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[OpenStack Infra <1653953@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/457886
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d89e7d7857e0ab56c3b088338272c24d0618c07f
Submitter: Zuul
Branch:    master

commit d89e7d7857e0ab56c3b088338272c24d0618c07f
Author: rsritesh <rsritesh@xxxxxxxxxx>
Date:   Wed Apr 19 12:02:30 2017 +0530

    libvirt: flatten rbd images when unshelving an instance
    
    Previously attempts to remove the shelved snapshot of an unshelved
    instance when using the rbd backends for both Nova and Glance would
    fail. This was due to the instance disk being cloned from and still
    referencing the shelved snapshot image in Glance, blocking any attempt
    to remove this image later in the unshelve process.
    
    After much debate this change attempts to fix this issue by flattening
    the instance disk while the instance is being spawned as part of an
    unshelve. For the rbd imagebackend this removes any reference to the
    shelved snapshot in Glance allowing this image to be removed. For all
    other imagebackends the call to flatten the image is currently a no-op.
    
    Co-Authored-By: Lee Yarwood <lyarwood@xxxxxxxxxx>
    Co-Authored-By: Vladyslav Drok <vdrok@xxxxxxxxxxxx>
    
    Closes-Bug: #1653953
    Change-Id: If3c9d1de3ce0fe394405bd1e1f0fa08ce2baeda8


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

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https://bugs.launchpad.net/bugs/1653953

Title:
  Unable to remove snapshots after an instance is unshelved when using
  the rbd imagebackend

Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) queens series:
  New
Status in OpenStack Compute (nova) rocky series:
  New
Status in OpenStack Compute (nova) stein series:
  New

Bug description:
  Description
  ===========

  I'm not entirely convinced that this is a bug but wanted to document
  and discuss this upstream.

  When using the rbd imagebackend, snapshots used to shelve an instance
  cannot be removed after unshelving as they are cloned and as a result
  are now the parents of the recreated instance disks.

  This is in line with the behaviour of the imagebackend when initially
  spawning an instance from an image but has caused confusion for
  operators downstream who assume that the snapshot can be removed once
  the instance has been unshelved.

  We could flatten the instance disk when spawning during an unshelve
  but to do so would mean extending the imagebackend to handle yet
  another corner case for rbd.

  Steps to reproduce
  ==================

  $ nova boot --image cirros-raw --flavor 1 test-shelve
  [..]
  $ nova shelve test-shelve
  [..]
  $ nova unshelve test-shelve
  [..]
  $ sudo rbd -p vms ls -l
  NAME                                       SIZE PARENT                                           FMT PROT LOCK 
  4c843671-879d-4ba6-b4e8-8eefdced5393_disk 1024M images/df96af36-5a97-4f47-a79f-f3f3c85a21d9@snap   2 
  $ glance image-delete df96af36-5a97-4f47-a79f-f3f3c85a21d9
  Unable to delete image 'df96af36-5a97-4f47-a79f-f3f3c85a21d9' because it is in use.

  We can easily workaround this by manually flattening the instance disk
  :

  $ nova stop test-shelve
  $ sudo rbd -p vms flatten 4c843671-879d-4ba6-b4e8-8eefdced5393_disk
  Image flatten: 100% complete...done.
  $ nova start test-shelve
  $ glance image-delete df96af36-5a97-4f47-a79f-f3f3c85a21d9

  Expected result
  ===============
  Able to remove the shelved snapshot from Glance after unshelve.

  Actual result
  =============
  Unable to remove the shelved snapshot from Glance after unshelve.

  Environment
  ===========
  1. Exact version of OpenStack you are running. See the following
     list for all releases: http://docs.openstack.org/releases/

     $ pwd
     /opt/stack/nova
     $ git rev-parse HEAD
     d768bfa2c2fb774154a5268f58b28537f7b39f69
     
  2. Which hypervisor did you use?
     (For example: Libvirt + KVM, Libvirt + XEN, Hyper-V, PowerKVM, ...)
     What's the version of that?

     libvirt + kvm

  2. Which storage type did you use?
     (For example: Ceph, LVM, GPFS, ...)
     What's the version of that?

     ceph

  3. Which networking type did you use?
     (For example: nova-network, Neutron with OpenVSwitch, ...)

     N/A

  Logs & Configs
  ==============

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