tools: add selftest for BPF_F_ZERO_SEED

Check that iterating two separate hash maps produces the same
order of keys if BPF_F_ZERO_SEED is used.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/test_maps.c

@@ -258,24 +258,36 @@ static void test_hashmap_percpu(int task, void *data)
 	close(fd);
 }
 
-static void test_hashmap_walk(int task, void *data)
+static int helper_fill_hashmap(int max_entries)
 {
-	int fd, i, max_entries = 1000;
-	long long key, value, next_key;
-	bool next_key_valid = true;
+	int i, fd, ret;
+	long long key, value;
 
 	fd = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value),
 			    max_entries, map_flags);
-	if (fd < 0) {
-		printf("Failed to create hashmap '%s'!\n", strerror(errno));
-		exit(1);
-	}
+	CHECK(fd < 0,
+	      "failed to create hashmap",
+	      "err: %s, flags: 0x%x\n", strerror(errno), map_flags);
 
 	for (i = 0; i < max_entries; i++) {
 		key = i; value = key;
-		assert(bpf_map_update_elem(fd, &key, &value, BPF_NOEXIST) == 0);
+		ret = bpf_map_update_elem(fd, &key, &value, BPF_NOEXIST);
+		CHECK(ret != 0,
+		      "can't update hashmap",
+		      "err: %s\n", strerror(ret));
 	}
 
+	return fd;
+}
+
+static void test_hashmap_walk(int task, void *data)
+{
+	int fd, i, max_entries = 1000;
+	long long key, value, next_key;
+	bool next_key_valid = true;
+
+	fd = helper_fill_hashmap(max_entries);
+
 	for (i = 0; bpf_map_get_next_key(fd, !i ? NULL : &key,
 					 &next_key) == 0; i++) {
 		key = next_key;
@@ -306,6 +318,39 @@ static void test_hashmap_walk(int task, void *data)
 	close(fd);
 }
 
+static void test_hashmap_zero_seed(void)
+{
+	int i, first, second, old_flags;
+	long long key, next_first, next_second;
+
+	old_flags = map_flags;
+	map_flags |= BPF_F_ZERO_SEED;
+
+	first = helper_fill_hashmap(3);
+	second = helper_fill_hashmap(3);
+
+	for (i = 0; ; i++) {
+		void *key_ptr = !i ? NULL : &key;
+
+		if (bpf_map_get_next_key(first, key_ptr, &next_first) != 0)
+			break;
+
+		CHECK(bpf_map_get_next_key(second, key_ptr, &next_second) != 0,
+		      "next_key for second map must succeed",
+		      "key_ptr: %p", key_ptr);
+		CHECK(next_first != next_second,
+		      "keys must match",
+		      "i: %d first: %lld second: %lld\n", i,
+		      next_first, next_second);
+
+		key = next_first;
+	}
+
+	map_flags = old_flags;
+	close(first);
+	close(second);
+}
+
 static void test_arraymap(int task, void *data)
 {
 	int key, next_key, fd;
@@ -1534,6 +1579,7 @@ static void run_all_tests(void)
 	test_hashmap(0, NULL);
 	test_hashmap_percpu(0, NULL);
 	test_hashmap_walk(0, NULL);
+	test_hashmap_zero_seed();
 
 	test_arraymap(0, NULL);
 	test_arraymap_percpu(0, NULL);