Re: [PATCH nf-next] netfilter: nf_tables: add ebpf expression

Florian Westphal
2022-08-31T21:58:50Z

Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > This helps gradually moving towards move epbf for those that
> > still heavily rely on the classic forwarding path.
>
> No one is using it.
> If it was, we would have seen at least one bug report over
> all these years. We've seen none.

Err, it IS used, else I would not have sent this patch.

> very reasonable early on and turned out to be useless with
> zero users.
> BPF_PROG_TYPE_SCHED_ACT and BPF_PROG_TYPE_LWT*
> are in this category.

I doubt it had 0 users. Those users probably moved to something
better?

> As a minimum we shouldn't step on the same rakes.
> xt_ebpf would be the same dead code as xt_bpf.

Its just 160 LOC or so, I don't see it has a huge technical debt.

> > If you are open to BPF_PROG_TYPE_NETFILTER I can go that route
> > as well, raw bpf program attachment via NF_HOOK and the bpf dispatcher,
> > but it will take significantly longer to get there.
> >
> > It involves reviving
> > https://lore.kernel.org/netfilter-devel/20211014121046.29329-1-fw@strlen.de/
>
> I missed it earlier. What is the end goal ?

Immediate goal: get rid of all indirect calls from NF_HOOK()
invocations. Its about 2% speedup in my tests (with connection
tracking+defrag enabled).

This series changes prototype of the callbacks to int foo(struct *),
so I think it would be possible to build on this and allow attaching raw
bpf progs/implement what is now a netfilter kernel module as a bpf
program.

I have not spent time on this so far though, so I don't know yet
how the "please attach prog id 12345 at FORWARD with prio 42" should
be done.

> Optimize nft run-time with on the fly generation of bpf byte code ?

This could be done too, so far this JITs nf_hook_slow() only.
The big question for nft run-time would be how and where to do the JIT
translation.

I think that "nft run time jit" would be step 3, after allowing
(re)implementation of netfilter modules via bpf programs.