lwip/linux: Add lwip support for networking component under linux

linux/lwip: Wrap some IO posix functions
* to workaourd the FreeRTOS EINTR issue (when building without lwip)
* to correctly choose the sub-system based on fd (when building with
lwip) -- passing control to either linux/system or to lwip
This commit also addapts tapio-if to provide DHCP client by default and
configurable settings for static IP

examples/common_components/protocol_examples_tapif_io/Kconfig.projbuild

@@ -3,7 +3,7 @@ menu "Example Connection Configuration"
     config EXAMPLE_CONNECT_LWIP_TAPIF
         bool "connect using lwip to linux tap interface"
         depends on IDF_TARGET_LINUX && ESP_NETIF_TCPIP_LWIP
-        default n
+        default y
 
     if EXAMPLE_CONNECT_LWIP_TAPIF
         config EXAMPLE_CONNECT_IPV4
@@ -18,24 +18,28 @@ menu "Example Connection Configuration"
             help
                 Set to true to setup link local address and wait until it's valid
 
+        config EXAMPLE_CONNECT_WAIT_FOR_IP
+            bool "run DHCP and wait for IP"
+            default y
+
         config EXAMPLE_CONNECT_TAPIF_IP_ADDR
             string "Static IP address"
             default "192.168.5.100"
-            depends on EXAMPLE_CONNECT_IPV4
+            depends on EXAMPLE_CONNECT_IPV4 && !EXAMPLE_CONNECT_WAIT_FOR_IP
             help
                 Set static IP address.
 
         config EXAMPLE_CONNECT_TAPIF_NETMASK
             string "Static netmask address"
             default "255.255.255.0"
-            depends on EXAMPLE_CONNECT_IPV4
+            depends on EXAMPLE_CONNECT_IPV4 && !EXAMPLE_CONNECT_WAIT_FOR_IP
             help
                 Set static netmask address.
 
         config EXAMPLE_CONNECT_TAPIF_GW
             string "Static gateway address"
             default "192.168.5.1"
-            depends on EXAMPLE_CONNECT_IPV4
+            depends on EXAMPLE_CONNECT_IPV4 && !EXAMPLE_CONNECT_WAIT_FOR_IP
             help
                 Set static gateway address.
 

examples/common_components/protocol_examples_tapif_io/README.md

@@ -110,6 +110,8 @@ sudo iptables -A FORWARD -i tap0 -o eth0 -j ACCEPT
 It's also possible to configure the lwip interface to use DHCP client (common setup for most default network interfaces, such as Ethernet or WiFi station)
 and set up a DHCP server on the host machine to assign the IP address dynamically.
 
+This component sets up a DHCP client if `CONFIG_EXAMPLE_CONNECT_WAIT_FOR_IP` is enabled and waits for assigning an IP address. See below the description of DHCP client workflow for tap interface:
+
 1) **Configure and set the `esp-netif` up**
 
 * Same as in [API usage](#Usage-of-the-API), but update the base esp-netif config `3c)` to enable DHCP client
@@ -125,14 +127,17 @@ and set up a DHCP server on the host machine to assign the IP address dynamicall
     esp_netif_action_connected(tap_netif, 0, 0, 0);
 ```
 * Wait for the IP address to be assigned.
-This could be implemented as a wait loop below, as the esp-event currently doesn't support IP events on Linux target.
+This could be implemented using an event handler
 ```cpp
+    esp_netif_inherent_config_t base_cfg = {
+        ...
+       .get_ip_event = TAP0_GOT_IP,
+       ...
+    };
+    ESP_ERROR_CHECK(esp_event_handler_register(IP_EVENT, TAP0_GOT_IP, event_handler, NULL));
+    // wait for the IP event (e.g. using signalling semaphores from the handler)
+    // ...
     esp_netif_ip_info_t ip_info = {};
-    while (ip_info.ip.addr == 0) {
-        ESP_LOGI("tap-init", "No IP assigned, waiting...");
-        usleep(1000000);
-        esp_netif_get_ip_info(tap_netif, &ip_info);
-    }
     ESP_LOGI("tap-init", "Assigned IP address:"IPSTR ",", IP2STR(&ip_info.ip));
 ```
 

examples/common_components/protocol_examples_tapif_io/linux/tapio.c

@@ -4,26 +4,25 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 #include <stdlib.h>
-#include "esp_err.h"
-#include "esp_log.h"
-#include <stdlib.h>
-#include "esp_netif.h"
-#include <fcntl.h>
-#include <stdlib.h>
-#include <stdio.h>
 #include <unistd.h>
 #include <string.h>
+#include "esp_err.h"
+#include "esp_log.h"
+#include "esp_netif.h"
+
+// Use linux system sockets to connect to tap interface
+#define LWIP_HDR_LINUX_SYS_SOCKETS_H
+#include <sys/socket.h>
+#include <fcntl.h>
+
 #include <sys/ioctl.h>
 #include <sys/types.h>
 #include <sys/ioctl.h>
 #include <lwip/sys.h>
 #include "errno.h"
 
-#define LWIP_HDR_LINUX_SYS_SOCKETS_H
-
 #include <linux/if.h>
 #include <linux/if_tun.h>
-#include <esp_netif_net_stack.h>
 
 #define DEVTAP "/dev/net/tun"
 #define DEVTAP_NAME "tap0"

examples/common_components/protocol_examples_tapif_io/linux_connect.c

@@ -7,6 +7,26 @@
 #include "esp_netif.h"      // esp-netif
 #include "tapio.h"          // esp-netif's driver side
 #include "lwip/tapif.h"     // esp-netif's network stack side
+#include "esp_log.h"
+
+#if CONFIG_EXAMPLE_CONNECT_WAIT_FOR_IP
+#include "esp_event.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "freertos/event_groups.h"
+
+static const char *TAG = "linux_connect";
+
+static EventGroupHandle_t s_events;
+
+static void event_handler(void* arg, esp_event_base_t event_base, int32_t event_id, void* event_data)
+{
+    xEventGroupSetBits(s_events, 1);
+}
+
+#endif // CONFIG_EXAMPLE_CONNECT_WAIT_FOR_IP
+
+#define TAP0_GOT_IP (0x1234)
 
 esp_err_t example_connect(void)
 {
@@ -25,14 +45,20 @@ esp_err_t example_connect(void)
     };
     // configure inherent esp-netif parameters
     esp_netif_ip_info_t ip_info = {};
+    esp_netif_flags_t netif_flags = (ESP_NETIF_FLAG_EVENT_IP_MODIFIED | ESP_NETIF_FLAG_AUTOUP);
+#if !CONFIG_EXAMPLE_CONNECT_WAIT_FOR_IP
     ip_info.ip.addr = ipaddr_addr(CONFIG_EXAMPLE_CONNECT_TAPIF_IP_ADDR);
     ip_info.netmask.addr = ipaddr_addr(CONFIG_EXAMPLE_CONNECT_TAPIF_NETMASK);
     ip_info.gw.addr = ipaddr_addr(CONFIG_EXAMPLE_CONNECT_TAPIF_GW);
+#else
+    netif_flags |= ESP_NETIF_DHCP_CLIENT;
+#endif
 
     esp_netif_inherent_config_t base_cfg = {
             .if_key = "TAP",
-            .flags = ESP_NETIF_FLAG_AUTOUP,
             .ip_info = &ip_info,
+            .flags = netif_flags,
+            .get_ip_event = TAP0_GOT_IP,
             .route_prio = 100
     };
 
@@ -46,6 +72,15 @@ esp_err_t example_connect(void)
     // create the interface and attach it to the tapio-handle
     esp_netif_t *tap_netif = esp_netif_new(&cfg);
     esp_netif_attach(tap_netif, driver_cfg.handle);
+#if CONFIG_EXAMPLE_CONNECT_WAIT_FOR_IP
+    ESP_LOGI(TAG, "Waiting for IP addresses...");
+    esp_netif_action_connected(tap_netif, 0, 0, 0);
+    ESP_ERROR_CHECK(esp_event_handler_register(IP_EVENT, TAP0_GOT_IP, event_handler, NULL));
+    s_events = xEventGroupCreate();
+    xEventGroupWaitBits(s_events, 1, pdFALSE, pdFALSE, portMAX_DELAY);
+    esp_netif_get_ip_info(tap_netif, &ip_info);
+    ESP_LOGI(TAG, "Assigned IP address:"IPSTR ",", IP2STR(&ip_info.ip));
+#endif // CONFIG_EXAMPLE_CONNECT_WAIT_FOR_IP
 #endif // EXAMPLE_CONNECT_LWIP_TAPIF
     return ESP_OK;
 }