David Ahern <dsahern@xxxxxxxxx> writes: > On 10/9/20 3:13 AM, 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, at the cost of a bit of duplicated work. >> >> 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. So let's just >> always return the ifindex, and also add a flag that lets the caller turn >> off the neighbour lookup entirely in bpf_fib_lookup(). > > seems really odd to do the fib lookup only to skip the neighbor lookup > and defer to a second helper to do a second fib lookup and send out. > > The better back-to-back calls is to return the ifindex and gateway on > successful fib lookup regardless of valid neighbor. If the call to > bpf_redirect_neigh is needed, it can have a flag to skip the fib lookup > and just redirect to the given nexthop address + ifindex. ie., > bpf_redirect_neigh only does neighbor handling in this case. Hmm, yeah, I guess it would make sense to cache and reuse the lookup - maybe stick it in bpf_redirect_info()? However, given the imminent opening of the merge window, I don't see this landing before then. So I'm going to respin this patch with just the original change to always return the ifindex, then we can revisit the flags/reuse of the fib lookup later. -Toke
