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

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Date:	Tue, 21 Nov 2006 12:06:14 +0000
From:	Alan <alan@...rguk.ukuu.org.uk>
To:	avl@...ic.at
Cc:	linux-kernel@...r.kernel.org
Subject: Re: possible bug in ide-disk.c (2.6.18.2 but also older)

> After reading it a second time, I'll see if I got it straight now:
> 
> .) the kernel always loads even-aligned pairs of sectors.
> .) for an odd-sectored disk, this results in the GPT plus the
>      following (non-existent) sector being accessed from disk.

Yes

> .) the old, unmaintained ide-driver generally does not handle
>      the odd-size case right, as it misinterprets the harddisks
>      error for the second sector (the one after the end) as a
>      general error causing dma to be turned off, after some retries.
>      It would also do that, if I later accessed the last sector
>      (e.g. dd if=/dev/hda ..., or by accessing a file that happens
>      to be stored there per filesystem, if at all possible),
>      not just during the initial GPT-check.

Only ever seen during the partition check

> .) If I remove the "addr++;", then the harddisk is actually
>      believed to be 1 sector smaller than it really is, which
>      means that it looks like an even-sized disk. This could mean
>      that an eventually existing GPT could be missed. What would
>      be the "worst-case" consequences?
> .) if ((old ide-driver) && (odd # of sectors)) youre_doomed_anyway(); ?

Not in any normal situation it appears, just the partition code seems to
trip it up.
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