Re: [PATCH 4/9 RESEND] RFC: timekeeping: introduce flag systime_was_set

From: John Stultz
Date: Fri Jun 14 2013 - 13:41:32 EST

On 06/14/2013 09:52 AM, Alexander Holler wrote:
In order to let an RTC set the time at boot without the problem that a
second RTC overwrites it, the flag systime_was_set is introduced.

systime_was_set will be true, if a persistent clock sets the time at boot,
or if do_settimeofday() is called (e.g. by the RTC subsystem or userspace).

Signed-off-by: Alexander Holler <holler@xxxxxxxxxxxxx>
include/linux/time.h | 6 ++++++
kernel/time/timekeeping.c | 10 +++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/time.h b/include/linux/time.h
index d5d229b..888280f 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -129,6 +129,12 @@ extern int update_persistent_clock(struct timespec now);
void timekeeping_init(void);
extern int timekeeping_suspended;
+ * Will be true if the system time was set at least once by
+ * a persistent clock, RTC or userspace.
+ */
+extern bool systime_was_set;

Probably should make this static to timekeeping.c and create an accessor function so you don't have to export locking rules on this.

unsigned long get_seconds(void);
struct timespec current_kernel_time(void);
struct timespec __current_kernel_time(void); /* does not take xtime_lock */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index baeeb5c..07d8531 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -37,6 +37,9 @@ int __read_mostly timekeeping_suspended;
/* Flag for if there is a persistent clock on this platform */
bool __read_mostly persistent_clock_exist = false;
+/* Flag for if the system time was set at least once */
+bool __read_mostly systime_was_set;
Probably should also move this to be part of the timekeeper structure (since it will be protected by the timekeeper lock.

static inline void tk_normalize_xtime(struct timekeeper *tk)
while (tk->xtime_nsec >= ((u64)NSEC_PER_SEC << tk->shift)) {
@@ -498,6 +501,9 @@ int do_settimeofday(const struct timespec *tv)
raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ systime_was_set = true;
xt = tk_xtime(tk);

Might also want to add the flag to inject_offset as well, since that could be used to set the time.


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