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Subject[PATCH 06/11] 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>
---
Documentation/watchdog/watchdog-kernel-api.txt | 7 ++++++
drivers/watchdog/watchdog_dev.c | 28 ++++++++++++++++++++---
include/linux/watchdog.h | 1 +
3 files changed, 32 insertions(+), 4 deletions(-)
diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
index 3085c5c..8e5867c 100644
--- a/Documentation/watchdog/watchdog-kernel-api.txt
+++ b/Documentation/watchdog/watchdog-kernel-api.txt
@@ -125,3 +125,10 @@ 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.
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 0d4b16d..c9ab89e 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -133,6 +133,8 @@ 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,
@@ -144,9 +146,18 @@ 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 */
@@ -272,15 +283,24 @@ 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);

- /* stop the watchdog */
- err = watchdog_stop(wdd);
+ /* If the watchdog was not stopped, sent 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 7e37fdf..8406ed5 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -85,6 +85,7 @@ 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 ? */
};

/* drivers/watchdog/core/watchdog_core.c */
--
1.7.6


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