While creating an image, if we want to extend the volume
(to accomodate the image), we need to first detach the volume,
perform the extend and attach it again. This is inefficient
for backends that support extending attached volumes since we
are performing 3 cinder operations (the attachment call
includes 3 API calls which sum to a total of 5 API calls for 3
operations) instead of directly extending it which requires only
1 API call to cinder.
The support for extending attached volumes was added in cinder
microversion 3.42.
This patch adds a new boolean config option
``cinder_do_extend_attached`` which allows operators to specify
if the cinder backend they are using supports extending
attached (in-use) volumes. By default this will be ``false``.
Based on the parameter, we will perform the extend operation,
online (if cinder_do_extend_attached is true) and offline otherwise.
Spec: https://review.opendev.org/c/openstack/glance-specs/+/868901
Depends-On: https://review.opendev.org/c/openstack/glance/+/869021
Depends-On: https://review.opendev.org/c/openstack/cinder/+/869051
Change-Id: I5e70824e9abc5277ea25ba95704b358fe3686037
a7edc87b0e