On Mon, Nov 26, 2018 at 10:17:18AM +0800, Ming Lei wrote:
> 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.

Reviewed-by: Omar Sandoval <osan...@fb.com>

> Signed-off-by: Ming Lei <ming....@redhat.com>
> ---
>  Documentation/block/biovecs.txt | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt
> index 25689584e6e0..ce6eccaf5df7 100644
> --- a/Documentation/block/biovecs.txt
> +++ b/Documentation/block/biovecs.txt
> @@ -117,3 +117,28 @@ 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. They are usually used by filesystem code. Drivers
> +shouldn't use them because the bio may have been split before it reached 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 segment. The passed 'struct
> +bio_vec' will contain a single-page IO vector during the iteration
> +
> +     bio_for_each_segment()
> +     bio_for_each_segment_all()
> +
> +* The following helpers iterate over multi-page bvec. The passed 'struct
> +bio_vec' will contain a multi-page IO vector during the iteration
> +
> +     bio_for_each_bvec()
> +     rq_for_each_bvec()
> -- 
> 2.9.5
> 

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