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Linux Loadable Kernel Module HOWTO

Bryan Henderson

2006-09-24

Revision History
Revision v1.09 2006-09-24 Revised by: bjh
Fix typos.
Revision v1.08 2006-03-03 Revised by: bjh
Add copyright information.
Revision v1.07 2005-07-20 Revised by: bjh
Add some 2.6 info and disclaimers. Update references to Linux Device Drivers book, Linux Kernel Module Programming Guide.
Revision v1.06 2005-01-12 Revised by: bjh
Cover Linux 2.6 briefly. Update hello.c and reference to Lkmpg. Add information about perils of unloading. Mention dmesg as way to see kernel messages.
Revision v1.05 2004-01-05 Revised by: bjh
Add information on module.h and -DMODULE. Fix tldb.org to tldp.org. Add information on kallsyms.
Revision v1.04 2003-10-10 Revised by: bjh
Fix typo: AHA154x should be AHA152x Add information on what module names the kernel module loader calls for. Add information on what an LKM does when you first load it. Add information on loop module. Change linuxdoc.org to tldp.org.
Revision v1.03 2003-07-03 Revised by: bjh
Update on kernels that don't load into vmalloc space. Add explanation of "deleted" state of an LKM. Explain GPLONLY.
Revision v1.02 2002-05-21 Revised by: bjh
Correct explanation of symbol versioning. Correct author of Linux Device Drivers. Add info about memory allocation penalty of LKM vs bound-in. Add LKM-to-LKM symbol matching requirement. Add open source licensing issue in LKM symbol resolution. Add SMP symbol versioning info.
Revision v1.01 2001-08-18 Revised by: bjh
Add material on various features created in the last few years: kernel module loader, ksymoops symbols, kernel-version-dependent LKM file location.
Revision v1.00 2001-06-14 Revised by: bjh
Initial release.

This is the HOWTO for Linux loadable kernel modules (LKMs). It explains what they are and how to use and create them. It also includes documentation of parameters and other details of use of some particular modules.


Table of Contents
1. Preface
2. Introduction to Linux Loadable Kernel Modules
2.1. Terminology
2.2. History of Loadable Kernel Modules
2.3. The Case For Loadable Kernel Modules
2.4. What LKMs Can't Do
2.5. What LKMs Are Used For
3. Making Loadable Kernel Modules
4. LKM Utilities
5. How To Insert And Remove LKMs
5.1. Could Not Find Kernel Version...
5.2. What Happens When An LKM Loads
5.3. Intelligent Loading Of LKMs - Modprobe
5.4. Automatic LKM Loading and Unloading
5.5. /proc/modules
5.6. Where Are My LKM Files On My System?
6. Unresolved Symbols
6.1. Some LKMs Prerequire Other LKMs
6.2. An LKM Must Match The Base Kernel
6.3. If You Run Multiple Kernels
6.4. SMP symbols
6.5. You Are Not Licensed To Access The Symbol
6.6. An LKM Must Match Prerequisite LKMs
7. How To Boot Without A Disk Device Driver
8. About Module Parameters
9. Persistent Data
10. Technical Details
10.1. How They Work
10.2. The .modinfo Section
10.3. The __ksymtab And .kstrtab Sections
10.4. Ksymoops Symbols
10.5. Other Symbols
10.6. Debugging Symbols
10.7. Memory Allocation For Loading
10.8. Linux internals
11. Writing Your Own Loadable Kernel Module
11.1. Simpler hello.c
11.2. Using the Kernel Build System
11.3. Rubini et al: Linux Device Drivers
11.4. Module Use Counts
12. Differences Between Versions Of Linux
12.1. Linux 2.4 - Linux 2.6
13. Copyright Considerations With LKMs
14. Related Documentation
15. Individual Modules
15.1. Executable Interpreters
15.2. Block Device Drivers
15.3. SCSI Drivers
15.4. Network Device Drivers
15.5. CDROM Device Drivers
15.6. Filesystem Drivers
15.7. Miscellaneous Device Driver
15.8. Serial Device Drivers
15.9. Parallel Device Drivers
15.10. Bus Mouse Device Drivers
15.11. Tape Device Drivers
15.12. Watchdog Timers
15.13. Sound Device Drivers
16. Maintenance Of This Document
17. History
18. Copyright