WSL2-Linux-Kernel/drivers/dax/bus.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright(c) 2017-2018 Intel Corporation. All rights reserved. */
#include <linux/memremap.h>
#include <linux/device.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/dax.h>
#include "dax-private.h"
#include "bus.h"

static struct class *dax_class;

static DEFINE_MUTEX(dax_bus_lock);

#define DAX_NAME_LEN 30
struct dax_id {
	struct list_head list;
	char dev_name[DAX_NAME_LEN];
};

static int dax_bus_uevent(struct device *dev, struct kobj_uevent_env *env)
{
	/*
	 * We only ever expect to handle device-dax instances, i.e. the
	 * @type argument to MODULE_ALIAS_DAX_DEVICE() is always zero
	 */
	return add_uevent_var(env, "MODALIAS=" DAX_DEVICE_MODALIAS_FMT, 0);
}

static struct dax_device_driver *to_dax_drv(struct device_driver *drv)
{
	return container_of(drv, struct dax_device_driver, drv);
}

static struct dax_id *__dax_match_id(struct dax_device_driver *dax_drv,
		const char *dev_name)
{
	struct dax_id *dax_id;

	lockdep_assert_held(&dax_bus_lock);

	list_for_each_entry(dax_id, &dax_drv->ids, list)
		if (sysfs_streq(dax_id->dev_name, dev_name))
			return dax_id;
	return NULL;
}

static int dax_match_id(struct dax_device_driver *dax_drv, struct device *dev)
{
	int match;

	mutex_lock(&dax_bus_lock);
	match = !!__dax_match_id(dax_drv, dev_name(dev));
	mutex_unlock(&dax_bus_lock);

	return match;
}

enum id_action {
	ID_REMOVE,
	ID_ADD,
};

static ssize_t do_id_store(struct device_driver *drv, const char *buf,
		size_t count, enum id_action action)
{
	struct dax_device_driver *dax_drv = to_dax_drv(drv);
	unsigned int region_id, id;
	char devname[DAX_NAME_LEN];
	struct dax_id *dax_id;
	ssize_t rc = count;
	int fields;

	fields = sscanf(buf, "dax%d.%d", &region_id, &id);
	if (fields != 2)
		return -EINVAL;
	sprintf(devname, "dax%d.%d", region_id, id);
	if (!sysfs_streq(buf, devname))
		return -EINVAL;

	mutex_lock(&dax_bus_lock);
	dax_id = __dax_match_id(dax_drv, buf);
	if (!dax_id) {
		if (action == ID_ADD) {
			dax_id = kzalloc(sizeof(*dax_id), GFP_KERNEL);
			if (dax_id) {
				strncpy(dax_id->dev_name, buf, DAX_NAME_LEN);
				list_add(&dax_id->list, &dax_drv->ids);
			} else
				rc = -ENOMEM;
		} else
			/* nothing to remove */;
	} else if (action == ID_REMOVE) {
		list_del(&dax_id->list);
		kfree(dax_id);
	} else
		/* dax_id already added */;
	mutex_unlock(&dax_bus_lock);

	if (rc < 0)
		return rc;
	if (action == ID_ADD)
		rc = driver_attach(drv);
	if (rc)
		return rc;
	return count;
}

static ssize_t new_id_store(struct device_driver *drv, const char *buf,
		size_t count)
{
	return do_id_store(drv, buf, count, ID_ADD);
}
static DRIVER_ATTR_WO(new_id);

static ssize_t remove_id_store(struct device_driver *drv, const char *buf,
		size_t count)
{
	return do_id_store(drv, buf, count, ID_REMOVE);
}
static DRIVER_ATTR_WO(remove_id);

static struct attribute *dax_drv_attrs[] = {
	&driver_attr_new_id.attr,
	&driver_attr_remove_id.attr,
	NULL,
};
ATTRIBUTE_GROUPS(dax_drv);

static int dax_bus_match(struct device *dev, struct device_driver *drv);

static bool is_static(struct dax_region *dax_region)
{
	return (dax_region->res.flags & IORESOURCE_DAX_STATIC) != 0;
}

static int dax_bus_probe(struct device *dev)
{
	struct dax_device_driver *dax_drv = to_dax_drv(dev->driver);
	struct dev_dax *dev_dax = to_dev_dax(dev);
	struct dax_region *dax_region = dev_dax->region;
	struct range *range = &dev_dax->range;
	int rc;

	if (range_len(range) == 0 || dev_dax->id < 0)
		return -ENXIO;

	rc = dax_drv->probe(dev_dax);

	if (rc || is_static(dax_region))
		return rc;

	/*
	 * Track new seed creation only after successful probe of the
	 * previous seed.
	 */
	if (dax_region->seed == dev)
		dax_region->seed = NULL;

	return 0;
}

static int dax_bus_remove(struct device *dev)
{
	struct dax_device_driver *dax_drv = to_dax_drv(dev->driver);
	struct dev_dax *dev_dax = to_dev_dax(dev);

	return dax_drv->remove(dev_dax);
}

static struct bus_type dax_bus_type = {
	.name = "dax",
	.uevent = dax_bus_uevent,
	.match = dax_bus_match,
	.probe = dax_bus_probe,
	.remove = dax_bus_remove,
	.drv_groups = dax_drv_groups,
};

static int dax_bus_match(struct device *dev, struct device_driver *drv)
{
	struct dax_device_driver *dax_drv = to_dax_drv(drv);

	/*
	 * All but the 'device-dax' driver, which has 'match_always'
	 * set, requires an exact id match.
	 */
	if (dax_drv->match_always)
		return 1;

	return dax_match_id(dax_drv, dev);
}

/*
 * Rely on the fact that drvdata is set before the attributes are
 * registered, and that the attributes are unregistered before drvdata
 * is cleared to assume that drvdata is always valid.
 */
static ssize_t id_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);

	return sprintf(buf, "%d\n", dax_region->id);
}
static DEVICE_ATTR_RO(id);

static ssize_t region_size_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);

	return sprintf(buf, "%llu\n", (unsigned long long)
			resource_size(&dax_region->res));
}
static struct device_attribute dev_attr_region_size = __ATTR(size, 0444,
		region_size_show, NULL);

static ssize_t align_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);

	return sprintf(buf, "%u\n", dax_region->align);
}
static DEVICE_ATTR_RO(align);

#define for_each_dax_region_resource(dax_region, res) \
	for (res = (dax_region)->res.child; res; res = res->sibling)

static unsigned long long dax_region_avail_size(struct dax_region *dax_region)
{
	resource_size_t size = resource_size(&dax_region->res);
	struct resource *res;

	device_lock_assert(dax_region->dev);

	for_each_dax_region_resource(dax_region, res)
		size -= resource_size(res);
	return size;
}

static ssize_t available_size_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);
	unsigned long long size;

	device_lock(dev);
	size = dax_region_avail_size(dax_region);
	device_unlock(dev);

	return sprintf(buf, "%llu\n", size);
}
static DEVICE_ATTR_RO(available_size);

static ssize_t seed_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);
	struct device *seed;
	ssize_t rc;

	if (is_static(dax_region))
		return -EINVAL;

	device_lock(dev);
	seed = dax_region->seed;
	rc = sprintf(buf, "%s\n", seed ? dev_name(seed) : "");
	device_unlock(dev);

	return rc;
}
static DEVICE_ATTR_RO(seed);

static ssize_t create_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);
	struct device *youngest;
	ssize_t rc;

	if (is_static(dax_region))
		return -EINVAL;

	device_lock(dev);
	youngest = dax_region->youngest;
	rc = sprintf(buf, "%s\n", youngest ? dev_name(youngest) : "");
	device_unlock(dev);

	return rc;
}

static ssize_t create_store(struct device *dev, struct device_attribute *attr,
		const char *buf, size_t len)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);
	unsigned long long avail;
	ssize_t rc;
	int val;

	if (is_static(dax_region))
		return -EINVAL;

	rc = kstrtoint(buf, 0, &val);
	if (rc)
		return rc;
	if (val != 1)
		return -EINVAL;

	device_lock(dev);
	avail = dax_region_avail_size(dax_region);
	if (avail == 0)
		rc = -ENOSPC;
	else {
		struct dev_dax_data data = {
			.dax_region = dax_region,
			.size = 0,
			.id = -1,
		};
		struct dev_dax *dev_dax = devm_create_dev_dax(&data);

		if (IS_ERR(dev_dax))
			rc = PTR_ERR(dev_dax);
		else {
			/*
			 * In support of crafting multiple new devices
			 * simultaneously multiple seeds can be created,
			 * but only the first one that has not been
			 * successfully bound is tracked as the region
			 * seed.
			 */
			if (!dax_region->seed)
				dax_region->seed = &dev_dax->dev;
			dax_region->youngest = &dev_dax->dev;
			rc = len;
		}
	}
	device_unlock(dev);

	return rc;
}
static DEVICE_ATTR_RW(create);

void kill_dev_dax(struct dev_dax *dev_dax)
{
	struct dax_device *dax_dev = dev_dax->dax_dev;
	struct inode *inode = dax_inode(dax_dev);

	kill_dax(dax_dev);
	unmap_mapping_range(inode->i_mapping, 0, 0, 1);
}
EXPORT_SYMBOL_GPL(kill_dev_dax);

static void free_dev_dax_range(struct dev_dax *dev_dax)
{
	struct dax_region *dax_region = dev_dax->region;
	struct range *range = &dev_dax->range;

	device_lock_assert(dax_region->dev);
	if (range_len(range))
		__release_region(&dax_region->res, range->start,
				range_len(range));
}

static void unregister_dev_dax(void *dev)
{
	struct dev_dax *dev_dax = to_dev_dax(dev);

	dev_dbg(dev, "%s\n", __func__);

	kill_dev_dax(dev_dax);
	free_dev_dax_range(dev_dax);
	device_del(dev);
	put_device(dev);
}

/* a return value >= 0 indicates this invocation invalidated the id */
static int __free_dev_dax_id(struct dev_dax *dev_dax)
{
	struct dax_region *dax_region = dev_dax->region;
	struct device *dev = &dev_dax->dev;
	int rc = dev_dax->id;

	device_lock_assert(dev);

	if (is_static(dax_region) || dev_dax->id < 0)
		return -1;
	ida_free(&dax_region->ida, dev_dax->id);
	dev_dax->id = -1;
	return rc;
}

static int free_dev_dax_id(struct dev_dax *dev_dax)
{
	struct device *dev = &dev_dax->dev;
	int rc;

	device_lock(dev);
	rc = __free_dev_dax_id(dev_dax);
	device_unlock(dev);
	return rc;
}

static ssize_t delete_store(struct device *dev, struct device_attribute *attr,
		const char *buf, size_t len)
{
	struct dax_region *dax_region = dev_get_drvdata(dev);
	struct dev_dax *dev_dax;
	struct device *victim;
	bool do_del = false;
	int rc;

	if (is_static(dax_region))
		return -EINVAL;

	victim = device_find_child_by_name(dax_region->dev, buf);
	if (!victim)
		return -ENXIO;

	device_lock(dev);
	device_lock(victim);
	dev_dax = to_dev_dax(victim);
	if (victim->driver || range_len(&dev_dax->range))
		rc = -EBUSY;
	else {
		/*
		 * Invalidate the device so it does not become active
		 * again, but always preserve device-id-0 so that
		 * /sys/bus/dax/ is guaranteed to be populated while any
		 * dax_region is registered.
		 */
		if (dev_dax->id > 0) {
			do_del = __free_dev_dax_id(dev_dax) >= 0;
			rc = len;
			if (dax_region->seed == victim)
				dax_region->seed = NULL;
			if (dax_region->youngest == victim)
				dax_region->youngest = NULL;
		} else
			rc = -EBUSY;
	}
	device_unlock(victim);

	/* won the race to invalidate the device, clean it up */
	if (do_del)
		devm_release_action(dev, unregister_dev_dax, victim);
	device_unlock(dev);
	put_device(victim);

	return rc;
}
static DEVICE_ATTR_WO(delete);

static umode_t dax_region_visible(struct kobject *kobj, struct attribute *a,
		int n)
{
	struct device *dev = container_of(kobj, struct device, kobj);
	struct dax_region *dax_region = dev_get_drvdata(dev);

	if (is_static(dax_region))
		if (a == &dev_attr_available_size.attr
				|| a == &dev_attr_create.attr
				|| a == &dev_attr_seed.attr
				|| a == &dev_attr_delete.attr)
			return 0;
	return a->mode;
}

static struct attribute *dax_region_attributes[] = {
	&dev_attr_available_size.attr,
	&dev_attr_region_size.attr,
	&dev_attr_align.attr,
	&dev_attr_create.attr,
	&dev_attr_seed.attr,
	&dev_attr_delete.attr,
	&dev_attr_id.attr,
	NULL,
};

static const struct attribute_group dax_region_attribute_group = {
	.name = "dax_region",
	.attrs = dax_region_attributes,
	.is_visible = dax_region_visible,
};

static const struct attribute_group *dax_region_attribute_groups[] = {
	&dax_region_attribute_group,
	NULL,
};

static void dax_region_free(struct kref *kref)
{
	struct dax_region *dax_region;

	dax_region = container_of(kref, struct dax_region, kref);
	kfree(dax_region);
}

void dax_region_put(struct dax_region *dax_region)
{
	kref_put(&dax_region->kref, dax_region_free);
}
EXPORT_SYMBOL_GPL(dax_region_put);

static void dax_region_unregister(void *region)
{
	struct dax_region *dax_region = region;

	sysfs_remove_groups(&dax_region->dev->kobj,
			dax_region_attribute_groups);
	dax_region_put(dax_region);
}

struct dax_region *alloc_dax_region(struct device *parent, int region_id,
		struct resource *res, int target_node, unsigned int align,
		unsigned long flags)
{
	struct dax_region *dax_region;

	/*
	 * The DAX core assumes that it can store its private data in
	 * parent->driver_data. This WARN is a reminder / safeguard for
	 * developers of device-dax drivers.
	 */
	if (dev_get_drvdata(parent)) {
		dev_WARN(parent, "dax core failed to setup private data\n");
		return NULL;
	}

	if (!IS_ALIGNED(res->start, align)
			|| !IS_ALIGNED(resource_size(res), align))
		return NULL;

	dax_region = kzalloc(sizeof(*dax_region), GFP_KERNEL);
	if (!dax_region)
		return NULL;

	dev_set_drvdata(parent, dax_region);
	kref_init(&dax_region->kref);
	dax_region->id = region_id;
	dax_region->align = align;
	dax_region->dev = parent;
	dax_region->target_node = target_node;
	ida_init(&dax_region->ida);
	dax_region->res = (struct resource) {
		.start = res->start,
		.end = res->end,
		.flags = IORESOURCE_MEM | flags,
	};

	if (sysfs_create_groups(&parent->kobj, dax_region_attribute_groups)) {
		kfree(dax_region);
		return NULL;
	}

	kref_get(&dax_region->kref);
	if (devm_add_action_or_reset(parent, dax_region_unregister, dax_region))
		return NULL;
	return dax_region;
}
EXPORT_SYMBOL_GPL(alloc_dax_region);

static int alloc_dev_dax_range(struct dev_dax *dev_dax, resource_size_t size)
{
	struct dax_region *dax_region = dev_dax->region;
	struct resource *res = &dax_region->res;
	struct device *dev = &dev_dax->dev;
	struct resource *alloc;

	device_lock_assert(dax_region->dev);

	/* handle the seed alloc special case */
	if (!size) {
		dev_dax->range = (struct range) {
			.start = res->start,
			.end = res->start - 1,
		};
		return 0;
	}

	/* TODO: handle multiple allocations per region */
	if (res->child)
		return -ENOMEM;

	alloc = __request_region(res, res->start, size, dev_name(dev), 0);

	if (!alloc)
		return -ENOMEM;

	dev_dax->range = (struct range) {
		.start = alloc->start,
		.end = alloc->end,
	};

	return 0;
}

static ssize_t size_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dev_dax *dev_dax = to_dev_dax(dev);
	unsigned long long size = range_len(&dev_dax->range);

	return sprintf(buf, "%llu\n", size);
}
static DEVICE_ATTR_RO(size);

static int dev_dax_target_node(struct dev_dax *dev_dax)
{
	struct dax_region *dax_region = dev_dax->region;

	return dax_region->target_node;
}

static ssize_t target_node_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dev_dax *dev_dax = to_dev_dax(dev);

	return sprintf(buf, "%d\n", dev_dax_target_node(dev_dax));
}
static DEVICE_ATTR_RO(target_node);

static ssize_t resource_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct dev_dax *dev_dax = to_dev_dax(dev);

	return sprintf(buf, "%#llx\n", dev_dax->range.start);
}
static DEVICE_ATTR(resource, 0400, resource_show, NULL);

static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
		char *buf)
{
	/*
	 * We only ever expect to handle device-dax instances, i.e. the
	 * @type argument to MODULE_ALIAS_DAX_DEVICE() is always zero
	 */
	return sprintf(buf, DAX_DEVICE_MODALIAS_FMT "\n", 0);
}
static DEVICE_ATTR_RO(modalias);

static ssize_t numa_node_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	return sprintf(buf, "%d\n", dev_to_node(dev));
}
static DEVICE_ATTR_RO(numa_node);

static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
{
	struct device *dev = container_of(kobj, struct device, kobj);
	struct dev_dax *dev_dax = to_dev_dax(dev);

	if (a == &dev_attr_target_node.attr && dev_dax_target_node(dev_dax) < 0)
		return 0;
	if (a == &dev_attr_numa_node.attr && !IS_ENABLED(CONFIG_NUMA))
		return 0;
	return a->mode;
}

static struct attribute *dev_dax_attributes[] = {
	&dev_attr_modalias.attr,
	&dev_attr_size.attr,
	&dev_attr_target_node.attr,
	&dev_attr_resource.attr,
	&dev_attr_numa_node.attr,
	NULL,
};

static const struct attribute_group dev_dax_attribute_group = {
	.attrs = dev_dax_attributes,
	.is_visible = dev_dax_visible,
};

static const struct attribute_group *dax_attribute_groups[] = {
	&dev_dax_attribute_group,
	NULL,
};

static void dev_dax_release(struct device *dev)
{
	struct dev_dax *dev_dax = to_dev_dax(dev);
	struct dax_region *dax_region = dev_dax->region;
	struct dax_device *dax_dev = dev_dax->dax_dev;

	put_dax(dax_dev);
	free_dev_dax_id(dev_dax);
	dax_region_put(dax_region);
	kfree(dev_dax->pgmap);
	kfree(dev_dax);
}

static const struct device_type dev_dax_type = {
	.release = dev_dax_release,
	.groups = dax_attribute_groups,
};

struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
{
	struct dax_region *dax_region = data->dax_region;
	struct device *parent = dax_region->dev;
	struct dax_device *dax_dev;
	struct dev_dax *dev_dax;
	struct inode *inode;
	struct device *dev;
	int rc;

	dev_dax = kzalloc(sizeof(*dev_dax), GFP_KERNEL);
	if (!dev_dax)
		return ERR_PTR(-ENOMEM);

	if (is_static(dax_region)) {
		if (dev_WARN_ONCE(parent, data->id < 0,
				"dynamic id specified to static region\n")) {
			rc = -EINVAL;
			goto err_id;
		}

		dev_dax->id = data->id;
	} else {
		if (dev_WARN_ONCE(parent, data->id >= 0,
				"static id specified to dynamic region\n")) {
			rc = -EINVAL;
			goto err_id;
		}

		rc = ida_alloc(&dax_region->ida, GFP_KERNEL);
		if (rc < 0)
			goto err_id;
		dev_dax->id = rc;
	}

	dev_dax->region = dax_region;
	dev = &dev_dax->dev;
	device_initialize(dev);
	dev_set_name(dev, "dax%d.%d", dax_region->id, dev_dax->id);

	rc = alloc_dev_dax_range(dev_dax, data->size);
	if (rc)
		goto err_range;

	if (data->pgmap) {
		dev_WARN_ONCE(parent, !is_static(dax_region),
			"custom dev_pagemap requires a static dax_region\n");

		dev_dax->pgmap = kmemdup(data->pgmap,
				sizeof(struct dev_pagemap), GFP_KERNEL);
		if (!dev_dax->pgmap) {
			rc = -ENOMEM;
			goto err_pgmap;
		}
	}

	/*
	 * No 'host' or dax_operations since there is no access to this
	 * device outside of mmap of the resulting character device.
	 */
	dax_dev = alloc_dax(dev_dax, NULL, NULL, DAXDEV_F_SYNC);
	if (IS_ERR(dax_dev)) {
		rc = PTR_ERR(dax_dev);
		goto err_alloc_dax;
	}

	/* a device_dax instance is dead while the driver is not attached */
	kill_dax(dax_dev);

	/* from here on we're committed to teardown via dev_dax_release() */
	dev_dax->dax_dev = dax_dev;
	dev_dax->target_node = dax_region->target_node;
	kref_get(&dax_region->kref);

	inode = dax_inode(dax_dev);
	dev->devt = inode->i_rdev;
	if (data->subsys == DEV_DAX_BUS)
		dev->bus = &dax_bus_type;
	else
		dev->class = dax_class;
	dev->parent = parent;
	dev->type = &dev_dax_type;

	rc = device_add(dev);
	if (rc) {
		kill_dev_dax(dev_dax);
		put_device(dev);
		return ERR_PTR(rc);
	}

	rc = devm_add_action_or_reset(dax_region->dev, unregister_dev_dax, dev);
	if (rc)
		return ERR_PTR(rc);

	return dev_dax;

err_alloc_dax:
	kfree(dev_dax->pgmap);
err_pgmap:
	free_dev_dax_range(dev_dax);
err_range:
	free_dev_dax_id(dev_dax);
err_id:
	kfree(dev_dax);

	return ERR_PTR(rc);
}
EXPORT_SYMBOL_GPL(devm_create_dev_dax);

static int match_always_count;

int __dax_driver_register(struct dax_device_driver *dax_drv,
		struct module *module, const char *mod_name)
{
	struct device_driver *drv = &dax_drv->drv;
	int rc = 0;

	INIT_LIST_HEAD(&dax_drv->ids);
	drv->owner = module;
	drv->name = mod_name;
	drv->mod_name = mod_name;
	drv->bus = &dax_bus_type;

	/* there can only be one default driver */
	mutex_lock(&dax_bus_lock);
	match_always_count += dax_drv->match_always;
	if (match_always_count > 1) {
		match_always_count--;
		WARN_ON(1);
		rc = -EINVAL;
	}
	mutex_unlock(&dax_bus_lock);
	if (rc)
		return rc;
	return driver_register(drv);
}
EXPORT_SYMBOL_GPL(__dax_driver_register);

void dax_driver_unregister(struct dax_device_driver *dax_drv)
{
	struct device_driver *drv = &dax_drv->drv;
	struct dax_id *dax_id, *_id;

	mutex_lock(&dax_bus_lock);
	match_always_count -= dax_drv->match_always;
	list_for_each_entry_safe(dax_id, _id, &dax_drv->ids, list) {
		list_del(&dax_id->list);
		kfree(dax_id);
	}
	mutex_unlock(&dax_bus_lock);
	driver_unregister(drv);
}
EXPORT_SYMBOL_GPL(dax_driver_unregister);

int __init dax_bus_init(void)
{
	int rc;

	if (IS_ENABLED(CONFIG_DEV_DAX_PMEM_COMPAT)) {
		dax_class = class_create(THIS_MODULE, "dax");
		if (IS_ERR(dax_class))
			return PTR_ERR(dax_class);
	}

	rc = bus_register(&dax_bus_type);
	if (rc)
		class_destroy(dax_class);
	return rc;
}

void __exit dax_bus_exit(void)
{
	bus_unregister(&dax_bus_type);
	class_destroy(dax_class);
}