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EVENTHANDLER(9)		 BSD Kernel Developer's	Manual	       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 subsystems to	regis-
     ter interest in kernel events and have their callback functions invoked
     when these	events occur.

     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 prior-
	     ity 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 suc-
	     cessful, 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 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 func-
	     tion.

     The macros	are implemented	using the following functions:

     eventhandler_register()
	     The eventhandler_register() function is used to register a	call-
	     back 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
		       passed to the callback function func as its first argu-
		       ment 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 asso-
	     ciated 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 inter-
	     face.

     if_clone_event
	     Callbacks invoked when an interface is cloned.

     ifnet_arrival_event
	     Callbacks invoked when a new network interface appears.

     ifnet_departure_event
	     Callbacks invoked when a network interface	is taken down.

     bpf_track
	     Callbacks invoked when a BPF listener attaches to/detaches	from
	     network interface.

     kld_load
	     Callbacks invoked after a linker file has been loaded.

     kld_unload
	     Callbacks invoked after a linker file has been successfully un-
	     loaded.

     kld_unload_try
	     Callbacks invoked before a	linker file is about to	be unloaded.
	     These callbacks may be used to return an error and	prevent	the
	     unload from proceeding.

     power_profile_change
	     Callbacks invoked when the	power profile of the system 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 systems are syn-
	     chronized.

     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 reinitial-
	     ized.

RETURN VALUES
     The macro EVENTHANDLER_REGISTER() and function eventhandler_register()
     return a cookie of	type eventhandler_tag, which may be used in a subse-
     quent call	to EVENTHANDLER_DEREGISTER() or	eventhandler_deregister().

     The eventhandler_find_list() function returns a pointer to	an event han-
     dler 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@FreeBSD.org>.

BSD				August 1, 2013				   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | HISTORY | AUTHORS

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