Re: [PATCH 07/11] vfs: copy_file_range should update file timestamps

[Amir Goldstein <amir73il@gmail.com>]

On Mon, Dec 3, 2018 at 10:34 AM Dave Chinner <david@fromorbit.com> wrote:
>
> From: Dave Chinner <dchinner@redhat.com>
>
> Timestamps are not updated right now, so programs looking for
> timestamp updates for file modifications (like rsync) will not
> detect that files have changed. We are also accessing the source
> data when doing a copy (but not when cloning) so we need to update
> atime on the source file as well.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/read_write.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 3b101183ea19..3288db1d5f21 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1576,6 +1576,16 @@ static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in,
>  {
>         ssize_t ret;
>
> +       /* Update source timestamps, because we are accessing file data */
> +       file_accessed(file_in);
> +
> +       /* Update destination timestamps, since we can alter file contents. */
> +       if (!(file_out->f_mode & FMODE_NOCMTIME)) {
> +               ret = file_update_time(file_out);
> +               if (ret)
> +                       return ret;
> +       }
> +

If there is a consistency about who is responsible of calling file_accessed()
and file_update_time() it eludes me. grep tells me that they are mostly
handled by filesystem code or generic helpers called by filesystem code
and not in the vfs helpers.

FMODE_NOCMTIME seems like an xfs specific flag (for DMAPI?), which
most generic callers of file_update_time() completely ignore.
This seems like another argument in favor of leaving the responsibility
of the timestamp updates to the filesystem.

Maybe I am missing something?

Thanks,
Amir.