From 642dc19c2554e376fad1bdfaff8fda5adb791688 Mon Sep 17 00:00:00 2001
From: Roland Dobai <roland@espressif.com>
Date: Tue, 14 Jan 2020 13:48:36 +0100
Subject: [PATCH] VFS: Check in select() if the UART driver is installed or not

Closes https://github.com/espressif/esp-idf/issues/4627
---
 components/driver/include/driver/uart.h | 11 +++++++++++
 components/driver/uart.c                |  5 +++++
 components/vfs/vfs_uart.c               |  8 ++++++++
 3 files changed, 24 insertions(+)

diff --git a/components/driver/include/driver/uart.h b/components/driver/include/driver/uart.h
index 4bf855c186..5b5ffce2e4 100644
--- a/components/driver/include/driver/uart.h
+++ b/components/driver/include/driver/uart.h
@@ -155,6 +155,17 @@ typedef struct {
 
 typedef intr_handle_t uart_isr_handle_t;
 
+/**
+ * @brief Checks whether the driver is installed or not
+ *
+ * @param uart_num UART port number, the max port number is (UART_NUM_MAX -1).
+ *
+ * @return
+ *     - true  driver is installed
+ *     - false driver is not installed
+ */
+bool uart_is_driver_installed(uart_port_t uart_num);
+
 /**
  * @brief Set UART data bits.
  *
diff --git a/components/driver/uart.c b/components/driver/uart.c
index dba3c585d7..8186214702 100644
--- a/components/driver/uart.c
+++ b/components/driver/uart.c
@@ -1485,6 +1485,11 @@ esp_err_t uart_driver_delete(uart_port_t uart_num)
     return ESP_OK;
 }
 
+bool uart_is_driver_installed(uart_port_t uart_num)
+{
+    return uart_num < UART_NUM_MAX && (p_uart_obj[uart_num] != NULL);
+}
+
 void uart_set_select_notif_callback(uart_port_t uart_num, uart_select_notif_callback_t uart_select_notif_callback)
 {
     if (uart_num < UART_NUM_MAX && p_uart_obj[uart_num]) {
diff --git a/components/vfs/vfs_uart.c b/components/vfs/vfs_uart.c
index c413cbfb00..20cd17db77 100644
--- a/components/vfs/vfs_uart.c
+++ b/components/vfs/vfs_uart.c
@@ -420,6 +420,14 @@ static esp_err_t uart_start_select(int nfds, fd_set *readfds, fd_set *writefds,
     const int max_fds = MIN(nfds, UART_NUM);
     *end_select_args = NULL;
 
+    for (int i = 0; i < max_fds; ++i) {
+        if (FD_ISSET(i, readfds) || FD_ISSET(i, writefds) || FD_ISSET(i, exceptfds)) {
+            if (!uart_is_driver_installed(i)) {
+                return ESP_ERR_INVALID_STATE;
+            }
+        }
+    }
+
     uart_select_args_t *args = malloc(sizeof(uart_select_args_t));
 
     if (args == NULL) {