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$FreeBSD: releng/10.2/share/man/man9/EVENTHANDLER.9 254813 2013-08-24 21:13:38Z markj $
.Dd August 1, 2013 .Dt EVENTHANDLER 9 .Os .Sh NAME .Nm EVENTHANDLER .Nd kernel event handling functions .Sh SYNOPSIS n 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" .Sh DESCRIPTION The .Nm mechanism provides a way for kernel subsystems to register interest in kernel events and have their callback functions invoked when these events occur.
p 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: l -tag -width indent t Fn EVENTHANDLER_DECLARE This macro declares an event handler named by argument .Fa name with callback functions of type .Fa type . t 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 .Dv EVENTHANDLER_PRI_FIRST (highest priority), to .Dv EVENTHANDLER_PRI_LAST (lowest priority). The symbol .Dv 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 . t Fn EVENTHANDLER_DEREGISTER This macro removes a previously registered callback associated with tag .Fa tag from the event handler named by argument .Fa name . t 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. .El
p The macros are implemented using the following functions: l -tag -width indent t 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: l -tag -width ".Fa priority" t Fa list A pointer to an existing event handler list, or .Dv NULL . If .Fa list is .Dv NULL , the event handler list corresponding to argument .Fa name is used. t Fa name The name of the event handler list. t 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. t Fa priority The relative priority of this callback among all the callbacks registered for this event. Valid values are those in the range .Dv EVENTHANDLER_PRI_FIRST to .Dv EVENTHANDLER_PRI_LAST . .El
p The .Fn eventhandler_register function returns a .Fa tag that can later be used with .Fn eventhandler_deregister to remove the particular callback function. t 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. t Fn eventhandler_find_list The .Fn eventhandler_find_list function returns a pointer to event handler list structure corresponding to event .Fa name . t Fn eventhandler_prune_list The .Fn eventhandler_prune_list function removes all deregistered callbacks from the event list .Fa list . .El .Ss Kernel Event Handlers The following event handlers are present in the kernel: l -tag -width indent t Vt acpi_sleep_event Callbacks invoked when the system is being sent to sleep. t Vt acpi_wakeup_event Callbacks invoked when the system is being woken up. t Vt dev_clone Callbacks invoked when a new entry is created under
a /dev . t Vt ifaddr_event Callbacks invoked when an address is set up on a network interface. t Vt if_clone_event Callbacks invoked when an interface is cloned. t Vt ifnet_arrival_event Callbacks invoked when a new network interface appears. t Vt ifnet_departure_event Callbacks invoked when a network interface is taken down. t Vt bpf_track Callbacks invoked when a BPF listener attaches to/detaches from network interface. t Vt kld_load Callbacks invoked after a linker file has been loaded. t Vt kld_unload Callbacks invoked after a linker file has been successfully unloaded. t 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. t Vt power_profile_change Callbacks invoked when the power profile of the system changes. t Vt process_exec Callbacks invoked when a process performs an .Fn exec operation. t Vt process_exit Callbacks invoked when a process exits. t Vt process_fork Callbacks invoked when a process forks a child. t Vt shutdown_pre_sync Callbacks invoked at shutdown time, before file systems are synchronized. t Vt shutdown_post_sync Callbacks invoked at shutdown time, after all file systems are synchronized. t Vt shutdown_final Callbacks invoked just before halting the system. t Vt vm_lowmem Callbacks invoked when virtual memory is low. t Vt watchdog_list Callbacks invoked when the system watchdog timer is reinitialized. .El .Sh 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 .
p The .Fn eventhandler_find_list function returns a pointer to an event handler list corresponding to parameter .Fa name , or .Dv NULL if no such list was found. .Sh HISTORY The .Nm facility first appeared in .Fx 4.0 . .Sh AUTHORS This manual page was written by .An Joseph Koshy Aq jkoshy@FreeBSD.org .