From d7dc4fde4080513e2a62fabbdeee546bd74b9a0d Mon Sep 17 00:00:00 2001
From: Gary Lockyer <gary@catalyst.net.nz>
Date: Thu, 7 Mar 2019 10:18:00 +1300
Subject: [PATCH] lib ldb key value backends: Add nested txn support

Add limited nested transaction support to the back ends to make the key value
operations atomic (for those back ends that support nested transactions).

Note: that only the lmdb backend currently supports nested transactions.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
---
 lib/ldb/ldb_key_value/ldb_kv.h |  3 +++
 lib/ldb/ldb_mdb/ldb_mdb.c      | 33 +++++++++++++++++++++++++++++++++
 lib/ldb/ldb_tdb/ldb_tdb.c      | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+)

diff --git a/lib/ldb/ldb_key_value/ldb_kv.h b/lib/ldb/ldb_key_value/ldb_kv.h
index 3de29039a98..e7fcbd9be8d 100644
--- a/lib/ldb/ldb_key_value/ldb_kv.h
+++ b/lib/ldb/ldb_key_value/ldb_kv.h
@@ -51,6 +51,9 @@ struct kv_db_ops {
 	bool (*has_changed)(struct ldb_kv_private *ldb_kv);
 	bool (*transaction_active)(struct ldb_kv_private *ldb_kv);
 	size_t (*get_size)(struct ldb_kv_private *ldb_kv);
+	int (*begin_nested_write)(struct ldb_kv_private *);
+	int (*finish_nested_write)(struct ldb_kv_private *);
+	int (*abort_nested_write)(struct ldb_kv_private *);
 };
 
 /* this private structure is used by the key value backends in the
diff --git a/lib/ldb/ldb_mdb/ldb_mdb.c b/lib/ldb/ldb_mdb/ldb_mdb.c
index 9fa10e9e470..35e21434ff0 100644
--- a/lib/ldb/ldb_mdb/ldb_mdb.c
+++ b/lib/ldb/ldb_mdb/ldb_mdb.c
@@ -739,6 +739,36 @@ static size_t lmdb_get_size(struct ldb_kv_private *ldb_kv)
 	return stats.ms_entries;
 }
 
+/*
+ * Start a sub transaction
+ * As lmdb supports nested transactions we can start a new transaction
+ */
+static int lmdb_nested_transaction_start(struct ldb_kv_private *ldb_kv)
+{
+	int ret = lmdb_transaction_start(ldb_kv);
+	return ret;
+}
+
+/*
+ * Commit a sub transaction
+ * As lmdb supports nested transactions we can commit the nested transaction
+ */
+static int lmdb_nested_transaction_commit(struct ldb_kv_private *ldb_kv)
+{
+	int ret = lmdb_transaction_commit(ldb_kv);
+	return ret;
+}
+
+/*
+ * Cancel a sub transaction
+ * As lmdb supports nested transactions we can cancel the nested transaction
+ */
+static int lmdb_nested_transaction_cancel(struct ldb_kv_private *ldb_kv)
+{
+	int ret = lmdb_transaction_cancel(ldb_kv);
+	return ret;
+}
+
 static struct kv_db_ops lmdb_key_value_ops = {
 	.options            = LDB_KV_OPTION_STABLE_READ_LOCK,
 
@@ -760,6 +790,9 @@ static struct kv_db_ops lmdb_key_value_ops = {
 	.has_changed        = lmdb_changed,
 	.transaction_active = lmdb_transaction_active,
 	.get_size           = lmdb_get_size,
+	.begin_nested_write = lmdb_nested_transaction_start,
+	.finish_nested_write = lmdb_nested_transaction_commit,
+	.abort_nested_write = lmdb_nested_transaction_cancel,
 };
 
 static const char *lmdb_get_path(const char *url)
diff --git a/lib/ldb/ldb_tdb/ldb_tdb.c b/lib/ldb/ldb_tdb/ldb_tdb.c
index 6e2cb633a4d..77cd5e9726b 100644
--- a/lib/ldb/ldb_tdb/ldb_tdb.c
+++ b/lib/ldb/ldb_tdb/ldb_tdb.c
@@ -437,6 +437,36 @@ static size_t ltdb_get_size(struct ldb_kv_private *ldb_kv)
 	return size;
 }
 
+/*
+ * Start a sub transaction
+ * As TDB does not currently support nested transactions, we do nothing and
+ * return LDB_SUCCESS
+ */
+static int ltdb_nested_transaction_start(struct ldb_kv_private *ldb_kv)
+{
+	return LDB_SUCCESS;
+}
+
+/*
+ * Commit a sub transaction
+ * As TDB does not currently support nested transactions, we do nothing and
+ * return LDB_SUCCESS
+ */
+static int ltdb_nested_transaction_commit(struct ldb_kv_private *ldb_kv)
+{
+	return LDB_SUCCESS;
+}
+
+/*
+ * Cancel a sub transaction
+ * As TDB does not currently support nested transactions, we do nothing and
+ * return LDB_SUCCESS
+ */
+static int ltdb_nested_transaction_cancel(struct ldb_kv_private *ldb_kv)
+{
+	return LDB_SUCCESS;
+}
+
 static const struct kv_db_ops key_value_ops = {
 	/* No support for any additional features */
 	.options = 0,
@@ -459,6 +489,9 @@ static const struct kv_db_ops key_value_ops = {
 	.has_changed = ltdb_changed,
 	.transaction_active = ltdb_transaction_active,
 	.get_size = ltdb_get_size,
+	.begin_nested_write = ltdb_nested_transaction_start,
+	.finish_nested_write = ltdb_nested_transaction_commit,
+	.abort_nested_write = ltdb_nested_transaction_cancel,
 };
 
 /*
-- 
2.47.3