Bug#590221: Package: nvidia-glx-legacy-173xx

[Russ Allbery]

Steven Altermatt <stevealcnm at gmail.com> writes:

> Thanks for your explanations, although I do have a couple ?s. I have
> been investigating this issue further lately but was unable to send an
> e-mail due to surgery on my right hand. I see that there are 2 source
> pkgs, nvidia-kernel-legacy-173xx-source &
> nvidia-kernel-legacy-173xx-dkms. The former for people like me using
> make-kpkg or those using m-a. The latter for the auto install with dkms
> users. The pkg description, of the former, states:

> "PLEASE read
> /usr/share/doc/nvidia-kernel-legacy-173xx-source/README.Debian.gz for
> building information. If you want the kernel module to be automatically
> installed via DKMS, install nvidia-kernel-legacy-173xx-dkms instead."

> In the testing, my main system, it is way at the bottom and likely missed,
> whereas in the unstable it is near the top. So it appears these 2 source
> pkgs are mutually exclusive.

They are not mutually exclusive.  You can install both.  You probably
don't care about -source if you have -dkms installed, but there are some
edge cases where that's a useful thing to do (if you're using -dkms for
your local system, for instance, but want to build Debian packages with
the kernel module using -source for other systems).

> The depends, recommends and suggests listing for each seem to be correct
> and should not cause a problem.

The Recommends for -source of nvidia-glx is the root of your problem.

> Before the newest source pkg upgrade I always just upgraded the source
> first and then upgraded the glx whenever I got around to building and
> installing the new module.

Right.

> If I understand correctly, there was a change in the glx pkg that caused
> the problem I experienced.

Only because DKMS now provides a way to immediately satisfy the
requirement for the kernel module when upgrading nvidia-glx.  In the past,
there was no way to satisfy that dependency, so upgrading nvidia-glx would
block until you had built a kernel module.  Now, with DKMS, there's a way
to not wait, and apt-get and aptitude will find it.

> I see in the glx pkg description it lists a virtual pkg;
> nvidia-kernel-173(version) which is provided by
> nvidia-kernel-legacy-173xx-dkms. Shouldn't it also be provided by the
> other source pkg, nvidia-kernel-legacy-173xx-source?

No, because just installing the -source package does not actually satisfy
that dependency.  You have to actually have a kernel module.  The -source
package does not provide a kernel module, only the means to create one.
So if we let the -source package satisfy the dependency, apt would think
everything was fine, but the user would have a broken video driver until
they built a kernel module.

> Maybe that's where the confusion starts.  Of course I knew the module
> had to be built and installed before the glx due to dependency issues,
> but for some reason just installing the source pkg wanted to pull in all
> the other stuff.

Installing the source package pulls in nvidia-glx via Recommends.
nvidia-glx in turn requires a kernel module, so apt-get and aptitude look
for some way to get a kernel module, find DKMS, and install the -dkms
package and its requirements, which include such things as kernel headers
and a compiler matching the compiler used for your kernel.

> I used to build the kernel headers pkg also when I needed several kernel
> modules, but now only use the nvidia one. I guess I always thought quite
> a few users *did* build custom kernels, maybe that has changed in the
> past few years with more people using Debian and the ubuntus.

My subjective impression is that the number of people building custom
kernels has dropped steadily as the quality of the Debian-provided kernels
has increased.  I stopped building custom kernels about eight years ago
since the Debian-provided kernels started just working for me and I had
better things to do with that time I was spending.

-- 
Russ Allbery (rra at debian.org)               <http://www.eyrie.org/~eagle/>