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[OpenStack Infra <1605720@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/346263
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d7b831e38cbc029b7975d1059ed212762a5f6a5e
Submitter: Jenkins
Branch:    master

commit d7b831e38cbc029b7975d1059ed212762a5f6a5e
Author: Chris Friesen <chris.friesen@xxxxxxxxxxxxx>
Date:   Fri Jul 22 16:33:43 2016 -0600

    Fix cold migration with qcow2 ephemeral disks
    
    If we have qcow2 ephemeral disks we need to ensure that the
    backing file gets created on a cold migration.
    
    This requires passing in the block_device_info when calling
    _create_image() so that we can loop over the ephemeral disks.
    
    Closes-Bug: #1605720
    Co-Authored-By: Feodor Tersin <ftersin@xxxxxxxxxxx>
    Change-Id: Ie278bb10e1675ba1d903aaa3c0249be0d1cf147b


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1605720

Title:
  backing store missing for ephemeral disk on cold migration

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  I'm on stable/mitaka, but the master code looks similar.

  I have compute nodes configured to use qcow2 and libvirt.  The flavor
  has an ephemeral disk and a swap disk, with root disk size of "0" for
  auto-size.  I boot an instance with this flavor.

  When I try to cold-migrate the instance, I get an error:
  2016-07-21 23:33:48.561 46340 ERROR nova.compute.manager [instance: 4e52bfd8-0c71-48dc-89fb-6f6b31dc06bb] libvirtError: Cannot access backing file '/etc/nova/instances/_base/ephemeral_1_0706d66' of storage file '/etc/nova/instances/4e52bfd8-0c71-48dc-89fb-6f6b31dc06bb/disk.eph0' (as uid:0, gid:0): No such file or directory

  The problem seems to be that in
  nova.virt.libvirt.driver.LibvirtDriver.finish_migration() we call
  self._create_image(...block_device_info=None...)

  Down in _create_image() we handle the case of a "disk.local" ephemeral
  device, but that doesn't help because the device is actually named
  "disk.eph0".   It looks like we then try to loop over any ephemerals
  in block_device_info, but that's None so we don't handle any of those
  (which is too bad since it looks like they would be named correctly).

  The end result is that we have a qcow2 "disk.eph0" image, but with
  potentially no backing store in <instances_path>/_base.  When we tell
  libvirt to start the instance, this results in the above error.

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