Re: [PATCH v6 14/42] sequencer.c: use ref transactions for all ref updates

--- a/sequencer.c
+++ b/sequencer.c

@@ -272,23 +272,31 @@ static int error_dirty_index(struct replay_opts *opts)
 static int fast_forward_to(const unsigned char *to, const unsigned char *from,
 			int unborn, struct replay_opts *opts)
 {
-	struct ref_lock *ref_lock;
+	struct ref_transaction *transaction;
 	struct strbuf sb = STRBUF_INIT;
-	int ret;
+	struct strbuf err = STRBUF_INIT;
 
 	read_cache();
 	if (checkout_fast_forward(from, to, 1))
 		exit(1); /* the callee should have complained already */
-	ref_lock = lock_any_ref_for_update("HEAD", unborn ? null_sha1 : from,
-					   0, NULL);
-	if (!ref_lock)
-		return error(_("Failed to lock HEAD during fast_forward_to"));
 
 	strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
-	ret = write_ref_sha1(ref_lock, to, sb.buf);
+
+	transaction = ref_transaction_begin();
+	if ((!transaction ||
+	    ref_transaction_update(transaction, "HEAD", to, from,
+				   0, !unborn)) ||

+	    (ref_transaction_commit(transaction, sb.buf, &err) &&
+	     !(transaction = NULL))) {
+		ref_transaction_rollback(transaction);