Alexei Starovoitov [off-list ref] wrote:

quoted

See my reply to Alexey, immediate goal was to get rid of the indirect
calls by providing a tailored/jitted equivalent of nf_hook_slow().

The next step could be to allow implementation of netfilter hooks
(i.e., kernel modules that call nf_register_net_hook()) in bpf
but AFAIU it requires addition of BPF_PROG_TYPE_NETFILTER etc.

We were adding new prog and maps types in the past.
Now new features are being added differently.
All of the networking either works with sk_buff-s or xdp frames.
We try hard not to add any new uapi helpers.
Everything is moving to kfuncs.
Other sub-systems should be able to use bpf without touching
the bpf core. See hid-bpf as an example.
It needs several verifier improvements, but doesn't need
new prog types, helpers, etc.

I don't see how it can be done without a new prog type, the bpf progs
would need access to "nf_hook_state" struct, passed as argument
to nf_hook_slow() (and down to the individual xt_foo modules...).

We can't change the existing netfilter hook prototype to go by
sk_buff * as that doesn't have all information, most prominent are
the input and output net_device, but also okfn is needed for async
reinject (nf_queue), the hook location and so on.

quoted

After that, yes, one could think about how to jit nft_do_chain() and
all the rest of the nft machinery.

Sounds like a ton of work. All that just to accelerate nft a bit?
I think there are more impactful projects to work on.
For example, accelerating classic iptables with bpf would immediately
help a bunch of users.

Maybe, but from the problem points and the required effort it doesn't matter
if the chosen target is iptables or nftables; as far as the time/effort
needed I'd say they are identical.

The hard issues that need to be solved first are the same; they reside
in the netfilter core and not in the specific interpreter (nft_do_chain
vs. ipt_do_table and friends).

nf_tables might be *slightly* easier once that point would be reached
because the core functionality is more integrated with nf_tables whereas
in iptables there is more copypastry (ipt_do_table, ip6t_do_table,
ebt_do_table, ...).