linux-kernel - Re: [PATCH 3/3] ovl: Use real disk UUID for origin file handles

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Message-ID: <5334ebc6-ceee-4262-b477-6b161c5ca704@igalia.com>
Date: Wed, 14 Jan 2026 13:17:15 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Christoph Hellwig <hch@....de>
Cc: Chuck Lever <chuck.lever@...cle.com>, Jeff Layton <jlayton@...nel.org>,
 NeilBrown <neil@...wn.name>, Olga Kornievskaia <okorniev@...hat.com>,
 Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>,
 Carlos Maiolino <cem@...nel.org>, Amir Goldstein <amir73il@...il.com>,
 Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
 Miklos Szeredi <miklos@...redi.hu>, Christian Brauner <brauner@...nel.org>,
 Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
 linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-btrfs@...r.kernel.org, linux-unionfs@...r.kernel.org,
 kernel-dev@...lia.com
Subject: Re: [PATCH 3/3] ovl: Use real disk UUID for origin file handles

Em 14/01/2026 03:26, Christoph Hellwig escreveu:
> On Wed, Jan 14, 2026 at 01:31:43AM -0300, André Almeida wrote:
>> Some filesystem, like btrfs, supports mounting cloned images, but assign
>> random UUIDs for them to avoid conflicts. This breaks overlayfs "index"
>> check, given that every time the same image is mounted, it get's
>> assigned a new UUID.
> 
> ... and the fix is to not assign random uuid, but to assign a new uuid
> to the cloned image that is persisted.  That might need a new field
> to distintguish the stamped into the format uuid from the visible
> uuid like the xfs metauuid, but not hacks like this.
> 

How can I create this non random and persisting UUID? I was thinking of 
doing some operation on top the original UUID, like a circular shift, 
some sort of rearrangement of the original value that we can always 
reproduce. Is this in the right direction do you think?