accf_dns man page on FreeBSD

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ACCF_DNS(9)		 BSD Kernel Developer's Manual		   ACCF_DNS(9)

     accf_dns — buffer incoming DNS requests until the whole first request is

     options INET
     options ACCEPT_FILTER_DNS
     kldload accf_dns

     This is a filter to be placed on a socket that will be using accept() to
     receive incoming connections.

     It prevents the application from receiving the connected descriptor via
     accept() until a whole DNS request is available on the socket.  It does
     this by reading the first two bytes of the request, to determine its
     size, and waiting until the required amount of data is available to be

     The ACCEPT_FILTER_DNS kernel option is also a module that can be enabled
     at runtime via kldload(8) if the INET option has been compiled into the

     If the accf_dns module is available in the kernel, the following code
     will enable the DNS accept filter on a socket sok.

	     struct accept_filter_arg afa;

	     bzero(&afa, sizeof(afa));
	     strcpy(afa.af_name, "dnsready");
	     setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));

     setsockopt(2), accept_filter(9), accf_http(9) accf_data(9)

     The accept filter mechanism was introduced in FreeBSD 4.0.

     This manual page and the filter were written by David Malone.

BSD				 July 16, 2008				   BSD

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