+static int persistent_prepare_merge(struct dm_exception_store *store,
+ chunk_t *last_old_chunk,
+ chunk_t *last_new_chunk)
+{
+ struct pstore *ps = get_info(store);
+ struct disk_exception de;
+ int nr_consecutive;
+ int r;
+
+ /*
+ * When current area is empty, move back to preceding area.
+ */
+ if (!ps->current_committed) {
+ /*
+ * Have we finished?
+ */
+ if (!ps->current_area)
+ return 0;
+
+ ps->current_area--;
+ r = area_io(ps, READ);
+ if (r < 0)
+ return r;
+ ps->current_committed = ps->exceptions_per_area;
+ }
+
+ read_exception(ps, ps->current_committed - 1, &de);
+ *last_old_chunk = de.old_chunk;
+ *last_new_chunk = de.new_chunk;
+
+ /*
+ * Find number of consecutive chunks within the current area,
+ * working backwards.
+ */
+ for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
+ nr_consecutive++) {
+ read_exception(ps, ps->current_committed - 1 - nr_consecutive,
+ &de);
+ if (de.old_chunk != *last_old_chunk - nr_consecutive ||
+ de.new_chunk != *last_new_chunk - nr_consecutive)
+ break;
+ }
+
+ return nr_consecutive;
+}
+
+static int persistent_commit_merge(struct dm_exception_store *store,
+ int nr_merged)
+{
+ int r, i;
+ struct pstore *ps = get_info(store);
+
+ BUG_ON(nr_merged > ps->current_committed);
+
+ for (i = 0; i < nr_merged; i++)
+ clear_exception(ps, ps->current_committed - 1 - i);
+
+ r = area_io(ps, WRITE);
+ if (r < 0)
+ return r;
+
+ ps->current_committed -= nr_merged;
+
+ /*
+ * At this stage, only persistent_usage() uses ps->next_free, so
+ * we make no attempt to keep ps->next_free strictly accurate
+ * as exceptions may have been committed out-of-order originally.
+ * Once a snapshot has become merging, we set it to the value it
+ * would have held had all the exceptions been committed in order.
+ *
+ * ps->current_area does not get reduced by prepare_merge() until
+ * after commit_merge() has removed the nr_merged previous exceptions.
+ */
+ ps->next_free = (area_location(ps, ps->current_area) - 1) +
+ (ps->current_committed + 1) + NUM_SNAPSHOT_HDR_CHUNKS;
+
+ return 0;
+}
+