On Thu, 30 Jun 2011, Alexander Graf wrote: > On 06/30/2011 12:21 PM, Stefano Stabellini wrote: > > On Thu, 30 Jun 2011, Wei Liu wrote: > >> On Thu, Jun 30, 2011 at 4:31 PM, Alexander Graf<ag...@suse.de> wrote: > >>> On 29.06.2011, at 15:59, Wei Liu<l...@liuw.name> 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. > > What's keeping us from doing so? Doesn't MMIO emulation work with Xen PV?
No, it does not. The only realistic way that I can see to make virtio work with PV guests is to write "virtio-xenstore".
