slirp/tcp_timer.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
  30  * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
  31  */
  32
  33 #include <slirp.h>
  34
  35 static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);
  36
  37 /*
  38  * Fast timeout routine for processing delayed acks
  39  */
  40 void
  41 tcp_fasttimo(Slirp *slirp)
  42 {
  43         register struct socket *so;
  44         register struct tcpcb *tp;
  45
  46         DEBUG_CALL("tcp_fasttimo");
  47
  48         so = slirp->tcb.so_next;
  49         if (so)
  50         for (; so != &slirp->tcb; so = so->so_next)
  51                 if ((tp = (struct tcpcb *)so->so_tcpcb) &&
  52                     (tp->t_flags & TF_DELACK)) {
  53                         tp->t_flags &= ~TF_DELACK;
  54                         tp->t_flags |= TF_ACKNOW;
  55                         (void) tcp_output(tp);
  56                 }
  57 }
  58
  59 /*
  60  * Tcp protocol timeout routine called every 500 ms.
  61  * Updates the timers in all active tcb's and
  62  * causes finite state machine actions if timers expire.
  63  */
  64 void
  65 tcp_slowtimo(Slirp *slirp)
  66 {
  67         register struct socket *ip, *ipnxt;
  68         register struct tcpcb *tp;
  69         register int i;
  70
  71         DEBUG_CALL("tcp_slowtimo");
  72
  73         /*
  74          * Search through tcb's and update active timers.
  75          */
  76         ip = slirp->tcb.so_next;
  77         if (ip == 0)
  78            return;
  79         for (; ip != &slirp->tcb; ip = ipnxt) {
  80                 ipnxt = ip->so_next;
  81                 tp = sototcpcb(ip);
  82                 if (tp == 0)
  83                         continue;
  84                 for (i = 0; i < TCPT_NTIMERS; i++) {
  85                         if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
  86                                 tcp_timers(tp,i);
  87                                 if (ipnxt->so_prev != ip)
  88                                         goto tpgone;
  89                         }
  90                 }
  91                 tp->t_idle++;
  92                 if (tp->t_rtt)
  93                    tp->t_rtt++;
  94 tpgone:
  95                 ;
  96         }
  97         slirp->tcp_iss += TCP_ISSINCR/PR_SLOWHZ;        /* increment iss */
  98         slirp->tcp_now++;                               /* for timestamps */
  99 }
 100
 101 /*
 102  * Cancel all timers for TCP tp.
 103  */
 104 void
 105 tcp_canceltimers(struct tcpcb *tp)
 106 {
 107         register int i;
 108
 109         for (i = 0; i < TCPT_NTIMERS; i++)
 110                 tp->t_timer[i] = 0;
 111 }
 112
 113 const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 114    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
 115
 116 /*
 117  * TCP timer processing.
 118  */
 119 static struct tcpcb *
 120 tcp_timers(register struct tcpcb *tp, int timer)
 121 {
 122         register int rexmt;
 123
 124         DEBUG_CALL("tcp_timers");
 125
 126         switch (timer) {
 127
 128         /*
 129          * 2 MSL timeout in shutdown went off.  If we're closed but
 130          * still waiting for peer to close and connection has been idle
 131          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 132          * control block.  Otherwise, check again in a bit.
 133          */
 134         case TCPT_2MSL:
 135                 if (tp->t_state != TCPS_TIME_WAIT &&
 136                     tp->t_idle <= TCP_MAXIDLE)
 137                         tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;
 138                 else
 139                         tp = tcp_close(tp);
 140                 break;
 141
 142         /*
 143          * Retransmission timer went off.  Message has not
 144          * been acked within retransmit interval.  Back off
 145          * to a longer retransmit interval and retransmit one segment.
 146          */
 147         case TCPT_REXMT:
 148
 149                 /*
 150                  * XXXXX If a packet has timed out, then remove all the queued
 151                  * packets for that session.
 152                  */
 153
 154                 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 155                         /*
 156                          * This is a hack to suit our terminal server here at the uni of canberra
 157                          * since they have trouble with zeroes... It usually lets them through
 158                          * unharmed, but under some conditions, it'll eat the zeros.  If we
 159                          * keep retransmitting it, it'll keep eating the zeroes, so we keep
 160                          * retransmitting, and eventually the connection dies...
 161                          * (this only happens on incoming data)
 162                          *
 163                          * So, if we were gonna drop the connection from too many retransmits,
 164                          * don't... instead halve the t_maxseg, which might break up the NULLs and
 165                          * let them through
 166                          *
 167                          * *sigh*
 168                          */
 169
 170                         tp->t_maxseg >>= 1;
 171                         if (tp->t_maxseg < 32) {
 172                                 /*
 173                                  * We tried our best, now the connection must die!
 174                                  */
 175                                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 176                                 tp = tcp_drop(tp, tp->t_softerror);
 177                                 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
 178                                 return (tp); /* XXX */
 179                         }
 180
 181                         /*
 182                          * Set rxtshift to 6, which is still at the maximum
 183                          * backoff time
 184                          */
 185                         tp->t_rxtshift = 6;
 186                 }
 187                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 188                 TCPT_RANGESET(tp->t_rxtcur, rexmt,
 189                     (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
 190                 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
 191                 /*
 192                  * If losing, let the lower level know and try for
 193                  * a better route.  Also, if we backed off this far,
 194                  * our srtt estimate is probably bogus.  Clobber it
 195                  * so we'll take the next rtt measurement as our srtt;
 196                  * move the current srtt into rttvar to keep the current
 197                  * retransmit times until then.
 198                  */
 199                 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 200                         tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 201                         tp->t_srtt = 0;
 202                 }
 203                 tp->snd_nxt = tp->snd_una;
 204                 /*
 205                  * If timing a segment in this window, stop the timer.
 206                  */
 207                 tp->t_rtt = 0;
 208                 /*
 209                  * Close the congestion window down to one segment
 210                  * (we'll open it by one segment for each ack we get).
 211                  * Since we probably have a window's worth of unacked
 212                  * data accumulated, this "slow start" keeps us from
 213                  * dumping all that data as back-to-back packets (which
 214                  * might overwhelm an intermediate gateway).
 215                  *
 216                  * There are two phases to the opening: Initially we
 217                  * open by one mss on each ack.  This makes the window
 218                  * size increase exponentially with time.  If the
 219                  * window is larger than the path can handle, this
 220                  * exponential growth results in dropped packet(s)
 221                  * almost immediately.  To get more time between
 222                  * drops but still "push" the network to take advantage
 223                  * of improving conditions, we switch from exponential
 224                  * to linear window opening at some threshold size.
 225                  * For a threshold, we use half the current window
 226                  * size, truncated to a multiple of the mss.
 227                  *
 228                  * (the minimum cwnd that will give us exponential
 229                  * growth is 2 mss.  We don't allow the threshold
 230                  * to go below this.)
 231                  */
 232                 {
 233                 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
 234                 if (win < 2)
 235                         win = 2;
 236                 tp->snd_cwnd = tp->t_maxseg;
 237                 tp->snd_ssthresh = win * tp->t_maxseg;
 238                 tp->t_dupacks = 0;
 239                 }
 240                 (void) tcp_output(tp);
 241                 break;
 242
 243         /*
 244          * Persistence timer into zero window.
 245          * Force a byte to be output, if possible.
 246          */
 247         case TCPT_PERSIST:
 248                 tcp_setpersist(tp);
 249                 tp->t_force = 1;
 250                 (void) tcp_output(tp);
 251                 tp->t_force = 0;
 252                 break;
 253
 254         /*
 255          * Keep-alive timer went off; send something
 256          * or drop connection if idle for too long.
 257          */
 258         case TCPT_KEEP:
 259                 if (tp->t_state < TCPS_ESTABLISHED)
 260                         goto dropit;
 261
 262                 if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {
 263                         if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)
 264                                 goto dropit;
 265                         /*
 266                          * Send a packet designed to force a response
 267                          * if the peer is up and reachable:
 268                          * either an ACK if the connection is still alive,
 269                          * or an RST if the peer has closed the connection
 270                          * due to timeout or reboot.
 271                          * Using sequence number tp->snd_una-1
 272                          * causes the transmitted zero-length segment
 273                          * to lie outside the receive window;
 274                          * by the protocol spec, this requires the
 275                          * correspondent TCP to respond.
 276                          */
 277                         tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
 278                             tp->rcv_nxt, tp->snd_una - 1, 0);
 279                         tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
 280                 } else
 281                         tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
 282                 break;
 283
 284         dropit:
 285                 tp = tcp_drop(tp, 0);
 286                 break;
 287         }
 288
 289         return (tp);
 290 }