Problem in sysdeps/unix/sysv/linux/tcsetattr.c

[Franz Sirl <Franz dot Sirl-kernel at lauterbach dot com>]

Hi,

in this file we have:

  if (retval == 0 && cmd == TCSETS)
    {
      /* The Linux kernel has a bug which silently ignore the invalid
         c_cflag on pty. We have to check it here. */
      int save = errno;
      retval = __ioctl (fd, TCGETS, &k_termios);
      if (retval)
        {
          /* We cannot verify if the setting is ok. We don't return
             an error (?). */
          __set_errno (save);
          retval = 0;
        }
      else if ((termios_p->c_cflag & (PARENB | CREAD))
               != (k_termios.c_cflag & (PARENB | CREAD))
               || ((termios_p->c_cflag & CSIZE)
                   && ((termios_p->c_cflag & CSIZE)
                       != (k_termios.c_cflag & CSIZE))))
        {
          /* It looks like the Linux kernel silently changed the
             PARENB/CREAD/CSIZE bits in c_cflag. Report it as an
             error. */
          __set_errno (EINVAL);
          retval = -1;
        }
    }

How is this "error checking" supposed to work against PTYs with this in the 
kernel (2.5.61 drivers/char/pty.c):

static void pty_set_termios(struct tty_struct *tty, struct termios 
*old_termios)
{
        tty->termios->c_cflag &= ~(CSIZE | PARENB);
        tty->termios->c_cflag |= (CS8 | CREAD);
}

This lets 7bit xterm fail with:

[fsirl@enzo:~]$ xterm
xterm: fatal pty error 23 (errno=22) on tty /dev/pts/11

Was the above error check possibly be obsoleted by newer kernel versions? Then 
we could handle that with an __ASSUME_WORKING_TCSETS.

Franz.