NAME
accept_filter,
accept_filt_add,
accept_filt_del,
accept_filt_generic_mod_event,
accept_filt_get —
filter incoming
connections
SYNOPSIS
#define ACCEPT_FILTER_MOD
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/signalvar.h>
#include <sys/socketvar.h>
#include <netinet/accept_filter.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. This manual page describes the kernel interface for
accept filters. User applications request accept filters 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 accept filters currently provided with
NetBSD
(
accf_data(9) and
accf_http(9)) are implemented
as pseudo-devices, but an accept filter may use any supported means of
initializing and registering itself at system startup or later, including the
module framework if supported by the running kernel.
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 can be used by
accept filters which are loadable kernel modules to add and delete themselves.
SEE ALSO
setsockopt(2),
accf_data(9),
accf_http(9),
malloc(9)
HISTORY
The accept filter mechanism was introduced in
FreeBSD
4.0. It was ported to
NetBSD by Coyote Point
Systems, Inc. and appeared in
NetBSD 5.0.
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.