rbd: add support for block-devices in NodeGetVolumeStats()
rbd: add support for block-devices in NodeGetVolumeStats()

The NodeGetVolumeStats procedure can now be used to fetch the capacity
of the RBD block-device. By default this is a thin-provisioned device,
which means that the capacity is not reserved in the Ceph cluster. This
makes it possible to over-provision the cluster.

In order to detect the amount of storage used by the RBD block-device
(when thin-provisioned), it is required to connect to the Ceph cluster.
Unfortunately, the NodeGetVolumeStats CSI procedure does not provide
enough parameters to connect to the Ceph cluster and fetch more details
about the RBD image.

Signed-off-by: Niels de Vos <7bda0c0ee7f47171cc808e9e60292cbc5d8140dd@redhat.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi