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, 17 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 34407f15e6d3..456e0b891238 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1445,6 +1445,23 @@ config SYSCTL_SYSCALL
 
           If unsure say N here.
 
+config POSIX_TIMERS
+        bool "Posix Clocks & timers" if EXPERT
+        default y
+        help
+          This includes native support for POSIX timers to the kernel.
+          Some embedded systems have no use for them and therefore they
+          can be configured out to reduce the size of the kernel image.
+
+          When this option is disabled, the following syscalls won't be
+          available: timer_create, timer_gettime: timer_getoverrun,
+          timer_settime, timer_delete, clock_adjtime, getitimer,
+          setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
+          clock_getres and clock_nanosleep syscalls will be limited to
+          CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
+
+          If unsure say y.
+
 config KALLSYMS
          bool "Load all symbols for debugging/ksymoops" if EXPERT
          default y