tty: Move packet mode flow control notifications to pty driver

When a master pty is set to packet mode, flow control changes to
the slave pty cause notifications to the master pty via reads and
polls. However, these tests are occurring for all ttys, not
just ptys.

Implement flow control packet mode notifications in the pty driver.
Only the slave side implements the flow control handlers since
packet mode is asymmetric; the master pty receives notifications
for slave-side changes, but not vice versa.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 41 insertions, 0 deletions

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 9bbdb1de12e2..7c4447a5c0f4 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -24,6 +24,7 @@
 #include <linux/devpts_fs.h>
 #include <linux/slab.h>
 #include <linux/mutex.h>
+#include <linux/poll.h>
 
 
 #ifdef CONFIG_UNIX98_PTYS
@@ -313,6 +314,42 @@ done:
 }
 
 /**
+ *	pty_start - start() handler
+ *	pty_stop  - stop() handler
+ *	@tty: tty being flow-controlled
+ *
+ *	Propagates the TIOCPKT status to the master pty.
+ *
+ *	NB: only the master pty can be in packet mode so only the slave
+ *	    needs start()/stop() handlers
+ */
+static void pty_start(struct tty_struct *tty)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&tty->ctrl_lock, flags);
+	if (tty->link && tty->link->packet) {
+		tty->ctrl_status &= ~TIOCPKT_STOP;
+		tty->ctrl_status |= TIOCPKT_START;
+		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
+	}
+	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+}
+
+static void pty_stop(struct tty_struct *tty)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&tty->ctrl_lock, flags);
+	if (tty->link && tty->link->packet) {
+		tty->ctrl_status &= ~TIOCPKT_START;
+		tty->ctrl_status |= TIOCPKT_STOP;
+		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
+	}
+	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+}
+
+/**
  *	pty_common_install		-	set up the pty pair
  *	@driver: the pty driver
  *	@tty: the tty being instantiated
@@ -471,6 +508,8 @@ static const struct tty_operations slave_pty_ops_bsd = {
 	.set_termios = pty_set_termios,
 	.cleanup = pty_cleanup,
 	.resize = pty_resize,
+	.start = pty_start,
+	.stop = pty_stop,
 	.remove = pty_remove
 };
 
@@ -646,6 +685,8 @@ static const struct tty_operations pty_unix98_ops = {
 	.chars_in_buffer = pty_chars_in_buffer,
 	.unthrottle = pty_unthrottle,
 	.set_termios = pty_set_termios,
+	.start = pty_start,
+	.stop = pty_stop,
 	.shutdown = pty_unix98_shutdown,
 	.cleanup = pty_cleanup,
 };