Add programs.ecryptfs for mount wrappers.

The `ecryptfs` package refers to the setuid wrapper paths, but they do
not exist so far in NixOS.

nixos/modules/module-list.nix

@@ -163,6 +163,7 @@
   ./programs/direnv.nix
   ./programs/dmrconfig.nix
   ./programs/droidcam.nix
+  ./programs/ecryptfs.nix
   ./programs/environment.nix
   ./programs/evince.nix
   ./programs/extra-container.nix

nixos/modules/programs/ecryptfs.nix

@@ -0,0 +1,31 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.programs.ecryptfs;
+
+in {
+  options.programs.ecryptfs = {
+    enable = mkEnableOption (lib.mdDoc "ecryptfs setuid mount wrappers");
+  };
+
+  config = mkIf cfg.enable {
+    security.wrappers = {
+
+      "mount.ecryptfs_private" = {
+        setuid = true;
+        owner = "root";
+        group = "root";
+        source = "${lib.getBin pkgs.ecryptfs}/bin/mount.ecryptfs_private";
+      };
+      "umount.ecryptfs_private" = {
+        setuid = true;
+        owner = "root";
+        group = "root";
+        source = "${lib.getBin pkgs.ecryptfs}/bin/umount.ecryptfs_private";
+      };
+
+    };
+  };
+}