Re: [PATCH 06/12] hw/xen: add get_frontend_path() method to XenDeviceClass

[Paul Durrant]

On 24/10/2023 13:56, David Woodhouse wrote:
> On Tue, 2023-10-24 at 13:42 +0100, Paul Durrant wrote:
> > > --- a/hw/xen/xen-bus.c
> > > +++ b/hw/xen/xen-bus.c
> > > @@ -711,8 +711,16 @@ static void xen_device_frontend_create(XenDevice *xendev, 
> > > Error **errp)
> > >     {
> > >         ERRP_GUARD();
> > >         XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
> > > +    XenDeviceClass *xendev_class = XEN_DEVICE_GET_CLASS(xendev);
> > >     
> > > -    xendev->frontend_path = xen_device_get_frontend_path(xendev);
> > > +    if (xendev_class->get_frontend_path) {
> > > +        xendev->frontend_path = xendev_class->get_frontend_path(xendev, errp);
> > > +        if (!xendev->frontend_path) {
> > > +            return;
> >
> > I think you need to update errp here to note that you are failing to
> > create the frontend.
>
> If xendev_class->get_frontend_path returned NULL it will have filled in errp.

Ok, but a prepend to say that a lack of path there means we skip 
frontend creation seems reasonable?

> As a general rule (I'll be doing a bombing run on xen-bus once I get my
> patch queue down into single digits) we should never check 'if (*errp)'
> to check if a function had an error. It should *also* return a success
> or failure indication, and we should cope with errp being NULL.

I'm pretty sure someone told me the exact opposite a few years back.

  Paul