[libvirt-users] libvirt domain configuration xml

[Laine Stump]

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:

vm.defineXML(xml)

That's it.

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


>
> Andrei
>
> On Fri, Dec 11, 2015 at 5:25 PM, Eric Blake <eblake at redhat.com 
> <mailto:eblake at 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:
>
>     vm.defineXML(xml)
>
>     > 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:
>     <!--
>     WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY
>     TO BE
>     OVERWRITTEN AND LOST. Changes to this xml configuration should be made
>     using:
>       virsh edit domain
>     or other application using the libvirt API.
>     -->
>
>     --
>     Eric Blake   eblake redhat com +1-919-301-3266 <tel:%2B1-919-301-3266>
>     Libvirt virtualization library http://libvirt.org
>
>
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