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