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

[duchangbin <changbin.du@huawei.com>]

On Wed, Sep 11, 2024 at 10:45:16AM +0100, James Clark wrote:
> 
> 
> 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@huawei.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;
> > +	}
> > +
> 
> 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.
>
Thansk, I will rebase this on perf-tools-next branch.

> Either way:
> 
> Reviewed-by: James Clark <james.clark@linaro.org>

-- 
Cheers,
Changbin Du