Small course Loadable Kernel Modules in linux Kernel 2.6

Loadable Kernel Modules in linux Kernel 2.6

Learning Objectives

Reference

History of Loadable Module

Loadable Kernel Modules did not exist in Linux in the beginning.
Loadable Kernel Modules have been around at least since Linux1.2 (1995).
Device drivers were always quite modular, and only small amount of work was needed to make them Loadable Kernel Module.
Since about 2000 everything that make sense as an LKM had the option of being LKM.

Advantages of using LKMs

What LKMs can Do

Building Kernel Modules

Loadable Kernel Modules are also know as Kernel Modules.
After building the Kernel image issue following commands: make modules Above command compiles the source code and creates module object files
Then issue the following commandsmake modules_installAbove command will copy all modules over to the conventional locations

Loadable kernel Module Utilities

insmod Insert an LKM into the kernel.
rmmod Remove an LKM from the kernel.
depmod Determine interdependencies between LKMs.
lsmod List currently loaded LKMs.
modinfo Display contents of .modinfo section in an LKM object file.
modprobe Insert or remove an LKM or set of LKMs intelligently. For example, if load A before loading B, Modprobe will automatically load A when you tell it to load B.

Inserting kernel Modules

Try following commands to load the modules msdos, the path for module may change depending on your Kernel Version:
# cd /lib/modules/2.6.18-53el5/kernel/fs
# insmod msdos/msdos.ko

Listing the loaded modules

Loaded modules may be listed by using the “lsmod” command.
You may also get information about modules from “/proc/modules”cat /proc/modules

You may also get information about “devices” and “interrupts” from “/proc/devices” and “/proc/interrupts”

Removing Modules

Using modprobe

Using modprobe is a better way of loading modules. Modprobe checks dependencies and also loads the modules needed to support the module being loaded.
Many modules such as some CDROM Drivers and Networks Drivers require certain parameters to be passed with the modules.
The files “/etc/modprobe.conf”, “/etc/modprobe.conf.local” and the directory “/etc/modprobe.d” contains parameters for modules that directly access the hardware. As modprobe can use information from these files it is a better method to load modules.
There are no standard module parameters, drivers may have their own set of parameters. To find out parameters of a driver read the documentation for that module in the directory “/usr/src/linux/documentation”.

Kmod – The Kernel Module Loader

Kmod automates the process of loading Kernel Module.
Kmod keeps on running in the background and automatically loads a kernel Module using “modprobe” whenever a desired feature is needed in the Kernel.
Kmod does not unload the modules if not required in feature but with Amount of RAM available this is not a big issue.

Modules in Linux kernel 2.6

The Linux 2.6 kernel introduces a new, unified framework for device drivers, which requires changes to custom device drivers developed to run under earlier versions of the Linux kernel.
The new driver model provides a framework for full and complete support for

device Plug and Play
power management
Defines the interfaces that these subsystems can use when communicating with individual drivers.

The new driver framework provides a much cleaner separation of responsibilities between buses and drivers.
The 2.6 Linux kernel also introduces the sysfs filesystem to provide a hierarchical view of each system's device tree (and to prevent further overloading of the proc filesystem).
A new naming convention for loadable kernel modules, using the .ko extension (kernel object) rather than the standard .o (object) extension used in all previous stable releases of the Linux kernel.

Summary