libvirt users - Oct 2016 - Re: Libvirt adds extra parameters in domain XML

On Mon, Oct 17, 2016 at 02:29:10PM +0200, Marina Danial
wrote:
>I have a predetermined set of commands that I want to launch qemu with:
>
>sudo `which qemu-system-x86_64` -m 4G $(IMAGE) -enable-kvm \
>-nographic \
>-net nic,model=virtio,netdev=net0,macaddr=$(MAC),vlan=0 \
>-netdev tap,id=net0,ifname=tap01,vhost=on,script=no,downscript=no \
>-net nic,model=virtio,netdev=net1,macaddr=$(MANAGE_MAC),vlan=1 \
>-netdev tap,id=net1,ifname=tap02,vhost=on,script=no,downscript=no \
>
>I dont need any extra configuration from libvirt. is this possible? Or can
>anyone help with a possible xml configuration ?
>
Why do you need libvirt, then?  If you need something from libvirt,
we'll need to add some things.  But if you don't need libvirt, then you
can just run that command.  Maybe I'm missing something.
>
>
>On Thu, Oct 13, 2016 at 1:13 PM, Martin Kletzander
<mkletzan@redhat.com>
>wrote:
>
>> On Thu, Oct 13, 2016 at 11:49:44AM +0200, Marina Danial wrote:
>>
>>> Hello,
>>>
>>> In my C++ code, I generate my own domain XML file and I
>>> use virDomainCreateXML or virDomainDefineXML to launch my qemu VM.
>>> However,
>>> when I get to check which commands are sent to the qemu
commandline, I
>>> find
>>> that libvirt has added so many extra parameters to the ones I have
already
>>> set. How can I prevent libvirt from adding any extra parameters to
the
>>> ones
>>> I originally defined in the domain XML?
>>>
>>>
>> What problems are you having with those?  What specific ones are
>> problematic for you?  Libvirt adds a lot of things so that the domain
is
>> predictable, it can talk to it later on and so on.  Some of them are
>> adding the same things you would have there without -no-defconfig and
>> similar.  Just so we can guarantee some compatibility etc.
>>
>> Help will be highly appreciated.
>>>
>>>
>>> Thanks
>>>
>>
>> _______________________________________________
>>> libvirt-users mailing list
>>> libvirt-users@redhat.com
>>> https://www.redhat.com/mailman/listinfo/libvirt-users
>>>
>>

I need write the domain XML in libvirt to eventually convert it into these
qemu commands.. I don't want to call qemu directly with these commands. So
I needed assistance with that

On Oct 17, 2016 9:34 PM, "Martin Kletzander"
<mkletzan@redhat.com> wrote:
> On Mon, Oct 17, 2016 at 02:29:10PM +0200, Marina Danial wrote:
>
>> I have a predetermined set of commands that I want to launch qemu with:
>>
>> sudo `which qemu-system-x86_64` -m 4G $(IMAGE) -enable-kvm \
>> -nographic \
>> -net nic,model=virtio,netdev=net0,macaddr=$(MAC),vlan=0 \
>> -netdev tap,id=net0,ifname=tap01,vhost=on,script=no,downscript=no \
>> -net nic,model=virtio,netdev=net1,macaddr=$(MANAGE_MAC),vlan=1 \
>> -netdev tap,id=net1,ifname=tap02,vhost=on,script=no,downscript=no \
>>
>> I dont need any extra configuration from libvirt. is this possible? Or
can
>> anyone help with a possible xml configuration ?
>>
>>
> Why do you need libvirt, then?  If you need something from libvirt,
> we'll need to add some things.  But if you don't need libvirt, then
you
> can just run that command.  Maybe I'm missing something.
>
>
>>
>> On Thu, Oct 13, 2016 at 1:13 PM, Martin Kletzander
<mkletzan@redhat.com>
>> wrote:
>>
>> On Thu, Oct 13, 2016 at 11:49:44AM +0200, Marina Danial wrote:
>>>
>>> Hello,
>>>>
>>>> In my C++ code, I generate my own domain XML file and I
>>>> use virDomainCreateXML or virDomainDefineXML to launch my qemu
VM.
>>>> However,
>>>> when I get to check which commands are sent to the qemu
commandline, I
>>>> find
>>>> that libvirt has added so many extra parameters to the ones I
have
>>>> already
>>>> set. How can I prevent libvirt from adding any extra parameters
to the
>>>> ones
>>>> I originally defined in the domain XML?
>>>>
>>>>
>>>> What problems are you having with those?  What specific ones
are
>>> problematic for you?  Libvirt adds a lot of things so that the
domain is
>>> predictable, it can talk to it later on and so on.  Some of them
are
>>> adding the same things you would have there without -no-defconfig
and
>>> similar.  Just so we can guarantee some compatibility etc.
>>>
>>> Help will be highly appreciated.
>>>
>>>>
>>>>
>>>> Thanks
>>>>
>>>>
>>> _______________________________________________
>>>
>>>> libvirt-users mailing list
>>>> libvirt-users@redhat.com
>>>> https://www.redhat.com/mailman/listinfo/libvirt-users
>>>>
>>>>
>>>

On Mon, 2016-10-17 at 21:37 +0200, Marina Danial wrote:
> I need write the domain XML in libvirt to eventually convert
> it into these qemu commands.. I don't want to call qemu
> directly with these commands. So I needed assistance with
> that
If you're dead set on executing QEMU with those options,
and *only* those options, then libvirt is quite simply
not the tool you're looking for.

When you use libvirt, by definition you're giving up
fine-grained control of the specific options passed to
the underlying hypervisor and trust libvirt to translate
an high-level virtual hardware definition (guest XML)
into an appropriate QEMU command line.

Just to give you an example of why libvirt will never be
able to build exactly the command line you provided, we
rely on the QEMU monitor to eg. perform device hotplug,
so you will never see a QEMU process spawned by libvirt
that lacks the '-mon' option.

So your options are basically:

  1) switch to libvirt and accept the fact that your QEMU
     command lines will be quite a bit more verbose than
     they currently are

  2) keep spawning QEMU processes with hand-crafted
     command lines

I would of course recommend going for 1), as that will
allow you to use all of libvirt's features down the line,
when it eventually turns out you need them ;)

-- 
Andrea Bolognani / Red Hat / Virtualization