#ifndef _LINUX_VIRTIO_H
  #define _LINUX_VIRTIO_H
  /* Everything a virtio driver needs to work with any particular virtio
   * implementation. */
  #include <linux/types.h>
  #include <linux/scatterlist.h>
  #include <linux/spinlock.h>
  #include <linux/device.h>
  #include <linux/mod_devicetable.h>

  #include <linux/gfp.h>

  #include <linux/vringh.h>

  
  /**
   * virtqueue - a queue to register buffers for sending or receiving.

   * @list: the chain of virtqueues for this device

   * @callback: the function to call when buffers are consumed (can be NULL).

   * @name: the name of this virtqueue (mainly for debugging)

   * @vdev: the virtio device this queue was created for.

   * @priv: a pointer for the virtqueue implementation to use.

   * @index: the zero-based ordinal number for this queue.
   * @num_free: number of elements we expect to be able to fit.
   *
   * A note on @num_free: with indirect buffers, each buffer needs one
   * element in the queue, otherwise a buffer will need one element per
   * sg element.

   */

  struct virtqueue {
  	struct list_head list;

  	void (*callback)(struct virtqueue *vq);

  	const char *name;

  	struct virtio_device *vdev;

  	unsigned int index;
  	unsigned int num_free;

  	void *priv;
  };

  int virtqueue_add_outbuf(struct virtqueue *vq,
  			 struct scatterlist sg[], unsigned int num,
  			 void *data,
  			 gfp_t gfp);
  
  int virtqueue_add_inbuf(struct virtqueue *vq,
  			struct scatterlist sg[], unsigned int num,
  			void *data,
  			gfp_t gfp);

  int virtqueue_add_sgs(struct virtqueue *vq,
  		      struct scatterlist *sgs[],
  		      unsigned int out_sgs,
  		      unsigned int in_sgs,
  		      void *data,
  		      gfp_t gfp);

  bool virtqueue_kick(struct virtqueue *vq);

  bool virtqueue_kick_prepare(struct virtqueue *vq);

  bool virtqueue_notify(struct virtqueue *vq);

  void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);

  void virtqueue_disable_cb(struct virtqueue *vq);

  bool virtqueue_enable_cb(struct virtqueue *vq);

  unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
  
  bool virtqueue_poll(struct virtqueue *vq, unsigned);

  bool virtqueue_enable_cb_delayed(struct virtqueue *vq);

  void *virtqueue_detach_unused_buf(struct virtqueue *vq);

  unsigned int virtqueue_get_vring_size(struct virtqueue *vq);

  bool virtqueue_is_broken(struct virtqueue *vq);

  const struct vring *virtqueue_get_vring(struct virtqueue *vq);
  dma_addr_t virtqueue_get_desc_addr(struct virtqueue *vq);
  dma_addr_t virtqueue_get_avail_addr(struct virtqueue *vq);
  dma_addr_t virtqueue_get_used_addr(struct virtqueue *vq);
  
  /*
   * Legacy accessors -- in almost all cases, these are the wrong functions
   * to use.
   */
  static inline void *virtqueue_get_desc(struct virtqueue *vq)
  {
  	return virtqueue_get_vring(vq)->desc;
  }
  static inline void *virtqueue_get_avail(struct virtqueue *vq)
  {
  	return virtqueue_get_vring(vq)->avail;
  }
  static inline void *virtqueue_get_used(struct virtqueue *vq)
  {
  	return virtqueue_get_vring(vq)->used;
  }

  /**
   * virtio_device - representation of a device using virtio
   * @index: unique position on the virtio bus

   * @failed: saved value for VIRTIO_CONFIG_S_FAILED bit (for restore)

   * @config_enabled: configuration change reporting enabled
   * @config_change_pending: configuration change reported while disabled
   * @config_lock: protects configuration change reporting

   * @dev: underlying device.
   * @id: the device type identification (used to match it with a driver).
   * @config: the configuration ops for this device.

   * @vringh_config: configuration ops for host vrings.

   * @vqs: the list of virtqueues for this device.

   * @features: the features supported by both driver and device.

   * @priv: private pointer for the driver's use.
   */

  struct virtio_device {

  	int index;

  	bool failed;

  	bool config_enabled;
  	bool config_change_pending;
  	spinlock_t config_lock;

  	struct device dev;
  	struct virtio_device_id id;

  	const struct virtio_config_ops *config;

  	const struct vringh_config_ops *vringh_config;

  	struct list_head vqs;

  	u64 features;

  	void *priv;
  };

  static inline struct virtio_device *dev_to_virtio(struct device *_dev)
  {
  	return container_of(_dev, struct virtio_device, dev);
  }

  int register_virtio_device(struct virtio_device *dev);
  void unregister_virtio_device(struct virtio_device *dev);

  void virtio_break_device(struct virtio_device *dev);

  void virtio_config_changed(struct virtio_device *dev);

  #ifdef CONFIG_PM_SLEEP
  int virtio_device_freeze(struct virtio_device *dev);
  int virtio_device_restore(struct virtio_device *dev);
  #endif

  /**
   * virtio_driver - operations for a virtio I/O driver
   * @driver: underlying device driver (populate name and owner).
   * @id_table: the ids serviced by this driver.

   * @feature_table: an array of feature numbers supported by this driver.

   * @feature_table_size: number of entries in the feature table array.

   * @feature_table_legacy: same as feature_table but when working in legacy mode.
   * @feature_table_size_legacy: number of entries in feature table legacy array.

   * @probe: the function to call when a device is found.  Returns 0 or -errno.

   * @remove: the function to call when a device is removed.

   * @config_changed: optional function to call when the device configuration
   *    changes; may be called in interrupt context.

   */
  struct virtio_driver {
  	struct device_driver driver;
  	const struct virtio_device_id *id_table;

  	const unsigned int *feature_table;
  	unsigned int feature_table_size;

  	const unsigned int *feature_table_legacy;
  	unsigned int feature_table_size_legacy;

  	int (*probe)(struct virtio_device *dev);

  	void (*scan)(struct virtio_device *dev);

  	void (*remove)(struct virtio_device *dev);

  	void (*config_changed)(struct virtio_device *dev);

  #ifdef CONFIG_PM
  	int (*freeze)(struct virtio_device *dev);

  	int (*restore)(struct virtio_device *dev);
  #endif

  };

  static inline struct virtio_driver *drv_to_virtio(struct device_driver *drv)
  {
  	return container_of(drv, struct virtio_driver, driver);
  }

  int register_virtio_driver(struct virtio_driver *drv);
  void unregister_virtio_driver(struct virtio_driver *drv);

  
  /* module_virtio_driver() - Helper macro for drivers that don't do
   * anything special in module init/exit.  This eliminates a lot of
   * boilerplate.  Each module may only use this macro once, and
   * calling it replaces module_init() and module_exit()
   */
  #define module_virtio_driver(__virtio_driver) \
  	module_driver(__virtio_driver, register_virtio_driver, \
  			unregister_virtio_driver)

  #endif /* _LINUX_VIRTIO_H */