2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
3 * The Regents of the University of California.
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7 * modification, are permitted provided that the following conditions
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
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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
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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
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30 * @(#)tcp_sack.c 8.12 (Berkeley) 5/24/95
34 * @@(#)COPYRIGHT 1.1 (NRL) 17 January 1995
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:
40 * 1. Redistributions of source code must retain the above copyright
41 * notice, this list of conditions and the following disclaimer.
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46 * must display the following acknowledgements:
47 * This product includes software developed by the University of
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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.
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.
67 * The views and conclusions contained in the software and documentation
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70 * Research Laboratory (NRL).
73 #include <sys/cdefs.h>
74 __FBSDID("$FreeBSD$");
77 #include "opt_inet6.h"
78 #include "opt_tcpdebug.h"
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>
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>
93 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
98 #include <net/if_var.h>
99 #include <net/route.h>
100 #include <net/vnet.h>
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>
121 #include <netinet/tcp_debug.h>
122 #endif /* TCPDEBUG */
124 #include <machine/in_cksum.h>
126 VNET_DECLARE(struct uma_zone *, sack_hole_zone);
127 #define V_sack_hole_zone VNET(sack_hole_zone)
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");
135 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
136 #define V_tcp_sack_maxholes VNET(tcp_sack_maxholes)
137 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
138 &VNET_NAME(tcp_sack_maxholes), 0,
139 "Maximum number of TCP SACK holes allowed per connection");
141 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
142 #define V_tcp_sack_globalmaxholes VNET(tcp_sack_globalmaxholes)
143 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
144 &VNET_NAME(tcp_sack_globalmaxholes), 0,
145 "Global maximum number of TCP SACK holes");
147 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
148 #define V_tcp_sack_globalholes VNET(tcp_sack_globalholes)
149 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
150 &VNET_NAME(tcp_sack_globalholes), 0,
151 "Global number of TCP SACK holes currently allocated");
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.
158 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
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.
166 struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
167 int num_head, num_saved, i;
169 INP_WLOCK_ASSERT(tp->t_inpcb);
171 /* Check arguments. */
172 KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
174 /* SACK block for the received segment. */
175 head_blk.start = rcv_start;
176 head_blk.end = rcv_end;
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
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)) {
189 * Discard this SACK block.
191 } else if (SEQ_LEQ(head_blk.start, end) &&
192 SEQ_GEQ(head_blk.end, start)) {
194 * Merge this SACK block into head_blk. This SACK
195 * block itself will be discarded.
197 if (SEQ_GT(head_blk.start, start))
198 head_blk.start = start;
199 if (SEQ_LT(head_blk.end, end))
203 * Save this SACK block.
205 saved_blks[num_saved].start = start;
206 saved_blks[num_saved].end = end;
212 * Update SACK list in tp->sackblks[].
215 if (SEQ_GT(head_blk.start, tp->rcv_nxt)) {
217 * The received data segment is an out-of-order segment. Put
218 * head_blk at the top of SACK list.
220 tp->sackblks[0] = head_blk;
223 * If the number of saved SACK blocks exceeds its limit,
224 * discard the last SACK block.
226 if (num_saved >= MAX_SACK_BLKS)
231 * Copy the saved SACK blocks back.
233 bcopy(saved_blks, &tp->sackblks[num_head],
234 sizeof(struct sackblk) * num_saved);
237 /* Save the number of SACK blocks. */
238 tp->rcv_numsacks = num_head + num_saved;
242 * Delete all receiver-side SACK information.
245 tcp_clean_sackreport(struct tcpcb *tp)
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;
256 * Allocate struct sackhole.
258 static struct sackhole *
259 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
261 struct sackhole *hole;
263 if (tp->snd_numholes >= V_tcp_sack_maxholes ||
264 V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
265 TCPSTAT_INC(tcps_sack_sboverflow);
269 hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
278 atomic_add_int(&V_tcp_sack_globalholes, 1);
284 * Free struct sackhole.
287 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
290 uma_zfree(V_sack_hole_zone, hole);
293 atomic_subtract_int(&V_tcp_sack_globalholes, 1);
295 KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
296 KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
300 * Insert new SACK hole into scoreboard.
302 static struct sackhole *
303 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
304 struct sackhole *after)
306 struct sackhole *hole;
308 /* Allocate a new SACK hole. */
309 hole = tcp_sackhole_alloc(tp, start, end);
313 /* Insert the new SACK hole into scoreboard. */
315 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
317 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
319 /* Update SACK hint. */
320 if (tp->sackhint.nexthole == NULL)
321 tp->sackhint.nexthole = hole;
327 * Remove SACK hole from scoreboard.
330 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
333 /* Update SACK hint. */
334 if (tp->sackhint.nexthole == hole)
335 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
337 /* Remove this SACK hole. */
338 TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
340 /* Free this SACK hole. */
341 tcp_sackhole_free(tp, hole);
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 * Returns 1 if incoming ACK has previously unknown SACK information,
349 * 0 otherwise. Note: We treat (snd_una, th_ack) as a sack block so any changes
350 * to that (i.e. left edge moving) would also be considered a change in SACK
351 * information which is slightly different than rfc6675.
354 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
356 struct sackhole *cur, *temp;
357 struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
358 int i, j, num_sack_blks, sack_changed;
360 INP_WLOCK_ASSERT(tp->t_inpcb);
365 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
366 * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
368 if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
369 sack_blocks[num_sack_blks].start = tp->snd_una;
370 sack_blocks[num_sack_blks++].end = th_ack;
373 * Append received valid SACK blocks to sack_blocks[], but only if we
374 * received new blocks from the other side.
376 if (to->to_flags & TOF_SACK) {
377 tp->sackhint.sacked_bytes = 0; /* reset */
378 for (i = 0; i < to->to_nsacks; i++) {
379 bcopy((to->to_sacks + i * TCPOLEN_SACK),
380 &sack, sizeof(sack));
381 sack.start = ntohl(sack.start);
382 sack.end = ntohl(sack.end);
383 if (SEQ_GT(sack.end, sack.start) &&
384 SEQ_GT(sack.start, tp->snd_una) &&
385 SEQ_GT(sack.start, th_ack) &&
386 SEQ_LT(sack.start, tp->snd_max) &&
387 SEQ_GT(sack.end, tp->snd_una) &&
388 SEQ_LEQ(sack.end, tp->snd_max)) {
389 sack_blocks[num_sack_blks++] = sack;
390 tp->sackhint.sacked_bytes +=
391 (sack.end-sack.start);
396 * Return if SND.UNA is not advanced and no valid SACK block is
399 if (num_sack_blks == 0)
400 return (sack_changed);
403 * Sort the SACK blocks so we can update the scoreboard with just one
404 * pass. The overhead of sorting up to 4+1 elements is less than
405 * making up to 4+1 passes over the scoreboard.
407 for (i = 0; i < num_sack_blks; i++) {
408 for (j = i + 1; j < num_sack_blks; j++) {
409 if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
410 sack = sack_blocks[i];
411 sack_blocks[i] = sack_blocks[j];
412 sack_blocks[j] = sack;
416 if (TAILQ_EMPTY(&tp->snd_holes))
418 * Empty scoreboard. Need to initialize snd_fack (it may be
419 * uninitialized or have a bogus value). Scoreboard holes
420 * (from the sack blocks received) are created later below
421 * (in the logic that adds holes to the tail of the
424 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
426 * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
427 * SACK holes (snd_holes) are traversed from their tails with just
428 * one pass in order to reduce the number of compares especially when
429 * the bandwidth-delay product is large.
431 * Note: Typically, in the first RTT of SACK recovery, the highest
432 * three or four SACK blocks with the same ack number are received.
433 * In the second RTT, if retransmitted data segments are not lost,
434 * the highest three or four SACK blocks with ack number advancing
437 sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */
438 tp->sackhint.last_sack_ack = sblkp->end;
439 if (SEQ_LT(tp->snd_fack, sblkp->start)) {
441 * The highest SACK block is beyond fack. Append new SACK
442 * hole at the tail. If the second or later highest SACK
443 * blocks are also beyond the current fack, they will be
444 * inserted by way of hole splitting in the while-loop below.
446 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
448 tp->snd_fack = sblkp->end;
449 /* Go to the previous sack block. */
454 * We failed to add a new hole based on the current
455 * sack block. Skip over all the sack blocks that
456 * fall completely to the right of snd_fack and
457 * proceed to trim the scoreboard based on the
458 * remaining sack blocks. This also trims the
459 * scoreboard for th_ack (which is sack_blocks[0]).
461 while (sblkp >= sack_blocks &&
462 SEQ_LT(tp->snd_fack, sblkp->start))
464 if (sblkp >= sack_blocks &&
465 SEQ_LT(tp->snd_fack, sblkp->end))
466 tp->snd_fack = sblkp->end;
468 } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
469 /* fack is advanced. */
470 tp->snd_fack = sblkp->end;
473 cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
475 * Since the incoming sack blocks are sorted, we can process them
476 * making one sweep of the scoreboard.
478 while (sblkp >= sack_blocks && cur != NULL) {
479 if (SEQ_GEQ(sblkp->start, cur->end)) {
481 * SACKs data beyond the current hole. Go to the
482 * previous sack block.
487 if (SEQ_LEQ(sblkp->end, cur->start)) {
489 * SACKs data before the current hole. Go to the
492 cur = TAILQ_PREV(cur, sackhole_head, scblink);
495 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
496 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
497 ("sackhint bytes rtx >= 0"));
499 if (SEQ_LEQ(sblkp->start, cur->start)) {
500 /* Data acks at least the beginning of hole. */
501 if (SEQ_GEQ(sblkp->end, cur->end)) {
502 /* Acks entire hole, so delete hole. */
504 cur = TAILQ_PREV(cur, sackhole_head, scblink);
505 tcp_sackhole_remove(tp, temp);
507 * The sack block may ack all or part of the
508 * next hole too, so continue onto the next
513 /* Move start of hole forward. */
514 cur->start = sblkp->end;
515 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
518 /* Data acks at least the end of hole. */
519 if (SEQ_GEQ(sblkp->end, cur->end)) {
520 /* Move end of hole backward. */
521 cur->end = sblkp->start;
522 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
525 * ACKs some data in middle of a hole; need
526 * to split current hole
528 temp = tcp_sackhole_insert(tp, sblkp->end,
531 if (SEQ_GT(cur->rxmit, temp->rxmit)) {
532 temp->rxmit = cur->rxmit;
533 tp->sackhint.sack_bytes_rexmit
537 cur->end = sblkp->start;
538 cur->rxmit = SEQ_MIN(cur->rxmit,
543 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
545 * Testing sblkp->start against cur->start tells us whether
546 * we're done with the sack block or the sack hole.
547 * Accordingly, we advance one or the other.
549 if (SEQ_LEQ(sblkp->start, cur->start))
550 cur = TAILQ_PREV(cur, sackhole_head, scblink);
554 return (sack_changed);
558 * Free all SACK holes to clear the scoreboard.
561 tcp_free_sackholes(struct tcpcb *tp)
565 INP_WLOCK_ASSERT(tp->t_inpcb);
566 while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
567 tcp_sackhole_remove(tp, q);
568 tp->sackhint.sack_bytes_rexmit = 0;
570 KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
571 KASSERT(tp->sackhint.nexthole == NULL,
572 ("tp->sackhint.nexthole == NULL"));
576 * Partial ack handling within a sack recovery episode. Keeping this very
577 * simple for now. When a partial ack is received, force snd_cwnd to a value
578 * that will allow the sender to transmit no more than 2 segments. If
579 * necessary, a better scheme can be adopted at a later point, but for now,
580 * the goal is to prevent the sender from bursting a large amount of data in
581 * the midst of sack recovery.
584 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
588 INP_WLOCK_ASSERT(tp->t_inpcb);
589 tcp_timer_activate(tp, TT_REXMT, 0);
591 /* Send one or 2 segments based on how much new data was acked. */
592 if ((BYTES_THIS_ACK(tp, th) / tp->t_maxseg) >= 2)
594 tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
595 (tp->snd_nxt - tp->sack_newdata) + num_segs * tp->t_maxseg);
596 if (tp->snd_cwnd > tp->snd_ssthresh)
597 tp->snd_cwnd = tp->snd_ssthresh;
598 tp->t_flags |= TF_ACKNOW;
599 (void) tp->t_fb->tfb_tcp_output(tp);
604 * Debug version of tcp_sack_output() that walks the scoreboard. Used for
605 * now to sanity check the hint.
607 static struct sackhole *
608 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
612 INP_WLOCK_ASSERT(tp->t_inpcb);
613 *sack_bytes_rexmt = 0;
614 TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
615 if (SEQ_LT(p->rxmit, p->end)) {
616 if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
619 *sack_bytes_rexmt += (p->rxmit - p->start);
622 *sack_bytes_rexmt += (p->rxmit - p->start);
629 * Returns the next hole to retransmit and the number of retransmitted bytes
630 * from the scoreboard. We store both the next hole and the number of
631 * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
632 * reception). This avoids scoreboard traversals completely.
634 * The loop here will traverse *at most* one link. Here's the argument. For
635 * the loop to traverse more than 1 link before finding the next hole to
636 * retransmit, we would need to have at least 1 node following the current
637 * hint with (rxmit == end). But, for all holes following the current hint,
638 * (start == rxmit), since we have not yet retransmitted from them.
639 * Therefore, in order to traverse more 1 link in the loop below, we need to
640 * have at least one node following the current hint with (start == rxmit ==
641 * end). But that can't happen, (start == end) means that all the data in
642 * that hole has been sacked, in which case, the hole would have been removed
643 * from the scoreboard.
646 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
648 struct sackhole *hole = NULL;
650 INP_WLOCK_ASSERT(tp->t_inpcb);
651 *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
652 hole = tp->sackhint.nexthole;
653 if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
655 while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
656 if (SEQ_LT(hole->rxmit, hole->end)) {
657 tp->sackhint.nexthole = hole;
666 * After a timeout, the SACK list may be rebuilt. This SACK information
667 * should be used to avoid retransmitting SACKed data. This function
668 * traverses the SACK list to see if snd_nxt should be moved forward.
671 tcp_sack_adjust(struct tcpcb *tp)
673 struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
675 INP_WLOCK_ASSERT(tp->t_inpcb);
677 return; /* No holes */
678 if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
679 return; /* We're already beyond any SACKed blocks */
681 * Two cases for which we want to advance snd_nxt:
682 * i) snd_nxt lies between end of one hole and beginning of another
683 * ii) snd_nxt lies between end of last hole and snd_fack
685 while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
686 if (SEQ_LT(tp->snd_nxt, cur->end))
688 if (SEQ_GEQ(tp->snd_nxt, p->start))
691 tp->snd_nxt = p->start;
695 if (SEQ_LT(tp->snd_nxt, cur->end))
697 tp->snd_nxt = tp->snd_fack;