base: add Child_policy::session_state_changed()

This method is a hook to enable a runtime to respond to state changes.
In particular, in init this hook is used to trigger the generation of a
new state report, if configured.

Furthermore, the patch introduces the 'generate_client_side_info' and
'generate_server_side_info' methods to the 'Session_state', which
generates an XML representation of the session states to appear in
reports produced by init.

Issue #2246

repos/base/include/base/child.h

@@ -187,6 +187,11 @@ struct Genode::Child_policy
 	 */
 	virtual Id_space<Parent::Server> &server_id_space() { throw Nonexistent_id_space(); }
 
+	/**
+	 * Notification hook invoked each time a session state is modified
+	 */
+	virtual void session_state_changed() { }
+
 	/**
 	 * Return region map for the child's address space
 	 *
@@ -562,6 +567,12 @@ class Genode::Child : protected Rpc_object<Parent>,
 			     2*Rom_connection::RAM_QUOTA;
 		}
 
+		template <typename FN>
+		void for_each_session(FN const &fn) const
+		{
+			_id_space.for_each<Session_state const>(fn);
+		}
+
 		/**
 		 * Deduce session costs from usable ram quota
 		 */

repos/base/include/base/session_state.h

@@ -167,7 +167,12 @@ class Genode::Session_state : public Parent::Client, public Parent::Server,
 
 		Affinity const &affinity() const { return _affinity; }
 
-		void generate_session_request(Xml_generator &xml) const;
+		void generate_session_request(Xml_generator &) const;
+
+		struct Detail { enum Args { NO_ARGS, ARGS } args; };
+
+		void generate_client_side_info(Xml_generator &, Detail detail) const;
+		void generate_server_side_info(Xml_generator &, Detail detail) const;
 
 		size_t donated_ram_quota() const { return _donated_ram_quota; }
 

repos/base/lib/symbols/ld

@@ -312,6 +312,8 @@ _ZN6Genode8ipc_callENS_17Native_capabilityERNS_11Msgbuf_baseES2_m T
 _ZN6Genode9ipc_replyENS_17Native_capabilityENS_18Rpc_exception_codeERNS_11Msgbuf_baseE T
 _ZNK6Genode11Sliced_heap8overheadEm T
 _ZNK6Genode13Session_state24generate_session_requestERNS_13Xml_generatorE T
+_ZNK6Genode13Session_state25generate_client_side_infoERNS_13Xml_generatorENS0_6DetailE T
+_ZNK6Genode13Session_state25generate_server_side_infoERNS_13Xml_generatorENS0_6DetailE T
 _ZNK6Genode13Session_state5printERNS_6OutputE T
 _ZNK6Genode13Shared_object7_lookupEPKc T
 _ZNK6Genode13Shared_object8link_mapEv T

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

@@ -238,6 +238,8 @@ Session_capability Child::session(Parent::Client::Id id,
 		create_session(_policy.name(), service, route.label, *_session_factory,
 		               _id_space, id, argbuf, filtered_affinity);
 
+	_policy.session_state_changed();
+
 	session.ready_callback = this;
 	session.closed_callback = this;
 
@@ -322,6 +324,7 @@ Session_capability Child::session_cap(Client::Id id)
 	catch (Id_space<Parent::Client>::Unknown_id) {
 		warning(_policy.name(), " requested session cap for unknown ID"); }
 
+	_policy.session_state_changed();
 	return cap;
 }
 
@@ -369,11 +372,13 @@ Parent::Upgrade_result Child::upgrade(Client::Id id, Parent::Upgrade_args const
 
 		if (session.phase == Session_state::CAP_HANDED_OUT) {
 			result = UPGRADE_DONE;
+			_policy.session_state_changed();
 			return;
 		}
 
 		session.service().wakeup();
 	});
+	_policy.session_state_changed();
 	return result;
 }
 
@@ -396,6 +401,7 @@ void Child::_revert_quota_and_destroy(Session_state &session)
 		warning(_policy.name(), ": could not revert session quota (", session, ")"); }
 
 	session.destroy();
+	_policy.session_state_changed();
 }
 
 
@@ -427,6 +433,8 @@ Child::Close_result Child::_close(Session_state &session)
 		return CLOSE_DONE;
 	}
 
+	_policy.session_state_changed();
+
 	session.discard_id_at_client();
 	session.service().wakeup();
 

repos/base/src/lib/base/session_state.cc

@@ -18,12 +18,36 @@
 using namespace Genode;
 
 
+struct Formatted_phase
+{
+	Session_state::Phase _phase;
+
+	Formatted_phase(Session_state::Phase phase) : _phase(phase) { }
+
+	void print(Output &output) const
+	{
+		using Genode::print;
+		typedef Genode::Session_state State;
+
+		switch (_phase) {
+		case State::CREATE_REQUESTED:   print(output, "CREATE_REQUESTED");  break;
+		case State::INVALID_ARGS:       print(output, "INVALID_ARGS");      break;
+		case State::AVAILABLE:          print(output, "AVAILABLE");         break;
+		case State::CAP_HANDED_OUT:     print(output, "CAP_HANDED_OUT");    break;
+		case State::UPGRADE_REQUESTED:  print(output, "UPGRADE_REQUESTED"); break;
+		case State::CLOSE_REQUESTED:    print(output, "CLOSE_REQUESTED");   break;
+		case State::CLOSED:             print(output, "CLOSED");            break;
+		}
+	}
+};
+
+
 void Session_state::print(Output &out) const
 {
 	using Genode::print;
 
 	print(out, "service=", _service.name(), " cid=", _id_at_client, " "
-	      "args='", _args, "' state=", (int)phase, " "
+	      "args='", _args, "' state=", Formatted_phase(phase), " "
 	      "ram_quota=", _donated_ram_quota);
 }
 
@@ -70,6 +94,24 @@ void Session_state::generate_session_request(Xml_generator &xml) const
 }
 
 
+void Session_state::generate_client_side_info(Xml_generator &xml, Detail detail) const
+{
+	xml.attribute("service", _service.name());
+	xml.attribute("label", _label);
+	xml.attribute("state", String<32>(Formatted_phase(phase)));
+	xml.attribute("ram", String<32>(Number_of_bytes(_donated_ram_quota)));
+
+	if (detail.args == Detail::ARGS)
+		xml.node("args", [&] () { xml.append_sanitized(_args.string()); });
+}
+
+
+void Session_state::generate_server_side_info(Xml_generator &xml, Detail detail) const
+{
+	generate_client_side_info(xml, detail);
+}
+
+
 void Session_state::destroy()
 {
 	/*