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Tue, 14 Oct 2025 16:46:40 -0700 (PDT) Message-ID: <5137ce36-c3b4-4a0a-83af-e00892feaf43@gmail.com> Date: Wed, 15 Oct 2025 07:46:34 +0800 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/1] ovl: Use fsid as unique identifier for trusted origin Content-Language: en-GB To: Christoph Hellwig , =?UTF-8?Q?Andr=C3=A9_Almeida?= Cc: linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, kernel-dev@igalia.com, Miklos Szeredi , Amir Goldstein , Chris Mason , David Sterba , "Guilherme G . Piccoli" References: <20251014015707.129013-1-andrealmeid@igalia.com> <20251014015707.129013-2-andrealmeid@igalia.com> From: Anand Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 14-Oct-25 12:39 PM, Christoph Hellwig wrote: > On Mon, Oct 13, 2025 at 10:57:07PM -0300, André Almeida wrote: >> Some filesystem have non-persistent UUIDs, that can change between >> mounting, even if the filesystem is not modified. To prevent >> false-positives when mounting overlayfs with index enabled, use the fsid >> reported from statfs that is persistent across mounts. > > Please fix btrfs to not change uuids, as that completely defeats the > point of uuids. 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.