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.Dd November 23, 2004
.Dt EVENTHANDLER 9
.Os
.Sh NAME
.Nm EVENTHANDLER
.Nd kernel event handling functions
.Sh SYNOPSIS
.In 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.
.Pp
The normal way to use this subsystem is via the macro interface.
.Pp
The macro
.Fn EVENTHANDLER_DECLARE
declares an event handler named by argument
.Fa name
with callback functions of type
.Fa type .
.Pp
The macro
.Fn EVENTHANDLER_REGISTER
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 this callback among other callbacks
associated with this 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 .
.Pp
The macro
.Fn EVENTHANDLER_DEREGISTER
removes a previously registered callback associated with
tag
.Fa tag
from the event handler named by argument
.Fa name .
.Pp
The macro
.Fn EVENTHANDLER_INVOKE
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.
.Pp
The macros are implemented using the following functions:
.Pp
The function
.Fn eventhandler_register
is used to register a callback with a given event.
The argument
.Fa list
is pointer to an existing event handler list, or
.Dv NULL .
If argument
.Fa list
is
.Dv NULL ,
the event handler list corresponding to argument
.Fa name
is used.
Argument
.Fa func
is a pointer to a callback function.
Argument
.Fa arg
is a passed in to callback function
.Fa func
as its first argument when it is invoked.
Argument
.Fa priority
ranges from
.Dv EVENTHANDLER_PRI_FIRST
to
.Dv EVENTHANDLER_PRI_LAST ,
and determines the relative priority of this callback among all the
callbacks registered for this event.
.Pp
Function
.Fn eventhandler_deregister
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.
.Pp
Function
.Fn eventhandler_find_list
returns a pointer to event handler list structure corresponding to
event
.Fa name .
.Pp
Function
.Fn eventhandler_prune_list
removes all deregistered callbacks from the event list
.Fa list .
.Ss Kernel Event Handlers
The following event handlers are present in the kernel:
.Bl -tag -width indent
.It Vt acpi_sleep_event
Callbacks invoked when the system is being sent to sleep.
.It Vt acpi_wakeup_event
Callbacks invoked when the system is being woken up.
.It Vt dev_clone
Callbacks invoked when a new entry is created under
.Pa /dev .
.It Vt ifaddr_event
Callbacks invoked when an address is set up on a network interface.
.It Vt if_clone_event
Callbacks invoked when an interface is cloned.
.It Vt ifnet_arrival_event
Callbacks invoked when a new network interface appears.
.It Vt ifnet_departure_event
Callbacks invoked when a network interface is taken down.
.It Vt power_profile_change
Callbacks invoked when the power profile of the system changes.
.It Vt process_exec
Callbacks invoked when a process performs an
.Fn exec
operation.
.It Vt process_exit
Callbacks invoked when a process exits.
.It Vt process_fork
Callbacks invoked when a process forks a child.
.It Vt shutdown_pre_sync
Callbacks invoked at shutdown time, before file systems are synchronized.
.It Vt shutdown_post_sync
Callbacks invoked at shutdown time, after all file systems are synchronized.
.It Vt shutdown_final
Callbacks invoked just before halting the system.
.It Vt vm_lowmem
Callbacks invoked when virtual memory is low.
.It 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 .
.Pp
Function
.Fn eventhandler_find_list
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 .