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Re: Specifying names for tap interfaces

On Wed, Jun 20, 2012 at 06:31:42PM +0100, Roger Pau Monne wrote:
> Mouse wrote:
> >>So, we would like to be able to create interface alias, here is what
> >>I think should be doable (from my PoV):
> >
> >Here are some thoughts that come to mind.  I'm not sure they're all
> >points worth worrying about.
> Thanks for the information, it has been really helpful.
> >>Adding a field to ifnet to contain that alias, something like
> >>if_xalias, then being able to set that name with an ioctl [...]
> >
> >Is a maximum of one alias per interface sufficient?  I once saw it said
> >that "the number two is ludicrous" - having one of something is fine,
> >but as soon as you have two, why not an unlimited number?  In this
> >case, the "something" is names per interface.
> Well, I think that adding one or more than one is not really a
> problem. I will start working on adding one alias per interface, but
> we can always extend that code to add more than one.
> >Why draw a distinction between the name and the alias?  (I actually can
> >see some potential answers to this; I mention it more to provoke
> >thought than because I think it's a serious issue.)
> >
> >>What I'm not sure is how to propagate that change to every tool that
> >>interacts with network interfaces, we should of course change
> >>ifconfig to be able to set/get this aliases, but then changes will
> >>also be required to brconfig, pf...?
> >
> >I see no need for all tools to be aware of aliases.  Many (most?) tools
> >just use names to refer to interfaces and don't care about the finer
> >points of it.  So as long as the names are valid for the purposes the
> >tools are using them for, I see no reason for, eg, brconfig to care
> >whether an interface it's trying to add is an alias or not.
> True.
> >>Also, when the user specifies something like ifconfig alias:foo up,
> >>how do we know to what is alias:foo mapped to?
> >
> >Who is "we"?  I see no reason for ifconfig to care; it just does the
> >ioctl with "alias:foo" in the interface name field and doesn't care
> >whether it's an alias, even, much less what it's an alias for.  Inside
> >the kernel, for most purposes, this is entirely hidden within the "look
> >up an interface given its name" code; as far as I can see, the only
> >other things that have occasion to care are the specifcally alias-aware
> >ones, like the code to set and get alias names.
> Yes.
> >If it turns out there is reason for userland to care - and reason to
> >draw a distinction between an interface's alias and its real name -
> >then an interface could be added to return the real name corresponding
> >to a possibly-aliased name.
> Well, now I have a clearer idea of what should be done, I will start
> working on this tomorrow morning, let's see if I can get it ready
> for a backport to 6.0.

Don't rush, the discussion is not over.
Also, I think it's too late anyway for 6.0. But it can be in 6.1.

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference

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