2 * SPDX-License-Identifier: BSD-3-Clause
4 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
5 * The Regents of the University of California.
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15 * documentation and/or other materials provided with the distribution.
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17 * may be used to endorse or promote products derived from this software
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21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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32 * @(#)tcp_sack.c 8.12 (Berkeley) 5/24/95
36 * @@(#)COPYRIGHT 1.1 (NRL) 17 January 1995
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:
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43 * notice, this list of conditions and the following disclaimer.
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49 * This product includes software developed by the University of
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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.
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.
69 * The views and conclusions contained in the software and documentation
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72 * Research Laboratory (NRL).
75 #include <sys/cdefs.h>
76 __FBSDID("$FreeBSD$");
79 #include "opt_inet6.h"
80 #include "opt_tcpdebug.h"
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>
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>
95 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
100 #include <net/if_var.h>
101 #include <net/route.h>
102 #include <net/vnet.h>
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 #include <netinet/cc/cc.h>
124 #include <netinet/tcp_debug.h>
125 #endif /* TCPDEBUG */
127 #include <machine/in_cksum.h>
129 VNET_DECLARE(struct uma_zone *, sack_hole_zone);
130 #define V_sack_hole_zone VNET(sack_hole_zone)
132 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
135 VNET_DEFINE(int, tcp_do_sack) = 1;
136 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
137 &VNET_NAME(tcp_do_sack), 0,
138 "Enable/Disable TCP SACK support");
140 VNET_DEFINE(int, tcp_do_newsack) = 1;
141 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, revised, CTLFLAG_VNET | CTLFLAG_RW,
142 &VNET_NAME(tcp_do_newsack), 0,
143 "Use revised SACK loss recovery per RFC 6675");
145 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
146 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
147 &VNET_NAME(tcp_sack_maxholes), 0,
148 "Maximum number of TCP SACK holes allowed per connection");
150 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
151 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
152 &VNET_NAME(tcp_sack_globalmaxholes), 0,
153 "Global maximum number of TCP SACK holes");
155 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
156 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
157 &VNET_NAME(tcp_sack_globalholes), 0,
158 "Global number of TCP SACK holes currently allocated");
161 tcp_dsack_block_exists(struct tcpcb *tp)
163 /* Return true if a DSACK block exists */
164 if (tp->rcv_numsacks == 0)
166 if (SEQ_LEQ(tp->sackblks[0].end, tp->rcv_nxt))
172 * This function will find overlaps with the currently stored sackblocks
173 * and add any overlap as a dsack block upfront
176 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
178 struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
179 int i, j, n, identical;
182 INP_WLOCK_ASSERT(tp->t_inpcb);
184 KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
186 if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
187 ((rcv_end == tp->rcv_nxt) &&
188 (tp->rcv_numsacks > 0 ) &&
189 (tp->sackblks[0].end == tp->rcv_nxt))) {
190 saved_blks[0].start = rcv_start;
191 saved_blks[0].end = rcv_end;
193 saved_blks[0].start = saved_blks[0].end = 0;
196 head_blk.start = head_blk.end = 0;
197 mid_blk.start = rcv_start;
198 mid_blk.end = rcv_end;
201 for (i = 0; i < tp->rcv_numsacks; i++) {
202 start = tp->sackblks[i].start;
203 end = tp->sackblks[i].end;
204 if (SEQ_LT(rcv_end, start)) {
205 /* pkt left to sack blk */
208 if (SEQ_GT(rcv_start, end)) {
209 /* pkt right to sack blk */
212 if (SEQ_GT(tp->rcv_nxt, end)) {
213 if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
214 (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
215 (head_blk.start == head_blk.end))) {
216 head_blk.start = SEQ_MAX(rcv_start, start);
217 head_blk.end = SEQ_MIN(rcv_end, end);
221 if (((head_blk.start == head_blk.end) ||
222 SEQ_LT(start, head_blk.start)) &&
223 (SEQ_GT(end, rcv_start) &&
224 SEQ_LEQ(start, rcv_end))) {
225 head_blk.start = start;
228 mid_blk.start = SEQ_MIN(mid_blk.start, start);
229 mid_blk.end = SEQ_MAX(mid_blk.end, end);
230 if ((mid_blk.start == start) &&
231 (mid_blk.end == end))
234 if (SEQ_LT(head_blk.start, head_blk.end)) {
235 /* store overlapping range */
236 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
237 saved_blks[0].end = SEQ_MIN(rcv_end, head_blk.end);
241 * Second, if not ACKed, store the SACK block that
242 * overlaps with the DSACK block unless it is identical
244 if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
245 !((mid_blk.start == saved_blks[0].start) &&
246 (mid_blk.end == saved_blks[0].end))) ||
248 saved_blks[n].start = mid_blk.start;
249 saved_blks[n++].end = mid_blk.end;
251 for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
252 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
253 SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
254 (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
255 saved_blks[n++] = tp->sackblks[j];
258 for (i = 0; i < n; i++) {
259 /* we can end up with a stale initial entry */
260 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
261 tp->sackblks[j++] = saved_blks[i];
264 tp->rcv_numsacks = j;
268 * This function is called upon receipt of new valid data (while not in
269 * header prediction mode), and it updates the ordered list of sacks.
272 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
275 * First reported block MUST be the most recent one. Subsequent
276 * blocks SHOULD be in the order in which they arrived at the
277 * receiver. These two conditions make the implementation fully
278 * compliant with RFC 2018.
280 struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
281 int num_head, num_saved, i;
283 INP_WLOCK_ASSERT(tp->t_inpcb);
285 /* Check arguments. */
286 KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
288 if ((rcv_start == rcv_end) &&
289 (tp->rcv_numsacks >= 1) &&
290 (rcv_end == tp->sackblks[0].end)) {
291 /* retaining DSACK block below rcv_nxt (todrop) */
292 head_blk = tp->sackblks[0];
294 /* SACK block for the received segment. */
295 head_blk.start = rcv_start;
296 head_blk.end = rcv_end;
300 * Merge updated SACK blocks into head_blk, and save unchanged SACK
301 * blocks into saved_blks[]. num_saved will have the number of the
305 for (i = 0; i < tp->rcv_numsacks; i++) {
306 tcp_seq start = tp->sackblks[i].start;
307 tcp_seq end = tp->sackblks[i].end;
308 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
310 * Discard this SACK block.
312 } else if (SEQ_LEQ(head_blk.start, end) &&
313 SEQ_GEQ(head_blk.end, start)) {
315 * Merge this SACK block into head_blk. This SACK
316 * block itself will be discarded.
329 * |-----| DSACK smaller
331 if (head_blk.start == end)
332 head_blk.start = start;
333 else if (head_blk.end == start)
336 if (SEQ_LT(head_blk.start, start)) {
337 tcp_seq temp = start;
338 start = head_blk.start;
339 head_blk.start = temp;
341 if (SEQ_GT(head_blk.end, end)) {
346 if ((head_blk.start != start) ||
347 (head_blk.end != end)) {
348 if ((num_saved >= 1) &&
349 SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
350 SEQ_LEQ(saved_blks[num_saved-1].end, end))
352 saved_blks[num_saved].start = start;
353 saved_blks[num_saved].end = end;
359 * This block supercedes the prior block
361 if ((num_saved >= 1) &&
362 SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
363 SEQ_LEQ(saved_blks[num_saved-1].end, end))
366 * Save this SACK block.
368 saved_blks[num_saved].start = start;
369 saved_blks[num_saved].end = end;
375 * Update SACK list in tp->sackblks[].
378 if (SEQ_LT(rcv_start, rcv_end)) {
380 * The received data segment is an out-of-order segment. Put
381 * head_blk at the top of SACK list.
383 tp->sackblks[0] = head_blk;
386 * If the number of saved SACK blocks exceeds its limit,
387 * discard the last SACK block.
389 if (num_saved >= MAX_SACK_BLKS)
392 if ((rcv_start == rcv_end) &&
393 (rcv_start == tp->sackblks[0].end)) {
398 * Copy the saved SACK blocks back.
400 bcopy(saved_blks, &tp->sackblks[num_head],
401 sizeof(struct sackblk) * num_saved);
404 /* Save the number of SACK blocks. */
405 tp->rcv_numsacks = num_head + num_saved;
409 tcp_clean_dsack_blocks(struct tcpcb *tp)
411 struct sackblk saved_blks[MAX_SACK_BLKS];
414 INP_WLOCK_ASSERT(tp->t_inpcb);
416 * Clean up any DSACK blocks that
417 * are in our queue of sack blocks.
421 for (i = 0; i < tp->rcv_numsacks; i++) {
422 tcp_seq start = tp->sackblks[i].start;
423 tcp_seq end = tp->sackblks[i].end;
424 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
426 * Discard this D-SACK block.
431 * Save this SACK block.
433 saved_blks[num_saved].start = start;
434 saved_blks[num_saved].end = end;
439 * Copy the saved SACK blocks back.
441 bcopy(saved_blks, &tp->sackblks[0],
442 sizeof(struct sackblk) * num_saved);
444 tp->rcv_numsacks = num_saved;
448 * Delete all receiver-side SACK information.
451 tcp_clean_sackreport(struct tcpcb *tp)
455 INP_WLOCK_ASSERT(tp->t_inpcb);
456 tp->rcv_numsacks = 0;
457 for (i = 0; i < MAX_SACK_BLKS; i++)
458 tp->sackblks[i].start = tp->sackblks[i].end=0;
462 * Allocate struct sackhole.
464 static struct sackhole *
465 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
467 struct sackhole *hole;
469 if (tp->snd_numholes >= V_tcp_sack_maxholes ||
470 V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
471 TCPSTAT_INC(tcps_sack_sboverflow);
475 hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
484 atomic_add_int(&V_tcp_sack_globalholes, 1);
490 * Free struct sackhole.
493 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
496 uma_zfree(V_sack_hole_zone, hole);
499 atomic_subtract_int(&V_tcp_sack_globalholes, 1);
501 KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
502 KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
506 * Insert new SACK hole into scoreboard.
508 static struct sackhole *
509 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
510 struct sackhole *after)
512 struct sackhole *hole;
514 /* Allocate a new SACK hole. */
515 hole = tcp_sackhole_alloc(tp, start, end);
519 /* Insert the new SACK hole into scoreboard. */
521 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
523 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
525 /* Update SACK hint. */
526 if (tp->sackhint.nexthole == NULL)
527 tp->sackhint.nexthole = hole;
533 * Remove SACK hole from scoreboard.
536 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
539 /* Update SACK hint. */
540 if (tp->sackhint.nexthole == hole)
541 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
543 /* Remove this SACK hole. */
544 TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
546 /* Free this SACK hole. */
547 tcp_sackhole_free(tp, hole);
551 * Process cumulative ACK and the TCP SACK option to update the scoreboard.
552 * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
553 * the sequence space).
554 * Returns 1 if incoming ACK has previously unknown SACK information,
558 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
560 struct sackhole *cur, *temp;
561 struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
562 int i, j, num_sack_blks, sack_changed;
563 int delivered_data, left_edge_delta;
565 INP_WLOCK_ASSERT(tp->t_inpcb);
572 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
573 * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
574 * Account changes to SND.UNA always in delivered data.
576 if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
577 left_edge_delta = th_ack - tp->snd_una;
578 sack_blocks[num_sack_blks].start = tp->snd_una;
579 sack_blocks[num_sack_blks++].end = th_ack;
581 * Pulling snd_fack forward if we got here
582 * due to DSACK blocks
584 if (SEQ_LT(tp->snd_fack, th_ack)) {
585 delivered_data += th_ack - tp->snd_una;
586 tp->snd_fack = th_ack;
591 * Append received valid SACK blocks to sack_blocks[], but only if we
592 * received new blocks from the other side.
594 if (to->to_flags & TOF_SACK) {
595 for (i = 0; i < to->to_nsacks; i++) {
596 bcopy((to->to_sacks + i * TCPOLEN_SACK),
597 &sack, sizeof(sack));
598 sack.start = ntohl(sack.start);
599 sack.end = ntohl(sack.end);
600 if (SEQ_GT(sack.end, sack.start) &&
601 SEQ_GT(sack.start, tp->snd_una) &&
602 SEQ_GT(sack.start, th_ack) &&
603 SEQ_LT(sack.start, tp->snd_max) &&
604 SEQ_GT(sack.end, tp->snd_una) &&
605 SEQ_LEQ(sack.end, tp->snd_max)) {
606 sack_blocks[num_sack_blks++] = sack;
607 } else if (SEQ_LEQ(sack.start, th_ack) &&
608 SEQ_LEQ(sack.end, th_ack)) {
610 * Its a D-SACK block.
612 tcp_record_dsack(tp, sack.start, sack.end, 0);
617 * Return if SND.UNA is not advanced and no valid SACK block is
620 if (num_sack_blks == 0)
621 return (sack_changed);
624 * Sort the SACK blocks so we can update the scoreboard with just one
625 * pass. The overhead of sorting up to 4+1 elements is less than
626 * making up to 4+1 passes over the scoreboard.
628 for (i = 0; i < num_sack_blks; i++) {
629 for (j = i + 1; j < num_sack_blks; j++) {
630 if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
631 sack = sack_blocks[i];
632 sack_blocks[i] = sack_blocks[j];
633 sack_blocks[j] = sack;
637 if (TAILQ_EMPTY(&tp->snd_holes)) {
639 * Empty scoreboard. Need to initialize snd_fack (it may be
640 * uninitialized or have a bogus value). Scoreboard holes
641 * (from the sack blocks received) are created later below
642 * (in the logic that adds holes to the tail of the
645 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
646 tp->sackhint.sacked_bytes = 0; /* reset */
649 * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
650 * SACK holes (snd_holes) are traversed from their tails with just
651 * one pass in order to reduce the number of compares especially when
652 * the bandwidth-delay product is large.
654 * Note: Typically, in the first RTT of SACK recovery, the highest
655 * three or four SACK blocks with the same ack number are received.
656 * In the second RTT, if retransmitted data segments are not lost,
657 * the highest three or four SACK blocks with ack number advancing
660 sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */
661 tp->sackhint.last_sack_ack = sblkp->end;
662 if (SEQ_LT(tp->snd_fack, sblkp->start)) {
664 * The highest SACK block is beyond fack. First,
665 * check if there was a successful Rescue Retransmission,
666 * and move this hole left. With normal holes, snd_fack
667 * is always to the right of the end.
669 if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
670 SEQ_LEQ(tp->snd_fack,temp->end)) {
671 temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
672 temp->end = sblkp->start;
673 temp->rxmit = temp->start;
674 delivered_data += sblkp->end - sblkp->start;
675 tp->snd_fack = sblkp->end;
680 * Append a new SACK hole at the tail. If the
681 * second or later highest SACK blocks are also
682 * beyond the current fack, they will be inserted
683 * by way of hole splitting in the while-loop below.
685 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
687 delivered_data += sblkp->end - sblkp->start;
688 tp->snd_fack = sblkp->end;
689 /* Go to the previous sack block. */
694 * We failed to add a new hole based on the current
695 * sack block. Skip over all the sack blocks that
696 * fall completely to the right of snd_fack and
697 * proceed to trim the scoreboard based on the
698 * remaining sack blocks. This also trims the
699 * scoreboard for th_ack (which is sack_blocks[0]).
701 while (sblkp >= sack_blocks &&
702 SEQ_LT(tp->snd_fack, sblkp->start))
704 if (sblkp >= sack_blocks &&
705 SEQ_LT(tp->snd_fack, sblkp->end)) {
706 delivered_data += sblkp->end - tp->snd_fack;
707 tp->snd_fack = sblkp->end;
712 } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
713 /* fack is advanced. */
714 delivered_data += sblkp->end - tp->snd_fack;
715 tp->snd_fack = sblkp->end;
718 cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
720 * Since the incoming sack blocks are sorted, we can process them
721 * making one sweep of the scoreboard.
723 while (sblkp >= sack_blocks && cur != NULL) {
724 if (SEQ_GEQ(sblkp->start, cur->end)) {
726 * SACKs data beyond the current hole. Go to the
727 * previous sack block.
732 if (SEQ_LEQ(sblkp->end, cur->start)) {
734 * SACKs data before the current hole. Go to the
737 cur = TAILQ_PREV(cur, sackhole_head, scblink);
740 tp->sackhint.sack_bytes_rexmit -=
741 (SEQ_MIN(cur->rxmit, cur->end) - cur->start);
742 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
743 ("sackhint bytes rtx >= 0"));
745 if (SEQ_LEQ(sblkp->start, cur->start)) {
746 /* Data acks at least the beginning of hole. */
747 if (SEQ_GEQ(sblkp->end, cur->end)) {
748 /* Acks entire hole, so delete hole. */
749 delivered_data += (cur->end - cur->start);
751 cur = TAILQ_PREV(cur, sackhole_head, scblink);
752 tcp_sackhole_remove(tp, temp);
754 * The sack block may ack all or part of the
755 * next hole too, so continue onto the next
760 /* Move start of hole forward. */
761 delivered_data += (sblkp->end - cur->start);
762 cur->start = sblkp->end;
763 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
766 /* Data acks at least the end of hole. */
767 if (SEQ_GEQ(sblkp->end, cur->end)) {
768 /* Move end of hole backward. */
769 delivered_data += (cur->end - sblkp->start);
770 cur->end = sblkp->start;
771 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
772 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
773 cur->rxmit = tp->snd_recover;
776 * ACKs some data in middle of a hole; need
777 * to split current hole
779 temp = tcp_sackhole_insert(tp, sblkp->end,
782 if (SEQ_GT(cur->rxmit, temp->rxmit)) {
783 temp->rxmit = cur->rxmit;
784 tp->sackhint.sack_bytes_rexmit +=
785 (SEQ_MIN(temp->rxmit,
786 temp->end) - temp->start);
788 cur->end = sblkp->start;
789 cur->rxmit = SEQ_MIN(cur->rxmit,
791 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
792 cur->rxmit = tp->snd_recover;
793 delivered_data += (sblkp->end - sblkp->start);
797 tp->sackhint.sack_bytes_rexmit +=
798 (SEQ_MIN(cur->rxmit, cur->end) - cur->start);
800 * Testing sblkp->start against cur->start tells us whether
801 * we're done with the sack block or the sack hole.
802 * Accordingly, we advance one or the other.
804 if (SEQ_LEQ(sblkp->start, cur->start))
805 cur = TAILQ_PREV(cur, sackhole_head, scblink);
809 if (!(to->to_flags & TOF_SACK))
811 * If this ACK did not contain any
812 * SACK blocks, any only moved the
813 * left edge right, it is a pure
814 * cumulative ACK. Do not count
815 * DupAck for this. Also required
816 * for RFC6675 rescue retransmission.
819 tp->sackhint.delivered_data = delivered_data;
820 tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
821 KASSERT((delivered_data >= 0), ("delivered_data < 0"));
822 KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
823 return (sack_changed);
827 * Free all SACK holes to clear the scoreboard.
830 tcp_free_sackholes(struct tcpcb *tp)
834 INP_WLOCK_ASSERT(tp->t_inpcb);
835 while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
836 tcp_sackhole_remove(tp, q);
837 tp->sackhint.sack_bytes_rexmit = 0;
839 KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
840 KASSERT(tp->sackhint.nexthole == NULL,
841 ("tp->sackhint.nexthole == NULL"));
845 * Partial ack handling within a sack recovery episode. Keeping this very
846 * simple for now. When a partial ack is received, force snd_cwnd to a value
847 * that will allow the sender to transmit no more than 2 segments. If
848 * necessary, a better scheme can be adopted at a later point, but for now,
849 * the goal is to prevent the sender from bursting a large amount of data in
850 * the midst of sack recovery.
853 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
856 u_int maxseg = tcp_maxseg(tp);
858 INP_WLOCK_ASSERT(tp->t_inpcb);
859 tcp_timer_activate(tp, TT_REXMT, 0);
861 /* Send one or 2 segments based on how much new data was acked. */
862 if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
864 tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
865 (tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
866 if (tp->snd_cwnd > tp->snd_ssthresh)
867 tp->snd_cwnd = tp->snd_ssthresh;
868 tp->t_flags |= TF_ACKNOW;
870 * RFC6675 rescue retransmission
871 * Add a hole between th_ack (snd_una is not yet set) and snd_max,
872 * if this was a pure cumulative ACK and no data was send beyond
873 * recovery point. Since the data in the socket has not been freed
874 * at this point, we check if the scoreboard is empty, and the ACK
875 * delivered some new data, indicating a full ACK. Also, if the
876 * recovery point is still at snd_max, we are probably application
877 * limited. However, this inference might not always be true. The
878 * rescue retransmission may rarely be slightly premature
879 * compared to RFC6675.
880 * The corresponding ACK+SACK will cause any further outstanding
881 * segments to be retransmitted. This addresses a corner case, when
882 * the trailing packets of a window are lost and no further data
883 * is available for sending.
885 if ((V_tcp_do_newsack) &&
886 SEQ_LT(th->th_ack, tp->snd_recover) &&
887 (tp->snd_recover == tp->snd_max) &&
888 TAILQ_EMPTY(&tp->snd_holes) &&
889 (tp->sackhint.delivered_data > 0)) {
891 * Exclude FIN sequence space in
892 * the hole for the rescue retransmission,
893 * and also don't create a hole, if only
894 * the ACK for a FIN is outstanding.
896 tcp_seq highdata = tp->snd_max;
897 if (tp->t_flags & TF_SENTFIN)
899 if (th->th_ack != highdata) {
900 tp->snd_fack = th->th_ack;
901 (void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
902 highdata - maxseg), highdata, NULL);
905 (void) tcp_output(tp);
910 * Debug version of tcp_sack_output() that walks the scoreboard. Used for
911 * now to sanity check the hint.
913 static struct sackhole *
914 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
918 INP_WLOCK_ASSERT(tp->t_inpcb);
919 *sack_bytes_rexmt = 0;
920 TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
921 if (SEQ_LT(p->rxmit, p->end)) {
922 if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
925 *sack_bytes_rexmt += (p->rxmit - p->start);
928 *sack_bytes_rexmt += (SEQ_MIN(p->rxmit, p->end) - p->start);
935 * Returns the next hole to retransmit and the number of retransmitted bytes
936 * from the scoreboard. We store both the next hole and the number of
937 * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
938 * reception). This avoids scoreboard traversals completely.
940 * The loop here will traverse *at most* one link. Here's the argument. For
941 * the loop to traverse more than 1 link before finding the next hole to
942 * retransmit, we would need to have at least 1 node following the current
943 * hint with (rxmit == end). But, for all holes following the current hint,
944 * (start == rxmit), since we have not yet retransmitted from them.
945 * Therefore, in order to traverse more 1 link in the loop below, we need to
946 * have at least one node following the current hint with (start == rxmit ==
947 * end). But that can't happen, (start == end) means that all the data in
948 * that hole has been sacked, in which case, the hole would have been removed
949 * from the scoreboard.
952 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
954 struct sackhole *hole = NULL;
956 INP_WLOCK_ASSERT(tp->t_inpcb);
957 *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
958 hole = tp->sackhint.nexthole;
961 if (SEQ_GEQ(hole->rxmit, hole->end)) {
963 hole = TAILQ_NEXT(hole, scblink);
966 if (SEQ_LT(hole->rxmit, hole->end)) {
967 tp->sackhint.nexthole = hole;
972 KASSERT(SEQ_LT(hole->start, hole->end), ("%s: hole.start >= hole.end", __func__));
973 if (!(V_tcp_do_newsack)) {
974 KASSERT(SEQ_LT(hole->start, tp->snd_fack), ("%s: hole.start >= snd.fack", __func__));
975 KASSERT(SEQ_LT(hole->end, tp->snd_fack), ("%s: hole.end >= snd.fack", __func__));
976 KASSERT(SEQ_LT(hole->rxmit, tp->snd_fack), ("%s: hole.rxmit >= snd.fack", __func__));
977 if (SEQ_GEQ(hole->start, hole->end) ||
978 SEQ_GEQ(hole->start, tp->snd_fack) ||
979 SEQ_GEQ(hole->end, tp->snd_fack) ||
980 SEQ_GEQ(hole->rxmit, tp->snd_fack)) {
981 log(LOG_CRIT,"tcp: invalid SACK hole (%u-%u,%u) vs fwd ack %u, ignoring.\n",
982 hole->start, hole->end, hole->rxmit, tp->snd_fack);
990 * After a timeout, the SACK list may be rebuilt. This SACK information
991 * should be used to avoid retransmitting SACKed data. This function
992 * traverses the SACK list to see if snd_nxt should be moved forward.
995 tcp_sack_adjust(struct tcpcb *tp)
997 struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
999 INP_WLOCK_ASSERT(tp->t_inpcb);
1001 return; /* No holes */
1002 if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
1003 return; /* We're already beyond any SACKed blocks */
1005 * Two cases for which we want to advance snd_nxt:
1006 * i) snd_nxt lies between end of one hole and beginning of another
1007 * ii) snd_nxt lies between end of last hole and snd_fack
1009 while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
1010 if (SEQ_LT(tp->snd_nxt, cur->end))
1012 if (SEQ_GEQ(tp->snd_nxt, p->start))
1015 tp->snd_nxt = p->start;
1019 if (SEQ_LT(tp->snd_nxt, cur->end))
1021 tp->snd_nxt = tp->snd_fack;
1025 * Lost Retransmission Detection
1026 * Check is FACK is beyond the rexmit of the leftmost hole.
1027 * If yes, we restart sending from still existing holes,
1028 * and adjust cwnd via the congestion control module.
1031 tcp_sack_lost_retransmission(struct tcpcb *tp, struct tcphdr *th)
1033 struct sackhole *temp;
1035 if (IN_RECOVERY(tp->t_flags) &&
1036 SEQ_GT(tp->snd_fack, tp->snd_recover) &&
1037 ((temp = TAILQ_FIRST(&tp->snd_holes)) != NULL) &&
1038 SEQ_GEQ(temp->rxmit, temp->end) &&
1039 SEQ_GEQ(tp->snd_fack, temp->rxmit)) {
1040 TCPSTAT_INC(tcps_sack_lostrexmt);
1042 * Start retransmissions from the first hole, and
1043 * subsequently all other remaining holes, including
1044 * those, which had been sent completely before.
1046 tp->sackhint.nexthole = temp;
1047 TAILQ_FOREACH(temp, &tp->snd_holes, scblink) {
1048 if (SEQ_GEQ(tp->snd_fack, temp->rxmit) &&
1049 SEQ_GEQ(temp->rxmit, temp->end))
1050 temp->rxmit = temp->start;
1053 * Remember the old ssthresh, to deduct the beta factor used
1054 * by the CC module. Finally, set cwnd to ssthresh just
1055 * prior to invoking another cwnd reduction by the CC
1056 * module, to not shrink it excessively.
1058 tp->snd_cwnd = tp->snd_ssthresh;
1060 * Formally exit recovery, and let the CC module adjust
1061 * ssthresh as intended.
1063 EXIT_RECOVERY(tp->t_flags);
1064 cc_cong_signal(tp, th, CC_NDUPACK);
1066 * For PRR, adjust recover_fs as if this new reduction
1067 * initialized this variable.
1068 * cwnd will be adjusted by SACK or PRR processing
1069 * subsequently, only set it to a safe value here.
1071 tp->snd_cwnd = tcp_maxseg(tp);
1072 tp->sackhint.recover_fs = (tp->snd_max - tp->snd_una) -
1073 tp->sackhint.recover_fs;