WIP : Run as snapshot for macos "Apple Virtualisation"

Configuration/UTMAppleConfiguration.swift

@@ -275,6 +275,7 @@ final class UTMAppleConfiguration: UTMConfigurable, Codable, ObservableObject {
 
     @Published var isSerialEnabled: Bool
     @Published var isConsoleDisplay: Bool
+    @Published var isRunAsSnapshot: Bool
 
     @available(macOS 12, *)
     var isKeyboardEnabled: Bool {
@@ -337,6 +338,7 @@ final class UTMAppleConfiguration: UTMConfigurable, Codable, ObservableObject {
         case isConsoleDisplay
         case isKeyboardEnabled
         case isPointingEnabled
+        case isRunAsSnapshot
     }
 
     init() {
@@ -357,6 +359,7 @@ final class UTMAppleConfiguration: UTMConfigurable, Codable, ObservableObject {
         isAppleVirtualization = true
         isSerialEnabled = false
         isConsoleDisplay = false
+        isRunAsSnapshot = false
         memorySize = 4 * 1024 * 1024 * 1024
         cpuCount = 4
     }
@@ -398,6 +401,7 @@ final class UTMAppleConfiguration: UTMConfigurable, Codable, ObservableObject {
         isEntropyEnabled = try values.decode(Bool.self, forKey: .isEntropyEnabled)
         isSerialEnabled = try values.decode(Bool.self, forKey: .isSerialEnabled)
         isConsoleDisplay = try values.decode(Bool.self, forKey: .isConsoleDisplay)
+        isRunAsSnapshot = try values.decode(Bool.self, forKey: .isRunAsSnapshot)
         name = try values.decode(String.self, forKey: .name)
         architecture = try values.decode(String.self, forKey: .architecture)
         icon = try values.decodeIfPresent(String.self, forKey: .icon)
@@ -435,6 +439,7 @@ final class UTMAppleConfiguration: UTMConfigurable, Codable, ObservableObject {
         try container.encode(isEntropyEnabled, forKey: .isEntropyEnabled)
         try container.encode(isSerialEnabled, forKey: .isSerialEnabled)
         try container.encode(isConsoleDisplay, forKey: .isConsoleDisplay)
+        try container.encode(isRunAsSnapshot, forKey: .isRunAsSnapshot)
         try container.encode(name, forKey: .name)
         try container.encode(architecture, forKey: .architecture)
         try container.encodeIfPresent(icon, forKey: .icon)
@@ -616,6 +621,29 @@ final class UTMAppleConfiguration: UTMConfigurable, Codable, ObservableObject {
         }
         return urls
     }
+
+    /// Remove the snapshot URL image, this can be done as part of VM cleanup
+    func cleanupDriveSnapshot() throws {
+        for i in diskImages.indices {
+            try diskImages[i].cleanupDriveSnapshot()
+        }
+    }
+
+    /// Perform a snapshot clone of the current image URL to the snapshot URL
+    /// this is required for the snapshotURL image to "work"
+    func setupDriveSnapshot() throws {
+        for i in diskImages.indices {
+            // Apply --snapshot on all volumes if its configured systemwide
+            if self.isRunAsSnapshot {
+                diskImages[i].runAsSnapshot = true
+            }
+
+            // Setup the --snapshot on a per drive level
+            if diskImages[i].runAsSnapshot {
+                try diskImages[i].setupDriveSnapshot()
+            }
+        }
+    }
 }
 
 struct Bootloader: Codable {
@@ -864,13 +892,15 @@ struct DiskImage: Codable, Hashable, Identifiable {
     var sizeMib: Int
     var isReadOnly: Bool
     var isExternal: Bool
+    var runAsSnapshot: Bool
     var imageURL: URL?
     private var uuid = UUID() // for identifiable
 
     private enum CodingKeys: String, CodingKey {
         case sizeMib
         case isReadOnly
         case isExternal
+        case runAsSnapshot
         case imagePath
         case imageBookmark
     }
@@ -891,12 +921,14 @@ struct DiskImage: Codable, Hashable, Identifiable {
         sizeMib = newSize
         isReadOnly = false
         isExternal = false
+        runAsSnapshot = false
     }
 
-    init(importImage url: URL, isReadOnly: Bool = false, isExternal: Bool = false) {
+    init(importImage url: URL, isReadOnly: Bool = false, isExternal: Bool = false, runAsSnapshot: Bool = false) {
         self.imageURL = url
         self.isReadOnly = isReadOnly
         self.isExternal = isExternal
+        self.runAsSnapshot = runAsSnapshot
         if let attributes = try? url.resourceValues(forKeys: [.fileSizeKey]), let fileSize = attributes.fileSize {
             sizeMib = fileSize / bytesInMib
         } else {
@@ -912,6 +944,7 @@ struct DiskImage: Codable, Hashable, Identifiable {
         sizeMib = try container.decode(Int.self, forKey: .sizeMib)
         isReadOnly = try container.decode(Bool.self, forKey: .isReadOnly)
         isExternal = try container.decode(Bool.self, forKey: .isExternal)
+        runAsSnapshot = try container.decode(Bool.self, forKey: .runAsSnapshot)
         if !isExternal, let imagePath = try container.decodeIfPresent(String.self, forKey: .imagePath) {
             imageURL = dataURL.appendingPathComponent(imagePath)
         } else if let bookmark = try container.decodeIfPresent(Data.self, forKey: .imageBookmark) {
@@ -925,6 +958,7 @@ struct DiskImage: Codable, Hashable, Identifiable {
         try container.encode(sizeMib, forKey: .sizeMib)
         try container.encode(isReadOnly, forKey: .isReadOnly)
         try container.encode(isExternal, forKey: .isExternal)
+        try container.encode(runAsSnapshot, forKey: .runAsSnapshot)
         if !isExternal {
             try container.encodeIfPresent(imageURL?.lastPathComponent, forKey: .imagePath)
         } else {
@@ -941,7 +975,43 @@ struct DiskImage: Codable, Hashable, Identifiable {
         }
     }
 
+    /// Returns the snapshot equivalent URL for the current image
+    /// Does not actually prepare the snapshot (this is done via setupDriveSnapshot)
+    func snapshotURL() throws -> URL? {
+        return imageURL?.appendingPathComponent(".snapshot")
+    }
+
+    /// Remove the snapshot URL image, this can be done as part of VM cleanup
+    func cleanupDriveSnapshot() throws {
+        if let snapshotURL = try snapshotURL() {
+            // The file may not exists, if so nothing happens
+            try FileManager.default.removeItem(at: snapshotURL)
+        }
+    }
+
+    /// Perform a snapshot clone of the current image URL to the snapshot URL
+    /// this is required for the snapshotURL image to "work"
+    func setupDriveSnapshot() throws {
+        // Perform any needed cleanup first
+        try cleanupDriveSnapshot()
+
+        // and make a copy of the provided imageURL
+        if let snapshotURL = try snapshotURL(), let imageURL = imageURL {
+            // lets setup the snapshot file 
+            // AFAICT this does a shallow copy on APFS drives
+            try FileManager.default.copyItem(at: imageURL, to: snapshotURL)
+        }
+    }
+
+    /// Return the VZDiskImageStorageDeviceAttachment using the snapshotURL if runAsSnapshot is enabled
+    /// else returns using the imageURL if its configured.
     func vzDiskImage() throws -> VZDiskImageStorageDeviceAttachment? {
+        if runAsSnapshot, let snapshotURL = try snapshotURL() {
+            return try VZDiskImageStorageDeviceAttachment(url: snapshotURL, readOnly: isReadOnly)
+        } else {
+            return nil
+        }
+
         if let imageURL = imageURL {
             return try VZDiskImageStorageDeviceAttachment(url: imageURL, readOnly: isReadOnly)
         } else {

Managers/UTMAppleVirtualMachine.swift

@@ -190,6 +190,12 @@ import Virtualization
                 }
             }
         }
+
+
+        // This perform any cleanup for the "--snapshot" feature, 
+        // if it was initialized previously
+        try appleConfig.cleanupDriveSnapshot()
+
     }
 
     override func vmStop(force: Bool) async throws {
@@ -324,6 +330,10 @@ import Virtualization
                 fsConfig.share = self?.makeDirectoryShare(from: newShares)
             }
         }
+
+        // This perform any reset's needed for the "--snapshot" feature (if its in use)
+        try appleConfig.setupDriveSnapshot()
+
         apple = VZVirtualMachine(configuration: appleConfig.apple, queue: vmQueue)
         apple.delegate = self
     }

Platform/macOS/VMConfigAppleDriveDetailsView.swift

@@ -25,6 +25,7 @@ struct VMConfigAppleDriveDetailsView: View {
             TextField("Name", text: .constant(diskImage.imageURL?.lastPathComponent ?? NSLocalizedString("(New Drive)", comment: "VMConfigAppleDriveDetailsView")))
                 .disabled(true)
             Toggle("Read Only?", isOn: $diskImage.isReadOnly)
+            Toggle("Run using a snapshot? (similar to qemu --snapshot)", isOn: $diskImage.runAsSnapshot)
             Button(action: onDelete) {
                 Label("Delete Drive", systemImage: "externaldrive.badge.minus")
                     .foregroundColor(.red)

Platform/macOS/VMConfigAppleSystemView.swift

@@ -75,6 +75,9 @@ struct VMConfigAppleSystemView: View {
                         Toggle("Enable Keyboard", isOn: $config.isKeyboardEnabled)
                         Toggle("Enable Pointer", isOn: $config.isPointingEnabled)
                     }
+
+                    // System wide --snapshot toggle, if enabled this would be set as "true" on all drives
+                    Toggle("Enable 'Run using a snapshot' on all drives", isOn: $config.isRunAsSnapshot)
                 }
             }
         }