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 | CTLFLAG_MPSAFE, 0,
 132     "TCP SACK");
 133 VNET_DEFINE(int, tcp_do_sack) = 1;
 134 #define V_tcp_do_sack                   VNET(tcp_do_sack)
 135 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
 136     &VNET_NAME(tcp_do_sack), 0, "Enable/Disable TCP SACK support");
 137
 138 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
 139 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
 140     &VNET_NAME(tcp_sack_maxholes), 0,
 141     "Maximum number of TCP SACK holes allowed per connection");
 142
 143 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
 144 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
 145     &VNET_NAME(tcp_sack_globalmaxholes), 0,
 146     "Global maximum number of TCP SACK holes");
 147
 148 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
 149 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
 150     &VNET_NAME(tcp_sack_globalholes), 0,
 151     "Global number of TCP SACK holes currently allocated");
 152
 153
 154 /*
 155  * This function will find overlaps with the currently stored sackblocks
 156  * and add any overlap as a dsack block upfront
 157  */
 158 void
 159 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 160 {
 161         struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
 162         int i, j, n, identical;
 163         tcp_seq start, end;
 164
 165         INP_WLOCK_ASSERT(tp->t_inpcb);
 166
 167         KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
 168
 169         if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
 170             ((rcv_end == tp->rcv_nxt) &&
 171              (tp->rcv_numsacks > 0 ) &&
 172              (tp->sackblks[0].end == tp->rcv_nxt))) {
 173                 saved_blks[0].start = rcv_start;
 174                 saved_blks[0].end = rcv_end;
 175         } else {
 176                 saved_blks[0].start = saved_blks[0].end = 0;
 177         }
 178
 179         head_blk.start = head_blk.end = 0;
 180         mid_blk.start = rcv_start;
 181         mid_blk.end = rcv_end;
 182         identical = 0;
 183
 184         for (i = 0; i < tp->rcv_numsacks; i++) {
 185                 start = tp->sackblks[i].start;
 186                 end = tp->sackblks[i].end;
 187                 if (SEQ_LT(rcv_end, start)) {
 188                         /* pkt left to sack blk */
 189                         continue;
 190                 }
 191                 if (SEQ_GT(rcv_start, end)) {
 192                         /* pkt right to sack blk */
 193                         continue;
 194                 }
 195                 if (SEQ_GT(tp->rcv_nxt, end)) {
 196                         if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
 197                             (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
 198                             (head_blk.start == head_blk.end))) {
 199                                 head_blk.start = SEQ_MAX(rcv_start, start);
 200                                 head_blk.end = SEQ_MIN(rcv_end, end);
 201                         }
 202                         continue;
 203                 }
 204                 if (((head_blk.start == head_blk.end) ||
 205                      SEQ_LT(start, head_blk.start)) &&
 206                      (SEQ_GT(end, rcv_start) &&
 207                       SEQ_LEQ(start, rcv_end))) {
 208                         head_blk.start = start;
 209                         head_blk.end = end;
 210                 }
 211                 mid_blk.start = SEQ_MIN(mid_blk.start, start);
 212                 mid_blk.end = SEQ_MAX(mid_blk.end, end);
 213                 if ((mid_blk.start == start) &&
 214                     (mid_blk.end == end))
 215                         identical = 1;
 216         }
 217         if (SEQ_LT(head_blk.start, head_blk.end)) {
 218                 /* store overlapping range */
 219                 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
 220                 saved_blks[0].end   = SEQ_MIN(rcv_end, head_blk.end);
 221         }
 222         n = 1;
 223         /*
 224          * Second, if not ACKed, store the SACK block that
 225          * overlaps with the DSACK block unless it is identical
 226          */
 227         if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
 228             !((mid_blk.start == saved_blks[0].start) &&
 229             (mid_blk.end == saved_blks[0].end))) ||
 230             identical == 1) {
 231                 saved_blks[n].start = mid_blk.start;
 232                 saved_blks[n++].end = mid_blk.end;
 233         }
 234         for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
 235                 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
 236                       SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
 237                     (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
 238                 saved_blks[n++] = tp->sackblks[j];
 239         }
 240         j = 0;
 241         for (i = 0; i < n; i++) {
 242                 /* we can end up with a stale initial entry */
 243                 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
 244                         tp->sackblks[j++] = saved_blks[i];
 245                 }
 246         }
 247         tp->rcv_numsacks = j;
 248 }
 249
 250 /*
 251  * This function is called upon receipt of new valid data (while not in
 252  * header prediction mode), and it updates the ordered list of sacks.
 253  */
 254 void
 255 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 256 {
 257         /*
 258          * First reported block MUST be the most recent one.  Subsequent
 259          * blocks SHOULD be in the order in which they arrived at the
 260          * receiver.  These two conditions make the implementation fully
 261          * compliant with RFC 2018.
 262          */
 263         struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
 264         int num_head, num_saved, i;
 265
 266         INP_WLOCK_ASSERT(tp->t_inpcb);
 267
 268         /* Check arguments. */
 269         KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
 270
 271         if ((rcv_start == rcv_end) &&
 272             (tp->rcv_numsacks >= 1) &&
 273             (rcv_end == tp->sackblks[0].end)) {
 274                 /* retaining DSACK block below rcv_nxt (todrop) */
 275                 head_blk = tp->sackblks[0];
 276         } else {
 277                 /* SACK block for the received segment. */
 278                 head_blk.start = rcv_start;
 279                 head_blk.end = rcv_end;
 280         }
 281
 282         /*
 283          * Merge updated SACK blocks into head_blk, and save unchanged SACK
 284          * blocks into saved_blks[].  num_saved will have the number of the
 285          * saved SACK blocks.
 286          */
 287         num_saved = 0;
 288         for (i = 0; i < tp->rcv_numsacks; i++) {
 289                 tcp_seq start = tp->sackblks[i].start;
 290                 tcp_seq end = tp->sackblks[i].end;
 291                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 292                         /*
 293                          * Discard this SACK block.
 294                          */
 295                 } else if (SEQ_LEQ(head_blk.start, end) &&
 296                            SEQ_GEQ(head_blk.end, start)) {
 297                         /*
 298                          * Merge this SACK block into head_blk.  This SACK
 299                          * block itself will be discarded.
 300                          */
 301                         /*
 302                          * |-|
 303                          *   |---|  merge
 304                          *
 305                          *     |-|
 306                          * |---|    merge
 307                          *
 308                          * |-----|
 309                          *   |-|    DSACK smaller
 310                          *
 311                          *   |-|
 312                          * |-----|  DSACK smaller
 313                          */
 314                         if (head_blk.start == end)
 315                                 head_blk.start = start;
 316                         else if (head_blk.end == start)
 317                                 head_blk.end = end;
 318                         else {
 319                                 if (SEQ_LT(head_blk.start, start)) {
 320                                         tcp_seq temp = start;
 321                                         start = head_blk.start;
 322                                         head_blk.start = temp;
 323                                 }
 324                                 if (SEQ_GT(head_blk.end, end)) {
 325                                         tcp_seq temp = end;
 326                                         end = head_blk.end;
 327                                         head_blk.end = temp;
 328                                 }
 329                                 if ((head_blk.start != start) ||
 330                                     (head_blk.end != end)) {
 331                                         if ((num_saved >= 1) &&
 332                                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 333                                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 334                                                 num_saved--;
 335                                         saved_blks[num_saved].start = start;
 336                                         saved_blks[num_saved].end = end;
 337                                         num_saved++;
 338                                 }
 339                         }
 340                 } else {
 341                         /*
 342                          * This block supercedes the prior block
 343                          */
 344                         if ((num_saved >= 1) &&
 345                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 346                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 347                                 num_saved--;
 348                         /*
 349                          * Save this SACK block.
 350                          */
 351                         saved_blks[num_saved].start = start;
 352                         saved_blks[num_saved].end = end;
 353                         num_saved++;
 354                 }
 355         }
 356
 357         /*
 358          * Update SACK list in tp->sackblks[].
 359          */
 360         num_head = 0;
 361         if (SEQ_LT(rcv_start, rcv_end)) {
 362                 /*
 363                  * The received data segment is an out-of-order segment.  Put
 364                  * head_blk at the top of SACK list.
 365                  */
 366                 tp->sackblks[0] = head_blk;
 367                 num_head = 1;
 368                 /*
 369                  * If the number of saved SACK blocks exceeds its limit,
 370                  * discard the last SACK block.
 371                  */
 372                 if (num_saved >= MAX_SACK_BLKS)
 373                         num_saved--;
 374         }
 375         if ((rcv_start == rcv_end) &&
 376             (rcv_start == tp->sackblks[0].end)) {
 377                 num_head = 1;
 378         }
 379         if (num_saved > 0) {
 380                 /*
 381                  * Copy the saved SACK blocks back.
 382                  */
 383                 bcopy(saved_blks, &tp->sackblks[num_head],
 384                       sizeof(struct sackblk) * num_saved);
 385         }
 386
 387         /* Save the number of SACK blocks. */
 388         tp->rcv_numsacks = num_head + num_saved;
 389 }
 390
 391 void
 392 tcp_clean_dsack_blocks(struct tcpcb *tp)
 393 {
 394         struct sackblk saved_blks[MAX_SACK_BLKS];
 395         int num_saved, i;
 396
 397         INP_WLOCK_ASSERT(tp->t_inpcb);
 398         /*
 399          * Clean up any DSACK blocks that
 400          * are in our queue of sack blocks.
 401          *
 402          */
 403         num_saved = 0;
 404         for (i = 0; i < tp->rcv_numsacks; i++) {
 405                 tcp_seq start = tp->sackblks[i].start;
 406                 tcp_seq end = tp->sackblks[i].end;
 407                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 408                         /*
 409                          * Discard this D-SACK block.
 410                          */
 411                         continue;
 412                 }
 413                 /*
 414                  * Save this SACK block.
 415                  */
 416                 saved_blks[num_saved].start = start;
 417                 saved_blks[num_saved].end = end;
 418                 num_saved++;
 419         }
 420         if (num_saved > 0) {
 421                 /*
 422                  * Copy the saved SACK blocks back.
 423                  */
 424                 bcopy(saved_blks, &tp->sackblks[0],
 425                       sizeof(struct sackblk) * num_saved);
 426         }
 427         tp->rcv_numsacks = num_saved;
 428 }
 429
 430 /*
 431  * Delete all receiver-side SACK information.
 432  */
 433 void
 434 tcp_clean_sackreport(struct tcpcb *tp)
 435 {
 436         int i;
 437
 438         INP_WLOCK_ASSERT(tp->t_inpcb);
 439         tp->rcv_numsacks = 0;
 440         for (i = 0; i < MAX_SACK_BLKS; i++)
 441                 tp->sackblks[i].start = tp->sackblks[i].end=0;
 442 }
 443
 444 /*
 445  * Allocate struct sackhole.
 446  */
 447 static struct sackhole *
 448 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 449 {
 450         struct sackhole *hole;
 451
 452         if (tp->snd_numholes >= V_tcp_sack_maxholes ||
 453             V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
 454                 TCPSTAT_INC(tcps_sack_sboverflow);
 455                 return NULL;
 456         }
 457
 458         hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
 459         if (hole == NULL)
 460                 return NULL;
 461
 462         hole->start = start;
 463         hole->end = end;
 464         hole->rxmit = start;
 465
 466         tp->snd_numholes++;
 467         atomic_add_int(&V_tcp_sack_globalholes, 1);
 468
 469         return hole;
 470 }
 471
 472 /*
 473  * Free struct sackhole.
 474  */
 475 static void
 476 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
 477 {
 478
 479         uma_zfree(V_sack_hole_zone, hole);
 480
 481         tp->snd_numholes--;
 482         atomic_subtract_int(&V_tcp_sack_globalholes, 1);
 483
 484         KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
 485         KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
 486 }
 487
 488 /*
 489  * Insert new SACK hole into scoreboard.
 490  */
 491 static struct sackhole *
 492 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
 493     struct sackhole *after)
 494 {
 495         struct sackhole *hole;
 496
 497         /* Allocate a new SACK hole. */
 498         hole = tcp_sackhole_alloc(tp, start, end);
 499         if (hole == NULL)
 500                 return NULL;
 501
 502         /* Insert the new SACK hole into scoreboard. */
 503         if (after != NULL)
 504                 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
 505         else
 506                 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
 507
 508         /* Update SACK hint. */
 509         if (tp->sackhint.nexthole == NULL)
 510                 tp->sackhint.nexthole = hole;
 511
 512         return hole;
 513 }
 514
 515 /*
 516  * Remove SACK hole from scoreboard.
 517  */
 518 static void
 519 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
 520 {
 521
 522         /* Update SACK hint. */
 523         if (tp->sackhint.nexthole == hole)
 524                 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
 525
 526         /* Remove this SACK hole. */
 527         TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
 528
 529         /* Free this SACK hole. */
 530         tcp_sackhole_free(tp, hole);
 531 }
 532
 533 /*
 534  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
 535  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
 536  * the sequence space).
 537  * Returns 1 if incoming ACK has previously unknown SACK information,
 538  * 0 otherwise.
 539  */
 540 int
 541 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
 542 {
 543         struct sackhole *cur, *temp;
 544         struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 545         int i, j, num_sack_blks, sack_changed;
 546         int delivered_data, left_edge_delta;
 547
 548         INP_WLOCK_ASSERT(tp->t_inpcb);
 549
 550         num_sack_blks = 0;
 551         sack_changed = 0;
 552         delivered_data = 0;
 553         left_edge_delta = 0;
 554         /*
 555          * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 556          * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
 557          * Account changes to SND.UNA always in delivered data.
 558          */
 559         if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
 560                 left_edge_delta = th_ack - tp->snd_una;
 561                 sack_blocks[num_sack_blks].start = tp->snd_una;
 562                 sack_blocks[num_sack_blks++].end = th_ack;
 563         }
 564         /*
 565          * Append received valid SACK blocks to sack_blocks[], but only if we
 566          * received new blocks from the other side.
 567          */
 568         if (to->to_flags & TOF_SACK) {
 569                 for (i = 0; i < to->to_nsacks; i++) {
 570                         bcopy((to->to_sacks + i * TCPOLEN_SACK),
 571                             &sack, sizeof(sack));
 572                         sack.start = ntohl(sack.start);
 573                         sack.end = ntohl(sack.end);
 574                         if (SEQ_GT(sack.end, sack.start) &&
 575                             SEQ_GT(sack.start, tp->snd_una) &&
 576                             SEQ_GT(sack.start, th_ack) &&
 577                             SEQ_LT(sack.start, tp->snd_max) &&
 578                             SEQ_GT(sack.end, tp->snd_una) &&
 579                             SEQ_LEQ(sack.end, tp->snd_max)) {
 580                                 sack_blocks[num_sack_blks++] = sack;
 581                         }
 582                 }
 583         }
 584         /*
 585          * Return if SND.UNA is not advanced and no valid SACK block is
 586          * received.
 587          */
 588         if (num_sack_blks == 0)
 589                 return (sack_changed);
 590
 591         /*
 592          * Sort the SACK blocks so we can update the scoreboard with just one
 593          * pass. The overhead of sorting up to 4+1 elements is less than
 594          * making up to 4+1 passes over the scoreboard.
 595          */
 596         for (i = 0; i < num_sack_blks; i++) {
 597                 for (j = i + 1; j < num_sack_blks; j++) {
 598                         if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
 599                                 sack = sack_blocks[i];
 600                                 sack_blocks[i] = sack_blocks[j];
 601                                 sack_blocks[j] = sack;
 602                         }
 603                 }
 604         }
 605         if (TAILQ_EMPTY(&tp->snd_holes)) {
 606                 /*
 607                  * Empty scoreboard. Need to initialize snd_fack (it may be
 608                  * uninitialized or have a bogus value). Scoreboard holes
 609                  * (from the sack blocks received) are created later below
 610                  * (in the logic that adds holes to the tail of the
 611                  * scoreboard).
 612                  */
 613                 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
 614                 tp->sackhint.sacked_bytes = 0;  /* reset */
 615         }
 616         /*
 617          * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
 618          * SACK holes (snd_holes) are traversed from their tails with just
 619          * one pass in order to reduce the number of compares especially when
 620          * the bandwidth-delay product is large.
 621          *
 622          * Note: Typically, in the first RTT of SACK recovery, the highest
 623          * three or four SACK blocks with the same ack number are received.
 624          * In the second RTT, if retransmitted data segments are not lost,
 625          * the highest three or four SACK blocks with ack number advancing
 626          * are received.
 627          */
 628         sblkp = &sack_blocks[num_sack_blks - 1];        /* Last SACK block */
 629         tp->sackhint.last_sack_ack = sblkp->end;
 630         if (SEQ_LT(tp->snd_fack, sblkp->start)) {
 631                 /*
 632                  * The highest SACK block is beyond fack.  Append new SACK
 633                  * hole at the tail.  If the second or later highest SACK
 634                  * blocks are also beyond the current fack, they will be
 635                  * inserted by way of hole splitting in the while-loop below.
 636                  */
 637                 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
 638                 if (temp != NULL) {
 639                         delivered_data += sblkp->end - sblkp->start;
 640                         tp->snd_fack = sblkp->end;
 641                         /* Go to the previous sack block. */
 642                         sblkp--;
 643                         sack_changed = 1;
 644                 } else {
 645                         /*
 646                          * We failed to add a new hole based on the current
 647                          * sack block.  Skip over all the sack blocks that
 648                          * fall completely to the right of snd_fack and
 649                          * proceed to trim the scoreboard based on the
 650                          * remaining sack blocks.  This also trims the
 651                          * scoreboard for th_ack (which is sack_blocks[0]).
 652                          */
 653                         while (sblkp >= sack_blocks &&
 654                                SEQ_LT(tp->snd_fack, sblkp->start))
 655                                 sblkp--;
 656                         if (sblkp >= sack_blocks &&
 657                             SEQ_LT(tp->snd_fack, sblkp->end)) {
 658                                 delivered_data += sblkp->end - tp->snd_fack;
 659                                 tp->snd_fack = sblkp->end;
 660                                 sack_changed = 1;
 661                         }
 662                 }
 663         } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
 664                 /* fack is advanced. */
 665                 delivered_data += sblkp->end - tp->snd_fack;
 666                 tp->snd_fack = sblkp->end;
 667                 sack_changed = 1;
 668         }
 669         cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
 670         /*
 671          * Since the incoming sack blocks are sorted, we can process them
 672          * making one sweep of the scoreboard.
 673          */
 674         while (sblkp >= sack_blocks  && cur != NULL) {
 675                 if (SEQ_GEQ(sblkp->start, cur->end)) {
 676                         /*
 677                          * SACKs data beyond the current hole.  Go to the
 678                          * previous sack block.
 679                          */
 680                         sblkp--;
 681                         continue;
 682                 }
 683                 if (SEQ_LEQ(sblkp->end, cur->start)) {
 684                         /*
 685                          * SACKs data before the current hole.  Go to the
 686                          * previous hole.
 687                          */
 688                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 689                         continue;
 690                 }
 691                 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
 692                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 693                     ("sackhint bytes rtx >= 0"));
 694                 sack_changed = 1;
 695                 if (SEQ_LEQ(sblkp->start, cur->start)) {
 696                         /* Data acks at least the beginning of hole. */
 697                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 698                                 /* Acks entire hole, so delete hole. */
 699                                 delivered_data += (cur->end - cur->start);
 700                                 temp = cur;
 701                                 cur = TAILQ_PREV(cur, sackhole_head, scblink);
 702                                 tcp_sackhole_remove(tp, temp);
 703                                 /*
 704                                  * The sack block may ack all or part of the
 705                                  * next hole too, so continue onto the next
 706                                  * hole.
 707                                  */
 708                                 continue;
 709                         } else {
 710                                 /* Move start of hole forward. */
 711                                 delivered_data += (sblkp->end - cur->start);
 712                                 cur->start = sblkp->end;
 713                                 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 714                         }
 715                 } else {
 716                         /* Data acks at least the end of hole. */
 717                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 718                                 /* Move end of hole backward. */
 719                                 delivered_data += (cur->end - sblkp->start);
 720                                 cur->end = sblkp->start;
 721                                 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 722                         } else {
 723                                 /*
 724                                  * ACKs some data in middle of a hole; need
 725                                  * to split current hole
 726                                  */
 727                                 temp = tcp_sackhole_insert(tp, sblkp->end,
 728                                     cur->end, cur);
 729                                 if (temp != NULL) {
 730                                         if (SEQ_GT(cur->rxmit, temp->rxmit)) {
 731                                                 temp->rxmit = cur->rxmit;
 732                                                 tp->sackhint.sack_bytes_rexmit
 733                                                     += (temp->rxmit
 734                                                     - temp->start);
 735                                         }
 736                                         cur->end = sblkp->start;
 737                                         cur->rxmit = SEQ_MIN(cur->rxmit,
 738                                             cur->end);
 739                                         delivered_data += (sblkp->end - sblkp->start);
 740                                 }
 741                         }
 742                 }
 743                 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
 744                 /*
 745                  * Testing sblkp->start against cur->start tells us whether
 746                  * we're done with the sack block or the sack hole.
 747                  * Accordingly, we advance one or the other.
 748                  */
 749                 if (SEQ_LEQ(sblkp->start, cur->start))
 750                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 751                 else
 752                         sblkp--;
 753         }
 754         tp->sackhint.delivered_data = delivered_data;
 755         tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
 756         KASSERT((delivered_data >= 0), ("delivered_data < 0"));
 757         KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
 758         return (sack_changed);
 759 }
 760
 761 /*
 762  * Free all SACK holes to clear the scoreboard.
 763  */
 764 void
 765 tcp_free_sackholes(struct tcpcb *tp)
 766 {
 767         struct sackhole *q;
 768
 769         INP_WLOCK_ASSERT(tp->t_inpcb);
 770         while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
 771                 tcp_sackhole_remove(tp, q);
 772         tp->sackhint.sack_bytes_rexmit = 0;
 773
 774         KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
 775         KASSERT(tp->sackhint.nexthole == NULL,
 776                 ("tp->sackhint.nexthole == NULL"));
 777 }
 778
 779 /*
 780  * Partial ack handling within a sack recovery episode.  Keeping this very
 781  * simple for now.  When a partial ack is received, force snd_cwnd to a value
 782  * that will allow the sender to transmit no more than 2 segments.  If
 783  * necessary, a better scheme can be adopted at a later point, but for now,
 784  * the goal is to prevent the sender from bursting a large amount of data in
 785  * the midst of sack recovery.
 786  */
 787 void
 788 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 789 {
 790         int num_segs = 1;
 791
 792         INP_WLOCK_ASSERT(tp->t_inpcb);
 793         tcp_timer_activate(tp, TT_REXMT, 0);
 794         tp->t_rtttime = 0;
 795         /* Send one or 2 segments based on how much new data was acked. */
 796         if ((BYTES_THIS_ACK(tp, th) / tp->t_maxseg) >= 2)
 797                 num_segs = 2;
 798         tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
 799             (tp->snd_nxt - tp->snd_recover) + num_segs * tp->t_maxseg);
 800         if (tp->snd_cwnd > tp->snd_ssthresh)
 801                 tp->snd_cwnd = tp->snd_ssthresh;
 802         tp->t_flags |= TF_ACKNOW;
 803         (void) tp->t_fb->tfb_tcp_output(tp);
 804 }
 805
 806 #if 0
 807 /*
 808  * Debug version of tcp_sack_output() that walks the scoreboard.  Used for
 809  * now to sanity check the hint.
 810  */
 811 static struct sackhole *
 812 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
 813 {
 814         struct sackhole *p;
 815
 816         INP_WLOCK_ASSERT(tp->t_inpcb);
 817         *sack_bytes_rexmt = 0;
 818         TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
 819                 if (SEQ_LT(p->rxmit, p->end)) {
 820                         if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 821                                 continue;
 822                         }
 823                         *sack_bytes_rexmt += (p->rxmit - p->start);
 824                         break;
 825                 }
 826                 *sack_bytes_rexmt += (p->rxmit - p->start);
 827         }
 828         return (p);
 829 }
 830 #endif
 831
 832 /*
 833  * Returns the next hole to retransmit and the number of retransmitted bytes
 834  * from the scoreboard.  We store both the next hole and the number of
 835  * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
 836  * reception).  This avoids scoreboard traversals completely.
 837  *
 838  * The loop here will traverse *at most* one link.  Here's the argument.  For
 839  * the loop to traverse more than 1 link before finding the next hole to
 840  * retransmit, we would need to have at least 1 node following the current
 841  * hint with (rxmit == end).  But, for all holes following the current hint,
 842  * (start == rxmit), since we have not yet retransmitted from them.
 843  * Therefore, in order to traverse more 1 link in the loop below, we need to
 844  * have at least one node following the current hint with (start == rxmit ==
 845  * end).  But that can't happen, (start == end) means that all the data in
 846  * that hole has been sacked, in which case, the hole would have been removed
 847  * from the scoreboard.
 848  */
 849 struct sackhole *
 850 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 851 {
 852         struct sackhole *hole = NULL;
 853
 854         INP_WLOCK_ASSERT(tp->t_inpcb);
 855         *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
 856         hole = tp->sackhint.nexthole;
 857         if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
 858                 goto out;
 859         while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
 860                 if (SEQ_LT(hole->rxmit, hole->end)) {
 861                         tp->sackhint.nexthole = hole;
 862                         break;
 863                 }
 864         }
 865 out:
 866         return (hole);
 867 }
 868
 869 /*
 870  * After a timeout, the SACK list may be rebuilt.  This SACK information
 871  * should be used to avoid retransmitting SACKed data.  This function
 872  * traverses the SACK list to see if snd_nxt should be moved forward.
 873  */
 874 void
 875 tcp_sack_adjust(struct tcpcb *tp)
 876 {
 877         struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 878
 879         INP_WLOCK_ASSERT(tp->t_inpcb);
 880         if (cur == NULL)
 881                 return; /* No holes */
 882         if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
 883                 return; /* We're already beyond any SACKed blocks */
 884         /*-
 885          * Two cases for which we want to advance snd_nxt:
 886          * i) snd_nxt lies between end of one hole and beginning of another
 887          * ii) snd_nxt lies between end of last hole and snd_fack
 888          */
 889         while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
 890                 if (SEQ_LT(tp->snd_nxt, cur->end))
 891                         return;
 892                 if (SEQ_GEQ(tp->snd_nxt, p->start))
 893                         cur = p;
 894                 else {
 895                         tp->snd_nxt = p->start;
 896                         return;
 897                 }
 898         }
 899         if (SEQ_LT(tp->snd_nxt, cur->end))
 900                 return;
 901         tp->snd_nxt = tp->snd_fack;
 902 }