md: add ->takeover method to support changing the personality managing an array

Implement this for RAID6 to be able to 'takeover' a RAID5 array.  The
new RAID6 will use a layout which places Q on the last device, and
that device will be missing.
If there are any available spares, one will immediately have Q
recovered onto it.

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

1 files changed, 59 insertions, 5 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 81789fa7a023..5b346b41e515 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -933,8 +933,10 @@ static int grow_stripes(raid5_conf_t *conf, int num)
         struct kmem_cache *sc;
         int devs = conf->raid_disks;
 
-        sprintf(conf->cache_name[0], "raid5-%s", mdname(conf->mddev));
-        sprintf(conf->cache_name[1], "raid5-%s-alt", mdname(conf->mddev));
+        sprintf(conf->cache_name[0],
+                "raid%d-%s", conf->level, mdname(conf->mddev));
+        sprintf(conf->cache_name[1],
+                "raid%d-%s-alt", conf->level, mdname(conf->mddev));
         conf->active_name = 0;
         sc = kmem_cache_create(conf->cache_name[conf->active_name],
                                sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
@@ -4361,10 +4363,12 @@ static int run(mddev_t *mddev)
                 BUG_ON(mddev->chunk_size != mddev->new_chunk);
                 BUG_ON(mddev->delta_disks != 0);
         }
-        conf = setup_conf(mddev);
 
-        if (conf == NULL)
-                return -EIO;
+        if (mddev->private == NULL)
+                conf = setup_conf(mddev);
+        else
+                conf = mddev->private;
+
         if (IS_ERR(conf))
                 return PTR_ERR(conf);
 
@@ -4880,6 +4884,55 @@ static void raid5_quiesce(mddev_t *mddev, int state)
         }
 }
 
+static struct mdk_personality raid5_personality;
+
+static void *raid6_takeover(mddev_t *mddev)
+{
+        /* Currently can only take over a raid5.  We map the
+         * personality to an equivalent raid6 personality
+         * with the Q block at the end.
+         */
+        int new_layout;
+
+        if (mddev->pers != &raid5_personality)
+                return ERR_PTR(-EINVAL);
+        if (mddev->degraded > 1)
+                return ERR_PTR(-EINVAL);
+        if (mddev->raid_disks > 253)
+                return ERR_PTR(-EINVAL);
+        if (mddev->raid_disks < 3)
+                return ERR_PTR(-EINVAL);
+
+        switch (mddev->layout) {
+        case ALGORITHM_LEFT_ASYMMETRIC:
+                new_layout = ALGORITHM_LEFT_ASYMMETRIC_6;
+                break;
+        case ALGORITHM_RIGHT_ASYMMETRIC:
+                new_layout = ALGORITHM_RIGHT_ASYMMETRIC_6;
+                break;
+        case ALGORITHM_LEFT_SYMMETRIC:
+                new_layout = ALGORITHM_LEFT_SYMMETRIC_6;
+                break;
+        case ALGORITHM_RIGHT_SYMMETRIC:
+                new_layout = ALGORITHM_RIGHT_SYMMETRIC_6;
+                break;
+        case ALGORITHM_PARITY_0:
+                new_layout = ALGORITHM_PARITY_0_6;
+                break;
+        case ALGORITHM_PARITY_N:
+                new_layout = ALGORITHM_PARITY_N;
+                break;
+        default:
+                return ERR_PTR(-EINVAL);
+        }
+        mddev->new_level = 6;
+        mddev->new_layout = new_layout;
+        mddev->delta_disks = 1;
+        mddev->raid_disks += 1;
+        return setup_conf(mddev);
+}
+
+
 static struct mdk_personality raid6_personality =
 {
         .name           = "raid6",
@@ -4900,6 +4953,7 @@ static struct mdk_personality raid6_personality =
         .start_reshape  = raid5_start_reshape,
 #endif
         .quiesce        = raid5_quiesce,
+        .takeover       = raid6_takeover,
 };
 static struct mdk_personality raid5_personality =
 {