Re: Configuration vs. compat hints [was Re: [Qemu-devel] [PATCHv3 03/13] qemu: add routines to manage PCI capabilities]

Avi Kivity
2009-06-15T11:34:36Z

On 06/15/2009 12:09 PM, Mark McLoughlin wrote:
>>>> I think the point is that you don't need version numbers if you have a
>>>> proper device tree.
>>>>
>>>>
>>> How do you add a new attribute to the device tree and, when a supplied
>>> device tree lacking said attribute, distinguish between a device tree
>>> from an old version of qemu (i.e. use the old default) and a partial
>>> device tree from the VM manager (i.e. use the new default) ?
>>>
>>>
>> -baseline 0.10
>>
>
> That's a version number :-)
>
> (I was responding to Anthony's "you don't need a version number")
>

If you want to prevent incompatibilities, you need to make everything
new (potentially including bugfixes) non-default. Eventually the
default configuration becomes increasingly unusable and you need a new
baseline. You must still be able to fall back to the old baseline for
older guests. I don't think games with configuration files can hide that.

--
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