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31 .Nd kernel event handling functions
33 .In sys/eventhandler.h
34 .Fn EVENTHANDLER_DECLARE name type
35 .Fn EVENTHANDLER_INVOKE name ...
37 .Fn EVENTHANDLER_REGISTER name func arg priority
38 .Fn EVENTHANDLER_DEREGISTER name tag
40 .Fo eventhandler_register
41 .Fa "struct eventhandler_list *list"
42 .Fa "const char *name"
48 .Fo eventhandler_deregister
49 .Fa "struct eventhandler_list *list"
50 .Fa "eventhandler_tag tag"
52 .Ft "struct eventhandler_list *"
53 .Fn eventhandler_find_list "const char *name"
55 .Fn eventhandler_prune_list "struct eventhandler_list *list"
59 mechanism provides a way for kernel subsystems to register interest in
60 kernel events and have their callback functions invoked when these
63 The normal way to use this subsystem is via the macro interface.
64 The macros that can be used for working with event handlers and callback
66 .Bl -tag -width indent
67 .It Fn EVENTHANDLER_DECLARE
68 This macro declares an event handler named by argument
70 with callback functions of type
72 .It Fn EVENTHANDLER_REGISTER
73 This macro registers a callback function
77 When invoked, function
79 will be invoked with argument
81 as its first parameter along with any additional parameters passed in
83 .Fn EVENTHANDLER_INVOKE
85 Callback functions are invoked in order of priority.
86 The relative priority of each callback among other callbacks
87 associated with an event is given by argument
89 which is an integer ranging from
90 .Dv EVENTHANDLER_PRI_FIRST
91 (highest priority), to
92 .Dv EVENTHANDLER_PRI_LAST
95 .Dv EVENTHANDLER_PRI_ANY
96 may be used if the handler does not have a specific priority
98 If registration is successful,
99 .Fn EVENTHANDLER_REGISTER
100 returns a cookie of type
101 .Vt eventhandler_tag .
102 .It Fn EVENTHANDLER_DEREGISTER
103 This macro removes a previously registered callback associated with tag
105 from the event handler named by argument
107 .It Fn EVENTHANDLER_INVOKE
108 This macro is used to invoke all the callbacks associated with event
111 This macro is a variadic one.
112 Additional arguments to the macro after the
114 parameter are passed as the second and subsequent arguments to each
115 registered callback function.
118 The macros are implemented using the following functions:
119 .Bl -tag -width indent
120 .It Fn eventhandler_register
122 .Fn eventhandler_register
123 function is used to register a callback with a given event.
124 The arguments expected by this function are:
125 .Bl -tag -width ".Fa priority"
127 A pointer to an existing event handler list, or
133 the event handler list corresponding to argument
137 The name of the event handler list.
139 A pointer to a callback function.
142 is passed to the callback function
144 as its first argument when it is invoked.
146 The relative priority of this callback among all the callbacks
147 registered for this event.
148 Valid values are those in the range
149 .Dv EVENTHANDLER_PRI_FIRST
151 .Dv EVENTHANDLER_PRI_LAST .
155 .Fn eventhandler_register
158 that can later be used with
159 .Fn eventhandler_deregister
160 to remove the particular callback function.
161 .It Fn eventhandler_deregister
163 .Fn eventhandler_deregister
164 function removes the callback associated with tag
166 from the event handler list pointed to by
168 This function is safe to call from inside an event handler
170 .It Fn eventhandler_find_list
172 .Fn eventhandler_find_list
173 function returns a pointer to event handler list structure corresponding
176 .It Fn eventhandler_prune_list
178 .Fn eventhandler_prune_list
179 function removes all deregistered callbacks from the event list
182 .Ss Kernel Event Handlers
183 The following event handlers are present in the kernel:
184 .Bl -tag -width indent
185 .It Vt acpi_sleep_event
186 Callbacks invoked when the system is being sent to sleep.
187 .It Vt acpi_wakeup_event
188 Callbacks invoked when the system is being woken up.
190 Callbacks invoked when a new entry is created under
193 Callbacks invoked when an address is set up on a network interface.
194 .It Vt if_clone_event
195 Callbacks invoked when an interface is cloned.
196 .It Vt ifnet_arrival_event
197 Callbacks invoked when a new network interface appears.
198 .It Vt ifnet_departure_event
199 Callbacks invoked when a network interface is taken down.
201 Callbacks invoked when a BPF listener attaches to/detaches from network interface.
203 Callbacks invoked after a linker file has been loaded.
205 Callbacks invoked after a linker file has been successfully unloaded.
206 .It Vt kld_unload_try
207 Callbacks invoked before a linker file is about to be unloaded.
208 These callbacks may be used to return an error and prevent the unload from
210 .It Vt power_profile_change
211 Callbacks invoked when the power profile of the system changes.
213 Callbacks invoked when a process performs an
217 Callbacks invoked when a process exits.
219 Callbacks invoked when a process forks a child.
220 .It Vt shutdown_pre_sync
221 Callbacks invoked at shutdown time, before file systems are synchronized.
222 .It Vt shutdown_post_sync
223 Callbacks invoked at shutdown time, after all file systems are synchronized.
224 .It Vt shutdown_final
225 Callbacks invoked just before halting the system.
227 Callbacks invoked when virtual memory is low.
229 Callbacks invoked when the system watchdog timer is reinitialized.
233 .Fn EVENTHANDLER_REGISTER
235 .Fn eventhandler_register
236 return a cookie of type
237 .Vt eventhandler_tag ,
238 which may be used in a subsequent call to
239 .Fn EVENTHANDLER_DEREGISTER
241 .Fn eventhandler_deregister .
244 .Fn eventhandler_find_list
246 returns a pointer to an event handler list corresponding to parameter
250 if no such list was found.
254 facility first appeared in
257 This manual page was written by
258 .An Joseph Koshy Aq jkoshy@FreeBSD.org .