systemd: support systemd.tmpfiles.settings

[phanirithvij]

copied verbatim from nixpkgs

since this is writing to a single file, I am adding comments for each settings section to distinguish it. edit: it is now writing to different files, one per settings option.

cc: @r-vdp

#146

[r-vdp]

Thanks!

Did you copy this code over from nixpkgs or you wrote it from scratch?
In the long run, it would be nice if we could factor out this code and reuse it between here and nixpkgs. But that's a longterm goal.

I'm also wondering if we should actually generate multiple files, like we do in nixpkgs, which gives more control to users, and it makes sure that modules that rely on this, are portable. You think that that would be feasible?

[r-vdp]

A test would also be nice.

[phanirithvij]

Yes I copied it from nixpkgs, as I don't know how to reuse it.

I'll see if I can get it working with multiple files same as in nixpkgs. And test it as well.

[phanirithvij]

Let me preface this by saying I don't have much experience with rust.

In tmp_files.rs activate function

    let mut cmd = process::Command::new("systemd-tmpfiles");
    cmd.arg("--create")
        .arg("--remove")
        .arg("/etc/tmpfiles.d/00-system-manager.conf");

Here, I need to change it to something like systemd-tmpfiles --create --remove /etc/tmpfiles.d/*.conf
But the existing ubuntu (host os) already has some services and tmpfiles configured, so it affects the existing tmpfiles.

• So I read from etc_tree and got the tmpfiles.d entry and looped over the files inside it.

I heard unwrap should be avoided, because it panics at runtime.
In this case since /etc/tmpfiles.d/00-system-manager.conf is guaranteed to exist, meaning /etc/tmpfiles.d for sure will be in etc_tree, and thus we shouldn't panic at all?

[phanirithvij]

Here it differs from nixpkgs version

orig nixpkgs version https://github.com/NixOS/nixpkgs/blob/01ddc67fd61124e3c9df1438e6874731af6d3f06/nixos/modules/system/boot/systemd/tmpfiles.nix#L240-L243

        '' + concatMapStrings (name: optionalString (hasPrefix "tmpfiles.d/" name) ''
          rm -f $out/${removePrefix "tmpfiles.d/" name}
        '') config.system.build.etc.passthru.targets;
      }) + "/*";

• there is no support for globs in system-manager's environment.etc.source so + "/*"; is out.
• I don't know what config.system.build.etc.passthru.targets is tbh, can't find it in system-manager codebase

[phanirithvij]

  etc' = lib.filter (f: f.enable) (lib.attrValues config.environment.etc);

  etc = pkgs.runCommandLocal "etc" {
    # This is needed for the systemd module
    passthru.targets = map (x: x.target) etc';
  } /* sh */ ''

from nixos/modules/system/etc/etc.nix

I don't know if it is needed for system-manager?

[r-vdp]

One small change to avoid having to call unwrap, besides that, this looks good to me!

It's really unfortunate that we need to copy all this code from nixpkgs, but I don't think we have a real alternative currently. If at some point this project gets more traction, we could have a discussion in the community to see if we can have some sort of re-usable modules that we can share to lower the maintenance burden.