Re: [PATCH 2/4] perf ftrace: Factor out check_ftrace_capable()

[Namhyung Kim]

Hi Ian,

On Mon, Jul 29, 2024 at 11:23 AM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> On Sun, Jul 28, 2024 at 5:41 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> >
> > The check is a common part of the ftrace commands, let's move it out.
> >
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
>
> The whole ifdefs and perf_cap__capable seemed wrong, not least as we'd
> like the error message to be accurate not just when libcap is present,
> so I sent out;
> https://lore.kernel.org/lkml/20240729181931.2870851-1-irogers@xxxxxxxxxx/
> which I think can supersede this.

Thanks for the change!  I'll reply to the patch.
Namhyung

>
> > ---
> >  tools/perf/builtin-ftrace.c | 44 +++++++++++++++++--------------------
> >  1 file changed, 20 insertions(+), 24 deletions(-)
> >
> > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> > index 33c52ebda2fd..978608ecd89c 100644
> > --- a/tools/perf/builtin-ftrace.c
> > +++ b/tools/perf/builtin-ftrace.c
> > @@ -59,6 +59,22 @@ static void ftrace__workload_exec_failed_signal(int signo __maybe_unused,
> >         done = true;
> >  }
> >
> > +static int check_ftrace_capable(void)
> > +{
> > +       if (!(perf_cap__capable(CAP_PERFMON) ||
> > +             perf_cap__capable(CAP_SYS_ADMIN))) {
> > +               pr_err("ftrace only works for %s!\n",
> > +#ifdef HAVE_LIBCAP_SUPPORT
> > +               "users with the CAP_PERFMON or CAP_SYS_ADMIN capability"
> > +#else
> > +               "root"
> > +#endif
> > +               );
> > +               return -1;
> > +       }
> > +       return 0;
> > +}
> > +
> >  static int __write_tracing_file(const char *name, const char *val, bool append)
> >  {
> >         char *file;
> > @@ -586,18 +602,6 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace)
> >                 .events = POLLIN,
> >         };
> >
> > -       if (!(perf_cap__capable(CAP_PERFMON) ||
> > -             perf_cap__capable(CAP_SYS_ADMIN))) {
> > -               pr_err("ftrace only works for %s!\n",
> > -#ifdef HAVE_LIBCAP_SUPPORT
> > -               "users with the CAP_PERFMON or CAP_SYS_ADMIN capability"
> > -#else
> > -               "root"
> > -#endif
> > -               );
> > -               return -1;
> > -       }
> > -
> >         select_tracer(ftrace);
> >
> >         if (reset_tracing_files(ftrace) < 0) {
> > @@ -902,18 +906,6 @@ static int __cmd_latency(struct perf_ftrace *ftrace)
> >         };
> >         int buckets[NUM_BUCKET] = { };
> >
> > -       if (!(perf_cap__capable(CAP_PERFMON) ||
> > -             perf_cap__capable(CAP_SYS_ADMIN))) {
> > -               pr_err("ftrace only works for %s!\n",
> > -#ifdef HAVE_LIBCAP_SUPPORT
> > -               "users with the CAP_PERFMON or CAP_SYS_ADMIN capability"
> > -#else
> > -               "root"
> > -#endif
> > -               );
> > -               return -1;
> > -       }
> > -
> >         trace_fd = prepare_func_latency(ftrace);
> >         if (trace_fd < 0)
> >                 goto out;
> > @@ -1220,6 +1212,10 @@ int cmd_ftrace(int argc, const char **argv)
> >         signal(SIGCHLD, sig_handler);
> >         signal(SIGPIPE, sig_handler);
> >
> > +       ret = check_ftrace_capable();
> > +       if (ret < 0)
> > +               return -1;
> > +
> >         ret = perf_config(perf_ftrace_config, &ftrace);
> >         if (ret < 0)
> >                 return -1;
> > --
> > 2.46.0.rc1.232.g9752f9e123-goog
> >