From 591f35be8717ce023a8f2bb95d433c6ca612a001 Mon Sep 17 00:00:00 2001
From: Stefan Kolb <Stefan.Kolb@avat.de>
Date: Wed, 10 May 2017 07:56:17 -0600
Subject: [PATCH] =?UTF-8?q?I=20discovered=20a=20problem=20in=20the=20file?=
 =?UTF-8?q?=20drivers/serial/serial.c=20concerning=20the=20function=20uart?=
 =?UTF-8?q?=5Fclose(=E2=80=A6).=20In=20the=20case=20that=20a=20serial=20de?=
 =?UTF-8?q?vice=20is=20opened=20with=20the=20flag=20O=5FNONBLOCK=20the=20f?=
 =?UTF-8?q?unction=20uart=5Fclose(=E2=80=A6)=20blocks=20until=20all=20data?=
 =?UTF-8?q?=20in=20the=20buffer=20is=20transmitted.=20The=20function=20clo?=
 =?UTF-8?q?se(=E2=80=A6)=20called=20on=20an=20handle=20opened=20with=20O?=
 =?UTF-8?q?=5FNONBLOCK=20should=20not=20block.=20The=20problem=20occurred?=
 =?UTF-8?q?=20with=20a=20CDC/ACM=20device.?=
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---
 Documentation/README.html |  2 +-
 drivers/serial/serial.c   | 35 ++++++++++++++++++++---------------
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/Documentation/README.html b/Documentation/README.html
index 02a3042b484..fe4dced9adb 100644
--- a/Documentation/README.html
+++ b/Documentation/README.html
@@ -8,7 +8,7 @@
   <tr align="center" bgcolor="#e4e4e4">
     <td>
       <h1><big><font color="#3c34ec"><i>NuttX README Files</i></font></big></h1>
-      <p>Last Updated: April 18, 2017</p>
+      <p>Last Updated: May 9, 2017</p>
     </td>
   </tr>
 </table>
diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
index 85fded4e470..775fa3a97a7 100644
--- a/drivers/serial/serial.c
+++ b/drivers/serial/serial.c
@@ -1,7 +1,7 @@
 /************************************************************************************
  * drivers/serial/serial.c
  *
- *   Copyright (C) 2007-2009, 2011-2013, 2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009, 2011-2013, 2016-2017 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -1207,26 +1207,31 @@ static int uart_close(FAR struct file *filep)
 
   uart_disablerxint(dev);
 
-  /* Now we wait for the transmit buffer to clear */
+  /* Prevent blocking if the device is opened with O_NONBLOCK */
 
-  while (dev->xmit.head != dev->xmit.tail)
+  if ((filep->f_oflags & O_NONBLOCK) == 0)
     {
-#ifndef CONFIG_DISABLE_SIGNALS
-      usleep(HALF_SECOND_USEC);
-#else
-      up_mdelay(HALF_SECOND_MSEC);
-#endif
-    }
+      /* Now we wait for the transmit buffer to clear */
 
-  /* And wait for the TX fifo to drain */
-
-  while (!uart_txempty(dev))
-    {
+      while (dev->xmit.head != dev->xmit.tail)
+        {
 #ifndef CONFIG_DISABLE_SIGNALS
-      usleep(HALF_SECOND_USEC);
+          usleep(HALF_SECOND_USEC);
 #else
-      up_mdelay(HALF_SECOND_MSEC);
+          up_mdelay(HALF_SECOND_MSEC);
 #endif
+        }
+
+     /* And wait for the TX fifo to drain */
+
+      while (!uart_txempty(dev))
+        {
+#ifndef CONFIG_DISABLE_SIGNALS
+          usleep(HALF_SECOND_USEC);
+#else
+          up_mdelay(HALF_SECOND_MSEC);
+#endif
+        }
     }
 
   /* Free the IRQ and disable the UART */