perf tool: Provide an option to print perf_event_open args and return value

Perf record with verbose=2 already prints this information along with
whole lot of other traces which requires lot of scrolling. Introduce
an option to print only perf_event_open() arguments and return value.

Sample o/p:

  $ perf --debug perf-event-open=1 record -- ls > /dev/null
  ------------------------------------------------------------
  perf_event_attr:
    size                             112
    { sample_period, sample_freq }   4000
    sample_type                      IP|TID|TIME|PERIOD
    read_format                      ID
    disabled                         1
    inherit                          1
    exclude_kernel                   1
    mmap                             1
    comm                             1
    freq                             1
    enable_on_exec                   1
    task                             1
    precise_ip                       3
    sample_id_all                    1
    exclude_guest                    1
    mmap2                            1
    comm_exec                        1
    ksymbol                          1
    bpf_event                        1
  ------------------------------------------------------------
  sys_perf_event_open: pid 4308  cpu 0  group_fd -1  flags 0x8 = 4
  sys_perf_event_open: pid 4308  cpu 1  group_fd -1  flags 0x8 = 5
  sys_perf_event_open: pid 4308  cpu 2  group_fd -1  flags 0x8 = 6
  sys_perf_event_open: pid 4308  cpu 3  group_fd -1  flags 0x8 = 8
  sys_perf_event_open: pid 4308  cpu 4  group_fd -1  flags 0x8 = 9
  sys_perf_event_open: pid 4308  cpu 5  group_fd -1  flags 0x8 = 10
  sys_perf_event_open: pid 4308  cpu 6  group_fd -1  flags 0x8 = 11
  sys_perf_event_open: pid 4308  cpu 7  group_fd -1  flags 0x8 = 12
  ------------------------------------------------------------
  perf_event_attr:
    type                             1
    size                             112
    config                           0x9
    watermark                        1
    sample_id_all                    1
    bpf_event                        1
    { wakeup_events, wakeup_watermark } 1
  ------------------------------------------------------------
  sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8
  sys_perf_event_open failed, error -13
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.002 MB perf.data (9 samples) ]

Committer notes:

Just like the 'verbose' variable this new 'debug_peo_args' needs to be
added to util/python.c, since we don't link the debug.o file in the
python binding, which ended up making 'perf test python' fail with:

  # perf test -v python
  18: 'import perf' in python                               :
  --- start ---
  test child forked, pid 19237
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  ImportError: /tmp/build/perf/python/perf.so: undefined symbol: debug_peo_args
  test child finished with -1
  ---- end ----
  'import perf' in python: FAILED!
  #

After adding that new variable to util/python.c:

  # perf test -v python
  18: 'import perf' in python                               :
  --- start ---
  test child forked, pid 22364
  test child finished with 0
  ---- end ----
  'import perf' in python: Ok
  #

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20191108094128.28769-1-ravi.bangoria@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/tools/perf/util/debug.c b/tools/perf/util/debug.c
index e55114f0336f..adb656745ecc 100644
--- a/tools/perf/util/debug.c
+++ b/tools/perf/util/debug.c
@@ -24,6 +24,7 @@
 #include <linux/ctype.h>
 
 int verbose;
+int debug_peo_args;
 bool dump_trace = false, quiet = false;
 int debug_ordered_events;
 static int redirect_to_stderr;
@@ -180,6 +181,7 @@ static struct debug_variable {
 	{ .name = "ordered-events",	.ptr = &debug_ordered_events},
 	{ .name = "stderr",		.ptr = &redirect_to_stderr},
 	{ .name = "data-convert",	.ptr = &debug_data_convert },
+	{ .name = "perf-event-open",	.ptr = &debug_peo_args },
 	{ .name = NULL, }
 };