[NETFILTER]: Simplify netbios helper
[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                         pcount = tcp_skb_pcount(skb);
983
984                         if (pcount > 1 &&
985                             (after(start_seq, TCP_SKB_CB(skb)->seq) ||
986                              before(end_seq, TCP_SKB_CB(skb)->end_seq))) {
987                                 unsigned int pkt_len;
988
989                                 if (after(start_seq, TCP_SKB_CB(skb)->seq))
990                                         pkt_len = (start_seq -
991                                                    TCP_SKB_CB(skb)->seq);
992                                 else
993                                         pkt_len = (end_seq -
994                                                    TCP_SKB_CB(skb)->seq);
995                                 if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->tso_size))
996                                         break;
997                                 pcount = tcp_skb_pcount(skb);
998                         }
999
1000                         fack_count += pcount;
1001
1002                         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1003                                 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1004
1005                         sacked = TCP_SKB_CB(skb)->sacked;
1006
1007                         /* Account D-SACK for retransmitted packet. */
1008                         if ((dup_sack && in_sack) &&
1009                             (sacked & TCPCB_RETRANS) &&
1010                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1011                                 tp->undo_retrans--;
1012
1013                         /* The frame is ACKed. */
1014                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1015                                 if (sacked&TCPCB_RETRANS) {
1016                                         if ((dup_sack && in_sack) &&
1017                                             (sacked&TCPCB_SACKED_ACKED))
1018                                                 reord = min(fack_count, reord);
1019                                 } else {
1020                                         /* If it was in a hole, we detected reordering. */
1021                                         if (fack_count < prior_fackets &&
1022                                             !(sacked&TCPCB_SACKED_ACKED))
1023                                                 reord = min(fack_count, reord);
1024                                 }
1025
1026                                 /* Nothing to do; acked frame is about to be dropped. */
1027                                 continue;
1028                         }
1029
1030                         if ((sacked&TCPCB_SACKED_RETRANS) &&
1031                             after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1032                             (!lost_retrans || after(end_seq, lost_retrans)))
1033                                 lost_retrans = end_seq;
1034
1035                         if (!in_sack)
1036                                 continue;
1037
1038                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1039                                 if (sacked & TCPCB_SACKED_RETRANS) {
1040                                         /* If the segment is not tagged as lost,
1041                                          * we do not clear RETRANS, believing
1042                                          * that retransmission is still in flight.
1043                                          */
1044                                         if (sacked & TCPCB_LOST) {
1045                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1046                                                 tp->lost_out -= tcp_skb_pcount(skb);
1047                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1048                                         }
1049                                 } else {
1050                                         /* New sack for not retransmitted frame,
1051                                          * which was in hole. It is reordering.
1052                                          */
1053                                         if (!(sacked & TCPCB_RETRANS) &&
1054                                             fack_count < prior_fackets)
1055                                                 reord = min(fack_count, reord);
1056
1057                                         if (sacked & TCPCB_LOST) {
1058                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1059                                                 tp->lost_out -= tcp_skb_pcount(skb);
1060                                         }
1061                                 }
1062
1063                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1064                                 flag |= FLAG_DATA_SACKED;
1065                                 tp->sacked_out += tcp_skb_pcount(skb);
1066
1067                                 if (fack_count > tp->fackets_out)
1068                                         tp->fackets_out = fack_count;
1069                         } else {
1070                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1071                                         reord = min(fack_count, reord);
1072                         }
1073
1074                         /* D-SACK. We can detect redundant retransmission
1075                          * in S|R and plain R frames and clear it.
1076                          * undo_retrans is decreased above, L|R frames
1077                          * are accounted above as well.
1078                          */
1079                         if (dup_sack &&
1080                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1081                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1082                                 tp->retrans_out -= tcp_skb_pcount(skb);
1083                         }
1084                 }
1085         }
1086
1087         /* Check for lost retransmit. This superb idea is
1088          * borrowed from "ratehalving". Event "C".
1089          * Later note: FACK people cheated me again 8),
1090          * we have to account for reordering! Ugly,
1091          * but should help.
1092          */
1093         if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
1094                 struct sk_buff *skb;
1095
1096                 sk_stream_for_retrans_queue(skb, sk) {
1097                         if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1098                                 break;
1099                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1100                                 continue;
1101                         if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1102                             after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1103                             (IsFack(tp) ||
1104                              !before(lost_retrans,
1105                                      TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1106                                      tp->mss_cache))) {
1107                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1108                                 tp->retrans_out -= tcp_skb_pcount(skb);
1109
1110                                 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1111                                         tp->lost_out += tcp_skb_pcount(skb);
1112                                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1113                                         flag |= FLAG_DATA_SACKED;
1114                                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1115                                 }
1116                         }
1117                 }
1118         }
1119
1120         tp->left_out = tp->sacked_out + tp->lost_out;
1121
1122         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss)
1123                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1124
1125 #if FASTRETRANS_DEBUG > 0
1126         BUG_TRAP((int)tp->sacked_out >= 0);
1127         BUG_TRAP((int)tp->lost_out >= 0);
1128         BUG_TRAP((int)tp->retrans_out >= 0);
1129         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1130 #endif
1131         return flag;
1132 }
1133
1134 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new
1135  * segments to see from the next ACKs whether any data was really missing.
1136  * If the RTO was spurious, new ACKs should arrive.
1137  */
1138 void tcp_enter_frto(struct sock *sk)
1139 {
1140         const struct inet_connection_sock *icsk = inet_csk(sk);
1141         struct tcp_sock *tp = tcp_sk(sk);
1142         struct sk_buff *skb;
1143
1144         tp->frto_counter = 1;
1145
1146         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1147             tp->snd_una == tp->high_seq ||
1148             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1149                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1150                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1151                 tcp_ca_event(sk, CA_EVENT_FRTO);
1152         }
1153
1154         /* Have to clear retransmission markers here to keep the bookkeeping
1155          * in shape, even though we are not yet in Loss state.
1156          * If something was really lost, it is eventually caught up
1157          * in tcp_enter_frto_loss.
1158          */
1159         tp->retrans_out = 0;
1160         tp->undo_marker = tp->snd_una;
1161         tp->undo_retrans = 0;
1162
1163         sk_stream_for_retrans_queue(skb, sk) {
1164                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
1165         }
1166         tcp_sync_left_out(tp);
1167
1168         tcp_set_ca_state(sk, TCP_CA_Open);
1169         tp->frto_highmark = tp->snd_nxt;
1170 }
1171
1172 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1173  * which indicates that we should follow the traditional RTO recovery,
1174  * i.e. mark everything lost and do go-back-N retransmission.
1175  */
1176 static void tcp_enter_frto_loss(struct sock *sk)
1177 {
1178         struct tcp_sock *tp = tcp_sk(sk);
1179         struct sk_buff *skb;
1180         int cnt = 0;
1181
1182         tp->sacked_out = 0;
1183         tp->lost_out = 0;
1184         tp->fackets_out = 0;
1185
1186         sk_stream_for_retrans_queue(skb, sk) {
1187                 cnt += tcp_skb_pcount(skb);
1188                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1189                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1190
1191                         /* Do not mark those segments lost that were
1192                          * forward transmitted after RTO
1193                          */
1194                         if (!after(TCP_SKB_CB(skb)->end_seq,
1195                                    tp->frto_highmark)) {
1196                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1197                                 tp->lost_out += tcp_skb_pcount(skb);
1198                         }
1199                 } else {
1200                         tp->sacked_out += tcp_skb_pcount(skb);
1201                         tp->fackets_out = cnt;
1202                 }
1203         }
1204         tcp_sync_left_out(tp);
1205
1206         tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
1207         tp->snd_cwnd_cnt = 0;
1208         tp->snd_cwnd_stamp = tcp_time_stamp;
1209         tp->undo_marker = 0;
1210         tp->frto_counter = 0;
1211
1212         tp->reordering = min_t(unsigned int, tp->reordering,
1213                                              sysctl_tcp_reordering);
1214         tcp_set_ca_state(sk, TCP_CA_Loss);
1215         tp->high_seq = tp->frto_highmark;
1216         TCP_ECN_queue_cwr(tp);
1217 }
1218
1219 void tcp_clear_retrans(struct tcp_sock *tp)
1220 {
1221         tp->left_out = 0;
1222         tp->retrans_out = 0;
1223
1224         tp->fackets_out = 0;
1225         tp->sacked_out = 0;
1226         tp->lost_out = 0;
1227
1228         tp->undo_marker = 0;
1229         tp->undo_retrans = 0;
1230 }
1231
1232 /* Enter Loss state. If "how" is not zero, forget all SACK information
1233  * and reset tags completely, otherwise preserve SACKs. If receiver
1234  * dropped its ofo queue, we will know this due to reneging detection.
1235  */
1236 void tcp_enter_loss(struct sock *sk, int how)
1237 {
1238         const struct inet_connection_sock *icsk = inet_csk(sk);
1239         struct tcp_sock *tp = tcp_sk(sk);
1240         struct sk_buff *skb;
1241         int cnt = 0;
1242
1243         /* Reduce ssthresh if it has not yet been made inside this window. */
1244         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1245             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1246                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1247                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1248                 tcp_ca_event(sk, CA_EVENT_LOSS);
1249         }
1250         tp->snd_cwnd       = 1;
1251         tp->snd_cwnd_cnt   = 0;
1252         tp->snd_cwnd_stamp = tcp_time_stamp;
1253
1254         tcp_clear_retrans(tp);
1255
1256         /* Push undo marker, if it was plain RTO and nothing
1257          * was retransmitted. */
1258         if (!how)
1259                 tp->undo_marker = tp->snd_una;
1260
1261         sk_stream_for_retrans_queue(skb, sk) {
1262                 cnt += tcp_skb_pcount(skb);
1263                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1264                         tp->undo_marker = 0;
1265                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1266                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1267                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1268                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1269                         tp->lost_out += tcp_skb_pcount(skb);
1270                 } else {
1271                         tp->sacked_out += tcp_skb_pcount(skb);
1272                         tp->fackets_out = cnt;
1273                 }
1274         }
1275         tcp_sync_left_out(tp);
1276
1277         tp->reordering = min_t(unsigned int, tp->reordering,
1278                                              sysctl_tcp_reordering);
1279         tcp_set_ca_state(sk, TCP_CA_Loss);
1280         tp->high_seq = tp->snd_nxt;
1281         TCP_ECN_queue_cwr(tp);
1282 }
1283
1284 static int tcp_check_sack_reneging(struct sock *sk)
1285 {
1286         struct sk_buff *skb;
1287
1288         /* If ACK arrived pointing to a remembered SACK,
1289          * it means that our remembered SACKs do not reflect
1290          * real state of receiver i.e.
1291          * receiver _host_ is heavily congested (or buggy).
1292          * Do processing similar to RTO timeout.
1293          */
1294         if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
1295             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1296                 struct inet_connection_sock *icsk = inet_csk(sk);
1297                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1298
1299                 tcp_enter_loss(sk, 1);
1300                 icsk->icsk_retransmits++;
1301                 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
1302                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1303                                           icsk->icsk_rto, TCP_RTO_MAX);
1304                 return 1;
1305         }
1306         return 0;
1307 }
1308
1309 static inline int tcp_fackets_out(struct tcp_sock *tp)
1310 {
1311         return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1312 }
1313
1314 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1315 {
1316         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1317 }
1318
1319 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
1320 {
1321         return tp->packets_out &&
1322                tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
1323 }
1324
1325 /* Linux NewReno/SACK/FACK/ECN state machine.
1326  * --------------------------------------
1327  *
1328  * "Open"       Normal state, no dubious events, fast path.
1329  * "Disorder"   In all the respects it is "Open",
1330  *              but requires a bit more attention. It is entered when
1331  *              we see some SACKs or dupacks. It is split of "Open"
1332  *              mainly to move some processing from fast path to slow one.
1333  * "CWR"        CWND was reduced due to some Congestion Notification event.
1334  *              It can be ECN, ICMP source quench, local device congestion.
1335  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1336  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1337  *
1338  * tcp_fastretrans_alert() is entered:
1339  * - each incoming ACK, if state is not "Open"
1340  * - when arrived ACK is unusual, namely:
1341  *      * SACK
1342  *      * Duplicate ACK.
1343  *      * ECN ECE.
1344  *
1345  * Counting packets in flight is pretty simple.
1346  *
1347  *      in_flight = packets_out - left_out + retrans_out
1348  *
1349  *      packets_out is SND.NXT-SND.UNA counted in packets.
1350  *
1351  *      retrans_out is number of retransmitted segments.
1352  *
1353  *      left_out is number of segments left network, but not ACKed yet.
1354  *
1355  *              left_out = sacked_out + lost_out
1356  *
1357  *     sacked_out: Packets, which arrived to receiver out of order
1358  *                 and hence not ACKed. With SACKs this number is simply
1359  *                 amount of SACKed data. Even without SACKs
1360  *                 it is easy to give pretty reliable estimate of this number,
1361  *                 counting duplicate ACKs.
1362  *
1363  *       lost_out: Packets lost by network. TCP has no explicit
1364  *                 "loss notification" feedback from network (for now).
1365  *                 It means that this number can be only _guessed_.
1366  *                 Actually, it is the heuristics to predict lossage that
1367  *                 distinguishes different algorithms.
1368  *
1369  *      F.e. after RTO, when all the queue is considered as lost,
1370  *      lost_out = packets_out and in_flight = retrans_out.
1371  *
1372  *              Essentially, we have now two algorithms counting
1373  *              lost packets.
1374  *
1375  *              FACK: It is the simplest heuristics. As soon as we decided
1376  *              that something is lost, we decide that _all_ not SACKed
1377  *              packets until the most forward SACK are lost. I.e.
1378  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1379  *              It is absolutely correct estimate, if network does not reorder
1380  *              packets. And it loses any connection to reality when reordering
1381  *              takes place. We use FACK by default until reordering
1382  *              is suspected on the path to this destination.
1383  *
1384  *              NewReno: when Recovery is entered, we assume that one segment
1385  *              is lost (classic Reno). While we are in Recovery and
1386  *              a partial ACK arrives, we assume that one more packet
1387  *              is lost (NewReno). This heuristics are the same in NewReno
1388  *              and SACK.
1389  *
1390  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1391  *  deflation etc. CWND is real congestion window, never inflated, changes
1392  *  only according to classic VJ rules.
1393  *
1394  * Really tricky (and requiring careful tuning) part of algorithm
1395  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1396  * The first determines the moment _when_ we should reduce CWND and,
1397  * hence, slow down forward transmission. In fact, it determines the moment
1398  * when we decide that hole is caused by loss, rather than by a reorder.
1399  *
1400  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1401  * holes, caused by lost packets.
1402  *
1403  * And the most logically complicated part of algorithm is undo
1404  * heuristics. We detect false retransmits due to both too early
1405  * fast retransmit (reordering) and underestimated RTO, analyzing
1406  * timestamps and D-SACKs. When we detect that some segments were
1407  * retransmitted by mistake and CWND reduction was wrong, we undo
1408  * window reduction and abort recovery phase. This logic is hidden
1409  * inside several functions named tcp_try_undo_<something>.
1410  */
1411
1412 /* This function decides, when we should leave Disordered state
1413  * and enter Recovery phase, reducing congestion window.
1414  *
1415  * Main question: may we further continue forward transmission
1416  * with the same cwnd?
1417  */
1418 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
1419 {
1420         __u32 packets_out;
1421
1422         /* Trick#1: The loss is proven. */
1423         if (tp->lost_out)
1424                 return 1;
1425
1426         /* Not-A-Trick#2 : Classic rule... */
1427         if (tcp_fackets_out(tp) > tp->reordering)
1428                 return 1;
1429
1430         /* Trick#3 : when we use RFC2988 timer restart, fast
1431          * retransmit can be triggered by timeout of queue head.
1432          */
1433         if (tcp_head_timedout(sk, tp))
1434                 return 1;
1435
1436         /* Trick#4: It is still not OK... But will it be useful to delay
1437          * recovery more?
1438          */
1439         packets_out = tp->packets_out;
1440         if (packets_out <= tp->reordering &&
1441             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1442             !tcp_may_send_now(sk, tp)) {
1443                 /* We have nothing to send. This connection is limited
1444                  * either by receiver window or by application.
1445                  */
1446                 return 1;
1447         }
1448
1449         return 0;
1450 }
1451
1452 /* If we receive more dupacks than we expected counting segments
1453  * in assumption of absent reordering, interpret this as reordering.
1454  * The only another reason could be bug in receiver TCP.
1455  */
1456 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1457 {
1458         struct tcp_sock *tp = tcp_sk(sk);
1459         u32 holes;
1460
1461         holes = max(tp->lost_out, 1U);
1462         holes = min(holes, tp->packets_out);
1463
1464         if ((tp->sacked_out + holes) > tp->packets_out) {
1465                 tp->sacked_out = tp->packets_out - holes;
1466                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1467         }
1468 }
1469
1470 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1471
1472 static void tcp_add_reno_sack(struct sock *sk)
1473 {
1474         struct tcp_sock *tp = tcp_sk(sk);
1475         tp->sacked_out++;
1476         tcp_check_reno_reordering(sk, 0);
1477         tcp_sync_left_out(tp);
1478 }
1479
1480 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1481
1482 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
1483 {
1484         if (acked > 0) {
1485                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1486                 if (acked-1 >= tp->sacked_out)
1487                         tp->sacked_out = 0;
1488                 else
1489                         tp->sacked_out -= acked-1;
1490         }
1491         tcp_check_reno_reordering(sk, acked);
1492         tcp_sync_left_out(tp);
1493 }
1494
1495 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1496 {
1497         tp->sacked_out = 0;
1498         tp->left_out = tp->lost_out;
1499 }
1500
1501 /* Mark head of queue up as lost. */
1502 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
1503                                int packets, u32 high_seq)
1504 {
1505         struct sk_buff *skb;
1506         int cnt = packets;
1507
1508         BUG_TRAP(cnt <= tp->packets_out);
1509
1510         sk_stream_for_retrans_queue(skb, sk) {
1511                 cnt -= tcp_skb_pcount(skb);
1512                 if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1513                         break;
1514                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1515                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1516                         tp->lost_out += tcp_skb_pcount(skb);
1517                 }
1518         }
1519         tcp_sync_left_out(tp);
1520 }
1521
1522 /* Account newly detected lost packet(s) */
1523
1524 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
1525 {
1526         if (IsFack(tp)) {
1527                 int lost = tp->fackets_out - tp->reordering;
1528                 if (lost <= 0)
1529                         lost = 1;
1530                 tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
1531         } else {
1532                 tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
1533         }
1534
1535         /* New heuristics: it is possible only after we switched
1536          * to restart timer each time when something is ACKed.
1537          * Hence, we can detect timed out packets during fast
1538          * retransmit without falling to slow start.
1539          */
1540         if (tcp_head_timedout(sk, tp)) {
1541                 struct sk_buff *skb;
1542
1543                 sk_stream_for_retrans_queue(skb, sk) {
1544                         if (tcp_skb_timedout(sk, skb) &&
1545                             !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1546                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1547                                 tp->lost_out += tcp_skb_pcount(skb);
1548                         }
1549                 }
1550                 tcp_sync_left_out(tp);
1551         }
1552 }
1553
1554 /* CWND moderation, preventing bursts due to too big ACKs
1555  * in dubious situations.
1556  */
1557 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1558 {
1559         tp->snd_cwnd = min(tp->snd_cwnd,
1560                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1561         tp->snd_cwnd_stamp = tcp_time_stamp;
1562 }
1563
1564 /* Decrease cwnd each second ack. */
1565 static void tcp_cwnd_down(struct sock *sk)
1566 {
1567         const struct inet_connection_sock *icsk = inet_csk(sk);
1568         struct tcp_sock *tp = tcp_sk(sk);
1569         int decr = tp->snd_cwnd_cnt + 1;
1570
1571         tp->snd_cwnd_cnt = decr&1;
1572         decr >>= 1;
1573
1574         if (decr && tp->snd_cwnd > icsk->icsk_ca_ops->min_cwnd(sk))
1575                 tp->snd_cwnd -= decr;
1576
1577         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1578         tp->snd_cwnd_stamp = tcp_time_stamp;
1579 }
1580
1581 /* Nothing was retransmitted or returned timestamp is less
1582  * than timestamp of the first retransmission.
1583  */
1584 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1585 {
1586         return !tp->retrans_stamp ||
1587                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1588                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1589 }
1590
1591 /* Undo procedures. */
1592
1593 #if FASTRETRANS_DEBUG > 1
1594 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
1595 {
1596         struct inet_sock *inet = inet_sk(sk);
1597         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1598                msg,
1599                NIPQUAD(inet->daddr), ntohs(inet->dport),
1600                tp->snd_cwnd, tp->left_out,
1601                tp->snd_ssthresh, tp->prior_ssthresh,
1602                tp->packets_out);
1603 }
1604 #else
1605 #define DBGUNDO(x...) do { } while (0)
1606 #endif
1607
1608 static void tcp_undo_cwr(struct sock *sk, const int undo)
1609 {
1610         struct tcp_sock *tp = tcp_sk(sk);
1611
1612         if (tp->prior_ssthresh) {
1613                 const struct inet_connection_sock *icsk = inet_csk(sk);
1614
1615                 if (icsk->icsk_ca_ops->undo_cwnd)
1616                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
1617                 else
1618                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1619
1620                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1621                         tp->snd_ssthresh = tp->prior_ssthresh;
1622                         TCP_ECN_withdraw_cwr(tp);
1623                 }
1624         } else {
1625                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1626         }
1627         tcp_moderate_cwnd(tp);
1628         tp->snd_cwnd_stamp = tcp_time_stamp;
1629 }
1630
1631 static inline int tcp_may_undo(struct tcp_sock *tp)
1632 {
1633         return tp->undo_marker &&
1634                 (!tp->undo_retrans || tcp_packet_delayed(tp));
1635 }
1636
1637 /* People celebrate: "We love our President!" */
1638 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
1639 {
1640         if (tcp_may_undo(tp)) {
1641                 /* Happy end! We did not retransmit anything
1642                  * or our original transmission succeeded.
1643                  */
1644                 DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
1645                 tcp_undo_cwr(sk, 1);
1646                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
1647                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1648                 else
1649                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1650                 tp->undo_marker = 0;
1651         }
1652         if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1653                 /* Hold old state until something *above* high_seq
1654                  * is ACKed. For Reno it is MUST to prevent false
1655                  * fast retransmits (RFC2582). SACK TCP is safe. */
1656                 tcp_moderate_cwnd(tp);
1657                 return 1;
1658         }
1659         tcp_set_ca_state(sk, TCP_CA_Open);
1660         return 0;
1661 }
1662
1663 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1664 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
1665 {
1666         if (tp->undo_marker && !tp->undo_retrans) {
1667                 DBGUNDO(sk, tp, "D-SACK");
1668                 tcp_undo_cwr(sk, 1);
1669                 tp->undo_marker = 0;
1670                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1671         }
1672 }
1673
1674 /* Undo during fast recovery after partial ACK. */
1675
1676 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
1677                                 int acked)
1678 {
1679         /* Partial ACK arrived. Force Hoe's retransmit. */
1680         int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1681
1682         if (tcp_may_undo(tp)) {
1683                 /* Plain luck! Hole if filled with delayed
1684                  * packet, rather than with a retransmit.
1685                  */
1686                 if (tp->retrans_out == 0)
1687                         tp->retrans_stamp = 0;
1688
1689                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
1690
1691                 DBGUNDO(sk, tp, "Hoe");
1692                 tcp_undo_cwr(sk, 0);
1693                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1694
1695                 /* So... Do not make Hoe's retransmit yet.
1696                  * If the first packet was delayed, the rest
1697                  * ones are most probably delayed as well.
1698                  */
1699                 failed = 0;
1700         }
1701         return failed;
1702 }
1703
1704 /* Undo during loss recovery after partial ACK. */
1705 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
1706 {
1707         if (tcp_may_undo(tp)) {
1708                 struct sk_buff *skb;
1709                 sk_stream_for_retrans_queue(skb, sk) {
1710                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1711                 }
1712                 DBGUNDO(sk, tp, "partial loss");
1713                 tp->lost_out = 0;
1714                 tp->left_out = tp->sacked_out;
1715                 tcp_undo_cwr(sk, 1);
1716                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1717                 inet_csk(sk)->icsk_retransmits = 0;
1718                 tp->undo_marker = 0;
1719                 if (!IsReno(tp))
1720                         tcp_set_ca_state(sk, TCP_CA_Open);
1721                 return 1;
1722         }
1723         return 0;
1724 }
1725
1726 static inline void tcp_complete_cwr(struct sock *sk)
1727 {
1728         struct tcp_sock *tp = tcp_sk(sk);
1729         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
1730         tp->snd_cwnd_stamp = tcp_time_stamp;
1731         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
1732 }
1733
1734 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
1735 {
1736         tp->left_out = tp->sacked_out;
1737
1738         if (tp->retrans_out == 0)
1739                 tp->retrans_stamp = 0;
1740
1741         if (flag&FLAG_ECE)
1742                 tcp_enter_cwr(sk);
1743
1744         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
1745                 int state = TCP_CA_Open;
1746
1747                 if (tp->left_out || tp->retrans_out || tp->undo_marker)
1748                         state = TCP_CA_Disorder;
1749
1750                 if (inet_csk(sk)->icsk_ca_state != state) {
1751                         tcp_set_ca_state(sk, state);
1752                         tp->high_seq = tp->snd_nxt;
1753                 }
1754                 tcp_moderate_cwnd(tp);
1755         } else {
1756                 tcp_cwnd_down(sk);
1757         }
1758 }
1759
1760 /* Process an event, which can update packets-in-flight not trivially.
1761  * Main goal of this function is to calculate new estimate for left_out,
1762  * taking into account both packets sitting in receiver's buffer and
1763  * packets lost by network.
1764  *
1765  * Besides that it does CWND reduction, when packet loss is detected
1766  * and changes state of machine.
1767  *
1768  * It does _not_ decide what to send, it is made in function
1769  * tcp_xmit_retransmit_queue().
1770  */
1771 static void
1772 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
1773                       int prior_packets, int flag)
1774 {
1775         struct inet_connection_sock *icsk = inet_csk(sk);
1776         struct tcp_sock *tp = tcp_sk(sk);
1777         int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
1778
1779         /* Some technical things:
1780          * 1. Reno does not count dupacks (sacked_out) automatically. */
1781         if (!tp->packets_out)
1782                 tp->sacked_out = 0;
1783         /* 2. SACK counts snd_fack in packets inaccurately. */
1784         if (tp->sacked_out == 0)
1785                 tp->fackets_out = 0;
1786
1787         /* Now state machine starts.
1788          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
1789         if (flag&FLAG_ECE)
1790                 tp->prior_ssthresh = 0;
1791
1792         /* B. In all the states check for reneging SACKs. */
1793         if (tp->sacked_out && tcp_check_sack_reneging(sk))
1794                 return;
1795
1796         /* C. Process data loss notification, provided it is valid. */
1797         if ((flag&FLAG_DATA_LOST) &&
1798             before(tp->snd_una, tp->high_seq) &&
1799             icsk->icsk_ca_state != TCP_CA_Open &&
1800             tp->fackets_out > tp->reordering) {
1801                 tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
1802                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
1803         }
1804
1805         /* D. Synchronize left_out to current state. */
1806         tcp_sync_left_out(tp);
1807
1808         /* E. Check state exit conditions. State can be terminated
1809          *    when high_seq is ACKed. */
1810         if (icsk->icsk_ca_state == TCP_CA_Open) {
1811                 if (!sysctl_tcp_frto)
1812                         BUG_TRAP(tp->retrans_out == 0);
1813                 tp->retrans_stamp = 0;
1814         } else if (!before(tp->snd_una, tp->high_seq)) {
1815                 switch (icsk->icsk_ca_state) {
1816                 case TCP_CA_Loss:
1817                         icsk->icsk_retransmits = 0;
1818                         if (tcp_try_undo_recovery(sk, tp))
1819                                 return;
1820                         break;
1821
1822                 case TCP_CA_CWR:
1823                         /* CWR is to be held something *above* high_seq
1824                          * is ACKed for CWR bit to reach receiver. */
1825                         if (tp->snd_una != tp->high_seq) {
1826                                 tcp_complete_cwr(sk);
1827                                 tcp_set_ca_state(sk, TCP_CA_Open);
1828                         }
1829                         break;
1830
1831                 case TCP_CA_Disorder:
1832                         tcp_try_undo_dsack(sk, tp);
1833                         if (!tp->undo_marker ||
1834                             /* For SACK case do not Open to allow to undo
1835                              * catching for all duplicate ACKs. */
1836                             IsReno(tp) || tp->snd_una != tp->high_seq) {
1837                                 tp->undo_marker = 0;
1838                                 tcp_set_ca_state(sk, TCP_CA_Open);
1839                         }
1840                         break;
1841
1842                 case TCP_CA_Recovery:
1843                         if (IsReno(tp))
1844                                 tcp_reset_reno_sack(tp);
1845                         if (tcp_try_undo_recovery(sk, tp))
1846                                 return;
1847                         tcp_complete_cwr(sk);
1848                         break;
1849                 }
1850         }
1851
1852         /* F. Process state. */
1853         switch (icsk->icsk_ca_state) {
1854         case TCP_CA_Recovery:
1855                 if (prior_snd_una == tp->snd_una) {
1856                         if (IsReno(tp) && is_dupack)
1857                                 tcp_add_reno_sack(sk);
1858                 } else {
1859                         int acked = prior_packets - tp->packets_out;
1860                         if (IsReno(tp))
1861                                 tcp_remove_reno_sacks(sk, tp, acked);
1862                         is_dupack = tcp_try_undo_partial(sk, tp, acked);
1863                 }
1864                 break;
1865         case TCP_CA_Loss:
1866                 if (flag&FLAG_DATA_ACKED)
1867                         icsk->icsk_retransmits = 0;
1868                 if (!tcp_try_undo_loss(sk, tp)) {
1869                         tcp_moderate_cwnd(tp);
1870                         tcp_xmit_retransmit_queue(sk);
1871                         return;
1872                 }
1873                 if (icsk->icsk_ca_state != TCP_CA_Open)
1874                         return;
1875                 /* Loss is undone; fall through to processing in Open state. */
1876         default:
1877                 if (IsReno(tp)) {
1878                         if (tp->snd_una != prior_snd_una)
1879                                 tcp_reset_reno_sack(tp);
1880                         if (is_dupack)
1881                                 tcp_add_reno_sack(sk);
1882                 }
1883
1884                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
1885                         tcp_try_undo_dsack(sk, tp);
1886
1887                 if (!tcp_time_to_recover(sk, tp)) {
1888                         tcp_try_to_open(sk, tp, flag);
1889                         return;
1890                 }
1891
1892                 /* Otherwise enter Recovery state */
1893
1894                 if (IsReno(tp))
1895                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
1896                 else
1897                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
1898
1899                 tp->high_seq = tp->snd_nxt;
1900                 tp->prior_ssthresh = 0;
1901                 tp->undo_marker = tp->snd_una;
1902                 tp->undo_retrans = tp->retrans_out;
1903
1904                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
1905                         if (!(flag&FLAG_ECE))
1906                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1907                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1908                         TCP_ECN_queue_cwr(tp);
1909                 }
1910
1911                 tp->snd_cwnd_cnt = 0;
1912                 tcp_set_ca_state(sk, TCP_CA_Recovery);
1913         }
1914
1915         if (is_dupack || tcp_head_timedout(sk, tp))
1916                 tcp_update_scoreboard(sk, tp);
1917         tcp_cwnd_down(sk);
1918         tcp_xmit_retransmit_queue(sk);
1919 }
1920
1921 /* Read draft-ietf-tcplw-high-performance before mucking
1922  * with this code. (Superceeds RFC1323)
1923  */
1924 static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
1925 {
1926         /* RTTM Rule: A TSecr value received in a segment is used to
1927          * update the averaged RTT measurement only if the segment
1928          * acknowledges some new data, i.e., only if it advances the
1929          * left edge of the send window.
1930          *
1931          * See draft-ietf-tcplw-high-performance-00, section 3.3.
1932          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
1933          *
1934          * Changed: reset backoff as soon as we see the first valid sample.
1935          * If we do not, we get strongly overstimated rto. With timestamps
1936          * samples are accepted even from very old segments: f.e., when rtt=1
1937          * increases to 8, we retransmit 5 times and after 8 seconds delayed
1938          * answer arrives rto becomes 120 seconds! If at least one of segments
1939          * in window is lost... Voila.                          --ANK (010210)
1940          */
1941         struct tcp_sock *tp = tcp_sk(sk);
1942         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
1943         tcp_rtt_estimator(sk, seq_rtt, usrtt);
1944         tcp_set_rto(sk);
1945         inet_csk(sk)->icsk_backoff = 0;
1946         tcp_bound_rto(sk);
1947 }
1948
1949 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag)
1950 {
1951         /* We don't have a timestamp. Can only use
1952          * packets that are not retransmitted to determine
1953          * rtt estimates. Also, we must not reset the
1954          * backoff for rto until we get a non-retransmitted
1955          * packet. This allows us to deal with a situation
1956          * where the network delay has increased suddenly.
1957          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
1958          */
1959
1960         if (flag & FLAG_RETRANS_DATA_ACKED)
1961                 return;
1962
1963         tcp_rtt_estimator(sk, seq_rtt, usrtt);
1964         tcp_set_rto(sk);
1965         inet_csk(sk)->icsk_backoff = 0;
1966         tcp_bound_rto(sk);
1967 }
1968
1969 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
1970                                       const s32 seq_rtt, u32 *usrtt)
1971 {
1972         const struct tcp_sock *tp = tcp_sk(sk);
1973         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
1974         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
1975                 tcp_ack_saw_tstamp(sk, usrtt, flag);
1976         else if (seq_rtt >= 0)
1977                 tcp_ack_no_tstamp(sk, seq_rtt, usrtt, flag);
1978 }
1979
1980 static inline void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
1981                                   u32 in_flight, int good)
1982 {
1983         const struct inet_connection_sock *icsk = inet_csk(sk);
1984         icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
1985         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
1986 }
1987
1988 /* Restart timer after forward progress on connection.
1989  * RFC2988 recommends to restart timer to now+rto.
1990  */
1991
1992 static inline void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
1993 {
1994         if (!tp->packets_out) {
1995                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
1996         } else {
1997                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
1998         }
1999 }
2000
2001 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
2002                          __u32 now, __s32 *seq_rtt)
2003 {
2004         struct tcp_sock *tp = tcp_sk(sk);
2005         struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2006         __u32 seq = tp->snd_una;
2007         __u32 packets_acked;
2008         int acked = 0;
2009
2010         /* If we get here, the whole TSO packet has not been
2011          * acked.
2012          */
2013         BUG_ON(!after(scb->end_seq, seq));
2014
2015         packets_acked = tcp_skb_pcount(skb);
2016         if (tcp_trim_head(sk, skb, seq - scb->seq))
2017                 return 0;
2018         packets_acked -= tcp_skb_pcount(skb);
2019
2020         if (packets_acked) {
2021                 __u8 sacked = scb->sacked;
2022
2023                 acked |= FLAG_DATA_ACKED;
2024                 if (sacked) {
2025                         if (sacked & TCPCB_RETRANS) {
2026                                 if (sacked & TCPCB_SACKED_RETRANS)
2027                                         tp->retrans_out -= packets_acked;
2028                                 acked |= FLAG_RETRANS_DATA_ACKED;
2029                                 *seq_rtt = -1;
2030                         } else if (*seq_rtt < 0)
2031                                 *seq_rtt = now - scb->when;
2032                         if (sacked & TCPCB_SACKED_ACKED)
2033                                 tp->sacked_out -= packets_acked;
2034                         if (sacked & TCPCB_LOST)
2035                                 tp->lost_out -= packets_acked;
2036                         if (sacked & TCPCB_URG) {
2037                                 if (tp->urg_mode &&
2038                                     !before(seq, tp->snd_up))
2039                                         tp->urg_mode = 0;
2040                         }
2041                 } else if (*seq_rtt < 0)
2042                         *seq_rtt = now - scb->when;
2043
2044                 if (tp->fackets_out) {
2045                         __u32 dval = min(tp->fackets_out, packets_acked);
2046                         tp->fackets_out -= dval;
2047                 }
2048                 tp->packets_out -= packets_acked;
2049
2050                 BUG_ON(tcp_skb_pcount(skb) == 0);
2051                 BUG_ON(!before(scb->seq, scb->end_seq));
2052         }
2053
2054         return acked;
2055 }
2056
2057
2058 /* Remove acknowledged frames from the retransmission queue. */
2059 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt)
2060 {
2061         struct tcp_sock *tp = tcp_sk(sk);
2062         struct sk_buff *skb;
2063         __u32 now = tcp_time_stamp;
2064         int acked = 0;
2065         __s32 seq_rtt = -1;
2066         struct timeval usnow;
2067         u32 pkts_acked = 0;
2068
2069         if (seq_usrtt)
2070                 do_gettimeofday(&usnow);
2071
2072         while ((skb = skb_peek(&sk->sk_write_queue)) &&
2073                skb != sk->sk_send_head) {
2074                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2075                 __u8 sacked = scb->sacked;
2076
2077                 /* If our packet is before the ack sequence we can
2078                  * discard it as it's confirmed to have arrived at
2079                  * the other end.
2080                  */
2081                 if (after(scb->end_seq, tp->snd_una)) {
2082                         if (tcp_skb_pcount(skb) > 1 &&
2083                             after(tp->snd_una, scb->seq))
2084                                 acked |= tcp_tso_acked(sk, skb,
2085                                                        now, &seq_rtt);
2086                         break;
2087                 }
2088
2089                 /* Initial outgoing SYN's get put onto the write_queue
2090                  * just like anything else we transmit.  It is not
2091                  * true data, and if we misinform our callers that
2092                  * this ACK acks real data, we will erroneously exit
2093                  * connection startup slow start one packet too
2094                  * quickly.  This is severely frowned upon behavior.
2095                  */
2096                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2097                         acked |= FLAG_DATA_ACKED;
2098                         ++pkts_acked;
2099                 } else {
2100                         acked |= FLAG_SYN_ACKED;
2101                         tp->retrans_stamp = 0;
2102                 }
2103
2104                 if (sacked) {
2105                         if (sacked & TCPCB_RETRANS) {
2106                                 if(sacked & TCPCB_SACKED_RETRANS)
2107                                         tp->retrans_out -= tcp_skb_pcount(skb);
2108                                 acked |= FLAG_RETRANS_DATA_ACKED;
2109                                 seq_rtt = -1;
2110                         } else if (seq_rtt < 0)
2111                                 seq_rtt = now - scb->when;
2112                         if (seq_usrtt) {
2113                                 struct timeval tv;
2114                         
2115                                 skb_get_timestamp(skb, &tv);
2116                                 *seq_usrtt = (usnow.tv_sec - tv.tv_sec) * 1000000
2117                                         + (usnow.tv_usec - tv.tv_usec);
2118                         }
2119
2120                         if (sacked & TCPCB_SACKED_ACKED)
2121                                 tp->sacked_out -= tcp_skb_pcount(skb);
2122                         if (sacked & TCPCB_LOST)
2123                                 tp->lost_out -= tcp_skb_pcount(skb);
2124                         if (sacked & TCPCB_URG) {
2125                                 if (tp->urg_mode &&
2126                                     !before(scb->end_seq, tp->snd_up))
2127                                         tp->urg_mode = 0;
2128                         }
2129                 } else if (seq_rtt < 0)
2130                         seq_rtt = now - scb->when;
2131                 tcp_dec_pcount_approx(&tp->fackets_out, skb);
2132                 tcp_packets_out_dec(tp, skb);
2133                 __skb_unlink(skb, &sk->sk_write_queue);
2134                 sk_stream_free_skb(sk, skb);
2135         }
2136
2137         if (acked&FLAG_ACKED) {
2138                 const struct inet_connection_sock *icsk = inet_csk(sk);
2139                 tcp_ack_update_rtt(sk, acked, seq_rtt, seq_usrtt);
2140                 tcp_ack_packets_out(sk, tp);
2141
2142                 if (icsk->icsk_ca_ops->pkts_acked)
2143                         icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
2144         }
2145
2146 #if FASTRETRANS_DEBUG > 0
2147         BUG_TRAP((int)tp->sacked_out >= 0);
2148         BUG_TRAP((int)tp->lost_out >= 0);
2149         BUG_TRAP((int)tp->retrans_out >= 0);
2150         if (!tp->packets_out && tp->rx_opt.sack_ok) {
2151                 const struct inet_connection_sock *icsk = inet_csk(sk);
2152                 if (tp->lost_out) {
2153                         printk(KERN_DEBUG "Leak l=%u %d\n",
2154                                tp->lost_out, icsk->icsk_ca_state);
2155                         tp->lost_out = 0;
2156                 }
2157                 if (tp->sacked_out) {
2158                         printk(KERN_DEBUG "Leak s=%u %d\n",
2159                                tp->sacked_out, icsk->icsk_ca_state);
2160                         tp->sacked_out = 0;
2161                 }
2162                 if (tp->retrans_out) {
2163                         printk(KERN_DEBUG "Leak r=%u %d\n",
2164                                tp->retrans_out, icsk->icsk_ca_state);
2165                         tp->retrans_out = 0;
2166                 }
2167         }
2168 #endif
2169         *seq_rtt_p = seq_rtt;
2170         return acked;
2171 }
2172
2173 static void tcp_ack_probe(struct sock *sk)
2174 {
2175         const struct tcp_sock *tp = tcp_sk(sk);
2176         struct inet_connection_sock *icsk = inet_csk(sk);
2177
2178         /* Was it a usable window open? */
2179
2180         if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
2181                    tp->snd_una + tp->snd_wnd)) {
2182                 icsk->icsk_backoff = 0;
2183                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2184                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2185                  * This function is not for random using!
2186                  */
2187         } else {
2188                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2189                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2190                                           TCP_RTO_MAX);
2191         }
2192 }
2193
2194 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2195 {
2196         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2197                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2198 }
2199
2200 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2201 {
2202         const struct tcp_sock *tp = tcp_sk(sk);
2203         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2204                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2205 }
2206
2207 /* Check that window update is acceptable.
2208  * The function assumes that snd_una<=ack<=snd_next.
2209  */
2210 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2211                                         const u32 ack_seq, const u32 nwin)
2212 {
2213         return (after(ack, tp->snd_una) ||
2214                 after(ack_seq, tp->snd_wl1) ||
2215                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2216 }
2217
2218 /* Update our send window.
2219  *
2220  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2221  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2222  */
2223 static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
2224                                  struct sk_buff *skb, u32 ack, u32 ack_seq)
2225 {
2226         int flag = 0;
2227         u32 nwin = ntohs(skb->h.th->window);
2228
2229         if (likely(!skb->h.th->syn))
2230                 nwin <<= tp->rx_opt.snd_wscale;
2231
2232         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2233                 flag |= FLAG_WIN_UPDATE;
2234                 tcp_update_wl(tp, ack, ack_seq);
2235
2236                 if (tp->snd_wnd != nwin) {
2237                         tp->snd_wnd = nwin;
2238
2239                         /* Note, it is the only place, where
2240                          * fast path is recovered for sending TCP.
2241                          */
2242                         tcp_fast_path_check(sk, tp);
2243
2244                         if (nwin > tp->max_window) {
2245                                 tp->max_window = nwin;
2246                                 tcp_sync_mss(sk, tp->pmtu_cookie);
2247                         }
2248                 }
2249         }
2250
2251         tp->snd_una = ack;
2252
2253         return flag;
2254 }
2255
2256 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
2257 {
2258         struct tcp_sock *tp = tcp_sk(sk);
2259         
2260         tcp_sync_left_out(tp);
2261         
2262         if (tp->snd_una == prior_snd_una ||
2263             !before(tp->snd_una, tp->frto_highmark)) {
2264                 /* RTO was caused by loss, start retransmitting in
2265                  * go-back-N slow start
2266                  */
2267                 tcp_enter_frto_loss(sk);
2268                 return;
2269         }
2270
2271         if (tp->frto_counter == 1) {
2272                 /* First ACK after RTO advances the window: allow two new
2273                  * segments out.
2274                  */
2275                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2276         } else {
2277                 /* Also the second ACK after RTO advances the window.
2278                  * The RTO was likely spurious. Reduce cwnd and continue
2279                  * in congestion avoidance
2280                  */
2281                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2282                 tcp_moderate_cwnd(tp);
2283         }
2284
2285         /* F-RTO affects on two new ACKs following RTO.
2286          * At latest on third ACK the TCP behavor is back to normal.
2287          */
2288         tp->frto_counter = (tp->frto_counter + 1) % 3;
2289 }
2290
2291 /* This routine deals with incoming acks, but not outgoing ones. */
2292 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2293 {
2294         struct inet_connection_sock *icsk = inet_csk(sk);
2295         struct tcp_sock *tp = tcp_sk(sk);
2296         u32 prior_snd_una = tp->snd_una;
2297         u32 ack_seq = TCP_SKB_CB(skb)->seq;
2298         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2299         u32 prior_in_flight;
2300         s32 seq_rtt;
2301         s32 seq_usrtt = 0;
2302         int prior_packets;
2303
2304         /* If the ack is newer than sent or older than previous acks
2305          * then we can probably ignore it.
2306          */
2307         if (after(ack, tp->snd_nxt))
2308                 goto uninteresting_ack;
2309
2310         if (before(ack, prior_snd_una))
2311                 goto old_ack;
2312
2313         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
2314                 /* Window is constant, pure forward advance.
2315                  * No more checks are required.
2316                  * Note, we use the fact that SND.UNA>=SND.WL2.
2317                  */
2318                 tcp_update_wl(tp, ack, ack_seq);
2319                 tp->snd_una = ack;
2320                 flag |= FLAG_WIN_UPDATE;
2321
2322                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
2323
2324                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
2325         } else {
2326                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
2327                         flag |= FLAG_DATA;
2328                 else
2329                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
2330
2331                 flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);
2332
2333                 if (TCP_SKB_CB(skb)->sacked)
2334                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2335
2336                 if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
2337                         flag |= FLAG_ECE;
2338
2339                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
2340         }
2341
2342         /* We passed data and got it acked, remove any soft error
2343          * log. Something worked...
2344          */
2345         sk->sk_err_soft = 0;
2346         tp->rcv_tstamp = tcp_time_stamp;
2347         prior_packets = tp->packets_out;
2348         if (!prior_packets)
2349                 goto no_queue;
2350
2351         prior_in_flight = tcp_packets_in_flight(tp);
2352
2353         /* See if we can take anything off of the retransmit queue. */
2354         flag |= tcp_clean_rtx_queue(sk, &seq_rtt,
2355                                     icsk->icsk_ca_ops->rtt_sample ? &seq_usrtt : NULL);
2356
2357         if (tp->frto_counter)
2358                 tcp_process_frto(sk, prior_snd_una);
2359
2360         if (tcp_ack_is_dubious(sk, flag)) {
2361                 /* Advanve CWND, if state allows this. */
2362                 if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
2363                         tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
2364                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2365         } else {
2366                 if ((flag & FLAG_DATA_ACKED))
2367                         tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
2368         }
2369
2370         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2371                 dst_confirm(sk->sk_dst_cache);
2372
2373         return 1;
2374
2375 no_queue:
2376         icsk->icsk_probes_out = 0;
2377
2378         /* If this ack opens up a zero window, clear backoff.  It was
2379          * being used to time the probes, and is probably far higher than
2380          * it needs to be for normal retransmission.
2381          */
2382         if (sk->sk_send_head)
2383                 tcp_ack_probe(sk);
2384         return 1;
2385
2386 old_ack:
2387         if (TCP_SKB_CB(skb)->sacked)
2388                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2389
2390 uninteresting_ack:
2391         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2392         return 0;
2393 }
2394
2395
2396 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2397  * But, this can also be called on packets in the established flow when
2398  * the fast version below fails.
2399  */
2400 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2401 {
2402         unsigned char *ptr;
2403         struct tcphdr *th = skb->h.th;
2404         int length=(th->doff*4)-sizeof(struct tcphdr);
2405
2406         ptr = (unsigned char *)(th + 1);
2407         opt_rx->saw_tstamp = 0;
2408
2409         while(length>0) {
2410                 int opcode=*ptr++;
2411                 int opsize;
2412
2413                 switch (opcode) {
2414                         case TCPOPT_EOL:
2415                                 return;
2416                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
2417                                 length--;
2418                                 continue;
2419                         default:
2420                                 opsize=*ptr++;
2421                                 if (opsize < 2) /* "silly options" */
2422                                         return;
2423                                 if (opsize > length)
2424                                         return; /* don't parse partial options */
2425                                 switch(opcode) {
2426                                 case TCPOPT_MSS:
2427                                         if(opsize==TCPOLEN_MSS && th->syn && !estab) {
2428                                                 u16 in_mss = ntohs(get_unaligned((__u16 *)ptr));
2429                                                 if (in_mss) {
2430                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2431                                                                 in_mss = opt_rx->user_mss;
2432                                                         opt_rx->mss_clamp = in_mss;
2433                                                 }
2434                                         }
2435                                         break;
2436                                 case TCPOPT_WINDOW:
2437                                         if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
2438                                                 if (sysctl_tcp_window_scaling) {
2439                                                         __u8 snd_wscale = *(__u8 *) ptr;
2440                                                         opt_rx->wscale_ok = 1;
2441                                                         if (snd_wscale > 14) {
2442                                                                 if(net_ratelimit())
2443                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
2444                                                                                "scaling value %d >14 received.\n",
2445                                                                                snd_wscale);
2446                                                                 snd_wscale = 14;
2447                                                         }
2448                                                         opt_rx->snd_wscale = snd_wscale;
2449                                                 }
2450                                         break;
2451                                 case TCPOPT_TIMESTAMP:
2452                                         if(opsize==TCPOLEN_TIMESTAMP) {
2453                                                 if ((estab && opt_rx->tstamp_ok) ||
2454                                                     (!estab && sysctl_tcp_timestamps)) {
2455                                                         opt_rx->saw_tstamp = 1;
2456                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr));
2457                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4)));
2458                                                 }
2459                                         }
2460                                         break;
2461                                 case TCPOPT_SACK_PERM:
2462                                         if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2463                                                 if (sysctl_tcp_sack) {
2464                                                         opt_rx->sack_ok = 1;
2465                                                         tcp_sack_reset(opt_rx);
2466                                                 }
2467                                         }
2468                                         break;
2469
2470                                 case TCPOPT_SACK:
2471                                         if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2472                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2473                                            opt_rx->sack_ok) {
2474                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2475                                         }
2476                                 };
2477                                 ptr+=opsize-2;
2478                                 length-=opsize;
2479                 };
2480         }
2481 }
2482
2483 /* Fast parse options. This hopes to only see timestamps.
2484  * If it is wrong it falls back on tcp_parse_options().
2485  */
2486 static inline int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2487                                          struct tcp_sock *tp)
2488 {
2489         if (th->doff == sizeof(struct tcphdr)>>2) {
2490                 tp->rx_opt.saw_tstamp = 0;
2491                 return 0;
2492         } else if (tp->rx_opt.tstamp_ok &&
2493                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2494                 __u32 *ptr = (__u32 *)(th + 1);
2495                 if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2496                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2497                         tp->rx_opt.saw_tstamp = 1;
2498                         ++ptr;
2499                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
2500                         ++ptr;
2501                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2502                         return 1;
2503                 }
2504         }
2505         tcp_parse_options(skb, &tp->rx_opt, 1);
2506         return 1;
2507 }
2508
2509 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2510 {
2511         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2512         tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
2513 }
2514
2515 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2516 {
2517         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2518                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
2519                  * extra check below makes sure this can only happen
2520                  * for pure ACK frames.  -DaveM
2521                  *
2522                  * Not only, also it occurs for expired timestamps.
2523                  */
2524
2525                 if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2526                    xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2527                         tcp_store_ts_recent(tp);
2528         }
2529 }
2530
2531 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2532  *
2533  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2534  * it can pass through stack. So, the following predicate verifies that
2535  * this segment is not used for anything but congestion avoidance or
2536  * fast retransmit. Moreover, we even are able to eliminate most of such
2537  * second order effects, if we apply some small "replay" window (~RTO)
2538  * to timestamp space.
2539  *
2540  * All these measures still do not guarantee that we reject wrapped ACKs
2541  * on networks with high bandwidth, when sequence space is recycled fastly,
2542  * but it guarantees that such events will be very rare and do not affect
2543  * connection seriously. This doesn't look nice, but alas, PAWS is really
2544  * buggy extension.
2545  *
2546  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
2547  * states that events when retransmit arrives after original data are rare.
2548  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
2549  * the biggest problem on large power networks even with minor reordering.
2550  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
2551  * up to bandwidth of 18Gigabit/sec. 8) ]
2552  */
2553
2554 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
2555 {
2556         struct tcp_sock *tp = tcp_sk(sk);
2557         struct tcphdr *th = skb->h.th;
2558         u32 seq = TCP_SKB_CB(skb)->seq;
2559         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2560
2561         return (/* 1. Pure ACK with correct sequence number. */
2562                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
2563
2564                 /* 2. ... and duplicate ACK. */
2565                 ack == tp->snd_una &&
2566
2567                 /* 3. ... and does not update window. */
2568                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
2569
2570                 /* 4. ... and sits in replay window. */
2571                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
2572 }
2573
2574 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
2575 {
2576         const struct tcp_sock *tp = tcp_sk(sk);
2577         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
2578                 xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2579                 !tcp_disordered_ack(sk, skb));
2580 }
2581
2582 /* Check segment sequence number for validity.
2583  *
2584  * Segment controls are considered valid, if the segment
2585  * fits to the window after truncation to the window. Acceptability
2586  * of data (and SYN, FIN, of course) is checked separately.
2587  * See tcp_data_queue(), for example.
2588  *
2589  * Also, controls (RST is main one) are accepted using RCV.WUP instead
2590  * of RCV.NXT. Peer still did not advance his SND.UNA when we
2591  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
2592  * (borrowed from freebsd)
2593  */
2594
2595 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
2596 {
2597         return  !before(end_seq, tp->rcv_wup) &&
2598                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
2599 }
2600
2601 /* When we get a reset we do this. */
2602 static void tcp_reset(struct sock *sk)
2603 {
2604         /* We want the right error as BSD sees it (and indeed as we do). */
2605         switch (sk->sk_state) {
2606                 case TCP_SYN_SENT:
2607                         sk->sk_err = ECONNREFUSED;
2608                         break;
2609                 case TCP_CLOSE_WAIT:
2610                         sk->sk_err = EPIPE;
2611                         break;
2612                 case TCP_CLOSE:
2613                         return;
2614                 default:
2615                         sk->sk_err = ECONNRESET;
2616         }
2617
2618         if (!sock_flag(sk, SOCK_DEAD))
2619                 sk->sk_error_report(sk);
2620
2621         tcp_done(sk);
2622 }
2623
2624 /*
2625  *      Process the FIN bit. This now behaves as it is supposed to work
2626  *      and the FIN takes effect when it is validly part of sequence
2627  *      space. Not before when we get holes.
2628  *
2629  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
2630  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
2631  *      TIME-WAIT)
2632  *
2633  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
2634  *      close and we go into CLOSING (and later onto TIME-WAIT)
2635  *
2636  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
2637  */
2638 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
2639 {
2640         struct tcp_sock *tp = tcp_sk(sk);
2641
2642         inet_csk_schedule_ack(sk);
2643
2644         sk->sk_shutdown |= RCV_SHUTDOWN;
2645         sock_set_flag(sk, SOCK_DONE);
2646
2647         switch (sk->sk_state) {
2648                 case TCP_SYN_RECV:
2649                 case TCP_ESTABLISHED:
2650                         /* Move to CLOSE_WAIT */
2651                         tcp_set_state(sk, TCP_CLOSE_WAIT);
2652                         inet_csk(sk)->icsk_ack.pingpong = 1;
2653                         break;
2654
2655                 case TCP_CLOSE_WAIT:
2656                 case TCP_CLOSING:
2657                         /* Received a retransmission of the FIN, do
2658                          * nothing.
2659                          */
2660                         break;
2661                 case TCP_LAST_ACK:
2662                         /* RFC793: Remain in the LAST-ACK state. */
2663                         break;
2664
2665                 case TCP_FIN_WAIT1:
2666                         /* This case occurs when a simultaneous close
2667                          * happens, we must ack the received FIN and
2668                          * enter the CLOSING state.
2669                          */
2670                         tcp_send_ack(sk);
2671                         tcp_set_state(sk, TCP_CLOSING);
2672                         break;
2673                 case TCP_FIN_WAIT2:
2674                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
2675                         tcp_send_ack(sk);
2676                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
2677                         break;
2678                 default:
2679                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
2680                          * cases we should never reach this piece of code.
2681                          */
2682                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
2683                                __FUNCTION__, sk->sk_state);
2684                         break;
2685         };
2686
2687         /* It _is_ possible, that we have something out-of-order _after_ FIN.
2688          * Probably, we should reset in this case. For now drop them.
2689          */
2690         __skb_queue_purge(&tp->out_of_order_queue);
2691         if (tp->rx_opt.sack_ok)
2692                 tcp_sack_reset(&tp->rx_opt);
2693         sk_stream_mem_reclaim(sk);
2694
2695         if (!sock_flag(sk, SOCK_DEAD)) {
2696                 sk->sk_state_change(sk);
2697
2698                 /* Do not send POLL_HUP for half duplex close. */
2699                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
2700                     sk->sk_state == TCP_CLOSE)
2701                         sk_wake_async(sk, 1, POLL_HUP);
2702                 else
2703                         sk_wake_async(sk, 1, POLL_IN);
2704         }
2705 }
2706
2707 static __inline__ int
2708 tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
2709 {
2710         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
2711                 if (before(seq, sp->start_seq))
2712                         sp->start_seq = seq;
2713                 if (after(end_seq, sp->end_seq))
2714                         sp->end_seq = end_seq;
2715                 return 1;
2716         }
2717         return 0;
2718 }
2719
2720 static inline void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
2721 {
2722         if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2723                 if (before(seq, tp->rcv_nxt))
2724                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
2725                 else
2726                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
2727
2728                 tp->rx_opt.dsack = 1;
2729                 tp->duplicate_sack[0].start_seq = seq;
2730                 tp->duplicate_sack[0].end_seq = end_seq;
2731                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
2732         }
2733 }
2734
2735 static inline void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
2736 {
2737         if (!tp->rx_opt.dsack)
2738                 tcp_dsack_set(tp, seq, end_seq);
2739         else
2740                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
2741 }
2742
2743 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
2744 {
2745         struct tcp_sock *tp = tcp_sk(sk);
2746
2747         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
2748             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2749                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2750                 tcp_enter_quickack_mode(sk);
2751
2752                 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2753                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2754
2755                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
2756                                 end_seq = tp->rcv_nxt;
2757                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
2758                 }
2759         }
2760
2761         tcp_send_ack(sk);
2762 }
2763
2764 /* These routines update the SACK block as out-of-order packets arrive or
2765  * in-order packets close up the sequence space.
2766  */
2767 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
2768 {
2769         int this_sack;
2770         struct tcp_sack_block *sp = &tp->selective_acks[0];
2771         struct tcp_sack_block *swalk = sp+1;
2772
2773         /* See if the recent change to the first SACK eats into
2774          * or hits the sequence space of other SACK blocks, if so coalesce.
2775          */
2776         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
2777                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
2778                         int i;
2779
2780                         /* Zap SWALK, by moving every further SACK up by one slot.
2781                          * Decrease num_sacks.
2782                          */
2783                         tp->rx_opt.num_sacks--;
2784                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2785                         for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
2786                                 sp[i] = sp[i+1];
2787                         continue;
2788                 }
2789                 this_sack++, swalk++;
2790         }
2791 }
2792
2793 static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
2794 {
2795         __u32 tmp;
2796
2797         tmp = sack1->start_seq;
2798         sack1->start_seq = sack2->start_seq;
2799         sack2->start_seq = tmp;
2800
2801         tmp = sack1->end_seq;
2802         sack1->end_seq = sack2->end_seq;
2803         sack2->end_seq = tmp;
2804 }
2805
2806 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
2807 {
2808         struct tcp_sock *tp = tcp_sk(sk);
2809         struct tcp_sack_block *sp = &tp->selective_acks[0];
2810         int cur_sacks = tp->rx_opt.num_sacks;
2811         int this_sack;
2812
2813         if (!cur_sacks)
2814                 goto new_sack;
2815
2816         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
2817                 if (tcp_sack_extend(sp, seq, end_seq)) {
2818                         /* Rotate this_sack to the first one. */
2819                         for (; this_sack>0; this_sack--, sp--)
2820                                 tcp_sack_swap(sp, sp-1);
2821                         if (cur_sacks > 1)
2822                                 tcp_sack_maybe_coalesce(tp);
2823                         return;
2824                 }
2825         }
2826
2827         /* Could not find an adjacent existing SACK, build a new one,
2828          * put it at the front, and shift everyone else down.  We
2829          * always know there is at least one SACK present already here.
2830          *
2831          * If the sack array is full, forget about the last one.
2832          */
2833         if (this_sack >= 4) {
2834                 this_sack--;
2835                 tp->rx_opt.num_sacks--;
2836                 sp--;
2837         }
2838         for(; this_sack > 0; this_sack--, sp--)
2839                 *sp = *(sp-1);
2840
2841 new_sack:
2842         /* Build the new head SACK, and we're done. */
2843         sp->start_seq = seq;
2844         sp->end_seq = end_seq;
2845         tp->rx_opt.num_sacks++;
2846         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2847 }
2848
2849 /* RCV.NXT advances, some SACKs should be eaten. */
2850
2851 static void tcp_sack_remove(struct tcp_sock *tp)
2852 {
2853         struct tcp_sack_block *sp = &tp->selective_acks[0];
2854         int num_sacks = tp->rx_opt.num_sacks;
2855         int this_sack;
2856
2857         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
2858         if (skb_queue_empty(&tp->out_of_order_queue)) {
2859                 tp->rx_opt.num_sacks = 0;
2860                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
2861                 return;
2862         }
2863
2864         for(this_sack = 0; this_sack < num_sacks; ) {
2865                 /* Check if the start of the sack is covered by RCV.NXT. */
2866                 if (!before(tp->rcv_nxt, sp->start_seq)) {
2867                         int i;
2868
2869                         /* RCV.NXT must cover all the block! */
2870                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
2871
2872                         /* Zap this SACK, by moving forward any other SACKS. */
2873                         for (i=this_sack+1; i < num_sacks; i++)
2874                                 tp->selective_acks[i-1] = tp->selective_acks[i];
2875                         num_sacks--;
2876                         continue;
2877                 }
2878                 this_sack++;
2879                 sp++;
2880         }
2881         if (num_sacks != tp->rx_opt.num_sacks) {
2882                 tp->rx_opt.num_sacks = num_sacks;
2883                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2884         }
2885 }
2886
2887 /* This one checks to see if we can put data from the
2888  * out_of_order queue into the receive_queue.
2889  */
2890 static void tcp_ofo_queue(struct sock *sk)
2891 {
2892         struct tcp_sock *tp = tcp_sk(sk);
2893         __u32 dsack_high = tp->rcv_nxt;
2894         struct sk_buff *skb;
2895
2896         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
2897                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
2898                         break;
2899
2900                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
2901                         __u32 dsack = dsack_high;
2902                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
2903                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
2904                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
2905                 }
2906
2907                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
2908                         SOCK_DEBUG(sk, "ofo packet was already received \n");
2909                         __skb_unlink(skb, &tp->out_of_order_queue);
2910                         __kfree_skb(skb);
2911                         continue;
2912                 }
2913                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
2914                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
2915                            TCP_SKB_CB(skb)->end_seq);
2916
2917                 __skb_unlink(skb, &tp->out_of_order_queue);
2918                 __skb_queue_tail(&sk->sk_receive_queue, skb);
2919                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2920                 if(skb->h.th->fin)
2921                         tcp_fin(skb, sk, skb->h.th);
2922         }
2923 }
2924
2925 static int tcp_prune_queue(struct sock *sk);
2926
2927 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
2928 {
2929         struct tcphdr *th = skb->h.th;
2930         struct tcp_sock *tp = tcp_sk(sk);
2931         int eaten = -1;
2932
2933         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
2934                 goto drop;
2935
2936         __skb_pull(skb, th->doff*4);
2937
2938         TCP_ECN_accept_cwr(tp, skb);
2939
2940         if (tp->rx_opt.dsack) {
2941                 tp->rx_opt.dsack = 0;
2942                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
2943                                                     4 - tp->rx_opt.tstamp_ok);
2944         }
2945
2946         /*  Queue data for delivery to the user.
2947          *  Packets in sequence go to the receive queue.
2948          *  Out of sequence packets to the out_of_order_queue.
2949          */
2950         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
2951                 if (tcp_receive_window(tp) == 0)
2952                         goto out_of_window;
2953
2954                 /* Ok. In sequence. In window. */
2955                 if (tp->ucopy.task == current &&
2956                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
2957                     sock_owned_by_user(sk) && !tp->urg_data) {
2958                         int chunk = min_t(unsigned int, skb->len,
2959                                                         tp->ucopy.len);
2960
2961                         __set_current_state(TASK_RUNNING);
2962
2963                         local_bh_enable();
2964                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
2965                                 tp->ucopy.len -= chunk;
2966                                 tp->copied_seq += chunk;
2967                                 eaten = (chunk == skb->len && !th->fin);
2968                                 tcp_rcv_space_adjust(sk);
2969                         }
2970                         local_bh_disable();
2971                 }
2972
2973                 if (eaten <= 0) {
2974 queue_and_out:
2975                         if (eaten < 0 &&
2976                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
2977                              !sk_stream_rmem_schedule(sk, skb))) {
2978                                 if (tcp_prune_queue(sk) < 0 ||
2979                                     !sk_stream_rmem_schedule(sk, skb))
2980                                         goto drop;
2981                         }
2982                         sk_stream_set_owner_r(skb, sk);
2983                         __skb_queue_tail(&sk->sk_receive_queue, skb);
2984                 }
2985                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2986                 if(skb->len)
2987                         tcp_event_data_recv(sk, tp, skb);
2988                 if(th->fin)
2989                         tcp_fin(skb, sk, th);
2990
2991                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
2992                         tcp_ofo_queue(sk);
2993
2994                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
2995                          * gap in queue is filled.
2996                          */
2997                         if (skb_queue_empty(&tp->out_of_order_queue))
2998                                 inet_csk(sk)->icsk_ack.pingpong = 0;
2999                 }
3000
3001                 if (tp->rx_opt.num_sacks)
3002                         tcp_sack_remove(tp);
3003
3004                 tcp_fast_path_check(sk, tp);
3005
3006                 if (eaten > 0)
3007                         __kfree_skb(skb);
3008                 else if (!sock_flag(sk, SOCK_DEAD))
3009                         sk->sk_data_ready(sk, 0);
3010                 return;
3011         }
3012
3013         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3014                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3015                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3016                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3017
3018 out_of_window:
3019                 tcp_enter_quickack_mode(sk);
3020                 inet_csk_schedule_ack(sk);
3021 drop:
3022                 __kfree_skb(skb);
3023                 return;
3024         }
3025
3026         /* Out of window. F.e. zero window probe. */
3027         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3028                 goto out_of_window;
3029
3030         tcp_enter_quickack_mode(sk);
3031
3032         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3033                 /* Partial packet, seq < rcv_next < end_seq */
3034                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3035                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3036                            TCP_SKB_CB(skb)->end_seq);
3037
3038                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3039                 
3040                 /* If window is closed, drop tail of packet. But after
3041                  * remembering D-SACK for its head made in previous line.
3042                  */
3043                 if (!tcp_receive_window(tp))
3044                         goto out_of_window;
3045                 goto queue_and_out;
3046         }
3047
3048         TCP_ECN_check_ce(tp, skb);
3049
3050         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3051             !sk_stream_rmem_schedule(sk, skb)) {
3052                 if (tcp_prune_queue(sk) < 0 ||
3053                     !sk_stream_rmem_schedule(sk, skb))
3054                         goto drop;
3055         }
3056
3057         /* Disable header prediction. */
3058         tp->pred_flags = 0;
3059         inet_csk_schedule_ack(sk);
3060
3061         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3062                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3063
3064         sk_stream_set_owner_r(skb, sk);
3065
3066         if (!skb_peek(&tp->out_of_order_queue)) {
3067                 /* Initial out of order segment, build 1 SACK. */
3068                 if (tp->rx_opt.sack_ok) {
3069                         tp->rx_opt.num_sacks = 1;
3070                         tp->rx_opt.dsack     = 0;
3071                         tp->rx_opt.eff_sacks = 1;
3072                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3073                         tp->selective_acks[0].end_seq =
3074                                                 TCP_SKB_CB(skb)->end_seq;
3075                 }
3076                 __skb_queue_head(&tp->out_of_order_queue,skb);
3077         } else {
3078                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3079                 u32 seq = TCP_SKB_CB(skb)->seq;
3080                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3081
3082                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3083                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3084
3085                         if (!tp->rx_opt.num_sacks ||
3086                             tp->selective_acks[0].end_seq != seq)
3087                                 goto add_sack;
3088
3089                         /* Common case: data arrive in order after hole. */
3090                         tp->selective_acks[0].end_seq = end_seq;
3091                         return;
3092                 }
3093
3094                 /* Find place to insert this segment. */
3095                 do {
3096                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3097                                 break;
3098                 } while ((skb1 = skb1->prev) !=
3099                          (struct sk_buff*)&tp->out_of_order_queue);
3100
3101                 /* Do skb overlap to previous one? */
3102                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3103                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3104                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3105                                 /* All the bits are present. Drop. */
3106                                 __kfree_skb(skb);
3107                                 tcp_dsack_set(tp, seq, end_seq);
3108                                 goto add_sack;
3109                         }
3110                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3111                                 /* Partial overlap. */
3112                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3113                         } else {
3114                                 skb1 = skb1->prev;
3115                         }
3116                 }
3117                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3118                 
3119                 /* And clean segments covered by new one as whole. */
3120                 while ((skb1 = skb->next) !=
3121                        (struct sk_buff*)&tp->out_of_order_queue &&
3122                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3123                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3124                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3125                                break;
3126                        }
3127                        __skb_unlink(skb1, &tp->out_of_order_queue);
3128                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3129                        __kfree_skb(skb1);
3130                 }
3131
3132 add_sack:
3133                 if (tp->rx_opt.sack_ok)
3134                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3135         }
3136 }
3137
3138 /* Collapse contiguous sequence of skbs head..tail with
3139  * sequence numbers start..end.
3140  * Segments with FIN/SYN are not collapsed (only because this
3141  * simplifies code)
3142  */
3143 static void
3144 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3145              struct sk_buff *head, struct sk_buff *tail,
3146              u32 start, u32 end)
3147 {
3148         struct sk_buff *skb;
3149
3150         /* First, check that queue is collapsable and find
3151          * the point where collapsing can be useful. */
3152         for (skb = head; skb != tail; ) {
3153                 /* No new bits? It is possible on ofo queue. */
3154                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3155                         struct sk_buff *next = skb->next;
3156                         __skb_unlink(skb, list);
3157                         __kfree_skb(skb);
3158                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3159                         skb = next;
3160                         continue;
3161                 }
3162
3163                 /* The first skb to collapse is:
3164                  * - not SYN/FIN and
3165                  * - bloated or contains data before "start" or
3166                  *   overlaps to the next one.
3167                  */
3168                 if (!skb->h.th->syn && !skb->h.th->fin &&
3169                     (tcp_win_from_space(skb->truesize) > skb->len ||
3170                      before(TCP_SKB_CB(skb)->seq, start) ||
3171                      (skb->next != tail &&
3172                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3173                         break;
3174
3175                 /* Decided to skip this, advance start seq. */
3176                 start = TCP_SKB_CB(skb)->end_seq;
3177                 skb = skb->next;
3178         }
3179         if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3180                 return;
3181
3182         while (before(start, end)) {
3183                 struct sk_buff *nskb;
3184                 int header = skb_headroom(skb);
3185                 int copy = SKB_MAX_ORDER(header, 0);
3186
3187                 /* Too big header? This can happen with IPv6. */
3188                 if (copy < 0)
3189                         return;
3190                 if (end-start < copy)
3191                         copy = end-start;
3192                 nskb = alloc_skb(copy+header, GFP_ATOMIC);
3193                 if (!nskb)
3194                         return;
3195                 skb_reserve(nskb, header);
3196                 memcpy(nskb->head, skb->head, header);
3197                 nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head);
3198                 nskb->h.raw = nskb->head + (skb->h.raw-skb->head);
3199                 nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head);
3200                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3201                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3202                 __skb_insert(nskb, skb->prev, skb, list);
3203                 sk_stream_set_owner_r(nskb, sk);
3204
3205                 /* Copy data, releasing collapsed skbs. */
3206                 while (copy > 0) {
3207                         int offset = start - TCP_SKB_CB(skb)->seq;
3208                         int size = TCP_SKB_CB(skb)->end_seq - start;
3209
3210                         if (offset < 0) BUG();
3211                         if (size > 0) {
3212                                 size = min(copy, size);
3213                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3214                                         BUG();
3215                                 TCP_SKB_CB(nskb)->end_seq += size;
3216                                 copy -= size;
3217                                 start += size;
3218                         }
3219                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3220                                 struct sk_buff *next = skb->next;
3221                                 __skb_unlink(skb, list);
3222                                 __kfree_skb(skb);
3223                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3224                                 skb = next;
3225                                 if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3226                                         return;
3227                         }
3228                 }
3229         }
3230 }
3231
3232 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3233  * and tcp_collapse() them until all the queue is collapsed.
3234  */
3235 static void tcp_collapse_ofo_queue(struct sock *sk)
3236 {
3237         struct tcp_sock *tp = tcp_sk(sk);
3238         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3239         struct sk_buff *head;
3240         u32 start, end;
3241
3242         if (skb == NULL)
3243                 return;
3244
3245         start = TCP_SKB_CB(skb)->seq;
3246         end = TCP_SKB_CB(skb)->end_seq;
3247         head = skb;
3248
3249         for (;;) {
3250                 skb = skb->next;
3251
3252                 /* Segment is terminated when we see gap or when
3253                  * we are at the end of all the queue. */
3254                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
3255                     after(TCP_SKB_CB(skb)->seq, end) ||
3256                     before(TCP_SKB_CB(skb)->end_seq, start)) {
3257                         tcp_collapse(sk, &tp->out_of_order_queue,
3258                                      head, skb, start, end);
3259                         head = skb;
3260                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
3261                                 break;
3262                         /* Start new segment */
3263                         start = TCP_SKB_CB(skb)->seq;
3264                         end = TCP_SKB_CB(skb)->end_seq;
3265                 } else {
3266                         if (before(TCP_SKB_CB(skb)->seq, start))
3267                                 start = TCP_SKB_CB(skb)->seq;
3268                         if (after(TCP_SKB_CB(skb)->end_seq, end))
3269                                 end = TCP_SKB_CB(skb)->end_seq;
3270                 }
3271         }
3272 }
3273
3274 /* Reduce allocated memory if we can, trying to get
3275  * the socket within its memory limits again.
3276  *
3277  * Return less than zero if we should start dropping frames
3278  * until the socket owning process reads some of the data
3279  * to stabilize the situation.
3280  */
3281 static int tcp_prune_queue(struct sock *sk)
3282 {
3283         struct tcp_sock *tp = tcp_sk(sk); 
3284
3285         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
3286
3287         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
3288
3289         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
3290                 tcp_clamp_window(sk, tp);
3291         else if (tcp_memory_pressure)
3292                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
3293
3294         tcp_collapse_ofo_queue(sk);
3295         tcp_collapse(sk, &sk->sk_receive_queue,
3296                      sk->sk_receive_queue.next,
3297                      (struct sk_buff*)&sk->sk_receive_queue,
3298                      tp->copied_seq, tp->rcv_nxt);
3299         sk_stream_mem_reclaim(sk);
3300
3301         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3302                 return 0;
3303
3304         /* Collapsing did not help, destructive actions follow.
3305          * This must not ever occur. */
3306
3307         /* First, purge the out_of_order queue. */
3308         if (!skb_queue_empty(&tp->out_of_order_queue)) {
3309                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
3310                 __skb_queue_purge(&tp->out_of_order_queue);
3311
3312                 /* Reset SACK state.  A conforming SACK implementation will
3313                  * do the same at a timeout based retransmit.  When a connection
3314                  * is in a sad state like this, we care only about integrity
3315                  * of the connection not performance.
3316                  */
3317                 if (tp->rx_opt.sack_ok)
3318                         tcp_sack_reset(&tp->rx_opt);
3319                 sk_stream_mem_reclaim(sk);
3320         }
3321
3322         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3323                 return 0;
3324
3325         /* If we are really being abused, tell the caller to silently
3326          * drop receive data on the floor.  It will get retransmitted
3327          * and hopefully then we'll have sufficient space.
3328          */
3329         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
3330
3331         /* Massive buffer overcommit. */
3332         tp->pred_flags = 0;
3333         return -1;
3334 }
3335
3336
3337 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
3338  * As additional protections, we do not touch cwnd in retransmission phases,
3339  * and if application hit its sndbuf limit recently.
3340  */
3341 void tcp_cwnd_application_limited(struct sock *sk)
3342 {
3343         struct tcp_sock *tp = tcp_sk(sk);
3344
3345         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
3346             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
3347                 /* Limited by application or receiver window. */
3348                 u32 win_used = max(tp->snd_cwnd_used, 2U);
3349                 if (win_used < tp->snd_cwnd) {
3350                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
3351                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
3352                 }
3353                 tp->snd_cwnd_used = 0;
3354         }
3355         tp->snd_cwnd_stamp = tcp_time_stamp;
3356 }
3357
3358 static inline int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp)
3359 {
3360         /* If the user specified a specific send buffer setting, do
3361          * not modify it.
3362          */
3363         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
3364                 return 0;
3365
3366         /* If we are under global TCP memory pressure, do not expand.  */
3367         if (tcp_memory_pressure)
3368                 return 0;
3369
3370         /* If we are under soft global TCP memory pressure, do not expand.  */
3371         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
3372                 return 0;
3373
3374         /* If we filled the congestion window, do not expand.  */
3375         if (tp->packets_out >= tp->snd_cwnd)
3376                 return 0;
3377
3378         return 1;
3379 }
3380
3381 /* When incoming ACK allowed to free some skb from write_queue,
3382  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
3383  * on the exit from tcp input handler.
3384  *
3385  * PROBLEM: sndbuf expansion does not work well with largesend.
3386  */
3387 static void tcp_new_space(struct sock *sk)
3388 {
3389         struct tcp_sock *tp = tcp_sk(sk);
3390
3391         if (tcp_should_expand_sndbuf(sk, tp)) {
3392                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
3393                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
3394                     demanded = max_t(unsigned int, tp->snd_cwnd,
3395                                                    tp->reordering + 1);
3396                 sndmem *= 2*demanded;
3397                 if (sndmem > sk->sk_sndbuf)
3398                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
3399                 tp->snd_cwnd_stamp = tcp_time_stamp;
3400         }
3401
3402         sk->sk_write_space(sk);
3403 }
3404
3405 static inline void tcp_check_space(struct sock *sk)
3406 {
3407         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
3408                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
3409                 if (sk->sk_socket &&
3410                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
3411                         tcp_new_space(sk);
3412         }
3413 }
3414
3415 static __inline__ void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
3416 {
3417         tcp_push_pending_frames(sk, tp);
3418         tcp_check_space(sk);
3419 }
3420
3421 /*
3422  * Check if sending an ack is needed.
3423  */
3424 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
3425 {
3426         struct tcp_sock *tp = tcp_sk(sk);
3427
3428             /* More than one full frame received... */
3429         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
3430              /* ... and right edge of window advances far enough.
3431               * (tcp_recvmsg() will send ACK otherwise). Or...
3432               */
3433              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
3434             /* We ACK each frame or... */
3435             tcp_in_quickack_mode(sk) ||
3436             /* We have out of order data. */
3437             (ofo_possible &&
3438              skb_peek(&tp->out_of_order_queue))) {
3439                 /* Then ack it now */
3440                 tcp_send_ack(sk);
3441         } else {
3442                 /* Else, send delayed ack. */
3443                 tcp_send_delayed_ack(sk);
3444         }
3445 }
3446
3447 static __inline__ void tcp_ack_snd_check(struct sock *sk)
3448 {
3449         if (!inet_csk_ack_scheduled(sk)) {
3450                 /* We sent a data segment already. */
3451                 return;
3452         }
3453         __tcp_ack_snd_check(sk, 1);
3454 }
3455
3456 /*
3457  *      This routine is only called when we have urgent data
3458  *      signalled. Its the 'slow' part of tcp_urg. It could be
3459  *      moved inline now as tcp_urg is only called from one
3460  *      place. We handle URGent data wrong. We have to - as
3461  *      BSD still doesn't use the correction from RFC961.
3462  *      For 1003.1g we should support a new option TCP_STDURG to permit
3463  *      either form (or just set the sysctl tcp_stdurg).
3464  */
3465  
3466 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
3467 {
3468         struct tcp_sock *tp = tcp_sk(sk);
3469         u32 ptr = ntohs(th->urg_ptr);
3470
3471         if (ptr && !sysctl_tcp_stdurg)
3472                 ptr--;
3473         ptr += ntohl(th->seq);
3474
3475         /* Ignore urgent data that we've already seen and read. */
3476         if (after(tp->copied_seq, ptr))
3477                 return;
3478
3479         /* Do not replay urg ptr.
3480          *
3481          * NOTE: interesting situation not covered by specs.
3482          * Misbehaving sender may send urg ptr, pointing to segment,
3483          * which we already have in ofo queue. We are not able to fetch
3484          * such data and will stay in TCP_URG_NOTYET until will be eaten
3485          * by recvmsg(). Seems, we are not obliged to handle such wicked
3486          * situations. But it is worth to think about possibility of some
3487          * DoSes using some hypothetical application level deadlock.
3488          */
3489         if (before(ptr, tp->rcv_nxt))
3490                 return;
3491
3492         /* Do we already have a newer (or duplicate) urgent pointer? */
3493         if (tp->urg_data && !after(ptr, tp->urg_seq))
3494                 return;
3495
3496         /* Tell the world about our new urgent pointer. */
3497         sk_send_sigurg(sk);
3498
3499         /* We may be adding urgent data when the last byte read was
3500          * urgent. To do this requires some care. We cannot just ignore
3501          * tp->copied_seq since we would read the last urgent byte again
3502          * as data, nor can we alter copied_seq until this data arrives
3503          * or we break the sematics of SIOCATMARK (and thus sockatmark())
3504          *
3505          * NOTE. Double Dutch. Rendering to plain English: author of comment
3506          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
3507          * and expect that both A and B disappear from stream. This is _wrong_.
3508          * Though this happens in BSD with high probability, this is occasional.
3509          * Any application relying on this is buggy. Note also, that fix "works"
3510          * only in this artificial test. Insert some normal data between A and B and we will
3511          * decline of BSD again. Verdict: it is better to remove to trap
3512          * buggy users.
3513          */
3514         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
3515             !sock_flag(sk, SOCK_URGINLINE) &&
3516             tp->copied_seq != tp->rcv_nxt) {
3517                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
3518                 tp->copied_seq++;
3519                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
3520                         __skb_unlink(skb, &sk->sk_receive_queue);
3521                         __kfree_skb(skb);
3522                 }
3523         }
3524
3525         tp->urg_data   = TCP_URG_NOTYET;
3526         tp->urg_seq    = ptr;
3527
3528         /* Disable header prediction. */
3529         tp->pred_flags = 0;
3530 }
3531
3532 /* This is the 'fast' part of urgent handling. */
3533 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
3534 {
3535         struct tcp_sock *tp = tcp_sk(sk);
3536
3537         /* Check if we get a new urgent pointer - normally not. */
3538         if (th->urg)
3539                 tcp_check_urg(sk,th);
3540
3541         /* Do we wait for any urgent data? - normally not... */
3542         if (tp->urg_data == TCP_URG_NOTYET) {
3543                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
3544                           th->syn;
3545
3546                 /* Is the urgent pointer pointing into this packet? */   
3547                 if (ptr < skb->len) {
3548                         u8 tmp;
3549                         if (skb_copy_bits(skb, ptr, &tmp, 1))
3550                                 BUG();
3551                         tp->urg_data = TCP_URG_VALID | tmp;
3552                         if (!sock_flag(sk, SOCK_DEAD))
3553                                 sk->sk_data_ready(sk, 0);
3554                 }
3555         }
3556 }
3557
3558 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
3559 {
3560         struct tcp_sock *tp = tcp_sk(sk);
3561         int chunk = skb->len - hlen;
3562         int err;
3563
3564         local_bh_enable();
3565         if (skb->ip_summed==CHECKSUM_UNNECESSARY)
3566                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
3567         else
3568                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
3569                                                        tp->ucopy.iov);
3570
3571         if (!err) {
3572                 tp->ucopy.len -= chunk;
3573                 tp->copied_seq += chunk;
3574                 tcp_rcv_space_adjust(sk);
3575         }
3576
3577         local_bh_disable();
3578         return err;
3579 }
3580
3581 static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3582 {
3583         int result;
3584
3585         if (sock_owned_by_user(sk)) {
3586                 local_bh_enable();
3587                 result = __tcp_checksum_complete(skb);
3588                 local_bh_disable();
3589         } else {
3590                 result = __tcp_checksum_complete(skb);
3591         }
3592         return result;
3593 }
3594
3595 static __inline__ int
3596 tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3597 {
3598         return skb->ip_summed != CHECKSUM_UNNECESSARY &&
3599                 __tcp_checksum_complete_user(sk, skb);
3600 }
3601
3602 /*
3603  *      TCP receive function for the ESTABLISHED state. 
3604  *
3605  *      It is split into a fast path and a slow path. The fast path is 
3606  *      disabled when:
3607  *      - A zero window was announced from us - zero window probing
3608  *        is only handled properly in the slow path. 
3609  *      - Out of order segments arrived.
3610  *      - Urgent data is expected.
3611  *      - There is no buffer space left
3612  *      - Unexpected TCP flags/window values/header lengths are received
3613  *        (detected by checking the TCP header against pred_flags) 
3614  *      - Data is sent in both directions. Fast path only supports pure senders
3615  *        or pure receivers (this means either the sequence number or the ack
3616  *        value must stay constant)
3617  *      - Unexpected TCP option.
3618  *
3619  *      When these conditions are not satisfied it drops into a standard 
3620  *      receive procedure patterned after RFC793 to handle all cases.
3621  *      The first three cases are guaranteed by proper pred_flags setting,
3622  *      the rest is checked inline. Fast processing is turned on in 
3623  *      tcp_data_queue when everything is OK.
3624  */
3625 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
3626                         struct tcphdr *th, unsigned len)
3627 {
3628         struct tcp_sock *tp = tcp_sk(sk);
3629
3630         /*
3631          *      Header prediction.
3632          *      The code loosely follows the one in the famous 
3633          *      "30 instruction TCP receive" Van Jacobson mail.
3634          *      
3635          *      Van's trick is to deposit buffers into socket queue 
3636          *      on a device interrupt, to call tcp_recv function
3637          *      on the receive process context and checksum and copy
3638          *      the buffer to user space. smart...
3639          *
3640          *      Our current scheme is not silly either but we take the 
3641          *      extra cost of the net_bh soft interrupt processing...
3642          *      We do checksum and copy also but from device to kernel.
3643          */
3644
3645         tp->rx_opt.saw_tstamp = 0;
3646
3647         /*      pred_flags is 0xS?10 << 16 + snd_wnd
3648          *      if header_predition is to be made
3649          *      'S' will always be tp->tcp_header_len >> 2
3650          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
3651          *  turn it off (when there are holes in the receive 
3652          *       space for instance)
3653          *      PSH flag is ignored.
3654          */
3655
3656         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
3657                 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3658                 int tcp_header_len = tp->tcp_header_len;
3659
3660                 /* Timestamp header prediction: tcp_header_len
3661                  * is automatically equal to th->doff*4 due to pred_flags
3662                  * match.
3663                  */
3664
3665                 /* Check timestamp */
3666                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
3667                         __u32 *ptr = (__u32 *)(th + 1);
3668
3669                         /* No? Slow path! */
3670                         if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3671                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
3672                                 goto slow_path;
3673
3674                         tp->rx_opt.saw_tstamp = 1;
3675                         ++ptr; 
3676                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
3677                         ++ptr;
3678                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3679
3680                         /* If PAWS failed, check it more carefully in slow path */
3681                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
3682                                 goto slow_path;
3683
3684                         /* DO NOT update ts_recent here, if checksum fails
3685                          * and timestamp was corrupted part, it will result
3686                          * in a hung connection since we will drop all
3687                          * future packets due to the PAWS test.
3688                          */
3689                 }
3690
3691                 if (len <= tcp_header_len) {
3692                         /* Bulk data transfer: sender */
3693                         if (len == tcp_header_len) {
3694                                 /* Predicted packet is in window by definition.
3695                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3696                                  * Hence, check seq<=rcv_wup reduces to:
3697                                  */
3698                                 if (tcp_header_len ==
3699                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3700                                     tp->rcv_nxt == tp->rcv_wup)
3701                                         tcp_store_ts_recent(tp);
3702
3703                                 tcp_rcv_rtt_measure_ts(sk, skb);
3704
3705                                 /* We know that such packets are checksummed
3706                                  * on entry.
3707                                  */
3708                                 tcp_ack(sk, skb, 0);
3709                                 __kfree_skb(skb); 
3710                                 tcp_data_snd_check(sk, tp);
3711                                 return 0;
3712                         } else { /* Header too small */
3713                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
3714                                 goto discard;
3715                         }
3716                 } else {
3717                         int eaten = 0;
3718
3719                         if (tp->ucopy.task == current &&
3720                             tp->copied_seq == tp->rcv_nxt &&
3721                             len - tcp_header_len <= tp->ucopy.len &&
3722                             sock_owned_by_user(sk)) {
3723                                 __set_current_state(TASK_RUNNING);
3724
3725                                 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
3726                                         /* Predicted packet is in window by definition.
3727                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3728                                          * Hence, check seq<=rcv_wup reduces to:
3729                                          */
3730                                         if (tcp_header_len ==
3731                                             (sizeof(struct tcphdr) +
3732                                              TCPOLEN_TSTAMP_ALIGNED) &&
3733                                             tp->rcv_nxt == tp->rcv_wup)
3734                                                 tcp_store_ts_recent(tp);
3735
3736                                         tcp_rcv_rtt_measure_ts(sk, skb);
3737
3738                                         __skb_pull(skb, tcp_header_len);
3739                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3740                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
3741                                         eaten = 1;
3742                                 }
3743                         }
3744                         if (!eaten) {
3745                                 if (tcp_checksum_complete_user(sk, skb))
3746                                         goto csum_error;
3747
3748                                 /* Predicted packet is in window by definition.
3749                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3750                                  * Hence, check seq<=rcv_wup reduces to:
3751                                  */
3752                                 if (tcp_header_len ==
3753                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3754                                     tp->rcv_nxt == tp->rcv_wup)
3755                                         tcp_store_ts_recent(tp);
3756
3757                                 tcp_rcv_rtt_measure_ts(sk, skb);
3758
3759                                 if ((int)skb->truesize > sk->sk_forward_alloc)
3760                                         goto step5;
3761
3762                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
3763
3764                                 /* Bulk data transfer: receiver */
3765                                 __skb_pull(skb,tcp_header_len);
3766                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3767                                 sk_stream_set_owner_r(skb, sk);
3768                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3769                         }
3770
3771                         tcp_event_data_recv(sk, tp, skb);
3772
3773                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
3774                                 /* Well, only one small jumplet in fast path... */
3775                                 tcp_ack(sk, skb, FLAG_DATA);
3776                                 tcp_data_snd_check(sk, tp);
3777                                 if (!inet_csk_ack_scheduled(sk))
3778                                         goto no_ack;
3779                         }
3780
3781                         __tcp_ack_snd_check(sk, 0);
3782 no_ack:
3783                         if (eaten)
3784                                 __kfree_skb(skb);
3785                         else
3786                                 sk->sk_data_ready(sk, 0);
3787                         return 0;
3788                 }
3789         }
3790
3791 slow_path:
3792         if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
3793                 goto csum_error;
3794
3795         /*
3796          * RFC1323: H1. Apply PAWS check first.
3797          */
3798         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
3799             tcp_paws_discard(sk, skb)) {
3800                 if (!th->rst) {
3801                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
3802                         tcp_send_dupack(sk, skb);
3803                         goto discard;
3804                 }
3805                 /* Resets are accepted even if PAWS failed.
3806
3807                    ts_recent update must be made after we are sure
3808                    that the packet is in window.
3809                  */
3810         }
3811
3812         /*
3813          *      Standard slow path.
3814          */
3815
3816         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
3817                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
3818                  * (RST) segments are validated by checking their SEQ-fields."
3819                  * And page 69: "If an incoming segment is not acceptable,
3820                  * an acknowledgment should be sent in reply (unless the RST bit
3821                  * is set, if so drop the segment and return)".
3822                  */
3823                 if (!th->rst)
3824                         tcp_send_dupack(sk, skb);
3825                 goto discard;
3826         }
3827
3828         if(th->rst) {
3829                 tcp_reset(sk);
3830                 goto discard;
3831         }
3832
3833         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3834
3835         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3836                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
3837                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
3838                 tcp_reset(sk);
3839                 return 1;
3840         }
3841
3842 step5:
3843         if(th->ack)
3844                 tcp_ack(sk, skb, FLAG_SLOWPATH);
3845
3846         tcp_rcv_rtt_measure_ts(sk, skb);
3847
3848         /* Process urgent data. */
3849         tcp_urg(sk, skb, th);
3850
3851         /* step 7: process the segment text */
3852         tcp_data_queue(sk, skb);
3853
3854         tcp_data_snd_check(sk, tp);
3855         tcp_ack_snd_check(sk);
3856         return 0;
3857
3858 csum_error:
3859         TCP_INC_STATS_BH(TCP_MIB_INERRS);
3860
3861 discard:
3862         __kfree_skb(skb);
3863         return 0;
3864 }
3865
3866 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
3867                                          struct tcphdr *th, unsigned len)
3868 {
3869         struct tcp_sock *tp = tcp_sk(sk);
3870         int saved_clamp = tp->rx_opt.mss_clamp;
3871
3872         tcp_parse_options(skb, &tp->rx_opt, 0);
3873
3874         if (th->ack) {
3875                 struct inet_connection_sock *icsk;
3876                 /* rfc793:
3877                  * "If the state is SYN-SENT then
3878                  *    first check the ACK bit
3879                  *      If the ACK bit is set
3880                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
3881                  *        a reset (unless the RST bit is set, if so drop
3882                  *        the segment and return)"
3883                  *
3884                  *  We do not send data with SYN, so that RFC-correct
3885                  *  test reduces to:
3886                  */
3887                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
3888                         goto reset_and_undo;
3889
3890                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3891                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
3892                              tcp_time_stamp)) {
3893                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
3894                         goto reset_and_undo;
3895                 }
3896
3897                 /* Now ACK is acceptable.
3898                  *
3899                  * "If the RST bit is set
3900                  *    If the ACK was acceptable then signal the user "error:
3901                  *    connection reset", drop the segment, enter CLOSED state,
3902                  *    delete TCB, and return."
3903                  */
3904
3905                 if (th->rst) {
3906                         tcp_reset(sk);
3907                         goto discard;
3908                 }
3909
3910                 /* rfc793:
3911                  *   "fifth, if neither of the SYN or RST bits is set then
3912                  *    drop the segment and return."
3913                  *
3914                  *    See note below!
3915                  *                                        --ANK(990513)
3916                  */
3917                 if (!th->syn)
3918                         goto discard_and_undo;
3919
3920                 /* rfc793:
3921                  *   "If the SYN bit is on ...
3922                  *    are acceptable then ...
3923                  *    (our SYN has been ACKed), change the connection
3924                  *    state to ESTABLISHED..."
3925                  */
3926
3927                 TCP_ECN_rcv_synack(tp, th);
3928                 if (tp->ecn_flags&TCP_ECN_OK)
3929                         sock_set_flag(sk, SOCK_NO_LARGESEND);
3930
3931                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
3932                 tcp_ack(sk, skb, FLAG_SLOWPATH);
3933
3934                 /* Ok.. it's good. Set up sequence numbers and
3935                  * move to established.
3936                  */
3937                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
3938                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
3939
3940                 /* RFC1323: The window in SYN & SYN/ACK segments is
3941                  * never scaled.
3942                  */
3943                 tp->snd_wnd = ntohs(th->window);
3944                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
3945
3946                 if (!tp->rx_opt.wscale_ok) {
3947                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
3948                         tp->window_clamp = min(tp->window_clamp, 65535U);
3949                 }
3950
3951                 if (tp->rx_opt.saw_tstamp) {
3952                         tp->rx_opt.tstamp_ok       = 1;
3953                         tp->tcp_header_len =
3954                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
3955                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
3956                         tcp_store_ts_recent(tp);
3957                 } else {
3958                         tp->tcp_header_len = sizeof(struct tcphdr);
3959                 }
3960
3961                 if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
3962                         tp->rx_opt.sack_ok |= 2;
3963
3964                 tcp_sync_mss(sk, tp->pmtu_cookie);
3965                 tcp_initialize_rcv_mss(sk);
3966
3967                 /* Remember, tcp_poll() does not lock socket!
3968                  * Change state from SYN-SENT only after copied_seq
3969                  * is initialized. */
3970                 tp->copied_seq = tp->rcv_nxt;
3971                 mb();
3972                 tcp_set_state(sk, TCP_ESTABLISHED);
3973
3974                 /* Make sure socket is routed, for correct metrics.  */
3975                 tp->af_specific->rebuild_header(sk);
3976
3977                 tcp_init_metrics(sk);
3978
3979                 tcp_init_congestion_control(sk);
3980
3981                 /* Prevent spurious tcp_cwnd_restart() on first data
3982                  * packet.
3983                  */
3984                 tp->lsndtime = tcp_time_stamp;
3985
3986                 tcp_init_buffer_space(sk);
3987
3988                 if (sock_flag(sk, SOCK_KEEPOPEN))
3989                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
3990
3991                 if (!tp->rx_opt.snd_wscale)
3992                         __tcp_fast_path_on(tp, tp->snd_wnd);
3993                 else
3994                         tp->pred_flags = 0;
3995
3996                 if (!sock_flag(sk, SOCK_DEAD)) {
3997                         sk->sk_state_change(sk);
3998                         sk_wake_async(sk, 0, POLL_OUT);
3999                 }
4000
4001                 icsk = inet_csk(sk);
4002
4003                 if (sk->sk_write_pending ||
4004                     icsk->icsk_accept_queue.rskq_defer_accept ||
4005                     icsk->icsk_ack.pingpong) {
4006                         /* Save one ACK. Data will be ready after
4007                          * several ticks, if write_pending is set.
4008                          *
4009                          * It may be deleted, but with this feature tcpdumps
4010                          * look so _wonderfully_ clever, that I was not able
4011                          * to stand against the temptation 8)     --ANK
4012                          */
4013                         inet_csk_schedule_ack(sk);
4014                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4015                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4016                         tcp_incr_quickack(sk);
4017                         tcp_enter_quickack_mode(sk);
4018                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4019                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4020
4021 discard:
4022                         __kfree_skb(skb);
4023                         return 0;
4024                 } else {
4025                         tcp_send_ack(sk);
4026                 }
4027                 return -1;
4028         }
4029
4030         /* No ACK in the segment */
4031
4032         if (th->rst) {
4033                 /* rfc793:
4034                  * "If the RST bit is set
4035                  *
4036                  *      Otherwise (no ACK) drop the segment and return."
4037                  */
4038
4039                 goto discard_and_undo;
4040         }
4041
4042         /* PAWS check. */
4043         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4044                 goto discard_and_undo;
4045
4046         if (th->syn) {
4047                 /* We see SYN without ACK. It is attempt of
4048                  * simultaneous connect with crossed SYNs.
4049                  * Particularly, it can be connect to self.
4050                  */
4051                 tcp_set_state(sk, TCP_SYN_RECV);
4052
4053                 if (tp->rx_opt.saw_tstamp) {
4054                         tp->rx_opt.tstamp_ok = 1;
4055                         tcp_store_ts_recent(tp);
4056                         tp->tcp_header_len =
4057                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4058                 } else {
4059                         tp->tcp_header_len = sizeof(struct tcphdr);
4060                 }
4061
4062                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4063                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4064
4065                 /* RFC1323: The window in SYN & SYN/ACK segments is
4066                  * never scaled.
4067                  */
4068                 tp->snd_wnd    = ntohs(th->window);
4069                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4070                 tp->max_window = tp->snd_wnd;
4071
4072                 TCP_ECN_rcv_syn(tp, th);
4073                 if (tp->ecn_flags&TCP_ECN_OK)
4074                         sock_set_flag(sk, SOCK_NO_LARGESEND);
4075
4076                 tcp_sync_mss(sk, tp->pmtu_cookie);
4077                 tcp_initialize_rcv_mss(sk);
4078
4079
4080                 tcp_send_synack(sk);
4081 #if 0
4082                 /* Note, we could accept data and URG from this segment.
4083                  * There are no obstacles to make this.
4084                  *
4085                  * However, if we ignore data in ACKless segments sometimes,
4086                  * we have no reasons to accept it sometimes.
4087                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
4088                  * is not flawless. So, discard packet for sanity.
4089                  * Uncomment this return to process the data.
4090                  */
4091                 return -1;
4092 #else
4093                 goto discard;
4094 #endif
4095         }
4096         /* "fifth, if neither of the SYN or RST bits is set then
4097          * drop the segment and return."
4098          */
4099
4100 discard_and_undo:
4101         tcp_clear_options(&tp->rx_opt);
4102         tp->rx_opt.mss_clamp = saved_clamp;
4103         goto discard;
4104
4105 reset_and_undo:
4106         tcp_clear_options(&tp->rx_opt);
4107         tp->rx_opt.mss_clamp = saved_clamp;
4108         return 1;
4109 }
4110
4111
4112 /*
4113  *      This function implements the receiving procedure of RFC 793 for
4114  *      all states except ESTABLISHED and TIME_WAIT. 
4115  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4116  *      address independent.
4117  */
4118         
4119 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4120                           struct tcphdr *th, unsigned len)
4121 {
4122         struct tcp_sock *tp = tcp_sk(sk);
4123         int queued = 0;
4124
4125         tp->rx_opt.saw_tstamp = 0;
4126
4127         switch (sk->sk_state) {
4128         case TCP_CLOSE:
4129                 goto discard;
4130
4131         case TCP_LISTEN:
4132                 if(th->ack)
4133                         return 1;
4134
4135                 if(th->rst)
4136                         goto discard;
4137
4138                 if(th->syn) {
4139                         if(tp->af_specific->conn_request(sk, skb) < 0)
4140                                 return 1;
4141
4142                         /* Now we have several options: In theory there is 
4143                          * nothing else in the frame. KA9Q has an option to 
4144                          * send data with the syn, BSD accepts data with the
4145                          * syn up to the [to be] advertised window and 
4146                          * Solaris 2.1 gives you a protocol error. For now 
4147                          * we just ignore it, that fits the spec precisely 
4148                          * and avoids incompatibilities. It would be nice in
4149                          * future to drop through and process the data.
4150                          *
4151                          * Now that TTCP is starting to be used we ought to 
4152                          * queue this data.
4153                          * But, this leaves one open to an easy denial of
4154                          * service attack, and SYN cookies can't defend
4155                          * against this problem. So, we drop the data
4156                          * in the interest of security over speed.
4157                          */
4158                         goto discard;
4159                 }
4160                 goto discard;
4161
4162         case TCP_SYN_SENT:
4163                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4164                 if (queued >= 0)
4165                         return queued;
4166
4167                 /* Do step6 onward by hand. */
4168                 tcp_urg(sk, skb, th);
4169                 __kfree_skb(skb);
4170                 tcp_data_snd_check(sk, tp);
4171                 return 0;
4172         }
4173
4174         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4175             tcp_paws_discard(sk, skb)) {
4176                 if (!th->rst) {
4177                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4178                         tcp_send_dupack(sk, skb);
4179                         goto discard;
4180                 }
4181                 /* Reset is accepted even if it did not pass PAWS. */
4182         }
4183
4184         /* step 1: check sequence number */
4185         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4186                 if (!th->rst)
4187                         tcp_send_dupack(sk, skb);
4188                 goto discard;
4189         }
4190
4191         /* step 2: check RST bit */
4192         if(th->rst) {
4193                 tcp_reset(sk);
4194                 goto discard;
4195         }
4196
4197         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4198
4199         /* step 3: check security and precedence [ignored] */
4200
4201         /*      step 4:
4202          *
4203          *      Check for a SYN in window.
4204          */
4205         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4206                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4207                 tcp_reset(sk);
4208                 return 1;
4209         }
4210
4211         /* step 5: check the ACK field */
4212         if (th->ack) {
4213                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
4214
4215                 switch(sk->sk_state) {
4216                 case TCP_SYN_RECV:
4217                         if (acceptable) {
4218                                 tp->copied_seq = tp->rcv_nxt;
4219                                 mb();
4220                                 tcp_set_state(sk, TCP_ESTABLISHED);
4221                                 sk->sk_state_change(sk);
4222
4223                                 /* Note, that this wakeup is only for marginal
4224                                  * crossed SYN case. Passively open sockets
4225                                  * are not waked up, because sk->sk_sleep ==
4226                                  * NULL and sk->sk_socket == NULL.
4227                                  */
4228                                 if (sk->sk_socket) {
4229                                         sk_wake_async(sk,0,POLL_OUT);
4230                                 }
4231
4232                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
4233                                 tp->snd_wnd = ntohs(th->window) <<
4234                                               tp->rx_opt.snd_wscale;
4235                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
4236                                             TCP_SKB_CB(skb)->seq);
4237
4238                                 /* tcp_ack considers this ACK as duplicate
4239                                  * and does not calculate rtt.
4240                                  * Fix it at least with timestamps.
4241                                  */
4242                                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4243                                     !tp->srtt)
4244                                         tcp_ack_saw_tstamp(sk, NULL, 0);
4245
4246                                 if (tp->rx_opt.tstamp_ok)
4247                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
4248
4249                                 /* Make sure socket is routed, for
4250                                  * correct metrics.
4251                                  */
4252                                 tp->af_specific->rebuild_header(sk);
4253
4254                                 tcp_init_metrics(sk);
4255
4256                                 tcp_init_congestion_control(sk);
4257
4258                                 /* Prevent spurious tcp_cwnd_restart() on
4259                                  * first data packet.
4260                                  */
4261                                 tp->lsndtime = tcp_time_stamp;
4262
4263                                 tcp_initialize_rcv_mss(sk);
4264                                 tcp_init_buffer_space(sk);
4265                                 tcp_fast_path_on(tp);
4266                         } else {
4267                                 return 1;
4268                         }
4269                         break;
4270
4271                 case TCP_FIN_WAIT1:
4272                         if (tp->snd_una == tp->write_seq) {
4273                                 tcp_set_state(sk, TCP_FIN_WAIT2);
4274                                 sk->sk_shutdown |= SEND_SHUTDOWN;
4275                                 dst_confirm(sk->sk_dst_cache);
4276
4277                                 if (!sock_flag(sk, SOCK_DEAD))
4278                                         /* Wake up lingering close() */
4279                                         sk->sk_state_change(sk);
4280                                 else {
4281                                         int tmo;
4282
4283                                         if (tp->linger2 < 0 ||
4284                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4285                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
4286                                                 tcp_done(sk);
4287                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4288                                                 return 1;
4289                                         }
4290
4291                                         tmo = tcp_fin_time(sk);
4292                                         if (tmo > TCP_TIMEWAIT_LEN) {
4293                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
4294                                         } else if (th->fin || sock_owned_by_user(sk)) {
4295                                                 /* Bad case. We could lose such FIN otherwise.
4296                                                  * It is not a big problem, but it looks confusing
4297                                                  * and not so rare event. We still can lose it now,
4298                                                  * if it spins in bh_lock_sock(), but it is really
4299                                                  * marginal case.
4300                                                  */
4301                                                 inet_csk_reset_keepalive_timer(sk, tmo);
4302                                         } else {
4303                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
4304                                                 goto discard;
4305                                         }
4306                                 }
4307                         }
4308                         break;
4309
4310                 case TCP_CLOSING:
4311                         if (tp->snd_una == tp->write_seq) {
4312                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4313                                 goto discard;
4314                         }
4315                         break;
4316
4317                 case TCP_LAST_ACK:
4318                         if (tp->snd_una == tp->write_seq) {
4319                                 tcp_update_metrics(sk);
4320                                 tcp_done(sk);
4321                                 goto discard;
4322                         }
4323                         break;
4324                 }
4325         } else
4326                 goto discard;
4327
4328         /* step 6: check the URG bit */
4329         tcp_urg(sk, skb, th);
4330
4331         /* step 7: process the segment text */
4332         switch (sk->sk_state) {
4333         case TCP_CLOSE_WAIT:
4334         case TCP_CLOSING:
4335         case TCP_LAST_ACK:
4336                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4337                         break;
4338         case TCP_FIN_WAIT1:
4339         case TCP_FIN_WAIT2:
4340                 /* RFC 793 says to queue data in these states,
4341                  * RFC 1122 says we MUST send a reset. 
4342                  * BSD 4.4 also does reset.
4343                  */
4344                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
4345                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4346                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
4347                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4348                                 tcp_reset(sk);
4349                                 return 1;
4350                         }
4351                 }
4352                 /* Fall through */
4353         case TCP_ESTABLISHED: 
4354                 tcp_data_queue(sk, skb);
4355                 queued = 1;
4356                 break;
4357         }
4358
4359         /* tcp_data could move socket to TIME-WAIT */
4360         if (sk->sk_state != TCP_CLOSE) {
4361                 tcp_data_snd_check(sk, tp);
4362                 tcp_ack_snd_check(sk);
4363         }
4364
4365         if (!queued) { 
4366 discard:
4367                 __kfree_skb(skb);
4368         }
4369         return 0;
4370 }
4371
4372 EXPORT_SYMBOL(sysctl_tcp_ecn);
4373 EXPORT_SYMBOL(sysctl_tcp_reordering);
4374 EXPORT_SYMBOL(tcp_parse_options);
4375 EXPORT_SYMBOL(tcp_rcv_established);
4376 EXPORT_SYMBOL(tcp_rcv_state_process);