On 10/9/20 11:42 AM, Toke Høiland-Jørgensen wrote: > 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 That is not needed. > 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. > What I am suggesting is a change in API to bpf_redirect_neigh which should be done now, before the merge window, before it comes a locked API. Right now, bpf_redirect_neigh does a lookup to get the nexthop. It should take the gateway as an input argument. If set, then the lookup is not done - only the neighbor redirect.
