X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=libringbuffer%2Fshm.c;h=3dbb9f4928a6d81b43c01fc1dbd4dbd3620ebf0c;hb=c0c0989ab70574e09b2f7e8b48c2da6af664a849;hp=9160c2184f9874841e30802bab2288be30f36894;hpb=b72687b85f4f07a9b63be329ad1fe95b36d24900;p=lttng-ust.git

diff --git a/libringbuffer/shm.c b/libringbuffer/shm.c
index 9160c218..3dbb9f49 100644
--- a/libringbuffer/shm.c
+++ b/libringbuffer/shm.c
@@ -1,21 +1,7 @@
 /*
- * libringbuffer/shm.c
+ * SPDX-License-Identifier: LGPL-2.1-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
  */
 
 #define _LGPL_SOURCE
@@ -128,25 +114,35 @@ struct shm_object *_shm_object_table_alloc_shm(struct shm_object_table *table,
 	}
 	memcpy(obj->wait_fd, waitfd, sizeof(waitfd));
 
-	/* create shm */
+	/*
+	 * Set POSIX shared memory object size
+	 *
+	 * First, use ftruncate() to set its size, some implementations won't
+	 * allow writes past the size set by ftruncate.
+	 * Then, use write() to fill it with zeros, this allows us to fully
+	 * allocate it and detect a shortage of shm space without dealing with
+	 * a SIGBUS.
+	 */
 
 	shmfd = stream_fd;
-	ret = zero_file(shmfd, memory_map_size);
-	if (ret) {
-		PERROR("zero_file");
-		goto error_zero_file;
-	}
 	ret = ftruncate(shmfd, memory_map_size);
 	if (ret) {
 		PERROR("ftruncate");
 		goto error_ftruncate;
 	}
+	ret = zero_file(shmfd, memory_map_size);
+	if (ret) {
+		PERROR("zero_file");
+		goto error_zero_file;
+	}
+
 	/*
 	 * Also ensure the file metadata is synced with the storage by using
-	 * fsync(2).
+	 * fsync(2). Some platforms don't allow fsync on POSIX shm fds, ignore
+	 * EINVAL accordingly.
 	 */
 	ret = fsync(shmfd);
-	if (ret) {
+	if (ret && errno != EINVAL) {
 		PERROR("fsync");
 		goto error_fsync;
 	}