sctp: assure at least one T3-rtx timer is running if a FORWARD TSN is sent
[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_CID_DATA == chunk->chunk_hdr->type) {
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                 /* Attempt to append this chunk to the packet. */
602                 status = sctp_packet_append_chunk(pkt, chunk);
603
604                 switch (status) {
605                 case SCTP_XMIT_PMTU_FULL:
606                         /* Send this packet.  */
607                         error = sctp_packet_transmit(pkt);
608
609                         /* If we are retransmitting, we should only
610                          * send a single packet.
611                          */
612                         if (rtx_timeout || fast_rtx)
613                                 done = 1;
614
615                         /* Bundle next chunk in the next round.  */
616                         break;
617
618                 case SCTP_XMIT_RWND_FULL:
619                         /* Send this packet. */
620                         error = sctp_packet_transmit(pkt);
621
622                         /* Stop sending DATA as there is no more room
623                          * at the receiver.
624                          */
625                         done = 1;
626                         break;
627
628                 case SCTP_XMIT_NAGLE_DELAY:
629                         /* Send this packet. */
630                         error = sctp_packet_transmit(pkt);
631
632                         /* Stop sending DATA because of nagle delay. */
633                         done = 1;
634                         break;
635
636                 default:
637                         /* The append was successful, so add this chunk to
638                          * the transmitted list.
639                          */
640                         list_del(&chunk->transmitted_list);
641                         list_add_tail(&chunk->transmitted_list,
642                                         &transport->transmitted);
643
644                         /* Mark the chunk as ineligible for fast retransmit
645                          * after it is retransmitted.
646                          */
647                         if (chunk->fast_retransmit == SCTP_NEED_FRTX)
648                                 chunk->fast_retransmit = SCTP_DONT_FRTX;
649
650                         /* Force start T3-rtx timer when fast retransmitting
651                          * the earliest outstanding TSN
652                          */
653                         if (!timer && fast_rtx &&
654                             ntohl(chunk->subh.data_hdr->tsn) ==
655                                              asoc->ctsn_ack_point + 1)
656                                 timer = 2;
657
658                         q->empty = 0;
659                         break;
660                 }
661
662                 /* Set the timer if there were no errors */
663                 if (!error && !timer)
664                         timer = 1;
665
666                 if (done)
667                         break;
668         }
669
670         /* If we are here due to a retransmit timeout or a fast
671          * retransmit and if there are any chunks left in the retransmit
672          * queue that could not fit in the PMTU sized packet, they need
673          * to be marked as ineligible for a subsequent fast retransmit.
674          */
675         if (rtx_timeout || fast_rtx) {
676                 list_for_each_entry(chunk1, lqueue, transmitted_list) {
677                         if (chunk1->fast_retransmit == SCTP_NEED_FRTX)
678                                 chunk1->fast_retransmit = SCTP_DONT_FRTX;
679                 }
680         }
681
682         *start_timer = timer;
683
684         /* Clear fast retransmit hint */
685         if (fast_rtx)
686                 q->fast_rtx = 0;
687
688         return error;
689 }
690
691 /* Cork the outqueue so queued chunks are really queued. */
692 int sctp_outq_uncork(struct sctp_outq *q)
693 {
694         int error = 0;
695         if (q->cork)
696                 q->cork = 0;
697         error = sctp_outq_flush(q, 0);
698         return error;
699 }
700
701
702 /*
703  * Try to flush an outqueue.
704  *
705  * Description: Send everything in q which we legally can, subject to
706  * congestion limitations.
707  * * Note: This function can be called from multiple contexts so appropriate
708  * locking concerns must be made.  Today we use the sock lock to protect
709  * this function.
710  */
711 static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout)
712 {
713         struct sctp_packet *packet;
714         struct sctp_packet singleton;
715         struct sctp_association *asoc = q->asoc;
716         __u16 sport = asoc->base.bind_addr.port;
717         __u16 dport = asoc->peer.port;
718         __u32 vtag = asoc->peer.i.init_tag;
719         struct sctp_transport *transport = NULL;
720         struct sctp_transport *new_transport;
721         struct sctp_chunk *chunk, *tmp;
722         sctp_xmit_t status;
723         int error = 0;
724         int start_timer = 0;
725         int one_packet = 0;
726
727         /* These transports have chunks to send. */
728         struct list_head transport_list;
729         struct list_head *ltransport;
730
731         INIT_LIST_HEAD(&transport_list);
732         packet = NULL;
733
734         /*
735          * 6.10 Bundling
736          *   ...
737          *   When bundling control chunks with DATA chunks, an
738          *   endpoint MUST place control chunks first in the outbound
739          *   SCTP packet.  The transmitter MUST transmit DATA chunks
740          *   within a SCTP packet in increasing order of TSN.
741          *   ...
742          */
743
744         list_for_each_entry_safe(chunk, tmp, &q->control_chunk_list, list) {
745                 list_del_init(&chunk->list);
746
747                 /* Pick the right transport to use. */
748                 new_transport = chunk->transport;
749
750                 if (!new_transport) {
751                         /*
752                          * If we have a prior transport pointer, see if
753                          * the destination address of the chunk
754                          * matches the destination address of the
755                          * current transport.  If not a match, then
756                          * try to look up the transport with a given
757                          * destination address.  We do this because
758                          * after processing ASCONFs, we may have new
759                          * transports created.
760                          */
761                         if (transport &&
762                             sctp_cmp_addr_exact(&chunk->dest,
763                                                 &transport->ipaddr))
764                                         new_transport = transport;
765                         else
766                                 new_transport = sctp_assoc_lookup_paddr(asoc,
767                                                                 &chunk->dest);
768
769                         /* if we still don't have a new transport, then
770                          * use the current active path.
771                          */
772                         if (!new_transport)
773                                 new_transport = asoc->peer.active_path;
774                 } else if ((new_transport->state == SCTP_INACTIVE) ||
775                            (new_transport->state == SCTP_UNCONFIRMED)) {
776                         /* If the chunk is Heartbeat or Heartbeat Ack,
777                          * send it to chunk->transport, even if it's
778                          * inactive.
779                          *
780                          * 3.3.6 Heartbeat Acknowledgement:
781                          * ...
782                          * A HEARTBEAT ACK is always sent to the source IP
783                          * address of the IP datagram containing the
784                          * HEARTBEAT chunk to which this ack is responding.
785                          * ...
786                          *
787                          * ASCONF_ACKs also must be sent to the source.
788                          */
789                         if (chunk->chunk_hdr->type != SCTP_CID_HEARTBEAT &&
790                             chunk->chunk_hdr->type != SCTP_CID_HEARTBEAT_ACK &&
791                             chunk->chunk_hdr->type != SCTP_CID_ASCONF_ACK)
792                                 new_transport = asoc->peer.active_path;
793                 }
794
795                 /* Are we switching transports?
796                  * Take care of transport locks.
797                  */
798                 if (new_transport != transport) {
799                         transport = new_transport;
800                         if (list_empty(&transport->send_ready)) {
801                                 list_add_tail(&transport->send_ready,
802                                               &transport_list);
803                         }
804                         packet = &transport->packet;
805                         sctp_packet_config(packet, vtag,
806                                            asoc->peer.ecn_capable);
807                 }
808
809                 switch (chunk->chunk_hdr->type) {
810                 /*
811                  * 6.10 Bundling
812                  *   ...
813                  *   An endpoint MUST NOT bundle INIT, INIT ACK or SHUTDOWN
814                  *   COMPLETE with any other chunks.  [Send them immediately.]
815                  */
816                 case SCTP_CID_INIT:
817                 case SCTP_CID_INIT_ACK:
818                 case SCTP_CID_SHUTDOWN_COMPLETE:
819                         sctp_packet_init(&singleton, transport, sport, dport);
820                         sctp_packet_config(&singleton, vtag, 0);
821                         sctp_packet_append_chunk(&singleton, chunk);
822                         error = sctp_packet_transmit(&singleton);
823                         if (error < 0)
824                                 return error;
825                         break;
826
827                 case SCTP_CID_ABORT:
828                         if (sctp_test_T_bit(chunk)) {
829                                 packet->vtag = asoc->c.my_vtag;
830                         }
831                 /* The following chunks are "response" chunks, i.e.
832                  * they are generated in response to something we
833                  * received.  If we are sending these, then we can
834                  * send only 1 packet containing these chunks.
835                  */
836                 case SCTP_CID_HEARTBEAT_ACK:
837                 case SCTP_CID_SHUTDOWN_ACK:
838                 case SCTP_CID_COOKIE_ACK:
839                 case SCTP_CID_COOKIE_ECHO:
840                 case SCTP_CID_ERROR:
841                 case SCTP_CID_ECN_CWR:
842                 case SCTP_CID_ASCONF_ACK:
843                         one_packet = 1;
844                         /* Fall throught */
845
846                 case SCTP_CID_SACK:
847                 case SCTP_CID_HEARTBEAT:
848                 case SCTP_CID_SHUTDOWN:
849                 case SCTP_CID_ECN_ECNE:
850                 case SCTP_CID_ASCONF:
851                 case SCTP_CID_FWD_TSN:
852                         status = sctp_packet_transmit_chunk(packet, chunk,
853                                                             one_packet);
854                         if (status  != SCTP_XMIT_OK) {
855                                 /* put the chunk back */
856                                 list_add(&chunk->list, &q->control_chunk_list);
857                         } else if (chunk->chunk_hdr->type == SCTP_CID_FWD_TSN) {
858                                 /* PR-SCTP C5) If a FORWARD TSN is sent, the
859                                  * sender MUST assure that at least one T3-rtx
860                                  * timer is running.
861                                  */
862                                 sctp_transport_reset_timers(transport, 0);
863                         }
864                         break;
865
866                 default:
867                         /* We built a chunk with an illegal type! */
868                         BUG();
869                 }
870         }
871
872         /* Is it OK to send data chunks?  */
873         switch (asoc->state) {
874         case SCTP_STATE_COOKIE_ECHOED:
875                 /* Only allow bundling when this packet has a COOKIE-ECHO
876                  * chunk.
877                  */
878                 if (!packet || !packet->has_cookie_echo)
879                         break;
880
881                 /* fallthru */
882         case SCTP_STATE_ESTABLISHED:
883         case SCTP_STATE_SHUTDOWN_PENDING:
884         case SCTP_STATE_SHUTDOWN_RECEIVED:
885                 /*
886                  * RFC 2960 6.1  Transmission of DATA Chunks
887                  *
888                  * C) When the time comes for the sender to transmit,
889                  * before sending new DATA chunks, the sender MUST
890                  * first transmit any outstanding DATA chunks which
891                  * are marked for retransmission (limited by the
892                  * current cwnd).
893                  */
894                 if (!list_empty(&q->retransmit)) {
895                         if (transport == asoc->peer.retran_path)
896                                 goto retran;
897
898                         /* Switch transports & prepare the packet.  */
899
900                         transport = asoc->peer.retran_path;
901
902                         if (list_empty(&transport->send_ready)) {
903                                 list_add_tail(&transport->send_ready,
904                                               &transport_list);
905                         }
906
907                         packet = &transport->packet;
908                         sctp_packet_config(packet, vtag,
909                                            asoc->peer.ecn_capable);
910                 retran:
911                         error = sctp_outq_flush_rtx(q, packet,
912                                                     rtx_timeout, &start_timer);
913
914                         if (start_timer)
915                                 sctp_transport_reset_timers(transport,
916                                                             start_timer-1);
917
918                         /* This can happen on COOKIE-ECHO resend.  Only
919                          * one chunk can get bundled with a COOKIE-ECHO.
920                          */
921                         if (packet->has_cookie_echo)
922                                 goto sctp_flush_out;
923
924                         /* Don't send new data if there is still data
925                          * waiting to retransmit.
926                          */
927                         if (!list_empty(&q->retransmit))
928                                 goto sctp_flush_out;
929                 }
930
931                 /* Apply Max.Burst limitation to the current transport in
932                  * case it will be used for new data.  We are going to
933                  * rest it before we return, but we want to apply the limit
934                  * to the currently queued data.
935                  */
936                 if (transport)
937                         sctp_transport_burst_limited(transport);
938
939                 /* Finally, transmit new packets.  */
940                 while ((chunk = sctp_outq_dequeue_data(q)) != NULL) {
941                         /* RFC 2960 6.5 Every DATA chunk MUST carry a valid
942                          * stream identifier.
943                          */
944                         if (chunk->sinfo.sinfo_stream >=
945                             asoc->c.sinit_num_ostreams) {
946
947                                 /* Mark as failed send. */
948                                 sctp_chunk_fail(chunk, SCTP_ERROR_INV_STRM);
949                                 sctp_chunk_free(chunk);
950                                 continue;
951                         }
952
953                         /* Has this chunk expired? */
954                         if (sctp_chunk_abandoned(chunk)) {
955                                 sctp_chunk_fail(chunk, 0);
956                                 sctp_chunk_free(chunk);
957                                 continue;
958                         }
959
960                         /* If there is a specified transport, use it.
961                          * Otherwise, we want to use the active path.
962                          */
963                         new_transport = chunk->transport;
964                         if (!new_transport ||
965                             ((new_transport->state == SCTP_INACTIVE) ||
966                              (new_transport->state == SCTP_UNCONFIRMED)))
967                                 new_transport = asoc->peer.active_path;
968
969                         /* Change packets if necessary.  */
970                         if (new_transport != transport) {
971                                 transport = new_transport;
972
973                                 /* Schedule to have this transport's
974                                  * packet flushed.
975                                  */
976                                 if (list_empty(&transport->send_ready)) {
977                                         list_add_tail(&transport->send_ready,
978                                                       &transport_list);
979                                 }
980
981                                 packet = &transport->packet;
982                                 sctp_packet_config(packet, vtag,
983                                                    asoc->peer.ecn_capable);
984                                 /* We've switched transports, so apply the
985                                  * Burst limit to the new transport.
986                                  */
987                                 sctp_transport_burst_limited(transport);
988                         }
989
990                         SCTP_DEBUG_PRINTK("sctp_outq_flush(%p, %p[%s]), ",
991                                           q, chunk,
992                                           chunk && chunk->chunk_hdr ?
993                                           sctp_cname(SCTP_ST_CHUNK(
994                                                   chunk->chunk_hdr->type))
995                                           : "Illegal Chunk");
996
997                         SCTP_DEBUG_PRINTK("TX TSN 0x%x skb->head "
998                                         "%p skb->users %d.\n",
999                                         ntohl(chunk->subh.data_hdr->tsn),
1000                                         chunk->skb ?chunk->skb->head : NULL,
1001                                         chunk->skb ?
1002                                         atomic_read(&chunk->skb->users) : -1);
1003
1004                         /* Add the chunk to the packet.  */
1005                         status = sctp_packet_transmit_chunk(packet, chunk, 0);
1006
1007                         switch (status) {
1008                         case SCTP_XMIT_PMTU_FULL:
1009                         case SCTP_XMIT_RWND_FULL:
1010                         case SCTP_XMIT_NAGLE_DELAY:
1011                                 /* We could not append this chunk, so put
1012                                  * the chunk back on the output queue.
1013                                  */
1014                                 SCTP_DEBUG_PRINTK("sctp_outq_flush: could "
1015                                         "not transmit TSN: 0x%x, status: %d\n",
1016                                         ntohl(chunk->subh.data_hdr->tsn),
1017                                         status);
1018                                 sctp_outq_head_data(q, chunk);
1019                                 goto sctp_flush_out;
1020                                 break;
1021
1022                         case SCTP_XMIT_OK:
1023                                 /* The sender is in the SHUTDOWN-PENDING state,
1024                                  * The sender MAY set the I-bit in the DATA
1025                                  * chunk header.
1026                                  */
1027                                 if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING)
1028                                         chunk->chunk_hdr->flags |= SCTP_DATA_SACK_IMM;
1029
1030                                 break;
1031
1032                         default:
1033                                 BUG();
1034                         }
1035
1036                         /* BUG: We assume that the sctp_packet_transmit()
1037                          * call below will succeed all the time and add the
1038                          * chunk to the transmitted list and restart the
1039                          * timers.
1040                          * It is possible that the call can fail under OOM
1041                          * conditions.
1042                          *
1043                          * Is this really a problem?  Won't this behave
1044                          * like a lost TSN?
1045                          */
1046                         list_add_tail(&chunk->transmitted_list,
1047                                       &transport->transmitted);
1048
1049                         sctp_transport_reset_timers(transport, 0);
1050
1051                         q->empty = 0;
1052
1053                         /* Only let one DATA chunk get bundled with a
1054                          * COOKIE-ECHO chunk.
1055                          */
1056                         if (packet->has_cookie_echo)
1057                                 goto sctp_flush_out;
1058                 }
1059                 break;
1060
1061         default:
1062                 /* Do nothing.  */
1063                 break;
1064         }
1065
1066 sctp_flush_out:
1067
1068         /* Before returning, examine all the transports touched in
1069          * this call.  Right now, we bluntly force clear all the
1070          * transports.  Things might change after we implement Nagle.
1071          * But such an examination is still required.
1072          *
1073          * --xguo
1074          */
1075         while ((ltransport = sctp_list_dequeue(&transport_list)) != NULL ) {
1076                 struct sctp_transport *t = list_entry(ltransport,
1077                                                       struct sctp_transport,
1078                                                       send_ready);
1079                 packet = &t->packet;
1080                 if (!sctp_packet_empty(packet))
1081                         error = sctp_packet_transmit(packet);
1082
1083                 /* Clear the burst limited state, if any */
1084                 sctp_transport_burst_reset(t);
1085         }
1086
1087         return error;
1088 }
1089
1090 /* Update unack_data based on the incoming SACK chunk */
1091 static void sctp_sack_update_unack_data(struct sctp_association *assoc,
1092                                         struct sctp_sackhdr *sack)
1093 {
1094         sctp_sack_variable_t *frags;
1095         __u16 unack_data;
1096         int i;
1097
1098         unack_data = assoc->next_tsn - assoc->ctsn_ack_point - 1;
1099
1100         frags = sack->variable;
1101         for (i = 0; i < ntohs(sack->num_gap_ack_blocks); i++) {
1102                 unack_data -= ((ntohs(frags[i].gab.end) -
1103                                 ntohs(frags[i].gab.start) + 1));
1104         }
1105
1106         assoc->unack_data = unack_data;
1107 }
1108
1109 /* Return the highest new tsn that is acknowledged by the given SACK chunk. */
1110 static __u32 sctp_highest_new_tsn(struct sctp_sackhdr *sack,
1111                                   struct sctp_association *asoc)
1112 {
1113         struct sctp_transport *transport;
1114         struct sctp_chunk *chunk;
1115         __u32 highest_new_tsn, tsn;
1116         struct list_head *transport_list = &asoc->peer.transport_addr_list;
1117
1118         highest_new_tsn = ntohl(sack->cum_tsn_ack);
1119
1120         list_for_each_entry(transport, transport_list, transports) {
1121                 list_for_each_entry(chunk, &transport->transmitted,
1122                                 transmitted_list) {
1123                         tsn = ntohl(chunk->subh.data_hdr->tsn);
1124
1125                         if (!chunk->tsn_gap_acked &&
1126                             TSN_lt(highest_new_tsn, tsn) &&
1127                             sctp_acked(sack, tsn))
1128                                 highest_new_tsn = tsn;
1129                 }
1130         }
1131
1132         return highest_new_tsn;
1133 }
1134
1135 /* This is where we REALLY process a SACK.
1136  *
1137  * Process the SACK against the outqueue.  Mostly, this just frees
1138  * things off the transmitted queue.
1139  */
1140 int sctp_outq_sack(struct sctp_outq *q, struct sctp_sackhdr *sack)
1141 {
1142         struct sctp_association *asoc = q->asoc;
1143         struct sctp_transport *transport;
1144         struct sctp_chunk *tchunk = NULL;
1145         struct list_head *lchunk, *transport_list, *temp;
1146         sctp_sack_variable_t *frags = sack->variable;
1147         __u32 sack_ctsn, ctsn, tsn;
1148         __u32 highest_tsn, highest_new_tsn;
1149         __u32 sack_a_rwnd;
1150         unsigned outstanding;
1151         struct sctp_transport *primary = asoc->peer.primary_path;
1152         int count_of_newacks = 0;
1153         int gap_ack_blocks;
1154
1155         /* Grab the association's destination address list. */
1156         transport_list = &asoc->peer.transport_addr_list;
1157
1158         sack_ctsn = ntohl(sack->cum_tsn_ack);
1159         gap_ack_blocks = ntohs(sack->num_gap_ack_blocks);
1160         /*
1161          * SFR-CACC algorithm:
1162          * On receipt of a SACK the sender SHOULD execute the
1163          * following statements.
1164          *
1165          * 1) If the cumulative ack in the SACK passes next tsn_at_change
1166          * on the current primary, the CHANGEOVER_ACTIVE flag SHOULD be
1167          * cleared. The CYCLING_CHANGEOVER flag SHOULD also be cleared for
1168          * all destinations.
1169          * 2) If the SACK contains gap acks and the flag CHANGEOVER_ACTIVE
1170          * is set the receiver of the SACK MUST take the following actions:
1171          *
1172          * A) Initialize the cacc_saw_newack to 0 for all destination
1173          * addresses.
1174          *
1175          * Only bother if changeover_active is set. Otherwise, this is
1176          * totally suboptimal to do on every SACK.
1177          */
1178         if (primary->cacc.changeover_active) {
1179                 u8 clear_cycling = 0;
1180
1181                 if (TSN_lte(primary->cacc.next_tsn_at_change, sack_ctsn)) {
1182                         primary->cacc.changeover_active = 0;
1183                         clear_cycling = 1;
1184                 }
1185
1186                 if (clear_cycling || gap_ack_blocks) {
1187                         list_for_each_entry(transport, transport_list,
1188                                         transports) {
1189                                 if (clear_cycling)
1190                                         transport->cacc.cycling_changeover = 0;
1191                                 if (gap_ack_blocks)
1192                                         transport->cacc.cacc_saw_newack = 0;
1193                         }
1194                 }
1195         }
1196
1197         /* Get the highest TSN in the sack. */
1198         highest_tsn = sack_ctsn;
1199         if (gap_ack_blocks)
1200                 highest_tsn += ntohs(frags[gap_ack_blocks - 1].gab.end);
1201
1202         if (TSN_lt(asoc->highest_sacked, highest_tsn)) {
1203                 highest_new_tsn = highest_tsn;
1204                 asoc->highest_sacked = highest_tsn;
1205         } else {
1206                 highest_new_tsn = sctp_highest_new_tsn(sack, asoc);
1207         }
1208
1209
1210         /* Run through the retransmit queue.  Credit bytes received
1211          * and free those chunks that we can.
1212          */
1213         sctp_check_transmitted(q, &q->retransmit, NULL, sack, highest_new_tsn);
1214
1215         /* Run through the transmitted queue.
1216          * Credit bytes received and free those chunks which we can.
1217          *
1218          * This is a MASSIVE candidate for optimization.
1219          */
1220         list_for_each_entry(transport, transport_list, transports) {
1221                 sctp_check_transmitted(q, &transport->transmitted,
1222                                        transport, sack, highest_new_tsn);
1223                 /*
1224                  * SFR-CACC algorithm:
1225                  * C) Let count_of_newacks be the number of
1226                  * destinations for which cacc_saw_newack is set.
1227                  */
1228                 if (transport->cacc.cacc_saw_newack)
1229                         count_of_newacks ++;
1230         }
1231
1232         if (gap_ack_blocks) {
1233                 list_for_each_entry(transport, transport_list, transports)
1234                         sctp_mark_missing(q, &transport->transmitted, transport,
1235                                           highest_new_tsn, count_of_newacks);
1236         }
1237
1238         /* Move the Cumulative TSN Ack Point if appropriate.  */
1239         if (TSN_lt(asoc->ctsn_ack_point, sack_ctsn))
1240                 asoc->ctsn_ack_point = sack_ctsn;
1241
1242         /* Update unack_data field in the assoc. */
1243         sctp_sack_update_unack_data(asoc, sack);
1244
1245         ctsn = asoc->ctsn_ack_point;
1246
1247         /* Throw away stuff rotting on the sack queue.  */
1248         list_for_each_safe(lchunk, temp, &q->sacked) {
1249                 tchunk = list_entry(lchunk, struct sctp_chunk,
1250                                     transmitted_list);
1251                 tsn = ntohl(tchunk->subh.data_hdr->tsn);
1252                 if (TSN_lte(tsn, ctsn)) {
1253                         list_del_init(&tchunk->transmitted_list);
1254                         sctp_chunk_free(tchunk);
1255                 }
1256         }
1257
1258         /* ii) Set rwnd equal to the newly received a_rwnd minus the
1259          *     number of bytes still outstanding after processing the
1260          *     Cumulative TSN Ack and the Gap Ack Blocks.
1261          */
1262
1263         sack_a_rwnd = ntohl(sack->a_rwnd);
1264         outstanding = q->outstanding_bytes;
1265
1266         if (outstanding < sack_a_rwnd)
1267                 sack_a_rwnd -= outstanding;
1268         else
1269                 sack_a_rwnd = 0;
1270
1271         asoc->peer.rwnd = sack_a_rwnd;
1272
1273         sctp_generate_fwdtsn(q, sack_ctsn);
1274
1275         SCTP_DEBUG_PRINTK("%s: sack Cumulative TSN Ack is 0x%x.\n",
1276                           __func__, sack_ctsn);
1277         SCTP_DEBUG_PRINTK("%s: Cumulative TSN Ack of association, "
1278                           "%p is 0x%x. Adv peer ack point: 0x%x\n",
1279                           __func__, asoc, ctsn, asoc->adv_peer_ack_point);
1280
1281         /* See if all chunks are acked.
1282          * Make sure the empty queue handler will get run later.
1283          */
1284         q->empty = (list_empty(&q->out_chunk_list) &&
1285                     list_empty(&q->retransmit));
1286         if (!q->empty)
1287                 goto finish;
1288
1289         list_for_each_entry(transport, transport_list, transports) {
1290                 q->empty = q->empty && list_empty(&transport->transmitted);
1291                 if (!q->empty)
1292                         goto finish;
1293         }
1294
1295         SCTP_DEBUG_PRINTK("sack queue is empty.\n");
1296 finish:
1297         return q->empty;
1298 }
1299
1300 /* Is the outqueue empty?  */
1301 int sctp_outq_is_empty(const struct sctp_outq *q)
1302 {
1303         return q->empty;
1304 }
1305
1306 /********************************************************************
1307  * 2nd Level Abstractions
1308  ********************************************************************/
1309
1310 /* Go through a transport's transmitted list or the association's retransmit
1311  * list and move chunks that are acked by the Cumulative TSN Ack to q->sacked.
1312  * The retransmit list will not have an associated transport.
1313  *
1314  * I added coherent debug information output.   --xguo
1315  *
1316  * Instead of printing 'sacked' or 'kept' for each TSN on the
1317  * transmitted_queue, we print a range: SACKED: TSN1-TSN2, TSN3, TSN4-TSN5.
1318  * KEPT TSN6-TSN7, etc.
1319  */
1320 static void sctp_check_transmitted(struct sctp_outq *q,
1321                                    struct list_head *transmitted_queue,
1322                                    struct sctp_transport *transport,
1323                                    struct sctp_sackhdr *sack,
1324                                    __u32 highest_new_tsn_in_sack)
1325 {
1326         struct list_head *lchunk;
1327         struct sctp_chunk *tchunk;
1328         struct list_head tlist;
1329         __u32 tsn;
1330         __u32 sack_ctsn;
1331         __u32 rtt;
1332         __u8 restart_timer = 0;
1333         int bytes_acked = 0;
1334         int migrate_bytes = 0;
1335
1336         /* These state variables are for coherent debug output. --xguo */
1337
1338 #if SCTP_DEBUG
1339         __u32 dbg_ack_tsn = 0;  /* An ACKed TSN range starts here... */
1340         __u32 dbg_last_ack_tsn = 0;  /* ...and finishes here.        */
1341         __u32 dbg_kept_tsn = 0; /* An un-ACKed range starts here...  */
1342         __u32 dbg_last_kept_tsn = 0; /* ...and finishes here.        */
1343
1344         /* 0 : The last TSN was ACKed.
1345          * 1 : The last TSN was NOT ACKed (i.e. KEPT).
1346          * -1: We need to initialize.
1347          */
1348         int dbg_prt_state = -1;
1349 #endif /* SCTP_DEBUG */
1350
1351         sack_ctsn = ntohl(sack->cum_tsn_ack);
1352
1353         INIT_LIST_HEAD(&tlist);
1354
1355         /* The while loop will skip empty transmitted queues. */
1356         while (NULL != (lchunk = sctp_list_dequeue(transmitted_queue))) {
1357                 tchunk = list_entry(lchunk, struct sctp_chunk,
1358                                     transmitted_list);
1359
1360                 if (sctp_chunk_abandoned(tchunk)) {
1361                         /* Move the chunk to abandoned list. */
1362                         sctp_insert_list(&q->abandoned, lchunk);
1363
1364                         /* If this chunk has not been acked, stop
1365                          * considering it as 'outstanding'.
1366                          */
1367                         if (!tchunk->tsn_gap_acked) {
1368                                 if (tchunk->transport)
1369                                         tchunk->transport->flight_size -=
1370                                                         sctp_data_size(tchunk);
1371                                 q->outstanding_bytes -= sctp_data_size(tchunk);
1372                         }
1373                         continue;
1374                 }
1375
1376                 tsn = ntohl(tchunk->subh.data_hdr->tsn);
1377                 if (sctp_acked(sack, tsn)) {
1378                         /* If this queue is the retransmit queue, the
1379                          * retransmit timer has already reclaimed
1380                          * the outstanding bytes for this chunk, so only
1381                          * count bytes associated with a transport.
1382                          */
1383                         if (transport) {
1384                                 /* If this chunk is being used for RTT
1385                                  * measurement, calculate the RTT and update
1386                                  * the RTO using this value.
1387                                  *
1388                                  * 6.3.1 C5) Karn's algorithm: RTT measurements
1389                                  * MUST NOT be made using packets that were
1390                                  * retransmitted (and thus for which it is
1391                                  * ambiguous whether the reply was for the
1392                                  * first instance of the packet or a later
1393                                  * instance).
1394                                  */
1395                                 if (!tchunk->tsn_gap_acked &&
1396                                     !tchunk->resent &&
1397                                     tchunk->rtt_in_progress) {
1398                                         tchunk->rtt_in_progress = 0;
1399                                         rtt = jiffies - tchunk->sent_at;
1400                                         sctp_transport_update_rto(transport,
1401                                                                   rtt);
1402                                 }
1403                         }
1404
1405                         /* If the chunk hasn't been marked as ACKED,
1406                          * mark it and account bytes_acked if the
1407                          * chunk had a valid transport (it will not
1408                          * have a transport if ASCONF had deleted it
1409                          * while DATA was outstanding).
1410                          */
1411                         if (!tchunk->tsn_gap_acked) {
1412                                 tchunk->tsn_gap_acked = 1;
1413                                 bytes_acked += sctp_data_size(tchunk);
1414                                 if (!tchunk->transport)
1415                                         migrate_bytes += sctp_data_size(tchunk);
1416                         }
1417
1418                         if (TSN_lte(tsn, sack_ctsn)) {
1419                                 /* RFC 2960  6.3.2 Retransmission Timer Rules
1420                                  *
1421                                  * R3) Whenever a SACK is received
1422                                  * that acknowledges the DATA chunk
1423                                  * with the earliest outstanding TSN
1424                                  * for that address, restart T3-rtx
1425                                  * timer for that address with its
1426                                  * current RTO.
1427                                  */
1428                                 restart_timer = 1;
1429
1430                                 if (!tchunk->tsn_gap_acked) {
1431                                         /*
1432                                          * SFR-CACC algorithm:
1433                                          * 2) If the SACK contains gap acks
1434                                          * and the flag CHANGEOVER_ACTIVE is
1435                                          * set the receiver of the SACK MUST
1436                                          * take the following action:
1437                                          *
1438                                          * B) For each TSN t being acked that
1439                                          * has not been acked in any SACK so
1440                                          * far, set cacc_saw_newack to 1 for
1441                                          * the destination that the TSN was
1442                                          * sent to.
1443                                          */
1444                                         if (transport &&
1445                                             sack->num_gap_ack_blocks &&
1446                                             q->asoc->peer.primary_path->cacc.
1447                                             changeover_active)
1448                                                 transport->cacc.cacc_saw_newack
1449                                                         = 1;
1450                                 }
1451
1452                                 list_add_tail(&tchunk->transmitted_list,
1453                                               &q->sacked);
1454                         } else {
1455                                 /* RFC2960 7.2.4, sctpimpguide-05 2.8.2
1456                                  * M2) Each time a SACK arrives reporting
1457                                  * 'Stray DATA chunk(s)' record the highest TSN
1458                                  * reported as newly acknowledged, call this
1459                                  * value 'HighestTSNinSack'. A newly
1460                                  * acknowledged DATA chunk is one not
1461                                  * previously acknowledged in a SACK.
1462                                  *
1463                                  * When the SCTP sender of data receives a SACK
1464                                  * chunk that acknowledges, for the first time,
1465                                  * the receipt of a DATA chunk, all the still
1466                                  * unacknowledged DATA chunks whose TSN is
1467                                  * older than that newly acknowledged DATA
1468                                  * chunk, are qualified as 'Stray DATA chunks'.
1469                                  */
1470                                 list_add_tail(lchunk, &tlist);
1471                         }
1472
1473 #if SCTP_DEBUG
1474                         switch (dbg_prt_state) {
1475                         case 0: /* last TSN was ACKed */
1476                                 if (dbg_last_ack_tsn + 1 == tsn) {
1477                                         /* This TSN belongs to the
1478                                          * current ACK range.
1479                                          */
1480                                         break;
1481                                 }
1482
1483                                 if (dbg_last_ack_tsn != dbg_ack_tsn) {
1484                                         /* Display the end of the
1485                                          * current range.
1486                                          */
1487                                         SCTP_DEBUG_PRINTK("-%08x",
1488                                                           dbg_last_ack_tsn);
1489                                 }
1490
1491                                 /* Start a new range.  */
1492                                 SCTP_DEBUG_PRINTK(",%08x", tsn);
1493                                 dbg_ack_tsn = tsn;
1494                                 break;
1495
1496                         case 1: /* The last TSN was NOT ACKed. */
1497                                 if (dbg_last_kept_tsn != dbg_kept_tsn) {
1498                                         /* Display the end of current range. */
1499                                         SCTP_DEBUG_PRINTK("-%08x",
1500                                                           dbg_last_kept_tsn);
1501                                 }
1502
1503                                 SCTP_DEBUG_PRINTK("\n");
1504
1505                                 /* FALL THROUGH... */
1506                         default:
1507                                 /* This is the first-ever TSN we examined.  */
1508                                 /* Start a new range of ACK-ed TSNs.  */
1509                                 SCTP_DEBUG_PRINTK("ACKed: %08x", tsn);
1510                                 dbg_prt_state = 0;
1511                                 dbg_ack_tsn = tsn;
1512                         }
1513
1514                         dbg_last_ack_tsn = tsn;
1515 #endif /* SCTP_DEBUG */
1516
1517                 } else {
1518                         if (tchunk->tsn_gap_acked) {
1519                                 SCTP_DEBUG_PRINTK("%s: Receiver reneged on "
1520                                                   "data TSN: 0x%x\n",
1521                                                   __func__,
1522                                                   tsn);
1523                                 tchunk->tsn_gap_acked = 0;
1524
1525                                 if (tchunk->transport)
1526                                         bytes_acked -= sctp_data_size(tchunk);
1527
1528                                 /* RFC 2960 6.3.2 Retransmission Timer Rules
1529                                  *
1530                                  * R4) Whenever a SACK is received missing a
1531                                  * TSN that was previously acknowledged via a
1532                                  * Gap Ack Block, start T3-rtx for the
1533                                  * destination address to which the DATA
1534                                  * chunk was originally
1535                                  * transmitted if it is not already running.
1536                                  */
1537                                 restart_timer = 1;
1538                         }
1539
1540                         list_add_tail(lchunk, &tlist);
1541
1542 #if SCTP_DEBUG
1543                         /* See the above comments on ACK-ed TSNs. */
1544                         switch (dbg_prt_state) {
1545                         case 1:
1546                                 if (dbg_last_kept_tsn + 1 == tsn)
1547                                         break;
1548
1549                                 if (dbg_last_kept_tsn != dbg_kept_tsn)
1550                                         SCTP_DEBUG_PRINTK("-%08x",
1551                                                           dbg_last_kept_tsn);
1552
1553                                 SCTP_DEBUG_PRINTK(",%08x", tsn);
1554                                 dbg_kept_tsn = tsn;
1555                                 break;
1556
1557                         case 0:
1558                                 if (dbg_last_ack_tsn != dbg_ack_tsn)
1559                                         SCTP_DEBUG_PRINTK("-%08x",
1560                                                           dbg_last_ack_tsn);
1561                                 SCTP_DEBUG_PRINTK("\n");
1562
1563                                 /* FALL THROUGH... */
1564                         default:
1565                                 SCTP_DEBUG_PRINTK("KEPT: %08x",tsn);
1566                                 dbg_prt_state = 1;
1567                                 dbg_kept_tsn = tsn;
1568                         }
1569
1570                         dbg_last_kept_tsn = tsn;
1571 #endif /* SCTP_DEBUG */
1572                 }
1573         }
1574
1575 #if SCTP_DEBUG
1576         /* Finish off the last range, displaying its ending TSN.  */
1577         switch (dbg_prt_state) {
1578         case 0:
1579                 if (dbg_last_ack_tsn != dbg_ack_tsn) {
1580                         SCTP_DEBUG_PRINTK("-%08x\n", dbg_last_ack_tsn);
1581                 } else {
1582                         SCTP_DEBUG_PRINTK("\n");
1583                 }
1584         break;
1585
1586         case 1:
1587                 if (dbg_last_kept_tsn != dbg_kept_tsn) {
1588                         SCTP_DEBUG_PRINTK("-%08x\n", dbg_last_kept_tsn);
1589                 } else {
1590                         SCTP_DEBUG_PRINTK("\n");
1591                 }
1592         }
1593 #endif /* SCTP_DEBUG */
1594         if (transport) {
1595                 if (bytes_acked) {
1596                         /* We may have counted DATA that was migrated
1597                          * to this transport due to DEL-IP operation.
1598                          * Subtract those bytes, since the were never
1599                          * send on this transport and shouldn't be
1600                          * credited to this transport.
1601                          */
1602                         bytes_acked -= migrate_bytes;
1603
1604                         /* 8.2. When an outstanding TSN is acknowledged,
1605                          * the endpoint shall clear the error counter of
1606                          * the destination transport address to which the
1607                          * DATA chunk was last sent.
1608                          * The association's overall error counter is
1609                          * also cleared.
1610                          */
1611                         transport->error_count = 0;
1612                         transport->asoc->overall_error_count = 0;
1613
1614                         /* Mark the destination transport address as
1615                          * active if it is not so marked.
1616                          */
1617                         if ((transport->state == SCTP_INACTIVE) ||
1618                             (transport->state == SCTP_UNCONFIRMED)) {
1619                                 sctp_assoc_control_transport(
1620                                         transport->asoc,
1621                                         transport,
1622                                         SCTP_TRANSPORT_UP,
1623                                         SCTP_RECEIVED_SACK);
1624                         }
1625
1626                         sctp_transport_raise_cwnd(transport, sack_ctsn,
1627                                                   bytes_acked);
1628
1629                         transport->flight_size -= bytes_acked;
1630                         if (transport->flight_size == 0)
1631                                 transport->partial_bytes_acked = 0;
1632                         q->outstanding_bytes -= bytes_acked + migrate_bytes;
1633                 } else {
1634                         /* RFC 2960 6.1, sctpimpguide-06 2.15.2
1635                          * When a sender is doing zero window probing, it
1636                          * should not timeout the association if it continues
1637                          * to receive new packets from the receiver. The
1638                          * reason is that the receiver MAY keep its window
1639                          * closed for an indefinite time.
1640                          * A sender is doing zero window probing when the
1641                          * receiver's advertised window is zero, and there is
1642                          * only one data chunk in flight to the receiver.
1643                          */
1644                         if (!q->asoc->peer.rwnd &&
1645                             !list_empty(&tlist) &&
1646                             (sack_ctsn+2 == q->asoc->next_tsn)) {
1647                                 SCTP_DEBUG_PRINTK("%s: SACK received for zero "
1648                                                   "window probe: %u\n",
1649                                                   __func__, sack_ctsn);
1650                                 q->asoc->overall_error_count = 0;
1651                                 transport->error_count = 0;
1652                         }
1653                 }
1654
1655                 /* RFC 2960 6.3.2 Retransmission Timer Rules
1656                  *
1657                  * R2) Whenever all outstanding data sent to an address have
1658                  * been acknowledged, turn off the T3-rtx timer of that
1659                  * address.
1660                  */
1661                 if (!transport->flight_size) {
1662                         if (timer_pending(&transport->T3_rtx_timer) &&
1663                             del_timer(&transport->T3_rtx_timer)) {
1664                                 sctp_transport_put(transport);
1665                         }
1666                 } else if (restart_timer) {
1667                         if (!mod_timer(&transport->T3_rtx_timer,
1668                                        jiffies + transport->rto))
1669                                 sctp_transport_hold(transport);
1670                 }
1671         }
1672
1673         list_splice(&tlist, transmitted_queue);
1674 }
1675
1676 /* Mark chunks as missing and consequently may get retransmitted. */
1677 static void sctp_mark_missing(struct sctp_outq *q,
1678                               struct list_head *transmitted_queue,
1679                               struct sctp_transport *transport,
1680                               __u32 highest_new_tsn_in_sack,
1681                               int count_of_newacks)
1682 {
1683         struct sctp_chunk *chunk;
1684         __u32 tsn;
1685         char do_fast_retransmit = 0;
1686         struct sctp_transport *primary = q->asoc->peer.primary_path;
1687
1688         list_for_each_entry(chunk, transmitted_queue, transmitted_list) {
1689
1690                 tsn = ntohl(chunk->subh.data_hdr->tsn);
1691
1692                 /* RFC 2960 7.2.4, sctpimpguide-05 2.8.2 M3) Examine all
1693                  * 'Unacknowledged TSN's', if the TSN number of an
1694                  * 'Unacknowledged TSN' is smaller than the 'HighestTSNinSack'
1695                  * value, increment the 'TSN.Missing.Report' count on that
1696                  * chunk if it has NOT been fast retransmitted or marked for
1697                  * fast retransmit already.
1698                  */
1699                 if (chunk->fast_retransmit == SCTP_CAN_FRTX &&
1700                     !chunk->tsn_gap_acked &&
1701                     TSN_lt(tsn, highest_new_tsn_in_sack)) {
1702
1703                         /* SFR-CACC may require us to skip marking
1704                          * this chunk as missing.
1705                          */
1706                         if (!transport || !sctp_cacc_skip(primary, transport,
1707                                             count_of_newacks, tsn)) {
1708                                 chunk->tsn_missing_report++;
1709
1710                                 SCTP_DEBUG_PRINTK(
1711                                         "%s: TSN 0x%x missing counter: %d\n",
1712                                         __func__, tsn,
1713                                         chunk->tsn_missing_report);
1714                         }
1715                 }
1716                 /*
1717                  * M4) If any DATA chunk is found to have a
1718                  * 'TSN.Missing.Report'
1719                  * value larger than or equal to 3, mark that chunk for
1720                  * retransmission and start the fast retransmit procedure.
1721                  */
1722
1723                 if (chunk->tsn_missing_report >= 3) {
1724                         chunk->fast_retransmit = SCTP_NEED_FRTX;
1725                         do_fast_retransmit = 1;
1726                 }
1727         }
1728
1729         if (transport) {
1730                 if (do_fast_retransmit)
1731                         sctp_retransmit(q, transport, SCTP_RTXR_FAST_RTX);
1732
1733                 SCTP_DEBUG_PRINTK("%s: transport: %p, cwnd: %d, "
1734                                   "ssthresh: %d, flight_size: %d, pba: %d\n",
1735                                   __func__, transport, transport->cwnd,
1736                                   transport->ssthresh, transport->flight_size,
1737                                   transport->partial_bytes_acked);
1738         }
1739 }
1740
1741 /* Is the given TSN acked by this packet?  */
1742 static int sctp_acked(struct sctp_sackhdr *sack, __u32 tsn)
1743 {
1744         int i;
1745         sctp_sack_variable_t *frags;
1746         __u16 gap;
1747         __u32 ctsn = ntohl(sack->cum_tsn_ack);
1748
1749         if (TSN_lte(tsn, ctsn))
1750                 goto pass;
1751
1752         /* 3.3.4 Selective Acknowledgement (SACK) (3):
1753          *
1754          * Gap Ack Blocks:
1755          *  These fields contain the Gap Ack Blocks. They are repeated
1756          *  for each Gap Ack Block up to the number of Gap Ack Blocks
1757          *  defined in the Number of Gap Ack Blocks field. All DATA
1758          *  chunks with TSNs greater than or equal to (Cumulative TSN
1759          *  Ack + Gap Ack Block Start) and less than or equal to
1760          *  (Cumulative TSN Ack + Gap Ack Block End) of each Gap Ack
1761          *  Block are assumed to have been received correctly.
1762          */
1763
1764         frags = sack->variable;
1765         gap = tsn - ctsn;
1766         for (i = 0; i < ntohs(sack->num_gap_ack_blocks); ++i) {
1767                 if (TSN_lte(ntohs(frags[i].gab.start), gap) &&
1768                     TSN_lte(gap, ntohs(frags[i].gab.end)))
1769                         goto pass;
1770         }
1771
1772         return 0;
1773 pass:
1774         return 1;
1775 }
1776
1777 static inline int sctp_get_skip_pos(struct sctp_fwdtsn_skip *skiplist,
1778                                     int nskips, __be16 stream)
1779 {
1780         int i;
1781
1782         for (i = 0; i < nskips; i++) {
1783                 if (skiplist[i].stream == stream)
1784                         return i;
1785         }
1786         return i;
1787 }
1788
1789 /* Create and add a fwdtsn chunk to the outq's control queue if needed. */
1790 static void sctp_generate_fwdtsn(struct sctp_outq *q, __u32 ctsn)
1791 {
1792         struct sctp_association *asoc = q->asoc;
1793         struct sctp_chunk *ftsn_chunk = NULL;
1794         struct sctp_fwdtsn_skip ftsn_skip_arr[10];
1795         int nskips = 0;
1796         int skip_pos = 0;
1797         __u32 tsn;
1798         struct sctp_chunk *chunk;
1799         struct list_head *lchunk, *temp;
1800
1801         if (!asoc->peer.prsctp_capable)
1802                 return;
1803
1804         /* PR-SCTP C1) Let SackCumAck be the Cumulative TSN ACK carried in the
1805          * received SACK.
1806          *
1807          * If (Advanced.Peer.Ack.Point < SackCumAck), then update
1808          * Advanced.Peer.Ack.Point to be equal to SackCumAck.
1809          */
1810         if (TSN_lt(asoc->adv_peer_ack_point, ctsn))
1811                 asoc->adv_peer_ack_point = ctsn;
1812
1813         /* PR-SCTP C2) Try to further advance the "Advanced.Peer.Ack.Point"
1814          * locally, that is, to move "Advanced.Peer.Ack.Point" up as long as
1815          * the chunk next in the out-queue space is marked as "abandoned" as
1816          * shown in the following example:
1817          *
1818          * Assuming that a SACK arrived with the Cumulative TSN ACK 102
1819          * and the Advanced.Peer.Ack.Point is updated to this value:
1820          *
1821          *   out-queue at the end of  ==>   out-queue after Adv.Ack.Point
1822          *   normal SACK processing           local advancement
1823          *                ...                           ...
1824          *   Adv.Ack.Pt-> 102 acked                     102 acked
1825          *                103 abandoned                 103 abandoned
1826          *                104 abandoned     Adv.Ack.P-> 104 abandoned
1827          *                105                           105
1828          *                106 acked                     106 acked
1829          *                ...                           ...
1830          *
1831          * In this example, the data sender successfully advanced the
1832          * "Advanced.Peer.Ack.Point" from 102 to 104 locally.
1833          */
1834         list_for_each_safe(lchunk, temp, &q->abandoned) {
1835                 chunk = list_entry(lchunk, struct sctp_chunk,
1836                                         transmitted_list);
1837                 tsn = ntohl(chunk->subh.data_hdr->tsn);
1838
1839                 /* Remove any chunks in the abandoned queue that are acked by
1840                  * the ctsn.
1841                  */
1842                 if (TSN_lte(tsn, ctsn)) {
1843                         list_del_init(lchunk);
1844                         sctp_chunk_free(chunk);
1845                 } else {
1846                         if (TSN_lte(tsn, asoc->adv_peer_ack_point+1)) {
1847                                 asoc->adv_peer_ack_point = tsn;
1848                                 if (chunk->chunk_hdr->flags &
1849                                          SCTP_DATA_UNORDERED)
1850                                         continue;
1851                                 skip_pos = sctp_get_skip_pos(&ftsn_skip_arr[0],
1852                                                 nskips,
1853                                                 chunk->subh.data_hdr->stream);
1854                                 ftsn_skip_arr[skip_pos].stream =
1855                                         chunk->subh.data_hdr->stream;
1856                                 ftsn_skip_arr[skip_pos].ssn =
1857                                          chunk->subh.data_hdr->ssn;
1858                                 if (skip_pos == nskips)
1859                                         nskips++;
1860                                 if (nskips == 10)
1861                                         break;
1862                         } else
1863                                 break;
1864                 }
1865         }
1866
1867         /* PR-SCTP C3) If, after step C1 and C2, the "Advanced.Peer.Ack.Point"
1868          * is greater than the Cumulative TSN ACK carried in the received
1869          * SACK, the data sender MUST send the data receiver a FORWARD TSN
1870          * chunk containing the latest value of the
1871          * "Advanced.Peer.Ack.Point".
1872          *
1873          * C4) For each "abandoned" TSN the sender of the FORWARD TSN SHOULD
1874          * list each stream and sequence number in the forwarded TSN. This
1875          * information will enable the receiver to easily find any
1876          * stranded TSN's waiting on stream reorder queues. Each stream
1877          * SHOULD only be reported once; this means that if multiple
1878          * abandoned messages occur in the same stream then only the
1879          * highest abandoned stream sequence number is reported. If the
1880          * total size of the FORWARD TSN does NOT fit in a single MTU then
1881          * the sender of the FORWARD TSN SHOULD lower the
1882          * Advanced.Peer.Ack.Point to the last TSN that will fit in a
1883          * single MTU.
1884          */
1885         if (asoc->adv_peer_ack_point > ctsn)
1886                 ftsn_chunk = sctp_make_fwdtsn(asoc, asoc->adv_peer_ack_point,
1887                                               nskips, &ftsn_skip_arr[0]);
1888
1889         if (ftsn_chunk) {
1890                 list_add_tail(&ftsn_chunk->list, &q->control_chunk_list);
1891                 SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
1892         }
1893 }