Re: Disabling watchdog when closing /dev/watchdog

[Guenter Roeck <linux@roeck-us.net>]

On 10/09/2013 04:47 PM, Markus Mayer wrote:
> Currently, the watchdog framework works such that upon closing
> /dev/watchdog it will attempt to disable the watchdog timer and,
> failing that, will poke the watchdog (via the watchdog_release()
> function).
>
> I am working on a new watchdog driver for a Broadcom SoC, and for test
> purposes at least, it would be helpful if the watchdog could be left
> alone when the device is closed (i.e. the watchdog is neither stopped
> nor poked). That way I could use a command line utility to issue ioctl
> calls and observe the effect of these calls.
>
> Right now, using my line tool to check the "time left" will return the
> proper amount of time left, but it will also poke the watchdog,
> therefore changing the time that's actually left until the watchdog
> expires (the command line tool opens /dev/watchdog, issues an ioctl
> and closes /dev/watchdog), turning a "read-only" operation into one
> that actually changes the watchdog's status.
>
> Automatically stopping or poking the watchdog upon close only makes
> sense in the case of a continuously running daemon that keeps
> /dev/watchdog open at all times. It doesn't work for case where an
> application would open the watchdog device only for brief amounts of
> time.
>
> Would it make sense to add a flag like "WDOG_LEAVE_ON" to, say, struct
> watchdog_device's "status" values, which the driver could set,
> allowing watchdog_release() to leave the watchdog alone upon closing
> the device? Or is there a different way to achieve this? A daemon is
> not practicable for me at this point, and even later on, we may not
> want to go with a daemon solution, but may want to rely on the
> watchdog continuing to run even if the device is closed.
>

It might make more sense to use sysfs attributes to provide this
functionality (name, status, ping, configured timeout, time left,
reboot reason, ...). I think that would be much cleaner and accomplish
the same. Another option might be debugfs if this is supposed
to be used for debugging only.

Thanks,
Guenter