#ifndef _LINUX_VIRTIO_CONFIG_H
  #define _LINUX_VIRTIO_CONFIG_H
  
  #include <linux/err.h>
  #include <linux/bug.h>
  #include <linux/virtio.h>
  #include <uapi/linux/virtio_config.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
   * @reset: reset the device
   *	vdev: the virtio device
   *	After this, status and feature negotiation must be done again
   *	Device must not be reset from its vq/config callbacks, or in
   *	parallel with being added/removed.
   * @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
   *		include a NULL entry for vqs that do not need a callback
   *	names: array of virtqueue names (mainly for debugging)
   *		include a NULL entry for vqs unused by driver
   *	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.
   * @bus_name: return the bus name associated with the device
   *	vdev: the virtio_device
   *      This returns a pointer to the bus name a la pci_name from which
   *      the caller can then copy.
   * @set_vq_affinity: set the affinity for a virtqueue.
   */
  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);
  	const char *(*bus_name)(struct virtio_device *vdev);
  	int (*set_vq_affinity)(struct virtqueue *vq, int cpu);
  };
  
  /* 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);
  }
  
  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;
  }
  
  static inline
  const char *virtio_bus_name(struct virtio_device *vdev)
  {
  	if (!vdev->config->bus_name)
  		return "virtio";
  	return vdev->config->bus_name(vdev);
  }
  
  /**
   * virtqueue_set_affinity - setting affinity for a virtqueue
   * @vq: the virtqueue
   * @cpu: the cpu no.
   *
   * Pay attention the function are best-effort: the affinity hint may not be set
   * due to config support, irq type and sharing.
   *
   */
  static inline
  int virtqueue_set_affinity(struct virtqueue *vq, int cpu)
  {
  	struct virtio_device *vdev = vq->vdev;
  	if (vdev->config->set_vq_affinity)
  		return vdev->config->set_vq_affinity(vq, cpu);
  	return 0;
  }
  
  /* Config space accessors. */
  #define virtio_cread(vdev, structname, member, ptr)			\
  	do {								\
  		/* Must match the member's type, and be integer */	\
  		if (!typecheck(typeof((((structname*)0)->member)), *(ptr))) \
  			(*ptr) = 1;					\
  									\
  		switch (sizeof(*ptr)) {					\
  		case 1:							\
  			*(ptr) = virtio_cread8(vdev,			\
  					       offsetof(structname, member)); \
  			break;						\
  		case 2:							\
  			*(ptr) = virtio_cread16(vdev,			\
  						offsetof(structname, member)); \
  			break;						\
  		case 4:							\
  			*(ptr) = virtio_cread32(vdev,			\
  						offsetof(structname, member)); \
  			break;						\
  		case 8:							\
  			*(ptr) = virtio_cread64(vdev,			\
  						offsetof(structname, member)); \
  			break;						\
  		default:						\
  			BUG();						\
  		}							\
  	} while(0)
  
  /* Config space accessors. */
  #define virtio_cwrite(vdev, structname, member, ptr)			\
  	do {								\
  		/* Must match the member's type, and be integer */	\
  		if (!typecheck(typeof((((structname*)0)->member)), *(ptr))) \
  			BUG_ON((*ptr) == 1);				\
  									\
  		switch (sizeof(*ptr)) {					\
  		case 1:							\
  			virtio_cwrite8(vdev,				\
  				       offsetof(structname, member),	\
  				       *(ptr));				\
  			break;						\
  		case 2:							\
  			virtio_cwrite16(vdev,				\
  					offsetof(structname, member),	\
  					*(ptr));			\
  			break;						\
  		case 4:							\
  			virtio_cwrite32(vdev,				\
  					offsetof(structname, member),	\
  					*(ptr));			\
  			break;						\
  		case 8:							\
  			virtio_cwrite64(vdev,				\
  					offsetof(structname, member),	\
  					*(ptr));			\
  			break;						\
  		default:						\
  			BUG();						\
  		}							\
  	} while(0)
  
  static inline u8 virtio_cread8(struct virtio_device *vdev, unsigned int offset)
  {
  	u8 ret;
  	vdev->config->get(vdev, offset, &ret, sizeof(ret));
  	return ret;
  }
  
  static inline void virtio_cread_bytes(struct virtio_device *vdev,
  				      unsigned int offset,
  				      void *buf, size_t len)
  {
  	vdev->config->get(vdev, offset, buf, len);
  }
  
  static inline void virtio_cwrite8(struct virtio_device *vdev,
  				  unsigned int offset, u8 val)
  {
  	vdev->config->set(vdev, offset, &val, sizeof(val));
  }
  
  static inline u16 virtio_cread16(struct virtio_device *vdev,
  				 unsigned int offset)
  {
  	u16 ret;
  	vdev->config->get(vdev, offset, &ret, sizeof(ret));
  	return ret;
  }
  
  static inline void virtio_cwrite16(struct virtio_device *vdev,
  				   unsigned int offset, u16 val)
  {
  	vdev->config->set(vdev, offset, &val, sizeof(val));
  }
  
  static inline u32 virtio_cread32(struct virtio_device *vdev,
  				 unsigned int offset)
  {
  	u32 ret;
  	vdev->config->get(vdev, offset, &ret, sizeof(ret));
  	return ret;
  }
  
  static inline void virtio_cwrite32(struct virtio_device *vdev,
  				   unsigned int offset, u32 val)
  {
  	vdev->config->set(vdev, offset, &val, sizeof(val));
  }
  
  static inline u64 virtio_cread64(struct virtio_device *vdev,
  				 unsigned int offset)
  {
  	u64 ret;
  	vdev->config->get(vdev, offset, &ret, sizeof(ret));
  	return ret;
  }
  
  static inline void virtio_cwrite64(struct virtio_device *vdev,
  				   unsigned int offset, u64 val)
  {
  	vdev->config->set(vdev, offset, &val, sizeof(val));
  }
  
  /* Conditional config space accessors. */
  #define virtio_cread_feature(vdev, fbit, structname, member, ptr)	\
  	({								\
  		int _r = 0;						\
  		if (!virtio_has_feature(vdev, fbit))			\
  			_r = -ENOENT;					\
  		else							\
  			virtio_cread((vdev), structname, member, ptr);	\
  		_r;							\
  	})
  
  #endif /* _LINUX_VIRTIO_CONFIG_H */