.\"	$NetBSD: ppsratecheck.9,v 1.6 2008/04/30 13:10:58 martin Exp $
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.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jun-ichiro itojun Hagino.
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.Dd August 3, 2000
.Dt PPSRATECHECK 9
.Os
.Sh NAME
.Nm ppsratecheck
.Nd function to help implement rate-limited actions
.Sh SYNOPSIS
.In sys/time.h
.Ft int
.Fn ppsratecheck "struct timeval *lasttime" "int *curpps" "int maxpps"
.Sh DESCRIPTION
The
.Fn ppsratecheck
function provides easy way to perform packet-per-sec,
or event-per-sec, rate limitation.
The motivation for implementing
.Fn ppsratecheck
was to provide a mechanism that could be used to add rate limitation to
network packet output.
For certain network packets, we may want to impose rate limitation,
to avoid denial-of-service attack possibilities.
.Pp
.Fa maxpps
specifies maximum permitted packets, or events, per second.
If
.Fn ppsratecheck
is called more than
.Fa maxpps
times in a given one second period,
the function will return 0, indicating that we exceeded the limit.
If we are below the limit, the function will return 1.
If
.Fa maxpps
is set to 0, the function will always return 0
.Pq no packets/events are permitted .
Negative
.Fa maxpps
indicates that rate limitation is disabled, and
.Fa ppsratecheck
will always return 1.
.Pp
.Fa curpps
and
.Fa lasttime
are used to maintain the number of recent calls.
.Fa curpps
will be incremented every time
.Fn ppsratecheck
is called, and will be reset whenever necessary.
.Sh SEE ALSO
.Xr log 9 ,
.Xr printf 9 ,
.Xr ratecheck 9 ,
.Xr time_second 9
.Sh HISTORY
The
.Fn ppsratecheck
function appeared in
.Nx 1.5 .