lib: Add tst_timer functions.

* Add struct timespec conversions and arithmetic

* Add timer functions simplify elapsed time measurement.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
diff --git a/lib/tst_timer.c b/lib/tst_timer.c
new file mode 100644
index 0000000..5f0cfc4
--- /dev/null
+++ b/lib/tst_timer.c
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2015 Cyril Hrubis <chrubis@suse.cz>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * Further, this software is distributed without any warranty that it is
+ * free of the rightful claim of any third person regarding infringement
+ * or the like.  Any license provided herein, whether implied or
+ * otherwise, applies only to this software file.  Patent licenses, if
+ * any, provided herein do not apply to combinations of this program with
+ * other software, or any other product whatsoever.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <errno.h>
+
+#include "test.h"
+#include "tst_timer.h"
+#include "lapi/posix_clocks.h"
+
+static struct timespec start_time, stop_time;
+static clockid_t clock_id;
+
+static const char *clock_name(clockid_t clk_id)
+{
+	switch (clk_id) {
+	case CLOCK_REALTIME:
+		return "CLOCK_REALTIME";
+	case CLOCK_REALTIME_COARSE:
+		return "CLOCK_REALTIME_COARSE";
+	case CLOCK_MONOTONIC:
+		return "CLOCK_MONOTONIC";
+	case CLOCK_MONOTONIC_COARSE:
+		return "CLOCK_MONOTONIC_COARSE";
+	case CLOCK_MONOTONIC_RAW:
+		return "CLOCK_MONOTONIC_RAW";
+	case CLOCK_BOOTTIME:
+		return "CLOCK_BOOTTIME";
+	case CLOCK_PROCESS_CPUTIME_ID:
+		return "CLOCK_PROCESS_CPUTIME_ID";
+	case CLOCK_THREAD_CPUTIME_ID:
+		return "CLOCK_THREAD_CPUTIME_ID";
+	default:
+		return "UNKNOWN/INVALID";
+	}
+}
+
+void tst_timer_check(clockid_t clk_id)
+{
+	if (clock_gettime(clk_id, &start_time)) {
+		if (errno == EINVAL) {
+			tst_brkm(TCONF, NULL,
+			         "Clock id %s(%u) not supported by kernel",
+				 clock_name(clk_id), clk_id);
+		}
+
+		tst_brkm(TBROK | TERRNO, NULL, "clock_gettime() failed");
+	}
+}
+
+void tst_timer_start(clockid_t clk_id)
+{
+	clock_id = clk_id;
+
+	if (clock_gettime(clock_id, &start_time))
+		tst_resm(TWARN | TERRNO, "clock_gettime() failed");
+}
+
+void tst_timer_stop(void)
+{
+	if (clock_gettime(clock_id, &stop_time))
+		tst_resm(TWARN | TERRNO, "clock_gettime() failed");
+}
+
+struct timespec tst_timer_elapsed(void)
+{
+	return tst_timespec_diff(stop_time, start_time);
+}