Kontron KTAM3874-pITX - Manual (Page 263)

KTD-S0057-I Page 259 Linux® Programming Examples (DebianTM)
KTAM3874/pITX Software Guide
10.13 Interprocess Communication (Root/User)
Many examples in this guide require root access. If you want to retain the user permissions the easiest way
is based on InterProcess Communication (IPC) between a root (server) and a user (client) program. For
background operation the server part can be realized as a Daemon. A number of possible communication
types exist: shared memory, mapped memory, pipes, FIFOs (named pipes) and sockets. The following
demonstration programs only use FIFOs. Any process has the ability to open or close the FIFO; the proces-
ses on either end of the pipe need not be related to each other. A FIFO can possess multiple readers or
multiple writers.
As a first step the sample programs run as normal applications in a terminal window, one as root (server)
and the other one as user (client).
One possible Makefile (server) might look like this:
CC := arm-linux-gnueabihf-gcc -march=armv7
all: server
server.o: server.c
server: server.o
$(CC) -o $@ server.o
clean:
rm server server.o
One possible Makefile (client) might look like this:
CC := arm-linux-gnueabihf-gcc -march=armv7
all: client
client.o: client.c
client: client.o
$(CC) -o $@ client.o
clean:
rm client client.o
and now the Include-file 'fifo.h':
/* Include file for server & client application
* Copyright (c) 2014 Kontron Technology A/S
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License. */
#ifndef FIFO_H
#define FIFO_H
#define RD_SIZE 32
#define WR_SIZE 32
#define POLL_TIME 5 /* milliseconds */