From 0998cc370d09e0240732482662459eca22a2a234 Mon Sep 17 00:00:00 2001
From: Kevin Pearson <kevin.pearson@ortmanconsulting.com>
Date: Thu, 1 Oct 2020 10:55:03 -0400
Subject: [PATCH] Add error context to failures to open devices

This should address common misconceptions of "No matching or compatible
device found" by isolating permission problems from lack of a matching
device in the system.
---
 src/classes/Keyboard.cpp |  8 ++++++++
 src/main.cpp             | 12 +++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/classes/Keyboard.cpp b/src/classes/Keyboard.cpp
index b34b74d..74817d5 100644
--- a/src/classes/Keyboard.cpp
+++ b/src/classes/Keyboard.cpp
@@ -20,6 +20,7 @@
 #include <unistd.h>
 #include <vector>
 #include <map>
+#include <cerrno>
 
 #if defined(hidapi)
 	#include <locale>
@@ -200,6 +201,8 @@ bool LedKeyboard::open(uint16_t vendorID, uint16_t productID, string serial) {
 
 		if (! dev) {
 			currentDevice.model = KeyboardModel::unknown;
+			errno = ENODEV;
+
 			hid_exit();
 			return false;
 		}
@@ -209,6 +212,7 @@ bool LedKeyboard::open(uint16_t vendorID, uint16_t productID, string serial) {
 
 		if(m_hidHandle == 0) {
 			hid_exit();
+			errno = EACCES;
 			return false;
 		}
 
@@ -294,6 +298,7 @@ bool LedKeyboard::open(uint16_t vendorID, uint16_t productID, string serial) {
 
 		if (currentDevice.model == KeyboardModel::unknown) {
 			libusb_exit(m_ctx);
+			errno = ENODEV;
 			m_ctx = NULL;
 			return false;
 		}
@@ -303,6 +308,7 @@ bool LedKeyboard::open(uint16_t vendorID, uint16_t productID, string serial) {
 
 		if(m_hidHandle == NULL) {
 			libusb_exit(m_ctx);
+			errno = EACCES;
 			m_ctx = NULL;
 			return false;
 		}
@@ -310,6 +316,7 @@ bool LedKeyboard::open(uint16_t vendorID, uint16_t productID, string serial) {
 		if(libusb_kernel_driver_active(m_hidHandle, 1) == 1) {
 			if(libusb_detach_kernel_driver(m_hidHandle, 1) != 0) {
 				libusb_exit(m_ctx);
+				errno = EACCES;
 				m_ctx = NULL;
 				return false;
 			}
@@ -322,6 +329,7 @@ bool LedKeyboard::open(uint16_t vendorID, uint16_t productID, string serial) {
 				m_isKernellDetached = false;
 			}
 			libusb_exit(m_ctx);
+			errno = EACCES;
 			m_ctx = NULL;
 			return false;
 		}
diff --git a/src/main.cpp b/src/main.cpp
index e867327..2099027 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -323,7 +323,17 @@ int main(int argc, char **argv) {
 
 		//Initialize the device for use
 		if (!kbd.open(vendorID, productID, serial)) {
-			std::cout << "Matching or compatible device not found !" << std::endl;
+			switch (errno)
+			{
+				case ENODEV:
+					std::cout << "Matching or compatible device not found" << std::endl;
+					break;
+				case EACCES:
+					std::cout << "Access denied: Check device access permissions or run as a privileged user (root/sudo)" << std::endl;
+					break;
+				default:
+					std::cout << "Unknown error: errno=" << errno << std::endl;
+			}
 			return 2;
 		}