ptyfork.c

#include "apue.h"
#include <termios.h>

pid_t
pty_fork (int *ptrfdm, char *slave_name, int slave_namesz,
	  const struct termios *slave_termios,
	  const struct winsize *slave_winsize)
{
  int fdm, fds;
  pid_t pid;
  char pts_name[20];

  if ((fdm = ptym_open (pts_name, sizeof (pts_name))) < 0)
    err_sys ("can't open master pty: %s, error %d", pts_name, fdm);

  if (slave_name != NULL)
    {
      /*
       * Return name of slave.  Null terminate to handle case
       * where strlen(pts_name) > slave_namesz.
       */
      strncpy (slave_name, pts_name, slave_namesz);
      slave_name[slave_namesz - 1] = '\0';
    }

  if ((pid = fork ()) < 0)
    {
      return (-1);
    }
  else if (pid == 0)
    {				/* child */
      if (setsid () < 0)
	err_sys ("setsid error");

      /*
       * System V acquires controlling terminal on open().
       */
      if ((fds = ptys_open (pts_name)) < 0)
	err_sys ("can't open slave pty");
      close (fdm);		/* all done with master in child */

#if	defined(BSD)
      /*
       * TIOCSCTTY is the BSD way to acquire a controlling terminal.
       */
      if (ioctl (fds, TIOCSCTTY, (char *) 0) < 0)
	err_sys ("TIOCSCTTY error");
#endif
      /*
       * Set slave's termios and window size.
       */
      if (slave_termios != NULL)
	{
	  if (tcsetattr (fds, TCSANOW, slave_termios) < 0)
	    err_sys ("tcsetattr error on slave pty");
	}
      if (slave_winsize != NULL)
	{
	  if (ioctl (fds, TIOCSWINSZ, slave_winsize) < 0)
	    err_sys ("TIOCSWINSZ error on slave pty");
	}

      /*
       * Slave becomes stdin/stdout/stderr of child.
       */
      if (dup2 (fds, STDIN_FILENO) != STDIN_FILENO)
	err_sys ("dup2 error to stdin");
      if (dup2 (fds, STDOUT_FILENO) != STDOUT_FILENO)
	err_sys ("dup2 error to stdout");
      if (dup2 (fds, STDERR_FILENO) != STDERR_FILENO)
	err_sys ("dup2 error to stderr");
      if (fds != STDIN_FILENO && fds != STDOUT_FILENO && fds != STDERR_FILENO)
	close (fds);
      return (0);		/* child returns 0 just like fork() */
    }
  else
    {				/* parent */
      *ptrfdm = fdm;		/* return fd of master */
      return (pid);		/* parent returns pid of child */
    }
}