On 06/27/2018 05:45 AM, Ming Lei wrote:
> Now multipage bvec is supported, and some helpers may return page by
> page, and some may return segment by segment, this patch documents the
> usage for helping us use them correctly.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> Documentation/block/biovecs.txt | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt
> index 25689584e6e0..f63af564ae89 100644
> --- a/Documentation/block/biovecs.txt
> +++ b/Documentation/block/biovecs.txt
> @@ -117,3 +117,30 @@ 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 which name has suffix of "_all" can only be used on
helpers whose names have the suffix of "_all" can only be used on
> +non-BIO_CLONED bio, and ususally they are used by filesystem code, and driver
usually
> +shouldn't use them becasue bio may have been splitted before they got to the
because split
> +driver:
> +
> + bio_for_each_segment_all()
> + bio_first_bvec_all()
> + bio_first_page_all()
> + bio_last_bvec_all()
> +
> +* The following helpers iterate over singlepage bvec, and the local
preferably: single-page
> +variable of 'struct bio_vec' or the reference records single page io
IO or I/O
> +vector during the itearation:
> +
> + bio_for_each_segment()
> + bio_for_each_segment_all()
> +
> +* The following helper iterates over multipage bvec, and each bvec may
preferably: multi-page
> +include multiple physically contiguous pages, and the local variable of
> +'struct bio_vec' or the reference records multi page io vector during the
multi-page IO or I/O
> +itearation:
> +
> + bio_for_each_bvec()
>
--
~Randy
