1.\" $NetBSD: ppsratecheck.9,v 1.6 2008/04/30 13:10:58 martin Exp $ 2.\" 3.\" Copyright (c) 2000 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Jun-ichiro itojun Hagino. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd August 3, 2000 31.Dt PPSRATECHECK 9 32.Os 33.Sh NAME 34.Nm ppsratecheck 35.Nd function to help implement rate-limited actions 36.Sh SYNOPSIS 37.In sys/time.h 38.Ft int 39.Fn ppsratecheck "struct timeval *lasttime" "int *curpps" "int maxpps" 40.Sh DESCRIPTION 41The 42.Fn ppsratecheck 43function provides easy way to perform packet-per-sec, 44or event-per-sec, rate limitation. 45The motivation for implementing 46.Fn ppsratecheck 47was to provide a mechanism that could be used to add rate limitation to 48network packet output. 49For certain network packets, we may want to impose rate limitation, 50to avoid denial-of-service attack possibilities. 51.Pp 52.Fa maxpps 53specifies maximum permitted packets, or events, per second. 54If 55.Fn ppsratecheck 56is called more than 57.Fa maxpps 58times in a given one second period, 59the function will return 0, indicating that we exceeded the limit. 60If we are below the limit, the function will return 1. 61If 62.Fa maxpps 63is set to 0, the function will always return 0 64.Pq no packets/events are permitted . 65Negative 66.Fa maxpps 67indicates that rate limitation is disabled, and 68.Fa ppsratecheck 69will always return 1. 70.Pp 71.Fa curpps 72and 73.Fa lasttime 74are used to maintain the number of recent calls. 75.Fa curpps 76will be incremented every time 77.Fn ppsratecheck 78is called, and will be reset whenever necessary. 79.Sh SEE ALSO 80.Xr log 9 , 81.Xr printf 9 , 82.Xr ratecheck 9 , 83.Xr time_second 9 84.Sh HISTORY 85The 86.Fn ppsratecheck 87function appeared in 88.Nx 1.5 . 89