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