[PATCH v8 06/18] perf ftrace: add option '--inherit' to trace children processes

[Changbin Du]

This adds an option '--inherit' to allow us trace children
processes spawned by our target.

Signed-off-by: Changbin Du <changbin...@gmail.com>

---
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 7a5d915f60b0..c46d0a09b38c 100644
--- a/tools/perf/Documentation/perf-ftrace.txt
+++ b/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
diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 39c694be2b71..07b81d0c1658 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/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()
        };
 
-- 
2.25.1