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 12:32:24 +0200
Cornelia Huck <cornelia.huck@de.ibm.com> wrote:

> On Fri, 22 Jul 2016 12:11:11 +0200
> Greg Kurz <groug@kaod.org> wrote:
> 
> > 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().  
> 
> I don't know, I'd find that a bit surprising, especially as I would end
> up with a legacy-capable device if I did not specify anything in
> the !pcie case.
> 

Isn't it already what happens with legacy being the default in pre-2.7 QEMU ?

Do you think we should have separate checks for pcie and !pcie ?

> >   
> > > > +        error_setg(errp, "device cannot work when both modern and legacy modes"
> > > > +                   " are disabled");  
> 
> Suggest to change this wording to:
> 
> "device cannot work as neither modern nor legacy mode is enabled"
> 
> as this more accurately reflects what happened (the user did not
> actively disable legacy in the case above).
> 

Thanks ! This is THE wording I was looking for :)

> > > > +        error_append_hint(errp, "Set either disable-modern or disable-legacy"
> > > > +                          " to off\n");  
> 
> The hint looks fine to me :)
> 

It was the easy part :)

> > > > +        return;
> > > > +    }
> > > > +
> > > >      if (!(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_PCIE) &&
> > > >          virtio_pci_modern(proxy)) {
> > > >          pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;
> > > >     
> > >   
> >   
> 
>