trace: redirect logs to trace based on policy

If trace is enabled for component than an attempt to put message into
trace buffer is performed using log_output policy. If it succeeds than
message is not put to logs using log service.

Fixes #3714

repos/base/include/base/thread.h

@@ -417,6 +417,16 @@ class Genode::Thread
 			_logger()->log(cstring, strlen(cstring));
 		}
 
+		/**
+		 * Log null-terminated string as trace event using log_output policy
+		 *
+		 * \return true if trace is really put to buffer
+		 */
+		static bool trace_captured(char const *cstring)
+		{
+			return _logger()->log_captured(cstring, strlen(cstring));
+		}
+
 		/**
 		 * Log binary data as trace event
 		 */

repos/base/include/base/trace/logger.h

@@ -67,6 +67,13 @@ struct Genode::Trace::Logger
 		 */
 		void log(char const *, size_t);
 
+		/**
+		 * Log binary data to trace buffer using log_output policy
+		 *
+		 * \return true if log is really put to buffer
+		 */
+		bool log_captured(char const *, size_t);
+
 		/**
 		 * Log event to trace buffer
 		 */

repos/base/src/lib/base/default_log.cc

@@ -98,7 +98,12 @@ void Genode::init_log(Parent &parent)
 
 	back_end_ptr = unmanaged_singleton<Back_end>(parent);
 
-	struct Write_fn { void operator () (char const *s) { back_end_ptr->write(s); } };
+	struct Write_fn {
+		void operator () (char const *s) {
+			if (Thread::trace_captured(s)) return;
+			back_end_ptr->write(s);
+		}
+	};
 
 	typedef Buffered_output<Log_session::MAX_STRING_LEN, Write_fn>
 	        Buffered_log_output;

repos/base/src/lib/base/trace.cc

@@ -157,6 +157,18 @@ void Trace::Logger::log(char const *msg, size_t len)
 }
 
 
+__attribute__((optimize("-fno-delete-null-pointer-checks")))
+bool Trace::Logger::log_captured(char const *msg, size_t len)
+{
+	if (!this || !_evaluate_control()) return false;
+
+	len = policy_module->log_output(buffer->reserve(len), msg, len);
+	buffer->commit(len);
+
+	return len != 0;
+}
+
+
 void Trace::Logger::init(Thread_capability thread, Cpu_session *cpu_session,
                          Trace::Control *attached_control)
 {