+ * @complete_unwritten: The filesystem method used to convert unwritten blocks
+ * to written so the data written to them is exposed. This is required for
+ * required by write faults for filesystems that will return unwritten
+ * extent mappings from @get_block, but it is optional for reads as
+ * dax_insert_mapping() will always zero unwritten blocks. If the fs does
+ * not support unwritten extents, the it should pass NULL.