From f40fa3e0296c5b7c4b0f3467c6c690e334fd7b08 Mon Sep 17 00:00:00 2001
From: Michal Bloch <m.bloch@samsung.com>
Date: Fri, 13 Jan 2023 21:08:28 +0100
Subject: [PATCH] dlog_logger: cull unused logger readers

This will avoid unnecessary resource usage, in particular
needless threads when the transition happens.

Change-Id: Ia2a057b964f1ab0e9cefc582214495d37984ed4c
---
 src/logger/logger.c | 59 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 46 insertions(+), 13 deletions(-)

diff --git a/src/logger/logger.c b/src/logger/logger.c
index e219644..d95bc7c 100644
--- a/src/logger/logger.c
+++ b/src/logger/logger.c
@@ -243,6 +243,11 @@ int add_reader_memory(struct logger *server, struct reader_memory *reader)
 	return 0;
 }
 
+#ifndef UNIT_TEST
+/* This really belongs to the UNIT_TEST block at the bottom since it is only used
+ * by a function living there, but has not been moved there to keep patches small
+ * and because this function is going to be removed soon in an upcoming patch. */
+
 static int add_reader_logger(struct logger *server, struct reader_logger *reader)
 {
 	assert(reader);
@@ -271,6 +276,7 @@ failure:
 
 	return ret;
 }
+#endif
 
 int create_fifo_fds(struct logger *server, int pipe_fd[2], int flags, bool dump)
 {
@@ -733,13 +739,16 @@ int logger_create(struct logger_config_data *data, struct logger *l)
 
 			if (qos_is_enabled(&l->qos)) {
 				r = reader_add_subreader_metrics(&g_backend.logger_readers[id]->common, &l->qos);
-				if (r < 0)
+				if (r < 0) {
+					reader_free(&g_backend.logger_readers[id]->common);
+					g_backend.logger_readers[id] = NULL;
 					return r;
+				}
 			}
 
-			r = add_reader_logger(l, g_backend.logger_readers[id]);
-			if (r < 0)
-				return r;
+			/* The reader is not yet complete; later in `finalize_init`
+			 * it will receive further readers and be added to epoll
+			 * or alternatively get culled if it gets no sub-readers. */
 		}
 
 	for (log_id_t id = 0; id < LOG_ID_MAX; id++)
@@ -1325,6 +1334,29 @@ static int finalize_init(struct logger_config_data *data, struct logger *server)
 		.data = data,
 	}, parse_logfile_config);
 
+	/* The above created subs for logger readers.
+	 * There is no way for them to gain more at
+	 * runtime, so this is the time to do some
+	 * processing that relies on subs being ready. */
+	for (log_id_t id = 0; id < LOG_ID_MAX; ++id) {
+		struct reader_logger *const reader = g_backend.logger_readers[id];
+		if (!reader)
+			continue;
+
+		if (reader->common.subs == NULL) {
+			reader_free(&reader->common);
+			g_backend.logger_readers[id] = NULL;
+			continue;
+		}
+
+		r = add_reader_logger(server, reader);
+		if (r < 0) {
+			reader_free(&reader->common);
+			g_backend.logger_readers[id] = NULL;
+			return r;
+		}
+	}
+
 	return 0;
 }
 
@@ -1347,15 +1379,16 @@ bool early_termination(const struct logger_config_data *data, const struct logge
 	/* In order to check if the deamon will be doing nothing
 	 * and can quit instantaneously, we do three checks: */
 
-	/* 1. We make sure that there are no logger subreaders.
-	 * When the logger backend is being used, the daemon reads the data
-	 * in order to use it internally. The daemon always reads each buffer
-	 * to a separate reader and each concrete usage has its own subreader.
-	 * Therefore, we need to check if no subreaders exist. */
-	for (list_head l = logger->readers_logger; l != NULL; list_next(&l)) {
-		struct reader_logger *reader = list_at(l);
-		if (reader->common.subs != NULL)
-			return false;
+	/* 1. We make sure that there are no Android Logger readers.
+	 * Note that an earlier function gets rid of any readers that
+	 * don't do anything (i.e. have no subs and no way to get them). */
+	for (log_id_t id = 0; id < LOG_ID_MAX; ++id) {
+		const struct reader_logger *const reader = g_backend.logger_readers[id];
+		if (!reader)
+			continue;
+
+		assert(reader->common.subs != NULL);
+		return false;
 	}
 
 	/* 2. We make sure that no pipe-like buffer is enabled.
-- 
2.7.4