udf_readatoffset
error = udf_readatoffset(node, &size, offset, &bp, &data);
error = udf_readatoffset(ds->node, &ds->size, ds->offset,
error = udf_readatoffset(ds->node, &ds->size, ds->offset,
static int udf_readatoffset(struct udf_node *, int *, int, struct buf **, uint8_t **);