[gentoo-server] Kernel configuration management

[Matthias-Christian Ott <ott@mirix.org>]

I'm planning to migrate several computers to Gentoo. At the moment I'm
running two machines with ad-hoc kernel configurations based on the
kernel configuration from the installation CD (which was created for
2.6.26). In order to keep the maintenance effort for the new machines
low, I would like to have a unified/baseline kernel configuration with
minor adjustments for some machines.

I have been thinking about this for several weeks now and came to the
conclusion, that there are two sub-problems: Creating a universal kernel
configuration and merging and maintaining specific configurations with
the baseline configuration.

The second problem can be solved by simple concatenation and/or
defconfigman, kccmp and make silentoldconfig. OpenWRT does this pretty
much the same way.

Creating the baseline configuration is much harder. So far I tried make
defconfig, the installation CD configuration and kernel-seeds.org. None
really satisfied my requirements and often resulted in ad-hoc changes
when I simply went through a compile and reboot cycle until everything
worked. I had a look at policies of other GNU/Linux distributions [1,2]
and found that I need to develop or adopt a policy for my systems (the
Ubuntu "modular where possible" policy seems reasonable to me and
probably makes the curent ad-hoc configuration unnecessary). I also
thought about reusing kernel configurations from other distributions,
but have some doubts about kernel version mismatches (i.e. the kernel
versions of Gentoo and the other distribution differ) and about
unintended implications of kernel options that I don't fully understand.

The mailing list archives show that this topic has been partly discussed
before (especially whether Gentoo should have a default kernel
configuration like other distributions), so I don't want to start a
lengthy discussion about this here. I'm more interested in what other
people do for larger deployments/installations on heterogeneous hardware.

Regards,
Matthias-Christian

[1] https://wiki.ubuntu.com/Kernel/Dev/KernelConfig
[2] https://wiki.linaro.org/KernelConfigPolicyDraft