Re: [Qemu-devel] [PATCH v3 00/20] qom: dynamic properties and composition tree

[Anthony Liguori]

On 12/16/2011 06:24 AM, Paolo Bonzini wrote:
> On 12/16/2011 11:36 AM, Kevin Wolf wrote:
> > > I think actually this is not the biggest problem. child properties are
> > > dynamic, and it's not a problem IMO if they are created like that.
> >
> > That they are added in an init function is an indicator that they aren't
> > really dynamic.
>
> That's true. However, another indicator is that anything that does not have a
> struct field is also not really static. :)
>
> So right now, child properties are all "dynamic" in this sense. This could
> change when Anthony converts buses to QOM. The bus right now is embedded into
> the HBA's struct, is not a pointer. This likely would change when buses are
> QOM-ized, but then the bus would indeed be a 100% static child.
>
> > I think having a child property that can be NULL could be
> > reasonable.
>
> I think Anthony convinced me this is not the case (unlike links). Even if buses
> and similar objects are changed to pointers because the implementation needs
> that, those pointers should never be NULL (or if they can, the child property
> should not exist when they are NULL).

What I would like to get to eventually is:

struct ISASerial {
   Device parent;

   UART _child uart;
   ISABus _link *bus;
};

A child should be able to be part of the parent devices memory with its life 
cycle bound to the parents life cycle.  This is why a child property shouldn't 
be nullable.

Regards,

Anthony Liguori

> Paolo