+ struct list_head list;
+
+ /*
+ * The primary pending_exception is the one that holds
+ * the sibling_count and the list of origin_bios for a
+ * group of pending_exceptions. It is always last to get freed.
+ * These fields get set up when writing to the origin.
+ */
+ struct pending_exception *primary_pe;
+
+ /*
+ * Number of pending_exceptions processing this chunk.
+ * When this drops to zero we must complete the origin bios.
+ * If incrementing or decrementing this, hold pe->snap->lock for
+ * the sibling concerned and not pe->primary_pe->snap->lock unless
+ * they are the same.
+ */
+ atomic_t sibling_count;