linux-kernel - Re: [RFC PATCH 1/1] ovl: Use fsid as unique identifier for trusted origin

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Message-ID: <aO73YTmDIhHkg3XB@infradead.org>
Date: Tue, 14 Oct 2025 18:22:41 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Anand Jain <anajain.sg@...il.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	André Almeida <andrealmeid@...lia.com>,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kernel-dev@...lia.com, Miklos Szeredi <miklos@...redi.hu>,
	Amir Goldstein <amir73il@...il.com>, Chris Mason <clm@...com>,
	David Sterba <dsterba@...e.com>,
	"Guilherme G . Piccoli" <gpiccoli@...lia.com>
Subject: Re: [RFC PATCH 1/1] ovl: Use fsid as unique identifier for trusted
 origin

On Wed, Oct 15, 2025 at 07:46:34AM +0800, Anand Jain wrote:
> We needed cloned device mount support for an A/B testing
> use case, but changing the on-disk UUID defeats the purpose.
> 
> Right now, ext4 and Btrfs can mount identical devices,
> but XFS can't. How about extending this to the common
> VFS layer and adding a parameter to tell apart a cloned
> device from the same device accessed through multiple
> paths? I haven't looked into the details yet, but I can
> dig it further.

If you clone a device you need to change the user visible uuid/fsid,
and you need to do that explicitly to a known either saved or user
controlled value.  Assigning a random ID is highly dangerous as seen
here.