X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=liblttng-ust%2Flttng-ust-comm.c;fp=liblttng-ust%2Flttng-ust-comm.c;h=e8c85304e798b446ecf17110cc9e3fd70464527f;hb=5d32ea4466f42665808fe8cf7ac8b533cb512aee;hp=1c7584ddd51e84ed3d1d55015467101791bd4657;hpb=75b46fdf889cde49b02a7e15cae52e2e2d3e94bc;p=lttng-ust.git

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index 1c7584dd..e8c85304 100644
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -689,6 +689,30 @@ int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
 	 */
 	wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 	if (wait_shm_fd >= 0) {
+		int32_t tmp_read;
+		ssize_t len;
+		size_t bytes_read = 0;
+
+		/*
+		 * Try to read the fd. If unable to do so, try opening
+		 * it in write mode.
+		 */
+		do {
+			len = read(wait_shm_fd,
+				&((char *) &tmp_read)[bytes_read],
+				sizeof(tmp_read) - bytes_read);
+			if (len > 0) {
+				bytes_read += len;
+			}
+		} while ((len < 0 && errno == EINTR)
+			|| (len > 0 && bytes_read < sizeof(tmp_read)));
+		if (bytes_read != sizeof(tmp_read)) {
+			ret = close(wait_shm_fd);
+			if (ret) {
+				ERR("close wait_shm_fd");
+			}
+			goto open_write;
+		}
 		goto end;
 	} else if (wait_shm_fd < 0 && errno != ENOENT) {
 		/*
@@ -699,9 +723,11 @@ int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
 		ERR("Error opening shm %s", sock_info->wait_shm_path);
 		goto end;
 	}
+
+open_write:
 	/*
-	 * If the open failed because the file did not exist, try
-	 * creating it ourself.
+	 * If the open failed because the file did not exist, or because
+	 * the file was not truncated yet, try creating it ourself.
 	 */
 	URCU_TLS(lttng_ust_nest_count)++;
 	pid = fork();