qcow2 disk size not set to auto

[a-h]

The qcow2 disk image seems set to 8192 in https://github.com/nix-community/nixos-generators/blob/896f6589db5b25023b812bbb6c1f5d3a499b1132/formats/qcow.nix#L32C16-L32C20

When building a large disk image, it's likely you'll receive the following error:

ERROR: cptofs failed. diskSize might be too small for closure.

This comment suggests using a module to override the behaviour: #150 (comment)

However, applying the module within the flake.nix doesn't make any difference.

      packages.vm = forAllHostnames ({ system, pkgs, hostname }: nixos-generators.nixosGenerate {
        system = system;
        modules = [
          # Pin nixpkgs to the flake input, so that the packages installed
          # come from the flake inputs.nixpkgs.url.
          ({ ... }: { nix.registry.nixpkgs.flake = nixpkgs; })
          # Make the disk bigger to avoid "ERROR: cptofs failed. diskSize might be too small for closure."
          ({ lib, ... }: {
            system.build.qcow = lib.mkDefault {
              diskSize = lib.mkForce "auto";
              additionalSpace = "10G";
            };
          })
          # Install all tools.
          ./tools.nix
          # Apply the rest of the config.
          ./configuration.nix
        ];
        format = "qcow2";
      });

And neither does setting it in the configuration.nix:

{ pkgs, lib, hostname, github-url, ... }: {
  networking = {
    hostName = hostname;
  };
  # Enable the OpenSSH server.
  services.openssh = {
    enable = true;
  };
  # Lots of other stuff...
  system.build.qcow = lib.mkDefault {
    diskSize = lib.mkForce "auto";
    additionalSpace = "10G";
  };
  system.stateVersion = "23.11";
}

However, if I switch to the raw image format, everything works well. Presumably because raw images use the "auto" setting?

Is there a reason why diskSize isn't set to auto for qcow2 images?

[a-h]

The change to add auto resizing images was added in NixOS/nixpkgs#89331

Not sure if this is the same issue, but in a different format: #279

There's some people out there running out of /tmp space, but that's not me, I've got >100GB free (https://discourse.nixos.org/t/disk-size-too-small-when-generating-qcow2-image/35281)

[jalseth]

I had a similar problem, except that I want to use a specific size rather than "auto", so I opened a PR: #292.

[a-h]

From reading @jalseth's PR, it looks like it resolves this issue. I've moved to using raw images as a result of the issue, so I haven't got a test to hand.

I'll close this.