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.
The module utilities are available from wherever you got your kernel
source as modules-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 modules-x.y.z.tar.gz',
cd to the directory it creates (modules-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
memory, 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.
As of version 1.2.2, many filesystems, a few SCSI drivers, several ethernet
adapter drivers, and other odds and ends are loadable as 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.