[Fedora-xen] netloop

[Daniel P. Berrange]

On Sat, Apr 14, 2007 at 08:26:16PM +0300, Pasi K?rkk?inen wrote:
> On Sat, Apr 14, 2007 at 12:18:26AM +0100, Daniel P. Berrange wrote:
> > On Fri, Apr 13, 2007 at 01:52:46PM -0700, Curtis Doty wrote:
> > > Am I going about this wrong? It's quite trivial to deadlock the Fedora 
> > > kernel.
> > > 
> > > # modprobe netloop ; rmmod netloop
> > > unregister_netdevice: waiting for veth3 to become free. Usage count = 1
> > > unregister_netdevice: waiting for veth3 to become free. Usage count = 1
> > > unregister_netdevice: waiting for veth3 to become free. Usage count = 1
> > > ...
> > > 
> > > This is without doing anything else with xend or the other modules. So 
> > > why/who/what grabbed a hold of that veth?
> > 
> > This is basically a limitation of the netloop module - its not written to
> > allow its removal once loaded. Fortunately we don't need to worry about
> > fixing this, because in the very near future we will be blasting netloop
> > into oblivion :-)  This will make networking in Dom0 much simpler because
> > you won't have this crazy set of extra devices for Dom0 - just the real
> > eth*, the bridge device & any VIFs for guest VMs.
> > 
> 
> Can you tell more about this? Redhat is planning not to use the xen
> network-bridge script anymore and allow more flexible configuration with
> the tools provided by the distro? 

For compatability with FC5/6 we need to keep using network-bridge in the
default RPM setup. What we're trying to do is alter the network-bridge
script so that it doesn't need to use the netloop module. Part of this
work involves kernel changes to the way the Xen network module transfer
data to avoid some potential denial-of-service conditions that arise if
you're not using netloop.

So we'll have a simplified network-bridge, but will also have the option 
of just setting the config file option '(network-script /bin/true)' and 
then using normal distro networking scripts for bridging/bonding/whatever.

> What does "in the very near future" mean.. ? for fc7? fc8?

Fedora 7 is the goal.

> I'm interested in this because I've made my own scripts for use in dom0
> instead of xen network-bridge.. kind of "add-on" scripts for standard fedora
> network scripts.

You'll be able to keep using these - netloop will still exist for compatability
with any user custom scripts, we simply won't use it in the default scripts


Dan.
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