Date: Wed, 31 May 2000 10:06:11 +0900 From: itojun@iijlab.net To: Archie Cobbs <archie@whistle.com> Cc: freebsd-net@FreeBSD.ORG Subject: Re: BPF fix to if_loop.c Message-ID: <4814.959735171@coconut.itojun.org> In-Reply-To: archie's message of Tue, 30 May 2000 14:55:26 MST. <200005302155.OAA00803@bubba.whistle.com>
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>> sorry this was incorrect. however, I think there should be check
>> if ifp really wants DLT_NULL encapsulation or not.
>Hmm.. maybe a better fix is to remove this BPF section altogether.. ?
>It's only going to result in showing the same packet twice, right?
there are couple of different stories here.
note that you can pass any ifp to if_simloop().
a. when if_simloop(ifp = lo0), there must be call to bpf_mtap,
with DLT_NULL encapsulation. if we don't do it here, nobody will.
b. when if_simloop(ifp = non-lo0), there are two cases.
b1. if it was called from layer 2 specific code like
if_ethersubr.c, if_simloop may want to inject the packet
with no encapsulation change.
b2. if it was called from ip{6,}_mloopback, if_simloop() must
not call bpf_mtap. with the current code, ifp_simloop
injects packet as is (with no layer 2 header) into, for
example to bpf for ethernet interface, passing junk to bpf
listeners. this is the problem I experienced.
in case of b1, your description should be correct (seeing same
packet twice). in case of b2, I'm still not sure how to resolve it.
maybe I don't get the ultimate goal for this change from 4.4BSD.
itojun
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