ldisc n_tty: add new method n_tty_inherit_ops()

This new method can be used to init a new struct tty_ldisc_ops as the
default tty_ldisc_N_TTY struct.
Signed-off-by: Rodolfo Giometti <giometti@linux.it>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg KH <greg@kroah.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/n_tty.c

@@ -48,6 +48,7 @@
 #include <linux/audit.h>
 #include <linux/file.h>
 #include <linux/uaccess.h>
+#include <linux/module.h>
 
 #include <asm/system.h>
 
@@ -2091,3 +2092,19 @@ struct tty_ldisc_ops tty_ldisc_N_TTY = {
 	.receive_buf     = n_tty_receive_buf,
 	.write_wakeup    = n_tty_write_wakeup
 };
+
+/**
+ *	n_tty_inherit_ops	-	inherit N_TTY methods
+ *	@ops: struct tty_ldisc_ops where to save N_TTY methods
+ *
+ *	Used by a generic struct tty_ldisc_ops to easily inherit N_TTY
+ *	methods.
+ */
+
+void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
+{
+	*ops = tty_ldisc_N_TTY;
+	ops->owner = NULL;
+	ops->refcount = ops->flags = 0;
+}
+EXPORT_SYMBOL_GPL(n_tty_inherit_ops);

include/linux/tty.h

@@ -514,6 +514,7 @@ extern void tty_ldisc_enable(struct tty_struct *tty);
 
 /* n_tty.c */
 extern struct tty_ldisc_ops tty_ldisc_N_TTY;
+extern void n_tty_inherit_ops(struct tty_ldisc_ops *ops);
 
 /* tty_audit.c */
 #ifdef CONFIG_AUDIT