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

[Anthony Liguori]

On 04/12/2012 11:52 AM, Andreas Färber wrote:
> Am 12.04.2012 17:41, schrieb Anthony Liguori:
> > On 04/12/2012 09:04 AM, Andreas Färber wrote:
> > > Am 12.04.2012 16:59, schrieb Paolo Bonzini:
> > > > Il 12/04/2012 16:47, Anthony Liguori ha scritto:
> > > > > > Wrap setting of Object::realized property, error reporting and exit(1)
> > > > > > into a helper function. It is the equivalent of qdev_init_nofail().
> > > > >
> > > > > I don't like this.
> > > > >
> > > > > If for no reason other than, a much more specific justification is
> > > > > needed for this.  I absolutely don't want to repeat the error handling
> > > > > mistakes of qdev.  I would rather we refactor all of the users of
> > > > > qdev_init_nofail() to propagate errors.
> > > >
> > > > I agree about this in general, but for a different reason.  There
> > > > should be
> > > > only one call to object_realize_nofail, in vl.c, which might as well be
> > > > inlined---I'll include it in my series.  All calls to qdev_init_nofail
> > > > and qdev_init should disappear from boards that are properly converted
> > > > to QOM.
> > >
> > > We had talked about this on IRC and found that it won't work for
> > > selecting the type of an object.
> >
> > Can you be more specific?
> >
> > 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!

No, you misunderstood.  A link allows a user to create an object and make an 
associate.  If you want to let a user choose a type, just have them make an 
object.  Since you need no parameters to create an object, there's no advantage 
of telling something about a type name vs. giving it an object of that type.

Regards,

Anthony Liguori

> 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!
>
> https://github.com/afaerber/qemu-cpu/commit/32e4dd701694fffcf312d111c79eedad243be2b3
>
> Andreas