tcp_sack.c revision 196019
1/*- 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995 3 * The Regents of the University of California. 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 4. Neither the name of the University nor the names of its contributors 15 * may be used to endorse or promote products derived from this software 16 * without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 * 30 * @(#)tcp_sack.c 8.12 (Berkeley) 5/24/95 31 */ 32 33/*- 34 * @@(#)COPYRIGHT 1.1 (NRL) 17 January 1995 35 * 36 * NRL grants permission for redistribution and use in source and binary 37 * forms, with or without modification, of the software and documentation 38 * created at NRL provided that the following conditions are met: 39 * 40 * 1. Redistributions of source code must retain the above copyright 41 * notice, this list of conditions and the following disclaimer. 42 * 2. Redistributions in binary form must reproduce the above copyright 43 * notice, this list of conditions and the following disclaimer in the 44 * documentation and/or other materials provided with the distribution. 45 * 3. All advertising materials mentioning features or use of this software 46 * must display the following acknowledgements: 47 * This product includes software developed by the University of 48 * California, Berkeley and its contributors. 49 * This product includes software developed at the Information 50 * Technology Division, US Naval Research Laboratory. 51 * 4. Neither the name of the NRL nor the names of its contributors 52 * may be used to endorse or promote products derived from this software 53 * without specific prior written permission. 54 * 55 * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS 56 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 57 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 58 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NRL OR 59 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 60 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 61 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 62 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 63 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 64 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 65 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 66 * 67 * The views and conclusions contained in the software and documentation 68 * are those of the authors and should not be interpreted as representing 69 * official policies, either expressed or implied, of the US Naval 70 * Research Laboratory (NRL). 71 */ 72 73#include <sys/cdefs.h> 74__FBSDID("$FreeBSD: head/sys/netinet/tcp_sack.c 196019 2009-08-01 19:26:27Z rwatson $"); 75 76#include "opt_inet.h" 77#include "opt_inet6.h" 78#include "opt_tcpdebug.h" 79 80#include <sys/param.h> 81#include <sys/systm.h> 82#include <sys/kernel.h> 83#include <sys/sysctl.h> 84#include <sys/malloc.h> 85#include <sys/mbuf.h> 86#include <sys/proc.h> /* for proc0 declaration */ 87#include <sys/protosw.h> 88#include <sys/socket.h> 89#include <sys/socketvar.h> 90#include <sys/syslog.h> 91#include <sys/systm.h> 92 93#include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */ 94 95#include <vm/uma.h> 96 97#include <net/if.h> 98#include <net/route.h> 99#include <net/vnet.h> 100 101#include <netinet/in.h> 102#include <netinet/in_systm.h> 103#include <netinet/ip.h> 104#include <netinet/in_var.h> 105#include <netinet/in_pcb.h> 106#include <netinet/ip_var.h> 107#include <netinet/ip6.h> 108#include <netinet/icmp6.h> 109#include <netinet6/nd6.h> 110#include <netinet6/ip6_var.h> 111#include <netinet6/in6_pcb.h> 112#include <netinet/tcp.h> 113#include <netinet/tcp_fsm.h> 114#include <netinet/tcp_seq.h> 115#include <netinet/tcp_timer.h> 116#include <netinet/tcp_var.h> 117#include <netinet6/tcp6_var.h> 118#include <netinet/tcpip.h> 119#ifdef TCPDEBUG 120#include <netinet/tcp_debug.h> 121#endif /* TCPDEBUG */ 122 123#include <machine/in_cksum.h> 124 125VNET_DECLARE(struct uma_zone *, sack_hole_zone); 126VNET_DEFINE(int, tcp_do_sack); 127VNET_DEFINE(int, tcp_sack_maxholes); 128VNET_DEFINE(int, tcp_sack_globalmaxholes); 129VNET_DEFINE(int, tcp_sack_globalholes); 130 131#define V_sack_hole_zone VNET(sack_hole_zone) 132#define V_tcp_do_sack VNET(tcp_do_sack) 133#define V_tcp_sack_maxholes VNET(tcp_sack_maxholes) 134#define V_tcp_sack_globalmaxholes VNET(tcp_sack_globalmaxholes) 135#define V_tcp_sack_globalholes VNET(tcp_sack_globalholes) 136 137SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW, 0, "TCP SACK"); 138SYSCTL_VNET_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_RW, 139 &VNET_NAME(tcp_do_sack), 0, "Enable/Disable TCP SACK support"); 140 141SYSCTL_VNET_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_RW, 142 &VNET_NAME(tcp_sack_maxholes), 0, 143 "Maximum number of TCP SACK holes allowed per connection"); 144 145SYSCTL_VNET_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_RW, 146 &VNET_NAME(tcp_sack_globalmaxholes), 0, 147 "Global maximum number of TCP SACK holes"); 148 149SYSCTL_VNET_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_RD, 150 &VNET_NAME(tcp_sack_globalholes), 0, 151 "Global number of TCP SACK holes currently allocated"); 152 153/* 154 * This function is called upon receipt of new valid data (while not in 155 * header prediction mode), and it updates the ordered list of sacks. 156 */ 157void 158tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end) 159{ 160 /* 161 * First reported block MUST be the most recent one. Subsequent 162 * blocks SHOULD be in the order in which they arrived at the 163 * receiver. These two conditions make the implementation fully 164 * compliant with RFC 2018. 165 */ 166 struct sackblk head_blk, saved_blks[MAX_SACK_BLKS]; 167 int num_head, num_saved, i; 168 169 INP_WLOCK_ASSERT(tp->t_inpcb); 170 171 /* Check arguments. */ 172 KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end")); 173 174 /* SACK block for the received segment. */ 175 head_blk.start = rcv_start; 176 head_blk.end = rcv_end; 177 178 /* 179 * Merge updated SACK blocks into head_blk, and save unchanged SACK 180 * blocks into saved_blks[]. num_saved will have the number of the 181 * saved SACK blocks. 182 */ 183 num_saved = 0; 184 for (i = 0; i < tp->rcv_numsacks; i++) { 185 tcp_seq start = tp->sackblks[i].start; 186 tcp_seq end = tp->sackblks[i].end; 187 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) { 188 /* 189 * Discard this SACK block. 190 */ 191 } else if (SEQ_LEQ(head_blk.start, end) && 192 SEQ_GEQ(head_blk.end, start)) { 193 /* 194 * Merge this SACK block into head_blk. This SACK 195 * block itself will be discarded. 196 */ 197 if (SEQ_GT(head_blk.start, start)) 198 head_blk.start = start; 199 if (SEQ_LT(head_blk.end, end)) 200 head_blk.end = end; 201 } else { 202 /* 203 * Save this SACK block. 204 */ 205 saved_blks[num_saved].start = start; 206 saved_blks[num_saved].end = end; 207 num_saved++; 208 } 209 } 210 211 /* 212 * Update SACK list in tp->sackblks[]. 213 */ 214 num_head = 0; 215 if (SEQ_GT(head_blk.start, tp->rcv_nxt)) { 216 /* 217 * The received data segment is an out-of-order segment. Put 218 * head_blk at the top of SACK list. 219 */ 220 tp->sackblks[0] = head_blk; 221 num_head = 1; 222 /* 223 * If the number of saved SACK blocks exceeds its limit, 224 * discard the last SACK block. 225 */ 226 if (num_saved >= MAX_SACK_BLKS) 227 num_saved--; 228 } 229 if (num_saved > 0) { 230 /* 231 * Copy the saved SACK blocks back. 232 */ 233 bcopy(saved_blks, &tp->sackblks[num_head], 234 sizeof(struct sackblk) * num_saved); 235 } 236 237 /* Save the number of SACK blocks. */ 238 tp->rcv_numsacks = num_head + num_saved; 239} 240 241/* 242 * Delete all receiver-side SACK information. 243 */ 244void 245tcp_clean_sackreport(struct tcpcb *tp) 246{ 247 int i; 248 249 INP_WLOCK_ASSERT(tp->t_inpcb); 250 tp->rcv_numsacks = 0; 251 for (i = 0; i < MAX_SACK_BLKS; i++) 252 tp->sackblks[i].start = tp->sackblks[i].end=0; 253} 254 255/* 256 * Allocate struct sackhole. 257 */ 258static struct sackhole * 259tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end) 260{ 261 struct sackhole *hole; 262 263 if (tp->snd_numholes >= V_tcp_sack_maxholes || 264 V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) { 265 TCPSTAT_INC(tcps_sack_sboverflow); 266 return NULL; 267 } 268 269 hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT); 270 if (hole == NULL) 271 return NULL; 272 273 hole->start = start; 274 hole->end = end; 275 hole->rxmit = start; 276 277 tp->snd_numholes++; 278 atomic_add_int(&V_tcp_sack_globalholes, 1); 279 280 return hole; 281} 282 283/* 284 * Free struct sackhole. 285 */ 286static void 287tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole) 288{ 289 290 uma_zfree(V_sack_hole_zone, hole); 291 292 tp->snd_numholes--; 293 atomic_subtract_int(&V_tcp_sack_globalholes, 1); 294 295 KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0")); 296 KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0")); 297} 298 299/* 300 * Insert new SACK hole into scoreboard. 301 */ 302static struct sackhole * 303tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end, 304 struct sackhole *after) 305{ 306 struct sackhole *hole; 307 308 /* Allocate a new SACK hole. */ 309 hole = tcp_sackhole_alloc(tp, start, end); 310 if (hole == NULL) 311 return NULL; 312 313 /* Insert the new SACK hole into scoreboard. */ 314 if (after != NULL) 315 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink); 316 else 317 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink); 318 319 /* Update SACK hint. */ 320 if (tp->sackhint.nexthole == NULL) 321 tp->sackhint.nexthole = hole; 322 323 return hole; 324} 325 326/* 327 * Remove SACK hole from scoreboard. 328 */ 329static void 330tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole) 331{ 332 333 /* Update SACK hint. */ 334 if (tp->sackhint.nexthole == hole) 335 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink); 336 337 /* Remove this SACK hole. */ 338 TAILQ_REMOVE(&tp->snd_holes, hole, scblink); 339 340 /* Free this SACK hole. */ 341 tcp_sackhole_free(tp, hole); 342} 343 344/* 345 * Process cumulative ACK and the TCP SACK option to update the scoreboard. 346 * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of 347 * the sequence space). 348 */ 349void 350tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack) 351{ 352 struct sackhole *cur, *temp; 353 struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp; 354 int i, j, num_sack_blks; 355 356 INP_WLOCK_ASSERT(tp->t_inpcb); 357 358 num_sack_blks = 0; 359 /* 360 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist, 361 * treat [SND.UNA, SEG.ACK) as if it is a SACK block. 362 */ 363 if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) { 364 sack_blocks[num_sack_blks].start = tp->snd_una; 365 sack_blocks[num_sack_blks++].end = th_ack; 366 } 367 /* 368 * Append received valid SACK blocks to sack_blocks[], but only if we 369 * received new blocks from the other side. 370 */ 371 if (to->to_flags & TOF_SACK) { 372 for (i = 0; i < to->to_nsacks; i++) { 373 bcopy((to->to_sacks + i * TCPOLEN_SACK), 374 &sack, sizeof(sack)); 375 sack.start = ntohl(sack.start); 376 sack.end = ntohl(sack.end); 377 if (SEQ_GT(sack.end, sack.start) && 378 SEQ_GT(sack.start, tp->snd_una) && 379 SEQ_GT(sack.start, th_ack) && 380 SEQ_LT(sack.start, tp->snd_max) && 381 SEQ_GT(sack.end, tp->snd_una) && 382 SEQ_LEQ(sack.end, tp->snd_max)) 383 sack_blocks[num_sack_blks++] = sack; 384 } 385 } 386 /* 387 * Return if SND.UNA is not advanced and no valid SACK block is 388 * received. 389 */ 390 if (num_sack_blks == 0) 391 return; 392 393 /* 394 * Sort the SACK blocks so we can update the scoreboard with just one 395 * pass. The overhead of sorting upto 4+1 elements is less than 396 * making upto 4+1 passes over the scoreboard. 397 */ 398 for (i = 0; i < num_sack_blks; i++) { 399 for (j = i + 1; j < num_sack_blks; j++) { 400 if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) { 401 sack = sack_blocks[i]; 402 sack_blocks[i] = sack_blocks[j]; 403 sack_blocks[j] = sack; 404 } 405 } 406 } 407 if (TAILQ_EMPTY(&tp->snd_holes)) 408 /* 409 * Empty scoreboard. Need to initialize snd_fack (it may be 410 * uninitialized or have a bogus value). Scoreboard holes 411 * (from the sack blocks received) are created later below 412 * (in the logic that adds holes to the tail of the 413 * scoreboard). 414 */ 415 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack); 416 /* 417 * In the while-loop below, incoming SACK blocks (sack_blocks[]) and 418 * SACK holes (snd_holes) are traversed from their tails with just 419 * one pass in order to reduce the number of compares especially when 420 * the bandwidth-delay product is large. 421 * 422 * Note: Typically, in the first RTT of SACK recovery, the highest 423 * three or four SACK blocks with the same ack number are received. 424 * In the second RTT, if retransmitted data segments are not lost, 425 * the highest three or four SACK blocks with ack number advancing 426 * are received. 427 */ 428 sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */ 429 if (SEQ_LT(tp->snd_fack, sblkp->start)) { 430 /* 431 * The highest SACK block is beyond fack. Append new SACK 432 * hole at the tail. If the second or later highest SACK 433 * blocks are also beyond the current fack, they will be 434 * inserted by way of hole splitting in the while-loop below. 435 */ 436 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL); 437 if (temp != NULL) { 438 tp->snd_fack = sblkp->end; 439 /* Go to the previous sack block. */ 440 sblkp--; 441 } else { 442 /* 443 * We failed to add a new hole based on the current 444 * sack block. Skip over all the sack blocks that 445 * fall completely to the right of snd_fack and 446 * proceed to trim the scoreboard based on the 447 * remaining sack blocks. This also trims the 448 * scoreboard for th_ack (which is sack_blocks[0]). 449 */ 450 while (sblkp >= sack_blocks && 451 SEQ_LT(tp->snd_fack, sblkp->start)) 452 sblkp--; 453 if (sblkp >= sack_blocks && 454 SEQ_LT(tp->snd_fack, sblkp->end)) 455 tp->snd_fack = sblkp->end; 456 } 457 } else if (SEQ_LT(tp->snd_fack, sblkp->end)) 458 /* fack is advanced. */ 459 tp->snd_fack = sblkp->end; 460 /* We must have at least one SACK hole in scoreboard. */ 461 KASSERT(!TAILQ_EMPTY(&tp->snd_holes), 462 ("SACK scoreboard must not be empty")); 463 cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */ 464 /* 465 * Since the incoming sack blocks are sorted, we can process them 466 * making one sweep of the scoreboard. 467 */ 468 while (sblkp >= sack_blocks && cur != NULL) { 469 if (SEQ_GEQ(sblkp->start, cur->end)) { 470 /* 471 * SACKs data beyond the current hole. Go to the 472 * previous sack block. 473 */ 474 sblkp--; 475 continue; 476 } 477 if (SEQ_LEQ(sblkp->end, cur->start)) { 478 /* 479 * SACKs data before the current hole. Go to the 480 * previous hole. 481 */ 482 cur = TAILQ_PREV(cur, sackhole_head, scblink); 483 continue; 484 } 485 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start); 486 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0, 487 ("sackhint bytes rtx >= 0")); 488 if (SEQ_LEQ(sblkp->start, cur->start)) { 489 /* Data acks at least the beginning of hole. */ 490 if (SEQ_GEQ(sblkp->end, cur->end)) { 491 /* Acks entire hole, so delete hole. */ 492 temp = cur; 493 cur = TAILQ_PREV(cur, sackhole_head, scblink); 494 tcp_sackhole_remove(tp, temp); 495 /* 496 * The sack block may ack all or part of the 497 * next hole too, so continue onto the next 498 * hole. 499 */ 500 continue; 501 } else { 502 /* Move start of hole forward. */ 503 cur->start = sblkp->end; 504 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start); 505 } 506 } else { 507 /* Data acks at least the end of hole. */ 508 if (SEQ_GEQ(sblkp->end, cur->end)) { 509 /* Move end of hole backward. */ 510 cur->end = sblkp->start; 511 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end); 512 } else { 513 /* 514 * ACKs some data in middle of a hole; need 515 * to split current hole 516 */ 517 temp = tcp_sackhole_insert(tp, sblkp->end, 518 cur->end, cur); 519 if (temp != NULL) { 520 if (SEQ_GT(cur->rxmit, temp->rxmit)) { 521 temp->rxmit = cur->rxmit; 522 tp->sackhint.sack_bytes_rexmit 523 += (temp->rxmit 524 - temp->start); 525 } 526 cur->end = sblkp->start; 527 cur->rxmit = SEQ_MIN(cur->rxmit, 528 cur->end); 529 } 530 } 531 } 532 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start); 533 /* 534 * Testing sblkp->start against cur->start tells us whether 535 * we're done with the sack block or the sack hole. 536 * Accordingly, we advance one or the other. 537 */ 538 if (SEQ_LEQ(sblkp->start, cur->start)) 539 cur = TAILQ_PREV(cur, sackhole_head, scblink); 540 else 541 sblkp--; 542 } 543} 544 545/* 546 * Free all SACK holes to clear the scoreboard. 547 */ 548void 549tcp_free_sackholes(struct tcpcb *tp) 550{ 551 struct sackhole *q; 552 553 INP_WLOCK_ASSERT(tp->t_inpcb); 554 while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL) 555 tcp_sackhole_remove(tp, q); 556 tp->sackhint.sack_bytes_rexmit = 0; 557 558 KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0")); 559 KASSERT(tp->sackhint.nexthole == NULL, 560 ("tp->sackhint.nexthole == NULL")); 561} 562 563/* 564 * Partial ack handling within a sack recovery episode. Keeping this very 565 * simple for now. When a partial ack is received, force snd_cwnd to a value 566 * that will allow the sender to transmit no more than 2 segments. If 567 * necessary, a better scheme can be adopted at a later point, but for now, 568 * the goal is to prevent the sender from bursting a large amount of data in 569 * the midst of sack recovery. 570 */ 571void 572tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th) 573{ 574 int num_segs = 1; 575 576 INP_WLOCK_ASSERT(tp->t_inpcb); 577 tcp_timer_activate(tp, TT_REXMT, 0); 578 tp->t_rtttime = 0; 579 /* Send one or 2 segments based on how much new data was acked. */ 580 if (((th->th_ack - tp->snd_una) / tp->t_maxseg) > 2) 581 num_segs = 2; 582 tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit + 583 (tp->snd_nxt - tp->sack_newdata) + num_segs * tp->t_maxseg); 584 if (tp->snd_cwnd > tp->snd_ssthresh) 585 tp->snd_cwnd = tp->snd_ssthresh; 586 tp->t_flags |= TF_ACKNOW; 587 (void) tcp_output(tp); 588} 589 590#if 0 591/* 592 * Debug version of tcp_sack_output() that walks the scoreboard. Used for 593 * now to sanity check the hint. 594 */ 595static struct sackhole * 596tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt) 597{ 598 struct sackhole *p; 599 600 INP_WLOCK_ASSERT(tp->t_inpcb); 601 *sack_bytes_rexmt = 0; 602 TAILQ_FOREACH(p, &tp->snd_holes, scblink) { 603 if (SEQ_LT(p->rxmit, p->end)) { 604 if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */ 605 continue; 606 } 607 *sack_bytes_rexmt += (p->rxmit - p->start); 608 break; 609 } 610 *sack_bytes_rexmt += (p->rxmit - p->start); 611 } 612 return (p); 613} 614#endif 615 616/* 617 * Returns the next hole to retransmit and the number of retransmitted bytes 618 * from the scoreboard. We store both the next hole and the number of 619 * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK 620 * reception). This avoids scoreboard traversals completely. 621 * 622 * The loop here will traverse *at most* one link. Here's the argument. For 623 * the loop to traverse more than 1 link before finding the next hole to 624 * retransmit, we would need to have at least 1 node following the current 625 * hint with (rxmit == end). But, for all holes following the current hint, 626 * (start == rxmit), since we have not yet retransmitted from them. 627 * Therefore, in order to traverse more 1 link in the loop below, we need to 628 * have at least one node following the current hint with (start == rxmit == 629 * end). But that can't happen, (start == end) means that all the data in 630 * that hole has been sacked, in which case, the hole would have been removed 631 * from the scoreboard. 632 */ 633struct sackhole * 634tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt) 635{ 636 struct sackhole *hole = NULL; 637 638 INP_WLOCK_ASSERT(tp->t_inpcb); 639 *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit; 640 hole = tp->sackhint.nexthole; 641 if (hole == NULL || SEQ_LT(hole->rxmit, hole->end)) 642 goto out; 643 while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) { 644 if (SEQ_LT(hole->rxmit, hole->end)) { 645 tp->sackhint.nexthole = hole; 646 break; 647 } 648 } 649out: 650 return (hole); 651} 652 653/* 654 * After a timeout, the SACK list may be rebuilt. This SACK information 655 * should be used to avoid retransmitting SACKed data. This function 656 * traverses the SACK list to see if snd_nxt should be moved forward. 657 */ 658void 659tcp_sack_adjust(struct tcpcb *tp) 660{ 661 struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes); 662 663 INP_WLOCK_ASSERT(tp->t_inpcb); 664 if (cur == NULL) 665 return; /* No holes */ 666 if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack)) 667 return; /* We're already beyond any SACKed blocks */ 668 /*- 669 * Two cases for which we want to advance snd_nxt: 670 * i) snd_nxt lies between end of one hole and beginning of another 671 * ii) snd_nxt lies between end of last hole and snd_fack 672 */ 673 while ((p = TAILQ_NEXT(cur, scblink)) != NULL) { 674 if (SEQ_LT(tp->snd_nxt, cur->end)) 675 return; 676 if (SEQ_GEQ(tp->snd_nxt, p->start)) 677 cur = p; 678 else { 679 tp->snd_nxt = p->start; 680 return; 681 } 682 } 683 if (SEQ_LT(tp->snd_nxt, cur->end)) 684 return; 685 tp->snd_nxt = tp->snd_fack; 686} 687