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NetBSD/sys/netinet/tcp_subr.c

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/* $NetBSD: tcp_subr.c,v 1.32 1997/10/18 21:18:33 kml Exp $ */
/*
* Copyright (c) 1982, 1986, 1988, 1990, 1993
* 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. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 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_subr.c 8.1 (Berkeley) 6/10/93
*/
#include "rnd.h"
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/errno.h>
#include <sys/kernel.h>
#if NRND > 0
#include <sys/rnd.h>
#endif
#include <net/route.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip_icmp.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 <netinet/tcpip.h>
/* patchable/settable parameters for tcp */
int tcp_mssdflt = TCP_MSS;
int tcp_rttdflt = TCPTV_SRTTDFLT / PR_SLOWHZ;
int tcp_do_rfc1323 = 1;
#ifndef TCBHASHSIZE
#define TCBHASHSIZE 128
#endif
int tcbhashsize = TCBHASHSIZE;
/*
* Tcp initialization
*/
void
tcp_init()
{
in_pcbinit(&tcbtable, tcbhashsize, tcbhashsize);
if (max_protohdr < sizeof(struct tcpiphdr))
max_protohdr = sizeof(struct tcpiphdr);
if (max_linkhdr + sizeof(struct tcpiphdr) > MHLEN)
panic("tcp_init");
}
/*
* Create template to be used to send tcp packets on a connection.
* Call after host entry created, allocates an mbuf and fills
* in a skeletal tcp/ip header, minimizing the amount of work
* necessary when the connection is used.
*/
struct tcpiphdr *
tcp_template(tp)
struct tcpcb *tp;
{
register struct inpcb *inp = tp->t_inpcb;
register struct tcpiphdr *n;
if ((n = tp->t_template) == 0) {
MALLOC(n, struct tcpiphdr *, sizeof (struct tcpiphdr),
M_MBUF, M_NOWAIT);
if (n == NULL)
return (0);
}
bzero(n->ti_x1, sizeof n->ti_x1);
n->ti_pr = IPPROTO_TCP;
n->ti_len = htons(sizeof (struct tcpiphdr) - sizeof (struct ip));
n->ti_src = inp->inp_laddr;
n->ti_dst = inp->inp_faddr;
n->ti_sport = inp->inp_lport;
n->ti_dport = inp->inp_fport;
n->ti_seq = 0;
n->ti_ack = 0;
n->ti_x2 = 0;
n->ti_off = 5;
n->ti_flags = 0;
n->ti_win = 0;
n->ti_sum = 0;
n->ti_urp = 0;
return (n);
}
/*
* Send a single message to the TCP at address specified by
* the given TCP/IP header. If m == 0, then we make a copy
* of the tcpiphdr at ti and send directly to the addressed host.
* This is used to force keep alive messages out using the TCP
* template for a connection tp->t_template. If flags are given
* then we send a message back to the TCP which originated the
* segment ti, and discard the mbuf containing it and any other
* attached mbufs.
*
* In any case the ack and sequence number of the transmitted
* segment are as specified by the parameters.
*/
int
tcp_respond(tp, ti, m, ack, seq, flags)
struct tcpcb *tp;
register struct tcpiphdr *ti;
register struct mbuf *m;
tcp_seq ack, seq;
int flags;
{
register int tlen;
int win = 0;
struct route *ro = 0;
if (tp) {
win = sbspace(&tp->t_inpcb->inp_socket->so_rcv);
ro = &tp->t_inpcb->inp_route;
}
if (m == 0) {
m = m_gethdr(M_DONTWAIT, MT_HEADER);
if (m == NULL)
return (ENOBUFS);
#ifdef TCP_COMPAT_42
tlen = 1;
#else
tlen = 0;
#endif
m->m_data += max_linkhdr;
*mtod(m, struct tcpiphdr *) = *ti;
ti = mtod(m, struct tcpiphdr *);
flags = TH_ACK;
} else {
m_freem(m->m_next);
m->m_next = 0;
m->m_data = (caddr_t)ti;
m->m_len = sizeof (struct tcpiphdr);
tlen = 0;
#define xchg(a,b,type) { type t; t=a; a=b; b=t; }
xchg(ti->ti_dst.s_addr, ti->ti_src.s_addr, u_int32_t);
xchg(ti->ti_dport, ti->ti_sport, u_int16_t);
#undef xchg
}
bzero(ti->ti_x1, sizeof ti->ti_x1);
ti->ti_seq = htonl(seq);
ti->ti_ack = htonl(ack);
ti->ti_x2 = 0;
if ((flags & TH_SYN) == 0) {
if (tp)
ti->ti_win = htons((u_int16_t) (win >> tp->rcv_scale));
else
ti->ti_win = htons((u_int16_t)win);
ti->ti_off = sizeof (struct tcphdr) >> 2;
tlen += sizeof (struct tcphdr);
} else
tlen += ti->ti_off << 2;
ti->ti_len = htons((u_int16_t)tlen);
tlen += sizeof (struct ip);
m->m_len = tlen;
m->m_pkthdr.len = tlen;
m->m_pkthdr.rcvif = (struct ifnet *) 0;
ti->ti_flags = flags;
ti->ti_urp = 0;
ti->ti_sum = 0;
ti->ti_sum = in_cksum(m, tlen);
((struct ip *)ti)->ip_len = tlen;
((struct ip *)ti)->ip_ttl = ip_defttl;
return ip_output(m, NULL, ro, 0, NULL);
}
/*
* Create a new TCP control block, making an
* empty reassembly queue and hooking it to the argument
* protocol control block.
*/
struct tcpcb *
tcp_newtcpcb(inp)
struct inpcb *inp;
{
register struct tcpcb *tp;
tp = malloc(sizeof(*tp), M_PCB, M_NOWAIT);
if (tp == NULL)
return ((struct tcpcb *)0);
bzero((caddr_t)tp, sizeof(struct tcpcb));
LIST_INIT(&tp->segq);
tp->t_maxseg = tcp_mssdflt;
tp->t_ourmss = tcp_mssdflt;
tp->t_flags = tcp_do_rfc1323 ? (TF_REQ_SCALE|TF_REQ_TSTMP) : 0;
tp->t_inpcb = inp;
/*
* Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
* rtt estimate. Set rttvar so that srtt + 2 * rttvar gives
* reasonable initial retransmit time.
*/
tp->t_srtt = TCPTV_SRTTBASE;
tp->t_rttvar = tcp_rttdflt * PR_SLOWHZ << (TCP_RTTVAR_SHIFT + 2 - 1);
tp->t_rttmin = TCPTV_MIN;
TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
TCPTV_MIN, TCPTV_REXMTMAX);
tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT;
tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
inp->inp_ip.ip_ttl = ip_defttl;
inp->inp_ppcb = (caddr_t)tp;
return (tp);
}
/*
* Drop a TCP connection, reporting
* the specified error. If connection is synchronized,
* then send a RST to peer.
*/
struct tcpcb *
tcp_drop(tp, errno)
register struct tcpcb *tp;
int errno;
{
struct socket *so = tp->t_inpcb->inp_socket;
if (TCPS_HAVERCVDSYN(tp->t_state)) {
tp->t_state = TCPS_CLOSED;
(void) tcp_output(tp);
tcpstat.tcps_drops++;
} else
tcpstat.tcps_conndrops++;
if (errno == ETIMEDOUT && tp->t_softerror)
errno = tp->t_softerror;
so->so_error = errno;
return (tcp_close(tp));
}
/*
* Close a TCP control block:
* discard all space held by the tcp
* discard internet protocol block
* wake up any sleepers
*/
struct tcpcb *
tcp_close(tp)
register struct tcpcb *tp;
{
register struct ipqent *qe;
struct inpcb *inp = tp->t_inpcb;
struct socket *so = inp->inp_socket;
#ifdef RTV_RTT
register struct rtentry *rt;
/*
* If we sent enough data to get some meaningful characteristics,
* save them in the routing entry. 'Enough' is arbitrarily
* defined as the sendpipesize (default 4K) * 16. This would
* give us 16 rtt samples assuming we only get one sample per
* window (the usual case on a long haul net). 16 samples is
* enough for the srtt filter to converge to within 5% of the correct
* value; fewer samples and we could save a very bogus rtt.
*
* Don't update the default route's characteristics and don't
* update anything that the user "locked".
*/
if (SEQ_LT(tp->iss + so->so_snd.sb_hiwat * 16, tp->snd_max) &&
(rt = inp->inp_route.ro_rt) &&
!in_nullhost(satosin(rt_key(rt))->sin_addr)) {
register u_long i = 0;
if ((rt->rt_rmx.rmx_locks & RTV_RTT) == 0) {
i = tp->t_srtt *
((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTT_SHIFT + 2));
if (rt->rt_rmx.rmx_rtt && i)
/*
* filter this update to half the old & half
* the new values, converting scale.
* See route.h and tcp_var.h for a
* description of the scaling constants.
*/
rt->rt_rmx.rmx_rtt =
(rt->rt_rmx.rmx_rtt + i) / 2;
else
rt->rt_rmx.rmx_rtt = i;
}
if ((rt->rt_rmx.rmx_locks & RTV_RTTVAR) == 0) {
i = tp->t_rttvar *
((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTTVAR_SHIFT + 2));
if (rt->rt_rmx.rmx_rttvar && i)
rt->rt_rmx.rmx_rttvar =
(rt->rt_rmx.rmx_rttvar + i) / 2;
else
rt->rt_rmx.rmx_rttvar = i;
}
/*
* update the pipelimit (ssthresh) if it has been updated
* already or if a pipesize was specified & the threshhold
* got below half the pipesize. I.e., wait for bad news
* before we start updating, then update on both good
* and bad news.
*/
if (((rt->rt_rmx.rmx_locks & RTV_SSTHRESH) == 0 &&
(i = tp->snd_ssthresh) && rt->rt_rmx.rmx_ssthresh) ||
i < (rt->rt_rmx.rmx_sendpipe / 2)) {
/*
* convert the limit from user data bytes to
* packets then to packet data bytes.
*/
i = (i + tp->t_maxseg / 2) / tp->t_maxseg;
if (i < 2)
i = 2;
i *= (u_long)(tp->t_maxseg + sizeof (struct tcpiphdr));
if (rt->rt_rmx.rmx_ssthresh)
rt->rt_rmx.rmx_ssthresh =
(rt->rt_rmx.rmx_ssthresh + i) / 2;
else
rt->rt_rmx.rmx_ssthresh = i;
}
}
#endif /* RTV_RTT */
/* free the reassembly queue, if any */
while ((qe = tp->segq.lh_first) != NULL) {
LIST_REMOVE(qe, ipqe_q);
m_freem(qe->ipqe_m);
FREE(qe, M_IPQ);
}
if (tp->t_template)
FREE(tp->t_template, M_MBUF);
free(tp, M_PCB);
inp->inp_ppcb = 0;
soisdisconnected(so);
in_pcbdetach(inp);
tcpstat.tcps_closed++;
return ((struct tcpcb *)0);
}
void
tcp_drain()
{
}
/*
* Notify a tcp user of an asynchronous error;
* store error as soft error, but wake up user
* (for now, won't do anything until can select for soft error).
*/
void
tcp_notify(inp, error)
struct inpcb *inp;
int error;
{
register struct tcpcb *tp = (struct tcpcb *)inp->inp_ppcb;
register struct socket *so = inp->inp_socket;
/*
* Ignore some errors if we are hooked up.
* If connection hasn't completed, has retransmitted several times,
* and receives a second error, give up now. This is better
* than waiting a long time to establish a connection that
* can never complete.
*/
if (tp->t_state == TCPS_ESTABLISHED &&
(error == EHOSTUNREACH || error == ENETUNREACH ||
error == EHOSTDOWN)) {
return;
} else if (TCPS_HAVEESTABLISHED(tp->t_state) == 0 &&
tp->t_rxtshift > 3 && tp->t_softerror)
so->so_error = error;
else
tp->t_softerror = error;
wakeup((caddr_t) &so->so_timeo);
sorwakeup(so);
sowwakeup(so);
}
void *
tcp_ctlinput(cmd, sa, v)
int cmd;
struct sockaddr *sa;
register void *v;
{
register struct ip *ip = v;
register struct tcphdr *th;
extern int inetctlerrmap[];
void (*notify) __P((struct inpcb *, int)) = tcp_notify;
int errno;
int nmatch;
if ((unsigned)cmd >= PRC_NCMDS)
return NULL;
errno = inetctlerrmap[cmd];
if (cmd == PRC_QUENCH)
notify = tcp_quench;
else if (PRC_IS_REDIRECT(cmd))
notify = in_rtchange, ip = 0;
else if (cmd == PRC_MSGSIZE && ip_mtudisc)
notify = tcp_mtudisc, ip = 0;
else if (cmd == PRC_HOSTDEAD)
ip = 0;
else if (errno == 0)
return NULL;
if (ip) {
th = (struct tcphdr *)((caddr_t)ip + (ip->ip_hl << 2));
nmatch = in_pcbnotify(&tcbtable, satosin(sa)->sin_addr,
th->th_dport, ip->ip_src, th->th_sport, errno, notify);
if (nmatch == 0 && syn_cache_count &&
(inetctlerrmap[cmd] == EHOSTUNREACH ||
inetctlerrmap[cmd] == ENETUNREACH ||
inetctlerrmap[cmd] == EHOSTDOWN))
syn_cache_unreach(ip, th);
} else
(void)in_pcbnotifyall(&tcbtable, satosin(sa)->sin_addr, errno,
notify);
return NULL;
}
/*
* When a source quench is received, close congestion window
* to one segment. We will gradually open it again as we proceed.
*/
void
tcp_quench(inp, errno)
struct inpcb *inp;
int errno;
{
struct tcpcb *tp = intotcpcb(inp);
if (tp)
tp->snd_cwnd = tp->t_maxseg;
}
/*
* On receipt of path MTU corrections, flush old route and replace it
* with the new one. Retransmit all unacknowledged packets, to ensure
* that all packets will be received.
*/
void
tcp_mtudisc(inp, errno)
struct inpcb *inp;
int errno;
{
struct tcpcb *tp = intotcpcb(inp);
struct rtentry *rt = in_pcbrtentry(inp);
if (tp != 0) {
if (rt != 0) {
/* If this was not a host route, remove and realloc */
if ((rt->rt_flags & RTF_HOST) == 0) {
in_rtchange(inp, errno);
rtfree(rt);
if ((rt = in_pcbrtentry(inp)) == 0)
return;
}
}
/* Resend unacknowledged packets: */
tp->snd_nxt = tp->snd_una;
tcp_output(tp);
}
}
/*
* Compute the MSS to advertise to the peer. Called only during
* the 3-way handshake. If we are the server (peer initiated
* connection), we are called with the TCPCB for the listen
* socket. If we are the client (we initiated connection), we
* are called witht he TCPCB for the actual connection.
*/
int
tcp_mss_to_advertise(tp)
const struct tcpcb *tp;
{
extern u_long in_maxmtu;
struct inpcb *inp;
struct socket *so;
int mss;
inp = tp->t_inpcb;
so = inp->inp_socket;
/*
* In order to avoid defeating path MTU discovery on the peer,
* we advertise the max MTU of all attached networks as our MSS,
* per RFC 1191, section 3.1.
*
* XXX Should we allow room for the timestamp option if
* XXX rfc1323 is enabled?
*/
mss = in_maxmtu - sizeof(struct tcpiphdr);
return (mss);
}
/*
* Set connection variables based on the peer's advertised MSS.
* We are passed the TCPCB for the actual connection. If we
* are the server, we are called by the compressed state engine
* when the 3-way handshake is complete. If we are the client,
* we are called when we recieve the SYN,ACK from the server.
*
* NOTE: Our advertised MSS value must be initialized in the TCPCB
* before this routine is called!
*/
void
tcp_mss_from_peer(tp, offer)
struct tcpcb *tp;
int offer;
{
struct inpcb *inp = tp->t_inpcb;
struct socket *so = inp->inp_socket;
#if defined(RTV_SPIPE) || defined(RTV_SSTHRESH)
struct rtentry *rt = in_pcbrtentry(inp);
#endif
u_long bufsize;
int mss;
/*
* Assume our MSS is the MSS of the peer, unless they sent us
* an offer. Do not accept offers less than 32 bytes.
*/
mss = tp->t_ourmss;
if (offer)
mss = offer;
mss = max(mss, 32); /* sanity */
/*
* If there's a pipesize, change the socket buffer to that size.
* Make the socket buffer an integral number of MSS units. If
* the MSS is larger than the socket buffer, artificially decrease
* the MSS.
*/
#ifdef RTV_SPIPE
if (rt != NULL && rt->rt_rmx.rmx_sendpipe != 0)
bufsize = rt->rt_rmx.rmx_sendpipe;
else
#endif
bufsize = so->so_snd.sb_hiwat;
if (bufsize < mss)
mss = bufsize;
else {
bufsize = roundup(bufsize, mss);
if (bufsize > sb_max)
bufsize = sb_max;
(void) sbreserve(&so->so_snd, bufsize);
}
tp->t_maxseg = mss;
/* Initialize the initial congestion window. */
tp->snd_cwnd = mss;
#ifdef RTV_SSTHRESH
if (rt != NULL && rt->rt_rmx.rmx_ssthresh) {
/*
* There's some sort of gateway or interface buffer
* limit on the path. Use this to set the slow
* start threshold, but set the threshold to no less
* than 2 * MSS.
*/
tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
}
#endif
}
/*
* Processing necessary when a TCP connection is established.
*/
void
tcp_established(tp)
struct tcpcb *tp;
{
struct inpcb *inp = tp->t_inpcb;
struct socket *so = inp->inp_socket;
#ifdef RTV_RPIPE
struct rtentry *rt = in_pcbrtentry(inp);
#endif
u_long bufsize;
tp->t_state = TCPS_ESTABLISHED;
tp->t_timer[TCPT_KEEP] = tcp_keepidle;
#ifdef RTV_RPIPE
if (rt != NULL && rt->rt_rmx.rmx_recvpipe != 0)
bufsize = rt->rt_rmx.rmx_recvpipe;
else
#endif
bufsize = so->so_rcv.sb_hiwat;
if (bufsize > tp->t_ourmss) {
bufsize = roundup(bufsize, tp->t_ourmss);
if (bufsize > sb_max)
bufsize = sb_max;
(void) sbreserve(&so->so_rcv, bufsize);
}
}
/*
* Check if there's an initial rtt or rttvar. Convert from the
* route-table units to scaled multiples of the slow timeout timer.
* Called only during the 3-way handshake.
*/
void
tcp_rmx_rtt(tp)
struct tcpcb *tp;
{
#ifdef RTV_RTT
struct rtentry *rt;
int rtt;
if ((rt = in_pcbrtentry(tp->t_inpcb)) == NULL)
return;
if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
/*
* XXX The lock bit for MTU indicates that the value
* is also a minimum value; this is subject to time.
*/
if (rt->rt_rmx.rmx_locks & RTV_RTT)
tp->t_rttmin = rtt / (RTM_RTTUNIT / PR_SLOWHZ);
tp->t_srtt = rtt /
((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTT_SHIFT + 2));
if (rt->rt_rmx.rmx_rttvar) {
tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
((RTM_RTTUNIT / PR_SLOWHZ) >>
(TCP_RTTVAR_SHIFT + 2));
} else {
/* Default variation is +- 1 rtt */
tp->t_rttvar =
tp->t_srtt >> (TCP_RTT_SHIFT - TCP_RTTVAR_SHIFT);
}
TCPT_RANGESET(tp->t_rxtcur,
((tp->t_srtt >> 2) + tp->t_rttvar) >> (1 + 2),
tp->t_rttmin, TCPTV_REXMTMAX);
}
#endif
}
tcp_seq tcp_iss_seq = 0; /* tcp initial seq # */
/*
* Get a new sequence value given a tcp control block
*/
tcp_seq
tcp_new_iss(tp, len, addin)
void *tp;
u_long len;
tcp_seq addin;
{
tcp_seq tcp_iss;
/*
* add randomness about this connection, but do not estimate
* entropy from the timing, since the physical device driver would
* have done that for us.
*/
#if NRND > 0
if (tp != NULL)
rnd_add_data(NULL, tp, len, 0);
#endif
/*
* randomize.
*/
#if NRND > 0
rnd_extract_data(&tcp_iss, sizeof(tcp_iss), RND_EXTRACT_ANY);
#else
tcp_iss = random();
#endif
/*
* If we were asked to add some amount to a known value,
* we will take a random value obtained above, mask off the upper
* bits, and add in the known value. We also add in a constant to
* ensure that we are at least a certain distance from the original
* value.
*
* This is used when an old connection is in timed wait
* and we have a new one coming in, for instance.
*/
if (addin != 0) {
#ifdef TCPISS_DEBUG
printf("Random %08x, ", tcp_iss);
#endif
tcp_iss &= TCP_ISS_RANDOM_MASK;
tcp_iss = tcp_iss + addin + TCP_ISSINCR;
tcp_iss_seq += TCP_ISSINCR;
tcp_iss += tcp_iss_seq;
#ifdef TCPISS_DEBUG
printf("Old ISS %08x, ISS %08x\n", addin, tcp_iss);
#endif
} else {
tcp_iss &= TCP_ISS_RANDOM_MASK;
tcp_iss_seq += TCP_ISSINCR;
tcp_iss += tcp_iss_seq;
#ifdef TCPISS_DEBUG
printf("ISS %08x\n", tcp_iss);
#endif
}
#ifdef TCP_COMPAT_42
/*
* limit it to the positive range for really old TCP implementations
*/
if ((int)tcp_iss < 0)
tcp_iss &= 0x7fffffff; /* XXX */
#endif
return tcp_iss;
}
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