Ability to create a volume already present in the storage backend

It would be nice to have the possibility to 'add' a volume instead of creating it, the latest implies a block creation. The purpose of this new command and API implementation is close the glance image-create. With glance, it will go like this:

$ glance image-create --size 2147483648 --name foo --store rbd --disk-format raw --container-format ovf --location rbd://ubuntu-raw

Basically:

As an administrator, I would like to be able to import existing volumes from a storage backend without having to extract them and then re-import them.

From a DB perspective, the operation is just a registration of a new volume nothing less nothing more.