linux-kernel - [PATCH v8 2/2] timekeeping: Added a function to return tv_sec portion of ktime_get_real

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Date:	Wed, 29 Oct 2014 16:01:50 +0530
From:	Heena Sirwani <heenasirwani@...il.com>
To:	opw-kernel@...glegroups.com
Cc:	linux-kernel@...r.kernel.org, john.stultz@...aro.org,
	tglx@...utronix.de, arnd@...db.de
Subject: [PATCH v8 2/2] timekeeping: Added a function to return tv_sec
 portion of ktime_get_real_ts64()

The following patch adds a function to return tv_sec portion of
ktime_get_real_ts64() function in order to have a function that returns
seconds as 64-bit integers instead of 32-bit integers to address the
y2038 problem.

The function is similar to get_seconds() function except that it
includes read_seqcount_retry loop which is required for 32-bit
architectures. This is because 32-bit machines cannot access 64-bit
tk->xtime_sec variable atomically, requiring two 32-bit register loads.

Signed-off-by: Heena Sirwani <heenasirwani@...il.com>
---
 include/linux/timekeeping.h |  1 +
 kernel/time/timekeeping.c   | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 115d55e..91454de 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -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);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e42da92..d731e7a 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -664,6 +664,25 @@ time64_t ktime_get_seconds(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_seconds);
 
+time64_t ktime_get_real_seconds(void)
+{
+	time64_t seconds;
+	struct timekeeper *tk = &tk_core.timekeeper;
+	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
 
 /**
-- 
1.9.1

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