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