libvirt users - Oct 2018 - Re: How to explain this libvirt oddity w.r.t machine types?

On Sun, Oct 14, 2018 at 02:28:07PM +0200, Andrea Bolognani
wrote:
> On Fri, 2018-10-12 at 22:38 +0200, Kashyap Chamarthy wrote:
[...]
> > Now check the machine type again.  Bizarrely enough, libvirt
"helpfully"
> > auto-adds QEMU *2.11* machine type, which is obviously no longer on
the
> > system!
> > 
> >     # grep machine= /etc/libvirt/qemu/cirros.xml
> >     <type arch='x86_64'
machine='pc-i440fx-2.11'>hvm</type>
> > 
> >     # virsh dumpxml cirros | grep -i machine> >     <type
arch='x86_64' machine='pc-i440fx-2.11'>hvm</type>
> > 
> > How to explain this?  Is this even a "valid test"?
> > 
> > (To undo the nuisance, obviously, I had to `virsh edit cirros` again
and
> > change it to 2.10.)
> > 
> > Note, I *don't* have 2.11 QEMU on the system:
[...]
> If I had to guess, I would say the <emulator> element of your guest
> is probably pointing to a custom-built QEMU 2.11 binary rather than
> the default one installed from RPMs.
Your guess made me curious enough to check the remote machine one last
time before I went to sleep, but unfortunately the <emulator> element is
pointing to the plain `/usr/bin/qemu-kvm`, which in turn exec()'s
`/usr/bin/qemu-system-x86_64`.

(I attached the nothing-special, full guest XML.)


-- 
/kashyap

On Mon, 2018-10-15 at 08:21 +0200, Kashyap Chamarthy
wrote:
> On Sun, Oct 14, 2018 at 02:28:07PM +0200, Andrea Bolognani wrote:
> > If I had to guess, I would say the <emulator> element of your
guest
> > is probably pointing to a custom-built QEMU 2.11 binary rather than
> > the default one installed from RPMs.
> 
> Your guess made me curious enough to check the remote machine one last
> time before I went to sleep, but unfortunately the <emulator> element
is
> pointing to the plain `/usr/bin/qemu-kvm`, which in turn exec()'s
> `/usr/bin/qemu-system-x86_64`.
> 
> (I attached the nothing-special, full guest XML.)
Interesting. What is the output of 'virsh capabilities'?

More interesting still is the fact that the guest XML you shared
looks like an *active* XML, ie. one taken from a running guest...
Does that mean the guest can start even though it's using the 2.11
machine type?

-- 
Andrea Bolognani / Red Hat / Virtualization

On Mon, Oct 15, 2018 at 09:05:16AM +0200, Andrea Bolognani wrote:

[...]
> Interesting. What is the output of 'virsh capabilities'?
In attachment.
> More interesting still is the fact that the guest XML you shared
> looks like an *active* XML, ie. one taken from a running guest...
> Does that mean the guest can start even though it's using the 2.11
> machine type?
No, of course it doesn't; the guest is running because I `virsh-edit`ed
it to use 2.10 machine type :-)

-- 
/kashyap