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1 /*
2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
3  *              operating system.  INET is implemented using the  BSD Socket
4  *              interface as the means of communication with the user level.
5  *
6  *              Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Version:     $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
9  *
10  * Authors:     Ross Biro
11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
14  *              Florian La Roche, <flla@stud.uni-sb.de>
15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20  *              Jorge Cwik, <jorge@laser.satlink.net>
21  */
22
23 /*
24  * Changes:
25  *              Pedro Roque     :       Fast Retransmit/Recovery.
26  *                                      Two receive queues.
27  *                                      Retransmit queue handled by TCP.
28  *                                      Better retransmit timer handling.
29  *                                      New congestion avoidance.
30  *                                      Header prediction.
31  *                                      Variable renaming.
32  *
33  *              Eric            :       Fast Retransmit.
34  *              Randy Scott     :       MSS option defines.
35  *              Eric Schenk     :       Fixes to slow start algorithm.
36  *              Eric Schenk     :       Yet another double ACK bug.
37  *              Eric Schenk     :       Delayed ACK bug fixes.
38  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
39  *              David S. Miller :       Don't allow zero congestion window.
40  *              Eric Schenk     :       Fix retransmitter so that it sends
41  *                                      next packet on ack of previous packet.
42  *              Andi Kleen      :       Moved open_request checking here
43  *                                      and process RSTs for open_requests.
44  *              Andi Kleen      :       Better prune_queue, and other fixes.
45  *              Andrey Savochkin:       Fix RTT measurements in the presnce of
46  *                                      timestamps.
47  *              Andrey Savochkin:       Check sequence numbers correctly when
48  *                                      removing SACKs due to in sequence incoming
49  *                                      data segments.
50  *              Andi Kleen:             Make sure we never ack data there is not
51  *                                      enough room for. Also make this condition
52  *                                      a fatal error if it might still happen.
53  *              Andi Kleen:             Add tcp_measure_rcv_mss to make 
54  *                                      connections with MSS<min(MTU,ann. MSS)
55  *                                      work without delayed acks. 
56  *              Andi Kleen:             Process packets with PSH set in the
57  *                                      fast path.
58  *              J Hadi Salim:           ECN support
59  *              Andrei Gurtov,
60  *              Pasi Sarolahti,
61  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
62  *                                      engine. Lots of bugs are found.
63  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
64  */
65
66 #include <linux/config.h>
67 #include <linux/mm.h>
68 #include <linux/module.h>
69 #include <linux/sysctl.h>
70 #include <net/tcp.h>
71 #include <net/inet_common.h>
72 #include <linux/ipsec.h>
73 #include <asm/unaligned.h>
74
75 int sysctl_tcp_timestamps = 1;
76 int sysctl_tcp_window_scaling = 1;
77 int sysctl_tcp_sack = 1;
78 int sysctl_tcp_fack = 1;
79 int sysctl_tcp_reordering = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn;
81 int sysctl_tcp_dsack = 1;
82 int sysctl_tcp_app_win = 31;
83 int sysctl_tcp_adv_win_scale = 2;
84
85 int sysctl_tcp_stdurg;
86 int sysctl_tcp_rfc1337;
87 int sysctl_tcp_max_orphans = NR_FILE;
88 int sysctl_tcp_frto;
89 int sysctl_tcp_nometrics_save;
90
91 int sysctl_tcp_moderate_rcvbuf = 1;
92
93 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
94 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
95 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
96 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
97 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
98 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
99 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
100 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
101 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
102
103 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
104 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
105 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
106 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
107
108 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
109 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
110 #define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
111
112 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
113
114 /* Adapt the MSS value used to make delayed ack decision to the 
115  * real world.
116  */ 
117 static inline void tcp_measure_rcv_mss(struct tcp_sock *tp,
118                                        struct sk_buff *skb)
119 {
120         unsigned int len, lss;
121
122         lss = tp->ack.last_seg_size; 
123         tp->ack.last_seg_size = 0; 
124
125         /* skb->len may jitter because of SACKs, even if peer
126          * sends good full-sized frames.
127          */
128         len = skb->len;
129         if (len >= tp->ack.rcv_mss) {
130                 tp->ack.rcv_mss = len;
131         } else {
132                 /* Otherwise, we make more careful check taking into account,
133                  * that SACKs block is variable.
134                  *
135                  * "len" is invariant segment length, including TCP header.
136                  */
137                 len += skb->data - skb->h.raw;
138                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
139                     /* If PSH is not set, packet should be
140                      * full sized, provided peer TCP is not badly broken.
141                      * This observation (if it is correct 8)) allows
142                      * to handle super-low mtu links fairly.
143                      */
144                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
145                      !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) {
146                         /* Subtract also invariant (if peer is RFC compliant),
147                          * tcp header plus fixed timestamp option length.
148                          * Resulting "len" is MSS free of SACK jitter.
149                          */
150                         len -= tp->tcp_header_len;
151                         tp->ack.last_seg_size = len;
152                         if (len == lss) {
153                                 tp->ack.rcv_mss = len;
154                                 return;
155                         }
156                 }
157                 tp->ack.pending |= TCP_ACK_PUSHED;
158         }
159 }
160
161 static void tcp_incr_quickack(struct tcp_sock *tp)
162 {
163         unsigned quickacks = tp->rcv_wnd/(2*tp->ack.rcv_mss);
164
165         if (quickacks==0)
166                 quickacks=2;
167         if (quickacks > tp->ack.quick)
168                 tp->ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
169 }
170
171 void tcp_enter_quickack_mode(struct tcp_sock *tp)
172 {
173         tcp_incr_quickack(tp);
174         tp->ack.pingpong = 0;
175         tp->ack.ato = TCP_ATO_MIN;
176 }
177
178 /* Send ACKs quickly, if "quick" count is not exhausted
179  * and the session is not interactive.
180  */
181
182 static __inline__ int tcp_in_quickack_mode(struct tcp_sock *tp)
183 {
184         return (tp->ack.quick && !tp->ack.pingpong);
185 }
186
187 /* Buffer size and advertised window tuning.
188  *
189  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
190  */
191
192 static void tcp_fixup_sndbuf(struct sock *sk)
193 {
194         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
195                      sizeof(struct sk_buff);
196
197         if (sk->sk_sndbuf < 3 * sndmem)
198                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
199 }
200
201 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
202  *
203  * All tcp_full_space() is split to two parts: "network" buffer, allocated
204  * forward and advertised in receiver window (tp->rcv_wnd) and
205  * "application buffer", required to isolate scheduling/application
206  * latencies from network.
207  * window_clamp is maximal advertised window. It can be less than
208  * tcp_full_space(), in this case tcp_full_space() - window_clamp
209  * is reserved for "application" buffer. The less window_clamp is
210  * the smoother our behaviour from viewpoint of network, but the lower
211  * throughput and the higher sensitivity of the connection to losses. 8)
212  *
213  * rcv_ssthresh is more strict window_clamp used at "slow start"
214  * phase to predict further behaviour of this connection.
215  * It is used for two goals:
216  * - to enforce header prediction at sender, even when application
217  *   requires some significant "application buffer". It is check #1.
218  * - to prevent pruning of receive queue because of misprediction
219  *   of receiver window. Check #2.
220  *
221  * The scheme does not work when sender sends good segments opening
222  * window and then starts to feed us spagetti. But it should work
223  * in common situations. Otherwise, we have to rely on queue collapsing.
224  */
225
226 /* Slow part of check#2. */
227 static int __tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
228                              struct sk_buff *skb)
229 {
230         /* Optimize this! */
231         int truesize = tcp_win_from_space(skb->truesize)/2;
232         int window = tcp_full_space(sk)/2;
233
234         while (tp->rcv_ssthresh <= window) {
235                 if (truesize <= skb->len)
236                         return 2*tp->ack.rcv_mss;
237
238                 truesize >>= 1;
239                 window >>= 1;
240         }
241         return 0;
242 }
243
244 static inline void tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
245                                    struct sk_buff *skb)
246 {
247         /* Check #1 */
248         if (tp->rcv_ssthresh < tp->window_clamp &&
249             (int)tp->rcv_ssthresh < tcp_space(sk) &&
250             !tcp_memory_pressure) {
251                 int incr;
252
253                 /* Check #2. Increase window, if skb with such overhead
254                  * will fit to rcvbuf in future.
255                  */
256                 if (tcp_win_from_space(skb->truesize) <= skb->len)
257                         incr = 2*tp->advmss;
258                 else
259                         incr = __tcp_grow_window(sk, tp, skb);
260
261                 if (incr) {
262                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
263                         tp->ack.quick |= 1;
264                 }
265         }
266 }
267
268 /* 3. Tuning rcvbuf, when connection enters established state. */
269
270 static void tcp_fixup_rcvbuf(struct sock *sk)
271 {
272         struct tcp_sock *tp = tcp_sk(sk);
273         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
274
275         /* Try to select rcvbuf so that 4 mss-sized segments
276          * will fit to window and correspoding skbs will fit to our rcvbuf.
277          * (was 3; 4 is minimum to allow fast retransmit to work.)
278          */
279         while (tcp_win_from_space(rcvmem) < tp->advmss)
280                 rcvmem += 128;
281         if (sk->sk_rcvbuf < 4 * rcvmem)
282                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
283 }
284
285 /* 4. Try to fixup all. It is made iimediately after connection enters
286  *    established state.
287  */
288 static void tcp_init_buffer_space(struct sock *sk)
289 {
290         struct tcp_sock *tp = tcp_sk(sk);
291         int maxwin;
292
293         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
294                 tcp_fixup_rcvbuf(sk);
295         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
296                 tcp_fixup_sndbuf(sk);
297
298         tp->rcvq_space.space = tp->rcv_wnd;
299
300         maxwin = tcp_full_space(sk);
301
302         if (tp->window_clamp >= maxwin) {
303                 tp->window_clamp = maxwin;
304
305                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
306                         tp->window_clamp = max(maxwin -
307                                                (maxwin >> sysctl_tcp_app_win),
308                                                4 * tp->advmss);
309         }
310
311         /* Force reservation of one segment. */
312         if (sysctl_tcp_app_win &&
313             tp->window_clamp > 2 * tp->advmss &&
314             tp->window_clamp + tp->advmss > maxwin)
315                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
316
317         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
318         tp->snd_cwnd_stamp = tcp_time_stamp;
319 }
320
321 /* 5. Recalculate window clamp after socket hit its memory bounds. */
322 static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp)
323 {
324         struct sk_buff *skb;
325         unsigned int app_win = tp->rcv_nxt - tp->copied_seq;
326         int ofo_win = 0;
327
328         tp->ack.quick = 0;
329
330         skb_queue_walk(&tp->out_of_order_queue, skb) {
331                 ofo_win += skb->len;
332         }
333
334         /* If overcommit is due to out of order segments,
335          * do not clamp window. Try to expand rcvbuf instead.
336          */
337         if (ofo_win) {
338                 if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
339                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
340                     !tcp_memory_pressure &&
341                     atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0])
342                         sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
343                                             sysctl_tcp_rmem[2]);
344         }
345         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) {
346                 app_win += ofo_win;
347                 if (atomic_read(&sk->sk_rmem_alloc) >= 2 * sk->sk_rcvbuf)
348                         app_win >>= 1;
349                 if (app_win > tp->ack.rcv_mss)
350                         app_win -= tp->ack.rcv_mss;
351                 app_win = max(app_win, 2U*tp->advmss);
352
353                 if (!ofo_win)
354                         tp->window_clamp = min(tp->window_clamp, app_win);
355                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
356         }
357 }
358
359 /* Receiver "autotuning" code.
360  *
361  * The algorithm for RTT estimation w/o timestamps is based on
362  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
363  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
364  *
365  * More detail on this code can be found at
366  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
367  * though this reference is out of date.  A new paper
368  * is pending.
369  */
370 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
371 {
372         u32 new_sample = tp->rcv_rtt_est.rtt;
373         long m = sample;
374
375         if (m == 0)
376                 m = 1;
377
378         if (new_sample != 0) {
379                 /* If we sample in larger samples in the non-timestamp
380                  * case, we could grossly overestimate the RTT especially
381                  * with chatty applications or bulk transfer apps which
382                  * are stalled on filesystem I/O.
383                  *
384                  * Also, since we are only going for a minimum in the
385                  * non-timestamp case, we do not smoothe things out
386                  * else with timestamps disabled convergance takes too
387                  * long.
388                  */
389                 if (!win_dep) {
390                         m -= (new_sample >> 3);
391                         new_sample += m;
392                 } else if (m < new_sample)
393                         new_sample = m << 3;
394         } else {
395                 /* No previous mesaure. */
396                 new_sample = m << 3;
397         }
398
399         if (tp->rcv_rtt_est.rtt != new_sample)
400                 tp->rcv_rtt_est.rtt = new_sample;
401 }
402
403 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
404 {
405         if (tp->rcv_rtt_est.time == 0)
406                 goto new_measure;
407         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
408                 return;
409         tcp_rcv_rtt_update(tp,
410                            jiffies - tp->rcv_rtt_est.time,
411                            1);
412
413 new_measure:
414         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
415         tp->rcv_rtt_est.time = tcp_time_stamp;
416 }
417
418 static inline void tcp_rcv_rtt_measure_ts(struct tcp_sock *tp, struct sk_buff *skb)
419 {
420         if (tp->rx_opt.rcv_tsecr &&
421             (TCP_SKB_CB(skb)->end_seq -
422              TCP_SKB_CB(skb)->seq >= tp->ack.rcv_mss))
423                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
424 }
425
426 /*
427  * This function should be called every time data is copied to user space.
428  * It calculates the appropriate TCP receive buffer space.
429  */
430 void tcp_rcv_space_adjust(struct sock *sk)
431 {
432         struct tcp_sock *tp = tcp_sk(sk);
433         int time;
434         int space;
435         
436         if (tp->rcvq_space.time == 0)
437                 goto new_measure;
438         
439         time = tcp_time_stamp - tp->rcvq_space.time;
440         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
441             tp->rcv_rtt_est.rtt == 0)
442                 return;
443         
444         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
445
446         space = max(tp->rcvq_space.space, space);
447
448         if (tp->rcvq_space.space != space) {
449                 int rcvmem;
450
451                 tp->rcvq_space.space = space;
452
453                 if (sysctl_tcp_moderate_rcvbuf) {
454                         int new_clamp = space;
455
456                         /* Receive space grows, normalize in order to
457                          * take into account packet headers and sk_buff
458                          * structure overhead.
459                          */
460                         space /= tp->advmss;
461                         if (!space)
462                                 space = 1;
463                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
464                                   16 + sizeof(struct sk_buff));
465                         while (tcp_win_from_space(rcvmem) < tp->advmss)
466                                 rcvmem += 128;
467                         space *= rcvmem;
468                         space = min(space, sysctl_tcp_rmem[2]);
469                         if (space > sk->sk_rcvbuf) {
470                                 sk->sk_rcvbuf = space;
471
472                                 /* Make the window clamp follow along.  */
473                                 tp->window_clamp = new_clamp;
474                         }
475                 }
476         }
477         
478 new_measure:
479         tp->rcvq_space.seq = tp->copied_seq;
480         tp->rcvq_space.time = tcp_time_stamp;
481 }
482
483 /* There is something which you must keep in mind when you analyze the
484  * behavior of the tp->ato delayed ack timeout interval.  When a
485  * connection starts up, we want to ack as quickly as possible.  The
486  * problem is that "good" TCP's do slow start at the beginning of data
487  * transmission.  The means that until we send the first few ACK's the
488  * sender will sit on his end and only queue most of his data, because
489  * he can only send snd_cwnd unacked packets at any given time.  For
490  * each ACK we send, he increments snd_cwnd and transmits more of his
491  * queue.  -DaveM
492  */
493 static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
494 {
495         u32 now;
496
497         tcp_schedule_ack(tp);
498
499         tcp_measure_rcv_mss(tp, skb);
500
501         tcp_rcv_rtt_measure(tp);
502         
503         now = tcp_time_stamp;
504
505         if (!tp->ack.ato) {
506                 /* The _first_ data packet received, initialize
507                  * delayed ACK engine.
508                  */
509                 tcp_incr_quickack(tp);
510                 tp->ack.ato = TCP_ATO_MIN;
511         } else {
512                 int m = now - tp->ack.lrcvtime;
513
514                 if (m <= TCP_ATO_MIN/2) {
515                         /* The fastest case is the first. */
516                         tp->ack.ato = (tp->ack.ato>>1) + TCP_ATO_MIN/2;
517                 } else if (m < tp->ack.ato) {
518                         tp->ack.ato = (tp->ack.ato>>1) + m;
519                         if (tp->ack.ato > tp->rto)
520                                 tp->ack.ato = tp->rto;
521                 } else if (m > tp->rto) {
522                         /* Too long gap. Apparently sender falled to
523                          * restart window, so that we send ACKs quickly.
524                          */
525                         tcp_incr_quickack(tp);
526                         sk_stream_mem_reclaim(sk);
527                 }
528         }
529         tp->ack.lrcvtime = now;
530
531         TCP_ECN_check_ce(tp, skb);
532
533         if (skb->len >= 128)
534                 tcp_grow_window(sk, tp, skb);
535 }
536
537 /* Called to compute a smoothed rtt estimate. The data fed to this
538  * routine either comes from timestamps, or from segments that were
539  * known _not_ to have been retransmitted [see Karn/Partridge
540  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
541  * piece by Van Jacobson.
542  * NOTE: the next three routines used to be one big routine.
543  * To save cycles in the RFC 1323 implementation it was better to break
544  * it up into three procedures. -- erics
545  */
546 static void tcp_rtt_estimator(struct tcp_sock *tp, __u32 mrtt, u32 *usrtt)
547 {
548         long m = mrtt; /* RTT */
549
550         /*      The following amusing code comes from Jacobson's
551          *      article in SIGCOMM '88.  Note that rtt and mdev
552          *      are scaled versions of rtt and mean deviation.
553          *      This is designed to be as fast as possible 
554          *      m stands for "measurement".
555          *
556          *      On a 1990 paper the rto value is changed to:
557          *      RTO = rtt + 4 * mdev
558          *
559          * Funny. This algorithm seems to be very broken.
560          * These formulae increase RTO, when it should be decreased, increase
561          * too slowly, when it should be incresed fastly, decrease too fastly
562          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
563          * does not matter how to _calculate_ it. Seems, it was trap
564          * that VJ failed to avoid. 8)
565          */
566         if(m == 0)
567                 m = 1;
568         if (tp->srtt != 0) {
569                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
570                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
571                 if (m < 0) {
572                         m = -m;         /* m is now abs(error) */
573                         m -= (tp->mdev >> 2);   /* similar update on mdev */
574                         /* This is similar to one of Eifel findings.
575                          * Eifel blocks mdev updates when rtt decreases.
576                          * This solution is a bit different: we use finer gain
577                          * for mdev in this case (alpha*beta).
578                          * Like Eifel it also prevents growth of rto,
579                          * but also it limits too fast rto decreases,
580                          * happening in pure Eifel.
581                          */
582                         if (m > 0)
583                                 m >>= 3;
584                 } else {
585                         m -= (tp->mdev >> 2);   /* similar update on mdev */
586                 }
587                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
588                 if (tp->mdev > tp->mdev_max) {
589                         tp->mdev_max = tp->mdev;
590                         if (tp->mdev_max > tp->rttvar)
591                                 tp->rttvar = tp->mdev_max;
592                 }
593                 if (after(tp->snd_una, tp->rtt_seq)) {
594                         if (tp->mdev_max < tp->rttvar)
595                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
596                         tp->rtt_seq = tp->snd_nxt;
597                         tp->mdev_max = TCP_RTO_MIN;
598                 }
599         } else {
600                 /* no previous measure. */
601                 tp->srtt = m<<3;        /* take the measured time to be rtt */
602                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
603                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
604                 tp->rtt_seq = tp->snd_nxt;
605         }
606
607         if (tp->ca_ops->rtt_sample)
608                 tp->ca_ops->rtt_sample(tp, *usrtt);
609 }
610
611 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
612  * routine referred to above.
613  */
614 static inline void tcp_set_rto(struct tcp_sock *tp)
615 {
616         /* Old crap is replaced with new one. 8)
617          *
618          * More seriously:
619          * 1. If rtt variance happened to be less 50msec, it is hallucination.
620          *    It cannot be less due to utterly erratic ACK generation made
621          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
622          *    to do with delayed acks, because at cwnd>2 true delack timeout
623          *    is invisible. Actually, Linux-2.4 also generates erratic
624          *    ACKs in some curcumstances.
625          */
626         tp->rto = (tp->srtt >> 3) + tp->rttvar;
627
628         /* 2. Fixups made earlier cannot be right.
629          *    If we do not estimate RTO correctly without them,
630          *    all the algo is pure shit and should be replaced
631          *    with correct one. It is exaclty, which we pretend to do.
632          */
633 }
634
635 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
636  * guarantees that rto is higher.
637  */
638 static inline void tcp_bound_rto(struct tcp_sock *tp)
639 {
640         if (tp->rto > TCP_RTO_MAX)
641                 tp->rto = TCP_RTO_MAX;
642 }
643
644 /* Save metrics learned by this TCP session.
645    This function is called only, when TCP finishes successfully
646    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
647  */
648 void tcp_update_metrics(struct sock *sk)
649 {
650         struct tcp_sock *tp = tcp_sk(sk);
651         struct dst_entry *dst = __sk_dst_get(sk);
652
653         if (sysctl_tcp_nometrics_save)
654                 return;
655
656         dst_confirm(dst);
657
658         if (dst && (dst->flags&DST_HOST)) {
659                 int m;
660
661                 if (tp->backoff || !tp->srtt) {
662                         /* This session failed to estimate rtt. Why?
663                          * Probably, no packets returned in time.
664                          * Reset our results.
665                          */
666                         if (!(dst_metric_locked(dst, RTAX_RTT)))
667                                 dst->metrics[RTAX_RTT-1] = 0;
668                         return;
669                 }
670
671                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
672
673                 /* If newly calculated rtt larger than stored one,
674                  * store new one. Otherwise, use EWMA. Remember,
675                  * rtt overestimation is always better than underestimation.
676                  */
677                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
678                         if (m <= 0)
679                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
680                         else
681                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
682                 }
683
684                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
685                         if (m < 0)
686                                 m = -m;
687
688                         /* Scale deviation to rttvar fixed point */
689                         m >>= 1;
690                         if (m < tp->mdev)
691                                 m = tp->mdev;
692
693                         if (m >= dst_metric(dst, RTAX_RTTVAR))
694                                 dst->metrics[RTAX_RTTVAR-1] = m;
695                         else
696                                 dst->metrics[RTAX_RTTVAR-1] -=
697                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
698                 }
699
700                 if (tp->snd_ssthresh >= 0xFFFF) {
701                         /* Slow start still did not finish. */
702                         if (dst_metric(dst, RTAX_SSTHRESH) &&
703                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
704                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
705                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
706                         if (!dst_metric_locked(dst, RTAX_CWND) &&
707                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
708                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
709                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
710                            tp->ca_state == TCP_CA_Open) {
711                         /* Cong. avoidance phase, cwnd is reliable. */
712                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
713                                 dst->metrics[RTAX_SSTHRESH-1] =
714                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
715                         if (!dst_metric_locked(dst, RTAX_CWND))
716                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
717                 } else {
718                         /* Else slow start did not finish, cwnd is non-sense,
719                            ssthresh may be also invalid.
720                          */
721                         if (!dst_metric_locked(dst, RTAX_CWND))
722                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
723                         if (dst->metrics[RTAX_SSTHRESH-1] &&
724                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
725                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
726                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
727                 }
728
729                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
730                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
731                             tp->reordering != sysctl_tcp_reordering)
732                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
733                 }
734         }
735 }
736
737 /* Numbers are taken from RFC2414.  */
738 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
739 {
740         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
741
742         if (!cwnd) {
743                 if (tp->mss_cache_std > 1460)
744                         cwnd = 2;
745                 else
746                         cwnd = (tp->mss_cache_std > 1095) ? 3 : 4;
747         }
748         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
749 }
750
751 /* Initialize metrics on socket. */
752
753 static void tcp_init_metrics(struct sock *sk)
754 {
755         struct tcp_sock *tp = tcp_sk(sk);
756         struct dst_entry *dst = __sk_dst_get(sk);
757
758         if (dst == NULL)
759                 goto reset;
760
761         dst_confirm(dst);
762
763         if (dst_metric_locked(dst, RTAX_CWND))
764                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
765         if (dst_metric(dst, RTAX_SSTHRESH)) {
766                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
767                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
768                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
769         }
770         if (dst_metric(dst, RTAX_REORDERING) &&
771             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
772                 tp->rx_opt.sack_ok &= ~2;
773                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
774         }
775
776         if (dst_metric(dst, RTAX_RTT) == 0)
777                 goto reset;
778
779         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
780                 goto reset;
781
782         /* Initial rtt is determined from SYN,SYN-ACK.
783          * The segment is small and rtt may appear much
784          * less than real one. Use per-dst memory
785          * to make it more realistic.
786          *
787          * A bit of theory. RTT is time passed after "normal" sized packet
788          * is sent until it is ACKed. In normal curcumstances sending small
789          * packets force peer to delay ACKs and calculation is correct too.
790          * The algorithm is adaptive and, provided we follow specs, it
791          * NEVER underestimate RTT. BUT! If peer tries to make some clever
792          * tricks sort of "quick acks" for time long enough to decrease RTT
793          * to low value, and then abruptly stops to do it and starts to delay
794          * ACKs, wait for troubles.
795          */
796         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
797                 tp->srtt = dst_metric(dst, RTAX_RTT);
798                 tp->rtt_seq = tp->snd_nxt;
799         }
800         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
801                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
802                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
803         }
804         tcp_set_rto(tp);
805         tcp_bound_rto(tp);
806         if (tp->rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
807                 goto reset;
808         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
809         tp->snd_cwnd_stamp = tcp_time_stamp;
810         return;
811
812 reset:
813         /* Play conservative. If timestamps are not
814          * supported, TCP will fail to recalculate correct
815          * rtt, if initial rto is too small. FORGET ALL AND RESET!
816          */
817         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
818                 tp->srtt = 0;
819                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
820                 tp->rto = TCP_TIMEOUT_INIT;
821         }
822 }
823
824 static void tcp_update_reordering(struct tcp_sock *tp, int metric, int ts)
825 {
826         if (metric > tp->reordering) {
827                 tp->reordering = min(TCP_MAX_REORDERING, metric);
828
829                 /* This exciting event is worth to be remembered. 8) */
830                 if (ts)
831                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
832                 else if (IsReno(tp))
833                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
834                 else if (IsFack(tp))
835                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
836                 else
837                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
838 #if FASTRETRANS_DEBUG > 1
839                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
840                        tp->rx_opt.sack_ok, tp->ca_state,
841                        tp->reordering,
842                        tp->fackets_out,
843                        tp->sacked_out,
844                        tp->undo_marker ? tp->undo_retrans : 0);
845 #endif
846                 /* Disable FACK yet. */
847                 tp->rx_opt.sack_ok &= ~2;
848         }
849 }
850
851 /* This procedure tags the retransmission queue when SACKs arrive.
852  *
853  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
854  * Packets in queue with these bits set are counted in variables
855  * sacked_out, retrans_out and lost_out, correspondingly.
856  *
857  * Valid combinations are:
858  * Tag  InFlight        Description
859  * 0    1               - orig segment is in flight.
860  * S    0               - nothing flies, orig reached receiver.
861  * L    0               - nothing flies, orig lost by net.
862  * R    2               - both orig and retransmit are in flight.
863  * L|R  1               - orig is lost, retransmit is in flight.
864  * S|R  1               - orig reached receiver, retrans is still in flight.
865  * (L|S|R is logically valid, it could occur when L|R is sacked,
866  *  but it is equivalent to plain S and code short-curcuits it to S.
867  *  L|S is logically invalid, it would mean -1 packet in flight 8))
868  *
869  * These 6 states form finite state machine, controlled by the following events:
870  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
871  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
872  * 3. Loss detection event of one of three flavors:
873  *      A. Scoreboard estimator decided the packet is lost.
874  *         A'. Reno "three dupacks" marks head of queue lost.
875  *         A''. Its FACK modfication, head until snd.fack is lost.
876  *      B. SACK arrives sacking data transmitted after never retransmitted
877  *         hole was sent out.
878  *      C. SACK arrives sacking SND.NXT at the moment, when the
879  *         segment was retransmitted.
880  * 4. D-SACK added new rule: D-SACK changes any tag to S.
881  *
882  * It is pleasant to note, that state diagram turns out to be commutative,
883  * so that we are allowed not to be bothered by order of our actions,
884  * when multiple events arrive simultaneously. (see the function below).
885  *
886  * Reordering detection.
887  * --------------------
888  * Reordering metric is maximal distance, which a packet can be displaced
889  * in packet stream. With SACKs we can estimate it:
890  *
891  * 1. SACK fills old hole and the corresponding segment was not
892  *    ever retransmitted -> reordering. Alas, we cannot use it
893  *    when segment was retransmitted.
894  * 2. The last flaw is solved with D-SACK. D-SACK arrives
895  *    for retransmitted and already SACKed segment -> reordering..
896  * Both of these heuristics are not used in Loss state, when we cannot
897  * account for retransmits accurately.
898  */
899 static int
900 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
901 {
902         struct tcp_sock *tp = tcp_sk(sk);
903         unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
904         struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2);
905         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
906         int reord = tp->packets_out;
907         int prior_fackets;
908         u32 lost_retrans = 0;
909         int flag = 0;
910         int i;
911
912         /* So, SACKs for already sent large segments will be lost.
913          * Not good, but alternative is to resegment the queue. */
914         if (sk->sk_route_caps & NETIF_F_TSO) {
915                 sk->sk_route_caps &= ~NETIF_F_TSO;
916                 sock_set_flag(sk, SOCK_NO_LARGESEND);
917                 tp->mss_cache = tp->mss_cache_std;
918         }
919
920         if (!tp->sacked_out)
921                 tp->fackets_out = 0;
922         prior_fackets = tp->fackets_out;
923
924         for (i=0; i<num_sacks; i++, sp++) {
925                 struct sk_buff *skb;
926                 __u32 start_seq = ntohl(sp->start_seq);
927                 __u32 end_seq = ntohl(sp->end_seq);
928                 int fack_count = 0;
929                 int dup_sack = 0;
930
931                 /* Check for D-SACK. */
932                 if (i == 0) {
933                         u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;
934
935                         if (before(start_seq, ack)) {
936                                 dup_sack = 1;
937                                 tp->rx_opt.sack_ok |= 4;
938                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
939                         } else if (num_sacks > 1 &&
940                                    !after(end_seq, ntohl(sp[1].end_seq)) &&
941                                    !before(start_seq, ntohl(sp[1].start_seq))) {
942                                 dup_sack = 1;
943                                 tp->rx_opt.sack_ok |= 4;
944                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
945                         }
946
947                         /* D-SACK for already forgotten data...
948                          * Do dumb counting. */
949                         if (dup_sack &&
950                             !after(end_seq, prior_snd_una) &&
951                             after(end_seq, tp->undo_marker))
952                                 tp->undo_retrans--;
953
954                         /* Eliminate too old ACKs, but take into
955                          * account more or less fresh ones, they can
956                          * contain valid SACK info.
957                          */
958                         if (before(ack, prior_snd_una - tp->max_window))
959                                 return 0;
960                 }
961
962                 /* Event "B" in the comment above. */
963                 if (after(end_seq, tp->high_seq))
964                         flag |= FLAG_DATA_LOST;
965
966                 sk_stream_for_retrans_queue(skb, sk) {
967                         u8 sacked = TCP_SKB_CB(skb)->sacked;
968                         int in_sack;
969
970                         /* The retransmission queue is always in order, so
971                          * we can short-circuit the walk early.
972                          */
973                         if(!before(TCP_SKB_CB(skb)->seq, end_seq))
974                                 break;
975
976                         fack_count += tcp_skb_pcount(skb);
977
978                         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
979                                 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
980
981                         /* Account D-SACK for retransmitted packet. */
982                         if ((dup_sack && in_sack) &&
983                             (sacked & TCPCB_RETRANS) &&
984                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
985                                 tp->undo_retrans--;
986
987                         /* The frame is ACKed. */
988                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
989                                 if (sacked&TCPCB_RETRANS) {
990                                         if ((dup_sack && in_sack) &&
991                                             (sacked&TCPCB_SACKED_ACKED))
992                                                 reord = min(fack_count, reord);
993                                 } else {
994                                         /* If it was in a hole, we detected reordering. */
995                                         if (fack_count < prior_fackets &&
996                                             !(sacked&TCPCB_SACKED_ACKED))
997                                                 reord = min(fack_count, reord);
998                                 }
999
1000                                 /* Nothing to do; acked frame is about to be dropped. */
1001                                 continue;
1002                         }
1003
1004                         if ((sacked&TCPCB_SACKED_RETRANS) &&
1005                             after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1006                             (!lost_retrans || after(end_seq, lost_retrans)))
1007                                 lost_retrans = end_seq;
1008
1009                         if (!in_sack)
1010                                 continue;
1011
1012                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1013                                 if (sacked & TCPCB_SACKED_RETRANS) {
1014                                         /* If the segment is not tagged as lost,
1015                                          * we do not clear RETRANS, believing
1016                                          * that retransmission is still in flight.
1017                                          */
1018                                         if (sacked & TCPCB_LOST) {
1019                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1020                                                 tp->lost_out -= tcp_skb_pcount(skb);
1021                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1022                                         }
1023                                 } else {
1024                                         /* New sack for not retransmitted frame,
1025                                          * which was in hole. It is reordering.
1026                                          */
1027                                         if (!(sacked & TCPCB_RETRANS) &&
1028                                             fack_count < prior_fackets)
1029                                                 reord = min(fack_count, reord);
1030
1031                                         if (sacked & TCPCB_LOST) {
1032                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1033                                                 tp->lost_out -= tcp_skb_pcount(skb);
1034                                         }
1035                                 }
1036
1037                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1038                                 flag |= FLAG_DATA_SACKED;
1039                                 tp->sacked_out += tcp_skb_pcount(skb);
1040
1041                                 if (fack_count > tp->fackets_out)
1042                                         tp->fackets_out = fack_count;
1043                         } else {
1044                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1045                                         reord = min(fack_count, reord);
1046                         }
1047
1048                         /* D-SACK. We can detect redundant retransmission
1049                          * in S|R and plain R frames and clear it.
1050                          * undo_retrans is decreased above, L|R frames
1051                          * are accounted above as well.
1052                          */
1053                         if (dup_sack &&
1054                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1055                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1056                                 tp->retrans_out -= tcp_skb_pcount(skb);
1057                         }
1058                 }
1059         }
1060
1061         /* Check for lost retransmit. This superb idea is
1062          * borrowed from "ratehalving". Event "C".
1063          * Later note: FACK people cheated me again 8),
1064          * we have to account for reordering! Ugly,
1065          * but should help.
1066          */
1067         if (lost_retrans && tp->ca_state == TCP_CA_Recovery) {
1068                 struct sk_buff *skb;
1069
1070                 sk_stream_for_retrans_queue(skb, sk) {
1071                         if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1072                                 break;
1073                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1074                                 continue;
1075                         if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1076                             after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1077                             (IsFack(tp) ||
1078                              !before(lost_retrans,
1079                                      TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1080                                      tp->mss_cache_std))) {
1081                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1082                                 tp->retrans_out -= tcp_skb_pcount(skb);
1083
1084                                 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1085                                         tp->lost_out += tcp_skb_pcount(skb);
1086                                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1087                                         flag |= FLAG_DATA_SACKED;
1088                                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1089                                 }
1090                         }
1091                 }
1092         }
1093
1094         tp->left_out = tp->sacked_out + tp->lost_out;
1095
1096         if ((reord < tp->fackets_out) && tp->ca_state != TCP_CA_Loss)
1097                 tcp_update_reordering(tp, ((tp->fackets_out + 1) - reord), 0);
1098
1099 #if FASTRETRANS_DEBUG > 0
1100         BUG_TRAP((int)tp->sacked_out >= 0);
1101         BUG_TRAP((int)tp->lost_out >= 0);
1102         BUG_TRAP((int)tp->retrans_out >= 0);
1103         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1104 #endif
1105         return flag;
1106 }
1107
1108 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new
1109  * segments to see from the next ACKs whether any data was really missing.
1110  * If the RTO was spurious, new ACKs should arrive.
1111  */
1112 void tcp_enter_frto(struct sock *sk)
1113 {
1114         struct tcp_sock *tp = tcp_sk(sk);
1115         struct sk_buff *skb;
1116
1117         tp->frto_counter = 1;
1118
1119         if (tp->ca_state <= TCP_CA_Disorder ||
1120             tp->snd_una == tp->high_seq ||
1121             (tp->ca_state == TCP_CA_Loss && !tp->retransmits)) {
1122                 tp->prior_ssthresh = tcp_current_ssthresh(tp);
1123                 tp->snd_ssthresh = tp->ca_ops->ssthresh(tp);
1124                 tcp_ca_event(tp, CA_EVENT_FRTO);
1125         }
1126
1127         /* Have to clear retransmission markers here to keep the bookkeeping
1128          * in shape, even though we are not yet in Loss state.
1129          * If something was really lost, it is eventually caught up
1130          * in tcp_enter_frto_loss.
1131          */
1132         tp->retrans_out = 0;
1133         tp->undo_marker = tp->snd_una;
1134         tp->undo_retrans = 0;
1135
1136         sk_stream_for_retrans_queue(skb, sk) {
1137                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
1138         }
1139         tcp_sync_left_out(tp);
1140
1141         tcp_set_ca_state(tp, TCP_CA_Open);
1142         tp->frto_highmark = tp->snd_nxt;
1143 }
1144
1145 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1146  * which indicates that we should follow the traditional RTO recovery,
1147  * i.e. mark everything lost and do go-back-N retransmission.
1148  */
1149 static void tcp_enter_frto_loss(struct sock *sk)
1150 {
1151         struct tcp_sock *tp = tcp_sk(sk);
1152         struct sk_buff *skb;
1153         int cnt = 0;
1154
1155         tp->sacked_out = 0;
1156         tp->lost_out = 0;
1157         tp->fackets_out = 0;
1158
1159         sk_stream_for_retrans_queue(skb, sk) {
1160                 cnt += tcp_skb_pcount(skb);
1161                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1162                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1163
1164                         /* Do not mark those segments lost that were
1165                          * forward transmitted after RTO
1166                          */
1167                         if (!after(TCP_SKB_CB(skb)->end_seq,
1168                                    tp->frto_highmark)) {
1169                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1170                                 tp->lost_out += tcp_skb_pcount(skb);
1171                         }
1172                 } else {
1173                         tp->sacked_out += tcp_skb_pcount(skb);
1174                         tp->fackets_out = cnt;
1175                 }
1176         }
1177         tcp_sync_left_out(tp);
1178
1179         tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
1180         tp->snd_cwnd_cnt = 0;
1181         tp->snd_cwnd_stamp = tcp_time_stamp;
1182         tp->undo_marker = 0;
1183         tp->frto_counter = 0;
1184
1185         tp->reordering = min_t(unsigned int, tp->reordering,
1186                                              sysctl_tcp_reordering);
1187         tcp_set_ca_state(tp, TCP_CA_Loss);
1188         tp->high_seq = tp->frto_highmark;
1189         TCP_ECN_queue_cwr(tp);
1190 }
1191
1192 void tcp_clear_retrans(struct tcp_sock *tp)
1193 {
1194         tp->left_out = 0;
1195         tp->retrans_out = 0;
1196
1197         tp->fackets_out = 0;
1198         tp->sacked_out = 0;
1199         tp->lost_out = 0;
1200
1201         tp->undo_marker = 0;
1202         tp->undo_retrans = 0;
1203 }
1204
1205 /* Enter Loss state. If "how" is not zero, forget all SACK information
1206  * and reset tags completely, otherwise preserve SACKs. If receiver
1207  * dropped its ofo queue, we will know this due to reneging detection.
1208  */
1209 void tcp_enter_loss(struct sock *sk, int how)
1210 {
1211         struct tcp_sock *tp = tcp_sk(sk);
1212         struct sk_buff *skb;
1213         int cnt = 0;
1214
1215         /* Reduce ssthresh if it has not yet been made inside this window. */
1216         if (tp->ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1217             (tp->ca_state == TCP_CA_Loss && !tp->retransmits)) {
1218                 tp->prior_ssthresh = tcp_current_ssthresh(tp);
1219                 tp->snd_ssthresh = tp->ca_ops->ssthresh(tp);
1220                 tcp_ca_event(tp, CA_EVENT_LOSS);
1221         }
1222         tp->snd_cwnd       = 1;
1223         tp->snd_cwnd_cnt   = 0;
1224         tp->snd_cwnd_stamp = tcp_time_stamp;
1225
1226         tcp_clear_retrans(tp);
1227
1228         /* Push undo marker, if it was plain RTO and nothing
1229          * was retransmitted. */
1230         if (!how)
1231                 tp->undo_marker = tp->snd_una;
1232
1233         sk_stream_for_retrans_queue(skb, sk) {
1234                 cnt += tcp_skb_pcount(skb);
1235                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1236                         tp->undo_marker = 0;
1237                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1238                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1239                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1240                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1241                         tp->lost_out += tcp_skb_pcount(skb);
1242                 } else {
1243                         tp->sacked_out += tcp_skb_pcount(skb);
1244                         tp->fackets_out = cnt;
1245                 }
1246         }
1247         tcp_sync_left_out(tp);
1248
1249         tp->reordering = min_t(unsigned int, tp->reordering,
1250                                              sysctl_tcp_reordering);
1251         tcp_set_ca_state(tp, TCP_CA_Loss);
1252         tp->high_seq = tp->snd_nxt;
1253         TCP_ECN_queue_cwr(tp);
1254 }
1255
1256 static int tcp_check_sack_reneging(struct sock *sk, struct tcp_sock *tp)
1257 {
1258         struct sk_buff *skb;
1259
1260         /* If ACK arrived pointing to a remembered SACK,
1261          * it means that our remembered SACKs do not reflect
1262          * real state of receiver i.e.
1263          * receiver _host_ is heavily congested (or buggy).
1264          * Do processing similar to RTO timeout.
1265          */
1266         if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
1267             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1268                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1269
1270                 tcp_enter_loss(sk, 1);
1271                 tp->retransmits++;
1272                 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
1273                 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1274                 return 1;
1275         }
1276         return 0;
1277 }
1278
1279 static inline int tcp_fackets_out(struct tcp_sock *tp)
1280 {
1281         return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1282 }
1283
1284 static inline int tcp_skb_timedout(struct tcp_sock *tp, struct sk_buff *skb)
1285 {
1286         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > tp->rto);
1287 }
1288
1289 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
1290 {
1291         return tp->packets_out &&
1292                tcp_skb_timedout(tp, skb_peek(&sk->sk_write_queue));
1293 }
1294
1295 /* Linux NewReno/SACK/FACK/ECN state machine.
1296  * --------------------------------------
1297  *
1298  * "Open"       Normal state, no dubious events, fast path.
1299  * "Disorder"   In all the respects it is "Open",
1300  *              but requires a bit more attention. It is entered when
1301  *              we see some SACKs or dupacks. It is split of "Open"
1302  *              mainly to move some processing from fast path to slow one.
1303  * "CWR"        CWND was reduced due to some Congestion Notification event.
1304  *              It can be ECN, ICMP source quench, local device congestion.
1305  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1306  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1307  *
1308  * tcp_fastretrans_alert() is entered:
1309  * - each incoming ACK, if state is not "Open"
1310  * - when arrived ACK is unusual, namely:
1311  *      * SACK
1312  *      * Duplicate ACK.
1313  *      * ECN ECE.
1314  *
1315  * Counting packets in flight is pretty simple.
1316  *
1317  *      in_flight = packets_out - left_out + retrans_out
1318  *
1319  *      packets_out is SND.NXT-SND.UNA counted in packets.
1320  *
1321  *      retrans_out is number of retransmitted segments.
1322  *
1323  *      left_out is number of segments left network, but not ACKed yet.
1324  *
1325  *              left_out = sacked_out + lost_out
1326  *
1327  *     sacked_out: Packets, which arrived to receiver out of order
1328  *                 and hence not ACKed. With SACKs this number is simply
1329  *                 amount of SACKed data. Even without SACKs
1330  *                 it is easy to give pretty reliable estimate of this number,
1331  *                 counting duplicate ACKs.
1332  *
1333  *       lost_out: Packets lost by network. TCP has no explicit
1334  *                 "loss notification" feedback from network (for now).
1335  *                 It means that this number can be only _guessed_.
1336  *                 Actually, it is the heuristics to predict lossage that
1337  *                 distinguishes different algorithms.
1338  *
1339  *      F.e. after RTO, when all the queue is considered as lost,
1340  *      lost_out = packets_out and in_flight = retrans_out.
1341  *
1342  *              Essentially, we have now two algorithms counting
1343  *              lost packets.
1344  *
1345  *              FACK: It is the simplest heuristics. As soon as we decided
1346  *              that something is lost, we decide that _all_ not SACKed
1347  *              packets until the most forward SACK are lost. I.e.
1348  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1349  *              It is absolutely correct estimate, if network does not reorder
1350  *              packets. And it loses any connection to reality when reordering
1351  *              takes place. We use FACK by default until reordering
1352  *              is suspected on the path to this destination.
1353  *
1354  *              NewReno: when Recovery is entered, we assume that one segment
1355  *              is lost (classic Reno). While we are in Recovery and
1356  *              a partial ACK arrives, we assume that one more packet
1357  *              is lost (NewReno). This heuristics are the same in NewReno
1358  *              and SACK.
1359  *
1360  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1361  *  deflation etc. CWND is real congestion window, never inflated, changes
1362  *  only according to classic VJ rules.
1363  *
1364  * Really tricky (and requiring careful tuning) part of algorithm
1365  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1366  * The first determines the moment _when_ we should reduce CWND and,
1367  * hence, slow down forward transmission. In fact, it determines the moment
1368  * when we decide that hole is caused by loss, rather than by a reorder.
1369  *
1370  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1371  * holes, caused by lost packets.
1372  *
1373  * And the most logically complicated part of algorithm is undo
1374  * heuristics. We detect false retransmits due to both too early
1375  * fast retransmit (reordering) and underestimated RTO, analyzing
1376  * timestamps and D-SACKs. When we detect that some segments were
1377  * retransmitted by mistake and CWND reduction was wrong, we undo
1378  * window reduction and abort recovery phase. This logic is hidden
1379  * inside several functions named tcp_try_undo_<something>.
1380  */
1381
1382 /* This function decides, when we should leave Disordered state
1383  * and enter Recovery phase, reducing congestion window.
1384  *
1385  * Main question: may we further continue forward transmission
1386  * with the same cwnd?
1387  */
1388 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
1389 {
1390         __u32 packets_out;
1391
1392         /* Trick#1: The loss is proven. */
1393         if (tp->lost_out)
1394                 return 1;
1395
1396         /* Not-A-Trick#2 : Classic rule... */
1397         if (tcp_fackets_out(tp) > tp->reordering)
1398                 return 1;
1399
1400         /* Trick#3 : when we use RFC2988 timer restart, fast
1401          * retransmit can be triggered by timeout of queue head.
1402          */
1403         if (tcp_head_timedout(sk, tp))
1404                 return 1;
1405
1406         /* Trick#4: It is still not OK... But will it be useful to delay
1407          * recovery more?
1408          */
1409         packets_out = tp->packets_out;
1410         if (packets_out <= tp->reordering &&
1411             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1412             !tcp_may_send_now(sk, tp)) {
1413                 /* We have nothing to send. This connection is limited
1414                  * either by receiver window or by application.
1415                  */
1416                 return 1;
1417         }
1418
1419         return 0;
1420 }
1421
1422 /* If we receive more dupacks than we expected counting segments
1423  * in assumption of absent reordering, interpret this as reordering.
1424  * The only another reason could be bug in receiver TCP.
1425  */
1426 static void tcp_check_reno_reordering(struct tcp_sock *tp, int addend)
1427 {
1428         u32 holes;
1429
1430         holes = max(tp->lost_out, 1U);
1431         holes = min(holes, tp->packets_out);
1432
1433         if ((tp->sacked_out + holes) > tp->packets_out) {
1434                 tp->sacked_out = tp->packets_out - holes;
1435                 tcp_update_reordering(tp, tp->packets_out+addend, 0);
1436         }
1437 }
1438
1439 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1440
1441 static void tcp_add_reno_sack(struct tcp_sock *tp)
1442 {
1443         tp->sacked_out++;
1444         tcp_check_reno_reordering(tp, 0);
1445         tcp_sync_left_out(tp);
1446 }
1447
1448 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1449
1450 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
1451 {
1452         if (acked > 0) {
1453                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1454                 if (acked-1 >= tp->sacked_out)
1455                         tp->sacked_out = 0;
1456                 else
1457                         tp->sacked_out -= acked-1;
1458         }
1459         tcp_check_reno_reordering(tp, acked);
1460         tcp_sync_left_out(tp);
1461 }
1462
1463 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1464 {
1465         tp->sacked_out = 0;
1466         tp->left_out = tp->lost_out;
1467 }
1468
1469 /* Mark head of queue up as lost. */
1470 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
1471                                int packets, u32 high_seq)
1472 {
1473         struct sk_buff *skb;
1474         int cnt = packets;
1475
1476         BUG_TRAP(cnt <= tp->packets_out);
1477
1478         sk_stream_for_retrans_queue(skb, sk) {
1479                 cnt -= tcp_skb_pcount(skb);
1480                 if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1481                         break;
1482                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1483                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1484                         tp->lost_out += tcp_skb_pcount(skb);
1485                 }
1486         }
1487         tcp_sync_left_out(tp);
1488 }
1489
1490 /* Account newly detected lost packet(s) */
1491
1492 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
1493 {
1494         if (IsFack(tp)) {
1495                 int lost = tp->fackets_out - tp->reordering;
1496                 if (lost <= 0)
1497                         lost = 1;
1498                 tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
1499         } else {
1500                 tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
1501         }
1502
1503         /* New heuristics: it is possible only after we switched
1504          * to restart timer each time when something is ACKed.
1505          * Hence, we can detect timed out packets during fast
1506          * retransmit without falling to slow start.
1507          */
1508         if (tcp_head_timedout(sk, tp)) {
1509                 struct sk_buff *skb;
1510
1511                 sk_stream_for_retrans_queue(skb, sk) {
1512                         if (tcp_skb_timedout(tp, skb) &&
1513                             !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1514                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1515                                 tp->lost_out += tcp_skb_pcount(skb);
1516                         }
1517                 }
1518                 tcp_sync_left_out(tp);
1519         }
1520 }
1521
1522 /* CWND moderation, preventing bursts due to too big ACKs
1523  * in dubious situations.
1524  */
1525 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1526 {
1527         tp->snd_cwnd = min(tp->snd_cwnd,
1528                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1529         tp->snd_cwnd_stamp = tcp_time_stamp;
1530 }
1531
1532 /* Decrease cwnd each second ack. */
1533 static void tcp_cwnd_down(struct tcp_sock *tp)
1534 {
1535         int decr = tp->snd_cwnd_cnt + 1;
1536
1537         tp->snd_cwnd_cnt = decr&1;
1538         decr >>= 1;
1539
1540         if (decr && tp->snd_cwnd > tp->ca_ops->min_cwnd(tp))
1541                 tp->snd_cwnd -= decr;
1542
1543         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1544         tp->snd_cwnd_stamp = tcp_time_stamp;
1545 }
1546
1547 /* Nothing was retransmitted or returned timestamp is less
1548  * than timestamp of the first retransmission.
1549  */
1550 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1551 {
1552         return !tp->retrans_stamp ||
1553                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1554                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1555 }
1556
1557 /* Undo procedures. */
1558
1559 #if FASTRETRANS_DEBUG > 1
1560 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
1561 {
1562         struct inet_sock *inet = inet_sk(sk);
1563         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1564                msg,
1565                NIPQUAD(inet->daddr), ntohs(inet->dport),
1566                tp->snd_cwnd, tp->left_out,
1567                tp->snd_ssthresh, tp->prior_ssthresh,
1568                tp->packets_out);
1569 }
1570 #else
1571 #define DBGUNDO(x...) do { } while (0)
1572 #endif
1573
1574 static void tcp_undo_cwr(struct tcp_sock *tp, int undo)
1575 {
1576         if (tp->prior_ssthresh) {
1577                 if (tp->ca_ops->undo_cwnd)
1578                         tp->snd_cwnd = tp->ca_ops->undo_cwnd(tp);
1579                 else
1580                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1581
1582                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1583                         tp->snd_ssthresh = tp->prior_ssthresh;
1584                         TCP_ECN_withdraw_cwr(tp);
1585                 }
1586         } else {
1587                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1588         }
1589         tcp_moderate_cwnd(tp);
1590         tp->snd_cwnd_stamp = tcp_time_stamp;
1591 }
1592
1593 static inline int tcp_may_undo(struct tcp_sock *tp)
1594 {
1595         return tp->undo_marker &&
1596                 (!tp->undo_retrans || tcp_packet_delayed(tp));
1597 }
1598
1599 /* People celebrate: "We love our President!" */
1600 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
1601 {
1602         if (tcp_may_undo(tp)) {
1603                 /* Happy end! We did not retransmit anything
1604                  * or our original transmission succeeded.
1605                  */
1606                 DBGUNDO(sk, tp, tp->ca_state == TCP_CA_Loss ? "loss" : "retrans");
1607                 tcp_undo_cwr(tp, 1);
1608                 if (tp->ca_state == TCP_CA_Loss)
1609                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1610                 else
1611                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1612                 tp->undo_marker = 0;
1613         }
1614         if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1615                 /* Hold old state until something *above* high_seq
1616                  * is ACKed. For Reno it is MUST to prevent false
1617                  * fast retransmits (RFC2582). SACK TCP is safe. */
1618                 tcp_moderate_cwnd(tp);
1619                 return 1;
1620         }
1621         tcp_set_ca_state(tp, TCP_CA_Open);
1622         return 0;
1623 }
1624
1625 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1626 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
1627 {
1628         if (tp->undo_marker && !tp->undo_retrans) {
1629                 DBGUNDO(sk, tp, "D-SACK");
1630                 tcp_undo_cwr(tp, 1);
1631                 tp->undo_marker = 0;
1632                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1633         }
1634 }
1635
1636 /* Undo during fast recovery after partial ACK. */
1637
1638 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
1639                                 int acked)
1640 {
1641         /* Partial ACK arrived. Force Hoe's retransmit. */
1642         int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1643
1644         if (tcp_may_undo(tp)) {
1645                 /* Plain luck! Hole if filled with delayed
1646                  * packet, rather than with a retransmit.
1647                  */
1648                 if (tp->retrans_out == 0)
1649                         tp->retrans_stamp = 0;
1650
1651                 tcp_update_reordering(tp, tcp_fackets_out(tp)+acked, 1);
1652
1653                 DBGUNDO(sk, tp, "Hoe");
1654                 tcp_undo_cwr(tp, 0);
1655                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1656
1657                 /* So... Do not make Hoe's retransmit yet.
1658                  * If the first packet was delayed, the rest
1659                  * ones are most probably delayed as well.
1660                  */
1661                 failed = 0;
1662         }
1663         return failed;
1664 }
1665
1666 /* Undo during loss recovery after partial ACK. */
1667 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
1668 {
1669         if (tcp_may_undo(tp)) {
1670                 struct sk_buff *skb;
1671                 sk_stream_for_retrans_queue(skb, sk) {
1672                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1673                 }
1674                 DBGUNDO(sk, tp, "partial loss");
1675                 tp->lost_out = 0;
1676                 tp->left_out = tp->sacked_out;
1677                 tcp_undo_cwr(tp, 1);
1678                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1679                 tp->retransmits = 0;
1680                 tp->undo_marker = 0;
1681                 if (!IsReno(tp))
1682                         tcp_set_ca_state(tp, TCP_CA_Open);
1683                 return 1;
1684         }
1685         return 0;
1686 }
1687
1688 static inline void tcp_complete_cwr(struct tcp_sock *tp)
1689 {
1690         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
1691         tp->snd_cwnd_stamp = tcp_time_stamp;
1692         tcp_ca_event(tp, CA_EVENT_COMPLETE_CWR);
1693 }
1694
1695 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
1696 {
1697         tp->left_out = tp->sacked_out;
1698
1699         if (tp->retrans_out == 0)
1700                 tp->retrans_stamp = 0;
1701
1702         if (flag&FLAG_ECE)
1703                 tcp_enter_cwr(tp);
1704
1705         if (tp->ca_state != TCP_CA_CWR) {
1706                 int state = TCP_CA_Open;
1707
1708                 if (tp->left_out || tp->retrans_out || tp->undo_marker)
1709                         state = TCP_CA_Disorder;
1710
1711                 if (tp->ca_state != state) {
1712                         tcp_set_ca_state(tp, state);
1713                         tp->high_seq = tp->snd_nxt;
1714                 }
1715                 tcp_moderate_cwnd(tp);
1716         } else {
1717                 tcp_cwnd_down(tp);
1718         }
1719 }
1720
1721 /* Process an event, which can update packets-in-flight not trivially.
1722  * Main goal of this function is to calculate new estimate for left_out,
1723  * taking into account both packets sitting in receiver's buffer and
1724  * packets lost by network.
1725  *
1726  * Besides that it does CWND reduction, when packet loss is detected
1727  * and changes state of machine.
1728  *
1729  * It does _not_ decide what to send, it is made in function
1730  * tcp_xmit_retransmit_queue().
1731  */
1732 static void
1733 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
1734                       int prior_packets, int flag)
1735 {
1736         struct tcp_sock *tp = tcp_sk(sk);
1737         int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
1738
1739         /* Some technical things:
1740          * 1. Reno does not count dupacks (sacked_out) automatically. */
1741         if (!tp->packets_out)
1742                 tp->sacked_out = 0;
1743         /* 2. SACK counts snd_fack in packets inaccurately. */
1744         if (tp->sacked_out == 0)
1745                 tp->fackets_out = 0;
1746
1747         /* Now state machine starts.
1748          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
1749         if (flag&FLAG_ECE)
1750                 tp->prior_ssthresh = 0;
1751
1752         /* B. In all the states check for reneging SACKs. */
1753         if (tp->sacked_out && tcp_check_sack_reneging(sk, tp))
1754                 return;
1755
1756         /* C. Process data loss notification, provided it is valid. */
1757         if ((flag&FLAG_DATA_LOST) &&
1758             before(tp->snd_una, tp->high_seq) &&
1759             tp->ca_state != TCP_CA_Open &&
1760             tp->fackets_out > tp->reordering) {
1761                 tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
1762                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
1763         }
1764
1765         /* D. Synchronize left_out to current state. */
1766         tcp_sync_left_out(tp);
1767
1768         /* E. Check state exit conditions. State can be terminated
1769          *    when high_seq is ACKed. */
1770         if (tp->ca_state == TCP_CA_Open) {
1771                 if (!sysctl_tcp_frto)
1772                         BUG_TRAP(tp->retrans_out == 0);
1773                 tp->retrans_stamp = 0;
1774         } else if (!before(tp->snd_una, tp->high_seq)) {
1775                 switch (tp->ca_state) {
1776                 case TCP_CA_Loss:
1777                         tp->retransmits = 0;
1778                         if (tcp_try_undo_recovery(sk, tp))
1779                                 return;
1780                         break;
1781
1782                 case TCP_CA_CWR:
1783                         /* CWR is to be held something *above* high_seq
1784                          * is ACKed for CWR bit to reach receiver. */
1785                         if (tp->snd_una != tp->high_seq) {
1786                                 tcp_complete_cwr(tp);
1787                                 tcp_set_ca_state(tp, TCP_CA_Open);
1788                         }
1789                         break;
1790
1791                 case TCP_CA_Disorder:
1792                         tcp_try_undo_dsack(sk, tp);
1793                         if (!tp->undo_marker ||
1794                             /* For SACK case do not Open to allow to undo
1795                              * catching for all duplicate ACKs. */
1796                             IsReno(tp) || tp->snd_una != tp->high_seq) {
1797                                 tp->undo_marker = 0;
1798                                 tcp_set_ca_state(tp, TCP_CA_Open);
1799                         }
1800                         break;
1801
1802                 case TCP_CA_Recovery:
1803                         if (IsReno(tp))
1804                                 tcp_reset_reno_sack(tp);
1805                         if (tcp_try_undo_recovery(sk, tp))
1806                                 return;
1807                         tcp_complete_cwr(tp);
1808                         break;
1809                 }
1810         }
1811
1812         /* F. Process state. */
1813         switch (tp->ca_state) {
1814         case TCP_CA_Recovery:
1815                 if (prior_snd_una == tp->snd_una) {
1816                         if (IsReno(tp) && is_dupack)
1817                                 tcp_add_reno_sack(tp);
1818                 } else {
1819                         int acked = prior_packets - tp->packets_out;
1820                         if (IsReno(tp))
1821                                 tcp_remove_reno_sacks(sk, tp, acked);
1822                         is_dupack = tcp_try_undo_partial(sk, tp, acked);
1823                 }
1824                 break;
1825         case TCP_CA_Loss:
1826                 if (flag&FLAG_DATA_ACKED)
1827                         tp->retransmits = 0;
1828                 if (!tcp_try_undo_loss(sk, tp)) {
1829                         tcp_moderate_cwnd(tp);
1830                         tcp_xmit_retransmit_queue(sk);
1831                         return;
1832                 }
1833                 if (tp->ca_state != TCP_CA_Open)
1834                         return;
1835                 /* Loss is undone; fall through to processing in Open state. */
1836         default:
1837                 if (IsReno(tp)) {
1838                         if (tp->snd_una != prior_snd_una)
1839                                 tcp_reset_reno_sack(tp);
1840                         if (is_dupack)
1841                                 tcp_add_reno_sack(tp);
1842                 }
1843
1844                 if (tp->ca_state == TCP_CA_Disorder)
1845                         tcp_try_undo_dsack(sk, tp);
1846
1847                 if (!tcp_time_to_recover(sk, tp)) {
1848                         tcp_try_to_open(sk, tp, flag);
1849                         return;
1850                 }
1851
1852                 /* Otherwise enter Recovery state */
1853
1854                 if (IsReno(tp))
1855                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
1856                 else
1857                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
1858
1859                 tp->high_seq = tp->snd_nxt;
1860                 tp->prior_ssthresh = 0;
1861                 tp->undo_marker = tp->snd_una;
1862                 tp->undo_retrans = tp->retrans_out;
1863
1864                 if (tp->ca_state < TCP_CA_CWR) {
1865                         if (!(flag&FLAG_ECE))
1866                                 tp->prior_ssthresh = tcp_current_ssthresh(tp);
1867                         tp->snd_ssthresh = tp->ca_ops->ssthresh(tp);
1868                         TCP_ECN_queue_cwr(tp);
1869                 }
1870
1871                 tp->snd_cwnd_cnt = 0;
1872                 tcp_set_ca_state(tp, TCP_CA_Recovery);
1873         }
1874
1875         if (is_dupack || tcp_head_timedout(sk, tp))
1876                 tcp_update_scoreboard(sk, tp);
1877         tcp_cwnd_down(tp);
1878         tcp_xmit_retransmit_queue(sk);
1879 }
1880
1881 /* Read draft-ietf-tcplw-high-performance before mucking
1882  * with this code. (Superceeds RFC1323)
1883  */
1884 static void tcp_ack_saw_tstamp(struct tcp_sock *tp, u32 *usrtt, int flag)
1885 {
1886         __u32 seq_rtt;
1887
1888         /* RTTM Rule: A TSecr value received in a segment is used to
1889          * update the averaged RTT measurement only if the segment
1890          * acknowledges some new data, i.e., only if it advances the
1891          * left edge of the send window.
1892          *
1893          * See draft-ietf-tcplw-high-performance-00, section 3.3.
1894          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
1895          *
1896          * Changed: reset backoff as soon as we see the first valid sample.
1897          * If we do not, we get strongly overstimated rto. With timestamps
1898          * samples are accepted even from very old segments: f.e., when rtt=1
1899          * increases to 8, we retransmit 5 times and after 8 seconds delayed
1900          * answer arrives rto becomes 120 seconds! If at least one of segments
1901          * in window is lost... Voila.                          --ANK (010210)
1902          */
1903         seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
1904         tcp_rtt_estimator(tp, seq_rtt, usrtt);
1905         tcp_set_rto(tp);
1906         tp->backoff = 0;
1907         tcp_bound_rto(tp);
1908 }
1909
1910 static void tcp_ack_no_tstamp(struct tcp_sock *tp, u32 seq_rtt, u32 *usrtt, int flag)
1911 {
1912         /* We don't have a timestamp. Can only use
1913          * packets that are not retransmitted to determine
1914          * rtt estimates. Also, we must not reset the
1915          * backoff for rto until we get a non-retransmitted
1916          * packet. This allows us to deal with a situation
1917          * where the network delay has increased suddenly.
1918          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
1919          */
1920
1921         if (flag & FLAG_RETRANS_DATA_ACKED)
1922                 return;
1923
1924         tcp_rtt_estimator(tp, seq_rtt, usrtt);
1925         tcp_set_rto(tp);
1926         tp->backoff = 0;
1927         tcp_bound_rto(tp);
1928 }
1929
1930 static inline void tcp_ack_update_rtt(struct tcp_sock *tp,
1931                                       int flag, s32 seq_rtt, u32 *usrtt)
1932 {
1933         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
1934         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
1935                 tcp_ack_saw_tstamp(tp, usrtt, flag);
1936         else if (seq_rtt >= 0)
1937                 tcp_ack_no_tstamp(tp, seq_rtt, usrtt, flag);
1938 }
1939
1940 static inline void tcp_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,
1941                                   u32 in_flight, int good)
1942 {
1943         tp->ca_ops->cong_avoid(tp, ack, rtt, in_flight, good);
1944         tp->snd_cwnd_stamp = tcp_time_stamp;
1945 }
1946
1947 /* Restart timer after forward progress on connection.
1948  * RFC2988 recommends to restart timer to now+rto.
1949  */
1950
1951 static inline void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
1952 {
1953         if (!tp->packets_out) {
1954                 tcp_clear_xmit_timer(sk, TCP_TIME_RETRANS);
1955         } else {
1956                 tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
1957         }
1958 }
1959
1960 /* There is one downside to this scheme.  Although we keep the
1961  * ACK clock ticking, adjusting packet counters and advancing
1962  * congestion window, we do not liberate socket send buffer
1963  * space.
1964  *
1965  * Mucking with skb->truesize and sk->sk_wmem_alloc et al.
1966  * then making a write space wakeup callback is a possible
1967  * future enhancement.  WARNING: it is not trivial to make.
1968  */
1969 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
1970                          __u32 now, __s32 *seq_rtt)
1971 {
1972         struct tcp_sock *tp = tcp_sk(sk);
1973         struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
1974         __u32 seq = tp->snd_una;
1975         __u32 packets_acked;
1976         int acked = 0;
1977
1978         /* If we get here, the whole TSO packet has not been
1979          * acked.
1980          */
1981         BUG_ON(!after(scb->end_seq, seq));
1982
1983         packets_acked = tcp_skb_pcount(skb);
1984         if (tcp_trim_head(sk, skb, seq - scb->seq))
1985                 return 0;
1986         packets_acked -= tcp_skb_pcount(skb);
1987
1988         if (packets_acked) {
1989                 __u8 sacked = scb->sacked;
1990
1991                 acked |= FLAG_DATA_ACKED;
1992                 if (sacked) {
1993                         if (sacked & TCPCB_RETRANS) {
1994                                 if (sacked & TCPCB_SACKED_RETRANS)
1995                                         tp->retrans_out -= packets_acked;
1996                                 acked |= FLAG_RETRANS_DATA_ACKED;
1997                                 *seq_rtt = -1;
1998                         } else if (*seq_rtt < 0)
1999                                 *seq_rtt = now - scb->when;
2000                         if (sacked & TCPCB_SACKED_ACKED)
2001                                 tp->sacked_out -= packets_acked;
2002                         if (sacked & TCPCB_LOST)
2003                                 tp->lost_out -= packets_acked;
2004                         if (sacked & TCPCB_URG) {
2005                                 if (tp->urg_mode &&
2006                                     !before(seq, tp->snd_up))
2007                                         tp->urg_mode = 0;
2008                         }
2009                 } else if (*seq_rtt < 0)
2010                         *seq_rtt = now - scb->when;
2011
2012                 if (tp->fackets_out) {
2013                         __u32 dval = min(tp->fackets_out, packets_acked);
2014                         tp->fackets_out -= dval;
2015                 }
2016                 tp->packets_out -= packets_acked;
2017
2018                 BUG_ON(tcp_skb_pcount(skb) == 0);
2019                 BUG_ON(!before(scb->seq, scb->end_seq));
2020         }
2021
2022         return acked;
2023 }
2024
2025
2026 /* Remove acknowledged frames from the retransmission queue. */
2027 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt)
2028 {
2029         struct tcp_sock *tp = tcp_sk(sk);
2030         struct sk_buff *skb;
2031         __u32 now = tcp_time_stamp;
2032         int acked = 0;
2033         __s32 seq_rtt = -1;
2034         struct timeval usnow;
2035         u32 pkts_acked = 0;
2036
2037         if (seq_usrtt)
2038                 do_gettimeofday(&usnow);
2039
2040         while ((skb = skb_peek(&sk->sk_write_queue)) &&
2041                skb != sk->sk_send_head) {
2042                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2043                 __u8 sacked = scb->sacked;
2044
2045                 /* If our packet is before the ack sequence we can
2046                  * discard it as it's confirmed to have arrived at
2047                  * the other end.
2048                  */
2049                 if (after(scb->end_seq, tp->snd_una)) {
2050                         if (tcp_skb_pcount(skb) > 1)
2051                                 acked |= tcp_tso_acked(sk, skb,
2052                                                        now, &seq_rtt);
2053                         break;
2054                 }
2055
2056                 /* Initial outgoing SYN's get put onto the write_queue
2057                  * just like anything else we transmit.  It is not
2058                  * true data, and if we misinform our callers that
2059                  * this ACK acks real data, we will erroneously exit
2060                  * connection startup slow start one packet too
2061                  * quickly.  This is severely frowned upon behavior.
2062                  */
2063                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2064                         acked |= FLAG_DATA_ACKED;
2065                         ++pkts_acked;
2066                 } else {
2067                         acked |= FLAG_SYN_ACKED;
2068                         tp->retrans_stamp = 0;
2069                 }
2070
2071                 if (sacked) {
2072                         if (sacked & TCPCB_RETRANS) {
2073                                 if(sacked & TCPCB_SACKED_RETRANS)
2074                                         tp->retrans_out -= tcp_skb_pcount(skb);
2075                                 acked |= FLAG_RETRANS_DATA_ACKED;
2076                                 seq_rtt = -1;
2077                         } else if (seq_rtt < 0)
2078                                 seq_rtt = now - scb->when;
2079                         if (seq_usrtt)
2080                                 *seq_usrtt = (usnow.tv_sec - skb->stamp.tv_sec) * 1000000
2081                                         + (usnow.tv_usec - skb->stamp.tv_usec);
2082
2083                         if (sacked & TCPCB_SACKED_ACKED)
2084                                 tp->sacked_out -= tcp_skb_pcount(skb);
2085                         if (sacked & TCPCB_LOST)
2086                                 tp->lost_out -= tcp_skb_pcount(skb);
2087                         if (sacked & TCPCB_URG) {
2088                                 if (tp->urg_mode &&
2089                                     !before(scb->end_seq, tp->snd_up))
2090                                         tp->urg_mode = 0;
2091                         }
2092                 } else if (seq_rtt < 0)
2093                         seq_rtt = now - scb->when;
2094                 tcp_dec_pcount_approx(&tp->fackets_out, skb);
2095                 tcp_packets_out_dec(tp, skb);
2096                 __skb_unlink(skb, skb->list);
2097                 sk_stream_free_skb(sk, skb);
2098         }
2099
2100         if (acked&FLAG_ACKED) {
2101                 tcp_ack_update_rtt(tp, acked, seq_rtt, seq_usrtt);
2102                 tcp_ack_packets_out(sk, tp);
2103
2104                 if (tp->ca_ops->pkts_acked)
2105                         tp->ca_ops->pkts_acked(tp, pkts_acked);
2106         }
2107
2108 #if FASTRETRANS_DEBUG > 0
2109         BUG_TRAP((int)tp->sacked_out >= 0);
2110         BUG_TRAP((int)tp->lost_out >= 0);
2111         BUG_TRAP((int)tp->retrans_out >= 0);
2112         if (!tp->packets_out && tp->rx_opt.sack_ok) {
2113                 if (tp->lost_out) {
2114                         printk(KERN_DEBUG "Leak l=%u %d\n",
2115                                tp->lost_out, tp->ca_state);
2116                         tp->lost_out = 0;
2117                 }
2118                 if (tp->sacked_out) {
2119                         printk(KERN_DEBUG "Leak s=%u %d\n",
2120                                tp->sacked_out, tp->ca_state);
2121                         tp->sacked_out = 0;
2122                 }
2123                 if (tp->retrans_out) {
2124                         printk(KERN_DEBUG "Leak r=%u %d\n",
2125                                tp->retrans_out, tp->ca_state);
2126                         tp->retrans_out = 0;
2127                 }
2128         }
2129 #endif
2130         *seq_rtt_p = seq_rtt;
2131         return acked;
2132 }
2133
2134 static void tcp_ack_probe(struct sock *sk)
2135 {
2136         struct tcp_sock *tp = tcp_sk(sk);
2137
2138         /* Was it a usable window open? */
2139
2140         if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
2141                    tp->snd_una + tp->snd_wnd)) {
2142                 tp->backoff = 0;
2143                 tcp_clear_xmit_timer(sk, TCP_TIME_PROBE0);
2144                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2145                  * This function is not for random using!
2146                  */
2147         } else {
2148                 tcp_reset_xmit_timer(sk, TCP_TIME_PROBE0,
2149                                      min(tp->rto << tp->backoff, TCP_RTO_MAX));
2150         }
2151 }
2152
2153 static inline int tcp_ack_is_dubious(struct tcp_sock *tp, int flag)
2154 {
2155         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2156                 tp->ca_state != TCP_CA_Open);
2157 }
2158
2159 static inline int tcp_may_raise_cwnd(struct tcp_sock *tp, int flag)
2160 {
2161         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2162                 !((1<<tp->ca_state)&(TCPF_CA_Recovery|TCPF_CA_CWR));
2163 }
2164
2165 /* Check that window update is acceptable.
2166  * The function assumes that snd_una<=ack<=snd_next.
2167  */
2168 static inline int tcp_may_update_window(struct tcp_sock *tp, u32 ack,
2169                                         u32 ack_seq, u32 nwin)
2170 {
2171         return (after(ack, tp->snd_una) ||
2172                 after(ack_seq, tp->snd_wl1) ||
2173                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2174 }
2175
2176 /* Update our send window.
2177  *
2178  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2179  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2180  */
2181 static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
2182                                  struct sk_buff *skb, u32 ack, u32 ack_seq)
2183 {
2184         int flag = 0;
2185         u32 nwin = ntohs(skb->h.th->window);
2186
2187         if (likely(!skb->h.th->syn))
2188                 nwin <<= tp->rx_opt.snd_wscale;
2189
2190         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2191                 flag |= FLAG_WIN_UPDATE;
2192                 tcp_update_wl(tp, ack, ack_seq);
2193
2194                 if (tp->snd_wnd != nwin) {
2195                         tp->snd_wnd = nwin;
2196
2197                         /* Note, it is the only place, where
2198                          * fast path is recovered for sending TCP.
2199                          */
2200                         tcp_fast_path_check(sk, tp);
2201
2202                         if (nwin > tp->max_window) {
2203                                 tp->max_window = nwin;
2204                                 tcp_sync_mss(sk, tp->pmtu_cookie);
2205                         }
2206                 }
2207         }
2208
2209         tp->snd_una = ack;
2210
2211         return flag;
2212 }
2213
2214 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
2215 {
2216         struct tcp_sock *tp = tcp_sk(sk);
2217         
2218         tcp_sync_left_out(tp);
2219         
2220         if (tp->snd_una == prior_snd_una ||
2221             !before(tp->snd_una, tp->frto_highmark)) {
2222                 /* RTO was caused by loss, start retransmitting in
2223                  * go-back-N slow start
2224                  */
2225                 tcp_enter_frto_loss(sk);
2226                 return;
2227         }
2228
2229         if (tp->frto_counter == 1) {
2230                 /* First ACK after RTO advances the window: allow two new
2231                  * segments out.
2232                  */
2233                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2234         } else {
2235                 /* Also the second ACK after RTO advances the window.
2236                  * The RTO was likely spurious. Reduce cwnd and continue
2237                  * in congestion avoidance
2238                  */
2239                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2240                 tcp_moderate_cwnd(tp);
2241         }
2242
2243         /* F-RTO affects on two new ACKs following RTO.
2244          * At latest on third ACK the TCP behavor is back to normal.
2245          */
2246         tp->frto_counter = (tp->frto_counter + 1) % 3;
2247 }
2248
2249 /* This routine deals with incoming acks, but not outgoing ones. */
2250 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2251 {
2252         struct tcp_sock *tp = tcp_sk(sk);
2253         u32 prior_snd_una = tp->snd_una;
2254         u32 ack_seq = TCP_SKB_CB(skb)->seq;
2255         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2256         u32 prior_in_flight;
2257         s32 seq_rtt;
2258         s32 seq_usrtt = 0;
2259         int prior_packets;
2260
2261         /* If the ack is newer than sent or older than previous acks
2262          * then we can probably ignore it.
2263          */
2264         if (after(ack, tp->snd_nxt))
2265                 goto uninteresting_ack;
2266
2267         if (before(ack, prior_snd_una))
2268                 goto old_ack;
2269
2270         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
2271                 /* Window is constant, pure forward advance.
2272                  * No more checks are required.
2273                  * Note, we use the fact that SND.UNA>=SND.WL2.
2274                  */
2275                 tcp_update_wl(tp, ack, ack_seq);
2276                 tp->snd_una = ack;
2277                 flag |= FLAG_WIN_UPDATE;
2278
2279                 tcp_ca_event(tp, CA_EVENT_FAST_ACK);
2280
2281                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
2282         } else {
2283                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
2284                         flag |= FLAG_DATA;
2285                 else
2286                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
2287
2288                 flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);
2289
2290                 if (TCP_SKB_CB(skb)->sacked)
2291                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2292
2293                 if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
2294                         flag |= FLAG_ECE;
2295
2296                 tcp_ca_event(tp, CA_EVENT_SLOW_ACK);
2297         }
2298
2299         /* We passed data and got it acked, remove any soft error
2300          * log. Something worked...
2301          */
2302         sk->sk_err_soft = 0;
2303         tp->rcv_tstamp = tcp_time_stamp;
2304         prior_packets = tp->packets_out;
2305         if (!prior_packets)
2306                 goto no_queue;
2307
2308         prior_in_flight = tcp_packets_in_flight(tp);
2309
2310         /* See if we can take anything off of the retransmit queue. */
2311         flag |= tcp_clean_rtx_queue(sk, &seq_rtt,
2312                                     tp->ca_ops->rtt_sample ? &seq_usrtt : NULL);
2313
2314         if (tp->frto_counter)
2315                 tcp_process_frto(sk, prior_snd_una);
2316
2317         if (tcp_ack_is_dubious(tp, flag)) {
2318                 /* Advanve CWND, if state allows this. */
2319                 if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(tp, flag))
2320                         tcp_cong_avoid(tp, ack,  seq_rtt, prior_in_flight, 0);
2321                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2322         } else {
2323                 if ((flag & FLAG_DATA_ACKED))
2324                         tcp_cong_avoid(tp, ack, seq_rtt, prior_in_flight, 1);
2325         }
2326
2327         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2328                 dst_confirm(sk->sk_dst_cache);
2329
2330         return 1;
2331
2332 no_queue:
2333         tp->probes_out = 0;
2334
2335         /* If this ack opens up a zero window, clear backoff.  It was
2336          * being used to time the probes, and is probably far higher than
2337          * it needs to be for normal retransmission.
2338          */
2339         if (sk->sk_send_head)
2340                 tcp_ack_probe(sk);
2341         return 1;
2342
2343 old_ack:
2344         if (TCP_SKB_CB(skb)->sacked)
2345                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2346
2347 uninteresting_ack:
2348         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2349         return 0;
2350 }
2351
2352
2353 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2354  * But, this can also be called on packets in the established flow when
2355  * the fast version below fails.
2356  */
2357 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2358 {
2359         unsigned char *ptr;
2360         struct tcphdr *th = skb->h.th;
2361         int length=(th->doff*4)-sizeof(struct tcphdr);
2362
2363         ptr = (unsigned char *)(th + 1);
2364         opt_rx->saw_tstamp = 0;
2365
2366         while(length>0) {
2367                 int opcode=*ptr++;
2368                 int opsize;
2369
2370                 switch (opcode) {
2371                         case TCPOPT_EOL:
2372                                 return;
2373                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
2374                                 length--;
2375                                 continue;
2376                         default:
2377                                 opsize=*ptr++;
2378                                 if (opsize < 2) /* "silly options" */
2379                                         return;
2380                                 if (opsize > length)
2381                                         return; /* don't parse partial options */
2382                                 switch(opcode) {
2383                                 case TCPOPT_MSS:
2384                                         if(opsize==TCPOLEN_MSS && th->syn && !estab) {
2385                                                 u16 in_mss = ntohs(get_unaligned((__u16 *)ptr));
2386                                                 if (in_mss) {
2387                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2388                                                                 in_mss = opt_rx->user_mss;
2389                                                         opt_rx->mss_clamp = in_mss;
2390                                                 }
2391                                         }
2392                                         break;
2393                                 case TCPOPT_WINDOW:
2394                                         if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
2395                                                 if (sysctl_tcp_window_scaling) {
2396                                                         __u8 snd_wscale = *(__u8 *) ptr;
2397                                                         opt_rx->wscale_ok = 1;
2398                                                         if (snd_wscale > 14) {
2399                                                                 if(net_ratelimit())
2400                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
2401                                                                                "scaling value %d >14 received.\n",
2402                                                                                snd_wscale);
2403                                                                 snd_wscale = 14;
2404                                                         }
2405                                                         opt_rx->snd_wscale = snd_wscale;
2406                                                 }
2407                                         break;
2408                                 case TCPOPT_TIMESTAMP:
2409                                         if(opsize==TCPOLEN_TIMESTAMP) {
2410                                                 if ((estab && opt_rx->tstamp_ok) ||
2411                                                     (!estab && sysctl_tcp_timestamps)) {
2412                                                         opt_rx->saw_tstamp = 1;
2413                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr));
2414                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4)));
2415                                                 }
2416                                         }
2417                                         break;
2418                                 case TCPOPT_SACK_PERM:
2419                                         if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2420                                                 if (sysctl_tcp_sack) {
2421                                                         opt_rx->sack_ok = 1;
2422                                                         tcp_sack_reset(opt_rx);
2423                                                 }
2424                                         }
2425                                         break;
2426
2427                                 case TCPOPT_SACK:
2428                                         if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2429                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2430                                            opt_rx->sack_ok) {
2431                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2432                                         }
2433                                 };
2434                                 ptr+=opsize-2;
2435                                 length-=opsize;
2436                 };
2437         }
2438 }
2439
2440 /* Fast parse options. This hopes to only see timestamps.
2441  * If it is wrong it falls back on tcp_parse_options().
2442  */
2443 static inline int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2444                                          struct tcp_sock *tp)
2445 {
2446         if (th->doff == sizeof(struct tcphdr)>>2) {
2447                 tp->rx_opt.saw_tstamp = 0;
2448                 return 0;
2449         } else if (tp->rx_opt.tstamp_ok &&
2450                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2451                 __u32 *ptr = (__u32 *)(th + 1);
2452                 if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2453                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2454                         tp->rx_opt.saw_tstamp = 1;
2455                         ++ptr;
2456                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
2457                         ++ptr;
2458                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2459                         return 1;
2460                 }
2461         }
2462         tcp_parse_options(skb, &tp->rx_opt, 1);
2463         return 1;
2464 }
2465
2466 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2467 {
2468         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2469         tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
2470 }
2471
2472 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2473 {
2474         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2475                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
2476                  * extra check below makes sure this can only happen
2477                  * for pure ACK frames.  -DaveM
2478                  *
2479                  * Not only, also it occurs for expired timestamps.
2480                  */
2481
2482                 if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2483                    xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2484                         tcp_store_ts_recent(tp);
2485         }
2486 }
2487
2488 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2489  *
2490  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2491  * it can pass through stack. So, the following predicate verifies that
2492  * this segment is not used for anything but congestion avoidance or
2493  * fast retransmit. Moreover, we even are able to eliminate most of such
2494  * second order effects, if we apply some small "replay" window (~RTO)
2495  * to timestamp space.
2496  *
2497  * All these measures still do not guarantee that we reject wrapped ACKs
2498  * on networks with high bandwidth, when sequence space is recycled fastly,
2499  * but it guarantees that such events will be very rare and do not affect
2500  * connection seriously. This doesn't look nice, but alas, PAWS is really
2501  * buggy extension.
2502  *
2503  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
2504  * states that events when retransmit arrives after original data are rare.
2505  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
2506  * the biggest problem on large power networks even with minor reordering.
2507  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
2508  * up to bandwidth of 18Gigabit/sec. 8) ]
2509  */
2510
2511 static int tcp_disordered_ack(struct tcp_sock *tp, struct sk_buff *skb)
2512 {
2513         struct tcphdr *th = skb->h.th;
2514         u32 seq = TCP_SKB_CB(skb)->seq;
2515         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2516
2517         return (/* 1. Pure ACK with correct sequence number. */
2518                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
2519
2520                 /* 2. ... and duplicate ACK. */
2521                 ack == tp->snd_una &&
2522
2523                 /* 3. ... and does not update window. */
2524                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
2525
2526                 /* 4. ... and sits in replay window. */
2527                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (tp->rto*1024)/HZ);
2528 }
2529
2530 static inline int tcp_paws_discard(struct tcp_sock *tp, struct sk_buff *skb)
2531 {
2532         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
2533                 xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2534                 !tcp_disordered_ack(tp, skb));
2535 }
2536
2537 /* Check segment sequence number for validity.
2538  *
2539  * Segment controls are considered valid, if the segment
2540  * fits to the window after truncation to the window. Acceptability
2541  * of data (and SYN, FIN, of course) is checked separately.
2542  * See tcp_data_queue(), for example.
2543  *
2544  * Also, controls (RST is main one) are accepted using RCV.WUP instead
2545  * of RCV.NXT. Peer still did not advance his SND.UNA when we
2546  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
2547  * (borrowed from freebsd)
2548  */
2549
2550 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
2551 {
2552         return  !before(end_seq, tp->rcv_wup) &&
2553                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
2554 }
2555
2556 /* When we get a reset we do this. */
2557 static void tcp_reset(struct sock *sk)
2558 {
2559         /* We want the right error as BSD sees it (and indeed as we do). */
2560         switch (sk->sk_state) {
2561                 case TCP_SYN_SENT:
2562                         sk->sk_err = ECONNREFUSED;
2563                         break;
2564                 case TCP_CLOSE_WAIT:
2565                         sk->sk_err = EPIPE;
2566                         break;
2567                 case TCP_CLOSE:
2568                         return;
2569                 default:
2570                         sk->sk_err = ECONNRESET;
2571         }
2572
2573         if (!sock_flag(sk, SOCK_DEAD))
2574                 sk->sk_error_report(sk);
2575
2576         tcp_done(sk);
2577 }
2578
2579 /*
2580  *      Process the FIN bit. This now behaves as it is supposed to work
2581  *      and the FIN takes effect when it is validly part of sequence
2582  *      space. Not before when we get holes.
2583  *
2584  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
2585  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
2586  *      TIME-WAIT)
2587  *
2588  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
2589  *      close and we go into CLOSING (and later onto TIME-WAIT)
2590  *
2591  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
2592  */
2593 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
2594 {
2595         struct tcp_sock *tp = tcp_sk(sk);
2596
2597         tcp_schedule_ack(tp);
2598
2599         sk->sk_shutdown |= RCV_SHUTDOWN;
2600         sock_set_flag(sk, SOCK_DONE);
2601
2602         switch (sk->sk_state) {
2603                 case TCP_SYN_RECV:
2604                 case TCP_ESTABLISHED:
2605                         /* Move to CLOSE_WAIT */
2606                         tcp_set_state(sk, TCP_CLOSE_WAIT);
2607                         tp->ack.pingpong = 1;
2608                         break;
2609
2610                 case TCP_CLOSE_WAIT:
2611                 case TCP_CLOSING:
2612                         /* Received a retransmission of the FIN, do
2613                          * nothing.
2614                          */
2615                         break;
2616                 case TCP_LAST_ACK:
2617                         /* RFC793: Remain in the LAST-ACK state. */
2618                         break;
2619
2620                 case TCP_FIN_WAIT1:
2621                         /* This case occurs when a simultaneous close
2622                          * happens, we must ack the received FIN and
2623                          * enter the CLOSING state.
2624                          */
2625                         tcp_send_ack(sk);
2626                         tcp_set_state(sk, TCP_CLOSING);
2627                         break;
2628                 case TCP_FIN_WAIT2:
2629                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
2630                         tcp_send_ack(sk);
2631                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
2632                         break;
2633                 default:
2634                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
2635                          * cases we should never reach this piece of code.
2636                          */
2637                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
2638                                __FUNCTION__, sk->sk_state);
2639                         break;
2640         };
2641
2642         /* It _is_ possible, that we have something out-of-order _after_ FIN.
2643          * Probably, we should reset in this case. For now drop them.
2644          */
2645         __skb_queue_purge(&tp->out_of_order_queue);
2646         if (tp->rx_opt.sack_ok)
2647                 tcp_sack_reset(&tp->rx_opt);
2648         sk_stream_mem_reclaim(sk);
2649
2650         if (!sock_flag(sk, SOCK_DEAD)) {
2651                 sk->sk_state_change(sk);
2652
2653                 /* Do not send POLL_HUP for half duplex close. */
2654                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
2655                     sk->sk_state == TCP_CLOSE)
2656                         sk_wake_async(sk, 1, POLL_HUP);
2657                 else
2658                         sk_wake_async(sk, 1, POLL_IN);
2659         }
2660 }
2661
2662 static __inline__ int
2663 tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
2664 {
2665         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
2666                 if (before(seq, sp->start_seq))
2667                         sp->start_seq = seq;
2668                 if (after(end_seq, sp->end_seq))
2669                         sp->end_seq = end_seq;
2670                 return 1;
2671         }
2672         return 0;
2673 }
2674
2675 static inline void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
2676 {
2677         if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2678                 if (before(seq, tp->rcv_nxt))
2679                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
2680                 else
2681                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
2682
2683                 tp->rx_opt.dsack = 1;
2684                 tp->duplicate_sack[0].start_seq = seq;
2685                 tp->duplicate_sack[0].end_seq = end_seq;
2686                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
2687         }
2688 }
2689
2690 static inline void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
2691 {
2692         if (!tp->rx_opt.dsack)
2693                 tcp_dsack_set(tp, seq, end_seq);
2694         else
2695                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
2696 }
2697
2698 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
2699 {
2700         struct tcp_sock *tp = tcp_sk(sk);
2701
2702         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
2703             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2704                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2705                 tcp_enter_quickack_mode(tp);
2706
2707                 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2708                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2709
2710                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
2711                                 end_seq = tp->rcv_nxt;
2712                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
2713                 }
2714         }
2715
2716         tcp_send_ack(sk);
2717 }
2718
2719 /* These routines update the SACK block as out-of-order packets arrive or
2720  * in-order packets close up the sequence space.
2721  */
2722 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
2723 {
2724         int this_sack;
2725         struct tcp_sack_block *sp = &tp->selective_acks[0];
2726         struct tcp_sack_block *swalk = sp+1;
2727
2728         /* See if the recent change to the first SACK eats into
2729          * or hits the sequence space of other SACK blocks, if so coalesce.
2730          */
2731         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
2732                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
2733                         int i;
2734
2735                         /* Zap SWALK, by moving every further SACK up by one slot.
2736                          * Decrease num_sacks.
2737                          */
2738                         tp->rx_opt.num_sacks--;
2739                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2740                         for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
2741                                 sp[i] = sp[i+1];
2742                         continue;
2743                 }
2744                 this_sack++, swalk++;
2745         }
2746 }
2747
2748 static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
2749 {
2750         __u32 tmp;
2751
2752         tmp = sack1->start_seq;
2753         sack1->start_seq = sack2->start_seq;
2754         sack2->start_seq = tmp;
2755
2756         tmp = sack1->end_seq;
2757         sack1->end_seq = sack2->end_seq;
2758         sack2->end_seq = tmp;
2759 }
2760
2761 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
2762 {
2763         struct tcp_sock *tp = tcp_sk(sk);
2764         struct tcp_sack_block *sp = &tp->selective_acks[0];
2765         int cur_sacks = tp->rx_opt.num_sacks;
2766         int this_sack;
2767
2768         if (!cur_sacks)
2769                 goto new_sack;
2770
2771         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
2772                 if (tcp_sack_extend(sp, seq, end_seq)) {
2773                         /* Rotate this_sack to the first one. */
2774                         for (; this_sack>0; this_sack--, sp--)
2775                                 tcp_sack_swap(sp, sp-1);
2776                         if (cur_sacks > 1)
2777                                 tcp_sack_maybe_coalesce(tp);
2778                         return;
2779                 }
2780         }
2781
2782         /* Could not find an adjacent existing SACK, build a new one,
2783          * put it at the front, and shift everyone else down.  We
2784          * always know there is at least one SACK present already here.
2785          *
2786          * If the sack array is full, forget about the last one.
2787          */
2788         if (this_sack >= 4) {
2789                 this_sack--;
2790                 tp->rx_opt.num_sacks--;
2791                 sp--;
2792         }
2793         for(; this_sack > 0; this_sack--, sp--)
2794                 *sp = *(sp-1);
2795
2796 new_sack:
2797         /* Build the new head SACK, and we're done. */
2798         sp->start_seq = seq;
2799         sp->end_seq = end_seq;
2800         tp->rx_opt.num_sacks++;
2801         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2802 }
2803
2804 /* RCV.NXT advances, some SACKs should be eaten. */
2805
2806 static void tcp_sack_remove(struct tcp_sock *tp)
2807 {
2808         struct tcp_sack_block *sp = &tp->selective_acks[0];
2809         int num_sacks = tp->rx_opt.num_sacks;
2810         int this_sack;
2811
2812         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
2813         if (skb_queue_len(&tp->out_of_order_queue) == 0) {
2814                 tp->rx_opt.num_sacks = 0;
2815                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
2816                 return;
2817         }
2818
2819         for(this_sack = 0; this_sack < num_sacks; ) {
2820                 /* Check if the start of the sack is covered by RCV.NXT. */
2821                 if (!before(tp->rcv_nxt, sp->start_seq)) {
2822                         int i;
2823
2824                         /* RCV.NXT must cover all the block! */
2825                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
2826
2827                         /* Zap this SACK, by moving forward any other SACKS. */
2828                         for (i=this_sack+1; i < num_sacks; i++)
2829                                 tp->selective_acks[i-1] = tp->selective_acks[i];
2830                         num_sacks--;
2831                         continue;
2832                 }
2833                 this_sack++;
2834                 sp++;
2835         }
2836         if (num_sacks != tp->rx_opt.num_sacks) {
2837                 tp->rx_opt.num_sacks = num_sacks;
2838                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2839         }
2840 }
2841
2842 /* This one checks to see if we can put data from the
2843  * out_of_order queue into the receive_queue.
2844  */
2845 static void tcp_ofo_queue(struct sock *sk)
2846 {
2847         struct tcp_sock *tp = tcp_sk(sk);
2848         __u32 dsack_high = tp->rcv_nxt;
2849         struct sk_buff *skb;
2850
2851         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
2852                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
2853                         break;
2854
2855                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
2856                         __u32 dsack = dsack_high;
2857                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
2858                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
2859                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
2860                 }
2861
2862                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
2863                         SOCK_DEBUG(sk, "ofo packet was already received \n");
2864                         __skb_unlink(skb, skb->list);
2865                         __kfree_skb(skb);
2866                         continue;
2867                 }
2868                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
2869                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
2870                            TCP_SKB_CB(skb)->end_seq);
2871
2872                 __skb_unlink(skb, skb->list);
2873                 __skb_queue_tail(&sk->sk_receive_queue, skb);
2874                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2875                 if(skb->h.th->fin)
2876                         tcp_fin(skb, sk, skb->h.th);
2877         }
2878 }
2879
2880 static int tcp_prune_queue(struct sock *sk);
2881
2882 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
2883 {
2884         struct tcphdr *th = skb->h.th;
2885         struct tcp_sock *tp = tcp_sk(sk);
2886         int eaten = -1;
2887
2888         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
2889                 goto drop;
2890
2891         __skb_pull(skb, th->doff*4);
2892
2893         TCP_ECN_accept_cwr(tp, skb);
2894
2895         if (tp->rx_opt.dsack) {
2896                 tp->rx_opt.dsack = 0;
2897                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
2898                                                     4 - tp->rx_opt.tstamp_ok);
2899         }
2900
2901         /*  Queue data for delivery to the user.
2902          *  Packets in sequence go to the receive queue.
2903          *  Out of sequence packets to the out_of_order_queue.
2904          */
2905         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
2906                 if (tcp_receive_window(tp) == 0)
2907                         goto out_of_window;
2908
2909                 /* Ok. In sequence. In window. */
2910                 if (tp->ucopy.task == current &&
2911                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
2912                     sock_owned_by_user(sk) && !tp->urg_data) {
2913                         int chunk = min_t(unsigned int, skb->len,
2914                                                         tp->ucopy.len);
2915
2916                         __set_current_state(TASK_RUNNING);
2917
2918                         local_bh_enable();
2919                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
2920                                 tp->ucopy.len -= chunk;
2921                                 tp->copied_seq += chunk;
2922                                 eaten = (chunk == skb->len && !th->fin);
2923                                 tcp_rcv_space_adjust(sk);
2924                         }
2925                         local_bh_disable();
2926                 }
2927
2928                 if (eaten <= 0) {
2929 queue_and_out:
2930                         if (eaten < 0 &&
2931                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
2932                              !sk_stream_rmem_schedule(sk, skb))) {
2933                                 if (tcp_prune_queue(sk) < 0 ||
2934                                     !sk_stream_rmem_schedule(sk, skb))
2935                                         goto drop;
2936                         }
2937                         sk_stream_set_owner_r(skb, sk);
2938                         __skb_queue_tail(&sk->sk_receive_queue, skb);
2939                 }
2940                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2941                 if(skb->len)
2942                         tcp_event_data_recv(sk, tp, skb);
2943                 if(th->fin)
2944                         tcp_fin(skb, sk, th);
2945
2946                 if (skb_queue_len(&tp->out_of_order_queue)) {
2947                         tcp_ofo_queue(sk);
2948
2949                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
2950                          * gap in queue is filled.
2951                          */
2952                         if (!skb_queue_len(&tp->out_of_order_queue))
2953                                 tp->ack.pingpong = 0;
2954                 }
2955
2956                 if (tp->rx_opt.num_sacks)
2957                         tcp_sack_remove(tp);
2958
2959                 tcp_fast_path_check(sk, tp);
2960
2961                 if (eaten > 0)
2962                         __kfree_skb(skb);
2963                 else if (!sock_flag(sk, SOCK_DEAD))
2964                         sk->sk_data_ready(sk, 0);
2965                 return;
2966         }
2967
2968         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
2969                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
2970                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2971                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
2972
2973 out_of_window:
2974                 tcp_enter_quickack_mode(tp);
2975                 tcp_schedule_ack(tp);
2976 drop:
2977                 __kfree_skb(skb);
2978                 return;
2979         }
2980
2981         /* Out of window. F.e. zero window probe. */
2982         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
2983                 goto out_of_window;
2984
2985         tcp_enter_quickack_mode(tp);
2986
2987         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2988                 /* Partial packet, seq < rcv_next < end_seq */
2989                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
2990                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
2991                            TCP_SKB_CB(skb)->end_seq);
2992
2993                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
2994                 
2995                 /* If window is closed, drop tail of packet. But after
2996                  * remembering D-SACK for its head made in previous line.
2997                  */
2998                 if (!tcp_receive_window(tp))
2999                         goto out_of_window;
3000                 goto queue_and_out;
3001         }
3002
3003         TCP_ECN_check_ce(tp, skb);
3004
3005         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3006             !sk_stream_rmem_schedule(sk, skb)) {
3007                 if (tcp_prune_queue(sk) < 0 ||
3008                     !sk_stream_rmem_schedule(sk, skb))
3009                         goto drop;
3010         }
3011
3012         /* Disable header prediction. */
3013         tp->pred_flags = 0;
3014         tcp_schedule_ack(tp);
3015
3016         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3017                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3018
3019         sk_stream_set_owner_r(skb, sk);
3020
3021         if (!skb_peek(&tp->out_of_order_queue)) {
3022                 /* Initial out of order segment, build 1 SACK. */
3023                 if (tp->rx_opt.sack_ok) {
3024                         tp->rx_opt.num_sacks = 1;
3025                         tp->rx_opt.dsack     = 0;
3026                         tp->rx_opt.eff_sacks = 1;
3027                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3028                         tp->selective_acks[0].end_seq =
3029                                                 TCP_SKB_CB(skb)->end_seq;
3030                 }
3031                 __skb_queue_head(&tp->out_of_order_queue,skb);
3032         } else {
3033                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3034                 u32 seq = TCP_SKB_CB(skb)->seq;
3035                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3036
3037                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3038                         __skb_append(skb1, skb);
3039
3040                         if (!tp->rx_opt.num_sacks ||
3041                             tp->selective_acks[0].end_seq != seq)
3042                                 goto add_sack;
3043
3044                         /* Common case: data arrive in order after hole. */
3045                         tp->selective_acks[0].end_seq = end_seq;
3046                         return;
3047                 }
3048
3049                 /* Find place to insert this segment. */
3050                 do {
3051                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3052                                 break;
3053                 } while ((skb1 = skb1->prev) !=
3054                          (struct sk_buff*)&tp->out_of_order_queue);
3055
3056                 /* Do skb overlap to previous one? */
3057                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3058                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3059                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3060                                 /* All the bits are present. Drop. */
3061                                 __kfree_skb(skb);
3062                                 tcp_dsack_set(tp, seq, end_seq);
3063                                 goto add_sack;
3064                         }
3065                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3066                                 /* Partial overlap. */
3067                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3068                         } else {
3069                                 skb1 = skb1->prev;
3070                         }
3071                 }
3072                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3073                 
3074                 /* And clean segments covered by new one as whole. */
3075                 while ((skb1 = skb->next) !=
3076                        (struct sk_buff*)&tp->out_of_order_queue &&
3077                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3078                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3079                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3080                                break;
3081                        }
3082                        __skb_unlink(skb1, skb1->list);
3083                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3084                        __kfree_skb(skb1);
3085                 }
3086
3087 add_sack:
3088                 if (tp->rx_opt.sack_ok)
3089                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3090         }
3091 }
3092
3093 /* Collapse contiguous sequence of skbs head..tail with
3094  * sequence numbers start..end.
3095  * Segments with FIN/SYN are not collapsed (only because this
3096  * simplifies code)
3097  */
3098 static void
3099 tcp_collapse(struct sock *sk, struct sk_buff *head,
3100              struct sk_buff *tail, u32 start, u32 end)
3101 {
3102         struct sk_buff *skb;
3103
3104         /* First, check that queue is collapsable and find
3105          * the point where collapsing can be useful. */
3106         for (skb = head; skb != tail; ) {
3107                 /* No new bits? It is possible on ofo queue. */
3108                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3109                         struct sk_buff *next = skb->next;
3110                         __skb_unlink(skb, skb->list);
3111                         __kfree_skb(skb);
3112                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3113                         skb = next;
3114                         continue;
3115                 }
3116
3117                 /* The first skb to collapse is:
3118                  * - not SYN/FIN and
3119                  * - bloated or contains data before "start" or
3120                  *   overlaps to the next one.
3121                  */
3122                 if (!skb->h.th->syn && !skb->h.th->fin &&
3123                     (tcp_win_from_space(skb->truesize) > skb->len ||
3124                      before(TCP_SKB_CB(skb)->seq, start) ||
3125                      (skb->next != tail &&
3126                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3127                         break;
3128
3129                 /* Decided to skip this, advance start seq. */
3130                 start = TCP_SKB_CB(skb)->end_seq;
3131                 skb = skb->next;
3132         }
3133         if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3134                 return;
3135
3136         while (before(start, end)) {