libc: add adjtime() system call.

Implement the adjtime() system call and add a test for it to test69.
Additionally, install the adjtime.2 and clock_*.2 man pages.

kernel/clock.c

@@ -20,6 +20,7 @@
  *   clock_stop:	called just before MINIX shutdown
  *   get_realtime:	get wall time since boot in clock ticks
  *   set_realtime:	set wall time since boot in clock ticks
+ *   set_adjtime_delta:	set the number of ticks to adjust realtime
  *   get_monotonic:	get monotonic time since boot in clock ticks
  *   set_timer:		set a watchdog timer (+)
  *   reset_timer:	reset a watchdog timer (+)
@@ -63,6 +64,11 @@ static clock_t monotonic = 0;
  */
 static clock_t realtime = 0;
 
+/* Number of ticks to adjust realtime by. A negative value implies slowing
+ * down realtime, a positive value implies speeding it up.
+ */
+static clock_t adjtime_delta = 0;
+
 /*
  * The boot processor's timer interrupt handler. In addition to non-boot cpus
  * it keeps real time and notifies the clock task if need be.
@@ -90,7 +96,17 @@ int timer_int_handler(void)
 
 	if (cpu_is_bsp(cpuid)) {
 		monotonic++;
-		realtime++;
+
+		/* if adjtime_delta has ticks remaining, apply one to realtime.
+		 * limit changes to every other interrupt.
+		 */
+		if (adjtime_delta != 0 && monotonic & 0x1) {
+			/* go forward or stay behind */
+			realtime += (adjtime_delta > 0) ? 2 : 0;
+			adjtime_delta += (adjtime_delta > 0) ? -1 : +1;
+		} else {
+			realtime++;
+		}
 	}
 
 	/* Update user and system accounting times. Charge the current process
@@ -176,6 +192,14 @@ void set_realtime(clock_t newrealtime)
   realtime = newrealtime;
 }
 
+/*===========================================================================*
+ *				set_adjtime_delta			     *
+ *===========================================================================*/
+void set_adjtime_delta(clock_t ticks)
+{
+  adjtime_delta = ticks;
+}
+
 /*===========================================================================*
  *				get_monotonic				     *
  *===========================================================================*/

kernel/proto.h

@@ -17,6 +17,7 @@ struct timer;
 /* clock.c */
 clock_t get_realtime(void);
 void set_realtime(clock_t);
+void set_adjtime_delta(clock_t);
 clock_t get_monotonic(void);
 void set_timer(struct timer *tp, clock_t t, tmr_func_t f);
 void reset_timer(struct timer *tp);

kernel/system/do_settime.c

@@ -17,12 +17,20 @@
  *===========================================================================*/
 int do_settime(struct proc * caller, message * m_ptr)
 {
-  clock_t newclock;
+  clock_t newclock, ticks;
   time_t timediff;
 
   if (m_ptr->T_CLOCK_ID != CLOCK_REALTIME) /* only realtime can change */
 	return EINVAL;
 
+  if (m_ptr->T_SETTIME_NOW == 0) { /* user just wants to adjtime() */
+	/* convert delta value from seconds and nseconds to ticks */
+	ticks = (m_ptr->T_TIME_SEC * system_hz) +
+				(m_ptr->T_TIME_NSEC/(1000000000/system_hz));
+	set_adjtime_delta(ticks);
+	return(OK);
+  } /* else user wants to set the time */
+
   /* prevent a negative value for realtime */
   if (m_ptr->T_TIME_SEC <= boottime) {
   	/* boottime was likely wrong, try to correct it. */
@@ -35,9 +43,7 @@ int do_settime(struct proc * caller, message * m_ptr)
   timediff = m_ptr->T_TIME_SEC - boottime;
   newclock = (timediff*system_hz) + (m_ptr->T_TIME_NSEC/(1000000000/system_hz));
 
-  if (m_ptr->T_SETTIME_NOW) {
-	set_realtime(newclock);
-  } /* else used adjtime() method (to be implemented) */
+  set_realtime(newclock);
 
   return(OK);
 }