+#define DM_TRACKED_CHUNK_HASH_SIZE 16
+#define DM_TRACKED_CHUNK_HASH(x) ((unsigned long)(x) & \
+ (DM_TRACKED_CHUNK_HASH_SIZE - 1))
+
+struct exception_table {
+ uint32_t hash_mask;
+ unsigned hash_shift;
+ struct list_head *table;
+};
+
+struct dm_snapshot {
+ struct rw_semaphore lock;
+
+ struct dm_dev *origin;
+
+ /* List of snapshots per Origin */
+ struct list_head list;
+
+ /* You can't use a snapshot if this is 0 (e.g. if full) */
+ int valid;
+
+ /* Origin writes don't trigger exceptions until this is set */
+ int active;
+
+ mempool_t *pending_pool;
+
+ atomic_t pending_exceptions_count;
+
+ struct exception_table pending;
+ struct exception_table complete;
+
+ /*
+ * pe_lock protects all pending_exception operations and access
+ * as well as the snapshot_bios list.
+ */
+ spinlock_t pe_lock;
+
+ /* The on disk metadata handler */
+ struct dm_exception_store *store;
+
+ struct dm_kcopyd_client *kcopyd_client;
+
+ /* Queue of snapshot writes for ksnapd to flush */
+ struct bio_list queued_bios;
+ struct work_struct queued_bios_work;
+
+ /* Chunks with outstanding reads */
+ mempool_t *tracked_chunk_pool;
+ spinlock_t tracked_chunk_lock;
+ struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
+};
+