Change pack_firmware_image::EntryBlob behavior

utility/pack_firmware_image

 #!/usr/bin/env python2.6
 
 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os
 import re
 import struct
 import subprocess
@@ skipping 111 matching lines @@
 
 
 class EntryBlob(EntryFmapArea):
 
   def __init__(self, **kwargs):
     Entry._CheckFields(kwargs, ('path',))
     super(EntryBlob, self).__init__(**kwargs)
 
   def Pack(self, firmware_image, entries):
     size = os.stat(self.path).st_size
-    if size > 0:
-      size = min(size, self.length)
-    else:
+    if size > self.length:
+        raise PackError('blob too large: %d > %d' % (size, self.length))
+    if size == 0: # special case for files like /dev/zero
       size = self.length
     with open(self.path, 'rb') as blob_image:
       firmware_image.seek(self.offset)
       firmware_image.write(blob_image.read(size))
 
 
 class EntryKeyBlock(EntryFmapArea):
 
   stdout = None
   stderr = None
@@ skipping 112 matching lines @@
       raise ConfigError('undefined variable: %s' % varname)
     _Info('%s = %s' % (varname, repr(env[varname])))
 
   pack_firmware_image(env['ENTRIES'], env['OUTPUT'], env['SIZE'])
 
   sys.exit(0)
 
 
 if __name__ == '__main__':
   main()