TTY: provide tty_standard_install helper

There are currently many cut&paste copies of what
tty_driver_install_tty does when custom ->install method is not
provided. Let's get rid of the copies and create a helper with this
setup code.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Havard Skinnemoen <hskinnemoen@google.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -1271,6 +1271,19 @@ int tty_init_termios(struct tty_struct *tty)
 }
 EXPORT_SYMBOL_GPL(tty_init_termios);
 
+int tty_standard_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	int ret = tty_init_termios(tty);
+	if (ret)
+		return ret;
+
+	tty_driver_kref_get(driver);
+	tty->count++;
+	driver->ttys[tty->index] = tty;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tty_standard_install);
+
 /**
  *	tty_driver_install_tty() - install a tty entry in the driver
  *	@driver: the driver for the tty
@@ -1286,21 +1299,8 @@ EXPORT_SYMBOL_GPL(tty_init_termios);
 static int tty_driver_install_tty(struct tty_driver *driver,
 						struct tty_struct *tty)
 {
-	int idx = tty->index;
-	int ret;
-
-	if (driver->ops->install) {
-		ret = driver->ops->install(driver, tty);
-		return ret;
-	}
-
-	if (tty_init_termios(tty) == 0) {
-		tty_driver_kref_get(driver);
-		tty->count++;
-		driver->ttys[idx] = tty;
-		return 0;
-	}
-	return -ENOMEM;
+	return driver->ops->install ? driver->ops->install(driver, tty) :
+		tty_standard_install(driver, tty);
 }
 
 /**

include/linux/tty.h

@@ -484,6 +484,8 @@ extern void deinitialize_tty_struct(struct tty_struct *tty);
 extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx);
 extern int tty_release(struct inode *inode, struct file *filp);
 extern int tty_init_termios(struct tty_struct *tty);
+extern int tty_standard_install(struct tty_driver *driver,
+		struct tty_struct *tty);
 
 extern struct tty_struct *tty_pair_get_tty(struct tty_struct *tty);
 extern struct tty_struct *tty_pair_get_pty(struct tty_struct *tty);