TTY: add support for unnumbered device nodes

This allows drivers like ttyprintk to avoid hacks to create an
unnumbered node in /dev. It used to set TTY_DRIVER_DYNAMIC_DEV in
flags and call device_create on its own. That is incorrect, because
TTY_DRIVER_DYNAMIC_DEV may be set only if tty_register_device is
called explicitly.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index a67609b..4d9898c 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1216,7 +1216,10 @@
  */
 static void tty_line_name(struct tty_driver *driver, int index, char *p)
 {
-	sprintf(p, "%s%d", driver->name, index + driver->name_base);
+	if (driver->flags & TTY_DRIVER_UNNUMBERED_NODE)
+		strcpy(p, driver->name);
+	else
+		sprintf(p, "%s%d", driver->name, index + driver->name_base);
 }
 
 /**
@@ -3076,7 +3079,7 @@
 	struct tty_driver *driver;
 	int err;
 
-	if (!lines)
+	if (!lines || (flags & TTY_DRIVER_UNNUMBERED_NODE && lines > 1))
 		return ERR_PTR(-EINVAL);
 
 	driver = kzalloc(sizeof(struct tty_driver), GFP_KERNEL);