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+.\"	$NetBSD: lkm.4,v 1.4 1994/11/30 16:22:22 jtc Exp $
+.\"
+.\" Copyright (c) 1993 Christopher G. Demetriou
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.Dd September 4, 1993
+.Dt LKM 4
+.Os NetBSD 0.9a
+.Sh NAME
+.Nm LKM
+.Nd Loadable Kernel Modules interface
+.Sh SYNOPSIS
+.Cd "options LKM"
+.Sh 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.
+.Pp
+Various types of modules can be loaded into the sytem.
+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.
+.Pp
+The
+.Nm
+interface is used by performing
+.Xr ioctl 2
+calls on the
+.Pa /dev/lkm
+device.  Normally all operations involving
+Loadable Kernel Modules are handled by the
+.Xr modload 8 ,
+.Xr modunload 8 ,
+and
+.Xr modstat 8
+programs.  Users should never have to interact with
+.Pa /dev/lkm
+directly.
+.Sh "MODULE TYPES"
+.Bl -tag -width indent
+.It System Call modules
+System calls may be replaced by loading
+new ones via the
+.Nm
+interface.  All system calls may be
+replaced, but special care should
+be taken with the
+.Xr ioctl 2
+system call, as it is used to load and
+unload modules.
+.Pp
+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.
+.It Virtual File System modules
+Virtual file systems may be added
+via the
+.Nm
+interface.  At this time, only
+file systems which are already
+known to the system can be added,
+because of the way the
+.Xr mount 2
+system call is implemented.
+.It Device Driver modules
+New block and character device
+drivers may be loaded into the system with
+.Nm LKM .
+The major problem with loading
+a device driver is that the driver's
+device nodes must be exist for the
+devices to be accessed.  They are usually
+created by instructing
+.Xr modload 8
+to run an appropriate program when
+the driver has been successfully loaded.
+.It Execution Interpreters
+Execution interpreters allow
+the loading and execution of
+binaries which are normally not
+usable by the operating system.
+.It 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.
+.El
+.Sh FILES
+.Bl -tag -width /usr/include/sys/lkm.h -compact
+.It Pa /dev/lkm
+.Nm
+interface device
+.It Pa /usr/include/sys/lkm.h
+file containing defitions of module types
+.It Pa /usr/share/lkm
+example source code implementing several of the modules types
+.Sh SEE ALSO
+.Xr modload 8 ,
+.Xr modunload 8 ,
+.Xr modstat 8
+.Sh HISTORY
+The
+.Nm
+facility was designed to be similar in functionality
+to the loadable kernel modules facility provided by
+.Tn "SunOS 4.1.3" .
+.Sh AUTHOR
+.Bl -tag
+Terrence R. Lambert, terry@cs.weber.edu
+.El
+.Sh BUGS
+Loading a bogus module is likely to kill your machine.
+.Pp
+Loadable streams modules should and will be implemented
+when a streams implementation is written.