.. versionadded:: 2019.2.0

    Returns the glusterfs volume's max op-version value
    Requires Glusterfs version > 3.9

    CLI Example:
    .. code-block:: bash

        salt '*' glusterfs.get_max_op_version

def get_max_op_version():
    '''
    .. versionadded:: 2019.2.0

    Returns the glusterfs volume's max op-version value
    Requires Glusterfs version > 3.9

    CLI Example:
    .. code-block:: bash

        salt '*' glusterfs.get_max_op_version
    '''
    if _get_version() < (3, 10,):
        return False, 'Glusterfs version must be 3.10+.  Your version is {0}.'.format(str('.'.join(str(i) for i in _get_version())))

    cmd = 'volume get all cluster.max-op-version'
    root = _gluster_xml(cmd)

    if not _gluster_ok(root):
        return False, root.find('opErrstr').text

    result = {}
    for max_op_version in _iter(root, 'volGetopts'):
        for item in max_op_version:
            if item.tag == 'Value':
                result = item.text
            elif item.tag == 'Opt':
                for child in item:
                    if child.tag == 'Value':
                        result = child.text

    return result