EVENTHANDLER (9) | Kernel routines | Unix Manual Pages

EVENTHANDLER (9) | Kernel routines | Unix Manual Pages | :man▋

The normal way to use this subsystem is via the macro interface. 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 argument 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 below). Callback functions are invoked in order of priority. The relative priority of each callback among other callbacks associated with an event is given by argument priority, which is an integer 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 registration is successful, `EVENTHANDLER_REGISTER` returns a cookie of type .Vt eventhandler_tag .
`EVENTHANDLER_DEREGISTER`
	This macro removes a previously registered callback associated with tag tag from the event handler named by argument name.
`EVENTHANDLER_INVOKE`
	This macro is used to invoke all the callbacks associated 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 register 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 handler list corresponding to argument name is used.
name	The name of the event handler list.
func	A pointer to a callback function. Argument 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 `EVENTHANDLER_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:

Vt acpi_sleep_event
	Callbacks invoked when the system is being sent to sleep.
Vt acpi_wakeup_event
	Callbacks invoked when the system is being woken up.
Vt dev_clone
	Callbacks invoked when a new entry is created under `/dev`.
Vt ifaddr_event
	Callbacks invoked when an address is set up on a network interface.
Vt if_clone_event
	Callbacks invoked when an interface is cloned.
Vt ifnet_arrival_event
	Callbacks invoked when a new network interface appears.
Vt ifnet_departure_event
	Callbacks invoked when a network interface is taken down.
Vt power_profile_change
	Callbacks invoked when the power profile of the system changes.
Vt process_exec
	Callbacks invoked when a process performs an `exec` operation.
Vt process_exit
	Callbacks invoked when a process exits.
Vt process_fork
	Callbacks invoked when a process forks a child.
Vt shutdown_pre_sync
	Callbacks invoked at shutdown time, before file systems are synchronized.
Vt shutdown_post_sync
	Callbacks invoked at shutdown time, after all file systems are synchronized.
Vt shutdown_final
	Callbacks invoked just before halting the system.
Vt vm_lowmem
	Callbacks invoked when virtual memory is low.
Vt watchdog_list
	Callbacks invoked when the system watchdog timer is reinitialized.