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Date:      Mon, 16 Feb 1998 14:38:16 -0800 (PST)
From:      Julian Elischer <julian@whistle.com>
To:        Simon Shapiro <shimon@simon-shapiro.org>
Cc:        freebsd-hackers@FreeBSD.ORG
Subject:   Re: WatchDog Timer
Message-ID:  <Pine.BSF.3.95.980216143351.8949O-100000@current1.whistle.com>
In-Reply-To: <XFMail.980216142345.shimon@simon-shapiro.org>

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look in wd.c (for example) for the code:

#ifdef	HW_WDOG
	if (wdog_tickler)
		(*wdog_tickler)();
#endif


this is in the code to make a core dump and it tickles the watchdog
each 1MB of core saved...

we added it for our h/w watchdog at whistle.  the existance of the
function pointer is the entire support in freeBSD for a hardware watchdog,
and took a whole 4 bytes :)

we got tired of getting HALF of a core-dump :)

under normal circumstances, the watchdog is tickled by a userland process.


On Mon, 16 Feb 1998, Simon Shapiro wrote:

> 
> On 16-Feb-98 Julian Elischer wrote:
> > eh?
> > what watchdog?
> > we have a hook that is called by the kernel
> > when it is doing long uninterrupted operations (e.g. dumping core)
> > but it's just a hook. The user needs to supply their own hardware
> > watchdog.. (and code to tickle it)
> > 
> > julian
> 
> If there is no driver for such hardware today, I'll write it this week.
> This is really not the same as a kernel's internal watchdog..  What we are
> talking about here is used to build a dead-man switch;  In case of O/S
> catastrophic failure, this device will reboot the machine, or in the case
> of HA/FT, signal to the rest of the ``system'' that a Unix instance just
> died.
> 
> I simply do not want to write a driver that was already written.
> What is the kernel's hook name/path?  Maybe we can merge the two, or at
> least relate to each other.  As in ``If the kernel is busy with a long,
> uninterrupted operation, we automatically mask off the dead-man switch''.
> 
> ----------
> 
> 
> Sincerely Yours, 
> 
> Simon Shapiro
> Shimon@Simon-Shapiro.ORG                      Voice:   503.708.7858
> 


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