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-rw-r--r--drivers/md/dm-clone-metadata.h17
1 files changed, 17 insertions, 0 deletions
diff --git a/drivers/md/dm-clone-metadata.h b/drivers/md/dm-clone-metadata.h
index 3fe50a781c11..14af1ebd853f 100644
--- a/drivers/md/dm-clone-metadata.h
+++ b/drivers/md/dm-clone-metadata.h
@@ -75,7 +75,23 @@ void dm_clone_metadata_close(struct dm_clone_metadata *cmd);
/*
* Commit dm-clone metadata to disk.
+ *
+ * We use a two phase commit:
+ *
+ * 1. dm_clone_metadata_pre_commit(): Prepare the current transaction for
+ * committing. After this is called, all subsequent metadata updates, done
+ * through either dm_clone_set_region_hydrated() or
+ * dm_clone_cond_set_range(), will be part of the **next** transaction.
+ *
+ * 2. dm_clone_metadata_commit(): Actually commit the current transaction to
+ * disk and start a new transaction.
+ *
+ * This allows dm-clone to flush the destination device after step (1) to
+ * ensure that all freshly hydrated regions, for which we are updating the
+ * metadata, are properly written to non-volatile storage and won't be lost in
+ * case of a crash.
*/
+int dm_clone_metadata_pre_commit(struct dm_clone_metadata *cmd);
int dm_clone_metadata_commit(struct dm_clone_metadata *cmd);
/*
@@ -112,6 +128,7 @@ int dm_clone_metadata_abort(struct dm_clone_metadata *cmd);
* Switches metadata to a read only mode. Once read-only mode has been entered
* the following functions will return -EPERM:
*
+ * dm_clone_metadata_pre_commit()
* dm_clone_metadata_commit()
* dm_clone_set_region_hydrated()
* dm_clone_cond_set_range()