sys/netinet/tcp_sack.c

   1 /*
   2  * Copyright (c) 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
   3  * Copyright (c) 2003, 2004 The DragonFly Project.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to The DragonFly Project
   6  * by Jeffrey M. Hsu.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of The DragonFly Project nor the names of its
  17  *    contributors may be used to endorse or promote products derived
  18  *    from this software without specific, prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  24  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  25  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  27  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  30  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * $DragonFly: src/sys/netinet/tcp_sack.c,v 1.8 2008/08/15 21:37:16 nth Exp $
  34  */
  35
  36 #include <sys/param.h>
  37 #include <sys/systm.h>
  38 #include <sys/kernel.h>
  39 #include <sys/malloc.h>
  40 #include <sys/queue.h>
  41 #include <sys/thread.h>
  42 #include <sys/types.h>
  43 #include <sys/socket.h>
  44 #include <sys/socketvar.h>
  45
  46 #include <net/if.h>
  47
  48 #include <netinet/in.h>
  49 #include <netinet/in_systm.h>
  50 #include <netinet/ip.h>
  51 #include <netinet/in_var.h>
  52 #include <netinet/in_pcb.h>
  53 #include <netinet/ip_var.h>
  54 #include <netinet/tcp.h>
  55 #include <netinet/tcp_seq.h>
  56 #include <netinet/tcp_var.h>
  57
  58 /*
  59  * Implemented:
  60  *
  61  * RFC 2018
  62  * RFC 2883
  63  * RFC 3517
  64  */
  65
  66 struct sackblock {
  67         tcp_seq                 sblk_start;
  68         tcp_seq                 sblk_end;
  69         TAILQ_ENTRY(sackblock)  sblk_list;
  70 };
  71
  72 #define MAXSAVEDBLOCKS  8                       /* per connection limit */
  73
  74 static int insert_block(struct scoreboard *scb,
  75                         const struct raw_sackblock *raw_sb, boolean_t *update);
  76 static void update_lostseq(struct scoreboard *scb, tcp_seq snd_una,
  77                            u_int maxseg, int rxtthresh);
  78
  79 static MALLOC_DEFINE(M_SACKBLOCK, "sblk", "sackblock struct");
  80
  81 /*
  82  * Per-tcpcb initialization.
  83  */
  84 void
  85 tcp_sack_tcpcb_init(struct tcpcb *tp)
  86 {
  87         struct scoreboard *scb = &tp->scb;
  88
  89         scb->nblocks = 0;
  90         TAILQ_INIT(&scb->sackblocks);
  91         scb->lastfound = NULL;
  92 }
  93
  94 /*
  95  * Find the SACK block containing or immediately preceding "seq".
  96  * The boolean result indicates whether the sequence is actually
  97  * contained in the SACK block.
  98  */
  99 static boolean_t
 100 sack_block_lookup(struct scoreboard *scb, tcp_seq seq, struct sackblock **sb)
 101 {
 102         struct sackblock *hint = scb->lastfound;
 103         struct sackblock *cur, *last, *prev;
 104
 105         if (TAILQ_EMPTY(&scb->sackblocks)) {
 106                 *sb = NULL;
 107                 return FALSE;
 108         }
 109
 110         if (hint == NULL) {
 111                 /* No hint.  Search from start to end. */
 112                 cur = TAILQ_FIRST(&scb->sackblocks);
 113                 last = NULL;
 114                 prev = TAILQ_LAST(&scb->sackblocks, sackblock_list);
 115         } else  {
 116                 if (SEQ_GEQ(seq, hint->sblk_start)) {
 117                         /* Search from hint to end of list. */
 118                         cur = hint;
 119                         last = NULL;
 120                         prev = TAILQ_LAST(&scb->sackblocks, sackblock_list);
 121                 } else {
 122                         /* Search from front of list to hint. */
 123                         cur = TAILQ_FIRST(&scb->sackblocks);
 124                         last = hint;
 125                         prev = TAILQ_PREV(hint, sackblock_list, sblk_list);
 126                 }
 127         }
 128
 129         do {
 130                 if (SEQ_GT(cur->sblk_end, seq)) {
 131                         if (SEQ_GEQ(seq, cur->sblk_start)) {
 132                                 *sb = scb->lastfound = cur;
 133                                 return TRUE;
 134                         } else {
 135                                 *sb = scb->lastfound =
 136                                     TAILQ_PREV(cur, sackblock_list, sblk_list);
 137                                 return FALSE;
 138                         }
 139                 }
 140                 cur = TAILQ_NEXT(cur, sblk_list);
 141         } while (cur != last);
 142
 143         *sb = scb->lastfound = prev;
 144         return FALSE;
 145 }
 146
 147 /*
 148  * Allocate a SACK block.
 149  */
 150 static __inline struct sackblock *
 151 alloc_sackblock(struct scoreboard *scb, const struct raw_sackblock *raw_sb)
 152 {
 153         struct sackblock *sb;
 154
 155         if (scb->freecache != NULL) {
 156                 sb = scb->freecache;
 157                 scb->freecache = NULL;
 158                 tcpstat.tcps_sacksbfast++;
 159         } else {
 160                 sb = kmalloc(sizeof(struct sackblock), M_SACKBLOCK, M_NOWAIT);
 161                 if (sb == NULL) {
 162                         tcpstat.tcps_sacksbfailed++;
 163                         return NULL;
 164                 }
 165         }
 166         sb->sblk_start = raw_sb->rblk_start;
 167         sb->sblk_end = raw_sb->rblk_end;
 168         return sb;
 169 }
 170
 171 static __inline struct sackblock *
 172 alloc_sackblock_limit(struct scoreboard *scb,
 173     const struct raw_sackblock *raw_sb)
 174 {
 175         if (scb->nblocks == MAXSAVEDBLOCKS) {
 176                 /*
 177                  * Should try to kick out older blocks XXX JH
 178                  * May be able to coalesce with existing block.
 179                  * Or, go other way and free all blocks if we hit
 180                  * this limit.
 181                  */
 182                 tcpstat.tcps_sacksboverflow++;
 183                 return NULL;
 184         }
 185         return alloc_sackblock(scb, raw_sb);
 186 }
 187
 188 /*
 189  * Free a SACK block.
 190  */
 191 static __inline void
 192 free_sackblock(struct scoreboard *scb, struct sackblock *s)
 193 {
 194         if (scb->freecache == NULL) {
 195                 /* YYY Maybe use the latest freed block? */
 196                 scb->freecache = s;
 197                 return;
 198         }
 199         kfree(s, M_SACKBLOCK);
 200 }
 201
 202 /*
 203  * Free up SACK blocks for data that's been acked.
 204  */
 205 static void
 206 tcp_sack_ack_blocks(struct scoreboard *scb, tcp_seq th_ack)
 207 {
 208         struct sackblock *sb, *nb;
 209
 210         sb = TAILQ_FIRST(&scb->sackblocks);
 211         while (sb && SEQ_LEQ(sb->sblk_end, th_ack)) {
 212                 nb = TAILQ_NEXT(sb, sblk_list);
 213                 if (scb->lastfound == sb)
 214                         scb->lastfound = NULL;
 215                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 216                 free_sackblock(scb, sb);
 217                 --scb->nblocks;
 218                 KASSERT(scb->nblocks >= 0,
 219                     ("SACK block count underflow: %d < 0", scb->nblocks));
 220                 sb = nb;
 221         }
 222         if (sb && SEQ_GT(th_ack, sb->sblk_start))
 223                 sb->sblk_start = th_ack;        /* other side reneged? XXX */
 224 }
 225
 226 /*
 227  * Delete and free SACK blocks saved in scoreboard.
 228  */
 229 void
 230 tcp_sack_cleanup(struct scoreboard *scb)
 231 {
 232         struct sackblock *sb, *nb;
 233
 234         TAILQ_FOREACH_MUTABLE(sb, &scb->sackblocks, sblk_list, nb) {
 235                 free_sackblock(scb, sb);
 236                 --scb->nblocks;
 237         }
 238         KASSERT(scb->nblocks == 0,
 239             ("SACK block %d count not zero", scb->nblocks));
 240         TAILQ_INIT(&scb->sackblocks);
 241         scb->lastfound = NULL;
 242 }
 243
 244 /*
 245  * Delete and free SACK blocks saved in scoreboard.
 246  * Delete the one slot block cache.
 247  */
 248 void
 249 tcp_sack_destroy(struct scoreboard *scb)
 250 {
 251         tcp_sack_cleanup(scb);
 252         if (scb->freecache != NULL) {
 253                 kfree(scb->freecache, M_SACKBLOCK);
 254                 scb->freecache = NULL;
 255         }
 256 }
 257
 258 /*
 259  * Cleanup the reported SACK block information
 260  */
 261 void
 262 tcp_sack_report_cleanup(struct tcpcb *tp)
 263 {
 264         tp->sack_flags &=
 265             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
 266         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
 267 }
 268
 269 /*
 270  * Returns      0 if not D-SACK block,
 271  *              1 if D-SACK,
 272  *              2 if duplicate of out-of-order D-SACK block.
 273  */
 274 int
 275 tcp_sack_ndsack_blocks(struct raw_sackblock *blocks, const int numblocks,
 276                        tcp_seq snd_una)
 277 {
 278         if (numblocks == 0)
 279                 return 0;
 280
 281         if (SEQ_LT(blocks[0].rblk_start, snd_una))
 282                 return 1;
 283
 284         /* block 0 inside block 1 */
 285         if (numblocks > 1 &&
 286             SEQ_GEQ(blocks[0].rblk_start, blocks[1].rblk_start) &&
 287             SEQ_LEQ(blocks[0].rblk_end, blocks[1].rblk_end))
 288                 return 2;
 289
 290         return 0;
 291 }
 292
 293 /*
 294  * Update scoreboard on new incoming ACK.
 295  */
 296 static void
 297 tcp_sack_add_blocks(struct tcpcb *tp, struct tcpopt *to)
 298 {
 299         const int numblocks = to->to_nsackblocks;
 300         struct raw_sackblock *blocks = to->to_sackblocks;
 301         struct scoreboard *scb = &tp->scb;
 302         int startblock, i;
 303
 304         if (tcp_sack_ndsack_blocks(blocks, numblocks, tp->snd_una) > 0)
 305                 startblock = 1;
 306         else
 307                 startblock = 0;
 308
 309         to->to_flags |= TOF_SACK_REDUNDANT;
 310         for (i = startblock; i < numblocks; i++) {
 311                 struct raw_sackblock *newsackblock = &blocks[i];
 312                 boolean_t update;
 313                 int error;
 314
 315                 /* Guard against ACK reordering */
 316                 if (SEQ_LT(newsackblock->rblk_start, tp->snd_una))
 317                         continue;
 318
 319                 /* Don't accept bad SACK blocks */
 320                 if (SEQ_GT(newsackblock->rblk_end, tp->snd_max)) {
 321                         tcpstat.tcps_rcvbadsackopt++;
 322                         break;          /* skip all other blocks */
 323                 }
 324                 tcpstat.tcps_sacksbupdate++;
 325
 326                 error = insert_block(scb, newsackblock, &update);
 327                 if (update)
 328                         to->to_flags &= ~TOF_SACK_REDUNDANT;
 329                 if (error)
 330                         break;
 331         }
 332 }
 333
 334 void
 335 tcp_sack_update_scoreboard(struct tcpcb *tp, struct tcpopt *to)
 336 {
 337         struct scoreboard *scb = &tp->scb;
 338         int rexmt_high_update = 0;
 339
 340         tcp_sack_ack_blocks(scb, tp->snd_una);
 341         tcp_sack_add_blocks(tp, to);
 342         update_lostseq(scb, tp->snd_una, tp->t_maxseg, tp->t_rxtthresh);
 343         if (SEQ_LT(tp->rexmt_high, tp->snd_una)) {
 344                 tp->rexmt_high = tp->snd_una;
 345                 rexmt_high_update = 1;
 346         }
 347         if (tp->sack_flags & TSACK_F_SACKRESCUED) {
 348                 if (SEQ_LT(tp->rexmt_rescue, tp->snd_una)) {
 349                         tp->sack_flags &= ~TSACK_F_SACKRESCUED;
 350                 } else if (tcp_aggressive_rescuesack && rexmt_high_update &&
 351                     SEQ_LT(tp->rexmt_rescue, tp->rexmt_high)) {
 352                         /* Drag RescueRxt along with HighRxt */
 353                         tp->rexmt_rescue = tp->rexmt_high;
 354                 }
 355         }
 356 }
 357
 358 /*
 359  * Insert SACK block into sender's scoreboard.
 360  */
 361 static int
 362 insert_block(struct scoreboard *scb, const struct raw_sackblock *raw_sb,
 363     boolean_t *update)
 364 {
 365         struct sackblock *sb, *workingblock;
 366         boolean_t overlap_front;
 367
 368         *update = TRUE;
 369         if (TAILQ_EMPTY(&scb->sackblocks)) {
 370                 struct sackblock *newblock;
 371
 372                 KASSERT(scb->nblocks == 0, ("emply scb w/ blocks"));
 373
 374                 newblock = alloc_sackblock(scb, raw_sb);
 375                 if (newblock == NULL)
 376                         return ENOMEM;
 377                 TAILQ_INSERT_HEAD(&scb->sackblocks, newblock, sblk_list);
 378                 scb->nblocks = 1;
 379                 return 0;
 380         }
 381
 382         KASSERT(scb->nblocks > 0, ("insert_block() called w/ no blocks"));
 383         KASSERT(scb->nblocks <= MAXSAVEDBLOCKS,
 384             ("too many SACK blocks %d", scb->nblocks));
 385
 386         overlap_front = sack_block_lookup(scb, raw_sb->rblk_start, &sb);
 387
 388         if (sb == NULL) {
 389                 workingblock = alloc_sackblock_limit(scb, raw_sb);
 390                 if (workingblock == NULL)
 391                         return ENOMEM;
 392                 TAILQ_INSERT_HEAD(&scb->sackblocks, workingblock, sblk_list);
 393                 ++scb->nblocks;
 394         } else {
 395                 if (overlap_front || sb->sblk_end == raw_sb->rblk_start) {
 396                         /* Extend old block */
 397                         workingblock = sb;
 398                         if (SEQ_GT(raw_sb->rblk_end, sb->sblk_end))
 399                                 sb->sblk_end = raw_sb->rblk_end;
 400                         else
 401                                 *update = FALSE;
 402                         tcpstat.tcps_sacksbreused++;
 403                 } else {
 404                         workingblock = alloc_sackblock_limit(scb, raw_sb);
 405                         if (workingblock == NULL)
 406                                 return ENOMEM;
 407                         TAILQ_INSERT_AFTER(&scb->sackblocks, sb, workingblock,
 408                             sblk_list);
 409                         ++scb->nblocks;
 410                 }
 411         }
 412
 413         /* Consolidate right-hand side. */
 414         sb = TAILQ_NEXT(workingblock, sblk_list);
 415         while (sb != NULL &&
 416             SEQ_GEQ(workingblock->sblk_end, sb->sblk_end)) {
 417                 struct sackblock *nextblock;
 418
 419                 nextblock = TAILQ_NEXT(sb, sblk_list);
 420                 if (scb->lastfound == sb)
 421                         scb->lastfound = NULL;
 422                 /* Remove completely overlapped block */
 423                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 424                 free_sackblock(scb, sb);
 425                 --scb->nblocks;
 426                 KASSERT(scb->nblocks > 0,
 427                     ("removed overlapped block: %d blocks left", scb->nblocks));
 428                 sb = nextblock;
 429         }
 430         if (sb != NULL &&
 431             SEQ_GEQ(workingblock->sblk_end, sb->sblk_start)) {
 432                 /* Extend new block to cover partially overlapped old block. */
 433                 workingblock->sblk_end = sb->sblk_end;
 434                 if (scb->lastfound == sb)
 435                         scb->lastfound = NULL;
 436                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 437                 free_sackblock(scb, sb);
 438                 --scb->nblocks;
 439                 KASSERT(scb->nblocks > 0,
 440                     ("removed partial right: %d blocks left", scb->nblocks));
 441         }
 442         return 0;
 443 }
 444
 445 #ifdef DEBUG_SACK_BLOCKS
 446 static void
 447 tcp_sack_dump_blocks(struct scoreboard *scb)
 448 {
 449         struct sackblock *sb;
 450
 451         kprintf("%d blocks:", scb->nblocks);
 452         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
 453                 kprintf(" [%u, %u)", sb->sblk_start, sb->sblk_end);
 454         kprintf("\n");
 455 }
 456 #else
 457 static __inline void
 458 tcp_sack_dump_blocks(struct scoreboard *scb)
 459 {
 460 }
 461 #endif
 462
 463 /*
 464  * Optimization to quickly determine which packets are lost.
 465  */
 466 static void
 467 update_lostseq(struct scoreboard *scb, tcp_seq snd_una, u_int maxseg,
 468     int rxtthresh)
 469 {
 470         struct sackblock *sb;
 471         int nsackblocks = 0;
 472         int bytes_sacked = 0;
 473         int rxtthresh_bytes;
 474
 475         /*
 476          * XXX
 477          * The RFC3517bis recommends to reduce the byte threshold.
 478          * However, it will cause extra spurious retransmit if
 479          * segments are reordered.  Before certain DupThresh adaptive
 480          * algorithm is implemented, we don't reduce the byte
 481          * threshold (tcp_rfc3517bis_rxt is off by default).
 482          */
 483         if (tcp_do_rfc3517bis && tcp_rfc3517bis_rxt)
 484                 rxtthresh_bytes = (rxtthresh - 1) * maxseg;
 485         else
 486                 rxtthresh_bytes = rxtthresh * maxseg;
 487
 488         sb = TAILQ_LAST(&scb->sackblocks, sackblock_list);
 489         while (sb != NULL) {
 490                 ++nsackblocks;
 491                 bytes_sacked += sb->sblk_end - sb->sblk_start;
 492                 if (nsackblocks == rxtthresh ||
 493                     bytes_sacked >= rxtthresh_bytes) {
 494                         scb->lostseq = sb->sblk_start;
 495                         return;
 496                 }
 497                 sb = TAILQ_PREV(sb, sackblock_list, sblk_list);
 498         }
 499         scb->lostseq = snd_una;
 500 }
 501
 502 /*
 503  * Return whether the given sequence number is considered lost.
 504  */
 505 boolean_t
 506 tcp_sack_islost(struct scoreboard *scb, tcp_seq seqnum)
 507 {
 508         return SEQ_LT(seqnum, scb->lostseq);
 509 }
 510
 511 /*
 512  * True if at least "amount" has been SACKed.  Used by Early Retransmit.
 513  */
 514 boolean_t
 515 tcp_sack_has_sacked(struct scoreboard *scb, u_int amount)
 516 {
 517         struct sackblock *sb;
 518         int bytes_sacked = 0;
 519
 520         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
 521                 bytes_sacked += sb->sblk_end - sb->sblk_start;
 522                 if (bytes_sacked >= amount)
 523                         return TRUE;
 524         }
 525         return FALSE;
 526 }
 527
 528 /*
 529  * Number of bytes SACKed below seq.
 530  */
 531 int
 532 tcp_sack_bytes_below(struct scoreboard *scb, tcp_seq seq)
 533 {
 534         struct sackblock *sb;
 535         int bytes_sacked = 0;
 536
 537         sb = TAILQ_FIRST(&scb->sackblocks);
 538         while (sb && SEQ_GT(seq, sb->sblk_start)) {
 539                 bytes_sacked += seq_min(seq, sb->sblk_end) - sb->sblk_start;
 540                 sb = TAILQ_NEXT(sb, sblk_list);
 541         }
 542         return bytes_sacked;
 543 }
 544
 545 /*
 546  * Return estimate of the number of bytes outstanding in the network.
 547  */
 548 uint32_t
 549 tcp_sack_compute_pipe(struct tcpcb *tp)
 550 {
 551         struct scoreboard *scb = &tp->scb;
 552         struct sackblock *sb;
 553         int nlost, nretransmitted;
 554         tcp_seq end;
 555
 556         nlost = tp->snd_max - scb->lostseq;
 557         nretransmitted = tp->rexmt_high - tp->snd_una;
 558
 559         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
 560                 if (SEQ_LT(sb->sblk_start, tp->rexmt_high)) {
 561                         end = seq_min(sb->sblk_end, tp->rexmt_high);
 562                         nretransmitted -= end - sb->sblk_start;
 563                 }
 564                 if (SEQ_GEQ(sb->sblk_start, scb->lostseq))
 565                         nlost -= sb->sblk_end - sb->sblk_start;
 566         }
 567
 568         return (nlost + nretransmitted);
 569 }
 570
 571 /*
 572  * Return the sequence number and length of the next segment to transmit
 573  * when in Fast Recovery.
 574  */
 575 boolean_t
 576 tcp_sack_nextseg(struct tcpcb *tp, tcp_seq *nextrexmt, uint32_t *plen,
 577     boolean_t *rescue)
 578 {
 579         struct scoreboard *scb = &tp->scb;
 580         struct socket *so = tp->t_inpcb->inp_socket;
 581         struct sackblock *sb;
 582         const struct sackblock *lastblock =
 583             TAILQ_LAST(&scb->sackblocks, sackblock_list);
 584         tcp_seq torexmt;
 585         long len, off;
 586
 587         /* skip SACKed data */
 588         tcp_sack_skip_sacked(scb, &tp->rexmt_high);
 589
 590         /* Look for lost data. */
 591         torexmt = tp->rexmt_high;
 592         *rescue = FALSE;
 593         if (lastblock != NULL) {
 594                 if (SEQ_LT(torexmt, lastblock->sblk_end) &&
 595                     tcp_sack_islost(scb, torexmt)) {
 596 sendunsacked:
 597                         *nextrexmt = torexmt;
 598                         /* If the left-hand edge has been SACKed, pull it in. */
 599                         if (sack_block_lookup(scb, torexmt + tp->t_maxseg, &sb))
 600                                 *plen = sb->sblk_start - torexmt;
 601                         else
 602                                 *plen = tp->t_maxseg;
 603                         return TRUE;
 604                 }
 605         }
 606
 607         /* See if unsent data available within send window. */
 608         off = tp->snd_max - tp->snd_una;
 609         len = (long) ulmin(so->so_snd.ssb_cc, tp->snd_wnd) - off;
 610         if (len > 0) {
 611                 *nextrexmt = tp->snd_max;       /* Send new data. */
 612                 *plen = tp->t_maxseg;
 613                 return TRUE;
 614         }
 615
 616         /* We're less certain this data has been lost. */
 617         if (lastblock != NULL && SEQ_LT(torexmt, lastblock->sblk_end))
 618                 goto sendunsacked;
 619
 620         /* Rescue retransmission */
 621         if (tcp_do_rescuesack || tcp_do_rfc3517bis) {
 622                 tcpstat.tcps_sackrescue_try++;
 623                 if (tp->sack_flags & TSACK_F_SACKRESCUED) {
 624                         if (!tcp_aggressive_rescuesack)
 625                                 return FALSE;
 626
 627                         /*
 628                          * Aggressive variant of the rescue retransmission.
 629                          *
 630                          * The idea of the rescue retransmission is to sustain
 631                          * the ACK clock thus to avoid timeout retransmission.
 632                          *
 633                          * Under some situations, the conservative approach
 634                          * suggested in the draft
 635                          * http://tools.ietf.org/html/
 636                          * draft-nishida-tcpm-rescue-retransmission-00
 637                          * could not sustain ACK clock, since it only allows
 638                          * one rescue retransmission before a cumulative ACK
 639                          * covers the segement transmitted by rescue
 640                          * retransmission.
 641                          *
 642                          * We try to locate the next unSACKed segment which
 643                          * follows the previously sent rescue segment.  If
 644                          * there is no such segment, we loop back to the first
 645                          * unacknowledged segment.
 646                          */
 647
 648                         /*
 649                          * Skip SACKed data, but here we follow
 650                          * the last transmitted rescue segment.
 651                          */
 652                         torexmt = tp->rexmt_rescue;
 653                         tcp_sack_skip_sacked(scb, &torexmt);
 654                         if (torexmt == tp->snd_max) {
 655                                 /* Nothing left to retransmit; restart */
 656                                 torexmt = tp->snd_una;
 657                         }
 658                 }
 659                 *rescue = TRUE;
 660                 goto sendunsacked;
 661         } else if (tcp_do_smartsack && lastblock == NULL) {
 662                 tcpstat.tcps_sackrescue_try++;
 663                 *rescue = TRUE;
 664                 goto sendunsacked;
 665         }
 666
 667         return FALSE;
 668 }
 669
 670 /*
 671  * Return the next sequence number higher than "*prexmt" that has
 672  * not been SACKed.
 673  */
 674 void
 675 tcp_sack_skip_sacked(struct scoreboard *scb, tcp_seq *prexmt)
 676 {
 677         struct sackblock *sb;
 678
 679         /* skip SACKed data */
 680         if (sack_block_lookup(scb, *prexmt, &sb))
 681                 *prexmt = sb->sblk_end;
 682 }
 683
 684 #ifdef later
 685 void
 686 tcp_sack_save_scoreboard(struct scoreboard *scb)
 687 {
 688         struct scoreboard *scb = &tp->scb;
 689
 690         scb->sackblocks_prev = scb->sackblocks;
 691         TAILQ_INIT(&scb->sackblocks);
 692 }
 693
 694 void
 695 tcp_sack_revert_scoreboard(struct scoreboard *scb, tcp_seq snd_una,
 696                            u_int maxseg)
 697 {
 698         struct sackblock *sb;
 699
 700         scb->sackblocks = scb->sackblocks_prev;
 701         scb->nblocks = 0;
 702         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
 703                 ++scb->nblocks;
 704         tcp_sack_ack_blocks(scb, snd_una);
 705         scb->lastfound = NULL;
 706 }
 707 #endif
 708
 709 #ifdef DEBUG_SACK_HISTORY
 710 static void
 711 tcp_sack_dump_history(char *msg, struct tcpcb *tp)
 712 {
 713         int i;
 714         static int ndumped;
 715
 716         /* only need a couple of these to debug most problems */
 717         if (++ndumped > 900)
 718                 return;
 719
 720         kprintf("%s:\tnsackhistory %d: ", msg, tp->nsackhistory);
 721         for (i = 0; i < tp->nsackhistory; ++i)
 722                 kprintf("[%u, %u) ", tp->sackhistory[i].rblk_start,
 723                     tp->sackhistory[i].rblk_end);
 724         kprintf("\n");
 725 }
 726 #else
 727 static __inline void
 728 tcp_sack_dump_history(char *msg, struct tcpcb *tp)
 729 {
 730 }
 731 #endif
 732
 733 /*
 734  * Remove old SACK blocks from the SACK history that have already been ACKed.
 735  */
 736 static void
 737 tcp_sack_ack_history(struct tcpcb *tp)
 738 {
 739         int i, nblocks, openslot;
 740
 741         tcp_sack_dump_history("before tcp_sack_ack_history", tp);
 742         nblocks = tp->nsackhistory;
 743         for (i = openslot = 0; i < nblocks; ++i) {
 744                 if (SEQ_LEQ(tp->sackhistory[i].rblk_end, tp->rcv_nxt)) {
 745                         --tp->nsackhistory;
 746                         continue;
 747                 }
 748                 if (SEQ_LT(tp->sackhistory[i].rblk_start, tp->rcv_nxt))
 749                         tp->sackhistory[i].rblk_start = tp->rcv_nxt;
 750                 if (i == openslot)
 751                         ++openslot;
 752                 else
 753                         tp->sackhistory[openslot++] = tp->sackhistory[i];
 754         }
 755         tcp_sack_dump_history("after tcp_sack_ack_history", tp);
 756         KASSERT(openslot == tp->nsackhistory,
 757             ("tcp_sack_ack_history miscounted: %d != %d",
 758             openslot, tp->nsackhistory));
 759 }
 760
 761 /*
 762  * Add or merge newblock into reported history.
 763  * Also remove or update SACK blocks that will be acked.
 764  */
 765 static void
 766 tcp_sack_update_reported_history(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 767 {
 768         struct raw_sackblock copy[MAX_SACK_REPORT_BLOCKS];
 769         int i, cindex;
 770
 771         tcp_sack_dump_history("before tcp_sack_update_reported_history", tp);
 772         /*
 773          * Six cases:
 774          *      0) no overlap
 775          *      1) newblock == oldblock
 776          *      2) oldblock contains newblock
 777          *      3) newblock contains oldblock
 778          *      4) tail of oldblock overlaps or abuts start of newblock
 779          *      5) tail of newblock overlaps or abuts head of oldblock
 780          */
 781         for (i = cindex = 0; i < tp->nsackhistory; ++i) {
 782                 struct raw_sackblock *oldblock = &tp->sackhistory[i];
 783                 tcp_seq old_start = oldblock->rblk_start;
 784                 tcp_seq old_end = oldblock->rblk_end;
 785
 786                 if (SEQ_LT(end, old_start) || SEQ_GT(start, old_end)) {
 787                         /* Case 0:  no overlap.  Copy old block. */
 788                         copy[cindex++] = *oldblock;
 789                         continue;
 790                 }
 791
 792                 if (SEQ_GEQ(start, old_start) && SEQ_LEQ(end, old_end)) {
 793                         /* Cases 1 & 2.  Move block to front of history. */
 794                         int j;
 795
 796                         start = old_start;
 797                         end = old_end;
 798                         /* no need to check rest of blocks */
 799                         for (j = i + 1; j < tp->nsackhistory; ++j)
 800                                 copy[cindex++] = tp->sackhistory[j];
 801                         break;
 802                 }
 803
 804                 if (SEQ_GEQ(old_end, start) && SEQ_LT(old_start, start)) {
 805                         /* Case 4:  extend start of new block. */
 806                         start = old_start;
 807                 } else if (SEQ_GEQ(end, old_start) && SEQ_GT(old_end, end)) {
 808                         /* Case 5: extend end of new block */
 809                         end = old_end;
 810                 } else {
 811                         /* Case 3.  Delete old block by not copying it. */
 812                         KASSERT(SEQ_LEQ(start, old_start) &&
 813                                 SEQ_GEQ(end, old_end),
 814                             ("bad logic: old [%u, %u), new [%u, %u)",
 815                              old_start, old_end, start, end));
 816                 }
 817         }
 818
 819         /* insert new block */
 820         tp->sackhistory[0].rblk_start = start;
 821         tp->sackhistory[0].rblk_end = end;
 822         cindex = min(cindex, MAX_SACK_REPORT_BLOCKS - 1);
 823         for (i = 0; i < cindex; ++i)
 824                 tp->sackhistory[i + 1] = copy[i];
 825         tp->nsackhistory = cindex + 1;
 826         tcp_sack_dump_history("after tcp_sack_update_reported_history", tp);
 827 }
 828
 829 /*
 830  * Fill in SACK report to return to data sender.
 831  */
 832 void
 833 tcp_sack_fill_report(struct tcpcb *tp, u_char *opt, u_int *plen)
 834 {
 835         u_int optlen = *plen;
 836         uint32_t *lp = (uint32_t *)(opt + optlen);
 837         uint32_t *olp;
 838         tcp_seq hstart = tp->rcv_nxt, hend;
 839         int nblocks;
 840
 841         KASSERT(TCP_MAXOLEN - optlen >=
 842             TCPOLEN_SACK_ALIGNED + TCPOLEN_SACK_BLOCK,
 843             ("no room for SACK header and one block: optlen %d", optlen));
 844
 845         if (tp->sack_flags & TSACK_F_DUPSEG)
 846                 tcpstat.tcps_snddsackopt++;
 847         else
 848                 tcpstat.tcps_sndsackopt++;
 849
 850         olp = lp++;
 851         optlen += TCPOLEN_SACK_ALIGNED;
 852
 853         tcp_sack_ack_history(tp);
 854         if (tp->reportblk.rblk_start != tp->reportblk.rblk_end) {
 855                 *lp++ = htonl(tp->reportblk.rblk_start);
 856                 *lp++ = htonl(tp->reportblk.rblk_end);
 857                 optlen += TCPOLEN_SACK_BLOCK;
 858                 hstart = tp->reportblk.rblk_start;
 859                 hend = tp->reportblk.rblk_end;
 860                 if (tp->sack_flags & TSACK_F_ENCLOSESEG) {
 861                         KASSERT(TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK,
 862                             ("no room for enclosing SACK block: oplen %d",
 863                             optlen));
 864                         *lp++ = htonl(tp->encloseblk.rblk_start);
 865                         *lp++ = htonl(tp->encloseblk.rblk_end);
 866                         optlen += TCPOLEN_SACK_BLOCK;
 867                         hstart = tp->encloseblk.rblk_start;
 868                         hend = tp->encloseblk.rblk_end;
 869                 }
 870                 if (SEQ_GT(hstart, tp->rcv_nxt))
 871                         tcp_sack_update_reported_history(tp, hstart, hend);
 872         }
 873         if (tcp_do_smartsack && (tp->sack_flags & TSACK_F_SACKLEFT)) {
 874                 /* Fill in from left!  Walk re-assembly queue. */
 875                 struct tseg_qent *q;
 876
 877                 q = LIST_FIRST(&tp->t_segq);
 878                 while (q != NULL &&
 879                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
 880                         *lp++ = htonl(q->tqe_th->th_seq);
 881                         *lp++ = htonl(TCP_SACK_BLKEND(
 882                             q->tqe_th->th_seq + q->tqe_len,
 883                             q->tqe_th->th_flags));
 884                         optlen += TCPOLEN_SACK_BLOCK;
 885                         q = LIST_NEXT(q, tqe_q);
 886                 }
 887         } else {
 888                 int n = 0;
 889
 890                 /* Fill in SACK blocks from right side. */
 891                 while (n < tp->nsackhistory &&
 892                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
 893                         if (tp->sackhistory[n].rblk_start != hstart) {
 894                                 *lp++ = htonl(tp->sackhistory[n].rblk_start);
 895                                 *lp++ = htonl(tp->sackhistory[n].rblk_end);
 896                                 optlen += TCPOLEN_SACK_BLOCK;
 897                         }
 898                         ++n;
 899                 }
 900         }
 901         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
 902         tp->sack_flags &=
 903             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
 904         nblocks = (lp - olp - 1) / 2;
 905         *olp = htonl(TCPOPT_SACK_ALIGNED |
 906                      (TCPOLEN_SACK + nblocks * TCPOLEN_SACK_BLOCK));
 907         *plen = optlen;
 908 }