source: vbox/trunk/src/VBox/Devices/Network/slirp/tcp_timer.c

/* $Id: tcp_timer.c 98103 2023-01-17 14:15:46Z vboxsync $ */
/** @file
 * NAT - TCP timers.
 */

/*
 * Copyright (C) 2006-2023 Oracle and/or its affiliates.
 *
 * This file is part of VirtualBox base platform packages, as
 * available from https://www.virtualbox.org.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation, in version 3 of the
 * License.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <https://www.gnu.org/licenses>.
 *
 * SPDX-License-Identifier: GPL-3.0-only
 */

/*
 * This code is based on:
 *
 * 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(PNATState pData, register struct tcpcb *tp, int timer);
/*
 * Fast timeout routine for processing delayed acks
 */
void
tcp_fasttimo(PNATState pData)
{
    register struct socket *so, *so_next;
    register struct tcpcb *tp;

    LogFlowFuncEnter();

    so = tcb.so_next;
    if (so)
        QSOCKET_FOREACH (so, so_next, tcp)
        /* { */
            if (   (tp = (struct tcpcb *)so->so_tcpcb)
                && (tp->t_flags & TF_DELACK))
            {
                tp->t_flags &= ~TF_DELACK;
                tp->t_flags |= TF_ACKNOW;
                tcpstat.tcps_delack++;
                TCP_OUTPUT(pData, tp);
            }
        LOOP_LABEL(tcp, so, so_next);
        }
}

/*
 * 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(PNATState pData)
{
    register struct socket *ip, *ipnxt;
    register struct tcpcb *tp;
    register int i;

    LogFlowFuncEnter();

    /*
     * Search through tcb's and update active timers.
     */
    ip = tcb.so_next;
    if (ip == 0)
        return;
    QSOCKET_FOREACH(ip, ipnxt, tcp)
    /* { */
        ipnxt = ip->so_next;
        tp = sototcpcb(ip);
        if (tp == 0)
            CONTINUE(tcp);
        for (i = 0; i < TCPT_NTIMERS; i++)
        {
            if (tp->t_timer[i] && --tp->t_timer[i] == 0)
            {
                tcp_timers(pData, tp, i);
                if (ipnxt->so_prev != ip)
                    goto tpgone;
            }
        }
        tp->t_idle++;
        if (tp->t_rtt)
            tp->t_rtt++;
tpgone:
        ;
    LOOP_LABEL(tcp, ip, ipnxt);
    }
    tcp_iss += TCP_ISSINCR / PR_SLOWHZ;         /* increment iss */
#ifdef TCP_COMPAT_42
    if ((int)tcp_iss < 0)
        tcp_iss = 0;                            /* XXX */
#endif
    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(PNATState pData, register struct tcpcb *tp, int timer)
{
    register int rexmt;
    int fUninitializedTemplate = 0;

    LogFlowFunc(("ENTER: tp:%R[tcpcb793], timer:%d\n", tp, timer));
    fUninitializedTemplate = RT_BOOL((   tp->t_template.ti_src.s_addr == INADDR_ANY
                                      || tp->t_template.ti_dst.s_addr == INADDR_ANY));
    if (fUninitializedTemplate)
    {
        tp = tcp_drop(pData, tp, 0);
        return tp;
    }

    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(pData, 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:
            STAM_COUNTER_INC(&pData->StatTCP_retransmit);
            /*
             * XXX 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;
                    tcpstat.tcps_timeoutdrop++;
                    tp = tcp_drop(pData, 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;
            }
            tcpstat.tcps_rexmttimeo++;
            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)
            {
/*              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 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(pData, tp);
            break;

        /*
         * Persistence 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(pData, 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_socket->so_options & SO_KEEPALIVE && */
            if ((so_options) && 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(pData, 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(pData, tp, 0); /* ETIMEDOUT); */
            break;
    }

    return tp;
}