Re: Working around bogus HPAs in libata

[Ben Hutchings <ben@decadent.org.uk>]

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On Tue, 2010-04-06 at 11:01 +0900, Tejun Heo wrote:
> Hello,
> 
> On 04/03/2010 06:57 AM, Ben Hutchings wrote:
> > Several distributions have turned on the switch by default.  As I said
> > previously, this turned out to be a bad idea.
> 
> Heh, yeah, I did that on openSUSE which was mandatory for backward
> compatibility because ide unlocked HPA by default (at least on
> openSUSE).  Do you know how common are these problem cases w/ default
> HPA unlocking?

No idea, but they look serious enough to worry about.

> Diddling with HPAs and writing stuff to disks from
> BIOS is generally a very bad idea because it means that switching BIOS
> options or attaching a hard drive to a different motherboard can lead
> to data corruption.

If a system vendor puts its own name or model numbers on the disks it
ships then I think the BIOS or other platform firmware can reasonably
assume that it 'owns' and can write to the HPA on a disk with the
vendor's identification.  (I wouldn't be at all surprised to find that
some vendors take shortcuts though.)

[...]
> > My test case also revealed a bug in the partition scanning retry:
> > partition 2 is an extended partition and wholly within the HPA, so the
> > extended partition table is not accessible until the HPA is disabled.
> > But it is not rescanned after the HPA is disabled.  However, this is is
> > consistent between IDE and libata drivers and will not be a regression
> > when making the transition.
> 
> Ah... I see, but let's fix that up too.  It could be worse to have
> half working workaround than not working around at all.  I'll update
> the patch once the currently pending HPA updates are in.

Oh, what are those?

I want to apply some version of this fix in Debian soon so we can
complete the transition to libata.  I would very much appreciate it if
you could answer whether or not the multiple 'capacity change' messages
may indicate a problem.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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