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Re: [PATCH v4 2/5] qcow2: introduce compression type feature

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH v4 2/5] qcow2: introduce compression type feature
Date: Tue, 3 Mar 2020 17:32:30 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

03.03.2020 16:34, Denis Plotnikov 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 all the 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 feture compression type
       backing_file_offset += 56 (8 + 48 -> header_change + fature_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<address@hidden>

Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

Best regards,

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