eventhandler(9)

NAME

EVENTHANDLER - kernel event handling functions

SYNOPSIS

#include <sys/eventhandler.h>
EVENTHANDLER_DECLARE(name, type);
EVENTHANDLER_INVOKE(name, ...);
eventhandler_tag
EVENTHANDLER_REGISTER(name, func, arg, priority);
EVENTHANDLER_DEREGISTER(name, tag);
eventhandler_tag
eventhandler_register(struct eventhandler_list *list,  const
char *name,
        void *func, void *arg, int priority);
void
eventhandler_deregister(struct eventhandler_list *list,
        eventhandler_tag tag);
struct eventhandler_list *
eventhandler_find_list(const char *name);
void
eventhandler_prune_list(struct eventhandler_list *list);

DESCRIPTION

The EVENTHANDLER mechanism provides a way for kernel subsys

tems to register interest in kernel events and have their callback func

tions invoked
when these events occur.

The normal way to use this subsystem is via the macro inter

face. The
macros that can be used for working with event handlers and

callback
function lists are:

EVENTHANDLER_DECLARE()

This macro declares an event handler named by argu

ment name with
callback functions of type type.

EVENTHANDLER_REGISTER()

This macro registers a callback function func with

event handler
name. When invoked, function func will be invoked

with argument
arg as its first parameter along with any additional

parameters
passed in via macro EVENTHANDLER_INVOKE() (see be

low). Callback
functions are invoked in order of priority. The

relative priority of each callback among other callbacks associat

ed with an
event is given by argument priority, which is an in

teger ranging
from EVENTHANDLER_PRI_FIRST (highest priority), to
EVENTHANDLER_PRI_LAST (lowest priority). The symbol
EVENTHANDLER_PRI_ANY may be used if the handler does

not have a
specific priority associated with it. If registra

tion is successful, EVENTHANDLER_REGISTER() returns a cookie of

type
eventhandler_tag.

EVENTHANDLER_DEREGISTER()

This macro removes a previously registered callback

associated
with tag tag from the event handler named by argu

ment name.

EVENTHANDLER_INVOKE()

This macro is used to invoke all the callbacks asso

ciated with
event handler name. This macro is a variadic one.

Additional
arguments to the macro after the name parameter are

passed as the
second and subsequent arguments to each registered

callback function.

The macros are implemented using the following functions:

eventhandler_register()

The eventhandler_register() function is used to reg

ister a callback with a given event. The arguments expected by

this function
are:

list A pointer to an existing event handler

list, or

NULL. If list is NULL, the event han

dler list corresponding to argument name is used.

name The name of the event handler list.

func A pointer to a callback function. Ar

gument arg is

a passed to the callback function func

as its first
argument when it is invoked.

priority The relative priority of this callback

among all

the callbacks registered for this

event. Valid
values are those in the range
EVENTHANDLER_PRI_FIRST to EVEN

THANDLER_PRI_LAST.

The eventhandler_register() function returns a tag

that can later
be used with eventhandler_deregister() to remove the

particular
callback function.

eventhandler_deregister()

The eventhandler_deregister() function removes the

callback associated with tag tag from the event handler list

pointed to by
list. This function is safe to call from inside an

event handler
callback.

eventhandler_find_list()

The eventhandler_find_list() function returns a

pointer to event
handler list structure corresponding to event name.

eventhandler_prune_list()

The eventhandler_prune_list() function removes all

deregistered
callbacks from the event list list.

Kernel Event Handlers

The following event handlers are present in the kernel:

acpi_sleep_event

Callbacks invoked when the system is being sent to

sleep.

acpi_wakeup_event

Callbacks invoked when the system is being woken up.

dev_clone

Callbacks invoked when a new entry is created under

/dev.

ifaddr_event

Callbacks invoked when an address is set up on a

network interface.

if_clone_event

Callbacks invoked when an interface is cloned.

ifnet_arrival_event

Callbacks invoked when a new network interface ap

pears.

ifnet_departure_event

Callbacks invoked when a network interface is taken

down.

power_profile_change

Callbacks invoked when the power profile of the sys

tem changes.

process_exec

Callbacks invoked when a process performs an exec()

operation.

process_exit

Callbacks invoked when a process exits.

process_fork

Callbacks invoked when a process forks a child.

shutdown_pre_sync

Callbacks invoked at shutdown time, before file sys

tems are synchronized.

shutdown_post_sync

Callbacks invoked at shutdown time, after all file

systems are
synchronized.

shutdown_final

Callbacks invoked just before halting the system.

vm_lowmem

Callbacks invoked when virtual memory is low.

watchdog_list

Callbacks invoked when the system watchdog timer is

reinitialized.

RETURN VALUES

The macro EVENTHANDLER_REGISTER() and function

eventhandler_register()
return a cookie of type eventhandler_tag, which may be used

in a subsequent call to EVENTHANDLER_DEREGISTER() or

eventhandler_deregister().

The eventhandler_find_list() function returns a pointer to

an event handler list corresponding to parameter name, or NULL if no

such list was
found.

HISTORY

The EVENTHANDLER facility first appeared in FreeBSD 4.0.

AUTHORS

This manual page was written by Joseph Koshy <jkoshy@FreeB

SD.org>.

BSD January 7, 2005

BSD