base: add Child_policy::Route::Diag flag

The 'diag' flag can be defined by a target node of a route in init's
configuration. It is propagated as session argument to the server, which
may evaluate the flag to enable diagnostic output for the corresponding
session.

Issue #2398

repos/base/include/base/child.h

@@ -86,7 +86,8 @@ struct Genode::Child_policy
 	struct Route
 	{
 		Service &service;
-		Session_label const label;
+		Session::Label const label;
+		Session::Diag  const diag;
 	};
 
 	/**
@@ -543,7 +544,7 @@ class Genode::Child : protected Rpc_object<Parent>,
 					_env_service.construct(_child, route.service);
 					_connection.construct(*_env_service, _child._id_space, _client_id,
 					                      _args, _child._policy.filter_session_affinity(Affinity()),
-					                      route.label);
+					                      route.label, route.diag);
 				}
 				catch (Parent::Service_denied) {
 					error(_child._policy.name(), ": ", _service_name(), " "

repos/base/include/base/local_connection.h

@@ -39,7 +39,8 @@ struct Genode::Local_connection_base : Noncopyable
 
 	private:
 
-		static Args _init_args(Args const &args, size_t const &ram_quota)
+		static Args _init_args(Args const &args, size_t const &ram_quota,
+		                       Session::Diag diag)
 		{
 			/* copy original arguments into modifiable buffer */
 			char buf[Args::capacity()];
@@ -47,6 +48,7 @@ struct Genode::Local_connection_base : Noncopyable
 
 			Arg_string::set_arg(buf, sizeof(buf), "ram_quota",
 			                    String<64>(ram_quota).string());
+			Arg_string::set_arg(buf, sizeof(buf), "diag", diag.enabled);
 
 			/* return result as a copy  */
 			return Args(Cstring(buf));
@@ -58,13 +60,15 @@ struct Genode::Local_connection_base : Noncopyable
 		                      Id_space<Parent::Client>         &id_space,
 		                      Parent::Client::Id                id,
 		                      Args const &args, Affinity const &affinity,
-		                      Session_label              const &label,
+		                      Session::Label             const &label,
+		                      Session::Diag                     diag,
 		                      size_t                            ram_quota)
 		{
 			enum { NUM_ATTEMPTS = 10 };
 			for (unsigned i = 0; i < NUM_ATTEMPTS; i++) {
 				_session_state.construct(service, id_space, id, label,
-				                         _init_args(args, ram_quota), affinity);
+				                         _init_args(args, ram_quota, diag),
+				                         affinity);
 
 				_session_state->service().initiate_request(*_session_state);
 
@@ -143,10 +147,12 @@ class Genode::Local_connection : Local_connection_base
 		Local_connection(Service &service, Id_space<Parent::Client> &id_space,
 		                 Parent::Client::Id id, Args const &args,
 		                 Affinity const &affinity,
-		                 Session_label const &label = Session_label())
+		                 Session::Label const &label = Session_label(),
+		                 Session::Diag diag = { false })
 		:
 			Local_connection_base(service, id_space, id, args, affinity,
 			                      label.valid() ? label : label_from_args(args.string()),
+			                      diag,
 			                      CONNECTION::RAM_QUOTA)
 		{
 			service.wakeup();

repos/base/src/lib/base/child.cc

@@ -138,8 +138,8 @@ Child_policy::Route Child::_resolve_session_request(Child_policy &policy,
 	try {
 
 		Session_state::Args args(argbuf);
-		return Child_policy::Route {
+		return { policy.resolve_session_request(name, args), label,
-			policy.resolve_session_request(name, args), label };
+		         session_diag_from_args(argbuf) };
 	}
 	catch (Parent::Service_denied) { }
 
@@ -187,6 +187,9 @@ Session_capability Child::session(Parent::Client::Id id,
 	Child_policy::Route route = _resolve_session_request(_policy, name.string(), argbuf);
 	Service &service = route.service;
 
+	/* propagate diag flag */
+	Arg_string::set_arg(argbuf, sizeof(argbuf), "diag", route.diag.enabled);
+
 	Session_state &session =
 		create_session(_policy.name(), service, route.label,
 		               _session_factory, _id_space, id, argbuf, filtered_affinity);

repos/os/src/init/child.cc

@@ -441,12 +441,15 @@ Init::Child::Route Init::Child::resolve_session_request(Service::Name const &ser
 				Label const target_label =
 					target.attribute_value("label", Label(label.string()));
 
+				Session::Diag const
+					target_diag { target.attribute_value("diag", false) };
+
 				if (target.has_type("parent")) {
 
 					Parent_service *service = nullptr;
 
 					if ((service = find_service(_parent_services, service_name)))
-						return Route { *service, target_label };
+						return Route { *service, target_label, target_diag };
 
 					if (service && service->abandoned())
 						throw Parent::Service_denied();
@@ -475,7 +478,7 @@ Init::Child::Route Init::Child::resolve_session_request(Service::Name const &ser
 						throw Parent::Service_denied();
 
 					if (service)
-						return Route { *service, target_label };
+						return Route { *service, target_label, target_diag };
 
 					if (!service_wildcard) {
 						warning(name(), ": lookup to child "
@@ -495,7 +498,7 @@ Init::Child::Route Init::Child::resolve_session_request(Service::Name const &ser
 					Routed_service *service = nullptr;
 
 					if ((service = find_service(_child_services, service_name)))
-						return Route { *service, target_label };
+						return Route { *service, target_label, target_diag };
 
 					if (!service_wildcard) {
 						warning(name(), ": lookup for service "