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Re: [virt-tools-list] virt-what detection on Citrix XenServer 5.5



On Fri, Aug 26, 2011 at 03:24:58PM +0100, Mark Phillips wrote:
> Hi,
> 
> Just been recommended to look at virt-what by Dom Cleal, after struggling with
> Facter/Puppet.
> 
> I've a RHEL (well, CentOS) 5.5 virtual running on Citrix XenServer 5.5.0 -
> virt-what reports the virtual as being on hyperv though:
> 
> [root jusbeta virt-what]# PATH=.:$PATH ./virt-what
> hyperv
> [root jusbeta virt-what]# ./virt-what-cpuid-helper 
> Microsoft Hv
> [root jusbeta virt-what]# dmidecode | egrep '(Vendor|Manufact|Product)'
>         Vendor: Xen
>         Manufacturer: Xen
>         Product Name: HVM domU
>         Manufacturer: Xen
>         Manufacturer: AMD
> 
> I can gather it's down to virt-what-cpuid-helper that this is the discovery,
> but not being a C coder I don't know why - I guess you guys probably do. 
> 
> If there's anything else I can provide that will help resolve this, please let
> me know.

Sadly this is a nice example of the hazards with detecting hypervisors,
rather than detecting features you actually want. IIUC, to make Windows
guests run better, Xen supports some of the Hyper-V paravirt ABIs, and
as such the Xen hypervisor may advertize itself as being Hyper-V. I
thought they only enables this for Windows guests though, so surprised
to see it for your RHEL guest, but its always possible they changed
to make the hyperv always be active.

If my hypothesis is correct, then virt-what is technically correct in
what it reports, while at the same time it is obviously wrong. Perhaps
virt-what has to report that it is both hyperv and xen...

You can get similar situation with KVM running Xenner, where CPUID would
show that the hypervisor is KVM and Xen at the same time :-)

Daniel
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