netdev - Re: [PATCH nf-next 7/8] netfilter: nf_tables: add flowtable map for xdp offload

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Date: Thu, 30 Nov 2023 14:53:08 +0100
From: Florian Westphal <fw@...len.de>
To: Toke Høiland-Jørgensen <toke@...e.dk>
Cc: Florian Westphal <fw@...len.de>, netfilter-devel@...r.kernel.org,
	lorenzo@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH nf-next 7/8] netfilter: nf_tables: add flowtable map for
 xdp offload

Toke Høiland-Jørgensen <toke@...e.dk> wrote:
> I am not a huge fan of this flag, especially not as UAPI. Using the XDP
> offload functionality is already an explicit opt-in by userspace (you
> need to load the XDP program). So adding a second UAPI flag that you
> have to set for the flowtable to be compatible with XDP seems to just
> constrain things needlessly (and is bound to lead to bugs)?

I can remove it.  But it leads to issues, for example one flowtable
can shadow another one.

I'd prefer to handle this from control plane and reject such config.
Alternative is to ignore this and handle it as "self sabotage, don't
care" combined with "do not do that, then".

> If we can't change the behaviour, we could change the lookup mechanism?
> BPF is pretty flexible, nothing says it has to use an ifindex as the
> lookup key? The neatest thing would be to have some way for userspace to
> directly populate a reference to the flowtable struct in a map, but a
> simpler solution would be to just introduce an opaque ID for each
> flowtable instance and use that as the lookup key (userspace could
> trivially put that into a map for the BPF program to find)?

Won't that complicate things?  Userspace will have to use netlink
events to discover when a flowtable is removed, no?