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 register interest in
     kernel events and have their callback functions invoked when these events occur.

     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.

     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 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.  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 deregister, 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 function.

     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 definition.

     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 variadic 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 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.  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 function is
             not safe to call from inside an event handler callback.

     eventhandler_deregister_nowait()
             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.

     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 interface 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 interface.

     ifaddr_event_ext
             Callback invoked when an address has been added or removed from an interface.

     if_clone_event
             Callbacks invoked when an interface is cloned.

     iflladdr_event
             Callback invoked when an if link layer address event has happened.

     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 synchronized.

     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 connections.

     tcp_offload_listen_stop
             Callback invoked ror TCP Offload to stop listening for new connections.

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