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/if_var.h> 99 #include <net/route.h> 100 #include <net/vnet.h> 101 102 #include <netinet/in.h> 103 #include <netinet/in_systm.h> 104 #include <netinet/ip.h> 105 #include <netinet/in_var.h> 106 #include <netinet/in_pcb.h> 107 #include <netinet/ip_var.h> 108 #include <netinet/ip6.h> 109 #include <netinet/icmp6.h> 110 #include <netinet6/nd6.h> 111 #include <netinet6/ip6_var.h> 112 #include <netinet6/in6_pcb.h> 113 #include <netinet/tcp.h> 114 #include <netinet/tcp_fsm.h> 115 #include <netinet/tcp_seq.h> 116 #include <netinet/tcp_timer.h> 117 #include <netinet/tcp_var.h> 118 #include <netinet6/tcp6_var.h> 119 #include <netinet/tcpip.h> 120 #ifdef TCPDEBUG 121 #include <netinet/tcp_debug.h> 122 #endif /* TCPDEBUG */ 123 124 #include <machine/in_cksum.h> 125 126 VNET_DECLARE(struct uma_zone *, sack_hole_zone); 127 #define V_sack_hole_zone VNET(sack_hole_zone) 128 129 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW, 0, "TCP SACK"); 130 VNET_DEFINE(int, tcp_do_sack) = 1; 131 #define V_tcp_do_sack VNET(tcp_do_sack) 132 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW, 133 &VNET_NAME(tcp_do_sack), 0, "Enable/Disable TCP SACK support"); 134 135 VNET_DEFINE(int, tcp_sack_maxholes) = 128; 136 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW, 137 &VNET_NAME(tcp_sack_maxholes), 0, 138 "Maximum number of TCP SACK holes allowed per connection"); 139 140 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536; 141 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW, 142 &VNET_NAME(tcp_sack_globalmaxholes), 0, 143 "Global maximum number of TCP SACK holes"); 144 145 VNET_DEFINE(int, tcp_sack_globalholes) = 0; 146 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD, 147 &VNET_NAME(tcp_sack_globalholes), 0, 148 "Global number of TCP SACK holes currently allocated"); 149 150 /* 151 * This function is called upon receipt of new valid data (while not in 152 * header prediction mode), and it updates the ordered list of sacks. 153 */ 154 void 155 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end) 156 { 157 /* 158 * First reported block MUST be the most recent one. Subsequent 159 * blocks SHOULD be in the order in which they arrived at the 160 * receiver. These two conditions make the implementation fully 161 * compliant with RFC 2018. 162 */ 163 struct sackblk head_blk, saved_blks[MAX_SACK_BLKS]; 164 int num_head, num_saved, i; 165 166 INP_WLOCK_ASSERT(tp->t_inpcb); 167 168 /* Check arguments. */ 169 KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end")); 170 171 /* SACK block for the received segment. */ 172 head_blk.start = rcv_start; 173 head_blk.end = rcv_end; 174 175 /* 176 * Merge updated SACK blocks into head_blk, and save unchanged SACK 177 * blocks into saved_blks[]. num_saved will have the number of the 178 * saved SACK blocks. 179 */ 180 num_saved = 0; 181 for (i = 0; i < tp->rcv_numsacks; i++) { 182 tcp_seq start = tp->sackblks[i].start; 183 tcp_seq end = tp->sackblks[i].end; 184 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) { 185 /* 186 * Discard this SACK block. 187 */ 188 } else if (SEQ_LEQ(head_blk.start, end) && 189 SEQ_GEQ(head_blk.end, start)) { 190 /* 191 * Merge this SACK block into head_blk. This SACK 192 * block itself will be discarded. 193 */ 194 if (SEQ_GT(head_blk.start, start)) 195 head_blk.start = start; 196 if (SEQ_LT(head_blk.end, end)) 197 head_blk.end = end; 198 } else { 199 /* 200 * Save this SACK block. 201 */ 202 saved_blks[num_saved].start = start; 203 saved_blks[num_saved].end = end; 204 num_saved++; 205 } 206 } 207 208 /* 209 * Update SACK list in tp->sackblks[]. 210 */ 211 num_head = 0; 212 if (SEQ_GT(head_blk.start, tp->rcv_nxt)) { 213 /* 214 * The received data segment is an out-of-order segment. Put 215 * head_blk at the top of SACK list. 216 */ 217 tp->sackblks[0] = head_blk; 218 num_head = 1; 219 /* 220 * If the number of saved SACK blocks exceeds its limit, 221 * discard the last SACK block. 222 */ 223 if (num_saved >= MAX_SACK_BLKS) 224 num_saved--; 225 } 226 if (num_saved > 0) { 227 /* 228 * Copy the saved SACK blocks back. 229 */ 230 bcopy(saved_blks, &tp->sackblks[num_head], 231 sizeof(struct sackblk) * num_saved); 232 } 233 234 /* Save the number of SACK blocks. */ 235 tp->rcv_numsacks = num_head + num_saved; 236 } 237 238 /* 239 * Delete all receiver-side SACK information. 240 */ 241 void 242 tcp_clean_sackreport(struct tcpcb *tp) 243 { 244 int i; 245 246 INP_WLOCK_ASSERT(tp->t_inpcb); 247 tp->rcv_numsacks = 0; 248 for (i = 0; i < MAX_SACK_BLKS; i++) 249 tp->sackblks[i].start = tp->sackblks[i].end=0; 250 } 251 252 /* 253 * Allocate struct sackhole. 254 */ 255 static struct sackhole * 256 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end) 257 { 258 struct sackhole *hole; 259 260 if (tp->snd_numholes >= V_tcp_sack_maxholes || 261 V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) { 262 TCPSTAT_INC(tcps_sack_sboverflow); 263 return NULL; 264 } 265 266 hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT); 267 if (hole == NULL) 268 return NULL; 269 270 hole->start = start; 271 hole->end = end; 272 hole->rxmit = start; 273 274 tp->snd_numholes++; 275 atomic_add_int(&V_tcp_sack_globalholes, 1); 276 277 return hole; 278 } 279 280 /* 281 * Free struct sackhole. 282 */ 283 static void 284 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole) 285 { 286 287 uma_zfree(V_sack_hole_zone, hole); 288 289 tp->snd_numholes--; 290 atomic_subtract_int(&V_tcp_sack_globalholes, 1); 291 292 KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0")); 293 KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0")); 294 } 295 296 /* 297 * Insert new SACK hole into scoreboard. 298 */ 299 static struct sackhole * 300 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end, 301 struct sackhole *after) 302 { 303 struct sackhole *hole; 304 305 /* Allocate a new SACK hole. */ 306 hole = tcp_sackhole_alloc(tp, start, end); 307 if (hole == NULL) 308 return NULL; 309 310 /* Insert the new SACK hole into scoreboard. */ 311 if (after != NULL) 312 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink); 313 else 314 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink); 315 316 /* Update SACK hint. */ 317 if (tp->sackhint.nexthole == NULL) 318 tp->sackhint.nexthole = hole; 319 320 return hole; 321 } 322 323 /* 324 * Remove SACK hole from scoreboard. 325 */ 326 static void 327 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole) 328 { 329 330 /* Update SACK hint. */ 331 if (tp->sackhint.nexthole == hole) 332 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink); 333 334 /* Remove this SACK hole. */ 335 TAILQ_REMOVE(&tp->snd_holes, hole, scblink); 336 337 /* Free this SACK hole. */ 338 tcp_sackhole_free(tp, hole); 339 } 340 341 /* 342 * Process cumulative ACK and the TCP SACK option to update the scoreboard. 343 * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of 344 * the sequence space). 345 * Returns 1 if incoming ACK has previously unknown SACK information, 346 * 0 otherwise. Note: We treat (snd_una, th_ack) as a sack block so any changes 347 * to that (i.e. left edge moving) would also be considered a change in SACK 348 * information which is slightly different than rfc6675. 349 */ 350 int 351 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack) 352 { 353 struct sackhole *cur, *temp; 354 struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp; 355 int i, j, num_sack_blks, sack_changed; 356 357 INP_WLOCK_ASSERT(tp->t_inpcb); 358 359 num_sack_blks = 0; 360 sack_changed = 0; 361 /* 362 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist, 363 * treat [SND.UNA, SEG.ACK) as if it is a SACK block. 364 */ 365 if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) { 366 sack_blocks[num_sack_blks].start = tp->snd_una; 367 sack_blocks[num_sack_blks++].end = th_ack; 368 } 369 /* 370 * Append received valid SACK blocks to sack_blocks[], but only if we 371 * received new blocks from the other side. 372 */ 373 if (to->to_flags & TOF_SACK) { 374 tp->sackhint.sacked_bytes = 0; /* reset */ 375 for (i = 0; i < to->to_nsacks; i++) { 376 bcopy((to->to_sacks + i * TCPOLEN_SACK), 377 &sack, sizeof(sack)); 378 sack.start = ntohl(sack.start); 379 sack.end = ntohl(sack.end); 380 if (SEQ_GT(sack.end, sack.start) && 381 SEQ_GT(sack.start, tp->snd_una) && 382 SEQ_GT(sack.start, th_ack) && 383 SEQ_LT(sack.start, tp->snd_max) && 384 SEQ_GT(sack.end, tp->snd_una) && 385 SEQ_LEQ(sack.end, tp->snd_max)) { 386 sack_blocks[num_sack_blks++] = sack; 387 tp->sackhint.sacked_bytes += 388 (sack.end-sack.start); 389 } 390 } 391 } 392 /* 393 * Return if SND.UNA is not advanced and no valid SACK block is 394 * received. 395 */ 396 if (num_sack_blks == 0) 397 return (sack_changed); 398 399 /* 400 * Sort the SACK blocks so we can update the scoreboard with just one 401 * pass. The overhead of sorting up to 4+1 elements is less than 402 * making up to 4+1 passes over the scoreboard. 403 */ 404 for (i = 0; i < num_sack_blks; i++) { 405 for (j = i + 1; j < num_sack_blks; j++) { 406 if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) { 407 sack = sack_blocks[i]; 408 sack_blocks[i] = sack_blocks[j]; 409 sack_blocks[j] = sack; 410 } 411 } 412 } 413 if (TAILQ_EMPTY(&tp->snd_holes)) 414 /* 415 * Empty scoreboard. Need to initialize snd_fack (it may be 416 * uninitialized or have a bogus value). Scoreboard holes 417 * (from the sack blocks received) are created later below 418 * (in the logic that adds holes to the tail of the 419 * scoreboard). 420 */ 421 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack); 422 /* 423 * In the while-loop below, incoming SACK blocks (sack_blocks[]) and 424 * SACK holes (snd_holes) are traversed from their tails with just 425 * one pass in order to reduce the number of compares especially when 426 * the bandwidth-delay product is large. 427 * 428 * Note: Typically, in the first RTT of SACK recovery, the highest 429 * three or four SACK blocks with the same ack number are received. 430 * In the second RTT, if retransmitted data segments are not lost, 431 * the highest three or four SACK blocks with ack number advancing 432 * are received. 433 */ 434 sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */ 435 tp->sackhint.last_sack_ack = sblkp->end; 436 if (SEQ_LT(tp->snd_fack, sblkp->start)) { 437 /* 438 * The highest SACK block is beyond fack. Append new SACK 439 * hole at the tail. If the second or later highest SACK 440 * blocks are also beyond the current fack, they will be 441 * inserted by way of hole splitting in the while-loop below. 442 */ 443 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL); 444 if (temp != NULL) { 445 tp->snd_fack = sblkp->end; 446 /* Go to the previous sack block. */ 447 sblkp--; 448 sack_changed = 1; 449 } else { 450 /* 451 * We failed to add a new hole based on the current 452 * sack block. Skip over all the sack blocks that 453 * fall completely to the right of snd_fack and 454 * proceed to trim the scoreboard based on the 455 * remaining sack blocks. This also trims the 456 * scoreboard for th_ack (which is sack_blocks[0]). 457 */ 458 while (sblkp >= sack_blocks && 459 SEQ_LT(tp->snd_fack, sblkp->start)) 460 sblkp--; 461 if (sblkp >= sack_blocks && 462 SEQ_LT(tp->snd_fack, sblkp->end)) 463 tp->snd_fack = sblkp->end; 464 } 465 } else if (SEQ_LT(tp->snd_fack, sblkp->end)) { 466 /* fack is advanced. */ 467 tp->snd_fack = sblkp->end; 468 sack_changed = 1; 469 } 470 cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */ 471 /* 472 * Since the incoming sack blocks are sorted, we can process them 473 * making one sweep of the scoreboard. 474 */ 475 while (sblkp >= sack_blocks && cur != NULL) { 476 if (SEQ_GEQ(sblkp->start, cur->end)) { 477 /* 478 * SACKs data beyond the current hole. Go to the 479 * previous sack block. 480 */ 481 sblkp--; 482 continue; 483 } 484 if (SEQ_LEQ(sblkp->end, cur->start)) { 485 /* 486 * SACKs data before the current hole. Go to the 487 * previous hole. 488 */ 489 cur = TAILQ_PREV(cur, sackhole_head, scblink); 490 continue; 491 } 492 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start); 493 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0, 494 ("sackhint bytes rtx >= 0")); 495 sack_changed = 1; 496 if (SEQ_LEQ(sblkp->start, cur->start)) { 497 /* Data acks at least the beginning of hole. */ 498 if (SEQ_GEQ(sblkp->end, cur->end)) { 499 /* Acks entire hole, so delete hole. */ 500 temp = cur; 501 cur = TAILQ_PREV(cur, sackhole_head, scblink); 502 tcp_sackhole_remove(tp, temp); 503 /* 504 * The sack block may ack all or part of the 505 * next hole too, so continue onto the next 506 * hole. 507 */ 508 continue; 509 } else { 510 /* Move start of hole forward. */ 511 cur->start = sblkp->end; 512 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start); 513 } 514 } else { 515 /* Data acks at least the end of hole. */ 516 if (SEQ_GEQ(sblkp->end, cur->end)) { 517 /* Move end of hole backward. */ 518 cur->end = sblkp->start; 519 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end); 520 } else { 521 /* 522 * ACKs some data in middle of a hole; need 523 * to split current hole 524 */ 525 temp = tcp_sackhole_insert(tp, sblkp->end, 526 cur->end, cur); 527 if (temp != NULL) { 528 if (SEQ_GT(cur->rxmit, temp->rxmit)) { 529 temp->rxmit = cur->rxmit; 530 tp->sackhint.sack_bytes_rexmit 531 += (temp->rxmit 532 - temp->start); 533 } 534 cur->end = sblkp->start; 535 cur->rxmit = SEQ_MIN(cur->rxmit, 536 cur->end); 537 } 538 } 539 } 540 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start); 541 /* 542 * Testing sblkp->start against cur->start tells us whether 543 * we're done with the sack block or the sack hole. 544 * Accordingly, we advance one or the other. 545 */ 546 if (SEQ_LEQ(sblkp->start, cur->start)) 547 cur = TAILQ_PREV(cur, sackhole_head, scblink); 548 else 549 sblkp--; 550 } 551 return (sack_changed); 552 } 553 554 /* 555 * Free all SACK holes to clear the scoreboard. 556 */ 557 void 558 tcp_free_sackholes(struct tcpcb *tp) 559 { 560 struct sackhole *q; 561 562 INP_WLOCK_ASSERT(tp->t_inpcb); 563 while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL) 564 tcp_sackhole_remove(tp, q); 565 tp->sackhint.sack_bytes_rexmit = 0; 566 567 KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0")); 568 KASSERT(tp->sackhint.nexthole == NULL, 569 ("tp->sackhint.nexthole == NULL")); 570 } 571 572 /* 573 * Partial ack handling within a sack recovery episode. Keeping this very 574 * simple for now. When a partial ack is received, force snd_cwnd to a value 575 * that will allow the sender to transmit no more than 2 segments. If 576 * necessary, a better scheme can be adopted at a later point, but for now, 577 * the goal is to prevent the sender from bursting a large amount of data in 578 * the midst of sack recovery. 579 */ 580 void 581 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th) 582 { 583 int num_segs = 1; 584 585 INP_WLOCK_ASSERT(tp->t_inpcb); 586 tcp_timer_activate(tp, TT_REXMT, 0); 587 tp->t_rtttime = 0; 588 /* Send one or 2 segments based on how much new data was acked. */ 589 if ((BYTES_THIS_ACK(tp, th) / tp->t_maxseg) >= 2) 590 num_segs = 2; 591 tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit + 592 (tp->snd_nxt - tp->sack_newdata) + num_segs * tp->t_maxseg); 593 if (tp->snd_cwnd > tp->snd_ssthresh) 594 tp->snd_cwnd = tp->snd_ssthresh; 595 tp->t_flags |= TF_ACKNOW; 596 (void) tp->t_fb->tfb_tcp_output(tp); 597 } 598 599 #if 0 600 /* 601 * Debug version of tcp_sack_output() that walks the scoreboard. Used for 602 * now to sanity check the hint. 603 */ 604 static struct sackhole * 605 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt) 606 { 607 struct sackhole *p; 608 609 INP_WLOCK_ASSERT(tp->t_inpcb); 610 *sack_bytes_rexmt = 0; 611 TAILQ_FOREACH(p, &tp->snd_holes, scblink) { 612 if (SEQ_LT(p->rxmit, p->end)) { 613 if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */ 614 continue; 615 } 616 *sack_bytes_rexmt += (p->rxmit - p->start); 617 break; 618 } 619 *sack_bytes_rexmt += (p->rxmit - p->start); 620 } 621 return (p); 622 } 623 #endif 624 625 /* 626 * Returns the next hole to retransmit and the number of retransmitted bytes 627 * from the scoreboard. We store both the next hole and the number of 628 * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK 629 * reception). This avoids scoreboard traversals completely. 630 * 631 * The loop here will traverse *at most* one link. Here's the argument. For 632 * the loop to traverse more than 1 link before finding the next hole to 633 * retransmit, we would need to have at least 1 node following the current 634 * hint with (rxmit == end). But, for all holes following the current hint, 635 * (start == rxmit), since we have not yet retransmitted from them. 636 * Therefore, in order to traverse more 1 link in the loop below, we need to 637 * have at least one node following the current hint with (start == rxmit == 638 * end). But that can't happen, (start == end) means that all the data in 639 * that hole has been sacked, in which case, the hole would have been removed 640 * from the scoreboard. 641 */ 642 struct sackhole * 643 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt) 644 { 645 struct sackhole *hole = NULL; 646 647 INP_WLOCK_ASSERT(tp->t_inpcb); 648 *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit; 649 hole = tp->sackhint.nexthole; 650 if (hole == NULL || SEQ_LT(hole->rxmit, hole->end)) 651 goto out; 652 while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) { 653 if (SEQ_LT(hole->rxmit, hole->end)) { 654 tp->sackhint.nexthole = hole; 655 break; 656 } 657 } 658 out: 659 return (hole); 660 } 661 662 /* 663 * After a timeout, the SACK list may be rebuilt. This SACK information 664 * should be used to avoid retransmitting SACKed data. This function 665 * traverses the SACK list to see if snd_nxt should be moved forward. 666 */ 667 void 668 tcp_sack_adjust(struct tcpcb *tp) 669 { 670 struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes); 671 672 INP_WLOCK_ASSERT(tp->t_inpcb); 673 if (cur == NULL) 674 return; /* No holes */ 675 if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack)) 676 return; /* We're already beyond any SACKed blocks */ 677 /*- 678 * Two cases for which we want to advance snd_nxt: 679 * i) snd_nxt lies between end of one hole and beginning of another 680 * ii) snd_nxt lies between end of last hole and snd_fack 681 */ 682 while ((p = TAILQ_NEXT(cur, scblink)) != NULL) { 683 if (SEQ_LT(tp->snd_nxt, cur->end)) 684 return; 685 if (SEQ_GEQ(tp->snd_nxt, p->start)) 686 cur = p; 687 else { 688 tp->snd_nxt = p->start; 689 return; 690 } 691 } 692 if (SEQ_LT(tp->snd_nxt, cur->end)) 693 return; 694 tp->snd_nxt = tp->snd_fack; 695 } 696