tty_ioctl(): start taking TIOC[SG]SERIAL into separate methods

->set_serial() and ->get_serial() resp., both taking tty and
a kernel pointer to serial_struct.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/tty/tty_io.c

@@ -2456,22 +2456,40 @@ static int tty_tiocgicount(struct tty_struct *tty, void __user *arg)
 	return 0;
 }
 
-static void tty_warn_deprecated_flags(struct serial_struct __user *ss)
+static int tty_tiocsserial(struct tty_struct *tty, struct serial_struct __user *ss)
 {
 	static DEFINE_RATELIMIT_STATE(depr_flags,
 			DEFAULT_RATELIMIT_INTERVAL,
 			DEFAULT_RATELIMIT_BURST);
 	char comm[TASK_COMM_LEN];
+	struct serial_struct v;
 	int flags;
 
-	if (get_user(flags, &ss->flags))
-		return;
+	if (copy_from_user(&v, ss, sizeof(struct serial_struct)))
+		return -EFAULT;
 
-	flags &= ASYNC_DEPRECATED;
+	flags = v.flags & ASYNC_DEPRECATED;
 
 	if (flags && __ratelimit(&depr_flags))
 		pr_warn("%s: '%s' is using deprecated serial flags (with no effect): %.8x\n",
 			__func__, get_task_comm(comm, current), flags);
+	if (!tty->ops->set_serial)
+		return -ENOIOCTLCMD;
+	return tty->ops->set_serial(tty, &v);
+}
+
+static int tty_tiocgserial(struct tty_struct *tty, struct serial_struct __user *ss)
+{
+	struct serial_struct v;
+	int err;
+
+	memset(&v, 0, sizeof(struct serial_struct));
+	if (!tty->ops->get_serial)
+		return -ENOIOCTLCMD;
+	err = tty->ops->get_serial(tty, &v);
+	if (!err && copy_to_user(ss, &v, sizeof(struct serial_struct)))
+		err = -EFAULT;
+	return err;
 }
 
 /*
@@ -2603,7 +2621,14 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		}
 		break;
 	case TIOCSSERIAL:
-		tty_warn_deprecated_flags(p);
+		retval = tty_tiocsserial(tty, p);
+		if (retval != -ENOIOCTLCMD)
+			return retval;
+		break;
+	case TIOCGSERIAL:
+		retval = tty_tiocgserial(tty, p);
+		if (retval != -ENOIOCTLCMD)
+			return retval;
 		break;
 	case TIOCGPTPEER:
 		/* Special because the struct file is needed */

include/linux/tty_driver.h

@@ -249,6 +249,7 @@
 struct tty_struct;
 struct tty_driver;
 struct serial_icounter_struct;
+struct serial_struct;
 
 struct tty_operations {
 	struct tty_struct * (*lookup)(struct tty_driver *driver,
@@ -287,6 +288,8 @@ struct tty_operations {
 	int (*set_termiox)(struct tty_struct *tty, struct termiox *tnew);
 	int (*get_icount)(struct tty_struct *tty,
 				struct serial_icounter_struct *icount);
+	int  (*get_serial)(struct tty_struct *tty, struct serial_struct *p);
+	int  (*set_serial)(struct tty_struct *tty, struct serial_struct *p);
 	void (*show_fdinfo)(struct tty_struct *tty, struct seq_file *m);
 #ifdef CONFIG_CONSOLE_POLL
 	int (*poll_init)(struct tty_driver *driver, int line, char *options);