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.

     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 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.

     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>.