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From: Markus Armbruster <armbru@redhat.com>
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Date: Thu, 08 Sep 2016 09:15:28 +0200
In-Reply-To: <147326877255.8546.8636563472418354481.stgit@bahia.lan> (Greg
	Kurz's message of "Wed, 07 Sep 2016 19:19:32 +0200")
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Subject: Re: [Qemu-devel] [PATCH 2/2] virtio-pci: error out when both legacy
 and modern modes are disabled
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To: Greg Kurz <groug@kaod.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

Greg Kurz <groug@kaod.org> writes:

> 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>
> Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
>  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 268fd8ebb219..4b6a8a356621 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))) {
> +        error_setg(errp, "device cannot work as neither modern nor legacy mode"
> +                   " is enabled");
> +        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;

Pardon my ignorance... is this a device-specific restriction, or is it
the same for more (all?) virtio devices?