watchdog: WatchDog Timer Driver Core - Add nowayout feature

Add support for the nowayout feature to the
WatchDog Timer Driver Core framework.
This feature prevents the watchdog timer from being
stopped.

Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>

1 files changed, 13 insertions, 5 deletions

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index db40c6c79ef..ac20f92347b 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -98,11 +98,18 @@ static int watchdog_start(struct watchdog_device *wddev)
  *      Stop the watchdog if it is still active and unmark it active.
  *      This function returns zero on success or a negative errno code for
  *      failure.
+ *      If the 'nowayout' feature was set, the watchdog cannot be stopped.
  */
 
 static int watchdog_stop(struct watchdog_device *wddev)
 {
-        int err;
+        int err = -EBUSY;
+
+        if (test_bit(WDOG_NO_WAY_OUT, &wdd->status)) {
+                pr_info("%s: nowayout prevents watchdog to be stopped!\n",
+                                                        wdd->info->identity);
+                return err;
+        }
 
         if (test_bit(WDOG_ACTIVE, &wdd->status)) {
                 err = wddev->ops->stop(wddev);
@@ -123,7 +130,7 @@ static int watchdog_stop(struct watchdog_device *wddev)
  *
  *      A write to a watchdog device is defined as a keepalive ping.
  *      Writing the magic 'V' sequence allows the next close to turn
- *      off the watchdog.
+ *      off the watchdog (if 'nowayout' is not set).
  */
 
 static ssize_t watchdog_write(struct file *file, const char __user *data,
@@ -271,8 +278,8 @@ out:
  *      @file: file handle to device
  *
  *      This is the code for when /dev/watchdog gets closed. We will only
- *      stop the watchdog when we have received the magic char, else the
- *      watchdog will keep running.
+ *      stop the watchdog when we have received the magic char (and nowayout
+ *      was not set), else the watchdog will keep running.
  */
 
 static int watchdog_release(struct inode *inode, struct file *file)
@@ -281,7 +288,8 @@ static int watchdog_release(struct inode *inode, struct file *file)
 
         /*
          * We only stop the watchdog if we received the magic character
-         * or if WDIOF_MAGICCLOSE is not set
+         * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
+         * watchdog_stop will fail.
          */
         if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
             !(wdd->info->options & WDIOF_MAGICCLOSE))