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 }