perf python: Add metrics function

The metrics function returns a list dictionaries describing metrics as
strings mapping to strings, except for metric groups that are a string
mapping to a list of strings. For example:
```
>>> import perf
>>> perf.metrics()[0]
{'MetricGroup': ['Power'], 'MetricName': 'C10_Pkg_Residency',
'PMU': 'default_core', 'MetricExpr': 'cstate_pkg@c10\\-residency@ / TSC',
'ScaleUnit': '100%', 'BriefDescription': 'C10 residency percent per package'}
```

Reviewed-by: Howard Chu <[e-mail]>
Signed-off-by: Ian Rogers <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Chun-Tse Shao <[e-mail]>
Cc: Collin Funk <[e-mail]>
Cc: Dr. David Alan Gilbert <[e-mail]>
Cc: Gautam Menghani <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Masami Hiramatsu <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Falcon <[e-mail]>
Cc: Thomas Richter <[e-mail]>
Cc: Tiezhu Yang <[e-mail]>
Cc: Weilin Wang <[e-mail]>
Cc: Xu Yang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/python.c

···
 	return result;
 }
 
+static PyObject *pyrf__metrics_groups(const struct pmu_metric *pm)
+{
+	PyObject *groups = PyList_New(/*len=*/0);
+	const char *mg = pm->metric_group;
+
+	if (!groups)
+		return NULL;
+
+	while (mg) {
+		PyObject *val = NULL;
+		const char *sep = strchr(mg, ';');
+		size_t len = sep ? (size_t)(sep - mg) : strlen(mg);
+
+		if (len > 0) {
+			val = PyUnicode_FromStringAndSize(mg, len);
+			if (val)
+				PyList_Append(groups, val);
+
+			Py_XDECREF(val);
+		}
+		mg = sep ? sep + 1 : NULL;
+	}
+	return groups;
+}
+
+static int pyrf__metrics_cb(const struct pmu_metric *pm,
+			    const struct pmu_metrics_table *table __maybe_unused,
+			    void *vdata)
+{
+	PyObject *py_list = vdata;
+	PyObject *dict = PyDict_New();
+	PyObject *key = dict ? PyUnicode_FromString("MetricGroup") : NULL;
+	PyObject *value = key ? pyrf__metrics_groups(pm) : NULL;
+
+	if (!value || PyDict_SetItem(dict, key, value) != 0) {
+		Py_XDECREF(key);
+		Py_XDECREF(value);
+		Py_XDECREF(dict);
+		return -ENOMEM;
+	}
+
+	if (!add_to_dict(dict, "MetricName", pm->metric_name) ||
+	    !add_to_dict(dict, "PMU", pm->pmu) ||
+	    !add_to_dict(dict, "MetricExpr", pm->metric_expr) ||
+	    !add_to_dict(dict, "MetricThreshold", pm->metric_threshold) ||
+	    !add_to_dict(dict, "ScaleUnit", pm->unit) ||
+	    !add_to_dict(dict, "Compat", pm->compat) ||
+	    !add_to_dict(dict, "BriefDescription", pm->desc) ||
+	    !add_to_dict(dict, "PublicDescription", pm->long_desc) ||
+	    PyList_Append(py_list, dict) != 0) {
+		Py_DECREF(dict);
+		return -ENOMEM;
+	}
+	Py_DECREF(dict);
+	return 0;
+}
+
+static PyObject *pyrf__metrics(PyObject *self, PyObject *args)
+{
+	const struct pmu_metrics_table *table = pmu_metrics_table__find();
+	PyObject *list = PyList_New(/*len=*/0);
+	int ret;
+
+	if (!list)
+		return NULL;
+
+	ret = pmu_metrics_table__for_each_metric(table, pyrf__metrics_cb, list);
+	if (!ret)
+		ret = pmu_for_each_sys_metric(pyrf__metrics_cb, list);
+
+	if (ret) {
+		Py_DECREF(list);
+		errno = -ret;
+		PyErr_SetFromErrno(PyExc_OSError);
+		return NULL;
+	}
+	return list;
+}
+
 static PyMethodDef perf__methods[] = {
+	{
+		.ml_name  = "metrics",
+		.ml_meth  = (PyCFunction) pyrf__metrics,
+		.ml_flags = METH_NOARGS,
+		.ml_doc	  = PyDoc_STR(
+			"Returns a list of metrics represented as string values in dictionaries.")
+	},
 	{
 		.ml_name  = "tracepoint",
 		.ml_meth  = (PyCFunction) pyrf__tracepoint,