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Date:   Fri, 14 Aug 2020 08:35:35 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 02/18] perf ftrace: add option '-F/--funcs' to list
 available functions

Em Sat, Aug 08, 2020 at 10:31:25AM +0800, Changbin Du escreveu:
> 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>
> 
> ---
> v3: fix return value issue.
> v2: option name '-l/--list-functions' -> '-F/--funcs'
> ---
>  tools/perf/Documentation/perf-ftrace.txt |  4 +++
>  tools/perf/builtin-ftrace.c              | 46 ++++++++++++++++++++++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
> index 821d4d334a09..4f5628445a63 100644
> --- a/tools/perf/Documentation/perf-ftrace.txt
> +++ b/tools/perf/Documentation/perf-ftrace.txt
> @@ -31,6 +31,10 @@ 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 048a11192b59..1ebf71ecc1a8 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -33,6 +33,7 @@ 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;
> @@ -128,6 +129,46 @@ 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)
> +			break;
> +		else 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);
>  
> @@ -302,6 +343,9 @@ 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;
> @@ -487,6 +531,8 @@ int cmd_ftrace(int argc, const char **argv)
>  	const struct option ftrace_options[] = {
>  	OPT_STRING('t', "tracer", &ftrace.tracer, "tracer",
>  		   "tracer to use: function_graph(default) or function"),
> +	OPT_BOOLEAN('F', "funcs", &ftrace.list_avail_functions,
> +		    "Show available functions to filter"),

A boolean? I guess this can be a first step, but why not do it like
'perf probe' and accept a patterna? Allows for less typing:

  # perf probe -h -F

    -F, --funcs <[FILTER]>
                          Show potential probe-able functions.

[root@...co ~]#

# perf probe -F '*btf_parse*'
btf_parse_hdr
btf_parse_str_sec
btf_parse_vmlinux
#
# perf ftrace -F | grep btf_parse
btf_parse_str_sec
btf_parse_hdr
btf_parse_vmlinux
#

I'm applying this to make progress, but please consider sending a patch
to make this behave in the same way as 'perf probe'.

- Arnaldo


>  	OPT_STRING('p', "pid", &ftrace.target.pid, "pid",
>  		   "trace on existing process id"),
>  	OPT_INCR('v', "verbose", &verbose,
> -- 
> 2.25.1
> 

-- 

- Arnaldo

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