From a3ccff4ffbfa87702cf3bc4693f86c2aaac27be2 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 26 Jan 2012 21:36:06 -0500
Subject: [PATCH] clock: output clock description in metadata

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 lttng-events.c        | 77 +++++++++++++++++++++++++++++++++++++++----
 wrapper/trace-clock.h |  8 ++---
 2 files changed, 75 insertions(+), 10 deletions(-)

diff --git a/lttng-events.c b/lttng-events.c
index 0ef87a8c..6dd3ba4e 100644
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -794,8 +794,8 @@ int _lttng_stream_packet_context_declare(struct lttng_session *session)
 {
 	return lttng_metadata_printf(session,
 		"struct packet_context {\n"
-		"	uint64_t timestamp_begin;\n"
-		"	uint64_t timestamp_end;\n"
+		"	uint64_clock_monotonic_t timestamp_begin;\n"
+		"	uint64_clock_monotonic_t timestamp_end;\n"
 		"	uint32_t events_discarded;\n"
 		"	uint32_t content_size;\n"
 		"	uint32_t packet_size;\n"
@@ -821,11 +821,11 @@ int _lttng_event_header_declare(struct lttng_session *session)
 	"	enum : uint5_t { compact = 0 ... 30, extended = 31 } id;\n"
 	"	variant <id> {\n"
 	"		struct {\n"
-	"			uint27_t timestamp;\n"
+	"			uint27_clock_monotonic_t timestamp;\n"
 	"		} compact;\n"
 	"		struct {\n"
 	"			uint32_t id;\n"
-	"			uint64_t timestamp;\n"
+	"			uint64_clock_monotonic_t timestamp;\n"
 	"		} extended;\n"
 	"	} v;\n"
 	"} align(%u);\n"
@@ -834,11 +834,11 @@ int _lttng_event_header_declare(struct lttng_session *session)
 	"	enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;\n"
 	"	variant <id> {\n"
 	"		struct {\n"
-	"			uint32_t timestamp;\n"
+	"			uint32_clock_monotonic_t timestamp;\n"
 	"		} compact;\n"
 	"		struct {\n"
 	"			uint32_t id;\n"
-	"			uint64_t timestamp;\n"
+	"			uint64_clock_monotonic_t timestamp;\n"
 	"		} extended;\n"
 	"	} v;\n"
 	"} align(%u);\n\n",
@@ -847,6 +847,33 @@ int _lttng_event_header_declare(struct lttng_session *session)
 	);
 }
 
+ /*
+ * Approximation of NTP time of day to clock monotonic correlation,
+ * taken at start of trace.
+ * Yes, this is only an approximation. Yes, we can (and will) do better
+ * in future versions.
+ */
+static
+uint64_t measure_clock_offset(void)
+{
+	uint64_t offset, monotonic[2], realtime;
+	struct timespec rts = { 0, 0 };
+	unsigned long flags;
+
+	/* Disable interrupts to increase correlation precision. */
+	local_irq_save(flags);
+	monotonic[0] = trace_clock_read64();
+	getnstimeofday(&rts);      
+	monotonic[1] = trace_clock_read64();
+	local_irq_restore(flags);
+
+	offset = (monotonic[0] + monotonic[1]) >> 1;
+	realtime = rts.tv_sec * NSEC_PER_SEC;
+	realtime += rts.tv_nsec;
+	offset = realtime - offset;
+	return offset;
+}
+
 /*
  * Output metadata into this session's metadata buffers.
  */
@@ -910,6 +937,44 @@ int _lttng_session_metadata_statedump(struct lttng_session *session)
 	if (ret)
 		goto end;
 
+	ret = lttng_metadata_printf(session,
+		"clock {\n"
+		"	name = %s;\n"
+		"	uuid = %s;\n"
+		"	description = \"Monotonic Clock\";\n"
+		"	freq = %llu; /* Frequency, in Hz */\n"
+		"	/* clock value offset from Epoch is: offset * (1/freq) */\n"
+		"	offset = %llu;\n"
+		"};\n\n",
+		"monotonic",
+		trace_clock_uuid(),
+		(unsigned long long) trace_clock_freq(),
+		(unsigned long long) measure_clock_offset()
+		);
+	if (ret)
+		goto end;
+
+	ret = lttng_metadata_printf(session,
+		"typealias integer {\n"
+		"	size = 27; align = 1; signed = false;\n"
+		"	map = clock.monotonic.value;\n"
+		"} := uint27_clock_monotonic_t;\n"
+		"\n"
+		"typealias integer {\n"
+		"	size = 32; align = %u; signed = false;\n"
+		"	map = clock.monotonic.value;\n"
+		"} := uint32_clock_monotonic_t;\n"
+		"\n"
+		"typealias integer {\n"
+		"	size = 64; align = %u; signed = false;\n"
+		"	map = clock.monotonic.value;\n"
+		"} := uint64_clock_monotonic_t;\n\n",
+		lttng_alignof(uint32_t) * CHAR_BIT,
+		lttng_alignof(uint64_t) * CHAR_BIT
+		);
+	if (ret)
+		goto end;
+
 	ret = _lttng_stream_packet_context_declare(session);
 	if (ret)
 		goto end;
diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index d2579725..1140b94b 100644
--- a/wrapper/trace-clock.h
+++ b/wrapper/trace-clock.h
@@ -44,14 +44,14 @@ static inline u64 trace_clock_read64(void)
 	return (u64) trace_clock_monotonic_wrapper();
 }
 
-static inline u64 trace_clock_frequency(void)
+static inline u64 trace_clock_freq(void)
 {
-	return (u64)NSEC_PER_SEC;
+	return (u64) NSEC_PER_SEC;
 }
 
-static inline u32 trace_clock_freq_scale(void)
+static inline const char *trace_clock_uuid(void)
 {
-	return 1;
+	return "CLOCK_MONOTONIC";
 }
 
 static inline int get_trace_clock(void)
-- 
2.34.1