Cloned from launchpad blueprint https://blueprints.launchpad.net/cinder/+spec/add-flat-volume-api.

Description:

For some backends  such like ceph and nexenta , they use CoW/Layering mechanism for cloning, that introduce a dependency between child volume and its parent snapshot/volumes. I want to add a flat_volume api extenssion(include api extension and also a dummy implementation in volume/driver.py), that willing to allow user to flat the child volume , thus remove the dependency.
Currently ,with such dependency, user cannot delete the parent volume/snapshot unless they deleted all child volumes cloned from them.This may not make sense for some use cases such like a tenant admin want to delete a base volume image,but there are still some running VMs using the child volumes.
With the flat_volume api(and also its implementation in backend driver), it allow such use case.

Specification URL (additional information):

None