[RFC PATCH 2/6] vdpa: add should_enable op

[Eugenio Pérez]

To restore the device at the destination of a live migration we send the
commands through control virtqueue.  For a device to read CVQ it must
have received the DRIVER_OK status bit.

However this opens a window where the device could start receiving
packets in rx queue 0 before it receives the RSS configuration.  To
avoid that, we will not send vring_enable until all configuration is
used by the device.

As a first step, enable a new vitio ops per vhost_vdpa device to know if
we should enable a virtqueue or not.  This srtuct can be reused in the
future to add more actions to vhost_vdpa that depend on the virtIO kind
of device.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 include/hw/virtio/vhost-vdpa.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/hw/virtio/vhost-vdpa.h b/include/hw/virtio/vhost-vdpa.h
index 5407d54fd7..3d330d439a 100644
--- a/include/hw/virtio/vhost-vdpa.h
+++ b/include/hw/virtio/vhost-vdpa.h
@@ -30,6 +30,13 @@ typedef struct VhostVDPAHostNotifier {
     void *addr;
 } VhostVDPAHostNotifier;
 
+struct vhost_vdpa;
+typedef bool (*vhost_vdpa_virtio_should_enable_op)(const struct vhost_vdpa *v);
+
+typedef struct VhostVDPAVirtIOOps {
+    vhost_vdpa_virtio_should_enable_op should_enable;
+} VhostVDPAVirtIOOps;
+
 typedef struct vhost_vdpa {
     int device_fd;
     int index;
@@ -48,6 +55,7 @@ typedef struct vhost_vdpa {
     VhostIOVATree *iova_tree;
     GPtrArray *shadow_vqs;
     const VhostShadowVirtqueueOps *shadow_vq_ops;
+    const VhostVDPAVirtIOOps *virtio_ops;
     void *shadow_vq_ops_opaque;
     struct vhost_dev *dev;
     Error *migration_blocker;
-- 
2.39.3