new time code problem

From: George Anzinger <george@mvista.com>
To: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>, linux-kernel@vger.kernel.org
Subject: new time code problem
Date: Tue, 10 Jan 2006 15:58:52 -0800	[thread overview]
Message-ID: <43C44A3C.6010803@mvista.com> (raw)
In-Reply-To: <1136935211.2890.11.camel@cog.beaverton.ibm.com>

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The 64-bit conversion routine to convert 64-bit nsec time to a time spec. 
gives an unnormalized result if the value being converted is negative.  I 
think there are two ways to go about fixing this.  Most systems will give a 
negative remainder and so need to just normalize.  On the other hand, some 
systems will use div64 to do the division and, I think, it expects unsigned 
numbers.  The attached patch uses the conservative approach of expecting the 
div to be set up for unsigned numbers.

I came accross this when one of my tests set a time near 1 Jan 1970, i.e. it 
is a real problem.
-- 
George Anzinger   george@mvista.com
HRT (High-res-timers):  http://sourceforge.net/projects/high-res-timers/

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 kernel/time.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

Index: linux-2.6.16-rc/kernel/time.c
===================================================================

--- linux-2.6.16-rc.orig/kernel/time.c
+++ linux-2.6.16-rc/kernel/time.c
@@ -702,16 +702,19 @@ void set_normalized_timespec(struct time
  *
  * Returns the timespec representation of the nsec parameter.
  */
-inline struct timespec ns_to_timespec(const nsec_t nsec)
+struct timespec ns_to_timespec(const nsec_t nsec)
 {
 	struct timespec ts;
 
-	if (nsec)
+	if (nsec) return (struct timespec){0, 0};
+
+	if (nsec < 0) {
+		ts.tv_sec = div_long_long_rem_signed(-nsec, NSEC_PER_SEC,
+						     &ts.tv_nsec);
+		set_normalized_timespec(&ts, -ts.tv_sec, -ts.tv_nsec);
+	} else
 		ts.tv_sec = div_long_long_rem_signed(nsec, NSEC_PER_SEC,
 						     &ts.tv_nsec);
-	else
-		ts.tv_sec = ts.tv_nsec = 0;
-
 	return ts;
 }
 
