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Emile Clark-Boman 2025-07-22 02:42:34 +10:00
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/*
* 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. 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_timer.c 8.1 (Berkeley) 6/10/93
* tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
*/
#include "slirp.h"
static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);
/*
* Fast timeout routine for processing delayed acks
*/
void
tcp_fasttimo(Slirp *slirp)
{
register struct socket *so;
register struct tcpcb *tp;
DEBUG_CALL("tcp_fasttimo");
so = slirp->tcb.so_next;
if (so)
for (; so != &slirp->tcb; so = so->so_next)
if ((tp = (struct tcpcb *)so->so_tcpcb) &&
(tp->t_flags & TF_DELACK)) {
tp->t_flags &= ~TF_DELACK;
tp->t_flags |= TF_ACKNOW;
(void) tcp_output(tp);
}
}
/*
* Tcp protocol timeout routine called every 500 ms.
* Updates the timers in all active tcb's and
* causes finite state machine actions if timers expire.
*/
void
tcp_slowtimo(Slirp *slirp)
{
register struct socket *ip, *ipnxt;
register struct tcpcb *tp;
register int i;
DEBUG_CALL("tcp_slowtimo");
/*
* Search through tcb's and update active timers.
*/
ip = slirp->tcb.so_next;
if (ip == NULL) {
return;
}
for (; ip != &slirp->tcb; ip = ipnxt) {
ipnxt = ip->so_next;
tp = sototcpcb(ip);
if (tp == NULL) {
continue;
}
for (i = 0; i < TCPT_NTIMERS; i++) {
if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
tcp_timers(tp,i);
if (ipnxt->so_prev != ip)
goto tpgone;
}
}
tp->t_idle++;
if (tp->t_rtt)
tp->t_rtt++;
tpgone:
;
}
slirp->tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */
slirp->tcp_now++; /* for timestamps */
}
/*
* Cancel all timers for TCP tp.
*/
void
tcp_canceltimers(struct tcpcb *tp)
{
register int i;
for (i = 0; i < TCPT_NTIMERS; i++)
tp->t_timer[i] = 0;
}
const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
{ 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
/*
* TCP timer processing.
*/
static struct tcpcb *
tcp_timers(register struct tcpcb *tp, int timer)
{
register int rexmt;
DEBUG_CALL("tcp_timers");
switch (timer) {
/*
* 2 MSL timeout in shutdown went off. If we're closed but
* still waiting for peer to close and connection has been idle
* too long, or if 2MSL time is up from TIME_WAIT, delete connection
* control block. Otherwise, check again in a bit.
*/
case TCPT_2MSL:
if (tp->t_state != TCPS_TIME_WAIT &&
tp->t_idle <= TCP_MAXIDLE)
tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;
else
tp = tcp_close(tp);
break;
/*
* Retransmission timer went off. Message has not
* been acked within retransmit interval. Back off
* to a longer retransmit interval and retransmit one segment.
*/
case TCPT_REXMT:
/*
* XXXXX If a packet has timed out, then remove all the queued
* packets for that session.
*/
if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
/*
* This is a hack to suit our terminal server here at the uni of canberra
* since they have trouble with zeroes... It usually lets them through
* unharmed, but under some conditions, it'll eat the zeros. If we
* keep retransmitting it, it'll keep eating the zeroes, so we keep
* retransmitting, and eventually the connection dies...
* (this only happens on incoming data)
*
* So, if we were gonna drop the connection from too many retransmits,
* don't... instead halve the t_maxseg, which might break up the NULLs and
* let them through
*
* *sigh*
*/
tp->t_maxseg >>= 1;
if (tp->t_maxseg < 32) {
/*
* We tried our best, now the connection must die!
*/
tp->t_rxtshift = TCP_MAXRXTSHIFT;
tp = tcp_drop(tp, tp->t_softerror);
/* tp->t_softerror : ETIMEDOUT); */ /* XXX */
return (tp); /* XXX */
}
/*
* Set rxtshift to 6, which is still at the maximum
* backoff time
*/
tp->t_rxtshift = 6;
}
rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
TCPT_RANGESET(tp->t_rxtcur, rexmt,
(short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
/*
* If losing, let the lower level know and try for
* a better route. Also, if we backed off this far,
* our srtt estimate is probably bogus. Clobber it
* so we'll take the next rtt measurement as our srtt;
* move the current srtt into rttvar to keep the current
* retransmit times until then.
*/
if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
tp->t_srtt = 0;
}
tp->snd_nxt = tp->snd_una;
/*
* If timing a segment in this window, stop the timer.
*/
tp->t_rtt = 0;
/*
* Close the congestion window down to one segment
* (we'll open it by one segment for each ack we get).
* Since we probably have a window's worth of unacked
* data accumulated, this "slow start" keeps us from
* dumping all that data as back-to-back packets (which
* might overwhelm an intermediate gateway).
*
* There are two phases to the opening: Initially we
* open by one mss on each ack. This makes the window
* size increase exponentially with time. If the
* window is larger than the path can handle, this
* exponential growth results in dropped packet(s)
* almost immediately. To get more time between
* drops but still "push" the network to take advantage
* of improving conditions, we switch from exponential
* to linear window opening at some threshold size.
* For a threshold, we use half the current window
* size, truncated to a multiple of the mss.
*
* (the minimum cwnd that will give us exponential
* growth is 2 mss. We don't allow the threshold
* to go below this.)
*/
{
u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
if (win < 2)
win = 2;
tp->snd_cwnd = tp->t_maxseg;
tp->snd_ssthresh = win * tp->t_maxseg;
tp->t_dupacks = 0;
}
(void) tcp_output(tp);
break;
/*
* Persistence timer into zero window.
* Force a byte to be output, if possible.
*/
case TCPT_PERSIST:
tcp_setpersist(tp);
tp->t_force = 1;
(void) tcp_output(tp);
tp->t_force = 0;
break;
/*
* Keep-alive timer went off; send something
* or drop connection if idle for too long.
*/
case TCPT_KEEP:
if (tp->t_state < TCPS_ESTABLISHED)
goto dropit;
if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {
if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)
goto dropit;
/*
* Send a packet designed to force a response
* if the peer is up and reachable:
* either an ACK if the connection is still alive,
* or an RST if the peer has closed the connection
* due to timeout or reboot.
* Using sequence number tp->snd_una-1
* causes the transmitted zero-length segment
* to lie outside the receive window;
* by the protocol spec, this requires the
* correspondent TCP to respond.
*/
tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
tp->rcv_nxt, tp->snd_una - 1, 0);
tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
} else
tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
break;
dropit:
tp = tcp_drop(tp, 0);
break;
}
return (tp);
}