[PATCH] virtio-balloon-pci: Allow setting nvectors, so we can use MSI-X

[Reza Arbab]

Most virtio-pci devices allow MSI-X. Add it to virtio-balloon-pci, but
only enable it in new machine types, so we don't break migration of
existing machine types between different qemu versions.

This copies what was done for virtio-rng-pci in:
9ea02e8f1306 ("virtio-rng-pci: Allow setting nvectors, so we can use MSI-X")
bad9c5a5166f ("virtio-rng-pci: fix migration compat for vectors")
62bdb8871512 ("virtio-rng-pci: fix transitional migration compat for vectors")

Signed-off-by: Reza Arbab <ar...@linux.ibm.com>
---
 hw/core/machine.c              |  6 +++++-
 hw/virtio/virtio-balloon-pci.c | 13 +++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index e6900b43efa2..db59c7771ec4 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -36,7 +36,11 @@
 #include "hw/virtio/virtio-iommu.h"
 #include "audio/audio.h"
 
-GlobalProperty hw_compat_9_2[] = {};
+GlobalProperty hw_compat_9_2[] = {
+    { "virtio-balloon-pci", "vectors", "0" },
+    { "virtio-balloon-pci-transitional", "vectors", "0" },
+    { "virtio-balloon-pci-non-transitional", "vectors", "0" },
+};
 const size_t hw_compat_9_2_len = G_N_ELEMENTS(hw_compat_9_2);
 
 GlobalProperty hw_compat_9_1[] = {
diff --git a/hw/virtio/virtio-balloon-pci.c b/hw/virtio/virtio-balloon-pci.c
index ce2645ba7187..1c2b071eff0c 100644
--- a/hw/virtio/virtio-balloon-pci.c
+++ b/hw/virtio/virtio-balloon-pci.c
@@ -35,11 +35,23 @@ struct VirtIOBalloonPCI {
     VirtIOBalloon vdev;
 };
 
+static Property virtio_balloon_properties[] = {
+    DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
+    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
+                       DEV_NVECTORS_UNSPECIFIED),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void virtio_balloon_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
 {
     VirtIOBalloonPCI *dev = VIRTIO_BALLOON_PCI(vpci_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
 
+    if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
+        vpci_dev->nvectors = 2;
+    }
+
     vpci_dev->class_code = PCI_CLASS_OTHERS;
     qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
 }
@@ -55,6 +67,7 @@ static void virtio_balloon_pci_class_init(ObjectClass *klass, 
void *data)
     pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_BALLOON;
     pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
     pcidev_k->class_id = PCI_CLASS_OTHERS;
+    device_class_set_props(dc, virtio_balloon_properties);
 }
 
 static void virtio_balloon_pci_instance_init(Object *obj)

base-commit: ca80a5d026a280762e0772615f1988db542b3ade
-- 
2.47.1