Source to osfmk/kern/clock.c


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/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @[email protected]
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @[email protected]
 */
/*
 * @[email protected]
 */
/*
 *	File:		kern/clock.c
 *	Purpose:	Routines for the creation and use of kernel
 *			alarm clock services. This file and the ipc
 *			routines in kern/ipc_clock.c constitute the
 *			machine-independent clock service layer.
 */

#include <cpus.h>
#include <mach_host.h>

#include <mach/boolean.h>
#include <mach/policy.h>
#include <mach/processor_info.h>
#include <mach/vm_param.h>
#include <machine/mach_param.h>
#include <kern/cpu_number.h>
#include <kern/misc_protos.h>
#include <kern/lock.h>
#include <kern/host.h>
#include <kern/processor.h>
#include <kern/sched.h>
#include <kern/spl.h>
#include <kern/thread.h>
#include <kern/thread_swap.h>
#include <kern/ipc_host.h>
#include <kern/clock.h>
#include <kern/zalloc.h>
#include <kern/sf.h>
#include <ipc/ipc_port.h>
#include <mach/mach_syscalls.h>

#include <mach/clock_reply.h>

/*
 * Exported interface
 */

#include <mach/clock_server.h>
#include <mach/mach_host_server.h>

/* local data declarations */
decl_simple_lock_data(static,ClockLock)		/* clock system synchronization */
static struct	zone		*alarm_zone;	/* zone for user alarms */
static struct	alarm		*alrmfree;		/* alarm free list pointer */
static struct	alarm		*alrmdone;		/* alarm done list pointer */
static long					alrm_seqno;		/* uniquely identifies alarms */
static thread_call_data_t	alarm_deliver;

/* backwards compatibility */
int             hz = HZ;                /* GET RID OF THIS !!! */
int             tick = (1000000 / HZ);  /* GET RID OF THIS !!! */

/* external declarations */
extern	struct clock	clock_list[];
extern	int		clock_count;

/* local clock subroutines */
static
void	flush_alarms(
			clock_t			clock);

static
void	post_alarm(
			clock_t			clock,
			alarm_t			alarm);

static
int		check_time(
			alarm_type_t	alarm_type,
			mach_timespec_t	*alarm_time,
			mach_timespec_t	*clock_time);

static void		clock_alarm_deliver(void);

/*
 *	Macros to lock/unlock clock system.
 */
#define LOCK_CLOCK(s)			\
	s = splclock();			\
	simple_lock(&ClockLock);

#define UNLOCK_CLOCK(s)			\
	simple_unlock(&ClockLock);	\
	splx(s);

/*
 * Configure the clock system. (Not sure if we need this,
 * as separate from clock_init()).
 */
void
clock_config(void)
{
	clock_t			clock;
	register int 	i;

	if (cpu_number() != master_cpu)
		panic("clock_config");

	/*
	 * Configure clock devices.
	 */
	simple_lock_init(&ClockLock, ETAP_MISC_CLOCK);
	for (i = 0; i < clock_count; i++) {
		clock = &clock_list[i];
		if (clock->cl_ops) {
			if ((*clock->cl_ops->c_config)() == 0)
				clock->cl_ops = 0;
		}
	}

	/* start alarm sequence numbers at 0 */
	alrm_seqno = 0;
}

/*
 * Initialize the clock system.
 */
void
clock_init(void)
{
	clock_t			clock;
	register int	i;

	/*
	 * Initialize basic clock structures.
	 */
	for (i = 0; i < clock_count; i++) {
		clock = &clock_list[i];
		if (clock->cl_ops)
			(*clock->cl_ops->c_init)();
	}
}

/*
 * Initialize the clock ipc service facility.
 */
void
clock_service_create(void)
{
	clock_t			clock;
	register int	i;

	/*
	 * Initialize ipc clock services.
	 */
	for (i = 0; i < clock_count; i++) {
		clock = &clock_list[i];
		if (clock->cl_ops) {
			ipc_clock_init(clock);
			ipc_clock_enable(clock);
		}
	}

	/*
	 * Initialize clock service alarms.
	 */
	i = sizeof(struct alarm);
	alarm_zone = zinit(i, (4096/i)*i, 10*i, "alarms");

	/*
	 * Initialize the clock alarm delivery mechanism.
	 */
	thread_call_setup(&alarm_deliver, clock_alarm_deliver, NULL);
}

/*
 * Get the service port on a clock.
 */
kern_return_t
host_get_clock_service(
	host_t			host,
	clock_id_t		clock_id,
	clock_t			*clock)		/* OUT */
{
	if (host == HOST_NULL || clock_id < 0 || clock_id >= clock_count) {
		*clock = CLOCK_NULL;
		return (KERN_INVALID_ARGUMENT);
	}

	*clock = &clock_list[clock_id];
	if ((*clock)->cl_ops == 0)
		return (KERN_FAILURE);
	return (KERN_SUCCESS);
}

/*
 * Get the control port on a clock.
 */
kern_return_t
host_get_clock_control(
	host_t			host,
	clock_id_t		clock_id,
	clock_t			*clock)		/* OUT */
{
	if (host == HOST_NULL || clock_id < 0 || clock_id >= clock_count) {
		*clock = CLOCK_NULL;
		return (KERN_INVALID_ARGUMENT);
	}

	*clock = &clock_list[clock_id];
	if ((*clock)->cl_ops == 0)
		return (KERN_FAILURE);
	return (KERN_SUCCESS);
}

/*
 * Get the current clock time.
 */
kern_return_t
clock_get_time(
	clock_t			clock,
	mach_timespec_t	*cur_time)	/* OUT */
{
	if (clock == CLOCK_NULL)
		return (KERN_INVALID_ARGUMENT);
	return ((*clock->cl_ops->c_gettime)(cur_time));
}

/*
 * Get clock attributes.
 */
kern_return_t
clock_get_attributes(
	clock_t					clock,
	clock_flavor_t			flavor,
	clock_attr_t			attr,		/* OUT */
	mach_msg_type_number_t	*count)		/* IN/OUT */
{
	kern_return_t	(*getattr)(
						clock_flavor_t			flavor,
						clock_attr_t			attr,
						mach_msg_type_number_t	*count);

	if (clock == CLOCK_NULL)
		return (KERN_INVALID_ARGUMENT);
	if (getattr = clock->cl_ops->c_getattr)
		return((*getattr)(flavor, attr, count));
	else
		return (KERN_FAILURE);
}

/*
 * Set the current clock time.
 */
kern_return_t
clock_set_time(
	clock_t			clock,
	mach_timespec_t	new_time)
{
	mach_timespec_t	*clock_time;
	kern_return_t	(*settime)(
						mach_timespec_t		*clock_time);

	if (clock == CLOCK_NULL)
		return (KERN_INVALID_ARGUMENT);
	if ((settime = clock->cl_ops->c_settime) == 0)
		return (KERN_FAILURE);
	clock_time = &new_time;
	if (BAD_MACH_TIMESPEC(clock_time))
		return (KERN_INVALID_VALUE);

	/*
	 * Flush all outstanding alarms.
	 */
	flush_alarms(clock);

	/*
	 * Set the new time.
	 */
	return ((*settime)(clock_time));
}

/*
 * Set the clock alarm resolution.
 */
kern_return_t
clock_set_attributes(
	clock_t					clock,
	clock_flavor_t			flavor,
	clock_attr_t			attr,
	mach_msg_type_number_t	count)
{
	kern_return_t	(*setattr)(
						clock_flavor_t			flavor,
						clock_attr_t			attr,
						mach_msg_type_number_t	count);

	if (clock == CLOCK_NULL)
		return (KERN_INVALID_ARGUMENT);
	if (setattr = clock->cl_ops->c_setattr)
		return ((*setattr)(flavor, attr, count));
	else
		return (KERN_FAILURE);
}

/*
 * Setup a clock alarm.
 */
kern_return_t
clock_alarm(
	clock_t					clock,
	alarm_type_t			alarm_type,
	mach_timespec_t			alarm_time,
	ipc_port_t				alarm_port,
	mach_msg_type_name_t	alarm_port_type)
{
	alarm_t					alarm;
	mach_timespec_t			clock_time;
	int						chkstat;
	kern_return_t			reply_code;
	spl_t					s;

	if (clock == CLOCK_NULL)
		return (KERN_INVALID_ARGUMENT);
	if (clock->cl_ops->c_setalrm == 0)
		return (KERN_FAILURE);
	if (IP_VALID(alarm_port) == 0)
		return (KERN_INVALID_CAPABILITY);

	/*
	 * Check alarm parameters. If parameters are invalid,
	 * send alarm message immediately.
	 */
	(*clock->cl_ops->c_gettime)(&clock_time);
	chkstat = check_time(alarm_type, &alarm_time, &clock_time);
	if (chkstat <= 0) {
		reply_code = (chkstat < 0 ? KERN_INVALID_VALUE : KERN_SUCCESS);
		clock_alarm_reply(alarm_port, alarm_port_type,
				  reply_code, alarm_type, clock_time);
		return (KERN_SUCCESS);
	}

	/*
	 * Get alarm and add to clock alarm list.
	 */

	LOCK_CLOCK(s);
	if ((alarm = alrmfree) == 0) {
		UNLOCK_CLOCK(s);
		alarm = (alarm_t) zalloc(alarm_zone);
		if (alarm == 0)
			return (KERN_RESOURCE_SHORTAGE);
		LOCK_CLOCK(s);
	}
	else
		alrmfree = alarm->al_next;

	alarm->al_status = ALARM_CLOCK;
	alarm->al_time = alarm_time;
	alarm->al_type = alarm_type;
	alarm->al_port = alarm_port;
	alarm->al_port_type = alarm_port_type;
	alarm->al_clock = clock;
	alarm->al_policy = POLICY_NULL;
	alarm->al_seqno = alrm_seqno++;
	post_alarm(clock, alarm);
	UNLOCK_CLOCK(s);

	return (KERN_SUCCESS);
}

/*
 * Set a clock alarm for a scheduling policy.
 */
kern_return_t
clock_alarm_sp(
	alarm_type_t		alarm_type,
	mach_timespec_t		alarm_time,
	long				*alarm_id,
	int					policy,
	void				*alarm_data,
	alarm_t				alarm)
{
	clock_t				clock;
	mach_timespec_t		clock_time;
	int					chkstat;
	spl_t				s;

	/* Always use system clock. */
	clock = &clock_list[SYSTEM_CLOCK];

	if (clock->cl_ops->c_setalrm == 0)
		return (KERN_FAILURE);

	assert(alarm != 0);

	/*
	 * Check alarm parameters. If parameters are invalid,
	 * send alarm message immediately.
	 */
	(*clock->cl_ops->c_gettime)(&clock_time);
	chkstat = check_time(alarm_type, &alarm_time, &clock_time);
	if (chkstat <= 0) {
		return(chkstat < 0 ? KERN_INVALID_VALUE : KERN_RETURN_MAX);
		/*** ??? define a better value for `KERN_RETURN_MAX' ***/
	}

	/*
	 * Get alarm and add to clock alarm list.
	 */

	LOCK_CLOCK(s);
	alarm->al_status = ALARM_CLOCK;
	alarm->al_time = alarm_time;
	alarm->al_type = alarm_type;
	alarm->al_port = IP_NULL;
	alarm->al_port_type = 0;
	alarm->al_clock = clock;
	alarm->al_data = alarm_data;
	alarm->al_policy = policy;
	alarm->al_seqno = alrm_seqno++;
	*alarm_id = alarm->al_seqno;
	post_alarm(clock, alarm);
	UNLOCK_CLOCK(s);

	return (KERN_SUCCESS);
}

/*
 * Cancel a clock alarm on behalf of a scheduling policy.
 */
kern_return_t
clock_alarm_cancel_sp(
	long				alarm_id)
{
	clock_t				clock;
	alarm_t				alrm1, alrm2;
	kern_return_t		kr = KERN_FAILURE;
	spl_t				s;

	/*
	 * Cancel alarm with ID `alarm_id.'
	 */

	/* Always use system clock. */
	clock = &clock_list[SYSTEM_CLOCK];

	/* Assume you can't cancel alarms if you can't set them */
	if (clock->cl_ops->c_setalrm == 0)
		return (KERN_FAILURE);

	LOCK_CLOCK(s);
	alrm1 = (alarm_t) &clock->cl_alarm;
	while (alrm2 = alrm1->al_next) {
		/*
		 * See if alarm is still in alarm list.
		 */
		if (alrm2->al_seqno == alarm_id) {
			/* Found it.  Now remove it. */
			if (alrm1->al_next = alrm2->al_next) {
				(alrm1->al_next)->al_prev = alrm1;
			}

			/* Indicate success */
			kr = KERN_SUCCESS;

			/*
			 * If the canceled alarm is the 'earliest' alarm,
			 * reset the device layer alarm time accordingly.
			 */
			if (clock->cl_alarm.al_next == alrm2)
				(*clock->cl_ops->c_setalrm)
				  (&((clock->cl_alarm.al_next)->al_time));

			/* Quit looking */
			break;
		}
	}
	UNLOCK_CLOCK(s);

	return(kr);
}

/*
 * Sleep on a clock. System trap. User-level libmach clock_sleep
 * interface call takes a mach_timespec_t sleep_time argument which it
 * converts to sleep_sec and sleep_nsec arguments which are then
 * passed to clock_sleep_trap.
 */
kern_return_t
clock_sleep_trap(
	mach_port_name_t	clock_name,
	sleep_type_t		sleep_type,
	int					sleep_sec,
	int					sleep_nsec,
	mach_timespec_t		*wakeup_time)
{
	clock_t				clock;
	mach_timespec_t		swtime;
	kern_return_t		rvalue;

	/*
	 * Convert the trap parameters.
	 */
	clock = port_name_to_clock(clock_name);
	swtime.tv_sec  = sleep_sec;
	swtime.tv_nsec = sleep_nsec;

	/*
	 * Call the actual clock_sleep routine.
	 */
	rvalue = clock_sleep_internal(clock, sleep_type, &swtime);

	/*
	 * Return current time as wakeup time.
	 */
	if (rvalue != KERN_INVALID_ARGUMENT && rvalue != KERN_FAILURE) {
		copyout((char *)&swtime, (char *)wakeup_time,
			sizeof(mach_timespec_t));
	}
	return (rvalue);
}	

/*
 * Kernel internally callable clock sleep routine. The calling
 * thread is suspended until the requested sleep time is reached.
 */
kern_return_t
clock_sleep_internal(
	clock_t				clock,
	sleep_type_t		sleep_type,
	mach_timespec_t		*sleep_time)
{
	alarm_t				alarm;
	mach_timespec_t		clock_time;
	kern_return_t		rvalue;
	int					chkstat;
	spl_t				s;

	if (clock == CLOCK_NULL)
		return (KERN_INVALID_ARGUMENT);
	if (clock->cl_ops->c_setalrm == 0)
		return (KERN_FAILURE);

	/*
	 * Check sleep parameters. If parameters are invalid
	 * return an error, otherwise post alarm request.
	 */
	(*clock->cl_ops->c_gettime)(&clock_time);

	chkstat = check_time(sleep_type, sleep_time, &clock_time);
	if (chkstat < 0)
		return (KERN_INVALID_VALUE);
	rvalue = KERN_SUCCESS;
	if (chkstat > 0) {
		/*
		 * Get alarm and add to clock alarm list.
		 */

		LOCK_CLOCK(s);
		if ((alarm = alrmfree) == 0) {
			UNLOCK_CLOCK(s);
			alarm = (alarm_t) zalloc(alarm_zone);
			if (alarm == 0)
				return (KERN_RESOURCE_SHORTAGE);
			LOCK_CLOCK(s);
		}
		else
			alrmfree = alarm->al_next;

		alarm->al_time = *sleep_time;
		alarm->al_status = ALARM_SLEEP;
		post_alarm(clock, alarm);

		/*
		 * Wait for alarm to occur.
		 */
		assert_wait((event_t)alarm, THREAD_ABORTSAFE);
		UNLOCK_CLOCK(s);
		/* should we force spl(0) at this point? */
		thread_block((void (*)(void)) 0);
		/* we should return here at ipl0 */

		/*
		 * Note if alarm expired normally or whether it
		 * was aborted. If aborted, delete alarm from
		 * clock alarm list. Return alarm to free list.
		 */
		LOCK_CLOCK(s);
		if (alarm->al_status != ALARM_DONE) {
			/* This means we were interrupted and that
			   thread->wait_result != THREAD_AWAKENED. */
			if ((alarm->al_prev)->al_next = alarm->al_next)
				(alarm->al_next)->al_prev = alarm->al_prev;
			rvalue = KERN_ABORTED;
		}
		*sleep_time = alarm->al_time;
		alarm->al_status = ALARM_FREE;
		alarm->al_next = alrmfree;
		alrmfree = alarm;
		UNLOCK_CLOCK(s);
	}
	else
		*sleep_time = clock_time;

	return (rvalue);
}

/*
 * CLOCK INTERRUPT SERVICE ROUTINES.
 */

/*
 * Service clock alarm interrupts. Called from machine dependent
 * layer at splclock(). The clock_id argument specifies the clock,
 * and the clock_time argument gives that clock's current time.
 */
void
clock_alarm_intr(
	clock_id_t			clock_id,
	mach_timespec_t		*clock_time)
{
	clock_t				clock;
	register alarm_t	alrm1;
	register alarm_t	alrm2;
	mach_timespec_t		*alarm_time;
	spl_t				s;

	clock = &clock_list[clock_id];

	/*
	 * Update clock alarm list. All alarms that are due are moved
	 * to the alarmdone list to be serviced by the alarm_thread.
	 */

	LOCK_CLOCK(s);
	alrm1 = (alarm_t) &clock->cl_alarm;
	while (alrm2 = alrm1->al_next) {
		alarm_time = &alrm2->al_time;
		if (CMP_MACH_TIMESPEC(alarm_time, clock_time) > 0)
			break;

		/*
		 * Alarm has expired, so remove it from the
		 * clock alarm list.
		 */  
		if (alrm1->al_next = alrm2->al_next)
			(alrm1->al_next)->al_prev = alrm1;

		/*
		 * If a clock_sleep() alarm, wakeup the thread
		 * which issued the clock_sleep() call.
		 */
		if (alrm2->al_status == ALARM_SLEEP) {
			alrm2->al_next = 0;
			alrm2->al_status = ALARM_DONE;
			alrm2->al_time = *clock_time;
			thread_wakeup((event_t)alrm2);
		}

 		/*
		 * If a clock_alarm() alarm, place the alarm on
		 * the alarm done list and schedule the alarm
		 * delivery mechanism.
		 */
		else {
			assert(alrm2->al_status == ALARM_CLOCK);
			if (alrm2->al_next = alrmdone)
				alrmdone->al_prev = alrm2;
			else
				thread_call_enter(&alarm_deliver);
			alrm2->al_prev = (alarm_t) &alrmdone;
			alrmdone = alrm2;
			alrm2->al_status = ALARM_DONE;
			alrm2->al_time = *clock_time;
		}
	}

	/*
	 * Setup the clock dependent layer to deliver another
	 * interrupt for the next pending alarm.
	 */
	if (alrm2)
		(*clock->cl_ops->c_setalrm)(alarm_time);
	UNLOCK_CLOCK(s);
}

/*
 * ALARM DELIVERY ROUTINES.
 */

static
void
clock_alarm_deliver(void)
{
	register alarm_t	alrm;
	kern_return_t		code;
	sched_policy_t		*policy;
	spl_t				s;

	LOCK_CLOCK(s);
	while (alrm = alrmdone) {
		if (alrmdone = alrm->al_next)
			alrmdone->al_prev = (alarm_t) &alrmdone;
		UNLOCK_CLOCK(s);

		code = (alrm->al_status == ALARM_DONE? KERN_SUCCESS: KERN_ABORTED);
		if (alrm->al_port != IP_NULL) {
			/* Deliver message to designated port */
			if (IP_VALID(alrm->al_port)) {
				clock_alarm_reply(alrm->al_port, alrm->al_port_type, code,
								  				alrm->al_type, alrm->al_time);
			}

			LOCK_CLOCK(s);
			alrm->al_status = ALARM_FREE;
			alrm->al_next = alrmfree;
			alrmfree = alrm;
		}
		else {
			/* Call designated scheduling policy's alarm routine */
			assert(alrm->al_policy != POLICY_NULL);
			policy = &sched_policy[alrm->al_policy];
			policy->sp_ops.sp_alarm_expired(policy, alrm->al_seqno, code,
								alrm->al_type, alrm->al_time, alrm->al_data);

			LOCK_CLOCK(s);
		}
	}

	UNLOCK_CLOCK(s);
}

/*
 * CLOCK PRIVATE SERVICING SUBROUTINES.
 */

/*
 * Flush all pending alarms on a clock. All alarms
 * are activated and timestamped correctly, so any
 * programs waiting on alarms/threads will proceed
 * with accurate information.
 */
static
void
flush_alarms(
	clock_t				clock)
{
	register alarm_t	alrm1, alrm2;
	spl_t				s;

	/*
	 * Flush all outstanding alarms.
	 */
	LOCK_CLOCK(s);
	alrm1 = (alarm_t) &clock->cl_alarm;
	while (alrm2 = alrm1->al_next) {
		/*
		 * Remove alarm from the clock alarm list.
		 */  
		if (alrm1->al_next = alrm2->al_next)
			(alrm1->al_next)->al_prev = alrm1;

		/*
		 * If a clock_sleep() alarm, wakeup the thread
		 * which issued the clock_sleep() call.
		 */
		if (alrm2->al_status == ALARM_SLEEP) {
			alrm2->al_next = 0;
			thread_wakeup((event_t)alrm2);
		}
		else {
			/*
			 * If a clock_alarm() alarm, place the alarm on
			 * the alarm done list and wakeup the dedicated
			 * kernel alarm_thread to service the alarm.
			 */
			assert(alrm2->al_status == ALARM_CLOCK);
			if (alrm2->al_next = alrmdone)
				alrmdone->al_prev = alrm2;
			else
				thread_wakeup((event_t)&alrmdone);
			alrm2->al_prev = (alarm_t) &alrmdone;
			alrmdone = alrm2;
		}
	}
	UNLOCK_CLOCK(s);
}

/*
 * Post an alarm on a clock's active alarm list. The alarm is
 * inserted in time-order into the clock's active alarm list.
 * Always called from within a LOCK_CLOCK() code section.
 */
static
void
post_alarm(
	clock_t				clock,
	alarm_t				alarm)
{
	register alarm_t	alrm1, alrm2;
	mach_timespec_t		*alarm_time;
	mach_timespec_t		*queue_time;

	/*
	 * Traverse alarm list until queue time is greater
	 * than alarm time, then insert alarm.
	 */
	alarm_time = &alarm->al_time;
	alrm1 = (alarm_t) &clock->cl_alarm;
	while (alrm2 = alrm1->al_next) {
		queue_time = &alrm2->al_time;
		if (CMP_MACH_TIMESPEC(queue_time, alarm_time) > 0)
			break;
		alrm1 = alrm2;
	}
	alrm1->al_next = alarm;
	alarm->al_next = alrm2;
	alarm->al_prev = alrm1;
	if (alrm2)
		alrm2->al_prev  = alarm;

	/*
	 * If the inserted alarm is the 'earliest' alarm,
	 * reset the device layer alarm time accordingly.
	 */
	if (clock->cl_alarm.al_next == alarm)
		(*clock->cl_ops->c_setalrm)(alarm_time);
}

/*
 * Check the validity of 'alarm_time' and 'alarm_type'. If either
 * argument is invalid, return a negative value. If the 'alarm_time'
 * is now, return a 0 value. If the 'alarm_time' is in the future,
 * return a positive value.
 */
static
int
check_time(
	alarm_type_t		alarm_type,
	mach_timespec_t		*alarm_time,
	mach_timespec_t		*clock_time)
{
	int					result;

	if (BAD_ALRMTYPE(alarm_type))
		return (-1);
	if (BAD_MACH_TIMESPEC(alarm_time))
		return (-1);
	if ((alarm_type & ALRMTYPE) == TIME_RELATIVE)
		ADD_MACH_TIMESPEC(alarm_time, clock_time);

	result = CMP_MACH_TIMESPEC(alarm_time, clock_time);

	return ((result >= 0)? result: 0);
}

mach_timespec_t
clock_get_system_value(void)
{
	clock_t				clock = &clock_list[SYSTEM_CLOCK];
	mach_timespec_t		value;

	(void) (*clock->cl_ops->c_gettime)(&value);

	return value;
}

mach_timespec_t
clock_get_calendar_value(void)
{
	clock_t				clock = &clock_list[CALENDAR_CLOCK];
	mach_timespec_t		value = MACH_TIMESPEC_ZERO;

	(void) (*clock->cl_ops->c_gettime)(&value);

	return value;
}

void
clock_set_calendar_value(
	mach_timespec_t		value)
{
	clock_t				clock = &clock_list[CALENDAR_CLOCK];

	(void) (*clock->cl_ops->c_settime)(&value);
}

void
clock_deadline_for_periodic_event(
	AbsoluteTime		interval,
	AbsoluteTime		abstime,
	AbsoluteTime		*deadline)
{
	assert(AbsoluteTime_to_scalar(&interval) != 0);

	ADD_ABSOLUTETIME(deadline, &interval);

	if (	AbsoluteTime_to_scalar(deadline)	<=
			AbsoluteTime_to_scalar(&abstime)		) {
		*deadline = abstime;
		clock_get_uptime(&abstime);
		ADD_ABSOLUTETIME(deadline, &interval);

		if (	AbsoluteTime_to_scalar(deadline)	<=
				AbsoluteTime_to_scalar(&abstime)		) {
			*deadline = abstime;
			ADD_ABSOLUTETIME(deadline, &interval);
		}
	}
}