Date:   Wed, 8 Jun 2022 21:56:53 -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>,
        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 1/6] net: ieee802154: Drop coordinator interface type

Hi,

On Wed, Jun 8, 2022 at 9:47 AM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
>
> Hi Alex,
>
> > > 3. coordinator (any $TYPE specific) userspace software
> > >
> > > May the main argument. Some coordinator specific user space daemon
> > > does specific type handling (e.g. hostapd) maybe because some library
> > > is required. It is a pain to deal with changing roles during the
> > > lifetime of an interface and synchronize user space software with it.
> > > We should keep in mind that some of those handlings will maybe be
> > > moved to user space instead of doing it in the kernel. I am fine with
> > > the solution now, but keep in mind to offer such a possibility.
> > >
> > > I think the above arguments are probably the same why wireless is
> > > doing something similar and I would avoid running into issues or it's
> > > really difficult to handle because you need to solve other Linux net
> > > architecture handling at first.
> >
> > Yep.
>
> The spec makes a difference between "coordinator" and "PAN
> coordinator", which one is the "coordinator" interface type supposed to
> picture? I believe we are talking about being a "PAN coordinator", but
> I want to be sure that we are aligned on the terms.
>

I think it depends what exactly the difference is. So far I see for
address filtering it should be the same. Maybe this is an interface
option then?

> > > > > You are mixing things here with "role in the network" and what
> > > > > the transceiver capability (RFD, FFD) is, which are two
> > > > > different things.
> > > >
> > > > I don't think I am, however maybe our vision differ on what an
> > > > interface should be.
> > > >
> > > > > You should use those defines and the user needs to create a new
> > > > > interface type and probably have a different extended address
> > > > > to act as a coordinator.
> > > >
> > > > Can't we just simply switch from coordinator to !coordinator
> > > > (that's what I currently implemented)? Why would we need the user
> > > > to create a new interface type *and* to provide a new address?
> > > >
> > > > Note that these are real questions that I am asking myself. I'm
> > > > fine adapting my implementation, as long as I get the main idea.
> > > >
> > >
> > > See above.
> >
> > That's okay for me. I will adapt my implementation to use the
> > interface thing. In the mean time additional details about what a
> > coordinator interface should do differently (above question) is
> > welcome because this is not something I am really comfortable with.
>
> I've updated the implementation to use the IFACE_COORD interface and it
> works fine, besides one question below.
>
> Also, I read the spec once again (soon I'll sleep with it) and
> actually what I extracted is that:
>
> * A FFD, when turned on, will perform a scan, then associate to any PAN
>   it found (algorithm is beyond the spec) or otherwise create a PAN ID
>   and start its own PAN. In both cases, it finishes its setup by
>   starting to send beacons.
>

What does it mean "algorithm is beyond the spec" - build your own?

> * A RFD will behave more or less the same, without the PAN creation
>   possibility of course. RFD-RX and RFD-TX are not required to support
>   any of that, I'll assume none of the scanning features is suitable
>   for them.
>
> I have a couple of questions however:
>
> - Creating an interface (let's call it wpancoord) out of wpan0 means
>   that two interfaces can be used in different ways and one can use
>   wpan0 as a node while using wpancoord as a PAN coordinator. Is that
>   really allowed? How should we prevent this from happening?
>

When the hardware does not support it, it should be forbidden. As most
transceivers have only one address filter it should be forbidden
then... but there exists a way to indeed have such a setup (which you
probably don't need to think about). It's better to forbid something
now, with the possibility later allowing it. So it should not break
any existing behaviour.

> - Should the device always wait for the user(space) to provide the PAN
>   to associate to after the scan procedure right after the
>   add_interface()? (like an information that must be provided prior to
>   set the interface up?)
>
> - How does an orphan FFD should pick the PAN ID for a PAN creation?
>   Should we use a random number? Start from 0 upwards? Start from
>   0xfffd downwards? Should the user always provide it?
>

I think this can be done all with some "fallback strategies" (build
your own) if it's not given as a parameter.

> - Should an FFD be able to create its own PAN on demand? Shall we
>   allow to do that at the creation of the new interface?
>

I thought the spec said "or otherwise"? That means if nothing can be
found, create one?

- Alex

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