| Message ID | 20191105205118.11359-1-linux@rasmusvillemoes.dk (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v2] watchdog: make nowayout sysfs file writable | expand |
On 11/5/19 12:51 PM, Rasmus Villemoes wrote: > 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> > --- > v2: drop redundant "current" variable and !!. > > .../ABI/testing/sysfs-class-watchdog | 9 ++++++-- > drivers/watchdog/watchdog_dev.c | 21 ++++++++++++++++++- > 2 files changed, 27 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@iguana.be> > 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..d3bdcb144657 100644 > --- a/drivers/watchdog/watchdog_dev.c > +++ b/drivers/watchdog/watchdog_dev.c > @@ -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)); > } > -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, > char *buf) >
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@iguana.be> 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..d3bdcb144657 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -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)); } -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, char *buf)
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> --- v2: drop redundant "current" variable and !!. .../ABI/testing/sysfs-class-watchdog | 9 ++++++-- drivers/watchdog/watchdog_dev.c | 21 ++++++++++++++++++- 2 files changed, 27 insertions(+), 3 deletions(-)