80dd3f5e73
called after the module has been loaded, and the unload handlers are called before the module is unloaded. Moreover, the module unload handlers may return an error to prevent the unload from proceeding. Reviewed by: avg MFC after: 2 weeks
257 lines
7.5 KiB
Groff
257 lines
7.5 KiB
Groff
.\" Copyright (c) 2004 Joseph Koshy
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\" $FreeBSD$
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.\"
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.Dd August 1, 2013
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.Dt EVENTHANDLER 9
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.Os
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.Sh NAME
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.Nm EVENTHANDLER
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.Nd kernel event handling functions
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.Sh SYNOPSIS
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.In sys/eventhandler.h
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.Fn EVENTHANDLER_DECLARE name type
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.Fn EVENTHANDLER_INVOKE name ...
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.Ft eventhandler_tag
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.Fn EVENTHANDLER_REGISTER name func arg priority
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.Fn EVENTHANDLER_DEREGISTER name tag
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.Ft eventhandler_tag
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.Fo eventhandler_register
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.Fa "struct eventhandler_list *list"
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.Fa "const char *name"
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.Fa "void *func"
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.Fa "void *arg"
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.Fa "int priority"
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.Fc
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.Ft void
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.Fo eventhandler_deregister
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.Fa "struct eventhandler_list *list"
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.Fa "eventhandler_tag tag"
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.Fc
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.Ft "struct eventhandler_list *"
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.Fn eventhandler_find_list "const char *name"
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.Ft void
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.Fn eventhandler_prune_list "struct eventhandler_list *list"
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.Sh DESCRIPTION
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The
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.Nm
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mechanism provides a way for kernel subsystems to register interest in
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kernel events and have their callback functions invoked when these
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events occur.
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.Pp
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The normal way to use this subsystem is via the macro interface.
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The macros that can be used for working with event handlers and callback
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function lists are:
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.Bl -tag -width indent
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.It Fn EVENTHANDLER_DECLARE
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This macro declares an event handler named by argument
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.Fa name
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with callback functions of type
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.Fa type .
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.It Fn EVENTHANDLER_REGISTER
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This macro registers a callback function
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.Fa func
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with event handler
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.Fa name .
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When invoked, function
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.Fa func
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will be invoked with argument
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.Fa arg
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as its first parameter along with any additional parameters passed in
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via macro
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.Fn EVENTHANDLER_INVOKE
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(see below).
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Callback functions are invoked in order of priority.
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The relative priority of each callback among other callbacks
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associated with an event is given by argument
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.Fa priority ,
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which is an integer ranging from
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.Dv EVENTHANDLER_PRI_FIRST
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(highest priority), to
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.Dv EVENTHANDLER_PRI_LAST
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(lowest priority).
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The symbol
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.Dv EVENTHANDLER_PRI_ANY
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may be used if the handler does not have a specific priority
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associated with it.
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If registration is successful,
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.Fn EVENTHANDLER_REGISTER
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returns a cookie of type
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.Vt eventhandler_tag .
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.It Fn EVENTHANDLER_DEREGISTER
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This macro removes a previously registered callback associated with tag
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.Fa tag
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from the event handler named by argument
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.Fa name .
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.It Fn EVENTHANDLER_INVOKE
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This macro is used to invoke all the callbacks associated with event
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handler
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.Fa name .
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This macro is a variadic one.
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Additional arguments to the macro after the
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.Fa name
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parameter are passed as the second and subsequent arguments to each
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registered callback function.
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.El
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.Pp
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The macros are implemented using the following functions:
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.Bl -tag -width indent
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.It Fn eventhandler_register
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The
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.Fn eventhandler_register
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function is used to register a callback with a given event.
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The arguments expected by this function are:
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.Bl -tag -width ".Fa priority"
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.It Fa list
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A pointer to an existing event handler list, or
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.Dv NULL .
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If
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.Fa list
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is
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.Dv NULL ,
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the event handler list corresponding to argument
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.Fa name
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is used.
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.It Fa name
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The name of the event handler list.
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.It Fa func
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A pointer to a callback function.
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Argument
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.Fa arg
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is passed to the callback function
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.Fa func
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as its first argument when it is invoked.
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.It Fa priority
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The relative priority of this callback among all the callbacks
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registered for this event.
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Valid values are those in the range
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.Dv EVENTHANDLER_PRI_FIRST
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to
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.Dv EVENTHANDLER_PRI_LAST .
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.El
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.Pp
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The
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.Fn eventhandler_register
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function returns a
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.Fa tag
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that can later be used with
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.Fn eventhandler_deregister
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to remove the particular callback function.
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.It Fn eventhandler_deregister
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The
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.Fn eventhandler_deregister
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function removes the callback associated with tag
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.Fa tag
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from the event handler list pointed to by
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.Fa list .
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This function is safe to call from inside an event handler
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callback.
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.It Fn eventhandler_find_list
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The
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.Fn eventhandler_find_list
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function returns a pointer to event handler list structure corresponding
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to event
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.Fa name .
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.It Fn eventhandler_prune_list
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The
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.Fn eventhandler_prune_list
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function removes all deregistered callbacks from the event list
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.Fa list .
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.El
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.Ss Kernel Event Handlers
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The following event handlers are present in the kernel:
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.Bl -tag -width indent
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.It Vt acpi_sleep_event
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Callbacks invoked when the system is being sent to sleep.
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.It Vt acpi_wakeup_event
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Callbacks invoked when the system is being woken up.
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.It Vt dev_clone
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Callbacks invoked when a new entry is created under
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.Pa /dev .
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.It Vt ifaddr_event
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Callbacks invoked when an address is set up on a network interface.
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.It Vt if_clone_event
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Callbacks invoked when an interface is cloned.
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.It Vt ifnet_arrival_event
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Callbacks invoked when a new network interface appears.
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.It Vt ifnet_departure_event
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Callbacks invoked when a network interface is taken down.
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.It Vt bpf_track
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Callbacks invoked when a BPF listener attaches to/detaches from network interface.
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.It Vt mod_load
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Callbacks invoked after a module has been loaded.
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.It Vt mod_unload
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Callbacks invoked before a module is about to be unloaded.
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These callbacks may be used to return an error and prevent the unload from
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proceeding.
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.It Vt power_profile_change
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Callbacks invoked when the power profile of the system changes.
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.It Vt process_exec
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Callbacks invoked when a process performs an
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.Fn exec
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operation.
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.It Vt process_exit
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Callbacks invoked when a process exits.
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.It Vt process_fork
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Callbacks invoked when a process forks a child.
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.It Vt shutdown_pre_sync
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Callbacks invoked at shutdown time, before file systems are synchronized.
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.It Vt shutdown_post_sync
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Callbacks invoked at shutdown time, after all file systems are synchronized.
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.It Vt shutdown_final
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Callbacks invoked just before halting the system.
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.It Vt vm_lowmem
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Callbacks invoked when virtual memory is low.
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.It Vt watchdog_list
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Callbacks invoked when the system watchdog timer is reinitialized.
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.El
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.Sh RETURN VALUES
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The macro
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.Fn EVENTHANDLER_REGISTER
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and function
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.Fn eventhandler_register
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return a cookie of type
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.Vt eventhandler_tag ,
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which may be used in a subsequent call to
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.Fn EVENTHANDLER_DEREGISTER
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or
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.Fn eventhandler_deregister .
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.Pp
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The
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.Fn eventhandler_find_list
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function
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returns a pointer to an event handler list corresponding to parameter
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.Fa name ,
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or
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.Dv NULL
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if no such list was found.
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.Sh HISTORY
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The
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.Nm
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facility first appeared in
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.Fx 4.0 .
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.Sh AUTHORS
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This manual page was written by
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.An Joseph Koshy Aq jkoshy@FreeBSD.org .
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