Re: [PATCH 0/8] watchdog: Add support for keepalives triggered by infrastructure

Uwe Kleine-König
2015-08-05T07:36:05Z

Hello Pádraig,

On Wed, Aug 05, 2015 at 12:43:39AM +0100, Pádraig Brady wrote:
> On 04/08/15 03:13, Guenter Roeck wrote:
> > The watchdog infrastructure is currently purely passive, meaning
> > it only passes information from user space to drivers and vice versa.
> >
> > Since watchdog hardware tends to have its own quirks, this can result
> > in quite complex watchdog drivers. A number of scanarios are especially common.
> >
> > - A watchdog is always active and can not be disabled, or can not be disabled
> > once enabled. To support such hardware, watchdog drivers have to implement
> > their own timers and use those timers to trigger watchdog keepalives while
> > the watchdog device is not or not yet opened.
> > - A variant of this is the desire to enable a watchdog as soon as its driver
> > has been instantiated, to protect the system while it is still booting up,
> > but the watchdog daemon is not yet running.
>
> Just mentioning that patting the watchdog in the boot loader
> (by patching grub etc.) can be a more general solution here as it
> avoids hangs if the kernel crashes before it runs the watchdog driver,
> which is especially true if PXE loaded across the net for example.
> Also this tends to be better spaced between boot start and user space loading.

the watchdog I'm currently working with on a powerpc platform has a
unchangable timeout of ~1 s. To make the machine boot I patched the
bootloader and need some automatic pinging in the kernel before
userspace takes over.

Best regards
Uwe

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