Re: [PATCH] perf ftrace: Detect whether ftrace is enabled on system

[James Clark]

On 10/09/2024 04:36, 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@xxxxxxxxxx>
> ---
>   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;
> +	}
> +

Very minor nit, but you could probably put this earlier next to 
check_ftrace_capable(). It didn't look like it used any of the config or 
parsing results.

Either way:

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