Fix: sessiond: sessiond and agent deadlock on destroy

[lttng-tools.git] / src / bin / lttng-sessiond / session.h

diff --git a/src/bin/lttng-sessiond/session.h b/src/bin/lttng-sessiond/session.h
index da3805658cd28e1255292d6250ae6882f779a6d0..1df70a4747a8341d93b8b3185603ccddcfb23782 100644 (file)
--- a/src/bin/lttng-sessiond/session.h
+++ b/src/bin/lttng-sessiond/session.h
@@ -1,18 +1,8 @@
 /*
- * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
+ * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License, version 2 only,
- * as published by the Free Software Foundation.
+ * SPDX-License-Identifier: GPL-2.0-only
  *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
 #ifndef _LTT_SESSION_H
@@ -172,7 +162,8 @@ struct ltt_session {
         * Keep a state if this session was rotated after the last stop command.
         * We only allow one rotation after a stop. At destroy, we also need to
         * know if a rotation occurred since the last stop to rename the current
-        * chunk.
+        * chunk. After a stop followed by rotate, all subsequent clear
+        * (without prior start) will succeed, but will be effect-less.
         */
        bool rotated_after_last_stop;
        /*
@@ -181,6 +172,10 @@ struct ltt_session {
         * subsequent rotate (without prior start) will return an error.
         */
        bool cleared_after_last_stop;
+       /*
+        * True if the session has had an explicit non-quiet rotation.
+        */
+       bool rotated;
        /*
         * Condition and trigger for size-based rotations.
         */
@@ -200,13 +195,22 @@ struct ltt_session {
        char *base_path;
 };
 
-/* Prototypes */
 enum lttng_error_code session_create(const char *name, uid_t uid, gid_t gid,
                struct ltt_session **out_session);
 void session_lock(struct ltt_session *session);
+void session_unlock(struct ltt_session *session);
+
+/*
+ * The session list lock covers more ground than its name implies. While
+ * it does protect against concurent mutations of the session list, it is
+ * also used as a multi-session lock when synchronizing newly-registered
+ * 'user space tracer' and 'agent' applications.
+ *
+ * In other words, it prevents session configurations from changing while they
+ * are being transmitted to the various applications.
+ */
 void session_lock_list(void);
 int session_trylock_list(void);
-void session_unlock(struct ltt_session *session);
 void session_unlock_list(void);
 
 void session_destroy(struct ltt_session *session);