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Date: Fri, 15 Feb 2019 19:13:22 +0800 From: Ming Lei <ming.lei@...hat.com> To: Jens Axboe <axboe@...nel.dk> Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Theodore Ts'o <tytso@....edu>, Omar Sandoval <osandov@...com>, Sagi Grimberg <sagi@...mberg.me>, Dave Chinner <dchinner@...hat.com>, Kent Overstreet <kent.overstreet@...il.com>, Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com, Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, linux-raid@...r.kernel.org, David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org, "Darrick J . Wong" <darrick.wong@...cle.com>, linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>, Christoph Hellwig <hch@....de>, linux-ext4@...r.kernel.org, Coly Li <colyli@...e.de>, linux-bcache@...r.kernel.org, Boaz Harrosh <ooo@...ctrozaur.com>, Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com, Ming Lei <ming.lei@...hat.com> Subject: [PATCH V15 16/18] block: document usage of bio iterator helpers Now multi-page bvec is supported, some helpers may return page by page, meantime some may return segment by segment, this patch documents the usage. Reviewed-by: Christoph Hellwig <hch@....de> Reviewed-by: Omar Sandoval <osandov@...com> Signed-off-by: Ming Lei <ming.lei@...hat.com> --- Documentation/block/biovecs.txt | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt index 25689584e6e0..ce6eccaf5df7 100644 --- a/Documentation/block/biovecs.txt +++ b/Documentation/block/biovecs.txt @@ -117,3 +117,28 @@ Other implications: size limitations and the limitations of the underlying devices. Thus there's no need to define ->merge_bvec_fn() callbacks for individual block drivers. + +Usage of helpers: +================= + +* The following helpers whose names have the suffix of "_all" can only be used +on non-BIO_CLONED bio. They are usually used by filesystem code. Drivers +shouldn't use them because the bio may have been split before it reached the +driver. + + bio_for_each_segment_all() + bio_first_bvec_all() + bio_first_page_all() + bio_last_bvec_all() + +* The following helpers iterate over single-page segment. The passed 'struct +bio_vec' will contain a single-page IO vector during the iteration + + bio_for_each_segment() + bio_for_each_segment_all() + +* The following helpers iterate over multi-page bvec. The passed 'struct +bio_vec' will contain a multi-page IO vector during the iteration + + bio_for_each_bvec() + rq_for_each_bvec() -- 2.9.5
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