[PATCH v5 4/6] perf config: Add 'get' functionality

[Taeung Song <treeze.taeung@gmail.com>]

This patch consists of functions
which can get specific config variables.
For the syntax examples,

   perf config [options] [section.name ...]

   display key-value pairs of specific config variables
   # perf config report.queue-size report.children

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
---
 tools/perf/Documentation/perf-config.txt |  2 +
 tools/perf/builtin-config.c              | 79 ++++++++++++++++++++++++++++++--
 tools/perf/util/cache.h                  |  1 +
 3 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-config.txt b/tools/perf/Documentation/perf-config.txt
index d95baad..691d52b 100644
--- a/tools/perf/Documentation/perf-config.txt
+++ b/tools/perf/Documentation/perf-config.txt
@@ -8,6 +8,8 @@ perf-config - Get and set variables in a configuration file.
 SYNOPSIS
 --------
 [verse]
+'perf config' [<file-option>] [section.name ...]
+or
 'perf config' [<file-option>] -l | --list
 or
 'perf config' [<file-option>] -a | --list-all
diff --git a/tools/perf/builtin-config.c b/tools/perf/builtin-config.c
index ac13aaf..0f2193a 100644
--- a/tools/perf/builtin-config.c
+++ b/tools/perf/builtin-config.c
@@ -17,7 +17,7 @@ static bool use_system_config, use_user_config;
 static const char *config_file_name;
 
 static const char * const config_usage[] = {
-	"perf config [options]",
+	"perf config [options] [section.name ...]",
 	NULL
 };
 
@@ -412,6 +412,37 @@ static void find_config(struct config_section **section_node,
 		*element_node = NULL;
 }
 
+static int show_spec_config(const char *section_name, const char *name)
+{
+	int i;
+	struct config_section *section_node = NULL;
+	struct config_element *element_node = NULL;
+	char key[BUFSIZ];
+
+	find_config(&section_node, &element_node, section_name, name);
+
+	if (section_node && element_node) {
+		scnprintf(key, sizeof(key), "%s.%s",
+			  section_node->name, element_node->name);
+		return show_config(key, element_node->value, NULL);
+	}
+
+	for (i = 0; default_configsets[i].section_name != NULL; i++) {
+		struct default_configset *config = &default_configsets[i];
+
+		if (!strcmp(config->section_name, section_name) &&
+		    !strcmp(config->name, name)) {
+			printf("%s.%s=%s (default)\n", config->section_name,
+			       config->name, config->value);
+			return 0;
+		}
+	}
+
+	pr_err("Error: %s.%s: failed to find the variable.\n", section_name, name);
+
+	return 0;
+}
+
 static char *normalize_value(const char *section_name, const char *name, const char *value)
 {
 	int i, ret = 0;
@@ -526,9 +557,44 @@ static int show_all_config(void)
 	return 0;
 }
 
+static int perf_configset_with_option(configset_fn_t fn, const char *var)
+{
+	char *section_name;
+	char *name;
+	const char *last_dot;
+	char *key = strdup(var);
+
+	if (!key) {
+		pr_err("%s: strdup failed\n", __func__);
+		return -1;
+	}
+	last_dot = strchr(key, '.');
+	/*
+	 * Since "key" actually contains the section name and the real
+	 * key name separated by a dot, we have to know where the dot is.
+	 */
+	if (last_dot == NULL || last_dot == key) {
+		pr_err("The config variable does not contain a section: %s\n", key);
+		return -1;
+	}
+	if (!last_dot[1]) {
+		pr_err("The config varible does not contain variable name: %s\n", key);
+		return -1;
+	}
+
+	section_name = strsep(&key, ".");
+	name = strsep(&key, ".");
+	free(key);
+
+	return fn(section_name, name);
+
+	pr_err("invalid key: %s\n", var);
+	return -1;
+}
+
 int cmd_config(int argc, const char **argv, const char *prefix __maybe_unused)
 {
-	int ret = 0;
+	int i, ret = 0;
 
 	argc = parse_options(argc, argv, config_options, config_usage,
 			     PARSE_OPT_STOP_AT_NON_OPTION);
@@ -552,10 +618,17 @@ int cmd_config(int argc, const char **argv, const char *prefix __maybe_unused)
 			break;
 		}
 	case ACTION_LIST:
-	default:
 		if (argc) {
 			pr_err("Error: unknown argument\n");
 			goto out_err;
+		}
+	default:
+		if (argc) {
+			for (i = 0; argv[i]; i++) {
+				ret = perf_configset_with_option(show_spec_config, argv[i]);
+				if (ret < 0)
+					break;
+			}
 		} else
 			ret = perf_config_from_file(show_config, config_file_name, NULL);
 	}
diff --git a/tools/perf/util/cache.h b/tools/perf/util/cache.h
index f49a5e2..6fe734c 100644
--- a/tools/perf/util/cache.h
+++ b/tools/perf/util/cache.h
@@ -34,6 +34,7 @@ struct config_section {
 
 struct list_head sections;
 
+typedef int (*configset_fn_t)(const char *, const char *);
 typedef int (*config_fn_t)(const char *, const char *, void *);
 extern int perf_default_config(const char *, const char *, void *);
 extern int perf_config(config_fn_t fn, void *);
-- 
1.9.1