libvirt users - Nov 2014 - Re: Is there a way to disable libvirt qemu monitor while creating kvm vm using virsh?

Hi Kashyap,

Thanks for the reply. 
>> 
>> Now for some reason, I need to add “ -qmp tcp:127.0.0.1:1235” when
>> creating a KVM VM using libvirt.
> 
> You might need to elaborate how exactly you're doing this.
I wanted to add “-qmp tcp:127.0.0.1:1235” when creating VM because I was using a
multi-level debugger which needs this option to get more information of the VM
kernel debuginfo and the processes running inside the VM besides gdb attach.
> 
>> This command meaning in “qemu-kvm --help” is: -qmp dev        like
>> -monitor but opens in 'control' mode.
> 
> The above is used if you want to explicitly control a running QEMU
> instance via QMP, e.g. manually issue them QMP commands via telnet(1)
> for development/testing/debugging.
This is exactly what I need - for debugging. Is there a way to achieve this
while still using the default monitor libvirt provides?
> 
>> I added command-line equivalent options into the xml file, like below
>> format:
>> 
>>  <qemu:commandline> <qemu:arg value="-s"/>
<qemu:arg value="-qmp"/>
>>  <qemu:arg value="tcp:127.0.0.1:1235"/>
</qemu:commandline>
> 
> In guests created in a regular fashion (e.g. virt-install,
> virt-manager), this is all handled by libvirt for you via its APIs.
> 
>> However when I create VM using this xml file, I got the error:
>> 
>> # virsh create instance-libvirt.xml error: Failed to create domain
>> from instance-libvirt.xml error: internal error process exited while
>> connecting to monitor: qemu-kvm: -qmp tcp:127.0.0.1:1235: Duplicate ID
>> 'monitor' for mon duplicate chardev: monitor
>> 
>> The VM I created, without “—qmp” option, has below options showing in
>> “ps aux | grep qemu-kvm”:
>> 
>> -chardev
>>
socket,id=charmonitor,path=/var/lib/libvirt/qemu/vmifs_test.monitor,server,nowait
>> -mon chardev=charmonitor,id=monitor,mode=control
>> 
>> Looks like libvirt automatically adds the monitor options upon VM
>> creation.
> 
> As I understand it, libvirt uses its own APIs to handle interactions
> with QEMU monitor console, e.g. qemuMonitorOpen(), etc.
> 
> If you're fine delving into code, you might want to libvirt
> sources, specificially this directory: libvirt/src/qemu.
Messing up the source code is the last thing I want to do. I am using the
default libvirt coming with CentOs6.5, last time I modified and installed the
libvirt source code, I got seriously version-not-match problem.
> 
>> Is there a way to disable this and use “—qmp” instead when creating
>> VM?
> 
> I doubt libvirt developers will agree with this proposal. But if you're
> intending to try QEMU monitor console for testing, here's some old
notes
> on different ways to access QEMU monitor via QMP:
> 
>   
http://kashyapc.com/2013/03/31/multiple-ways-to-access-qemu-monitor-protocol-qmp/

I’ve read this and looks like you’re also using command line to create a KVM
machine while enabling “—qmp” option. Is there a way to do this but still
creating VM through libvirt?

Thank you very much for your time!


Best Regards,
Min

On Nov 9, 2014, at 11:34 AM, Kashyap Chamarthy <kchamart@redhat.com>
wrote:
> On Fri, Nov 07, 2014 at 03:28:57PM -0700, Min Du wrote:
>> Hi,
>> 
>> Now for some reason, I need to add “ -qmp tcp:127.0.0.1:1235” when
>> creating a KVM VM using libvirt.
> 
> You might need to elaborate how exactly you're doing this.
> 
>> This command meaning in “qemu-kvm --help” is: -qmp dev        like
>> -monitor but opens in 'control' mode.
> 
> The above is used if you want to explicitly control a running QEMU
> instance via QMP, e.g. manually issue them QMP commands via telnet(1)
> for development/testing/debugging.
> 
>> I added command-line equivalent options into the xml file, like below
>> format:
>> 
>>  <qemu:commandline> <qemu:arg value="-s"/>
<qemu:arg value="-qmp"/>
>>  <qemu:arg value="tcp:127.0.0.1:1235"/>
</qemu:commandline>
> 
> In guests created in a regular fashion (e.g. virt-install,
> virt-manager), this is all handled by libvirt for you via its APIs.
> 
>> However when I create VM using this xml file, I got the error:
>> 
>> # virsh create instance-libvirt.xml error: Failed to create domain
>> from instance-libvirt.xml error: internal error process exited while
>> connecting to monitor: qemu-kvm: -qmp tcp:127.0.0.1:1235: Duplicate ID
>> 'monitor' for mon duplicate chardev: monitor
>> 
>> The VM I created, without “—qmp” option, has below options showing in
>> “ps aux | grep qemu-kvm”:
>> 
>> -chardev
>>
socket,id=charmonitor,path=/var/lib/libvirt/qemu/vmifs_test.monitor,server,nowait
>> -mon chardev=charmonitor,id=monitor,mode=control
>> 
>> Looks like libvirt automatically adds the monitor options upon VM
>> creation.
> 
> As I understand it, libvirt uses its own APIs to handle interactions
> with QEMU monitor console, e.g. qemuMonitorOpen(), etc.
> 
> If you're fine delving into code, you might want to libvirt
> sources, specificially this directory: libvirt/src/qemu.
> 
>> Is there a way to disable this and use “—qmp” instead when creating
>> VM?
> 
> I doubt libvirt developers will agree with this proposal. But if you're
> intending to try QEMU monitor console for testing, here's some old
notes
> on different ways to access QEMU monitor via QMP:
> 
>   
http://kashyapc.com/2013/03/31/multiple-ways-to-access-qemu-monitor-protocol-qmp/
> 
> -- 
> /kashyap

On Mon, Nov 10, 2014 at 06:54:58PM -0700, Min Du wrote:
> Hi Kashyap,
> 
> Thanks for the reply. 
> 
> >> 
> >> Now for some reason, I need to add “ -qmp tcp:127.0.0.1:1235” when
> >> creating a KVM VM using libvirt.
> > 
> > You might need to elaborate how exactly you're doing this.
> 
> I wanted to add “-qmp tcp:127.0.0.1:1235” when creating VM because I
> was using a multi-level debugger which needs this option to get more
> information of the VM kernel debuginfo and the processes running inside
> the VM besides gdb attach.
That's impossible, because libvirt owns the QMP monitor and cannot delegate
use to another process. A core part of the VM startup process requires that
libvirt talk to the QMP monitor to accomplish work, as well as to receive
ongoing notifications of changes in state.

What is the debugger program you are using ?  It really needs to be updated
to use the libvirt APIs instead of QEMU monitor directly. Libvirt provides
an API for issuing monitor commands which it should be able to use. It is
just a question of re-writing the debugger to know about this.

Regards,
Daniel
-- 
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Hi Daniel,

Thanks. The debugger program I used is a multi-level debugging tool called
StackDB developed in our department. It was developed for Xen initially, and KVM
support was only added recently.

I've forwarded your email to the developer and hopefully it should be pretty
straightforward to do so.



Best Regards,
Min

On Nov 11, 2014, at 2:32 AM, Daniel P. Berrange <berrange@redhat.com>
wrote:
> On Mon, Nov 10, 2014 at 06:54:58PM -0700, Min Du wrote:
>> Hi Kashyap,
>> 
>> Thanks for the reply. 
>> 
>>>> 
>>>> Now for some reason, I need to add “ -qmp tcp:127.0.0.1:1235”
when
>>>> creating a KVM VM using libvirt.
>>> 
>>> You might need to elaborate how exactly you're doing this.
>> 
>> I wanted to add “-qmp tcp:127.0.0.1:1235” when creating VM because I
>> was using a multi-level debugger which needs this option to get more
>> information of the VM kernel debuginfo and the processes running inside
>> the VM besides gdb attach.
> 
> That's impossible, because libvirt owns the QMP monitor and cannot
delegate
> use to another process. A core part of the VM startup process requires that
> libvirt talk to the QMP monitor to accomplish work, as well as to receive
> ongoing notifications of changes in state.
> 
> What is the debugger program you are using ?  It really needs to be updated
> to use the libvirt APIs instead of QEMU monitor directly. Libvirt provides
> an API for issuing monitor commands which it should be able to use. It is
> just a question of re-writing the debugger to know about this.
> 
> Regards,
> Daniel
> -- 
> |: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/
:|
> |: http://libvirt.org              -o-             http://virt-manager.org
:|
> |: http://autobuild.org       -o-         http://search.cpan.org/~danberr/
:|
> |: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc
:|