bpf_perf_event_output() outputs data through sample->raw_data. This
patch adds support to convert those data into CTF. A python script then
can be used to process output data from BPF programs.

Test result:

  # cat ./test_bpf_output_2.c
  /************************ BEGIN **************************/
  #include <uapi/linux/bpf.h>
  struct bpf_map_def {
 	unsigned int type;
 	unsigned int key_size;
 	unsigned int value_size;
 	unsigned int max_entries;
  };
  #define SEC(NAME) __attribute__((section(NAME), used))
  static u64 (*ktime_get_ns)(void) =
 	(void *)BPF_FUNC_ktime_get_ns;
  static int (*trace_printk)(const char *fmt, int fmt_size, ...) =
 	(void *)BPF_FUNC_trace_printk;
  static int (*get_smp_processor_id)(void) =
 	(void *)BPF_FUNC_get_smp_processor_id;
  static int (*perf_event_output)(void *, struct bpf_map_def *, int, void *, unsigned long) =
 	(void *)BPF_FUNC_perf_event_output;

  struct bpf_map_def SEC("maps") channel = {
 	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
 	.key_size = sizeof(int),
 	.value_size = sizeof(u32),
 	.max_entries = __NR_CPUS__,
  };

  static inline int __attribute__((always_inline))
  func(void *ctx, int type)
  {
 	struct {
 		u64 ktime;
 		int type;
 	} __attribute__((packed)) output_data;
 	char error_data[] = "Error: failed to output\n";
 	int err;

 	output_data.type = type;
 	output_data.ktime = ktime_get_ns();
 	err = perf_event_output(ctx, &channel, get_smp_processor_id(),
 				&output_data, sizeof(output_data));
 	if (err)
 		trace_printk(error_data, sizeof(error_data));
 	return 0;
  }
  SEC("func_begin=sys_nanosleep")
  int func_begin(void *ctx) {return func(ctx, 1);}
  SEC("func_end=sys_nanosleep%return")
  int func_end(void *ctx) { return func(ctx, 2);}
  char _license[] SEC("license") = "GPL";
  int _version SEC("version") = LINUX_VERSION_CODE;
  /************************* END ***************************/

  # ./perf record -e bpf-output/no-inherit,name=evt/ \
                 -e ./test_bpf_output_2.c/map:channel.event=evt/ \
                 usleep 100000
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.012 MB perf.data (2 samples) ]

  # ./perf script
          usleep 14942 92503.198504: evt:  ffffffff810e0ba1 sys_nanosleep (/lib/modules/4.3.0....
          usleep 14942 92503.298562: evt:  ffffffff810585e9 kretprobe_trampoline_holder (/lib....

  # ./perf data convert --to-ctf ./out.ctf
  [ perf data convert: Converted 'perf.data' into CTF data './out.ctf' ]
  [ perf data convert: Converted and wrote 0.000 MB (2 samples) ]

  # babeltrace ./out.ctf
  [01:41:43.198504134] (+?.?????????) evt: { cpu_id = 0 }, { perf_ip = 0xFFFFFFFF810E0BA1, perf_tid = 14942, perf_pid = 14942, perf_id = 1044, raw_len = 3, raw_data = [ [0] = 0x32C0C07B, [1] = 0x5421, [2] = 0x1 ] }
  [01:41:43.298562257] (+0.100058123) evt: { cpu_id = 0 }, { perf_ip = 0xFFFFFFFF810585E9, perf_tid = 14942, perf_pid = 14942, perf_id = 1044, raw_len = 3, raw_data = [ [0] = 0x38B77FAA, [1] = 0x5421, [2] = 0x2 ] }

  # cat ./test_bpf_output_2.py
  from babeltrace import TraceCollection
  tc = TraceCollection()
  tc.add_trace('./out.ctf', 'ctf')
  d = {1:[], 2:[]}
  for event in tc.events:
     if not event.name.startswith('evt'):
         continue
     raw_data = event['raw_data']
     (time, type) = ((raw_data[0] + (raw_data[1] << 32)), raw_data[2])
     d[type].append(time)
  print(list(map(lambda i: d[2][i] - d[1][i], range(len(d[1])))));

  # python3 ./test_bpf_output_2.py
  [100056879]

Committer note:

Make sure you have python3-devel installed, not python-devel, which may
be for python2, which will lead to some "PyInstance_Type" errors. Also
make sure that you use the right libbabeltrace, because it is shipped
in Fedora, for instance, but an older version.

To build libbabeltrace's python binding one also needs to use:

 ./configure --enable-python-bindings

And then set PYTHONPATH=/usr/local/lib64/python3.4/site-packages/.
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1456479154-136027-9-git-send-email-wangnan0@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>