Re: [Qemu-block] [Qemu-devel] [PATCH 1/4] block/qcow2: add compression_algorithm create option

[Peter Lieven]

Am 27.06.2017 um 15:20 schrieb Daniel P. Berrange:
> On Tue, Jun 27, 2017 at 02:34:07PM +0200, Peter Lieven wrote:
> > this patch adds a new compression_algorithm option when creating qcow2 images.
> > The current default for the compresison algorithm is zlib and zlib will be
> > used when this option is omitted (like before).
> >
> > If the option is specified e.g. with:
> >
> >   qemu-img create -f qcow2 -o compression_algorithm=zlib image.qcow2 1G
> IMHO we should introduce a nested struct "compress" struct to hold the format
> name, and any other format specific arguments, in a way that maps nicely to
> any future QAPI representmatch of create options. eg
>
> { 'enum': 'BlockdevQcow2CompressFormat',
>    'data': [ 'zlib', 'lzo' ] }
>
> { 'union': 'BlockdevQcow2Compress',
>    'base': { 'format': 'BlockdevQcow2CompressFormat' },
>    'discriminator': 'format',
>    'data': { 'zlib': 'BlockdevQcow2CompressZLib',
>              'lzo': 'BlockdevQcow2CompressLZO'} }
>
> so it would map to
>
>   qemu-img create -f qcow2 -o compress.format=zlib image.qcow2 1G
>
> and let us have other compress.XXXX options specific to each format

Or would it be possible to start with just a compress.level (int) parameter.
In fact that would be sufficient for almost all formats (or better use 
algorithms?).
The windowBits can be default to -15 in the future. It seems the old choice of 
-12
was just not optimal. We just have to use it for backwards compatiblity if the 
compress
options are not specified.

Peter