vfs: support watch handlers on application signal level

Fixes #4092

repos/gems/src/app/menu_view/main.cc

@@ -103,8 +103,8 @@ struct Menu_view::Main
 	Directory _fonts_dir  { _root_dir, "fonts" };
 	Directory _styles_dir { _root_dir, "styles" };
 
-	Style_database _styles { _env.ram(), _env.rm(), _heap, _fonts_dir, _styles_dir,
+	Style_database _styles { _env.ep(), _env.ram(), _env.rm(), _heap,
-	                         _dialog_update_handler };
+	                         _fonts_dir, _styles_dir, _dialog_update_handler };
 
 	Animator _animator { };
 

repos/gems/src/app/menu_view/style_database.h

@@ -148,19 +148,21 @@ class Menu_view::Style_database
 			 *
 			 * \throw Reading_failed
 			 */
-			Font_entry(Directory const &fonts_dir, Path const &path, Allocator &alloc,
+			Font_entry(Entrypoint &ep, Directory const &fonts_dir,
+			           Path const &path, Allocator &alloc,
 			           Style_database const &style_database)
 			try :
 				path(path),
 				_style_database(style_database),
 				_vfs_font(alloc, fonts_dir, path),
 				_cached_font(alloc, _vfs_font, _font_cache_limit),
-				_glyphs_changed_handler(fonts_dir, Path(path, "/glyphs"),
+				_glyphs_changed_handler(ep, fonts_dir, Path(path, "/glyphs"),
 				                        *this, &Font_entry::_handle_glyphs_changed)
 			{ }
 			catch (...) { throw Reading_failed(); }
 		};
 
+		Entrypoint      &_ep;
 		Ram_allocator   &_ram;
 		Region_map      &_rm;
 		Allocator       &_alloc;
@@ -228,11 +230,12 @@ class Menu_view::Style_database
 
 	public:
 
-		Style_database(Ram_allocator &ram, Region_map &rm, Allocator &alloc,
+		Style_database(Entrypoint &ep, Ram_allocator &ram, Region_map &rm,
+		               Allocator &alloc,
 		               Directory const &fonts_dir, Directory const &styles_dir,
 		               Signal_context_capability style_changed_sigh)
 		:
-			_ram(ram), _rm(rm), _alloc(alloc),
+			_ep(ep), _ram(ram), _rm(rm), _alloc(alloc),
 			_fonts_dir(fonts_dir), _styles_dir(styles_dir),
 			_style_changed_sigh(style_changed_sigh)
 		{ }
@@ -273,7 +276,7 @@ class Menu_view::Style_database
 			 */
 			try {
 				Font_entry *e = new (_alloc)
-					Font_entry(_fonts_dir, path, _alloc, *this);
+					Font_entry(_ep, _fonts_dir, path, _alloc, *this);
 
 				_fonts.insert(e);
 				return &e->font();

repos/gems/src/app/text_area/main.cc

@@ -136,7 +136,8 @@ struct Text_area::Main : Text_area_widget::Action
 
 	void _watch(bool enabled)
 	{
-		_watch_handler.conditional(enabled, _vfs, _path(), *this, &Main::_handle_watch);
+		_watch_handler.conditional(enabled, _env.ep(), _vfs, _path(), *this,
+		                           &Main::_handle_watch);
 	}
 
 	bool _editable() const { return !_watch_handler.constructed(); }

repos/gems/src/lib/vfs/trace/vfs.cc

@@ -279,12 +279,12 @@ class Vfs_trace::Subject : private Subject_factory,
 
 		typedef String<200> Config;
 
-		Watch_handler<Subject> _enable_handler {
+		Io::Watch_handler<Subject> _enable_handler {
 		  _enabled_fs, "/enable",
 		  Subject_factory::_env.alloc(),
 		  *this, &Subject::_enable_subject };
 
-		Watch_handler<Subject> _buffer_size_handler {
+		Io::Watch_handler<Subject> _buffer_size_handler {
 		  _buffer_size_fs, "/buffer_size",
 		  Subject_factory::_env.alloc(),
 		  *this, &Subject::_buffer_size };

repos/gems/src/server/terminal/main.cc

@@ -80,8 +80,15 @@ struct Terminal::Main : Character_consumer
 			_config_handler.local_submit();
 	}
 
-	Watch_handler<Main> _glyphs_changed_handler {
+	/*
-		_root_dir, "fonts/monospace/regular/glyphs", *this, &Main::_handle_glyphs_changed };
+	 * XXX Currently an I/O-level watch handler is used
+	 *     to prevent a config/watch handler cycle as
+	 *     side-effect of '_root_dir.apply_config()' with
+	 *     an application-level watch handler.
+	 */
+	Io::Watch_handler<Main> _glyphs_changed_handler {
+		_root_dir, "fonts/monospace/regular/glyphs", *this,
+		&Main::_handle_glyphs_changed };
 
 	Color_palette _color_palette { };
 

repos/libports/src/lib/libc/internal/kernel.h

@@ -202,12 +202,12 @@ struct Libc::Kernel final : Vfs::Read_ready_response_handler,
 		Constructible<Rtc> _rtc { };
 
 		/* handler for watching the stdout's info pseudo file */
-		Constructible<Watch_handler<Kernel>> _terminal_resize_handler { };
+		Constructible<Io::Watch_handler<Kernel>> _terminal_resize_handler { };
 
 		void _handle_terminal_resize();
 
 		/* handler for watching user interrupts (control-c) */
-		Constructible<Watch_handler<Kernel>> _user_interrupt_handler { };
+		Constructible<Io::Watch_handler<Kernel>> _user_interrupt_handler { };
 
 		void _handle_user_interrupt();
 

repos/libports/src/lib/vfs/oss/vfs_oss.cc

@@ -813,55 +813,55 @@ struct Vfs::Oss_file_system::Local_factory : File_system_factory
 
 	Audio _audio { _env.env(), _info, _info_fs };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _enable_input_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _enable_input_handler {
 		_enable_input_fs, "/enable_input",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_enable_input_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _enable_output_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _enable_output_handler {
 		_enable_output_fs, "/enable_output",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_enable_output_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _halt_input_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _halt_input_handler {
 		_halt_input_fs, "/halt_input",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_halt_input_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _halt_output_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _halt_output_handler {
 		_halt_output_fs, "/halt_output",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_halt_output_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _ifrag_total_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _ifrag_total_handler {
 		_ifrag_total_fs, "/ifrag_total",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_ifrag_total_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _ifrag_size_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _ifrag_size_handler {
 		_ifrag_size_fs, "/ifrag_size",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_ofrag_size_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _ofrag_total_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _ofrag_total_handler {
 		_ofrag_total_fs, "/ofrag_total",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_ofrag_total_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _ofrag_size_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _ofrag_size_handler {
 		_ofrag_size_fs, "/ofrag_size",
 		_env.alloc(),
 		*this,
 		&Vfs::Oss_file_system::Local_factory::_ofrag_size_changed };
 
-	Genode::Watch_handler<Vfs::Oss_file_system::Local_factory> _play_underruns_handler {
+	Genode::Io::Watch_handler<Vfs::Oss_file_system::Local_factory> _play_underruns_handler {
 		_play_underruns_fs, "/play_underruns",
 		_env.alloc(),
 		*this,

repos/os/include/os/vfs.h

@@ -31,6 +31,10 @@ namespace Genode {
 	class  Append_file;
 	class  New_file;
 	class  Watcher;
+	namespace Io {
+		template <typename>
+		class Watch_handler;
+	}
 	template <typename>
 	class  Watch_handler;
 	template <typename FN>
@@ -954,9 +958,12 @@ class Genode::Watcher
 };
 
 
+/**
+ * Watch handler that operates on I/O signal level
+ */
 template <typename T>
-class Genode::Watch_handler : public Vfs::Watch_response_handler,
+class Genode::Io::Watch_handler : public Vfs::Watch_response_handler,
-                              private Watcher
+                                  private Watcher
 
 {
 	private:
@@ -981,4 +988,39 @@ class Genode::Watch_handler : public Vfs::Watch_response_handler,
 		void watch_response() override { (_obj.*_member)(); }
 };
 
+
+/**
+ * Watch handler that operates on application signal level
+ */
+template <typename T>
+class Genode::Watch_handler : public Signal_handler<Watch_handler<T>>
+{
+	private:
+
+		Io::Watch_handler<Watch_handler> _io_watch_handler;
+
+		T  &_obj;
+		void (T::*_member) ();
+
+		void _handle_watch_response()
+		{
+			Signal_handler<Watch_handler<T>>::local_submit();
+		}
+
+		void _handle_signal()
+		{
+			(_obj.*_member)();
+		}
+
+	public:
+
+		Watch_handler(Genode::Entrypoint &ep, Directory const &dir,
+		              Directory::Path const &rel_path,
+		              T &obj, void (T::*member)())
+		: Signal_handler<Watch_handler<T>>(ep, *this, &Watch_handler<T>::_handle_signal),
+		  _io_watch_handler(dir, rel_path, *this, &Watch_handler<T>::_handle_watch_response),
+		  _obj(obj), _member(member)
+		{ }
+};
+
 #endif /* _INCLUDE__OS__VFS_H_ */

repos/os/src/lib/vfs/tap/vfs_tap.cc

@@ -244,7 +244,7 @@ struct Vfs::Tap_file_system::Local_factory : File_system_factory,
 	 ** Watch handlers **
 	 ********************/
 
-	Genode::Watch_handler<Vfs::Tap_file_system::Local_factory<FS>> _mac_addr_changed_handler {
+	Genode::Io::Watch_handler<Vfs::Tap_file_system::Local_factory<FS>> _mac_addr_changed_handler {
 		_mac_addr_fs, "/mac_addr",
 		_env.alloc(),
 		*this,