/*
 * Program to test for possible misbehaviour upon accessing /dev/tty
 *  when the `real' ctty device isn't open.
 *
 * Run this with a tty device pathname as an argument.  For the test to
 *  be valid, the tty device must be one nothing else has open.
 */

#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <termios.h>
#include <strings.h>
#include <sys/wait.h>
#include <sys/ioctl.h>

extern const char *__progname;

static const char *ttydev;
static int ttyfd;
static int devttyfd;

static void forkchild(void)
{
 pid_t kid;
 int status;

 fflush(0);
 kid = fork();
 if (kid == 0) return;
 wait(&status);
 if (WIFEXITED(status))
  { if (WEXITSTATUS(status) == 0) exit(0);
    printf("exit %d\n",(int)WEXITSTATUS(status));
    exit(1);
  }
 if (WIFSIGNALED(status))
  { printf("signal %d (%s)%s\n",WTERMSIG(status),(WTERMSIG(status)>=NSIG)?"unknown":sys_siglist[WTERMSIG(status)],WCOREDUMP(status)?" - core dumped":"");
    exit(1);
  }
 printf("incomprehensible exit status %d (%#x)\n",status,status);
 exit(1);
}

int main(int, char **);
int main(int ac, char **av)
{
 int n;

 if (ac != 2)
  { fprintf(stderr,"Usage: %s tty-device\n",__progname);
    exit(1);
  }
 ttydev = av[1];
 // setsid() is defined to fail for process group leaders (why?!)
 if (getpgrp() == getpid()) forkchild();
 // Make us session leader of a new session
 if (setsid() < 0)
  { fprintf(stderr,"%s: setsid() failed: %s\n",__progname,strerror(errno));
    exit(1);
  }
 // We want to be able to print stuff even if stdout is a tty...
 signal(SIGTTOU,SIG_IGN);
 // Open the specified tty device.
 ttyfd = open(ttydev,O_RDWR|O_NONBLOCK,0);
 if (ttyfd < 0)
  { fprintf(stderr,"%s: can't open %s: %s\n",__progname,ttydev,strerror(errno));
    exit(1);
  }
 // Make it our ctty
 if (ioctl(ttyfd,TIOCSCTTY,0) < 0)
  { fprintf(stderr,"%s: TIOCSCTTY failed: %s\n",__progname,strerror(errno));
    exit(1);
  }
 // Open /dev/tty
 devttyfd = open("/dev/tty",O_RDWR|O_NONBLOCK,0);
 if (ttyfd < 0)
  { fprintf(stderr,"%s: can't open /dev/tty: %s\n",__progname,strerror(errno));
    exit(1);
  }
 // Close the real ctty
 close(ttyfd);
 // Test: try to access it via /dev/tty
 n = write(devttyfd,"hello\r\n",7);
 if (n < 0)
  { fprintf(stderr,"%s: test write failed: %s\n",__progname,strerror(errno));
    exit(1);
  }
 if (n != 7)
  { fprintf(stderr,"%s: test write returned %d, not 7\n",__progname,n);
    exit(1);
  }
 fprintf(stderr,"%s: test write worked\n",__progname);
 exit(0);
}