tart delete: prevent the deletion of running VMs (#676)

And introduce a VMDirectory.lock() method to avoid duplication of
the PIDLock(lockURL: vmDir.configURL) snippet.

Sources/tart/Commands/Run.swift

@@ -224,7 +224,7 @@ struct Run: AsyncParsableCommand {
     // configuration file, otherwise we will loose the lock.
     //
     // [1]: https://man.openbsd.org/fcntl
-    let lock = try PIDLock(lockURL: vmDir.configURL)
+    let lock = try vmDir.lock()
     if try !lock.trylock() {
       throw RuntimeError.VMAlreadyRunning("VM \"\(name)\" is already running!")
     }

Sources/tart/Commands/Stop.swift

@@ -29,12 +29,12 @@ struct Stop: AsyncParsableCommand {
   }
 
   func stopRunning(_ vmDir: VMDirectory) async throws {
-    let lock = try PIDLock(lockURL: vmDir.configURL)
+    let lock = try vmDir.lock()
 
     // Find the VM's PID
     var pid = try lock.pid()
     if pid == 0 {
-      throw RuntimeError.VMNotRunning("VM \"\(name)\" is not running")
+      throw RuntimeError.VMNotRunning(name)
     }
 
     // Try to gracefully terminate the VM

Sources/tart/Commands/Suspend.swift

@@ -11,7 +11,7 @@ struct Suspend: AsyncParsableCommand {
 
   func run() async throws {
     let vmDir = try VMStorageLocal().open(name)
-    let lock = try PIDLock(lockURL: vmDir.configURL)
+    let lock = try vmDir.lock()
 
     // Find the VM's PID
     var pid = try lock.pid()

Sources/tart/VMDirectory.swift

@@ -30,13 +30,17 @@ struct VMDirectory: Prunable {
     baseURL
   }
 
+  func lock() throws -> PIDLock {
+    try PIDLock(lockURL: configURL)
+  }
+
   func running() throws -> Bool {
     // The most common reason why PIDLock() instantiation fails is a race with "tart delete" (ENOENT),
     // which is fine to report as "not running".
     //
     // The other reasons are unlikely and the cost of getting a false positive is way less than
     // the cost of crashing with an exception when calling "tart list" on a busy machine, for example.
-    guard let lock = try? PIDLock(lockURL: configURL) else {
+    guard let lock = try? lock() else {
       return false
     }
 
@@ -137,7 +141,15 @@ struct VMDirectory: Prunable {
   }
 
   func delete() throws {
+    let lock = try lock()
+
+    if try !lock.trylock() {
+      throw RuntimeError.VMIsRunning(name)
+    }
+
     try FileManager.default.removeItem(at: baseURL)
+
+    try lock.unlock()
   }
 
   func accessDate() throws -> Date {

Sources/tart/VMStorageHelper.swift

@@ -50,7 +50,8 @@ enum RuntimeError : Error {
   case VMConfigurationError(_ message: String)
   case VMDoesNotExist(name: String)
   case VMMissingFiles(_ message: String)
-  case VMNotRunning(_ message: String)
+  case VMIsRunning(_ name: String)
+  case VMNotRunning(_ name: String)
   case VMAlreadyRunning(_ message: String)
   case NoIPAddressFound(_ message: String)
   case DiskAlreadyInUse(_ message: String)
@@ -81,8 +82,10 @@ extension RuntimeError : CustomStringConvertible {
       return "the specified VM \"\(name)\" does not exist"
     case .VMMissingFiles(let message):
       return message
-    case .VMNotRunning(let message):
-      return message
+    case .VMIsRunning(let name):
+      return "VM \"\(name)\" is running"
+    case .VMNotRunning(let name):
+      return "VM \"\(name)\" is not running"
     case .VMAlreadyRunning(let message):
       return message
     case .NoIPAddressFound(let message):

Sources/tart/VMStorageLocal.swift

@@ -39,7 +39,7 @@ class VMStorageLocal: PrunableStorage {
   }
 
   func delete(_ name: String) throws {
-    try FileManager.default.removeItem(at: vmURL(name))
+    try VMDirectory(baseURL: vmURL(name)).delete()
   }
 
   func list() throws -> [(String, VMDirectory)] {