1 files changed, 24 insertions, 1 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 7d66ae508e5c..358a337af598 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -14,6 +14,29 @@
 #include <linux/llist.h>
 
 
+/*
+ * Lock subclasses for tty locks
+ *
+ * TTY_LOCK_NORMAL is for normal ttys and master ptys.
+ * TTY_LOCK_SLAVE is for slave ptys only.
+ *
+ * Lock subclasses are necessary for handling nested locking with pty pairs.
+ * tty locks which use nested locking:
+ *
+ * legacy_mutex - Nested tty locks are necessary for releasing pty pairs.
+ *                The stable lock order is master pty first, then slave pty.
+ * termios_rwsem - The stable lock order is tty_buffer lock->termios_rwsem.
+ *                 Subclassing this lock enables the slave pty to hold its
+ *                 termios_rwsem when claiming the master tty_buffer lock.
+ * tty_buffer lock - slave ptys can claim nested buffer lock when handling
+ *                   signal chars. The stable lock order is slave pty, then
+ *                   master.
+ */
+
+enum {
+        TTY_LOCK_NORMAL = 0,
+        TTY_LOCK_SLAVE,
+};
 
 /*
  * (Note: the *_driver.minor_start values 1, 64, 128, 192 are
@@ -443,6 +466,7 @@ extern void tty_flush_to_ldisc(struct tty_struct *tty);
 extern void tty_buffer_free_all(struct tty_port *port);
 extern void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld);
 extern void tty_buffer_init(struct tty_port *port);
+extern void tty_buffer_set_lock_subclass(struct tty_port *port);
 extern speed_t tty_termios_baud_rate(struct ktermios *termios);
 extern speed_t tty_termios_input_baud_rate(struct ktermios *termios);
 extern void tty_termios_encode_baud_rate(struct ktermios *termios,
@@ -467,7 +491,6 @@ static inline speed_t tty_get_baud_rate(struct tty_struct *tty)
 
 extern void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old);
 extern int tty_termios_hw_change(struct ktermios *a, struct ktermios *b);
-extern int tty_set_termios(struct tty_struct *tty, struct ktermios *kt);
 
 extern struct tty_ldisc *tty_ldisc_ref(struct tty_struct *);
 extern void tty_ldisc_deref(struct tty_ldisc *);