#ifndef _LINUX_VIRTIO_CONFIG_H
  #define _LINUX_VIRTIO_CONFIG_H
  /* Virtio devices use a standardized configuration space to define their
   * features and pass configuration information, but each implementation can
   * store and access that space differently. */
  #include <linux/types.h>

  /* Status byte for guest to report progress, and synchronize features. */

  /* We have seen device and processed generic fields (VIRTIO_CONFIG_F_VIRTIO) */
  #define VIRTIO_CONFIG_S_ACKNOWLEDGE	1
  /* We have found a driver for the device. */
  #define VIRTIO_CONFIG_S_DRIVER		2
  /* Driver has used its parts of the config, and is happy */
  #define VIRTIO_CONFIG_S_DRIVER_OK	4
  /* We've given up on this device. */
  #define VIRTIO_CONFIG_S_FAILED		0x80

  #ifdef __KERNEL__
  struct virtio_device;
  
  /**
   * virtio_config_ops - operations for configuring a virtio device

   * @feature: search for a feature in this config

   *	vdev: the virtio_device

   *	bit: the feature bit
   *	Returns true if the feature is supported.  Acknowledges the feature
   *	so the host can see it.
   * @get: read the value of a configuration field

   *	vdev: the virtio_device

   *	offset: the offset of the configuration field

   *	buf: the buffer to write the field value into.

   *	len: the length of the buffer

   *	Note that contents are conventionally little-endian.

   * @set: write the value of a configuration field

   *	vdev: the virtio_device

   *	offset: the offset of the configuration field

   *	buf: the buffer to read the field value from.

   *	len: the length of the buffer

   *	Note that contents are conventionally little-endian.
   * @get_status: read the status byte
   *	vdev: the virtio_device
   *	Returns the status byte
   * @set_status: write the status byte
   *	vdev: the virtio_device
   *	status: the new status byte

   * @reset: reset the device
   *	vdev: the virtio device
   *	After this, status and feature negotiation must be done again

   * @find_vq: find a virtqueue and instantiate it.

   *	vdev: the virtio_device

   *	index: the 0-based virtqueue number in case there's more than one.

   *	callback: the virqtueue callback

   *	Returns the new virtqueue or ERR_PTR() (eg. -ENOENT).

   * @del_vq: free a virtqueue found by find_vq().
   */
  struct virtio_config_ops
  {

  	bool (*feature)(struct virtio_device *vdev, unsigned bit);
  	void (*get)(struct virtio_device *vdev, unsigned offset,

  		    void *buf, unsigned len);

  	void (*set)(struct virtio_device *vdev, unsigned offset,

  		    const void *buf, unsigned len);
  	u8 (*get_status)(struct virtio_device *vdev);
  	void (*set_status)(struct virtio_device *vdev, u8 status);

  	void (*reset)(struct virtio_device *vdev);

  	struct virtqueue *(*find_vq)(struct virtio_device *vdev,

  				     unsigned index,

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

  	void (*del_vq)(struct virtqueue *vq);
  };
  
  /**

   * virtio_config_val - look for a feature and get a single virtio config.
   * @vdev: the virtio device
   * @fbit: the feature bit
   * @offset: the type to search for.

   * @val: a pointer to the value to fill in.
   *

   * The return value is -ENOENT if the feature doesn't exist.  Otherwise
   * the value is endian-corrected and returned in v. */
  #define virtio_config_val(vdev, fbit, offset, v) ({			\
  	int _err;							\
  	if ((vdev)->config->feature((vdev), (fbit))) {			\
  		__virtio_config_val((vdev), (offset), (v));		\
  		_err = 0;						\
  	} else								\
  		_err = -ENOENT;						\

  	_err;								\
  })

  /**

   * __virtio_config_val - get a single virtio config without feature check.
   * @vdev: the virtio device
   * @offset: the type to search for.
   * @val: a pointer to the value to fill in.

   *

   * The value is endian-corrected and returned in v. */
  #define __virtio_config_val(vdev, offset, v) do {			\
  	BUILD_BUG_ON(sizeof(*(v)) != 1 && sizeof(*(v)) != 2		\
  		     && sizeof(*(v)) != 4 && sizeof(*(v)) != 8);	\
  	(vdev)->config->get((vdev), (offset), (v), sizeof(*(v)));	\
  	switch (sizeof(*(v))) {						\
  	case 2: le16_to_cpus((__u16 *) v); break;			\
  	case 4: le32_to_cpus((__u32 *) v); break;			\
  	case 8: le64_to_cpus((__u64 *) v); break;			\
  	}								\
  } while(0)

  #endif /* __KERNEL__ */
  #endif /* _LINUX_VIRTIO_CONFIG_H */