selftests/bpf: Optionally select broadcasting flags

Broadcasting flags are hardcoded for each kind for protocol.

Create a redirect_flags map that allows to select the broadcasting flags
to use in the bpf_redirect_map(). The protocol ID is used as a key.
Set the old hardcoded values as default if the map isn't filled by the
BPF caller.

Signed-off-by: Bastien Curutchet (eBPF Foundation) <bastien.curutchet@bootlin.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250212-redirect-multi-v5-3-fd0d39fca6e6@bootlin.com

tools/testing/selftests/bpf/progs/xdp_redirect_multi_kern.c

@@ -34,32 +34,49 @@ struct {
 	__uint(max_entries, 128);
 } mac_map SEC(".maps");
 
+/* map to store redirect flags for each protocol*/
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, __u16);
+	__type(value, __u64);
+	__uint(max_entries, 16);
+} redirect_flags SEC(".maps");
+
 SEC("xdp")
 int xdp_redirect_map_multi_prog(struct xdp_md *ctx)
 {
 	void *data_end = (void *)(long)ctx->data_end;
 	void *data = (void *)(long)ctx->data;
 	int if_index = ctx->ingress_ifindex;
 	struct ethhdr *eth = data;
+	__u64 *flags_from_map;
 	__u16 h_proto;
 	__u64 nh_off;
+	__u64 flags;
 
 	nh_off = sizeof(*eth);
 	if (data + nh_off > data_end)
 		return XDP_DROP;
 
-	h_proto = eth->h_proto;
-
-	/* Using IPv4 for (BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS) testing */
-	if (h_proto == bpf_htons(ETH_P_IP))
-		return bpf_redirect_map(&map_all, 0,
-					BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS);
-	/* Using IPv6 for none flag testing */
-	else if (h_proto == bpf_htons(ETH_P_IPV6))
-		return bpf_redirect_map(&map_all, if_index, 0);
-	/* All others for BPF_F_BROADCAST testing */
-	else
-		return bpf_redirect_map(&map_all, 0, BPF_F_BROADCAST);
+	h_proto = bpf_htons(eth->h_proto);
+
+	flags_from_map = bpf_map_lookup_elem(&redirect_flags, &h_proto);
+
+	/* Default flags for IPv4 : (BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS) */
+	if (h_proto == ETH_P_IP) {
+		flags = flags_from_map ? *flags_from_map : BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS;
+		return bpf_redirect_map(&map_all, 0, flags);
+	}
+	/* Default flags for IPv6 : 0 */
+	if (h_proto == ETH_P_IPV6) {
+		flags = flags_from_map ? *flags_from_map : 0;
+		return bpf_redirect_map(&map_all, if_index, flags);
+	}
+	/* Default flags for others BPF_F_BROADCAST : 0 */
+	else {
+		flags = flags_from_map ? *flags_from_map : BPF_F_BROADCAST;
+		return bpf_redirect_map(&map_all, 0, flags);
+	}
 }
 
 /* The following 2 progs are for 2nd devmap prog testing */