Re: [PATCH] qcow2: Fix preallocation on images with unaligned sizes

[Eric Blake <eblake@redhat.com>]

On 6/10/20 4:46 AM, Alberto Garcia wrote:
> When resizing an image with qcow2_co_truncate() using the falloc or
> full preallocation modes the code assumes that both the old and new
> sizes are cluster-aligned.
> 
> There are two problems with this:
> 
>    1) The calculation of how many clusters are involved does not always
>       get the right result.
> 
>       Example: creating a 60KB image and resizing it (with
>       preallocation=full) to 80KB won't allocate the second cluster.
> 
>    2) No copy-on-write is performed, so in the previous example if
>       there is a backing file then the first 60KB of the first cluster
>       won't be filled with data from the backing file.
> 
> This patch fixes both issues.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>   block/qcow2.c              | 17 ++++++++++++++---
>   tests/qemu-iotests/125     | 21 +++++++++++++++++++++
>   tests/qemu-iotests/125.out |  9 +++++++++
>   3 files changed, 44 insertions(+), 3 deletions(-)
> 

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

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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