linux-kernel - Re: [PATCH V10 05/19] block: introduce bvec_last

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Date:   Thu, 15 Nov 2018 15:23:56 -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,
        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, linux-erofs@...ts.ozlabs.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>, Theodore Ts'o <tytso@....edu>,
        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 V10 05/19] block: introduce bvec_last_segment()

On Thu, Nov 15, 2018 at 04:52:52PM +0800, Ming Lei wrote:
> BTRFS and guard_bio_eod() need to get the last singlepage segment
> from one multipage bvec, so introduce this helper to make them happy.
> 
> Cc: Dave Chinner <dchinner@...hat.com>
> Cc: Kent Overstreet <kent.overstreet@...il.com>
> Cc: Mike Snitzer <snitzer@...hat.com>
> Cc: dm-devel@...hat.com
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: Shaohua Li <shli@...nel.org>
> Cc: linux-raid@...r.kernel.org
> Cc: linux-erofs@...ts.ozlabs.org
> Cc: David Sterba <dsterba@...e.com>
> Cc: linux-btrfs@...r.kernel.org
> Cc: Darrick J. Wong <darrick.wong@...cle.com>
> Cc: linux-xfs@...r.kernel.org
> Cc: Gao Xiang <gaoxiang25@...wei.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Theodore Ts'o <tytso@....edu>
> Cc: linux-ext4@...r.kernel.org
> Cc: Coly Li <colyli@...e.de>
> Cc: linux-bcache@...r.kernel.org
> Cc: Boaz Harrosh <ooo@...ctrozaur.com>
> Cc: Bob Peterson <rpeterso@...hat.com>
> Cc: cluster-devel@...hat.com

Reviewed-by: Omar Sandoval <osandov@...com>

Minor comments below.

> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---
>  include/linux/bvec.h | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/include/linux/bvec.h b/include/linux/bvec.h
> index 3d61352cd8cf..01616a0b6220 100644
> --- a/include/linux/bvec.h
> +++ b/include/linux/bvec.h
> @@ -216,4 +216,29 @@ static inline bool mp_bvec_iter_advance(const struct bio_vec *bv,
>  	.bi_bvec_done	= 0,						\
>  }
>  
> +/*
> + * Get the last singlepage segment from the multipage bvec and store it
> + * in @seg
> + */
> +static inline void bvec_last_segment(const struct bio_vec *bvec,
> +		struct bio_vec *seg)

Indentation is all messed up here.

> +{
> +	unsigned total = bvec->bv_offset + bvec->bv_len;
> +	unsigned last_page = total / PAGE_SIZE;
> +
> +	if (last_page * PAGE_SIZE == total)
> +		last_page--;

I think this could just be

	unsigned int last_page = (total - 1) / PAGE_SIZE;

> +	seg->bv_page = nth_page(bvec->bv_page, last_page);
> +
> +	/* the whole segment is inside the last page */
> +	if (bvec->bv_offset >= last_page * PAGE_SIZE) {
> +		seg->bv_offset = bvec->bv_offset % PAGE_SIZE;
> +		seg->bv_len = bvec->bv_len;
> +	} else {
> +		seg->bv_offset = 0;
> +		seg->bv_len = total - last_page * PAGE_SIZE;
> +	}
> +}
> +
>  #endif /* __LINUX_BVEC_ITER_H */
> -- 
> 2.9.5
>