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Date: Wed, 14 Jan 2026 07:24:24 +0100
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: =?iso-8859-1?Q?Andr=E9?= Almeida <andrealmeid@igalia.com>,
	Christoph Hellwig <hch@lst.de>,
	Chuck Lever <chuck.lever@oracle.com>,
	Jeff Layton <jlayton@kernel.org>, NeilBrown <neil@brown.name>,
	Olga Kornievskaia <okorniev@redhat.com>,
	Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>,
	Carlos Maiolino <cem@kernel.org>,
	Amir Goldstein <amir73il@gmail.com>, Chris Mason <clm@fb.com>,
	David Sterba <dsterba@suse.com>, Miklos Szeredi <miklos@szeredi.hu>,
	Christian Brauner <brauner@kernel.org>,
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	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-unionfs@vger.kernel.org,
	kernel-dev@igalia.com
Subject: Re: [PATCH 1/3] exportfs: Rename get_uuid() to get_disk_uuid()
Message-ID: <20260114062424.GA10805@lst.de>
References: <20260114-tonyk-get_disk_uuid-v1-0-e6a319e25d57@igalia.com> <20260114-tonyk-get_disk_uuid-v1-1-e6a319e25d57@igalia.com> <20260114061028.GF15551@frogsfrogsfrogs>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Jan 13, 2026 at 10:10:28PM -0800, Darrick J. Wong wrote:
> On Wed, Jan 14, 2026 at 01:31:41AM -0300, André Almeida wrote:
> > To make clear which UUID is being returned, rename get_uuid() to
> > get_disk_uuid(). Expand the function documentation to note that this
> > function can be also used for filesystem that supports cloned devices
> > that might have different UUIDs for userspace tools, while having the
> > same UUID for internal usage.
> 
> I'm not sure what a "disk uuid" is -- XFS can store two of them in the
> ondisk superblock: the admin-modifiable one that blkid reports, and the
> secret one that's stamped in all the metadata and cannot change.

It isn't.  Totally independent of the rest of the discussion, the
get_uuid exportfs operation is not useful for anything but the original
pNFS block layout.  Which is actually pretty broken and should be slowly
phased out.

> IIRC XFS only shares the user-visible UUID, but they're both from the
> disk.   Also I'm not sure what a non-disk filesystem is supposed to
> provide here?

Yeah.