The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_timer.c

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    1 /*
    2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
    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 8.2 (Berkeley) 5/24/95
   34  * $FreeBSD: src/sys/netinet/tcp_timer.c,v 1.20.2.3 1999/09/05 08:18:44 peter Exp $
   35  */
   36 
   37 #include "opt_tcpdebug.h"
   38 
   39 #ifndef TUBA_INCLUDE
   40 #include <sys/param.h>
   41 #include <sys/queue.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/sysctl.h>
   45 #include <sys/malloc.h>
   46 #include <sys/mbuf.h>
   47 #include <sys/socket.h>
   48 #include <sys/socketvar.h>
   49 #include <sys/protosw.h>
   50 #include <sys/errno.h>
   51 
   52 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
   53 
   54 #include <net/if.h>
   55 #include <net/route.h>
   56 
   57 #include <netinet/in.h>
   58 #include <netinet/in_systm.h>
   59 #include <netinet/ip.h>
   60 #include <netinet/in_pcb.h>
   61 #include <netinet/ip_var.h>
   62 #include <netinet/tcp.h>
   63 #include <netinet/tcp_fsm.h>
   64 #include <netinet/tcp_seq.h>
   65 #include <netinet/tcp_timer.h>
   66 #include <netinet/tcp_var.h>
   67 #include <netinet/tcpip.h>
   68 #ifdef TCPDEBUG
   69 #include <netinet/tcp_debug.h>
   70 #endif
   71 
   72 int     tcp_keepinit = TCPTV_KEEP_INIT;
   73 SYSCTL_INT(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit,
   74         CTLFLAG_RW, &tcp_keepinit , 0, "");
   75 
   76 int     tcp_keepidle = TCPTV_KEEP_IDLE;
   77 SYSCTL_INT(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle,
   78         CTLFLAG_RW, &tcp_keepidle , 0, "");
   79 
   80 static int      tcp_keepintvl = TCPTV_KEEPINTVL;
   81 SYSCTL_INT(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl,
   82         CTLFLAG_RW, &tcp_keepintvl , 0, "");
   83 
   84 static int      always_keepalive = 0;
   85 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive,
   86         CTLFLAG_RW, &always_keepalive , 0, "");
   87 
   88 static int      tcp_keepcnt = TCPTV_KEEPCNT;
   89         /* max idle probes */
   90 static int      tcp_maxpersistidle = TCPTV_KEEP_IDLE;
   91         /* max idle time in persist */
   92 int     tcp_maxidle;
   93 #else /* TUBA_INCLUDE */
   94 
   95 static  int tcp_maxpersistidle;
   96 #endif /* TUBA_INCLUDE */
   97 
   98 /*
   99  * Fast timeout routine for processing delayed acks
  100  */
  101 void
  102 tcp_fasttimo()
  103 {
  104         register struct inpcb *inp;
  105         register struct tcpcb *tp;
  106         int s;
  107 
  108         s = splnet();
  109 
  110         for (inp = tcb.lh_first; inp != NULL; inp = inp->inp_list.le_next) {
  111                 if ((tp = (struct tcpcb *)inp->inp_ppcb) &&
  112                     (tp->t_flags & TF_DELACK)) {
  113                         tp->t_flags &= ~TF_DELACK;
  114                         tp->t_flags |= TF_ACKNOW;
  115                         tcpstat.tcps_delack++;
  116                         (void) tcp_output(tp);
  117                 }
  118         }
  119         splx(s);
  120 }
  121 
  122 /*
  123  * Tcp protocol timeout routine called every 500 ms.
  124  * Updates the timers in all active tcb's and
  125  * causes finite state machine actions if timers expire.
  126  */
  127 void
  128 tcp_slowtimo()
  129 {
  130         register struct inpcb *ip, *ipnxt;
  131         register struct tcpcb *tp;
  132         register int i;
  133         int s;
  134 #ifdef TCPDEBUG
  135         int ostate;
  136 #endif
  137 
  138         s = splnet();
  139 
  140         tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
  141 
  142         ip = tcb.lh_first;
  143         if (ip == NULL) {
  144                 splx(s);
  145                 return;
  146         }
  147         /*
  148          * Search through tcb's and update active timers.
  149          */
  150         for (; ip != NULL; ip = ipnxt) {
  151                 ipnxt = ip->inp_list.le_next;
  152                 tp = intotcpcb(ip);
  153                 if (tp == 0 || tp->t_state == TCPS_LISTEN)
  154                         continue;
  155                 for (i = 0; i < TCPT_NTIMERS; i++) {
  156                         if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
  157 #ifdef TCPDEBUG
  158                                 ostate = tp->t_state;
  159 #endif
  160                                 tp = tcp_timers(tp, i);
  161                                 if (tp == NULL)
  162                                         goto tpgone;
  163 #ifdef TCPDEBUG
  164                                 if (tp->t_inpcb->inp_socket->so_options
  165                                     & SO_DEBUG)
  166                                         tcp_trace(TA_USER, ostate, tp,
  167                                                   (struct tcpiphdr *)0,
  168                                                   PRU_SLOWTIMO);
  169 #endif
  170                         }
  171                 }
  172                 tp->t_idle++;
  173                 tp->t_duration++;
  174                 if (tp->t_rtt)
  175                         tp->t_rtt++;
  176 tpgone:
  177                 ;
  178         }
  179         tcp_iss += TCP_ISSINCR/PR_SLOWHZ;               /* increment iss */
  180 #ifdef TCP_COMPAT_42
  181         if ((int)tcp_iss < 0)
  182                 tcp_iss = TCP_ISSINCR;                  /* XXX */
  183 #endif
  184         tcp_now++;                                      /* for timestamps */
  185         splx(s);
  186 }
  187 #ifndef TUBA_INCLUDE
  188 
  189 /*
  190  * Cancel all timers for TCP tp.
  191  */
  192 void
  193 tcp_canceltimers(tp)
  194         struct tcpcb *tp;
  195 {
  196         register int i;
  197 
  198         for (i = 0; i < TCPT_NTIMERS; i++)
  199                 tp->t_timer[i] = 0;
  200 }
  201 
  202 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
  203     { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
  204 
  205 static int tcp_totbackoff = 511;        /* sum of tcp_backoff[] */
  206 
  207 /*
  208  * TCP timer processing.
  209  */
  210 struct tcpcb *
  211 tcp_timers(tp, timer)
  212         register struct tcpcb *tp;
  213         int timer;
  214 {
  215         register int rexmt;
  216 
  217         switch (timer) {
  218 
  219         /*
  220          * 2 MSL timeout in shutdown went off.  If we're closed but
  221          * still waiting for peer to close and connection has been idle
  222          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
  223          * control block.  Otherwise, check again in a bit.
  224          */
  225         case TCPT_2MSL:
  226                 if (tp->t_state != TCPS_TIME_WAIT &&
  227                     tp->t_idle <= tcp_maxidle)
  228                         tp->t_timer[TCPT_2MSL] = tcp_keepintvl;
  229                 else
  230                         tp = tcp_close(tp);
  231                 break;
  232 
  233         /*
  234          * Retransmission timer went off.  Message has not
  235          * been acked within retransmit interval.  Back off
  236          * to a longer retransmit interval and retransmit one segment.
  237          */
  238         case TCPT_REXMT:
  239                 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
  240                         tp->t_rxtshift = TCP_MAXRXTSHIFT;
  241                         tcpstat.tcps_timeoutdrop++;
  242                         tp = tcp_drop(tp, tp->t_softerror ?
  243                             tp->t_softerror : ETIMEDOUT);
  244                         break;
  245                 }
  246                 tcpstat.tcps_rexmttimeo++;
  247                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
  248                 TCPT_RANGESET(tp->t_rxtcur, rexmt,
  249                     tp->t_rttmin, TCPTV_REXMTMAX);
  250                 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
  251                 /*
  252                  * If losing, let the lower level know and try for
  253                  * a better route.  Also, if we backed off this far,
  254                  * our srtt estimate is probably bogus.  Clobber it
  255                  * so we'll take the next rtt measurement as our srtt;
  256                  * move the current srtt into rttvar to keep the current
  257                  * retransmit times until then.
  258                  */
  259                 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
  260                         in_losing(tp->t_inpcb);
  261                         tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
  262                         tp->t_srtt = 0;
  263                 }
  264                 tp->snd_nxt = tp->snd_una;
  265                 /*
  266                  * Force a segment to be sent.
  267                  */
  268                 tp->t_flags |= TF_ACKNOW;
  269                 /*
  270                  * If timing a segment in this window, stop the timer.
  271                  */
  272                 tp->t_rtt = 0;
  273                 /*
  274                  * Close the congestion window down to one segment
  275                  * (we'll open it by one segment for each ack we get).
  276                  * Since we probably have a window's worth of unacked
  277                  * data accumulated, this "slow start" keeps us from
  278                  * dumping all that data as back-to-back packets (which
  279                  * might overwhelm an intermediate gateway).
  280                  *
  281                  * There are two phases to the opening: Initially we
  282                  * open by one mss on each ack.  This makes the window
  283                  * size increase exponentially with time.  If the
  284                  * window is larger than the path can handle, this
  285                  * exponential growth results in dropped packet(s)
  286                  * almost immediately.  To get more time between
  287                  * drops but still "push" the network to take advantage
  288                  * of improving conditions, we switch from exponential
  289                  * to linear window opening at some threshhold size.
  290                  * For a threshhold, we use half the current window
  291                  * size, truncated to a multiple of the mss.
  292                  *
  293                  * (the minimum cwnd that will give us exponential
  294                  * growth is 2 mss.  We don't allow the threshhold
  295                  * to go below this.)
  296                  */
  297                 {
  298                 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
  299                 if (win < 2)
  300                         win = 2;
  301                 tp->snd_cwnd = tp->t_maxseg;
  302                 tp->snd_ssthresh = win * tp->t_maxseg;
  303                 tp->t_dupacks = 0;
  304                 }
  305                 (void) tcp_output(tp);
  306                 break;
  307 
  308         /*
  309          * Persistance timer into zero window.
  310          * Force a byte to be output, if possible.
  311          */
  312         case TCPT_PERSIST:
  313                 tcpstat.tcps_persisttimeo++;
  314                 /*
  315                  * Hack: if the peer is dead/unreachable, we do not
  316                  * time out if the window is closed.  After a full
  317                  * backoff, drop the connection if the idle time
  318                  * (no responses to probes) reaches the maximum
  319                  * backoff that we would use if retransmitting.
  320                  */
  321                 if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
  322                     (tp->t_idle >= tcp_maxpersistidle ||
  323                     tp->t_idle >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
  324                         tcpstat.tcps_persistdrop++;
  325                         tp = tcp_drop(tp, ETIMEDOUT);
  326                         break;
  327                 }
  328                 tcp_setpersist(tp);
  329                 tp->t_force = 1;
  330                 (void) tcp_output(tp);
  331                 tp->t_force = 0;
  332                 break;
  333 
  334         /*
  335          * Keep-alive timer went off; send something
  336          * or drop connection if idle for too long.
  337          */
  338         case TCPT_KEEP:
  339                 tcpstat.tcps_keeptimeo++;
  340                 if (tp->t_state < TCPS_ESTABLISHED)
  341                         goto dropit;
  342                 if ((always_keepalive ||
  343                     tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE) &&
  344                     tp->t_state <= TCPS_CLOSING) {
  345                         if (tp->t_idle >= tcp_keepidle + tcp_maxidle)
  346                                 goto dropit;
  347                         /*
  348                          * Send a packet designed to force a response
  349                          * if the peer is up and reachable:
  350                          * either an ACK if the connection is still alive,
  351                          * or an RST if the peer has closed the connection
  352                          * due to timeout or reboot.
  353                          * Using sequence number tp->snd_una-1
  354                          * causes the transmitted zero-length segment
  355                          * to lie outside the receive window;
  356                          * by the protocol spec, this requires the
  357                          * correspondent TCP to respond.
  358                          */
  359                         tcpstat.tcps_keepprobe++;
  360 #ifdef TCP_COMPAT_42
  361                         /*
  362                          * The keepalive packet must have nonzero length
  363                          * to get a 4.2 host to respond.
  364                          */
  365                         tcp_respond(tp, tp->t_template, (struct mbuf *)NULL,
  366                             tp->rcv_nxt - 1, tp->snd_una - 1, 0);
  367 #else
  368                         tcp_respond(tp, tp->t_template, (struct mbuf *)NULL,
  369                             tp->rcv_nxt, tp->snd_una - 1, 0);
  370 #endif
  371                         tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
  372                 } else
  373                         tp->t_timer[TCPT_KEEP] = tcp_keepidle;
  374                 break;
  375         dropit:
  376                 tcpstat.tcps_keepdrops++;
  377                 tp = tcp_drop(tp, ETIMEDOUT);
  378                 break;
  379         }
  380         return (tp);
  381 }
  382 #endif /* TUBA_INCLUDE */

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