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Hi Nova and Cinder developers.

As I reported in a bug report [1], nova swap volume
(updating an attached volume) fuction does not work
in the case of non admin users by default. 
(Volumes are stuck.)

Before I was working for fixing another swap volume bug [2][3].
But Ryan fixed it on the Cinder side [4].
As a result, admin users can execute swap volume function,
but it was not fixed in the case of non admin users.
So I reported the bug report [1].

In the patch[5], I tried to change the default cinder's policy
to allow non admin users to execute migrate_volume_completion API.
But it was rejected by the cinder project ('-2' was voted).

In the patch[5], it was suggested to make the swap volume API admin only
on the Nova side.
But IMO, the swap volume function should be allowed to non admin users
because attaching a volume and detaching a volume can be performed
by non admin users.

If migrate_volume_completion is only allowed to admin users
by default on the Cinder side, attaching a new volume and
detaching an old volume should be performed on the Nova side
when swapping volumes.

If you have a good idea, please let me know it.

[1] Cinder volumes are stuck when non admin user executes nova swap volume API
    https://bugs.launchpad.net/cinder/+bug/1522705

[2] Cinder volume stuck in swap_volume
    https://bugs.launchpad.net/nova/+bug/1471098

[3] Fix cinder volume stuck in swap_volume
    https://review.openstack.org/#/c/207385/

[4] Fix swap_volume for case without migration
    https://review.openstack.org/#/c/247767/

[5] Enable volume owners to execute migrate_volume_completion
    https://review.openstack.org/#/c/253363/

Regards,
Takashi Natsume
NTT Software Innovation Center
E-mail: natsume.takashi at lab.ntt.co.jp