On Tue, 07 Dec 2010 08:25:26 +0100, Henrik Rydberg said:

Today, userspace sets up an input device based on the data it emits.
This is not always enough; a tablet and a touchscreen may emit exactly
the same data, for instance, but the former should be set up with a
pointer whereas the latter does not need to. Recently, a new type of
touchpad has emerged where the buttons are under the pad, which changes
handling logic without changing the emitted data. This patch introduces
a new ioctl, EVIOCGDEVINFO, which allows userspace to extract information
about the device resulting in proper setup.

 /*
+ * Device types
+ */
+
+#define DEVTYPE_KEYBOARD	0
+#define DEVTYPE_MOUSE		1
+#define DEVTYPE_JOYSTICK	2
+#define DEVTYPE_TOUCHPAD	3
+#define DEVTYPE_TABLET		4
+#define DEVTYPE_TOUCHSCREEN	5

Add a #define DEVTYPE_UNKNOWN 0 and push everybody else down one. That way,
an uninitialized 'struct input_devinfo' won't claim to be a keyboard.