according to linux device drivers, POSIX standard is to return -ENOTTY for

invalid ioctl number

diff --git a/comedi/comedi_fops.c b/comedi/comedi_fops.c
index 7217ba87c07288108f0be8a913b043d01a2f3652..c53ff45d09c83c7c0a46154e776a6a935cd5a723 100644 (file)
--- a/comedi/comedi_fops.c
+++ b/comedi/comedi_fops.c
@@ -123,9 +123,8 @@ static int comedi_ioctl(struct inode * inode,struct file * file,
        case COMEDI_POLL:
                return do_poll_ioctl(dev,arg,file);
        default:
-               return -EIO;
+               return -ENOTTY;
        }
-       return -EIO;
 }