linux-kernel - Re: watchdog start on restart

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Message-ID: <2b14920abf9f430731ec11c1df6c0253185c7ce7.camel@yadro.com>
Date:   Thu, 3 Sep 2020 13:23:09 +0300
From:   Ivan Mikhaylov <i.mikhaylov@...ro.com>
To:     Guenter Roeck <linux@...ck-us.net>
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 Wed, 2020-09-02 at 06:36 -0700, Guenter Roeck wrote:
> 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).

If it's only driver level decision then it makes sense.

> 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.

I understand that it can be started from userspace. As example, I want the
watchdog trigger with guarantee that the userspace will be properly shut on
reboot, how can I get it with current interface? Just start before the reboot
doesn't guarantee that it will be triggered or will be triggered in middle
of reboot/restart.

Thanks.