How to identify a disconnecting USB device using udev rules?

Question

I have two LCD's using Xorg's xinerama feature. Each LCD screen has a touchscreen which are connected to their respective USB lines.

Looking into the '/var/log/messages' file, I see the following:

kernel: input: Analog Resistive as /class/input/input0
kernel: input: USB HID v1.01 Mouse [Analog Resistive] on usb-0000:00:1d.3-1
kernel: input: Analog Resistive as /class/input/input1
kernel: input: USB HID v1.01 Mouse [Analog Resistive] on usb-0000:00:1d.3-2

For some reason, at some point in time the USB bus seems to reset (or something weird) and my two touchscreens get inverted (press the left LCD and the mouse moves on the right and if I press the right LCD the mouse moves on the left).

To try and debug the problem, I tried to write a udev rule to log when my devices get reset/disconnected (or whatever). But it seems as though udev will report full details (product, manufacturer, idProduct, idVendor, etc) on the device when it connects, but gives you nothing but a few bus numbers when it is removed. Why is this?

When I get an ACTION=="remove", KERNEL=="input*" rule, there is no way for me to know which device it is! Does anyone know a way around this?

Answer 1

I have run into the same problem in Linux. The information sent on a remove is minimal and cannot be used to uniquely identify the device being removed. I use to use the PHYDEVPATH (which is unique on plug in and unplug for a given machine and USB port), but very unfortunately, that has been deprecated in later versions of udev.