1.\" 2.\" Copyright (c) 2008 David Malone 3.\" 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" " 28.Dd July 16, 2008 29.Dt ACCF_DNS 9 30.Os 31.Sh NAME 32.Nm accf_dns 33.Nd buffer incoming DNS requests until the whole first request is present 34.Sh SYNOPSIS 35.Nm options INET 36.Nm options ACCEPT_FILTER_DNS 37.Nm kldload accf_dns 38.Sh DESCRIPTION 39This is a filter to be placed on a socket that will be using 40.Fn accept 41to receive incoming connections. 42.Pp 43It prevents the application from receiving the connected descriptor via 44.Fn accept 45until a whole DNS request is available on the socket. 46It does this by reading the first two bytes of the request, 47to determine its size, 48and waiting until the required amount of data is available to be read. 49.Pp 50The 51.Fa ACCEPT_FILTER_DNS 52kernel option is also a module that can be enabled at runtime via 53.Xr kldload 8 54if the INET option has been compiled into the kernel. 55.Sh EXAMPLES 56If the 57.Nm 58module is available in the kernel, 59the following code will enable the DNS accept filter 60on a socket 61.Fa sok . 62.Bd -literal -offset 0i 63 struct accept_filter_arg afa; 64 65 bzero(&afa, sizeof(afa)); 66 strcpy(afa.af_name, "dnsready"); 67 setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa)); 68.Ed 69.Sh SEE ALSO 70.Xr setsockopt 2 , 71.Xr accept_filter 9 , 72.Xr accf_data 9 , 73.Xr accf_http 9 74.Sh HISTORY 75The accept filter mechanism was introduced in 76.Fx 4.0 . 77.Sh AUTHORS 78This manual page and the filter were written by 79.An David Malone . 80