slirp/src/tcp_var.h

   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  */
  43 struct 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         uint32_t snd_cwnd;              /* congestion-controlled window */
  96         uint32_t snd_ssthresh;          /* snd_cwnd size threshold for
  97                                          * for slow start exponential to
  98                                          * linear switch
  99                                          */
 100 /*
 101  * transmit timing stuff.  See below for scale of srtt and rttvar.
 102  * "Variance" is actually smoothed difference.
 103  */
 104         short   t_idle;                 /* inactivity time */
 105         short   t_rtt;                  /* round trip time */
 106         tcp_seq t_rtseq;                /* sequence number being timed */
 107         short   t_srtt;                 /* smoothed round-trip time */
 108         short   t_rttvar;               /* variance in round-trip time */
 109         uint16_t        t_rttmin;               /* minimum rtt allowed */
 110         uint32_t max_sndwnd;            /* largest window peer has offered */
 111
 112 /* out-of-band data */
 113         uint8_t t_oobflags;             /* have some */
 114         uint8_t t_iobc;                 /* input character */
 115 #define TCPOOB_HAVEDATA 0x01
 116 #define TCPOOB_HADDATA  0x02
 117         short   t_softerror;            /* possible error not yet reported */
 118
 119 /* RFC 1323 variables */
 120         uint8_t snd_scale;              /* window scaling for send window */
 121         uint8_t rcv_scale;              /* window scaling for recv window */
 122         uint8_t request_r_scale;        /* pending window scaling */
 123         uint8_t requested_s_scale;
 124         uint32_t        ts_recent;              /* timestamp echo data */
 125         uint32_t        ts_recent_age;          /* when last updated */
 126         tcp_seq last_ack_sent;
 127
 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) \
 160         (((tp)->t_srtt >> TCP_RTT_SHIFT) + (tp)->t_rttvar)
 161
 162 #endif