Working around bogus HPAs in libata

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

[-- Attachment #1: Type: text/plain, Size: 1450 bytes --]

Since SCSI has no concept of the Host Protected Area (HPA) supported by
ATA, ATA disks handled by libata have no set_capacity() operation and it
appears to be impossible to override an HPA except through the libata
module parameter.

In particular, this means that the workaround for bogus HPAs in
rescan_partitions() does not work:

			if (bdops->set_capacity &&
			    (disk->flags & GENHD_FL_NATIVE_CAPACITY) == 0) {
				printk(KERN_CONT "enabling native capacity\n");
				capacity = bdops->set_capacity(disk, ~0ULL);
				disk->flags |= GENHD_FL_NATIVE_CAPACITY;
				if (capacity > get_capacity(disk)) {
					set_capacity(disk, capacity);
					check_disk_size_change(disk, bdev);
					bdev->bd_invalidated = 0;
				}
				...

This creates a serious problem when transitioning from IDE drivers to
libata-based drivers: partitions may disappear or be truncated.  For
example, see <http://bugs.debian.org/574795>.

One workaround is to ignore the HPA by default, but this can result in
data loss:
<https://bugs.launchpad.net/ubuntu/+source/linux/+bug/380138>.

I think that sd should implement set_capacity() and somehow pass through
requests to libata.  This could perhaps be done using the new ATA
PASS-THROUGH commands in the SATL, but I regret that I do not know
enough about either ATA or SCSI to produce a patch.

Ben.

-- 
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 828 bytes --]