v2

Add tests
Modify syntax to be clearer
Add Query function

Assets/Plugins/UnityGameMode/LinuxGameMode.cs

@@ -0,0 +1,42 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using System.Runtime.InteropServices;
+
+public class LinuxGameMode : MonoBehaviour
+{
+#if UNITY_EDITOR_LINUX || UNITY_STANDALONE_LINUX
+    
+    // Import functions from native lib
+    [DllImport("UnityGameMode")]
+    public static extern int GameModeRequestStart();
+    [DllImport("UnityGameMode")]
+    public static extern int GameModeRequestEnd();
+    [DllImport("UnityGameMode")]
+    public static extern int GameModeQueryStatus();
+    
+    private void Start()
+    {
+        Debug.Log("Requesting Linux GameMode Start");
+        var ret = GameModeRequestStart();
+        if (ret != 0)
+        {
+            Debug.Log($"Linux GameMode Start Failed: #{ret}");
+        }
+    }
+    
+    private void OnApplicationQuit()
+    {
+        Debug.Log("Requesting Linux GameMode End");
+        var ret = GameModeRequestEnd();
+        if (ret != 0)
+        {
+            Debug.Log($"Linux GameMode End failed: #{ret}");
+        }
+    }
+#else
+    public static int GameModeRequestStart() { return 0; }
+    public static int GameModeRequestEnd() { return 0; }
+    public static int GameModeQueryStatus() { return 0; }
+#endif // UNITY_EDITOR_LINUX || UNITY_STANDALONE_LINUX
+}

Assets/Plugins/UnityGameMode/LinuxGameMode.cs.meta

@@ -0,0 +1,11 @@
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Assets/Plugins/UnityGameMode/Tests.meta

@@ -0,0 +1,8 @@
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Assets/Plugins/UnityGameMode/Tests/LinuxGameModeTests.cs

@@ -0,0 +1,42 @@
+using System.Collections;
+using System.Collections.Generic;
+using NUnit.Framework;
+using UnityEngine;
+using UnityEngine.TestTools;
+
+#if UNITY_EDITOR_LINUX || UNITY_STANDALONE_LINUX
+namespace Tests
+{
+    public class LinuxGameModeTests
+    {
+        [Test]
+        public void GameModeRequestStartWorks()
+        {
+            var ret = LinuxGameMode.GameModeRequestStart();
+            Assert.IsTrue( ret == 0 );
+        }
+        
+        [Test]
+        public void GameModeRequestEndWorks()
+        {
+            var ret = LinuxGameMode.GameModeRequestStart();
+            Assert.IsTrue( ret == 0 );
+            ret = LinuxGameMode.GameModeRequestEnd();
+            Assert.IsTrue( ret == 0 );
+        }
+        
+        [Test]
+        public void GameModeGameModeQueryStatusWorks()
+        {
+            var ret = LinuxGameMode.GameModeRequestStart();
+            Assert.IsTrue( ret == 0 );
+
+            ret = LinuxGameMode.GameModeQueryStatus();
+            Assert.IsTrue( ret == 2 );
+            
+            ret = LinuxGameMode.GameModeRequestEnd();
+            Assert.IsTrue( ret == 0 );
+        }
+    }
+}
+#endif

Assets/Plugins/UnityGameMode/Tests/LinuxGameModeTests.cs.meta

@@ -0,0 +1,11 @@
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Assets/Plugins/UnityGameMode/Tests/Tests.asmdef

@@ -0,0 +1,16 @@
+{
+    "name": "Tests",
+    "references": [
+        "UnityGameMode"
+    ],
+    "optionalUnityReferences": [
+        "TestAssemblies"
+    ],
+    "includePlatforms": [],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": false,
+    "precompiledReferences": [],
+    "autoReferenced": true,
+    "defineConstraints": []
+}

Assets/Plugins/UnityGameMode/Tests/Tests.asmdef.meta

@@ -0,0 +1,7 @@
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Assets/Plugins/UnityGameMode/UnityGameMode.asmdef

@@ -0,0 +1,3 @@
+{
+	"name": "UnityGameMode"
+}

Assets/Plugins/UnityGameMode/UnityGameMode.asmdef.meta

@@ -0,0 +1,7 @@
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Assets/Plugins/UnityGameMode/compile.sh

@@ -1,2 +1,3 @@
 #!/bin/bash
 g++ unitygamemode.c -shared -ldl -o libUnityGameMode.so
+nm -C libUnityGameMode.so | grep GameMode

Assets/Plugins/UnityGameMode/compile.sh.meta

@@ -0,0 +1,7 @@
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Assets/Plugins/UnityGameMode/unitygamemode.c

@@ -1,9 +1,13 @@
 #include "gamemode_client.h"
 
-extern "C" int UnityEnterGameMode() {
-	gamemode_request_start();
+extern "C" int GameModeRequestStart() {
+	return gamemode_request_start();
 }
 
-extern "C" int UnityExitGameMode() {
-	gamemode_request_end();
+extern "C" int GameModeRequestEnd() {
+	return gamemode_request_end();
+}
+
+extern "C" int GameModeQueryStatus() {
+	return gamemode_query_status();
 }