EVENTHANDLER
—
kernel event handling functions
#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);
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.
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.
The EVENTHANDLER
facility first appeared
in FreeBSD 4.0.