odb: prepare `struct odb_transaction` to become generic

An ODB transaction handles how objects are stored temporarily and
eventually committed. Due to object storage being implemented
differently for a given ODB source, the ODB transactions must be
implemented in a manner specific to the source the objects are being
written to. To provide generic transactions, `struct odb_transaction` is
updated to store a commit callback that can be configured to support a
specific ODB source. For now `struct odb_transaction_files` is the
only transaction type and what is always returned when starting a
transaction.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/odb.c b/odb.c
index a5e6fd01a9..349b4218a5 100644
--- a/odb.c
+++ b/odb.c
@@ -1158,5 +1158,8 @@ struct odb_transaction *odb_transaction_begin(struct object_database *odb)
 
 void odb_transaction_commit(struct odb_transaction *transaction)
 {
-	odb_transaction_files_commit(transaction);
+	if (!transaction)
+		return;
+
+	transaction->commit(transaction);
 }