@fpletz you looked interested :p

I think we have to be careful about moving computations that are currently done in builder (like generate-config.pl) to Nix because NixOS evaluation is already very slow.

at first, I had moved the check to a check-config.pl but I was not sure how to integrate with nixos/modules/system/boot/kernel.nix (I believe it's an IFD situation ? frowned upon) so I translated it to nix.
Maybe we could disable these checks by default ? nixpkgs currently runs the check only for linuxManualConfig I believe because of:
assertions = if config.boot.kernelPackages.kernel ? features then []
so that wouldn't change much.

I've added a commit that kinda reverts to the current behavior, i.e., it only runs the check when the kernel is built with no features set, aka when built with linuxManualConfig. This way, the extra penalty should only concern few people.

Another aspect (regardless of the implementation) is that I wanted a way to decouple the check from the build. For instance in nixops, I want to check if guest kernels have VIRTIO without rebuilding their kernels.

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still care. For reference, a new project appeared a few days ago to fix kernel configs https://bitbucket.org/easelab/configfix/src/master/

I marked this as stale due to inactivity. → More info

If this PR is not accepted, should system.requiredKernelConfig be removed then?
It is used across nixpkgs but has no effect and that is confusing

And, ... I might be wrong, but it looks like IFD in the present form of Nix-implementation (because of builtins.readFile), but bash/perl/whatsoever-implemenation will not be IFD (just like configchecking of webservers are done)