The solution (3)

• Problem: Notifying a waiting program that udev has finished running its rules so it is safe to proceed and use it.

• Solution: This was the trickiest problem to deal with as udev has only a primitive transactional model, with a simple transaction counter that can be queried to determine that all transactions up to the one returned have been completed but later ones may or may not have been. Our transactions could get 'stuck' behind slow ones (probing unreliable devices perhaps). In the end we could not find a way of using this and our current proposal adds our own transaction id – or cookie as we decided to call it.