1/* $OpenBSD: tcp_timer.h,v 1.28 2025/12/31 03:47:04 jsg Exp $ */
2/* $NetBSD: tcp_timer.h,v 1.6 1995/03/26 20:32:37 jtc Exp $ */
3
4/*
5 * Copyright (c) 1982, 1986, 1993
6 * The Regents of the University of California. All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 *
32 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
33 */
34
35#ifndef _NETINET_TCP_TIMER_H_
36#define _NETINET_TCP_TIMER_H_
37
38/*
39 * Definitions of the TCP timers.
40 */
41#define TCPT_REXMT 0 /* retransmit */
42#define TCPT_PERSIST 1 /* retransmit persistence */
43#define TCPT_KEEP 2 /* keep alive */
44#define TCPT_2MSL 3 /* 2*msl quiet time timer */
45#define TCPT_DELACK 4 /* delayed ack timeout */
46
47#define TCPT_NTIMERS 5
48
49/*
50 * The TCPT_REXMT timer is used to force retransmissions.
51 * The TCP has the TCPT_REXMT timer set whenever segments
52 * have been sent for which ACKs are expected but not yet
53 * received. If an ACK is received which advances tp->snd_una,
54 * then the retransmit timer is cleared (if there are no more
55 * outstanding segments) or reset to the base value (if there
56 * are more ACKs expected). Whenever the retransmit timer goes off,
57 * we retransmit one unacknowledged segment, and do a backoff
58 * on the retransmit timer.
59 *
60 * The TCPT_PERSIST timer is used to keep window size information
61 * flowing even if the window goes shut. If all previous transmissions
62 * have been acknowledged (so that there are no retransmissions in progress),
63 * and the window is too small to bother sending anything, then we start
64 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
65 * we go to transmit state. Otherwise, at intervals send a single byte
66 * into the peer's window to force him to update our window information.
67 * We do this at most as often as TCPT_PERSMIN time intervals,
68 * but no more frequently than the current estimate of round-trip
69 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
70 * a window update from the peer.
71 *
72 * The TCPT_KEEP timer is used to keep connections alive. If an
73 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
74 * but not yet established, then we drop the connection. Once the connection
75 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
76 * (and keepalives have been enabled on the socket), we begin to probe
77 * the connection. We force the peer to send us a segment by sending:
78 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
79 * This segment is (deliberately) outside the window, and should elicit
80 * an ack segment in response from the peer. If, despite the TCPT_KEEP
81 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
82 * amount of time probing, then we drop the connection.
83 */
84
85/*
86 * Time constants.
87 */
88#define TCPTV_MSL TCP_TIME(30) /* max seg lifetime (hah!) */
89#define TCPTV_SRTTBASE 0 /* base roundtrip time;
90 if 0, no idea yet */
91#define TCPTV_SRTTDFLT TCP_TIME(3) /* assumed RTT if no info */
92
93#define TCPTV_PERSMIN TCP_TIME(5) /* retransmit persistence */
94#define TCPTV_PERSMAX TCP_TIME(60) /* maximum persist interval */
95
96#define TCPTV_KEEPINIT TCP_TIME(75) /* initial connect keep alive */
97#define TCPTV_KEEPIDLE TCP_TIME(120*60) /* dflt time before probing */
98#define TCPTV_KEEPINTVL TCP_TIME(75) /* default probe interval */
99#define TCPTV_KEEPCNT 8 /* max probes before drop */
100
101#define TCPTV_MIN TCP_TIME(1) /* minimum allowable value */
102#define TCPTV_REXMTMAX TCP_TIME(64) /* 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#define TCP_DELACK_MSECS 200 /* time to delay ACK */
109
110#ifdef TCPTIMERS
111const char *tcptimers[TCPT_NTIMERS] =
112 { "REXMT", "PERSIST", "KEEP", "2MSL", "DELACK" };
113#endif /* TCPTIMERS */
114
115/*
116 * Init, arm, disarm, and test TCP timers.
117 */
118#define TCP_TIMER_INIT(tp, timer) \
119 timeout_set_flags(&(tp)->t_timer[(timer)], \
120 tcp_timer_funcs[(timer)], (tp)->t_inpcb, \
121 KCLOCK_NONE, TIMEOUT_PROC | TIMEOUT_MPSAFE)
122
123#define TCP_TIMER_ARM(tp, timer, msecs) \
124do { \
125 SET((tp)->t_flags, TF_TIMER << (timer)); \
126 if (timeout_add_msec(&(tp)->t_timer[(timer)], (msecs))) \
127 in_pcbref((tp)->t_inpcb); \
128} while (0)
129
130#define TCP_TIMER_DISARM(tp, timer) \
131do { \
132 CLR((tp)->t_flags, TF_TIMER << (timer)); \
133 if (timeout_del(&(tp)->t_timer[(timer)])) \
134 in_pcbunref((tp)->t_inpcb); \
135} while (0)
136
137#define TCP_TIMER_ISARMED(tp, timer) \
138 ISSET((tp)->t_flags, TF_TIMER << (timer))
139
140/*
141 * Force a time value to be in a certain range.
142 */
143#define TCPT_RANGESET(tv, value, tvmin, tvmax) \
144do { \
145 (tv) = (value); \
146 if ((tv) < (tvmin)) \
147 (tv) = (tvmin); \
148 else if ((tv) > (tvmax)) \
149 (tv) = (tvmax); \
150} while (/* CONSTCOND */ 0)
151
152#ifdef _KERNEL
153typedef void (*tcp_timer_func_t)(void *);
154
155extern const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS];
156
157extern int tcp_delack_msecs; /* [I] delayed ACK timeout in millisecs */
158extern int tcp_always_keepalive;/* [a] assume SO_KEEPALIVE always set */
159extern int tcp_keepinit; /* [a] time to keep alive initial SYN packet */
160extern int tcp_keepidle; /* [a] time before keepalive probes begin */
161extern int tcp_keepintvl; /* [a] time between keepalive probes */
162extern int tcp_keepinit_sec; /* [a] copy of above in seconds for sysctl */
163extern int tcp_keepidle_sec; /* [a] copy of above in seconds for sysctl */
164extern int tcp_keepintvl_sec; /* [a] copy of above in seconds for sysctl */
165extern const int tcp_backoff[];
166#endif /* _KERNEL */
167#endif /* _NETINET_TCP_TIMER_H_ */