[Qemu-devel] [PATCH v3] 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>
---
v3: - rebased on top of:
    https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg04744.html
    - use virtio_pci_legacy/modern helpers
    - rephrased error message to be shorter and use the on/off logic

Marcel, this still results in > 80 char line in the code but I'd rather not
split it to ease grepping, nor shorten the message even more to keep it
meaningful.
---
 hw/virtio/virtio-pci.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 755f9218b77d..1f5f00a50a0b 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1842,6 +1842,11 @@ 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 disable-modern and 
disable-legacy are set to on.");
+        return;
+    }
+
     if (!(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_PCIE) &&
         virtio_pci_modern(proxy)) {
         pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;