[PATCH 2/3] configure.ac,trace.c: check for CLOCK_MONOTONIC

[Reuben Hawkins <reubenhwk@gmail.com>]

CLOCK_MONOTONIC isn't available on RHEL3, but there are still RHEL3
systems being used in production.  This change makes compiling git
less tedious on older platforms.
---
 configure.ac | 26 ++++++++++++++++++++++++++
 trace.c      |  2 +-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 3cfdd51..3900044 100644
--- a/configure.ac
+++ b/configure.ac
@@ -736,8 +736,10 @@ GIT_UNSTASH_FLAGS($ICONVDIR)
 
 GIT_CONF_SUBST([OLD_ICONV])
 
+
 ## Checks for typedefs, structures, and compiler characteristics.
 AC_MSG_NOTICE([CHECKS for typedefs, structures, and compiler characteristics])
+
 #
 TYPE_SOCKLEN_T
 case $ac_cv_type_socklen_t in
@@ -930,6 +932,30 @@ AC_CHECK_LIB([iconv], [locale_charset],
                      [CHARSET_LIB=-lcharset])])
 GIT_CONF_SUBST([CHARSET_LIB])
 #
+# Define NO_CLOCK_GETTIME if you don't have clock_gettime.
+GIT_CHECK_FUNC(clock_gettime,
+[HAVE_CLOCK_GETTIME=Yes],
+[HAVE_CLOCK_GETTIME=])
+GIT_CONF_SUBST([HAVE_CLOCK_GETTIME])
+
+AC_DEFUN([CLOCK_MONOTONIC_SRC], [
+AC_LANG_PROGRAM([[
+#include <time.h>
+clockid_t id = CLOCK_MONOTONIC;
+]], [])])
+
+#
+# Define NO_CLOCK_MONOTONIC on really old systems that are still in production
+# if you need GIT to compile but can't update the machine otherwise.
+AC_MSG_CHECKING([for CLOCK_MONOTONIC])
+AC_COMPILE_IFELSE([CLOCK_MONOTONIC_SRC],
+	[AC_MSG_RESULT([yes])
+	HAVE_CLOCK_MONOTONIC=Yes],
+	[AC_MSG_RESULT([no])
+	HAVE_CLOCK_MONOTONIC=])
+
+GIT_CONF_SUBST([HAVE_CLOCK_MONOTONIC])
+#
 # Define NO_SETITIMER if you don't have setitimer.
 GIT_CHECK_FUNC(setitimer,
 [NO_SETITIMER=],
diff --git a/trace.c b/trace.c
index 4778608..bfbd48f 100644
--- a/trace.c
+++ b/trace.c
@@ -324,7 +324,7 @@ int trace_want(struct trace_key *key)
 	return !!get_trace_fd(key);
 }
 
-#ifdef HAVE_CLOCK_GETTIME
+#if defined(HAVE_CLOCK_GETTIME) && defined(HAVE_CLOCK_MONOTONIC)
 
 static inline uint64_t highres_nanos(void)
 {
-- 
2.2.0.GIT