blkdev_get_no_open
bdev = blkdev_get_no_open(dev, true);
bdev = blkdev_get_no_open(d_backing_inode(path->dentry)->i_rdev, false);
bdev = blkdev_get_no_open(MKDEV(major, minor), false);
struct block_device *blkdev_get_no_open(dev_t dev, bool autoload);
bdev = blkdev_get_no_open(inode->i_rdev, true);