Re: [PATCH v20 1/4] qcow2: introduce compression type feature

[Alberto Garcia <berto@igalia.com>]

On Tue 21 Apr 2020 10:11:14 AM CEST, Denis Plotnikov <dplotnikov@virtuozzo.com> wrote:
> The patch adds some preparation parts for incompatible compression type
> feature to qcow2 allowing the use different compression methods for
> image clusters (de)compressing.
>
> It is implied that the compression type is set on the image creation and
> can be changed only later by image conversion, thus compression type
> defines the only compression algorithm used for the image, and thus,
> for all image clusters.
>
> The goal of the feature is to add support of other compression methods
> to qcow2. For example, ZSTD which is more effective on compression than ZLIB.
>
> The default compression is ZLIB. Images created with ZLIB compression type
> are backward compatible with older qemu versions.
>
> Adding of the compression type breaks a number of tests because now the
> compression type is reported on image creation and there are some changes
> in the qcow2 header in size and offsets.
>
> The tests are fixed in the following ways:
>     * filter out compression_type for many tests
>     * fix header size, feature table size and backing file offset
>       affected tests: 031, 036, 061, 080
>       header_size +=8: 1 byte compression type
>                        7 bytes padding
>       feature_table += 48: incompatible feature compression type
>       backing_file_offset += 56 (8 + 48 -> header_change + feature_table_change)
>     * add "compression type" for test output matching when it isn't filtered
>       affected tests: 049, 060, 061, 065, 144, 182, 242, 255
>
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> QAPI part:
> Acked-by: Markus Armbruster <armbru@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto