slirp/src/tcp_timer.h

   1 /* SPDX-License-Identifier: BSD-3-Clause */
   2 /*
   3  * Copyright (c) 1982, 1986, 1993
   4  *      The Regents of the University of California.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. Neither the name of the University nor the names of its contributors
  15  *    may be used to endorse or promote products derived from this software
  16  *    without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  28  * SUCH DAMAGE.
  29  *
  30  *      @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
  31  * tcp_timer.h,v 1.4 1994/08/21 05:27:38 paul Exp
  32  */
  33
  34 #ifndef TCP_TIMER_H
  35 #define TCP_TIMER_H
  36
  37 /*
  38  * Definitions of the TCP timers.  These timers are counted
  39  * down PR_SLOWHZ times a second.
  40  */
  41 #define TCPT_NTIMERS    4
  42
  43 #define TCPT_REXMT      0               /* retransmit */
  44 #define TCPT_PERSIST    1               /* retransmit persistence */
  45 #define TCPT_KEEP       2               /* keep alive */
  46 #define TCPT_2MSL       3               /* 2*msl quiet time timer */
  47
  48 /*
  49  * The TCPT_REXMT timer is used to force retransmissions.
  50  * The TCP has the TCPT_REXMT timer set whenever segments
  51  * have been sent for which ACKs are expected but not yet
  52  * received.  If an ACK is received which advances tp->snd_una,
  53  * then the retransmit timer is cleared (if there are no more
  54  * outstanding segments) or reset to the base value (if there
  55  * are more ACKs expected).  Whenever the retransmit timer goes off,
  56  * we retransmit one unacknowledged segment, and do a backoff
  57  * on the retransmit timer.
  58  *
  59  * The TCPT_PERSIST timer is used to keep window size information
  60  * flowing even if the window goes shut.  If all previous transmissions
  61  * have been acknowledged (so that there are no retransmissions in progress),
  62  * and the window is too small to bother sending anything, then we start
  63  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
  64  * we go to transmit state.  Otherwise, at intervals send a single byte
  65  * into the peer's window to force him to update our window information.
  66  * We do this at most as often as TCPT_PERSMIN time intervals,
  67  * but no more frequently than the current estimate of round-trip
  68  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
  69  * a window update from the peer.
  70  *
  71  * The TCPT_KEEP timer is used to keep connections alive.  If an
  72  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
  73  * but not yet established, then we drop the connection.  Once the connection
  74  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
  75  * (and keepalives have been enabled on the socket), we begin to probe
  76  * the connection.  We force the peer to send us a segment by sending:
  77  *      <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
  78  * This segment is (deliberately) outside the window, and should elicit
  79  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
  80  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
  81  * amount of time probing, then we drop the connection.
  82  */
  83
  84 /*
  85  * Time constants.
  86  */
  87 #define TCPTV_MSL       ( 5*PR_SLOWHZ)          /* max seg lifetime (hah!) */
  88
  89 #define TCPTV_SRTTBASE  0                       /* base roundtrip time;
  90                                                    if 0, no idea yet */
  91 #define TCPTV_SRTTDFLT  (  3*PR_SLOWHZ)         /* assumed RTT if no info */
  92
  93 #define TCPTV_PERSMIN   (  5*PR_SLOWHZ)         /* retransmit persistence */
  94 #define TCPTV_PERSMAX   ( 60*PR_SLOWHZ)         /* maximum persist interval */
  95
  96 #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ)         /* initial connect keep alive */
  97 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ)      /* dflt time before probing */
  98 #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ)         /* default probe interval */
  99 #define TCPTV_KEEPCNT   8                       /* max probes before drop */
 100
 101 #define TCPTV_MIN       (  1*PR_SLOWHZ)         /* minimum allowable value */
 102 #define TCPTV_REXMTMAX  ( 12*PR_SLOWHZ)         /* max allowable REXMT value */
 103
 104 #define TCP_LINGERTIME  120                     /* linger at most 2 minutes */
 105
 106 #define TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
 107
 108
 109 /*
 110  * Force a time value to be in a certain range.
 111  */
 112 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \
 113         (tv) = (value); \
 114         if ((tv) < (tvmin)) \
 115                 (tv) = (tvmin); \
 116         else if ((tv) > (tvmax)) \
 117                 (tv) = (tvmax); \
 118 }
 119
 120 extern const int tcp_backoff[];
 121
 122 struct tcpcb;
 123
 124 void tcp_fasttimo(Slirp *);
 125 void tcp_slowtimo(Slirp *);
 126 void tcp_canceltimers(struct tcpcb *);
 127
 128 #endif