xref: /xnu-8796.101.5/bsd/netinet/tcp_timer.h (revision aca3beaa3dfbd42498b42c5e5ce20a938e6554e5)

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/*
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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
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 * 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: src/sys/netinet/tcp_timer.h,v 1.18 1999/12/29 04:41:03 peter Exp $
 */

#ifndef _NETINET_TCP_TIMER_H_
#define _NETINET_TCP_TIMER_H_
#include <sys/appleapiopts.h>

#ifdef BSD_KERNEL_PRIVATE
#include <kern/thread_call.h>
#endif /* BSD_KERNEL_PRIVATE */

/* Keep the external definition the same for binary compatibility */
#define TCPT_NTIMERS_EXT        4

/*
 * Definitions of the TCP timers.
 *
 * The TCPT_PTO timer is used for probing for a tail loss in a send window.
 * If this probe gets acknowledged using SACK, it will allow the connection
 * to enter fast-recovery instead of hitting a retransmit timeout. A probe
 * timeout will send the last unacknowledged segment to generate more acks
 * with SACK information which can be used for fast-retransmiting the lost
 * packets. This will fire in the order of 10ms.
 *
 * 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_DELACK timer is used for transmitting delayed acknowledgements
 * if an acknowledgement was delayed in anticipation of a new segment.
 *
 * 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.
 *
 * The TCPT_2MSL timer is used for keeping the conenction in Time-wait state
 * before fully closing it so that the connection 4-tuple can be reused.
 */
#ifdef BSD_KERNEL_PRIVATE

#define TCPT_PTO        0       /* Probe timeout */
#define TCPT_DELAYFR    1       /* Delay recovery if there is reordering */
#define TCPT_REXMT      2       /* retransmit */
#define TCPT_DELACK     3       /* delayed ack */
#define TCPT_PERSIST    4       /* retransmit persistence */
#define TCPT_KEEP       5       /* keep alive */
#define TCPT_2MSL       6       /* 2*msl quiet time timer */
#if MPTCP
#define TCPT_JACK_RXMT  7       /* retransmit timer for join ack */
#define TCPT_CELLICON   8       /* Timer to check for cell-activity */
#define TCPT_MAX        8
#else /* MPTCP */
#define TCPT_MAX        6
#endif /* !MPTCP */

#define TCPT_NONE       (TCPT_MAX + 1)
#define TCPT_NTIMERS    (TCPT_MAX + 1)

/* External definitions */
#define TCPT_REXMT_EXT          0
#define TCPT_PERSIST_EXT        1
#define TCPT_KEEP_EXT           2
#define TCPT_2MSL_EXT           3
#define TCPT_DELACK_EXT         4

#else /* !BSD_KERNEL_PRIVATE */
#define TCPT_REXMT      0               /* retransmit */
#define TCPT_PERSIST    1               /* retransmit persistence */
#define TCPT_KEEP       2               /* keep alive */
#define TCPT_2MSL       3               /* 2*msl quiet time timer */
#define TCPT_DELACK     4               /* delayed ack timer */
#if MPTCP
#define TCPT_JACK_RXMT  5       /* retransmit timer for join ack */
#define TCPT_MAX        5
#else /* MPTCP */
#define TCPT_MAX        4
#endif /* !MPTCP */
#define TCPT_NONE       (TCPT_MAX + 1)
#define TCPT_NTIMERS    (TCPT_MAX + 1)

#endif /* BSD_KERNEL_PRIVATE */

#ifdef BSD_KERNEL_PRIVATE
/*
 * Time constants.
 */
#define TCPTV_MSL       ( 15*TCP_RETRANSHZ)     /* max seg lifetime */
#define TCPTV_SRTTBASE  0       /* base roundtrip time; if 0, no idea yet */
#define TCPTV_RTOBASE   (  1*TCP_RETRANSHZ)     /* assumed RTO if no info */
#define TCPTV_SRTTDFLT  (  1*TCP_RETRANSHZ)     /* assumed RTT if no info */
#define TCPTV_PERSMIN   (  5*TCP_RETRANSHZ)     /* retransmit persistence */
#define TCPTV_PERSMAX   ( 60*TCP_RETRANSHZ)     /* maximum persist interval */

extern int tcptv_persmin_val;

#define TCPTV_KEEP_INIT ( 75*TCP_RETRANSHZ)     /* connect keep alive */
#define TCPTV_KEEP_IDLE (120*60*TCP_RETRANSHZ)  /* time before probing */
#define TCPTV_KEEPINTVL ( 75*TCP_RETRANSHZ)     /* default probe interval */
#define TCPTV_KEEPCNT   8                       /* max probes before drop */

#define TCPTV_REXMTMAX  ( 64*TCP_RETRANSHZ )    /* max REXMT value */
#define TCPTV_REXMTMIN  ( TCP_RETRANSHZ/33 )    /* min REXMT for non-local connections */

#define TCPTV_FINWAIT2  ( 60*TCP_RETRANSHZ)     /* timeout to get out of FIN_WAIT_2 */

/*
 * Window for counting received bytes to see if ack-stretching
 * can start (default 100 ms)
 */
#define TCPTV_UNACKWIN  ( TCP_RETRANSHZ/10 )

/* Receiver idle time, avoid ack-stretching after this idle time */
#define TCPTV_MAXRCVIDLE (TCP_RETRANSHZ/5 )

/*
 * No ack stretching during slow-start, until we see some packets.
 * By the time the receiver gets 512 packets, the senders cwnd
 * should open by a few hundred packets consdering the
 * slow-start progression.
 */
#define TCP_RCV_SS_PKTCOUNT     512

#define TCPTV_TWTRUNC   8               /* RTO factor to truncate TW */

#define TCP_LINGERTIME  120             /* linger at most 2 minutes */

#define TCP_MAXRXTSHIFT 12              /* maximum retransmits */

#ifdef  TCPTIMERS
static char *tcptimers[] =
{ "REXMT", "PERSIST", "KEEP", "2MSL", "DELACK"};
#endif /* TCPTIMERS */

/*
 * Persist, keep, 2msl and MPTCP's join-ack timer as slow timers which can
 * be coalesced at a higher granularity (500 ms).
 *
 * Rexmt and delayed ack timers are considered as fast timers which run
 * in the order of 100ms.
 *
 * Probe timeout is a quick timer which will run in the order of 10ms.
 */
#define IS_TIMER_HZ_500MS(i)    ((i) >= TCPT_PERSIST)
#define IS_TIMER_HZ_100MS(i)    ((i) >= TCPT_REXMT && (i) < TCPT_PERSIST)
#define IS_TIMER_HZ_10MS(i)     ((i) < TCPT_REXMT)

struct tcptimerlist;

struct tcptimerentry {
	LIST_ENTRY(tcptimerentry) le;   /* links for timer list */
	uint32_t timer_start;   /* tcp clock when the timer was started */
	uint16_t index;         /* index of lowest timer that needs to run first */
	uint16_t mode;          /* Bit-wise OR of timers that are active */
	uint32_t runtime;       /* deadline at which the first timer has to fire */
};

LIST_HEAD(timerlisthead, tcptimerentry);

struct tcptimerlist {
	struct timerlisthead lhead;     /* head of the list */
	lck_mtx_t mtx;          /* lock to protect the list */
	lck_grp_t *mtx_grp;     /* mutex group definition */
	thread_call_t call;     /* call entry */
	uint32_t runtime;       /* time at which this list is going to run */
	uint32_t schedtime;     /* time at which this list was scheduled */
	uint32_t entries;       /* Number of entries on the list */
	uint32_t maxentries;    /* Max number of entries at any time */

	/* Set desired mode when timer list running */
	boolean_t running;      /* Set when timer list is being processed */
	boolean_t scheduled;    /* set when the timer is scheduled */
#define TCP_TIMERLIST_10MS_MODE 0x1
#define TCP_TIMERLIST_100MS_MODE 0x2
#define TCP_TIMERLIST_500MS_MODE 0x4
	uint32_t mode;          /* Current mode of the timer */
	uint32_t pref_mode;     /* Preferred mode set by a connection */
	uint32_t pref_offset;   /* Preferred offset set by a connection */
	uint32_t idleruns;      /* Number of times the list has been idle in fast mode */
	struct tcptimerentry *next_te;  /* next timer entry pointer to process */
	u_int16_t probe_if_index; /* Interface index that needs to send probes */
};

/* number of idle runs allowed for TCP timer list in fast or quick modes */
#define TCP_FASTMODE_IDLERUN_MAX 10

/*
 * Minimum retransmit timeout is set to 30ms. We add a slop of
 * 200 ms to the retransmit value to account for processing
 * variance and delayed ack. This extra 200ms will help to avoid
 * spurious retransmits by taking into consideration the receivers
 * that wait for delayed ack timer instead of generating an ack
 * for every two packets.
 *
 * On a local link, the minimum retransmit timeout is 100ms and
 * variance is set to 0. This will make the sender a little bit more
 * aggressive on local link. When the connection is not established yet,
 * there is no need to add an extra 200ms to retransmit timeout because
 * the initial value is high (1s) and delayed ack is not a problem in
 * that case.
 */
#define TCPTV_REXMTSLOP ( TCP_RETRANSHZ/5 )     /* extra 200 ms slop */

/* macro to decide when retransmit slop (described above) should be added */
#define TCP_ADD_REXMTSLOP(tp) (tp->t_state >= TCPS_ESTABLISHED)

#define TCPT_RANGESET(tv, value, tvmin, tvmax, addslop) do { \
	(tv) = ((addslop) ? tcp_rexmt_slop : 0) + (value); \
	if ((uint32_t)(tv) < (uint32_t)(tvmin)) \
	        (tv) = (tvmin); \
	else if ((uint32_t)(tv) > (uint32_t)(tvmax)) \
	        (tv) = (tvmax); \
} while(0)

#define TCP_CONN_KEEPIDLE(tp) \
	((tp)->t_keepidle && \
	((tp)->t_inpcb->inp_socket->so_options & SO_KEEPALIVE) ? \
	        (tp)->t_keepidle : (uint32_t)tcp_keepidle)
#define TCP_CONN_KEEPINIT(tp) \
	(((tp)->t_keepinit > 0) ? (tp)->t_keepinit : (uint32_t)tcp_keepinit)
#define TCP_CONN_KEEPCNT(tp) \
	(((tp)->t_keepcnt > 0) ? (tp)->t_keepcnt : (uint32_t)tcp_keepcnt)
#define TCP_CONN_KEEPINTVL(tp) \
	(((tp)->t_keepintvl > 0) ? (tp)->t_keepintvl : (uint32_t)tcp_keepintvl)
#define TCP_CONN_MAXIDLE(tp) \
	(TCP_CONN_KEEPCNT(tp) * TCP_CONN_KEEPINTVL(tp))

#define TCP_IDLETIMEOUT(tp) \
	(((TCP_ADD_REXMTSLOP(tp)) ? 0 : tcp_rexmt_slop) + tp->t_rxtcur)

TAILQ_HEAD(tcptailq, tcpcb);

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_delack;          /* delayed ack timer */
extern int tcp_maxpersistidle;
extern int tcp_msl;
extern int tcp_ttl;             /* time to live for TCP segs */
extern int tcp_backoff[];
extern int tcp_rexmt_slop;
extern u_int32_t tcp_max_persist_timeout;       /* Maximum persistence for Zero Window Probes */

#define OFFSET_FROM_START(tp, off) ((tcp_now + (off)) - (tp)->tentry.timer_start)

#endif /* BSD_KERNEL_PRIVATE */
#endif /* !_NETINET_TCP_TIMER_H_ */