[PATCH 1/1] Add poll method to mkiss let notify hangup to the user process.

[Jean-Christian de Rivaz <jc@eclis.ch>]

Without this the application that use the mkiss line discipline have
no way to terminate in case the corresponding serial device is
removed, for example when a USB TNC is unplugged. The application must
wait on poll().

The kissattach application must be patched to take advantage of this
feature.

Signed-off-by: Jean-Christian de Rivaz <jc@eclis.ch>
---
 drivers/net/hamradio/mkiss.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/net/hamradio/mkiss.c b/drivers/net/hamradio/mkiss.c
index fba41e9..50cd36c 100644
--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -893,6 +893,20 @@ static long mkiss_compat_ioctl(struct tty_struct *tty, struct file *file,
 #endif
 
 /*
+ * Waiting until hangup is the only allowed operation. This is used
+ * to notify the application in case the serial deivce is removed
+ * (ex. USB). The tty_ldisc_hangup() will wake up the process.
+ */
+static unsigned int mkiss_poll(struct tty_struct *tty, struct file *file,
+							poll_table *wait)
+{
+	poll_wait(file, &tty->read_wait, wait);
+	poll_wait(file, &tty->write_wait, wait);
+
+	return 0;
+}
+
+/*
  * Handle the 'receiver data ready' interrupt.
  * This function is called by the 'tty_io' module in the kernel when
  * a block of data has been received, which can now be decapsulated
@@ -969,6 +983,7 @@ static struct tty_ldisc_ops ax_ldisc = {
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= mkiss_compat_ioctl,
 #endif
+	.poll           = mkiss_poll,
 	.receive_buf	= mkiss_receive_buf,
 	.write_wakeup	= mkiss_write_wakeup
 };
-- 
1.7.10.4