diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 6e211b6..108a1e99 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -274,7 +274,8 @@
 	int capabilities;
 	char serverName[SERVER_NAME_LEN_WITH_NULL * 2];	/* BB make bigger for
 				TCP names - will ipv6 and sctp addresses fit? */
-	char *user_name;
+	char *user_name;	/* must not be null except during init of sess
+				   and after mount option parsing we fill it */
 	char *domainName;
 	char *password;
 	struct session_key auth_key;