[Patch 1/6] Delay accounting: timespec diff

[Shailabh Nagar <nagar@watson.ibm.com>]

nstimestamp_diff.patch

Add kernel utility function for measuring the
interval (diff) between two timespec values, adjusting for overflow

Signed-off-by: Shailabh Nagar <nagar@watson.ibm.com>

 include/linux/time.h |   15 +++++++++++++++
 1 files changed, 15 insertions(+)

Index: linux-2.6.15-rc7/include/linux/time.h
===================================================================
--- linux-2.6.15-rc7.orig/include/linux/time.h
+++ linux-2.6.15-rc7/include/linux/time.h
@@ -114,6 +114,21 @@ set_normalized_timespec (struct timespec
 	ts->tv_nsec = nsec;
 }

+/*
+ * timespec_diff_ns - Return difference of two timestamps in nanoseconds
+ * In the rare case of @end being earlier than @start, return zero
+ */
+static inline unsigned long long
+timespec_diff_ns(struct timespec *start, struct timespec *end)
+{
+	long long ret;
+
+	ret = end->tv_sec*(1000000000) + end->tv_nsec;
+	ret -= start->tv_sec*(1000000000) + start->tv_nsec;
+	if (ret < 0)
+		return 0;
+	return ret;
+}
 #endif /* __KERNEL__ */

 #define NFDBITS			__NFDBITS