Re: [Qemu-devel] [PATCH v2] virtio-pci: error out when both legacy and modern modes are disabled

[Greg Kurz <groug@kaod.org>]

On Thu, 21 Jul 2016 19:02:39 +0200
Greg Kurz <groug@kaod.org> wrote:

> On Thu, 21 Jul 2016 19:52:28 +0300
> Marcel Apfelbaum <marcel.apfelbaum@gmail.com> wrote:
> 
> > On 07/21/2016 06:52 PM, Greg Kurz 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>
> > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > ---
> > > v2: - error out at realize time as suggested by Connie
> > >      - updated title and changelog
> > > ---
> > >   hw/virtio/virtio-pci.c |    6 ++++++
> > >   1 file changed, 6 insertions(+)
> > >
> > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > > index f0677b73d860..8d707aac0c21 100644
> > > --- a/hw/virtio/virtio-pci.c
> > > +++ b/hw/virtio/virtio-pci.c
> > > @@ -1838,6 +1838,12 @@ static void virtio_pci_dc_realize(DeviceState *qdev, Error **errp)
> > >       VirtIOPCIProxy *proxy = VIRTIO_PCI(qdev);
> > >       PCIDevice *pci_dev = &proxy->pci_dev;
> > >
> > > +    if (proxy->flags & VIRTIO_PCI_FLAG_DISABLE_LEGACY &&
> > > +        proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN) {
> > > +        error_setg(errp, "device is unserviceable when both legacy and modern modes are disabled. At least one of the disable-modern or disable-legacy properties should be set to false.");
> > > +        return;
> > > +    }
> > > +  
> > 
> > Hi Greg,
> > 
> > I agree with the patch, but other patch in the mailing list
> > replaces the flags with standalone fields:
> > 
> > https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg04744.html
> > 
> 
> v3 will be using virtio_pci_legacy() and virtio_pci_modern().
> 
> > Also the error line may be too long and need to be truncated.
> > 
> 
> I'll rephrase the message. BTW is there a formal limit for the length
> of error lines ? 80 chars ?
> 

Not even sure it makes sense since the final error message contains the
full -device command line option which can be of arbitrary length...

> > Thanks,
> > Marcel
> > 
> > >       if (!(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_PCIE) &&
> > >           !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN)) {
> > >           pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;
> > >
> > >  
> > 
>