Re: [PATCH v5 07/17] perf ftrace: add option '--inherit' to trace children processes

[Namhyung Kim]

On Sat, Jul 11, 2020 at 9:42 PM Changbin Du <changbin.du@xxxxxxxxx> wrote:
>
> This adds an option '--inherit' to allow us trace children
> processes spawned by our target.
>
> Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>
>
> ---
> v2: option name '--trace-children' -> '--inherit'.
> ---
>  tools/perf/Documentation/perf-ftrace.txt |  3 ++
>  tools/perf/builtin-ftrace.c              | 38 ++++++++++++++++++++++++
>  2 files changed, 41 insertions(+)
>
> diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
> index 98fe01d354d1..fd632bd9b2c1 100644
> --- a/tools/perf/Documentation/perf-ftrace.txt
> +++ b/tools/perf/Documentation/perf-ftrace.txt
> @@ -61,6 +61,9 @@ OPTIONS
>         Set the size of per-cpu tracing buffer, <size> is expected to
>         be a number with appended unit character - B/K/M/G.
>
> +--inherit::
> +       Trace children processes spawned by our target.
> +
>  -T::
>  --trace-funcs=::
>         Only trace functions given by the argument.  Multiple functions
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 887e78b23a82..4efaa7b6a906 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -39,6 +39,7 @@ struct perf_ftrace {
>         struct list_head        nograph_funcs;
>         int                     graph_depth;
>         unsigned long           percpu_buffer_size;
> +       bool                    inherit;
>  };
>
>  struct filter_entry {
> @@ -177,9 +178,27 @@ static int write_tracing_file_int(const char *name, int value)
>         return 0;
>  }
>
> +static int write_tracing_option_file(const char *name, const char *val)
> +{
> +       char *file;
> +       int ret;
> +
> +       if (asprintf(&file, "options/%s", name) < 0)
> +               return -1;
> +
> +       ret = __write_tracing_file(file, val, false);
> +       free(file);
> +       return ret;
> +}
> +
>  static int reset_tracing_cpu(void);
>  static void reset_tracing_filters(void);
>
> +static void reset_tracing_options(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +       write_tracing_option_file("function-fork", "0");
> +}
> +
>  static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
>  {
>         if (write_tracing_file("tracing_on", "0") < 0)
> @@ -198,6 +217,7 @@ static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
>                 return -1;
>
>         reset_tracing_filters();
> +       reset_tracing_options(ftrace);
>         return 0;
>  }
>
> @@ -336,6 +356,17 @@ static int set_tracing_percpu_buffer_size(struct perf_ftrace *ftrace)
>         return 0;
>  }
>
> +static int set_tracing_trace_inherit(struct perf_ftrace *ftrace)
> +{
> +       if (!ftrace->inherit)
> +               return 0;
> +
> +       if (write_tracing_option_file("function-fork", "1") < 0)
> +               return -1;
> +
> +       return 0;
> +}
> +
>  static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
>  {
>         char *trace_file;
> @@ -405,6 +436,11 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
>                 goto out_reset;
>         }
>
> +       if (set_tracing_trace_inherit(ftrace) < 0) {
> +               pr_err("failed to set tracing option function-fork\n");
> +               goto out_reset;
> +       }

Can we have set_tracing_options() here instead to make
the __cmd_ftrace() shorter?  It'd set other options added later.
It's also symmetric to reset_tracing_options().

Thanks
Namhyung

> +
>         if (write_tracing_file("current_tracer", ftrace->tracer) < 0) {
>                 pr_err("failed to set current_tracer to %s\n", ftrace->tracer);
>                 goto out_reset;
> @@ -599,6 +635,8 @@ int cmd_ftrace(int argc, const char **argv)
>                     "Max depth for function graph tracer"),
>         OPT_CALLBACK('m', "buffer-size", &ftrace.percpu_buffer_size, "size",
>                      "size of per cpu buffer", parse_buffer_size),
> +       OPT_BOOLEAN(0, "inherit", &ftrace.inherit,
> +                   "trace children processes"),
>         OPT_END()
>         };
>
> --
> 2.25.1
>