Re: [PATCH] DAX: enable iostat for read/write

[Dan Williams]

On Fri, Oct 14, 2016 at 10:25 AM, Toshi Kani <toshi.kani@xxxxxxx> wrote:
> DAX IO path does not support iostat, but its metadata IO path does.
> Therefore, iostat shows metadata IO statistics only, which has been
> confusing to users.
>
> Add iostat support to the DAX read/write path.
>
> Note, iostat still does not support the DAX mmap path as it allows
> user applications to access directly.
>
> Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> ---
>  fs/dax.c |   37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 014defd..3aaaac2 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -144,6 +144,34 @@ static sector_t to_sector(const struct buffer_head *bh,
>         return sector;
>  }
>
> +static void dax_iostat_start(struct gendisk *disk, struct iov_iter *iter,
> +                            unsigned long *start)
> +{
> +       int rw = iov_iter_rw(iter);
> +       int sec = iov_iter_count(iter) >> 9;

Should this be a minimum of one sector since we allow unaligned
transfers through this interface?

...or is iov_iter_count() somehow guaranteed to be sector aligned here?