Re: [PATCH v14 091/138] block: Add bio_for_each_folio_all()

On Thu, Jul 15, 2021 at 02:12:54PM -0700, Darrick J. Wong wrote:

On Thu, Jul 15, 2021 at 04:36:17AM +0100, Matthew Wilcox (Oracle) wrote:

quoted

+struct folio_iter {
+	struct folio *folio;
+	size_t offset;
+	size_t length;

Hm... so after every bio_{first,next}_folio call, we can access the
folio, the offset, and the length (both in units of bytes) within the
folio?

Correct.

quoted

+	size_t _seg_count;
+	int _i;

And these are private variables that the iteration code should not
scribble over?

Indeed!

quoted

+/*
+ * Iterate over each folio in a bio.
+ */
+#define bio_for_each_folio_all(fi, bio)				\
+	for (bio_first_folio(&fi, bio, 0); fi.folio; bio_next_folio(&fi, bio))

...so I guess a sample iteration loop would be something like:

	struct bio *bio = <get one from somewhere>;
	struct folio_iter fi;

	bio_for_each_folio_all(fi, bio) {
		if (folio_test_dirty(fi.folio))
			printk("folio idx 0x%lx is dirty, i hates dirty data!",
					folio_index(fi.folio));
			panic();
	}

I'll go look through the rest of the patches, but this so far looks
pretty straightforward to me.

Something very much like that!

+static void iomap_read_end_io(struct bio *bio)
 {
+       struct folio_iter fi;
+       bio_for_each_folio_all(fi, bio)
+               iomap_finish_folio_read(fi.folio, fi.offset, fi.length, error);