Comment 11 for bug 1792077

Ah, I think you're right.

It seems to me that we shouldn't be creating the address tag at all unless we intend to set the unit as well. So, I wonder if we should do something like this then:

--- a/nova/virt/libvirt/volume/volume.py
+++ b/nova/virt/libvirt/volume/volume.py
@@ -94,16 +94,15 @@ class LibvirtBaseVolumeDriver(object):
         if data.get('discard', False) is True:
             conf.driver_discard = 'unmap'

- if disk_info['bus'] == 'scsi':
+ if disk_info['bus'] == 'scsi' and 'unit' in disk_info:
             # The driver is responsible to create the SCSI controller
             # at index 0.
             conf.device_addr = vconfig.LibvirtConfigGuestDeviceAddressDrive()
             conf.device_addr.controller = 0
- if 'unit' in disk_info:
- # In order to allow up to 256 disks handled by one
- # virtio-scsi controller, the device addr should be
- # specified.
- conf.device_addr.unit = disk_info['unit']
+ # In order to allow up to 256 disks handled by one
+ # virtio-scsi controller, the device addr should be
+ # specified.
+ conf.device_addr.unit = disk_info['unit']

         if connection_info.get('multiattach', False):
             # Note that driver_cache should be disabled (none) when using