[PATCH v4 07/11] odb/transaction: propagate commit errors

[Justin Tobler <jltobler@gmail.com>]

When `odb_transaction_commit()` is invoked, the return value of the
backend commit callback is silently discarded. A backend has no way
to signal that committing failed, such as when the "files" backend
cannot migrate its temporary object directory into the permanent
ODB.

In a subsequent commit, git-receive-pack(1) starts using ODB transaction
to stage objects and consequently cares about such failures so it can
handle the error appropriately. Change the commit callback signature to
return an int error code and have `odb_transaction_commit()` forward it
accordingly.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
---
 odb/transaction.c | 10 +++++++---
 odb/transaction.h |  7 ++++---
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/odb/transaction.c b/odb/transaction.c
index b6da4a3942..249ef4d9b7 100644
--- a/odb/transaction.c
+++ b/odb/transaction.c
@@ -18,19 +18,23 @@ int odb_transaction_begin(struct object_database *odb,
 	return ret;
 }
 
-void odb_transaction_commit(struct odb_transaction *transaction)
+int odb_transaction_commit(struct odb_transaction *transaction)
 {
+	int ret;
+
 	if (!transaction)
-		return;
+		return 0;
 
 	/*
 	 * Ensure the transaction ending matches the pending transaction.
 	 */
 	ASSERT(transaction == transaction->source->odb->transaction);
 
-	transaction->commit(transaction);
+	ret = transaction->commit(transaction);
 	transaction->source->odb->transaction = NULL;
 	free(transaction);
+
+	return ret;
 }
 
 int odb_transaction_write_object_stream(struct odb_transaction *transaction,
diff --git a/odb/transaction.h b/odb/transaction.h
index f5c43187c9..3b0a5a78e5 100644
--- a/odb/transaction.h
+++ b/odb/transaction.h
@@ -54,10 +54,11 @@ static inline void odb_transaction_begin_or_die(struct object_database *odb,
 }
 
 /*
- * Commits an ODB transaction making the written objects visible. If the
- * specified transaction is NULL, the function is a no-op.
+ * Commits an ODB transaction making the written objects visible. Returns 0 on
+ * success, a negative error code otherwise. Note that, if the specified
+ * transaction is NULL, the function is a no-op and no error is returned.
  */
-void odb_transaction_commit(struct odb_transaction *transaction);
+int odb_transaction_commit(struct odb_transaction *transaction);
 
 /*
  * Writes the object in the provided stream into the transaction. The resulting
-- 
2.55.0.122.gf85a7e6620