linux-ext4 - Re: [PATCH 4/6] ubifs: Maintain a parent pointer

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Date:   Tue, 23 May 2017 01:37:58 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Richard Weinberger <richard@....at>
Cc:     linux-mtd@...ts.infradead.org, david@...ma-star.at,
        dedekind1@...il.com, adrian.hunter@...el.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        adilger.kernel@...ger.ca, akpm@...ux-foundation.org,
        linux-ext4@...r.kernel.org, bfields@...hat.com,
        marcus.folkesson@...il.com, hyc.lee@...il.com,
        rockdotlee@...il.com, leon.pollak@...il.com
Subject: Re: [PATCH 4/6] ubifs: Maintain a parent pointer

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.