[libvirt] Is possible that cpu_maps.xml changed during different releases?

[Jiang, Yunhong]

Any idea on my assumed scenario?
If this is really an issue, it's something we need fix it IMHO.

Thanks
--jyh

> -----Original Message-----
> From: Jiang, Yunhong
> Sent: Friday, November 02, 2012 4:52 PM
> To: Eric Blake
> Cc: libvir-list at redhat.com
> Subject: RE: [libvirt] Is possible that cpu_maps.xml changed during different
> releases?
> 
> One question come to my mind for "but such changes will only be additive",
> which may be an issue in cloud environment:
> 
> Considering following assumed situation:
> 	In release 1.0's cpu_maps.xml, core2duo include feature "a, b, c"
> 	In release 1.1's cpu_maps.xml, core2duo include "a, b, c, d"
> 	Two hosts, with different CPU features:
> 	Host A with feature "a, b, c, d, e" and 1.1 release, capabilities will be:
> 		Model: Core2duo (assume core2duo is the only match one)
> 		Features: e
> 	Host B with feature "a, b, c, e", and 1.0 release, capabilities will be:
> 		Models: Core2Duo (again, assume core2duo is the only match one)
> 		Features: e
> 
> 	When we compare the capabilities in Host A, I think comparCPU will pass,
> because host A will use 1.1 release definition to check Host B's capabilities, this
> is sure to be wrong, since host B does not have feature 'd'.
> 
> 	I think the key point is, capabilities describe features with information
> from cpu_maps.xml, which is a per-host file.
> 
> Thanks
> --jyh
> 
> 
> Will depends on
> > -----Original Message-----
> > From: Jiang, Yunhong
> > Sent: Friday, November 02, 2012 9:39 AM
> > To: Eric Blake
> > Cc: libvir-list at redhat.com
> > Subject: RE: [libvirt] Is possible that cpu_maps.xml changed during different
> > releases?
> >
> > Eric, thanks for the answer very .much, that's really helpful.
> > Sorry for the wrong format, I'm using outlook and possibly some setting
> wrong.
> >
> > Thanks
> > --jyh
> >
> > > -----Original Message-----
> > > From: Eric Blake [mailto:eblake at redhat.com]
> > > Sent: Thursday, November 01, 2012 11:23 PM
> > > To: Jiang, Yunhong
> > > Cc: libvir-list at redhat.com
> > > Subject: Re: [libvirt] Is possible that cpu_maps.xml changed during
> > > different releases?
> > >
> > > On 10/31/2012 02:20 AM, Jiang, Yunhong wrote:
> > > > Hi, all
> > >
> > > [your mailer doesn't know how to wrap long lines, which makes it
> > > awkward to read your message]
> > >
> > > > 	I have two questions to the cpu_maps.xml in different releases,
> > > > hope
> > > someone can give me some hints:
> > > >
> > > > 	a) Will it be possible that the features defined in cpu_maps.xml
> > > > for one
> > > specific CPU model (like Nehalem) will be different? For example, one
> > > feature is not listed for Nehalem in release x.y, and added in release x.y+1?
> > >
> > > XML does have the possibility to change between releases, but such
> > > changes will only be additive (we will never remove support for a
> > > feature once it is listed).
> > >
> > > >
> > > > 	2) Is the format of the cpu_maps.xml fine defined or will be it
> > > > changed
> > > during releases? I asked this because currently the features defined
> > > in the capabilities only list features not included in the definition
> > > in cpu_maps.xml for the corresponding model. So if I want to get the
> > > full features supported by the host, I have to parse the capabilities
> > > and the cpu_maps.xml. I didn't find the definition for cpu_maps.xml
> > > format, although the capabilities format is well defined in
> > > http://libvirt.org/guide/html/Application_Development_Guide-Connection
> > > s-Ca
> > > pability_Info.html.
> > >
> > > The format should be well-defined; again, our requirement is that
> > > upgrades might add new xml attributes or elements, but will never
> > > remove elements that have been valid in previous releases.  To some
> > > extent, docs/schemas/capability.rng in libvirt.git gives an RNG
> > > grammar for what capabilities will look like, although someone else
> > > may be able to point to a better documentation of what will be in
> > cpu_maps.xml.
> > >
> > > --
> > > Eric Blake   eblake at redhat.com    +1-919-301-3266
> > > Libvirt virtualization library http://libvirt.org