New HOWTO: The Linux Kernel HOWTO - page 11

Table of Contents

  10.  Modules

  Loadable kernel modules can save memory and ease configuration. The
  scope of modules has grown to include filesystems, ethernet card
  drivers, tape drivers, printer drivers, and more.

  10.1.  Installing the module utilities

  The module utilities are available from wherever you got your kernel
  source as modutils-x.y.z.tar.gz; choose the highest patchlevel x.y.z
  that is equal to or below that of your current kernel. Unpack it with
  `tar zxvf modutils-x.y.z.tar.gz', cd to the directory it creates
  (modutils-x.y.z), look over the README, and carry out its installation
  instructions (which is usually something simple, such as make
  install). You should now have the programs insmod, rmmod, ksyms,
  lsmod, genksyms, modprobe, and depmod in /sbin. If you wish, test out
  the utilities with the ``hw'' example driver in insmod; look over the
  INSTALL file in that subdirectory for details.

  insmod inserts a module into the running kernel. Modules usually have
  a .o extension; the example driver mentioned above is called
  drv_hello.o, so to insert this, one would say `insmod drv_hello.o'. To
  see the modules that the kernel is currently using, use lsmod. The
  output looks like this:

      blah# lsmod
      Module:        #pages:  Used by:
      drv_hello          1

  `drv_hello' is the name of the module, it uses one page (4k) of mem�
  ory, and no other kernel modules depend on it at the moment. To remove
  this module, use `rmmod drv_hello'. Note that rmmod wants a module
  name, not a filename; you get this from lsmod's listing. The other
  module utilities' purposes are documented in their manual pages.
  10.2.  Modules distributed with the kernel

  As of version 2.0.30, most of everything is available as a loadable
  modules. To use them, first make sure that you don't configure them
  into the regular kernel; that is, don't say y to it during `make
  config'.  Compile a new kernel and reboot with it. Then, cd to
  /usr/src/linux again, and do a `make modules'. This compiles all of
  the modules which you did not specify in the kernel configuration, and
  places links to them in /usr/src/linux/modules.  You can use them
  straight from that directory or execute `make modules_install', which
  installs them in /lib/modules/x.y.z, where x.y.z is the kernel
  release.

  This can be especially handy with filesystems. You may not use the
  minix or msdos filesystems frequently. For example, if I encountered
  an msdos (shudder) floppy, I would insmod
  /usr/src/linux/modules/msdos.o, and then rmmod msdos when finished.
  This procedure saves about 50k of RAM in the kernel during normal
  operation. A small note is in order for the minix filesystem: you
  should always configure it directly into the kernel for use in
  ``rescue'' disks.