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

Darrick J. Wong
2021-07-15T21:12:57Z

On Thu, Jul 15, 2021 at 04:36:17AM +0100, Matthew Wilcox (Oracle) wrote:
> Allow callers to iterate over each folio instead of each page. The
> bio need not have been constructed using folios originally.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> include/linux/bio.h | 43 ++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index ade93e2de6a1..d462bbc95c4b 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -189,7 +189,7 @@ static inline void bio_advance_iter_single(const struct bio *bio,
> */
> #define bio_for_each_bvec_all(bvl, bio, i) \
> for (i = 0, bvl = bio_first_bvec_all(bio); \
> - i < (bio)->bi_vcnt; i++, bvl++) \
> + i < (bio)->bi_vcnt; i++, bvl++)
>
> #define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)
>
> @@ -314,6 +314,47 @@ static inline struct bio_vec *bio_last_bvec_all(struct bio *bio)
> return &bio->bi_io_vec[bio->bi_vcnt - 1];
> }
>
> +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?

> + size_t _seg_count;
> + int _i;

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

> +};
> +
> +static inline
> +void bio_first_folio(struct folio_iter *fi, struct bio *bio, int i)
> +{
> + struct bio_vec *bvec = bio_first_bvec_all(bio) + i;
> +
> + fi->folio = page_folio(bvec->bv_page);
> + fi->offset = bvec->bv_offset +
> + PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
> + fi->_seg_count = bvec->bv_len;
> + fi->length = min(folio_size(fi->folio) - fi->offset, fi->_seg_count);
> + fi->_i = i;
> +}
> +
> +static inline void bio_next_folio(struct folio_iter *fi, struct bio *bio)
> +{
> + fi->_seg_count -= fi->length;
> + if (fi->_seg_count) {
> + fi->folio = folio_next(fi->folio);
> + fi->offset = 0;
> + fi->length = min(folio_size(fi->folio), fi->_seg_count);
> + } else if (fi->_i + 1 < bio->bi_vcnt) {
> + bio_first_folio(fi, bio, fi->_i + 1);
> + } else {
> + fi->folio = NULL;
> + }
> +}
> +
> +/*
> + * 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.

--D

> +
> enum bip_flags {
> BIP_BLOCK_INTEGRITY = 1 << 0, /* block layer owns integrity data */
> BIP_MAPPED_INTEGRITY = 1 << 1, /* ref tag has been remapped */
> --
> 2.30.2
>