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Subject[PATCH] time: Make NTP optionnal
Date
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@gmail.com>
---
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
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