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 <[email protected]> Cc: Kent Overstreet <[email protected]> Cc: Mike Snitzer <[email protected]> Cc: [email protected] Cc: Alexander Viro <[email protected]> Cc: [email protected] Cc: Shaohua Li <[email protected]> Cc: [email protected] Cc: [email protected] Cc: David Sterba <[email protected]> Cc: [email protected] Cc: Darrick J. Wong <[email protected]> Cc: [email protected] Cc: Gao Xiang <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: Theodore Ts'o <[email protected]> Cc: [email protected] Cc: Coly Li <[email protected]> Cc: [email protected] Cc: Boaz Harrosh <[email protected]> Cc: Bob Peterson <[email protected]> Cc: [email protected] Signed-off-by: Ming Lei <[email protected]> --- 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
