ovl: copy up before encoding non-connectable dir file handle

 * --------------------------------

 *  Pure upper		| U

 *  Non-indexed upper	| U

 *  Indexed upper	| L

 *  Non-upper		| L

 *  Indexed upper	| L (*)

 *  Non-upper		| L (*)

 *

 * U = upper file handle

 * L = lower file handle

 *

 * (*) Connecting an overlay dir from real lower dentry is not always

 * possible when there are redirects in lower layers. To mitigate this case,

 * we copy up the lower dir first and then encode an upper dir file handle.

 */

static bool ovl_should_encode_origin(struct dentry *dentry)

{

	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;

	if (!ovl_dentry_lower(dentry))

		return false;

	/*

	 * Decoding a merge dir, whose origin's parent is under a redirected

	 * lower dir is not always possible. As a simple aproximation, we do

	 * not encode lower dir file handles when overlay has multiple lower

	 * layers and origin is below the topmost lower layer.

	 *

	 * TODO: copy up only the parent that is under redirected lower.

	 */

	if (d_is_dir(dentry) && ofs->upper_mnt &&

	    OVL_E(dentry)->lowerstack[0].layer->idx > 1)

		return false;

	/* Decoding a non-indexed upper from origin is not implemented */

	if (ovl_dentry_upper(dentry) &&

	    !ovl_test_flag(OVL_INDEX, d_inode(dentry)))

	return true;

}

static int ovl_encode_maybe_copy_up(struct dentry *dentry)

{

	int err;

	if (ovl_dentry_upper(dentry))

		return 0;

	err = ovl_want_write(dentry);

	if (err)

		return err;

	err = ovl_copy_up(dentry);

	ovl_drop_write(dentry);

	return err;

}

static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)

{

	struct dentry *upper = ovl_dentry_upper(dentry);

	struct dentry *upper;

	struct dentry *origin = ovl_dentry_lower(dentry);

	struct ovl_fh *fh = NULL;

	int err;

	if (!ovl_should_encode_origin(dentry))

	/*

	 * If we should not encode a lower dir file handle, copy up and encode

	 * an upper dir file handle.

	 */

	if (!ovl_should_encode_origin(dentry)) {

		err = ovl_encode_maybe_copy_up(dentry);

		if (err)

			goto fail;

		origin = NULL;

	}

	upper = ovl_dentry_upper(dentry);

	err = -EACCES;

	if (!upper || origin)

		goto fail;