LKM(4) OpenBSD Programmer's Manual LKM(4)NAME
LKM - Loadable Kernel Modules interface
SYNOPSIS
option LKM
DESCRIPTION
Loadable kernel modules allow the system administrator to dynamically add
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 the
system 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 the /dev/lkm
device. Normally all operations involving Loadable Kernel Modules are
handled by the modload(8), modunload(8), and modstat(8) programs. Users
should never have to interact with /dev/lkm directly. The loading and
unloading of modules is also dependent on the system securelevel(7).
MODULE TYPES
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 rightful place
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 into the
system with LKM. The major problem with loading a device driver
is that the driver's device nodes must exist for the devices to
be accessed. They are usually created by instructing modload(8)
to run an appropriate program when the driver has been
successfully loaded.
Execution Interpreters
Execution interpreters allow the loading and execution of
binaries which are normally not usable by the operating system.
Miscellaneous modules
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.
FILES
/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 modules types.
SEE ALSOsecurelevel(7), modload(8), modstat(8), modunload(8)HISTORY
The LKM facility was designed to be similar in functionality to the
loadable kernel modules facility provided by SunOS 4.1.3.
AUTHORS
Terrence R. Lambert <terry@cs.weber.edu>
BUGS
Loading a bogus module is likely to kill your machine.
Loadable streams modules should and will be implemented when a streams
implementation is written.
OpenBSD 4.9 August 2, 2008 OpenBSD 4.9