Commit 551879a4 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: clarify that bio_add_page() and related helpers can add multi pages 



bio_add_page() and __bio_add_page() are capable of adding pages into
bio, and now we have at least two such usages alreay:

	- __bio_iov_bvec_add_pages()
	- nvmet_bdev_execute_rw().

So update comments on these two helpers.

The thing is a bit special for __bio_try_merge_page(), given the caller
needs to know if the new added page is same with the last added page,
then it isn't safe to pass multi-page in case that 'same_page' is true,
so adds warning on potential misuse, and updates comment on
__bio_try_merge_page().

Cc: linux-xfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Reviewed-by: default avatarChristoph Hellwig <hch@infradead.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 6c88d735

block/bio.c

+15 −11
Original line number Diff line number Diff line
@@ -667,6 +667,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv, 
			return false;

	}



	WARN_ON_ONCE(same_page && (len + off) > PAGE_SIZE);



	return true;

}
@@ -786,9 +788,9 @@ EXPORT_SYMBOL(bio_add_pc_page); 
/**

 * __bio_try_merge_page - try appending data to an existing bvec.

 * @bio: destination bio

 * @page: page to add

 * @page: start page to add

 * @len: length of the data to add

 * @off: offset of the data in @page

 * @off: offset of the data relative to @page

 * @same_page: if %true only merge if the new data is in the same physical

 *		page as the last segment of the bio.

 *
@@ -796,6 +798,8 @@ EXPORT_SYMBOL(bio_add_pc_page); 
 * a useful optimisation for file systems with a block size smaller than the

 * page size.

 *

 * Warn if (@len, @off) crosses pages in case that @same_page is true.

 *

 * Return %true on success or %false on failure.

 */

bool __bio_try_merge_page(struct bio *bio, struct page *page,
@@ -818,11 +822,11 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page, 
EXPORT_SYMBOL_GPL(__bio_try_merge_page);



/**

 * __bio_add_page - add page to a bio in a new segment

 * __bio_add_page - add page(s) 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

 * @page: start page to add

 * @len: length of the data to add, may cross pages

 * @off: offset of the data relative to @page, may cross pages

 *

 * Add the data at @page + @off to @bio as a new bvec.  The caller must ensure

 * that @bio has space for another bvec.
@@ -845,13 +849,13 @@ void __bio_add_page(struct bio *bio, struct page *page, 
EXPORT_SYMBOL_GPL(__bio_add_page);



/**

 *	bio_add_page	-	attempt to add page to bio

 *	bio_add_page	-	attempt to add page(s) to bio

 *	@bio: destination bio

 *	@page: page to add

 *	@len: vec entry length

 *	@offset: vec entry offset

 *	@page: start page to add

 *	@len: vec entry length, may cross pages

 *	@offset: vec entry offset relative to @page, may cross pages

 *

 *	Attempt to add a page to the bio_vec maplist. This will only fail

 *	Attempt to add page(s) to the bio_vec maplist. This will only fail

 *	if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.

 */

int bio_add_page(struct bio *bio, struct page *page,

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