Index: uspace/srv/net/include/device.h
===================================================================
--- uspace/srv/net/include/device.h	(revision daecfed36380a6e328ff223e435bda5697785880)
+++ uspace/srv/net/include/device.h	(revision c92a5753b68f5804744c1b828ba80a97caaa5ce0)
@@ -47,4 +47,8 @@
  */
 #define DEVICE_MAP_IMPLEMENT	INT_MAP_IMPLEMENT
+
+/** Invalid device identifier.
+ */
+#define DEVICE_INVALID_ID		( -1 )
 
 /** Device identifier type.