From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 19 Apr 2016 22:42:06 +0000 (-0400)
Subject: Fix: lttng-live flush when output to file
X-Git-Tag: v1.4.0-rc1~100
X-Git-Url: http://git.efficios.com/?p=babeltrace.git;a=commitdiff_plain;h=857eaa682bde4acfb5b9437ac9ace2d429d7107a

Fix: lttng-live flush when output to file

When the standard output is redirected to a file, we need to flush the
output between each packet, otherwise the stream buffering may keep us
from seeing events for a while in a low-throughput trace.

While we are there, document that lttng-live does now support the
--output option in babeltrace 1.x.

Fixes #1010

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/doc/babeltrace.1 b/doc/babeltrace.1
index 929c5634..1ee2281f 100644
--- a/doc/babeltrace.1
+++ b/doc/babeltrace.1
@@ -97,7 +97,8 @@ babeltrace-log(1), lttng(1), lttng-ust(3), lttng-sessiond(8)
 .SH "BUGS"
 
 .PP
-No known bugs at this point.
+The lttng-live plugin does not honor the the "--output" command line
+option.
 
 If you encounter any issues or usability problem, please report it on
 our mailing list <lttng-dev@lists.lttng.org> to help improve this
diff --git a/formats/lttng-live/lttng-live-comm.c b/formats/lttng-live/lttng-live-comm.c
index 492125a7..fdecf31c 100644
--- a/formats/lttng-live/lttng-live-comm.c
+++ b/formats/lttng-live/lttng-live-comm.c
@@ -246,7 +246,7 @@ void print_session_list(GPtrArray *session_list, const char *path)
 
 	for (i = 0; i < session_list->len; i++) {
 		relay_session = g_ptr_array_index(session_list, i);
-		fprintf(stdout, "%s/host/%s/%s (timer = %u, "
+		fprintf(LTTNG_LIVE_OUTPUT_FP, "%s/host/%s/%s (timer = %u, "
 				"%u stream(s), %u client(s) connected)\n",
 				path, relay_session->hostname,
 				relay_session->name, relay_session->timer,
@@ -649,6 +649,18 @@ retry:
 		ret = -1;
 		goto end;
 	}
+
+	/*
+	 * Flush the output between attempts to grab a packet, thus
+	 * ensuring we flush at least at the periodical timer period.
+	 * This ensures the output remains reactive for interactive users and
+	 * that the output is flushed when redirected to a file by the shell.
+	 */
+	if (fflush(LTTNG_LIVE_OUTPUT_FP) < 0) {
+		perror("fflush");
+		goto error;
+	}
+
 	cmd.cmd = htobe32(LTTNG_VIEWER_GET_PACKET);
 	cmd.data_size = htobe64(sizeof(rq));
 	cmd.cmd_version = htobe32(0);
diff --git a/formats/lttng-live/lttng-live-plugin.c b/formats/lttng-live/lttng-live-plugin.c
index bf71b2bf..771801ce 100644
--- a/formats/lttng-live/lttng-live-plugin.c
+++ b/formats/lttng-live/lttng-live-plugin.c
@@ -292,6 +292,12 @@ struct bt_trace_descriptor *lttng_live_open_trace(const char *path, int flags,
 	pos->parent.rw_table = NULL;
 	pos->parent.event_cb = NULL;
 	pos->parent.trace = &pos->trace_descriptor;
+	/*
+	 * Since we do *everything* in this function, we are skipping
+	 * the output plugin handling that is part of Babeltrace 1.x.
+	 * Therefore, don't expect the --output cmd line option to work.
+	 * This limits the output of lttng-live to stderr and stdout.
+	 */
 	if (lttng_live_open_trace_read(path) < 0) {
 		goto error;
 	}
diff --git a/formats/lttng-live/lttng-live.h b/formats/lttng-live/lttng-live.h
index 4ab641d5..56492be0 100644
--- a/formats/lttng-live/lttng-live.h
+++ b/formats/lttng-live/lttng-live.h
@@ -32,6 +32,13 @@
 #define LTTNG_LIVE_MAJOR			2
 #define LTTNG_LIVE_MINOR			4
 
+/*
+ * The lttng-live output file pointer is currently hardcoded to stdout,
+ * and is expected to be hardcoded to this by fflush() performed between
+ * each packet.
+ */
+#define LTTNG_LIVE_OUTPUT_FP			stdout
+
 struct lttng_live_ctx {
 	char traced_hostname[MAXNAMLEN];
 	char session_name[MAXNAMLEN];