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

[Taeung Song]

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 <namhy...@kernel.org>
Cc: Jiri Olsa <jo...@kernel.org>
Cc: Wang Nan <wangn...@huawei.com>
Signed-off-by: Taeung Song <treeze.tae...@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