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| author | Heena Sirwani <heenasirwani@gmail.com> | 2014-10-29 16:01:50 +0530 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2014-10-29 15:15:40 +0100 |
| commit | dbe7aa622db96b5cd601f59d09c4f00b98b76079 (patch) | |
| tree | 303b3f8f88b40b4529f3a37ea20ca8f4f46694e5 /kernel/time | |
| parent | 9e3680b1750b9a62680b0262c9f438de98b77655 (diff) | |
| download | linux-dbe7aa622db96b5cd601f59d09c4f00b98b76079.tar.bz2 | |
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: Heena Sirwani <heenasirwani@gmail.com>
Reviewed-by: Arnd 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: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/timekeeping.c | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index a693270efafb..0aef92a0a701 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -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 /** |