Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
[sfrench/cifs-2.6.git] / net / ipv4 / tcp_input.c
1 /*
2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
3  *              operating system.  INET is implemented using the  BSD Socket
4  *              interface as the means of communication with the user level.
5  *
6  *              Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Version:     $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
9  *
10  * Authors:     Ross Biro
11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
14  *              Florian La Roche, <flla@stud.uni-sb.de>
15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20  *              Jorge Cwik, <jorge@laser.satlink.net>
21  */
22
23 /*
24  * Changes:
25  *              Pedro Roque     :       Fast Retransmit/Recovery.
26  *                                      Two receive queues.
27  *                                      Retransmit queue handled by TCP.
28  *                                      Better retransmit timer handling.
29  *                                      New congestion avoidance.
30  *                                      Header prediction.
31  *                                      Variable renaming.
32  *
33  *              Eric            :       Fast Retransmit.
34  *              Randy Scott     :       MSS option defines.
35  *              Eric Schenk     :       Fixes to slow start algorithm.
36  *              Eric Schenk     :       Yet another double ACK bug.
37  *              Eric Schenk     :       Delayed ACK bug fixes.
38  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
39  *              David S. Miller :       Don't allow zero congestion window.
40  *              Eric Schenk     :       Fix retransmitter so that it sends
41  *                                      next packet on ack of previous packet.
42  *              Andi Kleen      :       Moved open_request checking here
43  *                                      and process RSTs for open_requests.
44  *              Andi Kleen      :       Better prune_queue, and other fixes.
45  *              Andrey Savochkin:       Fix RTT measurements in the presence of
46  *                                      timestamps.
47  *              Andrey Savochkin:       Check sequence numbers correctly when
48  *                                      removing SACKs due to in sequence incoming
49  *                                      data segments.
50  *              Andi Kleen:             Make sure we never ack data there is not
51  *                                      enough room for. Also make this condition
52  *                                      a fatal error if it might still happen.
53  *              Andi Kleen:             Add tcp_measure_rcv_mss to make 
54  *                                      connections with MSS<min(MTU,ann. MSS)
55  *                                      work without delayed acks. 
56  *              Andi Kleen:             Process packets with PSH set in the
57  *                                      fast path.
58  *              J Hadi Salim:           ECN support
59  *              Andrei Gurtov,
60  *              Pasi Sarolahti,
61  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
62  *                                      engine. Lots of bugs are found.
63  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
64  */
65
66 #include <linux/mm.h>
67 #include <linux/module.h>
68 #include <linux/sysctl.h>
69 #include <net/tcp.h>
70 #include <net/inet_common.h>
71 #include <linux/ipsec.h>
72 #include <asm/unaligned.h>
73 #include <net/netdma.h>
74
75 int sysctl_tcp_timestamps __read_mostly = 1;
76 int sysctl_tcp_window_scaling __read_mostly = 1;
77 int sysctl_tcp_sack __read_mostly = 1;
78 int sysctl_tcp_fack __read_mostly = 1;
79 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn __read_mostly;
81 int sysctl_tcp_dsack __read_mostly = 1;
82 int sysctl_tcp_app_win __read_mostly = 31;
83 int sysctl_tcp_adv_win_scale __read_mostly = 2;
84
85 int sysctl_tcp_stdurg __read_mostly;
86 int sysctl_tcp_rfc1337 __read_mostly;
87 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
88 int sysctl_tcp_frto __read_mostly;
89 int sysctl_tcp_nometrics_save __read_mostly;
90
91 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
92 int sysctl_tcp_abc __read_mostly;
93
94 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
95 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
96 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
97 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
98 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
99 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
100 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
101 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
102 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
103
104 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
105 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
106 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
107 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
108
109 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
110 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
111 #define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
112
113 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
114
115 /* Adapt the MSS value used to make delayed ack decision to the 
116  * real world.
117  */ 
118 static void tcp_measure_rcv_mss(struct sock *sk,
119                                 const struct sk_buff *skb)
120 {
121         struct inet_connection_sock *icsk = inet_csk(sk);
122         const unsigned int lss = icsk->icsk_ack.last_seg_size; 
123         unsigned int len;
124
125         icsk->icsk_ack.last_seg_size = 0; 
126
127         /* skb->len may jitter because of SACKs, even if peer
128          * sends good full-sized frames.
129          */
130         len = skb_shinfo(skb)->gso_size ?: skb->len;
131         if (len >= icsk->icsk_ack.rcv_mss) {
132                 icsk->icsk_ack.rcv_mss = len;
133         } else {
134                 /* Otherwise, we make more careful check taking into account,
135                  * that SACKs block is variable.
136                  *
137                  * "len" is invariant segment length, including TCP header.
138                  */
139                 len += skb->data - skb->h.raw;
140                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
141                     /* If PSH is not set, packet should be
142                      * full sized, provided peer TCP is not badly broken.
143                      * This observation (if it is correct 8)) allows
144                      * to handle super-low mtu links fairly.
145                      */
146                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
147                      !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) {
148                         /* Subtract also invariant (if peer is RFC compliant),
149                          * tcp header plus fixed timestamp option length.
150                          * Resulting "len" is MSS free of SACK jitter.
151                          */
152                         len -= tcp_sk(sk)->tcp_header_len;
153                         icsk->icsk_ack.last_seg_size = len;
154                         if (len == lss) {
155                                 icsk->icsk_ack.rcv_mss = len;
156                                 return;
157                         }
158                 }
159                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
160                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
161                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
162         }
163 }
164
165 static void tcp_incr_quickack(struct sock *sk)
166 {
167         struct inet_connection_sock *icsk = inet_csk(sk);
168         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
169
170         if (quickacks==0)
171                 quickacks=2;
172         if (quickacks > icsk->icsk_ack.quick)
173                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
174 }
175
176 void tcp_enter_quickack_mode(struct sock *sk)
177 {
178         struct inet_connection_sock *icsk = inet_csk(sk);
179         tcp_incr_quickack(sk);
180         icsk->icsk_ack.pingpong = 0;
181         icsk->icsk_ack.ato = TCP_ATO_MIN;
182 }
183
184 /* Send ACKs quickly, if "quick" count is not exhausted
185  * and the session is not interactive.
186  */
187
188 static inline int tcp_in_quickack_mode(const struct sock *sk)
189 {
190         const struct inet_connection_sock *icsk = inet_csk(sk);
191         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
192 }
193
194 /* Buffer size and advertised window tuning.
195  *
196  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
197  */
198
199 static void tcp_fixup_sndbuf(struct sock *sk)
200 {
201         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
202                      sizeof(struct sk_buff);
203
204         if (sk->sk_sndbuf < 3 * sndmem)
205                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
206 }
207
208 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
209  *
210  * All tcp_full_space() is split to two parts: "network" buffer, allocated
211  * forward and advertised in receiver window (tp->rcv_wnd) and
212  * "application buffer", required to isolate scheduling/application
213  * latencies from network.
214  * window_clamp is maximal advertised window. It can be less than
215  * tcp_full_space(), in this case tcp_full_space() - window_clamp
216  * is reserved for "application" buffer. The less window_clamp is
217  * the smoother our behaviour from viewpoint of network, but the lower
218  * throughput and the higher sensitivity of the connection to losses. 8)
219  *
220  * rcv_ssthresh is more strict window_clamp used at "slow start"
221  * phase to predict further behaviour of this connection.
222  * It is used for two goals:
223  * - to enforce header prediction at sender, even when application
224  *   requires some significant "application buffer". It is check #1.
225  * - to prevent pruning of receive queue because of misprediction
226  *   of receiver window. Check #2.
227  *
228  * The scheme does not work when sender sends good segments opening
229  * window and then starts to feed us spaghetti. But it should work
230  * in common situations. Otherwise, we have to rely on queue collapsing.
231  */
232
233 /* Slow part of check#2. */
234 static int __tcp_grow_window(const struct sock *sk, struct tcp_sock *tp,
235                              const struct sk_buff *skb)
236 {
237         /* Optimize this! */
238         int truesize = tcp_win_from_space(skb->truesize)/2;
239         int window = tcp_win_from_space(sysctl_tcp_rmem[2])/2;
240
241         while (tp->rcv_ssthresh <= window) {
242                 if (truesize <= skb->len)
243                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
244
245                 truesize >>= 1;
246                 window >>= 1;
247         }
248         return 0;
249 }
250
251 static void tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
252                             struct sk_buff *skb)
253 {
254         /* Check #1 */
255         if (tp->rcv_ssthresh < tp->window_clamp &&
256             (int)tp->rcv_ssthresh < tcp_space(sk) &&
257             !tcp_memory_pressure) {
258                 int incr;
259
260                 /* Check #2. Increase window, if skb with such overhead
261                  * will fit to rcvbuf in future.
262                  */
263                 if (tcp_win_from_space(skb->truesize) <= skb->len)
264                         incr = 2*tp->advmss;
265                 else
266                         incr = __tcp_grow_window(sk, tp, skb);
267
268                 if (incr) {
269                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
270                         inet_csk(sk)->icsk_ack.quick |= 1;
271                 }
272         }
273 }
274
275 /* 3. Tuning rcvbuf, when connection enters established state. */
276
277 static void tcp_fixup_rcvbuf(struct sock *sk)
278 {
279         struct tcp_sock *tp = tcp_sk(sk);
280         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
281
282         /* Try to select rcvbuf so that 4 mss-sized segments
283          * will fit to window and corresponding skbs will fit to our rcvbuf.
284          * (was 3; 4 is minimum to allow fast retransmit to work.)
285          */
286         while (tcp_win_from_space(rcvmem) < tp->advmss)
287                 rcvmem += 128;
288         if (sk->sk_rcvbuf < 4 * rcvmem)
289                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
290 }
291
292 /* 4. Try to fixup all. It is made immediately after connection enters
293  *    established state.
294  */
295 static void tcp_init_buffer_space(struct sock *sk)
296 {
297         struct tcp_sock *tp = tcp_sk(sk);
298         int maxwin;
299
300         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
301                 tcp_fixup_rcvbuf(sk);
302         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
303                 tcp_fixup_sndbuf(sk);
304
305         tp->rcvq_space.space = tp->rcv_wnd;
306
307         maxwin = tcp_full_space(sk);
308
309         if (tp->window_clamp >= maxwin) {
310                 tp->window_clamp = maxwin;
311
312                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
313                         tp->window_clamp = max(maxwin -
314                                                (maxwin >> sysctl_tcp_app_win),
315                                                4 * tp->advmss);
316         }
317
318         /* Force reservation of one segment. */
319         if (sysctl_tcp_app_win &&
320             tp->window_clamp > 2 * tp->advmss &&
321             tp->window_clamp + tp->advmss > maxwin)
322                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
323
324         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
325         tp->snd_cwnd_stamp = tcp_time_stamp;
326 }
327
328 /* 5. Recalculate window clamp after socket hit its memory bounds. */
329 static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp)
330 {
331         struct inet_connection_sock *icsk = inet_csk(sk);
332
333         icsk->icsk_ack.quick = 0;
334
335         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
336             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
337             !tcp_memory_pressure &&
338             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
339                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
340                                     sysctl_tcp_rmem[2]);
341         }
342         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
343                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
344 }
345
346
347 /* Initialize RCV_MSS value.
348  * RCV_MSS is an our guess about MSS used by the peer.
349  * We haven't any direct information about the MSS.
350  * It's better to underestimate the RCV_MSS rather than overestimate.
351  * Overestimations make us ACKing less frequently than needed.
352  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
353  */
354 void tcp_initialize_rcv_mss(struct sock *sk)
355 {
356         struct tcp_sock *tp = tcp_sk(sk);
357         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
358
359         hint = min(hint, tp->rcv_wnd/2);
360         hint = min(hint, TCP_MIN_RCVMSS);
361         hint = max(hint, TCP_MIN_MSS);
362
363         inet_csk(sk)->icsk_ack.rcv_mss = hint;
364 }
365
366 /* Receiver "autotuning" code.
367  *
368  * The algorithm for RTT estimation w/o timestamps is based on
369  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
370  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
371  *
372  * More detail on this code can be found at
373  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
374  * though this reference is out of date.  A new paper
375  * is pending.
376  */
377 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
378 {
379         u32 new_sample = tp->rcv_rtt_est.rtt;
380         long m = sample;
381
382         if (m == 0)
383                 m = 1;
384
385         if (new_sample != 0) {
386                 /* If we sample in larger samples in the non-timestamp
387                  * case, we could grossly overestimate the RTT especially
388                  * with chatty applications or bulk transfer apps which
389                  * are stalled on filesystem I/O.
390                  *
391                  * Also, since we are only going for a minimum in the
392                  * non-timestamp case, we do not smooth things out
393                  * else with timestamps disabled convergence takes too
394                  * long.
395                  */
396                 if (!win_dep) {
397                         m -= (new_sample >> 3);
398                         new_sample += m;
399                 } else if (m < new_sample)
400                         new_sample = m << 3;
401         } else {
402                 /* No previous measure. */
403                 new_sample = m << 3;
404         }
405
406         if (tp->rcv_rtt_est.rtt != new_sample)
407                 tp->rcv_rtt_est.rtt = new_sample;
408 }
409
410 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
411 {
412         if (tp->rcv_rtt_est.time == 0)
413                 goto new_measure;
414         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
415                 return;
416         tcp_rcv_rtt_update(tp,
417                            jiffies - tp->rcv_rtt_est.time,
418                            1);
419
420 new_measure:
421         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
422         tp->rcv_rtt_est.time = tcp_time_stamp;
423 }
424
425 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
426 {
427         struct tcp_sock *tp = tcp_sk(sk);
428         if (tp->rx_opt.rcv_tsecr &&
429             (TCP_SKB_CB(skb)->end_seq -
430              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
431                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
432 }
433
434 /*
435  * This function should be called every time data is copied to user space.
436  * It calculates the appropriate TCP receive buffer space.
437  */
438 void tcp_rcv_space_adjust(struct sock *sk)
439 {
440         struct tcp_sock *tp = tcp_sk(sk);
441         int time;
442         int space;
443         
444         if (tp->rcvq_space.time == 0)
445                 goto new_measure;
446         
447         time = tcp_time_stamp - tp->rcvq_space.time;
448         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
449             tp->rcv_rtt_est.rtt == 0)
450                 return;
451         
452         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
453
454         space = max(tp->rcvq_space.space, space);
455
456         if (tp->rcvq_space.space != space) {
457                 int rcvmem;
458
459                 tp->rcvq_space.space = space;
460
461                 if (sysctl_tcp_moderate_rcvbuf &&
462                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
463                         int new_clamp = space;
464
465                         /* Receive space grows, normalize in order to
466                          * take into account packet headers and sk_buff
467                          * structure overhead.
468                          */
469                         space /= tp->advmss;
470                         if (!space)
471                                 space = 1;
472                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
473                                   16 + sizeof(struct sk_buff));
474                         while (tcp_win_from_space(rcvmem) < tp->advmss)
475                                 rcvmem += 128;
476                         space *= rcvmem;
477                         space = min(space, sysctl_tcp_rmem[2]);
478                         if (space > sk->sk_rcvbuf) {
479                                 sk->sk_rcvbuf = space;
480
481                                 /* Make the window clamp follow along.  */
482                                 tp->window_clamp = new_clamp;
483                         }
484                 }
485         }
486         
487 new_measure:
488         tp->rcvq_space.seq = tp->copied_seq;
489         tp->rcvq_space.time = tcp_time_stamp;
490 }
491
492 /* There is something which you must keep in mind when you analyze the
493  * behavior of the tp->ato delayed ack timeout interval.  When a
494  * connection starts up, we want to ack as quickly as possible.  The
495  * problem is that "good" TCP's do slow start at the beginning of data
496  * transmission.  The means that until we send the first few ACK's the
497  * sender will sit on his end and only queue most of his data, because
498  * he can only send snd_cwnd unacked packets at any given time.  For
499  * each ACK we send, he increments snd_cwnd and transmits more of his
500  * queue.  -DaveM
501  */
502 static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
503 {
504         struct inet_connection_sock *icsk = inet_csk(sk);
505         u32 now;
506
507         inet_csk_schedule_ack(sk);
508
509         tcp_measure_rcv_mss(sk, skb);
510
511         tcp_rcv_rtt_measure(tp);
512         
513         now = tcp_time_stamp;
514
515         if (!icsk->icsk_ack.ato) {
516                 /* The _first_ data packet received, initialize
517                  * delayed ACK engine.
518                  */
519                 tcp_incr_quickack(sk);
520                 icsk->icsk_ack.ato = TCP_ATO_MIN;
521         } else {
522                 int m = now - icsk->icsk_ack.lrcvtime;
523
524                 if (m <= TCP_ATO_MIN/2) {
525                         /* The fastest case is the first. */
526                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
527                 } else if (m < icsk->icsk_ack.ato) {
528                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
529                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
530                                 icsk->icsk_ack.ato = icsk->icsk_rto;
531                 } else if (m > icsk->icsk_rto) {
532                         /* Too long gap. Apparently sender failed to
533                          * restart window, so that we send ACKs quickly.
534                          */
535                         tcp_incr_quickack(sk);
536                         sk_stream_mem_reclaim(sk);
537                 }
538         }
539         icsk->icsk_ack.lrcvtime = now;
540
541         TCP_ECN_check_ce(tp, skb);
542
543         if (skb->len >= 128)
544                 tcp_grow_window(sk, tp, skb);
545 }
546
547 /* Called to compute a smoothed rtt estimate. The data fed to this
548  * routine either comes from timestamps, or from segments that were
549  * known _not_ to have been retransmitted [see Karn/Partridge
550  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
551  * piece by Van Jacobson.
552  * NOTE: the next three routines used to be one big routine.
553  * To save cycles in the RFC 1323 implementation it was better to break
554  * it up into three procedures. -- erics
555  */
556 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
557 {
558         struct tcp_sock *tp = tcp_sk(sk);
559         long m = mrtt; /* RTT */
560
561         /*      The following amusing code comes from Jacobson's
562          *      article in SIGCOMM '88.  Note that rtt and mdev
563          *      are scaled versions of rtt and mean deviation.
564          *      This is designed to be as fast as possible 
565          *      m stands for "measurement".
566          *
567          *      On a 1990 paper the rto value is changed to:
568          *      RTO = rtt + 4 * mdev
569          *
570          * Funny. This algorithm seems to be very broken.
571          * These formulae increase RTO, when it should be decreased, increase
572          * too slowly, when it should be increased quickly, decrease too quickly
573          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
574          * does not matter how to _calculate_ it. Seems, it was trap
575          * that VJ failed to avoid. 8)
576          */
577         if(m == 0)
578                 m = 1;
579         if (tp->srtt != 0) {
580                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
581                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
582                 if (m < 0) {
583                         m = -m;         /* m is now abs(error) */
584                         m -= (tp->mdev >> 2);   /* similar update on mdev */
585                         /* This is similar to one of Eifel findings.
586                          * Eifel blocks mdev updates when rtt decreases.
587                          * This solution is a bit different: we use finer gain
588                          * for mdev in this case (alpha*beta).
589                          * Like Eifel it also prevents growth of rto,
590                          * but also it limits too fast rto decreases,
591                          * happening in pure Eifel.
592                          */
593                         if (m > 0)
594                                 m >>= 3;
595                 } else {
596                         m -= (tp->mdev >> 2);   /* similar update on mdev */
597                 }
598                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
599                 if (tp->mdev > tp->mdev_max) {
600                         tp->mdev_max = tp->mdev;
601                         if (tp->mdev_max > tp->rttvar)
602                                 tp->rttvar = tp->mdev_max;
603                 }
604                 if (after(tp->snd_una, tp->rtt_seq)) {
605                         if (tp->mdev_max < tp->rttvar)
606                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
607                         tp->rtt_seq = tp->snd_nxt;
608                         tp->mdev_max = TCP_RTO_MIN;
609                 }
610         } else {
611                 /* no previous measure. */
612                 tp->srtt = m<<3;        /* take the measured time to be rtt */
613                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
614                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
615                 tp->rtt_seq = tp->snd_nxt;
616         }
617 }
618
619 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
620  * routine referred to above.
621  */
622 static inline void tcp_set_rto(struct sock *sk)
623 {
624         const struct tcp_sock *tp = tcp_sk(sk);
625         /* Old crap is replaced with new one. 8)
626          *
627          * More seriously:
628          * 1. If rtt variance happened to be less 50msec, it is hallucination.
629          *    It cannot be less due to utterly erratic ACK generation made
630          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
631          *    to do with delayed acks, because at cwnd>2 true delack timeout
632          *    is invisible. Actually, Linux-2.4 also generates erratic
633          *    ACKs in some circumstances.
634          */
635         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
636
637         /* 2. Fixups made earlier cannot be right.
638          *    If we do not estimate RTO correctly without them,
639          *    all the algo is pure shit and should be replaced
640          *    with correct one. It is exactly, which we pretend to do.
641          */
642 }
643
644 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
645  * guarantees that rto is higher.
646  */
647 static inline void tcp_bound_rto(struct sock *sk)
648 {
649         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
650                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
651 }
652
653 /* Save metrics learned by this TCP session.
654    This function is called only, when TCP finishes successfully
655    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
656  */
657 void tcp_update_metrics(struct sock *sk)
658 {
659         struct tcp_sock *tp = tcp_sk(sk);
660         struct dst_entry *dst = __sk_dst_get(sk);
661
662         if (sysctl_tcp_nometrics_save)
663                 return;
664
665         dst_confirm(dst);
666
667         if (dst && (dst->flags&DST_HOST)) {
668                 const struct inet_connection_sock *icsk = inet_csk(sk);
669                 int m;
670
671                 if (icsk->icsk_backoff || !tp->srtt) {
672                         /* This session failed to estimate rtt. Why?
673                          * Probably, no packets returned in time.
674                          * Reset our results.
675                          */
676                         if (!(dst_metric_locked(dst, RTAX_RTT)))
677                                 dst->metrics[RTAX_RTT-1] = 0;
678                         return;
679                 }
680
681                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
682
683                 /* If newly calculated rtt larger than stored one,
684                  * store new one. Otherwise, use EWMA. Remember,
685                  * rtt overestimation is always better than underestimation.
686                  */
687                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
688                         if (m <= 0)
689                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
690                         else
691                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
692                 }
693
694                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
695                         if (m < 0)
696                                 m = -m;
697
698                         /* Scale deviation to rttvar fixed point */
699                         m >>= 1;
700                         if (m < tp->mdev)
701                                 m = tp->mdev;
702
703                         if (m >= dst_metric(dst, RTAX_RTTVAR))
704                                 dst->metrics[RTAX_RTTVAR-1] = m;
705                         else
706                                 dst->metrics[RTAX_RTTVAR-1] -=
707                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
708                 }
709
710                 if (tp->snd_ssthresh >= 0xFFFF) {
711                         /* Slow start still did not finish. */
712                         if (dst_metric(dst, RTAX_SSTHRESH) &&
713                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
714                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
715                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
716                         if (!dst_metric_locked(dst, RTAX_CWND) &&
717                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
718                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
719                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
720                            icsk->icsk_ca_state == TCP_CA_Open) {
721                         /* Cong. avoidance phase, cwnd is reliable. */
722                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
723                                 dst->metrics[RTAX_SSTHRESH-1] =
724                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
725                         if (!dst_metric_locked(dst, RTAX_CWND))
726                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
727                 } else {
728                         /* Else slow start did not finish, cwnd is non-sense,
729                            ssthresh may be also invalid.
730                          */
731                         if (!dst_metric_locked(dst, RTAX_CWND))
732                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
733                         if (dst->metrics[RTAX_SSTHRESH-1] &&
734                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
735                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
736                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
737                 }
738
739                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
740                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
741                             tp->reordering != sysctl_tcp_reordering)
742                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
743                 }
744         }
745 }
746
747 /* Numbers are taken from RFC2414.  */
748 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
749 {
750         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
751
752         if (!cwnd) {
753                 if (tp->mss_cache > 1460)
754                         cwnd = 2;
755                 else
756                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
757         }
758         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
759 }
760
761 /* Set slow start threshold and cwnd not falling to slow start */
762 void tcp_enter_cwr(struct sock *sk)
763 {
764         struct tcp_sock *tp = tcp_sk(sk);
765
766         tp->prior_ssthresh = 0;
767         tp->bytes_acked = 0;
768         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
769                 tp->undo_marker = 0;
770                 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
771                 tp->snd_cwnd = min(tp->snd_cwnd,
772                                    tcp_packets_in_flight(tp) + 1U);
773                 tp->snd_cwnd_cnt = 0;
774                 tp->high_seq = tp->snd_nxt;
775                 tp->snd_cwnd_stamp = tcp_time_stamp;
776                 TCP_ECN_queue_cwr(tp);
777
778                 tcp_set_ca_state(sk, TCP_CA_CWR);
779         }
780 }
781
782 /* Initialize metrics on socket. */
783
784 static void tcp_init_metrics(struct sock *sk)
785 {
786         struct tcp_sock *tp = tcp_sk(sk);
787         struct dst_entry *dst = __sk_dst_get(sk);
788
789         if (dst == NULL)
790                 goto reset;
791
792         dst_confirm(dst);
793
794         if (dst_metric_locked(dst, RTAX_CWND))
795                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
796         if (dst_metric(dst, RTAX_SSTHRESH)) {
797                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
798                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
799                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
800         }
801         if (dst_metric(dst, RTAX_REORDERING) &&
802             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
803                 tp->rx_opt.sack_ok &= ~2;
804                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
805         }
806
807         if (dst_metric(dst, RTAX_RTT) == 0)
808                 goto reset;
809
810         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
811                 goto reset;
812
813         /* Initial rtt is determined from SYN,SYN-ACK.
814          * The segment is small and rtt may appear much
815          * less than real one. Use per-dst memory
816          * to make it more realistic.
817          *
818          * A bit of theory. RTT is time passed after "normal" sized packet
819          * is sent until it is ACKed. In normal circumstances sending small
820          * packets force peer to delay ACKs and calculation is correct too.
821          * The algorithm is adaptive and, provided we follow specs, it
822          * NEVER underestimate RTT. BUT! If peer tries to make some clever
823          * tricks sort of "quick acks" for time long enough to decrease RTT
824          * to low value, and then abruptly stops to do it and starts to delay
825          * ACKs, wait for troubles.
826          */
827         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
828                 tp->srtt = dst_metric(dst, RTAX_RTT);
829                 tp->rtt_seq = tp->snd_nxt;
830         }
831         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
832                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
833                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
834         }
835         tcp_set_rto(sk);
836         tcp_bound_rto(sk);
837         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
838                 goto reset;
839         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
840         tp->snd_cwnd_stamp = tcp_time_stamp;
841         return;
842
843 reset:
844         /* Play conservative. If timestamps are not
845          * supported, TCP will fail to recalculate correct
846          * rtt, if initial rto is too small. FORGET ALL AND RESET!
847          */
848         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
849                 tp->srtt = 0;
850                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
851                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
852         }
853 }
854
855 static void tcp_update_reordering(struct sock *sk, const int metric,
856                                   const int ts)
857 {
858         struct tcp_sock *tp = tcp_sk(sk);
859         if (metric > tp->reordering) {
860                 tp->reordering = min(TCP_MAX_REORDERING, metric);
861
862                 /* This exciting event is worth to be remembered. 8) */
863                 if (ts)
864                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
865                 else if (IsReno(tp))
866                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
867                 else if (IsFack(tp))
868                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
869                 else
870                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
871 #if FASTRETRANS_DEBUG > 1
872                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
873                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
874                        tp->reordering,
875                        tp->fackets_out,
876                        tp->sacked_out,
877                        tp->undo_marker ? tp->undo_retrans : 0);
878 #endif
879                 /* Disable FACK yet. */
880                 tp->rx_opt.sack_ok &= ~2;
881         }
882 }
883
884 /* This procedure tags the retransmission queue when SACKs arrive.
885  *
886  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
887  * Packets in queue with these bits set are counted in variables
888  * sacked_out, retrans_out and lost_out, correspondingly.
889  *
890  * Valid combinations are:
891  * Tag  InFlight        Description
892  * 0    1               - orig segment is in flight.
893  * S    0               - nothing flies, orig reached receiver.
894  * L    0               - nothing flies, orig lost by net.
895  * R    2               - both orig and retransmit are in flight.
896  * L|R  1               - orig is lost, retransmit is in flight.
897  * S|R  1               - orig reached receiver, retrans is still in flight.
898  * (L|S|R is logically valid, it could occur when L|R is sacked,
899  *  but it is equivalent to plain S and code short-curcuits it to S.
900  *  L|S is logically invalid, it would mean -1 packet in flight 8))
901  *
902  * These 6 states form finite state machine, controlled by the following events:
903  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
904  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
905  * 3. Loss detection event of one of three flavors:
906  *      A. Scoreboard estimator decided the packet is lost.
907  *         A'. Reno "three dupacks" marks head of queue lost.
908  *         A''. Its FACK modfication, head until snd.fack is lost.
909  *      B. SACK arrives sacking data transmitted after never retransmitted
910  *         hole was sent out.
911  *      C. SACK arrives sacking SND.NXT at the moment, when the
912  *         segment was retransmitted.
913  * 4. D-SACK added new rule: D-SACK changes any tag to S.
914  *
915  * It is pleasant to note, that state diagram turns out to be commutative,
916  * so that we are allowed not to be bothered by order of our actions,
917  * when multiple events arrive simultaneously. (see the function below).
918  *
919  * Reordering detection.
920  * --------------------
921  * Reordering metric is maximal distance, which a packet can be displaced
922  * in packet stream. With SACKs we can estimate it:
923  *
924  * 1. SACK fills old hole and the corresponding segment was not
925  *    ever retransmitted -> reordering. Alas, we cannot use it
926  *    when segment was retransmitted.
927  * 2. The last flaw is solved with D-SACK. D-SACK arrives
928  *    for retransmitted and already SACKed segment -> reordering..
929  * Both of these heuristics are not used in Loss state, when we cannot
930  * account for retransmits accurately.
931  */
932 static int
933 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
934 {
935         const struct inet_connection_sock *icsk = inet_csk(sk);
936         struct tcp_sock *tp = tcp_sk(sk);
937         unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
938         struct tcp_sack_block_wire *sp = (struct tcp_sack_block_wire *)(ptr+2);
939         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
940         int reord = tp->packets_out;
941         int prior_fackets;
942         u32 lost_retrans = 0;
943         int flag = 0;
944         int dup_sack = 0;
945         int i;
946
947         if (!tp->sacked_out)
948                 tp->fackets_out = 0;
949         prior_fackets = tp->fackets_out;
950
951         /* SACK fastpath:
952          * if the only SACK change is the increase of the end_seq of
953          * the first block then only apply that SACK block
954          * and use retrans queue hinting otherwise slowpath */
955         flag = 1;
956         for (i = 0; i< num_sacks; i++) {
957                 __u32 start_seq = ntohl(sp[i].start_seq);
958                 __u32 end_seq =  ntohl(sp[i].end_seq);
959
960                 if (i == 0){
961                         if (tp->recv_sack_cache[i].start_seq != start_seq)
962                                 flag = 0;
963                 } else {
964                         if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
965                             (tp->recv_sack_cache[i].end_seq != end_seq))
966                                 flag = 0;
967                 }
968                 tp->recv_sack_cache[i].start_seq = start_seq;
969                 tp->recv_sack_cache[i].end_seq = end_seq;
970
971                 /* Check for D-SACK. */
972                 if (i == 0) {
973                         u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;
974
975                         if (before(start_seq, ack)) {
976                                 dup_sack = 1;
977                                 tp->rx_opt.sack_ok |= 4;
978                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
979                         } else if (num_sacks > 1 &&
980                                    !after(end_seq, ntohl(sp[1].end_seq)) &&
981                                    !before(start_seq, ntohl(sp[1].start_seq))) {
982                                 dup_sack = 1;
983                                 tp->rx_opt.sack_ok |= 4;
984                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
985                         }
986
987                         /* D-SACK for already forgotten data...
988                          * Do dumb counting. */
989                         if (dup_sack &&
990                             !after(end_seq, prior_snd_una) &&
991                             after(end_seq, tp->undo_marker))
992                                 tp->undo_retrans--;
993
994                         /* Eliminate too old ACKs, but take into
995                          * account more or less fresh ones, they can
996                          * contain valid SACK info.
997                          */
998                         if (before(ack, prior_snd_una - tp->max_window))
999                                 return 0;
1000                 }
1001         }
1002
1003         if (flag)
1004                 num_sacks = 1;
1005         else {
1006                 int j;
1007                 tp->fastpath_skb_hint = NULL;
1008
1009                 /* order SACK blocks to allow in order walk of the retrans queue */
1010                 for (i = num_sacks-1; i > 0; i--) {
1011                         for (j = 0; j < i; j++){
1012                                 if (after(ntohl(sp[j].start_seq),
1013                                           ntohl(sp[j+1].start_seq))){
1014                                         struct tcp_sack_block_wire tmp;
1015
1016                                         tmp = sp[j];
1017                                         sp[j] = sp[j+1];
1018                                         sp[j+1] = tmp;
1019                                 }
1020
1021                         }
1022                 }
1023         }
1024
1025         /* clear flag as used for different purpose in following code */
1026         flag = 0;
1027
1028         for (i=0; i<num_sacks; i++, sp++) {
1029                 struct sk_buff *skb;
1030                 __u32 start_seq = ntohl(sp->start_seq);
1031                 __u32 end_seq = ntohl(sp->end_seq);
1032                 int fack_count;
1033
1034                 /* Use SACK fastpath hint if valid */
1035                 if (tp->fastpath_skb_hint) {
1036                         skb = tp->fastpath_skb_hint;
1037                         fack_count = tp->fastpath_cnt_hint;
1038                 } else {
1039                         skb = sk->sk_write_queue.next;
1040                         fack_count = 0;
1041                 }
1042
1043                 /* Event "B" in the comment above. */
1044                 if (after(end_seq, tp->high_seq))
1045                         flag |= FLAG_DATA_LOST;
1046
1047                 sk_stream_for_retrans_queue_from(skb, sk) {
1048                         int in_sack, pcount;
1049                         u8 sacked;
1050
1051                         tp->fastpath_skb_hint = skb;
1052                         tp->fastpath_cnt_hint = fack_count;
1053
1054                         /* The retransmission queue is always in order, so
1055                          * we can short-circuit the walk early.
1056                          */
1057                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1058                                 break;
1059
1060                         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1061                                 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1062
1063                         pcount = tcp_skb_pcount(skb);
1064
1065                         if (pcount > 1 && !in_sack &&
1066                             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1067                                 unsigned int pkt_len;
1068
1069                                 in_sack = !after(start_seq,
1070                                                  TCP_SKB_CB(skb)->seq);
1071
1072                                 if (!in_sack)
1073                                         pkt_len = (start_seq -
1074                                                    TCP_SKB_CB(skb)->seq);
1075                                 else
1076                                         pkt_len = (end_seq -
1077                                                    TCP_SKB_CB(skb)->seq);
1078                                 if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size))
1079                                         break;
1080                                 pcount = tcp_skb_pcount(skb);
1081                         }
1082
1083                         fack_count += pcount;
1084
1085                         sacked = TCP_SKB_CB(skb)->sacked;
1086
1087                         /* Account D-SACK for retransmitted packet. */
1088                         if ((dup_sack && in_sack) &&
1089                             (sacked & TCPCB_RETRANS) &&
1090                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1091                                 tp->undo_retrans--;
1092
1093                         /* The frame is ACKed. */
1094                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1095                                 if (sacked&TCPCB_RETRANS) {
1096                                         if ((dup_sack && in_sack) &&
1097                                             (sacked&TCPCB_SACKED_ACKED))
1098                                                 reord = min(fack_count, reord);
1099                                 } else {
1100                                         /* If it was in a hole, we detected reordering. */
1101                                         if (fack_count < prior_fackets &&
1102                                             !(sacked&TCPCB_SACKED_ACKED))
1103                                                 reord = min(fack_count, reord);
1104                                 }
1105
1106                                 /* Nothing to do; acked frame is about to be dropped. */
1107                                 continue;
1108                         }
1109
1110                         if ((sacked&TCPCB_SACKED_RETRANS) &&
1111                             after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1112                             (!lost_retrans || after(end_seq, lost_retrans)))
1113                                 lost_retrans = end_seq;
1114
1115                         if (!in_sack)
1116                                 continue;
1117
1118                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1119                                 if (sacked & TCPCB_SACKED_RETRANS) {
1120                                         /* If the segment is not tagged as lost,
1121                                          * we do not clear RETRANS, believing
1122                                          * that retransmission is still in flight.
1123                                          */
1124                                         if (sacked & TCPCB_LOST) {
1125                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1126                                                 tp->lost_out -= tcp_skb_pcount(skb);
1127                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1128
1129                                                 /* clear lost hint */
1130                                                 tp->retransmit_skb_hint = NULL;
1131                                         }
1132                                 } else {
1133                                         /* New sack for not retransmitted frame,
1134                                          * which was in hole. It is reordering.
1135                                          */
1136                                         if (!(sacked & TCPCB_RETRANS) &&
1137                                             fack_count < prior_fackets)
1138                                                 reord = min(fack_count, reord);
1139
1140                                         if (sacked & TCPCB_LOST) {
1141                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1142                                                 tp->lost_out -= tcp_skb_pcount(skb);
1143
1144                                                 /* clear lost hint */
1145                                                 tp->retransmit_skb_hint = NULL;
1146                                         }
1147                                 }
1148
1149                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1150                                 flag |= FLAG_DATA_SACKED;
1151                                 tp->sacked_out += tcp_skb_pcount(skb);
1152
1153                                 if (fack_count > tp->fackets_out)
1154                                         tp->fackets_out = fack_count;
1155                         } else {
1156                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1157                                         reord = min(fack_count, reord);
1158                         }
1159
1160                         /* D-SACK. We can detect redundant retransmission
1161                          * in S|R and plain R frames and clear it.
1162                          * undo_retrans is decreased above, L|R frames
1163                          * are accounted above as well.
1164                          */
1165                         if (dup_sack &&
1166                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1167                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1168                                 tp->retrans_out -= tcp_skb_pcount(skb);
1169                                 tp->retransmit_skb_hint = NULL;
1170                         }
1171                 }
1172         }
1173
1174         /* Check for lost retransmit. This superb idea is
1175          * borrowed from "ratehalving". Event "C".
1176          * Later note: FACK people cheated me again 8),
1177          * we have to account for reordering! Ugly,
1178          * but should help.
1179          */
1180         if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
1181                 struct sk_buff *skb;
1182
1183                 sk_stream_for_retrans_queue(skb, sk) {
1184                         if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1185                                 break;
1186                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1187                                 continue;
1188                         if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1189                             after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1190                             (IsFack(tp) ||
1191                              !before(lost_retrans,
1192                                      TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1193                                      tp->mss_cache))) {
1194                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1195                                 tp->retrans_out -= tcp_skb_pcount(skb);
1196
1197                                 /* clear lost hint */
1198                                 tp->retransmit_skb_hint = NULL;
1199
1200                                 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1201                                         tp->lost_out += tcp_skb_pcount(skb);
1202                                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1203                                         flag |= FLAG_DATA_SACKED;
1204                                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1205                                 }
1206                         }
1207                 }
1208         }
1209
1210         tp->left_out = tp->sacked_out + tp->lost_out;
1211
1212         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss)
1213                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1214
1215 #if FASTRETRANS_DEBUG > 0
1216         BUG_TRAP((int)tp->sacked_out >= 0);
1217         BUG_TRAP((int)tp->lost_out >= 0);
1218         BUG_TRAP((int)tp->retrans_out >= 0);
1219         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1220 #endif
1221         return flag;
1222 }
1223
1224 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new
1225  * segments to see from the next ACKs whether any data was really missing.
1226  * If the RTO was spurious, new ACKs should arrive.
1227  */
1228 void tcp_enter_frto(struct sock *sk)
1229 {
1230         const struct inet_connection_sock *icsk = inet_csk(sk);
1231         struct tcp_sock *tp = tcp_sk(sk);
1232         struct sk_buff *skb;
1233
1234         tp->frto_counter = 1;
1235
1236         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1237             tp->snd_una == tp->high_seq ||
1238             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1239                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1240                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1241                 tcp_ca_event(sk, CA_EVENT_FRTO);
1242         }
1243
1244         /* Have to clear retransmission markers here to keep the bookkeeping
1245          * in shape, even though we are not yet in Loss state.
1246          * If something was really lost, it is eventually caught up
1247          * in tcp_enter_frto_loss.
1248          */
1249         tp->retrans_out = 0;
1250         tp->undo_marker = tp->snd_una;
1251         tp->undo_retrans = 0;
1252
1253         sk_stream_for_retrans_queue(skb, sk) {
1254                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
1255         }
1256         tcp_sync_left_out(tp);
1257
1258         tcp_set_ca_state(sk, TCP_CA_Open);
1259         tp->frto_highmark = tp->snd_nxt;
1260 }
1261
1262 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1263  * which indicates that we should follow the traditional RTO recovery,
1264  * i.e. mark everything lost and do go-back-N retransmission.
1265  */
1266 static void tcp_enter_frto_loss(struct sock *sk)
1267 {
1268         struct tcp_sock *tp = tcp_sk(sk);
1269         struct sk_buff *skb;
1270         int cnt = 0;
1271
1272         tp->sacked_out = 0;
1273         tp->lost_out = 0;
1274         tp->fackets_out = 0;
1275
1276         sk_stream_for_retrans_queue(skb, sk) {
1277                 cnt += tcp_skb_pcount(skb);
1278                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1279                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1280
1281                         /* Do not mark those segments lost that were
1282                          * forward transmitted after RTO
1283                          */
1284                         if (!after(TCP_SKB_CB(skb)->end_seq,
1285                                    tp->frto_highmark)) {
1286                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1287                                 tp->lost_out += tcp_skb_pcount(skb);
1288                         }
1289                 } else {
1290                         tp->sacked_out += tcp_skb_pcount(skb);
1291                         tp->fackets_out = cnt;
1292                 }
1293         }
1294         tcp_sync_left_out(tp);
1295
1296         tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
1297         tp->snd_cwnd_cnt = 0;
1298         tp->snd_cwnd_stamp = tcp_time_stamp;
1299         tp->undo_marker = 0;
1300         tp->frto_counter = 0;
1301
1302         tp->reordering = min_t(unsigned int, tp->reordering,
1303                                              sysctl_tcp_reordering);
1304         tcp_set_ca_state(sk, TCP_CA_Loss);
1305         tp->high_seq = tp->frto_highmark;
1306         TCP_ECN_queue_cwr(tp);
1307
1308         clear_all_retrans_hints(tp);
1309 }
1310
1311 void tcp_clear_retrans(struct tcp_sock *tp)
1312 {
1313         tp->left_out = 0;
1314         tp->retrans_out = 0;
1315
1316         tp->fackets_out = 0;
1317         tp->sacked_out = 0;
1318         tp->lost_out = 0;
1319
1320         tp->undo_marker = 0;
1321         tp->undo_retrans = 0;
1322 }
1323
1324 /* Enter Loss state. If "how" is not zero, forget all SACK information
1325  * and reset tags completely, otherwise preserve SACKs. If receiver
1326  * dropped its ofo queue, we will know this due to reneging detection.
1327  */
1328 void tcp_enter_loss(struct sock *sk, int how)
1329 {
1330         const struct inet_connection_sock *icsk = inet_csk(sk);
1331         struct tcp_sock *tp = tcp_sk(sk);
1332         struct sk_buff *skb;
1333         int cnt = 0;
1334
1335         /* Reduce ssthresh if it has not yet been made inside this window. */
1336         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1337             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1338                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1339                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1340                 tcp_ca_event(sk, CA_EVENT_LOSS);
1341         }
1342         tp->snd_cwnd       = 1;
1343         tp->snd_cwnd_cnt   = 0;
1344         tp->snd_cwnd_stamp = tcp_time_stamp;
1345
1346         tp->bytes_acked = 0;
1347         tcp_clear_retrans(tp);
1348
1349         /* Push undo marker, if it was plain RTO and nothing
1350          * was retransmitted. */
1351         if (!how)
1352                 tp->undo_marker = tp->snd_una;
1353
1354         sk_stream_for_retrans_queue(skb, sk) {
1355                 cnt += tcp_skb_pcount(skb);
1356                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1357                         tp->undo_marker = 0;
1358                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1359                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1360                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1361                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1362                         tp->lost_out += tcp_skb_pcount(skb);
1363                 } else {
1364                         tp->sacked_out += tcp_skb_pcount(skb);
1365                         tp->fackets_out = cnt;
1366                 }
1367         }
1368         tcp_sync_left_out(tp);
1369
1370         tp->reordering = min_t(unsigned int, tp->reordering,
1371                                              sysctl_tcp_reordering);
1372         tcp_set_ca_state(sk, TCP_CA_Loss);
1373         tp->high_seq = tp->snd_nxt;
1374         TCP_ECN_queue_cwr(tp);
1375
1376         clear_all_retrans_hints(tp);
1377 }
1378
1379 static int tcp_check_sack_reneging(struct sock *sk)
1380 {
1381         struct sk_buff *skb;
1382
1383         /* If ACK arrived pointing to a remembered SACK,
1384          * it means that our remembered SACKs do not reflect
1385          * real state of receiver i.e.
1386          * receiver _host_ is heavily congested (or buggy).
1387          * Do processing similar to RTO timeout.
1388          */
1389         if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
1390             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1391                 struct inet_connection_sock *icsk = inet_csk(sk);
1392                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1393
1394                 tcp_enter_loss(sk, 1);
1395                 icsk->icsk_retransmits++;
1396                 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
1397                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1398                                           icsk->icsk_rto, TCP_RTO_MAX);
1399                 return 1;
1400         }
1401         return 0;
1402 }
1403
1404 static inline int tcp_fackets_out(struct tcp_sock *tp)
1405 {
1406         return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1407 }
1408
1409 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1410 {
1411         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1412 }
1413
1414 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
1415 {
1416         return tp->packets_out &&
1417                tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
1418 }
1419
1420 /* Linux NewReno/SACK/FACK/ECN state machine.
1421  * --------------------------------------
1422  *
1423  * "Open"       Normal state, no dubious events, fast path.
1424  * "Disorder"   In all the respects it is "Open",
1425  *              but requires a bit more attention. It is entered when
1426  *              we see some SACKs or dupacks. It is split of "Open"
1427  *              mainly to move some processing from fast path to slow one.
1428  * "CWR"        CWND was reduced due to some Congestion Notification event.
1429  *              It can be ECN, ICMP source quench, local device congestion.
1430  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1431  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1432  *
1433  * tcp_fastretrans_alert() is entered:
1434  * - each incoming ACK, if state is not "Open"
1435  * - when arrived ACK is unusual, namely:
1436  *      * SACK
1437  *      * Duplicate ACK.
1438  *      * ECN ECE.
1439  *
1440  * Counting packets in flight is pretty simple.
1441  *
1442  *      in_flight = packets_out - left_out + retrans_out
1443  *
1444  *      packets_out is SND.NXT-SND.UNA counted in packets.
1445  *
1446  *      retrans_out is number of retransmitted segments.
1447  *
1448  *      left_out is number of segments left network, but not ACKed yet.
1449  *
1450  *              left_out = sacked_out + lost_out
1451  *
1452  *     sacked_out: Packets, which arrived to receiver out of order
1453  *                 and hence not ACKed. With SACKs this number is simply
1454  *                 amount of SACKed data. Even without SACKs
1455  *                 it is easy to give pretty reliable estimate of this number,
1456  *                 counting duplicate ACKs.
1457  *
1458  *       lost_out: Packets lost by network. TCP has no explicit
1459  *                 "loss notification" feedback from network (for now).
1460  *                 It means that this number can be only _guessed_.
1461  *                 Actually, it is the heuristics to predict lossage that
1462  *                 distinguishes different algorithms.
1463  *
1464  *      F.e. after RTO, when all the queue is considered as lost,
1465  *      lost_out = packets_out and in_flight = retrans_out.
1466  *
1467  *              Essentially, we have now two algorithms counting
1468  *              lost packets.
1469  *
1470  *              FACK: It is the simplest heuristics. As soon as we decided
1471  *              that something is lost, we decide that _all_ not SACKed
1472  *              packets until the most forward SACK are lost. I.e.
1473  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1474  *              It is absolutely correct estimate, if network does not reorder
1475  *              packets. And it loses any connection to reality when reordering
1476  *              takes place. We use FACK by default until reordering
1477  *              is suspected on the path to this destination.
1478  *
1479  *              NewReno: when Recovery is entered, we assume that one segment
1480  *              is lost (classic Reno). While we are in Recovery and
1481  *              a partial ACK arrives, we assume that one more packet
1482  *              is lost (NewReno). This heuristics are the same in NewReno
1483  *              and SACK.
1484  *
1485  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1486  *  deflation etc. CWND is real congestion window, never inflated, changes
1487  *  only according to classic VJ rules.
1488  *
1489  * Really tricky (and requiring careful tuning) part of algorithm
1490  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1491  * The first determines the moment _when_ we should reduce CWND and,
1492  * hence, slow down forward transmission. In fact, it determines the moment
1493  * when we decide that hole is caused by loss, rather than by a reorder.
1494  *
1495  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1496  * holes, caused by lost packets.
1497  *
1498  * And the most logically complicated part of algorithm is undo
1499  * heuristics. We detect false retransmits due to both too early
1500  * fast retransmit (reordering) and underestimated RTO, analyzing
1501  * timestamps and D-SACKs. When we detect that some segments were
1502  * retransmitted by mistake and CWND reduction was wrong, we undo
1503  * window reduction and abort recovery phase. This logic is hidden
1504  * inside several functions named tcp_try_undo_<something>.
1505  */
1506
1507 /* This function decides, when we should leave Disordered state
1508  * and enter Recovery phase, reducing congestion window.
1509  *
1510  * Main question: may we further continue forward transmission
1511  * with the same cwnd?
1512  */
1513 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
1514 {
1515         __u32 packets_out;
1516
1517         /* Trick#1: The loss is proven. */
1518         if (tp->lost_out)
1519                 return 1;
1520
1521         /* Not-A-Trick#2 : Classic rule... */
1522         if (tcp_fackets_out(tp) > tp->reordering)
1523                 return 1;
1524
1525         /* Trick#3 : when we use RFC2988 timer restart, fast
1526          * retransmit can be triggered by timeout of queue head.
1527          */
1528         if (tcp_head_timedout(sk, tp))
1529                 return 1;
1530
1531         /* Trick#4: It is still not OK... But will it be useful to delay
1532          * recovery more?
1533          */
1534         packets_out = tp->packets_out;
1535         if (packets_out <= tp->reordering &&
1536             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1537             !tcp_may_send_now(sk, tp)) {
1538                 /* We have nothing to send. This connection is limited
1539                  * either by receiver window or by application.
1540                  */
1541                 return 1;
1542         }
1543
1544         return 0;
1545 }
1546
1547 /* If we receive more dupacks than we expected counting segments
1548  * in assumption of absent reordering, interpret this as reordering.
1549  * The only another reason could be bug in receiver TCP.
1550  */
1551 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1552 {
1553         struct tcp_sock *tp = tcp_sk(sk);
1554         u32 holes;
1555
1556         holes = max(tp->lost_out, 1U);
1557         holes = min(holes, tp->packets_out);
1558
1559         if ((tp->sacked_out + holes) > tp->packets_out) {
1560                 tp->sacked_out = tp->packets_out - holes;
1561                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1562         }
1563 }
1564
1565 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1566
1567 static void tcp_add_reno_sack(struct sock *sk)
1568 {
1569         struct tcp_sock *tp = tcp_sk(sk);
1570         tp->sacked_out++;
1571         tcp_check_reno_reordering(sk, 0);
1572         tcp_sync_left_out(tp);
1573 }
1574
1575 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1576
1577 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
1578 {
1579         if (acked > 0) {
1580                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1581                 if (acked-1 >= tp->sacked_out)
1582                         tp->sacked_out = 0;
1583                 else
1584                         tp->sacked_out -= acked-1;
1585         }
1586         tcp_check_reno_reordering(sk, acked);
1587         tcp_sync_left_out(tp);
1588 }
1589
1590 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1591 {
1592         tp->sacked_out = 0;
1593         tp->left_out = tp->lost_out;
1594 }
1595
1596 /* Mark head of queue up as lost. */
1597 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
1598                                int packets, u32 high_seq)
1599 {
1600         struct sk_buff *skb;
1601         int cnt;
1602
1603         BUG_TRAP(packets <= tp->packets_out);
1604         if (tp->lost_skb_hint) {
1605                 skb = tp->lost_skb_hint;
1606                 cnt = tp->lost_cnt_hint;
1607         } else {
1608                 skb = sk->sk_write_queue.next;
1609                 cnt = 0;
1610         }
1611
1612         sk_stream_for_retrans_queue_from(skb, sk) {
1613                 /* TODO: do this better */
1614                 /* this is not the most efficient way to do this... */
1615                 tp->lost_skb_hint = skb;
1616                 tp->lost_cnt_hint = cnt;
1617                 cnt += tcp_skb_pcount(skb);
1618                 if (cnt > packets || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1619                         break;
1620                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1621                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1622                         tp->lost_out += tcp_skb_pcount(skb);
1623
1624                         /* clear xmit_retransmit_queue hints
1625                          *  if this is beyond hint */
1626                         if(tp->retransmit_skb_hint != NULL &&
1627                            before(TCP_SKB_CB(skb)->seq,
1628                                   TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) {
1629
1630                                 tp->retransmit_skb_hint = NULL;
1631                         }
1632                 }
1633         }
1634         tcp_sync_left_out(tp);
1635 }
1636
1637 /* Account newly detected lost packet(s) */
1638
1639 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
1640 {
1641         if (IsFack(tp)) {
1642                 int lost = tp->fackets_out - tp->reordering;
1643                 if (lost <= 0)
1644                         lost = 1;
1645                 tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
1646         } else {
1647                 tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
1648         }
1649
1650         /* New heuristics: it is possible only after we switched
1651          * to restart timer each time when something is ACKed.
1652          * Hence, we can detect timed out packets during fast
1653          * retransmit without falling to slow start.
1654          */
1655         if (!IsReno(tp) && tcp_head_timedout(sk, tp)) {
1656                 struct sk_buff *skb;
1657
1658                 skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
1659                         : sk->sk_write_queue.next;
1660
1661                 sk_stream_for_retrans_queue_from(skb, sk) {
1662                         if (!tcp_skb_timedout(sk, skb))
1663                                 break;
1664
1665                         if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1666                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1667                                 tp->lost_out += tcp_skb_pcount(skb);
1668
1669                                 /* clear xmit_retrans hint */
1670                                 if (tp->retransmit_skb_hint &&
1671                                     before(TCP_SKB_CB(skb)->seq,
1672                                            TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
1673
1674                                         tp->retransmit_skb_hint = NULL;
1675                         }
1676                 }
1677
1678                 tp->scoreboard_skb_hint = skb;
1679
1680                 tcp_sync_left_out(tp);
1681         }
1682 }
1683
1684 /* CWND moderation, preventing bursts due to too big ACKs
1685  * in dubious situations.
1686  */
1687 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1688 {
1689         tp->snd_cwnd = min(tp->snd_cwnd,
1690                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1691         tp->snd_cwnd_stamp = tcp_time_stamp;
1692 }
1693
1694 /* Lower bound on congestion window is slow start threshold
1695  * unless congestion avoidance choice decides to overide it.
1696  */
1697 static inline u32 tcp_cwnd_min(const struct sock *sk)
1698 {
1699         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1700
1701         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
1702 }
1703
1704 /* Decrease cwnd each second ack. */
1705 static void tcp_cwnd_down(struct sock *sk)
1706 {
1707         struct tcp_sock *tp = tcp_sk(sk);
1708         int decr = tp->snd_cwnd_cnt + 1;
1709
1710         tp->snd_cwnd_cnt = decr&1;
1711         decr >>= 1;
1712
1713         if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
1714                 tp->snd_cwnd -= decr;
1715
1716         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1717         tp->snd_cwnd_stamp = tcp_time_stamp;
1718 }
1719
1720 /* Nothing was retransmitted or returned timestamp is less
1721  * than timestamp of the first retransmission.
1722  */
1723 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1724 {
1725         return !tp->retrans_stamp ||
1726                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1727                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1728 }
1729
1730 /* Undo procedures. */
1731
1732 #if FASTRETRANS_DEBUG > 1
1733 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
1734 {
1735         struct inet_sock *inet = inet_sk(sk);
1736         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1737                msg,
1738                NIPQUAD(inet->daddr), ntohs(inet->dport),
1739                tp->snd_cwnd, tp->left_out,
1740                tp->snd_ssthresh, tp->prior_ssthresh,
1741                tp->packets_out);
1742 }
1743 #else
1744 #define DBGUNDO(x...) do { } while (0)
1745 #endif
1746
1747 static void tcp_undo_cwr(struct sock *sk, const int undo)
1748 {
1749         struct tcp_sock *tp = tcp_sk(sk);
1750
1751         if (tp->prior_ssthresh) {
1752                 const struct inet_connection_sock *icsk = inet_csk(sk);
1753
1754                 if (icsk->icsk_ca_ops->undo_cwnd)
1755                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
1756                 else
1757                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1758
1759                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1760                         tp->snd_ssthresh = tp->prior_ssthresh;
1761                         TCP_ECN_withdraw_cwr(tp);
1762                 }
1763         } else {
1764                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1765         }
1766         tcp_moderate_cwnd(tp);
1767         tp->snd_cwnd_stamp = tcp_time_stamp;
1768
1769         /* There is something screwy going on with the retrans hints after
1770            an undo */
1771         clear_all_retrans_hints(tp);
1772 }
1773
1774 static inline int tcp_may_undo(struct tcp_sock *tp)
1775 {
1776         return tp->undo_marker &&
1777                 (!tp->undo_retrans || tcp_packet_delayed(tp));
1778 }
1779
1780 /* People celebrate: "We love our President!" */
1781 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
1782 {
1783         if (tcp_may_undo(tp)) {
1784                 /* Happy end! We did not retransmit anything
1785                  * or our original transmission succeeded.
1786                  */
1787                 DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
1788                 tcp_undo_cwr(sk, 1);
1789                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
1790                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1791                 else
1792                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1793                 tp->undo_marker = 0;
1794         }
1795         if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1796                 /* Hold old state until something *above* high_seq
1797                  * is ACKed. For Reno it is MUST to prevent false
1798                  * fast retransmits (RFC2582). SACK TCP is safe. */
1799                 tcp_moderate_cwnd(tp);
1800                 return 1;
1801         }
1802         tcp_set_ca_state(sk, TCP_CA_Open);
1803         return 0;
1804 }
1805
1806 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1807 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
1808 {
1809         if (tp->undo_marker && !tp->undo_retrans) {
1810                 DBGUNDO(sk, tp, "D-SACK");
1811                 tcp_undo_cwr(sk, 1);
1812                 tp->undo_marker = 0;
1813                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1814         }
1815 }
1816
1817 /* Undo during fast recovery after partial ACK. */
1818
1819 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
1820                                 int acked)
1821 {
1822         /* Partial ACK arrived. Force Hoe's retransmit. */
1823         int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1824
1825         if (tcp_may_undo(tp)) {
1826                 /* Plain luck! Hole if filled with delayed
1827                  * packet, rather than with a retransmit.
1828                  */
1829                 if (tp->retrans_out == 0)
1830                         tp->retrans_stamp = 0;
1831
1832                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
1833
1834                 DBGUNDO(sk, tp, "Hoe");
1835                 tcp_undo_cwr(sk, 0);
1836                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1837
1838                 /* So... Do not make Hoe's retransmit yet.
1839                  * If the first packet was delayed, the rest
1840                  * ones are most probably delayed as well.
1841                  */
1842                 failed = 0;
1843         }
1844         return failed;
1845 }
1846
1847 /* Undo during loss recovery after partial ACK. */
1848 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
1849 {
1850         if (tcp_may_undo(tp)) {
1851                 struct sk_buff *skb;
1852                 sk_stream_for_retrans_queue(skb, sk) {
1853                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1854                 }
1855
1856                 clear_all_retrans_hints(tp);
1857
1858                 DBGUNDO(sk, tp, "partial loss");
1859                 tp->lost_out = 0;
1860                 tp->left_out = tp->sacked_out;
1861                 tcp_undo_cwr(sk, 1);
1862                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1863                 inet_csk(sk)->icsk_retransmits = 0;
1864                 tp->undo_marker = 0;
1865                 if (!IsReno(tp))
1866                         tcp_set_ca_state(sk, TCP_CA_Open);
1867                 return 1;
1868         }
1869         return 0;
1870 }
1871
1872 static inline void tcp_complete_cwr(struct sock *sk)
1873 {
1874         struct tcp_sock *tp = tcp_sk(sk);
1875         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
1876         tp->snd_cwnd_stamp = tcp_time_stamp;
1877         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
1878 }
1879
1880 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
1881 {
1882         tp->left_out = tp->sacked_out;
1883
1884         if (tp->retrans_out == 0)
1885                 tp->retrans_stamp = 0;
1886
1887         if (flag&FLAG_ECE)
1888                 tcp_enter_cwr(sk);
1889
1890         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
1891                 int state = TCP_CA_Open;
1892
1893                 if (tp->left_out || tp->retrans_out || tp->undo_marker)
1894                         state = TCP_CA_Disorder;
1895
1896                 if (inet_csk(sk)->icsk_ca_state != state) {
1897                         tcp_set_ca_state(sk, state);
1898                         tp->high_seq = tp->snd_nxt;
1899                 }
1900                 tcp_moderate_cwnd(tp);
1901         } else {
1902                 tcp_cwnd_down(sk);
1903         }
1904 }
1905
1906 static void tcp_mtup_probe_failed(struct sock *sk)
1907 {
1908         struct inet_connection_sock *icsk = inet_csk(sk);
1909
1910         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
1911         icsk->icsk_mtup.probe_size = 0;
1912 }
1913
1914 static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
1915 {
1916         struct tcp_sock *tp = tcp_sk(sk);
1917         struct inet_connection_sock *icsk = inet_csk(sk);
1918
1919         /* FIXME: breaks with very large cwnd */
1920         tp->prior_ssthresh = tcp_current_ssthresh(sk);
1921         tp->snd_cwnd = tp->snd_cwnd *
1922                        tcp_mss_to_mtu(sk, tp->mss_cache) /
1923                        icsk->icsk_mtup.probe_size;
1924         tp->snd_cwnd_cnt = 0;
1925         tp->snd_cwnd_stamp = tcp_time_stamp;
1926         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
1927
1928         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
1929         icsk->icsk_mtup.probe_size = 0;
1930         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
1931 }
1932
1933
1934 /* Process an event, which can update packets-in-flight not trivially.
1935  * Main goal of this function is to calculate new estimate for left_out,
1936  * taking into account both packets sitting in receiver's buffer and
1937  * packets lost by network.
1938  *
1939  * Besides that it does CWND reduction, when packet loss is detected
1940  * and changes state of machine.
1941  *
1942  * It does _not_ decide what to send, it is made in function
1943  * tcp_xmit_retransmit_queue().
1944  */
1945 static void
1946 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
1947                       int prior_packets, int flag)
1948 {
1949         struct inet_connection_sock *icsk = inet_csk(sk);
1950         struct tcp_sock *tp = tcp_sk(sk);
1951         int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
1952
1953         /* Some technical things:
1954          * 1. Reno does not count dupacks (sacked_out) automatically. */
1955         if (!tp->packets_out)
1956                 tp->sacked_out = 0;
1957         /* 2. SACK counts snd_fack in packets inaccurately. */
1958         if (tp->sacked_out == 0)
1959                 tp->fackets_out = 0;
1960
1961         /* Now state machine starts.
1962          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
1963         if (flag&FLAG_ECE)
1964                 tp->prior_ssthresh = 0;
1965
1966         /* B. In all the states check for reneging SACKs. */
1967         if (tp->sacked_out && tcp_check_sack_reneging(sk))
1968                 return;
1969
1970         /* C. Process data loss notification, provided it is valid. */
1971         if ((flag&FLAG_DATA_LOST) &&
1972             before(tp->snd_una, tp->high_seq) &&
1973             icsk->icsk_ca_state != TCP_CA_Open &&
1974             tp->fackets_out > tp->reordering) {
1975                 tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
1976                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
1977         }
1978
1979         /* D. Synchronize left_out to current state. */
1980         tcp_sync_left_out(tp);
1981
1982         /* E. Check state exit conditions. State can be terminated
1983          *    when high_seq is ACKed. */
1984         if (icsk->icsk_ca_state == TCP_CA_Open) {
1985                 if (!sysctl_tcp_frto)
1986                         BUG_TRAP(tp->retrans_out == 0);
1987                 tp->retrans_stamp = 0;
1988         } else if (!before(tp->snd_una, tp->high_seq)) {
1989                 switch (icsk->icsk_ca_state) {
1990                 case TCP_CA_Loss:
1991                         icsk->icsk_retransmits = 0;
1992                         if (tcp_try_undo_recovery(sk, tp))
1993                                 return;
1994                         break;
1995
1996                 case TCP_CA_CWR:
1997                         /* CWR is to be held something *above* high_seq
1998                          * is ACKed for CWR bit to reach receiver. */
1999                         if (tp->snd_una != tp->high_seq) {
2000                                 tcp_complete_cwr(sk);
2001                                 tcp_set_ca_state(sk, TCP_CA_Open);
2002                         }
2003                         break;
2004
2005                 case TCP_CA_Disorder:
2006                         tcp_try_undo_dsack(sk, tp);
2007                         if (!tp->undo_marker ||
2008                             /* For SACK case do not Open to allow to undo
2009                              * catching for all duplicate ACKs. */
2010                             IsReno(tp) || tp->snd_una != tp->high_seq) {
2011                                 tp->undo_marker = 0;
2012                                 tcp_set_ca_state(sk, TCP_CA_Open);
2013                         }
2014                         break;
2015
2016                 case TCP_CA_Recovery:
2017                         if (IsReno(tp))
2018                                 tcp_reset_reno_sack(tp);
2019                         if (tcp_try_undo_recovery(sk, tp))
2020                                 return;
2021                         tcp_complete_cwr(sk);
2022                         break;
2023                 }
2024         }
2025
2026         /* F. Process state. */
2027         switch (icsk->icsk_ca_state) {
2028         case TCP_CA_Recovery:
2029                 if (prior_snd_una == tp->snd_una) {
2030                         if (IsReno(tp) && is_dupack)
2031                                 tcp_add_reno_sack(sk);
2032                 } else {
2033                         int acked = prior_packets - tp->packets_out;
2034                         if (IsReno(tp))
2035                                 tcp_remove_reno_sacks(sk, tp, acked);
2036                         is_dupack = tcp_try_undo_partial(sk, tp, acked);
2037                 }
2038                 break;
2039         case TCP_CA_Loss:
2040                 if (flag&FLAG_DATA_ACKED)
2041                         icsk->icsk_retransmits = 0;
2042                 if (!tcp_try_undo_loss(sk, tp)) {
2043                         tcp_moderate_cwnd(tp);
2044                         tcp_xmit_retransmit_queue(sk);
2045                         return;
2046                 }
2047                 if (icsk->icsk_ca_state != TCP_CA_Open)
2048                         return;
2049                 /* Loss is undone; fall through to processing in Open state. */
2050         default:
2051                 if (IsReno(tp)) {
2052                         if (tp->snd_una != prior_snd_una)
2053                                 tcp_reset_reno_sack(tp);
2054                         if (is_dupack)
2055                                 tcp_add_reno_sack(sk);
2056                 }
2057
2058                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
2059                         tcp_try_undo_dsack(sk, tp);
2060
2061                 if (!tcp_time_to_recover(sk, tp)) {
2062                         tcp_try_to_open(sk, tp, flag);
2063                         return;
2064                 }
2065
2066                 /* MTU probe failure: don't reduce cwnd */
2067                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2068                     icsk->icsk_mtup.probe_size &&
2069                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2070                         tcp_mtup_probe_failed(sk);
2071                         /* Restores the reduction we did in tcp_mtup_probe() */
2072                         tp->snd_cwnd++;
2073                         tcp_simple_retransmit(sk);
2074                         return;
2075                 }
2076
2077                 /* Otherwise enter Recovery state */
2078
2079                 if (IsReno(tp))
2080                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
2081                 else
2082                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
2083
2084                 tp->high_seq = tp->snd_nxt;
2085                 tp->prior_ssthresh = 0;
2086                 tp->undo_marker = tp->snd_una;
2087                 tp->undo_retrans = tp->retrans_out;
2088
2089                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
2090                         if (!(flag&FLAG_ECE))
2091                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2092                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2093                         TCP_ECN_queue_cwr(tp);
2094                 }
2095
2096                 tp->bytes_acked = 0;
2097                 tp->snd_cwnd_cnt = 0;
2098                 tcp_set_ca_state(sk, TCP_CA_Recovery);
2099         }
2100
2101         if (is_dupack || tcp_head_timedout(sk, tp))
2102                 tcp_update_scoreboard(sk, tp);
2103         tcp_cwnd_down(sk);
2104         tcp_xmit_retransmit_queue(sk);
2105 }
2106
2107 /* Read draft-ietf-tcplw-high-performance before mucking
2108  * with this code. (Supersedes RFC1323)
2109  */
2110 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
2111 {
2112         /* RTTM Rule: A TSecr value received in a segment is used to
2113          * update the averaged RTT measurement only if the segment
2114          * acknowledges some new data, i.e., only if it advances the
2115          * left edge of the send window.
2116          *
2117          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2118          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
2119          *
2120          * Changed: reset backoff as soon as we see the first valid sample.
2121          * If we do not, we get strongly overestimated rto. With timestamps
2122          * samples are accepted even from very old segments: f.e., when rtt=1
2123          * increases to 8, we retransmit 5 times and after 8 seconds delayed
2124          * answer arrives rto becomes 120 seconds! If at least one of segments
2125          * in window is lost... Voila.                          --ANK (010210)
2126          */
2127         struct tcp_sock *tp = tcp_sk(sk);
2128         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
2129         tcp_rtt_estimator(sk, seq_rtt);
2130         tcp_set_rto(sk);
2131         inet_csk(sk)->icsk_backoff = 0;
2132         tcp_bound_rto(sk);
2133 }
2134
2135 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
2136 {
2137         /* We don't have a timestamp. Can only use
2138          * packets that are not retransmitted to determine
2139          * rtt estimates. Also, we must not reset the
2140          * backoff for rto until we get a non-retransmitted
2141          * packet. This allows us to deal with a situation
2142          * where the network delay has increased suddenly.
2143          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
2144          */
2145
2146         if (flag & FLAG_RETRANS_DATA_ACKED)
2147                 return;
2148
2149         tcp_rtt_estimator(sk, seq_rtt);
2150         tcp_set_rto(sk);
2151         inet_csk(sk)->icsk_backoff = 0;
2152         tcp_bound_rto(sk);
2153 }
2154
2155 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
2156                                       const s32 seq_rtt)
2157 {
2158         const struct tcp_sock *tp = tcp_sk(sk);
2159         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
2160         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
2161                 tcp_ack_saw_tstamp(sk, flag);
2162         else if (seq_rtt >= 0)
2163                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
2164 }
2165
2166 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
2167                            u32 in_flight, int good)
2168 {
2169         const struct inet_connection_sock *icsk = inet_csk(sk);
2170         icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
2171         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2172 }
2173
2174 /* Restart timer after forward progress on connection.
2175  * RFC2988 recommends to restart timer to now+rto.
2176  */
2177
2178 static void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
2179 {
2180         if (!tp->packets_out) {
2181                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2182         } else {
2183                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2184         }
2185 }
2186
2187 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
2188                          __u32 now, __s32 *seq_rtt)
2189 {
2190         struct tcp_sock *tp = tcp_sk(sk);
2191         struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2192         __u32 seq = tp->snd_una;
2193         __u32 packets_acked;
2194         int acked = 0;
2195
2196         /* If we get here, the whole TSO packet has not been
2197          * acked.
2198          */
2199         BUG_ON(!after(scb->end_seq, seq));
2200
2201         packets_acked = tcp_skb_pcount(skb);
2202         if (tcp_trim_head(sk, skb, seq - scb->seq))
2203                 return 0;
2204         packets_acked -= tcp_skb_pcount(skb);
2205
2206         if (packets_acked) {
2207                 __u8 sacked = scb->sacked;
2208
2209                 acked |= FLAG_DATA_ACKED;
2210                 if (sacked) {
2211                         if (sacked & TCPCB_RETRANS) {
2212                                 if (sacked & TCPCB_SACKED_RETRANS)
2213                                         tp->retrans_out -= packets_acked;
2214                                 acked |= FLAG_RETRANS_DATA_ACKED;
2215                                 *seq_rtt = -1;
2216                         } else if (*seq_rtt < 0)
2217                                 *seq_rtt = now - scb->when;
2218                         if (sacked & TCPCB_SACKED_ACKED)
2219                                 tp->sacked_out -= packets_acked;
2220                         if (sacked & TCPCB_LOST)
2221                                 tp->lost_out -= packets_acked;
2222                         if (sacked & TCPCB_URG) {
2223                                 if (tp->urg_mode &&
2224                                     !before(seq, tp->snd_up))
2225                                         tp->urg_mode = 0;
2226                         }
2227                 } else if (*seq_rtt < 0)
2228                         *seq_rtt = now - scb->when;
2229
2230                 if (tp->fackets_out) {
2231                         __u32 dval = min(tp->fackets_out, packets_acked);
2232                         tp->fackets_out -= dval;
2233                 }
2234                 tp->packets_out -= packets_acked;
2235
2236                 BUG_ON(tcp_skb_pcount(skb) == 0);
2237                 BUG_ON(!before(scb->seq, scb->end_seq));
2238         }
2239
2240         return acked;
2241 }
2242
2243 static u32 tcp_usrtt(struct timeval *tv)
2244 {
2245         struct timeval now;
2246
2247         do_gettimeofday(&now);
2248         return (now.tv_sec - tv->tv_sec) * 1000000 + (now.tv_usec - tv->tv_usec);
2249 }
2250
2251 /* Remove acknowledged frames from the retransmission queue. */
2252 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
2253 {
2254         struct tcp_sock *tp = tcp_sk(sk);
2255         const struct inet_connection_sock *icsk = inet_csk(sk);
2256         struct sk_buff *skb;
2257         __u32 now = tcp_time_stamp;
2258         int acked = 0;
2259         __s32 seq_rtt = -1;
2260         u32 pkts_acked = 0;
2261         void (*rtt_sample)(struct sock *sk, u32 usrtt)
2262                 = icsk->icsk_ca_ops->rtt_sample;
2263         struct timeval tv = { .tv_sec = 0, .tv_usec = 0 };
2264
2265         while ((skb = skb_peek(&sk->sk_write_queue)) &&
2266                skb != sk->sk_send_head) {
2267                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2268                 __u8 sacked = scb->sacked;
2269
2270                 /* If our packet is before the ack sequence we can
2271                  * discard it as it's confirmed to have arrived at
2272                  * the other end.
2273                  */
2274                 if (after(scb->end_seq, tp->snd_una)) {
2275                         if (tcp_skb_pcount(skb) > 1 &&
2276                             after(tp->snd_una, scb->seq))
2277                                 acked |= tcp_tso_acked(sk, skb,
2278                                                        now, &seq_rtt);
2279                         break;
2280                 }
2281
2282                 /* Initial outgoing SYN's get put onto the write_queue
2283                  * just like anything else we transmit.  It is not
2284                  * true data, and if we misinform our callers that
2285                  * this ACK acks real data, we will erroneously exit
2286                  * connection startup slow start one packet too
2287                  * quickly.  This is severely frowned upon behavior.
2288                  */
2289                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2290                         acked |= FLAG_DATA_ACKED;
2291                         ++pkts_acked;
2292                 } else {
2293                         acked |= FLAG_SYN_ACKED;
2294                         tp->retrans_stamp = 0;
2295                 }
2296
2297                 /* MTU probing checks */
2298                 if (icsk->icsk_mtup.probe_size) {
2299                         if (!after(tp->mtu_probe.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {
2300                                 tcp_mtup_probe_success(sk, skb);
2301                         }
2302                 }
2303
2304                 if (sacked) {
2305                         if (sacked & TCPCB_RETRANS) {
2306                                 if(sacked & TCPCB_SACKED_RETRANS)
2307                                         tp->retrans_out -= tcp_skb_pcount(skb);
2308                                 acked |= FLAG_RETRANS_DATA_ACKED;
2309                                 seq_rtt = -1;
2310                         } else if (seq_rtt < 0) {
2311                                 seq_rtt = now - scb->when;
2312                                 skb_get_timestamp(skb, &tv);
2313                         }
2314                         if (sacked & TCPCB_SACKED_ACKED)
2315                                 tp->sacked_out -= tcp_skb_pcount(skb);
2316                         if (sacked & TCPCB_LOST)
2317                                 tp->lost_out -= tcp_skb_pcount(skb);
2318                         if (sacked & TCPCB_URG) {
2319                                 if (tp->urg_mode &&
2320                                     !before(scb->end_seq, tp->snd_up))
2321                                         tp->urg_mode = 0;
2322                         }
2323                 } else if (seq_rtt < 0) {
2324                         seq_rtt = now - scb->when;
2325                         skb_get_timestamp(skb, &tv);
2326                 }
2327                 tcp_dec_pcount_approx(&tp->fackets_out, skb);
2328                 tcp_packets_out_dec(tp, skb);
2329                 __skb_unlink(skb, &sk->sk_write_queue);
2330                 sk_stream_free_skb(sk, skb);
2331                 clear_all_retrans_hints(tp);
2332         }
2333
2334         if (acked&FLAG_ACKED) {
2335                 tcp_ack_update_rtt(sk, acked, seq_rtt);
2336                 tcp_ack_packets_out(sk, tp);
2337                 if (rtt_sample && !(acked & FLAG_RETRANS_DATA_ACKED))
2338                         (*rtt_sample)(sk, tcp_usrtt(&tv));
2339
2340                 if (icsk->icsk_ca_ops->pkts_acked)
2341                         icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
2342         }
2343
2344 #if FASTRETRANS_DEBUG > 0
2345         BUG_TRAP((int)tp->sacked_out >= 0);
2346         BUG_TRAP((int)tp->lost_out >= 0);
2347         BUG_TRAP((int)tp->retrans_out >= 0);
2348         if (!tp->packets_out && tp->rx_opt.sack_ok) {
2349                 const struct inet_connection_sock *icsk = inet_csk(sk);
2350                 if (tp->lost_out) {
2351                         printk(KERN_DEBUG "Leak l=%u %d\n",
2352                                tp->lost_out, icsk->icsk_ca_state);
2353                         tp->lost_out = 0;
2354                 }
2355                 if (tp->sacked_out) {
2356                         printk(KERN_DEBUG "Leak s=%u %d\n",
2357                                tp->sacked_out, icsk->icsk_ca_state);
2358                         tp->sacked_out = 0;
2359                 }
2360                 if (tp->retrans_out) {
2361                         printk(KERN_DEBUG "Leak r=%u %d\n",
2362                                tp->retrans_out, icsk->icsk_ca_state);
2363                         tp->retrans_out = 0;
2364                 }
2365         }
2366 #endif
2367         *seq_rtt_p = seq_rtt;
2368         return acked;
2369 }
2370
2371 static void tcp_ack_probe(struct sock *sk)
2372 {
2373         const struct tcp_sock *tp = tcp_sk(sk);
2374         struct inet_connection_sock *icsk = inet_csk(sk);
2375
2376         /* Was it a usable window open? */
2377
2378         if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
2379                    tp->snd_una + tp->snd_wnd)) {
2380                 icsk->icsk_backoff = 0;
2381                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2382                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2383                  * This function is not for random using!
2384                  */
2385         } else {
2386                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2387                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2388                                           TCP_RTO_MAX);
2389         }
2390 }
2391
2392 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2393 {
2394         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2395                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2396 }
2397
2398 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2399 {
2400         const struct tcp_sock *tp = tcp_sk(sk);
2401         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2402                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2403 }
2404
2405 /* Check that window update is acceptable.
2406  * The function assumes that snd_una<=ack<=snd_next.
2407  */
2408 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2409                                         const u32 ack_seq, const u32 nwin)
2410 {
2411         return (after(ack, tp->snd_una) ||
2412                 after(ack_seq, tp->snd_wl1) ||
2413                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2414 }
2415
2416 /* Update our send window.
2417  *
2418  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2419  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2420  */
2421 static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
2422                                  struct sk_buff *skb, u32 ack, u32 ack_seq)
2423 {
2424         int flag = 0;
2425         u32 nwin = ntohs(skb->h.th->window);
2426
2427         if (likely(!skb->h.th->syn))
2428                 nwin <<= tp->rx_opt.snd_wscale;
2429
2430         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2431                 flag |= FLAG_WIN_UPDATE;
2432                 tcp_update_wl(tp, ack, ack_seq);
2433
2434                 if (tp->snd_wnd != nwin) {
2435                         tp->snd_wnd = nwin;
2436
2437                         /* Note, it is the only place, where
2438                          * fast path is recovered for sending TCP.
2439                          */
2440                         tp->pred_flags = 0;
2441                         tcp_fast_path_check(sk, tp);
2442
2443                         if (nwin > tp->max_window) {
2444                                 tp->max_window = nwin;
2445                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
2446                         }
2447                 }
2448         }
2449
2450         tp->snd_una = ack;
2451
2452         return flag;
2453 }
2454
2455 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
2456 {
2457         struct tcp_sock *tp = tcp_sk(sk);
2458         
2459         tcp_sync_left_out(tp);
2460         
2461         if (tp->snd_una == prior_snd_una ||
2462             !before(tp->snd_una, tp->frto_highmark)) {
2463                 /* RTO was caused by loss, start retransmitting in
2464                  * go-back-N slow start
2465                  */
2466                 tcp_enter_frto_loss(sk);
2467                 return;
2468         }
2469
2470         if (tp->frto_counter == 1) {
2471                 /* First ACK after RTO advances the window: allow two new
2472                  * segments out.
2473                  */
2474                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2475         } else {
2476                 /* Also the second ACK after RTO advances the window.
2477                  * The RTO was likely spurious. Reduce cwnd and continue
2478                  * in congestion avoidance
2479                  */
2480                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2481                 tcp_moderate_cwnd(tp);
2482         }
2483
2484         /* F-RTO affects on two new ACKs following RTO.
2485          * At latest on third ACK the TCP behavior is back to normal.
2486          */
2487         tp->frto_counter = (tp->frto_counter + 1) % 3;
2488 }
2489
2490 /* This routine deals with incoming acks, but not outgoing ones. */
2491 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2492 {
2493         struct inet_connection_sock *icsk = inet_csk(sk);
2494         struct tcp_sock *tp = tcp_sk(sk);
2495         u32 prior_snd_una = tp->snd_una;
2496         u32 ack_seq = TCP_SKB_CB(skb)->seq;
2497         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2498         u32 prior_in_flight;
2499         s32 seq_rtt;
2500         int prior_packets;
2501
2502         /* If the ack is newer than sent or older than previous acks
2503          * then we can probably ignore it.
2504          */
2505         if (after(ack, tp->snd_nxt))
2506                 goto uninteresting_ack;
2507
2508         if (before(ack, prior_snd_una))
2509                 goto old_ack;
2510
2511         if (sysctl_tcp_abc) {
2512                 if (icsk->icsk_ca_state < TCP_CA_CWR)
2513                         tp->bytes_acked += ack - prior_snd_una;
2514                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
2515                         /* we assume just one segment left network */
2516                         tp->bytes_acked += min(ack - prior_snd_una, tp->mss_cache);
2517         }
2518
2519         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
2520                 /* Window is constant, pure forward advance.
2521                  * No more checks are required.
2522                  * Note, we use the fact that SND.UNA>=SND.WL2.
2523                  */
2524                 tcp_update_wl(tp, ack, ack_seq);
2525                 tp->snd_una = ack;
2526                 flag |= FLAG_WIN_UPDATE;
2527
2528                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
2529
2530                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
2531         } else {
2532                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
2533                         flag |= FLAG_DATA;
2534                 else
2535                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
2536
2537                 flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);
2538
2539                 if (TCP_SKB_CB(skb)->sacked)
2540                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2541
2542                 if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
2543                         flag |= FLAG_ECE;
2544
2545                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
2546         }
2547
2548         /* We passed data and got it acked, remove any soft error
2549          * log. Something worked...
2550          */
2551         sk->sk_err_soft = 0;
2552         tp->rcv_tstamp = tcp_time_stamp;
2553         prior_packets = tp->packets_out;
2554         if (!prior_packets)
2555                 goto no_queue;
2556
2557         prior_in_flight = tcp_packets_in_flight(tp);
2558
2559         /* See if we can take anything off of the retransmit queue. */
2560         flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
2561
2562         if (tp->frto_counter)
2563                 tcp_process_frto(sk, prior_snd_una);
2564
2565         if (tcp_ack_is_dubious(sk, flag)) {
2566                 /* Advance CWND, if state allows this. */
2567                 if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
2568                         tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
2569                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2570         } else {
2571                 if ((flag & FLAG_DATA_ACKED))
2572                         tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
2573         }
2574
2575         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2576                 dst_confirm(sk->sk_dst_cache);
2577
2578         return 1;
2579
2580 no_queue:
2581         icsk->icsk_probes_out = 0;
2582
2583         /* If this ack opens up a zero window, clear backoff.  It was
2584          * being used to time the probes, and is probably far higher than
2585          * it needs to be for normal retransmission.
2586          */
2587         if (sk->sk_send_head)
2588                 tcp_ack_probe(sk);
2589         return 1;
2590
2591 old_ack:
2592         if (TCP_SKB_CB(skb)->sacked)
2593                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2594
2595 uninteresting_ack:
2596         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2597         return 0;
2598 }
2599
2600
2601 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2602  * But, this can also be called on packets in the established flow when
2603  * the fast version below fails.
2604  */
2605 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2606 {
2607         unsigned char *ptr;
2608         struct tcphdr *th = skb->h.th;
2609         int length=(th->doff*4)-sizeof(struct tcphdr);
2610
2611         ptr = (unsigned char *)(th + 1);
2612         opt_rx->saw_tstamp = 0;
2613
2614         while(length>0) {
2615                 int opcode=*ptr++;
2616                 int opsize;
2617
2618                 switch (opcode) {
2619                         case TCPOPT_EOL:
2620                                 return;
2621                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
2622                                 length--;
2623                                 continue;
2624                         default:
2625                                 opsize=*ptr++;
2626                                 if (opsize < 2) /* "silly options" */
2627                                         return;
2628                                 if (opsize > length)
2629                                         return; /* don't parse partial options */
2630                                 switch(opcode) {
2631                                 case TCPOPT_MSS:
2632                                         if(opsize==TCPOLEN_MSS && th->syn && !estab) {
2633                                                 u16 in_mss = ntohs(get_unaligned((__be16 *)ptr));
2634                                                 if (in_mss) {
2635                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2636                                                                 in_mss = opt_rx->user_mss;
2637                                                         opt_rx->mss_clamp = in_mss;
2638                                                 }
2639                                         }
2640                                         break;
2641                                 case TCPOPT_WINDOW:
2642                                         if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
2643                                                 if (sysctl_tcp_window_scaling) {
2644                                                         __u8 snd_wscale = *(__u8 *) ptr;
2645                                                         opt_rx->wscale_ok = 1;
2646                                                         if (snd_wscale > 14) {
2647                                                                 if(net_ratelimit())
2648                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
2649                                                                                "scaling value %d >14 received.\n",
2650                                                                                snd_wscale);
2651                                                                 snd_wscale = 14;
2652                                                         }
2653                                                         opt_rx->snd_wscale = snd_wscale;
2654                                                 }
2655                                         break;
2656                                 case TCPOPT_TIMESTAMP:
2657                                         if(opsize==TCPOLEN_TIMESTAMP) {
2658                                                 if ((estab && opt_rx->tstamp_ok) ||
2659                                                     (!estab && sysctl_tcp_timestamps)) {
2660                                                         opt_rx->saw_tstamp = 1;
2661                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__be32 *)ptr));
2662                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4)));
2663                                                 }
2664                                         }
2665                                         break;
2666                                 case TCPOPT_SACK_PERM:
2667                                         if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2668                                                 if (sysctl_tcp_sack) {
2669                                                         opt_rx->sack_ok = 1;
2670                                                         tcp_sack_reset(opt_rx);
2671                                                 }
2672                                         }
2673                                         break;
2674
2675                                 case TCPOPT_SACK:
2676                                         if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2677                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2678                                            opt_rx->sack_ok) {
2679                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2680                                         }
2681 #ifdef CONFIG_TCP_MD5SIG
2682                                 case TCPOPT_MD5SIG:
2683                                         /*
2684                                          * The MD5 Hash has already been
2685                                          * checked (see tcp_v{4,6}_do_rcv()).
2686                                          */
2687                                         break;
2688 #endif
2689                                 };
2690                                 ptr+=opsize-2;
2691                                 length-=opsize;
2692                 };
2693         }
2694 }
2695
2696 /* Fast parse options. This hopes to only see timestamps.
2697  * If it is wrong it falls back on tcp_parse_options().
2698  */
2699 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2700                                   struct tcp_sock *tp)
2701 {
2702         if (th->doff == sizeof(struct tcphdr)>>2) {
2703                 tp->rx_opt.saw_tstamp = 0;
2704                 return 0;
2705         } else if (tp->rx_opt.tstamp_ok &&
2706                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2707                 __be32 *ptr = (__be32 *)(th + 1);
2708                 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2709                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2710                         tp->rx_opt.saw_tstamp = 1;
2711                         ++ptr;
2712                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
2713                         ++ptr;
2714                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2715                         return 1;
2716                 }
2717         }
2718         tcp_parse_options(skb, &tp->rx_opt, 1);
2719         return 1;
2720 }
2721
2722 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2723 {
2724         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2725         tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
2726 }
2727
2728 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2729 {
2730         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2731                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
2732                  * extra check below makes sure this can only happen
2733                  * for pure ACK frames.  -DaveM
2734                  *
2735                  * Not only, also it occurs for expired timestamps.
2736                  */
2737
2738                 if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2739                    xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2740                         tcp_store_ts_recent(tp);
2741         }
2742 }
2743
2744 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2745  *
2746  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2747  * it can pass through stack. So, the following predicate verifies that
2748  * this segment is not used for anything but congestion avoidance or
2749  * fast retransmit. Moreover, we even are able to eliminate most of such
2750  * second order effects, if we apply some small "replay" window (~RTO)
2751  * to timestamp space.
2752  *
2753  * All these measures still do not guarantee that we reject wrapped ACKs
2754  * on networks with high bandwidth, when sequence space is recycled fastly,
2755  * but it guarantees that such events will be very rare and do not affect
2756  * connection seriously. This doesn't look nice, but alas, PAWS is really
2757  * buggy extension.
2758  *
2759  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
2760  * states that events when retransmit arrives after original data are rare.
2761  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
2762  * the biggest problem on large power networks even with minor reordering.
2763  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
2764  * up to bandwidth of 18Gigabit/sec. 8) ]
2765  */
2766
2767 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
2768 {
2769         struct tcp_sock *tp = tcp_sk(sk);
2770         struct tcphdr *th = skb->h.th;
2771         u32 seq = TCP_SKB_CB(skb)->seq;
2772         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2773
2774         return (/* 1. Pure ACK with correct sequence number. */
2775                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
2776
2777                 /* 2. ... and duplicate ACK. */
2778                 ack == tp->snd_una &&
2779
2780                 /* 3. ... and does not update window. */
2781                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
2782
2783                 /* 4. ... and sits in replay window. */
2784                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
2785 }
2786
2787 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
2788 {
2789         const struct tcp_sock *tp = tcp_sk(sk);
2790         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
2791                 xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2792                 !tcp_disordered_ack(sk, skb));
2793 }
2794
2795 /* Check segment sequence number for validity.
2796  *
2797  * Segment controls are considered valid, if the segment
2798  * fits to the window after truncation to the window. Acceptability
2799  * of data (and SYN, FIN, of course) is checked separately.
2800  * See tcp_data_queue(), for example.
2801  *
2802  * Also, controls (RST is main one) are accepted using RCV.WUP instead
2803  * of RCV.NXT. Peer still did not advance his SND.UNA when we
2804  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
2805  * (borrowed from freebsd)
2806  */
2807
2808 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
2809 {
2810         return  !before(end_seq, tp->rcv_wup) &&
2811                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
2812 }
2813
2814 /* When we get a reset we do this. */
2815 static void tcp_reset(struct sock *sk)
2816 {
2817         /* We want the right error as BSD sees it (and indeed as we do). */
2818         switch (sk->sk_state) {
2819                 case TCP_SYN_SENT:
2820                         sk->sk_err = ECONNREFUSED;
2821                         break;
2822                 case TCP_CLOSE_WAIT:
2823                         sk->sk_err = EPIPE;
2824                         break;
2825                 case TCP_CLOSE:
2826                         return;
2827                 default:
2828                         sk->sk_err = ECONNRESET;
2829         }
2830
2831         if (!sock_flag(sk, SOCK_DEAD))
2832                 sk->sk_error_report(sk);
2833
2834         tcp_done(sk);
2835 }
2836
2837 /*
2838  *      Process the FIN bit. This now behaves as it is supposed to work
2839  *      and the FIN takes effect when it is validly part of sequence
2840  *      space. Not before when we get holes.
2841  *
2842  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
2843  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
2844  *      TIME-WAIT)
2845  *
2846  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
2847  *      close and we go into CLOSING (and later onto TIME-WAIT)
2848  *
2849  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
2850  */
2851 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
2852 {
2853         struct tcp_sock *tp = tcp_sk(sk);
2854
2855         inet_csk_schedule_ack(sk);
2856
2857         sk->sk_shutdown |= RCV_SHUTDOWN;
2858         sock_set_flag(sk, SOCK_DONE);
2859
2860         switch (sk->sk_state) {
2861                 case TCP_SYN_RECV:
2862                 case TCP_ESTABLISHED:
2863                         /* Move to CLOSE_WAIT */
2864                         tcp_set_state(sk, TCP_CLOSE_WAIT);
2865                         inet_csk(sk)->icsk_ack.pingpong = 1;
2866                         break;
2867
2868                 case TCP_CLOSE_WAIT:
2869                 case TCP_CLOSING:
2870                         /* Received a retransmission of the FIN, do
2871                          * nothing.
2872                          */
2873                         break;
2874                 case TCP_LAST_ACK:
2875                         /* RFC793: Remain in the LAST-ACK state. */
2876                         break;
2877
2878                 case TCP_FIN_WAIT1:
2879                         /* This case occurs when a simultaneous close
2880                          * happens, we must ack the received FIN and
2881                          * enter the CLOSING state.
2882                          */
2883                         tcp_send_ack(sk);
2884                         tcp_set_state(sk, TCP_CLOSING);
2885                         break;
2886                 case TCP_FIN_WAIT2:
2887                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
2888                         tcp_send_ack(sk);
2889                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
2890                         break;
2891                 default:
2892                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
2893                          * cases we should never reach this piece of code.
2894                          */
2895                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
2896                                __FUNCTION__, sk->sk_state);
2897                         break;
2898         };
2899
2900         /* It _is_ possible, that we have something out-of-order _after_ FIN.
2901          * Probably, we should reset in this case. For now drop them.
2902          */
2903         __skb_queue_purge(&tp->out_of_order_queue);
2904         if (tp->rx_opt.sack_ok)
2905                 tcp_sack_reset(&tp->rx_opt);
2906         sk_stream_mem_reclaim(sk);
2907
2908         if (!sock_flag(sk, SOCK_DEAD)) {
2909                 sk->sk_state_change(sk);
2910
2911                 /* Do not send POLL_HUP for half duplex close. */
2912                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
2913                     sk->sk_state == TCP_CLOSE)
2914                         sk_wake_async(sk, 1, POLL_HUP);
2915                 else
2916                         sk_wake_async(sk, 1, POLL_IN);
2917         }
2918 }
2919
2920 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
2921 {
2922         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
2923                 if (before(seq, sp->start_seq))
2924                         sp->start_seq = seq;
2925                 if (after(end_seq, sp->end_seq))
2926                         sp->end_seq = end_seq;
2927                 return 1;
2928         }
2929         return 0;
2930 }
2931
2932 static void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
2933 {
2934         if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2935                 if (before(seq, tp->rcv_nxt))
2936                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
2937                 else
2938                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
2939
2940                 tp->rx_opt.dsack = 1;
2941                 tp->duplicate_sack[0].start_seq = seq;
2942                 tp->duplicate_sack[0].end_seq = end_seq;
2943                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
2944         }
2945 }
2946
2947 static void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
2948 {
2949         if (!tp->rx_opt.dsack)
2950                 tcp_dsack_set(tp, seq, end_seq);
2951         else
2952                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
2953 }
2954
2955 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
2956 {
2957         struct tcp_sock *tp = tcp_sk(sk);
2958
2959         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
2960             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2961                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2962                 tcp_enter_quickack_mode(sk);
2963
2964                 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2965                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2966
2967                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
2968                                 end_seq = tp->rcv_nxt;
2969                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
2970                 }
2971         }
2972
2973         tcp_send_ack(sk);
2974 }
2975
2976 /* These routines update the SACK block as out-of-order packets arrive or
2977  * in-order packets close up the sequence space.
2978  */
2979 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
2980 {
2981         int this_sack;
2982         struct tcp_sack_block *sp = &tp->selective_acks[0];
2983         struct tcp_sack_block *swalk = sp+1;
2984
2985         /* See if the recent change to the first SACK eats into
2986          * or hits the sequence space of other SACK blocks, if so coalesce.
2987          */
2988         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
2989                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
2990                         int i;
2991
2992                         /* Zap SWALK, by moving every further SACK up by one slot.
2993                          * Decrease num_sacks.
2994                          */
2995                         tp->rx_opt.num_sacks--;
2996                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2997                         for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
2998                                 sp[i] = sp[i+1];
2999                         continue;
3000                 }
3001                 this_sack++, swalk++;
3002         }
3003 }
3004
3005 static inline void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
3006 {
3007         __u32 tmp;
3008
3009         tmp = sack1->start_seq;
3010         sack1->start_seq = sack2->start_seq;
3011         sack2->start_seq = tmp;
3012
3013         tmp = sack1->end_seq;
3014         sack1->end_seq = sack2->end_seq;
3015         sack2->end_seq = tmp;
3016 }
3017
3018 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
3019 {
3020         struct tcp_sock *tp = tcp_sk(sk);
3021         struct tcp_sack_block *sp = &tp->selective_acks[0];
3022         int cur_sacks = tp->rx_opt.num_sacks;
3023         int this_sack;
3024
3025         if (!cur_sacks)
3026                 goto new_sack;
3027
3028         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
3029                 if (tcp_sack_extend(sp, seq, end_seq)) {
3030                         /* Rotate this_sack to the first one. */
3031                         for (; this_sack>0; this_sack--, sp--)
3032                                 tcp_sack_swap(sp, sp-1);
3033                         if (cur_sacks > 1)
3034                                 tcp_sack_maybe_coalesce(tp);
3035                         return;
3036                 }
3037         }
3038
3039         /* Could not find an adjacent existing SACK, build a new one,
3040          * put it at the front, and shift everyone else down.  We
3041          * always know there is at least one SACK present already here.
3042          *
3043          * If the sack array is full, forget about the last one.
3044          */
3045         if (this_sack >= 4) {