nixos/systemd-tmpfiles: add settings option

nixos/modules/system/boot/systemd/tmpfiles.nix

@@ -20,6 +20,102 @@ in
       '';
     };
 
+    systemd.tmpfiles.settings = mkOption {
+      description = lib.mdDoc ''
+        Declare systemd-tmpfiles rules to create, delete, and clean up volatile
+        and temporary files and directories.
+
+        Even though the service is called `*tmp*files` you can also create
+        persistent files.
+      '';
+      example = {
+        "10-mypackage" = {
+          "/var/lib/my-service/statefolder".d = {
+            mode = "0755";
+            user = "root";
+            group = "root";
+          };
+        };
+      };
+      default = {};
+      type = types.attrsOf (types.attrsOf (types.attrsOf (types.submodule ({ name, config, ... }: {
+        options.type = mkOption {
+          type = types.str;
+          default = name;
+          example = "d";
+          description = lib.mdDoc ''
+            The type of operation to perform on the file.
+
+            The type consists of a single letter and optionally one or more
+            modifier characters.
+
+            Please see the upstream documentation for the available types and
+            more details:
+            <https://www.freedesktop.org/software/systemd/man/tmpfiles.d>
+          '';
+        };
+        options.mode = mkOption {
+          type = types.str;
+          default = "-";
+          example = "0755";
+          description = lib.mdDoc ''
+            The file access mode to use when creating this file or directory.
+          '';
+        };
+        options.user = mkOption {
+          type = types.str;
+          default = "-";
+          example = "root";
+          description = lib.mdDoc ''
+            The user of the file.
+
+            This may either be a numeric ID or a user/group name.
+
+            If omitted or when set to `"-"`, the user and group of the user who
+            invokes systemd-tmpfiles is used.
+          '';
+        };
+        options.group = mkOption {
+          type = types.str;
+          default = "-";
+          example = "root";
+          description = lib.mdDoc ''
+            The group of the file.
+
+            This may either be a numeric ID or a user/group name.
+
+            If omitted or when set to `"-"`, the user and group of the user who
+            invokes systemd-tmpfiles is used.
+          '';
+        };
+        options.age = mkOption {
+          type = types.str;
+          default = "-";
+          example = "10d";
+          description = lib.mdDoc ''
+            Delete a file when it reaches a certain age.
+
+            If a file or directory is older than the current time minus the age
+            field, it is deleted.
+
+            If set to `"-"` no automatic clean-up is done.
+          '';
+        };
+        options.argument = mkOption {
+          type = types.str;
+          default = "";
+          example = "";
+          description = lib.mdDoc ''
+            An argument whose meaning depends on the type of operation.
+
+            Please see the upstream documentation for the meaning of this
+            parameter in different situations:
+            <https://www.freedesktop.org/software/systemd/man/tmpfiles.d>
+          '';
+        };
+      }))));
+    };
+
     systemd.tmpfiles.packages = mkOption {
       type = types.listOf types.package;
       default = [];
@@ -100,7 +196,13 @@ in
           ${concatStringsSep "\n" cfg.rules}
         '';
       })
-    ];
+    ] ++ (mapAttrsToList (name: paths:
+      pkgs.writeTextDir "lib/tmpfiles.d/${name}.conf" (concatStrings (mapAttrsToList (path: types:
+        concatStrings (mapAttrsToList (_type: entry: ''
+          '${entry.type}' '${path}' '${entry.mode}' '${entry.user}' '${entry.group}' '${entry.age}' ${entry.argument}
+        '') types)
+      ) paths ))
+    ) cfg.settings);
 
     systemd.tmpfiles.rules = [
       "d  /nix/var                           0755 root root - -"

nixos/tests/misc.nix

@@ -13,6 +13,7 @@ in {
       environment.variables.EDITOR = lib.mkOverride 0 "emacs";
       documentation.nixos.enable = lib.mkOverride 0 true;
       systemd.tmpfiles.rules = [ "d /tmp 1777 root root 10d" ];
+      systemd.tmpfiles.settings."10-test"."/tmp/somefile".d = {};
       virtualisation.fileSystems = { "/tmp2" =
         { fsType = "tmpfs";
           options = [ "mode=1777" "noauto" ];
@@ -117,6 +118,9 @@ in {
           )
           machine.fail("[ -e /tmp/foo ]")
 
+      with subtest("whether systemd-tmpfiles settings works"):
+          machine.succeed("[ -e /tmp/somefile ]")
+
       with subtest("whether automounting works"):
           machine.fail("grep '/tmp2 tmpfs' /proc/mounts")
           machine.succeed("touch /tmp2/x")