selftests/timens: handle a case when alarm clocks are not supported

This can happen if a testing node doesn't have RTC (real time clock)
hardware or it doesn't support alarms.

Fixes: 61c57676035d ("selftests/timens: Add Time Namespace test for supported clocks")
Acked-by: Vincenzo Frascino <[e-mail]>
Reported-by: Vincenzo Frascino <[e-mail]>
Signed-off-by: Andrei Vagin <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/timens/clock_nanosleep.c

···
 
 	ksft_set_plan(4);
 
-	check_config_posix_timers();
+	check_supported_timers();
 
 	if (unshare_timens())
 		return 1;

tools/testing/selftests/timens/timens.c

···
 
 	nscheck();
 
-	check_config_posix_timers();
+	check_supported_timers();
 
 	ksft_set_plan(ARRAY_SIZE(clocks) * 2);
 

tools/testing/selftests/timens/timens.h

···
 #endif
 
 static int config_posix_timers = true;
+static int config_alarm_timers = true;
 
-static inline void check_config_posix_timers(void)
+static inline void check_supported_timers(void)
 {
+	struct timespec ts;
+
 	if (timer_create(-1, 0, 0) == -1 && errno == ENOSYS)
 		config_posix_timers = false;
+
+	if (clock_gettime(CLOCK_BOOTTIME_ALARM, &ts) == -1 && errno == EINVAL)
+		config_alarm_timers = false;
 }
 
 static inline bool check_skip(int clockid)
 {
+	if (!config_alarm_timers && clockid == CLOCK_BOOTTIME_ALARM) {
+		ksft_test_result_skip("CLOCK_BOOTTIME_ALARM isn't supported\n");
+		return true;
+	}
+
 	if (config_posix_timers)
 		return false;
 

tools/testing/selftests/timens/timer.c

···
 	timer_t fd;
 	int i;
 
+	if (check_skip(clockid))
+		return 0;
+
 	for (i = 0; i < 2; i++) {
 		struct sigevent sevp = {.sigev_notify = SIGEV_NONE};
 		int flags = 0;
···
 	struct timespec btime_now, mtime_now;
 
 	nscheck();
+
+	check_supported_timers();
 
 	ksft_set_plan(3);
 

tools/testing/selftests/timens/timerfd.c

···
 	long long elapsed;
 	int fd, i;
 
+	if (check_skip(clockid))
+		return 0;
+
 	if (tclock_gettime(clockid, &now))
 		return pr_perror("clock_gettime(%d)", clockid);
 
···
 	struct timespec btime_now, mtime_now;
 
 	nscheck();
+
+	check_supported_timers();
 
 	ksft_set_plan(3);