nixos/autotierfs: init module

nixos/modules/module-list.nix

@@ -417,6 +417,7 @@
   ./services/audio/squeezelite.nix
   ./services/audio/tts.nix
   ./services/audio/ympd.nix
+  ./services/autotierfs.nix
   ./services/backup/automysqlbackup.nix
   ./services/backup/bacula.nix
   ./services/backup/borgbackup.nix

nixos/modules/services/autotierfs.nix

@@ -0,0 +1,94 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.services.autotierfs;
+  ini = pkgs.formats.ini { };
+  format = lib.types.attrsOf ini.type;
+  stateDir = "/var/lib/autotier";
+
+  generateConfigName =
+    name: builtins.replaceStrings [ "/" ] [ "-" ] (lib.strings.removePrefix "/" name);
+  configFiles = builtins.mapAttrs (
+    name: val: ini.generate "${generateConfigName name}.conf" val
+  ) cfg.settings;
+
+  getMountDeps = settings: builtins.concatStringsSep " " (builtins.catAttrs "Path" (builtins.attrValues settings));
+
+  mountPaths = builtins.attrNames cfg.settings;
+in
+{
+  options.services.autotierfs = {
+    enable = lib.mkEnableOption "the autotier passthrough tiering filesystem";
+    package = lib.mkPackageOption pkgs "autotier" { };
+    settings = lib.mkOption {
+      type = lib.types.submodule {
+        freeformType = format;
+      };
+      default = {};
+      description = ''
+        The contents of the configuration file for autotier.
+        See the [autotier repo](https://github.com/45Drives/autotier#configuration) for supported values.
+      '';
+      example = lib.literalExpression ''
+        {
+          "/mnt/autotier" = {
+            Global = {
+              "Log Level" = 1;
+              "Tier Period" = 1000;
+              "Copy Buffer Size" = "1 MiB";
+            };
+            "Tier 1" = {
+              Path = "/mnt/tier1";
+              Quota = "30GiB";
+            };
+            "Tier 2" = {
+              Path = "/mnt/tier2";
+              Quota = "200GiB";
+            };
+          };
+        }
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.enable -> cfg.settings != { };
+        message = "Autotier needs a config file to know how to tier your paths.";
+      }
+    ];
+
+    system.fsPackages = [ cfg.package ];
+
+    # Not necessary for module to work but makes it easier to pass config into cli
+    environment.etc = lib.attrsets.mapAttrs' (
+      name: value:
+      lib.attrsets.nameValuePair "autotier/${(generateConfigName name)}.conf" { source = value; }
+    ) configFiles;
+
+    systemd.tmpfiles.rules = (map (path: "d ${path} 0770 - autotier - -") mountPaths) ++ [
+      "d ${stateDir} 0774 - autotier - -"
+    ];
+
+    users.groups.autotier = { };
+
+    systemd.services = lib.attrsets.mapAttrs' (
+      path: values:
+      lib.attrsets.nameValuePair (generateConfigName path) {
+        description = "Mount autotierfs virtual path ${path}";
+        unitConfig.RequiresMountsFor = getMountDeps values;
+        wantedBy = [ "local-fs.target" ];
+        serviceConfig = {
+          Type = "forking";
+          ExecStart = "${lib.getExe' cfg.package "autotierfs"} -c /etc/autotier/${generateConfigName path}.conf ${path} -o allow_other,default_permissions";
+          ExecStop = "umount ${path}";
+        };
+      }
+    ) cfg.settings;
+  };
+}