Re: libvirt domain configuration xml

Laine Stump <laine@xxxxxxxxx> · Tue, 15 Dec 2015 16:50:29 -0500



    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@xxxxxxxxxx>
            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

                  Libvirt virtualization library http://libvirt.org

                  
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