Subject: tools/pygrub: Fix error handling if no valid partitions are found
From: Andrew Cooper andrew.cooper3@citrix.com Sat May 10 02:18:33 2014 +0100
Date: Mon May 12 15:52:43 2014 +0100:
Git: d75215805ce6ed20b3807955fab6a7f7a3368bee

If no partitions at all are found, pygrub never creates the name 'fs',
resulting in a NameError indicating the lack of fs, rather than a
RuntimeError explaining that no partitions were found.

Set fs to None right at the start, and use the pythonic idiom "if fs is None:"
to protect against otherwise valid values for fs which compare equal to
0/False.

Reported-by: Sven Köhler <sven.koehler@gmail.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

Index: xen-4.4.0-testing/tools/pygrub/src/pygrub
===================================================================
--- xen-4.4.0-testing.orig/tools/pygrub/src/pygrub
+++ xen-4.4.0-testing/tools/pygrub/src/pygrub
@@ -760,7 +760,7 @@ if __name__ == "__main__":
         usage()
         sys.exit(1)
     file = args[0]
-        
+    fs = None
     output = None
     entry = None
     interactive = True
@@ -882,7 +882,7 @@ if __name__ == "__main__":
         sys.exit(0)
 
     # Did looping through partitions find us a kernel?
-    if not fs:
+    if fs is None:
         raise RuntimeError, "Unable to find partition containing kernel"
 
     bootcfg["kernel"] = copy_from_image(fs, chosencfg["kernel"], "kernel",