base: add 'Session_object' class

The 'Session_object' unifies several aspects of server-component
implementations:

* It keeps track of session quotas and is equipped with standardized
  interfaces (Quota_guard) to upgrade (and in the future potentially
  downgrade) session quotas in a uniform way.

* It follows the pattern of modern RPC objects / signal handlers that
  manage/dissolve themselves at the entrypoint given as constructor
  argument. Thereby, the relationship with its entrypoint is always
  coupled with the lifetime of the session-component object.

* It stores the session label, which was previously done manually by
  most but not all server-component implementations.

* It stores the session 'diag' flag.

* It is equipped with output methods 'diag', 'error', and 'warning'.
  All messages printed from the context of a session component is
  automatically prefixed with the session type and client label.
  Messages passed via 'diag' are only printed if the 'diag' flag of
  the session is set.

Issue #2398

repos/base/include/base/session_object.h

@@ -0,0 +1,120 @@
+/*
+ * \brief  RPC object that owns client-provided RAM and capability quotas
+ * \author Norman Feske
+ * \date   2017-04-28
+ */
+
+/*
+ * Copyright (C) 2017 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _INCLUDE__BASE__SESSION_OBJECT_H_
+#define _INCLUDE__BASE__SESSION_OBJECT_H_
+
+#include <util/arg_string.h>
+#include <base/entrypoint.h>
+#include <session/session.h>
+
+namespace Genode { template <typename, typename> struct Session_object; }
+
+template <typename RPC_INTERFACE, typename SERVER = RPC_INTERFACE>
+class Genode::Session_object : public Ram_quota_guard,
+                               public Cap_quota_guard,
+                               public Rpc_object<RPC_INTERFACE, SERVER>
+{
+	public:
+
+		typedef Session::Label     Label;
+		typedef Session::Diag      Diag;
+		typedef Session::Resources Resources;
+
+	private:
+
+		Rpc_entrypoint &_ep;
+
+		Diag _diag;
+
+	protected:
+
+		Label const _label;
+
+	public:
+
+		/**
+		 * Constructor
+		 */
+		Session_object(Entrypoint &ep, Resources const &resources,
+		               Label const &label, Diag diag)
+		:
+			Session_object(ep.rpc_ep(), resources, label, diag)
+		{ }
+
+		/**
+		 * Constructor
+		 *
+		 * \deprecated This constructor exists for backward compatibility only
+		 *             and will eventually be removed.
+		 */
+		Session_object(Rpc_entrypoint &ep, Resources const &resources,
+		               Label const &label, Diag diag)
+		:
+			Ram_quota_guard(resources.ram_quota),
+			Cap_quota_guard(resources.cap_quota),
+			_ep(ep), _diag(diag), _label(label)
+		{
+			Cap_quota_guard::withdraw(Cap_quota{1});
+			_ep.manage(this);
+		}
+
+		~Session_object()
+		{
+			_ep.dissolve(this);
+			Cap_quota_guard::replenish(Cap_quota{1});
+		}
+
+		/**
+		 * Hook called whenever the session quota was upgraded by the client
+		 */
+		virtual void session_quota_upgraded() { }
+
+		/**
+		 * Return client-specific session label
+		 */
+		Label label() const { return _label; }
+
+		/**
+		 * Output label-prefixed diagnostic message conditionally
+		 *
+		 * The method produces output only if the session is in diagnostic
+		 * mode (defined via the 'diag' session argument).
+		 */
+		template <typename... ARGS>
+		void diag(ARGS &&... args)
+		{
+			if (_diag.enabled)
+				log(RPC_INTERFACE::service_name(), " (", _label, ") ", args...);
+		}
+
+		/**
+		 * Output label-prefixed error message
+		 */
+		template <typename... ARGS>
+		void error(ARGS &&... args)
+		{
+			Genode::error(RPC_INTERFACE::service_name(), " (", _label, ") ", args...);
+		}
+
+		/**
+		 * Output label-prefixed error message
+		 */
+		template <typename... ARGS>
+		void warning(ARGS &&... args)
+		{
+			Genode::warning(RPC_INTERFACE::service_name(), " (", _label, ") ", args...);
+		}
+};
+
+#endif /* _INCLUDE__BASE__SESSION_OBJECT_H_ */