os: add black hole component

The 'black_hole' component provides dummy implementations of common
session interfaces.

At this time, only the 'Audio_out' session is provided if enabled
in the configuration of the component:

<config>
	<audio_out/>
</config>

Issue #3653

repos/os/recipes/pkg/black_hole/README

@@ -0,0 +1,2 @@
+
+   Runtime for deploying the black hole component from the depot

repos/os/recipes/pkg/black_hole/archives

@@ -0,0 +1 @@
+_/src/black_hole

repos/os/recipes/pkg/black_hole/hash

@@ -0,0 +1 @@
+2021-08-24 3200fb247859dffd0825d7ed21be65932cc6c752

repos/os/recipes/pkg/black_hole/runtime

@@ -0,0 +1,16 @@
+<runtime ram="8M" caps="100" binary="black_hole">
+
+	<provides>
+		<audio_out/>
+	</provides>
+
+	<config>
+		<audio_out/>
+	</config>
+
+	<content>
+		<rom label="ld.lib.so"/>
+		<rom label="black_hole"/>
+	</content>
+
+</runtime>

repos/os/recipes/src/black_hole/content.mk

@@ -0,0 +1,2 @@
+SRC_DIR = src/server/black_hole
+include $(GENODE_DIR)/repos/base/recipes/src/content.inc

repos/os/recipes/src/black_hole/hash

@@ -0,0 +1 @@
+2021-08-24 0dd5287293a6c95313cd5f82c56a14e174e8bf35

repos/os/recipes/src/black_hole/used_apis

@@ -0,0 +1,2 @@
+base
+audio_out_session

repos/os/src/server/black_hole/README

@@ -0,0 +1,9 @@
+The 'black_hole' component provides dummy implementations of common
+session interfaces.
+
+At this time, only the 'Audio_out' session is provided if enabled
+in the configuration of the component:
+
+<config>
+	<audio_out/>
+</config>

repos/os/src/server/black_hole/audio_out.h

@@ -0,0 +1,162 @@
+/*
+ * \brief  'Audio_out' part of black hole component
+ * \author Christian Prochaska
+ * \date   2021-07-07
+ *
+ */
+
+/*
+ * Copyright (C) 2021 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 _AUDIO_OUT_H_
+#define _AUDIO_OUT_H_
+
+/* Genode includes */
+#include <audio_out_session/rpc_object.h>
+#include <timer_session/connection.h>
+
+
+namespace Audio_out
+{
+	class Session_component_base;
+	class Session_component;
+	class Root;
+}
+
+
+/**
+ * This base struct is needed to get the 'Signal_handler' constructed
+ * before the 'Session_rpc_object' constructor is called with the handler
+ * as argument.
+ */
+
+struct Audio_out::Session_component_base
+{
+	Genode::Signal_handler<Session_component_base>  _data_available_handler;
+	Timer::One_shot_timeout<Session_component_base> _timeout;
+
+	virtual void _handle_data_available() = 0;
+	virtual void _handle_timeout(Genode::Duration) = 0;
+
+	Session_component_base(Genode::Env &env, Timer::Connection &timer)
+	: _data_available_handler(env.ep(),
+		                      *this,
+		                      &Session_component_base::_handle_data_available),
+	  _timeout(timer, *this, &Session_component_base::_handle_timeout)
+	{ }
+
+	virtual ~Session_component_base() { }
+};
+
+
+class Audio_out::Session_component : Audio_out::Session_component_base,
+                                     public Audio_out::Session_rpc_object
+{
+	private:
+
+		/* subtract 200ms for overhead */
+		Genode::Microseconds _delay {
+			((Audio_out::PERIOD * 1000 * 1000) / Audio_out::SAMPLE_RATE) - 200 };
+
+		void _handle_data_available() override
+		{
+			_timeout.schedule(_delay);
+		}
+
+		void _handle_timeout(Genode::Duration) override
+		{
+			if (stream()->empty())
+				return;
+
+			bool const full = stream()->full();
+
+			Packet *p = stream()->get(stream()->pos());
+			p->invalidate();
+			p->mark_as_played();
+			stream()->increment_position();
+			progress_submit();
+
+			if (full) alloc_submit();
+
+			if (!stream()->empty())
+				_timeout.schedule(_delay);
+		}
+
+	public:
+
+		Session_component(Genode::Env &env, Timer::Connection &timer)
+		: Session_component_base(env, timer),
+		  Session_rpc_object(env, _data_available_handler)
+		{ }
+
+		~Session_component()
+		{
+			if (Session_rpc_object::active()) stop();
+		}
+
+		void start() override
+		{
+			Session_rpc_object::start();
+			stream()->pos(0);
+		}
+
+		void stop() override
+		{
+			Session_rpc_object::stop();
+		}
+};
+
+
+namespace Audio_out {
+	typedef Genode::Root_component<Session_component, Genode::Multiple_clients> Root_component;
+}
+
+
+class Audio_out::Root : public Audio_out::Root_component
+{
+	private:
+
+		Genode::Env &_env;
+		Timer::Connection _timer;
+
+		Session_component *_create_session(const char *args) override
+		{
+			using namespace Genode;
+
+			size_t ram_quota =
+				Arg_string::find_arg(args, "ram_quota").ulong_value(0);
+
+			size_t session_size = align_addr(sizeof(Session_component), 12);
+
+			if ((ram_quota < session_size) ||
+			    (sizeof(Stream) > ram_quota - session_size)) {
+				Genode::error("insufficient 'ram_quota', got ", ram_quota, ", "
+				              "need ", sizeof(Stream) + session_size);
+				throw Insufficient_ram_quota();
+			}
+
+			Session_component *session = new (md_alloc())
+				Session_component(_env, _timer);
+
+			return session;
+
+		}
+
+		void _destroy_session(Session_component *session) override
+		{
+			Genode::destroy(md_alloc(), session);
+		}
+
+	public:
+
+		Root(Genode::Env        &env,
+		     Genode::Allocator  &md_alloc)
+		: Root_component(env.ep(), md_alloc),
+		  _env(env), _timer(env) { }
+};
+
+#endif /* _AUDIO_OUT_H_ */

repos/os/src/server/black_hole/main.cc

@@ -0,0 +1,54 @@
+/*
+ * \brief  Black hole component
+ * \author Christian Prochaska
+ * \date   2021-07-07
+ *
+ */
+
+/*
+ * Copyright (C) 2021 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.
+ */
+
+
+/* Genode includes */
+#include <base/attached_rom_dataspace.h>
+#include <base/component.h>
+#include <base/heap.h>
+#include <base/log.h>
+#include <root/component.h>
+
+/* local includes */
+#include "audio_out.h"
+
+
+/***************
+ ** Component **
+ ***************/
+
+namespace Black_hole { struct Main; }
+
+struct Black_hole::Main
+{
+	Genode::Env &env;
+
+	Genode::Sliced_heap heap { env.ram(), env.rm() };
+
+	Genode::Constructible<Audio_out::Root> audio_out_root { };
+
+	Main(Genode::Env &env) : env(env)
+	{
+		Genode::Attached_rom_dataspace _config_rom { env, "config" };
+
+		if (_config_rom.xml().has_sub_node("audio_out")) {
+			audio_out_root.construct(env, heap);
+			env.parent().announce(env.ep().manage(*audio_out_root));
+		}
+	}
+};
+
+
+void Component::construct(Genode::Env &env)
+{ static Black_hole::Main inst(env); }

repos/os/src/server/black_hole/target.mk

@@ -0,0 +1,3 @@
+TARGET = black_hole
+SRC_CC = main.cc
+LIBS = base