LKM - Loadable Kernel Modules interface
Loadable kernel modules allow the system administrator to
and remove functionality from a running system. This ability also helps
software developers to develop new parts of the kernel without constantly
rebooting to test their changes.
Various types of modules can be loaded into the system.
There are several
defined module types, listed below, which can be added to
in a predefined way. In addition, there is a generic type,
for which the
module itself handles loading and unloading.
The LKM interface is used by performing ioctl(2) calls on
device. Normally all operations involving Loadable Kernel
handled by the modload(8), modunload(8), and modstat(8) programs. Users
should never have to interact with /dev/lkm directly.
System Call modules
System calls may be replaced by loading new ones via
the LKM interface.
All system calls may be replaced, but special care
should be taken with the ioctl(2) system call, as it
is used to
load and unload modules.
When a system call module is unloaded, the system
call which was
replaced by the loadable module is returned to its
in the system call table.
Virtual File System modules
Virtual file systems may be added via the LKM interface.
Device Driver modules
New block and character device drivers may be loaded
system with LKM. The major problem with loading a
is that the driver's device nodes must be exist for
to be accessed. They are usually created by instructing
modload(8) to run an appropriate program when the
driver has been
Execution interpreters allow the loading and execution of binaries
which are normally not usable by the operating
Miscellaneous modules are modules for which there
are not currently
well-defined or well-used interfaces for extension. The
user is expected to write their own loader to manipulate whatever
kernel data structures necessary to enable and disable the new
module when it is loaded and unloaded.
/dev/lkm LKM interface device
/usr/include/sys/lkm.h file containing definitions of module types
/usr/share/lkm example source code implementing
several of the
modload(8), modstat(8), modunload(8)
The LKM facility was designed to be similar in functionality
to the loadable
kernel modules facility provided by SunOS 4.1.3.
Terrence R. Lambert <email@example.com>
Loading a bogus module is likely to kill your machine.
Loadable streams modules should and will be implemented when
implementation is written.
OpenBSD 3.6 September 4, 1993
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