libvirt users - Apr 2015 - Re: <qemu:commandline> domain XML tag is not working?

Hi,

I tried to enable virtio-blk data plane feature for VMs in my openstack
environment,  the hypervisor is ubuntu 14.04, libvirt 1.2.2 and QEMU 2.0.
As nova doesn't support that parameter yet, I did belows

1. nova boot a VM with raw disk image.
2. nova stop the VM.
3. run "virsh edit <instance-id>" on the hyprvisor node, and
adding below
into instance xml just before </domain>.

However, the <qemu:commandline> part is ignored and not saved after
closing
virsh edit, seems that libvirt rejected these changes. Is there any XML
syntax error here? Or libvirt doesn't support <qemu:commandline> tag?

<qemu:commandline>
    <qemu:arg value='-set'/>
    <qemu:arg value='device.drive-virtio-disk0.x-data-plane=on'/>
</qemu:commandline>


Regards,
Chengyuan.

On Mon, Apr 20, 2015 at 10:37:13PM +0800, Chengyuan Li
wrote:
> Hi,
> 
> I tried to enable virtio-blk data plane feature for VMs in my openstack
> environment,  the hypervisor is ubuntu 14.04, libvirt 1.2.2 
[I haven't tested the virtio-blk data plane myself.]

This libvirt version seems a little old (from March 2014), you might
want to move to a bit newer.
> and QEMU 2.0.
> As nova doesn't support that parameter yet, I did belows
> 
> 1. nova boot a VM with raw disk image.
> 2. nova stop the VM.
> 3. run "virsh edit <instance-id>" on the hyprvisor node,
and adding below
> into instance xml just before </domain>.
You're modifying the guest definition behind Nova's back, so you get to
keep all the pieces if something breaks. :-)
> However, the <qemu:commandline> part is ignored and not saved after
closing
> virsh edit, seems that libvirt rejected these changes. Is there any XML
> syntax error here? Or libvirt doesn't support <qemu:commandline>
tag?
> 
> <qemu:commandline>
>     <qemu:arg value='-set'/>
>     <qemu:arg
value='device.drive-virtio-disk0.x-data-plane=on'/>
> </qemu:commandline>
 
-- 
/kashyap

On 04/20/2015 08:37 AM, Chengyuan Li wrote:
> Hi,
> 
> I tried to enable virtio-blk data plane feature for VMs in my openstack
> environment,  the hypervisor is ubuntu 14.04, libvirt 1.2.2 and QEMU 2.0.
> As nova doesn't support that parameter yet, I did belows
> 
> 1. nova boot a VM with raw disk image.
> 2. nova stop the VM.
> 3. run "virsh edit <instance-id>" on the hyprvisor node,
and adding below
> into instance xml just before </domain>.
> 
> However, the <qemu:commandline> part is ignored and not saved after
closing
> virsh edit, seems that libvirt rejected these changes. Is there any XML
> syntax error here? Or libvirt doesn't support <qemu:commandline>
tag?
If XML changes disappear after virsh edit, then it is a case of you
using XML that wasn't recognized by libvirt.
> 
> <qemu:commandline>
>     <qemu:arg value='-set'/>
>     <qemu:arg
value='device.drive-virtio-disk0.x-data-plane=on'/>
> </qemu:commandline>
Did you also remember to declare the namespace? Per
http://libvirt.org/drvqemu.html#qemucommand

it is essential to have something like:

<domain type='qemu'
xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>

before any other <qemu:...> will be recognized.  (The namespace does not
have to be named 'qemu:', but it makes it easier to stick to the naming
used by the examples)

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Hi Eric,

Thanks!
You are right, I missed declaring namespace, now, the <qemu:commandline>
is
saved after virsh edit.
However, both namespace and  <qemu:commandline> tag are lost after I run
"nova start" to launch the VM.
Any idea that how could I make this qemu command take effect ?

Regards,
CY.

On Mon, Apr 20, 2015 at 11:41 PM, Eric Blake <eblake@redhat.com> wrote:
> On 04/20/2015 08:37 AM, Chengyuan Li wrote:
> > Hi,
> >
> > I tried to enable virtio-blk data plane feature for VMs in my
openstack
> > environment,  the hypervisor is ubuntu 14.04, libvirt 1.2.2 and QEMU
2.0.
> > As nova doesn't support that parameter yet, I did belows
> >
> > 1. nova boot a VM with raw disk image.
> > 2. nova stop the VM.
> > 3. run "virsh edit <instance-id>" on the hyprvisor
node, and adding below
> > into instance xml just before </domain>.
> >
> > However, the <qemu:commandline> part is ignored and not saved
after
> closing
> > virsh edit, seems that libvirt rejected these changes. Is there any
XML
> > syntax error here? Or libvirt doesn't support
<qemu:commandline> tag?
>
> If XML changes disappear after virsh edit, then it is a case of you
> using XML that wasn't recognized by libvirt.
>
> >
> > <qemu:commandline>
> >     <qemu:arg value='-set'/>
> >     <qemu:arg
value='device.drive-virtio-disk0.x-data-plane=on'/>
> > </qemu:commandline>
>
> Did you also remember to declare the namespace? Per
> http://libvirt.org/drvqemu.html#qemucommand
>
> it is essential to have something like:
>
> <domain type='qemu'
xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0
> '>
>
> before any other <qemu:...> will be recognized.  (The namespace does
not
> have to be named 'qemu:', but it makes it easier to stick to the
naming
> used by the examples)
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>

Hi Kashyap,

Here I want to test and see how much I/O performance could be improved by
virtio-blk data plane feature.
Yes, this is a dirty way to enable it :-), You mentioned using newer
libvirt, is there parameter similar "x-data-plane=on" in new version
libvirt?
Please let know me you if you have better solution.



Regards,
CY.

On Mon, Apr 20, 2015 at 10:51 PM, Kashyap Chamarthy <kchamart@redhat.com>
wrote:
> On Mon, Apr 20, 2015 at 10:37:13PM +0800, Chengyuan Li wrote:
> > Hi,
> >
> > I tried to enable virtio-blk data plane feature for VMs in my
openstack
> > environment,  the hypervisor is ubuntu 14.04, libvirt 1.2.2
>
> [I haven't tested the virtio-blk data plane myself.]
>
> This libvirt version seems a little old (from March 2014), you might
> want to move to a bit newer.
>
> > and QEMU 2.0.
> > As nova doesn't support that parameter yet, I did belows
> >
> > 1. nova boot a VM with raw disk image.
> > 2. nova stop the VM.
> > 3. run "virsh edit <instance-id>" on the hyprvisor
node, and adding below
> > into instance xml just before </domain>.
>
> You're modifying the guest definition behind Nova's back, so you
get to
> keep all the pieces if something breaks. :-)
>
> > However, the <qemu:commandline> part is ignored and not saved
after
> closing
> > virsh edit, seems that libvirt rejected these changes. Is there any
XML
> > syntax error here? Or libvirt doesn't support
<qemu:commandline> tag?
> >
> > <qemu:commandline>
> >     <qemu:arg value='-set'/>
> >     <qemu:arg
value='device.drive-virtio-disk0.x-data-plane=on'/>
> > </qemu:commandline>
>
>
> --
> /kashyap
>