server/log_tee: shim to duplicate log streams

Fixes #28

run/log_tee.run

@@ -0,0 +1,33 @@
+build "core init server/log_tee test/printf"
+
+create_boot_directory
+
+install_config {
+	<config>
+		<parent-provides>
+			<service name="LOG"/>
+			<service name="RM"/>
+		</parent-provides>
+		<default-route>
+			<any-service> <parent/> </any-service>
+		</default-route>
+
+		<start name="log_tee">
+			<resource name="RAM" quantum="2M"/>
+			<provides> <service name="LOG"/> </provides>
+		</start>
+
+		<start name="test-printf">
+			<resource name="RAM" quantum="2M"/>
+			<route>
+				<any-service> <child name="log_tee"/> <parent/> </any-service>
+			</route>
+		</start>
+	</config>
+}
+
+build_boot_image "core init log_tee test-printf"
+
+append qemu_args "-nographic -m 64"
+
+run_genode_until {child "test-printf" exited with exit value 0} 10

src/server/log_tee/README

@@ -0,0 +1,41 @@
+Log_tee is a LOG shim server that writes client messages to
+dedicated LOG sessions as well as a global component log. The
+effect is that log messages are duplicated into two streams.
+
+This component pays for each client session from its own quota,
+client quota donations are forwarded to the LOG backends. This
+is to prevent naive client donations from being depleted before
+reaching the final logging destination.
+
+Example: log messages should be written to the file-system,
+the screen, and the kernel log.
+
+     ⇊
+  log_tee → terminal_log (on-screen)
+     ⇊
+  log_tee → parent (kernel)
+     ⇊
+   fs_log (file-system)
+
+!
+! <start name="terminal_log"> ... </start>
+! <start name="fs_log">       ... </start>
+!
+! <start name="log_tee_2">
+!    <binary name="log_tee"/>
+!    <resource name="RAM" quantum="4M"/>
+!      <provides> <service name="LOG"/> </provides>
+!      <route>
+!        <service name="LOG" label=""> <child name="terminal_log"/> </service>
+!        <service name="LOG">          <child name="log_tee_1"/>    </service>
+!    </start>
+! 
+! <start name="log_tee_1">
+!    <binary name="log_tee"/>
+!    <resource name="RAM" quantum="4M"/>
+!      <provides> <service name="LOG"/> </provides>
+!      <route>
+!        <service name="LOG" label=""> <parent/>              </service>
+!        <service name="LOG">          <child name="fs_log"/> </service>
+!    </start>
+!

src/server/log_tee/component.cc

@@ -0,0 +1,109 @@
+/*
+ * \brief  Server that duplicates log streams
+ * \author Emery Hemingway
+ * \date   2016-07-28
+ */
+
+/*
+ * Copyright (C) 2016 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+/* Genode includes */
+#include <log_session/connection.h>
+#include <root/component.h>
+#include <base/component.h>
+#include <base/session_label.h>
+#include <base/log.h>
+#include <base/snprintf.h>
+#include <util/list.h>
+
+namespace Log_tee {
+
+	using namespace Genode;
+	class Session_component;
+	class Root_component;
+
+}
+
+
+class Log_tee::Session_component : public Rpc_object<Log_session>
+{
+	private:
+
+		/* craft our own connection to get a label in */
+		struct Log_connection : Connection<Log_session>, Log_session_client
+		{
+			Log_connection(Env &env, char const *args)
+			:
+				Connection<Log_session>(env, session(env.parent(), args)),
+				Log_session_client(cap())
+			{ }
+		} _log;
+
+		char _prefix[Session_label::capacity()+3];
+
+	public:
+
+		Session_component(Env &env, Session_label const &label, char const *args)
+		: _log(env, args)
+		{ snprintf(_prefix, sizeof(_prefix), "[%s] ", label.string()); }
+
+		size_t write(Log_session::String const &msg) override
+		{
+			/* write to the dedicated client log session */
+			size_t n = _log.write(msg);
+
+			/* write to our own log session */
+			log((char const *)_prefix, msg.string());
+
+			return n;
+		}
+};
+
+
+class Log_tee::Root_component :
+	public Genode::Root_component<Log_tee::Session_component>
+{
+	private:
+
+		Env &_env;
+
+	protected:
+
+		Log_tee::Session_component *_create_session(char const *args) override
+		{
+			Session_label const label = label_from_args(args);
+
+			try { return new (md_alloc()) Session_component(_env, label, args); }
+			catch (Genode::Parent::Service_denied) { throw Root::Unavailable(); }
+		}
+
+	public:
+
+		Root_component(Env &env, Allocator &alloc)
+		:
+			Genode::Root_component<Log_tee::Session_component>(env.ep(), alloc),
+			_env(env)
+		{ }
+};
+
+
+Genode::size_t Component::stack_size() { return 2*1024*sizeof(Genode::addr_t); }
+
+void Component::construct(Genode::Env &env)
+{
+	/*
+	 * Client sessions are not allocated on seperate dataspaces,
+	 * they are allocated on a heap against the component's own
+	 * RAM quota. The session RAM donation is passed verbatim to
+	 * the backend session.
+	 */
+
+	static Genode::Heap heap(env.ram(), env.rm());
+	static Log_tee::Root_component root(env, heap);
+
+	env.parent().announce(env.ep().manage(root));
+}

src/server/log_tee/target.mk

@@ -0,0 +1,3 @@
+TARGET := log_tee
+SRC_CC := component.cc
+LIBS   := base