linux-kernel - Re: [PATCH 2/4] libata: Implement disk shock protection support

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Date:	Fri, 12 Sep 2008 01:25:07 +0200
From:	Tejun Heo <htejun@...il.com>
To:	Valdis.Kletnieks@...edu
CC:	Elias Oltmanns <eo@...ensachen.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Jeff Garzik <jeff@...zik.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] libata: Implement disk shock protection support

Valdis.Kletnieks@...edu wrote:
> On Thu, 11 Sep 2008 15:01:00 +0200, Tejun Heo said:
>> Ah.. just one more thing.
>>
>> I think it would be easier on the application if the written timeout
>> value is cropped if it's over the maximum instead of failing the
>> write.
> 
> Which is better, failing the write so the application *knows* there is a
> problem, or letting the application proceed with a totally incorrect idea of
> what the value is set to?

It depends.  As -EINVAL either results in program failure or no
protection for the event.

> For instance, what happens if the program tries to set 100, it's silently
> clamped to 10, and it then tries to set a timer for itself to '90% of the
> value'?  It might be in for an unpleasant surprise when it finds out that
> it's overshot by 81....

Hitting the limit would be a pretty rare occasion and which way we go
it's not gonna be too pretty.  e.g. Let's say a program calculates
timeout according to some algorithm which 99.9% of the time stays in
the limit but once in the blue moon hits the ceiling.  Given the
characteristics of the problem and very high limit value, I think it's
better to have cropped value.

How about returning -OVERFLOW while still setting the timeout to the
maximum?

Thanks.

-- 
tejun
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