[PATCH 3/5] trace-cmd library: Store the timestamp of the first event when reading a trace file

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

When reading a trace file, detect and store the timestamp of the first
recorded event. A new API is introduced to get the first ts from an input
handler:
 tracecmd_get_first_ts()
The first ts can be used by the library users to align timestamps of the
events, when displaying them.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/trace-cmd/trace-cmd.h |  1 +
 lib/trace-cmd/trace-input.c   | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/include/trace-cmd/trace-cmd.h b/include/trace-cmd/trace-cmd.h
index 162cd318..022720b0 100644
--- a/include/trace-cmd/trace-cmd.h
+++ b/include/trace-cmd/trace-cmd.h
@@ -37,6 +37,7 @@ int tracecmd_get_guest_cpumap(struct tracecmd_input *handle,
 			      unsigned long long trace_id,
 			      const char **name,
 			      int *vcpu_count, const int **cpu_pid);
+unsigned long long tracecmd_get_first_ts(struct tracecmd_input *handle);
 int tracecmd_buffer_instances(struct tracecmd_input *handle);
 const char *tracecmd_buffer_instance_name(struct tracecmd_input *handle, int indx);
 struct tracecmd_input *tracecmd_buffer_instance_handle(struct tracecmd_input *handle, int indx);
diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index bacf9ccf..284f25e8 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -61,6 +61,7 @@ struct cpu_data {
 	unsigned long long	offset;
 	unsigned long long	size;
 	unsigned long long	timestamp;
+	unsigned long long	first_ts;
 	struct list_head	page_maps;
 	struct page_map		*page_map;
 	struct page		**pages;
@@ -2273,6 +2274,7 @@ static int init_cpu(struct tracecmd_input *handle, int cpu)
 
 	if (update_page_info(handle, cpu))
 		goto fail;
+	cpu_data->first_ts = cpu_data->timestamp;
 
 	return 0;
  fail:
@@ -4072,6 +4074,27 @@ unsigned long long tracecmd_get_traceid(struct tracecmd_input *handle)
 	return handle->trace_id;
 }
 
+/**
+ * tracecmd_get_first_ts - get the timestamp of the first recorded event
+ * @handle: input handle for the trace.dat file
+ *
+ * Returns the timestamp of the first recorded event
+ */
+unsigned long long tracecmd_get_first_ts(struct tracecmd_input *handle)
+{
+	unsigned long long ts = 0;
+	bool first = true;
+	int i;
+
+	for (i = 0; i < handle->cpus; i++) {
+		if (first || ts > handle->cpu_data[i].first_ts)
+			ts = handle->cpu_data[i].first_ts;
+		first = false;
+	}
+
+	return ts;
+}
+
 /**
  * tracecmd_get_guest_cpumap - get the mapping of guest VCPU to host process
  * @handle: input handle for the trace.dat file
-- 
2.30.2