The conceptual change is that the mode in which a volume gets handled
is derived from it's spec, not from the ability of the driver. In
practice, that is already how the code worked because it didn't
actually look at CSIDriver.Spec.Mode at all.
Therefore the code change itself is mostly just renaming "driver mode"
to "volume mode". In some places (CanDeviceMount, CanAttach) the
feature check that was used elsewhere seemed to be missing. Now their
code path for ephemeral volumes are also only entered if that feature
is enabled.
The sanity check whether a CSI driver is being used correctly still
needs to be implemented.
Related-to: https://github.com/kubernetes/kubernetes/issues/79624
555ff7ef10