#ifndef _LINUX_VIRTIO_CONFIG_H
  #define _LINUX_VIRTIO_CONFIG_H

  /* This header, excluding the #ifdef __KERNEL__ part, is BSD licensed so

   * anyone can use the definitions to implement compatible drivers/servers.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of IBM nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE. */

  /* 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

  /* Some virtio feature bits (currently bits 28 through 31) are reserved for the
   * transport being used (eg. virtio_ring), the rest are per-device feature
   * bits. */
  #define VIRTIO_TRANSPORT_F_START	28
  #define VIRTIO_TRANSPORT_F_END		32

  /* Do we get callbacks when the ring is completely used, even if we've
   * suppressed them? */
  #define VIRTIO_F_NOTIFY_ON_EMPTY	24

  #ifdef __KERNEL__

  #include <linux/err.h>

  #include <linux/virtio.h>

  
  /**
   * virtio_config_ops - operations for configuring a virtio device

   * @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

   * @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

   * @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

   * @request_vqs: request the specified number of virtqueues
   *	vdev: the virtio_device
   *	max_vqs: the max number of virtqueues we want
   *      If supplied, must call before any virtqueues are instantiated.
   *      To modify the max number of virtqueues after request_vqs has been
   *      called, call free_vqs and then request_vqs with a new value.
   * @free_vqs: cleanup resources allocated by request_vqs
   *	vdev: the virtio_device
   *      If supplied, must call after all virtqueues have been deleted.

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

   * @find_vqs: find virtqueues and instantiate them.

   *	vdev: the virtio_device

   *	nvqs: the number of virtqueues to find
   *	vqs: on success, includes new virtqueues
   *	callbacks: array of callbacks, for each virtqueue
   *	names: array of virtqueue names (mainly for debugging)
   *	Returns 0 on success or error status
   * @del_vqs: free virtqueues found by find_vqs().

   * @get_features: get the array of feature bits for this device.
   *	vdev: the virtio_device
   *	Returns the first 32 feature bits (all we currently need).

   * @finalize_features: confirm what device features we'll be using.

   *	vdev: the virtio_device

   *	This gives the final feature bits for the device: it can change
   *	the dev->feature bits if it wants.

   */

  typedef void vq_callback_t(struct virtqueue *);

  struct virtio_config_ops {

  	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);

  	int (*find_vqs)(struct virtio_device *, unsigned nvqs,
  			struct virtqueue *vqs[],
  			vq_callback_t *callbacks[],
  			const char *names[]);
  	void (*del_vqs)(struct virtio_device *);

  	u32 (*get_features)(struct virtio_device *vdev);

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

  };

  /* If driver didn't advertise the feature, it will never appear. */
  void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
  					 unsigned int fbit);
  
  /**
   * virtio_has_feature - helper to determine if this device has this feature.
   * @vdev: the device
   * @fbit: the feature bit
   */
  static inline bool virtio_has_feature(const struct virtio_device *vdev,
  				      unsigned int fbit)
  {
  	/* Did you forget to fix assumptions on max features? */

  	if (__builtin_constant_p(fbit))
  		BUILD_BUG_ON(fbit >= 32);
  	else
  		BUG_ON(fbit >= 32);

  	if (fbit < VIRTIO_TRANSPORT_F_START)
  		virtio_check_driver_offered_feature(vdev, fbit);

  	return test_bit(fbit, vdev->features);
  }

  /**

   * virtio_config_val - look for a feature and get a virtio config entry.

   * @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 config value is copied into whatever is pointed to by v. */
  #define virtio_config_val(vdev, fbit, offset, v) \

  	virtio_config_buf((vdev), (fbit), (offset), (v), sizeof(*v))

  static inline int virtio_config_buf(struct virtio_device *vdev,
  				    unsigned int fbit,
  				    unsigned int offset,
  				    void *buf, unsigned len)
  {

  	if (!virtio_has_feature(vdev, fbit))

  		return -ENOENT;
  
  	vdev->config->get(vdev, offset, buf, len);
  	return 0;
  }

  
  static inline
  struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
  					vq_callback_t *c, const char *n)
  {
  	vq_callback_t *callbacks[] = { c };
  	const char *names[] = { n };
  	struct virtqueue *vq;
  	int err = vdev->config->find_vqs(vdev, 1, &vq, callbacks, names);
  	if (err < 0)
  		return ERR_PTR(err);
  	return vq;
  }

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