ublk_get_registered_fd
io_uring_prep_fsync(sqe[0], ublk_get_registered_fd(q, 1) /*fds[1]*/, IORING_FSYNC_DATASYNC);
io_uring_prep_rw(op, sqe[0], ublk_get_registered_fd(q, 2),
io_uring_prep_rw(op, sqe[0], ublk_get_registered_fd(q, 1) /*fds[1]*/,
io_uring_prep_rw(op, sqe[1], ublk_get_registered_fd(q, 1) /*fds[1]*/, 0,
sqe[0]->fd = ublk_get_registered_fd(q, 0); /* dev->fds[0] */
int dev_fd = ublk_get_registered_fd(q, 0);