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 <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Corey Ashford <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jean Pihet <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/sort.c

···
 	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)) {
 			/*