The reason seems to be the fact that Cinder expects the connector provided through the "attachment_update" call to include the requested attach mode [1], otherwise assuming it to be 'rw'. As Nova won't provide it, Cinder will then error because of an access mode mismatch.
The introduction of "new style volume attachments" seems to have caused a regression, breaking read-only volume attachments.
Trace: http:// paste.openstack .org/raw/ 639097/
The reason seems to be the fact that Cinder expects the connector provided through the "attachment_update" call to include the requested attach mode [1], otherwise assuming it to be 'rw'. As Nova won't provide it, Cinder will then error because of an access mode mismatch.
[1] https:/ /github. com/openstack/ cinder/ blob/d96b6dfba0 3424baf8b3ddc75 39347554892e941 /cinder/ volume/ manager. py#L4374- L4393