By default, an open file description does not have an id by itself. In picotm, we construct the id from the file id of the open file description's file and a file descriptor that refers to the open file description.

If two file descriptors refer to the same open file description, they create two different ids. Even though the open file description is the same, these ids must compare as different. The look-up code fixes this ad-hoc. It's a short coming resulting fom the non-existance of unique system ids for open file descriptions.