Re: [PATCH net-next RFC 0/5] ipv6: sr: introduce seg6local End.BPF action

On Wed, Apr 4, 2018 at 2:34 AM, Mathieu Xhonneux [off-list ref] wrote:

2018-04-03 16:25 GMT+02:00 David Lebrun [off-list ref]:

quoted

Actually I'm wrong here. dst_input() will call either ip6_input() or
ip6_forward(), not ipv6_rcv(). Both functions expect IP6CB() to be set,
so using skb->cb here will interfere with them.

What about saving and restoring the IPv6 CB, similarly to what TCP does with
tcp_v6_restore_cb() ?

Yes. I can change the call to bpf_prog_run_save_cb to bpf_prog_run_clear_cb,
and then manually save/restore the IPv6 CB in input_action_end_bpf.

Or is there maybe a better solution to share some state between the bpf caller
and helpers, that does not need access to skb->cb ?

I think per-cpu scratch buffer approach can work for this
situation. Similar to one used by do_redirect and sockmap.