perf data: Add tracepoint fields when converting to JSON

When converting recorded data into JSON format, perf data omits probe
variables. Add them to the output in the format "field name": "field value"
using tep_print_field:

    $ perf data convert --to-json output.json

    // output.json
    {
        "linux-perf-json-version": 1,
        "headers": { ... },
        "samples": [
            {
            "timestamp": 29182079082999,
            "pid": 309194,
                    [...]
            "__probe_ip": "0x93ee35",
            "query_string_string": "select 2;",
            "nxids": "0"
            }
        ]
    }

Signed-off-by: Dmitrii Dolgov <[email protected]>
Acked-by: Ian Rogers <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/util/data-convert-json.c

@@ -217,6 +217,26 @@ static int process_sample_event(struct perf_tool *tool,
 	}
 	output_json_format(out, false, 3, "]");
 
+	if (sample->raw_data) {
+		int i;
+		struct tep_format_field **fields;
+
+		fields = tep_event_fields(evsel->tp_format);
+		if (fields) {
+			i = 0;
+			while (fields[i]) {
+				struct trace_seq s;
+
+				trace_seq_init(&s);
+				tep_print_field(&s, sample->raw_data, fields[i]);
+				output_json_key_string(out, true, 3, fields[i]->name, s.buffer);
+
+				i++;
+			}
+			free(fields);
+		}
+	}
+
 	output_json_format(out, false, 2, "}");
 	return 0;
 }