1 files changed, 709 insertions, 0 deletions

diff --git a/drivers/dax/device.c b/drivers/dax/device.c
new file mode 100644
index 000000000000..19a42edbfa03
--- /dev/null
+++ b/drivers/dax/device.c
@@ -0,0 +1,709 @@
+/*
+ * Copyright(c) 2016 - 2017 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#include <linux/pagemap.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/pfn_t.h>
+#include <linux/cdev.h>
+#include <linux/slab.h>
+#include <linux/dax.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include "dax.h"
+
+static struct class *dax_class;
+
+/**
+ * struct dax_region - mapping infrastructure for dax devices
+ * @id: kernel-wide unique region for a memory range
+ * @base: linear address corresponding to @res
+ * @kref: to pin while other agents have a need to do lookups
+ * @dev: parent device backing this region
+ * @align: allocation and mapping alignment for child dax devices
+ * @res: physical address range of the region
+ * @pfn_flags: identify whether the pfns are paged back or not
+ */
+struct dax_region {
+	int id;
+	struct ida ida;
+	void *base;
+	struct kref kref;
+	struct device *dev;
+	unsigned int align;
+	struct resource res;
+	unsigned long pfn_flags;
+};
+
+/**
+ * struct dev_dax - instance data for a subdivision of a dax region
+ * @region - parent region
+ * @dax_dev - core dax functionality
+ * @dev - device core
+ * @id - child id in the region
+ * @num_resources - number of physical address extents in this device
+ * @res - array of physical address ranges
+ */
+struct dev_dax {
+	struct dax_region *region;
+	struct dax_device *dax_dev;
+	struct device dev;
+	int id;
+	int num_resources;
+	struct resource res[0];
+};
+
+static ssize_t id_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dax_region *dax_region;
+	ssize_t rc = -ENXIO;
+
+	device_lock(dev);
+	dax_region = dev_get_drvdata(dev);
+	if (dax_region)
+		rc = sprintf(buf, "%d\n", dax_region->id);
+	device_unlock(dev);
+
+	return rc;
+}
+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;
+	ssize_t rc = -ENXIO;
+
+	device_lock(dev);
+	dax_region = dev_get_drvdata(dev);
+	if (dax_region)
+		rc = sprintf(buf, "%llu\n", (unsigned long long)
+				resource_size(&dax_region->res));
+	device_unlock(dev);
+
+	return rc;
+}
+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;
+	ssize_t rc = -ENXIO;
+
+	device_lock(dev);
+	dax_region = dev_get_drvdata(dev);
+	if (dax_region)
+		rc = sprintf(buf, "%u\n", dax_region->align);
+	device_unlock(dev);
+
+	return rc;
+}
+static DEVICE_ATTR_RO(align);
+
+static struct attribute *dax_region_attributes[] = {
+	&dev_attr_region_size.attr,
+	&dev_attr_align.attr,
+	&dev_attr_id.attr,
+	NULL,
+};
+
+static const struct attribute_group dax_region_attribute_group = {
+	.name = "dax_region",
+	.attrs = dax_region_attributes,
+};
+
+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, unsigned int align, void *addr,
+		unsigned long pfn_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);
+	memcpy(&dax_region->res, res, sizeof(*res));
+	dax_region->pfn_flags = pfn_flags;
+	kref_init(&dax_region->kref);
+	dax_region->id = region_id;
+	ida_init(&dax_region->ida);
+	dax_region->align = align;
+	dax_region->dev = parent;
+	dax_region->base = addr;
+	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 struct dev_dax *to_dev_dax(struct device *dev)
+{
+	return container_of(dev, struct dev_dax, dev);
+}
+
+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 = 0;
+	int i;
+
+	for (i = 0; i < dev_dax->num_resources; i++)
+		size += resource_size(&dev_dax->res[i]);
+
+	return sprintf(buf, "%llu\n", size);
+}
+static DEVICE_ATTR_RO(size);
+
+static struct attribute *dev_dax_attributes[] = {
+	&dev_attr_size.attr,
+	NULL,
+};
+
+static const struct attribute_group dev_dax_attribute_group = {
+	.attrs = dev_dax_attributes,
+};
+
+static const struct attribute_group *dax_attribute_groups[] = {
+	&dev_dax_attribute_group,
+	NULL,
+};
+
+static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
+		const char *func)
+{
+	struct dax_region *dax_region = dev_dax->region;
+	struct device *dev = &dev_dax->dev;
+	unsigned long mask;
+
+	if (!dax_alive(dev_dax->dax_dev))
+		return -ENXIO;
+
+	/* prevent private mappings from being established */
+	if ((vma->vm_flags & VM_MAYSHARE) != VM_MAYSHARE) {
+		dev_info(dev, "%s: %s: fail, attempted private mapping\n",
+				current->comm, func);
+		return -EINVAL;
+	}
+
+	mask = dax_region->align - 1;
+	if (vma->vm_start & mask || vma->vm_end & mask) {
+		dev_info(dev, "%s: %s: fail, unaligned vma (%#lx - %#lx, %#lx)\n",
+				current->comm, func, vma->vm_start, vma->vm_end,
+				mask);
+		return -EINVAL;
+	}
+
+	if ((dax_region->pfn_flags & (PFN_DEV|PFN_MAP)) == PFN_DEV
+			&& (vma->vm_flags & VM_DONTCOPY) == 0) {
+		dev_info(dev, "%s: %s: fail, dax range requires MADV_DONTFORK\n",
+				current->comm, func);
+		return -EINVAL;
+	}
+
+	if (!vma_is_dax(vma)) {
+		dev_info(dev, "%s: %s: fail, vma is not DAX capable\n",
+				current->comm, func);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static phys_addr_t pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
+		unsigned long size)
+{
+	struct resource *res;
+	phys_addr_t phys;
+	int i;
+
+	for (i = 0; i < dev_dax->num_resources; i++) {
+		res = &dev_dax->res[i];
+		phys = pgoff * PAGE_SIZE + res->start;
+		if (phys >= res->start && phys <= res->end)
+			break;
+		pgoff -= PHYS_PFN(resource_size(res));
+	}
+
+	if (i < dev_dax->num_resources) {
+		res = &dev_dax->res[i];
+		if (phys + size - 1 <= res->end)
+			return phys;
+	}
+
+	return -1;
+}
+
+static int __dev_dax_pte_fault(struct dev_dax *dev_dax, struct vm_fault *vmf)
+{
+	struct device *dev = &dev_dax->dev;
+	struct dax_region *dax_region;
+	int rc = VM_FAULT_SIGBUS;
+	phys_addr_t phys;
+	pfn_t pfn;
+	unsigned int fault_size = PAGE_SIZE;
+
+	if (check_vma(dev_dax, vmf->vma, __func__))
+		return VM_FAULT_SIGBUS;
+
+	dax_region = dev_dax->region;
+	if (dax_region->align > PAGE_SIZE) {
+		dev_dbg(dev, "%s: alignment (%#x) > fault size (%#x)\n",
+			__func__, dax_region->align, fault_size);
+		return VM_FAULT_SIGBUS;
+	}
+
+	if (fault_size != dax_region->align)
+		return VM_FAULT_SIGBUS;
+
+	phys = pgoff_to_phys(dev_dax, vmf->pgoff, PAGE_SIZE);
+	if (phys == -1) {
+		dev_dbg(dev, "%s: pgoff_to_phys(%#lx) failed\n", __func__,
+				vmf->pgoff);
+		return VM_FAULT_SIGBUS;
+	}
+
+	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
+
+	rc = vm_insert_mixed(vmf->vma, vmf->address, pfn);
+
+	if (rc == -ENOMEM)
+		return VM_FAULT_OOM;
+	if (rc < 0 && rc != -EBUSY)
+		return VM_FAULT_SIGBUS;
+
+	return VM_FAULT_NOPAGE;
+}
+
+static int __dev_dax_pmd_fault(struct dev_dax *dev_dax, struct vm_fault *vmf)
+{
+	unsigned long pmd_addr = vmf->address & PMD_MASK;
+	struct device *dev = &dev_dax->dev;
+	struct dax_region *dax_region;
+	phys_addr_t phys;
+	pgoff_t pgoff;
+	pfn_t pfn;
+	unsigned int fault_size = PMD_SIZE;
+
+	if (check_vma(dev_dax, vmf->vma, __func__))
+		return VM_FAULT_SIGBUS;
+
+	dax_region = dev_dax->region;
+	if (dax_region->align > PMD_SIZE) {
+		dev_dbg(dev, "%s: alignment (%#x) > fault size (%#x)\n",
+			__func__, dax_region->align, fault_size);
+		return VM_FAULT_SIGBUS;
+	}
+
+	/* dax pmd mappings require pfn_t_devmap() */
+	if ((dax_region->pfn_flags & (PFN_DEV|PFN_MAP)) != (PFN_DEV|PFN_MAP)) {
+		dev_dbg(dev, "%s: region lacks devmap flags\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	if (fault_size < dax_region->align)
+		return VM_FAULT_SIGBUS;
+	else if (fault_size > dax_region->align)
+		return VM_FAULT_FALLBACK;
+
+	/* if we are outside of the VMA */
+	if (pmd_addr < vmf->vma->vm_start ||
+			(pmd_addr + PMD_SIZE) > vmf->vma->vm_end)
+		return VM_FAULT_SIGBUS;
+
+	pgoff = linear_page_index(vmf->vma, pmd_addr);
+	phys = pgoff_to_phys(dev_dax, pgoff, PMD_SIZE);
+	if (phys == -1) {
+		dev_dbg(dev, "%s: pgoff_to_phys(%#lx) failed\n", __func__,
+				pgoff);
+		return VM_FAULT_SIGBUS;
+	}
+
+	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
+
+	return vmf_insert_pfn_pmd(vmf->vma, vmf->address, vmf->pmd, pfn,
+			vmf->flags & FAULT_FLAG_WRITE);
+}
+
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+static int __dev_dax_pud_fault(struct dev_dax *dev_dax, struct vm_fault *vmf)
+{
+	unsigned long pud_addr = vmf->address & PUD_MASK;
+	struct device *dev = &dev_dax->dev;
+	struct dax_region *dax_region;
+	phys_addr_t phys;
+	pgoff_t pgoff;
+	pfn_t pfn;
+	unsigned int fault_size = PUD_SIZE;
+
+
+	if (check_vma(dev_dax, vmf->vma, __func__))
+		return VM_FAULT_SIGBUS;
+
+	dax_region = dev_dax->region;
+	if (dax_region->align > PUD_SIZE) {
+		dev_dbg(dev, "%s: alignment (%#x) > fault size (%#x)\n",
+			__func__, dax_region->align, fault_size);
+		return VM_FAULT_SIGBUS;
+	}
+
+	/* dax pud mappings require pfn_t_devmap() */
+	if ((dax_region->pfn_flags & (PFN_DEV|PFN_MAP)) != (PFN_DEV|PFN_MAP)) {
+		dev_dbg(dev, "%s: region lacks devmap flags\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	if (fault_size < dax_region->align)
+		return VM_FAULT_SIGBUS;
+	else if (fault_size > dax_region->align)
+		return VM_FAULT_FALLBACK;
+
+	/* if we are outside of the VMA */
+	if (pud_addr < vmf->vma->vm_start ||
+			(pud_addr + PUD_SIZE) > vmf->vma->vm_end)
+		return VM_FAULT_SIGBUS;
+
+	pgoff = linear_page_index(vmf->vma, pud_addr);
+	phys = pgoff_to_phys(dev_dax, pgoff, PUD_SIZE);
+	if (phys == -1) {
+		dev_dbg(dev, "%s: pgoff_to_phys(%#lx) failed\n", __func__,
+				pgoff);
+		return VM_FAULT_SIGBUS;
+	}
+
+	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
+
+	return vmf_insert_pfn_pud(vmf->vma, vmf->address, vmf->pud, pfn,
+			vmf->flags & FAULT_FLAG_WRITE);
+}
+#else
+static int __dev_dax_pud_fault(struct dev_dax *dev_dax, struct vm_fault *vmf)
+{
+	return VM_FAULT_FALLBACK;
+}
+#endif /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
+
+static int dev_dax_huge_fault(struct vm_fault *vmf,
+		enum page_entry_size pe_size)
+{
+	int rc, id;
+	struct file *filp = vmf->vma->vm_file;
+	struct dev_dax *dev_dax = filp->private_data;
+
+	dev_dbg(&dev_dax->dev, "%s: %s: %s (%#lx - %#lx) size = %d\n", __func__,
+			current->comm, (vmf->flags & FAULT_FLAG_WRITE)
+			? "write" : "read",
+			vmf->vma->vm_start, vmf->vma->vm_end, pe_size);
+
+	id = dax_read_lock();
+	switch (pe_size) {
+	case PE_SIZE_PTE:
+		rc = __dev_dax_pte_fault(dev_dax, vmf);
+		break;
+	case PE_SIZE_PMD:
+		rc = __dev_dax_pmd_fault(dev_dax, vmf);
+		break;
+	case PE_SIZE_PUD:
+		rc = __dev_dax_pud_fault(dev_dax, vmf);
+		break;
+	default:
+		rc = VM_FAULT_SIGBUS;
+	}
+	dax_read_unlock(id);
+
+	return rc;
+}
+
+static int dev_dax_fault(struct vm_fault *vmf)
+{
+	return dev_dax_huge_fault(vmf, PE_SIZE_PTE);
+}
+
+static const struct vm_operations_struct dax_vm_ops = {
+	.fault = dev_dax_fault,
+	.huge_fault = dev_dax_huge_fault,
+};
+
+static int dax_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	struct dev_dax *dev_dax = filp->private_data;
+	int rc, id;
+
+	dev_dbg(&dev_dax->dev, "%s\n", __func__);
+
+	/*
+	 * We lock to check dax_dev liveness and will re-check at
+	 * fault time.
+	 */
+	id = dax_read_lock();
+	rc = check_vma(dev_dax, vma, __func__);
+	dax_read_unlock(id);
+	if (rc)
+		return rc;
+
+	vma->vm_ops = &dax_vm_ops;
+	vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
+	return 0;
+}
+
+/* return an unmapped area aligned to the dax region specified alignment */
+static unsigned long dax_get_unmapped_area(struct file *filp,
+		unsigned long addr, unsigned long len, unsigned long pgoff,
+		unsigned long flags)
+{
+	unsigned long off, off_end, off_align, len_align, addr_align, align;
+	struct dev_dax *dev_dax = filp ? filp->private_data : NULL;
+	struct dax_region *dax_region;
+
+	if (!dev_dax || addr)
+		goto out;
+
+	dax_region = dev_dax->region;
+	align = dax_region->align;
+	off = pgoff << PAGE_SHIFT;
+	off_end = off + len;
+	off_align = round_up(off, align);
+
+	if ((off_end <= off_align) || ((off_end - off_align) < align))
+		goto out;
+
+	len_align = len + align;
+	if ((off + len_align) < off)
+		goto out;
+
+	addr_align = current->mm->get_unmapped_area(filp, addr, len_align,
+			pgoff, flags);
+	if (!IS_ERR_VALUE(addr_align)) {
+		addr_align += (off - addr_align) & (align - 1);
+		return addr_align;
+	}
+ out:
+	return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
+}
+
+static int dax_open(struct inode *inode, struct file *filp)
+{
+	struct dax_device *dax_dev = inode_dax(inode);
+	struct inode *__dax_inode = dax_inode(dax_dev);
+	struct dev_dax *dev_dax = dax_get_private(dax_dev);
+
+	dev_dbg(&dev_dax->dev, "%s\n", __func__);
+	inode->i_mapping = __dax_inode->i_mapping;
+	inode->i_mapping->host = __dax_inode;
+	filp->f_mapping = inode->i_mapping;
+	filp->private_data = dev_dax;
+	inode->i_flags = S_DAX;
+
+	return 0;
+}
+
+static int dax_release(struct inode *inode, struct file *filp)
+{
+	struct dev_dax *dev_dax = filp->private_data;
+
+	dev_dbg(&dev_dax->dev, "%s\n", __func__);
+	return 0;
+}
+
+static const struct file_operations dax_fops = {
+	.llseek = noop_llseek,
+	.owner = THIS_MODULE,
+	.open = dax_open,
+	.release = dax_release,
+	.get_unmapped_area = dax_get_unmapped_area,
+	.mmap = dax_mmap,
+};
+
+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;
+
+	ida_simple_remove(&dax_region->ida, dev_dax->id);
+	dax_region_put(dax_region);
+	put_dax(dax_dev);
+	kfree(dev_dax);
+}
+
+static 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);
+}
+
+static void unregister_dev_dax(void *dev)
+{
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+	struct dax_device *dax_dev = dev_dax->dax_dev;
+	struct inode *inode = dax_inode(dax_dev);
+	struct cdev *cdev = inode->i_cdev;
+
+	dev_dbg(dev, "%s\n", __func__);
+
+	kill_dev_dax(dev_dax);
+	cdev_device_del(cdev, dev);
+	put_device(dev);
+}
+
+struct dev_dax *devm_create_dev_dax(struct dax_region *dax_region,
+		struct resource *res, int count)
+{
+	struct device *parent = dax_region->dev;
+	struct dax_device *dax_dev;
+	struct dev_dax *dev_dax;
+	struct inode *inode;
+	struct device *dev;
+	struct cdev *cdev;
+	int rc = 0, i;
+
+	dev_dax = kzalloc(sizeof(*dev_dax) + sizeof(*res) * count, GFP_KERNEL);
+	if (!dev_dax)
+		return ERR_PTR(-ENOMEM);
+
+	for (i = 0; i < count; i++) {
+		if (!IS_ALIGNED(res[i].start, dax_region->align)
+				|| !IS_ALIGNED(resource_size(&res[i]),
+					dax_region->align)) {
+			rc = -EINVAL;
+			break;
+		}
+		dev_dax->res[i].start = res[i].start;
+		dev_dax->res[i].end = res[i].end;
+	}
+
+	if (i < count)
+		goto err_id;
+
+	dev_dax->id = ida_simple_get(&dax_region->ida, 0, 0, GFP_KERNEL);
+	if (dev_dax->id < 0) {
+		rc = dev_dax->id;
+		goto err_id;
+	}
+
+	dax_dev = alloc_dax(dev_dax);
+	if (!dax_dev)
+		goto err_dax;
+
+	/* from here on we're committed to teardown via dax_dev_release() */
+	dev = &dev_dax->dev;
+	device_initialize(dev);
+
+	inode = dax_inode(dax_dev);
+	cdev = inode->i_cdev;
+	cdev_init(cdev, &dax_fops);
+	cdev->owner = parent->driver->owner;
+
+	dev_dax->num_resources = count;
+	dev_dax->dax_dev = dax_dev;
+	dev_dax->region = dax_region;
+	kref_get(&dax_region->kref);
+
+	dev->devt = inode->i_rdev;
+	dev->class = dax_class;
+	dev->parent = parent;
+	dev->groups = dax_attribute_groups;
+	dev->release = dev_dax_release;
+	dev_set_name(dev, "dax%d.%d", dax_region->id, dev_dax->id);
+
+	rc = cdev_device_add(cdev, 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_dax:
+	ida_simple_remove(&dax_region->ida, dev_dax->id);
+ err_id:
+	kfree(dev_dax);
+
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_GPL(devm_create_dev_dax);
+
+static int __init dax_init(void)
+{
+	dax_class = class_create(THIS_MODULE, "dax");
+	return PTR_ERR_OR_ZERO(dax_class);
+}
+
+static void __exit dax_exit(void)
+{
+	class_destroy(dax_class);
+}
+
+MODULE_AUTHOR("Intel Corporation");
+MODULE_LICENSE("GPL v2");
+subsys_initcall(dax_init);
+module_exit(dax_exit);