[RFC PATCH 3/4] perf data-convert: Add perf.data to trace.dat conversion backend

[Tanushree Shah <tshah@linux.ibm.com>]

Add data-convert-trace.c implementing trace_convert__perf2dat() to
convert perf.data tracepoint events to trace.dat format.

process_sample_event() is invoked for each PERF_TYPE_TRACEPOINT sample
during perf_session__process_events(), storing raw event bytes per-cpu
via trace_dat__collect_cpu_event().

Once all samples are collected:
- trace_dat__write_options_section1() writes the OPTIONS section with
  CPUCOUNT, TRACECLOCK, HEADER_INFO, FTRACE_EVENTS, EVENT_FORMATS,
  KALLSYMS, CMDLINES and DONE options.
- trace_dat__write__options_section2() writes the OPTIONS section with
  BUFFER option holding per-cpu data offset placeholders and the DONE
  option.
- trace_dat__write_flyrecord_section() builds ring buffer pages
  per-cpu and patches BUFFER option with final offsets and sizes

Per-cpu buffers are sized to tep_get_page_size() from the session
tep handle and released on all exit paths.

Signed-off-by: Tanushree Shah <tshah@linux.ibm.com>
---
 tools/perf/util/Build                |   1 +
 tools/perf/util/data-convert-trace.c | 152 +++++++++++++++++++++++++++
 tools/perf/util/data-convert.h       |   4 +
 3 files changed, 157 insertions(+)
 create mode 100644 tools/perf/util/data-convert-trace.c

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index c000d8032d25..88022b24e170 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -236,6 +236,7 @@ ifeq ($(CONFIG_LIBTRACEEVENT),y)
 endif
 
 perf-util-y += data-convert-json.o
+perf-util-$(CONFIG_LIBTRACEEVENT) += data-convert-trace.o
 
 perf-util-y += scripting-engines/
 
diff --git a/tools/perf/util/data-convert-trace.c b/tools/perf/util/data-convert-trace.c
new file mode 100644
index 000000000000..e4f8b817be36
--- /dev/null
+++ b/tools/perf/util/data-convert-trace.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 2026, IBM Corporation
+ * Author: Tanushree Shah <tshah@linux.ibm.com>
+ *
+ * data-convert-trace.c
+ *
+ * Implements perf.data to trace.dat format conversion for tracepoint events.
+ */
+
+#include <errno.h>
+#include <inttypes.h>
+#include <linux/compiler.h>
+#include <linux/err.h>
+
+#include "data-convert.h"
+#include "session.h"
+#include "evsel.h"
+#include "tool.h"
+#include "debug.h"
+#include "trace-dat.h"
+#include "trace-event.h"
+#include "event.h"
+#include "sample.h"
+#include "evlist.h"
+
+struct trace_convert {
+	struct perf_tool tool;
+	u64 events_count;
+};
+
+/* Store raw tracepoint event data in per-cpu buffer for trace.dat flyrecord */
+static int process_sample_event(const struct perf_tool *tool,
+				union perf_event *event __maybe_unused,
+				struct perf_sample *sample,
+				struct evsel *evsel,
+				struct machine *machine __maybe_unused)
+{
+	struct trace_convert *tc = container_of(tool, struct trace_convert, tool);
+
+	/* Collect raw tracepoint data per-cpu */
+	if (trace_dat_fp && sample->raw_size > 0 &&
+	    evsel->core.attr.type == PERF_TYPE_TRACEPOINT) {
+		if (trace_dat__collect_cpu_event(sample->cpu, sample->time,
+					sample->raw_data, sample->raw_size) < 0) {
+			pr_err("Failed to collect CPU event\n");
+			return -ENOMEM;
+		}
+		tc->events_count++;
+	}
+
+	return 0;
+}
+
+/* Convert perf.data tracepoint events to trace.dat format */
+int trace_convert__perf2dat(const char *input, const char *to_trace,
+			   struct perf_data_convert_opts *opts)
+{
+	struct perf_session *session;
+	struct trace_convert tc = {
+		.events_count = 0,
+	};
+	struct perf_data data = {
+		.path = input,
+		.mode = PERF_DATA_MODE_READ,
+		.force = opts->force,
+	};
+	int ret = -EINVAL;
+	bool cpu_buffers_initialized = false;
+
+	/* Initialize tool with all required callbacks */
+	perf_tool__init(&tc.tool, /*ordered_events=*/true);
+	tc.tool.sample = process_sample_event;
+
+	/* Open output trace.dat file */
+	trace_dat_fp = fopen(to_trace, "wb");
+	if (!trace_dat_fp) {
+		pr_err("Failed to open output file: %s\n", to_trace);
+		return -EINVAL;
+	}
+
+	/* Open perf.data session - this writes trace.dat metadata sections */
+	session = perf_session__new(&data, &tc.tool);
+	if (IS_ERR(session)) {
+		pr_err("Failed to open perf.data file\n");
+		ret = PTR_ERR(session);
+		goto out_close;
+	}
+
+	/* Initialize per-CPU buffers for flyrecord data */
+	if (session->tevent.pevent) {
+		trace_dat_page_size = tep_get_page_size(session->tevent.pevent);
+		if (trace_dat__init_cpu_buffers(session->header.env.nr_cpus_online) < 0) {
+			pr_err("Failed to initialize CPU buffers\n");
+			ret = -ENOMEM;
+			goto out_delete;
+		}
+		cpu_buffers_initialized = true;
+	}
+
+	/* Process all events - collects raw data per-cpu */
+	ret = perf_session__process_events(session);
+	if (ret < 0) {
+		pr_err("Failed to process events\n");
+		goto out_delete;
+	}
+
+	/* Skip file creation if no tracepoint events found */
+	if (tc.events_count == 0) {
+		pr_warning("No tracepoint events found in '%s', skipping trace.dat creation\n",
+			input);
+		ret = -EINVAL;
+		goto out_delete;
+	}
+
+	/* Write trace.dat options and flyrecord sections */
+	if (trace_dat__write_options_section1() < 0) {
+		pr_err("Failed to write options section1\n");
+		ret = -EIO;
+		goto out_delete;
+	}
+	if (trace_dat__write_options_section2() < 0) {
+		pr_err("Failed to write options section2\n");
+		ret = -EIO;
+		goto out_delete;
+	}
+	if (trace_dat__write_flyrecord_section() < 0) {
+		pr_err("Failed to write flyrecord section\n");
+		ret = -EIO;
+		goto out_delete;
+	}
+
+	pr_info("[ perf data convert: Converted '%s' into trace.dat format '%s' ]\n",
+		input, to_trace);
+	pr_info("[ perf data convert: Converted %llu events ]\n",
+		(unsigned long long)tc.events_count);
+
+	ret = 0;
+
+out_delete:
+	if (cpu_buffers_initialized)
+		trace_dat__free_cpu_buffers();
+	perf_session__delete(session);
+out_close:
+	if (trace_dat_fp) {
+		fclose(trace_dat_fp);
+		trace_dat_fp = NULL;
+	}
+	if (ret != 0)
+		unlink(to_trace);
+	return ret;
+}
diff --git a/tools/perf/util/data-convert.h b/tools/perf/util/data-convert.h
index ee651fa680a1..d958e68367fe 100644
--- a/tools/perf/util/data-convert.h
+++ b/tools/perf/util/data-convert.h
@@ -19,4 +19,8 @@ int bt_convert__perf2ctf(const char *input_name, const char *to_ctf,
 int bt_convert__perf2json(const char *input_name, const char *to_ctf,
 			 struct perf_data_convert_opts *opts);
 
+#ifdef HAVE_LIBTRACEEVENT
+int trace_convert__perf2dat(const char *input, const char *to_trace,
+			   struct perf_data_convert_opts *opts);
+#endif /* HAVE_LIBTRACEEVENT */
 #endif /* __DATA_CONVERT_H */
-- 
2.53.0