linux-ext4 - Re: [PATCH V12 18/20] block: document usage of bio iterator helpers

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Date:   Mon, 26 Nov 2018 14:43:51 -0800
From:   Omar Sandoval <osandov@...ndov.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, 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 V12 18/20] block: document usage of bio iterator helpers

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 <osandov@...com>

> Signed-off-by: Ming Lei <ming.lei@...hat.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
>