[Bug 1906266] Re: After upgrade: "libvirt.libvirtError: Requested operation is not valid: format of backing image %s of image %s was not specified"

[Christian Ehrhardt ]

Thanks everyone, I agree that we'd want to consider this for Focals libvirt.
But there is a quite excessive series of changes in v6.0.0 -> v6.1.0 before the referenced change took place. So it will either be a massive backport (picking much more related changes to cherry-pick) or have a rather big set of backporting changes.

I wanted to ask if out of all your testing above there is already a simpler testcase that one can use without nova and all such. Just a) how to create a broken image + b) how to make libvirt stumble over it.
We will need this for the SRU process anyway if we want to bring it to Focal.

Also for severity - since didn't have this show up in any other place
yet I wonder how common this case would be? Any comment on that?

For the time being (while discussing) I have tried to rather "bluntly" backport the change.
If it builds would you be able to try this PPA [1] in your existing test environment?
If it works then MP [2] could be a simpler change than what I was afraid it could be.

[1]: https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/4388/+packages
[2]: https://code.launchpad.net/~paelzer/ubuntu/+source/libvirt/+git/libvirt/+merge/395778

** Changed in: libvirt (Ubuntu Focal)
       Status: New => Triaged

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https://bugs.launchpad.net/bugs/1906266

Title:
  After upgrade: "libvirt.libvirtError: Requested operation is not
  valid: format of backing image %s of image %s was not specified"

Status in OpenStack Compute (nova):
  Won't Fix
Status in libvirt package in Ubuntu:
  Fix Released
Status in nova package in Ubuntu:
  New
Status in libvirt source package in Focal:
  Triaged
Status in nova source package in Focal:
  New
Status in libvirt source package in Groovy:
  Invalid
Status in nova source package in Groovy:
  New

Bug description:
  In a site upgraded to Ussuri we are getting faults starting instances

  2020-11-30 13:41:40.586 232871 ERROR oslo_messaging.rpc.server
  libvirt.libvirtError: Requested operation is not valid: format of
  backing image '/var/lib/nova/instances/_base/xxx' of image
  '/var/lib/nova/instances/xxx' was not specified in the image metadata
  (See https://libvirt.org/kbase/backing_chains.html for
  troubleshooting)

  Bug #1864020 reports similar symptoms, where due to an upstream change
  in Libvirt v6.0.0+ images need the backing format specified.

  The fix for Bug #1864020 handles the case for new instances. However,
  for upgraded instances we're hitting the same problem, as those still
  don't have backing format specified.

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