#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>

  
  /**
   * 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.
   */

  struct virtqueue {
  	struct list_head list;

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

  	const char *name;

  	struct virtio_device *vdev;

  	void *priv;
  };

  int virtqueue_add_buf(struct virtqueue *vq,
  		      struct scatterlist sg[],
  		      unsigned int out_num,
  		      unsigned int in_num,
  		      void *data,
  		      gfp_t gfp);

  void virtqueue_kick(struct virtqueue *vq);

  bool virtqueue_kick_prepare(struct virtqueue *vq);
  
  void 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);

  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);

  /**
   * virtio_device - representation of a device using virtio
   * @index: unique position on the virtio bus
   * @dev: underlying device.
   * @id: the device type identification (used to match it with a driver).
   * @config: the configuration ops for this device.

   * @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;
  	struct device dev;
  	struct virtio_device_id id;
  	struct virtio_config_ops *config;

  	struct list_head vqs;

  	/* Note that this is a Linux set_bit-style bitmap. */
  	unsigned long features[1];

  	void *priv;
  };

  #define dev_to_virtio(dev) container_of(dev, struct virtio_device, dev)

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

   * @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;

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

  };
  
  int register_virtio_driver(struct virtio_driver *drv);
  void unregister_virtio_driver(struct virtio_driver *drv);
  #endif /* _LINUX_VIRTIO_H */