3 files changed, 58 insertions, 3 deletions

diff --git a/lib/tdb/common/open.c b/lib/tdb/common/open.c
index 4ea4499dc1..4d4f95a3da 100644
--- a/lib/tdb/common/open.c
+++ b/lib/tdb/common/open.c
@@ -202,6 +202,23 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 		tdb->flags &= ~TDB_CLEAR_IF_FIRST;
 	}
 
+	if ((tdb->flags & TDB_ALLOW_NESTING) &&
+	    (tdb->flags & TDB_DISALLOW_NESTING)) {
+		tdb->ecode = TDB_ERR_NESTING;
+		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_open_ex: "
+			"allow_nesting and disallow_nesting are not allowed together!"));
+		errno = EINVAL;
+		goto fail;
+	}
+
+	/*
+	 * TDB_ALLOW_NESTING is the default behavior.
+	 * Note: this may change in future versions!
+	 */
+	if (!(tdb->flags & TDB_DISALLOW_NESTING)) {
+		tdb->flags |= TDB_ALLOW_NESTING;
+	}
+
 	/* internal databases don't mmap or lock, and start off cleared */
 	if (tdb->flags & TDB_INTERNAL) {
 		tdb->flags |= (TDB_NOLOCK | TDB_NOMMAP);
diff --git a/lib/tdb/common/tdb.c b/lib/tdb/common/tdb.c
index 564c5fed5c..d2688def04 100644
--- a/lib/tdb/common/tdb.c
+++ b/lib/tdb/common/tdb.c
@@ -730,11 +730,41 @@ int tdb_get_flags(struct tdb_context *tdb)
 
 void tdb_add_flags(struct tdb_context *tdb, unsigned flags)
 {
+	if ((flags & TDB_ALLOW_NESTING) &&
+	    (flags & TDB_DISALLOW_NESTING)) {
+		tdb->ecode = TDB_ERR_NESTING;
+		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_add_flags: "
+			"allow_nesting and disallow_nesting are not allowed together!"));
+		return;
+	}
+
+	if (flags & TDB_ALLOW_NESTING) {
+		tdb->flags &= ~TDB_DISALLOW_NESTING;
+	}
+	if (flags & TDB_DISALLOW_NESTING) {
+		tdb->flags &= ~TDB_ALLOW_NESTING;
+	}
+
 	tdb->flags |= flags;
 }
 
 void tdb_remove_flags(struct tdb_context *tdb, unsigned flags)
 {
+	if ((flags & TDB_ALLOW_NESTING) &&
+	    (flags & TDB_DISALLOW_NESTING)) {
+		tdb->ecode = TDB_ERR_NESTING;
+		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_remove_flags: "
+			"allow_nesting and disallow_nesting are not allowed together!"));
+		return;
+	}
+
+	if (flags & TDB_ALLOW_NESTING) {
+		tdb->flags |= TDB_DISALLOW_NESTING;
+	}
+	if (flags & TDB_DISALLOW_NESTING) {
+		tdb->flags |= TDB_ALLOW_NESTING;
+	}
+
 	tdb->flags &= ~flags;
 }
 
diff --git a/lib/tdb/common/transaction.c b/lib/tdb/common/transaction.c
index 501cd62b96..20f2bfc2cd 100644
--- a/lib/tdb/common/transaction.c
+++ b/lib/tdb/common/transaction.c
@@ -86,12 +86,20 @@
     fsync/msync calls are made.
 
   - if TDB_ALLOW_NESTING is passed to flags in tdb open, or added using
-    tdb_add_flags() transaction is enabled.
-    The default is that transaction nesting is not allowed and an attempt
-    to create a nested transaction will fail with TDB_ERR_NESTING.
+    tdb_add_flags() transaction nesting is enabled.
+    It resets the TDB_DISALLOW_NESTING flag, as both cannot be used together.
+    The default is that transaction nesting is allowed.
+    Note: this default may change in future versions of tdb.
 
     Beware. when transactions are nested a transaction successfully
     completed with tdb_transaction_commit() can be silently unrolled later.
+
+  - if TDB_DISALLOW_NESTING is passed to flags in tdb open, or added using
+    tdb_add_flags() transaction nesting is disabled.
+    It resets the TDB_ALLOW_NESTING flag, as both cannot be used together.
+    An attempt create a nested transaction will fail with TDB_ERR_NESTING.
+    The default is that transaction nesting is allowed.
+    Note: this default may change in future versions of tdb.
 */