+enum virtio_config_status {
+    VIRTIO_CONFIG_SUPPORT,
+    VIRTIO_CONFIG_WORK,
+    VIRTIO_CONFIG_STOP,
+    VIRTIO_CONFIG_STATUS_UNKNOWN,

Any reason for this extra state? I think we can know whether the config
interrupt is being used through a

Thanks

The problem is I need to split the backend devices into 3 types,
1） normal device
2）vdpa support config interrupt. and the configur interrupt is active now
3）vdpa not support config interrupt.
So I  add this bit and this bit will init in vpda /vhost modules and
qemu can check this bit to know the  which behariver we will do in
virtio bus  and other modules,

I wonder whether it's a must. We can setup guest notifiers unconditionally, so if it's an vhost bakcend without config interrupt support, such notifiers won't be used.

Thanks

 Maybe I need to change this bit's name
to make it more clearly

Thanks
Cindy