linux-kernel - Re: [PATCH v5 02/17] perf ftrace: add option '-F/--funcs' to list available functions

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Date:   Fri, 17 Jul 2020 11:05:04 -0400
From:   Steven Rostedt <rostedt@...dmis.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>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org,
        "linux-trace-devel@...r.kernel.org" 
        <linux-trace-devel@...r.kernel.org>
Subject: Re: [PATCH v5 02/17] perf ftrace: add option '-F/--funcs' to list
 available functions

On Sat, 11 Jul 2020 20:40:20 +0800
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)
> +{

All this is looking like its duplicating code that we are working on
for libtracefs. 

Would you like to start contributing to that, and when we get the
libtracefs.so packed in distributions, we can easily create the
perf ftrace without having to rewrite the wheel 10 times?

-- Steve


> +	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;
> +
> +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,