KVM : Virtio ring size

Hi all,

I was experimenting on Virtio-net frontend driver. And I observed that the virtio ring size is communicated to guest as 256 from the qemu-backend.
I tried changing backend-qemu code manually, to propagate 512 as ring size. It worked fine.

But I was wondering if there is another sophisticated mechanism to change the ring size.
Other than changing backend code and hard-coding, Is there anyway to configure the virtio ring size ?

Thanks in advance.