[libvirt] Question about virtio-pci in Aarch64

[Kevin Zhao]

Yeah I see.
  In virt-manager ,aarch64 can realize hotplug by virtio-scsi .
  Thanks Cole ~

On Mon, 13 Jun 2016 at 22:07 Cole Robinson <crobinso at redhat.com> wrote:

> On 06/12/2016 10:08 PM, Kevin Zhao wrote:
> > Hi Cole,
> >      Thanks for your kindly help.
> >
> > On 13 June 2016 at 06:21, Cole Robinson <crobinso at redhat.com
> > <mailto:crobinso at redhat.com>> wrote:
> >
> >     On 06/12/2016 10:29 AM, Kevin Zhao wrote:
> >     > Hi Cole && All,
> >     >      Nice meeting you in the libvirt mail-list. Greetings from
> Linaro !!!
> >     >      I am Kevin Zhao from Linaro and working for OpenStack on
> Aarch64.
> >     > Nowadays I find that the default "virtio" bus is "virtio-mmio" ,
> not
> >     > "virtio-pci". Since virtio-mmio do not has the host plugged
> function ,
> >     > something is wrong with the function in OpenStack Nova.
> >     >
> >     >       Then I search and find some mail information as belows by
> Cole :-)
> >     >       1)
> https://www.redhat.com/archives/libvir-list/2015-December/msg00217.html
> >     >       2)
> https://www.redhat.com/archives/libvir-list/2016-March/msg00167.html
> >     >
> >     >        I see some efforts have been doing by you. Really thanks
> for your
> >     > efforts for Aarch64. And I have some small questions.
> >     >       1. Is Libvirt planning to replace the default virtio-mmio to
> virtio-pci
> >     > for Aarch64?
> >
> >     We have vague plans to maybe change the virtio-mmio default to
> virtio-pci at
> >     some future point, based on some new enough qemu machine type. But
> the main
> >     blocker is that most linux distributions currently don't work out of
> the box
> >     with virtio-pci, at least Fedora doesn't as far as I know. So
> changing the
> >     default now is pre-mature
> >
> > OK . Hope it will be true in the future.
> >
> >     >       2. If not , how can I change the xml file(generated by
> Virsh) for
> >     > virtio-pci  so that Qemu can recognize it ?
> >     >
> >
> >     The latest libvirt-1.3.5 release accepts device XML containing
> <address
> >     type='pci'/> . The address block is an explicit request to libvirt to
> >     'allocate a PCI address' rather than the default virtio-mmio. So for
> example
> >     if you want to specify a virtio nic, but have it use virtio-pci
> rather than
> >     virtio-mmio, you can do something like:
> >
> >         <interface type='network'>
> >           <source network='default'/>
> >           <model type='virtio'/>
> >           <address type='pci'/>
> >         </interface>
> >
> >     But there isn't currently any switch to say 'always give me
> virtio-pci instead
> >     of virtio-mmio'
> >
> > In my opinion, that is to say, when I want to attach a block device to a
> guest
> > and hope it
> > take effects soon,*the only way is using 'scsi' instead of 'virtio'* in
> > Aarch64 just like what
> > virt-manager does since scsi supports hot plugged. Am I right?
>
> On x86 at least virtio-blk + pci supports hotplug, but I don't know if that
> combo works for aarch64 at the moment. However disk=scsi hotplug should
> currently work on aarch64 with controller=virtio-scsi, I've tested that
> before
>
> Thanks,
> Cole
>
>
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