diff --git a/components/dfs/filesystems/lwip/lwip_select.c b/components/dfs/filesystems/lwip/lwip_select.c
index 4d74406ade7b7b6ad049e67aa0755fd8ccd9deb3..7e97d37416e533f730afd77e8b689e6112ea561e 100644
--- a/components/dfs/filesystems/lwip/lwip_select.c
+++ b/components/dfs/filesystems/lwip/lwip_select.c
@@ -1,3 +1,27 @@
+/*
+ * File      : lwip_select.c
+ * This file is part of RT-Thread RTOS
+ * COPYRIGHT (C) 2015, RT-Thread Development Team
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Change Logs:
+ * Date           Author       Notes
+ * 2015-05-05     Bernard      First version
+ */
+
 #include <rtthread.h>
 #include <sys/select.h>
 
@@ -21,28 +45,28 @@ select(int maxfdp1, fd_set *readset, fd_set *writeset, fd_set *exceptset,
     maxfd = 0;
     for (index = 0; index < maxfdp1; index ++)
     {
+        /* convert fd to sock */
+        sock = dfs_lwip_getsocket(index);
+        if (sock == -1) continue;
+
+        if (sock > maxfd) maxfd = sock;
+
+        /* if FD is set, set the socket set */
         if (readset && FD_ISSET(index, readset))
         {
-            sock = dfs_lwip_getsocket(index);
-            if (sock > maxfd) maxfd = sock;
             FD_SET(sock, &sock_readset);
         }
-        
         if (writeset && FD_ISSET(index, writeset))
         {
-            sock = dfs_lwip_getsocket(index);
-            if (sock > maxfd) maxfd = sock;
             FD_SET(sock, &sock_writeset);
         }
-        
         if (exceptset && FD_ISSET(index, exceptset))
         {
-            sock = dfs_lwip_getsocket(index);
-            if (sock > maxfd) maxfd = sock;
             FD_SET(sock, &sock_exceptset);
         }
     }
 
+    /* no socket found, return bad file descriptor */
     if (maxfd == 0) return -EBADF;
     maxfd += 1;