open() returns error when daemonized

Question

In my case I'm trying to write to frame buffer /dev/fb1. As soon as I daemonize the program I get no valid file descriptor. I tried it with a regular file (with correct permissions) - same result. When I comment out daemonize(); everything runs fine.

int fbfd;

void initFB()
{
    fbfd = open("/dev/fb1", O_RDWR);
    if (!fbfd) 
    {
        exit(EXIT_FAILURE);
    }
    ...
}

int daemonize()
{
    pid_t pid,sid;
    int lockFile;
    char ProcessID[10];

    pid = fork();
    if (pid < 0)
    {
        exit(EXIT_FAILURE);
    } else if (pid != 0) 
    {
        exit(EXIT_SUCCESS);
    }

    umask(0);

    sid = setsid();
    if(sid < 0)
    {
        exit(EXIT_FAILURE);
    }

    lockFile = open("/var/run/program.pid",O_RDWR|O_CREAT,0640);
    if (lockFile < 0)
    {
        exit(EXIT_FAILURE);
    }
    if (lockf(lockFile,F_TLOCK,0)<0)
    {
        exit(EXIT_SUCCESS);
    }

    sprintf(ProcessID,"%d\n",getpid());
    write(lockFile,ProcessID,strlen(ProcessID));

    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);
    signal(SIGCHLD,SIG_IGN);
    signal(SIGTSTP,SIG_IGN);
    signal(SIGTTOU,SIG_IGN);
    signal(SIGTTIN,SIG_IGN);
    signal(SIGHUP,signal_handler);
    signal(SIGTERM,signal_handler);

   return(1);
}


int main(int argc,char **argv)
{
    daemonize();
    initFB();
    ...
}

Answer 1

Your check for the result of open() is incorrect. On failure, open() returns -1, not 0. In your case, this happens because open() will end up with the lowest available file descriptor, which is 0 here, as you've closed stdin.