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 #include "opt_inet.h"
  77 #include "opt_inet6.h"
  78 #include "opt_tcpdebug.h"
  79
  80 #include <sys/param.h>
  81 #include <sys/systm.h>
  82 #include <sys/kernel.h>
  83 #include <sys/sysctl.h>
  84 #include <sys/malloc.h>
  85 #include <sys/mbuf.h>
  86 #include <sys/proc.h>           /* for proc0 declaration */
  87 #include <sys/protosw.h>
  88 #include <sys/socket.h>
  89 #include <sys/socketvar.h>
  90 #include <sys/syslog.h>
  91 #include <sys/systm.h>
  92
  93 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  94
  95 #include <vm/uma.h>
  96
  97 #include <net/if.h>
  98 #include <net/if_var.h>
  99 #include <net/route.h>
 100 #include <net/vnet.h>
 101
 102 #include <netinet/in.h>
 103 #include <netinet/in_systm.h>
 104 #include <netinet/ip.h>
 105 #include <netinet/in_var.h>
 106 #include <netinet/in_pcb.h>
 107 #include <netinet/ip_var.h>
 108 #include <netinet/ip6.h>
 109 #include <netinet/icmp6.h>
 110 #include <netinet6/nd6.h>
 111 #include <netinet6/ip6_var.h>
 112 #include <netinet6/in6_pcb.h>
 113 #include <netinet/tcp.h>
 114 #include <netinet/tcp_fsm.h>
 115 #include <netinet/tcp_seq.h>
 116 #include <netinet/tcp_timer.h>
 117 #include <netinet/tcp_var.h>
 118 #include <netinet6/tcp6_var.h>
 119 #include <netinet/tcpip.h>
 120 #ifdef TCPDEBUG
 121 #include <netinet/tcp_debug.h>
 122 #endif /* TCPDEBUG */
 123
 124 #include <machine/in_cksum.h>
 125
 126 VNET_DECLARE(struct uma_zone *, sack_hole_zone);
 127 #define V_sack_hole_zone                VNET(sack_hole_zone)
 128
 129 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
 130     "TCP SACK");
 131 VNET_DEFINE(int, tcp_do_sack) = 1;
 132 #define V_tcp_do_sack                   VNET(tcp_do_sack)
 133 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
 134     &VNET_NAME(tcp_do_sack), 0, "Enable/Disable TCP SACK support");
 135
 136 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
 137 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
 138     &VNET_NAME(tcp_sack_maxholes), 0,
 139     "Maximum number of TCP SACK holes allowed per connection");
 140
 141 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
 142 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
 143     &VNET_NAME(tcp_sack_globalmaxholes), 0,
 144     "Global maximum number of TCP SACK holes");
 145
 146 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
 147 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
 148     &VNET_NAME(tcp_sack_globalholes), 0,
 149     "Global number of TCP SACK holes currently allocated");
 150
 151 int
 152 tcp_dsack_block_exists(struct tcpcb *tp)
 153 {
 154         /* Return true if a DSACK block exists */
 155         if (tp->rcv_numsacks == 0)
 156                 return (0);
 157         if (SEQ_LEQ(tp->sackblks[0].end, tp->rcv_nxt))
 158                 return(1);
 159         return (0);
 160 }
 161
 162 /*
 163  * This function will find overlaps with the currently stored sackblocks
 164  * and add any overlap as a dsack block upfront
 165  */
 166 void
 167 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 168 {
 169         struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
 170         int i, j, n, identical;
 171         tcp_seq start, end;
 172
 173         INP_WLOCK_ASSERT(tp->t_inpcb);
 174
 175         KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
 176
 177         if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
 178             ((rcv_end == tp->rcv_nxt) &&
 179              (tp->rcv_numsacks > 0 ) &&
 180              (tp->sackblks[0].end == tp->rcv_nxt))) {
 181                 saved_blks[0].start = rcv_start;
 182                 saved_blks[0].end = rcv_end;
 183         } else {
 184                 saved_blks[0].start = saved_blks[0].end = 0;
 185         }
 186
 187         head_blk.start = head_blk.end = 0;
 188         mid_blk.start = rcv_start;
 189         mid_blk.end = rcv_end;
 190         identical = 0;
 191
 192         for (i = 0; i < tp->rcv_numsacks; i++) {
 193                 start = tp->sackblks[i].start;
 194                 end = tp->sackblks[i].end;
 195                 if (SEQ_LT(rcv_end, start)) {
 196                         /* pkt left to sack blk */
 197                         continue;
 198                 }
 199                 if (SEQ_GT(rcv_start, end)) {
 200                         /* pkt right to sack blk */
 201                         continue;
 202                 }
 203                 if (SEQ_GT(tp->rcv_nxt, end)) {
 204                         if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
 205                             (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
 206                             (head_blk.start == head_blk.end))) {
 207                                 head_blk.start = SEQ_MAX(rcv_start, start);
 208                                 head_blk.end = SEQ_MIN(rcv_end, end);
 209                         }
 210                         continue;
 211                 }
 212                 if (((head_blk.start == head_blk.end) ||
 213                      SEQ_LT(start, head_blk.start)) &&
 214                      (SEQ_GT(end, rcv_start) &&
 215                       SEQ_LEQ(start, rcv_end))) {
 216                         head_blk.start = start;
 217                         head_blk.end = end;
 218                 }
 219                 mid_blk.start = SEQ_MIN(mid_blk.start, start);
 220                 mid_blk.end = SEQ_MAX(mid_blk.end, end);
 221                 if ((mid_blk.start == start) &&
 222                     (mid_blk.end == end))
 223                         identical = 1;
 224         }
 225         if (SEQ_LT(head_blk.start, head_blk.end)) {
 226                 /* store overlapping range */
 227                 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
 228                 saved_blks[0].end   = SEQ_MIN(rcv_end, head_blk.end);
 229         }
 230         n = 1;
 231         /*
 232          * Second, if not ACKed, store the SACK block that
 233          * overlaps with the DSACK block unless it is identical
 234          */
 235         if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
 236             !((mid_blk.start == saved_blks[0].start) &&
 237             (mid_blk.end == saved_blks[0].end))) ||
 238             identical == 1) {
 239                 saved_blks[n].start = mid_blk.start;
 240                 saved_blks[n++].end = mid_blk.end;
 241         }
 242         for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
 243                 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
 244                       SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
 245                     (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
 246                 saved_blks[n++] = tp->sackblks[j];
 247         }
 248         j = 0;
 249         for (i = 0; i < n; i++) {
 250                 /* we can end up with a stale initial entry */
 251                 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
 252                         tp->sackblks[j++] = saved_blks[i];
 253                 }
 254         }
 255         tp->rcv_numsacks = j;
 256 }
 257
 258 /*
 259  * This function is called upon receipt of new valid data (while not in
 260  * header prediction mode), and it updates the ordered list of sacks.
 261  */
 262 void
 263 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 264 {
 265         /*
 266          * First reported block MUST be the most recent one.  Subsequent
 267          * blocks SHOULD be in the order in which they arrived at the
 268          * receiver.  These two conditions make the implementation fully
 269          * compliant with RFC 2018.
 270          */
 271         struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
 272         int num_head, num_saved, i;
 273
 274         INP_WLOCK_ASSERT(tp->t_inpcb);
 275
 276         /* Check arguments. */
 277         KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
 278
 279         if ((rcv_start == rcv_end) &&
 280             (tp->rcv_numsacks >= 1) &&
 281             (rcv_end == tp->sackblks[0].end)) {
 282                 /* retaining DSACK block below rcv_nxt (todrop) */
 283                 head_blk = tp->sackblks[0];
 284         } else {
 285                 /* SACK block for the received segment. */
 286                 head_blk.start = rcv_start;
 287                 head_blk.end = rcv_end;
 288         }
 289
 290         /*
 291          * Merge updated SACK blocks into head_blk, and save unchanged SACK
 292          * blocks into saved_blks[].  num_saved will have the number of the
 293          * saved SACK blocks.
 294          */
 295         num_saved = 0;
 296         for (i = 0; i < tp->rcv_numsacks; i++) {
 297                 tcp_seq start = tp->sackblks[i].start;
 298                 tcp_seq end = tp->sackblks[i].end;
 299                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 300                         /*
 301                          * Discard this SACK block.
 302                          */
 303                 } else if (SEQ_LEQ(head_blk.start, end) &&
 304                            SEQ_GEQ(head_blk.end, start)) {
 305                         /*
 306                          * Merge this SACK block into head_blk.  This SACK
 307                          * block itself will be discarded.
 308                          */
 309                         /*
 310                          * |-|
 311                          *   |---|  merge
 312                          *
 313                          *     |-|
 314                          * |---|    merge
 315                          *
 316                          * |-----|
 317                          *   |-|    DSACK smaller
 318                          *
 319                          *   |-|
 320                          * |-----|  DSACK smaller
 321                          */
 322                         if (head_blk.start == end)
 323                                 head_blk.start = start;
 324                         else if (head_blk.end == start)
 325                                 head_blk.end = end;
 326                         else {
 327                                 if (SEQ_LT(head_blk.start, start)) {
 328                                         tcp_seq temp = start;
 329                                         start = head_blk.start;
 330                                         head_blk.start = temp;
 331                                 }
 332                                 if (SEQ_GT(head_blk.end, end)) {
 333                                         tcp_seq temp = end;
 334                                         end = head_blk.end;
 335                                         head_blk.end = temp;
 336                                 }
 337                                 if ((head_blk.start != start) ||
 338                                     (head_blk.end != end)) {
 339                                         if ((num_saved >= 1) &&
 340                                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 341                                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 342                                                 num_saved--;
 343                                         saved_blks[num_saved].start = start;
 344                                         saved_blks[num_saved].end = end;
 345                                         num_saved++;
 346                                 }
 347                         }
 348                 } else {
 349                         /*
 350                          * This block supercedes the prior block
 351                          */
 352                         if ((num_saved >= 1) &&
 353                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 354                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 355                                 num_saved--;
 356                         /*
 357                          * Save this SACK block.
 358                          */
 359                         saved_blks[num_saved].start = start;
 360                         saved_blks[num_saved].end = end;
 361                         num_saved++;
 362                 }
 363         }
 364
 365         /*
 366          * Update SACK list in tp->sackblks[].
 367          */
 368         num_head = 0;
 369         if (SEQ_LT(rcv_start, rcv_end)) {
 370                 /*
 371                  * The received data segment is an out-of-order segment.  Put
 372                  * head_blk at the top of SACK list.
 373                  */
 374                 tp->sackblks[0] = head_blk;
 375                 num_head = 1;
 376                 /*
 377                  * If the number of saved SACK blocks exceeds its limit,
 378                  * discard the last SACK block.
 379                  */
 380                 if (num_saved >= MAX_SACK_BLKS)
 381                         num_saved--;
 382         }
 383         if ((rcv_start == rcv_end) &&
 384             (rcv_start == tp->sackblks[0].end)) {
 385                 num_head = 1;
 386         }
 387         if (num_saved > 0) {
 388                 /*
 389                  * Copy the saved SACK blocks back.
 390                  */
 391                 bcopy(saved_blks, &tp->sackblks[num_head],
 392                       sizeof(struct sackblk) * num_saved);
 393         }
 394
 395         /* Save the number of SACK blocks. */
 396         tp->rcv_numsacks = num_head + num_saved;
 397 }
 398
 399 void
 400 tcp_clean_dsack_blocks(struct tcpcb *tp)
 401 {
 402         struct sackblk saved_blks[MAX_SACK_BLKS];
 403         int num_saved, i;
 404
 405         INP_WLOCK_ASSERT(tp->t_inpcb);
 406         /*
 407          * Clean up any DSACK blocks that
 408          * are in our queue of sack blocks.
 409          *
 410          */
 411         num_saved = 0;
 412         for (i = 0; i < tp->rcv_numsacks; i++) {
 413                 tcp_seq start = tp->sackblks[i].start;
 414                 tcp_seq end = tp->sackblks[i].end;
 415                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 416                         /*
 417                          * Discard this D-SACK block.
 418                          */
 419                         continue;
 420                 }
 421                 /*
 422                  * Save this SACK block.
 423                  */
 424                 saved_blks[num_saved].start = start;
 425                 saved_blks[num_saved].end = end;
 426                 num_saved++;
 427         }
 428         if (num_saved > 0) {
 429                 /*
 430                  * Copy the saved SACK blocks back.
 431                  */
 432                 bcopy(saved_blks, &tp->sackblks[0],
 433                       sizeof(struct sackblk) * num_saved);
 434         }
 435         tp->rcv_numsacks = num_saved;
 436 }
 437
 438 /*
 439  * Delete all receiver-side SACK information.
 440  */
 441 void
 442 tcp_clean_sackreport(struct tcpcb *tp)
 443 {
 444         int i;
 445
 446         INP_WLOCK_ASSERT(tp->t_inpcb);
 447         tp->rcv_numsacks = 0;
 448         for (i = 0; i < MAX_SACK_BLKS; i++)
 449                 tp->sackblks[i].start = tp->sackblks[i].end=0;
 450 }
 451
 452 /*
 453  * Allocate struct sackhole.
 454  */
 455 static struct sackhole *
 456 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 457 {
 458         struct sackhole *hole;
 459
 460         if (tp->snd_numholes >= V_tcp_sack_maxholes ||
 461             V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
 462                 TCPSTAT_INC(tcps_sack_sboverflow);
 463                 return NULL;
 464         }
 465
 466         hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
 467         if (hole == NULL)
 468                 return NULL;
 469
 470         hole->start = start;
 471         hole->end = end;
 472         hole->rxmit = start;
 473
 474         tp->snd_numholes++;
 475         atomic_add_int(&V_tcp_sack_globalholes, 1);
 476
 477         return hole;
 478 }
 479
 480 /*
 481  * Free struct sackhole.
 482  */
 483 static void
 484 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
 485 {
 486
 487         uma_zfree(V_sack_hole_zone, hole);
 488
 489         tp->snd_numholes--;
 490         atomic_subtract_int(&V_tcp_sack_globalholes, 1);
 491
 492         KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
 493         KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
 494 }
 495
 496 /*
 497  * Insert new SACK hole into scoreboard.
 498  */
 499 static struct sackhole *
 500 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
 501     struct sackhole *after)
 502 {
 503         struct sackhole *hole;
 504
 505         /* Allocate a new SACK hole. */
 506         hole = tcp_sackhole_alloc(tp, start, end);
 507         if (hole == NULL)
 508                 return NULL;
 509
 510         /* Insert the new SACK hole into scoreboard. */
 511         if (after != NULL)
 512                 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
 513         else
 514                 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
 515
 516         /* Update SACK hint. */
 517         if (tp->sackhint.nexthole == NULL)
 518                 tp->sackhint.nexthole = hole;
 519
 520         return hole;
 521 }
 522
 523 /*
 524  * Remove SACK hole from scoreboard.
 525  */
 526 static void
 527 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
 528 {
 529
 530         /* Update SACK hint. */
 531         if (tp->sackhint.nexthole == hole)
 532                 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
 533
 534         /* Remove this SACK hole. */
 535         TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
 536
 537         /* Free this SACK hole. */
 538         tcp_sackhole_free(tp, hole);
 539 }
 540
 541 /*
 542  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
 543  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
 544  * the sequence space).
 545  * Returns 1 if incoming ACK has previously unknown SACK information,
 546  * 0 otherwise.
 547  */
 548 int
 549 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
 550 {
 551         struct sackhole *cur, *temp;
 552         struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 553         int i, j, num_sack_blks, sack_changed;
 554         int delivered_data, left_edge_delta;
 555
 556         INP_WLOCK_ASSERT(tp->t_inpcb);
 557
 558         num_sack_blks = 0;
 559         sack_changed = 0;
 560         delivered_data = 0;
 561         left_edge_delta = 0;
 562         /*
 563          * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 564          * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
 565          * Account changes to SND.UNA always in delivered data.
 566          */
 567         if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
 568                 left_edge_delta = th_ack - tp->snd_una;
 569                 sack_blocks[num_sack_blks].start = tp->snd_una;
 570                 sack_blocks[num_sack_blks++].end = th_ack;
 571                 /*
 572                  * Pulling snd_fack forward if we got here
 573                  * due to DSACK blocks
 574                  */
 575                 if (SEQ_LT(tp->snd_fack, th_ack)) {
 576                         delivered_data += th_ack - tp->snd_una;
 577                         tp->snd_fack = th_ack;
 578                         sack_changed = 1;
 579                 }
 580         }
 581         /*
 582          * Append received valid SACK blocks to sack_blocks[], but only if we
 583          * received new blocks from the other side.
 584          */
 585         if (to->to_flags & TOF_SACK) {
 586                 for (i = 0; i < to->to_nsacks; i++) {
 587                         bcopy((to->to_sacks + i * TCPOLEN_SACK),
 588                             &sack, sizeof(sack));
 589                         sack.start = ntohl(sack.start);
 590                         sack.end = ntohl(sack.end);
 591                         if (SEQ_GT(sack.end, sack.start) &&
 592                             SEQ_GT(sack.start, tp->snd_una) &&
 593                             SEQ_GT(sack.start, th_ack) &&
 594                             SEQ_LT(sack.start, tp->snd_max) &&
 595                             SEQ_GT(sack.end, tp->snd_una) &&
 596                             SEQ_LEQ(sack.end, tp->snd_max)) {
 597                                 sack_blocks[num_sack_blks++] = sack;
 598                         }
 599                 }
 600         }
 601         /*
 602          * Return if SND.UNA is not advanced and no valid SACK block is
 603          * received.
 604          */
 605         if (num_sack_blks == 0)
 606                 return (sack_changed);
 607
 608         /*
 609          * Sort the SACK blocks so we can update the scoreboard with just one
 610          * pass. The overhead of sorting up to 4+1 elements is less than
 611          * making up to 4+1 passes over the scoreboard.
 612          */
 613         for (i = 0; i < num_sack_blks; i++) {
 614                 for (j = i + 1; j < num_sack_blks; j++) {
 615                         if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
 616                                 sack = sack_blocks[i];
 617                                 sack_blocks[i] = sack_blocks[j];
 618                                 sack_blocks[j] = sack;
 619                         }
 620                 }
 621         }
 622         if (TAILQ_EMPTY(&tp->snd_holes)) {
 623                 /*
 624                  * Empty scoreboard. Need to initialize snd_fack (it may be
 625                  * uninitialized or have a bogus value). Scoreboard holes
 626                  * (from the sack blocks received) are created later below
 627                  * (in the logic that adds holes to the tail of the
 628                  * scoreboard).
 629                  */
 630                 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
 631                 tp->sackhint.sacked_bytes = 0;  /* reset */
 632         }
 633         /*
 634          * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
 635          * SACK holes (snd_holes) are traversed from their tails with just
 636          * one pass in order to reduce the number of compares especially when
 637          * the bandwidth-delay product is large.
 638          *
 639          * Note: Typically, in the first RTT of SACK recovery, the highest
 640          * three or four SACK blocks with the same ack number are received.
 641          * In the second RTT, if retransmitted data segments are not lost,
 642          * the highest three or four SACK blocks with ack number advancing
 643          * are received.
 644          */
 645         sblkp = &sack_blocks[num_sack_blks - 1];        /* Last SACK block */
 646         tp->sackhint.last_sack_ack = sblkp->end;
 647         if (SEQ_LT(tp->snd_fack, sblkp->start)) {
 648                 /*
 649                  * The highest SACK block is beyond fack.  First,
 650                  * check if there was a successful Rescue Retransmission,
 651                  * and move this hole left. With normal holes, snd_fack
 652                  * is always to the right of the end.
 653                  */
 654                 if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
 655                     SEQ_LEQ(tp->snd_fack,temp->end)) {
 656                         temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
 657                         temp->end = sblkp->start;
 658                         temp->rxmit = temp->start;
 659                         delivered_data += sblkp->end - sblkp->start;
 660                         tp->snd_fack = sblkp->end;
 661                         sblkp--;
 662                         sack_changed = 1;
 663                 } else {
 664                         /*
 665                          * Append a new SACK hole at the tail.  If the
 666                          * second or later highest SACK blocks are also
 667                          * beyond the current fack, they will be inserted
 668                          * by way of hole splitting in the while-loop below.
 669                          */
 670                         temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
 671                         if (temp != NULL) {
 672                                 delivered_data += sblkp->end - sblkp->start;
 673                                 tp->snd_fack = sblkp->end;
 674                                 /* Go to the previous sack block. */
 675                                 sblkp--;
 676                                 sack_changed = 1;
 677                         } else {
 678                                 /*
 679                                  * We failed to add a new hole based on the current
 680                                  * sack block.  Skip over all the sack blocks that
 681                                  * fall completely to the right of snd_fack and
 682                                  * proceed to trim the scoreboard based on the
 683                                  * remaining sack blocks.  This also trims the
 684                                  * scoreboard for th_ack (which is sack_blocks[0]).
 685                                  */
 686                                 while (sblkp >= sack_blocks &&
 687                                        SEQ_LT(tp->snd_fack, sblkp->start))
 688                                         sblkp--;
 689                                 if (sblkp >= sack_blocks &&
 690                                     SEQ_LT(tp->snd_fack, sblkp->end)) {
 691                                         delivered_data += sblkp->end - tp->snd_fack;
 692                                         tp->snd_fack = sblkp->end;
 693                                         sack_changed = 1;
 694                                 }
 695                         }
 696                 }
 697         } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
 698                 /* fack is advanced. */
 699                 delivered_data += sblkp->end - tp->snd_fack;
 700                 tp->snd_fack = sblkp->end;
 701                 sack_changed = 1;
 702         }
 703         cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
 704         /*
 705          * Since the incoming sack blocks are sorted, we can process them
 706          * making one sweep of the scoreboard.
 707          */
 708         while (sblkp >= sack_blocks  && cur != NULL) {
 709                 if (SEQ_GEQ(sblkp->start, cur->end)) {
 710                         /*
 711                          * SACKs data beyond the current hole.  Go to the
 712                          * previous sack block.
 713                          */
 714                         sblkp--;
 715                         continue;
 716                 }
 717                 if (SEQ_LEQ(sblkp->end, cur->start)) {
 718                         /*
 719                          * SACKs data before the current hole.  Go to the
 720                          * previous hole.
 721                          */
 722                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 723                         continue;
 724                 }
 725                 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
 726                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 727                     ("sackhint bytes rtx >= 0"));
 728                 sack_changed = 1;
 729                 if (SEQ_LEQ(sblkp->start, cur->start)) {
 730                         /* Data acks at least the beginning of hole. */
 731                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 732                                 /* Acks entire hole, so delete hole. */
 733                                 delivered_data += (cur->end - cur->start);
 734                                 temp = cur;
 735                                 cur = TAILQ_PREV(cur, sackhole_head, scblink);
 736                                 tcp_sackhole_remove(tp, temp);
 737                                 /*
 738                                  * The sack block may ack all or part of the
 739                                  * next hole too, so continue onto the next
 740                                  * hole.
 741                                  */
 742                                 continue;
 743                         } else {
 744                                 /* Move start of hole forward. */
 745                                 delivered_data += (sblkp->end - cur->start);
 746                                 cur->start = sblkp->end;
 747                                 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 748                         }
 749                 } else {
 750                         /* Data acks at least the end of hole. */
 751                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 752                                 /* Move end of hole backward. */
 753                                 delivered_data += (cur->end - sblkp->start);
 754                                 cur->end = sblkp->start;
 755                                 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 756                         } else {
 757                                 /*
 758                                  * ACKs some data in middle of a hole; need
 759                                  * to split current hole
 760                                  */
 761                                 temp = tcp_sackhole_insert(tp, sblkp->end,
 762                                     cur->end, cur);
 763                                 if (temp != NULL) {
 764                                         if (SEQ_GT(cur->rxmit, temp->rxmit)) {
 765                                                 temp->rxmit = cur->rxmit;
 766                                                 tp->sackhint.sack_bytes_rexmit
 767                                                     += (temp->rxmit
 768                                                     - temp->start);
 769                                         }
 770                                         cur->end = sblkp->start;
 771                                         cur->rxmit = SEQ_MIN(cur->rxmit,
 772                                             cur->end);
 773                                         delivered_data += (sblkp->end - sblkp->start);
 774                                 }
 775                         }
 776                 }
 777                 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
 778                 /*
 779                  * Testing sblkp->start against cur->start tells us whether
 780                  * we're done with the sack block or the sack hole.
 781                  * Accordingly, we advance one or the other.
 782                  */
 783                 if (SEQ_LEQ(sblkp->start, cur->start))
 784                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 785                 else
 786                         sblkp--;
 787         }
 788         if (!(to->to_flags & TOF_SACK))
 789                 /*
 790                  * If this ACK did not contain any
 791                  * SACK blocks, any only moved the
 792                  * left edge right, it is a pure
 793                  * cumulative ACK. Do not count
 794                  * DupAck for this. Also required
 795                  * for RFC6675 rescue retransmission.
 796                  */
 797                 sack_changed = 0;
 798         tp->sackhint.delivered_data = delivered_data;
 799         tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
 800         KASSERT((delivered_data >= 0), ("delivered_data < 0"));
 801         KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
 802         return (sack_changed);
 803 }
 804
 805 /*
 806  * Free all SACK holes to clear the scoreboard.
 807  */
 808 void
 809 tcp_free_sackholes(struct tcpcb *tp)
 810 {
 811         struct sackhole *q;
 812
 813         INP_WLOCK_ASSERT(tp->t_inpcb);
 814         while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
 815                 tcp_sackhole_remove(tp, q);
 816         tp->sackhint.sack_bytes_rexmit = 0;
 817
 818         KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
 819         KASSERT(tp->sackhint.nexthole == NULL,
 820                 ("tp->sackhint.nexthole == NULL"));
 821 }
 822
 823 /*
 824  * Partial ack handling within a sack recovery episode.  Keeping this very
 825  * simple for now.  When a partial ack is received, force snd_cwnd to a value
 826  * that will allow the sender to transmit no more than 2 segments.  If
 827  * necessary, a better scheme can be adopted at a later point, but for now,
 828  * the goal is to prevent the sender from bursting a large amount of data in
 829  * the midst of sack recovery.
 830  */
 831 void
 832 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 833 {
 834         int num_segs = 1;
 835         u_int maxseg = tcp_maxseg(tp);
 836
 837         INP_WLOCK_ASSERT(tp->t_inpcb);
 838         tcp_timer_activate(tp, TT_REXMT, 0);
 839         tp->t_rtttime = 0;
 840         /* Send one or 2 segments based on how much new data was acked. */
 841         if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
 842                 num_segs = 2;
 843         tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
 844             (tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
 845         if (tp->snd_cwnd > tp->snd_ssthresh)
 846                 tp->snd_cwnd = tp->snd_ssthresh;
 847         tp->t_flags |= TF_ACKNOW;
 848         /*
 849          * RFC6675 rescue retransmission
 850          * Add a hole between th_ack (snd_una is not yet set) and snd_max,
 851          * if this was a pure cumulative ACK and no data was send beyond
 852          * recovery point. Since the data in the socket has not been freed
 853          * at this point, we check if the scoreboard is empty, and the ACK
 854          * delivered some new data, indicating a full ACK. Also, if the
 855          * recovery point is still at snd_max, we are probably application
 856          * limited. However, this inference might not always be true. The
 857          * rescue retransmission may rarely be slightly premature
 858          * compared to RFC6675.
 859          * The corresponding ACK+SACK will cause any further outstanding
 860          * segments to be retransmitted. This addresses a corner case, when
 861          * the trailing packets of a window are lost and no further data
 862          * is available for sending.
 863          */
 864         if ((V_tcp_do_rfc6675_pipe) &&
 865             SEQ_LT(th->th_ack, tp->snd_recover) &&
 866             (tp->snd_recover == tp->snd_max) &&
 867             TAILQ_EMPTY(&tp->snd_holes) &&
 868             (tp->sackhint.delivered_data > 0)) {
 869                 /*
 870                  * Exclude FIN sequence space in
 871                  * the hole for the rescue retransmission,
 872                  * and also don't create a hole, if only
 873                  * the ACK for a FIN is outstanding.
 874                  */
 875                 tcp_seq highdata = tp->snd_max;
 876                 if (tp->t_flags & TF_SENTFIN)
 877                         highdata--;
 878                 if (th->th_ack != highdata) {
 879                         tp->snd_fack = th->th_ack;
 880                         (void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
 881                             highdata - maxseg), highdata, NULL);
 882                 }
 883         }
 884         (void) tp->t_fb->tfb_tcp_output(tp);
 885 }
 886
 887 #if 0
 888 /*
 889  * Debug version of tcp_sack_output() that walks the scoreboard.  Used for
 890  * now to sanity check the hint.
 891  */
 892 static struct sackhole *
 893 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
 894 {
 895         struct sackhole *p;
 896
 897         INP_WLOCK_ASSERT(tp->t_inpcb);
 898         *sack_bytes_rexmt = 0;
 899         TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
 900                 if (SEQ_LT(p->rxmit, p->end)) {
 901                         if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 902                                 continue;
 903                         }
 904                         *sack_bytes_rexmt += (p->rxmit - p->start);
 905                         break;
 906                 }
 907                 *sack_bytes_rexmt += (p->rxmit - p->start);
 908         }
 909         return (p);
 910 }
 911 #endif
 912
 913 /*
 914  * Returns the next hole to retransmit and the number of retransmitted bytes
 915  * from the scoreboard.  We store both the next hole and the number of
 916  * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
 917  * reception).  This avoids scoreboard traversals completely.
 918  *
 919  * The loop here will traverse *at most* one link.  Here's the argument.  For
 920  * the loop to traverse more than 1 link before finding the next hole to
 921  * retransmit, we would need to have at least 1 node following the current
 922  * hint with (rxmit == end).  But, for all holes following the current hint,
 923  * (start == rxmit), since we have not yet retransmitted from them.
 924  * Therefore, in order to traverse more 1 link in the loop below, we need to
 925  * have at least one node following the current hint with (start == rxmit ==
 926  * end).  But that can't happen, (start == end) means that all the data in
 927  * that hole has been sacked, in which case, the hole would have been removed
 928  * from the scoreboard.
 929  */
 930 struct sackhole *
 931 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 932 {
 933         struct sackhole *hole = NULL;
 934
 935         INP_WLOCK_ASSERT(tp->t_inpcb);
 936         *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
 937         hole = tp->sackhint.nexthole;
 938         if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
 939                 goto out;
 940         while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
 941                 if (SEQ_LT(hole->rxmit, hole->end)) {
 942                         tp->sackhint.nexthole = hole;
 943                         break;
 944                 }
 945         }
 946 out:
 947         return (hole);
 948 }
 949
 950 /*
 951  * After a timeout, the SACK list may be rebuilt.  This SACK information
 952  * should be used to avoid retransmitting SACKed data.  This function
 953  * traverses the SACK list to see if snd_nxt should be moved forward.
 954  */
 955 void
 956 tcp_sack_adjust(struct tcpcb *tp)
 957 {
 958         struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 959
 960         INP_WLOCK_ASSERT(tp->t_inpcb);
 961         if (cur == NULL)
 962                 return; /* No holes */
 963         if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
 964                 return; /* We're already beyond any SACKed blocks */
 965         /*-
 966          * Two cases for which we want to advance snd_nxt:
 967          * i) snd_nxt lies between end of one hole and beginning of another
 968          * ii) snd_nxt lies between end of last hole and snd_fack
 969          */
 970         while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
 971                 if (SEQ_LT(tp->snd_nxt, cur->end))
 972                         return;
 973                 if (SEQ_GEQ(tp->snd_nxt, p->start))
 974                         cur = p;
 975                 else {
 976                         tp->snd_nxt = p->start;
 977                         return;
 978                 }
 979         }
 980         if (SEQ_LT(tp->snd_nxt, cur->end))
 981                 return;
 982         tp->snd_nxt = tp->snd_fack;
 983 }