Re: [Qemu-devel] [PATCH v2 1/1] mirror: do not increase offset during initial zero_or_discard phase

[Eric Blake <eblake@redhat.com>]

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On 02/02/2017 08:25 AM, Denis V. Lunev wrote:
> From: Anton Nefedov <anton.nefedov@virtuozzo.com>
> 
> If explicit zeroing out before mirroring is required for the target image,
> it moves the block job offset counter to EOF, then offset and len counters
> count the image size twice. There is no harm but stats are confusing,
> specifically the progress of the operation is always reported as 99% by
> management tools.
> 
> The patch skips offset increase for the first "technical" pass over the
> image. This should not cause any further harm.
> 
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Jeff Cody <jcody@redhat.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Max Reitz <mreitz@redhat.com>
> CC: Eric Blake <eblake@redhat.com>
> ---

> +    bool initial_zeroing_ongoing;

Long name. With a bit of bikeshedding, I might have used 'init_pass' for
a shorter name (particularly if some later patch introduces another
aspect of initialization that is not zeroing but is worth ignoring with
respects to progress reporting).

>  } MirrorBlockJob;
>  
>  typedef struct MirrorOp {
> @@ -117,9 +118,10 @@ static void mirror_iteration_done(MirrorOp *op, int ret)
>          if (s->cow_bitmap) {
>              bitmap_set(s->cow_bitmap, chunk_num, nb_chunks);
>          }
> -        s->common.offset += (uint64_t)op->nb_sectors * BDRV_SECTOR_SIZE;
> +        if (!s->initial_zeroing_ongoing) {
> +            s->common.offset += (uint64_t)op->nb_sectors * BDRV_SECTOR_SIZE;
> +        }
>      }
> -
>      qemu_iovec_destroy(&op->qiov);

Why are you deleting the blank line?

Other than naming, the patch looks reasonable.  If you spin a v3 with
only the name changed, you can add:

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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