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 <dchin...@redhat.com> Cc: Kent Overstreet <kent.overstr...@gmail.com> Cc: Mike Snitzer <snit...@redhat.com> Cc: dm-de...@redhat.com Cc: Alexander Viro <v...@zeniv.linux.org.uk> Cc: linux-fsde...@vger.kernel.org Cc: Shaohua Li <s...@kernel.org> Cc: linux-r...@vger.kernel.org Cc: linux-er...@lists.ozlabs.org Cc: David Sterba <dste...@suse.com> Cc: linux-btrfs@vger.kernel.org Cc: Darrick J. Wong <darrick.w...@oracle.com> Cc: linux-...@vger.kernel.org Cc: Gao Xiang <gaoxian...@huawei.com> Cc: Christoph Hellwig <h...@lst.de> Cc: Theodore Ts'o <ty...@mit.edu> Cc: linux-e...@vger.kernel.org Cc: Coly Li <col...@suse.de> Cc: linux-bca...@vger.kernel.org Cc: Boaz Harrosh <o...@electrozaur.com> Cc: Bob Peterson <rpete...@redhat.com> Cc: cluster-de...@redhat.com Signed-off-by: Ming Lei <ming....@redhat.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