Implement auto subtree watching of a directory

Allow recursively watching a directory while adding newly created
subdirectories to the inotify watch list.

Sources/Inotify/InotifyWatchManager.swift

@@ -1,18 +1,46 @@
 struct InotifyWatchManager {
 	private var watchPaths: [CInt: String] = [:]
+	private var watchMasks: [CInt: InotifyEventMask] = [:]
 	private var activeWatches: Set<CInt> = []
+	private var watchesWithAutomaticSubtreeWatching: Set<CInt> = []
 
-	mutating func add(_ path: String, withId watchDescriptor: CInt) {
+	mutating func add(_ path: String, withId watchDescriptor: CInt, mask: InotifyEventMask) {
 		self.watchPaths[watchDescriptor] = path
+		self.watchMasks[watchDescriptor] = mask
 		self.activeWatches.insert(watchDescriptor)
 	}
 
+	mutating func enableAutomaticSubtreeWatching(forId watchDescriptor: CInt) {
+		assert(self.activeWatches.contains(watchDescriptor))
+		self.watchesWithAutomaticSubtreeWatching.insert(watchDescriptor)
+	}
+
+	mutating func enableAutomaticSubtreeWatching(forIds watchDescriptors: CInt...) {
+		self.enableAutomaticSubtreeWatching(forIds: watchDescriptors)
+	}
+
+	mutating func enableAutomaticSubtreeWatching(forIds watchDescriptors: [CInt]) {
+		for watchDescriptor in watchDescriptors {
+			self.enableAutomaticSubtreeWatching(forId: watchDescriptor)
+		}
+	}
+
 	mutating func remove(forId watchDescriptor: CInt) {
 		self.watchPaths.removeValue(forKey: watchDescriptor)
+		self.watchMasks.removeValue(forKey: watchDescriptor)
 		self.activeWatches.remove(watchDescriptor)
+		self.watchesWithAutomaticSubtreeWatching.remove(watchDescriptor)
 	}
 
 	func path(forId watchDescriptor: CInt) -> String? {
 		return self.watchPaths[watchDescriptor]
 	}
+
+	func mask(forId watchDescriptor: CInt) -> InotifyEventMask? {
+		return self.watchMasks[watchDescriptor]
+	}
+
+	func isAutomaticSubtreeWatching(_ watchDescriptor: CInt) -> Bool {
+		return self.watchesWithAutomaticSubtreeWatching.contains(watchDescriptor)
+	}
 }