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+.\"
+.\" Copyright (c) 2000 Alfred Perlstein
+.\"
+.\" All rights reserved.
+.\"
+.\" 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 DEVELOPERS ``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 DEVELOPERS 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.
+.\"
+.\" $FreeBSD$
+.\" "
+.Dd November 15, 2000
+.Dt ACCF_DATA 9
+.Os
+.Sh NAME
+.Nm accf_data
+.Nd buffer incoming connections until data arrives
+.Sh SYNOPSIS
+.Nm options INET
+.Nm options ACCEPT_FILTER_DATA
+.Nm kldload accf_data
+.Sh DESCRIPTION
+This is a filter to be placed on a socket that will be using
+.Fn accept
+to receive incoming connections.
+.Pp
+It prevents the application from receiving the connected descriptor via
+.Fn accept
+until data arrives on the connection.
+.Pp
+The
+.Fa ACCEPT_FILTER_DATA
+kernel option is also a module that can be enabled at runtime via
+.Xr kldload 8
+if the INET option has been compiled into the kernel.
+.Sh EXAMPLES
+Assuming ACCEPT_FILTER_DATA has been included in the kernel config
+file or the
+.Nm
+module
+has been loaded, this will enable the data accept filter
+on the socket
+.Fa sok .
+.Bd -literal -offset 0i
+	struct accept_filter_arg afa;
+
+	bzero(&afa, sizeof(afa));
+	strcpy(afa.af_name, "dataready");
+	setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));
+.Ed
+.Sh SEE ALSO
+.Xr setsockopt 2 ,
+.Xr accept_filter 9 ,
+.Xr accf_dns 9
+.Xr accf_http 9
+.Sh HISTORY
+The accept filter mechanism and the
+accf_data filter were introduced in
+.Fx 4.0 .
+.Sh AUTHORS
+This manual page and the filter were written by
+.An Alfred Perlstein .