refactor(nixos): make ZFS configuration optional

- move ZFS and snapshot manager settings out of the global base
- group snapshot files under common/optional/zfs
- enable the ZFS module on existing ZFS hosts
- make the global tmpfs setting overridable

common/global/default.nix

@@ -17,16 +17,11 @@
     ./nix.nix
     ./programs.nix
     ./ssh.nix
-    ./snapshot_manager.nix
   ];
 
   boot = {
-    tmp.useTmpfs = true;
+    tmp.useTmpfs = lib.mkDefault true;
     kernelPackages = lib.mkDefault pkgs.linuxPackages_6_12;
-    zfs = {
-      package = lib.mkDefault pkgs.zfs_2_4;
-      forceImportRoot = lib.mkDefault false;
-    };
   };
 
   hardware.enableRedistributableFirmware = true;
@@ -50,16 +45,6 @@
 
     # firmware update
     fwupd.enable = true;
-
-    snapshot_manager = {
-      enable = lib.mkDefault true;
-      PYTHONPATH = "${inputs.self}/";
-    };
-
-    zfs = {
-      trim.enable = lib.mkDefault true;
-      autoScrub.enable = lib.mkDefault true;
-    };
   };
 
   powerManagement.powertop.enable = lib.mkDefault true;

common/global/snapshot_config.toml

@@ -1,29 +0,0 @@
-["default"]
-15_min = 8
-hourly = 24
-daily = 0
-monthly = 0
-
-["root_pool/home"]
-15_min = 8
-hourly = 12
-daily = 1
-monthly = 0
-
-["root_pool/root"]
-15_min = 8
-hourly = 24
-daily = 0
-monthly = 0
-
-["root_pool/nix"]
-15_min = 4
-hourly = 0
-daily = 0
-monthly = 0
-
-["root_pool/var"]
-15_min = 8
-hourly = 24
-daily = 30
-monthly = 6

common/global/snapshot_manager.nix

@@ -1,64 +0,0 @@
-{
-  pkgs,
-  lib,
-  config,
-  ...
-}:
-let
-  cfg = config.services.snapshot_manager;
-in
-{
-  options = {
-    services.snapshot_manager = {
-      enable = lib.mkEnableOption "ZFS snapshot manager";
-      path = lib.mkOption {
-        type = lib.types.path;
-        default = ./snapshot_config.toml;
-        description = "Path to the snapshot_manager TOML config.";
-      };
-      PYTHONPATH = lib.mkOption {
-        type = lib.types.str;
-        description = ''
-          the PYTHONPATH to use for the snapshot_manager service.
-        '';
-      };
-      EnvironmentFile = lib.mkOption {
-        type = lib.types.nullOr (lib.types.coercedTo lib.types.path toString lib.types.str);
-        default = null;
-        description = ''
-          Single environment file for the service (e.g. /etc/snapshot-manager/env).
-          Use a leading "-" to ignore if missing (systemd feature).
-        '';
-      };
-    };
-  };
-
-  config = lib.mkIf cfg.enable {
-    systemd = {
-      services.snapshot_manager = {
-        description = "ZFS Snapshot Manager";
-        requires = [ "zfs-import.target" ];
-        after = [ "zfs-import.target" ];
-        path = [ pkgs.zfs ];
-        environment = {
-          PYTHONPATH = cfg.PYTHONPATH;
-        };
-        serviceConfig = {
-          Type = "oneshot";
-          ExecStart = "${pkgs.my_python}/bin/python -m python.tools.snapshot_manager ${lib.escapeShellArg cfg.path}";
-        }
-        // lib.optionalAttrs (cfg.EnvironmentFile != null) {
-          EnvironmentFile = cfg.EnvironmentFile;
-        };
-      };
-      timers.snapshot_manager = {
-        wantedBy = [ "timers.target" ];
-        timerConfig = {
-          OnBootSec = "15m";
-          OnUnitActiveSec = "15m";
-          Unit = "snapshot_manager.service";
-        };
-      };
-    };
-  };
-}