When VTAM® invokes the USERVAR exit routine because a USERVAR is being added, the exit attempts to allocate a UVCB for the USERVAR. If the exit allocates the UVCB successfully, the exit initializes the UVCB and adds it to the UVCB queue. If the exit does not allocate the UVCB successfully, the exit sets the return code to 0 and returns control. Likewise, if any of the processing required to add the USERVAR fails, the exit sets the return code to 0, returns control, and processing continues.