[Rpm-ecosystem] Writing a dnf plugin to better deal with out of tree kernel modules

Vít Ondruch vondruch at redhat.com
Thu Oct 6 10:16:36 UTC 2016


Actually is this really DNF issue?

DNF resolves the dependencies properly and installs what can be
installed. E.g. it keeps the kernel-core-4.6.1-1 which is compatible
with the module on the system as long as the module is installed, while
nothing prohibits installation of more recent kernel.

The problem is that the default boot loader entry is modified. Or that
kernel is blindly trying to load inappropriate modules.


Vít



Dne 6.10.2016 v 11:28 Hans de Goede napsal(a):
> Hi All,
>
> There has been some discussion about giving end users a smoother
> nvidia binary driver experience (or a smoother experience with
> any out of tree kernel module they depend on really).
>
> The problem with out of tree kernel modules installed via
> a repo is that as soon as the Fedora kernel pkg gets updated,
> the module needs to be rebuild and typically there will be
> some lag between the repo hosting the module doing that
> rebuild and the user receiving the kernel update.
>
> akmods, or dkms are 2 solutions to this, but we really do
> not want end users to depend on automatically building
> stuff from source on their system, this is undesirable
> in general, and is esp. problematic since this may
> break if the (glue) code needs some minor fix because
> of e.g. a kernel function getting an extra argument.
>
> When things break this way, then the user may end up
> with an unusable system (e.g. black screen after boot),
> and this is something which we ought to fix.
>
> I believe that a possible solution for this updates
> problem is a dnf plugin which knows about kernel module
> packages and which will consider the following scenario
> broken deps and thus will skip the kernel update:
>
> installed
> kernel-core-4.6.1-1
> nvidia-kernel-module-4.6.1-1 (requiring kernel-core=4.6.1-1)
> nvidia-xorg-driver (requiring nvidia-kernel-module)
>
> available as update:
> kernel-core-4.6.2-1
>
> Currently dnf will happily install the update
> and then without dkms / akmod on the next reboot the nvidia
> binary driver will not work since there is no
> nvidia-kernel-module available for the running kernel,
> typically resulting in a black screen, which is a quite
> bad user experience. And as said we really want to avoid
> dkms / akmod.
>
> So the idea is to have a new dnf-plugin which understands
> that if an extra kernel-module is installed that then not
> having that module available for a newer kernel should
> be treated as that kernel having broken deps causing dnf
> to skip the kerel update, unless --best is used in which
> case this will be an error.
>
> So 2 questions:
>
> 1) Any better ideas to delay a kernel update until
> matching extra-module pkgs are available for all
> extra-modules the user has installed ?
>
> 2) Would it be feasible to write such a dnf plugin?
>
> Regards,
>
> Hans
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