1.\" Copyright (c) 2004 Joseph Koshy 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" $FreeBSD$ 25.\" 26.Dd January 7, 2005 27.Dt EVENTHANDLER 9 28.Os 29.Sh NAME 30.Nm EVENTHANDLER 31.Nd kernel event handling functions 32.Sh SYNOPSIS 33.In sys/eventhandler.h 34.Fn EVENTHANDLER_DECLARE name type 35.Fn EVENTHANDLER_INVOKE name ... 36.Ft eventhandler_tag 37.Fn EVENTHANDLER_REGISTER name func arg priority 38.Fn EVENTHANDLER_DEREGISTER name tag 39.Ft eventhandler_tag 40.Fo eventhandler_register 41.Fa "struct eventhandler_list *list" 42.Fa "const char *name" 43.Fa "void *func" 44.Fa "void *arg" 45.Fa "int priority" 46.Fc 47.Ft void 48.Fo eventhandler_deregister 49.Fa "struct eventhandler_list *list" 50.Fa "eventhandler_tag tag" 51.Fc 52.Ft "struct eventhandler_list *" 53.Fn eventhandler_find_list "const char *name" 54.Ft void 55.Fn eventhandler_prune_list "struct eventhandler_list *list" 56.Sh DESCRIPTION 57The 58.Nm 59mechanism provides a way for kernel subsystems to register interest in 60kernel events and have their callback functions invoked when these 61events occur. 62.Pp 63The normal way to use this subsystem is via the macro interface. 64The macros that can be used for working with event handlers and callback 65function lists are: 66.Bl -tag -width indent 67.It Fn EVENTHANDLER_DECLARE 68This macro declares an event handler named by argument 69.Fa name 70with callback functions of type 71.Fa type . 72.It Fn EVENTHANDLER_REGISTER 73This macro registers a callback function 74.Fa func 75with event handler 76.Fa name . 77When invoked, function 78.Fa func 79will be invoked with argument 80.Fa arg 81as its first parameter along with any additional parameters passed in 82via macro 83.Fn EVENTHANDLER_INVOKE 84(see below). 85Callback functions are invoked in order of priority. 86The relative priority of each callback among other callbacks 87associated with an event is given by argument 88.Fa priority , 89which is an integer ranging from 90.Dv EVENTHANDLER_PRI_FIRST 91(highest priority), to 92.Dv EVENTHANDLER_PRI_LAST 93(lowest priority). 94The symbol 95.Dv EVENTHANDLER_PRI_ANY 96may be used if the handler does not have a specific priority 97associated with it. 98If registration is successful, 99.Fn EVENTHANDLER_REGISTER 100returns a cookie of type 101.Vt eventhandler_tag . 102.It Fn EVENTHANDLER_DEREGISTER 103This macro removes a previously registered callback associated with tag 104.Fa tag 105from the event handler named by argument 106.Fa name . 107.It Fn EVENTHANDLER_INVOKE 108This macro is used to invoke all the callbacks associated with event 109handler 110.Fa name . 111This macro is a variadic one. 112Additional arguments to the macro after the 113.Fa name 114parameter are passed as the second and subsequent arguments to each 115registered callback function. 116.El 117.Pp 118The macros are implemented using the following functions: 119.Bl -tag -width indent 120.It Fn eventhandler_register 121The 122.Fn eventhandler_register 123function is used to register a callback with a given event. 124The arguments expected by this function are: 125.Bl -tag -width ".Fa priority" 126.It Fa list 127A pointer to an existing event handler list, or 128.Dv NULL . 129If 130.Fa list 131is 132.Dv NULL , 133the event handler list corresponding to argument 134.Fa name 135is used. 136.It Fa name 137The name of the event handler list. 138.It Fa func 139A pointer to a callback function. 140Argument 141.Fa arg 142is passed to the callback function 143.Fa func 144as its first argument when it is invoked. 145.It Fa priority 146The relative priority of this callback among all the callbacks 147registered for this event. 148Valid values are those in the range 149.Dv EVENTHANDLER_PRI_FIRST 150to 151.Dv EVENTHANDLER_PRI_LAST . 152.El 153.Pp 154The 155.Fn eventhandler_register 156function returns a 157.Fa tag 158that can later be used with 159.Fn eventhandler_deregister 160to remove the particular callback function. 161.It Fn eventhandler_deregister 162The 163.Fn eventhandler_deregister 164function removes the callback associated with tag 165.Fa tag 166from the event handler list pointed to by 167.Fa list . 168This function is safe to call from inside an event handler 169callback. 170.It Fn eventhandler_find_list 171The 172.Fn eventhandler_find_list 173function returns a pointer to event handler list structure corresponding 174to event 175.Fa name . 176.It Fn eventhandler_prune_list 177The 178.Fn eventhandler_prune_list 179function removes all deregistered callbacks from the event list 180.Fa list . 181.El 182.Ss Kernel Event Handlers 183The following event handlers are present in the kernel: 184.Bl -tag -width indent 185.It Vt acpi_sleep_event 186Callbacks invoked when the system is being sent to sleep. 187.It Vt acpi_wakeup_event 188Callbacks invoked when the system is being woken up. 189.It Vt dev_clone 190Callbacks invoked when a new entry is created under 191.Pa /dev . 192.It Vt ifaddr_event 193Callbacks invoked when an address is set up on a network interface. 194.It Vt if_clone_event 195Callbacks invoked when an interface is cloned. 196.It Vt ifnet_arrival_event 197Callbacks invoked when a new network interface appears. 198.It Vt ifnet_departure_event 199Callbacks invoked when a network interface is taken down. 200.It Vt power_profile_change 201Callbacks invoked when the power profile of the system changes. 202.It Vt process_exec 203Callbacks invoked when a process performs an 204.Fn exec 205operation. 206.It Vt process_exit 207Callbacks invoked when a process exits. 208.It Vt process_fork 209Callbacks invoked when a process forks a child. 210.It Vt shutdown_pre_sync 211Callbacks invoked at shutdown time, before file systems are synchronized. 212.It Vt shutdown_post_sync 213Callbacks invoked at shutdown time, after all file systems are synchronized. 214.It Vt shutdown_final 215Callbacks invoked just before halting the system. 216.It Vt vm_lowmem 217Callbacks invoked when virtual memory is low. 218.It Vt watchdog_list 219Callbacks invoked when the system watchdog timer is reinitialized. 220.El 221.Sh RETURN VALUES 222The macro 223.Fn EVENTHANDLER_REGISTER 224and function 225.Fn eventhandler_register 226return a cookie of type 227.Vt eventhandler_tag , 228which may be used in a subsequent call to 229.Fn EVENTHANDLER_DEREGISTER 230or 231.Fn eventhandler_deregister . 232.Pp 233The 234.Fn eventhandler_find_list 235function 236returns a pointer to an event handler list corresponding to parameter 237.Fa name , 238or 239.Dv NULL 240if no such list was found. 241.Sh HISTORY 242The 243.Nm 244facility first appeared in 245.Fx 4.0 . 246.Sh AUTHORS 247This manual page was written by 248.An Joseph Koshy Aq jkoshy@FreeBSD.org . 249