perf scripting python: Add function to get a config value

This can be used to get config values like which objdump Perf uses for
disassembly.

Reviewed-by: Leo Yan <[e-mail]>
Signed-off-by: James Clark <[e-mail]>
Tested-by: Ganapatrao Kulkarni <[e-mail]>
Cc: Ben Gainey <[e-mail]>
Cc: Suzuki K Poulose <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Mathieu Poirier <[e-mail]>
Cc: Mike Leach <[e-mail]>
Cc: Ruidong Tian <[e-mail]>
Cc: Leo Yan <[e-mail]>
Cc: Benjamin Gray <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: John Garry <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/Documentation/perf-script-python.txt

···
  perf_set_itrace_options(context, itrace_options) - set --itrace options if they have not been set already
  perf_sample_srcline(context) - returns source_file_name, line_number
  perf_sample_srccode(context) - returns source_file_name, line_number, source_line
-
+ perf_config_get(config_name) - returns the value of the named config item, or None if unset
 
 Util.py Module
 ~~~~~~~~~~~~~~

tools/perf/scripts/python/Perf-Trace-Util/Context.c

···
 #define PY_SSIZE_T_CLEAN
 
 #include <Python.h>
+#include "../../../util/config.h"
 #include "../../../util/trace-event.h"
 #include "../../../util/event.h"
 #include "../../../util/symbol.h"
···
 	return perf_sample_src(obj, args, true);
 }
 
+static PyObject *__perf_config_get(PyObject *obj, PyObject *args)
+{
+	const char *config_name;
+
+	if (!PyArg_ParseTuple(args, "s", &config_name))
+		return NULL;
+	return Py_BuildValue("s", perf_config_get(config_name));
+}
+
 static PyMethodDef ContextMethods[] = {
 #ifdef HAVE_LIBTRACEEVENT
 	{ "common_pc", perf_trace_context_common_pc, METH_VARARGS,
···
 	  METH_VARARGS,	"Get source file name and line number."},
 	{ "perf_sample_srccode", perf_sample_srccode,
 	  METH_VARARGS,	"Get source file name, line number and line."},
+	{ "perf_config_get", __perf_config_get, METH_VARARGS, "Get perf config entry"},
 	{ NULL, NULL, 0, NULL}
 };
 

tools/perf/util/config.c

···
 struct perf_config_scan_data {
 	const char *name;
 	const char *fmt;
+	const char *value;
 	va_list args;
 	int ret;
 };
···
 	va_end(d.args);
 
 	return d.ret;
+}
+
+static int perf_config_get_cb(const char *var, const char *value, void *data)
+{
+	struct perf_config_scan_data *d = data;
+
+	if (!strcmp(var, d->name))
+		d->value = value;
+
+	return 0;
+}
+
+const char *perf_config_get(const char *name)
+{
+	struct perf_config_scan_data d = {
+		.name = name,
+		.value = NULL,
+	};
+
+	perf_config(perf_config_get_cb, &d);
+	return d.value;
 }

tools/perf/util/config.h

···
 int perf_default_config(const char *, const char *, void *);
 int perf_config(config_fn_t fn, void *);
 int perf_config_scan(const char *name, const char *fmt, ...) __scanf(2, 3);
+const char *perf_config_get(const char *name);
 int perf_config_set(struct perf_config_set *set,
 		    config_fn_t fn, void *data);
 int perf_config_int(int *dest, const char *, const char *);