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