ovl: constant st_ino/st_dev across copy up

		       u32 request_mask, unsigned int flags)

{

	struct dentry *dentry = path->dentry;

	enum ovl_path_type type;

	struct path realpath;

	const struct cred *old_cred;

	int err;

	ovl_path_real(dentry, &realpath);

	type = ovl_path_real(dentry, &realpath);

	old_cred = ovl_override_creds(dentry->d_sb);

	err = vfs_getattr(&realpath, stat, request_mask, flags);

	if (err)

		goto out;

	/*

	 * When all layers are on the same fs, all real inode number are

	 * unique, so we use the overlay st_dev, which is friendly to du -x.

	 *

	 * We also use st_ino of the copy up origin, if we know it.

	 * This guaranties constant st_dev/st_ino across copy up.

	 *

	 * If filesystem supports NFS export ops, this also guaranties

	 * persistent st_ino across mount cycle.

	 */

	if (ovl_same_sb(dentry->d_sb)) {

		if (OVL_TYPE_ORIGIN(type)) {

			struct kstat lowerstat;

			ovl_path_lower(dentry, &realpath);

			err = vfs_getattr(&realpath, &lowerstat,

					  STATX_INO | STATX_NLINK, flags);

			if (err)

				goto out;

			WARN_ON_ONCE(stat->dev != lowerstat.dev);

			/*

			 * Lower hardlinks are broken on copy up to different

			 * upper files, so we cannot use the lower origin st_ino

			 * for those different files, even for the same fs case.

			 */

			if (lowerstat.nlink == 1)

				stat->ino = lowerstat.ino;

		}

		stat->dev = dentry->d_sb->s_dev;

	}

out:

	revert_creds(old_cred);

	return err;

}