Re: [Qemu-devel] Questions on DeviceState and Virtio infrastructure

[Alexander Graf]

On 29.06.2011, at 15:59, Wei Liu <address@hidden> wrote:

> 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).

I'm not a huge fan of adding multiple different transports for virtio if we 
don't have to. IIRC Xen PV guests can do PCI device assignment, right? That 
means there is a PCI bus for them which we could reuse to run virtio-pci on.

By then, you'd get all the virtio code for free and don't have to worry about 
maintaining yet another transport (which _is_ cumbersome)

Alex

> 
> 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.
>