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>

1 files changed, 35 insertions, 0 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 95953273c4d9..70b50af2bcd7 100644
--- 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);
 }