Message-ID: <CAK-6q+gbRZ_w-G7WBTQNfjnpawQ0EJ4DuR9tsGPbZpT6MN35cw@mail.gmail.com>
Date:   Thu, 1 Sep 2022 22:23:02 -0400
From:   Alexander Aring <aahringo@...hat.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan - ML <linux-wpan@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Network Development <netdev@...r.kernel.org>,
        David Girault <david.girault@...vo.com>,
        Romuald Despres <romuald.despres@...vo.com>,
        Frederic Blain <frederic.blain@...vo.com>,
        Nicolas Schodet <nico@...fr.eu.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH wpan-next 01/20] net: mac802154: Allow the creation of
 coordinator interfaces

Hi,

On Wed, Aug 31, 2022 at 8:09 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
>
> Hello again,
>
> miquel.raynal@...tlin.com wrote on Wed, 31 Aug 2022 17:39:03 +0200:
>
> > Hi Alexander & Stefan,
> >
> > aahringo@...hat.com wrote on Mon, 29 Aug 2022 22:23:09 -0400:
> >
> > I am currently testing my code with the ATUSB devices, the association
> > works, so it's a good news! However I am struggling to get the
> > association working for a simple reason: the crafted ACKs are
> > transmitted (the ATUSB in monitor mode sees it) but I get absolutely
> > nothing on the receiver side.
> >
> > The logic is:
> >
> > coord0                 coord1
> > association req ->
> >                 <-     ack
> >                 <-     association response
> > ack             ->
> >
> > The first ack is sent by coord1 but coord0 never sees anything. In
> > practice coord0 has sent an association request and received a single
> > one-byte packet in return which I guess is the firmware saying "okay, Tx
> > has been performed". Shall I interpret this byte differently? Does it
> > mean that the ack has also been received?
>
> I think I now have a clearer understanding on how the devices behave.
>
> I turned the devices into promiscuous mode and could observe that some
> frames were considered wrong. Indeed, it looks like the PHYs add the
> FCS themselves, while the spec says that the FCS should be provided to
> the PHY. Anyway, I dropped the FCS calculations from the different MLME
> frames forged and it helped a lot.
>

This is currently the case because monitor interfaces and AF_PACKET
will not have the FCS in the payload. As you already figured out you
can't refer 802.15.4 promiscuous mode to mac802154 promiscuous mode,
it was a historically growing term as people wanted to have a sniffer
device and used a promiscuous term from a datasheet (my guess).
Vendors has a different meaning of promiscuous mode as the one from
802.15.4. IFF_PROMISC should be mapped to non-filtered mode which is
more equal to a sniffer device. However we need to find solutions
which fulfill everybody.

> I also kind of "discovered" the concept of hardware address filtering
> on atusb which makes me realize that maybe we were not talking about
> the same "filtering" until now.
>
> Associations and disassociations now work properly, I'm glad I fixed
> "everything". I still need to figure out if using the promiscuous mode
> everywhere is really useful or not (maybe the hardware filters were
> disabled in this mode and it made it work). However, using the
> promiscuous mode was the only way I had to receive acknowledgements,
> otherwise they were filtered out by the hardware (the monitor was
> showing that the ack frames were actually being sent).
>

This is correct, the most hardware will turn off automatic
ackknowledge handling if address filtering is off (I am sure I said
that before). We cannot handle acks on mac802154 if they are time
critical.

> Finally, changing the channel was also a piece of the puzzle, because I
> think some of my smart light bulbs tried to say hello and it kind of
> disturbed me :)
>
> > I could not find a documentation of the firmware interface, I went
> > through the wiki but I did not find something clear about what to
> > expect or "what the driver should do". But perhaps this will ring a
> > bell on your side?
> >
> > [...]
> >
> > > I did not see the v2 until now. Sorry for that.
> >
> > Ah! Ok, no problem :)
> >
> > >
> > > However I think there are missing bits here at the receive handling
> > > side. Which are:
> > >
> > > 1. Do a stop_tx(), stop_rx(), start_rx(filtering_level) to go into
> > > other filtering modes while ifup.
> >
> > Who is supposed to change the filtering level?
> >
> > For now there is only the promiscuous mode being applied and the user
> > has no knowledge about it, it's just something internal.
> >
> > Changing how the promiscuous mode is applied (using a filtering level
> > instead of a "promiscuous on" boolean) would impact all the drivers
> > and for now we don't really need it.
> >
> > > I don't want to see all filtering modes here, just what we currently
> > > support with NONE (then with FCS check on software if necessary),
> > > ?THIRD/FOURTH? LEVEL filtering and that's it. What I don't want to see
> > > is runtime changes of phy flags. To tell the receive path what to
> > > filter and what's not.
> >
> > Runtime changes on a dedicated "filtering" PHY flag is what I've used
> > and it works okay for this situation, why don't you want that? It
> > avoids the need for (yet) another rework of the API with the drivers,
> > no?
> >
> > > 2. set the pan coordinator bit for hw address filter. And there is a
> > > TODO about setting pkt_type in mac802154 receive path which we should
> > > take a look into. This bit should be addressed for coordinator support
> > > even if there is the question about coordinator vs pan coordinator,
> > > then the kernel needs a bit as coordinator iface type parameter to
> > > know if it's a pan coordinator and not coordinator.
> >
> > This is not really something that we can "set". Either the device
> > had performed an association and it is a child device: it is not the
> > PAN coordinator, or it initiated the PAN and it is the PAN coordinator.
> > There are commands to change that later on but those are not supported.
> >
> > The "PAN coordinator" information is being added in the association
> > series (which comes after the scan). I have handled the pkt_type you are
> > mentioning.
> >
> > > I think it makes total sense to split this work in transmit handling,
> > > where we had no support at all to send something besides the usual
> > > data path, and receive handling, where we have no way to change the
> > > filtering level besides interface type and ifup time of an interface.
> > > We are currently trying to make a receive path working in a way that
> > > "the other ideas flying around which are good" can be introduced in
> > > future.
> > > If this is done, then take care about how to add the rest of it.
> > >
> > > I will look into v2 the next few days.
>
> If possible, I would really like to understand what you expect in terms
> of filtering. Maybe as well a short snippet of code showing what kind
> of interface you have in mind. Are we talking about a rework of the
> promiscuous callback? Are we talking about the hardware filters? What

I try to do that over the weekend. Monday is a holiday here.

> are the inputs and outputs for these callbacks? What do we expect from
> the drivers in terms of advertising? I will be glad to make the
> relevant changes once I understand what is needed because on this topic
> I have a clear lack of experience, so I will try to judge what is
> reachable based on your inputs.

ok.

Thanks.

- Alex

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