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

[Stefano Stabellini]

On Thu, 30 Jun 2011, Wei Liu wrote:
> On Thu, Jun 30, 2011 at 4:31 PM, Alexander Graf <address@hidden> wrote:
> >
> > 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)
> >
> 
> Good point, I will check this.
> 
> I thought that Xen pv pci assignment is only used for pci passthrough.
> But I will check the possibility to assign pv backend to guest.
> 
> Stefano, how would you say about this?
 
Yes, the PCI bus is an empty PCI bus created by xen-pcifront and it is
only used for PCI passthrough. It couldn't be used as is for virtio-pci.