disk_has_backing_file
Description:
return whether disk has a backing file
Detect and return whether the disk image filename has a backing file.
Note that detecting disk features can be insecure under some circumstances. See "CVE-2010-3851" in guestfs(3).
Parameters:
| this | 
           A GuestfsSession object  | 
      
Returns:
| 
           the returned value, or -1 on error  |