[Fwd: regarding libata HPA default behavior]

Scott James Remnant scott at ubuntu.com
Mon Sep 3 15:38:56 BST 2007

Question concerning our kernels

-------- Forwarded Message --------
From: Tejun Heo <htejun at gmail.com>
To: Dave Jones <davej at redhat.com>, Jeff Garzik <jgarzik at pobox.com>, Alan
Cox <alan at lxorguk.ukuu.org.uk>, hmh at hmh.eng.br, scott at ubuntu.com,
lcapitulino at mandriva.com.br
Subject: regarding libata HPA default behavior
Date: Mon, 03 Sep 2007 21:22:08 +0900

Hello, all.  Feel free to add other people to the thread.

The upcoming version of openSUSE is switching over to libata completely
and it seems we have some problems with backward compatibility.
Mainline libata defaults to not unlocking HPA and we can't change that
easily as it breaks compatibility with older libata.  Unfortunately, not
unlocking HPA breaks compatibility with IDE drivers.

SUSE is leaning toward unlocking HPA by default as not being able to
access partitions during upgrade can be pretty bad but that would make
SUSE kernel behave differently from vanilla and kernels from other
distros and it can be quite annoying for users trying to use vanilla
kernels or other distros on the same machine.

The best way out would be being able to detect whether the current
on-disk format requires HPA unlocking and unlock automatically if
necessary.  Implementing kernel side of it shouldn't be too difficult
(snoop SET_MAX, change size and revalidate) but detecting whether HPA
unlocking is necessary seems to be a problem.  It's possible with DOS
style partition table but there are dm, md and plethora of other on-disk
formats, and some of them put the partition table at the end of the disk...

I think it would be nice to have a unified front on this problem as
mixing one behavior with the other can be disorienting and there's
possibility of mass data loss.  So, how are you guys dealing with this


Scott James Remnant
Ubuntu Development Manager
scott at ubuntu.com
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