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

Matthew Wilcox
2021-07-15T22:38:58Z

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:
> > +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.

> > + size_t _seg_count;
> > + int _i;
>
> And these are private variables that the iteration code should not
> scribble over?

Indeed!

> > +/*
> > + * 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);