md: separate meta and data devs
Allow the metadata to be on a separate device from the
data.
This doesn't mean the data and metadata will by on separate
physical devices - it simply gives device-mapper and userspace
tools more flexibility.
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 7e4f358..eec517c 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -60,6 +60,12 @@
mddev_t *mddev; /* RAID array if running */
int last_events; /* IO event timestamp */
+ /*
+ * If meta_bdev is non-NULL, it means that a separate device is
+ * being used to store the metadata (superblock/bitmap) which
+ * would otherwise be contained on the same device as the data (bdev).
+ */
+ struct block_device *meta_bdev;
struct block_device *bdev; /* block device handle */
struct page *sb_page;