watchdog: WatchDog Timer Driver Core - Add Magic Close feature

Add support for the Magic Close feature to the
WatchDog Timer Driver Core framework.

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>

3 files changed, 32 insertions, 3 deletions

diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
index acdee39fb08a..41d552698ada 100644
--- a/Documentation/watchdog/watchdog-kernel-api.txt
+++ b/Documentation/watchdog/watchdog-kernel-api.txt
@@ -127,6 +127,13 @@ bit-operations. The status bits that are defined are:
 * WDOG_DEV_OPEN: this status bit shows whether or not the watchdog device
   was opened via /dev/watchdog.
   (This bit should only be used by the WatchDog Timer Driver Core).
+* WDOG_ALLOW_RELEASE: this bit stores whether or not the magic close character
+  has been sent (so that we can support the magic close feature).
+  (This bit should only be used by the WatchDog Timer Driver Core).
+
+Note: The WatchDog Timer Driver Core supports the magic close feature. To use
+the magic close feature you must set the WDIOF_MAGICCLOSE bit in the options
+field of the watchdog's info structure.
 
 To get or set driver specific data the following two helper functions should be
 used:
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 2c0289deaadd..db40c6c79ef8 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -122,6 +122,8 @@ static int watchdog_stop(struct watchdog_device *wddev)
  *      @ppos: pointer to the file offset
  *
  *      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.
  */
 
 static ssize_t watchdog_write(struct file *file, const char __user *data,
@@ -133,9 +135,18 @@ static ssize_t watchdog_write(struct file *file, const char __user *data,
         if (len == 0)
                 return 0;
 
+        /*
+         * Note: just in case someone wrote the magic character
+         * five months ago...
+         */
+        clear_bit(WDOG_ALLOW_RELEASE, &wdd->status);
+
+        /* scan to see whether or not we got the magic character */
         for (i = 0; i != len; i++) {
                 if (get_user(c, data + i))
                         return -EFAULT;
+                if (c == 'V')
+                        set_bit(WDOG_ALLOW_RELEASE, &wdd->status);
         }
 
         /* someone wrote to us, so we send the watchdog a keepalive ping */
@@ -259,14 +270,24 @@ out:
  *      @inode: inode of device
  *      @file: file handle to device
  *
- *      This is the code for when /dev/watchdog gets closed.
+ *      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.
  */
 
 static int watchdog_release(struct inode *inode, struct file *file)
 {
-        int err;
+        int err = -EBUSY;
+
+        /*
+         * We only stop the watchdog if we received the magic character
+         * or if WDIOF_MAGICCLOSE is not set
+         */
+        if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
+            !(wdd->info->options & WDIOF_MAGICCLOSE))
+                err = watchdog_stop(wdd);
 
-        err = watchdog_stop(wdd);
+        /* If the watchdog was not stopped, send a keepalive ping */
         if (err < 0) {
                 pr_crit("%s: watchdog did not stop!\n", wdd->info->identity);
                 watchdog_ping(wdd);
diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
index 9f33efe199d1..e9881ca2452b 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -112,6 +112,7 @@ struct watchdog_device {
 /* Bit numbers for status flags */
 #define WDOG_ACTIVE             0       /* Is the watchdog running/active */
 #define WDOG_DEV_OPEN           1       /* Opened via /dev/watchdog ? */
+#define WDOG_ALLOW_RELEASE      2       /* Did we receive the magic char ? */
 };
 
 /* Use the following functions to manipulate watchdog driver specific data */