tty: fix return value for unsupported ioctls

Drivers should return -ENOTTY ("Inappropriate I/O control operation")
when an ioctl isn't supported, while -EINVAL is used for invalid
arguments.

Fix up the TIOCMGET, TIOCMSET and TIOCGICOUNT helpers which returned
-EINVAL when a tty driver did not implement the corresponding
operations.

Note that the TIOCMGET and TIOCMSET helpers predate git and do not get a
corresponding Fixes tag below.

Fixes: d281da7f ("tty: Make tiocgicount a handler")
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407095208.31838-3-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -2529,14 +2529,14 @@ static int send_break(struct tty_struct *tty, unsigned int duration)
  *	@p: pointer to result
  *
  *	Obtain the modem status bits from the tty driver if the feature
- *	is supported. Return -EINVAL if it is not available.
+ *	is supported. Return -ENOTTY if it is not available.
  *
  *	Locking: none (up to the driver)
  */
 
 static int tty_tiocmget(struct tty_struct *tty, int __user *p)
 {
-	int retval = -EINVAL;
+	int retval = -ENOTTY;
 
 	if (tty->ops->tiocmget) {
 		retval = tty->ops->tiocmget(tty);
@@ -2554,7 +2554,7 @@ static int tty_tiocmget(struct tty_struct *tty, int __user *p)
  *	@p: pointer to desired bits
  *
  *	Set the modem status bits from the tty driver if the feature
- *	is supported. Return -EINVAL if it is not available.
+ *	is supported. Return -ENOTTY if it is not available.
  *
  *	Locking: none (up to the driver)
  */
@@ -2566,7 +2566,7 @@ static int tty_tiocmset(struct tty_struct *tty, unsigned int cmd,
 	unsigned int set, clear, val;
 
 	if (tty->ops->tiocmset == NULL)
-		return -EINVAL;
+		return -ENOTTY;
 
 	retval = get_user(val, p);
 	if (retval)
@@ -2606,7 +2606,7 @@ int tty_get_icount(struct tty_struct *tty,
 	if (tty->ops->get_icount)
 		return tty->ops->get_icount(tty, icount);
 	else
-		return -EINVAL;
+		return -ENOTTY;
 }
 EXPORT_SYMBOL_GPL(tty_get_icount);
 

include/linux/tty_driver.h

@@ -228,7 +228,7 @@
  *
  *	Called when the device receives a TIOCGICOUNT ioctl. Passed a kernel
  *	structure to complete. This method is optional and will only be called
- *	if provided (otherwise EINVAL will be returned).
+ *	if provided (otherwise ENOTTY will be returned).
  */
 
 #include <linux/export.h>