sctp: Do not force T3 timer on fast retransmissions.
[linux-3.10.git] / net / sctp / outqueue.c
1 /* SCTP kernel implementation
2  * (C) Copyright IBM Corp. 2001, 2004
3  * Copyright (c) 1999-2000 Cisco, Inc.
4  * Copyright (c) 1999-2001 Motorola, Inc.
5  * Copyright (c) 2001-2003 Intel Corp.
6  *
7  * This file is part of the SCTP kernel implementation
8  *
9  * These functions implement the sctp_outq class.   The outqueue handles
10  * bundling and queueing of outgoing SCTP chunks.
11  *
12  * This SCTP implementation is free software;
13  * you can redistribute it and/or modify it under the terms of
14  * the GNU General Public License as published by
15  * the Free Software Foundation; either version 2, or (at your option)
16  * any later version.
17  *
18  * This SCTP implementation is distributed in the hope that it
19  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
20  *                 ************************
21  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
22  * See the GNU General Public License for more details.
23  *
24  * You should have received a copy of the GNU General Public License
25  * along with GNU CC; see the file COPYING.  If not, write to
26  * the Free Software Foundation, 59 Temple Place - Suite 330,
27  * Boston, MA 02111-1307, USA.
28  *
29  * Please send any bug reports or fixes you make to the
30  * email address(es):
31  *    lksctp developers <lksctp-developers@lists.sourceforge.net>
32  *
33  * Or submit a bug report through the following website:
34  *    http://www.sf.net/projects/lksctp
35  *
36  * Written or modified by:
37  *    La Monte H.P. Yarroll <piggy@acm.org>
38  *    Karl Knutson          <karl@athena.chicago.il.us>
39  *    Perry Melange         <pmelange@null.cc.uic.edu>
40  *    Xingang Guo           <xingang.guo@intel.com>
41  *    Hui Huang             <hui.huang@nokia.com>
42  *    Sridhar Samudrala     <sri@us.ibm.com>
43  *    Jon Grimm             <jgrimm@us.ibm.com>
44  *
45  * Any bugs reported given to us we will try to fix... any fixes shared will
46  * be incorporated into the next SCTP release.
47  */
48
49 #include <linux/types.h>
50 #include <linux/list.h>   /* For struct list_head */
51 #include <linux/socket.h>
52 #include <linux/ip.h>
53 #include <linux/slab.h>
54 #include <net/sock.h>     /* For skb_set_owner_w */
55
56 #include <net/sctp/sctp.h>
57 #include <net/sctp/sm.h>
58
59 /* Declare internal functions here.  */
60 static int sctp_acked(struct sctp_sackhdr *sack, __u32 tsn);
61 static void sctp_check_transmitted(struct sctp_outq *q,
62                                    struct list_head *transmitted_queue,
63                                    struct sctp_transport *transport,
64                                    struct sctp_sackhdr *sack,
65                                    __u32 highest_new_tsn);
66
67 static void sctp_mark_missing(struct sctp_outq *q,
68                               struct list_head *transmitted_queue,
69                               struct sctp_transport *transport,
70                               __u32 highest_new_tsn,
71                               int count_of_newacks);
72
73 static void sctp_generate_fwdtsn(struct sctp_outq *q, __u32 sack_ctsn);
74
75 static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout);
76
77 /* Add data to the front of the queue. */
78 static inline void sctp_outq_head_data(struct sctp_outq *q,
79                                         struct sctp_chunk *ch)
80 {
81         list_add(&ch->list, &q->out_chunk_list);
82         q->out_qlen += ch->skb->len;
83         return;
84 }
85
86 /* Take data from the front of the queue. */
87 static inline struct sctp_chunk *sctp_outq_dequeue_data(struct sctp_outq *q)
88 {
89         struct sctp_chunk *ch = NULL;
90
91         if (!list_empty(&q->out_chunk_list)) {
92                 struct list_head *entry = q->out_chunk_list.next;
93
94                 ch = list_entry(entry, struct sctp_chunk, list);
95                 list_del_init(entry);
96                 q->out_qlen -= ch->skb->len;
97         }
98         return ch;
99 }
100 /* Add data chunk to the end of the queue. */
101 static inline void sctp_outq_tail_data(struct sctp_outq *q,
102                                        struct sctp_chunk *ch)
103 {
104         list_add_tail(&ch->list, &q->out_chunk_list);
105         q->out_qlen += ch->skb->len;
106         return;
107 }
108
109 /*
110  * SFR-CACC algorithm:
111  * D) If count_of_newacks is greater than or equal to 2
112  * and t was not sent to the current primary then the
113  * sender MUST NOT increment missing report count for t.
114  */
115 static inline int sctp_cacc_skip_3_1_d(struct sctp_transport *primary,
116                                        struct sctp_transport *transport,
117                                        int count_of_newacks)
118 {
119         if (count_of_newacks >=2 && transport != primary)
120                 return 1;
121         return 0;
122 }
123
124 /*
125  * SFR-CACC algorithm:
126  * F) If count_of_newacks is less than 2, let d be the
127  * destination to which t was sent. If cacc_saw_newack
128  * is 0 for destination d, then the sender MUST NOT
129  * increment missing report count for t.
130  */
131 static inline int sctp_cacc_skip_3_1_f(struct sctp_transport *transport,
132                                        int count_of_newacks)
133 {
134         if (count_of_newacks < 2 && !transport->cacc.cacc_saw_newack)
135                 return 1;
136         return 0;
137 }
138
139 /*
140  * SFR-CACC algorithm:
141  * 3.1) If CYCLING_CHANGEOVER is 0, the sender SHOULD
142  * execute steps C, D, F.
143  *
144  * C has been implemented in sctp_outq_sack
145  */
146 static inline int sctp_cacc_skip_3_1(struct sctp_transport *primary,
147                                      struct sctp_transport *transport,
148                                      int count_of_newacks)
149 {
150         if (!primary->cacc.cycling_changeover) {
151                 if (sctp_cacc_skip_3_1_d(primary, transport, count_of_newacks))
152                         return 1;
153                 if (sctp_cacc_skip_3_1_f(transport, count_of_newacks))
154                         return 1;
155                 return 0;
156         }
157         return 0;
158 }
159
160 /*
161  * SFR-CACC algorithm:
162  * 3.2) Else if CYCLING_CHANGEOVER is 1, and t is less
163  * than next_tsn_at_change of the current primary, then
164  * the sender MUST NOT increment missing report count
165  * for t.
166  */
167 static inline int sctp_cacc_skip_3_2(struct sctp_transport *primary, __u32 tsn)
168 {
169         if (primary->cacc.cycling_changeover &&
170             TSN_lt(tsn, primary->cacc.next_tsn_at_change))
171                 return 1;
172         return 0;
173 }
174
175 /*
176  * SFR-CACC algorithm:
177  * 3) If the missing report count for TSN t is to be
178  * incremented according to [RFC2960] and
179  * [SCTP_STEWART-2002], and CHANGEOVER_ACTIVE is set,
180  * then the sender MUST futher execute steps 3.1 and
181  * 3.2 to determine if the missing report count for
182  * TSN t SHOULD NOT be incremented.
183  *
184  * 3.3) If 3.1 and 3.2 do not dictate that the missing
185  * report count for t should not be incremented, then
186  * the sender SOULD increment missing report count for
187  * t (according to [RFC2960] and [SCTP_STEWART_2002]).
188  */
189 static inline int sctp_cacc_skip(struct sctp_transport *primary,
190                                  struct sctp_transport *transport,
191                                  int count_of_newacks,
192                                  __u32 tsn)
193 {
194         if (primary->cacc.changeover_active &&
195             (sctp_cacc_skip_3_1(primary, transport, count_of_newacks) ||
196              sctp_cacc_skip_3_2(primary, tsn)))
197                 return 1;
198         return 0;
199 }
200
201 /* Initialize an existing sctp_outq.  This does the boring stuff.
202  * You still need to define handlers if you really want to DO
203  * something with this structure...
204  */
205 void sctp_outq_init(struct sctp_association *asoc, struct sctp_outq *q)
206 {
207         q->asoc = asoc;
208         INIT_LIST_HEAD(&q->out_chunk_list);
209         INIT_LIST_HEAD(&q->control_chunk_list);
210         INIT_LIST_HEAD(&q->retransmit);
211         INIT_LIST_HEAD(&q->sacked);
212         INIT_LIST_HEAD(&q->abandoned);
213
214         q->fast_rtx = 0;
215         q->outstanding_bytes = 0;
216         q->empty = 1;
217         q->cork  = 0;
218
219         q->malloced = 0;
220         q->out_qlen = 0;
221 }
222
223 /* Free the outqueue structure and any related pending chunks.
224  */
225 void sctp_outq_teardown(struct sctp_outq *q)
226 {
227         struct sctp_transport *transport;
228         struct list_head *lchunk, *temp;
229         struct sctp_chunk *chunk, *tmp;
230
231         /* Throw away unacknowledged chunks. */
232         list_for_each_entry(transport, &q->asoc->peer.transport_addr_list,
233                         transports) {
234                 while ((lchunk = sctp_list_dequeue(&transport->transmitted)) != NULL) {
235                         chunk = list_entry(lchunk, struct sctp_chunk,
236                                            transmitted_list);
237                         /* Mark as part of a failed message. */
238                         sctp_chunk_fail(chunk, q->error);
239                         sctp_chunk_free(chunk);
240                 }
241         }
242
243         /* Throw away chunks that have been gap ACKed.  */
244         list_for_each_safe(lchunk, temp, &q->sacked) {
245                 list_del_init(lchunk);
246                 chunk = list_entry(lchunk, struct sctp_chunk,
247                                    transmitted_list);
248                 sctp_chunk_fail(chunk, q->error);
249                 sctp_chunk_free(chunk);
250         }
251
252         /* Throw away any chunks in the retransmit queue. */
253         list_for_each_safe(lchunk, temp, &q->retransmit) {
254                 list_del_init(lchunk);
255                 chunk = list_entry(lchunk, struct sctp_chunk,
256                                    transmitted_list);
257                 sctp_chunk_fail(chunk, q->error);
258                 sctp_chunk_free(chunk);
259         }
260
261         /* Throw away any chunks that are in the abandoned queue. */
262         list_for_each_safe(lchunk, temp, &q->abandoned) {
263                 list_del_init(lchunk);
264                 chunk = list_entry(lchunk, struct sctp_chunk,
265                                    transmitted_list);
266                 sctp_chunk_fail(chunk, q->error);
267                 sctp_chunk_free(chunk);
268         }
269
270         /* Throw away any leftover data chunks. */
271         while ((chunk = sctp_outq_dequeue_data(q)) != NULL) {
272
273                 /* Mark as send failure. */
274                 sctp_chunk_fail(chunk, q->error);
275                 sctp_chunk_free(chunk);
276         }
277
278         q->error = 0;
279
280         /* Throw away any leftover control chunks. */
281         list_for_each_entry_safe(chunk, tmp, &q->control_chunk_list, list) {
282                 list_del_init(&chunk->list);
283                 sctp_chunk_free(chunk);
284         }
285 }
286
287 /* Free the outqueue structure and any related pending chunks.  */
288 void sctp_outq_free(struct sctp_outq *q)
289 {
290         /* Throw away leftover chunks. */
291         sctp_outq_teardown(q);
292
293         /* If we were kmalloc()'d, free the memory.  */
294         if (q->malloced)
295                 kfree(q);
296 }
297
298 /* Put a new chunk in an sctp_outq.  */
299 int sctp_outq_tail(struct sctp_outq *q, struct sctp_chunk *chunk)
300 {
301         int error = 0;
302
303         SCTP_DEBUG_PRINTK("sctp_outq_tail(%p, %p[%s])\n",
304                           q, chunk, chunk && chunk->chunk_hdr ?
305                           sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type))
306                           : "Illegal Chunk");
307
308         /* If it is data, queue it up, otherwise, send it
309          * immediately.
310          */
311         if (sctp_chunk_is_data(chunk)) {
312                 /* Is it OK to queue data chunks?  */
313                 /* From 9. Termination of Association
314                  *
315                  * When either endpoint performs a shutdown, the
316                  * association on each peer will stop accepting new
317                  * data from its user and only deliver data in queue
318                  * at the time of sending or receiving the SHUTDOWN
319                  * chunk.
320                  */
321                 switch (q->asoc->state) {
322                 case SCTP_STATE_EMPTY:
323                 case SCTP_STATE_CLOSED:
324                 case SCTP_STATE_SHUTDOWN_PENDING:
325                 case SCTP_STATE_SHUTDOWN_SENT:
326                 case SCTP_STATE_SHUTDOWN_RECEIVED:
327                 case SCTP_STATE_SHUTDOWN_ACK_SENT:
328                         /* Cannot send after transport endpoint shutdown */
329                         error = -ESHUTDOWN;
330                         break;
331
332                 default:
333                         SCTP_DEBUG_PRINTK("outqueueing (%p, %p[%s])\n",
334                           q, chunk, chunk && chunk->chunk_hdr ?
335                           sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type))
336                           : "Illegal Chunk");
337
338                         sctp_outq_tail_data(q, chunk);
339                         if (chunk->chunk_hdr->flags & SCTP_DATA_UNORDERED)
340                                 SCTP_INC_STATS(SCTP_MIB_OUTUNORDERCHUNKS);
341                         else
342                                 SCTP_INC_STATS(SCTP_MIB_OUTORDERCHUNKS);
343                         q->empty = 0;
344                         break;
345                 }
346         } else {
347                 list_add_tail(&chunk->list, &q->control_chunk_list);
348                 SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
349         }
350
351         if (error < 0)
352                 return error;
353
354         if (!q->cork)
355                 error = sctp_outq_flush(q, 0);
356
357         return error;
358 }
359
360 /* Insert a chunk into the sorted list based on the TSNs.  The retransmit list
361  * and the abandoned list are in ascending order.
362  */
363 static void sctp_insert_list(struct list_head *head, struct list_head *new)
364 {
365         struct list_head *pos;
366         struct sctp_chunk *nchunk, *lchunk;
367         __u32 ntsn, ltsn;
368         int done = 0;
369
370         nchunk = list_entry(new, struct sctp_chunk, transmitted_list);
371         ntsn = ntohl(nchunk->subh.data_hdr->tsn);
372
373         list_for_each(pos, head) {
374                 lchunk = list_entry(pos, struct sctp_chunk, transmitted_list);
375                 ltsn = ntohl(lchunk->subh.data_hdr->tsn);
376                 if (TSN_lt(ntsn, ltsn)) {
377                         list_add(new, pos->prev);
378                         done = 1;
379                         break;
380                 }
381         }
382         if (!done)
383                 list_add_tail(new, head);
384 }
385
386 /* Mark all the eligible packets on a transport for retransmission.  */
387 void sctp_retransmit_mark(struct sctp_outq *q,
388                           struct sctp_transport *transport,
389                           __u8 reason)
390 {
391         struct list_head *lchunk, *ltemp;
392         struct sctp_chunk *chunk;
393
394         /* Walk through the specified transmitted queue.  */
395         list_for_each_safe(lchunk, ltemp, &transport->transmitted) {
396                 chunk = list_entry(lchunk, struct sctp_chunk,
397                                    transmitted_list);
398
399                 /* If the chunk is abandoned, move it to abandoned list. */
400                 if (sctp_chunk_abandoned(chunk)) {
401                         list_del_init(lchunk);
402                         sctp_insert_list(&q->abandoned, lchunk);
403
404                         /* If this chunk has not been previousely acked,
405                          * stop considering it 'outstanding'.  Our peer
406                          * will most likely never see it since it will
407                          * not be retransmitted
408                          */
409                         if (!chunk->tsn_gap_acked) {
410                                 if (chunk->transport)
411                                         chunk->transport->flight_size -=
412                                                         sctp_data_size(chunk);
413                                 q->outstanding_bytes -= sctp_data_size(chunk);
414                                 q->asoc->peer.rwnd += (sctp_data_size(chunk) +
415                                                         sizeof(struct sk_buff));
416                         }
417                         continue;
418                 }
419
420                 /* If we are doing  retransmission due to a timeout or pmtu
421                  * discovery, only the  chunks that are not yet acked should
422                  * be added to the retransmit queue.
423                  */
424                 if ((reason == SCTP_RTXR_FAST_RTX  &&
425                             (chunk->fast_retransmit == SCTP_NEED_FRTX)) ||
426                     (reason != SCTP_RTXR_FAST_RTX  && !chunk->tsn_gap_acked)) {
427                         /* RFC 2960 6.2.1 Processing a Received SACK
428                          *
429                          * C) Any time a DATA chunk is marked for
430                          * retransmission (via either T3-rtx timer expiration
431                          * (Section 6.3.3) or via fast retransmit
432                          * (Section 7.2.4)), add the data size of those
433                          * chunks to the rwnd.
434                          */
435                         q->asoc->peer.rwnd += (sctp_data_size(chunk) +
436                                                 sizeof(struct sk_buff));
437                         q->outstanding_bytes -= sctp_data_size(chunk);
438                         if (chunk->transport)
439                                 transport->flight_size -= sctp_data_size(chunk);
440
441                         /* sctpimpguide-05 Section 2.8.2
442                          * M5) If a T3-rtx timer expires, the
443                          * 'TSN.Missing.Report' of all affected TSNs is set
444                          * to 0.
445                          */
446                         chunk->tsn_missing_report = 0;
447
448                         /* If a chunk that is being used for RTT measurement
449                          * has to be retransmitted, we cannot use this chunk
450                          * anymore for RTT measurements. Reset rto_pending so
451                          * that a new RTT measurement is started when a new
452                          * data chunk is sent.
453                          */
454                         if (chunk->rtt_in_progress) {
455                                 chunk->rtt_in_progress = 0;
456                                 transport->rto_pending = 0;
457                         }
458
459                         /* Move the chunk to the retransmit queue. The chunks
460                          * on the retransmit queue are always kept in order.
461                          */
462                         list_del_init(lchunk);
463                         sctp_insert_list(&q->retransmit, lchunk);
464                 }
465         }
466
467         SCTP_DEBUG_PRINTK("%s: transport: %p, reason: %d, "
468                           "cwnd: %d, ssthresh: %d, flight_size: %d, "
469                           "pba: %d\n", __func__,
470                           transport, reason,
471                           transport->cwnd, transport->ssthresh,
472                           transport->flight_size,
473                           transport->partial_bytes_acked);
474
475 }
476
477 /* Mark all the eligible packets on a transport for retransmission and force
478  * one packet out.
479  */
480 void sctp_retransmit(struct sctp_outq *q, struct sctp_transport *transport,
481                      sctp_retransmit_reason_t reason)
482 {
483         int error = 0;
484
485         switch(reason) {
486         case SCTP_RTXR_T3_RTX:
487                 SCTP_INC_STATS(SCTP_MIB_T3_RETRANSMITS);
488                 sctp_transport_lower_cwnd(transport, SCTP_LOWER_CWND_T3_RTX);
489                 /* Update the retran path if the T3-rtx timer has expired for
490                  * the current retran path.
491                  */
492                 if (transport == transport->asoc->peer.retran_path)
493                         sctp_assoc_update_retran_path(transport->asoc);
494                 transport->asoc->rtx_data_chunks +=
495                         transport->asoc->unack_data;
496                 break;
497         case SCTP_RTXR_FAST_RTX:
498                 SCTP_INC_STATS(SCTP_MIB_FAST_RETRANSMITS);
499                 sctp_transport_lower_cwnd(transport, SCTP_LOWER_CWND_FAST_RTX);
500                 q->fast_rtx = 1;
501                 break;
502         case SCTP_RTXR_PMTUD:
503                 SCTP_INC_STATS(SCTP_MIB_PMTUD_RETRANSMITS);
504                 break;
505         case SCTP_RTXR_T1_RTX:
506                 SCTP_INC_STATS(SCTP_MIB_T1_RETRANSMITS);
507                 transport->asoc->init_retries++;
508                 break;
509         default:
510                 BUG();
511         }
512
513         sctp_retransmit_mark(q, transport, reason);
514
515         /* PR-SCTP A5) Any time the T3-rtx timer expires, on any destination,
516          * the sender SHOULD try to advance the "Advanced.Peer.Ack.Point" by
517          * following the procedures outlined in C1 - C5.
518          */
519         if (reason == SCTP_RTXR_T3_RTX)
520                 sctp_generate_fwdtsn(q, q->asoc->ctsn_ack_point);
521
522         /* Flush the queues only on timeout, since fast_rtx is only
523          * triggered during sack processing and the queue
524          * will be flushed at the end.
525          */
526         if (reason != SCTP_RTXR_FAST_RTX)
527                 error = sctp_outq_flush(q, /* rtx_timeout */ 1);
528
529         if (error)
530                 q->asoc->base.sk->sk_err = -error;
531 }
532
533 /*
534  * Transmit DATA chunks on the retransmit queue.  Upon return from
535  * sctp_outq_flush_rtx() the packet 'pkt' may contain chunks which
536  * need to be transmitted by the caller.
537  * We assume that pkt->transport has already been set.
538  *
539  * The return value is a normal kernel error return value.
540  */
541 static int sctp_outq_flush_rtx(struct sctp_outq *q, struct sctp_packet *pkt,
542                                int rtx_timeout, int *start_timer)
543 {
544         struct list_head *lqueue;
545         struct sctp_transport *transport = pkt->transport;
546         sctp_xmit_t status;
547         struct sctp_chunk *chunk, *chunk1;
548         struct sctp_association *asoc;
549         int fast_rtx;
550         int error = 0;
551         int timer = 0;
552         int done = 0;
553
554         asoc = q->asoc;
555         lqueue = &q->retransmit;
556         fast_rtx = q->fast_rtx;
557
558         /* This loop handles time-out retransmissions, fast retransmissions,
559          * and retransmissions due to opening of whindow.
560          *
561          * RFC 2960 6.3.3 Handle T3-rtx Expiration
562          *
563          * E3) Determine how many of the earliest (i.e., lowest TSN)
564          * outstanding DATA chunks for the address for which the
565          * T3-rtx has expired will fit into a single packet, subject
566          * to the MTU constraint for the path corresponding to the
567          * destination transport address to which the retransmission
568          * is being sent (this may be different from the address for
569          * which the timer expires [see Section 6.4]). Call this value
570          * K. Bundle and retransmit those K DATA chunks in a single
571          * packet to the destination endpoint.
572          *
573          * [Just to be painfully clear, if we are retransmitting
574          * because a timeout just happened, we should send only ONE
575          * packet of retransmitted data.]
576          *
577          * For fast retransmissions we also send only ONE packet.  However,
578          * if we are just flushing the queue due to open window, we'll
579          * try to send as much as possible.
580          */
581         list_for_each_entry_safe(chunk, chunk1, lqueue, transmitted_list) {
582
583                 /* Make sure that Gap Acked TSNs are not retransmitted.  A
584                  * simple approach is just to move such TSNs out of the
585                  * way and into a 'transmitted' queue and skip to the
586                  * next chunk.
587                  */
588                 if (chunk->tsn_gap_acked) {
589                         list_del(&chunk->transmitted_list);
590                         list_add_tail(&chunk->transmitted_list,
591                                         &transport->transmitted);
592                         continue;
593                 }
594
595                 /* If we are doing fast retransmit, ignore non-fast_rtransmit
596                  * chunks
597                  */
598                 if (fast_rtx && !chunk->fast_retransmit)
599                         continue;
600
601 redo:
602                 /* Attempt to append this chunk to the packet. */
603                 status = sctp_packet_append_chunk(pkt, chunk);
604
605                 switch (status) {
606                 case SCTP_XMIT_PMTU_FULL:
607                         if (!pkt->has_data && !pkt->has_cookie_echo) {
608                                 /* If this packet did not contain DATA then
609                                  * retransmission did not happen, so do it
610                                  * again.  We'll ignore the error here since
611                                  * control chunks are already freed so there
612                                  * is nothing we can do.
613                                  */
614                                 sctp_packet_transmit(pkt);
615                                 goto redo;
616                         }
617
618                         /* Send this packet.  */
619                         error = sctp_packet_transmit(pkt);
620
621                         /* If we are retransmitting, we should only
622                          * send a single packet.
623                          */
624                         if (rtx_timeout || fast_rtx)
625                                 done = 1;
626
627                         /* Bundle next chunk in the next round.  */
628                         break;
629
630                 case SCTP_XMIT_RWND_FULL:
631                         /* Send this packet. */
632                         error = sctp_packet_transmit(pkt);
633
634                         /* Stop sending DATA as there is no more room
635                          * at the receiver.
636                          */
637                         done = 1;
638                         break;
639
640                 case SCTP_XMIT_NAGLE_DELAY:
641                         /* Send this packet. */
642                         error = sctp_packet_transmit(pkt);
643
644                         /* Stop sending DATA because of nagle delay. */
645                         done = 1;
646                         break;
647
648                 default:
649                         /* The append was successful, so add this chunk to
650                          * the transmitted list.
651                          */
652                         list_del(&chunk->transmitted_list);
653                         list_add_tail(&chunk->transmitted_list,
654                                         &transport->transmitted);
655
656                         /* Mark the chunk as ineligible for fast retransmit
657                          * after it is retransmitted.
658                          */
659                         if (chunk->fast_retransmit == SCTP_NEED_FRTX)
660                                 chunk->fast_retransmit = SCTP_DONT_FRTX;
661
662                         q->empty = 0;
663                         break;
664                 }
665
666                 /* Set the timer if there were no errors */
667                 if (!error && !timer)
668                         timer = 1;
669
670                 if (done)
671                         break;
672         }
673
674         /* If we are here due to a retransmit timeout or a fast
675          * retransmit and if there are any chunks left in the retransmit
676          * queue that could not fit in the PMTU sized packet, they need
677          * to be marked as ineligible for a subsequent fast retransmit.
678          */
679         if (rtx_timeout || fast_rtx) {
680                 list_for_each_entry(chunk1, lqueue, transmitted_list) {
681                         if (chunk1->fast_retransmit == SCTP_NEED_FRTX)
682                                 chunk1->fast_retransmit = SCTP_DONT_FRTX;
683                 }
684         }
685
686         *start_timer = timer;
687
688         /* Clear fast retransmit hint */
689         if (fast_rtx)
690                 q->fast_rtx = 0;
691
692         return error;
693 }
694
695 /* Cork the outqueue so queued chunks are really queued. */
696 int sctp_outq_uncork(struct sctp_outq *q)
697 {
698         int error = 0;
699         if (q->cork)
700                 q->cork = 0;
701         error = sctp_outq_flush(q, 0);
702         return error;
703 }
704
705
706 /*
707  * Try to flush an outqueue.
708  *
709  * Description: Send everything in q which we legally can, subject to
710  * congestion limitations.
711  * * Note: This function can be called from multiple contexts so appropriate
712  * locking concerns must be made.  Today we use the sock lock to protect
713  * this function.
714  */
715 static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout)
716 {
717         struct sctp_packet *packet;
718         struct sctp_packet singleton;
719         struct sctp_association *asoc = q->asoc;
720         __u16 sport = asoc->base.bind_addr.port;
721         __u16 dport = asoc->peer.port;
722         __u32 vtag = asoc->peer.i.init_tag;
723         struct sctp_transport *transport = NULL;
724         struct sctp_transport *new_transport;
725         struct sctp_chunk *chunk, *tmp;
726         sctp_xmit_t status;
727         int error = 0;
728         int start_timer = 0;
729         int one_packet = 0;
730
731         /* These transports have chunks to send. */
732         struct list_head transport_list;
733         struct list_head *ltransport;
734
735         INIT_LIST_HEAD(&transport_list);
736         packet = NULL;
737
738         /*
739          * 6.10 Bundling
740          *   ...
741          *   When bundling control chunks with DATA chunks, an
742          *   endpoint MUST place control chunks first in the outbound
743          *   SCTP packet.  The transmitter MUST transmit DATA chunks
744          *   within a SCTP packet in increasing order of TSN.
745          *   ...
746          */
747
748         list_for_each_entry_safe(chunk, tmp, &q->control_chunk_list, list) {
749                 list_del_init(&chunk->list);
750
751                 /* Pick the right transport to use. */
752                 new_transport = chunk->transport;
753
754                 if (!new_transport) {
755                         /*
756                          * If we have a prior transport pointer, see if
757                          * the destination address of the chunk
758                          * matches the destination address of the
759                          * current transport.  If not a match, then
760                          * try to look up the transport with a given
761                          * destination address.  We do this because
762                          * after processing ASCONFs, we may have new
763                          * transports created.
764                          */
765                         if (transport &&
766                             sctp_cmp_addr_exact(&chunk->dest,
767                                                 &transport->ipaddr))
768                                         new_transport = transport;
769                         else
770                                 new_transport = sctp_assoc_lookup_paddr(asoc,
771                                                                 &chunk->dest);
772
773                         /* if we still don't have a new transport, then
774                          * use the current active path.
775                          */
776                         if (!new_transport)
777                                 new_transport = asoc->peer.active_path;
778                 } else if ((new_transport->state == SCTP_INACTIVE) ||
779                            (new_transport->state == SCTP_UNCONFIRMED)) {
780                         /* If the chunk is Heartbeat or Heartbeat Ack,
781                          * send it to chunk->transport, even if it's
782                          * inactive.
783                          *
784                          * 3.3.6 Heartbeat Acknowledgement:
785                          * ...
786                          * A HEARTBEAT ACK is always sent to the source IP
787                          * address of the IP datagram containing the
788                          * HEARTBEAT chunk to which this ack is responding.
789                          * ...
790                          *
791                          * ASCONF_ACKs also must be sent to the source.
792                          */
793                         if (chunk->chunk_hdr->type != SCTP_CID_HEARTBEAT &&
794                             chunk->chunk_hdr->type != SCTP_CID_HEARTBEAT_ACK &&
795                             chunk->chunk_hdr->type != SCTP_CID_ASCONF_ACK)
796                                 new_transport = asoc->peer.active_path;
797                 }
798
799                 /* Are we switching transports?
800                  * Take care of transport locks.
801                  */
802                 if (new_transport != transport) {
803                         transport = new_transport;
804                         if (list_empty(&transport->send_ready)) {
805                                 list_add_tail(&transport->send_ready,
806                                               &transport_list);
807                         }
808                         packet = &transport->packet;
809                         sctp_packet_config(packet, vtag,
810                                            asoc->peer.ecn_capable);
811                 }
812
813                 switch (chunk->chunk_hdr->type) {
814                 /*
815                  * 6.10 Bundling
816                  *   ...
817                  *   An endpoint MUST NOT bundle INIT, INIT ACK or SHUTDOWN
818                  *   COMPLETE with any other chunks.  [Send them immediately.]
819                  */
820                 case SCTP_CID_INIT:
821                 case SCTP_CID_INIT_ACK:
822                 case SCTP_CID_SHUTDOWN_COMPLETE:
823                         sctp_packet_init(&singleton, transport, sport, dport);
824                         sctp_packet_config(&singleton, vtag, 0);
825                         sctp_packet_append_chunk(&singleton, chunk);
826                         error = sctp_packet_transmit(&singleton);
827                         if (error < 0)
828                                 return error;
829                         break;
830
831                 case SCTP_CID_ABORT:
832                         if (sctp_test_T_bit(chunk)) {
833                                 packet->vtag = asoc->c.my_vtag;
834                         }
835                 /* The following chunks are "response" chunks, i.e.
836                  * they are generated in response to something we
837                  * received.  If we are sending these, then we can
838                  * send only 1 packet containing these chunks.
839                  */
840                 case SCTP_CID_HEARTBEAT_ACK:
841                 case SCTP_CID_SHUTDOWN_ACK:
842                 case SCTP_CID_COOKIE_ACK:
843                 case SCTP_CID_COOKIE_ECHO:
844                 case SCTP_CID_ERROR:
845                 case SCTP_CID_ECN_CWR:
846                 case SCTP_CID_ASCONF_ACK:
847                         one_packet = 1;
848                         /* Fall throught */
849
850                 case SCTP_CID_SACK:
851                 case SCTP_CID_HEARTBEAT:
852                 case SCTP_CID_SHUTDOWN:
853                 case SCTP_CID_ECN_ECNE:
854                 case SCTP_CID_ASCONF:
855                 case SCTP_CID_FWD_TSN:
856                         status = sctp_packet_transmit_chunk(packet, chunk,
857                                                             one_packet);
858                         if (status  != SCTP_XMIT_OK) {
859                                 /* put the chunk back */
860                                 list_add(&chunk->list, &q->control_chunk_list);
861                         } else if (chunk->chunk_hdr->type == SCTP_CID_FWD_TSN) {
862                                 /* PR-SCTP C5) If a FORWARD TSN is sent, the
863                                  * sender MUST assure that at least one T3-rtx
864                                  * timer is running.
865                                  */
866                                 sctp_transport_reset_timers(transport);
867                         }
868                         break;
869
870                 default:
871                         /* We built a chunk with an illegal type! */
872                         BUG();
873                 }
874         }
875
876         /* Is it OK to send data chunks?  */
877         switch (asoc->state) {
878         case SCTP_STATE_COOKIE_ECHOED:
879                 /* Only allow bundling when this packet has a COOKIE-ECHO
880                  * chunk.
881                  */
882                 if (!packet || !packet->has_cookie_echo)
883                         break;
884
885                 /* fallthru */
886         case SCTP_STATE_ESTABLISHED:
887         case SCTP_STATE_SHUTDOWN_PENDING:
888         case SCTP_STATE_SHUTDOWN_RECEIVED:
889                 /*
890                  * RFC 2960 6.1  Transmission of DATA Chunks
891                  *
892                  * C) When the time comes for the sender to transmit,
893                  * before sending new DATA chunks, the sender MUST
894                  * first transmit any outstanding DATA chunks which
895                  * are marked for retransmission (limited by the
896                  * current cwnd).
897                  */
898                 if (!list_empty(&q->retransmit)) {
899                         if (transport == asoc->peer.retran_path)
900                                 goto retran;
901
902                         /* Switch transports & prepare the packet.  */
903
904                         transport = asoc->peer.retran_path;
905
906                         if (list_empty(&transport->send_ready)) {
907                                 list_add_tail(&transport->send_ready,
908                                               &transport_list);
909                         }
910
911                         packet = &transport->packet;
912                         sctp_packet_config(packet, vtag,
913                                            asoc->peer.ecn_capable);
914                 retran:
915                         error = sctp_outq_flush_rtx(q, packet,
916                                                     rtx_timeout, &start_timer);
917
918                         if (start_timer)
919                                 sctp_transport_reset_timers(transport);
920
921                         /* This can happen on COOKIE-ECHO resend.  Only
922                          * one chunk can get bundled with a COOKIE-ECHO.
923                          */
924                         if (packet->has_cookie_echo)
925                                 goto sctp_flush_out;
926
927                         /* Don't send new data if there is still data
928                          * waiting to retransmit.
929                          */
930                         if (!list_empty(&q->retransmit))
931                                 goto sctp_flush_out;
932                 }
933
934                 /* Apply Max.Burst limitation to the current transport in
935                  * case it will be used for new data.  We are going to
936                  * rest it before we return, but we want to apply the limit
937                  * to the currently queued data.
938                  */
939                 if (transport)
940                         sctp_transport_burst_limited(transport);
941
942                 /* Finally, transmit new packets.  */
943                 while ((chunk = sctp_outq_dequeue_data(q)) != NULL) {
944                         /* RFC 2960 6.5 Every DATA chunk MUST carry a valid
945                          * stream identifier.
946                          */
947                         if (chunk->sinfo.sinfo_stream >=
948                             asoc->c.sinit_num_ostreams) {
949
950                                 /* Mark as failed send. */
951                                 sctp_chunk_fail(chunk, SCTP_ERROR_INV_STRM);
952                                 sctp_chunk_free(chunk);
953                                 continue;
954                         }
955
956                         /* Has this chunk expired? */
957                         if (sctp_chunk_abandoned(chunk)) {
958                                 sctp_chunk_fail(chunk, 0);
959                                 sctp_chunk_free(chunk);
960                                 continue;
961                         }
962
963                         /* If there is a specified transport, use it.
964                          * Otherwise, we want to use the active path.
965                          */
966                         new_transport = chunk->transport;
967                         if (!new_transport ||
968                             ((new_transport->state == SCTP_INACTIVE) ||
969                              (new_transport->state == SCTP_UNCONFIRMED)))
970                                 new_transport = asoc->peer.active_path;
971
972                         /* Change packets if necessary.  */
973                         if (new_transport != transport) {
974                                 transport = new_transport;
975
976                                 /* Schedule to have this transport's
977                                  * packet flushed.
978                                  */
979                                 if (list_empty(&transport->send_ready)) {
980                                         list_add_tail(&transport->send_ready,
981                                                       &transport_list);
982                                 }
983
984                                 packet = &transport->packet;
985                                 sctp_packet_config(packet, vtag,
986                                                    asoc->peer.ecn_capable);
987                                 /* We've switched transports, so apply the
988                                  * Burst limit to the new transport.
989                                  */
990                                 sctp_transport_burst_limited(transport);
991                         }
992
993                         SCTP_DEBUG_PRINTK("sctp_outq_flush(%p, %p[%s]), ",
994                                           q, chunk,
995                                           chunk && chunk->chunk_hdr ?
996                                           sctp_cname(SCTP_ST_CHUNK(
997                                                   chunk->chunk_hdr->type))
998                                           : "Illegal Chunk");
999
1000                         SCTP_DEBUG_PRINTK("TX TSN 0x%x skb->head "
1001                                         "%p skb->users %d.\n",
1002                                         ntohl(chunk->subh.data_hdr->tsn),
1003                                         chunk->skb ?chunk->skb->head : NULL,
1004                                         chunk->skb ?
1005                                         atomic_read(&chunk->skb->users) : -1);
1006
1007                         /* Add the chunk to the packet.  */
1008                         status = sctp_packet_transmit_chunk(packet, chunk, 0);
1009
1010                         switch (status) {
1011                         case SCTP_XMIT_PMTU_FULL:
1012                         case SCTP_XMIT_RWND_FULL:
1013                         case SCTP_XMIT_NAGLE_DELAY:
1014                                 /* We could not append this chunk, so put
1015                                  * the chunk back on the output queue.
1016                                  */
1017                                 SCTP_DEBUG_PRINTK("sctp_outq_flush: could "
1018                                         "not transmit TSN: 0x%x, status: %d\n",
1019                                         ntohl(chunk->subh.data_hdr->tsn),
1020                                         status);
1021                                 sctp_outq_head_data(q, chunk);
1022                                 goto sctp_flush_out;
1023                                 break;
1024
1025                         case SCTP_XMIT_OK:
1026                                 /* The sender is in the SHUTDOWN-PENDING state,
1027                                  * The sender MAY set the I-bit in the DATA
1028                                  * chunk header.
1029                                  */
1030                                 if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING)
1031                                         chunk->chunk_hdr->flags |= SCTP_DATA_SACK_IMM;
1032
1033                                 break;
1034
1035                         default:
1036                                 BUG();
1037                         }
1038
1039                         /* BUG: We assume that the sctp_packet_transmit()
1040                          * call below will succeed all the time and add the
1041                          * chunk to the transmitted list and restart the
1042                          * timers.
1043                          * It is possible that the call can fail under OOM
1044                          * conditions.
1045                          *
1046                          * Is this really a problem?  Won't this behave
1047                          * like a lost TSN?
1048                          */
1049                         list_add_tail(&chunk->transmitted_list,
1050                                       &transport->transmitted);
1051
1052                         sctp_transport_reset_timers(transport);
1053
1054                         q->empty = 0;
1055
1056                         /* Only let one DATA chunk get bundled with a
1057                          * COOKIE-ECHO chunk.
1058                          */
1059                         if (packet->has_cookie_echo)
1060                                 goto sctp_flush_out;
1061                 }
1062                 break;
1063
1064         default:
1065                 /* Do nothing.  */
1066                 break;
1067         }
1068
1069 sctp_flush_out:
1070
1071         /* Before returning, examine all the transports touched in
1072          * this call.  Right now, we bluntly force clear all the
1073          * transports.  Things might change after we implement Nagle.
1074          * But such an examination is still required.
1075          *
1076          * --xguo
1077          */
1078         while ((ltransport = sctp_list_dequeue(&transport_list)) != NULL ) {
1079                 struct sctp_transport *t = list_entry(ltransport,
1080                                                       struct sctp_transport,
1081                                                       send_ready);
1082                 packet = &t->packet;
1083                 if (!sctp_packet_empty(packet))
1084                         error = sctp_packet_transmit(packet);
1085
1086                 /* Clear the burst limited state, if any */
1087                 sctp_transport_burst_reset(t);
1088         }
1089
1090         return error;
1091 }
1092
1093 /* Update unack_data based on the incoming SACK chunk */
1094 static void sctp_sack_update_unack_data(struct sctp_association *assoc,
1095                                         struct sctp_sackhdr *sack)
1096 {
1097         sctp_sack_variable_t *frags;
1098         __u16 unack_data;
1099         int i;
1100
1101         unack_data = assoc->next_tsn - assoc->ctsn_ack_point - 1;
1102
1103         frags = sack->variable;
1104         for (i = 0; i < ntohs(sack->num_gap_ack_blocks); i++) {
1105                 unack_data -= ((ntohs(frags[i].gab.end) -
1106                                 ntohs(frags[i].gab.start) + 1));
1107         }
1108
1109         assoc->unack_data = unack_data;
1110 }
1111
1112 /* Return the highest new tsn that is acknowledged by the given SACK chunk. */
1113 static __u32 sctp_highest_new_tsn(struct sctp_sackhdr *sack,
1114                                   struct sctp_association *asoc)
1115 {
1116         struct sctp_transport *transport;
1117         struct sctp_chunk *chunk;
1118         __u32 highest_new_tsn, tsn;
1119         struct list_head *transport_list = &asoc->peer.transport_addr_list;
1120
1121         highest_new_tsn = ntohl(sack->cum_tsn_ack);
1122
1123         list_for_each_entry(transport, transport_list, transports) {
1124                 list_for_each_entry(chunk, &transport->transmitted,
1125                                 transmitted_list) {
1126                         tsn = ntohl(chunk->subh.data_hdr->tsn);
1127
1128                         if (!chunk->tsn_gap_acked &&
1129                             TSN_lt(highest_new_tsn, tsn) &&
1130                             sctp_acked(sack, tsn))
1131                                 highest_new_tsn = tsn;
1132                 }
1133         }
1134
1135         return highest_new_tsn;
1136 }
1137
1138 /* This is where we REALLY process a SACK.
1139  *
1140  * Process the SACK against the outqueue.  Mostly, this just frees
1141  * things off the transmitted queue.
1142  */
1143 int sctp_outq_sack(struct sctp_outq *q, struct sctp_sackhdr *sack)
1144 {
1145         struct sctp_association *asoc = q->asoc;
1146         struct sctp_transport *transport;
1147         struct sctp_chunk *tchunk = NULL;
1148         struct list_head *lchunk, *transport_list, *temp;
1149         sctp_sack_variable_t *frags = sack->variable;
1150         __u32 sack_ctsn, ctsn, tsn;
1151         __u32 highest_tsn, highest_new_tsn;
1152         __u32 sack_a_rwnd;
1153         unsigned outstanding;
1154         struct sctp_transport *primary = asoc->peer.primary_path;
1155         int count_of_newacks = 0;
1156         int gap_ack_blocks;
1157
1158         /* Grab the association's destination address list. */
1159         transport_list = &asoc->peer.transport_addr_list;
1160
1161         sack_ctsn = ntohl(sack->cum_tsn_ack);
1162         gap_ack_blocks = ntohs(sack->num_gap_ack_blocks);
1163         /*
1164          * SFR-CACC algorithm:
1165          * On receipt of a SACK the sender SHOULD execute the
1166          * following statements.
1167          *
1168          * 1) If the cumulative ack in the SACK passes next tsn_at_change
1169          * on the current primary, the CHANGEOVER_ACTIVE flag SHOULD be
1170          * cleared. The CYCLING_CHANGEOVER flag SHOULD also be cleared for
1171          * all destinations.
1172          * 2) If the SACK contains gap acks and the flag CHANGEOVER_ACTIVE
1173          * is set the receiver of the SACK MUST take the following actions:
1174          *
1175          * A) Initialize the cacc_saw_newack to 0 for all destination
1176          * addresses.
1177          *
1178          * Only bother if changeover_active is set. Otherwise, this is
1179          * totally suboptimal to do on every SACK.
1180          */
1181         if (primary->cacc.changeover_active) {
1182                 u8 clear_cycling = 0;
1183
1184                 if (TSN_lte(primary->cacc.next_tsn_at_change, sack_ctsn)) {
1185                         primary->cacc.changeover_active = 0;
1186                         clear_cycling = 1;
1187                 }
1188
1189                 if (clear_cycling || gap_ack_blocks) {
1190                         list_for_each_entry(transport, transport_list,
1191                                         transports) {
1192                                 if (clear_cycling)
1193                                         transport->cacc.cycling_changeover = 0;
1194                                 if (gap_ack_blocks)
1195                                         transport->cacc.cacc_saw_newack = 0;
1196                         }
1197                 }
1198         }
1199
1200         /* Get the highest TSN in the sack. */
1201         highest_tsn = sack_ctsn;
1202         if (gap_ack_blocks)
1203                 highest_tsn += ntohs(frags[gap_ack_blocks - 1].gab.end);
1204
1205         if (TSN_lt(asoc->highest_sacked, highest_tsn)) {
1206                 highest_new_tsn = highest_tsn;
1207                 asoc->highest_sacked = highest_tsn;
1208         } else {
1209                 highest_new_tsn = sctp_highest_new_tsn(sack, asoc);
1210         }
1211
1212
1213         /* Run through the retransmit queue.  Credit bytes received
1214          * and free those chunks that we can.
1215          */
1216         sctp_check_transmitted(q, &q->retransmit, NULL, sack, highest_new_tsn);
1217
1218         /* Run through the transmitted queue.
1219          * Credit bytes received and free those chunks which we can.
1220          *
1221          * This is a MASSIVE candidate for optimization.
1222          */
1223         list_for_each_entry(transport, transport_list, transports) {
1224                 sctp_check_transmitted(q, &transport->transmitted,
1225                                        transport, sack, highest_new_tsn);
1226                 /*
1227                  * SFR-CACC algorithm:
1228                  * C) Let count_of_newacks be the number of
1229                  * destinations for which cacc_saw_newack is set.
1230                  */
1231                 if (transport->cacc.cacc_saw_newack)
1232                         count_of_newacks ++;
1233         }
1234
1235         if (gap_ack_blocks) {
1236                 list_for_each_entry(transport, transport_list, transports)
1237                         sctp_mark_missing(q, &transport->transmitted, transport,
1238                                           highest_new_tsn, count_of_newacks);
1239         }
1240
1241         /* Move the Cumulative TSN Ack Point if appropriate.  */
1242         if (TSN_lt(asoc->ctsn_ack_point, sack_ctsn))
1243                 asoc->ctsn_ack_point = sack_ctsn;
1244
1245         /* Update unack_data field in the assoc. */
1246         sctp_sack_update_unack_data(asoc, sack);
1247
1248         ctsn = asoc->ctsn_ack_point;
1249
1250         /* Throw away stuff rotting on the sack queue.  */
1251         list_for_each_safe(lchunk, temp, &q->sacked) {
1252                 tchunk = list_entry(lchunk, struct sctp_chunk,
1253                                     transmitted_list);
1254                 tsn = ntohl(tchunk->subh.data_hdr->tsn);
1255                 if (TSN_lte(tsn, ctsn)) {
1256                         list_del_init(&tchunk->transmitted_list);
1257                         sctp_chunk_free(tchunk);
1258                 }
1259         }
1260
1261         /* ii) Set rwnd equal to the newly received a_rwnd minus the
1262          *     number of bytes still outstanding after processing the
1263          *     Cumulative TSN Ack and the Gap Ack Blocks.
1264          */
1265
1266         sack_a_rwnd = ntohl(sack->a_rwnd);
1267         outstanding = q->outstanding_bytes;
1268
1269         if (outstanding < sack_a_rwnd)
1270                 sack_a_rwnd -= outstanding;
1271         else
1272                 sack_a_rwnd = 0;
1273
1274         asoc->peer.rwnd = sack_a_rwnd;
1275
1276         sctp_generate_fwdtsn(q, sack_ctsn);
1277
1278         SCTP_DEBUG_PRINTK("%s: sack Cumulative TSN Ack is 0x%x.\n",
1279                           __func__, sack_ctsn);
1280         SCTP_DEBUG_PRINTK("%s: Cumulative TSN Ack of association, "
1281                           "%p is 0x%x. Adv peer ack point: 0x%x\n",
1282                           __func__, asoc, ctsn, asoc->adv_peer_ack_point);
1283
1284         /* See if all chunks are acked.
1285          * Make sure the empty queue handler will get run later.
1286          */
1287         q->empty = (list_empty(&q->out_chunk_list) &&
1288                     list_empty(&q->retransmit));
1289         if (!q->empty)
1290                 goto finish;
1291
1292         list_for_each_entry(transport, transport_list, transports) {
1293                 q->empty = q->empty && list_empty(&transport->transmitted);
1294                 if (!q->empty)
1295                         goto finish;
1296         }
1297
1298         SCTP_DEBUG_PRINTK("sack queue is empty.\n");
1299 finish:
1300         return q->empty;
1301 }
1302
1303 /* Is the outqueue empty?  */
1304 int sctp_outq_is_empty(const struct sctp_outq *q)
1305 {
1306         return q->empty;
1307 }
1308
1309 /********************************************************************
1310  * 2nd Level Abstractions
1311  ********************************************************************/
1312
1313 /* Go through a transport's transmitted list or the association's retransmit
1314  * list and move chunks that are acked by the Cumulative TSN Ack to q->sacked.
1315  * The retransmit list will not have an associated transport.
1316  *
1317  * I added coherent debug information output.   --xguo
1318  *
1319  * Instead of printing 'sacked' or 'kept' for each TSN on the
1320  * transmitted_queue, we print a range: SACKED: TSN1-TSN2, TSN3, TSN4-TSN5.
1321  * KEPT TSN6-TSN7, etc.
1322  */
1323 static void sctp_check_transmitted(struct sctp_outq *q,
1324                                    struct list_head *transmitted_queue,
1325                                    struct sctp_transport *transport,
1326                                    struct sctp_sackhdr *sack,
1327                                    __u32 highest_new_tsn_in_sack)
1328 {
1329         struct list_head *lchunk;
1330         struct sctp_chunk *tchunk;
1331         struct list_head tlist;
1332         __u32 tsn;
1333         __u32 sack_ctsn;
1334         __u32 rtt;
1335         __u8 restart_timer = 0;
1336         int bytes_acked = 0;
1337         int migrate_bytes = 0;
1338
1339         /* These state variables are for coherent debug output. --xguo */
1340
1341 #if SCTP_DEBUG
1342         __u32 dbg_ack_tsn = 0;  /* An ACKed TSN range starts here... */
1343         __u32 dbg_last_ack_tsn = 0;  /* ...and finishes here.        */
1344         __u32 dbg_kept_tsn = 0; /* An un-ACKed range starts here...  */
1345         __u32 dbg_last_kept_tsn = 0; /* ...and finishes here.        */
1346
1347         /* 0 : The last TSN was ACKed.
1348          * 1 : The last TSN was NOT ACKed (i.e. KEPT).
1349          * -1: We need to initialize.
1350          */
1351         int dbg_prt_state = -1;
1352 #endif /* SCTP_DEBUG */
1353
1354         sack_ctsn = ntohl(sack->cum_tsn_ack);
1355
1356         INIT_LIST_HEAD(&tlist);
1357
1358         /* The while loop will skip empty transmitted queues. */
1359         while (NULL != (lchunk = sctp_list_dequeue(transmitted_queue))) {
1360                 tchunk = list_entry(lchunk, struct sctp_chunk,
1361                                     transmitted_list);
1362
1363                 if (sctp_chunk_abandoned(tchunk)) {
1364                         /* Move the chunk to abandoned list. */
1365                         sctp_insert_list(&q->abandoned, lchunk);
1366
1367                         /* If this chunk has not been acked, stop
1368                          * considering it as 'outstanding'.
1369                          */
1370                         if (!tchunk->tsn_gap_acked) {
1371                                 if (tchunk->transport)
1372                                         tchunk->transport->flight_size -=
1373                                                         sctp_data_size(tchunk);
1374                                 q->outstanding_bytes -= sctp_data_size(tchunk);
1375                         }
1376                         continue;
1377                 }
1378
1379                 tsn = ntohl(tchunk->subh.data_hdr->tsn);
1380                 if (sctp_acked(sack, tsn)) {
1381                         /* If this queue is the retransmit queue, the
1382                          * retransmit timer has already reclaimed
1383                          * the outstanding bytes for this chunk, so only
1384                          * count bytes associated with a transport.
1385                          */
1386                         if (transport) {
1387                                 /* If this chunk is being used for RTT
1388                                  * measurement, calculate the RTT and update
1389                                  * the RTO using this value.
1390                                  *
1391                                  * 6.3.1 C5) Karn's algorithm: RTT measurements
1392                                  * MUST NOT be made using packets that were
1393                                  * retransmitted (and thus for which it is
1394                                  * ambiguous whether the reply was for the
1395                                  * first instance of the packet or a later
1396                                  * instance).
1397                                  */
1398                                 if (!tchunk->tsn_gap_acked &&
1399                                     tchunk->rtt_in_progress) {
1400                                         tchunk->rtt_in_progress = 0;
1401                                         rtt = jiffies - tchunk->sent_at;
1402                                         sctp_transport_update_rto(transport,
1403                                                                   rtt);
1404                                 }
1405                         }
1406
1407                         /* If the chunk hasn't been marked as ACKED,
1408                          * mark it and account bytes_acked if the
1409                          * chunk had a valid transport (it will not
1410                          * have a transport if ASCONF had deleted it
1411                          * while DATA was outstanding).
1412                          */
1413                         if (!tchunk->tsn_gap_acked) {
1414                                 tchunk->tsn_gap_acked = 1;
1415                                 bytes_acked += sctp_data_size(tchunk);
1416                                 if (!tchunk->transport)
1417                                         migrate_bytes += sctp_data_size(tchunk);
1418                         }
1419
1420                         if (TSN_lte(tsn, sack_ctsn)) {
1421                                 /* RFC 2960  6.3.2 Retransmission Timer Rules
1422                                  *
1423                                  * R3) Whenever a SACK is received
1424                                  * that acknowledges the DATA chunk
1425                                  * with the earliest outstanding TSN
1426                                  * for that address, restart T3-rtx
1427                                  * timer for that address with its
1428                                  * current RTO.
1429                                  */
1430                                 restart_timer = 1;
1431
1432                                 if (!tchunk->tsn_gap_acked) {
1433                                         /*
1434                                          * SFR-CACC algorithm:
1435                                          * 2) If the SACK contains gap acks
1436                                          * and the flag CHANGEOVER_ACTIVE is
1437                                          * set the receiver of the SACK MUST
1438                                          * take the following action:
1439                                          *
1440                                          * B) For each TSN t being acked that
1441                                          * has not been acked in any SACK so
1442                                          * far, set cacc_saw_newack to 1 for
1443                                          * the destination that the TSN was
1444                                          * sent to.
1445                                          */
1446                                         if (transport &&
1447                                             sack->num_gap_ack_blocks &&
1448                                             q->asoc->peer.primary_path->cacc.
1449                                             changeover_active)
1450                                                 transport->cacc.cacc_saw_newack
1451                                                         = 1;
1452                                 }
1453
1454                                 list_add_tail(&tchunk->transmitted_list,
1455                                               &q->sacked);
1456                         } else {
1457                                 /* RFC2960 7.2.4, sctpimpguide-05 2.8.2
1458                                  * M2) Each time a SACK arrives reporting
1459                                  * 'Stray DATA chunk(s)' record the highest TSN
1460                                  * reported as newly acknowledged, call this
1461                                  * value 'HighestTSNinSack'. A newly
1462                                  * acknowledged DATA chunk is one not
1463                                  * previously acknowledged in a SACK.
1464                                  *
1465                                  * When the SCTP sender of data receives a SACK
1466                                  * chunk that acknowledges, for the first time,
1467                                  * the receipt of a DATA chunk, all the still
1468                                  * unacknowledged DATA chunks whose TSN is
1469                                  * older than that newly acknowledged DATA
1470                                  * chunk, are qualified as 'Stray DATA chunks'.
1471                                  */
1472                                 list_add_tail(lchunk, &tlist);
1473                         }
1474
1475 #if SCTP_DEBUG
1476                         switch (dbg_prt_state) {
1477                         case 0: /* last TSN was ACKed */
1478                                 if (dbg_last_ack_tsn + 1 == tsn) {
1479                                         /* This TSN belongs to the
1480                                          * current ACK range.
1481                                          */
1482                                         break;
1483                                 }
1484
1485                                 if (dbg_last_ack_tsn != dbg_ack_tsn) {
1486                                         /* Display the end of the
1487                                          * current range.
1488                                          */
1489                                         SCTP_DEBUG_PRINTK("-%08x",
1490                                                           dbg_last_ack_tsn);
1491                                 }
1492
1493                                 /* Start a new range.  */
1494                                 SCTP_DEBUG_PRINTK(",%08x", tsn);
1495                                 dbg_ack_tsn = tsn;
1496                                 break;
1497
1498                         case 1: /* The last TSN was NOT ACKed. */
1499                                 if (dbg_last_kept_tsn != dbg_kept_tsn) {
1500                                         /* Display the end of current range. */
1501                                         SCTP_DEBUG_PRINTK("-%08x",
1502                                                           dbg_last_kept_tsn);
1503                                 }
1504
1505                                 SCTP_DEBUG_PRINTK("\n");
1506
1507                                 /* FALL THROUGH... */
1508                         default:
1509                                 /* This is the first-ever TSN we examined.  */
1510                                 /* Start a new range of ACK-ed TSNs.  */
1511                                 SCTP_DEBUG_PRINTK("ACKed: %08x", tsn);
1512                                 dbg_prt_state = 0;
1513                                 dbg_ack_tsn = tsn;
1514                         }
1515
1516                         dbg_last_ack_tsn = tsn;
1517 #endif /* SCTP_DEBUG */
1518
1519                 } else {
1520                         if (tchunk->tsn_gap_acked) {
1521                                 SCTP_DEBUG_PRINTK("%s: Receiver reneged on "
1522                                                   "data TSN: 0x%x\n",
1523                                                   __func__,
1524                                                   tsn);
1525                                 tchunk->tsn_gap_acked = 0;
1526
1527                                 if (tchunk->transport)
1528                                         bytes_acked -= sctp_data_size(tchunk);
1529
1530                                 /* RFC 2960 6.3.2 Retransmission Timer Rules
1531                                  *
1532                                  * R4) Whenever a SACK is received missing a
1533                                  * TSN that was previously acknowledged via a
1534                                  * Gap Ack Block, start T3-rtx for the
1535                                  * destination address to which the DATA
1536                                  * chunk was originally
1537                                  * transmitted if it is not already running.
1538                                  */
1539                                 restart_timer = 1;
1540                         }
1541
1542                         list_add_tail(lchunk, &tlist);
1543
1544 #if SCTP_DEBUG
1545                         /* See the above comments on ACK-ed TSNs. */
1546                         switch (dbg_prt_state) {
1547                         case 1:
1548                                 if (dbg_last_kept_tsn + 1 == tsn)
1549                                         break;
1550
1551                                 if (dbg_last_kept_tsn != dbg_kept_tsn)
1552                                         SCTP_DEBUG_PRINTK("-%08x",
1553                                                           dbg_last_kept_tsn);
1554
1555                                 SCTP_DEBUG_PRINTK(",%08x", tsn);
1556                                 dbg_kept_tsn = tsn;
1557                                 break;
1558
1559                         case 0:
1560                                 if (dbg_last_ack_tsn != dbg_ack_tsn)
1561                                         SCTP_DEBUG_PRINTK("-%08x",
1562                                                           dbg_last_ack_tsn);
1563                                 SCTP_DEBUG_PRINTK("\n");
1564
1565                                 /* FALL THROUGH... */
1566                         default:
1567                                 SCTP_DEBUG_PRINTK("KEPT: %08x",tsn);
1568                                 dbg_prt_state = 1;
1569                                 dbg_kept_tsn = tsn;
1570                         }
1571
1572                         dbg_last_kept_tsn = tsn;
1573 #endif /* SCTP_DEBUG */
1574                 }
1575         }
1576
1577 #if SCTP_DEBUG
1578         /* Finish off the last range, displaying its ending TSN.  */
1579         switch (dbg_prt_state) {
1580         case 0:
1581                 if (dbg_last_ack_tsn != dbg_ack_tsn) {
1582                         SCTP_DEBUG_PRINTK("-%08x\n", dbg_last_ack_tsn);
1583                 } else {
1584                         SCTP_DEBUG_PRINTK("\n");
1585                 }
1586         break;
1587
1588         case 1:
1589                 if (dbg_last_kept_tsn != dbg_kept_tsn) {
1590                         SCTP_DEBUG_PRINTK("-%08x\n", dbg_last_kept_tsn);
1591                 } else {
1592                         SCTP_DEBUG_PRINTK("\n");
1593                 }
1594         }
1595 #endif /* SCTP_DEBUG */
1596         if (transport) {
1597                 if (bytes_acked) {
1598                         /* We may have counted DATA that was migrated
1599                          * to this transport due to DEL-IP operation.
1600                          * Subtract those bytes, since the were never
1601                          * send on this transport and shouldn't be
1602                          * credited to this transport.
1603                          */
1604                         bytes_acked -= migrate_bytes;
1605
1606                         /* 8.2. When an outstanding TSN is acknowledged,
1607                          * the endpoint shall clear the error counter of
1608                          * the destination transport address to which the
1609                          * DATA chunk was last sent.
1610                          * The association's overall error counter is
1611                          * also cleared.
1612                          */
1613                         transport->error_count = 0;
1614                         transport->asoc->overall_error_count = 0;
1615
1616                         /* Mark the destination transport address as
1617                          * active if it is not so marked.
1618                          */
1619                         if ((transport->state == SCTP_INACTIVE) ||
1620                             (transport->state == SCTP_UNCONFIRMED)) {
1621                                 sctp_assoc_control_transport(
1622                                         transport->asoc,
1623                                         transport,
1624                                         SCTP_TRANSPORT_UP,
1625                                         SCTP_RECEIVED_SACK);
1626                         }
1627
1628                         sctp_transport_raise_cwnd(transport, sack_ctsn,
1629                                                   bytes_acked);
1630
1631                         transport->flight_size -= bytes_acked;
1632                         if (transport->flight_size == 0)
1633                                 transport->partial_bytes_acked = 0;
1634                         q->outstanding_bytes -= bytes_acked + migrate_bytes;
1635                 } else {
1636                         /* RFC 2960 6.1, sctpimpguide-06 2.15.2
1637                          * When a sender is doing zero window probing, it
1638                          * should not timeout the association if it continues
1639                          * to receive new packets from the receiver. The
1640                          * reason is that the receiver MAY keep its window
1641                          * closed for an indefinite time.
1642                          * A sender is doing zero window probing when the
1643                          * receiver's advertised window is zero, and there is
1644                          * only one data chunk in flight to the receiver.
1645                          */
1646                         if (!q->asoc->peer.rwnd &&
1647                             !list_empty(&tlist) &&
1648                             (sack_ctsn+2 == q->asoc->next_tsn)) {
1649                                 SCTP_DEBUG_PRINTK("%s: SACK received for zero "
1650                                                   "window probe: %u\n",
1651                                                   __func__, sack_ctsn);
1652                                 q->asoc->overall_error_count = 0;
1653                                 transport->error_count = 0;
1654                         }
1655                 }
1656
1657                 /* RFC 2960 6.3.2 Retransmission Timer Rules
1658                  *
1659                  * R2) Whenever all outstanding data sent to an address have
1660                  * been acknowledged, turn off the T3-rtx timer of that
1661                  * address.
1662                  */
1663                 if (!transport->flight_size) {
1664                         if (timer_pending(&transport->T3_rtx_timer) &&
1665                             del_timer(&transport->T3_rtx_timer)) {
1666                                 sctp_transport_put(transport);
1667                         }
1668                 } else if (restart_timer) {
1669                         if (!mod_timer(&transport->T3_rtx_timer,
1670                                        jiffies + transport->rto))
1671                                 sctp_transport_hold(transport);
1672                 }
1673         }
1674
1675         list_splice(&tlist, transmitted_queue);
1676 }
1677
1678 /* Mark chunks as missing and consequently may get retransmitted. */
1679 static void sctp_mark_missing(struct sctp_outq *q,
1680                               struct list_head *transmitted_queue,
1681                               struct sctp_transport *transport,
1682                               __u32 highest_new_tsn_in_sack,
1683                               int count_of_newacks)
1684 {
1685         struct sctp_chunk *chunk;
1686         __u32 tsn;
1687         char do_fast_retransmit = 0;
1688         struct sctp_transport *primary = q->asoc->peer.primary_path;
1689
1690         list_for_each_entry(chunk, transmitted_queue, transmitted_list) {
1691
1692                 tsn = ntohl(chunk->subh.data_hdr->tsn);
1693
1694                 /* RFC 2960 7.2.4, sctpimpguide-05 2.8.2 M3) Examine all
1695                  * 'Unacknowledged TSN's', if the TSN number of an
1696                  * 'Unacknowledged TSN' is smaller than the 'HighestTSNinSack'
1697                  * value, increment the 'TSN.Missing.Report' count on that
1698                  * chunk if it has NOT been fast retransmitted or marked for
1699                  * fast retransmit already.
1700                  */
1701                 if (chunk->fast_retransmit == SCTP_CAN_FRTX &&
1702                     !chunk->tsn_gap_acked &&
1703                     TSN_lt(tsn, highest_new_tsn_in_sack)) {
1704
1705                         /* SFR-CACC may require us to skip marking
1706                          * this chunk as missing.
1707                          */
1708                         if (!transport || !sctp_cacc_skip(primary, transport,
1709                                             count_of_newacks, tsn)) {
1710                                 chunk->tsn_missing_report++;
1711
1712                                 SCTP_DEBUG_PRINTK(
1713                                         "%s: TSN 0x%x missing counter: %d\n",
1714                                         __func__, tsn,
1715                                         chunk->tsn_missing_report);
1716                         }
1717                 }
1718                 /*
1719                  * M4) If any DATA chunk is found to have a
1720                  * 'TSN.Missing.Report'
1721                  * value larger than or equal to 3, mark that chunk for
1722                  * retransmission and start the fast retransmit procedure.
1723                  */
1724
1725                 if (chunk->tsn_missing_report >= 3) {
1726                         chunk->fast_retransmit = SCTP_NEED_FRTX;
1727                         do_fast_retransmit = 1;
1728                 }
1729         }
1730
1731         if (transport) {
1732                 if (do_fast_retransmit)
1733                         sctp_retransmit(q, transport, SCTP_RTXR_FAST_RTX);
1734
1735                 SCTP_DEBUG_PRINTK("%s: transport: %p, cwnd: %d, "
1736                                   "ssthresh: %d, flight_size: %d, pba: %d\n",
1737                                   __func__, transport, transport->cwnd,
1738                                   transport->ssthresh, transport->flight_size,
1739                                   transport->partial_bytes_acked);
1740         }
1741 }
1742
1743 /* Is the given TSN acked by this packet?  */
1744 static int sctp_acked(struct sctp_sackhdr *sack, __u32 tsn)
1745 {
1746         int i;
1747         sctp_sack_variable_t *frags;
1748         __u16 gap;
1749         __u32 ctsn = ntohl(sack->cum_tsn_ack);
1750
1751         if (TSN_lte(tsn, ctsn))
1752                 goto pass;
1753
1754         /* 3.3.4 Selective Acknowledgement (SACK) (3):
1755          *
1756          * Gap Ack Blocks:
1757          *  These fields contain the Gap Ack Blocks. They are repeated
1758          *  for each Gap Ack Block up to the number of Gap Ack Blocks
1759          *  defined in the Number of Gap Ack Blocks field. All DATA
1760          *  chunks with TSNs greater than or equal to (Cumulative TSN
1761          *  Ack + Gap Ack Block Start) and less than or equal to
1762          *  (Cumulative TSN Ack + Gap Ack Block End) of each Gap Ack
1763          *  Block are assumed to have been received correctly.
1764          */
1765
1766         frags = sack->variable;
1767         gap = tsn - ctsn;
1768         for (i = 0; i < ntohs(sack->num_gap_ack_blocks); ++i) {
1769                 if (TSN_lte(ntohs(frags[i].gab.start), gap) &&
1770                     TSN_lte(gap, ntohs(frags[i].gab.end)))
1771                         goto pass;
1772         }
1773
1774         return 0;
1775 pass:
1776         return 1;
1777 }
1778
1779 static inline int sctp_get_skip_pos(struct sctp_fwdtsn_skip *skiplist,
1780                                     int nskips, __be16 stream)
1781 {
1782         int i;
1783
1784         for (i = 0; i < nskips; i++) {
1785                 if (skiplist[i].stream == stream)
1786                         return i;
1787         }
1788         return i;
1789 }
1790
1791 /* Create and add a fwdtsn chunk to the outq's control queue if needed. */
1792 static void sctp_generate_fwdtsn(struct sctp_outq *q, __u32 ctsn)
1793 {
1794         struct sctp_association *asoc = q->asoc;
1795         struct sctp_chunk *ftsn_chunk = NULL;
1796         struct sctp_fwdtsn_skip ftsn_skip_arr[10];
1797         int nskips = 0;
1798         int skip_pos = 0;
1799         __u32 tsn;
1800         struct sctp_chunk *chunk;
1801         struct list_head *lchunk, *temp;
1802
1803         if (!asoc->peer.prsctp_capable)
1804                 return;
1805
1806         /* PR-SCTP C1) Let SackCumAck be the Cumulative TSN ACK carried in the
1807          * received SACK.
1808          *
1809          * If (Advanced.Peer.Ack.Point < SackCumAck), then update
1810          * Advanced.Peer.Ack.Point to be equal to SackCumAck.
1811          */
1812         if (TSN_lt(asoc->adv_peer_ack_point, ctsn))
1813                 asoc->adv_peer_ack_point = ctsn;
1814
1815         /* PR-SCTP C2) Try to further advance the "Advanced.Peer.Ack.Point"
1816          * locally, that is, to move "Advanced.Peer.Ack.Point" up as long as
1817          * the chunk next in the out-queue space is marked as "abandoned" as
1818          * shown in the following example:
1819          *
1820          * Assuming that a SACK arrived with the Cumulative TSN ACK 102
1821          * and the Advanced.Peer.Ack.Point is updated to this value:
1822          *
1823          *   out-queue at the end of  ==>   out-queue after Adv.Ack.Point
1824          *   normal SACK processing           local advancement
1825          *                ...                           ...
1826          *   Adv.Ack.Pt-> 102 acked                     102 acked
1827          *                103 abandoned                 103 abandoned
1828          *                104 abandoned     Adv.Ack.P-> 104 abandoned
1829          *                105                           105
1830          *                106 acked                     106 acked
1831          *                ...                           ...
1832          *
1833          * In this example, the data sender successfully advanced the
1834          * "Advanced.Peer.Ack.Point" from 102 to 104 locally.
1835          */
1836         list_for_each_safe(lchunk, temp, &q->abandoned) {
1837                 chunk = list_entry(lchunk, struct sctp_chunk,
1838                                         transmitted_list);
1839                 tsn = ntohl(chunk->subh.data_hdr->tsn);
1840
1841                 /* Remove any chunks in the abandoned queue that are acked by
1842                  * the ctsn.
1843                  */
1844                 if (TSN_lte(tsn, ctsn)) {
1845                         list_del_init(lchunk);
1846                         sctp_chunk_free(chunk);
1847                 } else {
1848                         if (TSN_lte(tsn, asoc->adv_peer_ack_point+1)) {
1849                                 asoc->adv_peer_ack_point = tsn;
1850                                 if (chunk->chunk_hdr->flags &
1851                                          SCTP_DATA_UNORDERED)
1852                                         continue;
1853                                 skip_pos = sctp_get_skip_pos(&ftsn_skip_arr[0],
1854                                                 nskips,
1855                                                 chunk->subh.data_hdr->stream);
1856                                 ftsn_skip_arr[skip_pos].stream =
1857                                         chunk->subh.data_hdr->stream;
1858                                 ftsn_skip_arr[skip_pos].ssn =
1859                                          chunk->subh.data_hdr->ssn;
1860                                 if (skip_pos == nskips)
1861                                         nskips++;
1862                                 if (nskips == 10)
1863                                         break;
1864                         } else
1865                                 break;
1866                 }
1867         }
1868
1869         /* PR-SCTP C3) If, after step C1 and C2, the "Advanced.Peer.Ack.Point"
1870          * is greater than the Cumulative TSN ACK carried in the received
1871          * SACK, the data sender MUST send the data receiver a FORWARD TSN
1872          * chunk containing the latest value of the
1873          * "Advanced.Peer.Ack.Point".
1874          *
1875          * C4) For each "abandoned" TSN the sender of the FORWARD TSN SHOULD
1876          * list each stream and sequence number in the forwarded TSN. This
1877          * information will enable the receiver to easily find any
1878          * stranded TSN's waiting on stream reorder queues. Each stream
1879          * SHOULD only be reported once; this means that if multiple
1880          * abandoned messages occur in the same stream then only the
1881          * highest abandoned stream sequence number is reported. If the
1882          * total size of the FORWARD TSN does NOT fit in a single MTU then
1883          * the sender of the FORWARD TSN SHOULD lower the
1884          * Advanced.Peer.Ack.Point to the last TSN that will fit in a
1885          * single MTU.
1886          */
1887         if (asoc->adv_peer_ack_point > ctsn)
1888                 ftsn_chunk = sctp_make_fwdtsn(asoc, asoc->adv_peer_ack_point,
1889                                               nskips, &ftsn_skip_arr[0]);
1890
1891         if (ftsn_chunk) {
1892                 list_add_tail(&ftsn_chunk->list, &q->control_chunk_list);
1893                 SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
1894         }
1895 }