[Qemu-devel] [PATCH v4] 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>
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))) {
+        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;