bpf: add devmap, a map for storing net device references

Device map (devmap) is a BPF map, primarily useful for networking
applications, that uses a key to lookup a reference to a netdevice.

The map provides a clean way for BPF programs to build virtual port
to physical port maps. Additionally, it provides a scoping function
for the redirect action itself allowing multiple optimizations. Future
patches will leverage the map to provide batching at the XDP layer.

Another optimization/feature, that is not yet implemented, would be
to support multiple netdevices per key to support efficient multicast
and broadcast support.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/bpf/test_maps.c

@@ -438,6 +438,21 @@ static void test_arraymap_percpu_many_keys(void)
 	close(fd);
 }
 
+static void test_devmap(int task, void *data)
+{
+	int next_key, fd;
+	__u32 key, value;
+
+	fd = bpf_create_map(BPF_MAP_TYPE_DEVMAP, sizeof(key), sizeof(value),
+			    2, 0);
+	if (fd < 0) {
+		printf("Failed to create arraymap '%s'!\n", strerror(errno));
+		exit(1);
+	}
+
+	close(fd);
+}
+
 #define MAP_SIZE (32 * 1024)
 
 static void test_map_large(void)