perf ftrace: Add option '--inherit' to trace children processes

This adds an option '--inherit' to allow us trace children
processes spawned by our target.
Signed-off-by: Changbin Du <changbin.du@gmail.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: http://lore.kernel.org/lkml/20200808023141.14227-7-changbin.du@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-ftrace.txt

@@ -58,6 +58,9 @@ 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=::
 	Select function tracer and set function filter on the given

tools/perf/builtin-ftrace.c

@@ -41,6 +41,7 @@ struct perf_ftrace {
 	struct list_head	nograph_funcs;
 	int			graph_depth;
 	unsigned long		percpu_buffer_size;
+	bool			inherit;
 };
 
 struct filter_entry {
@@ -182,9 +183,27 @@ 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)
@@ -203,6 +222,7 @@ static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
 		return -1;
 
 	reset_tracing_filters();
+	reset_tracing_options(ftrace);
 	return 0;
 }
 
@@ -341,6 +361,17 @@ 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;
@@ -410,6 +441,11 @@ 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;
+	}
+
 	if (write_tracing_file("current_tracer", ftrace->tracer) < 0) {
 		pr_err("failed to set current_tracer to %s\n", ftrace->tracer);
 		goto out_reset;
@@ -618,6 +654,8 @@ 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()
 	};