posix-timers: Make them configurable

Some embedded systems have no use for them.  This removes about
25KB from the kernel binary size when configured out.

Corresponding syscalls are routed to a stub logging the attempt to
use those syscalls which should be enough of a clue if they were
disabled without proper consideration. They are: timer_create,
timer_gettime: timer_getoverrun, timer_settime, timer_delete,
clock_adjtime, setitimer, getitimer, alarm.

The clock_settime, clock_gettime, clock_getres and clock_nanosleep
syscalls are replaced by simple wrappers compatible with CLOCK_REALTIME,
CLOCK_MONOTONIC and CLOCK_BOOTTIME only which should cover the vast
majority of use cases with very little code.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-kbuild@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Michal Marek <mmarek@suse.com>
Cc: Edward Cree <ecree@solarflare.com>
Link: http://lkml.kernel.org/r/1478841010-28605-7-git-send-email-nicolas.pitre@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 12dd190634ab..a15caa3d1721 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -846,8 +846,10 @@ static int __init alarmtimer_init(void)
 
 	alarmtimer_rtc_timer_init();
 
-	posix_timers_register_clock(CLOCK_REALTIME_ALARM, &alarm_clock);
-	posix_timers_register_clock(CLOCK_BOOTTIME_ALARM, &alarm_clock);
+	if (IS_ENABLED(CONFIG_POSIX_TIMERS)) {
+		posix_timers_register_clock(CLOCK_REALTIME_ALARM, &alarm_clock);
+		posix_timers_register_clock(CLOCK_BOOTTIME_ALARM, &alarm_clock);
+	}
 
 	/* Initialize alarm bases */
 	alarm_bases[ALARM_REALTIME].base_clockid = CLOCK_REALTIME;