2.11BSD/sys/netinet/tcp_timer.c
/*
* Copyright (c) 1982, 1986 Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that this notice is preserved and that due credit is given
* to the University of California at Berkeley. The name of the University
* may not be used to endorse or promote products derived from this
* software without specific prior written permission. This software
* is provided ``as is'' without express or implied warranty.
*
* @(#)tcp_timer.c 7.11.1.2 (Berkeley) 3/16/88
*/
#include "param.h"
#include "systm.h"
#include "mbuf.h"
#include "socket.h"
#include "socketvar.h"
#include "protosw.h"
#include "errno.h"
#include "../net/if.h"
#include "../net/route.h"
#include "domain.h"
#include "in.h"
#include "in_pcb.h"
#include "in_systm.h"
#include "ip.h"
#include "ip_var.h"
#include "tcp.h"
#include "tcp_fsm.h"
#include "tcp_seq.h"
#include "tcp_timer.h"
#include "tcp_var.h"
#include "tcpip.h"
int tcpnodelack = 0;
int tcp_keepidle = TCPTV_KEEP_IDLE;
int tcp_keepintvl = TCPTV_KEEPINTVL;
int tcp_maxidle;
/*
* Fast timeout routine for processing delayed acks
*/
tcp_fasttimo()
{
register struct inpcb *inp;
register struct tcpcb *tp;
int s = splnet();
inp = tcb.inp_next;
if (inp)
for (; inp != &tcb; inp = inp->inp_next)
if ((tp = (struct tcpcb *)inp->inp_ppcb) &&
(tp->t_flags & TF_DELACK)) {
tp->t_flags &= ~TF_DELACK;
tp->t_flags |= TF_ACKNOW;
tcpstat.tcps_delack++;
(void) tcp_output(tp);
}
splx(s);
}
/*
* 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.
*/
tcp_slowtimo()
{
register struct inpcb *ip, *ipnxt;
register struct tcpcb *tp;
int s = splnet();
register int i;
tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl;
/*
* Search through tcb's and update active timers.
*/
ip = tcb.inp_next;
if (ip == 0) {
splx(s);
return;
}
for (; ip != &tcb; ip = ipnxt) {
ipnxt = ip->inp_next;
tp = intotcpcb(ip);
if (tp == 0)
continue;
for (i = 0; i < TCPT_NTIMERS; i++) {
if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
(void) tcp_usrreq(tp->t_inpcb->inp_socket,
PRU_SLOWTIMO, (struct mbuf *)0,
(struct mbuf *)i, (struct mbuf *)0);
if (ipnxt->inp_prev != ip)
goto tpgone;
}
}
tp->t_idle++;
if (tp->t_rtt)
tp->t_rtt++;
tpgone:
;
}
tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */
#ifdef TCP_COMPAT_42
if ((long)tcp_iss < 0)
tcp_iss = 0; /* XXX */
#endif
splx(s);
}
/*
* Cancel all timers for TCP tp.
*/
tcp_canceltimers(tp)
struct tcpcb *tp;
{
register int i;
for (i = 0; i < TCPT_NTIMERS; i++)
tp->t_timer[i] = 0;
}
int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
{ 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
/*
* TCP timer processing.
*/
struct tcpcb *
tcp_timers(tp, timer)
register struct tcpcb *tp;
int timer;
{
register int rexmt;
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] = tcp_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:
if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
tp->t_rxtshift = TCP_MAXRXTSHIFT;
tcpstat.tcps_timeoutdrop++;
tp = tcp_drop(tp, ETIMEDOUT);
break;
}
tcpstat.tcps_rexmttimeo++;
rexmt = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
rexmt *= tcp_backoff[tp->t_rxtshift];
TCPT_RANGESET(tp->t_rxtcur, rexmt, TCPTV_MIN, TCPTV_REXMTMAX);
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) {
#if BSD>=43
in_losing(tp->t_inpcb);
#endif
tp->t_rttvar += (tp->t_srtt >> 2);
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 threshhold size.
* For a threshhold, 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 threshhold
* 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;
}
(void) tcp_output(tp);
break;
/*
* Persistance timer into zero window.
* Force a byte to be output, if possible.
*/
case TCPT_PERSIST:
tcpstat.tcps_persisttimeo++;
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:
tcpstat.tcps_keeptimeo++;
if (tp->t_state < TCPS_ESTABLISHED)
goto dropit;
if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE &&
tp->t_state <= TCPS_CLOSE_WAIT) {
if (tp->t_idle >= tcp_keepidle + 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.
*/
tcpstat.tcps_keepprobe++;
#ifdef TCP_COMPAT_42
/*
* The keepalive packet must have nonzero length
* to get a 4.2 host to respond.
*/
tcp_respond(tp, tp->t_template,
tp->rcv_nxt - 1, tp->snd_una - 1, 0);
#else
tcp_respond(tp, tp->t_template,
tp->rcv_nxt, tp->snd_una - 1, 0);
#endif
tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
} else
tp->t_timer[TCPT_KEEP] = tcp_keepidle;
break;
dropit:
tcpstat.tcps_keepdrops++;
tp = tcp_drop(tp, ETIMEDOUT);
break;
}
return (tp);
}