Dave Scott's added support for a low-bandwidth channel into XL with the intention of reusing virtio-rng (and virtio-serial and friends). http://lists.xen.org/archives/html/xen-devel/2014-06/msg0293...

On the other hand, I disagree that we're reinventing an ABI given that:

1) virtio isn't the supported PV interface in Xen -- rndfront/back follows the same design principles as net/blk/fb/usb/pci/console etc.

2) The Xen shared-ring interface is older than virtio, and much simpler for pure PV guests such as Mirage (no PCI emulation to worry about). I do wonder what happened to that GSoC project from a few years to add virtio support to Xen though...I don't think any patches ever appeared.