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+.\"	$OpenBSD: ppsratecheck.9,v 1.7 2020/06/26 18:48:31 cheloha Exp $
+.\"	$NetBSD: ppsratecheck.9,v 1.1 2000/08/03 00:09:39 itojun Exp $
+.\"
+.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
+.\" All rights reserved.
+.\"
+.\" This code is derived from software contributed to The NetBSD Foundation
+.\" by Jun-ichiro itojun Hagino.
+.\"
+.\" 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.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
+.\"
+.Dd $Mdocdate: June 26 2020 $
+.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 an 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
+.Fn 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 microtime 9 ,
+.Xr printf 9 ,
+.Xr ratecheck 9
+.Sh HISTORY
+The
+.Fn ppsratecheck
+function appeared in
+.Nx 1.5 .