linux-kernel - [PATCH 1/1] pty: BREAK for pseudoterminals

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Date:	Fri,  6 Feb 2015 03:11:29 +0800
From:	Nan Li <nli@...e.com>
To:	gregkh@...uxfoundation.org, jslaby@...e.cz
Cc:	linux-kernel@...r.kernel.org, ptesarik@...e.cz,
	Nan Li <nli@...e.com>
Subject: [PATCH 1/1] pty: BREAK for pseudoterminals

This will greatly enhance the usefulness of QEMU virtual serial ports, because the Linux kernel interprets a break on the serial console as a SysRq, but there is currently no way to pass this signal over a pseudo-terminal. This patch will work for transmitting BREAK from master to slave through pseudo-terminal.

Signed-off-by: Nan Li <nli@...e.com>
---
 drivers/tty/pty.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index e72ee62..ac8893a 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -31,6 +31,7 @@
 static struct tty_driver *ptm_driver;
 static struct tty_driver *pts_driver;
 static DEFINE_MUTEX(devpts_mutex);
+#define BREAK_STRING '\0'
 #endif
 
 static void pty_close(struct tty_struct *tty, struct file *filp)
@@ -674,6 +675,23 @@ static void pty_unix98_shutdown(struct tty_struct *tty)
 	devpts_kill_index(tty->driver_data, tty->index);
 }
 
+static int pty_unix98_break_ctl(struct tty_struct *tty, int break_state)
+{
+	int c;
+	struct tty_struct *to = tty->link;
+
+	if (break_state) {
+		/* Stuff the break data into the input queue of the other end */
+		c = tty_insert_flip_char(to->port, BREAK_STRING, TTY_BREAK);
+		/* And shovel */
+		if (c)
+			tty_flip_buffer_push(to->port);
+		else
+			return -ENOMEM;
+	}
+	return 0;
+}
+
 static const struct tty_operations ptm_unix98_ops = {
 	.lookup = ptm_unix98_lookup,
 	.install = pty_unix98_install,
@@ -686,6 +704,7 @@ static const struct tty_operations ptm_unix98_ops = {
 	.chars_in_buffer = pty_chars_in_buffer,
 	.unthrottle = pty_unthrottle,
 	.ioctl = pty_unix98_ioctl,
+	.break_ctl = pty_unix98_break_ctl,
 	.resize = pty_resize,
 	.shutdown = pty_unix98_shutdown,
 	.cleanup = pty_cleanup
-- 
1.7.12.4

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