KernelModuleDisabler: allow disabling the kernel module backend

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui/src/main/java/com/wireguard/android/Application.java

@@ -75,7 +75,7 @@ public class Application extends android.app.Application implements SharedPrefer
                     } catch (final Exception ignored) {
                     }
                 }
-                if (ModuleLoader.isModuleLoaded()) {
+                if (!app.sharedPreferences.getBoolean("disable_kernel_module", false) && ModuleLoader.isModuleLoaded()) {
                     try {
                         if (!didStartRootShell)
                             app.rootShell.start();

ui/src/main/java/com/wireguard/android/activity/SettingsActivity.java

@@ -117,10 +117,12 @@ public class SettingsActivity extends ThemeChangeAwareActivity {
             });
 
             final Preference moduleInstaller = getPreferenceManager().findPreference("module_downloader");
+            final Preference kernelModuleDisabler = getPreferenceManager().findPreference("kernel_module_disabler");
             moduleInstaller.setVisible(false);
             if (ModuleLoader.isModuleLoaded()) {
                 screen.removePreference(moduleInstaller);
             } else {
+                screen.removePreference(kernelModuleDisabler);
                 Application.getAsyncWorker().runAsync(Application.getRootShell()::start).whenComplete((v, e) -> {
                     if (e == null)
                         moduleInstaller.setVisible(true);

ui/src/main/java/com/wireguard/android/preference/KernelModuleDisablerPreference.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright © 2020 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.preference;
+
+import android.content.Context;
+import android.content.Intent;
+import android.util.AttributeSet;
+
+import com.wireguard.android.Application;
+import com.wireguard.android.R;
+import com.wireguard.android.backend.WgQuickBackend;
+import com.wireguard.util.NonNullForAll;
+
+import androidx.preference.Preference;
+
+@NonNullForAll
+public class KernelModuleDisablerPreference extends Preference {
+    private State state;
+
+    public KernelModuleDisablerPreference(final Context context, final AttributeSet attrs) {
+        super(context, attrs);
+        state = Application.getBackend() instanceof WgQuickBackend ? State.ENABLED : State.DISABLED;
+    }
+
+    @Override
+    public CharSequence getSummary() {
+        return getContext().getString(state.summaryResourceId);
+    }
+
+    @Override
+    public CharSequence getTitle() {
+        return getContext().getString(state.titleResourceId);
+    }
+
+    @Override
+    protected void onClick() {
+        if (state == State.DISABLED) {
+            setState(State.ENABLING);
+            Application.getSharedPreferences().edit().putBoolean("disable_kernel_module", false).apply();
+        } else if (state == State.ENABLED) {
+            setState(State.DISABLING);
+            Application.getSharedPreferences().edit().putBoolean("disable_kernel_module", true).apply();
+        }
+        Application.getAsyncWorker().runAsync(() -> {
+            Thread.sleep(1000 * 5);
+            Intent i = getContext().getPackageManager().getLaunchIntentForPackage(getContext().getPackageName());
+            if (i == null)
+                return;
+            i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
+            i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
+            Application.get().startActivity(i);
+            System.exit(0);
+        });
+    }
+
+    private void setState(final State state) {
+        if (this.state == state)
+            return;
+        this.state = state;
+        if (isEnabled() != state.shouldEnableView)
+            setEnabled(state.shouldEnableView);
+        notifyChanged();
+    }
+
+    private enum State {
+        ENABLED(R.string.module_disabler_enabled_title, R.string.module_disabler_enabled_summary, true),
+        DISABLED(R.string.module_disabler_disabled_title, R.string.module_disabler_disabled_summary, true),
+        ENABLING(R.string.module_disabler_disabled_title, R.string.module_disabler_working, false),
+        DISABLING(R.string.module_disabler_enabled_title, R.string.module_disabler_working, false);
+
+        private final boolean shouldEnableView;
+        private final int summaryResourceId;
+        private final int titleResourceId;
+
+        State(final int titleResourceId, final int summaryResourceId, final boolean shouldEnableView) {
+            this.summaryResourceId = summaryResourceId;
+            this.titleResourceId = titleResourceId;
+            this.shouldEnableView = shouldEnableView;
+        }
+    }
+}

ui/src/main/res/values/strings.xml

@@ -103,6 +103,11 @@
     <string name="module_installer_title">Download and install kernel module</string>
     <string name="module_installer_working">Downloading and installing…</string>
     <string name="module_installer_error">Something went wrong. Please try again</string>
+    <string name="module_disabler_disabled_title">Enable kernel module backend</string>
+    <string name="module_disabler_disabled_summary">The experimental kernel module can improve performance</string>
+    <string name="module_disabler_enabled_title">Disable kernel module backend</string>
+    <string name="module_disabler_enabled_summary">The slower userspace backend may improve stability</string>
+    <string name="module_disabler_working">The application will restart in 5 seconds</string>
     <string name="mtu">MTU</string>
     <string name="multiple_tunnels_title">Allow multiple simultaneous tunnels</string>
     <string name="multiple_tunnels_summary_on">Multiple tunnels may be turned on simultaneously</string>

ui/src/main/res/xml/preferences.xml

@@ -23,4 +23,5 @@
         android:summaryOff="@string/dark_theme_summary_off"
         android:summaryOn="@string/dark_theme_summary_on"
         android:title="@string/dark_theme_title" />
+    <com.wireguard.android.preference.KernelModuleDisablerPreference android:key="kernel_module_disabler" />
 </androidx.preference.PreferenceScreen>