1/* SPDX-License-Identifier: BSD-3-Clause */
2/*
3 * Copyright (c) 1982, 1986, 1993, 1994
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_var.h 8.3 (Berkeley) 4/10/94
31 * tcp_var.h,v 1.3 1994/08/21 05:27:39 paul Exp
32 */
33
34#ifndef TCP_VAR_H
35#define TCP_VAR_H
36
37#include "tcpip.h"
38#include "tcp_timer.h"
39
40/*
41 * Tcp control block, one per tcp; fields:
42 */
43struct tcpcb {
44 struct tcpiphdr *seg_next; /* sequencing queue */
45 struct tcpiphdr *seg_prev;
46 short t_state; /* state of this connection */
47 short t_timer[TCPT_NTIMERS]; /* tcp timers */
48 short t_rxtshift; /* log(2) of rexmt exp. backoff */
49 short t_rxtcur; /* current retransmit value */
50 short t_dupacks; /* consecutive dup acks recd */
51 uint16_t t_maxseg; /* maximum segment size */
52 uint8_t t_force; /* 1 if forcing out a byte */
53 uint16_t t_flags;
54#define TF_ACKNOW 0x0001 /* ack peer immediately */
55#define TF_DELACK 0x0002 /* ack, but try to delay it */
56#define TF_NODELAY 0x0004 /* don't delay packets to coalesce */
57#define TF_NOOPT 0x0008 /* don't use tcp options */
58#define TF_SENTFIN 0x0010 /* have sent FIN */
59#define TF_REQ_SCALE 0x0020 /* have/will request window scaling */
60#define TF_RCVD_SCALE 0x0040 /* other side has requested scaling */
61#define TF_REQ_TSTMP 0x0080 /* have/will request timestamps */
62#define TF_RCVD_TSTMP 0x0100 /* a timestamp was received in SYN */
63#define TF_SACK_PERMIT 0x0200 /* other side said I could SACK */
64
65 struct tcpiphdr t_template; /* static skeletal packet for xmit */
66
67 struct socket *t_socket; /* back pointer to socket */
68 /*
69 * The following fields are used as in the protocol specification.
70 * See RFC783, Dec. 1981, page 21.
71 */
72 /* send sequence variables */
73 tcp_seq snd_una; /* send unacknowledged */
74 tcp_seq snd_nxt; /* send next */
75 tcp_seq snd_up; /* send urgent pointer */
76 tcp_seq snd_wl1; /* window update seg seq number */
77 tcp_seq snd_wl2; /* window update seg ack number */
78 tcp_seq iss; /* initial send sequence number */
79 uint32_t snd_wnd; /* send window */
80 /* receive sequence variables */
81 uint32_t rcv_wnd; /* receive window */
82 tcp_seq rcv_nxt; /* receive next */
83 tcp_seq rcv_up; /* receive urgent pointer */
84 tcp_seq irs; /* initial receive sequence number */
85 /*
86 * Additional variables for this implementation.
87 */
88 /* receive variables */
89 tcp_seq rcv_adv; /* advertised window */
90 /* retransmit variables */
91 tcp_seq snd_max; /* highest sequence number sent;
92 * used to recognize retransmits
93 */
94 /* congestion control (for slow start, source quench, retransmit after loss)
95 */
96 uint32_t snd_cwnd; /* congestion-controlled window */
97 uint32_t snd_ssthresh; /* snd_cwnd size threshold for
98 * for slow start exponential to
99 * linear switch
100 */
101 /*
102 * transmit timing stuff. See below for scale of srtt and rttvar.
103 * "Variance" is actually smoothed difference.
104 */
105 short t_idle; /* inactivity time */
106 short t_rtt; /* round trip time */
107 tcp_seq t_rtseq; /* sequence number being timed */
108 short t_srtt; /* smoothed round-trip time */
109 short t_rttvar; /* variance in round-trip time */
110 uint16_t t_rttmin; /* minimum rtt allowed */
111 uint32_t max_sndwnd; /* largest window peer has offered */
112
113 /* out-of-band data */
114 uint8_t t_oobflags; /* have some */
115 uint8_t t_iobc; /* input character */
116#define TCPOOB_HAVEDATA 0x01
117#define TCPOOB_HADDATA 0x02
118 short t_softerror; /* possible error not yet reported */
119
120 /* RFC 1323 variables */
121 uint8_t snd_scale; /* window scaling for send window */
122 uint8_t rcv_scale; /* window scaling for recv window */
123 uint8_t request_r_scale; /* pending window scaling */
124 uint8_t requested_s_scale;
125 uint32_t ts_recent; /* timestamp echo data */
126 uint32_t ts_recent_age; /* when last updated */
127 tcp_seq last_ack_sent;
128};
129
130#define sototcpcb(so) ((so)->so_tcpcb)
131
132/*
133 * The smoothed round-trip time and estimated variance
134 * are stored as fixed point numbers scaled by the values below.
135 * For convenience, these scales are also used in smoothing the average
136 * (smoothed = (1/scale)sample + ((scale-1)/scale)smoothed).
137 * With these scales, srtt has 3 bits to the right of the binary point,
138 * and thus an "ALPHA" of 0.875. rttvar has 2 bits to the right of the
139 * binary point, and is smoothed with an ALPHA of 0.75.
140 */
141#define TCP_RTT_SCALE 8 /* multiplier for srtt; 3 bits frac. */
142#define TCP_RTT_SHIFT 3 /* shift for srtt; 3 bits frac. */
143#define TCP_RTTVAR_SCALE 4 /* multiplier for rttvar; 2 bits */
144#define TCP_RTTVAR_SHIFT 2 /* multiplier for rttvar; 2 bits */
145
146/*
147 * The initial retransmission should happen at rtt + 4 * rttvar.
148 * Because of the way we do the smoothing, srtt and rttvar
149 * will each average +1/2 tick of bias. When we compute
150 * the retransmit timer, we want 1/2 tick of rounding and
151 * 1 extra tick because of +-1/2 tick uncertainty in the
152 * firing of the timer. The bias will give us exactly the
153 * 1.5 tick we need. But, because the bias is
154 * statistical, we have to test that we don't drop below
155 * the minimum feasible timer (which is 2 ticks).
156 * This macro assumes that the value of TCP_RTTVAR_SCALE
157 * is the same as the multiplier for rttvar.
158 */
159#define TCP_REXMTVAL(tp) (((tp)->t_srtt >> TCP_RTT_SHIFT) + (tp)->t_rttvar)
160
161#endif
162