Comment 0 for bug 1667667

How to reproduce it:

Two images, one of them with with hw_disk_bus=scsi and hw_scsi_model=virtio-scsi properties:

$ glance image-show 48888bbf-ddbf-4ede-a30f-b5b4a8e68876
+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| checksum | 79b4436412283bb63c2cba4ac796bcd9 |
| container_format | bare |
| created_at | 2017-02-24T08:45:48Z |
| disk_format | qcow2 |
| id | 48888bbf-ddbf-4ede-a30f-b5b4a8e68876 |
| min_disk | 0 |
| min_ram | 0 |
| name | cirros-0.3.4-i386-disk |
| owner | 277132bf94b040f0842bd66d71a0d574 |
| protected | False |
| size | 12506112 |
| status | active |
| tags | [] |
| updated_at | 2017-02-24T08:45:52Z |
| virtual_size | None |
| visibility | public |
+------------------+--------------------------------------+

$ glance image-show 8ce9540e-a802-4e39-a1b4-20cbff14ec18
+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| checksum | 79b4436412283bb63c2cba4ac796bcd9 |
| container_format | bare |
| created_at | 2017-02-24T09:07:44Z |
| disk_format | qcow2 |
| hw_disk_bus | scsi |
| hw_scsi_model | virtio-scsi |
| id | 8ce9540e-a802-4e39-a1b4-20cbff14ec18 |
| min_disk | 0 |
| min_ram | 0 |
| name | cirros-scsi |
| owner | bd560276f6bd48219ddcd7c9fb245ec1 |
| protected | False |
| size | 12506112 |
| status | active |
| tags | [] |
| updated_at | 2017-02-24T09:07:45Z |
| virtual_size | None |
| visibility | shared |
+------------------+--------------------------------------+

$ nova boot --flavor m1.small --image 48888bbf-ddbf-4ede-a30f-b5b4a8e68876 vm1
$ virsh dumpxml instance-00000003 | grep '.*target.*bus'
      <target dev='vda' bus='virtio'/>

$ nova rebuild vm1 cirros-scsi
$ stack@devstack-adam:~/devstack$ nova show vm1 | grep image
| image | cirros-scsi (8ce9540e-a802-4e39-a1b4-20cbff14ec18)
$ virsh dumpxml instance-00000003 | grep '.*target.*bus'
      <target dev='vda' bus='virtio'/>

The problem is that despite property hw_disk_bus set on cirros-scsi (8ce9540e-a802-4e39-a1b4-20cbff14ec18), 'virtio' (and vda) is not replaced in the instance's XML file.

The expected result IMO should be like a normal boot from this image:

$ nova boot --flavor m1.small --image 8ce9540e-a802-4e39-a1b4-20cbff14ec18 vm2
$ virsh dumpxml instance-00000004 | grep '.*target.*bus'
      <target dev='sda' bus='scsi'/>