#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

#define SYSFS_CLASS_USID        "/sys/class/efuse/usid"
#define USID_LEN        16

int main(int argc, char *argv[])
{
        int fd, len;
        char buf[USID_LEN];

        fd = open(SYSFS_CLASS_USID, O_RDONLY);
        if (fd < 0)
                printf("Open error! \n");

        read(fd, buf, USID_LEN);

        printf("S/N is '%s'\n", buf);

        close(fd);

        return 0;
}