From 5d678dba9edd6e45c5657b27a09b34592572ae6e Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Wed, 17 Jun 2015 13:25:51 +0200
Subject: [PATCH] core: throw Trace::Out_of_metadata in subjects()

While importing trace sources as trace subjects into a TRACE session,
the session quota might become depleted. The TRACE session already keeps
track of the session quota via an allocator guard but the 'subjects' RPC
function missed to handle the out-of-memory condition. This patch
reflects the error condition as an 'Out_of_metadata' exception to the
TRACE client. It also contains an extension of the trace test to
exercise the corner case.
---
 repos/base/include/trace_session/client.h     |  2 ++
 .../include/trace_session/trace_session.h     |  3 +-
 .../base/src/core/trace_session_component.cc  | 11 ++++--
 repos/os/src/test/trace/main.cc               | 36 +++++++++++++++++++
 4 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/repos/base/include/trace_session/client.h b/repos/base/include/trace_session/client.h
index b8882e700..9a1a95ec0 100644
--- a/repos/base/include/trace_session/client.h
+++ b/repos/base/include/trace_session/client.h
@@ -61,6 +61,8 @@ struct Genode::Trace::Session_client : Genode::Rpc_client<Genode::Trace::Session
 
 		/**
 		 * Retrieve subject directory
+		 *
+		 * \throw Out_of_metadata
 		 */
 		size_t subjects(Subject_id *dst, size_t dst_len)
 		{
diff --git a/repos/base/include/trace_session/trace_session.h b/repos/base/include/trace_session/trace_session.h
index 42a4550c6..a693c3c5f 100644
--- a/repos/base/include/trace_session/trace_session.h
+++ b/repos/base/include/trace_session/trace_session.h
@@ -131,7 +131,8 @@ struct Genode::Trace::Session : Genode::Session
 	GENODE_RPC_THROW(Rpc_resume, void, resume,
 	                 GENODE_TYPE_LIST(Nonexistent_subject, Source_is_dead),
 	                 Subject_id);
-	GENODE_RPC(Rpc_subjects, size_t, subjects);
+	GENODE_RPC_THROW(Rpc_subjects, size_t, subjects,
+	                 GENODE_TYPE_LIST(Out_of_metadata));
 	GENODE_RPC_THROW(Rpc_subject_info, Subject_info, subject_info,
 	                 GENODE_TYPE_LIST(Nonexistent_subject), Subject_id);
 	GENODE_RPC_THROW(Rpc_buffer, Dataspace_capability, buffer,
diff --git a/repos/base/src/core/trace_session_component.cc b/repos/base/src/core/trace_session_component.cc
index 527980122..e0e25b7fb 100644
--- a/repos/base/src/core/trace_session_component.cc
+++ b/repos/base/src/core/trace_session_component.cc
@@ -29,7 +29,14 @@ Dataspace_capability Session_component::dataspace()
 
 size_t Session_component::subjects()
 {
-	_subjects.import_new_sources(_sources);
+	try {
+		_subjects.import_new_sources(_sources);
+
+	} catch (Allocator::Out_of_memory) {
+
+		PWRN("TRACE session ran out of memory");
+		throw Out_of_metadata();
+	}
 
 	return _subjects.subjects((Subject_id *)_argument_buffer.base,
 	                          _argument_buffer.size/sizeof(Subject_id));
@@ -155,7 +162,7 @@ Session_component::Session_component(Allocator &md_alloc, size_t ram_quota,
 	_subjects(_subjects_slab, _ram, _sources),
 	_argument_buffer(_ram, arg_buffer_size)
 {
-	_md_alloc.withdraw(arg_buffer_size);
+	_md_alloc.withdraw(_argument_buffer.size);
 }
 
 
diff --git a/repos/os/src/test/trace/main.cc b/repos/os/src/test/trace/main.cc
index 304f48249..975003c96 100644
--- a/repos/os/src/test/trace/main.cc
+++ b/repos/os/src/test/trace/main.cc
@@ -16,6 +16,7 @@
 #include <trace_session/connection.h>
 #include <timer_session/connection.h>
 #include <os/config.h>
+#include <base/sleep.h>
 
 static char const *state_name(Genode::Trace::Subject_info::State state)
 {
@@ -117,12 +118,47 @@ class Trace_buffer_monitor
 };
 
 
+static void test_out_of_metadata()
+{
+	printf("test Out_of_metadata exception of Trace::Session::subjects call\n");
+
+	/*
+	 * The call of 'subjects' will prompt core's TRACE service to import those
+	 * threads as trace subjects into the TRACE session. This step should fail
+	 * because we dimensioned the TRACE session with a very low amount of
+	 * session quota. The allocation failure is propagated to the TRACE client
+	 * by the 'Out_of_metadata' exception. The test validates this
+	 * error-handling procedure.
+	 */
+
+	enum { MAX_SUBJECT_IDS = 16 };
+	Genode::Trace::Subject_id subject_ids[MAX_SUBJECT_IDS];
+
+	Genode::Trace::Connection trace(sizeof(subject_ids) + 4096, sizeof(subject_ids), 0);
+
+	try {
+		trace.subjects(subject_ids, MAX_SUBJECT_IDS);
+
+		/* we should never arrive here */
+		struct Unexpectedly_got_no_exception{};
+		throw  Unexpectedly_got_no_exception();
+
+	} catch (Trace::Out_of_metadata) {
+		printf("got Trace::Out_of_metadata exception as expected\n");
+	}
+
+	printf("passed Out_of_metadata test\n");
+}
+
+
 int main(int argc, char **argv)
 {
 	using namespace Genode;
 
 	printf("--- test-trace started ---\n");
 
+	test_out_of_metadata();
+
 	static Genode::Trace::Connection trace(1024*1024, 64*1024, 0);
 
 	static Timer::Connection timer;