@@ -100,6 +100,9 @@ struct btrfs_ordered_sum;
 /* tracks free space in block groups. */
 #define BTRFS_FREE_SPACE_TREE_OBJECTID 10ULL
 
+/* on-disk dedup tree (EXPERIMENTAL) */
+#define BTRFS_DEDUP_TREE_OBJECTID 11ULL
+
 /* for storing balance parameters in the root tree */
 #define BTRFS_BALANCE_OBJECTID -4ULL
 

@@ -505,6 +508,7 @@ struct btrfs_super_block {
  * ones specified below then we will fail to mount
  */
 #define BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE	(1ULL << 0)
+#define BTRFS_FEATURE_COMPAT_RO_DEDUP		(1ULL << 1)
 
 #define BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF	(1ULL << 0)
 #define BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL	(1ULL << 1)

@@ -534,7 +538,8 @@ struct btrfs_super_block {
 #define BTRFS_FEATURE_COMPAT_SAFE_CLEAR		0ULL
 
 #define BTRFS_FEATURE_COMPAT_RO_SUPP			\
-	(BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE)
+	(BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE |	\
+	 BTRFS_FEATURE_COMPAT_RO_DEDUP)
 
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_SET	0ULL
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_CLEAR	0ULL

@@ -964,6 +969,46 @@ struct btrfs_csum_item {
 	u8 csum;
 } __attribute__ ((__packed__));
 
+/*
+ * Objectid: 0
+ * Type: BTRFS_DEDUP_STATUS_ITEM_KEY
+ * Offset: 0
+ */
+struct btrfs_dedup_status_item {
+	__le64 blocksize;
+	__le64 limit_nr;
+	__le16 hash_type;
+	__le16 backend;
+} __attribute__ ((__packed__));
+
+/*
+ * Objectid: Last 64 bit of the hash
+ * Type: BTRFS_DEDUP_HASH_ITEM_KEY
+ * Offset: Bytenr of the hash
+ *
+ * Used for hash <-> bytenr search
+ * XXX: On-disk format not stable yet, see the unsed one
+ */
+struct btrfs_dedup_hash_item {
+	/* on disk length of dedup range */
+	__le64 len;
+
+	/* Spare space */
+	u8 __unused[16];
+
+	/* Hash follows */
+} __attribute__ ((__packed__));
+
+/*
+ * Objectid: bytenr
+ * Type: BTRFS_DEDUP_BYTENR_ITEM_KEY
+ * offset: Last 64 bit of the hash
+ *
+ * Used for bytenr <-> hash search (for free_extent)
+ * all its content is hash.
+ * So no special item struct is needed.
+ */
+
 struct btrfs_dev_stats_item {
 	/*
 	 * grow this item struct at the end for future enhancements and keep

@@ -2167,6 +2212,13 @@ struct btrfs_ioctl_defrag_range_args {
 #define BTRFS_CHUNK_ITEM_KEY	228
 
 /*
+ * Dedup item and status
+ */
+#define BTRFS_DEDUP_STATUS_ITEM_KEY	230
+#define BTRFS_DEDUP_HASH_ITEM_KEY	231
+#define BTRFS_DEDUP_BYTENR_ITEM_KEY	232
+
+/*
  * Records the overall state of the qgroups.
  * There's only one instance of this key present,
  * (0, BTRFS_QGROUP_STATUS_KEY, 0)

@@ -3229,6 +3281,19 @@ static inline unsigned long btrfs_leaf_data(struct extent_buffer *l)
 	return offsetof(struct btrfs_leaf, items);
 }
 
+/* btrfs_dedup_status */
+BTRFS_SETGET_FUNCS(dedup_status_blocksize, struct btrfs_dedup_status_item,
+		   blocksize, 64);
+BTRFS_SETGET_FUNCS(dedup_status_limit, struct btrfs_dedup_status_item,
+		   limit_nr, 64);
+BTRFS_SETGET_FUNCS(dedup_status_hash_type, struct btrfs_dedup_status_item,
+		   hash_type, 16);
+BTRFS_SETGET_FUNCS(dedup_status_backend, struct btrfs_dedup_status_item,
+		   backend, 16);
+
+/* btrfs_dedup_hash_item */
+BTRFS_SETGET_FUNCS(dedup_hash_len, struct btrfs_dedup_hash_item, len, 64);
+
 /* struct btrfs_file_extent_item */
 BTRFS_SETGET_FUNCS(file_extent_type, struct btrfs_file_extent_item, type, 8);
 BTRFS_SETGET_STACK_FUNCS(stack_file_extent_disk_bytenr,

@@ -58,6 +58,8 @@ struct btrfs_dedup_hash {
 	u8 hash[];
 };
 
+struct btrfs_root;
+
 struct btrfs_dedup_info {
 	/* dedup blocksize */
 	u64 blocksize;

@@ -73,6 +75,9 @@ struct btrfs_dedup_info {
 	struct list_head lru_list;
 	u64 limit_nr;
 	u64 current_nr;
+
+	/* for persist data like dedup-hash and dedup status */
+	struct btrfs_root *dedup_root;
 };
 
 struct btrfs_trans_handle;

@@ -183,6 +183,7 @@ static struct btrfs_lockdep_keyset {
 	{ .id = BTRFS_DATA_RELOC_TREE_OBJECTID,	.name_stem = "dreloc"	},
 	{ .id = BTRFS_UUID_TREE_OBJECTID,	.name_stem = "uuid"	},
 	{ .id = BTRFS_FREE_SPACE_TREE_OBJECTID,	.name_stem = "free-space" },
+	{ .id = BTRFS_DEDUP_TREE_OBJECTID,	.name_stem = "dedup"	},
 	{ .id = 0,				.name_stem = "tree"	},
 };
 

@@ -47,12 +47,13 @@ struct btrfs_qgroup_operation;
 		{ BTRFS_TREE_RELOC_OBJECTID,	"TREE_RELOC"	},	\
 		{ BTRFS_UUID_TREE_OBJECTID,	"UUID_TREE"	},	\
 		{ BTRFS_FREE_SPACE_TREE_OBJECTID, "FREE_SPACE_TREE" },	\
+		{ BTRFS_DEDUP_TREE_OBJECTID,	"DEDUP_TREE"	},	\
 		{ BTRFS_DATA_RELOC_TREE_OBJECTID, "DATA_RELOC_TREE" })
 
 #define show_root_type(obj)						\
 	obj, ((obj >= BTRFS_DATA_RELOC_TREE_OBJECTID) ||		\
 	      (obj >= BTRFS_ROOT_TREE_OBJECTID &&			\
-	       obj <= BTRFS_QUOTA_TREE_OBJECTID)) ? __show_root_type(obj) : "-"
+	       obj <= BTRFS_DEDUP_TREE_OBJECTID)) ? __show_root_type(obj) : "-"
 
 #define BTRFS_GROUP_FLAGS	\
 	{ BTRFS_BLOCK_GROUP_DATA,	"DATA"},	\