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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
     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:

     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
             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
                       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:

     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 appears.

     ifnet_departure_event
             Callbacks invoked when a network interface is taken down.

     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
             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@FreeBSD.org〉.