VDEV_LABEL_START_SIZE
VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE;
asize += VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE;
offset + VDEV_LABEL_START_SIZE, bytes));
((off_t)(VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE))
off += VDEV_LABEL_START_SIZE;