/*
 * return timer owned by the process, used by exit_itimers
 */
static void itimer_delete(struct k_itimer *timer)
{
	unsigned long flags;

retry_delete:
	spin_lock_irqsave(&timer->it_lock, flags);

	/* On RT we can race with a deletion */
	if (!timer->it_signal) {
		unlock_timer(timer, flags);
		return;
	}

	if (timer_delete_hook(timer) == TIMER_RETRY) {
		rcu_read_lock();
		unlock_timer(timer, flags);
		timer_wait_for_callback(clockid_to_kclock(timer->it_clock),
					timer);
		rcu_read_unlock();
		goto retry_delete;
	}
	list_del(&timer->list);
	/*
	 * This keeps any tasks waiting on the spin lock from thinking
	 * they got something (see the lock code above).
	 */
	timer->it_signal = NULL;

	unlock_timer(timer, flags);
	release_posix_timer(timer, IT_ID_SET);
}

//.........这里部分代码省略.........
        ulong_t itx=time_to_ticks(&tspec.it_interval);

        /* We need to hold the lock during the whole process, so lookup
         * target timer explicitely.
         */
        LOCK_POSIX_STUFF_W(stuff);
        ptimer=(posix_timer_t*)__posix_locate_object(stuff,id,POSIX_OBJ_TIMER);
        if( !ptimer ) {
          break;
        }

        ktimer=&ptimer->ktimer;
        if( !(tspec.it_value.tv_sec | tspec.it_value.tv_nsec) ) {
          if( ktimer->time_x && posix_timer_active(ptimer) ) { /* Disarm active timer */
#ifdef CONFIG_DEBUG_TIMERS
            kprintf_fault("sys_timer_control() [%d:%d]: Tick=%d, deactivating timer %p:(P=%d) to %d\n",
                          current_task()->pid,current_task()->tid,
                          system_ticks,ktimer,ptimer->interval,tx);
#endif
            deactivate_posix_timer(ptimer);
            delete_timer(ktimer);
          }
          r=0;
        } else if( valid_timeval ) {
          if( !(arg1 & TIMER_ABSTIME) ) {
            tx+=system_ticks;
          }

          ptimer->interval=itx;
          activate_posix_timer(ptimer);
          if( ktimer->time_x ) { /* New time for active timer. */
#ifdef CONFIG_DEBUG_TIMERS
            kprintf_fault("sys_timer_control() [%d:%d] <RE-ARM> Tick=%d, timer=%p:(Tv=%d/%d,Pv=%d/%d,ABS=%d) to %d\n",
                          current_task()->pid,current_task()->tid,
                          system_ticks,ktimer,
                          tspec.it_value.tv_sec,tspec.it_value.tv_nsec,
                          tspec.it_interval.tv_sec,tspec.it_interval.tv_nsec,
                          (arg1 & TIMER_ABSTIME) != 0,
                          tx);
#endif

            r=modify_timer(ktimer,tx);
          } else {
            TIMER_RESET_TIME(ktimer,tx);

#ifdef CONFIG_DEBUG_TIMERS
            kprintf_fault("sys_timer_control() <ARM> [%d:%d] Tick=%d, timer=%p:(Tv=%d/%d,Pv=%d/%d,ABS=%d) to %d\n",
                          current_task()->pid,current_task()->tid,
                          system_ticks,ktimer,
                          tspec.it_value.tv_sec,tspec.it_value.tv_nsec,
                          tspec.it_interval.tv_sec,tspec.it_interval.tv_nsec,
                          (arg1 & TIMER_ABSTIME) != 0,
                          tx);
#endif

            r=add_timer(ktimer);
          }
        }
        UNLOCK_POSIX_STUFF_W(stuff);

        if( !r && arg3 ) {
          __get_timer_status(ptimer,&kspec);
          if( copy_to_user((itimerspec_t *)arg3,&kspec,sizeof(kspec)) )  {
            r=-EFAULT;
            /* TODO: [mt] Cleanup timer upon -EFAULT. */
          }
        }
      }
      break;
    case __POSIX_TIMER_GETTIME:
      ptimer=posix_lookup_timer(stuff,id);
      if( !ptimer ) {
        break;
      }
      __get_timer_status(ptimer,&kspec);
      r=copy_to_user((itimerspec_t *)arg1,&kspec,sizeof(kspec)) ? -EFAULT : 0;
      break;
    case __POSIX_TIMER_GETOVERRUN:
      ptimer=posix_lookup_timer(stuff,id);
      if( !ptimer ) {
        break;
      }
      r=ptimer->overrun;
      break;
    default:
      r=-EINVAL;
      break;
  }

  if( ptimer ) {
    release_posix_timer(ptimer);
  }

#ifdef CONFIG_DEBUG_TIMERS
  kprintf_fault("sys_timer_control(<END>) [%d:%d]: Tick=%d, (cmd=%d,id=%d), result=%d\n",
                current_task()->pid,current_task()->tid,
                system_ticks,cmd,id,r);
#endif
  return ERR(r);
}