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[Launchpad Bug Tracker <1561246@xxxxxxxxxxxxxxxxxx>]

[Expired for OpenStack Compute (nova) because there has been no activity
for 60 days.]

** Changed in: nova
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1561246

Title:
  user cannot choose disk bus when attaching volume to instance

Status in OpenStack Compute (nova):
  Expired

Bug description:
  After https://review.openstack.org/#/c/189632/, since the device name
  specified by the user is ignored when attaching volumes to a VM, the
  user now has no way to configure the disk bus that the volume is
  attached to.

  Before the change, if user specifies device name like "/dev/hda" then
  it will be attached with ide driver, or "/dev/vda" with virtio driver
  (for KVM).

  Now, the device name is ignored. Instead, the disk bus is determined
  first based on the image metadata of the VM instance, and then based
  on the device type (e.g. "virtio" for a KVM disk). Note that the
  former is based on the VM image metadata, not the volume image
  metadata. So, if the VM is booted from an image that uses ide disk
  bus, then the volume will also be attached with ide disk bus instead
  of virtio. If it is based on the volume image metadata or volume
  metadata instead, then that would solve the bug.

  We added a temporary hack to mitigate the issue, so that the device
  name is not completely ignored:

  --- novaa/virt/libvirt/driver.py	2016-03-23 18:40:52.000000000 -0400
  +++ novab/virt/libvirt/driver.py	2016-03-23 18:41:40.800635279 -0400
  @@ -7278,7 +7278,14 @@

           # NOTE(ndipanov): get_info_from_bdm will generate the new device name
           #                 only when it's actually not set on the bd object
  -        block_device_obj.device_name = None
  +        if block_device_obj.device_name is not None:
  +            if len(block_device_obj.device_name) >= 6 and block_device_obj.device_name[0:5] == '/dev/' and block_device_obj.get('disk_bus') is None:
  +                if block_device_obj.device_name[5] == 'v':
  +                    block_device_obj.disk_bus = 'virtio'
  +                elif block_device_obj.device_name[5] == 'h':
  +                    block_device_obj.disk_bus = 'ide'
  +            block_device_obj.device_name = None
  +
           disk_info = blockinfo.get_info_from_bdm(
               instance, CONF.libvirt.virt_type, image_meta,
               block_device_obj, mapping=instance_info['mapping'])

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