Merge branch 'for-linus' of master.kernel.org:/pub/scm/linux/kernel/git/roland/infiniband
[linux-2.6] / net / ipv4 / tcp_input.c
1 /*
2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
3  *              operating system.  INET is implemented using the  BSD Socket
4  *              interface as the means of communication with the user level.
5  *
6  *              Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Version:     $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
9  *
10  * Authors:     Ross Biro
11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
14  *              Florian La Roche, <flla@stud.uni-sb.de>
15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20  *              Jorge Cwik, <jorge@laser.satlink.net>
21  */
22
23 /*
24  * Changes:
25  *              Pedro Roque     :       Fast Retransmit/Recovery.
26  *                                      Two receive queues.
27  *                                      Retransmit queue handled by TCP.
28  *                                      Better retransmit timer handling.
29  *                                      New congestion avoidance.
30  *                                      Header prediction.
31  *                                      Variable renaming.
32  *
33  *              Eric            :       Fast Retransmit.
34  *              Randy Scott     :       MSS option defines.
35  *              Eric Schenk     :       Fixes to slow start algorithm.
36  *              Eric Schenk     :       Yet another double ACK bug.
37  *              Eric Schenk     :       Delayed ACK bug fixes.
38  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
39  *              David S. Miller :       Don't allow zero congestion window.
40  *              Eric Schenk     :       Fix retransmitter so that it sends
41  *                                      next packet on ack of previous packet.
42  *              Andi Kleen      :       Moved open_request checking here
43  *                                      and process RSTs for open_requests.
44  *              Andi Kleen      :       Better prune_queue, and other fixes.
45  *              Andrey Savochkin:       Fix RTT measurements in the presence of
46  *                                      timestamps.
47  *              Andrey Savochkin:       Check sequence numbers correctly when
48  *                                      removing SACKs due to in sequence incoming
49  *                                      data segments.
50  *              Andi Kleen:             Make sure we never ack data there is not
51  *                                      enough room for. Also make this condition
52  *                                      a fatal error if it might still happen.
53  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
54  *                                      connections with MSS<min(MTU,ann. MSS)
55  *                                      work without delayed acks.
56  *              Andi Kleen:             Process packets with PSH set in the
57  *                                      fast path.
58  *              J Hadi Salim:           ECN support
59  *              Andrei Gurtov,
60  *              Pasi Sarolahti,
61  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
62  *                                      engine. Lots of bugs are found.
63  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
64  */
65
66 #include <linux/mm.h>
67 #include <linux/module.h>
68 #include <linux/sysctl.h>
69 #include <net/tcp.h>
70 #include <net/inet_common.h>
71 #include <linux/ipsec.h>
72 #include <asm/unaligned.h>
73 #include <net/netdma.h>
74
75 int sysctl_tcp_timestamps __read_mostly = 1;
76 int sysctl_tcp_window_scaling __read_mostly = 1;
77 int sysctl_tcp_sack __read_mostly = 1;
78 int sysctl_tcp_fack __read_mostly = 1;
79 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn __read_mostly;
81 int sysctl_tcp_dsack __read_mostly = 1;
82 int sysctl_tcp_app_win __read_mostly = 31;
83 int sysctl_tcp_adv_win_scale __read_mostly = 2;
84
85 int sysctl_tcp_stdurg __read_mostly;
86 int sysctl_tcp_rfc1337 __read_mostly;
87 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
88 int sysctl_tcp_frto __read_mostly;
89 int sysctl_tcp_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
106 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
107 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
108 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
109 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
110
111 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
112 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
113 #define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
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
119 /* Adapt the MSS value used to make delayed ack decision to the
120  * real world.
121  */
122 static void tcp_measure_rcv_mss(struct sock *sk,
123                                 const struct sk_buff *skb)
124 {
125         struct inet_connection_sock *icsk = inet_csk(sk);
126         const unsigned int lss = icsk->icsk_ack.last_seg_size;
127         unsigned int len;
128
129         icsk->icsk_ack.last_seg_size = 0;
130
131         /* skb->len may jitter because of SACKs, even if peer
132          * sends good full-sized frames.
133          */
134         len = skb_shinfo(skb)->gso_size ?: skb->len;
135         if (len >= icsk->icsk_ack.rcv_mss) {
136                 icsk->icsk_ack.rcv_mss = len;
137         } else {
138                 /* Otherwise, we make more careful check taking into account,
139                  * that SACKs block is variable.
140                  *
141                  * "len" is invariant segment length, including TCP header.
142                  */
143                 len += skb->data - skb_transport_header(skb);
144                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
145                     /* If PSH is not set, packet should be
146                      * full sized, provided peer TCP is not badly broken.
147                      * This observation (if it is correct 8)) allows
148                      * to handle super-low mtu links fairly.
149                      */
150                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
151                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
152                         /* Subtract also invariant (if peer is RFC compliant),
153                          * tcp header plus fixed timestamp option length.
154                          * Resulting "len" is MSS free of SACK jitter.
155                          */
156                         len -= tcp_sk(sk)->tcp_header_len;
157                         icsk->icsk_ack.last_seg_size = len;
158                         if (len == lss) {
159                                 icsk->icsk_ack.rcv_mss = len;
160                                 return;
161                         }
162                 }
163                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
164                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
165                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
166         }
167 }
168
169 static void tcp_incr_quickack(struct sock *sk)
170 {
171         struct inet_connection_sock *icsk = inet_csk(sk);
172         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
173
174         if (quickacks==0)
175                 quickacks=2;
176         if (quickacks > icsk->icsk_ack.quick)
177                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
178 }
179
180 void tcp_enter_quickack_mode(struct sock *sk)
181 {
182         struct inet_connection_sock *icsk = inet_csk(sk);
183         tcp_incr_quickack(sk);
184         icsk->icsk_ack.pingpong = 0;
185         icsk->icsk_ack.ato = TCP_ATO_MIN;
186 }
187
188 /* Send ACKs quickly, if "quick" count is not exhausted
189  * and the session is not interactive.
190  */
191
192 static inline int tcp_in_quickack_mode(const struct sock *sk)
193 {
194         const struct inet_connection_sock *icsk = inet_csk(sk);
195         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
196 }
197
198 /* Buffer size and advertised window tuning.
199  *
200  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
201  */
202
203 static void tcp_fixup_sndbuf(struct sock *sk)
204 {
205         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
206                      sizeof(struct sk_buff);
207
208         if (sk->sk_sndbuf < 3 * sndmem)
209                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
210 }
211
212 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
213  *
214  * All tcp_full_space() is split to two parts: "network" buffer, allocated
215  * forward and advertised in receiver window (tp->rcv_wnd) and
216  * "application buffer", required to isolate scheduling/application
217  * latencies from network.
218  * window_clamp is maximal advertised window. It can be less than
219  * tcp_full_space(), in this case tcp_full_space() - window_clamp
220  * is reserved for "application" buffer. The less window_clamp is
221  * the smoother our behaviour from viewpoint of network, but the lower
222  * throughput and the higher sensitivity of the connection to losses. 8)
223  *
224  * rcv_ssthresh is more strict window_clamp used at "slow start"
225  * phase to predict further behaviour of this connection.
226  * It is used for two goals:
227  * - to enforce header prediction at sender, even when application
228  *   requires some significant "application buffer". It is check #1.
229  * - to prevent pruning of receive queue because of misprediction
230  *   of receiver window. Check #2.
231  *
232  * The scheme does not work when sender sends good segments opening
233  * window and then starts to feed us spaghetti. But it should work
234  * in common situations. Otherwise, we have to rely on queue collapsing.
235  */
236
237 /* Slow part of check#2. */
238 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
239 {
240         struct tcp_sock *tp = tcp_sk(sk);
241         /* Optimize this! */
242         int truesize = tcp_win_from_space(skb->truesize)/2;
243         int window = tcp_win_from_space(sysctl_tcp_rmem[2])/2;
244
245         while (tp->rcv_ssthresh <= window) {
246                 if (truesize <= skb->len)
247                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
248
249                 truesize >>= 1;
250                 window >>= 1;
251         }
252         return 0;
253 }
254
255 static void tcp_grow_window(struct sock *sk,
256                             struct sk_buff *skb)
257 {
258         struct tcp_sock *tp = tcp_sk(sk);
259
260         /* Check #1 */
261         if (tp->rcv_ssthresh < tp->window_clamp &&
262             (int)tp->rcv_ssthresh < tcp_space(sk) &&
263             !tcp_memory_pressure) {
264                 int incr;
265
266                 /* Check #2. Increase window, if skb with such overhead
267                  * will fit to rcvbuf in future.
268                  */
269                 if (tcp_win_from_space(skb->truesize) <= skb->len)
270                         incr = 2*tp->advmss;
271                 else
272                         incr = __tcp_grow_window(sk, skb);
273
274                 if (incr) {
275                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
276                         inet_csk(sk)->icsk_ack.quick |= 1;
277                 }
278         }
279 }
280
281 /* 3. Tuning rcvbuf, when connection enters established state. */
282
283 static void tcp_fixup_rcvbuf(struct sock *sk)
284 {
285         struct tcp_sock *tp = tcp_sk(sk);
286         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
287
288         /* Try to select rcvbuf so that 4 mss-sized segments
289          * will fit to window and corresponding skbs will fit to our rcvbuf.
290          * (was 3; 4 is minimum to allow fast retransmit to work.)
291          */
292         while (tcp_win_from_space(rcvmem) < tp->advmss)
293                 rcvmem += 128;
294         if (sk->sk_rcvbuf < 4 * rcvmem)
295                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
296 }
297
298 /* 4. Try to fixup all. It is made immediately after connection enters
299  *    established state.
300  */
301 static void tcp_init_buffer_space(struct sock *sk)
302 {
303         struct tcp_sock *tp = tcp_sk(sk);
304         int maxwin;
305
306         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
307                 tcp_fixup_rcvbuf(sk);
308         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
309                 tcp_fixup_sndbuf(sk);
310
311         tp->rcvq_space.space = tp->rcv_wnd;
312
313         maxwin = tcp_full_space(sk);
314
315         if (tp->window_clamp >= maxwin) {
316                 tp->window_clamp = maxwin;
317
318                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
319                         tp->window_clamp = max(maxwin -
320                                                (maxwin >> sysctl_tcp_app_win),
321                                                4 * tp->advmss);
322         }
323
324         /* Force reservation of one segment. */
325         if (sysctl_tcp_app_win &&
326             tp->window_clamp > 2 * tp->advmss &&
327             tp->window_clamp + tp->advmss > maxwin)
328                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
329
330         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
331         tp->snd_cwnd_stamp = tcp_time_stamp;
332 }
333
334 /* 5. Recalculate window clamp after socket hit its memory bounds. */
335 static void tcp_clamp_window(struct sock *sk)
336 {
337         struct tcp_sock *tp = tcp_sk(sk);
338         struct inet_connection_sock *icsk = inet_csk(sk);
339
340         icsk->icsk_ack.quick = 0;
341
342         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
343             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
344             !tcp_memory_pressure &&
345             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
346                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
347                                     sysctl_tcp_rmem[2]);
348         }
349         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
350                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
351 }
352
353
354 /* Initialize RCV_MSS value.
355  * RCV_MSS is an our guess about MSS used by the peer.
356  * We haven't any direct information about the MSS.
357  * It's better to underestimate the RCV_MSS rather than overestimate.
358  * Overestimations make us ACKing less frequently than needed.
359  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
360  */
361 void tcp_initialize_rcv_mss(struct sock *sk)
362 {
363         struct tcp_sock *tp = tcp_sk(sk);
364         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
365
366         hint = min(hint, tp->rcv_wnd/2);
367         hint = min(hint, TCP_MIN_RCVMSS);
368         hint = max(hint, TCP_MIN_MSS);
369
370         inet_csk(sk)->icsk_ack.rcv_mss = hint;
371 }
372
373 /* Receiver "autotuning" code.
374  *
375  * The algorithm for RTT estimation w/o timestamps is based on
376  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
377  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
378  *
379  * More detail on this code can be found at
380  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
381  * though this reference is out of date.  A new paper
382  * is pending.
383  */
384 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
385 {
386         u32 new_sample = tp->rcv_rtt_est.rtt;
387         long m = sample;
388
389         if (m == 0)
390                 m = 1;
391
392         if (new_sample != 0) {
393                 /* If we sample in larger samples in the non-timestamp
394                  * case, we could grossly overestimate the RTT especially
395                  * with chatty applications or bulk transfer apps which
396                  * are stalled on filesystem I/O.
397                  *
398                  * Also, since we are only going for a minimum in the
399                  * non-timestamp case, we do not smooth things out
400                  * else with timestamps disabled convergence takes too
401                  * long.
402                  */
403                 if (!win_dep) {
404                         m -= (new_sample >> 3);
405                         new_sample += m;
406                 } else if (m < new_sample)
407                         new_sample = m << 3;
408         } else {
409                 /* No previous measure. */
410                 new_sample = m << 3;
411         }
412
413         if (tp->rcv_rtt_est.rtt != new_sample)
414                 tp->rcv_rtt_est.rtt = new_sample;
415 }
416
417 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
418 {
419         if (tp->rcv_rtt_est.time == 0)
420                 goto new_measure;
421         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
422                 return;
423         tcp_rcv_rtt_update(tp,
424                            jiffies - tp->rcv_rtt_est.time,
425                            1);
426
427 new_measure:
428         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
429         tp->rcv_rtt_est.time = tcp_time_stamp;
430 }
431
432 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
433 {
434         struct tcp_sock *tp = tcp_sk(sk);
435         if (tp->rx_opt.rcv_tsecr &&
436             (TCP_SKB_CB(skb)->end_seq -
437              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
438                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
439 }
440
441 /*
442  * This function should be called every time data is copied to user space.
443  * It calculates the appropriate TCP receive buffer space.
444  */
445 void tcp_rcv_space_adjust(struct sock *sk)
446 {
447         struct tcp_sock *tp = tcp_sk(sk);
448         int time;
449         int space;
450
451         if (tp->rcvq_space.time == 0)
452                 goto new_measure;
453
454         time = tcp_time_stamp - tp->rcvq_space.time;
455         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
456             tp->rcv_rtt_est.rtt == 0)
457                 return;
458
459         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
460
461         space = max(tp->rcvq_space.space, space);
462
463         if (tp->rcvq_space.space != space) {
464                 int rcvmem;
465
466                 tp->rcvq_space.space = space;
467
468                 if (sysctl_tcp_moderate_rcvbuf &&
469                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
470                         int new_clamp = space;
471
472                         /* Receive space grows, normalize in order to
473                          * take into account packet headers and sk_buff
474                          * structure overhead.
475                          */
476                         space /= tp->advmss;
477                         if (!space)
478                                 space = 1;
479                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
480                                   16 + sizeof(struct sk_buff));
481                         while (tcp_win_from_space(rcvmem) < tp->advmss)
482                                 rcvmem += 128;
483                         space *= rcvmem;
484                         space = min(space, sysctl_tcp_rmem[2]);
485                         if (space > sk->sk_rcvbuf) {
486                                 sk->sk_rcvbuf = space;
487
488                                 /* Make the window clamp follow along.  */
489                                 tp->window_clamp = new_clamp;
490                         }
491                 }
492         }
493
494 new_measure:
495         tp->rcvq_space.seq = tp->copied_seq;
496         tp->rcvq_space.time = tcp_time_stamp;
497 }
498
499 /* There is something which you must keep in mind when you analyze the
500  * behavior of the tp->ato delayed ack timeout interval.  When a
501  * connection starts up, we want to ack as quickly as possible.  The
502  * problem is that "good" TCP's do slow start at the beginning of data
503  * transmission.  The means that until we send the first few ACK's the
504  * sender will sit on his end and only queue most of his data, because
505  * he can only send snd_cwnd unacked packets at any given time.  For
506  * each ACK we send, he increments snd_cwnd and transmits more of his
507  * queue.  -DaveM
508  */
509 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
510 {
511         struct tcp_sock *tp = tcp_sk(sk);
512         struct inet_connection_sock *icsk = inet_csk(sk);
513         u32 now;
514
515         inet_csk_schedule_ack(sk);
516
517         tcp_measure_rcv_mss(sk, skb);
518
519         tcp_rcv_rtt_measure(tp);
520
521         now = tcp_time_stamp;
522
523         if (!icsk->icsk_ack.ato) {
524                 /* The _first_ data packet received, initialize
525                  * delayed ACK engine.
526                  */
527                 tcp_incr_quickack(sk);
528                 icsk->icsk_ack.ato = TCP_ATO_MIN;
529         } else {
530                 int m = now - icsk->icsk_ack.lrcvtime;
531
532                 if (m <= TCP_ATO_MIN/2) {
533                         /* The fastest case is the first. */
534                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
535                 } else if (m < icsk->icsk_ack.ato) {
536                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
537                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
538                                 icsk->icsk_ack.ato = icsk->icsk_rto;
539                 } else if (m > icsk->icsk_rto) {
540                         /* Too long gap. Apparently sender failed to
541                          * restart window, so that we send ACKs quickly.
542                          */
543                         tcp_incr_quickack(sk);
544                         sk_stream_mem_reclaim(sk);
545                 }
546         }
547         icsk->icsk_ack.lrcvtime = now;
548
549         TCP_ECN_check_ce(tp, skb);
550
551         if (skb->len >= 128)
552                 tcp_grow_window(sk, skb);
553 }
554
555 /* Called to compute a smoothed rtt estimate. The data fed to this
556  * routine either comes from timestamps, or from segments that were
557  * known _not_ to have been retransmitted [see Karn/Partridge
558  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
559  * piece by Van Jacobson.
560  * NOTE: the next three routines used to be one big routine.
561  * To save cycles in the RFC 1323 implementation it was better to break
562  * it up into three procedures. -- erics
563  */
564 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
565 {
566         struct tcp_sock *tp = tcp_sk(sk);
567         long m = mrtt; /* RTT */
568
569         /*      The following amusing code comes from Jacobson's
570          *      article in SIGCOMM '88.  Note that rtt and mdev
571          *      are scaled versions of rtt and mean deviation.
572          *      This is designed to be as fast as possible
573          *      m stands for "measurement".
574          *
575          *      On a 1990 paper the rto value is changed to:
576          *      RTO = rtt + 4 * mdev
577          *
578          * Funny. This algorithm seems to be very broken.
579          * These formulae increase RTO, when it should be decreased, increase
580          * too slowly, when it should be increased quickly, decrease too quickly
581          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
582          * does not matter how to _calculate_ it. Seems, it was trap
583          * that VJ failed to avoid. 8)
584          */
585         if (m == 0)
586                 m = 1;
587         if (tp->srtt != 0) {
588                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
589                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
590                 if (m < 0) {
591                         m = -m;         /* m is now abs(error) */
592                         m -= (tp->mdev >> 2);   /* similar update on mdev */
593                         /* This is similar to one of Eifel findings.
594                          * Eifel blocks mdev updates when rtt decreases.
595                          * This solution is a bit different: we use finer gain
596                          * for mdev in this case (alpha*beta).
597                          * Like Eifel it also prevents growth of rto,
598                          * but also it limits too fast rto decreases,
599                          * happening in pure Eifel.
600                          */
601                         if (m > 0)
602                                 m >>= 3;
603                 } else {
604                         m -= (tp->mdev >> 2);   /* similar update on mdev */
605                 }
606                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
607                 if (tp->mdev > tp->mdev_max) {
608                         tp->mdev_max = tp->mdev;
609                         if (tp->mdev_max > tp->rttvar)
610                                 tp->rttvar = tp->mdev_max;
611                 }
612                 if (after(tp->snd_una, tp->rtt_seq)) {
613                         if (tp->mdev_max < tp->rttvar)
614                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
615                         tp->rtt_seq = tp->snd_nxt;
616                         tp->mdev_max = TCP_RTO_MIN;
617                 }
618         } else {
619                 /* no previous measure. */
620                 tp->srtt = m<<3;        /* take the measured time to be rtt */
621                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
622                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
623                 tp->rtt_seq = tp->snd_nxt;
624         }
625 }
626
627 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
628  * routine referred to above.
629  */
630 static inline void tcp_set_rto(struct sock *sk)
631 {
632         const struct tcp_sock *tp = tcp_sk(sk);
633         /* Old crap is replaced with new one. 8)
634          *
635          * More seriously:
636          * 1. If rtt variance happened to be less 50msec, it is hallucination.
637          *    It cannot be less due to utterly erratic ACK generation made
638          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
639          *    to do with delayed acks, because at cwnd>2 true delack timeout
640          *    is invisible. Actually, Linux-2.4 also generates erratic
641          *    ACKs in some circumstances.
642          */
643         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
644
645         /* 2. Fixups made earlier cannot be right.
646          *    If we do not estimate RTO correctly without them,
647          *    all the algo is pure shit and should be replaced
648          *    with correct one. It is exactly, which we pretend to do.
649          */
650 }
651
652 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
653  * guarantees that rto is higher.
654  */
655 static inline void tcp_bound_rto(struct sock *sk)
656 {
657         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
658                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
659 }
660
661 /* Save metrics learned by this TCP session.
662    This function is called only, when TCP finishes successfully
663    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
664  */
665 void tcp_update_metrics(struct sock *sk)
666 {
667         struct tcp_sock *tp = tcp_sk(sk);
668         struct dst_entry *dst = __sk_dst_get(sk);
669
670         if (sysctl_tcp_nometrics_save)
671                 return;
672
673         dst_confirm(dst);
674
675         if (dst && (dst->flags&DST_HOST)) {
676                 const struct inet_connection_sock *icsk = inet_csk(sk);
677                 int m;
678
679                 if (icsk->icsk_backoff || !tp->srtt) {
680                         /* This session failed to estimate rtt. Why?
681                          * Probably, no packets returned in time.
682                          * Reset our results.
683                          */
684                         if (!(dst_metric_locked(dst, RTAX_RTT)))
685                                 dst->metrics[RTAX_RTT-1] = 0;
686                         return;
687                 }
688
689                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
690
691                 /* If newly calculated rtt larger than stored one,
692                  * store new one. Otherwise, use EWMA. Remember,
693                  * rtt overestimation is always better than underestimation.
694                  */
695                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
696                         if (m <= 0)
697                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
698                         else
699                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
700                 }
701
702                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
703                         if (m < 0)
704                                 m = -m;
705
706                         /* Scale deviation to rttvar fixed point */
707                         m >>= 1;
708                         if (m < tp->mdev)
709                                 m = tp->mdev;
710
711                         if (m >= dst_metric(dst, RTAX_RTTVAR))
712                                 dst->metrics[RTAX_RTTVAR-1] = m;
713                         else
714                                 dst->metrics[RTAX_RTTVAR-1] -=
715                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
716                 }
717
718                 if (tp->snd_ssthresh >= 0xFFFF) {
719                         /* Slow start still did not finish. */
720                         if (dst_metric(dst, RTAX_SSTHRESH) &&
721                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
722                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
723                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
724                         if (!dst_metric_locked(dst, RTAX_CWND) &&
725                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
726                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
727                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
728                            icsk->icsk_ca_state == TCP_CA_Open) {
729                         /* Cong. avoidance phase, cwnd is reliable. */
730                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
731                                 dst->metrics[RTAX_SSTHRESH-1] =
732                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
733                         if (!dst_metric_locked(dst, RTAX_CWND))
734                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
735                 } else {
736                         /* Else slow start did not finish, cwnd is non-sense,
737                            ssthresh may be also invalid.
738                          */
739                         if (!dst_metric_locked(dst, RTAX_CWND))
740                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
741                         if (dst->metrics[RTAX_SSTHRESH-1] &&
742                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
743                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
744                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
745                 }
746
747                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
748                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
749                             tp->reordering != sysctl_tcp_reordering)
750                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
751                 }
752         }
753 }
754
755 /* Numbers are taken from RFC2414.  */
756 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
757 {
758         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
759
760         if (!cwnd) {
761                 if (tp->mss_cache > 1460)
762                         cwnd = 2;
763                 else
764                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
765         }
766         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
767 }
768
769 /* Set slow start threshold and cwnd not falling to slow start */
770 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
771 {
772         struct tcp_sock *tp = tcp_sk(sk);
773         const struct inet_connection_sock *icsk = inet_csk(sk);
774
775         tp->prior_ssthresh = 0;
776         tp->bytes_acked = 0;
777         if (icsk->icsk_ca_state < TCP_CA_CWR) {
778                 tp->undo_marker = 0;
779                 if (set_ssthresh)
780                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
781                 tp->snd_cwnd = min(tp->snd_cwnd,
782                                    tcp_packets_in_flight(tp) + 1U);
783                 tp->snd_cwnd_cnt = 0;
784                 tp->high_seq = tp->snd_nxt;
785                 tp->snd_cwnd_stamp = tcp_time_stamp;
786                 TCP_ECN_queue_cwr(tp);
787
788                 tcp_set_ca_state(sk, TCP_CA_CWR);
789         }
790 }
791
792 /* Initialize metrics on socket. */
793
794 static void tcp_init_metrics(struct sock *sk)
795 {
796         struct tcp_sock *tp = tcp_sk(sk);
797         struct dst_entry *dst = __sk_dst_get(sk);
798
799         if (dst == NULL)
800                 goto reset;
801
802         dst_confirm(dst);
803
804         if (dst_metric_locked(dst, RTAX_CWND))
805                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
806         if (dst_metric(dst, RTAX_SSTHRESH)) {
807                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
808                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
809                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
810         }
811         if (dst_metric(dst, RTAX_REORDERING) &&
812             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
813                 tp->rx_opt.sack_ok &= ~2;
814                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
815         }
816
817         if (dst_metric(dst, RTAX_RTT) == 0)
818                 goto reset;
819
820         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
821                 goto reset;
822
823         /* Initial rtt is determined from SYN,SYN-ACK.
824          * The segment is small and rtt may appear much
825          * less than real one. Use per-dst memory
826          * to make it more realistic.
827          *
828          * A bit of theory. RTT is time passed after "normal" sized packet
829          * is sent until it is ACKed. In normal circumstances sending small
830          * packets force peer to delay ACKs and calculation is correct too.
831          * The algorithm is adaptive and, provided we follow specs, it
832          * NEVER underestimate RTT. BUT! If peer tries to make some clever
833          * tricks sort of "quick acks" for time long enough to decrease RTT
834          * to low value, and then abruptly stops to do it and starts to delay
835          * ACKs, wait for troubles.
836          */
837         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
838                 tp->srtt = dst_metric(dst, RTAX_RTT);
839                 tp->rtt_seq = tp->snd_nxt;
840         }
841         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
842                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
843                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
844         }
845         tcp_set_rto(sk);
846         tcp_bound_rto(sk);
847         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
848                 goto reset;
849         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
850         tp->snd_cwnd_stamp = tcp_time_stamp;
851         return;
852
853 reset:
854         /* Play conservative. If timestamps are not
855          * supported, TCP will fail to recalculate correct
856          * rtt, if initial rto is too small. FORGET ALL AND RESET!
857          */
858         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
859                 tp->srtt = 0;
860                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
861                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
862         }
863 }
864
865 static void tcp_update_reordering(struct sock *sk, const int metric,
866                                   const int ts)
867 {
868         struct tcp_sock *tp = tcp_sk(sk);
869         if (metric > tp->reordering) {
870                 tp->reordering = min(TCP_MAX_REORDERING, metric);
871
872                 /* This exciting event is worth to be remembered. 8) */
873                 if (ts)
874                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
875                 else if (IsReno(tp))
876                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
877                 else if (IsFack(tp))
878                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
879                 else
880                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
881 #if FASTRETRANS_DEBUG > 1
882                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
883                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
884                        tp->reordering,
885                        tp->fackets_out,
886                        tp->sacked_out,
887                        tp->undo_marker ? tp->undo_retrans : 0);
888 #endif
889                 /* Disable FACK yet. */
890                 tp->rx_opt.sack_ok &= ~2;
891         }
892 }
893
894 /* This procedure tags the retransmission queue when SACKs arrive.
895  *
896  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
897  * Packets in queue with these bits set are counted in variables
898  * sacked_out, retrans_out and lost_out, correspondingly.
899  *
900  * Valid combinations are:
901  * Tag  InFlight        Description
902  * 0    1               - orig segment is in flight.
903  * S    0               - nothing flies, orig reached receiver.
904  * L    0               - nothing flies, orig lost by net.
905  * R    2               - both orig and retransmit are in flight.
906  * L|R  1               - orig is lost, retransmit is in flight.
907  * S|R  1               - orig reached receiver, retrans is still in flight.
908  * (L|S|R is logically valid, it could occur when L|R is sacked,
909  *  but it is equivalent to plain S and code short-curcuits it to S.
910  *  L|S is logically invalid, it would mean -1 packet in flight 8))
911  *
912  * These 6 states form finite state machine, controlled by the following events:
913  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
914  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
915  * 3. Loss detection event of one of three flavors:
916  *      A. Scoreboard estimator decided the packet is lost.
917  *         A'. Reno "three dupacks" marks head of queue lost.
918  *         A''. Its FACK modfication, head until snd.fack is lost.
919  *      B. SACK arrives sacking data transmitted after never retransmitted
920  *         hole was sent out.
921  *      C. SACK arrives sacking SND.NXT at the moment, when the
922  *         segment was retransmitted.
923  * 4. D-SACK added new rule: D-SACK changes any tag to S.
924  *
925  * It is pleasant to note, that state diagram turns out to be commutative,
926  * so that we are allowed not to be bothered by order of our actions,
927  * when multiple events arrive simultaneously. (see the function below).
928  *
929  * Reordering detection.
930  * --------------------
931  * Reordering metric is maximal distance, which a packet can be displaced
932  * in packet stream. With SACKs we can estimate it:
933  *
934  * 1. SACK fills old hole and the corresponding segment was not
935  *    ever retransmitted -> reordering. Alas, we cannot use it
936  *    when segment was retransmitted.
937  * 2. The last flaw is solved with D-SACK. D-SACK arrives
938  *    for retransmitted and already SACKed segment -> reordering..
939  * Both of these heuristics are not used in Loss state, when we cannot
940  * account for retransmits accurately.
941  */
942 static int
943 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
944 {
945         const struct inet_connection_sock *icsk = inet_csk(sk);
946         struct tcp_sock *tp = tcp_sk(sk);
947         unsigned char *ptr = (skb_transport_header(ack_skb) +
948                               TCP_SKB_CB(ack_skb)->sacked);
949         struct tcp_sack_block_wire *sp = (struct tcp_sack_block_wire *)(ptr+2);
950         struct sk_buff *cached_skb;
951         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
952         int reord = tp->packets_out;
953         int prior_fackets;
954         u32 lost_retrans = 0;
955         int flag = 0;
956         int dup_sack = 0;
957         int cached_fack_count;
958         int i;
959         int first_sack_index;
960
961         if (!tp->sacked_out)
962                 tp->fackets_out = 0;
963         prior_fackets = tp->fackets_out;
964
965         /* Check for D-SACK. */
966         if (before(ntohl(sp[0].start_seq), TCP_SKB_CB(ack_skb)->ack_seq)) {
967                 dup_sack = 1;
968                 tp->rx_opt.sack_ok |= 4;
969                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
970         } else if (num_sacks > 1 &&
971                         !after(ntohl(sp[0].end_seq), ntohl(sp[1].end_seq)) &&
972                         !before(ntohl(sp[0].start_seq), ntohl(sp[1].start_seq))) {
973                 dup_sack = 1;
974                 tp->rx_opt.sack_ok |= 4;
975                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
976         }
977
978         /* D-SACK for already forgotten data...
979          * Do dumb counting. */
980         if (dup_sack &&
981                         !after(ntohl(sp[0].end_seq), prior_snd_una) &&
982                         after(ntohl(sp[0].end_seq), tp->undo_marker))
983                 tp->undo_retrans--;
984
985         /* Eliminate too old ACKs, but take into
986          * account more or less fresh ones, they can
987          * contain valid SACK info.
988          */
989         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
990                 return 0;
991
992         /* SACK fastpath:
993          * if the only SACK change is the increase of the end_seq of
994          * the first block then only apply that SACK block
995          * and use retrans queue hinting otherwise slowpath */
996         flag = 1;
997         for (i = 0; i < num_sacks; i++) {
998                 __be32 start_seq = sp[i].start_seq;
999                 __be32 end_seq = sp[i].end_seq;
1000
1001                 if (i == 0) {
1002                         if (tp->recv_sack_cache[i].start_seq != start_seq)
1003                                 flag = 0;
1004                 } else {
1005                         if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
1006                             (tp->recv_sack_cache[i].end_seq != end_seq))
1007                                 flag = 0;
1008                 }
1009                 tp->recv_sack_cache[i].start_seq = start_seq;
1010                 tp->recv_sack_cache[i].end_seq = end_seq;
1011         }
1012         /* Clear the rest of the cache sack blocks so they won't match mistakenly. */
1013         for (; i < ARRAY_SIZE(tp->recv_sack_cache); i++) {
1014                 tp->recv_sack_cache[i].start_seq = 0;
1015                 tp->recv_sack_cache[i].end_seq = 0;
1016         }
1017
1018         first_sack_index = 0;
1019         if (flag)
1020                 num_sacks = 1;
1021         else {
1022                 int j;
1023                 tp->fastpath_skb_hint = NULL;
1024
1025                 /* order SACK blocks to allow in order walk of the retrans queue */
1026                 for (i = num_sacks-1; i > 0; i--) {
1027                         for (j = 0; j < i; j++){
1028                                 if (after(ntohl(sp[j].start_seq),
1029                                           ntohl(sp[j+1].start_seq))){
1030                                         struct tcp_sack_block_wire tmp;
1031
1032                                         tmp = sp[j];
1033                                         sp[j] = sp[j+1];
1034                                         sp[j+1] = tmp;
1035
1036                                         /* Track where the first SACK block goes to */
1037                                         if (j == first_sack_index)
1038                                                 first_sack_index = j+1;
1039                                 }
1040
1041                         }
1042                 }
1043         }
1044
1045         /* clear flag as used for different purpose in following code */
1046         flag = 0;
1047
1048         /* Use SACK fastpath hint if valid */
1049         cached_skb = tp->fastpath_skb_hint;
1050         cached_fack_count = tp->fastpath_cnt_hint;
1051         if (!cached_skb) {
1052                 cached_skb = tcp_write_queue_head(sk);
1053                 cached_fack_count = 0;
1054         }
1055
1056         for (i=0; i<num_sacks; i++, sp++) {
1057                 struct sk_buff *skb;
1058                 __u32 start_seq = ntohl(sp->start_seq);
1059                 __u32 end_seq = ntohl(sp->end_seq);
1060                 int fack_count;
1061
1062                 skb = cached_skb;
1063                 fack_count = cached_fack_count;
1064
1065                 /* Event "B" in the comment above. */
1066                 if (after(end_seq, tp->high_seq))
1067                         flag |= FLAG_DATA_LOST;
1068
1069                 tcp_for_write_queue_from(skb, sk) {
1070                         int in_sack, pcount;
1071                         u8 sacked;
1072
1073                         if (skb == tcp_send_head(sk))
1074                                 break;
1075
1076                         cached_skb = skb;
1077                         cached_fack_count = fack_count;
1078                         if (i == first_sack_index) {
1079                                 tp->fastpath_skb_hint = skb;
1080                                 tp->fastpath_cnt_hint = fack_count;
1081                         }
1082
1083                         /* The retransmission queue is always in order, so
1084                          * we can short-circuit the walk early.
1085                          */
1086                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1087                                 break;
1088
1089                         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1090                                 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1091
1092                         pcount = tcp_skb_pcount(skb);
1093
1094                         if (pcount > 1 && !in_sack &&
1095                             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1096                                 unsigned int pkt_len;
1097
1098                                 in_sack = !after(start_seq,
1099                                                  TCP_SKB_CB(skb)->seq);
1100
1101                                 if (!in_sack)
1102                                         pkt_len = (start_seq -
1103                                                    TCP_SKB_CB(skb)->seq);
1104                                 else
1105                                         pkt_len = (end_seq -
1106                                                    TCP_SKB_CB(skb)->seq);
1107                                 if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size))
1108                                         break;
1109                                 pcount = tcp_skb_pcount(skb);
1110                         }
1111
1112                         fack_count += pcount;
1113
1114                         sacked = TCP_SKB_CB(skb)->sacked;
1115
1116                         /* Account D-SACK for retransmitted packet. */
1117                         if ((dup_sack && in_sack) &&
1118                             (sacked & TCPCB_RETRANS) &&
1119                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1120                                 tp->undo_retrans--;
1121
1122                         /* The frame is ACKed. */
1123                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1124                                 if (sacked&TCPCB_RETRANS) {
1125                                         if ((dup_sack && in_sack) &&
1126                                             (sacked&TCPCB_SACKED_ACKED))
1127                                                 reord = min(fack_count, reord);
1128                                 } else {
1129                                         /* If it was in a hole, we detected reordering. */
1130                                         if (fack_count < prior_fackets &&
1131                                             !(sacked&TCPCB_SACKED_ACKED))
1132                                                 reord = min(fack_count, reord);
1133                                 }
1134
1135                                 /* Nothing to do; acked frame is about to be dropped. */
1136                                 continue;
1137                         }
1138
1139                         if ((sacked&TCPCB_SACKED_RETRANS) &&
1140                             after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
1141                             (!lost_retrans || after(end_seq, lost_retrans)))
1142                                 lost_retrans = end_seq;
1143
1144                         if (!in_sack)
1145                                 continue;
1146
1147                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1148                                 if (sacked & TCPCB_SACKED_RETRANS) {
1149                                         /* If the segment is not tagged as lost,
1150                                          * we do not clear RETRANS, believing
1151                                          * that retransmission is still in flight.
1152                                          */
1153                                         if (sacked & TCPCB_LOST) {
1154                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1155                                                 tp->lost_out -= tcp_skb_pcount(skb);
1156                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1157
1158                                                 /* clear lost hint */
1159                                                 tp->retransmit_skb_hint = NULL;
1160                                         }
1161                                 } else {
1162                                         /* New sack for not retransmitted frame,
1163                                          * which was in hole. It is reordering.
1164                                          */
1165                                         if (!(sacked & TCPCB_RETRANS) &&
1166                                             fack_count < prior_fackets)
1167                                                 reord = min(fack_count, reord);
1168
1169                                         if (sacked & TCPCB_LOST) {
1170                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1171                                                 tp->lost_out -= tcp_skb_pcount(skb);
1172
1173                                                 /* clear lost hint */
1174                                                 tp->retransmit_skb_hint = NULL;
1175                                         }
1176                                         /* SACK enhanced F-RTO detection.
1177                                          * Set flag if and only if non-rexmitted
1178                                          * segments below frto_highmark are
1179                                          * SACKed (RFC4138; Appendix B).
1180                                          * Clearing correct due to in-order walk
1181                                          */
1182                                         if (after(end_seq, tp->frto_highmark)) {
1183                                                 flag &= ~FLAG_ONLY_ORIG_SACKED;
1184                                         } else {
1185                                                 if (!(sacked & TCPCB_RETRANS))
1186                                                         flag |= FLAG_ONLY_ORIG_SACKED;
1187                                         }
1188                                 }
1189
1190                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1191                                 flag |= FLAG_DATA_SACKED;
1192                                 tp->sacked_out += tcp_skb_pcount(skb);
1193
1194                                 if (fack_count > tp->fackets_out)
1195                                         tp->fackets_out = fack_count;
1196                         } else {
1197                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1198                                         reord = min(fack_count, reord);
1199                         }
1200
1201                         /* D-SACK. We can detect redundant retransmission
1202                          * in S|R and plain R frames and clear it.
1203                          * undo_retrans is decreased above, L|R frames
1204                          * are accounted above as well.
1205                          */
1206                         if (dup_sack &&
1207                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1208                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1209                                 tp->retrans_out -= tcp_skb_pcount(skb);
1210                                 tp->retransmit_skb_hint = NULL;
1211                         }
1212                 }
1213         }
1214
1215         /* Check for lost retransmit. This superb idea is
1216          * borrowed from "ratehalving". Event "C".
1217          * Later note: FACK people cheated me again 8),
1218          * we have to account for reordering! Ugly,
1219          * but should help.
1220          */
1221         if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
1222                 struct sk_buff *skb;
1223
1224                 tcp_for_write_queue(skb, sk) {
1225                         if (skb == tcp_send_head(sk))
1226                                 break;
1227                         if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
1228                                 break;
1229                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1230                                 continue;
1231                         if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
1232                             after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
1233                             (IsFack(tp) ||
1234                              !before(lost_retrans,
1235                                      TCP_SKB_CB(skb)->ack_seq + tp->reordering *
1236                                      tp->mss_cache))) {
1237                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1238                                 tp->retrans_out -= tcp_skb_pcount(skb);
1239
1240                                 /* clear lost hint */
1241                                 tp->retransmit_skb_hint = NULL;
1242
1243                                 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1244                                         tp->lost_out += tcp_skb_pcount(skb);
1245                                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1246                                         flag |= FLAG_DATA_SACKED;
1247                                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1248                                 }
1249                         }
1250                 }
1251         }
1252
1253         tp->left_out = tp->sacked_out + tp->lost_out;
1254
1255         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss &&
1256             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1257                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1258
1259 #if FASTRETRANS_DEBUG > 0
1260         BUG_TRAP((int)tp->sacked_out >= 0);
1261         BUG_TRAP((int)tp->lost_out >= 0);
1262         BUG_TRAP((int)tp->retrans_out >= 0);
1263         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1264 #endif
1265         return flag;
1266 }
1267
1268 /* F-RTO can only be used if TCP has never retransmitted anything other than
1269  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
1270  */
1271 int tcp_use_frto(struct sock *sk)
1272 {
1273         const struct tcp_sock *tp = tcp_sk(sk);
1274         struct sk_buff *skb;
1275
1276         if (!sysctl_tcp_frto)
1277                 return 0;
1278
1279         if (IsSackFrto())
1280                 return 1;
1281
1282         /* Avoid expensive walking of rexmit queue if possible */
1283         if (tp->retrans_out > 1)
1284                 return 0;
1285
1286         skb = tcp_write_queue_head(sk);
1287         skb = tcp_write_queue_next(sk, skb);    /* Skips head */
1288         tcp_for_write_queue_from(skb, sk) {
1289                 if (skb == tcp_send_head(sk))
1290                         break;
1291                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1292                         return 0;
1293                 /* Short-circuit when first non-SACKed skb has been checked */
1294                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED))
1295                         break;
1296         }
1297         return 1;
1298 }
1299
1300 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
1301  * recovery a bit and use heuristics in tcp_process_frto() to detect if
1302  * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
1303  * keep retrans_out counting accurate (with SACK F-RTO, other than head
1304  * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
1305  * bits are handled if the Loss state is really to be entered (in
1306  * tcp_enter_frto_loss).
1307  *
1308  * Do like tcp_enter_loss() would; when RTO expires the second time it
1309  * does:
1310  *  "Reduce ssthresh if it has not yet been made inside this window."
1311  */
1312 void tcp_enter_frto(struct sock *sk)
1313 {
1314         const struct inet_connection_sock *icsk = inet_csk(sk);
1315         struct tcp_sock *tp = tcp_sk(sk);
1316         struct sk_buff *skb;
1317
1318         if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
1319             tp->snd_una == tp->high_seq ||
1320             ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
1321              !icsk->icsk_retransmits)) {
1322                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1323                 /* Our state is too optimistic in ssthresh() call because cwnd
1324                  * is not reduced until tcp_enter_frto_loss() when previous FRTO
1325                  * recovery has not yet completed. Pattern would be this: RTO,
1326                  * Cumulative ACK, RTO (2xRTO for the same segment does not end
1327                  * up here twice).
1328                  * RFC4138 should be more specific on what to do, even though
1329                  * RTO is quite unlikely to occur after the first Cumulative ACK
1330                  * due to back-off and complexity of triggering events ...
1331                  */
1332                 if (tp->frto_counter) {
1333                         u32 stored_cwnd;
1334                         stored_cwnd = tp->snd_cwnd;
1335                         tp->snd_cwnd = 2;
1336                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1337                         tp->snd_cwnd = stored_cwnd;
1338                 } else {
1339                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1340                 }
1341                 /* ... in theory, cong.control module could do "any tricks" in
1342                  * ssthresh(), which means that ca_state, lost bits and lost_out
1343                  * counter would have to be faked before the call occurs. We
1344                  * consider that too expensive, unlikely and hacky, so modules
1345                  * using these in ssthresh() must deal these incompatibility
1346                  * issues if they receives CA_EVENT_FRTO and frto_counter != 0
1347                  */
1348                 tcp_ca_event(sk, CA_EVENT_FRTO);
1349         }
1350
1351         tp->undo_marker = tp->snd_una;
1352         tp->undo_retrans = 0;
1353
1354         skb = tcp_write_queue_head(sk);
1355         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
1356                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1357                 tp->retrans_out -= tcp_skb_pcount(skb);
1358         }
1359         tcp_sync_left_out(tp);
1360
1361         /* Earlier loss recovery underway (see RFC4138; Appendix B).
1362          * The last condition is necessary at least in tp->frto_counter case.
1363          */
1364         if (IsSackFrto() && (tp->frto_counter ||
1365             ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
1366             after(tp->high_seq, tp->snd_una)) {
1367                 tp->frto_highmark = tp->high_seq;
1368         } else {
1369                 tp->frto_highmark = tp->snd_nxt;
1370         }
1371         tcp_set_ca_state(sk, TCP_CA_Disorder);
1372         tp->high_seq = tp->snd_nxt;
1373         tp->frto_counter = 1;
1374 }
1375
1376 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1377  * which indicates that we should follow the traditional RTO recovery,
1378  * i.e. mark everything lost and do go-back-N retransmission.
1379  */
1380 static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
1381 {
1382         struct tcp_sock *tp = tcp_sk(sk);
1383         struct sk_buff *skb;
1384         int cnt = 0;
1385
1386         tp->sacked_out = 0;
1387         tp->lost_out = 0;
1388         tp->fackets_out = 0;
1389         tp->retrans_out = 0;
1390
1391         tcp_for_write_queue(skb, sk) {
1392                 if (skb == tcp_send_head(sk))
1393                         break;
1394                 cnt += tcp_skb_pcount(skb);
1395                 /*
1396                  * Count the retransmission made on RTO correctly (only when
1397                  * waiting for the first ACK and did not get it)...
1398                  */
1399                 if ((tp->frto_counter == 1) && !(flag&FLAG_DATA_ACKED)) {
1400                         tp->retrans_out += tcp_skb_pcount(skb);
1401                         /* ...enter this if branch just for the first segment */
1402                         flag |= FLAG_DATA_ACKED;
1403                 } else {
1404                         TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1405                 }
1406                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1407
1408                         /* Do not mark those segments lost that were
1409                          * forward transmitted after RTO
1410                          */
1411                         if (!after(TCP_SKB_CB(skb)->end_seq,
1412                                    tp->frto_highmark)) {
1413                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1414                                 tp->lost_out += tcp_skb_pcount(skb);
1415                         }
1416                 } else {
1417                         tp->sacked_out += tcp_skb_pcount(skb);
1418                         tp->fackets_out = cnt;
1419                 }
1420         }
1421         tcp_sync_left_out(tp);
1422
1423         tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
1424         tp->snd_cwnd_cnt = 0;
1425         tp->snd_cwnd_stamp = tcp_time_stamp;
1426         tp->undo_marker = 0;
1427         tp->frto_counter = 0;
1428
1429         tp->reordering = min_t(unsigned int, tp->reordering,
1430                                              sysctl_tcp_reordering);
1431         tcp_set_ca_state(sk, TCP_CA_Loss);
1432         tp->high_seq = tp->frto_highmark;
1433         TCP_ECN_queue_cwr(tp);
1434
1435         clear_all_retrans_hints(tp);
1436 }
1437
1438 void tcp_clear_retrans(struct tcp_sock *tp)
1439 {
1440         tp->left_out = 0;
1441         tp->retrans_out = 0;
1442
1443         tp->fackets_out = 0;
1444         tp->sacked_out = 0;
1445         tp->lost_out = 0;
1446
1447         tp->undo_marker = 0;
1448         tp->undo_retrans = 0;
1449 }
1450
1451 /* Enter Loss state. If "how" is not zero, forget all SACK information
1452  * and reset tags completely, otherwise preserve SACKs. If receiver
1453  * dropped its ofo queue, we will know this due to reneging detection.
1454  */
1455 void tcp_enter_loss(struct sock *sk, int how)
1456 {
1457         const struct inet_connection_sock *icsk = inet_csk(sk);
1458         struct tcp_sock *tp = tcp_sk(sk);
1459         struct sk_buff *skb;
1460         int cnt = 0;
1461
1462         /* Reduce ssthresh if it has not yet been made inside this window. */
1463         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1464             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1465                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1466                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1467                 tcp_ca_event(sk, CA_EVENT_LOSS);
1468         }
1469         tp->snd_cwnd       = 1;
1470         tp->snd_cwnd_cnt   = 0;
1471         tp->snd_cwnd_stamp = tcp_time_stamp;
1472
1473         tp->bytes_acked = 0;
1474         tcp_clear_retrans(tp);
1475
1476         /* Push undo marker, if it was plain RTO and nothing
1477          * was retransmitted. */
1478         if (!how)
1479                 tp->undo_marker = tp->snd_una;
1480
1481         tcp_for_write_queue(skb, sk) {
1482                 if (skb == tcp_send_head(sk))
1483                         break;
1484                 cnt += tcp_skb_pcount(skb);
1485                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1486                         tp->undo_marker = 0;
1487                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1488                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1489                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1490                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1491                         tp->lost_out += tcp_skb_pcount(skb);
1492                 } else {
1493                         tp->sacked_out += tcp_skb_pcount(skb);
1494                         tp->fackets_out = cnt;
1495                 }
1496         }
1497         tcp_sync_left_out(tp);
1498
1499         tp->reordering = min_t(unsigned int, tp->reordering,
1500                                              sysctl_tcp_reordering);
1501         tcp_set_ca_state(sk, TCP_CA_Loss);
1502         tp->high_seq = tp->snd_nxt;
1503         TCP_ECN_queue_cwr(tp);
1504
1505         clear_all_retrans_hints(tp);
1506 }
1507
1508 static int tcp_check_sack_reneging(struct sock *sk)
1509 {
1510         struct sk_buff *skb;
1511
1512         /* If ACK arrived pointing to a remembered SACK,
1513          * it means that our remembered SACKs do not reflect
1514          * real state of receiver i.e.
1515          * receiver _host_ is heavily congested (or buggy).
1516          * Do processing similar to RTO timeout.
1517          */
1518         if ((skb = tcp_write_queue_head(sk)) != NULL &&
1519             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1520                 struct inet_connection_sock *icsk = inet_csk(sk);
1521                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1522
1523                 tcp_enter_loss(sk, 1);
1524                 icsk->icsk_retransmits++;
1525                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
1526                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1527                                           icsk->icsk_rto, TCP_RTO_MAX);
1528                 return 1;
1529         }
1530         return 0;
1531 }
1532
1533 static inline int tcp_fackets_out(struct tcp_sock *tp)
1534 {
1535         return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1536 }
1537
1538 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1539 {
1540         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1541 }
1542
1543 static inline int tcp_head_timedout(struct sock *sk)
1544 {
1545         struct tcp_sock *tp = tcp_sk(sk);
1546
1547         return tp->packets_out &&
1548                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
1549 }
1550
1551 /* Linux NewReno/SACK/FACK/ECN state machine.
1552  * --------------------------------------
1553  *
1554  * "Open"       Normal state, no dubious events, fast path.
1555  * "Disorder"   In all the respects it is "Open",
1556  *              but requires a bit more attention. It is entered when
1557  *              we see some SACKs or dupacks. It is split of "Open"
1558  *              mainly to move some processing from fast path to slow one.
1559  * "CWR"        CWND was reduced due to some Congestion Notification event.
1560  *              It can be ECN, ICMP source quench, local device congestion.
1561  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1562  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1563  *
1564  * tcp_fastretrans_alert() is entered:
1565  * - each incoming ACK, if state is not "Open"
1566  * - when arrived ACK is unusual, namely:
1567  *      * SACK
1568  *      * Duplicate ACK.
1569  *      * ECN ECE.
1570  *
1571  * Counting packets in flight is pretty simple.
1572  *
1573  *      in_flight = packets_out - left_out + retrans_out
1574  *
1575  *      packets_out is SND.NXT-SND.UNA counted in packets.
1576  *
1577  *      retrans_out is number of retransmitted segments.
1578  *
1579  *      left_out is number of segments left network, but not ACKed yet.
1580  *
1581  *              left_out = sacked_out + lost_out
1582  *
1583  *     sacked_out: Packets, which arrived to receiver out of order
1584  *                 and hence not ACKed. With SACKs this number is simply
1585  *                 amount of SACKed data. Even without SACKs
1586  *                 it is easy to give pretty reliable estimate of this number,
1587  *                 counting duplicate ACKs.
1588  *
1589  *       lost_out: Packets lost by network. TCP has no explicit
1590  *                 "loss notification" feedback from network (for now).
1591  *                 It means that this number can be only _guessed_.
1592  *                 Actually, it is the heuristics to predict lossage that
1593  *                 distinguishes different algorithms.
1594  *
1595  *      F.e. after RTO, when all the queue is considered as lost,
1596  *      lost_out = packets_out and in_flight = retrans_out.
1597  *
1598  *              Essentially, we have now two algorithms counting
1599  *              lost packets.
1600  *
1601  *              FACK: It is the simplest heuristics. As soon as we decided
1602  *              that something is lost, we decide that _all_ not SACKed
1603  *              packets until the most forward SACK are lost. I.e.
1604  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1605  *              It is absolutely correct estimate, if network does not reorder
1606  *              packets. And it loses any connection to reality when reordering
1607  *              takes place. We use FACK by default until reordering
1608  *              is suspected on the path to this destination.
1609  *
1610  *              NewReno: when Recovery is entered, we assume that one segment
1611  *              is lost (classic Reno). While we are in Recovery and
1612  *              a partial ACK arrives, we assume that one more packet
1613  *              is lost (NewReno). This heuristics are the same in NewReno
1614  *              and SACK.
1615  *
1616  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1617  *  deflation etc. CWND is real congestion window, never inflated, changes
1618  *  only according to classic VJ rules.
1619  *
1620  * Really tricky (and requiring careful tuning) part of algorithm
1621  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1622  * The first determines the moment _when_ we should reduce CWND and,
1623  * hence, slow down forward transmission. In fact, it determines the moment
1624  * when we decide that hole is caused by loss, rather than by a reorder.
1625  *
1626  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1627  * holes, caused by lost packets.
1628  *
1629  * And the most logically complicated part of algorithm is undo
1630  * heuristics. We detect false retransmits due to both too early
1631  * fast retransmit (reordering) and underestimated RTO, analyzing
1632  * timestamps and D-SACKs. When we detect that some segments were
1633  * retransmitted by mistake and CWND reduction was wrong, we undo
1634  * window reduction and abort recovery phase. This logic is hidden
1635  * inside several functions named tcp_try_undo_<something>.
1636  */
1637
1638 /* This function decides, when we should leave Disordered state
1639  * and enter Recovery phase, reducing congestion window.
1640  *
1641  * Main question: may we further continue forward transmission
1642  * with the same cwnd?
1643  */
1644 static int tcp_time_to_recover(struct sock *sk)
1645 {
1646         struct tcp_sock *tp = tcp_sk(sk);
1647         __u32 packets_out;
1648
1649         /* Do not perform any recovery during FRTO algorithm */
1650         if (tp->frto_counter)
1651                 return 0;
1652
1653         /* Trick#1: The loss is proven. */
1654         if (tp->lost_out)
1655                 return 1;
1656
1657         /* Not-A-Trick#2 : Classic rule... */
1658         if (tcp_fackets_out(tp) > tp->reordering)
1659                 return 1;
1660
1661         /* Trick#3 : when we use RFC2988 timer restart, fast
1662          * retransmit can be triggered by timeout of queue head.
1663          */
1664         if (tcp_head_timedout(sk))
1665                 return 1;
1666
1667         /* Trick#4: It is still not OK... But will it be useful to delay
1668          * recovery more?
1669          */
1670         packets_out = tp->packets_out;
1671         if (packets_out <= tp->reordering &&
1672             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1673             !tcp_may_send_now(sk)) {
1674                 /* We have nothing to send. This connection is limited
1675                  * either by receiver window or by application.
1676                  */
1677                 return 1;
1678         }
1679
1680         return 0;
1681 }
1682
1683 /* If we receive more dupacks than we expected counting segments
1684  * in assumption of absent reordering, interpret this as reordering.
1685  * The only another reason could be bug in receiver TCP.
1686  */
1687 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1688 {
1689         struct tcp_sock *tp = tcp_sk(sk);
1690         u32 holes;
1691
1692         holes = max(tp->lost_out, 1U);
1693         holes = min(holes, tp->packets_out);
1694
1695         if ((tp->sacked_out + holes) > tp->packets_out) {
1696                 tp->sacked_out = tp->packets_out - holes;
1697                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1698         }
1699 }
1700
1701 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1702
1703 static void tcp_add_reno_sack(struct sock *sk)
1704 {
1705         struct tcp_sock *tp = tcp_sk(sk);
1706         tp->sacked_out++;
1707         tcp_check_reno_reordering(sk, 0);
1708         tcp_sync_left_out(tp);
1709 }
1710
1711 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1712
1713 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1714 {
1715         struct tcp_sock *tp = tcp_sk(sk);
1716
1717         if (acked > 0) {
1718                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1719                 if (acked-1 >= tp->sacked_out)
1720                         tp->sacked_out = 0;
1721                 else
1722                         tp->sacked_out -= acked-1;
1723         }
1724         tcp_check_reno_reordering(sk, acked);
1725         tcp_sync_left_out(tp);
1726 }
1727
1728 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1729 {
1730         tp->sacked_out = 0;
1731         tp->left_out = tp->lost_out;
1732 }
1733
1734 /* Mark head of queue up as lost. */
1735 static void tcp_mark_head_lost(struct sock *sk,
1736                                int packets, u32 high_seq)
1737 {
1738         struct tcp_sock *tp = tcp_sk(sk);
1739         struct sk_buff *skb;
1740         int cnt;
1741
1742         BUG_TRAP(packets <= tp->packets_out);
1743         if (tp->lost_skb_hint) {
1744                 skb = tp->lost_skb_hint;
1745                 cnt = tp->lost_cnt_hint;
1746         } else {
1747                 skb = tcp_write_queue_head(sk);
1748                 cnt = 0;
1749         }
1750
1751         tcp_for_write_queue_from(skb, sk) {
1752                 if (skb == tcp_send_head(sk))
1753                         break;
1754                 /* TODO: do this better */
1755                 /* this is not the most efficient way to do this... */
1756                 tp->lost_skb_hint = skb;
1757                 tp->lost_cnt_hint = cnt;
1758                 cnt += tcp_skb_pcount(skb);
1759                 if (cnt > packets || after(TCP_SKB_CB(skb)->end_seq, high_seq))
1760                         break;
1761                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1762                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1763                         tp->lost_out += tcp_skb_pcount(skb);
1764
1765                         /* clear xmit_retransmit_queue hints
1766                          *  if this is beyond hint */
1767                         if (tp->retransmit_skb_hint != NULL &&
1768                             before(TCP_SKB_CB(skb)->seq,
1769                                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
1770                                 tp->retransmit_skb_hint = NULL;
1771
1772                 }
1773         }
1774         tcp_sync_left_out(tp);
1775 }
1776
1777 /* Account newly detected lost packet(s) */
1778
1779 static void tcp_update_scoreboard(struct sock *sk)
1780 {
1781         struct tcp_sock *tp = tcp_sk(sk);
1782
1783         if (IsFack(tp)) {
1784                 int lost = tp->fackets_out - tp->reordering;
1785                 if (lost <= 0)
1786                         lost = 1;
1787                 tcp_mark_head_lost(sk, lost, tp->high_seq);
1788         } else {
1789                 tcp_mark_head_lost(sk, 1, tp->high_seq);
1790         }
1791
1792         /* New heuristics: it is possible only after we switched
1793          * to restart timer each time when something is ACKed.
1794          * Hence, we can detect timed out packets during fast
1795          * retransmit without falling to slow start.
1796          */
1797         if (!IsReno(tp) && tcp_head_timedout(sk)) {
1798                 struct sk_buff *skb;
1799
1800                 skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
1801                         : tcp_write_queue_head(sk);
1802
1803                 tcp_for_write_queue_from(skb, sk) {
1804                         if (skb == tcp_send_head(sk))
1805                                 break;
1806                         if (!tcp_skb_timedout(sk, skb))
1807                                 break;
1808
1809                         if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
1810                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1811                                 tp->lost_out += tcp_skb_pcount(skb);
1812
1813                                 /* clear xmit_retrans hint */
1814                                 if (tp->retransmit_skb_hint &&
1815                                     before(TCP_SKB_CB(skb)->seq,
1816                                            TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
1817
1818                                         tp->retransmit_skb_hint = NULL;
1819                         }
1820                 }
1821
1822                 tp->scoreboard_skb_hint = skb;
1823
1824                 tcp_sync_left_out(tp);
1825         }
1826 }
1827
1828 /* CWND moderation, preventing bursts due to too big ACKs
1829  * in dubious situations.
1830  */
1831 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
1832 {
1833         tp->snd_cwnd = min(tp->snd_cwnd,
1834                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
1835         tp->snd_cwnd_stamp = tcp_time_stamp;
1836 }
1837
1838 /* Lower bound on congestion window is slow start threshold
1839  * unless congestion avoidance choice decides to overide it.
1840  */
1841 static inline u32 tcp_cwnd_min(const struct sock *sk)
1842 {
1843         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1844
1845         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
1846 }
1847
1848 /* Decrease cwnd each second ack. */
1849 static void tcp_cwnd_down(struct sock *sk)
1850 {
1851         struct tcp_sock *tp = tcp_sk(sk);
1852         int decr = tp->snd_cwnd_cnt + 1;
1853
1854         tp->snd_cwnd_cnt = decr&1;
1855         decr >>= 1;
1856
1857         if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
1858                 tp->snd_cwnd -= decr;
1859
1860         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
1861         tp->snd_cwnd_stamp = tcp_time_stamp;
1862 }
1863
1864 /* Nothing was retransmitted or returned timestamp is less
1865  * than timestamp of the first retransmission.
1866  */
1867 static inline int tcp_packet_delayed(struct tcp_sock *tp)
1868 {
1869         return !tp->retrans_stamp ||
1870                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
1871                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
1872 }
1873
1874 /* Undo procedures. */
1875
1876 #if FASTRETRANS_DEBUG > 1
1877 static void DBGUNDO(struct sock *sk, const char *msg)
1878 {
1879         struct tcp_sock *tp = tcp_sk(sk);
1880         struct inet_sock *inet = inet_sk(sk);
1881
1882         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
1883                msg,
1884                NIPQUAD(inet->daddr), ntohs(inet->dport),
1885                tp->snd_cwnd, tp->left_out,
1886                tp->snd_ssthresh, tp->prior_ssthresh,
1887                tp->packets_out);
1888 }
1889 #else
1890 #define DBGUNDO(x...) do { } while (0)
1891 #endif
1892
1893 static void tcp_undo_cwr(struct sock *sk, const int undo)
1894 {
1895         struct tcp_sock *tp = tcp_sk(sk);
1896
1897         if (tp->prior_ssthresh) {
1898                 const struct inet_connection_sock *icsk = inet_csk(sk);
1899
1900                 if (icsk->icsk_ca_ops->undo_cwnd)
1901                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
1902                 else
1903                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
1904
1905                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
1906                         tp->snd_ssthresh = tp->prior_ssthresh;
1907                         TCP_ECN_withdraw_cwr(tp);
1908                 }
1909         } else {
1910                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
1911         }
1912         tcp_moderate_cwnd(tp);
1913         tp->snd_cwnd_stamp = tcp_time_stamp;
1914
1915         /* There is something screwy going on with the retrans hints after
1916            an undo */
1917         clear_all_retrans_hints(tp);
1918 }
1919
1920 static inline int tcp_may_undo(struct tcp_sock *tp)
1921 {
1922         return tp->undo_marker &&
1923                 (!tp->undo_retrans || tcp_packet_delayed(tp));
1924 }
1925
1926 /* People celebrate: "We love our President!" */
1927 static int tcp_try_undo_recovery(struct sock *sk)
1928 {
1929         struct tcp_sock *tp = tcp_sk(sk);
1930
1931         if (tcp_may_undo(tp)) {
1932                 /* Happy end! We did not retransmit anything
1933                  * or our original transmission succeeded.
1934                  */
1935                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
1936                 tcp_undo_cwr(sk, 1);
1937                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
1938                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
1939                 else
1940                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
1941                 tp->undo_marker = 0;
1942         }
1943         if (tp->snd_una == tp->high_seq && IsReno(tp)) {
1944                 /* Hold old state until something *above* high_seq
1945                  * is ACKed. For Reno it is MUST to prevent false
1946                  * fast retransmits (RFC2582). SACK TCP is safe. */
1947                 tcp_moderate_cwnd(tp);
1948                 return 1;
1949         }
1950         tcp_set_ca_state(sk, TCP_CA_Open);
1951         return 0;
1952 }
1953
1954 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
1955 static void tcp_try_undo_dsack(struct sock *sk)
1956 {
1957         struct tcp_sock *tp = tcp_sk(sk);
1958
1959         if (tp->undo_marker && !tp->undo_retrans) {
1960                 DBGUNDO(sk, "D-SACK");
1961                 tcp_undo_cwr(sk, 1);
1962                 tp->undo_marker = 0;
1963                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
1964         }
1965 }
1966
1967 /* Undo during fast recovery after partial ACK. */
1968
1969 static int tcp_try_undo_partial(struct sock *sk, int acked)
1970 {
1971         struct tcp_sock *tp = tcp_sk(sk);
1972         /* Partial ACK arrived. Force Hoe's retransmit. */
1973         int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
1974
1975         if (tcp_may_undo(tp)) {
1976                 /* Plain luck! Hole if filled with delayed
1977                  * packet, rather than with a retransmit.
1978                  */
1979                 if (tp->retrans_out == 0)
1980                         tp->retrans_stamp = 0;
1981
1982                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
1983
1984                 DBGUNDO(sk, "Hoe");
1985                 tcp_undo_cwr(sk, 0);
1986                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
1987
1988                 /* So... Do not make Hoe's retransmit yet.
1989                  * If the first packet was delayed, the rest
1990                  * ones are most probably delayed as well.
1991                  */
1992                 failed = 0;
1993         }
1994         return failed;
1995 }
1996
1997 /* Undo during loss recovery after partial ACK. */
1998 static int tcp_try_undo_loss(struct sock *sk)
1999 {
2000         struct tcp_sock *tp = tcp_sk(sk);
2001
2002         if (tcp_may_undo(tp)) {
2003                 struct sk_buff *skb;
2004                 tcp_for_write_queue(skb, sk) {
2005                         if (skb == tcp_send_head(sk))
2006                                 break;
2007                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2008                 }
2009
2010                 clear_all_retrans_hints(tp);
2011
2012                 DBGUNDO(sk, "partial loss");
2013                 tp->lost_out = 0;
2014                 tp->left_out = tp->sacked_out;
2015                 tcp_undo_cwr(sk, 1);
2016                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
2017                 inet_csk(sk)->icsk_retransmits = 0;
2018                 tp->undo_marker = 0;
2019                 if (!IsReno(tp))
2020                         tcp_set_ca_state(sk, TCP_CA_Open);
2021                 return 1;
2022         }
2023         return 0;
2024 }
2025
2026 static inline void tcp_complete_cwr(struct sock *sk)
2027 {
2028         struct tcp_sock *tp = tcp_sk(sk);
2029         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2030         tp->snd_cwnd_stamp = tcp_time_stamp;
2031         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2032 }
2033
2034 static void tcp_try_to_open(struct sock *sk, int flag)
2035 {
2036         struct tcp_sock *tp = tcp_sk(sk);
2037
2038         tp->left_out = tp->sacked_out;
2039
2040         if (tp->retrans_out == 0)
2041                 tp->retrans_stamp = 0;
2042
2043         if (flag&FLAG_ECE)
2044                 tcp_enter_cwr(sk, 1);
2045
2046         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2047                 int state = TCP_CA_Open;
2048
2049                 if (tp->left_out || tp->retrans_out || tp->undo_marker)
2050                         state = TCP_CA_Disorder;
2051
2052                 if (inet_csk(sk)->icsk_ca_state != state) {
2053                         tcp_set_ca_state(sk, state);
2054                         tp->high_seq = tp->snd_nxt;
2055                 }
2056                 tcp_moderate_cwnd(tp);
2057         } else {
2058                 tcp_cwnd_down(sk);
2059         }
2060 }
2061
2062 static void tcp_mtup_probe_failed(struct sock *sk)
2063 {
2064         struct inet_connection_sock *icsk = inet_csk(sk);
2065
2066         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2067         icsk->icsk_mtup.probe_size = 0;
2068 }
2069
2070 static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
2071 {
2072         struct tcp_sock *tp = tcp_sk(sk);
2073         struct inet_connection_sock *icsk = inet_csk(sk);
2074
2075         /* FIXME: breaks with very large cwnd */
2076         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2077         tp->snd_cwnd = tp->snd_cwnd *
2078                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2079                        icsk->icsk_mtup.probe_size;
2080         tp->snd_cwnd_cnt = 0;
2081         tp->snd_cwnd_stamp = tcp_time_stamp;
2082         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
2083
2084         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2085         icsk->icsk_mtup.probe_size = 0;
2086         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2087 }
2088
2089
2090 /* Process an event, which can update packets-in-flight not trivially.
2091  * Main goal of this function is to calculate new estimate for left_out,
2092  * taking into account both packets sitting in receiver's buffer and
2093  * packets lost by network.
2094  *
2095  * Besides that it does CWND reduction, when packet loss is detected
2096  * and changes state of machine.
2097  *
2098  * It does _not_ decide what to send, it is made in function
2099  * tcp_xmit_retransmit_queue().
2100  */
2101 static void
2102 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
2103                       int prior_packets, int flag)
2104 {
2105         struct inet_connection_sock *icsk = inet_csk(sk);
2106         struct tcp_sock *tp = tcp_sk(sk);
2107         int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
2108
2109         /* Some technical things:
2110          * 1. Reno does not count dupacks (sacked_out) automatically. */
2111         if (!tp->packets_out)
2112                 tp->sacked_out = 0;
2113         /* 2. SACK counts snd_fack in packets inaccurately. */
2114         if (tp->sacked_out == 0)
2115                 tp->fackets_out = 0;
2116
2117         /* Now state machine starts.
2118          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2119         if (flag&FLAG_ECE)
2120                 tp->prior_ssthresh = 0;
2121
2122         /* B. In all the states check for reneging SACKs. */
2123         if (tp->sacked_out && tcp_check_sack_reneging(sk))
2124                 return;
2125
2126         /* C. Process data loss notification, provided it is valid. */
2127         if ((flag&FLAG_DATA_LOST) &&
2128             before(tp->snd_una, tp->high_seq) &&
2129             icsk->icsk_ca_state != TCP_CA_Open &&
2130             tp->fackets_out > tp->reordering) {
2131                 tcp_mark_head_lost(sk, tp->fackets_out-tp->reordering, tp->high_seq);
2132                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
2133         }
2134
2135         /* D. Synchronize left_out to current state. */
2136         tcp_sync_left_out(tp);
2137
2138         /* E. Check state exit conditions. State can be terminated
2139          *    when high_seq is ACKed. */
2140         if (icsk->icsk_ca_state == TCP_CA_Open) {
2141                 BUG_TRAP(tp->retrans_out == 0);
2142                 tp->retrans_stamp = 0;
2143         } else if (!before(tp->snd_una, tp->high_seq)) {
2144                 switch (icsk->icsk_ca_state) {
2145                 case TCP_CA_Loss:
2146                         icsk->icsk_retransmits = 0;
2147                         if (tcp_try_undo_recovery(sk))
2148                                 return;
2149                         break;
2150
2151                 case TCP_CA_CWR:
2152                         /* CWR is to be held something *above* high_seq
2153                          * is ACKed for CWR bit to reach receiver. */
2154                         if (tp->snd_una != tp->high_seq) {
2155                                 tcp_complete_cwr(sk);
2156                                 tcp_set_ca_state(sk, TCP_CA_Open);
2157                         }
2158                         break;
2159
2160                 case TCP_CA_Disorder:
2161                         tcp_try_undo_dsack(sk);
2162                         if (!tp->undo_marker ||
2163                             /* For SACK case do not Open to allow to undo
2164                              * catching for all duplicate ACKs. */
2165                             IsReno(tp) || tp->snd_una != tp->high_seq) {
2166                                 tp->undo_marker = 0;
2167                                 tcp_set_ca_state(sk, TCP_CA_Open);
2168                         }
2169                         break;
2170
2171                 case TCP_CA_Recovery:
2172                         if (IsReno(tp))
2173                                 tcp_reset_reno_sack(tp);
2174                         if (tcp_try_undo_recovery(sk))
2175                                 return;
2176                         tcp_complete_cwr(sk);
2177                         break;
2178                 }
2179         }
2180
2181         /* F. Process state. */
2182         switch (icsk->icsk_ca_state) {
2183         case TCP_CA_Recovery:
2184                 if (prior_snd_una == tp->snd_una) {
2185                         if (IsReno(tp) && is_dupack)
2186                                 tcp_add_reno_sack(sk);
2187                 } else {
2188                         int acked = prior_packets - tp->packets_out;
2189                         if (IsReno(tp))
2190                                 tcp_remove_reno_sacks(sk, acked);
2191                         is_dupack = tcp_try_undo_partial(sk, acked);
2192                 }
2193                 break;
2194         case TCP_CA_Loss:
2195                 if (flag&FLAG_DATA_ACKED)
2196                         icsk->icsk_retransmits = 0;
2197                 if (!tcp_try_undo_loss(sk)) {
2198                         tcp_moderate_cwnd(tp);
2199                         tcp_xmit_retransmit_queue(sk);
2200                         return;
2201                 }
2202                 if (icsk->icsk_ca_state != TCP_CA_Open)
2203                         return;
2204                 /* Loss is undone; fall through to processing in Open state. */
2205         default:
2206                 if (IsReno(tp)) {
2207                         if (tp->snd_una != prior_snd_una)
2208                                 tcp_reset_reno_sack(tp);
2209                         if (is_dupack)
2210                                 tcp_add_reno_sack(sk);
2211                 }
2212
2213                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
2214                         tcp_try_undo_dsack(sk);
2215
2216                 if (!tcp_time_to_recover(sk)) {
2217                         tcp_try_to_open(sk, flag);
2218                         return;
2219                 }
2220
2221                 /* MTU probe failure: don't reduce cwnd */
2222                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2223                     icsk->icsk_mtup.probe_size &&
2224                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2225                         tcp_mtup_probe_failed(sk);
2226                         /* Restores the reduction we did in tcp_mtup_probe() */
2227                         tp->snd_cwnd++;
2228                         tcp_simple_retransmit(sk);
2229                         return;
2230                 }
2231
2232                 /* Otherwise enter Recovery state */
2233
2234                 if (IsReno(tp))
2235                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
2236                 else
2237                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
2238
2239                 tp->high_seq = tp->snd_nxt;
2240                 tp->prior_ssthresh = 0;
2241                 tp->undo_marker = tp->snd_una;
2242                 tp->undo_retrans = tp->retrans_out;
2243
2244                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
2245                         if (!(flag&FLAG_ECE))
2246                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2247                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2248                         TCP_ECN_queue_cwr(tp);
2249                 }
2250
2251                 tp->bytes_acked = 0;
2252                 tp->snd_cwnd_cnt = 0;
2253                 tcp_set_ca_state(sk, TCP_CA_Recovery);
2254         }
2255
2256         if (is_dupack || tcp_head_timedout(sk))
2257                 tcp_update_scoreboard(sk);
2258         tcp_cwnd_down(sk);
2259         tcp_xmit_retransmit_queue(sk);
2260 }
2261
2262 /* Read draft-ietf-tcplw-high-performance before mucking
2263  * with this code. (Supersedes RFC1323)
2264  */
2265 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
2266 {
2267         /* RTTM Rule: A TSecr value received in a segment is used to
2268          * update the averaged RTT measurement only if the segment
2269          * acknowledges some new data, i.e., only if it advances the
2270          * left edge of the send window.
2271          *
2272          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2273          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
2274          *
2275          * Changed: reset backoff as soon as we see the first valid sample.
2276          * If we do not, we get strongly overestimated rto. With timestamps
2277          * samples are accepted even from very old segments: f.e., when rtt=1
2278          * increases to 8, we retransmit 5 times and after 8 seconds delayed
2279          * answer arrives rto becomes 120 seconds! If at least one of segments
2280          * in window is lost... Voila.                          --ANK (010210)
2281          */
2282         struct tcp_sock *tp = tcp_sk(sk);
2283         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
2284         tcp_rtt_estimator(sk, seq_rtt);
2285         tcp_set_rto(sk);
2286         inet_csk(sk)->icsk_backoff = 0;
2287         tcp_bound_rto(sk);
2288 }
2289
2290 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
2291 {
2292         /* We don't have a timestamp. Can only use
2293          * packets that are not retransmitted to determine
2294          * rtt estimates. Also, we must not reset the
2295          * backoff for rto until we get a non-retransmitted
2296          * packet. This allows us to deal with a situation
2297          * where the network delay has increased suddenly.
2298          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
2299          */
2300
2301         if (flag & FLAG_RETRANS_DATA_ACKED)
2302                 return;
2303
2304         tcp_rtt_estimator(sk, seq_rtt);
2305         tcp_set_rto(sk);
2306         inet_csk(sk)->icsk_backoff = 0;
2307         tcp_bound_rto(sk);
2308 }
2309
2310 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
2311                                       const s32 seq_rtt)
2312 {
2313         const struct tcp_sock *tp = tcp_sk(sk);
2314         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
2315         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
2316                 tcp_ack_saw_tstamp(sk, flag);
2317         else if (seq_rtt >= 0)
2318                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
2319 }
2320
2321 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
2322                            u32 in_flight, int good)
2323 {
2324         const struct inet_connection_sock *icsk = inet_csk(sk);
2325         icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
2326         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2327 }
2328
2329 /* Restart timer after forward progress on connection.
2330  * RFC2988 recommends to restart timer to now+rto.
2331  */
2332
2333 static void tcp_ack_packets_out(struct sock *sk)
2334 {
2335         struct tcp_sock *tp = tcp_sk(sk);
2336
2337         if (!tp->packets_out) {
2338                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2339         } else {
2340                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2341         }
2342 }
2343
2344 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
2345                          __u32 now, __s32 *seq_rtt)
2346 {
2347         struct tcp_sock *tp = tcp_sk(sk);
2348         struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
2349         __u32 seq = tp->snd_una;
2350         __u32 packets_acked;
2351         int acked = 0;
2352
2353         /* If we get here, the whole TSO packet has not been
2354          * acked.
2355          */
2356         BUG_ON(!after(scb->end_seq, seq));
2357
2358         packets_acked = tcp_skb_pcount(skb);
2359         if (tcp_trim_head(sk, skb, seq - scb->seq))
2360                 return 0;
2361         packets_acked -= tcp_skb_pcount(skb);
2362
2363         if (packets_acked) {
2364                 __u8 sacked = scb->sacked;
2365
2366                 acked |= FLAG_DATA_ACKED;
2367                 if (sacked) {
2368                         if (sacked & TCPCB_RETRANS) {
2369                                 if (sacked & TCPCB_SACKED_RETRANS)
2370                                         tp->retrans_out -= packets_acked;
2371                                 acked |= FLAG_RETRANS_DATA_ACKED;
2372                                 *seq_rtt = -1;
2373                         } else if (*seq_rtt < 0)
2374                                 *seq_rtt = now - scb->when;
2375                         if (sacked & TCPCB_SACKED_ACKED)
2376                                 tp->sacked_out -= packets_acked;
2377                         if (sacked & TCPCB_LOST)
2378                                 tp->lost_out -= packets_acked;
2379                         if (sacked & TCPCB_URG) {
2380                                 if (tp->urg_mode &&
2381                                     !before(seq, tp->snd_up))
2382                                         tp->urg_mode = 0;
2383                         }
2384                 } else if (*seq_rtt < 0)
2385                         *seq_rtt = now - scb->when;
2386
2387                 if (tp->fackets_out) {
2388                         __u32 dval = min(tp->fackets_out, packets_acked);
2389                         tp->fackets_out -= dval;
2390                 }
2391                 tp->packets_out -= packets_acked;
2392
2393                 BUG_ON(tcp_skb_pcount(skb) == 0);
2394                 BUG_ON(!before(scb->seq, scb->end_seq));
2395         }
2396
2397         return acked;
2398 }
2399
2400 /* Remove acknowledged frames from the retransmission queue. */
2401 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
2402 {
2403         struct tcp_sock *tp = tcp_sk(sk);
2404         const struct inet_connection_sock *icsk = inet_csk(sk);
2405         struct sk_buff *skb;
2406         __u32 now = tcp_time_stamp;
2407         int acked = 0;
2408         __s32 seq_rtt = -1;
2409         u32 pkts_acked = 0;
2410         ktime_t last_ackt = ktime_set(0,0);
2411
2412         while ((skb = tcp_write_queue_head(sk)) &&
2413                skb != tcp_send_head(sk)) {
2414                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
2415                 __u8 sacked = scb->sacked;
2416
2417                 /* If our packet is before the ack sequence we can
2418                  * discard it as it's confirmed to have arrived at
2419                  * the other end.
2420                  */
2421                 if (after(scb->end_seq, tp->snd_una)) {
2422                         if (tcp_skb_pcount(skb) > 1 &&
2423                             after(tp->snd_una, scb->seq))
2424                                 acked |= tcp_tso_acked(sk, skb,
2425                                                        now, &seq_rtt);
2426                         break;
2427                 }
2428
2429                 /* Initial outgoing SYN's get put onto the write_queue
2430                  * just like anything else we transmit.  It is not
2431                  * true data, and if we misinform our callers that
2432                  * this ACK acks real data, we will erroneously exit
2433                  * connection startup slow start one packet too
2434                  * quickly.  This is severely frowned upon behavior.
2435                  */
2436                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2437                         acked |= FLAG_DATA_ACKED;
2438                         ++pkts_acked;
2439                 } else {
2440                         acked |= FLAG_SYN_ACKED;
2441                         tp->retrans_stamp = 0;
2442                 }
2443
2444                 /* MTU probing checks */
2445                 if (icsk->icsk_mtup.probe_size) {
2446                         if (!after(tp->mtu_probe.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {
2447                                 tcp_mtup_probe_success(sk, skb);
2448                         }
2449                 }
2450
2451                 if (sacked) {
2452                         if (sacked & TCPCB_RETRANS) {
2453                                 if (sacked & TCPCB_SACKED_RETRANS)
2454                                         tp->retrans_out -= tcp_skb_pcount(skb);
2455                                 acked |= FLAG_RETRANS_DATA_ACKED;
2456                                 seq_rtt = -1;
2457                         } else if (seq_rtt < 0) {
2458                                 seq_rtt = now - scb->when;
2459                                 last_ackt = skb->tstamp;
2460                         }
2461                         if (sacked & TCPCB_SACKED_ACKED)
2462                                 tp->sacked_out -= tcp_skb_pcount(skb);
2463                         if (sacked & TCPCB_LOST)
2464                                 tp->lost_out -= tcp_skb_pcount(skb);
2465                         if (sacked & TCPCB_URG) {
2466                                 if (tp->urg_mode &&
2467                                     !before(scb->end_seq, tp->snd_up))
2468                                         tp->urg_mode = 0;
2469                         }
2470                 } else if (seq_rtt < 0) {
2471                         seq_rtt = now - scb->when;
2472                         last_ackt = skb->tstamp;
2473                 }
2474                 tcp_dec_pcount_approx(&tp->fackets_out, skb);
2475                 tcp_packets_out_dec(tp, skb);
2476                 tcp_unlink_write_queue(skb, sk);
2477                 sk_stream_free_skb(sk, skb);
2478                 clear_all_retrans_hints(tp);
2479         }
2480
2481         if (acked&FLAG_ACKED) {
2482                 const struct tcp_congestion_ops *ca_ops
2483                         = inet_csk(sk)->icsk_ca_ops;
2484
2485                 tcp_ack_update_rtt(sk, acked, seq_rtt);
2486                 tcp_ack_packets_out(sk);
2487
2488                 if (ca_ops->pkts_acked)
2489                         ca_ops->pkts_acked(sk, pkts_acked, last_ackt);
2490         }
2491
2492 #if FASTRETRANS_DEBUG > 0
2493         BUG_TRAP((int)tp->sacked_out >= 0);
2494         BUG_TRAP((int)tp->lost_out >= 0);
2495         BUG_TRAP((int)tp->retrans_out >= 0);
2496         if (!tp->packets_out && tp->rx_opt.sack_ok) {
2497                 const struct inet_connection_sock *icsk = inet_csk(sk);
2498                 if (tp->lost_out) {
2499                         printk(KERN_DEBUG "Leak l=%u %d\n",
2500                                tp->lost_out, icsk->icsk_ca_state);
2501                         tp->lost_out = 0;
2502                 }
2503                 if (tp->sacked_out) {
2504                         printk(KERN_DEBUG "Leak s=%u %d\n",
2505                                tp->sacked_out, icsk->icsk_ca_state);
2506                         tp->sacked_out = 0;
2507                 }
2508                 if (tp->retrans_out) {
2509                         printk(KERN_DEBUG "Leak r=%u %d\n",
2510                                tp->retrans_out, icsk->icsk_ca_state);
2511                         tp->retrans_out = 0;
2512                 }
2513         }
2514 #endif
2515         *seq_rtt_p = seq_rtt;
2516         return acked;
2517 }
2518
2519 static void tcp_ack_probe(struct sock *sk)
2520 {
2521         const struct tcp_sock *tp = tcp_sk(sk);
2522         struct inet_connection_sock *icsk = inet_csk(sk);
2523
2524         /* Was it a usable window open? */
2525
2526         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
2527                    tp->snd_una + tp->snd_wnd)) {
2528                 icsk->icsk_backoff = 0;
2529                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2530                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2531                  * This function is not for random using!
2532                  */
2533         } else {
2534                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2535                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2536                                           TCP_RTO_MAX);
2537         }
2538 }
2539
2540 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2541 {
2542         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2543                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2544 }
2545
2546 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2547 {
2548         const struct tcp_sock *tp = tcp_sk(sk);
2549         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2550                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2551 }
2552
2553 /* Check that window update is acceptable.
2554  * The function assumes that snd_una<=ack<=snd_next.
2555  */
2556 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2557                                         const u32 ack_seq, const u32 nwin)
2558 {
2559         return (after(ack, tp->snd_una) ||
2560                 after(ack_seq, tp->snd_wl1) ||
2561                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2562 }
2563
2564 /* Update our send window.
2565  *
2566  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2567  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2568  */
2569 static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
2570                                  u32 ack_seq)
2571 {
2572         struct tcp_sock *tp = tcp_sk(sk);
2573         int flag = 0;
2574         u32 nwin = ntohs(tcp_hdr(skb)->window);
2575
2576         if (likely(!tcp_hdr(skb)->syn))
2577                 nwin <<= tp->rx_opt.snd_wscale;
2578
2579         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2580                 flag |= FLAG_WIN_UPDATE;
2581                 tcp_update_wl(tp, ack, ack_seq);
2582
2583                 if (tp->snd_wnd != nwin) {
2584                         tp->snd_wnd = nwin;
2585
2586                         /* Note, it is the only place, where
2587                          * fast path is recovered for sending TCP.
2588                          */
2589                         tp->pred_flags = 0;
2590                         tcp_fast_path_check(sk);
2591
2592                         if (nwin > tp->max_window) {
2593                                 tp->max_window = nwin;
2594                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
2595                         }
2596                 }
2597         }
2598
2599         tp->snd_una = ack;
2600
2601         return flag;
2602 }
2603
2604 /* A very conservative spurious RTO response algorithm: reduce cwnd and
2605  * continue in congestion avoidance.
2606  */
2607 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
2608 {
2609         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2610         tp->snd_cwnd_cnt = 0;
2611         tcp_moderate_cwnd(tp);
2612 }
2613
2614 /* A conservative spurious RTO response algorithm: reduce cwnd using
2615  * rate halving and continue in congestion avoidance.
2616  */
2617 static void tcp_ratehalving_spur_to_response(struct sock *sk)
2618 {
2619         tcp_enter_cwr(sk, 0);
2620 }
2621
2622 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
2623 {
2624         if (flag&FLAG_ECE)
2625                 tcp_ratehalving_spur_to_response(sk);
2626         else
2627                 tcp_undo_cwr(sk, 1);
2628 }
2629
2630 /* F-RTO spurious RTO detection algorithm (RFC4138)
2631  *
2632  * F-RTO affects during two new ACKs following RTO (well, almost, see inline
2633  * comments). State (ACK number) is kept in frto_counter. When ACK advances
2634  * window (but not to or beyond highest sequence sent before RTO):
2635  *   On First ACK,  send two new segments out.
2636  *   On Second ACK, RTO was likely spurious. Do spurious response (response
2637  *                  algorithm is not part of the F-RTO detection algorithm
2638  *                  given in RFC4138 but can be selected separately).
2639  * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
2640  * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
2641  * of Nagle, this is done using frto_counter states 2 and 3, when a new data
2642  * segment of any size sent during F-RTO, state 2 is upgraded to 3.
2643  *
2644  * Rationale: if the RTO was spurious, new ACKs should arrive from the
2645  * original window even after we transmit two new data segments.
2646  *
2647  * SACK version:
2648  *   on first step, wait until first cumulative ACK arrives, then move to
2649  *   the second step. In second step, the next ACK decides.
2650  *
2651  * F-RTO is implemented (mainly) in four functions:
2652  *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
2653  *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
2654  *     called when tcp_use_frto() showed green light
2655  *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
2656  *   - tcp_enter_frto_loss() is called if there is not enough evidence
2657  *     to prove that the RTO is indeed spurious. It transfers the control
2658  *     from F-RTO to the conventional RTO recovery
2659  */
2660 static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
2661 {
2662         struct tcp_sock *tp = tcp_sk(sk);
2663
2664         tcp_sync_left_out(tp);
2665
2666         /* Duplicate the behavior from Loss state (fastretrans_alert) */
2667         if (flag&FLAG_DATA_ACKED)
2668                 inet_csk(sk)->icsk_retransmits = 0;
2669
2670         if (!before(tp->snd_una, tp->frto_highmark)) {
2671                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
2672                 return 1;
2673         }
2674
2675         if (!IsSackFrto() || IsReno(tp)) {
2676                 /* RFC4138 shortcoming in step 2; should also have case c):
2677                  * ACK isn't duplicate nor advances window, e.g., opposite dir
2678                  * data, winupdate
2679                  */
2680                 if ((tp->snd_una == prior_snd_una) && (flag&FLAG_NOT_DUP) &&
2681                     !(flag&FLAG_FORWARD_PROGRESS))
2682                         return 1;
2683
2684                 if (!(flag&FLAG_DATA_ACKED)) {
2685                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
2686                                             flag);
2687                         return 1;
2688                 }
2689         } else {
2690                 if (!(flag&FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
2691                         /* Prevent sending of new data. */
2692                         tp->snd_cwnd = min(tp->snd_cwnd,
2693                                            tcp_packets_in_flight(tp));
2694                         return 1;
2695                 }
2696
2697                 if ((tp->frto_counter >= 2) &&
2698                     (!(flag&FLAG_FORWARD_PROGRESS) ||
2699                      ((flag&FLAG_DATA_SACKED) && !(flag&FLAG_ONLY_ORIG_SACKED)))) {
2700                         /* RFC4138 shortcoming (see comment above) */
2701                         if (!(flag&FLAG_FORWARD_PROGRESS) && (flag&FLAG_NOT_DUP))
2702                                 return 1;
2703
2704                         tcp_enter_frto_loss(sk, 3, flag);
2705                         return 1;
2706                 }
2707         }
2708
2709         if (tp->frto_counter == 1) {
2710                 /* Sending of the next skb must be allowed or no FRTO */
2711                 if (!tcp_send_head(sk) ||
2712                     after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
2713                                      tp->snd_una + tp->snd_wnd)) {
2714                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3),
2715                                             flag);
2716                         return 1;
2717                 }
2718
2719                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2720                 tp->frto_counter = 2;
2721                 return 1;
2722         } else {
2723                 switch (sysctl_tcp_frto_response) {
2724                 case 2:
2725                         tcp_undo_spur_to_response(sk, flag);
2726                         break;
2727                 case 1:
2728                         tcp_conservative_spur_to_response(tp);
2729                         break;
2730                 default:
2731                         tcp_ratehalving_spur_to_response(sk);
2732                         break;
2733                 }
2734                 tp->frto_counter = 0;
2735         }
2736         return 0;
2737 }
2738
2739 /* This routine deals with incoming acks, but not outgoing ones. */
2740 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
2741 {
2742         struct inet_connection_sock *icsk = inet_csk(sk);
2743         struct tcp_sock *tp = tcp_sk(sk);
2744         u32 prior_snd_una = tp->snd_una;
2745         u32 ack_seq = TCP_SKB_CB(skb)->seq;
2746         u32 ack = TCP_SKB_CB(skb)->ack_seq;
2747         u32 prior_in_flight;
2748         s32 seq_rtt;
2749         int prior_packets;
2750         int frto_cwnd = 0;
2751
2752         /* If the ack is newer than sent or older than previous acks
2753          * then we can probably ignore it.
2754          */
2755         if (after(ack, tp->snd_nxt))
2756                 goto uninteresting_ack;
2757
2758         if (before(ack, prior_snd_una))
2759                 goto old_ack;
2760
2761         if (sysctl_tcp_abc) {
2762                 if (icsk->icsk_ca_state < TCP_CA_CWR)
2763                         tp->bytes_acked += ack - prior_snd_una;
2764                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
2765                         /* we assume just one segment left network */
2766                         tp->bytes_acked += min(ack - prior_snd_una, tp->mss_cache);
2767         }
2768
2769         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
2770                 /* Window is constant, pure forward advance.
2771                  * No more checks are required.
2772                  * Note, we use the fact that SND.UNA>=SND.WL2.
2773                  */
2774                 tcp_update_wl(tp, ack, ack_seq);
2775                 tp->snd_una = ack;
2776                 flag |= FLAG_WIN_UPDATE;
2777
2778                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
2779
2780                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
2781         } else {
2782                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
2783                         flag |= FLAG_DATA;
2784                 else
2785                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
2786
2787                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
2788
2789                 if (TCP_SKB_CB(skb)->sacked)
2790                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2791
2792                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
2793                         flag |= FLAG_ECE;
2794
2795                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
2796         }
2797
2798         /* We passed data and got it acked, remove any soft error
2799          * log. Something worked...
2800          */
2801         sk->sk_err_soft = 0;
2802         tp->rcv_tstamp = tcp_time_stamp;
2803         prior_packets = tp->packets_out;
2804         if (!prior_packets)
2805                 goto no_queue;
2806
2807         prior_in_flight = tcp_packets_in_flight(tp);
2808
2809         /* See if we can take anything off of the retransmit queue. */
2810         flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
2811
2812         if (tp->frto_counter)
2813                 frto_cwnd = tcp_process_frto(sk, prior_snd_una, flag);
2814
2815         if (tcp_ack_is_dubious(sk, flag)) {
2816                 /* Advance CWND, if state allows this. */
2817                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
2818                     tcp_may_raise_cwnd(sk, flag))
2819                         tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
2820                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
2821         } else {
2822                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
2823                         tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
2824         }
2825
2826         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
2827                 dst_confirm(sk->sk_dst_cache);
2828
2829         return 1;
2830
2831 no_queue:
2832         icsk->icsk_probes_out = 0;
2833
2834         /* If this ack opens up a zero window, clear backoff.  It was
2835          * being used to time the probes, and is probably far higher than
2836          * it needs to be for normal retransmission.
2837          */
2838         if (tcp_send_head(sk))
2839                 tcp_ack_probe(sk);
2840         return 1;
2841
2842 old_ack:
2843         if (TCP_SKB_CB(skb)->sacked)
2844                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
2845
2846 uninteresting_ack:
2847         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
2848         return 0;
2849 }
2850
2851
2852 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
2853  * But, this can also be called on packets in the established flow when
2854  * the fast version below fails.
2855  */
2856 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
2857 {
2858         unsigned char *ptr;
2859         struct tcphdr *th = tcp_hdr(skb);
2860         int length=(th->doff*4)-sizeof(struct tcphdr);
2861
2862         ptr = (unsigned char *)(th + 1);
2863         opt_rx->saw_tstamp = 0;
2864
2865         while (length > 0) {
2866                 int opcode=*ptr++;
2867                 int opsize;
2868
2869                 switch (opcode) {
2870                         case TCPOPT_EOL:
2871                                 return;
2872                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
2873                                 length--;
2874                                 continue;
2875                         default:
2876                                 opsize=*ptr++;
2877                                 if (opsize < 2) /* "silly options" */
2878                                         return;
2879                                 if (opsize > length)
2880                                         return; /* don't parse partial options */
2881                                 switch (opcode) {
2882                                 case TCPOPT_MSS:
2883                                         if (opsize==TCPOLEN_MSS && th->syn && !estab) {
2884                                                 u16 in_mss = ntohs(get_unaligned((__be16 *)ptr));
2885                                                 if (in_mss) {
2886                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
2887                                                                 in_mss = opt_rx->user_mss;
2888                                                         opt_rx->mss_clamp = in_mss;
2889                                                 }
2890                                         }
2891                                         break;
2892                                 case TCPOPT_WINDOW:
2893                                         if (opsize==TCPOLEN_WINDOW && th->syn && !estab)
2894                                                 if (sysctl_tcp_window_scaling) {
2895                                                         __u8 snd_wscale = *(__u8 *) ptr;
2896                                                         opt_rx->wscale_ok = 1;
2897                                                         if (snd_wscale > 14) {
2898                                                                 if (net_ratelimit())
2899                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
2900                                                                                "scaling value %d >14 received.\n",
2901                                                                                snd_wscale);
2902                                                                 snd_wscale = 14;
2903                                                         }
2904                                                         opt_rx->snd_wscale = snd_wscale;
2905                                                 }
2906                                         break;
2907                                 case TCPOPT_TIMESTAMP:
2908                                         if (opsize==TCPOLEN_TIMESTAMP) {
2909                                                 if ((estab && opt_rx->tstamp_ok) ||
2910                                                     (!estab && sysctl_tcp_timestamps)) {
2911                                                         opt_rx->saw_tstamp = 1;
2912                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__be32 *)ptr));
2913                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4)));
2914                                                 }
2915                                         }
2916                                         break;
2917                                 case TCPOPT_SACK_PERM:
2918                                         if (opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
2919                                                 if (sysctl_tcp_sack) {
2920                                                         opt_rx->sack_ok = 1;
2921                                                         tcp_sack_reset(opt_rx);
2922                                                 }
2923                                         }
2924                                         break;
2925
2926                                 case TCPOPT_SACK:
2927                                         if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
2928                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
2929                                            opt_rx->sack_ok) {
2930                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
2931                                         }
2932 #ifdef CONFIG_TCP_MD5SIG
2933                                 case TCPOPT_MD5SIG:
2934                                         /*
2935                                          * The MD5 Hash has already been
2936                                          * checked (see tcp_v{4,6}_do_rcv()).
2937                                          */
2938                                         break;
2939 #endif
2940                                 }
2941
2942                                 ptr+=opsize-2;
2943                                 length-=opsize;
2944                 }
2945         }
2946 }
2947
2948 /* Fast parse options. This hopes to only see timestamps.
2949  * If it is wrong it falls back on tcp_parse_options().
2950  */
2951 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
2952                                   struct tcp_sock *tp)
2953 {
2954         if (th->doff == sizeof(struct tcphdr)>>2) {
2955                 tp->rx_opt.saw_tstamp = 0;
2956                 return 0;
2957         } else if (tp->rx_opt.tstamp_ok &&
2958                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
2959                 __be32 *ptr = (__be32 *)(th + 1);
2960                 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
2961                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
2962                         tp->rx_opt.saw_tstamp = 1;
2963                         ++ptr;
2964                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
2965                         ++ptr;
2966                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
2967                         return 1;
2968                 }
2969         }
2970         tcp_parse_options(skb, &tp->rx_opt, 1);
2971         return 1;
2972 }
2973
2974 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
2975 {
2976         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
2977         tp->rx_opt.ts_recent_stamp = get_seconds();
2978 }
2979
2980 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
2981 {
2982         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
2983                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
2984                  * extra check below makes sure this can only happen
2985                  * for pure ACK frames.  -DaveM
2986                  *
2987                  * Not only, also it occurs for expired timestamps.
2988                  */
2989
2990                 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
2991                    get_seconds() >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
2992                         tcp_store_ts_recent(tp);
2993         }
2994 }
2995
2996 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
2997  *
2998  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
2999  * it can pass through stack. So, the following predicate verifies that
3000  * this segment is not used for anything but congestion avoidance or
3001  * fast retransmit. Moreover, we even are able to eliminate most of such
3002  * second order effects, if we apply some small "replay" window (~RTO)
3003  * to timestamp space.
3004  *
3005  * All these measures still do not guarantee that we reject wrapped ACKs
3006  * on networks with high bandwidth, when sequence space is recycled fastly,
3007  * but it guarantees that such events will be very rare and do not affect
3008  * connection seriously. This doesn't look nice, but alas, PAWS is really
3009  * buggy extension.
3010  *
3011  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3012  * states that events when retransmit arrives after original data are rare.
3013  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3014  * the biggest problem on large power networks even with minor reordering.
3015  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3016  * up to bandwidth of 18Gigabit/sec. 8) ]
3017  */
3018
3019 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3020 {
3021         struct tcp_sock *tp = tcp_sk(sk);
3022         struct tcphdr *th = tcp_hdr(skb);
3023         u32 seq = TCP_SKB_CB(skb)->seq;
3024         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3025
3026         return (/* 1. Pure ACK with correct sequence number. */
3027                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3028
3029                 /* 2. ... and duplicate ACK. */
3030                 ack == tp->snd_una &&
3031
3032                 /* 3. ... and does not update window. */
3033                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3034
3035                 /* 4. ... and sits in replay window. */
3036                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3037 }
3038
3039 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
3040 {
3041         const struct tcp_sock *tp = tcp_sk(sk);
3042         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
3043                 get_seconds() < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
3044                 !tcp_disordered_ack(sk, skb));
3045 }
3046
3047 /* Check segment sequence number for validity.
3048  *
3049  * Segment controls are considered valid, if the segment
3050  * fits to the window after truncation to the window. Acceptability
3051  * of data (and SYN, FIN, of course) is checked separately.
3052  * See tcp_data_queue(), for example.
3053  *
3054  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3055  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3056  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3057  * (borrowed from freebsd)
3058  */
3059
3060 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
3061 {
3062         return  !before(end_seq, tp->rcv_wup) &&
3063                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3064 }
3065
3066 /* When we get a reset we do this. */
3067 static void tcp_reset(struct sock *sk)
3068 {
3069         /* We want the right error as BSD sees it (and indeed as we do). */
3070         switch (sk->sk_state) {
3071                 case TCP_SYN_SENT:
3072                         sk->sk_err = ECONNREFUSED;
3073                         break;
3074                 case TCP_CLOSE_WAIT:
3075                         sk->sk_err = EPIPE;
3076                         break;
3077                 case TCP_CLOSE:
3078                         return;
3079                 default:
3080                         sk->sk_err = ECONNRESET;
3081         }
3082
3083         if (!sock_flag(sk, SOCK_DEAD))
3084                 sk->sk_error_report(sk);
3085
3086         tcp_done(sk);
3087 }
3088
3089 /*
3090  *      Process the FIN bit. This now behaves as it is supposed to work
3091  *      and the FIN takes effect when it is validly part of sequence
3092  *      space. Not before when we get holes.
3093  *
3094  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3095  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3096  *      TIME-WAIT)
3097  *
3098  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3099  *      close and we go into CLOSING (and later onto TIME-WAIT)
3100  *
3101  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3102  */
3103 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
3104 {
3105         struct tcp_sock *tp = tcp_sk(sk);
3106
3107         inet_csk_schedule_ack(sk);
3108
3109         sk->sk_shutdown |= RCV_SHUTDOWN;
3110         sock_set_flag(sk, SOCK_DONE);
3111
3112         switch (sk->sk_state) {
3113                 case TCP_SYN_RECV:
3114                 case TCP_ESTABLISHED:
3115                         /* Move to CLOSE_WAIT */
3116                         tcp_set_state(sk, TCP_CLOSE_WAIT);
3117                         inet_csk(sk)->icsk_ack.pingpong = 1;
3118                         break;
3119
3120                 case TCP_CLOSE_WAIT:
3121                 case TCP_CLOSING:
3122                         /* Received a retransmission of the FIN, do
3123                          * nothing.
3124                          */
3125                         break;
3126                 case TCP_LAST_ACK:
3127                         /* RFC793: Remain in the LAST-ACK state. */
3128                         break;
3129
3130                 case TCP_FIN_WAIT1:
3131                         /* This case occurs when a simultaneous close
3132                          * happens, we must ack the received FIN and
3133                          * enter the CLOSING state.
3134                          */
3135                         tcp_send_ack(sk);
3136                         tcp_set_state(sk, TCP_CLOSING);
3137                         break;
3138                 case TCP_FIN_WAIT2:
3139                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
3140                         tcp_send_ack(sk);
3141                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
3142                         break;
3143                 default:
3144                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
3145                          * cases we should never reach this piece of code.
3146                          */
3147                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
3148                                __FUNCTION__, sk->sk_state);
3149                         break;
3150         }
3151
3152         /* It _is_ possible, that we have something out-of-order _after_ FIN.
3153          * Probably, we should reset in this case. For now drop them.
3154          */
3155         __skb_queue_purge(&tp->out_of_order_queue);
3156         if (tp->rx_opt.sack_ok)
3157                 tcp_sack_reset(&tp->rx_opt);
3158         sk_stream_mem_reclaim(sk);
3159
3160         if (!sock_flag(sk, SOCK_DEAD)) {
3161                 sk->sk_state_change(sk);
3162
3163                 /* Do not send POLL_HUP for half duplex close. */
3164                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
3165                     sk->sk_state == TCP_CLOSE)
3166                         sk_wake_async(sk, 1, POLL_HUP);
3167                 else
3168                         sk_wake_async(sk, 1, POLL_IN);
3169         }
3170 }
3171
3172 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
3173 {
3174         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
3175                 if (before(seq, sp->start_seq))
3176                         sp->start_seq = seq;
3177                 if (after(end_seq, sp->end_seq))
3178                         sp->end_seq = end_seq;
3179                 return 1;
3180         }
3181         return 0;
3182 }
3183
3184 static void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
3185 {
3186         if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
3187                 if (before(seq, tp->rcv_nxt))
3188                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
3189                 else
3190                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
3191
3192                 tp->rx_opt.dsack = 1;
3193                 tp->duplicate_sack[0].start_seq = seq;
3194                 tp->duplicate_sack[0].end_seq = end_seq;
3195                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
3196         }
3197 }
3198
3199 static void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
3200 {
3201         if (!tp->rx_opt.dsack)
3202                 tcp_dsack_set(tp, seq, end_seq);
3203         else
3204                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
3205 }
3206
3207 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
3208 {
3209         struct tcp_sock *tp = tcp_sk(sk);
3210
3211         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
3212             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3213                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3214                 tcp_enter_quickack_mode(sk);
3215
3216                 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
3217                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3218
3219                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
3220                                 end_seq = tp->rcv_nxt;
3221                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
3222                 }
3223         }
3224
3225         tcp_send_ack(sk);
3226 }
3227
3228 /* These routines update the SACK block as out-of-order packets arrive or
3229  * in-order packets close up the sequence space.
3230  */
3231 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
3232 {
3233         int this_sack;
3234         struct tcp_sack_block *sp = &tp->selective_acks[0];
3235         struct tcp_sack_block *swalk = sp+1;
3236
3237         /* See if the recent change to the first SACK eats into
3238          * or hits the sequence space of other SACK blocks, if so coalesce.
3239          */
3240         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
3241                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
3242                         int i;
3243
3244                         /* Zap SWALK, by moving every further SACK up by one slot.
3245                          * Decrease num_sacks.
3246                          */
3247                         tp->rx_opt.num_sacks--;
3248                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3249                         for (i=this_sack; i < tp->rx_opt.num_sacks; i++)
3250                                 sp[i] = sp[i+1];
3251                         continue;
3252                 }
3253                 this_sack++, swalk++;
3254         }
3255 }
3256
3257 static inline void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
3258 {
3259         __u32 tmp;
3260
3261         tmp = sack1->start_seq;
3262         sack1->start_seq = sack2->start_seq;
3263         sack2->start_seq = tmp;
3264
3265         tmp = sack1->end_seq;
3266         sack1->end_seq = sack2->end_seq;
3267         sack2->end_seq = tmp;
3268 }
3269
3270 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
3271 {
3272         struct tcp_sock *tp = tcp_sk(sk);
3273         struct tcp_sack_block *sp = &tp->selective_acks[0];
3274         int cur_sacks = tp->rx_opt.num_sacks;
3275         int this_sack;
3276
3277         if (!cur_sacks)
3278                 goto new_sack;
3279
3280         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
3281                 if (tcp_sack_extend(sp, seq, end_seq)) {
3282                         /* Rotate this_sack to the first one. */
3283                         for (; this_sack>0; this_sack--, sp--)
3284                                 tcp_sack_swap(sp, sp-1);
3285                         if (cur_sacks > 1)
3286                                 tcp_sack_maybe_coalesce(tp);
3287                         return;
3288                 }
3289         }
3290
3291         /* Could not find an adjacent existing SACK, build a new one,
3292          * put it at the front, and shift everyone else down.  We
3293          * always know there is at least one SACK present already here.
3294          *
3295          * If the sack array is full, forget about the last one.
3296          */
3297         if (this_sack >= 4) {
3298                 this_sack--;
3299                 tp->rx_opt.num_sacks--;
3300                 sp--;
3301         }
3302         for (; this_sack > 0; this_sack--, sp--)
3303                 *sp = *(sp-1);
3304
3305 new_sack:
3306         /* Build the new head SACK, and we're done. */
3307         sp->start_seq = seq;
3308         sp->end_seq = end_seq;
3309         tp->rx_opt.num_sacks++;
3310         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3311 }
3312
3313 /* RCV.NXT advances, some SACKs should be eaten. */
3314
3315 static void tcp_sack_remove(struct tcp_sock *tp)
3316 {
3317         struct tcp_sack_block *sp = &tp->selective_acks[0];
3318         int num_sacks = tp->rx_opt.num_sacks;
3319         int this_sack;
3320
3321         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
3322         if (skb_queue_empty(&tp->out_of_order_queue)) {
3323                 tp->rx_opt.num_sacks = 0;
3324                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
3325                 return;
3326         }
3327
3328         for (this_sack = 0; this_sack < num_sacks; ) {
3329                 /* Check if the start of the sack is covered by RCV.NXT. */
3330                 if (!before(tp->rcv_nxt, sp->start_seq)) {
3331                         int i;
3332
3333                         /* RCV.NXT must cover all the block! */
3334                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
3335
3336                         /* Zap this SACK, by moving forward any other SACKS. */
3337                         for (i=this_sack+1; i < num_sacks; i++)
3338                                 tp->selective_acks[i-1] = tp->selective_acks[i];
3339                         num_sacks--;
3340                         continue;
3341                 }
3342                 this_sack++;
3343                 sp++;
3344         }
3345         if (num_sacks != tp->rx_opt.num_sacks) {
3346                 tp->rx_opt.num_sacks = num_sacks;
3347                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3348         }
3349 }
3350
3351 /* This one checks to see if we can put data from the
3352  * out_of_order queue into the receive_queue.
3353  */
3354 static void tcp_ofo_queue(struct sock *sk)
3355 {
3356         struct tcp_sock *tp = tcp_sk(sk);
3357         __u32 dsack_high = tp->rcv_nxt;
3358         struct sk_buff *skb;
3359
3360         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
3361                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
3362                         break;
3363
3364                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
3365                         __u32 dsack = dsack_high;
3366                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
3367                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
3368                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
3369                 }
3370
3371                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3372                         SOCK_DEBUG(sk, "ofo packet was already received \n");
3373                         __skb_unlink(skb, &tp->out_of_order_queue);
3374                         __kfree_skb(skb);
3375                         continue;
3376                 }
3377                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
3378                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3379                            TCP_SKB_CB(skb)->end_seq);
3380
3381                 __skb_unlink(skb, &tp->out_of_order_queue);
3382                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3383                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3384                 if (tcp_hdr(skb)->fin)
3385                         tcp_fin(skb, sk, tcp_hdr(skb));
3386         }
3387 }
3388
3389 static int tcp_prune_queue(struct sock *sk);
3390
3391 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
3392 {
3393         struct tcphdr *th = tcp_hdr(skb);
3394         struct tcp_sock *tp = tcp_sk(sk);
3395         int eaten = -1;
3396
3397         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
3398                 goto drop;
3399
3400         __skb_pull(skb, th->doff*4);
3401
3402         TCP_ECN_accept_cwr(tp, skb);
3403
3404         if (tp->rx_opt.dsack) {
3405                 tp->rx_opt.dsack = 0;
3406                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
3407                                                     4 - tp->rx_opt.tstamp_ok);
3408         }
3409
3410         /*  Queue data for delivery to the user.
3411          *  Packets in sequence go to the receive queue.
3412          *  Out of sequence packets to the out_of_order_queue.
3413          */
3414         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3415                 if (tcp_receive_window(tp) == 0)
3416                         goto out_of_window;
3417
3418                 /* Ok. In sequence. In window. */
3419                 if (tp->ucopy.task == current &&
3420                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
3421                     sock_owned_by_user(sk) && !tp->urg_data) {
3422                         int chunk = min_t(unsigned int, skb->len,
3423                                                         tp->ucopy.len);
3424
3425                         __set_current_state(TASK_RUNNING);
3426
3427                         local_bh_enable();
3428                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
3429                                 tp->ucopy.len -= chunk;
3430                                 tp->copied_seq += chunk;
3431                                 eaten = (chunk == skb->len && !th->fin);
3432                                 tcp_rcv_space_adjust(sk);
3433                         }
3434                         local_bh_disable();
3435                 }
3436
3437                 if (eaten <= 0) {
3438 queue_and_out:
3439                         if (eaten < 0 &&
3440                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3441                              !sk_stream_rmem_schedule(sk, skb))) {
3442                                 if (tcp_prune_queue(sk) < 0 ||
3443                                     !sk_stream_rmem_schedule(sk, skb))
3444                                         goto drop;
3445                         }
3446                         sk_stream_set_owner_r(skb, sk);
3447                         __skb_queue_tail(&sk->sk_receive_queue, skb);
3448                 }
3449                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3450                 if (skb->len)
3451                         tcp_event_data_recv(sk, skb);
3452                 if (th->fin)
3453                         tcp_fin(skb, sk, th);
3454
3455                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
3456                         tcp_ofo_queue(sk);
3457
3458                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
3459                          * gap in queue is filled.
3460                          */
3461                         if (skb_queue_empty(&tp->out_of_order_queue))
3462                                 inet_csk(sk)->icsk_ack.pingpong = 0;
3463                 }
3464
3465                 if (tp->rx_opt.num_sacks)
3466                         tcp_sack_remove(tp);
3467
3468                 tcp_fast_path_check(sk);
3469
3470                 if (eaten > 0)
3471                         __kfree_skb(skb);
3472                 else if (!sock_flag(sk, SOCK_DEAD))
3473                         sk->sk_data_ready(sk, 0);
3474                 return;
3475         }
3476
3477         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3478                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3479                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3480                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3481
3482 out_of_window:
3483                 tcp_enter_quickack_mode(sk);
3484                 inet_csk_schedule_ack(sk);
3485 drop:
3486                 __kfree_skb(skb);
3487                 return;
3488         }
3489
3490         /* Out of window. F.e. zero window probe. */
3491         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3492                 goto out_of_window;
3493
3494         tcp_enter_quickack_mode(sk);
3495
3496         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3497                 /* Partial packet, seq < rcv_next < end_seq */
3498                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3499                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3500                            TCP_SKB_CB(skb)->end_seq);
3501
3502                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3503
3504                 /* If window is closed, drop tail of packet. But after
3505                  * remembering D-SACK for its head made in previous line.
3506                  */
3507                 if (!tcp_receive_window(tp))
3508                         goto out_of_window;
3509                 goto queue_and_out;
3510         }
3511
3512         TCP_ECN_check_ce(tp, skb);
3513
3514         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3515             !sk_stream_rmem_schedule(sk, skb)) {
3516                 if (tcp_prune_queue(sk) < 0 ||
3517                     !sk_stream_rmem_schedule(sk, skb))
3518                         goto drop;
3519         }
3520
3521         /* Disable header prediction. */
3522         tp->pred_flags = 0;
3523         inet_csk_schedule_ack(sk);
3524
3525         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3526                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3527
3528         sk_stream_set_owner_r(skb, sk);
3529
3530         if (!skb_peek(&tp->out_of_order_queue)) {
3531                 /* Initial out of order segment, build 1 SACK. */
3532                 if (tp->rx_opt.sack_ok) {
3533                         tp->rx_opt.num_sacks = 1;
3534                         tp->rx_opt.dsack     = 0;
3535                         tp->rx_opt.eff_sacks = 1;
3536                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3537                         tp->selective_acks[0].end_seq =
3538                                                 TCP_SKB_CB(skb)->end_seq;
3539                 }
3540                 __skb_queue_head(&tp->out_of_order_queue,skb);
3541         } else {
3542                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3543                 u32 seq = TCP_SKB_CB(skb)->seq;
3544                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3545
3546                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3547                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3548
3549                         if (!tp->rx_opt.num_sacks ||
3550                             tp->selective_acks[0].end_seq != seq)
3551                                 goto add_sack;
3552
3553                         /* Common case: data arrive in order after hole. */
3554                         tp->selective_acks[0].end_seq = end_seq;
3555                         return;
3556                 }
3557
3558                 /* Find place to insert this segment. */
3559                 do {
3560                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3561                                 break;
3562                 } while ((skb1 = skb1->prev) !=
3563                          (struct sk_buff*)&tp->out_of_order_queue);
3564
3565                 /* Do skb overlap to previous one? */
3566                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3567                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3568                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3569                                 /* All the bits are present. Drop. */
3570                                 __kfree_skb(skb);
3571                                 tcp_dsack_set(tp, seq, end_seq);
3572                                 goto add_sack;
3573                         }
3574                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3575                                 /* Partial overlap. */
3576                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3577                         } else {
3578                                 skb1 = skb1->prev;
3579                         }
3580                 }
3581                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3582
3583                 /* And clean segments covered by new one as whole. */
3584                 while ((skb1 = skb->next) !=
3585                        (struct sk_buff*)&tp->out_of_order_queue &&
3586                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3587                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3588                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3589                                break;
3590                        }
3591                        __skb_unlink(skb1, &tp->out_of_order_queue);
3592                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3593                        __kfree_skb(skb1);
3594                 }
3595
3596 add_sack:
3597                 if (tp->rx_opt.sack_ok)
3598                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3599         }
3600 }
3601
3602 /* Collapse contiguous sequence of skbs head..tail with
3603  * sequence numbers start..end.
3604  * Segments with FIN/SYN are not collapsed (only because this
3605  * simplifies code)
3606  */
3607 static void
3608 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3609              struct sk_buff *head, struct sk_buff *tail,
3610              u32 start, u32 end)
3611 {
3612         struct sk_buff *skb;
3613
3614         /* First, check that queue is collapsible and find
3615          * the point where collapsing can be useful. */
3616         for (skb = head; skb != tail; ) {
3617                 /* No new bits? It is possible on ofo queue. */
3618                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3619                         struct sk_buff *next = skb->next;
3620                         __skb_unlink(skb, list);
3621                         __kfree_skb(skb);
3622                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3623                         skb = next;
3624                         continue;
3625                 }
3626
3627                 /* The first skb to collapse is:
3628                  * - not SYN/FIN and
3629                  * - bloated or contains data before "start" or
3630                  *   overlaps to the next one.
3631                  */
3632                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
3633                     (tcp_win_from_space(skb->truesize) > skb->len ||
3634                      before(TCP_SKB_CB(skb)->seq, start) ||
3635                      (skb->next != tail &&
3636                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3637                         break;
3638
3639                 /* Decided to skip this, advance start seq. */
3640                 start = TCP_SKB_CB(skb)->end_seq;
3641                 skb = skb->next;
3642         }
3643         if (skb == tail || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
3644                 return;
3645
3646         while (before(start, end)) {
3647                 struct sk_buff *nskb;
3648                 int header = skb_headroom(skb);
3649                 int copy = SKB_MAX_ORDER(header, 0);
3650
3651                 /* Too big header? This can happen with IPv6. */
3652                 if (copy < 0)
3653                         return;
3654                 if (end-start < copy)
3655                         copy = end-start;
3656                 nskb = alloc_skb(copy+header, GFP_ATOMIC);
3657                 if (!nskb)
3658                         return;
3659
3660                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
3661                 skb_set_network_header(nskb, (skb_network_header(skb) -
3662                                               skb->head));
3663                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
3664                                                 skb->head));
3665                 skb_reserve(nskb, header);
3666                 memcpy(nskb->head, skb->head, header);
3667                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3668                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3669                 __skb_insert(nskb, skb->prev, skb, list);
3670                 sk_stream_set_owner_r(nskb, sk);
3671
3672                 /* Copy data, releasing collapsed skbs. */
3673                 while (copy > 0) {
3674                         int offset = start - TCP_SKB_CB(skb)->seq;
3675                         int size = TCP_SKB_CB(skb)->end_seq - start;
3676
3677                         BUG_ON(offset < 0);
3678                         if (size > 0) {
3679                                 size = min(copy, size);
3680                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3681                                         BUG();
3682                                 TCP_SKB_CB(nskb)->end_seq += size;
3683                                 copy -= size;
3684                                 start += size;
3685                         }
3686                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3687                                 struct sk_buff *next = skb->next;
3688                                 __skb_unlink(skb, list);
3689                                 __kfree_skb(skb);
3690                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3691                                 skb = next;
3692                                 if (skb == tail ||
3693                                     tcp_hdr(skb)->syn ||
3694                                     tcp_hdr(skb)->fin)
3695                                         return;
3696                         }
3697                 }
3698         }
3699 }
3700
3701 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3702  * and tcp_collapse() them until all the queue is collapsed.
3703  */
3704 static void tcp_collapse_ofo_queue(struct sock *sk)
3705 {
3706         struct tcp_sock *tp = tcp_sk(sk);
3707         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3708         struct sk_buff *head;
3709         u32 start, end;
3710
3711         if (skb == NULL)
3712                 return;
3713
3714         start = TCP_SKB_CB(skb)->seq;
3715         end = TCP_SKB_CB(skb)->end_seq;
3716         head = skb;
3717
3718         for (;;) {
3719                 skb = skb->next;
3720
3721                 /* Segment is terminated when we see gap or when
3722                  * we are at the end of all the queue. */
3723                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
3724                     after(TCP_SKB_CB(skb)->seq, end) ||
3725                     before(TCP_SKB_CB(skb)->end_seq, start)) {
3726                         tcp_collapse(sk, &tp->out_of_order_queue,
3727                                      head, skb, start, end);
3728                         head = skb;
3729                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
3730                                 break;
3731                         /* Start new segment */
3732                         start = TCP_SKB_CB(skb)->seq;
3733                         end = TCP_SKB_CB(skb)->end_seq;
3734                 } else {
3735                         if (before(TCP_SKB_CB(skb)->seq, start))
3736                                 start = TCP_SKB_CB(skb)->seq;
3737                         if (after(TCP_SKB_CB(skb)->end_seq, end))
3738                                 end = TCP_SKB_CB(skb)->end_seq;
3739                 }
3740         }
3741 }
3742
3743 /* Reduce allocated memory if we can, trying to get
3744  * the socket within its memory limits again.
3745  *
3746  * Return less than zero if we should start dropping frames
3747  * until the socket owning process reads some of the data
3748  * to stabilize the situation.
3749  */
3750 static int tcp_prune_queue(struct sock *sk)
3751 {
3752         struct tcp_sock *tp = tcp_sk(sk);
3753
3754         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
3755
3756         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
3757
3758         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
3759                 tcp_clamp_window(sk);
3760         else if (tcp_memory_pressure)
3761                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
3762
3763         tcp_collapse_ofo_queue(sk);
3764         tcp_collapse(sk, &sk->sk_receive_queue,
3765                      sk->sk_receive_queue.next,
3766                      (struct sk_buff*)&sk->sk_receive_queue,
3767                      tp->copied_seq, tp->rcv_nxt);
3768         sk_stream_mem_reclaim(sk);
3769
3770         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3771                 return 0;
3772
3773         /* Collapsing did not help, destructive actions follow.
3774          * This must not ever occur. */
3775
3776         /* First, purge the out_of_order queue. */
3777         if (!skb_queue_empty(&tp->out_of_order_queue)) {
3778                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
3779                 __skb_queue_purge(&tp->out_of_order_queue);
3780
3781                 /* Reset SACK state.  A conforming SACK implementation will
3782                  * do the same at a timeout based retransmit.  When a connection
3783                  * is in a sad state like this, we care only about integrity
3784                  * of the connection not performance.
3785                  */
3786                 if (tp->rx_opt.sack_ok)
3787                         tcp_sack_reset(&tp->rx_opt);
3788                 sk_stream_mem_reclaim(sk);
3789         }
3790
3791         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
3792                 return 0;
3793
3794         /* If we are really being abused, tell the caller to silently
3795          * drop receive data on the floor.  It will get retransmitted
3796          * and hopefully then we'll have sufficient space.
3797          */
3798         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
3799
3800         /* Massive buffer overcommit. */
3801         tp->pred_flags = 0;
3802         return -1;
3803 }
3804
3805
3806 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
3807  * As additional protections, we do not touch cwnd in retransmission phases,
3808  * and if application hit its sndbuf limit recently.
3809  */
3810 void tcp_cwnd_application_limited(struct sock *sk)
3811 {
3812         struct tcp_sock *tp = tcp_sk(sk);
3813
3814         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
3815             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
3816                 /* Limited by application or receiver window. */
3817                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
3818                 u32 win_used = max(tp->snd_cwnd_used, init_win);
3819                 if (win_used < tp->snd_cwnd) {
3820                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
3821                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
3822                 }
3823                 tp->snd_cwnd_used = 0;
3824         }
3825         tp->snd_cwnd_stamp = tcp_time_stamp;
3826 }
3827
3828 static int tcp_should_expand_sndbuf(struct sock *sk)
3829 {
3830         struct tcp_sock *tp = tcp_sk(sk);
3831
3832         /* If the user specified a specific send buffer setting, do
3833          * not modify it.
3834          */
3835         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
3836                 return 0;
3837
3838         /* If we are under global TCP memory pressure, do not expand.  */
3839         if (tcp_memory_pressure)
3840                 return 0;
3841
3842         /* If we are under soft global TCP memory pressure, do not expand.  */
3843         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
3844                 return 0;
3845
3846         /* If we filled the congestion window, do not expand.  */
3847         if (tp->packets_out >= tp->snd_cwnd)
3848                 return 0;
3849
3850         return 1;
3851 }
3852
3853 /* When incoming ACK allowed to free some skb from write_queue,
3854  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
3855  * on the exit from tcp input handler.
3856  *
3857  * PROBLEM: sndbuf expansion does not work well with largesend.
3858  */
3859 static void tcp_new_space(struct sock *sk)
3860 {
3861         struct tcp_sock *tp = tcp_sk(sk);
3862
3863         if (tcp_should_expand_sndbuf(sk)) {
3864                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
3865                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
3866                     demanded = max_t(unsigned int, tp->snd_cwnd,
3867                                                    tp->reordering + 1);
3868                 sndmem *= 2*demanded;
3869                 if (sndmem > sk->sk_sndbuf)
3870                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
3871                 tp->snd_cwnd_stamp = tcp_time_stamp;
3872         }
3873
3874         sk->sk_write_space(sk);
3875 }
3876
3877 static void tcp_check_space(struct sock *sk)
3878 {
3879         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
3880                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
3881                 if (sk->sk_socket &&
3882                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
3883                         tcp_new_space(sk);
3884         }
3885 }
3886
3887 static inline void tcp_data_snd_check(struct sock *sk)
3888 {
3889         tcp_push_pending_frames(sk);
3890         tcp_check_space(sk);
3891 }
3892
3893 /*
3894  * Check if sending an ack is needed.
3895  */
3896 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
3897 {
3898         struct tcp_sock *tp = tcp_sk(sk);
3899
3900             /* More than one full frame received... */
3901         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
3902              /* ... and right edge of window advances far enough.
3903               * (tcp_recvmsg() will send ACK otherwise). Or...
3904               */
3905              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
3906             /* We ACK each frame or... */
3907             tcp_in_quickack_mode(sk) ||
3908             /* We have out of order data. */
3909             (ofo_possible &&
3910              skb_peek(&tp->out_of_order_queue))) {
3911                 /* Then ack it now */
3912                 tcp_send_ack(sk);
3913         } else {
3914                 /* Else, send delayed ack. */
3915                 tcp_send_delayed_ack(sk);
3916         }
3917 }
3918
3919 static inline void tcp_ack_snd_check(struct sock *sk)
3920 {
3921         if (!inet_csk_ack_scheduled(sk)) {
3922                 /* We sent a data segment already. */
3923                 return;
3924         }
3925         __tcp_ack_snd_check(sk, 1);
3926 }
3927
3928 /*
3929  *      This routine is only called when we have urgent data
3930  *      signaled. Its the 'slow' part of tcp_urg. It could be
3931  *      moved inline now as tcp_urg is only called from one
3932  *      place. We handle URGent data wrong. We have to - as
3933  *      BSD still doesn't use the correction from RFC961.
3934  *      For 1003.1g we should support a new option TCP_STDURG to permit
3935  *      either form (or just set the sysctl tcp_stdurg).
3936  */
3937
3938 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
3939 {
3940         struct tcp_sock *tp = tcp_sk(sk);
3941         u32 ptr = ntohs(th->urg_ptr);
3942
3943         if (ptr && !sysctl_tcp_stdurg)
3944                 ptr--;
3945         ptr += ntohl(th->seq);
3946
3947         /* Ignore urgent data that we've already seen and read. */
3948         if (after(tp->copied_seq, ptr))
3949                 return;
3950
3951         /* Do not replay urg ptr.
3952          *
3953          * NOTE: interesting situation not covered by specs.
3954          * Misbehaving sender may send urg ptr, pointing to segment,
3955          * which we already have in ofo queue. We are not able to fetch
3956          * such data and will stay in TCP_URG_NOTYET until will be eaten
3957          * by recvmsg(). Seems, we are not obliged to handle such wicked
3958          * situations. But it is worth to think about possibility of some
3959          * DoSes using some hypothetical application level deadlock.
3960          */
3961         if (before(ptr, tp->rcv_nxt))
3962                 return;
3963
3964         /* Do we already have a newer (or duplicate) urgent pointer? */
3965         if (tp->urg_data && !after(ptr, tp->urg_seq))
3966                 return;
3967
3968         /* Tell the world about our new urgent pointer. */
3969         sk_send_sigurg(sk);
3970
3971         /* We may be adding urgent data when the last byte read was
3972          * urgent. To do this requires some care. We cannot just ignore
3973          * tp->copied_seq since we would read the last urgent byte again
3974          * as data, nor can we alter copied_seq until this data arrives
3975          * or we break the semantics of SIOCATMARK (and thus sockatmark())
3976          *
3977          * NOTE. Double Dutch. Rendering to plain English: author of comment
3978          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
3979          * and expect that both A and B disappear from stream. This is _wrong_.
3980          * Though this happens in BSD with high probability, this is occasional.
3981          * Any application relying on this is buggy. Note also, that fix "works"
3982          * only in this artificial test. Insert some normal data between A and B and we will
3983          * decline of BSD again. Verdict: it is better to remove to trap
3984          * buggy users.
3985          */
3986         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
3987             !sock_flag(sk, SOCK_URGINLINE) &&
3988             tp->copied_seq != tp->rcv_nxt) {
3989                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
3990                 tp->copied_seq++;
3991                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
3992                         __skb_unlink(skb, &sk->sk_receive_queue);
3993                         __kfree_skb(skb);
3994                 }
3995         }
3996
3997         tp->urg_data   = TCP_URG_NOTYET;
3998         tp->urg_seq    = ptr;
3999
4000         /* Disable header prediction. */
4001         tp->pred_flags = 0;
4002 }
4003
4004 /* This is the 'fast' part of urgent handling. */
4005 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
4006 {
4007         struct tcp_sock *tp = tcp_sk(sk);
4008
4009         /* Check if we get a new urgent pointer - normally not. */
4010         if (th->urg)
4011                 tcp_check_urg(sk,th);
4012
4013         /* Do we wait for any urgent data? - normally not... */
4014         if (tp->urg_data == TCP_URG_NOTYET) {
4015                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4016                           th->syn;
4017
4018                 /* Is the urgent pointer pointing into this packet? */
4019                 if (ptr < skb->len) {
4020                         u8 tmp;
4021                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4022                                 BUG();
4023                         tp->urg_data = TCP_URG_VALID | tmp;
4024                         if (!sock_flag(sk, SOCK_DEAD))
4025                                 sk->sk_data_ready(sk, 0);
4026                 }
4027         }
4028 }
4029
4030 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4031 {
4032         struct tcp_sock *tp = tcp_sk(sk);
4033         int chunk = skb->len - hlen;
4034         int err;
4035
4036         local_bh_enable();
4037         if (skb_csum_unnecessary(skb))
4038                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4039         else
4040                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4041                                                        tp->ucopy.iov);
4042
4043         if (!err) {
4044                 tp->ucopy.len -= chunk;
4045                 tp->copied_seq += chunk;
4046                 tcp_rcv_space_adjust(sk);
4047         }
4048
4049         local_bh_disable();
4050         return err;
4051 }
4052
4053 static __sum16 __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
4054 {
4055         __sum16 result;
4056
4057         if (sock_owned_by_user(sk)) {
4058                 local_bh_enable();
4059                 result = __tcp_checksum_complete(skb);
4060                 local_bh_disable();
4061         } else {
4062                 result = __tcp_checksum_complete(skb);
4063         }
4064         return result;
4065 }
4066
4067 static inline int tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
4068 {
4069         return !skb_csum_unnecessary(skb) &&
4070                 __tcp_checksum_complete_user(sk, skb);
4071 }
4072
4073 #ifdef CONFIG_NET_DMA
4074 static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb, int hlen)
4075 {
4076         struct tcp_sock *tp = tcp_sk(sk);
4077         int chunk = skb->len - hlen;
4078         int dma_cookie;
4079         int copied_early = 0;
4080
4081         if (tp->ucopy.wakeup)
4082                 return 0;
4083
4084         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
4085                 tp->ucopy.dma_chan = get_softnet_dma();
4086
4087         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
4088
4089                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
4090                         skb, hlen, tp->ucopy.iov, chunk, tp->ucopy.pinned_list);
4091
4092                 if (dma_cookie < 0)
4093                         goto out;
4094
4095                 tp->ucopy.dma_cookie = dma_cookie;
4096                 copied_early = 1;
4097
4098                 tp->ucopy.len -= chunk;
4099                 tp->copied_seq += chunk;
4100                 tcp_rcv_space_adjust(sk);
4101
4102                 if ((tp->ucopy.len == 0) ||
4103                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
4104                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
4105                         tp->ucopy.wakeup = 1;
4106                         sk->sk_data_ready(sk, 0);
4107                 }
4108         } else if (chunk > 0) {
4109                 tp->ucopy.wakeup = 1;
4110                 sk->sk_data_ready(sk, 0);
4111         }
4112 out:
4113         return copied_early;
4114 }
4115 #endif /* CONFIG_NET_DMA */
4116
4117 /*
4118  *      TCP receive function for the ESTABLISHED state.
4119  *
4120  *      It is split into a fast path and a slow path. The fast path is
4121  *      disabled when:
4122  *      - A zero window was announced from us - zero window probing
4123  *        is only handled properly in the slow path.
4124  *      - Out of order segments arrived.
4125  *      - Urgent data is expected.
4126  *      - There is no buffer space left
4127  *      - Unexpected TCP flags/window values/header lengths are received
4128  *        (detected by checking the TCP header against pred_flags)
4129  *      - Data is sent in both directions. Fast path only supports pure senders
4130  *        or pure receivers (this means either the sequence number or the ack
4131  *        value must stay constant)
4132  *      - Unexpected TCP option.
4133  *
4134  *      When these conditions are not satisfied it drops into a standard
4135  *      receive procedure patterned after RFC793 to handle all cases.
4136  *      The first three cases are guaranteed by proper pred_flags setting,
4137  *      the rest is checked inline. Fast processing is turned on in
4138  *      tcp_data_queue when everything is OK.
4139  */
4140 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
4141                         struct tcphdr *th, unsigned len)
4142 {
4143         struct tcp_sock *tp = tcp_sk(sk);
4144
4145         /*
4146          *      Header prediction.
4147          *      The code loosely follows the one in the famous
4148          *      "30 instruction TCP receive" Van Jacobson mail.
4149          *
4150          *      Van's trick is to deposit buffers into socket queue
4151          *      on a device interrupt, to call tcp_recv function
4152          *      on the receive process context and checksum and copy
4153          *      the buffer to user space. smart...
4154          *
4155          *      Our current scheme is not silly either but we take the
4156          *      extra cost of the net_bh soft interrupt processing...
4157          *      We do checksum and copy also but from device to kernel.
4158          */
4159
4160         tp->rx_opt.saw_tstamp = 0;
4161
4162         /*      pred_flags is 0xS?10 << 16 + snd_wnd
4163          *      if header_prediction is to be made
4164          *      'S' will always be tp->tcp_header_len >> 2
4165          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
4166          *  turn it off (when there are holes in the receive
4167          *       space for instance)
4168          *      PSH flag is ignored.
4169          */
4170
4171         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
4172                 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4173                 int tcp_header_len = tp->tcp_header_len;
4174
4175                 /* Timestamp header prediction: tcp_header_len
4176                  * is automatically equal to th->doff*4 due to pred_flags
4177                  * match.
4178                  */
4179
4180                 /* Check timestamp */
4181                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
4182                         __be32 *ptr = (__be32 *)(th + 1);
4183
4184                         /* No? Slow path! */
4185                         if (*ptr != htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4186                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
4187                                 goto slow_path;
4188
4189                         tp->rx_opt.saw_tstamp = 1;
4190                         ++ptr;
4191                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
4192                         ++ptr;
4193                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
4194
4195                         /* If PAWS failed, check it more carefully in slow path */
4196                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
4197                                 goto slow_path;
4198
4199                         /* DO NOT update ts_recent here, if checksum fails
4200                          * and timestamp was corrupted part, it will result
4201                          * in a hung connection since we will drop all
4202                          * future packets due to the PAWS test.
4203                          */
4204                 }
4205
4206                 if (len <= tcp_header_len) {
4207                         /* Bulk data transfer: sender */
4208                         if (len == tcp_header_len) {
4209                                 /* Predicted packet is in window by definition.
4210                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4211                                  * Hence, check seq<=rcv_wup reduces to:
4212                                  */
4213                                 if (tcp_header_len ==
4214                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4215                                     tp->rcv_nxt == tp->rcv_wup)
4216                                         tcp_store_ts_recent(tp);
4217
4218                                 /* We know that such packets are checksummed
4219                                  * on entry.
4220                                  */
4221                                 tcp_ack(sk, skb, 0);
4222                                 __kfree_skb(skb);
4223                                 tcp_data_snd_check(sk);
4224                                 return 0;
4225                         } else { /* Header too small */
4226                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4227                                 goto discard;
4228                         }
4229                 } else {
4230                         int eaten = 0;
4231                         int copied_early = 0;
4232
4233                         if (tp->copied_seq == tp->rcv_nxt &&
4234                             len - tcp_header_len <= tp->ucopy.len) {
4235 #ifdef CONFIG_NET_DMA
4236                                 if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
4237                                         copied_early = 1;
4238                                         eaten = 1;
4239                                 }
4240 #endif
4241                                 if (tp->ucopy.task == current && sock_owned_by_user(sk) && !copied_early) {
4242                                         __set_current_state(TASK_RUNNING);
4243
4244                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
4245                                                 eaten = 1;
4246                                 }
4247                                 if (eaten) {
4248                                         /* Predicted packet is in window by definition.
4249                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4250                                          * Hence, check seq<=rcv_wup reduces to:
4251                                          */
4252                                         if (tcp_header_len ==
4253                                             (sizeof(struct tcphdr) +
4254                                              TCPOLEN_TSTAMP_ALIGNED) &&
4255                                             tp->rcv_nxt == tp->rcv_wup)
4256                                                 tcp_store_ts_recent(tp);
4257
4258                                         tcp_rcv_rtt_measure_ts(sk, skb);
4259
4260                                         __skb_pull(skb, tcp_header_len);
4261                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4262                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
4263                                 }
4264                                 if (copied_early)
4265                                         tcp_cleanup_rbuf(sk, skb->len);
4266                         }
4267                         if (!eaten) {
4268                                 if (tcp_checksum_complete_user(sk, skb))
4269                                         goto csum_error;
4270
4271                                 /* Predicted packet is in window by definition.
4272                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4273                                  * Hence, check seq<=rcv_wup reduces to:
4274                                  */
4275                                 if (tcp_header_len ==
4276                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4277                                     tp->rcv_nxt == tp->rcv_wup)
4278                                         tcp_store_ts_recent(tp);
4279
4280                                 tcp_rcv_rtt_measure_ts(sk, skb);
4281
4282                                 if ((int)skb->truesize > sk->sk_forward_alloc)
4283                                         goto step5;
4284
4285                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
4286
4287                                 /* Bulk data transfer: receiver */
4288                                 __skb_pull(skb,tcp_header_len);
4289                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4290                                 sk_stream_set_owner_r(skb, sk);
4291                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4292                         }
4293
4294                         tcp_event_data_recv(sk, skb);
4295
4296                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
4297                                 /* Well, only one small jumplet in fast path... */
4298                                 tcp_ack(sk, skb, FLAG_DATA);
4299                                 tcp_data_snd_check(sk);
4300                                 if (!inet_csk_ack_scheduled(sk))
4301                                         goto no_ack;
4302                         }
4303
4304                         __tcp_ack_snd_check(sk, 0);
4305 no_ack:
4306 #ifdef CONFIG_NET_DMA
4307                         if (copied_early)
4308                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
4309                         else
4310 #endif
4311                         if (eaten)
4312                                 __kfree_skb(skb);
4313                         else
4314                                 sk->sk_data_ready(sk, 0);
4315                         return 0;
4316                 }
4317         }
4318
4319 slow_path:
4320         if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
4321                 goto csum_error;
4322
4323         /*
4324          * RFC1323: H1. Apply PAWS check first.
4325          */
4326         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4327             tcp_paws_discard(sk, skb)) {
4328                 if (!th->rst) {
4329                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4330                         tcp_send_dupack(sk, skb);
4331                         goto discard;
4332                 }
4333                 /* Resets are accepted even if PAWS failed.
4334
4335                    ts_recent update must be made after we are sure
4336                    that the packet is in window.
4337                  */
4338         }
4339
4340         /*
4341          *      Standard slow path.
4342          */
4343
4344         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4345                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
4346                  * (RST) segments are validated by checking their SEQ-fields."
4347                  * And page 69: "If an incoming segment is not acceptable,
4348                  * an acknowledgment should be sent in reply (unless the RST bit
4349                  * is set, if so drop the segment and return)".
4350                  */
4351                 if (!th->rst)
4352                         tcp_send_dupack(sk, skb);
4353                 goto discard;
4354         }
4355
4356         if (th->rst) {
4357                 tcp_reset(sk);
4358                 goto discard;
4359         }
4360
4361         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4362
4363         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4364                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4365                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4366                 tcp_reset(sk);
4367                 return 1;
4368         }
4369
4370 step5:
4371         if (th->ack)
4372                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4373
4374         tcp_rcv_rtt_measure_ts(sk, skb);
4375
4376         /* Process urgent data. */
4377         tcp_urg(sk, skb, th);
4378
4379         /* step 7: process the segment text */
4380         tcp_data_queue(sk, skb);
4381
4382         tcp_data_snd_check(sk);
4383         tcp_ack_snd_check(sk);
4384         return 0;
4385
4386 csum_error:
4387         TCP_INC_STATS_BH(TCP_MIB_INERRS);
4388
4389 discard:
4390         __kfree_skb(skb);
4391         return 0;
4392 }
4393
4394 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
4395                                          struct tcphdr *th, unsigned len)
4396 {
4397         struct tcp_sock *tp = tcp_sk(sk);
4398         struct inet_connection_sock *icsk = inet_csk(sk);
4399         int saved_clamp = tp->rx_opt.mss_clamp;
4400
4401         tcp_parse_options(skb, &tp->rx_opt, 0);
4402
4403         if (th->ack) {
4404                 /* rfc793:
4405                  * "If the state is SYN-SENT then
4406                  *    first check the ACK bit
4407                  *      If the ACK bit is set
4408                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
4409                  *        a reset (unless the RST bit is set, if so drop
4410                  *        the segment and return)"
4411                  *
4412                  *  We do not send data with SYN, so that RFC-correct
4413                  *  test reduces to:
4414                  */
4415                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
4416                         goto reset_and_undo;
4417
4418                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4419                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
4420                              tcp_time_stamp)) {
4421                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
4422                         goto reset_and_undo;
4423                 }
4424
4425                 /* Now ACK is acceptable.
4426                  *
4427                  * "If the RST bit is set
4428                  *    If the ACK was acceptable then signal the user "error:
4429                  *    connection reset", drop the segment, enter CLOSED state,
4430                  *    delete TCB, and return."
4431                  */
4432
4433                 if (th->rst) {
4434                         tcp_reset(sk);
4435                         goto discard;
4436                 }
4437
4438                 /* rfc793:
4439                  *   "fifth, if neither of the SYN or RST bits is set then
4440                  *    drop the segment and return."
4441                  *
4442                  *    See note below!
4443                  *                                        --ANK(990513)
4444                  */
4445                 if (!th->syn)
4446                         goto discard_and_undo;
4447
4448                 /* rfc793:
4449                  *   "If the SYN bit is on ...
4450                  *    are acceptable then ...
4451                  *    (our SYN has been ACKed), change the connection
4452                  *    state to ESTABLISHED..."
4453                  */
4454
4455                 TCP_ECN_rcv_synack(tp, th);
4456
4457                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
4458                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4459
4460                 /* Ok.. it's good. Set up sequence numbers and
4461                  * move to established.
4462                  */
4463                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4464                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4465
4466                 /* RFC1323: The window in SYN & SYN/ACK segments is
4467                  * never scaled.
4468                  */
4469                 tp->snd_wnd = ntohs(th->window);
4470                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
4471
4472                 if (!tp->rx_opt.wscale_ok) {
4473                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
4474                         tp->window_clamp = min(tp->window_clamp, 65535U);
4475                 }
4476
4477                 if (tp->rx_opt.saw_tstamp) {
4478                         tp->rx_opt.tstamp_ok       = 1;
4479                         tp->tcp_header_len =
4480                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4481                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
4482                         tcp_store_ts_recent(tp);
4483                 } else {
4484                         tp->tcp_header_len = sizeof(struct tcphdr);
4485                 }
4486
4487                 if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
4488                         tp->rx_opt.sack_ok |= 2;
4489
4490                 tcp_mtup_init(sk);
4491                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4492                 tcp_initialize_rcv_mss(sk);
4493
4494                 /* Remember, tcp_poll() does not lock socket!
4495                  * Change state from SYN-SENT only after copied_seq
4496                  * is initialized. */
4497                 tp->copied_seq = tp->rcv_nxt;
4498                 smp_mb();
4499                 tcp_set_state(sk, TCP_ESTABLISHED);
4500
4501                 security_inet_conn_established(sk, skb);
4502
4503                 /* Make sure socket is routed, for correct metrics.  */
4504                 icsk->icsk_af_ops->rebuild_header(sk);
4505
4506                 tcp_init_metrics(sk);
4507
4508                 tcp_init_congestion_control(sk);
4509
4510                 /* Prevent spurious tcp_cwnd_restart() on first data
4511                  * packet.
4512                  */
4513                 tp->lsndtime = tcp_time_stamp;
4514
4515                 tcp_init_buffer_space(sk);
4516
4517                 if (sock_flag(sk, SOCK_KEEPOPEN))
4518                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
4519
4520                 if (!tp->rx_opt.snd_wscale)
4521                         __tcp_fast_path_on(tp, tp->snd_wnd);
4522                 else
4523                         tp->pred_flags = 0;
4524
4525                 if (!sock_flag(sk, SOCK_DEAD)) {
4526                         sk->sk_state_change(sk);
4527                         sk_wake_async(sk, 0, POLL_OUT);
4528                 }
4529
4530                 if (sk->sk_write_pending ||
4531                     icsk->icsk_accept_queue.rskq_defer_accept ||
4532                     icsk->icsk_ack.pingpong) {
4533                         /* Save one ACK. Data will be ready after
4534                          * several ticks, if write_pending is set.
4535                          *
4536                          * It may be deleted, but with this feature tcpdumps
4537                          * look so _wonderfully_ clever, that I was not able
4538                          * to stand against the temptation 8)     --ANK
4539                          */
4540                         inet_csk_schedule_ack(sk);
4541                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4542                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4543                         tcp_incr_quickack(sk);
4544                         tcp_enter_quickack_mode(sk);
4545                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4546                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4547
4548 discard:
4549                         __kfree_skb(skb);
4550                         return 0;
4551                 } else {
4552                         tcp_send_ack(sk);
4553                 }
4554                 return -1;
4555         }
4556
4557         /* No ACK in the segment */
4558
4559         if (th->rst) {
4560                 /* rfc793:
4561                  * "If the RST bit is set
4562                  *
4563                  *      Otherwise (no ACK) drop the segment and return."
4564                  */
4565
4566                 goto discard_and_undo;
4567         }
4568
4569         /* PAWS check. */
4570         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4571                 goto discard_and_undo;
4572
4573         if (th->syn) {
4574                 /* We see SYN without ACK. It is attempt of
4575                  * simultaneous connect with crossed SYNs.
4576                  * Particularly, it can be connect to self.
4577                  */
4578                 tcp_set_state(sk, TCP_SYN_RECV);
4579
4580                 if (tp->rx_opt.saw_tstamp) {
4581                         tp->rx_opt.tstamp_ok = 1;
4582                         tcp_store_ts_recent(tp);
4583                         tp->tcp_header_len =
4584                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4585                 } else {
4586                         tp->tcp_header_len = sizeof(struct tcphdr);
4587                 }
4588
4589                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4590                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4591
4592                 /* RFC1323: The window in SYN & SYN/ACK segments is
4593                  * never scaled.
4594                  */
4595                 tp->snd_wnd    = ntohs(th->window);
4596                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4597                 tp->max_window = tp->snd_wnd;
4598
4599                 TCP_ECN_rcv_syn(tp, th);
4600
4601                 tcp_mtup_init(sk);
4602                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4603                 tcp_initialize_rcv_mss(sk);
4604
4605
4606                 tcp_send_synack(sk);
4607 #if 0
4608                 /* Note, we could accept data and URG from this segment.
4609                  * There are no obstacles to make this.
4610                  *
4611                  * However, if we ignore data in ACKless segments sometimes,
4612                  * we have no reasons to accept it sometimes.
4613                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
4614                  * is not flawless. So, discard packet for sanity.
4615                  * Uncomment this return to process the data.
4616                  */
4617                 return -1;
4618 #else
4619                 goto discard;
4620 #endif
4621         }
4622         /* "fifth, if neither of the SYN or RST bits is set then
4623          * drop the segment and return."
4624          */
4625
4626 discard_and_undo:
4627         tcp_clear_options(&tp->rx_opt);
4628         tp->rx_opt.mss_clamp = saved_clamp;
4629         goto discard;
4630
4631 reset_and_undo:
4632         tcp_clear_options(&tp->rx_opt);
4633         tp->rx_opt.mss_clamp = saved_clamp;
4634         return 1;
4635 }
4636
4637
4638 /*
4639  *      This function implements the receiving procedure of RFC 793 for
4640  *      all states except ESTABLISHED and TIME_WAIT.
4641  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4642  *      address independent.
4643  */
4644
4645 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4646                           struct tcphdr *th, unsigned len)
4647 {
4648         struct tcp_sock *tp = tcp_sk(sk);
4649         struct inet_connection_sock *icsk = inet_csk(sk);
4650         int queued = 0;
4651
4652         tp->rx_opt.saw_tstamp = 0;
4653
4654         switch (sk->sk_state) {
4655         case TCP_CLOSE:
4656                 goto discard;
4657
4658         case TCP_LISTEN:
4659                 if (th->ack)
4660                         return 1;
4661
4662                 if (th->rst)
4663                         goto discard;
4664
4665                 if (th->syn) {
4666                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
4667                                 return 1;
4668
4669                         /* Now we have several options: In theory there is
4670                          * nothing else in the frame. KA9Q has an option to
4671                          * send data with the syn, BSD accepts data with the
4672                          * syn up to the [to be] advertised window and
4673                          * Solaris 2.1 gives you a protocol error. For now
4674                          * we just ignore it, that fits the spec precisely
4675                          * and avoids incompatibilities. It would be nice in
4676                          * future to drop through and process the data.
4677                          *
4678                          * Now that TTCP is starting to be used we ought to
4679                          * queue this data.
4680                          * But, this leaves one open to an easy denial of
4681                          * service attack, and SYN cookies can't defend
4682                          * against this problem. So, we drop the data
4683                          * in the interest of security over speed unless
4684                          * it's still in use.
4685                          */
4686                         kfree_skb(skb);
4687                         return 0;
4688                 }
4689                 goto discard;
4690
4691         case TCP_SYN_SENT:
4692                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4693                 if (queued >= 0)
4694                         return queued;
4695
4696                 /* Do step6 onward by hand. */
4697                 tcp_urg(sk, skb, th);
4698                 __kfree_skb(skb);
4699                 tcp_data_snd_check(sk);
4700                 return 0;
4701         }
4702
4703         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4704             tcp_paws_discard(sk, skb)) {
4705                 if (!th->rst) {
4706                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4707                         tcp_send_dupack(sk, skb);
4708                         goto discard;
4709                 }
4710                 /* Reset is accepted even if it did not pass PAWS. */
4711         }
4712
4713         /* step 1: check sequence number */
4714         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4715                 if (!th->rst)
4716                         tcp_send_dupack(sk, skb);
4717                 goto discard;
4718         }
4719
4720         /* step 2: check RST bit */
4721         if (th->rst) {
4722                 tcp_reset(sk);
4723                 goto discard;
4724         }
4725
4726         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4727
4728         /* step 3: check security and precedence [ignored] */
4729
4730         /*      step 4:
4731          *
4732          *      Check for a SYN in window.
4733          */
4734         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4735                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4736                 tcp_reset(sk);
4737                 return 1;
4738         }
4739
4740         /* step 5: check the ACK field */
4741         if (th->ack) {
4742                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
4743
4744                 switch (sk->sk_state) {
4745                 case TCP_SYN_RECV:
4746                         if (acceptable) {
4747                                 tp->copied_seq = tp->rcv_nxt;
4748                                 smp_mb();
4749                                 tcp_set_state(sk, TCP_ESTABLISHED);
4750                                 sk->sk_state_change(sk);
4751
4752                                 /* Note, that this wakeup is only for marginal
4753                                  * crossed SYN case. Passively open sockets
4754                                  * are not waked up, because sk->sk_sleep ==
4755                                  * NULL and sk->sk_socket == NULL.
4756                                  */
4757                                 if (sk->sk_socket) {
4758                                         sk_wake_async(sk,0,POLL_OUT);
4759                                 }
4760
4761                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
4762                                 tp->snd_wnd = ntohs(th->window) <<
4763                                               tp->rx_opt.snd_wscale;
4764                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
4765                                             TCP_SKB_CB(skb)->seq);
4766
4767                                 /* tcp_ack considers this ACK as duplicate
4768                                  * and does not calculate rtt.
4769                                  * Fix it at least with timestamps.
4770                                  */
4771                                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4772                                     !tp->srtt)
4773                                         tcp_ack_saw_tstamp(sk, 0);
4774
4775                                 if (tp->rx_opt.tstamp_ok)
4776                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
4777
4778                                 /* Make sure socket is routed, for
4779                                  * correct metrics.
4780                                  */
4781                                 icsk->icsk_af_ops->rebuild_header(sk);
4782
4783                                 tcp_init_metrics(sk);
4784
4785                                 tcp_init_congestion_control(sk);
4786
4787                                 /* Prevent spurious tcp_cwnd_restart() on
4788                                  * first data packet.
4789                                  */
4790                                 tp->lsndtime = tcp_time_stamp;
4791
4792                                 tcp_mtup_init(sk);
4793                                 tcp_initialize_rcv_mss(sk);
4794                                 tcp_init_buffer_space(sk);
4795                                 tcp_fast_path_on(tp);
4796                         } else {
4797                                 return 1;
4798                         }
4799                         break;
4800
4801                 case TCP_FIN_WAIT1:
4802                         if (tp->snd_una == tp->write_seq) {
4803                                 tcp_set_state(sk, TCP_FIN_WAIT2);
4804                                 sk->sk_shutdown |= SEND_SHUTDOWN;
4805                                 dst_confirm(sk->sk_dst_cache);
4806
4807                                 if (!sock_flag(sk, SOCK_DEAD))
4808                                         /* Wake up lingering close() */
4809                                         sk->sk_state_change(sk);
4810                                 else {
4811                                         int tmo;
4812
4813                                         if (tp->linger2 < 0 ||
4814                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4815                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
4816                                                 tcp_done(sk);
4817                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4818                                                 return 1;
4819                                         }
4820
4821                                         tmo = tcp_fin_time(sk);
4822                                         if (tmo > TCP_TIMEWAIT_LEN) {
4823                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
4824                                         } else if (th->fin || sock_owned_by_user(sk)) {
4825                                                 /* Bad case. We could lose such FIN otherwise.
4826                                                  * It is not a big problem, but it looks confusing
4827                                                  * and not so rare event. We still can lose it now,
4828                                                  * if it spins in bh_lock_sock(), but it is really
4829                                                  * marginal case.
4830                                                  */
4831                                                 inet_csk_reset_keepalive_timer(sk, tmo);
4832                                         } else {
4833                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
4834                                                 goto discard;
4835                                         }
4836                                 }
4837                         }
4838                         break;
4839
4840                 case TCP_CLOSING:
4841                         if (tp->snd_una == tp->write_seq) {
4842                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4843                                 goto discard;
4844                         }
4845                         break;
4846
4847                 case TCP_LAST_ACK:
4848                         if (tp->snd_una == tp->write_seq) {
4849                                 tcp_update_metrics(sk);
4850                                 tcp_done(sk);
4851                                 goto discard;
4852                         }
4853                         break;
4854                 }
4855         } else
4856                 goto discard;
4857
4858         /* step 6: check the URG bit */
4859         tcp_urg(sk, skb, th);
4860
4861         /* step 7: process the segment text */
4862         switch (sk->sk_state) {
4863         case TCP_CLOSE_WAIT:
4864         case TCP_CLOSING:
4865         case TCP_LAST_ACK:
4866                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4867                         break;
4868         case TCP_FIN_WAIT1:
4869         case TCP_FIN_WAIT2:
4870                 /* RFC 793 says to queue data in these states,
4871                  * RFC 1122 says we MUST send a reset.
4872                  * BSD 4.4 also does reset.
4873                  */
4874                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
4875                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4876                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
4877                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
4878                                 tcp_reset(sk);
4879                                 return 1;
4880                         }
4881                 }
4882                 /* Fall through */
4883         case TCP_ESTABLISHED:
4884                 tcp_data_queue(sk, skb);
4885                 queued = 1;
4886                 break;
4887         }
4888
4889         /* tcp_data could move socket to TIME-WAIT */
4890         if (sk->sk_state != TCP_CLOSE) {
4891                 tcp_data_snd_check(sk);
4892                 tcp_ack_snd_check(sk);
4893         }
4894
4895         if (!queued) {
4896 discard:
4897                 __kfree_skb(skb);
4898         }
4899         return 0;
4900 }
4901
4902 EXPORT_SYMBOL(sysctl_tcp_ecn);
4903 EXPORT_SYMBOL(sysctl_tcp_reordering);
4904 EXPORT_SYMBOL(tcp_parse_options);
4905 EXPORT_SYMBOL(tcp_rcv_established);
4906 EXPORT_SYMBOL(tcp_rcv_state_process);
4907 EXPORT_SYMBOL(tcp_initialize_rcv_mss);