md/raid5: finish support for DDF/raid6

DDF requires RAID6 calculations over different devices in a different
order.
For md/raid6, we calculate over just the data devices, starting
immediately after the 'Q' block.
For ddf/raid6 we calculate over all devices, using zeros in place of
the P and Q blocks.

This requires unfortunately complex loops...

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 633d79289616..84456b1af204 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -201,6 +201,7 @@ struct stripe_head {
         sector_t                sector;         /* sector of this row */
         short                   pd_idx;         /* parity disk index */
         short                   qd_idx;         /* 'Q' disk index for raid6 */
+        short                   ddf_layout;/* use DDF ordering to calculate Q */
         unsigned long           state;          /* state flags */
         atomic_t                count;        /* nr of active thread/requests */
         spinlock_t              lock;