def METHOD_NAME(node_name, path, backing=None, fmt=None, throttle=None):
    if fmt is None:
        fmt = iotests.imgfmt
    res = {
        'node-name': node_name,
        'driver': fmt,
        'file': {
            'driver': 'file',
            'filename': path
        }
    }
    if backing is not None:
        res['backing'] = backing
    if throttle:
        res['file'] = {
            'driver': 'throttle',
            'throttle-group': throttle,
            'file': res['file']
        }
    return res