On 22.12.19 12:37, Alberto Garcia wrote:
> The bdrv_co_pwrite_zeroes() call here fills complete clusters with
> zeroes, but it can happen that some subclusters are not part of the
> write request or the copy-on-write. This patch makes sure that only
> the affected subclusters are overwritten.
> 
> A potential improvement would be to also fill with zeroes the other
> subclusters if we can guarantee that we are not overwriting existing
> data. However this would waste more disk space, so we should first
> evaluate if it's really worth doing.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>