'Validate the components of an existing masking view.
:param serial_number: the array serial number
:param masking_view_dict: the masking view dict
:param maskingview_name: the amsking view name
:param default_sg_name: the default sg name
:param extra_specs: the extra specifications
:returns: storage_group_name -- string, msg -- string'

def _validate_existing_masking_view(self, serial_number, masking_view_dict, maskingview_name, default_sg_name, extra_specs):

    (storage_group_name, msg) = self._check_existing_storage_group(serial_number, maskingview_name, default_sg_name, masking_view_dict)
    if (not msg):
        portgroup_name = self.rest.get_element_from_masking_view(serial_number, maskingview_name, portgroup=True)
        (__, msg) = self._check_port_group(serial_number, portgroup_name)
        if (not msg):
            (initiator_group, msg) = self._check_existing_initiator_group(serial_number, maskingview_name, masking_view_dict, storage_group_name, portgroup_name, extra_specs)
    return (storage_group_name, msg)
