From 939950af98d044a3b0632cad5293f91cb1493ef8 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 30 Jan 2012 09:02:04 -0500
Subject: [PATCH] Use boot_id as monotonic clock uuid

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 liblttng-ust/clock.h      | 31 +++++++++++++++++++++++++++++--
 liblttng-ust/ltt-events.c | 22 +++++++++++++++++-----
 2 files changed, 46 insertions(+), 7 deletions(-)

diff --git a/liblttng-ust/clock.h b/liblttng-ust/clock.h
index 95e3e43b..82a7b45c 100644
--- a/liblttng-ust/clock.h
+++ b/liblttng-ust/clock.h
@@ -24,6 +24,12 @@
 #include <sys/time.h>
 #include <stdint.h>
 #include <stddef.h>
+#include <stdio.h>
+
+/*
+ * Includes final \0.
+ */
+#define CLOCK_UUID_LEN		37
 
 /* TRACE CLOCK */
 
@@ -50,9 +56,30 @@ uint64_t trace_clock_freq(void)
 }
 
 static __inline__
-const char *trace_clock_uuid(void)
+const int trace_clock_uuid(char *uuid)
 {
-	return "CLOCK_MONOTONIC";
+	int ret = 0;
+	size_t len;
+	FILE *fp;
+
+	/*
+	 * boot_id needs to be read once before being used concurrently
+	 * to deal with a Linux kernel race. A fix is proposed for
+	 * upstream, but the work-around is needed for older kernels.
+	 */
+	fp = fopen("/proc/sys/kernel/random/boot_id", "r");
+	if (!fp) {
+		return -ENOENT;
+	}
+	len = fread(uuid, 1, CLOCK_UUID_LEN - 1, fp);
+	if (len < CLOCK_UUID_LEN - 1) {
+		ret = -EINVAL;
+		goto end;
+	}
+	uuid[CLOCK_UUID_LEN - 1] = '\0';
+end:
+	fclose(fp);
+	return ret;
 }
 
 #endif /* _UST_CLOCK_H */
diff --git a/liblttng-ust/ltt-events.c b/liblttng-ust/ltt-events.c
index 7d2dc31a..85afc1ba 100644
--- a/liblttng-ust/ltt-events.c
+++ b/liblttng-ust/ltt-events.c
@@ -1075,7 +1075,7 @@ static
 int _ltt_session_metadata_statedump(struct ltt_session *session)
 {
 	unsigned char *uuid_c = session->uuid;
-	char uuid_s[37];
+	char uuid_s[37], clock_uuid_s[CLOCK_UUID_LEN];
 	struct ltt_channel *chan;
 	struct ltt_event *event;
 	int ret = 0;
@@ -1133,15 +1133,27 @@ int _ltt_session_metadata_statedump(struct ltt_session *session)
 
 	ret = lttng_metadata_printf(session,
 		"clock {\n"
-		"	name = %s;\n"
-		"	uuid = %s;\n"
+		"	name = %s;\n",
+		"monotonic"
+		);
+	if (ret)
+		goto end;
+
+	if (!trace_clock_uuid(clock_uuid_s)) {
+		ret = lttng_metadata_printf(session,
+			"	uuid = \"%s\";\n",
+			clock_uuid_s
+			);
+		if (ret)
+			goto end;
+	}
+
+	ret = lttng_metadata_printf(session,
 		"	description = \"Monotonic Clock\";\n"
 		"	freq = %" PRIu64 "; /* Frequency, in Hz */\n"
 		"	/* clock value offset from Epoch is: offset * (1/freq) */\n"
 		"	offset = %" PRIu64 ";\n"
 		"};\n\n",
-		"monotonic",
-		trace_clock_uuid(),
 		trace_clock_freq(),
 		measure_clock_offset()
 		);
-- 
2.34.1