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

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Date:   Mon, 6 Jun 2022 17:43:19 +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 Alexander,

aahringo@...hat.com wrote on Fri, 3 Jun 2022 22:01:38 -0400:

> Hi,
> 
> On Fri, Jun 3, 2022 at 2:34 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> >
> > The current enum is wrong. A device can either be an RFD, an RFD-RX, an
> > RFD-TX or an FFD. If it is an FFD, it can also be a coordinator. While
> > defining a node type might make sense from a strict software point of
> > view, opposing node and coordinator seems meaningless in the ieee
> > 802.15.4 world. As this enumeration is not used anywhere, let's just
> > drop it. We will in a second time add a new "node type" enumeration
> > which apply only to nodes, and does differentiates the type of devices
> > mentioned above.
> >  
> 
> First you cannot say if this is not used anywhere else.

Mmmh, that's tricky, I really don't see how that might be a
problem because there is literally nowhere in the kernel that uses this
type, besides ieee802154_setup_sdata() which would just BUG() if this
type was to be used. So I assumed it was safe to be removed.

> Second I have
> a different opinion here that you cannot just "switch" the role from
> RFD, FFD, whatever.

I agree with this, and that's why I don't understand this enum.

A device can either be a NODE (an active device) or a MONITOR (a
passive device) at a time. We can certainly switch from one to
another at run time.

A NODE can be either an RFD or an FFD. That is a static property which
cannot change.

However being a coordinator is just an additional property of a NODE
which is of type FFD, and this can change over time.

So I don't get what having a coordinator interface would bring. What
was the idea behind its introduction 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.

Thanks,
Miquèl