From: Daniel Borkmann <dan...@iogearbox.net>
Date: Sat, 1 Aug 2015 00:46:29 +0200
> Add skb->hash to the __sk_buff offset map, so it can be accessed from
> an eBPF program. We currently already do this for classic BPF filters,
> but not yet on eBPF, it might be useful as a demuxer in combination with
> helpers like bpf_clone_redirect(), toy example:
>
> __section("cls-lb") int ingress_main(struct __sk_buff *skb)
> {
> unsigned int which = 3 + (skb->hash & 7);
> /* bpf_skb_store_bytes(skb, ...); */
> /* bpf_l{3,4}_csum_replace(skb, ...); */
> bpf_clone_redirect(skb, which, 0);
> return -1;
> }
>
> I was thinking whether to add skb_get_hash(), but then concluded the
> raw skb->hash seems fine in this case: we can directly access the hash
> w/o extra eBPF helper function call, it's filled out by many NICs on
> ingress, and in case the entropy level would not be sufficient, people
> can still implement their own specific sw fallback hash mix anyway.
>
> Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
> Acked-by: Alexei Starovoitov <a...@plumgrid.com>
Applied, thanks Daniel.
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