Date:   Mon, 13 Jul 2020 10:49:40 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 02/17] perf ftrace: add option '-F/--funcs' to list
 available functions

Hello,

On Sat, Jul 11, 2020 at 9:42 PM Changbin Du <changbin.du@...il.com> wrote:
>
> This adds an option '-F/--funcs' to list all available functions to trace,
> which is read from tracing file 'available_filter_functions'.
>
> $ sudo ./perf ftrace -F | head
> trace_initcall_finish_cb
> initcall_blacklisted
> do_one_initcall
> do_one_initcall
> trace_initcall_start_cb
> run_init_process
> try_to_run_init_process
> match_dev_by_label
> match_dev_by_uuid
> rootfs_init_fs_context
>
> Signed-off-by: Changbin Du <changbin.du@...il.com>
>
> ---
> v2: option name '-l/--list-functions' -> '-F/--funcs'
> ---
>  tools/perf/Documentation/perf-ftrace.txt |  4 +++
>  tools/perf/builtin-ftrace.c              | 43 ++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
>
> diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
> index 952e46669168..d79560dea19f 100644
> --- a/tools/perf/Documentation/perf-ftrace.txt
> +++ b/tools/perf/Documentation/perf-ftrace.txt
> @@ -30,6 +30,10 @@ OPTIONS
>  --verbose=::
>          Verbosity level.
>
> +-F::
> +--funcs::
> +        List all available functions to trace.
> +
>  -p::
>  --pid=::
>         Trace on existing process id (comma separated list).
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 5f53da87040d..244cc8e6bd60 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -32,6 +32,7 @@ struct perf_ftrace {
>         struct evlist           *evlist;
>         struct target           target;
>         const char              *tracer;
> +       bool                    list_avail_functions;
>         struct list_head        filters;
>         struct list_head        notrace;
>         struct list_head        graph_funcs;
> @@ -127,6 +128,43 @@ static int append_tracing_file(const char *name, const char *val)
>         return __write_tracing_file(name, val, true);
>  }
>
> +static int read_tracing_file_to_stdout(const char *name)
> +{
> +       char buf[4096];
> +       char *file;
> +       int fd;
> +       int ret = -1;
> +
> +       file = get_tracing_file(name);
> +       if (!file) {
> +               pr_debug("cannot get tracing file: %s\n", name);
> +               return -1;
> +       }
> +
> +       fd = open(file, O_RDONLY);
> +       if (fd < 0) {
> +               pr_debug("cannot open tracing file: %s: %s\n",
> +                        name, str_error_r(errno, buf, sizeof(buf)));
> +               goto out;
> +       }
> +
> +       /* read contents to stdout */
> +       while (true) {
> +               int n = read(fd, buf, sizeof(buf));
> +               if (n <= 0)
> +                       goto out_close;
> +               if (fwrite(buf, n, 1, stdout) != 1)
> +                       goto out_close;
> +       }
> +       ret = 0;

As I said before, there's no break in the loop above
so the ret can never be 0.

Thanks
Namhyung

> +
> +out_close:
> +       close(fd);
> +out:
> +       put_tracing_file(file);
> +       return ret;
> +}
> +
>  static int reset_tracing_cpu(void);
>  static void reset_tracing_filters(void);
>
> @@ -301,6 +339,9 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
>         signal(SIGCHLD, sig_handler);
>         signal(SIGPIPE, sig_handler);
>
> +       if (ftrace->list_avail_functions)
> +               return read_tracing_file_to_stdout("available_filter_functions");
> +
>         if (reset_tracing_files(ftrace) < 0) {
>                 pr_err("failed to reset ftrace\n");
>                 goto out;
> @@ -470,6 +511,8 @@ int cmd_ftrace(int argc, const char **argv)
>         const struct option ftrace_options[] = {
>         OPT_STRING('t', "tracer", &ftrace.tracer, "tracer",
>                    "tracer to use: function or function_graph (This option is deprecated)"),
> +       OPT_BOOLEAN('F', "funcs", &ftrace.list_avail_functions,
> +                   "Show available functions to filter"),
>         OPT_STRING('p', "pid", &ftrace.target.pid, "pid",
>                    "trace on existing process id"),
>         OPT_INCR('v', "verbose", &verbose,
> --
> 2.25.1
>

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