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Re: [libvirt-users] libvirt domain configuration xml

On 12/15/2015 04:36 AM, Andrei Perietanu wrote:
Tanks for the reply Eric.
  The only reason I'm not going through the API is because there is nothing in the API (AFIK), that will allow you to modify the VNC settings, i.e. enable/disable, change port number. So I figured, the only way to do it is to modify the XML. 
   I can't use virsh edit because I need this whole behavior scripted.
   So now if I want to change the VNC settings it looks like I have to read the XML, modify it, define it, actually re-define it (maybe I have to undefine it first?! ) and that's it - correct?

If you "define" a domain that already exists, the new definition replaces the existing one, but not until the domain has been powered off - the next time it is started, the new config takes effect. There is no need to "undefine" or separately "re-define".

So the solution to your problem is to simply replace the final two lines of your example code (open() and f.write()) with Eric's suggested line:


That's it.

(BTW, please make your replies inline rather that top-posting. It makes it much easier to follow the discussion)


On Fri, Dec 11, 2015 at 5:25 PM, Eric Blake <eblake redhat com> wrote:
On 12/11/2015 07:26 AM, Andrei Perietanu wrote:
> I am trying to change a domain configuration from a python script. More
> specific, I want to edit the VNC settings. You can't do this using the
> libvirt API so you have to edit the domain configuration:

Umm, the libvirt API _is_ how you edit the domain configuration.

> Fo exmple, to disable VNC for a domain 'test1':
> vmXml = vm.XMLDesc(0)
> root = ET.fromstring(vmXml)
> devices = root.find('./devices')
> graphics = devices.find('graphics')
> devices.remove(graphics)
> xml = ET.tostring(root)
> with open('path_to/test1.xml', 'w') as f:
> f.write(xml)

Writing to path_to/test1.xml is not necessary (it's merely a convenient
way for you to have a point-in-time snapshot of what the domain XML
was); what you are really looking for is to write the XML back to
libvirt, via:


> So the question really is: where is the domain configuration stored? Am I
> editing the write file, or am I missing something?

The official copy is stored in memory, so the only supported way to
manipulate it is via libvirt API.  Libvirt happens to copy its memory
into files located under /etc/libvirt for persistence reasons, but
modifying those files behind libvirt's back is not a good idea - in
fact, those files start with the disclaimer:
OVERWRITTEN AND LOST. Changes to this xml configuration should be made
  virsh edit domain
or other application using the libvirt API.

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

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