Comment 5 for bug 1792077

@melanie: what happens is the the generated XML lacks the unit (for the disk address) altogether. If you omit the address tag, libvirt will autogenerate it, but if you send it and omit the unit field, it assumes zero, and that's where the conflict comes in.

Look at this part of the XML in the above report: <address type="drive" controller="0"/>
There is a controller number, but no unit.