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Re: [libvirt] Bridge interface and script



On Mon, Jan 12, 2009 at 09:09:32PM +0000, John Levon wrote:
> On Mon, Jan 12, 2009 at 10:54:58AM +0000, Daniel P. Berrange wrote:
> 
> > > With current libvirt, it's not possible to specify a script for
> > > VIR_DOMAIN_NET_TYPE_BRIDGE. Is this just an oversight, or intentional?
> > 
> > That's intentional - if you want to use a generic network script then
> > use the type=ethernet style of network config instead of type=bridge
> 
> OK, why? Is there a reason for this restriction?

Take Xen on Linux as an example. There are 3 scripts that ship
with Xen

 - vif-bridge
 - vif-route
 - vif-nat

Only one of those scripts provides bridging of the VMs. There's no
easy way for libvirt to determine which script is bridging the VM
and which is doing something entirely different. So we have little
practical choice but to determine type=ethernet vs type=bridge based
on the name of the script.

> > > Suggestions on how to fix this? Should I just add script handling to
> > > this net type?
> > 
> > If the Solaris VIF setup script isn't called 'vif-bridge', then we can
> > just #ifdef the alternate name required for Solaris & everything else
> > should just work
> 
> Nope, since we have at least two standard scripts that are usable. Also,
> this is a back-compat issue (presumably, even for Linux...) that I don't
> think we can avoid.

What's the functional difference between the scripts ?

Converting from Xen -> SEXPR is the easy part - we can accept type=bridge
and an arbitrary script name without, but when we go back in the other
direction we need to be accurate about what we generate in the XML. We
don't want to report  type=bridge if the VM is in fact being setup with
routed networking. Hence we have to check for certain known script names

Daniel
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