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.h

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1982, 1986, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  * 3. Neither the name of the University nor the names of its contributors
   16  *    may be used to endorse or promote products derived from this software
   17  *    without specific prior written permission.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  *
   31  *      @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
   32  * $FreeBSD: stable/12/sys/netinet/tcp_timer.h 335924 2018-07-04 02:47:16Z mmacy $
   33  */
   34 
   35 #ifndef _NETINET_TCP_TIMER_H_
   36 #define _NETINET_TCP_TIMER_H_
   37 
   38 /*
   39  * The TCPT_REXMT timer is used to force retransmissions.
   40  * The TCP has the TCPT_REXMT timer set whenever segments
   41  * have been sent for which ACKs are expected but not yet
   42  * received.  If an ACK is received which advances tp->snd_una,
   43  * then the retransmit timer is cleared (if there are no more
   44  * outstanding segments) or reset to the base value (if there
   45  * are more ACKs expected).  Whenever the retransmit timer goes off,
   46  * we retransmit one unacknowledged segment, and do a backoff
   47  * on the retransmit timer.
   48  *
   49  * The TCPT_PERSIST timer is used to keep window size information
   50  * flowing even if the window goes shut.  If all previous transmissions
   51  * have been acknowledged (so that there are no retransmissions in progress),
   52  * and the window is too small to bother sending anything, then we start
   53  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
   54  * we go to transmit state.  Otherwise, at intervals send a single byte
   55  * into the peer's window to force him to update our window information.
   56  * We do this at most as often as TCPT_PERSMIN time intervals,
   57  * but no more frequently than the current estimate of round-trip
   58  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
   59  * a window update from the peer.
   60  *
   61  * The TCPT_KEEP timer is used to keep connections alive.  If an
   62  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
   63  * but not yet established, then we drop the connection.  Once the connection
   64  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
   65  * (and keepalives have been enabled on the socket), we begin to probe
   66  * the connection.  We force the peer to send us a segment by sending:
   67  *      <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
   68  * This segment is (deliberately) outside the window, and should elicit
   69  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
   70  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
   71  * amount of time probing, then we drop the connection.
   72  */
   73 
   74 /*
   75  * Time constants.
   76  */
   77 #define TCPTV_MSL       ( 30*hz)                /* max seg lifetime (hah!) */
   78 #define TCPTV_SRTTBASE  0                       /* base roundtrip time;
   79                                                    if 0, no idea yet */
   80 #define TCPTV_RTOBASE   (  3*hz)                /* assumed RTO if no info */
   81 
   82 #define TCPTV_PERSMIN   (  5*hz)                /* minimum persist interval */
   83 #define TCPTV_PERSMAX   ( 60*hz)                /* maximum persist interval */
   84 
   85 #define TCPTV_KEEP_INIT ( 75*hz)                /* initial connect keepalive */
   86 #define TCPTV_KEEP_IDLE (120*60*hz)             /* dflt time before probing */
   87 #define TCPTV_KEEPINTVL ( 75*hz)                /* default probe interval */
   88 #define TCPTV_KEEPCNT   8                       /* max probes before drop */
   89 
   90 #define TCPTV_FINWAIT2_TIMEOUT (60*hz)         /* FIN_WAIT_2 timeout if no receiver */
   91 
   92 /*
   93  * Minimum retransmit timer is 3 ticks, for algorithmic stability.
   94  * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
   95  * the expected worst-case processing variances by the kernels
   96  * representing the end points.  Such variances do not always show
   97  * up in the srtt because the timestamp is often calculated at
   98  * the interface rather then at the TCP layer.  This value is
   99  * typically 50ms.  However, it is also possible that delayed
  100  * acks (typically 100ms) could create issues so we set the slop
  101  * to 200ms to try to cover it.  Note that, properly speaking,
  102  * delayed-acks should not create a major issue for interactive
  103  * environments which 'P'ush the last segment, at least as
  104  * long as implementations do the required 'at least one ack
  105  * for every two packets' for the non-interactive streaming case.
  106  * (maybe the RTO calculation should use 2*RTT instead of RTT
  107  * to handle the ack-every-other-packet case).
  108  *
  109  * The prior minimum of 1*hz (1 second) badly breaks throughput on any
  110  * networks faster then a modem that has minor (e.g. 1%) packet loss.
  111  */
  112 #define TCPTV_MIN       ( hz/33 )               /* minimum allowable value */
  113 #define TCPTV_CPU_VAR   ( hz/5 )                /* cpu variance allowed (200ms) */
  114 #define TCPTV_REXMTMAX  ( 64*hz)                /* max allowable REXMT value */
  115 
  116 #define TCPTV_TWTRUNC   8                       /* RTO factor to truncate TW */
  117 
  118 #define TCP_LINGERTIME  120                     /* linger at most 2 minutes */
  119 
  120 #define TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
  121 
  122 #define TCPTV_DELACK    ( hz/10 )               /* 100ms timeout */
  123 
  124 /*
  125  * If we exceed this number of retransmits for a single segment, we'll consider
  126  * the current srtt measurement no longer valid and will recalculate from
  127  * scratch starting with the next ACK.
  128  */
  129 #define TCP_RTT_INVALIDATE (TCP_MAXRXTSHIFT / 4)
  130 
  131 #ifdef  TCPTIMERS
  132 static const char *tcptimers[] =
  133     { "REXMT", "PERSIST", "KEEP", "2MSL", "DELACK" };
  134 #endif
  135 
  136 /*
  137  * Force a time value to be in a certain range.
  138  */
  139 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
  140         (tv) = (value) + tcp_rexmit_slop; \
  141         if ((u_long)(tv) < (u_long)(tvmin)) \
  142                 (tv) = (tvmin); \
  143         if ((u_long)(tv) > (u_long)(tvmax)) \
  144                 (tv) = (tvmax); \
  145 } while(0)
  146 
  147 #ifdef _KERNEL
  148 
  149 struct xtcp_timer;
  150 
  151 struct tcp_timer {
  152         struct  callout tt_rexmt;       /* retransmit timer */
  153         struct  callout tt_persist;     /* retransmit persistence */
  154         struct  callout tt_keep;        /* keepalive */
  155         struct  callout tt_2msl;        /* 2*msl TIME_WAIT timer */
  156         struct  callout tt_delack;      /* delayed ACK timer */
  157         uint32_t        tt_flags;       /* Timers flags */
  158         uint32_t        tt_draincnt;    /* Count being drained */
  159 };
  160 
  161 /*
  162  * Flags for the tt_flags field.
  163  */
  164 #define TT_DELACK       0x0001
  165 #define TT_REXMT        0x0002
  166 #define TT_PERSIST      0x0004
  167 #define TT_KEEP         0x0008
  168 #define TT_2MSL         0x0010
  169 #define TT_MASK         (TT_DELACK|TT_REXMT|TT_PERSIST|TT_KEEP|TT_2MSL)
  170 
  171 /* 
  172  * Suspend flags - used when suspending a timer
  173  * from ever running again.
  174  */
  175 #define TT_DELACK_SUS   0x0100
  176 #define TT_REXMT_SUS    0x0200
  177 #define TT_PERSIST_SUS  0x0400
  178 #define TT_KEEP_SUS     0x0800
  179 #define TT_2MSL_SUS     0x1000
  180 
  181 #define TT_STOPPED      0x00010000
  182 
  183 #define TP_KEEPINIT(tp) ((tp)->t_keepinit ? (tp)->t_keepinit : tcp_keepinit)
  184 #define TP_KEEPIDLE(tp) ((tp)->t_keepidle ? (tp)->t_keepidle : tcp_keepidle)
  185 #define TP_KEEPINTVL(tp) ((tp)->t_keepintvl ? (tp)->t_keepintvl : tcp_keepintvl)
  186 #define TP_KEEPCNT(tp)  ((tp)->t_keepcnt ? (tp)->t_keepcnt : tcp_keepcnt)
  187 #define TP_MAXIDLE(tp)  (TP_KEEPCNT(tp) * TP_KEEPINTVL(tp))
  188 
  189 extern int tcp_persmin;                 /* minimum persist interval */
  190 extern int tcp_persmax;                 /* maximum persist interval */
  191 extern int tcp_keepinit;                /* time to establish connection */
  192 extern int tcp_keepidle;                /* time before keepalive probes begin */
  193 extern int tcp_keepintvl;               /* time between keepalive probes */
  194 extern int tcp_keepcnt;                 /* number of keepalives */
  195 extern int tcp_delacktime;              /* time before sending a delayed ACK */
  196 extern int tcp_maxpersistidle;
  197 extern int tcp_rexmit_min;
  198 extern int tcp_rexmit_slop;
  199 extern int tcp_msl;
  200 extern int tcp_ttl;                     /* time to live for TCP segs */
  201 extern int tcp_backoff[];
  202 extern int tcp_syn_backoff[];
  203 extern int tcp_totbackoff;
  204 extern int tcp_rexmit_drop_options;
  205 
  206 extern int tcp_always_keepalive;
  207 extern int tcp_finwait2_timeout;
  208 extern int tcp_fast_finwait2_recycle;
  209 
  210 VNET_DECLARE(int, tcp_pmtud_blackhole_detect);
  211 #define V_tcp_pmtud_blackhole_detect    VNET(tcp_pmtud_blackhole_detect)
  212 VNET_DECLARE(int, tcp_pmtud_blackhole_mss);
  213 #define V_tcp_pmtud_blackhole_mss       VNET(tcp_pmtud_blackhole_mss)
  214 VNET_DECLARE(int, tcp_v6pmtud_blackhole_mss);
  215 #define V_tcp_v6pmtud_blackhole_mss     VNET(tcp_v6pmtud_blackhole_mss)
  216 
  217 void tcp_inpinfo_lock_del(struct inpcb *inp, struct tcpcb *tp);
  218 
  219 void    tcp_timer_init(void);
  220 void    tcp_timer_2msl(void *xtp);
  221 void    tcp_timer_discard(void *);
  222 struct tcptw *
  223         tcp_tw_2msl_scan(int reuse);    /* XXX temporary? */
  224 void    tcp_timer_keep(void *xtp);
  225 void    tcp_timer_persist(void *xtp);
  226 void    tcp_timer_rexmt(void *xtp);
  227 void    tcp_timer_delack(void *xtp);
  228 
  229 #endif /* _KERNEL */
  230 
  231 #endif /* !_NETINET_TCP_TIMER_H_ */

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