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Commit dbe7aa62 authored by Heena Sirwani's avatar Heena Sirwani Committed by Thomas Gleixner
Browse files

timekeeping: Provide y2038 safe accessor to the seconds portion of CLOCK_REALTIME 



ktime_get_real_seconds() is the replacement function for get_seconds()
returning the seconds portion of CLOCK_REALTIME in a time64_t. For
64bit the function is equivivalent to get_seconds(), but for 32bit it
protects the readout with the timekeeper sequence count. This is
required because 32-bit machines cannot access 64-bit tk->xtime_sec
variable atomically.

[tglx: Massaged changelog and added docbook comment ]

Signed-off-by: default avatarHeena Sirwani <heenasirwani@gmail.com>
Reviewed-by: default avatarArnd Bergman <arnd@arndb.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: opw-kernel@googlegroups.com
Link: http://lkml.kernel.org/r/7adcfaa8962b8ad58785d9a2456c3f77d93c0ffb.1414578445.git.heenasirwani@gmail.com


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 9e3680b1

include/linux/timekeeping.h

+1 −0
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ struct timespec get_monotonic_coarse(void); 
extern void getrawmonotonic(struct timespec *ts);

extern void ktime_get_ts64(struct timespec64 *ts);

extern time64_t ktime_get_seconds(void);

extern time64_t ktime_get_real_seconds(void);



extern int __getnstimeofday64(struct timespec64 *tv);

extern void getnstimeofday64(struct timespec64 *tv);

kernel/time/timekeeping.c

+30 −0
Original line number Diff line number Diff line
@@ -676,6 +676,36 @@ time64_t ktime_get_seconds(void) 
}

EXPORT_SYMBOL_GPL(ktime_get_seconds);



/**

 * ktime_get_real_seconds - Get the seconds portion of CLOCK_REALTIME

 *

 * Returns the wall clock seconds since 1970. This replaces the

 * get_seconds() interface which is not y2038 safe on 32bit systems.

 *

 * For 64bit systems the fast access to tk->xtime_sec is preserved. On

 * 32bit systems the access must be protected with the sequence

 * counter to provide "atomic" access to the 64bit tk->xtime_sec

 * value.

 */

time64_t ktime_get_real_seconds(void)

{

	struct timekeeper *tk = &tk_core.timekeeper;

	time64_t seconds;

	unsigned int seq;



	if (IS_ENABLED(CONFIG_64BIT))

		return tk->xtime_sec;



	do {

		seq = read_seqcount_begin(&tk_core.seq);

		seconds = tk->xtime_sec;



	} while (read_seqcount_retry(&tk_core.seq, seq));



	return seconds;

}

EXPORT_SYMBOL_GPL(ktime_get_real_seconds);



#ifdef CONFIG_NTP_PPS



/**