On 16.05.2019 13:40, Max Reitz wrote: > 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.
Thanks for clarification. Will do that way. Denis > > Max > -- Best, Denis
