1 files changed, 73 insertions, 8 deletions

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 465dcd7317d5..ebf43f531ada 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -14,16 +14,13 @@
 #include <linux/module.h>
 #include <linux/mount.h>
 #include <linux/magic.h>
+#include <linux/genhd.h>
 #include <linux/cdev.h>
 #include <linux/hash.h>
 #include <linux/slab.h>
 #include <linux/dax.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;
@@ -47,6 +44,75 @@ void dax_read_unlock(int id)
 }
 EXPORT_SYMBOL_GPL(dax_read_unlock);
 
+int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
+		pgoff_t *pgoff)
+{
+	phys_addr_t phys_off = (get_start_sect(bdev) + sector) * 512;
+
+	if (pgoff)
+		*pgoff = PHYS_PFN(phys_off);
+	if (phys_off % PAGE_SIZE || size % PAGE_SIZE)
+		return -EINVAL;
+	return 0;
+}
+EXPORT_SYMBOL(bdev_dax_pgoff);
+
+/**
+ * __bdev_dax_supported() - Check if the device supports dax for filesystem
+ * @sb: The superblock of the device
+ * @blocksize: The block size of the device
+ *
+ * This is a library function for filesystems to check if the block device
+ * can be mounted with dax option.
+ *
+ * Return: negative errno if unsupported, 0 if supported.
+ */
+int __bdev_dax_supported(struct super_block *sb, int blocksize)
+{
+	struct block_device *bdev = sb->s_bdev;
+	struct dax_device *dax_dev;
+	pgoff_t pgoff;
+	int err, id;
+	void *kaddr;
+	pfn_t pfn;
+	long len;
+
+	if (blocksize != PAGE_SIZE) {
+		pr_err("VFS (%s): error: unsupported blocksize for dax\n",
+				sb->s_id);
+		return -EINVAL;
+	}
+
+	err = bdev_dax_pgoff(bdev, 0, PAGE_SIZE, &pgoff);
+	if (err) {
+		pr_err("VFS (%s): error: unaligned partition for dax\n",
+				sb->s_id);
+		return err;
+	}
+
+	dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
+	if (!dax_dev) {
+		pr_err("VFS (%s): error: device does not support dax\n",
+				sb->s_id);
+		return -EOPNOTSUPP;
+	}
+
+	id = dax_read_lock();
+	len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
+	dax_read_unlock(id);
+
+	put_dax(dax_dev);
+
+	if (len < 1) {
+		pr_err("VFS (%s): error: dax access failed (%ld)",
+				sb->s_id, len);
+		return len < 0 ? len : -EIO;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__bdev_dax_supported);
+
 /**
  * struct dax_device - anchor object for dax services
  * @inode: core vfs
@@ -261,7 +327,7 @@ struct dax_device *alloc_dax(void *private, const char *__host,
 	if (__host && !host)
 		return NULL;
 
-	minor = ida_simple_get(&dax_minor_ida, 0, nr_dax, GFP_KERNEL);
+	minor = ida_simple_get(&dax_minor_ida, 0, MINORMASK+1, GFP_KERNEL);
 	if (minor < 0)
 		goto err_minor;
 
@@ -405,8 +471,7 @@ static int __init dax_fs_init(void)
 	if (rc)
 		return rc;
 
-	nr_dax = max(nr_dax, 256);
-	rc = alloc_chrdev_region(&dax_devt, 0, nr_dax, "dax");
+	rc = alloc_chrdev_region(&dax_devt, 0, MINORMASK+1, "dax");
 	if (rc)
 		__dax_fs_exit();
 	return rc;
@@ -414,7 +479,7 @@ static int __init dax_fs_init(void)
 
 static void __exit dax_fs_exit(void)
 {
-	unregister_chrdev_region(dax_devt, nr_dax);
+	unregister_chrdev_region(dax_devt, MINORMASK+1);
 	ida_destroy(&dax_minor_ida);
 	__dax_fs_exit();
 }