xref: /freebsd/share/man/man9/accf_dns.9 (revision 42249ef2)
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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