1 .\" Copyright (c) 1993 Christopher G. Demetriou
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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15 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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26 .\" $FreeBSD: src/share/man/man4/kld.4,v 1.5.2.6 2001/08/17 13:08:38 ru Exp $
33 .Nd dynamic kernel linker facility
35 The LKM (Loadable Kernel Modules) facility has been deprecated in
37 and above in favor of the
40 This interface, like its
41 predecessor, allows the system administrator to dynamically add and remove
42 functionality from a running system. This ability also helps software
43 developers to develop new parts of the kernel without constantly rebooting
44 to test their changes.
46 Various types of modules can be loaded into the system.
47 There are several defined module types, listed below, which can
48 be added to the system in a predefined way. In addition, there
49 is a generic type, for which the module itself handles loading and
54 system makes extensive use of loadable kernel modules, and provides loadable
55 versions of most filesystems, the
57 client and server, all the screen-savers, and the
63 modules are placed by default in the
69 interface is used through the
78 program can load either
80 or ELF formatted loadable modules.
83 program unloads any given loaded module, if no other module is dependent
84 upon the given module.
87 program is used to check the status of the modules currently loaded into the
91 .It Em "Device Driver modules"
92 New block and character device
93 drivers may be loaded into the system with
95 The major problem with loading
96 a device driver is that the driver's
97 device nodes must exist for the
98 devices to be accessed. They are usually
103 (if the device is not supported by the
105 script) or, by writing a
108 which should run the appropriate program to create the devices when the
109 driver has been successfully loaded.
112 .Bl -tag -width /usr/include/sys/module.h -compact
114 directory containing module binaries shipped with the system
115 .It Pa /usr/include/sys/module.h
116 file containing definitions required to compile a
119 .It Pa /usr/share/examples/kld
120 example source code implementing a sample kld module
133 If a module B, is dependent on another module A, but is not compiled with
134 module A as a dependency, then
136 fails to load module B, even if module A is already present in the system.
138 If multiple modules are dependent on module A, and are compiled with module
139 A as a dependency, then
141 loads an instance of module A when any of the modules are loaded.
143 If a custom entry point is used for a module, and the module is compiled as
148 fails to execute the entry point.
151 returns the cryptic message
152 .Sq Li "ENOEXEC (Exec format error)"
153 for any error encountered while loading a module.
155 When system internal interfaces change, old modules often cannot
156 detect this, and such modules when loaded will often cause crashes or
161 facility was originally implemented by
162 .An Doug Rabson Aq dfr@FreeBSD.org .
168 and was designed as a replacement for the
170 facility, which was similar in functionality to the loadable kernel modules