nixos: Fix lvm2 sd stage 1 tests

[ElvishJerricco]

Description of changes

Now that useBootLoader implies a whole root fs disk image, we can't just change the root device like this anymore.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.05 Release Notes (or backporting 22.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[ElvishJerricco]

@RaitoBezarius Is it possible to make it not build the store image at all? Even with useNixStoreImage = false, it still builds one.

fwiw, this is why I think we shouldn't be using a store image by default with useBootLoader = true. It's good to be able to do that, but aren't there other tests that assume the root disk is an empty image and can therefore be trivially replaced?

[ElvishJerricco]

Hm, only seems to work with the linux-latest versions... not sure why the device times out on the others.

[RaitoBezarius]

@RaitoBezarius Is it possible to make it not build the store image at all? Even with useNixStoreImage = false, it still builds one.

fwiw, this is why I think we shouldn't be using a store image by default with useBootLoader = true. It's good to be able to do that, but aren't there other tests that assume the root disk is an empty image and can therefore be trivially replaced?

What do you mean by store image? It never builds a store image if you don't use one.

It only builds a system image, containing a nix store.

We should not use a store image by default with useBootLoader = true AFAIK. I don't know much about tests that assume the root disk is an empty image, if there are some like those, they should probably direct boot with a bootloader and not use the default filesystems and they can do their stuff like this.

[ElvishJerricco]

It only builds a system image, containing a nix store

This is what I meant by store image, and what I expected to be disabled by useNixStoreImage = false. But if I check the derivation closure for the test, I do find a derivation called nixos-disk-image containing a roughly 1G disk image file.

[ElvishJerricco]

Closed by #234030