176 lines
5.2 KiB
Groff
176 lines
5.2 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 November 8, 1998
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.Dt KLD 4
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.Os
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.Sh NAME
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.Nm kld
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.Nd dynamic kernel linker facility
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.Sh DESCRIPTION
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The LKM (Loadable Kernel Modules) facility has been deprecated in
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.Fx 3.0
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and above in favor of the
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.Nm
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interface.
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This interface, like its
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predecessor, allows the system administrator to dynamically add and remove
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functionality from a running system.
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This ability also helps software
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developers to develop new parts of the kernel without constantly rebooting
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to 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.
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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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.Fx
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system makes extensive use of loadable kernel modules, and provides loadable
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versions of most file systems, 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.
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.Nm
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modules are placed by default in the
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.Pa /boot/kernel
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directory along with their matching kernel.
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.Pp
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The
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.Nm
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interface is used through the
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.Xr kldload 8 ,
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.Xr kldunload 8
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and
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.Xr kldstat 8
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programs.
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.Pp
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The
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.Xr kldload 8
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program can load either
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.Xr a.out 5
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or ELF formatted loadable modules.
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The
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.Xr kldunload 8
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program unloads any given loaded module, if no other module is dependent
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upon the given module.
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The
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.Xr kldstat 8
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program is used to check the status of the modules currently loaded into the
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system.
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.Pp
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Kernel modules may only be loaded or unloaded if the system security level
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.Va kern.securelevel
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is less than one.
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.Sh "MODULE TYPES"
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.Bl -ohang
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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 .
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Device nodes for the loaded drivers are automatically created when a
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module is loaded and destroyed when it is unloaded by
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.Xr devfs 5 .
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You can specify userland programs that will run when new devices
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become available as a result of loading modules, or existing devices
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go away when modules are unloaded, by configuring
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.Xr devd 8 .
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.El
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.Sh FILES
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.Bl -tag -width /usr/include/sys/module.h -compact
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.It Pa /boot/kernel
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directory containing module binaries built for the kernel also
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residing in the directory.
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.It Pa /usr/include/sys/module.h
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file containing definitions required to compile a
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.Nm
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module
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.It Pa /usr/share/examples/kld
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example source code implementing a sample kld module
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.El
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.Sh SEE ALSO
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.Xr kldfind 2 ,
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.Xr kldfirstmod 2 ,
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.Xr kldload 2 ,
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.Xr kldnext 2 ,
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.Xr kldstat 2 ,
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.Xr kldunload 2 ,
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.Xr devfs 5 ,
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.Xr devd 8 ,
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.Xr kldload 8 ,
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.Xr kldstat 8 ,
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.Xr kldunload 8 ,
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.Xr sysctl 8
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.Sh HISTORY
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The
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.Nm
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facility appeared in
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.Fx 3.0
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and was designed as a replacement for the
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.Xr lkm 4
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facility, which was similar in functionality to the loadable kernel modules
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facility provided by
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.Tn SunOS
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4.1.3.
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.Sh AUTHORS
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The
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.Nm
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facility was originally implemented by
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.An Doug Rabson Aq dfr@FreeBSD.org .
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.Sh BUGS
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If a module B, is dependent on another module A, but is not compiled with
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module A as a dependency, then
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.Xr kldload 8
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fails to load module B, even if module A is already present in the system.
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.Pp
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If multiple modules are dependent on module A, and are compiled with module
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A as a dependency, then
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.Xr kldload 8
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loads an instance of module A when any of the modules are loaded.
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.Pp
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If a custom entry point is used for a module, and the module is compiled as
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an
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.Sq ELF
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binary, then
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.Xr kldload 8
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fails to execute the entry point.
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.Pp
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.Xr kldload 8
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returns the cryptic message
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.Sq Li "ENOEXEC (Exec format error)"
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for any error encountered while loading a module.
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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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