update: job ID must be positive

The documentation for directory_update_init() was incorrect: a job ID
must be positive, not non-negative.  If the update queue is full and
no job was created, it makes more sense to return 0 instead of -1,
because it is more consistent with the return value of isUpdatingDB().

src/command.c

@@ -803,31 +803,27 @@ static int handlePlaylistMove(struct client *client,
 	return print_playlist_result(client, result);
 }
 
-static int print_update_result(struct client *client, int ret)
-{
-	if (ret >= 0) {
-		client_printf(client, "updating_db: %i\n", ret);
-		return 0;
-	}
-	if (ret == -2)
-		command_error(client, ACK_ERROR_ARG, "invalid path");
-	else
-		command_error(client, ACK_ERROR_UPDATE_ALREADY,
-			      "already updating");
-	return -1;
-}
-
 static int handleUpdate(struct client *client,
 			mpd_unused int argc, char *argv[])
 {
 	char *path = NULL;
+	int ret;
 
 	assert(argc <= 2);
 	if (argc == 2 && !(path = sanitizePathDup(argv[1]))) {
 		command_error(client, ACK_ERROR_ARG, "invalid path");
 		return -1;
 	}
-	return print_update_result(client, directory_update_init(path));
+
+	ret = directory_update_init(path);
+	if (ret > 0) {
+		client_printf(client, "updating_db: %i\n", ret);
+		return 0;
+	} else {
+		command_error(client, ACK_ERROR_UPDATE_ALREADY,
+			      "already updating");
+		return -1;
+	}
 }
 
 static int handleNext(mpd_unused struct client *client,

src/database.c

@@ -46,7 +46,7 @@ db_init(void)
 	music_root = directory_new("", NULL);
 
 	ret = directory_update_init(NULL);
-	if (ret < 0)
+	if (ret == 0)
 		FATAL("directory update failed\n");
 
 	do {

src/update.c

@@ -436,9 +436,9 @@ int directory_update_init(char *path)
 		int next_task_id;
 
 		if (!path)
-			return -1;
+			return 0;
 		if (update_paths_nr == ARRAY_SIZE(update_paths))
-			return -1;
+			return 0;
 		assert(update_paths_nr < ARRAY_SIZE(update_paths));
 		update_paths[update_paths_nr++] = path;
 		next_task_id = update_task_id + update_paths_nr;

src/update.h

@@ -23,8 +23,8 @@
 int isUpdatingDB(void);
 
 /*
- * returns the non-negative update job ID on success,
- * returns -1 if busy
+ * returns the positive update job ID on success,
+ * returns 0 if busy
  * @path will be freed by this function and should not be reused
  */
 int directory_update_init(char *path);