Comment 9 for bug 1591827

Hi Daniel,
    Nova has hardcode the config drive --> cdrom as the last device name sdz. With your method, we can change the cdrom dev name to the front of the devname such as sda,sdb,,, That will work due to add controller:
<controller type="scsi" model="virtio-scsi"/>
The default index for controller virtio-scsi is index=0, which corresponding to sda to sdg. But for example, sdh, it needs virtio-scsi controller that has index=1 and so as sdz need index=3. So...
    Actually I meet another problem by virtio-scsi mode here. When I set hw_scsi_model=virtio-scsi and hw_disk_bus=scsi, then I use "nova volume-attach" to add the volume to an existing instanc, I have add device one by one. Adding volume as sdb, sdc,sde are all OK, they can be hotplug. When the adding device has devname "sdh", it can't be recognized by the instance, due to the controller index problem.
    So I think maybe add the index calculator according to its devname and add the controller xml corresponding devname can solve the problem.
    Thanks~