On Wed, Dec 08, 2021 at 04:22:14AM +0000, Matthew Wilcox (Oracle) wrote:

+static inline size_t copy_folio_to_iter(struct folio *folio, size_t offset,
+		size_t bytes, struct iov_iter *i)
+{
+	return copy_page_to_iter((struct page *)folio, offset, bytes, i);
+}

I think we had this 2 or three series ago, but these open coded casts
are a bad idea.  I think we need a proper and well documented helper for
them.