Merge branch 'for-linus' of master.kernel.org:/pub/scm/linux/kernel/git/shaggy/jfs-2.6
[linux-2.6] / 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 presnce of
46  *                                      timestamps.
47  *              Andrey Savochkin:       Check sequence numbers correctly when
48  *                                      removing SACKs due to in sequence incoming
49  *                                      data segments.
50  *              Andi Kleen:             Make sure we never ack data there is not
51  *                                      enough room for. Also make this condition
52  *                                      a fatal error if it might still happen.
53  *              Andi Kleen:             Add tcp_measure_rcv_mss to make 
54  *                                      connections with MSS<min(MTU,ann. MSS)
55  *                                      work without delayed acks. 
56  *              Andi Kleen:             Process packets with PSH set in the
57  *                                      fast path.
58  *              J Hadi Salim:           ECN support
59  *              Andrei Gurtov,
60  *              Pasi Sarolahti,
61  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
62  *                                      engine. Lots of bugs are found.
63  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
64  */
65
66 #include <linux/config.h>
67 #include <linux/mm.h>
68 #include <linux/module.h>
69 #include <linux/sysctl.h>
70 #include <net/tcp.h>
71 #include <net/inet_common.h>
72 #include <linux/ipsec.h>
73 #include <asm/unaligned.h>
74
75 int sysctl_tcp_timestamps = 1;
76 int sysctl_tcp_window_scaling = 1;
77 int sysctl_tcp_sack = 1;
78 int sysctl_tcp_fack = 1;
79 int sysctl_tcp_reordering = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn;
81 int sysctl_tcp_dsack = 1;
82 int sysctl_tcp_app_win = 31;
83 int sysctl_tcp_adv_win_scale = 2;
84
85 int sysctl_tcp_stdurg;
86 int sysctl_tcp_rfc1337;
87 int sysctl_tcp_max_orphans = NR_FILE;
88 int sysctl_tcp_frto;
89 int sysctl_tcp_nometrics_save;
90
91 int sysctl_tcp_moderate_rcvbuf = 1;
92
93 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
94 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
95 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
96 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
97 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
98 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
99 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
100 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
101 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
102
103 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
104 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
105 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
106 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
107
108 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
109 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
110 #define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
111
112 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
113
114 /* Adapt the MSS value used to make delayed ack decision to the 
115  * real world.
116  */ 
117 static inline void tcp_measure_rcv_mss(struct sock *sk,
118                                        const struct sk_buff *skb)
119 {
120         struct inet_connection_sock *icsk = inet_csk(sk);
121         const unsigned int lss = icsk->icsk_ack.last_seg_size; 
122         unsigned int len;
123
124         icsk->icsk_ack.last_seg_size = 0; 
125
126         /* skb->len may jitter because of SACKs, even if peer
127          * sends good full-sized frames.
128          */
129         len = skb->len;
130         if (len >= icsk->icsk_ack.rcv_mss) {
131                 icsk->icsk_ack.rcv_mss = len;
132         } else {
133                 /* Otherwise, we make more careful check taking into account,
134                  * that SACKs block is variable.
135                  *
136                  * "len" is invariant segment length, including TCP header.
137                  */
138                 len += skb->data - skb->h.raw;
139                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
140                     /* If PSH is not set, packet should be
141                      * full sized, provided peer TCP is not badly broken.
142                      * This observation (if it is correct 8)) allows
143                      * to handle super-low mtu links fairly.
144                      */
145                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
146                      !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) {
147                         /* Subtract also invariant (if peer is RFC compliant),
148                          * tcp header plus fixed timestamp option length.
149                          * Resulting "len" is MSS free of SACK jitter.
150                          */
151                         len -= tcp_sk(sk)->tcp_header_len;
152                         icsk->icsk_ack.last_seg_size = len;
153                         if (len == lss) {
154                                 icsk->icsk_ack.rcv_mss = len;
155                                 return;
156                         }
157                 }
158                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
159         }
160 }
161
162 static void tcp_incr_quickack(struct sock *sk)
163 {
164         struct inet_connection_sock *icsk = inet_csk(sk);
165         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
166
167         if (quickacks==0)
168                 quickacks=2;
169         if (quickacks > icsk->icsk_ack.quick)
170                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
171 }
172
173 void tcp_enter_quickack_mode(struct sock *sk)
174 {
175         struct inet_connection_sock *icsk = inet_csk(sk);
176         tcp_incr_quickack(sk);
177         icsk->icsk_ack.pingpong = 0;
178         icsk->icsk_ack.ato = TCP_ATO_MIN;
179 }
180
181 /* Send ACKs quickly, if "quick" count is not exhausted
182  * and the session is not interactive.
183  */
184
185 static inline int tcp_in_quickack_mode(const struct sock *sk)
186 {
187         const struct inet_connection_sock *icsk = inet_csk(sk);
188         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
189 }
190
191 /* Buffer size and advertised window tuning.
192  *
193  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
194  */
195
196 static void tcp_fixup_sndbuf(struct sock *sk)
197 {
198         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
199                      sizeof(struct sk_buff);
200
201         if (sk->sk_sndbuf < 3 * sndmem)
202                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
203 }
204
205 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
206  *
207  * All tcp_full_space() is split to two parts: "network" buffer, allocated
208  * forward and advertised in receiver window (tp->rcv_wnd) and
209  * "application buffer", required to isolate scheduling/application
210  * latencies from network.
211  * window_clamp is maximal advertised window. It can be less than
212  * tcp_full_space(), in this case tcp_full_space() - window_clamp
213  * is reserved for "application" buffer. The less window_clamp is
214  * the smoother our behaviour from viewpoint of network, but the lower
215  * throughput and the higher sensitivity of the connection to losses. 8)
216  *
217  * rcv_ssthresh is more strict window_clamp used at "slow start"
218  * phase to predict further behaviour of this connection.
219  * It is used for two goals:
220  * - to enforce header prediction at sender, even when application
221  *   requires some significant "application buffer". It is check #1.
222  * - to prevent pruning of receive queue because of misprediction
223  *   of receiver window. Check #2.
224  *
225  * The scheme does not work when sender sends good segments opening
226  * window and then starts to feed us spagetti. But it should work
227  * in common situations. Otherwise, we have to rely on queue collapsing.
228  */
229
230 /* Slow part of check#2. */
231 static int __tcp_grow_window(const struct sock *sk, struct tcp_sock *tp,
232                              const struct sk_buff *skb)
233 {
234         /* Optimize this! */
235         int truesize = tcp_win_from_space(skb->truesize)/2;
236         int window = tcp_full_space(sk)/2;
237
238         while (tp->rcv_ssthresh <= window) {
239                 if (truesize <= skb->len)
240                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
241
242                 truesize >>= 1;
243                 window >>= 1;
244         }
245         return 0;
246 }
247
248 static inline void tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
249                                    struct sk_buff *skb)
250 {
251         /* Check #1 */
252         if (tp->rcv_ssthresh < tp->window_clamp &&
253             (int)tp->rcv_ssthresh < tcp_space(sk) &&
254             !tcp_memory_pressure) {
255                 int incr;
256
257                 /* Check #2. Increase window, if skb with such overhead
258                  * will fit to rcvbuf in future.
259                  */
260                 if (tcp_win_from_space(skb->truesize) <= skb->len)
261                         incr = 2*tp->advmss;
262                 else
263                         incr = __tcp_grow_window(sk, tp, skb);
264
265                 if (incr) {
266                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
267                         inet_csk(sk)->icsk_ack.quick |= 1;
268                 }
269         }
270 }
271
272 /* 3. Tuning rcvbuf, when connection enters established state. */
273
274 static void tcp_fixup_rcvbuf(struct sock *sk)
275 {
276         struct tcp_sock *tp = tcp_sk(sk);
277         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
278
279         /* Try to select rcvbuf so that 4 mss-sized segments
280          * will fit to window and correspoding skbs will fit to our rcvbuf.
281          * (was 3; 4 is minimum to allow fast retransmit to work.)
282          */
283         while (tcp_win_from_space(rcvmem) < tp->advmss)
284                 rcvmem += 128;
285         if (sk->sk_rcvbuf < 4 * rcvmem)
286                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
287 }
288
289 /* 4. Try to fixup all. It is made iimediately after connection enters
290  *    established state.
291  */
292 static void tcp_init_buffer_space(struct sock *sk)
293 {
294         struct tcp_sock *tp = tcp_sk(sk);
295         int maxwin;
296
297         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
298                 tcp_fixup_rcvbuf(sk);
299         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
300                 tcp_fixup_sndbuf(sk);
301
302         tp->rcvq_space.space = tp->rcv_wnd;
303
304         maxwin = tcp_full_space(sk);
305
306         if (tp->window_clamp >= maxwin) {
307                 tp->window_clamp = maxwin;
308
309                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
310                         tp->window_clamp = max(maxwin -
311                                                (maxwin >> sysctl_tcp_app_win),
312                                                4 * tp->advmss);
313         }
314
315         /* Force reservation of one segment. */
316         if (sysctl_tcp_app_win &&
317             tp->window_clamp > 2 * tp->advmss &&
318             tp->window_clamp + tp->advmss > maxwin)
319                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
320
321         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
322         tp->snd_cwnd_stamp = tcp_time_stamp;
323 }
324
325 /* 5. Recalculate window clamp after socket hit its memory bounds. */
326 static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp)
327 {
328         struct inet_connection_sock *icsk = inet_csk(sk);
329         struct sk_buff *skb;
330         unsigned int app_win = tp->rcv_nxt - tp->copied_seq;
331         int ofo_win = 0;
332
333         icsk->icsk_ack.quick = 0;
334
335         skb_queue_walk(&tp->out_of_order_queue, skb) {
336                 ofo_win += skb->len;
337         }
338
339         /* If overcommit is due to out of order segments,
340          * do not clamp window. Try to expand rcvbuf instead.
341          */
342         if (ofo_win) {
343                 if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
344                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
345                     !tcp_memory_pressure &&
346                     atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0])
347                         sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
348                                             sysctl_tcp_rmem[2]);
349         }
350         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) {
351                 app_win += ofo_win;
352                 if (atomic_read(&sk->sk_rmem_alloc) >= 2 * sk->sk_rcvbuf)
353                         app_win >>= 1;
354                 if (app_win > icsk->icsk_ack.rcv_mss)
355                         app_win -= icsk->icsk_ack.rcv_mss;
356                 app_win = max(app_win, 2U*tp->advmss);
357
358                 if (!ofo_win)
359                         tp->window_clamp = min(tp->window_clamp, app_win);
360                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
361         }
362 }
363
364 /* Receiver "autotuning" code.
365  *
366  * The algorithm for RTT estimation w/o timestamps is based on
367  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
368  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
369  *
370  * More detail on this code can be found at
371  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
372  * though this reference is out of date.  A new paper
373  * is pending.
374  */
375 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
376 {
377         u32 new_sample = tp->rcv_rtt_est.rtt;
378         long m = sample;
379
380         if (m == 0)
381                 m = 1;
382
383         if (new_sample != 0) {
384                 /* If we sample in larger samples in the non-timestamp
385                  * case, we could grossly overestimate the RTT especially
386                  * with chatty applications or bulk transfer apps which
387                  * are stalled on filesystem I/O.
388                  *
389                  * Also, since we are only going for a minimum in the
390                  * non-timestamp case, we do not smoothe things out
391                  * else with timestamps disabled convergance takes too
392                  * long.
393                  */
394                 if (!win_dep) {
395                         m -= (new_sample >> 3);
396                         new_sample += m;
397                 } else if (m < new_sample)
398                         new_sample = m << 3;
399         } else {
400                 /* No previous mesaure. */
401                 new_sample = m << 3;
402         }
403
404         if (tp->rcv_rtt_est.rtt != new_sample)
405                 tp->rcv_rtt_est.rtt = new_sample;
406 }
407
408 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
409 {
410         if (tp->rcv_rtt_est.time == 0)
411                 goto new_measure;
412         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
413                 return;
414         tcp_rcv_rtt_update(tp,
415                            jiffies - tp->rcv_rtt_est.time,
416                            1);
417
418 new_measure:
419         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
420         tp->rcv_rtt_est.time = tcp_time_stamp;
421 }
422
423 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
424 {
425         struct tcp_sock *tp = tcp_sk(sk);
426         if (tp->rx_opt.rcv_tsecr &&
427             (TCP_SKB_CB(skb)->end_seq -
428              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
429                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
430 }
431
432 /*
433  * This function should be called every time data is copied to user space.
434  * It calculates the appropriate TCP receive buffer space.
435  */
436 void tcp_rcv_space_adjust(struct sock *sk)
437 {
438         struct tcp_sock *tp = tcp_sk(sk);
439         int time;
440         int space;
441         
442         if (tp->rcvq_space.time == 0)
443                 goto new_measure;
444         
445         time = tcp_time_stamp - tp->rcvq_space.time;
446         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
447             tp->rcv_rtt_est.rtt == 0)
448                 return;
449         
450         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
451
452         space = max(tp->rcvq_space.space, space);
453
454         if (tp->rcvq_space.space != space) {
455                 int rcvmem;
456
457                 tp->rcvq_space.space = space;
458
459                 if (sysctl_tcp_moderate_rcvbuf) {
460                         int new_clamp = space;
461
462                         /* Receive space grows, normalize in order to
463                          * take into account packet headers and sk_buff
464                          * structure overhead.
465                          */
466                         space /= tp->advmss;
467                         if (!space)
468                                 space = 1;
469                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
470                                   16 + sizeof(struct sk_buff));
471                         while (tcp_win_from_space(rcvmem) < tp->advmss)
472                                 rcvmem += 128;
473                         space *= rcvmem;
474                         space = min(space, sysctl_tcp_rmem[2]);
475                         if (space > sk->sk_rcvbuf) {
476                                 sk->sk_rcvbuf = space;
477
478                                 /* Make the window clamp follow along.  */
479                                 tp->window_clamp = new_clamp;
480                         }
481                 }
482         }
483         
484 new_measure:
485         tp->rcvq_space.seq = tp->copied_seq;
486         tp->rcvq_space.time = tcp_time_stamp;
487 }
488
489 /* There is something which you must keep in mind when you analyze the
490  * behavior of the tp->ato delayed ack timeout interval.  When a
491  * connection starts up, we want to ack as quickly as possible.  The
492  * problem is that "good" TCP's do slow start at the beginning of data
493  * transmission.  The means that until we send the first few ACK's the
494  * sender will sit on his end and only queue most of his data, because
495  * he can only send snd_cwnd unacked packets at any given time.  For
496  * each ACK we send, he increments snd_cwnd and transmits more of his
497  * queue.  -DaveM
498  */
499 static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
500 {
501         struct inet_connection_sock *icsk = inet_csk(sk);
502         u32 now;
503
504         inet_csk_schedule_ack(sk);
505
506         tcp_measure_rcv_mss(sk, skb);
507
508         tcp_rcv_rtt_measure(tp);
509         
510         now = tcp_time_stamp;
511
512         if (!icsk->icsk_ack.ato) {
513                 /* The _first_ data packet received, initialize
514                  * delayed ACK engine.
515                  */
516                 tcp_incr_quickack(sk);
517                 icsk->icsk_ack.ato = TCP_ATO_MIN;
518         } else {
519                 int m = now - icsk->icsk_ack.lrcvtime;
520
521                 if (m <= TCP_ATO_MIN/2) {
522                         /* The fastest case is the first. */
523                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
524                 } else if (m < icsk->icsk_ack.ato) {
525                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
526                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
527                                 icsk->icsk_ack.ato = icsk->icsk_rto;
528                 } else if (m > icsk->icsk_rto) {
529                         /* Too long gap. Apparently sender falled to
530                          * restart window, so that we send ACKs quickly.
531                          */
532                         tcp_incr_quickack(sk);
533                         sk_stream_mem_reclaim(sk);
534                 }
535         }
536         icsk->icsk_ack.lrcvtime = now;
537
538         TCP_ECN_check_ce(tp, skb);
539
540         if (skb->len >= 128)
541                 tcp_grow_window(sk, tp, skb);
542 }
543
544 /* Called to compute a smoothed rtt estimate. The data fed to this
545  * routine either comes from timestamps, or from segments that were
546  * known _not_ to have been retransmitted [see Karn/Partridge
547  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
548  * piece by Van Jacobson.
549  * NOTE: the next three routines used to be one big routine.
550  * To save cycles in the RFC 1323 implementation it was better to break
551  * it up into three procedures. -- erics
552  */
553 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt, u32 *usrtt)
554 {
555         struct tcp_sock *tp = tcp_sk(sk);
556         const struct inet_connection_sock *icsk = inet_csk(sk);
557         long m = mrtt; /* RTT */
558
559         /*      The following amusing code comes from Jacobson's
560          *      article in SIGCOMM '88.  Note that rtt and mdev
561          *      are scaled versions of rtt and mean deviation.
562          *      This is designed to be as fast as possible 
563          *      m stands for "measurement".
564          *
565          *      On a 1990 paper the rto value is changed to:
566          *      RTO = rtt + 4 * mdev
567          *
568          * Funny. This algorithm seems to be very broken.
569          * These formulae increase RTO, when it should be decreased, increase
570          * too slowly, when it should be incresed fastly, decrease too fastly
571          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
572          * does not matter how to _calculate_ it. Seems, it was trap
573          * that VJ failed to avoid. 8)
574          */
575         if(m == 0)
576                 m = 1;
577         if (tp->srtt != 0) {
578                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
579                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
580                 if (m < 0) {
581                         m = -m;         /* m is now abs(error) */
582                         m -= (tp->mdev >> 2);   /* similar update on mdev */
583                         /* This is similar to one of Eifel findings.
584                          * Eifel blocks mdev updates when rtt decreases.
585                          * This solution is a bit different: we use finer gain
586                          * for mdev in this case (alpha*beta).
587                          * Like Eifel it also prevents growth of rto,
588                          * but also it limits too fast rto decreases,
589                          * happening in pure Eifel.
590                          */
591                         if (m > 0)
592                                 m >>= 3;
593                 } else {
594                         m -= (tp->mdev >> 2);   /* similar update on mdev */
595                 }
596                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
597                 if (tp->mdev > tp->mdev_max) {
598                         tp->mdev_max = tp->mdev;
599                         if (tp->mdev_max > tp->rttvar)
600                                 tp->rttvar = tp->mdev_max;
601                 }
602                 if (after(tp->snd_una, tp->rtt_seq)) {
603                         if (tp->mdev_max < tp->rttvar)
604                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
605                         tp->rtt_seq = tp->snd_nxt;
606                         tp->mdev_max = TCP_RTO_MIN;
607                 }
608         } else {
609                 /* no previous measure. */
610                 tp->srtt = m<<3;        /* take the measured time to be rtt */
611                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
612                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
613                 tp->rtt_seq = tp->snd_nxt;
614         }
615
616         if (icsk->icsk_ca_ops->rtt_sample)
617                 icsk->icsk_ca_ops->rtt_sample(sk, *usrtt);
618 }
619
620 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
621  * routine referred to above.
622  */
623 static inline void tcp_set_rto(struct sock *sk)
624 {
625         const struct tcp_sock *tp = tcp_sk(sk);
626         /* Old crap is replaced with new one. 8)
627          *
628          * More seriously:
629          * 1. If rtt variance happened to be less 50msec, it is hallucination.
630          *    It cannot be less due to utterly erratic ACK generation made
631          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
632          *    to do with delayed acks, because at cwnd>2 true delack timeout
633          *    is invisible. Actually, Linux-2.4 also generates erratic
634          *    ACKs in some curcumstances.
635          */
636         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
637
638         /* 2. Fixups made earlier cannot be right.
639          *    If we do not estimate RTO correctly without them,
640          *    all the algo is pure shit and should be replaced
641          *    with correct one. It is exaclty, which we pretend to do.
642          */
643 }
644
645 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
646  * guarantees that rto is higher.
647  */
648 static inline void tcp_bound_rto(struct sock *sk)
649 {
650         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
651                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
652 }
653
654 /* Save metrics learned by this TCP session.
655    This function is called only, when TCP finishes successfully
656    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
657  */
658 void tcp_update_metrics(struct sock *sk)
659 {
660         struct tcp_sock *tp = tcp_sk(sk);
661         struct dst_entry *dst = __sk_dst_get(sk);
662
663         if (sysctl_tcp_nometrics_save)
664                 return;
665
666         dst_confirm(dst);
667
668         if (dst && (dst->flags&DST_HOST)) {
669                 const struct inet_connection_sock *icsk = inet_csk(sk);
670                 int m;
671
672                 if (icsk->icsk_backoff || !tp->srtt) {
673                         /* This session failed to estimate rtt. Why?
674                          * Probably, no packets returned in time.
675                          * Reset our results.
676                          */
677                         if (!(dst_metric_locked(dst, RTAX_RTT)))
678                                 dst->metrics[RTAX_RTT-1] = 0;
679                         return;
680                 }
681
682                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
683
684                 /* If newly calculated rtt larger than stored one,
685                  * store new one. Otherwise, use EWMA. Remember,
686                  * rtt overestimation is always better than underestimation.
687                  */
688                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
689                         if (m <= 0)
690                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
691                         else
692                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
693                 }
694
695                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
696                         if (m < 0)
697                                 m = -m;
698
699                         /* Scale deviation to rttvar fixed point */
700                         m >>= 1;
701                         if (m < tp->mdev)
702                                 m = tp->mdev;
703
704                         if (m >= dst_metric(dst, RTAX_RTTVAR))
705                                 dst->metrics[RTAX_RTTVAR-1] = m;
706                         else
707                                 dst->metrics[RTAX_RTTVAR-1] -=
708                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
709                 }
710
711                 if (tp->snd_ssthresh >= 0xFFFF) {
712                         /* Slow start still did not finish. */
713                         if (dst_metric(dst, RTAX_SSTHRESH) &&
714                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
715                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
716                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
717                         if (!dst_metric_locked(dst, RTAX_CWND) &&
718                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
719                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
720                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
721                            icsk->icsk_ca_state == TCP_CA_Open) {
722                         /* Cong. avoidance phase, cwnd is reliable. */
723                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
724                                 dst->metrics[RTAX_SSTHRESH-1] =
725                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
726                         if (!dst_metric_locked(dst, RTAX_CWND))
727                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
728                 } else {
729                         /* Else slow start did not finish, cwnd is non-sense,
730                            ssthresh may be also invalid.
731                          */
732                         if (!dst_metric_locked(dst, RTAX_CWND))
733                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
734                         if (dst->metrics[RTAX_SSTHRESH-1] &&
735                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
736                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
737                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
738                 }
739
740                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
741                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
742                             tp->reordering != sysctl_tcp_reordering)
743                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
744                 }
745         }
746 }
747
748 /* Numbers are taken from RFC2414.  */
749 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
750 {
751         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
752
753         if (!cwnd) {
754                 if (tp->mss_cache > 1460)
755                         cwnd = 2;
756                 else
757                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
758         }
759         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
760 }
761
762 /* Initialize metrics on socket. */
763
764 static void tcp_init_metrics(struct sock *sk)
765 {
766         struct tcp_sock *tp = tcp_sk(sk);
767         struct dst_entry *dst = __sk_dst_get(sk);
768
769         if (dst == NULL)
770                 goto reset;
771
772         dst_confirm(dst);
773
774         if (dst_metric_locked(dst, RTAX_CWND))
775                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
776         if (dst_metric(dst, RTAX_SSTHRESH)) {
777                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
778                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
779                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
780         }
781         if (dst_metric(dst, RTAX_REORDERING) &&
782             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
783                 tp->rx_opt.sack_ok &= ~2;
784                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
785         }
786
787         if (dst_metric(dst, RTAX_RTT) == 0)
788                 goto reset;
789
790         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
791                 goto reset;
792
793         /* Initial rtt is determined from SYN,SYN-ACK.
794          * The segment is small and rtt may appear much
795          * less than real one. Use per-dst memory
796          * to make it more realistic.
797          *
798          * A bit of theory. RTT is time passed after "normal" sized packet
799          * is sent until it is ACKed. In normal curcumstances sending small
800          * packets force peer to delay ACKs and calculation is correct too.
801          * The algorithm is adaptive and, provided we follow specs, it
802          * NEVER underestimate RTT. BUT! If peer tries to make some clever
803          * tricks sort of "quick acks" for time long enough to decrease RTT
804          * to low value, and then abruptly stops to do it and starts to delay
805          * ACKs, wait for troubles.
806          */
807         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
808                 tp->srtt = dst_metric(dst, RTAX_RTT);
809                 tp->rtt_seq = tp->snd_nxt;
810         }
811         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
812                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
813                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
814         }
815         tcp_set_rto(sk);
816         tcp_bound_rto(sk);
817         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
818                 goto reset;
819         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
820         tp->snd_cwnd_stamp = tcp_time_stamp;
821         return;
822
823 reset:
824         /* Play conservative. If timestamps are not
825          * supported, TCP will fail to recalculate correct
826          * rtt, if initial rto is too small. FORGET ALL AND RESET!
827          */
828         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
829                 tp->srtt = 0;
830                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
831                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
832         }
833 }
834
835 static void tcp_update_reordering(struct sock *sk, const int metric,
836                                   const int ts)
837 {
838         struct tcp_sock *tp = tcp_sk(sk);
839         if (metric > tp->reordering) {
840                 tp->reordering = min(TCP_MAX_REORDERING, metric);
841
842                 /* This exciting event is worth to be remembered. 8) */
843                 if (ts)
844                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
845                 else if (IsReno(tp))
846                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
847                 else if (IsFack(tp))
848                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
849                 else
850                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
851 #if FASTRETRANS_DEBUG > 1
852                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
853                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
854                        tp->reordering,
855                        tp->fackets_out,
856                        tp->sacked_out,
857                        tp->undo_marker ? tp->undo_retrans : 0);
858 #endif
859                 /* Disable FACK yet. */
860                 tp->rx_opt.sack_ok &= ~2;
861         }
862 }
863
864 /* This procedure tags the retransmission queue when SACKs arrive.
865  *
866  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
867  * Packets in queue with these bits set are counted in variables
868  * sacked_out, retrans_out and lost_out, correspondingly.
869  *
870  * Valid combinations are:
871  * Tag  InFlight        Description
872  * 0    1               - orig segment is in flight.
873  * S    0               - nothing flies, orig reached receiver.
874  * L    0               - nothing flies, orig lost by net.
875  * R    2               - both orig and retransmit are in flight.
876  * L|R  1               - orig is lost, retransmit is in flight.
877  * S|R  1               - orig reached receiver, retrans is still in flight.
878  * (L|S|R is logically valid, it could occur when L|R is sacked,
879  *  but it is equivalent to plain S and code short-curcuits it to S.
880  *  L|S is logically invalid, it would mean -1 packet in flight 8))
881  *
882  * These 6 states form finite state machine, controlled by the following events:
883  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
884  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
885  * 3. Loss detection event of one of three flavors:
886  *      A. Scoreboard estimator decided the packet is lost.
887  *         A'. Reno "three dupacks" marks head of queue lost.
888  *         A''. Its FACK modfication, head until snd.fack is lost.
889  *      B. SACK arrives sacking data transmitted after never retransmitted
890  *         hole was sent out.
891  *      C. SACK arrives sacking SND.NXT at the moment, when the
892  *         segment was retransmitted.
893  * 4. D-SACK added new rule: D-SACK changes any tag to S.
894  *
895  * It is pleasant to note, that state diagram turns out to be commutative,
896  * so that we are allowed not to be bothered by order of our actions,
897  * when multiple events arrive simultaneously. (see the function below).
898  *
899  * Reordering detection.
900  * --------------------
901  * Reordering metric is maximal distance, which a packet can be displaced
902  * in packet stream. With SACKs we can estimate it:
903  *
904  * 1. SACK fills old hole and the corresponding segment was not
905  *    ever retransmitted -> reordering. Alas, we cannot use it
906  *    when segment was retransmitted.
907  * 2. The last flaw is solved with D-SACK. D-SACK arrives
908  *    for retransmitted and already SACKed segment -> reordering..
909  * Both of these heuristics are not used in Loss state, when we cannot
910  * account for retransmits accurately.
911  */
912 static int
913 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
914 {
915         const struct inet_connection_sock *icsk = inet_csk(sk);
916         struct tcp_sock *tp = tcp_sk(sk);
917         unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
918         struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2);
919         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
920         int reord = tp->packets_out;
921         int prior_fackets;
922         u32 lost_retrans = 0;
923         int flag = 0;
924         int i;
925
926         if (!tp->sacked_out)
927                 tp->fackets_out = 0;
928         prior_fackets = tp->fackets_out;
929
930         for (i=0; i<num_sacks; i++, sp++) {
931                 struct sk_buff *skb;
932                 __u32 start_seq = ntohl(sp->start_seq);
933                 __u32 end_seq = ntohl(sp->end_seq);
934                 int fack_count = 0;
935                 int dup_sack = 0;
936
937                 /* Check for D-SACK. */
938                 if (i == 0) {
939                         u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;
940
941                         if (before(start_seq, ack)) {
942                                 dup_sack = 1;
943                                 tp->rx_opt.sack_ok |= 4;
944                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
945                         } else if (num_sacks > 1 &&
946                                    !after(end_seq, ntohl(sp[1].end_seq)) &&
947                                    !before(start_seq, ntohl(sp[1].start_seq))) {
948                                 dup_sack = 1;
949                                 tp->rx_opt.sack_ok |= 4;
950                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
951                         }
952
953                         /* D-SACK for already forgotten data...
954                          * Do dumb counting. */
955                         if (dup_sack &&
956                             !after(end_seq, prior_snd_una) &&
957                             after(end_seq, tp->undo_marker))
958                                 tp->undo_retrans--;
959
960                         /* Eliminate too old ACKs, but take into
961                          * account more or less fresh ones, they can
962                          * contain valid SACK info.
963                          */
964                         if (before(ack, prior_snd_una - tp->max_window))
965                                 return 0;
966                 }
967
968                 /* Event "B" in the comment above. */
969                 if (after(end_seq, tp->high_seq))
970                         flag |= FLAG_DATA_LOST;
971
972                 sk_stream_for_retrans_queue(skb, sk) {
973                         int in_sack, pcount;
974                         u8 sacked;
975
976                         /* The retransmission queue is always in order, so
977                          * we can short-circuit the walk early.
978                          */
979                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
980                                 break;
981
982                         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
983                                 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
984
985                         pcount = tcp_skb_pcount(skb);
986
987                         if (pcount > 1 && !in_sack &&
988                             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
989                                 unsigned int pkt_len;
990
991                                 in_sack = !after(start_seq,
992                                                  TCP_SKB_CB(skb)->seq);
993
994                                 if (!in_sack)
995                                         pkt_len = (start_seq -
996                                                    TCP_SKB_CB(skb)->seq);
997                                 else
998                                         pkt_len = (end_seq -
999                                                    TCP_SKB_CB(skb)->seq);
1000                                 if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->tso_size))
1001                                         break;
1002                                 pcount = tcp_skb_pcount(skb);
1003                         }
1004
1005                         fack_count += pcount;
1006
1007                         sacked = TCP_SKB_CB(skb)->sacked;
1008
1009                         /* Account D-SACK for retransmitted packet. */
1010                         if ((dup_sack && in_sack) &&
1011                             (sacked & TCPCB_RETRANS) &&
1012                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1013                                 tp->undo_retrans--;
1014
1015                         /* The frame is ACKed. */
1016                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1017                                 if (sacked&TCPCB_RETRANS) {
1018                                         if ((dup_sack && in_sack) &&
1019                                             (sacked&TCPCB_SACKED_ACKED))
1020                                                 reord = min(fack_count, reord);
1021                                 } else {
1022                                         /* If it was in a hole, we detected reordering. */
1023                                         if (fack_count < prior_fackets &&
1024                                             !(sacked&TCPCB_SACKED_ACKED))
1025                                                 reord = min(fack_count, reord);
1026                                 }
1027
1028                                 /* Nothing to do; acked frame is about to be dropped. */
1029                                 continue;
1030                         }
1031
1032                         if ((sacked&TCPCB_SACKED_RETRANS) &&
1033                             after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1034                             (!lost_retrans || after(end_seq, lost_retrans)))
1035                                 lost_retrans = end_seq;
1036
1037                         if (!in_sack)
1038                                 continue;
1039
1040                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1041                                 if (sacked & TCPCB_SACKED_RETRANS) {
1042                                         /* If the segment is not tagged as lost,
1043                                          * we do not clear RETRANS, believing
1044                                          * that retransmission is still in flight.
1045                                          */
1046                                         if (sacked & TCPCB_LOST) {
1047                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1048                                                 tp->lost_out -= tcp_skb_pcount(skb);
1049                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1050                                         }
1051                                 } else {
1052                                         /* New sack for not retransmitted frame,
1053                                          * which was in hole. It is reordering.
1054                                          */
1055                                         if (!(sacked & TCPCB_RETRANS) &&
1056                                             fack_count < prior_fackets)
1057                                                 reord = min(fack_count, reord);
1058
1059                                         if (sacked & TCPCB_LOST) {
1060                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1061                                                 tp->lost_out -= tcp_skb_pcount(skb);
1062                                         }
1063                                 }
1064
1065                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1066                                 flag |= FLAG_DATA_SACKED;
1067                                 tp->sacked_out += tcp_skb_pcount(skb);
1068
1069                                 if (fack_count > tp->fackets_out)
1070                                         tp->fackets_out = fack_count;
1071                         } else {
1072                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1073                                         reord = min(fack_count, reord);
1074                         }
1075
1076                         /* D-SACK. We can detect redundant retransmission
1077                          * in S|R and plain R frames and clear it.
1078                          * undo_retrans is decreased above, L|R frames
1079                          * are accounted above as well.
1080                          */
1081                         if (dup_sack &&
1082                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1083                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1084                                 tp->retrans_out -= tcp_skb_pcount(skb);
1085                         }
1086                 }
1087         }
1088
1089         /* Check for lost retransmit. This superb idea is
1090          * borrowed from "ratehalving". Event "C".
1091          * Later note: FACK people cheated me again 8),
1092          * we have to account for reordering! Ugly,
1093          * but should help.
1094          */
1095         if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
1096                 struct sk_buff *skb;
1097
1098                 sk_stream_for_retrans_queue(skb, sk) {
1099                         if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1100                                 break;
1101                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1102                                 continue;
1103                         if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1104                             after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1105                             (IsFack(tp) ||
1106                              !before(lost_retrans,
1107                                      TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1108                                      tp->mss_cache))) {
1109                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1110                                 tp->retrans_out -= tcp_skb_pcount(skb);
1111
1112                                 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1113                                         tp->lost_out += tcp_skb_pcount(skb);
1114                                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1115                                         flag |= FLAG_DATA_SACKED;
1116                                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1117                                 }
1118                         }
1119                 }
1120         }
1121
1122         tp->left_out = tp->sacked_out + tp->lost_out;
1123
1124         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss)
1125                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1126
1127 #if FASTRETRANS_DEBUG > 0
1128         BUG_TRAP((int)tp->sacked_out >= 0);
1129         BUG_TRAP((int)tp->lost_out >= 0);
1130         BUG_TRAP((int)tp->retrans_out >= 0);
1131         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1132 #endif
1133         return flag;
1134 }
1135
1136 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new
1137  * segments to see from the next ACKs whether any data was really missing.
1138  * If the RTO was spurious, new ACKs should arrive.
1139  */
1140 void tcp_enter_frto(struct sock *sk)
1141 {
1142         const struct inet_connection_sock *icsk = inet_csk(sk);
1143         struct tcp_sock *tp = tcp_sk(sk);
1144         struct sk_buff *skb;
1145
1146         tp->frto_counter = 1;
1147
1148         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1149             tp->snd_una == tp->high_seq ||
1150             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1151                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1152                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1153                 tcp_ca_event(sk, CA_EVENT_FRTO);
1154         }
1155
1156         /* Have to clear retransmission markers here to keep the bookkeeping
1157          * in shape, even though we are not yet in Loss state.
1158          * If something was really lost, it is eventually caught up
1159          * in tcp_enter_frto_loss.
1160          */
1161         tp->retrans_out = 0;
1162         tp->undo_marker = tp->snd_una;
1163         tp->undo_retrans = 0;
1164
1165         sk_stream_for_retrans_queue(skb, sk) {
1166                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
1167         }
1168         tcp_sync_left_out(tp);
1169
1170         tcp_set_ca_state(sk, TCP_CA_Open);
1171         tp->frto_highmark = tp->snd_nxt;
1172 }
1173
1174 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1175  * which indicates that we should follow the traditional RTO recovery,
1176  * i.e. mark everything lost and do go-back-N retransmission.
1177  */
1178 static void tcp_enter_frto_loss(struct sock *sk)
1179 {
1180         struct tcp_sock *tp = tcp_sk(sk);
1181         struct sk_buff *skb;
1182         int cnt = 0;
1183
1184         tp->sacked_out = 0;
1185         tp->lost_out = 0;
1186         tp->fackets_out = 0;
1187
1188         sk_stream_for_retrans_queue(skb, sk) {
1189                 cnt += tcp_skb_pcount(skb);
1190                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1191                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1192
1193                         /* Do not mark those segments lost that were
1194                          * forward transmitted after RTO
1195                          */
1196                         if (!after(TCP_SKB_CB(skb)->end_seq,
1197                                    tp->frto_highmark)) {
1198                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1199                                 tp->lost_out += tcp_skb_pcount(skb);
1200                         }
1201                 } else {
1202                         tp->sacked_out += tcp_skb_pcount(skb);
1203                         tp->fackets_out = cnt;
1204                 }
1205         }
1206         tcp_sync_left_out(tp);
1207
1208         tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
1209         tp->snd_cwnd_cnt = 0;
1210         tp->snd_cwnd_stamp = tcp_time_stamp;
1211         tp->undo_marker = 0;
1212         tp->frto_counter = 0;
1213
1214         tp->reordering = min_t(unsigned int, tp->reordering,
1215                                              sysctl_tcp_reordering);
1216         tcp_set_ca_state(sk, TCP_CA_Loss);
1217         tp->high_seq = tp->frto_highmark;
1218         TCP_ECN_queue_cwr(tp);
1219 }
1220
1221 void tcp_clear_retrans(struct tcp_sock *tp)
1222 {
1223         tp->left_out = 0;
1224         tp->retrans_out = 0;
1225
1226         tp->fackets_out = 0;
1227         tp->sacked_out = 0;
1228         tp->lost_out = 0;
1229
1230         tp->undo_marker = 0;
1231         tp->undo_retrans = 0;
1232 }
1233
1234 /* Enter Loss state. If "how" is not zero, forget all SACK information
1235  * and reset tags completely, otherwise preserve SACKs. If receiver
1236  * dropped its ofo queue, we will know this due to reneging detection.
1237  */
1238 void tcp_enter_loss(struct sock *sk, int how)
1239 {
1240         const struct inet_connection_sock *icsk = inet_csk(sk);
1241         struct tcp_sock *tp = tcp_sk(sk);
1242         struct sk_buff *skb;
1243         int cnt = 0;
1244
1245         /* Reduce ssthresh if it has not yet been made inside this window. */
1246         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1247             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1248                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1249                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1250                 tcp_ca_event(sk, CA_EVENT_LOSS);
1251         }
1252         tp->snd_cwnd       = 1;
1253         tp->snd_cwnd_cnt   = 0;
1254         tp->snd_cwnd_stamp = tcp_time_stamp;
1255
1256         tcp_clear_retrans(tp);
1257
1258         /* Push undo marker, if it was plain RTO and nothing
1259          * was retransmitted. */
1260         if (!how)
1261                 tp->undo_marker = tp->snd_una;
1262
1263         sk_stream_for_retrans_queue(skb, sk) {
1264                 cnt += tcp_skb_pcount(skb);
1265                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1266                         tp->undo_marker = 0;
1267                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1268                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1269                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1270                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1271                         tp->lost_out += tcp_skb_pcount(skb);
1272                 } else {
1273                         tp->sacked_out += tcp_skb_pcount(skb);
1274                         tp->fackets_out = cnt;
1275                 }
1276         }
1277         tcp_sync_left_out(tp);
1278
1279         tp->reordering = min_t(unsigned int, tp->reordering,
1280                                              sysctl_tcp_reordering);
1281         tcp_set_ca_state(sk, TCP_CA_Loss);
1282         tp->high_seq = tp->snd_nxt;
1283         TCP_ECN_queue_cwr(tp);
1284 }
1285
1286 static int tcp_check_sack_reneging(struct sock *sk)
1287 {
1288         struct sk_buff *skb;
1289
1290         /* If ACK arrived pointing to a remembered SACK,
1291          * it means that our remembered SACKs do not reflect
1292          * real state of receiver i.e.
1293          * receiver _host_ is heavily congested (or buggy).
1294          * Do processing similar to RTO timeout.
1295          */
1296         if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
1297             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1298                 struct inet_connection_sock *icsk = inet_csk(sk);
1299                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1300
1301                 tcp_enter_loss(sk, 1);
1302                 icsk->icsk_retransmits++;
1303                 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
1304                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1305                                           icsk->icsk_rto, TCP_RTO_MAX);
1306                 return 1;
1307         }
1308         return 0;
1309 }
1310
1311 static inline int tcp_fackets_out(struct tcp_sock *tp)
1312 {
1313         return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1314 }
1315
1316 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1317 {
1318         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1319 }
1320
1321 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
1322 {
1323         return tp->packets_out &&
1324                tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
1325 }
1326
1327 /* Linux NewReno/SACK/FACK/ECN state machine.
1328  * --------------------------------------
1329  *
1330  * "Open"       Normal state, no dubious events, fast path.
1331  * "Disorder"   In all the respects it is "Open",
1332  *              but requires a bit more attention. It is entered when
1333  *              we see some SACKs or dupacks. It is split of "Open"
1334  *              mainly to move some processing from fast path to slow one.
1335  * "CWR"        CWND was reduced due to some Congestion Notification event.
1336  *              It can be ECN, ICMP source quench, local device congestion.
1337  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1338  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1339  *
1340  * tcp_fastretrans_alert() is entered:
1341  * - each incoming ACK, if state is not "Open"
1342  * - when arrived ACK is unusual, namely:
1343  *      * SACK
1344  *      * Duplicate ACK.
1345  *      * ECN ECE.
1346  *
1347  * Counting packets in flight is pretty simple.
1348  *
1349  *      in_flight = packets_out - left_out + retrans_out
1350  *
1351  *      packets_out is SND.NXT-SND.UNA counted in packets.
1352  *
1353  *      retrans_out is number of retransmitted segments.
1354  *
1355  *      left_out is number of segments left network, but not ACKed yet.
1356  *
1357  *              left_out = sacked_out + lost_out
1358  *
1359  *     sacked_out: Packets, which arrived to receiver out of order
1360  *                 and hence not ACKed. With SACKs this number is simply
1361  *                 amount of SACKed data. Even without SACKs
1362  *                 it is easy to give pretty reliable estimate of this number,
1363  *                 counting duplicate ACKs.
1364  *
1365  *       lost_out: Packets lost by network. TCP has no explicit
1366  *                 "loss notification" feedback from network (for now).
1367  *                 It means that this number can be only _guessed_.
1368  *                 Actually, it is the heuristics to predict lossage that
1369  *                 distinguishes different algorithms.
1370  *
1371  *      F.e. after RTO, when all the queue is considered as lost,
1372  *      lost_out = packets_out and in_flight = retrans_out.
1373  *
1374  *              Essentially, we have now two algorithms counting
1375  *              lost packets.
1376  *
1377  *              FACK: It is the simplest heuristics. As soon as we decided
1378  *              that something is lost, we decide that _all_ not SACKed
1379  *              packets until the most forward SACK are lost. I.e.
1380  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1381  *              It is absolutely correct estimate, if network does not reorder
1382  *              packets. And it loses any connection to reality when reordering
1383  *              takes place. We use FACK by default until reordering
1384  *              is suspected on the path to this destination.
1385  *
1386  *              NewReno: when Recovery is entered, we assume that one segment
1387  *              is lost (classic Reno). While we are in Recovery and
1388  *              a partial ACK arrives, we assume that one more packet
1389  *              is lost (NewReno). This heuristics are the same in NewReno
1390  *              and SACK.
1391  *
1392  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1393  *  deflation etc. CWND is real congestion window, never inflated, changes
1394  *  only according to classic VJ rules.
1395  *
1396  * Really tricky (and requiring careful tuning) part of algorithm
1397  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1398  * The first determines the moment _when_ we should reduce CWND and,
1399  * hence, slow down forward transmission. In fact, it determines the moment
1400  * when we decide that hole is caused by loss, rather than by a reorder.
1401  *
1402  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1403  * holes, caused by lost packets.
1404  *
1405  * And the most logically complicated part of algorithm is undo
1406  * heuristics. We detect false retransmits due to both too early
1407  * fast retransmit (reordering) and underestimated RTO, analyzing
1408  * timestamps and D-SACKs. When we detect that some segments were
1409  * retransmitted by mistake and CWND reduction was wrong, we undo
1410  * window reduction and abort recovery phase. This logic is hidden
1411  * inside several functions named tcp_try_undo_<something>.
1412  */
1413
1414 /* This function decides, when we should leave Disordered state
1415  * and enter Recovery phase, reducing congestion window.
1416  *
1417  * Main question: may we further continue forward transmission
1418  * with the same cwnd?
1419  */
1420 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
1421 {
1422         __u32 packets_out;
1423
1424         /* Trick#1: The loss is proven. */
1425         if (tp->lost_out)
1426                 return 1;
1427
1428         /* Not-A-Trick#2 : Classic rule... */
1429         if (tcp_fackets_out(tp) > tp->reordering)
1430                 return 1;
1431
1432         /* Trick#3 : when we use RFC2988 timer restart, fast
1433          * retransmit can be triggered by timeout of queue head.
1434          */
1435         if (tcp_head_timedout(sk, tp))
1436                 return 1;
1437
1438         /* Trick#4: It is still not OK... But will it be useful to delay
1439          * recovery more?
1440          */
1441         packets_out = tp->packets_out;
1442         if (packets_out <= tp->reordering &&
1443             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1444             !tcp_may_send_now(sk, tp)) {
1445                 /* We have nothing to send. This connection is limited
1446                  * either by receiver window or by application.
1447                  */
1448                 return 1;
1449         }
1450
1451         return 0;
1452 }
1453
1454 /* If we receive more dupacks than we expected counting segments
1455  * in assumption of absent reordering, interpret this as reordering.
1456  * The only another reason could be bug in receiver TCP.
1457  */
1458 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1459 {
1460         struct tcp_sock *tp = tcp_sk(sk);
1461         u32 holes;
1462
1463         holes = max(tp->lost_out, 1U);
1464         holes = min(holes, tp->packets_out);
1465
1466         if ((tp->sacked_out + holes) > tp->packets_out) {
1467                 tp->sacked_out = tp->packets_out - holes;
1468                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1469         }
1470 }
1471
1472 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1473
1474 static void tcp_add_reno_sack(struct sock *sk)
1475 {
1476         struct tcp_sock *tp = tcp_sk(sk);
1477         tp->sacked_out++;
1478         tcp_check_reno_reordering(sk, 0);
1479         tcp_sync_left_out(tp);
1480 }
1481
1482 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1483
1484 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
1485 {
1486         if (acked > 0) {
1487                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1488                 if (acked-1 >= tp->sacked_out)
1489                         tp->sacked_out = 0;
1490                 else
1491                         tp->sacked_out -= acked-1;
1492         }
1493         tcp_check_reno_reordering(sk, acked);
1494         tcp_sync_left_out(tp);
1495 }
1496
1497 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1498 {
1499         tp->sacked_out = 0;
1500         tp->left_out = tp->lost_out;
1501 }
1502
1503 /* Mark head of queue up as lost. */
1504 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
1505                                int packets, u32 high_seq)
1506 {
1507         struct sk_buff *skb;
1508         int cnt = packets;
1509
1510         BUG_TRAP(cnt <= tp->packets_out);
1511
1512         sk_stream_for_retrans_queue(skb, sk) {
1513                 cnt -= tcp_skb_pcount(skb);
1514                 if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1515                         break;
1516                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1517                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1518                         tp->lost_out += tcp_skb_pcount(skb);
1519                 }
1520         }
1521         tcp_sync_left_out(tp);
1522 }
1523
1524 /* Account newly detected lost packet(s) */
1525
1526 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
1527 {
1528         if (IsFack(tp)) {
1529                 int lost = tp->fackets_out - tp->reordering;
1530                 if (lost <= 0)
1531                         lost = 1;
1532                 tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
1533         } else {
1534                 tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
1535         }
1536
1537         /* New heuristics: it is possible only after we switched
1538          * to restart timer each time when something is ACKed.
1539          * Hence, we can detect timed out packets during fast
1540          * retransmit without falling to slow start.
1541          */
1542         if (tcp_head_timedout(sk, tp)) {
1543                 struct sk_buff *skb;
1544
1545                 sk_stream_for_retrans_queue(skb, sk) {
1546                         if (tcp_skb_timedout(sk, skb) &&
1547                             !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1548                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1549                                 tp->lost_out += tcp_skb_pcount(skb);
1550                         }
1551                 }
1552                 tcp_sync_left_out(tp);
1553         }
1554 }
1555
1556 /* CWND moderation, preventing bursts due to too big ACKs
1557  * in dubious situations.
1558  */
1559 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1560 {
1561         tp->snd_cwnd = min(tp->snd_cwnd,
1562                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1563         tp->snd_cwnd_stamp = tcp_time_stamp;
1564 }
1565
1566 /* Decrease cwnd each second ack. */
1567 static void tcp_cwnd_down(struct sock *sk)
1568 {
1569         const struct inet_connection_sock *icsk = inet_csk(sk);
1570         struct tcp_sock *tp = tcp_sk(sk);
1571         int decr = tp->snd_cwnd_cnt + 1;
1572
1573         tp->snd_cwnd_cnt = decr&1;
1574         decr >>= 1;
1575
1576         if (decr && tp->snd_cwnd > icsk->icsk_ca_ops->min_cwnd(sk))
1577                 tp->snd_cwnd -= decr;
1578
1579         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1580         tp->snd_cwnd_stamp = tcp_time_stamp;
1581 }
1582
1583 /* Nothing was retransmitted or returned timestamp is less
1584  * than timestamp of the first retransmission.
1585  */
1586 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1587 {
1588         return !tp->retrans_stamp ||
1589                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1590                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1591 }
1592
1593 /* Undo procedures. */
1594
1595 #if FASTRETRANS_DEBUG > 1
1596 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
1597 {
1598         struct inet_sock *inet = inet_sk(sk);
1599         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1600                msg,
1601                NIPQUAD(inet->daddr), ntohs(inet->dport),
1602                tp->snd_cwnd, tp->left_out,
1603                tp->snd_ssthresh, tp->prior_ssthresh,
1604                tp->packets_out);
1605 }
1606 #else
1607 #define DBGUNDO(x...) do { } while (0)
1608 #endif
1609
1610 static void tcp_undo_cwr(struct sock *sk, const int undo)
1611 {
1612         struct tcp_sock *tp = tcp_sk(sk);
1613
1614         if (tp->prior_ssthresh) {
1615                 const struct inet_connection_sock *icsk = inet_csk(sk);
1616
1617                 if (icsk->icsk_ca_ops->undo_cwnd)
1618                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
1619                 else
1620                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1621
1622                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1623                         tp->snd_ssthresh = tp->prior_ssthresh;
1624                         TCP_ECN_withdraw_cwr(tp);
1625                 }
1626         } else {
1627                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1628         }
1629         tcp_moderate_cwnd(tp);
1630         tp->snd_cwnd_stamp = tcp_time_stamp;
1631 }
1632
1633 static inline int tcp_may_undo(struct tcp_sock *tp)
1634 {
1635         return tp->undo_marker &&
1636                 (!tp->undo_retrans || tcp_packet_delayed(tp));
1637 }
1638
1639 /* People celebrate: "We love our President!" */
1640 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
1641 {
1642         if (tcp_may_undo(tp)) {
1643                 /* Happy end! We did not retransmit anything
1644                  * or our original transmission succeeded.
1645                  */
1646                 DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
1647                 tcp_undo_cwr(sk, 1);
1648                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
1649                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1650                 else
1651                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1652                 tp->undo_marker = 0;
1653         }
1654         if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1655                 /* Hold old state until something *above* high_seq
1656                  * is ACKed. For Reno it is MUST to prevent false
1657                  * fast retransmits (RFC2582). SACK TCP is safe. */
1658                 tcp_moderate_cwnd(tp);
1659                 return 1;
1660         }
1661         tcp_set_ca_state(sk, TCP_CA_Open);
1662         return 0;
1663 }
1664
1665 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1666 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
1667 {
1668         if (tp->undo_marker && !tp->undo_retrans) {
1669                 DBGUNDO(sk, tp, "D-SACK");
1670                 tcp_undo_cwr(sk, 1);
1671                 tp->undo_marker = 0;
1672                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1673         }
1674 }
1675
1676 /* Undo during fast recovery after partial ACK. */
1677
1678 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
1679                                 int acked)
1680 {
1681         /* Partial ACK arrived. Force Hoe's retransmit. */
1682         int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1683
1684         if (tcp_may_undo(tp)) {
1685                 /* Plain luck! Hole if filled with delayed
1686                  * packet, rather than with a retransmit.
1687                  */
1688                 if (tp->retrans_out == 0)
1689                         tp->retrans_stamp = 0;
1690
1691                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
1692
1693                 DBGUNDO(sk, tp, "Hoe");
1694                 tcp_undo_cwr(sk, 0);
1695                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1696
1697                 /* So... Do not make Hoe's retransmit yet.
1698                  * If the first packet was delayed, the rest
1699                  * ones are most probably delayed as well.
1700                  */
1701                 failed = 0;
1702         }
1703         return failed;
1704 }
1705
1706 /* Undo during loss recovery after partial ACK. */
1707 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
1708 {
1709         if (tcp_may_undo(tp)) {
1710                 struct sk_buff *skb;
1711                 sk_stream_for_retrans_queue(skb, sk) {
1712                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1713                 }
1714                 DBGUNDO(sk, tp, "partial loss");
1715                 tp->lost_out = 0;
1716                 tp->left_out = tp->sacked_out;
1717                 tcp_undo_cwr(sk, 1);
1718                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1719                 inet_csk(sk)->icsk_retransmits = 0;
1720                 tp->undo_marker = 0;
1721                 if (!IsReno(tp))
1722                         tcp_set_ca_state(sk, TCP_CA_Open);
1723                 return 1;
1724         }
1725         return 0;
1726 }
1727
1728 static inline void tcp_complete_cwr(struct sock *sk)
1729 {
1730         struct tcp_sock *tp = tcp_sk(sk);
1731         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
1732         tp->snd_cwnd_stamp = tcp_time_stamp;
1733         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
1734 }
1735
1736 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
1737 {
1738         tp->left_out = tp->sacked_out;
1739
1740         if (tp->retrans_out == 0)
1741                 tp->retrans_stamp = 0;
1742
1743         if (flag&FLAG_ECE)
1744                 tcp_enter_cwr(sk);
1745
1746         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
1747                 int state = TCP_CA_Open;
1748
1749                 if (tp->left_out || tp->retrans_out || tp->undo_marker)
1750                         state = TCP_CA_Disorder;
1751
1752                 if (inet_csk(sk)->icsk_ca_state != state) {
1753                         tcp_set_ca_state(sk, state);
1754                         tp->high_seq = tp->snd_nxt;
1755                 }
1756                 tcp_moderate_cwnd(tp);
1757         } else {
1758                 tcp_cwnd_down(sk);
1759         }
1760 }
1761
1762 /* Process an event, which can update packets-in-flight not trivially.
1763  * Main goal of this function is to calculate new estimate for left_out,
1764  * taking into account both packets sitting in receiver's buffer and
1765  * packets lost by network.
1766  *
1767  * Besides that it does CWND reduction, when packet loss is detected
1768  * and changes state of machine.
1769  *
1770  * It does _not_ decide what to send, it is made in function
1771  * tcp_xmit_retransmit_queue().
1772  */
1773 static void
1774 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
1775                       int prior_packets, int flag)
1776 {
1777         struct inet_connection_sock *icsk = inet_csk(sk);
1778         struct tcp_sock *tp = tcp_sk(sk);
1779         int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
1780
1781         /* Some technical things:
1782          * 1. Reno does not count dupacks (sacked_out) automatically. */
1783         if (!tp->packets_out)
1784                 tp->sacked_out = 0;
1785         /* 2. SACK counts snd_fack in packets inaccurately. */
1786         if (tp->sacked_out == 0)
1787                 tp->fackets_out = 0;
1788
1789         /* Now state machine starts.
1790          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
1791         if (flag&FLAG_ECE)
1792                 tp->prior_ssthresh = 0;
1793
1794         /* B. In all the states check for reneging SACKs. */
1795         if (tp->sacked_out && tcp_check_sack_reneging(sk))
1796                 return;
1797
1798         /* C. Process data loss notification, provided it is valid. */
1799         if ((flag&FLAG_DATA_LOST) &&
1800             before(tp->snd_una, tp->high_seq) &&
1801             icsk->icsk_ca_state != TCP_CA_Open &&
1802             tp->fackets_out > tp->reordering) {
1803                 tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
1804                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
1805         }
1806
1807         /* D. Synchronize left_out to current state. */
1808         tcp_sync_left_out(tp);
1809
1810         /* E. Check state exit conditions. State can be terminated
1811          *    when high_seq is ACKed. */
1812         if (icsk->icsk_ca_state == TCP_CA_Open) {
1813                 if (!sysctl_tcp_frto)
1814                         BUG_TRAP(tp->retrans_out == 0);
1815                 tp->retrans_stamp = 0;
1816         } else if (!before(tp->snd_una, tp->high_seq)) {
1817                 switch (icsk->icsk_ca_state) {
1818                 case TCP_CA_Loss:
1819                         icsk->icsk_retransmits = 0;
1820                         if (tcp_try_undo_recovery(sk, tp))
1821                                 return;
1822                         break;
1823
1824                 case TCP_CA_CWR:
1825                         /* CWR is to be held something *above* high_seq
1826                          * is ACKed for CWR bit to reach receiver. */
1827                         if (tp->snd_una != tp->high_seq) {
1828                                 tcp_complete_cwr(sk);
1829                                 tcp_set_ca_state(sk, TCP_CA_Open);
1830                         }
1831                         break;
1832
1833                 case TCP_CA_Disorder:
1834                         tcp_try_undo_dsack(sk, tp);
1835                         if (!tp->undo_marker ||
1836                             /* For SACK case do not Open to allow to undo
1837                              * catching for all duplicate ACKs. */
1838                             IsReno(tp) || tp->snd_una != tp->high_seq) {
1839                                 tp->undo_marker = 0;
1840                                 tcp_set_ca_state(sk, TCP_CA_Open);
1841                         }
1842                         break;
1843
1844                 case TCP_CA_Recovery:
1845                         if (IsReno(tp))
1846                                 tcp_reset_reno_sack(tp);
1847                         if (tcp_try_undo_recovery(sk, tp))
1848                                 return;
1849                         tcp_complete_cwr(sk);
1850                         break;
1851                 }
1852         }
1853
1854         /* F. Process state. */
1855         switch (icsk->icsk_ca_state) {
1856         case TCP_CA_Recovery:
1857                 if (prior_snd_una == tp->snd_una) {
1858                         if (IsReno(tp) && is_dupack)
1859                                 tcp_add_reno_sack(sk);
1860                 } else {
1861                         int acked = prior_packets - tp->packets_out;
1862                         if (IsReno(tp))
1863                                 tcp_remove_reno_sacks(sk, tp, acked);
1864                         is_dupack = tcp_try_undo_partial(sk, tp, acked);
1865                 }
1866                 break;
1867         case TCP_CA_Loss:
1868                 if (flag&FLAG_DATA_ACKED)
1869                         icsk->icsk_retransmits = 0;
1870                 if (!tcp_try_undo_loss(sk, tp)) {
1871                         tcp_moderate_cwnd(tp);
1872                         tcp_xmit_retransmit_queue(sk);
1873                         return;
1874                 }
1875                 if (icsk->icsk_ca_state != TCP_CA_Open)
1876                         return;
1877                 /* Loss is undone; fall through to processing in Open state. */
1878         default:
1879                 if (IsReno(tp)) {
1880                         if (tp->snd_una != prior_snd_una)
1881                                 tcp_reset_reno_sack(tp);
1882                         if (is_dupack)
1883                                 tcp_add_reno_sack(sk);
1884                 }
1885
1886                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
1887                         tcp_try_undo_dsack(sk, tp);
1888
1889                 if (!tcp_time_to_recover(sk, tp)) {
1890                         tcp_try_to_open(sk, tp, flag);
1891                         return;
1892                 }
1893
1894                 /* Otherwise enter Recovery state */
1895
1896                 if (IsReno(tp))
1897                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
1898                 else
1899                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
1900
1901                 tp->high_seq = tp->snd_nxt;
1902                 tp->prior_ssthresh = 0;
1903                 tp->undo_marker = tp->snd_una;
1904                 tp->undo_retrans = tp->retrans_out;
1905
1906                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
1907                         if (!(flag&FLAG_ECE))
1908                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1909                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1910                         TCP_ECN_queue_cwr(tp);
1911                 }
1912
1913                 tp->snd_cwnd_cnt = 0;
1914                 tcp_set_ca_state(sk, TCP_CA_Recovery);
1915         }
1916
1917         if (is_dupack || tcp_head_timedout(sk, tp))
1918                 tcp_update_scoreboard(sk, tp);
1919         tcp_cwnd_down(sk);
1920         tcp_xmit_retransmit_queue(sk);
1921 }
1922
1923 /* Read draft-ietf-tcplw-high-performance before mucking
1924  * with this code. (Superceeds RFC1323)
1925  */
1926 static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
1927 {
1928         /* RTTM Rule: A TSecr value received in a segment is used to
1929          * update the averaged RTT measurement only if the segment
1930          * acknowledges some new data, i.e., only if it advances the
1931          * left edge of the send window.
1932          *
1933          * See draft-ietf-tcplw-high-performance-00, section 3.3.
1934          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
1935          *
1936          * Changed: reset backoff as soon as we see the first valid sample.
1937          * If we do not, we get strongly overstimated rto. With timestamps
1938          * samples are accepted even from very old segments: f.e., when rtt=1
1939          * increases to 8, we retransmit 5 times and after 8 seconds delayed
1940          * answer arrives rto becomes 120 seconds! If at least one of segments
1941          * in window is lost... Voila.                          --ANK (010210)
1942          */
1943         struct tcp_sock *tp = tcp_sk(sk);
1944         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
1945         tcp_rtt_estimator(sk, seq_rtt, usrtt);
1946         tcp_set_rto(sk);
1947         inet_csk(sk)->icsk_backoff = 0;
1948         tcp_bound_rto(sk);
1949 }
1950
1951 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag)
1952 {
1953         /* We don't have a timestamp. Can only use
1954          * packets that are not retransmitted to determine
1955          * rtt estimates. Also, we must not reset the
1956          * backoff for rto until we get a non-retransmitted
1957          * packet. This allows us to deal with a situation
1958          * where the network delay has increased suddenly.
1959          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
1960          */
1961
1962         if (flag & FLAG_RETRANS_DATA_ACKED)
1963                 return;
1964
1965         tcp_rtt_estimator(sk, seq_rtt, usrtt);
1966         tcp_set_rto(sk);
1967         inet_csk(sk)->icsk_backoff = 0;
1968         tcp_bound_rto(sk);
1969 }
1970
1971 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
1972                                       const s32 seq_rtt, u32 *usrtt)
1973 {
1974         const struct tcp_sock *tp = tcp_sk(sk);
1975         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
1976         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
1977                 tcp_ack_saw_tstamp(sk, usrtt, flag);
1978         else if (seq_rtt >= 0)
1979                 tcp_ack_no_tstamp(sk, seq_rtt, usrtt, flag);
1980 }
1981
1982 static inline void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
1983                                   u32 in_flight, int good)
1984 {
1985         const struct inet_connection_sock *icsk = inet_csk(sk);
1986         icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
1987         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
1988 }
1989
1990 /* Restart timer after forward progress on connection.
1991  * RFC2988 recommends to restart timer to now+rto.
1992  */
1993
1994 static inline void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
1995 {
1996         if (!tp->packets_out) {
1997                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
1998         } else {
1999                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2000         }
2001 }
2002
2003 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
2004                          __u32 now, __s32 *seq_rtt)
2005 {
2006         struct tcp_sock *tp = tcp_sk(sk);
2007         struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2008         __u32 seq = tp->snd_una;
2009         __u32 packets_acked;
2010         int acked = 0;
2011
2012         /* If we get here, the whole TSO packet has not been
2013          * acked.
2014          */
2015         BUG_ON(!after(scb->end_seq, seq));
2016
2017         packets_acked = tcp_skb_pcount(skb);
2018         if (tcp_trim_head(sk, skb, seq - scb->seq))
2019                 return 0;
2020         packets_acked -= tcp_skb_pcount(skb);
2021
2022         if (packets_acked) {
2023                 __u8 sacked = scb->sacked;
2024
2025                 acked |= FLAG_DATA_ACKED;
2026                 if (sacked) {
2027                         if (sacked & TCPCB_RETRANS) {
2028                                 if (sacked & TCPCB_SACKED_RETRANS)
2029                                         tp->retrans_out -= packets_acked;
2030                                 acked |= FLAG_RETRANS_DATA_ACKED;
2031                                 *seq_rtt = -1;
2032                         } else if (*seq_rtt < 0)
2033                                 *seq_rtt = now - scb->when;
2034                         if (sacked & TCPCB_SACKED_ACKED)
2035                                 tp->sacked_out -= packets_acked;
2036                         if (sacked & TCPCB_LOST)
2037                                 tp->lost_out -= packets_acked;
2038                         if (sacked & TCPCB_URG) {
2039                                 if (tp->urg_mode &&
2040                                     !before(seq, tp->snd_up))
2041                                         tp->urg_mode = 0;
2042                         }
2043                 } else if (*seq_rtt < 0)
2044                         *seq_rtt = now - scb->when;
2045
2046                 if (tp->fackets_out) {
2047                         __u32 dval = min(tp->fackets_out, packets_acked);
2048                         tp->fackets_out -= dval;
2049                 }
2050                 tp->packets_out -= packets_acked;
2051
2052                 BUG_ON(tcp_skb_pcount(skb) == 0);
2053                 BUG_ON(!before(scb->seq, scb->end_seq));
2054         }
2055
2056         return acked;
2057 }
2058
2059
2060 /* Remove acknowledged frames from the retransmission queue. */
2061 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt)
2062 {
2063         struct tcp_sock *tp = tcp_sk(sk);
2064         struct sk_buff *skb;
2065         __u32 now = tcp_time_stamp;
2066         int acked = 0;
2067         __s32 seq_rtt = -1;
2068         struct timeval usnow;
2069         u32 pkts_acked = 0;
2070
2071         if (seq_usrtt)
2072                 do_gettimeofday(&usnow);
2073
2074         while ((skb = skb_peek(&sk->sk_write_queue)) &&
2075                skb != sk->sk_send_head) {
2076                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2077                 __u8 sacked = scb->sacked;
2078
2079                 /* If our packet is before the ack sequence we can
2080                  * discard it as it's confirmed to have arrived at
2081                  * the other end.
2082                  */
2083                 if (after(scb->end_seq, tp->snd_una)) {
2084                         if (tcp_skb_pcount(skb) > 1 &&
2085                             after(tp->snd_una, scb->seq))
2086                                 acked |= tcp_tso_acked(sk, skb,
2087                                                        now, &seq_rtt);
2088                         break;
2089                 }
2090
2091                 /* Initial outgoing SYN's get put onto the write_queue
2092                  * just like anything else we transmit.  It is not
2093                  * true data, and if we misinform our callers that
2094                  * this ACK acks real data, we will erroneously exit
2095                  * connection startup slow start one packet too
2096                  * quickly.  This is severely frowned upon behavior.
2097                  */
2098                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2099                         acked |= FLAG_DATA_ACKED;
2100                         ++pkts_acked;
2101                 } else {
2102                         acked |= FLAG_SYN_ACKED;
2103                         tp->retrans_stamp = 0;
2104                 }
2105
2106                 if (sacked) {
2107                         if (sacked & TCPCB_RETRANS) {
2108                                 if(sacked & TCPCB_SACKED_RETRANS)
2109                                         tp->retrans_out -= tcp_skb_pcount(skb);
2110                                 acked |= FLAG_RETRANS_DATA_ACKED;
2111                                 seq_rtt = -1;
2112                         } else if (seq_rtt < 0)
2113                                 seq_rtt = now - scb->when;
2114                         if (seq_usrtt) {
2115                                 struct timeval tv;
2116                         
2117                                 skb_get_timestamp(skb, &tv);
2118                                 *seq_usrtt = (usnow.tv_sec - tv.tv_sec) * 1000000
2119                                         + (usnow.tv_usec - tv.tv_usec);
2120                         }
2121
2122                         if (sacked & TCPCB_SACKED_ACKED)
2123                                 tp->sacked_out -= tcp_skb_pcount(skb);
2124                         if (sacked & TCPCB_LOST)
2125                                 tp->lost_out -= tcp_skb_pcount(skb);
2126                         if (sacked & TCPCB_URG) {
2127                                 if (tp->urg_mode &&
2128                                     !before(scb->end_seq, tp->snd_up))
2129                                         tp->urg_mode = 0;
2130                         }
2131                 } else if (seq_rtt < 0)
2132                         seq_rtt = now - scb->when;
2133                 tcp_dec_pcount_approx(&tp->fackets_out, skb);
2134                 tcp_packets_out_dec(tp, skb);
2135                 __skb_unlink(skb, &sk->sk_write_queue);
2136                 sk_stream_free_skb(sk, skb);
2137         }
2138
2139         if (acked&FLAG_ACKED) {
2140                 const struct inet_connection_sock *icsk = inet_csk(sk);
2141                 tcp_ack_update_rtt(sk, acked, seq_rtt, seq_usrtt);
2142                 tcp_ack_packets_out(sk, tp);
2143
2144                 if (icsk->icsk_ca_ops->pkts_acked)
2145                         icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
2146         }
2147
2148 #if FASTRETRANS_DEBUG > 0
2149         BUG_TRAP((int)tp->sacked_out >= 0);
2150         BUG_TRAP((int)tp->lost_out >= 0);
2151         BUG_TRAP((int)tp->retrans_out >= 0);
2152         if (!tp->packets_out && tp->rx_opt.sack_ok) {
2153                 const struct inet_connection_sock *icsk = inet_csk(sk);
2154                 if (tp->lost_out) {
2155                         printk(KERN_DEBUG "Leak l=%u %d\n",
2156                                tp->lost_out, icsk->icsk_ca_state);
2157                         tp->lost_out = 0;
2158                 }
2159                 if (tp->sacked_out) {
2160                         printk(KERN_DEBUG "Leak s=%u %d\n",
2161                                tp->sacked_out, icsk->icsk_ca_state);
2162                         tp->sacked_out = 0;
2163                 }
2164                 if (tp->retrans_out) {
2165                         printk(KERN_DEBUG "Leak r=%u %d\n",
2166                                tp->retrans_out, icsk->icsk_ca_state);
2167                         tp->retrans_out = 0;
2168                 }
2169         }
2170 #endif
2171         *seq_rtt_p = seq_rtt;
2172         return acked;
2173 }
2174
2175 static void tcp_ack_probe(struct sock *sk)
2176 {
2177         const struct tcp_sock *tp = tcp_sk(sk);
2178         struct inet_connection_sock *icsk = inet_csk(sk);
2179
2180         /* Was it a usable window open? */
2181
2182         if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
2183                    tp->snd_una + tp->snd_wnd)) {
2184                 icsk->icsk_backoff = 0;
2185                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2186                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2187                  * This function is not for random using!
2188                  */
2189         } else {
2190                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2191                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2192                                           TCP_RTO_MAX);
2193         }
2194 }
2195
2196 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2197 {
2198         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2199                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2200 }
2201
2202 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2203 {
2204         const struct tcp_sock *tp = tcp_sk(sk);
2205         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2206                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2207 }
2208
2209 /* Check that window update is acceptable.
2210  * The function assumes that snd_una<=ack<=snd_next.
2211  */
2212 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2213                                         const u32 ack_seq, const u32 nwin)
2214 {
2215         return (after(ack, tp->snd_una) ||
2216                 after(ack_seq, tp->snd_wl1) ||
2217                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2218 }
2219
2220 /* Update our send window.
2221  *
2222  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2223  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2224  */
2225 static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
2226                                  struct sk_buff *skb, u32 ack, u32 ack_seq)
2227 {
2228         int flag = 0;
2229         u32 nwin = ntohs(skb->h.th->window);
2230
2231         if (likely(!skb->h.th->syn))
2232                 nwin <<= tp->rx_opt.snd_wscale;
2233
2234         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2235                 flag |= FLAG_WIN_UPDATE;
2236                 tcp_update_wl(tp, ack, ack_seq);
2237
2238                 if (tp->snd_wnd != nwin) {
2239                         tp->snd_wnd = nwin;
2240
2241                         /* Note, it is the only place, where
2242                          * fast path is recovered for sending TCP.
2243                          */
2244                         tcp_fast_path_check(sk, tp);
2245
2246                         if (nwin > tp->max_window) {
2247                                 tp->max_window = nwin;
2248                                 tcp_sync_mss(sk, tp->pmtu_cookie);
2249                         }
2250                 }
2251         }
2252
2253         tp->snd_una = ack;
2254
2255         return flag;
2256 }
2257
2258 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
2259 {
2260         struct tcp_sock *tp = tcp_sk(sk);
2261         
2262         tcp_sync_left_out(tp);
2263         
2264         if (tp->snd_una == prior_snd_una ||
2265             !before(tp->snd_una, tp->frto_highmark)) {
2266                 /* RTO was caused by loss, start retransmitting in
2267                  * go-back-N slow start
2268                  */
2269                 tcp_enter_frto_loss(sk);
2270                 return;
2271         }
2272
2273         if (tp->frto_counter == 1) {
2274                 /* First ACK after RTO advances the window: allow two new
2275                  * segments out.
2276                  */
2277                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2278         } else {
2279                 /* Also the second ACK after RTO advances the window.
2280                  * The RTO was likely spurious. Reduce cwnd and continue
2281                  * in congestion avoidance
2282                  */
2283                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2284                 tcp_moderate_cwnd(tp);
2285         }
2286
2287         /* F-RTO affects on two new ACKs following RTO.
2288          * At latest on third ACK the TCP behavor is back to normal.
2289          */
2290         tp->frto_counter = (tp->frto_counter + 1) % 3;
2291 }
2292
2293 /* This routine deals with incoming acks, but not outgoing ones. */
2294 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2295 {
2296         struct inet_connection_sock *icsk = inet_csk(sk);
2297         struct tcp_sock *tp = tcp_sk(sk);
2298         u32 prior_snd_una = tp->snd_una;
2299         u32 ack_seq = TCP_SKB_CB(skb)->seq;
2300         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2301         u32 prior_in_flight;
2302         s32 seq_rtt;
2303         s32 seq_usrtt = 0;
2304         int prior_packets;
2305
2306         /* If the ack is newer than sent or older than previous acks
2307          * then we can probably ignore it.
2308          */
2309         if (after(ack, tp->snd_nxt))
2310                 goto uninteresting_ack;
2311
2312         if (before(ack, prior_snd_una))
2313                 goto old_ack;
2314
2315         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
2316                 /* Window is constant, pure forward advance.
2317                  * No more checks are required.
2318                  * Note, we use the fact that SND.UNA>=SND.WL2.
2319                  */
2320                 tcp_update_wl(tp, ack, ack_seq);
2321                 tp->snd_una = ack;
2322                 flag |= FLAG_WIN_UPDATE;
2323
2324                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
2325
2326                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
2327         } else {
2328                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
2329                         flag |= FLAG_DATA;
2330                 else
2331                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
2332
2333                 flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);
2334
2335                 if (TCP_SKB_CB(skb)->sacked)
2336                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2337
2338                 if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
2339                         flag |= FLAG_ECE;
2340
2341                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
2342         }
2343
2344         /* We passed data and got it acked, remove any soft error
2345          * log. Something worked...
2346          */
2347         sk->sk_err_soft = 0;
2348         tp->rcv_tstamp = tcp_time_stamp;
2349         prior_packets = tp->packets_out;
2350         if (!prior_packets)
2351                 goto no_queue;
2352
2353         prior_in_flight = tcp_packets_in_flight(tp);
2354
2355         /* See if we can take anything off of the retransmit queue. */
2356         flag |= tcp_clean_rtx_queue(sk, &seq_rtt,
2357                                     icsk->icsk_ca_ops->rtt_sample ? &seq_usrtt : NULL);
2358
2359         if (tp->frto_counter)
2360                 tcp_process_frto(sk, prior_snd_una);
2361
2362         if (tcp_ack_is_dubious(sk, flag)) {
2363                 /* Advanve CWND, if state allows this. */
2364                 if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
2365                         tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
2366                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2367         } else {
2368                 if ((flag & FLAG_DATA_ACKED))
2369                         tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
2370         }
2371
2372         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2373                 dst_confirm(sk->sk_dst_cache);
2374
2375         return 1;
2376
2377 no_queue:
2378         icsk->icsk_probes_out = 0;
2379
2380         /* If this ack opens up a zero window, clear backoff.  It was
2381          * being used to time the probes, and is probably far higher than
2382          * it needs to be for normal retransmission.
2383          */
2384         if (sk->sk_send_head)
2385                 tcp_ack_probe(sk);
2386         return 1;
2387
2388 old_ack:
2389         if (TCP_SKB_CB(skb)->sacked)
2390                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2391
2392 uninteresting_ack:
2393         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2394         return 0;
2395 }
2396
2397
2398 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2399  * But, this can also be called on packets in the established flow when
2400  * the fast version below fails.
2401  */
2402 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2403 {
2404         unsigned char *ptr;
2405         struct tcphdr *th = skb->h.th;
2406         int length=(th->doff*4)-sizeof(struct tcphdr);
2407
2408         ptr = (unsigned char *)(th + 1);
2409         opt_rx->saw_tstamp = 0;
2410
2411         while(length>0) {
2412                 int opcode=*ptr++;
2413                 int opsize;
2414
2415                 switch (opcode) {
2416                         case TCPOPT_EOL:
2417                                 return;
2418                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
2419                                 length--;
2420                                 continue;
2421                         default:
2422                                 opsize=*ptr++;
2423                                 if (opsize < 2) /* "silly options" */
2424                                         return;
2425                                 if (opsize > length)
2426                                         return; /* don't parse partial options */
2427                                 switch(opcode) {
2428                                 case TCPOPT_MSS:
2429                                         if(opsize==TCPOLEN_MSS && th->syn && !estab) {
2430                                                 u16 in_mss = ntohs(get_unaligned((__u16 *)ptr));
2431                                                 if (in_mss) {
2432                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2433                                                                 in_mss = opt_rx->user_mss;
2434                                                         opt_rx->mss_clamp = in_mss;
2435                                                 }
2436                                         }
2437                                         break;
2438                                 case TCPOPT_WINDOW:
2439                                         if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
2440                                                 if (sysctl_tcp_window_scaling) {
2441                                                         __u8 snd_wscale = *(__u8 *) ptr;
2442                                                         opt_rx->wscale_ok = 1;
2443                                                         if (snd_wscale > 14) {
2444                                                                 if(net_ratelimit())
2445                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
2446                                                                                "scaling value %d >14 received.\n",
2447                                                                                snd_wscale);
2448                                                                 snd_wscale = 14;
2449                                                         }
2450                                                         opt_rx->snd_wscale = snd_wscale;
2451                                                 }
2452                                         break;
2453                                 case TCPOPT_TIMESTAMP:
2454                                         if(opsize==TCPOLEN_TIMESTAMP) {
2455                                                 if ((estab && opt_rx->tstamp_ok) ||
2456                                                     (!estab && sysctl_tcp_timestamps)) {
2457                                                         opt_rx->saw_tstamp = 1;
2458                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr));
2459                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4)));
2460                                                 }
2461                                         }
2462                                         break;
2463                                 case TCPOPT_SACK_PERM:
2464                                         if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2465                                                 if (sysctl_tcp_sack) {
2466                                                         opt_rx->sack_ok = 1;
2467                                                         tcp_sack_reset(opt_rx);
2468                                                 }
2469                                         }
2470                                         break;
2471
2472                                 case TCPOPT_SACK:
2473                                         if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2474                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2475                                            opt_rx->sack_ok) {
2476                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2477                                         }
2478                                 };
2479                                 ptr+=opsize-2;
2480                                 length-=opsize;
2481                 };
2482         }
2483 }
2484
2485 /* Fast parse options. This hopes to only see timestamps.
2486  * If it is wrong it falls back on tcp_parse_options().
2487  */
2488 static inline int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2489                                          struct tcp_sock *tp)
2490 {
2491         if (th->doff == sizeof(struct tcphdr)>>2) {
2492                 tp->rx_opt.saw_tstamp = 0;
2493                 return 0;
2494         } else if (tp->rx_opt.tstamp_ok &&
2495                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2496                 __u32 *ptr = (__u32 *)(th + 1);
2497                 if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2498                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2499                         tp->rx_opt.saw_tstamp = 1;
2500                         ++ptr;
2501                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
2502                         ++ptr;
2503                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2504                         return 1;
2505                 }
2506         }
2507         tcp_parse_options(skb, &tp->rx_opt, 1);
2508         return 1;
2509 }
2510
2511 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2512 {
2513         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2514         tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
2515 }
2516
2517 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2518 {
2519         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2520                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
2521                  * extra check below makes sure this can only happen
2522                  * for pure ACK frames.  -DaveM
2523                  *
2524                  * Not only, also it occurs for expired timestamps.
2525                  */
2526
2527                 if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2528                    xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2529                         tcp_store_ts_recent(tp);
2530         }
2531 }
2532
2533 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2534  *
2535  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2536  * it can pass through stack. So, the following predicate verifies that
2537  * this segment is not used for anything but congestion avoidance or
2538  * fast retransmit. Moreover, we even are able to eliminate most of such
2539  * second order effects, if we apply some small "replay" window (~RTO)
2540  * to timestamp space.
2541  *
2542  * All these measures still do not guarantee that we reject wrapped ACKs
2543  * on networks with high bandwidth, when sequence space is recycled fastly,
2544  * but it guarantees that such events will be very rare and do not affect
2545  * connection seriously. This doesn't look nice, but alas, PAWS is really
2546  * buggy extension.
2547  *
2548  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
2549  * states that events when retransmit arrives after original data are rare.
2550  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
2551  * the biggest problem on large power networks even with minor reordering.
2552  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
2553  * up to bandwidth of 18Gigabit/sec. 8) ]
2554  */
2555
2556 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
2557 {
2558         struct tcp_sock *tp = tcp_sk(sk);
2559         struct tcphdr *th = skb->h.th;
2560         u32 seq = TCP_SKB_CB(skb)->seq;
2561         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2562
2563         return (/* 1. Pure ACK with correct sequence number. */
2564                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
2565
2566                 /* 2. ... and duplicate ACK. */
2567                 ack == tp->snd_una &&
2568
2569                 /* 3. ... and does not update window. */
2570                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
2571
2572                 /* 4. ... and sits in replay window. */
2573                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
2574 }
2575
2576 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
2577 {
2578         const struct tcp_sock *tp = tcp_sk(sk);
2579         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
2580                 xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2581                 !tcp_disordered_ack(sk, skb));
2582 }
2583
2584 /* Check segment sequence number for validity.
2585  *
2586  * Segment controls are considered valid, if the segment
2587  * fits to the window after truncation to the window. Acceptability
2588  * of data (and SYN, FIN, of course) is checked separately.
2589  * See tcp_data_queue(), for example.
2590  *
2591  * Also, controls (RST is main one) are accepted using RCV.WUP instead
2592  * of RCV.NXT. Peer still did not advance his SND.UNA when we
2593  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
2594  * (borrowed from freebsd)
2595  */
2596
2597 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
2598 {
2599         return  !before(end_seq, tp->rcv_wup) &&
2600                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
2601 }
2602
2603 /* When we get a reset we do this. */
2604 static void tcp_reset(struct sock *sk)
2605 {
2606         /* We want the right error as BSD sees it (and indeed as we do). */
2607         switch (sk->sk_state) {
2608                 case TCP_SYN_SENT:
2609                         sk->sk_err = ECONNREFUSED;
2610                         break;
2611                 case TCP_CLOSE_WAIT:
2612                         sk->sk_err = EPIPE;
2613                         break;
2614                 case TCP_CLOSE:
2615                         return;
2616                 default:
2617                         sk->sk_err = ECONNRESET;
2618         }
2619
2620         if (!sock_flag(sk, SOCK_DEAD))
2621                 sk->sk_error_report(sk);
2622
2623         tcp_done(sk);
2624 }
2625
2626 /*
2627  *      Process the FIN bit. This now behaves as it is supposed to work
2628  *      and the FIN takes effect when it is validly part of sequence
2629  *      space. Not before when we get holes.
2630  *
2631  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
2632  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
2633  *      TIME-WAIT)
2634  *
2635  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
2636  *      close and we go into CLOSING (and later onto TIME-WAIT)
2637  *
2638  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
2639  */
2640 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
2641 {
2642         struct tcp_sock *tp = tcp_sk(sk);
2643
2644         inet_csk_schedule_ack(sk);
2645
2646         sk->sk_shutdown |= RCV_SHUTDOWN;
2647         sock_set_flag(sk, SOCK_DONE);
2648
2649         switch (sk->sk_state) {
2650                 case TCP_SYN_RECV:
2651                 case TCP_ESTABLISHED:
2652                         /* Move to CLOSE_WAIT */
2653                         tcp_set_state(sk, TCP_CLOSE_WAIT);
2654                         inet_csk(sk)->icsk_ack.pingpong = 1;
2655                         break;
2656
2657                 case TCP_CLOSE_WAIT:
2658                 case TCP_CLOSING:
2659                         /* Received a retransmission of the FIN, do
2660                          * nothing.
2661                          */
2662                         break;
2663                 case TCP_LAST_ACK:
2664                         /* RFC793: Remain in the LAST-ACK state. */
2665                         break;
2666
2667                 case TCP_FIN_WAIT1:
2668                         /* This case occurs when a simultaneous close
2669                          * happens, we must ack the received FIN and
2670                          * enter the CLOSING state.
2671                          */
2672                         tcp_send_ack(sk);
2673                         tcp_set_state(sk, TCP_CLOSING);
2674                         break;
2675                 case TCP_FIN_WAIT2:
2676                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
2677                         tcp_send_ack(sk);
2678                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
2679                         break;
2680                 default:
2681                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
2682                          * cases we should never reach this piece of code.
2683                          */
2684                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
2685                                __FUNCTION__, sk->sk_state);
2686                         break;
2687         };
2688
2689         /* It _is_ possible, that we have something out-of-order _after_ FIN.
2690          * Probably, we should reset in this case. For now drop them.
2691          */
2692         __skb_queue_purge(&tp->out_of_order_queue);
2693         if (tp->rx_opt.sack_ok)
2694                 tcp_sack_reset(&tp->rx_opt);
2695         sk_stream_mem_reclaim(sk);
2696
2697         if (!sock_flag(sk, SOCK_DEAD)) {
2698                 sk->sk_state_change(sk);
2699
2700                 /* Do not send POLL_HUP for half duplex close. */
2701                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
2702                     sk->sk_state == TCP_CLOSE)
2703                         sk_wake_async(sk, 1, POLL_HUP);
2704                 else
2705                         sk_wake_async(sk, 1, POLL_IN);
2706         }
2707 }
2708
2709 static __inline__ int
2710 tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
2711 {
2712         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
2713                 if (before(seq, sp->start_seq))
2714                         sp->start_seq = seq;
2715                 if (after(end_seq, sp->end_seq))
2716                         sp->end_seq = end_seq;
2717                 return 1;
2718         }
2719         return 0;
2720 }
2721
2722 static inline void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
2723 {
2724         if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2725                 if (before(seq, tp->rcv_nxt))
2726                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
2727                 else
2728                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
2729
2730                 tp->rx_opt.dsack = 1;
2731                 tp->duplicate_sack[0].start_seq = seq;
2732                 tp->duplicate_sack[0].end_seq = end_seq;
2733                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
2734         }
2735 }
2736
2737 static inline void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
2738 {
2739         if (!tp->rx_opt.dsack)
2740                 tcp_dsack_set(tp, seq, end_seq);
2741         else
2742                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
2743 }
2744
2745 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
2746 {
2747         struct tcp_sock *tp = tcp_sk(sk);
2748
2749         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
2750             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2751                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2752                 tcp_enter_quickack_mode(sk);
2753
2754                 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2755                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2756
2757                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
2758                                 end_seq = tp->rcv_nxt;
2759                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
2760                 }
2761         }
2762
2763         tcp_send_ack(sk);
2764 }
2765
2766 /* These routines update the SACK block as out-of-order packets arrive or
2767  * in-order packets close up the sequence space.
2768  */
2769 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
2770 {
2771         int this_sack;
2772         struct tcp_sack_block *sp = &tp->selective_acks[0];
2773         struct tcp_sack_block *swalk = sp+1;
2774
2775         /* See if the recent change to the first SACK eats into
2776          * or hits the sequence space of other SACK blocks, if so coalesce.
2777          */
2778         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
2779                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
2780                         int i;
2781
2782                         /* Zap SWALK, by moving every further SACK up by one slot.
2783                          * Decrease num_sacks.
2784                          */
2785                         tp->rx_opt.num_sacks--;
2786                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2787                         for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
2788                                 sp[i] = sp[i+1];
2789                         continue;
2790                 }
2791                 this_sack++, swalk++;
2792         }
2793 }
2794
2795 static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
2796 {
2797         __u32 tmp;
2798
2799         tmp = sack1->start_seq;
2800         sack1->start_seq = sack2->start_seq;
2801         sack2->start_seq = tmp;
2802
2803         tmp = sack1->end_seq;
2804         sack1->end_seq = sack2->end_seq;
2805         sack2->end_seq = tmp;
2806 }
2807
2808 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
2809 {
2810         struct tcp_sock *tp = tcp_sk(sk);
2811         struct tcp_sack_block *sp = &tp->selective_acks[0];
2812         int cur_sacks = tp->rx_opt.num_sacks;
2813         int this_sack;
2814
2815         if (!cur_sacks)
2816                 goto new_sack;
2817
2818         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
2819                 if (tcp_sack_extend(sp, seq, end_seq)) {
2820                         /* Rotate this_sack to the first one. */
2821                         for (; this_sack>0; this_sack--, sp--)
2822                                 tcp_sack_swap(sp, sp-1);
2823                         if (cur_sacks > 1)
2824                                 tcp_sack_maybe_coalesce(tp);
2825                         return;
2826                 }
2827         }
2828
2829         /* Could not find an adjacent existing SACK, build a new one,
2830          * put it at the front, and shift everyone else down.  We
2831          * always know there is at least one SACK present already here.
2832          *
2833          * If the sack array is full, forget about the last one.
2834          */
2835         if (this_sack >= 4) {
2836                 this_sack--;
2837                 tp->rx_opt.num_sacks--;
2838                 sp--;
2839         }
2840         for(; this_sack > 0; this_sack--, sp--)
2841                 *sp = *(sp-1);
2842
2843 new_sack:
2844         /* Build the new head SACK, and we're done. */
2845         sp->start_seq = seq;
2846         sp->end_seq = end_seq;
2847         tp->rx_opt.num_sacks++;
2848         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2849 }
2850
2851 /* RCV.NXT advances, some SACKs should be eaten. */
2852
2853 static void tcp_sack_remove(struct tcp_sock *tp)
2854 {
2855         struct tcp_sack_block *sp = &tp->selective_acks[0];
2856         int num_sacks = tp->rx_opt.num_sacks;
2857         int this_sack;
2858
2859         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
2860         if (skb_queue_empty(&tp->out_of_order_queue)) {
2861                 tp->rx_opt.num_sacks = 0;
2862                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
2863                 return;
2864         }
2865
2866         for(this_sack = 0; this_sack < num_sacks; ) {
2867                 /* Check if the start of the sack is covered by RCV.NXT. */
2868                 if (!before(tp->rcv_nxt, sp->start_seq)) {
2869                         int i;
2870
2871                         /* RCV.NXT must cover all the block! */
2872                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
2873
2874                         /* Zap this SACK, by moving forward any other SACKS. */
2875                         for (i=this_sack+1; i < num_sacks; i++)
2876                                 tp->selective_acks[i-1] = tp->selective_acks[i];
2877                         num_sacks--;
2878                         continue;
2879                 }
2880                 this_sack++;
2881                 sp++;
2882         }
2883         if (num_sacks != tp->rx_opt.num_sacks) {
2884                 tp->rx_opt.num_sacks = num_sacks;
2885                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2886         }
2887 }
2888
2889 /* This one checks to see if we can put data from the
2890  * out_of_order queue into the receive_queue.
2891  */
2892 static void tcp_ofo_queue(struct sock *sk)
2893 {
2894         struct tcp_sock *tp = tcp_sk(sk);
2895         __u32 dsack_high = tp->rcv_nxt;
2896         struct sk_buff *skb;
2897
2898         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
2899                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
2900                         break;
2901
2902                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
2903                         __u32 dsack = dsack_high;
2904                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
2905                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
2906                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
2907                 }
2908
2909                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
2910                         SOCK_DEBUG(sk, "ofo packet was already received \n");
2911                         __skb_unlink(skb, &tp->out_of_order_queue);
2912                         __kfree_skb(skb);
2913                         continue;
2914                 }
2915                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
2916                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
2917                            TCP_SKB_CB(skb)->end_seq);
2918
2919                 __skb_unlink(skb, &tp->out_of_order_queue);
2920                 __skb_queue_tail(&sk->sk_receive_queue, skb);
2921                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2922                 if(skb->h.th->fin)
2923                         tcp_fin(skb, sk, skb->h.th);
2924         }
2925 }
2926
2927 static int tcp_prune_queue(struct sock *sk);
2928
2929 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
2930 {
2931         struct tcphdr *th = skb->h.th;
2932         struct tcp_sock *tp = tcp_sk(sk);
2933         int eaten = -1;
2934
2935         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
2936                 goto drop;
2937
2938         __skb_pull(skb, th->doff*4);
2939
2940         TCP_ECN_accept_cwr(tp, skb);
2941
2942         if (tp->rx_opt.dsack) {
2943                 tp->rx_opt.dsack = 0;
2944                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
2945                                                     4 - tp->rx_opt.tstamp_ok);
2946         }
2947
2948         /*  Queue data for delivery to the user.
2949          *  Packets in sequence go to the receive queue.
2950          *  Out of sequence packets to the out_of_order_queue.
2951          */
2952         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
2953                 if (tcp_receive_window(tp) == 0)
2954                         goto out_of_window;
2955
2956                 /* Ok. In sequence. In window. */
2957                 if (tp->ucopy.task == current &&
2958                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
2959                     sock_owned_by_user(sk) && !tp->urg_data) {
2960                         int chunk = min_t(unsigned int, skb->len,
2961                                                         tp->ucopy.len);
2962
2963                         __set_current_state(TASK_RUNNING);
2964
2965                         local_bh_enable();
2966                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
2967                                 tp->ucopy.len -= chunk;
2968                                 tp->copied_seq += chunk;
2969                                 eaten = (chunk == skb->len && !th->fin);
2970                                 tcp_rcv_space_adjust(sk);
2971                         }
2972                         local_bh_disable();
2973                 }
2974
2975                 if (eaten <= 0) {
2976 queue_and_out:
2977                         if (eaten < 0 &&
2978                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
2979                              !sk_stream_rmem_schedule(sk, skb))) {
2980                                 if (tcp_prune_queue(sk) < 0 ||
2981                                     !sk_stream_rmem_schedule(sk, skb))
2982                                         goto drop;
2983                         }
2984                         sk_stream_set_owner_r(skb, sk);
2985                         __skb_queue_tail(&sk->sk_receive_queue, skb);
2986                 }
2987                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2988                 if(skb->len)
2989                         tcp_event_data_recv(sk, tp, skb);
2990                 if(th->fin)
2991                         tcp_fin(skb, sk, th);
2992
2993                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
2994                         tcp_ofo_queue(sk);
2995
2996                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
2997                          * gap in queue is filled.
2998                          */
2999                         if (skb_queue_empty(&tp->out_of_order_queue))
3000                                 inet_csk(sk)->icsk_ack.pingpong = 0;
3001                 }
3002
3003                 if (tp->rx_opt.num_sacks)
3004                         tcp_sack_remove(tp);
3005
3006                 tcp_fast_path_check(sk, tp);
3007
3008                 if (eaten > 0)
3009                         __kfree_skb(skb);
3010                 else if (!sock_flag(sk, SOCK_DEAD))
3011                         sk->sk_data_ready(sk, 0);
3012                 return;
3013         }
3014
3015         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3016                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3017                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3018                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3019
3020 out_of_window:
3021                 tcp_enter_quickack_mode(sk);
3022                 inet_csk_schedule_ack(sk);
3023 drop:
3024                 __kfree_skb(skb);
3025                 return;
3026         }
3027
3028         /* Out of window. F.e. zero window probe. */
3029         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3030                 goto out_of_window;
3031
3032         tcp_enter_quickack_mode(sk);
3033
3034         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3035                 /* Partial packet, seq < rcv_next < end_seq */
3036                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3037                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3038                            TCP_SKB_CB(skb)->end_seq);
3039
3040                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3041                 
3042                 /* If window is closed, drop tail of packet. But after
3043                  * remembering D-SACK for its head made in previous line.
3044                  */
3045                 if (!tcp_receive_window(tp))
3046                         goto out_of_window;
3047                 goto queue_and_out;
3048         }
3049
3050         TCP_ECN_check_ce(tp, skb);
3051
3052         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3053             !sk_stream_rmem_schedule(sk, skb)) {
3054                 if (tcp_prune_queue(sk) < 0 ||
3055                     !sk_stream_rmem_schedule(sk, skb))
3056                         goto drop;
3057         }
3058
3059         /* Disable header prediction. */
3060         tp->pred_flags = 0;
3061         inet_csk_schedule_ack(sk);
3062
3063         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3064                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3065
3066         sk_stream_set_owner_r(skb, sk);
3067
3068         if (!skb_peek(&tp->out_of_order_queue)) {
3069                 /* Initial out of order segment, build 1 SACK. */
3070                 if (tp->rx_opt.sack_ok) {
3071                         tp->rx_opt.num_sacks = 1;
3072                         tp->rx_opt.dsack     = 0;
3073                         tp->rx_opt.eff_sacks = 1;
3074                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3075                         tp->selective_acks[0].end_seq =
3076                                                 TCP_SKB_CB(skb)->end_seq;
3077                 }
3078                 __skb_queue_head(&tp->out_of_order_queue,skb);
3079         } else {
3080                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3081                 u32 seq = TCP_SKB_CB(skb)->seq;
3082                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3083
3084                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3085                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3086
3087                         if (!tp->rx_opt.num_sacks ||
3088                             tp->selective_acks[0].end_seq != seq)
3089                                 goto add_sack;
3090
3091                         /* Common case: data arrive in order after hole. */
3092                         tp->selective_acks[0].end_seq = end_seq;
3093                         return;
3094                 }
3095
3096                 /* Find place to insert this segment. */
3097                 do {
3098                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3099                                 break;
3100                 } while ((skb1 = skb1->prev) !=
3101                          (struct sk_buff*)&tp->out_of_order_queue);
3102
3103                 /* Do skb overlap to previous one? */
3104                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3105                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3106                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3107                                 /* All the bits are present. Drop. */
3108                                 __kfree_skb(skb);
3109                                 tcp_dsack_set(tp, seq, end_seq);
3110                                 goto add_sack;
3111                         }
3112                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3113                                 /* Partial overlap. */
3114                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3115                         } else {
3116                                 skb1 = skb1->prev;
3117                         }
3118                 }
3119                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3120                 
3121                 /* And clean segments covered by new one as whole. */
3122                 while ((skb1 = skb->next) !=
3123                        (struct sk_buff*)&tp->out_of_order_queue &&
3124                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3125                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3126                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3127                                break;
3128                        }
3129                        __skb_unlink(skb1, &tp->out_of_order_queue);
3130                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3131                        __kfree_skb(skb1);
3132                 }
3133
3134 add_sack:
3135                 if (tp->rx_opt.sack_ok)
3136                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3137         }
3138 }
3139
3140 /* Collapse contiguous sequence of skbs head..tail with
3141  * sequence numbers start..end.
3142  * Segments with FIN/SYN are not collapsed (only because this
3143  * simplifies code)
3144  */
3145 static void
3146 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3147              struct sk_buff *head, struct sk_buff *tail,
3148              u32 start, u32 end)
3149 {
3150         struct sk_buff *skb;
3151
3152         /* First, check that queue is collapsable and find
3153          * the point where collapsing can be useful. */
3154         for (skb = head; skb != tail; ) {
3155                 /* No new bits? It is possible on ofo queue. */
3156                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3157                         struct sk_buff *next = skb->next;
3158                         __skb_unlink(skb, list);
3159                         __kfree_skb(skb);
3160                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3161                         skb = next;
3162                         continue;
3163                 }
3164
3165                 /* The first skb to collapse is:
3166                  * - not SYN/FIN and
3167                  * - bloated or contains data before "start" or
3168                  *   overlaps to the next one.
3169                  */
3170                 if (!skb->h.th->syn && !skb->h.th->fin &&
3171                     (tcp_win_from_space(skb->truesize) > skb->len ||
3172                      before(TCP_SKB_CB(skb)->seq, start) ||
3173                      (skb->next != tail &&
3174                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3175                         break;
3176
3177                 /* Decided to skip this, advance start seq. */
3178                 start = TCP_SKB_CB(skb)->end_seq;
3179                 skb = skb->next;
3180         }
3181         if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3182                 return;
3183
3184         while (before(start, end)) {
3185                 struct sk_buff *nskb;
3186                 int header = skb_headroom(skb);
3187                 int copy = SKB_MAX_ORDER(header, 0);
3188
3189                 /* Too big header? This can happen with IPv6. */
3190                 if (copy < 0)
3191                         return;
3192                 if (end-start < copy)
3193                         copy = end-start;
3194                 nskb = alloc_skb(copy+header, GFP_ATOMIC);
3195                 if (!nskb)
3196                         return;
3197                 skb_reserve(nskb, header);
3198                 memcpy(nskb->head, skb->head, header);
3199                 nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head);
3200                 nskb->h.raw = nskb->head + (skb->h.raw-skb->head);
3201                 nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head);
3202                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3203                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3204                 __skb_insert(nskb, skb->prev, skb, list);
3205                 sk_stream_set_owner_r(nskb, sk);
3206
3207                 /* Copy data, releasing collapsed skbs. */
3208                 while (copy > 0) {
3209                         int offset = start - TCP_SKB_CB(skb)->seq;
3210                         int size = TCP_SKB_CB(skb)->end_seq - start;
3211
3212                         if (offset < 0) BUG();
3213                         if (size > 0) {
3214                                 size = min(copy, size);
3215                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3216                                         BUG();
3217                                 TCP_SKB_CB(nskb)->end_seq += size;
3218                                 copy -= size;
3219                                 start += size;
3220                         }
3221                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3222                                 struct sk_buff *next = skb->next;
3223                                 __skb_unlink(skb, list);
3224                                 __kfree_skb(skb);
3225                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3226                                 skb = next;
3227                                 if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3228                                         return;
3229                         }
3230                 }
3231         }
3232 }
3233
3234 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3235  * and tcp_collapse() them until all the queue is collapsed.
3236  */
3237 static void tcp_collapse_ofo_queue(struct sock *sk)
3238 {
3239         struct tcp_sock *tp = tcp_sk(sk);
3240         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3241         struct sk_buff *head;
3242         u32 start, end;
3243
3244         if (skb == NULL)
3245                 return;
3246
3247         start = TCP_SKB_CB(skb)->seq;
3248         end = TCP_SKB_CB(skb)->end_seq;
3249         head = skb;
3250
3251         for (;;) {
3252                 skb = skb->next;
3253
3254                 /* Segment is terminated when we see gap or when
3255                  * we are at the end of all the queue. */
3256                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
3257                     after(TCP_SKB_CB(skb)->seq, end) ||
3258                     before(TCP_SKB_CB(skb)->end_seq, start)) {
3259                         tcp_collapse(sk, &tp->out_of_order_queue,
3260                                      head, skb, start, end);
3261                         head = skb;
3262                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
3263                                 break;
3264                         /* Start new segment */
3265                         start = TCP_SKB_CB(skb)->seq;
3266                         end = TCP_SKB_CB(skb)->end_seq;
3267                 } else {
3268                         if (before(TCP_SKB_CB(skb)->seq, start))
3269                                 start = TCP_SKB_CB(skb)->seq;
3270                         if (after(TCP_SKB_CB(skb)->end_seq, end))
3271                                 end = TCP_SKB_CB(skb)->end_seq;
3272                 }
3273         }
3274 }
3275
3276 /* Reduce allocated memory if we can, trying to get
3277  * the socket within its memory limits again.
3278  *
3279  * Return less than zero if we should start dropping frames
3280  * until the socket owning process reads some of the data
3281  * to stabilize the situation.
3282  */
3283 static int tcp_prune_queue(struct sock *sk)
3284 {
3285         struct tcp_sock *tp = tcp_sk(sk); 
3286
3287         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
3288
3289         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
3290
3291         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
3292                 tcp_clamp_window(sk, tp);
3293         else if (tcp_memory_pressure)
3294                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
3295
3296         tcp_collapse_ofo_queue(sk);
3297         tcp_collapse(sk, &sk->sk_receive_queue,
3298                      sk->sk_receive_queue.next,
3299                      (struct sk_buff*)&sk->sk_receive_queue,
3300                      tp->copied_seq, tp->rcv_nxt);
3301         sk_stream_mem_reclaim(sk);
3302
3303         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3304                 return 0;
3305
3306         /* Collapsing did not help, destructive actions follow.
3307          * This must not ever occur. */
3308
3309         /* First, purge the out_of_order queue. */
3310         if (!skb_queue_empty(&tp->out_of_order_queue)) {
3311                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
3312                 __skb_queue_purge(&tp->out_of_order_queue);
3313
3314                 /* Reset SACK state.  A conforming SACK implementation will
3315                  * do the same at a timeout based retransmit.  When a connection
3316                  * is in a sad state like this, we care only about integrity
3317                  * of the connection not performance.
3318                  */
3319                 if (tp->rx_opt.sack_ok)
3320                         tcp_sack_reset(&tp->rx_opt);
3321                 sk_stream_mem_reclaim(sk);
3322         }
3323
3324         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3325                 return 0;
3326
3327         /* If we are really being abused, tell the caller to silently
3328          * drop receive data on the floor.  It will get retransmitted
3329          * and hopefully then we'll have sufficient space.
3330          */
3331         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
3332
3333         /* Massive buffer overcommit. */
3334         tp->pred_flags = 0;
3335         return -1;
3336 }
3337
3338
3339 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
3340  * As additional protections, we do not touch cwnd in retransmission phases,
3341  * and if application hit its sndbuf limit recently.
3342  */
3343 void tcp_cwnd_application_limited(struct sock *sk)
3344 {
3345         struct tcp_sock *tp = tcp_sk(sk);
3346
3347         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
3348             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
3349                 /* Limited by application or receiver window. */
3350                 u32 win_used = max(tp->snd_cwnd_used, 2U);
3351                 if (win_used < tp->snd_cwnd) {
3352                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
3353                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
3354                 }
3355                 tp->snd_cwnd_used = 0;
3356         }
3357         tp->snd_cwnd_stamp = tcp_time_stamp;
3358 }
3359
3360 static inline int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp)
3361 {
3362         /* If the user specified a specific send buffer setting, do
3363          * not modify it.
3364          */
3365         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
3366                 return 0;
3367
3368         /* If we are under global TCP memory pressure, do not expand.  */
3369         if (tcp_memory_pressure)
3370                 return 0;
3371
3372         /* If we are under soft global TCP memory pressure, do not expand.  */
3373         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
3374                 return 0;
3375
3376         /* If we filled the congestion window, do not expand.  */
3377         if (tp->packets_out >= tp->snd_cwnd)
3378                 return 0;
3379
3380         return 1;
3381 }
3382
3383 /* When incoming ACK allowed to free some skb from write_queue,
3384  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
3385  * on the exit from tcp input handler.
3386  *
3387  * PROBLEM: sndbuf expansion does not work well with largesend.
3388  */
3389 static void tcp_new_space(struct sock *sk)
3390 {
3391         struct tcp_sock *tp = tcp_sk(sk);
3392
3393         if (tcp_should_expand_sndbuf(sk, tp)) {
3394                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
3395                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
3396                     demanded = max_t(unsigned int, tp->snd_cwnd,
3397                                                    tp->reordering + 1);
3398                 sndmem *= 2*demanded;
3399                 if (sndmem > sk->sk_sndbuf)
3400                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
3401                 tp->snd_cwnd_stamp = tcp_time_stamp;
3402         }
3403
3404         sk->sk_write_space(sk);
3405 }
3406
3407 static inline void tcp_check_space(struct sock *sk)
3408 {
3409         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
3410                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
3411                 if (sk->sk_socket &&
3412                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
3413                         tcp_new_space(sk);
3414         }
3415 }
3416
3417 static __inline__ void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
3418 {
3419         tcp_push_pending_frames(sk, tp);
3420         tcp_check_space(sk);
3421 }
3422
3423 /*
3424  * Check if sending an ack is needed.
3425  */
3426 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
3427 {
3428         struct tcp_sock *tp = tcp_sk(sk);
3429
3430             /* More than one full frame received... */
3431         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
3432              /* ... and right edge of window advances far enough.
3433               * (tcp_recvmsg() will send ACK otherwise). Or...
3434               */
3435              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
3436             /* We ACK each frame or... */
3437             tcp_in_quickack_mode(sk) ||
3438             /* We have out of order data. */
3439             (ofo_possible &&
3440              skb_peek(&tp->out_of_order_queue))) {
3441                 /* Then ack it now */
3442                 tcp_send_ack(sk);
3443         } else {
3444                 /* Else, send delayed ack. */
3445                 tcp_send_delayed_ack(sk);
3446         }
3447 }
3448
3449 static __inline__ void tcp_ack_snd_check(struct sock *sk)
3450 {
3451         if (!inet_csk_ack_scheduled(sk)) {
3452                 /* We sent a data segment already. */
3453                 return;
3454         }
3455         __tcp_ack_snd_check(sk, 1);
3456 }
3457
3458 /*
3459  *      This routine is only called when we have urgent data
3460  *      signalled. Its the 'slow' part of tcp_urg. It could be
3461  *      moved inline now as tcp_urg is only called from one
3462  *      place. We handle URGent data wrong. We have to - as
3463  *      BSD still doesn't use the correction from RFC961.
3464  *      For 1003.1g we should support a new option TCP_STDURG to permit
3465  *      either form (or just set the sysctl tcp_stdurg).
3466  */
3467  
3468 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
3469 {
3470         struct tcp_sock *tp = tcp_sk(sk);
3471         u32 ptr = ntohs(th->urg_ptr);
3472
3473         if (ptr && !sysctl_tcp_stdurg)
3474                 ptr--;
3475         ptr += ntohl(th->seq);
3476
3477         /* Ignore urgent data that we've already seen and read. */
3478         if (after(tp->copied_seq, ptr))
3479                 return;
3480
3481         /* Do not replay urg ptr.
3482          *
3483          * NOTE: interesting situation not covered by specs.
3484          * Misbehaving sender may send urg ptr, pointing to segment,
3485          * which we already have in ofo queue. We are not able to fetch
3486          * such data and will stay in TCP_URG_NOTYET until will be eaten
3487          * by recvmsg(). Seems, we are not obliged to handle such wicked
3488          * situations. But it is worth to think about possibility of some
3489          * DoSes using some hypothetical application level deadlock.
3490          */
3491         if (before(ptr, tp->rcv_nxt))
3492                 return;
3493
3494         /* Do we already have a newer (or duplicate) urgent pointer? */
3495         if (tp->urg_data && !after(ptr, tp->urg_seq))
3496                 return;
3497
3498         /* Tell the world about our new urgent pointer. */
3499         sk_send_sigurg(sk);
3500
3501         /* We may be adding urgent data when the last byte read was
3502          * urgent. To do this requires some care. We cannot just ignore
3503          * tp->copied_seq since we would read the last urgent byte again
3504          * as data, nor can we alter copied_seq until this data arrives
3505          * or we break the sematics of SIOCATMARK (and thus sockatmark())
3506          *
3507          * NOTE. Double Dutch. Rendering to plain English: author of comment
3508          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
3509          * and expect that both A and B disappear from stream. This is _wrong_.
3510          * Though this happens in BSD with high probability, this is occasional.
3511          * Any application relying on this is buggy. Note also, that fix "works"
3512          * only in this artificial test. Insert some normal data between A and B and we will
3513          * decline of BSD again. Verdict: it is better to remove to trap
3514          * buggy users.
3515          */
3516         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
3517             !sock_flag(sk, SOCK_URGINLINE) &&
3518             tp->copied_seq != tp->rcv_nxt) {
3519                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
3520                 tp->copied_seq++;
3521                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
3522                         __skb_unlink(skb, &sk->sk_receive_queue);
3523                         __kfree_skb(skb);
3524                 }
3525         }
3526
3527         tp->urg_data   = TCP_URG_NOTYET;
3528         tp->urg_seq    = ptr;
3529
3530         /* Disable header prediction. */
3531         tp->pred_flags = 0;
3532 }
3533
3534 /* This is the 'fast' part of urgent handling. */
3535 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
3536 {
3537         struct tcp_sock *tp = tcp_sk(sk);
3538
3539         /* Check if we get a new urgent pointer - normally not. */
3540         if (th->urg)
3541                 tcp_check_urg(sk,th);
3542
3543         /* Do we wait for any urgent data? - normally not... */
3544         if (tp->urg_data == TCP_URG_NOTYET) {
3545                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
3546                           th->syn;
3547
3548                 /* Is the urgent pointer pointing into this packet? */   
3549                 if (ptr < skb->len) {
3550                         u8 tmp;
3551                         if (skb_copy_bits(skb, ptr, &tmp, 1))
3552                                 BUG();
3553                         tp->urg_data = TCP_URG_VALID | tmp;
3554                         if (!sock_flag(sk, SOCK_DEAD))
3555                                 sk->sk_data_ready(sk, 0);
3556                 }
3557         }
3558 }
3559
3560 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
3561 {
3562         struct tcp_sock *tp = tcp_sk(sk);
3563         int chunk = skb->len - hlen;
3564         int err;
3565
3566         local_bh_enable();
3567         if (skb->ip_summed==CHECKSUM_UNNECESSARY)
3568                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
3569         else
3570                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
3571                                                        tp->ucopy.iov);
3572
3573         if (!err) {
3574                 tp->ucopy.len -= chunk;
3575                 tp->copied_seq += chunk;
3576                 tcp_rcv_space_adjust(sk);
3577         }
3578
3579         local_bh_disable();
3580         return err;
3581 }
3582
3583 static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3584 {
3585         int result;
3586
3587         if (sock_owned_by_user(sk)) {
3588                 local_bh_enable();
3589                 result = __tcp_checksum_complete(skb);
3590                 local_bh_disable();
3591         } else {
3592                 result = __tcp_checksum_complete(skb);
3593         }
3594         return result;
3595 }
3596
3597 static __inline__ int
3598 tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3599 {
3600         return skb->ip_summed != CHECKSUM_UNNECESSARY &&
3601                 __tcp_checksum_complete_user(sk, skb);
3602 }
3603
3604 /*
3605  *      TCP receive function for the ESTABLISHED state. 
3606  *
3607  *      It is split into a fast path and a slow path. The fast path is 
3608  *      disabled when:
3609  *      - A zero window was announced from us - zero window probing
3610  *        is only handled properly in the slow path. 
3611  *      - Out of order segments arrived.
3612  *      - Urgent data is expected.
3613  *      - There is no buffer space left
3614  *      - Unexpected TCP flags/window values/header lengths are received
3615  *        (detected by checking the TCP header against pred_flags) 
3616  *      - Data is sent in both directions. Fast path only supports pure senders
3617  *        or pure receivers (this means either the sequence number or the ack
3618  *        value must stay constant)
3619  *      - Unexpected TCP option.
3620  *
3621  *      When these conditions are not satisfied it drops into a standard 
3622  *      receive procedure patterned after RFC793 to handle all cases.
3623  *      The first three cases are guaranteed by proper pred_flags setting,
3624  *      the rest is checked inline. Fast processing is turned on in 
3625  *      tcp_data_queue when everything is OK.
3626  */
3627 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
3628                         struct tcphdr *th, unsigned len)
3629 {
3630         struct tcp_sock *tp = tcp_sk(sk);
3631
3632         /*
3633          *      Header prediction.
3634          *      The code loosely follows the one in the famous 
3635          *      "30 instruction TCP receive" Van Jacobson mail.
3636          *      
3637          *      Van's trick is to deposit buffers into socket queue 
3638          *      on a device interrupt, to call tcp_recv function
3639          *      on the receive process context and checksum and copy
3640          *      the buffer to user space. smart...
3641          *
3642          *      Our current scheme is not silly either but we take the 
3643          *      extra cost of the net_bh soft interrupt processing...
3644          *      We do checksum and copy also but from device to kernel.
3645          */
3646
3647         tp->rx_opt.saw_tstamp = 0;
3648
3649         /*      pred_flags is 0xS?10 << 16 + snd_wnd
3650          *      if header_predition is to be made
3651          *      'S' will always be tp->tcp_header_len >> 2
3652          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
3653          *  turn it off (when there are holes in the receive 
3654          *       space for instance)
3655          *      PSH flag is ignored.
3656          */
3657
3658         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
3659                 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3660                 int tcp_header_len = tp->tcp_header_len;
3661
3662                 /* Timestamp header prediction: tcp_header_len
3663                  * is automatically equal to th->doff*4 due to pred_flags
3664                  * match.
3665                  */
3666
3667                 /* Check timestamp */
3668                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
3669                         __u32 *ptr = (__u32 *)(th + 1);
3670
3671                         /* No? Slow path! */
3672                         if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3673                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
3674                                 goto slow_path;
3675
3676                         tp->rx_opt.saw_tstamp = 1;
3677                         ++ptr; 
3678                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
3679                         ++ptr;
3680                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3681
3682                         /* If PAWS failed, check it more carefully in slow path */
3683                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
3684                                 goto slow_path;
3685
3686                         /* DO NOT update ts_recent here, if checksum fails
3687                          * and timestamp was corrupted part, it will result
3688                          * in a hung connection since we will drop all
3689                          * future packets due to the PAWS test.
3690                          */
3691                 }
3692
3693                 if (len <= tcp_header_len) {
3694                         /* Bulk data transfer: sender */
3695                         if (len == tcp_header_len) {
3696                                 /* Predicted packet is in window by definition.
3697                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3698                                  * Hence, check seq<=rcv_wup reduces to:
3699                                  */
3700                                 if (tcp_header_len ==
3701                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3702                                     tp->rcv_nxt == tp->rcv_wup)
3703                                         tcp_store_ts_recent(tp);
3704
3705                                 tcp_rcv_rtt_measure_ts(sk, skb);
3706
3707                                 /* We know that such packets are checksummed
3708                                  * on entry.
3709                                  */
3710                                 tcp_ack(sk, skb, 0);
3711                                 __kfree_skb(skb); 
3712                                 tcp_data_snd_check(sk, tp);
3713                                 return 0;
3714                         } else { /* Header too small */
3715                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
3716                                 goto discard;
3717                         }
3718                 } else {
3719                         int eaten = 0;
3720
3721                         if (tp->ucopy.task == current &&
3722                             tp->copied_seq == tp->rcv_nxt &&
3723                             len - tcp_header_len <= tp->ucopy.len &&
3724                             sock_owned_by_user(sk)) {
3725                                 __set_current_state(TASK_RUNNING);
3726
3727                                 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
3728                                         /* Predicted packet is in window by definition.
3729                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3730                                          * Hence, check seq<=rcv_wup reduces to:
3731                                          */
3732                                         if (tcp_header_len ==
3733                                             (sizeof(struct tcphdr) +
3734                                              TCPOLEN_TSTAMP_ALIGNED) &&
3735                                             tp->rcv_nxt == tp->rcv_wup)
3736                                                 tcp_store_ts_recent(tp);
3737
3738                                         tcp_rcv_rtt_measure_ts(sk, skb);
3739
3740                                         __skb_pull(skb, tcp_header_len);
3741                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3742                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
3743                                         eaten = 1;
3744                                 }
3745                         }
3746                         if (!eaten) {
3747                                 if (tcp_checksum_complete_user(sk, skb))
3748                                         goto csum_error;
3749
3750                                 /* Predicted packet is in window by definition.
3751                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3752                                  * Hence, check seq<=rcv_wup reduces to:
3753                                  */
3754                                 if (tcp_header_len ==
3755                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3756                                     tp->rcv_nxt == tp->rcv_wup)
3757                                         tcp_store_ts_recent(tp);
3758
3759                                 tcp_rcv_rtt_measure_ts(sk, skb);
3760
3761                                 if ((int)skb->truesize > sk->sk_forward_alloc)
3762                                         goto step5;
3763
3764                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
3765
3766                                 /* Bulk data transfer: receiver */
3767                                 __skb_pull(skb,tcp_header_len);
3768                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3769                                 sk_stream_set_owner_r(skb, sk);
3770                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3771                         }
3772
3773                         tcp_event_data_recv(sk, tp, skb);
3774
3775                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
3776                                 /* Well, only one small jumplet in fast path... */
3777                                 tcp_ack(sk, skb, FLAG_DATA);
3778                                 tcp_data_snd_check(sk, tp);
3779                                 if (!inet_csk_ack_scheduled(sk))
3780                                         goto no_ack;
3781                         }
3782
3783                         __tcp_ack_snd_check(sk, 0);
3784 no_ack:
3785                         if (eaten)
3786                                 __kfree_skb(skb);
3787                         else
3788                                 sk->sk_data_ready(sk, 0);
3789                         return 0;
3790                 }
3791         }
3792
3793 slow_path:
3794         if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
3795                 goto csum_error;
3796
3797         /*
3798          * RFC1323: H1. Apply PAWS check first.
3799          */
3800         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
3801             tcp_paws_discard(sk, skb)) {
3802                 if (!th->rst) {
3803                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
3804                         tcp_send_dupack(sk, skb);
3805                         goto discard;
3806                 }
3807                 /* Resets are accepted even if PAWS failed.
3808
3809                    ts_recent update must be made after we are sure
3810                    that the packet is in window.
3811                  */
3812         }
3813
3814         /*
3815          *      Standard slow path.
3816          */
3817
3818         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
3819                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
3820                  * (RST) segments are validated by checking their SEQ-fields."
3821                  * And page 69: "If an incoming segment is not acceptable,
3822                  * an acknowledgment should be sent in reply (unless the RST bit
3823                  * is set, if so drop the segment and return)".
3824                  */
3825                 if (!th->rst)
3826                         tcp_send_dupack(sk, skb);
3827                 goto discard;
3828         }
3829
3830         if(th->rst) {
3831                 tcp_reset(sk);
3832                 goto discard;
3833         }
3834
3835         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3836
3837         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3838                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
3839                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
3840                 tcp_reset(sk);
3841                 return 1;
3842         }
3843
3844 step5:
3845         if(th->ack)
3846                 tcp_ack(sk, skb, FLAG_SLOWPATH);
3847
3848         tcp_rcv_rtt_measure_ts(sk, skb);
3849
3850         /* Process urgent data. */
3851         tcp_urg(sk, skb, th);
3852
3853         /* step 7: process the segment text */
3854         tcp_data_queue(sk, skb);
3855
3856         tcp_data_snd_check(sk, tp);
3857         tcp_ack_snd_check(sk);
3858         return 0;
3859
3860 csum_error:
3861         TCP_INC_STATS_BH(TCP_MIB_INERRS);
3862
3863 discard:
3864         __kfree_skb(skb);
3865         return 0;
3866 }
3867
3868 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
3869                                          struct tcphdr *th, unsigned len)
3870 {
3871         struct tcp_sock *tp = tcp_sk(sk);
3872         int saved_clamp = tp->rx_opt.mss_clamp;
3873
3874         tcp_parse_options(skb, &tp->rx_opt, 0);
3875
3876         if (th->ack) {
3877                 struct inet_connection_sock *icsk;
3878                 /* rfc793:
3879                  * "If the state is SYN-SENT then
3880                  *    first check the ACK bit
3881                  *      If the ACK bit is set
3882                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
3883                  *        a reset (unless the RST bit is set, if so drop
3884                  *        the segment and return)"
3885                  *
3886                  *  We do not send data with SYN, so that RFC-correct
3887                  *  test reduces to:
3888                  */
3889                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
3890                         goto reset_and_undo;
3891
3892                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3893                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
3894                              tcp_time_stamp)) {
3895                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
3896                         goto reset_and_undo;
3897                 }
3898
3899                 /* Now ACK is acceptable.
3900                  *
3901                  * "If the RST bit is set
3902                  *    If the ACK was acceptable then signal the user "error:
3903                  *    connection reset", drop the segment, enter CLOSED state,
3904                  *    delete TCB, and return."
3905                  */
3906
3907                 if (th->rst) {
3908                         tcp_reset(sk);
3909                         goto discard;
3910                 }
3911
3912                 /* rfc793:
3913                  *   "fifth, if neither of the SYN or RST bits is set then
3914                  *    drop the segment and return."
3915                  *
3916                  *    See note below!
3917                  *                                        --ANK(990513)
3918                  */
3919                 if (!th->syn)
3920                         goto discard_and_undo;
3921
3922                 /* rfc793:
3923                  *   "If the SYN bit is on ...
3924                  *    are acceptable then ...
3925                  *    (our SYN has been ACKed), change the connection
3926                  *    state to ESTABLISHED..."
3927                  */
3928
3929                 TCP_ECN_rcv_synack(tp, th);
3930                 if (tp->ecn_flags&TCP_ECN_OK)
3931                         sock_set_flag(sk, SOCK_NO_LARGESEND);
3932
3933                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
3934                 tcp_ack(sk, skb, FLAG_SLOWPATH);
3935
3936                 /* Ok.. it's good. Set up sequence numbers and
3937                  * move to established.
3938                  */
3939                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
3940                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
3941
3942                 /* RFC1323: The window in SYN & SYN/ACK segments is
3943                  * never scaled.
3944                  */
3945                 tp->snd_wnd = ntohs(th->window);
3946                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
3947
3948                 if (!tp->rx_opt.wscale_ok) {
3949                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
3950                         tp->window_clamp = min(tp->window_clamp, 65535U);
3951                 }
3952
3953                 if (tp->rx_opt.saw_tstamp) {
3954                         tp->rx_opt.tstamp_ok       = 1;
3955                         tp->tcp_header_len =
3956                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
3957                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
3958                         tcp_store_ts_recent(tp);
3959                 } else {
3960                         tp->tcp_header_len = sizeof(struct tcphdr);
3961                 }
3962
3963                 if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
3964                         tp->rx_opt.sack_ok |= 2;
3965
3966                 tcp_sync_mss(sk, tp->pmtu_cookie);
3967                 tcp_initialize_rcv_mss(sk);
3968
3969                 /* Remember, tcp_poll() does not lock socket!
3970                  * Change state from SYN-SENT only after copied_seq
3971                  * is initialized. */
3972                 tp->copied_seq = tp->rcv_nxt;
3973                 mb();
3974                 tcp_set_state(sk, TCP_ESTABLISHED);
3975
3976                 /* Make sure socket is routed, for correct metrics.  */
3977                 tp->af_specific->rebuild_header(sk);
3978
3979                 tcp_init_metrics(sk);
3980
3981                 tcp_init_congestion_control(sk);
3982
3983                 /* Prevent spurious tcp_cwnd_restart() on first data
3984                  * packet.
3985                  */
3986                 tp->lsndtime = tcp_time_stamp;
3987
3988                 tcp_init_buffer_space(sk);
3989
3990                 if (sock_flag(sk, SOCK_KEEPOPEN))
3991                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
3992
3993                 if (!tp->rx_opt.snd_wscale)
3994                         __tcp_fast_path_on(tp, tp->snd_wnd);
3995                 else
3996                         tp->pred_flags = 0;
3997
3998                 if (!sock_flag(sk, SOCK_DEAD)) {
3999                         sk->sk_state_change(sk);
4000                         sk_wake_async(sk, 0, POLL_OUT);
4001                 }
4002
4003                 icsk = inet_csk(sk);
4004
4005                 if (sk->sk_write_pending ||
4006                     icsk->icsk_accept_queue.rskq_defer_accept ||
4007                     icsk->icsk_ack.pingpong) {
4008                         /* Save one ACK. Data will be ready after
4009                          * several ticks, if write_pending is set.
4010                          *
4011                          * It may be deleted, but with this feature tcpdumps
4012                          * look so _wonderfully_ clever, that I was not able
4013                          * to stand against the temptation 8)     --ANK
4014                          */
4015                         inet_csk_schedule_ack(sk);
4016                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4017                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4018                         tcp_incr_quickack(sk);
4019                         tcp_enter_quickack_mode(sk);
4020                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4021                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4022
4023 discard:
4024                         __kfree_skb(skb);
4025                         return 0;
4026                 } else {
4027                         tcp_send_ack(sk);
4028                 }
4029                 return -1;
4030         }
4031
4032         /* No ACK in the segment */
4033
4034         if (th->rst) {
4035                 /* rfc793:
4036                  * "If the RST bit is set
4037                  *
4038                  *      Otherwise (no ACK) drop the segment and return."
4039                  */
4040
4041                 goto discard_and_undo;
4042         }
4043
4044         /* PAWS check. */
4045         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4046                 goto discard_and_undo;
4047
4048         if (th->syn) {
4049                 /* We see SYN without ACK. It is attempt of
4050                  * simultaneous connect with crossed SYNs.
4051                  * Particularly, it can be connect to self.
4052                  */
4053                 tcp_set_state(sk, TCP_SYN_RECV);
4054
4055                 if (tp->rx_opt.saw_tstamp) {
4056                         tp->rx_opt.tstamp_ok = 1;
4057                         tcp_store_ts_recent(tp);
4058                         tp->tcp_header_len =
4059                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4060                 } else {
4061                         tp->tcp_header_len = sizeof(struct tcphdr);
4062                 }
4063
4064                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4065                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4066
4067                 /* RFC1323: The window in SYN & SYN/ACK segments is
4068                  * never scaled.
4069                  */
4070                 tp->snd_wnd    = ntohs(th->window);
4071                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4072                 tp->max_window = tp->snd_wnd;
4073
4074                 TCP_ECN_rcv_syn(tp, th);
4075                 if (tp->ecn_flags&TCP_ECN_OK)
4076                         sock_set_flag(sk, SOCK_NO_LARGESEND);
4077
4078                 tcp_sync_mss(sk, tp->pmtu_cookie);
4079                 tcp_initialize_rcv_mss(sk);
4080
4081
4082                 tcp_send_synack(sk);
4083 #if 0
4084                 /* Note, we could accept data and URG from this segment.
4085                  * There are no obstacles to make this.
4086                  *
4087                  * However, if we ignore data in ACKless segments sometimes,
4088                  * we have no reasons to accept it sometimes.
4089                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
4090                  * is not flawless. So, discard packet for sanity.
4091                  * Uncomment this return to process the data.
4092                  */
4093                 return -1;
4094 #else
4095                 goto discard;
4096 #endif
4097         }
4098         /* "fifth, if neither of the SYN or RST bits is set then
4099          * drop the segment and return."
4100          */
4101
4102 discard_and_undo:
4103         tcp_clear_options(&tp->rx_opt);
4104         tp->rx_opt.mss_clamp = saved_clamp;
4105         goto discard;
4106
4107 reset_and_undo:
4108         tcp_clear_options(&tp->rx_opt);
4109         tp->rx_opt.mss_clamp = saved_clamp;
4110         return 1;
4111 }
4112
4113
4114 /*
4115  *      This function implements the receiving procedure of RFC 793 for
4116  *      all states except ESTABLISHED and TIME_WAIT. 
4117  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4118  *      address independent.
4119  */
4120         
4121 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4122                           struct tcphdr *th, unsigned len)
4123 {
4124         struct tcp_sock *tp = tcp_sk(sk);
4125         int queued = 0;
4126
4127         tp->rx_opt.saw_tstamp = 0;
4128
4129         switch (sk->sk_state) {
4130         case TCP_CLOSE:
4131                 goto discard;
4132
4133         case TCP_LISTEN:
4134                 if(th->ack)
4135                         return 1;
4136
4137                 if(th->rst)
4138                         goto discard;
4139
4140                 if(th->syn) {
4141                         if(tp->af_specific->conn_request(sk, skb) < 0)
4142                                 return 1;
4143
4144                         /* Now we have several options: In theory there is 
4145                          * nothing else in the frame. KA9Q has an option to 
4146                          * send data with the syn, BSD accepts data with the
4147                          * syn up to the [to be] advertised window and 
4148                          * Solaris 2.1 gives you a protocol error. For now 
4149                          * we just ignore it, that fits the spec precisely 
4150                          * and avoids incompatibilities. It would be nice in
4151                          * future to drop through and process the data.
4152                          *
4153                          * Now that TTCP is starting to be used we ought to 
4154                          * queue this data.
4155                          * But, this leaves one open to an easy denial of
4156                          * service attack, and SYN cookies can't defend
4157                          * against this problem. So, we drop the data
4158                          * in the interest of security over speed.
4159                          */
4160                         goto discard;
4161                 }
4162                 goto discard;
4163
4164         case TCP_SYN_SENT:
4165                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4166                 if (queued >= 0)
4167                         return queued;
4168
4169                 /* Do step6 onward by hand. */
4170                 tcp_urg(sk, skb, th);
4171                 __kfree_skb(skb);
4172                 tcp_data_snd_check(sk, tp);
4173                 return 0;
4174         }
4175
4176         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4177             tcp_paws_discard(sk, skb)) {
4178                 if (!th->rst) {
4179                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4180                         tcp_send_dupack(sk, skb);
4181                         goto discard;
4182                 }
4183                 /* Reset is accepted even if it did not pass PAWS. */
4184         }
4185
4186         /* step 1: check sequence number */
4187         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4188                 if (!th->rst)
4189                         tcp_send_dupack(sk, skb);
4190                 goto discard;
4191         }
4192
4193         /* step 2: check RST bit */
4194         if(th->rst) {
4195                 tcp_reset(sk);
4196                 goto discard;
4197         }
4198
4199         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4200
4201         /* step 3: check security and precedence [ignored] */
4202
4203         /*      step 4:
4204          *
4205          *      Check for a SYN in window.
4206          */
4207         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4208                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4209                 tcp_reset(sk);
4210                 return 1;
4211         }
4212
4213         /* step 5: check the ACK field */
4214         if (th->ack) {
4215                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
4216
4217                 switch(sk->sk_state) {
4218                 case TCP_SYN_RECV:
4219                         if (acceptable) {
4220                                 tp->copied_seq = tp->rcv_nxt;
4221                                 mb();
4222                                 tcp_set_state(sk, TCP_ESTABLISHED);
4223                                 sk->sk_state_change(sk);
4224
4225                                 /* Note, that this wakeup is only for marginal
4226                                  * crossed SYN case. Passively open sockets
4227                                  * are not waked up, because sk->sk_sleep ==
4228                                  * NULL and sk->sk_socket == NULL.
4229                                  */
4230                                 if (sk->sk_socket) {
4231                                         sk_wake_async(sk,0,POLL_OUT);
4232                                 }
4233
4234                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
4235                                 tp->snd_wnd = ntohs(th->window) <<
4236                                               tp->rx_opt.snd_wscale;
4237                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
4238                                             TCP_SKB_CB(skb)->seq);
4239
4240                                 /* tcp_ack considers this ACK as duplicate
4241                                  * and does not calculate rtt.
4242                                  * Fix it at least with timestamps.
4243                                  */
4244                                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4245                                     !tp->srtt)
4246                                         tcp_ack_saw_tstamp(sk, NULL, 0);
4247
4248                                 if (tp->rx_opt.tstamp_ok)
4249                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
4250
4251                                 /* Make sure socket is routed, for
4252                                  * correct metrics.
4253                                  */
4254                                 tp->af_specific->rebuild_header(sk);
4255
4256                                 tcp_init_metrics(sk);
4257
4258                                 tcp_init_congestion_control(sk);
4259
4260                                 /* Prevent spurious tcp_cwnd_restart() on
4261                                  * first data packet.
4262                                  */
4263                                 tp->lsndtime = tcp_time_stamp;
4264
4265                                 tcp_initialize_rcv_mss(sk);
4266                                 tcp_init_buffer_space(sk);
4267                                 tcp_fast_path_on(tp);
4268                         } else {
4269                                 return 1;
4270                         }
4271                         break;
4272
4273                 case TCP_FIN_WAIT1:
4274                         if (tp->snd_una == tp->write_seq) {
4275                                 tcp_set_state(sk, TCP_FIN_WAIT2);
4276                                 sk->sk_shutdown |= SEND_SHUTDOWN;
4277                                 dst_confirm(sk->sk_dst_cache);
4278
4279                                 if (!sock_flag(sk, SOCK_DEAD))
4280                                         /* Wake up lingering close() */
4281                                         sk->sk_state_change(sk);
4282                                 else {
4283                                         int tmo;
4284
4285                                         if (tp->linger2 < 0 ||
4286                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4287                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
4288                                                 tcp_done(sk);
4289                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4290                                                 return 1;
4291                                         }
4292
4293                                         tmo = tcp_fin_time(sk);
4294                                         if (tmo > TCP_TIMEWAIT_LEN) {
4295                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
4296                                         } else if (th->fin || sock_owned_by_user(sk)) {
4297                                                 /* Bad case. We could lose such FIN otherwise.
4298                                                  * It is not a big problem, but it looks confusing
4299                                                  * and not so rare event. We still can lose it now,
4300                                                  * if it spins in bh_lock_sock(), but it is really
4301                                                  * marginal case.
4302                                                  */
4303                                                 inet_csk_reset_keepalive_timer(sk, tmo);
4304                                         } else {
4305                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
4306                                                 goto discard;
4307                                         }
4308                                 }
4309                         }
4310                         break;
4311
4312                 case TCP_CLOSING:
4313                         if (tp->snd_una == tp->write_seq) {
4314                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4315                                 goto discard;
4316                         }
4317                         break;
4318
4319                 case TCP_LAST_ACK:
4320                         if (tp->snd_una == tp->write_seq) {
4321                                 tcp_update_metrics(sk);
4322                                 tcp_done(sk);
4323                                 goto discard;
4324                         }
4325                         break;
4326                 }
4327         } else
4328                 goto discard;
4329
4330         /* step 6: check the URG bit */
4331         tcp_urg(sk, skb, th);
4332
4333         /* step 7: process the segment text */
4334         switch (sk->sk_state) {
4335         case TCP_CLOSE_WAIT:
4336         case TCP_CLOSING:
4337         case TCP_LAST_ACK:
4338                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4339                         break;
4340         case TCP_FIN_WAIT1:
4341         case TCP_FIN_WAIT2:
4342                 /* RFC 793 says to queue data in these states,
4343                  * RFC 1122 says we MUST send a reset. 
4344                  * BSD 4.4 also does reset.
4345                  */
4346                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
4347                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4348                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
4349                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4350                                 tcp_reset(sk);
4351                                 return 1;
4352                         }
4353                 }
4354                 /* Fall through */
4355         case TCP_ESTABLISHED: 
4356                 tcp_data_queue(sk, skb);
4357                 queued = 1;
4358                 break;
4359         }
4360
4361         /* tcp_data could move socket to TIME-WAIT */
4362         if (sk->sk_state != TCP_CLOSE) {
4363                 tcp_data_snd_check(sk, tp);
4364                 tcp_ack_snd_check(sk);
4365         }
4366
4367         if (!queued) { 
4368 discard:
4369                 __kfree_skb(skb);
4370         }
4371         return 0;
4372 }
4373
4374 EXPORT_SYMBOL(sysctl_tcp_ecn);
4375 EXPORT_SYMBOL(sysctl_tcp_reordering);
4376 EXPORT_SYMBOL(tcp_parse_options);
4377 EXPORT_SYMBOL(tcp_rcv_established);
4378 EXPORT_SYMBOL(tcp_rcv_state_process);