bpftool: make key and value optional in update command

Bpftool expects both key and value for 'update' operations. For some
map types, key should not be specified. Support updating those map types.

Before:
bpftool map create /sys/fs/bpf/q type queue value 4 entries 10 name q
bpftool map update pinned /sys/fs/bpf/q value 0 1 2 3
Error: did not find key

After:
bpftool map create /sys/fs/bpf/q type queue value 4 entries 10 name q
bpftool map update pinned /sys/fs/bpf/q value 0 1 2 3
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/Documentation/bpftool-map.rst

@@ -25,7 +25,7 @@ MAP COMMANDS
 |	**bpftool** **map create**     *FILE* **type** *TYPE* **key** *KEY_SIZE* **value** *VALUE_SIZE* \
 |		**entries** *MAX_ENTRIES* **name** *NAME* [**flags** *FLAGS*] [**dev** *NAME*]
 |	**bpftool** **map dump**       *MAP*
-|	**bpftool** **map update**     *MAP*  **key** *DATA*   **value** *VALUE* [*UPDATE_FLAGS*]
+|	**bpftool** **map update**     *MAP* [**key** *DATA*] [**value** *VALUE*] [*UPDATE_FLAGS*]
 |	**bpftool** **map lookup**     *MAP*  **key** *DATA*
 |	**bpftool** **map getnext**    *MAP* [**key** *DATA*]
 |	**bpftool** **map delete**     *MAP*  **key** *DATA*
@@ -62,7 +62,7 @@ DESCRIPTION
 	**bpftool map dump**    *MAP*
 		  Dump all entries in a given *MAP*.
 
-	**bpftool map update**  *MAP*  **key** *DATA*   **value** *VALUE* [*UPDATE_FLAGS*]
+	**bpftool map update**  *MAP* [**key** *DATA*] [**value** *VALUE*] [*UPDATE_FLAGS*]
 		  Update map entry for a given *KEY*.
 
 		  *UPDATE_FLAGS* can be one of: **any** update existing entry

tools/bpf/bpftool/map.c

@@ -779,6 +779,32 @@ static int do_dump(int argc, char **argv)
 	return err;
 }
 
+static int alloc_key_value(struct bpf_map_info *info, void **key, void **value)
+{
+	*key = NULL;
+	*value = NULL;
+
+	if (info->key_size) {
+		*key = malloc(info->key_size);
+		if (!*key) {
+			p_err("key mem alloc failed");
+			return -1;
+		}
+	}
+
+	if (info->value_size) {
+		*value = alloc_value(info);
+		if (!*value) {
+			p_err("value mem alloc failed");
+			free(*key);
+			*key = NULL;
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
 static int do_update(int argc, char **argv)
 {
 	struct bpf_map_info info = {};
@@ -795,13 +821,9 @@ static int do_update(int argc, char **argv)
 	if (fd < 0)
 		return -1;
 
-	key = malloc(info.key_size);
-	value = alloc_value(&info);
-	if (!key || !value) {
-		p_err("mem alloc failed");
-		err = -1;
+	err = alloc_key_value(&info, &key, &value);
+	if (err)
 		goto exit_free;
-	}
 
 	err = parse_elem(argv, &info, key, value, info.key_size,
 			 info.value_size, &flags, &value_fd);
@@ -1135,7 +1157,7 @@ static int do_help(int argc, char **argv)
 		"                              entries MAX_ENTRIES name NAME [flags FLAGS] \\\n"
 		"                              [dev NAME]\n"
 		"       %s %s dump       MAP\n"
-		"       %s %s update     MAP  key DATA value VALUE [UPDATE_FLAGS]\n"
+		"       %s %s update     MAP [key DATA] [value VALUE] [UPDATE_FLAGS]\n"
 		"       %s %s lookup     MAP  key DATA\n"
 		"       %s %s getnext    MAP [key DATA]\n"
 		"       %s %s delete     MAP  key DATA\n"