From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Alexander Aring <aahringo@redhat.com>
Cc: Alexander Aring <alex.aring@gmail.com>,
Stefan Schmidt <stefan@datenfreihafen.org>,
linux-wpan@vger.kernel.org,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Eric Dumazet <edumazet@google.com>,
netdev@vger.kernel.org, David Girault <david.girault@qorvo.com>,
Romuald Despres <romuald.despres@qorvo.com>,
Frederic Blain <frederic.blain@qorvo.com>,
Nicolas Schodet <nico@ni.fr.eu.org>,
Guilhem Imberton <guilhem.imberton@qorvo.com>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH wpan-next 07/11] mac802154: Handle association requests from peers
Date: Fri, 1 Sep 2023 18:25:28 +0200 [thread overview]
Message-ID: <20230901182528.7c35f71e@xps-13> (raw)
In-Reply-To: <20230901174537.50f88d60@xps-13>
miquel.raynal@bootlin.com wrote on Fri, 1 Sep 2023 17:45:37 +0200:
> Hi Alexander,
>
> > > > --- a/net/ieee802154/pan.c
> > > > +++ b/net/ieee802154/pan.c
> > > > @@ -66,3 +66,30 @@ cfg802154_device_is_child(struct wpan_dev *wpan_dev,
> > > > return NULL;
> > > > }
> > > > EXPORT_SYMBOL_GPL(cfg802154_device_is_child);
> > > > +
> > > > +__le16 cfg802154_get_free_short_addr(struct wpan_dev *wpan_dev)
> > > > +{
> > > > + struct ieee802154_pan_device *child;
> > > > + __le16 addr;
> > > > +
> > > > + lockdep_assert_held(&wpan_dev->association_lock);
> > > > +
> > > > + do {
> > > > + get_random_bytes(&addr, 2);
> > >
> > > This is combined with the max associations setting? I am not sure if
> > > this is the best way to get free values from a u16 value where we have
> > > some data structure of "given" addresses to a node. I recently was
> > > looking into idr/xarray data structure... maybe we can use something
> > > from there.
> >
> > I actually thought about using an increasing index, but the pseudo
> > random generator seemed appropriate because of its "unpredictability",
> > but there is not real use for that (besides maybe testing purposes). I
> > can definitely switch to another solution.
>
> I looked into this deeper. I didn't felt like idr would be so much
> useful, but I started converting the code to use ida instead (so the
> simplest approach, with no associated pointer). There are actually two
> use cases which clearly match better the random address mechanism.
>
> a/ One can freely decide the short address of the coordinator (it is
> freely selectable by the user) but ida has no mechanism to handle this
> with an API which would prevent such "number to be used".
>
> In practice, this could be workarounded "easily", even though the
> implementation would be dirty IMHO: getting an IDA, if it matches ours,
> just try again without freeing it. TBH I don't like much this idea.
>
> b/ In case we ever want to support master handover, the ida solution
> does not work well...
c/ Technically speaking, leaf devices can connect to a PAN coordinator
which is not the top-level coordinator in case it is out of reach.
So the coordinator receiving the association request needs to allocate
a random address for this leaf device, without knowing all the
addresses the top-level coordinator already allocated. In case the
devices move or a coordinator detects two different devices within the
same PAN with the same short addres, it must trigger a realignment
procedure (not implemented yet). Therefore, following a linear scheme
when allocating children short addresses sounds like an endless source
of conflicts and realignments, whereas random addressing would prevent
most of these situations on regular sized networks?
> For now I've kept the current approach (actually adding a missing
> check), but if you know how to solve that I can either update the
> implementation or make a followup patch, especially since the current
> approach is not bounded (in the theoretical case where we have 65k
> devices in the same PAN).
>
> I believe the allocation strategies are not set in stone anyway and can
> easily evolve.
>
> Thanks,
> Miquèl
next prev parent reply other threads:[~2023-09-01 16:25 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-01 15:48 [PATCH wpan-next 00/11] ieee802154: Associations between devices Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 01/11] ieee802154: Let PAN IDs be reset Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 02/11] ieee802154: Internal PAN management Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 03/11] ieee802154: Add support for user association requests Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 04/11] mac802154: Handle associating Miquel Raynal
2023-06-02 15:54 ` Simon Horman
2023-08-18 14:17 ` Miquel Raynal
2023-06-03 10:09 ` Alexander Aring
2023-07-04 11:34 ` Alexander Aring
2023-09-01 15:01 ` Miquel Raynal
2023-09-01 15:31 ` Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 05/11] ieee802154: Add support for user disassociation requests Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 06/11] mac802154: Handle disassociations Miquel Raynal
2023-06-03 11:30 ` Alexander Aring
2023-08-21 9:02 ` Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 07/11] mac802154: Handle association requests from peers Miquel Raynal
2023-06-03 11:28 ` Alexander Aring
2023-08-21 8:52 ` Miquel Raynal
2023-09-01 15:45 ` Miquel Raynal
2023-09-01 16:25 ` Miquel Raynal [this message]
2023-06-01 15:48 ` [PATCH wpan-next 08/11] ieee802154: Add support for limiting the number of associated devices Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 09/11] mac802154: Follow " Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 10/11] mac802154: Handle disassociation notifications from peers Miquel Raynal
2023-06-01 15:48 ` [PATCH wpan-next 11/11] ieee802154: Give the user the association list Miquel Raynal
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