Re: [Qemu-devel] [PATCH 07/18] qom: add link properties

[Anthony Liguori]

On 12/01/2011 05:21 AM, Avi Kivity wrote:
> On 11/30/2011 11:03 PM, Anthony Liguori wrote:
> > Links represent an ephemeral relationship between devices.  They are meant to
> > replace the qdev concept of busses by allowing more informal relationships
> > between devices.
>
> So, links are equivalent to pointers?

Yup.  Once we have qom inheritance (next stage), we can have a link<PCIDevice> 
property and you'll be able to set it to an E1000State with the appropriate 
casting and error checking taking place.

> > Links are fairly limited in their usefulness without implementing QOM-style
> > subclassing and interfaces.
> >
> >
> > +static void qdev_get_link_property(DeviceState *dev, Visitor *v, void *opaque,
> > +                                   const char *name, Error **errp)
> > +{
> > +    DeviceState **child = opaque;
> > +    gchar *path;
> > +
> > +    if (*child) {
> > +        path = qdev_get_canonical_path(*child);
> > +        visit_type_str(v,&path, name, errp);
> > +        g_free(path);
> > +    } else {
> > +        path = (gchar *)"";
>
> If gchar != char, this is wrong.  Also, you're converting a const
> pointer into a non-const pointer, discarding type safety.

I'll address this later in the thread.

> > +        visit_type_str(v,&path, name, errp);
> > +    }
>
> Shouldn't this be visit_type_link()?

link isn't a primitive type for visitors.   visit_type_link() would just call 
visit_type_str() so I don't think there's a ton of value in introducing the 
extra layer.

The accessors are the only places that should be marshaling links.

Regards,

Anthony Liguori

>