linux-kernel - Re: [PATCH v5 0/3] watchdog: allow setting deadline for opening /dev/watchdogN

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Date:   Mon, 22 May 2017 19:07:51 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     <linux-watchdog@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        <esben.haabendal@...il.com>, Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v5 0/3] watchdog: allow setting deadline for opening
 /dev/watchdogN

On Mon, 22 May 2017 16:06:36 +0200
Rasmus Villemoes <rasmus.villemoes@...vas.dk> wrote:

> If a watchdog driver tells the framework that the device is running,
> the framework takes care of feeding the watchdog until userspace opens
> the device. If the userspace application which is supposed to do that
> never comes up properly, the watchdog is fed indefinitely by the
> kernel. This can be especially problematic for embedded devices.
> 
> These patches allow one to set a maximum time for which the kernel
> will feed the watchdog, thus ensuring that either userspace has come
> up, or the board gets reset. This allows fallback logic in the
> bootloader to attempt some recovery (for example, if an automatic
> update is in progress, it could roll back to the previous version).


This makes sense except for being a CONFIG_ option not a boot parameter.
If it's a boot parameter then the same kernel works for multiple systems
and is general. If it's compile time then you have to build a custom
kernel.

For some embedded stuff that might not matter (although I bet they'd
prefer it command line/device tree too) but for something like an x86
platform where you are deploying a standard vendor supplied kernel it's
bad to do it that way IMHO.

In other words I think you should drop patch 3 but the rest is good.

Alan