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

[Cornelia Huck]

On Fri, 22 Jul 2016 15:23:19 +0200
Greg Kurz <address@hidden> wrote:

> On Fri, 22 Jul 2016 12:32:24 +0200
> Cornelia Huck <address@hidden> wrote:
> 
> > On Fri, 22 Jul 2016 12:11:11 +0200
> > Greg Kurz <address@hidden> wrote:
> > 
> > > On Fri, 22 Jul 2016 10:04:35 +0200
> > > Cornelia Huck <address@hidden> wrote:
> > >   
> > > > On Thu, 21 Jul 2016 23:21:16 +0200
> > > > Greg Kurz <address@hidden> wrote:
> > > >   
> > > > > From: Greg Kurz <address@hidden>
> > > > > 
> > > > > 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 <address@hidden>
> > > > > Reviewed-by: Marcel Apfelbaum <address@hidden>
> > > > > Signed-off-by: Greg Kurz <address@hidden>
> > > > > ---
> > > > > 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 ?

Well, that is exactly my point; users may be surprised.

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

I don't think we should overengineer this.

> 
> > >   
> > > > > +        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 :)

:)

I'm fine with the patch with the changed wording, as it less confusing
for the user.

<I'll be offline next week so please just attach my

Reviewed-by: Cornelia Huck <address@hidden>

if the only thing you change is the message>