usr/src/sys/netinet/tcp_timer.c

/*
 * Copyright (c) 1982, 1986, 1988, 1990 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution is only permitted until one year after the first shipment
 * of 4.4BSD by the Regents.  Otherwise, redistribution and use in source and
 * binary forms are permitted provided that: (1) source distributions retain
 * this entire copyright notice and comment, and (2) distributions including
 * binaries display the following acknowledgement:  This product includes
 * software developed by the University of California, Berkeley and its
 * contributors'' in the documentation or other materials provided with the
 * distribution and in all advertising materials mentioning features or use
 * of this software.  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 AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *      @(#)tcp_timer.c 7.18 (Berkeley) 6/28/90
 */

#include "param.h"
#include "systm.h"
#include "malloc.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 "in.h"
#include "in_systm.h"
#include "ip.h"
#include "in_pcb.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     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 ((int)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, tp->t_softerror ?
                            tp->t_softerror : ETIMEDOUT);
                        break;
                }
                tcpstat.tcps_rexmttimeo++;
                rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
                TCPT_RANGESET(tp->t_rxtcur, rexmt,
                    tp->t_rttmin, 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) {
                        in_losing(tp->t_inpcb);
                        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 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;
                tp->t_dupacks = 0;
                }
                (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, (struct mbuf *)NULL,
                            tp->rcv_nxt - 1, tp->snd_una - 1, 0);
#else
                        tcp_respond(tp, tp->t_template, (struct mbuf *)NULL,
                            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);
}