Re: Specifying names for tap interfaces

[Roger Pau Monne <roger.pau%citrix.com@localhost>]

Martin Husemann wrote:
> On Wed, Jun 20, 2012 at 11:39:14PM +0100, Roger Pau Monné wrote:
> > Well this might be ok with firewalls, but it's not applicable to guest
> > interfaces, there's still the problem with persistent interfaces for
> > DomUs, which this doesn't solve.
>
> I have never administered a dom0, so I clearly lack understanding here.
> Can you please explain why this needs kernel help at all (maybe again,
> I didn't get it earlier)?
>
> It sounds to me like xen would have a config file to fire up the domU,
> and there could be an entry saying "this domU will use tap14".
> So assumming we know what tap device we want upfront, there is already
> a simple API to create it, without renaming it later.
>
> What am I missing?

While this is true if you give a name to the interface on the config 
file, but how can the toolstack (xl, that launches Qemu) choose an 
interface name and pass it to Qemu when no one is specified? Well, we 
might be able to search for a free tap device and pass this as the 
desired name, but this is a really racy solution, as someone else might 
request a tap device while we are launching Qemu, and take our chosen 
tap device behind our back, so we will end up failing to create that domain.

Also, I don't think there's anyway to create vifs interfaces with an 
specific name, which I think will also be an interesting feature to have.