add missing libelf dependency to kernel-module-injector image

[kvaps]

this PR fixes problem of compiling DRBD module on Rocky Linux 9
more details: deckhouse/deckhouse#2268

[rck]

why does this introduce a new Dockerfile? there is already an image for almalinux9 which should work. In general the build process depends a lot on the compiler version, how the distribution ships the kernel sources, and the version of the kernel (e.g., not all of them need libelf-dev) and that is the reason why we have different Dockerfiles for different distributions, I do not want to endorse some magic Dockerfile that is supposed to magically build for all distros/kernels/compilers.

So this needs more explanation, convincing, as is: NACK

[kvaps]

Which is the Dockerfie used by piraeus-operator by default?
I would like to update just this, because having libelf-dev makes it working on Rocky Linux 9 as well.

[WanzenBug]

I guess for Piraeus, which uses the Compile method by default, we really could have just a single image. I believe as long as the GCC version is modern enough to support all compile options on modern kernels we should be good.

But that's just speculation. KBuild will issue a warning if you use a different compiler when building the kmod compared to the kernel, and I assume that warning exists for a reason.

[kvaps]

Can't we just put a few compilers into the image?
Or even better: try using gcc from the host namespace. User needs to install kernel-headers anyway, installing gcc shouldn't be a big deal though.

ref to the discussion about the warning https://patchwork.kernel.org/project/linux-kbuild/patch/20210801025346.93877-1-masahiroy@kernel.org/