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

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1982, 1986, 1993
      *      The Regents of the University of California.  All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
     * $FreeBSD: releng/12.0/sys/netinet/tcp_timer.h 335924 2018-07-04 02:47:16Z mmacy $
     */
    
    #ifndef _NETINET_TCP_TIMER_H_
    #define _NETINET_TCP_TIMER_H_
    
    /*
     * The TCPT_REXMT timer is used to force retransmissions.
     * The TCP has the TCPT_REXMT timer set whenever segments
     * have been sent for which ACKs are expected but not yet
     * received.  If an ACK is received which advances tp->snd_una,
     * then the retransmit timer is cleared (if there are no more
     * outstanding segments) or reset to the base value (if there
     * are more ACKs expected).  Whenever the retransmit timer goes off,
     * we retransmit one unacknowledged segment, and do a backoff
     * on the retransmit timer.
     *
     * The TCPT_PERSIST timer is used to keep window size information
     * flowing even if the window goes shut.  If all previous transmissions
     * have been acknowledged (so that there are no retransmissions in progress),
     * and the window is too small to bother sending anything, then we start
     * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
     * we go to transmit state.  Otherwise, at intervals send a single byte
     * into the peer's window to force him to update our window information.
     * We do this at most as often as TCPT_PERSMIN time intervals,
     * but no more frequently than the current estimate of round-trip
     * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
     * a window update from the peer.
     *
     * The TCPT_KEEP timer is used to keep connections alive.  If an
     * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
     * but not yet established, then we drop the connection.  Once the connection
     * is established, if the connection is idle for TCPTV_KEEP_IDLE time
     * (and keepalives have been enabled on the socket), we begin to probe
     * the connection.  We force the peer to send us a segment by sending:
     *      <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
     * This segment is (deliberately) outside the window, and should elicit
     * an ack segment in response from the peer.  If, despite the TCPT_KEEP
     * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
     * amount of time probing, then we drop the connection.
     */
    
    /*
     * Time constants.
     */
    #define TCPTV_MSL       ( 30*hz)                /* max seg lifetime (hah!) */
    #define TCPTV_SRTTBASE  0                       /* base roundtrip time;
                                                       if 0, no idea yet */
    #define TCPTV_RTOBASE   (  3*hz)                /* assumed RTO if no info */
    
    #define TCPTV_PERSMIN   (  5*hz)                /* minimum persist interval */
    #define TCPTV_PERSMAX   ( 60*hz)                /* maximum persist interval */
    
    #define TCPTV_KEEP_INIT ( 75*hz)                /* initial connect keepalive */
    #define TCPTV_KEEP_IDLE (120*60*hz)             /* dflt time before probing */
    #define TCPTV_KEEPINTVL ( 75*hz)                /* default probe interval */
    #define TCPTV_KEEPCNT   8                       /* max probes before drop */
    
    #define TCPTV_FINWAIT2_TIMEOUT (60*hz)         /* FIN_WAIT_2 timeout if no receiver */
    
    /*
     * Minimum retransmit timer is 3 ticks, for algorithmic stability.
     * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
     * the expected worst-case processing variances by the kernels
     * representing the end points.  Such variances do not always show
     * up in the srtt because the timestamp is often calculated at
     * the interface rather then at the TCP layer.  This value is
     * typically 50ms.  However, it is also possible that delayed
    * acks (typically 100ms) could create issues so we set the slop
    * to 200ms to try to cover it.  Note that, properly speaking,
    * delayed-acks should not create a major issue for interactive
    * environments which 'P'ush the last segment, at least as
    * long as implementations do the required 'at least one ack
    * for every two packets' for the non-interactive streaming case.
    * (maybe the RTO calculation should use 2*RTT instead of RTT
    * to handle the ack-every-other-packet case).
    *
    * The prior minimum of 1*hz (1 second) badly breaks throughput on any
    * networks faster then a modem that has minor (e.g. 1%) packet loss.
    */
   #define TCPTV_MIN       ( hz/33 )               /* minimum allowable value */
   #define TCPTV_CPU_VAR   ( hz/5 )                /* cpu variance allowed (200ms) */
   #define TCPTV_REXMTMAX  ( 64*hz)                /* max allowable REXMT value */
   
   #define TCPTV_TWTRUNC   8                       /* RTO factor to truncate TW */
   
   #define TCP_LINGERTIME  120                     /* linger at most 2 minutes */
   
   #define TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
   
   #define TCPTV_DELACK    ( hz/10 )               /* 100ms timeout */
   
   /*
    * If we exceed this number of retransmits for a single segment, we'll consider
    * the current srtt measurement no longer valid and will recalculate from
    * scratch starting with the next ACK.
    */
   #define TCP_RTT_INVALIDATE (TCP_MAXRXTSHIFT / 4)
   
   #ifdef  TCPTIMERS
   static const char *tcptimers[] =
       { "REXMT", "PERSIST", "KEEP", "2MSL", "DELACK" };
   #endif
   
   /*
    * Force a time value to be in a certain range.
    */
   #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
           (tv) = (value) + tcp_rexmit_slop; \
           if ((u_long)(tv) < (u_long)(tvmin)) \
                   (tv) = (tvmin); \
           if ((u_long)(tv) > (u_long)(tvmax)) \
                   (tv) = (tvmax); \
   } while(0)
   
   #ifdef _KERNEL
   
   struct xtcp_timer;
   
   struct tcp_timer {
           struct  callout tt_rexmt;       /* retransmit timer */
           struct  callout tt_persist;     /* retransmit persistence */
           struct  callout tt_keep;        /* keepalive */
           struct  callout tt_2msl;        /* 2*msl TIME_WAIT timer */
           struct  callout tt_delack;      /* delayed ACK timer */
           uint32_t        tt_flags;       /* Timers flags */
           uint32_t        tt_draincnt;    /* Count being drained */
   };
   
   /*
    * Flags for the tt_flags field.
    */
   #define TT_DELACK       0x0001
   #define TT_REXMT        0x0002
   #define TT_PERSIST      0x0004
   #define TT_KEEP         0x0008
   #define TT_2MSL         0x0010
   #define TT_MASK         (TT_DELACK|TT_REXMT|TT_PERSIST|TT_KEEP|TT_2MSL)
   
   /* 
    * Suspend flags - used when suspending a timer
    * from ever running again.
    */
   #define TT_DELACK_SUS   0x0100
   #define TT_REXMT_SUS    0x0200
   #define TT_PERSIST_SUS  0x0400
   #define TT_KEEP_SUS     0x0800
   #define TT_2MSL_SUS     0x1000
   
   #define TT_STOPPED      0x00010000
   
   #define TP_KEEPINIT(tp) ((tp)->t_keepinit ? (tp)->t_keepinit : tcp_keepinit)
   #define TP_KEEPIDLE(tp) ((tp)->t_keepidle ? (tp)->t_keepidle : tcp_keepidle)
   #define TP_KEEPINTVL(tp) ((tp)->t_keepintvl ? (tp)->t_keepintvl : tcp_keepintvl)
   #define TP_KEEPCNT(tp)  ((tp)->t_keepcnt ? (tp)->t_keepcnt : tcp_keepcnt)
   #define TP_MAXIDLE(tp)  (TP_KEEPCNT(tp) * TP_KEEPINTVL(tp))
   
   extern int tcp_persmin;                 /* minimum persist interval */
   extern int tcp_persmax;                 /* maximum persist interval */
   extern int tcp_keepinit;                /* time to establish connection */
   extern int tcp_keepidle;                /* time before keepalive probes begin */
   extern int tcp_keepintvl;               /* time between keepalive probes */
   extern int tcp_keepcnt;                 /* number of keepalives */
   extern int tcp_delacktime;              /* time before sending a delayed ACK */
   extern int tcp_maxpersistidle;
   extern int tcp_rexmit_min;
   extern int tcp_rexmit_slop;
   extern int tcp_msl;
   extern int tcp_ttl;                     /* time to live for TCP segs */
   extern int tcp_backoff[];
   extern int tcp_syn_backoff[];
   extern int tcp_totbackoff;
   extern int tcp_rexmit_drop_options;
   
   extern int tcp_always_keepalive;
   extern int tcp_finwait2_timeout;
   extern int tcp_fast_finwait2_recycle;
   
   VNET_DECLARE(int, tcp_pmtud_blackhole_detect);
   #define V_tcp_pmtud_blackhole_detect    VNET(tcp_pmtud_blackhole_detect)
   VNET_DECLARE(int, tcp_pmtud_blackhole_mss);
   #define V_tcp_pmtud_blackhole_mss       VNET(tcp_pmtud_blackhole_mss)
   VNET_DECLARE(int, tcp_v6pmtud_blackhole_mss);
   #define V_tcp_v6pmtud_blackhole_mss     VNET(tcp_v6pmtud_blackhole_mss)
   
   void tcp_inpinfo_lock_del(struct inpcb *inp, struct tcpcb *tp);
   
   void    tcp_timer_init(void);
   void    tcp_timer_2msl(void *xtp);
   void    tcp_timer_discard(void *);
   struct tcptw *
           tcp_tw_2msl_scan(int reuse);    /* XXX temporary? */
   void    tcp_timer_keep(void *xtp);
   void    tcp_timer_persist(void *xtp);
   void    tcp_timer_rexmt(void *xtp);
   void    tcp_timer_delack(void *xtp);
   
   #endif /* _KERNEL */
   
   #endif /* !_NETINET_TCP_TIMER_H_ */

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