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

[Greg Kurz]

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>
Signed-off-by: Greg Kurz <address@hidden>
---
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;
+    }
+
     if (!(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_PCIE) &&
         !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN)) {
         pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;