[resend PATCH v2 02/33] dax: refactor dax-fs into a generic provider of 'struct dax_device' instances

From: Dan Williams
Date: Mon Apr 17 2017 - 15:14:53 EST

We want dax capable drivers to be able to publish a set of dax
operations [1]. However, we do not want to further abuse block_devices
to advertise these operations. Instead we will attach these operations
to a dax device and add a lookup mechanism to go from block device path
to a dax device. A dax capable driver like pmem or brd is responsible
for registering a dax device, alongside a block device, and then a dax
capable filesystem is responsible for retrieving the dax device by path
name if it wants to call dax_operations.

For now, we refactor the dax pseudo-fs to be a generic facility, rather
than an implementation detail, of the device-dax use case. Where a "dax
device" is just an inode + dax infrastructure, and "Device DAX" is a
mapping service layered on top of that base 'struct dax_device'.
"Filesystem DAX" is then a mapping service that layers a filesystem on
top of that same base device. Filesystem DAX is associated with a
block_device for now, but perhaps directly to a dax device in the
future, or for new pmem-only filesystems.

[1]: https://lkml.org/lkml/2017/1/19/880

Suggested-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
drivers/Makefile | 2
drivers/dax/Kconfig | 10 +
drivers/dax/Makefile | 5 +
drivers/dax/dax.h | 20 +--
drivers/dax/device-dax.h | 25 ++++
drivers/dax/device.c | 241 ++++++----------------------------
drivers/dax/pmem.c | 2
drivers/dax/super.c | 303 +++++++++++++++++++++++++++++++++++++++++++
include/linux/dax.h | 3
tools/testing/nvdimm/Kbuild | 10 +
10 files changed, 404 insertions(+), 217 deletions(-)
create mode 100644 drivers/dax/device-dax.h
rename drivers/dax/{dax.c => device.c} (77%)
create mode 100644 drivers/dax/super.c

diff --git a/drivers/Makefile b/drivers/Makefile
index 2eced9afba53..0442e982cf35 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -71,7 +71,7 @@ obj-$(CONFIG_PARPORT) += parport/
obj-$(CONFIG_NVM) += lightnvm/
obj-y += base/ block/ misc/ mfd/ nfc/
obj-$(CONFIG_LIBNVDIMM) += nvdimm/
-obj-$(CONFIG_DEV_DAX) += dax/
+obj-$(CONFIG_DAX) += dax/
obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf/
obj-$(CONFIG_NUBUS) += nubus/
obj-y += macintosh/
diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index 9e95bf94eb13..b7053eafd88e 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -1,8 +1,13 @@
-menuconfig DEV_DAX
+menuconfig DAX
tristate "DAX: direct access to differentiated memory"
+ select SRCU
default m if NVDIMM_DAX
+
+if DAX
+
+config DEV_DAX
+ tristate "Device DAX: direct access mapping device"
depends on TRANSPARENT_HUGEPAGE
- select SRCU
help
Support raw access to differentiated (persistence, bandwidth,
latency...) memory via an mmap(2) capable character
@@ -11,7 +16,6 @@ menuconfig DEV_DAX
baseline memory pool. Mappings of a /dev/daxX.Y device impose
restrictions that make the mapping behavior deterministic.

-if DEV_DAX

config DEV_DAX_PMEM
tristate "PMEM DAX: direct access to persistent memory"
diff --git a/drivers/dax/Makefile b/drivers/dax/Makefile
index 27c54e38478a..dc7422530462 100644
--- a/drivers/dax/Makefile
+++ b/drivers/dax/Makefile
@@ -1,4 +1,7 @@
-obj-$(CONFIG_DEV_DAX) += dax.o
+obj-$(CONFIG_DAX) += dax.o
+obj-$(CONFIG_DEV_DAX) += device_dax.o
obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem.o

+dax-y := super.o
dax_pmem-y := pmem.o
+device_dax-y := device.o
diff --git a/drivers/dax/dax.h b/drivers/dax/dax.h
index ea176d875d60..2472d9da96db 100644
--- a/drivers/dax/dax.h
+++ b/drivers/dax/dax.h
@@ -1,5 +1,5 @@
/*
- * Copyright(c) 2016 Intel Corporation. All rights reserved.
+ * 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
@@ -12,14 +12,12 @@
*/
#ifndef __DAX_H__
#define __DAX_H__
-struct device;
-struct dev_dax;
-struct resource;
-struct dax_region;
-void dax_region_put(struct dax_region *dax_region);
-struct dax_region *alloc_dax_region(struct device *parent,
- int region_id, struct resource *res, unsigned int align,
- void *addr, unsigned long flags);
-struct dev_dax *devm_create_dev_dax(struct dax_region *dax_region,
- struct resource *res, int count);
+struct dax_device;
+struct dax_device *alloc_dax(void *private);
+void put_dax(struct dax_device *dax_dev);
+bool dax_alive(struct dax_device *dax_dev);
+void kill_dax(struct dax_device *dax_dev);
+struct dax_device *inode_dax(struct inode *inode);
+struct inode *dax_inode(struct dax_device *dax_dev);
+void *dax_get_private(struct dax_device *dax_dev);
#endif /* __DAX_H__ */
diff --git a/drivers/dax/device-dax.h b/drivers/dax/device-dax.h
new file mode 100644
index 000000000000..fdcd9769ffde
--- /dev/null
+++ b/drivers/dax/device-dax.h
@@ -0,0 +1,25 @@
+/*
+ * Copyright(c) 2016 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.
+ */
+#ifndef __DEVICE_DAX_H__
+#define __DEVICE_DAX_H__
+struct device;
+struct dev_dax;
+struct resource;
+struct dax_region;
+void dax_region_put(struct dax_region *dax_region);
+struct dax_region *alloc_dax_region(struct device *parent,
+ int region_id, struct resource *res, unsigned int align,
+ void *addr, unsigned long flags);
+struct dev_dax *devm_create_dev_dax(struct dax_region *dax_region,
+ struct resource *res, int count);
+#endif /* __DEVICE_DAX_H__ */
diff --git a/drivers/dax/dax.c b/drivers/dax/device.c
similarity index 77%
rename from drivers/dax/dax.c
rename to drivers/dax/device.c
index 376fdd353aea..19a42edbfa03 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/device.c
@@ -1,5 +1,5 @@
/*
- * Copyright(c) 2016 Intel Corporation. All rights reserved.
+ * 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
@@ -13,10 +13,7 @@
#include <linux/pagemap.h>
#include <linux/module.h>
#include <linux/device.h>
-#include <linux/magic.h>
-#include <linux/mount.h>
#include <linux/pfn_t.h>
-#include <linux/hash.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <linux/dax.h>
@@ -24,16 +21,7 @@
#include <linux/mm.h>
#include "dax.h"

-static dev_t dax_devt;
-DEFINE_STATIC_SRCU(dax_srcu);
static struct class *dax_class;
-static DEFINE_IDA(dax_minor_ida);
-static int nr_dax = CONFIG_NR_DEV_DAX;
-module_param(nr_dax, int, S_IRUGO);
-static struct vfsmount *dax_mnt;
-static struct kmem_cache *dax_cache __read_mostly;
-static struct super_block *dax_superblock __read_mostly;
-MODULE_PARM_DESC(nr_dax, "max number of device-dax instances");

/**
* struct dax_region - mapping infrastructure for dax devices
@@ -59,19 +47,16 @@ struct dax_region {
/**
* struct dev_dax - instance data for a subdivision of a dax region
* @region - parent region
- * @dev - device backing the character device
- * @cdev - core chardev data
- * @alive - !alive + srcu grace period == no new mappings can be established
+ * @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 inode *inode;
+ struct dax_device *dax_dev;
struct device dev;
- struct cdev cdev;
- bool alive;
int id;
int num_resources;
struct resource res[0];
@@ -144,117 +129,6 @@ static const struct attribute_group *dax_region_attribute_groups[] = {
NULL,
};

-static struct inode *dax_alloc_inode(struct super_block *sb)
-{
- return kmem_cache_alloc(dax_cache, GFP_KERNEL);
-}
-
-static void dax_i_callback(struct rcu_head *head)
-{
- struct inode *inode = container_of(head, struct inode, i_rcu);
-
- kmem_cache_free(dax_cache, inode);
-}
-
-static void dax_destroy_inode(struct inode *inode)
-{
- call_rcu(&inode->i_rcu, dax_i_callback);
-}
-
-static const struct super_operations dax_sops = {
- .statfs = simple_statfs,
- .alloc_inode = dax_alloc_inode,
- .destroy_inode = dax_destroy_inode,
- .drop_inode = generic_delete_inode,
-};
-
-static struct dentry *dax_mount(struct file_system_type *fs_type,
- int flags, const char *dev_name, void *data)
-{
- return mount_pseudo(fs_type, "dax:", &dax_sops, NULL, DAXFS_MAGIC);
-}
-
-static struct file_system_type dax_type = {
- .name = "dax",
- .mount = dax_mount,
- .kill_sb = kill_anon_super,
-};
-
-static int dax_test(struct inode *inode, void *data)
-{
- return inode->i_cdev == data;
-}
-
-static int dax_set(struct inode *inode, void *data)
-{
- inode->i_cdev = data;
- return 0;
-}
-
-static struct inode *dax_inode_get(struct cdev *cdev, dev_t devt)
-{
- struct inode *inode;
-
- inode = iget5_locked(dax_superblock, hash_32(devt + DAXFS_MAGIC, 31),
- dax_test, dax_set, cdev);
-
- if (!inode)
- return NULL;
-
- if (inode->i_state & I_NEW) {
- inode->i_mode = S_IFCHR;
- inode->i_flags = S_DAX;
- inode->i_rdev = devt;
- mapping_set_gfp_mask(&inode->i_data, GFP_USER);
- unlock_new_inode(inode);
- }
- return inode;
-}
-
-static void init_once(void *inode)
-{
- inode_init_once(inode);
-}
-
-static int dax_inode_init(void)
-{
- int rc;
-
- dax_cache = kmem_cache_create("dax_cache", sizeof(struct inode), 0,
- (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
- SLAB_MEM_SPREAD|SLAB_ACCOUNT),
- init_once);
- if (!dax_cache)
- return -ENOMEM;
-
- rc = register_filesystem(&dax_type);
- if (rc)
- goto err_register_fs;
-
- dax_mnt = kern_mount(&dax_type);
- if (IS_ERR(dax_mnt)) {
- rc = PTR_ERR(dax_mnt);
- goto err_mount;
- }
- dax_superblock = dax_mnt->mnt_sb;
-
- return 0;
-
- err_mount:
- unregister_filesystem(&dax_type);
- err_register_fs:
- kmem_cache_destroy(dax_cache);
-
- return rc;
-}
-
-static void dax_inode_exit(void)
-{
- kern_unmount(dax_mnt);
- unregister_filesystem(&dax_type);
- kmem_cache_destroy(dax_cache);
-}
-
static void dax_region_free(struct kref *kref)
{
struct dax_region *dax_region;
@@ -363,7 +237,7 @@ static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
struct device *dev = &dev_dax->dev;
unsigned long mask;

- if (!dev_dax->alive)
+ if (!dax_alive(dev_dax->dax_dev))
return -ENXIO;

/* prevent private mappings from being established */
@@ -582,7 +456,7 @@ static int dev_dax_huge_fault(struct vm_fault *vmf,
? "write" : "read",
vmf->vma->vm_start, vmf->vma->vm_end, pe_size);

- id = srcu_read_lock(&dax_srcu);
+ id = dax_read_lock();
switch (pe_size) {
case PE_SIZE_PTE:
rc = __dev_dax_pte_fault(dev_dax, vmf);
@@ -596,7 +470,7 @@ static int dev_dax_huge_fault(struct vm_fault *vmf,
default:
rc = VM_FAULT_SIGBUS;
}
- srcu_read_unlock(&dax_srcu, id);
+ dax_read_unlock(id);

return rc;
}
@@ -614,11 +488,17 @@ static const struct vm_operations_struct dax_vm_ops = {
static int dax_mmap(struct file *filp, struct vm_area_struct *vma)
{
struct dev_dax *dev_dax = filp->private_data;
- int rc;
+ 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;

@@ -664,12 +544,13 @@ static unsigned long dax_get_unmapped_area(struct file *filp,

static int dax_open(struct inode *inode, struct file *filp)
{
- struct dev_dax *dev_dax;
+ 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_dax = container_of(inode->i_cdev, struct dev_dax, cdev);
dev_dbg(&dev_dax->dev, "%s\n", __func__);
- inode->i_mapping = dev_dax->inode->i_mapping;
- inode->i_mapping->host = dev_dax->inode;
+ 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;
@@ -698,36 +579,34 @@ 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);
- ida_simple_remove(&dax_minor_ida, MINOR(dev->devt));
dax_region_put(dax_region);
- iput(dev_dax->inode);
+ put_dax(dax_dev);
kfree(dev_dax);
}

static void kill_dev_dax(struct dev_dax *dev_dax)
{
- /*
- * Note, rcu is not protecting the liveness of dev_dax, rcu is
- * ensuring that any fault handlers that might have seen
- * dev_dax->alive == true, have completed. Any fault handlers
- * that start after synchronize_srcu() has started will abort
- * upon seeing dev_dax->alive == false.
- */
- dev_dax->alive = false;
- synchronize_srcu(&dax_srcu);
- unmap_mapping_range(dev_dax->inode->i_mapping, 0, 0, 1);
+ 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(&dev_dax->cdev, dev);
+ cdev_device_del(cdev, dev);
put_device(dev);
}

@@ -735,11 +614,12 @@ 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;
- int rc = 0, minor, i;
+ struct inode *inode;
struct device *dev;
struct cdev *cdev;
- dev_t dev_t;
+ int rc = 0, i;

dev_dax = kzalloc(sizeof(*dev_dax) + sizeof(*res) * count, GFP_KERNEL);
if (!dev_dax)
@@ -765,33 +645,25 @@ struct dev_dax *devm_create_dev_dax(struct dax_region *dax_region,
goto err_id;
}

- minor = ida_simple_get(&dax_minor_ida, 0, 0, GFP_KERNEL);
- if (minor < 0) {
- rc = minor;
- goto err_minor;
- }
+ dax_dev = alloc_dax(dev_dax);
+ if (!dax_dev)
+ goto err_dax;

- dev_t = MKDEV(MAJOR(dax_devt), minor);
+ /* from here on we're committed to teardown via dax_dev_release() */
dev = &dev_dax->dev;
- dev_dax->inode = dax_inode_get(&dev_dax->cdev, dev_t);
- if (!dev_dax->inode) {
- rc = -ENOMEM;
- goto err_inode;
- }
-
- /* from here on we're committed to teardown via dev_dax_release() */
device_initialize(dev);

- cdev = &dev_dax->cdev;
+ 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->alive = true;
+ dev_dax->dax_dev = dax_dev;
dev_dax->region = dax_region;
kref_get(&dax_region->kref);

- dev->devt = dev_t;
+ dev->devt = inode->i_rdev;
dev->class = dax_class;
dev->parent = parent;
dev->groups = dax_attribute_groups;
@@ -811,9 +683,7 @@ struct dev_dax *devm_create_dev_dax(struct dax_region *dax_region,

return dev_dax;

- err_inode:
- ida_simple_remove(&dax_minor_ida, minor);
- err_minor:
+ err_dax:
ida_simple_remove(&dax_region->ida, dev_dax->id);
err_id:
kfree(dev_dax);
@@ -824,38 +694,13 @@ EXPORT_SYMBOL_GPL(devm_create_dev_dax);

static int __init dax_init(void)
{
- int rc;
-
- rc = dax_inode_init();
- if (rc)
- return rc;
-
- nr_dax = max(nr_dax, 256);
- rc = alloc_chrdev_region(&dax_devt, 0, nr_dax, "dax");
- if (rc)
- goto err_chrdev;
-
dax_class = class_create(THIS_MODULE, "dax");
- if (IS_ERR(dax_class)) {
- rc = PTR_ERR(dax_class);
- goto err_class;
- }
-
- return 0;
-
- err_class:
- unregister_chrdev_region(dax_devt, nr_dax);
- err_chrdev:
- dax_inode_exit();
- return rc;
+ return PTR_ERR_OR_ZERO(dax_class);
}

static void __exit dax_exit(void)
{
class_destroy(dax_class);
- unregister_chrdev_region(dax_devt, nr_dax);
- ida_destroy(&dax_minor_ida);
- dax_inode_exit();
}

MODULE_AUTHOR("Intel Corporation");
diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
index 2c736fc4508b..d4ca19bd74eb 100644
--- a/drivers/dax/pmem.c
+++ b/drivers/dax/pmem.c
@@ -16,7 +16,7 @@
#include <linux/pfn_t.h>
#include "../nvdimm/pfn.h"
#include "../nvdimm/nd.h"
-#include "dax.h"
+#include "device-dax.h"

struct dax_pmem {
struct device *dev;
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
new file mode 100644
index 000000000000..c9f85f1c086e
--- /dev/null
+++ b/drivers/dax/super.c
@@ -0,0 +1,303 @@
+/*
+ * Copyright(c) 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/mount.h>
+#include <linux/magic.h>
+#include <linux/cdev.h>
+#include <linux/hash.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+
+static int nr_dax = CONFIG_NR_DEV_DAX;
+module_param(nr_dax, int, S_IRUGO);
+MODULE_PARM_DESC(nr_dax, "max number of dax device instances");
+
+static dev_t dax_devt;
+DEFINE_STATIC_SRCU(dax_srcu);
+static struct vfsmount *dax_mnt;
+static DEFINE_IDA(dax_minor_ida);
+static struct kmem_cache *dax_cache __read_mostly;
+static struct super_block *dax_superblock __read_mostly;
+
+int dax_read_lock(void)
+{
+ return srcu_read_lock(&dax_srcu);
+}
+EXPORT_SYMBOL_GPL(dax_read_lock);
+
+void dax_read_unlock(int id)
+{
+ srcu_read_unlock(&dax_srcu, id);
+}
+EXPORT_SYMBOL_GPL(dax_read_unlock);
+
+/**
+ * struct dax_device - anchor object for dax services
+ * @inode: core vfs
+ * @cdev: optional character interface for "device dax"
+ * @private: dax driver private data
+ * @alive: !alive + rcu grace period == no new operations / mappings
+ */
+struct dax_device {
+ struct inode inode;
+ struct cdev cdev;
+ void *private;
+ bool alive;
+};
+
+bool dax_alive(struct dax_device *dax_dev)
+{
+ lockdep_assert_held(&dax_srcu);
+ return dax_dev->alive;
+}
+EXPORT_SYMBOL_GPL(dax_alive);
+
+/*
+ * Note, rcu is not protecting the liveness of dax_dev, rcu is ensuring
+ * that any fault handlers or operations that might have seen
+ * dax_alive(), have completed. Any operations that start after
+ * synchronize_srcu() has run will abort upon seeing !dax_alive().
+ */
+void kill_dax(struct dax_device *dax_dev)
+{
+ if (!dax_dev)
+ return;
+
+ dax_dev->alive = false;
+ synchronize_srcu(&dax_srcu);
+ dax_dev->private = NULL;
+}
+EXPORT_SYMBOL_GPL(kill_dax);
+
+static struct inode *dax_alloc_inode(struct super_block *sb)
+{
+ struct dax_device *dax_dev;
+
+ dax_dev = kmem_cache_alloc(dax_cache, GFP_KERNEL);
+ return &dax_dev->inode;
+}
+
+static struct dax_device *to_dax_dev(struct inode *inode)
+{
+ return container_of(inode, struct dax_device, inode);
+}
+
+static void dax_i_callback(struct rcu_head *head)
+{
+ struct inode *inode = container_of(head, struct inode, i_rcu);
+ struct dax_device *dax_dev = to_dax_dev(inode);
+
+ ida_simple_remove(&dax_minor_ida, MINOR(inode->i_rdev));
+ kmem_cache_free(dax_cache, dax_dev);
+}
+
+static void dax_destroy_inode(struct inode *inode)
+{
+ struct dax_device *dax_dev = to_dax_dev(inode);
+
+ WARN_ONCE(dax_dev->alive,
+ "kill_dax() must be called before final iput()\n");
+ call_rcu(&inode->i_rcu, dax_i_callback);
+}
+
+static const struct super_operations dax_sops = {
+ .statfs = simple_statfs,
+ .alloc_inode = dax_alloc_inode,
+ .destroy_inode = dax_destroy_inode,
+ .drop_inode = generic_delete_inode,
+};
+
+static struct dentry *dax_mount(struct file_system_type *fs_type,
+ int flags, const char *dev_name, void *data)
+{
+ return mount_pseudo(fs_type, "dax:", &dax_sops, NULL, DAXFS_MAGIC);
+}
+
+static struct file_system_type dax_fs_type = {
+ .name = "dax",
+ .mount = dax_mount,
+ .kill_sb = kill_anon_super,
+};
+
+static int dax_test(struct inode *inode, void *data)
+{
+ dev_t devt = *(dev_t *) data;
+
+ return inode->i_rdev == devt;
+}
+
+static int dax_set(struct inode *inode, void *data)
+{
+ dev_t devt = *(dev_t *) data;
+
+ inode->i_rdev = devt;
+ return 0;
+}
+
+static struct dax_device *dax_dev_get(dev_t devt)
+{
+ struct dax_device *dax_dev;
+ struct inode *inode;
+
+ inode = iget5_locked(dax_superblock, hash_32(devt + DAXFS_MAGIC, 31),
+ dax_test, dax_set, &devt);
+
+ if (!inode)
+ return NULL;
+
+ dax_dev = to_dax_dev(inode);
+ if (inode->i_state & I_NEW) {
+ dax_dev->alive = true;
+ inode->i_cdev = &dax_dev->cdev;
+ inode->i_mode = S_IFCHR;
+ inode->i_flags = S_DAX;
+ mapping_set_gfp_mask(&inode->i_data, GFP_USER);
+ unlock_new_inode(inode);
+ }
+
+ return dax_dev;
+}
+
+struct dax_device *alloc_dax(void *private)
+{
+ struct dax_device *dax_dev;
+ dev_t devt;
+ int minor;
+
+ minor = ida_simple_get(&dax_minor_ida, 0, nr_dax, GFP_KERNEL);
+ if (minor < 0)
+ return NULL;
+
+ devt = MKDEV(MAJOR(dax_devt), minor);
+ dax_dev = dax_dev_get(devt);
+ if (!dax_dev)
+ goto err_inode;
+
+ dax_dev->private = private;
+ return dax_dev;
+
+ err_inode:
+ ida_simple_remove(&dax_minor_ida, minor);
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(alloc_dax);
+
+void put_dax(struct dax_device *dax_dev)
+{
+ if (!dax_dev)
+ return;
+ iput(&dax_dev->inode);
+}
+EXPORT_SYMBOL_GPL(put_dax);
+
+/**
+ * inode_dax: convert a public inode into its dax_dev
+ * @inode: An inode with i_cdev pointing to a dax_dev
+ *
+ * Note this is not equivalent to to_dax_dev() which is for private
+ * internal use where we know the inode filesystem type == dax_fs_type.
+ */
+struct dax_device *inode_dax(struct inode *inode)
+{
+ struct cdev *cdev = inode->i_cdev;
+
+ return container_of(cdev, struct dax_device, cdev);
+}
+EXPORT_SYMBOL_GPL(inode_dax);
+
+struct inode *dax_inode(struct dax_device *dax_dev)
+{
+ return &dax_dev->inode;
+}
+EXPORT_SYMBOL_GPL(dax_inode);
+
+void *dax_get_private(struct dax_device *dax_dev)
+{
+ return dax_dev->private;
+}
+EXPORT_SYMBOL_GPL(dax_get_private);
+
+static void init_once(void *_dax_dev)
+{
+ struct dax_device *dax_dev = _dax_dev;
+ struct inode *inode = &dax_dev->inode;
+
+ inode_init_once(inode);
+}
+
+static int __dax_fs_init(void)
+{
+ int rc;
+
+ dax_cache = kmem_cache_create("dax_cache", sizeof(struct dax_device), 0,
+ (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
+ SLAB_MEM_SPREAD|SLAB_ACCOUNT),
+ init_once);
+ if (!dax_cache)
+ return -ENOMEM;
+
+ rc = register_filesystem(&dax_fs_type);
+ if (rc)
+ goto err_register_fs;
+
+ dax_mnt = kern_mount(&dax_fs_type);
+ if (IS_ERR(dax_mnt)) {
+ rc = PTR_ERR(dax_mnt);
+ goto err_mount;
+ }
+ dax_superblock = dax_mnt->mnt_sb;
+
+ return 0;
+
+ err_mount:
+ unregister_filesystem(&dax_fs_type);
+ err_register_fs:
+ kmem_cache_destroy(dax_cache);
+
+ return rc;
+}
+
+static void __dax_fs_exit(void)
+{
+ kern_unmount(dax_mnt);
+ unregister_filesystem(&dax_fs_type);
+ kmem_cache_destroy(dax_cache);
+}
+
+static int __init dax_fs_init(void)
+{
+ int rc;
+
+ rc = __dax_fs_init();
+ if (rc)
+ return rc;
+
+ nr_dax = max(nr_dax, 256);
+ rc = alloc_chrdev_region(&dax_devt, 0, nr_dax, "dax");
+ if (rc)
+ __dax_fs_exit();
+ return rc;
+}
+
+static void __exit dax_fs_exit(void)
+{
+ unregister_chrdev_region(dax_devt, nr_dax);
+ ida_destroy(&dax_minor_ida);
+ __dax_fs_exit();
+}
+
+MODULE_AUTHOR("Intel Corporation");
+MODULE_LICENSE("GPL v2");
+subsys_initcall(dax_fs_init);
+module_exit(dax_fs_exit);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index d8a3dc042e1c..5b62f5d19aea 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -8,6 +8,9 @@

struct iomap_ops;

+int dax_read_lock(void);
+void dax_read_unlock(int id);
+
/*
* We use lowest available bit in exceptional entry for locking, one bit for
* the entry size (PMD) and two more to tell us if the entry is a huge zero
diff --git a/tools/testing/nvdimm/Kbuild b/tools/testing/nvdimm/Kbuild
index 405212be044a..2033ad03b8cd 100644
--- a/tools/testing/nvdimm/Kbuild
+++ b/tools/testing/nvdimm/Kbuild
@@ -28,7 +28,10 @@ obj-$(CONFIG_ND_BTT) += nd_btt.o
obj-$(CONFIG_ND_BLK) += nd_blk.o
obj-$(CONFIG_X86_PMEM_LEGACY) += nd_e820.o
obj-$(CONFIG_ACPI_NFIT) += nfit.o
-obj-$(CONFIG_DEV_DAX) += dax.o
+ifeq ($(CONFIG_DAX),m)
+obj-$(CONFIG_DAX) += dax.o
+endif
+obj-$(CONFIG_DEV_DAX) += device_dax.o
obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem.o

nfit-y := $(ACPI_SRC)/core.o
@@ -48,9 +51,12 @@ nd_blk-y += config_check.o
nd_e820-y := $(NVDIMM_SRC)/e820.o
nd_e820-y += config_check.o

-dax-y := $(DAX_SRC)/dax.o
+dax-y := $(DAX_SRC)/super.o
dax-y += config_check.o

+device_dax-y := $(DAX_SRC)/device.o
+device_dax-y += config_check.o
+
dax_pmem-y := $(DAX_SRC)/pmem.o
dax_pmem-y += config_check.o