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

[Cornelia Huck <cornelia.huck@de.ibm.com>]

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.

> +        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;
>