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1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
162 lines
5.1 KiB
Groff
162 lines
5.1 KiB
Groff
.\" Copyright (c) 1993 Christopher G. Demetriou
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 17, 1996
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.Dt LKM 4
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.Os FreeBSD 2.0
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.Sh NAME
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.Nm lkm
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.Nd loadable kernel module facility
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.Sh DESCRIPTION
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Loadable kernel modules allow the system administrator to
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dynamically add and remove functionality from a running system.
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This ability also helps software developers to develop
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new parts of the kernel without constantly rebooting to
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test their changes.
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.Pp
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Various types of modules can be loaded into the system.
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There are several defined module types, listed below, which can
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be added to the system in a predefined way. In addition, there
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is a generic type, for which the module itself handles loading and
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unloading.
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.Pp
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The
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.Tn FreeBSD
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system makes extensive use of loadable kernel modules, and provides
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loadable versions of most filesystems, the
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.Tn NFS
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client and server, all the screen-savers, and the
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.Tn iBCS2
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and
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.Tn Linux
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emulators. Modules distributed with the system are found in the
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.Pa /lkm
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directory.
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.Pp
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The
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.Nm
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interface is used by performing
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.Xr ioctl 2
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calls on the
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.Pa /dev/lkm
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device. Normally all operations involving
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Loadable Kernel Modules are handled by the
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.Xr modload 8 ,
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.Xr modunload 8 ,
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and
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.Xr modstat 8
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programs. Users should never have to interact with
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.Pa /dev/lkm
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directly.
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.Sh "MODULE TYPES"
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.Bl -ohang
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.It Em "System Call modules"
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System calls may be replaced by loading
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new ones via the
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.Nm
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interface. All system calls may be
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replaced, but special care should
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be taken with the
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.Xr ioctl 2
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system call, as it is used to load and
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unload modules.
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.Pp
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When a system call module is unloaded,
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the system call which
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was replaced by the loadable module
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is returned to its rightful place
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in the system call table.
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.It Em "Virtual File System modules"
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Virtual file systems may be added
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via the
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.Nm
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interface.
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.It Em "Device Driver modules"
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New block and character device
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drivers may be loaded into the system with
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.Nm LKM .
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The major problem with loading
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a device driver is that the driver's
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device nodes must be exist for the
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devices to be accessed. They are usually
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created by instructing
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.Xr modload 8
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to run an appropriate program when
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the driver has been successfully loaded.
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.It Em "Execution classes"
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Also known as image activators, execution classes are the mechanisms
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by which the
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.Xr execve 2
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system call is able to recognize an executable file's format and load it
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into memory.
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.It Em "Miscellaneous modules"
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Miscellaneous modules are modules
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for which there are not currently
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well-defined or well-used interfaces
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for extension. Users are expected
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to write their own loaders to manipulate
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whatever kernel data structures necessary
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to enable and disable the new module
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when it is loaded and unloaded.
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.El
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.Sh FILES
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.Bl -tag -width /usr/share/examples/lkm -compact
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.It Pa /dev/lkm
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.Nm
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interface device
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.It Pa /lkm
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directory containing module binaries shipped with the system
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.It Pa /usr/include/sys/lkm.h
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file containing definitions of module types
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.It Pa /usr/share/examples/lkm
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example source code implementing two of the module types
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.Sh SEE ALSO
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.Xr modload 8 ,
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.Xr modstat 8 ,
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.Xr modunload 8
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.Sh BUGS
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If a module fails to initialize itself correctly, and the system is
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able to detect this failure, it will panic immediately.
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.Pp
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When system internal interfaces change, old modules often cannot
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detect this, and such modules when loaded will often cause crashes or
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mysterious failures.
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.Sh AUTHOR
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The
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.Nm
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facility was originally implemented by Terrence R. Lambert. Loadable
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filesystems were implemented by Garrett Wollman, and loadable
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execution classes were implemented by David Greenman, Soren Schmidt,
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and Garrett Wollman.
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.Sh HISTORY
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The
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.Nm
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facility was designed to be similar in functionality
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to the loadable kernel modules facility provided by
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.Tn SunOS
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4.1.3.
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