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EVENTHANDLER(9)	       FreeBSD Kernel Developer's Manual       EVENTHANDLER(9)

NAME
     EVENTHANDLER -- kernel event handling functions

SYNOPSIS
     #include <sys/eventhandler.h>

     EVENTHANDLER_DECLARE(name,	type);

     EVENTHANDLER_DEFINE(name, func, arg, priority);

     EVENTHANDLER_INVOKE(name, ...);

     eventhandler_tag
     EVENTHANDLER_REGISTER(name, func, arg, priority);

     EVENTHANDLER_DEREGISTER(name, tag);

     EVENTHANDLER_DEREGISTER_NOWAIT(name, tag);

     EVENTHANDLER_LIST_DECLARE(name);

     EVENTHANDLER_LIST_DEFINE(name);

     EVENTHANDLER_DIRECT_INVOKE(name);

     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);

     void
     eventhandler_deregister_nowait(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.

     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 (low-
     est priority).  The symbol	EVENTHANDLER_PRI_ANY may be used if the	han-
     dler does not have	a specific priority associated with it.

     The normal	way to use this	subsystem is via the macro interface.  For
     events that are high frequency it is suggested that you additionally use
     EVENTHANDLER_LIST_DEFINE()	so that	the event handlers can be invoked
     directly using EVENTHANDLER_DIRECT_INVOKE() (see below).  This saves the
     invoker from having to do a locked	traversal of a global list of event
     handler lists.

     EVENTHANDLER_DECLARE()
	     This macro	declares an event handler named	by argument name with
	     callback functions	of type	type.

     EVENTHANDLER_DEFINE()
	     This macro	uses SYSINIT(9)	to register 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).

     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).  If	regis-
	     tration 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 argument name.  It
	     waits until no threads are	running	handlers for this event	before
	     returning,	making it safe to unload a module immediately upon
	     return from this function.

     EVENTHANDLER_DEREGISTER_NOWAIT()
	     This macro	removes	a previously registered	callback associated
	     with tag tag from the event handler named by argument name.  Upon
	     return, one or more threads could still be	running	the removed
	     function(s), but no new calls will	be made.  To remove a handler
	     function from within that function, use this version of deregis-
	     ter, to avoid a deadlock.

     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.

     EVENTHANDLER_LIST_DEFINE()
	     This macro	defines	a reference to an event	handler	list named by
	     argument name.  It	uses SYSINIT(9)	to initialize the reference
	     and the eventhandler list.

     EVENTHANDLER_LIST_DECLARE()
	     This macro	declares an event handler list named by	argument name.
	     This is only needed for users of EVENTHANDLER_DIRECT_INVOKE()
	     which are not in the same compilation unit	of that	list's defini-
	     tion.

     EVENTHANDLER_DIRECT_INVOKE()
	     This macro	invokes	the event handlers registered for the list
	     named by argument name.  This macro can only be used if the list
	     was defined with EVENTHANDLER_LIST_DEFINE().  The macro is	vari-
	     adic with the same	semantics as EVENTHANDLER_INVOKE().

     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.  If tag is NULL, all	callback functions for the event are
	     removed.  This function will not return until all threads have
	     exited from the removed handler callback function(s).  This func-
	     tion is not safe to call from inside an event handler callback.

     eventhandler_deregister_nowait()
	     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.

     app_coredump_start
	     Callbacks invoked at start	of application core dump.

     app_coredump_progress
	     Callbacks invoked during progress of application core dump.

     app_coredump_finish
	     Callbacks invoked at finish of application	core dump.

     app_coredump_error
	     Callbacks invoked on error	of application core dump.

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

     cpufreq_levels_changed
	     Callback invoked when cpu frequency levels	have changed.

     cpufreq_post_change
	     Callback invoked after cpu	frequency has changed.

     cpufreq_pre_change
	     Callback invoked before cpu frequency has changed.

     dcons_poll
	     Callback invoked to poll for dcons	changes.

     device_attach
	     Callback invoked after a device has attached.

     device_detach
	     Callbacks invoked before and after	a device has detached.

     dev_clone
	     Callbacks invoked when a new entry	is created under /dev.

     group_attach_event
	     Callback invoked when an interfance has been added	to an inter-
	     face group.

     group_change_event
	     Callback invoked when an change has been made to an interface
	     group.

     group_detach_event
	     Callback invoked when an interfance has been removed from an
	     interface group.

     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.

     iflladdr_event
	     Callback invoked when an if link layer address event has hap-
	     pened.

     ifnet_arrival_event
	     Callbacks invoked when a new network interface appears.

     ifnet_departure_event
	     Callbacks invoked when a network interface	is taken down.

     ifnet_link_event
	     Callback invoked when an interfance link event has	happened.

     kld_load
	     Callbacks invoked after a linker file has been loaded.

     kld_unload
	     Callbacks invoked after a linker file has been successfully
	     unloaded.

     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.

     lle_event
	     Callback invoked when an link layer event has happened.

     nmbclusters_change
	     Callback invoked when the number of mbuf clusters has changed.

     nmbufs_change
	     Callback invoked when the number of mbufs has changed.

     maxsockets_change
	     Callback invoked when the maximum number of sockets has changed.

     mountroot
	     Callback invoked when root	has been mounted.

     power_profile_change
	     Callbacks invoked when the	power profile of the system changes.

     power_resume
	     Callback invoked when the system has resumed.

     power_suspend
	     Callback invoked just before the system is	suspended.

     process_ctor
	     Callback invoked when a process is	created.

     process_dtor
	     Callback invoked when a process is	destroyed.

     process_exec
	     Callbacks invoked when a process performs an exec() operation.

     process_exit
	     Callbacks invoked when a process exits.

     process_fini
	     Callback invoked when a process memory is destroyed.  This	is
	     never called.

     process_fork
	     Callbacks invoked when a process forks a child.

     process_init
	     Callback invoked when a process is	initialized.

     random_adaptor_attach
	     Callback invoked when a new random	module has been	loaded.

     register_framebuffer
	     Callback invoked when a new frame buffer is registered.

     route_redirect_event
	     Callback invoked when a route gets	redirected to a	new location.

     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.

     tcp_offload_listen_start
	     Callback invoked for TCP Offload to start listening for new con-
	     nections.

     tcp_offload_listen_stop
	     Callback invoked ror TCP Offload to stop listening	for new	con-
	     nections.

     thread_ctor
	     Callback invoked when a thread object is created.

     thread_dtor
	     Callback invoked when a thread object is destroyed.

     thread_init
	     Callback invoked when a thread object is initialized.

     thread_fini
	     Callback invoked when a thread object is deinitalized.

     usb_dev_configured
	     Callback invoked when a USB device	is configured

     unregister_framebuffer
	     Callback invoked when a frame buffer is deregistered.

     vfs_mounted
	     Callback invoked when a file system is mounted.

     vfs_unmounted
	     Callback invoked when a file system is unmounted.

     vlan_config
	     Callback invoked when the vlan configuration has changed.

     vlan_unconfig
	     Callback invoked when a vlan is destroyed.

     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> and
     Matt Joras	<mjoras@FreeBSD.org>.

FreeBSD	Ports 11.2	       September 6, 2018	    FreeBSD Ports 11.2

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

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