[PATCH v2 1/7] perf config: Add support for getting functionality

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

Add a functionality getting particular config key-value pairs.
For the syntax examples,

    perf config [<file-option>] [section.name ...]

e.g. To query config items 'report.queue-size' and 'report.children', do

    # perf config report.queue-size report.children

Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
---
 tools/perf/builtin-config.c | 42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-config.c b/tools/perf/builtin-config.c
index e4207a2..7b24789 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 * const config_usage[] = {
-	"perf config [<file-option>] [options]",
+	"perf config [<file-option>] [options] [section.name ...]",
 	NULL
 };
 
@@ -33,6 +33,36 @@ static struct option config_options[] = {
 	OPT_END()
 };
 
+static int show_spec_config(struct perf_config_set *set, const char *var)
+{
+	struct perf_config_section *section;
+	struct perf_config_item *item;
+
+	if (set == NULL || var == NULL)
+		return -1;
+
+	perf_config_items__for_each_entry(&set->sections, section) {
+		if (prefixcmp(var, section->name) != 0)
+			continue;
+
+		perf_config_items__for_each_entry(&section->items, item) {
+			const char *name = var + strlen(section->name) + 1;
+
+			if (strcmp(name, item->name) == 0) {
+				char *value = item->value;
+
+				if (value) {
+					printf("%s=%s\n", var, value);
+					return 0;
+				}
+			}
+
+		}
+	}
+
+	return 0;
+}
+
 static int show_config(struct perf_config_set *set)
 {
 	struct perf_config_section *section;
@@ -54,7 +84,7 @@ static int show_config(struct perf_config_set *set)
 
 int cmd_config(int argc, const char **argv, const char *prefix __maybe_unused)
 {
-	int ret = 0;
+	int i, ret = 0;
 	struct perf_config_set *set;
 	char *user_config = mkpath("%s/.perfconfig", getenv("HOME"));
 
@@ -100,7 +130,13 @@ int cmd_config(int argc, const char **argv, const char *prefix __maybe_unused)
 		}
 		break;
 	default:
-		usage_with_options(config_usage, config_options);
+		if (argc == 0) {
+			usage_with_options(config_usage, config_options);
+			break;
+		}
+
+		for (i = 0; argv[i]; i++)
+			ret = show_spec_config(set, argv[i]);
 	}
 
 	perf_config_set__delete(set);
-- 
2.7.4