linux-kernel - Re: [PATCH V11 17/19] block: document usage of bio iterator helpers

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Date:   Wed, 21 Nov 2018 09:45:25 +0200
From:   Nikolay Borisov <nborisov@...e.com>
To:     Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Theodore Ts'o <tytso@....edu>,
        Omar Sandoval <osandov@...com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Dave Chinner <dchinner@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, David Sterba <dsterba@...e.com>,
        linux-btrfs@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>,
        Christoph Hellwig <hch@....de>, linux-ext4@...r.kernel.org,
        Coly Li <colyli@...e.de>, linux-bcache@...r.kernel.org,
        Boaz Harrosh <ooo@...ctrozaur.com>,
        Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com
Subject: Re: [PATCH V11 17/19] block: document usage of bio iterator helpers



On 21.11.18 г. 5:23 ч., 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.
> 
> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---
>  Documentation/block/biovecs.txt | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt
> index 25689584e6e0..bb008f7afb05 100644
> --- a/Documentation/block/biovecs.txt
> +++ b/Documentation/block/biovecs.txt
> @@ -117,3 +117,27 @@ 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 bvecs. 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 single-page bvecs. The passed 'struct
> +bio_vec' will contain a single-page IO vector during the iteration
> +
> +	bio_for_each_bvec()

Just put this helper right below the above 2, no need to repeat the
explanation. Also I'd suggest introducing another catch-all sentence
"All other helpers are assumed to iterate multipage bio vecs" and
perhaps give an example with 1-2 helpers.

>