trace: make trace buffer resizeable

Trace buffers a re-allocated during subsequent calls to 'trace'.

issue #3294

repos/base/src/core/include/trace/subject_registry.h

@@ -79,19 +79,18 @@ class Genode::Trace::Subject
 
 				/**
 				 * Allocate new dataspace
-				 *
-				 * \return true on success, false on the attempt to call setup
-				 *         twice.
 				 */
-				bool setup(Ram_allocator &ram, size_t size)
+				void setup(Ram_allocator &ram, size_t size)
 				{
+					if (_size && _size == size)
+						return;
+
 					if (_size)
-						return false;
+						_ram_ptr->free(_ds);
 
 					_ram_ptr = &ram;
 					_size    = size;
 					_ds      = ram.alloc(size);
-					return true;
 				}
 
 				/**
@@ -103,6 +102,9 @@ class Genode::Trace::Subject
 					if (!from_ds.valid())
 						return false;
 
+					if (_size)
+						flush();
+
 					_ram_ptr = &ram;
 					_size    = size;
 					_ds      = ram.alloc(_size);
@@ -144,6 +146,7 @@ class Genode::Trace::Subject
 		Ram_dataspace       _buffer { };
 		Ram_dataspace       _policy { };
 		Policy_id           _policy_id { };
+		size_t              _allocated_memory { 0 };
 
 		Subject_info::State _state()
 		{
@@ -162,6 +165,18 @@ class Genode::Trace::Subject
 			return Subject_info::UNTRACED;
 		}
 
+		void _traceable_or_throw()
+		{
+			switch(_state()) {
+				case Subject_info::DEAD    : throw Source_is_dead();
+				case Subject_info::FOREIGN : throw Traced_by_other_session();
+				case Subject_info::ERROR   : throw Source_is_dead();
+				case Subject_info::INVALID : throw Nonexistent_subject();
+				case Subject_info::UNTRACED: return;
+				case Subject_info::TRACED  : return;
+			}
+		}
+
 	public:
 
 		/**
@@ -184,6 +199,9 @@ class Genode::Trace::Subject
 		 */
 		bool has_source_id(unsigned id) const { return id == _source_id; }
 
+		size_t allocated_memory() const { return _allocated_memory; }
+		void   reset_allocated_memory() { _allocated_memory = 0; }
+
 		/**
 		 * Start tracing
 		 *
@@ -199,21 +217,23 @@ class Genode::Trace::Subject
 		           size_t policy_size, Ram_allocator &ram,
 		           Region_map &local_rm, size_t size)
 		{
+			/* check state and throw error in case subject is not traceable */
+			_traceable_or_throw();
+
 			_policy_id = policy_id;
 
-			if (!_buffer.setup(ram, size)
+			_buffer.setup(ram, size);
-			 || !_policy.setup(ram, local_rm, policy_ds, policy_size))
+			if(!_policy.setup(ram, local_rm, policy_ds, policy_size))
-				throw Already_traced();
+					throw Already_traced();
 
 			/* inform trace source about the new buffer */
 			Locked_ptr<Source> source(_source);
 
-			if (!source.valid())
-				throw Source_is_dead();
-
 			if (!source->try_acquire(*this))
 				throw Traced_by_other_session();
 
+			_allocated_memory = policy_size + size;
+
 			source->trace(_policy.dataspace(), _buffer.dataspace());
 		}
 

repos/base/src/core/trace_session_component.cc

@@ -82,21 +82,28 @@ void Session_component::trace(Subject_id subject_id, Policy_id policy_id,
 	size_t const  policy_size = _policies.size(*this, policy_id);
 	size_t const required_ram = buffer_size + policy_size;
 
+	Trace::Subject &subject = _subjects.lookup_by_id(subject_id);
+	/* revert quota from previous call to trace */
+	if (subject.allocated_memory()) {
+		_md_alloc.upgrade(subject.allocated_memory());
+		subject.reset_allocated_memory();
+	}
+
 	/*
 	 * Account RAM needed for trace buffer and policy buffer to the trace
 	 * session.
 	 */
-	if (!_md_alloc.withdraw(required_ram))
+	if (!_md_alloc.withdraw(required_ram)) {
 		throw Out_of_ram();
+	}
 
 	try {
-		Trace::Subject &subject = _subjects.lookup_by_id(subject_id);
 		subject.trace(policy_id, _policies.dataspace(*this, policy_id),
 		              policy_size, _ram, _local_rm, buffer_size);
 	} catch (...) {
 		/* revert withdrawal or quota */
 		_md_alloc.upgrade(required_ram);
-		throw Out_of_ram();
+		throw;
 	}
 }