void bdrv_register(BlockDriver *bdrv)

{

    

    if (!bdrv->bdrv_co_readv) {

        bdrv->bdrv_co_readv = bdrv_co_readv_em;

        bdrv->bdrv_co_writev = bdrv_co_writev_em;



        if (!bdrv->bdrv_aio_readv) {

            

            bdrv->bdrv_aio_readv = bdrv_aio_readv_em;

            bdrv->bdrv_aio_writev = bdrv_aio_writev_em;

        } else if (!bdrv->bdrv_read) {

            

            bdrv->bdrv_read = bdrv_read_em;

            bdrv->bdrv_write = bdrv_write_em;

        }

    }



    if (!bdrv->bdrv_aio_flush)

        bdrv->bdrv_aio_flush = bdrv_aio_flush_em;



    QLIST_INSERT_HEAD(&bdrv_drivers, bdrv, list);

}
