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.