Re: Specifying names for tap interfaces

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sat, Jun 30, 2012 at 10:32:42AM +0100, Iain Hibbert wrote:
> > No, I'm saying it's incompatible with one of the goal of label, which
> > is to have a user-specifed interface identifier.
> 
> Sorry, was there a design document for this that I didn't see? This seems
> rather like a circular argument and you have not explained the reason for
> the restriction.

I posted a mail earlier in this thread where I explained how I would
see it work.

> 
> > If the label is not unique, it can't be used as identifier.
> 
> Why not? If you want to select to an item using a label, just have the
> tools find the first one with the matching label. Don't worry that there
> might be another, it will be hidden if you only use that label, until the
> first item has its label removed..

This all started with interraction between qemu and xen: qemu create a tap
interface with an unpredictible name (really, an unpredictible index) and
no way for qemu to give back the name it created to xen, so that xen tools
can configure the tap device created by qemu.

It was proposed to be able to create tap devices with arbitrary names.
I proposed, instead of changing the device name, to create a different
string (the label) and being able to lookup interfaces using labels instead
of names. Then you could use labels in various tools and config
files instead of names if you want to.
Now, if you allow more than one interface with the same label this opens
a whole can of worm, because the reasonable behavior will be tool-dependant.
For example, what should ipf do with
block in quick on label,foo
if label,foo refers to more than one interface ? I'd expect packets to be
blocked on all interfaces with the same label.
But should
dhclient label,foo
really configure all interfaces with this label ?
If I use label,foo in mrtg it won't be happy if it gets more than one
interface back.
And if the same label points to 2 interfaces with different properties
(say a hardware one and a tap), things get really messy.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--