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Date: Tue, 2 May 2017 16:17:51 +0200
From: Christoph Hellwig <hch@lst.de>
To: Amir Goldstein <amir73il@gmail.com>
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        "Darrick J . Wong" <darrick.wong@oracle.com>,
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Subject: Re: [PATCH v2] xfs: publish UUID in struct super_block
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On Tue, May 02, 2017 at 05:13:56PM +0300, Amir Goldstein wrote:
> How can it create problems if uniqueness is not guaranteed with
> Current s_uuid? Even if we did make the xfs uuid table code generic
> It couldn't be the vfs default. Filesystems will have to opt in.

It creates problems if you e.g. mount an ext4 fs and a dm snaphot of
it.  The non-XFS file systems are simply buggy in this regard.

Non-uniqueue uuids are an absolute no-go.