On 2/5/07, Bruce M. Simpson <[EMAIL PROTECTED]> wrote:
Jouke Witteveen wrote:
> Hello all,
>
> I'm in need of some information on how to utilize SIOCADDMULTI. It is
> supposed to be demonstrated by the mtest [1] program, but that doesn't
> do anything (on an SIOCDELMULTI rn it appears nothing was added:
> ENOENT), At least not for the values I tested, 1.80.c2.0.0.1 in
> particular. I presume it doesn't work because the program has not been
> revised in 3 years and revision 1.4 notes that it might not work.
> If this ioctl is depricated then please tell me what is the best way
> to receive multicast messages from the 01.80.c2.00.00.0x (802.1)
> range? It is ofcourse possible to go into ALLMULTI-mode and check on
> all datagrams, but the NIC's I use are suited with a very nice
> hardware filter (21143 chip) that should be able to do this more
> effectively. Anyway, I believe Linux still programs the hardware
> filter through SIOCADDMULTI so is a bit easier on this.
> I tracked down the source from the ioctl call to the network driver
> for some time now and could find no obvious fault, except for quite
> much casting, and inconsistent use of types (checks happen on all
> sorts of casts: socket, sokcet_dl, multiaddr, ...).
It's quite possible that path is broken, as hardly anyone else out there
needs to directly join a link-layer multicast group, and there is no
regression test for it.
The IP paths are known to work A-OK. If you didn't have code hooked up
to ether_demux() to see this traffic, you'd never see it in userland anyway.
As such, it's not a priority for me to fix , but will try to help anyway.
Are there specific performance constraints for your app? If not you
should just be able to use pcap (or bpf) to get the traffic. Admittedly
this is a performance hit, but with the optimization work on bpf and
ever more powerful CPUs, this shouldn't be a big issue.
You can write a regression test for this though with getifmaddrs().
anglepoise:~/head/src/sys/net % s mtest
Password:
multicast membership test program; enter ? for list of commands
a fxp0 01.80.c2.00.00.02
ether address added
should yield route -nv monitor output
got message of size 128 on Mon Feb 5 21:23:57 2007
RTM_NEWMADDR: new multicast group membership on iface: len 128,
sockaddrs: <IFP,IFA>
fxp0:0.90.27.59.40.2c 1.80.c2.0.0.2
Of course, netstat -g won't show you this, because it's concerned with
IP/IPv6 only.
netstat -ian should however tell you which link-layer multicast
addresses are configured.
When I add an ethernet multicast address manually with mtest, I see
vmstat -m | grep ether_multi increment as I'd expect.
It looks like there may be a missing piece somewhere. The code which I
see is OK but the results aren't as I'd expect. I am quite tired at the
moment so I may be way off.
Regards,
BMS
Further investigation showed that the address gets to the driver just
fine. I also saw with tcpdump that it actualy works: with `tcpdump -i
dc0 -p multicast` I could see traffic that I didn't see when I hadn't
added the multicast address.
So my apologies for suggesting it doesn't work at all; it seems that
the application I'm trying to get to work (wpa_supplicant for wired
interfaces) just doesn't _send_ its packets the right way.
Things aren't perfect though. In if.c the if_findmulti function is
broken (always returns NULL). I presume just comparing the
*LLADDR((sockaddr *)sa) data on both sockets is a better check, though
my knowledge on these things is limited.
As for netstat, I do not really know what is keeping it from showing
the Multicast addresses. Again: my knowledge on this matter is
limited. All I can think of is that getifmaddrs is forgetting
something (perhaps the lack of a group membership). Maybe you can take
a look at it (I believe you wrote it).
As I am still learning how best to contribute to a project as big as
FreeBSD and I do not think I am skilled enough yet in C I refrain from
writing a patch. I am eager to see one though, be it only out of
curiosity to know what would be considered a proper fix.
I hope someone can find a spare minute to look at if_findmulti. It
would help me quite much.
Kind regards,
- Jouke
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