[PATCH 14/15] kernel-shark: Add methods for time calibration

["Yordan Karadzhov (VMware)" <y.karadz@gmail.com>]

We add an infrastructure for correcting the timestamps of the entries.
This is needed in order to correlate Data streams that have been
recorded using non-synchronized clocks. The infrastructure can handle
an arbitrary timestamps correction formula, however for the moment we
only provide calibration that adds a constant offset.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
 src/libkshark.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/libkshark.h |  6 +++++
 2 files changed, 73 insertions(+)

diff --git a/src/libkshark.c b/src/libkshark.c
index 02927d2..667ebbe 100644
--- a/src/libkshark.c
+++ b/src/libkshark.c
@@ -1184,6 +1184,73 @@ kshark_get_entry_back(const struct kshark_entry_request *req,
 	return get_entry(req, data, index, req->first, end, -1);
 }
 
+static int compare_time(const void* a, const void* b)
+{
+	const struct kshark_entry *entry_a, *entry_b;
+
+	entry_a = *(const struct kshark_entry **) a;
+	entry_b = *(const struct kshark_entry **) b;
+
+	if (entry_a->ts > entry_b->ts)
+		return 1;
+
+	if (entry_a->ts < entry_b->ts)
+		return -1;
+
+	return 0;
+}
+
+static void kshark_data_qsort(struct kshark_entry **entries, size_t size)
+{
+	qsort(entries, size, sizeof(struct kshark_entry *), compare_time);
+}
+
+/**
+ * Add constant offset to the timestamp of the entry. To be used by the sream
+ * object as a System clock calibration callback function.
+ */
+void kshark_offset_calib(int64_t *ts, int64_t *argv)
+{
+	*ts += argv[0];
+}
+
+/**
+ * @brief Apply constant offset to the timestamps of all entries from a given
+ *	  Data stream.
+ *
+ * @param kshark_ctx: Input location for the session context pointer.
+ * @param entries: Input location for the trace data.
+ * @param size: The size of the trace data.
+ * @param sd: Data stream identifier.
+ * @param offset: The constant offset to be added (in nanosecond).
+ */
+void kshark_set_clock_offset(struct kshark_context *kshark_ctx,
+			     struct kshark_entry **entries, size_t size,
+			     int sd, int64_t offset)
+{
+	struct kshark_data_stream *stream;
+	int64_t correction;
+
+	stream = kshark_get_data_stream(kshark_ctx, sd);
+	if (!stream)
+		return;
+
+	if (!stream->calib_array) {
+		stream->calib = kshark_offset_calib;
+		stream->calib_array = calloc(1, sizeof(*stream->calib_array));
+		stream->calib_array_size = 1;
+	}
+
+	correction = offset - stream->calib_array[0];
+	stream->calib_array[0] = offset;
+
+	for (size_t i = 0; i < size; ++i)
+		if (entries[i]->stream_id == sd)
+			entries[i]->ts += correction;
+
+	kshark_data_qsort(entries, size);
+}
+
 static int first_in_time_entry(struct kshark_entry_data_set *buffer, int n_buffers, size_t *count)
 {
 	int64_t t_min = INT64_MAX;
diff --git a/src/libkshark.h b/src/libkshark.h
index 6878d6d..b39a107 100644
--- a/src/libkshark.h
+++ b/src/libkshark.h
@@ -1096,6 +1096,12 @@ struct kshark_config_doc *kshark_open_config_file(const char *file_name,
 
 struct kshark_config_doc *kshark_json_to_conf(struct json_object *jobj);
 
+void kshark_offset_calib(int64_t *ts, int64_t *atgv);
+
+void kshark_set_clock_offset(struct kshark_context *kshark_ctx,
+			     struct kshark_entry **entries, size_t size,
+			     int sd, int64_t offset);
+
 /** Structure representing a data set made of KernelShark entries. */
 struct kshark_entry_data_set {
 	/** Array of entries pointers. */
-- 
2.25.1