/*
 * wtime, short for wall time, count the time in nanoseconds elapsed 
 * since 1970/1/1, 0:0:0am.  It maintains a strict relationship with
 * mtime as follows:
 *
 * 	wtime = epoch + mtime
 *
 * where epoch is the initial wtime when machine starts.
 *
 * It is a 64-bit variable counted in units of nanoseconds, which gives
 * ~584 - <curr_year - 1970> years.
 *
 * wtime is implemented on top of mtime.  Whenever mtime advances
 * wtime advances naturally due to the fixed difference between them. 
 *
 * wtime can be changed.  No monotonicity is assumed.
 *
 * wtimers are timers that expire in wtime.  The callback of wtimer
 * when it expires is run in a process context (a daemon).
 *
 * Read/write of wtime is guarded by a reader/writer semaphore.  Callbacks
 * of wtimer are executed with reader semaphore acquired.  One must
 * acquire writer semaphore to change wtime, which implies wtime can
 * only be changed from process context.
 */

#ifndef _LINUX_MTIME_H
#define _LINUX_MTIME_H

#include <linux/types.h>
#include <linux/mtime.h>

extern u64 wtime_epoch;

/*
 * latch mtime and return current wtime
 */
u64 wtime_get(void);

/*
 * return current epoch value
 */
u64 wtime_get_epoch(void);

/*
 * Set wtime.  Must acquire writer semaphore first.
 */
int wtime_set(u64);

/*
 * wtimers
 */
void wtimer_add(struct wtimer_struct *);
void wtimer_del(struct wtimer_struct *);
void wtimer_mod(struct wtimer_struct *, u64 new_expire);

#endif