Add support for running VM as temporary snapshot

Managers/UTMQemuSystem.h

@@ -24,6 +24,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic) NSURL *imgPath;
 @property (nonatomic, nullable) NSString *snapshot;
 @property (nonatomic) NSInteger qmpPort;
+@property (nonatomic) BOOL runAsSnapshot;
 
 - (instancetype)init NS_UNAVAILABLE;
 - (instancetype)initWithConfiguration:(UTMQemuConfiguration *)configuration imgPath:(NSURL *)imgPath;

Managers/UTMQemuSystem.m

@@ -735,6 +735,10 @@ - (void)argsFromConfiguration {
         [self pushArgv:@"-device"];
         [self pushArgv:@"virtio-rng-pci"];
     }
+
+    if (self.runAsSnapshot) {
+        [self pushArgv:@"-snapshot"];
+    }
 }
 
 - (void)argsFromUser {

Managers/UTMQemuVirtualMachine.m

@@ -300,6 +300,15 @@ - (void)_vmStartWithCompletion:(void (^)(NSError * _Nullable))completion {
         }
     }
 
+    if (self.isRunningAsSnapshot) {
+        self.system.runAsSnapshot = self.isRunningAsSnapshot;
+    } else {
+        // Loading save states isn't possible when -snapshot is used
+        if (self.viewState.hasSaveState) {
+            self.system.snapshot = kSuspendSnapshotName;
+        }
+    }
+
     if (!_ioService) {
         _ioService = [self inputOutputService];
     }
@@ -309,9 +318,6 @@ - (void)_vmStartWithCompletion:(void (^)(NSError * _Nullable))completion {
         completion(spiceError);
         return;
     }
-    if (self.viewState.hasSaveState) {
-        self.system.snapshot = kSuspendSnapshotName;
-    }
     // start QEMU (this can be in parallel with QMP connect below)
     __weak typeof(self) weakSelf = self;
     __block NSError *qemuStartError = nil;

Managers/UTMVirtualMachine.h

@@ -76,6 +76,14 @@ NS_ASSUME_NONNULL_BEGIN
 /// This property is observable and must only be accessed on the main thread.
 @property (nonatomic, readonly) BOOL isBusy;
 
+/// Whether the next start of this VM should have the -snapshot flag set
+///
+/// This will be passed to UTMQemuSystem,
+/// and will be cleared when the VM stops or has an error.
+///
+/// This property is observable and must only be accessed on the main thread.
+@property (nonatomic) BOOL isRunningAsSnapshot;
+
 /// Checks if a save state exists
 ///
 /// This property is observable and must only be accessed on the main thread.

Managers/UTMVirtualMachine.m

@@ -101,6 +101,11 @@ - (BOOL)isBusy {
     return (_state == kVMPausing || _state == kVMResuming || _state == kVMStarting || _state == kVMStopping);
 }
 
+- (void)setIsRunningAsSnapshot:(BOOL)isNextRunAsSnapshot {
+    [self propertyWillChange];
+    _isRunningAsSnapshot = isNextRunAsSnapshot;
+}
+
 - (NSString *)stateLabel {
     switch (_state) {
         case kVMStopped:
@@ -274,6 +279,9 @@ - (void)changeState:(UTMVMState)state {
     if (state == kVMStarted) {
         [self startScreenshotTimer];
     }
+    if (state == kVMStopped) {
+        [self setIsRunningAsSnapshot:NO];
+    }
 }
 
 - (NSURL *)packageURLForName:(NSString *)name {

Platform/Shared/VMContextMenuModifier.swift

@@ -48,11 +48,22 @@ struct VMContextMenuModifier: ViewModifier {
                     Label("Stop", systemImage: "stop.fill")
                 }.help("Stop the running VM.")
             } else {
+                Divider()
+
                 Button {
                     data.run(vm: vm)
                 } label: {
                     Label("Run", systemImage: "play.fill")
                 }.help("Run the VM in the foreground.")
+
+                Button {
+                    vm.isRunningAsSnapshot = true
+                    data.run(vm: vm)
+                } label: {
+                    Label("Run without saving changes", systemImage: "play")
+                }.help("Run the VM in the foreground, without saving data changes to disk.")
+
+                Divider()
             }
             Button {
                 shareItem = .utmCopy(vm)

Platform/iOS/Display/VMToolbarActions.swift

@@ -89,6 +89,13 @@ import SwiftUI
         }
     }
 
+    var isRunningAsSnapshot: Bool {
+        guard let viewController = viewController else {
+            return false
+        }
+        return viewController.vm.isRunningAsSnapshot
+    }
+
     private func optionalObjectWillChange() {
         if #available(iOS 14, *) {
             self.objectWillChange.send()

Platform/iOS/Display/VMToolbarView.swift

@@ -90,6 +90,8 @@ struct VMToolbarView: View {
                 } label: {
                     Label(state.isRunning ? "Pause" : "Play", systemImage: state.isRunning ? "pause" : "play")
                 }.offset(offset(for: 6))
+                .disabled(state.isRunningAsSnapshot)
+                .opacity(state.isRunningAsSnapshot ? 0.5 : 1.0)
                 Button {
                     state.restartPressed()
                 } label: {

Platform/macOS/Display/VMDisplayMetalWindowController.swift

@@ -345,7 +345,7 @@ extension VMDisplayMetalWindowController: VMMetalViewInputDelegate {
         syncCapsLock()
         qemuVM.requestInputTablet(true)
         metalView?.releaseMouse()
-        self.window?.subtitle = ""
+        self.window?.subtitle = defaultSubtitle
     }
 
     func mouseMove(absolutePoint: CGPoint, button: CSInputButton) {

Platform/macOS/Display/VMDisplayQemuDisplayController.swift

@@ -23,6 +23,14 @@ class VMDisplayQemuWindowController: VMDisplayWindowController {
         vm?.config as? UTMQemuConfiguration
     }
 
+    var defaultSubtitle: String {
+        if qemuVM.isRunningAsSnapshot {
+            return NSLocalizedString("Disposable Mode", comment: "VMDisplayQemuDisplayController")
+        } else {
+            return ""
+        }
+    }
+
     override func enterLive() {
         qemuVM.ioDelegate = self
         startPauseToolbarItem.isEnabled = true
@@ -32,10 +40,15 @@ class VMDisplayQemuWindowController: VMDisplayWindowController {
             startPauseToolbarItem.isEnabled = false
         }
         #endif
+        if qemuVM.isRunningAsSnapshot {
+            startPauseToolbarItem.isEnabled = false
+            startPauseToolbarItem.toolTip = NSLocalizedString("Disabled when running without saving changes.", comment: "VMDisplayQemuDisplayController")
+        }
         drivesToolbarItem.isEnabled = vmQemuConfig.countDrives > 0
         sharedFolderToolbarItem.isEnabled = qemuVM.hasShareDirectoryEnabled
         usbToolbarItem.isEnabled = qemuVM.hasUsbRedirection
         window!.title = vmQemuConfig.name
+        window!.subtitle = defaultSubtitle
         super.enterLive()
     }
 }