NAME

       accept_filter,  accept_filt_add, accept_filt_del, accept_filt_generic_mod_event, accept_filt_get — filter
       incoming connections

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(),  passing 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 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.

       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 argument 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.

Debian                                            June 25, 2000                                 ACCEPT_FILTER(9)