nixos/ecryptfs: init

Currently, ecryptfs support is coupled to `security.pam.enableEcryptfs`, but one
might want to use ecryptfs without enabling the PAM functionality. This commit
splits it out into a `boot.supportedFilesystems` switch.

nixos/modules/tasks/filesystems/ecryptfs.nix

@@ -0,0 +1,14 @@
+{ config, lib, pkgs, ... }:
+# TODO: make ecryptfs work in initramfs?
+
+with lib;
+
+{
+  config = mkIf (any (fs: fs == "ecryptfs") config.boot.supportedFilesystems) {
+    system.fsPackages = [ pkgs.ecryptfs ];
+    security.wrappers = {
+      "mount.ecryptfs_private".source = "${pkgs.ecryptfs.out}/bin/mount.ecryptfs_private";
+      "umount.ecryptfs_private".source = "${pkgs.ecryptfs.out}/bin/umount.ecryptfs_private";
+    };
+  };
+}