Date: Fri, 28 Aug 1998 08:56:15 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: net@FreeBSD.ORG Subject: Proposal for (minimal) change to network drivers in promisc. mode Message-ID: <199808280656.IAA04891@labinfo.iet.unipi.it>
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In most (all ?) network card drivers, there are comments like the
following (generally copied from one driver to the other...):
/*
* Note that the interface cannot be in promiscuous mode if
* there are no BPF listeners. And if we are in promiscuous
now, isn't that a strong assumption ? There could be more reasons
to enable promiscuous mode on a machine (e.g. the bridging code i
am writing now, and possibly others), and the savings in the code
deriving from that assumption are really negligible: typically the
code would go from
if (sc->arpcom.ac_if.if_bpf) {
bpf_mtap(&sc->arpcom.ac_if, m);
if ((sc->arpcom.ac_if.if_flags & IFF_PROMISC) && pkt is not for us)
drop pkt ;
}
to
if (sc->arpcom.ac_if.if_bpf)
bpf_mtap(&sc->arpcom.ac_if, m);
if ((sc->arpcom.ac_if.if_flags & IFF_PROMISC) && pkt is not for us)
drop pkt ;
where the second 'if' is very cheap when not in promiscuous mode.
Some drivers already decouple bpf and PROMISC handling in the way
shown above, and i think this is all in the interest of clarity.
For others the modifications would be trivial. At a
first scan of the code i see the following:
"de", "fe", "ie", "lnc" already fixed.
"ed", "fxp", "ep", "wl", "zp": one-line fix as shown above
Note: the ep" driver one seems to have a redundant expensive
check for broadcast address
"le", "ze" almost as simple as above
"eg", "el", "ex", "tx" seem not to support multicast/promisc mode
so this is less of a problem.
What do you think, can i submit patches for at least a few of these drivers
with the hope that they get committed ?
luigi
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