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Subject[PATCH 6/7] dax: define a unified inode/address_space for device-dax mappings
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Date
In support of enabling resize / truncate of device-dax instances, define
a pseudo-fs to provide a unified inode/address space for vm operations.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/dax/dax.c | 150 +++++++++++++++++++++++++++++++++++++++++++-
fs/char_dev.c | 1
include/uapi/linux/magic.h | 1
3 files changed, 148 insertions(+), 4 deletions(-)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index 17715773c097..e8b9319aeadb 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -13,7 +13,9 @@
#include <linux/pagemap.h>
#include <linux/module.h>
#include <linux/device.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>
@@ -26,6 +28,9 @@ 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");

/**
@@ -61,6 +66,7 @@ struct dax_region {
*/
struct dax_dev {
struct dax_region *region;
+ struct inode *inode;
struct device dev;
struct cdev cdev;
bool alive;
@@ -69,6 +75,117 @@ struct dax_dev {
struct resource res[0];
};

+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;
@@ -379,6 +496,9 @@ static int dax_open(struct inode *inode, struct file *filp)

dax_dev = container_of(inode->i_cdev, struct dax_dev, cdev);
dev_dbg(&dax_dev->dev, "%s\n", __func__);
+ inode->i_mapping = dax_dev->inode->i_mapping;
+ inode->i_mapping->host = dax_dev->inode;
+ filp->f_mapping = inode->i_mapping;
filp->private_data = dax_dev;
inode->i_flags = S_DAX;

@@ -410,6 +530,7 @@ static void dax_dev_release(struct device *dev)
ida_simple_remove(&dax_region->ida, dax_dev->id);
ida_simple_remove(&dax_minor_ida, MINOR(dev->devt));
dax_region_put(dax_region);
+ iput(dax_dev->inode);
kfree(dax_dev);
}

@@ -459,6 +580,12 @@ int devm_create_dax_dev(struct dax_region *dax_region, struct resource *res,
goto err_minor;
}

+ dax_dev->inode = dax_inode_get(&dax_dev->cdev, dev_t);
+ if (!dax_dev->inode) {
+ rc = -ENOMEM;
+ goto err_inode;
+ }
+
/* device_initialize() so cdev can reference kobj parent */
dev_t = MKDEV(MAJOR(dax_devt), minor);
dev = &dax_dev->dev;
@@ -494,6 +621,8 @@ int devm_create_dax_dev(struct dax_region *dax_region, struct resource *res,
return devm_add_action_or_reset(dax_region->dev, unregister_dax_dev, dev);

err_cdev:
+ iput(dax_dev->inode);
+ err_inode:
ida_simple_remove(&dax_minor_ida, minor);
err_minor:
ida_simple_remove(&dax_region->ida, dax_dev->id);
@@ -508,16 +637,28 @@ 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)
- return rc;
+ goto err_chrdev;

dax_class = class_create(THIS_MODULE, "dax");
- if (IS_ERR(dax_class))
- unregister_chrdev_region(dax_devt, nr_dax);
+ if (IS_ERR(dax_class)) {
+ rc = PTR_ERR(dax_class);
+ goto err_class;
+ }

- return PTR_ERR_OR_ZERO(dax_class);
+ return 0;
+
+ err_class:
+ unregister_chrdev_region(dax_devt, nr_dax);
+ err_chrdev:
+ dax_inode_exit();
+ return rc;
}

static void __exit dax_exit(void)
@@ -525,6 +666,7 @@ 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/fs/char_dev.c b/fs/char_dev.c
index 6edd825231c5..44a240c4bb65 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -406,6 +406,7 @@ void cd_forget(struct inode *inode)
spin_lock(&cdev_lock);
list_del_init(&inode->i_devices);
inode->i_cdev = NULL;
+ inode->i_mapping = &inode->i_data;
spin_unlock(&cdev_lock);
}

diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index e398beac67b8..9bd559472c92 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -65,6 +65,7 @@
#define V9FS_MAGIC 0x01021997

#define BDEVFS_MAGIC 0x62646576
+#define DAXFS_MAGIC 0x64646178
#define BINFMTFS_MAGIC 0x42494e4d
#define DEVPTS_SUPER_MAGIC 0x1cd1
#define FUTEXFS_SUPER_MAGIC 0xBAD1DEA
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