Listing 9. Sample Data Write Function
/*
 * 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, or 
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */


#include <stdlib.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <asm/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdint.h>
#include <errno.h>

#include <linux/input.h>


int main (int argc, char **argv) {

    int fd = -1;           /* the file descriptor for the device */
    int retval = 0;        /* bytes written in write() */
    struct input_event ev; /* the event */

    /* read() requires a file descriptor, so we check for one, and then open it */
    if (argc != 2) {
	fprintf(stderr, "usage: %s event-device - probably /dev/input/event0\n", argv[0]);
	exit(1);
    }
    if ((fd = open(argv[1], O_WRONLY)) < 0) {
	perror("evdev open");
	exit(1);
    }

    /* we turn off all the LEDs to start */
    ev.type = EV_LED;
    ev.code = LED_CAPSL;
    ev.value = 0;
    retval = write(fd, &ev, sizeof(struct input_event));
    ev.code = LED_NUML;
    retval = write(fd, &ev, sizeof(struct input_event));
    ev.code = LED_SCROLLL;
    retval = write(fd, &ev, sizeof(struct input_event));

    while (1)
	{
	    ev.code = LED_CAPSL;
	    ev.value = 1;
	    retval = write(fd, &ev, sizeof(struct input_event));
	    usleep(200000);
	    ev.value = 0;
	    retval = write(fd, &ev, sizeof(struct input_event));

	    ev.code = LED_NUML;
	    ev.value = 1;
	    write(fd, &ev, sizeof(struct input_event));
	    usleep(200000);
	    ev.value = 0;
	    retval = write(fd, &ev, sizeof(struct input_event));
	}

    close(fd);

    exit(0);
}