sys/netinet/tcp_sack.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   5  *      The Regents of the University of California.
   6  * All rights reserved.
   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 University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  *      @(#)tcp_sack.c  8.12 (Berkeley) 5/24/95
  33  */
  34
  35 /*-
  36  *      @@(#)COPYRIGHT  1.1 (NRL) 17 January 1995
  37  *
  38  * NRL grants permission for redistribution and use in source and binary
  39  * forms, with or without modification, of the software and documentation
  40  * created at NRL provided that the following conditions are met:
  41  *
  42  * 1. Redistributions of source code must retain the above copyright
  43  *    notice, this list of conditions and the following disclaimer.
  44  * 2. Redistributions in binary form must reproduce the above copyright
  45  *    notice, this list of conditions and the following disclaimer in the
  46  *    documentation and/or other materials provided with the distribution.
  47  * 3. All advertising materials mentioning features or use of this software
  48  *    must display the following acknowledgements:
  49  *      This product includes software developed by the University of
  50  *      California, Berkeley and its contributors.
  51  *      This product includes software developed at the Information
  52  *      Technology Division, US Naval Research Laboratory.
  53  * 4. Neither the name of the NRL nor the names of its contributors
  54  *    may be used to endorse or promote products derived from this software
  55  *    without specific prior written permission.
  56  *
  57  * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS
  58  * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  59  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  60  * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL NRL OR
  61  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  62  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  63  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  64  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  65  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  66  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  67  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  68  *
  69  * The views and conclusions contained in the software and documentation
  70  * are those of the authors and should not be interpreted as representing
  71  * official policies, either expressed or implied, of the US Naval
  72  * Research Laboratory (NRL).
  73  */
  74
  75 #include <sys/cdefs.h>
  76 __FBSDID("$FreeBSD$");
  77
  78 #include "opt_inet.h"
  79 #include "opt_inet6.h"
  80 #include "opt_tcpdebug.h"
  81
  82 #include <sys/param.h>
  83 #include <sys/systm.h>
  84 #include <sys/kernel.h>
  85 #include <sys/sysctl.h>
  86 #include <sys/malloc.h>
  87 #include <sys/mbuf.h>
  88 #include <sys/proc.h>           /* for proc0 declaration */
  89 #include <sys/protosw.h>
  90 #include <sys/socket.h>
  91 #include <sys/socketvar.h>
  92 #include <sys/syslog.h>
  93 #include <sys/systm.h>
  94
  95 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  96
  97 #include <vm/uma.h>
  98
  99 #include <net/if.h>
 100 #include <net/if_var.h>
 101 #include <net/route.h>
 102 #include <net/vnet.h>
 103
 104 #include <netinet/in.h>
 105 #include <netinet/in_systm.h>
 106 #include <netinet/ip.h>
 107 #include <netinet/in_var.h>
 108 #include <netinet/in_pcb.h>
 109 #include <netinet/ip_var.h>
 110 #include <netinet/ip6.h>
 111 #include <netinet/icmp6.h>
 112 #include <netinet6/nd6.h>
 113 #include <netinet6/ip6_var.h>
 114 #include <netinet6/in6_pcb.h>
 115 #include <netinet/tcp.h>
 116 #include <netinet/tcp_fsm.h>
 117 #include <netinet/tcp_seq.h>
 118 #include <netinet/tcp_timer.h>
 119 #include <netinet/tcp_var.h>
 120 #include <netinet6/tcp6_var.h>
 121 #include <netinet/tcpip.h>
 122 #ifdef TCPDEBUG
 123 #include <netinet/tcp_debug.h>
 124 #endif /* TCPDEBUG */
 125
 126 #include <machine/in_cksum.h>
 127
 128 VNET_DECLARE(struct uma_zone *, sack_hole_zone);
 129 #define V_sack_hole_zone                VNET(sack_hole_zone)
 130
 131 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW, 0, "TCP SACK");
 132 VNET_DEFINE(int, tcp_do_sack) = 1;
 133 #define V_tcp_do_sack                   VNET(tcp_do_sack)
 134 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
 135     &VNET_NAME(tcp_do_sack), 0, "Enable/Disable TCP SACK support");
 136
 137 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
 138 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
 139     &VNET_NAME(tcp_sack_maxholes), 0,
 140     "Maximum number of TCP SACK holes allowed per connection");
 141
 142 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
 143 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
 144     &VNET_NAME(tcp_sack_globalmaxholes), 0,
 145     "Global maximum number of TCP SACK holes");
 146
 147 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
 148 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
 149     &VNET_NAME(tcp_sack_globalholes), 0,
 150     "Global number of TCP SACK holes currently allocated");
 151
 152
 153 /*
 154  * This function will find overlaps with the currently stored sackblocks
 155  * and add any overlap as a dsack block upfront
 156  */
 157 void
 158 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 159 {
 160         struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
 161         int i, j, n, identical;
 162         tcp_seq start, end;
 163
 164         INP_WLOCK_ASSERT(tp->t_inpcb);
 165
 166         KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
 167
 168         if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) {
 169                 log(LOG_DEBUG, "\nDSACK update: %d..%d, rcv_nxt: %u\n",
 170                 rcv_start, rcv_end, tp->rcv_nxt);
 171         }
 172
 173         if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
 174             ((rcv_end == tp->rcv_nxt) &&
 175              (tp->rcv_numsacks > 0 ) &&
 176              (tp->sackblks[0].end == tp->rcv_nxt))) {
 177                 saved_blks[0].start = rcv_start;
 178                 saved_blks[0].end = rcv_end;
 179         } else {
 180                 saved_blks[0].start = saved_blks[0].end = 0;
 181         }
 182
 183         head_blk.start = head_blk.end = 0;
 184         mid_blk.start = rcv_start;
 185         mid_blk.end = rcv_end;
 186         identical = 0;
 187
 188         for (i = 0; i < tp->rcv_numsacks; i++) {
 189                 start = tp->sackblks[i].start;
 190                 end = tp->sackblks[i].end;
 191                 if (SEQ_LT(rcv_end, start)) {
 192                         /* pkt left to sack blk */
 193                         continue;
 194                 }
 195                 if (SEQ_GT(rcv_start, end)) {
 196                         /* pkt right to sack blk */
 197                         continue;
 198                 }
 199                 if (SEQ_GT(tp->rcv_nxt, end)) {
 200                         if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
 201                             (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
 202                             (head_blk.start == head_blk.end))) {
 203                                 head_blk.start = SEQ_MAX(rcv_start, start);
 204                                 head_blk.end = SEQ_MIN(rcv_end, end);
 205                         }
 206                         continue;
 207                 }
 208                 if (((head_blk.start == head_blk.end) ||
 209                      SEQ_LT(start, head_blk.start)) &&
 210                      (SEQ_GT(end, rcv_start) &&
 211                       SEQ_LEQ(start, rcv_end))) {
 212                         head_blk.start = start;
 213                         head_blk.end = end;
 214                 }
 215                 mid_blk.start = SEQ_MIN(mid_blk.start, start);
 216                 mid_blk.end = SEQ_MAX(mid_blk.end, end);
 217                 if ((mid_blk.start == start) &&
 218                     (mid_blk.end == end))
 219                         identical = 1;
 220         }
 221         if (SEQ_LT(head_blk.start, head_blk.end)) {
 222                 /* store overlapping range */
 223                 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
 224                 saved_blks[0].end   = SEQ_MIN(rcv_end, head_blk.end);
 225         }
 226         n = 1;
 227         /*
 228          * Second, if not ACKed, store the SACK block that
 229          * overlaps with the DSACK block unless it is identical
 230          */
 231         if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
 232             !((mid_blk.start == saved_blks[0].start) &&
 233             (mid_blk.end == saved_blks[0].end))) ||
 234             identical == 1) {
 235                 saved_blks[n].start = mid_blk.start;
 236                 saved_blks[n++].end = mid_blk.end;
 237         }
 238         for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
 239                 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
 240                       SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
 241                     (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
 242                 saved_blks[n++] = tp->sackblks[j];
 243         }
 244         j = 0;
 245         for (i = 0; i < n; i++) {
 246                 /* we can end up with a stale inital entry */
 247                 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
 248                         tp->sackblks[j++] = saved_blks[i];
 249                 }
 250         }
 251         tp->rcv_numsacks = j;
 252 }
 253
 254 /*
 255  * This function is called upon receipt of new valid data (while not in
 256  * header prediction mode), and it updates the ordered list of sacks.
 257  */
 258 void
 259 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 260 {
 261         /*
 262          * First reported block MUST be the most recent one.  Subsequent
 263          * blocks SHOULD be in the order in which they arrived at the
 264          * receiver.  These two conditions make the implementation fully
 265          * compliant with RFC 2018.
 266          */
 267         struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
 268         int num_head, num_saved, i;
 269
 270         INP_WLOCK_ASSERT(tp->t_inpcb);
 271
 272         /* Check arguments. */
 273         KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
 274
 275         if ((rcv_start == rcv_end) &&
 276             (tp->rcv_numsacks >= 1) &&
 277             (rcv_end == tp->sackblks[0].end)) {
 278                 /* retaining DSACK block below rcv_nxt (todrop) */
 279                 head_blk = tp->sackblks[0];
 280         } else {
 281                 /* SACK block for the received segment. */
 282                 head_blk.start = rcv_start;
 283                 head_blk.end = rcv_end;
 284         }
 285
 286         /*
 287          * Merge updated SACK blocks into head_blk, and save unchanged SACK
 288          * blocks into saved_blks[].  num_saved will have the number of the
 289          * saved SACK blocks.
 290          */
 291         num_saved = 0;
 292         for (i = 0; i < tp->rcv_numsacks; i++) {
 293                 tcp_seq start = tp->sackblks[i].start;
 294                 tcp_seq end = tp->sackblks[i].end;
 295                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 296                         /*
 297                          * Discard this SACK block.
 298                          */
 299                 } else if (SEQ_LEQ(head_blk.start, end) &&
 300                            SEQ_GEQ(head_blk.end, start)) {
 301                         /*
 302                          * Merge this SACK block into head_blk.  This SACK
 303                          * block itself will be discarded.
 304                          */
 305                         /*
 306                          * |-|
 307                          *   |---|  merge
 308                          *
 309                          *     |-|
 310                          * |---|    merge
 311                          *
 312                          * |-----|
 313                          *   |-|    DSACK smaller
 314                          *
 315                          *   |-|
 316                          * |-----|  DSACK smaller
 317                          */
 318                         if (head_blk.start == end)
 319                                 head_blk.start = start;
 320                         else if (head_blk.end == start)
 321                                 head_blk.end = end;
 322                         else {
 323                                 if (SEQ_LT(head_blk.start, start)) {
 324                                         tcp_seq temp = start;
 325                                         start = head_blk.start;
 326                                         head_blk.start = temp;
 327                                 }
 328                                 if (SEQ_GT(head_blk.end, end)) {
 329                                         tcp_seq temp = end;
 330                                         end = head_blk.end;
 331                                         head_blk.end = temp;
 332                                 }
 333                                 if ((head_blk.start != start) ||
 334                                     (head_blk.end != end)) {
 335                                         if ((num_saved >= 1) &&
 336                                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 337                                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 338                                                 num_saved--;
 339                                         saved_blks[num_saved].start = start;
 340                                         saved_blks[num_saved].end = end;
 341                                         num_saved++;
 342                                 }
 343                         }
 344                 } else {
 345                         /*
 346                          * This block supercedes the prior block
 347                          */
 348                         if ((num_saved >= 1) &&
 349                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 350                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 351                                 num_saved--;
 352                         /*
 353                          * Save this SACK block.
 354                          */
 355                         saved_blks[num_saved].start = start;
 356                         saved_blks[num_saved].end = end;
 357                         num_saved++;
 358                 }
 359         }
 360
 361         /*
 362          * Update SACK list in tp->sackblks[].
 363          */
 364         num_head = 0;
 365         if (SEQ_LT(rcv_start, rcv_end)) {
 366                 /*
 367                  * The received data segment is an out-of-order segment.  Put
 368                  * head_blk at the top of SACK list.
 369                  */
 370                 tp->sackblks[0] = head_blk;
 371                 num_head = 1;
 372                 /*
 373                  * If the number of saved SACK blocks exceeds its limit,
 374                  * discard the last SACK block.
 375                  */
 376                 if (num_saved >= MAX_SACK_BLKS)
 377                         num_saved--;
 378         }
 379         if ((rcv_start == rcv_end) &&
 380             (rcv_start == tp->sackblks[0].end)) {
 381                 num_head = 1;
 382         }
 383         if (num_saved > 0) {
 384                 /*
 385                  * Copy the saved SACK blocks back.
 386                  */
 387                 bcopy(saved_blks, &tp->sackblks[num_head],
 388                       sizeof(struct sackblk) * num_saved);
 389         }
 390
 391         /* Save the number of SACK blocks. */
 392         tp->rcv_numsacks = num_head + num_saved;
 393 }
 394
 395 void
 396 tcp_clean_dsack_blocks(struct tcpcb *tp)
 397 {
 398         struct sackblk saved_blks[MAX_SACK_BLKS];
 399         int num_saved, i;
 400
 401         INP_WLOCK_ASSERT(tp->t_inpcb);
 402         /*
 403          * Clean up any DSACK blocks that
 404          * are in our queue of sack blocks.
 405          *
 406          */
 407         num_saved = 0;
 408         for (i = 0; i < tp->rcv_numsacks; i++) {
 409                 tcp_seq start = tp->sackblks[i].start;
 410                 tcp_seq end = tp->sackblks[i].end;
 411                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 412                         /*
 413                          * Discard this D-SACK block.
 414                          */
 415                         continue;
 416                 }
 417                 /*
 418                  * Save this SACK block.
 419                  */
 420                 saved_blks[num_saved].start = start;
 421                 saved_blks[num_saved].end = end;
 422                 num_saved++;
 423         }
 424         if (num_saved > 0) {
 425                 /*
 426                  * Copy the saved SACK blocks back.
 427                  */
 428                 bcopy(saved_blks, &tp->sackblks[0],
 429                       sizeof(struct sackblk) * num_saved);
 430         }
 431         tp->rcv_numsacks = num_saved;
 432 }
 433
 434 /*
 435  * Delete all receiver-side SACK information.
 436  */
 437 void
 438 tcp_clean_sackreport(struct tcpcb *tp)
 439 {
 440         int i;
 441
 442         INP_WLOCK_ASSERT(tp->t_inpcb);
 443         tp->rcv_numsacks = 0;
 444         for (i = 0; i < MAX_SACK_BLKS; i++)
 445                 tp->sackblks[i].start = tp->sackblks[i].end=0;
 446 }
 447
 448 /*
 449  * Allocate struct sackhole.
 450  */
 451 static struct sackhole *
 452 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 453 {
 454         struct sackhole *hole;
 455
 456         if (tp->snd_numholes >= V_tcp_sack_maxholes ||
 457             V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
 458                 TCPSTAT_INC(tcps_sack_sboverflow);
 459                 return NULL;
 460         }
 461
 462         hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
 463         if (hole == NULL)
 464                 return NULL;
 465
 466         hole->start = start;
 467         hole->end = end;
 468         hole->rxmit = start;
 469
 470         tp->snd_numholes++;
 471         atomic_add_int(&V_tcp_sack_globalholes, 1);
 472
 473         return hole;
 474 }
 475
 476 /*
 477  * Free struct sackhole.
 478  */
 479 static void
 480 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
 481 {
 482
 483         uma_zfree(V_sack_hole_zone, hole);
 484
 485         tp->snd_numholes--;
 486         atomic_subtract_int(&V_tcp_sack_globalholes, 1);
 487
 488         KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
 489         KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
 490 }
 491
 492 /*
 493  * Insert new SACK hole into scoreboard.
 494  */
 495 static struct sackhole *
 496 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
 497     struct sackhole *after)
 498 {
 499         struct sackhole *hole;
 500
 501         /* Allocate a new SACK hole. */
 502         hole = tcp_sackhole_alloc(tp, start, end);
 503         if (hole == NULL)
 504                 return NULL;
 505
 506         /* Insert the new SACK hole into scoreboard. */
 507         if (after != NULL)
 508                 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
 509         else
 510                 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
 511
 512         /* Update SACK hint. */
 513         if (tp->sackhint.nexthole == NULL)
 514                 tp->sackhint.nexthole = hole;
 515
 516         return hole;
 517 }
 518
 519 /*
 520  * Remove SACK hole from scoreboard.
 521  */
 522 static void
 523 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
 524 {
 525
 526         /* Update SACK hint. */
 527         if (tp->sackhint.nexthole == hole)
 528                 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
 529
 530         /* Remove this SACK hole. */
 531         TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
 532
 533         /* Free this SACK hole. */
 534         tcp_sackhole_free(tp, hole);
 535 }
 536
 537 /*
 538  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
 539  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
 540  * the sequence space).
 541  * Returns 1 if incoming ACK has previously unknown SACK information,
 542  * 0 otherwise. Note: We treat (snd_una, th_ack) as a sack block so any changes
 543  * to that (i.e. left edge moving) would also be considered a change in SACK
 544  * information which is slightly different than rfc6675.
 545  */
 546 int
 547 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
 548 {
 549         struct sackhole *cur, *temp;
 550         struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 551         int i, j, num_sack_blks, sack_changed;
 552
 553         INP_WLOCK_ASSERT(tp->t_inpcb);
 554
 555         num_sack_blks = 0;
 556         sack_changed = 0;
 557         /*
 558          * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 559          * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
 560          */
 561         if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
 562                 sack_blocks[num_sack_blks].start = tp->snd_una;
 563                 sack_blocks[num_sack_blks++].end = th_ack;
 564         }
 565         /*
 566          * Append received valid SACK blocks to sack_blocks[], but only if we
 567          * received new blocks from the other side.
 568          */
 569         if (to->to_flags & TOF_SACK) {
 570                 tp->sackhint.sacked_bytes = 0;  /* reset */
 571                 for (i = 0; i < to->to_nsacks; i++) {
 572                         bcopy((to->to_sacks + i * TCPOLEN_SACK),
 573                             &sack, sizeof(sack));
 574                         sack.start = ntohl(sack.start);
 575                         sack.end = ntohl(sack.end);
 576                         if (SEQ_GT(sack.end, sack.start) &&
 577                             SEQ_GT(sack.start, tp->snd_una) &&
 578                             SEQ_GT(sack.start, th_ack) &&
 579                             SEQ_LT(sack.start, tp->snd_max) &&
 580                             SEQ_GT(sack.end, tp->snd_una) &&
 581                             SEQ_LEQ(sack.end, tp->snd_max)) {
 582                                 sack_blocks[num_sack_blks++] = sack;
 583                                 tp->sackhint.sacked_bytes +=
 584                                     (sack.end-sack.start);
 585                         }
 586                 }
 587         }
 588         /*
 589          * Return if SND.UNA is not advanced and no valid SACK block is
 590          * received.
 591          */
 592         if (num_sack_blks == 0)
 593                 return (sack_changed);
 594
 595         /*
 596          * Sort the SACK blocks so we can update the scoreboard with just one
 597          * pass. The overhead of sorting up to 4+1 elements is less than
 598          * making up to 4+1 passes over the scoreboard.
 599          */
 600         for (i = 0; i < num_sack_blks; i++) {
 601                 for (j = i + 1; j < num_sack_blks; j++) {
 602                         if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
 603                                 sack = sack_blocks[i];
 604                                 sack_blocks[i] = sack_blocks[j];
 605                                 sack_blocks[j] = sack;
 606                         }
 607                 }
 608         }
 609         if (TAILQ_EMPTY(&tp->snd_holes))
 610                 /*
 611                  * Empty scoreboard. Need to initialize snd_fack (it may be
 612                  * uninitialized or have a bogus value). Scoreboard holes
 613                  * (from the sack blocks received) are created later below
 614                  * (in the logic that adds holes to the tail of the
 615                  * scoreboard).
 616                  */
 617                 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
 618         /*
 619          * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
 620          * SACK holes (snd_holes) are traversed from their tails with just
 621          * one pass in order to reduce the number of compares especially when
 622          * the bandwidth-delay product is large.
 623          *
 624          * Note: Typically, in the first RTT of SACK recovery, the highest
 625          * three or four SACK blocks with the same ack number are received.
 626          * In the second RTT, if retransmitted data segments are not lost,
 627          * the highest three or four SACK blocks with ack number advancing
 628          * are received.
 629          */
 630         sblkp = &sack_blocks[num_sack_blks - 1];        /* Last SACK block */
 631         tp->sackhint.last_sack_ack = sblkp->end;
 632         if (SEQ_LT(tp->snd_fack, sblkp->start)) {
 633                 /*
 634                  * The highest SACK block is beyond fack.  Append new SACK
 635                  * hole at the tail.  If the second or later highest SACK
 636                  * blocks are also beyond the current fack, they will be
 637                  * inserted by way of hole splitting in the while-loop below.
 638                  */
 639                 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
 640                 if (temp != NULL) {
 641                         tp->snd_fack = sblkp->end;
 642                         /* Go to the previous sack block. */
 643                         sblkp--;
 644                         sack_changed = 1;
 645                 } else {
 646                         /*
 647                          * We failed to add a new hole based on the current
 648                          * sack block.  Skip over all the sack blocks that
 649                          * fall completely to the right of snd_fack and
 650                          * proceed to trim the scoreboard based on the
 651                          * remaining sack blocks.  This also trims the
 652                          * scoreboard for th_ack (which is sack_blocks[0]).
 653                          */
 654                         while (sblkp >= sack_blocks &&
 655                                SEQ_LT(tp->snd_fack, sblkp->start))
 656                                 sblkp--;
 657                         if (sblkp >= sack_blocks &&
 658                             SEQ_LT(tp->snd_fack, sblkp->end))
 659                                 tp->snd_fack = sblkp->end;
 660                 }
 661         } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
 662                 /* fack is advanced. */
 663                 tp->snd_fack = sblkp->end;
 664                 sack_changed = 1;
 665         }
 666         cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
 667         /*
 668          * Since the incoming sack blocks are sorted, we can process them
 669          * making one sweep of the scoreboard.
 670          */
 671         while (sblkp >= sack_blocks  && cur != NULL) {
 672                 if (SEQ_GEQ(sblkp->start, cur->end)) {
 673                         /*
 674                          * SACKs data beyond the current hole.  Go to the
 675                          * previous sack block.
 676                          */
 677                         sblkp--;
 678                         continue;
 679                 }
 680                 if (SEQ_LEQ(sblkp->end, cur->start)) {
 681                         /*
 682                          * SACKs data before the current hole.  Go to the
 683                          * previous hole.
 684                          */
 685                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 686                         continue;
 687                 }
 688                 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
 689                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 690                     ("sackhint bytes rtx >= 0"));
 691                 sack_changed = 1;
 692                 if (SEQ_LEQ(sblkp->start, cur->start)) {
 693                         /* Data acks at least the beginning of hole. */
 694                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 695                                 /* Acks entire hole, so delete hole. */
 696                                 temp = cur;
 697                                 cur = TAILQ_PREV(cur, sackhole_head, scblink);
 698                                 tcp_sackhole_remove(tp, temp);
 699                                 /*
 700                                  * The sack block may ack all or part of the
 701                                  * next hole too, so continue onto the next
 702                                  * hole.
 703                                  */
 704                                 continue;
 705                         } else {
 706                                 /* Move start of hole forward. */
 707                                 cur->start = sblkp->end;
 708                                 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 709                         }
 710                 } else {
 711                         /* Data acks at least the end of hole. */
 712                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 713                                 /* Move end of hole backward. */
 714                                 cur->end = sblkp->start;
 715                                 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 716                         } else {
 717                                 /*
 718                                  * ACKs some data in middle of a hole; need
 719                                  * to split current hole
 720                                  */
 721                                 temp = tcp_sackhole_insert(tp, sblkp->end,
 722                                     cur->end, cur);
 723                                 if (temp != NULL) {
 724                                         if (SEQ_GT(cur->rxmit, temp->rxmit)) {
 725                                                 temp->rxmit = cur->rxmit;
 726                                                 tp->sackhint.sack_bytes_rexmit
 727                                                     += (temp->rxmit
 728                                                     - temp->start);
 729                                         }
 730                                         cur->end = sblkp->start;
 731                                         cur->rxmit = SEQ_MIN(cur->rxmit,
 732                                             cur->end);
 733                                 }
 734                         }
 735                 }
 736                 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
 737                 /*
 738                  * Testing sblkp->start against cur->start tells us whether
 739                  * we're done with the sack block or the sack hole.
 740                  * Accordingly, we advance one or the other.
 741                  */
 742                 if (SEQ_LEQ(sblkp->start, cur->start))
 743                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 744                 else
 745                         sblkp--;
 746         }
 747         return (sack_changed);
 748 }
 749
 750 /*
 751  * Free all SACK holes to clear the scoreboard.
 752  */
 753 void
 754 tcp_free_sackholes(struct tcpcb *tp)
 755 {
 756         struct sackhole *q;
 757
 758         INP_WLOCK_ASSERT(tp->t_inpcb);
 759         while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
 760                 tcp_sackhole_remove(tp, q);
 761         tp->sackhint.sack_bytes_rexmit = 0;
 762
 763         KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
 764         KASSERT(tp->sackhint.nexthole == NULL,
 765                 ("tp->sackhint.nexthole == NULL"));
 766 }
 767
 768 /*
 769  * Partial ack handling within a sack recovery episode.  Keeping this very
 770  * simple for now.  When a partial ack is received, force snd_cwnd to a value
 771  * that will allow the sender to transmit no more than 2 segments.  If
 772  * necessary, a better scheme can be adopted at a later point, but for now,
 773  * the goal is to prevent the sender from bursting a large amount of data in
 774  * the midst of sack recovery.
 775  */
 776 void
 777 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 778 {
 779         int num_segs = 1;
 780
 781         INP_WLOCK_ASSERT(tp->t_inpcb);
 782         tcp_timer_activate(tp, TT_REXMT, 0);
 783         tp->t_rtttime = 0;
 784         /* Send one or 2 segments based on how much new data was acked. */
 785         if ((BYTES_THIS_ACK(tp, th) / tp->t_maxseg) >= 2)
 786                 num_segs = 2;
 787         tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
 788             (tp->snd_nxt - tp->sack_newdata) + num_segs * tp->t_maxseg);
 789         if (tp->snd_cwnd > tp->snd_ssthresh)
 790                 tp->snd_cwnd = tp->snd_ssthresh;
 791         tp->t_flags |= TF_ACKNOW;
 792         (void) tp->t_fb->tfb_tcp_output(tp);
 793 }
 794
 795 #if 0
 796 /*
 797  * Debug version of tcp_sack_output() that walks the scoreboard.  Used for
 798  * now to sanity check the hint.
 799  */
 800 static struct sackhole *
 801 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
 802 {
 803         struct sackhole *p;
 804
 805         INP_WLOCK_ASSERT(tp->t_inpcb);
 806         *sack_bytes_rexmt = 0;
 807         TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
 808                 if (SEQ_LT(p->rxmit, p->end)) {
 809                         if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 810                                 continue;
 811                         }
 812                         *sack_bytes_rexmt += (p->rxmit - p->start);
 813                         break;
 814                 }
 815                 *sack_bytes_rexmt += (p->rxmit - p->start);
 816         }
 817         return (p);
 818 }
 819 #endif
 820
 821 /*
 822  * Returns the next hole to retransmit and the number of retransmitted bytes
 823  * from the scoreboard.  We store both the next hole and the number of
 824  * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
 825  * reception).  This avoids scoreboard traversals completely.
 826  *
 827  * The loop here will traverse *at most* one link.  Here's the argument.  For
 828  * the loop to traverse more than 1 link before finding the next hole to
 829  * retransmit, we would need to have at least 1 node following the current
 830  * hint with (rxmit == end).  But, for all holes following the current hint,
 831  * (start == rxmit), since we have not yet retransmitted from them.
 832  * Therefore, in order to traverse more 1 link in the loop below, we need to
 833  * have at least one node following the current hint with (start == rxmit ==
 834  * end).  But that can't happen, (start == end) means that all the data in
 835  * that hole has been sacked, in which case, the hole would have been removed
 836  * from the scoreboard.
 837  */
 838 struct sackhole *
 839 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 840 {
 841         struct sackhole *hole = NULL;
 842
 843         INP_WLOCK_ASSERT(tp->t_inpcb);
 844         *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
 845         hole = tp->sackhint.nexthole;
 846         if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
 847                 goto out;
 848         while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
 849                 if (SEQ_LT(hole->rxmit, hole->end)) {
 850                         tp->sackhint.nexthole = hole;
 851                         break;
 852                 }
 853         }
 854 out:
 855         return (hole);
 856 }
 857
 858 /*
 859  * After a timeout, the SACK list may be rebuilt.  This SACK information
 860  * should be used to avoid retransmitting SACKed data.  This function
 861  * traverses the SACK list to see if snd_nxt should be moved forward.
 862  */
 863 void
 864 tcp_sack_adjust(struct tcpcb *tp)
 865 {
 866         struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 867
 868         INP_WLOCK_ASSERT(tp->t_inpcb);
 869         if (cur == NULL)
 870                 return; /* No holes */
 871         if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
 872                 return; /* We're already beyond any SACKed blocks */
 873         /*-
 874          * Two cases for which we want to advance snd_nxt:
 875          * i) snd_nxt lies between end of one hole and beginning of another
 876          * ii) snd_nxt lies between end of last hole and snd_fack
 877          */
 878         while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
 879                 if (SEQ_LT(tp->snd_nxt, cur->end))
 880                         return;
 881                 if (SEQ_GEQ(tp->snd_nxt, p->start))
 882                         cur = p;
 883                 else {
 884                         tp->snd_nxt = p->start;
 885                         return;
 886                 }
 887         }
 888         if (SEQ_LT(tp->snd_nxt, cur->end))
 889                 return;
 890         tp->snd_nxt = tp->snd_fack;
 891 }