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ACCEPT_FILTER(9)       FreeBSD Kernel Developer's Manual      ACCEPT_FILTER(9)

NAME
     accept_filter, accept_filt_add, accept_filt_del,
     accept_filt_generic_mod_event, accept_filt_get -- filter incoming connec-
     tions

SYNOPSIS
     #include <sys/types.h>
     #include <sys/module.h>
     #include <sys/socket.h>
     #define ACCEPT_FILTER_MOD
     #include <sys/socketvar.h>

     int
     accept_filt_add(struct accept_filter *filt);

     int
     accept_filt_del(char *name);

     int
     accept_filt_generic_mod_event(module_t mod, int event, void *data);

     struct accept_filter *
     accept_filt_get(char *name);

DESCRIPTION
     Accept filters allow an application to request that the kernel pre-
     process incoming connections.  An accept filter is	requested via the
     setsockopt(2) system call,	passing	in an optname of SO_ACCEPTFILTER.

IMPLEMENTATION NOTES
     A module that wants to be an accept filter	must provide a struct
     accept_filter to the system:

     struct accept_filter {
	     char    accf_name[16];
	     void    (*accf_callback)(struct socket *so, void *arg, int	waitflag);
	     void *  (*accf_create)(struct socket *so, char *arg);
	     void    (*accf_destroy)(struct socket *so);
	     SLIST_ENTRY(accept_filter)	accf_next;   /*	next on	the list */
     };

     The module	should register	it with	the function accept_filt_add(),	pass-
     ing a pointer to a	struct accept_filter, allocated	with malloc(9).

     The fields	of struct accept_filter	are as follows:

     accf_name	    Name of the	filter;	this is	how it will be accessed	from
		    userland.

     accf_callback  The	callback that the kernel will do once the connection
		    is established.  It	is the same as a socket	upcall and
		    will be called when	the connection is established and
		    whenever new data arrives on the socket, unless the	call-
		    back modifies the socket's flags.

     accf_create    Called whenever a setsockopt(2) installs the filter	onto a
		    listening socket.

     accf_destroy   Called whenever the	user removes the accept	filter on the
		    socket.

     The accept_filt_del() function passed the same string used	in
     accept_filter.accf_name during registration with accept_filt_add(), the
     kernel will then disallow and further userland use	of the filter.

     The accept_filt_get() function is used internally to locate which accept
     filter to use via the setsockopt(2) system	call.

     The accept_filt_generic_mod_event() function provides a simple way	to
     avoid duplication of code for accept filters which	do not use the argu-
     ment field	to load	and unload themselves.	This function can be used in
     the moduledata_t struct for the DECLARE_MODULE(9) macro.

SEE ALSO
     setsockopt(2), accf_data(9), accf_dns(9), accf_http(9), malloc(9)

HISTORY
     The accept	filter mechanism was introduced	in FreeBSD 4.0.

AUTHORS
     This manual page was written by Alfred Perlstein, Sheldon Hearn and
     Jeroen Ruigrok van	der Werven.

     The accept	filter concept was pioneered by	David Filo at Yahoo! and
     refined to	be a loadable module system by Alfred Perlstein.

FreeBSD	10.1			 June 25, 2000			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | IMPLEMENTATION NOTES | SEE ALSO | HISTORY | AUTHORS

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<https://www.freebsd.org/cgi/man.cgi?query=accept_filter&manpath=FreeBSD+10.1-RELEASE>

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