[PATCH 3/3] trace-cmd: Get the timestamp of the first recorded event as TSC offset

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>]

When converting TSC timestamps to nanoseconds, an offset is used. That
offset is subtracted from each TSC timestamp, before the conversion. At
the end of the trace, the lowest recorded TSC timestamp is selected as
TSC offset, that will be used for tsc2nsec conversion.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 tracecmd/include/trace-local.h |   1 +
 tracecmd/trace-record.c        | 146 ++++++++++++++++++++++++++-------
 2 files changed, 116 insertions(+), 31 deletions(-)

diff --git a/tracecmd/include/trace-local.h b/tracecmd/include/trace-local.h
index 1218de12..d504ea14 100644
--- a/tracecmd/include/trace-local.h
+++ b/tracecmd/include/trace-local.h
@@ -213,6 +213,7 @@ struct buffer_instance {
 	char			*name;
 	struct tracefs_instance	*tracefs;
 	unsigned long long	trace_id;
+	unsigned long long	first_ts;
 	char			*cpumask;
 	char			*output_file;
 	struct event_list	*events;
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index fd03a605..a7093fa2 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -40,6 +40,7 @@
 #ifdef VSOCK
 #include <linux/vm_sockets.h>
 #endif
+#include <traceevent/kbuffer.h>
 
 #include "tracefs.h"
 #include "version.h"
@@ -685,34 +686,6 @@ add_tsc2nsec(struct tracecmd_output *handle, struct tsc_nsec *tsc2nsec)
 	tracecmd_add_option_v(handle, TRACECMD_OPTION_TSC2NSEC, vector, 3);
 }
 
-static void host_tsync_complete(struct common_record_context *ctx,
-				struct buffer_instance *instance)
-{
-	struct tracecmd_output *handle = NULL;
-	int fd = -1;
-	int ret;
-
-	ret = tracecmd_tsync_with_guest_stop(instance->tsync);
-	if (!ret) {
-		fd = open(instance->output_file, O_RDWR);
-		if (fd < 0)
-			die("error opening %s", instance->output_file);
-		handle = tracecmd_get_output_handle_fd(fd);
-		if (!handle)
-			die("cannot create output handle");
-
-		if (ctx->tsc2nsec.mult)
-			add_tsc2nsec(handle, &ctx->tsc2nsec);
-
-		tracecmd_write_guest_time_shift(handle, instance->tsync);
-		tracecmd_append_options(handle);
-		tracecmd_output_close(handle);
-	}
-
-	tracecmd_tsync_free(instance->tsync);
-	instance->tsync = NULL;
-}
-
 static void tell_guests_to_stop(struct common_record_context *ctx)
 {
 	struct buffer_instance *instance;
@@ -725,7 +698,7 @@ static void tell_guests_to_stop(struct common_record_context *ctx)
 
 	for_all_instances(instance) {
 		if (is_guest(instance))
-			host_tsync_complete(ctx, instance);
+			tracecmd_tsync_with_guest_stop(instance->tsync);
 	}
 
 	/* Wait for guests to acknowledge */
@@ -4183,7 +4156,100 @@ static void add_options(struct tracecmd_output *handle, struct common_record_con
 	free(clocks);
 }
 
-static void write_guest_file(struct buffer_instance *instance)
+int get_first_ts(char *file, unsigned long long *ts)
+{
+	enum kbuffer_long_size long_size;
+	enum kbuffer_endian endian;
+	struct kbuffer *kbuf = NULL;
+	int psize, rsize;
+	char *page = NULL;
+	int ret = -1;
+	char *data;
+	int fd;
+
+	fd = open(file, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	psize = getpagesize();
+	page = calloc(1, psize);
+	if (!page)
+		goto error;
+
+	rsize = read(fd, page, psize);
+	if (rsize <= 0)
+		goto error;
+
+	if (tracecmd_host_bigendian())
+		endian = KBUFFER_ENDIAN_BIG;
+	else
+		endian = KBUFFER_ENDIAN_LITTLE;
+	if (sizeof(long) == 8)
+		long_size = KBUFFER_LSIZE_8;
+	else
+		long_size = KBUFFER_LSIZE_4;
+
+	kbuf = kbuffer_alloc(long_size, endian);
+	if (!kbuf)
+		goto error;
+
+	kbuffer_load_subbuffer(kbuf, page);
+	if (kbuffer_subbuffer_size(kbuf) > rsize)
+		goto error;
+
+	data = kbuffer_read_event(kbuf, ts);
+	if (!data)
+		goto error;
+
+	ret = 0;
+error:
+	if (kbuf)
+		kbuffer_free(kbuf);
+	free(page);
+	close(fd);
+	return ret;
+}
+
+void get_first_ts_instance(struct buffer_instance *instance)
+{
+	struct tracecmd_ts_corrections corrections;
+	unsigned long long first_ts = 0;
+	unsigned long long ts;
+	unsigned int flags;
+	int first_ts_cpu;
+	char *file;
+	int ret;
+	int i;
+
+	for (i = 0; i < instance->cpu_count; i++) {
+		file = get_temp_file(instance, i);
+		if (!file)
+			continue;
+		if (!get_first_ts(file, &ts)) {
+			if (!first_ts || ts < first_ts) {
+				first_ts = ts;
+				first_ts_cpu = i;
+			}
+		}
+		put_temp_file(file);
+	}
+	if (first_ts) {
+		if (is_guest(instance)) {
+			ret = tracecmd_tsync_get_proto_flags(instance->tsync, &flags);
+			if (ret)
+				return;
+			ret =  tracecmd_tsync_get_offsets(instance->tsync, first_ts_cpu, &corrections);
+			if (ret)
+				return;
+			instance->first_ts = tracecmd_guest_ts_calc(first_ts, &corrections, flags);
+			free(corrections.ts_samples);
+		} else  {
+			instance->first_ts = first_ts;
+		}
+	}
+}
+
+static void write_guest_file(struct common_record_context *ctx, struct buffer_instance *instance)
 {
 	struct tracecmd_output *handle;
 	int cpu_count = instance->cpu_count;
@@ -4201,6 +4267,12 @@ static void write_guest_file(struct buffer_instance *instance)
 		die("error writing to %s", file);
 	if (instance->flags & BUFFER_FL_TSC2NSEC)
 		tracecmd_set_out_clock(handle, TSCNSEC_CLOCK);
+
+	if (ctx->tsc2nsec.mult)
+		add_tsc2nsec(handle, &ctx->tsc2nsec);
+	tracecmd_write_guest_time_shift(handle, instance->tsync);
+	tracecmd_append_options(handle);
+
 	temp_files = malloc(sizeof(*temp_files) * cpu_count);
 	if (!temp_files)
 		die("failed to allocate temp_files for %d cpus",
@@ -4219,6 +4291,9 @@ static void write_guest_file(struct buffer_instance *instance)
 	for (i = 0; i < cpu_count; i++)
 		put_temp_file(temp_files[i]);
 	free(temp_files);
+
+	tracecmd_tsync_free(instance->tsync);
+	instance->tsync = NULL;
 }
 
 static void record_data(struct common_record_context *ctx)
@@ -4231,9 +4306,18 @@ static void record_data(struct common_record_context *ctx)
 	char **temp_files;
 	int i;
 
+	if (ctx->tsc2nsec.mult) {
+		for_all_instances(instance) {
+			get_first_ts_instance(instance);
+			if (instance->first_ts &&
+			    (!ctx->tsc2nsec.offset || ctx->tsc2nsec.offset > instance->first_ts))
+				ctx->tsc2nsec.offset = instance->first_ts;
+		}
+	}
+
 	for_all_instances(instance) {
 		if (is_guest(instance))
-			write_guest_file(instance);
+			write_guest_file(ctx, instance);
 		else if (host && instance->msg_handle)
 			finish_network(instance->msg_handle);
 		else
-- 
2.30.2