--- a/mercurial/posix.py	Fri Dec 22 23:17:04 2017 +0800
+++ b/mercurial/posix.py	Sat Dec 30 21:07:03 2017 -0500
@@ -24,9 +24,12 @@
 from . import (
     encoding,
     error,
+    policy,
     pycompat,
 )
 
+osutil = policy.importmod(r'osutil')
+
 posixfile = open
 normpath = os.path.normpath
 samestat = os.path.samestat
@@ -302,6 +305,13 @@
     Returns None if the path is ok, or a UI string describing the problem.'''
     return None # on posix platforms, every path is ok
 
+def getfstype(dirpath):
+    '''Get the filesystem type name from a directory (best-effort)
+
+    Returns None if we are unsure. Raises OSError on ENOENT, EPERM, etc.
+    '''
+    return getattr(osutil, 'getfstype', lambda x: None)(dirpath)
+
 def setbinary(fd):
     pass