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Re: [PATCH v9 32/34] qcow2: Allow preallocation and backing files if ext
From: |
Max Reitz |
Subject: |
Re: [PATCH v9 32/34] qcow2: Allow preallocation and backing files if extended_l2 is set |
Date: |
Fri, 3 Jul 2020 09:45:56 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 |
On 28.06.20 13:02, 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>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
> block/qcow2.c | 7 ++++---
> tests/qemu-iotests/206.out | 2 +-
> 2 files changed, 5 insertions(+), 4 deletions(-)
Reviewed-by: Max Reitz <mreitz@redhat.com>
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