Re: [Qemu-devel] [PATCH v4] virtio-pci: error out when both legacy and modern modes are disabled

[Greg Kurz <groug@kaod.org>]

On Fri, 22 Jul 2016 10:04:35 +0200
Cornelia Huck <cornelia.huck@de.ibm.com> wrote:

> On Thu, 21 Jul 2016 23:21:16 +0200
> Greg Kurz <groug@kaod.org> wrote:
> 
> > 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>
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> > v4: - rephrased error message and provide a hint to the user
> >     - split string literals to stay below 80 characters
> >     - added Marcel's R-b tag
> > ---
> >  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 755f9218b77d..72c4b392ffda 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))) {  
> 
> I'm not sure that I didn't mess up the sequence of the realize
> callbacks, but could disable_legacy still be AUTO here? In that case,
> we'd fail for disable-modern=on and disable-legacy unset (i.e., AUTO),
> which would be ok for pcie but not for !pcie.
> 

Marcel made the same comment in:

https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg05225.html

If the user explicitly disables modern, she shouldn't rely on QEMU
implicitly enabling legacy, hence the suggestion in error_append_hint().

> > +        error_setg(errp, "device cannot work when both modern and legacy modes"
> > +                   " are disabled");
> > +        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;
> >   
>