accept_filter(9)

NAME

accept_filter, accept_filt_add, accept_filt_del, accept_filt_generic_mod_event, accept_filt_get - filter in

coming 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 ker

nel pre-process incoming connections. An accept filter is requested

via the
setsockopt(2) system call, passing in an optname of SO_AC

CEPTFILTER.

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 mal

loc(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 con

nection 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 ac

cept 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 sim

ple 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_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 Ya

hoo! and
refined to be a loadable module system by Alfred Perlstein.

BSD June 25, 2000

BSD