tty: new helper function tty_get_icount()

For a given struct tty_struct this yields the corresponding statistics
about sent and received characters (and some more) which is needed to
implement an LED trigger for tty devices.

The new function is then used to simplify tty_tiocgicount().
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20201218104246.591315-3-u.kleine-koenig@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -2488,15 +2488,36 @@ static int tty_tiocmset(struct tty_struct *tty, unsigned int cmd,
 	return tty->ops->tiocmset(tty, set, clear);
 }
 
+/**
+ *	tty_get_icount		-	get tty statistics
+ *	@tty: tty device
+ *	@icount: output parameter
+ *
+ *	Gets a copy of the tty's icount statistics.
+ *
+ *	Locking: none (up to the driver)
+ */
+int tty_get_icount(struct tty_struct *tty,
+		   struct serial_icounter_struct *icount)
+{
+	memset(icount, 0, sizeof(*icount));
+
+	if (tty->ops->get_icount)
+		return tty->ops->get_icount(tty, icount);
+	else
+		return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(tty_get_icount);
+
 static int tty_tiocgicount(struct tty_struct *tty, void __user *arg)
 {
-	int retval = -EINVAL;
 	struct serial_icounter_struct icount;
-	memset(&icount, 0, sizeof(icount));
-	if (tty->ops->get_icount)
-		retval = tty->ops->get_icount(tty, &icount);
+	int retval;
+
+	retval = tty_get_icount(tty, &icount);
 	if (retval != 0)
 		return retval;
+
 	if (copy_to_user(arg, &icount, sizeof(icount)))
 		return -EFAULT;
 	return 0;

include/linux/tty.h

@@ -500,6 +500,8 @@ extern void tty_unthrottle(struct tty_struct *tty);
 extern int tty_throttle_safe(struct tty_struct *tty);
 extern int tty_unthrottle_safe(struct tty_struct *tty);
 extern int tty_do_resize(struct tty_struct *tty, struct winsize *ws);
+extern int tty_get_icount(struct tty_struct *tty,
+			  struct serial_icounter_struct *icount);
 extern int is_current_pgrp_orphaned(void);
 extern void tty_hangup(struct tty_struct *tty);
 extern void tty_vhangup(struct tty_struct *tty);