Support CUDA in WSL2

[Atry]

/usr/lib/wsl/lib includes CUDA drivers for WSL2, which should be exposed to the FHS environment in order to use CUDA.

Note that both this PR and nix-community/NixOS-WSL#221 are required in order to enable CUDA in WSL2 in the VS Code Terminal

[SuperSandro2000]

Can we symlink?

[Atry]

cp -rsHf is already symlinking.

[Atry]

See https://linux.die.net/man/1/cp#:~:text=%2Dn%20option)-,%2DH,-follow%20command%2Dline

[Atry]

It seems cp -rsHf is used in nixpkgs to link other libraries.

https://github.com/NixOS/nixpkgs/blob/3d53723112c6045bd6534ebeb536056fec5a16f8/pkgs/build-support/build-fhs-userenv/env.nix#L192

[msteen]

@Atry Thanks for clarifying, I wasn't aware it was symlinking either. I will keep it as it is then in PR #47, but I will add a comment about it actually symlinking for clarify sake.

[msteen]

Closed in favor of #47.

[soleera]

Won't these symlinks just become self-referential once the FHS environment is created? Hard links are a no-go as well since wsl/libs and wsl/drivers are actually mount points to a different filesystem... I think the only way to avoid making a full copy would be if we could prevent /usr/lib/wsl from being unshared by bwrap in the first place...

[soleera]

So I managed to get this working by overriding buildFHSUserEnvBubblewrap with an overlay in my flake.nix:

(self: super: {
  buildFHSUserEnvBubblewrap = {...}@args: super.buildFHSUserEnvBubblewrap (args // {
    extraBwrapArgs = [ "--tmpfs /wsl" "--ro-bind /usr/lib/wsl /wsl" ];
    extraBuildCommands = "ln -s /wsl $out/usr/lib/wsl";
  });
})

probably best for this sort of thing to added to buildFHSUserEnvBubblewrap itself rather than being re-implemented in every package that uses it.