initial commit

modules/impermanence.nix

@@ -0,0 +1,49 @@
+{
+  config,
+  lib,
+  ...
+}: {
+  options.weinturm = with lib; {
+    impermanence = {
+      enable = mkOption {
+        type = types.bool;
+        default = true;
+        description = "Whether to enable impermanence";
+      };
+      rootDevice = with types;
+        mkOption {
+          type = nullOr str;
+          default = null;
+          description = ''
+            The device which contains the btrfs root subvolume
+          '';
+        };
+    };
+  };
+  config = let
+    cfg = config.weinturm.impermanence;
+  in
+    lib.mkIf cfg.enable {
+      fileSystems."/persist".neededForBoot = true;
+
+      environment.persistence."/persist".directories = [
+        "/var/lib/nixos"
+      ];
+
+      boot.initrd.postDeviceCommands = let
+        rootDevice =
+          if cfg.rootDevice == null
+          then ""
+          else cfg.rootDevice;
+      in
+        lib.mkAfter ''
+          mkdir /mnt
+          mount -t btrfs "${rootDevice}" /mnt
+          btrfs subvolume list -o /mnt/root | cut -f9 -d' ' | while read subvolume; do
+            btrfs subvolume delete "/mnt/$subvolume"
+          done
+          btrfs subvolume delete /mnt/root
+          btrfs subvolume snapshot /mnt/root-blank /mnt/root
+        '';
+    };
+}