util/qemu-timer.c - third_party/qemu - Git at Google

 /*
  * QEMU System Emulator
  *
  * Copyright (c) 2003-2008 Fabrice Bellard
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */

 #include "qemu/osdep.h"
 #include "qemu/main-loop.h"
 #include "qemu/timer.h"
 #include "qemu/lockable.h"
 #include "sysemu/replay.h"
 #include "sysemu/cpus.h"

 #ifdef CONFIG_POSIX
 #include <pthread.h>
 #endif

 #ifdef CONFIG_PPOLL
 #include <poll.h>
 #endif

 #ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
 #include <sys/prctl.h>
 #endif

 /***********************************************************/
 /* timers */

 typedef struct QEMUClock {
     /* We rely on BQL to protect the timerlists */
     QLIST_HEAD(, QEMUTimerList) timerlists;

     QEMUClockType type;
     bool enabled;
 } QEMUClock;

 QEMUTimerListGroup main_loop_tlg;
 static QEMUClock qemu_clocks[QEMU_CLOCK_MAX];

 /* A QEMUTimerList is a list of timers attached to a clock. More
  * than one QEMUTimerList can be attached to each clock, for instance
  * used by different AioContexts / threads. Each clock also has
  * a list of the QEMUTimerLists associated with it, in order that
  * reenabling the clock can call all the notifiers.
  */

 struct QEMUTimerList {
     QEMUClock *clock;
     QemuMutex active_timers_lock;
     QEMUTimer *active_timers;
     QLIST_ENTRY(QEMUTimerList) list;
     QEMUTimerListNotifyCB *notify_cb;
     void *notify_opaque;

     /* lightweight method to mark the end of timerlist's running */
     QemuEvent timers_done_ev;
 };

 /**
  * qemu_clock_ptr:
  * @type: type of clock
  *
  * Translate a clock type into a pointer to QEMUClock object.
  *
  * Returns: a pointer to the QEMUClock object
  */
 static inline QEMUClock *qemu_clock_ptr(QEMUClockType type)
 {
     return &qemu_clocks[type];
 }

 static bool timer_expired_ns(QEMUTimer *timer_head, int64_t current_time)
 {
     return timer_head && (timer_head->expire_time <= current_time);
 }

 QEMUTimerList *timerlist_new(QEMUClockType type,
                              QEMUTimerListNotifyCB *cb,
                              void *opaque)
 {
     QEMUTimerList *timer_list;
     QEMUClock *clock = qemu_clock_ptr(type);

     timer_list = g_malloc0(sizeof(QEMUTimerList));
     qemu_event_init(&timer_list->timers_done_ev, true);
     timer_list->clock = clock;
     timer_list->notify_cb = cb;
     timer_list->notify_opaque = opaque;
     qemu_mutex_init(&timer_list->active_timers_lock);
     QLIST_INSERT_HEAD(&clock->timerlists, timer_list, list);
     return timer_list;
 }

 void timerlist_free(QEMUTimerList *timer_list)
 {
     assert(!timerlist_has_timers(timer_list));
     if (timer_list->clock) {
         QLIST_REMOVE(timer_list, list);
     }
     qemu_mutex_destroy(&timer_list->active_timers_lock);
     g_free(timer_list);
 }

 static void qemu_clock_init(QEMUClockType type, QEMUTimerListNotifyCB *notify_cb)
 {
     QEMUClock *clock = qemu_clock_ptr(type);

     /* Assert that the clock of type TYPE has not been initialized yet. */
     assert(main_loop_tlg.tl[type] == NULL);

     clock->type = type;
     clock->enabled = (type == QEMU_CLOCK_VIRTUAL ? false : true);
     QLIST_INIT(&clock->timerlists);
     main_loop_tlg.tl[type] = timerlist_new(type, notify_cb, NULL);
 }

 bool qemu_clock_use_for_deadline(QEMUClockType type)
 {
     return !(use_icount && (type == QEMU_CLOCK_VIRTUAL));
 }

 void qemu_clock_notify(QEMUClockType type)
 {
     QEMUTimerList *timer_list;
     QEMUClock *clock = qemu_clock_ptr(type);
     QLIST_FOREACH(timer_list, &clock->timerlists, list) {
         timerlist_notify(timer_list);
     }
 }

 /* Disabling the clock will wait for related timerlists to stop
  * executing qemu_run_timers.  Thus, this functions should not
  * be used from the callback of a timer that is based on @clock.
  * Doing so would cause a deadlock.
  *
  * Caller should hold BQL.
  */
 void qemu_clock_enable(QEMUClockType type, bool enabled)
 {
     QEMUClock *clock = qemu_clock_ptr(type);
     QEMUTimerList *tl;
     bool old = clock->enabled;
     clock->enabled = enabled;
     if (enabled && !old) {
         qemu_clock_notify(type);
     } else if (!enabled && old) {
         QLIST_FOREACH(tl, &clock->timerlists, list) {
             qemu_event_wait(&tl->timers_done_ev);
         }
     }
 }

 bool timerlist_has_timers(QEMUTimerList *timer_list)
 {
     return !!atomic_read(&timer_list->active_timers);
 }

 bool qemu_clock_has_timers(QEMUClockType type)
 {
     return timerlist_has_timers(
         main_loop_tlg.tl[type]);
 }

 bool timerlist_expired(QEMUTimerList *timer_list)
 {
     int64_t expire_time;

     if (!atomic_read(&timer_list->active_timers)) {
         return false;
     }

     WITH_QEMU_LOCK_GUARD(&timer_list->active_timers_lock) {
         if (!timer_list->active_timers) {
             return false;
         }
         expire_time = timer_list->active_timers->expire_time;
     }

     return expire_time <= qemu_clock_get_ns(timer_list->clock->type);
 }

 bool qemu_clock_expired(QEMUClockType type)
 {
     return timerlist_expired(
         main_loop_tlg.tl[type]);
 }

 /*
  * As above, but return -1 for no deadline, and do not cap to 2^32
  * as we know the result is always positive.
  */

 int64_t timerlist_deadline_ns(QEMUTimerList *timer_list)
 {
     int64_t delta;
     int64_t expire_time;

     if (!atomic_read(&timer_list->active_timers)) {
         return -1;
     }

     if (!timer_list->clock->enabled) {
         return -1;
     }

     /* The active timers list may be modified before the caller uses our return
      * value but ->notify_cb() is called when the deadline changes.  Therefore
      * the caller should notice the change and there is no race condition.
      */
     WITH_QEMU_LOCK_GUARD(&timer_list->active_timers_lock) {
         if (!timer_list->active_timers) {
             return -1;
         }
         expire_time = timer_list->active_timers->expire_time;
     }

     delta = expire_time - qemu_clock_get_ns(timer_list->clock->type);

     if (delta <= 0) {
         return 0;
     }

     return delta;
 }

 /* Calculate the soonest deadline across all timerlists attached
  * to the clock. This is used for the icount timeout so we
  * ignore whether or not the clock should be used in deadline
  * calculations.
  */
 int64_t qemu_clock_deadline_ns_all(QEMUClockType type, int attr_mask)
 {
     int64_t deadline = -1;
     int64_t delta;
     int64_t expire_time;
     QEMUTimer *ts;
     QEMUTimerList *timer_list;
     QEMUClock *clock = qemu_clock_ptr(type);

     if (!clock->enabled) {
         return -1;
     }

     QLIST_FOREACH(timer_list, &clock->timerlists, list) {
         qemu_mutex_lock(&timer_list->active_timers_lock);
         ts = timer_list->active_timers;
         /* Skip all external timers */
         while (ts && (ts->attributes & ~attr_mask)) {
             ts = ts->next;
         }
         if (!ts) {
             qemu_mutex_unlock(&timer_list->active_timers_lock);
             continue;
         }
         expire_time = ts->expire_time;
         qemu_mutex_unlock(&timer_list->active_timers_lock);

         delta = expire_time - qemu_clock_get_ns(type);
         if (delta <= 0) {
             delta = 0;
         }
         deadline = qemu_soonest_timeout(deadline, delta);
     }
     return deadline;
 }

 QEMUClockType timerlist_get_clock(QEMUTimerList *timer_list)
 {
     return timer_list->clock->type;
 }

 QEMUTimerList *qemu_clock_get_main_loop_timerlist(QEMUClockType type)
 {
     return main_loop_tlg.tl[type];
 }

 void timerlist_notify(QEMUTimerList *timer_list)
 {
     if (timer_list->notify_cb) {
         timer_list->notify_cb(timer_list->notify_opaque, timer_list->clock->type);
     } else {
         qemu_notify_event();
     }
 }

 /* Transition function to convert a nanosecond timeout to ms
  * This is used where a system does not support ppoll
  */
 int qemu_timeout_ns_to_ms(int64_t ns)
 {
     int64_t ms;
     if (ns < 0) {
         return -1;
     }

     if (!ns) {
         return 0;
     }

     /* Always round up, because it's better to wait too long than to wait too
      * little and effectively busy-wait
      */
     ms = DIV_ROUND_UP(ns, SCALE_MS);

     /* To avoid overflow problems, limit this to 2^31, i.e. approx 25 days */
     return MIN(ms, INT32_MAX);
 }


 /* qemu implementation of g_poll which uses a nanosecond timeout but is
  * otherwise identical to g_poll
  */
 int qemu_poll_ns(GPollFD *fds, guint nfds, int64_t timeout)
 {
 #ifdef CONFIG_PPOLL
     if (timeout < 0) {
         return ppoll((struct pollfd *)fds, nfds, NULL, NULL);
     } else {
         struct timespec ts;
         int64_t tvsec = timeout / 1000000000LL;
         /* Avoid possibly overflowing and specifying a negative number of
          * seconds, which would turn a very long timeout into a busy-wait.
          */
         if (tvsec > (int64_t)INT32_MAX) {
             tvsec = INT32_MAX;
         }
         ts.tv_sec = tvsec;
         ts.tv_nsec = timeout % 1000000000LL;
         return ppoll((struct pollfd *)fds, nfds, &ts, NULL);
     }
 #else
     return g_poll(fds, nfds, qemu_timeout_ns_to_ms(timeout));
 #endif
 }


 void timer_init_full(QEMUTimer *ts,
                      QEMUTimerListGroup *timer_list_group, QEMUClockType type,
                      int scale, int attributes,
                      QEMUTimerCB *cb, void *opaque)
 {
     if (!timer_list_group) {
         timer_list_group = &main_loop_tlg;
     }
     ts->timer_list = timer_list_group->tl[type];
     ts->cb = cb;
     ts->opaque = opaque;
     ts->scale = scale;
     ts->attributes = attributes;
     ts->expire_time = -1;
 }

 void timer_deinit(QEMUTimer *ts)
 {
     assert(ts->expire_time == -1);
     ts->timer_list = NULL;
 }

 static void timer_del_locked(QEMUTimerList *timer_list, QEMUTimer *ts)
 {
     QEMUTimer **pt, *t;

     ts->expire_time = -1;
     pt = &timer_list->active_timers;
     for(;;) {
         t = *pt;
         if (!t)
             break;
         if (t == ts) {
             atomic_set(pt, t->next);
             break;
         }
         pt = &t->next;
     }
 }

 static bool timer_mod_ns_locked(QEMUTimerList *timer_list,
                                 QEMUTimer *ts, int64_t expire_time)
 {
     QEMUTimer **pt, *t;

     /* add the timer in the sorted list */
     pt = &timer_list->active_timers;
     for (;;) {
         t = *pt;
         if (!timer_expired_ns(t, expire_time)) {
             break;
         }
         pt = &t->next;
     }
     ts->expire_time = MAX(expire_time, 0);
     ts->next = *pt;
     atomic_set(pt, ts);

     return pt == &timer_list->active_timers;
 }

 static void timerlist_rearm(QEMUTimerList *timer_list)
 {
     /* Interrupt execution to force deadline recalculation.  */
     if (timer_list->clock->type == QEMU_CLOCK_VIRTUAL) {
         qemu_start_warp_timer();
     }
     timerlist_notify(timer_list);
 }

 /* stop a timer, but do not dealloc it */
 void timer_del(QEMUTimer *ts)
 {
     QEMUTimerList *timer_list = ts->timer_list;

     if (timer_list) {
         qemu_mutex_lock(&timer_list->active_timers_lock);
         timer_del_locked(timer_list, ts);
         qemu_mutex_unlock(&timer_list->active_timers_lock);
     }
 }

 /* modify the current timer so that it will be fired when current_time
    >= expire_time. The corresponding callback will be called. */
 void timer_mod_ns(QEMUTimer *ts, int64_t expire_time)
 {
     QEMUTimerList *timer_list = ts->timer_list;
     bool rearm;

     qemu_mutex_lock(&timer_list->active_timers_lock);
     timer_del_locked(timer_list, ts);
     rearm = timer_mod_ns_locked(timer_list, ts, expire_time);
     qemu_mutex_unlock(&timer_list->active_timers_lock);

     if (rearm) {
         timerlist_rearm(timer_list);
     }
 }

 /* modify the current timer so that it will be fired when current_time
    >= expire_time or the current deadline, whichever comes earlier.
    The corresponding callback will be called. */
 void timer_mod_anticipate_ns(QEMUTimer *ts, int64_t expire_time)
 {
     QEMUTimerList *timer_list = ts->timer_list;
     bool rearm;

     qemu_mutex_lock(&timer_list->active_timers_lock);
     if (ts->expire_time == -1 || ts->expire_time > expire_time) {
         if (ts->expire_time != -1) {
             timer_del_locked(timer_list, ts);
         }
         rearm = timer_mod_ns_locked(timer_list, ts, expire_time);
     } else {
         rearm = false;
     }
     qemu_mutex_unlock(&timer_list->active_timers_lock);

     if (rearm) {
         timerlist_rearm(timer_list);
     }
 }

 void timer_mod(QEMUTimer *ts, int64_t expire_time)
 {
     timer_mod_ns(ts, expire_time * ts->scale);
 }

 void timer_mod_anticipate(QEMUTimer *ts, int64_t expire_time)
 {
     timer_mod_anticipate_ns(ts, expire_time * ts->scale);
 }

 bool timer_pending(QEMUTimer *ts)
 {
     return ts->expire_time >= 0;
 }

 bool timer_expired(QEMUTimer *timer_head, int64_t current_time)
 {
     return timer_expired_ns(timer_head, current_time * timer_head->scale);
 }

 bool timerlist_run_timers(QEMUTimerList *timer_list)
 {
     QEMUTimer *ts;
     int64_t current_time;
     bool progress = false;
     QEMUTimerCB *cb;
     void *opaque;
     bool need_replay_checkpoint = false;

     if (!atomic_read(&timer_list->active_timers)) {
         return false;
     }

     qemu_event_reset(&timer_list->timers_done_ev);
     if (!timer_list->clock->enabled) {
         goto out;
     }

     switch (timer_list->clock->type) {
     case QEMU_CLOCK_REALTIME:
         break;
     default:
     case QEMU_CLOCK_VIRTUAL:
         if (replay_mode != REPLAY_MODE_NONE) {
             /* Checkpoint for virtual clock is redundant in cases where
              * it's being triggered with only non-EXTERNAL timers, because
              * these timers don't change guest state directly.
              * Since it has conditional dependence on specific timers, it is
              * subject to race conditions and requires special handling.
              * See below.
              */
             need_replay_checkpoint = true;
         }
         break;
     case QEMU_CLOCK_HOST:
         if (!replay_checkpoint(CHECKPOINT_CLOCK_HOST)) {
             goto out;
         }
         break;
     case QEMU_CLOCK_VIRTUAL_RT:
         if (!replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL_RT)) {
             goto out;
         }
         break;
     }

     /*
      * Extract expired timers from active timers list and and process them.
      *
      * In rr mode we need "filtered" checkpointing for virtual clock.  The
      * checkpoint must be recorded/replayed before processing any non-EXTERNAL timer,
      * and that must only be done once since the clock value stays the same. Because
      * non-EXTERNAL timers may appear in the timers list while it being processed,
      * the checkpoint can be issued at a time until no timers are left and we are
      * done".
      */
     current_time = qemu_clock_get_ns(timer_list->clock->type);
     qemu_mutex_lock(&timer_list->active_timers_lock);
     while ((ts = timer_list->active_timers)) {
         if (!timer_expired_ns(ts, current_time)) {
             /* No expired timers left.  The checkpoint can be skipped
              * if no timers fired or they were all external.
              */
             break;
         }
         if (need_replay_checkpoint
                 && !(ts->attributes & QEMU_TIMER_ATTR_EXTERNAL)) {
             /* once we got here, checkpoint clock only once */
             need_replay_checkpoint = false;
             qemu_mutex_unlock(&timer_list->active_timers_lock);
             if (!replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL)) {
                 goto out;
             }
             qemu_mutex_lock(&timer_list->active_timers_lock);
             /* The lock was released; start over again in case the list was
              * modified.
              */
             continue;
         }

         /* remove timer from the list before calling the callback */
         timer_list->active_timers = ts->next;
         ts->next = NULL;
         ts->expire_time = -1;
         cb = ts->cb;
         opaque = ts->opaque;

         /* run the callback (the timer list can be modified) */
         qemu_mutex_unlock(&timer_list->active_timers_lock);
         cb(opaque);
         qemu_mutex_lock(&timer_list->active_timers_lock);

         progress = true;
     }
     qemu_mutex_unlock(&timer_list->active_timers_lock);

 out:
     qemu_event_set(&timer_list->timers_done_ev);
     return progress;
 }

 bool qemu_clock_run_timers(QEMUClockType type)
 {
     return timerlist_run_timers(main_loop_tlg.tl[type]);
 }

 void timerlistgroup_init(QEMUTimerListGroup *tlg,
                          QEMUTimerListNotifyCB *cb, void *opaque)
 {
     QEMUClockType type;
     for (type = 0; type < QEMU_CLOCK_MAX; type++) {
         tlg->tl[type] = timerlist_new(type, cb, opaque);
     }
 }

 void timerlistgroup_deinit(QEMUTimerListGroup *tlg)
 {
     QEMUClockType type;
     for (type = 0; type < QEMU_CLOCK_MAX; type++) {
         timerlist_free(tlg->tl[type]);
     }
 }

 bool timerlistgroup_run_timers(QEMUTimerListGroup *tlg)
 {
     QEMUClockType type;
     bool progress = false;
     for (type = 0; type < QEMU_CLOCK_MAX; type++) {
         progress |= timerlist_run_timers(tlg->tl[type]);
     }
     return progress;
 }

 int64_t timerlistgroup_deadline_ns(QEMUTimerListGroup *tlg)
 {
     int64_t deadline = -1;
     QEMUClockType type;
     for (type = 0; type < QEMU_CLOCK_MAX; type++) {
         if (qemu_clock_use_for_deadline(type)) {
             deadline = qemu_soonest_timeout(deadline,
                                             timerlist_deadline_ns(tlg->tl[type]));
         }
     }
     return deadline;
 }

 int64_t qemu_clock_get_ns(QEMUClockType type)
 {
     switch (type) {
     case QEMU_CLOCK_REALTIME:
         return get_clock();
     default:
     case QEMU_CLOCK_VIRTUAL:
         if (use_icount) {
             return cpu_get_icount();
         } else {
             return cpu_get_clock();
         }
     case QEMU_CLOCK_HOST:
         return REPLAY_CLOCK(REPLAY_CLOCK_HOST, get_clock_realtime());
     case QEMU_CLOCK_VIRTUAL_RT:
         return REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT, cpu_get_clock());
     }
 }

 void init_clocks(QEMUTimerListNotifyCB *notify_cb)
 {
     QEMUClockType type;
     for (type = 0; type < QEMU_CLOCK_MAX; type++) {
         qemu_clock_init(type, notify_cb);
     }

 #ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
     prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
 #endif
 }

 uint64_t timer_expire_time_ns(QEMUTimer *ts)
 {
     return timer_pending(ts) ? ts->expire_time : -1;
 }

 bool qemu_clock_run_all_timers(void)
 {
     bool progress = false;
     QEMUClockType type;

     for (type = 0; type < QEMU_CLOCK_MAX; type++) {
         if (qemu_clock_use_for_deadline(type)) {
             progress |= qemu_clock_run_timers(type);
         }
     }

     return progress;
 }
	/*
	* QEMU System Emulator
	*
	* Copyright (c) 2003-2008 Fabrice Bellard
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/

	#include "qemu/osdep.h"
	#include "qemu/main-loop.h"
	#include "qemu/timer.h"
	#include "qemu/lockable.h"
	#include "sysemu/replay.h"
	#include "sysemu/cpus.h"

	#ifdef CONFIG_POSIX
	#include <pthread.h>
	#endif

	#ifdef CONFIG_PPOLL
	#include <poll.h>
	#endif

	#ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
	#include <sys/prctl.h>
	#endif

	/***********************************************************/
	/* timers */

	typedef struct QEMUClock {
	/* We rely on BQL to protect the timerlists */
	QLIST_HEAD(, QEMUTimerList) timerlists;

	QEMUClockType type;
	bool enabled;
	} QEMUClock;

	QEMUTimerListGroup main_loop_tlg;
	static QEMUClock qemu_clocks[QEMU_CLOCK_MAX];

	/* A QEMUTimerList is a list of timers attached to a clock. More
	* than one QEMUTimerList can be attached to each clock, for instance
	* used by different AioContexts / threads. Each clock also has
	* a list of the QEMUTimerLists associated with it, in order that
	* reenabling the clock can call all the notifiers.
	*/

	struct QEMUTimerList {
	QEMUClock *clock;
	QemuMutex active_timers_lock;
	QEMUTimer *active_timers;
	QLIST_ENTRY(QEMUTimerList) list;
	QEMUTimerListNotifyCB *notify_cb;
	void *notify_opaque;

	/* lightweight method to mark the end of timerlist's running */
	QemuEvent timers_done_ev;
	};

	/**
	* qemu_clock_ptr:
	* @type: type of clock
	*
	* Translate a clock type into a pointer to QEMUClock object.
	*
	* Returns: a pointer to the QEMUClock object
	*/
	static inline QEMUClock *qemu_clock_ptr(QEMUClockType type)
	{
	return &qemu_clocks[type];
	}

	static bool timer_expired_ns(QEMUTimer *timer_head, int64_t current_time)
	{
	return timer_head && (timer_head->expire_time <= current_time);
	}

	QEMUTimerList *timerlist_new(QEMUClockType type,
	QEMUTimerListNotifyCB *cb,
	void *opaque)
	{
	QEMUTimerList *timer_list;
	QEMUClock *clock = qemu_clock_ptr(type);

	timer_list = g_malloc0(sizeof(QEMUTimerList));
	qemu_event_init(&timer_list->timers_done_ev, true);
	timer_list->clock = clock;
	timer_list->notify_cb = cb;
	timer_list->notify_opaque = opaque;
	qemu_mutex_init(&timer_list->active_timers_lock);
	QLIST_INSERT_HEAD(&clock->timerlists, timer_list, list);
	return timer_list;
	}

	void timerlist_free(QEMUTimerList *timer_list)
	{
	assert(!timerlist_has_timers(timer_list));
	if (timer_list->clock) {
	QLIST_REMOVE(timer_list, list);
	}
	qemu_mutex_destroy(&timer_list->active_timers_lock);
	g_free(timer_list);
	}

	static void qemu_clock_init(QEMUClockType type, QEMUTimerListNotifyCB *notify_cb)
	{
	QEMUClock *clock = qemu_clock_ptr(type);

	/* Assert that the clock of type TYPE has not been initialized yet. */
	assert(main_loop_tlg.tl[type] == NULL);

	clock->type = type;
	clock->enabled = (type == QEMU_CLOCK_VIRTUAL ? false : true);
	QLIST_INIT(&clock->timerlists);
	main_loop_tlg.tl[type] = timerlist_new(type, notify_cb, NULL);
	}

	bool qemu_clock_use_for_deadline(QEMUClockType type)
	{
	return !(use_icount && (type == QEMU_CLOCK_VIRTUAL));
	}

	void qemu_clock_notify(QEMUClockType type)
	{
	QEMUTimerList *timer_list;
	QEMUClock *clock = qemu_clock_ptr(type);
	QLIST_FOREACH(timer_list, &clock->timerlists, list) {
	timerlist_notify(timer_list);
	}
	}

	/* Disabling the clock will wait for related timerlists to stop
	* executing qemu_run_timers. Thus, this functions should not
	* be used from the callback of a timer that is based on @clock.
	* Doing so would cause a deadlock.
	*
	* Caller should hold BQL.
	*/
	void qemu_clock_enable(QEMUClockType type, bool enabled)
	{
	QEMUClock *clock = qemu_clock_ptr(type);
	QEMUTimerList *tl;
	bool old = clock->enabled;
	clock->enabled = enabled;
	if (enabled && !old) {
	qemu_clock_notify(type);
	} else if (!enabled && old) {
	QLIST_FOREACH(tl, &clock->timerlists, list) {
	qemu_event_wait(&tl->timers_done_ev);
	}
	}
	}

	bool timerlist_has_timers(QEMUTimerList *timer_list)
	{
	return !!atomic_read(&timer_list->active_timers);
	}

	bool qemu_clock_has_timers(QEMUClockType type)
	{
	return timerlist_has_timers(
	main_loop_tlg.tl[type]);
	}

	bool timerlist_expired(QEMUTimerList *timer_list)
	{
	int64_t expire_time;

	if (!atomic_read(&timer_list->active_timers)) {
	return false;
	}

	WITH_QEMU_LOCK_GUARD(&timer_list->active_timers_lock) {
	if (!timer_list->active_timers) {
	return false;
	}
	expire_time = timer_list->active_timers->expire_time;
	}

	return expire_time <= qemu_clock_get_ns(timer_list->clock->type);
	}

	bool qemu_clock_expired(QEMUClockType type)
	{
	return timerlist_expired(
	main_loop_tlg.tl[type]);
	}

	/*
	* As above, but return -1 for no deadline, and do not cap to 2^32
	* as we know the result is always positive.
	*/

	int64_t timerlist_deadline_ns(QEMUTimerList *timer_list)
	{
	int64_t delta;
	int64_t expire_time;

	if (!atomic_read(&timer_list->active_timers)) {
	return -1;
	}

	if (!timer_list->clock->enabled) {
	return -1;
	}

	/* The active timers list may be modified before the caller uses our return
	* value but ->notify_cb() is called when the deadline changes. Therefore
	* the caller should notice the change and there is no race condition.
	*/
	WITH_QEMU_LOCK_GUARD(&timer_list->active_timers_lock) {
	if (!timer_list->active_timers) {
	return -1;
	}
	expire_time = timer_list->active_timers->expire_time;
	}

	delta = expire_time - qemu_clock_get_ns(timer_list->clock->type);

	if (delta <= 0) {
	return 0;
	}

	return delta;
	}

	/* Calculate the soonest deadline across all timerlists attached
	* to the clock. This is used for the icount timeout so we
	* ignore whether or not the clock should be used in deadline
	* calculations.
	*/
	int64_t qemu_clock_deadline_ns_all(QEMUClockType type, int attr_mask)
	{
	int64_t deadline = -1;
	int64_t delta;
	int64_t expire_time;
	QEMUTimer *ts;
	QEMUTimerList *timer_list;
	QEMUClock *clock = qemu_clock_ptr(type);

	if (!clock->enabled) {
	return -1;
	}

	QLIST_FOREACH(timer_list, &clock->timerlists, list) {
	qemu_mutex_lock(&timer_list->active_timers_lock);
	ts = timer_list->active_timers;
	/* Skip all external timers */
	while (ts && (ts->attributes & ~attr_mask)) {
	ts = ts->next;
	}
	if (!ts) {
	qemu_mutex_unlock(&timer_list->active_timers_lock);
	continue;
	}
	expire_time = ts->expire_time;
	qemu_mutex_unlock(&timer_list->active_timers_lock);

	delta = expire_time - qemu_clock_get_ns(type);
	if (delta <= 0) {
	delta = 0;
	}
	deadline = qemu_soonest_timeout(deadline, delta);
	}
	return deadline;
	}

	QEMUClockType timerlist_get_clock(QEMUTimerList *timer_list)
	{
	return timer_list->clock->type;
	}

	QEMUTimerList *qemu_clock_get_main_loop_timerlist(QEMUClockType type)
	{
	return main_loop_tlg.tl[type];
	}

	void timerlist_notify(QEMUTimerList *timer_list)
	{
	if (timer_list->notify_cb) {
	timer_list->notify_cb(timer_list->notify_opaque, timer_list->clock->type);
	} else {
	qemu_notify_event();
	}
	}

	/* Transition function to convert a nanosecond timeout to ms
	* This is used where a system does not support ppoll
	*/
	int qemu_timeout_ns_to_ms(int64_t ns)
	{
	int64_t ms;
	if (ns < 0) {
	return -1;
	}

	if (!ns) {
	return 0;
	}

	/* Always round up, because it's better to wait too long than to wait too
	* little and effectively busy-wait
	*/
	ms = DIV_ROUND_UP(ns, SCALE_MS);

	/* To avoid overflow problems, limit this to 2^31, i.e. approx 25 days */
	return MIN(ms, INT32_MAX);
	}


	/* qemu implementation of g_poll which uses a nanosecond timeout but is
	* otherwise identical to g_poll
	*/
	int qemu_poll_ns(GPollFD *fds, guint nfds, int64_t timeout)
	{
	#ifdef CONFIG_PPOLL
	if (timeout < 0) {
	return ppoll((struct pollfd *)fds, nfds, NULL, NULL);
	} else {
	struct timespec ts;
	int64_t tvsec = timeout / 1000000000LL;
	/* Avoid possibly overflowing and specifying a negative number of
	* seconds, which would turn a very long timeout into a busy-wait.
	*/
	if (tvsec > (int64_t)INT32_MAX) {
	tvsec = INT32_MAX;
	}
	ts.tv_sec = tvsec;
	ts.tv_nsec = timeout % 1000000000LL;
	return ppoll((struct pollfd *)fds, nfds, &ts, NULL);
	}
	#else
	return g_poll(fds, nfds, qemu_timeout_ns_to_ms(timeout));
	#endif
	}


	void timer_init_full(QEMUTimer *ts,
	QEMUTimerListGroup *timer_list_group, QEMUClockType type,
	int scale, int attributes,
	QEMUTimerCB cb, void opaque)
	{
	if (!timer_list_group) {
	timer_list_group = &main_loop_tlg;
	}
	ts->timer_list = timer_list_group->tl[type];
	ts->cb = cb;
	ts->opaque = opaque;
	ts->scale = scale;
	ts->attributes = attributes;
	ts->expire_time = -1;
	}

	void timer_deinit(QEMUTimer *ts)
	{
	assert(ts->expire_time == -1);
	ts->timer_list = NULL;
	}

	static void timer_del_locked(QEMUTimerList timer_list, QEMUTimer ts)
	{
	QEMUTimer *pt, t;

	ts->expire_time = -1;
	pt = &timer_list->active_timers;
	for(;;) {
	t = *pt;
	if (!t)
	break;
	if (t == ts) {
	atomic_set(pt, t->next);
	break;
	}
	pt = &t->next;
	}
	}

	static bool timer_mod_ns_locked(QEMUTimerList *timer_list,
	QEMUTimer *ts, int64_t expire_time)
	{
	QEMUTimer *pt, t;

	/* add the timer in the sorted list */
	pt = &timer_list->active_timers;
	for (;;) {
	t = *pt;
	if (!timer_expired_ns(t, expire_time)) {
	break;
	}
	pt = &t->next;
	}
	ts->expire_time = MAX(expire_time, 0);
	ts->next = *pt;
	atomic_set(pt, ts);

	return pt == &timer_list->active_timers;
	}

	static void timerlist_rearm(QEMUTimerList *timer_list)
	{
	/* Interrupt execution to force deadline recalculation. */
	if (timer_list->clock->type == QEMU_CLOCK_VIRTUAL) {
	qemu_start_warp_timer();
	}
	timerlist_notify(timer_list);
	}

	/* stop a timer, but do not dealloc it */
	void timer_del(QEMUTimer *ts)
	{
	QEMUTimerList *timer_list = ts->timer_list;

	if (timer_list) {
	qemu_mutex_lock(&timer_list->active_timers_lock);
	timer_del_locked(timer_list, ts);
	qemu_mutex_unlock(&timer_list->active_timers_lock);
	}
	}

	/* modify the current timer so that it will be fired when current_time
	>= expire_time. The corresponding callback will be called. */
	void timer_mod_ns(QEMUTimer *ts, int64_t expire_time)
	{
	QEMUTimerList *timer_list = ts->timer_list;
	bool rearm;

	qemu_mutex_lock(&timer_list->active_timers_lock);
	timer_del_locked(timer_list, ts);
	rearm = timer_mod_ns_locked(timer_list, ts, expire_time);
	qemu_mutex_unlock(&timer_list->active_timers_lock);

	if (rearm) {
	timerlist_rearm(timer_list);
	}
	}

	/* modify the current timer so that it will be fired when current_time
	>= expire_time or the current deadline, whichever comes earlier.
	The corresponding callback will be called. */
	void timer_mod_anticipate_ns(QEMUTimer *ts, int64_t expire_time)
	{
	QEMUTimerList *timer_list = ts->timer_list;
	bool rearm;

	qemu_mutex_lock(&timer_list->active_timers_lock);
	if (ts->expire_time == -1 \|\| ts->expire_time > expire_time) {
	if (ts->expire_time != -1) {
	timer_del_locked(timer_list, ts);
	}
	rearm = timer_mod_ns_locked(timer_list, ts, expire_time);
	} else {
	rearm = false;
	}
	qemu_mutex_unlock(&timer_list->active_timers_lock);

	if (rearm) {
	timerlist_rearm(timer_list);
	}
	}

	void timer_mod(QEMUTimer *ts, int64_t expire_time)
	{
	timer_mod_ns(ts, expire_time * ts->scale);
	}

	void timer_mod_anticipate(QEMUTimer *ts, int64_t expire_time)
	{
	timer_mod_anticipate_ns(ts, expire_time * ts->scale);
	}

	bool timer_pending(QEMUTimer *ts)
	{
	return ts->expire_time >= 0;
	}

	bool timer_expired(QEMUTimer *timer_head, int64_t current_time)
	{
	return timer_expired_ns(timer_head, current_time * timer_head->scale);
	}

	bool timerlist_run_timers(QEMUTimerList *timer_list)
	{
	QEMUTimer *ts;
	int64_t current_time;
	bool progress = false;
	QEMUTimerCB *cb;
	void *opaque;
	bool need_replay_checkpoint = false;

	if (!atomic_read(&timer_list->active_timers)) {
	return false;
	}

	qemu_event_reset(&timer_list->timers_done_ev);
	if (!timer_list->clock->enabled) {
	goto out;
	}

	switch (timer_list->clock->type) {
	case QEMU_CLOCK_REALTIME:
	break;
	default:
	case QEMU_CLOCK_VIRTUAL:
	if (replay_mode != REPLAY_MODE_NONE) {
	/* Checkpoint for virtual clock is redundant in cases where
	* it's being triggered with only non-EXTERNAL timers, because
	* these timers don't change guest state directly.
	* Since it has conditional dependence on specific timers, it is
	* subject to race conditions and requires special handling.
	* See below.
	*/
	need_replay_checkpoint = true;
	}
	break;
	case QEMU_CLOCK_HOST:
	if (!replay_checkpoint(CHECKPOINT_CLOCK_HOST)) {
	goto out;
	}
	break;
	case QEMU_CLOCK_VIRTUAL_RT:
	if (!replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL_RT)) {
	goto out;
	}
	break;
	}

	/*
	* Extract expired timers from active timers list and and process them.
	*
	* In rr mode we need "filtered" checkpointing for virtual clock. The
	* checkpoint must be recorded/replayed before processing any non-EXTERNAL timer,
	* and that must only be done once since the clock value stays the same. Because
	* non-EXTERNAL timers may appear in the timers list while it being processed,
	* the checkpoint can be issued at a time until no timers are left and we are
	* done".
	*/
	current_time = qemu_clock_get_ns(timer_list->clock->type);
	qemu_mutex_lock(&timer_list->active_timers_lock);
	while ((ts = timer_list->active_timers)) {
	if (!timer_expired_ns(ts, current_time)) {
	/* No expired timers left. The checkpoint can be skipped
	* if no timers fired or they were all external.
	*/
	break;
	}
	if (need_replay_checkpoint
	&& !(ts->attributes & QEMU_TIMER_ATTR_EXTERNAL)) {
	/* once we got here, checkpoint clock only once */
	need_replay_checkpoint = false;
	qemu_mutex_unlock(&timer_list->active_timers_lock);
	if (!replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL)) {
	goto out;
	}
	qemu_mutex_lock(&timer_list->active_timers_lock);
	/* The lock was released; start over again in case the list was
	* modified.
	*/
	continue;
	}

	/* remove timer from the list before calling the callback */
	timer_list->active_timers = ts->next;
	ts->next = NULL;
	ts->expire_time = -1;
	cb = ts->cb;
	opaque = ts->opaque;

	/* run the callback (the timer list can be modified) */
	qemu_mutex_unlock(&timer_list->active_timers_lock);
	cb(opaque);
	qemu_mutex_lock(&timer_list->active_timers_lock);

	progress = true;
	}
	qemu_mutex_unlock(&timer_list->active_timers_lock);

	out:
	qemu_event_set(&timer_list->timers_done_ev);
	return progress;
	}

	bool qemu_clock_run_timers(QEMUClockType type)
	{
	return timerlist_run_timers(main_loop_tlg.tl[type]);
	}

	void timerlistgroup_init(QEMUTimerListGroup *tlg,
	QEMUTimerListNotifyCB cb, void opaque)
	{
	QEMUClockType type;
	for (type = 0; type < QEMU_CLOCK_MAX; type++) {
	tlg->tl[type] = timerlist_new(type, cb, opaque);
	}
	}

	void timerlistgroup_deinit(QEMUTimerListGroup *tlg)
	{
	QEMUClockType type;
	for (type = 0; type < QEMU_CLOCK_MAX; type++) {
	timerlist_free(tlg->tl[type]);
	}
	}

	bool timerlistgroup_run_timers(QEMUTimerListGroup *tlg)
	{
	QEMUClockType type;
	bool progress = false;
	for (type = 0; type < QEMU_CLOCK_MAX; type++) {
	progress \|= timerlist_run_timers(tlg->tl[type]);
	}
	return progress;
	}

	int64_t timerlistgroup_deadline_ns(QEMUTimerListGroup *tlg)
	{
	int64_t deadline = -1;
	QEMUClockType type;
	for (type = 0; type < QEMU_CLOCK_MAX; type++) {
	if (qemu_clock_use_for_deadline(type)) {
	deadline = qemu_soonest_timeout(deadline,
	timerlist_deadline_ns(tlg->tl[type]));
	}
	}
	return deadline;
	}

	int64_t qemu_clock_get_ns(QEMUClockType type)
	{
	switch (type) {
	case QEMU_CLOCK_REALTIME:
	return get_clock();
	default:
	case QEMU_CLOCK_VIRTUAL:
	if (use_icount) {
	return cpu_get_icount();
	} else {
	return cpu_get_clock();
	}
	case QEMU_CLOCK_HOST:
	return REPLAY_CLOCK(REPLAY_CLOCK_HOST, get_clock_realtime());
	case QEMU_CLOCK_VIRTUAL_RT:
	return REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT, cpu_get_clock());
	}
	}

	void init_clocks(QEMUTimerListNotifyCB *notify_cb)
	{
	QEMUClockType type;
	for (type = 0; type < QEMU_CLOCK_MAX; type++) {
	qemu_clock_init(type, notify_cb);
	}

	#ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
	prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
	#endif
	}

	uint64_t timer_expire_time_ns(QEMUTimer *ts)
	{
	return timer_pending(ts) ? ts->expire_time : -1;
	}

	bool qemu_clock_run_all_timers(void)
	{
	bool progress = false;
	QEMUClockType type;

	for (type = 0; type < QEMU_CLOCK_MAX; type++) {
	if (qemu_clock_use_for_deadline(type)) {
	progress \|= qemu_clock_run_timers(type);
	}
	}

	return progress;
	}