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 <dsahern@xxxxxxxxx>
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
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
