int gre_io_send_mdata(
    gre_io_t *                  handle,  
    gre_io_serialized_data_t *  md_buffer  
)
            Send a serialized buffer of mdata (data manager key/value pairs) to the
                        handle. The handle must have been opened for writing using
                            GRE_IO_WRONLY.
Parameters:
        handle  A valid handle created with gre_io_open()  
        buffer  A data buffer containing a serialized data  
Returns:
        -1 on failure anything else is success