filesystems/btrfs: add btrfs module

modules/modules/filesystems/btrfs.nix

@@ -0,0 +1,21 @@
+{ config, options, lib, pkgs, ... }:
+with lib;
+with lib.hlissner;
+let
+  cfg = config.modules.filesystems.btrfs;
+  opt = options.modules.filesystems.btrfs;
+in
+{
+  options.modules.filesystems.btrfs = with types; {
+    enable = mkBoolOpt false;
+    scrub = mkOpt attrs { };
+  };
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = with pkgs; [
+      btrfs-progs
+    ];
+
+    services.btrfs.autoScrub = mkAliasDefinitions opt.scrub;
+  };
+}