/*
   *  fs/timerfd.c
   *
   *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   *
   *
   *  Thanks to Thomas Gleixner for code reviews and useful comments.
   *
   */
  
  #include <linux/file.h>
  #include <linux/poll.h>
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/sched.h>
  #include <linux/kernel.h>

  #include <linux/slab.h>

  #include <linux/list.h>
  #include <linux/spinlock.h>
  #include <linux/time.h>
  #include <linux/hrtimer.h>
  #include <linux/anon_inodes.h>
  #include <linux/timerfd.h>

  #include <linux/syscalls.h>

  #include <linux/rcupdate.h>

  
  struct timerfd_ctx {
  	struct hrtimer tmr;
  	ktime_t tintv;

  	ktime_t moffs;

  	wait_queue_head_t wqh;

  	u64 ticks;

  	int expired;

  	int clockid;

  	struct rcu_head rcu;
  	struct list_head clist;

  	bool might_cancel;

  };

  static LIST_HEAD(cancel_list);
  static DEFINE_SPINLOCK(cancel_lock);

  /*
   * This gets called when the timer event triggers. We set the "expired"
   * flag, but we do not re-arm the timer (in case it's necessary,

   * tintv.tv64 != 0) until the timer is accessed.

   */
  static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
  {
  	struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
  	unsigned long flags;

  	spin_lock_irqsave(&ctx->wqh.lock, flags);

  	ctx->expired = 1;

  	ctx->ticks++;

  	wake_up_locked(&ctx->wqh);

  	spin_unlock_irqrestore(&ctx->wqh.lock, flags);

  
  	return HRTIMER_NORESTART;
  }

  /*
   * Called when the clock was set to cancel the timers in the cancel

   * list. This will wake up processes waiting on these timers. The
   * wake-up requires ctx->ticks to be non zero, therefore we increment
   * it before calling wake_up_locked().

   */
  void timerfd_clock_was_set(void)

  {

  	ktime_t moffs = ktime_get_monotonic_offset();
  	struct timerfd_ctx *ctx;
  	unsigned long flags;

  	rcu_read_lock();
  	list_for_each_entry_rcu(ctx, &cancel_list, clist) {
  		if (!ctx->might_cancel)
  			continue;
  		spin_lock_irqsave(&ctx->wqh.lock, flags);
  		if (ctx->moffs.tv64 != moffs.tv64) {
  			ctx->moffs.tv64 = KTIME_MAX;

  			ctx->ticks++;

  			wake_up_locked(&ctx->wqh);
  		}
  		spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  	}
  	rcu_read_unlock();

  }

  static void timerfd_remove_cancel(struct timerfd_ctx *ctx)

  {

  	if (ctx->might_cancel) {
  		ctx->might_cancel = false;
  		spin_lock(&cancel_lock);
  		list_del_rcu(&ctx->clist);
  		spin_unlock(&cancel_lock);
  	}
  }

  static bool timerfd_canceled(struct timerfd_ctx *ctx)
  {
  	if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)

  		return false;

  	ctx->moffs = ktime_get_monotonic_offset();
  	return true;
  }

  static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
  {
  	if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
  	    (flags & TFD_TIMER_CANCEL_ON_SET)) {
  		if (!ctx->might_cancel) {
  			ctx->might_cancel = true;
  			spin_lock(&cancel_lock);
  			list_add_rcu(&ctx->clist, &cancel_list);
  			spin_unlock(&cancel_lock);
  		}
  	} else if (ctx->might_cancel) {
  		timerfd_remove_cancel(ctx);
  	}
  }

  static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
  {
  	ktime_t remaining;

  	remaining = hrtimer_expires_remaining(&ctx->tmr);
  	return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;

  }
  
  static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
  			 const struct itimerspec *ktmr)

  {
  	enum hrtimer_mode htmode;
  	ktime_t texp;

  	int clockid = ctx->clockid;

  
  	htmode = (flags & TFD_TIMER_ABSTIME) ?
  		HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
  
  	texp = timespec_to_ktime(ktmr->it_value);
  	ctx->expired = 0;

  	ctx->ticks = 0;

  	ctx->tintv = timespec_to_ktime(ktmr->it_interval);

  	hrtimer_init(&ctx->tmr, clockid, htmode);

  	hrtimer_set_expires(&ctx->tmr, texp);

  	ctx->tmr.function = timerfd_tmrproc;

  	if (texp.tv64 != 0) {

  		hrtimer_start(&ctx->tmr, texp, htmode);

  		if (timerfd_canceled(ctx))
  			return -ECANCELED;
  	}
  	return 0;

  }
  
  static int timerfd_release(struct inode *inode, struct file *file)
  {
  	struct timerfd_ctx *ctx = file->private_data;

  	timerfd_remove_cancel(ctx);

  	hrtimer_cancel(&ctx->tmr);

  	kfree_rcu(ctx, rcu);

  	return 0;
  }
  
  static unsigned int timerfd_poll(struct file *file, poll_table *wait)
  {
  	struct timerfd_ctx *ctx = file->private_data;
  	unsigned int events = 0;
  	unsigned long flags;
  
  	poll_wait(file, &ctx->wqh, wait);

  	spin_lock_irqsave(&ctx->wqh.lock, flags);

  	if (ctx->ticks)

  		events |= POLLIN;

  	spin_unlock_irqrestore(&ctx->wqh.lock, flags);

  
  	return events;
  }
  
  static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
  			    loff_t *ppos)
  {
  	struct timerfd_ctx *ctx = file->private_data;
  	ssize_t res;

  	u64 ticks = 0;

  
  	if (count < sizeof(ticks))
  		return -EINVAL;

  	spin_lock_irq(&ctx->wqh.lock);

  	if (file->f_flags & O_NONBLOCK)
  		res = -EAGAIN;
  	else
  		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);

  	/*
  	 * If clock has changed, we do not care about the
  	 * ticks and we do not rearm the timer. Userspace must
  	 * reevaluate anyway.
  	 */
  	if (timerfd_canceled(ctx)) {
  		ctx->ticks = 0;
  		ctx->expired = 0;
  		res = -ECANCELED;
  	}

  	if (ctx->ticks) {
  		ticks = ctx->ticks;

  		if (ctx->expired && ctx->tintv.tv64) {

  			/*
  			 * If tintv.tv64 != 0, this is a periodic timer that
  			 * needs to be re-armed. We avoid doing it in the timer
  			 * callback to avoid DoS attacks specifying a very
  			 * short timer period.
  			 */

  			ticks += hrtimer_forward_now(&ctx->tmr,
  						     ctx->tintv) - 1;

  			hrtimer_restart(&ctx->tmr);

  		}
  		ctx->expired = 0;
  		ctx->ticks = 0;

  	}

  	spin_unlock_irq(&ctx->wqh.lock);

  	if (ticks)

  		res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);

  	return res;
  }
  
  static const struct file_operations timerfd_fops = {
  	.release	= timerfd_release,
  	.poll		= timerfd_poll,
  	.read		= timerfd_read,

  	.llseek		= noop_llseek,

  };

  static struct file *timerfd_fget(int fd)
  {
  	struct file *file;
  
  	file = fget(fd);
  	if (!file)
  		return ERR_PTR(-EBADF);
  	if (file->f_op != &timerfd_fops) {
  		fput(file);
  		return ERR_PTR(-EINVAL);
  	}
  
  	return file;
  }

  SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)

  {

  	int ufd;

  	struct timerfd_ctx *ctx;

  	/* Check the TFD_* constants for consistency.  */
  	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
  	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);

  	if ((flags & ~TFD_CREATE_FLAGS) ||
  	    (clockid != CLOCK_MONOTONIC &&
  	     clockid != CLOCK_REALTIME))

  		return -EINVAL;

  
  	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
  	if (!ctx)
  		return -ENOMEM;
  
  	init_waitqueue_head(&ctx->wqh);
  	ctx->clockid = clockid;
  	hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);

  	ctx->moffs = ktime_get_monotonic_offset();

  	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,

  			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));

  	if (ufd < 0)

  		kfree(ctx);

  
  	return ufd;
  }

  SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
  		const struct itimerspec __user *, utmr,
  		struct itimerspec __user *, otmr)

  {
  	struct file *file;
  	struct timerfd_ctx *ctx;
  	struct itimerspec ktmr, kotmr;

  	int ret;

  
  	if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
  		return -EFAULT;

  	if ((flags & ~TFD_SETTIME_FLAGS) ||
  	    !timespec_valid(&ktmr.it_value) ||

  	    !timespec_valid(&ktmr.it_interval))
  		return -EINVAL;

  	file = timerfd_fget(ufd);
  	if (IS_ERR(file))
  		return PTR_ERR(file);
  	ctx = file->private_data;

  	timerfd_setup_cancel(ctx, flags);

  	/*
  	 * We need to stop the existing timer before reprogramming
  	 * it to the new values.
  	 */
  	for (;;) {
  		spin_lock_irq(&ctx->wqh.lock);
  		if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
  			break;

  		spin_unlock_irq(&ctx->wqh.lock);

  		cpu_relax();

  	}

  	/*
  	 * If the timer is expired and it's periodic, we need to advance it
  	 * because the caller may want to know the previous expiration time.
  	 * We do not update "ticks" and "expired" since the timer will be
  	 * re-programmed again in the following timerfd_setup() call.
  	 */
  	if (ctx->expired && ctx->tintv.tv64)
  		hrtimer_forward_now(&ctx->tmr, ctx->tintv);

  	kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
  	kotmr.it_interval = ktime_to_timespec(ctx->tintv);
  
  	/*
  	 * Re-program the timer to the new value ...
  	 */

  	ret = timerfd_setup(ctx, flags, &ktmr);

  
  	spin_unlock_irq(&ctx->wqh.lock);
  	fput(file);
  	if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
  		return -EFAULT;

  	return ret;

  }

  SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)

  {
  	struct file *file;
  	struct timerfd_ctx *ctx;
  	struct itimerspec kotmr;
  
  	file = timerfd_fget(ufd);
  	if (IS_ERR(file))
  		return PTR_ERR(file);
  	ctx = file->private_data;
  
  	spin_lock_irq(&ctx->wqh.lock);
  	if (ctx->expired && ctx->tintv.tv64) {
  		ctx->expired = 0;
  		ctx->ticks +=
  			hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
  		hrtimer_restart(&ctx->tmr);
  	}
  	kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
  	kotmr.it_interval = ktime_to_timespec(ctx->tintv);
  	spin_unlock_irq(&ctx->wqh.lock);
  	fput(file);
  
  	return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;

  }