From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Lei Date: Thu, 15 Nov 2018 16:53:03 +0800 Subject: [Cluster-devel] [PATCH V10 16/19] block: document usage of bio iterator helpers In-Reply-To: <20181115085306.9910-1-ming.lei@redhat.com> References: <20181115085306.9910-1-ming.lei@redhat.com> Message-ID: <20181115085306.9910-17-ming.lei@redhat.com> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 Cc: Kent Overstreet Cc: Mike Snitzer Cc: dm-devel at redhat.com Cc: Alexander Viro Cc: linux-fsdevel at vger.kernel.org Cc: Shaohua Li Cc: linux-raid at vger.kernel.org Cc: linux-erofs at lists.ozlabs.org Cc: David Sterba Cc: linux-btrfs at vger.kernel.org Cc: Darrick J. Wong Cc: linux-xfs at vger.kernel.org Cc: Gao Xiang Cc: Christoph Hellwig Cc: Theodore Ts'o Cc: linux-ext4 at vger.kernel.org Cc: Coly Li Cc: linux-bcache at vger.kernel.org Cc: Boaz Harrosh Cc: Bob Peterson Cc: cluster-devel at redhat.com Signed-off-by: Ming Lei --- 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