Re: [Qemu-devel] [PATCH v2] qom: Introduce object_realize_nofail()

[Anthony Liguori]

On 04/12/2012 12:02 PM, Paolo Bonzini wrote:
> Il 12/04/2012 18:52, Andreas Färber ha scritto:
> > > Selecting the type of an object should be done by having a link<>
> > > property and letting the user create an object and setup the link.
> >
> > No, that's not what a link does. A link<>  property lets the user
> > associate one instance, not a type that can be used for multiple
> > instances. We'd need a template<>  or clone<>  mechanism for that!
> >
> > For example, the user specifies -cpu cortex-a9,+neon,-fpu and we have a
> > dual-core exynos4210 SoC.
> >
> > I originally had a patch on my qom-cpu-sh4 v1 series where exactly such
> > a link got criticized by Peter:
> >
> > http://patchwork.ozlabs.org/patch/146669/
> >
> > And I agree, it was an ugly workaround around the missing two-stage
> > constructor support. Therefore I had posted my object_realize() series!
>
> I think this is difficult to reconcile for now.  I can see Anthony's
> point, which makes a lot of sense from the PC point of view, but then
> "magic" configuration can also be important when working with SoC boards.

I don't see such "magic" configurations.  Either a SoC has a chip that's 
soldered to the board and cannot be changed (it's a child<>) or the SoC has a 
socket and you can add in a different component (it's a link<>).

Where does the "magic" come in?

> I've added a missing_property hook to my series that can be used to this
> end.  Accessing a property can trigger creation of the device with the
> appropriate class before realization.

I think we need to stick close to something that looks like it could be a real 
piece of hardware.  Once you add too much magic, it's too easy to do things the 
wrong way.

Regards,

Anthony Liguori

> Paolo