sys/netinet/tcp_sack.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   5  *      The Regents of the University of California.
   6  * All rights reserved.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  *      @(#)tcp_sack.c  8.12 (Berkeley) 5/24/95
  33  */
  34
  35 /*-
  36  *      @@(#)COPYRIGHT  1.1 (NRL) 17 January 1995
  37  *
  38  * NRL grants permission for redistribution and use in source and binary
  39  * forms, with or without modification, of the software and documentation
  40  * created at NRL provided that the following conditions are met:
  41  *
  42  * 1. Redistributions of source code must retain the above copyright
  43  *    notice, this list of conditions and the following disclaimer.
  44  * 2. Redistributions in binary form must reproduce the above copyright
  45  *    notice, this list of conditions and the following disclaimer in the
  46  *    documentation and/or other materials provided with the distribution.
  47  * 3. All advertising materials mentioning features or use of this software
  48  *    must display the following acknowledgements:
  49  *      This product includes software developed by the University of
  50  *      California, Berkeley and its contributors.
  51  *      This product includes software developed at the Information
  52  *      Technology Division, US Naval Research Laboratory.
  53  * 4. Neither the name of the NRL nor the names of its contributors
  54  *    may be used to endorse or promote products derived from this software
  55  *    without specific prior written permission.
  56  *
  57  * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS
  58  * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  59  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  60  * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL NRL OR
  61  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  62  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  63  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  64  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  65  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  66  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  67  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  68  *
  69  * The views and conclusions contained in the software and documentation
  70  * are those of the authors and should not be interpreted as representing
  71  * official policies, either expressed or implied, of the US Naval
  72  * Research Laboratory (NRL).
  73  */
  74
  75 #include <sys/cdefs.h>
  76 __FBSDID("$FreeBSD$");
  77
  78 #include "opt_inet.h"
  79 #include "opt_inet6.h"
  80 #include "opt_tcpdebug.h"
  81
  82 #include <sys/param.h>
  83 #include <sys/systm.h>
  84 #include <sys/kernel.h>
  85 #include <sys/sysctl.h>
  86 #include <sys/malloc.h>
  87 #include <sys/mbuf.h>
  88 #include <sys/proc.h>           /* for proc0 declaration */
  89 #include <sys/protosw.h>
  90 #include <sys/socket.h>
  91 #include <sys/socketvar.h>
  92 #include <sys/syslog.h>
  93 #include <sys/systm.h>
  94
  95 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  96
  97 #include <vm/uma.h>
  98
  99 #include <net/if.h>
 100 #include <net/if_var.h>
 101 #include <net/route.h>
 102 #include <net/vnet.h>
 103
 104 #include <netinet/in.h>
 105 #include <netinet/in_systm.h>
 106 #include <netinet/ip.h>
 107 #include <netinet/in_var.h>
 108 #include <netinet/in_pcb.h>
 109 #include <netinet/ip_var.h>
 110 #include <netinet/ip6.h>
 111 #include <netinet/icmp6.h>
 112 #include <netinet6/nd6.h>
 113 #include <netinet6/ip6_var.h>
 114 #include <netinet6/in6_pcb.h>
 115 #include <netinet/tcp.h>
 116 #include <netinet/tcp_fsm.h>
 117 #include <netinet/tcp_seq.h>
 118 #include <netinet/tcp_timer.h>
 119 #include <netinet/tcp_var.h>
 120 #include <netinet6/tcp6_var.h>
 121 #include <netinet/tcpip.h>
 122 #ifdef TCPDEBUG
 123 #include <netinet/tcp_debug.h>
 124 #endif /* TCPDEBUG */
 125
 126 #include <machine/in_cksum.h>
 127
 128 VNET_DECLARE(struct uma_zone *, sack_hole_zone);
 129 #define V_sack_hole_zone                VNET(sack_hole_zone)
 130
 131 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
 132     "TCP SACK");
 133 VNET_DEFINE(int, tcp_do_sack) = 1;
 134 #define V_tcp_do_sack                   VNET(tcp_do_sack)
 135 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
 136     &VNET_NAME(tcp_do_sack), 0, "Enable/Disable TCP SACK support");
 137
 138 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
 139 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
 140     &VNET_NAME(tcp_sack_maxholes), 0,
 141     "Maximum number of TCP SACK holes allowed per connection");
 142
 143 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
 144 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
 145     &VNET_NAME(tcp_sack_globalmaxholes), 0,
 146     "Global maximum number of TCP SACK holes");
 147
 148 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
 149 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
 150     &VNET_NAME(tcp_sack_globalholes), 0,
 151     "Global number of TCP SACK holes currently allocated");
 152
 153 /*
 154  * This function will find overlaps with the currently stored sackblocks
 155  * and add any overlap as a dsack block upfront
 156  */
 157 void
 158 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 159 {
 160         struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
 161         int i, j, n, identical;
 162         tcp_seq start, end;
 163
 164         INP_WLOCK_ASSERT(tp->t_inpcb);
 165
 166         KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
 167
 168         if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
 169             ((rcv_end == tp->rcv_nxt) &&
 170              (tp->rcv_numsacks > 0 ) &&
 171              (tp->sackblks[0].end == tp->rcv_nxt))) {
 172                 saved_blks[0].start = rcv_start;
 173                 saved_blks[0].end = rcv_end;
 174         } else {
 175                 saved_blks[0].start = saved_blks[0].end = 0;
 176         }
 177
 178         head_blk.start = head_blk.end = 0;
 179         mid_blk.start = rcv_start;
 180         mid_blk.end = rcv_end;
 181         identical = 0;
 182
 183         for (i = 0; i < tp->rcv_numsacks; i++) {
 184                 start = tp->sackblks[i].start;
 185                 end = tp->sackblks[i].end;
 186                 if (SEQ_LT(rcv_end, start)) {
 187                         /* pkt left to sack blk */
 188                         continue;
 189                 }
 190                 if (SEQ_GT(rcv_start, end)) {
 191                         /* pkt right to sack blk */
 192                         continue;
 193                 }
 194                 if (SEQ_GT(tp->rcv_nxt, end)) {
 195                         if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
 196                             (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
 197                             (head_blk.start == head_blk.end))) {
 198                                 head_blk.start = SEQ_MAX(rcv_start, start);
 199                                 head_blk.end = SEQ_MIN(rcv_end, end);
 200                         }
 201                         continue;
 202                 }
 203                 if (((head_blk.start == head_blk.end) ||
 204                      SEQ_LT(start, head_blk.start)) &&
 205                      (SEQ_GT(end, rcv_start) &&
 206                       SEQ_LEQ(start, rcv_end))) {
 207                         head_blk.start = start;
 208                         head_blk.end = end;
 209                 }
 210                 mid_blk.start = SEQ_MIN(mid_blk.start, start);
 211                 mid_blk.end = SEQ_MAX(mid_blk.end, end);
 212                 if ((mid_blk.start == start) &&
 213                     (mid_blk.end == end))
 214                         identical = 1;
 215         }
 216         if (SEQ_LT(head_blk.start, head_blk.end)) {
 217                 /* store overlapping range */
 218                 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
 219                 saved_blks[0].end   = SEQ_MIN(rcv_end, head_blk.end);
 220         }
 221         n = 1;
 222         /*
 223          * Second, if not ACKed, store the SACK block that
 224          * overlaps with the DSACK block unless it is identical
 225          */
 226         if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
 227             !((mid_blk.start == saved_blks[0].start) &&
 228             (mid_blk.end == saved_blks[0].end))) ||
 229             identical == 1) {
 230                 saved_blks[n].start = mid_blk.start;
 231                 saved_blks[n++].end = mid_blk.end;
 232         }
 233         for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
 234                 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
 235                       SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
 236                     (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
 237                 saved_blks[n++] = tp->sackblks[j];
 238         }
 239         j = 0;
 240         for (i = 0; i < n; i++) {
 241                 /* we can end up with a stale initial entry */
 242                 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
 243                         tp->sackblks[j++] = saved_blks[i];
 244                 }
 245         }
 246         tp->rcv_numsacks = j;
 247 }
 248
 249 /*
 250  * This function is called upon receipt of new valid data (while not in
 251  * header prediction mode), and it updates the ordered list of sacks.
 252  */
 253 void
 254 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 255 {
 256         /*
 257          * First reported block MUST be the most recent one.  Subsequent
 258          * blocks SHOULD be in the order in which they arrived at the
 259          * receiver.  These two conditions make the implementation fully
 260          * compliant with RFC 2018.
 261          */
 262         struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
 263         int num_head, num_saved, i;
 264
 265         INP_WLOCK_ASSERT(tp->t_inpcb);
 266
 267         /* Check arguments. */
 268         KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
 269
 270         if ((rcv_start == rcv_end) &&
 271             (tp->rcv_numsacks >= 1) &&
 272             (rcv_end == tp->sackblks[0].end)) {
 273                 /* retaining DSACK block below rcv_nxt (todrop) */
 274                 head_blk = tp->sackblks[0];
 275         } else {
 276                 /* SACK block for the received segment. */
 277                 head_blk.start = rcv_start;
 278                 head_blk.end = rcv_end;
 279         }
 280
 281         /*
 282          * Merge updated SACK blocks into head_blk, and save unchanged SACK
 283          * blocks into saved_blks[].  num_saved will have the number of the
 284          * saved SACK blocks.
 285          */
 286         num_saved = 0;
 287         for (i = 0; i < tp->rcv_numsacks; i++) {
 288                 tcp_seq start = tp->sackblks[i].start;
 289                 tcp_seq end = tp->sackblks[i].end;
 290                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 291                         /*
 292                          * Discard this SACK block.
 293                          */
 294                 } else if (SEQ_LEQ(head_blk.start, end) &&
 295                            SEQ_GEQ(head_blk.end, start)) {
 296                         /*
 297                          * Merge this SACK block into head_blk.  This SACK
 298                          * block itself will be discarded.
 299                          */
 300                         /*
 301                          * |-|
 302                          *   |---|  merge
 303                          *
 304                          *     |-|
 305                          * |---|    merge
 306                          *
 307                          * |-----|
 308                          *   |-|    DSACK smaller
 309                          *
 310                          *   |-|
 311                          * |-----|  DSACK smaller
 312                          */
 313                         if (head_blk.start == end)
 314                                 head_blk.start = start;
 315                         else if (head_blk.end == start)
 316                                 head_blk.end = end;
 317                         else {
 318                                 if (SEQ_LT(head_blk.start, start)) {
 319                                         tcp_seq temp = start;
 320                                         start = head_blk.start;
 321                                         head_blk.start = temp;
 322                                 }
 323                                 if (SEQ_GT(head_blk.end, end)) {
 324                                         tcp_seq temp = end;
 325                                         end = head_blk.end;
 326                                         head_blk.end = temp;
 327                                 }
 328                                 if ((head_blk.start != start) ||
 329                                     (head_blk.end != end)) {
 330                                         if ((num_saved >= 1) &&
 331                                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 332                                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 333                                                 num_saved--;
 334                                         saved_blks[num_saved].start = start;
 335                                         saved_blks[num_saved].end = end;
 336                                         num_saved++;
 337                                 }
 338                         }
 339                 } else {
 340                         /*
 341                          * This block supercedes the prior block
 342                          */
 343                         if ((num_saved >= 1) &&
 344                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 345                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 346                                 num_saved--;
 347                         /*
 348                          * Save this SACK block.
 349                          */
 350                         saved_blks[num_saved].start = start;
 351                         saved_blks[num_saved].end = end;
 352                         num_saved++;
 353                 }
 354         }
 355
 356         /*
 357          * Update SACK list in tp->sackblks[].
 358          */
 359         num_head = 0;
 360         if (SEQ_LT(rcv_start, rcv_end)) {
 361                 /*
 362                  * The received data segment is an out-of-order segment.  Put
 363                  * head_blk at the top of SACK list.
 364                  */
 365                 tp->sackblks[0] = head_blk;
 366                 num_head = 1;
 367                 /*
 368                  * If the number of saved SACK blocks exceeds its limit,
 369                  * discard the last SACK block.
 370                  */
 371                 if (num_saved >= MAX_SACK_BLKS)
 372                         num_saved--;
 373         }
 374         if ((rcv_start == rcv_end) &&
 375             (rcv_start == tp->sackblks[0].end)) {
 376                 num_head = 1;
 377         }
 378         if (num_saved > 0) {
 379                 /*
 380                  * Copy the saved SACK blocks back.
 381                  */
 382                 bcopy(saved_blks, &tp->sackblks[num_head],
 383                       sizeof(struct sackblk) * num_saved);
 384         }
 385
 386         /* Save the number of SACK blocks. */
 387         tp->rcv_numsacks = num_head + num_saved;
 388 }
 389
 390 void
 391 tcp_clean_dsack_blocks(struct tcpcb *tp)
 392 {
 393         struct sackblk saved_blks[MAX_SACK_BLKS];
 394         int num_saved, i;
 395
 396         INP_WLOCK_ASSERT(tp->t_inpcb);
 397         /*
 398          * Clean up any DSACK blocks that
 399          * are in our queue of sack blocks.
 400          *
 401          */
 402         num_saved = 0;
 403         for (i = 0; i < tp->rcv_numsacks; i++) {
 404                 tcp_seq start = tp->sackblks[i].start;
 405                 tcp_seq end = tp->sackblks[i].end;
 406                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 407                         /*
 408                          * Discard this D-SACK block.
 409                          */
 410                         continue;
 411                 }
 412                 /*
 413                  * Save this SACK block.
 414                  */
 415                 saved_blks[num_saved].start = start;
 416                 saved_blks[num_saved].end = end;
 417                 num_saved++;
 418         }
 419         if (num_saved > 0) {
 420                 /*
 421                  * Copy the saved SACK blocks back.
 422                  */
 423                 bcopy(saved_blks, &tp->sackblks[0],
 424                       sizeof(struct sackblk) * num_saved);
 425         }
 426         tp->rcv_numsacks = num_saved;
 427 }
 428
 429 /*
 430  * Delete all receiver-side SACK information.
 431  */
 432 void
 433 tcp_clean_sackreport(struct tcpcb *tp)
 434 {
 435         int i;
 436
 437         INP_WLOCK_ASSERT(tp->t_inpcb);
 438         tp->rcv_numsacks = 0;
 439         for (i = 0; i < MAX_SACK_BLKS; i++)
 440                 tp->sackblks[i].start = tp->sackblks[i].end=0;
 441 }
 442
 443 /*
 444  * Allocate struct sackhole.
 445  */
 446 static struct sackhole *
 447 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 448 {
 449         struct sackhole *hole;
 450
 451         if (tp->snd_numholes >= V_tcp_sack_maxholes ||
 452             V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
 453                 TCPSTAT_INC(tcps_sack_sboverflow);
 454                 return NULL;
 455         }
 456
 457         hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
 458         if (hole == NULL)
 459                 return NULL;
 460
 461         hole->start = start;
 462         hole->end = end;
 463         hole->rxmit = start;
 464
 465         tp->snd_numholes++;
 466         atomic_add_int(&V_tcp_sack_globalholes, 1);
 467
 468         return hole;
 469 }
 470
 471 /*
 472  * Free struct sackhole.
 473  */
 474 static void
 475 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
 476 {
 477
 478         uma_zfree(V_sack_hole_zone, hole);
 479
 480         tp->snd_numholes--;
 481         atomic_subtract_int(&V_tcp_sack_globalholes, 1);
 482
 483         KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
 484         KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
 485 }
 486
 487 /*
 488  * Insert new SACK hole into scoreboard.
 489  */
 490 static struct sackhole *
 491 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
 492     struct sackhole *after)
 493 {
 494         struct sackhole *hole;
 495
 496         /* Allocate a new SACK hole. */
 497         hole = tcp_sackhole_alloc(tp, start, end);
 498         if (hole == NULL)
 499                 return NULL;
 500
 501         /* Insert the new SACK hole into scoreboard. */
 502         if (after != NULL)
 503                 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
 504         else
 505                 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
 506
 507         /* Update SACK hint. */
 508         if (tp->sackhint.nexthole == NULL)
 509                 tp->sackhint.nexthole = hole;
 510
 511         return hole;
 512 }
 513
 514 /*
 515  * Remove SACK hole from scoreboard.
 516  */
 517 static void
 518 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
 519 {
 520
 521         /* Update SACK hint. */
 522         if (tp->sackhint.nexthole == hole)
 523                 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
 524
 525         /* Remove this SACK hole. */
 526         TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
 527
 528         /* Free this SACK hole. */
 529         tcp_sackhole_free(tp, hole);
 530 }
 531
 532 /*
 533  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
 534  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
 535  * the sequence space).
 536  * Returns 1 if incoming ACK has previously unknown SACK information,
 537  * 0 otherwise.
 538  */
 539 int
 540 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
 541 {
 542         struct sackhole *cur, *temp;
 543         struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 544         int i, j, num_sack_blks, sack_changed;
 545         int delivered_data, left_edge_delta;
 546
 547         INP_WLOCK_ASSERT(tp->t_inpcb);
 548
 549         num_sack_blks = 0;
 550         sack_changed = 0;
 551         delivered_data = 0;
 552         left_edge_delta = 0;
 553         /*
 554          * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 555          * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
 556          * Account changes to SND.UNA always in delivered data.
 557          */
 558         if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
 559                 left_edge_delta = th_ack - tp->snd_una;
 560                 sack_blocks[num_sack_blks].start = tp->snd_una;
 561                 sack_blocks[num_sack_blks++].end = th_ack;
 562         }
 563         /*
 564          * Append received valid SACK blocks to sack_blocks[], but only if we
 565          * received new blocks from the other side.
 566          */
 567         if (to->to_flags & TOF_SACK) {
 568                 for (i = 0; i < to->to_nsacks; i++) {
 569                         bcopy((to->to_sacks + i * TCPOLEN_SACK),
 570                             &sack, sizeof(sack));
 571                         sack.start = ntohl(sack.start);
 572                         sack.end = ntohl(sack.end);
 573                         if (SEQ_GT(sack.end, sack.start) &&
 574                             SEQ_GT(sack.start, tp->snd_una) &&
 575                             SEQ_GT(sack.start, th_ack) &&
 576                             SEQ_LT(sack.start, tp->snd_max) &&
 577                             SEQ_GT(sack.end, tp->snd_una) &&
 578                             SEQ_LEQ(sack.end, tp->snd_max)) {
 579                                 sack_blocks[num_sack_blks++] = sack;
 580                         }
 581                 }
 582         }
 583         /*
 584          * Return if SND.UNA is not advanced and no valid SACK block is
 585          * received.
 586          */
 587         if (num_sack_blks == 0)
 588                 return (sack_changed);
 589
 590         /*
 591          * Sort the SACK blocks so we can update the scoreboard with just one
 592          * pass. The overhead of sorting up to 4+1 elements is less than
 593          * making up to 4+1 passes over the scoreboard.
 594          */
 595         for (i = 0; i < num_sack_blks; i++) {
 596                 for (j = i + 1; j < num_sack_blks; j++) {
 597                         if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
 598                                 sack = sack_blocks[i];
 599                                 sack_blocks[i] = sack_blocks[j];
 600                                 sack_blocks[j] = sack;
 601                         }
 602                 }
 603         }
 604         if (TAILQ_EMPTY(&tp->snd_holes)) {
 605                 /*
 606                  * Empty scoreboard. Need to initialize snd_fack (it may be
 607                  * uninitialized or have a bogus value). Scoreboard holes
 608                  * (from the sack blocks received) are created later below
 609                  * (in the logic that adds holes to the tail of the
 610                  * scoreboard).
 611                  */
 612                 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
 613                 tp->sackhint.sacked_bytes = 0;  /* reset */
 614         }
 615         /*
 616          * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
 617          * SACK holes (snd_holes) are traversed from their tails with just
 618          * one pass in order to reduce the number of compares especially when
 619          * the bandwidth-delay product is large.
 620          *
 621          * Note: Typically, in the first RTT of SACK recovery, the highest
 622          * three or four SACK blocks with the same ack number are received.
 623          * In the second RTT, if retransmitted data segments are not lost,
 624          * the highest three or four SACK blocks with ack number advancing
 625          * are received.
 626          */
 627         sblkp = &sack_blocks[num_sack_blks - 1];        /* Last SACK block */
 628         tp->sackhint.last_sack_ack = sblkp->end;
 629         if (SEQ_LT(tp->snd_fack, sblkp->start)) {
 630                 /*
 631                  * The highest SACK block is beyond fack.  Append new SACK
 632                  * hole at the tail.  If the second or later highest SACK
 633                  * blocks are also beyond the current fack, they will be
 634                  * inserted by way of hole splitting in the while-loop below.
 635                  */
 636                 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
 637                 if (temp != NULL) {
 638                         delivered_data += sblkp->end - sblkp->start;
 639                         tp->snd_fack = sblkp->end;
 640                         /* Go to the previous sack block. */
 641                         sblkp--;
 642                         sack_changed = 1;
 643                 } else {
 644                         /*
 645                          * We failed to add a new hole based on the current
 646                          * sack block.  Skip over all the sack blocks that
 647                          * fall completely to the right of snd_fack and
 648                          * proceed to trim the scoreboard based on the
 649                          * remaining sack blocks.  This also trims the
 650                          * scoreboard for th_ack (which is sack_blocks[0]).
 651                          */
 652                         while (sblkp >= sack_blocks &&
 653                                SEQ_LT(tp->snd_fack, sblkp->start))
 654                                 sblkp--;
 655                         if (sblkp >= sack_blocks &&
 656                             SEQ_LT(tp->snd_fack, sblkp->end)) {
 657                                 delivered_data += sblkp->end - tp->snd_fack;
 658                                 tp->snd_fack = sblkp->end;
 659                                 sack_changed = 1;
 660                         }
 661                 }
 662         } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
 663                 /* fack is advanced. */
 664                 delivered_data += sblkp->end - tp->snd_fack;
 665                 tp->snd_fack = sblkp->end;
 666                 sack_changed = 1;
 667         }
 668         cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
 669         /*
 670          * Since the incoming sack blocks are sorted, we can process them
 671          * making one sweep of the scoreboard.
 672          */
 673         while (sblkp >= sack_blocks  && cur != NULL) {
 674                 if (SEQ_GEQ(sblkp->start, cur->end)) {
 675                         /*
 676                          * SACKs data beyond the current hole.  Go to the
 677                          * previous sack block.
 678                          */
 679                         sblkp--;
 680                         continue;
 681                 }
 682                 if (SEQ_LEQ(sblkp->end, cur->start)) {
 683                         /*
 684                          * SACKs data before the current hole.  Go to the
 685                          * previous hole.
 686                          */
 687                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 688                         continue;
 689                 }
 690                 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
 691                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 692                     ("sackhint bytes rtx >= 0"));
 693                 sack_changed = 1;
 694                 if (SEQ_LEQ(sblkp->start, cur->start)) {
 695                         /* Data acks at least the beginning of hole. */
 696                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 697                                 /* Acks entire hole, so delete hole. */
 698                                 delivered_data += (cur->end - cur->start);
 699                                 temp = cur;
 700                                 cur = TAILQ_PREV(cur, sackhole_head, scblink);
 701                                 tcp_sackhole_remove(tp, temp);
 702                                 /*
 703                                  * The sack block may ack all or part of the
 704                                  * next hole too, so continue onto the next
 705                                  * hole.
 706                                  */
 707                                 continue;
 708                         } else {
 709                                 /* Move start of hole forward. */
 710                                 delivered_data += (sblkp->end - cur->start);
 711                                 cur->start = sblkp->end;
 712                                 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 713                         }
 714                 } else {
 715                         /* Data acks at least the end of hole. */
 716                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 717                                 /* Move end of hole backward. */
 718                                 delivered_data += (cur->end - sblkp->start);
 719                                 cur->end = sblkp->start;
 720                                 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 721                         } else {
 722                                 /*
 723                                  * ACKs some data in middle of a hole; need
 724                                  * to split current hole
 725                                  */
 726                                 temp = tcp_sackhole_insert(tp, sblkp->end,
 727                                     cur->end, cur);
 728                                 if (temp != NULL) {
 729                                         if (SEQ_GT(cur->rxmit, temp->rxmit)) {
 730                                                 temp->rxmit = cur->rxmit;
 731                                                 tp->sackhint.sack_bytes_rexmit
 732                                                     += (temp->rxmit
 733                                                     - temp->start);
 734                                         }
 735                                         cur->end = sblkp->start;
 736                                         cur->rxmit = SEQ_MIN(cur->rxmit,
 737                                             cur->end);
 738                                         delivered_data += (sblkp->end - sblkp->start);
 739                                 }
 740                         }
 741                 }
 742                 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
 743                 /*
 744                  * Testing sblkp->start against cur->start tells us whether
 745                  * we're done with the sack block or the sack hole.
 746                  * Accordingly, we advance one or the other.
 747                  */
 748                 if (SEQ_LEQ(sblkp->start, cur->start))
 749                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 750                 else
 751                         sblkp--;
 752         }
 753         tp->sackhint.delivered_data = delivered_data;
 754         tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
 755         KASSERT((delivered_data >= 0), ("delivered_data < 0"));
 756         KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
 757         return (sack_changed);
 758 }
 759
 760 /*
 761  * Free all SACK holes to clear the scoreboard.
 762  */
 763 void
 764 tcp_free_sackholes(struct tcpcb *tp)
 765 {
 766         struct sackhole *q;
 767
 768         INP_WLOCK_ASSERT(tp->t_inpcb);
 769         while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
 770                 tcp_sackhole_remove(tp, q);
 771         tp->sackhint.sack_bytes_rexmit = 0;
 772
 773         KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
 774         KASSERT(tp->sackhint.nexthole == NULL,
 775                 ("tp->sackhint.nexthole == NULL"));
 776 }
 777
 778 /*
 779  * Partial ack handling within a sack recovery episode.  Keeping this very
 780  * simple for now.  When a partial ack is received, force snd_cwnd to a value
 781  * that will allow the sender to transmit no more than 2 segments.  If
 782  * necessary, a better scheme can be adopted at a later point, but for now,
 783  * the goal is to prevent the sender from bursting a large amount of data in
 784  * the midst of sack recovery.
 785  */
 786 void
 787 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 788 {
 789         int num_segs = 1;
 790         u_int maxseg = tcp_maxseg(tp);
 791
 792         INP_WLOCK_ASSERT(tp->t_inpcb);
 793         tcp_timer_activate(tp, TT_REXMT, 0);
 794         tp->t_rtttime = 0;
 795         /* Send one or 2 segments based on how much new data was acked. */
 796         if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
 797                 num_segs = 2;
 798         tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
 799             (tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
 800         if (tp->snd_cwnd > tp->snd_ssthresh)
 801                 tp->snd_cwnd = tp->snd_ssthresh;
 802         tp->t_flags |= TF_ACKNOW;
 803         (void) tp->t_fb->tfb_tcp_output(tp);
 804 }
 805
 806 #if 0
 807 /*
 808  * Debug version of tcp_sack_output() that walks the scoreboard.  Used for
 809  * now to sanity check the hint.
 810  */
 811 static struct sackhole *
 812 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
 813 {
 814         struct sackhole *p;
 815
 816         INP_WLOCK_ASSERT(tp->t_inpcb);
 817         *sack_bytes_rexmt = 0;
 818         TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
 819                 if (SEQ_LT(p->rxmit, p->end)) {
 820                         if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 821                                 continue;
 822                         }
 823                         *sack_bytes_rexmt += (p->rxmit - p->start);
 824                         break;
 825                 }
 826                 *sack_bytes_rexmt += (p->rxmit - p->start);
 827         }
 828         return (p);
 829 }
 830 #endif
 831
 832 /*
 833  * Returns the next hole to retransmit and the number of retransmitted bytes
 834  * from the scoreboard.  We store both the next hole and the number of
 835  * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
 836  * reception).  This avoids scoreboard traversals completely.
 837  *
 838  * The loop here will traverse *at most* one link.  Here's the argument.  For
 839  * the loop to traverse more than 1 link before finding the next hole to
 840  * retransmit, we would need to have at least 1 node following the current
 841  * hint with (rxmit == end).  But, for all holes following the current hint,
 842  * (start == rxmit), since we have not yet retransmitted from them.
 843  * Therefore, in order to traverse more 1 link in the loop below, we need to
 844  * have at least one node following the current hint with (start == rxmit ==
 845  * end).  But that can't happen, (start == end) means that all the data in
 846  * that hole has been sacked, in which case, the hole would have been removed
 847  * from the scoreboard.
 848  */
 849 struct sackhole *
 850 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 851 {
 852         struct sackhole *hole = NULL;
 853
 854         INP_WLOCK_ASSERT(tp->t_inpcb);
 855         *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
 856         hole = tp->sackhint.nexthole;
 857         if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
 858                 goto out;
 859         while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
 860                 if (SEQ_LT(hole->rxmit, hole->end)) {
 861                         tp->sackhint.nexthole = hole;
 862                         break;
 863                 }
 864         }
 865 out:
 866         return (hole);
 867 }
 868
 869 /*
 870  * After a timeout, the SACK list may be rebuilt.  This SACK information
 871  * should be used to avoid retransmitting SACKed data.  This function
 872  * traverses the SACK list to see if snd_nxt should be moved forward.
 873  */
 874 void
 875 tcp_sack_adjust(struct tcpcb *tp)
 876 {
 877         struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 878
 879         INP_WLOCK_ASSERT(tp->t_inpcb);
 880         if (cur == NULL)
 881                 return; /* No holes */
 882         if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
 883                 return; /* We're already beyond any SACKed blocks */
 884         /*-
 885          * Two cases for which we want to advance snd_nxt:
 886          * i) snd_nxt lies between end of one hole and beginning of another
 887          * ii) snd_nxt lies between end of last hole and snd_fack
 888          */
 889         while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
 890                 if (SEQ_LT(tp->snd_nxt, cur->end))
 891                         return;
 892                 if (SEQ_GEQ(tp->snd_nxt, p->start))
 893                         cur = p;
 894                 else {
 895                         tp->snd_nxt = p->start;
 896                         return;
 897                 }
 898         }
 899         if (SEQ_LT(tp->snd_nxt, cur->end))
 900                 return;
 901         tp->snd_nxt = tp->snd_fack;
 902 }