freebsd-dev/sys/netinet/tcp_sack.c
Paul Saab a6235da61e - Make the sack scoreboard logic use the TAILQ macros. This improves
code readability and facilitates some anticipated optimizations in
  tcp_sack_option().
- Remove tcp_print_holes() and TCP_SACK_DEBUG.

Submitted by:	Raja Mukerji.
Reviewed by:	Mohan Srinivasan, Noritoshi Demizu.
2005-04-21 20:11:01 +00:00

623 lines
20 KiB
C

/*-
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)tcp_sack.c 8.12 (Berkeley) 5/24/95
* $FreeBSD$
*/
/*-
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @@(#)COPYRIGHT 1.1 (NRL) 17 January 1995
*
* NRL grants permission for redistribution and use in source and binary
* forms, with or without modification, of the software and documentation
* created at NRL provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgements:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* This product includes software developed at the Information
* Technology Division, US Naval Research Laboratory.
* 4. Neither the name of the NRL nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS
* IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NRL OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* The views and conclusions contained in the software and documentation
* are those of the authors and should not be interpreted as representing
* official policies, either expressed or implied, of the US Naval
* Research Laboratory (NRL).
*/
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_tcpdebug.h"
#include "opt_tcp_input.h"
#include "opt_tcp_sack.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/proc.h> /* for proc0 declaration */
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/syslog.h>
#include <sys/systm.h>
#include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
#include <vm/uma.h>
#include <net/if.h>
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h> /* for ICMP_BANDLIM */
#include <netinet/in_var.h>
#include <netinet/icmp_var.h> /* for ICMP_BANDLIM */
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_pcb.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet6/tcp6_var.h>
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif /* TCPDEBUG */
#ifdef FAST_IPSEC
#include <netipsec/ipsec.h>
#include <netipsec/ipsec6.h>
#endif
#ifdef IPSEC
#include <netinet6/ipsec.h>
#include <netinet6/ipsec6.h>
#include <netkey/key.h>
#endif /*IPSEC*/
#include <machine/in_cksum.h>
extern struct uma_zone *sack_hole_zone;
SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW, 0, "TCP SACK");
int tcp_do_sack = 1;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_RW,
&tcp_do_sack, 0, "Enable/Disable TCP SACK support");
TUNABLE_INT("net.inet.tcp.sack.enable", &tcp_do_sack);
static int tcp_sack_maxholes = 128;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_RW,
&tcp_sack_maxholes, 0,
"Maximum number of TCP SACK holes allowed per connection");
static int tcp_sack_globalmaxholes = 65536;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_RW,
&tcp_sack_globalmaxholes, 0,
"Global maximum number of TCP SACK holes");
static int tcp_sack_globalholes = 0;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_RD,
&tcp_sack_globalholes, 0,
"Global number of TCP SACK holes currently allocated");
/*
* This function is called upon receipt of new valid data (while not in header
* prediction mode), and it updates the ordered list of sacks.
*/
void
tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
{
/*
* First reported block MUST be the most recent one. Subsequent
* blocks SHOULD be in the order in which they arrived at the
* receiver. These two conditions make the implementation fully
* compliant with RFC 2018.
*/
struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
int num_head, num_saved, i;
INP_LOCK_ASSERT(tp->t_inpcb);
/* Check arguments */
KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
/* SACK block for the received segment. */
head_blk.start = rcv_start;
head_blk.end = rcv_end;
/*
* Merge updated SACK blocks into head_blk, and
* save unchanged SACK blocks into saved_blks[].
* num_saved will have the number of the saved SACK blocks.
*/
num_saved = 0;
for (i = 0; i < tp->rcv_numsacks; i++) {
tcp_seq start = tp->sackblks[i].start;
tcp_seq end = tp->sackblks[i].end;
if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
/*
* Discard this SACK block.
*/
} else if (SEQ_LEQ(head_blk.start, end) &&
SEQ_GEQ(head_blk.end, start)) {
/*
* Merge this SACK block into head_blk.
* This SACK block itself will be discarded.
*/
if (SEQ_GT(head_blk.start, start))
head_blk.start = start;
if (SEQ_LT(head_blk.end, end))
head_blk.end = end;
} else {
/*
* Save this SACK block.
*/
saved_blks[num_saved].start = start;
saved_blks[num_saved].end = end;
num_saved++;
}
}
/*
* Update SACK list in tp->sackblks[].
*/
num_head = 0;
if (SEQ_GT(head_blk.start, tp->rcv_nxt)) {
/*
* The received data segment is an out-of-order segment.
* Put head_blk at the top of SACK list.
*/
tp->sackblks[0] = head_blk;
num_head = 1;
/*
* If the number of saved SACK blocks exceeds its limit,
* discard the last SACK block.
*/
if (num_saved >= MAX_SACK_BLKS)
num_saved--;
}
if (num_saved > 0) {
/*
* Copy the saved SACK blocks back.
*/
bcopy(saved_blks, &tp->sackblks[num_head],
sizeof(struct sackblk) * num_saved);
}
/* Save the number of SACK blocks. */
tp->rcv_numsacks = num_head + num_saved;
}
/*
* Delete all receiver-side SACK information.
*/
void
tcp_clean_sackreport(tp)
struct tcpcb *tp;
{
int i;
INP_LOCK_ASSERT(tp->t_inpcb);
tp->rcv_numsacks = 0;
for (i = 0; i < MAX_SACK_BLKS; i++)
tp->sackblks[i].start = tp->sackblks[i].end=0;
}
/*
* Process the TCP SACK option. Returns 1 if tcp_dooptions() should continue,
* and 0 otherwise, if the option was fine. tp->snd_holes is an ordered list
* of holes (oldest to newest, in terms of the sequence space).
*/
int
tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
{
int tmp_olen;
u_char *tmp_cp;
struct sackhole *cur, *temp;
INP_LOCK_ASSERT(tp->t_inpcb);
if (!tp->sack_enable)
return (1);
if ((th->th_flags & TH_ACK) == 0)
return (1);
/* Note: TCPOLEN_SACK must be 2*sizeof(tcp_seq) */
if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
return (1);
/* If ack is outside [snd_una, snd_max], ignore the SACK options */
if (SEQ_LT(th->th_ack, tp->snd_una) || SEQ_GT(th->th_ack, tp->snd_max))
return (1);
tmp_cp = cp + 2;
tmp_olen = optlen - 2;
tcpstat.tcps_sack_rcv_blocks++;
if (tp->snd_numholes < 0) /* XXX panic? */
tp->snd_numholes = 0;
if (tp->t_maxseg == 0)
panic("tcp_sack_option"); /* Should never happen */
while (tmp_olen > 0) {
struct sackblk sack;
bcopy(tmp_cp, (char *) &(sack.start), sizeof(tcp_seq));
sack.start = ntohl(sack.start);
bcopy(tmp_cp + sizeof(tcp_seq),
(char *) &(sack.end), sizeof(tcp_seq));
sack.end = ntohl(sack.end);
tmp_olen -= TCPOLEN_SACK;
tmp_cp += TCPOLEN_SACK;
if (SEQ_LEQ(sack.end, sack.start))
continue; /* bad SACK fields */
if (SEQ_LEQ(sack.end, tp->snd_una))
continue; /* old block */
if (SEQ_GT(th->th_ack, tp->snd_una)) {
if (SEQ_LT(sack.start, th->th_ack))
continue;
}
if (SEQ_GT(sack.end, tp->snd_max))
continue;
if (TAILQ_EMPTY(&tp->snd_holes)) { /* first hole */
if (tcp_sack_globalholes >= tcp_sack_globalmaxholes ||
tcp_sack_maxholes == 0) {
tcpstat.tcps_sack_sboverflow++;
continue;
}
cur = (struct sackhole *)
uma_zalloc(sack_hole_zone,M_NOWAIT);
if (cur == NULL) {
/* ENOBUFS, so ignore SACKed block for now*/
continue;
}
cur->start = th->th_ack;
cur->end = sack.start;
cur->rxmit = cur->start;
tp->snd_numholes = 1;
tcp_sack_globalholes++;
tp->rcv_lastsack = sack.end;
TAILQ_INSERT_HEAD(&tp->snd_holes, cur, scblink);
continue; /* with next sack block */
}
/* Go thru list of holes. */
cur = TAILQ_FIRST(&tp->snd_holes);
while (cur) {
if (SEQ_LEQ(sack.end, cur->start))
/* SACKs data before the current hole */
break; /* no use going through more holes */
if (SEQ_GEQ(sack.start, cur->end)) {
/* SACKs data beyond the current hole */
cur = TAILQ_NEXT(cur, scblink);
continue;
}
if (SEQ_LEQ(sack.start, cur->start)) {
/* Data acks at least the beginning of hole */
if (SEQ_GEQ(sack.end, cur->end)) {
/* Acks entire hole, so delete hole */
temp = cur;
cur = TAILQ_NEXT(cur, scblink);
TAILQ_REMOVE(&tp->snd_holes,
temp, scblink);
uma_zfree(sack_hole_zone, temp);
tp->snd_numholes--;
tcp_sack_globalholes--;
continue;
}
/* otherwise, move start of hole forward */
cur->start = sack.end;
cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
cur = TAILQ_NEXT(cur, scblink);
continue;
}
/* move end of hole backward */
if (SEQ_GEQ(sack.end, cur->end)) {
cur->end = sack.start;
cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
cur = TAILQ_NEXT(cur, scblink);
continue;
}
if (SEQ_LT(cur->start, sack.start) &&
SEQ_GT(cur->end, sack.end)) {
/*
* ACKs some data in middle of a hole; need to
* split current hole
*/
if (tp->snd_numholes >= tcp_sack_maxholes ||
tcp_sack_globalholes >=
tcp_sack_globalmaxholes) {
tcpstat.tcps_sack_sboverflow++;
continue;
}
temp = (struct sackhole *)
uma_zalloc(sack_hole_zone,M_NOWAIT);
if (temp == NULL)
continue; /* ENOBUFS */
temp->start = sack.end;
temp->end = cur->end;
temp->rxmit = SEQ_MAX(cur->rxmit, temp->start);
cur->end = sack.start;
cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
TAILQ_INSERT_AFTER(&tp->snd_holes,
cur, temp, scblink);
cur = TAILQ_NEXT(temp, scblink);
tp->snd_numholes++;
tcp_sack_globalholes++;
}
}
/* At this point, we are at the tail of the scoreboard. */
if (SEQ_LT(tp->rcv_lastsack, sack.start)) {
/* Need to append new hole at end. */
if (tp->snd_numholes >= tcp_sack_maxholes ||
tcp_sack_globalholes >= tcp_sack_globalmaxholes) {
tcpstat.tcps_sack_sboverflow++;
continue;
}
temp = (struct sackhole *)
uma_zalloc(sack_hole_zone,M_NOWAIT);
if (temp == NULL)
continue; /* ENOBUFS */
temp->start = tp->rcv_lastsack;
temp->end = sack.start;
temp->rxmit = temp->start;
tp->rcv_lastsack = sack.end;
tp->snd_numholes++;
tcp_sack_globalholes++;
TAILQ_INSERT_TAIL(&tp->snd_holes, temp, scblink);
}
if (SEQ_LT(tp->rcv_lastsack, sack.end))
tp->rcv_lastsack = sack.end;
}
return (0);
}
/*
* Delete stale (i.e, cumulatively ack'd) holes. Hole is deleted only if
* it is completely acked; otherwise, tcp_sack_option(), called from
* tcp_dooptions(), will fix up the hole.
*/
void
tcp_del_sackholes(tp, th)
struct tcpcb *tp;
struct tcphdr *th;
{
INP_LOCK_ASSERT(tp->t_inpcb);
if (tp->sack_enable && tp->t_state != TCPS_LISTEN) {
/* max because this could be an older ack just arrived */
tcp_seq lastack = SEQ_GT(th->th_ack, tp->snd_una) ?
th->th_ack : tp->snd_una;
struct sackhole *cur = TAILQ_FIRST(&tp->snd_holes);
struct sackhole *prev;
while (cur)
if (SEQ_LEQ(cur->end, lastack)) {
prev = cur;
cur = TAILQ_NEXT(cur, scblink);
TAILQ_REMOVE(&tp->snd_holes, prev, scblink);
uma_zfree(sack_hole_zone, prev);
tp->snd_numholes--;
tcp_sack_globalholes--;
} else if (SEQ_LT(cur->start, lastack)) {
cur->start = lastack;
if (SEQ_LT(cur->rxmit, cur->start))
cur->rxmit = cur->start;
break;
} else
break;
}
}
void
tcp_free_sackholes(struct tcpcb *tp)
{
struct sackhole *q;
INP_LOCK_ASSERT(tp->t_inpcb);
while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL) {
TAILQ_REMOVE(&tp->snd_holes, q, scblink);
uma_zfree(sack_hole_zone, q);
tcp_sack_globalholes--;
}
tp->snd_numholes = 0;
}
/*
* Partial ack handling within a sack recovery episode.
* Keeping this very simple for now. When a partial ack
* is received, force snd_cwnd to a value that will allow
* the sender to transmit no more than 2 segments.
* If necessary, a better scheme can be adopted at a
* later point, but for now, the goal is to prevent the
* sender from bursting a large amount of data in the midst
* of sack recovery.
*/
void
tcp_sack_partialack(tp, th)
struct tcpcb *tp;
struct tcphdr *th;
{
int num_segs = 1;
int sack_bytes_rxmt = 0;
INP_LOCK_ASSERT(tp->t_inpcb);
callout_stop(tp->tt_rexmt);
tp->t_rtttime = 0;
/* send one or 2 segments based on how much new data was acked */
if (((th->th_ack - tp->snd_una) / tp->t_maxseg) > 2)
num_segs = 2;
(void)tcp_sack_output(tp, &sack_bytes_rxmt);
tp->snd_cwnd = sack_bytes_rxmt + (tp->snd_nxt - tp->sack_newdata) +
num_segs * tp->t_maxseg;
if (tp->snd_cwnd > tp->snd_ssthresh)
tp->snd_cwnd = tp->snd_ssthresh;
tp->t_flags |= TF_ACKNOW;
(void) tcp_output(tp);
}
/*
* Returns pointer to a sackhole if there are any pending retransmissions;
* NULL otherwise.
*/
struct sackhole *
tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
{
struct sackhole *p;
INP_LOCK_ASSERT(tp->t_inpcb);
if (!tp->sack_enable)
return (NULL);
*sack_bytes_rexmt = 0;
TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
if (SEQ_LT(p->rxmit, p->end)) {
if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
continue;
}
*sack_bytes_rexmt += (p->rxmit - p->start);
break;
}
*sack_bytes_rexmt += (p->rxmit - p->start);
}
return (p);
}
/*
* After a timeout, the SACK list may be rebuilt. This SACK information
* should be used to avoid retransmitting SACKed data. This function
* traverses the SACK list to see if snd_nxt should be moved forward.
*/
void
tcp_sack_adjust(struct tcpcb *tp)
{
struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
INP_LOCK_ASSERT(tp->t_inpcb);
if (cur == NULL)
return; /* No holes */
if (SEQ_GEQ(tp->snd_nxt, tp->rcv_lastsack))
return; /* We're already beyond any SACKed blocks */
/*
* Two cases for which we want to advance snd_nxt:
* i) snd_nxt lies between end of one hole and beginning of another
* ii) snd_nxt lies between end of last hole and rcv_lastsack
*/
while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
if (SEQ_LT(tp->snd_nxt, cur->end))
return;
if (SEQ_GEQ(tp->snd_nxt, p->start))
cur = p;
else {
tp->snd_nxt = p->start;
return;
}
}
if (SEQ_LT(tp->snd_nxt, cur->end))
return;
tp->snd_nxt = tp->rcv_lastsack;
return;
}
/*
* Calculate the number of SACKed bytes in the scoreboard by
* subtracting the amount of data accounted for in sackholes
* from the total span of the scoreboard. Also returns the
* amount of data that is "lost" and has not yet been retransmitted.
*/
int
tcp_sacked_bytes(struct tcpcb *tp, int *lost_not_rexmitted)
{
INP_LOCK_ASSERT(tp->t_inpcb);
struct sackhole *cur = TAILQ_FIRST(&tp->snd_holes);
int sacked = 0;
int lost = 0;
if (cur == NULL) /* Scoreboard empty. */
goto out;
if (SEQ_GEQ(tp->snd_una, tp->rcv_lastsack)) /* Scoreboard is stale. */
goto out;
sacked = tp->rcv_lastsack - cur->start;
while (cur) {
lost += (cur->end - cur->rxmit);
sacked -= (cur->end - cur->start);
cur = TAILQ_NEXT(cur, scblink);
}
out:
if (lost_not_rexmitted)
*lost_not_rexmitted = lost;
return (sacked);
}