Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension

[Daniel P. Berrange]

On Thu, Jul 13, 2017 at 05:02:51PM +0200, Peter Lieven wrote:
> Am 13.07.2017 um 17:01 schrieb Daniel P. Berrange:
> > On Thu, Jul 13, 2017 at 05:00:39PM +0200, Peter Lieven wrote:
> > > Am 13.07.2017 um 16:58 schrieb Daniel P. Berrange:
> > > > On Thu, Jul 13, 2017 at 04:18:13PM +0200, Peter Lieven wrote:
> > > > > Okay, so it has to be a mix of QAPI parsing and manual parameter 
> > > > > checking,
> > > > > right?
> > > > Yeah. It does feel like a valid RFE for QAPI to add a permitted range to
> > > > 'int' types though, which would simplify the code in future.
> > > > 
> > > > > I currently have the following:
> > > > > 
> > > > >       options = qemu_opts_to_qdict(opts, NULL);
> > > > >       qdict_extract_subqdict(options, &compressopts, "compress.");
> > > > >       v = qobject_input_visitor_new_keyval(QOBJECT(compressopts));
> > > > >       visit_start_struct(v, NULL, NULL, 0, &local_err);
> > > > >       if (local_err) {
> > > > >           ret= -EINVAL;
> > > > >           goto finish;
> > > > >       }
> > > > >       visit_type_Qcow2Compress_members(v, &compress, &local_err);
> > > > >       if (local_err) {
> > > > >           ret= -EINVAL;
> > > > >           goto finish;
> > > > >       }
> > > > >       visit_end_struct(v, NULL);
> > > > >       visit_free(v);
> > > > >       QDECREF(compressopts);
> > > > >       QDECREF(options)
> > > > Looks good.
> > > > 
> > > > > And I have the following 2 questions:
> > > > >    a) I have to specifiy compress.format and compress.level otherwise 
> > > > > I will get an error. How can I fix that the settings are optional?
> > > > Put an '*' as the first character of any field name if it should be 
> > > > optional.
> > > > 
> > > > >    b) If I just specify a compress.format can I default the 
> > > > > compress.level to 0 without an error?
> > > > I believe you'd get compress.level as 0 automatically for an 'int' type.
> > > I still face the issue that I now always have to specify a 
> > > compress.format.
> > > I tried to solve it like this:
> > [snip]
> > 
> > that's not needed if you name the parameter '*level' in the QAPI schema
> 
> its not needed for the *level, but I still get the error that the format
> parameter is missing otherwise. And I can't make format optional.

Surely specifying compress.format is how you turn on compression in the
first place, so making that optional should not be necessary. eg the
simple case becomes:

  qemu-img create -f qcow2 -o compress.format=zlib  foo.qcow2 1G

Yes, there is no notion of a "default" format, but IMHO that's a good
thing - same way with encryption - it requires an explict encrypt.format=luks
to turn on encryption

Regards,
Daniel
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