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. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  *      @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
  34  * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
  35  */
  36
  37 #include <slirp.h>
  38
  39 #ifdef LOG_ENABLED
  40 struct   tcpstat tcpstat;        /* tcp statistics */
  41 #endif
  42
  43 u_int32_t        tcp_now;                /* for RFC 1323 timestamps */
  44
  45 static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);
  46
  47 /*
  48  * Fast timeout routine for processing delayed acks
  49  */
  50 void
  51 tcp_fasttimo()
  52 {
  53         register struct socket *so;
  54         register struct tcpcb *tp;
  55
  56         DEBUG_CALL("tcp_fasttimo");
  57
  58         so = tcb.so_next;
  59         if (so)
  60         for (; so != &tcb; so = so->so_next)
  61                 if ((tp = (struct tcpcb *)so->so_tcpcb) &&
  62                     (tp->t_flags & TF_DELACK)) {
  63                         tp->t_flags &= ~TF_DELACK;
  64                         tp->t_flags |= TF_ACKNOW;
  65                         STAT(tcpstat.tcps_delack++);
  66                         (void) tcp_output(tp);
  67                 }
  68 }
  69
  70 /*
  71  * Tcp protocol timeout routine called every 500 ms.
  72  * Updates the timers in all active tcb's and
  73  * causes finite state machine actions if timers expire.
  74  */
  75 void
  76 tcp_slowtimo()
  77 {
  78         register struct socket *ip, *ipnxt;
  79         register struct tcpcb *tp;
  80         register int i;
  81
  82         DEBUG_CALL("tcp_slowtimo");
  83
  84         /*
  85          * Search through tcb's and update active timers.
  86          */
  87         ip = tcb.so_next;
  88         if (ip == 0)
  89            return;
  90         for (; ip != &tcb; ip = ipnxt) {
  91                 ipnxt = ip->so_next;
  92                 tp = sototcpcb(ip);
  93                 if (tp == 0)
  94                         continue;
  95                 for (i = 0; i < TCPT_NTIMERS; i++) {
  96                         if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
  97                                 tcp_timers(tp,i);
  98                                 if (ipnxt->so_prev != ip)
  99                                         goto tpgone;
 100                         }
 101                 }
 102                 tp->t_idle++;
 103                 if (tp->t_rtt)
 104                    tp->t_rtt++;
 105 tpgone:
 106                 ;
 107         }
 108         tcp_iss += TCP_ISSINCR/PR_SLOWHZ;               /* increment iss */
 109 #ifdef TCP_COMPAT_42
 110         if ((int)tcp_iss < 0)
 111                 tcp_iss = 0;                            /* XXX */
 112 #endif
 113         tcp_now++;                                      /* for timestamps */
 114 }
 115
 116 /*
 117  * Cancel all timers for TCP tp.
 118  */
 119 void
 120 tcp_canceltimers(tp)
 121         struct tcpcb *tp;
 122 {
 123         register int i;
 124
 125         for (i = 0; i < TCPT_NTIMERS; i++)
 126                 tp->t_timer[i] = 0;
 127 }
 128
 129 const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 130    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
 131
 132 /*
 133  * TCP timer processing.
 134  */
 135 static struct tcpcb *
 136 tcp_timers(register struct tcpcb *tp, int timer)
 137 {
 138         register int rexmt;
 139
 140         DEBUG_CALL("tcp_timers");
 141
 142         switch (timer) {
 143
 144         /*
 145          * 2 MSL timeout in shutdown went off.  If we're closed but
 146          * still waiting for peer to close and connection has been idle
 147          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 148          * control block.  Otherwise, check again in a bit.
 149          */
 150         case TCPT_2MSL:
 151                 if (tp->t_state != TCPS_TIME_WAIT &&
 152                     tp->t_idle <= TCP_MAXIDLE)
 153                         tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;
 154                 else
 155                         tp = tcp_close(tp);
 156                 break;
 157
 158         /*
 159          * Retransmission timer went off.  Message has not
 160          * been acked within retransmit interval.  Back off
 161          * to a longer retransmit interval and retransmit one segment.
 162          */
 163         case TCPT_REXMT:
 164
 165                 /*
 166                  * XXXXX If a packet has timed out, then remove all the queued
 167                  * packets for that session.
 168                  */
 169
 170                 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 171                         /*
 172                          * This is a hack to suit our terminal server here at the uni of canberra
 173                          * since they have trouble with zeroes... It usually lets them through
 174                          * unharmed, but under some conditions, it'll eat the zeros.  If we
 175                          * keep retransmitting it, it'll keep eating the zeroes, so we keep
 176                          * retransmitting, and eventually the connection dies...
 177                          * (this only happens on incoming data)
 178                          *
 179                          * So, if we were gonna drop the connection from too many retransmits,
 180                          * don't... instead halve the t_maxseg, which might break up the NULLs and
 181                          * let them through
 182                          *
 183                          * *sigh*
 184                          */
 185
 186                         tp->t_maxseg >>= 1;
 187                         if (tp->t_maxseg < 32) {
 188                                 /*
 189                                  * We tried our best, now the connection must die!
 190                                  */
 191                                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 192                                 STAT(tcpstat.tcps_timeoutdrop++);
 193                                 tp = tcp_drop(tp, tp->t_softerror);
 194                                 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
 195                                 return (tp); /* XXX */
 196                         }
 197
 198                         /*
 199                          * Set rxtshift to 6, which is still at the maximum
 200                          * backoff time
 201                          */
 202                         tp->t_rxtshift = 6;
 203                 }
 204                 STAT(tcpstat.tcps_rexmttimeo++);
 205                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 206                 TCPT_RANGESET(tp->t_rxtcur, rexmt,
 207                     (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
 208                 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
 209                 /*
 210                  * If losing, let the lower level know and try for
 211                  * a better route.  Also, if we backed off this far,
 212                  * our srtt estimate is probably bogus.  Clobber it
 213                  * so we'll take the next rtt measurement as our srtt;
 214                  * move the current srtt into rttvar to keep the current
 215                  * retransmit times until then.
 216                  */
 217                 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 218 /*                      in_losing(tp->t_inpcb); */
 219                         tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 220                         tp->t_srtt = 0;
 221                 }
 222                 tp->snd_nxt = tp->snd_una;
 223                 /*
 224                  * If timing a segment in this window, stop the timer.
 225                  */
 226                 tp->t_rtt = 0;
 227                 /*
 228                  * Close the congestion window down to one segment
 229                  * (we'll open it by one segment for each ack we get).
 230                  * Since we probably have a window's worth of unacked
 231                  * data accumulated, this "slow start" keeps us from
 232                  * dumping all that data as back-to-back packets (which
 233                  * might overwhelm an intermediate gateway).
 234                  *
 235                  * There are two phases to the opening: Initially we
 236                  * open by one mss on each ack.  This makes the window
 237                  * size increase exponentially with time.  If the
 238                  * window is larger than the path can handle, this
 239                  * exponential growth results in dropped packet(s)
 240                  * almost immediately.  To get more time between
 241                  * drops but still "push" the network to take advantage
 242                  * of improving conditions, we switch from exponential
 243                  * to linear window opening at some threshold size.
 244                  * For a threshold, we use half the current window
 245                  * size, truncated to a multiple of the mss.
 246                  *
 247                  * (the minimum cwnd that will give us exponential
 248                  * growth is 2 mss.  We don't allow the threshold
 249                  * to go below this.)
 250                  */
 251                 {
 252                 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
 253                 if (win < 2)
 254                         win = 2;
 255                 tp->snd_cwnd = tp->t_maxseg;
 256                 tp->snd_ssthresh = win * tp->t_maxseg;
 257                 tp->t_dupacks = 0;
 258                 }
 259                 (void) tcp_output(tp);
 260                 break;
 261
 262         /*
 263          * Persistence timer into zero window.
 264          * Force a byte to be output, if possible.
 265          */
 266         case TCPT_PERSIST:
 267                 STAT(tcpstat.tcps_persisttimeo++);
 268                 tcp_setpersist(tp);
 269                 tp->t_force = 1;
 270                 (void) tcp_output(tp);
 271                 tp->t_force = 0;
 272                 break;
 273
 274         /*
 275          * Keep-alive timer went off; send something
 276          * or drop connection if idle for too long.
 277          */
 278         case TCPT_KEEP:
 279                 STAT(tcpstat.tcps_keeptimeo++);
 280                 if (tp->t_state < TCPS_ESTABLISHED)
 281                         goto dropit;
 282
 283 /*              if (tp->t_socket->so_options & SO_KEEPALIVE && */
 284                 if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {
 285                         if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)
 286                                 goto dropit;
 287                         /*
 288                          * Send a packet designed to force a response
 289                          * if the peer is up and reachable:
 290                          * either an ACK if the connection is still alive,
 291                          * or an RST if the peer has closed the connection
 292                          * due to timeout or reboot.
 293                          * Using sequence number tp->snd_una-1
 294                          * causes the transmitted zero-length segment
 295                          * to lie outside the receive window;
 296                          * by the protocol spec, this requires the
 297                          * correspondent TCP to respond.
 298                          */
 299                         STAT(tcpstat.tcps_keepprobe++);
 300 #ifdef TCP_COMPAT_42
 301                         /*
 302                          * The keepalive packet must have nonzero length
 303                          * to get a 4.2 host to respond.
 304                          */
 305                         tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
 306                             tp->rcv_nxt - 1, tp->snd_una - 1, 0);
 307 #else
 308                         tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
 309                             tp->rcv_nxt, tp->snd_una - 1, 0);
 310 #endif
 311                         tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
 312                 } else
 313                         tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
 314                 break;
 315
 316         dropit:
 317                 STAT(tcpstat.tcps_keepdrops++);
 318                 tp = tcp_drop(tp, 0); /* ETIMEDOUT); */
 319                 break;
 320         }
 321
 322         return (tp);
 323 }