On Tue, Jul 20, 2021 at 07:42:00AM +0100, Christoph Hellwig wrote:
> On Mon, Jul 19, 2021 at 07:39:45PM +0100, Matthew Wilcox (Oracle) wrote:
> > +/**
> > + * bio_add_folio - Attempt to add part of a folio to a bio.
> > + * @bio: Bio to add to.
> > + * @folio: Folio to add.
> > + * @len: How many bytes from the folio to add.
> > + * @off: First byte in this folio to add.
> > + *
> > + * Always uses the head page of the folio in the bio. If a submitter only
> > + * uses bio_add_folio(), it can count on never seeing tail pages in the
> > + * completion routine. BIOs do not support folios that are 4GiB or larger.
> > + *
> > + * Return: The number of bytes from this folio added to the bio.
> > + */
> > +size_t bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
> > + size_t off)
> > +{
> > + if (len > UINT_MAX || off > UINT_MAX)
> > + return 0;
> > + return bio_add_page(bio, &folio->page, len, off);
> > +}
>
> I'd use the opportunity to switch to a true/false return instead of
> the length. This has been on my todo list for bio_add_page for a while,
> so it might make sense to start out the new API the right way.
Looking at it with fresh eyes, I decided to rewrite the docs too.
ie this:
/**
* bio_add_folio - Attempt to add part of a folio to a bio.
- * @bio: Bio to add to.
+ * @bio: BIO to add to.
* @folio: Folio to add.
* @len: How many bytes from the folio to add.
* @off: First byte in this folio to add.
*
- * Always uses the head page of the folio in the bio. If a submitter only
- * uses bio_add_folio(), it can count on never seeing tail pages in the
- * completion routine. BIOs do not support folios that are 4GiB or larger.
+ * Filesystems that use folios can call this function instead of calling
+ * bio_add_page() for each page in the folio. If @off is bigger than
+ * PAGE_SIZE, this function can create a bio_vec that starts in a page
+ * after the bv_page. BIOs do not support folios that are 4GiB or larger.
*
- * Return: The number of bytes from this folio added to the bio.
+ * Return: Whether the addition was successful.
*/
-size_t bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
+bool bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
size_t off)
{
if (len > UINT_MAX || off > UINT_MAX)
return 0;
- return bio_add_page(bio, &folio->page, len, off);
+ return bio_add_page(bio, &folio->page, len, off) > 0;
}
(i decided to go with > 0 so it's impervious to when you change
bio_add_page())
