examples: Add common linux component tapif_io

That can be used with linux target on lwip to pass packets from lwip to
linux host networking stack, e.g. routing the trafic to internet.

examples/common_components/protocol_examples_tapif_io/linux/tapio.c

@@ -0,0 +1,135 @@
+/*
+ * SPDX-FileCopyrightText: 2022-2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * 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 <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"
+
+
+typedef struct tap_io {
+    esp_netif_driver_base_t base;
+    int fd;
+} tap_io_t;
+
+static const char *TAG = "tap-netif";
+
+static void tapio_input_task(void *arg)
+{
+    tap_io_t *io = arg;
+    fd_set fdset;
+    int ret;
+    while (1) {
+        FD_ZERO(&fdset);
+        FD_SET(io->fd, &fdset);
+
+        /* Wait for a packet to arrive. */
+        ret = select(io->fd + 1, &fdset, NULL, NULL, NULL);
+
+        if (ret == 1) {
+            /* Handle incoming packet. */
+            ssize_t readlen;
+            char buf[1518]; /* max packet size including VLAN excluding CRC */
+
+            /* Obtain the size of the packet and put it into the "len"
+               variable. */
+            readlen = read(io->fd, buf, sizeof(buf));
+            if (readlen < 0) {
+                ESP_LOGE(TAG, "Failed to read from tap fd: returned %ld", readlen);
+                exit(1);
+            }
+#if CONFIG_EXAMPLE_CONNECT_TAPIF_IN_LOSS
+            if (((double)rand()/(double)RAND_MAX) < ((double)CONFIG_EXAMPLE_CONNECT_TAPIF_IN_LOSS)/100.0) {
+                ESP_LOGW(TAG, "Simulated packet drop on input");
+                continue;
+            }
+#endif
+            esp_netif_receive(io->base.netif, buf, readlen, NULL);
+        } else if (ret == -1) {
+            if (errno == EINTR /* Interrupted system call (used by FreeRTOS simulated interrupts) */) {
+                vTaskDelay(1); // yield to the FreeRTOS simulator
+            } else {
+                ESP_LOGE(TAG, "tapif_thread: select() error(%d), %s", errno, strerror(errno));
+            }
+        }
+    }
+}
+
+static esp_err_t tapio_start(esp_netif_t *esp_netif, void *arg)
+{
+    tap_io_t *io = arg;
+    io->base.netif = esp_netif;
+    esp_netif_action_start(esp_netif, 0, 0, 0);
+
+    sys_thread_new("tapio_rx", tapio_input_task, io, DEFAULT_THREAD_STACKSIZE, DEFAULT_THREAD_PRIO);
+
+    return ESP_OK;
+}
+
+void *tapio_create(void)
+{
+    static tap_io_t tap_io = {};
+    tap_io.base.post_attach = tapio_start;
+    tap_io.fd = open(DEVTAP, O_RDWR);
+    if (tap_io.fd == -1) {
+        ESP_LOGE(TAG, "Cannot open tap device %s", DEVTAP);
+        return NULL;
+    }
+
+    struct ifreq ifr = {};
+    memset(&ifr, 0, sizeof(ifr));
+
+    strncpy(ifr.ifr_name, DEVTAP_NAME, sizeof(ifr.ifr_name));
+    ifr.ifr_name[sizeof(ifr.ifr_name)-1] = 0; /* ensure \0 termination */
+    ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
+    if (ioctl(tap_io.fd, TUNSETIFF, (void *) &ifr) < 0) {
+        ESP_LOGE(TAG, "Cannot configure ioctl(TUNSETIFF) for \"%s\"", DEVTAP);
+        return NULL;
+    }
+
+
+    return &tap_io;
+}
+
+esp_err_t tapio_output(void *h, void *buffer, size_t len)
+{
+    tap_io_t *io = h;
+    ssize_t written;
+
+#if CONFIG_EXAMPLE_CONNECT_TAPIF_OUT_LOSS
+    if (((double)rand()/(double)RAND_MAX) < ((double)CONFIG_EXAMPLE_CONNECT_TAPIF_OUT_LOSS)/100.0) {
+        ESP_LOGW(TAG, "Simulated packet drop on output");
+        return ESP_OK; /* ESP_OK because we simulate packet loss on cable */
+    }
+#endif
+
+    /* signal that packet should be sent(); */
+    written = write(io->fd, buffer, len);
+    if (written < len) {
+        ESP_LOGE(TAG, "Failed to write from tap fd: returned %ld", written);
+        return ESP_FAIL;
+    }
+    return ESP_OK;
+}