[S390] introduce vdso on s390

Add a vdso to speed up gettimeofday and clock_getres/clock_gettime for
CLOCK_REALTIME/CLOCK_MONOTONIC.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/vdso.h

@@ -0,0 +1,39 @@
+#ifndef __S390_VDSO_H__
+#define __S390_VDSO_H__
+
+#ifdef __KERNEL__
+
+/* Default link addresses for the vDSOs */
+#define VDSO32_LBASE	0
+#define VDSO64_LBASE	0
+
+#define VDSO_VERSION_STRING	LINUX_2.6.26
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Note about this structure:
+ *
+ * NEVER USE THIS IN USERSPACE CODE DIRECTLY. The layout of this
+ * structure is supposed to be known only to the function in the vdso
+ * itself and may change without notice.
+ */
+
+struct vdso_data {
+	__u64 tb_update_count;		/* Timebase atomicity ctr	0x00 */
+	__u64 xtime_tod_stamp;		/* TOD clock for xtime		0x08 */
+	__u64 xtime_clock_sec;		/* Kernel time			0x10 */
+	__u64 xtime_clock_nsec;		/*				0x18 */
+	__u64 wtom_clock_sec;		/* Wall to monotonic clock	0x20 */
+	__u64 wtom_clock_nsec;		/*				0x28 */
+	__u32 tz_minuteswest;		/* Minutes west of Greenwich	0x30 */
+	__u32 tz_dsttime;		/* Type of dst correction	0x34 */
+};
+
+extern struct vdso_data *vdso_data;
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __KERNEL__ */
+
+#endif /* __S390_VDSO_H__ */