diff options
| author | Jesper Dangaard Brouer | 2019-08-08 18:17:47 +0200 |
|---|---|---|
| committer | Daniel Borkmann | 2019-08-09 18:05:03 +0200 |
| commit | abcce733adb71013997fcb84142a5454ef133616 (patch) | |
| tree | 28659aea47a6a2c3135b3f97a4ecb3dae929f2d1 /samples | |
| parent | a32a32cb26eb6291125e4eb49b569874ca9a53b5 (diff) | |
samples/bpf: xdp_fwd explain bpf_fib_lookup return codes
Make it clear that this XDP program depend on the network
stack to do the ARP resolution. This is connected with the
BPF_FIB_LKUP_RET_NO_NEIGH return code from bpf_fib_lookup().
Another common mistake (seen via XDP-tutorial) is that users
don't realize that sysctl net.ipv{4,6}.conf.all.forwarding
setting is honored by bpf_fib_lookup.
Reported-by: Anton Protopopov <a.s.protopopov@gmail.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'samples')
| -rw-r--r-- | samples/bpf/xdp_fwd_kern.c | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/samples/bpf/xdp_fwd_kern.c b/samples/bpf/xdp_fwd_kern.c index a43d6953c054..701a30f258b1 100644 --- a/samples/bpf/xdp_fwd_kern.c +++ b/samples/bpf/xdp_fwd_kern.c @@ -103,8 +103,23 @@ static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags) fib_params.ifindex = ctx->ingress_ifindex; rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags); - - if (rc == 0) { + /* + * Some rc (return codes) from bpf_fib_lookup() are important, + * to understand how this XDP-prog interacts with network stack. + * + * BPF_FIB_LKUP_RET_NO_NEIGH: + * Even if route lookup was a success, then the MAC-addresses are also + * needed. This is obtained from arp/neighbour table, but if table is + * (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid + * doing ARP lookup directly from XDP, then send packet to normal + * network stack via XDP_PASS and expect it will do ARP resolution. + * + * BPF_FIB_LKUP_RET_FWD_DISABLED: + * The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding + * setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not + * enabled this on ingress device. + */ + if (rc == BPF_FIB_LKUP_RET_SUCCESS) { /* Verify egress index has been configured as TX-port. * (Note: User can still have inserted an egress ifindex that * doesn't support XDP xmit, which will result in packet drops). |