[TCP]: Limit processing lost_retrans loop to work-to-do cases
[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 presence of
46  *                                      timestamps.
47  *              Andrey Savochkin:       Check sequence numbers correctly when
48  *                                      removing SACKs due to in sequence incoming
49  *                                      data segments.
50  *              Andi Kleen:             Make sure we never ack data there is not
51  *                                      enough room for. Also make this condition
52  *                                      a fatal error if it might still happen.
53  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
54  *                                      connections with MSS<min(MTU,ann. MSS)
55  *                                      work without delayed acks.
56  *              Andi Kleen:             Process packets with PSH set in the
57  *                                      fast path.
58  *              J Hadi Salim:           ECN support
59  *              Andrei Gurtov,
60  *              Pasi Sarolahti,
61  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
62  *                                      engine. Lots of bugs are found.
63  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
64  */
65
66 #include <linux/mm.h>
67 #include <linux/module.h>
68 #include <linux/sysctl.h>
69 #include <net/tcp.h>
70 #include <net/inet_common.h>
71 #include <linux/ipsec.h>
72 #include <asm/unaligned.h>
73 #include <net/netdma.h>
74
75 int sysctl_tcp_timestamps __read_mostly = 1;
76 int sysctl_tcp_window_scaling __read_mostly = 1;
77 int sysctl_tcp_sack __read_mostly = 1;
78 int sysctl_tcp_fack __read_mostly = 1;
79 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn __read_mostly;
81 int sysctl_tcp_dsack __read_mostly = 1;
82 int sysctl_tcp_app_win __read_mostly = 31;
83 int sysctl_tcp_adv_win_scale __read_mostly = 2;
84
85 int sysctl_tcp_stdurg __read_mostly;
86 int sysctl_tcp_rfc1337 __read_mostly;
87 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
88 int sysctl_tcp_frto __read_mostly = 2;
89 int sysctl_tcp_frto_response __read_mostly;
90 int sysctl_tcp_nometrics_save __read_mostly;
91
92 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
93 int sysctl_tcp_abc __read_mostly;
94
95 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
96 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
97 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
98 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
99 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
100 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
101 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
102 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
103 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
104 #define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
105 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
106 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained DSACK info */
107 #define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
108
109 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
110 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
111 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
112 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
113 #define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
114
115 #define IsSackFrto() (sysctl_tcp_frto == 0x2)
116
117 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
118 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
119
120 /* Adapt the MSS value used to make delayed ack decision to the
121  * real world.
122  */
123 static void tcp_measure_rcv_mss(struct sock *sk,
124                                 const struct sk_buff *skb)
125 {
126         struct inet_connection_sock *icsk = inet_csk(sk);
127         const unsigned int lss = icsk->icsk_ack.last_seg_size;
128         unsigned int len;
129
130         icsk->icsk_ack.last_seg_size = 0;
131
132         /* skb->len may jitter because of SACKs, even if peer
133          * sends good full-sized frames.
134          */
135         len = skb_shinfo(skb)->gso_size ?: skb->len;
136         if (len >= icsk->icsk_ack.rcv_mss) {
137                 icsk->icsk_ack.rcv_mss = len;
138         } else {
139                 /* Otherwise, we make more careful check taking into account,
140                  * that SACKs block is variable.
141                  *
142                  * "len" is invariant segment length, including TCP header.
143                  */
144                 len += skb->data - skb_transport_header(skb);
145                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
146                     /* If PSH is not set, packet should be
147                      * full sized, provided peer TCP is not badly broken.
148                      * This observation (if it is correct 8)) allows
149                      * to handle super-low mtu links fairly.
150                      */
151                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
152                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
153                         /* Subtract also invariant (if peer is RFC compliant),
154                          * tcp header plus fixed timestamp option length.
155                          * Resulting "len" is MSS free of SACK jitter.
156                          */
157                         len -= tcp_sk(sk)->tcp_header_len;
158                         icsk->icsk_ack.last_seg_size = len;
159                         if (len == lss) {
160                                 icsk->icsk_ack.rcv_mss = len;
161                                 return;
162                         }
163                 }
164                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
165                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
166                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
167         }
168 }
169
170 static void tcp_incr_quickack(struct sock *sk)
171 {
172         struct inet_connection_sock *icsk = inet_csk(sk);
173         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
174
175         if (quickacks==0)
176                 quickacks=2;
177         if (quickacks > icsk->icsk_ack.quick)
178                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
179 }
180
181 void tcp_enter_quickack_mode(struct sock *sk)
182 {
183         struct inet_connection_sock *icsk = inet_csk(sk);
184         tcp_incr_quickack(sk);
185         icsk->icsk_ack.pingpong = 0;
186         icsk->icsk_ack.ato = TCP_ATO_MIN;
187 }
188
189 /* Send ACKs quickly, if "quick" count is not exhausted
190  * and the session is not interactive.
191  */
192
193 static inline int tcp_in_quickack_mode(const struct sock *sk)
194 {
195         const struct inet_connection_sock *icsk = inet_csk(sk);
196         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
197 }
198
199 static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
200 {
201         if (tp->ecn_flags&TCP_ECN_OK)
202                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
203 }
204
205 static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
206 {
207         if (tcp_hdr(skb)->cwr)
208                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
209 }
210
211 static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
212 {
213         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
214 }
215
216 static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb)
217 {
218         if (tp->ecn_flags&TCP_ECN_OK) {
219                 if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags))
220                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
221                 /* Funny extension: if ECT is not set on a segment,
222                  * it is surely retransmit. It is not in ECN RFC,
223                  * but Linux follows this rule. */
224                 else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags)))
225                         tcp_enter_quickack_mode((struct sock *)tp);
226         }
227 }
228
229 static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
230 {
231         if ((tp->ecn_flags&TCP_ECN_OK) && (!th->ece || th->cwr))
232                 tp->ecn_flags &= ~TCP_ECN_OK;
233 }
234
235 static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th)
236 {
237         if ((tp->ecn_flags&TCP_ECN_OK) && (!th->ece || !th->cwr))
238                 tp->ecn_flags &= ~TCP_ECN_OK;
239 }
240
241 static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
242 {
243         if (th->ece && !th->syn && (tp->ecn_flags&TCP_ECN_OK))
244                 return 1;
245         return 0;
246 }
247
248 /* Buffer size and advertised window tuning.
249  *
250  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
251  */
252
253 static void tcp_fixup_sndbuf(struct sock *sk)
254 {
255         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
256                      sizeof(struct sk_buff);
257
258         if (sk->sk_sndbuf < 3 * sndmem)
259                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
260 }
261
262 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
263  *
264  * All tcp_full_space() is split to two parts: "network" buffer, allocated
265  * forward and advertised in receiver window (tp->rcv_wnd) and
266  * "application buffer", required to isolate scheduling/application
267  * latencies from network.
268  * window_clamp is maximal advertised window. It can be less than
269  * tcp_full_space(), in this case tcp_full_space() - window_clamp
270  * is reserved for "application" buffer. The less window_clamp is
271  * the smoother our behaviour from viewpoint of network, but the lower
272  * throughput and the higher sensitivity of the connection to losses. 8)
273  *
274  * rcv_ssthresh is more strict window_clamp used at "slow start"
275  * phase to predict further behaviour of this connection.
276  * It is used for two goals:
277  * - to enforce header prediction at sender, even when application
278  *   requires some significant "application buffer". It is check #1.
279  * - to prevent pruning of receive queue because of misprediction
280  *   of receiver window. Check #2.
281  *
282  * The scheme does not work when sender sends good segments opening
283  * window and then starts to feed us spaghetti. But it should work
284  * in common situations. Otherwise, we have to rely on queue collapsing.
285  */
286
287 /* Slow part of check#2. */
288 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
289 {
290         struct tcp_sock *tp = tcp_sk(sk);
291         /* Optimize this! */
292         int truesize = tcp_win_from_space(skb->truesize)/2;
293         int window = tcp_win_from_space(sysctl_tcp_rmem[2])/2;
294
295         while (tp->rcv_ssthresh <= window) {
296                 if (truesize <= skb->len)
297                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
298
299                 truesize >>= 1;
300                 window >>= 1;
301         }
302         return 0;
303 }
304
305 static void tcp_grow_window(struct sock *sk,
306                             struct sk_buff *skb)
307 {
308         struct tcp_sock *tp = tcp_sk(sk);
309
310         /* Check #1 */
311         if (tp->rcv_ssthresh < tp->window_clamp &&
312             (int)tp->rcv_ssthresh < tcp_space(sk) &&
313             !tcp_memory_pressure) {
314                 int incr;
315
316                 /* Check #2. Increase window, if skb with such overhead
317                  * will fit to rcvbuf in future.
318                  */
319                 if (tcp_win_from_space(skb->truesize) <= skb->len)
320                         incr = 2*tp->advmss;
321                 else
322                         incr = __tcp_grow_window(sk, skb);
323
324                 if (incr) {
325                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
326                         inet_csk(sk)->icsk_ack.quick |= 1;
327                 }
328         }
329 }
330
331 /* 3. Tuning rcvbuf, when connection enters established state. */
332
333 static void tcp_fixup_rcvbuf(struct sock *sk)
334 {
335         struct tcp_sock *tp = tcp_sk(sk);
336         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
337
338         /* Try to select rcvbuf so that 4 mss-sized segments
339          * will fit to window and corresponding skbs will fit to our rcvbuf.
340          * (was 3; 4 is minimum to allow fast retransmit to work.)
341          */
342         while (tcp_win_from_space(rcvmem) < tp->advmss)
343                 rcvmem += 128;
344         if (sk->sk_rcvbuf < 4 * rcvmem)
345                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
346 }
347
348 /* 4. Try to fixup all. It is made immediately after connection enters
349  *    established state.
350  */
351 static void tcp_init_buffer_space(struct sock *sk)
352 {
353         struct tcp_sock *tp = tcp_sk(sk);
354         int maxwin;
355
356         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
357                 tcp_fixup_rcvbuf(sk);
358         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
359                 tcp_fixup_sndbuf(sk);
360
361         tp->rcvq_space.space = tp->rcv_wnd;
362
363         maxwin = tcp_full_space(sk);
364
365         if (tp->window_clamp >= maxwin) {
366                 tp->window_clamp = maxwin;
367
368                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
369                         tp->window_clamp = max(maxwin -
370                                                (maxwin >> sysctl_tcp_app_win),
371                                                4 * tp->advmss);
372         }
373
374         /* Force reservation of one segment. */
375         if (sysctl_tcp_app_win &&
376             tp->window_clamp > 2 * tp->advmss &&
377             tp->window_clamp + tp->advmss > maxwin)
378                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
379
380         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
381         tp->snd_cwnd_stamp = tcp_time_stamp;
382 }
383
384 /* 5. Recalculate window clamp after socket hit its memory bounds. */
385 static void tcp_clamp_window(struct sock *sk)
386 {
387         struct tcp_sock *tp = tcp_sk(sk);
388         struct inet_connection_sock *icsk = inet_csk(sk);
389
390         icsk->icsk_ack.quick = 0;
391
392         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
393             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
394             !tcp_memory_pressure &&
395             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
396                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
397                                     sysctl_tcp_rmem[2]);
398         }
399         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
400                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
401 }
402
403
404 /* Initialize RCV_MSS value.
405  * RCV_MSS is an our guess about MSS used by the peer.
406  * We haven't any direct information about the MSS.
407  * It's better to underestimate the RCV_MSS rather than overestimate.
408  * Overestimations make us ACKing less frequently than needed.
409  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
410  */
411 void tcp_initialize_rcv_mss(struct sock *sk)
412 {
413         struct tcp_sock *tp = tcp_sk(sk);
414         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
415
416         hint = min(hint, tp->rcv_wnd/2);
417         hint = min(hint, TCP_MIN_RCVMSS);
418         hint = max(hint, TCP_MIN_MSS);
419
420         inet_csk(sk)->icsk_ack.rcv_mss = hint;
421 }
422
423 /* Receiver "autotuning" code.
424  *
425  * The algorithm for RTT estimation w/o timestamps is based on
426  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
427  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
428  *
429  * More detail on this code can be found at
430  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
431  * though this reference is out of date.  A new paper
432  * is pending.
433  */
434 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
435 {
436         u32 new_sample = tp->rcv_rtt_est.rtt;
437         long m = sample;
438
439         if (m == 0)
440                 m = 1;
441
442         if (new_sample != 0) {
443                 /* If we sample in larger samples in the non-timestamp
444                  * case, we could grossly overestimate the RTT especially
445                  * with chatty applications or bulk transfer apps which
446                  * are stalled on filesystem I/O.
447                  *
448                  * Also, since we are only going for a minimum in the
449                  * non-timestamp case, we do not smooth things out
450                  * else with timestamps disabled convergence takes too
451                  * long.
452                  */
453                 if (!win_dep) {
454                         m -= (new_sample >> 3);
455                         new_sample += m;
456                 } else if (m < new_sample)
457                         new_sample = m << 3;
458         } else {
459                 /* No previous measure. */
460                 new_sample = m << 3;
461         }
462
463         if (tp->rcv_rtt_est.rtt != new_sample)
464                 tp->rcv_rtt_est.rtt = new_sample;
465 }
466
467 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
468 {
469         if (tp->rcv_rtt_est.time == 0)
470                 goto new_measure;
471         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
472                 return;
473         tcp_rcv_rtt_update(tp,
474                            jiffies - tp->rcv_rtt_est.time,
475                            1);
476
477 new_measure:
478         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
479         tp->rcv_rtt_est.time = tcp_time_stamp;
480 }
481
482 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
483 {
484         struct tcp_sock *tp = tcp_sk(sk);
485         if (tp->rx_opt.rcv_tsecr &&
486             (TCP_SKB_CB(skb)->end_seq -
487              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
488                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
489 }
490
491 /*
492  * This function should be called every time data is copied to user space.
493  * It calculates the appropriate TCP receive buffer space.
494  */
495 void tcp_rcv_space_adjust(struct sock *sk)
496 {
497         struct tcp_sock *tp = tcp_sk(sk);
498         int time;
499         int space;
500
501         if (tp->rcvq_space.time == 0)
502                 goto new_measure;
503
504         time = tcp_time_stamp - tp->rcvq_space.time;
505         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
506             tp->rcv_rtt_est.rtt == 0)
507                 return;
508
509         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
510
511         space = max(tp->rcvq_space.space, space);
512
513         if (tp->rcvq_space.space != space) {
514                 int rcvmem;
515
516                 tp->rcvq_space.space = space;
517
518                 if (sysctl_tcp_moderate_rcvbuf &&
519                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
520                         int new_clamp = space;
521
522                         /* Receive space grows, normalize in order to
523                          * take into account packet headers and sk_buff
524                          * structure overhead.
525                          */
526                         space /= tp->advmss;
527                         if (!space)
528                                 space = 1;
529                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
530                                   16 + sizeof(struct sk_buff));
531                         while (tcp_win_from_space(rcvmem) < tp->advmss)
532                                 rcvmem += 128;
533                         space *= rcvmem;
534                         space = min(space, sysctl_tcp_rmem[2]);
535                         if (space > sk->sk_rcvbuf) {
536                                 sk->sk_rcvbuf = space;
537
538                                 /* Make the window clamp follow along.  */
539                                 tp->window_clamp = new_clamp;
540                         }
541                 }
542         }
543
544 new_measure:
545         tp->rcvq_space.seq = tp->copied_seq;
546         tp->rcvq_space.time = tcp_time_stamp;
547 }
548
549 /* There is something which you must keep in mind when you analyze the
550  * behavior of the tp->ato delayed ack timeout interval.  When a
551  * connection starts up, we want to ack as quickly as possible.  The
552  * problem is that "good" TCP's do slow start at the beginning of data
553  * transmission.  The means that until we send the first few ACK's the
554  * sender will sit on his end and only queue most of his data, because
555  * he can only send snd_cwnd unacked packets at any given time.  For
556  * each ACK we send, he increments snd_cwnd and transmits more of his
557  * queue.  -DaveM
558  */
559 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
560 {
561         struct tcp_sock *tp = tcp_sk(sk);
562         struct inet_connection_sock *icsk = inet_csk(sk);
563         u32 now;
564
565         inet_csk_schedule_ack(sk);
566
567         tcp_measure_rcv_mss(sk, skb);
568
569         tcp_rcv_rtt_measure(tp);
570
571         now = tcp_time_stamp;
572
573         if (!icsk->icsk_ack.ato) {
574                 /* The _first_ data packet received, initialize
575                  * delayed ACK engine.
576                  */
577                 tcp_incr_quickack(sk);
578                 icsk->icsk_ack.ato = TCP_ATO_MIN;
579         } else {
580                 int m = now - icsk->icsk_ack.lrcvtime;
581
582                 if (m <= TCP_ATO_MIN/2) {
583                         /* The fastest case is the first. */
584                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
585                 } else if (m < icsk->icsk_ack.ato) {
586                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
587                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
588                                 icsk->icsk_ack.ato = icsk->icsk_rto;
589                 } else if (m > icsk->icsk_rto) {
590                         /* Too long gap. Apparently sender failed to
591                          * restart window, so that we send ACKs quickly.
592                          */
593                         tcp_incr_quickack(sk);
594                         sk_stream_mem_reclaim(sk);
595                 }
596         }
597         icsk->icsk_ack.lrcvtime = now;
598
599         TCP_ECN_check_ce(tp, skb);
600
601         if (skb->len >= 128)
602                 tcp_grow_window(sk, skb);
603 }
604
605 static u32 tcp_rto_min(struct sock *sk)
606 {
607         struct dst_entry *dst = __sk_dst_get(sk);
608         u32 rto_min = TCP_RTO_MIN;
609
610         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
611                 rto_min = dst->metrics[RTAX_RTO_MIN-1];
612         return rto_min;
613 }
614
615 /* Called to compute a smoothed rtt estimate. The data fed to this
616  * routine either comes from timestamps, or from segments that were
617  * known _not_ to have been retransmitted [see Karn/Partridge
618  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
619  * piece by Van Jacobson.
620  * NOTE: the next three routines used to be one big routine.
621  * To save cycles in the RFC 1323 implementation it was better to break
622  * it up into three procedures. -- erics
623  */
624 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
625 {
626         struct tcp_sock *tp = tcp_sk(sk);
627         long m = mrtt; /* RTT */
628
629         /*      The following amusing code comes from Jacobson's
630          *      article in SIGCOMM '88.  Note that rtt and mdev
631          *      are scaled versions of rtt and mean deviation.
632          *      This is designed to be as fast as possible
633          *      m stands for "measurement".
634          *
635          *      On a 1990 paper the rto value is changed to:
636          *      RTO = rtt + 4 * mdev
637          *
638          * Funny. This algorithm seems to be very broken.
639          * These formulae increase RTO, when it should be decreased, increase
640          * too slowly, when it should be increased quickly, decrease too quickly
641          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
642          * does not matter how to _calculate_ it. Seems, it was trap
643          * that VJ failed to avoid. 8)
644          */
645         if (m == 0)
646                 m = 1;
647         if (tp->srtt != 0) {
648                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
649                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
650                 if (m < 0) {
651                         m = -m;         /* m is now abs(error) */
652                         m -= (tp->mdev >> 2);   /* similar update on mdev */
653                         /* This is similar to one of Eifel findings.
654                          * Eifel blocks mdev updates when rtt decreases.
655                          * This solution is a bit different: we use finer gain
656                          * for mdev in this case (alpha*beta).
657                          * Like Eifel it also prevents growth of rto,
658                          * but also it limits too fast rto decreases,
659                          * happening in pure Eifel.
660                          */
661                         if (m > 0)
662                                 m >>= 3;
663                 } else {
664                         m -= (tp->mdev >> 2);   /* similar update on mdev */
665                 }
666                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
667                 if (tp->mdev > tp->mdev_max) {
668                         tp->mdev_max = tp->mdev;
669                         if (tp->mdev_max > tp->rttvar)
670                                 tp->rttvar = tp->mdev_max;
671                 }
672                 if (after(tp->snd_una, tp->rtt_seq)) {
673                         if (tp->mdev_max < tp->rttvar)
674                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
675                         tp->rtt_seq = tp->snd_nxt;
676                         tp->mdev_max = tcp_rto_min(sk);
677                 }
678         } else {
679                 /* no previous measure. */
680                 tp->srtt = m<<3;        /* take the measured time to be rtt */
681                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
682                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
683                 tp->rtt_seq = tp->snd_nxt;
684         }
685 }
686
687 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
688  * routine referred to above.
689  */
690 static inline void tcp_set_rto(struct sock *sk)
691 {
692         const struct tcp_sock *tp = tcp_sk(sk);
693         /* Old crap is replaced with new one. 8)
694          *
695          * More seriously:
696          * 1. If rtt variance happened to be less 50msec, it is hallucination.
697          *    It cannot be less due to utterly erratic ACK generation made
698          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
699          *    to do with delayed acks, because at cwnd>2 true delack timeout
700          *    is invisible. Actually, Linux-2.4 also generates erratic
701          *    ACKs in some circumstances.
702          */
703         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
704
705         /* 2. Fixups made earlier cannot be right.
706          *    If we do not estimate RTO correctly without them,
707          *    all the algo is pure shit and should be replaced
708          *    with correct one. It is exactly, which we pretend to do.
709          */
710 }
711
712 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
713  * guarantees that rto is higher.
714  */
715 static inline void tcp_bound_rto(struct sock *sk)
716 {
717         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
718                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
719 }
720
721 /* Save metrics learned by this TCP session.
722    This function is called only, when TCP finishes successfully
723    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
724  */
725 void tcp_update_metrics(struct sock *sk)
726 {
727         struct tcp_sock *tp = tcp_sk(sk);
728         struct dst_entry *dst = __sk_dst_get(sk);
729
730         if (sysctl_tcp_nometrics_save)
731                 return;
732
733         dst_confirm(dst);
734
735         if (dst && (dst->flags&DST_HOST)) {
736                 const struct inet_connection_sock *icsk = inet_csk(sk);
737                 int m;
738
739                 if (icsk->icsk_backoff || !tp->srtt) {
740                         /* This session failed to estimate rtt. Why?
741                          * Probably, no packets returned in time.
742                          * Reset our results.
743                          */
744                         if (!(dst_metric_locked(dst, RTAX_RTT)))
745                                 dst->metrics[RTAX_RTT-1] = 0;
746                         return;
747                 }
748
749                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
750
751                 /* If newly calculated rtt larger than stored one,
752                  * store new one. Otherwise, use EWMA. Remember,
753                  * rtt overestimation is always better than underestimation.
754                  */
755                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
756                         if (m <= 0)
757                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
758                         else
759                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
760                 }
761
762                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
763                         if (m < 0)
764                                 m = -m;
765
766                         /* Scale deviation to rttvar fixed point */
767                         m >>= 1;
768                         if (m < tp->mdev)
769                                 m = tp->mdev;
770
771                         if (m >= dst_metric(dst, RTAX_RTTVAR))
772                                 dst->metrics[RTAX_RTTVAR-1] = m;
773                         else
774                                 dst->metrics[RTAX_RTTVAR-1] -=
775                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
776                 }
777
778                 if (tp->snd_ssthresh >= 0xFFFF) {
779                         /* Slow start still did not finish. */
780                         if (dst_metric(dst, RTAX_SSTHRESH) &&
781                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
782                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
783                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
784                         if (!dst_metric_locked(dst, RTAX_CWND) &&
785                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
786                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
787                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
788                            icsk->icsk_ca_state == TCP_CA_Open) {
789                         /* Cong. avoidance phase, cwnd is reliable. */
790                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
791                                 dst->metrics[RTAX_SSTHRESH-1] =
792                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
793                         if (!dst_metric_locked(dst, RTAX_CWND))
794                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
795                 } else {
796                         /* Else slow start did not finish, cwnd is non-sense,
797                            ssthresh may be also invalid.
798                          */
799                         if (!dst_metric_locked(dst, RTAX_CWND))
800                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
801                         if (dst->metrics[RTAX_SSTHRESH-1] &&
802                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
803                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
804                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
805                 }
806
807                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
808                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
809                             tp->reordering != sysctl_tcp_reordering)
810                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
811                 }
812         }
813 }
814
815 /* Numbers are taken from RFC3390.
816  *
817  * John Heffner states:
818  *
819  *      The RFC specifies a window of no more than 4380 bytes
820  *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
821  *      is a bit misleading because they use a clamp at 4380 bytes
822  *      rather than use a multiplier in the relevant range.
823  */
824 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
825 {
826         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
827
828         if (!cwnd) {
829                 if (tp->mss_cache > 1460)
830                         cwnd = 2;
831                 else
832                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
833         }
834         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
835 }
836
837 /* Set slow start threshold and cwnd not falling to slow start */
838 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
839 {
840         struct tcp_sock *tp = tcp_sk(sk);
841         const struct inet_connection_sock *icsk = inet_csk(sk);
842
843         tp->prior_ssthresh = 0;
844         tp->bytes_acked = 0;
845         if (icsk->icsk_ca_state < TCP_CA_CWR) {
846                 tp->undo_marker = 0;
847                 if (set_ssthresh)
848                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
849                 tp->snd_cwnd = min(tp->snd_cwnd,
850                                    tcp_packets_in_flight(tp) + 1U);
851                 tp->snd_cwnd_cnt = 0;
852                 tp->high_seq = tp->snd_nxt;
853                 tp->snd_cwnd_stamp = tcp_time_stamp;
854                 TCP_ECN_queue_cwr(tp);
855
856                 tcp_set_ca_state(sk, TCP_CA_CWR);
857         }
858 }
859
860 /*
861  * Packet counting of FACK is based on in-order assumptions, therefore TCP
862  * disables it when reordering is detected
863  */
864 static void tcp_disable_fack(struct tcp_sock *tp)
865 {
866         tp->rx_opt.sack_ok &= ~2;
867 }
868
869 /* Take a notice that peer is sending DSACKs */
870 static void tcp_dsack_seen(struct tcp_sock *tp)
871 {
872         tp->rx_opt.sack_ok |= 4;
873 }
874
875 /* Initialize metrics on socket. */
876
877 static void tcp_init_metrics(struct sock *sk)
878 {
879         struct tcp_sock *tp = tcp_sk(sk);
880         struct dst_entry *dst = __sk_dst_get(sk);
881
882         if (dst == NULL)
883                 goto reset;
884
885         dst_confirm(dst);
886
887         if (dst_metric_locked(dst, RTAX_CWND))
888                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
889         if (dst_metric(dst, RTAX_SSTHRESH)) {
890                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
891                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
892                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
893         }
894         if (dst_metric(dst, RTAX_REORDERING) &&
895             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
896                 tcp_disable_fack(tp);
897                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
898         }
899
900         if (dst_metric(dst, RTAX_RTT) == 0)
901                 goto reset;
902
903         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
904                 goto reset;
905
906         /* Initial rtt is determined from SYN,SYN-ACK.
907          * The segment is small and rtt may appear much
908          * less than real one. Use per-dst memory
909          * to make it more realistic.
910          *
911          * A bit of theory. RTT is time passed after "normal" sized packet
912          * is sent until it is ACKed. In normal circumstances sending small
913          * packets force peer to delay ACKs and calculation is correct too.
914          * The algorithm is adaptive and, provided we follow specs, it
915          * NEVER underestimate RTT. BUT! If peer tries to make some clever
916          * tricks sort of "quick acks" for time long enough to decrease RTT
917          * to low value, and then abruptly stops to do it and starts to delay
918          * ACKs, wait for troubles.
919          */
920         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
921                 tp->srtt = dst_metric(dst, RTAX_RTT);
922                 tp->rtt_seq = tp->snd_nxt;
923         }
924         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
925                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
926                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
927         }
928         tcp_set_rto(sk);
929         tcp_bound_rto(sk);
930         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
931                 goto reset;
932         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
933         tp->snd_cwnd_stamp = tcp_time_stamp;
934         return;
935
936 reset:
937         /* Play conservative. If timestamps are not
938          * supported, TCP will fail to recalculate correct
939          * rtt, if initial rto is too small. FORGET ALL AND RESET!
940          */
941         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
942                 tp->srtt = 0;
943                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
944                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
945         }
946 }
947
948 static void tcp_update_reordering(struct sock *sk, const int metric,
949                                   const int ts)
950 {
951         struct tcp_sock *tp = tcp_sk(sk);
952         if (metric > tp->reordering) {
953                 tp->reordering = min(TCP_MAX_REORDERING, metric);
954
955                 /* This exciting event is worth to be remembered. 8) */
956                 if (ts)
957                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
958                 else if (tcp_is_reno(tp))
959                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
960                 else if (tcp_is_fack(tp))
961                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
962                 else
963                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
964 #if FASTRETRANS_DEBUG > 1
965                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
966                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
967                        tp->reordering,
968                        tp->fackets_out,
969                        tp->sacked_out,
970                        tp->undo_marker ? tp->undo_retrans : 0);
971 #endif
972                 tcp_disable_fack(tp);
973         }
974 }
975
976 /* This procedure tags the retransmission queue when SACKs arrive.
977  *
978  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
979  * Packets in queue with these bits set are counted in variables
980  * sacked_out, retrans_out and lost_out, correspondingly.
981  *
982  * Valid combinations are:
983  * Tag  InFlight        Description
984  * 0    1               - orig segment is in flight.
985  * S    0               - nothing flies, orig reached receiver.
986  * L    0               - nothing flies, orig lost by net.
987  * R    2               - both orig and retransmit are in flight.
988  * L|R  1               - orig is lost, retransmit is in flight.
989  * S|R  1               - orig reached receiver, retrans is still in flight.
990  * (L|S|R is logically valid, it could occur when L|R is sacked,
991  *  but it is equivalent to plain S and code short-curcuits it to S.
992  *  L|S is logically invalid, it would mean -1 packet in flight 8))
993  *
994  * These 6 states form finite state machine, controlled by the following events:
995  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
996  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
997  * 3. Loss detection event of one of three flavors:
998  *      A. Scoreboard estimator decided the packet is lost.
999  *         A'. Reno "three dupacks" marks head of queue lost.
1000  *         A''. Its FACK modfication, head until snd.fack is lost.
1001  *      B. SACK arrives sacking data transmitted after never retransmitted
1002  *         hole was sent out.
1003  *      C. SACK arrives sacking SND.NXT at the moment, when the
1004  *         segment was retransmitted.
1005  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1006  *
1007  * It is pleasant to note, that state diagram turns out to be commutative,
1008  * so that we are allowed not to be bothered by order of our actions,
1009  * when multiple events arrive simultaneously. (see the function below).
1010  *
1011  * Reordering detection.
1012  * --------------------
1013  * Reordering metric is maximal distance, which a packet can be displaced
1014  * in packet stream. With SACKs we can estimate it:
1015  *
1016  * 1. SACK fills old hole and the corresponding segment was not
1017  *    ever retransmitted -> reordering. Alas, we cannot use it
1018  *    when segment was retransmitted.
1019  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1020  *    for retransmitted and already SACKed segment -> reordering..
1021  * Both of these heuristics are not used in Loss state, when we cannot
1022  * account for retransmits accurately.
1023  *
1024  * SACK block validation.
1025  * ----------------------
1026  *
1027  * SACK block range validation checks that the received SACK block fits to
1028  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1029  * Note that SND.UNA is not included to the range though being valid because
1030  * it means that the receiver is rather inconsistent with itself reporting
1031  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1032  * perfectly valid, however, in light of RFC2018 which explicitly states
1033  * that "SACK block MUST reflect the newest segment.  Even if the newest
1034  * segment is going to be discarded ...", not that it looks very clever
1035  * in case of head skb. Due to potentional receiver driven attacks, we
1036  * choose to avoid immediate execution of a walk in write queue due to
1037  * reneging and defer head skb's loss recovery to standard loss recovery
1038  * procedure that will eventually trigger (nothing forbids us doing this).
1039  *
1040  * Implements also blockage to start_seq wrap-around. Problem lies in the
1041  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1042  * there's no guarantee that it will be before snd_nxt (n). The problem
1043  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1044  * wrap (s_w):
1045  *
1046  *         <- outs wnd ->                          <- wrapzone ->
1047  *         u     e      n                         u_w   e_w  s n_w
1048  *         |     |      |                          |     |   |  |
1049  * |<------------+------+----- TCP seqno space --------------+---------->|
1050  * ...-- <2^31 ->|                                           |<--------...
1051  * ...---- >2^31 ------>|                                    |<--------...
1052  *
1053  * Current code wouldn't be vulnerable but it's better still to discard such
1054  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1055  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1056  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1057  * equal to the ideal case (infinite seqno space without wrap caused issues).
1058  *
1059  * With D-SACK the lower bound is extended to cover sequence space below
1060  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1061  * again, DSACK block must not to go across snd_una (for the same reason as
1062  * for the normal SACK blocks, explained above). But there all simplicity
1063  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1064  * fully below undo_marker they do not affect behavior in anyway and can
1065  * therefore be safely ignored. In rare cases (which are more or less
1066  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1067  * fragmentation and packet reordering past skb's retransmission. To consider
1068  * them correctly, the acceptable range must be extended even more though
1069  * the exact amount is rather hard to quantify. However, tp->max_window can
1070  * be used as an exaggerated estimate.
1071  */
1072 static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1073                                   u32 start_seq, u32 end_seq)
1074 {
1075         /* Too far in future, or reversed (interpretation is ambiguous) */
1076         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1077                 return 0;
1078
1079         /* Nasty start_seq wrap-around check (see comments above) */
1080         if (!before(start_seq, tp->snd_nxt))
1081                 return 0;
1082
1083         /* In outstanding window? ...This is valid exit for DSACKs too.
1084          * start_seq == snd_una is non-sensical (see comments above)
1085          */
1086         if (after(start_seq, tp->snd_una))
1087                 return 1;
1088
1089         if (!is_dsack || !tp->undo_marker)
1090                 return 0;
1091
1092         /* ...Then it's D-SACK, and must reside below snd_una completely */
1093         if (!after(end_seq, tp->snd_una))
1094                 return 0;
1095
1096         if (!before(start_seq, tp->undo_marker))
1097                 return 1;
1098
1099         /* Too old */
1100         if (!after(end_seq, tp->undo_marker))
1101                 return 0;
1102
1103         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1104          *   start_seq < undo_marker and end_seq >= undo_marker.
1105          */
1106         return !before(start_seq, end_seq - tp->max_window);
1107 }
1108
1109 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1110  * Event "C". Later note: FACK people cheated me again 8), we have to account
1111  * for reordering! Ugly, but should help.
1112  *
1113  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1114  * less than what is now known to be received by the other end (derived from
1115  * SACK blocks by the caller). Also calculate the lowest snd_nxt among the
1116  * remaining retransmitted skbs to avoid some costly processing per ACKs.
1117  */
1118 static int tcp_mark_lost_retrans(struct sock *sk, u32 received_upto)
1119 {
1120         struct tcp_sock *tp = tcp_sk(sk);
1121         struct sk_buff *skb;
1122         int flag = 0;
1123         int cnt = 0;
1124         u32 new_low_seq = 0;
1125
1126         tcp_for_write_queue(skb, sk) {
1127                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1128
1129                 if (skb == tcp_send_head(sk))
1130                         break;
1131                 if (cnt == tp->retrans_out)
1132                         break;
1133                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1134                         continue;
1135
1136                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1137                         continue;
1138
1139                 if (after(received_upto, ack_seq) &&
1140                     (tcp_is_fack(tp) ||
1141                      !before(received_upto,
1142                              ack_seq + tp->reordering * tp->mss_cache))) {
1143                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1144                         tp->retrans_out -= tcp_skb_pcount(skb);
1145
1146                         /* clear lost hint */
1147                         tp->retransmit_skb_hint = NULL;
1148
1149                         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1150                                 tp->lost_out += tcp_skb_pcount(skb);
1151                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1152                                 flag |= FLAG_DATA_SACKED;
1153                                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1154                         }
1155                 } else {
1156                         if (!new_low_seq || before(ack_seq, new_low_seq))
1157                                 new_low_seq = ack_seq;
1158                         cnt += tcp_skb_pcount(skb);
1159                 }
1160         }
1161
1162         if (tp->retrans_out)
1163                 tp->lost_retrans_low = new_low_seq;
1164
1165         return flag;
1166 }
1167
1168 static int tcp_check_dsack(struct tcp_sock *tp, struct sk_buff *ack_skb,
1169                            struct tcp_sack_block_wire *sp, int num_sacks,
1170                            u32 prior_snd_una)
1171 {
1172         u32 start_seq_0 = ntohl(get_unaligned(&sp[0].start_seq));
1173         u32 end_seq_0 = ntohl(get_unaligned(&sp[0].end_seq));
1174         int dup_sack = 0;
1175
1176         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1177                 dup_sack = 1;
1178                 tcp_dsack_seen(tp);
1179                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
1180         } else if (num_sacks > 1) {
1181                 u32 end_seq_1 = ntohl(get_unaligned(&sp[1].end_seq));
1182                 u32 start_seq_1 = ntohl(get_unaligned(&sp[1].start_seq));
1183
1184                 if (!after(end_seq_0, end_seq_1) &&
1185                     !before(start_seq_0, start_seq_1)) {
1186                         dup_sack = 1;
1187                         tcp_dsack_seen(tp);
1188                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
1189                 }
1190         }
1191
1192         /* D-SACK for already forgotten data... Do dumb counting. */
1193         if (dup_sack &&
1194             !after(end_seq_0, prior_snd_una) &&
1195             after(end_seq_0, tp->undo_marker))
1196                 tp->undo_retrans--;
1197
1198         return dup_sack;
1199 }
1200
1201 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1202  * the incoming SACK may not exactly match but we can find smaller MSS
1203  * aligned portion of it that matches. Therefore we might need to fragment
1204  * which may fail and creates some hassle (caller must handle error case
1205  * returns).
1206  */
1207 int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1208                           u32 start_seq, u32 end_seq)
1209 {
1210         int in_sack, err;
1211         unsigned int pkt_len;
1212
1213         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1214                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1215
1216         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1217             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1218
1219                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1220
1221                 if (!in_sack)
1222                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1223                 else
1224                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1225                 err = tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size);
1226                 if (err < 0)
1227                         return err;
1228         }
1229
1230         return in_sack;
1231 }
1232
1233 static int
1234 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
1235 {
1236         const struct inet_connection_sock *icsk = inet_csk(sk);
1237         struct tcp_sock *tp = tcp_sk(sk);
1238         unsigned char *ptr = (skb_transport_header(ack_skb) +
1239                               TCP_SKB_CB(ack_skb)->sacked);
1240         struct tcp_sack_block_wire *sp = (struct tcp_sack_block_wire *)(ptr+2);
1241         struct sk_buff *cached_skb;
1242         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
1243         int reord = tp->packets_out;
1244         int prior_fackets;
1245         u32 highest_sack_end_seq = 0;
1246         int flag = 0;
1247         int found_dup_sack = 0;
1248         int cached_fack_count;
1249         int i;
1250         int first_sack_index;
1251
1252         if (!tp->sacked_out) {
1253                 if (WARN_ON(tp->fackets_out))
1254                         tp->fackets_out = 0;
1255                 tp->highest_sack = tp->snd_una;
1256         }
1257         prior_fackets = tp->fackets_out;
1258
1259         found_dup_sack = tcp_check_dsack(tp, ack_skb, sp,
1260                                          num_sacks, prior_snd_una);
1261         if (found_dup_sack)
1262                 flag |= FLAG_DSACKING_ACK;
1263
1264         /* Eliminate too old ACKs, but take into
1265          * account more or less fresh ones, they can
1266          * contain valid SACK info.
1267          */
1268         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1269                 return 0;
1270
1271         /* SACK fastpath:
1272          * if the only SACK change is the increase of the end_seq of
1273          * the first block then only apply that SACK block
1274          * and use retrans queue hinting otherwise slowpath */
1275         flag = 1;
1276         for (i = 0; i < num_sacks; i++) {
1277                 __be32 start_seq = sp[i].start_seq;
1278                 __be32 end_seq = sp[i].end_seq;
1279
1280                 if (i == 0) {
1281                         if (tp->recv_sack_cache[i].start_seq != start_seq)
1282                                 flag = 0;
1283                 } else {
1284                         if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
1285                             (tp->recv_sack_cache[i].end_seq != end_seq))
1286                                 flag = 0;
1287                 }
1288                 tp->recv_sack_cache[i].start_seq = start_seq;
1289                 tp->recv_sack_cache[i].end_seq = end_seq;
1290         }
1291         /* Clear the rest of the cache sack blocks so they won't match mistakenly. */
1292         for (; i < ARRAY_SIZE(tp->recv_sack_cache); i++) {
1293                 tp->recv_sack_cache[i].start_seq = 0;
1294                 tp->recv_sack_cache[i].end_seq = 0;
1295         }
1296
1297         first_sack_index = 0;
1298         if (flag)
1299                 num_sacks = 1;
1300         else {
1301                 int j;
1302                 tp->fastpath_skb_hint = NULL;
1303
1304                 /* order SACK blocks to allow in order walk of the retrans queue */
1305                 for (i = num_sacks-1; i > 0; i--) {
1306                         for (j = 0; j < i; j++){
1307                                 if (after(ntohl(sp[j].start_seq),
1308                                           ntohl(sp[j+1].start_seq))){
1309                                         struct tcp_sack_block_wire tmp;
1310
1311                                         tmp = sp[j];
1312                                         sp[j] = sp[j+1];
1313                                         sp[j+1] = tmp;
1314
1315                                         /* Track where the first SACK block goes to */
1316                                         if (j == first_sack_index)
1317                                                 first_sack_index = j+1;
1318                                 }
1319
1320                         }
1321                 }
1322         }
1323
1324         /* clear flag as used for different purpose in following code */
1325         flag = 0;
1326
1327         /* Use SACK fastpath hint if valid */
1328         cached_skb = tp->fastpath_skb_hint;
1329         cached_fack_count = tp->fastpath_cnt_hint;
1330         if (!cached_skb) {
1331                 cached_skb = tcp_write_queue_head(sk);
1332                 cached_fack_count = 0;
1333         }
1334
1335         for (i=0; i<num_sacks; i++, sp++) {
1336                 struct sk_buff *skb;
1337                 __u32 start_seq = ntohl(sp->start_seq);
1338                 __u32 end_seq = ntohl(sp->end_seq);
1339                 int fack_count;
1340                 int dup_sack = (found_dup_sack && (i == first_sack_index));
1341
1342                 if (!tcp_is_sackblock_valid(tp, dup_sack, start_seq, end_seq)) {
1343                         if (dup_sack) {
1344                                 if (!tp->undo_marker)
1345                                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDNOUNDO);
1346                                 else
1347                                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDOLD);
1348                         } else {
1349                                 /* Don't count olds caused by ACK reordering */
1350                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1351                                     !after(end_seq, tp->snd_una))
1352                                         continue;
1353                                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKDISCARD);
1354                         }
1355                         continue;
1356                 }
1357
1358                 skb = cached_skb;
1359                 fack_count = cached_fack_count;
1360
1361                 /* Event "B" in the comment above. */
1362                 if (after(end_seq, tp->high_seq))
1363                         flag |= FLAG_DATA_LOST;
1364
1365                 tcp_for_write_queue_from(skb, sk) {
1366                         int in_sack;
1367                         u8 sacked;
1368
1369                         if (skb == tcp_send_head(sk))
1370                                 break;
1371
1372                         cached_skb = skb;
1373                         cached_fack_count = fack_count;
1374                         if (i == first_sack_index) {
1375                                 tp->fastpath_skb_hint = skb;
1376                                 tp->fastpath_cnt_hint = fack_count;
1377                         }
1378
1379                         /* The retransmission queue is always in order, so
1380                          * we can short-circuit the walk early.
1381                          */
1382                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1383                                 break;
1384
1385                         in_sack = tcp_match_skb_to_sack(sk, skb, start_seq, end_seq);
1386                         if (in_sack < 0)
1387                                 break;
1388
1389                         fack_count += tcp_skb_pcount(skb);
1390
1391                         sacked = TCP_SKB_CB(skb)->sacked;
1392
1393                         /* Account D-SACK for retransmitted packet. */
1394                         if ((dup_sack && in_sack) &&
1395                             (sacked & TCPCB_RETRANS) &&
1396                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1397                                 tp->undo_retrans--;
1398
1399                         /* The frame is ACKed. */
1400                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1401                                 if (sacked&TCPCB_RETRANS) {
1402                                         if ((dup_sack && in_sack) &&
1403                                             (sacked&TCPCB_SACKED_ACKED))
1404                                                 reord = min(fack_count, reord);
1405                                 } else {
1406                                         /* If it was in a hole, we detected reordering. */
1407                                         if (fack_count < prior_fackets &&
1408                                             !(sacked&TCPCB_SACKED_ACKED))
1409                                                 reord = min(fack_count, reord);
1410                                 }
1411
1412                                 /* Nothing to do; acked frame is about to be dropped. */
1413                                 continue;
1414                         }
1415
1416                         if (!in_sack)
1417                                 continue;
1418
1419                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1420                                 if (sacked & TCPCB_SACKED_RETRANS) {
1421                                         /* If the segment is not tagged as lost,
1422                                          * we do not clear RETRANS, believing
1423                                          * that retransmission is still in flight.
1424                                          */
1425                                         if (sacked & TCPCB_LOST) {
1426                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1427                                                 tp->lost_out -= tcp_skb_pcount(skb);
1428                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1429
1430                                                 /* clear lost hint */
1431                                                 tp->retransmit_skb_hint = NULL;
1432                                         }
1433                                 } else {
1434                                         /* New sack for not retransmitted frame,
1435                                          * which was in hole. It is reordering.
1436                                          */
1437                                         if (!(sacked & TCPCB_RETRANS) &&
1438                                             fack_count < prior_fackets)
1439                                                 reord = min(fack_count, reord);
1440
1441                                         if (sacked & TCPCB_LOST) {
1442                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1443                                                 tp->lost_out -= tcp_skb_pcount(skb);
1444
1445                                                 /* clear lost hint */
1446                                                 tp->retransmit_skb_hint = NULL;
1447                                         }
1448                                         /* SACK enhanced F-RTO detection.
1449                                          * Set flag if and only if non-rexmitted
1450                                          * segments below frto_highmark are
1451                                          * SACKed (RFC4138; Appendix B).
1452                                          * Clearing correct due to in-order walk
1453                                          */
1454                                         if (after(end_seq, tp->frto_highmark)) {
1455                                                 flag &= ~FLAG_ONLY_ORIG_SACKED;
1456                                         } else {
1457                                                 if (!(sacked & TCPCB_RETRANS))
1458                                                         flag |= FLAG_ONLY_ORIG_SACKED;
1459                                         }
1460                                 }
1461
1462                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1463                                 flag |= FLAG_DATA_SACKED;
1464                                 tp->sacked_out += tcp_skb_pcount(skb);
1465
1466                                 if (fack_count > tp->fackets_out)
1467                                         tp->fackets_out = fack_count;
1468
1469                                 if (after(TCP_SKB_CB(skb)->seq, tp->highest_sack)) {
1470                                         tp->highest_sack = TCP_SKB_CB(skb)->seq;
1471                                         highest_sack_end_seq = TCP_SKB_CB(skb)->end_seq;
1472                                 }
1473                         } else {
1474                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1475                                         reord = min(fack_count, reord);
1476                         }
1477
1478                         /* D-SACK. We can detect redundant retransmission
1479                          * in S|R and plain R frames and clear it.
1480                          * undo_retrans is decreased above, L|R frames
1481                          * are accounted above as well.
1482                          */
1483                         if (dup_sack &&
1484                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1485                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1486                                 tp->retrans_out -= tcp_skb_pcount(skb);
1487                                 tp->retransmit_skb_hint = NULL;
1488                         }
1489                 }
1490         }
1491
1492         if (tp->retrans_out &&
1493             after(highest_sack_end_seq, tp->lost_retrans_low) &&
1494             icsk->icsk_ca_state == TCP_CA_Recovery)
1495                 flag |= tcp_mark_lost_retrans(sk, highest_sack_end_seq);
1496
1497         tcp_verify_left_out(tp);
1498
1499         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss &&
1500             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1501                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1502
1503 #if FASTRETRANS_DEBUG > 0
1504         BUG_TRAP((int)tp->sacked_out >= 0);
1505         BUG_TRAP((int)tp->lost_out >= 0);
1506         BUG_TRAP((int)tp->retrans_out >= 0);
1507         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1508 #endif
1509         return flag;
1510 }
1511
1512 /* If we receive more dupacks than we expected counting segments
1513  * in assumption of absent reordering, interpret this as reordering.
1514  * The only another reason could be bug in receiver TCP.
1515  */
1516 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1517 {
1518         struct tcp_sock *tp = tcp_sk(sk);
1519         u32 holes;
1520
1521         holes = max(tp->lost_out, 1U);
1522         holes = min(holes, tp->packets_out);
1523
1524         if ((tp->sacked_out + holes) > tp->packets_out) {
1525                 tp->sacked_out = tp->packets_out - holes;
1526                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1527         }
1528 }
1529
1530 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1531
1532 static void tcp_add_reno_sack(struct sock *sk)
1533 {
1534         struct tcp_sock *tp = tcp_sk(sk);
1535         tp->sacked_out++;
1536         tcp_check_reno_reordering(sk, 0);
1537         tcp_verify_left_out(tp);
1538 }
1539
1540 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1541
1542 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1543 {
1544         struct tcp_sock *tp = tcp_sk(sk);
1545
1546         if (acked > 0) {
1547                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1548                 if (acked-1 >= tp->sacked_out)
1549                         tp->sacked_out = 0;
1550                 else
1551                         tp->sacked_out -= acked-1;
1552         }
1553         tcp_check_reno_reordering(sk, acked);
1554         tcp_verify_left_out(tp);
1555 }
1556
1557 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1558 {
1559         tp->sacked_out = 0;
1560 }
1561
1562 /* F-RTO can only be used if TCP has never retransmitted anything other than
1563  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
1564  */
1565 int tcp_use_frto(struct sock *sk)
1566 {
1567         const struct tcp_sock *tp = tcp_sk(sk);
1568         struct sk_buff *skb;
1569
1570         if (!sysctl_tcp_frto)
1571                 return 0;
1572
1573         if (IsSackFrto())
1574                 return 1;
1575
1576         /* Avoid expensive walking of rexmit queue if possible */
1577         if (tp->retrans_out > 1)
1578                 return 0;
1579
1580         skb = tcp_write_queue_head(sk);
1581         skb = tcp_write_queue_next(sk, skb);    /* Skips head */
1582         tcp_for_write_queue_from(skb, sk) {
1583                 if (skb == tcp_send_head(sk))
1584                         break;
1585                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1586                         return 0;
1587                 /* Short-circuit when first non-SACKed skb has been checked */
1588                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED))
1589                         break;
1590         }
1591         return 1;
1592 }
1593
1594 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
1595  * recovery a bit and use heuristics in tcp_process_frto() to detect if
1596  * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
1597  * keep retrans_out counting accurate (with SACK F-RTO, other than head
1598  * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
1599  * bits are handled if the Loss state is really to be entered (in
1600  * tcp_enter_frto_loss).
1601  *
1602  * Do like tcp_enter_loss() would; when RTO expires the second time it
1603  * does:
1604  *  "Reduce ssthresh if it has not yet been made inside this window."
1605  */
1606 void tcp_enter_frto(struct sock *sk)
1607 {
1608         const struct inet_connection_sock *icsk = inet_csk(sk);
1609         struct tcp_sock *tp = tcp_sk(sk);
1610         struct sk_buff *skb;
1611
1612         if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
1613             tp->snd_una == tp->high_seq ||
1614             ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
1615              !icsk->icsk_retransmits)) {
1616                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1617                 /* Our state is too optimistic in ssthresh() call because cwnd
1618                  * is not reduced until tcp_enter_frto_loss() when previous FRTO
1619                  * recovery has not yet completed. Pattern would be this: RTO,
1620                  * Cumulative ACK, RTO (2xRTO for the same segment does not end
1621                  * up here twice).
1622                  * RFC4138 should be more specific on what to do, even though
1623                  * RTO is quite unlikely to occur after the first Cumulative ACK
1624                  * due to back-off and complexity of triggering events ...
1625                  */
1626                 if (tp->frto_counter) {
1627                         u32 stored_cwnd;
1628                         stored_cwnd = tp->snd_cwnd;
1629                         tp->snd_cwnd = 2;
1630                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1631                         tp->snd_cwnd = stored_cwnd;
1632                 } else {
1633                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1634                 }
1635                 /* ... in theory, cong.control module could do "any tricks" in
1636                  * ssthresh(), which means that ca_state, lost bits and lost_out
1637                  * counter would have to be faked before the call occurs. We
1638                  * consider that too expensive, unlikely and hacky, so modules
1639                  * using these in ssthresh() must deal these incompatibility
1640                  * issues if they receives CA_EVENT_FRTO and frto_counter != 0
1641                  */
1642                 tcp_ca_event(sk, CA_EVENT_FRTO);
1643         }
1644
1645         tp->undo_marker = tp->snd_una;
1646         tp->undo_retrans = 0;
1647
1648         skb = tcp_write_queue_head(sk);
1649         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1650                 tp->undo_marker = 0;
1651         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
1652                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1653                 tp->retrans_out -= tcp_skb_pcount(skb);
1654         }
1655         tcp_verify_left_out(tp);
1656
1657         /* Earlier loss recovery underway (see RFC4138; Appendix B).
1658          * The last condition is necessary at least in tp->frto_counter case.
1659          */
1660         if (IsSackFrto() && (tp->frto_counter ||
1661             ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
1662             after(tp->high_seq, tp->snd_una)) {
1663                 tp->frto_highmark = tp->high_seq;
1664         } else {
1665                 tp->frto_highmark = tp->snd_nxt;
1666         }
1667         tcp_set_ca_state(sk, TCP_CA_Disorder);
1668         tp->high_seq = tp->snd_nxt;
1669         tp->frto_counter = 1;
1670 }
1671
1672 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1673  * which indicates that we should follow the traditional RTO recovery,
1674  * i.e. mark everything lost and do go-back-N retransmission.
1675  */
1676 static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
1677 {
1678         struct tcp_sock *tp = tcp_sk(sk);
1679         struct sk_buff *skb;
1680
1681         tp->lost_out = 0;
1682         tp->retrans_out = 0;
1683         if (tcp_is_reno(tp))
1684                 tcp_reset_reno_sack(tp);
1685
1686         tcp_for_write_queue(skb, sk) {
1687                 if (skb == tcp_send_head(sk))
1688                         break;
1689                 /*
1690                  * Count the retransmission made on RTO correctly (only when
1691                  * waiting for the first ACK and did not get it)...
1692                  */
1693                 if ((tp->frto_counter == 1) && !(flag&FLAG_DATA_ACKED)) {
1694                         /* For some reason this R-bit might get cleared? */
1695                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1696                                 tp->retrans_out += tcp_skb_pcount(skb);
1697                         /* ...enter this if branch just for the first segment */
1698                         flag |= FLAG_DATA_ACKED;
1699                 } else {
1700                         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1701                                 tp->undo_marker = 0;
1702                         TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1703                 }
1704
1705                 /* Don't lost mark skbs that were fwd transmitted after RTO */
1706                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) &&
1707                     !after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark)) {
1708                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1709                         tp->lost_out += tcp_skb_pcount(skb);
1710                 }
1711         }
1712         tcp_verify_left_out(tp);
1713
1714         tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
1715         tp->snd_cwnd_cnt = 0;
1716         tp->snd_cwnd_stamp = tcp_time_stamp;
1717         tp->frto_counter = 0;
1718         tp->bytes_acked = 0;
1719
1720         tp->reordering = min_t(unsigned int, tp->reordering,
1721                                              sysctl_tcp_reordering);
1722         tcp_set_ca_state(sk, TCP_CA_Loss);
1723         tp->high_seq = tp->frto_highmark;
1724         TCP_ECN_queue_cwr(tp);
1725
1726         tcp_clear_retrans_hints_partial(tp);
1727 }
1728
1729 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
1730 {
1731         tp->retrans_out = 0;
1732         tp->lost_out = 0;
1733
1734         tp->undo_marker = 0;
1735         tp->undo_retrans = 0;
1736 }
1737
1738 void tcp_clear_retrans(struct tcp_sock *tp)
1739 {
1740         tcp_clear_retrans_partial(tp);
1741
1742         tp->fackets_out = 0;
1743         tp->sacked_out = 0;
1744 }
1745
1746 /* Enter Loss state. If "how" is not zero, forget all SACK information
1747  * and reset tags completely, otherwise preserve SACKs. If receiver
1748  * dropped its ofo queue, we will know this due to reneging detection.
1749  */
1750 void tcp_enter_loss(struct sock *sk, int how)
1751 {
1752         const struct inet_connection_sock *icsk = inet_csk(sk);
1753         struct tcp_sock *tp = tcp_sk(sk);
1754         struct sk_buff *skb;
1755
1756         /* Reduce ssthresh if it has not yet been made inside this window. */
1757         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1758             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1759                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1760                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1761                 tcp_ca_event(sk, CA_EVENT_LOSS);
1762         }
1763         tp->snd_cwnd       = 1;
1764         tp->snd_cwnd_cnt   = 0;
1765         tp->snd_cwnd_stamp = tcp_time_stamp;
1766
1767         tp->bytes_acked = 0;
1768         tcp_clear_retrans_partial(tp);
1769
1770         if (tcp_is_reno(tp))
1771                 tcp_reset_reno_sack(tp);
1772
1773         if (!how) {
1774                 /* Push undo marker, if it was plain RTO and nothing
1775                  * was retransmitted. */
1776                 tp->undo_marker = tp->snd_una;
1777                 tcp_clear_retrans_hints_partial(tp);
1778         } else {
1779                 tp->sacked_out = 0;
1780                 tp->fackets_out = 0;
1781                 tcp_clear_all_retrans_hints(tp);
1782         }
1783
1784         tcp_for_write_queue(skb, sk) {
1785                 if (skb == tcp_send_head(sk))
1786                         break;
1787
1788                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1789                         tp->undo_marker = 0;
1790                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1791                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1792                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1793                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1794                         tp->lost_out += tcp_skb_pcount(skb);
1795                 }
1796         }
1797         tcp_verify_left_out(tp);
1798
1799         tp->reordering = min_t(unsigned int, tp->reordering,
1800                                              sysctl_tcp_reordering);
1801         tcp_set_ca_state(sk, TCP_CA_Loss);
1802         tp->high_seq = tp->snd_nxt;
1803         TCP_ECN_queue_cwr(tp);
1804         /* Abort FRTO algorithm if one is in progress */
1805         tp->frto_counter = 0;
1806 }
1807
1808 static int tcp_check_sack_reneging(struct sock *sk)
1809 {
1810         struct sk_buff *skb;
1811
1812         /* If ACK arrived pointing to a remembered SACK,
1813          * it means that our remembered SACKs do not reflect
1814          * real state of receiver i.e.
1815          * receiver _host_ is heavily congested (or buggy).
1816          * Do processing similar to RTO timeout.
1817          */
1818         if ((skb = tcp_write_queue_head(sk)) != NULL &&
1819             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1820                 struct inet_connection_sock *icsk = inet_csk(sk);
1821                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1822
1823                 tcp_enter_loss(sk, 1);
1824                 icsk->icsk_retransmits++;
1825                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
1826                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1827                                           icsk->icsk_rto, TCP_RTO_MAX);
1828                 return 1;
1829         }
1830         return 0;
1831 }
1832
1833 static inline int tcp_fackets_out(struct tcp_sock *tp)
1834 {
1835         return tcp_is_reno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1836 }
1837
1838 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1839 {
1840         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1841 }
1842
1843 static inline int tcp_head_timedout(struct sock *sk)
1844 {
1845         struct tcp_sock *tp = tcp_sk(sk);
1846
1847         return tp->packets_out &&
1848                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
1849 }
1850
1851 /* Linux NewReno/SACK/FACK/ECN state machine.
1852  * --------------------------------------
1853  *
1854  * "Open"       Normal state, no dubious events, fast path.
1855  * "Disorder"   In all the respects it is "Open",
1856  *              but requires a bit more attention. It is entered when
1857  *              we see some SACKs or dupacks. It is split of "Open"
1858  *              mainly to move some processing from fast path to slow one.
1859  * "CWR"        CWND was reduced due to some Congestion Notification event.
1860  *              It can be ECN, ICMP source quench, local device congestion.
1861  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1862  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1863  *
1864  * tcp_fastretrans_alert() is entered:
1865  * - each incoming ACK, if state is not "Open"
1866  * - when arrived ACK is unusual, namely:
1867  *      * SACK
1868  *      * Duplicate ACK.
1869  *      * ECN ECE.
1870  *
1871  * Counting packets in flight is pretty simple.
1872  *
1873  *      in_flight = packets_out - left_out + retrans_out
1874  *
1875  *      packets_out is SND.NXT-SND.UNA counted in packets.
1876  *
1877  *      retrans_out is number of retransmitted segments.
1878  *
1879  *      left_out is number of segments left network, but not ACKed yet.
1880  *
1881  *              left_out = sacked_out + lost_out
1882  *
1883  *     sacked_out: Packets, which arrived to receiver out of order
1884  *                 and hence not ACKed. With SACKs this number is simply
1885  *                 amount of SACKed data. Even without SACKs
1886  *                 it is easy to give pretty reliable estimate of this number,
1887  *                 counting duplicate ACKs.
1888  *
1889  *       lost_out: Packets lost by network. TCP has no explicit
1890  *                 "loss notification" feedback from network (for now).
1891  *                 It means that this number can be only _guessed_.
1892  *                 Actually, it is the heuristics to predict lossage that
1893  *                 distinguishes different algorithms.
1894  *
1895  *      F.e. after RTO, when all the queue is considered as lost,
1896  *      lost_out = packets_out and in_flight = retrans_out.
1897  *
1898  *              Essentially, we have now two algorithms counting
1899  *              lost packets.
1900  *
1901  *              FACK: It is the simplest heuristics. As soon as we decided
1902  *              that something is lost, we decide that _all_ not SACKed
1903  *              packets until the most forward SACK are lost. I.e.
1904  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1905  *              It is absolutely correct estimate, if network does not reorder
1906  *              packets. And it loses any connection to reality when reordering
1907  *              takes place. We use FACK by default until reordering
1908  *              is suspected on the path to this destination.
1909  *
1910  *              NewReno: when Recovery is entered, we assume that one segment
1911  *              is lost (classic Reno). While we are in Recovery and
1912  *              a partial ACK arrives, we assume that one more packet
1913  *              is lost (NewReno). This heuristics are the same in NewReno
1914  *              and SACK.
1915  *
1916  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1917  *  deflation etc. CWND is real congestion window, never inflated, changes
1918  *  only according to classic VJ rules.
1919  *
1920  * Really tricky (and requiring careful tuning) part of algorithm
1921  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1922  * The first determines the moment _when_ we should reduce CWND and,
1923  * hence, slow down forward transmission. In fact, it determines the moment
1924  * when we decide that hole is caused by loss, rather than by a reorder.
1925  *
1926  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1927  * holes, caused by lost packets.
1928  *
1929  * And the most logically complicated part of algorithm is undo
1930  * heuristics. We detect false retransmits due to both too early
1931  * fast retransmit (reordering) and underestimated RTO, analyzing
1932  * timestamps and D-SACKs. When we detect that some segments were
1933  * retransmitted by mistake and CWND reduction was wrong, we undo
1934  * window reduction and abort recovery phase. This logic is hidden
1935  * inside several functions named tcp_try_undo_<something>.
1936  */
1937
1938 /* This function decides, when we should leave Disordered state
1939  * and enter Recovery phase, reducing congestion window.
1940  *
1941  * Main question: may we further continue forward transmission
1942  * with the same cwnd?
1943  */
1944 static int tcp_time_to_recover(struct sock *sk)
1945 {
1946         struct tcp_sock *tp = tcp_sk(sk);
1947         __u32 packets_out;
1948
1949         /* Do not perform any recovery during FRTO algorithm */
1950         if (tp->frto_counter)
1951                 return 0;
1952
1953         /* Trick#1: The loss is proven. */
1954         if (tp->lost_out)
1955                 return 1;
1956
1957         /* Not-A-Trick#2 : Classic rule... */
1958         if (tcp_fackets_out(tp) > tp->reordering)
1959                 return 1;
1960
1961         /* Trick#3 : when we use RFC2988 timer restart, fast
1962          * retransmit can be triggered by timeout of queue head.
1963          */
1964         if (tcp_head_timedout(sk))
1965                 return 1;
1966
1967         /* Trick#4: It is still not OK... But will it be useful to delay
1968          * recovery more?
1969          */
1970         packets_out = tp->packets_out;
1971         if (packets_out <= tp->reordering &&
1972             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1973             !tcp_may_send_now(sk)) {
1974                 /* We have nothing to send. This connection is limited
1975                  * either by receiver window or by application.
1976                  */
1977                 return 1;
1978         }
1979
1980         return 0;
1981 }
1982
1983 /* RFC: This is from the original, I doubt that this is necessary at all:
1984  * clear xmit_retrans hint if seq of this skb is beyond hint. How could we
1985  * retransmitted past LOST markings in the first place? I'm not fully sure
1986  * about undo and end of connection cases, which can cause R without L?
1987  */
1988 static void tcp_verify_retransmit_hint(struct tcp_sock *tp,
1989                                        struct sk_buff *skb)
1990 {
1991         if ((tp->retransmit_skb_hint != NULL) &&
1992             before(TCP_SKB_CB(skb)->seq,
1993             TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
1994                 tp->retransmit_skb_hint = NULL;
1995 }
1996
1997 /* Mark head of queue up as lost. */
1998 static void tcp_mark_head_lost(struct sock *sk,
1999                                int packets, u32 high_seq)
2000 {
2001         struct tcp_sock *tp = tcp_sk(sk);
2002         struct sk_buff *skb;
2003         int cnt;
2004
2005         BUG_TRAP(packets <= tp->packets_out);
2006         if (tp->lost_skb_hint) {
2007                 skb = tp->lost_skb_hint;
2008                 cnt = tp->lost_cnt_hint;
2009         } else {
2010                 skb = tcp_write_queue_head(sk);
2011                 cnt = 0;
2012         }
2013
2014         tcp_for_write_queue_from(skb, sk) {
2015                 if (skb == tcp_send_head(sk))
2016                         break;
2017                 /* TODO: do this better */
2018                 /* this is not the most efficient way to do this... */
2019                 tp->lost_skb_hint = skb;
2020                 tp->lost_cnt_hint = cnt;
2021                 cnt += tcp_skb_pcount(skb);
2022                 if (cnt > packets || after(TCP_SKB_CB(skb)->end_seq, high_seq))
2023                         break;
2024                 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_SACKED_ACKED|TCPCB_LOST))) {
2025                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2026                         tp->lost_out += tcp_skb_pcount(skb);
2027                         tcp_verify_retransmit_hint(tp, skb);
2028                 }
2029         }
2030         tcp_verify_left_out(tp);
2031 }
2032
2033 /* Account newly detected lost packet(s) */
2034
2035 static void tcp_update_scoreboard(struct sock *sk)
2036 {
2037         struct tcp_sock *tp = tcp_sk(sk);
2038
2039         if (tcp_is_fack(tp)) {
2040                 int lost = tp->fackets_out - tp->reordering;
2041                 if (lost <= 0)
2042                         lost = 1;
2043                 tcp_mark_head_lost(sk, lost, tp->high_seq);
2044         } else {
2045                 tcp_mark_head_lost(sk, 1, tp->high_seq);
2046         }
2047
2048         /* New heuristics: it is possible only after we switched
2049          * to restart timer each time when something is ACKed.
2050          * Hence, we can detect timed out packets during fast
2051          * retransmit without falling to slow start.
2052          */
2053         if (!tcp_is_reno(tp) && tcp_head_timedout(sk)) {
2054                 struct sk_buff *skb;
2055
2056                 skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
2057                         : tcp_write_queue_head(sk);
2058
2059                 tcp_for_write_queue_from(skb, sk) {
2060                         if (skb == tcp_send_head(sk))
2061                                 break;
2062                         if (!tcp_skb_timedout(sk, skb))
2063                                 break;
2064
2065                         if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
2066                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2067                                 tp->lost_out += tcp_skb_pcount(skb);
2068                                 tcp_verify_retransmit_hint(tp, skb);
2069                         }
2070                 }
2071
2072                 tp->scoreboard_skb_hint = skb;
2073
2074                 tcp_verify_left_out(tp);
2075         }
2076 }
2077
2078 /* CWND moderation, preventing bursts due to too big ACKs
2079  * in dubious situations.
2080  */
2081 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2082 {
2083         tp->snd_cwnd = min(tp->snd_cwnd,
2084                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
2085         tp->snd_cwnd_stamp = tcp_time_stamp;
2086 }
2087
2088 /* Lower bound on congestion window is slow start threshold
2089  * unless congestion avoidance choice decides to overide it.
2090  */
2091 static inline u32 tcp_cwnd_min(const struct sock *sk)
2092 {
2093         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2094
2095         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2096 }
2097
2098 /* Decrease cwnd each second ack. */
2099 static void tcp_cwnd_down(struct sock *sk, int flag)
2100 {
2101         struct tcp_sock *tp = tcp_sk(sk);
2102         int decr = tp->snd_cwnd_cnt + 1;
2103
2104         if ((flag&(FLAG_ANY_PROGRESS|FLAG_DSACKING_ACK)) ||
2105             (tcp_is_reno(tp) && !(flag&FLAG_NOT_DUP))) {
2106                 tp->snd_cwnd_cnt = decr&1;
2107                 decr >>= 1;
2108
2109                 if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2110                         tp->snd_cwnd -= decr;
2111
2112                 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
2113                 tp->snd_cwnd_stamp = tcp_time_stamp;
2114         }
2115 }
2116
2117 /* Nothing was retransmitted or returned timestamp is less
2118  * than timestamp of the first retransmission.
2119  */
2120 static inline int tcp_packet_delayed(struct tcp_sock *tp)
2121 {
2122         return !tp->retrans_stamp ||
2123                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2124                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
2125 }
2126
2127 /* Undo procedures. */
2128
2129 #if FASTRETRANS_DEBUG > 1
2130 static void DBGUNDO(struct sock *sk, const char *msg)
2131 {
2132         struct tcp_sock *tp = tcp_sk(sk);
2133         struct inet_sock *inet = inet_sk(sk);
2134
2135         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
2136                msg,
2137                NIPQUAD(inet->daddr), ntohs(inet->dport),
2138                tp->snd_cwnd, tcp_left_out(tp),
2139                tp->snd_ssthresh, tp->prior_ssthresh,
2140                tp->packets_out);
2141 }
2142 #else
2143 #define DBGUNDO(x...) do { } while (0)
2144 #endif
2145
2146 static void tcp_undo_cwr(struct sock *sk, const int undo)
2147 {
2148         struct tcp_sock *tp = tcp_sk(sk);
2149
2150         if (tp->prior_ssthresh) {
2151                 const struct inet_connection_sock *icsk = inet_csk(sk);
2152
2153                 if (icsk->icsk_ca_ops->undo_cwnd)
2154                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2155                 else
2156                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
2157
2158                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
2159                         tp->snd_ssthresh = tp->prior_ssthresh;
2160                         TCP_ECN_withdraw_cwr(tp);
2161                 }
2162         } else {
2163                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2164         }
2165         tcp_moderate_cwnd(tp);
2166         tp->snd_cwnd_stamp = tcp_time_stamp;
2167
2168         /* There is something screwy going on with the retrans hints after
2169            an undo */
2170         tcp_clear_all_retrans_hints(tp);
2171 }
2172
2173 static inline int tcp_may_undo(struct tcp_sock *tp)
2174 {
2175         return tp->undo_marker &&
2176                 (!tp->undo_retrans || tcp_packet_delayed(tp));
2177 }
2178
2179 /* People celebrate: "We love our President!" */
2180 static int tcp_try_undo_recovery(struct sock *sk)
2181 {
2182         struct tcp_sock *tp = tcp_sk(sk);
2183
2184         if (tcp_may_undo(tp)) {
2185                 /* Happy end! We did not retransmit anything
2186                  * or our original transmission succeeded.
2187                  */
2188                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2189                 tcp_undo_cwr(sk, 1);
2190                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2191                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
2192                 else
2193                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
2194                 tp->undo_marker = 0;
2195         }
2196         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2197                 /* Hold old state until something *above* high_seq
2198                  * is ACKed. For Reno it is MUST to prevent false
2199                  * fast retransmits (RFC2582). SACK TCP is safe. */
2200                 tcp_moderate_cwnd(tp);
2201                 return 1;
2202         }
2203         tcp_set_ca_state(sk, TCP_CA_Open);
2204         return 0;
2205 }
2206
2207 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2208 static void tcp_try_undo_dsack(struct sock *sk)
2209 {
2210         struct tcp_sock *tp = tcp_sk(sk);
2211
2212         if (tp->undo_marker && !tp->undo_retrans) {
2213                 DBGUNDO(sk, "D-SACK");
2214                 tcp_undo_cwr(sk, 1);
2215                 tp->undo_marker = 0;
2216                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
2217         }
2218 }
2219
2220 /* Undo during fast recovery after partial ACK. */
2221
2222 static int tcp_try_undo_partial(struct sock *sk, int acked)
2223 {
2224         struct tcp_sock *tp = tcp_sk(sk);
2225         /* Partial ACK arrived. Force Hoe's retransmit. */
2226         int failed = tcp_is_reno(tp) || tp->fackets_out>tp->reordering;
2227
2228         if (tcp_may_undo(tp)) {
2229                 /* Plain luck! Hole if filled with delayed
2230                  * packet, rather than with a retransmit.
2231                  */
2232                 if (tp->retrans_out == 0)
2233                         tp->retrans_stamp = 0;
2234
2235                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2236
2237                 DBGUNDO(sk, "Hoe");
2238                 tcp_undo_cwr(sk, 0);
2239                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
2240
2241                 /* So... Do not make Hoe's retransmit yet.
2242                  * If the first packet was delayed, the rest
2243                  * ones are most probably delayed as well.
2244                  */
2245                 failed = 0;
2246         }
2247         return failed;
2248 }
2249
2250 /* Undo during loss recovery after partial ACK. */
2251 static int tcp_try_undo_loss(struct sock *sk)
2252 {
2253         struct tcp_sock *tp = tcp_sk(sk);
2254
2255         if (tcp_may_undo(tp)) {
2256                 struct sk_buff *skb;
2257                 tcp_for_write_queue(skb, sk) {
2258                         if (skb == tcp_send_head(sk))
2259                                 break;
2260                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2261                 }
2262
2263                 tcp_clear_all_retrans_hints(tp);
2264
2265                 DBGUNDO(sk, "partial loss");
2266                 tp->lost_out = 0;
2267                 tcp_undo_cwr(sk, 1);
2268                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
2269                 inet_csk(sk)->icsk_retransmits = 0;
2270                 tp->undo_marker = 0;
2271                 if (tcp_is_sack(tp))
2272                         tcp_set_ca_state(sk, TCP_CA_Open);
2273                 return 1;
2274         }
2275         return 0;
2276 }
2277
2278 static inline void tcp_complete_cwr(struct sock *sk)
2279 {
2280         struct tcp_sock *tp = tcp_sk(sk);
2281         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2282         tp->snd_cwnd_stamp = tcp_time_stamp;
2283         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2284 }
2285
2286 static void tcp_try_to_open(struct sock *sk, int flag)
2287 {
2288         struct tcp_sock *tp = tcp_sk(sk);
2289
2290         tcp_verify_left_out(tp);
2291
2292         if (tp->retrans_out == 0)
2293                 tp->retrans_stamp = 0;
2294
2295         if (flag&FLAG_ECE)
2296                 tcp_enter_cwr(sk, 1);
2297
2298         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2299                 int state = TCP_CA_Open;
2300
2301                 if (tcp_left_out(tp) || tp->retrans_out || tp->undo_marker)
2302                         state = TCP_CA_Disorder;
2303
2304                 if (inet_csk(sk)->icsk_ca_state != state) {
2305                         tcp_set_ca_state(sk, state);
2306                         tp->high_seq = tp->snd_nxt;
2307                 }
2308                 tcp_moderate_cwnd(tp);
2309         } else {
2310                 tcp_cwnd_down(sk, flag);
2311         }
2312 }
2313
2314 static void tcp_mtup_probe_failed(struct sock *sk)
2315 {
2316         struct inet_connection_sock *icsk = inet_csk(sk);
2317
2318         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2319         icsk->icsk_mtup.probe_size = 0;
2320 }
2321
2322 static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
2323 {
2324         struct tcp_sock *tp = tcp_sk(sk);
2325         struct inet_connection_sock *icsk = inet_csk(sk);
2326
2327         /* FIXME: breaks with very large cwnd */
2328         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2329         tp->snd_cwnd = tp->snd_cwnd *
2330                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2331                        icsk->icsk_mtup.probe_size;
2332         tp->snd_cwnd_cnt = 0;
2333         tp->snd_cwnd_stamp = tcp_time_stamp;
2334         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
2335
2336         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2337         icsk->icsk_mtup.probe_size = 0;
2338         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2339 }
2340
2341
2342 /* Process an event, which can update packets-in-flight not trivially.
2343  * Main goal of this function is to calculate new estimate for left_out,
2344  * taking into account both packets sitting in receiver's buffer and
2345  * packets lost by network.
2346  *
2347  * Besides that it does CWND reduction, when packet loss is detected
2348  * and changes state of machine.
2349  *
2350  * It does _not_ decide what to send, it is made in function
2351  * tcp_xmit_retransmit_queue().
2352  */
2353 static void
2354 tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
2355 {
2356         struct inet_connection_sock *icsk = inet_csk(sk);
2357         struct tcp_sock *tp = tcp_sk(sk);
2358         int is_dupack = !(flag&(FLAG_SND_UNA_ADVANCED|FLAG_NOT_DUP));
2359         int do_lost = is_dupack || ((flag&FLAG_DATA_SACKED) &&
2360                                     (tp->fackets_out > tp->reordering));
2361
2362         /* Some technical things:
2363          * 1. Reno does not count dupacks (sacked_out) automatically. */
2364         if (!tp->packets_out)
2365                 tp->sacked_out = 0;
2366
2367         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2368                 tp->fackets_out = 0;
2369
2370         /* Now state machine starts.
2371          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2372         if (flag&FLAG_ECE)
2373                 tp->prior_ssthresh = 0;
2374
2375         /* B. In all the states check for reneging SACKs. */
2376         if (tp->sacked_out && tcp_check_sack_reneging(sk))
2377                 return;
2378
2379         /* C. Process data loss notification, provided it is valid. */
2380         if ((flag&FLAG_DATA_LOST) &&
2381             before(tp->snd_una, tp->high_seq) &&
2382             icsk->icsk_ca_state != TCP_CA_Open &&
2383             tp->fackets_out > tp->reordering) {
2384                 tcp_mark_head_lost(sk, tp->fackets_out-tp->reordering, tp->high_seq);
2385                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
2386         }
2387
2388         /* D. Check consistency of the current state. */
2389         tcp_verify_left_out(tp);
2390
2391         /* E. Check state exit conditions. State can be terminated
2392          *    when high_seq is ACKed. */
2393         if (icsk->icsk_ca_state == TCP_CA_Open) {
2394                 BUG_TRAP(tp->retrans_out == 0);
2395                 tp->retrans_stamp = 0;
2396         } else if (!before(tp->snd_una, tp->high_seq)) {
2397                 switch (icsk->icsk_ca_state) {
2398                 case TCP_CA_Loss:
2399                         icsk->icsk_retransmits = 0;
2400                         if (tcp_try_undo_recovery(sk))
2401                                 return;
2402                         break;
2403
2404                 case TCP_CA_CWR:
2405                         /* CWR is to be held something *above* high_seq
2406                          * is ACKed for CWR bit to reach receiver. */
2407                         if (tp->snd_una != tp->high_seq) {
2408                                 tcp_complete_cwr(sk);
2409                                 tcp_set_ca_state(sk, TCP_CA_Open);
2410                         }
2411                         break;
2412
2413                 case TCP_CA_Disorder:
2414                         tcp_try_undo_dsack(sk);
2415                         if (!tp->undo_marker ||
2416                             /* For SACK case do not Open to allow to undo
2417                              * catching for all duplicate ACKs. */
2418                             tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
2419                                 tp->undo_marker = 0;
2420                                 tcp_set_ca_state(sk, TCP_CA_Open);
2421                         }
2422                         break;
2423
2424                 case TCP_CA_Recovery:
2425                         if (tcp_is_reno(tp))
2426                                 tcp_reset_reno_sack(tp);
2427                         if (tcp_try_undo_recovery(sk))
2428                                 return;
2429                         tcp_complete_cwr(sk);
2430                         break;
2431                 }
2432         }
2433
2434         /* F. Process state. */
2435         switch (icsk->icsk_ca_state) {
2436         case TCP_CA_Recovery:
2437                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2438                         if (tcp_is_reno(tp) && is_dupack)
2439                                 tcp_add_reno_sack(sk);
2440                 } else
2441                         do_lost = tcp_try_undo_partial(sk, pkts_acked);
2442                 break;
2443         case TCP_CA_Loss:
2444                 if (flag&FLAG_DATA_ACKED)
2445                         icsk->icsk_retransmits = 0;
2446                 if (!tcp_try_undo_loss(sk)) {
2447                         tcp_moderate_cwnd(tp);
2448                         tcp_xmit_retransmit_queue(sk);
2449                         return;
2450                 }
2451                 if (icsk->icsk_ca_state != TCP_CA_Open)
2452                         return;
2453                 /* Loss is undone; fall through to processing in Open state. */
2454         default:
2455                 if (tcp_is_reno(tp)) {
2456                         if (flag & FLAG_SND_UNA_ADVANCED)
2457                                 tcp_reset_reno_sack(tp);
2458                         if (is_dupack)
2459                                 tcp_add_reno_sack(sk);
2460                 }
2461
2462                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
2463                         tcp_try_undo_dsack(sk);
2464
2465                 if (!tcp_time_to_recover(sk)) {
2466                         tcp_try_to_open(sk, flag);
2467                         return;
2468                 }
2469
2470                 /* MTU probe failure: don't reduce cwnd */
2471                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2472                     icsk->icsk_mtup.probe_size &&
2473                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2474                         tcp_mtup_probe_failed(sk);
2475                         /* Restores the reduction we did in tcp_mtup_probe() */
2476                         tp->snd_cwnd++;
2477                         tcp_simple_retransmit(sk);
2478                         return;
2479                 }
2480
2481                 /* Otherwise enter Recovery state */
2482
2483                 if (tcp_is_reno(tp))
2484                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
2485                 else
2486                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
2487
2488                 tp->high_seq = tp->snd_nxt;
2489                 tp->prior_ssthresh = 0;
2490                 tp->undo_marker = tp->snd_una;
2491                 tp->undo_retrans = tp->retrans_out;
2492
2493                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
2494                         if (!(flag&FLAG_ECE))
2495                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2496                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2497                         TCP_ECN_queue_cwr(tp);
2498                 }
2499
2500                 tp->bytes_acked = 0;
2501                 tp->snd_cwnd_cnt = 0;
2502                 tcp_set_ca_state(sk, TCP_CA_Recovery);
2503         }
2504
2505         if (do_lost || tcp_head_timedout(sk))
2506                 tcp_update_scoreboard(sk);
2507         tcp_cwnd_down(sk, flag);
2508         tcp_xmit_retransmit_queue(sk);
2509 }
2510
2511 /* Read draft-ietf-tcplw-high-performance before mucking
2512  * with this code. (Supersedes RFC1323)
2513  */
2514 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
2515 {
2516         /* RTTM Rule: A TSecr value received in a segment is used to
2517          * update the averaged RTT measurement only if the segment
2518          * acknowledges some new data, i.e., only if it advances the
2519          * left edge of the send window.
2520          *
2521          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2522          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
2523          *
2524          * Changed: reset backoff as soon as we see the first valid sample.
2525          * If we do not, we get strongly overestimated rto. With timestamps
2526          * samples are accepted even from very old segments: f.e., when rtt=1
2527          * increases to 8, we retransmit 5 times and after 8 seconds delayed
2528          * answer arrives rto becomes 120 seconds! If at least one of segments
2529          * in window is lost... Voila.                          --ANK (010210)
2530          */
2531         struct tcp_sock *tp = tcp_sk(sk);
2532         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
2533         tcp_rtt_estimator(sk, seq_rtt);
2534         tcp_set_rto(sk);
2535         inet_csk(sk)->icsk_backoff = 0;
2536         tcp_bound_rto(sk);
2537 }
2538
2539 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
2540 {
2541         /* We don't have a timestamp. Can only use
2542          * packets that are not retransmitted to determine
2543          * rtt estimates. Also, we must not reset the
2544          * backoff for rto until we get a non-retransmitted
2545          * packet. This allows us to deal with a situation
2546          * where the network delay has increased suddenly.
2547          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
2548          */
2549
2550         if (flag & FLAG_RETRANS_DATA_ACKED)
2551                 return;
2552
2553         tcp_rtt_estimator(sk, seq_rtt);
2554         tcp_set_rto(sk);
2555         inet_csk(sk)->icsk_backoff = 0;
2556         tcp_bound_rto(sk);
2557 }
2558
2559 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
2560                                       const s32 seq_rtt)
2561 {
2562         const struct tcp_sock *tp = tcp_sk(sk);
2563         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
2564         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
2565                 tcp_ack_saw_tstamp(sk, flag);
2566         else if (seq_rtt >= 0)
2567                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
2568 }
2569
2570 static void tcp_cong_avoid(struct sock *sk, u32 ack,
2571                            u32 in_flight, int good)
2572 {
2573         const struct inet_connection_sock *icsk = inet_csk(sk);
2574         icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight, good);
2575         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2576 }
2577
2578 /* Restart timer after forward progress on connection.
2579  * RFC2988 recommends to restart timer to now+rto.
2580  */
2581 static void tcp_rearm_rto(struct sock *sk)
2582 {
2583         struct tcp_sock *tp = tcp_sk(sk);
2584
2585         if (!tp->packets_out) {
2586                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2587         } else {
2588                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2589         }
2590 }
2591
2592 /* If we get here, the whole TSO packet has not been acked. */
2593 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
2594 {
2595         struct tcp_sock *tp = tcp_sk(sk);
2596         u32 packets_acked;
2597
2598         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
2599
2600         packets_acked = tcp_skb_pcount(skb);
2601         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2602                 return 0;
2603         packets_acked -= tcp_skb_pcount(skb);
2604
2605         if (packets_acked) {
2606                 BUG_ON(tcp_skb_pcount(skb) == 0);
2607                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
2608         }
2609
2610         return packets_acked;
2611 }
2612
2613 /* Remove acknowledged frames from the retransmission queue. If our packet
2614  * is before the ack sequence we can discard it as it's confirmed to have
2615  * arrived at the other end.
2616  */
2617 static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p)
2618 {
2619         struct tcp_sock *tp = tcp_sk(sk);
2620         const struct inet_connection_sock *icsk = inet_csk(sk);
2621         struct sk_buff *skb;
2622         u32 now = tcp_time_stamp;
2623         int fully_acked = 1;
2624         int flag = 0;
2625         int prior_packets = tp->packets_out;
2626         s32 seq_rtt = -1;
2627         ktime_t last_ackt = net_invalid_timestamp();
2628
2629         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
2630                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
2631                 u32 end_seq;
2632                 u32 packets_acked;
2633                 u8 sacked = scb->sacked;
2634
2635                 if (after(scb->end_seq, tp->snd_una)) {
2636                         if (tcp_skb_pcount(skb) == 1 ||
2637                             !after(tp->snd_una, scb->seq))
2638                                 break;
2639
2640                         packets_acked = tcp_tso_acked(sk, skb);
2641                         if (!packets_acked)
2642                                 break;
2643
2644                         fully_acked = 0;
2645                         end_seq = tp->snd_una;
2646                 } else {
2647                         packets_acked = tcp_skb_pcount(skb);
2648                         end_seq = scb->end_seq;
2649                 }
2650
2651                 /* MTU probing checks */
2652                 if (fully_acked && icsk->icsk_mtup.probe_size &&
2653                     !after(tp->mtu_probe.probe_seq_end, scb->end_seq)) {
2654                         tcp_mtup_probe_success(sk, skb);
2655                 }
2656
2657                 if (sacked) {
2658                         if (sacked & TCPCB_RETRANS) {
2659                                 if (sacked & TCPCB_SACKED_RETRANS)
2660                                         tp->retrans_out -= packets_acked;
2661                                 flag |= FLAG_RETRANS_DATA_ACKED;
2662                                 seq_rtt = -1;
2663                                 if ((flag & FLAG_DATA_ACKED) ||
2664                                     (packets_acked > 1))
2665                                         flag |= FLAG_NONHEAD_RETRANS_ACKED;
2666                         } else if (seq_rtt < 0) {
2667                                 seq_rtt = now - scb->when;
2668                                 if (fully_acked)
2669                                         last_ackt = skb->tstamp;
2670                         }
2671
2672                         if (sacked & TCPCB_SACKED_ACKED)
2673                                 tp->sacked_out -= packets_acked;
2674                         if (sacked & TCPCB_LOST)
2675                                 tp->lost_out -= packets_acked;
2676
2677                         if ((sacked & TCPCB_URG) && tp->urg_mode &&
2678                             !before(end_seq, tp->snd_up))
2679                                 tp->urg_mode = 0;
2680                 } else if (seq_rtt < 0) {
2681                         seq_rtt = now - scb->when;
2682                         if (fully_acked)
2683                                 last_ackt = skb->tstamp;
2684                 }
2685                 tp->packets_out -= packets_acked;
2686
2687                 /* Initial outgoing SYN's get put onto the write_queue
2688                  * just like anything else we transmit.  It is not
2689                  * true data, and if we misinform our callers that
2690                  * this ACK acks real data, we will erroneously exit
2691                  * connection startup slow start one packet too
2692                  * quickly.  This is severely frowned upon behavior.
2693                  */
2694                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2695                         flag |= FLAG_DATA_ACKED;
2696                 } else {
2697                         flag |= FLAG_SYN_ACKED;
2698                         tp->retrans_stamp = 0;
2699                 }
2700
2701                 if (!fully_acked)
2702                         break;
2703
2704                 tcp_unlink_write_queue(skb, sk);
2705                 sk_stream_free_skb(sk, skb);
2706                 tcp_clear_all_retrans_hints(tp);
2707         }
2708
2709         if (flag & FLAG_ACKED) {
2710                 u32 pkts_acked = prior_packets - tp->packets_out;
2711                 const struct tcp_congestion_ops *ca_ops
2712                         = inet_csk(sk)->icsk_ca_ops;
2713
2714                 tcp_ack_update_rtt(sk, flag, seq_rtt);
2715                 tcp_rearm_rto(sk);
2716
2717                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
2718                 /* hint's skb might be NULL but we don't need to care */
2719                 tp->fastpath_cnt_hint -= min_t(u32, pkts_acked,
2720                                                tp->fastpath_cnt_hint);
2721                 if (tcp_is_reno(tp))
2722                         tcp_remove_reno_sacks(sk, pkts_acked);
2723
2724                 if (ca_ops->pkts_acked) {
2725                         s32 rtt_us = -1;
2726
2727                         /* Is the ACK triggering packet unambiguous? */
2728                         if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
2729                                 /* High resolution needed and available? */
2730                                 if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
2731                                     !ktime_equal(last_ackt,
2732                                                  net_invalid_timestamp()))
2733                                         rtt_us = ktime_us_delta(ktime_get_real(),
2734                                                                 last_ackt);
2735                                 else if (seq_rtt > 0)
2736                                         rtt_us = jiffies_to_usecs(seq_rtt);
2737                         }
2738
2739                         ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
2740                 }
2741         }
2742
2743 #if FASTRETRANS_DEBUG > 0
2744         BUG_TRAP((int)tp->sacked_out >= 0);
2745         BUG_TRAP((int)tp->lost_out >= 0);
2746         BUG_TRAP((int)tp->retrans_out >= 0);
2747         if (!tp->packets_out && tcp_is_sack(tp)) {
2748                 icsk = inet_csk(sk);
2749                 if (tp->lost_out) {
2750                         printk(KERN_DEBUG "Leak l=%u %d\n",
2751                                tp->lost_out, icsk->icsk_ca_state);
2752                         tp->lost_out = 0;
2753                 }
2754                 if (tp->sacked_out) {
2755                         printk(KERN_DEBUG "Leak s=%u %d\n",
2756                                tp->sacked_out, icsk->icsk_ca_state);
2757                         tp->sacked_out = 0;
2758                 }
2759                 if (tp->retrans_out) {
2760                         printk(KERN_DEBUG "Leak r=%u %d\n",
2761                                tp->retrans_out, icsk->icsk_ca_state);
2762                         tp->retrans_out = 0;
2763                 }
2764         }
2765 #endif
2766         *seq_rtt_p = seq_rtt;
2767         return flag;
2768 }
2769
2770 static void tcp_ack_probe(struct sock *sk)
2771 {
2772         const struct tcp_sock *tp = tcp_sk(sk);
2773         struct inet_connection_sock *icsk = inet_csk(sk);
2774
2775         /* Was it a usable window open? */
2776
2777         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
2778                    tp->snd_una + tp->snd_wnd)) {
2779                 icsk->icsk_backoff = 0;
2780                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2781                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2782                  * This function is not for random using!
2783                  */
2784         } else {
2785                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2786                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2787                                           TCP_RTO_MAX);
2788         }
2789 }
2790
2791 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2792 {
2793         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2794                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2795 }
2796
2797 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2798 {
2799         const struct tcp_sock *tp = tcp_sk(sk);
2800         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2801                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2802 }
2803
2804 /* Check that window update is acceptable.
2805  * The function assumes that snd_una<=ack<=snd_next.
2806  */
2807 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2808                                         const u32 ack_seq, const u32 nwin)
2809 {
2810         return (after(ack, tp->snd_una) ||
2811                 after(ack_seq, tp->snd_wl1) ||
2812                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2813 }
2814
2815 /* Update our send window.
2816  *
2817  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2818  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2819  */
2820 static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
2821                                  u32 ack_seq)
2822 {
2823         struct tcp_sock *tp = tcp_sk(sk);
2824         int flag = 0;
2825         u32 nwin = ntohs(tcp_hdr(skb)->window);
2826
2827         if (likely(!tcp_hdr(skb)->syn))
2828                 nwin <<= tp->rx_opt.snd_wscale;
2829
2830         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2831                 flag |= FLAG_WIN_UPDATE;
2832                 tcp_update_wl(tp, ack, ack_seq);
2833
2834                 if (tp->snd_wnd != nwin) {
2835                         tp->snd_wnd = nwin;
2836
2837                         /* Note, it is the only place, where
2838                          * fast path is recovered for sending TCP.
2839                          */
2840                         tp->pred_flags = 0;
2841                         tcp_fast_path_check(sk);
2842
2843                         if (nwin > tp->max_window) {
2844                                 tp->max_window = nwin;
2845                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
2846                         }
2847                 }
2848         }
2849
2850         tp->snd_una = ack;
2851
2852         return flag;
2853 }
2854
2855 /* A very conservative spurious RTO response algorithm: reduce cwnd and
2856  * continue in congestion avoidance.
2857  */
2858 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
2859 {
2860         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2861         tp->snd_cwnd_cnt = 0;
2862         tp->bytes_acked = 0;
2863         TCP_ECN_queue_cwr(tp);
2864         tcp_moderate_cwnd(tp);
2865 }
2866
2867 /* A conservative spurious RTO response algorithm: reduce cwnd using
2868  * rate halving and continue in congestion avoidance.
2869  */
2870 static void tcp_ratehalving_spur_to_response(struct sock *sk)
2871 {
2872         tcp_enter_cwr(sk, 0);
2873 }
2874
2875 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
2876 {
2877         if (flag&FLAG_ECE)
2878                 tcp_ratehalving_spur_to_response(sk);
2879         else
2880                 tcp_undo_cwr(sk, 1);
2881 }
2882
2883 /* F-RTO spurious RTO detection algorithm (RFC4138)
2884  *
2885  * F-RTO affects during two new ACKs following RTO (well, almost, see inline
2886  * comments). State (ACK number) is kept in frto_counter. When ACK advances
2887  * window (but not to or beyond highest sequence sent before RTO):
2888  *   On First ACK,  send two new segments out.
2889  *   On Second ACK, RTO was likely spurious. Do spurious response (response
2890  *                  algorithm is not part of the F-RTO detection algorithm
2891  *                  given in RFC4138 but can be selected separately).
2892  * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
2893  * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
2894  * of Nagle, this is done using frto_counter states 2 and 3, when a new data
2895  * segment of any size sent during F-RTO, state 2 is upgraded to 3.
2896  *
2897  * Rationale: if the RTO was spurious, new ACKs should arrive from the
2898  * original window even after we transmit two new data segments.
2899  *
2900  * SACK version:
2901  *   on first step, wait until first cumulative ACK arrives, then move to
2902  *   the second step. In second step, the next ACK decides.
2903  *
2904  * F-RTO is implemented (mainly) in four functions:
2905  *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
2906  *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
2907  *     called when tcp_use_frto() showed green light
2908  *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
2909  *   - tcp_enter_frto_loss() is called if there is not enough evidence
2910  *     to prove that the RTO is indeed spurious. It transfers the control
2911  *     from F-RTO to the conventional RTO recovery
2912  */
2913 static int tcp_process_frto(struct sock *sk, int flag)
2914 {
2915         struct tcp_sock *tp = tcp_sk(sk);
2916
2917         tcp_verify_left_out(tp);
2918
2919         /* Duplicate the behavior from Loss state (fastretrans_alert) */
2920         if (flag&FLAG_DATA_ACKED)
2921                 inet_csk(sk)->icsk_retransmits = 0;
2922
2923         if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
2924             ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
2925                 tp->undo_marker = 0;
2926
2927         if (!before(tp->snd_una, tp->frto_highmark)) {
2928                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
2929                 return 1;
2930         }
2931
2932         if (!IsSackFrto() || tcp_is_reno(tp)) {
2933                 /* RFC4138 shortcoming in step 2; should also have case c):
2934                  * ACK isn't duplicate nor advances window, e.g., opposite dir
2935                  * data, winupdate
2936                  */
2937                 if (!(flag&FLAG_ANY_PROGRESS) && (flag&FLAG_NOT_DUP))
2938                         return 1;
2939
2940                 if (!(flag&FLAG_DATA_ACKED)) {
2941                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
2942                                             flag);
2943                         return 1;
2944                 }
2945         } else {
2946                 if (!(flag&FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
2947                         /* Prevent sending of new data. */
2948                         tp->snd_cwnd = min(tp->snd_cwnd,
2949                                            tcp_packets_in_flight(tp));
2950                         return 1;
2951                 }
2952
2953                 if ((tp->frto_counter >= 2) &&
2954                     (!(flag&FLAG_FORWARD_PROGRESS) ||
2955                      ((flag&FLAG_DATA_SACKED) && !(flag&FLAG_ONLY_ORIG_SACKED)))) {
2956                         /* RFC4138 shortcoming (see comment above) */
2957                         if (!(flag&FLAG_FORWARD_PROGRESS) && (flag&FLAG_NOT_DUP))
2958                                 return 1;
2959
2960                         tcp_enter_frto_loss(sk, 3, flag);
2961                         return 1;
2962                 }
2963         }
2964
2965         if (tp->frto_counter == 1) {
2966                 /* Sending of the next skb must be allowed or no FRTO */
2967                 if (!tcp_send_head(sk) ||
2968                     after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
2969                                      tp->snd_una + tp->snd_wnd)) {
2970                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3),
2971                                             flag);
2972                         return 1;
2973                 }
2974
2975                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2976                 tp->frto_counter = 2;
2977                 return 1;
2978         } else {
2979                 switch (sysctl_tcp_frto_response) {
2980                 case 2:
2981                         tcp_undo_spur_to_response(sk, flag);
2982                         break;
2983                 case 1:
2984                         tcp_conservative_spur_to_response(tp);
2985                         break;
2986                 default:
2987                         tcp_ratehalving_spur_to_response(sk);
2988                         break;
2989                 }
2990                 tp->frto_counter = 0;
2991                 tp->undo_marker = 0;
2992                 NET_INC_STATS_BH(LINUX_MIB_TCPSPURIOUSRTOS);
2993         }
2994         return 0;
2995 }
2996
2997 /* This routine deals with incoming acks, but not outgoing ones. */
2998 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2999 {
3000         struct inet_connection_sock *icsk = inet_csk(sk);
3001         struct tcp_sock *tp = tcp_sk(sk);
3002         u32 prior_snd_una = tp->snd_una;
3003         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3004         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3005         u32 prior_in_flight;
3006         s32 seq_rtt;
3007         int prior_packets;
3008         int frto_cwnd = 0;
3009
3010         /* If the ack is newer than sent or older than previous acks
3011          * then we can probably ignore it.
3012          */
3013         if (after(ack, tp->snd_nxt))
3014                 goto uninteresting_ack;
3015
3016         if (before(ack, prior_snd_una))
3017                 goto old_ack;
3018
3019         if (after(ack, prior_snd_una))
3020                 flag |= FLAG_SND_UNA_ADVANCED;
3021
3022         if (sysctl_tcp_abc) {
3023                 if (icsk->icsk_ca_state < TCP_CA_CWR)
3024                         tp->bytes_acked += ack - prior_snd_una;
3025                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
3026                         /* we assume just one segment left network */
3027                         tp->bytes_acked += min(ack - prior_snd_una, tp->mss_cache);
3028         }
3029
3030         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3031                 /* Window is constant, pure forward advance.
3032                  * No more checks are required.
3033                  * Note, we use the fact that SND.UNA>=SND.WL2.
3034                  */
3035                 tcp_update_wl(tp, ack, ack_seq);
3036                 tp->snd_una = ack;
3037                 flag |= FLAG_WIN_UPDATE;
3038
3039                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3040
3041                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
3042         } else {
3043                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3044                         flag |= FLAG_DATA;
3045                 else
3046                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
3047
3048                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3049
3050                 if (TCP_SKB_CB(skb)->sacked)
3051                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3052
3053                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3054                         flag |= FLAG_ECE;
3055
3056                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3057         }
3058
3059         /* We passed data and got it acked, remove any soft error
3060          * log. Something worked...
3061          */
3062         sk->sk_err_soft = 0;
3063         tp->rcv_tstamp = tcp_time_stamp;
3064         prior_packets = tp->packets_out;
3065         if (!prior_packets)
3066                 goto no_queue;
3067
3068         prior_in_flight = tcp_packets_in_flight(tp);
3069
3070         /* See if we can take anything off of the retransmit queue. */
3071         flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
3072
3073         /* Guarantee sacktag reordering detection against wrap-arounds */
3074         if (before(tp->frto_highmark, tp->snd_una))
3075                 tp->frto_highmark = 0;
3076         if (tp->frto_counter)
3077                 frto_cwnd = tcp_process_frto(sk, flag);
3078
3079         if (tcp_ack_is_dubious(sk, flag)) {
3080                 /* Advance CWND, if state allows this. */
3081                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3082                     tcp_may_raise_cwnd(sk, flag))
3083                         tcp_cong_avoid(sk, ack, prior_in_flight, 0);
3084                 tcp_fastretrans_alert(sk, prior_packets - tp->packets_out, flag);
3085         } else {
3086                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3087                         tcp_cong_avoid(sk, ack, prior_in_flight, 1);
3088         }
3089
3090         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
3091                 dst_confirm(sk->sk_dst_cache);
3092
3093         return 1;
3094
3095 no_queue:
3096         icsk->icsk_probes_out = 0;
3097
3098         /* If this ack opens up a zero window, clear backoff.  It was
3099          * being used to time the probes, and is probably far higher than
3100          * it needs to be for normal retransmission.
3101          */
3102         if (tcp_send_head(sk))
3103                 tcp_ack_probe(sk);
3104         return 1;
3105
3106 old_ack:
3107         if (TCP_SKB_CB(skb)->sacked)
3108                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3109
3110 uninteresting_ack:
3111         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3112         return 0;
3113 }
3114
3115
3116 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3117  * But, this can also be called on packets in the established flow when
3118  * the fast version below fails.
3119  */
3120 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
3121 {
3122         unsigned char *ptr;
3123         struct tcphdr *th = tcp_hdr(skb);
3124         int length=(th->doff*4)-sizeof(struct tcphdr);
3125
3126         ptr = (unsigned char *)(th + 1);
3127         opt_rx->saw_tstamp = 0;
3128
3129         while (length > 0) {
3130                 int opcode=*ptr++;
3131                 int opsize;
3132
3133                 switch (opcode) {
3134                         case TCPOPT_EOL:
3135                                 return;
3136                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3137                                 length--;
3138                                 continue;
3139                         default:
3140                                 opsize=*ptr++;
3141                                 if (opsize < 2) /* "silly options" */
3142                                         return;
3143                                 if (opsize > length)
3144                                         return; /* don't parse partial options */
3145                                 switch (opcode) {
3146                                 case TCPOPT_MSS:
3147                                         if (opsize==TCPOLEN_MSS && th->syn && !estab) {
3148                                                 u16 in_mss = ntohs(get_unaligned((__be16 *)ptr));
3149                                                 if (in_mss) {
3150                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
3151                                                                 in_mss = opt_rx->user_mss;
3152                                                         opt_rx->mss_clamp = in_mss;
3153                                                 }
3154                                         }
3155                                         break;
3156                                 case TCPOPT_WINDOW:
3157                                         if (opsize==TCPOLEN_WINDOW && th->syn && !estab)
3158                                                 if (sysctl_tcp_window_scaling) {
3159                                                         __u8 snd_wscale = *(__u8 *) ptr;
3160                                                         opt_rx->wscale_ok = 1;
3161                                                         if (snd_wscale > 14) {
3162                                                                 if (net_ratelimit())
3163                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
3164                                                                                "scaling value %d >14 received.\n",
3165                                                                                snd_wscale);
3166                                                                 snd_wscale = 14;
3167                                                         }
3168                                                         opt_rx->snd_wscale = snd_wscale;
3169                                                 }
3170                                         break;
3171                                 case TCPOPT_TIMESTAMP:
3172                                         if (opsize==TCPOLEN_TIMESTAMP) {
3173                                                 if ((estab && opt_rx->tstamp_ok) ||
3174                                                     (!estab && sysctl_tcp_timestamps)) {
3175                                                         opt_rx->saw_tstamp = 1;
3176                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__be32 *)ptr));
3177                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4)));
3178                                                 }
3179                                         }
3180                                         break;
3181                                 case TCPOPT_SACK_PERM:
3182                                         if (opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
3183                                                 if (sysctl_tcp_sack) {
3184                                                         opt_rx->sack_ok = 1;
3185                                                         tcp_sack_reset(opt_rx);
3186                                                 }
3187                                         }
3188                                         break;
3189
3190                                 case TCPOPT_SACK:
3191                                         if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3192                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3193                                            opt_rx->sack_ok) {
3194                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3195                                         }
3196                                         break;
3197 #ifdef CONFIG_TCP_MD5SIG
3198                                 case TCPOPT_MD5SIG:
3199                                         /*
3200                                          * The MD5 Hash has already been
3201                                          * checked (see tcp_v{4,6}_do_rcv()).
3202                                          */
3203                                         break;
3204 #endif
3205                                 }
3206
3207                                 ptr+=opsize-2;
3208                                 length-=opsize;
3209                 }
3210         }
3211 }
3212
3213 /* Fast parse options. This hopes to only see timestamps.
3214  * If it is wrong it falls back on tcp_parse_options().
3215  */
3216 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
3217                                   struct tcp_sock *tp)
3218 {
3219         if (th->doff == sizeof(struct tcphdr)>>2) {
3220                 tp->rx_opt.saw_tstamp = 0;
3221                 return 0;
3222         } else if (tp->rx_opt.tstamp_ok &&
3223                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
3224                 __be32 *ptr = (__be32 *)(th + 1);
3225                 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3226                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3227                         tp->rx_opt.saw_tstamp = 1;
3228                         ++ptr;
3229                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
3230                         ++ptr;
3231                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3232                         return 1;
3233                 }
3234         }
3235         tcp_parse_options(skb, &tp->rx_opt, 1);
3236         return 1;
3237 }
3238
3239 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
3240 {
3241         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3242         tp->rx_opt.ts_recent_stamp = get_seconds();
3243 }
3244
3245 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3246 {
3247         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3248                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3249                  * extra check below makes sure this can only happen
3250                  * for pure ACK frames.  -DaveM
3251                  *
3252                  * Not only, also it occurs for expired timestamps.
3253                  */
3254
3255                 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
3256                    get_seconds() >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
3257                         tcp_store_ts_recent(tp);
3258         }
3259 }
3260
3261 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3262  *
3263  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3264  * it can pass through stack. So, the following predicate verifies that
3265  * this segment is not used for anything but congestion avoidance or
3266  * fast retransmit. Moreover, we even are able to eliminate most of such
3267  * second order effects, if we apply some small "replay" window (~RTO)
3268  * to timestamp space.
3269  *
3270  * All these measures still do not guarantee that we reject wrapped ACKs
3271  * on networks with high bandwidth, when sequence space is recycled fastly,
3272  * but it guarantees that such events will be very rare and do not affect
3273  * connection seriously. This doesn't look nice, but alas, PAWS is really
3274  * buggy extension.
3275  *
3276  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3277  * states that events when retransmit arrives after original data are rare.
3278  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3279  * the biggest problem on large power networks even with minor reordering.
3280  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3281  * up to bandwidth of 18Gigabit/sec. 8) ]
3282  */
3283
3284 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3285 {
3286         struct tcp_sock *tp = tcp_sk(sk);
3287         struct tcphdr *th = tcp_hdr(skb);
3288         u32 seq = TCP_SKB_CB(skb)->seq;
3289         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3290
3291         return (/* 1. Pure ACK with correct sequence number. */
3292                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3293
3294                 /* 2. ... and duplicate ACK. */
3295                 ack == tp->snd_una &&
3296
3297                 /* 3. ... and does not update window. */
3298                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3299
3300                 /* 4. ... and sits in replay window. */
3301                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3302 }
3303
3304 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
3305 {
3306         const struct tcp_sock *tp = tcp_sk(sk);
3307         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
3308                 get_seconds() < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
3309                 !tcp_disordered_ack(sk, skb));
3310 }
3311
3312 /* Check segment sequence number for validity.
3313  *
3314  * Segment controls are considered valid, if the segment
3315  * fits to the window after truncation to the window. Acceptability
3316  * of data (and SYN, FIN, of course) is checked separately.
3317  * See tcp_data_queue(), for example.
3318  *
3319  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3320  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3321  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3322  * (borrowed from freebsd)
3323  */
3324
3325 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
3326 {
3327         return  !before(end_seq, tp->rcv_wup) &&
3328                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3329 }
3330
3331 /* When we get a reset we do this. */
3332 static void tcp_reset(struct sock *sk)
3333 {
3334         /* We want the right error as BSD sees it (and indeed as we do). */
3335         switch (sk->sk_state) {
3336                 case TCP_SYN_SENT:
3337                         sk->sk_err = ECONNREFUSED;
3338                         break;
3339                 case TCP_CLOSE_WAIT:
3340                         sk->sk_err = EPIPE;
3341                         break;
3342                 case TCP_CLOSE:
3343                         return;
3344                 default:
3345                         sk->sk_err = ECONNRESET;
3346         }
3347
3348         if (!sock_flag(sk, SOCK_DEAD))
3349                 sk->sk_error_report(sk);
3350
3351         tcp_done(sk);
3352 }
3353
3354 /*
3355  *      Process the FIN bit. This now behaves as it is supposed to work
3356  *      and the FIN takes effect when it is validly part of sequence
3357  *      space. Not before when we get holes.
3358  *
3359  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3360  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3361  *      TIME-WAIT)
3362  *
3363  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3364  *      close and we go into CLOSING (and later onto TIME-WAIT)
3365  *
3366  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3367  */
3368 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
3369 {
3370         struct tcp_sock *tp = tcp_sk(sk);
3371
3372         inet_csk_schedule_ack(sk);
3373
3374         sk->sk_shutdown |= RCV_SHUTDOWN;
3375         sock_set_flag(sk, SOCK_DONE);
3376
3377         switch (sk->sk_state) {
3378                 case TCP_SYN_RECV:
3379                 case TCP_ESTABLISHED:
3380                         /* Move to CLOSE_WAIT */
3381                         tcp_set_state(sk, TCP_CLOSE_WAIT);
3382                         inet_csk(sk)->icsk_ack.pingpong = 1;
3383                         break;
3384
3385                 case TCP_CLOSE_WAIT:
3386                 case TCP_CLOSING:
3387                         /* Received a retransmission of the FIN, do
3388                          * nothing.
3389                          */
3390                         break;
3391                 case TCP_LAST_ACK:
3392                         /* RFC793: Remain in the LAST-ACK state. */
3393                         break;
3394
3395                 case TCP_FIN_WAIT1:
3396                         /* This case occurs when a simultaneous close
3397                          * happens, we must ack the received FIN and
3398                          * enter the CLOSING state.
3399                          */
3400                         tcp_send_ack(sk);
3401                         tcp_set_state(sk, TCP_CLOSING);
3402                         break;
3403                 case TCP_FIN_WAIT2:
3404                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
3405                         tcp_send_ack(sk);
3406                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
3407                         break;
3408                 default:
3409                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
3410                          * cases we should never reach this piece of code.
3411                          */
3412                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
3413                                __FUNCTION__, sk->sk_state);
3414                         break;
3415         }
3416
3417         /* It _is_ possible, that we have something out-of-order _after_ FIN.
3418          * Probably, we should reset in this case. For now drop them.
3419          */
3420         __skb_queue_purge(&tp->out_of_order_queue);
3421         if (tcp_is_sack(tp))
3422                 tcp_sack_reset(&tp->rx_opt);
3423         sk_stream_mem_reclaim(sk);
3424
3425         if (!sock_flag(sk, SOCK_DEAD)) {
3426                 sk->sk_state_change(sk);
3427
3428                 /* Do not send POLL_HUP for half duplex close. */
3429                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
3430                     sk->sk_state == TCP_CLOSE)
3431                         sk_wake_async(sk, 1, POLL_HUP);
3432                 else
3433                         sk_wake_async(sk, 1, POLL_IN);
3434         }
3435 }
3436
3437 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
3438 {
3439         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
3440                 if (before(seq, sp->start_seq))
3441                         sp->start_seq = seq;
3442                 if (after(end_seq, sp->end_seq))
3443                         sp->end_seq = end_seq;
3444                 return 1;
3445         }
3446         return 0;
3447 }
3448
3449 static void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
3450 {
3451         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3452                 if (before(seq, tp->rcv_nxt))
3453                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
3454                 else
3455                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
3456
3457                 tp->rx_opt.dsack = 1;
3458                 tp->duplicate_sack[0].start_seq = seq;
3459                 tp->duplicate_sack[0].end_seq = end_seq;
3460                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
3461         }
3462 }
3463
3464 static void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
3465 {
3466         if (!tp->rx_opt.dsack)
3467                 tcp_dsack_set(tp, seq, end_seq);
3468         else
3469                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
3470 }
3471
3472 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
3473 {
3474         struct tcp_sock *tp = tcp_sk(sk);
3475
3476         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
3477             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3478                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3479                 tcp_enter_quickack_mode(sk);
3480
3481                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3482                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3483
3484                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
3485                                 end_seq = tp->rcv_nxt;
3486                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
3487                 }
3488         }
3489
3490         tcp_send_ack(sk);
3491 }
3492
3493 /* These routines update the SACK block as out-of-order packets arrive or
3494  * in-order packets close up the sequence space.
3495  */
3496 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
3497 {
3498         int this_sack;
3499         struct tcp_sack_block *sp = &tp->selective_acks[0];
3500         struct tcp_sack_block *swalk = sp+1;
3501
3502         /* See if the recent change to the first SACK eats into
3503          * or hits the sequence space of other SACK blocks, if so coalesce.
3504          */
3505         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
3506                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
3507                         int i;
3508
3509                         /* Zap SWALK, by moving every further SACK up by one slot.
3510                          * Decrease num_sacks.
3511                          */
3512                         tp->rx_opt.num_sacks--;
3513                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3514                         for (i=this_sack; i < tp->rx_opt.num_sacks; i++)
3515                                 sp[i] = sp[i+1];
3516                         continue;
3517                 }
3518                 this_sack++, swalk++;
3519         }
3520 }
3521
3522 static inline void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
3523 {
3524         __u32 tmp;
3525
3526         tmp = sack1->start_seq;
3527         sack1->start_seq = sack2->start_seq;
3528         sack2->start_seq = tmp;
3529
3530         tmp = sack1->end_seq;
3531         sack1->end_seq = sack2->end_seq;
3532         sack2->end_seq = tmp;
3533 }
3534
3535 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
3536 {
3537         struct tcp_sock *tp = tcp_sk(sk);
3538         struct tcp_sack_block *sp = &tp->selective_acks[0];
3539         int cur_sacks = tp->rx_opt.num_sacks;
3540         int this_sack;
3541
3542         if (!cur_sacks)
3543                 goto new_sack;
3544
3545         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
3546                 if (tcp_sack_extend(sp, seq, end_seq)) {
3547                         /* Rotate this_sack to the first one. */
3548                         for (; this_sack>0; this_sack--, sp--)
3549                                 tcp_sack_swap(sp, sp-1);
3550                         if (cur_sacks > 1)
3551                                 tcp_sack_maybe_coalesce(tp);
3552                         return;
3553                 }
3554         }
3555
3556         /* Could not find an adjacent existing SACK, build a new one,
3557          * put it at the front, and shift everyone else down.  We
3558          * always know there is at least one SACK present already here.
3559          *
3560          * If the sack array is full, forget about the last one.
3561          */
3562         if (this_sack >= 4) {
3563                 this_sack--;
3564                 tp->rx_opt.num_sacks--;
3565                 sp--;
3566         }
3567         for (; this_sack > 0; this_sack--, sp--)
3568                 *sp = *(sp-1);
3569
3570 new_sack:
3571         /* Build the new head SACK, and we're done. */
3572         sp->start_seq = seq;
3573         sp->end_seq = end_seq;
3574         tp->rx_opt.num_sacks++;
3575         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3576 }
3577
3578 /* RCV.NXT advances, some SACKs should be eaten. */
3579
3580 static void tcp_sack_remove(struct tcp_sock *tp)
3581 {
3582         struct tcp_sack_block *sp = &tp->selective_acks[0];
3583         int num_sacks = tp->rx_opt.num_sacks;
3584         int this_sack;
3585
3586         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
3587         if (skb_queue_empty(&tp->out_of_order_queue)) {
3588                 tp->rx_opt.num_sacks = 0;
3589                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
3590                 return;
3591         }
3592
3593         for (this_sack = 0; this_sack < num_sacks; ) {
3594                 /* Check if the start of the sack is covered by RCV.NXT. */
3595                 if (!before(tp->rcv_nxt, sp->start_seq)) {
3596                         int i;
3597
3598                         /* RCV.NXT must cover all the block! */
3599                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
3600
3601                         /* Zap this SACK, by moving forward any other SACKS. */
3602                         for (i=this_sack+1; i < num_sacks; i++)
3603                                 tp->selective_acks[i-1] = tp->selective_acks[i];
3604                         num_sacks--;
3605                         continue;
3606                 }
3607                 this_sack++;
3608                 sp++;
3609         }
3610         if (num_sacks != tp->rx_opt.num_sacks) {
3611                 tp->rx_opt.num_sacks = num_sacks;
3612                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3613         }
3614 }
3615
3616 /* This one checks to see if we can put data from the
3617  * out_of_order queue into the receive_queue.
3618  */
3619 static void tcp_ofo_queue(struct sock *sk)
3620 {
3621         struct tcp_sock *tp = tcp_sk(sk);
3622         __u32 dsack_high = tp->rcv_nxt;
3623         struct sk_buff *skb;
3624
3625         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
3626                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
3627                         break;
3628
3629                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
3630                         __u32 dsack = dsack_high;
3631                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
3632                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
3633                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
3634                 }
3635
3636                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3637                         SOCK_DEBUG(sk, "ofo packet was already received \n");
3638                         __skb_unlink(skb, &tp->out_of_order_queue);
3639                         __kfree_skb(skb);
3640                         continue;
3641                 }
3642                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
3643                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3644                            TCP_SKB_CB(skb)->end_seq);
3645
3646                 __skb_unlink(skb, &tp->out_of_order_queue);
3647                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3648                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3649                 if (tcp_hdr(skb)->fin)
3650                         tcp_fin(skb, sk, tcp_hdr(skb));
3651         }
3652 }
3653
3654 static int tcp_prune_queue(struct sock *sk);
3655
3656 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
3657 {
3658         struct tcphdr *th = tcp_hdr(skb);
3659         struct tcp_sock *tp = tcp_sk(sk);
3660         int eaten = -1;
3661
3662         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
3663                 goto drop;
3664
3665         __skb_pull(skb, th->doff*4);
3666
3667         TCP_ECN_accept_cwr(tp, skb);
3668
3669         if (tp->rx_opt.dsack) {
3670                 tp->rx_opt.dsack = 0;
3671                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
3672                                                     4 - tp->rx_opt.tstamp_ok);
3673         }
3674
3675         /*  Queue data for delivery to the user.
3676          *  Packets in sequence go to the receive queue.
3677          *  Out of sequence packets to the out_of_order_queue.
3678          */
3679         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3680                 if (tcp_receive_window(tp) == 0)
3681                         goto out_of_window;
3682
3683                 /* Ok. In sequence. In window. */
3684                 if (tp->ucopy.task == current &&
3685                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
3686                     sock_owned_by_user(sk) && !tp->urg_data) {
3687                         int chunk = min_t(unsigned int, skb->len,
3688                                                         tp->ucopy.len);
3689
3690                         __set_current_state(TASK_RUNNING);
3691
3692                         local_bh_enable();
3693                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
3694                                 tp->ucopy.len -= chunk;
3695                                 tp->copied_seq += chunk;
3696                                 eaten = (chunk == skb->len && !th->fin);
3697                                 tcp_rcv_space_adjust(sk);
3698                         }
3699                         local_bh_disable();
3700                 }
3701
3702                 if (eaten <= 0) {
3703 queue_and_out:
3704                         if (eaten < 0 &&
3705                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3706                              !sk_stream_rmem_schedule(sk, skb))) {
3707                                 if (tcp_prune_queue(sk) < 0 ||
3708                                     !sk_stream_rmem_schedule(sk, skb))
3709                                         goto drop;
3710                         }
3711                         sk_stream_set_owner_r(skb, sk);
3712                         __skb_queue_tail(&sk->sk_receive_queue, skb);
3713                 }
3714                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3715                 if (skb->len)
3716                         tcp_event_data_recv(sk, skb);
3717                 if (th->fin)
3718                         tcp_fin(skb, sk, th);
3719
3720                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
3721                         tcp_ofo_queue(sk);
3722
3723                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
3724                          * gap in queue is filled.
3725                          */
3726                         if (skb_queue_empty(&tp->out_of_order_queue))
3727                                 inet_csk(sk)->icsk_ack.pingpong = 0;
3728                 }
3729
3730                 if (tp->rx_opt.num_sacks)
3731                         tcp_sack_remove(tp);
3732
3733                 tcp_fast_path_check(sk);
3734
3735                 if (eaten > 0)
3736                         __kfree_skb(skb);
3737                 else if (!sock_flag(sk, SOCK_DEAD))
3738                         sk->sk_data_ready(sk, 0);
3739                 return;
3740         }
3741
3742         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3743                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3744                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3745                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3746
3747 out_of_window:
3748                 tcp_enter_quickack_mode(sk);
3749                 inet_csk_schedule_ack(sk);
3750 drop:
3751                 __kfree_skb(skb);
3752                 return;
3753         }
3754
3755         /* Out of window. F.e. zero window probe. */
3756         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3757                 goto out_of_window;
3758
3759         tcp_enter_quickack_mode(sk);
3760
3761         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3762                 /* Partial packet, seq < rcv_next < end_seq */
3763                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3764                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3765                            TCP_SKB_CB(skb)->end_seq);
3766
3767                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3768
3769                 /* If window is closed, drop tail of packet. But after
3770                  * remembering D-SACK for its head made in previous line.
3771                  */
3772                 if (!tcp_receive_window(tp))
3773                         goto out_of_window;
3774                 goto queue_and_out;
3775         }
3776
3777         TCP_ECN_check_ce(tp, skb);
3778
3779         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3780             !sk_stream_rmem_schedule(sk, skb)) {
3781                 if (tcp_prune_queue(sk) < 0 ||
3782                     !sk_stream_rmem_schedule(sk, skb))
3783                         goto drop;
3784         }
3785
3786         /* Disable header prediction. */
3787         tp->pred_flags = 0;
3788         inet_csk_schedule_ack(sk);
3789
3790         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3791                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3792
3793         sk_stream_set_owner_r(skb, sk);
3794
3795         if (!skb_peek(&tp->out_of_order_queue)) {
3796                 /* Initial out of order segment, build 1 SACK. */
3797                 if (tcp_is_sack(tp)) {
3798                         tp->rx_opt.num_sacks = 1;
3799                         tp->rx_opt.dsack     = 0;
3800                         tp->rx_opt.eff_sacks = 1;
3801                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3802                         tp->selective_acks[0].end_seq =
3803                                                 TCP_SKB_CB(skb)->end_seq;
3804                 }
3805                 __skb_queue_head(&tp->out_of_order_queue,skb);
3806         } else {
3807                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3808                 u32 seq = TCP_SKB_CB(skb)->seq;
3809                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3810
3811                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3812                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3813
3814                         if (!tp->rx_opt.num_sacks ||
3815                             tp->selective_acks[0].end_seq != seq)
3816                                 goto add_sack;
3817
3818                         /* Common case: data arrive in order after hole. */
3819                         tp->selective_acks[0].end_seq = end_seq;
3820                         return;
3821                 }
3822
3823                 /* Find place to insert this segment. */
3824                 do {
3825                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3826                                 break;
3827                 } while ((skb1 = skb1->prev) !=
3828                          (struct sk_buff*)&tp->out_of_order_queue);
3829
3830                 /* Do skb overlap to previous one? */
3831                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3832                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3833                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3834                                 /* All the bits are present. Drop. */
3835                                 __kfree_skb(skb);
3836                                 tcp_dsack_set(tp, seq, end_seq);
3837                                 goto add_sack;
3838                         }
3839                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3840                                 /* Partial overlap. */
3841                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3842                         } else {
3843                                 skb1 = skb1->prev;
3844                         }
3845                 }
3846                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3847
3848                 /* And clean segments covered by new one as whole. */
3849                 while ((skb1 = skb->next) !=
3850                        (struct sk_buff*)&tp->out_of_order_queue &&
3851                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3852                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3853                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3854                                break;
3855                        }
3856                        __skb_unlink(skb1, &tp->out_of_order_queue);
3857                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3858                        __kfree_skb(skb1);
3859                 }
3860
3861 add_sack:
3862                 if (tcp_is_sack(tp))
3863                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3864         }
3865 }
3866
3867 /* Collapse contiguous sequence of skbs head..tail with
3868  * sequence numbers start..end.
3869  * Segments with FIN/SYN are not collapsed (only because this
3870  * simplifies code)
3871  */
3872 static void
3873 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3874              struct sk_buff *head, struct sk_buff *tail,
3875              u32 start, u32 end)
3876 {
3877         struct sk_buff *skb;
3878
3879         /* First, check that queue is collapsible and find
3880          * the point where collapsing can be useful. */
3881         for (skb = head; skb != tail; ) {
3882                 /* No new bits? It is possible on ofo queue. */
3883                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3884                         struct sk_buff *next = skb->next;
3885                         __skb_unlink(skb, list);
3886                         __kfree_skb(skb);
3887                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3888                         skb = next;
3889                         continue;
3890                 }
3891
3892                 /* The first skb to collapse is:
3893                  * - not SYN/FIN and
3894                  * - bloated or contains data before "start" or
3895                  *   overlaps to the next one.
3896                  */
3897                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
3898                     (tcp_win_from_space(skb->truesize) > skb->len ||
3899                      before(TCP_SKB_CB(skb)->seq, start) ||
3900                      (skb->next != tail &&
3901                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3902                         break;
3903
3904                 /* Decided to skip this, advance start seq. */
3905                 start = TCP_SKB_CB(skb)->end_seq;
3906                 skb = skb->next;
3907         }
3908         if (skb == tail || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
3909                 return;
3910
3911         while (before(start, end)) {
3912                 struct sk_buff *nskb;
3913                 int header = skb_headroom(skb);
3914                 int copy = SKB_MAX_ORDER(header, 0);
3915
3916                 /* Too big header? This can happen with IPv6. */
3917                 if (copy < 0)
3918                         return;
3919                 if (end-start < copy)
3920                         copy = end-start;
3921                 nskb = alloc_skb(copy+header, GFP_ATOMIC);
3922                 if (!nskb)
3923                         return;
3924
3925                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
3926                 skb_set_network_header(nskb, (skb_network_header(skb) -
3927                                               skb->head));
3928                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
3929                                                 skb->head));
3930                 skb_reserve(nskb, header);
3931                 memcpy(nskb->head, skb->head, header);
3932                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3933                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3934                 __skb_insert(nskb, skb->prev, skb, list);
3935                 sk_stream_set_owner_r(nskb, sk);
3936
3937                 /* Copy data, releasing collapsed skbs. */
3938                 while (copy > 0) {
3939                         int offset = start - TCP_SKB_CB(skb)->seq;
3940                         int size = TCP_SKB_CB(skb)->end_seq - start;
3941
3942                         BUG_ON(offset < 0);
3943                         if (size > 0) {
3944                                 size = min(copy, size);
3945                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3946                                         BUG();
3947                                 TCP_SKB_CB(nskb)->end_seq += size;
3948                                 copy -= size;
3949                                 start += size;
3950                         }
3951                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3952                                 struct sk_buff *next = skb->next;
3953                                 __skb_unlink(skb, list);
3954                                 __kfree_skb(skb);
3955                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3956                                 skb = next;
3957                                 if (skb == tail ||
3958                                     tcp_hdr(skb)->syn ||
3959                                     tcp_hdr(skb)->fin)
3960                                         return;
3961                         }
3962                 }
3963         }
3964 }
3965
3966 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3967  * and tcp_collapse() them until all the queue is collapsed.
3968  */
3969 static void tcp_collapse_ofo_queue(struct sock *sk)
3970 {
3971         struct tcp_sock *tp = tcp_sk(sk);
3972         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3973         struct sk_buff *head;
3974         u32 start, end;
3975
3976         if (skb == NULL)
3977                 return;
3978
3979         start = TCP_SKB_CB(skb)->seq;
3980         end = TCP_SKB_CB(skb)->end_seq;
3981         head = skb;
3982
3983         for (;;) {
3984                 skb = skb->next;
3985
3986                 /* Segment is terminated when we see gap or when
3987                  * we are at the end of all the queue. */
3988                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
3989                     after(TCP_SKB_CB(skb)->seq, end) ||
3990                     before(TCP_SKB_CB(skb)->end_seq, start)) {
3991                         tcp_collapse(sk, &tp->out_of_order_queue,
3992                                      head, skb, start, end);
3993                         head = skb;
3994                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
3995                                 break;
3996                         /* Start new segment */
3997                         start = TCP_SKB_CB(skb)->seq;
3998                         end = TCP_SKB_CB(skb)->end_seq;
3999                 } else {
4000                         if (before(TCP_SKB_CB(skb)->seq, start))
4001                                 start = TCP_SKB_CB(skb)->seq;
4002                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4003                                 end = TCP_SKB_CB(skb)->end_seq;
4004                 }
4005         }
4006 }
4007
4008 /* Reduce allocated memory if we can, trying to get
4009  * the socket within its memory limits again.
4010  *
4011  * Return less than zero if we should start dropping frames
4012  * until the socket owning process reads some of the data
4013  * to stabilize the situation.
4014  */
4015 static int tcp_prune_queue(struct sock *sk)
4016 {
4017         struct tcp_sock *tp = tcp_sk(sk);
4018
4019         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4020
4021         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
4022
4023         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4024                 tcp_clamp_window(sk);
4025         else if (tcp_memory_pressure)
4026                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4027
4028         tcp_collapse_ofo_queue(sk);
4029         tcp_collapse(sk, &sk->sk_receive_queue,
4030                      sk->sk_receive_queue.next,
4031                      (struct sk_buff*)&sk->sk_receive_queue,
4032                      tp->copied_seq, tp->rcv_nxt);
4033         sk_stream_mem_reclaim(sk);
4034
4035         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4036                 return 0;
4037
4038         /* Collapsing did not help, destructive actions follow.
4039          * This must not ever occur. */
4040
4041         /* First, purge the out_of_order queue. */
4042         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4043                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
4044                 __skb_queue_purge(&tp->out_of_order_queue);
4045
4046                 /* Reset SACK state.  A conforming SACK implementation will
4047                  * do the same at a timeout based retransmit.  When a connection
4048                  * is in a sad state like this, we care only about integrity
4049                  * of the connection not performance.
4050                  */
4051                 if (tcp_is_sack(tp))
4052                         tcp_sack_reset(&tp->rx_opt);
4053                 sk_stream_mem_reclaim(sk);
4054         }
4055
4056         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4057                 return 0;
4058
4059         /* If we are really being abused, tell the caller to silently
4060          * drop receive data on the floor.  It will get retransmitted
4061          * and hopefully then we'll have sufficient space.
4062          */
4063         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
4064
4065         /* Massive buffer overcommit. */
4066         tp->pred_flags = 0;
4067         return -1;
4068 }
4069
4070
4071 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4072  * As additional protections, we do not touch cwnd in retransmission phases,
4073  * and if application hit its sndbuf limit recently.
4074  */
4075 void tcp_cwnd_application_limited(struct sock *sk)
4076 {
4077         struct tcp_sock *tp = tcp_sk(sk);
4078
4079         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4080             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4081                 /* Limited by application or receiver window. */
4082                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4083                 u32 win_used = max(tp->snd_cwnd_used, init_win);
4084                 if (win_used < tp->snd_cwnd) {
4085                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
4086                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4087                 }
4088                 tp->snd_cwnd_used = 0;
4089         }
4090         tp->snd_cwnd_stamp = tcp_time_stamp;
4091 }
4092
4093 static int tcp_should_expand_sndbuf(struct sock *sk)
4094 {
4095         struct tcp_sock *tp = tcp_sk(sk);
4096
4097         /* If the user specified a specific send buffer setting, do
4098          * not modify it.
4099          */
4100         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4101                 return 0;
4102
4103         /* If we are under global TCP memory pressure, do not expand.  */
4104         if (tcp_memory_pressure)
4105                 return 0;
4106
4107         /* If we are under soft global TCP memory pressure, do not expand.  */
4108         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
4109                 return 0;
4110
4111         /* If we filled the congestion window, do not expand.  */
4112         if (tp->packets_out >= tp->snd_cwnd)
4113                 return 0;
4114
4115         return 1;
4116 }
4117
4118 /* When incoming ACK allowed to free some skb from write_queue,
4119  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4120  * on the exit from tcp input handler.
4121  *
4122  * PROBLEM: sndbuf expansion does not work well with largesend.
4123  */
4124 static void tcp_new_space(struct sock *sk)
4125 {
4126         struct tcp_sock *tp = tcp_sk(sk);
4127
4128         if (tcp_should_expand_sndbuf(sk)) {
4129                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
4130                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
4131                     demanded = max_t(unsigned int, tp->snd_cwnd,
4132                                                    tp->reordering + 1);
4133                 sndmem *= 2*demanded;
4134                 if (sndmem > sk->sk_sndbuf)
4135                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
4136                 tp->snd_cwnd_stamp = tcp_time_stamp;
4137         }
4138
4139         sk->sk_write_space(sk);
4140 }
4141
4142 static void tcp_check_space(struct sock *sk)
4143 {
4144         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4145                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4146                 if (sk->sk_socket &&
4147                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4148                         tcp_new_space(sk);
4149         }
4150 }
4151
4152 static inline void tcp_data_snd_check(struct sock *sk)
4153 {
4154         tcp_push_pending_frames(sk);
4155         tcp_check_space(sk);
4156 }
4157
4158 /*
4159  * Check if sending an ack is needed.
4160  */
4161 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4162 {
4163         struct tcp_sock *tp = tcp_sk(sk);
4164
4165             /* More than one full frame received... */
4166         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
4167              /* ... and right edge of window advances far enough.
4168               * (tcp_recvmsg() will send ACK otherwise). Or...
4169               */
4170              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
4171             /* We ACK each frame or... */
4172             tcp_in_quickack_mode(sk) ||
4173             /* We have out of order data. */
4174             (ofo_possible &&
4175              skb_peek(&tp->out_of_order_queue))) {
4176                 /* Then ack it now */
4177                 tcp_send_ack(sk);
4178         } else {
4179                 /* Else, send delayed ack. */
4180                 tcp_send_delayed_ack(sk);
4181         }
4182 }
4183
4184 static inline void tcp_ack_snd_check(struct sock *sk)
4185 {
4186         if (!inet_csk_ack_scheduled(sk)) {
4187                 /* We sent a data segment already. */
4188                 return;
4189         }
4190         __tcp_ack_snd_check(sk, 1);
4191 }
4192
4193 /*
4194  *      This routine is only called when we have urgent data
4195  *      signaled. Its the 'slow' part of tcp_urg. It could be
4196  *      moved inline now as tcp_urg is only called from one
4197  *      place. We handle URGent data wrong. We have to - as
4198  *      BSD still doesn't use the correction from RFC961.
4199  *      For 1003.1g we should support a new option TCP_STDURG to permit
4200  *      either form (or just set the sysctl tcp_stdurg).
4201  */
4202
4203 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
4204 {
4205         struct tcp_sock *tp = tcp_sk(sk);
4206         u32 ptr = ntohs(th->urg_ptr);
4207
4208         if (ptr && !sysctl_tcp_stdurg)
4209                 ptr--;
4210         ptr += ntohl(th->seq);
4211
4212         /* Ignore urgent data that we've already seen and read. */
4213         if (after(tp->copied_seq, ptr))
4214                 return;
4215
4216         /* Do not replay urg ptr.
4217          *
4218          * NOTE: interesting situation not covered by specs.
4219          * Misbehaving sender may send urg ptr, pointing to segment,
4220          * which we already have in ofo queue. We are not able to fetch
4221          * such data and will stay in TCP_URG_NOTYET until will be eaten
4222          * by recvmsg(). Seems, we are not obliged to handle such wicked
4223          * situations. But it is worth to think about possibility of some
4224          * DoSes using some hypothetical application level deadlock.
4225          */
4226         if (before(ptr, tp->rcv_nxt))
4227                 return;
4228
4229         /* Do we already have a newer (or duplicate) urgent pointer? */
4230         if (tp->urg_data && !after(ptr, tp->urg_seq))
4231                 return;
4232
4233         /* Tell the world about our new urgent pointer. */
4234         sk_send_sigurg(sk);
4235
4236         /* We may be adding urgent data when the last byte read was
4237          * urgent. To do this requires some care. We cannot just ignore
4238          * tp->copied_seq since we would read the last urgent byte again
4239          * as data, nor can we alter copied_seq until this data arrives
4240          * or we break the semantics of SIOCATMARK (and thus sockatmark())
4241          *
4242          * NOTE. Double Dutch. Rendering to plain English: author of comment
4243          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
4244          * and expect that both A and B disappear from stream. This is _wrong_.
4245          * Though this happens in BSD with high probability, this is occasional.
4246          * Any application relying on this is buggy. Note also, that fix "works"
4247          * only in this artificial test. Insert some normal data between A and B and we will
4248          * decline of BSD again. Verdict: it is better to remove to trap
4249          * buggy users.
4250          */
4251         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4252             !sock_flag(sk, SOCK_URGINLINE) &&
4253             tp->copied_seq != tp->rcv_nxt) {
4254                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4255                 tp->copied_seq++;
4256                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4257                         __skb_unlink(skb, &sk->sk_receive_queue);
4258                         __kfree_skb(skb);
4259                 }
4260         }
4261
4262         tp->urg_data   = TCP_URG_NOTYET;
4263         tp->urg_seq    = ptr;
4264
4265         /* Disable header prediction. */
4266         tp->pred_flags = 0;
4267 }
4268
4269 /* This is the 'fast' part of urgent handling. */
4270 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
4271 {
4272         struct tcp_sock *tp = tcp_sk(sk);
4273
4274         /* Check if we get a new urgent pointer - normally not. */
4275         if (th->urg)
4276                 tcp_check_urg(sk,th);
4277
4278         /* Do we wait for any urgent data? - normally not... */
4279         if (tp->urg_data == TCP_URG_NOTYET) {
4280                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4281                           th->syn;
4282
4283                 /* Is the urgent pointer pointing into this packet? */
4284                 if (ptr < skb->len) {
4285                         u8 tmp;
4286                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4287                                 BUG();
4288                         tp->urg_data = TCP_URG_VALID | tmp;
4289                         if (!sock_flag(sk, SOCK_DEAD))
4290                                 sk->sk_data_ready(sk, 0);
4291                 }
4292         }
4293 }
4294
4295 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4296 {
4297         struct tcp_sock *tp = tcp_sk(sk);
4298         int chunk = skb->len - hlen;
4299         int err;
4300
4301         local_bh_enable();
4302         if (skb_csum_unnecessary(skb))
4303                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4304         else
4305                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4306                                                        tp->ucopy.iov);
4307
4308         if (!err) {
4309                 tp->ucopy.len -= chunk;
4310                 tp->copied_seq += chunk;
4311                 tcp_rcv_space_adjust(sk);
4312         }
4313
4314         local_bh_disable();
4315         return err;
4316 }
4317
4318 static __sum16 __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
4319 {
4320         __sum16 result;
4321
4322         if (sock_owned_by_user(sk)) {
4323                 local_bh_enable();
4324                 result = __tcp_checksum_complete(skb);
4325                 local_bh_disable();
4326         } else {
4327                 result = __tcp_checksum_complete(skb);
4328         }
4329         return result;
4330 }
4331
4332 static inline int tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
4333 {
4334         return !skb_csum_unnecessary(skb) &&
4335                 __tcp_checksum_complete_user(sk, skb);
4336 }
4337
4338 #ifdef CONFIG_NET_DMA
4339 static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb, int hlen)
4340 {
4341         struct tcp_sock *tp = tcp_sk(sk);
4342         int chunk = skb->len - hlen;
4343         int dma_cookie;
4344         int copied_early = 0;
4345
4346         if (tp->ucopy.wakeup)
4347                 return 0;
4348
4349         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
4350                 tp->ucopy.dma_chan = get_softnet_dma();
4351
4352         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
4353
4354                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
4355                         skb, hlen, tp->ucopy.iov, chunk, tp->ucopy.pinned_list);
4356
4357                 if (dma_cookie < 0)
4358                         goto out;
4359
4360                 tp->ucopy.dma_cookie = dma_cookie;
4361                 copied_early = 1;
4362
4363                 tp->ucopy.len -= chunk;
4364                 tp->copied_seq += chunk;
4365                 tcp_rcv_space_adjust(sk);
4366
4367                 if ((tp->ucopy.len == 0) ||
4368                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
4369                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
4370                         tp->ucopy.wakeup = 1;
4371                         sk->sk_data_ready(sk, 0);
4372                 }
4373         } else if (chunk > 0) {
4374                 tp->ucopy.wakeup = 1;
4375                 sk->sk_data_ready(sk, 0);
4376         }
4377 out:
4378         return copied_early;
4379 }
4380 #endif /* CONFIG_NET_DMA */
4381
4382 /*
4383  *      TCP receive function for the ESTABLISHED state.
4384  *
4385  *      It is split into a fast path and a slow path. The fast path is
4386  *      disabled when:
4387  *      - A zero window was announced from us - zero window probing
4388  *        is only handled properly in the slow path.
4389  *      - Out of order segments arrived.
4390  *      - Urgent data is expected.
4391  *      - There is no buffer space left
4392  *      - Unexpected TCP flags/window values/header lengths are received
4393  *        (detected by checking the TCP header against pred_flags)
4394  *      - Data is sent in both directions. Fast path only supports pure senders
4395  *        or pure receivers (this means either the sequence number or the ack
4396  *        value must stay constant)
4397  *      - Unexpected TCP option.
4398  *
4399  *      When these conditions are not satisfied it drops into a standard
4400  *      receive procedure patterned after RFC793 to handle all cases.
4401  *      The first three cases are guaranteed by proper pred_flags setting,
4402  *      the rest is checked inline. Fast processing is turned on in
4403  *      tcp_data_queue when everything is OK.
4404  */
4405 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
4406                         struct tcphdr *th, unsigned len)
4407 {
4408         struct tcp_sock *tp = tcp_sk(sk);
4409
4410         /*
4411          *      Header prediction.
4412          *      The code loosely follows the one in the famous
4413          *      "30 instruction TCP receive" Van Jacobson mail.
4414          *
4415          *      Van's trick is to deposit buffers into socket queue
4416          *      on a device interrupt, to call tcp_recv function
4417          *      on the receive process context and checksum and copy
4418          *      the buffer to user space. smart...
4419          *
4420          *      Our current scheme is not silly either but we take the
4421          *      extra cost of the net_bh soft interrupt processing...
4422          *      We do checksum and copy also but from device to kernel.
4423          */
4424
4425         tp->rx_opt.saw_tstamp = 0;
4426
4427         /*      pred_flags is 0xS?10 << 16 + snd_wnd
4428          *      if header_prediction is to be made
4429          *      'S' will always be tp->tcp_header_len >> 2
4430          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
4431          *  turn it off (when there are holes in the receive
4432          *       space for instance)
4433          *      PSH flag is ignored.
4434          */
4435
4436         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
4437                 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4438                 int tcp_header_len = tp->tcp_header_len;
4439
4440                 /* Timestamp header prediction: tcp_header_len
4441                  * is automatically equal to th->doff*4 due to pred_flags
4442                  * match.
4443                  */
4444
4445                 /* Check timestamp */
4446                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
4447                         __be32 *ptr = (__be32 *)(th + 1);
4448
4449                         /* No? Slow path! */
4450                         if (*ptr != htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4451                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
4452                                 goto slow_path;
4453
4454                         tp->rx_opt.saw_tstamp = 1;
4455                         ++ptr;
4456                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
4457                         ++ptr;
4458                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
4459
4460                         /* If PAWS failed, check it more carefully in slow path */
4461                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
4462                                 goto slow_path;
4463
4464                         /* DO NOT update ts_recent here, if checksum fails
4465                          * and timestamp was corrupted part, it will result
4466                          * in a hung connection since we will drop all
4467                          * future packets due to the PAWS test.
4468                          */
4469                 }
4470
4471                 if (len <= tcp_header_len) {
4472                         /* Bulk data transfer: sender */
4473                         if (len == tcp_header_len) {
4474                                 /* Predicted packet is in window by definition.
4475                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4476                                  * Hence, check seq<=rcv_wup reduces to:
4477                                  */
4478                                 if (tcp_header_len ==
4479                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4480                                     tp->rcv_nxt == tp->rcv_wup)
4481                                         tcp_store_ts_recent(tp);
4482
4483                                 /* We know that such packets are checksummed
4484                                  * on entry.
4485                                  */
4486                                 tcp_ack(sk, skb, 0);
4487                                 __kfree_skb(skb);
4488                                 tcp_data_snd_check(sk);
4489                                 return 0;
4490                         } else { /* Header too small */
4491                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4492                                 goto discard;
4493                         }
4494                 } else {
4495                         int eaten = 0;
4496                         int copied_early = 0;
4497
4498                         if (tp->copied_seq == tp->rcv_nxt &&
4499                             len - tcp_header_len <= tp->ucopy.len) {
4500 #ifdef CONFIG_NET_DMA
4501                                 if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
4502                                         copied_early = 1;
4503                                         eaten = 1;
4504                                 }
4505 #endif
4506                                 if (tp->ucopy.task == current && sock_owned_by_user(sk) && !copied_early) {
4507                                         __set_current_state(TASK_RUNNING);
4508
4509                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
4510                                                 eaten = 1;
4511                                 }
4512                                 if (eaten) {
4513                                         /* Predicted packet is in window by definition.
4514                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4515                                          * Hence, check seq<=rcv_wup reduces to:
4516                                          */
4517                                         if (tcp_header_len ==
4518                                             (sizeof(struct tcphdr) +
4519                                              TCPOLEN_TSTAMP_ALIGNED) &&
4520                                             tp->rcv_nxt == tp->rcv_wup)
4521                                                 tcp_store_ts_recent(tp);
4522
4523                                         tcp_rcv_rtt_measure_ts(sk, skb);
4524
4525                                         __skb_pull(skb, tcp_header_len);
4526                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4527                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
4528                                 }
4529                                 if (copied_early)
4530                                         tcp_cleanup_rbuf(sk, skb->len);
4531                         }
4532                         if (!eaten) {
4533                                 if (tcp_checksum_complete_user(sk, skb))
4534                                         goto csum_error;
4535
4536                                 /* Predicted packet is in window by definition.
4537                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4538                                  * Hence, check seq<=rcv_wup reduces to:
4539                                  */
4540                                 if (tcp_header_len ==
4541                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4542                                     tp->rcv_nxt == tp->rcv_wup)
4543                                         tcp_store_ts_recent(tp);
4544
4545                                 tcp_rcv_rtt_measure_ts(sk, skb);
4546
4547                                 if ((int)skb->truesize > sk->sk_forward_alloc)
4548                                         goto step5;
4549
4550                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
4551
4552                                 /* Bulk data transfer: receiver */
4553                                 __skb_pull(skb,tcp_header_len);
4554                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4555                                 sk_stream_set_owner_r(skb, sk);
4556                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4557                         }
4558
4559                         tcp_event_data_recv(sk, skb);
4560
4561                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
4562                                 /* Well, only one small jumplet in fast path... */
4563                                 tcp_ack(sk, skb, FLAG_DATA);
4564                                 tcp_data_snd_check(sk);
4565                                 if (!inet_csk_ack_scheduled(sk))
4566                                         goto no_ack;
4567                         }
4568
4569                         __tcp_ack_snd_check(sk, 0);
4570 no_ack:
4571 #ifdef CONFIG_NET_DMA
4572                         if (copied_early)
4573                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
4574                         else
4575 #endif
4576                         if (eaten)
4577                                 __kfree_skb(skb);
4578                         else
4579                                 sk->sk_data_ready(sk, 0);
4580                         return 0;
4581                 }
4582         }
4583
4584 slow_path:
4585         if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
4586                 goto csum_error;
4587
4588         /*
4589          * RFC1323: H1. Apply PAWS check first.
4590          */
4591         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4592             tcp_paws_discard(sk, skb)) {
4593                 if (!th->rst) {
4594                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4595                         tcp_send_dupack(sk, skb);
4596                         goto discard;
4597                 }
4598                 /* Resets are accepted even if PAWS failed.
4599
4600                    ts_recent update must be made after we are sure
4601                    that the packet is in window.
4602                  */
4603         }
4604
4605         /*
4606          *      Standard slow path.
4607          */
4608
4609         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4610                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
4611                  * (RST) segments are validated by checking their SEQ-fields."
4612                  * And page 69: "If an incoming segment is not acceptable,
4613                  * an acknowledgment should be sent in reply (unless the RST bit
4614                  * is set, if so drop the segment and return)".
4615                  */
4616                 if (!th->rst)
4617                         tcp_send_dupack(sk, skb);
4618                 goto discard;
4619         }
4620
4621         if (th->rst) {
4622                 tcp_reset(sk);
4623                 goto discard;
4624         }
4625
4626         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4627
4628         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4629                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4630                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4631                 tcp_reset(sk);
4632                 return 1;
4633         }
4634
4635 step5:
4636         if (th->ack)
4637                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4638
4639         tcp_rcv_rtt_measure_ts(sk, skb);
4640
4641         /* Process urgent data. */
4642         tcp_urg(sk, skb, th);
4643
4644         /* step 7: process the segment text */
4645         tcp_data_queue(sk, skb);
4646
4647         tcp_data_snd_check(sk);
4648         tcp_ack_snd_check(sk);
4649         return 0;
4650
4651 csum_error:
4652         TCP_INC_STATS_BH(TCP_MIB_INERRS);
4653
4654 discard:
4655         __kfree_skb(skb);
4656         return 0;
4657 }
4658
4659 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
4660                                          struct tcphdr *th, unsigned len)
4661 {
4662         struct tcp_sock *tp = tcp_sk(sk);
4663         struct inet_connection_sock *icsk = inet_csk(sk);
4664         int saved_clamp = tp->rx_opt.mss_clamp;
4665
4666         tcp_parse_options(skb, &tp->rx_opt, 0);
4667
4668         if (th->ack) {
4669                 /* rfc793:
4670                  * "If the state is SYN-SENT then
4671                  *    first check the ACK bit
4672                  *      If the ACK bit is set
4673                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
4674                  *        a reset (unless the RST bit is set, if so drop
4675                  *        the segment and return)"
4676                  *
4677                  *  We do not send data with SYN, so that RFC-correct
4678                  *  test reduces to:
4679                  */
4680                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
4681                         goto reset_and_undo;
4682
4683                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4684                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
4685                              tcp_time_stamp)) {
4686                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
4687                         goto reset_and_undo;
4688                 }
4689
4690                 /* Now ACK is acceptable.
4691                  *
4692                  * "If the RST bit is set
4693                  *    If the ACK was acceptable then signal the user "error:
4694                  *    connection reset", drop the segment, enter CLOSED state,
4695                  *    delete TCB, and return."
4696                  */
4697
4698                 if (th->rst) {
4699                         tcp_reset(sk);
4700                         goto discard;
4701                 }
4702
4703                 /* rfc793:
4704                  *   "fifth, if neither of the SYN or RST bits is set then
4705                  *    drop the segment and return."
4706                  *
4707                  *    See note below!
4708                  *                                        --ANK(990513)
4709                  */
4710                 if (!th->syn)
4711                         goto discard_and_undo;
4712
4713                 /* rfc793:
4714                  *   "If the SYN bit is on ...
4715                  *    are acceptable then ...
4716                  *    (our SYN has been ACKed), change the connection
4717                  *    state to ESTABLISHED..."
4718                  */
4719
4720                 TCP_ECN_rcv_synack(tp, th);
4721
4722                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
4723                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4724
4725                 /* Ok.. it's good. Set up sequence numbers and
4726                  * move to established.
4727                  */
4728                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4729                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4730
4731                 /* RFC1323: The window in SYN & SYN/ACK segments is
4732                  * never scaled.
4733                  */
4734                 tp->snd_wnd = ntohs(th->window);
4735                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
4736
4737                 if (!tp->rx_opt.wscale_ok) {
4738                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
4739                         tp->window_clamp = min(tp->window_clamp, 65535U);
4740                 }
4741
4742                 if (tp->rx_opt.saw_tstamp) {
4743                         tp->rx_opt.tstamp_ok       = 1;
4744                         tp->tcp_header_len =
4745                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4746                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
4747                         tcp_store_ts_recent(tp);
4748                 } else {
4749                         tp->tcp_header_len = sizeof(struct tcphdr);
4750                 }
4751
4752                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
4753                         tcp_enable_fack(tp);
4754
4755                 tcp_mtup_init(sk);
4756                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4757                 tcp_initialize_rcv_mss(sk);
4758
4759                 /* Remember, tcp_poll() does not lock socket!
4760                  * Change state from SYN-SENT only after copied_seq
4761                  * is initialized. */
4762                 tp->copied_seq = tp->rcv_nxt;
4763                 smp_mb();
4764                 tcp_set_state(sk, TCP_ESTABLISHED);
4765
4766                 security_inet_conn_established(sk, skb);
4767
4768                 /* Make sure socket is routed, for correct metrics.  */
4769                 icsk->icsk_af_ops->rebuild_header(sk);
4770
4771                 tcp_init_metrics(sk);
4772
4773                 tcp_init_congestion_control(sk);
4774
4775                 /* Prevent spurious tcp_cwnd_restart() on first data
4776                  * packet.
4777                  */
4778                 tp->lsndtime = tcp_time_stamp;
4779
4780                 tcp_init_buffer_space(sk);
4781
4782                 if (sock_flag(sk, SOCK_KEEPOPEN))
4783                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
4784
4785                 if (!tp->rx_opt.snd_wscale)
4786                         __tcp_fast_path_on(tp, tp->snd_wnd);
4787                 else
4788                         tp->pred_flags = 0;
4789
4790                 if (!sock_flag(sk, SOCK_DEAD)) {
4791                         sk->sk_state_change(sk);
4792                         sk_wake_async(sk, 0, POLL_OUT);
4793                 }
4794
4795                 if (sk->sk_write_pending ||
4796                     icsk->icsk_accept_queue.rskq_defer_accept ||
4797                     icsk->icsk_ack.pingpong) {
4798                         /* Save one ACK. Data will be ready after
4799                          * several ticks, if write_pending is set.
4800                          *
4801                          * It may be deleted, but with this feature tcpdumps
4802                          * look so _wonderfully_ clever, that I was not able
4803                          * to stand against the temptation 8)     --ANK
4804                          */
4805                         inet_csk_schedule_ack(sk);
4806                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4807                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4808                         tcp_incr_quickack(sk);
4809                         tcp_enter_quickack_mode(sk);
4810                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4811                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4812
4813 discard:
4814                         __kfree_skb(skb);
4815                         return 0;
4816                 } else {
4817                         tcp_send_ack(sk);
4818                 }
4819                 return -1;
4820         }
4821
4822         /* No ACK in the segment */
4823
4824         if (th->rst) {
4825                 /* rfc793:
4826                  * "If the RST bit is set
4827                  *
4828                  *      Otherwise (no ACK) drop the segment and return."
4829                  */
4830
4831                 goto discard_and_undo;
4832         }
4833
4834         /* PAWS check. */
4835         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4836                 goto discard_and_undo;
4837
4838         if (th->syn) {
4839                 /* We see SYN without ACK. It is attempt of
4840                  * simultaneous connect with crossed SYNs.
4841                  * Particularly, it can be connect to self.
4842                  */
4843                 tcp_set_state(sk, TCP_SYN_RECV);
4844
4845                 if (tp->rx_opt.saw_tstamp) {
4846                         tp->rx_opt.tstamp_ok = 1;
4847                         tcp_store_ts_recent(tp);
4848                         tp->tcp_header_len =
4849                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4850                 } else {
4851                         tp->tcp_header_len = sizeof(struct tcphdr);
4852                 }
4853
4854                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4855                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4856
4857                 /* RFC1323: The window in SYN & SYN/ACK segments is
4858                  * never scaled.
4859                  */
4860                 tp->snd_wnd    = ntohs(th->window);
4861                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4862                 tp->max_window = tp->snd_wnd;
4863
4864                 TCP_ECN_rcv_syn(tp, th);
4865
4866                 tcp_mtup_init(sk);
4867                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4868                 tcp_initialize_rcv_mss(sk);
4869
4870
4871                 tcp_send_synack(sk);
4872 #if 0
4873                 /* Note, we could accept data and URG from this segment.
4874                  * There are no obstacles to make this.
4875                  *
4876                  * However, if we ignore data in ACKless segments sometimes,
4877                  * we have no reasons to accept it sometimes.
4878                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
4879                  * is not flawless. So, discard packet for sanity.
4880                  * Uncomment this return to process the data.
4881                  */
4882                 return -1;
4883 #else
4884                 goto discard;
4885 #endif
4886         }
4887         /* "fifth, if neither of the SYN or RST bits is set then
4888          * drop the segment and return."
4889          */
4890
4891 discard_and_undo:
4892         tcp_clear_options(&tp->rx_opt);
4893         tp->rx_opt.mss_clamp = saved_clamp;
4894         goto discard;
4895
4896 reset_and_undo:
4897         tcp_clear_options(&tp->rx_opt);
4898         tp->rx_opt.mss_clamp = saved_clamp;
4899         return 1;
4900 }
4901
4902
4903 /*
4904  *      This function implements the receiving procedure of RFC 793 for
4905  *      all states except ESTABLISHED and TIME_WAIT.
4906  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4907  *      address independent.
4908  */
4909
4910 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4911                           struct tcphdr *th, unsigned len)
4912 {
4913         struct tcp_sock *tp = tcp_sk(sk);
4914         struct inet_connection_sock *icsk = inet_csk(sk);
4915         int queued = 0;
4916
4917         tp->rx_opt.saw_tstamp = 0;
4918
4919         switch (sk->sk_state) {
4920         case TCP_CLOSE:
4921                 goto discard;
4922
4923         case TCP_LISTEN:
4924                 if (th->ack)
4925                         return 1;
4926
4927                 if (th->rst)
4928                         goto discard;
4929
4930                 if (th->syn) {
4931                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
4932                                 return 1;
4933
4934                         /* Now we have several options: In theory there is
4935                          * nothing else in the frame. KA9Q has an option to
4936                          * send data with the syn, BSD accepts data with the
4937                          * syn up to the [to be] advertised window and
4938                          * Solaris 2.1 gives you a protocol error. For now
4939                          * we just ignore it, that fits the spec precisely
4940                          * and avoids incompatibilities. It would be nice in
4941                          * future to drop through and process the data.
4942                          *
4943                          * Now that TTCP is starting to be used we ought to
4944                          * queue this data.
4945                          * But, this leaves one open to an easy denial of
4946                          * service attack, and SYN cookies can't defend
4947                          * against this problem. So, we drop the data
4948                          * in the interest of security over speed unless
4949                          * it's still in use.
4950                          */
4951                         kfree_skb(skb);
4952                         return 0;
4953                 }
4954                 goto discard;
4955
4956         case TCP_SYN_SENT:
4957                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4958                 if (queued >= 0)
4959                         return queued;
4960
4961                 /* Do step6 onward by hand. */
4962                 tcp_urg(sk, skb, th);
4963                 __kfree_skb(skb);
4964                 tcp_data_snd_check(sk);
4965                 return 0;
4966         }
4967
4968         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4969             tcp_paws_discard(sk, skb)) {
4970                 if (!th->rst) {
4971                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4972                         tcp_send_dupack(sk, skb);
4973                         goto discard;
4974                 }
4975                 /* Reset is accepted even if it did not pass PAWS. */
4976         }
4977
4978         /* step 1: check sequence number */
4979         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4980                 if (!th->rst)
4981                         tcp_send_dupack(sk, skb);
4982                 goto discard;
4983         }
4984
4985         /* step 2: check RST bit */
4986         if (th->rst) {
4987                 tcp_reset(sk);
4988                 goto discard;
4989         }
4990
4991         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4992
4993         /* step 3: check security and precedence [ignored] */
4994
4995         /*      step 4:
4996          *
4997          *      Check for a SYN in window.
4998          */
4999         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5000                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
5001                 tcp_reset(sk);
5002                 return 1;
5003         }
5004
5005         /* step 5: check the ACK field */
5006         if (th->ack) {
5007                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
5008
5009                 switch (sk->sk_state) {
5010                 case TCP_SYN_RECV:
5011                         if (acceptable) {
5012                                 tp->copied_seq = tp->rcv_nxt;
5013                                 smp_mb();
5014                                 tcp_set_state(sk, TCP_ESTABLISHED);
5015                                 sk->sk_state_change(sk);
5016
5017                                 /* Note, that this wakeup is only for marginal
5018                                  * crossed SYN case. Passively open sockets
5019                                  * are not waked up, because sk->sk_sleep ==
5020                                  * NULL and sk->sk_socket == NULL.
5021                                  */
5022                                 if (sk->sk_socket) {
5023                                         sk_wake_async(sk,0,POLL_OUT);
5024                                 }
5025
5026                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5027                                 tp->snd_wnd = ntohs(th->window) <<
5028                                               tp->rx_opt.snd_wscale;
5029                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
5030                                             TCP_SKB_CB(skb)->seq);
5031
5032                                 /* tcp_ack considers this ACK as duplicate
5033                                  * and does not calculate rtt.
5034                                  * Fix it at least with timestamps.
5035                                  */
5036                                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5037                                     !tp->srtt)
5038                                         tcp_ack_saw_tstamp(sk, 0);
5039
5040                                 if (tp->rx_opt.tstamp_ok)
5041                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5042
5043                                 /* Make sure socket is routed, for
5044                                  * correct metrics.
5045                                  */
5046                                 icsk->icsk_af_ops->rebuild_header(sk);
5047
5048                                 tcp_init_metrics(sk);
5049
5050                                 tcp_init_congestion_control(sk);
5051
5052                                 /* Prevent spurious tcp_cwnd_restart() on
5053                                  * first data packet.
5054                                  */
5055                                 tp->lsndtime = tcp_time_stamp;
5056
5057                                 tcp_mtup_init(sk);
5058                                 tcp_initialize_rcv_mss(sk);
5059                                 tcp_init_buffer_space(sk);
5060                                 tcp_fast_path_on(tp);
5061                         } else {
5062                                 return 1;
5063                         }
5064                         break;
5065
5066                 case TCP_FIN_WAIT1:
5067                         if (tp->snd_una == tp->write_seq) {
5068                                 tcp_set_state(sk, TCP_FIN_WAIT2);
5069                                 sk->sk_shutdown |= SEND_SHUTDOWN;
5070                                 dst_confirm(sk->sk_dst_cache);
5071
5072                                 if (!sock_flag(sk, SOCK_DEAD))
5073                                         /* Wake up lingering close() */
5074                                         sk->sk_state_change(sk);
5075                                 else {
5076                                         int tmo;
5077
5078                                         if (tp->linger2 < 0 ||
5079                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5080                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5081                                                 tcp_done(sk);
5082                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
5083                                                 return 1;
5084                                         }
5085
5086                                         tmo = tcp_fin_time(sk);
5087                                         if (tmo > TCP_TIMEWAIT_LEN) {
5088                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5089                                         } else if (th->fin || sock_owned_by_user(sk)) {
5090                                                 /* Bad case. We could lose such FIN otherwise.
5091                                                  * It is not a big problem, but it looks confusing
5092                                                  * and not so rare event. We still can lose it now,
5093                                                  * if it spins in bh_lock_sock(), but it is really
5094                                                  * marginal case.
5095                                                  */
5096                                                 inet_csk_reset_keepalive_timer(sk, tmo);
5097                                         } else {
5098                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5099                                                 goto discard;
5100                                         }
5101                                 }
5102                         }
5103                         break;
5104
5105                 case TCP_CLOSING:
5106                         if (tp->snd_una == tp->write_seq) {
5107                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5108                                 goto discard;
5109                         }
5110                         break;
5111
5112                 case TCP_LAST_ACK:
5113                         if (tp->snd_una == tp->write_seq) {
5114                                 tcp_update_metrics(sk);
5115                                 tcp_done(sk);
5116                                 goto discard;
5117                         }
5118                         break;
5119                 }
5120         } else
5121                 goto discard;
5122
5123         /* step 6: check the URG bit */
5124         tcp_urg(sk, skb, th);
5125
5126         /* step 7: process the segment text */
5127         switch (sk->sk_state) {
5128         case TCP_CLOSE_WAIT:
5129         case TCP_CLOSING:
5130         case TCP_LAST_ACK:
5131                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5132                         break;
5133         case TCP_FIN_WAIT1:
5134         case TCP_FIN_WAIT2:
5135                 /* RFC 793 says to queue data in these states,
5136                  * RFC 1122 says we MUST send a reset.
5137                  * BSD 4.4 also does reset.
5138                  */
5139                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5140                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5141                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5142                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
5143                                 tcp_reset(sk);
5144                                 return 1;
5145                         }
5146                 }
5147                 /* Fall through */
5148         case TCP_ESTABLISHED:
5149                 tcp_data_queue(sk, skb);
5150                 queued = 1;
5151                 break;
5152         }
5153
5154         /* tcp_data could move socket to TIME-WAIT */
5155         if (sk->sk_state != TCP_CLOSE) {
5156                 tcp_data_snd_check(sk);
5157                 tcp_ack_snd_check(sk);
5158         }
5159
5160         if (!queued) {
5161 discard:
5162                 __kfree_skb(skb);
5163         }
5164         return 0;
5165 }
5166
5167 EXPORT_SYMBOL(sysctl_tcp_ecn);
5168 EXPORT_SYMBOL(sysctl_tcp_reordering);
5169 EXPORT_SYMBOL(tcp_parse_options);
5170 EXPORT_SYMBOL(tcp_rcv_established);
5171 EXPORT_SYMBOL(tcp_rcv_state_process);
5172 EXPORT_SYMBOL(tcp_initialize_rcv_mss);