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

[Martin Kletzander]

On Wed, Sep 05, 2018 at 03:37:22PM +0100, Daniel P. Berrangé wrote:
>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.
>

I'm not against that <device id =''/> but it is going to take some effort to
properly specify what is really meant by that.  The fact that some device model
was chosen for a particular device does not necessarily mean that it is
requested as the default.  It only means what is actually encoded in the XML
already, that is a particular model for a particular device.

>Regards,
>Daniel
>-- 
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