linux-kernel - Re: watchdog start on restart

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Message-ID: <1721f170-95df-2451-e3af-6369e830afad@roeck-us.net>
Date:   Wed, 2 Sep 2020 06:36:29 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Ivan Mikhaylov <i.mikhaylov@...ro.com>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: watchdog start on restart

On 9/2/20 6:02 AM, Ivan Mikhaylov wrote:
> Hello everyone. Currently, the watchdog interface only has "stop watchdog on
> restart" but lacks a "start watchdog on restart" one. Is there a way to achieve
> such functionality?
> 
> I'd like to know why "stop watchdog on restart" wasn't implemented via ioctl
> interface? It would be more convenient from user perspective and you can
> control that behavior whenever you want from application layer.
> 

Because it is and always was a driver level decision. The function was added
to replace lots of driver level code implementing this functionality.
Overriding it from userspace doesn't make sense because the driver is supposed
to have a reason for disabling it on reboot (for example due to clock issues
or power issues or becasue it has a short hardware timeout).

> I have some thoughts on this problem that solve the aforementioned
> issue with "start watchdog on restart" but I don't think that my solution is
> correct.
> 
That functionality doesn't make much sense. It can be accomplished by not
stopping the watchdog on reboot in the first place. And if the watchdog
wasn't running before, it can be started from userspace just before the
reboot.

Guenter