[libvirt] [PATCHv3 04/11] Add virtio revision attribute to controllers

[Ján Tomko]

On Thu, Aug 11, 2016 at 10:17:34AM -0400, Laine Stump wrote:
>On 08/11/2016 09:31 AM, Daniel P. Berrange wrote:
>> On Thu, Aug 11, 2016 at 03:25:53PM +0200, Ján Tomko wrote:
>>> On Thu, Aug 11, 2016 at 01:00:08PM +0100, Daniel P. Berrange wrote:
>>>> On Wed, Aug 10, 2016 at 03:27:15PM +0200, Ján Tomko wrote:
>>>>> <controller type='scsi' index='0' model='virtio-scsi'>
>>>>>      <virtio revision='0.9'/>
>>>> I'm wondering about generalizing this. eg what if there are
>>>> other device models where we want the ability to set a
>>>> revision. We don't really want to invent a new sub-elment
>>>> named after each device model
>>> Not even a new attribute? :)
>>>   <revision virtio='0.9'/>
>>>
>>> How about:
>>>   <revision type='virtio' version='0.9'/>
>> Both of those are quite repetative - we already know its virtio.
>>
>> Most devices we have alrady include a <driver> or <model> sub-element,
>> so we should really just add a revision= attrbute to those existing
>> elements. For places which don't already have this we can add a new
>> <driver> element
>
>Yeah, I was going to suggest <driver> as well.
>
>The only thing missing would be the ability to specify multiple versions.
>

I think that's something we want to allow - didn't you mention somewhere
that 'disable-legacy=off,disable-modern=off' gets different results than
omitting it completely?

Other than awkward enum values, it could be represented as a (rather
verbose) subelement:
<driver>
  <revision>0.9</revision>
  <revision>1.0</revision>
</driver>

>Also, it does make the parsing and formatting a bit awkward, since
><driver> has different parse/format functions for each device that uses
>it (necessary due to the difference in possible attributes).

That means more work for me, but should not be a factor when deciding
on better-looking XML.

>
>In spite of that, it would definitely look better from the outside.
>

Personally I liked the consistence of having the same element under each
device more (and the ability to have more of them), but putting it under
<driver>/<model> also has its beauty, if we can figure out how to
express multiple versions.

Jan
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