dcb.c

: dcb_alloc switched malloc to calloc, dcb->fd is initialized to -1. 
: dcb_process_zombies return value of close(fd) is checked. Closed fds are stored to conn_open array. 
: dcb_connect assigns new fd only if backend connection succeeds. Dcb is added to poll set in the same way, only if connect succeed.
gateway.c : conn_open array is initialized in main. For each created socket, a true is set to corresponding slot. Max. number of slots is 1024.
mysql_client_server_protocol.h : gw_do_connect_to declaration 
mysql_backend.c : gw_create_backend_connection returns rv >= 0 and a protocol which is assigned to backend_dcb. In error, -1 is returned and fd is not set.
mysql_client.c : conn_open array is kept up-to-date and protocol pointer is assigned also to dcb outside mysql_protocol_init.
mysql_common.c : gw_do_connect_to_backend 3rd argument is pointer to fd, not protocol. dcb is added to poll set later in dcb_connect.
skygw_debug.h : define conn_open[1024] array where open connections can be marked in debug build.

server/modules/include/mysql_client_server_protocol.h

@@ -251,7 +251,7 @@ int gw_send_authentication_to_backend(
         uint8_t *passwd,
         MySQLProtocol *conn);
 const char *gw_mysql_protocol_state2string(int state);
-int        gw_do_connect_to_backend(char *host, int port, MySQLProtocol *conn);
+int gw_do_connect_to_backend(char *host, int port, int* fd);
 int mysql_send_custom_error (
         DCB *dcb,
         int packet_number,