Each memory backend has to declare a CameraBuffer class implementation that bridges the API calls to each CameraBuffer::Private implementation. As the code is likely the same for most (if not all) backends, provide a convenience macro that expands to the CameraBuffer class declaration. Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>