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 int
 154 tcp_dsack_block_exists(struct tcpcb *tp)
 155 {
 156         /* Return true if a DSACK block exists */
 157         if (tp->rcv_numsacks == 0)
 158                 return (0);
 159         if (SEQ_LEQ(tp->sackblks[0].end, tp->rcv_nxt))
 160                 return(1);
 161         return (0);
 162 }
 163
 164 /*
 165  * This function will find overlaps with the currently stored sackblocks
 166  * and add any overlap as a dsack block upfront
 167  */
 168 void
 169 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 170 {
 171         struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
 172         int i, j, n, identical;
 173         tcp_seq start, end;
 174
 175         INP_WLOCK_ASSERT(tp->t_inpcb);
 176
 177         KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
 178
 179         if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
 180             ((rcv_end == tp->rcv_nxt) &&
 181              (tp->rcv_numsacks > 0 ) &&
 182              (tp->sackblks[0].end == tp->rcv_nxt))) {
 183                 saved_blks[0].start = rcv_start;
 184                 saved_blks[0].end = rcv_end;
 185         } else {
 186                 saved_blks[0].start = saved_blks[0].end = 0;
 187         }
 188
 189         head_blk.start = head_blk.end = 0;
 190         mid_blk.start = rcv_start;
 191         mid_blk.end = rcv_end;
 192         identical = 0;
 193
 194         for (i = 0; i < tp->rcv_numsacks; i++) {
 195                 start = tp->sackblks[i].start;
 196                 end = tp->sackblks[i].end;
 197                 if (SEQ_LT(rcv_end, start)) {
 198                         /* pkt left to sack blk */
 199                         continue;
 200                 }
 201                 if (SEQ_GT(rcv_start, end)) {
 202                         /* pkt right to sack blk */
 203                         continue;
 204                 }
 205                 if (SEQ_GT(tp->rcv_nxt, end)) {
 206                         if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
 207                             (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
 208                             (head_blk.start == head_blk.end))) {
 209                                 head_blk.start = SEQ_MAX(rcv_start, start);
 210                                 head_blk.end = SEQ_MIN(rcv_end, end);
 211                         }
 212                         continue;
 213                 }
 214                 if (((head_blk.start == head_blk.end) ||
 215                      SEQ_LT(start, head_blk.start)) &&
 216                      (SEQ_GT(end, rcv_start) &&
 217                       SEQ_LEQ(start, rcv_end))) {
 218                         head_blk.start = start;
 219                         head_blk.end = end;
 220                 }
 221                 mid_blk.start = SEQ_MIN(mid_blk.start, start);
 222                 mid_blk.end = SEQ_MAX(mid_blk.end, end);
 223                 if ((mid_blk.start == start) &&
 224                     (mid_blk.end == end))
 225                         identical = 1;
 226         }
 227         if (SEQ_LT(head_blk.start, head_blk.end)) {
 228                 /* store overlapping range */
 229                 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
 230                 saved_blks[0].end   = SEQ_MIN(rcv_end, head_blk.end);
 231         }
 232         n = 1;
 233         /*
 234          * Second, if not ACKed, store the SACK block that
 235          * overlaps with the DSACK block unless it is identical
 236          */
 237         if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
 238             !((mid_blk.start == saved_blks[0].start) &&
 239             (mid_blk.end == saved_blks[0].end))) ||
 240             identical == 1) {
 241                 saved_blks[n].start = mid_blk.start;
 242                 saved_blks[n++].end = mid_blk.end;
 243         }
 244         for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
 245                 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
 246                       SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
 247                     (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
 248                 saved_blks[n++] = tp->sackblks[j];
 249         }
 250         j = 0;
 251         for (i = 0; i < n; i++) {
 252                 /* we can end up with a stale initial entry */
 253                 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
 254                         tp->sackblks[j++] = saved_blks[i];
 255                 }
 256         }
 257         tp->rcv_numsacks = j;
 258 }
 259
 260 /*
 261  * This function is called upon receipt of new valid data (while not in
 262  * header prediction mode), and it updates the ordered list of sacks.
 263  */
 264 void
 265 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 266 {
 267         /*
 268          * First reported block MUST be the most recent one.  Subsequent
 269          * blocks SHOULD be in the order in which they arrived at the
 270          * receiver.  These two conditions make the implementation fully
 271          * compliant with RFC 2018.
 272          */
 273         struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
 274         int num_head, num_saved, i;
 275
 276         INP_WLOCK_ASSERT(tp->t_inpcb);
 277
 278         /* Check arguments. */
 279         KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
 280
 281         if ((rcv_start == rcv_end) &&
 282             (tp->rcv_numsacks >= 1) &&
 283             (rcv_end == tp->sackblks[0].end)) {
 284                 /* retaining DSACK block below rcv_nxt (todrop) */
 285                 head_blk = tp->sackblks[0];
 286         } else {
 287                 /* SACK block for the received segment. */
 288                 head_blk.start = rcv_start;
 289                 head_blk.end = rcv_end;
 290         }
 291
 292         /*
 293          * Merge updated SACK blocks into head_blk, and save unchanged SACK
 294          * blocks into saved_blks[].  num_saved will have the number of the
 295          * saved SACK blocks.
 296          */
 297         num_saved = 0;
 298         for (i = 0; i < tp->rcv_numsacks; i++) {
 299                 tcp_seq start = tp->sackblks[i].start;
 300                 tcp_seq end = tp->sackblks[i].end;
 301                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 302                         /*
 303                          * Discard this SACK block.
 304                          */
 305                 } else if (SEQ_LEQ(head_blk.start, end) &&
 306                            SEQ_GEQ(head_blk.end, start)) {
 307                         /*
 308                          * Merge this SACK block into head_blk.  This SACK
 309                          * block itself will be discarded.
 310                          */
 311                         /*
 312                          * |-|
 313                          *   |---|  merge
 314                          *
 315                          *     |-|
 316                          * |---|    merge
 317                          *
 318                          * |-----|
 319                          *   |-|    DSACK smaller
 320                          *
 321                          *   |-|
 322                          * |-----|  DSACK smaller
 323                          */
 324                         if (head_blk.start == end)
 325                                 head_blk.start = start;
 326                         else if (head_blk.end == start)
 327                                 head_blk.end = end;
 328                         else {
 329                                 if (SEQ_LT(head_blk.start, start)) {
 330                                         tcp_seq temp = start;
 331                                         start = head_blk.start;
 332                                         head_blk.start = temp;
 333                                 }
 334                                 if (SEQ_GT(head_blk.end, end)) {
 335                                         tcp_seq temp = end;
 336                                         end = head_blk.end;
 337                                         head_blk.end = temp;
 338                                 }
 339                                 if ((head_blk.start != start) ||
 340                                     (head_blk.end != end)) {
 341                                         if ((num_saved >= 1) &&
 342                                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 343                                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 344                                                 num_saved--;
 345                                         saved_blks[num_saved].start = start;
 346                                         saved_blks[num_saved].end = end;
 347                                         num_saved++;
 348                                 }
 349                         }
 350                 } else {
 351                         /*
 352                          * This block supercedes the prior block
 353                          */
 354                         if ((num_saved >= 1) &&
 355                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 356                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 357                                 num_saved--;
 358                         /*
 359                          * Save this SACK block.
 360                          */
 361                         saved_blks[num_saved].start = start;
 362                         saved_blks[num_saved].end = end;
 363                         num_saved++;
 364                 }
 365         }
 366
 367         /*
 368          * Update SACK list in tp->sackblks[].
 369          */
 370         num_head = 0;
 371         if (SEQ_LT(rcv_start, rcv_end)) {
 372                 /*
 373                  * The received data segment is an out-of-order segment.  Put
 374                  * head_blk at the top of SACK list.
 375                  */
 376                 tp->sackblks[0] = head_blk;
 377                 num_head = 1;
 378                 /*
 379                  * If the number of saved SACK blocks exceeds its limit,
 380                  * discard the last SACK block.
 381                  */
 382                 if (num_saved >= MAX_SACK_BLKS)
 383                         num_saved--;
 384         }
 385         if ((rcv_start == rcv_end) &&
 386             (rcv_start == tp->sackblks[0].end)) {
 387                 num_head = 1;
 388         }
 389         if (num_saved > 0) {
 390                 /*
 391                  * Copy the saved SACK blocks back.
 392                  */
 393                 bcopy(saved_blks, &tp->sackblks[num_head],
 394                       sizeof(struct sackblk) * num_saved);
 395         }
 396
 397         /* Save the number of SACK blocks. */
 398         tp->rcv_numsacks = num_head + num_saved;
 399 }
 400
 401 void
 402 tcp_clean_dsack_blocks(struct tcpcb *tp)
 403 {
 404         struct sackblk saved_blks[MAX_SACK_BLKS];
 405         int num_saved, i;
 406
 407         INP_WLOCK_ASSERT(tp->t_inpcb);
 408         /*
 409          * Clean up any DSACK blocks that
 410          * are in our queue of sack blocks.
 411          *
 412          */
 413         num_saved = 0;
 414         for (i = 0; i < tp->rcv_numsacks; i++) {
 415                 tcp_seq start = tp->sackblks[i].start;
 416                 tcp_seq end = tp->sackblks[i].end;
 417                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 418                         /*
 419                          * Discard this D-SACK block.
 420                          */
 421                         continue;
 422                 }
 423                 /*
 424                  * Save this SACK block.
 425                  */
 426                 saved_blks[num_saved].start = start;
 427                 saved_blks[num_saved].end = end;
 428                 num_saved++;
 429         }
 430         if (num_saved > 0) {
 431                 /*
 432                  * Copy the saved SACK blocks back.
 433                  */
 434                 bcopy(saved_blks, &tp->sackblks[0],
 435                       sizeof(struct sackblk) * num_saved);
 436         }
 437         tp->rcv_numsacks = num_saved;
 438 }
 439
 440 /*
 441  * Delete all receiver-side SACK information.
 442  */
 443 void
 444 tcp_clean_sackreport(struct tcpcb *tp)
 445 {
 446         int i;
 447
 448         INP_WLOCK_ASSERT(tp->t_inpcb);
 449         tp->rcv_numsacks = 0;
 450         for (i = 0; i < MAX_SACK_BLKS; i++)
 451                 tp->sackblks[i].start = tp->sackblks[i].end=0;
 452 }
 453
 454 /*
 455  * Allocate struct sackhole.
 456  */
 457 static struct sackhole *
 458 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 459 {
 460         struct sackhole *hole;
 461
 462         if (tp->snd_numholes >= V_tcp_sack_maxholes ||
 463             V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
 464                 TCPSTAT_INC(tcps_sack_sboverflow);
 465                 return NULL;
 466         }
 467
 468         hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
 469         if (hole == NULL)
 470                 return NULL;
 471
 472         hole->start = start;
 473         hole->end = end;
 474         hole->rxmit = start;
 475
 476         tp->snd_numholes++;
 477         atomic_add_int(&V_tcp_sack_globalholes, 1);
 478
 479         return hole;
 480 }
 481
 482 /*
 483  * Free struct sackhole.
 484  */
 485 static void
 486 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
 487 {
 488
 489         uma_zfree(V_sack_hole_zone, hole);
 490
 491         tp->snd_numholes--;
 492         atomic_subtract_int(&V_tcp_sack_globalholes, 1);
 493
 494         KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
 495         KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
 496 }
 497
 498 /*
 499  * Insert new SACK hole into scoreboard.
 500  */
 501 static struct sackhole *
 502 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
 503     struct sackhole *after)
 504 {
 505         struct sackhole *hole;
 506
 507         /* Allocate a new SACK hole. */
 508         hole = tcp_sackhole_alloc(tp, start, end);
 509         if (hole == NULL)
 510                 return NULL;
 511
 512         /* Insert the new SACK hole into scoreboard. */
 513         if (after != NULL)
 514                 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
 515         else
 516                 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
 517
 518         /* Update SACK hint. */
 519         if (tp->sackhint.nexthole == NULL)
 520                 tp->sackhint.nexthole = hole;
 521
 522         return hole;
 523 }
 524
 525 /*
 526  * Remove SACK hole from scoreboard.
 527  */
 528 static void
 529 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
 530 {
 531
 532         /* Update SACK hint. */
 533         if (tp->sackhint.nexthole == hole)
 534                 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
 535
 536         /* Remove this SACK hole. */
 537         TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
 538
 539         /* Free this SACK hole. */
 540         tcp_sackhole_free(tp, hole);
 541 }
 542
 543 /*
 544  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
 545  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
 546  * the sequence space).
 547  * Returns 1 if incoming ACK has previously unknown SACK information,
 548  * 0 otherwise.
 549  */
 550 int
 551 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
 552 {
 553         struct sackhole *cur, *temp;
 554         struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 555         int i, j, num_sack_blks, sack_changed;
 556         int delivered_data, left_edge_delta;
 557
 558         INP_WLOCK_ASSERT(tp->t_inpcb);
 559
 560         num_sack_blks = 0;
 561         sack_changed = 0;
 562         delivered_data = 0;
 563         left_edge_delta = 0;
 564         /*
 565          * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 566          * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
 567          * Account changes to SND.UNA always in delivered data.
 568          */
 569         if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
 570                 left_edge_delta = th_ack - tp->snd_una;
 571                 sack_blocks[num_sack_blks].start = tp->snd_una;
 572                 sack_blocks[num_sack_blks++].end = th_ack;
 573                 /*
 574                  * Pulling snd_fack forward if we got here
 575                  * due to DSACK blocks
 576                  */
 577                 if (SEQ_LT(tp->snd_fack, th_ack)) {
 578                         delivered_data += th_ack - tp->snd_una;
 579                         tp->snd_fack = th_ack;
 580                         sack_changed = 1;
 581                 }
 582         }
 583         /*
 584          * Append received valid SACK blocks to sack_blocks[], but only if we
 585          * received new blocks from the other side.
 586          */
 587         if (to->to_flags & TOF_SACK) {
 588                 for (i = 0; i < to->to_nsacks; i++) {
 589                         bcopy((to->to_sacks + i * TCPOLEN_SACK),
 590                             &sack, sizeof(sack));
 591                         sack.start = ntohl(sack.start);
 592                         sack.end = ntohl(sack.end);
 593                         if (SEQ_GT(sack.end, sack.start) &&
 594                             SEQ_GT(sack.start, tp->snd_una) &&
 595                             SEQ_GT(sack.start, th_ack) &&
 596                             SEQ_LT(sack.start, tp->snd_max) &&
 597                             SEQ_GT(sack.end, tp->snd_una) &&
 598                             SEQ_LEQ(sack.end, tp->snd_max)) {
 599                                 sack_blocks[num_sack_blks++] = sack;
 600                         }
 601                 }
 602         }
 603         /*
 604          * Return if SND.UNA is not advanced and no valid SACK block is
 605          * received.
 606          */
 607         if (num_sack_blks == 0)
 608                 return (sack_changed);
 609
 610         /*
 611          * Sort the SACK blocks so we can update the scoreboard with just one
 612          * pass. The overhead of sorting up to 4+1 elements is less than
 613          * making up to 4+1 passes over the scoreboard.
 614          */
 615         for (i = 0; i < num_sack_blks; i++) {
 616                 for (j = i + 1; j < num_sack_blks; j++) {
 617                         if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
 618                                 sack = sack_blocks[i];
 619                                 sack_blocks[i] = sack_blocks[j];
 620                                 sack_blocks[j] = sack;
 621                         }
 622                 }
 623         }
 624         if (TAILQ_EMPTY(&tp->snd_holes)) {
 625                 /*
 626                  * Empty scoreboard. Need to initialize snd_fack (it may be
 627                  * uninitialized or have a bogus value). Scoreboard holes
 628                  * (from the sack blocks received) are created later below
 629                  * (in the logic that adds holes to the tail of the
 630                  * scoreboard).
 631                  */
 632                 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
 633                 tp->sackhint.sacked_bytes = 0;  /* reset */
 634         }
 635         /*
 636          * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
 637          * SACK holes (snd_holes) are traversed from their tails with just
 638          * one pass in order to reduce the number of compares especially when
 639          * the bandwidth-delay product is large.
 640          *
 641          * Note: Typically, in the first RTT of SACK recovery, the highest
 642          * three or four SACK blocks with the same ack number are received.
 643          * In the second RTT, if retransmitted data segments are not lost,
 644          * the highest three or four SACK blocks with ack number advancing
 645          * are received.
 646          */
 647         sblkp = &sack_blocks[num_sack_blks - 1];        /* Last SACK block */
 648         tp->sackhint.last_sack_ack = sblkp->end;
 649         if (SEQ_LT(tp->snd_fack, sblkp->start)) {
 650                 /*
 651                  * The highest SACK block is beyond fack.  First,
 652                  * check if there was a successful Rescue Retransmission,
 653                  * and move this hole left. With normal holes, snd_fack
 654                  * is always to the right of the end.
 655                  */
 656                 if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
 657                     SEQ_LEQ(tp->snd_fack,temp->end)) {
 658                         temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
 659                         temp->end = sblkp->start;
 660                         temp->rxmit = temp->start;
 661                         delivered_data += sblkp->end - sblkp->start;
 662                         tp->snd_fack = sblkp->end;
 663                         sblkp--;
 664                         sack_changed = 1;
 665                 } else {
 666                         /*
 667                          * Append a new SACK hole at the tail.  If the
 668                          * second or later highest SACK blocks are also
 669                          * beyond the current fack, they will be inserted
 670                          * by way of hole splitting in the while-loop below.
 671                          */
 672                         temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
 673                         if (temp != NULL) {
 674                                 delivered_data += sblkp->end - sblkp->start;
 675                                 tp->snd_fack = sblkp->end;
 676                                 /* Go to the previous sack block. */
 677                                 sblkp--;
 678                                 sack_changed = 1;
 679                         } else {
 680                                 /*
 681                                  * We failed to add a new hole based on the current
 682                                  * sack block.  Skip over all the sack blocks that
 683                                  * fall completely to the right of snd_fack and
 684                                  * proceed to trim the scoreboard based on the
 685                                  * remaining sack blocks.  This also trims the
 686                                  * scoreboard for th_ack (which is sack_blocks[0]).
 687                                  */
 688                                 while (sblkp >= sack_blocks &&
 689                                        SEQ_LT(tp->snd_fack, sblkp->start))
 690                                         sblkp--;
 691                                 if (sblkp >= sack_blocks &&
 692                                     SEQ_LT(tp->snd_fack, sblkp->end)) {
 693                                         delivered_data += sblkp->end - tp->snd_fack;
 694                                         tp->snd_fack = sblkp->end;
 695                                         sack_changed = 1;
 696                                 }
 697                         }
 698                 }
 699         } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
 700                 /* fack is advanced. */
 701                 delivered_data += sblkp->end - tp->snd_fack;
 702                 tp->snd_fack = sblkp->end;
 703                 sack_changed = 1;
 704         }
 705         cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
 706         /*
 707          * Since the incoming sack blocks are sorted, we can process them
 708          * making one sweep of the scoreboard.
 709          */
 710         while (sblkp >= sack_blocks  && cur != NULL) {
 711                 if (SEQ_GEQ(sblkp->start, cur->end)) {
 712                         /*
 713                          * SACKs data beyond the current hole.  Go to the
 714                          * previous sack block.
 715                          */
 716                         sblkp--;
 717                         continue;
 718                 }
 719                 if (SEQ_LEQ(sblkp->end, cur->start)) {
 720                         /*
 721                          * SACKs data before the current hole.  Go to the
 722                          * previous hole.
 723                          */
 724                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 725                         continue;
 726                 }
 727                 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
 728                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 729                     ("sackhint bytes rtx >= 0"));
 730                 sack_changed = 1;
 731                 if (SEQ_LEQ(sblkp->start, cur->start)) {
 732                         /* Data acks at least the beginning of hole. */
 733                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 734                                 /* Acks entire hole, so delete hole. */
 735                                 delivered_data += (cur->end - cur->start);
 736                                 temp = cur;
 737                                 cur = TAILQ_PREV(cur, sackhole_head, scblink);
 738                                 tcp_sackhole_remove(tp, temp);
 739                                 /*
 740                                  * The sack block may ack all or part of the
 741                                  * next hole too, so continue onto the next
 742                                  * hole.
 743                                  */
 744                                 continue;
 745                         } else {
 746                                 /* Move start of hole forward. */
 747                                 delivered_data += (sblkp->end - cur->start);
 748                                 cur->start = sblkp->end;
 749                                 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 750                         }
 751                 } else {
 752                         /* Data acks at least the end of hole. */
 753                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 754                                 /* Move end of hole backward. */
 755                                 delivered_data += (cur->end - sblkp->start);
 756                                 cur->end = sblkp->start;
 757                                 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 758                         } else {
 759                                 /*
 760                                  * ACKs some data in middle of a hole; need
 761                                  * to split current hole
 762                                  */
 763                                 temp = tcp_sackhole_insert(tp, sblkp->end,
 764                                     cur->end, cur);
 765                                 if (temp != NULL) {
 766                                         if (SEQ_GT(cur->rxmit, temp->rxmit)) {
 767                                                 temp->rxmit = cur->rxmit;
 768                                                 tp->sackhint.sack_bytes_rexmit
 769                                                     += (temp->rxmit
 770                                                     - temp->start);
 771                                         }
 772                                         cur->end = sblkp->start;
 773                                         cur->rxmit = SEQ_MIN(cur->rxmit,
 774                                             cur->end);
 775                                         delivered_data += (sblkp->end - sblkp->start);
 776                                 }
 777                         }
 778                 }
 779                 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
 780                 /*
 781                  * Testing sblkp->start against cur->start tells us whether
 782                  * we're done with the sack block or the sack hole.
 783                  * Accordingly, we advance one or the other.
 784                  */
 785                 if (SEQ_LEQ(sblkp->start, cur->start))
 786                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 787                 else
 788                         sblkp--;
 789         }
 790         if (!(to->to_flags & TOF_SACK))
 791                 /*
 792                  * If this ACK did not contain any
 793                  * SACK blocks, any only moved the
 794                  * left edge right, it is a pure
 795                  * cumulative ACK. Do not count
 796                  * DupAck for this. Also required
 797                  * for RFC6675 rescue retransmission.
 798                  */
 799                 sack_changed = 0;
 800         tp->sackhint.delivered_data = delivered_data;
 801         tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
 802         KASSERT((delivered_data >= 0), ("delivered_data < 0"));
 803         KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
 804         return (sack_changed);
 805 }
 806
 807 /*
 808  * Free all SACK holes to clear the scoreboard.
 809  */
 810 void
 811 tcp_free_sackholes(struct tcpcb *tp)
 812 {
 813         struct sackhole *q;
 814
 815         INP_WLOCK_ASSERT(tp->t_inpcb);
 816         while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
 817                 tcp_sackhole_remove(tp, q);
 818         tp->sackhint.sack_bytes_rexmit = 0;
 819
 820         KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
 821         KASSERT(tp->sackhint.nexthole == NULL,
 822                 ("tp->sackhint.nexthole == NULL"));
 823 }
 824
 825 /*
 826  * Partial ack handling within a sack recovery episode.  Keeping this very
 827  * simple for now.  When a partial ack is received, force snd_cwnd to a value
 828  * that will allow the sender to transmit no more than 2 segments.  If
 829  * necessary, a better scheme can be adopted at a later point, but for now,
 830  * the goal is to prevent the sender from bursting a large amount of data in
 831  * the midst of sack recovery.
 832  */
 833 void
 834 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 835 {
 836         int num_segs = 1;
 837         u_int maxseg = tcp_maxseg(tp);
 838
 839         INP_WLOCK_ASSERT(tp->t_inpcb);
 840         tcp_timer_activate(tp, TT_REXMT, 0);
 841         tp->t_rtttime = 0;
 842         /* Send one or 2 segments based on how much new data was acked. */
 843         if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
 844                 num_segs = 2;
 845         tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
 846             (tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
 847         if (tp->snd_cwnd > tp->snd_ssthresh)
 848                 tp->snd_cwnd = tp->snd_ssthresh;
 849         tp->t_flags |= TF_ACKNOW;
 850         /*
 851          * RFC6675 rescue retransmission
 852          * Add a hole between th_ack (snd_una is not yet set) and snd_max,
 853          * if this was a pure cumulative ACK and no data was send beyond
 854          * recovery point. Since the data in the socket has not been freed
 855          * at this point, we check if the scoreboard is empty, and the ACK
 856          * delivered some new data, indicating a full ACK. Also, if the
 857          * recovery point is still at snd_max, we are probably application
 858          * limited. However, this inference might not always be true. The
 859          * rescue retransmission may rarely be slightly premature
 860          * compared to RFC6675.
 861          * The corresponding ACK+SACK will cause any further outstanding
 862          * segments to be retransmitted. This addresses a corner case, when
 863          * the trailing packets of a window are lost and no further data
 864          * is available for sending.
 865          */
 866         if ((V_tcp_do_rfc6675_pipe) &&
 867             SEQ_LT(th->th_ack, tp->snd_recover) &&
 868             (tp->snd_recover == tp->snd_max) &&
 869             TAILQ_EMPTY(&tp->snd_holes) &&
 870             (tp->sackhint.delivered_data > 0)) {
 871                 /*
 872                  * Exclude FIN sequence space in
 873                  * the hole for the rescue retransmission,
 874                  * and also don't create a hole, if only
 875                  * the ACK for a FIN is outstanding.
 876                  */
 877                 tcp_seq highdata = tp->snd_max;
 878                 if (tp->t_flags & TF_SENTFIN)
 879                         highdata--;
 880                 if (th->th_ack != highdata) {
 881                         tp->snd_fack = th->th_ack;
 882                         (void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
 883                             highdata - maxseg), highdata, NULL);
 884                 }
 885         }
 886         (void) tp->t_fb->tfb_tcp_output(tp);
 887 }
 888
 889 #if 0
 890 /*
 891  * Debug version of tcp_sack_output() that walks the scoreboard.  Used for
 892  * now to sanity check the hint.
 893  */
 894 static struct sackhole *
 895 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
 896 {
 897         struct sackhole *p;
 898
 899         INP_WLOCK_ASSERT(tp->t_inpcb);
 900         *sack_bytes_rexmt = 0;
 901         TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
 902                 if (SEQ_LT(p->rxmit, p->end)) {
 903                         if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 904                                 continue;
 905                         }
 906                         *sack_bytes_rexmt += (p->rxmit - p->start);
 907                         break;
 908                 }
 909                 *sack_bytes_rexmt += (p->rxmit - p->start);
 910         }
 911         return (p);
 912 }
 913 #endif
 914
 915 /*
 916  * Returns the next hole to retransmit and the number of retransmitted bytes
 917  * from the scoreboard.  We store both the next hole and the number of
 918  * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
 919  * reception).  This avoids scoreboard traversals completely.
 920  *
 921  * The loop here will traverse *at most* one link.  Here's the argument.  For
 922  * the loop to traverse more than 1 link before finding the next hole to
 923  * retransmit, we would need to have at least 1 node following the current
 924  * hint with (rxmit == end).  But, for all holes following the current hint,
 925  * (start == rxmit), since we have not yet retransmitted from them.
 926  * Therefore, in order to traverse more 1 link in the loop below, we need to
 927  * have at least one node following the current hint with (start == rxmit ==
 928  * end).  But that can't happen, (start == end) means that all the data in
 929  * that hole has been sacked, in which case, the hole would have been removed
 930  * from the scoreboard.
 931  */
 932 struct sackhole *
 933 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 934 {
 935         struct sackhole *hole = NULL;
 936
 937         INP_WLOCK_ASSERT(tp->t_inpcb);
 938         *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
 939         hole = tp->sackhint.nexthole;
 940         if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
 941                 goto out;
 942         while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
 943                 if (SEQ_LT(hole->rxmit, hole->end)) {
 944                         tp->sackhint.nexthole = hole;
 945                         break;
 946                 }
 947         }
 948 out:
 949         return (hole);
 950 }
 951
 952 /*
 953  * After a timeout, the SACK list may be rebuilt.  This SACK information
 954  * should be used to avoid retransmitting SACKed data.  This function
 955  * traverses the SACK list to see if snd_nxt should be moved forward.
 956  */
 957 void
 958 tcp_sack_adjust(struct tcpcb *tp)
 959 {
 960         struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 961
 962         INP_WLOCK_ASSERT(tp->t_inpcb);
 963         if (cur == NULL)
 964                 return; /* No holes */
 965         if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
 966                 return; /* We're already beyond any SACKed blocks */
 967         /*-
 968          * Two cases for which we want to advance snd_nxt:
 969          * i) snd_nxt lies between end of one hole and beginning of another
 970          * ii) snd_nxt lies between end of last hole and snd_fack
 971          */
 972         while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
 973                 if (SEQ_LT(tp->snd_nxt, cur->end))
 974                         return;
 975                 if (SEQ_GEQ(tp->snd_nxt, p->start))
 976                         cur = p;
 977                 else {
 978                         tp->snd_nxt = p->start;
 979                         return;
 980                 }
 981         }
 982         if (SEQ_LT(tp->snd_nxt, cur->end))
 983                 return;
 984         tp->snd_nxt = tp->snd_fack;
 985 }