Re: [Qemu-block] [Qemu-devel] storing machine data in qcow images?

[Richard W.M. Jones]

On Tue, May 29, 2018 at 11:14:11AM -0300, Eduardo Habkost wrote:
> On Tue, May 29, 2018 at 03:03:16PM +0100, Dr. David Alan Gilbert wrote:
> > * Richard W.M. Jones (address@hidden) wrote:
> > > On Fri, May 18, 2018 at 06:09:56PM +0100, Daniel P. Berrangé wrote:
> > > > The closest to a cross-hypervisor standard is OVF which can store
> > > > metadata about required hardware for a VM. I'm pretty sure it does
> > > > not have the concept of machine types, but maybe it has a way for
> > > > people to define metadata extensions. Since it is just XML at the
> > > > end of the day, even if there was nothing official in OVF, it would
> > > > be possible to just define a custom XML namespace and declare a
> > > > schema for that to follow.
> > > 
> > > I have a great deal of experience with the OVF "standard".
> > > TL;DR: DO NOT USE IT.
> > 
> > In addition to the detail below, from reading DMTF's OVF spec (DSP0243 v
> > 2.1.1) I see absolutely nothing specifying hardware type.
> > Sure it can specify size of storage, number of ether cards, MAC
> > addresses for them etc - but I don't see any where specify the type of 
> > emualted system.
> 
> Maybe the VirtualHardwareSection/System/vssd:VirtualSystemType
> element could be used for that.  (DSP0243 v2.1.1, line 650).
> 
> But based on Richard's feedback, I think we shouldn't even try to
> use it.

Yes, save yourself time and worry by avoiding OVF altogether.

Note that in any case you need something quite different from any
existing metadata format.  Most guests will support a variety of
driver models (eg. pc or q35, sata or virtio-blk or virtio-scsi, ...).

You need to express what device drivers are installed in the guest,
(separately for boot and running) and then the management layer needs
to match the devices the hypervisor can emulate with the required
devices, select the best performing ones in each class, and present
those to the guest.

As far as I know, there is no existing metadata format which expresses
this.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html