Re: [Qemu-devel] [PATCH 2/2] virtio-pci: error out when both legacy and modern modes are disabled

[Greg Kurz <groug@kaod.org>]

On Thu, 08 Sep 2016 09:15:28 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Greg Kurz <groug@kaod.org> writes:
> 
> > From: Greg Kurz <gkurz@linux.vnet.ibm.com>
> >
> > Without presuming if we got there because of a user mistake or some
> > more subtle bug in the tooling, it really does not make sense to
> > implement a non-functional device.
> >
> > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
> > Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> >  hw/virtio/virtio-pci.c |    8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > index 268fd8ebb219..4b6a8a356621 100644
> > --- a/hw/virtio/virtio-pci.c
> > +++ b/hw/virtio/virtio-pci.c
> > @@ -1842,6 +1842,14 @@ static void virtio_pci_dc_realize(DeviceState *qdev, Error **errp)
> >      VirtIOPCIProxy *proxy = VIRTIO_PCI(qdev);
> >      PCIDevice *pci_dev = &proxy->pci_dev;
> >  
> > +    if (!(virtio_pci_modern(proxy) || virtio_pci_legacy(proxy))) {
> > +        error_setg(errp, "device cannot work as neither modern nor legacy mode"
> > +                   " is enabled");
> > +        error_append_hint(errp, "Set either disable-modern or disable-legacy"
> > +                          " to off\n");
> > +        return;
> > +    }
> > +
> >      if (!(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_PCIE) &&
> >          virtio_pci_modern(proxy)) {
> >          pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;  
> 
> Pardon my ignorance... is this a device-specific restriction, or is it
> the same for more (all?) virtio devices?

Yes this for all virtio devices.

But wait, I now realize that the check isn't done in the right place because
if we don't pass an explicit disable-legacy=on then proxy->disable_legacy gets
its final value in virtio_pci_realize() which gets called after virtio_pci_dc_realize()...

I'll fix that.

Thanks !

--
Greg