zdev: Improve handling of invalid udev rules

Add basic checking when reading udev rules and print a warning when an
invalid udev rule file is found. This addresses the current inconsistent
behavior:

  - CCW devices: invalid udev rules are considered valid
  - CCW group devices: invalid udev rules are silently ignored
  - zFCP LUNs: invalid rules cause chzdev/lszdev to silently terminate
    with non-zero exit code

Checks include a test for empty or truncated rule files that might be
the result of an interrupted chzdev operation, or a file system or I/O
error.

Note: The recommended way to correct invalid udev rules is to either
remove the offending rules file, or to repeat the associated persistent
configuration step.

Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reported-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdev/src/udev.c

@@ -346,6 +346,21 @@ exit_code_t udev_read_file(const char *path, struct udev_file **file_ptr)
 	return EXIT_OK;
 }
 
+/* Check if a udev file does not contain any statements. */
+bool udev_file_is_empty(struct udev_file *file)
+{
+	struct udev_line_node *l;
+
+	if (!file)
+		return true;
+	util_list_iterate(&file->lines, l) {
+		if (l->line[0])
+			return false;
+	}
+
+	return true;
+}
+
 static bool get_ids_cb(const char *filename, void *data)
 {
 	char *prefix = data;