Re: [PATCH] sd: fixup capacity calculation for 4k drives

["Ewan D. Milne" <emilne@redhat.com>]

On Tue, 2016-03-22 at 08:14 +0100, Hannes Reinecke wrote:
> On 03/22/2016 02:16 AM, Martin K. Petersen wrote:
> >>>>>> "Hannes" == Hannes Reinecke <hare@suse.de> writes:
> > 
> > Hannes> in sd_read_capacity() the sdkp->capacity field changes its
> > Hannes> meaning: after the call to read_capacity_XX() it carries the
> > Hannes> _unscaled_ values, making the comparison between the original
> > Hannes> value and the new value always false for drives with a sector
> > Hannes> size != 512.  So introduce a 'new_capacity' carrying the new,
> > Hannes> scaled, capacity.
> > 
> > I agree with Christoph.
> > 
> > How about something like this instead?
> > 
> I've coded it somewhat different, but this one works as well.
> But please modify the description in sd.h, as with this patch
> 'sdkp->capacity' is the _unscaled_ value.
> Might lead to confusion otherwise.
> 
> diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
> index 5f2a84a..5ed7434 100644
> --- a/drivers/scsi/sd.h
> +++ b/drivers/scsi/sd.h
> @@ -65,7 +65,7 @@ struct scsi_disk {
>         struct device   dev;
>         struct gendisk  *disk;
>         atomic_t        openers;
> -       sector_t        capacity;       /* size in 512-byte sectors */
> +       sector_t        capacity;       /* size in logical sectors */
>         u32             max_xfer_blocks;
>         u32             opt_xfer_blocks;
>         u32             max_ws_blocks;
> 
> (Apologies for the mangled patch)
> 
> Cheers,
> 
> Hannes

If we change the meaning of the scsi_disk->capacity field to be logical
sectors, we also have to change sd_getgeo() in sd.c, do we not?

The ->capacity field is also accessed by last_sector_hacks() in
drivers/usb/storage/transport.c, although it kind of looks like
that code might not have been correct for 4K sectors with the
scaled value.

-Ewan