1.\" $NetBSD: ppsratecheck.9,v 1.3 2002/02/13 08:18:49 ross 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.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the NetBSD 20.\" Foundation, Inc. and its contributors. 21.\" 4. Neither the name of The NetBSD Foundation nor the names of its 22.\" contributors may be used to endorse or promote products derived 23.\" from this software without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 26.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 27.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 28.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 29.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 31.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 32.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 33.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 34.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35.\" POSSIBILITY OF SUCH DAMAGE. 36.\" 37.Dd August 3, 2000 38.Dt PPSRATECHECK 9 39.Os 40.Sh NAME 41.Nm ppsratecheck 42.Nd function to help implement rate-limited actions 43.Sh SYNOPSIS 44.Fd #include \*[Lt]sys/time.h\*[Gt] 45.Ft int 46.Fn ppsratecheck "struct timeval *lasttime" "int *curpps" "int maxpps" 47.Sh DESCRIPTION 48The 49.Fn ppsratecheck 50function provides easy way to perform packet-per-sec, 51or event-per-sec, rate limitation. 52The motivation for implementing 53.Fn ppsratecheck 54was to provide a mechanism that could be used to add rate limitation to 55network packet output. 56For certain network packets, we may want to impose rate limitation, 57to avoid denial-of-service attack possibilities. 58.Pp 59.Fa maxpps 60specifies maximum permitted packets, or events, per second. 61If 62.Fn ppsratecheck 63is called more than 64.Fa maxpps 65times in a given one second period, 66the function will return 0, indicating that we exceeded the limit. 67If we are below the limit, the function will return 1. 68If 69.Fa maxpps 70is set to 0, the function will always return 0 71.Pq no packets/events are permitted . 72Negative 73.Fa maxpps 74indicates that rate limitation is disabled, and 75.Fa ppsratecheck 76will always return 1. 77.Pp 78.Fa curpps 79and 80.Fa lasttime 81are used to maintain the number of recent calls. 82.Fa curpps 83will be incremented every time 84.Fn ppsratecheck 85is called, and will be reset whenever necessary. 86.Sh SEE ALSO 87.Xr log 9 , 88.Xr printf 9 , 89.Xr ratecheck 9 , 90.Xr time 9 91.Sh HISTORY 92The 93.Fn ppsratecheck 94function appeared in 95.Nx 1.5 . 96