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

[Ian Rogers]

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,
Ian

> ---
>  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
>