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From a3c400a8553b598bc2fd01eb0f63c5748b2147e1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
Date: Wed, 8 Nov 2017 17:02:42 +0100
Subject: [PATCH] Prefer clock_gettime(CLOCK_MONOTONIC)
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gettimeofday() reports wrong elapsed real time if a time step was
inserted while running a program. This can happen on initial time
adjustment from NTP server or by manual adjustement by date command.

This patch uses clock_gettime(CLOCK_MONOTONIC) instead (if available)
that does not suffer from the issue.

<http://lists.gnu.org/archive/html/bug-gnu-utils/2013-09/msg00008.html>

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 configure.ac |  3 +++
 src/resuse.c | 27 +++++++++++++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index ede8fd5..d2950bd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -72,6 +72,9 @@ dnl Checks for library functions.
 AC_FUNC_VPRINTF
 AC_FUNC_WAIT3
 AC_CHECK_FUNCS(strerror)
+AC_SEARCH_LIBS(clock_gettime, [rt])
+test "$ac_cv_search_clock_gettime" != "no" && \
+    AC_DEFINE([HAVE_CLOCK_GETTIME], [1], [System provides clock_gettime() call])
 
 
 # What memory units are reported by getrusage(2) ?
diff --git a/src/resuse.c b/src/resuse.c
index d2ab870..ec54863 100644
--- a/src/resuse.c
+++ b/src/resuse.c
@@ -26,7 +26,14 @@
 #include <sys/wait.h>
 #include <sys/resource.h>
 
-#if !HAVE_WAIT3
+#if HAVE_WAIT3
+# if HAVE_CLOCK_GETTIME
+#  ifndef _POSIX_C_SOURCE
+#   define _POSIX_C_SOURCE 199309L
+#  endif
+#  include <time.h>
+# endif
+#else
 # include <sys/times.h>
 # ifndef HZ
 #  include <sys/param.h>
@@ -51,7 +58,14 @@ resuse_start (resp)
      RESUSE *resp;
 {
 #if HAVE_WAIT3
+#if HAVE_CLOCK_GETTIME
+  struct timespec res;
+  clock_gettime(CLOCK_MONOTONIC, &res);
+  resp->start.tv_sec = res.tv_sec;
+  resp->start.tv_usec = res.tv_nsec / 1000;
+#else
   gettimeofday (&resp->start, (struct timezone *) 0);
+#endif /* !HAVE_CLOCK_GETTIME */
 #else
   long value;
   struct tms tms;
@@ -59,7 +73,7 @@ resuse_start (resp)
   value = times (&tms);
   resp->start.tv_sec = value / HZ;
   resp->start.tv_usec = value % HZ * (1000000 / HZ);
-#endif
+#endif /* !HAVE_WAIT3 */
 }
 
 /* Wait for and fill in data on child process PID.
@@ -79,6 +93,9 @@ resuse_end (pid, resp)
   int status;
 
 #if HAVE_WAIT3
+#if HAVE_CLOCK_GETTIME
+  struct timespec res;
+#endif
   pid_t caught;
 
   /* Ignore signals, but don't ignore the children.  When wait3
@@ -89,7 +106,13 @@ resuse_end (pid, resp)
 	return 0;
     }
 
+#if HAVE_CLOCK_GETTIME
+  clock_gettime(CLOCK_MONOTONIC, &res);
+  resp->elapsed.tv_sec = res.tv_sec;
+  resp->elapsed.tv_usec = res.tv_nsec / 1000;
+#else
   gettimeofday (&resp->elapsed, (struct timezone *) 0);
+#endif
 #else  /* !HAVE_WAIT3 */
   long value;
   struct tms tms;
-- 
2.13.6