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

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Message-ID: <20260116093643.GA23235@lst.de>
Date: Fri, 16 Jan 2026 10:36:43 +0100
From: Christoph Hellwig <hch@....de>
To: André Almeida <andrealmeid@...lia.com>
Cc: Amir Goldstein <amir73il@...il.com>, Christoph Hellwig <hch@....de>,
	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>, 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,
	Qu Wenruo <wqu@...e.com>, 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

On Thu, Jan 15, 2026 at 03:55:15PM -0300, André Almeida wrote:
>> Is there any guarantee that file handles are relevant and point to the
>> same objects?
>>
>> The whole point of the overlayfs index feature is that overlayfs inodes
>> can have a unique id across copy-up.
>>
>> Please explain in more details exactly which overlayfs setup you are
>> trying to do with index feature.
>>
>
> The problem happens _before_ switching from A to B, it happens when trying 
> to install the same image from A on B.
>
> During the image installation process, while running in A, the B image will 
> be mounted more than once for some setup steps, and overlayfs is used for 
> this. Because A have the same UUID, each time B is remouted will get a new 
> UUID and then the installation scripts fails mounting the image.

It sounds like the 'clones' really need different persistent uuids. Or
do you also have a requirement that the two images have the same ID,
which would require a noouid-like option and extremely careful handling.