Re: [Qemu-devel] [PATCH 17/23] qom: move properties from qdev to object

[Anthony Liguori]

On 01/31/2012 01:46 AM, Paolo Bonzini wrote:
> On 01/30/2012 10:08 PM, Anthony Liguori wrote:
> > This is mostly code movement although not entirely. This makes properties part
> > of the Object base class which means that we can now start using Object in a
> > meaningful way outside of qdev.
>
> Can we move them to an intermediate base class? I would like to use QOM
> refcounting for other objects, such as SCSIRequest, so it is important to have
> Object as a pretty light-weight class. Also (and perhaps more importantly),
> interface implementations are Objects too and they do not need properties.
>
> I cannot think of any better name than IntrospectableObject, which is quite a
> mouthful. I suppose that we could have the base class but still pass the objects
> to the function as Object * and use the OBJECT macro. Nothing of this is in a
> hot path anyway.

I'm just not sure how I feel about this.

The overhead of properties are small in terms of object size.  It's just 
sizeof(void *).

I think that read-only properties could be interesting for SCSIRequest.  For 
instance, I can imagine having SCSIRequest is-a BlockRequest and having an error 
property associated with it.  That would provide a nice way to have an info io 
operation that returned a list of failed I/O requests or something like that.

Regards,

Anthony Liguori

> Paolo