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

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