On 09/08/2015 03:10 AM, Wen Congyang wrote:

>> Design-wise, I think we really want to have the add-child operation be
>> handed a pre-opened BDS, rather than the options dictionary to open the
>> BDS itself.  That is, we should use the existing blockdev-add (and
>> enhance it to support everything) to open the BDS, and then this command
>> should just attach that BDS as the new child (which is why it IS
>> important that we validate that the new BDS being added doesn't create
>> an invalid loop).
>>
> 
> How to check it? The parent BDS can get all children. But the child doesn't
> know if it is some BDS's child.

If I'm not mistaken, a child DOES know what its parent(s) are, once we
have Max's series for NULL BDS representing a BB without media.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org