src/tcp_timer.h

/* SPDX-License-Identifier: BSD-3-Clause */
/*
 * Copyright (c) 1982, 1986, 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.h	8.1 (Berkeley) 6/10/93
 * tcp_timer.h,v 1.4 1994/08/21 05:27:38 paul Exp
 */

#ifndef TCP_TIMER_H
#define TCP_TIMER_H

/*
 * Definitions of the TCP timers.  These timers are counted
 * down PR_SLOWHZ times a second.
 */
#define TCPT_NTIMERS 4

#define TCPT_REXMT 0 /* retransmit */
#define TCPT_PERSIST 1 /* retransmit persistence */
#define TCPT_KEEP 2 /* keep alive */
#define TCPT_2MSL 3 /* 2*msl quiet time timer */

/*
 * The TCPT_REXMT timer is used to force retransmissions.
 * The TCP has the TCPT_REXMT timer set whenever segments
 * have been sent for which ACKs are expected but not yet
 * received.  If an ACK is received which advances tp->snd_una,
 * then the retransmit timer is cleared (if there are no more
 * outstanding segments) or reset to the base value (if there
 * are more ACKs expected).  Whenever the retransmit timer goes off,
 * we retransmit one unacknowledged segment, and do a backoff
 * on the retransmit timer.
 *
 * The TCPT_PERSIST timer is used to keep window size information
 * flowing even if the window goes shut.  If all previous transmissions
 * have been acknowledged (so that there are no retransmissions in progress),
 * and the window is too small to bother sending anything, then we start
 * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
 * we go to transmit state.  Otherwise, at intervals send a single byte
 * into the peer's window to force him to update our window information.
 * We do this at most as often as TCPT_PERSMIN time intervals,
 * but no more frequently than the current estimate of round-trip
 * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
 * a window update from the peer.
 *
 * The TCPT_KEEP timer is used to keep connections alive.  If an
 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
 * but not yet established, then we drop the connection.  Once the connection
 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
 * (and keepalives have been enabled on the socket), we begin to probe
 * the connection.  We force the peer to send us a segment by sending:
 *	<SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
 * This segment is (deliberately) outside the window, and should elicit
 * an ack segment in response from the peer.  If, despite the TCPT_KEEP
 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
 * amount of time probing, then we drop the connection.
 */

/*
 * Time constants.
 */
#define TCPTV_MSL (5 * PR_SLOWHZ) /* max seg lifetime (hah!) */

#define TCPTV_SRTTBASE        \
    0 /* base roundtrip time; \
         if 0, no idea yet */
#define TCPTV_SRTTDFLT (3 * PR_SLOWHZ) /* assumed RTT if no info */

#define TCPTV_PERSMIN (5 * PR_SLOWHZ) /* retransmit persistence */
#define TCPTV_PERSMAX (60 * PR_SLOWHZ) /* maximum persist interval */

#define TCPTV_KEEP_INIT (75 * PR_SLOWHZ) /* initial connect keep alive */
#define TCPTV_KEEP_IDLE (120 * 60 * PR_SLOWHZ) /* dflt time before probing */
#define TCPTV_KEEPINTVL (75 * PR_SLOWHZ) /* default probe interval */
#define TCPTV_KEEPCNT 8 /* max probes before drop */

#define TCPTV_MIN (1 * PR_SLOWHZ) /* minimum allowable value */
#define TCPTV_REXMTMAX (12 * PR_SLOWHZ) /* max allowable REXMT value */

#define TCP_LINGERTIME 120 /* linger at most 2 minutes */

#define TCP_MAXRXTSHIFT 12 /* maximum retransmits */


/*
 * Force a time value to be in a certain range.
 */
#define TCPT_RANGESET(tv, value, tvmin, tvmax) \
    {                                          \
        (tv) = (value);                        \
        if ((tv) < (tvmin))                    \
            (tv) = (tvmin);                    \
        else if ((tv) > (tvmax))               \
            (tv) = (tvmax);                    \
    }

extern const int tcp_backoff[];

struct tcpcb;

/* Process fast time-outs */
void tcp_fasttimo(Slirp *);
/* Process slow time-outs */
void tcp_slowtimo(Slirp *);
/* Cancel all timers for TCP tp */
void tcp_canceltimers(struct tcpcb *);

#endif