Linux 5.0 compat: Fix timespec_sub()

The 5.0 kernel no longer include timespec_sub().  It only has
timespec64_sub().  Add a compatibility function.

Signed-off-by:	Tony Hutter <hutter2@llnl.gov>

config/kernel-timespec_sub.m4

@@ -0,0 +1,20 @@
+dnl #
+dnl # 5.0 API change
+dnl #
+dnl # Does timespec_sub() exists?  If not, use timespec64_sub().
+dnl #
+AC_DEFUN([SPL_AC_KERNEL_TIMESPEC_SUB], [
+	AC_MSG_CHECKING([whether timespec_sub() exists])
+	SPL_LINUX_TRY_COMPILE([
+		#include <linux/time.h>
+	],[
+		struct timespec a = {0}, b = {0};
+		timespec_sub(a, b);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_KERNEL_TIMESPEC_SUB, 1,
+		    [kernel has timespec_sub])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/spl-build.m4

@@ -56,6 +56,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_KERNEL_TIMER_FUNCTION_TIMER_LIST
 	SPL_AC_KERNEL_KTIME_GET_COARSE_REAL_TS64
 	SPL_AC_KERNEL_TOTALRAM_PAGES_FUNC
+	SPL_AC_KERNEL_TIMESPEC_SUB
 ])
 
 AC_DEFUN([SPL_AC_MODULE_SYMVERS], [

include/sys/time.h

@@ -57,6 +57,17 @@ typedef struct timespec		timespec_t;
 
 static const int hz = HZ;
 
+/* 5.0 kernels no longer have timespec_sub(), only timespec64_sub() */
+#if !defined(HAVE_KERNEL_TIMESPEC_SUB) && defined(HAVE_INODE_TIMESPEC64_TIMES)
+static inline struct timespec timespec_sub(struct timespec a,
+    struct timespec b) {
+	struct timespec64 res;
+	res = timespec64_sub(timespec_to_timespec64(a),
+	    timespec_to_timespec64(b));
+	return timespec64_to_timespec(res);
+}
+#endif
+
 #define	TIMESPEC_OVERFLOW(ts)		\
 	((ts)->tv_sec < TIME_MIN || (ts)->tv_sec > TIME_MAX)
 

module/splat/splat-kmem.c

@@ -30,6 +30,7 @@
 #include <sys/random.h>
 #include <sys/thread.h>
 #include <sys/vmsystm.h>
+#include <sys/time.h>
 #include "splat-internal.h"
 
 #define SPLAT_KMEM_NAME			"kmem"