It can be useful to delay setting the nowayout feature for a watchdog
device. Moreover, not every driver (notably gpio_wdt) implements a
nowayout module parameter/otherwise respects CONFIG_WATCHDOG_NOWAYOUT,
and modifying those drivers carries a risk of causing a regression for
someone who has two watchdog devices, sets CONFIG_WATCHDOG_NOWAYOUT
and somehow relies on the gpio_wdt driver being ignorant of
that (i.e., allowing one to gracefully close a gpio_wdt but not the
other watchdog in the system).
So instead, simply make the nowayout sysfs file writable. Obviously,
setting nowayout is a one-way street.
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
.../ABI/testing/sysfs-class-watchdog | 9 ++++++--
drivers/watchdog/watchdog_dev.c | 22 ++++++++++++++++++-
2 files changed, 28 insertions(+), 3 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-class-watchdog b/Documentation/ABI/testing/sysfs-class-watchdog
index 675f9b537661..9860a8b2ba75 100644
--- a/Documentation/ABI/testing/sysfs-class-watchdog
+++ b/Documentation/ABI/testing/sysfs-class-watchdog
@@ -17,8 +17,13 @@ What: /sys/class/watchdog/watchdogn/nowayout
Date: August 2015
Contact: Wim Van Sebroeck <wim@xxxxxxxxx>
Description:
- It is a read only file. While reading, it gives '1' if that
- device supports nowayout feature else, it gives '0'.
+ It is a read/write file. While reading, it gives '1'
+ if the device has the nowayout feature set, otherwise
+ it gives '0'. Writing a '1' to the file enables the
+ nowayout feature. Once set, the nowayout feature
+ cannot be disabled, so writing a '0' either has no
+ effect (if the feature was already disabled) or
+ results in a permission error.
What: /sys/class/watchdog/watchdogn/state
Date: August 2015
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index dbd2ad4c9294..0c478b8f8d5a 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -452,7 +452,27 @@ static ssize_t nowayout_show(struct device *dev, struct device_attribute *attr,
return sprintf(buf, "%d\n", !!test_bit(WDOG_NO_WAY_OUT, &wdd->status));
}
-static DEVICE_ATTR_RO(nowayout);
+
+static ssize_t nowayout_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t len)
+{
+ struct watchdog_device *wdd = dev_get_drvdata(dev);
+ unsigned int value, current;
+ int ret;
+
+ ret = kstrtouint(buf, 0, &value);
+ if (ret)
+ return ret;
+ if (value > 1)
+ return -EINVAL;
+ current = !!test_bit(WDOG_NO_WAY_OUT, &wdd->status);
+ /* nowayout cannot be disabled once set */
+ if (current && !value)
+ return -EPERM;
+ watchdog_set_nowayout(wdd, value);
+ return len;
+}
+static DEVICE_ATTR_RW(nowayout);
static ssize_t status_show(struct device *dev, struct device_attribute *attr,
char *buf)
--
2.23.0
