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Date: Sat, 22 Aug 2015 17:56:40 +0200
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Subject: Re: [Qemu-devel] [PATCH v2 03/49] qapi: convert NumaOptions into a
	flat union
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>

2015-08-22 01:13 keltezéssel, Eduardo Habkost írta:
> On Fri, Aug 21, 2015 at 05:36:59PM +0200, Kővágó, Zoltán wrote:
>> Signed-off-by: Kővágó, Zoltán <DirtY.iCE.hu@gmail.com>
>
> I don't understand QAPI enough to understand why exactly this is needed
> (so I would like to get feedback from somebody who actually understands
> QAPI unions), but I have one comment below.

It's needed so the option visitor can support nested structures properly 
without flattening them (or breaking backward compatibility).

There is some discussion here:
http://lists.nongnu.org/archive/html/qemu-devel/2015-06/msg04438.html

But basically the thing is that with new new opts visitor, unless we 
convert NumaOptions into a flat union, the user would have to type -numa 
node,node.nodeid=foo instead of -numa node,nodeid=foo which would break 
backward compatibility.

>
> [...]
>>   ##
>> +# @NumaDriver
>> +#
>> +# List of possible numa drivers.
>> +#
>> +# Since: 2.5
>> +##
>> +{ 'enum': 'NumaDriver',
>> +  'data': [ 'node' ] }
>
> Why is the name "NumaDriver"? Below, the field is called "type", so why
> not something like "NumaOptionType"?

No particular reason other than the example in docs/qapi-code-gen.txt 
used driver.  The field is called type because in the non-flat union the 
discriminator is called type.

>> +
>> +##
>> +# @NumaCommonOptions
>> +#
>> +# Common set of numa options.
>> +#
>> +# @type: the numa driver to use
>> +#
>> +# Since: 2.5
>> +##
>> +{ 'struct': 'NumaCommonOptions',
>> +  'data': {
>> +    'type': 'NumaDriver' } }
>> +
>> +##
>> +# @NumaOptions
>> +#
>> +# A discriminated record of NUMA options. (for OptsVisitor)
>> +#
>> +# Since 2.1
>> +##
>> +{ 'union': 'NumaOptions',
>> +  'base': 'NumaCommonOptions',
>> +  'discriminator': 'type',
>> +  'data': {
>> +    'node': 'NumaNodeOptions' }}
>> +
>> +##
>>   # @HostMemPolicy
>>   #
>>   # Host memory policy types
>> --
>> 2.5.0
>>
>