X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=include%2Flinux%2Ftty.h;h=fe5623c9af715fda985da02bcecb1c9451b3789c;hb=d2b6f44779d3be22d32a5697bd30b59367fd2b33;hp=7d66ae508e5cc08c0ba8f91b09e55224a565f04d;hpb=5c68eac68bea2fc908b20b6df8654d50bd1a5d36;p=firefly-linux-kernel-4.4.55.git

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 7d66ae508e5c..fe5623c9af71 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,