A device in Linux has at least a minor number with a major number. In case of P-PCI-LV, the device driver has a major number while each P-PCI-LV has each minor number. The number number is determined in the device driver when it is loaded. It tries to find P-PCI-LV in PCI slot in order. The device near CPU will be found first. This means the minor number of P-PCI-LV depends on the position of PCI slot. If you change the position, the minor number may change. Thus, minor number is not convenient to identify the device. The device has Switch register. You can define the value as the identification of the device. Thus, you read the contents of the register after calling a open system call, and then use the value as the identification.