linux-kernel - Re: possible bug in ide-disk.c (2.6.18.2 but also older)

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Message-ID: <20061120175721.GT6851@gamma.logic.tuwien.ac.at>
Date:	Mon, 20 Nov 2006 18:57:21 +0100
From:	Andreas Leitgeb <avl@...ic.at>
To:	Alan <alan@...rguk.ukuu.org.uk>
Cc:	avl@...ic.at, linux-kernel@...r.kernel.org
Subject: Re: possible bug in ide-disk.c (2.6.18.2 but also older)

On Mon, Nov 20, 2006 at 05:28:12PM +0000, Alan wrote:
> > Alternatively, a kernel-option to manually disable hpa-checking
> > would be a good step to solve the problem even for drives like mine.
> It's a compile time option. If you don't have GPT partitioning support
> then the system ought to behave correctly.

To me it now seems that my symptoms have twofold cause:
  -) misinterpretation of that drive's reported number of sectors.
  -) accessing the last reported sector in search for a GPT.

If I turn off GPT, then perhaps the last (non-existent-but-
believed-by-the-kernel-to-exist) sector is likely never ever
accessed, and therefore the dma-switching-off doesn't happen.
(Well, at least not at boot time, but still, if anyone did 
"dd if=/dev/hda ..." without limiting count=...)

Otoh, patching out this "addr++;" leads to the GPT-test to 
access a valid (in HD's view) sector which contains (who knows,
I even might have a GPT without being aware) or doesn't contain
a GPT, but anyway everthing works.

This does make sense to me.
Please let me know if this makes no sense
  to anyone really knowing ide-stuff.

PS: If it weren't that the failure to access that last sector
    caused dma to be turned off, I'd never have noticed anything
    special.
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