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("$FreeBSD$"); 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> 99 100 #include <netinet/in.h> 101 #include <netinet/in_systm.h> 102 #include <netinet/ip.h> 103 #include <netinet/in_var.h> 104 #include <netinet/in_pcb.h> 105 #include <netinet/ip_var.h> 106 #include <netinet/ip6.h> 107 #include <netinet/icmp6.h> 108 #include <netinet6/nd6.h> 109 #include <netinet6/ip6_var.h> 110 #include <netinet6/in6_pcb.h> 111 #include <netinet/tcp.h> 112 #include <netinet/tcp_fsm.h> 113 #include <netinet/tcp_seq.h> 114 #include <netinet/tcp_timer.h> 115 #include <netinet/tcp_var.h> 116 #include <netinet6/tcp6_var.h> 117 #include <netinet/tcpip.h> 118 #ifdef TCPDEBUG 119 #include <netinet/tcp_debug.h> 120 #endif /* TCPDEBUG */ 121 122 #include <machine/in_cksum.h> 123 124 extern struct uma_zone *sack_hole_zone; 125 126 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW, 0, "TCP SACK"); 127 int tcp_do_sack = 1; 128 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_RW, 129 &tcp_do_sack, 0, "Enable/Disable TCP SACK support"); 130 TUNABLE_INT("net.inet.tcp.sack.enable", &tcp_do_sack); 131 132 static int tcp_sack_maxholes = 128; 133 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_RW, 134 &tcp_sack_maxholes, 0, 135 "Maximum number of TCP SACK holes allowed per connection"); 136 137 static int tcp_sack_globalmaxholes = 65536; 138 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_RW, 139 &tcp_sack_globalmaxholes, 0, 140 "Global maximum number of TCP SACK holes"); 141 142 static int tcp_sack_globalholes = 0; 143 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_RD, 144 &tcp_sack_globalholes, 0, 145 "Global number of TCP SACK holes currently allocated"); 146 147 /* 148 * This function is called upon receipt of new valid data (while not in 149 * header prediction mode), and it updates the ordered list of sacks. 150 */ 151 void 152 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end) 153 { 154 /* 155 * First reported block MUST be the most recent one. Subsequent 156 * blocks SHOULD be in the order in which they arrived at the 157 * receiver. These two conditions make the implementation fully 158 * compliant with RFC 2018. 159 */ 160 struct sackblk head_blk, saved_blks[MAX_SACK_BLKS]; 161 int num_head, num_saved, i; 162 163 INP_LOCK_ASSERT(tp->t_inpcb); 164 165 /* Check arguments. */ 166 KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end")); 167 168 /* SACK block for the received segment. */ 169 head_blk.start = rcv_start; 170 head_blk.end = rcv_end; 171 172 /* 173 * Merge updated SACK blocks into head_blk, and save unchanged SACK 174 * blocks into saved_blks[]. num_saved will have the number of the 175 * saved SACK blocks. 176 */ 177 num_saved = 0; 178 for (i = 0; i < tp->rcv_numsacks; i++) { 179 tcp_seq start = tp->sackblks[i].start; 180 tcp_seq end = tp->sackblks[i].end; 181 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) { 182 /* 183 * Discard this SACK block. 184 */ 185 } else if (SEQ_LEQ(head_blk.start, end) && 186 SEQ_GEQ(head_blk.end, start)) { 187 /* 188 * Merge this SACK block into head_blk. This SACK 189 * block itself will be discarded. 190 */ 191 if (SEQ_GT(head_blk.start, start)) 192 head_blk.start = start; 193 if (SEQ_LT(head_blk.end, end)) 194 head_blk.end = end; 195 } else { 196 /* 197 * Save this SACK block. 198 */ 199 saved_blks[num_saved].start = start; 200 saved_blks[num_saved].end = end; 201 num_saved++; 202 } 203 } 204 205 /* 206 * Update SACK list in tp->sackblks[]. 207 */ 208 num_head = 0; 209 if (SEQ_GT(head_blk.start, tp->rcv_nxt)) { 210 /* 211 * The received data segment is an out-of-order segment. Put 212 * head_blk at the top of SACK list. 213 */ 214 tp->sackblks[0] = head_blk; 215 num_head = 1; 216 /* 217 * If the number of saved SACK blocks exceeds its limit, 218 * discard the last SACK block. 219 */ 220 if (num_saved >= MAX_SACK_BLKS) 221 num_saved--; 222 } 223 if (num_saved > 0) { 224 /* 225 * Copy the saved SACK blocks back. 226 */ 227 bcopy(saved_blks, &tp->sackblks[num_head], 228 sizeof(struct sackblk) * num_saved); 229 } 230 231 /* Save the number of SACK blocks. */ 232 tp->rcv_numsacks = num_head + num_saved; 233 } 234 235 /* 236 * Delete all receiver-side SACK information. 237 */ 238 void 239 tcp_clean_sackreport(struct tcpcb *tp) 240 { 241 int i; 242 243 INP_LOCK_ASSERT(tp->t_inpcb); 244 tp->rcv_numsacks = 0; 245 for (i = 0; i < MAX_SACK_BLKS; i++) 246 tp->sackblks[i].start = tp->sackblks[i].end=0; 247 } 248 249 /* 250 * Allocate struct sackhole. 251 */ 252 static struct sackhole * 253 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end) 254 { 255 struct sackhole *hole; 256 257 if (tp->snd_numholes >= tcp_sack_maxholes || 258 tcp_sack_globalholes >= tcp_sack_globalmaxholes) { 259 tcpstat.tcps_sack_sboverflow++; 260 return NULL; 261 } 262 263 hole = (struct sackhole *)uma_zalloc(sack_hole_zone, M_NOWAIT); 264 if (hole == NULL) 265 return NULL; 266 267 hole->start = start; 268 hole->end = end; 269 hole->rxmit = start; 270 271 tp->snd_numholes++; 272 tcp_sack_globalholes++; 273 274 return hole; 275 } 276 277 /* 278 * Free struct sackhole. 279 */ 280 static void 281 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole) 282 { 283 284 uma_zfree(sack_hole_zone, hole); 285 286 tp->snd_numholes--; 287 tcp_sack_globalholes--; 288 289 KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0")); 290 KASSERT(tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0")); 291 } 292 293 /* 294 * Insert new SACK hole into scoreboard. 295 */ 296 static struct sackhole * 297 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end, 298 struct sackhole *after) 299 { 300 struct sackhole *hole; 301 302 /* Allocate a new SACK hole. */ 303 hole = tcp_sackhole_alloc(tp, start, end); 304 if (hole == NULL) 305 return NULL; 306 307 /* Insert the new SACK hole into scoreboard. */ 308 if (after != NULL) 309 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink); 310 else 311 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink); 312 313 /* Update SACK hint. */ 314 if (tp->sackhint.nexthole == NULL) 315 tp->sackhint.nexthole = hole; 316 317 return hole; 318 } 319 320 /* 321 * Remove SACK hole from scoreboard. 322 */ 323 static void 324 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole) 325 { 326 327 /* Update SACK hint. */ 328 if (tp->sackhint.nexthole == hole) 329 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink); 330 331 /* Remove this SACK hole. */ 332 TAILQ_REMOVE(&tp->snd_holes, hole, scblink); 333 334 /* Free this SACK hole. */ 335 tcp_sackhole_free(tp, hole); 336 } 337 338 /* 339 * Process cumulative ACK and the TCP SACK option to update the scoreboard. 340 * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of 341 * the sequence space). 342 */ 343 void 344 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack) 345 { 346 struct sackhole *cur, *temp; 347 struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp; 348 int i, j, num_sack_blks; 349 350 INP_LOCK_ASSERT(tp->t_inpcb); 351 352 num_sack_blks = 0; 353 /* 354 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist, 355 * treat [SND.UNA, SEG.ACK) as if it is a SACK block. 356 */ 357 if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) { 358 sack_blocks[num_sack_blks].start = tp->snd_una; 359 sack_blocks[num_sack_blks++].end = th_ack; 360 } 361 /* 362 * Append received valid SACK blocks to sack_blocks[], but only if we 363 * received new blocks from the other side. 364 */ 365 if (to->to_flags & TOF_SACK) { 366 for (i = 0; i < to->to_nsacks; i++) { 367 bcopy((to->to_sacks + i * TCPOLEN_SACK), 368 &sack, sizeof(sack)); 369 sack.start = ntohl(sack.start); 370 sack.end = ntohl(sack.end); 371 if (SEQ_GT(sack.end, sack.start) && 372 SEQ_GT(sack.start, tp->snd_una) && 373 SEQ_GT(sack.start, th_ack) && 374 SEQ_LT(sack.start, tp->snd_max) && 375 SEQ_GT(sack.end, tp->snd_una) && 376 SEQ_LEQ(sack.end, tp->snd_max)) 377 sack_blocks[num_sack_blks++] = sack; 378 } 379 } 380 /* 381 * Return if SND.UNA is not advanced and no valid SACK block is 382 * received. 383 */ 384 if (num_sack_blks == 0) 385 return; 386 387 /* 388 * Sort the SACK blocks so we can update the scoreboard with just one 389 * pass. The overhead of sorting upto 4+1 elements is less than 390 * making upto 4+1 passes over the scoreboard. 391 */ 392 for (i = 0; i < num_sack_blks; i++) { 393 for (j = i + 1; j < num_sack_blks; j++) { 394 if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) { 395 sack = sack_blocks[i]; 396 sack_blocks[i] = sack_blocks[j]; 397 sack_blocks[j] = sack; 398 } 399 } 400 } 401 if (TAILQ_EMPTY(&tp->snd_holes)) 402 /* 403 * Empty scoreboard. Need to initialize snd_fack (it may be 404 * uninitialized or have a bogus value). Scoreboard holes 405 * (from the sack blocks received) are created later below 406 * (in the logic that adds holes to the tail of the 407 * scoreboard). 408 */ 409 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack); 410 /* 411 * In the while-loop below, incoming SACK blocks (sack_blocks[]) and 412 * SACK holes (snd_holes) are traversed from their tails with just 413 * one pass in order to reduce the number of compares especially when 414 * the bandwidth-delay product is large. 415 * 416 * Note: Typically, in the first RTT of SACK recovery, the highest 417 * three or four SACK blocks with the same ack number are received. 418 * In the second RTT, if retransmitted data segments are not lost, 419 * the highest three or four SACK blocks with ack number advancing 420 * are received. 421 */ 422 sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */ 423 if (SEQ_LT(tp->snd_fack, sblkp->start)) { 424 /* 425 * The highest SACK block is beyond fack. Append new SACK 426 * hole at the tail. If the second or later highest SACK 427 * blocks are also beyond the current fack, they will be 428 * inserted by way of hole splitting in the while-loop below. 429 */ 430 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL); 431 if (temp != NULL) { 432 tp->snd_fack = sblkp->end; 433 /* Go to the previous sack block. */ 434 sblkp--; 435 } else { 436 /* 437 * We failed to add a new hole based on the current 438 * sack block. Skip over all the sack blocks that 439 * fall completely to the right of snd_fack and 440 * proceed to trim the scoreboard based on the 441 * remaining sack blocks. This also trims the 442 * scoreboard for th_ack (which is sack_blocks[0]). 443 */ 444 while (sblkp >= sack_blocks && 445 SEQ_LT(tp->snd_fack, sblkp->start)) 446 sblkp--; 447 if (sblkp >= sack_blocks && 448 SEQ_LT(tp->snd_fack, sblkp->end)) 449 tp->snd_fack = sblkp->end; 450 } 451 } else if (SEQ_LT(tp->snd_fack, sblkp->end)) 452 /* fack is advanced. */ 453 tp->snd_fack = sblkp->end; 454 /* We must have at least one SACK hole in scoreboard. */ 455 KASSERT(!TAILQ_EMPTY(&tp->snd_holes), 456 ("SACK scoreboard must not be empty")); 457 cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */ 458 /* 459 * Since the incoming sack blocks are sorted, we can process them 460 * making one sweep of the scoreboard. 461 */ 462 while (sblkp >= sack_blocks && cur != NULL) { 463 if (SEQ_GEQ(sblkp->start, cur->end)) { 464 /* 465 * SACKs data beyond the current hole. Go to the 466 * previous sack block. 467 */ 468 sblkp--; 469 continue; 470 } 471 if (SEQ_LEQ(sblkp->end, cur->start)) { 472 /* 473 * SACKs data before the current hole. Go to the 474 * previous hole. 475 */ 476 cur = TAILQ_PREV(cur, sackhole_head, scblink); 477 continue; 478 } 479 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start); 480 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0, 481 ("sackhint bytes rtx >= 0")); 482 if (SEQ_LEQ(sblkp->start, cur->start)) { 483 /* Data acks at least the beginning of hole. */ 484 if (SEQ_GEQ(sblkp->end, cur->end)) { 485 /* Acks entire hole, so delete hole. */ 486 temp = cur; 487 cur = TAILQ_PREV(cur, sackhole_head, scblink); 488 tcp_sackhole_remove(tp, temp); 489 /* 490 * The sack block may ack all or part of the 491 * next hole too, so continue onto the next 492 * hole. 493 */ 494 continue; 495 } else { 496 /* Move start of hole forward. */ 497 cur->start = sblkp->end; 498 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start); 499 } 500 } else { 501 /* Data acks at least the end of hole. */ 502 if (SEQ_GEQ(sblkp->end, cur->end)) { 503 /* Move end of hole backward. */ 504 cur->end = sblkp->start; 505 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end); 506 } else { 507 /* 508 * ACKs some data in middle of a hole; need 509 * to split current hole 510 */ 511 temp = tcp_sackhole_insert(tp, sblkp->end, 512 cur->end, cur); 513 if (temp != NULL) { 514 if (SEQ_GT(cur->rxmit, temp->rxmit)) { 515 temp->rxmit = cur->rxmit; 516 tp->sackhint.sack_bytes_rexmit 517 += (temp->rxmit 518 - temp->start); 519 } 520 cur->end = sblkp->start; 521 cur->rxmit = SEQ_MIN(cur->rxmit, 522 cur->end); 523 } 524 } 525 } 526 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start); 527 /* 528 * Testing sblkp->start against cur->start tells us whether 529 * we're done with the sack block or the sack hole. 530 * Accordingly, we advance one or the other. 531 */ 532 if (SEQ_LEQ(sblkp->start, cur->start)) 533 cur = TAILQ_PREV(cur, sackhole_head, scblink); 534 else 535 sblkp--; 536 } 537 } 538 539 /* 540 * Free all SACK holes to clear the scoreboard. 541 */ 542 void 543 tcp_free_sackholes(struct tcpcb *tp) 544 { 545 struct sackhole *q; 546 547 INP_LOCK_ASSERT(tp->t_inpcb); 548 while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL) 549 tcp_sackhole_remove(tp, q); 550 tp->sackhint.sack_bytes_rexmit = 0; 551 552 KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0")); 553 KASSERT(tp->sackhint.nexthole == NULL, 554 ("tp->sackhint.nexthole == NULL")); 555 } 556 557 /* 558 * Partial ack handling within a sack recovery episode. Keeping this very 559 * simple for now. When a partial ack is received, force snd_cwnd to a value 560 * that will allow the sender to transmit no more than 2 segments. If 561 * necessary, a better scheme can be adopted at a later point, but for now, 562 * the goal is to prevent the sender from bursting a large amount of data in 563 * the midst of sack recovery. 564 */ 565 void 566 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th) 567 { 568 int num_segs = 1; 569 570 INP_LOCK_ASSERT(tp->t_inpcb); 571 tcp_timer_activate(tp, TT_REXMT, 0); 572 tp->t_rtttime = 0; 573 /* Send one or 2 segments based on how much new data was acked. */ 574 if (((th->th_ack - tp->snd_una) / tp->t_maxseg) > 2) 575 num_segs = 2; 576 tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit + 577 (tp->snd_nxt - tp->sack_newdata) + num_segs * tp->t_maxseg); 578 if (tp->snd_cwnd > tp->snd_ssthresh) 579 tp->snd_cwnd = tp->snd_ssthresh; 580 tp->t_flags |= TF_ACKNOW; 581 (void) tcp_output(tp); 582 } 583 584 #if 0 585 /* 586 * Debug version of tcp_sack_output() that walks the scoreboard. Used for 587 * now to sanity check the hint. 588 */ 589 static struct sackhole * 590 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt) 591 { 592 struct sackhole *p; 593 594 INP_LOCK_ASSERT(tp->t_inpcb); 595 *sack_bytes_rexmt = 0; 596 TAILQ_FOREACH(p, &tp->snd_holes, scblink) { 597 if (SEQ_LT(p->rxmit, p->end)) { 598 if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */ 599 continue; 600 } 601 *sack_bytes_rexmt += (p->rxmit - p->start); 602 break; 603 } 604 *sack_bytes_rexmt += (p->rxmit - p->start); 605 } 606 return (p); 607 } 608 #endif 609 610 /* 611 * Returns the next hole to retransmit and the number of retransmitted bytes 612 * from the scoreboard. We store both the next hole and the number of 613 * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK 614 * reception). This avoids scoreboard traversals completely. 615 * 616 * The loop here will traverse *at most* one link. Here's the argument. For 617 * the loop to traverse more than 1 link before finding the next hole to 618 * retransmit, we would need to have at least 1 node following the current 619 * hint with (rxmit == end). But, for all holes following the current hint, 620 * (start == rxmit), since we have not yet retransmitted from them. 621 * Therefore, in order to traverse more 1 link in the loop below, we need to 622 * have at least one node following the current hint with (start == rxmit == 623 * end). But that can't happen, (start == end) means that all the data in 624 * that hole has been sacked, in which case, the hole would have been removed 625 * from the scoreboard. 626 */ 627 struct sackhole * 628 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt) 629 { 630 struct sackhole *hole = NULL; 631 632 INP_LOCK_ASSERT(tp->t_inpcb); 633 *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit; 634 hole = tp->sackhint.nexthole; 635 if (hole == NULL || SEQ_LT(hole->rxmit, hole->end)) 636 goto out; 637 while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) { 638 if (SEQ_LT(hole->rxmit, hole->end)) { 639 tp->sackhint.nexthole = hole; 640 break; 641 } 642 } 643 out: 644 return (hole); 645 } 646 647 /* 648 * After a timeout, the SACK list may be rebuilt. This SACK information 649 * should be used to avoid retransmitting SACKed data. This function 650 * traverses the SACK list to see if snd_nxt should be moved forward. 651 */ 652 void 653 tcp_sack_adjust(struct tcpcb *tp) 654 { 655 struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes); 656 657 INP_LOCK_ASSERT(tp->t_inpcb); 658 if (cur == NULL) 659 return; /* No holes */ 660 if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack)) 661 return; /* We're already beyond any SACKed blocks */ 662 /*- 663 * Two cases for which we want to advance snd_nxt: 664 * i) snd_nxt lies between end of one hole and beginning of another 665 * ii) snd_nxt lies between end of last hole and snd_fack 666 */ 667 while ((p = TAILQ_NEXT(cur, scblink)) != NULL) { 668 if (SEQ_LT(tp->snd_nxt, cur->end)) 669 return; 670 if (SEQ_GEQ(tp->snd_nxt, p->start)) 671 cur = p; 672 else { 673 tp->snd_nxt = p->start; 674 return; 675 } 676 } 677 if (SEQ_LT(tp->snd_nxt, cur->end)) 678 return; 679 tp->snd_nxt = tp->snd_fack; 680 return; 681 } 682