linux-kernel - [PATCH V10 16/19] block: document usage of bio iterator helpers

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Date:   Thu, 15 Nov 2018 16:53:03 +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, Ming Lei <ming.lei@...hat.com>,
        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, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, linux-erofs@...ts.ozlabs.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>, Theodore Ts'o <tytso@....edu>,
        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
Subject: [PATCH V10 16/19] 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.

Cc: Dave Chinner <dchinner@...hat.com>
Cc: Kent Overstreet <kent.overstreet@...il.com>
Cc: Mike Snitzer <snitzer@...hat.com>
Cc: dm-devel@...hat.com
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org
Cc: Shaohua Li <shli@...nel.org>
Cc: linux-raid@...r.kernel.org
Cc: linux-erofs@...ts.ozlabs.org
Cc: David Sterba <dsterba@...e.com>
Cc: linux-btrfs@...r.kernel.org
Cc: Darrick J. Wong <darrick.wong@...cle.com>
Cc: linux-xfs@...r.kernel.org
Cc: Gao Xiang <gaoxiang25@...wei.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Theodore Ts'o <tytso@....edu>
Cc: linux-ext4@...r.kernel.org
Cc: Coly Li <colyli@...e.de>
Cc: linux-bcache@...r.kernel.org
Cc: Boaz Harrosh <ooo@...ctrozaur.com>
Cc: Bob Peterson <rpeterso@...hat.com>
Cc: cluster-devel@...hat.com
Signed-off-by: Ming Lei <ming.lei@...hat.com>
---
 Documentation/block/biovecs.txt | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt
index 25689584e6e0..bfafb70d0d9e 100644
--- a/Documentation/block/biovecs.txt
+++ b/Documentation/block/biovecs.txt
@@ -117,3 +117,29 @@ 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, and usually they are used by filesystem code, and driver
+shouldn't use them because bio may have been split before they got to 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 bvec, and the local
+variable of 'struct bio_vec' or the reference records single-page IO
+vector during the itearation:
+
+	bio_for_each_segment()
+	bio_for_each_segment_all()
+
+* The following helper iterates over multi-page bvec, and each bvec may
+include multiple physically contiguous pages, and the local variable of
+'struct bio_vec' or the reference records multi-page IO vector during the
+itearation:
+
+	bio_for_each_bvec()
-- 
2.9.5