Move to kernel style SPDX license identifiers

[lttng-ust.git] / libringbuffer / frontend_internal.h

diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index 1a9c2d4b78e82e7645e1267430b41e6f0c3218c2..9c6a8db78ecdd50dc9d510e99cfdc182fa868a18 100644 (file)
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -1,39 +1,20 @@
-#ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
-#define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
-
 /*
- * libringbuffer/frontend_internal.h
- *
- * Ring Buffer Library Synchronization Header (internal helpers).
+ * SPDX-License-Identifier: (LGPL-2.1-only or GPL-2.0-only)
  *
  * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; only
- * version 2.1 of the License.
- *
- * This library 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
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
- *
- * Author:
- *     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Ring Buffer Library Synchronization Header (internal helpers).
  *
  * See ring_buffer_frontend.c for more information on wait-free algorithms.
- *
- * Dual LGPL v2.1/GPL v2 license.
  */
 
+#ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
+#define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
+
 #include <urcu/compiler.h>
 #include <urcu/tls-compat.h>
 #include <signal.h>
+#include <stdint.h>
 #include <pthread.h>
 
 #include <lttng/ringbuffer-config.h>
@@ -205,6 +186,15 @@ void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
                                              consumed_new) != consumed_old));
 }
 
+/*
+ * Move consumed position to the beginning of subbuffer in which the
+ * write offset is. Should only be used on ring buffers that are not
+ * actively being written into, because clear_reader does not take into
+ * account the commit counters when moving the consumed position, which
+ * can make concurrent trace producers or consumers observe consumed
+ * position further than the write offset, which breaks ring buffer
+ * algorithm guarantees.
+ */
 static inline
 void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
                                  struct lttng_ust_shm_handle *handle)
@@ -221,12 +211,10 @@ void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
        do {
                offset = v_read(config, &buf->offset);
                consumed_old = uatomic_read(&buf->consumed);
-               if (caa_unlikely(subbuf_trunc(offset, chan)
-                             - subbuf_trunc(consumed_old, chan)
-                            > 0))
-                       consumed_new = subbuf_trunc(offset, chan);
-               else
-                       return;
+               CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
+                               - subbuf_trunc(consumed_old, chan))
+                               < 0);
+               consumed_new = subbuf_trunc(offset, chan);
        } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
                                              consumed_new) != consumed_old));
 }