title: Unique device identifiers for USB, firewire, and serial ports
body: <p>I am working on a project that involves the auto-detection of USB and firewire devices being plugged and unplugged from an OS X system. For a given device, the system needs to recognise a device when it is plugged in (no matter which port) and load a device-specific bundle to deal with it.</p>
  
  <p>The key to making this work is obviously the unique identification of each device. I know that USB devices are identified by a combination of the vendor ID and product ID fields, but this does not provide a unique ID, only the "kind" of device. If I have two devices the same and I plug both of them in to the computer, I would like some way to distinguish them. Is there a general and reliable way to do this, perhaps using other fields in the USB descriptor?</p>
  
  <p>A related question, how does this work for USB serial ports? Suppose I plug in two USB serial ports of the same make/model. OS X should give them unique inodes in the /dev tree. However, suppose it calls them /dev/usbserial1 and /dev/usbserial2. If I then unplug the ports and plug in only one one of them, will that port be given the same name as it previously had, or will it just get /dev/usbserial1 (since it is the only) port plugged in?</p>
  
  <p>Same question for firewire devices, although I think firewire devices are supposed to have a 64-bit GUID. In this case I am looking for someone to verify that using the GUID for firewire device identification would be reliable. In other words, if I plugged in two separate cameras of the same make and model, would I expect them to have different GUIDs?</p>
  
  <p>I know I could test some of these with the appropriate hardware, but I don't have multiple bits of hardware at this time, so I am hoping someone may know at least some of the answers to the above questions.</p>