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 int     tcp_keepidle = TCPTV_KEEP_IDLE;
  40 int     tcp_keepintvl = TCPTV_KEEPINTVL;
  41 int     tcp_maxidle;
  42 int     so_options = DO_KEEPALIVE;
  43
  44 struct   tcpstat tcpstat;        /* tcp statistics */
  45 u_int32_t        tcp_now;                /* for RFC 1323 timestamps */
  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                         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         tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl;
  85         /*
  86          * Search through tcb's and update active timers.
  87          */
  88         ip = tcb.so_next;
  89         if (ip == 0)
  90            return;
  91         for (; ip != &tcb; ip = ipnxt) {
  92                 ipnxt = ip->so_next;
  93                 tp = sototcpcb(ip);
  94                 if (tp == 0)
  95                         continue;
  96                 for (i = 0; i < TCPT_NTIMERS; i++) {
  97                         if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
  98                                 tcp_timers(tp,i);
  99                                 if (ipnxt->so_prev != ip)
 100                                         goto tpgone;
 101                         }
 102                 }
 103                 tp->t_idle++;
 104                 if (tp->t_rtt)
 105                    tp->t_rtt++;
 106 tpgone:
 107                 ;
 108         }
 109         tcp_iss += TCP_ISSINCR/PR_SLOWHZ;               /* increment iss */
 110 #ifdef TCP_COMPAT_42
 111         if ((int)tcp_iss < 0)
 112                 tcp_iss = 0;                            /* XXX */
 113 #endif
 114         tcp_now++;                                      /* for timestamps */
 115 }
 116
 117 /*
 118  * Cancel all timers for TCP tp.
 119  */
 120 void
 121 tcp_canceltimers(tp)
 122         struct tcpcb *tp;
 123 {
 124         register int i;
 125
 126         for (i = 0; i < TCPT_NTIMERS; i++)
 127                 tp->t_timer[i] = 0;
 128 }
 129
 130 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 131    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
 132
 133 /*
 134  * TCP timer processing.
 135  */
 136 struct tcpcb *
 137 tcp_timers(tp, timer)
 138         register struct tcpcb *tp;
 139         int timer;
 140 {
 141         register int rexmt;
 142
 143         DEBUG_CALL("tcp_timers");
 144
 145         switch (timer) {
 146
 147         /*
 148          * 2 MSL timeout in shutdown went off.  If we're closed but
 149          * still waiting for peer to close and connection has been idle
 150          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 151          * control block.  Otherwise, check again in a bit.
 152          */
 153         case TCPT_2MSL:
 154                 if (tp->t_state != TCPS_TIME_WAIT &&
 155                     tp->t_idle <= tcp_maxidle)
 156                         tp->t_timer[TCPT_2MSL] = tcp_keepintvl;
 157                 else
 158                         tp = tcp_close(tp);
 159                 break;
 160
 161         /*
 162          * Retransmission timer went off.  Message has not
 163          * been acked within retransmit interval.  Back off
 164          * to a longer retransmit interval and retransmit one segment.
 165          */
 166         case TCPT_REXMT:
 167
 168                 /*
 169                  * XXXXX If a packet has timed out, then remove all the queued
 170                  * packets for that session.
 171                  */
 172
 173                 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 174                         /*
 175                          * This is a hack to suit our terminal server here at the uni of canberra
 176                          * since they have trouble with zeroes... It usually lets them through
 177                          * unharmed, but under some conditions, it'll eat the zeros.  If we
 178                          * keep retransmitting it, it'll keep eating the zeroes, so we keep
 179                          * retransmitting, and eventually the connection dies...
 180                          * (this only happens on incoming data)
 181                          *
 182                          * So, if we were gonna drop the connection from too many retransmits,
 183                          * don't... instead halve the t_maxseg, which might break up the NULLs and
 184                          * let them through
 185                          *
 186                          * *sigh*
 187                          */
 188
 189                         tp->t_maxseg >>= 1;
 190                         if (tp->t_maxseg < 32) {
 191                                 /*
 192                                  * We tried our best, now the connection must die!
 193                                  */
 194                                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 195                                 tcpstat.tcps_timeoutdrop++;
 196                                 tp = tcp_drop(tp, tp->t_softerror);
 197                                 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
 198                                 return (tp); /* XXX */
 199                         }
 200
 201                         /*
 202                          * Set rxtshift to 6, which is still at the maximum
 203                          * backoff time
 204                          */
 205                         tp->t_rxtshift = 6;
 206                 }
 207                 tcpstat.tcps_rexmttimeo++;
 208                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 209                 TCPT_RANGESET(tp->t_rxtcur, rexmt,
 210                     (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
 211                 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
 212                 /*
 213                  * If losing, let the lower level know and try for
 214                  * a better route.  Also, if we backed off this far,
 215                  * our srtt estimate is probably bogus.  Clobber it
 216                  * so we'll take the next rtt measurement as our srtt;
 217                  * move the current srtt into rttvar to keep the current
 218                  * retransmit times until then.
 219                  */
 220                 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 221 /*                      in_losing(tp->t_inpcb); */
 222                         tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 223                         tp->t_srtt = 0;
 224                 }
 225                 tp->snd_nxt = tp->snd_una;
 226                 /*
 227                  * If timing a segment in this window, stop the timer.
 228                  */
 229                 tp->t_rtt = 0;
 230                 /*
 231                  * Close the congestion window down to one segment
 232                  * (we'll open it by one segment for each ack we get).
 233                  * Since we probably have a window's worth of unacked
 234                  * data accumulated, this "slow start" keeps us from
 235                  * dumping all that data as back-to-back packets (which
 236                  * might overwhelm an intermediate gateway).
 237                  *
 238                  * There are two phases to the opening: Initially we
 239                  * open by one mss on each ack.  This makes the window
 240                  * size increase exponentially with time.  If the
 241                  * window is larger than the path can handle, this
 242                  * exponential growth results in dropped packet(s)
 243                  * almost immediately.  To get more time between
 244                  * drops but still "push" the network to take advantage
 245                  * of improving conditions, we switch from exponential
 246                  * to linear window opening at some threshold size.
 247                  * For a threshold, we use half the current window
 248                  * size, truncated to a multiple of the mss.
 249                  *
 250                  * (the minimum cwnd that will give us exponential
 251                  * growth is 2 mss.  We don't allow the threshold
 252                  * to go below this.)
 253                  */
 254                 {
 255                 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
 256                 if (win < 2)
 257                         win = 2;
 258                 tp->snd_cwnd = tp->t_maxseg;
 259                 tp->snd_ssthresh = win * tp->t_maxseg;
 260                 tp->t_dupacks = 0;
 261                 }
 262                 (void) tcp_output(tp);
 263                 break;
 264
 265         /*
 266          * Persistence timer into zero window.
 267          * Force a byte to be output, if possible.
 268          */
 269         case TCPT_PERSIST:
 270                 tcpstat.tcps_persisttimeo++;
 271                 tcp_setpersist(tp);
 272                 tp->t_force = 1;
 273                 (void) tcp_output(tp);
 274                 tp->t_force = 0;
 275                 break;
 276
 277         /*
 278          * Keep-alive timer went off; send something
 279          * or drop connection if idle for too long.
 280          */
 281         case TCPT_KEEP:
 282                 tcpstat.tcps_keeptimeo++;
 283                 if (tp->t_state < TCPS_ESTABLISHED)
 284                         goto dropit;
 285
 286 /*              if (tp->t_socket->so_options & SO_KEEPALIVE && */
 287                 if ((so_options) && tp->t_state <= TCPS_CLOSE_WAIT) {
 288                         if (tp->t_idle >= tcp_keepidle + tcp_maxidle)
 289                                 goto dropit;
 290                         /*
 291                          * Send a packet designed to force a response
 292                          * if the peer is up and reachable:
 293                          * either an ACK if the connection is still alive,
 294                          * or an RST if the peer has closed the connection
 295                          * due to timeout or reboot.
 296                          * Using sequence number tp->snd_una-1
 297                          * causes the transmitted zero-length segment
 298                          * to lie outside the receive window;
 299                          * by the protocol spec, this requires the
 300                          * correspondent TCP to respond.
 301                          */
 302                         tcpstat.tcps_keepprobe++;
 303 #ifdef TCP_COMPAT_42
 304                         /*
 305                          * The keepalive packet must have nonzero length
 306                          * to get a 4.2 host to respond.
 307                          */
 308                         tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
 309                             tp->rcv_nxt - 1, tp->snd_una - 1, 0);
 310 #else
 311                         tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
 312                             tp->rcv_nxt, tp->snd_una - 1, 0);
 313 #endif
 314                         tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
 315                 } else
 316                         tp->t_timer[TCPT_KEEP] = tcp_keepidle;
 317                 break;
 318
 319         dropit:
 320                 tcpstat.tcps_keepdrops++;
 321                 tp = tcp_drop(tp, 0); /* ETIMEDOUT); */
 322                 break;
 323         }
 324
 325         return (tp);
 326 }