Hi Vladimir,
Medvedkin, Vladimir, Mar 19, 2024 at 18:16:
> 2) Is it OK/safe to modify a fib from a control thread (read/write)
> while it is used by data path threads (read only)?
This part is a bit more complicated. In practice, I would say yes,
however, there is a possibility that if the lookup thread is preempted
in the middle of the lookup process, and at the same time the control
thread deletes the corresponding route, then the lookup result may
return outdated data. This problem is solved in LPM with RCU enabled.
I have plans to implement it in the near future in the FIB.
OK that's good to know, thanks.
> 3) There is no public API to list/walk all configured routes in
> a fib. Would that be possible/easy to implement?
Yes, it already there. FIB under the hood uses rte_rib to hold
existing routes. So walking through can be implemented like:
I had tried it and got confusing results out of this. This must have
been before I had realized that all addresses needed to be in host
order...
I tried again and it works as advertised with a small missing detail:
after configuring a default route, e.g.:
rte_fib_add(fib, RTE_IPV4(2, 2, 0, 0), 16, RTE_IPV4(1, 2, 3, 4));
rte_fib_add(fib, RTE_IPV4(3, 3, 3, 0), 24, RTE_IPV4(4, 3, 2, 1));
rte_fib_add(fib, RTE_IPV4(0, 0, 0, 0), 0, RTE_IPV4(9, 9, 9, 9));
It is not returned by rte_rib_get_nxt() successive calls. I only see the
other two routes:
2.2.0.0/16 via 1.2.3.4
3.3.3.0/24 via 4.3.2.1
Is this expected?
> 4) In rte_fib, every IPv4 address (route *and* next hop) needs to be
> in host order. This is not consistent with fib6 where addresses
> are stored in network order. It took me quite a while to figure
> out what was wrong with my code.
This API behavior was created in such a way that it is the same as
LPM.
As for LPM, I think it was done this way for performance reasons
because in some scenarios you only working with the host order ipv4
addresses.
This should really be advertised in strong capital letters in the API
docs. Or (preferably) hidden to the user. I don't see any valid scenario
where you would work with host order IPv4 addresses.
Do you think we could change that API or at least add a flag at FIB/RIB
creation to make it transparent to the user and consistent between IPv4
and IPv6?
Thanks!
