dax: define a unified inode/address_space for device-dax mappings

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>

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index 17715773c097de0b5bbc07067cf6e06df2caf6f8..e8b9319aeadb321e4c6a7b50dad5d77463254611 100644 (file)
--- 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 6edd825231c5d3d323d2e58cd2ac97189ab61470..44a240c4bb658149c2d2b5b527af35fbf1a95d49 100644 (file)
--- 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 e398beac67b89eb5afc863fc2f38fc9623e24211..9bd559472c9280a6317e336f3a62471fd0aafa49 100644 (file)
--- 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