On 10/8/20 4:53 PM, Toke Høiland-Jørgensen wrote:
The bpf_fib_lookup() helper performs a neighbour lookup for the destination IP and returns BPF_FIB_LKUP_NO_NEIGH if this fails, with the expectation that the BPF program will pass the packet up the stack in this case. However, with the addition of bpf_redirect_neigh() that can be used instead to perform the neighbour lookup.However, for that we still need the target ifindex, and since bpf_fib_lookup() already has that at the time it performs the neighbour lookup, there is really no reason why it can't just return it in any case. With this fix, a BPF program can do the following to perform a redirect based on the routing table that will succeed even if there is no neighbour entry: ret = bpf_fib_lookup(skb, &fib_params, sizeof(fib_params), 0); if (ret == BPF_FIB_LKUP_RET_SUCCESS) { __builtin_memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN); __builtin_memcpy(eth->h_source, fib_params.smac, ETH_ALEN); return bpf_redirect(fib_params.ifindex, 0); } else if (ret == BPF_FIB_LKUP_RET_NO_NEIGH) { return bpf_redirect_neigh(fib_params.ifindex, 0); } Cc: David Ahern <dsah...@gmail.com> Signed-off-by: Toke Høiland-Jørgensen <t...@redhat.com>
ACK, this looks super useful! Could you also add a new flag which would skip neighbor lookup in the helper while at it (follow-up would be totally fine from my pov since both are independent from each other)? Thanks, Daniel
