Index: kernel/generic/include/ipc/ipc.h
===================================================================
--- kernel/generic/include/ipc/ipc.h	(revision d51a0d61e43baaf646db5fd0827b7e8c89b0f4f5)
+++ kernel/generic/include/ipc/ipc.h	(revision 7c0e1f596a64720b6f6a6ec66b3499a9d26511cb)
@@ -106,4 +106,6 @@
 	/** Phone which made or last masqueraded this call. */
 	phone_t *phone;
+	/** User-defined label */
+	sysarg_t label;
 } ipc_data_t;
 
Index: kernel/generic/include/ipc/sysipc.h
===================================================================
--- kernel/generic/include/ipc/sysipc.h	(revision d51a0d61e43baaf646db5fd0827b7e8c89b0f4f5)
+++ kernel/generic/include/ipc/sysipc.h	(revision 7c0e1f596a64720b6f6a6ec66b3499a9d26511cb)
@@ -44,5 +44,5 @@
 extern sysarg_t sys_ipc_call_async_fast(sysarg_t, sysarg_t, sysarg_t,
     sysarg_t, sysarg_t, sysarg_t);
-extern sysarg_t sys_ipc_call_async_slow(sysarg_t, ipc_data_t *);
+extern sysarg_t sys_ipc_call_async_slow(sysarg_t, ipc_data_t *, sysarg_t);
 extern sysarg_t sys_ipc_answer_fast(sysarg_t, sysarg_t, sysarg_t, sysarg_t,
     sysarg_t, sysarg_t);