md: add takeover support for converting raid6 back into raid5

If a raid6 is still in the layout that comes from converting raid5
into a raid6. this will allow us to convert it back again.

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

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 9595327..70b50af 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4912,6 +4912,39 @@ static void *raid5_takeover_raid1(mddev_t *mddev)
        return setup_conf(mddev);
 }
 
+static void *raid5_takeover_raid6(mddev_t *mddev)
+{
+       int new_layout;
+
+       switch (mddev->layout) {
+       case ALGORITHM_LEFT_ASYMMETRIC_6:
+               new_layout = ALGORITHM_LEFT_ASYMMETRIC;
+               break;
+       case ALGORITHM_RIGHT_ASYMMETRIC_6:
+               new_layout = ALGORITHM_RIGHT_ASYMMETRIC;
+               break;
+       case ALGORITHM_LEFT_SYMMETRIC_6:
+               new_layout = ALGORITHM_LEFT_SYMMETRIC;
+               break;
+       case ALGORITHM_RIGHT_SYMMETRIC_6:
+               new_layout = ALGORITHM_RIGHT_SYMMETRIC;
+               break;
+       case ALGORITHM_PARITY_0_6:
+               new_layout = ALGORITHM_PARITY_0;
+               break;
+       case ALGORITHM_PARITY_N:
+               new_layout = ALGORITHM_PARITY_N;
+               break;
+       default:
+               return ERR_PTR(-EINVAL);
+       }
+       mddev->new_level = 5;
+       mddev->new_layout = new_layout;
+       mddev->delta_disks = -1;
+       mddev->raid_disks -= 1;
+       return setup_conf(mddev);
+}
+
 
 static int raid5_reconfig(mddev_t *mddev, int new_layout, int new_chunk)
 {
@@ -4972,6 +5005,8 @@ static void *raid5_takeover(mddev_t *mddev)
                mddev->new_level = 5;
                return setup_conf(mddev);
        }
+       if (mddev->level == 6)
+               return raid5_takeover_raid6(mddev);
 
        return ERR_PTR(-EINVAL);
 }