Re: current btle 6lowpan issues

[Jukka Rissanen <jukka.rissanen@linux.intel.com>]

Hi Alex,

On Thu, 2016-06-16 at 23:38 +0200, Alexander Aring wrote:
> Hi,
> 
> On 06/16/2016 03:41 PM, Patrik Flykt wrote:
> > 
> > On Thu, 2016-06-16 at 13:00 +0300, Jukka Rissanen wrote:
> > > 
> > > Yes you are right that there are issues. Fortunately the bt0 is
> > > currently a point-to-point link in which case ND is not really
> > > done
> > > and everything kind of "works" ok.
> > > 
> > > I added Patrik to cc: as he has been working to fix the issues
> > > but
> > > the patches are not yet ready. Perhaps we could combine the
> > > efforts
> > > here.
> > I had some patches that make BTLE interfaces non-point-to-point.
> > Let me
> > check that they can be applied on the latest bluetooth-next and
> > that
> > they still compile after a few months of sitting on an old version.
> > Then let's hope they also work as expected...
> > 
> With non-point-to-point you mean to remove the IFF_POINTOPOINT flag
> in
> net_device? Yes this should be removed.

Yes, agreed.

> 
> But I think this is one of the smallest issue in btle 6lowpan.
> 
> What means "ND is not really done", does that means you will not see
> btle neighbours by doing "ip -6 neigh" for your bt interface?

Yes.

> 
> I don't believe that and I think no matter if you set IFF_POINTOPOINT
> or
> not, the IPv6 stack will mostly ignore such flag. I did a grep and it
> seems the SIT stuff sets this flag and IPv6 stack does something with
> that, but not in case of ARPHRD_6LOWPAN, it's for ARPHRD_SIT only. So
> I
> think this flag makes some "peer" address in "ip a" handling instead
> of
> showing broadcast address. But nobody will make special handling in
> IPv6
> or btle 6lowpan if this flag is set.
> 
> What I mean is, you can set this flag on or off but it will don't
> change
> any behaviour.

Unfortunately there is a different behaviour. If the interface has
IFF_POINTTOPOINT, then kernel will not send neighbor discovery messages
to that link. I have not checked the kernel code where exactly that is
enforced but I have looked the wireshark output and there are no ND's
sent if bt0 is p-to-p link. If the flag is removed, the device starts
to send ND's to that interface.

Removing the IFF_POINTTOPPOINT is not enough as the MAC address will be
wrongly set in that case as you have noticed.


Cheers,
Jukka