[PATCH v2] libshouldbeinlibc: Use 64bit mapped time values in maptime_read when possible

[Zhaoming Luo]

Use 64bit mapped time values in maptime_read when the kernel and the
mapped_time_value structure in header file time_value.h support it.
Otherwise step back to use the 32bit time.

---
 configure.ac                |  3 +++
 libshouldbeinlibc/maptime.h | 16 ++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/configure.ac b/configure.ac
index 1f814438..d7e33e56 100644
--- a/configure.ac
+++ b/configure.ac
@@ -335,6 +335,9 @@ AC_SUBST([libdaemon_CFLAGS])
 AC_CHECK_MEMBERS([struct thread_sched_info.last_processor],,,
  [#include <mach/thread_info.h>])
 
+AC_CHECK_MEMBERS([struct mapped_time_value.time_value.seconds],,,
+ [#include <mach/time_value.h>])
+
 PKG_CHECK_MODULES([libblkid], [blkid],
   [AC_DEFINE([HAVE_BLKID], [1], [Use libblkid])],
   [true])
diff --git a/libshouldbeinlibc/maptime.h b/libshouldbeinlibc/maptime.h
index 04ce0353..3a595ae5 100644
--- a/libshouldbeinlibc/maptime.h
+++ b/libshouldbeinlibc/maptime.h
@@ -48,6 +48,22 @@ extern void maptime_read (volatile struct mapped_time_value 
*mtime, struct timev
 MAPTIME_EI void
 maptime_read (volatile struct mapped_time_value *mtime, struct timeval *tv)
 {
+#ifdef HAVE_STRUCT_MAPPED_TIME_VALUE_TIME_VALUE_SECONDS
+  /* Use the 64bit time if it is supported in the kernel.  Otherwise step
+     back to the 32bit time.  */
+  if (mtime->time_value.seconds != 0)
+    {
+      do
+       {
+         tv->tv_sec = mtime->time_value.seconds;
+         __sync_synchronize ();
+         tv->tv_usec = mtime->time_value.nanoseconds / 1000;
+         __sync_synchronize ();
+       }
+      while (tv->tv_sec != mtime->check_seconds64);
+      return;
+    }
+#endif
   do
     {
       tv->tv_sec = mtime->seconds;
-- 
2.49.0