md: add support for raid5 to raid4 conversion

This is unlikely to be wanted, but we may as well provide it
for completeness.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index bb28fd6b44f..020143dec18 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5788,6 +5788,18 @@ static void *raid5_takeover(mddev_t *mddev)
         return ERR_PTR(-EINVAL);
 }
 
+static void *raid4_takeover(mddev_t *mddev)
+{
+        /* raid4 can take over raid5 if layout is right.
+         */
+        if (mddev->level == 5 &&
+            mddev->layout == ALGORITHM_PARITY_N) {
+                mddev->new_layout = 0;
+                mddev->new_level = 4;
+                return setup_conf(mddev);
+        }
+        return ERR_PTR(-EINVAL);
+}
 
 static struct mdk_personality raid5_personality;
 
@@ -5903,6 +5915,7 @@ static struct mdk_personality raid4_personality =
         .start_reshape  = raid5_start_reshape,
         .finish_reshape = raid5_finish_reshape,
         .quiesce        = raid5_quiesce,
+        .takeover       = raid4_takeover,
 };
 
 static int __init raid5_init(void)