netdev - Re: [PATCH wpan-next 1/6] net: ieee802154: Drop coordinator interface type

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Message-ID: <20220608154749.06b62d59@xps-13>
Date:   Wed, 8 Jun 2022 15:47:49 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Alexander Aring <aahringo@...hat.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 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.

> > > > 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.

* 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?

- 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?

- 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?

Thanks,
Miquèl