dm exception store: add merge specific methods
Add functions that decide how many consecutive chunks of snapshot to
merge back into the origin next and to update the metadata afterwards.
prepare_merge provides a pointer to the most recent still-to-be-merged
chunk and returns how many previous ones are consecutive and can be
processed together.
commit_merge removes the nr_merged most-recent chunks permanently from
the exception store. The number must not exceed that returned by
prepare_merge.
Introduce NUM_SNAPSHOT_HDR_CHUNKS to show where the snapshot header
chunk is accounted for.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-exception-store.h b/drivers/md/dm-exception-store.h
index bb88746..c53e089 100644
--- a/drivers/md/dm-exception-store.h
+++ b/drivers/md/dm-exception-store.h
@@ -75,6 +75,23 @@
void *callback_context);
/*
+ * Returns 0 if the exception store is empty.
+ *
+ * If there are exceptions still to be merged, sets
+ * *last_old_chunk and *last_new_chunk to the most recent
+ * still-to-be-merged chunk and returns the number of
+ * consecutive previous ones.
+ */
+ int (*prepare_merge) (struct dm_exception_store *store,
+ chunk_t *last_old_chunk, chunk_t *last_new_chunk);
+
+ /*
+ * Clear the last n exceptions.
+ * nr_merged must be <= the value returned by prepare_merge.
+ */
+ int (*commit_merge) (struct dm_exception_store *store, int nr_merged);
+
+ /*
* The snapshot is invalid, note this in the metadata.
*/
void (*drop_snapshot) (struct dm_exception_store *store);