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

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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: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2019-04-23 10:51:04 +08:00 committed by Jens Axboe
parent 6c88d73515
commit 551879a48f
1 changed files with 15 additions and 11 deletions
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26
block/bio.c
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@ -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,