trace: support to request subject infos batched

Optimize requesting the Subject_infos from O(n) to O(1) RPC call.

Issue #3610

repos/base/include/trace_session/client.h

@@ -86,6 +86,22 @@ struct Genode::Trace::Session_client : Genode::Rpc_client<Genode::Trace::Session
 			return num_subjects;
 		}
 
+		template <typename FN>
+		size_t for_each_subject_info(FN const &fn)
+		{
+			size_t const num_subjects = call<Rpc_subject_infos>();
+			size_t const max_subjects = _argument_buffer.size / (sizeof(Subject_info) + sizeof(Subject_id));
+
+			Subject_info * const infos = reinterpret_cast<Subject_info *>(_argument_buffer.base);
+			Subject_id   * const ids   = reinterpret_cast<Subject_id *>(infos + max_subjects);
+
+			for (unsigned i = 0; i < num_subjects; i++) {
+				fn(ids[i], infos[i]);
+			}
+
+			return num_subjects;
+		}
+
 		Policy_id alloc_policy(size_t size) override {
 			return call<Rpc_alloc_policy>(size); }
 

repos/base/include/trace_session/trace_session.h

@@ -142,6 +142,8 @@ struct Genode::Trace::Session : Genode::Session
 	                 Subject_id);
 	GENODE_RPC_THROW(Rpc_subjects, size_t, subjects,
 	                 GENODE_TYPE_LIST(Out_of_ram, Out_of_caps));
+	GENODE_RPC_THROW(Rpc_subject_infos, size_t, subject_infos,
+	                 GENODE_TYPE_LIST(Out_of_ram, Out_of_caps));
 	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,
@@ -153,7 +155,7 @@ struct Genode::Trace::Session : Genode::Session
 	GENODE_RPC_INTERFACE(Rpc_dataspace, Rpc_alloc_policy, Rpc_policy,
 	                     Rpc_unload_policy, Rpc_trace, Rpc_rule, Rpc_pause,
 	                     Rpc_resume, Rpc_subjects, Rpc_subject_info, Rpc_buffer,
-	                     Rpc_free);
+	                     Rpc_free, Rpc_subject_infos);
 };
 
 #endif /* _INCLUDE__TRACE_SESSION__TRACE_SESSION_H_ */

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

@@ -74,6 +74,7 @@ class Genode::Trace::Session_component
 
 		Dataspace_capability dataspace();
 		size_t subjects();
+		size_t subject_infos();
 
 		Policy_id alloc_policy(size_t) override;
 		Dataspace_capability policy(Policy_id) override;

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

@@ -436,6 +436,22 @@ class Genode::Trace::Subject_registry
 			return i;
 		}
 
+		/**
+		 * Retrieve Subject_infos batched
+		 */
+		size_t subjects(Subject_info * const dst, Subject_id * ids, size_t const len)
+		{
+			Mutex::Guard guard(_mutex);
+
+			unsigned i = 0;
+			for (Subject *s = _entries.first(); s && i < len; s = s->next()) {
+				ids[i]   = s->id();
+				dst[i++] = s->info();
+			}
+
+			return i;
+		}
+
 		/**
 		 * Remove subject and release resources
 		 *

repos/base/src/core/trace_session_component.cc

@@ -36,6 +36,18 @@ size_t Session_component::subjects()
 }
 
 
+size_t Session_component::subject_infos()
+{
+	_subjects.import_new_sources(_sources);
+
+	size_t const count  = _argument_buffer.size() / (sizeof(Subject_info) + sizeof(Subject_id));
+	Subject_info *infos = _argument_buffer.local_addr<Subject_info>();
+	Subject_id   *ids   = reinterpret_cast<Subject_id *>(infos + count);
+
+	return _subjects.subjects(infos, ids, count);
+}
+
+
 Policy_id Session_component::alloc_policy(size_t size)
 {
 	if (size > _argument_buffer.size())