Kernel Korner - Exploring Dynamic Kernel Module Support (DKMS)

shows that each of the shell variable directives should be coded in all capital letters. One of the current exceptions to this rule is the MAKE_ directive. DKMS uses the generic MAKE= command to build your module. But, if a MAKE_kernel-regexp-text command exists and the text after the MAKE_ matches (as a substring) the kernel for which it is being built, then this alternate make command is used. In the above example, you can see how DKMS would use the MAKE_smp directive on any smp kernel for which it was building this module. Similar PATCH_ commands also exist. When the text after the underscore matches the kernel for which a module is being built, that patch first is applied to the module source. This allows developers to distribute one source tarball, with one dkms.conf and multiple patches. Yet, different patches can be applied as necessary to the source to ensure all modules function correctly on all kernels.

Also notice that dkms.conf accepts the $kernelver variable, which, at build time, is replaced with the kernel version for which the module is being built. This is especially important so the correct include directories are referenced when compiling a module for a kernel that is not currently running.

DKMS and RPM actually work quite well together. The only twist is that to make it function properly, you have to create an RPM that installs source. Although normal practice is to install source only with source RPMs, a source RPM does not necessarily work with DKMS; it will not let you do much besides install the source. Instead, your source tarball needs to be included with your RPM, so your source can be placed in /usr/src/module-module-version/ and the proper DMKS commands can be called. The %post and %preun basically are DKMS commands. Here is a sample .spec file:

%define module qla2x00

Summary: Qlogic HBA module
Name: %module_dkms
Version: v6.04.00
Release: 1
Vendor: Qlogic Corporation
Copyright: GPL
Packager: Gary Lerhaupt <gary_lerhaupt@dell.com>
Group: System Environment/Base
BuildArch: noarch
Requires: dkms gcc bash sed
Source0: qla2x00src-%version.tgz
Source1: dkms.conf
BuildRoot: %{_tmppath}/%{name}-%{version}-%{release}-root/

%description
This package contains Qlogic's qla2x00 HBA module meant
for the DKMS framework.

%prep
rm -rf qla2x00src-%version
mkdir qla2x00src-%version
cd qla2x00src-%version
tar xvzf $RPM_SOURCE_DIR/qla2x00src-%version.tgz

%install
if [ "$RPM_BUILD_ROOT" != "/" ]; then
	rm -rf $RPM_BUILD_ROOT
fi
mkdir -p $RPM_BUILD_ROOT/usr/src/%module-%version/
install -m 644 $RPM_SOURCE_DIR/dkms.conf
$RPM_BUILD_ROOT/usr/src/%module-%version
install -m 644 qla2x00src-%version/*
$RPM_BUILD_ROOT/usr/src/%module-%version

%clean
if [ "$RPM_BUILD_ROOT" != "/" ]; then
        rm -rf $RPM_BUILD_ROOT
fi

%files
%defattr(0644,root,root)
%attr(0755,root,root) /usr/src/%module-%version/

%pre

%post
/sbin/dkms add -m %module -v %version
/sbin/dkms build -m %module -v %version
/sbin/dkms install -m %module -v %version
exit 0

%preun
/sbin/dkms remove -m %module -v %version --all
exit 0

Because DKMS is a recently conceived framework, many things can be added, removed or recoded as the community decides. The latest project information for DKMS can be found at www.freshmeat.net/projects/dkms. You can ask questions and provide feedback by joining the DKMS-devel mailing list at lists.us.dell.com/mailman/listinfo.

In the December 2002 issue of Linux Journal, Linus Torvalds was quoted as saying, “Basically, all of the commercial people have their own agenda, and that's very healthy because you want to have these often-conflicting agendas to push the system into something that actually works for everybody.” As a commercial reseller of Linux-enabled products, Dell is interested in finding a good solution to the ongoing module/kernel issue, both to support the community and to create a better Linux experience for their customers. DKMS was designed with this in mind.