I'm trying to find a way to mark a USB flash device in a way that I can programmaticly test for without mounting it or changing the label.
Are there any properties I can modify about a device that will not cause it to behave/look differently to the user?
Running Ubuntu Jaunty.
You cannot modify this property, but the tuple (vendor_id, product_id, serial_number) is unique to each device, so you can use this as mark that is already there. You can enumerate the devices on the USB bus using lsusb or usblib.
Changing the VID/PID might make your device non-usable without custom drivers. HAL isn't supposed to auto-mount your flash drives for you.
That being said, you could always sneak something into the boot sector and/or the beginning part of the drive. There are a lot of spare bytes in there that can be used for custom purposes - both nefarious and otherwise.