linux-kernel - Re: [PATCH 19/60] fs/buffer: comment on direct access to bvec table

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Message-ID: <20161031153530.GJ30919@infradead.org>
Date:   Mon, 31 Oct 2016 08:35:30 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Kent Overstreet <kent.overstreet@...il.com>
Subject: Re: [PATCH 19/60] fs/buffer: comment on direct access to bvec table


I think we'll just need a version zero_fill_bio with a length argument
and let that handle all the bvec access.  I have vague memories that
Kent posted one a while ago, Ccing him.

On Sat, Oct 29, 2016 at 04:08:18PM +0800, Ming Lei wrote:
> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> ---
>  fs/buffer.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index b205a629001d..81c3793948b4 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -3018,8 +3018,13 @@ static void end_bio_bh_io_sync(struct bio *bio)
>  void guard_bio_eod(int op, struct bio *bio)
>  {
>  	sector_t maxsector;
> -	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
>  	unsigned truncated_bytes;
> +	/*
> +	 * It is safe to truncate the last bvec in the following way
> +	 * even though multipage bvec is supported, but we need to
> +	 * fix the parameters passed to zero_user().
> +	 */
> +	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
>  
>  	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
>  	if (!maxsector)
> -- 
> 2.7.4
> 
> --
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---end quoted text---