linux-kernel - Re: [PATCH v2] perf ftrace: Detect whether ftrace is enabled on system

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Message-ID: <c37492e5-6a1a-4506-810c-ec59056ee85b@linaro.org>
Date: Wed, 11 Sep 2024 11:15:19 +0100
From: James Clark <james.clark@...aro.org>
To: Changbin Du <changbin.du@...wei.com>
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, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v2] perf ftrace: Detect whether ftrace is enabled on
 system



On 11/09/2024 11:01, Changbin Du wrote:
> 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>
> 
> v2: rebase on perf-tools-next.
> ---
>   tools/perf/builtin-ftrace.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
> 
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 88a87bf387d2..abcdc49b7a98 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -80,6 +80,24 @@ static bool check_ftrace_capable(void)
>   	return false;
>   }
>   
> +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;
> +}
> +
>   static int __write_tracing_file(const char *name, const char *val, bool append)
>   {
>   	char *file;
> @@ -1583,6 +1601,11 @@ int cmd_ftrace(int argc, const char **argv)
>   	if (!check_ftrace_capable())
>   		return -1;
>   
> +	if (!is_ftrace_supported()) {
> +		pr_err("ftrace is not supported on this system\n");
> +		return -ENOTSUP;
> +	}
> +
>   	ret = perf_config(perf_ftrace_config, &ftrace);
>   	if (ret < 0)
>   		return -1;

Reviewed-by: James Clark <james.clark@...aro.org>