I.MX6 Android backlight modify by C demo

/**************************************************************************
*             I.MX6 Android backlight modify by C demo
* 说明：
*     因为一些特殊情况，需要添加一个这个简单的控制程序来控制android背光
* 亮度，个人感觉是没有必要的，但是应要求还是加上。
*
*                                      2016-5-14 深圳 南山平山村 曾剑锋
*************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <string.h>
#include <errno.h>

#define BACKLIGHT0_PATH "/sys/class/backlight/pwm-backlight.0/brightness"
#define BACKLIGHT1_PATH "/sys/class/backlight/pwm-backlight.1/brightness"

//#define BACKLIGHT0_PATH "brightness0"
//#define BACKLIGHT1_PATH "brightness1"

int help ( int argc );
int isDigitalStr(char *str);
int file_exists(char *filename);
void writeStringToFile(char *filePath, char *string);

int main(int argc, char **argv)
{
int bl0 = 0;
int bl1 = 0;

if ( help( argc ) != 0)
return -1;

if ( !isDigitalStr(argv[1]) ) {
printf("Please give a numeric string.\n");
return -1;
}

writeStringToFile(BACKLIGHT0_PATH, argv[1]);
writeStringToFile(BACKLIGHT1_PATH, argv[1]);
}

void writeStringToFile(char *filePath, char *string)
{
int fd = 0;

if ( file_exists(filePath) ) {

fd = open(filePath, O_RDWR);

ftruncate(fd, 0);
write(fd, string, strlen(string));

close(fd);

}
}

int isDigitalStr(char *str)
{
int len = strlen(str);
char *s = str;
int i = 0;

while( '0' <= *s && *s <= '9' && i < len){
s++;
i++;
}

if(i == len)
return 1;
else
return 0;
}

int file_exists(char *filename)
{
if (access(filename, F_OK) == 0) {
return 1;
} else {
printf("%s is not exist.\n", filename);
return 0;
}
}

int help( int argc )
{
if ( argc != 2 ) {
printf ( "USAGE:\n" );
printf ( "    backlight <value>\n" );
printf ( "    example:\n" );
printf ( "        backlight 0\n" );
return -1;
}

return 0;
}