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>
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 84b22d6..8034f62 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -321,6 +321,16 @@
* others - reserved
*/
void (*quiesce) (mddev_t *mddev, int state);
+ /* takeover is used to transition an array from one
+ * personality to another. The new personality must be able
+ * to handle the data in the current layout.
+ * e.g. 2drive raid1 -> 2drive raid5
+ * ndrive raid5 -> degraded n+1drive raid6 with special layout
+ * If the takeover succeeds, a new 'private' structure is returned.
+ * This needs to be installed and then ->run used to activate the
+ * array.
+ */
+ void *(*takeover) (mddev_t *mddev);
};