#include <linux/virtio.h>
  #include <linux/spinlock.h>
  #include <linux/virtio_config.h>
  #include <linux/module.h>
  #include <linux/idr.h>
  
  /* Unique numbering for virtio devices. */
  static DEFINE_IDA(virtio_index_ida);
  
  static ssize_t device_show(struct device *_d,
  			   struct device_attribute *attr, char *buf)
  {
  	struct virtio_device *dev = dev_to_virtio(_d);
  	return sprintf(buf, "0x%04x
  ", dev->id.device);
  }
  static DEVICE_ATTR_RO(device);
  
  static ssize_t vendor_show(struct device *_d,
  			   struct device_attribute *attr, char *buf)
  {
  	struct virtio_device *dev = dev_to_virtio(_d);
  	return sprintf(buf, "0x%04x
  ", dev->id.vendor);
  }
  static DEVICE_ATTR_RO(vendor);
  
  static ssize_t status_show(struct device *_d,
  			   struct device_attribute *attr, char *buf)
  {
  	struct virtio_device *dev = dev_to_virtio(_d);
  	return sprintf(buf, "0x%08x
  ", dev->config->get_status(dev));
  }
  static DEVICE_ATTR_RO(status);
  
  static ssize_t modalias_show(struct device *_d,
  			     struct device_attribute *attr, char *buf)
  {
  	struct virtio_device *dev = dev_to_virtio(_d);
  	return sprintf(buf, "virtio:d%08Xv%08X
  ",
  		       dev->id.device, dev->id.vendor);
  }
  static DEVICE_ATTR_RO(modalias);
  
  static ssize_t features_show(struct device *_d,
  			     struct device_attribute *attr, char *buf)
  {
  	struct virtio_device *dev = dev_to_virtio(_d);
  	unsigned int i;
  	ssize_t len = 0;
  
  	/* We actually represent this as a bitstring, as it could be
  	 * arbitrary length in future. */
  	for (i = 0; i < ARRAY_SIZE(dev->features)*BITS_PER_LONG; i++)
  		len += sprintf(buf+len, "%c",
  			       test_bit(i, dev->features) ? '1' : '0');
  	len += sprintf(buf+len, "
  ");
  	return len;
  }
  static DEVICE_ATTR_RO(features);
  
  static struct attribute *virtio_dev_attrs[] = {
  	&dev_attr_device.attr,
  	&dev_attr_vendor.attr,
  	&dev_attr_status.attr,
  	&dev_attr_modalias.attr,
  	&dev_attr_features.attr,
  	NULL,
  };
  ATTRIBUTE_GROUPS(virtio_dev);
  
  static inline int virtio_id_match(const struct virtio_device *dev,
  				  const struct virtio_device_id *id)
  {
  	if (id->device != dev->id.device && id->device != VIRTIO_DEV_ANY_ID)
  		return 0;
  
  	return id->vendor == VIRTIO_DEV_ANY_ID || id->vendor == dev->id.vendor;
  }
  
  /* This looks through all the IDs a driver claims to support.  If any of them
   * match, we return 1 and the kernel will call virtio_dev_probe(). */
  static int virtio_dev_match(struct device *_dv, struct device_driver *_dr)
  {
  	unsigned int i;
  	struct virtio_device *dev = dev_to_virtio(_dv);
  	const struct virtio_device_id *ids;
  
  	ids = drv_to_virtio(_dr)->id_table;
  	for (i = 0; ids[i].device; i++)
  		if (virtio_id_match(dev, &ids[i]))
  			return 1;
  	return 0;
  }
  
  static int virtio_uevent(struct device *_dv, struct kobj_uevent_env *env)
  {
  	struct virtio_device *dev = dev_to_virtio(_dv);
  
  	return add_uevent_var(env, "MODALIAS=virtio:d%08Xv%08X",
  			      dev->id.device, dev->id.vendor);
  }
  
  static void add_status(struct virtio_device *dev, unsigned status)
  {
  	dev->config->set_status(dev, dev->config->get_status(dev) | status);
  }
  
  void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
  					 unsigned int fbit)
  {
  	unsigned int i;
  	struct virtio_driver *drv = drv_to_virtio(vdev->dev.driver);
  
  	for (i = 0; i < drv->feature_table_size; i++)
  		if (drv->feature_table[i] == fbit)
  			return;
  	BUG();
  }
  EXPORT_SYMBOL_GPL(virtio_check_driver_offered_feature);
  
  static int virtio_dev_probe(struct device *_d)
  {
  	int err, i;
  	struct virtio_device *dev = dev_to_virtio(_d);
  	struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
  	u32 device_features;
  
  	/* We have a driver! */
  	add_status(dev, VIRTIO_CONFIG_S_DRIVER);
  
  	/* Figure out what features the device supports. */
  	device_features = dev->config->get_features(dev);
  
  	/* Features supported by both device and driver into dev->features. */
  	memset(dev->features, 0, sizeof(dev->features));
  	for (i = 0; i < drv->feature_table_size; i++) {
  		unsigned int f = drv->feature_table[i];
  		BUG_ON(f >= 32);
  		if (device_features & (1 << f))
  			set_bit(f, dev->features);
  	}
  
  	/* Transport features always preserved to pass to finalize_features. */
  	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++)
  		if (device_features & (1 << i))
  			set_bit(i, dev->features);
  
  	dev->config->finalize_features(dev);
  
  	err = drv->probe(dev);
  	if (err)
  		add_status(dev, VIRTIO_CONFIG_S_FAILED);
  	else {
  		add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
  		if (drv->scan)
  			drv->scan(dev);
  	}
  
  	return err;
  }
  
  static int virtio_dev_remove(struct device *_d)
  {
  	struct virtio_device *dev = dev_to_virtio(_d);
  	struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
  
  	drv->remove(dev);
  
  	/* Driver should have reset device. */
  	WARN_ON_ONCE(dev->config->get_status(dev));
  
  	/* Acknowledge the device's existence again. */
  	add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
  	return 0;
  }
  
  static struct bus_type virtio_bus = {
  	.name  = "virtio",
  	.match = virtio_dev_match,
  	.dev_groups = virtio_dev_groups,
  	.uevent = virtio_uevent,
  	.probe = virtio_dev_probe,
  	.remove = virtio_dev_remove,
  };
  
  int register_virtio_driver(struct virtio_driver *driver)
  {
  	/* Catch this early. */
  	BUG_ON(driver->feature_table_size && !driver->feature_table);
  	driver->driver.bus = &virtio_bus;
  	return driver_register(&driver->driver);
  }
  EXPORT_SYMBOL_GPL(register_virtio_driver);
  
  void unregister_virtio_driver(struct virtio_driver *driver)
  {
  	driver_unregister(&driver->driver);
  }
  EXPORT_SYMBOL_GPL(unregister_virtio_driver);
  
  int register_virtio_device(struct virtio_device *dev)
  {
  	int err;
  
  	dev->dev.bus = &virtio_bus;
  
  	/* Assign a unique device index and hence name. */
  	err = ida_simple_get(&virtio_index_ida, 0, 0, GFP_KERNEL);
  	if (err < 0)
  		goto out;
  
  	dev->index = err;
  	dev_set_name(&dev->dev, "virtio%u", dev->index);
  
  	/* We always start by resetting the device, in case a previous
  	 * driver messed it up.  This also tests that code path a little. */
  	dev->config->reset(dev);
  
  	/* Acknowledge that we've seen the device. */
  	add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
  
  	INIT_LIST_HEAD(&dev->vqs);
  
  	/* device_register() causes the bus infrastructure to look for a
  	 * matching driver. */
  	err = device_register(&dev->dev);
  out:
  	if (err)
  		add_status(dev, VIRTIO_CONFIG_S_FAILED);
  	return err;
  }
  EXPORT_SYMBOL_GPL(register_virtio_device);
  
  void unregister_virtio_device(struct virtio_device *dev)
  {
  	int index = dev->index; /* save for after device release */
  
  	device_unregister(&dev->dev);
  	ida_simple_remove(&virtio_index_ida, index);
  }
  EXPORT_SYMBOL_GPL(unregister_virtio_device);
  
  static int virtio_init(void)
  {
  	if (bus_register(&virtio_bus) != 0)
  		panic("virtio bus registration failed");
  	return 0;
  }
  
  static void __exit virtio_exit(void)
  {
  	bus_unregister(&virtio_bus);
  }
  core_initcall(virtio_init);
  module_exit(virtio_exit);
  
  MODULE_LICENSE("GPL");