nixos-container: minor fixes

[Ma27]

Motivation for this change

While there are plans to rework the nixos-container infrastructure (#69414) in the long-term, the imperative nixos-container tool is pretty helpful to e.g. test new modules in an isolated environment.

This PR fixes two issues that bothered me for quite some time:

• 3909f50990ef2a33828c2b43b89846f718d72ea2 - to avoid inconsistent state in case of a failing eval during nixos-container create, the entire state/config is removed in that case (until now you'd still have the /etc/containers/<name>.conf, but no running instance which breaks recreation-attempts).

• 7d51c490b58977f725710d839c8f0aefa39947ba - add --nixos-path to nixos-container update as well. Helpful when hacking e.g. on new modules in a local checkout.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[Ma27]

Resolved the merge conflicts that were caused by the introduction of initial flake support.

@GrahamcOfBorg test containers-imperative

[danbst]

[danbst@station:~/dev/nixpkgs]$ sudo ./result/bin/nixos-container --nixos-path nixos create test1 --config '{ services.nginx.enable = true; }'
host IP is 10.233.2.1, container IP is 10.233.2.2
error: syntax error, unexpected '{', at /var/lib/containers/test1/etc/nixos/configuration.nix:8:3
(use '--show-trace' to show detailed location information)
./result/bin/nixos-container: failed to build initial container configuration

[danbst@station:~/dev/nixpkgs]$ cat /var/lib/containers/test1/etc/nixos/configuration.nix
cat: /var/lib/containers/test1/etc/nixos/configuration.nix: No such file or directory

Maybe it is possible to leave configuration file, so inspection of a problem is easier?

[Ma27]

Maybe it is possible to leave configuration file, so inspection of a problem is easier?

Good idea 👍 . However I wouldn't keep the full data directory. We could either print the configs to stderr (which might be harmful though if the config is rather long) or move it to a temporary file and print the path to it in the error message if the initial setup fails.

Regarding your issue: in case you haven't found it yourself, --config doesn't need the brackets at the beginning and end :)

[Ma27]

@danbst IMHO this should be backported as well. Are there any reasons against this and if not, do you intend to do this or should I take care of this? :)

[danbst]

@Ma27 yeah, no objections, please you do

[Ma27]

Backported as 3d9983b, 73d246f.