perf config: Add support setting variables in a config file

Add setting feature that can add config variables with their values to a
config file (i.e. user or system config file) or modify config key-value
pairs in a config file.  For the syntax examples:

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

e.g. You can set the ui.show-headers to false with

    # perf config ui.show-headers=false

If you want to add or modify several config items, you can do like

    # perf config annotate.show_nr_jumps=false kmem.default=slab

Committer notes:

Testing it:

  $ perf config -l
  top.children=true
  report.children=false
  $
  $ perf config top.children=false
  $ perf config -l
  top.children=false
  report.children=false
  $
  $ perf config kmem.default=slab
  $ perf config -l
  top.children=false
  report.children=false
  kmem.default=slab
  $

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Nambong Ha <over3025@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Wookje Kwon <aweee0@gmail.com>
Link: http://lkml.kernel.org/r/1478241862-31230-5-git-send-email-treeze.taeung@gmail.com
[ Combined patch with docs update with this one ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/tools/perf/util/config.h b/tools/perf/util/config.h
index 6f813d46045e..0fcdb8c594b0 100644
--- a/tools/perf/util/config.h
+++ b/tools/perf/util/config.h
@@ -33,6 +33,8 @@ const char *perf_etc_perfconfig(void);
 
 struct perf_config_set *perf_config_set__new(void);
 void perf_config_set__delete(struct perf_config_set *set);
+int perf_config_set__collect(struct perf_config_set *set,
+			     const char *var, const char *value);
 void perf_config__init(void);
 void perf_config__exit(void);
 void perf_config__refresh(void);