Re: [Qemu-devel] [PATCH 03/14] qdev: add qdev_add_properties

[Anthony Liguori <aliguori@us.ibm.com>]

On 05/01/2012 03:57 PM, Peter Maydell wrote:
> On 1 May 2012 21:48, Anthony Liguori<aliguori@us.ibm.com>  wrote:
>> Legacy properties != static properties.
>>
>> qdev_add_properties adds both legacy and static properties.  I'm happy to
>> put static properties into object but not legacy properties.
>
> So, er, how are you defining legacy and static properties?
> I would have thought 'legacy property' was 'anything we happen
> to already have'...

No, per the naming convention Paolo introduced, it's roughly:

1) legacy properties can be get/set as strings using the qdev parsing methods. 
Via qdev, they're exposed as -device <type>,<prop-name>=<string>.

In QOM, they're exposed as:

/path/to/device/legacy-<prop-name> = <string>

2) static properties are well-behaved QOM properties that just happen to be 
defined by the DEFINE_PROP_XXX macros.  They use the get/set methods of the 
property types.  New code can (and probably should) make use of static properties.

There's magic in the qdev layer now to decide whether a Property in the array of 
properties becomes a legacy or static property (it's only ever exposed as one 
type).  When we move static properties to Object, I'd like to keep legacy 
strictly as a qdev concept so we don't accidentally introduce more legacy 
properties.

>> Base classes are free to call object_property_add_static directly and avoid
>> qdev_add_properties entirely but we need the later for backwards compat.
>
> If qdev_add_properties is purely for back-compat it should be
> clearly labelled so we don't use it in new code.

Yes, I expect it would be once we have Paolo's property series in.  For now, 
it's the only real interface we have for adding bulk properties.

Regards,

Anthony Liguori

>
> -- PMM
>