bpf: Add BPF_FIB_LOOKUP_SKIP_NEIGH for bpf_fib_lookup

The bpf_fib_lookup() also looks up the neigh table.
This was done before bpf_redirect_neigh() was added.

In the use case that does not manage the neigh table
and requires bpf_fib_lookup() to lookup a fib to
decide if it needs to redirect or not, the bpf prog can
depend only on using bpf_redirect_neigh() to lookup the
neigh. It also keeps the neigh entries fresh and connected.

This patch adds a bpf_fib_lookup flag, SKIP_NEIGH, to avoid
the double neigh lookup when the bpf prog always call
bpf_redirect_neigh() to do the neigh lookup. The params->smac
output is skipped together when SKIP_NEIGH is set because
bpf_redirect_neigh() will figure out the smac also.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230217205515.3583372-1-martin.lau@linux.dev

1 files changed, 6 insertions, 0 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1503f61336b6..62ce1f5d1b1d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3134,6 +3134,11 @@ union bpf_attr {
  *		**BPF_FIB_LOOKUP_OUTPUT**
  *			Perform lookup from an egress perspective (default is
  *			ingress).
+ *		**BPF_FIB_LOOKUP_SKIP_NEIGH**
+ *			Skip the neighbour table lookup. *params*->dmac
+ *			and *params*->smac will not be set as output. A common
+ *			use case is to call **bpf_redirect_neigh**\ () after
+ *			doing **bpf_fib_lookup**\ ().
  *
  *		*ctx* is either **struct xdp_md** for XDP programs or
  *		**struct sk_buff** tc cls_act programs.
@@ -6750,6 +6755,7 @@ struct bpf_raw_tracepoint_args {
 enum {
 	BPF_FIB_LOOKUP_DIRECT  = (1U << 0),
 	BPF_FIB_LOOKUP_OUTPUT  = (1U << 1),
+	BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
 };
 
 enum {