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By Root 1542 0

into the official kernel sources, or those that are simply too esoteric to be put into the kernel sources (e.g., a device driver for some custom-built hardware that is not publicly available) can be available as stand-alone, external modules. Unpack the archive of the module, compile it according to the instructions that are hopefully included, and copy the resulting module file to the appropriate subdirectory of /lib/modules/kernelversion. Some modules might have an install script or allow you to issue the command make install to perform the last step.

Loading a Module

Once you have a compiled module (either from the kernel sources or external), you can load it using the command:

insmod module

where module is the name of the module object file. For example:

insmod /lib/modules/2.6.11.4/kernel/drivers/parport/parport_pc.ko

installs the parport_pc driver if it is found in that file.

Once a module is installed, it may display some information to the console (as well as to the system logs), indicating that it is initialized. For example, the ftape driver might display the following:

Jul 26 13:08:41 tigger kernel: pnp: Device 00:09 activated.

Jul 26 13:08:41 tigger kernel: parport: PnPBIOS parport detected.

Jul 26 13:08:41 tigger kernel: parport0: PC-style at 0x378, irq 7 [PCSPP,TRISTATE]

The exact messages printed depend on the module, of course. Each module should come with ample documentation describing just what it does and how to debug it if there are problems.

It is likely that insmod will tell you it could not load the module into the kernel because there were "symbols missing ." This means that the module you want to load needs functionality from another part of the kernel that is neither compiled into the kernel nor contained in a module already loaded. In particular, the parport_pc module that we have been using as an example depends on the parport module that provides the general parallel port functionality. You could now try to find out which module contains those functions, load that module first with insmod, and try again. You will eventually succeed with this method, but it can be cumbersome, and this would not be Linux if there weren't a better way.

You first need a module database in the file /lib/modules/kernelversion/modules.dep. You can create this database by calling:

depmod -a

This goes through all the modules you have and records whether they need any other modules. With this database in place, you can simply replace the insmod command with the modprobe command, which checks the module database and loads any other modules that might be needed before loading the requested module. For example, our modules.dep file contains—among others—the following line:

/lib/modules/2.6.8/kernel/drivers/isdn/i4l/isdn.ko:/lib/modules/2.6.8/

kernel/drivers/net/slhc.ko

This means that in order to load the isdn module (a device driver for ISDN support), the slhc module (containing one of the ISDN protocol implementations) must be loaded. If we now load the isdn module with modprobe (this example is slightly simplified because the isdn module needs additional parameters):

modprobe hisax

modprobe will detect the dependency and load the slhc module. If you have compiled a module for the current kernel, you first need to run depmod -a, though, so that modprobe can find it.

Some modules need so-called module parameters. For example, a device driver might need to be assigned an IRQ. You can pass those parameters in the form parameter_name=parameter_value with both the insmod and the modprobe command. In the following example, several parameters are passed to the hisax module, which is a particular (and somewhat outdated) driver for a family of ISDN boards:

tigger # modprobe hisax type=3 protocol=2 io=0x280 irq=10

The documentation for each module should tell you which parameters the module supports. If you are too lazy to read the documentation, a nifty tool you can use is modinfo, which tells you—among other things—which parameters are accepted by the module you specify.

One caveat