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 tcpcb *tp, tcp_seq th_ack)
 205 {
 206         struct scoreboard *scb = &tp->scb;
 207         struct sackblock *sb, *nb;
 208
 209         sb = TAILQ_FIRST(&scb->sackblocks);
 210         while (sb && SEQ_LEQ(sb->sblk_end, th_ack)) {
 211                 nb = TAILQ_NEXT(sb, sblk_list);
 212                 if (scb->lastfound == sb)
 213                         scb->lastfound = NULL;
 214                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 215                 free_sackblock(scb, sb);
 216                 --scb->nblocks;
 217                 KASSERT(scb->nblocks >= 0,
 218                     ("SACK block count underflow: %d < 0", scb->nblocks));
 219                 sb = nb;
 220         }
 221         if (sb && SEQ_GEQ(th_ack, sb->sblk_start)) {
 222                 /* Other side reneged? XXX */
 223                 tcpstat.tcps_sackrenege++;
 224                 tcp_sack_discard(tp);
 225         }
 226 }
 227
 228 /*
 229  * Delete and free SACK blocks saved in scoreboard.
 230  */
 231 static void
 232 tcp_sack_cleanup(struct scoreboard *scb)
 233 {
 234         struct sackblock *sb, *nb;
 235
 236         TAILQ_FOREACH_MUTABLE(sb, &scb->sackblocks, sblk_list, nb) {
 237                 free_sackblock(scb, sb);
 238                 --scb->nblocks;
 239         }
 240         KASSERT(scb->nblocks == 0,
 241             ("SACK block %d count not zero", scb->nblocks));
 242         TAILQ_INIT(&scb->sackblocks);
 243         scb->lastfound = NULL;
 244 }
 245
 246 /*
 247  * Discard SACK scoreboard, HighRxt, RescueRxt and LostSeq.
 248  */
 249 void
 250 tcp_sack_discard(struct tcpcb *tp)
 251 {
 252         tcp_sack_cleanup(&tp->scb);
 253         tp->rexmt_high = tp->snd_una;
 254         tp->sack_flags &= ~TSACK_F_SACKRESCUED;
 255         tp->scb.lostseq = tp->snd_una;
 256 }
 257
 258 /*
 259  * Delete and free SACK blocks saved in scoreboard.
 260  * Delete the one slot block cache.
 261  */
 262 void
 263 tcp_sack_destroy(struct scoreboard *scb)
 264 {
 265         tcp_sack_cleanup(scb);
 266         if (scb->freecache != NULL) {
 267                 kfree(scb->freecache, M_SACKBLOCK);
 268                 scb->freecache = NULL;
 269         }
 270 }
 271
 272 /*
 273  * Cleanup the reported SACK block information
 274  */
 275 void
 276 tcp_sack_report_cleanup(struct tcpcb *tp)
 277 {
 278         tp->sack_flags &=
 279             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
 280         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
 281 }
 282
 283 /*
 284  * Returns      0 if not D-SACK block,
 285  *              1 if D-SACK,
 286  *              2 if duplicate of out-of-order D-SACK block.
 287  */
 288 int
 289 tcp_sack_ndsack_blocks(const struct raw_sackblock *blocks, const int numblocks,
 290     tcp_seq snd_una)
 291 {
 292         if (numblocks == 0)
 293                 return 0;
 294
 295         if (SEQ_LT(blocks[0].rblk_start, snd_una))
 296                 return 1;
 297
 298         /* block 0 inside block 1 */
 299         if (numblocks > 1 &&
 300             SEQ_GEQ(blocks[0].rblk_start, blocks[1].rblk_start) &&
 301             SEQ_LEQ(blocks[0].rblk_end, blocks[1].rblk_end))
 302                 return 2;
 303
 304         return 0;
 305 }
 306
 307 /*
 308  * Update scoreboard on new incoming ACK.
 309  */
 310 static void
 311 tcp_sack_add_blocks(struct tcpcb *tp, struct tcpopt *to)
 312 {
 313         const int numblocks = to->to_nsackblocks;
 314         struct raw_sackblock *blocks = to->to_sackblocks;
 315         struct scoreboard *scb = &tp->scb;
 316         int startblock, i;
 317
 318         if (tcp_sack_ndsack_blocks(blocks, numblocks, tp->snd_una) > 0)
 319                 startblock = 1;
 320         else
 321                 startblock = 0;
 322
 323         to->to_flags |= TOF_SACK_REDUNDANT;
 324         for (i = startblock; i < numblocks; i++) {
 325                 struct raw_sackblock *newsackblock = &blocks[i];
 326                 boolean_t update;
 327                 int error;
 328
 329                 /* Guard against ACK reordering */
 330                 if (SEQ_LEQ(newsackblock->rblk_start, tp->snd_una))
 331                         continue;
 332
 333                 /* Don't accept bad SACK blocks */
 334                 if (SEQ_GT(newsackblock->rblk_end, tp->snd_max)) {
 335                         tcpstat.tcps_rcvbadsackopt++;
 336                         break;          /* skip all other blocks */
 337                 }
 338                 tcpstat.tcps_sacksbupdate++;
 339
 340                 error = insert_block(scb, newsackblock, &update);
 341                 if (update)
 342                         to->to_flags &= ~TOF_SACK_REDUNDANT;
 343                 if (error)
 344                         break;
 345         }
 346 }
 347
 348 void
 349 tcp_sack_update_scoreboard(struct tcpcb *tp, struct tcpopt *to)
 350 {
 351         struct scoreboard *scb = &tp->scb;
 352         int rexmt_high_update = 0;
 353
 354         tcp_sack_ack_blocks(tp, tp->snd_una);
 355         tcp_sack_add_blocks(tp, to);
 356         tcp_sack_update_lostseq(scb, tp->snd_una, tp->t_maxseg,
 357             tp->t_rxtthresh);
 358         if (SEQ_LT(tp->rexmt_high, tp->snd_una)) {
 359                 tp->rexmt_high = tp->snd_una;
 360                 rexmt_high_update = 1;
 361         }
 362         if (tp->sack_flags & TSACK_F_SACKRESCUED) {
 363                 if (SEQ_LEQ(tp->rexmt_rescue, tp->snd_una)) {
 364                         tp->sack_flags &= ~TSACK_F_SACKRESCUED;
 365                 } else if (tcp_aggressive_rescuesack && rexmt_high_update &&
 366                     SEQ_LT(tp->rexmt_rescue, tp->rexmt_high)) {
 367                         /* Drag RescueRxt along with HighRxt */
 368                         tp->rexmt_rescue = tp->rexmt_high;
 369                 }
 370         }
 371 }
 372
 373 /*
 374  * Insert SACK block into sender's scoreboard.
 375  */
 376 static int
 377 insert_block(struct scoreboard *scb, const struct raw_sackblock *raw_sb,
 378     boolean_t *update)
 379 {
 380         struct sackblock *sb, *workingblock;
 381         boolean_t overlap_front;
 382
 383         *update = TRUE;
 384         if (TAILQ_EMPTY(&scb->sackblocks)) {
 385                 struct sackblock *newblock;
 386
 387                 KASSERT(scb->nblocks == 0, ("emply scb w/ blocks"));
 388
 389                 newblock = alloc_sackblock(scb, raw_sb);
 390                 if (newblock == NULL)
 391                         return ENOMEM;
 392                 TAILQ_INSERT_HEAD(&scb->sackblocks, newblock, sblk_list);
 393                 scb->nblocks = 1;
 394                 return 0;
 395         }
 396
 397         KASSERT(scb->nblocks > 0, ("insert_block() called w/ no blocks"));
 398         KASSERT(scb->nblocks <= MAXSAVEDBLOCKS,
 399             ("too many SACK blocks %d", scb->nblocks));
 400
 401         overlap_front = sack_block_lookup(scb, raw_sb->rblk_start, &sb);
 402
 403         if (sb == NULL) {
 404                 workingblock = alloc_sackblock_limit(scb, raw_sb);
 405                 if (workingblock == NULL)
 406                         return ENOMEM;
 407                 TAILQ_INSERT_HEAD(&scb->sackblocks, workingblock, sblk_list);
 408                 ++scb->nblocks;
 409         } else {
 410                 if (overlap_front || sb->sblk_end == raw_sb->rblk_start) {
 411                         tcpstat.tcps_sacksbreused++;
 412
 413                         /* Extend old block */
 414                         workingblock = sb;
 415                         if (SEQ_GT(raw_sb->rblk_end, sb->sblk_end)) {
 416                                 sb->sblk_end = raw_sb->rblk_end;
 417                         } else {
 418                                 /* Exact match, nothing to consolidate */
 419                                 *update = FALSE;
 420                                 return 0;
 421                         }
 422                 } else {
 423                         workingblock = alloc_sackblock_limit(scb, raw_sb);
 424                         if (workingblock == NULL)
 425                                 return ENOMEM;
 426                         TAILQ_INSERT_AFTER(&scb->sackblocks, sb, workingblock,
 427                             sblk_list);
 428                         ++scb->nblocks;
 429                 }
 430         }
 431
 432         /* Consolidate right-hand side. */
 433         sb = TAILQ_NEXT(workingblock, sblk_list);
 434         while (sb != NULL &&
 435             SEQ_GEQ(workingblock->sblk_end, sb->sblk_end)) {
 436                 struct sackblock *nextblock;
 437
 438                 nextblock = TAILQ_NEXT(sb, sblk_list);
 439                 if (scb->lastfound == sb)
 440                         scb->lastfound = NULL;
 441                 /* Remove completely overlapped block */
 442                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 443                 free_sackblock(scb, sb);
 444                 --scb->nblocks;
 445                 KASSERT(scb->nblocks > 0,
 446                     ("removed overlapped block: %d blocks left", scb->nblocks));
 447                 sb = nextblock;
 448         }
 449         if (sb != NULL &&
 450             SEQ_GEQ(workingblock->sblk_end, sb->sblk_start)) {
 451                 /* Extend new block to cover partially overlapped old block. */
 452                 workingblock->sblk_end = sb->sblk_end;
 453                 if (scb->lastfound == sb)
 454                         scb->lastfound = NULL;
 455                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
 456                 free_sackblock(scb, sb);
 457                 --scb->nblocks;
 458                 KASSERT(scb->nblocks > 0,
 459                     ("removed partial right: %d blocks left", scb->nblocks));
 460         }
 461         return 0;
 462 }
 463
 464 #ifdef DEBUG_SACK_BLOCKS
 465 static void
 466 tcp_sack_dump_blocks(const struct scoreboard *scb)
 467 {
 468         const struct sackblock *sb;
 469
 470         kprintf("%d blocks:", scb->nblocks);
 471         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
 472                 kprintf(" [%u, %u)", sb->sblk_start, sb->sblk_end);
 473         kprintf("\n");
 474 }
 475 #else
 476 static __inline void
 477 tcp_sack_dump_blocks(const struct scoreboard *scb)
 478 {
 479 }
 480 #endif
 481
 482 /*
 483  * Optimization to quickly determine which packets are lost.
 484  */
 485 void
 486 tcp_sack_update_lostseq(struct scoreboard *scb, tcp_seq snd_una, u_int maxseg,
 487     int rxtthresh)
 488 {
 489         struct sackblock *sb;
 490         int nsackblocks = 0;
 491         int bytes_sacked = 0;
 492         int rxtthresh_bytes;
 493
 494         if (tcp_do_rfc3517bis)
 495                 rxtthresh_bytes = (rxtthresh - 1) * maxseg;
 496         else
 497                 rxtthresh_bytes = rxtthresh * maxseg;
 498
 499         sb = TAILQ_LAST(&scb->sackblocks, sackblock_list);
 500         while (sb != NULL) {
 501                 ++nsackblocks;
 502                 bytes_sacked += sb->sblk_end - sb->sblk_start;
 503                 if (nsackblocks == rxtthresh ||
 504                     bytes_sacked >= rxtthresh_bytes) {
 505                         scb->lostseq = sb->sblk_start;
 506                         return;
 507                 }
 508                 sb = TAILQ_PREV(sb, sackblock_list, sblk_list);
 509         }
 510         scb->lostseq = snd_una;
 511 }
 512
 513 /*
 514  * Return whether the given sequence number is considered lost.
 515  */
 516 boolean_t
 517 tcp_sack_islost(const struct scoreboard *scb, tcp_seq seqnum)
 518 {
 519         return SEQ_LT(seqnum, scb->lostseq);
 520 }
 521
 522 /*
 523  * True if at least "amount" has been SACKed.  Used by Early Retransmit.
 524  */
 525 boolean_t
 526 tcp_sack_has_sacked(const struct scoreboard *scb, u_int amount)
 527 {
 528         const struct sackblock *sb;
 529         int bytes_sacked = 0;
 530
 531         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
 532                 bytes_sacked += sb->sblk_end - sb->sblk_start;
 533                 if (bytes_sacked >= amount)
 534                         return TRUE;
 535         }
 536         return FALSE;
 537 }
 538
 539 /*
 540  * Number of bytes SACKed below seq.
 541  */
 542 int
 543 tcp_sack_bytes_below(const struct scoreboard *scb, tcp_seq seq)
 544 {
 545         const struct sackblock *sb;
 546         int bytes_sacked = 0;
 547
 548         sb = TAILQ_FIRST(&scb->sackblocks);
 549         while (sb && SEQ_GT(seq, sb->sblk_start)) {
 550                 bytes_sacked += seq_min(seq, sb->sblk_end) - sb->sblk_start;
 551                 sb = TAILQ_NEXT(sb, sblk_list);
 552         }
 553         return bytes_sacked;
 554 }
 555
 556 /*
 557  * Return estimate of the number of bytes outstanding in the network.
 558  */
 559 uint32_t
 560 tcp_sack_compute_pipe(const struct tcpcb *tp)
 561 {
 562         const struct scoreboard *scb = &tp->scb;
 563         const struct sackblock *sb;
 564         int nlost, nretransmitted;
 565         tcp_seq end;
 566
 567         nlost = tp->snd_max - scb->lostseq;
 568         nretransmitted = tp->rexmt_high - tp->snd_una;
 569
 570         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
 571                 if (SEQ_LT(sb->sblk_start, tp->rexmt_high)) {
 572                         end = seq_min(sb->sblk_end, tp->rexmt_high);
 573                         nretransmitted -= end - sb->sblk_start;
 574                 }
 575                 if (SEQ_GEQ(sb->sblk_start, scb->lostseq))
 576                         nlost -= sb->sblk_end - sb->sblk_start;
 577         }
 578
 579         return (nlost + nretransmitted);
 580 }
 581
 582 /*
 583  * Return the sequence number and length of the next segment to transmit
 584  * when in Fast Recovery.
 585  */
 586 boolean_t
 587 tcp_sack_nextseg(struct tcpcb *tp, tcp_seq *nextrexmt, uint32_t *plen,
 588     boolean_t *rescue)
 589 {
 590         struct scoreboard *scb = &tp->scb;
 591         struct socket *so = tp->t_inpcb->inp_socket;
 592         struct sackblock *sb;
 593         const struct sackblock *lastblock =
 594             TAILQ_LAST(&scb->sackblocks, sackblock_list);
 595         tcp_seq torexmt;
 596         long len, off, sendwin;
 597
 598         /* skip SACKed data */
 599         tcp_sack_skip_sacked(scb, &tp->rexmt_high);
 600
 601         /* Look for lost data. */
 602         torexmt = tp->rexmt_high;
 603         *rescue = FALSE;
 604         if (lastblock != NULL) {
 605                 if (SEQ_LT(torexmt, lastblock->sblk_end) &&
 606                     tcp_sack_islost(scb, torexmt)) {
 607 sendunsacked:
 608                         *nextrexmt = torexmt;
 609                         /* If the left-hand edge has been SACKed, pull it in. */
 610                         if (sack_block_lookup(scb, torexmt + tp->t_maxseg, &sb))
 611                                 *plen = sb->sblk_start - torexmt;
 612                         else
 613                                 *plen = tp->t_maxseg;
 614                         return TRUE;
 615                 }
 616         }
 617
 618         /* See if unsent data available within send window. */
 619         off = tp->snd_max - tp->snd_una;
 620         sendwin = min(tp->snd_wnd, tp->snd_bwnd);
 621         len = (long) ulmin(so->so_snd.ssb_cc, sendwin) - off;
 622         if (len > 0) {
 623                 *nextrexmt = tp->snd_max;       /* Send new data. */
 624                 *plen = tp->t_maxseg;
 625                 return TRUE;
 626         }
 627
 628         /* We're less certain this data has been lost. */
 629         if (lastblock != NULL && SEQ_LT(torexmt, lastblock->sblk_end))
 630                 goto sendunsacked;
 631
 632         /* Rescue retransmission */
 633         if (tcp_do_rescuesack || tcp_do_rfc3517bis) {
 634                 tcpstat.tcps_sackrescue_try++;
 635                 if (tp->sack_flags & TSACK_F_SACKRESCUED) {
 636                         if (!tcp_aggressive_rescuesack)
 637                                 return FALSE;
 638
 639                         /*
 640                          * Aggressive variant of the rescue retransmission.
 641                          *
 642                          * The idea of the rescue retransmission is to sustain
 643                          * the ACK clock thus to avoid timeout retransmission.
 644                          *
 645                          * Under some situations, the conservative approach
 646                          * suggested in the draft
 647                          * http://tools.ietf.org/html/
 648                          * draft-nishida-tcpm-rescue-retransmission-00
 649                          * could not sustain ACK clock, since it only allows
 650                          * one rescue retransmission before a cumulative ACK
 651                          * covers the segement transmitted by rescue
 652                          * retransmission.
 653                          *
 654                          * We try to locate the next unSACKed segment which
 655                          * follows the previously sent rescue segment.  If
 656                          * there is no such segment, we loop back to the first
 657                          * unacknowledged segment.
 658                          */
 659
 660                         /*
 661                          * Skip SACKed data, but here we follow
 662                          * the last transmitted rescue segment.
 663                          */
 664                         torexmt = tp->rexmt_rescue;
 665                         tcp_sack_skip_sacked(scb, &torexmt);
 666                 }
 667                 if (torexmt == tp->snd_max) {
 668                         /* Nothing left to retransmit; restart */
 669                         torexmt = tp->snd_una;
 670                 }
 671                 *rescue = TRUE;
 672                 goto sendunsacked;
 673         } else if (tcp_do_smartsack && lastblock == NULL) {
 674                 tcpstat.tcps_sackrescue_try++;
 675                 *rescue = TRUE;
 676                 goto sendunsacked;
 677         }
 678
 679         return FALSE;
 680 }
 681
 682 /*
 683  * Return the next sequence number higher than "*prexmt" that has
 684  * not been SACKed.
 685  */
 686 void
 687 tcp_sack_skip_sacked(struct scoreboard *scb, tcp_seq *prexmt)
 688 {
 689         struct sackblock *sb;
 690
 691         /* skip SACKed data */
 692         if (sack_block_lookup(scb, *prexmt, &sb))
 693                 *prexmt = sb->sblk_end;
 694 }
 695
 696 /*
 697  * The length of the first amount of unSACKed data
 698  */
 699 uint32_t
 700 tcp_sack_first_unsacked_len(const struct tcpcb *tp)
 701 {
 702         const struct sackblock *sb;
 703
 704         sb = TAILQ_FIRST(&tp->scb.sackblocks);
 705         if (sb == NULL)
 706                 return tp->t_maxseg;
 707
 708         KASSERT(SEQ_LT(tp->snd_una, sb->sblk_start),
 709             ("invalid sb start %u, snd_una %u",
 710              sb->sblk_start, tp->snd_una));
 711         return (sb->sblk_start - tp->snd_una);
 712 }
 713
 714 #ifdef later
 715 void
 716 tcp_sack_save_scoreboard(struct scoreboard *scb)
 717 {
 718         struct scoreboard *scb = &tp->scb;
 719
 720         scb->sackblocks_prev = scb->sackblocks;
 721         TAILQ_INIT(&scb->sackblocks);
 722 }
 723
 724 void
 725 tcp_sack_revert_scoreboard(struct scoreboard *scb, tcp_seq snd_una,
 726                            u_int maxseg)
 727 {
 728         struct sackblock *sb;
 729
 730         scb->sackblocks = scb->sackblocks_prev;
 731         scb->nblocks = 0;
 732         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
 733                 ++scb->nblocks;
 734         tcp_sack_ack_blocks(scb, snd_una);
 735         scb->lastfound = NULL;
 736 }
 737 #endif
 738
 739 #ifdef DEBUG_SACK_HISTORY
 740 static void
 741 tcp_sack_dump_history(const char *msg, const struct tcpcb *tp)
 742 {
 743         int i;
 744         static int ndumped;
 745
 746         /* only need a couple of these to debug most problems */
 747         if (++ndumped > 900)
 748                 return;
 749
 750         kprintf("%s:\tnsackhistory %d: ", msg, tp->nsackhistory);
 751         for (i = 0; i < tp->nsackhistory; ++i)
 752                 kprintf("[%u, %u) ", tp->sackhistory[i].rblk_start,
 753                     tp->sackhistory[i].rblk_end);
 754         kprintf("\n");
 755 }
 756 #else
 757 static __inline void
 758 tcp_sack_dump_history(const char *msg, const struct tcpcb *tp)
 759 {
 760 }
 761 #endif
 762
 763 /*
 764  * Remove old SACK blocks from the SACK history that have already been ACKed.
 765  */
 766 static void
 767 tcp_sack_ack_history(struct tcpcb *tp)
 768 {
 769         int i, nblocks, openslot;
 770
 771         tcp_sack_dump_history("before tcp_sack_ack_history", tp);
 772         nblocks = tp->nsackhistory;
 773         for (i = openslot = 0; i < nblocks; ++i) {
 774                 if (SEQ_LEQ(tp->sackhistory[i].rblk_end, tp->rcv_nxt)) {
 775                         --tp->nsackhistory;
 776                         continue;
 777                 }
 778                 if (SEQ_LT(tp->sackhistory[i].rblk_start, tp->rcv_nxt))
 779                         tp->sackhistory[i].rblk_start = tp->rcv_nxt;
 780                 if (i == openslot)
 781                         ++openslot;
 782                 else
 783                         tp->sackhistory[openslot++] = tp->sackhistory[i];
 784         }
 785         tcp_sack_dump_history("after tcp_sack_ack_history", tp);
 786         KASSERT(openslot == tp->nsackhistory,
 787             ("tcp_sack_ack_history miscounted: %d != %d",
 788             openslot, tp->nsackhistory));
 789 }
 790
 791 /*
 792  * Add or merge newblock into reported history.
 793  * Also remove or update SACK blocks that will be acked.
 794  */
 795 static void
 796 tcp_sack_update_reported_history(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 797 {
 798         struct raw_sackblock copy[MAX_SACK_REPORT_BLOCKS];
 799         int i, cindex;
 800
 801         tcp_sack_dump_history("before tcp_sack_update_reported_history", tp);
 802         /*
 803          * Six cases:
 804          *      0) no overlap
 805          *      1) newblock == oldblock
 806          *      2) oldblock contains newblock
 807          *      3) newblock contains oldblock
 808          *      4) tail of oldblock overlaps or abuts start of newblock
 809          *      5) tail of newblock overlaps or abuts head of oldblock
 810          */
 811         for (i = cindex = 0; i < tp->nsackhistory; ++i) {
 812                 struct raw_sackblock *oldblock = &tp->sackhistory[i];
 813                 tcp_seq old_start = oldblock->rblk_start;
 814                 tcp_seq old_end = oldblock->rblk_end;
 815
 816                 if (SEQ_LT(end, old_start) || SEQ_GT(start, old_end)) {
 817                         /* Case 0:  no overlap.  Copy old block. */
 818                         copy[cindex++] = *oldblock;
 819                         continue;
 820                 }
 821
 822                 if (SEQ_GEQ(start, old_start) && SEQ_LEQ(end, old_end)) {
 823                         /* Cases 1 & 2.  Move block to front of history. */
 824                         int j;
 825
 826                         start = old_start;
 827                         end = old_end;
 828                         /* no need to check rest of blocks */
 829                         for (j = i + 1; j < tp->nsackhistory; ++j)
 830                                 copy[cindex++] = tp->sackhistory[j];
 831                         break;
 832                 }
 833
 834                 if (SEQ_GEQ(old_end, start) && SEQ_LT(old_start, start)) {
 835                         /* Case 4:  extend start of new block. */
 836                         start = old_start;
 837                 } else if (SEQ_GEQ(end, old_start) && SEQ_GT(old_end, end)) {
 838                         /* Case 5: extend end of new block */
 839                         end = old_end;
 840                 } else {
 841                         /* Case 3.  Delete old block by not copying it. */
 842                         KASSERT(SEQ_LEQ(start, old_start) &&
 843                                 SEQ_GEQ(end, old_end),
 844                             ("bad logic: old [%u, %u), new [%u, %u)",
 845                              old_start, old_end, start, end));
 846                 }
 847         }
 848
 849         /* insert new block */
 850         tp->sackhistory[0].rblk_start = start;
 851         tp->sackhistory[0].rblk_end = end;
 852         cindex = min(cindex, MAX_SACK_REPORT_BLOCKS - 1);
 853         for (i = 0; i < cindex; ++i)
 854                 tp->sackhistory[i + 1] = copy[i];
 855         tp->nsackhistory = cindex + 1;
 856         tcp_sack_dump_history("after tcp_sack_update_reported_history", tp);
 857 }
 858
 859 /*
 860  * Fill in SACK report to return to data sender.
 861  */
 862 void
 863 tcp_sack_fill_report(struct tcpcb *tp, u_char *opt, u_int *plen)
 864 {
 865         u_int optlen = *plen;
 866         uint32_t *lp = (uint32_t *)(opt + optlen);
 867         uint32_t *olp;
 868         tcp_seq hstart = tp->rcv_nxt, hend;
 869         int nblocks;
 870
 871         KASSERT(TCP_MAXOLEN - optlen >=
 872             TCPOLEN_SACK_ALIGNED + TCPOLEN_SACK_BLOCK,
 873             ("no room for SACK header and one block: optlen %d", optlen));
 874
 875         if (tp->sack_flags & TSACK_F_DUPSEG)
 876                 tcpstat.tcps_snddsackopt++;
 877         else
 878                 tcpstat.tcps_sndsackopt++;
 879
 880         olp = lp++;
 881         optlen += TCPOLEN_SACK_ALIGNED;
 882
 883         tcp_sack_ack_history(tp);
 884         if (tp->reportblk.rblk_start != tp->reportblk.rblk_end) {
 885                 *lp++ = htonl(tp->reportblk.rblk_start);
 886                 *lp++ = htonl(tp->reportblk.rblk_end);
 887                 optlen += TCPOLEN_SACK_BLOCK;
 888                 hstart = tp->reportblk.rblk_start;
 889                 hend = tp->reportblk.rblk_end;
 890                 if (tp->sack_flags & TSACK_F_ENCLOSESEG) {
 891                         KASSERT(TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK,
 892                             ("no room for enclosing SACK block: oplen %d",
 893                             optlen));
 894                         *lp++ = htonl(tp->encloseblk.rblk_start);
 895                         *lp++ = htonl(tp->encloseblk.rblk_end);
 896                         optlen += TCPOLEN_SACK_BLOCK;
 897                         hstart = tp->encloseblk.rblk_start;
 898                         hend = tp->encloseblk.rblk_end;
 899                 }
 900                 if (SEQ_GT(hstart, tp->rcv_nxt))
 901                         tcp_sack_update_reported_history(tp, hstart, hend);
 902         }
 903         if (tcp_do_smartsack && (tp->sack_flags & TSACK_F_SACKLEFT)) {
 904                 /* Fill in from left!  Walk re-assembly queue. */
 905                 struct tseg_qent *q;
 906
 907                 q = TAILQ_FIRST(&tp->t_segq);
 908                 while (q != NULL &&
 909                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
 910                         *lp++ = htonl(q->tqe_th->th_seq);
 911                         *lp++ = htonl(TCP_SACK_BLKEND(
 912                             q->tqe_th->th_seq + q->tqe_len,
 913                             q->tqe_th->th_flags));
 914                         optlen += TCPOLEN_SACK_BLOCK;
 915                         q = TAILQ_NEXT(q, tqe_q);
 916                 }
 917         } else {
 918                 int n = 0;
 919
 920                 /* Fill in SACK blocks from right side. */
 921                 while (n < tp->nsackhistory &&
 922                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
 923                         if (tp->sackhistory[n].rblk_start != hstart) {
 924                                 *lp++ = htonl(tp->sackhistory[n].rblk_start);
 925                                 *lp++ = htonl(tp->sackhistory[n].rblk_end);
 926                                 optlen += TCPOLEN_SACK_BLOCK;
 927                         }
 928                         ++n;
 929                 }
 930         }
 931         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
 932         tp->sack_flags &=
 933             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
 934         nblocks = (lp - olp - 1) / 2;
 935         *olp = htonl(TCPOPT_SACK_ALIGNED |
 936                      (TCPOLEN_SACK + nblocks * TCPOLEN_SACK_BLOCK));
 937         *plen = optlen;
 938 }