[Qemu-devel] Questions on DeviceState and Virtio infrastructure

[Wei Liu <liuw@liuw.name>]

Hi, QEMU folks

I know that I might have a bad title for this post, but I just don't
have better idea for the title.

I'm developing virtio support for Xen pv guest, hoping to reuse the
virtio infrastructure in qemu, i.e. I'm planning to use qemu as
"virtio backend" for Xen pv. And qemu can be run as pv backend if
proper "machine" option is given.

Maybe you've known that Xen pv guest utilizes Xenbus/Xenstore to
configure its paravirt devices. So I'm to configure virtio devices
with Xenbus/Xenstore as well. But in nowdays XenDevice in qemu does
not include a DeviceState. To my understanding, it is not connected to
qemu's internal buses or whatever (correct me if I'm wrong, I'm
relatively new to qemu).

Here is the problem, say I'm to implement virtio nic for Xen pv guest,
I use Xenbus to probe and initialize the device. When doing
initialization, I am to reuse virtio_net_init, which takes DeviceState
as the first argument -- but I just don't have one in XenDevice. All I
need is to use qemu's virtio infrastructure.

What's the purpose of this DeviceState argument?

If I just construct my own DeviceState and pass it to virtio_net_init,
what will happen? Will qemu emulates virtio nic as usual?

Thanks.

Wei.