miquel.raynal@xxxxxxxxxxx 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