Re: [PATCH v8 32/34] qcow2: Allow preallocation and backing files if extended_l2 is set

[Eric Blake]

On 6/10/20 10:03 AM, Alberto Garcia wrote:
> Traditional qcow2 images don't allow preallocation if a backing file
> is set. This is because once a cluster is allocated there is no way to
> tell that its data should be read from the backing file.
>
> Extended L2 entries have individual allocation bits for each
> subcluster, and therefore it is perfectly possible to have an
> allocated cluster with all its subclusters unallocated.
>
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>   block/qcow2.c              | 7 ++++---
>   tests/qemu-iotests/206.out | 2 +-
>   2 files changed, 5 insertions(+), 4 deletions(-)

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

--
Eric Blake, Principal Software Engineer
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