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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/socket.h>
     #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)
		     __P((struct socket *so, void *arg, int waitflag));
	     void *  (*accf_create)
		     __P((struct socket *so, char *arg));
	     void    (*accf_destroy)
		     __P((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 connec-
		       tion 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
		       callback 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.

     accept_filt_del() 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.

     accept_filt_get() is used internally to locate which accept filter to use
     via the setsockopt() syscall.

     accept_filt_generic_mod_event() provides a simple way to avoid duplicate
     code for accept filters which don't use argument field to load and unload
     themselves.  It is a function that can be put in the load/unload struct
     for the DECLARE_MODULE() macro.

SEE ALSO
     setsockopt(2), accf_data(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 4.9			 June 25, 2000			   FreeBSD 4.9