Fix qubes.storage.file pylint warnings

qubes/storage/file.py

@@ -86,7 +86,7 @@ class FilePool(Pool):
         ''' Expands volume, throws
             :py:class:`qubst.storage.StoragePoolException` if given size is
             less than current_size
-        '''
+        '''  # pylint: disable=no-self-use
         _type = volume.volume_type
         if _type not in ['origin', 'read-write', 'volatile']:
             raise StoragePoolException('Can not resize a %s volume %s' %
@@ -170,7 +170,7 @@ class FilePool(Pool):
 
     def start(self, volume):
         if volume.volume_type == 'volatile':
-            self._reset_volume(volume)
+            _reset_volume(volume)
         if volume.volume_type in ['origin', 'snapshot']:
             _check_path(volume.path_origin)
             _check_path(volume.path_cow)
@@ -182,18 +182,6 @@ class FilePool(Pool):
     def stop(self, volume):
         pass
 
-    @staticmethod
-    def _reset_volume(volume):
-        ''' Remove and recreate a volatile volume '''
-        assert volume.volume_type == 'volatile', "Not a volatile volume"
-        assert volume.size
-
-        _remove_if_exists(volume.path)
-
-        with open(volume.path, "w") as f_volatile:
-            f_volatile.truncate(volume.size)
-        return volume
-
     def target_dir(self, vm):
         """ Returns the path to vmdir depending on the type of the VM.
 
@@ -251,6 +239,7 @@ class FilePool(Pool):
                 expected_origin_type
 
             origin_pool = vm.app.get_pool(origin_vm.volume_config[name]['pool'])
+
             assert isinstance(origin_pool,
                               FilePool), 'Origin volume not a file volume'
 
@@ -513,7 +502,7 @@ def copy_file(source, destination):
 
 
 def _remove_if_exists(path):
-    ''' Removes a path if it exist, silently succeeds if file does not exist '''
+    ''' Removes a file if it exist, silently succeeds if file does not exist '''
     if os.path.exists(path):
         os.remove(path)
 
@@ -522,3 +511,16 @@ def _check_path(path):
     ''' Raise an StoragePoolException if ``path`` does not exist'''
     if not os.path.exists(path):
         raise StoragePoolException('Missing image file: %s' % path)
+
+
+def _reset_volume(volume):
+    ''' Remove and recreate a volatile volume '''
+    assert volume.volume_type == 'volatile', "Not a volatile volume"
+
+    assert volume.size
+
+    _remove_if_exists(volume)
+
+    with open(volume.path, "w") as f_volatile:
+        f_volatile.truncate(volume.size)
+    return volume