[PATCH 1/6] watchdog: watchdog_dev: WATCHDOG_KEEP_ON feature

[Janusz Uzycki]

Some applications require to start watchdog before userspace software.
This patch enables such feature. Only the flag is necessary
to enable it.
Moreover kernel's ping is re-enabled when userspace software closed
watchdog using the magic character. The features improves kernel's
reliability if hardware watchdog is available.

Signed-off-by: Janusz Uzycki <j.uzycki at elproma.com.pl>
---
 drivers/watchdog/watchdog_dev.c | 58 ++++++++++++++++++++++++++-
 include/linux/watchdog.h        |  5 +++
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 6aaefba..51a65f6 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -41,6 +41,7 @@
 #include <linux/miscdevice.h>	/* For handling misc devices */
 #include <linux/init.h>		/* For __init/__exit/... */
 #include <linux/uaccess.h>	/* For copy_to_user/put_user/... */
+#include <linux/jiffies.h>	/* for ping timer */
 
 #include "watchdog_core.h"
 
@@ -277,6 +278,27 @@ out_ioctl:
 	return err;
 }
 
+/* 'keep on' feature */
+static void watchdog_ping_timer_cb(unsigned long data)
+{
+	struct watchdog_device *wdd = (struct watchdog_device *)data;
+	watchdog_ping(wdd);
+	/* call next ping half the timeout value */
+	mod_timer(&wdd->ping_timer,
+			jiffies + msecs_to_jiffies(wdd->timeout * 500));
+}
+
+static void watchdog_keepon_start(struct watchdog_device *wdd)
+{
+	watchdog_start(wdd);
+	watchdog_ping_timer_cb((unsigned long)wdd);
+}
+
+static void watchdog_keepon_stop(struct watchdog_device *wdd)
+{
+	del_timer_sync(&wdd->ping_timer);
+}
+
 /*
  *	watchdog_write: writes to the watchdog.
  *	@file: file from VFS
@@ -430,6 +452,9 @@ static int watchdog_open(struct inode *inode, struct file *file)
 	if (!try_module_get(wdd->ops->owner))
 		goto out;
 
+	if (test_bit(WDOG_KEEP_ON, &wdd->status))
+		watchdog_keepon_stop(wdd);
+
 	err = watchdog_start(wdd);
 	if (err < 0)
 		goto out_mod;
@@ -472,8 +497,13 @@ static int watchdog_release(struct inode *inode, struct file *file)
 	if (!test_bit(WDOG_ACTIVE, &wdd->status))
 		err = 0;
 	else if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
-		 !(wdd->info->options & WDIOF_MAGICCLOSE))
-		err = watchdog_stop(wdd);
+		 !(wdd->info->options & WDIOF_MAGICCLOSE)) {
+		if (test_bit(WDOG_KEEP_ON, &wdd->status)) {
+			watchdog_keepon_start(wdd);
+			err = 0;
+		} else
+			err = watchdog_stop(wdd);
+	}
 
 	/* If the watchdog was not stopped, send a keepalive ping */
 	if (err < 0) {
@@ -524,6 +554,14 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
 {
 	int err, devno;
 
+	if (test_bit(WDOG_KEEP_ON, &watchdog->status)) {
+		if (!try_module_get(watchdog->ops->owner))
+			return -ENODEV;
+		setup_timer(&watchdog->ping_timer, watchdog_ping_timer_cb,
+				(unsigned long)watchdog);
+		watchdog_keepon_start(watchdog);
+	}
+
 	if (watchdog->id == 0) {
 		old_wdd = watchdog;
 		watchdog_miscdev.parent = watchdog->parent;
@@ -535,6 +573,11 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
 				pr_err("%s: a legacy watchdog module is probably present.\n",
 					watchdog->info->identity);
 			old_wdd = NULL;
+			if (test_bit(WDOG_KEEP_ON, &watchdog->status)) {
+				watchdog_keepon_stop(watchdog);
+				watchdog_stop(watchdog);
+				module_put(watchdog->ops->owner);
+			}
 			return err;
 		}
 	}
@@ -553,6 +596,11 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
 			misc_deregister(&watchdog_miscdev);
 			old_wdd = NULL;
 		}
+		if (test_bit(WDOG_KEEP_ON, &watchdog->status)) {
+			watchdog_keepon_stop(watchdog);
+			watchdog_stop(watchdog);
+			module_put(watchdog->ops->owner);
+		}
 	}
 	return err;
 }
@@ -575,6 +623,12 @@ int watchdog_dev_unregister(struct watchdog_device *watchdog)
 		misc_deregister(&watchdog_miscdev);
 		old_wdd = NULL;
 	}
+
+	if (test_bit(WDOG_KEEP_ON, &watchdog->status)) {
+		watchdog_keepon_stop(watchdog);
+		watchdog_stop(watchdog);
+		module_put(watchdog->ops->owner);
+	}
 	return 0;
 }
 
diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
index 2a3038e..650e0d5 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -12,6 +12,7 @@
 #include <linux/bitops.h>
 #include <linux/device.h>
 #include <linux/cdev.h>
+#include <linux/timer.h>		/* for ping timer */
 #include <uapi/linux/watchdog.h>
 
 struct watchdog_ops;
@@ -95,6 +96,8 @@ struct watchdog_device {
 #define WDOG_ALLOW_RELEASE	2	/* Did we receive the magic char ? */
 #define WDOG_NO_WAY_OUT		3	/* Is 'nowayout' feature set ? */
 #define WDOG_UNREGISTERED	4	/* Has the device been unregistered */
+#define WDOG_KEEP_ON		5	/* Is 'keep on' feature set? */
+	struct timer_list ping_timer;	/* timer to keep on hardware ping */
 };
 
 #ifdef CONFIG_WATCHDOG_NOWAYOUT
@@ -104,6 +107,8 @@ struct watchdog_device {
 #define WATCHDOG_NOWAYOUT		0
 #define WATCHDOG_NOWAYOUT_INIT_STATUS	0
 #endif
+/* other proposal: WATCHDOG_ALWAYS_ACTIVE */
+#define WATCHDOG_KEEP_ON		(1 << WDOG_KEEP_ON)
 
 /* Use the following function to check whether or not the watchdog is active */
 static inline bool watchdog_active(struct watchdog_device *wdd)
-- 
1.7.11.3