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
 134 VNET_DEFINE(int, tcp_do_sack) = 1;
 135 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
 136     &VNET_NAME(tcp_do_sack), 0,
 137     "Enable/Disable TCP SACK support");
 138
 139 VNET_DEFINE(int, tcp_do_newsack) = 1;
 140 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, revised, CTLFLAG_VNET | CTLFLAG_RW,
 141     &VNET_NAME(tcp_do_newsack), 0,
 142     "Use revised SACK loss recovery per RFC 6675");
 143
 144 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
 145 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
 146     &VNET_NAME(tcp_sack_maxholes), 0,
 147     "Maximum number of TCP SACK holes allowed per connection");
 148
 149 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
 150 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
 151     &VNET_NAME(tcp_sack_globalmaxholes), 0,
 152     "Global maximum number of TCP SACK holes");
 153
 154 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
 155 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
 156     &VNET_NAME(tcp_sack_globalholes), 0,
 157     "Global number of TCP SACK holes currently allocated");
 158
 159 int
 160 tcp_dsack_block_exists(struct tcpcb *tp)
 161 {
 162         /* Return true if a DSACK block exists */
 163         if (tp->rcv_numsacks == 0)
 164                 return (0);
 165         if (SEQ_LEQ(tp->sackblks[0].end, tp->rcv_nxt))
 166                 return(1);
 167         return (0);
 168 }
 169
 170 /*
 171  * This function will find overlaps with the currently stored sackblocks
 172  * and add any overlap as a dsack block upfront
 173  */
 174 void
 175 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 176 {
 177         struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
 178         int i, j, n, identical;
 179         tcp_seq start, end;
 180
 181         INP_WLOCK_ASSERT(tp->t_inpcb);
 182
 183         KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
 184
 185         if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
 186             ((rcv_end == tp->rcv_nxt) &&
 187              (tp->rcv_numsacks > 0 ) &&
 188              (tp->sackblks[0].end == tp->rcv_nxt))) {
 189                 saved_blks[0].start = rcv_start;
 190                 saved_blks[0].end = rcv_end;
 191         } else {
 192                 saved_blks[0].start = saved_blks[0].end = 0;
 193         }
 194
 195         head_blk.start = head_blk.end = 0;
 196         mid_blk.start = rcv_start;
 197         mid_blk.end = rcv_end;
 198         identical = 0;
 199
 200         for (i = 0; i < tp->rcv_numsacks; i++) {
 201                 start = tp->sackblks[i].start;
 202                 end = tp->sackblks[i].end;
 203                 if (SEQ_LT(rcv_end, start)) {
 204                         /* pkt left to sack blk */
 205                         continue;
 206                 }
 207                 if (SEQ_GT(rcv_start, end)) {
 208                         /* pkt right to sack blk */
 209                         continue;
 210                 }
 211                 if (SEQ_GT(tp->rcv_nxt, end)) {
 212                         if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
 213                             (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
 214                             (head_blk.start == head_blk.end))) {
 215                                 head_blk.start = SEQ_MAX(rcv_start, start);
 216                                 head_blk.end = SEQ_MIN(rcv_end, end);
 217                         }
 218                         continue;
 219                 }
 220                 if (((head_blk.start == head_blk.end) ||
 221                      SEQ_LT(start, head_blk.start)) &&
 222                      (SEQ_GT(end, rcv_start) &&
 223                       SEQ_LEQ(start, rcv_end))) {
 224                         head_blk.start = start;
 225                         head_blk.end = end;
 226                 }
 227                 mid_blk.start = SEQ_MIN(mid_blk.start, start);
 228                 mid_blk.end = SEQ_MAX(mid_blk.end, end);
 229                 if ((mid_blk.start == start) &&
 230                     (mid_blk.end == end))
 231                         identical = 1;
 232         }
 233         if (SEQ_LT(head_blk.start, head_blk.end)) {
 234                 /* store overlapping range */
 235                 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
 236                 saved_blks[0].end   = SEQ_MIN(rcv_end, head_blk.end);
 237         }
 238         n = 1;
 239         /*
 240          * Second, if not ACKed, store the SACK block that
 241          * overlaps with the DSACK block unless it is identical
 242          */
 243         if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
 244             !((mid_blk.start == saved_blks[0].start) &&
 245             (mid_blk.end == saved_blks[0].end))) ||
 246             identical == 1) {
 247                 saved_blks[n].start = mid_blk.start;
 248                 saved_blks[n++].end = mid_blk.end;
 249         }
 250         for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
 251                 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
 252                       SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
 253                     (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
 254                 saved_blks[n++] = tp->sackblks[j];
 255         }
 256         j = 0;
 257         for (i = 0; i < n; i++) {
 258                 /* we can end up with a stale initial entry */
 259                 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
 260                         tp->sackblks[j++] = saved_blks[i];
 261                 }
 262         }
 263         tp->rcv_numsacks = j;
 264 }
 265
 266 /*
 267  * This function is called upon receipt of new valid data (while not in
 268  * header prediction mode), and it updates the ordered list of sacks.
 269  */
 270 void
 271 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 272 {
 273         /*
 274          * First reported block MUST be the most recent one.  Subsequent
 275          * blocks SHOULD be in the order in which they arrived at the
 276          * receiver.  These two conditions make the implementation fully
 277          * compliant with RFC 2018.
 278          */
 279         struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
 280         int num_head, num_saved, i;
 281
 282         INP_WLOCK_ASSERT(tp->t_inpcb);
 283
 284         /* Check arguments. */
 285         KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
 286
 287         if ((rcv_start == rcv_end) &&
 288             (tp->rcv_numsacks >= 1) &&
 289             (rcv_end == tp->sackblks[0].end)) {
 290                 /* retaining DSACK block below rcv_nxt (todrop) */
 291                 head_blk = tp->sackblks[0];
 292         } else {
 293                 /* SACK block for the received segment. */
 294                 head_blk.start = rcv_start;
 295                 head_blk.end = rcv_end;
 296         }
 297
 298         /*
 299          * Merge updated SACK blocks into head_blk, and save unchanged SACK
 300          * blocks into saved_blks[].  num_saved will have the number of the
 301          * saved SACK blocks.
 302          */
 303         num_saved = 0;
 304         for (i = 0; i < tp->rcv_numsacks; i++) {
 305                 tcp_seq start = tp->sackblks[i].start;
 306                 tcp_seq end = tp->sackblks[i].end;
 307                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 308                         /*
 309                          * Discard this SACK block.
 310                          */
 311                 } else if (SEQ_LEQ(head_blk.start, end) &&
 312                            SEQ_GEQ(head_blk.end, start)) {
 313                         /*
 314                          * Merge this SACK block into head_blk.  This SACK
 315                          * block itself will be discarded.
 316                          */
 317                         /*
 318                          * |-|
 319                          *   |---|  merge
 320                          *
 321                          *     |-|
 322                          * |---|    merge
 323                          *
 324                          * |-----|
 325                          *   |-|    DSACK smaller
 326                          *
 327                          *   |-|
 328                          * |-----|  DSACK smaller
 329                          */
 330                         if (head_blk.start == end)
 331                                 head_blk.start = start;
 332                         else if (head_blk.end == start)
 333                                 head_blk.end = end;
 334                         else {
 335                                 if (SEQ_LT(head_blk.start, start)) {
 336                                         tcp_seq temp = start;
 337                                         start = head_blk.start;
 338                                         head_blk.start = temp;
 339                                 }
 340                                 if (SEQ_GT(head_blk.end, end)) {
 341                                         tcp_seq temp = end;
 342                                         end = head_blk.end;
 343                                         head_blk.end = temp;
 344                                 }
 345                                 if ((head_blk.start != start) ||
 346                                     (head_blk.end != end)) {
 347                                         if ((num_saved >= 1) &&
 348                                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 349                                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 350                                                 num_saved--;
 351                                         saved_blks[num_saved].start = start;
 352                                         saved_blks[num_saved].end = end;
 353                                         num_saved++;
 354                                 }
 355                         }
 356                 } else {
 357                         /*
 358                          * This block supercedes the prior block
 359                          */
 360                         if ((num_saved >= 1) &&
 361                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 362                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 363                                 num_saved--;
 364                         /*
 365                          * Save this SACK block.
 366                          */
 367                         saved_blks[num_saved].start = start;
 368                         saved_blks[num_saved].end = end;
 369                         num_saved++;
 370                 }
 371         }
 372
 373         /*
 374          * Update SACK list in tp->sackblks[].
 375          */
 376         num_head = 0;
 377         if (SEQ_LT(rcv_start, rcv_end)) {
 378                 /*
 379                  * The received data segment is an out-of-order segment.  Put
 380                  * head_blk at the top of SACK list.
 381                  */
 382                 tp->sackblks[0] = head_blk;
 383                 num_head = 1;
 384                 /*
 385                  * If the number of saved SACK blocks exceeds its limit,
 386                  * discard the last SACK block.
 387                  */
 388                 if (num_saved >= MAX_SACK_BLKS)
 389                         num_saved--;
 390         }
 391         if ((rcv_start == rcv_end) &&
 392             (rcv_start == tp->sackblks[0].end)) {
 393                 num_head = 1;
 394         }
 395         if (num_saved > 0) {
 396                 /*
 397                  * Copy the saved SACK blocks back.
 398                  */
 399                 bcopy(saved_blks, &tp->sackblks[num_head],
 400                       sizeof(struct sackblk) * num_saved);
 401         }
 402
 403         /* Save the number of SACK blocks. */
 404         tp->rcv_numsacks = num_head + num_saved;
 405 }
 406
 407 void
 408 tcp_clean_dsack_blocks(struct tcpcb *tp)
 409 {
 410         struct sackblk saved_blks[MAX_SACK_BLKS];
 411         int num_saved, i;
 412
 413         INP_WLOCK_ASSERT(tp->t_inpcb);
 414         /*
 415          * Clean up any DSACK blocks that
 416          * are in our queue of sack blocks.
 417          *
 418          */
 419         num_saved = 0;
 420         for (i = 0; i < tp->rcv_numsacks; i++) {
 421                 tcp_seq start = tp->sackblks[i].start;
 422                 tcp_seq end = tp->sackblks[i].end;
 423                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 424                         /*
 425                          * Discard this D-SACK block.
 426                          */
 427                         continue;
 428                 }
 429                 /*
 430                  * Save this SACK block.
 431                  */
 432                 saved_blks[num_saved].start = start;
 433                 saved_blks[num_saved].end = end;
 434                 num_saved++;
 435         }
 436         if (num_saved > 0) {
 437                 /*
 438                  * Copy the saved SACK blocks back.
 439                  */
 440                 bcopy(saved_blks, &tp->sackblks[0],
 441                       sizeof(struct sackblk) * num_saved);
 442         }
 443         tp->rcv_numsacks = num_saved;
 444 }
 445
 446 /*
 447  * Delete all receiver-side SACK information.
 448  */
 449 void
 450 tcp_clean_sackreport(struct tcpcb *tp)
 451 {
 452         int i;
 453
 454         INP_WLOCK_ASSERT(tp->t_inpcb);
 455         tp->rcv_numsacks = 0;
 456         for (i = 0; i < MAX_SACK_BLKS; i++)
 457                 tp->sackblks[i].start = tp->sackblks[i].end=0;
 458 }
 459
 460 /*
 461  * Allocate struct sackhole.
 462  */
 463 static struct sackhole *
 464 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 465 {
 466         struct sackhole *hole;
 467
 468         if (tp->snd_numholes >= V_tcp_sack_maxholes ||
 469             V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
 470                 TCPSTAT_INC(tcps_sack_sboverflow);
 471                 return NULL;
 472         }
 473
 474         hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
 475         if (hole == NULL)
 476                 return NULL;
 477
 478         hole->start = start;
 479         hole->end = end;
 480         hole->rxmit = start;
 481
 482         tp->snd_numholes++;
 483         atomic_add_int(&V_tcp_sack_globalholes, 1);
 484
 485         return hole;
 486 }
 487
 488 /*
 489  * Free struct sackhole.
 490  */
 491 static void
 492 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
 493 {
 494
 495         uma_zfree(V_sack_hole_zone, hole);
 496
 497         tp->snd_numholes--;
 498         atomic_subtract_int(&V_tcp_sack_globalholes, 1);
 499
 500         KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
 501         KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
 502 }
 503
 504 /*
 505  * Insert new SACK hole into scoreboard.
 506  */
 507 static struct sackhole *
 508 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
 509     struct sackhole *after)
 510 {
 511         struct sackhole *hole;
 512
 513         /* Allocate a new SACK hole. */
 514         hole = tcp_sackhole_alloc(tp, start, end);
 515         if (hole == NULL)
 516                 return NULL;
 517
 518         /* Insert the new SACK hole into scoreboard. */
 519         if (after != NULL)
 520                 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
 521         else
 522                 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
 523
 524         /* Update SACK hint. */
 525         if (tp->sackhint.nexthole == NULL)
 526                 tp->sackhint.nexthole = hole;
 527
 528         return hole;
 529 }
 530
 531 /*
 532  * Remove SACK hole from scoreboard.
 533  */
 534 static void
 535 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
 536 {
 537
 538         /* Update SACK hint. */
 539         if (tp->sackhint.nexthole == hole)
 540                 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
 541
 542         /* Remove this SACK hole. */
 543         TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
 544
 545         /* Free this SACK hole. */
 546         tcp_sackhole_free(tp, hole);
 547 }
 548
 549 /*
 550  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
 551  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
 552  * the sequence space).
 553  * Returns 1 if incoming ACK has previously unknown SACK information,
 554  * 0 otherwise.
 555  */
 556 int
 557 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
 558 {
 559         struct sackhole *cur, *temp;
 560         struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 561         int i, j, num_sack_blks, sack_changed;
 562         int delivered_data, left_edge_delta;
 563
 564         INP_WLOCK_ASSERT(tp->t_inpcb);
 565
 566         num_sack_blks = 0;
 567         sack_changed = 0;
 568         delivered_data = 0;
 569         left_edge_delta = 0;
 570         /*
 571          * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 572          * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
 573          * Account changes to SND.UNA always in delivered data.
 574          */
 575         if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
 576                 left_edge_delta = th_ack - tp->snd_una;
 577                 sack_blocks[num_sack_blks].start = tp->snd_una;
 578                 sack_blocks[num_sack_blks++].end = th_ack;
 579                 /*
 580                  * Pulling snd_fack forward if we got here
 581                  * due to DSACK blocks
 582                  */
 583                 if (SEQ_LT(tp->snd_fack, th_ack)) {
 584                         delivered_data += th_ack - tp->snd_una;
 585                         tp->snd_fack = th_ack;
 586                         sack_changed = 1;
 587                 }
 588         }
 589         /*
 590          * Append received valid SACK blocks to sack_blocks[], but only if we
 591          * received new blocks from the other side.
 592          */
 593         if (to->to_flags & TOF_SACK) {
 594                 for (i = 0; i < to->to_nsacks; i++) {
 595                         bcopy((to->to_sacks + i * TCPOLEN_SACK),
 596                             &sack, sizeof(sack));
 597                         sack.start = ntohl(sack.start);
 598                         sack.end = ntohl(sack.end);
 599                         if (SEQ_GT(sack.end, sack.start) &&
 600                             SEQ_GT(sack.start, tp->snd_una) &&
 601                             SEQ_GT(sack.start, th_ack) &&
 602                             SEQ_LT(sack.start, tp->snd_max) &&
 603                             SEQ_GT(sack.end, tp->snd_una) &&
 604                             SEQ_LEQ(sack.end, tp->snd_max)) {
 605                                 sack_blocks[num_sack_blks++] = sack;
 606                         }
 607                 }
 608         }
 609         /*
 610          * Return if SND.UNA is not advanced and no valid SACK block is
 611          * received.
 612          */
 613         if (num_sack_blks == 0)
 614                 return (sack_changed);
 615
 616         /*
 617          * Sort the SACK blocks so we can update the scoreboard with just one
 618          * pass. The overhead of sorting up to 4+1 elements is less than
 619          * making up to 4+1 passes over the scoreboard.
 620          */
 621         for (i = 0; i < num_sack_blks; i++) {
 622                 for (j = i + 1; j < num_sack_blks; j++) {
 623                         if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
 624                                 sack = sack_blocks[i];
 625                                 sack_blocks[i] = sack_blocks[j];
 626                                 sack_blocks[j] = sack;
 627                         }
 628                 }
 629         }
 630         if (TAILQ_EMPTY(&tp->snd_holes)) {
 631                 /*
 632                  * Empty scoreboard. Need to initialize snd_fack (it may be
 633                  * uninitialized or have a bogus value). Scoreboard holes
 634                  * (from the sack blocks received) are created later below
 635                  * (in the logic that adds holes to the tail of the
 636                  * scoreboard).
 637                  */
 638                 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
 639                 tp->sackhint.sacked_bytes = 0;  /* reset */
 640         }
 641         /*
 642          * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
 643          * SACK holes (snd_holes) are traversed from their tails with just
 644          * one pass in order to reduce the number of compares especially when
 645          * the bandwidth-delay product is large.
 646          *
 647          * Note: Typically, in the first RTT of SACK recovery, the highest
 648          * three or four SACK blocks with the same ack number are received.
 649          * In the second RTT, if retransmitted data segments are not lost,
 650          * the highest three or four SACK blocks with ack number advancing
 651          * are received.
 652          */
 653         sblkp = &sack_blocks[num_sack_blks - 1];        /* Last SACK block */
 654         tp->sackhint.last_sack_ack = sblkp->end;
 655         if (SEQ_LT(tp->snd_fack, sblkp->start)) {
 656                 /*
 657                  * The highest SACK block is beyond fack.  First,
 658                  * check if there was a successful Rescue Retransmission,
 659                  * and move this hole left. With normal holes, snd_fack
 660                  * is always to the right of the end.
 661                  */
 662                 if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
 663                     SEQ_LEQ(tp->snd_fack,temp->end)) {
 664                         temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
 665                         temp->end = sblkp->start;
 666                         temp->rxmit = temp->start;
 667                         delivered_data += sblkp->end - sblkp->start;
 668                         tp->snd_fack = sblkp->end;
 669                         sblkp--;
 670                         sack_changed = 1;
 671                 } else {
 672                         /*
 673                          * Append a new SACK hole at the tail.  If the
 674                          * second or later highest SACK blocks are also
 675                          * beyond the current fack, they will be inserted
 676                          * by way of hole splitting in the while-loop below.
 677                          */
 678                         temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
 679                         if (temp != NULL) {
 680                                 delivered_data += sblkp->end - sblkp->start;
 681                                 tp->snd_fack = sblkp->end;
 682                                 /* Go to the previous sack block. */
 683                                 sblkp--;
 684                                 sack_changed = 1;
 685                         } else {
 686                                 /*
 687                                  * We failed to add a new hole based on the current
 688                                  * sack block.  Skip over all the sack blocks that
 689                                  * fall completely to the right of snd_fack and
 690                                  * proceed to trim the scoreboard based on the
 691                                  * remaining sack blocks.  This also trims the
 692                                  * scoreboard for th_ack (which is sack_blocks[0]).
 693                                  */
 694                                 while (sblkp >= sack_blocks &&
 695                                        SEQ_LT(tp->snd_fack, sblkp->start))
 696                                         sblkp--;
 697                                 if (sblkp >= sack_blocks &&
 698                                     SEQ_LT(tp->snd_fack, sblkp->end)) {
 699                                         delivered_data += sblkp->end - tp->snd_fack;
 700                                         tp->snd_fack = sblkp->end;
 701                                         sack_changed = 1;
 702                                 }
 703                         }
 704                 }
 705         } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
 706                 /* fack is advanced. */
 707                 delivered_data += sblkp->end - tp->snd_fack;
 708                 tp->snd_fack = sblkp->end;
 709                 sack_changed = 1;
 710         }
 711         cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
 712         /*
 713          * Since the incoming sack blocks are sorted, we can process them
 714          * making one sweep of the scoreboard.
 715          */
 716         while (sblkp >= sack_blocks  && cur != NULL) {
 717                 if (SEQ_GEQ(sblkp->start, cur->end)) {
 718                         /*
 719                          * SACKs data beyond the current hole.  Go to the
 720                          * previous sack block.
 721                          */
 722                         sblkp--;
 723                         continue;
 724                 }
 725                 if (SEQ_LEQ(sblkp->end, cur->start)) {
 726                         /*
 727                          * SACKs data before the current hole.  Go to the
 728                          * previous hole.
 729                          */
 730                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 731                         continue;
 732                 }
 733                 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
 734                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 735                     ("sackhint bytes rtx >= 0"));
 736                 sack_changed = 1;
 737                 if (SEQ_LEQ(sblkp->start, cur->start)) {
 738                         /* Data acks at least the beginning of hole. */
 739                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 740                                 /* Acks entire hole, so delete hole. */
 741                                 delivered_data += (cur->end - cur->start);
 742                                 temp = cur;
 743                                 cur = TAILQ_PREV(cur, sackhole_head, scblink);
 744                                 tcp_sackhole_remove(tp, temp);
 745                                 /*
 746                                  * The sack block may ack all or part of the
 747                                  * next hole too, so continue onto the next
 748                                  * hole.
 749                                  */
 750                                 continue;
 751                         } else {
 752                                 /* Move start of hole forward. */
 753                                 delivered_data += (sblkp->end - cur->start);
 754                                 cur->start = sblkp->end;
 755                                 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 756                         }
 757                 } else {
 758                         /* Data acks at least the end of hole. */
 759                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 760                                 /* Move end of hole backward. */
 761                                 delivered_data += (cur->end - sblkp->start);
 762                                 cur->end = sblkp->start;
 763                                 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 764                         } else {
 765                                 /*
 766                                  * ACKs some data in middle of a hole; need
 767                                  * to split current hole
 768                                  */
 769                                 temp = tcp_sackhole_insert(tp, sblkp->end,
 770                                     cur->end, cur);
 771                                 if (temp != NULL) {
 772                                         if (SEQ_GT(cur->rxmit, temp->rxmit)) {
 773                                                 temp->rxmit = cur->rxmit;
 774                                                 tp->sackhint.sack_bytes_rexmit
 775                                                     += (temp->rxmit
 776                                                     - temp->start);
 777                                         }
 778                                         cur->end = sblkp->start;
 779                                         cur->rxmit = SEQ_MIN(cur->rxmit,
 780                                             cur->end);
 781                                         delivered_data += (sblkp->end - sblkp->start);
 782                                 }
 783                         }
 784                 }
 785                 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
 786                 /*
 787                  * Testing sblkp->start against cur->start tells us whether
 788                  * we're done with the sack block or the sack hole.
 789                  * Accordingly, we advance one or the other.
 790                  */
 791                 if (SEQ_LEQ(sblkp->start, cur->start))
 792                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 793                 else
 794                         sblkp--;
 795         }
 796         if (!(to->to_flags & TOF_SACK))
 797                 /*
 798                  * If this ACK did not contain any
 799                  * SACK blocks, any only moved the
 800                  * left edge right, it is a pure
 801                  * cumulative ACK. Do not count
 802                  * DupAck for this. Also required
 803                  * for RFC6675 rescue retransmission.
 804                  */
 805                 sack_changed = 0;
 806         tp->sackhint.delivered_data = delivered_data;
 807         tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
 808         KASSERT((delivered_data >= 0), ("delivered_data < 0"));
 809         KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
 810         return (sack_changed);
 811 }
 812
 813 /*
 814  * Free all SACK holes to clear the scoreboard.
 815  */
 816 void
 817 tcp_free_sackholes(struct tcpcb *tp)
 818 {
 819         struct sackhole *q;
 820
 821         INP_WLOCK_ASSERT(tp->t_inpcb);
 822         while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
 823                 tcp_sackhole_remove(tp, q);
 824         tp->sackhint.sack_bytes_rexmit = 0;
 825
 826         KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
 827         KASSERT(tp->sackhint.nexthole == NULL,
 828                 ("tp->sackhint.nexthole == NULL"));
 829 }
 830
 831 /*
 832  * Partial ack handling within a sack recovery episode.  Keeping this very
 833  * simple for now.  When a partial ack is received, force snd_cwnd to a value
 834  * that will allow the sender to transmit no more than 2 segments.  If
 835  * necessary, a better scheme can be adopted at a later point, but for now,
 836  * the goal is to prevent the sender from bursting a large amount of data in
 837  * the midst of sack recovery.
 838  */
 839 void
 840 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 841 {
 842         int num_segs = 1;
 843         u_int maxseg = tcp_maxseg(tp);
 844
 845         INP_WLOCK_ASSERT(tp->t_inpcb);
 846         tcp_timer_activate(tp, TT_REXMT, 0);
 847         tp->t_rtttime = 0;
 848         /* Send one or 2 segments based on how much new data was acked. */
 849         if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
 850                 num_segs = 2;
 851         tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
 852             (tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
 853         if (tp->snd_cwnd > tp->snd_ssthresh)
 854                 tp->snd_cwnd = tp->snd_ssthresh;
 855         tp->t_flags |= TF_ACKNOW;
 856         /*
 857          * RFC6675 rescue retransmission
 858          * Add a hole between th_ack (snd_una is not yet set) and snd_max,
 859          * if this was a pure cumulative ACK and no data was send beyond
 860          * recovery point. Since the data in the socket has not been freed
 861          * at this point, we check if the scoreboard is empty, and the ACK
 862          * delivered some new data, indicating a full ACK. Also, if the
 863          * recovery point is still at snd_max, we are probably application
 864          * limited. However, this inference might not always be true. The
 865          * rescue retransmission may rarely be slightly premature
 866          * compared to RFC6675.
 867          * The corresponding ACK+SACK will cause any further outstanding
 868          * segments to be retransmitted. This addresses a corner case, when
 869          * the trailing packets of a window are lost and no further data
 870          * is available for sending.
 871          */
 872         if ((V_tcp_do_newsack) &&
 873             SEQ_LT(th->th_ack, tp->snd_recover) &&
 874             (tp->snd_recover == tp->snd_max) &&
 875             TAILQ_EMPTY(&tp->snd_holes) &&
 876             (tp->sackhint.delivered_data > 0)) {
 877                 /*
 878                  * Exclude FIN sequence space in
 879                  * the hole for the rescue retransmission,
 880                  * and also don't create a hole, if only
 881                  * the ACK for a FIN is outstanding.
 882                  */
 883                 tcp_seq highdata = tp->snd_max;
 884                 if (tp->t_flags & TF_SENTFIN)
 885                         highdata--;
 886                 if (th->th_ack != highdata) {
 887                         tp->snd_fack = th->th_ack;
 888                         (void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
 889                             highdata - maxseg), highdata, NULL);
 890                 }
 891         }
 892         (void) tp->t_fb->tfb_tcp_output(tp);
 893 }
 894
 895 #if 0
 896 /*
 897  * Debug version of tcp_sack_output() that walks the scoreboard.  Used for
 898  * now to sanity check the hint.
 899  */
 900 static struct sackhole *
 901 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
 902 {
 903         struct sackhole *p;
 904
 905         INP_WLOCK_ASSERT(tp->t_inpcb);
 906         *sack_bytes_rexmt = 0;
 907         TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
 908                 if (SEQ_LT(p->rxmit, p->end)) {
 909                         if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 910                                 continue;
 911                         }
 912                         *sack_bytes_rexmt += (p->rxmit - p->start);
 913                         break;
 914                 }
 915                 *sack_bytes_rexmt += (p->rxmit - p->start);
 916         }
 917         return (p);
 918 }
 919 #endif
 920
 921 /*
 922  * Returns the next hole to retransmit and the number of retransmitted bytes
 923  * from the scoreboard.  We store both the next hole and the number of
 924  * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
 925  * reception).  This avoids scoreboard traversals completely.
 926  *
 927  * The loop here will traverse *at most* one link.  Here's the argument.  For
 928  * the loop to traverse more than 1 link before finding the next hole to
 929  * retransmit, we would need to have at least 1 node following the current
 930  * hint with (rxmit == end).  But, for all holes following the current hint,
 931  * (start == rxmit), since we have not yet retransmitted from them.
 932  * Therefore, in order to traverse more 1 link in the loop below, we need to
 933  * have at least one node following the current hint with (start == rxmit ==
 934  * end).  But that can't happen, (start == end) means that all the data in
 935  * that hole has been sacked, in which case, the hole would have been removed
 936  * from the scoreboard.
 937  */
 938 struct sackhole *
 939 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 940 {
 941         struct sackhole *hole = NULL;
 942
 943         INP_WLOCK_ASSERT(tp->t_inpcb);
 944         *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
 945         hole = tp->sackhint.nexthole;
 946         if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
 947                 goto out;
 948         while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
 949                 if (SEQ_LT(hole->rxmit, hole->end)) {
 950                         tp->sackhint.nexthole = hole;
 951                         break;
 952                 }
 953         }
 954 out:
 955         return (hole);
 956 }
 957
 958 /*
 959  * After a timeout, the SACK list may be rebuilt.  This SACK information
 960  * should be used to avoid retransmitting SACKed data.  This function
 961  * traverses the SACK list to see if snd_nxt should be moved forward.
 962  */
 963 void
 964 tcp_sack_adjust(struct tcpcb *tp)
 965 {
 966         struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 967
 968         INP_WLOCK_ASSERT(tp->t_inpcb);
 969         if (cur == NULL)
 970                 return; /* No holes */
 971         if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
 972                 return; /* We're already beyond any SACKed blocks */
 973         /*-
 974          * Two cases for which we want to advance snd_nxt:
 975          * i) snd_nxt lies between end of one hole and beginning of another
 976          * ii) snd_nxt lies between end of last hole and snd_fack
 977          */
 978         while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
 979                 if (SEQ_LT(tp->snd_nxt, cur->end))
 980                         return;
 981                 if (SEQ_GEQ(tp->snd_nxt, p->start))
 982                         cur = p;
 983                 else {
 984                         tp->snd_nxt = p->start;
 985                         return;
 986                 }
 987         }
 988         if (SEQ_LT(tp->snd_nxt, cur->end))
 989                 return;
 990         tp->snd_nxt = tp->snd_fack;
 991 }