ifconfig(8) refactoring -- YACC grammar now online

Robert Watson rwatson at freebsd.org
Sun Nov 30 14:43:49 PST 2003

On Sun, 30 Nov 2003, Bruce M Simpson wrote:

> On Sun, Nov 30, 2003 at 02:20:50PM -0500, Robert Watson wrote:
> > if_type seems like it will work for high level classes of interfaces, but
> > something more fine-grained will be required for interfaces that implement
> > multiple classes or subclasses (i.e., 802 generally, and also 802.11b).
> The idea just now is we look at if_media if we need to get specific with
> physical interfaces. 
> tap would seem to be missing from my list, actually; I note it's used to
> provide VMware support in the absence of Netgraph, amongst other things.

if_tap is actually quite useful, and in the same general class of
synthetic interfaces as if_tun.  I've used both in building tunneling and
topology-manipulation tools, as well as for debugging routing, etc. 
if_tap simulates an 802 device, and if_tun simulates a point-to-point
device.  VMware is the only application I know of using if_tap, although I
have a fair amount of my own code that uses it.  Userland ppp uses if_tun,
as to some of the third party crypto tunneling tools. 

> > Or likewise, tap interfaces might implement 802 generally, but also
> > if_tap-specific primitives.  Do we need to probe by-name for capabilities
> > using interface ioctls, or return a "list" of implemented
> > interfaces/classes to allow things to be a bit more multidimensional?
> That might work well, actually -- I already added a MIB to rtsock to
> deal with our lack of reporting multicast group memberships, I see no
> reason not to add one to enumerate loaded interface classes. 
> OTOH, for the 'could load kld' case, this falls down, until the instance
> is created, either through cloning or completing ifattach() for a
> physical interface -- but if CREATE is a separate operation this isn't a
> problem, it is a problem if we want to say something like this in one
> go:-
>   ifconfig gif0 create tunnel
> Then you do need a means for the ifconfig instance to ask gif0 if it
> speaks 'tunnel-ese' once it's loaded. 
> I have to find an abstraction to comfortably deal with this stacking of
> properties/methods, simple polymorphism (a la Java 'implements
> interface')  springs to mind. 

I think that would be a reasonable approach, although it seems to me that
both the "inheritance" and "implements" models might apply in looking at
sets of protocol relationships.  a tap interface is a synthetic interface,
it implements synthetic interface controls, as well as implementing 802.
However, it might be neat to hook up 802.11 to a tap-like interface
sometime as well.  Question: does 802.11 imply 802?  If so, a notion of
inheritence might be quite useful for driver implementors.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at fledge.watson.org      Senior Research Scientist, McAfee Research

More information about the freebsd-arch mailing list