libc: add VFS watch handle accessor

Issue #3450

repos/libports/src/lib/libc/task.cc

@@ -767,6 +767,17 @@ struct Libc::Kernel final : Vfs::Io_response_handler,
 			}
 		}
 
+		/**
+		 * Alloc new watch handler for given path
+		 */
+		Vfs::Vfs_watch_handle *alloc_watch_handle(char const *path)
+		{
+			Vfs::Vfs_watch_handle *watch_handle { nullptr };
+			typedef Vfs::Directory_service::Watch_result Result;
+			return _libc_env.vfs().watch(path, &watch_handle, _heap) == Result::WATCH_OK
+				? watch_handle : nullptr;
+		}
+
 
 		/****************************************
 		 ** Vfs::Io_response_handler interface **
@@ -857,6 +868,12 @@ void Libc::dispatch_pending_io_signals()
 }
 
 
+Vfs::Vfs_watch_handle *Libc::watch(char const *path)
+{
+	return kernel->alloc_watch_handle(path);
+}
+
+
 Genode::Duration Libc::current_time()
 {
 	return kernel->current_time();

repos/libports/src/lib/libc/task.h

@@ -23,6 +23,7 @@
 
 #include <base/duration.h>
 #include <util/xml_node.h>
+#include <vfs/vfs_handle.h>
 
 namespace Libc {
 
@@ -51,6 +52,16 @@ namespace Libc {
 
 	void dispatch_pending_io_signals();
 
+	/**
+	 * Get watch handle for given path
+	 *
+	 * \param path  path that should be be watched
+	 *
+	 * \return      point to the watch handle object or a nullptr
+	 *              when the watch operation failed
+	 */
+	Vfs::Vfs_watch_handle *watch(char const *path);
+
 	/**
 	 * Get time since startup in ms
 	 */