Date: Sun, 30 Nov 2003 17:41:08 -0500 (EST) From: Robert Watson <rwatson@freebsd.org> To: Bruce M Simpson <bms@spc.org> Cc: freebsd-arch@freebsd.org Subject: Re: ifconfig(8) refactoring -- YACC grammar now online Message-ID: <Pine.NEB.3.96L.1031130173735.66375g-100000@fledge.watson.org> In-Reply-To: <20031130194220.GB36456@saboteur.dek.spc.org>
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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 1.2.3.4 5.6.7.8 10.0.0.1 10.0.0.2 > > 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@fledge.watson.org Senior Research Scientist, McAfee Research
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