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                 LinuxPlanet / Tutorials
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               ---------------------------------------------------------------

                                   [Stock Market Analysis]

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                Linux Device Drivers Demystified
                All About Modules
                [Image]
                James Andrews

                Another much-trumpeted advantage of Linux is that it does not
                need to be rebooted as often as other operating systems. You
                might think that this is due to its rock solid stability. You
                may think I am now going to talk about the quality of the
                device drivers. But you'd be wrong. The reason that Linux
                device drivers lead to less rebooting is that we can
                reconfigure, load or unload them without restarting the
                system.

                To do this modular kernel drivers are used.

                How to load a module

                Most people configure their modules at install time and then
                leave them alone. All the major distributions have taken to
                modules because of another advantage they have: size.
                Distribution makers want to support all the possible cards and
                devices that Linux can. If we compiled all these into the
                kernel it would be huge. If several different static kernels
                for different devices were supplied then they would take up
                too much space, as well. With the modular system distribution
                makers supply a stripped down kernel plus a comprehensive set
                of device drivers. This typically only occupies two or three
                floppy disks in total.

                modprobe, lsmod and insmod

                if you want to load a module after system setup time, then the
                easiest way is as follows:

                modprobe hfs

                This example loads the Apple Mac disk subsystem driver (called
                hfs) with the modprobe command. If the module takes
                parameters, like IRQ numbers, then you can specify them with
                modprobe too.

                To see what modules are loaded and to see information on how
                they depend on each other we use lsmod. Here is some example
                output from lsmod.

                Module                  Size  Used by
                gus                     45016    0
                mad16                  6564    0
                sb                       31416   0
                ad1848                15112    0  [mad16]
                uart401                 5588    0  [mad16 sb]
                sound                 54368   0  [gus mad16 sb ad1848 uart401]

                In this example the mad16 kernel device driver depends on the
                ad1848 device driver.

                Yes, there really is a mad16 device driver. It is a soundcard
                chipset.

                /etc/modules, /etc/conf.modules

                In the normal course of events the modules we asked for when
                Linux was installed are loaded at boot time. To achieve this
                the file /etc/modules is used. This is a list of modules to be
                loaded.

                The options for the modules are stored in /etc/conf.modules.
                Recommended practice is to not edit /etc/conf.modules,
                however, but to use a script like update-modules; see the man
                pages for more details.

                      Next: Looking for the driver for a particular device? »

• Kernel updatesSkip Ahead
  and info site [Image]
  [Image]       1 Introduction
• Kernel Compili2 All About Modules
  Guide         3 Looking for the driver for a particular device?
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