qvm-block: fix handling unusual devices attached to dom0

Simply get device major-minor from /dev/ device file.
This is only partial solution, because this will work only for dom0
devices, but the same problem can apply to VM.

core/qubesutils.py

@@ -31,6 +31,7 @@ import re
 import shutil
 import time
 import grp,pwd
+import stat
 from datetime import datetime
 from qmemman_client import QMemmanClient
 
@@ -116,6 +117,11 @@ def block_name_to_majorminor(name):
     if name.isdigit():
         return (int(name) / 256, int(name) % 256)
 
+    if os.path.exists('/dev/%s' % name):
+        blk_info = os.stat(os.path.realpath('/dev/%s' % name))
+        if stat.S_ISBLK(blk_info.st_mode):
+            return (blk_info.st_rdev / 256, blk_info.st_rdev % 256)
+
     major = 0
     minor = 0
     dXpY_style = False