1 .\" Copyright (c) 1993 Christopher G. Demetriou
2 .\" All rights reserved.
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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 $
27 .\" $DragonFly: src/share/man/man4/kld.4,v 1.3 2004/03/11 12:28:55 hmp Exp $
34 .Nd dynamic kernel linker facility
36 The LKM (Loadable Kernel Modules) facility has been deprecated in
38 and above in favor of the
41 This interface, like its
42 predecessor, allows the system administrator to dynamically add and remove
43 functionality from a running system. This ability also helps software
44 developers to develop new parts of the kernel without constantly rebooting
45 to test their changes.
47 Various types of modules can be loaded into the system.
48 There are several defined module types, listed below, which can
49 be added to the system in a predefined way. In addition, there
50 is a generic type, for which the module itself handles loading and
55 system makes extensive use of loadable kernel modules, and provides loadable
56 versions of most filesystems, the
58 client and server, all the screen-savers, and the
64 modules are placed by default in the
70 interface is used through the
79 program can load either
81 or ELF formatted loadable modules.
84 program unloads any given loaded module, if no other module is dependent
85 upon the given module.
88 program is used to check the status of the modules currently loaded into the
92 .It Em "Device Driver modules"
93 New block and character device
94 drivers may be loaded into the system with
96 The major problem with loading
97 a device driver is that the driver's
98 device nodes must exist for the
99 devices to be accessed. They are usually
104 (if the device is not supported by the
106 script) or, by writing a
109 which should run the appropriate program to create the devices when the
110 driver has been successfully loaded.
113 .Bl -tag -width /usr/include/sys/module.h -compact
115 directory containing module binaries shipped with the system
116 .It Pa /usr/include/sys/module.h
117 file containing definitions required to compile a
120 .It Pa /usr/share/examples/kld
121 example source code implementing a sample kld module
134 If a module B, is dependent on another module A, but is not compiled with
135 module A as a dependency, then
137 fails to load module B, even if module A is already present in the system.
139 If multiple modules are dependent on module A, and are compiled with module
140 A as a dependency, then
142 loads an instance of module A when any of the modules are loaded.
144 If a custom entry point is used for a module, and the module is compiled as
149 fails to execute the entry point.
152 returns the cryptic message
153 .Sq Li "ENOEXEC (Exec format error)"
154 for any error encountered while loading a module.
156 When system internal interfaces change, old modules often cannot
157 detect this, and such modules when loaded will often cause crashes or
162 facility was originally implemented by
163 .An Doug Rabson Aq dfr@FreeBSD.org .
169 and was designed as a replacement for the
171 facility, which was similar in functionality to the loadable kernel modules