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

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Date:	Fri,  2 Oct 2015 23:46:13 +0200
From:	Jean-Christian de Rivaz <jc@...is.ch>
To:	Thomas Osterried <thomas@...erried.de>,
	David Ranch <dranch@...nnet.net>,
	Ralf Baechle DL5RB <ralf@...ux-mips.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Peter Hurley <peter@...leysoftware.com>
Cc:	linux-hams@...nnet.net, linux-hams@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] Add poll method to mkiss let notify hangup to the user process.

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@...is.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

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