open_db
retval = open_db(context, dbc,
retval = open_db(context, dbc, O_RDONLY, 0, &db);
retval = open_db(context, dbc, O_RDWR | O_CREAT | O_EXCL, 0600, &dbc->db);
if ((dbp = open_db(map, O_RDWR|O_EXLOCK|O_EXCL|O_CREAT)) == NULL)
dbp = open_db(map, O_RDONLY);