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[Lee Yarwood <1860913@xxxxxxxxxxxxxxxxxx>]

** No longer affects: nova

** Changed in: cinder
     Assignee: Lee Yarwood (lyarwood) => (unassigned)

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https://bugs.launchpad.net/bugs/1860913

Title:
  Instance uses base image file when it is rebooted after snapshot
  creation if cinder nfs backend is used

Status in Cinder:
  In Progress

Bug description:
  Description
  ===========
  When we use nfs backend in cinder and attach a cinder volume to an instance, the instance access to the file in nfs share, which is named like volume-<volume id>.

  When the volume is attached to an instance and we take snapshot with
  "openstack volume snapshot create <volume> --force", it will create
  the following 3 files in nfs share.

   (1) volume-<volume id>
     base image freezed when taking snapshot

   (2) volume-<volume id>-<snapshot id>
    diff image where instance should write into after taking snapshot

   (3) volume-<volume id>.info
     json file to manage active snapshot

  As described above, after taking snapshot, the instance should write into (2) volume-<volume id>-<snapshot id> .
  It works just after taking snapshot, but if we stop and start the instance, the instance starts to write into (1) volume-<volume id>, which it should not modify.

  Steps to reproduce
  ==================
  1. Create a volume in cinder nfs backend
  2. Create a bfv instance with the volume
  3. Take snapshot of the volume
  4. Stop and Start the instance

  Expected result
  ===============
  The instance keeps writing into volume-<volume id>-<snapshot id>

  Actual result
  =============
  The instance writes into volume-<volume id>

  Environment
  ===========
  I reproduced the issue with Queens release with
   nova: libvirt driver
   cinder: nfs backed, with nfs_snapshot_support=True

  As far as I see the implementation about file path handling, I don't
  see any changes in the way how we handle disk file path for nfs
  backend, so the problem should be reproduced with master.

  Logs & Configs
  ==============
  N/A

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