libperf: Add API for allocating new thread map array

The existing API perf_thread_map__new_dummy() allocates new thread map
for one thread. I couldn't find a way to reallocate the map with more
threads, or to allocate a new map for more than one thread.

Having multiple threads in a thread map is essential for some use cases.
That's why a new API is proposed, which allocates a new thread map for
given number of threads: perf_thread_map__new_array()

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/linux-perf-users/20220221102628.43904-1-tz.stoyanov@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/Documentation/libperf.txt

@@ -62,6 +62,7 @@ SYNOPSIS
   struct perf_thread_map;
 
   struct perf_thread_map *perf_thread_map__new_dummy(void);
+  struct perf_thread_map *perf_thread_map__new_array(int nr_threads, pid_t *array);
 
   void perf_thread_map__set_pid(struct perf_thread_map *map, int idx, pid_t pid);
   char *perf_thread_map__comm(struct perf_thread_map *map, int idx);

tools/lib/perf/include/perf/threadmap.h

@@ -8,6 +8,7 @@
 struct perf_thread_map;
 
 LIBPERF_API struct perf_thread_map *perf_thread_map__new_dummy(void);
+LIBPERF_API struct perf_thread_map *perf_thread_map__new_array(int nr_threads, pid_t *array);
 
 LIBPERF_API void perf_thread_map__set_pid(struct perf_thread_map *map, int idx, pid_t pid);
 LIBPERF_API char *perf_thread_map__comm(struct perf_thread_map *map, int idx);

tools/lib/perf/libperf.map

@@ -12,6 +12,7 @@ LIBPERF_0.0.1 {
 		perf_cpu_map__empty;
 		perf_cpu_map__max;
 		perf_cpu_map__has;
+		perf_thread_map__new_array;
 		perf_thread_map__new_dummy;
 		perf_thread_map__set_pid;
 		perf_thread_map__comm;

tools/lib/perf/tests/test-threadmap.c

@@ -11,9 +11,43 @@ static int libperf_print(enum libperf_print_level level,
 	return vfprintf(stderr, fmt, ap);
 }
 
+static int test_threadmap_array(int nr, pid_t *array)
+{
+	struct perf_thread_map *threads;
+	int i;
+
+	threads = perf_thread_map__new_array(nr, array);
+	__T("Failed to allocate new thread map", threads);
+
+	__T("Unexpected number of threads", perf_thread_map__nr(threads) == nr);
+
+	for (i = 0; i < nr; i++) {
+		__T("Unexpected initial value of thread",
+		    perf_thread_map__pid(threads, i) == (array ? array[i] : -1));
+	}
+
+	for (i = 1; i < nr; i++)
+		perf_thread_map__set_pid(threads, i, i * 100);
+
+	__T("Unexpected value of thread 0",
+	    perf_thread_map__pid(threads, 0) == (array ? array[0] : -1));
+
+	for (i = 1; i < nr; i++) {
+		__T("Unexpected thread value",
+		    perf_thread_map__pid(threads, i) == i * 100);
+	}
+
+	perf_thread_map__put(threads);
+
+	return 0;
+}
+
+#define THREADS_NR	10
 int test_threadmap(int argc, char **argv)
 {
 	struct perf_thread_map *threads;
+	pid_t thr_array[THREADS_NR];
+	int i;
 
 	__T_START;
 
@@ -27,6 +61,13 @@ int test_threadmap(int argc, char **argv)
 	perf_thread_map__put(threads);
 	perf_thread_map__put(threads);
 
+	test_threadmap_array(THREADS_NR, NULL);
+
+	for (i = 0; i < THREADS_NR; i++)
+		thr_array[i] = i + 100;
+
+	test_threadmap_array(THREADS_NR, thr_array);
+
 	__T_END;
 	return tests_failed == 0 ? 0 : -1;
 }

tools/lib/perf/threadmap.c

@@ -42,16 +42,26 @@ char *perf_thread_map__comm(struct perf_thread_map *map, int idx)
 	return map->map[idx].comm;
 }
 
+struct perf_thread_map *perf_thread_map__new_array(int nr_threads, pid_t *array)
+{
+	struct perf_thread_map *threads = thread_map__alloc(nr_threads);
+	int i;
+
+	if (!threads)
+		return NULL;
+
+	for (i = 0; i < nr_threads; i++)
+		perf_thread_map__set_pid(threads, i, array ? array[i] : -1);
+
+	threads->nr = nr_threads;
+	refcount_set(&threads->refcnt, 1);
+
+	return threads;
+}
+
 struct perf_thread_map *perf_thread_map__new_dummy(void)
 {
-	struct perf_thread_map *threads = thread_map__alloc(1);
-
-	if (threads != NULL) {
-		perf_thread_map__set_pid(threads, 0, -1);
-		threads->nr = 1;
-		refcount_set(&threads->refcnt, 1);
-	}
-	return threads;
+	return perf_thread_map__new_array(1, NULL);
 }
 
 static void perf_thread_map__delete(struct perf_thread_map *threads)