[PATCH v2 1/6] refs: construct transaction using a _begin callback

["Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Han-Wen Nienhuys <hanwen@xxxxxxxxxx>

This prepares for taking locks on constructing the transaction.

Signed-off-by: Han-Wen Nienhuys <hanwen@xxxxxxxxxx>
---
 refs.c                | 8 +++-----
 refs/debug.c          | 8 ++++++++
 refs/files-backend.c  | 8 ++++++++
 refs/packed-backend.c | 9 +++++++++
 refs/refs-internal.h  | 4 ++++
 5 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/refs.c b/refs.c
index fcae5dddc60..f7ba3e56284 100644
--- a/refs.c
+++ b/refs.c
@@ -1129,11 +1129,9 @@ int read_ref_at(struct ref_store *refs, const char *refname,
 struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
 						    struct strbuf *err)
 {
-	struct ref_transaction *tr;
-	assert(err);
-
-	CALLOC_ARRAY(tr, 1);
-	tr->ref_store = refs;
+	struct ref_transaction *tr = refs->be->transaction_begin(refs, err);
+	if (tr)
+		tr->ref_store = refs;
 	return tr;
 }
 
diff --git a/refs/debug.c b/refs/debug.c
index b7ffc4ce67e..95fb3eb4430 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -41,6 +41,13 @@ static int debug_init_db(struct ref_store *refs, struct strbuf *err)
 	return res;
 }
 
+static struct ref_transaction *debug_transaction_begin(struct ref_store *ref_store,
+						       struct strbuf *err) {
+	struct ref_transaction *tr;
+	CALLOC_ARRAY(tr, 1);
+	return tr;
+}
+
 static int debug_transaction_prepare(struct ref_store *refs,
 				     struct ref_transaction *transaction,
 				     struct strbuf *err)
@@ -451,6 +458,7 @@ struct ref_storage_be refs_be_debug = {
 	 * has a function we should also have a wrapper for it here.
 	 * Test the output with "GIT_TRACE_REFS=1".
 	 */
+	.transaction_begin = debug_transaction_begin,
 	.transaction_prepare = debug_transaction_prepare,
 	.transaction_finish = debug_transaction_finish,
 	.transaction_abort = debug_transaction_abort,
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 341354182bb..d83eea8b408 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2681,6 +2681,13 @@ static void files_transaction_cleanup(struct files_ref_store *refs,
 	transaction->state = REF_TRANSACTION_CLOSED;
 }
 
+static struct ref_transaction *files_transaction_begin(struct ref_store *ref_store,
+						       struct strbuf *err) {
+	struct ref_transaction *tr;
+	CALLOC_ARRAY(tr, 1);
+	return tr;
+}
+
 static int files_transaction_prepare(struct ref_store *ref_store,
 				     struct ref_transaction *transaction,
 				     struct strbuf *err)
@@ -3297,6 +3304,7 @@ struct ref_storage_be refs_be_files = {
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,
+	.transaction_begin = files_transaction_begin,
 	.transaction_prepare = files_transaction_prepare,
 	.transaction_finish = files_transaction_finish,
 	.transaction_abort = files_transaction_abort,
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 59c78d7941f..4f5b1025605 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1580,6 +1580,14 @@ static void packed_transaction_cleanup(struct packed_ref_store *refs,
 	transaction->state = REF_TRANSACTION_CLOSED;
 }
 
+
+static struct ref_transaction *packed_transaction_begin(struct ref_store *ref_store,
+							struct strbuf *err) {
+	struct ref_transaction *tr;
+	CALLOC_ARRAY(tr, 1);
+	return tr;
+}
+
 static int packed_transaction_prepare(struct ref_store *ref_store,
 				      struct ref_transaction *transaction,
 				      struct strbuf *err)
@@ -1758,6 +1766,7 @@ struct ref_storage_be refs_be_packed = {
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,
+	.transaction_begin = packed_transaction_begin,
 	.transaction_prepare = packed_transaction_prepare,
 	.transaction_finish = packed_transaction_finish,
 	.transaction_abort = packed_transaction_abort,
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 9db8aec4da8..0a15e8a2ac8 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -531,6 +531,9 @@ typedef struct ref_store *ref_store_init_fn(struct repository *repo,
 
 typedef int ref_init_db_fn(struct ref_store *refs, struct strbuf *err);
 
+typedef struct ref_transaction *ref_transaction_begin_fn(struct ref_store *refs,
+							 struct strbuf *err);
+
 typedef int ref_transaction_prepare_fn(struct ref_store *refs,
 				       struct ref_transaction *transaction,
 				       struct strbuf *err);
@@ -670,6 +673,7 @@ struct ref_storage_be {
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;
 
+	ref_transaction_begin_fn *transaction_begin;
 	ref_transaction_prepare_fn *transaction_prepare;
 	ref_transaction_finish_fn *transaction_finish;
 	ref_transaction_abort_fn *transaction_abort;
-- 
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