Re: [PATCH 01/33] block: add a lower-level bio_add_page interface

[Matthew Wilcox <willy@infradead.org>]

On Wed, May 09, 2018 at 09:47:58AM +0200, Christoph Hellwig wrote:
> +/**
> + * __bio_try_merge_page - try adding data to an existing bvec
> + * @bio: destination bio
> + * @page: page to add
> + * @len: length of the range to add
> + * @off: offset into @page
> + *
> + * Try adding the data described at @page + @offset to the last bvec of @bio.
> + * Return %true on success or %false on failure.  This can happen frequently
> + * for file systems with a block size smaller than the page size.
> + */

Could we make this:

/**
 * __bio_try_merge_page() - Try appending data to an existing bvec.
 * @bio: Destination bio.
 * @page: Page to add.
 * @len: Length of the data to add.
 * @off: Offset of the data in @page.
 *
 * Try to add the data at @page + @off to the last bvec of @bio.  This is
 * a useful optimisation for file systems with a block size smaller than
 * the page size.
 *
 * Context: Any context.
 * Return: %true on success or %false on failure.
 */

(page, len, off) is a bit weird to me.  Usually we do (page, off, len).

> +/**
> + * __bio_add_page - add page to a bio in a new segment
> + * @bio: destination bio
> + * @page: page to add
> + * @len: length of the range to add
> + * @off: offset into @page
> + *
> + * Add the data at @page + @offset to @bio as a new bvec.  The caller must
> + * ensure that @bio has space for another bvec.
> + */

/**
 * __bio_add_page - Add page to a bio in a new segment.
 * @bio: Destination bio.
 * @page: Page to add.
 * @len: Length of the data to add.
 * @off: Offset of the data in @page.
 *
 * Add the data at @page + @off to @bio as a new bvec.  The caller must
 * ensure that @bio has space for another bvec.
 *
 * Context: Any context.
 */

> +static inline bool bio_full(struct bio *bio)
> +{
> +	return bio->bi_vcnt >= bio->bi_max_vecs;
> +}

I really like this helper.