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watchdog: make nowayout sysfs file writable

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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@rasmusvillemoes.dk>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20191105205118.11359-1-linux@rasmusvillemoes.dk
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
This commit is contained in:
Rasmus Villemoes 2019-11-05 21:51:18 +01:00 committed by Wim Van Sebroeck
parent a19f89335f
commit bc44fa734c
2 changed files with 27 additions and 3 deletions
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9
Documentation/ABI/testing/sysfs-class-watchdog
View File

@ -17,8 +17,13 @@ What: /sys/class/watchdog/watchdogn/nowayout
Date: August 2015 Date: August 2015
Contact: Wim Van Sebroeck <wim@iguana.be> Contact: Wim Van Sebroeck <wim@iguana.be>
Description: Description:
It is a read only file. While reading, it gives '1' if that It is a read/write file. While reading, it gives '1'
device supports nowayout feature else, it gives '0'. 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 What: /sys/class/watchdog/watchdogn/state
Date: August 2015 Date: August 2015

21
drivers/watchdog/watchdog_dev.c
View File

@ -452,7 +452,26 @@ 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)); 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;
int ret;
ret = kstrtouint(buf, 0, &value);
if (ret)
return ret;
if (value > 1)
return -EINVAL;
/* nowayout cannot be disabled once set */
if (test_bit(WDOG_NO_WAY_OUT, &wdd->status) && !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, static ssize_t status_show(struct device *dev, struct device_attribute *attr,
char *buf) char *buf)