On 16.05.19 09:50, Denis Plotnikov wrote: > > > On 29.04.2019 1:32, Max Reitz wrote: >> On 05.02.19 10:08, Denis Plotnikov wrote: >>> The patch adds some preparation parts for incompatible compression type >>> feature into QCOW2 header that indicates that *all* compressed clusters >>> must be (de)compressed using a certain compression type. >>> >>> It is implied that the compression type is set on the image creation and >>> can be changed only later by image convertion, thus the only compression >>> algorithm is used for the image. >>> >>> The plan is to add support for ZSTD and then may be something more effective >>> in the future. >>> >>> ZSDT compression algorithm consumes 3-5 times less CPU power with a >>> comparable comression ratio with zlib. It would be wise to use it for >>> data compression f.e. for backups. >>> >>> The default compression is ZLIB. >>> >>> Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com> >>> --- >>> block/qcow2.c | 25 +++++++++++++++++++++++++ >>> block/qcow2.h | 26 ++++++++++++++++++++++---- >>> 2 files changed, 47 insertions(+), 4 deletions(-) >> >> Are there plans to pursue this further? > Yes, I'm going to come up with the first version in a few weeks
OK. >> [...] >> >>> diff --git a/block/qcow2.h b/block/qcow2.h >>> index 32cce9eee2..fdde5bbefd 100644 >>> --- a/block/qcow2.h >>> +++ b/block/qcow2.h >>> @@ -112,6 +112,10 @@ >>> #define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size" >>> #define QCOW2_OPT_CACHE_CLEAN_INTERVAL "cache-clean-interval" >>> >>> +/* Compression types */ >>> +#define QCOW2_COMPRESSION_TYPE_ZLIB 0 >>> +#define QCOW2_COMPRESSION_TYPE_ZSTD 1 >> >> We probably want QAPI types anyway (qemu-img info should report the >> compression type), so I think we could use them instead. > I'm not sure that I understood the idea. Could you please explain what > is meant here? We don't need those constants and should use the > constants defined somewhere else (where)? qemu-img info can report format-specific information. I think the compression type should be listed there as well, once there is more than one. Format-specific information is a QAPI type, namely ImageInfoSpecificQCow2. Therefore, everything it contains needs to be a QAPI object, and this includes potential compression information. We thus need a QAPI enum like Qcow2CompressionType, and that would automatically give us these values. Max
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