test(esp_netif): clear errno before L2TAP asserts

select() does not set errno on timeout per POSIX; remove the incorrect
EAGAIN check after select timeout and clear errno before asserting it.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/esp_netif/test_apps/test_app_vfs_l2tap/main/test_vfs_l2tap.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2025 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -527,6 +527,7 @@ TEST_CASE("esp32 l2tap - non blocking read", "[ethernet]")
 
     // Verify the read does not block
     while (loop_cnt < 100) {
+        errno = 0;
         if ((n = read(eth_tap_fd, in_buffer, IN_BUFFER_SIZE)) > 0) {
             ESP_LOG_BUFFER_HEX(TAG, in_buffer, n);
             ESP_LOGI(TAG, "recv test string: %s", ((test_vfs_eth_tap_msg_t *)in_buffer)->str);
@@ -594,8 +595,8 @@ TEST_CASE("esp32 l2tap - non blocking read", "[ethernet]")
     FD_SET(eth_tap_fd, &rfds);
 
     TEST_ASSERT_EQUAL(0, select(eth_tap_fd + 1, &rfds, NULL, NULL, &tv));
-    TEST_ASSERT_EQUAL(EAGAIN, errno);
 
+    errno = 0;
     n = read(eth_tap_fd, in_buffer, IN_BUFFER_SIZE);
     TEST_ASSERT_EQUAL(EAGAIN, errno);
     TEST_ASSERT_EQUAL(-1, n);
@@ -703,6 +704,7 @@ TEST_CASE("esp32 l2tap - write", "[ethernet]")
     esp_eth_ioctl(eth_network_hndls.eth_handle, ETH_CMD_G_MAC_ADDR, &test_msg.header.dest.addr);
     // set different Ethernet type than the fd is configured to
     test_msg.header.type = htons(ETH_FILTER_LE + 10);
+    errno = 0;
     TEST_ASSERT_EQUAL(-1, write(eth_tap_fd, &test_msg, sizeof(test_msg)));
     TEST_ASSERT_EQUAL(EBADMSG, errno);
 
@@ -904,9 +906,11 @@ TEST_CASE("esp32 l2tap - time stamping", "[ethernet]")
     ESP_LOGI(TAG, "Verify response when trying to write/read in standard way (input len > 0) but tap configured as TS enabled");
     test_ptp_msg.ptp_msg.ptp_hdr.sequence_id++;
     exp_sequence_id++;
+    errno = 0;
     n = write(eth_tap_fd, &test_ptp_msg, sizeof(test_ptp_msg));
     TEST_ASSERT_EQUAL(-1, n);
     TEST_ASSERT_EQUAL(EINVAL, errno);
+    errno = 0;
     n = read(eth_tap_fd, &in_buffer, sizeof(test_ptp_msg));
     TEST_ASSERT_EQUAL(-1, n);
     TEST_ASSERT_EQUAL(EINVAL, errno);
@@ -985,6 +989,7 @@ TEST_CASE("esp32 l2tap - time stamping", "[ethernet]")
     ts_info->len = L2TAP_IREC_LEN(sizeof(struct timespec));
     ptp_msg_ext_buff.buff = NULL;
     ptp_msg_ext_buff.buff_len = sizeof(test_ptp_msg);
+    errno = 0;
     n = write(eth_tap_fd, &ptp_msg_ext_buff, 0);
     TEST_ASSERT_EQUAL(-1, n);
     TEST_ASSERT_EQUAL(EFAULT, errno);
@@ -993,6 +998,7 @@ TEST_CASE("esp32 l2tap - time stamping", "[ethernet]")
     ts_info->len = L2TAP_IREC_LEN(1);
     ptp_msg_ext_buff.buff = NULL;
     ptp_msg_ext_buff.buff_len = IN_BUFFER_SIZE;
+    errno = 0;
     n = read(eth_tap_fd, &ptp_msg_ext_buff, 0);
     TEST_ASSERT_EQUAL(-1, n);
     TEST_ASSERT_EQUAL(EFAULT, errno);
@@ -1056,6 +1062,7 @@ TEST_CASE("esp32 l2tap - ioctl - RCV_FILTER", "[ethernet]")
     TEST_ASSERT_NOT_EQUAL(-1, eth_tap_fd);
     ESP_LOGI(TAG, "Verify that RCV_FILTER is allowed to be configured only after interface is set...");
     uint16_t eth_type_filter = ETH_FILTER_LE;
+    errno = 0;
     TEST_ASSERT_EQUAL(-1, ioctl(eth_tap_fd, L2TAP_S_RCV_FILTER, &eth_type_filter));
     TEST_ASSERT_EQUAL(EACCES, errno);
     TEST_ASSERT_EQUAL(0, close(eth_tap_fd));
@@ -1122,6 +1129,7 @@ TEST_CASE("esp32 l2tap - ioctl - RCV_FILTER", "[ethernet]")
     TEST_ASSERT_EQUAL_STRING("ETH_DEF", if_key_str);
 
     ESP_LOGI(TAG, "Verify that the setting the same Ethernet type to other fd at the same interface was unsuccessful...");
+    errno = 0;
     TEST_ASSERT_EQUAL(-1, ioctl(eth_tap_fd_2, L2TAP_S_RCV_FILTER, &eth_type_filter));
     TEST_ASSERT_EQUAL(EINVAL, errno);
     TEST_ASSERT_NOT_EQUAL(-1, ioctl(eth_tap_fd_2, L2TAP_G_RCV_FILTER, &eth_type_filter_get));
@@ -1182,6 +1190,7 @@ TEST_CASE("esp32 l2tap - ioctl - INTF_DEVICE/DEVICE_DRV_HNDL", "[ethernet]")
     TEST_ASSERT_EQUAL_UINT8_ARRAY(&s_test_msg, in_buffer, n);
 
     ESP_LOGI(TAG, "Try to set non-existing Ethernet interface...");
+    errno = 0;
     TEST_ASSERT_EQUAL(-1, ioctl(eth_tap_fd, L2TAP_S_INTF_DEVICE, "ETH_NOT_DEF"));
     TEST_ASSERT_EQUAL(ENODEV, errno);
     ESP_LOGI(TAG, "Verify that previous setting is kept...");
@@ -1302,6 +1311,7 @@ TEST_CASE("esp32 l2tap - fcntl", "[ethernet]")
     int loop_cnt = 0;
     xTaskCreate(send_task, "raw_eth_send_task", 1024, &send_task_ctrl, tskIDLE_PRIORITY + 2, NULL);
     while (loop_cnt < 100) {
+        errno = 0;
         if ((n = read(eth_tap_fd, in_buffer, IN_BUFFER_SIZE)) > 0) {
             TEST_ASSERT_EQUAL_UINT8_ARRAY(&s_test_msg, in_buffer, n);
             break;
@@ -1329,6 +1339,7 @@ TEST_CASE("esp32 l2tap - fcntl", "[ethernet]")
     loop_cnt = 0;
     xTaskCreate(send_task, "raw_eth_send_task", 1024, &send_task_ctrl, tskIDLE_PRIORITY + 2, NULL);
     while (loop_cnt < 100) {
+        errno = 0;
         if ((n = read(eth_tap_fd, in_buffer, IN_BUFFER_SIZE)) > 0) {
             TEST_ASSERT_EQUAL_UINT8_ARRAY(&s_test_msg, in_buffer, n);
             break;
@@ -1343,14 +1354,17 @@ TEST_CASE("esp32 l2tap - fcntl", "[ethernet]")
     TEST_ASSERT_EQUAL(0, loop_cnt);
 
     // Try to use unsupported operation
+    errno = 0;
     flags = fcntl(eth_tap_fd, F_DUPFD, 0);
     TEST_ASSERT_EQUAL(-1, flags);
     TEST_ASSERT_EQUAL(ENOSYS, errno);
 
     // Try to set unsupported flag
+    errno = 0;
     flags = fcntl(eth_tap_fd, F_SETFL, O_TRUNC);
     TEST_ASSERT_EQUAL(-1, flags);
     TEST_ASSERT_EQUAL(EINVAL, errno);
+    errno = 0;
     flags = fcntl(eth_tap_fd, F_SETFL, O_TRUNC | O_NONBLOCK);
     TEST_ASSERT_EQUAL(-1, flags);
     TEST_ASSERT_EQUAL(EINVAL, errno);