vfs: watch support for <rom> file system

Fixes #3606

repos/os/src/lib/vfs/rom_file_system.h

@@ -15,6 +15,7 @@
 #define _INCLUDE__VFS__ROM_FILE_SYSTEM_H_
 
 #include <base/attached_rom_dataspace.h>
+#include <base/registry.h>
 #include <vfs/file_system.h>
 
 namespace Vfs { class Rom_file_system; }
@@ -26,13 +27,33 @@ class Vfs::Rom_file_system : public Single_file_system
 
 		enum Rom_type { ROM_TEXT, ROM_BINARY };
 
+		Genode::Env &_env;
+
 		typedef String<64> Label;
 
 		Label const _label;
 
 		bool const _binary;
 
-		Genode::Attached_rom_dataspace _rom;
+		Genode::Attached_rom_dataspace _rom { _env, _label.string() };
+
+		file_size _init_content_size()
+		{
+			if (!_binary)
+				for (file_size pos = 0; pos < _rom.size(); pos++) 
+					if (_rom.local_addr<char>()[pos] == 0x00)
+						return pos;
+
+			return _rom.size();
+		}
+
+		file_size _content_size = _init_content_size();
+
+		void _update()
+		{
+			_rom.update();
+			_content_size = _init_content_size();
+		}
 
 		class Rom_vfs_handle : public Single_vfs_handle
 		{
@@ -40,18 +61,7 @@ class Vfs::Rom_file_system : public Single_file_system
 
 				Genode::Attached_rom_dataspace &_rom;
 
-				file_size const _content_size;
-
-				file_size _init_content_size(Rom_type type)
-				{
-					if (type == ROM_TEXT) {
-						for (file_size pos = 0; pos < _rom.size(); pos++) 
-							if (_rom.local_addr<char>()[pos] == 0x00)
-								return pos;
-					}
-
-					return _rom.size();
-				}
+				file_size const &_content_size;
 
 			public:
 
@@ -59,10 +69,10 @@ class Vfs::Rom_file_system : public Single_file_system
 				               File_io_service                &fs,
 				               Genode::Allocator              &alloc,
 				               Genode::Attached_rom_dataspace &rom,
-				               Rom_type                        type)
+				               file_size                const &content_size)
 				:
 					Single_vfs_handle(ds, fs, alloc, 0),
-					_rom(rom), _content_size(_init_content_size(type))
+					_rom(rom), _content_size(content_size)
 				{ }
 
 				Read_result read(char *dst, file_size count,
@@ -105,6 +115,20 @@ class Vfs::Rom_file_system : public Single_file_system
 				bool read_ready() override { return true; }
 		};
 
+		typedef Genode::Registered<Vfs_watch_handle>      Registered_watch_handle;
+		typedef Genode::Registry<Registered_watch_handle> Watch_handle_registry;
+
+		Watch_handle_registry _handle_registry { };
+
+		void _handle_rom_changed()
+		{
+			_handle_registry.for_each([this] (Registered_watch_handle &handle) {
+				handle.watch_response(); });
+		}
+
+		Genode::Constructible<Genode::Io_signal_handler<Rom_file_system>>
+			_rom_changed_handler { };
+
 	public:
 
 		Rom_file_system(Vfs::Env &env,
@@ -112,14 +136,13 @@ class Vfs::Rom_file_system : public Single_file_system
 		:
 			Single_file_system(Node_type::CONTINUOUS_FILE, name(),
 			                   Node_rwx::ro(), config),
+			_env(env.env()),
 
 			/* use 'label' attribute if present, fall back to 'name' if not */
 			_label(config.attribute_value("label",
 			                              config.attribute_value("name", Label()))),
 
-			_binary(config.attribute_value("binary", true)),
-
-			_rom(env.env(), _label.string())
+			_binary(config.attribute_value("binary", true))
 		{ }
 
 		static char const *name()   { return "rom"; }
@@ -136,11 +159,11 @@ class Vfs::Rom_file_system : public Single_file_system
 			if (!_single_file(path))
 				return OPEN_ERR_UNACCESSIBLE;
 
-			_rom.update();
+			_update();
 
 			try {
 				*out_handle = new (alloc)
-					Rom_vfs_handle(*this, *this, alloc, _rom, _binary ? ROM_BINARY : ROM_TEXT);
+					Rom_vfs_handle(*this, *this, alloc, _rom, _content_size);
 				return OPEN_OK;
 			}
 			catch (Genode::Out_of_ram)  { return OPEN_ERR_OUT_OF_RAM; }
@@ -166,8 +189,8 @@ class Vfs::Rom_file_system : public Single_file_system
 			 * version.
 			 */
 			if (out.type == Node_type::CONTINUOUS_FILE) {
-				_rom.update();
-				out.size = _rom.valid() ? _rom.size() : 0;
+				_update();
+				out.size = _content_size;
 				out.rwx  = { .readable   = true,
 				             .writeable  = false,
 				             .executable = true };
@@ -175,6 +198,34 @@ class Vfs::Rom_file_system : public Single_file_system
 
 			return result;
 		}
+
+		Watch_result watch(char const        *path,
+		                   Vfs_watch_handle **handle,
+		                   Allocator         &alloc) override
+		{
+			if (!_single_file(path))
+				return WATCH_ERR_UNACCESSIBLE;
+
+			if (!_rom_changed_handler.constructed()) {
+				_rom_changed_handler.construct(_env.ep(), *this,
+				                               &Rom_file_system::_handle_rom_changed);
+				_rom.sigh(*_rom_changed_handler);
+			}
+
+			try {
+				*handle = new (alloc)
+					Registered_watch_handle(_handle_registry, *this, alloc);
+				return WATCH_OK;
+			}
+			catch (Genode::Out_of_ram)  { return WATCH_ERR_OUT_OF_RAM;  }
+			catch (Genode::Out_of_caps) { return WATCH_ERR_OUT_OF_CAPS; }
+		}
+
+		void close(Vfs_watch_handle *handle) override
+		{
+			Genode::destroy(handle->alloc(),
+			                static_cast<Registered_watch_handle *>(handle));
+		}
 };
 
 #endif /* _INCLUDE__VFS__ROM_FILE_SYSTEM_H_ */