[PATCH 4/6] ubifs: Maintain a parent pointer

[Christoph Hellwig]

On Sun, May 21, 2017 at 10:20:49PM +0200, Richard Weinberger wrote:
> The new feature UBIFS_FLG_PARENTPOINTER allows looking
> up the parent. Usually the Linux VFS walks down the filesystem
> and no parent pointers are needed. But when a filesystem
> is exportable via NFS such a lookup is needed.
> We can use a padding field in struct ubifs_ino_node to
> maintain a pointer to the parent inode.

Note that nfsd/exportfs will only do this for directories, and beacause
we hardlinks for other objects that is an important distinction.

I think the ubifs code should make sure to only maintain the parent
pointers for directories, otherwise confusion and abuses will happen.