btrfs: introduce key type for persistent temporary items (0bbbccb1) · Commits · 戴 / test

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 <dsterba@suse.com>

fs/btrfs/ctree.h

+16 −0

Original line number	Diff line number	Diff line
		@@ -2185,8 +2185,24 @@ 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).

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