Re: [PATCH 2/2] perf: Fix ftrace builtin when kernel doesn't have function_graph

[Julien Thierry]

On 01/11/17 16:44, Steven Rostedt wrote:
> On Wed,  1 Nov 2017 14:33:44 +0000
> Julien Thierry <julien.thierry@xxxxxxx> wrote:
>
> > When linux is built without support for function graph tracer, the ftrace
> > builtin of perf will fail when trying to reset max_graph_depth because the
> > file does not exist. This prevents the use of function tracer from perf.
> >
> > Do not attempt to write this file when the tracer in use is not
> > function_graph.
> >
> > Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >   tools/perf/builtin-ftrace.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> > index 25a42ac..48120f2 100644
> > --- a/tools/perf/builtin-ftrace.c
> > +++ b/tools/perf/builtin-ftrace.c
> > @@ -130,7 +130,8 @@ static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
> >   	if (reset_tracing_cpu() < 0)
> >   		return -1;
> >
> > -	if (write_tracing_file("max_graph_depth", "0") < 0)
> > +	if (!strcmp(ftrace->tracer, "function_graph") &&
> > +	    write_tracing_file("max_graph_depth", "0") < 0)
>
> Hmm, instead of doing this, could we just do a stat on the file first.
> As with trace-cmd, I like to reset files like this even when not
> enabling function_graph tracer.

Sounds reasonable.

I'll include that change in the next version of the patches.

Thanks,

--
Julien Thierry