rtf_make_user_pair modifies the behaviour of the RT-FIFO N: user-space reads of the /dev/rtfN are now routed to RT-FIFO P. User-space writes to /dev/rtfN continue communicating with fifo N. This essentially makes /dev/rtfN bidirectional: data sent with rtf_put to FIFO P will be read from /dev/rtfN; rtf_get on FIFO N gets data written to /dev/rtfN. RT-FIFO handlers are affected similarly.
The RT-FIFO is a mechanism, implemented as a character device, to communicate between realtime tasks and ordinary Linux processes. The rtf_* functions are used by the realtime tasks; Linux processes use standard character device access functions such as read(2), write(2) and select(2).
N or P is greater than or equal to RTF_NO.
N or P is not a valid RT-FIFO identifier.