[PATCH] lib/util: fix timespec normalization

Philipp Gesang philipp.gesang at intra2net.com
Thu Jan 17 16:07:18 UTC 2019


-<| Quoting Volker Lendecke via samba-technical <Volker.Lendecke at SerNet.DE>, on Thursday, 2019-01-17 11:58:16 AM |>-
> On Thu, Jan 17, 2019 at 11:40:48AM +0100, Philipp Gesang via samba-technical wrote:
> > +
> > +/****************************************************************************
> > + Deal with nanoseconds overflow.
> > +****************************************************************************/
> > +
> > +void normalize_timespec(struct timespec *ts)
> > +{
> > +	while (ts->tv_nsec >= NSEC_PER_SEC) {
> > +		++ts->tv_sec;
> > +		ts->tv_nsec -= NSEC_PER_SEC;
> > +	}
> > +	while (ts->tv_nsec < 0) {
> > +		--ts->tv_sec;
> > +		ts->tv_nsec += NSEC_PER_SEC;
> > +	}
> > +}
> 
> This looks a bit inefficient to be honest. Shouldn't that be faster
> doing some modulo-magic?

Unless something is severely wrong, there shouldn’t be more than
the sum of two valid tv_nsec in there so the loop is unlikely to
run more than once. Also on 32 bit, it’ll run at most twice on
account of tv_nsec being long.

Anyways, attached is a variant that uses lldiv instead.

Regards,
Philipp

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From 3f9a4364be7be4761b5358078de1086a2b4201b6 Mon Sep 17 00:00:00 2001
From: Philipp Gesang <philipp.gesang at intra2net.com>
Date: Thu, 17 Jan 2019 11:06:26 +0100
Subject: [PATCH v2] lib/util: fix timespec normalization

When fixing up timespec structs, negative values for the ns part
should be taken into account. Also, the range for a valid ns part
is [0, 1000000000), not [0, 1000000000].

Signed-off-by: Philipp Gesang <philipp.gesang at intra2net.com>
---
 lib/util/tests/time.c | 45 +++++++++++++++++++++++++++++++++++++++++++
 lib/util/time.c       | 33 +++++++++++++++++++++++--------
 lib/util/time.h       |  1 +
 3 files changed, 71 insertions(+), 8 deletions(-)

diff --git a/lib/util/tests/time.c b/lib/util/tests/time.c
index fce0eef5e2e..890d5c2424f 100644
--- a/lib/util/tests/time.c
+++ b/lib/util/tests/time.c
@@ -82,6 +82,49 @@ static bool test_timestring(struct torture_context *tctx)
 	return true;
 }
 
+static bool test_normalize_timespec(struct torture_context *tctx)
+{
+	const struct {
+		time_t in_s; long in_ns;
+		time_t out_s; long out_ns;
+	} data [] = {
+		{ 0, 0, 0, 0 }
+		, { 1, 0, 1, 0 }
+		, { -1, 0, -1, 0 }
+		, { 0, 1000000000, 1, 0 }
+		, { 0, 2000000000, 2, 0 }
+		, { 0, 1000000001, 1, 1 }
+		, { 0, 2000000001, 2, 1 }
+		, { 0, -1000000000, -1, 0 }
+		, { 0, -2000000000, -2, 0 }
+		, { 0, -1000000001, -2, 999999999 }
+		, { 0, -2000000001, -3, 999999999 }
+		, { 0, -1, -1, 999999999 }
+		, { 1, -1, 0, 999999999 }
+		, { -1, -1, -2, 999999999 }
+		, { 0, 999999999, 0, 999999999 }
+		, { 0, 1999999999, 1, 999999999 }
+		, { 0, 2999999999, 2, 999999999 }
+		, { 0, -999999999, -1, 1 }
+		, { 0, -1999999999, -2, 1 }
+		, { 0, -2999999999, -3, 1 }
+	};
+
+	for (int i = 0; i < sizeof(data) / sizeof(data[0]); ++i) {
+		struct timespec ts = (struct timespec)
+				   { .tv_sec  = data[i].in_s
+				   , .tv_nsec = data[i].in_ns };
+		normalize_timespec(&ts);
+
+		torture_assert_int_equal(tctx, ts.tv_sec, data[i].out_s,
+					 "mismatch in tv_sec");
+		torture_assert_int_equal(tctx, ts.tv_nsec, data[i].out_ns,
+					 "mismatch in tv_nsec");
+	}
+
+	return true;
+}
+
 struct torture_suite *torture_local_util_time(TALLOC_CTX *mem_ctx)
 {
 	struct torture_suite *suite = torture_suite_create(mem_ctx, "time");
@@ -92,6 +135,8 @@ struct torture_suite *torture_local_util_time(TALLOC_CTX *mem_ctx)
 								  test_http_timestring);
 	torture_suite_add_simple_test(suite, "timestring", 
 								  test_timestring);
+	torture_suite_add_simple_test(suite, "normalize_timespec",
+				      test_normalize_timespec);
 
 	return suite;
 }
diff --git a/lib/util/time.c b/lib/util/time.c
index bd067f84e8e..d162bcb3940 100644
--- a/lib/util/time.c
+++ b/lib/util/time.c
@@ -39,6 +39,7 @@
 #endif
 
 
+#define NSEC_PER_SEC 1000000000
 
 /**
  External access to time_t_min and time_t_max.
@@ -88,10 +89,7 @@ _PUBLIC_ time_t time_mono(time_t *t)
 time_t convert_timespec_to_time_t(struct timespec ts)
 {
 	/* Ensure tv_nsec is less than 1sec. */
-	while (ts.tv_nsec > 1000000000) {
-		ts.tv_sec += 1;
-		ts.tv_nsec -= 1000000000;
-	}
+	normalize_timespec(&ts);
 
 	/* 1 ns == 1,000,000,000 - one thousand millionths of a second.
 	   increment if it's greater than 500 millionth of a second. */
@@ -950,10 +948,7 @@ void round_timespec_to_usec(struct timespec *ts)
 {
 	struct timeval tv = convert_timespec_to_timeval(*ts);
 	*ts = convert_timeval_to_timespec(tv);
-	while (ts->tv_nsec > 1000000000) {
-		ts->tv_sec += 1;
-		ts->tv_nsec -= 1000000000;
-	}
+	normalize_timespec(ts);
 }
 
 /****************************************************************************
@@ -982,3 +977,25 @@ _PUBLIC_ NTTIME unix_timespec_to_nt_time(struct timespec ts)
 
 	return d;
 }
+
+/****************************************************************************
+ Deal with nanoseconds overflow.
+****************************************************************************/
+
+void normalize_timespec(struct timespec *ts)
+{
+	lldiv_t dres;
+
+	/* most likely case: nsec is valid */
+	if ((unsigned long)ts->tv_nsec < NSEC_PER_SEC) return;
+
+	dres = lldiv(ts->tv_nsec, NSEC_PER_SEC);
+	ts->tv_nsec = dres.rem;
+	ts->tv_sec += dres.quot;
+
+	/* if the ns part was positive or muliple of -1000000000, we're done */
+	if (ts->tv_nsec > 0 || dres.rem == 0) return;
+
+	ts->tv_nsec += NSEC_PER_SEC;
+	--ts->tv_sec;
+}
diff --git a/lib/util/time.h b/lib/util/time.h
index 1988b330576..2cfa1fa9039 100644
--- a/lib/util/time.h
+++ b/lib/util/time.h
@@ -329,5 +329,6 @@ int timespec_compare(const struct timespec *ts1, const struct timespec *ts2);
 void round_timespec_to_sec(struct timespec *ts);
 void round_timespec_to_usec(struct timespec *ts);
 NTTIME unix_timespec_to_nt_time(struct timespec ts);
+void normalize_timespec(struct timespec *ts);
 
 #endif /* _SAMBA_TIME_H_ */
-- 
2.17.2

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