lwip: Route LWIP socket POSIX I/O functions via IDF VFS layer

No more conflicts between LWIP & newlib read(), write(), fcntl(), etc.

select() still only works if all of the fds are sockets.

Closes https://github.com/espressif/esp-idf/issues/273

components/lwip/include/lwip/port/arch/sys_arch.h

@@ -37,6 +37,7 @@
 #include "freertos/task.h"
 #include "freertos/queue.h"
 #include "freertos/semphr.h"
+#include "arch/vfs_lwip.h"
 
 #ifdef __cplusplus
 extern "C" {

components/lwip/include/lwip/port/arch/vfs_lwip.h

@@ -0,0 +1,28 @@
+// Copyright 2017 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Internal declarations used to ingreate LWIP port layer
+   to ESP-IDF VFS for POSIX I/O.
+*/
+extern unsigned lwip_socket_offset;
+
+void esp_vfs_lwip_sockets_register();
+
+#ifdef __cplusplus
+}
+#endif

components/lwip/include/lwip/port/lwipopts.h

@@ -34,6 +34,7 @@
 
 #include <stdlib.h>
 #include <time.h>
+#include <unistd.h>
 #include <sys/time.h>
 #include <sys/fcntl.h>
 #include "esp_task.h"
@@ -687,6 +688,19 @@
 #define ETHARP_TRUST_IP_MAC             CONFIG_LWIP_ETHARP_TRUST_IP_MAC
 
 
+/**
+ * POSIX I/O functions are mapped to LWIP via the VFS layer
+ * (see port/vfs_lwip.c)
+ */
+#define LWIP_POSIX_SOCKETS_IO_NAMES     0
+
+
+/**
+ * Socket offset is also determined via the VFS layer at
+ * filesystem registration time (see port/vfs_lwip.c)
+ */
+#define LWIP_SOCKET_OFFSET              lwip_socket_offset
+
 /* Enable all Espressif-only options */
 
 #define ESP_LWIP                        1