[INET]: Fix typo in Arnaldo's connection sock compat fixups.
[linux-2.6.git] / net / ipv4 / tcp_input.c
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 presence 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 int sysctl_tcp_abc = 1;
93
94 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
95 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
96 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
97 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
98 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
99 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
100 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
101 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
102 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
103
104 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
105 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
106 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
107 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
108
109 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
110 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
111 #define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
112
113 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
114
115 /* Adapt the MSS value used to make delayed ack decision to the 
116  * real world.
117  */ 
118 static void tcp_measure_rcv_mss(struct sock *sk,
119                                 const struct sk_buff *skb)
120 {
121         struct inet_connection_sock *icsk = inet_csk(sk);
122         const unsigned int lss = icsk->icsk_ack.last_seg_size; 
123         unsigned int len;
124
125         icsk->icsk_ack.last_seg_size = 0; 
126
127         /* skb->len may jitter because of SACKs, even if peer
128          * sends good full-sized frames.
129          */
130         len = skb->len;
131         if (len >= icsk->icsk_ack.rcv_mss) {
132                 icsk->icsk_ack.rcv_mss = len;
133         } else {
134                 /* Otherwise, we make more careful check taking into account,
135                  * that SACKs block is variable.
136                  *
137                  * "len" is invariant segment length, including TCP header.
138                  */
139                 len += skb->data - skb->h.raw;
140                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
141                     /* If PSH is not set, packet should be
142                      * full sized, provided peer TCP is not badly broken.
143                      * This observation (if it is correct 8)) allows
144                      * to handle super-low mtu links fairly.
145                      */
146                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
147                      !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) {
148                         /* Subtract also invariant (if peer is RFC compliant),
149                          * tcp header plus fixed timestamp option length.
150                          * Resulting "len" is MSS free of SACK jitter.
151                          */
152                         len -= tcp_sk(sk)->tcp_header_len;
153                         icsk->icsk_ack.last_seg_size = len;
154                         if (len == lss) {
155                                 icsk->icsk_ack.rcv_mss = len;
156                                 return;
157                         }
158                 }
159                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
160         }
161 }
162
163 static void tcp_incr_quickack(struct sock *sk)
164 {
165         struct inet_connection_sock *icsk = inet_csk(sk);
166         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
167
168         if (quickacks==0)
169                 quickacks=2;
170         if (quickacks > icsk->icsk_ack.quick)
171                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
172 }
173
174 void tcp_enter_quickack_mode(struct sock *sk)
175 {
176         struct inet_connection_sock *icsk = inet_csk(sk);
177         tcp_incr_quickack(sk);
178         icsk->icsk_ack.pingpong = 0;
179         icsk->icsk_ack.ato = TCP_ATO_MIN;
180 }
181
182 /* Send ACKs quickly, if "quick" count is not exhausted
183  * and the session is not interactive.
184  */
185
186 static inline int tcp_in_quickack_mode(const struct sock *sk)
187 {
188         const struct inet_connection_sock *icsk = inet_csk(sk);
189         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
190 }
191
192 /* Buffer size and advertised window tuning.
193  *
194  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
195  */
196
197 static void tcp_fixup_sndbuf(struct sock *sk)
198 {
199         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
200                      sizeof(struct sk_buff);
201
202         if (sk->sk_sndbuf < 3 * sndmem)
203                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
204 }
205
206 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
207  *
208  * All tcp_full_space() is split to two parts: "network" buffer, allocated
209  * forward and advertised in receiver window (tp->rcv_wnd) and
210  * "application buffer", required to isolate scheduling/application
211  * latencies from network.
212  * window_clamp is maximal advertised window. It can be less than
213  * tcp_full_space(), in this case tcp_full_space() - window_clamp
214  * is reserved for "application" buffer. The less window_clamp is
215  * the smoother our behaviour from viewpoint of network, but the lower
216  * throughput and the higher sensitivity of the connection to losses. 8)
217  *
218  * rcv_ssthresh is more strict window_clamp used at "slow start"
219  * phase to predict further behaviour of this connection.
220  * It is used for two goals:
221  * - to enforce header prediction at sender, even when application
222  *   requires some significant "application buffer". It is check #1.
223  * - to prevent pruning of receive queue because of misprediction
224  *   of receiver window. Check #2.
225  *
226  * The scheme does not work when sender sends good segments opening
227  * window and then starts to feed us spaghetti. But it should work
228  * in common situations. Otherwise, we have to rely on queue collapsing.
229  */
230
231 /* Slow part of check#2. */
232 static int __tcp_grow_window(const struct sock *sk, struct tcp_sock *tp,
233                              const struct sk_buff *skb)
234 {
235         /* Optimize this! */
236         int truesize = tcp_win_from_space(skb->truesize)/2;
237         int window = tcp_win_from_space(sysctl_tcp_rmem[2])/2;
238
239         while (tp->rcv_ssthresh <= window) {
240                 if (truesize <= skb->len)
241                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
242
243                 truesize >>= 1;
244                 window >>= 1;
245         }
246         return 0;
247 }
248
249 static void tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
250                             struct sk_buff *skb)
251 {
252         /* Check #1 */
253         if (tp->rcv_ssthresh < tp->window_clamp &&
254             (int)tp->rcv_ssthresh < tcp_space(sk) &&
255             !tcp_memory_pressure) {
256                 int incr;
257
258                 /* Check #2. Increase window, if skb with such overhead
259                  * will fit to rcvbuf in future.
260                  */
261                 if (tcp_win_from_space(skb->truesize) <= skb->len)
262                         incr = 2*tp->advmss;
263                 else
264                         incr = __tcp_grow_window(sk, tp, skb);
265
266                 if (incr) {
267                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
268                         inet_csk(sk)->icsk_ack.quick |= 1;
269                 }
270         }
271 }
272
273 /* 3. Tuning rcvbuf, when connection enters established state. */
274
275 static void tcp_fixup_rcvbuf(struct sock *sk)
276 {
277         struct tcp_sock *tp = tcp_sk(sk);
278         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
279
280         /* Try to select rcvbuf so that 4 mss-sized segments
281          * will fit to window and corresponding skbs will fit to our rcvbuf.
282          * (was 3; 4 is minimum to allow fast retransmit to work.)
283          */
284         while (tcp_win_from_space(rcvmem) < tp->advmss)
285                 rcvmem += 128;
286         if (sk->sk_rcvbuf < 4 * rcvmem)
287                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
288 }
289
290 /* 4. Try to fixup all. It is made immediately after connection enters
291  *    established state.
292  */
293 static void tcp_init_buffer_space(struct sock *sk)
294 {
295         struct tcp_sock *tp = tcp_sk(sk);
296         int maxwin;
297
298         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
299                 tcp_fixup_rcvbuf(sk);
300         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
301                 tcp_fixup_sndbuf(sk);
302
303         tp->rcvq_space.space = tp->rcv_wnd;
304
305         maxwin = tcp_full_space(sk);
306
307         if (tp->window_clamp >= maxwin) {
308                 tp->window_clamp = maxwin;
309
310                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
311                         tp->window_clamp = max(maxwin -
312                                                (maxwin >> sysctl_tcp_app_win),
313                                                4 * tp->advmss);
314         }
315
316         /* Force reservation of one segment. */
317         if (sysctl_tcp_app_win &&
318             tp->window_clamp > 2 * tp->advmss &&
319             tp->window_clamp + tp->advmss > maxwin)
320                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
321
322         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
323         tp->snd_cwnd_stamp = tcp_time_stamp;
324 }
325
326 /* 5. Recalculate window clamp after socket hit its memory bounds. */
327 static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp)
328 {
329         struct inet_connection_sock *icsk = inet_csk(sk);
330
331         icsk->icsk_ack.quick = 0;
332
333         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
334             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
335             !tcp_memory_pressure &&
336             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
337                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
338                                     sysctl_tcp_rmem[2]);
339         }
340         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
341                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
342 }
343
344
345 /* Initialize RCV_MSS value.
346  * RCV_MSS is an our guess about MSS used by the peer.
347  * We haven't any direct information about the MSS.
348  * It's better to underestimate the RCV_MSS rather than overestimate.
349  * Overestimations make us ACKing less frequently than needed.
350  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
351  */
352 void tcp_initialize_rcv_mss(struct sock *sk)
353 {
354         struct tcp_sock *tp = tcp_sk(sk);
355         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
356
357         hint = min(hint, tp->rcv_wnd/2);
358         hint = min(hint, TCP_MIN_RCVMSS);
359         hint = max(hint, TCP_MIN_MSS);
360
361         inet_csk(sk)->icsk_ack.rcv_mss = hint;
362 }
363
364 /* Receiver "autotuning" code.
365  *
366  * The algorithm for RTT estimation w/o timestamps is based on
367  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
368  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
369  *
370  * More detail on this code can be found at
371  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
372  * though this reference is out of date.  A new paper
373  * is pending.
374  */
375 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
376 {
377         u32 new_sample = tp->rcv_rtt_est.rtt;
378         long m = sample;
379
380         if (m == 0)
381                 m = 1;
382
383         if (new_sample != 0) {
384                 /* If we sample in larger samples in the non-timestamp
385                  * case, we could grossly overestimate the RTT especially
386                  * with chatty applications or bulk transfer apps which
387                  * are stalled on filesystem I/O.
388                  *
389                  * Also, since we are only going for a minimum in the
390                  * non-timestamp case, we do not smooth things out
391                  * else with timestamps disabled convergence takes too
392                  * long.
393                  */
394                 if (!win_dep) {
395                         m -= (new_sample >> 3);
396                         new_sample += m;
397                 } else if (m < new_sample)
398                         new_sample = m << 3;
399         } else {
400                 /* No previous measure. */
401                 new_sample = m << 3;
402         }
403
404         if (tp->rcv_rtt_est.rtt != new_sample)
405                 tp->rcv_rtt_est.rtt = new_sample;
406 }
407
408 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
409 {
410         if (tp->rcv_rtt_est.time == 0)
411                 goto new_measure;
412         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
413                 return;
414         tcp_rcv_rtt_update(tp,
415                            jiffies - tp->rcv_rtt_est.time,
416                            1);
417
418 new_measure:
419         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
420         tp->rcv_rtt_est.time = tcp_time_stamp;
421 }
422
423 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
424 {
425         struct tcp_sock *tp = tcp_sk(sk);
426         if (tp->rx_opt.rcv_tsecr &&
427             (TCP_SKB_CB(skb)->end_seq -
428              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
429                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
430 }
431
432 /*
433  * This function should be called every time data is copied to user space.
434  * It calculates the appropriate TCP receive buffer space.
435  */
436 void tcp_rcv_space_adjust(struct sock *sk)
437 {
438         struct tcp_sock *tp = tcp_sk(sk);
439         int time;
440         int space;
441         
442         if (tp->rcvq_space.time == 0)
443                 goto new_measure;
444         
445         time = tcp_time_stamp - tp->rcvq_space.time;
446         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
447             tp->rcv_rtt_est.rtt == 0)
448                 return;
449         
450         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
451
452         space = max(tp->rcvq_space.space, space);
453
454         if (tp->rcvq_space.space != space) {
455                 int rcvmem;
456
457                 tp->rcvq_space.space = space;
458
459                 if (sysctl_tcp_moderate_rcvbuf &&
460                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
461                         int new_clamp = space;
462
463                         /* Receive space grows, normalize in order to
464                          * take into account packet headers and sk_buff
465                          * structure overhead.
466                          */
467                         space /= tp->advmss;
468                         if (!space)
469                                 space = 1;
470                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
471                                   16 + sizeof(struct sk_buff));
472                         while (tcp_win_from_space(rcvmem) < tp->advmss)
473                                 rcvmem += 128;
474                         space *= rcvmem;
475                         space = min(space, sysctl_tcp_rmem[2]);
476                         if (space > sk->sk_rcvbuf) {
477                                 sk->sk_rcvbuf = space;
478
479                                 /* Make the window clamp follow along.  */
480                                 tp->window_clamp = new_clamp;
481                         }
482                 }
483         }
484         
485 new_measure:
486         tp->rcvq_space.seq = tp->copied_seq;
487         tp->rcvq_space.time = tcp_time_stamp;
488 }
489
490 /* There is something which you must keep in mind when you analyze the
491  * behavior of the tp->ato delayed ack timeout interval.  When a
492  * connection starts up, we want to ack as quickly as possible.  The
493  * problem is that "good" TCP's do slow start at the beginning of data
494  * transmission.  The means that until we send the first few ACK's the
495  * sender will sit on his end and only queue most of his data, because
496  * he can only send snd_cwnd unacked packets at any given time.  For
497  * each ACK we send, he increments snd_cwnd and transmits more of his
498  * queue.  -DaveM
499  */
500 static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
501 {
502         struct inet_connection_sock *icsk = inet_csk(sk);
503         u32 now;
504
505         inet_csk_schedule_ack(sk);
506
507         tcp_measure_rcv_mss(sk, skb);
508
509         tcp_rcv_rtt_measure(tp);
510         
511         now = tcp_time_stamp;
512
513         if (!icsk->icsk_ack.ato) {
514                 /* The _first_ data packet received, initialize
515                  * delayed ACK engine.
516                  */
517                 tcp_incr_quickack(sk);
518                 icsk->icsk_ack.ato = TCP_ATO_MIN;
519         } else {
520                 int m = now - icsk->icsk_ack.lrcvtime;
521
522                 if (m <= TCP_ATO_MIN/2) {
523                         /* The fastest case is the first. */
524                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
525                 } else if (m < icsk->icsk_ack.ato) {
526                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
527                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
528                                 icsk->icsk_ack.ato = icsk->icsk_rto;
529                 } else if (m > icsk->icsk_rto) {
530                         /* Too long gap. Apparently sender failed to
531                          * restart window, so that we send ACKs quickly.
532                          */
533                         tcp_incr_quickack(sk);
534                         sk_stream_mem_reclaim(sk);
535                 }
536         }
537         icsk->icsk_ack.lrcvtime = now;
538
539         TCP_ECN_check_ce(tp, skb);
540
541         if (skb->len >= 128)
542                 tcp_grow_window(sk, tp, skb);
543 }
544
545 /* Called to compute a smoothed rtt estimate. The data fed to this
546  * routine either comes from timestamps, or from segments that were
547  * known _not_ to have been retransmitted [see Karn/Partridge
548  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
549  * piece by Van Jacobson.
550  * NOTE: the next three routines used to be one big routine.
551  * To save cycles in the RFC 1323 implementation it was better to break
552  * it up into three procedures. -- erics
553  */
554 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
555 {
556         struct tcp_sock *tp = tcp_sk(sk);
557         long m = mrtt; /* RTT */
558
559         /*      The following amusing code comes from Jacobson's
560          *      article in SIGCOMM '88.  Note that rtt and mdev
561          *      are scaled versions of rtt and mean deviation.
562          *      This is designed to be as fast as possible 
563          *      m stands for "measurement".
564          *
565          *      On a 1990 paper the rto value is changed to:
566          *      RTO = rtt + 4 * mdev
567          *
568          * Funny. This algorithm seems to be very broken.
569          * These formulae increase RTO, when it should be decreased, increase
570          * too slowly, when it should be increased quickly, decrease too quickly
571          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
572          * does not matter how to _calculate_ it. Seems, it was trap
573          * that VJ failed to avoid. 8)
574          */
575         if(m == 0)
576                 m = 1;
577         if (tp->srtt != 0) {
578                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
579                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
580                 if (m < 0) {
581                         m = -m;         /* m is now abs(error) */
582                         m -= (tp->mdev >> 2);   /* similar update on mdev */
583                         /* This is similar to one of Eifel findings.
584                          * Eifel blocks mdev updates when rtt decreases.
585                          * This solution is a bit different: we use finer gain
586                          * for mdev in this case (alpha*beta).
587                          * Like Eifel it also prevents growth of rto,
588                          * but also it limits too fast rto decreases,
589                          * happening in pure Eifel.
590                          */
591                         if (m > 0)
592                                 m >>= 3;
593                 } else {
594                         m -= (tp->mdev >> 2);   /* similar update on mdev */
595                 }
596                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
597                 if (tp->mdev > tp->mdev_max) {
598                         tp->mdev_max = tp->mdev;
599                         if (tp->mdev_max > tp->rttvar)
600                                 tp->rttvar = tp->mdev_max;
601                 }
602                 if (after(tp->snd_una, tp->rtt_seq)) {
603                         if (tp->mdev_max < tp->rttvar)
604                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
605                         tp->rtt_seq = tp->snd_nxt;
606                         tp->mdev_max = TCP_RTO_MIN;
607                 }
608         } else {
609                 /* no previous measure. */
610                 tp->srtt = m<<3;        /* take the measured time to be rtt */
611                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
612                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
613                 tp->rtt_seq = tp->snd_nxt;
614         }
615 }
616
617 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
618  * routine referred to above.
619  */
620 static inline void tcp_set_rto(struct sock *sk)
621 {
622         const struct tcp_sock *tp = tcp_sk(sk);
623         /* Old crap is replaced with new one. 8)
624          *
625          * More seriously:
626          * 1. If rtt variance happened to be less 50msec, it is hallucination.
627          *    It cannot be less due to utterly erratic ACK generation made
628          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
629          *    to do with delayed acks, because at cwnd>2 true delack timeout
630          *    is invisible. Actually, Linux-2.4 also generates erratic
631          *    ACKs in some circumstances.
632          */
633         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
634
635         /* 2. Fixups made earlier cannot be right.
636          *    If we do not estimate RTO correctly without them,
637          *    all the algo is pure shit and should be replaced
638          *    with correct one. It is exactly, which we pretend to do.
639          */
640 }
641
642 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
643  * guarantees that rto is higher.
644  */
645 static inline void tcp_bound_rto(struct sock *sk)
646 {
647         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
648                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
649 }
650
651 /* Save metrics learned by this TCP session.
652    This function is called only, when TCP finishes successfully
653    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
654  */
655 void tcp_update_metrics(struct sock *sk)
656 {
657         struct tcp_sock *tp = tcp_sk(sk);
658         struct dst_entry *dst = __sk_dst_get(sk);
659
660         if (sysctl_tcp_nometrics_save)
661                 return;
662
663         dst_confirm(dst);
664
665         if (dst && (dst->flags&DST_HOST)) {
666                 const struct inet_connection_sock *icsk = inet_csk(sk);
667                 int m;
668
669                 if (icsk->icsk_backoff || !tp->srtt) {
670                         /* This session failed to estimate rtt. Why?
671                          * Probably, no packets returned in time.
672                          * Reset our results.
673                          */
674                         if (!(dst_metric_locked(dst, RTAX_RTT)))
675                                 dst->metrics[RTAX_RTT-1] = 0;
676                         return;
677                 }
678
679                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
680
681                 /* If newly calculated rtt larger than stored one,
682                  * store new one. Otherwise, use EWMA. Remember,
683                  * rtt overestimation is always better than underestimation.
684                  */
685                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
686                         if (m <= 0)
687                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
688                         else
689                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
690                 }
691
692                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
693                         if (m < 0)
694                                 m = -m;
695
696                         /* Scale deviation to rttvar fixed point */
697                         m >>= 1;
698                         if (m < tp->mdev)
699                                 m = tp->mdev;
700
701                         if (m >= dst_metric(dst, RTAX_RTTVAR))
702                                 dst->metrics[RTAX_RTTVAR-1] = m;
703                         else
704                                 dst->metrics[RTAX_RTTVAR-1] -=
705                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
706                 }
707
708                 if (tp->snd_ssthresh >= 0xFFFF) {
709                         /* Slow start still did not finish. */
710                         if (dst_metric(dst, RTAX_SSTHRESH) &&
711                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
712                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
713                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
714                         if (!dst_metric_locked(dst, RTAX_CWND) &&
715                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
716                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
717                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
718                            icsk->icsk_ca_state == TCP_CA_Open) {
719                         /* Cong. avoidance phase, cwnd is reliable. */
720                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
721                                 dst->metrics[RTAX_SSTHRESH-1] =
722                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
723                         if (!dst_metric_locked(dst, RTAX_CWND))
724                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
725                 } else {
726                         /* Else slow start did not finish, cwnd is non-sense,
727                            ssthresh may be also invalid.
728                          */
729                         if (!dst_metric_locked(dst, RTAX_CWND))
730                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
731                         if (dst->metrics[RTAX_SSTHRESH-1] &&
732                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
733                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
734                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
735                 }
736
737                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
738                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
739                             tp->reordering != sysctl_tcp_reordering)
740                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
741                 }
742         }
743 }
744
745 /* Numbers are taken from RFC2414.  */
746 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
747 {
748         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
749
750         if (!cwnd) {
751                 if (tp->mss_cache > 1460)
752                         cwnd = 2;
753                 else
754                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
755         }
756         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
757 }
758
759 /* Set slow start threshold and cwnd not falling to slow start */
760 void tcp_enter_cwr(struct sock *sk)
761 {
762         struct tcp_sock *tp = tcp_sk(sk);
763
764         tp->prior_ssthresh = 0;
765         tp->bytes_acked = 0;
766         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
767                 tp->undo_marker = 0;
768                 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
769                 tp->snd_cwnd = min(tp->snd_cwnd,
770                                    tcp_packets_in_flight(tp) + 1U);
771                 tp->snd_cwnd_cnt = 0;
772                 tp->high_seq = tp->snd_nxt;
773                 tp->snd_cwnd_stamp = tcp_time_stamp;
774                 TCP_ECN_queue_cwr(tp);
775
776                 tcp_set_ca_state(sk, TCP_CA_CWR);
777         }
778 }
779
780 /* Initialize metrics on socket. */
781
782 static void tcp_init_metrics(struct sock *sk)
783 {
784         struct tcp_sock *tp = tcp_sk(sk);
785         struct dst_entry *dst = __sk_dst_get(sk);
786
787         if (dst == NULL)
788                 goto reset;
789
790         dst_confirm(dst);
791
792         if (dst_metric_locked(dst, RTAX_CWND))
793                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
794         if (dst_metric(dst, RTAX_SSTHRESH)) {
795                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
796                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
797                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
798         }
799         if (dst_metric(dst, RTAX_REORDERING) &&
800             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
801                 tp->rx_opt.sack_ok &= ~2;
802                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
803         }
804
805         if (dst_metric(dst, RTAX_RTT) == 0)
806                 goto reset;
807
808         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
809                 goto reset;
810
811         /* Initial rtt is determined from SYN,SYN-ACK.
812          * The segment is small and rtt may appear much
813          * less than real one. Use per-dst memory
814          * to make it more realistic.
815          *
816          * A bit of theory. RTT is time passed after "normal" sized packet
817          * is sent until it is ACKed. In normal circumstances sending small
818          * packets force peer to delay ACKs and calculation is correct too.
819          * The algorithm is adaptive and, provided we follow specs, it
820          * NEVER underestimate RTT. BUT! If peer tries to make some clever
821          * tricks sort of "quick acks" for time long enough to decrease RTT
822          * to low value, and then abruptly stops to do it and starts to delay
823          * ACKs, wait for troubles.
824          */
825         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
826                 tp->srtt = dst_metric(dst, RTAX_RTT);
827                 tp->rtt_seq = tp->snd_nxt;
828         }
829         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
830                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
831                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
832         }
833         tcp_set_rto(sk);
834         tcp_bound_rto(sk);
835         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
836                 goto reset;
837         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
838         tp->snd_cwnd_stamp = tcp_time_stamp;
839         return;
840
841 reset:
842         /* Play conservative. If timestamps are not
843          * supported, TCP will fail to recalculate correct
844          * rtt, if initial rto is too small. FORGET ALL AND RESET!
845          */
846         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
847                 tp->srtt = 0;
848                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
849                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
850         }
851 }
852
853 static void tcp_update_reordering(struct sock *sk, const int metric,
854                                   const int ts)
855 {
856         struct tcp_sock *tp = tcp_sk(sk);
857         if (metric > tp->reordering) {
858                 tp->reordering = min(TCP_MAX_REORDERING, metric);
859
860                 /* This exciting event is worth to be remembered. 8) */
861                 if (ts)
862                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
863                 else if (IsReno(tp))
864                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
865                 else if (IsFack(tp))
866                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
867                 else
868                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
869 #if FASTRETRANS_DEBUG > 1
870                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
871                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
872                        tp->reordering,
873                        tp->fackets_out,
874                        tp->sacked_out,
875                        tp->undo_marker ? tp->undo_retrans : 0);
876 #endif
877                 /* Disable FACK yet. */
878                 tp->rx_opt.sack_ok &= ~2;
879         }
880 }
881
882 /* This procedure tags the retransmission queue when SACKs arrive.
883  *
884  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
885  * Packets in queue with these bits set are counted in variables
886  * sacked_out, retrans_out and lost_out, correspondingly.
887  *
888  * Valid combinations are:
889  * Tag  InFlight        Description
890  * 0    1               - orig segment is in flight.
891  * S    0               - nothing flies, orig reached receiver.
892  * L    0               - nothing flies, orig lost by net.
893  * R    2               - both orig and retransmit are in flight.
894  * L|R  1               - orig is lost, retransmit is in flight.
895  * S|R  1               - orig reached receiver, retrans is still in flight.
896  * (L|S|R is logically valid, it could occur when L|R is sacked,
897  *  but it is equivalent to plain S and code short-curcuits it to S.
898  *  L|S is logically invalid, it would mean -1 packet in flight 8))
899  *
900  * These 6 states form finite state machine, controlled by the following events:
901  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
902  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
903  * 3. Loss detection event of one of three flavors:
904  *      A. Scoreboard estimator decided the packet is lost.
905  *         A'. Reno "three dupacks" marks head of queue lost.
906  *         A''. Its FACK modfication, head until snd.fack is lost.
907  *      B. SACK arrives sacking data transmitted after never retransmitted
908  *         hole was sent out.
909  *      C. SACK arrives sacking SND.NXT at the moment, when the
910  *         segment was retransmitted.
911  * 4. D-SACK added new rule: D-SACK changes any tag to S.
912  *
913  * It is pleasant to note, that state diagram turns out to be commutative,
914  * so that we are allowed not to be bothered by order of our actions,
915  * when multiple events arrive simultaneously. (see the function below).
916  *
917  * Reordering detection.
918  * --------------------
919  * Reordering metric is maximal distance, which a packet can be displaced
920  * in packet stream. With SACKs we can estimate it:
921  *
922  * 1. SACK fills old hole and the corresponding segment was not
923  *    ever retransmitted -> reordering. Alas, we cannot use it
924  *    when segment was retransmitted.
925  * 2. The last flaw is solved with D-SACK. D-SACK arrives
926  *    for retransmitted and already SACKed segment -> reordering..
927  * Both of these heuristics are not used in Loss state, when we cannot
928  * account for retransmits accurately.
929  */
930 static int
931 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
932 {
933         const struct inet_connection_sock *icsk = inet_csk(sk);
934         struct tcp_sock *tp = tcp_sk(sk);
935         unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
936         struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2);
937         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
938         int reord = tp->packets_out;
939         int prior_fackets;
940         u32 lost_retrans = 0;
941         int flag = 0;
942         int dup_sack = 0;
943         int i;
944
945         if (!tp->sacked_out)
946                 tp->fackets_out = 0;
947         prior_fackets = tp->fackets_out;
948
949         /* SACK fastpath:
950          * if the only SACK change is the increase of the end_seq of
951          * the first block then only apply that SACK block
952          * and use retrans queue hinting otherwise slowpath */
953         flag = 1;
954         for (i = 0; i< num_sacks; i++) {
955                 __u32 start_seq = ntohl(sp[i].start_seq);
956                 __u32 end_seq =  ntohl(sp[i].end_seq);
957
958                 if (i == 0){
959                         if (tp->recv_sack_cache[i].start_seq != start_seq)
960                                 flag = 0;
961                 } else {
962                         if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
963                             (tp->recv_sack_cache[i].end_seq != end_seq))
964                                 flag = 0;
965                 }
966                 tp->recv_sack_cache[i].start_seq = start_seq;
967                 tp->recv_sack_cache[i].end_seq = end_seq;
968
969                 /* Check for D-SACK. */
970                 if (i == 0) {
971                         u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;
972
973                         if (before(start_seq, ack)) {
974                                 dup_sack = 1;
975                                 tp->rx_opt.sack_ok |= 4;
976                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
977                         } else if (num_sacks > 1 &&
978                                    !after(end_seq, ntohl(sp[1].end_seq)) &&
979                                    !before(start_seq, ntohl(sp[1].start_seq))) {
980                                 dup_sack = 1;
981                                 tp->rx_opt.sack_ok |= 4;
982                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
983                         }
984
985                         /* D-SACK for already forgotten data...
986                          * Do dumb counting. */
987                         if (dup_sack &&
988                             !after(end_seq, prior_snd_una) &&
989                             after(end_seq, tp->undo_marker))
990                                 tp->undo_retrans--;
991
992                         /* Eliminate too old ACKs, but take into
993                          * account more or less fresh ones, they can
994                          * contain valid SACK info.
995                          */
996                         if (before(ack, prior_snd_una - tp->max_window))
997                                 return 0;
998                 }
999         }
1000
1001         if (flag)
1002                 num_sacks = 1;
1003         else {
1004                 int j;
1005                 tp->fastpath_skb_hint = NULL;
1006
1007                 /* order SACK blocks to allow in order walk of the retrans queue */
1008                 for (i = num_sacks-1; i > 0; i--) {
1009                         for (j = 0; j < i; j++){
1010                                 if (after(ntohl(sp[j].start_seq),
1011                                           ntohl(sp[j+1].start_seq))){
1012                                         sp[j].start_seq = htonl(tp->recv_sack_cache[j+1].start_seq);
1013                                         sp[j].end_seq = htonl(tp->recv_sack_cache[j+1].end_seq);
1014                                         sp[j+1].start_seq = htonl(tp->recv_sack_cache[j].start_seq);
1015                                         sp[j+1].end_seq = htonl(tp->recv_sack_cache[j].end_seq);
1016                                 }
1017
1018                         }
1019                 }
1020         }
1021
1022         /* clear flag as used for different purpose in following code */
1023         flag = 0;
1024
1025         for (i=0; i<num_sacks; i++, sp++) {
1026                 struct sk_buff *skb;
1027                 __u32 start_seq = ntohl(sp->start_seq);
1028                 __u32 end_seq = ntohl(sp->end_seq);
1029                 int fack_count;
1030
1031                 /* Use SACK fastpath hint if valid */
1032                 if (tp->fastpath_skb_hint) {
1033                         skb = tp->fastpath_skb_hint;
1034                         fack_count = tp->fastpath_cnt_hint;
1035                 } else {
1036                         skb = sk->sk_write_queue.next;
1037                         fack_count = 0;
1038                 }
1039
1040                 /* Event "B" in the comment above. */
1041                 if (after(end_seq, tp->high_seq))
1042                         flag |= FLAG_DATA_LOST;
1043
1044                 sk_stream_for_retrans_queue_from(skb, sk) {
1045                         int in_sack, pcount;
1046                         u8 sacked;
1047
1048                         tp->fastpath_skb_hint = skb;
1049                         tp->fastpath_cnt_hint = fack_count;
1050
1051                         /* The retransmission queue is always in order, so
1052                          * we can short-circuit the walk early.
1053                          */
1054                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1055                                 break;
1056
1057                         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1058                                 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1059
1060                         pcount = tcp_skb_pcount(skb);
1061
1062                         if (pcount > 1 && !in_sack &&
1063                             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1064                                 unsigned int pkt_len;
1065
1066                                 in_sack = !after(start_seq,
1067                                                  TCP_SKB_CB(skb)->seq);
1068
1069                                 if (!in_sack)
1070                                         pkt_len = (start_seq -
1071                                                    TCP_SKB_CB(skb)->seq);
1072                                 else
1073                                         pkt_len = (end_seq -
1074                                                    TCP_SKB_CB(skb)->seq);
1075                                 if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->tso_size))
1076                                         break;
1077                                 pcount = tcp_skb_pcount(skb);
1078                         }
1079
1080                         fack_count += pcount;
1081
1082                         sacked = TCP_SKB_CB(skb)->sacked;
1083
1084                         /* Account D-SACK for retransmitted packet. */
1085                         if ((dup_sack && in_sack) &&
1086                             (sacked & TCPCB_RETRANS) &&
1087                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1088                                 tp->undo_retrans--;
1089
1090                         /* The frame is ACKed. */
1091                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1092                                 if (sacked&TCPCB_RETRANS) {
1093                                         if ((dup_sack && in_sack) &&
1094                                             (sacked&TCPCB_SACKED_ACKED))
1095                                                 reord = min(fack_count, reord);
1096                                 } else {
1097                                         /* If it was in a hole, we detected reordering. */
1098                                         if (fack_count < prior_fackets &&
1099                                             !(sacked&TCPCB_SACKED_ACKED))
1100                                                 reord = min(fack_count, reord);
1101                                 }
1102
1103                                 /* Nothing to do; acked frame is about to be dropped. */
1104                                 continue;
1105                         }
1106
1107                         if ((sacked&TCPCB_SACKED_RETRANS) &&
1108                             after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1109                             (!lost_retrans || after(end_seq, lost_retrans)))
1110                                 lost_retrans = end_seq;
1111
1112                         if (!in_sack)
1113                                 continue;
1114
1115                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1116                                 if (sacked & TCPCB_SACKED_RETRANS) {
1117                                         /* If the segment is not tagged as lost,
1118                                          * we do not clear RETRANS, believing
1119                                          * that retransmission is still in flight.
1120                                          */
1121                                         if (sacked & TCPCB_LOST) {
1122                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1123                                                 tp->lost_out -= tcp_skb_pcount(skb);
1124                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1125
1126                                                 /* clear lost hint */
1127                                                 tp->retransmit_skb_hint = NULL;
1128                                         }
1129                                 } else {
1130                                         /* New sack for not retransmitted frame,
1131                                          * which was in hole. It is reordering.
1132                                          */
1133                                         if (!(sacked & TCPCB_RETRANS) &&
1134                                             fack_count < prior_fackets)
1135                                                 reord = min(fack_count, reord);
1136
1137                                         if (sacked & TCPCB_LOST) {
1138                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1139                                                 tp->lost_out -= tcp_skb_pcount(skb);
1140
1141                                                 /* clear lost hint */
1142                                                 tp->retransmit_skb_hint = NULL;
1143                                         }
1144                                 }
1145
1146                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1147                                 flag |= FLAG_DATA_SACKED;
1148                                 tp->sacked_out += tcp_skb_pcount(skb);
1149
1150                                 if (fack_count > tp->fackets_out)
1151                                         tp->fackets_out = fack_count;
1152                         } else {
1153                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1154                                         reord = min(fack_count, reord);
1155                         }
1156
1157                         /* D-SACK. We can detect redundant retransmission
1158                          * in S|R and plain R frames and clear it.
1159                          * undo_retrans is decreased above, L|R frames
1160                          * are accounted above as well.
1161                          */
1162                         if (dup_sack &&
1163                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1164                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1165                                 tp->retrans_out -= tcp_skb_pcount(skb);
1166                                 tp->retransmit_skb_hint = NULL;
1167                         }
1168                 }
1169         }
1170
1171         /* Check for lost retransmit. This superb idea is
1172          * borrowed from "ratehalving". Event "C".
1173          * Later note: FACK people cheated me again 8),
1174          * we have to account for reordering! Ugly,
1175          * but should help.
1176          */
1177         if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
1178                 struct sk_buff *skb;
1179
1180                 sk_stream_for_retrans_queue(skb, sk) {
1181                         if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1182                                 break;
1183                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1184                                 continue;
1185                         if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1186                             after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1187                             (IsFack(tp) ||
1188                              !before(lost_retrans,
1189                                      TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1190                                      tp->mss_cache))) {
1191                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1192                                 tp->retrans_out -= tcp_skb_pcount(skb);
1193
1194                                 /* clear lost hint */
1195                                 tp->retransmit_skb_hint = NULL;
1196
1197                                 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1198                                         tp->lost_out += tcp_skb_pcount(skb);
1199                                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1200                                         flag |= FLAG_DATA_SACKED;
1201                                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1202                                 }
1203                         }
1204                 }
1205         }
1206
1207         tp->left_out = tp->sacked_out + tp->lost_out;
1208
1209         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss)
1210                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1211
1212 #if FASTRETRANS_DEBUG > 0
1213         BUG_TRAP((int)tp->sacked_out >= 0);
1214         BUG_TRAP((int)tp->lost_out >= 0);
1215         BUG_TRAP((int)tp->retrans_out >= 0);
1216         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1217 #endif
1218         return flag;
1219 }
1220
1221 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new
1222  * segments to see from the next ACKs whether any data was really missing.
1223  * If the RTO was spurious, new ACKs should arrive.
1224  */
1225 void tcp_enter_frto(struct sock *sk)
1226 {
1227         const struct inet_connection_sock *icsk = inet_csk(sk);
1228         struct tcp_sock *tp = tcp_sk(sk);
1229         struct sk_buff *skb;
1230
1231         tp->frto_counter = 1;
1232
1233         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1234             tp->snd_una == tp->high_seq ||
1235             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1236                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1237                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1238                 tcp_ca_event(sk, CA_EVENT_FRTO);
1239         }
1240
1241         /* Have to clear retransmission markers here to keep the bookkeeping
1242          * in shape, even though we are not yet in Loss state.
1243          * If something was really lost, it is eventually caught up
1244          * in tcp_enter_frto_loss.
1245          */
1246         tp->retrans_out = 0;
1247         tp->undo_marker = tp->snd_una;
1248         tp->undo_retrans = 0;
1249
1250         sk_stream_for_retrans_queue(skb, sk) {
1251                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
1252         }
1253         tcp_sync_left_out(tp);
1254
1255         tcp_set_ca_state(sk, TCP_CA_Open);
1256         tp->frto_highmark = tp->snd_nxt;
1257 }
1258
1259 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1260  * which indicates that we should follow the traditional RTO recovery,
1261  * i.e. mark everything lost and do go-back-N retransmission.
1262  */
1263 static void tcp_enter_frto_loss(struct sock *sk)
1264 {
1265         struct tcp_sock *tp = tcp_sk(sk);
1266         struct sk_buff *skb;
1267         int cnt = 0;
1268
1269         tp->sacked_out = 0;
1270         tp->lost_out = 0;
1271         tp->fackets_out = 0;
1272
1273         sk_stream_for_retrans_queue(skb, sk) {
1274                 cnt += tcp_skb_pcount(skb);
1275                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1276                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1277
1278                         /* Do not mark those segments lost that were
1279                          * forward transmitted after RTO
1280                          */
1281                         if (!after(TCP_SKB_CB(skb)->end_seq,
1282                                    tp->frto_highmark)) {
1283                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1284                                 tp->lost_out += tcp_skb_pcount(skb);
1285                         }
1286                 } else {
1287                         tp->sacked_out += tcp_skb_pcount(skb);
1288                         tp->fackets_out = cnt;
1289                 }
1290         }
1291         tcp_sync_left_out(tp);
1292
1293         tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
1294         tp->snd_cwnd_cnt = 0;
1295         tp->snd_cwnd_stamp = tcp_time_stamp;
1296         tp->undo_marker = 0;
1297         tp->frto_counter = 0;
1298
1299         tp->reordering = min_t(unsigned int, tp->reordering,
1300                                              sysctl_tcp_reordering);
1301         tcp_set_ca_state(sk, TCP_CA_Loss);
1302         tp->high_seq = tp->frto_highmark;
1303         TCP_ECN_queue_cwr(tp);
1304
1305         clear_all_retrans_hints(tp);
1306 }
1307
1308 void tcp_clear_retrans(struct tcp_sock *tp)
1309 {
1310         tp->left_out = 0;
1311         tp->retrans_out = 0;
1312
1313         tp->fackets_out = 0;
1314         tp->sacked_out = 0;
1315         tp->lost_out = 0;
1316
1317         tp->undo_marker = 0;
1318         tp->undo_retrans = 0;
1319 }
1320
1321 /* Enter Loss state. If "how" is not zero, forget all SACK information
1322  * and reset tags completely, otherwise preserve SACKs. If receiver
1323  * dropped its ofo queue, we will know this due to reneging detection.
1324  */
1325 void tcp_enter_loss(struct sock *sk, int how)
1326 {
1327         const struct inet_connection_sock *icsk = inet_csk(sk);
1328         struct tcp_sock *tp = tcp_sk(sk);
1329         struct sk_buff *skb;
1330         int cnt = 0;
1331
1332         /* Reduce ssthresh if it has not yet been made inside this window. */
1333         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1334             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1335                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1336                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1337                 tcp_ca_event(sk, CA_EVENT_LOSS);
1338         }
1339         tp->snd_cwnd       = 1;
1340         tp->snd_cwnd_cnt   = 0;
1341         tp->snd_cwnd_stamp = tcp_time_stamp;
1342
1343         tp->bytes_acked = 0;
1344         tcp_clear_retrans(tp);
1345
1346         /* Push undo marker, if it was plain RTO and nothing
1347          * was retransmitted. */
1348         if (!how)
1349                 tp->undo_marker = tp->snd_una;
1350
1351         sk_stream_for_retrans_queue(skb, sk) {
1352                 cnt += tcp_skb_pcount(skb);
1353                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1354                         tp->undo_marker = 0;
1355                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1356                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1357                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1358                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1359                         tp->lost_out += tcp_skb_pcount(skb);
1360                 } else {
1361                         tp->sacked_out += tcp_skb_pcount(skb);
1362                         tp->fackets_out = cnt;
1363                 }
1364         }
1365         tcp_sync_left_out(tp);
1366
1367         tp->reordering = min_t(unsigned int, tp->reordering,
1368                                              sysctl_tcp_reordering);
1369         tcp_set_ca_state(sk, TCP_CA_Loss);
1370         tp->high_seq = tp->snd_nxt;
1371         TCP_ECN_queue_cwr(tp);
1372
1373         clear_all_retrans_hints(tp);
1374 }
1375
1376 static int tcp_check_sack_reneging(struct sock *sk)
1377 {
1378         struct sk_buff *skb;
1379
1380         /* If ACK arrived pointing to a remembered SACK,
1381          * it means that our remembered SACKs do not reflect
1382          * real state of receiver i.e.
1383          * receiver _host_ is heavily congested (or buggy).
1384          * Do processing similar to RTO timeout.
1385          */
1386         if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
1387             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1388                 struct inet_connection_sock *icsk = inet_csk(sk);
1389                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1390
1391                 tcp_enter_loss(sk, 1);
1392                 icsk->icsk_retransmits++;
1393                 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
1394                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1395                                           icsk->icsk_rto, TCP_RTO_MAX);
1396                 return 1;
1397         }
1398         return 0;
1399 }
1400
1401 static inline int tcp_fackets_out(struct tcp_sock *tp)
1402 {
1403         return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1404 }
1405
1406 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1407 {
1408         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1409 }
1410
1411 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
1412 {
1413         return tp->packets_out &&
1414                tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
1415 }
1416
1417 /* Linux NewReno/SACK/FACK/ECN state machine.
1418  * --------------------------------------
1419  *
1420  * "Open"       Normal state, no dubious events, fast path.
1421  * "Disorder"   In all the respects it is "Open",
1422  *              but requires a bit more attention. It is entered when
1423  *              we see some SACKs or dupacks. It is split of "Open"
1424  *              mainly to move some processing from fast path to slow one.
1425  * "CWR"        CWND was reduced due to some Congestion Notification event.
1426  *              It can be ECN, ICMP source quench, local device congestion.
1427  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1428  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1429  *
1430  * tcp_fastretrans_alert() is entered:
1431  * - each incoming ACK, if state is not "Open"
1432  * - when arrived ACK is unusual, namely:
1433  *      * SACK
1434  *      * Duplicate ACK.
1435  *      * ECN ECE.
1436  *
1437  * Counting packets in flight is pretty simple.
1438  *
1439  *      in_flight = packets_out - left_out + retrans_out
1440  *
1441  *      packets_out is SND.NXT-SND.UNA counted in packets.
1442  *
1443  *      retrans_out is number of retransmitted segments.
1444  *
1445  *      left_out is number of segments left network, but not ACKed yet.
1446  *
1447  *              left_out = sacked_out + lost_out
1448  *
1449  *     sacked_out: Packets, which arrived to receiver out of order
1450  *                 and hence not ACKed. With SACKs this number is simply
1451  *                 amount of SACKed data. Even without SACKs
1452  *                 it is easy to give pretty reliable estimate of this number,
1453  *                 counting duplicate ACKs.
1454  *
1455  *       lost_out: Packets lost by network. TCP has no explicit
1456  *                 "loss notification" feedback from network (for now).
1457  *                 It means that this number can be only _guessed_.
1458  *                 Actually, it is the heuristics to predict lossage that
1459  *                 distinguishes different algorithms.
1460  *
1461  *      F.e. after RTO, when all the queue is considered as lost,
1462  *      lost_out = packets_out and in_flight = retrans_out.
1463  *
1464  *              Essentially, we have now two algorithms counting
1465  *              lost packets.
1466  *
1467  *              FACK: It is the simplest heuristics. As soon as we decided
1468  *              that something is lost, we decide that _all_ not SACKed
1469  *              packets until the most forward SACK are lost. I.e.
1470  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1471  *              It is absolutely correct estimate, if network does not reorder
1472  *              packets. And it loses any connection to reality when reordering
1473  *              takes place. We use FACK by default until reordering
1474  *              is suspected on the path to this destination.
1475  *
1476  *              NewReno: when Recovery is entered, we assume that one segment
1477  *              is lost (classic Reno). While we are in Recovery and
1478  *              a partial ACK arrives, we assume that one more packet
1479  *              is lost (NewReno). This heuristics are the same in NewReno
1480  *              and SACK.
1481  *
1482  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1483  *  deflation etc. CWND is real congestion window, never inflated, changes
1484  *  only according to classic VJ rules.
1485  *
1486  * Really tricky (and requiring careful tuning) part of algorithm
1487  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1488  * The first determines the moment _when_ we should reduce CWND and,
1489  * hence, slow down forward transmission. In fact, it determines the moment
1490  * when we decide that hole is caused by loss, rather than by a reorder.
1491  *
1492  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1493  * holes, caused by lost packets.
1494  *
1495  * And the most logically complicated part of algorithm is undo
1496  * heuristics. We detect false retransmits due to both too early
1497  * fast retransmit (reordering) and underestimated RTO, analyzing
1498  * timestamps and D-SACKs. When we detect that some segments were
1499  * retransmitted by mistake and CWND reduction was wrong, we undo
1500  * window reduction and abort recovery phase. This logic is hidden
1501  * inside several functions named tcp_try_undo_<something>.
1502  */
1503
1504 /* This function decides, when we should leave Disordered state
1505  * and enter Recovery phase, reducing congestion window.
1506  *
1507  * Main question: may we further continue forward transmission
1508  * with the same cwnd?
1509  */
1510 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
1511 {
1512         __u32 packets_out;
1513
1514         /* Trick#1: The loss is proven. */
1515         if (tp->lost_out)
1516                 return 1;
1517
1518         /* Not-A-Trick#2 : Classic rule... */
1519         if (tcp_fackets_out(tp) > tp->reordering)
1520                 return 1;
1521
1522         /* Trick#3 : when we use RFC2988 timer restart, fast
1523          * retransmit can be triggered by timeout of queue head.
1524          */
1525         if (tcp_head_timedout(sk, tp))
1526                 return 1;
1527
1528         /* Trick#4: It is still not OK... But will it be useful to delay
1529          * recovery more?
1530          */
1531         packets_out = tp->packets_out;
1532         if (packets_out <= tp->reordering &&
1533             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1534             !tcp_may_send_now(sk, tp)) {
1535                 /* We have nothing to send. This connection is limited
1536                  * either by receiver window or by application.
1537                  */
1538                 return 1;
1539         }
1540
1541         return 0;
1542 }
1543
1544 /* If we receive more dupacks than we expected counting segments
1545  * in assumption of absent reordering, interpret this as reordering.
1546  * The only another reason could be bug in receiver TCP.
1547  */
1548 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1549 {
1550         struct tcp_sock *tp = tcp_sk(sk);
1551         u32 holes;
1552
1553         holes = max(tp->lost_out, 1U);
1554         holes = min(holes, tp->packets_out);
1555
1556         if ((tp->sacked_out + holes) > tp->packets_out) {
1557                 tp->sacked_out = tp->packets_out - holes;
1558                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1559         }
1560 }
1561
1562 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1563
1564 static void tcp_add_reno_sack(struct sock *sk)
1565 {
1566         struct tcp_sock *tp = tcp_sk(sk);
1567         tp->sacked_out++;
1568         tcp_check_reno_reordering(sk, 0);
1569         tcp_sync_left_out(tp);
1570 }
1571
1572 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1573
1574 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
1575 {
1576         if (acked > 0) {
1577                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1578                 if (acked-1 >= tp->sacked_out)
1579                         tp->sacked_out = 0;
1580                 else
1581                         tp->sacked_out -= acked-1;
1582         }
1583         tcp_check_reno_reordering(sk, acked);
1584         tcp_sync_left_out(tp);
1585 }
1586
1587 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1588 {
1589         tp->sacked_out = 0;
1590         tp->left_out = tp->lost_out;
1591 }
1592
1593 /* Mark head of queue up as lost. */
1594 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
1595                                int packets, u32 high_seq)
1596 {
1597         struct sk_buff *skb;
1598         int cnt;
1599
1600         BUG_TRAP(packets <= tp->packets_out);
1601         if (tp->lost_skb_hint) {
1602                 skb = tp->lost_skb_hint;
1603                 cnt = tp->lost_cnt_hint;
1604         } else {
1605                 skb = sk->sk_write_queue.next;
1606                 cnt = 0;
1607         }
1608
1609         sk_stream_for_retrans_queue_from(skb, sk) {
1610                 /* TODO: do this better */
1611                 /* this is not the most efficient way to do this... */
1612                 tp->lost_skb_hint = skb;
1613                 tp->lost_cnt_hint = cnt;
1614                 cnt += tcp_skb_pcount(skb);
1615                 if (cnt > packets || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1616                         break;
1617                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1618                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1619                         tp->lost_out += tcp_skb_pcount(skb);
1620
1621                         /* clear xmit_retransmit_queue hints
1622                          *  if this is beyond hint */
1623                         if(tp->retransmit_skb_hint != NULL &&
1624                            before(TCP_SKB_CB(skb)->seq,
1625                                   TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) {
1626
1627                                 tp->retransmit_skb_hint = NULL;
1628                         }
1629                 }
1630         }
1631         tcp_sync_left_out(tp);
1632 }
1633
1634 /* Account newly detected lost packet(s) */
1635
1636 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
1637 {
1638         if (IsFack(tp)) {
1639                 int lost = tp->fackets_out - tp->reordering;
1640                 if (lost <= 0)
1641                         lost = 1;
1642                 tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
1643         } else {
1644                 tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
1645         }
1646
1647         /* New heuristics: it is possible only after we switched
1648          * to restart timer each time when something is ACKed.
1649          * Hence, we can detect timed out packets during fast
1650          * retransmit without falling to slow start.
1651          */
1652         if (tcp_head_timedout(sk, tp)) {
1653                 struct sk_buff *skb;
1654
1655                 skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
1656                         : sk->sk_write_queue.next;
1657
1658                 sk_stream_for_retrans_queue_from(skb, sk) {
1659                         if (!tcp_skb_timedout(sk, skb))
1660                                 break;
1661
1662                         if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1663                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1664                                 tp->lost_out += tcp_skb_pcount(skb);
1665
1666                                 /* clear xmit_retrans hint */
1667                                 if (tp->retransmit_skb_hint &&
1668                                     before(TCP_SKB_CB(skb)->seq,
1669                                            TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
1670
1671                                         tp->retransmit_skb_hint = NULL;
1672                         }
1673                 }
1674
1675                 tp->scoreboard_skb_hint = skb;
1676
1677                 tcp_sync_left_out(tp);
1678         }
1679 }
1680
1681 /* CWND moderation, preventing bursts due to too big ACKs
1682  * in dubious situations.
1683  */
1684 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1685 {
1686         tp->snd_cwnd = min(tp->snd_cwnd,
1687                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1688         tp->snd_cwnd_stamp = tcp_time_stamp;
1689 }
1690
1691 /* Decrease cwnd each second ack. */
1692 static void tcp_cwnd_down(struct sock *sk)
1693 {
1694         const struct inet_connection_sock *icsk = inet_csk(sk);
1695         struct tcp_sock *tp = tcp_sk(sk);
1696         int decr = tp->snd_cwnd_cnt + 1;
1697
1698         tp->snd_cwnd_cnt = decr&1;
1699         decr >>= 1;
1700
1701         if (decr && tp->snd_cwnd > icsk->icsk_ca_ops->min_cwnd(sk))
1702                 tp->snd_cwnd -= decr;
1703
1704         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1705         tp->snd_cwnd_stamp = tcp_time_stamp;
1706 }
1707
1708 /* Nothing was retransmitted or returned timestamp is less
1709  * than timestamp of the first retransmission.
1710  */
1711 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1712 {
1713         return !tp->retrans_stamp ||
1714                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1715                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1716 }
1717
1718 /* Undo procedures. */
1719
1720 #if FASTRETRANS_DEBUG > 1
1721 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
1722 {
1723         struct inet_sock *inet = inet_sk(sk);
1724         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1725                msg,
1726                NIPQUAD(inet->daddr), ntohs(inet->dport),
1727                tp->snd_cwnd, tp->left_out,
1728                tp->snd_ssthresh, tp->prior_ssthresh,
1729                tp->packets_out);
1730 }
1731 #else
1732 #define DBGUNDO(x...) do { } while (0)
1733 #endif
1734
1735 static void tcp_undo_cwr(struct sock *sk, const int undo)
1736 {
1737         struct tcp_sock *tp = tcp_sk(sk);
1738
1739         if (tp->prior_ssthresh) {
1740                 const struct inet_connection_sock *icsk = inet_csk(sk);
1741
1742                 if (icsk->icsk_ca_ops->undo_cwnd)
1743                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
1744                 else
1745                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1746
1747                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1748                         tp->snd_ssthresh = tp->prior_ssthresh;
1749                         TCP_ECN_withdraw_cwr(tp);
1750                 }
1751         } else {
1752                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1753         }
1754         tcp_moderate_cwnd(tp);
1755         tp->snd_cwnd_stamp = tcp_time_stamp;
1756
1757         /* There is something screwy going on with the retrans hints after
1758            an undo */
1759         clear_all_retrans_hints(tp);
1760 }
1761
1762 static inline int tcp_may_undo(struct tcp_sock *tp)
1763 {
1764         return tp->undo_marker &&
1765                 (!tp->undo_retrans || tcp_packet_delayed(tp));
1766 }
1767
1768 /* People celebrate: "We love our President!" */
1769 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
1770 {
1771         if (tcp_may_undo(tp)) {
1772                 /* Happy end! We did not retransmit anything
1773                  * or our original transmission succeeded.
1774                  */
1775                 DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
1776                 tcp_undo_cwr(sk, 1);
1777                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
1778                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1779                 else
1780                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1781                 tp->undo_marker = 0;
1782         }
1783         if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1784                 /* Hold old state until something *above* high_seq
1785                  * is ACKed. For Reno it is MUST to prevent false
1786                  * fast retransmits (RFC2582). SACK TCP is safe. */
1787                 tcp_moderate_cwnd(tp);
1788                 return 1;
1789         }
1790         tcp_set_ca_state(sk, TCP_CA_Open);
1791         return 0;
1792 }
1793
1794 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1795 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
1796 {
1797         if (tp->undo_marker && !tp->undo_retrans) {
1798                 DBGUNDO(sk, tp, "D-SACK");
1799                 tcp_undo_cwr(sk, 1);
1800                 tp->undo_marker = 0;
1801                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1802         }
1803 }
1804
1805 /* Undo during fast recovery after partial ACK. */
1806
1807 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
1808                                 int acked)
1809 {
1810         /* Partial ACK arrived. Force Hoe's retransmit. */
1811         int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1812
1813         if (tcp_may_undo(tp)) {
1814                 /* Plain luck! Hole if filled with delayed
1815                  * packet, rather than with a retransmit.
1816                  */
1817                 if (tp->retrans_out == 0)
1818                         tp->retrans_stamp = 0;
1819
1820                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
1821
1822                 DBGUNDO(sk, tp, "Hoe");
1823                 tcp_undo_cwr(sk, 0);
1824                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1825
1826                 /* So... Do not make Hoe's retransmit yet.
1827                  * If the first packet was delayed, the rest
1828                  * ones are most probably delayed as well.
1829                  */
1830                 failed = 0;
1831         }
1832         return failed;
1833 }
1834
1835 /* Undo during loss recovery after partial ACK. */
1836 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
1837 {
1838         if (tcp_may_undo(tp)) {
1839                 struct sk_buff *skb;
1840                 sk_stream_for_retrans_queue(skb, sk) {
1841                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1842                 }
1843
1844                 clear_all_retrans_hints(tp);
1845
1846                 DBGUNDO(sk, tp, "partial loss");
1847                 tp->lost_out = 0;
1848                 tp->left_out = tp->sacked_out;
1849                 tcp_undo_cwr(sk, 1);
1850                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1851                 inet_csk(sk)->icsk_retransmits = 0;
1852                 tp->undo_marker = 0;
1853                 if (!IsReno(tp))
1854                         tcp_set_ca_state(sk, TCP_CA_Open);
1855                 return 1;
1856         }
1857         return 0;
1858 }
1859
1860 static inline void tcp_complete_cwr(struct sock *sk)
1861 {
1862         struct tcp_sock *tp = tcp_sk(sk);
1863         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
1864         tp->snd_cwnd_stamp = tcp_time_stamp;
1865         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
1866 }
1867
1868 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
1869 {
1870         tp->left_out = tp->sacked_out;
1871
1872         if (tp->retrans_out == 0)
1873                 tp->retrans_stamp = 0;
1874
1875         if (flag&FLAG_ECE)
1876                 tcp_enter_cwr(sk);
1877
1878         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
1879                 int state = TCP_CA_Open;
1880
1881                 if (tp->left_out || tp->retrans_out || tp->undo_marker)
1882                         state = TCP_CA_Disorder;
1883
1884                 if (inet_csk(sk)->icsk_ca_state != state) {
1885                         tcp_set_ca_state(sk, state);
1886                         tp->high_seq = tp->snd_nxt;
1887                 }
1888                 tcp_moderate_cwnd(tp);
1889         } else {
1890                 tcp_cwnd_down(sk);
1891         }
1892 }
1893
1894 static void tcp_mtup_probe_failed(struct sock *sk)
1895 {
1896         struct inet_connection_sock *icsk = inet_csk(sk);
1897
1898         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
1899         icsk->icsk_mtup.probe_size = 0;
1900 }
1901
1902 static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
1903 {
1904         struct tcp_sock *tp = tcp_sk(sk);
1905         struct inet_connection_sock *icsk = inet_csk(sk);
1906
1907         /* FIXME: breaks with very large cwnd */
1908         tp->prior_ssthresh = tcp_current_ssthresh(sk);
1909         tp->snd_cwnd = tp->snd_cwnd *
1910                        tcp_mss_to_mtu(sk, tp->mss_cache) /
1911                        icsk->icsk_mtup.probe_size;
1912         tp->snd_cwnd_cnt = 0;
1913         tp->snd_cwnd_stamp = tcp_time_stamp;
1914         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
1915
1916         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
1917         icsk->icsk_mtup.probe_size = 0;
1918         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
1919 }
1920
1921
1922 /* Process an event, which can update packets-in-flight not trivially.
1923  * Main goal of this function is to calculate new estimate for left_out,
1924  * taking into account both packets sitting in receiver's buffer and
1925  * packets lost by network.
1926  *
1927  * Besides that it does CWND reduction, when packet loss is detected
1928  * and changes state of machine.
1929  *
1930  * It does _not_ decide what to send, it is made in function
1931  * tcp_xmit_retransmit_queue().
1932  */
1933 static void
1934 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
1935                       int prior_packets, int flag)
1936 {
1937         struct inet_connection_sock *icsk = inet_csk(sk);
1938         struct tcp_sock *tp = tcp_sk(sk);
1939         int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
1940
1941         /* Some technical things:
1942          * 1. Reno does not count dupacks (sacked_out) automatically. */
1943         if (!tp->packets_out)
1944                 tp->sacked_out = 0;
1945         /* 2. SACK counts snd_fack in packets inaccurately. */
1946         if (tp->sacked_out == 0)
1947                 tp->fackets_out = 0;
1948
1949         /* Now state machine starts.
1950          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
1951         if (flag&FLAG_ECE)
1952                 tp->prior_ssthresh = 0;
1953
1954         /* B. In all the states check for reneging SACKs. */
1955         if (tp->sacked_out && tcp_check_sack_reneging(sk))
1956                 return;
1957
1958         /* C. Process data loss notification, provided it is valid. */
1959         if ((flag&FLAG_DATA_LOST) &&
1960             before(tp->snd_una, tp->high_seq) &&
1961             icsk->icsk_ca_state != TCP_CA_Open &&
1962             tp->fackets_out > tp->reordering) {
1963                 tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
1964                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
1965         }
1966
1967         /* D. Synchronize left_out to current state. */
1968         tcp_sync_left_out(tp);
1969
1970         /* E. Check state exit conditions. State can be terminated
1971          *    when high_seq is ACKed. */
1972         if (icsk->icsk_ca_state == TCP_CA_Open) {
1973                 if (!sysctl_tcp_frto)
1974                         BUG_TRAP(tp->retrans_out == 0);
1975                 tp->retrans_stamp = 0;
1976         } else if (!before(tp->snd_una, tp->high_seq)) {
1977                 switch (icsk->icsk_ca_state) {
1978                 case TCP_CA_Loss:
1979                         icsk->icsk_retransmits = 0;
1980                         if (tcp_try_undo_recovery(sk, tp))
1981                                 return;
1982                         break;
1983
1984                 case TCP_CA_CWR:
1985                         /* CWR is to be held something *above* high_seq
1986                          * is ACKed for CWR bit to reach receiver. */
1987                         if (tp->snd_una != tp->high_seq) {
1988                                 tcp_complete_cwr(sk);
1989                                 tcp_set_ca_state(sk, TCP_CA_Open);
1990                         }
1991                         break;
1992
1993                 case TCP_CA_Disorder:
1994                         tcp_try_undo_dsack(sk, tp);
1995                         if (!tp->undo_marker ||
1996                             /* For SACK case do not Open to allow to undo
1997                              * catching for all duplicate ACKs. */
1998                             IsReno(tp) || tp->snd_una != tp->high_seq) {
1999                                 tp->undo_marker = 0;
2000                                 tcp_set_ca_state(sk, TCP_CA_Open);
2001                         }
2002                         break;
2003
2004                 case TCP_CA_Recovery:
2005                         if (IsReno(tp))
2006                                 tcp_reset_reno_sack(tp);
2007                         if (tcp_try_undo_recovery(sk, tp))
2008                                 return;
2009                         tcp_complete_cwr(sk);
2010                         break;
2011                 }
2012         }
2013
2014         /* F. Process state. */
2015         switch (icsk->icsk_ca_state) {
2016         case TCP_CA_Recovery:
2017                 if (prior_snd_una == tp->snd_una) {
2018                         if (IsReno(tp) && is_dupack)
2019                                 tcp_add_reno_sack(sk);
2020                 } else {
2021                         int acked = prior_packets - tp->packets_out;
2022                         if (IsReno(tp))
2023                                 tcp_remove_reno_sacks(sk, tp, acked);
2024                         is_dupack = tcp_try_undo_partial(sk, tp, acked);
2025                 }
2026                 break;
2027         case TCP_CA_Loss:
2028                 if (flag&FLAG_DATA_ACKED)
2029                         icsk->icsk_retransmits = 0;
2030                 if (!tcp_try_undo_loss(sk, tp)) {
2031                         tcp_moderate_cwnd(tp);
2032                         tcp_xmit_retransmit_queue(sk);
2033                         return;
2034                 }
2035                 if (icsk->icsk_ca_state != TCP_CA_Open)
2036                         return;
2037                 /* Loss is undone; fall through to processing in Open state. */
2038         default:
2039                 if (IsReno(tp)) {
2040                         if (tp->snd_una != prior_snd_una)
2041                                 tcp_reset_reno_sack(tp);
2042                         if (is_dupack)
2043                                 tcp_add_reno_sack(sk);
2044                 }
2045
2046                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
2047                         tcp_try_undo_dsack(sk, tp);
2048
2049                 if (!tcp_time_to_recover(sk, tp)) {
2050                         tcp_try_to_open(sk, tp, flag);
2051                         return;
2052                 }
2053
2054                 /* MTU probe failure: don't reduce cwnd */
2055                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2056                     icsk->icsk_mtup.probe_size &&
2057                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2058                         tcp_mtup_probe_failed(sk);
2059                         /* Restores the reduction we did in tcp_mtup_probe() */
2060                         tp->snd_cwnd++;
2061                         tcp_simple_retransmit(sk);
2062                         return;
2063                 }
2064
2065                 /* Otherwise enter Recovery state */
2066
2067                 if (IsReno(tp))
2068                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
2069                 else
2070                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
2071
2072                 tp->high_seq = tp->snd_nxt;
2073                 tp->prior_ssthresh = 0;
2074                 tp->undo_marker = tp->snd_una;
2075                 tp->undo_retrans = tp->retrans_out;
2076
2077                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
2078                         if (!(flag&FLAG_ECE))
2079                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2080                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2081                         TCP_ECN_queue_cwr(tp);
2082                 }
2083
2084                 tp->bytes_acked = 0;
2085                 tp->snd_cwnd_cnt = 0;
2086                 tcp_set_ca_state(sk, TCP_CA_Recovery);
2087         }
2088
2089         if (is_dupack || tcp_head_timedout(sk, tp))
2090                 tcp_update_scoreboard(sk, tp);
2091         tcp_cwnd_down(sk);
2092         tcp_xmit_retransmit_queue(sk);
2093 }
2094
2095 /* Read draft-ietf-tcplw-high-performance before mucking
2096  * with this code. (Supersedes RFC1323)
2097  */
2098 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
2099 {
2100         /* RTTM Rule: A TSecr value received in a segment is used to
2101          * update the averaged RTT measurement only if the segment
2102          * acknowledges some new data, i.e., only if it advances the
2103          * left edge of the send window.
2104          *
2105          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2106          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
2107          *
2108          * Changed: reset backoff as soon as we see the first valid sample.
2109          * If we do not, we get strongly overestimated rto. With timestamps
2110          * samples are accepted even from very old segments: f.e., when rtt=1
2111          * increases to 8, we retransmit 5 times and after 8 seconds delayed
2112          * answer arrives rto becomes 120 seconds! If at least one of segments
2113          * in window is lost... Voila.                          --ANK (010210)
2114          */
2115         struct tcp_sock *tp = tcp_sk(sk);
2116         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
2117         tcp_rtt_estimator(sk, seq_rtt);
2118         tcp_set_rto(sk);
2119         inet_csk(sk)->icsk_backoff = 0;
2120         tcp_bound_rto(sk);
2121 }
2122
2123 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
2124 {
2125         /* We don't have a timestamp. Can only use
2126          * packets that are not retransmitted to determine
2127          * rtt estimates. Also, we must not reset the
2128          * backoff for rto until we get a non-retransmitted
2129          * packet. This allows us to deal with a situation
2130          * where the network delay has increased suddenly.
2131          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
2132          */
2133
2134         if (flag & FLAG_RETRANS_DATA_ACKED)
2135                 return;
2136
2137         tcp_rtt_estimator(sk, seq_rtt);
2138         tcp_set_rto(sk);
2139         inet_csk(sk)->icsk_backoff = 0;
2140         tcp_bound_rto(sk);
2141 }
2142
2143 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
2144                                       const s32 seq_rtt)
2145 {
2146         const struct tcp_sock *tp = tcp_sk(sk);
2147         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
2148         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
2149                 tcp_ack_saw_tstamp(sk, flag);
2150         else if (seq_rtt >= 0)
2151                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
2152 }
2153
2154 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
2155                            u32 in_flight, int good)
2156 {
2157         const struct inet_connection_sock *icsk = inet_csk(sk);
2158         icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
2159         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2160 }
2161
2162 /* Restart timer after forward progress on connection.
2163  * RFC2988 recommends to restart timer to now+rto.
2164  */
2165
2166 static void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
2167 {
2168         if (!tp->packets_out) {
2169                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2170         } else {
2171                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2172         }
2173 }
2174
2175 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
2176                          __u32 now, __s32 *seq_rtt)
2177 {
2178         struct tcp_sock *tp = tcp_sk(sk);
2179         struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2180         __u32 seq = tp->snd_una;
2181         __u32 packets_acked;
2182         int acked = 0;
2183
2184         /* If we get here, the whole TSO packet has not been
2185          * acked.
2186          */
2187         BUG_ON(!after(scb->end_seq, seq));
2188
2189         packets_acked = tcp_skb_pcount(skb);
2190         if (tcp_trim_head(sk, skb, seq - scb->seq))
2191                 return 0;
2192         packets_acked -= tcp_skb_pcount(skb);
2193
2194         if (packets_acked) {
2195                 __u8 sacked = scb->sacked;
2196
2197                 acked |= FLAG_DATA_ACKED;
2198                 if (sacked) {
2199                         if (sacked & TCPCB_RETRANS) {
2200                                 if (sacked & TCPCB_SACKED_RETRANS)
2201                                         tp->retrans_out -= packets_acked;
2202                                 acked |= FLAG_RETRANS_DATA_ACKED;
2203                                 *seq_rtt = -1;
2204                         } else if (*seq_rtt < 0)
2205                                 *seq_rtt = now - scb->when;
2206                         if (sacked & TCPCB_SACKED_ACKED)
2207                                 tp->sacked_out -= packets_acked;
2208                         if (sacked & TCPCB_LOST)
2209                                 tp->lost_out -= packets_acked;
2210                         if (sacked & TCPCB_URG) {
2211                                 if (tp->urg_mode &&
2212                                     !before(seq, tp->snd_up))
2213                                         tp->urg_mode = 0;
2214                         }
2215                 } else if (*seq_rtt < 0)
2216                         *seq_rtt = now - scb->when;
2217
2218                 if (tp->fackets_out) {
2219                         __u32 dval = min(tp->fackets_out, packets_acked);
2220                         tp->fackets_out -= dval;
2221                 }
2222                 tp->packets_out -= packets_acked;
2223
2224                 BUG_ON(tcp_skb_pcount(skb) == 0);
2225                 BUG_ON(!before(scb->seq, scb->end_seq));
2226         }
2227
2228         return acked;
2229 }
2230
2231 static u32 tcp_usrtt(const struct sk_buff *skb)
2232 {
2233         struct timeval tv, now;
2234
2235         do_gettimeofday(&now);
2236         skb_get_timestamp(skb, &tv);
2237         return (now.tv_sec - tv.tv_sec) * 1000000 + (now.tv_usec - tv.tv_usec);
2238 }
2239
2240 /* Remove acknowledged frames from the retransmission queue. */
2241 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
2242 {
2243         struct tcp_sock *tp = tcp_sk(sk);
2244         const struct inet_connection_sock *icsk = inet_csk(sk);
2245         struct sk_buff *skb;
2246         __u32 now = tcp_time_stamp;
2247         int acked = 0;
2248         __s32 seq_rtt = -1;
2249         u32 pkts_acked = 0;
2250         void (*rtt_sample)(struct sock *sk, u32 usrtt)
2251                 = icsk->icsk_ca_ops->rtt_sample;
2252
2253         while ((skb = skb_peek(&sk->sk_write_queue)) &&
2254                skb != sk->sk_send_head) {
2255                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2256                 __u8 sacked = scb->sacked;
2257
2258                 /* If our packet is before the ack sequence we can
2259                  * discard it as it's confirmed to have arrived at
2260                  * the other end.
2261                  */
2262                 if (after(scb->end_seq, tp->snd_una)) {
2263                         if (tcp_skb_pcount(skb) > 1 &&
2264                             after(tp->snd_una, scb->seq))
2265                                 acked |= tcp_tso_acked(sk, skb,
2266                                                        now, &seq_rtt);
2267                         break;
2268                 }
2269
2270                 /* Initial outgoing SYN's get put onto the write_queue
2271                  * just like anything else we transmit.  It is not
2272                  * true data, and if we misinform our callers that
2273                  * this ACK acks real data, we will erroneously exit
2274                  * connection startup slow start one packet too
2275                  * quickly.  This is severely frowned upon behavior.
2276                  */
2277                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2278                         acked |= FLAG_DATA_ACKED;
2279                         ++pkts_acked;
2280                 } else {
2281                         acked |= FLAG_SYN_ACKED;
2282                         tp->retrans_stamp = 0;
2283                 }
2284
2285                 /* MTU probing checks */
2286                 if (icsk->icsk_mtup.probe_size) {
2287                         if (!after(tp->mtu_probe.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {
2288                                 tcp_mtup_probe_success(sk, skb);
2289                         }
2290                 }
2291
2292                 if (sacked) {
2293                         if (sacked & TCPCB_RETRANS) {
2294                                 if(sacked & TCPCB_SACKED_RETRANS)
2295                                         tp->retrans_out -= tcp_skb_pcount(skb);
2296                                 acked |= FLAG_RETRANS_DATA_ACKED;
2297                                 seq_rtt = -1;
2298                         } else if (seq_rtt < 0) {
2299                                 seq_rtt = now - scb->when;
2300                                 if (rtt_sample)
2301                                         (*rtt_sample)(sk, tcp_usrtt(skb));
2302                         }
2303                         if (sacked & TCPCB_SACKED_ACKED)
2304                                 tp->sacked_out -= tcp_skb_pcount(skb);
2305                         if (sacked & TCPCB_LOST)
2306                                 tp->lost_out -= tcp_skb_pcount(skb);
2307                         if (sacked & TCPCB_URG) {
2308                                 if (tp->urg_mode &&
2309                                     !before(scb->end_seq, tp->snd_up))
2310                                         tp->urg_mode = 0;
2311                         }
2312                 } else if (seq_rtt < 0) {
2313                         seq_rtt = now - scb->when;
2314                         if (rtt_sample)
2315                                 (*rtt_sample)(sk, tcp_usrtt(skb));
2316                 }
2317                 tcp_dec_pcount_approx(&tp->fackets_out, skb);
2318                 tcp_packets_out_dec(tp, skb);
2319                 __skb_unlink(skb, &sk->sk_write_queue);
2320                 sk_stream_free_skb(sk, skb);
2321                 clear_all_retrans_hints(tp);
2322         }
2323
2324         if (acked&FLAG_ACKED) {
2325                 tcp_ack_update_rtt(sk, acked, seq_rtt);
2326                 tcp_ack_packets_out(sk, tp);
2327
2328                 if (icsk->icsk_ca_ops->pkts_acked)
2329                         icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
2330         }
2331
2332 #if FASTRETRANS_DEBUG > 0
2333         BUG_TRAP((int)tp->sacked_out >= 0);
2334         BUG_TRAP((int)tp->lost_out >= 0);
2335         BUG_TRAP((int)tp->retrans_out >= 0);
2336         if (!tp->packets_out && tp->rx_opt.sack_ok) {
2337                 const struct inet_connection_sock *icsk = inet_csk(sk);
2338                 if (tp->lost_out) {
2339                         printk(KERN_DEBUG "Leak l=%u %d\n",
2340                                tp->lost_out, icsk->icsk_ca_state);
2341                         tp->lost_out = 0;
2342                 }
2343                 if (tp->sacked_out) {
2344                         printk(KERN_DEBUG "Leak s=%u %d\n",
2345                                tp->sacked_out, icsk->icsk_ca_state);
2346                         tp->sacked_out = 0;
2347                 }
2348                 if (tp->retrans_out) {
2349                         printk(KERN_DEBUG "Leak r=%u %d\n",
2350                                tp->retrans_out, icsk->icsk_ca_state);
2351                         tp->retrans_out = 0;
2352                 }
2353         }
2354 #endif
2355         *seq_rtt_p = seq_rtt;
2356         return acked;
2357 }
2358
2359 static void tcp_ack_probe(struct sock *sk)
2360 {
2361         const struct tcp_sock *tp = tcp_sk(sk);
2362         struct inet_connection_sock *icsk = inet_csk(sk);
2363
2364         /* Was it a usable window open? */
2365
2366         if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
2367                    tp->snd_una + tp->snd_wnd)) {
2368                 icsk->icsk_backoff = 0;
2369                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2370                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2371                  * This function is not for random using!
2372                  */
2373         } else {
2374                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2375                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2376                                           TCP_RTO_MAX);
2377         }
2378 }
2379
2380 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2381 {
2382         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2383                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2384 }
2385
2386 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2387 {
2388         const struct tcp_sock *tp = tcp_sk(sk);
2389         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2390                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2391 }
2392
2393 /* Check that window update is acceptable.
2394  * The function assumes that snd_una<=ack<=snd_next.
2395  */
2396 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2397                                         const u32 ack_seq, const u32 nwin)
2398 {
2399         return (after(ack, tp->snd_una) ||
2400                 after(ack_seq, tp->snd_wl1) ||
2401                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2402 }
2403
2404 /* Update our send window.
2405  *
2406  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2407  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2408  */
2409 static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
2410                                  struct sk_buff *skb, u32 ack, u32 ack_seq)
2411 {
2412         int flag = 0;
2413         u32 nwin = ntohs(skb->h.th->window);
2414
2415         if (likely(!skb->h.th->syn))
2416                 nwin <<= tp->rx_opt.snd_wscale;
2417
2418         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2419                 flag |= FLAG_WIN_UPDATE;
2420                 tcp_update_wl(tp, ack, ack_seq);
2421
2422                 if (tp->snd_wnd != nwin) {
2423                         tp->snd_wnd = nwin;
2424
2425                         /* Note, it is the only place, where
2426                          * fast path is recovered for sending TCP.
2427                          */
2428                         tp->pred_flags = 0;
2429                         tcp_fast_path_check(sk, tp);
2430
2431                         if (nwin > tp->max_window) {
2432                                 tp->max_window = nwin;
2433                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
2434                         }
2435                 }
2436         }
2437
2438         tp->snd_una = ack;
2439
2440         return flag;
2441 }
2442
2443 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
2444 {
2445         struct tcp_sock *tp = tcp_sk(sk);
2446         
2447         tcp_sync_left_out(tp);
2448         
2449         if (tp->snd_una == prior_snd_una ||
2450             !before(tp->snd_una, tp->frto_highmark)) {
2451                 /* RTO was caused by loss, start retransmitting in
2452                  * go-back-N slow start
2453                  */
2454                 tcp_enter_frto_loss(sk);
2455                 return;
2456         }
2457
2458         if (tp->frto_counter == 1) {
2459                 /* First ACK after RTO advances the window: allow two new
2460                  * segments out.
2461                  */
2462                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2463         } else {
2464                 /* Also the second ACK after RTO advances the window.
2465                  * The RTO was likely spurious. Reduce cwnd and continue
2466                  * in congestion avoidance
2467                  */
2468                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2469                 tcp_moderate_cwnd(tp);
2470         }
2471
2472         /* F-RTO affects on two new ACKs following RTO.
2473          * At latest on third ACK the TCP behavior is back to normal.
2474          */
2475         tp->frto_counter = (tp->frto_counter + 1) % 3;
2476 }
2477
2478 /* This routine deals with incoming acks, but not outgoing ones. */
2479 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2480 {
2481         struct inet_connection_sock *icsk = inet_csk(sk);
2482         struct tcp_sock *tp = tcp_sk(sk);
2483         u32 prior_snd_una = tp->snd_una;
2484         u32 ack_seq = TCP_SKB_CB(skb)->seq;
2485         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2486         u32 prior_in_flight;
2487         s32 seq_rtt;
2488         int prior_packets;
2489
2490         /* If the ack is newer than sent or older than previous acks
2491          * then we can probably ignore it.
2492          */
2493         if (after(ack, tp->snd_nxt))
2494                 goto uninteresting_ack;
2495
2496         if (before(ack, prior_snd_una))
2497                 goto old_ack;
2498
2499         if (sysctl_tcp_abc && icsk->icsk_ca_state < TCP_CA_CWR)
2500                 tp->bytes_acked += ack - prior_snd_una;
2501
2502         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
2503                 /* Window is constant, pure forward advance.
2504                  * No more checks are required.
2505                  * Note, we use the fact that SND.UNA>=SND.WL2.
2506                  */
2507                 tcp_update_wl(tp, ack, ack_seq);
2508                 tp->snd_una = ack;
2509                 flag |= FLAG_WIN_UPDATE;
2510
2511                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
2512
2513                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
2514         } else {
2515                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
2516                         flag |= FLAG_DATA;
2517                 else
2518                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
2519
2520                 flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);
2521
2522                 if (TCP_SKB_CB(skb)->sacked)
2523                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2524
2525                 if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
2526                         flag |= FLAG_ECE;
2527
2528                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
2529         }
2530
2531         /* We passed data and got it acked, remove any soft error
2532          * log. Something worked...
2533          */
2534         sk->sk_err_soft = 0;
2535         tp->rcv_tstamp = tcp_time_stamp;
2536         prior_packets = tp->packets_out;
2537         if (!prior_packets)
2538                 goto no_queue;
2539
2540         prior_in_flight = tcp_packets_in_flight(tp);
2541
2542         /* See if we can take anything off of the retransmit queue. */
2543         flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
2544
2545         if (tp->frto_counter)
2546                 tcp_process_frto(sk, prior_snd_una);
2547
2548         if (tcp_ack_is_dubious(sk, flag)) {
2549                 /* Advance CWND, if state allows this. */
2550                 if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
2551                         tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
2552                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2553         } else {
2554                 if ((flag & FLAG_DATA_ACKED))
2555                         tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
2556         }
2557
2558         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2559                 dst_confirm(sk->sk_dst_cache);
2560
2561         return 1;
2562
2563 no_queue:
2564         icsk->icsk_probes_out = 0;
2565
2566         /* If this ack opens up a zero window, clear backoff.  It was
2567          * being used to time the probes, and is probably far higher than
2568          * it needs to be for normal retransmission.
2569          */
2570         if (sk->sk_send_head)
2571                 tcp_ack_probe(sk);
2572         return 1;
2573
2574 old_ack:
2575         if (TCP_SKB_CB(skb)->sacked)
2576                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2577
2578 uninteresting_ack:
2579         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2580         return 0;
2581 }
2582
2583
2584 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2585  * But, this can also be called on packets in the established flow when
2586  * the fast version below fails.
2587  */
2588 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2589 {
2590         unsigned char *ptr;
2591         struct tcphdr *th = skb->h.th;
2592         int length=(th->doff*4)-sizeof(struct tcphdr);
2593
2594         ptr = (unsigned char *)(th + 1);
2595         opt_rx->saw_tstamp = 0;
2596
2597         while(length>0) {
2598                 int opcode=*ptr++;
2599                 int opsize;
2600
2601                 switch (opcode) {
2602                         case TCPOPT_EOL:
2603                                 return;
2604                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
2605                                 length--;
2606                                 continue;
2607                         default:
2608                                 opsize=*ptr++;
2609                                 if (opsize < 2) /* "silly options" */
2610                                         return;
2611                                 if (opsize > length)
2612                                         return; /* don't parse partial options */
2613                                 switch(opcode) {
2614                                 case TCPOPT_MSS:
2615                                         if(opsize==TCPOLEN_MSS && th->syn && !estab) {
2616                                                 u16 in_mss = ntohs(get_unaligned((__u16 *)ptr));
2617                                                 if (in_mss) {
2618                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2619                                                                 in_mss = opt_rx->user_mss;
2620                                                         opt_rx->mss_clamp = in_mss;
2621                                                 }
2622                                         }
2623                                         break;
2624                                 case TCPOPT_WINDOW:
2625                                         if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
2626                                                 if (sysctl_tcp_window_scaling) {
2627                                                         __u8 snd_wscale = *(__u8 *) ptr;
2628                                                         opt_rx->wscale_ok = 1;
2629                                                         if (snd_wscale > 14) {
2630                                                                 if(net_ratelimit())
2631                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
2632                                                                                "scaling value %d >14 received.\n",
2633                                                                                snd_wscale);
2634                                                                 snd_wscale = 14;
2635                                                         }
2636                                                         opt_rx->snd_wscale = snd_wscale;
2637                                                 }
2638                                         break;
2639                                 case TCPOPT_TIMESTAMP:
2640                                         if(opsize==TCPOLEN_TIMESTAMP) {
2641                                                 if ((estab && opt_rx->tstamp_ok) ||
2642                                                     (!estab && sysctl_tcp_timestamps)) {
2643                                                         opt_rx->saw_tstamp = 1;
2644                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr));
2645                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4)));
2646                                                 }
2647                                         }
2648                                         break;
2649                                 case TCPOPT_SACK_PERM:
2650                                         if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2651                                                 if (sysctl_tcp_sack) {
2652                                                         opt_rx->sack_ok = 1;
2653                                                         tcp_sack_reset(opt_rx);
2654                                                 }
2655                                         }
2656                                         break;
2657
2658                                 case TCPOPT_SACK:
2659                                         if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2660                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2661                                            opt_rx->sack_ok) {
2662                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2663                                         }
2664                                 };
2665                                 ptr+=opsize-2;
2666                                 length-=opsize;
2667                 };
2668         }
2669 }
2670
2671 /* Fast parse options. This hopes to only see timestamps.
2672  * If it is wrong it falls back on tcp_parse_options().
2673  */
2674 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2675                                   struct tcp_sock *tp)
2676 {
2677         if (th->doff == sizeof(struct tcphdr)>>2) {
2678                 tp->rx_opt.saw_tstamp = 0;
2679                 return 0;
2680         } else if (tp->rx_opt.tstamp_ok &&
2681                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2682                 __u32 *ptr = (__u32 *)(th + 1);
2683                 if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2684                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2685                         tp->rx_opt.saw_tstamp = 1;
2686                         ++ptr;
2687                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
2688                         ++ptr;
2689                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2690                         return 1;
2691                 }
2692         }
2693         tcp_parse_options(skb, &tp->rx_opt, 1);
2694         return 1;
2695 }
2696
2697 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2698 {
2699         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2700         tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
2701 }
2702
2703 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2704 {
2705         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2706                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
2707                  * extra check below makes sure this can only happen
2708                  * for pure ACK frames.  -DaveM
2709                  *
2710                  * Not only, also it occurs for expired timestamps.
2711                  */
2712
2713                 if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2714                    xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2715                         tcp_store_ts_recent(tp);
2716         }
2717 }
2718
2719 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2720  *
2721  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2722  * it can pass through stack. So, the following predicate verifies that
2723  * this segment is not used for anything but congestion avoidance or
2724  * fast retransmit. Moreover, we even are able to eliminate most of such
2725  * second order effects, if we apply some small "replay" window (~RTO)
2726  * to timestamp space.
2727  *
2728  * All these measures still do not guarantee that we reject wrapped ACKs
2729  * on networks with high bandwidth, when sequence space is recycled fastly,
2730  * but it guarantees that such events will be very rare and do not affect
2731  * connection seriously. This doesn't look nice, but alas, PAWS is really
2732  * buggy extension.
2733  *
2734  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
2735  * states that events when retransmit arrives after original data are rare.
2736  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
2737  * the biggest problem on large power networks even with minor reordering.
2738  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
2739  * up to bandwidth of 18Gigabit/sec. 8) ]
2740  */
2741
2742 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
2743 {
2744         struct tcp_sock *tp = tcp_sk(sk);
2745         struct tcphdr *th = skb->h.th;
2746         u32 seq = TCP_SKB_CB(skb)->seq;
2747         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2748
2749         return (/* 1. Pure ACK with correct sequence number. */
2750                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
2751
2752                 /* 2. ... and duplicate ACK. */
2753                 ack == tp->snd_una &&
2754
2755                 /* 3. ... and does not update window. */
2756                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
2757
2758                 /* 4. ... and sits in replay window. */
2759                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
2760 }
2761
2762 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
2763 {
2764         const struct tcp_sock *tp = tcp_sk(sk);
2765         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
2766                 xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2767                 !tcp_disordered_ack(sk, skb));
2768 }
2769
2770 /* Check segment sequence number for validity.
2771  *
2772  * Segment controls are considered valid, if the segment
2773  * fits to the window after truncation to the window. Acceptability
2774  * of data (and SYN, FIN, of course) is checked separately.
2775  * See tcp_data_queue(), for example.
2776  *
2777  * Also, controls (RST is main one) are accepted using RCV.WUP instead
2778  * of RCV.NXT. Peer still did not advance his SND.UNA when we
2779  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
2780  * (borrowed from freebsd)
2781  */
2782
2783 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
2784 {
2785         return  !before(end_seq, tp->rcv_wup) &&
2786                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
2787 }
2788
2789 /* When we get a reset we do this. */
2790 static void tcp_reset(struct sock *sk)
2791 {
2792         /* We want the right error as BSD sees it (and indeed as we do). */
2793         switch (sk->sk_state) {
2794                 case TCP_SYN_SENT:
2795                         sk->sk_err = ECONNREFUSED;
2796                         break;
2797                 case TCP_CLOSE_WAIT:
2798                         sk->sk_err = EPIPE;
2799                         break;
2800                 case TCP_CLOSE:
2801                         return;
2802                 default:
2803                         sk->sk_err = ECONNRESET;
2804         }
2805
2806         if (!sock_flag(sk, SOCK_DEAD))
2807                 sk->sk_error_report(sk);
2808
2809         tcp_done(sk);
2810 }
2811
2812 /*
2813  *      Process the FIN bit. This now behaves as it is supposed to work
2814  *      and the FIN takes effect when it is validly part of sequence
2815  *      space. Not before when we get holes.
2816  *
2817  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
2818  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
2819  *      TIME-WAIT)
2820  *
2821  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
2822  *      close and we go into CLOSING (and later onto TIME-WAIT)
2823  *
2824  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
2825  */
2826 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
2827 {
2828         struct tcp_sock *tp = tcp_sk(sk);
2829
2830         inet_csk_schedule_ack(sk);
2831
2832         sk->sk_shutdown |= RCV_SHUTDOWN;
2833         sock_set_flag(sk, SOCK_DONE);
2834
2835         switch (sk->sk_state) {
2836                 case TCP_SYN_RECV:
2837                 case TCP_ESTABLISHED:
2838                         /* Move to CLOSE_WAIT */
2839                         tcp_set_state(sk, TCP_CLOSE_WAIT);
2840                         inet_csk(sk)->icsk_ack.pingpong = 1;
2841                         break;
2842
2843                 case TCP_CLOSE_WAIT:
2844                 case TCP_CLOSING:
2845                         /* Received a retransmission of the FIN, do
2846                          * nothing.
2847                          */
2848                         break;
2849                 case TCP_LAST_ACK:
2850                         /* RFC793: Remain in the LAST-ACK state. */
2851                         break;
2852
2853                 case TCP_FIN_WAIT1:
2854                         /* This case occurs when a simultaneous close
2855                          * happens, we must ack the received FIN and
2856                          * enter the CLOSING state.
2857                          */
2858                         tcp_send_ack(sk);
2859                         tcp_set_state(sk, TCP_CLOSING);
2860                         break;
2861                 case TCP_FIN_WAIT2:
2862                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
2863                         tcp_send_ack(sk);
2864                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
2865                         break;
2866                 default:
2867                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
2868                          * cases we should never reach this piece of code.
2869                          */
2870                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
2871                                __FUNCTION__, sk->sk_state);
2872                         break;
2873         };
2874
2875         /* It _is_ possible, that we have something out-of-order _after_ FIN.
2876          * Probably, we should reset in this case. For now drop them.
2877          */
2878         __skb_queue_purge(&tp->out_of_order_queue);
2879         if (tp->rx_opt.sack_ok)
2880                 tcp_sack_reset(&tp->rx_opt);
2881         sk_stream_mem_reclaim(sk);
2882
2883         if (!sock_flag(sk, SOCK_DEAD)) {
2884                 sk->sk_state_change(sk);
2885
2886                 /* Do not send POLL_HUP for half duplex close. */
2887                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
2888                     sk->sk_state == TCP_CLOSE)
2889                         sk_wake_async(sk, 1, POLL_HUP);
2890                 else
2891                         sk_wake_async(sk, 1, POLL_IN);
2892         }
2893 }
2894
2895 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
2896 {
2897         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
2898                 if (before(seq, sp->start_seq))
2899                         sp->start_seq = seq;
2900                 if (after(end_seq, sp->end_seq))
2901                         sp->end_seq = end_seq;
2902                 return 1;
2903         }
2904         return 0;
2905 }
2906
2907 static void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
2908 {
2909         if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2910                 if (before(seq, tp->rcv_nxt))
2911                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
2912                 else
2913                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
2914
2915                 tp->rx_opt.dsack = 1;
2916                 tp->duplicate_sack[0].start_seq = seq;
2917                 tp->duplicate_sack[0].end_seq = end_seq;
2918                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
2919         }
2920 }
2921
2922 static void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
2923 {
2924         if (!tp->rx_opt.dsack)
2925                 tcp_dsack_set(tp, seq, end_seq);
2926         else
2927                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
2928 }
2929
2930 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
2931 {
2932         struct tcp_sock *tp = tcp_sk(sk);
2933
2934         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
2935             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2936                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2937                 tcp_enter_quickack_mode(sk);
2938
2939                 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2940                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2941
2942                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
2943                                 end_seq = tp->rcv_nxt;
2944                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
2945                 }
2946         }
2947
2948         tcp_send_ack(sk);
2949 }
2950
2951 /* These routines update the SACK block as out-of-order packets arrive or
2952  * in-order packets close up the sequence space.
2953  */
2954 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
2955 {
2956         int this_sack;
2957         struct tcp_sack_block *sp = &tp->selective_acks[0];
2958         struct tcp_sack_block *swalk = sp+1;
2959
2960         /* See if the recent change to the first SACK eats into
2961          * or hits the sequence space of other SACK blocks, if so coalesce.
2962          */
2963         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
2964                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
2965                         int i;
2966
2967                         /* Zap SWALK, by moving every further SACK up by one slot.
2968                          * Decrease num_sacks.
2969                          */
2970                         tp->rx_opt.num_sacks--;
2971                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2972                         for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
2973                                 sp[i] = sp[i+1];
2974                         continue;
2975                 }
2976                 this_sack++, swalk++;
2977         }
2978 }
2979
2980 static inline void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
2981 {
2982         __u32 tmp;
2983
2984         tmp = sack1->start_seq;
2985         sack1->start_seq = sack2->start_seq;
2986         sack2->start_seq = tmp;
2987
2988         tmp = sack1->end_seq;
2989         sack1->end_seq = sack2->end_seq;
2990         sack2->end_seq = tmp;
2991 }
2992
2993 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
2994 {
2995         struct tcp_sock *tp = tcp_sk(sk);
2996         struct tcp_sack_block *sp = &tp->selective_acks[0];
2997         int cur_sacks = tp->rx_opt.num_sacks;
2998         int this_sack;
2999
3000         if (!cur_sacks)
3001                 goto new_sack;
3002
3003         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
3004                 if (tcp_sack_extend(sp, seq, end_seq)) {
3005                         /* Rotate this_sack to the first one. */
3006                         for (; this_sack>0; this_sack--, sp--)
3007                                 tcp_sack_swap(sp, sp-1);
3008                         if (cur_sacks > 1)
3009                                 tcp_sack_maybe_coalesce(tp);
3010                         return;
3011                 }
3012         }
3013
3014         /* Could not find an adjacent existing SACK, build a new one,
3015          * put it at the front, and shift everyone else down.  We
3016          * always know there is at least one SACK present already here.
3017          *
3018          * If the sack array is full, forget about the last one.
3019          */
3020         if (this_sack >= 4) {
3021                 this_sack--;
3022                 tp->rx_opt.num_sacks--;
3023                 sp--;
3024         }
3025         for(; this_sack > 0; this_sack--, sp--)
3026                 *sp = *(sp-1);
3027
3028 new_sack:
3029         /* Build the new head SACK, and we're done. */
3030         sp->start_seq = seq;
3031         sp->end_seq = end_seq;
3032         tp->rx_opt.num_sacks++;
3033         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3034 }
3035
3036 /* RCV.NXT advances, some SACKs should be eaten. */
3037
3038 static void tcp_sack_remove(struct tcp_sock *tp)
3039 {
3040         struct tcp_sack_block *sp = &tp->selective_acks[0];
3041         int num_sacks = tp->rx_opt.num_sacks;
3042         int this_sack;
3043
3044         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
3045         if (skb_queue_empty(&tp->out_of_order_queue)) {
3046                 tp->rx_opt.num_sacks = 0;
3047                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
3048                 return;
3049         }
3050
3051         for(this_sack = 0; this_sack < num_sacks; ) {
3052                 /* Check if the start of the sack is covered by RCV.NXT. */
3053                 if (!before(tp->rcv_nxt, sp->start_seq)) {
3054                         int i;
3055
3056                         /* RCV.NXT must cover all the block! */
3057                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
3058
3059                         /* Zap this SACK, by moving forward any other SACKS. */
3060                         for (i=this_sack+1; i < num_sacks; i++)
3061                                 tp->selective_acks[i-1] = tp->selective_acks[i];
3062                         num_sacks--;
3063                         continue;
3064                 }
3065                 this_sack++;
3066                 sp++;
3067         }
3068         if (num_sacks != tp->rx_opt.num_sacks) {
3069                 tp->rx_opt.num_sacks = num_sacks;
3070                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3071         }
3072 }
3073
3074 /* This one checks to see if we can put data from the
3075  * out_of_order queue into the receive_queue.
3076  */
3077 static void tcp_ofo_queue(struct sock *sk)
3078 {
3079         struct tcp_sock *tp = tcp_sk(sk);
3080         __u32 dsack_high = tp->rcv_nxt;
3081         struct sk_buff *skb;
3082
3083         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
3084                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
3085                         break;
3086
3087                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
3088                         __u32 dsack = dsack_high;
3089                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
3090                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
3091                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
3092                 }
3093
3094                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3095                         SOCK_DEBUG(sk, "ofo packet was already received \n");
3096                         __skb_unlink(skb, &tp->out_of_order_queue);
3097                         __kfree_skb(skb);
3098                         continue;
3099                 }
3100                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
3101                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3102                            TCP_SKB_CB(skb)->end_seq);
3103
3104                 __skb_unlink(skb, &tp->out_of_order_queue);
3105                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3106                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3107                 if(skb->h.th->fin)
3108                         tcp_fin(skb, sk, skb->h.th);
3109         }
3110 }
3111
3112 static int tcp_prune_queue(struct sock *sk);
3113
3114 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
3115 {
3116         struct tcphdr *th = skb->h.th;
3117         struct tcp_sock *tp = tcp_sk(sk);
3118         int eaten = -1;
3119
3120         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
3121                 goto drop;
3122
3123         __skb_pull(skb, th->doff*4);
3124
3125         TCP_ECN_accept_cwr(tp, skb);
3126
3127         if (tp->rx_opt.dsack) {
3128                 tp->rx_opt.dsack = 0;
3129                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
3130                                                     4 - tp->rx_opt.tstamp_ok);
3131         }
3132
3133         /*  Queue data for delivery to the user.
3134          *  Packets in sequence go to the receive queue.
3135          *  Out of sequence packets to the out_of_order_queue.
3136          */
3137         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3138                 if (tcp_receive_window(tp) == 0)
3139                         goto out_of_window;
3140
3141                 /* Ok. In sequence. In window. */
3142                 if (tp->ucopy.task == current &&
3143                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
3144                     sock_owned_by_user(sk) && !tp->urg_data) {
3145                         int chunk = min_t(unsigned int, skb->len,
3146                                                         tp->ucopy.len);
3147
3148                         __set_current_state(TASK_RUNNING);
3149
3150                         local_bh_enable();
3151                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
3152                                 tp->ucopy.len -= chunk;
3153                                 tp->copied_seq += chunk;
3154                                 eaten = (chunk == skb->len && !th->fin);
3155                                 tcp_rcv_space_adjust(sk);
3156                         }
3157                         local_bh_disable();
3158                 }
3159
3160                 if (eaten <= 0) {
3161 queue_and_out:
3162                         if (eaten < 0 &&
3163                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3164                              !sk_stream_rmem_schedule(sk, skb))) {
3165                                 if (tcp_prune_queue(sk) < 0 ||
3166                                     !sk_stream_rmem_schedule(sk, skb))
3167                                         goto drop;
3168                         }
3169                         sk_stream_set_owner_r(skb, sk);
3170                         __skb_queue_tail(&sk->sk_receive_queue, skb);
3171                 }
3172                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3173                 if(skb->len)
3174                         tcp_event_data_recv(sk, tp, skb);
3175                 if(th->fin)
3176                         tcp_fin(skb, sk, th);
3177
3178                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
3179                         tcp_ofo_queue(sk);
3180
3181                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
3182                          * gap in queue is filled.
3183                          */
3184                         if (skb_queue_empty(&tp->out_of_order_queue))
3185                                 inet_csk(sk)->icsk_ack.pingpong = 0;
3186                 }
3187
3188                 if (tp->rx_opt.num_sacks)
3189                         tcp_sack_remove(tp);
3190
3191                 tcp_fast_path_check(sk, tp);
3192
3193                 if (eaten > 0)
3194                         __kfree_skb(skb);
3195                 else if (!sock_flag(sk, SOCK_DEAD))
3196                         sk->sk_data_ready(sk, 0);
3197                 return;
3198         }
3199
3200         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3201                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3202                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3203                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3204
3205 out_of_window:
3206                 tcp_enter_quickack_mode(sk);
3207                 inet_csk_schedule_ack(sk);
3208 drop:
3209                 __kfree_skb(skb);
3210                 return;
3211         }
3212
3213         /* Out of window. F.e. zero window probe. */
3214         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3215                 goto out_of_window;
3216
3217         tcp_enter_quickack_mode(sk);
3218
3219         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3220                 /* Partial packet, seq < rcv_next < end_seq */
3221                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3222                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3223                            TCP_SKB_CB(skb)->end_seq);
3224
3225                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3226                 
3227                 /* If window is closed, drop tail of packet. But after
3228                  * remembering D-SACK for its head made in previous line.
3229                  */
3230                 if (!tcp_receive_window(tp))
3231                         goto out_of_window;
3232                 goto queue_and_out;
3233         }
3234
3235         TCP_ECN_check_ce(tp, skb);
3236
3237         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3238             !sk_stream_rmem_schedule(sk, skb)) {
3239                 if (tcp_prune_queue(sk) < 0 ||
3240                     !sk_stream_rmem_schedule(sk, skb))
3241                         goto drop;
3242         }
3243
3244         /* Disable header prediction. */
3245         tp->pred_flags = 0;
3246         inet_csk_schedule_ack(sk);
3247
3248         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3249                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3250
3251         sk_stream_set_owner_r(skb, sk);
3252
3253         if (!skb_peek(&tp->out_of_order_queue)) {
3254                 /* Initial out of order segment, build 1 SACK. */
3255                 if (tp->rx_opt.sack_ok) {
3256                         tp->rx_opt.num_sacks = 1;
3257                         tp->rx_opt.dsack     = 0;
3258                         tp->rx_opt.eff_sacks = 1;
3259                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3260                         tp->selective_acks[0].end_seq =
3261                                                 TCP_SKB_CB(skb)->end_seq;
3262                 }
3263                 __skb_queue_head(&tp->out_of_order_queue,skb);
3264         } else {
3265                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3266                 u32 seq = TCP_SKB_CB(skb)->seq;
3267                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3268
3269                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3270                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3271
3272                         if (!tp->rx_opt.num_sacks ||
3273                             tp->selective_acks[0].end_seq != seq)
3274                                 goto add_sack;
3275
3276                         /* Common case: data arrive in order after hole. */
3277                         tp->selective_acks[0].end_seq = end_seq;
3278                         return;
3279                 }
3280
3281                 /* Find place to insert this segment. */
3282                 do {
3283                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3284                                 break;
3285                 } while ((skb1 = skb1->prev) !=
3286                          (struct sk_buff*)&tp->out_of_order_queue);
3287
3288                 /* Do skb overlap to previous one? */
3289                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3290                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3291                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3292                                 /* All the bits are present. Drop. */
3293                                 __kfree_skb(skb);
3294                                 tcp_dsack_set(tp, seq, end_seq);
3295                                 goto add_sack;
3296                         }
3297                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3298                                 /* Partial overlap. */
3299                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3300                         } else {
3301                                 skb1 = skb1->prev;
3302                         }
3303                 }
3304                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3305                 
3306                 /* And clean segments covered by new one as whole. */
3307                 while ((skb1 = skb->next) !=
3308                        (struct sk_buff*)&tp->out_of_order_queue &&
3309                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3310                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3311                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3312                                break;
3313                        }
3314                        __skb_unlink(skb1, &tp->out_of_order_queue);
3315                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3316                        __kfree_skb(skb1);
3317                 }
3318
3319 add_sack:
3320                 if (tp->rx_opt.sack_ok)
3321                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3322         }
3323 }
3324
3325 /* Collapse contiguous sequence of skbs head..tail with
3326  * sequence numbers start..end.
3327  * Segments with FIN/SYN are not collapsed (only because this
3328  * simplifies code)
3329  */
3330 static void
3331 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3332              struct sk_buff *head, struct sk_buff *tail,
3333              u32 start, u32 end)
3334 {
3335         struct sk_buff *skb;
3336
3337         /* First, check that queue is collapsible and find
3338          * the point where collapsing can be useful. */
3339         for (skb = head; skb != tail; ) {
3340                 /* No new bits? It is possible on ofo queue. */
3341                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3342                         struct sk_buff *next = skb->next;
3343                         __skb_unlink(skb, list);
3344                         __kfree_skb(skb);
3345                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3346                         skb = next;
3347                         continue;
3348                 }
3349
3350                 /* The first skb to collapse is:
3351                  * - not SYN/FIN and
3352                  * - bloated or contains data before "start" or
3353                  *   overlaps to the next one.
3354                  */
3355                 if (!skb->h.th->syn && !skb->h.th->fin &&
3356                     (tcp_win_from_space(skb->truesize) > skb->len ||
3357                      before(TCP_SKB_CB(skb)->seq, start) ||
3358                      (skb->next != tail &&
3359                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3360                         break;
3361
3362                 /* Decided to skip this, advance start seq. */
3363                 start = TCP_SKB_CB(skb)->end_seq;
3364                 skb = skb->next;
3365         }
3366         if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3367                 return;
3368
3369         while (before(start, end)) {
3370                 struct sk_buff *nskb;
3371                 int header = skb_headroom(skb);
3372                 int copy = SKB_MAX_ORDER(header, 0);
3373
3374                 /* Too big header? This can happen with IPv6. */
3375                 if (copy < 0)
3376                         return;
3377                 if (end-start < copy)
3378                         copy = end-start;
3379                 nskb = alloc_skb(copy+header, GFP_ATOMIC);
3380                 if (!nskb)
3381                         return;
3382                 skb_reserve(nskb, header);
3383                 memcpy(nskb->head, skb->head, header);
3384                 nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head);
3385                 nskb->h.raw = nskb->head + (skb->h.raw-skb->head);
3386                 nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head);
3387                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3388                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3389                 __skb_insert(nskb, skb->prev, skb, list);
3390                 sk_stream_set_owner_r(nskb, sk);
3391
3392                 /* Copy data, releasing collapsed skbs. */
3393                 while (copy > 0) {
3394                         int offset = start - TCP_SKB_CB(skb)->seq;
3395                         int size = TCP_SKB_CB(skb)->end_seq - start;
3396
3397                         BUG_ON(offset < 0);
3398                         if (size > 0) {
3399                                 size = min(copy, size);
3400                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3401                                         BUG();
3402                                 TCP_SKB_CB(nskb)->end_seq += size;
3403                                 copy -= size;
3404                                 start += size;
3405                         }
3406                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3407                                 struct sk_buff *next = skb->next;
3408                                 __skb_unlink(skb, list);
3409                                 __kfree_skb(skb);
3410                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3411                                 skb = next;
3412                                 if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3413                                         return;
3414                         }
3415                 }
3416         }
3417 }
3418
3419 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3420  * and tcp_collapse() them until all the queue is collapsed.
3421  */
3422 static void tcp_collapse_ofo_queue(struct sock *sk)
3423 {
3424         struct tcp_sock *tp = tcp_sk(sk);
3425         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3426         struct sk_buff *head;
3427         u32 start, end;
3428
3429         if (skb == NULL)
3430                 return;
3431
3432         start = TCP_SKB_CB(skb)->seq;
3433         end = TCP_SKB_CB(skb)->end_seq;
3434         head = skb;
3435
3436         for (;;) {
3437                 skb = skb->next;
3438
3439                 /* Segment is terminated when we see gap or when
3440                  * we are at the end of all the queue. */
3441                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
3442                     after(TCP_SKB_CB(skb)->seq, end) ||
3443                     before(TCP_SKB_CB(skb)->end_seq, start)) {
3444                         tcp_collapse(sk, &tp->out_of_order_queue,
3445                                      head, skb, start, end);
3446                         head = skb;
3447                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
3448                                 break;
3449                         /* Start new segment */
3450                         start = TCP_SKB_CB(skb)->seq;
3451                         end = TCP_SKB_CB(skb)->end_seq;
3452                 } else {
3453                         if (before(TCP_SKB_CB(skb)->seq, start))
3454                                 start = TCP_SKB_CB(skb)->seq;
3455                         if (after(TCP_SKB_CB(skb)->end_seq, end))
3456                                 end = TCP_SKB_CB(skb)->end_seq;
3457                 }
3458         }
3459 }
3460
3461 /* Reduce allocated memory if we can, trying to get
3462  * the socket within its memory limits again.
3463  *
3464  * Return less than zero if we should start dropping frames
3465  * until the socket owning process reads some of the data
3466  * to stabilize the situation.
3467  */
3468 static int tcp_prune_queue(struct sock *sk)
3469 {
3470         struct tcp_sock *tp = tcp_sk(sk); 
3471
3472         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
3473
3474         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
3475
3476         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
3477                 tcp_clamp_window(sk, tp);
3478         else if (tcp_memory_pressure)
3479                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
3480
3481         tcp_collapse_ofo_queue(sk);
3482         tcp_collapse(sk, &sk->sk_receive_queue,
3483                      sk->sk_receive_queue.next,
3484                      (struct sk_buff*)&sk->sk_receive_queue,
3485                      tp->copied_seq, tp->rcv_nxt);
3486         sk_stream_mem_reclaim(sk);
3487
3488         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3489                 return 0;
3490
3491         /* Collapsing did not help, destructive actions follow.
3492          * This must not ever occur. */
3493
3494         /* First, purge the out_of_order queue. */
3495         if (!skb_queue_empty(&tp->out_of_order_queue)) {
3496                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
3497                 __skb_queue_purge(&tp->out_of_order_queue);
3498
3499                 /* Reset SACK state.  A conforming SACK implementation will
3500                  * do the same at a timeout based retransmit.  When a connection
3501                  * is in a sad state like this, we care only about integrity
3502                  * of the connection not performance.
3503                  */
3504                 if (tp->rx_opt.sack_ok)
3505                         tcp_sack_reset(&tp->rx_opt);
3506                 sk_stream_mem_reclaim(sk);
3507         }
3508
3509         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3510                 return 0;
3511
3512         /* If we are really being abused, tell the caller to silently
3513          * drop receive data on the floor.  It will get retransmitted
3514          * and hopefully then we'll have sufficient space.
3515          */
3516         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
3517
3518         /* Massive buffer overcommit. */
3519         tp->pred_flags = 0;
3520         return -1;
3521 }
3522
3523
3524 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
3525  * As additional protections, we do not touch cwnd in retransmission phases,
3526  * and if application hit its sndbuf limit recently.
3527  */
3528 void tcp_cwnd_application_limited(struct sock *sk)
3529 {
3530         struct tcp_sock *tp = tcp_sk(sk);
3531
3532         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
3533             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
3534                 /* Limited by application or receiver window. */
3535                 u32 win_used = max(tp->snd_cwnd_used, 2U);
3536                 if (win_used < tp->snd_cwnd) {
3537                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
3538                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
3539                 }
3540                 tp->snd_cwnd_used = 0;
3541         }
3542         tp->snd_cwnd_stamp = tcp_time_stamp;
3543 }
3544
3545 static int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp)
3546 {
3547         /* If the user specified a specific send buffer setting, do
3548          * not modify it.
3549          */
3550         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
3551                 return 0;
3552
3553         /* If we are under global TCP memory pressure, do not expand.  */
3554         if (tcp_memory_pressure)
3555                 return 0;
3556
3557         /* If we are under soft global TCP memory pressure, do not expand.  */
3558         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
3559                 return 0;
3560
3561         /* If we filled the congestion window, do not expand.  */
3562         if (tp->packets_out >= tp->snd_cwnd)
3563                 return 0;
3564
3565         return 1;
3566 }
3567
3568 /* When incoming ACK allowed to free some skb from write_queue,
3569  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
3570  * on the exit from tcp input handler.
3571  *
3572  * PROBLEM: sndbuf expansion does not work well with largesend.
3573  */
3574 static void tcp_new_space(struct sock *sk)
3575 {
3576         struct tcp_sock *tp = tcp_sk(sk);
3577
3578         if (tcp_should_expand_sndbuf(sk, tp)) {
3579                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
3580                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
3581                     demanded = max_t(unsigned int, tp->snd_cwnd,
3582                                                    tp->reordering + 1);
3583                 sndmem *= 2*demanded;
3584                 if (sndmem > sk->sk_sndbuf)
3585                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
3586                 tp->snd_cwnd_stamp = tcp_time_stamp;
3587         }
3588
3589         sk->sk_write_space(sk);
3590 }
3591
3592 static void tcp_check_space(struct sock *sk)
3593 {
3594         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
3595                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
3596                 if (sk->sk_socket &&
3597                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
3598                         tcp_new_space(sk);
3599         }
3600 }
3601
3602 static inline void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
3603 {
3604         tcp_push_pending_frames(sk, tp);
3605         tcp_check_space(sk);
3606 }
3607
3608 /*
3609  * Check if sending an ack is needed.
3610  */
3611 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
3612 {
3613         struct tcp_sock *tp = tcp_sk(sk);
3614
3615             /* More than one full frame received... */
3616         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
3617              /* ... and right edge of window advances far enough.
3618               * (tcp_recvmsg() will send ACK otherwise). Or...
3619               */
3620              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
3621             /* We ACK each frame or... */
3622             tcp_in_quickack_mode(sk) ||
3623             /* We have out of order data. */
3624             (ofo_possible &&
3625              skb_peek(&tp->out_of_order_queue))) {
3626                 /* Then ack it now */
3627                 tcp_send_ack(sk);
3628         } else {
3629                 /* Else, send delayed ack. */
3630                 tcp_send_delayed_ack(sk);
3631         }
3632 }
3633
3634 static inline void tcp_ack_snd_check(struct sock *sk)
3635 {
3636         if (!inet_csk_ack_scheduled(sk)) {
3637                 /* We sent a data segment already. */
3638                 return;
3639         }
3640         __tcp_ack_snd_check(sk, 1);
3641 }
3642
3643 /*
3644  *      This routine is only called when we have urgent data
3645  *      signaled. Its the 'slow' part of tcp_urg. It could be
3646  *      moved inline now as tcp_urg is only called from one
3647  *      place. We handle URGent data wrong. We have to - as
3648  *      BSD still doesn't use the correction from RFC961.
3649  *      For 1003.1g we should support a new option TCP_STDURG to permit
3650  *      either form (or just set the sysctl tcp_stdurg).
3651  */
3652  
3653 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
3654 {
3655         struct tcp_sock *tp = tcp_sk(sk);
3656         u32 ptr = ntohs(th->urg_ptr);
3657
3658         if (ptr && !sysctl_tcp_stdurg)
3659                 ptr--;
3660         ptr += ntohl(th->seq);
3661
3662         /* Ignore urgent data that we've already seen and read. */
3663         if (after(tp->copied_seq, ptr))
3664                 return;
3665
3666         /* Do not replay urg ptr.
3667          *
3668          * NOTE: interesting situation not covered by specs.
3669          * Misbehaving sender may send urg ptr, pointing to segment,
3670          * which we already have in ofo queue. We are not able to fetch
3671          * such data and will stay in TCP_URG_NOTYET until will be eaten
3672          * by recvmsg(). Seems, we are not obliged to handle such wicked
3673          * situations. But it is worth to think about possibility of some
3674          * DoSes using some hypothetical application level deadlock.
3675          */
3676         if (before(ptr, tp->rcv_nxt))
3677                 return;
3678
3679         /* Do we already have a newer (or duplicate) urgent pointer? */
3680         if (tp->urg_data && !after(ptr, tp->urg_seq))
3681                 return;
3682
3683         /* Tell the world about our new urgent pointer. */
3684         sk_send_sigurg(sk);
3685
3686         /* We may be adding urgent data when the last byte read was
3687          * urgent. To do this requires some care. We cannot just ignore
3688          * tp->copied_seq since we would read the last urgent byte again
3689          * as data, nor can we alter copied_seq until this data arrives
3690          * or we break the semantics of SIOCATMARK (and thus sockatmark())
3691          *
3692          * NOTE. Double Dutch. Rendering to plain English: author of comment
3693          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
3694          * and expect that both A and B disappear from stream. This is _wrong_.
3695          * Though this happens in BSD with high probability, this is occasional.
3696          * Any application relying on this is buggy. Note also, that fix "works"
3697          * only in this artificial test. Insert some normal data between A and B and we will
3698          * decline of BSD again. Verdict: it is better to remove to trap
3699          * buggy users.
3700          */
3701         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
3702             !sock_flag(sk, SOCK_URGINLINE) &&
3703             tp->copied_seq != tp->rcv_nxt) {
3704                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
3705                 tp->copied_seq++;
3706                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
3707                         __skb_unlink(skb, &sk->sk_receive_queue);
3708                         __kfree_skb(skb);
3709                 }
3710         }
3711
3712         tp->urg_data   = TCP_URG_NOTYET;
3713         tp->urg_seq    = ptr;
3714
3715         /* Disable header prediction. */
3716         tp->pred_flags = 0;
3717 }
3718
3719 /* This is the 'fast' part of urgent handling. */
3720 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
3721 {
3722         struct tcp_sock *tp = tcp_sk(sk);
3723
3724         /* Check if we get a new urgent pointer - normally not. */
3725         if (th->urg)
3726                 tcp_check_urg(sk,th);
3727
3728         /* Do we wait for any urgent data? - normally not... */
3729         if (tp->urg_data == TCP_URG_NOTYET) {
3730                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
3731                           th->syn;
3732
3733                 /* Is the urgent pointer pointing into this packet? */   
3734                 if (ptr < skb->len) {
3735                         u8 tmp;
3736                         if (skb_copy_bits(skb, ptr, &tmp, 1))
3737                                 BUG();
3738                         tp->urg_data = TCP_URG_VALID | tmp;
3739                         if (!sock_flag(sk, SOCK_DEAD))
3740                                 sk->sk_data_ready(sk, 0);
3741                 }
3742         }
3743 }
3744
3745 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
3746 {
3747         struct tcp_sock *tp = tcp_sk(sk);
3748         int chunk = skb->len - hlen;
3749         int err;
3750
3751         local_bh_enable();
3752         if (skb->ip_summed==CHECKSUM_UNNECESSARY)
3753                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
3754         else
3755                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
3756                                                        tp->ucopy.iov);
3757
3758         if (!err) {
3759                 tp->ucopy.len -= chunk;
3760                 tp->copied_seq += chunk;
3761                 tcp_rcv_space_adjust(sk);
3762         }
3763
3764         local_bh_disable();
3765         return err;
3766 }
3767
3768 static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3769 {
3770         int result;
3771
3772         if (sock_owned_by_user(sk)) {
3773                 local_bh_enable();
3774                 result = __tcp_checksum_complete(skb);
3775                 local_bh_disable();
3776         } else {
3777                 result = __tcp_checksum_complete(skb);
3778         }
3779         return result;
3780 }
3781
3782 static inline int tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3783 {
3784         return skb->ip_summed != CHECKSUM_UNNECESSARY &&
3785                 __tcp_checksum_complete_user(sk, skb);
3786 }
3787
3788 /*
3789  *      TCP receive function for the ESTABLISHED state. 
3790  *
3791  *      It is split into a fast path and a slow path. The fast path is 
3792  *      disabled when:
3793  *      - A zero window was announced from us - zero window probing
3794  *        is only handled properly in the slow path. 
3795  *      - Out of order segments arrived.
3796  *      - Urgent data is expected.
3797  *      - There is no buffer space left
3798  *      - Unexpected TCP flags/window values/header lengths are received
3799  *        (detected by checking the TCP header against pred_flags) 
3800  *      - Data is sent in both directions. Fast path only supports pure senders
3801  *        or pure receivers (this means either the sequence number or the ack
3802  *        value must stay constant)
3803  *      - Unexpected TCP option.
3804  *
3805  *      When these conditions are not satisfied it drops into a standard 
3806  *      receive procedure patterned after RFC793 to handle all cases.
3807  *      The first three cases are guaranteed by proper pred_flags setting,
3808  *      the rest is checked inline. Fast processing is turned on in 
3809  *      tcp_data_queue when everything is OK.
3810  */
3811 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
3812                         struct tcphdr *th, unsigned len)
3813 {
3814         struct tcp_sock *tp = tcp_sk(sk);
3815
3816         /*
3817          *      Header prediction.
3818          *      The code loosely follows the one in the famous 
3819          *      "30 instruction TCP receive" Van Jacobson mail.
3820          *      
3821          *      Van's trick is to deposit buffers into socket queue 
3822          *      on a device interrupt, to call tcp_recv function
3823          *      on the receive process context and checksum and copy
3824          *      the buffer to user space. smart...
3825          *
3826          *      Our current scheme is not silly either but we take the 
3827          *      extra cost of the net_bh soft interrupt processing...
3828          *      We do checksum and copy also but from device to kernel.
3829          */
3830
3831         tp->rx_opt.saw_tstamp = 0;
3832
3833         /*      pred_flags is 0xS?10 << 16 + snd_wnd
3834          *      if header_prediction is to be made
3835          *      'S' will always be tp->tcp_header_len >> 2
3836          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
3837          *  turn it off (when there are holes in the receive 
3838          *       space for instance)
3839          *      PSH flag is ignored.
3840          */
3841
3842         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
3843                 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3844                 int tcp_header_len = tp->tcp_header_len;
3845
3846                 /* Timestamp header prediction: tcp_header_len
3847                  * is automatically equal to th->doff*4 due to pred_flags
3848                  * match.
3849                  */
3850
3851                 /* Check timestamp */
3852                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
3853                         __u32 *ptr = (__u32 *)(th + 1);
3854
3855                         /* No? Slow path! */
3856                         if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3857                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
3858                                 goto slow_path;
3859
3860                         tp->rx_opt.saw_tstamp = 1;
3861                         ++ptr; 
3862                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
3863                         ++ptr;
3864                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3865
3866                         /* If PAWS failed, check it more carefully in slow path */
3867                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
3868                                 goto slow_path;
3869
3870                         /* DO NOT update ts_recent here, if checksum fails
3871                          * and timestamp was corrupted part, it will result
3872                          * in a hung connection since we will drop all
3873                          * future packets due to the PAWS test.
3874                          */
3875                 }
3876
3877                 if (len <= tcp_header_len) {
3878                         /* Bulk data transfer: sender */
3879                         if (len == tcp_header_len) {
3880                                 /* Predicted packet is in window by definition.
3881                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3882                                  * Hence, check seq<=rcv_wup reduces to:
3883                                  */
3884                                 if (tcp_header_len ==
3885                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3886                                     tp->rcv_nxt == tp->rcv_wup)
3887                                         tcp_store_ts_recent(tp);
3888
3889                                 tcp_rcv_rtt_measure_ts(sk, skb);
3890
3891                                 /* We know that such packets are checksummed
3892                                  * on entry.
3893                                  */
3894                                 tcp_ack(sk, skb, 0);
3895                                 __kfree_skb(skb); 
3896                                 tcp_data_snd_check(sk, tp);
3897                                 return 0;
3898                         } else { /* Header too small */
3899                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
3900                                 goto discard;
3901                         }
3902                 } else {
3903                         int eaten = 0;
3904
3905                         if (tp->ucopy.task == current &&
3906                             tp->copied_seq == tp->rcv_nxt &&
3907                             len - tcp_header_len <= tp->ucopy.len &&
3908                             sock_owned_by_user(sk)) {
3909                                 __set_current_state(TASK_RUNNING);
3910
3911                                 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
3912                                         /* Predicted packet is in window by definition.
3913                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3914                                          * Hence, check seq<=rcv_wup reduces to:
3915                                          */
3916                                         if (tcp_header_len ==
3917                                             (sizeof(struct tcphdr) +
3918                                              TCPOLEN_TSTAMP_ALIGNED) &&
3919                                             tp->rcv_nxt == tp->rcv_wup)
3920                                                 tcp_store_ts_recent(tp);
3921
3922                                         tcp_rcv_rtt_measure_ts(sk, skb);
3923
3924                                         __skb_pull(skb, tcp_header_len);
3925                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3926                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
3927                                         eaten = 1;
3928                                 }
3929                         }
3930                         if (!eaten) {
3931                                 if (tcp_checksum_complete_user(sk, skb))
3932                                         goto csum_error;
3933
3934                                 /* Predicted packet is in window by definition.
3935                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3936                                  * Hence, check seq<=rcv_wup reduces to:
3937                                  */
3938                                 if (tcp_header_len ==
3939                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3940                                     tp->rcv_nxt == tp->rcv_wup)
3941                                         tcp_store_ts_recent(tp);
3942
3943                                 tcp_rcv_rtt_measure_ts(sk, skb);
3944
3945                                 if ((int)skb->truesize > sk->sk_forward_alloc)
3946                                         goto step5;
3947
3948                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
3949
3950                                 /* Bulk data transfer: receiver */
3951                                 __skb_pull(skb,tcp_header_len);
3952                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3953                                 sk_stream_set_owner_r(skb, sk);
3954                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3955                         }
3956
3957                         tcp_event_data_recv(sk, tp, skb);
3958
3959                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
3960                                 /* Well, only one small jumplet in fast path... */
3961                                 tcp_ack(sk, skb, FLAG_DATA);
3962                                 tcp_data_snd_check(sk, tp);
3963                                 if (!inet_csk_ack_scheduled(sk))
3964                                         goto no_ack;
3965                         }
3966
3967                         __tcp_ack_snd_check(sk, 0);
3968 no_ack:
3969                         if (eaten)
3970                                 __kfree_skb(skb);
3971                         else
3972                                 sk->sk_data_ready(sk, 0);
3973                         return 0;
3974                 }
3975         }
3976
3977 slow_path:
3978         if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
3979                 goto csum_error;
3980
3981         /*
3982          * RFC1323: H1. Apply PAWS check first.
3983          */
3984         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
3985             tcp_paws_discard(sk, skb)) {
3986                 if (!th->rst) {
3987                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
3988                         tcp_send_dupack(sk, skb);
3989                         goto discard;
3990                 }
3991                 /* Resets are accepted even if PAWS failed.
3992
3993                    ts_recent update must be made after we are sure
3994                    that the packet is in window.
3995                  */
3996         }
3997
3998         /*
3999          *      Standard slow path.
4000          */
4001
4002         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4003                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
4004                  * (RST) segments are validated by checking their SEQ-fields."
4005                  * And page 69: "If an incoming segment is not acceptable,
4006                  * an acknowledgment should be sent in reply (unless the RST bit
4007                  * is set, if so drop the segment and return)".
4008                  */
4009                 if (!th->rst)
4010                         tcp_send_dupack(sk, skb);
4011                 goto discard;
4012         }
4013
4014         if(th->rst) {
4015                 tcp_reset(sk);
4016                 goto discard;
4017         }
4018
4019         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4020
4021         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4022                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4023                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4024                 tcp_reset(sk);
4025                 return 1;
4026         }
4027
4028 step5:
4029         if(th->ack)
4030                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4031
4032         tcp_rcv_rtt_measure_ts(sk, skb);
4033
4034         /* Process urgent data. */
4035         tcp_urg(sk, skb, th);
4036
4037         /* step 7: process the segment text */
4038         tcp_data_queue(sk, skb);
4039
4040         tcp_data_snd_check(sk, tp);
4041         tcp_ack_snd_check(sk);
4042         return 0;
4043
4044 csum_error:
4045         TCP_INC_STATS_BH(TCP_MIB_INERRS);
4046
4047 discard:
4048         __kfree_skb(skb);
4049         return 0;
4050 }
4051
4052 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
4053                                          struct tcphdr *th, unsigned len)
4054 {
4055         struct tcp_sock *tp = tcp_sk(sk);
4056         struct inet_connection_sock *icsk = inet_csk(sk);
4057         int saved_clamp = tp->rx_opt.mss_clamp;
4058
4059         tcp_parse_options(skb, &tp->rx_opt, 0);
4060
4061         if (th->ack) {
4062                 /* rfc793:
4063                  * "If the state is SYN-SENT then
4064                  *    first check the ACK bit
4065                  *      If the ACK bit is set
4066                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
4067                  *        a reset (unless the RST bit is set, if so drop
4068                  *        the segment and return)"
4069                  *
4070                  *  We do not send data with SYN, so that RFC-correct
4071                  *  test reduces to:
4072                  */
4073                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
4074                         goto reset_and_undo;
4075
4076                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4077                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
4078                              tcp_time_stamp)) {
4079                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
4080                         goto reset_and_undo;
4081                 }
4082
4083                 /* Now ACK is acceptable.
4084                  *
4085                  * "If the RST bit is set
4086                  *    If the ACK was acceptable then signal the user "error:
4087                  *    connection reset", drop the segment, enter CLOSED state,
4088                  *    delete TCB, and return."
4089                  */
4090
4091                 if (th->rst) {
4092                         tcp_reset(sk);
4093                         goto discard;
4094                 }
4095
4096                 /* rfc793:
4097                  *   "fifth, if neither of the SYN or RST bits is set then
4098                  *    drop the segment and return."
4099                  *
4100                  *    See note below!
4101                  *                                        --ANK(990513)
4102                  */
4103                 if (!th->syn)
4104                         goto discard_and_undo;
4105
4106                 /* rfc793:
4107                  *   "If the SYN bit is on ...
4108                  *    are acceptable then ...
4109                  *    (our SYN has been ACKed), change the connection
4110                  *    state to ESTABLISHED..."
4111                  */
4112
4113                 TCP_ECN_rcv_synack(tp, th);
4114                 if (tp->ecn_flags&TCP_ECN_OK)
4115                         sock_set_flag(sk, SOCK_NO_LARGESEND);
4116
4117                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
4118                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4119
4120                 /* Ok.. it's good. Set up sequence numbers and
4121                  * move to established.
4122                  */
4123                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4124                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4125
4126                 /* RFC1323: The window in SYN & SYN/ACK segments is
4127                  * never scaled.
4128                  */
4129                 tp->snd_wnd = ntohs(th->window);
4130                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
4131
4132                 if (!tp->rx_opt.wscale_ok) {
4133                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
4134                         tp->window_clamp = min(tp->window_clamp, 65535U);
4135                 }
4136
4137                 if (tp->rx_opt.saw_tstamp) {
4138                         tp->rx_opt.tstamp_ok       = 1;
4139                         tp->tcp_header_len =
4140                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4141                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
4142                         tcp_store_ts_recent(tp);
4143                 } else {
4144                         tp->tcp_header_len = sizeof(struct tcphdr);
4145                 }
4146
4147                 if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
4148                         tp->rx_opt.sack_ok |= 2;
4149
4150                 tcp_mtup_init(sk);
4151                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4152                 tcp_initialize_rcv_mss(sk);
4153
4154                 /* Remember, tcp_poll() does not lock socket!
4155                  * Change state from SYN-SENT only after copied_seq
4156                  * is initialized. */
4157                 tp->copied_seq = tp->rcv_nxt;
4158                 mb();
4159                 tcp_set_state(sk, TCP_ESTABLISHED);
4160
4161                 /* Make sure socket is routed, for correct metrics.  */
4162                 icsk->icsk_af_ops->rebuild_header(sk);
4163
4164                 tcp_init_metrics(sk);
4165
4166                 tcp_init_congestion_control(sk);
4167
4168                 /* Prevent spurious tcp_cwnd_restart() on first data
4169                  * packet.
4170                  */
4171                 tp->lsndtime = tcp_time_stamp;
4172
4173                 tcp_init_buffer_space(sk);
4174
4175                 if (sock_flag(sk, SOCK_KEEPOPEN))
4176                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
4177
4178                 if (!tp->rx_opt.snd_wscale)
4179                         __tcp_fast_path_on(tp, tp->snd_wnd);
4180                 else
4181                         tp->pred_flags = 0;
4182
4183                 if (!sock_flag(sk, SOCK_DEAD)) {
4184                         sk->sk_state_change(sk);
4185                         sk_wake_async(sk, 0, POLL_OUT);
4186                 }
4187
4188                 if (sk->sk_write_pending ||
4189                     icsk->icsk_accept_queue.rskq_defer_accept ||
4190                     icsk->icsk_ack.pingpong) {
4191                         /* Save one ACK. Data will be ready after
4192                          * several ticks, if write_pending is set.
4193                          *
4194                          * It may be deleted, but with this feature tcpdumps
4195                          * look so _wonderfully_ clever, that I was not able
4196                          * to stand against the temptation 8)     --ANK
4197                          */
4198                         inet_csk_schedule_ack(sk);
4199                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4200                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4201                         tcp_incr_quickack(sk);
4202                         tcp_enter_quickack_mode(sk);
4203                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4204                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4205
4206 discard:
4207                         __kfree_skb(skb);
4208                         return 0;
4209                 } else {
4210                         tcp_send_ack(sk);
4211                 }
4212                 return -1;
4213         }
4214
4215         /* No ACK in the segment */
4216
4217         if (th->rst) {
4218                 /* rfc793:
4219                  * "If the RST bit is set
4220                  *
4221                  *      Otherwise (no ACK) drop the segment and return."
4222                  */
4223
4224                 goto discard_and_undo;
4225         }
4226
4227         /* PAWS check. */
4228         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4229                 goto discard_and_undo;
4230
4231         if (th->syn) {
4232                 /* We see SYN without ACK. It is attempt of
4233                  * simultaneous connect with crossed SYNs.
4234                  * Particularly, it can be connect to self.
4235                  */
4236                 tcp_set_state(sk, TCP_SYN_RECV);
4237
4238                 if (tp->rx_opt.saw_tstamp) {
4239                         tp->rx_opt.tstamp_ok = 1;
4240                         tcp_store_ts_recent(tp);
4241                         tp->tcp_header_len =
4242                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4243                 } else {
4244                         tp->tcp_header_len = sizeof(struct tcphdr);
4245                 }
4246
4247                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4248                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4249
4250                 /* RFC1323: The window in SYN & SYN/ACK segments is
4251                  * never scaled.
4252                  */
4253                 tp->snd_wnd    = ntohs(th->window);
4254                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4255                 tp->max_window = tp->snd_wnd;
4256
4257                 TCP_ECN_rcv_syn(tp, th);
4258                 if (tp->ecn_flags&TCP_ECN_OK)
4259                         sock_set_flag(sk, SOCK_NO_LARGESEND);
4260
4261                 tcp_mtup_init(sk);
4262                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4263                 tcp_initialize_rcv_mss(sk);
4264
4265
4266                 tcp_send_synack(sk);
4267 #if 0
4268                 /* Note, we could accept data and URG from this segment.
4269                  * There are no obstacles to make this.
4270                  *
4271                  * However, if we ignore data in ACKless segments sometimes,
4272                  * we have no reasons to accept it sometimes.
4273                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
4274                  * is not flawless. So, discard packet for sanity.
4275                  * Uncomment this return to process the data.
4276                  */
4277                 return -1;
4278 #else
4279                 goto discard;
4280 #endif
4281         }
4282         /* "fifth, if neither of the SYN or RST bits is set then
4283          * drop the segment and return."
4284          */
4285
4286 discard_and_undo:
4287         tcp_clear_options(&tp->rx_opt);
4288         tp->rx_opt.mss_clamp = saved_clamp;
4289         goto discard;
4290
4291 reset_and_undo:
4292         tcp_clear_options(&tp->rx_opt);
4293         tp->rx_opt.mss_clamp = saved_clamp;
4294         return 1;
4295 }
4296
4297
4298 /*
4299  *      This function implements the receiving procedure of RFC 793 for
4300  *      all states except ESTABLISHED and TIME_WAIT. 
4301  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4302  *      address independent.
4303  */
4304         
4305 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4306                           struct tcphdr *th, unsigned len)
4307 {
4308         struct tcp_sock *tp = tcp_sk(sk);
4309         struct inet_connection_sock *icsk = inet_csk(sk);
4310         int queued = 0;
4311
4312         tp->rx_opt.saw_tstamp = 0;
4313
4314         switch (sk->sk_state) {
4315         case TCP_CLOSE:
4316                 goto discard;
4317
4318         case TCP_LISTEN:
4319                 if(th->ack)
4320                         return 1;
4321
4322                 if(th->rst)
4323                         goto discard;
4324
4325                 if(th->syn) {
4326                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
4327                                 return 1;
4328
4329                         /* Now we have several options: In theory there is 
4330                          * nothing else in the frame. KA9Q has an option to 
4331                          * send data with the syn, BSD accepts data with the
4332                          * syn up to the [to be] advertised window and 
4333                          * Solaris 2.1 gives you a protocol error. For now 
4334                          * we just ignore it, that fits the spec precisely 
4335                          * and avoids incompatibilities. It would be nice in
4336                          * future to drop through and process the data.
4337                          *
4338                          * Now that TTCP is starting to be used we ought to 
4339                          * queue this data.
4340                          * But, this leaves one open to an easy denial of
4341                          * service attack, and SYN cookies can't defend
4342                          * against this problem. So, we drop the data
4343                          * in the interest of security over speed.
4344                          */
4345                         goto discard;
4346                 }
4347                 goto discard;
4348
4349         case TCP_SYN_SENT:
4350                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4351                 if (queued >= 0)
4352                         return queued;
4353
4354                 /* Do step6 onward by hand. */
4355                 tcp_urg(sk, skb, th);
4356                 __kfree_skb(skb);
4357                 tcp_data_snd_check(sk, tp);
4358                 return 0;
4359         }
4360
4361         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4362             tcp_paws_discard(sk, skb)) {
4363                 if (!th->rst) {
4364                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4365                         tcp_send_dupack(sk, skb);
4366                         goto discard;
4367                 }
4368                 /* Reset is accepted even if it did not pass PAWS. */
4369         }
4370
4371         /* step 1: check sequence number */
4372         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4373                 if (!th->rst)
4374                         tcp_send_dupack(sk, skb);
4375                 goto discard;
4376         }
4377
4378         /* step 2: check RST bit */
4379         if(th->rst) {
4380                 tcp_reset(sk);
4381                 goto discard;
4382         }
4383
4384         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4385
4386         /* step 3: check security and precedence [ignored] */
4387
4388         /*      step 4:
4389          *
4390          *      Check for a SYN in window.
4391          */
4392         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4393                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4394                 tcp_reset(sk);
4395                 return 1;
4396         }
4397
4398         /* step 5: check the ACK field */
4399         if (th->ack) {
4400                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
4401
4402                 switch(sk->sk_state) {
4403                 case TCP_SYN_RECV:
4404                         if (acceptable) {
4405                                 tp->copied_seq = tp->rcv_nxt;
4406                                 mb();
4407                                 tcp_set_state(sk, TCP_ESTABLISHED);
4408                                 sk->sk_state_change(sk);
4409
4410                                 /* Note, that this wakeup is only for marginal
4411                                  * crossed SYN case. Passively open sockets
4412                                  * are not waked up, because sk->sk_sleep ==
4413                                  * NULL and sk->sk_socket == NULL.
4414                                  */
4415                                 if (sk->sk_socket) {
4416                                         sk_wake_async(sk,0,POLL_OUT);
4417                                 }
4418
4419                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
4420                                 tp->snd_wnd = ntohs(th->window) <<
4421                                               tp->rx_opt.snd_wscale;
4422                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
4423                                             TCP_SKB_CB(skb)->seq);
4424
4425                                 /* tcp_ack considers this ACK as duplicate
4426                                  * and does not calculate rtt.
4427                                  * Fix it at least with timestamps.
4428                                  */
4429                                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4430                                     !tp->srtt)
4431                                         tcp_ack_saw_tstamp(sk, 0);
4432
4433                                 if (tp->rx_opt.tstamp_ok)
4434                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
4435
4436                                 /* Make sure socket is routed, for
4437                                  * correct metrics.
4438                                  */
4439                                 icsk->icsk_af_ops->rebuild_header(sk);
4440
4441                                 tcp_init_metrics(sk);
4442
4443                                 tcp_init_congestion_control(sk);
4444
4445                                 /* Prevent spurious tcp_cwnd_restart() on
4446                                  * first data packet.
4447                                  */
4448                                 tp->lsndtime = tcp_time_stamp;
4449
4450                                 tcp_mtup_init(sk);
4451                                 tcp_initialize_rcv_mss(sk);
4452                                 tcp_init_buffer_space(sk);
4453                                 tcp_fast_path_on(tp);
4454                         } else {
4455                                 return 1;
4456                         }
4457                         break;
4458
4459                 case TCP_FIN_WAIT1:
4460                         if (tp->snd_una == tp->write_seq) {
4461                                 tcp_set_state(sk, TCP_FIN_WAIT2);
4462                                 sk->sk_shutdown |= SEND_SHUTDOWN;
4463                                 dst_confirm(sk->sk_dst_cache);
4464
4465                                 if (!sock_flag(sk, SOCK_DEAD))
4466                                         /* Wake up lingering close() */
4467                                         sk->sk_state_change(sk);
4468                                 else {
4469                                         int tmo;
4470
4471                                         if (tp->linger2 < 0 ||
4472                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4473                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
4474                                                 tcp_done(sk);
4475                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4476                                                 return 1;
4477                                         }
4478
4479                                         tmo = tcp_fin_time(sk);
4480                                         if (tmo > TCP_TIMEWAIT_LEN) {
4481                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
4482                                         } else if (th->fin || sock_owned_by_user(sk)) {
4483                                                 /* Bad case. We could lose such FIN otherwise.
4484                                                  * It is not a big problem, but it looks confusing
4485                                                  * and not so rare event. We still can lose it now,
4486                                                  * if it spins in bh_lock_sock(), but it is really
4487                                                  * marginal case.
4488                                                  */
4489                                                 inet_csk_reset_keepalive_timer(sk, tmo);
4490                                         } else {
4491                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
4492                                                 goto discard;
4493                                         }
4494                                 }
4495                         }
4496                         break;
4497
4498                 case TCP_CLOSING:
4499                         if (tp->snd_una == tp->write_seq) {
4500                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4501                                 goto discard;
4502                         }
4503                         break;
4504
4505                 case TCP_LAST_ACK:
4506                         if (tp->snd_una == tp->write_seq) {
4507                                 tcp_update_metrics(sk);
4508                                 tcp_done(sk);
4509                                 goto discard;
4510                         }
4511                         break;
4512                 }
4513         } else
4514                 goto discard;
4515
4516         /* step 6: check the URG bit */
4517         tcp_urg(sk, skb, th);
4518
4519         /* step 7: process the segment text */
4520         switch (sk->sk_state) {
4521         case TCP_CLOSE_WAIT:
4522         case TCP_CLOSING:
4523         case TCP_LAST_ACK:
4524                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4525                         break;
4526         case TCP_FIN_WAIT1:
4527         case TCP_FIN_WAIT2:
4528                 /* RFC 793 says to queue data in these states,
4529                  * RFC 1122 says we MUST send a reset. 
4530                  * BSD 4.4 also does reset.
4531                  */
4532                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
4533                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4534                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
4535                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4536                                 tcp_reset(sk);
4537                                 return 1;
4538                         }
4539                 }
4540                 /* Fall through */
4541         case TCP_ESTABLISHED: 
4542                 tcp_data_queue(sk, skb);
4543                 queued = 1;
4544                 break;
4545         }
4546
4547         /* tcp_data could move socket to TIME-WAIT */
4548         if (sk->sk_state != TCP_CLOSE) {
4549                 tcp_data_snd_check(sk, tp);
4550                 tcp_ack_snd_check(sk);
4551         }
4552
4553         if (!queued) { 
4554 discard:
4555                 __kfree_skb(skb);
4556         }
4557         return 0;
4558 }
4559
4560 EXPORT_SYMBOL(sysctl_tcp_ecn);
4561 EXPORT_SYMBOL(sysctl_tcp_reordering);
4562 EXPORT_SYMBOL(sysctl_tcp_abc);
4563 EXPORT_SYMBOL(tcp_parse_options);
4564 EXPORT_SYMBOL(tcp_rcv_established);
4565 EXPORT_SYMBOL(tcp_rcv_state_process);
4566 EXPORT_SYMBOL(tcp_initialize_rcv_mss);