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.\" Copyright (c) 2004 Joseph Koshy
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\" $FreeBSD$
.\"
.Dd October 21, 2018
.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_DEFINE name func arg priority
.Fn EVENTHANDLER_INVOKE name ...
.Ft eventhandler_tag
.Fn EVENTHANDLER_REGISTER name func arg priority
.Fn EVENTHANDLER_DEREGISTER name tag
.Fn EVENTHANDLER_DEREGISTER_NOWAIT name tag
.Fn EVENTHANDLER_LIST_DECLARE name
.Fn EVENTHANDLER_LIST_DEFINE name
.Fn EVENTHANDLER_DIRECT_INVOKE name
.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 void
.Fo eventhandler_deregister_nowait
.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
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
.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.
.Pp
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
.Fn EVENTHANDLER_LIST_DEFINE
so that the event handlers can be invoked directly using
.Fn EVENTHANDLER_DIRECT_INVOKE
(see below).
This saves the invoker from having to do a locked traversal of a global
list of event handler lists.
.Bl -tag -width indent
.It Fn EVENTHANDLER_DECLARE
This macro declares an event handler named by argument
.Fa name
with callback functions of type
.Fa type .
.It Fn EVENTHANDLER_DEFINE
This macro uses
.Xr SYSINIT 9
to register 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).
.It Fn EVENTHANDLER_REGISTER
This macro 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).
If registration is successful,
.Fn EVENTHANDLER_REGISTER
returns a cookie of type
.Vt eventhandler_tag .
.It Fn EVENTHANDLER_DEREGISTER
This macro removes a previously registered callback associated with tag
.Fa tag
from the event handler named by argument
.Fa 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.
.It Fn EVENTHANDLER_DEREGISTER_NOWAIT
This macro removes a previously registered callback associated with tag
.Fa tag
from the event handler named by argument
.Fa 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.
.It Fn EVENTHANDLER_INVOKE
This macro 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.
.It Fn EVENTHANDLER_LIST_DEFINE
This macro defines a reference to an event handler list named by
argument
.Fa name .
It uses
.Xr SYSINIT 9
to initialize the reference and the eventhandler list.
.It Fn EVENTHANDLER_LIST_DECLARE
This macro declares an event handler list named by argument
.Fa name .
This is only needed for users of
.Fn EVENTHANDLER_DIRECT_INVOKE
which are not in the same compilation unit of that list's definition.
.It Fn EVENTHANDLER_DIRECT_INVOKE
This macro invokes the event handlers registered for the list named by
argument
.Fa name .
This macro can only be used if the list was defined with
.Fn EVENTHANDLER_LIST_DEFINE .
The macro is variadic with the same semantics as
.Fn EVENTHANDLER_INVOKE .
.El
.Pp
The macros are implemented using the following functions:
.Bl -tag -width indent
.It Fn eventhandler_register
The
.Fn eventhandler_register
function is used to register a callback with a given event.
The arguments expected by this function are:
.Bl -tag -width ".Fa priority"
.It Fa list
A pointer to an existing event handler list, or
.Dv NULL .
If
.Fa list
is
.Dv NULL ,
the event handler list corresponding to argument
.Fa name
is used.
.It Fa name
The name of the event handler list.
.It Fa func
A pointer to a callback function.
Argument
.Fa arg
is passed to the callback function
.Fa func
as its first argument when it is invoked.
.It Fa priority
The relative priority of this callback among all the callbacks
registered for this event.
Valid values are those in the range
.Dv EVENTHANDLER_PRI_FIRST
to
.Dv EVENTHANDLER_PRI_LAST .
.El
.Pp
The
.Fn eventhandler_register
function returns a
.Fa tag
that can later be used with
.Fn eventhandler_deregister
to remove the particular callback function.
.It Fn eventhandler_deregister
The
.Fn eventhandler_deregister
function removes the callback associated with tag
.Fa tag
from the event handler list pointed to by
.Fa list .
If
.Fa tag
is
.Va 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.
.It Fn eventhandler_deregister_nowait
The
.Fn eventhandler_deregister
function 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.
.It Fn eventhandler_find_list
The
.Fn eventhandler_find_list
function returns a pointer to event handler list structure corresponding
to event
.Fa name .
.It Fn eventhandler_prune_list
The
.Fn eventhandler_prune_list
function removes all deregistered callbacks from the event list
.Fa list .
.El
.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 app_coredump_start
Callbacks invoked at start of application core dump.
.It Vt app_coredump_progress
Callbacks invoked during progress of application core dump.
.It Vt app_coredump_finish
Callbacks invoked at finish of application core dump.
.It Vt app_coredump_error
Callbacks invoked on error of application core dump.
.It Vt bpf_track
Callbacks invoked when a BPF listener attaches to/detaches from network interface.
.It Vt cpufreq_levels_changed
Callback invoked when cpu frequency levels have changed.
.It Vt cpufreq_post_change
Callback invoked after cpu frequency has changed.
.It Vt cpufreq_pre_change
Callback invoked before cpu frequency has changed.
.It Vt dcons_poll
Callback invoked to poll for dcons changes.
.It Vt device_attach
Callback invoked after a device has attached.
.It Vt device_detach
Callbacks invoked before and after a device has detached.
.It Vt dev_clone
Callbacks invoked when a new entry is created under
.Pa /dev .
.It Vt group_attach_event
Callback invoked when an interfance has been added to an interface group.
.It Vt group_change_event
Callback invoked when an change has been made to an interface group.
.It Vt group_detach_event
Callback invoked when an interfance has been removed from an interface group.
.It Vt ifaddr_event
Callbacks invoked when an address is set up on a network interface.
.It Vt ifaddr_event_ext
Callback invoked when an address has been added or removed from an interface.
.It Vt if_clone_event
Callbacks invoked when an interface is cloned.
.It Vt iflladdr_event
Callback invoked when an if link layer address event has happened.
.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 ifnet_link_event
Callback invoked when an interfance link event has happened.
.It Vt kld_load
Callbacks invoked after a linker file has been loaded.
.It Vt kld_unload
Callbacks invoked after a linker file has been successfully unloaded.
.It Vt 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.
.It Vt lle_event
Callback invoked when an link layer event has happened.
.It Vt nmbclusters_change
Callback invoked when the number of mbuf clusters has changed.
.It Vt nmbufs_change
Callback invoked when the number of mbufs has changed.
.It Vt maxsockets_change
Callback invoked when the maximum number of sockets has changed.
.It Vt mountroot
Callback invoked when root has been mounted.
.It Vt power_profile_change
Callbacks invoked when the power profile of the system changes.
.It Vt power_resume
Callback invoked when the system has resumed.
.It Vt power_suspend
Callback invoked just before the system is suspended.
.It Vt process_ctor
Callback invoked when a process is created.
.It Vt process_dtor
Callback invoked when a process is destroyed.
.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_fini
Callback invoked when a process memory is destroyed.
This is never called.
.It Vt process_fork
Callbacks invoked when a process forks a child.
.It Vt process_init
Callback invoked when a process is initialized.
.It Vt random_adaptor_attach
Callback invoked when a new random module has been loaded.
.It Vt register_framebuffer
Callback invoked when a new frame buffer is registered.
.It Vt route_redirect_event
Callback invoked when a route gets redirected to a new location.
.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 tcp_offload_listen_start
Callback invoked for TCP Offload to start listening for new connections.
.It Vt tcp_offload_listen_stop
Callback invoked ror TCP Offload to stop listening for new connections.
.It Vt thread_ctor
Callback invoked when a thread object is created.
.It Vt thread_dtor
Callback invoked when a thread object is destroyed.
.It Vt thread_init
Callback invoked when a thread object is initialized.
.It Vt thread_fini
Callback invoked when a thread object is deinitalized.
.It Vt usb_dev_configured
Callback invoked when a USB device is configured
.It Vt unregister_framebuffer
Callback invoked when a frame buffer is deregistered.
.It Vt vfs_mounted
Callback invoked when a file system is mounted.
.It Vt vfs_unmounted
Callback invoked when a file system is unmounted.
.It Vt vlan_config
Callback invoked when the vlan configuration has changed.
.It Vt vlan_unconfig
Callback invoked when a vlan is destroyed.
.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
The
.Fn eventhandler_find_list
function
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 Mt jkoshy@FreeBSD.org
and
.An Matt Joras Aq Mt mjoras@FreeBSD.org .