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From: Amir Goldstein <amir73il@gmail.com>
Date: Fri, 5 Oct 2018 11:39:24 +0300
Message-ID: <CAOQ4uxha3=jyVmZ0ArbSsO-CSMeQb43p7YTMGazZRB_M8zS0SQ@mail.gmail.com>
Subject: Re: [PATCH 07/15] vfs: skip zero-length dedupe requests
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>,
        linux-xfs <linux-xfs@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Btrfs <linux-btrfs@vger.kernel.org>,
        ocfs2-devel@oss.oracle.com, Eric Sandeen <sandeen@redhat.com>
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On Fri, Oct 5, 2018 at 3:46 AM Darrick J. Wong <darrick.wong@oracle.com> wrote:
>
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> Don't bother calling the filesystem for a zero-length dedupe request;
> we can return zero and exit.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/read_write.c |    5 +++++
>  1 file changed, 5 insertions(+)
>
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 973d3da78c09..99b2f809180c 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1966,6 +1966,11 @@ int vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
>         if (!dst_file->f_op->dedupe_file_range)
>                 goto out_drop_write;
>
> +       if (len == 0) {
> +               ret = 0;
> +               goto out_drop_write;
> +       }
> +
>         ret = dst_file->f_op->dedupe_file_range(src_file, src_pos,
>                                                 dst_file, dst_pos, len);

I suppose it is best to let user get the same errors he would get
before this change rather than skipping zero length copy at
vfs_dedupe_file_range() level, so looks fine.

Thanks,
Amir.