[libvirt] libvirt not wanting to read back its own interface XML

[Marc Haber]

On Thu, Oct 19, 2017 at 10:08:37AM +0200, Martin Kletzander wrote:
> On Wed, Oct 18, 2017 at 04:48:45PM +0200, Marc Haber wrote:
> > Hi,
> > 
> > I'm trying to give libvirt knowlegde of a VLAN interface that is
> > configured by a different means and not by libvirt. To figure out the
> > syntax, I created a VLAN interface through virt-manager and dumped out
> > the XML:
> > 
> > <interface type='vlan' name='ens3.180'>
> >  <protocol family='ipv6'>
> >    <ip address='2a01:4f8:150:436c::55:100' prefix='64'/>
> >    <ip address='fe80::5054:ff:fe30:e0d1' prefix='64'/>
> >  </protocol>
> >  <link speed='4294967295' state='up'/>
> >  <vlan tag='180'>
> >    <interface name='ens3'/>
> >  </vlan>
> > </interface>
> > 
> > I then removed the Interface in virt-manager and tried to have libvirt
> > read back its own XML.
> > 
> > [12/784]mh at testsid85:~ $ virsh iface-dumpxml ens3.180 > ens3.180.xml
> > [13/785]mh at testsid85:~ $ virsh iface-define ens3.180.xml
> > error: Failed to define interface from ens3.180.xml
> > error: XML error: could not get interface XML description: XML invalid - Expecting an element start, got nothing
> > 
> > What is going on here? How do I define a VLAN interface via XML?
> > 
> 
> Hm, weird.  Before looking at where the problem is, it could be easier to find
> if we knew how virt-manager was able to define this.  Can you look at the logs
> for the XML from virt-manager?

[Mi, 18 Okt 2017 16:38:57 virt-manager 31596] DEBUG (interface:253) Creating int
erface 'ens3.180' with xml:
<interface type="vlan" name="ens3.180">
  <start mode="onboot"/>
  <vlan tag="180">
    <interface name="ens3"/>
  </vlan>
</interface>

This directly opens the next issue: I explicitly asked virt-manager to
do "no configuration" of IPv6, which seems to be the case in the XML
given to libvirt by virt-manager, but still, the libvirt-generated XML
contains the IPv6 configuration of the interface (which it shouldn't,
IMO).

I tried iface-define with

<interface type='vlan' name='ens3.180'>
 <link speed='4294967295' state='up'/>
 <vlan tag='180'>
   <interface name='ens3'/>
 </vlan>
</interface>

also with the link speed clause removed, but the error message remains
the same.

Greetings
Marc

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