perf tools: Add +field argument support for --sort option

Adding support to add field(s) to default sort order via using the '+'
prefix, like for report:

  $ perf report
  Samples: 2K of event 'cycles', Event count (approx.): 882172583
  Overhead  Command  Shared Object        Symbol
     7.39%  swapper  [kernel.kallsyms]    [k] intel_idle
     1.97%  firefox  libpthread-2.17.so   [.] pthread_mutex_lock
     1.39%  firefox  [snd_hda_intel]      [k] azx_get_position
     1.11%  firefox  libpthread-2.17.so   [.] pthread_mutex_unlock

  $ perf report -s +cpu
  Samples: 2K of event 'cycles', Event count (approx.): 882172583
  Overhead  Command  Shared Object        Symbol                  CPU
     2.89%  swapper  [kernel.kallsyms]    [k] intel_idle          000
     2.61%  swapper  [kernel.kallsyms]    [k] intel_idle          002
     1.20%  swapper  [kernel.kallsyms]    [k] intel_idle          001
     0.82%  firefox  libpthread-2.17.so   [.] pthread_mutex_lock  002

Works in general for commands using --sort option.

v2 with changes suggested:
  - Use dynamic memory instead static buffer
  - Fix error message typo

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20140823125948.GA1193@krava.brq.redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/sort.c

@@ -1446,12 +1446,47 @@ static const char *get_default_sort_order(void)
 	return default_sort_orders[sort__mode];
 }
 
+static int setup_sort_order(void)
+{
+	char *new_sort_order;
+
+	/*
+	 * Append '+'-prefixed sort order to the default sort
+	 * order string.
+	 */
+	if (!sort_order || is_strict_order(sort_order))
+		return 0;
+
+	if (sort_order[1] == '\0') {
+		error("Invalid --sort key: `+'");
+		return -EINVAL;
+	}
+
+	/*
+	 * We allocate new sort_order string, but we never free it,
+	 * because it's checked over the rest of the code.
+	 */
+	if (asprintf(&new_sort_order, "%s,%s",
+		     get_default_sort_order(), sort_order + 1) < 0) {
+		error("Not enough memory to set up --sort");
+		return -ENOMEM;
+	}
+
+	sort_order = new_sort_order;
+	return 0;
+}
+
 static int __setup_sorting(void)
 {
 	char *tmp, *tok, *str;
-	const char *sort_keys = sort_order;
+	const char *sort_keys;
 	int ret = 0;
 
+	ret = setup_sort_order();
+	if (ret)
+		return ret;
+
+	sort_keys = sort_order;
 	if (sort_keys == NULL) {
 		if (is_strict_order(field_order)) {
 			/*