[PATCH] time: Make NTP optionnal

[Romain Perier]

On embedded systems with limited space, synchronizing system clock via
NTP might be not needed.

This commit introduces a new Kconfig entry. When disabled, it compiles
out the adjtimex and clock_adjtimes system calls. The corresponding NTP
accessors are also disabled from timekeeping.c and their declaration are
replaced by no_op static inline functions in time.h

The bloat-o-meter output is the following:

add/remove: 1/35 grow/shrink: 2/9 up/down: 170/-3760 (-3590)
function                                     old     new   delta
tk_set_wall_to_mono.constprop                  -     164    +164
tk_xtime_add.constprop                       200     204      +4
timespec_trunc                                60      62      +2
ntp_notify_cmos_timer                          2       -      -2
k_itimer_rcu_free                             18      16      -2
timekeeping_forward_now.constprop            256     252      -4
time_status                                    4       -      -4
time_state                                     4       -      -4
time_maxerror                                  4       -      -4
time_esterror                                  4       -      -4
time_constant                                  4       -      -4
time_adjust                                    4       -      -4
tick_usec                                      4       -      -4
tick_nsec                                      4       -      -4
ntp_init                                       4       -      -4
posix_clock_realtime_adj                       6       -      -6
time_reftime                                   8       -      -8
time_offset                                    8       -      -8
time_freq                                      8       -      -8
tick_length_base                               8       -      -8
tick_length                                    8       -      -8
ntp_tick_adj                                   8       -      -8
ntp_next_leap_sec                              8       -      -8
mask_to_bit_num                                8       -      -8
mask_to_allowed_status                         8       -      -8
ntp_tick_length                               12       -     -12
__setup_ntp_tick_adj_setup                    12       -     -12
__setup_str_ntp_tick_adj_setup                14       -     -14
timekeeping_resume                           614     598     -16
timekeeping_inject_offset                    352     336     -16
timekeeping_init                             400     384     -16
do_settimeofday64                            342     326     -16
ntp_tick_adj_setup                            28       -     -28
timekeeping_update                           236     206     -30
branch_table                                  32       -     -32
sys_adjtimex                                  42       -     -42
sys_clock_adjtime                             64       -     -64
ntp_clear                                     72       -     -72
ntp_get_next_leap                             76       -     -76
ntp_validate_timex                            78       -     -78
tk_set_wall_to_mono                          166       -    -166
ntp_update_frequency                         180       -    -180
update_wall_time                            1846    1590    -256
do_adjtimex                                  272       -    -272
second_overflow                              476       -    -476
bcj_apply                                   1100     224    -876
__do_adjtimex                                888       -    -888

Signed-off-by: Romain Perier <romain.perier@xxxxxxxxx>
---
 include/linux/timex.h      | 14 +++++++++++---
 init/Kconfig               |  9 +++++++++
 kernel/compat.c            |  2 ++
 kernel/sys_ni.c            |  6 ++++++
 kernel/time/Makefile       |  6 +++++-
 kernel/time/ntp_internal.h | 29 +++++++++++++++++++++++++++++
 kernel/time/posix-timers.c | 13 ++++++++-----
 kernel/time/time.c         |  4 ++--
 kernel/time/timekeeping.c  |  2 ++
 9 files changed, 74 insertions(+), 11 deletions(-)

diff --git a/include/linux/timex.h b/include/linux/timex.h
index 39c25dbebfe8..5906b654821a 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -151,12 +151,20 @@ extern unsigned long tick_nsec;		/* SHIFTED_HZ period (nsec) */
 #define NTP_INTERVAL_FREQ  (HZ)
 #define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
 
+#ifdef CONFIG_NTP
 extern int do_adjtimex(struct timex *);
 extern void hardpps(const struct timespec64 *, const struct timespec64 *);
-
-int read_current_timer(unsigned long *timer_val);
 void ntp_notify_cmos_timer(void);
-
+#else
+static inline int do_adjtimex(struct timex *txc)
+{
+	return TIME_OK;
+}
+static inline void hardpps(const struct timespec64 *phase_ts,
+			   const struct timespec64 *raw_ts)
+{}
+#endif
+int read_current_timer(unsigned long *timer_val);
 /* The clock frequency of the i8253/i8254 PIT */
 #define PIT_TICK_RATE 1193182ul
 
diff --git a/init/Kconfig b/init/Kconfig
index 3c1faaa2af4a..d4b0b33f7e91 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1332,6 +1332,15 @@ config EVENTFD
 
 	  If unsure, say Y.
 
+config NTP
+	bool "Enable NTP support" if EXPERT
+	default y
+	help
+	  This enables support for synchronizing system clock with NTP
+	  and its corresponding syscalls adjtimex and clock_adjtimex.
+
+          If unsure, say Y.
+
 # syscall, maps, verifier
 config BPF_SYSCALL
 	bool "Enable bpf() system call"
diff --git a/kernel/compat.c b/kernel/compat.c
index 772e038d04d9..12945ae5ae94 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -30,6 +30,7 @@
 
 #include <linux/uaccess.h>
 
+#ifdef CONFIG_NTP
 int compat_get_timex(struct timex *txc, const struct compat_timex __user *utp)
 {
 	struct compat_timex tx32;
@@ -91,6 +92,7 @@ int compat_put_timex(struct compat_timex __user *utp, const struct timex *txc)
 		return -EFAULT;
 	return 0;
 }
+#endif
 
 static int __compat_get_timeval(struct timeval *tv, const struct compat_timeval __user *ctv)
 {
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 8acef8576ce9..f854d24b813c 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -258,3 +258,9 @@ cond_syscall(sys_membarrier);
 cond_syscall(sys_pkey_mprotect);
 cond_syscall(sys_pkey_alloc);
 cond_syscall(sys_pkey_free);
+#ifndef CONFIG_NTP
+cond_syscall(sys_adjtimex);
+cond_syscall(sys_clock_adjtime);
+cond_syscall(compat_sys_adjtimex);
+cond_syscall(compat_sys_clock_adjtime);
+#endif
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 938dbf33ef49..44bd321e4560 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -1,7 +1,11 @@
 obj-y += time.o timer.o hrtimer.o
-obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o
+obj-y += timekeeping.o clocksource.o jiffies.o timer_list.o
 obj-y += timeconv.o timecounter.o alarmtimer.o
 
+ifeq ($(CONFIG_NTP),y)
+ obj-y += ntp.o
+endif
+
 ifeq ($(CONFIG_POSIX_TIMERS),y)
  obj-y += posix-timers.o posix-cpu-timers.o posix-clock.o itimer.o
 else
diff --git a/kernel/time/ntp_internal.h b/kernel/time/ntp_internal.h
index d8a7c11fa71a..9d1ebc042968 100644
--- a/kernel/time/ntp_internal.h
+++ b/kernel/time/ntp_internal.h
@@ -1,6 +1,7 @@
 #ifndef _LINUX_NTP_INTERNAL_H
 #define _LINUX_NTP_INTERNAL_H
 
+#ifdef CONFIG_NTP
 extern void ntp_init(void);
 extern void ntp_clear(void);
 /* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
@@ -10,4 +11,32 @@ extern int second_overflow(time64_t secs);
 extern int ntp_validate_timex(struct timex *);
 extern int __do_adjtimex(struct timex *, struct timespec64 *, s32 *);
 extern void __hardpps(const struct timespec64 *, const struct timespec64 *);
+#else
+static inline void ntp_init(void)
+{}
+static inline void ntp_clear(void)
+{}
+static inline u64 ntp_tick_length(void)
+{
+	return 0;
+}
+static inline ktime_t ntp_get_next_leap(void)
+{
+	return KTIME_MAX;
+}
+static inline int second_overflow(time64_t secs)
+{
+	return 0;
+}
+static inline int ntp_validate_timex(struct timex *txc)
+{
+	return 0;
+}
+static inline int __do_adjtimex(struct timex *txc, struct timespec64 *ts,
+				s32 *time_tai)
+{
+	return TIME_OK;
+}
+#endif
+
 #endif /* _LINUX_NTP_INTERNAL_H */
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 13d6881f908b..dd31eaddc196 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -207,12 +207,13 @@ static int posix_clock_realtime_set(const clockid_t which_clock,
 	return do_sys_settimeofday64(tp, NULL);
 }
 
+#ifdef CONFIG_NTP
 static int posix_clock_realtime_adj(const clockid_t which_clock,
 				    struct timex *t)
 {
 	return do_adjtimex(t);
 }
-
+#endif
 /*
  * Get monotonic time for posix timers
  */
@@ -1065,7 +1066,7 @@ SYSCALL_DEFINE2(clock_gettime, const clockid_t, which_clock,
 
 	return error;
 }
-
+#ifdef CONFIG_NTP
 SYSCALL_DEFINE2(clock_adjtime, const clockid_t, which_clock,
 		struct timex __user *, utx)
 {
@@ -1088,7 +1089,7 @@ SYSCALL_DEFINE2(clock_adjtime, const clockid_t, which_clock,
 
 	return err;
 }
-
+#endif
 SYSCALL_DEFINE2(clock_getres, const clockid_t, which_clock,
 		struct timespec __user *, tp)
 {
@@ -1141,7 +1142,7 @@ COMPAT_SYSCALL_DEFINE2(clock_gettime, clockid_t, which_clock,
 
 	return err;
 }
-
+#ifdef CONFIG_NTP
 COMPAT_SYSCALL_DEFINE2(clock_adjtime, clockid_t, which_clock,
 		       struct compat_timex __user *, utp)
 {
@@ -1165,7 +1166,7 @@ COMPAT_SYSCALL_DEFINE2(clock_adjtime, clockid_t, which_clock,
 
 	return err;
 }
-
+#endif
 COMPAT_SYSCALL_DEFINE2(clock_getres, clockid_t, which_clock,
 		       struct compat_timespec __user *, tp)
 {
@@ -1252,7 +1253,9 @@ static const struct k_clock clock_realtime = {
 	.clock_getres		= posix_get_hrtimer_res,
 	.clock_get		= posix_clock_realtime_get,
 	.clock_set		= posix_clock_realtime_set,
+#ifdef CONFIG_NTP
 	.clock_adj		= posix_clock_realtime_adj,
+#endif
 	.nsleep			= common_nsleep,
 	.timer_create		= common_timer_create,
 	.timer_set		= common_timer_set,
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 44a8c1402133..413eca43a09c 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -297,7 +297,7 @@ COMPAT_SYSCALL_DEFINE2(settimeofday, struct compat_timeval __user *, tv,
 	return do_sys_settimeofday64(tv ? &new_ts : NULL, tz ? &new_tz : NULL);
 }
 #endif
-
+#ifdef CONFIG_NTP
 SYSCALL_DEFINE1(adjtimex, struct timex __user *, txc_p)
 {
 	struct timex txc;		/* Local copy of parameter */
@@ -333,7 +333,7 @@ COMPAT_SYSCALL_DEFINE1(adjtimex, struct compat_timex __user *, utp)
 	return ret;
 }
 #endif
-
+#endif
 /*
  * Convert jiffies to milliseconds and back.
  *
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 2cafb49aa65e..223fe15daa75 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2247,6 +2247,7 @@ ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
 	return base;
 }
 
+#ifdef CONFIG_NTP
 /**
  * do_adjtimex() - Accessor function to NTP __do_adjtimex function
  */
@@ -2317,6 +2318,7 @@ void hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts)
 }
 EXPORT_SYMBOL(hardpps);
 #endif /* CONFIG_NTP_PPS */
+#endif /* CONFIG_NTP */
 
 /**
  * xtime_update() - advances the timekeeping infrastructure
-- 
2.14.1