How gtk distinguish event from differnt input device?

[Lam Yick Yan <superylam netscape net>]

Dear Sir,

    I have asked similar question before but may be the subject
is not very attractive, I ask again, using a different subject.

    Suppose I have 3 input devices, one PS/2 and one COM port and
one USB mouse. Now I am writing a GTK application with a drawing area,
and I have a callback event handler to handle motion_notify_event.
Is it possible to distinguish from which device the motion
event is triggered?

    In the gint motion_notify(GtkWidget *widget, GdkEvent *event),
I have study throught every field in the event structure, and I
cannot find a way to tell from which device the event is generated,
can some one please instruct me how to do so? An example or a pointer
to webpage will be greatly appreciated.

Yick Lam
Hong Kong, Chna