def get_hit_count(self, image_id):
        if not self.is_cached(image_id):
            return 0

        path = self.get_image_filepath(image_id)
        return int(get_xattr(path, 'hits', default=0))
``BlockDeviceDeployer.calculate_changes`` recognizes a volume that is
dataset/ETHPy150Open rcbops/glance-buildpackage/glance/image_cache/drivers/xattr.py/Driver.get_hit_count--crossover with--dataset/ETHPy150Open ClusterHQ/flocker/flocker/node/agents/test/test_blockdevice.py/BlockDeviceDeployerDetachCalculateChangesTests.test_detach_deleted_manifestation