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
  77 static MALLOC_DEFINE(M_SACKBLOCK, "sblk", "sackblock struct");
  78
  79 /*
  80  * Per-tcpcb initialization.
  81  */
  82 void
  83 tcp_sack_tcpcb_init(struct tcpcb *tp)
  84 {
  85         struct scoreboard *scb = &tp->scb;
  86
  87         scb->nblocks = 0;
  88         TAILQ_INIT(&scb->sackblocks);
  89         scb->lastfound = NULL;
  90 }
  91
  92 /*
  93  * Find the SACK block containing or immediately preceding "seq".
  94  * The boolean result indicates whether the sequence is actually
  95  * contained in the SACK block.
  96  */
  97 static boolean_t
  98 sack_block_lookup(struct scoreboard *scb, tcp_seq seq, struct sackblock **sb)
  99 {
 100         struct sackblock *hint = scb->lastfound;
 101         struct sackblock *cur, *last, *prev;
 102
 103         if (TAILQ_EMPTY(&scb->sackblocks)) {
 104                 *sb = NULL;
 105                 return FALSE;
 106         }
 107
 108         if (hint == NULL) {
 109                 /* No hint.  Search from start to end. */
 110                 cur = TAILQ_FIRST(&scb->sackblocks);
 111                 last = NULL;
 112                 prev = TAILQ_LAST(&scb->sackblocks, sackblock_list);
 113         } else  {
 114                 if (SEQ_GEQ(seq, hint->sblk_start)) {
 115                         /* Search from hint to end of list. */
 116                         cur = hint;
 117                         last = NULL;
 118                         prev = TAILQ_LAST(&scb->sackblocks, sackblock_list);
 119                 } else {
 120                         /* Search from front of list to hint. */
 121                         cur = TAILQ_FIRST(&scb->sackblocks);
 122                         last = hint;
 123                         prev = TAILQ_PREV(hint, sackblock_list, sblk_list);
 124                 }
 125         }
 126
 127         do {
 128                 if (SEQ_GT(cur->sblk_end, seq)) {
 129                         if (SEQ_GEQ(seq, cur->sblk_start)) {
 130                                 *sb = scb->lastfound = cur;
 131                                 return TRUE;
 132                         } else {
 133                                 *sb = scb->lastfound =
 134                                     TAILQ_PREV(cur, sackblock_list, sblk_list);
 135                                 return FALSE;
 136                         }
 137                 }
 138                 cur = TAILQ_NEXT(cur, sblk_list);
 139         } while (cur != last);
 140
 141         *sb = scb->lastfound = prev;
 142         return FALSE;
 143 }
 144
 145 /*
 146  * Allocate a SACK block.
 147  */
 148 static __inline struct sackblock *
 149 alloc_sackblock(struct scoreboard *scb, const struct raw_sackblock *raw_sb)
 150 {
 151         struct sackblock *sb;
 152
 153         if (scb->freecache != NULL) {
 154                 sb = scb->freecache;
 155                 scb->freecache = NULL;
 156                 tcpstat.tcps_sacksbfast++;
 157         } else {
 158                 sb = kmalloc(sizeof(struct sackblock), M_SACKBLOCK, M_NOWAIT);
 159                 if (sb == NULL) {
 160                         tcpstat.tcps_sacksbfailed++;
 161                         return NULL;
 162                 }
 163         }
 164         sb->sblk_start = raw_sb->rblk_start;
 165         sb->sblk_end = raw_sb->rblk_end;
 166         return sb;
 167 }
 168
 169 static __inline struct sackblock *
 170 alloc_sackblock_limit(struct scoreboard *scb,
 171     const struct raw_sackblock *raw_sb)
 172 {
 173         if (scb->nblocks == MAXSAVEDBLOCKS) {
 174                 /*
 175                  * Should try to kick out older blocks XXX JH
 176                  * May be able to coalesce with existing block.
 177                  * Or, go other way and free all blocks if we hit
 178                  * this limit.
 179                  */
 180                 tcpstat.tcps_sacksboverflow++;
 181                 return NULL;
 182         }
 183         return alloc_sackblock(scb, raw_sb);
 184 }
 185
 186 /*
 187  * Free a SACK block.
 188  */
 189 static __inline void
 190 free_sackblock(struct scoreboard *scb, struct sackblock *s)
 191 {
 192         if (scb->freecache == NULL) {
 193                 /* YYY Maybe use the latest freed block? */
 194                 scb->freecache = s;
 195                 return;
 196         }
 197         kfree(s, M_SACKBLOCK);
 198 }
 199
 200 /*
 201  * Free up SACK blocks for data that's been acked.
 202  */
 203 static void
 204 tcp_sack_ack_blocks(struct scoreboard *scb, tcp_seq th_ack)
 205 {
 206         struct sackblock *sb, *nb;
 207
 208         sb = TAILQ_FIRST(&scb->sackblocks);
 209         while (sb && SEQ_LEQ(sb->sblk_end, th_ack)) {
 210                 nb = TAILQ_NEXT(sb, sblk_list);
 211                 if (scb->lastfound == sb)
 212                         scb->lastfound = NULL;
 213                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 214                 free_sackblock(scb, sb);
 215                 --scb->nblocks;
 216                 KASSERT(scb->nblocks >= 0,
 217                     ("SACK block count underflow: %d < 0", scb->nblocks));
 218                 sb = nb;
 219         }
 220         if (sb && SEQ_GT(th_ack, sb->sblk_start))
 221                 sb->sblk_start = th_ack;        /* other side reneged? XXX */
 222 }
 223
 224 /*
 225  * Delete and free SACK blocks saved in scoreboard.
 226  */
 227 void
 228 tcp_sack_cleanup(struct scoreboard *scb)
 229 {
 230         struct sackblock *sb, *nb;
 231
 232         TAILQ_FOREACH_MUTABLE(sb, &scb->sackblocks, sblk_list, nb) {
 233                 free_sackblock(scb, sb);
 234                 --scb->nblocks;
 235         }
 236         KASSERT(scb->nblocks == 0,
 237             ("SACK block %d count not zero", scb->nblocks));
 238         TAILQ_INIT(&scb->sackblocks);
 239         scb->lastfound = NULL;
 240 }
 241
 242 /*
 243  * Delete and free SACK blocks saved in scoreboard.
 244  * Delete the one slot block cache.
 245  */
 246 void
 247 tcp_sack_destroy(struct scoreboard *scb)
 248 {
 249         tcp_sack_cleanup(scb);
 250         if (scb->freecache != NULL) {
 251                 kfree(scb->freecache, M_SACKBLOCK);
 252                 scb->freecache = NULL;
 253         }
 254 }
 255
 256 /*
 257  * Cleanup the reported SACK block information
 258  */
 259 void
 260 tcp_sack_report_cleanup(struct tcpcb *tp)
 261 {
 262         tp->sack_flags &=
 263             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
 264         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
 265 }
 266
 267 /*
 268  * Returns      0 if not D-SACK block,
 269  *              1 if D-SACK,
 270  *              2 if duplicate of out-of-order D-SACK block.
 271  */
 272 int
 273 tcp_sack_ndsack_blocks(struct raw_sackblock *blocks, const int numblocks,
 274                        tcp_seq snd_una)
 275 {
 276         if (numblocks == 0)
 277                 return 0;
 278
 279         if (SEQ_LT(blocks[0].rblk_start, snd_una))
 280                 return 1;
 281
 282         /* block 0 inside block 1 */
 283         if (numblocks > 1 &&
 284             SEQ_GEQ(blocks[0].rblk_start, blocks[1].rblk_start) &&
 285             SEQ_LEQ(blocks[0].rblk_end, blocks[1].rblk_end))
 286                 return 2;
 287
 288         return 0;
 289 }
 290
 291 /*
 292  * Update scoreboard on new incoming ACK.
 293  */
 294 static void
 295 tcp_sack_add_blocks(struct tcpcb *tp, struct tcpopt *to)
 296 {
 297         const int numblocks = to->to_nsackblocks;
 298         struct raw_sackblock *blocks = to->to_sackblocks;
 299         struct scoreboard *scb = &tp->scb;
 300         int startblock, i;
 301
 302         if (tcp_sack_ndsack_blocks(blocks, numblocks, tp->snd_una) > 0)
 303                 startblock = 1;
 304         else
 305                 startblock = 0;
 306
 307         to->to_flags |= TOF_SACK_REDUNDANT;
 308         for (i = startblock; i < numblocks; i++) {
 309                 struct raw_sackblock *newsackblock = &blocks[i];
 310                 boolean_t update;
 311                 int error;
 312
 313                 /* Guard against ACK reordering */
 314                 if (SEQ_LT(newsackblock->rblk_start, tp->snd_una))
 315                         continue;
 316
 317                 /* Don't accept bad SACK blocks */
 318                 if (SEQ_GT(newsackblock->rblk_end, tp->snd_max)) {
 319                         tcpstat.tcps_rcvbadsackopt++;
 320                         break;          /* skip all other blocks */
 321                 }
 322                 tcpstat.tcps_sacksbupdate++;
 323
 324                 error = insert_block(scb, newsackblock, &update);
 325                 if (update)
 326                         to->to_flags &= ~TOF_SACK_REDUNDANT;
 327                 if (error)
 328                         break;
 329         }
 330 }
 331
 332 void
 333 tcp_sack_update_scoreboard(struct tcpcb *tp, struct tcpopt *to)
 334 {
 335         struct scoreboard *scb = &tp->scb;
 336         int rexmt_high_update = 0;
 337
 338         tcp_sack_ack_blocks(scb, tp->snd_una);
 339         tcp_sack_add_blocks(tp, to);
 340         tcp_sack_update_lostseq(scb, tp->snd_una, tp->t_maxseg,
 341             tp->t_rxtthresh);
 342         if (SEQ_LT(tp->rexmt_high, tp->snd_una)) {
 343                 tp->rexmt_high = tp->snd_una;
 344                 rexmt_high_update = 1;
 345         }
 346         if (tp->sack_flags & TSACK_F_SACKRESCUED) {
 347                 if (SEQ_LT(tp->rexmt_rescue, tp->snd_una)) {
 348                         tp->sack_flags &= ~TSACK_F_SACKRESCUED;
 349                 } else if (tcp_aggressive_rescuesack && rexmt_high_update &&
 350                     SEQ_LT(tp->rexmt_rescue, tp->rexmt_high)) {
 351                         /* Drag RescueRxt along with HighRxt */
 352                         tp->rexmt_rescue = tp->rexmt_high;
 353                 }
 354         }
 355 }
 356
 357 /*
 358  * Insert SACK block into sender's scoreboard.
 359  */
 360 static int
 361 insert_block(struct scoreboard *scb, const struct raw_sackblock *raw_sb,
 362     boolean_t *update)
 363 {
 364         struct sackblock *sb, *workingblock;
 365         boolean_t overlap_front;
 366
 367         *update = TRUE;
 368         if (TAILQ_EMPTY(&scb->sackblocks)) {
 369                 struct sackblock *newblock;
 370
 371                 KASSERT(scb->nblocks == 0, ("emply scb w/ blocks"));
 372
 373                 newblock = alloc_sackblock(scb, raw_sb);
 374                 if (newblock == NULL)
 375                         return ENOMEM;
 376                 TAILQ_INSERT_HEAD(&scb->sackblocks, newblock, sblk_list);
 377                 scb->nblocks = 1;
 378                 return 0;
 379         }
 380
 381         KASSERT(scb->nblocks > 0, ("insert_block() called w/ no blocks"));
 382         KASSERT(scb->nblocks <= MAXSAVEDBLOCKS,
 383             ("too many SACK blocks %d", scb->nblocks));
 384
 385         overlap_front = sack_block_lookup(scb, raw_sb->rblk_start, &sb);
 386
 387         if (sb == NULL) {
 388                 workingblock = alloc_sackblock_limit(scb, raw_sb);
 389                 if (workingblock == NULL)
 390                         return ENOMEM;
 391                 TAILQ_INSERT_HEAD(&scb->sackblocks, workingblock, sblk_list);
 392                 ++scb->nblocks;
 393         } else {
 394                 if (overlap_front || sb->sblk_end == raw_sb->rblk_start) {
 395                         tcpstat.tcps_sacksbreused++;
 396
 397                         /* Extend old block */
 398                         workingblock = sb;
 399                         if (SEQ_GT(raw_sb->rblk_end, sb->sblk_end)) {
 400                                 sb->sblk_end = raw_sb->rblk_end;
 401                         } else {
 402                                 /* Exact match, nothing to consolidate */
 403                                 *update = FALSE;
 404                                 return 0;
 405                         }
 406                 } else {
 407                         workingblock = alloc_sackblock_limit(scb, raw_sb);
 408                         if (workingblock == NULL)
 409                                 return ENOMEM;
 410                         TAILQ_INSERT_AFTER(&scb->sackblocks, sb, workingblock,
 411                             sblk_list);
 412                         ++scb->nblocks;
 413                 }
 414         }
 415
 416         /* Consolidate right-hand side. */
 417         sb = TAILQ_NEXT(workingblock, sblk_list);
 418         while (sb != NULL &&
 419             SEQ_GEQ(workingblock->sblk_end, sb->sblk_end)) {
 420                 struct sackblock *nextblock;
 421
 422                 nextblock = TAILQ_NEXT(sb, sblk_list);
 423                 if (scb->lastfound == sb)
 424                         scb->lastfound = NULL;
 425                 /* Remove completely overlapped block */
 426                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 427                 free_sackblock(scb, sb);
 428                 --scb->nblocks;
 429                 KASSERT(scb->nblocks > 0,
 430                     ("removed overlapped block: %d blocks left", scb->nblocks));
 431                 sb = nextblock;
 432         }
 433         if (sb != NULL &&
 434             SEQ_GEQ(workingblock->sblk_end, sb->sblk_start)) {
 435                 /* Extend new block to cover partially overlapped old block. */
 436                 workingblock->sblk_end = sb->sblk_end;
 437                 if (scb->lastfound == sb)
 438                         scb->lastfound = NULL;
 439                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 440                 free_sackblock(scb, sb);
 441                 --scb->nblocks;
 442                 KASSERT(scb->nblocks > 0,
 443                     ("removed partial right: %d blocks left", scb->nblocks));
 444         }
 445         return 0;
 446 }
 447
 448 #ifdef DEBUG_SACK_BLOCKS
 449 static void
 450 tcp_sack_dump_blocks(struct scoreboard *scb)
 451 {
 452         struct sackblock *sb;
 453
 454         kprintf("%d blocks:", scb->nblocks);
 455         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
 456                 kprintf(" [%u, %u)", sb->sblk_start, sb->sblk_end);
 457         kprintf("\n");
 458 }
 459 #else
 460 static __inline void
 461 tcp_sack_dump_blocks(struct scoreboard *scb)
 462 {
 463 }
 464 #endif
 465
 466 /*
 467  * Optimization to quickly determine which packets are lost.
 468  */
 469 void
 470 tcp_sack_update_lostseq(struct scoreboard *scb, tcp_seq snd_una, u_int maxseg,
 471     int rxtthresh)
 472 {
 473         struct sackblock *sb;
 474         int nsackblocks = 0;
 475         int bytes_sacked = 0;
 476         int rxtthresh_bytes;
 477
 478         /*
 479          * XXX
 480          * The RFC3517bis recommends to reduce the byte threshold.
 481          * However, it will cause extra spurious retransmit if
 482          * segments are reordered.  Before certain DupThresh adaptive
 483          * algorithm is implemented, we don't reduce the byte
 484          * threshold (tcp_rfc3517bis_rxt is off by default).
 485          */
 486         if (tcp_do_rfc3517bis && tcp_rfc3517bis_rxt)
 487                 rxtthresh_bytes = (rxtthresh - 1) * maxseg;
 488         else
 489                 rxtthresh_bytes = rxtthresh * maxseg;
 490
 491         sb = TAILQ_LAST(&scb->sackblocks, sackblock_list);
 492         while (sb != NULL) {
 493                 ++nsackblocks;
 494                 bytes_sacked += sb->sblk_end - sb->sblk_start;
 495                 if (nsackblocks == rxtthresh ||
 496                     bytes_sacked >= rxtthresh_bytes) {
 497                         scb->lostseq = sb->sblk_start;
 498                         return;
 499                 }
 500                 sb = TAILQ_PREV(sb, sackblock_list, sblk_list);
 501         }
 502         scb->lostseq = snd_una;
 503 }
 504
 505 /*
 506  * Return whether the given sequence number is considered lost.
 507  */
 508 boolean_t
 509 tcp_sack_islost(struct scoreboard *scb, tcp_seq seqnum)
 510 {
 511         return SEQ_LT(seqnum, scb->lostseq);
 512 }
 513
 514 /*
 515  * True if at least "amount" has been SACKed.  Used by Early Retransmit.
 516  */
 517 boolean_t
 518 tcp_sack_has_sacked(struct scoreboard *scb, u_int amount)
 519 {
 520         struct sackblock *sb;
 521         int bytes_sacked = 0;
 522
 523         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
 524                 bytes_sacked += sb->sblk_end - sb->sblk_start;
 525                 if (bytes_sacked >= amount)
 526                         return TRUE;
 527         }
 528         return FALSE;
 529 }
 530
 531 /*
 532  * Number of bytes SACKed below seq.
 533  */
 534 int
 535 tcp_sack_bytes_below(struct scoreboard *scb, tcp_seq seq)
 536 {
 537         struct sackblock *sb;
 538         int bytes_sacked = 0;
 539
 540         sb = TAILQ_FIRST(&scb->sackblocks);
 541         while (sb && SEQ_GT(seq, sb->sblk_start)) {
 542                 bytes_sacked += seq_min(seq, sb->sblk_end) - sb->sblk_start;
 543                 sb = TAILQ_NEXT(sb, sblk_list);
 544         }
 545         return bytes_sacked;
 546 }
 547
 548 /*
 549  * Return estimate of the number of bytes outstanding in the network.
 550  */
 551 uint32_t
 552 tcp_sack_compute_pipe(struct tcpcb *tp)
 553 {
 554         struct scoreboard *scb = &tp->scb;
 555         struct sackblock *sb;
 556         int nlost, nretransmitted;
 557         tcp_seq end;
 558
 559         nlost = tp->snd_max - scb->lostseq;
 560         nretransmitted = tp->rexmt_high - tp->snd_una;
 561
 562         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
 563                 if (SEQ_LT(sb->sblk_start, tp->rexmt_high)) {
 564                         end = seq_min(sb->sblk_end, tp->rexmt_high);
 565                         nretransmitted -= end - sb->sblk_start;
 566                 }
 567                 if (SEQ_GEQ(sb->sblk_start, scb->lostseq))
 568                         nlost -= sb->sblk_end - sb->sblk_start;
 569         }
 570
 571         return (nlost + nretransmitted);
 572 }
 573
 574 /*
 575  * Return the sequence number and length of the next segment to transmit
 576  * when in Fast Recovery.
 577  */
 578 boolean_t
 579 tcp_sack_nextseg(struct tcpcb *tp, tcp_seq *nextrexmt, uint32_t *plen,
 580     boolean_t *rescue)
 581 {
 582         struct scoreboard *scb = &tp->scb;
 583         struct socket *so = tp->t_inpcb->inp_socket;
 584         struct sackblock *sb;
 585         const struct sackblock *lastblock =
 586             TAILQ_LAST(&scb->sackblocks, sackblock_list);
 587         tcp_seq torexmt;
 588         long len, off;
 589
 590         /* skip SACKed data */
 591         tcp_sack_skip_sacked(scb, &tp->rexmt_high);
 592
 593         /* Look for lost data. */
 594         torexmt = tp->rexmt_high;
 595         *rescue = FALSE;
 596         if (lastblock != NULL) {
 597                 if (SEQ_LT(torexmt, lastblock->sblk_end) &&
 598                     tcp_sack_islost(scb, torexmt)) {
 599 sendunsacked:
 600                         *nextrexmt = torexmt;
 601                         /* If the left-hand edge has been SACKed, pull it in. */
 602                         if (sack_block_lookup(scb, torexmt + tp->t_maxseg, &sb))
 603                                 *plen = sb->sblk_start - torexmt;
 604                         else
 605                                 *plen = tp->t_maxseg;
 606                         return TRUE;
 607                 }
 608         }
 609
 610         /* See if unsent data available within send window. */
 611         off = tp->snd_max - tp->snd_una;
 612         len = (long) ulmin(so->so_snd.ssb_cc, tp->snd_wnd) - off;
 613         if (len > 0) {
 614                 *nextrexmt = tp->snd_max;       /* Send new data. */
 615                 *plen = tp->t_maxseg;
 616                 return TRUE;
 617         }
 618
 619         /* We're less certain this data has been lost. */
 620         if (lastblock != NULL && SEQ_LT(torexmt, lastblock->sblk_end))
 621                 goto sendunsacked;
 622
 623         /* Rescue retransmission */
 624         if (tcp_do_rescuesack || tcp_do_rfc3517bis) {
 625                 tcpstat.tcps_sackrescue_try++;
 626                 if (tp->sack_flags & TSACK_F_SACKRESCUED) {
 627                         if (!tcp_aggressive_rescuesack)
 628                                 return FALSE;
 629
 630                         /*
 631                          * Aggressive variant of the rescue retransmission.
 632                          *
 633                          * The idea of the rescue retransmission is to sustain
 634                          * the ACK clock thus to avoid timeout retransmission.
 635                          *
 636                          * Under some situations, the conservative approach
 637                          * suggested in the draft
 638                          * http://tools.ietf.org/html/
 639                          * draft-nishida-tcpm-rescue-retransmission-00
 640                          * could not sustain ACK clock, since it only allows
 641                          * one rescue retransmission before a cumulative ACK
 642                          * covers the segement transmitted by rescue
 643                          * retransmission.
 644                          *
 645                          * We try to locate the next unSACKed segment which
 646                          * follows the previously sent rescue segment.  If
 647                          * there is no such segment, we loop back to the first
 648                          * unacknowledged segment.
 649                          */
 650
 651                         /*
 652                          * Skip SACKed data, but here we follow
 653                          * the last transmitted rescue segment.
 654                          */
 655                         torexmt = tp->rexmt_rescue;
 656                         tcp_sack_skip_sacked(scb, &torexmt);
 657                 }
 658                 if (torexmt == tp->snd_max) {
 659                         /* Nothing left to retransmit; restart */
 660                         torexmt = tp->snd_una;
 661                 }
 662                 *rescue = TRUE;
 663                 goto sendunsacked;
 664         } else if (tcp_do_smartsack && lastblock == NULL) {
 665                 tcpstat.tcps_sackrescue_try++;
 666                 *rescue = TRUE;
 667                 goto sendunsacked;
 668         }
 669
 670         return FALSE;
 671 }
 672
 673 /*
 674  * Return the next sequence number higher than "*prexmt" that has
 675  * not been SACKed.
 676  */
 677 void
 678 tcp_sack_skip_sacked(struct scoreboard *scb, tcp_seq *prexmt)
 679 {
 680         struct sackblock *sb;
 681
 682         /* skip SACKed data */
 683         if (sack_block_lookup(scb, *prexmt, &sb))
 684                 *prexmt = sb->sblk_end;
 685 }
 686
 687 #ifdef later
 688 void
 689 tcp_sack_save_scoreboard(struct scoreboard *scb)
 690 {
 691         struct scoreboard *scb = &tp->scb;
 692
 693         scb->sackblocks_prev = scb->sackblocks;
 694         TAILQ_INIT(&scb->sackblocks);
 695 }
 696
 697 void
 698 tcp_sack_revert_scoreboard(struct scoreboard *scb, tcp_seq snd_una,
 699                            u_int maxseg)
 700 {
 701         struct sackblock *sb;
 702
 703         scb->sackblocks = scb->sackblocks_prev;
 704         scb->nblocks = 0;
 705         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
 706                 ++scb->nblocks;
 707         tcp_sack_ack_blocks(scb, snd_una);
 708         scb->lastfound = NULL;
 709 }
 710 #endif
 711
 712 #ifdef DEBUG_SACK_HISTORY
 713 static void
 714 tcp_sack_dump_history(char *msg, struct tcpcb *tp)
 715 {
 716         int i;
 717         static int ndumped;
 718
 719         /* only need a couple of these to debug most problems */
 720         if (++ndumped > 900)
 721                 return;
 722
 723         kprintf("%s:\tnsackhistory %d: ", msg, tp->nsackhistory);
 724         for (i = 0; i < tp->nsackhistory; ++i)
 725                 kprintf("[%u, %u) ", tp->sackhistory[i].rblk_start,
 726                     tp->sackhistory[i].rblk_end);
 727         kprintf("\n");
 728 }
 729 #else
 730 static __inline void
 731 tcp_sack_dump_history(char *msg, struct tcpcb *tp)
 732 {
 733 }
 734 #endif
 735
 736 /*
 737  * Remove old SACK blocks from the SACK history that have already been ACKed.
 738  */
 739 static void
 740 tcp_sack_ack_history(struct tcpcb *tp)
 741 {
 742         int i, nblocks, openslot;
 743
 744         tcp_sack_dump_history("before tcp_sack_ack_history", tp);
 745         nblocks = tp->nsackhistory;
 746         for (i = openslot = 0; i < nblocks; ++i) {
 747                 if (SEQ_LEQ(tp->sackhistory[i].rblk_end, tp->rcv_nxt)) {
 748                         --tp->nsackhistory;
 749                         continue;
 750                 }
 751                 if (SEQ_LT(tp->sackhistory[i].rblk_start, tp->rcv_nxt))
 752                         tp->sackhistory[i].rblk_start = tp->rcv_nxt;
 753                 if (i == openslot)
 754                         ++openslot;
 755                 else
 756                         tp->sackhistory[openslot++] = tp->sackhistory[i];
 757         }
 758         tcp_sack_dump_history("after tcp_sack_ack_history", tp);
 759         KASSERT(openslot == tp->nsackhistory,
 760             ("tcp_sack_ack_history miscounted: %d != %d",
 761             openslot, tp->nsackhistory));
 762 }
 763
 764 /*
 765  * Add or merge newblock into reported history.
 766  * Also remove or update SACK blocks that will be acked.
 767  */
 768 static void
 769 tcp_sack_update_reported_history(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 770 {
 771         struct raw_sackblock copy[MAX_SACK_REPORT_BLOCKS];
 772         int i, cindex;
 773
 774         tcp_sack_dump_history("before tcp_sack_update_reported_history", tp);
 775         /*
 776          * Six cases:
 777          *      0) no overlap
 778          *      1) newblock == oldblock
 779          *      2) oldblock contains newblock
 780          *      3) newblock contains oldblock
 781          *      4) tail of oldblock overlaps or abuts start of newblock
 782          *      5) tail of newblock overlaps or abuts head of oldblock
 783          */
 784         for (i = cindex = 0; i < tp->nsackhistory; ++i) {
 785                 struct raw_sackblock *oldblock = &tp->sackhistory[i];
 786                 tcp_seq old_start = oldblock->rblk_start;
 787                 tcp_seq old_end = oldblock->rblk_end;
 788
 789                 if (SEQ_LT(end, old_start) || SEQ_GT(start, old_end)) {
 790                         /* Case 0:  no overlap.  Copy old block. */
 791                         copy[cindex++] = *oldblock;
 792                         continue;
 793                 }
 794
 795                 if (SEQ_GEQ(start, old_start) && SEQ_LEQ(end, old_end)) {
 796                         /* Cases 1 & 2.  Move block to front of history. */
 797                         int j;
 798
 799                         start = old_start;
 800                         end = old_end;
 801                         /* no need to check rest of blocks */
 802                         for (j = i + 1; j < tp->nsackhistory; ++j)
 803                                 copy[cindex++] = tp->sackhistory[j];
 804                         break;
 805                 }
 806
 807                 if (SEQ_GEQ(old_end, start) && SEQ_LT(old_start, start)) {
 808                         /* Case 4:  extend start of new block. */
 809                         start = old_start;
 810                 } else if (SEQ_GEQ(end, old_start) && SEQ_GT(old_end, end)) {
 811                         /* Case 5: extend end of new block */
 812                         end = old_end;
 813                 } else {
 814                         /* Case 3.  Delete old block by not copying it. */
 815                         KASSERT(SEQ_LEQ(start, old_start) &&
 816                                 SEQ_GEQ(end, old_end),
 817                             ("bad logic: old [%u, %u), new [%u, %u)",
 818                              old_start, old_end, start, end));
 819                 }
 820         }
 821
 822         /* insert new block */
 823         tp->sackhistory[0].rblk_start = start;
 824         tp->sackhistory[0].rblk_end = end;
 825         cindex = min(cindex, MAX_SACK_REPORT_BLOCKS - 1);
 826         for (i = 0; i < cindex; ++i)
 827                 tp->sackhistory[i + 1] = copy[i];
 828         tp->nsackhistory = cindex + 1;
 829         tcp_sack_dump_history("after tcp_sack_update_reported_history", tp);
 830 }
 831
 832 /*
 833  * Fill in SACK report to return to data sender.
 834  */
 835 void
 836 tcp_sack_fill_report(struct tcpcb *tp, u_char *opt, u_int *plen)
 837 {
 838         u_int optlen = *plen;
 839         uint32_t *lp = (uint32_t *)(opt + optlen);
 840         uint32_t *olp;
 841         tcp_seq hstart = tp->rcv_nxt, hend;
 842         int nblocks;
 843
 844         KASSERT(TCP_MAXOLEN - optlen >=
 845             TCPOLEN_SACK_ALIGNED + TCPOLEN_SACK_BLOCK,
 846             ("no room for SACK header and one block: optlen %d", optlen));
 847
 848         if (tp->sack_flags & TSACK_F_DUPSEG)
 849                 tcpstat.tcps_snddsackopt++;
 850         else
 851                 tcpstat.tcps_sndsackopt++;
 852
 853         olp = lp++;
 854         optlen += TCPOLEN_SACK_ALIGNED;
 855
 856         tcp_sack_ack_history(tp);
 857         if (tp->reportblk.rblk_start != tp->reportblk.rblk_end) {
 858                 *lp++ = htonl(tp->reportblk.rblk_start);
 859                 *lp++ = htonl(tp->reportblk.rblk_end);
 860                 optlen += TCPOLEN_SACK_BLOCK;
 861                 hstart = tp->reportblk.rblk_start;
 862                 hend = tp->reportblk.rblk_end;
 863                 if (tp->sack_flags & TSACK_F_ENCLOSESEG) {
 864                         KASSERT(TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK,
 865                             ("no room for enclosing SACK block: oplen %d",
 866                             optlen));
 867                         *lp++ = htonl(tp->encloseblk.rblk_start);
 868                         *lp++ = htonl(tp->encloseblk.rblk_end);
 869                         optlen += TCPOLEN_SACK_BLOCK;
 870                         hstart = tp->encloseblk.rblk_start;
 871                         hend = tp->encloseblk.rblk_end;
 872                 }
 873                 if (SEQ_GT(hstart, tp->rcv_nxt))
 874                         tcp_sack_update_reported_history(tp, hstart, hend);
 875         }
 876         if (tcp_do_smartsack && (tp->sack_flags & TSACK_F_SACKLEFT)) {
 877                 /* Fill in from left!  Walk re-assembly queue. */
 878                 struct tseg_qent *q;
 879
 880                 q = TAILQ_FIRST(&tp->t_segq);
 881                 while (q != NULL &&
 882                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
 883                         *lp++ = htonl(q->tqe_th->th_seq);
 884                         *lp++ = htonl(TCP_SACK_BLKEND(
 885                             q->tqe_th->th_seq + q->tqe_len,
 886                             q->tqe_th->th_flags));
 887                         optlen += TCPOLEN_SACK_BLOCK;
 888                         q = TAILQ_NEXT(q, tqe_q);
 889                 }
 890         } else {
 891                 int n = 0;
 892
 893                 /* Fill in SACK blocks from right side. */
 894                 while (n < tp->nsackhistory &&
 895                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
 896                         if (tp->sackhistory[n].rblk_start != hstart) {
 897                                 *lp++ = htonl(tp->sackhistory[n].rblk_start);
 898                                 *lp++ = htonl(tp->sackhistory[n].rblk_end);
 899                                 optlen += TCPOLEN_SACK_BLOCK;
 900                         }
 901                         ++n;
 902                 }
 903         }
 904         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
 905         tp->sack_flags &=
 906             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
 907         nblocks = (lp - olp - 1) / 2;
 908         *olp = htonl(TCPOPT_SACK_ALIGNED |
 909                      (TCPOLEN_SACK + nblocks * TCPOLEN_SACK_BLOCK));
 910         *plen = optlen;
 911 }