Re: [PATCH v5 1/2] batman-adv: split DAT cache into DAT cache and DAT DHT

["Linus Lüssing" <linus.luessing@c0d3.blue>]

Hi Antonio,

Thanks for the feedback!

> I haven't followed previous discussions, therefore my question may just
> sound redundant, but if "cache_hash" is for ARP what is the "DAT DHT"? (the
> A in DAT stands for ARP).

The dht_hash would just store what was pushed to it from remote nodes
through the DAT DHT feature. So through a BATADV_P_DAT_DHT_PUT in
a batman-adv unicast4addr packet.

And would only be used for responses to a BATADV_P_DAT_DHT_GET.

The cache_hash would store all the other cases. That is local
additions learned through bat0. Or the responses this node got to
a BATADV_P_DAT_DHT_GET.

> Moreover, it seems with this approach you are converting the DAT concept
> into something "type specific" - am I wrong?

You mean to be able to use it for other types than ARP? Like the
patchset we had for IPv6 a while ago? Hm, no, that at least wasn't
the intention.

> 
> Is it truly required just to have a different timeout?
> Wouldn't a mark on entries be enough to instruct the subsystem about what
> timeout value to use?

That would work, too, right. I just found a split simpler and less
error-prone. With flags I'm always worried about missing potential
race conditions when flipping it back and forth. Especially with
the two different timeouts involved here.

For instance if I had an entry through a remote node
(BATADV_P_DAT_DHT_PUT) and therefore with a flag set. But now got an update for the same
address/entry through bat0 (maybe the client device roamed to us?
Or some collision / duplicate address usage?).
Should I now always unset the flag? Or should I check if its remaining
timeout is less than 5min and only if it is then unset the
flag?

Should a response to a BATADV_P_DAT_DHT_GET only be to an entry
with the flag set? Or independent to what the flag is set to?

.oO(Maybe a split could also be useful if one wanted to introduce
individual limits for additions? Against remote attackers trying to
DoS a node?)

Let me know if you'd still prefer a flag instead of a separate
hash table and I could change that.

Regards, Linus