btrfs_unlink_subvol
ret = btrfs_unlink_subvol(trans, dir, dentry);
ret = btrfs_unlink_subvol(trans, dir, dentry);
ret = btrfs_unlink_subvol(trans, BTRFS_I(old_dir), old_dentry);
ret = btrfs_unlink_subvol(trans, BTRFS_I(new_dir), new_dentry);
ret = btrfs_unlink_subvol(trans, BTRFS_I(old_dir), old_dentry);
ret = btrfs_unlink_subvol(trans, BTRFS_I(new_dir), new_dentry);