text: /*
   * v4l2-fh.h
   *
   * V4L2 file handle. Store per file handle data for the V4L2
   * framework. Using file handles is optional for the drivers.
   *
   * Copyright (C) 2009--2010 Nokia Corporation.
   *
   * Contact: Sakari Ailus <sakari.ailus@iki.fi>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * version 2 as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   */
  
  #ifndef V4L2_FH_H
  #define V4L2_FH_H
  
  #include <linux/fs.h>
  #include <linux/list.h>
  #include <linux/videodev2.h>
  
  struct video_device;
  struct v4l2_ctrl_handler;
  
  /**
   * struct v4l2_fh - Describes a V4L2 file handler
   *
   * @list: list of file handlers
   * @vdev: pointer to &struct video_device
   * @ctrl_handler: pointer to &struct v4l2_ctrl_handler
   * @prio: priority of the file handler, as defined by &enum v4l2_priority
   *
   * @wait: event' s wait queue
   * @subscribe_lock: serialise changes to the subscribed list; guarantee that
   *		    the add and del event callbacks are orderly called
   * @subscribed: list of subscribed events
   * @available: list of events waiting to be dequeued
   * @navailable: number of available events at @available list
   * @sequence: event sequence number
   *
   * @m2m_ctx: pointer to &struct v4l2_m2m_ctx
   */
  struct v4l2_fh {
  	struct list_head	list;
  	struct video_device	*vdev;
  	struct v4l2_ctrl_handler *ctrl_handler;
  	enum v4l2_priority	prio;
  
  	/* Events */
  	wait_queue_head_t	wait;
  	struct mutex		subscribe_lock;
  	struct list_head	subscribed;
  	struct list_head	available;
  	unsigned int		navailable;
  	u32			sequence;
  
  #if IS_ENABLED(CONFIG_V4L2_MEM2MEM_DEV)
  	struct v4l2_m2m_ctx	*m2m_ctx;
  #endif
  };
  
  /**
   * v4l2_fh_init - Initialise the file handle.
   *
   * @fh: pointer to &struct v4l2_fh
   * @vdev: pointer to &struct video_device
   *
   * Parts of the V4L2 framework using the
   * file handles should be initialised in this function. Must be called
   * from driver's v4l2_file_operations->open\(\) handler if the driver
   * uses &struct v4l2_fh.
   */
  void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev);
  
  /**
   * v4l2_fh_add - Add the fh to the list of file handles on a video_device.
   *
   * @fh: pointer to &struct v4l2_fh
   *
   * .. note::
   *    The @fh file handle must be initialised first.
   */
  void v4l2_fh_add(struct v4l2_fh *fh);
  
  /**
   * v4l2_fh_open - Ancillary routine that can be used as the open\(\) op
   *	of v4l2_file_operations.
   *
   * @filp: pointer to struct file
   *
   * It allocates a v4l2_fh and inits and adds it to the &struct video_device
   * associated with the file pointer.
   */
  int v4l2_fh_open(struct file *filp);
  
  /**
   * v4l2_fh_del - Remove file handle from the list of file handles.
   *
   * @fh: pointer to &struct v4l2_fh
   *
   * On error filp->private_data will be %NULL, otherwise it will point to
   * the &struct v4l2_fh.
   *
   * .. note::
   *    Must be called in v4l2_file_operations->release\(\) handler if the driver
   *    uses &struct v4l2_fh.
   */
  void v4l2_fh_del(struct v4l2_fh *fh);
  
  /**
   * v4l2_fh_exit - Release resources related to a file handle.
   *
   * @fh: pointer to &struct v4l2_fh
   *
   * Parts of the V4L2 framework using the v4l2_fh must release their
   * resources here, too.
   *
   * .. note::
   *    Must be called in v4l2_file_operations->release\(\) handler if the
   *    driver uses &struct v4l2_fh.
   */
  void v4l2_fh_exit(struct v4l2_fh *fh);
  
  /**
   * v4l2_fh_release - Ancillary routine that can be used as the release\(\) op
   *	of v4l2_file_operations.
   *
   * @filp: pointer to struct file
   *
   * It deletes and exits the v4l2_fh associated with the file pointer and
   * frees it. It will do nothing if filp->private_data (the pointer to the
   * v4l2_fh struct) is %NULL.
   *
   * This function always returns 0.
   */
  int v4l2_fh_release(struct file *filp);
  
  /**
   * v4l2_fh_is_singular - Returns 1 if this filehandle is the only filehandle
   *	 opened for the associated video_device.
   *
   * @fh: pointer to &struct v4l2_fh
   *
   * If @fh is NULL, then it returns 0.
   */
  int v4l2_fh_is_singular(struct v4l2_fh *fh);
  
  /**
   * v4l2_fh_is_singular_file - Returns 1 if this filehandle is the only
   *	filehandle opened for the associated video_device.
   *
   * @filp: pointer to struct file
   *
   * This is a helper function variant of v4l2_fh_is_singular() with uses
   * struct file as argument.
   *
   * If filp->private_data is %NULL, then it will return 0.
   */
  static inline int v4l2_fh_is_singular_file(struct file *filp)
  {
  	return v4l2_fh_is_singular(filp->private_data);
  }
  
  #endif /* V4L2_EVENT_H */
  