[Libosinfo] [libvirt] domain XML for tracking libosinfo ID

[Daniel P. Berrangé]

On Wed, Sep 05, 2018 at 02:01:42PM +0200, Martin Kletzander wrote:
> On Wed, Sep 05, 2018 at 09:28:52AM +0100, Daniel P. Berrangé wrote:
> > On Tue, Sep 04, 2018 at 03:44:12PM -0400, Cole Robinson wrote:
> > > Right now in virt-manager we only track a VM's OS name (win10, fedora28,
> > > etc.) during the VM install phase. This piece of data is important
> > > post-install though: if the user adds a new disk to the VM later, we want to
> > > be able to ask libosinfo about what devices the installed OS supports, so we
> > > can set optimal defaults, like enabling virtio.
> > > 
> > > There isn't any standard libvirt XML field to track this kind of info
> > > though, so apps have to invent their own schema. nova and rhev do it
> > > indirectly AFAICT. gnome-boxes does it directly with XML like this:
> > > 
> > >   <metadata>
> > >     <boxes:gnome-boxes xmlns:boxes="https://wiki.gnome.org/Apps/Boxes">
> > >       <os-id>http://fedoraproject.org/fedora/28</os-id>
> > >       ....
> > >     </boxes:gnome-boxes>
> > >   </metadata>
> > > 
> > > I want to add something similar to virt-manager but it seems a shame to
> > > invent our own private schema for something that most non-trivial virt apps
> > > will want to know about. I was thinking a schema we could document with
> > > libosinfo, something like
> > > 
> > > <metadata>
> > >   <libosinfo
> > > xmlns:libosinfo="http://libosinfo.org/xmlns/libvirt/domain/1.0">
> > >     <os-id>http://fedoraproject.org/fedora/28</os-id>
> > >   </libosinfo>
> > > </metadata>
> > 
> > Yes, I would like to see this standardized under <matadata>.
> > 
> 
> Me too and what Cole suggested looks fine.

It occurs to me that we actually need more than just the os-id value.

When you query devices for a given OS, you'll often be told that multiple
devices are compatible, and the mgmt app can decide which of them to then
use.

So if we want consistency when later hotplugging, we should make a record
of which devices we decided to use too, so if the mgmt app changes its
preference, we still know what we originally picked.

eg to express that we use virtio-net and virtio-blk (even if virtio-scsi
was supported by the OS):

   <metadata>
     <libosinfo xmlns:libosinfo="http://libosinfo.org/xmlns/libvirt/domain/1.0">
       <os id="http://fedoraproject.org/fedora/28"/>
       <device id="http://pcisig.com/pci/1af4/1000"/>
       <device id="http://pcisig.com/pci/1af4/1001"/>
     </libosinfo>
   </metadata>

Note, I'm suggesting using an 'id' attribute, rather than naming the
element 'os-id', to be more closely aligned with osinfo schema.

Regards,
Daniel
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