[1/6] btrfs: introduce key type for persistent temporary items

Commit Message

David Sterba Feb. 11, 2016, 5:23 p.m. UTC

The number of distinct key types is not that big that we could waste one
for something new we want to store in the tree. We'll introduce a new
name for an existing key value and use the objectid for further
extension.  The victim is the BTRFS_BALANCE_ITEM_KEY (248).

The nature of the balance status item is a good example of the temporary
item. It exists from beginning of the balance, keeps the status until it
finishes.

Signed-off-by: David Sterba <[e-mail]>
---
 fs/btrfs/ctree.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

Patch

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index bfe4a337fb4d..e20f40649917 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2185,9 +2185,25 @@  struct btrfs_ioctl_defrag_range_args {
  */
 #define BTRFS_QGROUP_RELATION_KEY       246
 
+/*
+ * Obsolete name, see BTRFS_TEMPORARY_ITEM_KEY.
+ */
 #define BTRFS_BALANCE_ITEM_KEY	248
 
 /*
+ * The key type for tree items that are stored persistently, but do not need to
+ * exist for extended period of time. The items can exist in any tree.
+ *
+ * [subtype, BTRFS_TEMPORARY_ITEM_KEY, data]
+ *
+ * Existing items:
+ *
+ * - balance status item
+ *   (BTRFS_BALANCE_OBJECTID, BTRFS_TEMPORARY_ITEM_KEY, 0)
+ */
+#define BTRFS_TEMPORARY_ITEM_KEY	248
+
+/*
  * Persistantly stores the io stats in the device tree.
  * One key for all stats, (0, BTRFS_DEV_STATS_KEY, devid).
  */