Re: WD_QUIRK_FORCE_LBA48

[Christoph Badura <bad%bsd.de@localhost>]

On Wed, Dec 16, 2009 at 10:13:23AM +0100, Manuel Bouyer wrote:
> Drives: most drives manufactured before 2004 with more than 138Gb I guess.
> The fact that it took 2 years for the problem to show up is enough
> of a proof.

And the fact that after two years a changed was committed to wd.c that
made it make illegal requests that cause the behaviour is merely coincidence?

> > > Yes. As I already said we got the sector 0xfffffff problem 2 years after
> > > we added LBA48 support. So the earlier LBA48 drives probably used
> > > 0x10000000 and not 0xfffffff for the max LBA28 capacity.
> > 
> > You haven't provided any evidence of that.
> 
> The fact that our driver worked with large drives before 2004 is enough.

OK, so lets look at the CVS history.

When the LBA48 support was committed in rev 1.220 in 2002 it used LBA48
access for all blocks unconditionally and there wasn't any problem with
large drives.

Then in rev. 1.256 the driver was changed to use LBA48 accesses only for
non-LBA28 addressable sectors.  But the constant for the threshold was
botched and it used LBA48 accesses for all sectores starting with sector 2^24.
No LBA28 access crossed the actual LBA48 border.  And there wasn't a any
problem with large drives.

Then on 2008-07-10 in rev 1.257 the threshold constant was corrected.  That
caused the driver to make illegal LBA28 accesses across the LBA48 border.

Then, a good year later the WD_QUIRK_FORCE_LBA48 was introduced to work around
the bug introduced in 1.257 with LBA28 accesses that go beyond the border
defined in words 60:61 (on LBA48 drives, obviously).

And you seriously want me to believe that it wasn't the bug introduced rev 1.257
that caused the issue but that somehow the disk drive manufacturers conspired
to flood the market with millions of drives with out of spec firmware?

Please note: I am not entirely ruling out that there might LBA48 drivers out
there that report 2^28 sectors as the LBA28 size.  But nobody else seems to
care and I think it is not worth to build convoluted software workarounds
unless we really know such drives exist.

--chris