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