SYNOPSIS

In sys/eventhandler.h Fn EVENTHANDLER_DECLARE name type Fn EVENTHANDLER_INVOKE name ... Ft eventhandler_tag Fn EVENTHANDLER_REGISTER name func arg priority Fn EVENTHANDLER_DEREGISTER name tag Ft eventhandler_tag Fo eventhandler_register Fa struct eventhandler_list *list Fa const char *name Fa void *func Fa void *arg Fa int priority Fc Ft void Fo eventhandler_deregister Fa struct eventhandler_list *list Fa eventhandler_tag tag Fc Ft struct eventhandler_list * Fn eventhandler_find_list const char *name Ft void Fn eventhandler_prune_list struct eventhandler_list *list

DESCRIPTION

The mechanism provides a way for kernel subsystems to register 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:

Fn EVENTHANDLER_DECLARE

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

Fn EVENTHANDLER_REGISTER

This macro registers a callback function Fa func with event handler Fa name . When invoked, function Fa func will be invoked with argument Fa arg as its first parameter along with any additional parameters passed in via macro Fn 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 Fa 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, Fn EVENTHANDLER_REGISTER returns a cookie of type Vt eventhandler_tag .

Fn EVENTHANDLER_DEREGISTER

This macro removes a previously registered callback associated with tag Fa tag from the event handler named by argument Fa name .

Fn EVENTHANDLER_INVOKE

This macro is used to invoke all the callbacks associated with event handler Fa name . This macro is a variadic one. Additional arguments to the macro after the Fa name parameter are passed as the second and subsequent arguments to each registered callback function.

The macros are implemented using the following functions:

Fn eventhandler_register

The Fn eventhandler_register function is used to register a callback with a given event. The arguments expected by this function are:

Fa list

A pointer to an existing event handler list, or NULL If Fa list is NULL the event handler list corresponding to argument Fa name is used.

Fa name

The name of the event handler list.

Fa func

A pointer to a callback function. Argument Fa arg is passed to the callback function Fa func as its first argument when it is invoked.

Fa 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 Fn eventhandler_register function returns a Fa tag that can later be used with Fn eventhandler_deregister to remove the particular callback function.

Fn eventhandler_deregister

The Fn eventhandler_deregister function removes the callback associated with tag Fa tag from the event handler list pointed to by Fa list . This function is safe to call from inside an event handler callback.

Fn eventhandler_find_list

The Fn eventhandler_find_list function returns a pointer to event handler list structure corresponding to event Fa name .

Fn eventhandler_prune_list

The Fn eventhandler_prune_list function removes all deregistered callbacks from the event list Fa 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 bpf_track

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

Vt kld_load

Callbacks invoked after a linker file has been loaded.

Vt kld_unload

Callbacks invoked after a linker file has been successfully unloaded.

Vt 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.

Vt power_profile_change

Callbacks invoked when the power profile of the system changes.

Vt process_exec

Callbacks invoked when a process performs an Fn 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.

RETURN VALUES

The macro Fn EVENTHANDLER_REGISTER and function Fn eventhandler_register return a cookie of type Vt eventhandler_tag , which may be used in a subsequent call to Fn EVENTHANDLER_DEREGISTER or Fn eventhandler_deregister .

The Fn eventhandler_find_list function returns a pointer to an event handler list corresponding to parameter Fa name , or NULL if no such list was found.

HISTORY

The facility first appeared in Fx 4.0 .

AUTHORS

This manual page was written by An Joseph Koshy Aq [email protected] .