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Date: Wed, 21 Jan 2026 01:17:14 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Jan Kara <jack@...e.cz>
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Subject: Re: [PATCH v2 02/31] exportfs: add new EXPORT_OP_STABLE_HANDLES flag

On Tue, Jan 20, 2026 at 09:40:07AM +0100, Jan Kara wrote:
> (with explanations before I couldn't quite see the difference between shmem
> and kernfs). I'd note that fat or shmem (which are both exportable)
> satisfy this only with reasonably high probability as they use
> get_random_u32() for initializing their i_generation but I guess it's as
> good as it gets for them.

For tmpfs random generations are as good as it gets, in fact that's what
XFS starts with when allocating new inode clusters (which could have
previous been used for for inodes as well).

fat on the other hand looks broken, as it also set a new generation when
reading inodes from disk.  So I don't think fat should be nfs exportable,
even if the export ops predate other uses.

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