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Date: Thu, 15 Jan 2026 17:08:16 +0100
From: Christoph Hellwig <hch@lst.de>
To: =?iso-8859-1?Q?Andr=E9?= Almeida <andrealmeid@igalia.com>
Cc: 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>,
	Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Qu Wenruo <wqu@suse.com>, linux-btrfs@vger.kernel.org,
	linux-unionfs@vger.kernel.org, kernel-dev@igalia.com
Subject: Re: [PATCH 3/3] ovl: Use real disk UUID for origin file handles
Message-ID: <20260115160816.GA16080@lst.de>
References: <20260114-tonyk-get_disk_uuid-v1-0-e6a319e25d57@igalia.com> <20260114-tonyk-get_disk_uuid-v1-3-e6a319e25d57@igalia.com> <20260114062608.GB10805@lst.de> <5334ebc6-ceee-4262-b477-6b161c5ca704@igalia.com> <20260115062944.GA9590@lst.de> <633bb5f3-4582-416c-b8b9-fd1f3b3452ab@suse.com> <20260115072311.GA10352@lst.de> <22b16e24-d10e-43f6-bc2b-eeaa94310e3a@igalia.com>
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On Thu, Jan 15, 2026 at 12:42:33PM -0300, André Almeida wrote:
>> So André, can you confirm this what you're worried about?  And btrfs
>> developers, I think the main problem is indeed that btrfs simply allows
>> mounting the same fsid twice.  Which is really fatal for anything using
>> the fsid/uuid, such NFS exports, mount by fs uuid or any sb->s_uuid user.
>>
>
> Yes, I'm would like to be able to mount two cloned btrfs images and to use 
> overlayfs with them. This is useful for SteamOS A/B partition scheme.

Then you'll really need to assign them different (persistent) fsids/uuids.