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

On Thu, 2013-01-24 at 11:48 +0000, James Harper wrote:
> > >  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,

I think the start of day networking setup should take care of resetting
things to a known good set of ports, which would involve clearing out
any stale ones caused by this

In the normal non-crashing world the vif script should be removing them
on domain shutdown (including on host reboot)

>  or at least it isn't if you expect the brctl compatibility layer to
> do the right thing.

Lets not go there...

> Is there some sort of rename operation that happens or are the vif and
> tap interfaces 'born' with their correct name?

In 4.2+ they are born with the vifX.Y(-emu) name and renamed to the name
specified in the config file (if any) in the vif hotplug script.


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