Re: [Qemu-block] [PATCH v2 3/7] qcow2: Make perform_cow() call do_perform_cow() twice

[Eric Blake]

On 06/07/2017 09:08 AM, Alberto Garcia wrote:
> Instead of calling perform_cow() twice with a different COW region
> each time, call it just once and make perform_cow() handle both
> regions.
> 
> This patch simply moves code around. The next one will do the actual
> reordering of the COW operations.
> 
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/qcow2-cluster.c | 38 +++++++++++++++++++++++---------------
>  1 file changed, 23 insertions(+), 15 deletions(-)

>      qemu_co_mutex_unlock(&s->lock);
> -    ret = do_perform_cow(bs, m->offset, m->alloc_offset, r->offset, 
> r->nb_bytes);
> +    ret = do_perform_cow(bs, m->offset, m->alloc_offset,
> +                         start->offset, start->nb_bytes);
> +    if (ret < 0) {
> +        goto fail;
> +    }
> +
> +    ret = do_perform_cow(bs, m->offset, m->alloc_offset,
> +                         end->offset, end->nb_bytes);
> +
> +fail:

Since you reach this label even on success, it feels a bit awkward. I
probably would have avoided the goto and used fewer lines by refactoring
the logic as:

ret = do_perform_cow(..., start->...);
if (ret >= 0) {
    ret = do_perform_cow(..., end->...);
}

But that doesn't affect correctness, so whether or not you redo the
logic in the shorter fashion:

Reviewed-by: Eric Blake <address@hidden>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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