Usage: int ddu_put_fev(struct fifo_entry fev)
Returns: 0 if good status, -1 if bad status, >0 if interrupted system call
Inserts a fifo entry fev to the DD system. The fev is inserted
at the INPUT_FIFO. This routine can be called by producers and consumers.
Care has to be taken in the case of a consumer using this routine: As
the fev is inserted at the INPUT_FIFO, the event might end up at the consumer
again (unless the latter modified the fev.ctl words).