eventhandler_prune_list

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.

Debian

eventhandler_prune_list

NAME

SYNOPSIS

DESCRIPTION

Kernel Event Handlers

RETURN VALUES

HISTORY

AUTHORS

Recommended readings

Questions & Answers