SQUASH into previous patch introducing shadow transactions

Signed-off-by: Paul Moore <paul@paul-moore.com>

src/db.c

@@ -909,6 +909,9 @@ static void _db_snap_release(struct db_filter_snap *snap)
 {
 	unsigned int iter;
 
+	if (snap == NULL)
+		return;
+
 	if (snap->filter_cnt > 0) {
 		for (iter = 0; iter < snap->filter_cnt; iter++) {
 			if (snap->filters[iter])
@@ -2475,14 +2478,24 @@ void db_col_transaction_commit(struct db_filter_col *col)
 	if (snap == NULL)
 		return;
 
+	/* check for a shadow set by a higher transaction commit */
+	if (snap->shadow) {
+		/* leave the shadow intact, but drop the next snapshot */
+		if (snap->next) {
+			snap->next = snap->next->next;
+			_db_snap_release(snap->next);
+		}
+		return;
+	}
+
 	/* adjust the number of filters if needed */
 	if (col->filter_cnt > snap->filter_cnt) {
 		unsigned int tmp_i;
 		struct db_filter **tmp_f;
 
 		/* add filters */
 		tmp_f = realloc(snap->filters,
-			      sizeof(struct db_filter *) * col->filter_cnt);
+				sizeof(struct db_filter *) * col->filter_cnt);
 		if (tmp_f == NULL)
 			goto shadow_err;
 		snap->filters = tmp_f;