[Libvir] Inconsistent networking between Xen & QEMU

Daniel P. Berrange berrange at redhat.com
Fri Mar 9 19:38:46 UTC 2007

On Fri, Mar 09, 2007 at 07:17:04PM +0000, Mark McLoughlin wrote:
> On Fri, 2007-03-09 at 18:52 +0000, Daniel P. Berrange wrote:
> > On Fri, Mar 09, 2007 at 04:44:17PM +0000, Mark McLoughlin wrote:
> > > 	Rather you suggest that if people want to use bridging, then they
> > > should modify the default network XML config by hand and not have the
> > > latter option in the UI?
> > 
> > How they configure the network XML is a completely separate issue - we could
> > easily have UI in virt-manager for creating/deleteing/editing networks in
> > the same way we have UI for creating/deleting/editing domains.
> 	... except you'd again have need an API for iterating physical network
> devices ...

You say that like its a bad thing ?   Virt-manager or other apps will need to
be able to enumerate physical devices somehow. So if libvirt is already 
providing APIs for virtual networks a VM can connect to, why not also provide
APIs for physical devices (or figure out a way to let the existing virtual
networks API also deal with phys devices).

> > > 	That introduces this user visible notion of a bridge vs. a router,
> > > which is just horrible. But, I guess you're saying you wouldn't have it
> > > in the UI.
> > 
> > Just because the different bridge vs routed confoigs are represented in the
> > libvirt XML one way, doesn't force our hand in our we present it to the user.
> > Any network with a '<device name='eth0'> tag could be displayed in the 
> > 'physical interfaces' drop down, while any without that tag would be
> > in the 'Network' drop down.
> 	Well, except that you're suggesting "connect to physical interface
> eth0" should be a property of a virtual network, but I think it makes
> more sense for it to be the property of a virtual nic.

Well actually I'm suggesting 'connect to the physical network that eth0
is a part of' which doesn't feel much different to 'connect to the
virtual network'

NB, in all this discussion I'm talking about a scenario where the guest
can be connect to eth0 via a bridge. I've not even thought about a case
where you'd NAT a VIF directly into eth0 - that's probably irrelevant
use case now we have proper virtual networks - i only bring it up because
that is what xen's  vif-route or vif-nat scripts do.

> 	e.g. connect your qemu guests to the default network, connect your Xen
> guests to the eth0 bridge.

I'm just wondering whether this is making a distinction, where no real
distinction exists? If you run 'ifconfig' or 'brctl show' in either
of these two cases its going to look basically identical to the admin.
ie, there a bridge device, with one of more NICs in it, some virtual
NICs or TAPs, some physical NICs. If you run 'virsh net-list' you're
only going to see one of those cases 

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