Dynamic Kernel Module Support

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Revision as of 15:19, 18 October 2012 by Lekensteyn (talk | contribs) (Should the .install file attempt to modprobe/rmmod the module?: no.)
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Dynamic Kernel Module Support allows one to compile and install kernel modules without recompiling the entire kernel.


Install package dkms in the Official Repositories.


Here are some guidelines to follow.

Package name

Since it is likely that the DKMS package duplicates a non-DKMS package, I am prefixing the DKMS-enabled package with "dkms-". If I were to package something that didn't have a non-DKMS counterpart, I would still use the "dkms-" prefix.

Where should source go?

DKMS by default uses /usr/src/, but [namcap] complains that is a non-standard directory. (Even though the FHS reference namcap uses states that /usr/src is "optional". One could place the source in /opt/<package> and then sym-link it (which is what some non-DKMS packages do.)

Sources should go into /usr/src/<package>-<package version> which is the default directory that DKMS commands use. <package> is the "true package name" (which is usually the PKGBUILD $_pkgname variable, which is the $pkgname minus the "dkms-" prefix). <package version> refers to the PACKAGE_VERSION field in dkms.conf. By convention, PKGBUILDs $pkgver should have the same value.

Where should patches be applied?

One could patch the source either in the PKGBUILD or through DKMS. Since non-DKMS packages patch from the PKGBUILD, and to keep the DKMS PKGBUILD as close to the non-DKMS version, I am patching in the PKGBUILD.

Should the .install file attempt to modprobe/rmmod the module?

No, it should not. Consider a module that crashes when loaded. That could halt a pacman upgrade or installation which has more severe consequences.

Loading/ removing modules is a task for the user.

How to create .install / dkms.conf files?

Try to avoid updating things like version numbers in multiple files. Try to avoid cluttering up PKGBUILDs/.install files with DKMS-specific stuff. (This keeps them closer to the non-DKMS files).

I've just started using a simple bash script to create the dkms.conf file and to replace text in an install.template file. This leads to much cleaner and easier to understand files.

You should not run depmod in your .install script, this is done automatically by dkms install. Running dkms install depends on dkms build which depends on dkms add and are executed automatically. Thus, you only need to put the sources in /usr/src/MODULE-VERSION and run dkms install in your .install script.

Example for a module put in /usr/src/MODULE-VERSION (substitute MODULE and PACKAGE_NAME accordingly):

post_install() {
    dkms install -m MODULE -v $1
pre_upgrade() {
    local curver=$2
    # $2 is unset due to a bug. Query current version using pacman as fallback
    [ -n "$curver" ] || curver=$(pacman -Qi PACKAGE_NAME | awk '/^Version/{print $3}')
    pre_remove $curver
post_upgrade() {
    post_install $1
pre_remove() {
    dkms remove -m MODULE -v $1 --all

DKMS breaks the ABS

Sort of, yes. The problem is that the resulting modules don't belong to the package, so pacman can't track or report on them.

I don't think that's a show-stopper, but it probably puts DKMS out on the fringe a bit. There is some talk about pacman adding similar support through pacman hooks. [1]. I think you could might "fake" the ownership, by installing the module as normal (or even a "dummy" file) and just letting DKMS overwrite it.

namcap issues

As mentioned earlier, namcap complains if you put source in /usr/src. Also, namcap can not detect that dkms is a dependency. (I guess maybe it's not technically a dependency, but...)

Basically, take the dependencies of the non-DKMS version, add 'dkms' and remove 'linux-headers' (since dkms optdepends on that)

See Also