text: /*
   *  fs/eventfd.c
   *
   *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   *
   */
  
  #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/anon_inodes.h>
  #include <linux/syscalls.h>
  #include <linux/export.h>
  #include <linux/kref.h>
  #include <linux/eventfd.h>
  #include <linux/proc_fs.h>
  #include <linux/seq_file.h>
  
  struct eventfd_ctx {
  	struct kref kref;
  	wait_queue_head_t wqh;
  	/*
  	 * Every time that a write(2) is performed on an eventfd, the
  	 * value of the __u64 being written is added to "count" and a
  	 * wakeup is performed on "wqh". A read(2) will return the "count"
  	 * value to userspace, and will reset "count" to zero. The kernel
  	 * side eventfd_signal() also, adds to the "count" counter and
  	 * issue a wakeup.
  	 */
  	__u64 count;
  	unsigned int flags;
  };
  
  /**
   * eventfd_signal - Adds @n to the eventfd counter.
   * @ctx: [in] Pointer to the eventfd context.
   * @n: [in] Value of the counter to be added to the eventfd internal counter.
   *          The value cannot be negative.
   *
   * This function is supposed to be called by the kernel in paths that do not
   * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
   * value, and we signal this as overflow condition by returining a POLLERR
   * to poll(2).
   *
   * Returns the amount by which the counter was incrememnted.  This will be less
   * than @n if the counter has overflowed.
   */
  __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&ctx->wqh.lock, flags);
  	if (ULLONG_MAX - ctx->count < n)
  		n = ULLONG_MAX - ctx->count;
  	ctx->count += n;
  	if (waitqueue_active(&ctx->wqh))
  		wake_up_locked_poll(&ctx->wqh, POLLIN);
  	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  
  	return n;
  }
  EXPORT_SYMBOL_GPL(eventfd_signal);
  
  static void eventfd_free_ctx(struct eventfd_ctx *ctx)
  {
  	kfree(ctx);
  }
  
  static void eventfd_free(struct kref *kref)
  {
  	struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
  
  	eventfd_free_ctx(ctx);
  }
  
  /**
   * eventfd_ctx_get - Acquires a reference to the internal eventfd context.
   * @ctx: [in] Pointer to the eventfd context.
   *
   * Returns: In case of success, returns a pointer to the eventfd context.
   */
  struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
  {
  	kref_get(&ctx->kref);
  	return ctx;
  }
  EXPORT_SYMBOL_GPL(eventfd_ctx_get);
  
  /**
   * eventfd_ctx_put - Releases a reference to the internal eventfd context.
   * @ctx: [in] Pointer to eventfd context.
   *
   * The eventfd context reference must have been previously acquired either
   * with eventfd_ctx_get() or eventfd_ctx_fdget().
   */
  void eventfd_ctx_put(struct eventfd_ctx *ctx)
  {
  	kref_put(&ctx->kref, eventfd_free);
  }
  EXPORT_SYMBOL_GPL(eventfd_ctx_put);
  
  static int eventfd_release(struct inode *inode, struct file *file)
  {
  	struct eventfd_ctx *ctx = file->private_data;
  
  	wake_up_poll(&ctx->wqh, POLLHUP);
  	eventfd_ctx_put(ctx);
  	return 0;
  }
  
  static unsigned int eventfd_poll(struct file *file, poll_table *wait)
  {
  	struct eventfd_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->count > 0)
  		events |= POLLIN;
  	if (ctx->count == ULLONG_MAX)
  		events |= POLLERR;
  	if (ULLONG_MAX - 1 > ctx->count)
  		events |= POLLOUT;
  	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  
  	return events;
  }
  
  static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
  {
  	*cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
  	ctx->count -= *cnt;
  }
  
  /**
   * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
   * @ctx: [in] Pointer to eventfd context.
   * @wait: [in] Wait queue to be removed.
   * @cnt: [out] Pointer to the 64-bit counter value.
   *
   * Returns %0 if successful, or the following error codes:
   *
   * -EAGAIN      : The operation would have blocked.
   *
   * This is used to atomically remove a wait queue entry from the eventfd wait
   * queue head, and read/reset the counter value.
   */
  int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
  				  __u64 *cnt)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&ctx->wqh.lock, flags);
  	eventfd_ctx_do_read(ctx, cnt);
  	__remove_wait_queue(&ctx->wqh, wait);
  	if (*cnt != 0 && waitqueue_active(&ctx->wqh))
  		wake_up_locked_poll(&ctx->wqh, POLLOUT);
  	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  
  	return *cnt != 0 ? 0 : -EAGAIN;
  }
  EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
  
  /**
   * eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
   * @ctx: [in] Pointer to eventfd context.
   * @no_wait: [in] Different from zero if the operation should not block.
   * @cnt: [out] Pointer to the 64-bit counter value.
   *
   * Returns %0 if successful, or the following error codes:
   *
   * -EAGAIN      : The operation would have blocked but @no_wait was non-zero.
   * -ERESTARTSYS : A signal interrupted the wait operation.
   *
   * If @no_wait is zero, the function might sleep until the eventfd internal
   * counter becomes greater than zero.
   */
  ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
  {
  	ssize_t res;
  	DECLARE_WAITQUEUE(wait, current);
  
  	spin_lock_irq(&ctx->wqh.lock);
  	*cnt = 0;
  	res = -EAGAIN;
  	if (ctx->count > 0)
  		res = 0;
  	else if (!no_wait) {
  		__add_wait_queue(&ctx->wqh, &wait);
  		for (;;) {
  			set_current_state(TASK_INTERRUPTIBLE);
  			if (ctx->count > 0) {
  				res = 0;
  				break;
  			}
  			if (signal_pending(current)) {
  				res = -ERESTARTSYS;
  				break;
  			}
  			spin_unlock_irq(&ctx->wqh.lock);
  			schedule();
  			spin_lock_irq(&ctx->wqh.lock);
  		}
  		__remove_wait_queue(&ctx->wqh, &wait);
  		__set_current_state(TASK_RUNNING);
  	}
  	if (likely(res == 0)) {
  		eventfd_ctx_do_read(ctx, cnt);
  		if (waitqueue_active(&ctx->wqh))
  			wake_up_locked_poll(&ctx->wqh, POLLOUT);
  	}
  	spin_unlock_irq(&ctx->wqh.lock);
  
  	return res;
  }
  EXPORT_SYMBOL_GPL(eventfd_ctx_read);
  
  static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
  			    loff_t *ppos)
  {
  	struct eventfd_ctx *ctx = file->private_data;
  	ssize_t res;
  	__u64 cnt;
  
  	if (count < sizeof(cnt))
  		return -EINVAL;
  	res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
  	if (res < 0)
  		return res;
  
  	return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
  }
  
  static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
  			     loff_t *ppos)
  {
  	struct eventfd_ctx *ctx = file->private_data;
  	ssize_t res;
  	__u64 ucnt;
  	DECLARE_WAITQUEUE(wait, current);
  
  	if (count < sizeof(ucnt))
  		return -EINVAL;
  	if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
  		return -EFAULT;
  	if (ucnt == ULLONG_MAX)
  		return -EINVAL;
  	spin_lock_irq(&ctx->wqh.lock);
  	res = -EAGAIN;
  	if (ULLONG_MAX - ctx->count > ucnt)
  		res = sizeof(ucnt);
  	else if (!(file->f_flags & O_NONBLOCK)) {
  		__add_wait_queue(&ctx->wqh, &wait);
  		for (res = 0;;) {
  			set_current_state(TASK_INTERRUPTIBLE);
  			if (ULLONG_MAX - ctx->count > ucnt) {
  				res = sizeof(ucnt);
  				break;
  			}
  			if (signal_pending(current)) {
  				res = -ERESTARTSYS;
  				break;
  			}
  			spin_unlock_irq(&ctx->wqh.lock);
  			schedule();
  			spin_lock_irq(&ctx->wqh.lock);
  		}
  		__remove_wait_queue(&ctx->wqh, &wait);
  		__set_current_state(TASK_RUNNING);
  	}
  	if (likely(res > 0)) {
  		ctx->count += ucnt;
  		if (waitqueue_active(&ctx->wqh))
  			wake_up_locked_poll(&ctx->wqh, POLLIN);
  	}
  	spin_unlock_irq(&ctx->wqh.lock);
  
  	return res;
  }
  
  #ifdef CONFIG_PROC_FS
  static int eventfd_show_fdinfo(struct seq_file *m, struct file *f)
  {
  	struct eventfd_ctx *ctx = f->private_data;
  	int ret;
  
  	spin_lock_irq(&ctx->wqh.lock);
  	ret = seq_printf(m, "eventfd-count: %16llx\n",
  			 (unsigned long long)ctx->count);
  	spin_unlock_irq(&ctx->wqh.lock);
  
  	return ret;
  }
  #endif
  
  static const struct file_operations eventfd_fops = {
  #ifdef CONFIG_PROC_FS
  	.show_fdinfo	= eventfd_show_fdinfo,
  #endif
  	.release	= eventfd_release,
  	.poll		= eventfd_poll,
  	.read		= eventfd_read,
  	.write		= eventfd_write,
  	.llseek		= noop_llseek,
  };
  
  /**
   * eventfd_fget - Acquire a reference of an eventfd file descriptor.
   * @fd: [in] Eventfd file descriptor.
   *
   * Returns a pointer to the eventfd file structure in case of success, or the
   * following error pointer:
   *
   * -EBADF    : Invalid @fd file descriptor.
   * -EINVAL   : The @fd file descriptor is not an eventfd file.
   */
  struct file *eventfd_fget(int fd)
  {
  	struct file *file;
  
  	file = fget(fd);
  	if (!file)
  		return ERR_PTR(-EBADF);
  	if (file->f_op != &eventfd_fops) {
  		fput(file);
  		return ERR_PTR(-EINVAL);
  	}
  
  	return file;
  }
  EXPORT_SYMBOL_GPL(eventfd_fget);
  
  /**
   * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
   * @fd: [in] Eventfd file descriptor.
   *
   * Returns a pointer to the internal eventfd context, otherwise the error
   * pointers returned by the following functions:
   *
   * eventfd_fget
   */
  struct eventfd_ctx *eventfd_ctx_fdget(int fd)
  {
  	struct file *file;
  	struct eventfd_ctx *ctx;
  
  	file = eventfd_fget(fd);
  	if (IS_ERR(file))
  		return (struct eventfd_ctx *) file;
  	ctx = eventfd_ctx_get(file->private_data);
  	fput(file);
  
  	return ctx;
  }
  EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
  
  /**
   * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
   * @file: [in] Eventfd file pointer.
   *
   * Returns a pointer to the internal eventfd context, otherwise the error
   * pointer:
   *
   * -EINVAL   : The @fd file descriptor is not an eventfd file.
   */
  struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
  {
  	if (file->f_op != &eventfd_fops)
  		return ERR_PTR(-EINVAL);
  
  	return eventfd_ctx_get(file->private_data);
  }
  EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
  
  /**
   * eventfd_file_create - Creates an eventfd file pointer.
   * @count: Initial eventfd counter value.
   * @flags: Flags for the eventfd file.
   *
   * This function creates an eventfd file pointer, w/out installing it into
   * the fd table. This is useful when the eventfd file is used during the
   * initialization of data structures that require extra setup after the eventfd
   * creation. So the eventfd creation is split into the file pointer creation
   * phase, and the file descriptor installation phase.
   * In this way races with userspace closing the newly installed file descriptor
   * can be avoided.
   * Returns an eventfd file pointer, or a proper error pointer.
   */
  struct file *eventfd_file_create(unsigned int count, int flags)
  {
  	struct file *file;
  	struct eventfd_ctx *ctx;
  
  	/* Check the EFD_* constants for consistency.  */
  	BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
  	BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
  
  	if (flags & ~EFD_FLAGS_SET)
  		return ERR_PTR(-EINVAL);
  
  	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
  	if (!ctx)
  		return ERR_PTR(-ENOMEM);
  
  	kref_init(&ctx->kref);
  	init_waitqueue_head(&ctx->wqh);
  	ctx->count = count;
  	ctx->flags = flags;
  
  	file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx,
  				  O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
  	if (IS_ERR(file))
  		eventfd_free_ctx(ctx);
  
  	return file;
  }
  
  SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
  {
  	int fd, error;
  	struct file *file;
  
  	error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS);
  	if (error < 0)
  		return error;
  	fd = error;
  
  	file = eventfd_file_create(count, flags);
  	if (IS_ERR(file)) {
  		error = PTR_ERR(file);
  		goto err_put_unused_fd;
  	}
  	fd_install(fd, file);
  
  	return fd;
  
  err_put_unused_fd:
  	put_unused_fd(fd);
  
  	return error;
  }
  
  SYSCALL_DEFINE1(eventfd, unsigned int, count)
  {
  	return sys_eventfd2(count, 0);
  }
  
  