--- a/configmix/compat.py	Thu Mar 14 00:21:30 2019 +0100
+++ b/configmix/compat.py	Thu Mar 14 01:35:16 2019 +0100
@@ -10,13 +10,15 @@
 from __future__ import division, absolute_import, print_function
 
 import sys
+import os
 import locale
 
 
 __all__ = ["PY2",
            "text_to_native_os_str",
            "native_os_str_to_text",
-           "u"]
+           "u",
+           "u2fs"]
 
 
 PY2 = sys.version_info[0] <= 2
@@ -26,6 +28,9 @@
 
     _OS_ENCODING = locale.getpreferredencoding()
 
+    _FS_ENCODING = sys.getfilesystemencoding() or _OS_ENCODING
+
+
     def text_to_native_os_str(s, encoding=None):
         if isinstance(s, unicode):
             return s.encode(encoding or _OS_ENCODING)
@@ -43,6 +48,21 @@
         else:
             return s.decode(encoding)
 
+
+    def u2fs(s, force=False):
+        """Convert a text (Unicode) string to the filesystem encoding.
+
+        .. note:: If `s` is already a byte string be permissive and
+                  return `s` unchanged.
+
+        """
+        if isinstance(s, str):
+            return s
+        if not force and os.name in ("nt", "ce"):
+            # WinNT and CE have native Unicode support: nothing to convert
+            return s
+        return s.encode(_FS_ENCODING)
+
 else:
 
     def text_to_native_os_str(s, encoding=None):
@@ -52,8 +72,20 @@
     def native_os_str_to_text(s, encoding=None):
         return s
 
+
     def u(s, encoding="utf-8"):
         if isinstance(s, str):
             return s
         else:
             return s.decode(encoding)
+
+
+    def u2fs(s, force=False):
+        """Convert a text (Unicode) string to the filesystem encoding.
+
+        .. note:: The filesystem encoding on Python 3 is a Unicode text
+                  string. The function is a noop when called on Python 3.
+
+        """
+        assert isinstance(s, str)
+        return s