 				case TCPOPT_MSS:
2428 					if(opsize==TCPOLEN_MSS && th->syn && !estab) {
2429 						u16 in_mss = ntohs(get_unaligned((__u16 *)ptr));
2430 						if (in_mss) {
2431 							if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2432 								in_mss = opt_rx->user_mss;
2433 							opt_rx->mss_clamp = in_mss;
2434 						}
2435 					}
2436 					break;
2437 				case TCPOPT_WINDOW:
2438 					if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
2439 						if (sysctl_tcp_window_scaling) {
2440 							__u8 snd_wscale = *(__u8 *) ptr;
2441 							opt_rx->wscale_ok = 1;
2442 							if (snd_wscale > 14) {
2443 								if(net_ratelimit())
2444 									printk(KERN_INFO "tcp_parse_options: Illegal window "
2445 									       "scaling value %d >14 received.\n",
2446 									       snd_wscale);
2447 								snd_wscale = 14;
2448 							}
2449 							opt_rx->snd_wscale = snd_wscale;
2450 						}
2451 					break;
2452 				case TCPOPT_TIMESTAMP:
2453 					if(opsize==TCPOLEN_TIMESTAMP) {
2454 						if ((estab && opt_rx->tstamp_ok) ||
2455 						    (!estab && sysctl_tcp_timestamps)) {
2456 							opt_rx->saw_tstamp = 1;
2457 							opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr));
2458 							opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4)));
2459 						}
2460 					}
2461 					break;
2462 				case TCPOPT_SACK_PERM:
2463 					if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2464 						if (sysctl_tcp_sack) {
2465 							opt_rx->sack_ok = 1;
2466 							tcp_sack_reset(opt_rx);
2467 						}
2468 					}
2469 					break;
2470 
2471 				case TCPOPT_SACK:
2472 					if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2473 					   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2474 					   opt_rx->sack_ok) {
2475 						TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2476 					}
2477 	  			};
2478 	  			ptr+=opsize-2;
2479 	  			length-=opsize;
2480 	  	};
2481 	}
2482 }
2483 
2484 /* Fast parse options. This hopes to only see timestamps.
2485  * If it is wrong it falls back on tcp_parse_options().
2486  */
2487 static inline int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2488 					 struct tcp_sock *tp)
2489 {
2490 	if (th->doff == sizeof(struct tcphdr)>>2) {
2491 		tp->rx_opt.saw_tstamp = 0;
2492 		return 0;
2493 	} else if (tp->rx_opt.tstamp_ok &&
2494 		   th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2495 		__u32 *ptr = (__u32 *)(th + 1);
2496 		if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2497 				  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2498 			tp->rx_opt.saw_tstamp = 1;
2499 			++ptr;
2500 			tp->rx_opt.rcv_tsval = ntohl(*ptr);
2501 			++ptr;
2502 			tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2503 			return 1;
2504 		}
2505 	}
2506 	tcp_parse_options(skb, &tp->rx_opt, 1);
2507 	return 1;
2508 }
2509 
2510 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2511 {
2512 	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2513 	tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
2514 }
2515 
2516 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2517 {
2518 	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2519 		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
2520 		 * extra check below makes sure this can only happen
2521 		 * for pure ACK frames.  -DaveM
2522 		 *
2523 		 * Not only, also it occurs for expired timestamps.
2524 		 */
2525 
2526 		if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2527 		   xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2528 			tcp_store_ts_recent(tp);
2529 	}
2530 }
2531 
2532 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2533  *
2534  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2535  * it can pass through stack. So, the following predicate verifies that
2536  * this segment is not used for anything but congestion avoidance or
2537  * fast retransmit. Moreover, we even are able to eliminate most of such
2538  * second order effects, if we apply some small "replay" window (~RTO)
2539  * to timestamp space.
2540  *
2541  * All these measures still do not guarantee that we reject wrapped ACKs
2542  * on networks with high bandwidth, when sequence space is recycled fastly,
2543  * but it guarantees that such events will be very rare and do not affect
2544  * connection seriously. This doesn't look nice, but alas, PAWS is really
2545  * buggy extension.
2546  *
2547  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
2548  * states that events when retransmit arrives after original data are rare.
2549  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
2550  * the biggest problem on large power networks even with minor reordering.
2551  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
2552  * up to bandwidth of 18Gigabit/sec. 8) ]
2553  */
2554 
2555 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
2556 {
2557 	struct tcp_sock *tp = tcp_sk(sk);
2558 	struct tcphdr *th = skb->h.th;
2559 	u32 seq = TCP_SKB_CB(skb)->seq;
2560 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
2561 
2562 	return (/* 1. Pure ACK with correct sequence number. */
2563 		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
2564 
2565 		/* 2. ... and duplicate ACK. */
2566 		ack == tp->snd_una &&
2567 
2568 		/* 3. ... and does not update window. */
2569 		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
2570 
2571 		/* 4. ... and sits in replay window. */
2572 		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
2573 }
2574 
2575 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
2576 {
2577 	const struct tcp_sock *tp = tcp_sk(sk);
2578 	return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
2579 		xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2580 		!tcp_disordered_ack(sk, skb));
2581 }
2582 
2583 /* Check segment sequence number for validity.
2584  *
2585  * Segment controls are considered valid, if the segment
2586  * fits to the window after truncation to the window. Acceptability
2587  * of data (and SYN, FIN, of course) is checked separately.
2588  * See tcp_data_queue(), for example.
2589  *
2590  * Also, controls (RST is main one) are accepted using RCV.WUP instead
2591  * of RCV.NXT. Peer still did not advance his SND.UNA when we
2592  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
2593  * (borrowed from freebsd)
2594  */
2595 
2596 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
2597 {
2598 	return	!before(end_seq, tp->rcv_wup) &&
2599 		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
2600 }
2601 
2602 /* When we get a reset we do this. */
2603 static void tcp_reset(struct sock *sk)
2604 {
2605 	/* We want the right error as BSD sees it (and indeed as we do). */
2606 	switch (sk->sk_state) {
2607 		case TCP_SYN_SENT:
2608 			sk->sk_err = ECONNREFUSED;
2609 			break;
2610 		case TCP_CLOSE_WAIT:
2611 			sk->sk_err = EPIPE;
2612 			break;
2613 		case TCP_CLOSE:
2614 			return;
2615 		default:
2616 			sk->sk_err = ECONNRESET;
2617 	}
2618 
2619 	if (!sock_flag(sk, SOCK_DEAD))
2620 		sk->sk_error_report(sk);
2621 
2622 	tcp_done(sk);
2623 }
2624 
2625 /*
2626  * 	Process the FIN bit. This now behaves as it is supposed to work
2627  *	and the FIN takes effect when it is validly part of sequence
2628  *	space. Not before when we get holes.
2629  *
2630  *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
2631  *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
2632  *	TIME-WAIT)
2633  *
2634  *	If we are in FINWAIT-1, a received FIN indicates simultaneous
2635  *	close and we go into CLOSING (and later onto TIME-WAIT)
2636  *
2637  *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
2638  */
2639 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
2640 {
2641 	struct tcp_sock *tp = tcp_sk(sk);
2642 
2643 	inet_csk_schedule_ack(sk);
2644 
2645 	sk->sk_shutdown |= RCV_SHUTDOWN;
2646 	sock_set_flag(sk, SOCK_DONE);
2647 
2648 	switch (sk->sk_state) {
2649 		case TCP_SYN_RECV:
2650 		case TCP_ESTABLISHED:
2651 			/* Move to CLOSE_WAIT */
2652 			tcp_set_state(sk, TCP_CLOSE_WAIT);
2653 			inet_csk(sk)->icsk_ack.pingpong = 1;
2654 			break;
2655 
2656 		case TCP_CLOSE_WAIT:
2657 		case TCP_CLOSING:
2658 			/* Received a retransmission of the FIN, do
2659 			 * nothing.
2660 			 */
2661 			break;
2662 		case TCP_LAST_ACK:
2663 			/* RFC793: Remain in the LAST-ACK state. */
2664 			break;
2665 
2666 		case TCP_FIN_WAIT1:
2667 			/* This case occurs when a simultaneous close
2668 			 * happens, we must ack the received FIN and
2669 			 * enter the CLOSING state.
2670 			 */
2671 			tcp_send_ack(sk);
2672 			tcp_set_state(sk, TCP_CLOSING);
2673 			break;
2674 		case TCP_FIN_WAIT2:
2675 			/* Received a FIN -- send ACK and enter TIME_WAIT. */
2676 			tcp_send_ack(sk);
2677 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
2678 			break;
2679 		default:
2680 			/* Only TCP_LISTEN and TCP_CLOSE are left, in these
2681 			 * cases we should never reach this piece of code.
2682 			 */
2683 			printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
2684 			       __FUNCTION__, sk->sk_state);
2685 			break;
2686 	};
2687 
2688 	/* It _is_ possible, that we have something out-of-order _after_ FIN.
2689 	 * Probably, we should reset in this case. For now drop them.
2690 	 */
2691 	__skb_queue_purge(&tp->out_of_order_queue);
2692 	if (tp->rx_opt.sack_ok)
2693 		tcp_sack_reset(&tp->rx_opt);
2694 	sk_stream_mem_reclaim(sk);
2695 
2696 	if (!sock_flag(sk, SOCK_DEAD)) {
2697 		sk->sk_state_change(sk);
2698 
2699 		/* Do not send POLL_HUP for half duplex close. */
2700 		if (sk->sk_shutdown == SHUTDOWN_MASK ||
2701 		    sk->sk_state == TCP_CLOSE)
2702 			sk_wake_async(sk, 1, POLL_HUP);
2703 		else
2704 			sk_wake_async(sk, 1, POLL_IN);
2705 	}
2706 }
2707 
2708 static __inline__ int
2709 tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
2710 {
2711 	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
2712 		if (before(seq, sp->start_seq))
2713 			sp->start_seq = seq;
2714 		if (after(end_seq, sp->end_seq))
2715 			sp->end_seq = end_seq;
2716 		return 1;
2717 	}
2718 	return 0;
2719 }
2720 
2721 static inline void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
2722 {
2723 	if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2724 		if (before(seq, tp->rcv_nxt))
2725 			NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
2726 		else
2727 			NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
2728 
2729 		tp->rx_opt.dsack = 1;
2730 		tp->duplicate_sack[0].start_seq = seq;
2731 		tp->duplicate_sack[0].end_seq = end_seq;
2732 		tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
2733 	}
2734 }
2735 
2736 static inline void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
2737 {
2738 	if (!tp->rx_opt.dsack)
2739 		tcp_dsack_set(tp, seq, end_seq);
2740 	else
2741 		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
2742 }
2743 
2744 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
2745 {
2746 	struct tcp_sock *tp = tcp_sk(sk);
2747 
2748 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
2749 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2750 		NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2751 		tcp_enter_quickack_mode(sk);
2752 
2753 		if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2754 			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2755 
2756 			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
2757 				end_seq = tp->rcv_nxt;
2758 			tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
2759 		}
2760 	}
2761 
2762 	tcp_send_ack(sk);
2763 }
2764 
2765 /* These routines update the SACK block as out-of-order packets arrive or
2766  * in-order packets close up the sequence space.
2767  */
2768 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
2769 {
2770 	int this_sack;
2771 	struct tcp_sack_block *sp = &tp->selective_acks[0];
2772 	struct tcp_sack_block *swalk = sp+1;
2773 
2774 	/* See if the recent change to the first SACK eats into
2775 	 * or hits the sequence space of other SACK blocks, if so coalesce.
2776 	 */
2777 	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
2778 		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
2779 			int i;
2780 
2781 			/* Zap SWALK, by moving every further SACK up by one slot.
2782 			 * Decrease num_sacks.
2783 			 */
2784 			tp->rx_opt.num_sacks--;
2785 			tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2786 			for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
2787 				sp[i] = sp[i+1];
2788 			continue;
2789 		}
2790 		this_sack++, swalk++;
2791 	}
2792 }
2793 
2794 static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
2795 {
2796 	__u32 tmp;
2797 
2798 	tmp = sack1->start_seq;
2799 	sack1->start_seq = sack2->start_seq;
2800 	sack2->start_seq = tmp;
2801 
2802 	tmp = sack1->end_seq;
2803 	sack1->end_seq = sack2->end_seq;
2804 	sack2->end_seq = tmp;
2805 }
2806 
2807 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
2808 {
2809 	struct tcp_sock *tp = tcp_sk(sk);
2810 	struct tcp_sack_block *sp = &tp->selective_acks[0];
2811 	int cur_sacks = tp->rx_opt.num_sacks;
2812 	int this_sack;
2813 
2814 	if (!cur_sacks)
2815 		goto new_sack;
2816 
2817 	for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
2818 		if (tcp_sack_extend(sp, seq, end_seq)) {
2819 			/* Rotate this_sack to the first one. */
2820 			for (; this_sack>0; this_sack--, sp--)
2821 				tcp_sack_swap(sp, sp-1);
2822 			if (cur_sacks > 1)
2823 				tcp_sack_maybe_coalesce(tp);
2824 			return;
2825 		}
2826 	}
2827 
2828 	/* Could not find an adjacent existing SACK, build a new one,
2829 	 * put it at the front, and shift everyone else down.  We
2830 	 * always know there is at least one SACK present already here.
2831 	 *
2832 	 * If the sack array is full, forget about the last one.
2833 	 */
2834 	if (this_sack >= 4) {
2835 		this_sack--;
2836 		tp->rx_opt.num_sacks--;
2837 		sp--;
2838 	}
2839 	for(; this_sack > 0; this_sack--, sp--)
2840 		*sp = *(sp-1);
2841 
2842 new_sack:
2843 	/* Build the new head SACK, and we're done. */
2844 	sp->start_seq = seq;
2845 	sp->end_seq = end_seq;
2846 	tp->rx_opt.num_sacks++;
2847 	tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2848 }
2849 
2850 /* RCV.NXT advances, some SACKs should be eaten. */
2851 
2852 static void tcp_sack_remove(struct tcp_sock *tp)
2853 {
2854 	struct tcp_sack_block *sp = &tp->selective_acks[0];
2855 	int num_sacks = tp->rx_opt.num_sacks;
2856 	int this_sack;
2857 
2858 	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
2859 	if (skb_queue_empty(&tp->out_of_order_queue)) {
2860 		tp->rx_opt.num_sacks = 0;
2861 		tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
2862 		return;
2863 	}
2864 
2865 	for(this_sack = 0; this_sack < num_sacks; ) {
2866 		/* Check if the start of the sack is covered by RCV.NXT. */
2867 		if (!before(tp->rcv_nxt, sp->start_seq)) {
2868 			int i;
2869 
2870 			/* RCV.NXT must cover all the block! */
2871 			BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
2872 
2873 			/* Zap this SACK, by moving forward any other SACKS. */
2874 			for (i=this_sack+1; i < num_sacks; i++)
2875 				tp->selective_acks[i-1] = tp->selective_acks[i];
2876 			num_sacks--;
2877 			continue;
2878 		}
2879 		this_sack++;
2880 		sp++;
2881 	}
2882 	if (num_sacks != tp->rx_opt.num_sacks) {
2883 		tp->rx_opt.num_sacks = num_sacks;
2884 		tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2885 	}
2886 }
2887 
2888 /* This one checks to see if we can put data from the
2889  * out_of_order queue into the receive_queue.
2890  */
2891 static void tcp_ofo_queue(struct sock *sk)
2892 {
2893 	struct tcp_sock *tp = tcp_sk(sk);
2894 	__u32 dsack_high = tp->rcv_nxt;
2895 	struct sk_buff *skb;
2896 
2897 	while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
2898 		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
2899 			break;
2900 
2901 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
2902 			__u32 dsack = dsack_high;
2903 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
2904 				dsack_high = TCP_SKB_CB(skb)->end_seq;
2905 			tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
2906 		}
2907 
2908 		if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
2909 			SOCK_DEBUG(sk, "ofo packet was already received \n");
2910 			__skb_unlink(skb, &tp->out_of_order_queue);
2911 			__kfree_skb(skb);
2912 			continue;
2913 		}
2914 		SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
2915 			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
2916 			   TCP_SKB_CB(skb)->end_seq);
2917 
2918 		__skb_unlink(skb, &tp->out_of_order_queue);
2919 		__skb_queue_tail(&sk->sk_receive_queue, skb);
2920 		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2921 		if(skb->h.th->fin)
2922 			tcp_fin(skb, sk, skb->h.th);
2923 	}
2924 }
2925 
2926 static int tcp_prune_queue(struct sock *sk);
2927 
2928 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
2929 {
2930 	struct tcphdr *th = skb->h.th;
2931 	struct tcp_sock *tp = tcp_sk(sk);
2932 	int eaten = -1;
2933 
2934 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
2935 		goto drop;
2936 
2937 	__skb_pull(skb, th->doff*4);
2938 
2939 	TCP_ECN_accept_cwr(tp, skb);
2940 
2941 	if (tp->rx_opt.dsack) {
2942 		tp->rx_opt.dsack = 0;
2943 		tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
2944 						    4 - tp->rx_opt.tstamp_ok);
2945 	}
2946 
2947 	/*  Queue data for delivery to the user.
2948 	 *  Packets in sequence go to the receive queue.
2949 	 *  Out of sequence packets to the out_of_order_queue.
2950 	 */
2951 	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
2952 		if (tcp_receive_window(tp) == 0)
2953 			goto out_of_window;
2954 
2955 		/* Ok. In sequence. In window. */
2956 		if (tp->ucopy.task == current &&
2957 		    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
2958 		    sock_owned_by_user(sk) && !tp->urg_data) {
2959 			int chunk = min_t(unsigned int, skb->len,
2960 							tp->ucopy.len);
2961 
2962 			__set_current_state(TASK_RUNNING);
2963 
2964 			local_bh_enable();
2965 			if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
2966 				tp->ucopy.len -= chunk;
2967 				tp->copied_seq += chunk;
2968 				eaten = (chunk == skb->len && !th->fin);
2969 				tcp_rcv_space_adjust(sk);
2970 			}
2971 			local_bh_disable();
2972 		}
2973 
2974 		if (eaten <= 0) {
2975 queue_and_out:
2976 			if (eaten < 0 &&
2977 			    (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
2978 			     !sk_stream_rmem_schedule(sk, skb))) {
2979 				if (tcp_prune_queue(sk) < 0 ||
2980 				    !sk_stream_rmem_schedule(sk, skb))
2981 					goto drop;
2982 			}
2983 			sk_stream_set_owner_r(skb, sk);
2984 			__skb_queue_tail(&sk->sk_receive_queue, skb);
2985 		}
2986 		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2987 		if(skb->len)
2988 			tcp_event_data_recv(sk, tp, skb);
2989 		if(th->fin)
2990 			tcp_fin(skb, sk, th);
2991 
2992 		if (!skb_queue_empty(&tp->out_of_order_queue)) {
2993 			tcp_ofo_queue(sk);
2994 
2995 			/* RFC2581. 4.2. SHOULD send immediate ACK, when
2996 			 * gap in queue is filled.
2997 			 */
2998 			if (skb_queue_empty(&tp->out_of_order_queue))
2999 				inet_csk(sk)->icsk_ack.pingpong = 0;
3000 		}
3001 
3002 		if (tp->rx_opt.num_sacks)
3003 			tcp_sack_remove(tp);
3004 
3005 		tcp_fast_path_check(sk, tp);
3006 
3007 		if (eaten > 0)
3008 			__kfree_skb(skb);
3009 		else if (!sock_flag(sk, SOCK_DEAD))
3010 			sk->sk_data_ready(sk, 0);
3011 		return;
3012 	}
3013 
3014 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3015 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
3016 		NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3017 		tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3018 
3019 out_of_window:
3020 		tcp_enter_quickack_mode(sk);
3021 		inet_csk_schedule_ack(sk);
3022 drop:
3023 		__kfree_skb(skb);
3024 		return;
3025 	}
3026 
3027 	/* Out of window. F.e. zero window probe. */
3028 	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3029 		goto out_of_window;
3030 
3031 	tcp_enter_quickack_mode(sk);
3032 
3033 	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3034 		/* Partial packet, seq < rcv_next < end_seq */
3035 		SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3036 			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3037 			   TCP_SKB_CB(skb)->end_seq);
3038 
3039 		tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3040 
3041 		/* If window is closed, drop tail of packet. But after
3042 		 * remembering D-SACK for its head made in previous line.
3043 		 */
3044 		if (!tcp_receive_window(tp))
3045 			goto out_of_window;
3046 		goto queue_and_out;
3047 	}
3048 
3049 	TCP_ECN_check_ce(tp, skb);
3050 
3051 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3052 	    !sk_stream_rmem_schedule(sk, skb)) {
3053 		if (tcp_prune_queue(sk) < 0 ||
3054 		    !sk_stream_rmem_schedule(sk, skb))
3055 			goto drop;
3056 	}
3057 
3058 	/* Disable header prediction. */
3059 	tp->pred_flags = 0;
3060 	inet_csk_schedule_ack(sk);
3061 
3062 	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3063 		   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3064 
3065 	sk_stream_set_owner_r(skb, sk);
3066 
3067 	if (!skb_peek(&tp->out_of_order_queue)) {
3068 		/* Initial out of order segment, build 1 SACK. */
3069 		if (tp->rx_opt.sack_ok) {
3070 			tp->rx_opt.num_sacks = 1;
3071 			tp->rx_opt.dsack     = 0;
3072 			tp->rx_opt.eff_sacks = 1;
3073 			tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3074 			tp->selective_acks[0].end_seq =
3075 						TCP_SKB_CB(skb)->end_seq;
3076 		}
3077 		__skb_queue_head(&tp->out_of_order_queue,skb);
3078 	} else {
3079 		struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3080 		u32 seq = TCP_SKB_CB(skb)->seq;
3081 		u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3082 
3083 		if (seq == TCP_SKB_CB(skb1)->end_seq) {
3084 			__skb_append(skb1, skb, &tp->out_of_order_queue);
3085 
3086 			if (!tp->rx_opt.num_sacks ||
3087 			    tp->selective_acks[0].end_seq != seq)
3088 				goto add_sack;
3089 
3090 			/* Common case: data arrive in order after hole. */
3091 			tp->selective_acks[0].end_seq = end_seq;
3092 			return;
3093 		}
3094 
3095 		/* Find place to insert this segment. */
3096 		do {
3097 			if (!after(TCP_SKB_CB(skb1)->seq, seq))
3098 				break;
3099 		} while ((skb1 = skb1->prev) !=
3100 			 (struct sk_buff*)&tp->out_of_order_queue);
3101 
3102 		/* Do skb overlap to previous one? */
3103 		if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3104 		    before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3105 			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3106 				/* All the bits are present. Drop. */
3107 				__kfree_skb(skb);
3108 				tcp_dsack_set(tp, seq, end_seq);
3109 				goto add_sack;
3110 			}
3111 			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3112 				/* Partial overlap. */
3113 				tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3114 			} else {
3115 				skb1 = skb1->prev;
3116 			}
3117 		}
3118 		__skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3119 
3120 		/* And clean segments covered by new one as whole. */
3121 		while ((skb1 = skb->next) !=
3122 		       (struct sk_buff*)&tp->out_of_order_queue &&
3123 		       after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3124 		       if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3125 			       tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3126 			       break;
3127 		       }
3128 		       __skb_unlink(skb1, &tp->out_of_order_queue);
3129 		       tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3130 		       __kfree_skb(skb1);
3131 		}
3132 
3133 add_sack:
3134 		if (tp->rx_opt.sack_ok)
3135 			tcp_sack_new_ofo_skb(sk, seq, end_seq);
3136 	}
3137 }
3138 
3139 /* Collapse contiguous sequence of skbs head..tail with
3140  * sequence numbers start..end.
3141  * Segments with FIN/SYN are not collapsed (only because this
3142  * simplifies code)
3143  */
3144 static void
3145 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3146 	     struct sk_buff *head, struct sk_buff *tail,
3147 	     u32 start, u32 end)
3148 {
3149 	struct sk_buff *skb;
3150 
3151 	/* First, check that queue is collapsable and find
3152 	 * the point where collapsing can be useful. */
3153 	for (skb = head; skb != tail; ) {
3154 		/* No new bits? It is possible on ofo queue. */
3155 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3156 			struct sk_buff *next = skb->next;
3157 			__skb_unlink(skb, list);
3158 			__kfree_skb(skb);
3159 			NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3160 			skb = next;
3161 			continue;
3162 		}
3163 
3164 		/* The first skb to collapse is:
3165 		 * - not SYN/FIN and
3166 		 * - bloated or contains data before "start" or
3167 		 *   overlaps to the next one.
3168 		 */
3169 		if (!skb->h.th->syn && !skb->h.th->fin &&
3170 		    (tcp_win_from_space(skb->truesize) > skb->len ||
3171 		     before(TCP_SKB_CB(skb)->seq, start) ||
3172 		     (skb->next != tail &&
3173 		      TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3174 			break;
3175 
3176 		/* Decided to skip this, advance start seq. */
3177 		start = TCP_SKB_CB(skb)->end_seq;
3178 		skb = skb->next;
3179 	}
3180 	if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3181 		return;
3182 
3183 	while (before(start, end)) {
3184 		struct sk_buff *nskb;
3185 		int header = skb_headroom(skb);
3186 		int copy = SKB_MAX_ORDER(header, 0);
3187 
3188 		/* Too big header? This can happen with IPv6. */
3189 		if (copy < 0)
3190 			return;
3191 		if (end-start < copy)
3192 			copy = end-start;
3193 		nskb = alloc_skb(copy+header, GFP_ATOMIC);
3194 		if (!nskb)
3195 			return;
3196 		skb_reserve(nskb, header);
3197 		memcpy(nskb->head, skb->head, header);
3198 		nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head);
3199 		nskb->h.raw = nskb->head + (skb->h.raw-skb->head);
3200 		nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head);
3201 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3202 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3203 		__skb_insert(nskb, skb->prev, skb, list);
3204 		sk_stream_set_owner_r(nskb, sk);
3205 
3206 		/* Copy data, releasing collapsed skbs. */
3207 		while (copy > 0) {
3208 			int offset = start - TCP_SKB_CB(skb)->seq;
3209 			int size = TCP_SKB_CB(skb)->end_seq - start;
3210 
3211 			if (offset < 0) BUG();
3212 			if (size > 0) {
3213 				size = min(copy, size);
3214 				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3215 					BUG();
3216 				TCP_SKB_CB(nskb)->end_seq += size;
3217 				copy -= size;
3218 				start += size;
3219 			}
3220 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3221 				struct sk_buff *next = skb->next;
3222 				__skb_unlink(skb, list);
3223 				__kfree_skb(skb);
3224 				NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3225 				skb = next;
3226 				if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3227 					return;
3228 			}
3229 		}
3230 	}
3231 }
3232 
3233 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3234  * and tcp_collapse() them until all the queue is collapsed.
3235  */
3236 static void tcp_collapse_ofo_queue(struct sock *sk)
3237 {
3238 	struct tcp_sock *tp = tcp_sk(sk);
3239 	struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3240 	struct sk_buff *head;
3241 	u32 start, end;
3242 
3243 	if (skb == NULL)
3244 		return;
3245 
3246 	start = TCP_SKB_CB(skb)->seq;
3247 	end = TCP_SKB_CB(skb)->end_seq;
3248 	head = skb;
3249 
3250 	for (;;) {
3251 		skb = skb->next;
3252 
3253 		/* Segment is terminated when we see gap or when
3254 		 * we are at the end of all the queue. */
3255 		if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
3256 		    after(TCP_SKB_CB(skb)->seq, end) ||
3257 		    before(TCP_SKB_CB(skb)->end_seq, start)) {
3258 			tcp_collapse(sk, &tp->out_of_order_queue,
3259 				     head, skb, start, end);
3260 			head = skb;
3261 			if (skb == (struct sk_buff *)&tp->out_of_order_queue)
3262 				break;
3263 			/* Start new segment */
3264 			start = TCP_SKB_CB(skb)->seq;
3265 			end = TCP_SKB_CB(skb)->end_seq;
3266 		} else {
3267 			if (before(TCP_SKB_CB(skb)->seq, start))
3268 				start = TCP_SKB_CB(skb)->seq;
3269 			if (after(TCP_SKB_CB(skb)->end_seq, end))
3270 				end = TCP_SKB_CB(skb)->end_seq;
3271 		}
3272 	}
3273 }
3274 
3275 /* Reduce allocated memory if we can, trying to get
3276  * the socket within its memory limits again.
3277  *
3278  * Return less than zero if we should start dropping frames
3279  * until the socket owning process reads some of the data
3280  * to stabilize the situation.
3281  */
3282 static int tcp_prune_queue(struct sock *sk)
3283 {
3284 	struct tcp_sock *tp = tcp_sk(sk);
3285 
3286 	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
3287 
3288 	NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
3289 
3290 	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
3291 		tcp_clamp_window(sk, tp);
3292 	else if (tcp_memory_pressure)
3293 		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
3294 
3295 	tcp_collapse_ofo_queue(sk);
3296 	tcp_collapse(sk, &sk->sk_receive_queue,
3297 		     sk->sk_receive_queue.next,
3298 		     (struct sk_buff*)&sk->sk_receive_queue,
3299 		     tp->copied_seq, tp->rcv_nxt);
3300 	sk_stream_mem_reclaim(sk);
3301 
3302 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3303 		return 0;
3304 
3305 	/* Collapsing did not help, destructive actions follow.
3306 	 * This must not ever occur. */
3307 
3308 	/* First, purge the out_of_order queue. */
3309 	if (!skb_queue_empty(&tp->out_of_order_queue)) {
3310 		NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
3311 		__skb_queue_purge(&tp->out_of_order_queue);
3312 
3313 		/* Reset SACK state.  A conforming SACK implementation will
3314 		 * do the same at a timeout based retransmit.  When a connection
3315 		 * is in a sad state like this, we care only about integrity
3316 		 * of the connection not performance.
3317 		 */
3318 		if (tp->rx_opt.sack_ok)
3319 			tcp_sack_reset(&tp->rx_opt);
3320 		sk_stream_mem_reclaim(sk);
3321 	}
3322 
3323 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3324 		return 0;
3325 
3326 	/* If we are really being abused, tell the caller to silently
3327 	 * drop receive data on the floor.  It will get retransmitted
3328 	 * and hopefully then we'll have sufficient space.
3329 	 */
3330 	NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
3331 
3332 	/* Massive buffer overcommit. */
3333 	tp->pred_flags = 0;
3334 	return -1;
3335 }
3336 
3337 
3338 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
3339  * As additional protections, we do not touch cwnd in retransmission phases,
3340  * and if application hit its sndbuf limit recently.
3341  */
3342 void tcp_cwnd_application_limited(struct sock *sk)
3343 {
3344 	struct tcp_sock *tp = tcp_sk(sk);
3345 
3346 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
3347 	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
3348 		/* Limited by application or receiver window. */
3349 		u32 win_used = max(tp->snd_cwnd_used, 2U);
3350 		if (win_used < tp->snd_cwnd) {
3351 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
3352 			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
3353 		}
3354 		tp->snd_cwnd_used = 0;
3355 	}
3356 	tp->snd_cwnd_stamp = tcp_time_stamp;
3357 }
3358 
3359 static inline int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp)
3360 {
3361 	/* If the user specified a specific send buffer setting, do
3362 	 * not modify it.
3363 	 */
3364 	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
3365 		return 0;
3366 
3367 	/* If we are under global TCP memory pressure, do not expand.  */
3368 	if (tcp_memory_pressure)
3369 		return 0;
3370 
3371 	/* If we are under soft global TCP memory pressure, do not expand.  */
3372 	if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
3373 		return 0;
3374 
3375 	/* If we filled the congestion window, do not expand.  */
3376 	if (tp->packets_out >= tp->snd_cwnd)
3377 		return 0;
3378 
3379 	return 1;
3380 }
3381 
3382 /* When incoming ACK allowed to free some skb from write_queue,
3383  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
3384  * on the exit from tcp input handler.
3385  *
3386  * PROBLEM: sndbuf expansion does not work well with largesend.
3387  */
3388 static void tcp_new_space(struct sock *sk)
3389 {
3390 	struct tcp_sock *tp = tcp_sk(sk);
3391 
3392 	if (tcp_should_expand_sndbuf(sk, tp)) {
3393  		int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
3394 			MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
3395 		    demanded = max_t(unsigned int, tp->snd_cwnd,
3396 						   tp->reordering + 1);
3397 		sndmem *= 2*demanded;
3398 		if (sndmem > sk->sk_sndbuf)
3399 			sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
3400 		tp->snd_cwnd_stamp = tcp_time_stamp;
3401 	}
3402 
3403 	sk->sk_write_space(sk);
3404 }
3405 
3406 static inline void tcp_check_space(struct sock *sk)
3407 {
3408 	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
3409 		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
3410 		if (sk->sk_socket &&
3411 		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
3412 			tcp_new_space(sk);
3413 	}
3414 }
3415 
3416 static __inline__ void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
3417 {
3418 	tcp_push_pending_frames(sk, tp);
3419 	tcp_check_space(sk);
3420 }
3421 
3422 /*
3423  * Check if sending an ack is needed.
3424  */
3425 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
3426 {
3427 	struct tcp_sock *tp = tcp_sk(sk);
3428 
3429 	    /* More than one full frame received... */
3430 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
3431 	     /* ... and right edge of window advances far enough.
3432 	      * (tcp_recvmsg() will send ACK otherwise). Or...
3433 	      */
3434 	     && __tcp_select_window(sk) >= tp->rcv_wnd) ||
3435 	    /* We ACK each frame or... */
3436 	    tcp_in_quickack_mode(sk) ||
3437 	    /* We have out of order data. */
3438 	    (ofo_possible &&
3439 	     skb_peek(&tp->out_of_order_queue))) {
3440 		/* Then ack it now */
3441 		tcp_send_ack(sk);
3442 	} else {
3443 		/* Else, send delayed ack. */
3444 		tcp_send_delayed_ack(sk);
3445 	}
3446 }
3447 
3448 static __inline__ void tcp_ack_snd_check(struct sock *sk)
3449 {
3450 	if (!inet_csk_ack_scheduled(sk)) {
3451 		/* We sent a data segment already. */
3452 		return;
3453 	}
3454 	__tcp_ack_snd_check(sk, 1);
3455 }
3456 
3457 /*
3458  *	This routine is only called when we have urgent data
3459  *	signalled. Its the 'slow' part of tcp_urg. It could be
3460  *	moved inline now as tcp_urg is only called from one
3461  *	place. We handle URGent data wrong. We have to - as
3462  *	BSD still doesn't use the correction from RFC961.
3463  *	For 1003.1g we should support a new option TCP_STDURG to permit
3464  *	either form (or just set the sysctl tcp_stdurg).
3465  */
3466 
3467 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
3468 {
3469 	struct tcp_sock *tp = tcp_sk(sk);
3470 	u32 ptr = ntohs(th->urg_ptr);
3471 
3472 	if (ptr && !sysctl_tcp_stdurg)
3473 		ptr--;
3474 	ptr += ntohl(th->seq);
3475 
3476 	/* Ignore urgent data that we've already seen and read. */
3477 	if (after(tp->copied_seq, ptr))
3478 		return;
3479 
3480 	/* Do not replay urg ptr.
3481 	 *
3482 	 * NOTE: interesting situation not covered by specs.
3483 	 * Misbehaving sender may send urg ptr, pointing to segment,
3484 	 * which we already have in ofo queue. We are not able to fetch
3485 	 * such data and will stay in TCP_URG_NOTYET until will be eaten
3486 	 * by recvmsg(). Seems, we are not obliged to handle such wicked
3487 	 * situations. But it is worth to think about possibility of some
3488 	 * DoSes using some hypothetical application level deadlock.
3489 	 */
3490 	if (before(ptr, tp->rcv_nxt))
3491 		return;
3492 
3493 	/* Do we already have a newer (or duplicate) urgent pointer? */
3494 	if (tp->urg_data && !after(ptr, tp->urg_seq))
3495 		return;
3496 
3497 	/* Tell the world about our new urgent pointer. */
3498 	sk_send_sigurg(sk);
3499 
3500 	/* We may be adding urgent data when the last byte read was
3501 	 * urgent. To do this requires some care. We cannot just ignore
3502 	 * tp->copied_seq since we would read the last urgent byte again
3503 	 * as data, nor can we alter copied_seq until this data arrives
3504 	 * or we break the sematics of SIOCATMARK (and thus sockatmark())
3505 	 *
3506 	 * NOTE. Double Dutch. Rendering to plain English: author of comment
3507 	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
3508 	 * and expect that both A and B disappear from stream. This is _wrong_.
3509 	 * Though this happens in BSD with high probability, this is occasional.
3510 	 * Any application relying on this is buggy. Note also, that fix "works"
3511 	 * only in this artificial test. Insert some normal data between A and B and we will
3512 	 * decline of BSD again. Verdict: it is better to remove to trap
3513 	 * buggy users.
3514 	 */
3515 	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
3516 	    !sock_flag(sk, SOCK_URGINLINE) &&
3517 	    tp->copied_seq != tp->rcv_nxt) {
3518 		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
3519 		tp->copied_seq++;
3520 		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
3521 			__skb_unlink(skb, &sk->sk_receive_queue);
3522 			__kfree_skb(skb);
3523 		}
3524 	}
3525 
3526 	tp->urg_data   = TCP_URG_NOTYET;
3527 	tp->urg_seq    = ptr;
3528 
3529 	/* Disable header prediction. */
3530 	tp->pred_flags = 0;
3531 }
3532 
3533 /* This is the 'fast' part of urgent handling. */
3534 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
3535 {
3536 	struct tcp_sock *tp = tcp_sk(sk);
3537 
3538 	/* Check if we get a new urgent pointer - normally not. */
3539 	if (th->urg)
3540 		tcp_check_urg(sk,th);
3541 
3542 	/* Do we wait for any urgent data? - normally not... */
3543 	if (tp->urg_data == TCP_URG_NOTYET) {
3544 		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
3545 			  th->syn;
3546 
3547 		/* Is the urgent pointer pointing into this packet? */
3548 		if (ptr < skb->len) {
3549 			u8 tmp;
3550 			if (skb_copy_bits(skb, ptr, &tmp, 1))
3551 				BUG();
3552 			tp->urg_data = TCP_URG_VALID | tmp;
3553 			if (!sock_flag(sk, SOCK_DEAD))
3554 				sk->sk_data_ready(sk, 0);
3555 		}
3556 	}
3557 }
3558 
3559 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
3560 {
3561 	struct tcp_sock *tp = tcp_sk(sk);
3562 	int chunk = skb->len - hlen;
3563 	int err;
3564 
3565 	local_bh_enable();
3566 	if (skb->ip_summed==CHECKSUM_UNNECESSARY)
3567 		err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
3568 	else
3569 		err = skb_copy_and_csum_datagram_iovec(skb, hlen,
3570 						       tp->ucopy.iov);
3571 
3572 	if (!err) {
3573 		tp->ucopy.len -= chunk;
3574 		tp->copied_seq += chunk;
3575 		tcp_rcv_space_adjust(sk);
3576 	}
3577 
3578 	local_bh_disable();
3579 	return err;
3580 }
3581 
3582 static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3583 {
3584 	int result;
3585 
3586 	if (sock_owned_by_user(sk)) {
3587 		local_bh_enable();
3588 		result = __tcp_checksum_complete(skb);
3589 		local_bh_disable();
3590 	} else {
3591 		result = __tcp_checksum_complete(skb);
3592 	}
3593 	return result;
3594 }
3595 
3596 static __inline__ int
3597 tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3598 {
3599 	return skb->ip_summed != CHECKSUM_UNNECESSARY &&
3600 		__tcp_checksum_complete_user(sk, skb);
3601 }
3602 
3603 /*
3604  *	TCP receive function for the ESTABLISHED state.
3605  *
3606  *	It is split into a fast path and a slow path. The fast path is
3607  * 	disabled when:
3608  *	- A zero window was announced from us - zero window probing
3609  *        is only handled properly in the slow path.
3610  *	- Out of order segments arrived.
3611  *	- Urgent data is expected.
3612  *	- There is no buffer space left
3613  *	- Unexpected TCP flags/window values/header lengths are received
3614  *	  (detected by checking the TCP header against pred_flags)
3615  *	- Data is sent in both directions. Fast path only supports pure senders
3616  *	  or pure receivers (this means either the sequence number or the ack
3617  *	  value must stay constant)
3618  *	- Unexpected TCP option.
3619  *
3620  *	When these conditions are not satisfied it drops into a standard
3621  *	receive procedure patterned after RFC793 to handle all cases.
3622  *	The first three cases are guaranteed by proper pred_flags setting,
3623  *	the rest is checked inline. Fast processing is turned on in
3624  *	tcp_data_queue when everything is OK.
3625  */
3626 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
3627 			struct tcphdr *th, unsigned len)
3628 {
3629 	struct tcp_sock *tp = tcp_sk(sk);
3630 
3631 	/*
3632 	 *	Header prediction.
3633 	 *	The code loosely follows the one in the famous
3634 	 *	"30 instruction TCP receive" Van Jacobson mail.
3635 	 *
3636 	 *	Van's trick is to deposit buffers into socket queue
3637 	 *	on a device interrupt, to call tcp_recv function
3638 	 *	on the receive process context and checksum and copy
3639 	 *	the buffer to user space. smart...
3640 	 *
3641 	 *	Our current scheme is not silly either but we take the
3642 	 *	extra cost of the net_bh soft interrupt processing...
3643 	 *	We do checksum and copy also but from device to kernel.
3644 	 */
3645 
3646 	tp->rx_opt.saw_tstamp = 0;
3647 
3648 	/*	pred_flags is 0xS?10 << 16 + snd_wnd
3649 	 *	if header_predition is to be made
3650 	 *	'S' will always be tp->tcp_header_len >> 2
3651 	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
3652 	 *  turn it off	(when there are holes in the receive
3653 	 *	 space for instance)
3654 	 *	PSH flag is ignored.
3655 	 */
3656 
3657 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
3658 		TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3659 		int tcp_header_len = tp->tcp_header_len;
3660 
3661 		/* Timestamp header prediction: tcp_header_len
3662 		 * is automatically equal to th->doff*4 due to pred_flags
3663 		 * match.
3664 		 */
3665 
3666 		/* Check timestamp */
3667 		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
3668 			__u32 *ptr = (__u32 *)(th + 1);
3669 
3670 			/* No? Slow path! */
3671 			if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3672 					  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
3673 				goto slow_path;
3674 
3675 			tp->rx_opt.saw_tstamp = 1;
3676 			++ptr;
3677 			tp->rx_opt.rcv_tsval = ntohl(*ptr);
3678 			++ptr;
3679 			tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3680 
3681 			/* If PAWS failed, check it more carefully in slow path */
3682 			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
3683 				goto slow_path;
3684 
3685 			/* DO NOT update ts_recent here, if checksum fails
3686 			 * and timestamp was corrupted part, it will result
3687 			 * in a hung connection since we will drop all
3688 			 * future packets due to the PAWS test.
3689 			 */
3690 		}
3691 
3692 		if (len <= tcp_header_len) {
3693 			/* Bulk data transfer: sender */
3694 			if (len == tcp_header_len) {
3695 				/* Predicted packet is in window by definition.
3696 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3697 				 * Hence, check seq<=rcv_wup reduces to:
3698 				 */
3699 				if (tcp_header_len ==
3700 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3701 				    tp->rcv_nxt == tp->rcv_wup)
3702 					tcp_store_ts_recent(tp);
3703 
3704 				tcp_rcv_rtt_measure_ts(sk, skb);
3705 
3706 				/* We know that such packets are checksummed
3707 				 * on entry.
3708 				 */
3709 				tcp_ack(sk, skb, 0);
3710 				__kfree_skb(skb);
3711 				tcp_data_snd_check(sk, tp);
3712 				return 0;
3713 			} else { /* Header too small */
3714 				TCP_INC_STATS_BH(TCP_MIB_INERRS);
3715 				goto discard;
3716 			}
3717 		} else {
3718 			int eaten = 0;
3719 
3720 			if (tp->ucopy.task == current &&
3721 			    tp->copied_seq == tp->rcv_nxt &&
3722 			    len - tcp_header_len <= tp->ucopy.len &&
3723 			    sock_owned_by_user(sk)) {
3724 				__set_current_state(TASK_RUNNING);
3725 
3726 				if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
3727 					/* Predicted packet is in window by definition.
3728 					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3729 					 * Hence, check seq<=rcv_wup reduces to:
3730 					 */
3731 					if (tcp_header_len ==
3732 					    (sizeof(struct tcphdr) +
3733 					     TCPOLEN_TSTAMP_ALIGNED) &&
3734 					    tp->rcv_nxt == tp->rcv_wup)
3735 						tcp_store_ts_recent(tp);
3736 
3737 					tcp_rcv_rtt_measure_ts(sk, skb);
3738 
3739 					__skb_pull(skb, tcp_header_len);
3740 					tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3741 					NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
3742 					eaten = 1;
3743 				}
3744 			}
3745 			if (!eaten) {
3746 				if (tcp_checksum_complete_user(sk, skb))
3747 					goto csum_error;
3748 
3749 				/* Predicted packet is in window by definition.
3750 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3751 				 * Hence, check seq<=rcv_wup reduces to:
3752 				 */
3753 				if (tcp_header_len ==
3754 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3755 				    tp->rcv_nxt == tp->rcv_wup)
3756 					tcp_store_ts_recent(tp);
3757 
3758 				tcp_rcv_rtt_measure_ts(sk, skb);
3759 
3760 				if ((int)skb->truesize > sk->sk_forward_alloc)
3761 					goto step5;
3762 
3763 				NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
3764 
3765 				/* Bulk data transfer: receiver */
3766 				__skb_pull(skb,tcp_header_len);
3767 				__skb_queue_tail(&sk->sk_receive_queue, skb);
3768 				sk_stream_set_owner_r(skb, sk);
3769 				tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3770 			}
3771 
3772 			tcp_event_data_recv(sk, tp, skb);
3773 
3774 			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
3775 				/* Well, only one small jumplet in fast path... */
3776 				tcp_ack(sk, skb, FLAG_DATA);
3777 				tcp_data_snd_check(sk, tp);
3778 				if (!inet_csk_ack_scheduled(sk))
3779 					goto no_ack;
3780 			}
3781 
3782 			__tcp_ack_snd_check(sk, 0);
3783 no_ack:
3784 			if (eaten)
3785 				__kfree_skb(skb);
3786 			else
3787 				sk->sk_data_ready(sk, 0);
3788 			return 0;
3789 		}
3790 	}
3791 
3792 slow_path:
3793 	if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
3794 		goto csum_error;
3795 
3796 	/*
3797 	 * RFC1323: H1. Apply PAWS check first.
3798 	 */
3799 	if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
3800 	    tcp_paws_discard(sk, skb)) {
3801 		if (!th->rst) {
3802 			NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
3803 			tcp_send_dupack(sk, skb);
3804 			goto discard;
3805 		}
3806 		/* Resets are accepted even if PAWS failed.
3807 
3808 		   ts_recent update must be made after we are sure
3809 		   that the packet is in window.
3810 		 */
3811 	}
3812 
3813 	/*
3814 	 *	Standard slow path.
3815 	 */
3816 
3817 	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
3818 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
3819 		 * (RST) segments are validated by checking their SEQ-fields."
3820 		 * And page 69: "If an incoming segment is not acceptable,
3821 		 * an acknowledgment should be sent in reply (unless the RST bit
3822 		 * is set, if so drop the segment and return)".
3823 		 */
3824 		if (!th->rst)
3825 			tcp_send_dupack(sk, skb);
3826 		goto discard;
3827 	}
3828 
3829 	if(th->rst) {
3830 		tcp_reset(sk);
3831 		goto discard;
3832 	}
3833 
3834 	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3835 
3836 	if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3837 		TCP_INC_STATS_BH(TCP_MIB_INERRS);
3838 		NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
3839 		tcp_reset(sk);
3840 		return 1;
3841 	}
3842 
3843 step5:
3844 	if(th->ack)
3845 		tcp_ack(sk, skb, FLAG_SLOWPATH);
3846 
3847 	tcp_rcv_rtt_measure_ts(sk, skb);
3848 
3849 	/* Process urgent data. */
3850 	tcp_urg(sk, skb, th);
3851 
3852 	/* step 7: process the segment text */
3853 	tcp_data_queue(sk, skb);
3854 
3855 	tcp_data_snd_check(sk, tp);
3856 	tcp_ack_snd_check(sk);
3857 	return 0;
3858 
3859 csum_error:
3860 	TCP_INC_STATS_BH(TCP_MIB_INERRS);
3861 
3862 discard:
3863 	__kfree_skb(skb);
3864 	return 0;
3865 }
3866 
3867 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
3868 					 struct tcphdr *th, unsigned len)
3869 {
3870 	struct tcp_sock *tp = tcp_sk(sk);
3871 	int saved_clamp = tp->rx_opt.mss_clamp;
3872 
3873 	tcp_parse_options(skb, &tp->rx_opt, 0);
3874 
3875 	if (th->ack) {
3876 		struct inet_connection_sock *icsk;
3877 		/* rfc793:
3878 		 * "If the state is SYN-SENT then
3879 		 *    first check the ACK bit
3880 		 *      If the ACK bit is set
3881 		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
3882 		 *        a reset (unless the RST bit is set, if so drop
3883 		 *        the segment and return)"
3884 		 *
3885 		 *  We do not send data with SYN, so that RFC-correct
3886 		 *  test reduces to:
3887 		 */
3888 		if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
3889 			goto reset_and_undo;
3890 
3891 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3892 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
3893 			     tcp_time_stamp)) {
3894 			NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
3895 			goto reset_and_undo;
3896 		}
3897 
3898 		/* Now ACK is acceptable.
3899 		 *
3900 		 * "If the RST bit is set
3901 		 *    If the ACK was acceptable then signal the user "error:
3902 		 *    connection reset", drop the segment, enter CLOSED state,
3903 		 *    delete TCB, and return."
3904 		 */
3905 
3906 		if (th->rst) {
3907 			tcp_reset(sk);
3908 			goto discard;
3909 		}
3910 
3911 		/* rfc793:
3912 		 *   "fifth, if neither of the SYN or RST bits is set then
3913 		 *    drop the segment and return."
3914 		 *
3915 		 *    See note below!
3916 		 *                                        --ANK(990513)
3917 		 */
3918 		if (!th->syn)
3919 			goto discard_and_undo;
3920 
3921 		/* rfc793:
3922 		 *   "If the SYN bit is on ...
3923 		 *    are acceptable then ...
3924 		 *    (our SYN has been ACKed), change the connection
3925 		 *    state to ESTABLISHED..."
3926 		 */
3927 
3928 		TCP_ECN_rcv_synack(tp, th);
3929 		if (tp->ecn_flags&TCP_ECN_OK)
3930 			sock_set_flag(sk, SOCK_NO_LARGESEND);
3931 
3932 		tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
3933 		tcp_ack(sk, skb, FLAG_SLOWPATH);
3934 
3935 		/* Ok.. it's good. Set up sequence numbers and
3936 		 * move to established.
3937 		 */
3938 		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
3939 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
3940 
3941 		/* RFC1323: The window in SYN & SYN/ACK segments is
3942 		 * never scaled.
3943 		 */
3944 		tp->snd_wnd = ntohs(th->window);
3945 		tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
3946 
3947 		if (!tp->rx_opt.wscale_ok) {
3948 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
3949 			tp->window_clamp = min(tp->window_clamp, 65535U);
3950 		}
3951 
3952 		if (tp->rx_opt.saw_tstamp) {
3953 			tp->rx_opt.tstamp_ok	   = 1;
3954 			tp->tcp_header_len =
3955 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
3956 			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
3957 			tcp_store_ts_recent(tp);
3958 		} else {
3959 			tp->tcp_header_len = sizeof(struct tcphdr);
3960 		}
3961 
3962 		if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
3963 			tp->rx_opt.sack_ok |= 2;
3964 
3965 		tcp_sync_mss(sk, tp->pmtu_cookie);
3966 		tcp_initialize_rcv_mss(sk);
3967 
3968 		/* Remember, tcp_poll() does not lock socket!
3969 		 * Change state from SYN-SENT only after copied_seq
3970 		 * is initialized. */
3971 		tp->copied_seq = tp->rcv_nxt;
3972 		mb();
3973 		tcp_set_state(sk, TCP_ESTABLISHED);
3974 
3975 		/* Make sure socket is routed, for correct metrics.  */
3976 		tp->af_specific->rebuild_header(sk);
3977 
3978 		tcp_init_metrics(sk);
3979 
3980 		tcp_init_congestion_control(sk);
3981 
3982 		/* Prevent spurious tcp_cwnd_restart() on first data
3983 		 * packet.
3984 		 */
3985 		tp->lsndtime = tcp_time_stamp;
3986 
3987 		tcp_init_buffer_space(sk);
3988 
3989 		if (sock_flag(sk, SOCK_KEEPOPEN))
3990 			inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
3991 
3992 		if (!tp->rx_opt.snd_wscale)
3993 			__tcp_fast_path_on(tp, tp->snd_wnd);
3994 		else
3995 			tp->pred_flags = 0;
3996 
3997 		if (!sock_flag(sk, SOCK_DEAD)) {
3998 			sk->sk_state_change(sk);
3999 			sk_wake_async(sk, 0, POLL_OUT);
4000 		}
4001 
4002 		icsk = inet_csk(sk);
4003 
4004 		if (sk->sk_write_pending ||
4005 		    icsk->icsk_accept_queue.rskq_defer_accept ||
4006 		    icsk->icsk_ack.pingpong) {
4007 			/* Save one ACK. Data will be ready after
4008 			 * several ticks, if write_pending is set.
4009 			 *
4010 			 * It may be deleted, but with this feature tcpdumps
4011 			 * look so _wonderfully_ clever, that I was not able
4012 			 * to stand against the temptation 8)     --ANK
4013 			 */
4014 			inet_csk_schedule_ack(sk);
4015 			icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4016 			icsk->icsk_ack.ato	 = TCP_ATO_MIN;
4017 			tcp_incr_quickack(sk);
4018 			tcp_enter_quickack_mode(sk);
4019 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4020 						  TCP_DELACK_MAX, TCP_RTO_MAX);
4021 
4022 discard:
4023 			__kfree_skb(skb);
4024 			return 0;
4025 		} else {
4026 			tcp_send_ack(sk);
4027 		}
4028 		return -1;
4029 	}
4030 
4031 	/* No ACK in the segment */
4032 
4033 	if (th->rst) {
4034 		/* rfc793:
4035 		 * "If the RST bit is set
4036 		 *
4037 		 *      Otherwise (no ACK) drop the segment and return."
4038 		 */
4039 
4040 		goto discard_and_undo;
4041 	}
4042 
4043 	/* PAWS check. */
4044 	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4045 		goto discard_and_undo;
4046 
4047 	if (th->syn) {
4048 		/* We see SYN without ACK. It is attempt of
4049 		 * simultaneous connect with crossed SYNs.
4050 		 * Particularly, it can be connect to self.
4051 		 */
4052 		tcp_set_state(sk, TCP_SYN_RECV);
4053 
4054 		if (tp->rx_opt.saw_tstamp) {
4055 			tp->rx_opt.tstamp_ok = 1;
4056 			tcp_store_ts_recent(tp);
4057 			tp->tcp_header_len =
4058 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4059 		} else {
4060 			tp->tcp_header_len = sizeof(struct tcphdr);
4061 		}
4062 
4063 		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4064 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4065 
4066 		/* RFC1323: The window in SYN & SYN/ACK segments is
4067 		 * never scaled.
4068 		 */
4069 		tp->snd_wnd    = ntohs(th->window);
4070 		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4071 		tp->max_window = tp->snd_wnd;
4072 
4073 		TCP_ECN_rcv_syn(tp, th);
4074 		if (tp->ecn_flags&TCP_ECN_OK)
4075 			sock_set_flag(sk, SOCK_NO_LARGESEND);
4076 
4077 		tcp_sync_mss(sk, tp->pmtu_cookie);
4078 		tcp_initialize_rcv_mss(sk);
4079 
4080 
4081 		tcp_send_synack(sk);
4082 #if 0
4083 		/* Note, we could accept data and URG from this segment.
4084 		 * There are no obstacles to make this.
4085 		 *
4086 		 * However, if we ignore data in ACKless segments sometimes,
4087 		 * we have no reasons to accept it sometimes.
4088 		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
4089 		 * is not flawless. So, discard packet for sanity.
4090 		 * Uncomment this return to process the data.
4091 		 */
4092 		return -1;
4093 #else
4094 		goto discard;
4095 #endif
4096 	}
4097 	/* "fifth, if neither of the SYN or RST bits is set then
4098 	 * drop the segment and return."
4099 	 */
4100 
4101 discard_and_undo:
4102 	tcp_clear_options(&tp->rx_opt);
4103 	tp->rx_opt.mss_clamp = saved_clamp;
4104 	goto discard;
4105 
4106 reset_and_undo:
4107 	tcp_clear_options(&tp->rx_opt);
4108 	tp->rx_opt.mss_clamp = saved_clamp;
4109 	return 1;
4110 }
4111 
4112 
4113 /*
4114  *	This function implements the receiving procedure of RFC 793 for
4115  *	all states except ESTABLISHED and TIME_WAIT.
4116  *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4117  *	address independent.
4118  */
4119 
4120 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4121 			  struct tcphdr *th, unsigned len)
4122 {
4123 	struct tcp_sock *tp = tcp_sk(sk);
4124 	int queued = 0;
4125 
4126 	tp->rx_opt.saw_tstamp = 0;
4127 
4128 	switch (sk->sk_state) {
4129 	case TCP_CLOSE:
4130 		goto discard;
4131 
4132 	case TCP_LISTEN:
4133 		if(th->ack)
4134 			return 1;
4135 
4136 		if(th->rst)
4137 			goto discard;
4138 
4139 		if(th->syn) {
4140 			if(tp->af_specific->conn_request(sk, skb) < 0)
4141 				return 1;
4142 
4143 			/* Now we have several options: In theory there is
4144 			 * nothing else in the frame. KA9Q has an option to
4145 			 * send data with the syn, BSD accepts data with the
4146 			 * syn up to the [to be] advertised window and
4147 			 * Solaris 2.1 gives you a protocol error. For now
4148 			 * we just ignore it, that fits the spec precisely
4149 			 * and avoids incompatibilities. It would be nice in
4150 			 * future to drop through and process the data.
4151 			 *
4152 			 * Now that TTCP is starting to be used we ought to
4153 			 * queue this data.
4154 			 * But, this leaves one open to an easy denial of
4155 		 	 * service attack, and SYN cookies can't defend
4156 			 * against this problem. So, we drop the data
4157 			 * in the interest of security over speed.
4158 			 */
4159 			goto discard;
4160 		}
4161 		goto discard;
4162 
4163 	case TCP_SYN_SENT:
4164 		queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4165 		if (queued >= 0)
4166 			return queued;
4167 
4168 		/* Do step6 onward by hand. */
4169 		tcp_urg(sk, skb, th);
4170 		__kfree_skb(skb);
4171 		tcp_data_snd_check(sk, tp);
4172 		return 0;
4173 	}
4174 
4175 	if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4176 	    tcp_paws_discard(sk, skb)) {
4177 		if (!th->rst) {
4178 			NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4179 			tcp_send_dupack(sk, skb);
4180 			goto discard;
4181 		}
4182 		/* Reset is accepted even if it did not pass PAWS. */
4183 	}
4184 
4185 	/* step 1: check sequence number */
4186 	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4187 		if (!th->rst)
4188 			tcp_send_dupack(sk, skb);
4189 		goto discard;
4190 	}
4191 
4192 	/* step 2: check RST bit */
4193 	if(th->rst) {
4194 		tcp_reset(sk);
4195 		goto discard;
4196 	}
4197 
4198 	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4199 
4200 	/* step 3: check security and precedence [ignored] */
4201 
4202 	/*	step 4:
4203 	 *
4204 	 *	Check for a SYN in window.
4205 	 */
4206 	if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4207 		NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4208 		tcp_reset(sk);
4209 		return 1;
4210 	}
4211 
4212 	/* step 5: check the ACK field */
4213 	if (th->ack) {
4214 		int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
4215 
4216 		switch(sk->sk_state) {
4217 		case TCP_SYN_RECV:
4218 			if (acceptable) {
4219 				tp->copied_seq = tp->rcv_nxt;
4220 				mb();
4221 				tcp_set_state(sk, TCP_ESTABLISHED);
4222 				sk->sk_state_change(sk);
4223 
4224 				/* Note, that this wakeup is only for marginal
4225 				 * crossed SYN case. Passively open sockets
4226 				 * are not waked up, because sk->sk_sleep ==
4227 				 * NULL and sk->sk_socket == NULL.
4228 				 */
4229 				if (sk->sk_socket) {
4230 					sk_wake_async(sk,0,POLL_OUT);
4231 				}
4232 
4233 				tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
4234 				tp->snd_wnd = ntohs(th->window) <<
4235 					      tp->rx_opt.snd_wscale;
4236 				tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
4237 					    TCP_SKB_CB(skb)->seq);
4238 
4239 				/* tcp_ack considers this ACK as duplicate
4240 				 * and does not calculate rtt.
4241 				 * Fix it at least with timestamps.
4242 				 */
4243 				if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4244 				    !tp->srtt)
4245 					tcp_ack_saw_tstamp(sk, NULL, 0);
4246 
4247 				if (tp->rx_opt.tstamp_ok)
4248 					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
4249 
4250 				/* Make sure socket is routed, for
4251 				 * correct metrics.
4252 				 */
4253 				tp->af_specific->rebuild_header(sk);
4254 
4255 				tcp_init_metrics(sk);
4256 
4257 				tcp_init_congestion_control(sk);
4258 
4259 				/* Prevent spurious tcp_cwnd_restart() on
4260 				 * first data packet.
4261 				 */
4262 				tp->lsndtime = tcp_time_stamp;
4263 
4264 				tcp_initialize_rcv_mss(sk);
4265 				tcp_init_buffer_space(sk);
4266 				tcp_fast_path_on(tp);
4267 			} else {
4268 				return 1;
4269 			}
4270 			break;
4271 
4272 		case TCP_FIN_WAIT1:
4273 			if (tp->snd_una == tp->write_seq) {
4274 				tcp_set_state(sk, TCP_FIN_WAIT2);
4275 				sk->sk_shutdown |= SEND_SHUTDOWN;
4276 				dst_confirm(sk->sk_dst_cache);
4277 
4278 				if (!sock_flag(sk, SOCK_DEAD))
4279 					/* Wake up lingering close() */
4280 					sk->sk_state_change(sk);
4281 				else {
4282 					int tmo;
4283 
4284 					if (tp->linger2 < 0 ||
4285 					    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4286 					     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
4287 						tcp_done(sk);
4288 						NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4289 						return 1;
4290 					}
4291 
4292 					tmo = tcp_fin_time(sk);
4293 					if (tmo > TCP_TIMEWAIT_LEN) {
4294 						inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
4295 					} else if (th->fin || sock_owned_by_user(sk)) {
4296 						/* Bad case. We could lose such FIN otherwise.
4297 						 * It is not a big problem, but it looks confusing
4298 						 * and not so rare event. We still can lose it now,
4299 						 * if it spins in bh_lock_sock(), but it is really
4300 						 * marginal case.
4301 						 */
4302 						inet_csk_reset_keepalive_timer(sk, tmo);
4303 					} else {
4304 						tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
4305 						goto discard;
4306 					}
4307 				}
4308 			}
4309 			break;
4310 
4311 		case TCP_CLOSING:
4312 			if (tp->snd_una == tp->write_seq) {
4313 				tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4314 				goto discard;
4315 			}
4316 			break;
4317 
4318 		case TCP_LAST_ACK:
4319 			if (tp->snd_una == tp->write_seq) {
4320 				tcp_update_metrics(sk);
4321 				tcp_done(sk);
4322 				goto discard;
4323 			}
4324 			break;
4325 		}
4326 	} else
4327 		goto discard;
4328 
4329 	/* step 6: check the URG bit */
4330 	tcp_urg(sk, skb, th);
4331 
4332 	/* step 7: process the segment text */
4333 	switch (sk->sk_state) {
4334 	case TCP_CLOSE_WAIT:
4335 	case TCP_CLOSING:
4336 	case TCP_LAST_ACK:
4337 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4338 			break;
4339 	case TCP_FIN_WAIT1:
4340 	case TCP_FIN_WAIT2:
4341 		/* RFC 793 says to queue data in these states,
4342 		 * RFC 1122 says we MUST send a reset.
4343 		 * BSD 4.4 also does reset.
4344 		 */
4345 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
4346 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4347 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
4348 				NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4349 				tcp_reset(sk);
4350 				return 1;
4351 			}
4352 		}
4353 		/* Fall through */
4354 	case TCP_ESTABLISHED:
4355 		tcp_data_queue(sk, skb);
4356 		queued = 1;
4357 		break;
4358 	}
4359 
4360 	/* tcp_data could move socket to TIME-WAIT */
4361 	if (sk->sk_state != TCP_CLOSE) {
4362 		tcp_data_snd_check(sk, tp);
4363 		tcp_ack_snd_check(sk);
4364 	}
4365 
4366 	if (!queued) {
4367 discard:
4368 		__kfree_skb(skb);
4369 	}
4370 	return 0;
4371 }
4372 
4373 EXPORT_SYMBOL(sysctl_tcp_ecn);
4374 EXPORT_SYMBOL(sysctl_tcp_reordering);
4375 EXPORT_SYMBOL(tcp_parse_options);
4376 EXPORT_SYMBOL(tcp_rcv_established);
4377 EXPORT_SYMBOL(tcp_rcv_state_process);
4378