Re: [Xen-devel] 4.3 Planning: Taking stock

[James Harper <james.harper@xxxxxxxxxxxxxxxx>]

> >  but even better would be that you manually create the port outside of
> > xen and the domu would plug into that port. I'm not sure if the
> > port/interface names are long enough to allow this in an intuitive way
> > though (eg to specify grokable port names).
> 
> I can never remember the OVS terminology but what you are saying is that
> you want to create ovsbr0 and several named ports (lets say, eth0, web
> and db) where eth0 is a real thing and web and db are "floating" ports
> where there is no corresponding network device. When the vif is created
> it can then be bound to the port?
> 
> This means that you can preconfigure the rules for web and db even
> before starting the domain?
> 
> Which ovs commands would you use to do this? If it can be done by hand
> then I expect it could also be done by extending the syntax Bastian
> added.
> 
> If you are just saying you want the vif to be named "web" then the
> existing vifname stuff (which the script should be applying prior to
> connecting to the bridge) would do the job.
> 
> <snip>
> 
> The lack of a cleanup script getting run correctly on network devices
> was something Roger solved with his hotplug rework for xl in 4.2
> (essentially the script used to be run after the backend was torn down
> in xenstore so it couldn't get at many of its parameters)

The problem here is that ovs remembers all the ports in its database. You do 
add-port once and the port is there forever until you remove it again, even 
over reboots. It's great for eth0 etc because everything "just works" once ovs 
is started, but it's not so great for your vif's if your Dom0 crashes and you 
have stale ports around, or at least it isn't if you expect the brctl 
compatibility layer to do the right thing.

I did experiment with seeing what would happen when the port suddenly appeared 
and if ovs would add it automatically, but this didnât seem to be the case. I'm 
not sure if it's something to do with the way the vif interfaces appear or what.

Is there some sort of rename operation that happens or are the vif and tap 
interfaces 'born' with their correct name? If it's the former then that might 
be why ovs can't match them up.

A 'transient' option to ovs to not keep the port in the database would solve 
that problem, but such a thing doesn't seem to exist.

> > Also there is a qemu-ifup script that does some brctl stuff too, and
> > also seems to race with the interface rename, at least under the
> > Debian Xen 4.1 packages.
> 
> In 4.2 I made it so that Xen emulated devices used the Xen hotplug
> scripts instead of the qemu-ifup script, for consistency.
> 

Perfect. qemu-ifup seemed a bit dodgy... it even has (had?) a bug where it said 
'echo -c' instead of 'echo -n' to avoid the trailing newline.

Thanks

James

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