Merge pull request #1114 from vivianQizhu/1496671

block_stream: Set default base to None.

qemu/tests/blk_stream.py

@@ -15,7 +15,7 @@ class BlockStream(block_copy.BlockCopy):
 
     def __init__(self, test, params, env, tag):
         super(BlockStream, self).__init__(test, params, env, tag)
-        self.base_image = self.image_file
+        self.base_image = None
         self.ext_args = {}
 
     def parser_test_args(self):

qemu/tests/block_stream_check_backingfile.py

@@ -36,6 +36,8 @@ class BlockStreamCheckBackingfile(blk_stream.BlockStream):
             self.test.fail(msg)
 
     def check_backingfile_exist(self):
+        if not self.base_image:
+            self.test.error("No backing file specified.")
         backingfile = self.get_backingfile()
         if backingfile != self.base_image:
             msg = "The backing file from monitor does not meet expectation. "
@@ -60,6 +62,7 @@ class BlockStreamCheckBackingfile(blk_stream.BlockStream):
         """
         Set values for backing-file option
         """
+        self.base_image = self.image_file
         absolute_path = self.params["absolute_path"]
         if absolute_path == "yes":
             backing_file = self.base_image