[PATCH] introduce __blkdev_driver_ioctl()

Analog of blkdev_driver_ioctl() with sane arguments.  For
now uses fake struct file, by the end of the series it won't
and blkdev_driver_ioctl() will become a wrapper around it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index fa35838..373442b 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -114,15 +114,7 @@
 			unsigned long arg)
 {
 	struct linear_c *lc = (struct linear_c *) ti->private;
-	struct block_device *bdev = lc->dev->bdev;
-	struct file fake_file = {};
-	struct dentry fake_dentry = {};
-
-	fake_file.f_mode = lc->dev->mode;
-	fake_file.f_path.dentry = &fake_dentry;
-	fake_dentry.d_inode = bdev->bd_inode;
-
-	return blkdev_driver_ioctl(bdev->bd_inode, &fake_file, bdev->bd_disk, cmd, arg);
+	return __blkdev_driver_ioctl(lc->dev->bdev, lc->dev->mode, cmd, arg);
 }
 
 static int linear_merge(struct dm_target *ti, struct bvec_merge_data *bvm,