e43065654930590d41317e7d42380cf8b143415f
[linux-2.6.git] / net / ipv4 / tcp_input.c
1 /*
2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
3  *              operating system.  INET is implemented using the  BSD Socket
4  *              interface as the means of communication with the user level.
5  *
6  *              Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Version:     $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
9  *
10  * Authors:     Ross Biro
11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
14  *              Florian La Roche, <flla@stud.uni-sb.de>
15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20  *              Jorge Cwik, <jorge@laser.satlink.net>
21  */
22
23 /*
24  * Changes:
25  *              Pedro Roque     :       Fast Retransmit/Recovery.
26  *                                      Two receive queues.
27  *                                      Retransmit queue handled by TCP.
28  *                                      Better retransmit timer handling.
29  *                                      New congestion avoidance.
30  *                                      Header prediction.
31  *                                      Variable renaming.
32  *
33  *              Eric            :       Fast Retransmit.
34  *              Randy Scott     :       MSS option defines.
35  *              Eric Schenk     :       Fixes to slow start algorithm.
36  *              Eric Schenk     :       Yet another double ACK bug.
37  *              Eric Schenk     :       Delayed ACK bug fixes.
38  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
39  *              David S. Miller :       Don't allow zero congestion window.
40  *              Eric Schenk     :       Fix retransmitter so that it sends
41  *                                      next packet on ack of previous packet.
42  *              Andi Kleen      :       Moved open_request checking here
43  *                                      and process RSTs for open_requests.
44  *              Andi Kleen      :       Better prune_queue, and other fixes.
45  *              Andrey Savochkin:       Fix RTT measurements in the 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                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
359         }
360 }
361
362 /* Receiver "autotuning" code.
363  *
364  * The algorithm for RTT estimation w/o timestamps is based on
365  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
366  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
367  *
368  * More detail on this code can be found at
369  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
370  * though this reference is out of date.  A new paper
371  * is pending.
372  */
373 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
374 {
375         u32 new_sample = tp->rcv_rtt_est.rtt;
376         long m = sample;
377
378         if (m == 0)
379                 m = 1;
380
381         if (new_sample != 0) {
382                 /* If we sample in larger samples in the non-timestamp
383                  * case, we could grossly overestimate the RTT especially
384                  * with chatty applications or bulk transfer apps which
385                  * are stalled on filesystem I/O.
386                  *
387                  * Also, since we are only going for a minimum in the
388                  * non-timestamp case, we do not smoothe things out
389                  * else with timestamps disabled convergance takes too
390                  * long.
391                  */
392                 if (!win_dep) {
393                         m -= (new_sample >> 3);
394                         new_sample += m;
395                 } else if (m < new_sample)
396                         new_sample = m << 3;
397         } else {
398                 /* No previous mesaure. */
399                 new_sample = m << 3;
400         }
401
402         if (tp->rcv_rtt_est.rtt != new_sample)
403                 tp->rcv_rtt_est.rtt = new_sample;
404 }
405
406 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
407 {
408         if (tp->rcv_rtt_est.time == 0)
409                 goto new_measure;
410         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
411                 return;
412         tcp_rcv_rtt_update(tp,
413                            jiffies - tp->rcv_rtt_est.time,
414                            1);
415
416 new_measure:
417         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
418         tp->rcv_rtt_est.time = tcp_time_stamp;
419 }
420
421 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
422 {
423         struct tcp_sock *tp = tcp_sk(sk);
424         if (tp->rx_opt.rcv_tsecr &&
425             (TCP_SKB_CB(skb)->end_seq -
426              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
427                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
428 }
429
430 /*
431  * This function should be called every time data is copied to user space.
432  * It calculates the appropriate TCP receive buffer space.
433  */
434 void tcp_rcv_space_adjust(struct sock *sk)
435 {
436         struct tcp_sock *tp = tcp_sk(sk);
437         int time;
438         int space;
439         
440         if (tp->rcvq_space.time == 0)
441                 goto new_measure;
442         
443         time = tcp_time_stamp - tp->rcvq_space.time;
444         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
445             tp->rcv_rtt_est.rtt == 0)
446                 return;
447         
448         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
449
450         space = max(tp->rcvq_space.space, space);
451
452         if (tp->rcvq_space.space != space) {
453                 int rcvmem;
454
455                 tp->rcvq_space.space = space;
456
457                 if (sysctl_tcp_moderate_rcvbuf) {
458                         int new_clamp = space;
459
460                         /* Receive space grows, normalize in order to
461                          * take into account packet headers and sk_buff
462                          * structure overhead.
463                          */
464                         space /= tp->advmss;
465                         if (!space)
466                                 space = 1;
467                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
468                                   16 + sizeof(struct sk_buff));
469                         while (tcp_win_from_space(rcvmem) < tp->advmss)
470                                 rcvmem += 128;
471                         space *= rcvmem;
472                         space = min(space, sysctl_tcp_rmem[2]);
473                         if (space > sk->sk_rcvbuf) {
474                                 sk->sk_rcvbuf = space;
475
476                                 /* Make the window clamp follow along.  */
477                                 tp->window_clamp = new_clamp;
478                         }
479                 }
480         }
481         
482 new_measure:
483         tp->rcvq_space.seq = tp->copied_seq;
484         tp->rcvq_space.time = tcp_time_stamp;
485 }
486
487 /* There is something which you must keep in mind when you analyze the
488  * behavior of the tp->ato delayed ack timeout interval.  When a
489  * connection starts up, we want to ack as quickly as possible.  The
490  * problem is that "good" TCP's do slow start at the beginning of data
491  * transmission.  The means that until we send the first few ACK's the
492  * sender will sit on his end and only queue most of his data, because
493  * he can only send snd_cwnd unacked packets at any given time.  For
494  * each ACK we send, he increments snd_cwnd and transmits more of his
495  * queue.  -DaveM
496  */
497 static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
498 {
499         struct inet_connection_sock *icsk = inet_csk(sk);
500         u32 now;
501
502         inet_csk_schedule_ack(sk);
503
504         tcp_measure_rcv_mss(sk, skb);
505
506         tcp_rcv_rtt_measure(tp);
507         
508         now = tcp_time_stamp;
509
510         if (!icsk->icsk_ack.ato) {
511                 /* The _first_ data packet received, initialize
512                  * delayed ACK engine.
513                  */
514                 tcp_incr_quickack(sk);
515                 icsk->icsk_ack.ato = TCP_ATO_MIN;
516         } else {
517                 int m = now - icsk->icsk_ack.lrcvtime;
518
519                 if (m <= TCP_ATO_MIN/2) {
520                         /* The fastest case is the first. */
521                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
522                 } else if (m < icsk->icsk_ack.ato) {
523                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
524                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
525                                 icsk->icsk_ack.ato = icsk->icsk_rto;
526                 } else if (m > icsk->icsk_rto) {
527                         /* Too long gap. Apparently sender falled to
528                          * restart window, so that we send ACKs quickly.
529                          */
530                         tcp_incr_quickack(sk);
531                         sk_stream_mem_reclaim(sk);
532                 }
533         }
534         icsk->icsk_ack.lrcvtime = now;
535
536         TCP_ECN_check_ce(tp, skb);
537
538         if (skb->len >= 128)
539                 tcp_grow_window(sk, tp, skb);
540 }
541
542 /* Called to compute a smoothed rtt estimate. The data fed to this
543  * routine either comes from timestamps, or from segments that were
544  * known _not_ to have been retransmitted [see Karn/Partridge
545  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
546  * piece by Van Jacobson.
547  * NOTE: the next three routines used to be one big routine.
548  * To save cycles in the RFC 1323 implementation it was better to break
549  * it up into three procedures. -- erics
550  */
551 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
552 {
553         struct tcp_sock *tp = tcp_sk(sk);
554         long m = mrtt; /* RTT */
555
556         /*      The following amusing code comes from Jacobson's
557          *      article in SIGCOMM '88.  Note that rtt and mdev
558          *      are scaled versions of rtt and mean deviation.
559          *      This is designed to be as fast as possible 
560          *      m stands for "measurement".
561          *
562          *      On a 1990 paper the rto value is changed to:
563          *      RTO = rtt + 4 * mdev
564          *
565          * Funny. This algorithm seems to be very broken.
566          * These formulae increase RTO, when it should be decreased, increase
567          * too slowly, when it should be incresed fastly, decrease too fastly
568          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
569          * does not matter how to _calculate_ it. Seems, it was trap
570          * that VJ failed to avoid. 8)
571          */
572         if(m == 0)
573                 m = 1;
574         if (tp->srtt != 0) {
575                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
576                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
577                 if (m < 0) {
578                         m = -m;         /* m is now abs(error) */
579                         m -= (tp->mdev >> 2);   /* similar update on mdev */
580                         /* This is similar to one of Eifel findings.
581                          * Eifel blocks mdev updates when rtt decreases.
582                          * This solution is a bit different: we use finer gain
583                          * for mdev in this case (alpha*beta).
584                          * Like Eifel it also prevents growth of rto,
585                          * but also it limits too fast rto decreases,
586                          * happening in pure Eifel.
587                          */
588                         if (m > 0)
589                                 m >>= 3;
590                 } else {
591                         m -= (tp->mdev >> 2);   /* similar update on mdev */
592                 }
593                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
594                 if (tp->mdev > tp->mdev_max) {
595                         tp->mdev_max = tp->mdev;
596                         if (tp->mdev_max > tp->rttvar)
597                                 tp->rttvar = tp->mdev_max;
598                 }
599                 if (after(tp->snd_una, tp->rtt_seq)) {
600                         if (tp->mdev_max < tp->rttvar)
601                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
602                         tp->rtt_seq = tp->snd_nxt;
603                         tp->mdev_max = TCP_RTO_MIN;
604                 }
605         } else {
606                 /* no previous measure. */
607                 tp->srtt = m<<3;        /* take the measured time to be rtt */
608                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
609                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
610                 tp->rtt_seq = tp->snd_nxt;
611         }
612 }
613
614 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
615  * routine referred to above.
616  */
617 static inline void tcp_set_rto(struct sock *sk)
618 {
619         const struct tcp_sock *tp = tcp_sk(sk);
620         /* Old crap is replaced with new one. 8)
621          *
622          * More seriously:
623          * 1. If rtt variance happened to be less 50msec, it is hallucination.
624          *    It cannot be less due to utterly erratic ACK generation made
625          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
626          *    to do with delayed acks, because at cwnd>2 true delack timeout
627          *    is invisible. Actually, Linux-2.4 also generates erratic
628          *    ACKs in some curcumstances.
629          */
630         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
631
632         /* 2. Fixups made earlier cannot be right.
633          *    If we do not estimate RTO correctly without them,
634          *    all the algo is pure shit and should be replaced
635          *    with correct one. It is exaclty, which we pretend to do.
636          */
637 }
638
639 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
640  * guarantees that rto is higher.
641  */
642 static inline void tcp_bound_rto(struct sock *sk)
643 {
644         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
645                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
646 }
647
648 /* Save metrics learned by this TCP session.
649    This function is called only, when TCP finishes successfully
650    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
651  */
652 void tcp_update_metrics(struct sock *sk)
653 {
654         struct tcp_sock *tp = tcp_sk(sk);
655         struct dst_entry *dst = __sk_dst_get(sk);
656
657         if (sysctl_tcp_nometrics_save)
658                 return;
659
660         dst_confirm(dst);
661
662         if (dst && (dst->flags&DST_HOST)) {
663                 const struct inet_connection_sock *icsk = inet_csk(sk);
664                 int m;
665
666                 if (icsk->icsk_backoff || !tp->srtt) {
667                         /* This session failed to estimate rtt. Why?
668                          * Probably, no packets returned in time.
669                          * Reset our results.
670                          */
671                         if (!(dst_metric_locked(dst, RTAX_RTT)))
672                                 dst->metrics[RTAX_RTT-1] = 0;
673                         return;
674                 }
675
676                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
677
678                 /* If newly calculated rtt larger than stored one,
679                  * store new one. Otherwise, use EWMA. Remember,
680                  * rtt overestimation is always better than underestimation.
681                  */
682                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
683                         if (m <= 0)
684                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
685                         else
686                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
687                 }
688
689                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
690                         if (m < 0)
691                                 m = -m;
692
693                         /* Scale deviation to rttvar fixed point */
694                         m >>= 1;
695                         if (m < tp->mdev)
696                                 m = tp->mdev;
697
698                         if (m >= dst_metric(dst, RTAX_RTTVAR))
699                                 dst->metrics[RTAX_RTTVAR-1] = m;
700                         else
701                                 dst->metrics[RTAX_RTTVAR-1] -=
702                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
703                 }
704
705                 if (tp->snd_ssthresh >= 0xFFFF) {
706                         /* Slow start still did not finish. */
707                         if (dst_metric(dst, RTAX_SSTHRESH) &&
708                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
709                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
710                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
711                         if (!dst_metric_locked(dst, RTAX_CWND) &&
712                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
713                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
714                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
715                            icsk->icsk_ca_state == TCP_CA_Open) {
716                         /* Cong. avoidance phase, cwnd is reliable. */
717                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
718                                 dst->metrics[RTAX_SSTHRESH-1] =
719                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
720                         if (!dst_metric_locked(dst, RTAX_CWND))
721                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
722                 } else {
723                         /* Else slow start did not finish, cwnd is non-sense,
724                            ssthresh may be also invalid.
725                          */
726                         if (!dst_metric_locked(dst, RTAX_CWND))
727                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
728                         if (dst->metrics[RTAX_SSTHRESH-1] &&
729                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
730                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
731                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
732                 }
733
734                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
735                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
736                             tp->reordering != sysctl_tcp_reordering)
737                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
738                 }
739         }
740 }
741
742 /* Numbers are taken from RFC2414.  */
743 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
744 {
745         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
746
747         if (!cwnd) {
748                 if (tp->mss_cache > 1460)
749                         cwnd = 2;
750                 else
751                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
752         }
753         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
754 }
755
756 /* Initialize metrics on socket. */
757
758 static void tcp_init_metrics(struct sock *sk)
759 {
760         struct tcp_sock *tp = tcp_sk(sk);
761         struct dst_entry *dst = __sk_dst_get(sk);
762
763         if (dst == NULL)
764                 goto reset;
765
766         dst_confirm(dst);
767
768         if (dst_metric_locked(dst, RTAX_CWND))
769                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
770         if (dst_metric(dst, RTAX_SSTHRESH)) {
771                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
772                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
773                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
774         }
775         if (dst_metric(dst, RTAX_REORDERING) &&
776             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
777                 tp->rx_opt.sack_ok &= ~2;
778                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
779         }
780
781         if (dst_metric(dst, RTAX_RTT) == 0)
782                 goto reset;
783
784         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
785                 goto reset;
786
787         /* Initial rtt is determined from SYN,SYN-ACK.
788          * The segment is small and rtt may appear much
789          * less than real one. Use per-dst memory
790          * to make it more realistic.
791          *
792          * A bit of theory. RTT is time passed after "normal" sized packet
793          * is sent until it is ACKed. In normal curcumstances sending small
794          * packets force peer to delay ACKs and calculation is correct too.
795          * The algorithm is adaptive and, provided we follow specs, it
796          * NEVER underestimate RTT. BUT! If peer tries to make some clever
797          * tricks sort of "quick acks" for time long enough to decrease RTT
798          * to low value, and then abruptly stops to do it and starts to delay
799          * ACKs, wait for troubles.
800          */
801         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
802                 tp->srtt = dst_metric(dst, RTAX_RTT);
803                 tp->rtt_seq = tp->snd_nxt;
804         }
805         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
806                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
807                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
808         }
809         tcp_set_rto(sk);
810         tcp_bound_rto(sk);
811         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
812                 goto reset;
813         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
814         tp->snd_cwnd_stamp = tcp_time_stamp;
815         return;
816
817 reset:
818         /* Play conservative. If timestamps are not
819          * supported, TCP will fail to recalculate correct
820          * rtt, if initial rto is too small. FORGET ALL AND RESET!
821          */
822         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
823                 tp->srtt = 0;
824                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
825                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
826         }
827 }
828
829 static void tcp_update_reordering(struct sock *sk, const int metric,
830                                   const int ts)
831 {
832         struct tcp_sock *tp = tcp_sk(sk);
833         if (metric > tp->reordering) {
834                 tp->reordering = min(TCP_MAX_REORDERING, metric);
835
836                 /* This exciting event is worth to be remembered. 8) */
837                 if (ts)
838                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
839                 else if (IsReno(tp))
840                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
841                 else if (IsFack(tp))
842                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
843                 else
844                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
845 #if FASTRETRANS_DEBUG > 1
846                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
847                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
848                        tp->reordering,
849                        tp->fackets_out,
850                        tp->sacked_out,
851                        tp->undo_marker ? tp->undo_retrans : 0);
852 #endif
853                 /* Disable FACK yet. */
854                 tp->rx_opt.sack_ok &= ~2;
855         }
856 }
857
858 /* This procedure tags the retransmission queue when SACKs arrive.
859  *
860  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
861  * Packets in queue with these bits set are counted in variables
862  * sacked_out, retrans_out and lost_out, correspondingly.
863  *
864  * Valid combinations are:
865  * Tag  InFlight        Description
866  * 0    1               - orig segment is in flight.
867  * S    0               - nothing flies, orig reached receiver.
868  * L    0               - nothing flies, orig lost by net.
869  * R    2               - both orig and retransmit are in flight.
870  * L|R  1               - orig is lost, retransmit is in flight.
871  * S|R  1               - orig reached receiver, retrans is still in flight.
872  * (L|S|R is logically valid, it could occur when L|R is sacked,
873  *  but it is equivalent to plain S and code short-curcuits it to S.
874  *  L|S is logically invalid, it would mean -1 packet in flight 8))
875  *
876  * These 6 states form finite state machine, controlled by the following events:
877  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
878  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
879  * 3. Loss detection event of one of three flavors:
880  *      A. Scoreboard estimator decided the packet is lost.
881  *         A'. Reno "three dupacks" marks head of queue lost.
882  *         A''. Its FACK modfication, head until snd.fack is lost.
883  *      B. SACK arrives sacking data transmitted after never retransmitted
884  *         hole was sent out.
885  *      C. SACK arrives sacking SND.NXT at the moment, when the
886  *         segment was retransmitted.
887  * 4. D-SACK added new rule: D-SACK changes any tag to S.
888  *
889  * It is pleasant to note, that state diagram turns out to be commutative,
890  * so that we are allowed not to be bothered by order of our actions,
891  * when multiple events arrive simultaneously. (see the function below).
892  *
893  * Reordering detection.
894  * --------------------
895  * Reordering metric is maximal distance, which a packet can be displaced
896  * in packet stream. With SACKs we can estimate it:
897  *
898  * 1. SACK fills old hole and the corresponding segment was not
899  *    ever retransmitted -> reordering. Alas, we cannot use it
900  *    when segment was retransmitted.
901  * 2. The last flaw is solved with D-SACK. D-SACK arrives
902  *    for retransmitted and already SACKed segment -> reordering..
903  * Both of these heuristics are not used in Loss state, when we cannot
904  * account for retransmits accurately.
905  */
906 static int
907 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
908 {
909         const struct inet_connection_sock *icsk = inet_csk(sk);
910         struct tcp_sock *tp = tcp_sk(sk);
911         unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
912         struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2);
913         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
914         int reord = tp->packets_out;
915         int prior_fackets;
916         u32 lost_retrans = 0;
917         int flag = 0;
918         int i;
919
920         if (!tp->sacked_out)
921                 tp->fackets_out = 0;
922         prior_fackets = tp->fackets_out;
923
924         for (i=0; i<num_sacks; i++, sp++) {
925                 struct sk_buff *skb;
926                 __u32 start_seq = ntohl(sp->start_seq);
927                 __u32 end_seq = ntohl(sp->end_seq);
928                 int fack_count = 0;
929                 int dup_sack = 0;
930
931                 /* Check for D-SACK. */
932                 if (i == 0) {
933                         u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;
934
935                         if (before(start_seq, ack)) {
936                                 dup_sack = 1;
937                                 tp->rx_opt.sack_ok |= 4;
938                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
939                         } else if (num_sacks > 1 &&
940                                    !after(end_seq, ntohl(sp[1].end_seq)) &&
941                                    !before(start_seq, ntohl(sp[1].start_seq))) {
942                                 dup_sack = 1;
943                                 tp->rx_opt.sack_ok |= 4;
944                                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
945                         }
946
947                         /* D-SACK for already forgotten data...
948                          * Do dumb counting. */
949                         if (dup_sack &&
950                             !after(end_seq, prior_snd_una) &&
951                             after(end_seq, tp->undo_marker))
952                                 tp->undo_retrans--;
953
954                         /* Eliminate too old ACKs, but take into
955                          * account more or less fresh ones, they can
956                          * contain valid SACK info.
957                          */
958                         if (before(ack, prior_snd_una - tp->max_window))
959                                 return 0;
960                 }
961
962                 /* Event "B" in the comment above. */
963                 if (after(end_seq, tp->high_seq))
964                         flag |= FLAG_DATA_LOST;
965
966                 sk_stream_for_retrans_queue(skb, sk) {
967                         int in_sack, pcount;
968                         u8 sacked;
969
970                         /* The retransmission queue is always in order, so
971                          * we can short-circuit the walk early.
972                          */
973                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
974                                 break;
975
976                         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
977                                 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
978
979                         pcount = tcp_skb_pcount(skb);
980
981                         if (pcount > 1 && !in_sack &&
982                             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
983                                 unsigned int pkt_len;
984
985                                 in_sack = !after(start_seq,
986                                                  TCP_SKB_CB(skb)->seq);
987
988                                 if (!in_sack)
989                                         pkt_len = (start_seq -
990                                                    TCP_SKB_CB(skb)->seq);
991                                 else
992                                         pkt_len = (end_seq -
993                                                    TCP_SKB_CB(skb)->seq);
994                                 if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->tso_size))
995                                         break;
996                                 pcount = tcp_skb_pcount(skb);
997                         }
998
999                         fack_count += pcount;
1000
1001                         sacked = TCP_SKB_CB(skb)->sacked;
1002
1003                         /* Account D-SACK for retransmitted packet. */
1004                         if ((dup_sack && in_sack) &&
1005                             (sacked & TCPCB_RETRANS) &&
1006                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1007                                 tp->undo_retrans--;
1008
1009                         /* The frame is ACKed. */
1010                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1011                                 if (sacked&TCPCB_RETRANS) {
1012                                         if ((dup_sack && in_sack) &&
1013                                             (sacked&TCPCB_SACKED_ACKED))
1014                                                 reord = min(fack_count, reord);
1015                                 } else {
1016                                         /* If it was in a hole, we detected reordering. */
1017                                         if (fack_count < prior_fackets &&
1018                                             !(sacked&TCPCB_SACKED_ACKED))
1019                                                 reord = min(fack_count, reord);
1020                                 }
1021
1022                                 /* Nothing to do; acked frame is about to be dropped. */
1023                                 continue;
1024                         }
1025
1026                         if ((sacked&TCPCB_SACKED_RETRANS) &&
1027                             after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1028                             (!lost_retrans || after(end_seq, lost_retrans)))
1029                                 lost_retrans = end_seq;
1030
1031                         if (!in_sack)
1032                                 continue;
1033
1034                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1035                                 if (sacked & TCPCB_SACKED_RETRANS) {
1036                                         /* If the segment is not tagged as lost,
1037                                          * we do not clear RETRANS, believing
1038                                          * that retransmission is still in flight.
1039                                          */
1040                                         if (sacked & TCPCB_LOST) {
1041                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1042                                                 tp->lost_out -= tcp_skb_pcount(skb);
1043                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1044                                         }
1045                                 } else {
1046                                         /* New sack for not retransmitted frame,
1047                                          * which was in hole. It is reordering.
1048                                          */
1049                                         if (!(sacked & TCPCB_RETRANS) &&
1050                                             fack_count < prior_fackets)
1051                                                 reord = min(fack_count, reord);
1052
1053                                         if (sacked & TCPCB_LOST) {
1054                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1055                                                 tp->lost_out -= tcp_skb_pcount(skb);
1056                                         }
1057                                 }
1058
1059                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1060                                 flag |= FLAG_DATA_SACKED;
1061                                 tp->sacked_out += tcp_skb_pcount(skb);
1062
1063                                 if (fack_count > tp->fackets_out)
1064                                         tp->fackets_out = fack_count;
1065                         } else {
1066                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1067                                         reord = min(fack_count, reord);
1068                         }
1069
1070                         /* D-SACK. We can detect redundant retransmission
1071                          * in S|R and plain R frames and clear it.
1072                          * undo_retrans is decreased above, L|R frames
1073                          * are accounted above as well.
1074                          */
1075                         if (dup_sack &&
1076                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1077                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1078                                 tp->retrans_out -= tcp_skb_pcount(skb);
1079                         }
1080                 }
1081         }
1082
1083         /* Check for lost retransmit. This superb idea is
1084          * borrowed from "ratehalving". Event "C".
1085          * Later note: FACK people cheated me again 8),
1086          * we have to account for reordering! Ugly,
1087          * but should help.
1088          */
1089         if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
1090                 struct sk_buff *skb;
1091
1092                 sk_stream_for_retrans_queue(skb, sk) {
1093                         if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1094                                 break;
1095                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1096                                 continue;
1097                         if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1098                             after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1099                             (IsFack(tp) ||
1100                              !before(lost_retrans,
1101                                      TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1102                                      tp->mss_cache))) {
1103                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1104                                 tp->retrans_out -= tcp_skb_pcount(skb);
1105
1106                                 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1107                                         tp->lost_out += tcp_skb_pcount(skb);
1108                                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1109                                         flag |= FLAG_DATA_SACKED;
1110                                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1111                                 }
1112                         }
1113                 }
1114         }
1115
1116         tp->left_out = tp->sacked_out + tp->lost_out;
1117
1118         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss)
1119                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1120
1121 #if FASTRETRANS_DEBUG > 0
1122         BUG_TRAP((int)tp->sacked_out >= 0);
1123         BUG_TRAP((int)tp->lost_out >= 0);
1124         BUG_TRAP((int)tp->retrans_out >= 0);
1125         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1126 #endif
1127         return flag;
1128 }
1129
1130 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new
1131  * segments to see from the next ACKs whether any data was really missing.
1132  * If the RTO was spurious, new ACKs should arrive.
1133  */
1134 void tcp_enter_frto(struct sock *sk)
1135 {
1136         const struct inet_connection_sock *icsk = inet_csk(sk);
1137         struct tcp_sock *tp = tcp_sk(sk);
1138         struct sk_buff *skb;
1139
1140         tp->frto_counter = 1;
1141
1142         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1143             tp->snd_una == tp->high_seq ||
1144             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1145                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1146                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1147                 tcp_ca_event(sk, CA_EVENT_FRTO);
1148         }
1149
1150         /* Have to clear retransmission markers here to keep the bookkeeping
1151          * in shape, even though we are not yet in Loss state.
1152          * If something was really lost, it is eventually caught up
1153          * in tcp_enter_frto_loss.
1154          */
1155         tp->retrans_out = 0;
1156         tp->undo_marker = tp->snd_una;
1157         tp->undo_retrans = 0;
1158
1159         sk_stream_for_retrans_queue(skb, sk) {
1160                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
1161         }
1162         tcp_sync_left_out(tp);
1163
1164         tcp_set_ca_state(sk, TCP_CA_Open);
1165         tp->frto_highmark = tp->snd_nxt;
1166 }
1167
1168 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1169  * which indicates that we should follow the traditional RTO recovery,
1170  * i.e. mark everything lost and do go-back-N retransmission.
1171  */
1172 static void tcp_enter_frto_loss(struct sock *sk)
1173 {
1174         struct tcp_sock *tp = tcp_sk(sk);
1175         struct sk_buff *skb;
1176         int cnt = 0;
1177
1178         tp->sacked_out = 0;
1179         tp->lost_out = 0;
1180         tp->fackets_out = 0;
1181
1182         sk_stream_for_retrans_queue(skb, sk) {
1183                 cnt += tcp_skb_pcount(skb);
1184                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1185                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1186
1187                         /* Do not mark those segments lost that were
1188                          * forward transmitted after RTO
1189                          */
1190                         if (!after(TCP_SKB_CB(skb)->end_seq,
1191                                    tp->frto_highmark)) {
1192                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1193                                 tp->lost_out += tcp_skb_pcount(skb);
1194                         }
1195                 } else {
1196                         tp->sacked_out += tcp_skb_pcount(skb);
1197                         tp->fackets_out = cnt;
1198                 }
1199         }
1200         tcp_sync_left_out(tp);
1201
1202         tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
1203         tp->snd_cwnd_cnt = 0;
1204         tp->snd_cwnd_stamp = tcp_time_stamp;
1205         tp->undo_marker = 0;
1206         tp->frto_counter = 0;
1207
1208         tp->reordering = min_t(unsigned int, tp->reordering,
1209                                              sysctl_tcp_reordering);
1210         tcp_set_ca_state(sk, TCP_CA_Loss);
1211         tp->high_seq = tp->frto_highmark;
1212         TCP_ECN_queue_cwr(tp);
1213 }
1214
1215 void tcp_clear_retrans(struct tcp_sock *tp)
1216 {
1217         tp->left_out = 0;
1218         tp->retrans_out = 0;
1219
1220         tp->fackets_out = 0;
1221         tp->sacked_out = 0;
1222         tp->lost_out = 0;
1223
1224         tp->undo_marker = 0;
1225         tp->undo_retrans = 0;
1226 }
1227
1228 /* Enter Loss state. If "how" is not zero, forget all SACK information
1229  * and reset tags completely, otherwise preserve SACKs. If receiver
1230  * dropped its ofo queue, we will know this due to reneging detection.
1231  */
1232 void tcp_enter_loss(struct sock *sk, int how)
1233 {
1234         const struct inet_connection_sock *icsk = inet_csk(sk);
1235         struct tcp_sock *tp = tcp_sk(sk);
1236         struct sk_buff *skb;
1237         int cnt = 0;
1238
1239         /* Reduce ssthresh if it has not yet been made inside this window. */
1240         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1241             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1242                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1243                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1244                 tcp_ca_event(sk, CA_EVENT_LOSS);
1245         }
1246         tp->snd_cwnd       = 1;
1247         tp->snd_cwnd_cnt   = 0;
1248         tp->snd_cwnd_stamp = tcp_time_stamp;
1249
1250         tcp_clear_retrans(tp);
1251
1252         /* Push undo marker, if it was plain RTO and nothing
1253          * was retransmitted. */
1254         if (!how)
1255                 tp->undo_marker = tp->snd_una;
1256
1257         sk_stream_for_retrans_queue(skb, sk) {
1258                 cnt += tcp_skb_pcount(skb);
1259                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1260                         tp->undo_marker = 0;
1261                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1262                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1263                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1264                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1265                         tp->lost_out += tcp_skb_pcount(skb);
1266                 } else {
1267                         tp->sacked_out += tcp_skb_pcount(skb);
1268                         tp->fackets_out = cnt;
1269                 }
1270         }
1271         tcp_sync_left_out(tp);
1272
1273         tp->reordering = min_t(unsigned int, tp->reordering,
1274                                              sysctl_tcp_reordering);
1275         tcp_set_ca_state(sk, TCP_CA_Loss);
1276         tp->high_seq = tp->snd_nxt;
1277         TCP_ECN_queue_cwr(tp);
1278 }
1279
1280 static int tcp_check_sack_reneging(struct sock *sk)
1281 {
1282         struct sk_buff *skb;
1283
1284         /* If ACK arrived pointing to a remembered SACK,
1285          * it means that our remembered SACKs do not reflect
1286          * real state of receiver i.e.
1287          * receiver _host_ is heavily congested (or buggy).
1288          * Do processing similar to RTO timeout.
1289          */
1290         if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
1291             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1292                 struct inet_connection_sock *icsk = inet_csk(sk);
1293                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1294
1295                 tcp_enter_loss(sk, 1);
1296                 icsk->icsk_retransmits++;
1297                 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
1298                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1299                                           icsk->icsk_rto, TCP_RTO_MAX);
1300                 return 1;
1301         }
1302         return 0;
1303 }
1304
1305 static inline int tcp_fackets_out(struct tcp_sock *tp)
1306 {
1307         return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1308 }
1309
1310 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1311 {
1312         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1313 }
1314
1315 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
1316 {
1317         return tp->packets_out &&
1318                tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
1319 }
1320
1321 /* Linux NewReno/SACK/FACK/ECN state machine.
1322  * --------------------------------------
1323  *
1324  * "Open"       Normal state, no dubious events, fast path.
1325  * "Disorder"   In all the respects it is "Open",
1326  *              but requires a bit more attention. It is entered when
1327  *              we see some SACKs or dupacks. It is split of "Open"
1328  *              mainly to move some processing from fast path to slow one.
1329  * "CWR"        CWND was reduced due to some Congestion Notification event.
1330  *              It can be ECN, ICMP source quench, local device congestion.
1331  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1332  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1333  *
1334  * tcp_fastretrans_alert() is entered:
1335  * - each incoming ACK, if state is not "Open"
1336  * - when arrived ACK is unusual, namely:
1337  *      * SACK
1338  *      * Duplicate ACK.
1339  *      * ECN ECE.
1340  *
1341  * Counting packets in flight is pretty simple.
1342  *
1343  *      in_flight = packets_out - left_out + retrans_out
1344  *
1345  *      packets_out is SND.NXT-SND.UNA counted in packets.
1346  *
1347  *      retrans_out is number of retransmitted segments.
1348  *
1349  *      left_out is number of segments left network, but not ACKed yet.
1350  *
1351  *              left_out = sacked_out + lost_out
1352  *
1353  *     sacked_out: Packets, which arrived to receiver out of order
1354  *                 and hence not ACKed. With SACKs this number is simply
1355  *                 amount of SACKed data. Even without SACKs
1356  *                 it is easy to give pretty reliable estimate of this number,
1357  *                 counting duplicate ACKs.
1358  *
1359  *       lost_out: Packets lost by network. TCP has no explicit
1360  *                 "loss notification" feedback from network (for now).
1361  *                 It means that this number can be only _guessed_.
1362  *                 Actually, it is the heuristics to predict lossage that
1363  *                 distinguishes different algorithms.
1364  *
1365  *      F.e. after RTO, when all the queue is considered as lost,
1366  *      lost_out = packets_out and in_flight = retrans_out.
1367  *
1368  *              Essentially, we have now two algorithms counting
1369  *              lost packets.
1370  *
1371  *              FACK: It is the simplest heuristics. As soon as we decided
1372  *              that something is lost, we decide that _all_ not SACKed
1373  *              packets until the most forward SACK are lost. I.e.
1374  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1375  *              It is absolutely correct estimate, if network does not reorder
1376  *              packets. And it loses any connection to reality when reordering
1377  *              takes place. We use FACK by default until reordering
1378  *              is suspected on the path to this destination.
1379  *
1380  *              NewReno: when Recovery is entered, we assume that one segment
1381  *              is lost (classic Reno). While we are in Recovery and
1382  *              a partial ACK arrives, we assume that one more packet
1383  *              is lost (NewReno). This heuristics are the same in NewReno
1384  *              and SACK.
1385  *
1386  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1387  *  deflation etc. CWND is real congestion window, never inflated, changes
1388  *  only according to classic VJ rules.
1389  *
1390  * Really tricky (and requiring careful tuning) part of algorithm
1391  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1392  * The first determines the moment _when_ we should reduce CWND and,
1393  * hence, slow down forward transmission. In fact, it determines the moment
1394  * when we decide that hole is caused by loss, rather than by a reorder.
1395  *
1396  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1397  * holes, caused by lost packets.
1398  *
1399  * And the most logically complicated part of algorithm is undo
1400  * heuristics. We detect false retransmits due to both too early
1401  * fast retransmit (reordering) and underestimated RTO, analyzing
1402  * timestamps and D-SACKs. When we detect that some segments were
1403  * retransmitted by mistake and CWND reduction was wrong, we undo
1404  * window reduction and abort recovery phase. This logic is hidden
1405  * inside several functions named tcp_try_undo_<something>.
1406  */
1407
1408 /* This function decides, when we should leave Disordered state
1409  * and enter Recovery phase, reducing congestion window.
1410  *
1411  * Main question: may we further continue forward transmission
1412  * with the same cwnd?
1413  */
1414 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
1415 {
1416         __u32 packets_out;
1417
1418         /* Trick#1: The loss is proven. */
1419         if (tp->lost_out)
1420                 return 1;
1421
1422         /* Not-A-Trick#2 : Classic rule... */
1423         if (tcp_fackets_out(tp) > tp->reordering)
1424                 return 1;
1425
1426         /* Trick#3 : when we use RFC2988 timer restart, fast
1427          * retransmit can be triggered by timeout of queue head.
1428          */
1429         if (tcp_head_timedout(sk, tp))
1430                 return 1;
1431
1432         /* Trick#4: It is still not OK... But will it be useful to delay
1433          * recovery more?
1434          */
1435         packets_out = tp->packets_out;
1436         if (packets_out <= tp->reordering &&
1437             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1438             !tcp_may_send_now(sk, tp)) {
1439                 /* We have nothing to send. This connection is limited
1440                  * either by receiver window or by application.
1441                  */
1442                 return 1;
1443         }
1444
1445         return 0;
1446 }
1447
1448 /* If we receive more dupacks than we expected counting segments
1449  * in assumption of absent reordering, interpret this as reordering.
1450  * The only another reason could be bug in receiver TCP.
1451  */
1452 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1453 {
1454         struct tcp_sock *tp = tcp_sk(sk);
1455         u32 holes;
1456
1457         holes = max(tp->lost_out, 1U);
1458         holes = min(holes, tp->packets_out);
1459
1460         if ((tp->sacked_out + holes) > tp->packets_out) {
1461                 tp->sacked_out = tp->packets_out - holes;
1462                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1463         }
1464 }
1465
1466 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1467
1468 static void tcp_add_reno_sack(struct sock *sk)
1469 {
1470         struct tcp_sock *tp = tcp_sk(sk);
1471         tp->sacked_out++;
1472         tcp_check_reno_reordering(sk, 0);
1473         tcp_sync_left_out(tp);
1474 }
1475
1476 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1477
1478 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
1479 {
1480         if (acked > 0) {
1481                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1482                 if (acked-1 >= tp->sacked_out)
1483                         tp->sacked_out = 0;
1484                 else
1485                         tp->sacked_out -= acked-1;
1486         }
1487         tcp_check_reno_reordering(sk, acked);
1488         tcp_sync_left_out(tp);
1489 }
1490
1491 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1492 {
1493         tp->sacked_out = 0;
1494         tp->left_out = tp->lost_out;
1495 }
1496
1497 /* Mark head of queue up as lost. */
1498 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
1499                                int packets, u32 high_seq)
1500 {
1501         struct sk_buff *skb;
1502         int cnt = packets;
1503
1504         BUG_TRAP(cnt <= tp->packets_out);
1505
1506         sk_stream_for_retrans_queue(skb, sk) {
1507                 cnt -= tcp_skb_pcount(skb);
1508                 if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1509                         break;
1510                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1511                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1512                         tp->lost_out += tcp_skb_pcount(skb);
1513                 }
1514         }
1515         tcp_sync_left_out(tp);
1516 }
1517
1518 /* Account newly detected lost packet(s) */
1519
1520 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
1521 {
1522         if (IsFack(tp)) {
1523                 int lost = tp->fackets_out - tp->reordering;
1524                 if (lost <= 0)
1525                         lost = 1;
1526                 tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
1527         } else {
1528                 tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
1529         }
1530
1531         /* New heuristics: it is possible only after we switched
1532          * to restart timer each time when something is ACKed.
1533          * Hence, we can detect timed out packets during fast
1534          * retransmit without falling to slow start.
1535          */
1536         if (tcp_head_timedout(sk, tp)) {
1537                 struct sk_buff *skb;
1538
1539                 sk_stream_for_retrans_queue(skb, sk) {
1540                         if (tcp_skb_timedout(sk, skb) &&
1541                             !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1542                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1543                                 tp->lost_out += tcp_skb_pcount(skb);
1544                         }
1545                 }
1546                 tcp_sync_left_out(tp);
1547         }
1548 }
1549
1550 /* CWND moderation, preventing bursts due to too big ACKs
1551  * in dubious situations.
1552  */
1553 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1554 {
1555         tp->snd_cwnd = min(tp->snd_cwnd,
1556                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1557         tp->snd_cwnd_stamp = tcp_time_stamp;
1558 }
1559
1560 /* Decrease cwnd each second ack. */
1561 static void tcp_cwnd_down(struct sock *sk)
1562 {
1563         const struct inet_connection_sock *icsk = inet_csk(sk);
1564         struct tcp_sock *tp = tcp_sk(sk);
1565         int decr = tp->snd_cwnd_cnt + 1;
1566
1567         tp->snd_cwnd_cnt = decr&1;
1568         decr >>= 1;
1569
1570         if (decr && tp->snd_cwnd > icsk->icsk_ca_ops->min_cwnd(sk))
1571                 tp->snd_cwnd -= decr;
1572
1573         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1574         tp->snd_cwnd_stamp = tcp_time_stamp;
1575 }
1576
1577 /* Nothing was retransmitted or returned timestamp is less
1578  * than timestamp of the first retransmission.
1579  */
1580 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1581 {
1582         return !tp->retrans_stamp ||
1583                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1584                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1585 }
1586
1587 /* Undo procedures. */
1588
1589 #if FASTRETRANS_DEBUG > 1
1590 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
1591 {
1592         struct inet_sock *inet = inet_sk(sk);
1593         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1594                msg,
1595                NIPQUAD(inet->daddr), ntohs(inet->dport),
1596                tp->snd_cwnd, tp->left_out,
1597                tp->snd_ssthresh, tp->prior_ssthresh,
1598                tp->packets_out);
1599 }
1600 #else
1601 #define DBGUNDO(x...) do { } while (0)
1602 #endif
1603
1604 static void tcp_undo_cwr(struct sock *sk, const int undo)
1605 {
1606         struct tcp_sock *tp = tcp_sk(sk);
1607
1608         if (tp->prior_ssthresh) {
1609                 const struct inet_connection_sock *icsk = inet_csk(sk);
1610
1611                 if (icsk->icsk_ca_ops->undo_cwnd)
1612                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
1613                 else
1614                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1615
1616                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1617                         tp->snd_ssthresh = tp->prior_ssthresh;
1618                         TCP_ECN_withdraw_cwr(tp);
1619                 }
1620         } else {
1621                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1622         }
1623         tcp_moderate_cwnd(tp);
1624         tp->snd_cwnd_stamp = tcp_time_stamp;
1625 }
1626
1627 static inline int tcp_may_undo(struct tcp_sock *tp)
1628 {
1629         return tp->undo_marker &&
1630                 (!tp->undo_retrans || tcp_packet_delayed(tp));
1631 }
1632
1633 /* People celebrate: "We love our President!" */
1634 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
1635 {
1636         if (tcp_may_undo(tp)) {
1637                 /* Happy end! We did not retransmit anything
1638                  * or our original transmission succeeded.
1639                  */
1640                 DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
1641                 tcp_undo_cwr(sk, 1);
1642                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
1643                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1644                 else
1645                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1646                 tp->undo_marker = 0;
1647         }
1648         if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1649                 /* Hold old state until something *above* high_seq
1650                  * is ACKed. For Reno it is MUST to prevent false
1651                  * fast retransmits (RFC2582). SACK TCP is safe. */
1652                 tcp_moderate_cwnd(tp);
1653                 return 1;
1654         }
1655         tcp_set_ca_state(sk, TCP_CA_Open);
1656         return 0;
1657 }
1658
1659 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1660 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
1661 {
1662         if (tp->undo_marker && !tp->undo_retrans) {
1663                 DBGUNDO(sk, tp, "D-SACK");
1664                 tcp_undo_cwr(sk, 1);
1665                 tp->undo_marker = 0;
1666                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1667         }
1668 }
1669
1670 /* Undo during fast recovery after partial ACK. */
1671
1672 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
1673                                 int acked)
1674 {
1675         /* Partial ACK arrived. Force Hoe's retransmit. */
1676         int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1677
1678         if (tcp_may_undo(tp)) {
1679                 /* Plain luck! Hole if filled with delayed
1680                  * packet, rather than with a retransmit.
1681                  */
1682                 if (tp->retrans_out == 0)
1683                         tp->retrans_stamp = 0;
1684
1685                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
1686
1687                 DBGUNDO(sk, tp, "Hoe");
1688                 tcp_undo_cwr(sk, 0);
1689                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1690
1691                 /* So... Do not make Hoe's retransmit yet.
1692                  * If the first packet was delayed, the rest
1693                  * ones are most probably delayed as well.
1694                  */
1695                 failed = 0;
1696         }
1697         return failed;
1698 }
1699
1700 /* Undo during loss recovery after partial ACK. */
1701 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
1702 {
1703         if (tcp_may_undo(tp)) {
1704                 struct sk_buff *skb;
1705                 sk_stream_for_retrans_queue(skb, sk) {
1706                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1707                 }
1708                 DBGUNDO(sk, tp, "partial loss");
1709                 tp->lost_out = 0;
1710                 tp->left_out = tp->sacked_out;
1711                 tcp_undo_cwr(sk, 1);
1712                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1713                 inet_csk(sk)->icsk_retransmits = 0;
1714                 tp->undo_marker = 0;
1715                 if (!IsReno(tp))
1716                         tcp_set_ca_state(sk, TCP_CA_Open);
1717                 return 1;
1718         }
1719         return 0;
1720 }
1721
1722 static inline void tcp_complete_cwr(struct sock *sk)
1723 {
1724         struct tcp_sock *tp = tcp_sk(sk);
1725         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
1726         tp->snd_cwnd_stamp = tcp_time_stamp;
1727         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
1728 }
1729
1730 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
1731 {
1732         tp->left_out = tp->sacked_out;
1733
1734         if (tp->retrans_out == 0)
1735                 tp->retrans_stamp = 0;
1736
1737         if (flag&FLAG_ECE)
1738                 tcp_enter_cwr(sk);
1739
1740         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
1741                 int state = TCP_CA_Open;
1742
1743                 if (tp->left_out || tp->retrans_out || tp->undo_marker)
1744                         state = TCP_CA_Disorder;
1745
1746                 if (inet_csk(sk)->icsk_ca_state != state) {
1747                         tcp_set_ca_state(sk, state);
1748                         tp->high_seq = tp->snd_nxt;
1749                 }
1750                 tcp_moderate_cwnd(tp);
1751         } else {
1752                 tcp_cwnd_down(sk);
1753         }
1754 }
1755
1756 /* Process an event, which can update packets-in-flight not trivially.
1757  * Main goal of this function is to calculate new estimate for left_out,
1758  * taking into account both packets sitting in receiver's buffer and
1759  * packets lost by network.
1760  *
1761  * Besides that it does CWND reduction, when packet loss is detected
1762  * and changes state of machine.
1763  *
1764  * It does _not_ decide what to send, it is made in function
1765  * tcp_xmit_retransmit_queue().
1766  */
1767 static void
1768 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
1769                       int prior_packets, int flag)
1770 {
1771         struct inet_connection_sock *icsk = inet_csk(sk);
1772         struct tcp_sock *tp = tcp_sk(sk);
1773         int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
1774
1775         /* Some technical things:
1776          * 1. Reno does not count dupacks (sacked_out) automatically. */
1777         if (!tp->packets_out)
1778                 tp->sacked_out = 0;
1779         /* 2. SACK counts snd_fack in packets inaccurately. */
1780         if (tp->sacked_out == 0)
1781                 tp->fackets_out = 0;
1782
1783         /* Now state machine starts.
1784          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
1785         if (flag&FLAG_ECE)
1786                 tp->prior_ssthresh = 0;
1787
1788         /* B. In all the states check for reneging SACKs. */
1789         if (tp->sacked_out && tcp_check_sack_reneging(sk))
1790                 return;
1791
1792         /* C. Process data loss notification, provided it is valid. */
1793         if ((flag&FLAG_DATA_LOST) &&
1794             before(tp->snd_una, tp->high_seq) &&
1795             icsk->icsk_ca_state != TCP_CA_Open &&
1796             tp->fackets_out > tp->reordering) {
1797                 tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
1798                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
1799         }
1800
1801         /* D. Synchronize left_out to current state. */
1802         tcp_sync_left_out(tp);
1803
1804         /* E. Check state exit conditions. State can be terminated
1805          *    when high_seq is ACKed. */
1806         if (icsk->icsk_ca_state == TCP_CA_Open) {
1807                 if (!sysctl_tcp_frto)
1808                         BUG_TRAP(tp->retrans_out == 0);
1809                 tp->retrans_stamp = 0;
1810         } else if (!before(tp->snd_una, tp->high_seq)) {
1811                 switch (icsk->icsk_ca_state) {
1812                 case TCP_CA_Loss:
1813                         icsk->icsk_retransmits = 0;
1814                         if (tcp_try_undo_recovery(sk, tp))
1815                                 return;
1816                         break;
1817
1818                 case TCP_CA_CWR:
1819                         /* CWR is to be held something *above* high_seq
1820                          * is ACKed for CWR bit to reach receiver. */
1821                         if (tp->snd_una != tp->high_seq) {
1822                                 tcp_complete_cwr(sk);
1823                                 tcp_set_ca_state(sk, TCP_CA_Open);
1824                         }
1825                         break;
1826
1827                 case TCP_CA_Disorder:
1828                         tcp_try_undo_dsack(sk, tp);
1829                         if (!tp->undo_marker ||
1830                             /* For SACK case do not Open to allow to undo
1831                              * catching for all duplicate ACKs. */
1832                             IsReno(tp) || tp->snd_una != tp->high_seq) {
1833                                 tp->undo_marker = 0;
1834                                 tcp_set_ca_state(sk, TCP_CA_Open);
1835                         }
1836                         break;
1837
1838                 case TCP_CA_Recovery:
1839                         if (IsReno(tp))
1840                                 tcp_reset_reno_sack(tp);
1841                         if (tcp_try_undo_recovery(sk, tp))
1842                                 return;
1843                         tcp_complete_cwr(sk);
1844                         break;
1845                 }
1846         }
1847
1848         /* F. Process state. */
1849         switch (icsk->icsk_ca_state) {
1850         case TCP_CA_Recovery:
1851                 if (prior_snd_una == tp->snd_una) {
1852                         if (IsReno(tp) && is_dupack)
1853                                 tcp_add_reno_sack(sk);
1854                 } else {
1855                         int acked = prior_packets - tp->packets_out;
1856                         if (IsReno(tp))
1857                                 tcp_remove_reno_sacks(sk, tp, acked);
1858                         is_dupack = tcp_try_undo_partial(sk, tp, acked);
1859                 }
1860                 break;
1861         case TCP_CA_Loss:
1862                 if (flag&FLAG_DATA_ACKED)
1863                         icsk->icsk_retransmits = 0;
1864                 if (!tcp_try_undo_loss(sk, tp)) {
1865                         tcp_moderate_cwnd(tp);
1866                         tcp_xmit_retransmit_queue(sk);
1867                         return;
1868                 }
1869                 if (icsk->icsk_ca_state != TCP_CA_Open)
1870                         return;
1871                 /* Loss is undone; fall through to processing in Open state. */
1872         default:
1873                 if (IsReno(tp)) {
1874                         if (tp->snd_una != prior_snd_una)
1875                                 tcp_reset_reno_sack(tp);
1876                         if (is_dupack)
1877                                 tcp_add_reno_sack(sk);
1878                 }
1879
1880                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
1881                         tcp_try_undo_dsack(sk, tp);
1882
1883                 if (!tcp_time_to_recover(sk, tp)) {
1884                         tcp_try_to_open(sk, tp, flag);
1885                         return;
1886                 }
1887
1888                 /* Otherwise enter Recovery state */
1889
1890                 if (IsReno(tp))
1891                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
1892                 else
1893                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
1894
1895                 tp->high_seq = tp->snd_nxt;
1896                 tp->prior_ssthresh = 0;
1897                 tp->undo_marker = tp->snd_una;
1898                 tp->undo_retrans = tp->retrans_out;
1899
1900                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
1901                         if (!(flag&FLAG_ECE))
1902                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1903                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1904                         TCP_ECN_queue_cwr(tp);
1905                 }
1906
1907                 tp->snd_cwnd_cnt = 0;
1908                 tcp_set_ca_state(sk, TCP_CA_Recovery);
1909         }
1910
1911         if (is_dupack || tcp_head_timedout(sk, tp))
1912                 tcp_update_scoreboard(sk, tp);
1913         tcp_cwnd_down(sk);
1914         tcp_xmit_retransmit_queue(sk);
1915 }
1916
1917 /* Read draft-ietf-tcplw-high-performance before mucking
1918  * with this code. (Superceeds RFC1323)
1919  */
1920 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
1921 {
1922         /* RTTM Rule: A TSecr value received in a segment is used to
1923          * update the averaged RTT measurement only if the segment
1924          * acknowledges some new data, i.e., only if it advances the
1925          * left edge of the send window.
1926          *
1927          * See draft-ietf-tcplw-high-performance-00, section 3.3.
1928          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
1929          *
1930          * Changed: reset backoff as soon as we see the first valid sample.
1931          * If we do not, we get strongly overstimated rto. With timestamps
1932          * samples are accepted even from very old segments: f.e., when rtt=1
1933          * increases to 8, we retransmit 5 times and after 8 seconds delayed
1934          * answer arrives rto becomes 120 seconds! If at least one of segments
1935          * in window is lost... Voila.                          --ANK (010210)
1936          */
1937         struct tcp_sock *tp = tcp_sk(sk);
1938         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
1939         tcp_rtt_estimator(sk, seq_rtt);
1940         tcp_set_rto(sk);
1941         inet_csk(sk)->icsk_backoff = 0;
1942         tcp_bound_rto(sk);
1943 }
1944
1945 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
1946 {
1947         /* We don't have a timestamp. Can only use
1948          * packets that are not retransmitted to determine
1949          * rtt estimates. Also, we must not reset the
1950          * backoff for rto until we get a non-retransmitted
1951          * packet. This allows us to deal with a situation
1952          * where the network delay has increased suddenly.
1953          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
1954          */
1955
1956         if (flag & FLAG_RETRANS_DATA_ACKED)
1957                 return;
1958
1959         tcp_rtt_estimator(sk, seq_rtt);
1960         tcp_set_rto(sk);
1961         inet_csk(sk)->icsk_backoff = 0;
1962         tcp_bound_rto(sk);
1963 }
1964
1965 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
1966                                       const s32 seq_rtt)
1967 {
1968         const struct tcp_sock *tp = tcp_sk(sk);
1969         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
1970         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
1971                 tcp_ack_saw_tstamp(sk, flag);
1972         else if (seq_rtt >= 0)
1973                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
1974 }
1975
1976 static inline void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
1977                                   u32 in_flight, int good)
1978 {
1979         const struct inet_connection_sock *icsk = inet_csk(sk);
1980         icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
1981         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
1982 }
1983
1984 /* Restart timer after forward progress on connection.
1985  * RFC2988 recommends to restart timer to now+rto.
1986  */
1987
1988 static inline void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
1989 {
1990         if (!tp->packets_out) {
1991                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
1992         } else {
1993                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
1994         }
1995 }
1996
1997 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
1998                          __u32 now, __s32 *seq_rtt)
1999 {
2000         struct tcp_sock *tp = tcp_sk(sk);
2001         struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2002         __u32 seq = tp->snd_una;
2003         __u32 packets_acked;
2004         int acked = 0;
2005
2006         /* If we get here, the whole TSO packet has not been
2007          * acked.
2008          */
2009         BUG_ON(!after(scb->end_seq, seq));
2010
2011         packets_acked = tcp_skb_pcount(skb);
2012         if (tcp_trim_head(sk, skb, seq - scb->seq))
2013                 return 0;
2014         packets_acked -= tcp_skb_pcount(skb);
2015
2016         if (packets_acked) {
2017                 __u8 sacked = scb->sacked;
2018
2019                 acked |= FLAG_DATA_ACKED;
2020                 if (sacked) {
2021                         if (sacked & TCPCB_RETRANS) {
2022                                 if (sacked & TCPCB_SACKED_RETRANS)
2023                                         tp->retrans_out -= packets_acked;
2024                                 acked |= FLAG_RETRANS_DATA_ACKED;
2025                                 *seq_rtt = -1;
2026                         } else if (*seq_rtt < 0)
2027                                 *seq_rtt = now - scb->when;
2028                         if (sacked & TCPCB_SACKED_ACKED)
2029                                 tp->sacked_out -= packets_acked;
2030                         if (sacked & TCPCB_LOST)
2031                                 tp->lost_out -= packets_acked;
2032                         if (sacked & TCPCB_URG) {
2033                                 if (tp->urg_mode &&
2034                                     !before(seq, tp->snd_up))
2035                                         tp->urg_mode = 0;
2036                         }
2037                 } else if (*seq_rtt < 0)
2038                         *seq_rtt = now - scb->when;
2039
2040                 if (tp->fackets_out) {
2041                         __u32 dval = min(tp->fackets_out, packets_acked);
2042                         tp->fackets_out -= dval;
2043                 }
2044                 tp->packets_out -= packets_acked;
2045
2046                 BUG_ON(tcp_skb_pcount(skb) == 0);
2047                 BUG_ON(!before(scb->seq, scb->end_seq));
2048         }
2049
2050         return acked;
2051 }
2052
2053 static inline u32 tcp_usrtt(const struct sk_buff *skb)
2054 {
2055         struct timeval tv, now;
2056
2057         do_gettimeofday(&now);
2058         skb_get_timestamp(skb, &tv);
2059         return (now.tv_sec - tv.tv_sec) * 1000000 + (now.tv_usec - tv.tv_usec);
2060 }
2061
2062 /* Remove acknowledged frames from the retransmission queue. */
2063 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
2064 {
2065         struct tcp_sock *tp = tcp_sk(sk);
2066         const struct inet_connection_sock *icsk = inet_csk(sk);
2067         struct sk_buff *skb;
2068         __u32 now = tcp_time_stamp;
2069         int acked = 0;
2070         __s32 seq_rtt = -1;
2071         u32 pkts_acked = 0;
2072         void (*rtt_sample)(struct sock *sk, u32 usrtt)
2073                 = icsk->icsk_ca_ops->rtt_sample;
2074
2075         while ((skb = skb_peek(&sk->sk_write_queue)) &&
2076                skb != sk->sk_send_head) {
2077                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
2078                 __u8 sacked = scb->sacked;
2079
2080                 /* If our packet is before the ack sequence we can
2081                  * discard it as it's confirmed to have arrived at
2082                  * the other end.
2083                  */
2084                 if (after(scb->end_seq, tp->snd_una)) {
2085                         if (tcp_skb_pcount(skb) > 1 &&
2086                             after(tp->snd_una, scb->seq))
2087                                 acked |= tcp_tso_acked(sk, skb,
2088                                                        now, &seq_rtt);
2089                         break;
2090                 }
2091
2092                 /* Initial outgoing SYN's get put onto the write_queue
2093                  * just like anything else we transmit.  It is not
2094                  * true data, and if we misinform our callers that
2095                  * this ACK acks real data, we will erroneously exit
2096                  * connection startup slow start one packet too
2097                  * quickly.  This is severely frowned upon behavior.
2098                  */
2099                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2100                         acked |= FLAG_DATA_ACKED;
2101                         ++pkts_acked;
2102                 } else {
2103                         acked |= FLAG_SYN_ACKED;
2104                         tp->retrans_stamp = 0;
2105                 }
2106
2107                 if (sacked) {
2108                         if (sacked & TCPCB_RETRANS) {
2109                                 if(sacked & TCPCB_SACKED_RETRANS)
2110                                         tp->retrans_out -= tcp_skb_pcount(skb);
2111                                 acked |= FLAG_RETRANS_DATA_ACKED;
2112                                 seq_rtt = -1;
2113                         } else if (seq_rtt < 0) {
2114                                 seq_rtt = now - scb->when;
2115                                 if (rtt_sample)
2116                                         (*rtt_sample)(sk, tcp_usrtt(skb));
2117                         }
2118                         if (sacked & TCPCB_SACKED_ACKED)
2119                                 tp->sacked_out -= tcp_skb_pcount(skb);
2120                         if (sacked & TCPCB_LOST)
2121                                 tp->lost_out -= tcp_skb_pcount(skb);
2122                         if (sacked & TCPCB_URG) {
2123                                 if (tp->urg_mode &&
2124                                     !before(scb->end_seq, tp->snd_up))
2125                                         tp->urg_mode = 0;
2126                         }
2127                 } else if (seq_rtt < 0) {
2128                         seq_rtt = now - scb->when;
2129                         if (rtt_sample)
2130                                 (*rtt_sample)(sk, tcp_usrtt(skb));
2131                 }
2132                 tcp_dec_pcount_approx(&tp->fackets_out, skb);
2133                 tcp_packets_out_dec(tp, skb);
2134                 __skb_unlink(skb, &sk->sk_write_queue);
2135                 sk_stream_free_skb(sk, skb);
2136         }
2137
2138         if (acked&FLAG_ACKED) {
2139                 tcp_ack_update_rtt(sk, acked, seq_rtt);
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                         tp->pred_flags = 0;
2243                         tcp_fast_path_check(sk, tp);
2244
2245                         if (nwin > tp->max_window) {
2246                                 tp->max_window = nwin;
2247                                 tcp_sync_mss(sk, tp->pmtu_cookie);
2248                         }
2249                 }
2250         }
2251
2252         tp->snd_una = ack;
2253
2254         return flag;
2255 }
2256
2257 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
2258 {
2259         struct tcp_sock *tp = tcp_sk(sk);
2260         
2261         tcp_sync_left_out(tp);
2262         
2263         if (tp->snd_una == prior_snd_una ||
2264             !before(tp->snd_una, tp->frto_highmark)) {
2265                 /* RTO was caused by loss, start retransmitting in
2266                  * go-back-N slow start
2267                  */
2268                 tcp_enter_frto_loss(sk);
2269                 return;
2270         }
2271
2272         if (tp->frto_counter == 1) {
2273                 /* First ACK after RTO advances the window: allow two new
2274                  * segments out.
2275                  */
2276                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2277         } else {
2278                 /* Also the second ACK after RTO advances the window.
2279                  * The RTO was likely spurious. Reduce cwnd and continue
2280                  * in congestion avoidance
2281                  */
2282                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2283                 tcp_moderate_cwnd(tp);
2284         }
2285
2286         /* F-RTO affects on two new ACKs following RTO.
2287          * At latest on third ACK the TCP behavor is back to normal.
2288          */
2289         tp->frto_counter = (tp->frto_counter + 1) % 3;
2290 }
2291
2292 /* This routine deals with incoming acks, but not outgoing ones. */
2293 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2294 {
2295         struct inet_connection_sock *icsk = inet_csk(sk);
2296         struct tcp_sock *tp = tcp_sk(sk);
2297         u32 prior_snd_una = tp->snd_una;
2298         u32 ack_seq = TCP_SKB_CB(skb)->seq;
2299         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2300         u32 prior_in_flight;
2301         s32 seq_rtt;
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
2356         if (tp->frto_counter)
2357                 tcp_process_frto(sk, prior_snd_una);
2358
2359         if (tcp_ack_is_dubious(sk, flag)) {
2360                 /* Advanve CWND, if state allows this. */
2361                 if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
2362                         tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
2363                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2364         } else {
2365                 if ((flag & FLAG_DATA_ACKED))
2366                         tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
2367         }
2368
2369         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2370                 dst_confirm(sk->sk_dst_cache);
2371
2372         return 1;
2373
2374 no_queue:
2375         icsk->icsk_probes_out = 0;
2376
2377         /* If this ack opens up a zero window, clear backoff.  It was
2378          * being used to time the probes, and is probably far higher than
2379          * it needs to be for normal retransmission.
2380          */
2381         if (sk->sk_send_head)
2382                 tcp_ack_probe(sk);
2383         return 1;
2384
2385 old_ack:
2386         if (TCP_SKB_CB(skb)->sacked)
2387                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2388
2389 uninteresting_ack:
2390         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2391         return 0;
2392 }
2393
2394
2395 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2396  * But, this can also be called on packets in the established flow when
2397  * the fast version below fails.
2398  */
2399 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2400 {
2401         unsigned char *ptr;
2402         struct tcphdr *th = skb->h.th;
2403         int length=(th->doff*4)-sizeof(struct tcphdr);
2404
2405         ptr = (unsigned char *)(th + 1);
2406         opt_rx->saw_tstamp = 0;
2407
2408         while(length>0) {
2409                 int opcode=*ptr++;
2410                 int opsize;
2411
2412                 switch (opcode) {
2413                         case TCPOPT_EOL:
2414                                 return;
2415                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
2416                                 length--;
2417                                 continue;
2418                         default:
2419                                 opsize=*ptr++;
2420                                 if (opsize < 2) /* "silly options" */
2421                                         return;
2422                                 if (opsize > length)
2423                                         return; /* don't parse partial options */
2424                                 switch(opcode) {
2425                                 case TCPOPT_MSS:
2426                                         if(opsize==TCPOLEN_MSS && th->syn && !estab) {
2427                                                 u16 in_mss = ntohs(get_unaligned((__u16 *)ptr));
2428                                                 if (in_mss) {
2429                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2430                                                                 in_mss = opt_rx->user_mss;
2431                                                         opt_rx->mss_clamp = in_mss;
2432                                                 }
2433                                         }
2434                                         break;
2435                                 case TCPOPT_WINDOW:
2436                                         if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
2437                                                 if (sysctl_tcp_window_scaling) {
2438                                                         __u8 snd_wscale = *(__u8 *) ptr;
2439                                                         opt_rx->wscale_ok = 1;
2440                                                         if (snd_wscale > 14) {
2441                                                                 if(net_ratelimit())
2442                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
2443                                                                                "scaling value %d >14 received.\n",
2444                                                                                snd_wscale);
2445                                                                 snd_wscale = 14;
2446                                                         }
2447                                                         opt_rx->snd_wscale = snd_wscale;
2448                                                 }
2449                                         break;
2450                                 case TCPOPT_TIMESTAMP:
2451                                         if(opsize==TCPOLEN_TIMESTAMP) {
2452                                                 if ((estab && opt_rx->tstamp_ok) ||
2453                                                     (!estab && sysctl_tcp_timestamps)) {
2454                                                         opt_rx->saw_tstamp = 1;
2455                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr));
2456                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4)));
2457                                                 }
2458                                         }
2459                                         break;
2460                                 case TCPOPT_SACK_PERM:
2461                                         if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2462                                                 if (sysctl_tcp_sack) {
2463                                                         opt_rx->sack_ok = 1;
2464                                                         tcp_sack_reset(opt_rx);
2465                                                 }
2466                                         }
2467                                         break;
2468
2469                                 case TCPOPT_SACK:
2470                                         if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2471                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2472                                            opt_rx->sack_ok) {
2473                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2474                                         }
2475                                 };
2476                                 ptr+=opsize-2;
2477                                 length-=opsize;
2478                 };
2479         }
2480 }
2481
2482 /* Fast parse options. This hopes to only see timestamps.
2483  * If it is wrong it falls back on tcp_parse_options().
2484  */
2485 static inline int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2486                                          struct tcp_sock *tp)
2487 {
2488         if (th->doff == sizeof(struct tcphdr)>>2) {
2489                 tp->rx_opt.saw_tstamp = 0;
2490                 return 0;
2491         } else if (tp->rx_opt.tstamp_ok &&
2492                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2493                 __u32 *ptr = (__u32 *)(th + 1);
2494                 if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2495                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2496                         tp->rx_opt.saw_tstamp = 1;
2497                         ++ptr;
2498                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
2499                         ++ptr;
2500                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2501                         return 1;
2502                 }
2503         }
2504         tcp_parse_options(skb, &tp->rx_opt, 1);
2505         return 1;
2506 }
2507
2508 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2509 {
2510         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2511         tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
2512 }
2513
2514 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2515 {
2516         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2517                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
2518                  * extra check below makes sure this can only happen
2519                  * for pure ACK frames.  -DaveM
2520                  *
2521                  * Not only, also it occurs for expired timestamps.
2522                  */
2523
2524                 if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2525                    xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2526                         tcp_store_ts_recent(tp);
2527         }
2528 }
2529
2530 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2531  *
2532  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2533  * it can pass through stack. So, the following predicate verifies that
2534  * this segment is not used for anything but congestion avoidance or
2535  * fast retransmit. Moreover, we even are able to eliminate most of such
2536  * second order effects, if we apply some small "replay" window (~RTO)
2537  * to timestamp space.
2538  *
2539  * All these measures still do not guarantee that we reject wrapped ACKs
2540  * on networks with high bandwidth, when sequence space is recycled fastly,
2541  * but it guarantees that such events will be very rare and do not affect
2542  * connection seriously. This doesn't look nice, but alas, PAWS is really
2543  * buggy extension.
2544  *
2545  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
2546  * states that events when retransmit arrives after original data are rare.
2547  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
2548  * the biggest problem on large power networks even with minor reordering.
2549  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
2550  * up to bandwidth of 18Gigabit/sec. 8) ]
2551  */
2552
2553 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
2554 {
2555         struct tcp_sock *tp = tcp_sk(sk);
2556         struct tcphdr *th = skb->h.th;
2557         u32 seq = TCP_SKB_CB(skb)->seq;
2558         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2559
2560         return (/* 1. Pure ACK with correct sequence number. */
2561                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
2562
2563                 /* 2. ... and duplicate ACK. */
2564                 ack == tp->snd_una &&
2565
2566                 /* 3. ... and does not update window. */
2567                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
2568
2569                 /* 4. ... and sits in replay window. */
2570                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
2571 }
2572
2573 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
2574 {
2575         const struct tcp_sock *tp = tcp_sk(sk);
2576         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
2577                 xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2578                 !tcp_disordered_ack(sk, skb));
2579 }
2580
2581 /* Check segment sequence number for validity.
2582  *
2583  * Segment controls are considered valid, if the segment
2584  * fits to the window after truncation to the window. Acceptability
2585  * of data (and SYN, FIN, of course) is checked separately.
2586  * See tcp_data_queue(), for example.
2587  *
2588  * Also, controls (RST is main one) are accepted using RCV.WUP instead
2589  * of RCV.NXT. Peer still did not advance his SND.UNA when we
2590  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
2591  * (borrowed from freebsd)
2592  */
2593
2594 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
2595 {
2596         return  !before(end_seq, tp->rcv_wup) &&
2597                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
2598 }
2599
2600 /* When we get a reset we do this. */
2601 static void tcp_reset(struct sock *sk)
2602 {
2603         /* We want the right error as BSD sees it (and indeed as we do). */
2604         switch (sk->sk_state) {
2605                 case TCP_SYN_SENT:
2606                         sk->sk_err = ECONNREFUSED;
2607                         break;
2608                 case TCP_CLOSE_WAIT:
2609                         sk->sk_err = EPIPE;
2610                         break;
2611                 case TCP_CLOSE:
2612                         return;
2613                 default:
2614                         sk->sk_err = ECONNRESET;
2615         }
2616
2617         if (!sock_flag(sk, SOCK_DEAD))
2618                 sk->sk_error_report(sk);
2619
2620         tcp_done(sk);
2621 }
2622
2623 /*
2624  *      Process the FIN bit. This now behaves as it is supposed to work
2625  *      and the FIN takes effect when it is validly part of sequence
2626  *      space. Not before when we get holes.
2627  *
2628  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
2629  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
2630  *      TIME-WAIT)
2631  *
2632  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
2633  *      close and we go into CLOSING (and later onto TIME-WAIT)
2634  *
2635  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
2636  */
2637 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
2638 {
2639         struct tcp_sock *tp = tcp_sk(sk);
2640
2641         inet_csk_schedule_ack(sk);
2642
2643         sk->sk_shutdown |= RCV_SHUTDOWN;
2644         sock_set_flag(sk, SOCK_DONE);
2645
2646         switch (sk->sk_state) {
2647                 case TCP_SYN_RECV:
2648                 case TCP_ESTABLISHED:
2649                         /* Move to CLOSE_WAIT */
2650                         tcp_set_state(sk, TCP_CLOSE_WAIT);
2651                         inet_csk(sk)->icsk_ack.pingpong = 1;
2652                         break;
2653
2654                 case TCP_CLOSE_WAIT:
2655                 case TCP_CLOSING:
2656                         /* Received a retransmission of the FIN, do
2657                          * nothing.
2658                          */
2659                         break;
2660                 case TCP_LAST_ACK:
2661                         /* RFC793: Remain in the LAST-ACK state. */
2662                         break;
2663
2664                 case TCP_FIN_WAIT1:
2665                         /* This case occurs when a simultaneous close
2666                          * happens, we must ack the received FIN and
2667                          * enter the CLOSING state.
2668                          */
2669                         tcp_send_ack(sk);
2670                         tcp_set_state(sk, TCP_CLOSING);
2671                         break;
2672                 case TCP_FIN_WAIT2:
2673                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
2674                         tcp_send_ack(sk);
2675                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
2676                         break;
2677                 default:
2678                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
2679                          * cases we should never reach this piece of code.
2680                          */
2681                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
2682                                __FUNCTION__, sk->sk_state);
2683                         break;
2684         };
2685
2686         /* It _is_ possible, that we have something out-of-order _after_ FIN.
2687          * Probably, we should reset in this case. For now drop them.
2688          */
2689         __skb_queue_purge(&tp->out_of_order_queue);
2690         if (tp->rx_opt.sack_ok)
2691                 tcp_sack_reset(&tp->rx_opt);
2692         sk_stream_mem_reclaim(sk);
2693
2694         if (!sock_flag(sk, SOCK_DEAD)) {
2695                 sk->sk_state_change(sk);
2696
2697                 /* Do not send POLL_HUP for half duplex close. */
2698                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
2699                     sk->sk_state == TCP_CLOSE)
2700                         sk_wake_async(sk, 1, POLL_HUP);
2701                 else
2702                         sk_wake_async(sk, 1, POLL_IN);
2703         }
2704 }
2705
2706 static __inline__ int
2707 tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
2708 {
2709         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
2710                 if (before(seq, sp->start_seq))
2711                         sp->start_seq = seq;
2712                 if (after(end_seq, sp->end_seq))
2713                         sp->end_seq = end_seq;
2714                 return 1;
2715         }
2716         return 0;
2717 }
2718
2719 static inline void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
2720 {
2721         if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2722                 if (before(seq, tp->rcv_nxt))
2723                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
2724                 else
2725                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
2726
2727                 tp->rx_opt.dsack = 1;
2728                 tp->duplicate_sack[0].start_seq = seq;
2729                 tp->duplicate_sack[0].end_seq = end_seq;
2730                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
2731         }
2732 }
2733
2734 static inline void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
2735 {
2736         if (!tp->rx_opt.dsack)
2737                 tcp_dsack_set(tp, seq, end_seq);
2738         else
2739                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
2740 }
2741
2742 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
2743 {
2744         struct tcp_sock *tp = tcp_sk(sk);
2745
2746         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
2747             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
2748                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2749                 tcp_enter_quickack_mode(sk);
2750
2751                 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
2752                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2753
2754                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
2755                                 end_seq = tp->rcv_nxt;
2756                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
2757                 }
2758         }
2759
2760         tcp_send_ack(sk);
2761 }
2762
2763 /* These routines update the SACK block as out-of-order packets arrive or
2764  * in-order packets close up the sequence space.
2765  */
2766 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
2767 {
2768         int this_sack;
2769         struct tcp_sack_block *sp = &tp->selective_acks[0];
2770         struct tcp_sack_block *swalk = sp+1;
2771
2772         /* See if the recent change to the first SACK eats into
2773          * or hits the sequence space of other SACK blocks, if so coalesce.
2774          */
2775         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
2776                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
2777                         int i;
2778
2779                         /* Zap SWALK, by moving every further SACK up by one slot.
2780                          * Decrease num_sacks.
2781                          */
2782                         tp->rx_opt.num_sacks--;
2783                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2784                         for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
2785                                 sp[i] = sp[i+1];
2786                         continue;
2787                 }
2788                 this_sack++, swalk++;
2789         }
2790 }
2791
2792 static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
2793 {
2794         __u32 tmp;
2795
2796         tmp = sack1->start_seq;
2797         sack1->start_seq = sack2->start_seq;
2798         sack2->start_seq = tmp;
2799
2800         tmp = sack1->end_seq;
2801         sack1->end_seq = sack2->end_seq;
2802         sack2->end_seq = tmp;
2803 }
2804
2805 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
2806 {
2807         struct tcp_sock *tp = tcp_sk(sk);
2808         struct tcp_sack_block *sp = &tp->selective_acks[0];
2809         int cur_sacks = tp->rx_opt.num_sacks;
2810         int this_sack;
2811
2812         if (!cur_sacks)
2813                 goto new_sack;
2814
2815         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
2816                 if (tcp_sack_extend(sp, seq, end_seq)) {
2817                         /* Rotate this_sack to the first one. */
2818                         for (; this_sack>0; this_sack--, sp--)
2819                                 tcp_sack_swap(sp, sp-1);
2820                         if (cur_sacks > 1)
2821                                 tcp_sack_maybe_coalesce(tp);
2822                         return;
2823                 }
2824         }
2825
2826         /* Could not find an adjacent existing SACK, build a new one,
2827          * put it at the front, and shift everyone else down.  We
2828          * always know there is at least one SACK present already here.
2829          *
2830          * If the sack array is full, forget about the last one.
2831          */
2832         if (this_sack >= 4) {
2833                 this_sack--;
2834                 tp->rx_opt.num_sacks--;
2835                 sp--;
2836         }
2837         for(; this_sack > 0; this_sack--, sp--)
2838                 *sp = *(sp-1);
2839
2840 new_sack:
2841         /* Build the new head SACK, and we're done. */
2842         sp->start_seq = seq;
2843         sp->end_seq = end_seq;
2844         tp->rx_opt.num_sacks++;
2845         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2846 }
2847
2848 /* RCV.NXT advances, some SACKs should be eaten. */
2849
2850 static void tcp_sack_remove(struct tcp_sock *tp)
2851 {
2852         struct tcp_sack_block *sp = &tp->selective_acks[0];
2853         int num_sacks = tp->rx_opt.num_sacks;
2854         int this_sack;
2855
2856         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
2857         if (skb_queue_empty(&tp->out_of_order_queue)) {
2858                 tp->rx_opt.num_sacks = 0;
2859                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
2860                 return;
2861         }
2862
2863         for(this_sack = 0; this_sack < num_sacks; ) {
2864                 /* Check if the start of the sack is covered by RCV.NXT. */
2865                 if (!before(tp->rcv_nxt, sp->start_seq)) {
2866                         int i;
2867
2868                         /* RCV.NXT must cover all the block! */
2869                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
2870
2871                         /* Zap this SACK, by moving forward any other SACKS. */
2872                         for (i=this_sack+1; i < num_sacks; i++)
2873                                 tp->selective_acks[i-1] = tp->selective_acks[i];
2874                         num_sacks--;
2875                         continue;
2876                 }
2877                 this_sack++;
2878                 sp++;
2879         }
2880         if (num_sacks != tp->rx_opt.num_sacks) {
2881                 tp->rx_opt.num_sacks = num_sacks;
2882                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
2883         }
2884 }
2885
2886 /* This one checks to see if we can put data from the
2887  * out_of_order queue into the receive_queue.
2888  */
2889 static void tcp_ofo_queue(struct sock *sk)
2890 {
2891         struct tcp_sock *tp = tcp_sk(sk);
2892         __u32 dsack_high = tp->rcv_nxt;
2893         struct sk_buff *skb;
2894
2895         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
2896                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
2897                         break;
2898
2899                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
2900                         __u32 dsack = dsack_high;
2901                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
2902                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
2903                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
2904                 }
2905
2906                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
2907                         SOCK_DEBUG(sk, "ofo packet was already received \n");
2908                         __skb_unlink(skb, &tp->out_of_order_queue);
2909                         __kfree_skb(skb);
2910                         continue;
2911                 }
2912                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
2913                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
2914                            TCP_SKB_CB(skb)->end_seq);
2915
2916                 __skb_unlink(skb, &tp->out_of_order_queue);
2917                 __skb_queue_tail(&sk->sk_receive_queue, skb);
2918                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2919                 if(skb->h.th->fin)
2920                         tcp_fin(skb, sk, skb->h.th);
2921         }
2922 }
2923
2924 static int tcp_prune_queue(struct sock *sk);
2925
2926 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
2927 {
2928         struct tcphdr *th = skb->h.th;
2929         struct tcp_sock *tp = tcp_sk(sk);
2930         int eaten = -1;
2931
2932         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
2933                 goto drop;
2934
2935         __skb_pull(skb, th->doff*4);
2936
2937         TCP_ECN_accept_cwr(tp, skb);
2938
2939         if (tp->rx_opt.dsack) {
2940                 tp->rx_opt.dsack = 0;
2941                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
2942                                                     4 - tp->rx_opt.tstamp_ok);
2943         }
2944
2945         /*  Queue data for delivery to the user.
2946          *  Packets in sequence go to the receive queue.
2947          *  Out of sequence packets to the out_of_order_queue.
2948          */
2949         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
2950                 if (tcp_receive_window(tp) == 0)
2951                         goto out_of_window;
2952
2953                 /* Ok. In sequence. In window. */
2954                 if (tp->ucopy.task == current &&
2955                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
2956                     sock_owned_by_user(sk) && !tp->urg_data) {
2957                         int chunk = min_t(unsigned int, skb->len,
2958                                                         tp->ucopy.len);
2959
2960                         __set_current_state(TASK_RUNNING);
2961
2962                         local_bh_enable();
2963                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
2964                                 tp->ucopy.len -= chunk;
2965                                 tp->copied_seq += chunk;
2966                                 eaten = (chunk == skb->len && !th->fin);
2967                                 tcp_rcv_space_adjust(sk);
2968                         }
2969                         local_bh_disable();
2970                 }
2971
2972                 if (eaten <= 0) {
2973 queue_and_out:
2974                         if (eaten < 0 &&
2975                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
2976                              !sk_stream_rmem_schedule(sk, skb))) {
2977                                 if (tcp_prune_queue(sk) < 0 ||
2978                                     !sk_stream_rmem_schedule(sk, skb))
2979                                         goto drop;
2980                         }
2981                         sk_stream_set_owner_r(skb, sk);
2982                         __skb_queue_tail(&sk->sk_receive_queue, skb);
2983                 }
2984                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
2985                 if(skb->len)
2986                         tcp_event_data_recv(sk, tp, skb);
2987                 if(th->fin)
2988                         tcp_fin(skb, sk, th);
2989
2990                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
2991                         tcp_ofo_queue(sk);
2992
2993                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
2994                          * gap in queue is filled.
2995                          */
2996                         if (skb_queue_empty(&tp->out_of_order_queue))
2997                                 inet_csk(sk)->icsk_ack.pingpong = 0;
2998                 }
2999
3000                 if (tp->rx_opt.num_sacks)
3001                         tcp_sack_remove(tp);
3002
3003                 tcp_fast_path_check(sk, tp);
3004
3005                 if (eaten > 0)
3006                         __kfree_skb(skb);
3007                 else if (!sock_flag(sk, SOCK_DEAD))
3008                         sk->sk_data_ready(sk, 0);
3009                 return;
3010         }
3011
3012         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3013                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3014                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3015                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3016
3017 out_of_window:
3018                 tcp_enter_quickack_mode(sk);
3019                 inet_csk_schedule_ack(sk);
3020 drop:
3021                 __kfree_skb(skb);
3022                 return;
3023         }
3024
3025         /* Out of window. F.e. zero window probe. */
3026         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3027                 goto out_of_window;
3028
3029         tcp_enter_quickack_mode(sk);
3030
3031         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3032                 /* Partial packet, seq < rcv_next < end_seq */
3033                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3034                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3035                            TCP_SKB_CB(skb)->end_seq);
3036
3037                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3038                 
3039                 /* If window is closed, drop tail of packet. But after
3040                  * remembering D-SACK for its head made in previous line.
3041                  */
3042                 if (!tcp_receive_window(tp))
3043                         goto out_of_window;
3044                 goto queue_and_out;
3045         }
3046
3047         TCP_ECN_check_ce(tp, skb);
3048
3049         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3050             !sk_stream_rmem_schedule(sk, skb)) {
3051                 if (tcp_prune_queue(sk) < 0 ||
3052                     !sk_stream_rmem_schedule(sk, skb))
3053                         goto drop;
3054         }
3055
3056         /* Disable header prediction. */
3057         tp->pred_flags = 0;
3058         inet_csk_schedule_ack(sk);
3059
3060         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3061                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3062
3063         sk_stream_set_owner_r(skb, sk);
3064
3065         if (!skb_peek(&tp->out_of_order_queue)) {
3066                 /* Initial out of order segment, build 1 SACK. */
3067                 if (tp->rx_opt.sack_ok) {
3068                         tp->rx_opt.num_sacks = 1;
3069                         tp->rx_opt.dsack     = 0;
3070                         tp->rx_opt.eff_sacks = 1;
3071                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3072                         tp->selective_acks[0].end_seq =
3073                                                 TCP_SKB_CB(skb)->end_seq;
3074                 }
3075                 __skb_queue_head(&tp->out_of_order_queue,skb);
3076         } else {
3077                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3078                 u32 seq = TCP_SKB_CB(skb)->seq;
3079                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3080
3081                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3082                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3083
3084                         if (!tp->rx_opt.num_sacks ||
3085                             tp->selective_acks[0].end_seq != seq)
3086                                 goto add_sack;
3087
3088                         /* Common case: data arrive in order after hole. */
3089                         tp->selective_acks[0].end_seq = end_seq;
3090                         return;
3091                 }
3092
3093                 /* Find place to insert this segment. */
3094                 do {
3095                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3096                                 break;
3097                 } while ((skb1 = skb1->prev) !=
3098                          (struct sk_buff*)&tp->out_of_order_queue);
3099
3100                 /* Do skb overlap to previous one? */
3101                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3102                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3103                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3104                                 /* All the bits are present. Drop. */
3105                                 __kfree_skb(skb);
3106                                 tcp_dsack_set(tp, seq, end_seq);
3107                                 goto add_sack;
3108                         }
3109                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3110                                 /* Partial overlap. */
3111                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3112                         } else {
3113                                 skb1 = skb1->prev;
3114                         }
3115                 }
3116                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3117                 
3118                 /* And clean segments covered by new one as whole. */
3119                 while ((skb1 = skb->next) !=
3120                        (struct sk_buff*)&tp->out_of_order_queue &&
3121                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3122                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3123                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3124                                break;
3125                        }
3126                        __skb_unlink(skb1, &tp->out_of_order_queue);
3127                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3128                        __kfree_skb(skb1);
3129                 }
3130
3131 add_sack:
3132                 if (tp->rx_opt.sack_ok)
3133                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3134         }
3135 }
3136
3137 /* Collapse contiguous sequence of skbs head..tail with
3138  * sequence numbers start..end.
3139  * Segments with FIN/SYN are not collapsed (only because this
3140  * simplifies code)
3141  */
3142 static void
3143 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3144              struct sk_buff *head, struct sk_buff *tail,
3145              u32 start, u32 end)
3146 {
3147         struct sk_buff *skb;
3148
3149         /* First, check that queue is collapsable and find
3150          * the point where collapsing can be useful. */
3151         for (skb = head; skb != tail; ) {
3152                 /* No new bits? It is possible on ofo queue. */
3153                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3154                         struct sk_buff *next = skb->next;
3155                         __skb_unlink(skb, list);
3156                         __kfree_skb(skb);
3157                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3158                         skb = next;
3159                         continue;
3160                 }
3161
3162                 /* The first skb to collapse is:
3163                  * - not SYN/FIN and
3164                  * - bloated or contains data before "start" or
3165                  *   overlaps to the next one.
3166                  */
3167                 if (!skb->h.th->syn && !skb->h.th->fin &&
3168                     (tcp_win_from_space(skb->truesize) > skb->len ||
3169                      before(TCP_SKB_CB(skb)->seq, start) ||
3170                      (skb->next != tail &&
3171                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3172                         break;
3173
3174                 /* Decided to skip this, advance start seq. */
3175                 start = TCP_SKB_CB(skb)->end_seq;
3176                 skb = skb->next;
3177         }
3178         if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3179                 return;
3180
3181         while (before(start, end)) {
3182                 struct sk_buff *nskb;
3183                 int header = skb_headroom(skb);
3184                 int copy = SKB_MAX_ORDER(header, 0);
3185
3186                 /* Too big header? This can happen with IPv6. */
3187                 if (copy < 0)
3188                         return;
3189                 if (end-start < copy)
3190                         copy = end-start;
3191                 nskb = alloc_skb(copy+header, GFP_ATOMIC);
3192                 if (!nskb)
3193                         return;
3194                 skb_reserve(nskb, header);
3195                 memcpy(nskb->head, skb->head, header);
3196                 nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head);
3197                 nskb->h.raw = nskb->head + (skb->h.raw-skb->head);
3198                 nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head);
3199                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3200                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3201                 __skb_insert(nskb, skb->prev, skb, list);
3202                 sk_stream_set_owner_r(nskb, sk);
3203
3204                 /* Copy data, releasing collapsed skbs. */
3205                 while (copy > 0) {
3206                         int offset = start - TCP_SKB_CB(skb)->seq;
3207                         int size = TCP_SKB_CB(skb)->end_seq - start;
3208
3209                         if (offset < 0) BUG();
3210                         if (size > 0) {
3211                                 size = min(copy, size);
3212                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3213                                         BUG();
3214                                 TCP_SKB_CB(nskb)->end_seq += size;
3215                                 copy -= size;
3216                                 start += size;
3217                         }
3218                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3219                                 struct sk_buff *next = skb->next;
3220                                 __skb_unlink(skb, list);
3221                                 __kfree_skb(skb);
3222                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3223                                 skb = next;
3224                                 if (skb == tail || skb->h.th->syn || skb->h.th->fin)
3225                                         return;
3226                         }
3227                 }
3228         }
3229 }
3230
3231 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3232  * and tcp_collapse() them until all the queue is collapsed.
3233  */
3234 static void tcp_collapse_ofo_queue(struct sock *sk)
3235 {
3236         struct tcp_sock *tp = tcp_sk(sk);
3237         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3238         struct sk_buff *head;
3239         u32 start, end;
3240
3241         if (skb == NULL)
3242                 return;
3243
3244         start = TCP_SKB_CB(skb)->seq;
3245         end = TCP_SKB_CB(skb)->end_seq;
3246         head = skb;
3247
3248         for (;;) {
3249                 skb = skb->next;
3250
3251                 /* Segment is terminated when we see gap or when
3252                  * we are at the end of all the queue. */
3253                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
3254                     after(TCP_SKB_CB(skb)->seq, end) ||
3255                     before(TCP_SKB_CB(skb)->end_seq, start)) {
3256                         tcp_collapse(sk, &tp->out_of_order_queue,
3257                                      head, skb, start, end);
3258                         head = skb;
3259                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
3260                                 break;
3261                         /* Start new segment */
3262                         start = TCP_SKB_CB(skb)->seq;
3263                         end = TCP_SKB_CB(skb)->end_seq;
3264                 } else {
3265                         if (before(TCP_SKB_CB(skb)->seq, start))
3266                                 start = TCP_SKB_CB(skb)->seq;
3267                         if (after(TCP_SKB_CB(skb)->end_seq, end))
3268                                 end = TCP_SKB_CB(skb)->end_seq;
3269                 }
3270         }
3271 }
3272
3273 /* Reduce allocated memory if we can, trying to get
3274  * the socket within its memory limits again.
3275  *
3276  * Return less than zero if we should start dropping frames
3277  * until the socket owning process reads some of the data
3278  * to stabilize the situation.
3279  */
3280 static int tcp_prune_queue(struct sock *sk)
3281 {
3282         struct tcp_sock *tp = tcp_sk(sk); 
3283
3284         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
3285
3286         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
3287
3288         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
3289                 tcp_clamp_window(sk, tp);
3290         else if (tcp_memory_pressure)
3291                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
3292
3293         tcp_collapse_ofo_queue(sk);
3294         tcp_collapse(sk, &sk->sk_receive_queue,
3295                      sk->sk_receive_queue.next,
3296                      (struct sk_buff*)&sk->sk_receive_queue,
3297                      tp->copied_seq, tp->rcv_nxt);
3298         sk_stream_mem_reclaim(sk);
3299
3300         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3301                 return 0;
3302
3303         /* Collapsing did not help, destructive actions follow.
3304          * This must not ever occur. */
3305
3306         /* First, purge the out_of_order queue. */
3307         if (!skb_queue_empty(&tp->out_of_order_queue)) {
3308                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
3309                 __skb_queue_purge(&tp->out_of_order_queue);
3310
3311                 /* Reset SACK state.  A conforming SACK implementation will
3312                  * do the same at a timeout based retransmit.  When a connection
3313                  * is in a sad state like this, we care only about integrity
3314                  * of the connection not performance.
3315                  */
3316                 if (tp->rx_opt.sack_ok)
3317                         tcp_sack_reset(&tp->rx_opt);
3318                 sk_stream_mem_reclaim(sk);
3319         }
3320
3321         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3322                 return 0;
3323
3324         /* If we are really being abused, tell the caller to silently
3325          * drop receive data on the floor.  It will get retransmitted
3326          * and hopefully then we'll have sufficient space.
3327          */
3328         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
3329
3330         /* Massive buffer overcommit. */
3331         tp->pred_flags = 0;
3332         return -1;
3333 }
3334
3335
3336 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
3337  * As additional protections, we do not touch cwnd in retransmission phases,
3338  * and if application hit its sndbuf limit recently.
3339  */
3340 void tcp_cwnd_application_limited(struct sock *sk)
3341 {
3342         struct tcp_sock *tp = tcp_sk(sk);
3343
3344         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
3345             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
3346                 /* Limited by application or receiver window. */
3347                 u32 win_used = max(tp->snd_cwnd_used, 2U);
3348                 if (win_used < tp->snd_cwnd) {
3349                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
3350                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
3351                 }
3352                 tp->snd_cwnd_used = 0;
3353         }
3354         tp->snd_cwnd_stamp = tcp_time_stamp;
3355 }
3356
3357 static inline int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp)
3358 {
3359         /* If the user specified a specific send buffer setting, do
3360          * not modify it.
3361          */
3362         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
3363                 return 0;
3364
3365         /* If we are under global TCP memory pressure, do not expand.  */
3366         if (tcp_memory_pressure)
3367                 return 0;
3368
3369         /* If we are under soft global TCP memory pressure, do not expand.  */
3370         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
3371                 return 0;
3372
3373         /* If we filled the congestion window, do not expand.  */
3374         if (tp->packets_out >= tp->snd_cwnd)
3375                 return 0;
3376
3377         return 1;
3378 }
3379
3380 /* When incoming ACK allowed to free some skb from write_queue,
3381  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
3382  * on the exit from tcp input handler.
3383  *
3384  * PROBLEM: sndbuf expansion does not work well with largesend.
3385  */
3386 static void tcp_new_space(struct sock *sk)
3387 {
3388         struct tcp_sock *tp = tcp_sk(sk);
3389
3390         if (tcp_should_expand_sndbuf(sk, tp)) {
3391                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
3392                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
3393                     demanded = max_t(unsigned int, tp->snd_cwnd,
3394                                                    tp->reordering + 1);
3395                 sndmem *= 2*demanded;
3396                 if (sndmem > sk->sk_sndbuf)
3397                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
3398                 tp->snd_cwnd_stamp = tcp_time_stamp;
3399         }
3400
3401         sk->sk_write_space(sk);
3402 }
3403
3404 static inline void tcp_check_space(struct sock *sk)
3405 {
3406         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
3407                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
3408                 if (sk->sk_socket &&
3409                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
3410                         tcp_new_space(sk);
3411         }
3412 }
3413
3414 static __inline__ void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
3415 {
3416         tcp_push_pending_frames(sk, tp);
3417         tcp_check_space(sk);
3418 }
3419
3420 /*
3421  * Check if sending an ack is needed.
3422  */
3423 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
3424 {
3425         struct tcp_sock *tp = tcp_sk(sk);
3426
3427             /* More than one full frame received... */
3428         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
3429              /* ... and right edge of window advances far enough.
3430               * (tcp_recvmsg() will send ACK otherwise). Or...
3431               */
3432              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
3433             /* We ACK each frame or... */
3434             tcp_in_quickack_mode(sk) ||
3435             /* We have out of order data. */
3436             (ofo_possible &&
3437              skb_peek(&tp->out_of_order_queue))) {
3438                 /* Then ack it now */
3439                 tcp_send_ack(sk);
3440         } else {
3441                 /* Else, send delayed ack. */
3442                 tcp_send_delayed_ack(sk);
3443         }
3444 }
3445
3446 static __inline__ void tcp_ack_snd_check(struct sock *sk)
3447 {
3448         if (!inet_csk_ack_scheduled(sk)) {
3449                 /* We sent a data segment already. */
3450                 return;
3451         }
3452         __tcp_ack_snd_check(sk, 1);
3453 }
3454
3455 /*
3456  *      This routine is only called when we have urgent data
3457  *      signalled. Its the 'slow' part of tcp_urg. It could be
3458  *      moved inline now as tcp_urg is only called from one
3459  *      place. We handle URGent data wrong. We have to - as
3460  *      BSD still doesn't use the correction from RFC961.
3461  *      For 1003.1g we should support a new option TCP_STDURG to permit
3462  *      either form (or just set the sysctl tcp_stdurg).
3463  */
3464  
3465 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
3466 {
3467         struct tcp_sock *tp = tcp_sk(sk);
3468         u32 ptr = ntohs(th->urg_ptr);
3469
3470         if (ptr && !sysctl_tcp_stdurg)
3471                 ptr--;
3472         ptr += ntohl(th->seq);
3473
3474         /* Ignore urgent data that we've already seen and read. */
3475         if (after(tp->copied_seq, ptr))
3476                 return;
3477
3478         /* Do not replay urg ptr.
3479          *
3480          * NOTE: interesting situation not covered by specs.
3481          * Misbehaving sender may send urg ptr, pointing to segment,
3482          * which we already have in ofo queue. We are not able to fetch
3483          * such data and will stay in TCP_URG_NOTYET until will be eaten
3484          * by recvmsg(). Seems, we are not obliged to handle such wicked
3485          * situations. But it is worth to think about possibility of some
3486          * DoSes using some hypothetical application level deadlock.
3487          */
3488         if (before(ptr, tp->rcv_nxt))
3489                 return;
3490
3491         /* Do we already have a newer (or duplicate) urgent pointer? */
3492         if (tp->urg_data && !after(ptr, tp->urg_seq))
3493                 return;
3494
3495         /* Tell the world about our new urgent pointer. */
3496         sk_send_sigurg(sk);
3497
3498         /* We may be adding urgent data when the last byte read was
3499          * urgent. To do this requires some care. We cannot just ignore
3500          * tp->copied_seq since we would read the last urgent byte again
3501          * as data, nor can we alter copied_seq until this data arrives
3502          * or we break the sematics of SIOCATMARK (and thus sockatmark())
3503          *
3504          * NOTE. Double Dutch. Rendering to plain English: author of comment
3505          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
3506          * and expect that both A and B disappear from stream. This is _wrong_.
3507          * Though this happens in BSD with high probability, this is occasional.
3508          * Any application relying on this is buggy. Note also, that fix "works"
3509          * only in this artificial test. Insert some normal data between A and B and we will
3510          * decline of BSD again. Verdict: it is better to remove to trap
3511          * buggy users.
3512          */
3513         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
3514             !sock_flag(sk, SOCK_URGINLINE) &&
3515             tp->copied_seq != tp->rcv_nxt) {
3516                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
3517                 tp->copied_seq++;
3518                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
3519                         __skb_unlink(skb, &sk->sk_receive_queue);
3520                         __kfree_skb(skb);
3521                 }
3522         }
3523
3524         tp->urg_data   = TCP_URG_NOTYET;
3525         tp->urg_seq    = ptr;
3526
3527         /* Disable header prediction. */
3528         tp->pred_flags = 0;
3529 }
3530
3531 /* This is the 'fast' part of urgent handling. */
3532 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
3533 {
3534         struct tcp_sock *tp = tcp_sk(sk);
3535
3536         /* Check if we get a new urgent pointer - normally not. */
3537         if (th->urg)
3538                 tcp_check_urg(sk,th);
3539
3540         /* Do we wait for any urgent data? - normally not... */
3541         if (tp->urg_data == TCP_URG_NOTYET) {
3542                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
3543                           th->syn;
3544
3545                 /* Is the urgent pointer pointing into this packet? */   
3546                 if (ptr < skb->len) {
3547                         u8 tmp;
3548                         if (skb_copy_bits(skb, ptr, &tmp, 1))
3549                                 BUG();
3550                         tp->urg_data = TCP_URG_VALID | tmp;
3551                         if (!sock_flag(sk, SOCK_DEAD))
3552                                 sk->sk_data_ready(sk, 0);
3553                 }
3554         }
3555 }
3556
3557 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
3558 {
3559         struct tcp_sock *tp = tcp_sk(sk);
3560         int chunk = skb->len - hlen;
3561         int err;
3562
3563         local_bh_enable();
3564         if (skb->ip_summed==CHECKSUM_UNNECESSARY)
3565                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
3566         else
3567                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
3568                                                        tp->ucopy.iov);
3569
3570         if (!err) {
3571                 tp->ucopy.len -= chunk;
3572                 tp->copied_seq += chunk;
3573                 tcp_rcv_space_adjust(sk);
3574         }
3575
3576         local_bh_disable();
3577         return err;
3578 }
3579
3580 static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3581 {
3582         int result;
3583
3584         if (sock_owned_by_user(sk)) {
3585                 local_bh_enable();
3586                 result = __tcp_checksum_complete(skb);
3587                 local_bh_disable();
3588         } else {
3589                 result = __tcp_checksum_complete(skb);
3590         }
3591         return result;
3592 }
3593
3594 static __inline__ int
3595 tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
3596 {
3597         return skb->ip_summed != CHECKSUM_UNNECESSARY &&
3598                 __tcp_checksum_complete_user(sk, skb);
3599 }
3600
3601 /*
3602  *      TCP receive function for the ESTABLISHED state. 
3603  *
3604  *      It is split into a fast path and a slow path. The fast path is 
3605  *      disabled when:
3606  *      - A zero window was announced from us - zero window probing
3607  *        is only handled properly in the slow path. 
3608  *      - Out of order segments arrived.
3609  *      - Urgent data is expected.
3610  *      - There is no buffer space left
3611  *      - Unexpected TCP flags/window values/header lengths are received
3612  *        (detected by checking the TCP header against pred_flags) 
3613  *      - Data is sent in both directions. Fast path only supports pure senders
3614  *        or pure receivers (this means either the sequence number or the ack
3615  *        value must stay constant)
3616  *      - Unexpected TCP option.
3617  *
3618  *      When these conditions are not satisfied it drops into a standard 
3619  *      receive procedure patterned after RFC793 to handle all cases.
3620  *      The first three cases are guaranteed by proper pred_flags setting,
3621  *      the rest is checked inline. Fast processing is turned on in 
3622  *      tcp_data_queue when everything is OK.
3623  */
3624 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
3625                         struct tcphdr *th, unsigned len)
3626 {
3627         struct tcp_sock *tp = tcp_sk(sk);
3628
3629         /*
3630          *      Header prediction.
3631          *      The code loosely follows the one in the famous 
3632          *      "30 instruction TCP receive" Van Jacobson mail.
3633          *      
3634          *      Van's trick is to deposit buffers into socket queue 
3635          *      on a device interrupt, to call tcp_recv function
3636          *      on the receive process context and checksum and copy
3637          *      the buffer to user space. smart...
3638          *
3639          *      Our current scheme is not silly either but we take the 
3640          *      extra cost of the net_bh soft interrupt processing...
3641          *      We do checksum and copy also but from device to kernel.
3642          */
3643
3644         tp->rx_opt.saw_tstamp = 0;
3645
3646         /*      pred_flags is 0xS?10 << 16 + snd_wnd
3647          *      if header_predition is to be made
3648          *      'S' will always be tp->tcp_header_len >> 2
3649          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
3650          *  turn it off (when there are holes in the receive 
3651          *       space for instance)
3652          *      PSH flag is ignored.
3653          */
3654
3655         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
3656                 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3657                 int tcp_header_len = tp->tcp_header_len;
3658
3659                 /* Timestamp header prediction: tcp_header_len
3660                  * is automatically equal to th->doff*4 due to pred_flags
3661                  * match.
3662                  */
3663
3664                 /* Check timestamp */
3665                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
3666                         __u32 *ptr = (__u32 *)(th + 1);
3667
3668                         /* No? Slow path! */
3669                         if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3670                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
3671                                 goto slow_path;
3672
3673                         tp->rx_opt.saw_tstamp = 1;
3674                         ++ptr; 
3675                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
3676                         ++ptr;
3677                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3678
3679                         /* If PAWS failed, check it more carefully in slow path */
3680                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
3681                                 goto slow_path;
3682
3683                         /* DO NOT update ts_recent here, if checksum fails
3684                          * and timestamp was corrupted part, it will result
3685                          * in a hung connection since we will drop all
3686                          * future packets due to the PAWS test.
3687                          */
3688                 }
3689
3690                 if (len <= tcp_header_len) {
3691                         /* Bulk data transfer: sender */
3692                         if (len == tcp_header_len) {
3693                                 /* Predicted packet is in window by definition.
3694                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3695                                  * Hence, check seq<=rcv_wup reduces to:
3696                                  */
3697                                 if (tcp_header_len ==
3698                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3699                                     tp->rcv_nxt == tp->rcv_wup)
3700                                         tcp_store_ts_recent(tp);
3701
3702                                 tcp_rcv_rtt_measure_ts(sk, skb);
3703
3704                                 /* We know that such packets are checksummed
3705                                  * on entry.
3706                                  */
3707                                 tcp_ack(sk, skb, 0);
3708                                 __kfree_skb(skb); 
3709                                 tcp_data_snd_check(sk, tp);
3710                                 return 0;
3711                         } else { /* Header too small */
3712                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
3713                                 goto discard;
3714                         }
3715                 } else {
3716                         int eaten = 0;
3717
3718                         if (tp->ucopy.task == current &&
3719                             tp->copied_seq == tp->rcv_nxt &&
3720                             len - tcp_header_len <= tp->ucopy.len &&
3721                             sock_owned_by_user(sk)) {
3722                                 __set_current_state(TASK_RUNNING);
3723
3724                                 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
3725                                         /* Predicted packet is in window by definition.
3726                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3727                                          * Hence, check seq<=rcv_wup reduces to:
3728                                          */
3729                                         if (tcp_header_len ==
3730                                             (sizeof(struct tcphdr) +
3731                                              TCPOLEN_TSTAMP_ALIGNED) &&
3732                                             tp->rcv_nxt == tp->rcv_wup)
3733                                                 tcp_store_ts_recent(tp);
3734
3735                                         tcp_rcv_rtt_measure_ts(sk, skb);
3736
3737                                         __skb_pull(skb, tcp_header_len);
3738                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3739                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
3740                                         eaten = 1;
3741                                 }
3742                         }
3743                         if (!eaten) {
3744                                 if (tcp_checksum_complete_user(sk, skb))
3745                                         goto csum_error;
3746
3747                                 /* Predicted packet is in window by definition.
3748                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
3749                                  * Hence, check seq<=rcv_wup reduces to:
3750                                  */
3751                                 if (tcp_header_len ==
3752                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
3753                                     tp->rcv_nxt == tp->rcv_wup)
3754                                         tcp_store_ts_recent(tp);
3755
3756                                 tcp_rcv_rtt_measure_ts(sk, skb);
3757
3758                                 if ((int)skb->truesize > sk->sk_forward_alloc)
3759                                         goto step5;
3760
3761                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
3762
3763                                 /* Bulk data transfer: receiver */
3764                                 __skb_pull(skb,tcp_header_len);
3765                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3766                                 sk_stream_set_owner_r(skb, sk);
3767                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3768                         }
3769
3770                         tcp_event_data_recv(sk, tp, skb);
3771
3772                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
3773                                 /* Well, only one small jumplet in fast path... */
3774                                 tcp_ack(sk, skb, FLAG_DATA);
3775                                 tcp_data_snd_check(sk, tp);
3776                                 if (!inet_csk_ack_scheduled(sk))
3777                                         goto no_ack;
3778                         }
3779
3780                         __tcp_ack_snd_check(sk, 0);
3781 no_ack:
3782                         if (eaten)
3783                                 __kfree_skb(skb);
3784                         else
3785                                 sk->sk_data_ready(sk, 0);
3786                         return 0;
3787                 }
3788         }
3789
3790 slow_path:
3791         if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
3792                 goto csum_error;
3793
3794         /*
3795          * RFC1323: H1. Apply PAWS check first.
3796          */
3797         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
3798             tcp_paws_discard(sk, skb)) {
3799                 if (!th->rst) {
3800                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
3801                         tcp_send_dupack(sk, skb);
3802                         goto discard;
3803                 }
3804                 /* Resets are accepted even if PAWS failed.
3805
3806                    ts_recent update must be made after we are sure
3807                    that the packet is in window.
3808                  */
3809         }
3810
3811         /*
3812          *      Standard slow path.
3813          */
3814
3815         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
3816                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
3817                  * (RST) segments are validated by checking their SEQ-fields."
3818                  * And page 69: "If an incoming segment is not acceptable,
3819                  * an acknowledgment should be sent in reply (unless the RST bit
3820                  * is set, if so drop the segment and return)".
3821                  */
3822                 if (!th->rst)
3823                         tcp_send_dupack(sk, skb);
3824                 goto discard;
3825         }
3826
3827         if(th->rst) {
3828                 tcp_reset(sk);
3829                 goto discard;
3830         }
3831
3832         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3833
3834         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3835                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
3836                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
3837                 tcp_reset(sk);
3838                 return 1;
3839         }
3840
3841 step5:
3842         if(th->ack)
3843                 tcp_ack(sk, skb, FLAG_SLOWPATH);
3844
3845         tcp_rcv_rtt_measure_ts(sk, skb);
3846
3847         /* Process urgent data. */
3848         tcp_urg(sk, skb, th);
3849
3850         /* step 7: process the segment text */
3851         tcp_data_queue(sk, skb);
3852
3853         tcp_data_snd_check(sk, tp);
3854         tcp_ack_snd_check(sk);
3855         return 0;
3856
3857 csum_error:
3858         TCP_INC_STATS_BH(TCP_MIB_INERRS);
3859
3860 discard:
3861         __kfree_skb(skb);
3862         return 0;
3863 }
3864
3865 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
3866                                          struct tcphdr *th, unsigned len)
3867 {
3868         struct tcp_sock *tp = tcp_sk(sk);
3869         int saved_clamp = tp->rx_opt.mss_clamp;
3870
3871         tcp_parse_options(skb, &tp->rx_opt, 0);
3872
3873         if (th->ack) {
3874                 struct inet_connection_sock *icsk;
3875                 /* rfc793:
3876                  * "If the state is SYN-SENT then
3877                  *    first check the ACK bit
3878                  *      If the ACK bit is set
3879                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
3880                  *        a reset (unless the RST bit is set, if so drop
3881                  *        the segment and return)"
3882                  *
3883                  *  We do not send data with SYN, so that RFC-correct
3884                  *  test reduces to:
3885                  */
3886                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
3887                         goto reset_and_undo;
3888
3889                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3890                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
3891                              tcp_time_stamp)) {
3892                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
3893                         goto reset_and_undo;
3894                 }
3895
3896                 /* Now ACK is acceptable.
3897                  *
3898                  * "If the RST bit is set
3899                  *    If the ACK was acceptable then signal the user "error:
3900                  *    connection reset", drop the segment, enter CLOSED state,
3901                  *    delete TCB, and return."
3902                  */
3903
3904                 if (th->rst) {
3905                         tcp_reset(sk);
3906                         goto discard;
3907                 }
3908
3909                 /* rfc793:
3910                  *   "fifth, if neither of the SYN or RST bits is set then
3911                  *    drop the segment and return."
3912                  *
3913                  *    See note below!
3914                  *                                        --ANK(990513)
3915                  */
3916                 if (!th->syn)
3917                         goto discard_and_undo;
3918
3919                 /* rfc793:
3920                  *   "If the SYN bit is on ...
3921                  *    are acceptable then ...
3922                  *    (our SYN has been ACKed), change the connection
3923                  *    state to ESTABLISHED..."
3924                  */
3925
3926                 TCP_ECN_rcv_synack(tp, th);
3927                 if (tp->ecn_flags&TCP_ECN_OK)
3928                         sock_set_flag(sk, SOCK_NO_LARGESEND);
3929
3930                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
3931                 tcp_ack(sk, skb, FLAG_SLOWPATH);
3932
3933                 /* Ok.. it's good. Set up sequence numbers and
3934                  * move to established.
3935                  */
3936                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
3937                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
3938
3939                 /* RFC1323: The window in SYN & SYN/ACK segments is
3940                  * never scaled.
3941                  */
3942                 tp->snd_wnd = ntohs(th->window);
3943                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
3944
3945                 if (!tp->rx_opt.wscale_ok) {
3946                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
3947                         tp->window_clamp = min(tp->window_clamp, 65535U);
3948                 }
3949
3950                 if (tp->rx_opt.saw_tstamp) {
3951                         tp->rx_opt.tstamp_ok       = 1;
3952                         tp->tcp_header_len =
3953                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
3954                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
3955                         tcp_store_ts_recent(tp);
3956                 } else {
3957                         tp->tcp_header_len = sizeof(struct tcphdr);
3958                 }
3959
3960                 if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
3961                         tp->rx_opt.sack_ok |= 2;
3962
3963                 tcp_sync_mss(sk, tp->pmtu_cookie);
3964                 tcp_initialize_rcv_mss(sk);
3965
3966                 /* Remember, tcp_poll() does not lock socket!
3967                  * Change state from SYN-SENT only after copied_seq
3968                  * is initialized. */
3969                 tp->copied_seq = tp->rcv_nxt;
3970                 mb();
3971                 tcp_set_state(sk, TCP_ESTABLISHED);
3972
3973                 /* Make sure socket is routed, for correct metrics.  */
3974                 tp->af_specific->rebuild_header(sk);
3975
3976                 tcp_init_metrics(sk);
3977
3978                 tcp_init_congestion_control(sk);
3979
3980                 /* Prevent spurious tcp_cwnd_restart() on first data
3981                  * packet.
3982                  */
3983                 tp->lsndtime = tcp_time_stamp;
3984
3985                 tcp_init_buffer_space(sk);
3986
3987                 if (sock_flag(sk, SOCK_KEEPOPEN))
3988                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
3989
3990                 if (!tp->rx_opt.snd_wscale)
3991                         __tcp_fast_path_on(tp, tp->snd_wnd);
3992                 else
3993                         tp->pred_flags = 0;
3994
3995                 if (!sock_flag(sk, SOCK_DEAD)) {
3996                         sk->sk_state_change(sk);
3997                         sk_wake_async(sk, 0, POLL_OUT);
3998                 }
3999
4000                 icsk = inet_csk(sk);
4001
4002                 if (sk->sk_write_pending ||
4003                     icsk->icsk_accept_queue.rskq_defer_accept ||
4004                     icsk->icsk_ack.pingpong) {
4005                         /* Save one ACK. Data will be ready after
4006                          * several ticks, if write_pending is set.
4007                          *
4008                          * It may be deleted, but with this feature tcpdumps
4009                          * look so _wonderfully_ clever, that I was not able
4010                          * to stand against the temptation 8)     --ANK
4011                          */
4012                         inet_csk_schedule_ack(sk);
4013                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4014                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4015                         tcp_incr_quickack(sk);
4016                         tcp_enter_quickack_mode(sk);
4017                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4018                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4019
4020 discard:
4021                         __kfree_skb(skb);
4022                         return 0;
4023                 } else {
4024                         tcp_send_ack(sk);
4025                 }
4026                 return -1;
4027         }
4028
4029         /* No ACK in the segment */
4030
4031         if (th->rst) {
4032                 /* rfc793:
4033                  * "If the RST bit is set
4034                  *
4035                  *      Otherwise (no ACK) drop the segment and return."
4036                  */
4037
4038                 goto discard_and_undo;
4039         }
4040
4041         /* PAWS check. */
4042         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4043                 goto discard_and_undo;
4044
4045         if (th->syn) {
4046                 /* We see SYN without ACK. It is attempt of
4047                  * simultaneous connect with crossed SYNs.
4048                  * Particularly, it can be connect to self.
4049                  */
4050                 tcp_set_state(sk, TCP_SYN_RECV);
4051
4052                 if (tp->rx_opt.saw_tstamp) {
4053                         tp->rx_opt.tstamp_ok = 1;
4054                         tcp_store_ts_recent(tp);
4055                         tp->tcp_header_len =
4056                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4057                 } else {
4058                         tp->tcp_header_len = sizeof(struct tcphdr);
4059                 }
4060
4061                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4062                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4063
4064                 /* RFC1323: The window in SYN & SYN/ACK segments is
4065                  * never scaled.
4066                  */
4067                 tp->snd_wnd    = ntohs(th->window);
4068                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4069                 tp->max_window = tp->snd_wnd;
4070
4071                 TCP_ECN_rcv_syn(tp, th);
4072                 if (tp->ecn_flags&TCP_ECN_OK)
4073                         sock_set_flag(sk, SOCK_NO_LARGESEND);
4074
4075                 tcp_sync_mss(sk, tp->pmtu_cookie);
4076                 tcp_initialize_rcv_mss(sk);
4077
4078
4079                 tcp_send_synack(sk);
4080 #if 0
4081                 /* Note, we could accept data and URG from this segment.
4082                  * There are no obstacles to make this.
4083                  *
4084                  * However, if we ignore data in ACKless segments sometimes,
4085                  * we have no reasons to accept it sometimes.
4086                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
4087                  * is not flawless. So, discard packet for sanity.
4088                  * Uncomment this return to process the data.
4089                  */
4090                 return -1;
4091 #else
4092                 goto discard;
4093 #endif
4094         }
4095         /* "fifth, if neither of the SYN or RST bits is set then
4096          * drop the segment and return."
4097          */
4098
4099 discard_and_undo:
4100         tcp_clear_options(&tp->rx_opt);
4101         tp->rx_opt.mss_clamp = saved_clamp;
4102         goto discard;
4103
4104 reset_and_undo:
4105         tcp_clear_options(&tp->rx_opt);
4106         tp->rx_opt.mss_clamp = saved_clamp;
4107         return 1;
4108 }
4109
4110
4111 /*
4112  *      This function implements the receiving procedure of RFC 793 for
4113  *      all states except ESTABLISHED and TIME_WAIT. 
4114  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4115  *      address independent.
4116  */
4117         
4118 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4119                           struct tcphdr *th, unsigned len)
4120 {
4121         struct tcp_sock *tp = tcp_sk(sk);
4122         int queued = 0;
4123
4124         tp->rx_opt.saw_tstamp = 0;
4125
4126         switch (sk->sk_state) {
4127         case TCP_CLOSE:
4128                 goto discard;
4129
4130         case TCP_LISTEN:
4131                 if(th->ack)
4132                         return 1;
4133
4134                 if(th->rst)
4135                         goto discard;
4136
4137                 if(th->syn) {
4138                         if(tp->af_specific->conn_request(sk, skb) < 0)
4139                                 return 1;
4140
4141                         /* Now we have several options: In theory there is 
4142                          * nothing else in the frame. KA9Q has an option to 
4143                          * send data with the syn, BSD accepts data with the
4144                          * syn up to the [to be] advertised window and 
4145                          * Solaris 2.1 gives you a protocol error. For now 
4146                          * we just ignore it, that fits the spec precisely 
4147                          * and avoids incompatibilities. It would be nice in
4148                          * future to drop through and process the data.
4149                          *
4150                          * Now that TTCP is starting to be used we ought to 
4151                          * queue this data.
4152                          * But, this leaves one open to an easy denial of
4153                          * service attack, and SYN cookies can't defend
4154                          * against this problem. So, we drop the data
4155                          * in the interest of security over speed.
4156                          */
4157                         goto discard;
4158                 }
4159                 goto discard;
4160
4161         case TCP_SYN_SENT:
4162                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4163                 if (queued >= 0)
4164                         return queued;
4165
4166                 /* Do step6 onward by hand. */
4167                 tcp_urg(sk, skb, th);
4168                 __kfree_skb(skb);
4169                 tcp_data_snd_check(sk, tp);
4170                 return 0;
4171         }
4172
4173         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4174             tcp_paws_discard(sk, skb)) {
4175                 if (!th->rst) {
4176                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4177                         tcp_send_dupack(sk, skb);
4178                         goto discard;
4179                 }
4180                 /* Reset is accepted even if it did not pass PAWS. */
4181         }
4182
4183         /* step 1: check sequence number */
4184         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4185                 if (!th->rst)
4186                         tcp_send_dupack(sk, skb);
4187                 goto discard;
4188         }
4189
4190         /* step 2: check RST bit */
4191         if(th->rst) {
4192                 tcp_reset(sk);
4193                 goto discard;
4194         }
4195
4196         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4197
4198         /* step 3: check security and precedence [ignored] */
4199
4200         /*      step 4:
4201          *
4202          *      Check for a SYN in window.
4203          */
4204         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4205                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4206                 tcp_reset(sk);
4207                 return 1;
4208         }
4209
4210         /* step 5: check the ACK field */
4211         if (th->ack) {
4212                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
4213
4214                 switch(sk->sk_state) {
4215                 case TCP_SYN_RECV:
4216                         if (acceptable) {
4217                                 tp->copied_seq = tp->rcv_nxt;
4218                                 mb();
4219                                 tcp_set_state(sk, TCP_ESTABLISHED);
4220                                 sk->sk_state_change(sk);
4221
4222                                 /* Note, that this wakeup is only for marginal
4223                                  * crossed SYN case. Passively open sockets
4224                                  * are not waked up, because sk->sk_sleep ==
4225                                  * NULL and sk->sk_socket == NULL.
4226                                  */
4227                                 if (sk->sk_socket) {
4228                                         sk_wake_async(sk,0,POLL_OUT);
4229                                 }
4230
4231                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
4232                                 tp->snd_wnd = ntohs(th->window) <<
4233                                               tp->rx_opt.snd_wscale;
4234                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
4235                                             TCP_SKB_CB(skb)->seq);
4236
4237                                 /* tcp_ack considers this ACK as duplicate
4238                                  * and does not calculate rtt.
4239                                  * Fix it at least with timestamps.
4240                                  */
4241                                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4242                                     !tp->srtt)
4243                                         tcp_ack_saw_tstamp(sk, 0);
4244
4245                                 if (tp->rx_opt.tstamp_ok)
4246                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
4247
4248                                 /* Make sure socket is routed, for
4249                                  * correct metrics.
4250                                  */
4251                                 tp->af_specific->rebuild_header(sk);
4252
4253                                 tcp_init_metrics(sk);
4254
4255                                 tcp_init_congestion_control(sk);
4256
4257                                 /* Prevent spurious tcp_cwnd_restart() on
4258                                  * first data packet.
4259                                  */
4260                                 tp->lsndtime = tcp_time_stamp;
4261
4262                                 tcp_initialize_rcv_mss(sk);
4263                                 tcp_init_buffer_space(sk);
4264                                 tcp_fast_path_on(tp);
4265                         } else {
4266                                 return 1;
4267                         }
4268                         break;
4269
4270                 case TCP_FIN_WAIT1:
4271                         if (tp->snd_una == tp->write_seq) {
4272                                 tcp_set_state(sk, TCP_FIN_WAIT2);
4273                                 sk->sk_shutdown |= SEND_SHUTDOWN;
4274                                 dst_confirm(sk->sk_dst_cache);
4275
4276                                 if (!sock_flag(sk, SOCK_DEAD))
4277                                         /* Wake up lingering close() */
4278                                         sk->sk_state_change(sk);
4279                                 else {
4280                                         int tmo;
4281
4282                                         if (tp->linger2 < 0 ||
4283                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4284                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
4285                                                 tcp_done(sk);
4286                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4287                                                 return 1;
4288                                         }
4289
4290                                         tmo = tcp_fin_time(sk);
4291                                         if (tmo > TCP_TIMEWAIT_LEN) {
4292                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
4293                                         } else if (th->fin || sock_owned_by_user(sk)) {
4294                                                 /* Bad case. We could lose such FIN otherwise.
4295                                                  * It is not a big problem, but it looks confusing
4296                                                  * and not so rare event. We still can lose it now,
4297                                                  * if it spins in bh_lock_sock(), but it is really
4298                                                  * marginal case.
4299                                                  */
4300                                                 inet_csk_reset_keepalive_timer(sk, tmo);
4301                                         } else {
4302                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
4303                                                 goto discard;
4304                                         }
4305                                 }
4306                         }
4307                         break;
4308
4309                 case TCP_CLOSING:
4310                         if (tp->snd_una == tp->write_seq) {
4311                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4312                                 goto discard;
4313                         }
4314                         break;
4315
4316                 case TCP_LAST_ACK:
4317                         if (tp->snd_una == tp->write_seq) {
4318                                 tcp_update_metrics(sk);
4319                                 tcp_done(sk);
4320                                 goto discard;
4321                         }
4322                         break;
4323                 }
4324         } else
4325                 goto discard;
4326
4327         /* step 6: check the URG bit */
4328         tcp_urg(sk, skb, th);
4329
4330         /* step 7: process the segment text */
4331         switch (sk->sk_state) {
4332         case TCP_CLOSE_WAIT:
4333         case TCP_CLOSING:
4334         case TCP_LAST_ACK:
4335                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4336                         break;
4337         case TCP_FIN_WAIT1:
4338         case TCP_FIN_WAIT2:
4339                 /* RFC 793 says to queue data in these states,
4340                  * RFC 1122 says we MUST send a reset. 
4341                  * BSD 4.4 also does reset.
4342                  */
4343                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
4344                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4345                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
4346                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4347                                 tcp_reset(sk);
4348                                 return 1;
4349                         }
4350                 }
4351                 /* Fall through */
4352         case TCP_ESTABLISHED: 
4353                 tcp_data_queue(sk, skb);
4354                 queued = 1;
4355                 break;
4356         }
4357
4358         /* tcp_data could move socket to TIME-WAIT */
4359         if (sk->sk_state != TCP_CLOSE) {
4360                 tcp_data_snd_check(sk, tp);
4361                 tcp_ack_snd_check(sk);
4362         }
4363
4364         if (!queued) { 
4365 discard:
4366                 __kfree_skb(skb);
4367         }
4368         return 0;
4369 }
4370
4371 EXPORT_SYMBOL(sysctl_tcp_ecn);
4372 EXPORT_SYMBOL(sysctl_tcp_reordering);
4373 EXPORT_SYMBOL(tcp_parse_options);
4374 EXPORT_SYMBOL(tcp_rcv_established);
4375 EXPORT_SYMBOL(tcp_rcv_state_process);