Re: [PATCH] libata: Don't trust current capacity values in identifywords 57-58

[Robert Hancock]

Mark Lord wrote:
> Robert Hancock wrote:
> > Hanno BÃck reported a problem where an old Conner CP30254 240MB hard 
> > drive
> > was reported as 1.1TB in capacity by libata:
> >
> > http://lkml.org/lkml/2009/2/13/134
> >
> > This was caused by libata trusting the drive's reported current 
> > capacity in sectors in identify words 57 and 58 if the drive does not 
> > support LBA and the
> > current CHS translation values appear valid. Unfortunately it seems older
> > ATA specs were vague about what this field should contain and a number 
> > of drives
> > used values with wrong byte order or that were totally bogus. There's no
> > unique information that it conveys and so we can just calculate the 
> > number
> > of sectors from the reported current CHS values.
> >
> > Signed-off-by: Robert Hancock <hancockrwd@xxxxxxxxx>
> ..
> >      } else {
> >          if (ata_id_current_chs_valid(id))
> > -            return ata_id_u32(id, 57);
> > +            return id[54] * id[55] * id[56];
> >          else
> >              return id[1] * id[3] * id[6];
> ..
>
> NAK.  That's not quite correct, either.
>
> The LBA capacity can be larger than the CHS capacity,
> so we have to use the reported LBA values if at all possible.
>
> That's why ata_id_is_lba_capacity_ok() exists,
> and why it looks so peculiar.
>
> Some of those early drives really did require that kind of logic.

This is the !ata_id_has_lba code path. If the drive supports LBA then 
the LBA capacity will always be used, that hasn't changed.
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