linux-kernel - [PATCH] perf ftrace: Detect whether ftrace is enabled on system

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Message-ID: <20240910033625.3569729-1-changbin.du@huawei.com>
Date: Tue, 10 Sep 2024 11:36:25 +0800
From: Changbin Du <changbin.du@...wei.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim
	<namhyung@...nel.org>
CC: Mark Rutland <mark.rutland@....com>, Alexander Shishkin
	<alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, Ian
 Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, "Liang,
 Kan" <kan.liang@...ux.intel.com>, <linux-perf-users@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Changbin Du <changbin.du@...wei.com>
Subject: [PATCH] perf ftrace: Detect whether ftrace is enabled on system

To make error messages more accurate, this change detects whether ftrace is
enabled on system by checking trace file "set_ftrace_pid".

Before:
~ # perf ftrace
failed to reset ftrace

After:
~ # perf ftrace
ftrace is not supported on this system

Signed-off-by: Changbin Du <changbin.du@...wei.com>
---
 tools/perf/builtin-ftrace.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index eb30c8eca488..e1dc2768bc0f 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -1112,6 +1112,24 @@ static int parse_graph_tracer_opts(const struct option *opt,
 	return 0;
 }
 
+static bool is_ftrace_supported(void)
+{
+	char *file;
+	bool supported = false;
+
+	file = get_tracing_file("set_ftrace_pid");
+	if (!file) {
+		pr_debug("cannot get tracing file set_ftrace_pid\n");
+		return false;
+	}
+
+	if (!access(file, F_OK))
+		supported = true;
+
+	put_tracing_file(file);
+	return supported;
+}
+
 enum perf_ftrace_subcommand {
 	PERF_FTRACE_NONE,
 	PERF_FTRACE_TRACE,
@@ -1254,6 +1272,12 @@ int cmd_ftrace(int argc, const char **argv)
 		goto out_delete_filters;
 	}
 
+	if (!is_ftrace_supported()) {
+		pr_err("ftrace is not supported on this system\n");
+		ret = -ENOTSUP;
+		goto out_delete_filters;
+	}
+
 	ret = target__validate(&ftrace.target);
 	if (ret) {
 		char errbuf[512];
-- 
2.34.1